Method for manufacturing non-oriented electrical steel sheet with excellent magnetic properties and non-oriented electrical steel sheet manufactured by the method

Abstract

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties and the non-oriented electrical steel sheet manufactured thereby. In one embodiment, the method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties includes the steps of: manufacturing a hot-rolled steel sheet using a slab containing 0.4 to 3.5 wt% silicon (Si), more than 0 to 0.05 wt% aluminum (Al), 0.002 to 3.5 wt% austenite stabilizing elements, and the balance being iron (Fe) and other unavoidable impurities; cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and cold-roll annealing the cold-rolled steel sheet, wherein the cold-roll annealing includes a first heat treatment of the cold-rolled steel sheet by heating it to a temperature in the austenite single-phase region and maintaining that temperature; and a second heat treatment of the first-heat-treated cold-rolled steel sheet by cooling it to a temperature in the ferrite-austenite two-phase region and maintaining that temperature.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties and a non-oriented electrical steel sheet manufactured by the method. [Background technology]

[0002] Electrical steel sheets are divided into oriented electrical steel sheets used in transformers and non-oriented electrical steel sheets used in rotating motor cores. Recently, interest in eco-friendly products has been increasing along with global environmental issues, and the automotive industry in particular is undergoing a paradigm shift toward reducing the production of internal combustion engine vehicles and increasing the production of electric vehicles. As demand for electric vehicles increases, there is also a demand for high-efficiency and high-power electrical steel sheets, a core component.

[0003] Two important properties of electrical steel sheets are magnetic flux density and core loss. Magnetic flux density, which indicates the number of magnetic lines of force induced in a material under a specific magnetic field, is generally expressed as B 50The magnetic flux density is primarily measured by the value, measured in Tesla units. Factors that can improve magnetic flux density include chemical composition, grain size, and texture. Iron loss, measured in watts per kilogram, is the energy loss that occurs during the magnetization process of electrical steel sheet materials. Iron loss can be divided into hysteresis loss, which occurs due to the magnetization phenomenon itself, and eddy current loss, which occurs due to eddy currents induced during magnetization. To improve the iron loss of electrical steel sheet, one can either increase resistivity by adding major alloying elements such as silicon, manganese, and aluminum, or thin the material. However, as the amount of alloying elements increases, magnetic flux density decreases and rollability deteriorates, making it difficult to thin the material. In addition, major alloying elements easily combine with impurity elements such as carbon, sulfur, nitrogen, and titanium to form precipitates. These precipitates impede the movement of magnetic spheres formed by an applied magnetic field, resulting in poor magnetic properties. In order to improve the properties of such electrical steel sheets, it is very important to optimize the alloying elements and impurity elements, and the properties can be improved by improving the microstructure and aggregate structure, which may affect the magnetic flux density and hysteresis loss.

[0004] Currently, electrical steel sheets are manufactured through the following process: steelmaking - continuous casting - hot rolling - hot rolling and annealing (APL) - cold rolling - cold rolling and annealing (ACL). However, with the currently known processes and composition, the effect of improving properties through improvements in microstructure and texture is minimal. In particular, it is difficult to obtain significant improvements in texture, which has a significant impact on magnetic properties, simply by improving additive elements or certain process conditions.

[0005] The background art of the present invention is disclosed in Korean Patent Publication No. 10-2325011 (published on November 11, 2021, title of invention: Non-oriented electrical steel sheet and manufacturing method thereof). Summary of the Invention [Problem to be solved by the invention]

[0006] According to one embodiment of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet having excellent effects of improving the microstructure and aggregate structure, minimizing iron loss, and having excellent magnetic properties.

[0007] According to one embodiment of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet that is effective in developing a texture advantageous for magnetic properties.

[0008] According to one embodiment of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet having excellent mechanical properties.

[0009] According to one embodiment of the present invention, there is provided a method for manufacturing a non-oriented electrical steel sheet that is excellent in productivity and economy.

[0010] According to one embodiment of the present invention, there is provided a non-oriented electrical steel sheet manufactured by the method for manufacturing a non-oriented electrical steel sheet. [Means for solving the problem]

[0011] One aspect of the present invention relates to a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties. In one specific example, the method for manufacturing the non-oriented electrical steel sheet includes the steps of: manufacturing a hot-rolled steel sheet using a slab containing 0.4 to 3.5 wt% silicon (Si), more than 0 to 0.05 wt% aluminum (Al), 0.002 to 3.5 wt% austenite stabilizing elements, and the balance being iron (Fe) and other unavoidable impurities; cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and cold-roll annealing the cold-rolled steel sheet, wherein the cold-roll annealing includes a first heat treatment of the cold-rolled steel sheet by heating it to a temperature in the austenite single-phase region and maintaining that temperature; and a second heat treatment of the first-heat-treated cold-rolled steel sheet by cooling it to a temperature in the ferrite-austenite two-phase region and maintaining that temperature.

