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, in wt%, 3.0% to 5.0% of Si, 0.1% to 1.4% of Mn, and 0.3% to 1.3% of Al, with the balance being Fe and unavoidable impurities. The non-oriented electrical steel sheet according to one embodiment of the present invention may have a length of irregularities having a height difference of 1.0 [mu] m or more with respect to the average height of 3 mm or less when a 5 mm * 5 mm region of the surface is observed.

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 reduce the temperature deviation of the overall length of the coil during hot rolling by performing accelerated rolling during hot rolling, thereby improving surface characteristics and 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. For this reason, a non-oriented electrical steel sheet with excellent magnetic properties and strength is required.

[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 efficient the electric motor can be manufactured under the same conditions. The higher the magnetic flux density, the smaller the electric 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 electric motor, the characteristics of the non-oriented electrical steel sheet to be considered also change. As a general standard for evaluating the characteristics of non-oriented electrical steel sheets used in electric 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 in 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, producing a strengthening effect, thereby increasing the strength. Conversely, as the addition amount of alloying elements such as Si, Al, Mn increases, there are disadvantages of decreased magnetic flux density and increased 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. The maximum value of the total content of commercially producible Si, Al, and Mn is limited. In addition to this, high-end non-oriented electrical steel sheets with excellent magnetic properties and strength can be produced by optimizing the content of trace elements.

[0006] On the other hand, the surface shape of the steel sheet also affects the magnetism, but no technology for improving it has been proposed. Summary of the Invention

[0007] (I) Technical Problems to be Solved

[0008] 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 and a manufacturing method thereof that improve surface characteristics and magnetism by performing accelerated rolling during the hot rolling process to reduce the temperature deviation of the overall length of the coil during hot rolling.

[0009] (II) Technical Solutions

[0010] The non-oriented electrical steel sheet according to an embodiment of the present invention contains 3.0% to 5.0% of Si, 0.1% to 1.4% of Mn, and 0.3% to 1.3% of Al by weight%, and contains the balance of Fe and inevitable impurities.

[0011] For the non-oriented electrical steel sheet according to an embodiment of the present invention, when observing a 5 mm × 5 mm area on the surface, the length of the unevenness with a height difference of 1.0 μm or more relative to the average height can be 3 mm or less.

[0012] The magnetic flux density B50 is 1.603 + 0.96 × t 2 (T) or more, and the iron loss W10 / 400 is 7.231 + 21.385 × t (W / kg) or less.

[0013] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of P at 0.1% by weight or less (excluding 0%), Sn at 0.1% by weight or less (excluding 0%), and Sb at 0.1% by weight or less (excluding 0%).

[0014] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of C of 0.005 wt% or less (excluding 0%), N 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%), Nb of 0.005 wt% or less (excluding 0%), and V of 0.005 wt% or less (excluding 0%).

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

[0016] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of Bi of 0.200 wt% or less (excluding 0%), Pb of 0.200 wt% or less (excluding 0%), Ge of 0.200 wt% or less (excluding 0%), and As of 0.200 wt% or less (excluding 0%).

[0017] 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%), Ca 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%).

[0018] 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, the slab containing 3.0% to 5.0% of Si, 0.1% to 1.4% of Mn, and 0.3% to 1.3% of Al by weight%, and containing the balance of Fe and inevitable impurities, a step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet, and a step of annealing the cold-rolled sheet; in the step of manufacturing the hot-rolled sheet, the speed at which the front end of the rough-rolled bar is loaded into the hot finish rolling mill is 300 m / min to 800 m / min, and the speed at which the rear end is loaded is 1.25 times or more relative to the front end of the rough-rolled bar.

[0019] The slab may further contain one or more of P of 0.1 wt% or less (excluding 0%), Sn of 0.1 wt% or less (excluding 0%), and Sb of 0.1 wt% or less (excluding 0%).

[0020] The slab may also contain one or more of C of 0.005 wt% or less (excluding 0%), N 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%), Nb of 0.005 wt% or less (excluding 0%), and V of 0.005 wt% or less (excluding 0%).

[0021] The slab may also contain one or more of Cu of 0.005 wt% to 0.2 wt%, Cr of 0.01 wt% to 0.5 wt%, Ni of 0.05 wt% or less (excluding 0%), and Zn of 0.01 wt% or less (excluding 0%).

[0022] The slab may also contain one or more of Bi of 0.200 wt% or less (excluding 0%), Pb of 0.200 wt% or less (excluding 0%), Ge of 0.200 wt% or less (excluding 0%), and As of 0.200 wt% or less (excluding 0%).

