Non-oriented electrical steel sheet and method for manufacturing non-oriented electrical steel sheet

Abstract

Provided according to an embodiment of the present invention are a non-oriented electrical steel sheet having excellent magnetic properties and a method for manufacturing the non-oriented electrical steel sheet, the method comprising the steps of: reheating a slab and then hot rolling same; performing hot annealing; performing cold rolling same; performing decarburization annealing, and performing final annealing, wherein the slab comprises 1.8 wt% to 4.0 wt% (both inclusive) of silicon (Si), 0.05 wt% to 0.5 wt% (both inclusive) of manganese (Mn), 0 wt% (exclusive) to 0.01 wt% (inclusive) of aluminum (Al), 0 wt% (exclusive) to 0.015 wt% (inclusive) of phosphorus (P), 0 wt% (exclusive) to 0.005 wt% (inclusive) of titanium (Ti), 0 wt% (exclusive) to 0.005 wt% (inclusive) of carbon (C), 0 wt% (exclusive) to 0.005 wt% (inclusive) of nitrogen (N), 0 wt% (exclusive) to 0.02 wt% (inclusive) of sulfur (S), and the balance of iron (Fe) and other inevitable impurities, and the decarburization annealing step satisfies equation 1 above.

Description

Non-oriented electrical steel sheet and method for manufacturing non-oriented electrical steel sheet

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing a non-oriented electrical steel sheet.

[0002] Recently, in accordance with global policies to reduce carbon dioxide emissions and prevent global warming, conventional internal combustion engine vehicles are being rapidly replaced by eco-friendly vehicles such as hybrid, electric, and hydrogen cars. Eco-friendly vehicles utilize electric motors to generate the driving force required for the vehicle and can reduce environmental pollution by significantly decreasing the emission of harmful exhaust gases.

[0003] As interest in and demand for such eco-friendly vehicles increase, the demand for electric motors, which generate the driving force of the vehicle, is also rising. An electric motor is a device that uses electricity to generate the driving force required for a vehicle, and it must have excellent energy efficiency to operate for a longer period using the same amount of energy. Furthermore, it must guarantee high output sufficient to replace the output of conventional internal combustion engines.

[0004] To improve the energy efficiency and output of electric motors, it is essential to enhance the magnetic performance of non-oriented electrical steel sheets used as core materials. Non-oriented electrical steel is a material that possesses uniform magnetic properties in all directions regardless of the rolling direction, and its representative magnetic properties include core loss and magnetic flux.

[0005] Iron loss is energy loss that occurs during the magnetization process of a material and can be expressed as energy loss occurring at a specific magnetic flux density and frequency, and can be divided into hysteresis loss and eddy current loss. In addition, magnetic flux density is the number of magnetic field lines induced under a specific magnetic field, and is generally evaluated as the value induced under a magnetic field of 5000 A / m.

[0006] In order to improve the aforementioned iron loss and magnetic flux density, it is necessary to control factors such as the chemical composition, sheet thickness, microstructure, and external shape of the non-oriented electrical steel sheet.

[0007] Conventionally, to reduce the iron loss of electrical steel sheets, methods were used to control the chemical composition of the steel sheet or to thin the material in order to increase the resistivity of the steel. In particular, if the amount of silicon (Si), aluminum (Al), manganese (Mn), etc. added to the steel is increased, the resistivity of the steel increases and the iron loss can be reduced to a certain range, but there is a problem that thinning is difficult because the magnetic flux density decreases and rolling performance deteriorates.

[0008] Furthermore, the magnetic flux density of electrical steel sheets is determined by the arrangement of crystal grains. In particular, magnetization is facilitated by the magnetic anisotropy of iron (Fe) atoms. <100> It is desirable to create an orientational texture uniformly throughout the plate.

[0009] Therefore, there is a need to develop technology that improves magnetic properties by increasing the texture of the tissue that is advantageous for magnetic properties.

[0010] [Prior Art Literature]

[0011] [Patent Literature]

[0012] (Patent Document 1) Korean Registered Patent No. 10-248364

[0013] The present invention has been devised to solve the above problems, and the objective of the present invention is to provide a non-oriented electrical steel sheet having excellent magnetic properties by controlling the alloy composition and a method for manufacturing a non-oriented electrical steel sheet.

[0014] The problems of the present invention are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0015] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of reheating a slab containing silicon (Si) 1.8 wt% or more and 4.0 wt% or less, manganese (Mn) 0.05 wt% or more and 0.5 wt% or less, aluminum (Al) 0 wt% or more and 0.01 wt% or less, phosphorus (P) 0 wt% or more and 0.015 wt% or less, titanium (Ti) 0 wt% or more and 0.005 wt% or less, carbon (C) 0 wt% or more and 0.005 wt% or less, nitrogen (N) 0 wt% or more and 0.005 wt% or less, sulfur (S) 0 wt% or more and 0.02 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities, followed by hot rolling, hot rolling annealing, cold rolling, decarburization annealing, and final annealing.

[0016] At this time, the above decarburization annealing step satisfies the following Equation 1.

[0017] [Equation 1]

[0018] T / (Dt) 2 ≤ 0.27

[0019] In the above Equation 1, T represents the heat treatment temperature during decarburization annealing, and Dt represents the dew point temperature during decarburization annealing.

[0020] In addition, the above decarburization annealing step may be performed by heat treatment at a temperature of 700°C or higher and 950°C or lower for a time of 1 minute or more and 10 minutes or less.

[0021] In addition, the non-oriented electrical steel sheet that has undergone the decarburization annealing step may have an average coating thickness of 1.2㎛ or more.

[0022] In addition, the non-oriented electrical steel sheet produced after the final annealing step can satisfy the following Equation 2.

