Double cold-rolled non-oriented electrical steel and method for manufacturing the non-oriented electrical steel.

Abstract

The present invention relates to a double cold-rolled non-oriented electrical steel sheet containing, in weight percent, the following elements: 0.0001% ≤ carbon ≤ 0.007%, 0.15% ≤ manganese ≤ 0.3%, 3.2% ≤ silicon ≤ 3.8%, 0.8% ≤ aluminum ≤ 1.1%, phosphorus ≤ 0.15%, sulfur ≤ 0.006%, nitrogen ≤ 0.09%, and one or more of the following optional elements: 0% ≤ niobium ≤ 0.1%, 0% ≤ titanium ≤ 0.1%, 0% ≤ vanadium ≤ 0.1%, 0% ≤ chromium ≤ 1%, 0% ≤ molybdenum ≤ 0.5%, 0% ≤ tungsten ≤ 0.1%, 0% ≤ cobalt ≤ 1%, 0% ≤ arsenic ≤ 0.05%, 0.001% ≤ calcium ≤ 0. A composition that may contain 0.1%, 0%≦copper≦1%, 0.001%≦nickel≦0.01%, 0%≦boron≦0.05%, 0%≦lead≦0.2%, 0%≦tin≦0.2%, and 0%≦antimony≦0.2%, wherein the remainder of the composition consists of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet is made from ferrite and comprises, in area fraction, 80%~100% recrystallized microstructure and 0%~20% non-recrystallized microstructure, the average grain size of the recrystallized microstructure is 20 microns~110 microns, and less than 30% when calculated according to the Bertotti method, IEC We handle double cold-rolled non-oriented electrical steel sheets that have a percentage of eddy current loss in total iron loss measured at 1T and 400Hz according to the 60404-2 standard, and simultaneously have magnetic polarization at 5000 A / m (J50) between 1.66T and 1.69T.

Description

Technical Field

[0001] The present invention relates to a double cold-rolled non-oriented electrical steel sheet and a method for producing the same. Specifically, the present invention relates to a double cold-rolled non-oriented electrical steel sheet having excellent mechanical properties and low iron loss, specifically low eddy current loss, and a method for producing the same.

Background Art

[0002] Therefore, intensive research and development efforts have been devoted, and due to the worldwide increase in energy conservation of electrical appliances, higher performance characteristics are required for using non-oriented electrical steel sheets as the core material of electric machines. In recent years, in particular, as motors used in electric vehicles, etc., the demand for small and high-output motors has been increasing. Such electric vehicle motors are designed to enable high-speed rotation, thereby obtaining high torque while having the least possible losses. This requires a light, highly efficient non-oriented electrical steel having low losses as its main characteristic. Finding a balance between loss, permeability, polarization, thermal conductivity, tensile strength, and yield strength is essential for non-oriented electrical steel.

[0003] The lower the iron loss in an electric machine, the higher the efficiency of the electric machine. Therefore, in order to reduce the amount of iron loss in an electric machine, the manufacturers of electric machines have several options, and their main option is to reduce either the hysteresis loss or the eddy current loss in order to improve the efficiency of the electric machine. Progress is often achieved by a combination of these two approaches. The present invention relates to the second option, i.e., the reduction of eddy current loss for electric machines. There are two options for reducing eddy current loss.

[0004] The first approach involves reducing the thickness of the steel plates used in electrical machinery, such as having a thickness of less than 0.35 mm or thinner. Unfortunately, this solution has limitations due to the reduction in the lamination ratio, which decreases the torque achievable for a given machine height, as well as a very significant decrease in the rigidity of certain automotive parts, and the emergence of acoustic problems that cause discomfort to the occupants.

[0005] The second method involves optimizing the elemental composition of the steel sheet by increasing the amount of alloying elements to limit eddy current losses. Among these alloying elements, aluminum and manganese, for example, have attractive mechanical and magnetic properties while significantly reducing eddy current losses. However, beyond a certain percentage, the presence of alloying elements affects hysteresis losses and magnetic polarization, so the addition of alloying elements can be limited.

[0006] Previous research and development in the field of high-strength non-oriented electrical steel have resulted in several methods for producing high-strength non-oriented electrical steel, some of which are listed herein for a thorough understanding of the present invention.