[0012] In one embodiment, the slab may further include, based on the total weight, one or more of: carbon (C) greater than 0 and less than 0.0050 wt %; sulfur (S) greater than 0 and less than 0.0050 wt %; nitrogen (N) greater than 0 and less than 0.0050 wt %; and titanium (Ti) greater than 0 and less than 0.0050 wt %.

[0013] In one specific example, the hot-rolled steel sheet may be produced by the steps of reheating the slab at a reheating temperature of 1110 to 1180°C; hot-rolling the reheated slab at a finish rolling temperature of 800 to 900°C; and coiling the hot-rolled slab at a coiling temperature of 500 to 700°C.

[0014] In one specific example, the method for manufacturing a non-oriented electrical steel sheet further includes, before the step of cold rolling the hot-rolled steel sheet, a step of hot-rolling annealing the hot-rolled steel sheet, wherein the hot-rolling annealing includes a step of raising the temperature of the hot-rolled steel sheet to 940 to 1110°C and maintaining the temperature; and a step of cooling the hot-rolled steel sheet.

[0015] In one specific example, the hot rolled annealing can be performed by raising the temperature of the hot rolled steel sheet at a heating rate of 20° C. / s or more and cooling it at a cooling rate of 20° C. / s or more.

[0016] In one specific example, the cold rolling is carried out at a rolling reduction of 50 to 90%, and the cold rolled steel sheet may have a thickness of 0.1 to 0.5 mm.

[0017] In one specific example, the first heat treatment may include a step of heating the cold-rolled steel sheet to 1000 to 1250°C and maintaining the temperature for 30 to 300 seconds, and the second heat treatment may include a step of cooling the primarily heat-treated cold-rolled steel sheet to a temperature in the ferrite-austenite two-phase region and maintaining the temperature for 5 to 300 seconds.

[0018] In one specific example, the secondary heat treatment may be performed by cooling the cold-rolled steel sheet that has been subjected to the primary heat treatment at a cooling rate of 10° C. / s or more.

[0019] Another aspect of the present invention relates to a non-oriented electrical steel sheet manufactured by the method for manufacturing a non-oriented electrical steel sheet. In one embodiment, the non-oriented electrical steel sheet contains 0.4 to 3.5 wt% silicon (Si), more than 0 to 0.05 wt% aluminum (Al), 0.002 to 3.5 wt% austenite stabilizing elements, the balance being iron (Fe) and other unavoidable impurities, and has a microstructure containing ferrite.

[0020] In one embodiment, the non-oriented electrical steel sheet may further include, based on the total weight, one or more of: carbon (C) greater than 0 and not greater than 0.0050 wt %; sulfur (S) greater than 0 and not greater than 0.0050 wt %; nitrogen (N) greater than 0 and not greater than 0.0050 wt %; and titanium (Ti) greater than 0 and not greater than 0.0050 wt %.

[0021] In one embodiment, the non-oriented electrical steel sheet has a thickness of 0.1 to 0.5 mm and a magnetic flux density (B 50 ) 1.65T or more and iron loss (W 15 / 50 ) 2.42 W / kg or less, a yield strength of 200 MPa or more, and a tensile strength of 300 MPa or more.

[0022] In one embodiment, the non-oriented electrical steel sheet is <100> / / ND aggregate tissue may be contained at least 15% by area. [Effects of the Invention]

[0023] The method for manufacturing a non-oriented electrical steel sheet according to the present invention and the non-oriented electrical steel sheet manufactured thereby have excellent effects in improving microstructure and texture, minimize iron loss, have excellent magnetic properties, are excellent in developing texture advantageous for magnetic properties, have excellent mechanical properties such as yield strength and tensile strength, and can be highly productive and economical. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 shows a method for producing a non-oriented electrical steel sheet according to one embodiment of the present invention. [Figure 2]FIG. 2 is a graph showing the heat treatment schedule during cold rolling and annealing for the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be described in detail below. Hereinafter, if it is determined that a detailed description of related publicly known techniques or configurations may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

[0026] The terms described below are defined taking into consideration their functions in the present invention, and since these may vary depending on the intentions or practices of the user or operator, their definitions must be determined based on the overall content of this specification which describes the present invention.

[0027] Manufacturing method for non-oriented electrical steel sheets with excellent magnetic properties One aspect of the present invention relates to a method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties. Fig. 1 shows a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. Referring to Fig. 1, the method for manufacturing a non-oriented electrical steel sheet includes a step of (S10) manufacturing a hot-rolled steel sheet, a step of (S20) cold-rolling, and a step of (S30) cold-rolling annealing.