[0023] The slab may also contain one or more of Mo of 0.03 wt% or less (excluding 0%), B of 0.0050 wt% or less (excluding 0%), Ca 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%).

[0024] The method for manufacturing the non-oriented electrical steel sheet may further include a step of heating the slab at 1200°C or less before the step of manufacturing the hot-rolled sheet.

[0025] In the step of manufacturing the hot-rolled sheet, it may include a step of rough rolling the slab to manufacture a bar, a step of finish rolling the bar, and a step of coiling the finish-rolled hot-rolled sheet; when starting the finish rolling step, the temperature deviation between the region from the most front end of the bar to 50 m and the region from the last end to 50 m is 30°C or less.

[0026] The speed at which the slab is charged into the hot roughing mill may be 40 m / min to 100 m / min.

[0027] The method for manufacturing the non-oriented electrical steel sheet may further include a hot-rolled sheet annealing step of annealing the hot-rolled sheet at 600°C to 1100°C after the step of manufacturing the hot-rolled sheet.

[0028] The step of manufacturing the cold-rolled sheet may include a step of first cold-rolling the hot-rolled sheet to manufacture a first cold-rolled sheet; a step of intermediate annealing the first cold-rolled sheet; and a step of second cold-rolling the first cold-rolled sheet to manufacture a second cold-rolled sheet.

[0029] (III) Advantageous Effects

[0030] The non-oriented electrical steel sheet according to an embodiment of the present invention has excellent surface shape, magnetic flux density, and iron loss at the same time.

[0031] Ultimately, the non-oriented electrical steel sheet according to an embodiment of the present invention can contribute to the manufacture of motors for eco-friendly vehicles, motors for high-efficiency household appliances, and ultra-high-end electric motors. Detailed Description of the Invention

[0032] The terms first, second, 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.

[0033] The technical terms used herein are only for referring to specific embodiments and are not intended to limit the present invention. Unless explicitly stated to the contrary, the singular forms used herein also include the plural forms. The meaning of "comprising" used in the specification is to specify a specific property, region, integer, step, action, element, and / or component, and does not exclude the existence or addition of other properties, regions, integers, steps, actions, elements, and / or components.

[0034] When referring to a certain part being "above" or "on" another part, this may mean that it is directly above or on the other part, or there may be other parts between them. In contrast, when referring to a certain part being "directly above" another part, there are no other parts between them.

[0035] Also, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

[0036] In an embodiment of the present invention, the meaning of further including additional elements means including the additional elements by substituting the additional amount of the additional elements for the remaining iron (Fe).

[0037] All terms, including technical terms and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs, although not defined otherwise. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the content currently disclosed. Unless defined otherwise, they should not be interpreted as ideal or overly formal meanings.

[0038] 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.

[0039] The nonoriented electrical steel sheet according to an embodiment of the present invention includes, by weight %, 3.0% to 5.0% of Si, 0.1% to 1.4% of Mn, and 0.3% to 1.3% of Al, and the balance of Fe and inevitable impurities.

[0040] Hereinafter, the reasons for limiting the composition of the non-oriented electrical steel sheet will be described.

[0041] Si: 3.0 wt% to 5.0 wt%

[0042] Silicon (Si) serves to increase the resistivity of the material to reduce iron loss. If too little Si is added, the effect of improving high-frequency iron loss 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. More specifically, 3.2 wt% to 4.5 wt% may be included. More specifically, 3.3 wt% to 4.0 wt% may be included.

[0043] Mn: 0.1 wt% to 1.4 wt%

[0044] Manganese (Mn) plays a role in increasing the specific resistance 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. More specifically, 0.3 wt% to 1.0 wt% may be included.

[0045] Al: 0.3% to 1.3%

[0046] Aluminum (Al) plays a role in increasing the resistivity of the material to reduce iron loss and improving strength through solid solution strengthening. If too little Al is added, fine nitrides are formed, and it may be 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. More specifically, 0.5 wt % to 1.0 wt % may be included. More specifically, 0.6 wt % to 0.9 wt % may be included.

[0047] 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% by weight or less (excluding 0%), Sn of 0.1% by weight or less (excluding 0%), and Sb of 0.1% by weight or less (excluding 0%).

[0048] P: 0.1% by weight or less

[0049] Phosphorus (P) is a grain boundary segregation element. If P is added excessively, the strength uniformity in the rolling direction and the direction perpendicular to rolling may deteriorate due to delayed recrystallization. More specifically, P may contain 0.0001% by weight to 0.05% by weight. More specifically, P may contain 0.001% by weight to 0.01% by weight.

