EP4640877A1

EP4640877A1 - Non-oriented electrical steel sheet and method of manufacturing same

Info

Publication number: EP4640877A1
Application number: EP23907562.5A
Authority: EP
Inventors: Seil LEE; Hyunwoo MUN
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2022-12-21
Filing date: 2023-12-13
Publication date: 2025-10-29
Also published as: CN120303427A; JP2025540883A; EP4640877A4; MX2025007233A; KR20240098846A; WO2024136276A1

Abstract

The present invention relates to a non-oriented electrical steel sheet and a method of manufacturing the same, and according to the non-oriented electrical steel sheet, an area fraction of grains having a grain size of less than 1/3 times an average grain size may be less than 5%, and an area fraction of grains having a dislocation density of more than 10¹²/m² and less than or equal to 10¹⁶/m² is less than 5% of a total area.

Description

[Technical Field]

The present invention relates to an electrical steel sheet, and more particularly, to a non-oriented electrical steel sheet and a method of manufacturing the same.

[Background Art]

Electrical steel sheets are products used as materials for transformers, motors, and electronic devices, and unlike general carbon steel, which prioritizes workability such as mechanical properties, electrical steel sheets are functional products that emphasize electrical properties. The electrical properties include iron loss, magnetic flux density, permeability, and fill factor, and the electrical steel sheet is characterized by having low iron loss and high magnetic flux density, permeability, and fill factor.
Electrical steel sheets are broadly classified into grain-oriented electrical steel sheets and non-oriented electrical steel sheets. The grain-oriented electrical steel sheet has excellent magnetic properties in a rolling direction by forming a Goss texture ({110}<001> texture) on an entire steel sheet by using an abnormal grain growth phenomenon called secondary recrystallization. The non-oriented electrical steel sheet is an electrical steel sheet with uniform magnetic properties in all directions on a rolled sheet.
The non-oriented electrical steel sheet is mainly used in motors that convert electrical energy into mechanical energy. To achieve high efficiency in this energy conversion process, the magnetic properties of the non-oriented electrical steel sheet must be excellent.
In addition, on a global scale, industrial structures are transitioning to environmentally-friendly and low-carbon industries in preparation for the carbonneutral era. In line with this trend, in the case of automobiles, internal combustion engines are being rapidly replaced by electric vehicles, and the driving motors used in the electric vehicles account for more than half of the electric energy consumed, so the demand for non-oriented electrical steel sheets used as core materials for the driving motors is continuously increasing. In this background, improving the iron loss of non-oriented electrical steel sheets is a very important method for increasing the efficiency of the driving motor.
For typical non-oriented electrical steel sheets, magnetic properties are mainly evaluated based on iron loss at 50 Hz and iron loss at 400 Hz. Since the iron loss refers to energy loss occurring at a specific magnetic flux density and frequency, the iron loss at 50 Hz is considered as energy loss occurring at a normal frequency, and the iron loss at 400 Hz is considered as energy loss occurring at a high frequency.
It is known that when a non-oriented electrical steel sheet with low iron loss is used in the core of the motor, heat loss generated in the core of the motor is reduced, making it possible to manufacture a motor with high efficiency. Since the motor driven by inverter control operates at various driving speeds, one way to manufacture a more efficient motor is to reduce the iron loss from normal frequency to high frequency, or even higher, ultra-high frequency.
One of the methods used to improve the iron loss of the non-oriented electrical steel sheet is to add alloying elements such as silicon (Si), aluminum (Al), and manganese (Mn), minimize impurities, and reduce the thickness of the steel sheet. As the specific resistance of the steel increases through the addition of the alloying elements, the eddy current loss decreases, thereby lowering the overall iron loss.
In addition, by minimizing the impurities, the structure of the magnetic domains within the steel sheet changes to a form that causes less loss during magnetization, and the number of dead domains fixed by inclusions or precipitates within the steel sheet decreases, thereby improving iron loss. Furthermore, if the thickness of the steel sheet is reduced, the iron loss can be effectively reduced because the eddy current loss, which increases in proportion to the square of the thickness, is reduced.
According to the design intent of the motor, the total iron loss, and in particular, the iron loss in the rolling direction, may act as a critical factor. Generally, in cases where the direction of magnetization does not rotate, such as in large-sized rotary machines or linear motors, or in motors that drive using reluctance during magnetization, electrical steel sheets with improved iron loss in the rolling direction are used.
However, among the technologies used to improve iron loss, increasing the amount of alloy increases production costs due to a rise in alloy raw material costs and a rapid decline in cold rollability, and there is a problem that it is impossible to increase the amount of alloy from the current level, and reducing the thickness of the steel sheet increases heat treatment and rolling times, causing a rapid increase in production costs and a rapid decrease in hourly production volume. In addition, lowering impurity levels is constrained by the limitations of steelmaking technology and the extension of refining time, thereby reducing productivity, and it may be difficult to reduce the iron loss due to problems such as increased cost due to the use of strict alloying raw material components.
In addition, in terms of improving the iron loss in the rolling direction, other than the aforementioned methods, there are very limited methods for improving the iron loss only in the rolling direction, making it difficult to apply to actual manufacturing processes. Accordingly, since conventional technologies increase manufacturing costs or reduce productivity and actual yield, research is needed on technologies that may solve the aforementioned problems and effectively reduce iron loss.

[Disclosure]

[Technical Problem]

An objective of the present invention attempts to provide a non-oriented electrical steel sheet that may reduce manufacturing costs, increases productivity and yield, and improves iron loss.
Another objective of the present invention attempts to provide a method for manufacturing a non-oriented electrical steel sheet having the aforementioned advantages.

[Technical Solution]

