Non-oriented electrical steel sheet and method for producing same

Abstract

A non-oriented electrical steel sheet according to one embodiment of the present invention contains 1.5% to 4.5% by weight of Si, 0.1% to 1.5% by weight of Al, and 0.1% to 0.5% by weight of Mn, with the remainder being Fe and unavoidable impurities, and has an orientation having the highest strength at {110} lt when a texture is represented by ODF; 115gt, 115gt; and the angle is within 5 degrees.

Description

Technical Field

[0001] An embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same. Specifically, an embodiment of the present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same, which omit the descaling process of the hot-rolled sheet and perform a pickling process after the first cold rolling, so as to develop grains with a specific orientation to improve magnetic properties. Background Art

[0002] Non-oriented electrical steel sheets are mainly used in electric motors that convert electrical energy into mechanical energy. In this process, in order to achieve high efficiency, excellent magnetic properties of the non-oriented electrical steel sheet are required. In particular, recently, as environmentally friendly vehicles driven by electric motors instead of internal combustion engines have received attention, the demand for non-oriented electrical steel sheets used as core materials for drive motors has increased. Therefore, a non-oriented electrical steel sheet with excellent magnetic properties and strength is needed.

[0003] The magnetic properties of non-oriented electrical steel sheets are mainly evaluated by iron loss and magnetic flux density. Iron loss refers to the energy loss that occurs at a specific magnetic flux density and frequency, and magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. The lower the iron loss, the more energy-efficient motors can be manufactured under the same conditions. The higher the magnetic flux density, the smaller the motor can be or the copper loss can be reduced. Therefore, a drive motor with excellent efficiency and torque can be manufactured by using a non-oriented electrical steel sheet with low iron loss and high magnetic flux density, thereby improving the driving range and output of environmentally friendly vehicles.

[0004] According to the operating conditions of the motor, the characteristics of the non-oriented electrical steel sheet that need to be considered also change. As a general standard for evaluating the characteristics of non-oriented electrical steel sheets used in motors, the iron loss W15 / 50 when a magnetic field of 1.5 T is applied at a commercial frequency of 50 Hz is widely used. However, in non-oriented electrical steel sheets with a thickness of 0.35 mm or less used for environmentally friendly vehicle drive motors, since magnetic properties are very important at low magnetic fields of 1.0 T or less and high frequencies of 400 Hz or more, the characteristics of non-oriented electrical steel sheets are usually evaluated by the iron loss W10 / 400.

[0005] In order to improve the magnetic properties of non-oriented electrical steel sheets, the commonly used method is to add alloying elements such as Si, Al, Mn, etc. By adding such alloying elements, when the specific resistance of the steel increases, the eddy current loss decreases, thereby reducing the overall iron loss. In addition, the alloying elements are dissolved in iron as substitutional elements, generating a strengthening effect, thereby improving the strength. Conversely, as the addition amount of alloying elements such as Si, Al, Mn, etc. increases, there are disadvantages of a decrease in magnetic flux density and an increase in brittleness. When the addition amount exceeds a certain level, cold rolling cannot be performed, making it difficult to achieve commercial production. In particular, the thinner the thickness of the electrical steel sheet, the more excellent the high-frequency iron loss, but the decrease in rolling performance due to brittleness becomes a key issue. It is known that the maximum value of the total content of Si, Al, Mn is about 4.5 wt%, and in addition, high-end non-oriented electrical steel sheets with excellent magnetic properties and strength can be produced by optimizing the content of trace elements.

[0006] However, when a large amount of alloying elements with high specific resistance such as Si, Al, Mn, Cr are added, the problem of a decrease in magnetic flux density occurs. In particular, for materials that continuously require lightweight, such as environmentally friendly electric vehicle drive motors, materials with high magnetic flux density must be used.

[0007] For this reason, a method of improving characteristics by thinning the hot-rolled sheet has been proposed, and a method of improving magnetism by including high Al and undergoing two annealing and two rolling processes has been proposed. In addition, a method of hot-rolling thinning by the thin slab manufacturing method has been proposed.

[0008] However, in the general hot-rolling process, the method of reducing the thickness of the hot-rolled sheet is difficult to mass-produce due to an increase in rolling load. Although the magnetism is improved to a certain extent by adding high Al, two annealing and two rolling processes, the {110}<001> Goss texture will develop at the same time. Therefore, the circumferential characteristics of the motor will deteriorate, and surface defects will increase significantly due to the addition of high Al. Summary of the Invention

[0009] (I) Technical Problems to be Solved

[0010] An embodiment of the present invention provides a non-oriented electrical steel sheet and a manufacturing method thereof. Specifically, an embodiment of the present invention provides a non-oriented electrical steel sheet that omits the descaling process of the hot-rolled sheet and performs a pickling process after the first cold rolling, thereby enabling the growth of grains with a specific orientation to improve magnetism, and a manufacturing method thereof.

[0011] (II) Technical Solutions

[0012] The non-oriented electrical steel sheet according to an embodiment of the present invention contains 1.5% to 4.5% of Si, 0.1% to 1.5% of Al, and 0.1% to 0.5% of Mn by weight, and contains the balance of Fe and inevitable impurities. When the texture is represented by ODF, the orientation with the highest strength is within 5° of {110}<115>.

[0013] For the non-oriented electrical steel sheet according to an embodiment of the present invention, when the texture is represented by ODF, the {110}<115> orientation strength can be more than 3 times the {001}<100> orientation strength.

[0014] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain 0.001% to 0.007% by weight of Te and one or more of Sn and Sb with their respective and total contents being 0.01% to 0.1% by weight.

[0015] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of 0.005% to 0.2% by weight of Cu, 0.01% to 0.5% by weight of Cr, 0.05% by weight or less (excluding 0%) of Ni, 0.01% by weight or less (excluding 0%) of Zn, and 0.05% by weight or less (excluding 0%) of Co.

