Non-oriented electrical steel sheet and manufacturing method therefor

Abstract

A manufacturing method for a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: a step of hot rolling a slab to manufacture a hot-rolled steel sheet; a step of hot-band annealing the hot-rolled steel sheet; a step of primarily cold rolling the hot-band-annealed hot-rolled steel sheet; a step of decarburization annealing the primarily cold-rolled steel sheet; a step of secondarily cold rolling the steel sheet that has been decarburization annealed; and a non-oxidizing annealing step of annealing, in a non-oxidization atmosphere, the steel sheet that has been secondarily cold-rolled.

Description

Non-oriented electrical steel sheet and manufacturing method thereof

[0001] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, wherein the non-oriented electrical steel sheet has improved magnetism in the rolling direction by including a decarburization annealing process between multiple cold rolling processes.

[0002] Non-oriented electrical steel sheets are used as core materials in rotating machines such as motors and generators and stationary machines such as small transformers, and play an important role in determining the energy efficiency of electrical equipment.

[0003] Recently, due to strengthened motor efficiency regulations, the use of high-efficiency motors has increased significantly.

[0004] To improve the efficiency of these motors, either the iron loss or the copper loss must be reduced.

[0005] These iron and copper losses are significantly affected by the magnetic properties of the electrical steel used in the motor core. Therefore, motor manufacturers are increasingly using low-iron-loss electrical steel instead of the traditional high-iron-loss electrical steel.

[0006] In order to reduce copper loss, a method is used to lower the design magnetic flux density than before or to lower the excitation current at the design magnetic flux. However, in order to use the latter method, it is necessary to improve the magnetic flux density of the electrical steel sheet.

[0007] High-flux-density electrical steel, in particular, offers the advantage of improved torque, enabling motors with frequent on / off cycles to generate high outputs quickly. Manufacturing high-flux-density electrical steel requires a reduced silicon content, but this low content, a resistivity-increasing element, leads to high core loss. Therefore, the development of electrical steel with both low core loss and high flux density is necessary.

[0008] Structurally, torque in a typical radial motor is proportional to the square of the rotor diameter times the length of the cylindrical stator. Therefore, to increase torque, the length of the motor's cylindrical stator must be increased, which increases the overall motor volume.

[0009] Meanwhile, unlike the conventional radial motor structure, the axial flux motor has a stator and rotor arranged axially parallel, so that magnetic force is transmitted to the rotor in the axial direction through the stator, generating torque. The magnitude of the torque is proportional to the cube of the cylindrical rotor diameter. In other words, it can be said to be a structure that can generate high torque even in a small space. Since the magnetic force generated by the current applied to the stator is transmitted to the rotor magnet in the axial direction, the application of a magnetic material with particularly excellent magnetic properties in one direction is required.

[0010] The normal oriented electrical steel sheet has a crystal orientation of {110}. <001> It is a soft magnetic material with excellent magnetic properties in the rolling direction, composed of crystal grains with the so-called Goss orientation. This grain-oriented electrical steel sheet is manufactured by rolling the final thickness through slab heating, hot rolling, hot-rolled sheet annealing, and cold rolling, and then going through primary recrystallization annealing and high-temperature annealing for secondary recrystallization formation.

[0011] Since MgO is coated on the surface after decarburization annealing and a metal oxide layer (also called a base coating layer) mainly composed of Mg2SiO4 is formed during high-temperature annealing, unlike non-oriented electrical steel sheets used in conventional motor cores, there is a problem that the mold is damaged during the punching process due to the metal oxide layer on the surface.

[0012] In addition, since the conventional oriented electrical steel sheet has a large number of Goss grains, the magnetic properties in the rolling direction are excellent, but the magnetic properties in the direction perpendicular to the rolling are inferior, so when used for an axial flux motor, there is a problem that the efficiency of the motor is reduced.

[0013] One embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, wherein the non-oriented electrical steel sheet has improved magnetism in the rolling direction by including a decarburization annealing process between multiple cold rolling processes.

[0014] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of hot-rolling a slab to manufacture a hot-rolled steel sheet; the step of first cold-rolling the hot-rolled steel sheet; the step of decarburization annealing the first cold-rolled steel sheet; the step of second cold-rolling the steel sheet on which decarburization annealing is completed; and the non-oxidation annealing step of annealing the steel sheet on which the second cold-rolling is completed in a non-oxidizing atmosphere.