[0050] Sn: 0.1% by weight or less (excluding 0%) and / or Sb: 0.1% by weight or less (excluding 0%)

[0051] Tin (Sn) and antimony (Sb) play a role in segregating at grain boundaries and on the surface to improve the texture of the material and inhibit surface oxidation. Therefore, they can be added to improve magnetism. If Sn and Sb are added excessively, severe grain boundary segregation will occur, deteriorating the surface quality, increasing the hardness, possibly causing fracture of the cold-rolled sheet, and reducing the rolling performance. Therefore, within the above ranges, one or more of Sn and Sb can be further added. More specifically, it may further contain one or more of Sn of 0.001% by weight to 0.08% by weight and Sb of 0.001% by weight to 0.08% by weight. More specifically, it may further contain one or more of Sn of 0.01% by weight to 0.05% by weight and Sb of 0.01% by weight to 0.05% by weight.

[0052] The non-oriented electrical steel sheet according to an embodiment of the present invention may further contain one or more of C of 0.005% by weight or less (excluding 0%), N of 0.005% by weight or less (excluding 0%), S of 0.005% by weight or less (excluding 0%), Ti of 0.005% by weight or less (excluding 0%), Nb of 0.005% by weight or less (excluding 0%), and V of 0.005% by weight or less (excluding 0%).

[0053] C: 0.0050% by weight or less

[0054] Carbon (C) causes magnetic aging, combines with other impurity elements to form carbides, thereby reducing magnetic properties, but increases strength by hindering dislocation movement. If too much C is included, the proportion of fine carbides increases, which may lead to magnetic deterioration. There is no particular limitation on the lower limit of C, but considering production efficiency, 0.0005% by weight or more can be included. That is, 0.0005% to 0.0050% by weight of C can be included. More specifically, 0.0010% to 0.0030% by weight can be included.

[0055] N: 0.0050% by weight or less

[0056] Nitrogen (N) not only forms fine AlN precipitates inside the base metal, but also combines with other impurities to form fine precipitates, thereby inhibiting grain growth and deteriorating iron loss. Therefore, 0.0050% by weight or less of N can be included. There is no particular limitation on the lower limit of N, but since N helps to increase strength, the lower limit can be set at 0.0003% by weight. That is, 0.0003% to 0.0050% by weight of N can be included. More specifically, 0.0010% to 0.0030% by weight can be included.

[0057] S: 0.0050% by weight or less

[0058] Sulfur (S) forms fine precipitates of MnS and CuS, thereby deteriorating magnetic properties and hot workability. However, in one embodiment of the present invention, since it helps the development of grains with a specific orientation and helps to increase magnetic flux density, in one embodiment of the present invention, 0.0005% by weight or more can be added. More specifically, 0.0010% to 0.0030% by weight of S can be included.

[0059] Ti: 0.0050% by weight or less

[0060] Titanium (Ti) has a strong tendency to form precipitates in steel and forms fine carbides, nitrides or sulfides inside the base metal, thereby inhibiting grain growth and domain wall movement, resulting in deterioration of iron loss. Therefore, the content of Ti can be 0.0050% by weight or less. There is no particular limitation on the lower limit, but considering the steelmaking cost, the content of Ti can be 0.0003% by weight. That is, 0.0003% to 0.0050% by weight of Ti can be included. More specifically, 0.0003% to 0.0030% by weight can be included.

[0061] Nb: 0.0050% by weight or less

[0062] Niobium (Nb) has a strong tendency to form precipitates in steel, and forms fine carbides, nitrides or sulfides inside the base material, thereby inhibiting grain growth and domain wall movement, resulting in iron loss degradation. Therefore, the content of Nb can be 0.0050 wt% or less. There is no particular lower limit, but considering the steelmaking cost, the content of Nb can be 0.0003 wt%. That is, 0.0003 wt% to 0.0050 wt% of Nb can be included. More specifically, 0.0003 wt% to 0.0030 wt% of Nb can be included.

[0063] V: 0.0050 wt% or less

[0064] Vanadium (V) has a strong tendency to form precipitates in steel, and forms fine carbides, nitrides or sulfides inside the base material, thereby inhibiting grain growth and domain wall movement, resulting in iron loss degradation. Therefore, the V content can be 0.0050 wt% or less. The lower limit is not particularly limited, but considering the steelmaking cost, the V content can be 0.0003 wt%. That is, 0.0003 wt% to 0.0050 wt% of V can be included. More specifically, 0.0003 wt% to 0.0030 wt% of V can be included.

[0065] The nonoriented electrical steel sheet according to an embodiment of the present invention may further include at least one of 0.005 wt % to 0.2 wt % of Cu, 0.01 wt % to 0.5 wt % of Cr, 0.05 wt % or less (excluding 0%) of Ni, and 0.01 wt % or less (excluding 0%) of Zn.