[0016] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of 0.1% by weight or less (excluding 0%) of P, 0.005% by weight or less (excluding 0%) of C, 0.005% by weight or less (excluding 0%) of S, 0.005% by weight or less (excluding 0%) of Ti, and 0.005% by weight or less (excluding 0%) of N.

[0017] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of 0.03% by weight or less (excluding 0%) of Mo, 0.0050% by weight or less (excluding 0%) of B, 0.0050% by weight or less (excluding 0%) of V, 0.0050% by weight or less (excluding 0%) of Ca, 0.0050% by weight or less (excluding 0%) of Nb, 0.005% by weight or less (excluding 0%) of Zr, and 0.0050% by weight or less (excluding 0%) of Mg.

[0018] The average grain size may be 50 μm to 150 μm.

[0019] The B50 magnetic flux density difference between the rolling direction and the direction perpendicular to rolling may be 0.05 T to 0.07 T.

[0020] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes a step of hot-rolling a slab to manufacture a hot-rolled sheet, wherein the slab contains 1.5% to 4.5% of Si, 0.1% to 1.5% of Al, and 0.1% to 0.5% of Mn by weight, and contains the balance of Fe and inevitable impurities; a step of performing first cold rolling on the hot-rolled sheet in a state where scale remains on the hot-rolled sheet to manufacture a first cold-rolled sheet; a step of pickling the first cold-rolled sheet; a step of performing second cold rolling on the pickled first cold-rolled sheet to manufacture a second cold-rolled sheet; and a step of annealing the second cold-rolled sheet, i.e., a cold-rolled sheet annealing step.

[0021] The slab may further contain 0.001% to 0.007% by weight of Te and one or more of Sn and Sb, each with a total content of 0.01% to 0.1% by weight.

[0022] The slab may further contain one or more of 0.005% to 0.2% by weight of Cu, 0.01% to 0.5% by weight of Cr, less than 0.1% (excluding 0%) by weight of Ni, less than 0.01% (excluding 0%) by weight of Zn, and less than 0.05% (excluding 0%) by weight of Co.

[0023] The slab may further contain one or more of less than 0.1% (excluding 0%) by weight of P, less than 0.005% (excluding 0%) by weight of C, less than 0.005% (excluding 0%) by weight of S, less than 0.005% (excluding 0%) by weight of Ti, and less than 0.005% (excluding 0%) by weight of N.

[0024] The slab may further contain one or more of less than 0.03% (excluding 0%) by weight of Mo, less than 0.0050% (excluding 0%) by weight of B, less than 0.0050% (excluding 0%) by weight of V, less than 0.0050% (excluding 0%) by weight of Ca, less than 0.0050% (excluding 0%) by weight of Nb, less than 0.005% (excluding 0%) by weight of Zr, and less than 0.0050% (excluding 0%) by weight of Mg.

[0025] The method for manufacturing a non-oriented electrical steel sheet may further include a step of heating the slab at 1200°C or lower before the step of manufacturing the hot-rolled sheet.

[0026] In the step of manufacturing the hot-rolled sheet, hot rolling may be performed at a finish rolling temperature of 800°C or higher and coiling may be performed at 550°C or lower.

[0027] After the step of manufacturing the hot-rolled sheet, the hot-rolled sheet may be cooled, and then first cold rolling may be performed on the cooled hot-rolled sheet.

[0028] The method for manufacturing an non-oriented electrical steel sheet may include: after the step of manufacturing a hot-rolled sheet, during the process of cooling the hot-rolled sheet, a step of re-coiling the coil at a temperature above 350°C, and performing a first cold rolling on the re-coiled hot-rolled sheet.

[0029] In the step of manufacturing the first cold-rolled sheet, the reduction ratio is 40% to 70%, and the friction coefficient between the cold rolling work roll and the steel sheet is 0.4 or more.

[0030] The method for manufacturing an non-oriented electrical steel sheet may further include: after the step of manufacturing the first cold-rolled sheet, an intermediate annealing step of annealing the first cold-rolled sheet at a temperature above 900°C.

[0031] In the step of manufacturing the second cold-rolled sheet, the reduction ratio may be 55% to 80%, and the friction coefficient between the cold rolling work roll and the steel sheet may be 0.2 or less.

[0032] The cold-rolled sheet annealing step is performed at a temperature above 850°C in an atmosphere of a mixed gas of hydrogen (H2) and nitrogen (N2).

[0033] (III) Advantageous Effects

[0034] The non-oriented electrical steel sheet according to an embodiment of the present invention improves the anisotropy of the magnetic flux density by optimizing the crystal orientation, and thus can have more excellent properties.

[0035] Ultimately, the non-oriented electrical steel sheet according to an embodiment of the present invention can contribute to the manufacture of motors for environmentally friendly vehicles, motors for high-efficiency household appliances, and ultra-high-end electric motors. Detailed Description

[0036] The terms first, second, and third, etc. are used to describe various parts, components, regions, layers, and / or elements, but are not limited thereto. These terms are only used to distinguish one part, component, region, layer, or element from another part, component, region, layer, or element. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, or element described below may be referred to as the second part, component, region, layer, or element.

[0037] The technical terms used herein are only used to refer to specific embodiments and are not intended to limit the present invention. Unless explicitly shown to have the opposite meaning, the singular form used herein also includes the plural form. The meaning of "including" used in the specification embodies specific characteristics, regions, integers, steps, actions, elements, and / or components, and does not exclude the existence or addition of other characteristics, regions, integers, steps, actions, elements, and / or components.

[0038] When a part is mentioned as being "above" or "over" another part, it may mean that it is directly above or above the other part, or there may be other parts between them. In contrast, when a part is mentioned as being "directly above" another part, there are no other parts between them.

[0039] Unless otherwise specified, % means % by weight, and 1 ppm means 0.0001 % by weight.

[0040] In one embodiment of the present invention, further including an additional element means that the additional element is included in an amount corresponding to the additional amount of the additional element instead of the balance of iron (Fe).