[0015] The slab may contain, by weight %, Si: 0.3% to 4.0%, C: 0.03% to 0.4%, and the remainder being Fe and unavoidable impurities.

[0016] The slab may further contain Mn: up to 0.1 wt% and S: up to 0.005 wt%.

[0017] The step of annealing the hot-rolled steel sheet may further include a step of annealing the hot-rolled steel sheet, and the step of annealing the hot-rolled steel sheet may include a decarburization process.

[0018] The hot-rolled plate annealing step can be performed at a temperature of 850℃ to 1000℃ and a dew point temperature of 70℃ or lower.

[0019] The decarburization annealing step can be performed at a temperature of 750°C to 1000°C and a dew point temperature of 25°C to 70°C.

[0020] The decarburization annealing step can be performed in the austenite single-phase region or in the region where a composite phase of ferrite and austenite exists.

[0021] After the decarburization annealing step, the carbon content in the steel sheet may be 0.005 wt% or less.

[0022] The decarburization annealing step and the secondary cold rolling step may be repeated two or more times.

[0023] The first cold rolling step may have a reduction ratio of 70 to 80%.

[0024] The non-oxidizing annealing step can be performed at a soaking temperature of 750 to 1050°C for 60 seconds to 5 minutes.

[0025] The non-oxidizing annealing step can be performed in an atmosphere with a dew point temperature of -20℃ or lower.

[0026] According to one embodiment of the present invention, a non-oriented electrical steel sheet is {110} <001> The area fraction of crystal grains forming an angle of less than 15˚ is 20 to 60%, and {100} <001> The area fraction of crystal grains forming an angle of 15˚ or less may be 5 to 20%.

[0027] Among all crystal grains, the ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) (D2 / D1) may be 0.5 or more, and may account for 95% or more of the total area of ​​the crystal grains.

[0028] The fraction of crystal grains having a crystal grain size of 30 ㎛ to 200 ㎛ among the entire crystal grains may be 80 area% or more.

[0029] Electrical steel sheets may contain, in weight %, Si: 0.3% to 4.0%, C: 0.005% or less (excluding 0%), and the remainder being Fe and unavoidable impurities.

[0030] The electrical steel sheet may further contain Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0031] A non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetism in all directions and at the same time excellent magnetism in the rolling direction, and thus can be particularly usefully used for an axial flux motor.

[0032] Additionally, since it can be manufactured through a continuous process, the manufacturing time can be relatively shortened and productivity can be improved.

[0033] Figure 1 is a photograph of the surface of a non-oriented electrical steel sheet manufactured by Steel No. 2, analyzed by EBSD.

[0034] Figure 2 is a photograph of the surface of a non-oriented electrical steel sheet manufactured from steel No. 2, analyzed by EBSD.

[0035]

[0036] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, 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.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0038] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0039] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0040] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0041] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0042] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0043]

[0044] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab to manufacture a hot-rolled steel sheet; hot-rolling the hot-rolled steel sheet; first cold-rolling the hot-rolled steel sheet annealed; decarburization annealing the first cold-rolled steel sheet; second cold-rolling the steel sheet on which decarburization annealing is completed; and a non-oxidation annealing step of annealing the steel sheet on which the second cold rolling is completed in a non-oxidizing atmosphere.

[0045] Below, each step is explained in detail.

[0046] First, the slab is hot rolled.

[0047] The slab may contain, by weight %, Si: 0.3% to 4.0%, C: 0.03% to 0.4%, and the remainder being Fe and unavoidable impurities.

[0048] The reasons for limiting the composition are as follows.

[0049] Si improves core loss by lowering the magnetic anisotropy of electrical steel and increasing the resistivity. When the Si content is less than 0.3 wt%, the core loss becomes poor, and when it exceeds 4.0 wt%, the brittleness increases. Therefore, the Si content in the non-oriented electrical steel after the slab and final non-oxidation annealing step may be 0.3% to 4.0 wt%. More specifically, the Si content may be 0.4% to 3.0 wt%. More specifically, the Si content may be 0.5% to 2.0 wt%.