[0023] [Equation 2]

[0024] Dmax / Davg ≥ 1.5

[0025] In Equation 2 above, Dmax represents the diameter of the largest grain, and Davg represents the average grain diameter.

[0026] In addition, the non-oriented electrical steel sheet that has undergone the final annealing step may have an area fraction of grains having (100) orientation of 50% or more.

[0027] In addition, the non-oriented electrical steel sheet that has undergone the final annealing step has iron loss (W 10 / 400 ) may be 12 W / kg or less.

[0028] A non-oriented electrical steel sheet according to one embodiment of the present invention comprises silicon (Si) 1.8 wt% or more and 4.0 wt% or less, manganese (Mn) 0.05 wt% or more and 0.5 wt% or less, aluminum (Al) 0 wt% or more and 0.01 wt% or less, phosphorus (P) 0 wt% or more and 0.015 wt% or less, titanium (Ti) 0 wt% or more and 0.005 wt% or less, carbon (C) 0 wt% or more and 0.005 wt% or less, nitrogen (N) 0 wt% or more and 0.005 wt% or less, sulfur (S) 0 wt% or more and 0.02 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities, and satisfies Formula 2 below.

[0029] [Equation 2]

[0030] Dmax / Davg ≥ 1.5

[0031] In Equation 2 above, Dmax represents the diameter of the largest grain, and Davg represents the average grain diameter.

[0032] In addition, the area fraction of crystal grains having (100) orientation may be 50% or more.

[0033] Also, iron loss (W 10 / 400 ) may be 12 W / kg or less.

[0034] According to one embodiment of the present invention, by performing decarburization annealing, a texture advantageous to magnetic properties is formed, thereby enabling the realization of a non-oriented electrical steel sheet having excellent magnetic properties and a method for manufacturing a non-oriented electrical steel sheet.

[0035] The effects of the present invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art from the description in the claims.

[0036] Hereinafter, preferred embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention is not limited or restricted by the following embodiments.

[0037] Additionally, when it is stated that a component (or area, layer, part, etc.) is "on," "connected," or "combined" with another component, it means that it may be directly placed / connected / combined with the other component, or that a third component may be placed between them.

[0038] Terms such as "include" or "have" are intended to indicate the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0039] In order to clearly explain the present invention, detailed descriptions of related prior art that are irrelevant to the explanation or that may unnecessarily obscure the essence of the invention have been omitted. Furthermore, when assigning reference numerals to the components of each drawing in this specification, identical or similar reference numerals are assigned to identical or similar components throughout the entire specification.

[0040] Furthermore, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0041] Unless otherwise specified, the notation 'A ~ B' for numerical values ​​A and B shall mean 'A or greater, B or less'. In such notation, if a unit is attached only to numerical value B, that unit shall also apply to numerical value A.

[0042] Also, unless specifically noted otherwise, 1 ppm is 0.0001 wt%.

[0043]

[0044] Method for manufacturing non-oriented electrical steel sheets

[0045] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment disclosed in this specification includes the steps of reheating a slab containing the alloy composition described above and then hot rolling, hot rolling annealing, cold rolling, decarburizing annealing, and final annealing.

[0046] At this time, the slab contains silicon (Si) 1.8 wt% or more and 4.0 wt% or less, manganese (Mn) 0.05 wt% or more and 0.5 wt% or less, aluminum (Al) 0 wt% or more and 0.01 wt% or less, phosphorus (P) 0 wt% or more and 0.015 wt% or less, titanium (Ti) 0 wt% or more and 0.005 wt% or less, carbon (C) 0 wt% or more and 0.005 wt% or less, nitrogen (N) 0 wt% or more and 0.005 wt% or less, sulfur (S) 0 wt% or more and 0.02 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities.

[0047] Before describing the method for manufacturing non-oriented electrical steel sheets, the role and content of alloying elements included in the non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail below.

[0048] Since the content of the alloy components does not substantially change during the manufacturing process of the non-oriented electrical steel sheet described below, the alloy composition of the slab and the alloy composition of the final product, the non-oriented electrical steel sheet, are substantially the same.

[0049]

[0050] Silicon (Si)

[0051] Silicon (Si) is a major additive element in electrical steel sheets and can reduce iron loss by increasing the resistivity of the steel. On the other hand, if silicon is added in small amounts, the effect of improving high-frequency iron loss may be insufficient. However, if silicon is added in excess, magnetic flux density may decrease, and a decrease in cold rolling performance may occur due to increased brittleness. Therefore, it is necessary to appropriately control the silicon content.

[0052] If the silicon content is less than 1.8 weight%, the above-described effect cannot be expected, and if the silicon content exceeds 4.0 weight%, brittleness increases and fracture may occur during cold rolling. Accordingly, the non-oriented electrical steel sheet according to one embodiment may contain silicon in an amount of 1.8 weight% or more and 4.0 weight% or less.

[0053]

[0054] Manganese (Mn)

[0055] Manganese (Mn) is an element that improves magnetic properties by increasing resistivity and reducing iron loss, along with silicon (Si). In addition, it can improve the fraction of textures that are favorable for magnetic properties.

[0056] In addition, manganese can combine with sulfur (S) present in the steel to form precipitates such as MnS. During cold rolling annealing in a reducing atmosphere, MnS reacts with hydrogen (H2) in the atmosphere, causing manganese (Mn) to be redissolved in the steel and sulfur (S) to vaporize in the form of hydrogen sulfide (H2S) and be absorbed into the atmosphere.

[0057] As a result, the surface energy of grains with the {100} orientation, which is favorable for magnetic properties, becomes lower than that of grains with the {111} orientation, which is unfavorable for magnetic properties, allowing grains with the {100} orientation to grow significantly. Additionally, as the amount of MnS that inhibited grain growth decreases, grains with the {100} orientation can grow significantly.

