JP2020076144A - Motor core and method for manufacturing the same - Google Patents

Abstract

To provide a motor core which is obtained by laminating a magnetic steel sheet and is excellent in fatigue strength, and a method for manufacturing the motor core.SOLUTION: The motor core is provided in which a tensile residual stress of a blanked end surface of the motor core is 250 MPa or less and hardness of the blanked end surface is 1.10 or more times the hardness of a base material. The method for manufacturing a motor core is provided that is composed of a blanking step of blanking a motor core material from a magnetic steel sheet that is used as the base material of the motor core, a laminating step of laminating the motor core material, and an annealing step in which the motor core material or a motor core is heated to a temperature T (°C) of 250°C or higher and 550°C or lower, and is held for time t (sec) satisfying 3350≤(T+273)×(2+logt)≤4650.SELECTED DRAWING: Figure 1

Description

  TECHNICAL FIELD The present invention relates to a motor core formed by laminating electromagnetic steel sheets and having excellent fatigue strength, and a method for manufacturing the motor core.

  With the increasing demand for energy saving in global electric equipment in recent years, even better magnetic properties are required for non-oriented electrical steel sheets used for iron cores of rotating machines. There is. In recent years, drive motors for HEVs (hybrid vehicles) and EVs (electric vehicles) have been strongly demanded for miniaturization and high output, and it is considered to increase the rotation speed of the motors in order to achieve this requirement. Has been done.

  The motor core is divided into a stator core and a rotor core, but the rotor core of the HEV drive motor has a large outer diameter, and thus a large centrifugal force acts. Further, the rotor core has a very narrow portion (1 to 2 mm) called a rotor core bridge portion due to its structure, and this portion is in a particularly high stress state during driving. Further, since the motor repeats rotation and stop, a large repetitive stress is exerted on the rotor core due to centrifugal force. Therefore, the magnetic steel sheet used for the rotor core needs to have excellent fatigue characteristics. On the other hand, the magnetic steel sheet used for the stator core preferably has high magnetic flux density and low iron loss in order to achieve downsizing and high output of the motor. That is, as the characteristics of the magnetic steel sheet used for the motor core, it is ideal that the rotor core has high fatigue characteristics and the stator core has high magnetic flux density and low iron loss.

  As described above, even in electromagnetic steel sheets used for the same motor core, the required characteristics are significantly different between the rotor core and the stator core. However, in manufacturing a motor core, in order to improve the material yield and productivity, the rotor core material and the stator core material are simultaneously punched from the same material steel sheet, and then the respective steel sheets are stacked to be assembled into the rotor core or the stator core. Is desirable.

  As a technique for producing a high-strength, low iron loss non-oriented electrical steel sheet for a motor core, for example, in Patent Document 1, a high-strength non-oriented electrical steel sheet is produced and a rotor core material is punched from the steel sheet. A technique for manufacturing a high-strength rotor core and a low iron loss stator core from the same material by collecting and stacking the stator core material, assembling the rotor core and the stator core, and then performing strain relief annealing only on the stator core is disclosed. ing.

JP, 2008-50686, A

  However, in the technique disclosed in Patent Document 1, although the yield stress is improved by using the high-strength non-oriented electrical steel sheet, the fatigue strength, which is the most important characteristic, is not necessarily improved. is there.

  The present invention has been made in view of the problems of the above-described conventional technology, and an object thereof is to provide a motor core having excellent fatigue strength and to propose an inexpensive manufacturing method thereof.

  The inventors have made earnest studies to solve the above problems and achieve the above objects. As a result, they have found that it is not always necessary to use high-strength steel plates to improve the fatigue strength of the motor core, especially the rotor core, and it is important to control the residual stress and the end surface hardness of the punched end surface within appropriate ranges.

  That is, the present invention is, firstly, a motor core formed by laminating electromagnetic steel sheets, wherein the punching end face of the motor core has a tensile residual stress of 250 MPa or less, and the punching end face has a hardness of 1. Provided is a motor core which is 10 times or more.

  The above-mentioned magnetic steel sheet of the present invention is C: 0.0050% or less, Si: 2.0% or more, 7.0% or less, Mn: 0.05% or more, 3.0% or less, Al: 3 in mass%. It is preferable to have a component composition containing 0.0% or less, P: 0.2% or less, S: 0.005% or less and N: 0.0050% or less, with the balance being Fe and inevitable impurities.

  In addition to the above-mentioned composition of ingredients, the above-mentioned magnetic steel sheet of the present invention is Cu: 0.10% or less, Ti: 0.010% or less, Nb: 0.010% or less, and V: 0.010 in mass%. It is preferable to contain one or two or more selected from the following.

