Non-oriented electrical steel sheet, method of manufacturing the same, and motor core

Abstract

The present invention provides a high-strength non-oriented electromagnetic steel sheet having good fatigue characteristics suitable for a rotor core and a non-oriented electromagnetic steel sheet having excellent magnetic characteristics suitable for a stator core. The non-oriented electromagnetic steel sheet has a composition consisting of, in mass%, C: 0.01% or less, Si: 2.0% to 5.0%, Mn: 0.05% to 5.00%, P: 0.1% or less, S: 0.01% or less, Al: 3.0% or less, and N: 0.005% or less, with Si+Al being 4.5% or more, and the remainder being Fe and inevitable impurities; for the grains in the steel sheet, the average crystal grain size X is 50 μm or less, the standard deviation S1 of the crystal grain size distribution satisfies S1 / X < 0.75, and the kurtosis γ1 of the crystal grain size distribution is 2.00 or less.

Description

Technical Field

[0001] This invention relates to non-directional electromagnetic steel sheets, methods for manufacturing the same, and motor cores using the non-directional electromagnetic steel sheets. Background Technology

[0002] In recent years, the demand for energy efficiency in electronic devices has been increasing worldwide. Consequently, there is a growing demand for superior magnetic properties in the non-directional electromagnetic steel sheets used in the cores of rotating machines. Furthermore, there is a strong recent demand for miniaturization and high output in drive motors for HEVs (hybrid electric vehicles) and EVs (electric vehicles), and research is underway to increase motor speeds to meet this need.

[0003] Motor cores are divided into stator cores and rotor cores. The rotor core of an HEV drive motor experiences significant centrifugal force due to its large outer diameter. Furthermore, the rotor core structure contains a very narrow section (width: 1-2 mm) called the rotor core bridging section, which experiences particularly high stress during motor operation. Consequently, the repeated rotation and stopping of the motor causes large repetitive stresses from centrifugal force on the rotor core; therefore, the electromagnetic steel sheet used for the rotor core needs to possess excellent fatigue characteristics.

[0004] On the other hand, in order to achieve miniaturization and high output of the motor, the electromagnetic steel plate used for the stator core is preferably high magnetic flux density and low iron loss. That is, as required characteristics for the electromagnetic steel plate used for the motor core, ideally the electromagnetic steel plate used for the rotor core has excellent fatigue characteristics, and the electromagnetic steel plate used for the stator core has high magnetic flux density and low iron loss.

[0005] Thus, even for electromagnetic steel sheets used in the same motor core, the required characteristics for the rotor core and stator core are quite different. However, in the manufacturing of motor cores, in order to improve material yield and productivity, it is preferable to take rotor core material and stator core material from the same blank steel sheet by punching, and then stack the individual steel sheets to assemble them into a rotor core or stator core.

[0006] As a technology for manufacturing high-strength and low-iron-loss non-directional electromagnetic steel sheets for motor cores, for example, Patent Document 1 discloses a technology for manufacturing high-strength rotor cores and low-iron-loss stator cores from the same blank as follows: manufacturing high-strength non-directional electromagnetic steel sheets, taking rotor core materials and stator core materials from the steel sheets by punching, stacking and assembling them into rotor cores and stator cores, and then performing stress-relief annealing only on the stator cores.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2008-50686 Summary of the Invention

[0010] However, as the inventors have observed, in the technology disclosed in Patent Document 1, while the yield stress is increased by using high-strength non-directional electromagnetic steel sheets, there is concern that the most important characteristic, the blanking fatigue strength, may not necessarily be improved. Here, blanking fatigue strength refers to the fatigue strength after blanking without end-face processing such as grinding. Furthermore, in the technology disclosed in Patent Document 1, there is a problem that the iron loss value after stress-relief annealing may not consistently reach the level required in industry.

[0011] The present invention was made in view of the problems existing in the prior art, and its purpose is to provide a high-strength non-directional electromagnetic steel plate with good fatigue characteristics suitable for rotor cores and a non-directional electromagnetic steel plate with excellent magnetic properties (low iron loss) suitable for stator cores, and to propose a low-cost method for manufacturing the non-directional electromagnetic steel plate.

[0012] To address the aforementioned problems, the inventors conducted in-depth research and discovered that by controlling the crystal grain size distribution, non-directional electromagnetic steel sheets with high punching fatigue strength can be obtained. Furthermore, by using stress-relief annealing (heat treatment) to promote grain growth in this non-directional electromagnetic steel sheet, excellent low iron loss can be stably achieved. Moreover, it was found that by optimizing the conditions of the final cold rolling pass, the crystal grain size distribution can be controlled.

[0013] This invention is based on this insight and has the following structure.

[0014] [1] A non-directional electromagnetic steel plate, characterized in that it has the following composition:

[0015] It contains, by mass%, less than 0.01% of C, 2.0% to 5.0% of Si, 0.05% to 5.00% of Mn, less than 0.1% of P, less than 0.01% of S, less than 3.0% of Al, and less than 0.0050% of N, with Si + Al being more than 4.5%, and the remainder being Fe and unavoidable impurities.

[0016] For the grains in the steel plate, the average grain size X is less than 50 μm, the standard deviation S1 of the grain size distribution satisfies the following formula (1), and the skewness γ1 of the grain size distribution is less than 2.00.

[0017] S1 / X < 0.75…(1)

[0018] [2] According to the non-directional electromagnetic steel sheet described in [1] above, the above-mentioned composition further includes Co: 0.0005% to 0.0050% by mass%.

[0019] [3] The non-directional electromagnetic steel sheet according to [1] or [2] above, wherein the above composition further includes Cr: 0.05% to 5.00% by mass%.

[0020] [4] The non-directional electromagnetic steel sheet according to any one of [1] to [3] above, wherein the above composition further includes, by mass%, any one or more of Ca: 0.001% to 0.100%, Mg: 0.001% to 0.100% and REM: 0.001% to 0.100%.

[0021] [5] The non-directional electromagnetic steel sheet according to any one of [1] to [4] above, wherein the above composition further comprises, by mass%, any one or two of Sn: 0.001% to 0.200% and Sb: 0.001% to 0.200%.

[0022] [6] The non-directional electromagnetic steel sheet according to any one of [1] to [5] above, wherein the above-mentioned composition further comprises, by mass %: any one or more of the following: Cu: 0% to 0.5%, Ni: 0% to 0.5%, Ti: 0% to 0.005%, Nb: 0% to 0.005%, V: 0% to 0.010%, Ta: 0% to 0.002%, B: 0% to 0.002%, Ga: 0% to 0.005%, Pb: 0% to 0.002%, Zn: 0% to 0.005%, Mo: 0% to 0.05%, W: 0% to 0.05%, Ge: 0% to 0.05%, and As: 0% to 0.05%.