[0028] More specifically, the method for manufacturing the non-oriented electrical steel sheet includes: (S10) a step of manufacturing a hot-rolled steel sheet using a slab containing 0.4 to 3.5 wt% of silicon (Si), more than 0 to 0.05 wt% of aluminum (Al), 0.002 to 3.5 wt% of austenite stabilizing elements, the balance being iron (Fe) and other unavoidable impurities; (S20) a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet; and (S30) a step of cold-roll annealing the cold-rolled steel sheet.

[0029] Hereinafter, the method for manufacturing a non-oriented electrical steel sheet according to the present invention will be described in detail step by step.

[0030] (S10) Hot-rolled steel sheet manufacturing step The step is a step of manufacturing a hot-rolled steel sheet using a slab containing 0.4 to 3.5 wt% silicon (Si), more than 0 to 0.05 wt% aluminum (Al), 0.002 to 3.5 wt% austenite stabilizing elements, the balance being iron (Fe) and other unavoidable impurities.

[0031] The constituent components of the slab will be described in detail below.

[0032] Silicone (Si) The silicone (Si) is added as a component to increase the resistivity of the material and reduce iron loss (eddy current loss).

[0033] In one embodiment, the silicone is contained in an amount of 0.4 to 3.5 wt% based on the total weight of the slab. If the silicone is contained in an amount less than 0.4 wt%, the iron loss improvement effect is insufficient, and if the silicone is contained in an amount more than 3.5 wt%, the magnetic flux density decreases due to an increase in alloying element components, and brittleness increases, which reduces cold rolling properties and may lead to a decrease in productivity.

[0034] Aluminum (Al) The aluminum (Al) is a main additive element that increases resistivity and reduces iron loss (eddy current loss) together with the silicone, and can also act as a ferrite stabilizing element.

[0035] In one embodiment, the aluminum (Al) is contained in an amount of more than 0 to 0.05 wt% based on the total weight of the slab. If the aluminum is contained in an amount of more than 0.05 wt%, the aluminum may reduce the phase transformation region and form secondary phases such as AlN, which may impair magnetic properties.

[0036] Austenite stabilizing elements The austenite stabilizing element may be added to ensure an austenite transformation region at high temperatures. In the process of increasing the amount of silicone added to improve iron loss of steel sheets, a problem may occur in which only a ferrite single-phase region exists and transformation to austenite is not possible when the silicone content exceeds about 1.7 wt. Therefore, the present invention adds the austenite stabilizing element to ensure an austenite transformation region at high temperatures.

[0037] In one embodiment, the austenite stabilizing element is included in an amount of 0.002 to 3.5 wt% based on the total weight of the slab. If the austenite stabilizing element is included in an amount less than 0.002 wt%, the austenite region cannot be secured, whereas if the austenite stabilizing element is included in an amount more than 3.5 wt%, the production cost may increase excessively and the magnetic property may be deteriorated.

[0038] In one embodiment, the austenite stabilizing elements may include manganese (Mn), cobalt (Co), nickel (Ni), chromium (Cr), etc. These may be included alone or in combination of two or more.

[0039] In one embodiment, the slab may further include, based on the total weight, one or more of: carbon (C) greater than 0 and less than 0.0050 wt %; sulfur (S) greater than 0 and less than 0.0050 wt %; nitrogen (N) greater than 0 and less than 0.0050 wt %; and titanium (Ti) greater than 0 and less than 0.0050 wt %.

[0040] Carbon (C) The carbon can secure the austenite phase transformation region, but is an element that forms carbides such as TiC and NbC and increases iron loss, so the smaller the amount of carbon added, the more advantageous it is.

[0041] In one embodiment, the carbon content may be greater than 0 and less than 0.0050 wt % based on the total weight of the slab. When the carbon content is within this range, it is possible to prevent an increase in iron loss while maintaining the austenite phase transformation region. For example, the carbon content may be greater than 0 and less than 0.0030 wt %.

[0042] Sulfur (S) The sulfur (S) forms precipitates such as MnS and CuS, which increase iron loss and inhibit grain growth, so the amount of sulfur added can be kept as low as possible.

[0043] In one embodiment, sulfur (S) may be contained in an amount of more than 0 to 0.0050 wt% based on the total weight of the slab. When contained within this content range, sulfur prevents the formation of precipitates such as MnS and CuS, thereby preventing an increase in iron loss and not inhibiting grain growth. For example, sulfur may be contained in an amount of more than 0 to 0.0030 wt%.

[0044] Nitrogen (N) Nitrogen (N) forms precipitates such as AlN, TiN, and NbN, which increase iron loss and inhibit grain growth, so it may be added in as small an amount as possible.

[0045] In one embodiment, nitrogen (N) may be contained in an amount of more than 0 to 0.0050 wt% based on the total weight of the slab. When contained within this content range, it prevents the formation of precipitates such as AlN, Tin, and NbN, thereby preventing an increase in iron loss and not inhibiting grain growth. For example, it may be contained in an amount of more than 0 to 0.0030 wt%.