[0007] U.S. Patent Application Publication No. 2021 / 371948 describes a non-oriented electrical steel sheet, 4.5 × 10 -6This is a non-oriented electrical steel sheet having the following average magnetostriction λp-p at 400 Hz and 1.0 T, and an area ratio of recrystallized crystal grains in the cross-section of the steel sheet in the rolling direction of the sheet of 40 to 95%, and containing, by mass%, C: 0.005% or less, Si: 2.8 to 6.5%, Mn: 0.05 to 2.0%, Al: 3.0% or less, P: 0.20% or less, S: 0.005% or less, N: 0.005% or less, Ti: 0.003% or less, V: 0.005% or less, and Nb: 0.005% or less, and satisfying Si-2A1-Mn≧0, and subjecting a steel slab to hot rolling, hot-rolled sheet annealing, appropriate cold rolling and finish annealing conditions to obtain an average grain size of 10 to 40 microns, and motor cores are manufactured from such a steel sheet. The specification of U.S. Patent Application Publication No. 2021 / 371948 does not demonstrate total elongation or eddy current losses at all.

[0008] European Patent Application Publication No. 4265749 discloses a non-oriented electrical steel sheet and a method for manufacturing the same, which suppress the formation of fine carbonitrides by appropriately adding Mo, Ti, and Nb and adjusting the time within a specific temperature range during the cooling process after final annealing. Accordingly, the invention relates to a non-oriented electrical steel sheet having excellent magnetic properties and strength, and a method for manufacturing the same.

[0009] European Patent Application Publication No. 4079893 discloses non-oriented electrical steel sheets and methods for manufacturing the same. Specifically, the invention relates to non-oriented electrical steel sheets and methods for manufacturing the same, which can improve magnetism by appropriately adding As and P and improving the texture. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent Application Publication No. 2021 / 371948 [Patent Document 2] European Patent Application Publication No. 4265749 [Patent Document 3] European Patent Application Publication No. 4079893 [Overview of the project] [Problems that the invention aims to solve]

[0011] The object of the present invention is to solve these problems by producing a double cold-rolled non-oriented electrical steel sheet that simultaneously has a magnetic polarization of 1.66T to 1.69T at 5000 A / m (J50), preferably 1.66T to 1.68T at 5000 A / m (J50), more preferably 1.664T to 1.675T at 5000 A / m (J50), and a percentage of eddy current loss in total iron loss of less than 30%, preferably 25% to 30%, more preferably 27% to 30%, when calculated according to the Bertotti method.

[0012] In preferred embodiments, the following additional properties can also be achieved, either alone or in combination: • Ultimate tensile strength of 500 MPa or more in both the direction perpendicular to rolling and the rolling direction, preferably exceeding 530 MPa in both the direction perpendicular to rolling and the rolling direction. • Yield strength of 390 MPa or more in both the direction perpendicular to rolling and the rolling direction, preferably 410 MPa or more in both the direction perpendicular to rolling and the rolling direction. • Total elongation of 19% or more in both the direction perpendicular to rolling and the rolling direction, preferably 21% or more in both the direction perpendicular to rolling and the rolling direction. • Total losses of 11-14 W / kg, preferably 12-13 W / kg, when measured at 1T and 400Hz.

[0013] Preferably, such steel can have good punchability and coating properties, and excellent suitability for rolling.

[0014] Preferably a hardness of 185 HV or higher, preferably 195 HV or higher.

[0015] Another objective of the present invention is to make available a method for manufacturing these plates that is compatible with conventional industrial applications while also being robust against changes in manufacturing parameters. [Means for solving the problem]

[0016] The above objects and other advantages of the present invention will become more apparent by describing preferred embodiments of the present invention in detail.

Embodiments for Carrying Out the Invention

[0017] The chemical composition of the non-oriented electromagnetic steel contains the following elements in weight percent: Carbon present in the steel of the present invention is 0.0001% to 0.007%. Since carbon is a precipitate-forming element, it is harmful to the magnetic properties of this steel. Therefore, the presence of carbon in this steel is 0.0001% to 0.007%. Since carbon promotes magnetic aging, the preferred content of carbon according to the present invention is 0.002% to 0.007%, more preferably 0.002% to 0.005%.