[0023] [7] A non-directional electromagnetic steel plate, characterized in that,

[0024] Composed of any one of the ingredients described in [1] to [6] above,

[0025] For the grains in the steel plate, the average grain size X' is above 80 μm, the standard deviation S2 of the grain size distribution satisfies the following formula (2), and the skewness γ2 of the grain size distribution is below 1.50.

[0026] S2 / X' < 0.75…(2)

[0027] [8] A method for manufacturing a non-directional electromagnetic steel sheet, comprising the following steps:

[0028] The hot rolling process involves hot rolling a steel billet having any one of the compositions described in [1] to [6] above to obtain a hot-rolled plate;

[0029] The pickling process involves pickling the aforementioned hot-rolled plates.

[0030] In the cold rolling process, the hot-rolled plate that has undergone the above pickling is subjected to a final pass entry temperature T1 of 50°C or higher, a final pass reduction r of 15% or higher, and a final pass strain rate ε. m For 100s －1 ~1000s －1 Cold-rolled sheets are obtained by cold rolling under certain conditions; and

[0031] In the annealing process, the above-mentioned cold-rolled sheet is heated to an annealing temperature T2 of 700°C to 850°C under the condition that the average heating rate V1 is 10°C / s or more from 500°C to 700°C, and then cooled to obtain a cold-rolled annealed sheet as a non-directional electromagnetic steel sheet.

[0032] [9] A method for manufacturing a non-directional electromagnetic steel sheet is a method for manufacturing the non-directional electromagnetic steel sheet described in [7] above, comprising a heat treatment step: heating the non-directional electromagnetic steel sheet described in any one of [1] to [6] above at a heat treatment temperature T3 of 750°C to 900°C.

[0033]

[10] A motor core is composed of a rotor core and a stator core, wherein the rotor core is a laminate of non-directional electromagnetic steel plates as described in any one of [1] to [6] above, and the stator core is a laminate of non-directional electromagnetic steel plates as described in [7] above.

[0034] According to the present invention, non-directional electromagnetic steel sheets with good fatigue characteristics suitable for rotor cores and non-directional electromagnetic steel sheets with excellent magnetic properties (low iron loss) suitable for stator cores can be provided. Furthermore, these non-directional electromagnetic steel sheets can be supplied from the same steel sheet. Therefore, by using the non-directional electromagnetic steel sheets of the present invention, high-performance motor cores can be provided with good material yield and low cost. The non-directional electromagnetic steel sheets of the present invention are also suitable for small and high-output motors. Detailed Implementation

[0035] The following is a detailed description of the present invention and the reasons for its limitations.

[0036] <Composition of Non-directional Electromagnetic Steel Sheets>

[0037] The preferred composition of the non-directional electromagnetic steel sheet and motor core of the present invention will be described. The unit of element content in the composition is "mass%"; unless otherwise specified, it will be expressed as "%".

[0038] It should be noted that, as examples of the non-directional electromagnetic steel sheet of the present invention, a first non-directional electromagnetic steel sheet mainly applicable to rotor cores and a second non-directional electromagnetic steel sheet mainly applicable to stator cores can be cited. However, since these non-directional electromagnetic steel sheets are obtained from the same steel sheet, the preferred composition is common to both the first and second non-directional electromagnetic steel sheets.

[0039] C: Below 0.01%

[0040] Carbon (C) is a harmful element that forms carbides during motor use, causing magnetic aging and deteriorating iron loss characteristics. To avoid magnetic aging, the C content in the steel sheet is 0.01% or less. Preferably, the C content is 0.004% or less. It should be noted that there is no particular lower limit for the C content, but steel sheets with excessively low C content are very expensive; therefore, the C content is preferably 0.0001% or more.

[0041] Si: 2.0%~5.0%

[0042] Si increases the inherent electrical resistance of steel and reduces iron loss. Furthermore, it enhances the strength of steel through solid solution strengthening. To achieve these effects, the Si content is 2.0% or higher. On the other hand, if the Si content exceeds 5.0%, the saturation magnetic flux density decreases significantly, therefore the upper limit for the Si content is 5.0%. Thus, the Si content is in the range of 2.0% to 5.0%. The Si content is preferably 2.5% to 5.0%, more preferably 3.0% to 5.0%.

[0043] Mn: 0.05%~5.00%

[0044] Like Si, manganese (Mn) is a useful element for improving the intrinsic electrical resistance and strength of steel. To achieve this effect, the Mn content needs to be 0.05% or higher. On the other hand, if the Mn content exceeds 5.00%, it can sometimes promote the precipitation of MnC, leading to a deterioration of magnetic properties; therefore, the upper limit for the Mn content is 5.00%. Thus, the Mn content is typically between 0.05% and 5.00%. The Mn content is preferably 0.1% or higher, and more preferably 3.0% or lower.

[0045] P: below 0.1%

[0046] Polymer (P) is a useful element for adjusting the strength (hardness) of steel. However, if the P content exceeds 0.1%, the toughness decreases, and cracks are easily generated during processing; therefore, the P content is 0.1% or less. It should be noted that there is no specific lower limit for the P content, but steel plates with excessively low P content are very expensive; therefore, the P content is preferably 0.001% or more. The P content is preferably 0.003% or more, and more preferably 0.08% or less.

[0047] S: below 0.01%

[0048] Sulfur (S) is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, its adverse effects become significant if the S content exceeds 0.01%, therefore the S content is 0.01% or less. It should be noted that there is no specific lower limit for the S content, but steel plates with excessively low S content are very expensive; therefore, the S content is preferably 0.0001% or more. The S content is preferably 0.0003% or more, and more preferably 0.0080% or less, and even more preferably 0.005% or less.

[0049] Al: Below 3.0%

[0050] Al, like Si, is a useful element that increases the inherent electrical resistance of steel and reduces iron loss. To achieve this effect, it is preferable that the Al content is 0.005% or more. More preferably, the Al content is 0.010% or more, and even more preferably 0.015% or more. On the other hand, if the Al content exceeds 3.0%, it may sometimes promote nitriding on the surface of the steel sheet, leading to a deterioration of magnetic properties; therefore, the upper limit for the Al content is 3.0%. The Al content is preferably 2.0% or less.

[0051] N: below 0.0050%

[0052] Nitrogen (N) is an element that forms fine precipitates, negatively impacting iron loss characteristics. In particular, its adverse effects become significant if the N content exceeds 0.0050%, therefore the N content is 0.0050% or less. The N content is preferably 0.0030% or less. It should be noted that there is no specific lower limit for the N content, but steel plates with excessively low N content are very expensive; therefore, the N content is preferably 0.0005% or more. The N content is preferably 0.0008% or more, and more preferably 0.0030% or less.