[0066] Cu: 0.005 wt% to 0.2 wt%

[0067] Copper (Cu) plays a role in forming sulfides together with Mn. When Cu is also added, if Cu is added too little, CuMnS is finely precipitated and the magnetic properties may be deteriorated. If Cu is added too much, high-temperature brittleness may occur and cracks may be formed during continuous casting or hot rolling. More specifically, 0.01 wt% to 0.1 wt% of Cu may be included.

[0068] Cr: 0.01 wt% to 0.50 wt%

[0069] Chromium (Cr) plays a role in improving the specific resistance to improve the iron loss. If too little Cr is added, the specific resistance improvement effect may be insufficient. If too much Cr is included, the magnetic flux density may be reduced. More specifically, when Cr is also included, 0.05 wt% to 0.30 wt% of Cr may be included.

[0070] Ni: 0.05 wt% or less

[0071] Nickel (Ni) reacts with impurity elements to form fine sulfides, carbides, and nitrides, which may have an adverse effect on magnetism. More specifically, it may contain 0.0001% to 0.0500% by weight of Ni. More specifically, it may contain 0.0010% to 0.0100% by weight.

[0072] Zn: 0.01% by weight or less

[0073] When the content of zinc (Zn) is excessive, it may act as an impurity and cause magnetic degradation. Therefore, Zn can also be added within the aforementioned range. More specifically, it may contain 0.0001% to 0.0100% by weight. More specifically, it may contain 0.0005% to 0.0050% by weight.

[0074] The non-oriented electrical steel sheet according to an embodiment of the present invention may also contain one or more of Bi of 0.200% by weight or less (excluding 0%), Pb of 0.200% by weight or less (excluding 0%), Ge of 0.200% by weight or less (excluding 0%), and As of 0.200% by weight or less (excluding 0%).

[0075] When bismuth (Bi), lead (Pb), germanium (Ge), and arsenic (As) are additionally added, they segregate at the grain boundaries, relieving the stress concentration at the grain boundaries during cold rolling, thereby suppressing the recrystallization of <111> / / ND orientation grains during subsequent recrystallization annealing, and thus improving the magnetic flux density. If these elements are added appropriately, the aforementioned effects can be additionally obtained, but if these elements are contained in excessive amounts, a large amount of segregation occurs and grain growth is inhibited, which may instead cause degradation of magnetic flux density and iron loss. More specifically, it may also contain one or more of Bi of 0.0001% to 0.200% by weight, Pb of 0.0001% to 0.200% by weight, Ge of 0.0001% to 0.200% by weight, and As of 0.0001% to 0.200% by weight. More specifically, it may also contain one or more of Bi of 0.0010% to 0.100% by weight, Pb of 0.0010% to 0.100% by weight, G of 0.0010% to 0.100% by weight, and As of 0.0010% to 0.100% by weight.

[0076] 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%), Ca 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%).

[0077] These elements may react with inevitably contained C, S, N, etc. to form fine carbides, nitrides or sulfides, thus having an adverse effect on magnetism. Therefore, the upper limits of these elements can be defined as described above.

[0078] More specifically, it may further contain one or more of Mo of 0.0001 wt% to 0.03 wt%, B of 0.0001 wt% to 0.0050 wt%, Ca of 0.0001 wt% to 0.0050 wt%, Zr of 0.0001 wt% to 0.005 wt%, and Mg of 0.0001 wt% to 0.0050 wt%. More specifically, it may further contain one or more of Mo of 0.001 wt% to 0.01 wt%, B of 0.0005 wt% to 0.0030 wt%, Ca of 0.0005 wt% to 0.0030 wt%, Zr of 0.0005 wt% to 0.0030 wt%, and Mg of 0.0005 wt% to 0.0030 wt%.

[0079] Other impurities

[0080] The balance contains Fe. In addition, it may further contain inevitably mixed impurities. Inevitable impurities refer to impurities mixed during the steelmaking process and the manufacturing process of the non-oriented electrical steel sheet. Since this is well known in the related art, its detailed description is omitted. In an embodiment of the present invention, adding elements other than the above alloy components is not excluded, and various elements can be included within the scope not damaging the technical idea of the present invention. When additional elements are further included, they are included in place of the balance of Fe.