[0050] Carbon (C) content in the slab may be 0.03 to 0.4 wt% because the Goss crystal grains in the surface layer need to diffuse to the center during decarburization annealing, and the C in the center needs to escape to the surface layer. More specifically, the C content in the slab may be 0.15 to 0.3 wt%. In addition, the carbon content in the finally manufactured non-oriented electrical steel sheet after decarburization is completed may be 0.0050 wt% or less. More specifically, it may be 0.002 wt% or less. More specifically, it may be 0.0005 to 0.0020 wt%.

[0051] The slab may further contain Mn: up to 0.1 wt% and S: up to 0.005 wt%.

[0052] Mn and S form MnS precipitates, which inhibit the growth of Goss grains that diffuse toward the center during the decarburization process. Therefore, it is preferable not to add Mn or S. However, considering the amount that is unavoidably mixed during the steelmaking process, the Mn and S contents in non-oriented electrical steel sheets after the slab and final annealing stages can be controlled to Mn: 0.1 wt% or less and S: 0.005 wt% or less, respectively.

[0053] The remainder includes Fe and unavoidable impurities. Unavoidable impurities are impurities mixed in during the steelmaking step and the manufacturing process of non-oriented electrical steel sheets, and since this is widely known in the field, a detailed description is omitted. Specifically, components such as Al, N, Ti, Mg, and Ca react with oxygen in steel to form oxides, and therefore, strong suppression is required, and therefore, each component can be managed to 0.005 wt% or less. In one embodiment of the present invention, the addition of elements other than the alloy components described above is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. When additional elements are further included, they are included in place of the remainder, Fe.

[0054] More specifically, the slab may be composed of, by weight %, Si: 0.3% to 4.0%, C: 0.03% to 0.4%, and the remainder being Fe and inevitable impurities.

[0055] The slab can be heated before hot rolling. The slab heating temperature can be 1050℃ to 1350℃, which is higher than the usual heating temperature. When the temperature is high during slab reheating, there is a problem that the hot-rolled structure becomes coarser, which adversely affects magnetism. However, the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention has a higher carbon content than in the past, so that even if the slab reheating temperature is high, the hot-rolled structure does not become coarser, and by reheating at a higher temperature than in the usual case, it is advantageous during hot rolling. However, when the reheating temperature is too high, the solid solubility of precipitates such as TiN and AlN increases, so that a large number of fine precipitates are distributed during cooling, which acts to hinder the growth of crystal grains on the surface.

[0056] Hot rolling can be used to manufacture hot-rolled sheets having a thickness of 1.50 to 4.00 mm by applying an appropriate rolling ratio in the final cold rolling stage so that the final product thickness can be manufactured. More specifically, hot-rolled sheets having a thickness of 1.80 to 2.60 mm can be manufactured.

[0057] There are no special restrictions on the hot rolling temperature or cooling temperature, but for example, if the magnetism is excellent, the hot rolling end temperature can be set to 950℃ or lower, and the cooling can be done rapidly with water so that the coiling can be done at 600℃ or lower.

[0058] After hot rolling, a step of hot-rolled sheet annealing may be further included. At this time, the hot-rolled sheet annealing may include a decarburization process. Specifically, the hot-rolled sheet annealing may be performed at a temperature of 850°C to 1000°C and a dew point temperature of 70°C or lower. More specifically, the annealing may be performed at a dew point temperature of -70°C to 70°C. After the annealing described above, additional annealing may be performed at a temperature of 1000°C to 1200°C and a dew point temperature of 0°C or lower. After the hot-rolled sheet annealing, pickling may be performed.

[0059] Next, primary cold rolling is performed to manufacture cold rolled steel sheets.

[0060] In the manufacturing process of conventional grain-oriented electrical steel sheets, it is known that it is effective to perform cold rolling once at a high pressure reduction rate close to 90%. This is because it creates an environment favorable for grain growth of only Goss grains among the primary recrystallized grains. However, the manufacturing method of a non-oriented electrical steel sheet according to an embodiment of the present invention does not utilize the abnormal grain growth of Goss grains, but internally diffuses Goss grains generated in the surface layer by decarburization annealing and cold rolling, so it is advantageous to form a large number of Goss grains distributed in the surface layer. In addition, in order to use it as a core for AFM, since a structure in which not only Goss but also Cube grains are mixed at an appropriate ratio is advantageous for generating magnetic field lines, a reduction rate that can simultaneously form Cube grains can be applied.