[0058] However, if MnS remains until the end of cold rolling annealing, MnS precipitates inhibit the growth of grains with {100} orientations favorable for magnetic properties, which may result in inferior magnetic properties.

[0059] If the manganese content is less than 0.05 weight%, the effect of improving magnetic properties cannot be expected. In addition, as sulfur (S) in the steel is not precipitated as MnS but is dissolved in atomic form, sulfur (S) is concentrated on the surface of the steel plate and may hinder the growth of crystal grains with {100} orientation.

[0060] On the other hand, if the manganese content exceeds 0.5 weight%, coarse MnS precipitates are formed, which lowers the magnetic flux density and may result in inferior magnetic properties and reduced cold rolling performance.

[0061] Accordingly, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain manganese in an amount of 0.05 weight% or more and 0.5 weight% or less.

[0062]

[0063] Aluminum (Al)

[0064] Aluminum (Al), along with silicon (Si) and manganese (Mn), is an element that increases resistivity and reduces iron loss, and is a major additive element in electrical steel sheets. Aluminum can reduce magnetic anisotropy and thus reduce magnetic deviation. However, aluminum can form fine AlN particles that hinder the movement of magnetic domain walls and affect surface energy, which can hinder the growth of crystal grains with (001) orientation, so it is necessary to control the amount of aluminum added.

[0065] If aluminum is not added, the increase in resistivity is insufficient, which may increase high-frequency iron loss. If the aluminum content exceeds 0.01 weight%, an excessive amount of oxides such as alumina (Al2O3) may be formed, hindering the movement of magnetic domain walls and degrading magnetic properties. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain aluminum in an amount greater than 0 weight% and less than or equal to 0.01 weight%.

[0066]

[0067] Ph(P)

[0068] Phosphorus is a grain boundary segregation element, and if added in excess, problems such as inhibition of grain growth, deterioration of magnetic properties, and reduction of cold rolling performance may occur due to the segregation effect. Therefore, it is desirable to add as little as possible, and a non-oriented electrical steel sheet according to one embodiment of the present invention may contain phosphorus in an amount greater than 0 weight% and less than or equal to 0.015 weight%.

[0069]

[0070] Titanium (Ti)

[0071] Titanium (Ti) is an element with a strong tendency to precipitate and combines with carbon (C), nitrogen (N), etc. in steel to form precipitates such as TiC and TiN. The formed precipitates can inhibit grain growth and degrade magnetic properties. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain titanium in an amount greater than 0 weight% and less than or equal to 0.005 weight%.

[0072]

[0073] Carbon (C)

[0074] Carbon (C) can combine with iron (Fe), titanium (Ti), etc., in the steel to form fine carbides. Fine carbides can reduce permeability and increase iron loss. In addition, if the carbon content exceeds 0.005 weight%, magnetic aging may occur, which may degrade magnetic properties. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain carbon in an amount greater than 0 weight% and less than or equal to 0.005 weight%.

[0075]

[0076] Nitrogen (N)

[0077] If the nitrogen (N) content exceeds 0.005 weight%, it may combine with aluminum (Al) in the steel to form precipitates such as AlN. These precipitates may impede magnetic properties by hindering domain wall movement and inhibiting grain growth. Therefore, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain nitrogen in an amount greater than 0 weight% and less than or equal to 0.005 weight%.

[0078]

[0079] Yellow (S)

[0080] Sulfur (S) is a grain boundary segregation element; when it exists in the form of free atoms, it can accumulate on the surface or grain boundaries of steel sheets during cold-rolled annealing, leading to segregation. In this case, the surface energy of grains with the {111} orientation, which is disadvantageous for magnetic properties, becomes lower than that of grains with the {100} orientation, which is advantageous for magnetic properties. Consequently, grains with the {111} orientation grow instead of grains with the {100} orientation, which can result in inferior magnetic properties.

[0081] In addition, if a large amount of sulfur is added, it may combine with manganese (Mn) to form a large amount of MnS precipitates, and since magnetic properties may be degraded by the precipitates, it is important to control the amount added to 0.02 weight% or less. Accordingly, a non-oriented electrical steel sheet according to one embodiment of the present invention may contain sulfur in an amount greater than 0 weight% and less than or equal to 0.02 weight%.

[0082]

[0083] In addition to the components of the steel described above, the remainder may contain Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking stage and the manufacturing process of non-oriented electrical steel sheets; as this is widely known in the field, a detailed explanation is omitted.

[0084] In one embodiment of the present invention, the addition of elements other than the aforementioned alloy components is not excluded, and various elements may be included within a scope that does not impair the technical spirit of the present invention. If additional elements are included, they may be included to replace the remainder of Fe.

[0085]

[0086] Hereinafter, each step of the method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention will be described in detail.

[0087] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform the step of reheating a slab and then hot rolling. More specifically, the step of reheating a slab and then hot rolling may include a reheating process, a hot rolling process, and a coiling process.

[0088] The reheating process is a process performed prior to the hot rolling process, and may involve reheating the steel for a subsequent process. More specifically, it may be a step of loading a slab into a furnace and heating it uniformly to facilitate plastic deformation.

[0089] At this time, if the reheating temperature is below 1000℃, the rolling load increases, which may cause difficulties in performing hot rolling. On the other hand, if the reheating temperature exceeds 1250℃, precipitates formed by carbon (C), sulfur (S), nitrogen (N), etc., within the steel are redissolved, and fine precipitates may be formed during the subsequent rolling and annealing processes. These fine precipitates can inhibit grain growth and increase iron loss.

[0090] In addition, the reheating time may be performed for 350 minutes or more and 850 minutes or less. If the reheating time is less than 350 minutes, sufficient time may not be secured for the precipitate to be sufficiently dissolved, and the material may be non-homogeneous. On the other hand, if the reheating time exceeds 850 minutes, the problem of increased production costs may arise due to prolonged heating.