[0081] The non-oriented electrical steel sheet according to an embodiment of the present invention has an excellent surface shape. If the surface shape is not good, the core shape during the manufacture of the motor is not good, thereby reducing the efficiency of the motor. The surface shape of the non-oriented electrical steel sheet is mainly determined during cold rolling, and one of the factors affecting cold rolling is the material of the hot-rolled sheet. The material deviation of the hot-rolled sheet is mainly caused by the temperature deviation between the front end and the rear end during the finish rolling of hot rolling, which can be achieved by accelerated rolling during hot rolling. A more specific method will be described in detail in the manufacturing method of the non-oriented electrical steel sheet according to an embodiment of the present invention.

[0082] The average grain size of the non-oriented electrical steel sheet according to an embodiment of the present invention may be from 25 μm to 125 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 a plane parallel to the rolling vertical plane (TD plane). The measurement position is not particularly limited, but it can be measured at a point from 1 / 4 to 3 / 4 of the overall thickness of the steel sheet. More specifically, the average grain size may be from 60 μm to 95 μm.

[0083] In addition, the non-oriented electrical steel sheet according to an embodiment of the present invention has an excellent surface shape. Specifically, in the non-oriented electrical steel sheet according to an embodiment of the present invention, when observing a 5 mm×5 mm area of the surface, the length of the unevenness with a height difference of 1.0 μm or more relative to the average height may be 3 mm or less. When there is an insulating coating on the non-oriented electrical steel sheet, after removing the insulating coating, the surface characteristics of the non-oriented electrical steel sheet can satisfy the above conditions. The method for removing the insulating coating is not particularly limited, and it can be removed by soaking in a NaOH solution at a temperature of 80 °C for 30 minutes. The average height refers to the average height of the overall sheet area (length) of the measurement object. The height difference can be + or -, and the length of the unevenness refers to the length in the specific direction with the longest length. The length of the unevenness can be measured by a method for measuring surface roughness, such as a method using a confocal laser.

[0084] In addition, the non-oriented electrical steel sheet according to an embodiment of the present invention has excellent magnetic flux density and iron loss. When using the non-oriented electrical steel sheet according to an embodiment of the present invention to manufacture an electric motor for environmentally friendly vehicle drive, it has advantages in terms of output and energy efficiency.

[0085] Specifically, the magnetic flux density B of the non-oriented electrical steel sheet 50 can be 1.603 + 0.96×t 2 (T) or more. At this time, t refers to the thickness (mm) of the steel sheet. B 50 refers to the magnetic flux density induced in a magnetic field of 5000 A / m. More specifically, when the thickness is 0.25 mm, the magnetic flux density B 50 can be from 1.67 T to 1.70 T, and when the thickness is 0.20 mm, the magnetic flux density B 50 can be from 1.65 T to 1.68 T, and when the thickness is 0.15 mm, the magnetic flux density B 50 can be from 1.63 T to 1.66 T, and when the thickness is 0.10 mm, the magnetic flux density B 50It can be from 1.62T to 1.65T.

[0086] Meanwhile, the iron loss (W 10 / 400 ) of the non-oriented electrical steel sheet can be 7.231 + 21.385×t or less. Here, t refers to the thickness (mm) of the steel sheet. More specifically, when the thickness is 0.25mm, the iron loss (W 10 / 400 ) can be from 12.3W / kg to 10.8W / kg; when the thickness is 0.20mm, the iron loss (W 10 / 400 ) can be from 11.3W / kg to 9.8W / kg; when the thickness is 0.15mm, the iron loss (W 10 / 400 ) can be from 10.1W / kg to 8.6W / kg; when the thickness is 0.10mm, the iron loss (W 10 / 400 ) can be from 9W / kg to 7.5W / kg.

[0087] 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 cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and a step of annealing the cold-rolled sheet.

[0088] First, the slab is hot rolled.

[0089] 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 composition of the non-oriented electrical steel sheet and the slab is substantially the same.

[0090] Specifically, the slab contains 3.0% to 5.0% of Si, 0.1% to 1.4% of Mn, and 0.3% to 1.3% of Al by weight%, and also contains the balance of Fe and inevitable impurities.

[0091] Regarding additional elements other than this, they have been described in the alloy composition of the non-oriented electrical steel sheet, so repeated description is omitted.

[0092] It is possible to heat the slab before hot rolling. There is no limitation on the heating temperature of the slab, but the slab can be heated at 1200°C or less. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab will re-dissolve and then precipitate finely during hot rolling and annealing, thereby suppressing grain growth and reducing magnetism.

[0093] Next, the slab is hot-rolled to produce a hot-rolled sheet. In an embodiment of the present invention, the speed at which the slab is loaded into the hot roughing mill is 40 m / min to 100 m / min, the speed at which the front end of the bar after rough rolling is loaded into the hot finishing mill is 300 m / min to 800 m / min, and the speed at which the slab is loaded into the hot roughing mill is 1.25 times or more relative to the speed at which the front end of the bar after rough rolling is loaded into the hot finishing mill. Here, the front end portion refers to a 50 m length starting from the foremost end portion, and the rear end portion refers to a 50 m length starting from the rearmost end portion.