An embodiment of present invention provides a non-oriented electrical steel sheet in which an area fraction of grains having a grain size of less than 1/3 times an average grain size may be less than 5%, and an area fraction of grains having a dislocation density of more than 10¹²/m² and less than or equal to 10¹⁶/m² is less than 5% of a total area. In the embodiment, an area fraction of grains having a grain size of more than 3 times the average grain size may be less than 5%.
In the embodiment, the non-oriented electrical steel sheet may include, in wt%, Si: 0.1 to 6.5%, Al: 0.001 to 6.5%, Mn: 0.01 to 20%, C: 0.0010 to 0.015%, N: 0.0003 to 0.001%, S: 0.0003 to 0.001%, Ti: 0.0003 to 0.001%, and the balance including Fe and inevitable impurities. In the embodiment, the average grain size may be 40 to 250 µm. In the embodiment, a thickness of the non-oriented electrical steel sheet may be 0.03 to 0.5 mm.
In the embodiment, an iron loss (W10/400) and the thickness (t) of the non-oriented electrical steel sheet may satisfy the following Equation 1: $W 10 / 400 Iron loss (W / kg) < 6 + {(t / 0.04)}^{1.1}$ (In Equation 1, t represents the thickness (mm) of the non-oriented electrical steel sheet).
In the embodiment, an iron loss (W15/50) and the thickness (t) of the non-oriented electrical steel sheet may satisfy the following Equation 2: $W 15 / 50 Iron loss (W / kg) < 0.7 + {(t / 0.03)}^{1 / 5}$ (In Equation 2, t represents the thickness (mm) of the non-oriented electrical steel sheet).
Another embodiment of the present invention provides a method of manufacturing a non-oriented electrical steel sheet, including: a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and a cold-rolled steel sheet annealing step of annealing the cold-rolled steel sheet, wherein in the cold-rolled steel sheet annealing step, a tensile stress of more than 0.01 to less than 1.0 kgf/mm² may be applied in a rolling direction (RD direction) of a coil at a temperature of 650 °C or higher, a direction of a tensile stress applied to the cold-rolled steel sheet forms an angle within 3 ° with the rolling direction (RD direction) of the coil, and an angle formed with a normal direction (ND direction) of a rolling surface of the cold-rolled steel sheet is greater than 87° and less than or equal to 93°. In the embodiment, the slab may include, in wt%, Si: 0.1 to 6.5%, Al: 0.001 to 6.5%, Mn: 0.01 to 20%, C: 0.0010 to 0.015%, N: 0.0003 to 0.01 %, S: 0.0003 to 0.01 %, Ti: 0.0003 to 0.01%, and the balance including Fe and inevitable impurities.
In the embodiment, the method of manufacturing the non-oriented electrical steel sheet may further include a hot-rolled steel sheet annealing step of heating the hot-rolled steel sheet, wherein the hot-rolled steel sheet annealing step may be a step of heating the hot-rolled steel sheet to 850 to 1,150 °C. In the embodiment, the cold-rolled steel sheet annealing step may include a heating step of heating the cold-rolled steel sheet to 820 °C or higher and a cooling step of cooling from 820 to 900 °C to 750 to 850 °C.
In the embodiment, in the cold-rolled steel sheet annealing step, the heating step may be performed for a time within 60 seconds. In the embodiment, in the cold-rolled steel sheet annealing step, the cooling step may be performed for a time of 5 seconds or more.
In the embodiment, in the cold-rolled steel sheet annealing step, the cooling step may cool a sheet surface perpendicular to the direction of gravity. In the embodiment, the cold-rolled steel sheet annealing step may be annealing in a reducing atmosphere.

[Advantageous Effects]

According to the embodiment of the present invention, a non-oriented electrical steel sheet is configured to reduce and improve iron loss in the rolling direction by controlling the area fraction of grain sizes, specifically the area fraction of grain sizes that are one-third of the average grain size, and dislocation density, and simultaneously, the distribution of grains is uniformly formed, and the density of dislocations is evenly maintained, thereby providing a non-oriented electrical steel sheet with enhanced properties.
According to another embodiment of the present invention, a method for manufacturing a non-oriented electrical steel sheet may provide a method for manufacturing a non-oriented electrical steel sheet having the aforementioned advantages by controlling the cooling rate and the direction and magnitude of tensile stress in a heat treatment process to distribute homogenized grains within the steel sheet.

[Description of the Drawings]

FIG. 1A illustrates a cold-rolled steel sheet arrangement during an annealing process according to an embodiment of the present invention, and FIG. 1B and FIG. 1C respectively illustrate plan views of a traveling direction of a steel sheet and a movement direction of the steel sheet along a tensile stress direction.
FIG. 2A and FIG. 2B respectively illustrate cross-sectional views of a traveling direction of a steel sheet and a movement direction of the steel sheet along a tensile stress direction.
FIG. 3 illustrates a region in which dislocations are concentrated according to an embodiment of the present invention.
FIG. 4A to FIG. 4E illustrate enlarged views of a region in which dislocations are concentrated according to an example of the present invention and a comparative example.

[Mode for Invention]

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, they are not limited thereto. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Therefore, a first part, component, area, layer, or section to be described below may be referred to as second part, component, area, layer, or section within the range of the present invention.
The technical terms used herein are to simply mention a particular embodiment and are not meant to limit the present invention. An expression used in the singular encompasses an expression of the plural, unless it has a clearly different meaning in the context. In the specification, it is to be understood that the terms such as "including", "having", etc., are intended to indicate the existence of specific features, regions, numbers, stages, operations, elements, components, and/or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, regions, numbers, stages, operations, elements, components, and/or combinations thereof may exist or may be added.
When referring to a part as being "on" or "above" another part, it may be positioned directly on or above the other part, or another part may be interposed therebetween. In contrast, when referring to a part being "directly above" another part, no other part is interposed therebetween.
Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those with ordinary knowledge in the field of art to which the present invention belongs. Terms defined in commonly used dictionaries are further interpreted as having meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as having idealized or very formal meanings unless defined otherwise.
Unless otherwise stated, % represents wt%, and 1 ppm is 0.0001 wt%. In embodiments of the present invention, inclusion of an additional element means replacing the remaining iron (Fe) by an additional amount of the additional elements.
In the present invention, the Goss orientation refers to an orientation corresponding to {110}<001> in Miller indices, and the Cube orientation refers to an orientation corresponding to {100}<001> in Miller indices.
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure.
A non-oriented electrical steel sheet according to an embodiment of the present invention includes, in wt%, Si: 0.1 to 6.5 wt%, Al: 0.001 to 6.5 wt%, Mn: 0.01 to 20 wt%, C: 0.0010 to 0.0150 wt%, at least one of N, S, and Ti: 0.0003 to 0.01 wt% each, and the balance of Fe and inevitable impurities.
Hereinafter, the reasons for limiting the composition of the non-oriented electrical steel sheet will be described.

Si: 0.1 to 6.5 wt%

Silicon (Si) serves to increase the specific resistance of the material to reduce iron loss, and is used as a deoxidizing agent in the steelmaking process. In addition, the silicon is an element inevitably added in the manufacturing process of the electrical steel sheet and is an element forming oxides during the manufacturing process. The Si content may be in the range of 0.1 to 6.5 wt%. Specifically, the Si content may be in the range of 1.0 to 4.5 wt%.
When the silicon content is excessively high, the brittleness of the material increases, which rapidly reduces rolling productivity, a thick oxide layer harmful to magnetism is formed, and iron loss may be inhibited by the oxide inside. In addition, when the silicon content is excessively high, a secondary phase is formed, which may significantly degrade magnetic properties. When the silicon content is excessively low, there is a problem that iron loss is deteriorated due to the formation of low-temperature Si oxides.

Al: 0.001 to 6.5 wt%

Aluminum (Al), like the above silicon, serves to reduce iron loss by increasing the specific resistance of the material, and may be used as a powerful deoxidizer in steelmaking. The aluminum content may be 0.001 to 6.5 wt%. Specifically, the aluminum content may be 0.1 to 2.0 wt%.