[0061] Therefore, when cold rolling is performed at a reduction ratio of 70% to 80%, Goss texture may be formed in large numbers in the surface layer. More specifically, it may be 72% to 80%.

[0062] Next, the first cold-rolled steel sheet is decarburized and annealed. At this time, the decarburization annealing step can be performed in the austenite single-phase region or the region where the ferrite and austenite composite phases exist. Specifically, the annealing can be performed at a temperature of 750°C to 1000°C and a dew point temperature of 25°C to 70°C. In addition, the atmosphere can be a mixed gas atmosphere of hydrogen and nitrogen. In addition, after the decarburization annealing, the carbon content in the steel sheet can be 0.005 wt% or less. More specifically, the annealing can be performed at a temperature of 750°C to 900°C. The annealing time can be performed for 60 seconds to 5 minutes. More specifically, it can be performed for 90 to 300 seconds.

[0063] During this decarburization annealing process, the grain size on the surface of the electrical steel sheet grows coarsely, but the grains inside the electrical steel sheet remain fine-grained. The average grain diameter after this decarburization annealing can be 150 to 250 μm. In this case, the grains are surface ferrite grains. In addition, the grain diameter refers to the diameter of an imaginary circle having the same area as the grains. The reference plane is a plane parallel to the rolling vertical plane (TD plane).

[0064] Next, the steel sheet, which has undergone decarburization annealing, undergoes a second cold rolling process. Since the second cold rolling process is identical to the first cold rolling process, a detailed description will be omitted. The reduction ratio during the second cold rolling process may range from 50 to 80%. More specifically, it may range from 50 to 70%.

[0065] The above-described decarburization annealing step and secondary cold rolling step can be repeated two or more times. By repeating the process two or more times, a large number of Goss grain structures and cube grain structures can be formed in the surface layer. In one embodiment of the present invention, the Goss grain structure means a grain structure that forms an angle of 15 degrees or less with the Goss direction. That is, the rolling surface (ND plane) and the rolling direction (RD direction) of the steel sheet are {110} of the crystal grains. <001> It refers to crystal grains that form an angle of less than 15 degrees with the direction. The cubic aggregate structure is {100} <001> It refers to crystal grains that form an angle of 15˚ or less with the direction.

[0066]

[0067] Next, the steel sheet that has undergone secondary cold rolling is annealed in a non-oxidizing atmosphere.

[0068] In one embodiment of the present invention, annealing is performed in a non-oxidizing atmosphere immediately after secondary cold rolling, and additional decarburization annealing can be omitted. If decarburization annealing is added after secondary cold rolling, the cubic structure within the steel sheet may be converted to a Goss structure, and the remaining cubic structure may become insufficient. As a result, while magnetism in the rolling direction may be improved, magnetism in directions other than the rolling direction may be significantly reduced.

[0069] The non-oxidizing annealing step can be performed at a soaking temperature of 750 to 1050°C for 60 seconds to 5 minutes.

[0070] The purpose of the non-oxidizing annealing step is to grow the grains to a certain size or larger. This can improve the magnetism, especially the high-frequency iron loss. If the soaking temperature is too low or the soaking time is too short, the Goss grains and cubic grains may not develop properly. If the soaking temperature is too high or the soaking time is too long, the Goss grains and cubic grains do not remain in a fine size that is advantageous for the high-frequency iron loss, but grow, and the problem of the fraction of Goss grains and cubic grains actually decreasing during the growth process may occur. More specifically, the soaking temperature of the non-oxidizing annealing can be 800 to 1000°C. More specifically, it can be 900 to 970°C.

[0071] The secondary non-oxidizing annealing step can be performed at a dew point temperature of -20°C or lower. If the dew point temperature is too high, an oxide layer may form on the surface, adversely affecting magnetism. More specifically, annealing can be performed in an atmosphere containing at least 99% hydrogen by volume and with a dew point temperature of -50°C to -30°C.