[0094] When the speed is too slow, the time for which the heated slab is placed varies depending on the slab length, and the temperature deviation in the slab length direction is aggravated, which appears as surface defects in the finally manufactured non-oriented electrical steel sheet. When the speed is too fast, the load on the rolling mill increases, and appropriate rolling may not be possible. More specifically, the speed at which the slab is loaded into the hot roughing mill is 50 m / min to 900 m / min, the speed at which the front end of the bar after rough rolling is loaded into the hot finishing mill is 350 m / min to 750 m / min, and the speed at which the front end of the bar after rough rolling is loaded into the hot finishing mill is 1.25 to 2.0 times relative to the speed at which the slab is loaded into the hot roughing mill. In the step of manufacturing the hot-rolled sheet, it includes: a step of rough rolling the slab to produce a bar; a step of finish rolling the bar; and a step of coiling the hot-rolled sheet after finish rolling.

[0095] When starting the finish rolling step, when measuring the temperature at any position between the 1 / 4 to 3 / 4 points in the width direction of the bar, the temperature deviation between the area from the foremost end of the bar to 50 m and the area from the rearmost end of the bar to 50 m can be 30°C or less.

[0096] When the temperature deviation is too large, in the finally manufactured non-oriented electrical steel sheet, unevenness is formed in the length direction, resulting in inferior surface shape.

[0097] The thickness of the hot-rolled sheet can be 1.8 mm to 2.5 mm. In the step of manufacturing the hot-rolled sheet, the finish rolling temperature can be 800°C or higher. When the hot-rolled finish rolling temperature is too low, the rolling load increases, thereby reducing the hot-rolling workability. However, a large amount of deformed structure remains in the hot-rolled steel sheet, and it becomes the cause of an increase in the rolling load during the subsequent cold rolling in the pre-rolling process. In addition, during intermediate annealing, the deformed structure promotes the recrystallization of <111> / / ND-oriented grains, resulting in inferior magnetic flux density. Specifically, it can be 800°C to 1000°C.

[0098] The hot-rolled sheet can be coiled at a temperature below 700°C. If the temperature in the coiling step is too low, the recovery and recrystallization of the hot-rolled deformed structure are difficult to proceed. In order to rapidly cool the steel sheet at a low temperature, the cooling load increases and coiling of the over-cooled coil may be difficult. Conversely, if the temperature is too high, although recovery and recrystallization can be promoted, additional oxidation may occur due to oxygen in the atmosphere during coiling, resulting in an increase in the thickness of the scale and possible problems of grain boundary oxidation. Grain boundary oxidation of the hot-rolled sheet promotes intergranular corrosion during subsequent pickling, thus increasing the possibility of surface stripe defects and may cause severe wear of the rolling rolls.

[0099] After the step of manufacturing the hot-rolled sheet, it may further include a step of annealing the hot-rolled sheet at a temperature range of 600°C to 1100°C. When the annealing temperature of the hot-rolled sheet is too low, the recrystallized structure may not form or grow slightly, resulting in a less effective increase in magnetic flux density. When the annealing temperature is too high, the magnetic properties will instead decrease, and the rolling operation efficiency may deteriorate due to deformation of the sheet shape. More specifically, the hot-rolled sheet annealing can be carried out at 850°C to 1000°C.

[0100] The hot-rolled sheet annealing is carried out as needed to increase the orientation favorable for magnetism, and it can also be omitted. That is, cold rolling can be carried out after cooling the hot-rolled hot-rolled sheet to 10°C to 50°C. The annealing form is not particularly limited, and batch or continuous annealing can be carried out.

[0101] The hot-rolled hot-rolled sheet can be pickled according to requirements.

[0102] Next, the hot-rolled sheet is cold-rolled.

[0103] The step of manufacturing the cold-rolled sheet may include: a step of performing the first cold rolling on the hot-rolled sheet to manufacture the first cold-rolled sheet; a step of performing intermediate annealing on the first cold-rolled sheet; and a step of performing the second cold rolling on the first cold-rolled sheet to manufacture the second cold-rolled sheet. One-time cold rolling can also be carried out.

[0104] When performing two-stage cold rolling, the thickness of the first cold-rolled sheet can be 0.5 mm to 1.2 mm. When the thickness of the first cold-rolled sheet is too thin, problems may occur such that the cold rolling itself becomes difficult and the unevenness defects on the surface become obvious. When the thickness of the first cold-rolled sheet is too thick, problems may occur such that it is difficult to ensure the magnetic properties of the final product. More specifically, the thickness of the first cold-rolled sheet can be 0.5 mm to 1.0 mm.