[0053] Si + Al: 4.5% or more

[0054] By ensuring that the Si + Al content (total Si and Al content) is 4.5% or higher and further performing cold rolling under appropriate conditions, the skewness of the grain size distribution in the cold-rolled annealed sheet is reduced. This improves punching fatigue strength, and excellent low iron loss characteristics can be expected during grain growth through stress-relief annealing (heat treatment). Therefore, the Si + Al content is 4.5% or higher. It should be noted that the reason for reducing the skewness of the grain size distribution by ensuring that the Si + Al content is 4.5% or higher and further combining it with appropriate cold rolling is not yet clear. However, the inventors speculate that this is due to a change in the equilibrium of the active slip system during cold rolling, resulting in the uniform dispersion of recrystallization nucleation sites within the cold-rolled sheet.

[0055] In one embodiment of the electromagnetic steel sheet composition, the remainder other than the aforementioned components is Fe and unavoidable impurities. However, in other embodiments of the electromagnetic steel sheet composition, depending on the required characteristics, it may further contain, in addition to the aforementioned components (elements), one or more elements selected from those described below in specified amounts.

[0056] Co: 0.0005%~0.0050%

[0057] Co has the effect of reducing the skewness of the grain size distribution in annealed sheets by properly controlling Si+Al and cold rolling conditions. That is, by adding trace amounts of Co, the skewness of the grain size distribution can be stably reduced. To achieve this effect, the Co content can be 0.0005% or more. On the other hand, if the Co content exceeds 0.0050%, the effect saturates, leading to unnecessary cost increases; therefore, when adding Co, the upper limit of the Co content is 0.0050%. Therefore, the above composition preferably further includes Co: 0.0005% to 0.0050%.

[0058] Cr: 0.05%~5.00%

[0059] Cr has the effect of increasing the inherent electrical resistance of steel and reducing iron loss. To achieve this effect, the Cr content can be 0.05% or more. On the other hand, if the Cr content exceeds 5.00%, the saturation magnetic flux density decreases significantly, so the upper limit of the Cr content is 5.00%. Therefore, the above composition preferably further includes Cr: 0.05% to 5.00%.

[0060] Ca: 0.001%~0.100%

[0061] Ca is an element that fixes sulfur (S) into sulfides, helping to reduce iron loss. To achieve this effect, the Ca content can be 0.001% or higher. On the other hand, if the Ca content exceeds 0.100%, the effect saturates, leading to unnecessary cost increases. Therefore, when adding Ca, the upper limit for the Ca content is 0.100%.

[0062] Mg: 0.001%~0.100%

[0063] Mg is an element that fixes sulfur (S) into sulfides, helping to reduce iron loss. To achieve this effect, the Mg content can be 0.001% or higher. On the other hand, if the Mg content exceeds 0.100%, the effect saturates, leading to unnecessary cost increases. Therefore, when adding Mg, the upper limit for the Mg content is 0.100%.

[0064] REM: 0.001%~0.100%

[0065] REM (refined iron oxide) is a group of elements that fixes sulfur (S) into sulfides, helping to reduce iron loss. To achieve this effect, the REM content can be 0.001% or higher. On the other hand, if the REM content exceeds 0.100%, the effect saturates, leading to unnecessary cost increases. Therefore, when adding REM, the upper limit for the REM content is 0.100%.

[0066] From the same point of view, the above-mentioned composition preferably further includes one or more of the following: Ca: 0.001% to 0.100%, Mg: 0.001% to 0.100%, and REM: 0.001% to 0.100%.

[0067] Sn: 0.001%~0.200%

[0068] Sn is an effective element for increasing magnetic flux density and reducing iron loss by improving texture. To achieve this effect, the Sn content can be 0.001% or higher. On the other hand, if the Sn content exceeds 0.200%, the effect saturates, leading to unnecessary cost increases. Therefore, when adding Sn, the upper limit of the Sn content is set at 0.200%.

[0069] Sb: 0.001%~0.200%

[0070] Sb is an effective element for increasing magnetic flux density and reducing iron loss by improving texture. To achieve this effect, the Sb content can be 0.001% or higher. On the other hand, if the Sb content exceeds 0.200%, the effect saturates, leading to unnecessary cost increases. Therefore, when adding Sb, the upper limit of the Sb content is set at 0.200%.

[0071] From the same point of view, the above-mentioned composition preferably further includes any one or two of Sn: 0.001% to 0.200% and Sb: 0.001% to 0.200%.

[0072] Cu: 0%~0.5%

[0073] Cu is an element that improves the toughness of steel and can be added appropriately. However, if the Cu content exceeds 0.5%, the effect becomes saturated; therefore, when adding Cu, the upper limit of the Cu content is 0.5%. When adding Cu, the Cu content is more preferably 0.01% or more, and even more preferably 0.1% or less. It should be noted that the Cu content can also be 0%.

[0074] Ni: 0%~0.5%

[0075] Ni is an element that improves the toughness of steel and can be added appropriately. However, if the Ni content exceeds 0.5%, the effect becomes saturated; therefore, when adding Ni, the upper limit of the Ni content is 0.5%. When adding Ni, the Ni content is more preferably 0.01% or more, and even more preferably 0.1% or less. It should be noted that the Ni content can also be 0%.

[0076] Ti: 0%~0.005%

[0077] Ti forms fine carbonitrides and improves the strength of steel sheets through precipitation strengthening, thereby increasing stamping fatigue strength; therefore, it can be added appropriately. On the other hand, if the Ti content exceeds 0.005%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding Ti, the upper limit of the Ti content is 0.005%. A Ti content of 0.002% or less is more preferable. It should be noted that the Ti content can also be 0%.

[0078] Nb: 0%~0.005%

[0079] Nitrogen b (Nb) forms fine carbonitrides and enhances the strength of steel sheets through precipitation strengthening, thereby improving stamping fatigue strength; therefore, it can be added appropriately. On the other hand, if the Nb content exceeds 0.005%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding Nb, the upper limit of the Nb content is 0.005%. More preferably, the Nb content is 0.002% or less. It should be noted that the Nb content can also be 0%.

[0080] V: 0%~0.010%

[0081] V forms fine carbonitrides and improves the strength of steel sheets through precipitation strengthening, thereby increasing punching fatigue strength; therefore, it can be added appropriately. On the other hand, if the V content exceeds 0.010%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding V, the upper limit of the V content is 0.010%. A V content of 0.005% or less is more preferable. It should be noted that the V content can also be 0%.