[0041] Although not otherwise defined, all terms used herein, including technical and scientific terms, have the same meanings as those generally understood by those of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with the relevant technical literature and the current disclosure, and unless defined, should not be interpreted as ideal or very formal meanings.

[0042] The following is a detailed description of the embodiments of the present invention so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein.

[0043] The non-oriented electrical steel sheet according to an embodiment of the present invention includes 1.5% to 4.5% of Si, 0.1% to 1.5% of Al, and 0.1% to 0.5% of Mn in weight %.

[0044] Hereinafter, the reasons for limiting the composition of the non-oriented electrical steel sheet will be described.

[0045] Si: 1.5 wt% to 4.5 wt%

[0046] Silicon (Si) serves to increase the resistivity of the material to reduce iron loss and improve strength through solid solution strengthening. If too little Si is added, the high-frequency iron loss and strength improvement effects may be minimal. If too much Si is added, the brittleness of the material increases, so that the rolling production efficiency drops sharply, and a surface oxide layer and oxide that are harmful to magnetism may be formed. Therefore, 1.5 wt % to 4.5 wt % may be included. More specifically, 2.0 wt % to 4.3 wt % may be included. More specifically, 3.0 wt % to 3.7 wt % may be included.

[0047] Al: 0.1 wt% to 1.5 wt%

[0048] Aluminum (Al) serves to increase the resistivity of the material to reduce iron loss and to increase strength by solid solution strengthening. If too little Al is added, fine nitrides are formed, which may make it difficult to obtain the effect of improving magnetic properties. If too much Al is added, too much nitride is formed to deteriorate magnetic properties, and causes problems in all processes such as steelmaking and continuous casting, which can significantly reduce production efficiency. Therefore, 0.1 wt % to 1.5 wt % of Al may be included. More specifically, 0.3 wt % to 1.2 wt % may be included. More specifically, 0.5 wt % to 1.0 wt % may be included.

[0049] Mn: 0.1 wt% to 0.5 wt%

[0050] Manganese (Mn) plays a role in increasing the resistivity of the material to improve iron loss and forming sulfides. If too little Mn is added, fine sulfides are formed to cause magnetic degradation, and if too much Mn is added, too much fine MnS is precipitated and the formation of a {111} texture that is harmful to magnetic properties is promoted, so that the magnetic flux density is sharply reduced. Therefore, 0.1 wt% to 0.5 wt% of Mn may be included. More specifically, 0.2 wt% to 0.4 wt% may be included.

[0051] The nonoriented electrical steel sheet according to an embodiment of the present invention may further include 0.001 wt % to 0.007 wt % of Te and 0.01 wt % to 0.1 wt % of one or more of Sn and Sb, each of which or the total content thereof.

[0052] Te: 0.001 wt% to 0.007 wt%

[0053] Tellurium (Te) diffuses into the oxide layer on the surface of the hot rolled coil, increases the friction coefficient between the oxide layer and the rolling work roll, and concentrates in the lower part of the oxide layer and increases the hardness, so Te can be added to prevent the oxide layer that breaks during rolling from being pressed into the base material and peeling off. When the amount of Te added is too small, its effect may not be obvious. When too much Te is added, the oxide layer is easily peeled off, causing the base material to directly contact the work roll, thereby reducing the effect, and excessive deformation bands are generated in the steel plate during cold rolling, which may lead to the development of {111} / / ND texture that is unfavorable to magnetic properties.

[0054] One or more of Sn and Sb: 0.01 wt% to 0.1 wt%

[0055] Tin (Sn) and antimony (Sb) play a role in segregating at grain boundaries and surfaces to improve the texture of the material and inhibit surface oxidation, so they can be added to improve magnetism. When the addition amounts of Sn and Sb are too small, the effects are not obvious, and the friction coefficient between the oxide layer on the surface of the hot-rolled coil and the rolling work roll is reduced, which may deteriorate the magnetic properties and surface quality. If too much Sn and Sb are added, severe segregation at grain boundaries will occur, deteriorating the surface quality, and the hardness will increase, which may cause the cold-rolled sheet to break and reduce the rolling performance. Therefore, within the above ranges, one or more of Sn and Sb can also be added. More specifically, it can contain 0.01 wt% to 0.05 wt% of Sn or 0.01 wt% to 0.05 wt% of Sb. More specifically, it can contain 0.01 wt% to 0.05 wt% of Sn and 0.01 wt% to 0.05 wt% of Sb. When Sn and Sb are added simultaneously, their total content can be 0.01 wt% to 0.1 wt%.

[0056] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of 0.005 wt% to 0.2 wt% of Cu, 0.01 wt% to 0.5 wt% of Cr, less than 0.05 wt% (excluding 0%) of Ni, less than 0.01 wt% (excluding 0%) of Zn, and less than 0.05 wt% (excluding 0%) of Co.

[0057] Cu: less than 0.01 wt%

[0058] Copper (Cu) plays a role in forming sulfides together with Mn. When Cu is also added, if too little Cu is added, CuMnS will precipitate finely and may deteriorate the magnetism. If too much Cu is added, high-temperature brittleness may occur and cracks may form during continuous casting or hot rolling. More specifically, it can contain 0.001 wt% to 0.01 wt% of Cu.

[0059] Cr: less than 0.50 wt%

[0060] Chromium (Cr) plays a role in increasing the specific resistance to improve iron loss. If too much Cr is contained, the magnetic flux density may be reduced. More specifically, when Cr is further contained, it can contain 0.01 wt% to 0.10 wt%.

[0061] Ni: less than 0.05 wt%

[0062] Nickel (Ni) does not form precipitates of fine sizes that reduce the magnetism of the steel sheet, but forms a concentrated layer on the surface or under the surface of the steel sheet, which can affect the workability during hot rolling or cold rolling.

[0063] Zn: less than 0.01 wt%

[0064] Zinc (Zn) does not form precipitates of a fine size that reduce the magnetic properties of the steel sheet, but since it is an element with a high oxygen affinity, it can promote the formation of an oxide layer on the surface of the steel sheet.