[0091] Accordingly, a reheating process according to one embodiment of the present invention can reheat a slab at a temperature within the range of 1000°C or higher and 1250°C or lower for 350 minutes or more and 850 minutes or less.

[0092] Next, a hot rolling process may be performed to form a hot-rolled steel sheet by hot rolling the reheated steel. The hot rolling process may include rough rolling and finish rolling. Here, rough rolling may refer to making the steel into a rolled material having a suitable shape, thickness, and width, and finish rolling may refer to adjusting the steel to a predetermined thickness and width and rolling it at a finishing temperature suitable for the application to achieve a good surface finish.

[0093] At this time, the finishing temperature of the hot rolling process may be carried out at a temperature for the formation of a uniform structure and appropriate strength improvement, and the hot rolling finishing temperature may be 850°C or higher and 1000°C or lower. If the finishing temperature is below 850°C, rolling is performed in a two-phase region, which may result in the formation of a non-uniform structure. If the finishing temperature exceeds 1000°C, a problem may arise in which the strength of the steel material decreases rapidly.

[0094] Subsequently, a coiling process may be performed to coil the hot-rolled steel sheet formed through the hot rolling process. At this time, the coiling temperature may be between 550°C and 750°C. If the coiling temperature is below 550°C, brittleness increases, which may cause the sheet to break during coiling, and the grain size may become too small, preventing sufficient grain growth even after annealing. On the other hand, if the coiling temperature exceeds 750°C, fine precipitates may be generated, which may increase iron loss.

[0095] The thickness of the hot-rolled steel sheet formed through the step of hot-rolling the steel may be 1.8 mm or more and 3.5 mm or less. If the thickness of the hot-rolled steel sheet is excessively thin, less than 1.8 mm, the thickness obtained after cold rolling is insufficient, which may cause shape defects when applied to products. On the other hand, if the thickness of the hot-rolled steel sheet exceeds 3.5 mm, the cold rolling reduction rate increases, which may cause defects such as breakage, roll marks, and camber during cold rolling.

[0096] The step of hot rolling annealing may be a step of hot rolling annealing the hot rolled steel plate to form a hot rolled annealed steel plate.

[0097] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a step of hot rolling annealing after the step of reheating the slab and then hot rolling. The hot rolling annealing step may be a step of performing heat treatment at an appropriate temperature to promote the recrystallization of unrecrystallized grains so as to have uniform equiaxed grains.

[0098] In the present invention, the appropriate temperature for hot rolling annealing may be 900°C or higher and 1100°C or lower. If the hot rolling annealing temperature is below 900°C, the elongated cast structure after hot rolling may remain, causing microstructural non-uniformity. On the other hand, if the hot rolling annealing temperature exceeds 1100°C, it may cause texture imbalance in the final product and degrade magnetic properties.

[0099] In addition, the hot rolling annealing step may have a hot rolling annealing time of 10 seconds or more and 180 seconds or less within the temperature range described above. If the hot rolling annealing time is less than 10 seconds, the annealing may be insufficient and the grains may not grow sufficiently, and if it exceeds 180 seconds, the grains may grow excessively.

[0100] At this time, the heating rate to the above temperature is preferably 20℃ / s or higher, and the cooling rate after heat treatment may be preferably 20℃ / s or higher. A method for manufacturing a non-oriented electrical steel sheet according to one embodiment may additionally perform shot blasting and pickling processes after the hot rolling annealing step and before the cold rolling step described later.

[0101] Specifically, shot blasting can be performed by rotating fine particles having a size of 2㎛ or more and 1200㎛ or less at a speed of 2000 rpm or more, and then spraying them under high-speed conditions of 50 m / s or more and 120 m / s or less. Pickling treatment may involve supplying hydrochloric acid to a pickling tank where it reacts with the steel plate to react with fine residual scale on the surface of the steel plate that has not been removed by mechanical means. At this time, the pickling treatment may be performed using a process known in the relevant technical field.

[0102] Subsequently, a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a cold rolling step. The cold rolling step may be a step of cold rolling a hot-rolled annealed steel sheet to form a cold-rolled steel sheet.

[0103] The cold rolling step involves cold rolling the hot-rolled steel sheet into a cold-rolled steel sheet having a thickness of 0.10 mm or more and 0.20 mm, and the reduction rate may be in the range of 70% or more and 97% or less.

[0104] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a decarburization annealing step after a cold rolling step. The decarburization annealing step is a step of removing carbon, which is treated as an impurity inside the steel, and forming a forsterite coating layer between the steel sheets.

[0105] The forsterite coating layer has a composition of Mg2SiO4 and is formed by the reaction of the oxide layer on the surface of the electrical steel sheet formed during the annealing process with MgO, an annealing separator applied to prevent adhesion between steel sheets during the decarburization annealing process. The forsterite coating layer formed in this way can prevent the steel sheets from fusing together due to heat during the annealing process.

[0106] In addition, iron loss can be reduced by increasing the resistance between plates and lowering eddy current losses, and the forsterite coating layer can form micro-stress on the surface of the steel plate, thereby providing an environment where grains with (100) orientation can be easily formed and / or grown during the final annealing step described later. As a result, the magnetic properties of the non-oriented electrical steel can be improved.

[0107] The effectiveness of the forsterite coating layer is influenced by the adhesion and average thickness of the coating layer. These adhesions and average thickness of the forsterite coating layer are affected by the heat treatment temperature and dew point temperature during decarburization annealing. Therefore, to obtain the aforementioned effectiveness of the forsterite coating layer, it is important to control the heat treatment temperature and dew point during decarburization annealing.

[0108] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention controls the appropriate temperature and dew point during decarburization annealing through the following Equation 1.