[0082] Ta: 0%~0.002%

[0083] Ta forms fine carbonitrides and improves the strength of steel sheets through precipitation strengthening, thereby increasing stamping fatigue strength; therefore, it can be added appropriately. On the other hand, if the Ta content exceeds 0.002%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding Ta, the upper limit of the Ta content is 0.0020%. The Ta content is more preferably 0.001% or less. It should be noted that the Ta content can also be 0%.

[0084] B: 0%~0.002%

[0085] Boron (B) forms fine nitrides and enhances the strength of steel sheets through precipitation strengthening, thereby improving stamping fatigue strength; therefore, it can be added appropriately. On the other hand, if the B content exceeds 0.002%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding B, the upper limit of the B content is 0.002%. A B content of 0.001% or less is more preferable. It should be noted that the B content can also be 0%.

[0086] Ga: 0%~0.005%

[0087] Ga forms fine nitrides and enhances the strength of steel sheets through precipitation strengthening, thereby improving stamping fatigue strength; therefore, it can be added appropriately. On the other hand, if the Ga content exceeds 0.005%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding Ga, the upper limit of the Ga content is 0.005%. A Ga content of 0.002% or less is more preferable. It should be noted that the Ga content can also be 0%.

[0088] Pb: 0%~0.002%

[0089] Pb forms fine Pb particles and enhances the strength of the steel sheet through precipitation strengthening, thereby improving the punching fatigue strength; therefore, it can be added appropriately. On the other hand, if the Pb content exceeds 0.002%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding Pb, the upper limit of the Pb content is 0.002%. A Pb content of 0.001% or less is more preferable. It should be noted that the Pb content can also be 0%.

[0090] Zn: 0%~0.005%

[0091] Zinc (Zn) is an element that increases fine inclusions and iron loss, especially when its content exceeds 0.005%, where the adverse effects become significant. Therefore, even when Zn is added, its content is in the range of 0% to 0.005%. A Zn content of 0.003% or less is more preferable. It should be noted that the Zn content can also be 0%.

[0092] Mo: 0%~0.05%

[0093] Mo forms fine carbides and improves the strength of steel sheets through precipitation strengthening, thereby increasing stamping fatigue strength; therefore, it can be added appropriately. On the other hand, if the Mo content exceeds 0.05%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding Mo, the upper limit of the Mo content is 0.05%. More preferably, the Mo content is 0.02% or less. It should be noted that the Mo content can also be 0%.

[0094] W: 0%~0.05%

[0095] W forms fine carbides and improves the strength of steel sheets through precipitation strengthening, thereby increasing punching fatigue strength; therefore, it can be added appropriately. On the other hand, if the W content exceeds 0.05%, it deteriorates grain growth during the heat treatment process, leading to increased iron loss. Therefore, when adding W, the upper limit of the W content is 0.05%. The W content is more preferably 0.02% or less. It should be noted that the W content can also be 0%.

[0096] Ge: 0%~0.05%

[0097] Ge is an effective element for improving magnetic flux density and reducing iron loss by improving texture, and therefore can be added appropriately. On the other hand, if the Ge content exceeds 0.05%, the effect saturates, so when adding Ge, the upper limit of the Ge content is kept to 0.05% or less. More preferably, the Ge content is 0.002% or more, and even more preferably 0.01% or less. It should be noted that the Ge content can also be 0%.

[0098] As: 0%~0.05%

[0099] As is an effective element for improving magnetic flux density and reducing iron loss by improving texture, and therefore can be added appropriately. On the other hand, if the As content exceeds 0.05%, the effect saturates, so when adding As, the upper limit of the As content is 0.05% or less. More preferably, the As content is 0.002% or more, and even more preferably 0.01% or less. It should be noted that the As content can also be 0%.

[0100] Of the above components, the remainder, besides the components mentioned above, consists of Fe and unavoidable impurities.

[0101] <Microstructure of the first non-directional electromagnetic steel sheet>

[0102] Next, the microstructure (grain morphology) of the first non-directional electromagnetic steel plate of the present invention will be described. This first non-directional electromagnetic steel plate is a material particularly suitable for rotor cores.

[0103] (Average crystal grain size X: less than 50 μm)

[0104] According to the research of the inventors, it has been clarified that the punching fatigue strength is improved due to the fineness of the grains in the steel sheet. Specifically, if the average grain size X is 50 μm or less, the punching fatigue strength can meet the requirements for rotor materials used in motors for HEVs or EVs (hereinafter referred to as HEV / EV motors). Therefore, in the first non-directional electromagnetic steel sheet, the average grain size X is made to be 50 μm or less. Here, the required value for punching fatigue strength for rotor materials is 430 MPa or more. On the other hand, there is no particular lower limit for the average grain size X, but if the grain size is excessively fine, the ductility of the steel sheet decreases, making processing difficult. Therefore, the average grain size X is preferably 1 μm or more.

[0105] (The standard deviation of the crystal grain size distribution S1 satisfies equation (1))

[0106] When the standard deviation of the crystal grain size distribution is greater than the average crystal grain size, stress concentration is increased during the punching and under stress loads of the steel sheet, thus reducing the punching fatigue strength. Therefore, in the first non-directional electromagnetic steel sheet, in order to ensure that the punching fatigue limit meets or exceeds the value required for the rotor material of the HEV / EV motor, the standard deviation S1 of the crystal grain size distribution should satisfy the following equation (1):

[0107] S1 / X < 0.75… (1).

[0108] Furthermore, the standard deviation S1 of the preferred crystal grain size distribution in the first non-directional electromagnetic steel plate satisfies the following equation (1'):

[0109] S1 / X < 0.70… (1').

[0110] (The skewness of the crystal grain size distribution γ1 is less than 2.00)

[0111] The inventors have discovered that by controlling the skewness of the grain size distribution, a non-directional electromagnetic steel sheet with excellent punching fatigue strength can be obtained, and excellent low iron loss can be achieved when grains grow through stress-relief annealing (heat treatment). This effect can be obtained by simultaneously controlling the skewness of the grain size distribution and the standard deviation S1 of the aforementioned grain size distribution. Specifically, a large skewness in the grain size distribution means that the grain size distribution exhibits a long tail distribution on the coarse grain side, with a high probability of grains that are considerably coarse relative to the average grain size. These coarse grains are prone to becoming crack initiation points during punching, thus deteriorating the punching fatigue characteristics. Specifically, if the skewness γ1 of the grain size distribution is 2.00 or less, the punching fatigue limit meets the aforementioned value required for rotor materials of HEV / EV motors, and low iron loss can be achieved after stress-relief annealing. Therefore, in the first non-directional electromagnetic steel sheet, the skewness γ1 of the grain size distribution is made to be 2.00 or less. The skewness γ1 of the crystal grain size distribution in the first non-directional electromagnetic steel sheet is preferably 1.50 or less. It should be noted that the lower limit of the above-mentioned skewness γ1 does not need to be specifically specified, but it is usually 0 or more even when manufactured using the method of the present invention.