[0065] Co: 0.05 wt% or less

[0066] Cobalt (Co) does not form precipitates of a fine size that reduce the magnetic properties of the steel sheet, but it increases the high-temperature strength, which can cause poor coil shape after hot rolling.

[0067] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of P of 0.1 wt% or less (excluding 0%), C of 0.005 wt% or less (excluding 0%), S of 0.005 wt% or less (excluding 0%), Ti of 0.005 wt% or less (excluding 0%), and N of 0.005 wt% or less (excluding 0%).

[0068] P: 0.100 wt% or less

[0069] Phosphorus (P) deteriorates the hot working performance, thereby reducing the production efficiency compared to magnetic improvement. Therefore, P of 0.100 wt% or less can be included. Its lower limit is not particularly limited, but by segregating at the surface and grain boundaries of the steel sheet, it inhibits surface oxidation during annealing, hinders the diffusion of elements through the grain boundaries, and hinders the recrystallization of the {111} / / ND orientation, thereby playing a role in improving the texture. Therefore, P of 0.005 wt% can be included. More specifically, P of 0.005 wt% to 0.050 wt% can be included. More specifically, P of 0.010 wt% to 0.030 wt% can be included.

[0070] C: 0.0050 wt% or less

[0071] Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, thereby reducing the magnetic properties, but it increases the strength by hindering the movement of dislocations. If C is included in excess, the proportion of fine carbides increases, which may cause magnetic deterioration. Therefore, C of 0.0050 wt% or less can be included. The lower limit of C is not particularly limited, but considering the production efficiency, C of 0.0010 wt% or more can be included. That is, C of 0.0010 wt% to 0.0050 wt% can be included. More specifically, C of 0.0010 wt% to 0.0030 wt% can be included.

[0072] S: 0.0050 wt% or less

[0073] Sulfur (S) forms fine precipitates of MnS and CuS, thereby deteriorating magnetic properties and hot workability. Therefore, S can be contained in an amount of 0.0050 wt% or less. However, in one embodiment of the present invention, since it contributes to the growth of grains having a specific orientation and contributes to an increase in magnetic flux density, in one embodiment of the present invention, it can be added in an amount of 0.0005 wt% or more. More specifically, S can be contained in an amount of 0.0010 wt% to 0.0030 wt%.

[0074] Ti: 0.0050 wt% or less

[0075] Titanium (Ti) has a strong tendency to form precipitates in steel and forms fine carbides, nitrides or sulfides inside the base metal, thereby suppressing grain growth and domain wall movement, resulting in deterioration of iron loss. Therefore, the content of Ti can be 0.0050 wt% or less. The lower limit is not particularly limited, but considering the steelmaking cost, the content of Ti can be 0.0003 wt%. That is, Ti can be contained in an amount of 0.0003 wt% to 0.0050 wt%. More specifically, it can be contained in an amount of 0.0003 wt% to 0.0030 wt%.

[0076] N: 0.0050 wt% or less

[0077] Nitrogen (N) not only forms fine AlN precipitates inside the base metal, but also combines with other impurities and forms fine precipitates, thereby suppressing grain growth and deteriorating iron loss. Therefore, N can be contained in an amount of 0.0050 wt% or less. The lower limit of N is not particularly limited, but since N contributes to an increase in strength, the lower limit can be set to 0.0003 wt%. That is, N can be contained in an amount of 0.0003 wt% to 0.0050 wt%. More specifically, it can be contained in an amount of 0.0010 wt% to 0.0030 wt%.

[0078] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Mo of 0.03 wt% or less (excluding 0%), B of 0.0050 wt% or less (excluding 0%), V of 0.0050 wt% or less (excluding 0%), Ca of 0.0050 wt% or less (excluding 0%), Nb of 0.0050 wt% or less (excluding 0%), Zr of 0.005 wt% or less (excluding 0%), and Mg of 0.0050 wt% or less (excluding 0%).

[0079] Mo: 0.030 wt% or less

[0080] When an excessive amount of molybdenum (Mo) is added, the texture improvement effect is reduced by suppressing the segregation of segregation elements. Therefore, Mo can be contained in an amount of 0.03% by weight or less. There is no particular limitation on its lower limit, but since it plays a role in improving the texture by segregating at the surface and grain boundaries, Mo can be contained in an amount of 0.001% by weight or more. More specifically, Mo can be contained in an amount of 0.001% by weight to 0.010% by weight. More specifically, Mo can be contained in an amount of 0.005% by weight to 0.010% by weight.

[0081] B: 0.005% by weight or less

[0082] When an excessive amount of boron (B) is added, magnetic properties may deteriorate due to the formation of inclusions in the steel. Therefore, B can be contained in an amount of 0.005% by weight or less. There is no particular limitation on its lower limit, but considering the steelmaking cost, B can be contained in an amount of 0.0001% by weight. More specifically, B can be contained in an amount of 0.0001% by weight to 0.0030% by weight.

[0083] V: 0.0050% by weight or less

[0084] Vanadium (V) has a strong tendency to form precipitates in the steel and forms fine carbides or nitrides inside the base metal, thus inhibiting grain growth and domain wall movement, resulting in deterioration of iron loss. Therefore, the content of V can be 0.0050% by weight or less. There is no particular limitation on its lower limit, but considering the steelmaking cost, the content of V can be 0.0003% by weight. That is, V can be contained in an amount of 0.0003% by weight to 0.0050% by weight. More specifically, V can be contained in an amount of 0.0003% by weight to 0.0030% by weight.

[0085] Ca: 0.0050% by weight or less

[0086] Calcium (Ca) has a strong tendency to form precipitates in the steel and forms fine sulfides inside the base metal, thus inhibiting grain growth and domain wall movement, resulting in deterioration of iron loss.