Mn: 0.01 to 20 wt%

Manganese (Mn) is an element capable of improving iron loss by increasing the specific resistance of the material, and may serve to form sulfides in the steel. The manganese content may be 0.01 to 20 wt%. Specifically, the manganese content may be 0.01 to 6.5 wt%. More specifically, the manganese content may be 0.01 to 2.0 wt%.
In an embodiment, the non-oriented electrical steel sheet may include at least one of N, S, and Ti of 0.0003 to 0.001 wt%, respectively. Specifically, it may include at least one of N, S, and Ti, and more specifically, it may include all of N, S, and Ti.

C: 0.0005 to 0.015 wt%

Carbon (C) is an element inevitably included in the manufacturing process of a non-oriented electrical steel sheet, and may serve to homogenize the rolling texture in the steel during rolling. Specifically, the carbon content may range from 0.0005 to 0.015 wt%, and more specifically, from 0.0015 to 0.004 wt%.
When the carbon content is excessively high, carbides are formed, which impede the movement of magnetic domains and require additional energy for magnetization during material magnetization. When the carbon content is excessively low, the material becomes non-uniform during rolling, resulting in non-uniform grain size of the recrystallized texture.

N: 0.0003 to 0.010 wt%

Nitrogen (N) not only forms fine AIN precipitates inside the steel sheet but also combines with other impurities to form fine precipitates and suppress grain growth, thereby worsening iron loss but improving strength. The nitrogen content may range from 0.0003 to 0.010 wt%. Specifically, the nitrogen content may range from 0.0003 to 0.004 wt%.

S: 0.0003 to 0.010 wt%

It is desirable to manage sulfur (S) to maintain a low content because it forms MnS, a fine precipitate, which deteriorates magnetic properties and hot workability. The sulfur content may range from 0.0003 to 0.010 wt%. Specifically, the sulfur content may range from 0.0003 to 0.004 wt%.
When the sulfur content is excessively high, cracks may occur during continuous casting. When the sulfur content is excessively low, it may be favorable for the properties of the steel sheet, but there is a problem in production cost because selected raw materials must be used to control the sulfur content to a value lower than the lower limit.

Ti: 0.0003 to 0.010 wt%

Titanium (Ti) has a strong tendency to form precipitates inside the steel sheet, and may deteriorate iron loss by forming fine carbides, nitrides, or sulfides inside the steel sheet and suppressing grain growth. The titanium content may range from 0.0003 to 0.010 wt%%. Specifically, the titanium content may range from 0.0003 to 0.003 wt%.
When the titanium content is excessively high, deterioration of iron loss may become a problem. When the titanium content is excessively low, there is a manufacturing cost problem that occurs because selected raw materials must be used to control the titanium content.
The non-oriented electrical steel sheet according to the embodiment of the present invention contains Fe and inevitable impurities as the balance. The inevitable impurities are impurities mixed in the steel-making and the manufacturing process of the non-oriented electrical steel sheet, which are widely known in the field, and thus a detailed description thereof will be omitted. In the embodiment of the present invention, the addition of elements other than the above-described alloy components is not excluded, and various elements may be included within a range that does not hinder the technical concept of the present invention. When the additional elements are further included, they replace the balance of Fe.
The non-oriented electrical steel sheet according to the embodiment of the present invention having the above-described composition has the following physical properties.
According to the embodiment of the present invention, the non-oriented electrical steel sheet may have an average grain size of 40 to 250 µm. The grains of the non-oriented electrical steel sheet are characterized by being evenly distributed. This is because the place where dislocations within the steel sheet are concentrated is the grain boundary, and the structural stability of the grain boundary may be obtained from the uniform distribution of grain sizes. Specifically, the average grain size may range from 50 µm to 120 µm.
In order to obtain the distribution of grain size, individual grains closed by grain boundaries are designated in a microscopic tissue photograph, the area of each grain is obtained, and the diameter of each grain may be expressed as the corresponding equivalent circle diameter (ECD). In this case, the distribution of grain diameters may be obtained using the ECD, and the average grain diameter may be calculated by taking the arithmetic mean thereof.
If the average grain diameter exceeds the upper limit of the range, the dispersion in grain size in the steel may increase. In a grain size distribution with a large dispersion, there may be a problem in which more dislocations are formed around large grains, resulting in the formation of sub-grain boundaries within the grains. If the average grain diameter exceeds the lower limit of the range, there is a problem in that the fraction of grain boundaries in the entire material increases and magnetization becomes difficult.
In an embodiment, the non-oriented electrical steel sheet may have an area fraction of less than 5% of grains having a grain size less than 1/3 times the average grain size. The grains having a grain size less than 1/3 of the average grain size mean grains having a grain size smaller than 1/3 of the average grain size calculated above.
The area fraction of grain sizes less than 1/3 of the average grain size refers to the ratio of the area occupied by grain sizes that are 1/3 of the average grain size in the entire structure of the non-oriented electrical steel sheet.
The texture fraction may be measured by calculating it using X-ray diffraction Pol Figure, calculating it using neutron diffraction, using X-ray transmission analysis, or analyzing it using electron microscope EBSD. The area fraction of grains with a misorientation within 15 degrees from the center of the Goss and Cube orientations may be calculated.
If the area fraction of grain sizes less than 1/3 of the average grain size is excessively large, there is a problem that magnetization is difficult in a low magnetic field and the permeability is low. In an embodiment, the area fraction of grain sizes greater than three times the average grain size may be less than 5%. The grain size greater than three times the average grain size mean grains having a grain size greater than three times the average grain size calculated above.
The area fraction of grains having a grain size exceeding three times the average grain size means the ratio of the area of grains having a grain size exceeding three times the average grain size in the entire structure of the non-oriented electrical steel sheet. If the area fraction of grains exceeding three times the average grain size is excessively large, there is a problem in that the dislocation distribution between grains becomes different, displacement is concentrated in locally coarse grains, and iron loss increases significantly.
In an embodiment, the sum of the fraction of grains having a Goss orientation and the fraction of grains having a Cube orientation in the non-oriented electrical steel sheet may exceed 5%.
In an embodiment, the dislocation density of the non-oriented electrical steel sheet may be greater than 10¹²/m² and less than or equal to 10¹⁶/m², and the fraction of the area where the dislocation is concentrated may be less than 5% of the total area. The dislocation density may be measured using a transmission electron microscope (TEM), or more simply calculated using a scanning electron microscope (SEM). The dislocation density may be measured using the line intercept method.
By controlling tensile stress during annealing according to the present invention, the formation of dislocations formed around grain boundaries after annealing is completed may be controlled. Dislocation formation at high temperatures occurs as the emission of dislocations from regions tens of nanometers away from grain boundaries to the grain boundaries is suppressed, resulting in their alignment into sub-grain boundaries within the grains. As the tensile stress during annealing increases, the amount of dislocations forming the sub-grain boundary increases, and accordingly, the orientation error angle between the regions between the sub-grain boundaries increases. As the orientation error angle increases, additional energy is consumed during magnetization, which deteriorates the magnetism. When there are sufficiently many grain boundaries and the size of each grain is uniform, the generation of dislocations due to tensile stress during annealing is suppressed by dislocation acceptance at the grain boundaries.
In an embodiment, the thickness of the non-oriented electrical steel sheet may range from 0.03 mm to 0.5 mm. Specifically, the thickness of the non-oriented electrical steel sheet may range from 0.15 mm to 0.3 mm.
If the thickness is excessively thick, there is a problem that the tensile stress during annealing differs depending on the sheet thickness, and dislocations are formed in a complex manner due to the generation of tensile stress in the thickness direction due to the difference in tensile stress between the surface and the center. If the thickness is excessively thin, there is a problem that tensile stress control in the annealing furnace becomes industrially impossible.
In an embodiment, the core loss (W10/400) of the non-oriented electrical steel sheet at a high frequency of 400 Hz and 1.0 T, and the thickness (t) of the non-oriented electrical steel sheet, may satisfy the following Equation 1: $W 10 / 400 Iron loss (W / kg) < 6 + {(t / 0.04)}^{1.1}$ (In Equation 1, t represents the thickness of the non-oriented electrical steel sheet)
By satisfying Equation 1, it is possible to provide a non-oriented electrical steel sheet in which magnetic properties such as iron loss are excellent. If Equation 1 is not satisfied, there is a problem that a steel sheet having excellent high-frequency iron loss compared to the sheet thickness cannot be obtained.
In an embodiment, the core loss of the non-oriented electrical steel sheet at a typical frequency of 50 Hz and 1.5 T, and the thickness (t) of the non-oriented electrical steel sheet, may satisfy the following Equation 2: $W 15 / 50 Iron loss (W / kg) < 0.7 + {(t / 0.03)}^{1 / 5}$ (In Equation 2, t represents the thickness of the non-oriented electrical steel sheet)
By satisfying Equation 2, it is possible to provide a non-oriented electrical steel sheet in which magnetic properties such as iron loss are excellent. If Equation 2 is not satisfied, there is a problem that the iron loss under high magnetic flux density conditions is inferior, and motor loss at high torque significantly increases.
In an embodiment, the core loss of the non-oriented electrical steel sheet at a typical frequency of 50 Hz and 1.5 T, and the thickness (t) of the non-oriented electrical steel sheet, may satisfy the following Equation 3: $W 15 / 50 Rolling direction iron loss (W / kg) < 0.6 + {(t / 0.03)}^{1 / 6}$ (In Equation 3, t represents the thickness of the non-oriented electrical steel sheet)
By satisfying Equation 3, it is possible to provide a non-oriented electrical steel sheet in which magnetic properties such as iron loss are excellent. If Equation 3 is not satisfied, there is a problem that motor loss at high torque increases when using a divided core made by cutting and assembling a part of a motor component in the rolling direction.
In an embodiment, the core loss (W10/400) of the non-oriented electrical steel sheet at a high frequency of 400 Hz and 1.0 T, and the thickness (t) of the non-oriented electrical steel sheet, may satisfy the following Equation 4: $W 10 / 400 Rolling direction iron loss (W / kg) < 5 + {(t / 0.04)}^{1.1}$