[0112] It should be noted that the skewness γ1 can be determined by following the steps described in the embodiments below.

[0113] <Microstructure of the Second Non-directional Electromagnetic Steel Sheet>

[0114] The first non-directional electromagnetic steel sheet having the above-described microstructure (grain morphology) can become a second non-directional electromagnetic steel sheet by performing heat treatment to grow grains, as described later. Therefore, the microstructure (grain morphology) of the second non-directional electromagnetic steel sheet of the present invention will be described next. This second non-directional electromagnetic steel sheet is a material particularly suitable for stator cores.

[0115] (Average crystal grain size X': ≥80μm)

[0116] The iron loss of non-directional electromagnetic steel sheets varies with the average crystal grain size. In a second non-directional electromagnetic steel sheet suitable for stator cores, the average crystal grain size X' is made to be 80 μm or higher. This allows the achievement of the target iron loss characteristics (W). 10／400 ≤11.0 (W / kg)).

[0117] (The standard deviation of the crystal grain size distribution S2 satisfies equation (2))

[0118] When the standard deviation of the crystal grain size distribution is greater than the average crystal grain size, there are many excessively fine grains and excessively coarse grains that are detrimental to reducing iron loss, thus increasing iron loss. Therefore, in the second non-directional electromagnetic steel sheet, in order to make the iron loss display the above-mentioned target value required for the stator material of the HEV / EV motor, the standard deviation S2 of the crystal grain size distribution should satisfy the following formula (2):

[0119] S2 / X' < 0.75… (2).

[0120] Furthermore, the standard deviation S2 of the preferred crystal grain size distribution in the second non-directional electromagnetic steel sheet satisfies the following equation (2'):

[0121] S2 / X' < 0.70… (2').

[0122] (The skewness γ2 of the crystal grain size distribution is less than 1.50)

[0123] The inventors have discovered that excellent low iron loss can be achieved by controlling the skewness of the crystal grain size distribution. This effect can be obtained by simultaneously controlling the skewness of the crystal grain size distribution and the standard deviation S2 of the crystal grain size distribution. As mentioned above, a large skewness of the crystal grain size distribution means that the crystal grain size distribution exhibits a long tail distribution on the coarse grain side, with a high probability of grains that are quite coarse relative to the average grain size. This increase in grain-induced eddy current loss deteriorates the overall iron loss characteristics of the steel sheet. Specifically, if the skewness γ2 of the crystal grain size distribution is 1.50 or less, the iron loss shows a good value required for the stator material of HEV / EV motors. Therefore, in the second non-directional electromagnetic steel sheet, the skewness γ2 of the crystal grain size distribution is made to be 1.50 or less. The skewness γ2 of the crystal grain size distribution in the second non-directional electromagnetic steel sheet is preferably 1.20 or less, more preferably 1.00 or less. On the other hand, the lower limit of the aforementioned skewness γ2 does not need to be specifically specified, but it is usually above 0 even when manufactured using the method of the present invention.

[0124] It should be noted that the skewness γ2 can be determined by following the steps described in the embodiments below.

[0125] <Motor core>

[0126] The motor core of the present invention comprises a rotor core consisting of a laminate of the first non-directional electromagnetic steel plate (i.e., a non-directional electromagnetic steel plate with an average crystal grain size X of 50 μm or less, a standard deviation S1 satisfying [S1 / X < 0.75], and a skewness γ1 of 2.00 or less) and a stator core consisting of the second non-directional electromagnetic steel plate (i.e., a non-directional electromagnetic steel plate with an average crystal grain size X' of 80 μm or more, a standard deviation S2 satisfying [S2 / X' < 0.75], and a skewness γ2 of 1.50 or less). Because the rotor core has high punching fatigue strength and the stator core has excellent magnetic properties, this motor core can be easily miniaturized and achieve high output.

[0127] <Manufacturing Method of Non-directional Electromagnetic Steel Sheets>

[0128] Next, the manufacturing method of the non-directional electromagnetic steel sheet of the present invention will be described.

[0129] In general, the method involves using a steel billet having the aforementioned composition as the starting material and sequentially performing a hot rolling process, an arbitrary hot-rolled plate annealing process, a pickling process, a cold rolling process, and an annealing process to obtain the first non-directional electromagnetic steel sheet of the present invention. Furthermore, by subjecting the first non-directional electromagnetic steel sheet to heat treatment, the second non-directional electromagnetic steel sheet of the present invention can be obtained. In the present invention, if the composition of the steel billet, the conditions of the cold rolling and annealing processes, and the conditions of the heat treatment process are within specified ranges, then other conditions are not particularly limited. It should be noted that the manufacturing method of the motor core is not particularly limited, and commonly known methods can be used.

[0130] (steel billet)

[0131] There are no particular limitations as long as the billet material is composed of the components of the non-directional electromagnetic steel sheet described above.

[0132] There are no particular limitations on the smelting method for steel billets; known smelting methods such as converters or electric furnaces can be used. Considering factors such as productivity, it is preferable to produce slabs (steel billets) by continuous casting after smelting, but slabs can also be produced by known casting methods such as ingot-rolling or thin slab continuous casting.

[0133] (Hot rolling process)

[0134] Hot rolling is a process of obtaining a hot-rolled plate by hot rolling a steel billet with the above-mentioned composition. There are no particular limitations on the hot rolling process; any process that involves heating and hot rolling a steel billet with the above-mentioned composition to obtain a hot-rolled plate of specified dimensions can be used.

[0135] A commonly used hot rolling process is as follows: heating the steel billet to a temperature of 1000℃~1200℃, hot rolling the heated steel billet at a finishing exit temperature of 800℃~950℃, and after hot rolling, performing appropriate post-rolling cooling (for example, cooling at an average cooling rate of 20℃ / s~100℃ / s in a temperature range of 450℃~950℃), and winding at a winding temperature of 400℃~700℃ to produce a hot-rolled plate of specified size and shape.

[0136] (Hot-rolled plate annealing process)

[0137] The hot-rolled sheet annealing process involves heating and maintaining the hot-rolled sheet at a high temperature to anneal it. There are no particular limitations on the hot-rolled sheet annealing process; commonly used hot-rolled sheet annealing processes can be used. It should be noted that this hot-rolled sheet annealing process is not mandatory and can be omitted.

[0138] (Pickling process)

[0139] The pickling process is a process of pickling hot-rolled steel sheets after the aforementioned hot rolling process or any of the aforementioned hot-rolled sheet annealing processes. There are no particular limitations on the pickling process, as long as it can pickle to a degree sufficient for cold rolling of the pickled steel sheet; for example, commonly used pickling processes using hydrochloric acid or sulfuric acid can be applied. When the aforementioned hot-rolled sheet annealing process is being performed, this pickling process can be carried out continuously on the same production line as the hot-rolled sheet annealing process, or it can be carried out on a separate production line.