[0087] Nb: 0.0050% by weight or less

[0088] Niobium (Nb) has a strong tendency to form precipitates in the steel and forms fine carbides or nitrides inside the base metal, thus inhibiting grain growth and domain wall movement, resulting in deterioration of iron loss. Therefore, the content of Nb can be 0.0050% by weight or less. There is no particular limitation on its lower limit, but considering the steelmaking cost, the content of Nb can be 0.0003% by weight. That is, Nb can be contained in an amount of 0.0003% by weight to 0.0050% by weight. More specifically, Nb can be contained in an amount of 0.0003% by weight to 0.0030% by weight.

[0089] Zr: 0.005 wt% or less

[0090] When an excessive amount of zirconium (Zr) is added, magnetic properties may deteriorate due to the formation of inclusions in the steel. Therefore, Zr may be included in an amount of 0.005 wt% or less. There is no particular limitation on the lower limit, but due to steelmaking costs, Zr may be included in an amount of 0.0001 wt%. That is, Zr may be included in an amount of 0.0001 wt% to 0.0050 wt%. More specifically, it may be included in an amount of 0.0005 wt% to 0.0030 wt%.

[0091] Mg: 0.0050 wt% or less

[0092] Magnesium (Mg) is an element that mainly combines with S to form sulfides and can affect the oxide layer on the surface of the iron material. Therefore, Mg may be included in an amount of 0.0050 wt% or less. There is no particular limitation on the lower limit, but due to steelmaking costs, Mg may be included in an amount of 0.0001 wt%. That is, Mg may be included in an amount of 0.0001 wt% to 0.0050 wt%. More specifically, it may be included in an amount of 0.0005 wt% to 0.0030 wt%.

[0093] The balance contains and inevitable impurities. Inevitable impurities refer to impurities mixed in during the steelmaking process and the manufacturing process of the non-oriented electrical steel sheet. Since this is well-known in the relevant field, detailed description thereof is omitted. In one embodiment of the present invention, addition of elements other than the above alloying components is not excluded, and various elements may be included within the scope not impairing the technical idea of the present invention. When additional elements are also included, Fe is included in place of the balance.

[0094] An non-oriented electrical steel sheet according to an embodiment of the present invention, when the texture is represented by an orientation distribution function (ODF), the orientation with the highest intensity is within 5° of {110}<115>. This means that a large number of grains with orientations near {110}<115> are formed, and the generation amount is significantly higher than that of other orientations. And {110}<115> can significantly improve the magnetic properties in the rolling direction and the direction perpendicular to rolling, thus contributing to improving the magnetism. More specifically, the orientation with the highest intensity can be within 5° of {110}<115>. The angle with {110}<115> refers to the angle formed by the {110}<115> direction and any direction in a plane including the {110}<115> direction and the arbitrary direction. There is no particular limitation on the analysis position of the ODF, but it can be analyzed by measuring the TD surface of the steel sheet wide enough. The ODF can be measured using EBSD and analyzed using OIM software. The harmonic series expansion method is used, and l (max) = 22 can be set for analysis. Specifically, the intensity at {110}<115> can be 3 to 15.

[0095] In order to form a large number of grains with orientations near {110}<115>, it is necessary to appropriately adjust the composition and manufacturing process of the steel. This will be described in detail in the manufacturing method of the non-oriented electrical steel sheet hereinafter, so the repeated description is omitted.

[0096] An non-oriented electrical steel sheet according to an embodiment of the present invention, when the texture is represented by the ODF, the intensity of the {110}<115> orientation can be more than 3 times the intensity of the {001}<100> orientation. The {001}<100> orientation is the orientation that theoretically makes the magnetic properties in the rolling direction and the direction perpendicular to rolling the most excellent. However, the {110}<115> orientation can also make the magnetic properties in the rolling direction and the direction perpendicular to rolling excellent. The fact that the intensity of the {110}<115> orientation is more than 3 times higher than that of the {001}<100> orientation means that the processes of deformation, recovery, and recrystallization applied to the material go through significantly different processes. More specifically, the intensity of the {110}<115> orientation can be 3.5 to 5 times the intensity of the {001}<100> orientation. The intensity of the {001}<100> orientation can be 0.3 to 1.5.

[0097] The average grain size of the non-oriented electrical steel sheet according to an embodiment of the present invention may be 50 μm to 150 μm. When an appropriate average grain size is ensured, the magnetic properties can be improved. In particular, the high-frequency iron loss can be improved. In an embodiment of the present invention, the grain size is a virtual circle having the same area as the area of the grain, and the diameter of the circle is defined as the grain size. The average grain size can be calculated as 2×(measured area÷number of grains÷π). 0.5 . The grain size can be measured based on the rolling vertical plane (TD plane). The measurement position is not particularly limited, but it can be measured at the 1 / 4 to 3 / 4 points of the overall thickness of the steel sheet. More specifically, the average grain size may be 60 μm to 95 μm.

[0098] The non-oriented electrical steel sheet according to an embodiment of the present invention has excellent anisotropy of magnetic flux density and excellent high-frequency iron loss. When manufacturing an electric motor for environmentally friendly vehicle drive using the non-oriented electrical steel sheet according to an embodiment of the present invention, while minimizing the cost increase, the efficiency of the motor is improved, thereby having the advantage of being able to increase the driving distance of the environmentally friendly vehicle on a single charge.

[0099] Specifically, based on a thickness of 0.25 mm of the non-oriented electrical steel sheet, the iron loss (W 10 / 400 ) can be 12.0 W / kg or less, the magnetic flux density (B 50L ) measured in the rolling direction can be 1.69 T or more, and the magnetic flux density (B 50C ) measured in the rolling vertical direction can be 1.65 T or more. More specifically, the iron loss (W 10 / 400 ) can be 10.5 W / kg to 11.5 W / kg, the magnetic flux density (B 50L ) measured in the rolling direction can be 1.70 T to 1.75 T, and the magnetic flux density (B 50C ) measured in the rolling vertical direction can be 1.66 T to 1.70 T.

[0100] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention includes: a step of hot rolling a slab to manufacture a hot-rolled sheet; a step of performing first cold rolling on the hot-rolled sheet in a state where scale remains to manufacture a first cold-rolled sheet; a step of pickling the first cold-rolled sheet; a step of performing second cold rolling on the pickled first cold-rolled sheet to manufacture a second cold-rolled sheet; and a cold-rolled sheet annealing step of annealing the second cold-rolled sheet.