By satisfying Equation 4, it is possible to provide a non-oriented electrical steel sheet in which magnetic properties such as iron loss are excellent. If Equation 4 is not satisfied, there is a problem that motor loss at high torque increases significantly when the rotation speed increases when using a divided core made by cutting and assembling a part of a motor component in the rolling direction.
A method of manufacturing a non-oriented electrical steel sheet according to another embodiment of the present invention includes a step of hot-rolling a slab to manufacture a hot-rolled steel sheet, a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet, and a cold-rolled steel sheet annealing step of annealing the cold-rolled steel sheet.
The step of hot-rolling the slab may hot-roll the slab satisfying the alloy composition of the present invention. Since the alloy composition of the slab has been described in the steel composition components of the non-oriented electrical steel sheet described above, a duplicate description thereof will be omitted. In the manufacturing process of the non-oriented electrical steel sheet, the alloy composition is substantially the same as the final product.
The step of hot-rolling the slab may include a step of heating the slab. In the step of heating the slab, the heating temperature is not limited, but specifically, it may be heated to 1,200 °C or less. If the slab heating temperature is excessively high, precipitates existing in the slab, for example, precipitates such as AIN and MnS, are re-dissolved and then finely precipitated during hot rolling and annealing, which may suppress grain growth and reduce magnetism.
Thereafter, the heated slab may be hot-rolled to manufacture a hot-rolled steel sheet. The hot-rolled steel sheet may be manufactured to have a thickness of 1 to 3 mm.
In an embodiment, in the step of hot-rolling the slab, the finishing rolling temperature may be 700 °C or higher. Specifically, the finishing rolling temperature may be 800 to 1,000 °C.
After the step of manufacturing the hot-rolled steel sheet, a hot-rolled sheet annealing step of heating the hot-rolled steel sheet may be included. In an embodiment, the hot-rolled sheet annealing step may be performed by heating the hot-rolled steel sheet to 850 to 1,150 °C.
In an embodiment, after the step of manufacturing the hot-rolled steel sheet, a step of pickling the annealed hot-rolled steel sheet may be included.
After the step of manufacturing the hot-rolled steel sheet, a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet may be included. The cold rolling may be finally rolled to a thickness of 0.03 to 0.5 mm. In an embodiment, the cold rolling step may further include an intermediate annealing step between a plurality of cold rolling steps.
After the step of cold-rolling the hot-rolled steel sheet to manufacture the cold-rolled steel sheet, a step of annealing the cold-rolled steel sheet may be included. The step of annealing the cold-rolled steel sheet may include a heating step of raising a temperature and a cooling step of cooling.
In an embodiment, the step of annealing the cold-rolled steel sheet may include a step of annealing the cold-rolled steel sheet at a crack temperature of 820 to 1,150 °C. If the upper limit of the crack temperature is exceeded, there is a problem that coarse grains are formed and the distribution of grain sizes goes beyond the scope of the invention, resulting in a significant increase in the area of high dislocation density, and if the lower limit of the crack temperature is exceeded, there is a problem that grains that have not completely recrystallized remain, resulting in deterioration of magnetism.
In an embodiment, the step of annealing the cold-rolled steel sheet may include a heating step of heating the cold-rolled steel sheet to 820 °C or higher and a cooling step of cooling from 820 to 900 °C to 750 to 820 °C. Specifically, the step of annealing the cold-rolled steel sheet may include a heating step of heating the cold-rolled steel sheet to 850 °C or higher and a cooling step of cooling from 850 to 900 °C to 750 to 850 °C.
In an embodiment, in the cold-rolled steel sheet annealing step, the heating step may be performed for a time within 60 seconds. If it is performed excessively over the time, there is a problem that the distribution of grains deviates from the scope of the invention and a grain size distribution with a wide dispersion occurs.
In an embodiment, in the cold-rolled steel sheet annealing step, the cooling step may be performed for a time of 5 seconds or more. If it is performed for a time less than the time, stress in the thickness direction occurs due to thermal contraction, and thermal stress occurs due to a difference in sheet surface cooling in the width direction of the sheet. In an embodiment, in the cold-rolled steel sheet annealing step, the cooling step may include a step of cooling the sheet surface perpendicular to the gravity direction.
In an embodiment, in the cold-rolled steel sheet annealing step, a tensile stress of more than 0.01 to less than 1.0 kgf/mm² may be applied in the rolling direction (RD) of the coil at a temperature of 650 °C or higher. Specifically, the tensile stress may be in the range of 0.05 to 0.8 kgf/mm². If the range of the tensile stress exceeds the upper limit, there is a problem that the area ratio of the region with high dislocation density significantly increases by the tensile stress. If the range of the tensile stress exceeds the lower limit, there is a problem that the traveling direction of the sheet is not in the horizontal plane or the stress of the sheet cannot be analyzed due to complex deformation stress.
FIG. 1A illustrates a cold-rolled steel sheet arrangement during an annealing process according to an embodiment of the present invention, and FIG. 1B and FIG. 1C respectively illustrate plan views of a traveling direction of a steel sheet and a movement direction of the steel sheet along a tensile stress direction.
Referring to FIG. 1A, when annealing the cold-rolled steel sheet, after disposing a cold-rolled steel sheet 10 on a roll 30 disposed in an annealing furnace 20, the cold-rolled steel sheet 10 moves and is annealed as the roll 30 rotates. Tension may be applied in the step of annealing the cold-rolled steel sheet, and the tensile stress may be calculated by a forward traveling force applied to the thickness and width of the steel sheet. Specifically, it is to measure the tensile stress applied to the sheet when the cooling of the furnace is performed, but when it is difficult to measure due to the structure of the annealing furnace in the actual manufacturing process, it is possible to calculate by a method of dividing the difference between the tensile stress measurement value of the sheet at the outlet side of the annealing furnace and the tensile stress measurement value measured at the inlet side of the annealing furnace by the cross-sectional area of the sheet in the annealing furnace. In this case, the cross-sectional area of the sheet in the annealing furnace may be regarded as the cross-sectional area value at the outlet side of the annealing furnace.
FIG. 1B illustrates a case in which the traveling direction of the cold-rolled steel sheet 10 and the tensile stress direction thereof are applied in a mutually coincident direction.
Referring to FIG. 1B, the tensile stress direction (TSD1_1) in which the tensile stress is applied may be generally applied in a direction coinciding with the traveling direction (D1) of the cold-rolled steel sheet.
FIG. 1C illustrates that the traveling direction (D2) of the cold-rolled steel sheet 10 and the tensile stress direction (TSD1_2) may form an angle of a predetermined range. In an embodiment, in the cold-rolled steel sheet annealing step, the direction (TSD1_2) of the tensile stress applied to the cold-rolled steel sheet may form an angle within 3° with the rolling direction (RD) of the coil. If the angle is excessively large, there is a problem that the stress applied to the sheet surface during cooling is not constant in the sheet width, and the region with high dislocation density in the sheet varies greatly depending on the position in the sheet. In addition, compared to the case where the direction (TSD) in which the tensile stress is applied and the rolling direction of the coil coincide, when the direction (TSD) in which the tensile stress is applied and the rolling direction of the coil form an angle within 3°, there is an advantage that the stress applied to the sheet surface during cooling is constant in the sheet width and high stress is not concentrated on a specific portion.
FIG. 2A and FIG. 2B respectively illustrate cross-sectional views of a traveling direction of a steel sheet and a movement direction of the steel sheet along a tensile stress direction.
FIG 2A illustrates the tensile stress direction (TSD) and the direction (SVD) perpendicular to the steel sheet surface when the direction of tensile stress applied to the cold-rolled steel sheet during the cold-rolled steel sheet annealing step forms an angle of more than 87° and less than 93° with the rolling surface normal direction (ND). When the angle range is achieved, it can be confirmed that the tensile stress direction (TSD) and the vertical direction (SVD) of the steel sheet surface are perpendicular.
FIG. 2B illustrates a case in which the angle deviates from the lower and upper limits of the range by more than 3° from the normal, and it can be seen that complex stress is applied in the thickness direction of the sheet, and the tensile stress direction (TSD) and the vertical direction (SVD) of the steel sheet surface are not constant, resulting in a problem that the stress is not constant.
As described above, the present invention minimizes the pulling force in the rolling traveling direction within the range of the tensile stress direction in the cold-rolled steel sheet annealing step, the rolling direction (RD) of the coil and the rolling surface normal direction (ND) of the cold-rolled steel sheet, while minimizing friction in the cooling zone considering the change in length due to friction and thermal expansion that occurs as the sheet progresses in the annealing furnace, thereby manufacturing a non-oriented electrical steel sheet having a uniform average grain size, good iron loss, and excellent magnetic properties.
In an embodiment, the cold-rolled steel sheet annealing step may be performed in a reducing atmosphere. The reducing atmosphere may include at least one of hydrogen (H₂), nitrogen (N₂), and an inert gas. As annealing is performed in the reducing atmosphere, it may be possible to manufacture a non-oriented electrical steel sheet with excellent iron loss.
Hereinafter, a specific example of the present invention will be described. However, the following example is only a specific example of the present invention, and the present invention is not limited to the following example.