[0105] In the step of intermediate annealing of the first cold-rolled sheet, annealing can be carried out at 950°C to 1100°C for 60 seconds to 150 seconds. When the intermediate annealing temperature is too low, there may be a problem of difficulty in ensuring the magnetic properties of the final product. When the intermediate annealing temperature is too high, there may be a problem of difficulty in cold rolling. More specifically, in the step of intermediate annealing, annealing can be carried out at 950°C to 1100°C for 60 seconds to 150 seconds.

[0106] After the step of intermediate annealing, pickling can be carried out according to requirements.

[0107] In the step of manufacturing the second cold-rolled sheet by performing second cold rolling on the first cold-rolled sheet, the thickness of the second cold-rolled sheet can be 0.10 mm to 0.30 mm. The thickness of the second cold-rolled sheet can be the same as the thickness of the finally manufactured non-oriented electrical steel sheet.

[0108] Next, cold-rolled sheet annealing is performed on the cold-rolled sheet.

[0109] When performing cold-rolled sheet annealing, soaking can be carried out at a soaking temperature of 900°C or higher. When the soaking temperature is too low, it may lead to insufficient grain growth. More specifically, the soaking temperature can be 900°C to 1050°C. The soaking step can be performed for 45 seconds to 100 seconds.

[0110] During soaking, all (i.e., more than 99%) of the processing structure formed in the cold rolling step can be recrystallized.

[0111] After soaking, 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.

[0112] 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.

[0113] Example 1

[0114] A slab is manufactured from the components of Table 1 including Fe with a remainder and inevitable impurities. It is heated at 1150°C and hot-rolled to a thickness of 2.0 mm. When loading into the hot rolling mill, the speed of the slab is adjusted as shown in Table 3, and the temperature deviation of the bars between the frontmost 50 m and the rearmost 50 m is measured at the start of finish rolling and tabulated in Table 3. Subsequently, the hot-rolled sheet is air-cooled to room temperature, cold-rolled once to a thickness of 0.8 mm, and intermediate annealed at a temperature of 1050°C for 2 minutes. After completion of annealing, pickling is carried out, and cold-rolled to a thickness of 0.25 mm.

[0115] The magnetic flux density and iron loss are measured by the Epstein test. At this time, the Epstein test pieces have dimensions of 305 mm × 30 mm respectively. The magnetic flux density B50 is the magnitude of the magnetic flux density (Tesla) induced in a magnetic field of 5000 A / m, and the iron loss W10 / 400 is the loss (W / kg) when a magnetic flux density of 1.0 Tesla is induced at a frequency of 400 Hz.

[0116] The surface shape is measured by a confocal laser measuring device capable of measuring roughness, a 3D surface roughness meter, etc. The unevenness with the maximum length in the sample is tabulated in Table 2 below.

[0117] Table 1

[0118]

[0119] Table 2

[0120]

[0121] Table 3

[0122]

[0123] As shown in Tables 1 to 3, in the inventive examples where the steel composition is appropriately adjusted and the charging speed is appropriately adjusted when charging into the hot rolling mill, it can be confirmed that a specific texture structure is developed and the surface shape, iron loss, and magnetic flux density are excellent.

[0124] Conversely, when the steel composition is not appropriately adjusted, it can be confirmed that the iron loss and magnetic flux density are inferior.

[0125] In addition, even when the steel composition is appropriately adjusted, when the charging speed is not appropriately adjusted when charging into the hot rolling mill, the specific texture structure is not developed and the surface shape, iron loss, and magnetic flux density are inferior.

[0126] Example 2

[0127] Using Steel Grades 1, 3, 4, 10, and 13 of the inventive examples, the magnetic properties at different thicknesses were confirmed.

[0128] Table 4

[0129]

[0130] The present invention is not limited to the embodiments, but can be made in various different forms from each other. 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 3.0% to 5.0% of Si, 0.1% to 1.4% of Mn, and 0.3% to 1.3% of Al by weight%, and contains the balance of Fe and inevitable impurities, when observing a 5 mm × 5 mm area on the surface, the length of the unevenness with a height difference of 1.0 μm or more with respect to the average height is 3 mm or less.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that, The magnetic flux density B50 is 1.603 + 0.96 × t with respect to the thickness t of the steel plate 2 Above, the iron loss W10 / 400 is 7.231 + 21.385 × t or less, where the unit of the magnetic flux density B50 is T, the unit of the thickness t is mm, and the unit of the iron loss W10 / 400 is W / kg.