  Further, the present invention is secondly a method for manufacturing a motor core, comprising a punching step of punching a motor core material from an electromagnetic steel sheet as a base material, a laminating step of laminating the motor core material, and a laminated motor core. An annealing step of heating to a temperature T of 250 ° C. or higher and 550 ° C. or lower, and holding the temperature for 3 t ≦ (T + 273) × (2 + logt) ≦ 4650 for t (seconds), or an electromagnetic wave serving as a base material A punching step of punching a motor core material from a steel plate, heating the motor core material to a temperature T of 250 ° C. or higher and 550 ° C. or lower, and maintaining the temperature t (seconds) for 3350 ≦ (T + 273) × (2 + logt) ≦ 4650. A method of manufacturing a motor core, which comprises a step of annealing and a step of laminating the annealed motor core material.

  In the motor core manufacturing method of the present invention, it is preferable that the punching clearance in the punching step is 3% or more and 15% or less of the plate thickness.

According to the present invention, it is possible to provide a rotor core excellent in fatigue strength, a stator core excellent in magnetic characteristics, and a method for manufacturing the same from the same material steel sheet by punching.
Therefore, according to the present invention, it is possible to provide a motor core suitable for use in a motor core of a high-output / high-speed rotation motor such as an HEV drive motor. It is possible to reduce the cost, and it is very effective in industry.

It is a graph which shows the influence which the ratio of the end surface hardness of a motor core and base material hardness has on a fatigue limit. It is a graph which shows the influence which the tensile residual stress of the end surface of a motor core has on a fatigue limit. 3 is a graph showing the influence of the annealing temperature T (° C.) and the holding time t (seconds) after punching on the characteristics of the motor core, wherein (a) the influence on the ratio of the end surface hardness to the base metal hardness, and ( b) Shows the effect on the tensile residual stress of the end face.

First, the motor core of the present invention will be described.
1. The tensile residual stress of the punched end face is 250 MPa or less. The tensile residual stress of the punched end face promotes the generation of fatigue cracks from the punched end face, resulting in a decrease in fatigue strength. In particular, in the rotor core, repeated stress due to centrifugal force acts in the plate surface direction, so it is necessary to reduce the tensile residual stress on the punched end surface. In order to sufficiently suppress the occurrence of fatigue cracks, the tensile residual stress of the punched end face must be 250 MPa or less. The tensile residual stress of the punched end face is preferably 200 MPa or less, more preferably 150 MPa or less. On the other hand, since the compressive residual stress does not contribute to the occurrence of fatigue cracks, it is not necessary to determine the lower limit of the tensile residual stress of the punched end face, but the tensile residual stress of the punched end face is usually -100 MPa or more (compressive residual stress is 100 MPa or less). is there. Here, the above-mentioned tensile residual stress is a residual stress in a direction perpendicular to the plate surface normal direction and parallel to the punched end face at the half thickness of the punched end face.

2. The hardness of the punched end surface is 1.10 times or more the hardness of the base material. The occurrence of fatigue cracks is generally suppressed as the strength of the steel sheet increases. On the other hand, in the case of punching fatigue, since the punching end face is inevitably roughened, fatigue cracks mostly occur from the punching end face. That is, in order to improve the punching fatigue characteristics, it is not necessary to increase the strength of the entire steel sheet, but it is important to increase the strength of the punched end portion that is the starting point of fatigue crack initiation. In order to sufficiently suppress the occurrence of fatigue cracks from the end face, the punched end face must have a hardness of 1.10 times or more the base metal hardness. It is preferably 1.2 times or more. On the other hand, if the hardness of the punched end face is too hard compared to the base metal, it may promote the occurrence of cracks due to the difference in hardness inside the steel sheet. It is preferably not more than 3 times the length. Here, the hardness of the punched end face is the plate thickness 1/2 and the micro Vickers hardness at a position 50 μm away from the end face, and the base material hardness is the plate thickness 1/2 and the plate thickness from the end face. The micro Vickers hardness is at a position three times or more away.

3. Component Composition of Steel Sheet Next, a suitable component composition of the electromagnetic steel sheet used in the motor core of the present invention will be described. The unit of the content of each element in the component composition is "mass%", but hereinafter, unless otherwise specified, simply indicated by "%".

C: 0.0050% or less C is a harmful element that forms carbides during use of the motor to cause magnetic aging and deteriorates iron loss characteristics. In order to avoid magnetic aging, C contained in the material is preferably 0.0050% or less. More preferably, it is 0.0040% or less. The lower limit of C is not particularly specified, but it is preferable to set it to about 0.0001% because a steel sheet in which C is excessively reduced is very expensive.