Slab Composition

Table 1 below shows the composition of the slab, and the slab was manufactured using the components listed in Table 1 below, with the balance including Fe and inevitable impurities. Thereafter, the slab was heated to 1,180°C and hot-rolled at a finishing temperature of 880°C to manufacture a hot-rolled steel sheet with a sheet thickness of 2.0 mm. The hot-rolled steel sheet was annealed under the pre-annealing conditions described in Table 1 below. The pre-annealing is specifically a step of heating the hot-rolled steel sheet at the temperature listed in Table 1 below.

(Table 1)

Steel Type	Si [wt%]	Al [wt%]	Mn [wt%]	N [wt%]	S [wt%]	Ti [wt%]	Hot-Rolled Steel Sheet Heating Temperature [°C]
Steel Type 1	3.3	1	0.5	0.0026	0.0027	0.0022	950
Steel Type 2	3.95	1.01	0.56	0.0110	0.0033	0.0022	1020
Steel Type 3	3.36	1.61	0.60	0.0024	0.0110	0.0020	1020
Steel Type 4	3.70	1.05	0.76	0.0037	0.0025	0.0110	1020
Steel Type 5	3.32	1.32	0.62	0.0025	0.0034	0.0013	1009
Steel Type 6	3.62	1.21	0.58	0.0029	0.0032	0.0017	1058
Steel Type 7	2.78	0.61	0.31	0.0040	0.0037	0.0007	1056
Steel Type 8	3.4	0.9	0.5	0.0019	0.0022	0.0025	967
Steel Type 9	307	1.0	0.37	0.0036	0.0035	0.0040	1084

Table 2 shows that the hot-rolled and annealed steel sheet manufactured from Table 1 was cold-rolled to the thickness of the steel sheet described in Table 2, and then cold-rolled sheet annealing was performed under the conditions described in Table 2. The reducing atmosphere below was used by mixing 80% nitrogen and 20% hydrogen when performing the cold rolled sheet annealing. When annealing was performed in the reducing atmosphere thus made, it was marked as "O", and when it was not performed in the reducing atmosphere, it was marked as "X". The heating time refers to the annealing time performed at 850°C or higher, and the cooling time refers to the time taken to cool from 850°C to 800°C.