[0109] [Equation 1]

[0110] T / (Dt) 2 ≤ 0.27

[0111] In the above Equation 1, T represents the heat treatment temperature during decarburization annealing, and Dt represents the dew point temperature during decarburization annealing.

[0112] If the value of the left side of Equation 1 above exceeds the upper limit described above, the forsterite coating layer may not develop sufficiently, and adhesion may be reduced. If the adhesion of the forsterite coating layer is reduced, the above-described effect is reduced, and it may be difficult to grow crystal grains having (100) orientation. In addition, if adhesion is reduced, insulation properties are reduced, and iron loss may decrease.

[0113] On the other hand, if the above Equation 1 is satisfied, the forsterite coating layer can be sufficiently developed and the adhesion can be excellent. At this time, the magnetic properties can be improved by increasing the resistance between plates and reducing eddy current losses. In addition, the magnetic properties can be improved by promoting the growth of crystal grains having (100) orientation.

[0114] In the step of decarburizing annealing according to one embodiment of the present invention, the decarburizing annealing temperature, time, and dew point can each be controlled.

[0115] Specifically, the decarburization annealing step can be performed by heat treatment at a temperature of 700°C or higher and 950°C or lower for a time of 1 minute or more and 10 minutes or less.

[0116] During decarburization annealing, the temperature can be controlled to be between 700°C and 950°C. If the decarburization annealing temperature is below 700°C, the forsterite coating layer may be formed unevenly or not formed locally. Additionally, the heat treatment time until the decarburization annealing is sufficiently completed increases significantly, which may lead to a decrease in productivity. On the other hand, if the decarburization annealing temperature exceeds 950°C, the texture of the steel sheet changes during the formation of the forsterite coating layer, and the grains grow excessively, which may result in a deterioration of magnetic properties.

[0117] During decarburization annealing, the dew point must be controlled within a range where decarburization can occur, and generally, the dew point at which decarburization occurs is 50°C or higher and 80°C or higher.

[0118] The steel material that has undergone the aforementioned decarburization annealing step can have an appropriate average coating thickness, which suppresses fusion between steel sheets during high-temperature annealing and can improve magnetic properties.

[0119] In a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention, the average coating thickness of the forsterite layer of the steel material that has undergone the decarburization annealing step may be 1.2 μm or more. If the average coating thickness of the forsterite layer is less than 1.2 μm, the forsterite coating layer may be formed unevenly or not formed locally.

[0120] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may perform a step of applying an annealing separator after a decarburization annealing step and before a final annealing step.

[0121] Subsequently, a final annealing step can be performed. The final annealing step can be performed at an appropriate temperature to improve magnetic and mechanical properties.

[0122] If the final annealing temperature is below 900°C, grains with the {001} orientation, which is advantageous for magnetic properties, may not grow sufficiently, resulting in inferior magnetic properties. On the other hand, if the final annealing temperature exceeds 1250°C, grains other than those with the {001} orientation may grow together, or process problems may occur due to the high temperature. In addition, excessive heat treatment may increase heat treatment costs and lead to increased production costs.

[0123] At this time, the final annealing may be performed for a period of 4 hours or more and 16 hours or less within the temperature range described above. If the final annealing heat treatment time is less than 4 hours, grains with {001} orientations favorable for magnetic properties may not grow sufficiently, and as a result, it may be difficult to improve magnetic properties. On the other hand, if the final annealing heat treatment time exceeds 16 hours, the grains may grow excessively, which may result in inferior magnetic properties, and problems such as increased production costs and reduced productivity due to the long heat treatment time may arise.

[0124] In addition, the heating rate up to the above-mentioned temperature range may be 10℃ / s or more.

[0125] In addition, the final annealing may be performed under mixed atmosphere conditions containing hydrogen (H2) and nitrogen (N2) to prevent oxidation and nitridation of the steel sheet surface. When cold-rolled annealing is performed in a mixed atmosphere containing hydrogen and nitrogen, the surface condition of the non-oriented electrical steel sheet can be made smoother and the surface quality can be improved.

[0126] In addition, as described above, by performing cold rolling annealing in a reducing atmosphere containing hydrogen (H2), the MnS precipitates decompose and the surface energy changes, allowing the selective growth of crystal grains having an orientation (100) that is advantageous for magnetic properties.

[0127] Accordingly, the final annealing process according to the present invention can secure excellent magnetic properties by maintaining a steel plate having the above-described composition ratio at a temperature of 1000°C or higher and 1250°C or lower for a period of 4 hours or more and 16 hours or less, thereby selectively growing crystal grains with (100) orientation.

[0128] A method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention may further perform a coating step after the final annealing step. The coating step may be performed to ensure the insulation properties and improve the punchability of the non-oriented electrical steel sheet, and may refer to forming an insulating film on the surface of the cold-rolled steel sheet that has undergone the final annealing step. The coating step may be performed using a process known in the art.

[0129]

[0130] A non-oriented electrical steel sheet produced by the method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention can satisfy the following Equation 2.

[0131] [Equation 2]

[0132] Dmax / Davg ≥ 1.5

[0133] In Equation 2, Dmax represents the diameter of the largest grain, and Davg represents the average grain diameter.

[0134] If Equation 2 is not satisfied, grain growth may be inhibited or excessive, which may have a negative effect on magnetic properties. This will be explained in more detail below.

[0135] If the Dmax / Davg value falls short of the lower limit described above, it may be that the various grains have grown uniformly. In this case, the fact that the various grains have grown uniformly may mean that the selective growth of the (100) orientation, which is the target of the present invention, has not been sufficiently achieved.

[0136] (100) If the growth of grains with an orientation is insufficient, the area fraction of grains with an orientation favorable to magnetic properties decreases, and the magnetic properties may be inferior.