[0072] After the primary cold rolling step, the non-oxidizing annealing step can be performed as a continuous process. A continuous process means that there is no need for batch processes, such as coiling the steel sheet and annealing it. As mentioned above, the decarburization annealing step and the non-oxidizing annealing step can be completed in a few minutes or less, making a continuous process possible.

[0073]

[0074] The final non-oriented electrical steel sheet manufactured after completing the non-oxidation annealing step is {110} <001> The area fraction of crystal grains forming an angle of less than 15˚ is 20 to 60%, and {100} <001> The area fraction of crystal grains forming an angle of 15˚ or less may be 5 to 20%.

[0075] At this time, the area fraction of the crystal grains is measured based on a plane parallel to the rolling plane (ND plane), and can be measured at points 1 / 4t to 3 / 4t of the steel sheet thickness. The measurement method is not particularly limited, but can be measured using EBSD.

[0076] In one embodiment of the present invention, since Goss crystal grains and cube crystal grains are appropriately present in the steel sheet, the magnetism in the overall direction is improved, and among them, the magnetism in the rolling direction is further improved, so that it can be usefully used for an axial flux motor. More specifically, {110} <001> The area fraction of crystal grains forming an angle of less than 15˚ is 40 to 55%, and {100} <001> The area fraction of crystal grains forming an angle of 15˚ or less may be 7 to 15%.

[0077] In one embodiment of the present invention, the ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) among all crystal grains (D2 / D1) may be 0.5 or more, and the crystal grains may account for 95% or more of the area.

[0078] In addition, the fraction of grains having a grain size of 30 ㎛ to 200 ㎛ among the total grains may be 80 area% or more. This is because in one embodiment of the present invention, decarburization annealing and non-oxidation annealing are performed for a short time. When annealing is performed for a long time of 1 hour or more through batch annealing as in the production of a conventional grain-oriented electrical steel sheet, the average grain size increases by 5 mm or more, which is completely different from the shape and size distribution of the grain size of the non-oriented electrical steel sheet according to one embodiment of the present invention. More specifically, the fraction of grains having a grain size of 30 ㎛ to 200 ㎛ among the total grains may be 90% to 99%. Such fine grains contribute to improving high-frequency iron loss. The fraction of grains refers to the area fraction, and can be obtained by calculating the area of ​​grains having the corresponding grain size in any cross-section of the steel sheet. More specifically, it can be obtained based on the steel sheet rolling vertical plane (ND plane). The grain size of a crystal can be calculated by assuming a virtual circle with the same area as the crystal grain and using the diameter of that circle.

[0079]

[0080] In one embodiment of the present invention, the effect may be realized by a unique manufacturing process and a unique microstructure generated by the manufacturing process rather than by the alloy composition of the non-oriented electrical steel sheet. Supplementary description of the alloy composition of the non-oriented electrical steel sheet will be given below. The non-oriented electrical steel sheet according to one embodiment of the present invention may include, in wt%, Si: 0.3% to 4.0%, C: 0.005% or less (excluding 0%), and the remainder being Fe and unavoidable impurities. In addition, the non-oriented electrical steel sheet according to one embodiment of the present invention may further include Mn: 0.1 wt% or less and S: 0.005 wt% or less. Since the description of the alloy composition of the non-oriented electrical steel sheet is the same as the description of the alloy composition of the slab described above, redundant description will be omitted.

[0081] In one embodiment of the present invention, the non-oriented electrical steel sheet has excellent magnetism, and particularly excellent magnetism in the rolling direction and the direction perpendicular to the rolling. Specifically, the average magnetic flux density (B) in the rolling direction and the direction perpendicular to the rolling 50 ) can be 1.78 to 1.88 T. In addition, the average iron loss (W) in the rolling direction and the direction perpendicular to the rolling 15 / 50 ) can be 1.5 to 2.0 W / kg. The magnetic flux density in the rolling direction (B 50 ) can be 1.95 to 2.05 T. Iron loss in the rolling direction (W 15 / 50 ) can be 0.80 to 1.5 W / kg.

[0082] In addition, at the same time, in one embodiment of the present invention, the non-oriented electrical steel sheet may have a small deviation in magnetic flux density in the rolling direction and the direction perpendicular to the rolling. Specifically, the deviation may be 5.0 to 15.0%. More specifically, the deviation may be 10.0 to 14.5%. The deviation may be calculated as (magnetic flux density in the rolling direction - magnetic flux density in the direction perpendicular to the rolling) / magnetic flux density in the rolling direction × 100.