(Table 2)

Steel Type	Reducing Atmosphere [Yes/No]	Heating Time [sec]	Cooling Time [sec]	Tensile Stress Rolling Direction Angle [°]	Tensile Stress Vertical Angle [°]	Tensile Stress Magnitude [kgf/mm²]	Steel Sheet Thickness [mm]
Steel Type 1	○	15	15	0.006	80.2	0.6	0.270
Steel Type 2	X	10	10	0.008	89.6	0.62	0.270
Steel Type 3	○	10	10	0.007	90.6	0.62	0.270
Steel Type 4	X	10	10	0.000	89.7	0.64	0.270
Steel Type 5	○	14	14	0.002	89.8	0.71	0.298
Steel Type 6	○	14	11	0.008	90.4	0.69	0.297
Steel Type 7	○	16	18	0.003	90.2	0.68	0.238
Steel Type 8	○	15	17	0.000	89.9	0.66	0.245
Steel Type 9	○	17	17	0.007	89.5	0.72	0.234

Table 3 shows the average grain size and the area fraction by grain size derived from the cold-rolled sheet annealed using an optical microscope, and the fraction of areas with high dislocation density in the steel sheet was measured using ECCI of an electron microscope. In addition, the iron loss of the manufactured steel sheet was measured, and the iron loss in the rolling direction was measured and recorded in Table 3. As described above, the average grain size was calculated by designating individual grains closed by grain boundaries in a microscopic tissue photograph, obtaining the area of each grain, and expressing the diameter of each grain as the corresponding equivalent circle diameter (ECD), and in this case, the distribution of grain diameters was obtained with the ECD, and the arithmetic mean was taken to calculate the average grain size.
In Table 3, the 1/3 grain size fraction refers to the area fraction of grains with a diameter less than 1/3 of the average grain diameter of the steel sheet, and the 3 times grain size fraction refers to the area fraction of grains with a diameter exceeding three times the average grain diameter of the steel sheet.
In addition, the texture fraction was analyzed using EBSD on the crosssection of the sheet. To measure the fraction in a sufficient area, the crosssections of the sheets were stacked and the texture fraction was measured in an area of 10 mm x 5 mm. The area fraction of grains with a misorientation within 15 degrees from the center of the Goss and Cube orientations was calculated. To measure the area fraction of the grains, the area of more than 2,000 grains with the average grain size was measured, and the area fraction was statistically determined.
For magnetic measurement, Epstein specimens were prepared and measured according to the IEC 60404 standard. The shape of the Epstein specimen is a rectangular shape with a long direction of 305 mm and a short direction of 30 mm, and the Epstein test specification for non-oriented electrical steel sheets was to derive the core loss by loading half of the specimen cut lengthwise in the rolling direction and half of the specimen cut lengthwise in the rolling vertical direction into the measuring device together. The iron loss in the rolling direction was measured by loading the specimens into an Epstein frame with the specimens cut so that the rolling direction was 305 mm and the direction perpendicular to the rolling was 30 mm.
In addition, the dislocation density was calculated using the electron channeling contrast image from a FE-SEM (Scanning Electron Microscope). The dislocation density was calculated through Equation 5 below using the line intercept method. $Dislocation density = 2 N / lt$
In Equation 5, N is the number of dislocations contacting a randomly drawn line, I is the length of the randomly drawn line, and t is the depth shown by the image. In ECCI, the value is proportional to the intensity of the electron beam, the composition of the specimen, and the intensity of the current, and since the depth of steel measured using a 15 kV electron beam is approximately 70 nm, the density was calculated by taking this into account.
FIG. 3 illustrates a region in which dislocations are concentrated according to an embodiment of the present invention.
Referring to FIG. 3, when measuring the surface of the non-oriented electrical steel sheet of Steel Type 2 as an example of the present invention using ECCI, regions of high dislocation density due to strain, for example, the red circled regions in FIG. 2, may be observed.
FIG. 4A to FIG. 4E illustrate enlarged views of regions of high dislocation density in Steel Type 2 as a comparative example and Steel Type 10 as an example of the present invention.
Referring to FIG. 4A and FIG. 4B, it can be confirmed that contrast is generated in the image locally due to strain, based on a 2 µm accumulation standard. Referring to FIG. 3C, when FIG. 3A and FIG. 3B are enlarged based on a 1 µm scale, it can be confirmed that the dislocation density can be observed to a degree that can be specifically calculated on the ECCI image.
FIG. 3D and FIG. 3E are enlarged regions where there is no shading in the ECCI image as a result of Steel Type 10 as an example of the present invention, and unlike FIG. 3A to FIG. 3C, dense regions of dislocations cannot be confirmed.

Based on the above, Table 3 below will be described as follows.

(Table 3)

Steel Type	Average Grain Size [µm]	1/3 Grain Fraction [%]	3x Grain Fraction [%]	Dislocation Density (m^-2) more than 10¹² less than 10¹⁶ Fraction [%]	W15/50 [W/kg]	W15/50 Rolling Direction [W/kg]	W10/400 [W/kg]	W10/400 Rolling Direction [W/kg]
Steel Type 1	81.5	3	3	0.93	1.95	1.69	12.1	11.07	Inventive Material
Steel Type 2	59.0	5.3	0.0	0.50	2.40	2.31	16.5	16.1	Comparative Material
Steel Type 3	55.0	5.1	0.0	0.41	2.45	2.38	17.8	17.1	Comparative Material
Steel Type 4	53.0	6.3	0.0	0.38	2.55	2.48	17.6	17.0	Comparative Material
Steel Type 5	62.8	3.1	3.3	0.64	2.27	1.80	14.3	12.6	Inventive Material
Steel Type 6	121.3	3.5	3.3	1.97	2.19	1.95	14.8	13.6	Inventive Material
Steel Type 7	40.4	2.7	2.6	0.11	1.43	1.32	12.8	11.7	Inventive Material
Steel Type 8	69.2	3.0	2.9	0.77	1.80	1.51	12.9	11.7	Inventive Material
Steel Type 9	72.2	2.8	2.5	0.87	1.74	1.56	12.7	11.8	Inventive Material

When the slab composition, the preliminary annealing condition, and the cold rolled sheet annealing condition, which are the conditions of the invention described in Table 1, Table 2, and Table 3, are satisfied, an electrical steel sheet having uniform grain sizes in the steel sheet, no concentrated dislocations in the steel sheet, excellent iron loss in the rolling direction, and excellent average iron loss in the rolling direction and the direction perpendicular to the rolling may be manufactured. Table 4 shows that a slab with a component including Si: 3.4 wt%, Al: 0.8 wt%, Mn: 0.5 wt%, N: 0.002 wt%, S: 0.002 wt%, Ti: 0.002 wt%, the balance being Fe and inevitable impurities was manufactured, heated to 1,150 °C, and then hot-rolled at a finishing temperature of 900 °C to manufacture a hot-rolled steel sheet with a thickness of 1.8 mm. The hot-rolled steel sheet was subjected to preliminary annealing at a temperature of 1,050 °C. It was cold-rolled to 0.3 mm, heated to a temperature of 850 °C or higher in a reducing atmosphere for 11 seconds, and then cooled from 850 °C to 800 °C for 10 seconds, thereby performing cold-rolled sheet annealing.