[0137] In addition, the upper limit of the desirable Dmax / Davg value may be 5.0 or less. If the Dmax / Davg value exceeds the aforementioned upper limit, it may indicate that the grains have grown excessively. If the grains grow excessively, it may cause a problem of increased iron loss, which may lead to a deterioration in magnetic properties.

[0138] On the other hand, the case satisfying Equation 2 above may be one in which the (100) orientation advantageous for magnetic properties is selectively grown. In addition, the case satisfying Equation 2 above may mean that the crystal grains have not grown excessively. Therefore, by satisfying Equation 2 above, the non-oriented electrical steel sheet according to one embodiment of the present invention has less increase in iron loss due to excessive crystal grain size and can have a texture advantageous for magnetic properties.

[0139] At this time, the non-oriented electrical steel sheet manufactured by the manufacturing method according to one embodiment of the present invention may have an area fraction of crystal grains having an orientation of (100) of 50% or more. The orientation of (100) is an orientation favorable to magnetic properties, and when the area fraction of crystal grains having an orientation of (100) is 50% or more, magnetic properties may be improved.

[0140] Thus, the non-oriented electrical steel sheet manufactured by the manufacturing method according to one embodiment of the present invention has a texture advantageous to magnetic properties, thereby securing excellent magnetic properties. More specifically, iron loss (W 10 / 400 ) may be 12 W / kg or less.

[0141]

[0142] Non-oriented electrical steel sheets

[0143] A non-oriented electrical steel sheet according to one embodiment comprises silicon (Si) 1.8 wt% or more and 4.0 wt% or less, manganese (Mn) 0.05 wt% or more and 0.5 wt% or less, aluminum (Al) 0 wt% or more and 0.01 wt% or less, phosphorus (P) 0 wt% or more and 0.015 wt% or less, titanium (Ti) 0 wt% or more and 0.005 wt% or less, carbon (C) 0 wt% or more and 0.005 wt% or less, nitrogen (N) 0 wt% or more and 0.005 wt% or less, sulfur (S) 0 wt% or more and 0.02 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities.

[0144] The content and role of the alloy components are as described above in the manufacturing method of non-oriented electrical steel sheets, and redundant descriptions will be omitted. In addition, since the content of the alloy components does not substantially change during the manufacturing process described above, the alloy composition of the slab disclosed in the above manufacturing method and the alloy composition of the final product, the non-oriented electrical steel sheet, are substantially the same.

[0145]

[0146] A non-oriented electrical steel sheet according to one embodiment of the present invention satisfies the following Equation 2.

[0147] [Equation 2]

[0148] Dmax / Davg ≥ 1.5

[0149] In Equation 2, Dmax represents the diameter of the largest grain, and Davg represents the average grain diameter.

[0150] If Equation 2 is not satisfied, grain growth may be inhibited or excessive, which may have a negative effect on magnetic properties. This will be explained in more detail below.

[0151] If the Dmax / Davg value falls short of the lower limit described above, it may be that the various grains have grown uniformly. In this case, the fact that the various grains have grown uniformly may mean that the selective growth of the (100) orientation, which is the target of the present invention, has not been sufficiently achieved.

[0152] (100) If the growth of grains with an orientation is insufficient, the area fraction of grains with an orientation favorable to magnetic properties decreases, and the magnetic properties may be inferior.

[0153] In addition, the upper limit of the desirable Dmax / Davg value may be 5.0 or less. If the Dmax / Davg value exceeds the aforementioned upper limit, it may indicate that the grains have grown excessively. If the grains grow excessively, it may cause a problem of increased iron loss, which may lead to a deterioration in magnetic properties.

[0154] On the other hand, the case satisfying Equation 2 above may be one in which the (100) orientation advantageous for magnetic properties is selectively grown. In addition, the case satisfying Equation 2 above may mean that the crystal grains have not grown excessively. Therefore, by satisfying Equation 2 above, the non-oriented electrical steel sheet according to one embodiment of the present invention has less increase in iron loss due to excessive crystal grain size and can have a texture advantageous for magnetic properties.

[0155] At this time, the non-oriented electrical steel sheet according to one embodiment of the present invention may have an area fraction of crystal grains having an orientation (100) of 50% or more. The orientation (100) is an orientation favorable to magnetic properties, and when the area fraction of crystal grains having an orientation (100) is 50% or more, magnetic properties may be improved.

[0156] Thus, the non-oriented electrical steel sheet according to one embodiment of the present invention has a texture advantageous for magnetic properties, thereby securing excellent magnetic properties. More specifically, iron loss (W 10 / 400) may be 12 W / kg or less.

[0157]

[0158] The structure and operation of the present invention will be explained below through experimental examples. However, these are presented as examples to aid in understanding the present invention and do not limit the invention.

[0159]

[0160] (Method for measuring the physical properties of non-oriented electrical steel specimens)

[0161] 1. Average thickness and adhesion of Forsterite coating layer

[0162] The average thickness of the forsterite coating layer was measured by the following method. First, 60×60 mm 2 Non-oriented electrical steel sheet specimens of a certain size were stacked, and the TD plane (Trasverse direction plane) of the stacked specimens was observed using an optical microscope (OM). Subsequently, the coating layer thickness was measured at five random points within 15 mm to the left and right of the center of the specimen, and the average of these values ​​was calculated and used as the average thickness of the coating layer. However, parts where the coating layer was not properly formed or where empty spaces were formed due to internal pores were excluded from the measurement.

[0163] To verify the adhesion of the forsterite coating layer, shear adhesion strength was evaluated by applying force in the plane direction to the surface of non-oriented electrical steel specimens. This was used to determine whether the coating layer detached. More specifically, adhesion was judged as poor if the coating layer detached upon application of force, and as good if it did not detach.