[0018] The manganese content of the steel of the present invention is 0.15% to 0.3%. Manganese provides solid solution strengthening and reduction of iron loss by increasing the specific resistance. If the addition amount of manganese exceeds 0.3%, the magnetic flux density may significantly decrease, and the recrystallization of the steel may be inhibited during annealing. The preferred limit for the presence of manganese is 0.18% to 0.27%, more preferably 0.21% to 0.25%.

[0019] The silicon content of the steel of the present invention is 3.2% to 3.8%. Silicon is an element that contributes to increasing the strength by solid solution strengthening, and is a central element for reducing the eddy current loss of iron loss by increasing the specific resistance of the steel. The above effects require a minimum silicon content of at least 3.2%. However, if the silicon content is more than 3.8%, rolling becomes difficult and significantly reduces the magnetic induction of the steel. The preferred limit for the presence of silicon is 3.2% to 3.7%, more preferably 3.2% to 3.5%.

[0020] The aluminum content is 0.8% - 1.1%. Aluminum can increase the electrical resistivity of the material and effectively reduce the iron loss of steel. When the aluminum content exceeds 1.1%, the magnetic induction of the steel is significantly reduced, which is also harmful to the rolling property of the cold rolling of the steel of the present invention. The preferable limit for the presence of aluminum is 0.85% - 1%, more preferably 0.85% - 0.95%.

[0021] Sulfur is not an essential element but may be contained as an impurity in steel. From the perspective of the present invention, the sulfur content is preferably as low as possible, but from the perspective of manufacturing cost, it is 0.006% or less. Furthermore, when higher sulfur is present in steel, sulfur combines to form sulfides that are harmful to the magnetic properties of the present invention.

[0022] The phosphorus component of the steel of the present invention is 0% - 0.15%. Phosphorus reduces hot and cold ductility due to its tendency to segregate particularly at grain boundaries or to co-segregate with manganese. For these reasons, its content is limited to 0.15%, preferably less than 0.09%.

[0023] Nitrogen is limited to 0.09% to minimize the precipitation of aluminum nitride during solidification, which is harmful to the magnetic properties of the steel.

[0024] Titanium is an optional element. When added to the steel of the present invention, it is 0% - 0.1%. Titanium forms titanium nitride that appears during the solidification of the casting. Therefore, the amount of titanium is limited to 0.1% to avoid the formation of titanium nitride that is harmful to the magnetic properties of the steel of the present invention. When the titanium content is less than 0.001%, it has no effect on the steel of the present invention.

[0025] Niobium is present in the steel of the present invention at a concentration of 0% to 0.1%, and is suitable for forming carbonitrides to increase the strength of the steel of the present invention through precipitation hardening. Niobium also affects the size of microstructural components by precipitating as carbonitrides. However, niobium content exceeding 0.1% is not economically interesting due to the saturation effect.

[0026] Vanadium is present in the steel of the present invention at a concentration of 0% to 0.1%, and is effective in increasing the strength of the steel by forming carbides or carbonitrides. From an economic standpoint, the upper limit is 0.1%.

[0027] Chromium is an optional element for the steel in this invention, present in concentrations of 0% to 1%. Chromium provides strength to the steel through solid solution strengthening, but using it in concentrations exceeding 1% impairs the magnetic properties of the steel.

[0028] Molybdenum is an optional element that constitutes 0% to 0.5% of the steel of the present invention.

[0029] Mo has the effect of reducing iron loss by coarsening carbides. When Mo exceeds 0.5%, the effect of improving iron loss saturates.

[0030] Tungsten is an optional element that constitutes 0% to 0.1% of the steel of the present invention. Like Mo, tungsten has the effect of coarsening carbides and reducing iron loss. However, if the amount added is less than 0.001% by mass, the above effect cannot be fully obtained, while if the amount added exceeds 0.1% by weight, the effect of improving iron loss saturates.

[0031] Cobalt is an optional element that constitutes 0% to 1% of the steel of the present invention. Cobalt is an element that increases the magnetic moment of Fe alloys, thereby increasing magnetic flux density and reducing iron loss. However, if the amount added is less than 0.01% by weight, the above effects cannot be fully obtained, while if the amount added exceeds 1% by weight, the raw material costs increase significantly.