In addition to the conditions described above, other conditions were implemented under the conditions described in Table 4, and the average grain size, the fraction of grains smaller than 1/3 of the average grain size, and the fraction of grains larger than 3 times the average grain size were measured, and the area in the region where dislocations were densely concentrated was derived. In addition, the magnetism was measured and recorded in Table 4.

(Table 4)

	Tensile Stress Rolling Direction Angle [°]	Tensile Stress Vertica I Angle [°]	Tensile Stress Magnitude [kgf/mm²]	Steel Sheet Thickness [mm]	Average Grain Size [µm]	1/3 Grain Fracti on [%]	3x Grain Size Fracti on [%]	Dislocatio n Density (m^-2) more than 10¹² less than 10¹⁶ Fraction [%]	W15/50 [W/kg]	W15/50 Rolling Direction [W/kg]	W10/400 [W/kg]	W10/400 Rolling Direction [W/kg]
Steel Type 10_1	0.01	90	0.60	0.30	75.0	2.5	3.0	0.3	1.95	1.85	14.5	13.5	Inventive Material
Steel Type10_2	2.5	90	0.60	0.30	75.0	2.5	3.0	2.3	2.00	1.90	14.7	13.7	Inventive material
Steel Type 10_3	5	90	1.00	0.30	75.0	2.5	3.0	5.7	2.03	1.95	14.9	14.2	Comparati ve Material
Steel Type10_4	0.01	85	1.00	0.30	75.0	2.5	3.0	6.1	2.05	1.98	15.0	14.6	Comparati ve Material
Steel Type10_5	0.01	94	1.00	0.30	75.0	2.5	3.0	5.3	2.10	2.03	15.0	14.7	Comparati ve Material

Referring to Table 4, it can be seen that the region where dislocations are concentrated differs significantly depending on the angular relationship between the tensile stress and the sheet surface in the cold-rolled sheet annealing, and accordingly, the iron loss in the rolling direction and the average iron loss change significantly. Table 5 shows that a slab containing components of Si: 3.4%, Al: 0.8%, Mn: 0.5%, N: 0.002%, S: 0.002%, and Ti: 0.002%, the balance being Fe and inevitable impurities, was manufactured, heated to 1,150 °C and hot-rolled at a finishing temperature of 900 °C to manufacture a hot-rolled steel sheet with a thickness of 1.8 mm. The hot-rolled steel sheet was pre-annealed at a temperature of 1,050 °C. It was cold-rolled to 0.3 mm, heated to a temperature of 850 °C or higher in a reducing atmosphere for 12 seconds, and then cooled from 850 °C to 800 °C for 10 seconds, thereby performing cold-rolled sheet annealing.

Steel Type	Re duc ing Atm osp her e	Heati ng Time [se]	Cooli ng Time [sec]	Tensil e Stress Rollin 9 Directi on Angle [°]	Tensil e Stres s Vertic al Angle [°]	Tensile Stress Magnitude [kgf/mm²]	Steel Sheet Thickn ess [mm]	Avera ge Grain Size [µm]	1/3 Grain Fracti on [%]	3x Grain Size Fracti on [%]	Dislocatio n Density (m^-2) more than 10¹² less than 10¹⁶ Fraction [%]	W15/50 [W/kg]	W15/50 Rolling Direction [W/kg]	W10/400 [W/kg]	W10/40 0 Rolling Directio n [W/kg]
Steel Type 11_1	○	12	10	0.01	90	0.10	0.30	75.0	2.5	3.0	0.0	2.00	1.96	14.4	14.1	Inventive material
Steel Type 11_2	○	12	10	0.02	90	0.80	0.30	75.0	2.5	3.0	1.0	1.95	1.85	14.5	13.5	Inventive Material
Steel Type 11_3	○	12	10	0.01	90	2.00	0.30	75.0	2.5	3.0	5.7	2.20	2.10	15.6	15.0	Comparati ve Material

In addition to the conditions described above, other conditions were implemented as described in Table 5, and the average grain size, the fraction of grains smaller than 1/3 of the average grain size, and the fraction of grains larger than 3 times the average grain size were measured, and the area of the region where dislocations were densely concentrated was derived. In addition, the magnetism was measured and recorded in Table 5.

(Table 5)

As shown in Table 5, it can be confirmed that the size of the tensile stress between the tensile stress and the sheet surface in the final annealing and the region of dislocation concentration significantly differ depending on the angle between the tensile stress and the sheet surface, and accordingly, it can be confirmed that the iron loss in the rolling direction and the average iron loss change significantly. Therefore, when the conditions of the present invention are satisfied, it is possible to manufacture a steel sheet having both excellent average iron loss and iron loss in the rolling direction. The average iron loss refers to the iron loss measurement of a typical non-oriented electrical steel sheet, and is the iron loss result measured by loading half of the sample of the Epstein measurement method in the iron loss measuring device in the rolling direction and the other half in the vertical rolling direction, and the iron loss in the rolling direction refers to the iron loss value measured by preparing the sample only in the rolling direction like a grain-oriented electrical steel sheet and loading it into an iron loss measuring device.

Table 6 below describes whether Steel Type 1 to Steel Type 11_3 satisfy Equation 1 to Equation 4 of the present invention.