[0046] Titanium (Ti) Titanium (Ti) forms fine precipitates such as TiC and TiN, which inhibits grain growth. The more titanium is added, the more the magnetic properties deteriorate, so the amount of titanium added should be kept as low as possible.

[0047] In one embodiment, titanium (Ti) may be included in an amount of more than 0 to 0.0050 wt% based on the total weight of the slab. When included within this content range, titanium (Ti) prevents the formation of fine precipitates such as TiC and TiN, does not inhibit grain growth, and does not impair magnetic properties. For example, titanium may be included in an amount of more than 0 to 0.0030 wt%.

[0048] In one specific example, the hot-rolled steel sheet may be produced by the steps of reheating the slab at a reheating temperature of 1110 to 1180°C; hot-rolling the reheated slab at a finish rolling temperature of 800 to 900°C; and coiling the hot-rolled slab at a coiling temperature of 500 to 700°C.

[0049] When the slab is reheated under the above reheating temperature conditions, precipitates formed by carbon, sulfur, nitrogen, etc. in the slab are prevented from redissolving, thereby preventing the formation of fine precipitates in the subsequent rolling and annealing processes, preventing rolling load, and not inhibiting grain growth, thereby easily ensuring magnetic properties.

[0050] The above finish rolling temperature conditions can prevent material deviation of the electrical steel sheet during hot rolling, and can result in excellent mechanical and magnetic properties.

[0051] When coiled under the above coiling temperature conditions, the electrical steel sheet can have excellent surface quality, mechanical properties, and magnetic properties.

[0052] In one embodiment, the hot-rolled steel sheet may have a thickness of 1.6 to 2.6 mm. Under these conditions, an increase in the reduction rate during cold rolling can be prevented, which can prevent deterioration of the texture and improve the magnetic properties of the electrical steel sheet.

[0053] (S11) Hot rolling and annealing step In one embodiment, the method for manufacturing a non-oriented electrical steel sheet may further include, before the step of cold rolling the hot-rolled steel sheet, the step of (S11) hot-rolling annealing the hot-rolled steel sheet.

[0054] The hot rolling annealing may include the steps of raising the temperature of the hot rolled steel sheet to 940 to 1110°C and maintaining the temperature; and cooling the hot rolled steel sheet.

[0055] When heated at the annealing temperature, the elongated cast structure is removed to form a uniform microstructure.

[0056] On the other hand, if the annealing temperature is too low, the elongated cast structure remaining after hot rolling may remain, causing uneven microstructure and small grains, which may act as an obstacle to cold rolling. On the other hand, if the annealing temperature is too high, unevenness in the aggregate structure of the final product may occur, causing anisotropy in properties. For example, the hot rolling annealing may involve heating the hot-rolled steel sheet to 940-1110°C and maintaining that temperature for 30-120 seconds. This annealing time may result in the formation of appropriate grain sizes, resulting in excellent magnetic properties of the electrical steel sheet.

[0057] In one embodiment, the hot-rolled annealing may be performed at a temperature rising rate of 20°C / s or more. Under these conditions, an appropriate grain size may be formed, resulting in excellent magnetic properties of the electrical steel sheet.

[0058] In one embodiment, the hot-rolled annealing may involve heating the hot-rolled steel sheet and maintaining the temperature, followed by cooling at a cooling rate of 20°C / s or more. Under these conditions, an appropriate grain size may be formed, resulting in excellent magnetic properties of the electrical steel sheet. For example, the steel sheet may be cooled to room temperature under these cooling rates.

[0059] (S20) Cold rolling step The step is a step of cold-rolling the hot-rolled steel sheet to manufacture a cold-rolled steel sheet. For example, the hot-rolled steel sheet may be pickled and then cold-rolled.

[0060] In one specific example, in order to facilitate the cold rolling, the temperature of the hot-rolled steel sheet can be increased to 75 to 200° C. and the rolling can be performed.

[0061] In one embodiment, the cold rolling can be performed at a rolling reduction (final rolling reduction) of 50 to 90%, which can prevent equipment load and provide the electrical steel sheet with excellent magnetic properties.

[0062] In one specific example, the cold rolled steel sheet may have a thickness of 0.1 to 0.5 mm. Under these conditions, the electrical steel sheet can have excellent magnetic properties and mechanical properties.

[0063] (S30) Cold rolling and annealing step The step is a step of cold-rolling annealing the cold-rolled steel sheet.

[0064] In one specific example, the cold roll annealing includes: (S31) a step of heating the cold rolled steel sheet to an austenite single phase temperature and maintaining the temperature therein, thereby performing a primary heat treatment; and (S32) a step of cooling the primarily heat-treated cold rolled steel sheet to a ferrite and austenite two-phase temperature and maintaining the temperature therein, thereby performing a secondary heat treatment.