[0164]

[0165] 2. Grain diameter

[0166] The grain size can be determined as follows. First, specimens are taken at the 1 / 4, 1 / 2, and 3 / 4 points along the width direction of the non-oriented electrical steel sheet, and 10×20 mm is prepared so that the ND plane (Normal Direction Plane) of the specimen is observed. 2 Test specimens for EBSD (Electron backscatter diffraction) measurement were prepared. Subsequently, the area of ​​each grain was calculated using TSL OIM software, an analysis software for EBSD measurements.

[0167] Subsequently, when the area of ​​each grain was converted into a virtual circle with the same area, the diameter of the virtual circle was taken as the grain size.

[0168]

[0169] 3. Area fraction of grains with (100) orientation

[0170] The grain size can be determined as follows. First, specimens are taken at the 1 / 4, 1 / 2, and 3 / 4 points along the width direction of the non-oriented electrical steel sheet, and 10×20 mm is prepared so that the ND plane (Normal Direction Plane) of the specimen is observed. 2 A specimen for EBSD (Electron backscatter diffraction) measurement was prepared. Subsequently, the area fraction of the grains was calculated using TSL OIM software, an analysis software for EBSD measurements.

[0171] At this time, the area fraction of grains with (100) orientation was calculated at three points within a single specimen using the method described above, and the average value of those values ​​was taken as the area fraction of grains with (100) orientation.

[0172]

[0173] 4. Iron loss (W 10 / 400 )

[0174] Iron loss (W) of the non-oriented electrical steel sheet specimen of the present invention 15 / 50) was measured using an SST (Single Sheet Tester). More specifically, it was measured based on the test method specified in IEC 60404-3.

[0175] In this experiment, non-oriented electrical steel sheet specimens were 60x60mm 2 A specimen of a certain size was fabricated, and the iron loss in the direction parallel to the rolling direction (RD, Rolling direction) and the direction perpendicular to the rolling direction (TD, Transverse direction) was measured, and the average value was used as the iron loss value of the specimen.

[0176]

[0177] (Preparation and Evaluation of Non-Oriented Electrical Steel Specimens)

[0178] The alloy composition of the non-oriented electrical steel sheet specimen of the present invention is as shown in Table 1 below. It includes the remainder of iron (Fe) other than the alloy composition listed in Table 1 below.

[0179] Alloy Composition (Weight%) Alloy Composition (ppm) SiMnAlPTiCNS 3.33 0.2323 10232393637

[0180] A slab having the alloy composition according to Table 1 above was manufactured, reheated to approximately 1200°C, and then hot-rolled to produce a hot-rolled steel sheet with a thickness of approximately 2.2 mm. The hot-rolled steel sheet was hot-rolled and annealed at approximately 1000°C for 60 seconds, and then cold-rolled to produce a cold-rolled steel sheet with a thickness of 0.2 mm. Subsequently, the cold-rolled steel sheet was decarburized and annealed for 10 minutes at the temperature and dew point listed in Table 2 below, and then the cold-rolled steel sheet that underwent decarburization and annealed was finally annealed at a temperature of approximately 1200°C for 16 hours.

[0181] The manufacturing method described above and other manufacturing process conditions not listed in Table 2 below were controlled as control variables and were equally controlled within the range described in the manufacturing method according to one embodiment of the present invention.

[0182] For the manufactured experimental example, the decarburization annealing condition, the thickness and adhesion of the forsterite coating layer, the value of Equation 2, the area fraction of crystal grains having (100) orientation, and the iron loss (W 10 / 400 The values ​​are shown in Table 2 below.

[0183] At this time, in Table 2 below, '(100) fraction' means the area fraction of crystal grains having (100) orientation.

[0184] In Table 2 below, the unit of temperature is '°C', the unit of coating layer thickness is '㎛', the unit of area fraction of crystal grains having (100) orientation is '%', and iron loss (W 10 / 400 The unit of ) is 'W / kg'.

[0185] Classification Decarburization Annealed Forsterite Coating Layer Type 2(100) fraction W 10 / 400Temperature Dew Point Type 1 Adhesion Average Thickness Comparison Example 1 700 500.28 Poor 0.3 11.09 17.3 14.24 Example 1 700 600.19 Good 1.4 21.95 50.6 11.96 Example 2 700 700.14 Good 2.5 42.86 59.4 11.62 Example 3 700 800.11 Good 4.8 53.12 64.7 11.89 Comparison Example 2 750 500.3 Poor 0.4 81.09 19.5 15.44 Example 4 750 600.21 Good 1.5 52.10 52.8 11.72 Good Example 5750700.15 Good 2.68 3.09 61.11 1.77 Example 6750800.12 Good 4.9 14.03 78.8 11.05 Comparative Example 3800500.32 Poor 0.59 1.21 19.8 14.07 Example 7800600.22 Good 1.68 2.43 53.5 11.58 Example 8800700.16 Good 2.75 3.55 64.7 11.16 Example 9800800.13 Good 5.12 4.24 82.5 10.89 Comparative Example 4 850 500.34 Poor 0.79 1.34 22.61 3.24 Example 10 850 600.24 Good 1.81 1.53 53.51 1.06 Example 11 850 700.17 Good 3.56 4.66 88.31 0.75 Example 12 850 800.13 Good 5.44 3.87 75.61 1.34 Comparative Example 5 900 500.36 Poor 0.88 1.27 25.81 2.32 Example 13 900 600.25 Good 2.11 4.17 81.81 0.71 Example Example 14 900 700.18 Good 3.88 4.819 0.210.54 Example 15 900 800.14 Good 5.89 2.946 0.311.74 Comparative Example 6 950 500.38 Poor 1.13 1.15 23.71 2.56 Example 16 950 600.26 Good 2.26 4.0879.811.06 Example 17 950 700.19 Good 4.12 4.7586.71 0.67 Example 18 950 800.15 Good 6.21 1.5356.11 1.80

[0186] Referring to Tables 1 and 2 above, it can be confirmed that Examples 1 to 13, which satisfy the alloy composition according to one embodiment of the present invention, the decarburization annealing temperature and dew point, and the above Equation 1, have good adhesion of the forsterite coating layer and an average coating thickness of 1.2 μm or more. At this time, it can be confirmed that the above Equation 2 is satisfied by the forsterite coating layer helping the growth of crystal grains having (100) orientation.