[0140] (Cold rolling process)

[0141] The cold rolling process is a process of cold rolling hot-rolled sheets (pickled sheets) that have undergone the above-mentioned pickling. More specifically, in the cold rolling process, the hot-rolled sheets that have undergone the above-mentioned pickling are subjected to a final pass entry temperature T1 of 50°C or higher, a final pass reduction r of 15% or higher, and a final pass strain rate ε. m For 100s －1 ~1000s －1 Cold rolling is performed under the specified conditions to obtain cold-rolled sheets. It should be noted that, in the cold rolling process, as long as the above cold rolling conditions are met, cold-rolled sheets of a specified size can also be produced by cold rolling twice or more, with intermediate annealing in between. Generally, there are no particular limitations on the conditions for intermediate annealing at this time, and commonly used intermediate annealing methods can be used.

[0142] [Final track inlet side temperature T1: above 50℃]

[0143] In the cold rolling process, the final pass entry temperature T1 is above 50°C. The reason for setting the final pass entry temperature T1 above 50°C is to ensure that the skewness γ1 of the crystal grain size distribution in the obtained first non-directional electromagnetic steel sheet is below 2.00, so as to form the desired steel sheet structure.

[0144] When the final pass inlet temperature T1 is less than 50°C, the strain distribution of the cold-rolled sheet deviates. In subsequent annealing processes, the selectivity of grain growth is emphasized, thus increasing the skewness of the grain size distribution in the annealed sheet. The reason for this is not yet clear, but the inventors speculate that by keeping the final pass inlet temperature T1 less than 50°C, the types of active slip systems are limited, making it easier to cause uneven deformation.

[0145] On the other hand, when the final pass inlet temperature T1 is above 50°C, after the annealing process described later, the skewness γ1 of the crystal grain size distribution becomes below 2.00. As a result, the desired steel sheet microstructure can be obtained.

[0146] The final pass inlet temperature T1 is preferably 55°C or higher, more preferably 60°C or higher. It should be noted that there is no particular upper limit to the final pass inlet temperature T1, but from the viewpoint of preventing the steel sheet from sticking to the roll, the final pass inlet temperature T1 is preferably 300°C or lower.

[0147] [Final pass reduction rate r: 15% or higher]

[0148] In the cold rolling process, the reduction rate r of the final pass is 15% or more. The reason for making the reduction rate r of the final pass 15% or more is to achieve a series of cold rolling control effects to form the desired steel sheet structure.

[0149] When the reduction rate r in the final pass is less than 15%, it is difficult to control the microstructure after annealing due to the excessively low reduction rate. On the other hand, when the reduction rate r in the final pass is 15% or more, a series of cold rolling control effects are achieved. As a result, the desired steel sheet microstructure can be obtained.

[0150] The reduction rate r of the final pass is preferably 20% or higher. It should be noted that there is no particular upper limit to the reduction rate r of the final pass, but an excessively high reduction rate requires a large amount of equipment capacity, and the shape control of the cold-rolled sheet also becomes difficult. Therefore, the reduction rate r of the final pass is usually below 50%.

[0151] [Strain velocity ε of the final pass] m 100s －1 ~1000s －1 ]

[0152] In the cold rolling process, the strain rate ε of the final passm For 100s －1 ~1000s －1 The strain rate ε of the final pass. m For 100s －1 ~1000s －1 The reason is that, while suppressing fracture during rolling, the skewness γ1 of the crystal grain size distribution in the first non-directional electromagnetic steel sheet is less than 2.00, so as to form the desired steel sheet structure.

[0153] The strain rate ε in the final pass m Less than 100s －1 In such cases, the strain distribution of the cold-rolled sheet deviates. In subsequent annealing processes, selective grain growth is emphasized, leading to a greater skewness in the grain size distribution of the annealed sheet. The reason for this is not yet clear, but the inventors speculate that due to the low strain rate and reduced flow stress, strain tends to concentrate on easily deformable grains with specific orientations, easily resulting in uneven deformation. On the other hand, at the strain rate ε in the final pass... m More than 1000s －1 Under certain conditions, excessive flow stress can easily lead to brittle fracture during rolling.

[0154] The strain rate ε in the final pass m For 100s －1 ~1000s －1 In this case, while suppressing fracture during rolling, the skewness γ1 of the grain size distribution becomes less than 2.00 after the annealing process described later. As a result, the desired steel sheet microstructure can be obtained.

[0155] The strain rate ε of the final pass m Preferred 150s －1 The above is also preferred, with 800s being the preferred option. －1 the following.

[0156] It should be noted that the strain rate ε in each pass of cold rolling... m It is derived using the following approximation of Ekelund.

[0157]

[0158] Here, v R R' is the roller circumferential speed (mm / s), h1 is the roller radius (mm), r is the roller inlet side plate thickness (mm), and r is the reduction rate (%).

[0159] (Annealing process)

[0160] The annealing process is a process of annealing cold-rolled sheets that have undergone the cold rolling process. More specifically, in the annealing process, the cold-rolled sheet is heated to an annealing temperature T2 of 700°C to 850°C under conditions where the average heating rate V1 from 500°C to 700°C is 10°C / s or higher, and then cooled to obtain a cold-rolled annealed sheet (first non-directional electromagnetic steel sheet). It should be noted that after the annealing process, an insulating coating can be applied to the surface. There are no particular limitations on the method and type of coating, and commonly used insulating coating processes can be used.

[0161] [Average heating rate V1 from 500℃ to 700℃: 10℃ / s or more]

[0162] In the annealing process, the average heating rate V1 from 500°C to 700°C is 10°C / s or more. The reason for making the average heating rate V1 10°C / s or more is to make the standard deviation S1 of the crystal grain size distribution in the obtained non-directional electromagnetic steel sheet satisfy the above formula (1) so as to form the desired steel sheet structure.

[0163] When the average heating rate V1 is less than 10℃ / s, the frequency of recrystallization nucleus formation decreases due to excessive recovery, and the position dependence of the number of recrystallization nuclei increases. As a result, fine and coarse grains coexist, the standard deviation S1 of the crystal grain size distribution increases, and the above equation (1) is no longer satisfied.

[0164] On the other hand, when the average heating rate V1 is 10℃ / s or higher, the frequency of recrystallization nucleus formation increases, and the positional dependence of the number of recrystallization nuclei decreases. As a result, the standard deviation S1 of the crystal grain size distribution decreases, satisfying the above equation (1).