[0065] In conventional technology, in order to improve the magnetic properties of non-oriented electrical steel sheets, a heat treatment method based on the phase transformation from austenite (γ) to ferrite (α) was used to induce the development of {100} / / ND planes in order to improve the texture. However, after the first rolling, a second rolling was performed to improve the surface, and then a second heat treatment was required to remove residual stress, which had the disadvantage of increasing production time and costs.

[0066] Other conventional techniques involve manufacturing non-oriented electrical steel sheets by heat treatment in the ferrite (α) single phase region without undergoing phase transformation. The sulfur (S) content is controlled to an extremely low level to induce the decomposition of MnS precipitates, and the decomposed S is then induced to segregate into the grains, thereby inducing the growth of the {100} / / ND plane. However, this method requires high-temperature conditions of over 1200°C and a long heat treatment period of at least 12 hours, which increases productivity time and costs.

[0067] In one embodiment, the first heat treatment may include a step of heating the cold-rolled steel sheet to 1000 to 1250°C and maintaining the temperature for 30 to 300 seconds. Under these conditions, the microstructure of the cold-rolled steel sheet during the first heat treatment can be easily transformed into a single-phase austenite region.

[0068] In one specific example, the secondary heat treatment may include cooling the primarily heat-treated cold-rolled steel sheet to a ferrite-austenite two-phase temperature range and maintaining that temperature for 5 to 300 seconds. For example, it may be performed by cooling to 700 to 980°C. Under these conditions, ferrite nucleation readily occurs during the secondary heat treatment, and the steel is readily transformed into austenite and ferrite microstructures. This increases the fraction of {100} / / ND orientation favorable for magnetic properties and reduces the fraction of orientation unfavorable for magnetic properties, resulting in excellent magnetic properties. For example, the secondary heat treatment may include cooling to a ferrite-austenite two-phase temperature range and maintaining that temperature for 10 to 100 seconds.

[0069] For example, the secondary heat treatment can be performed by cooling the cold-rolled steel sheet subjected to the primary heat treatment at a cooling rate of 10° C. / s or more.

[0070] In one specific example, after the second heat treatment, the second heat-treated cold-rolled steel sheet may be cooled at a cooling rate of 10° C. / s or more.

[0071] In one embodiment, the method may further include forming a coating layer on the surface of the cold-rolled and annealed cold-rolled steel sheet, the coating layer being formed to ensure insulation and improve punchability.

[0072] In contrast, in the present invention, when the phase transformation to the ferrite phase (α) occurs based on the phase transformation heat treatment, the orientation preferentially formed varies depending on the temperature conditions, and the effect of improving the texture is maximized by utilizing this fact.

[0073] The non-oriented electrical steel sheet also contained 0.4 to 3.5 wt% silicon (Si) as a major additive element. As the amount of silicon, a ferrite phase (α) stabilizing element, increases, the austenite phase transformation region disappears, so the amount of austenite phase (γ) stabilizing element was set to 0.002 to 3.5 wt% in proportion to the amount of silicon (Si) added to enable phase transformation heat treatment. Since the present invention is based on the phase transformation from austenite phase (γ) to ferrite phase (α), the austenite phase (γ) stabilizing element was added in proportion to the amount of Si added, thereby enabling the phase transformation.

[0074] Among the added elements, aluminum (Al) combines with nitrogen (N) to form AlN, which is unfavorable to magnetism, inhibiting magnetic properties, and acts as a ferrite phase (α) stabilizer like silicon (Si). Therefore, in order to minimize the amount added, the content was set to more than 0 and 0.05 wt%.

[0075] Meanwhile, in previous research, it was unknown what orientation would be preferentially formed due to temperature changes during phase transformation, and there was no purpose in applying this. Therefore, a method was chosen in which the temperature was raised and maintained during cold rolling annealing, and then cooled through continuous cooling to lower the temperature.

[0076] However, in the present invention, the austenite phase (γ) temperature is maintained for a certain period of time during cold rolling annealing to form a single phase, and then the orientation that is preferentially formed at each temperature where the austenite phase (γ) and the ferrite phase (α) are mixed is confirmed and applied.

[0077] Non-oriented electrical steel sheet manufactured by the non-oriented electrical steel sheet manufacturing method Another aspect of the present invention relates to a non-oriented electrical steel sheet manufactured by the method for manufacturing a non-oriented electrical steel sheet. In one embodiment, the non-oriented electrical steel sheet contains 0.4 to 3.5 wt% silicon (Si), more than 0 to 0.05 wt% aluminum (Al), 0.002 to 3.5 wt% austenite stabilizing elements, the balance being iron (Fe) and other unavoidable impurities, and has a microstructure containing ferrite.

[0078] In one embodiment, the austenite stabilizing elements may include manganese (Mn), cobalt (Co), nickel (Ni), and chromium (Cr).

[0079] These may be included alone or in combination of two or more.

[0080] The alloying elements and contents of the non-oriented electrical steel sheet may be the same as those of the slab.