(Table 6)

Steel Type	[Equation 1]	Whether Equation 1 is satisfied	[Equation 2]	Whether Equation 2 is satisfied	[Equation 3]	Whether Equation 3 is satisfied	[Equation 4]	Whether Equation 4 is satisfied
Steel Type	W10/400 Iron Loss (W/kg) < 6+ (t/0.04)^1.1	Whether Equation 1 is satisfied	W15/50 Iron Loss (W/kg) < 0.7+ (t/0.03)^1/5	Whether Equation 2 is satisfied	W15/50 Rolling Direction Iron Loss (W/kg) < 0.6+ (t/0.03)^1/6	Whether Equation 3 is satisfied	W10/400 Rolling Direction Iron Loss (W/kg) < 5+ (t/0.04)^1.1	Whether Equation 4 is satisfied
Steel Type 1	14.17	TRUE	2.50	TRUE	2.10	TRUE	13.17	TRUE
Steel Type 2	14.17	FALSE	2.50	TRUE	2.10	FALSE	13.17	FALSE
Steel Type 3	14.17	FALSE	2.50	TRUE	2.10	FALSE	13.17	FALSE
Steel Type 4	14.17	FALSE	2.50	FALSE	2.10	FALSE	13.17	FALSE
Steel Type 5	15.11	TRUE	2.69	TRUE	2.26	TRUE	14.11	TRUE
Steel Type 6	15.07	TRUE	2.68	TRUE	2.25	TRUE	14.07	TRUE
Steel Type 7	13.11	TRUE	2.29	TRUE	1.92	TRUE	12.11	TRUE
Steel Type 8	13.34	TRUE	2.33	TRUE	1.96	TRUE	12.34	TRUE
Steel Type 9	12.98	TRUE	2.26	TRUE	1.90	TRUE	11.98	TRUE
Steel Type 10_1	15.17	TRUE	2.70	TRUE	2.27	TRUE	14.17	TRUE
Steel Type 10_2	15.17	TRUE	2.70	TRUE	2.27	TRUE	14.17	TRUE
Steel Type 10_3	15.17	TRUE	2.70	TRUE	2.27	TRUE	14.17	FALSE
Steel Type 10_4	15.17	TRUE	2.70	TRUE	2.27	TRUE	14.17	FALSE
Steel Type 10_5	15.17	TRUE	2.70	TRUE	2.27	TRUE	14.17	FALSE
Steel Type 11_1	15.17	TRUE	2.70	TRUE	2.27	TRUE	14.17	TRUE
Steel Type 11_2	15.17	TRUE	2.70	TRUE	2.27	TRUE	14.17	TRUE
Steel Type 11_3	15.17	FALSE	2.70	TRUE	2.27	TRUE	14.17	FALSE

Referring to Table 6, it was confirmed that the examples of the present invention effectively reduced iron loss by satisfying Equation 1 to Equation 4. In contrast, it was confirmed that the comparative examples did not satisfy at least one of Equation 1 to Equation 4. As described above, the present invention has confirmed that, through Table 1 to Table 6, a steel sheet having excellent rolling direction and average iron loss may be manufactured by satisfying the conditions of the present invention. The present invention may be embodied in many different forms, and should not be construed as being limited to the disclosed embodiments and/or examples. In addition, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the technical spirit and essential features of the present invention. Therefore, it is to be understood that the above-described embodiments and/or examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

Claims

A non-oriented electrical steel sheet, wherein
an area fraction of grains having a grain size of less than 1/3 times an average grain size is less than 5%, and

an area fraction of grains having a dislocation density of more than 10¹²/m² and less than or equal to 10¹⁶/m² is less than 5% of a total area.
The non-oriented electrical steel sheet of claim 1, wherein
an area fraction of grains having a grain size of more than 3 times the average grain size is less than 5%.
The non-oriented electrical steel sheet of claim 1, wherein
the non-oriented electrical steel sheet includes, in wt%, Si: 0.1 to 6.5%, Al: 0.001 to 6.5%, Mn: 0.01 to 20%, C: 0.0010 to 0.015%, N: 0.0003 to 0.001%, S: 0.0003 to 0.001%, Ti: 0.0003 to 0.001%, and the balance including Fe and inevitable impurities.
The non-oriented electrical steel sheet of claim 1, wherein
the average grain size is 40 to 250 µm.
The non-oriented electrical steel sheet of claim 1, wherein
a thickness of the non-oriented electrical steel sheet is 0.03 to 0.5 mm.
The non-oriented electrical steel sheet of claim 5, wherein
an iron loss (W10/400) and the thickness (t) of the non-oriented electrical steel sheet satisfy the following Equation 1: $W 10 / 400 Iron loss (W / kg) < 6 + {(t / 0.04)}^{1.1}$

(In Equation 1, t represents the thickness (mm) of the non-oriented electrical steel sheet).
The non-oriented electrical steel sheet of claim 5, wherein
an iron loss (W15/50) and the thickness (t) of the non-oriented electrical steel sheet satisfy the following Equation 2: $W 15 / 50 Iron loss (W / kg) < 0.7 + {(t / 0.03)}^{1 / 5}$

(In Equation 2, t represents the thickness (mm) of the non-oriented electrical steel sheet).
A method of manufacturing a non-oriented electrical steel sheet, comprising:
a step of hot-rolling a slab to manufacture a hot-rolled steel sheet;

a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and

a cold-rolled steel sheet annealing step of annealing the cold-rolled steel sheet,

wherein in the cold-rolled steel sheet annealing step,

a tensile stress of more than 0.01 to less than 1.0 kgf/mm² may be applied in a rolling direction (RD direction) of a coil at a temperature of 650 °C or higher,

a direction of a tensile stress applied to the cold-rolled steel sheet forms an angle within 3 ° with the rolling direction (RD direction) of the coil, and

an angle formed with a normal direction (ND direction) of a rolling surface of the cold-rolled steel sheet is greater than 87° and less than or equal to 93°.
The method of manufacturing the non-oriented electrical steel sheet of claim 8, wherein
the slab includes, in wt%, Si: 0.1 to 6.5%, Al: 0.001 to 6.5%, Mn: 0.01 to 20%, C: 0.0010 to 0.015%, N: 0.0003 to 0.01 %, S: 0.0003 to 0.01 %, Ti: 0.0003 to 0.01%, and the balance including Fe and inevitable impurities.
The method of manufacturing the non-oriented electrical steel sheet of claim 8, further comprising
a hot-rolled steel sheet annealing step of heating the hot-rolled steel sheet, wherein the hot-rolled steel sheet annealing step is a step of heating the hot-rolled steel sheet to 850 to 1,150 °C.
The method of manufacturing the non-oriented electrical steel sheet of claim 8, wherein
the cold-rolled steel sheet annealing step includes a heating step of heating the cold-rolled steel sheet to 820 °C or higher and a cooling step of cooling from 820 to 900 °C to 750 to 850 °C.
The method of manufacturing the non-oriented electrical steel sheet of claim 8, wherein
in the cold-rolled steel sheet annealing step, the heating step is performed for a time within 60 seconds.
The method of manufacturing the non-oriented electrical steel sheet of claim 8, wherein
in the cold-rolled steel sheet annealing step, the cooling step is performed for a time of 5 seconds or more.
The method of manufacturing the non-oriented electrical steel sheet of claim 8, wherein
in the cold-rolled steel sheet annealing step, the cooling step cools a sheet surface perpendicular to the direction of gravity.
The method of manufacturing the non-oriented electrical steel sheet of claim 8, wherein
the cold-rolled steel sheet annealing step is annealing in a reducing atmosphere.