[0083] Magnetic flux density (B 50 ) means the magnetic flux density induced in a magnetic field of 5000 A / m. Iron loss (W 15 / 50 ) is the magnitude of the iron loss (W / kg) induced under 1.5 Tesla and 50 Hz conditions.

[0084] Specific examples of the present invention are described below. However, the following examples are merely specific examples of the present invention, and the present invention is not limited to the following examples.

[0085]

[0086] Example 1

[0087] A slab containing 2.0% Si, 0.085% C by weight, and the remainder Fe and unavoidable impurities was heated to 1150℃, hot-rolled to the thickness listed in Table 1 below, and then annealed as a hot-rolled sheet at an annealing temperature of 920℃. After cooling the steel sheet, pickling was performed, and cold-rolled at the reduction ratio listed in Table 1 below to produce a cold-rolled sheet. The cold-rolled sheet was heat-treated at a dew point temperature of 55℃ according to the decarburization annealing temperature and annealing time listed in Table 1 below. Thereafter, cold-rolled again at a reduction ratio of 56% to produce a cold-rolled sheet having a thickness of 0.22 mmt. Non-oxidizing annealing was performed for 2 minutes at a temperature of 950℃ in a mixed gas atmosphere of hydrogen and nitrogen and a dew point temperature of -30℃. The final C content, magnetic flux density, iron loss, and magnetic flux density deviation of the specimens after non-oxidizing annealing were measured and summarized in Table 2 below.

[0088] The crystal grain area fraction was measured using EBSD in the ND plane.

[0089] The magnetism was measured using a Single Sheet Tester.

[0090] Steel No. Hot rolled steel plate thickness (mm) Primary cold reduction ratio (%) Decarburization annealing temperature (℃) Decarburization annealing Time (seconds) 11.256088012521.807288012532.207788012542.558088012552.808288012563.348588012571.807275012581.807282012591.80721050125102.2077750125112.2077820125122.20771050125131.8072680125142.2077680125152.5580680125161.807288045172.207788045182.558088045

[0091] River No. Final C content (ppm) {110} <001> Crystalline grain fraction (area %) {100} <001> Grain fraction (area%) D2 / D1 is 0.5 or more Grain fraction (area%) 30㎛ to 200㎛ Grain fraction (area%) Rolling direction B50(T) Rolling direction perpendicular to the direction B50(T)Deviation(%)Remarks11578397962.031.6518.7Comparative Example21155797961.991.7114.1Example313501096971.991.7313.1Example415331598961.981.7511.6Example515181897981.871.699.6Comparative Example611252196971.821.687.7Comparative Example71353997961.981.7213.1Example81555797961.991.7114.1Example959332598981.881.6910.1B Example 1017461397961.961.7411.2Embodiment 11850996961.981.7213.1Embodiment 1285392295961.861.6710.2Comparative Example 13101521795961.841.679.2Comparative Example 1497412295961.861.6710.2Comparative Example 1585362795961.871.718.6Comparative Example 1659561495961.871.699.6Comparative Example 1766431997951.881.719.0Comparative Example 1874392296961.891.738.5Comparative Example

[0092] As shown in Tables 1 and 2, depending on the conditions during hot rolling, primary cold rolling, decarburization annealing, and non-oxidation annealing, a large number of cube grains and Goss grains are formed, which confirms that the magnetism is oriented in the overall direction and the rolling direction. On the other hand, No. 1, 5, and 6, which have primary cold reduction ratios outside the range, do not form a large number of cube grains or Goss grains, confirming that the magnetism is inferior.

[0093] No. 9 and No. 12, which had too high a temperature during decarburization annealing, showed poor magnetism due to the delayed decarburization and slow crystal growth caused by the formation of a dense oxide layer on the surface, making it difficult to form Goss and Cube orientations.

[0094] During decarburization annealing, No. 13 to 15, which have too low a temperature, show low carbon activity for decarburization, which delays decarburization and thus slows down crystal growth, delaying the formation of Goss and Cube crystal grains, resulting in poor magnetism.