[0187] As a result, Examples 1 to 13 can have a texture advantageous for magnetic properties, and specifically, it can be confirmed that the area fraction of crystal grains having (100) orientation satisfies 50% or more. In addition, by having a texture advantageous for magnetic properties, iron loss (W 10 / 400 It can be confirmed that ) is reduced and has a low iron loss value.

[0188] On the other hand, in the case of Comparative Examples 1, 3, 5 to 8, which do not satisfy the decarburization annealing temperature and dew point according to one embodiment of the present invention and Equation 1, it can be confirmed that the adhesion of the forsterite coating layer is poor. In addition, it can be confirmed that the forsterite coating layer is not formed well, so the average thickness of the forsterite coating layer does not satisfy 1.2 μm or more. At this time, it can be confirmed that Equation 2 is not satisfied because the growth of crystal grains with (100) orientation is insufficient.

[0189] As a result, it can be confirmed that the area fraction of crystal grains having the (100) orientation of Comparative Example 1, Comparative Example 3, and Comparative Example 5 is less than 50%. In addition, it can be confirmed that the iron loss value is higher compared to the embodiment according to one embodiment of the present invention.

[0190] Through this, it can be confirmed that when the method for manufacturing a non-oriented electrical steel sheet according to one embodiment disclosed in this specification is satisfied, a forsterite coating layer is appropriately formed, thereby improving the texture and securing excellent magnetic properties.

[0191] As described above, preferred embodiments according to the present invention have been examined. It is obvious to those skilled in the art that, in addition to the embodiments described above, the present invention may be embodied in other specific forms without departing from its spirit or scope. Therefore, the embodiments described above should be regarded as illustrative rather than restrictive, and accordingly, the present invention is not limited to the description above but may be modified within the scope of the appended claims and their equivalents.

Claims

1. A step of hot rolling a slab containing silicon (Si) 1.8 wt% or more and 4.0 wt% or less, manganese (Mn) 0.05 wt% or more and 0.5 wt% or less, aluminum (Al) greater than 0 wt% and 0.01 wt% or less, phosphorus (P) greater than 0 wt% and 0.015 wt% or less, titanium (Ti) greater than 0 wt% and 0.005 wt% or less, carbon (C) greater than 0 wt% and 0.005 wt% or less, nitrogen (N) greater than 0 wt% and 0.005 wt% or less, sulfur (S) greater than 0 wt% and 0.02 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities; Hot rolling and annealing step; cold rolling step; Step of decarburizing annealing; and It includes a final annealing step, The above decarburization annealing step is a method for manufacturing a non-oriented electrical steel sheet satisfying the following Formula 1: [Equation 1] T / (Dt) 2 ≤ 0.27 In the above Equation 1, T represents the heat treatment temperature during decarburization annealing, and Dt represents the dew point temperature during decarburization annealing.

2. In Paragraph 1, The above decarburization annealing step is, A method for manufacturing non-oriented electrical steel sheets, wherein heat treatment is performed at a temperature of 700°C or higher and 950°C or lower for a time of 1 minute or more and 10 minutes or less.

3. In Paragraph 1, Non-oriented electrical steel sheets that have undergone a decarburization annealing step are, A method for manufacturing a non-oriented electrical steel sheet having an average coating thickness of 1.2㎛ or more.

4. In Paragraph 1, Non-oriented electrical steel sheets manufactured after the final annealing step, A method for manufacturing non-oriented electrical steel sheets satisfying the following Equation 2: [Equation 2] Dmax / Davg ≥ 1.5 In Equation 2 above, Dmax represents the diameter of the largest grain, and Davg represents the average grain diameter.

5. In Paragraph 1, The non-oriented electrical steel sheet that has undergone the final annealing step is, (100) A method for manufacturing non-oriented electrical steel sheets in which the area fraction of the grains having orientation is 50% or more.

6. In Paragraph 1, The non-oriented electrical steel sheet that has undergone the final annealing step is, Iron loss (W 10 / 400 A method for manufacturing non-oriented electrical steel sheets having a value of 12 W / kg or less.

7. comprising silicon (Si) 1.8 wt% or more and 4.0 wt% or less, manganese (Mn) 0.05 wt% or more and 0.5 wt% or less, aluminum (Al) greater than 0 wt% and 0.01 wt% or less, phosphorus (P) greater than 0 wt% and 0.015 wt% or less, titanium (Ti) greater than 0 wt% and 0.005 wt% or less, carbon (C) greater than 0 wt% and 0.005 wt% or less, nitrogen (N) greater than 0 wt% and 0.005 wt% or less, sulfur (S) greater than 0 wt% and 0.02 wt% or less, and the remainder being iron (Fe) and other unavoidable impurities, Non-oriented electrical steel sheet satisfying the following Equation 2. [Equation 2] Dmax / Davg ≥ 1.5 In Equation 2 above, Dmax represents the diameter of the largest grain, and Davg represents the average grain diameter.

8. In Paragraph 7, (100) Non-oriented electrical steel sheet having an area fraction of 50% or more of the grains having orientation.

9. In Paragraph 7, Iron loss (W 10 / 400 Non-oriented electrical steel sheet with a ) of 12 W / kg or less.