[0032] Arsenic is an optional element that constitutes 0% to 0.05% of the steel of the present invention. As is a grain boundary segregation element that improves texture and thereby reduces iron loss. The above effect is obtained by adding 0.001% by weight or more. However, As is an element that causes grain boundary embrittlement, and this adverse effect becomes particularly pronounced when added in amounts exceeding 0.05% by weight. Therefore, it is preferable that As be added in the range of 0.001 to 0.05% by weight.

[0033] Nickel is an optional element and is present in an amount of 0.001% to 0.01% to increase the strength of the steel of the present invention and to improve its strength and elongation. In preferred embodiments, the nickel content is kept below 0.04%.

[0034] Copper is used to increase the strength and elongation of the steel of the present invention. , former As 0.01% It can be added in amounts of ~1%. However, if the content exceeds 1%, copper can degrade the surface morphology. 。

[0035] Boron is an optional element for the steel of the present invention and may be present in amounts of 0% to 0.05%. Boron forms boronitrides, and when added in an amount of at least 0.0001%, it imparts further strength to the steel of the present invention.

[0036] Calcium may be optionally present in the steel of the present invention, in amounts ranging from 0.001% to 0.01%. Calcium contributes to the refining of the steel by binding harmful sulfur-containing substances in a spherical manner, thereby delaying the harmful effects of sulfur.

[0037] Other elements such as Sn, Pb, or Sb can be added individually or in combination in the following proportions: Sn ≤ 0.2%, Pb ≤ 0.2%, and Sb ≤ 0.2%. Up to the indicated maximum content levels, these elements allow for grain refinement during solidification. In preferred embodiments, the Sn content is less than 0.04%.

[0038] The remainder of steel's composition consists of iron and unavoidable impurities resulting from processing.

[0039] Here, we will describe the microstructure of non-oriented electrical steel in detail, but all percentages are area fractions.

[0040] The microstructure is made from ferrite. The steel of the present invention has a recrystallized microstructure region with an area fraction of 80% to 100%, having crystal grains with an average grain size of 20 to 110 microns. The recrystallized structure with a high degree of recrystallization is due to homogeneous silicon enrichment, which improves the magnetic properties of the steel of the present invention. The controlled grain size ensures mechanical properties both perpendicular to and in the rolling direction. The preferred degree of recrystallization is 90% to 100%. The preferred average grain size for the present invention is 20 to 100 microns, more preferably 20 to 90 microns.

[0041] The steel of the present invention may have a non-recrystallized microstructure region of 0% to 20% in area fraction, with a preferred degree of non-recrystallization being 0% to 10%, more preferably 0% to 5%.

[0042] In addition to the microstructure described above, the microstructure of non-oriented electrical steel does not contain microstructure components such as martensite, bainite, pearlite, and cementite.

[0043] The steel according to the present invention can be manufactured by any suitable method. However, as a non-limiting example, it is preferable to use the method according to the present invention, which is detailed below.

[0044] Such a preferred method lies in providing a semi-finished casting of steel having the chemical composition of the steel according to the present invention. The casting may be in the form of an ingot, or in the form of a continuous thin slab or thin strip, i.e., a thickness in the range of less than about 240 mm for any form of the casting.

[0045] For example, a casting in the form of a slab is cast with the chemical composition according to the present invention and then reheated, with the slab reheating temperature being between 1050°C and 1200°C until the temperature is uniform throughout the slab. Below 1050°C, rolling becomes difficult and the force on the mill becomes too high. Above 1200°C, the high-silicon grade becomes very soft and may exhibit some deflection, making it difficult to handle. Preferably, the slab reheating temperature is between 1080°C and 1180°C, more preferably between 1080°C and 1150°C.

[0046] The reheated slab is subjected to hot rolling at a temperature of 840°C to 950°C, where the hot rolling finish temperature plays a role in the final hot rolling microstructure. If the finish rolling temperature is below 840°C, recrystallization is limited and the microstructure is highly deformed. If it is above 950°C, it means that there will be more impurities in the solid solution, which may result in precipitation and deterioration of magnetic properties. Preferably, the finish rolling temperature is 840°C to 940°C, more preferably 850°C to 900°C.