[0081] In one embodiment, the non-oriented electrical steel sheet may further include, based on the total weight, one or more of: carbon (C) greater than 0 and not greater than 0.0050 wt %; sulfur (S) greater than 0 and not greater than 0.0050 wt %; nitrogen (N) greater than 0 and not greater than 0.0050 wt %; and titanium (Ti) greater than 0 and not greater than 0.0050 wt %.

[0082] In one specific example, the non-oriented electrical steel sheet may have a thickness of 0.1 to 0.5 mm.

[0083] In one embodiment, the non-oriented electrical steel sheet may further have a coating layer formed on the surface thereof, which may be effective in ensuring insulation and improving punchability.

[0084] In one embodiment, the non-oriented electrical steel sheet has a magnetic flux density (B 50 ) 1.65T or more and iron loss (W 15 / 50 Under these conditions, the magnetic properties can be excellent.

[0085] The magnetic flux density (B 50 ) may be measured by applying a magnetic field of 5000 A / m to the electrical steel sheet.

[0086] The iron loss (W 15 / 50 ) may be measured by applying a magnetic flux density of 1.5 Tesla at a frequency of 50 Hz to the electrical steel sheet.

[0087] For example, the non-oriented electrical steel sheet has a magnetic flux density (B 50 ) 1.65~1.70T and iron loss (W 15 / 50 ) 2.28 to 2.42 W / kg.

[0088] In one embodiment, the non-oriented electrical steel sheet may have a yield strength of 200 MPa or more and a tensile strength of 300 MPa or more.

[0089] In one embodiment, the non-oriented electrical steel sheet is <100> / / The ND aggregate tissue may be contained in an amount of 15% or more by area. For example, it may be contained in an amount of 15 to 40% by area. As another example, it may be contained in an amount of 30 to 35% by area. Under these conditions, the magnetic force may be excellent.

[0090] The aforementioned <100> / / ND collective organization, <100> The term "xy plane" refers to an aggregate structure in which the planes are aligned parallel to the direction perpendicular to the sheet surface (ND) of the non-oriented electrical steel sheet. The plane of the non-oriented electrical steel sheet may refer to the xy plane, where the rolling direction (RD) of the steel sheet is the x axis and the transverse direction (TD) of the steel sheet is the y axis.

[0091] The texture of the non-oriented electrical steel sheet can be analyzed by using EBSD (Electron Backscatter Diffraction) based on the ND direction orientation under the R (Rolling), T (Transverse), and N (Vertical) conditions on the surface of the steel sheet, and the plane strength for each orientation can be analyzed using an orientation distribution function (ODF). [Example]

[0092] The present invention will be described in more detail with reference to preferred embodiments thereof below, which are merely examples of preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention in any way.

[0093] Example 1 (1) Hot-rolled steel sheet production: A slab containing 1.97 wt% silicon (Si), 1.0 wt% nickel (Ni), more than 0 but not more than 0.05 wt% aluminum (Al), 0.0040 wt% (40 ppm) carbon (C), 0.0040 wt% sulfur (S), 0.0015 wt% (15 ppm) nitrogen (N), and 0.0012 wt% titanium (Ti), with the remainder being iron (Fe) and other unavoidable impurities, was prepared. The slab with this alloy composition was heated to 1100°C to ensure the austenite phase (γ) stability region. The slab was then reheated at a reheating temperature (SRT) of 1170°C for 2 hours, hot-rolled at a finish rolling temperature of 850°C, and cooled and coiled at a coiling temperature of 600°C to produce a 2.0 mm thick hot-rolled steel sheet.

[0094] (2) Hot-rolled annealing and cold-rolling: The hot-rolled steel sheet was then heated to 975°C at a heating rate of 20°C / s or more, maintained at that temperature for 60 seconds, and then cooled to room temperature at a cooling rate of 20°C / s or more, thereby performing hot-rolled annealing. The hot-rolled steel sheet was then pickled and cold-rolled to produce a cold-rolled steel sheet with a thickness of 0.35 mm.

[0095] (3) Cold-rolled annealing: The cold-rolled steel sheet was then subjected to a primary heat treatment by heating it to 1100°C at a heating rate of 20°C / s or more and maintaining the temperature for 60 seconds, as shown in Figure 2. The cold-rolled steel sheet after the primary heat treatment was then cooled to 950°C at a cooling rate of 10°C / s or more and maintained at that temperature for 60 seconds, thereby performing a secondary heat treatment. The cold-rolled steel sheet after the secondary heat treatment was then cooled to room temperature at a cooling rate of 10°C / s or more to produce a non-oriented electrical steel sheet.

[0096] Example 2 As shown in FIG. 2, a non-oriented electrical steel sheet was manufactured in the same manner as in Example 1, except that the primary heat-treated cold-rolled steel sheet was cooled to 800°C at a cooling rate of 10°C / s or more during the secondary heat treatment and maintained at 800°C for 60 seconds.