[0101] First, the slab is hot rolled.

[0102] Regarding the alloy composition of the slab, it has been described in the alloy composition of the non-oriented electrical steel sheet above, so repeated description is omitted. Since there is no substantial change in the alloy composition during the manufacturing process of the non-oriented electrical steel sheet, the alloy compositions of the non-oriented electrical steel sheet and the slab are substantially the same.

[0103] Specifically, the slab contains 1.5% to 4.5% of Si, 0.1% to 1.5% of Al, 0.1% to 0.5% of Mn by weight%, and also contains the balance of Fe and inevitable impurities.

[0104] Regarding additional elements other than these, they have been described in the alloy composition of the non-oriented electrical steel sheet, so repeated description is omitted.

[0105] The slab can be heated before hot rolling. There is no limit to the heating temperature of the slab, but the slab can be heated at 1200°C or below. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab redissolve and then precipitate finely during hot rolling and annealing, thereby suppressing grain growth and reducing magnetism.

[0106] Next, the slab is hot rolled to manufacture a hot rolled sheet. The thickness of the hot rolled sheet can be 1.8 mm to 2.3 mm. In the step of manufacturing the hot rolled sheet, the finish rolling temperature can be 800°C or above. Specifically, it can be 800°C to 1000°C. The hot rolled sheet can be coiled at a temperature of 550°C or below. By coiling the hot rolled sheet at a lower temperature, it is beneficial to form an oxide layer that can increase the friction coefficient in the first cold rolling process. More specifically, the coiling temperature of the hot rolled sheet can be 400°C to 525°C.

[0107] Next, under the state of the residual scale on the hot-rolled sheet, the hot-rolled sheet is subjected to the first cold rolling. When hot rolling is performed, since it comes into contact with air at high temperature, scale is generated on the surface of the hot-rolled sheet. Conventionally, the scale is removed by pickling, sandblasting or surface grinding and then cold rolling is carried out. In an embodiment of the present invention, the scale removal processes such as pickling, sandblasting or surface grinding are omitted and cold rolling is performed. Since cold rolling is carried out in a state where the pickling process is omitted, the friction between the rolling work roll and the steel sheet is increased. Therefore, during the rolling process, in addition to plane deformation, shear deformation is also carried out simultaneously, and specific orientations are developed during recrystallization annealing. In an embodiment of the present invention, the scale refers to the part where elements such as Fe, Al, Si, etc. combine with oxygen on the surface of the steel sheet to form a phase different from the base material. The residual scale refers to the scale with a thickness of at least 1 μm remaining on the hot-rolled sheet. At this time, the scale thickness refers to the sum of the scale thicknesses formed on both surfaces of the steel sheet. When the thickness of the residual scale is too thin, the effects brought about by the remaining scale may not be fully exerted. Even if the scale thickness is thicker, the effects will not be improved, and there is a problem of reduced yield of the steel sheet. More specifically, a scale with a thickness of 0.1 μm to 1 μm can be left.

[0108] When cold rolling is carried out in a state where the scale remains, the scale may break and cause physical defects on the surface of the steel sheet. In an embodiment of the present invention, by controlling the holding time in the range of 400°C to 500°C after coiling the hot-rolled sheet, Te can be concentrated under the surface oxide layer of the steel sheet, so that the oxide layer can be easily peeled off during the first cold rolling, thereby solving the above problems.

[0109] After the step of manufacturing the hot-rolled sheet, the hot-rolled sheet is cooled, and the cooled hot-rolled sheet can be subjected to the first cold rolling. That is, after hot rolling, the annealing of the hot-rolled sheet can be omitted and the first cold rolling can be carried out. When the annealing of the hot-rolled sheet is omitted, the oxide layer that causes surface defects can be harmlessly removed by retaining the Te-concentrated layer under the surface oxide layer of the steel sheet.

[0110] It may include the step of re-coiling the coil at a temperature of 350°C or higher during the process of cooling the hot-rolled sheet. By re-coiling the coil, the oxide layer that may cause surface defects is pre-crushed, so that it can be easily partially removed during the first cold rolling. More specifically, the re-coiling can be carried out at a temperature of 375°C to 450°C.

[0111] In the step of manufacturing the first cold-rolled sheet, the reduction ratio can be 40% to 70%. The reduction ratio can be calculated by the following formula: (thickness before rolling - thickness after rolling) / thickness before rolling. When the reduction ratio is too low, the rolling load during the second cold rolling increases, resulting in a decrease in production efficiency and an increase in the reduction ratio of the second cold rolling. Therefore, it may be difficult to promote the recrystallization of the fine <111> / / ND orientation. Conversely, when the reduction ratio is too high, the cold rolling load increases and the possibility of sheet breakage also increases. More specifically, the reduction ratio can be 50% to 65%.

[0112] The first cold rolling step can be performed at a temperature of 60°C to 300°C. This temperature can be naturally increased due to the friction between the steel sheet and the roll or by heating externally. When the temperature is too low, the rolling load increases significantly, and problems such as slippage occur where the steel sheet does not roll between the rolls. When the temperature is too high, oxidation of Si and Al may occur on the surface of the steel sheet, magnetic degradation, and problems such as the combustion of rolling oil may occur. More specifically, preferably, it is performed at a temperature of 70°C to 250°C. The above temperature refers to the temperature of the steel sheet.

[0113] At this time, during the first cold rolling process, the friction coefficient between the cold rolling work roll and the steel sheet can be 0.4 or more. When there are multiple work rolls, the friction coefficient with the work roll in the first position can be 0.4 or more. The higher the friction coefficient, when performing the final recrystallization annealing, it is beneficial to develop a texture favorable for magnetism. More specifically, it can be 0.45 to 0.7.