[0047] Next, the hot-rolled steel sheet obtained in this manner is immediately cooled at a cooling rate of at least 10°C / second to the winding temperature of the hot-rolled steel sheet, which also serves the same role as the hot-rolled steel sheet, and the winding is performed at 500°C to 560°C. Winding at temperatures below 500°C does not result in a suitable distribution and size for the steel precipitates of the present invention. Above 560°C, a thick oxide layer appears, causing difficulties in subsequent processing steps such as cold rolling and / or pickling. Preferably, the cooling rate is 200°C / second or less, and more preferably, the cooling rate is 12°C / second to 75°C / second. Preferably, the winding temperature is 510°C to 560°C, and more preferably, 520°C to 555°C.

[0048] Next, after the rolled hot-rolled steel sheet has cooled to room temperature... ,heat It will be used for annealing rolled plates.

[0049] The hot-rolled steel sheet may be subjected to an optional descaling process to remove scale formed during hot rolling, prior to optional hot-rolled sheet annealing. The hot-rolled sheet is then subjected to an optional hot-rolled sheet annealing, which is carried out at a temperature of 780°C to 1000°C, preferably for at least 10 seconds and 96 hours or less, and the temperature is preferably maintained at 790°C to 980°C, more preferably 800°C to 950°C. Subsequently, the optional descaling process of the hot-rolled steel sheet may be carried out, for example, by pickling such a sheet.

[0050] Therefore, the resulting hot-rolled steel sheet may have a thickness of any choice between 0.8 mm and 3.5 mm, preferably between 0.9 mm and 3 mm, and more preferably between 1 mm and 2.8 mm.

[0051] Next, this hot-rolled steel sheet is subjected to a first cold-rolling process to obtain an intermediate cold-rolled steel sheet having a thickness reduction of 60-95%. Preferably, a thickness reduction of 65-95% results in an intermediate thickness of less than 1 mm.

[0052] Subsequently, the intermediate cold-rolled steel sheet is heat-treated, which imparts the mechanical properties and microstructure required for the steel of the present invention.

[0053] Next, the intermediate cold-rolled steel sheet is subjected to a first annealing, with heating starting from room temperature. The intermediate cold-rolled steel sheet is heated to a first annealing temperature TA1, which is 900°C to 1080°C, preferably 950°C to 1070°C, more preferably 990°C to 1050°C, at a heating rate HR1 of at least 1°C / second. In a preferred embodiment, the heating rate HR1 for heating is at least 2°C / second, more preferably at least 5°C / second. The intermediate cold-rolled steel sheet is kept at TA1 for 10 seconds to 5000 seconds to serve both the role of recrystallizing the intermediate cold-rolled steel with 80% to 100% recrystallization after the first cold rolling and the role of improving the magnetic properties of the steel of the present invention by dissolving carbides precipitated during sheet cooling and winding after hot rolling.

[0054] Next, the intermediate cold-rolled steel sheet is cooled, starting from TA1, and the intermediate cold-rolled steel sheet is cooled to a temperature T1 in the range of 20°C to 300°C at a cooling rate CR1 of 1°C / sec to 150°C / sec. In a preferred embodiment, the cooling rate CR1 is 3°C / sec to 120°C / sec. A preferred T1 temperature is 20°C to 200°C. At the end of cooling, a cold-rolled steel sheet that has undergone the first annealing is obtained.

[0055] Subsequently, the cold-rolled steel sheet that has undergone the first annealing is subjected to a second cold rolling to obtain a cold-rolled steel sheet having a thickness reduction of 50-95%. Preferably, the thickness reduction is 60-95%, more preferably 75-95%.

[0056] Subsequently, the cold-rolled steel sheet is subjected to a second annealing, with heating starting from room temperature, and the cold-rolled steel sheet is heated to a second annealing temperature TA2, which is 880°C to 1050°C, preferably 900°C to 1020°C, more preferably 930°C to 990°C, at a heating rate HR2 of at least 1°C / second. In a preferred embodiment, the heating rate HR2 for heating is at least 2°C / second, more preferably at least 5°C / second.

[0057] Cold-rolled steel sheets are maintained at TA2 for 10 to 5000 seconds to ensure 80% to 100% recrystallization.

[0058] Next, the cold-rolled steel sheet is cooled, starting from TA2, and the cold-rolled steel sheet is cooled to a temperature T2 in the range of 20°C to 300°C at a cooling rate CR2 of 1°C / sec to 150°C / sec. In a preferred embodiment, the cooling rate CR2 is 3°C / sec to 120°C / sec. A preferred T2 temperature is 20°C to 100°C.