[0165] The average heating rate V1 from 500°C to 700°C is preferably 20°C / s or more, more preferably 50°C / s or more. It should be noted that there is no particular upper limit to the average heating rate V1, but if the heating rate is too high, uneven temperature is likely to occur. Therefore, the average heating rate V1 is preferably 500°C / s or less.

[0166] [Annealing temperature T2: 700℃~850℃]

[0167] In the annealing process, the annealing temperature T2 is 700℃~850℃. The reason for setting the annealing temperature T2 to 700℃~850℃ is as follows.

[0168] When the annealing temperature T2 is less than 700°C, grain growth is suppressed, thus emphasizing the positional dependence of the number of recrystallization nuclei, resulting in a microstructure that retains the initial inhomogeneity. Consequently, the standard deviation S1 of the grain size distribution increases. On the other hand, when the annealing temperature T2 is 700°C or higher, sufficient grain growth can occur, allowing the standard deviation S1 of the grain size distribution to satisfy the above equation (1), thereby obtaining the desired steel sheet microstructure. The annealing temperature T2 is preferably 750°C or higher.

[0169] On the other hand, when the annealing temperature T2 exceeds 850°C, excessive recrystallization grain growth occurs, preventing the average crystal grain size X from being below 50 μm. Therefore, the annealing temperature T2 is below 850°C. Preferably, the annealing temperature T2 is below 825°C.

[0170] In the annealing process, the material is heated to the aforementioned annealing temperature T2 and then cooled. From the viewpoint of preventing uneven cooling, this cooling is preferably performed at a cooling rate of 50°C / s or less.

[0171] (Heat treatment process)

[0172] The heat treatment process is a process of heat-treating the cold-rolled annealed sheet (first non-directional electromagnetic steel sheet) that has undergone the above-described annealing process. More specifically, in the heat treatment process, the cold-rolled annealed sheet (first non-directional electromagnetic steel sheet) that has undergone the above-described annealing process is heated to a heat treatment temperature T3 of 750°C to 900°C. By cooling after heating, a heat-treated sheet (second non-directional electromagnetic steel sheet) can be obtained. It should be noted that the heat treatment process is usually performed on the stator core formed by stacking the above-described non-directional electromagnetic steel sheets, but the same effect can be obtained when the heat treatment process is performed on the above-described non-directional electromagnetic steel sheets before stacking.

[0173] [Heat treatment temperature T3: 750℃~900℃]

[0174] In the heat treatment process, the heat treatment temperature T3 is 750℃~900℃. The reasons for setting the heat treatment temperature T3 to 750℃~900℃ are as follows.

[0175] When the heat treatment temperature T3 is less than 750°C, grain growth is insufficient, and the average grain size X' in the obtained second non-directional electromagnetic steel sheet cannot be greater than 80 μm. Therefore, the heat treatment temperature T3 is 750°C or higher. Preferably, the heat treatment temperature T3 is 775°C or higher.

[0176] On the other hand, when the heat treatment temperature exceeds 900°C, the selectivity of grain growth is emphasized, and the skewness of the grain size distribution becomes excessive. As a result, the skewness γ2 of the grain size distribution in the obtained second non-directional electromagnetic steel sheet is not below 1.50. Therefore, the heat treatment temperature T3 is 900°C or below. The heat treatment temperature T3 is preferably 875°C or below.

[0177] By performing the above heat treatment process, the microstructure of the second non-directional electromagnetic steel sheet is obtained, namely, the average grain size X' is 80 μm or more, the standard deviation S2 satisfies [S2 / X' < 0.75], and the skewness γ2 is 1.50 or less. This microstructure change is affected by the microstructure of the steel sheet before the heat treatment process. That is, in order to obtain a microstructure with a standard deviation S2 satisfying [S2 / X' < 0.75] and a skewness γ2 of 1.50 or less by performing the heat treatment process, the steel sheet before the heat treatment process needs to satisfy a standard deviation S1 satisfying [S1 / X < 0.75] and a skewness γ1 of 2.00 or less.

[0178] Example

[0179] The following examples illustrate the present invention in detail. However, the present invention is not limited thereto.

[0180] <Manufacturing of Cold-Rolled Annealed Sheet (First Non-directional Electromagnetic Steel Sheet)>

[0181] Molten steel with the composition shown in Table 1 is smelted by commonly known methods and continuously cast to produce slabs (steel billets) with a thickness of 230 mm.

[0182] The obtained slab was hot-rolled to obtain a hot-rolled plate with a thickness of 2.0 mm. The hot-rolled plate was then annealed and pickled using known methods, and then cold-rolled to the thickness shown in Table 2 to obtain a cold-rolled plate.

[0183] The obtained cold-rolled sheet was annealed under the conditions shown in Table 2, and then coated by a known method to obtain a cold-rolled annealed sheet (first non-directional electromagnetic steel sheet).

[0184] <Manufacturing of Heat-Treated Plate (Second Non-directional Electromagnetic Steel Plate)>

[0185] The obtained cold-rolled annealed sheet was subjected to heat treatment under the conditions shown in Table 2 to obtain a heat-treated sheet (second non-directional electromagnetic steel sheet).

[0186] <Manufacturing of Motor Cores>

[0187] A motor core is obtained by combining a rotor core made of laminated cold-rolled annealed plates (first non-directional electromagnetic steel plates) and a stator core made of laminated heat-treated plates (second non-directional electromagnetic steel plates) using a known method.

[0188] <Evaluation>

[0189] (Observations on microstructures)

[0190] Test pieces for microstructure observation were taken from the obtained cold-rolled annealed sheets and heat-treated sheets. Next, the test pieces were thinned and mirror-finished using chemical polishing, with the observation surface located at approximately 1 / 4 of the sheet thickness on the rolled surface (ND surface). Electron backscatter diffraction (EBSD) was performed on the mirror-finished observation surface to obtain local orientation data. At this point, for the cold-rolled annealed sheet, the step size was 2 μm and the measurement area was 4 mm. 2 For the heat-treated plate, the step size is 10μm and the measurement area is 100mm. 2 That's all. Adjust the width of the measurement area appropriately to ensure that the number of grains in subsequent analyses exceeds 5000. It should be noted that the measurement can be performed on the entire area in a single scan, or the results of multiple scans can be combined using the Combo Scan function. Use the analysis software OIM Analysis 8 to analyze the obtained local orientation data.

[0191] Before data analysis, the analysis software's Partition Properties were used to screen grain-average data points under the condition that Formula: GCI[&;5.000,2,0.000,0,0,8.0,1,1,1.0,0;]>0.1, eliminating data points unsuitable for analysis. At this point, more than 97% of the data points were valid.