[0097] Comparative Example As shown in FIG. 2, a non-oriented electrical steel sheet was manufactured in the same manner as in Example 1, except that the primary heat-treated cold-rolled steel sheet was cooled to room temperature at a cooling rate of 10° C. / s or more.

[0098] Experimental Example (1) XRD analysis: In Examples 1 and 2, the cold-rolled steel sheets were measured for XRD at the cooling temperatures (950°C, 800°C) after the secondary heat treatment using an in-situ XRD analysis device, and the peak intensity ratio (I / Imax) of the XRD pattern was shown. In the comparative example, the random texture of the cold-rolled steel sheet was measured for XRD after cooling to room temperature, and the XRD peak intensity ratio was shown.

[0099] [Table 1]

[0100] Referring to Table 1, Example 1 was subjected to a first heat treatment in the cold rolling annealing process, where the temperature was raised to and maintained in the austenite phase (γ) region, and then cooled to 950°C during the second heat treatment. The XRD analysis results confirmed that there was no {110} peak, but only {200} and {112} peaks. Example 2 was performed in the same manner as Example 1, except that the temperature was cooled to 800°C during the second heat treatment. All of the {110}, {200}, and {112} peaks were observed. Compared to the random peaks in the comparative example, the {110} orientation peak fraction was relatively low, and the {200} and {112} orientation peaks were relatively high.

[0101] Taking the results of Table 1 together, it was experimentally confirmed that the preferential orientation changes depending on the temperature conditions when the austenite phase (γ) transforms to the ferrite phase (α). Furthermore, by applying the results of Table 1, the results of intentionally controlling the final texture depending on the process conditions can be confirmed in Table 2 below.

[0102] (2) Analysis of Steel Sheet Texture and Measurement of Magnetic Properties: The texture of the non-oriented electrical steel sheets finally manufactured in the Examples and Comparative Examples was analyzed, and the magnetic flux density and iron loss were measured. The results are shown in Table 2 below. 50 ) is measured on the electrical steel sheet under a magnetic field of 5000 A / m, and the iron loss (W 15 / 50 ) was measured by applying a magnetic flux density of 1.5 Tesla at a frequency of 50 Hz to the electrical steel sheet.

[0103] [Table 2]

[0104] The results in Table 2 above show the results of experiments conducted using a process designed based on the characteristics of Table 1. In the comparative example, the temperature was raised to 1100°C, maintained for 60 seconds, and then furnace cooled, which can be considered a general heat treatment cycle rather than one that induces growth under specific temperature conditions.

[0105] In Example 1, the primary heat treatment was performed at 1100°C for 60 seconds, where the austenite phase (γ) was stable. The secondary heat treatment was performed at 950°C for 60 seconds, where only the {200} and {112} peaks of the ferrite phase (α) exist, to intentionally induce nucleation. The furnace was then cooled. After the secondary heat treatment, the specimen was cooled to room temperature, and the developed aggregate structure was confirmed to be an orientation favorable for magnetism. <100> / / ND increases to 32.6% by area, which is an unfavorable orientation for magnetism <112> / / ND was reduced to 24.3% by area.

[0106] In Example 2, the secondary heat treatment cooling temperature (800°C) is more advantageous for magnetism than the comparative example. <100> / / Although the ND fraction increased, it was confirmed that it was formed relatively less than in Example 1. In addition, it is an orientation that is unfavorable for magnetism. <112> / / ND was also reduced compared to the comparative example, but it was confirmed that it was relatively increased compared to Example 1.

[0107] The non-oriented electrical steel sheet of the comparative example has a structure that is favorable for magnetism. <100> / / ND is formed in 12.1% of the area, which is an unfavorable orientation for magnetism <112> / / It can be seen that ND is formed at a high area rate of 56.9%.

[0108] Referring to the results in Table 2, Examples 1-2 and Comparative Example all had the same component composition, but simply improved the assembly structure. As a result, the magnetic flux density increased from 1.64 to 1.65 to 1.68 [T] from Comparative Example to Example 2 to Example 1, and the iron loss decreased from 2.45 to 2.42 to 2.36 [W / kg].

[0109] Comprehensive evaluation of the results in Table 2 reveals that by designing a component composition that allows for heat treatment to transform the austenite phase (γ) into the ferrite phase (α), and by setting process conditions that allow for the formation of orientations favorable to magnetism during the phase transformation, it was possible to intentionally increase the orientations favorable to magnetism and decrease the orientations unfavorable to magnetism, ultimately achieving improved magnetic properties.