[0114] After the step of manufacturing the first cold-rolled sheet, an intermediate annealing step of annealing the first cold-rolled sheet at 900°C can also be included. When the annealing temperature is too low, the grain size becomes fine, the grain boundaries increase, so that the number of recrystallization nuclei of the <111> / / ND orientation at the grain boundaries during the second cold rolling increases. The final magnetic flux density becomes inferior. Specifically, the temperature of the intermediate annealing step can be 900°C to 1100°C. The intermediate annealing time can be 10 seconds to 600 seconds.

[0115] Next, the first cold-rolled sheet is pickled. When scale remains on the finally manufactured non-oriented electrical steel sheet, the magnetism is damaged. In addition, when performing the second cold rolling in a state where scale remains, traces of the scale being pressed into the surface or peeled off from the surface form irregularities, which can deteriorate the operating stability and magnetic properties of the motor. After pickling, the scale is completely removed or exists with a thickness of 0.01μm or less. Pickling not only refers to acid pickling, but also includes all physical and chemical methods of removing scale. The pickling method can include acid pickling, sandblasting, or surface grinding.

[0116] Next, the pickled first cold-rolled sheet is subjected to a second cold rolling. At this time, the reduction ratio can be 55% to 80%. When the reduction ratio is too low, the strain energy accumulated in the rolled steel sheet is small, and recrystallization is difficult in the subsequent annealing process, resulting in the retention of the rolling texture, which may cause problems in improving the magnetic flux density and iron loss. On the contrary, when the reduction ratio is too high, the recrystallization of <111> / / ND-oriented grains is promoted in the subsequent annealing process, and the grains become fine, so problems such as inferior magnetic flux density and increased iron loss may occur. More specifically, the reduction ratio can be 60% to 75%.

[0117] At this time, when performing the second cold rolling, the friction coefficient between the cold rolling work roll and the steel sheet can be 0.2 or less. The lower the friction coefficient, the more beneficial it is to maintain the texture formed during the intermediate annealing without being transformed into a texture unfavorable to magnetism due to shear deformation. More specifically, it can be 0.01 to 0.15.

[0118] The final rolling thickness can be 0.1 mm to 0.35 mm.

[0119] Next, the second cold-rolled sheet is annealed. The cold-rolled sheet annealing step can be carried out in a mixed gas and atmosphere of hydrogen (H2) and nitrogen (N2). The mixed gas can contain 40% by volume or less of hydrogen and 60% by volume or more of nitrogen.

[0120] The cold-rolled sheet annealing step can be carried out at a temperature of 850 °C or higher. The above temperature refers to the soaking temperature. When the soaking temperature is too low, the grains cannot grow sufficiently, resulting in possible problems of increased hysteresis loss and deteriorated iron loss. When the soaking temperature is too high, there may be problems of increased eddy current loss and a sharp decrease in magnetic flux density. More specifically, annealing can be carried out at a temperature of 850 °C to 1100 °C. Annealing can be carried out for 30 seconds to 50 seconds.

[0121] During the annealing of the cold-rolled sheet, all (i.e., 99% or more) of the processing texture formed in the cold rolling step can be recrystallized.

[0122] After annealing the cold-rolled sheet, an insulating coating can be formed. The insulating coating can be treated by an organic, inorganic, or organic-inorganic composite coating, or can be treated by other insulating coating materials.

[0123] Hereinafter, the present invention will be described in more detail by way of examples. However, such examples are only for exemplifying the present invention, and the present invention is not limited thereto.

[0124] Example 1

[0125] A slab is manufactured from the composition shown in Table 1, containing Fe with a margin and inevitable impurities. It is heated to 1150 °C and hot-rolled at a final rolling temperature of 880 °C to produce a hot-rolled sheet with a thickness of 2.0 m. The specimen number B2 has the scale removed from the hot-rolled sheet by pickling.

[0126] After that, annealing of the hot-rolled sheet is omitted, and the first cold rolling is carried out under the conditions shown in the table, and the scale is completely removed by pickling. Intermediate annealing is carried out and the second cold rolling is carried out to a final thickness of 0.25 mm. The steel sheet after the second cold rolling is annealed at the temperature shown in the table.

[0127] The measurement methods for magnetic properties such as magnetic flux density and iron loss are as follows: Specimens with a width of 60 mm × a length of 60 mm × 5 pieces are cut from each specimen. The iron loss is measured in the rolling direction and the direction perpendicular to rolling using a single sheet tester, and the average value is shown. The magnetic flux density is measured in the rolling direction and the direction perpendicular to rolling.

[0128] At this time, W 10 / 400 refers to the iron loss when a magnetic flux density of 1.0 T is induced at a frequency of 400 Hz, and B 50 refers to the magnetic flux density induced under a magnetic field of 5000 A / m.

[0129] The ODF is analyzed using EBSD and OIM software. The harmonic series expansion method is used, and the analysis is carried out with l (maximum (max)) = 22 set.

[0130] Table 1

[0131]

[0132] Table 2

[0133]

[0134] Table 3

[0135]

[0136] Table 4

[0137]

[0138] Table 5

[0139]

[0140] As shown in Tables 1 to 3, in the inventive examples where the steel composition is appropriately adjusted and a part of the scale remains on the hot-rolled sheet, it can be confirmed that a specific texture structure is developed, and the iron loss and magnetic flux density are excellent. In particular, an appropriate magnetic flux density difference between the rolling direction and the direction perpendicular to rolling is obtained.

[0141] Conversely, when the steel composition is not appropriately adjusted, it can be confirmed that the iron loss and magnetic flux density are inferior.

[0142] In addition, even when the steel composition is appropriately adjusted, when the scale on the hot-rolled sheet is completely removed, it can be confirmed that a specific texture cannot develop, and thus the iron loss and magnetic flux density are inferior. In addition, when the scale is not removed after the first cold rolling, it can be confirmed that the iron loss and magnetic flux density are inferior due to the scale.