[0192] For the adjusted data above, as the definition of grain boundaries, Grain Tolerance Angle is set to 5°, Minimum Grain Size is set to 2, Minimum Anti Grain Size is set to 2, and Multiple RowsRequirement and Anti-Grain Multiple Rows Requirement are both set to OFF. The following analysis is then performed.

[0193] For preprocessed data, use the Export Grain File function to output grain information. Use the Grain Size (Diameter in microns) from Grain File Type 2 as the crystal grain size (X). iFor all the obtained grain information, calculate the average grain size X and X', standard deviation S1 and S2, and skewness γ1 and γ2 respectively. The following formulas are used in the calculations. It should be noted that the following formulas correspond to cold-rolled annealed plates with an additional subscript 1, representing X, S1, and γ1. However, in the case of heat-treated plates, the subscript 1 in each formula can be replaced with 2, representing X', S2, and γ2, and the following formulas are used in the same way.

[0194]

[0195] In the above formula, n is the number of grains, X i The data are for the crystal grain size (i: 1, 2, ..., n).

[0196] (Evaluation of punching fatigue strength)

[0197] Tensile fatigue test pieces (of the same shape as test piece No. 1 in JIS Z2275:1978, with b: 15 mm and R: 100 mm) were punched from the obtained cold-rolled annealed sheet and used for fatigue testing. The fatigue tests were conducted at the following conditions: test temperature: room temperature (25°C), tensile-tensile (pulse) test, stress ratio (=minimum stress / maximum stress): 0.1, and frequency: 20 Hz. The tests were performed after 10 repetitions. 7 The maximum stress that does not cause fatigue fracture is taken as the punching fatigue limit. When the punching fatigue limit is above 430 MPa, it is evaluated as having excellent punching fatigue strength.

[0198] (Evaluation of magnetic properties)

[0199] A magnetic testing piece with a width of 30 mm and a length of 280 mm was taken from the obtained heat-treated plate, with the length direction being the rolling direction and the rolling right angle direction. The iron loss W of the heat-treated plate was determined by the Epstein method according to JIS C2550-1:2011. 10／400 In W 10／400 When the iron loss is ≤11.0 (W / kg), it is evaluated as having good iron loss characteristics.

[0200] The results are shown in Table 3.

[0201]

[0202]

[0203]

[0204]

[0205]

[0206]

[0207] As shown in Table 3, the non-directional electromagnetic steel sheets according to the present invention exhibit excellent punching fatigue strength and excellent iron loss characteristics. It should be noted that the motor core obtained by combining a rotor core formed by laminating a cold-rolled annealed sheet according to the present invention with a stator core formed by laminating the same heat-treated sheet has excellent fatigue characteristics.

Claims

1. A non-directional electromagnetic steel plate, characterized in that, It has the following components composition: It contains, by mass%, less than 0.01% C, 2.0% to 5.0% Si, 0.05% to 5.00% Mn, less than 0.1% P, less than 0.01% S, less than 3.0% Al and less than 0.0050% N, with Si + Al being more than 4.5%, and the remainder being Fe and unavoidable impurities; For the grains in the steel plate, the average grain size X is less than 50 μm, the standard deviation S1 of the grain size distribution satisfies the following formula (1), and the skewness γ1 of the grain size distribution is less than 2.

00. S1 / X < 0.75…(1), Here, the skewness γ1 of the crystal grain size distribution is determined by electron backscattering diffraction (EBSD) at a position equivalent to 1 / 4 of the thickness of the non-directional electromagnetic steel plate, using the observation plane. The obtained local orientation data is analyzed, and the value of all obtained grain information is calculated using the following formula. In the above formula, n is the number of grains, X i Here are the crystal grain size data, where i is 1, 2, ..., n.

2. The non-directional electromagnetic steel plate according to claim 1, wherein, The composition further includes at least one group selected from groups A, B, C, D, and E below. Group A: Co: 0.0005%–0.0050% by mass. Group B: By mass%, Cr: 0.05%–5.00%, Group C: By mass%, any one or more of the following: Ca: 0.001%–0.100%, Mg: 0.001%–0.100%, and REM: 0.001%–0.100%. Group D: By mass%, any one or both of Sn: 0.001%–0.200% and Sb: 0.001%–0.200%. Group E: By mass%, any one or more of the following: Cu: 0%–0.5%, Ni: 0%–0.5%, Ti: 0%–0.005%, Nb: 0%–0.005%, V: 0%–0.010%, Ta: 0%–0.002%, B: 0%–0.002%, Ga: 0%–0.005%, Pb: 0%–0.002%, Zn: 0%–0.005%, Mo: 0%–0.05%, W: 0%–0.05%, Ge: 0%–0.05%, and As: 0%–0.05%.

3. A non-directional electromagnetic steel plate, characterized in that, Having the composition of the ingredients as described in claim 1 or 2, For the grains in the steel plate, the average grain size X' is above 80 μm, the standard deviation S2 of the grain size distribution satisfies the following formula (2), and the skewness γ2 of the grain size distribution is below 1.

50. S2 / X'<0.75…(2) Here, the skewness γ2 of the crystal grain size distribution is determined by electron backscattering diffraction (EBSD) at a position equivalent to 1 / 4 of the thickness of the non-directional electromagnetic steel plate, using the observation plane. The obtained local orientation data is analyzed, and the value of all obtained grain information is calculated using the following formula. In the above formula, n is the number of grains, X i Here are the crystal grain size data, where i is 1, 2, ..., n.

4. A method for manufacturing a non-directional electromagnetic steel sheet, comprising the steps described in claim 1 or 2: The hot rolling process involves hot rolling a steel billet having the composition described in claim 1 or 2 to obtain a hot-rolled plate. The pickling process involves pickling the hot-rolled plate. In the cold rolling process, the hot-rolled plate that has undergone pickling is subjected to a final pass entry temperature T1 of 50°C or higher, a final pass reduction r of 15% or higher, and a final pass strain rate ε. m For 100s －1 ~1000s －1 Cold-rolled sheets are obtained by cold rolling under certain conditions; and In the annealing process, the cold-rolled sheet is heated to an annealing temperature T2 of 700°C to 850°C under conditions where the average heating rate V1 is 10°C / s or more from 500°C to 700°C, and then cooled to obtain a cold-rolled annealed sheet as a non-directional electromagnetic steel sheet.

5. A method for manufacturing a non-directional electromagnetic steel sheet, comprising a heat treatment step of manufacturing the non-directional electromagnetic steel sheet of claim 3, wherein the non-directional electromagnetic steel sheet of claim 1 or 2 is heated at a heat treatment temperature T3 of 750°C to 900°C.

6. A motor core comprising a rotor core and a stator core, wherein the rotor core is a laminate of non-directional electromagnetic steel plates as described in claim 1 or 2, and the stator core is a laminate of non-directional electromagnetic steel plates as described in claim 3.

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