3. 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% by weight or less and excluding 0%, Sn of 0.1% by weight or less and excluding 0%, and Sb of 0.1% by weight or less and excluding 0%.

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 C of 0.005% by weight or less and excluding 0%, N of 0.005% by weight or less and excluding 0%, S of 0.005% by weight or less and excluding 0%, Ti of 0.005% by weight or less and excluding 0%, Nb of 0.005% by weight or less and excluding 0%, and V of 0.005% by weight or less and excluding 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 Cu of 0.005% to 0.2% by weight, Cr of 0.01% to 0.5% by weight, Ni of 0.05% by weight or less and excluding 0%, and Zn of 0.01% by weight or less and excluding 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 Bi of 0.200% by weight or less and excluding 0%, Pb of 0.200% by weight or less and excluding 0%, Ge of 0.200% by weight or less and excluding 0%, and As of 0.200% by weight or less and excluding 0%.

7. 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% by weight or less and excluding 0%, B of 0.0050% by weight or less and excluding 0%, Ca of 0.0050% by weight or less and excluding 0%, Zr of 0.005% by weight or less and excluding 0%, and Mg of 0.0050% by weight or less and excluding 0%.

8. A method for manufacturing a non-oriented electrical steel sheet, characterized in that, it includes: a step of hot rolling a slab to manufacture a hot rolled sheet, the slab containing 3.0% to 5.0% of Si, 0.1% to 1.4% of Mn, and 0.3% to 1.3% of Al by weight%, and containing the balance of Fe and inevitable impurities, a step of cold rolling the hot rolled sheet to manufacture a cold rolled sheet, and a step of annealing the cold rolled sheet; In the step of manufacturing the hot-rolled sheet, the speed at which the front end portion of the rough-rolled bar is loaded into the hot finish rolling mill is 300 m / min to 800 m / min, and the speed at which the rear end portion is loaded is 1.25 times or more with respect to the front end portion of the rough-rolled bar.

9. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of P of 0.1 wt% or less and excluding 0%, Sn of 0.1 wt% or less and excluding 0%, and Sb of 0.1 wt% or less and excluding 0%.

10. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of C of 0.005 wt% or less and excluding 0%, N of 0.005 wt% or less and excluding 0%, S of 0.005 wt% or less and excluding 0%, Ti of 0.005 wt% or less and excluding 0%, Nb of 0.005 wt% or less and excluding 0%, and V of 0.005 wt% or less and excluding 0%.

11. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Cu of 0.005 wt% to 0.2 wt%, Cr of 0.01 wt% to 0.5 wt%, Ni of 0.05 wt% or less and excluding 0%, and Zn of 0.01 wt% or less and excluding 0%.

12. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Bi of 0.200 wt% or less and excluding 0%, Pb of 0.200 wt% or less and excluding 0%, Ge of 0.200 wt% or less and excluding 0%, and As of 0.200 wt% or less and excluding 0%.

13. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the slab further contains one or more of Mo of 0.03 wt% or less and excluding 0%, B of 0.0050 wt% or less and excluding 0%, Ca of 0.0050 wt% or less and excluding 0%, Zr of 0.005 wt% or less and excluding 0%, and Mg of 0.0050 wt% or less and excluding 0%.

14. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the method for manufacturing the non-oriented electrical steel sheet further includes: a step of heating the slab at 1200 °C or lower before the step of manufacturing the hot-rolled sheet.

15. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein in the step of manufacturing the hot-rolled sheet, it includes: a step of rough rolling the slab to manufacture a bar, a step of finish rolling the bar, and a step of coiling the hot-rolled sheet obtained by finish rolling; when starting the finish rolling step, the temperature deviation between the region from the foremost end portion of the bar to 50 m and the region from the rearmost end portion to 50 m is 30 °C or less.

16. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein In the step of manufacturing the hot-rolled sheet, the speed at which the slab is charged into the hot roughing mill is 40 m / minute to 100 m / minute.

17. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the method for manufacturing the non-oriented electrical steel sheet further comprises: a hot-rolled sheet annealing step of annealing the hot-rolled sheet at 600°C to 1100°C after the step of manufacturing the hot-rolled sheet.

18. The method for manufacturing an non-oriented electrical steel sheet according to claim 8, wherein the step of manufacturing the cold-rolled sheet comprises: a step of performing a first cold rolling on the hot-rolled sheet to manufacture a first cold-rolled sheet; a step of performing an intermediate annealing on the first cold-rolled sheet; and a step of performing a second cold rolling on the first cold-rolled sheet to manufacture a second cold-rolled sheet.

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