[0059] The cold-rolled steel sheet obtained in this manner has a thickness of 0.23 mm to 0.26 mm, preferably 0.23 mm to 0.25 mm, and more preferably 0.24 mm to 0.25 mm.

[0060] Subsequently, the cold-rolled steel sheet is cooled to room temperature to obtain a double cold-rolled non-oriented electrical steel sheet.

[0061] The double cold-rolled non-oriented electrical steel sheet of the present invention may be optionally coated with an insulating coating, an organic coating, an inorganic coating, or a combination thereof, in order to improve its insulating properties. [Examples]

[0062] The following tests, examples, symbolic illustrations, and tables presented herein are not limiting in nature and should be considered for illustrative purposes only, and illustrate advantageous features of the present invention.

[0063] Table 1 summarizes steel sheets made from steel with different compositions, and each steel sheet is manufactured according to the process parameters specified in Table 2. Subsequently, Table 3 summarizes the results of the evaluation of the obtained properties.

[0064] All steels in Table 1 had a nitrogen content of less than 0.09%.

[0065] Table 2 summarizes the hot rolling and annealing process parameters performed on cold-rolled steel sheets to impart the mechanical and magnetic properties necessary to become non-oriented electrical steel to the steels in Table 1. All steels of the present invention from I1 to I4 are cooled at a cooling rate of 15°C / second after hot rolling. Furthermore, in the embodiments of the present invention, the heating rate HR1 to TA1 temperature is 5°C / second. For all embodiments of the present invention, the T1 temperature is 25°C, and the cooling rate CR1 is 5°C / second. For all embodiments of the present invention, the heating rate HR2 to TA2 temperature is 5°C / second. For all embodiments of the present invention, the T2 temperature is 25°C, and the cooling rate CR2 is 5°C / second.

[0066] All steels produced according to the parameters in Table 2 exhibited a recrystallized microstructure with over 95% recrystallization and grain size of 20–110 μm.

[0067] [Table 1]

[0068] [Table 2]

[0069] Table 3 The results of various mechanical tests conducted in accordance with the standards are summarized. Ultimate tensile strength, total elongation, and yield strength were measured according to the NF EN ISO 6892-1 standard, and J50 magnetic properties and total iron loss at 1T and 400Hz were measured according to the IEC 60404-2 standard. Eddy current loss is calculated according to the Bertotti method, as described in the paper "General Properties of Power Losses in Soft Ferromagnetic Materials" by Giorgio Berttoti, published in IEEE TRANSACTIONS ON MAGNETICS, Vol. 24, No. 1, January 1988. Equation 2 is referred to as eddy current loss in this invention (P class Identify the classical loss represented by ).

[0070] The average grain size of the recrystallized microstructure is measured by the linear intercept method according to ASTM E112 96(02) standard.

[0071] [Table 3]

Claims

1. Double cold-rolled non-oriented electrical steel sheet, comprising the following elements expressed in weight percentage: 0.0001% ≤ Carbon ≤ 0.007% 0.15% ≤ Manganese ≤ 0.3% 3.2% ≤ Silicon ≤ 3.8% 0.8% ≤ Aluminum ≤ 1.1% Phosphorus ≤ 0.15% Sulfur ≤ 0.006% Nitrogen ≤ 0.09% It includes and one or more of the following optional elements: 0% ≤ Niobium ≤ 0.1% 0% ≤ Titanium ≤ 0.1% 0% ≤ Vanadium ≤ 0.1% 0% ≤ Chromium ≤ 1% 0% ≤ Molybdenum ≤ 0.5% 0% ≤ Tungsten ≤ 0.1% 0% ≤ Cobalt ≤ 1% 0% ≤ Arsenic ≤ 0.05% 0.001% ≤ Calcium ≤ 0.01% 0%≦Copper≦1% 0.001% ≤ Nickel ≤ 0.01 0% ≤ Boron ≤ 0.05% 0%≦Lead≦0.2% 0% ≤ Tin ≤ 0.2% 0% ≤ Antimony ≤ 0.2% A double cold-rolled non-oriented electrical steel sheet having a composition that may contain, the remainder of which consists of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet being made of ferrite and comprising, in area fraction, 80% to 100% recrystallized microstructure and 0% to 20% non-recrystallized microstructure, the average grain size of the recrystallized microstructure being 20 to 110 microns, and having a percentage of eddy current loss in total iron loss measured at 1 T and 400 Hz according to IEC 60404-2 standard of less than 30% when calculated according to the Bertotti method, and simultaneously having magnetic polarization at 5000 A / m (J50) of 1.66 T to 1.69 T.