[0110] Based on the above, magnetically favorable <100> / / By maintaining the temperature at 950℃ for a certain period of time, the ND orientation is best developed. <100> / / We designed a heat treatment process that induces ND nucleation. As a result, we achieved magnetic properties that are favorable for existing continuous cooling conditions. <100> / / The effect of increasing ND direction by 20% can be obtained, and the magnetic disadvantage <112> / / ND orientation was reduced by 32.6%. The core of this invention is to use phase transformation to transform from austenite phase (γ) to ferrite phase (α), which is advantageous for magnetic properties. <100> It can be said that this is a non-oriented electrical steel sheet and manufacturing method that induces nucleation in a specific temperature range where ND orientation develops best, and then grows it to improve the texture.

[0111] Simple variations and modifications of the present invention can be easily implemented by a person having ordinary skill in the art, and all such variations and modifications can be considered to be included in the scope of the present invention.

Claims

1. A step of manufacturing a hot-rolled steel sheet using a slab containing 0.4 to 3.5 wt% silicon (Si), more than 0 to 0.05 wt% aluminum (Al), 0.002 to 3.5 wt% austenite stabilizing elements, the balance being iron (Fe) and other unavoidable impurities; cold rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet; and cold-rolling annealing the cold-rolled steel sheet; The cold rolling annealing is a step of performing a primary heat treatment by raising the temperature of the cold rolled steel sheet to an austenite single phase region temperature and maintaining the temperature; and a step of cooling the cold-rolled steel sheet after the primary heat treatment to a temperature in the ferrite-austenite two-phase region and maintaining the temperature therein, thereby subjecting the cold-rolled steel sheet to a secondary heat treatment.

2. 2. The method of manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the slab further comprises one or more of: carbon (C) greater than 0 and not greater than 0.0050 wt %; sulfur (S) greater than 0 and not greater than 0.0050 wt %; nitrogen (N) greater than 0 and not greater than 0.0050 wt %; and titanium (Ti) greater than 0 and not greater than 0.0050 wt % based on the total weight of the slab.

3. The hot-rolled steel sheet is Reheating the slab at a reheating temperature of 1110 to 1180°C; Hot rolling the reheated slab at a finish rolling temperature of 800 to 900°C; and 2. The method for producing a non-oriented electrical steel sheet according to claim 1, further comprising the step of: coiling the hot-rolled slab at a coiling temperature of 500 to 700°C.

4. The method further includes a step of hot-rolling annealing the hot-rolled steel sheet before the step of cold-rolling the hot-rolled steel sheet; The hot rolling annealing includes raising the temperature of the hot rolled steel sheet to 940 to 1110°C and maintaining the temperature; and The method for producing a non-oriented electrical steel sheet according to claim 1, further comprising the step of: cooling the hot-rolled steel sheet.

5. The hot rolling annealing is performed by raising the temperature of the hot-rolled steel sheet at a temperature rising rate of 20°C / s or more, The method for producing a non-oriented electrical steel sheet according to claim 4, wherein the cooling is carried out at a cooling rate of 20°C / s or more.

6. The cold rolling is carried out under the condition of a reduction ratio of 50 to 90%. The method for manufacturing a non-oriented electrical steel sheet according to claim 1, wherein the cold rolled steel sheet has a thickness of 0.1 to 0.5 mm.

7. The primary heat treatment includes a step of heating the cold-rolled steel sheet to 1000 to 1250°C and maintaining the temperature for 30 to 300 seconds; and 2. The method of claim 1, wherein the second heat treatment comprises cooling the first heat-treated cold-rolled steel sheet to a temperature in a ferrite-austenite two-phase region and maintaining the temperature therefor for 5 to 300 seconds.

8. The method for manufacturing a non-oriented electrical steel sheet according to claim 7, wherein the secondary heat treatment is performed by cooling the cold-rolled steel sheet subjected to the primary heat treatment at a cooling rate of 10°C / s or more.

9. Silicon (Si) 0.4 to 3.5 wt %, aluminum (Al) more than 0 to 0.05 wt %, austenite stabilizing elements 0.002 to 3.5 wt %, the balance being iron (Fe) and other unavoidable impurities, A non-oriented electrical steel sheet characterized in that the microstructure contains ferrite.

10. 10. The non-oriented electrical steel sheet according to claim 9, further comprising, based on a total weight of the non-oriented electrical steel sheet, one or more of: carbon (C) greater than 0 and not greater than 0.0050 wt %; sulfur (S) greater than 0 and not greater than 0.0050 wt %; nitrogen (N) greater than 0 and not greater than 0.0050 wt %; and titanium (Ti) greater than 0 and not greater than 0.0050 wt %.

11. The non-oriented electrical steel sheet has a thickness of 0.1 to 0.5 mm, Magnetic flux density (B ５０ ) 1.65T or more and iron loss (W １５／５０ ) 2.42 W / kg or less, 10. The non-oriented electrical steel sheet according to claim 9, having a yield strength of 200 MPa or more and a tensile strength of 300 MPa or more.

12. The non-oriented electrical steel sheet according to claim 9, wherein the non-oriented electrical steel sheet contains 15% by area or more of a <100> / / ND texture.

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