[0143] In addition, when a part of the scale on the hot-rolled sheet is removed, it can be confirmed that the development of a specific texture is insufficient and the magnetic properties are relatively inferior. In addition, when the scale is not sufficiently removed after the first cold rolling, it can be confirmed that the magnetic properties are relatively inferior.

[0144] The present invention is not limited to the embodiments, but can be made into various different forms. Those of ordinary skill in the technical field to which the present invention pertains should understand that it can also be implemented in other specific forms without changing the technical idea or essential features of the present invention. Therefore, the embodiments described above are to be understood as illustrative in all respects and not restrictive.

Claims

1. An non-oriented electrical steel sheet, characterized in that, it contains 1.5% to 4.5% of Si, 0.1% to 1.5% of Al and 0.1% to 0.5% of Mn by weight%, and contains the balance of Fe and inevitable impurities, when the texture is represented by ODF, the orientation with the highest strength is within 5° of {110}<115>.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that, when the texture is represented by ODF, the strength of the {110}<115> orientation is more than 3 times that of the {001}<100> orientation.

3. The non-oriented electrical steel sheet according to claim 1, characterized in that, the non-oriented electrical steel sheet further contains 0.001 wt% to 0.007 wt% of Te and one or more of Sn and Sb with their respective and total contents being 0.01 wt% to 0.1 wt%.

4. The non-oriented electrical steel sheet according to claim 1, characterized in that, the non-oriented electrical steel sheet further contains one or more of 0.005 wt% to 0.2 wt% of Cu, 0.01 wt% to 0.5 wt% of Cr, Ni of 0.05 wt% or less and not including 0%, Zn of 0.01 wt% or less and not including 0%, and Co of 0.05 wt% or less and not including 0%.

5. The non-oriented electrical steel sheet according to claim 1, characterized in that, the non-oriented electrical steel sheet further contains one or more of P of 0.1 wt% or less and not including 0%, C of 0.005 wt% or less and not including 0%, S of 0.005 wt% or less and not including 0%, Ti of 0.005 wt% or less and not including 0%, and N of 0.005 wt% or less and not including 0%.

6. The non-oriented electrical steel sheet according to claim 1, characterized in that, the non-oriented electrical steel sheet further contains one or more of Mo of 0.03 wt% or less and not including 0%, B of 0.0050 wt% or less and not including 0%, V of 0.0050 wt% or less and not including 0%, Ca of 0.0050 wt% or less and not including 0%, Nb of 0.0050 wt% or less and not including 0%, Zr of 0.005 wt% or less and not including 0%, and Mg of 0.0050 wt% or less and not including 0%.

7. The non-oriented electrical steel sheet according to claim 1, characterized in that, the average grain size is 50 μm to 150 μm.

8. A method for manufacturing an non-oriented electrical steel sheet, characterized in that, Comprising: a step of hot rolling a slab to produce a hot rolled sheet, the slab containing 1.5% to 4.5% of Si, 0.1% to 1.5% of Al and 0.1% to 0.5% of Mn by weight%, and containing the balance of Fe and inevitable impurities; a step of performing a first cold rolling on the hot rolled sheet in a state where the hot rolled sheet has residual scale to produce a first cold rolled sheet; a step of pickling the first cold rolled sheet; a step of performing a second cold rolling on the pickled first cold rolled sheet to produce a second cold rolled sheet; and a step of annealing the second cold rolled sheet, which is a cold rolled sheet annealing step.

9. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, the slab further contains 0.001% to 0.007% by weight of Te and one or more of Sn and Sb with their respective total contents being 0.01% to 0.1% by weight.

10. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, the slab further contains one or more of 0.005% to 0.2% by weight of Cu, 0.01% to 0.5% by weight of Cr, Ni of 0.1% or less and excluding 0%, Zn of 0.01% or less and excluding 0%, and Co of 0.05% or less and excluding 0%.

11. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, the slab further contains one or more of P of 0.1% or less and excluding 0%, C of 0.005% or less and excluding 0%, S of 0.005% or less and excluding 0%, Ti of 0.005% or less and excluding 0%, and N of 0.005% or less and excluding 0%.

12. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, the slab further contains one or more of Mo of 0.03% or less and excluding 0%, B of 0.0050% or less and excluding 0%, V of 0.0050% or less and excluding 0%, Ca of 0.0050% or less and excluding 0%, Nb of 0.0050% or less and excluding 0%, Zr of 0.005% or less and excluding 0%, and Mg of 0.0050% or less and excluding 0%.

13. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, the manufacturing method of the non-oriented electrical steel sheet further includes: before the step of manufacturing the hot-rolled sheet, a step of heating the slab at 1200°C or below.

14. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, in the step of manufacturing the hot-rolled sheet, hot rolling is performed at a finish rolling temperature of 800°C or above and coiling is performed at 550°C or below.

15. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, after the step of manufacturing the hot-rolled sheet, the hot-rolled sheet is cooled and the cooled hot-rolled sheet is subjected to first cold rolling.

16. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, the manufacturing method of the non-oriented electrical steel sheet includes: after the step of manufacturing the hot-rolled sheet, during the process of cooling the hot-rolled sheet, a step of re-coiling the coil at a temperature of 350°C or above, and the re-coiled hot-rolled sheet is subjected to first cold rolling.

17. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that, in the step of manufacturing the first cold-rolled sheet, the reduction ratio is 40% to 70%, and the friction coefficient between the cold rolling work roll and the steel sheet is 0.4 or above.

18. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that: The manufacturing method of the non-oriented electrical steel sheet further includes: An intermediate annealing step of annealing the first cold-rolled sheet at a temperature above 900 °C after the step of manufacturing the first cold-rolled sheet.

19. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that: In the step of manufacturing the second cold-rolled sheet, the reduction ratio is 55% to 80%, and the friction coefficient between the cold-rolling work roll and the steel sheet is 0.2 or less.

20. The manufacturing method of the non-oriented electrical steel sheet according to claim 8, characterized in that: The cold-rolled sheet annealing step is performed at a temperature above 850 °C in a mixed gas atmosphere of hydrogen and nitrogen.

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