[0095] No. 16 to 18, which have too short decarburization annealing times, show poor magnetism due to incomplete crystal growth, which delays the formation of Goss and Cube crystal grains, as decarburization is not completed.

[0096]

[0097] The present invention is not limited to the above-described embodiments and / or examples, but can be manufactured in various different forms. Those skilled in the art will understand that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments and / or examples should be understood as illustrative in all respects and not restrictive.

Claims

1. A step of manufacturing hot rolled steel plates by hot rolling slabs; A step of first cold rolling the above hot-rolled steel plate; A step of decarburization annealing the first cold rolled steel sheet; A step of performing secondary cold rolling on a steel sheet that has undergone decarburization annealing; and A method for manufacturing a non-oriented electrical steel sheet, comprising a non-oxidizing annealing step of annealing a steel sheet on which secondary cold rolling has been completed in a non-oxidizing atmosphere.

2. In paragraph 1, The above slab is a method for manufacturing a non-oriented electrical steel sheet containing, in wt%, Si: 0.3% to 4.0%, C: 0.03% to 0.4%, and the remainder being Fe and unavoidable impurities.

3. In paragraph 2, A method for manufacturing a non-oriented electrical steel sheet, wherein the above slab further contains Mn: 0.1 wt% or less and S: 0.005 wt% or less.

4. In paragraph 1, Further comprising a step of annealing the hot rolled steel sheet, A method for manufacturing a non-oriented electrical steel sheet including a decarburization process in the step of annealing the hot-rolled sheet.

5. In paragraph 4, A method for manufacturing a non-oriented electrical steel sheet, wherein the step of annealing the hot-rolled sheet is performed at a temperature of 850°C to 1000°C and a dew point temperature of 70°C or lower.

6. In paragraph 1, A method for manufacturing a non-oriented electrical steel sheet, wherein the above decarburization annealing step is performed at a temperature of 750°C to 1000°C and a dew point temperature of 25°C to 70°C.

7. In paragraph 1, A method for manufacturing a non-oriented electrical steel sheet in which the above decarburization annealing step is performed in an austenite single-phase region or a region in which a composite phase of ferrite and austenite exists.

8. In paragraph 1, A method for manufacturing a non-oriented electrical steel sheet having a carbon content of 0.005 wt% or less in the steel sheet after the above decarburization annealing step.

9. In paragraph 1, A method for manufacturing a non-oriented electrical steel sheet, wherein the above-mentioned decarburization annealing step and the above-mentioned secondary cold rolling step are repeated two or more times.

10. In paragraph 1, The above first cold rolling step is a method for manufacturing a non-oriented electrical steel sheet having a reduction ratio of 70 to 80%.

11. In paragraph 1, A method for manufacturing a non-oriented electrical steel sheet, wherein the above non-oxidation annealing step is performed at a soaking temperature of 750 to 1050°C for 60 seconds to 5 minutes.

12. In paragraph 1, The above non-oxidizing annealing step is a method for manufacturing a non-oriented electrical steel sheet in which annealing is performed in an atmosphere having a dew point temperature of -20℃ or lower. 13.{110} <001> The area fraction of crystal grains forming an angle of 15˚ or less is 20 to 60%, {100} <001> Non-oriented electrical steel sheet having an area fraction of grains forming an angle of 15˚ or less of 5 to 20%.

14. In paragraph 13, Non-oriented electrical steel sheet having a difference in magnetic flux density between the rolling direction and the direction perpendicular to the rolling of 10% or more and 20% or less.

15. In paragraph 13, Non-oriented electrical steel sheet having grains having a ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) of 0.5 or more (D2 / D1) in 95 area% or more of the total grains.

16. In paragraph 13, A non-oriented electrical steel sheet having a fraction of grains having a grain size of 30 ㎛ to 200 ㎛ of the total grain size of 80 area% or more.

17. In paragraph 13, The above electrical steel sheet is a non-oriented electrical steel sheet containing, in wt%, Si: 0.3% to 4.0%, C: 0.005% or less (excluding 0%), and the remainder being Fe and unavoidable impurities.

18. In paragraph 17, The above electrical steel sheet is a non-oriented electrical steel sheet further containing Mn: 0.1 wt% or less and S: 0.005 wt% or less.

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