2. The double cold-rolled non-oriented electrical steel sheet according to claim 1, wherein the composition contains 3.2% to 3.7% silicon.

3. A double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 or 2, wherein the composition contains 0.002% to 0.007% carbon.

4. A double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the composition contains 0.85% to 1% aluminum.

5. A double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the composition contains 0.18% to 0.27% manganese.

6. A double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 to 5, wherein the amount of non-recrystallized microstructure is 0% to 10%.

7. A double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 to 6, wherein the amount of recrystallized microstructure is 90% to 100%.

8. The double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 to 7, wherein the steel sheet has an ultimate tensile strength of at least 500 MPa in both the direction perpendicular to rolling and the rolling direction.

9. A non-oriented electrical steel sheet according to any one of claims 1 to 8, having a yield strength of 390 MPa or more in both the direction perpendicular to rolling and the rolling direction.

10. The double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 to 9, wherein the steel sheet has a total elongation of at least 19% in both the direction perpendicular to rolling and the rolling direction.

11. A method for manufacturing a double cold-rolled non-oriented electrical steel sheet according to any one of claims 1 to 10, The following are the sequential steps: - A step of providing a steel composition according to any one of claims 1 to 5; - A step of reheating the semi-finished product to a temperature of 1050°C to 1250°C; - A process for rolling the aforementioned semi-finished product, wherein the hot rolling finishing temperature is 840°C to 950°C, and a hot-rolled steel sheet is obtained. - A process of cooling the hot-rolled sheet immediately after the hot-rolling process is completed. Next, the hot-rolled steel sheet is cooled from the hot-rolling finish to a coiling temperature range of 500°C to 560°C at a cooling rate of at least 10°C / second. - Subsequently, the hot-rolled steel sheet is wound up within the aforementioned winding temperature range of 500°C to 560°C. - A step of optionally performing a scale removal process on the hot-rolled steel sheet; - A process in which hot-rolled steel sheets are optionally annealed at a temperature of 780°C to 1000°C for a period of 10 seconds to 96 hours; - A step of optionally performing a scale removal process on the hot-rolled steel sheet; - A process of cold-rolling the hot-rolled steel sheet at a reduction ratio of 60% to 95% to obtain an intermediate cold-rolled steel sheet; - Subsequently, the intermediate cold-rolled steel sheet is subjected to a first annealing process, wherein the heating for the first annealing process starts from room temperature and is performed at a heating rate HR1 of at least 1°C / second until it reaches a first annealing temperature range TA1 of 900°C to 1080°C. Next, a first annealing process is carried out at the TA1 temperature for 10 to 5000 seconds. Next, the intermediate cold-rolled steel sheet is cooled starting from the TA1 temperature and at a cooling rate CR1 of 1°C / sec to 150°C / sec, until it reaches a temperature T1 of 300°C to 20°C, thereby obtaining a cold-rolled steel sheet that has undergone the first annealing process. Subsequently, the cold-rolled steel sheet that has undergone the first annealing is subjected to cold rolling at a reduction ratio of 50% to 95% to obtain a cold-rolled steel sheet; - Subsequently, the cold-rolled steel sheet is subjected to a second annealing process, wherein the heating for the second annealing starts from room temperature and is performed at a heating rate HR2 of at least 1°C / second until it reaches an annealing temperature range TA2 of 880°C to 1050°C. Next, the process involves annealing at a TA2 temperature for 10 to 5000 seconds. Next, a process of cooling the cold-rolled steel sheet, starting from the TA2 temperature and reaching a temperature T2 of 300°C to 20°C at a cooling rate CR1 of 1°C / sec to 150°C / sec. Next, the process involves cooling to room temperature to obtain a double cold-rolled non-oriented electrical steel sheet. Methods that include...

12. The method according to claim 11, wherein the TA1 temperature for annealing is 950°C to 1070°C.

13. The method according to any one of claims 11 or 12, wherein the temperature T1 is 200°C to 20°C.

14. The method according to any one of claims 11 to 13, wherein the cooling rate CR1 is 3°C / sec to 120°C / sec.

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