Si: 2.0% or more and 7.0% or less Si has the effect of increasing the specific resistance of steel and reducing iron loss, and has the effect of increasing the strength of steel by solid solution strengthening. Further, since the work hardening coefficient of steel increases by the addition of Si, it also has the effect of promoting the increase in the hardness of the punched end. In order to surely obtain such an effect, the amount of Si added is preferably 2.0% or more. On the other hand, if it exceeds 7.0%, the toughness deteriorates and cracks are likely to occur, so the upper limit is preferably made 7.0%. Therefore, Si is preferably contained in the range of 2.0% or more and 7.0% or less. The range is more preferably 3.0% or more and 7.0% or less, and further preferably 3.7% or more and 7.0% or less.

Mn: 0.05% or more and 3.0% or less Mn, like Si, is an element useful for increasing the specific resistance and strength of steel, so it is preferable to contain 0.05% or more. On the other hand, if the content exceeds 3.0%, the toughness decreases and cracks are likely to occur during processing, so the upper limit is preferably set to 3.0%. Therefore, Mn is preferably contained in the range of 0.05% or more and 3.0% or less. The range is more preferably 0.1% or more and 2.0% or less.

Al: 3.0% or less Al, like Si, is a useful element that has the effect of increasing the specific resistance of steel and reducing iron loss. However, if it exceeds 3.0%, the toughness deteriorates and cracks are likely to occur during processing, so the upper limit is preferably made 3.0%. It is more preferably 2.0% or less.
When the Al content is in the range of more than 0.01% and less than 0.1%, fine AlN precipitates and iron loss is likely to increase. Therefore, Al is 0.01% or less or 0.1% or more. The range is more preferable. In particular, when Al is reduced, the texture is improved and the magnetic flux density is improved. Therefore, when the magnetic flux density is important, Al: 0.01% or less is preferable. It is more preferably 0.003% or less.

P: 0.2% or less P is a useful element used for adjusting the strength (hardness) of steel. However, if it exceeds 0.2%, the toughness deteriorates and cracks are likely to occur during processing, so the upper limit is preferably made 0.2%. The lower limit is not particularly specified, but a steel plate having an excessively reduced P is very expensive, so it is more preferably set to about 0.001%. More preferably, it is in the range of 0.005% or more and 0.1% or less.

S: 0.005% or less S is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, if it exceeds 0.005%, the adverse effect becomes remarkable, so 0.005% or less is preferable. It is more preferably 0.003% or less.

N: 0.0050% or less N is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, if it exceeds 0.0050%, the adverse effect becomes remarkable, so 0.0050% or less is preferable. It is more preferably 0.003% or less.

In the electromagnetic steel sheet used in the present invention, the balance other than the above components is Fe and inevitable impurities, but in addition to the above component composition, it is further selected from Cu, Ti, Nb and V depending on the required characteristics. One kind or two or more kinds can be contained in the following range.
Cu: 0.10% or less Cu is finely precipitated in the steel due to aging in the above-mentioned annealing step or the like, and contributes to the strength increase of the steel sheet by precipitation strengthening, so it is preferable to contain 0.005% or more. On the other hand, if added in excess of 0.10%, the precipitated Cu may prevent relaxation of the tensile residual stress in the annealing step, may become a starting point of fatigue cracking, and may deteriorate fatigue strength. Therefore, when Cu is added, its content is preferably 0.005% or more and 0.10% or less, and more preferably 0.005% or more and 0.05% or less.

Ti: 0.010% or less Ti is finely precipitated in the steel as a carbide due to aging in the above-mentioned annealing step or the like and contributes to the strength increase of the steel sheet by precipitation strengthening, so it is preferable to contain 0.0005% or more. .. On the other hand, if added in excess of 0.010%, the precipitated Ti carbide may interfere with relaxation of tensile residual stress in the annealing step, may become a starting point of fatigue cracking, and may deteriorate fatigue strength. Therefore, when Ti is added, the content is preferably 0.0005% or more and 0.010% or less, and more preferably 0.0005% or more and 0.005% or less.

Nb: 0.010% or less Nb is finely precipitated in the steel as a carbide due to aging in the above-mentioned annealing step or the like and contributes to the strength increase of the steel sheet by precipitation strengthening, so it is preferable to contain 0.0005% or more. .. On the other hand, if added in excess of 0.010%, the precipitated Nb carbide may prevent relaxation of tensile residual stress in the annealing step, may become a starting point of fatigue cracking, and may deteriorate fatigue strength. Therefore, when Nb is added, the content is preferably 0.0005% or more and 0.010% or less, and more preferably 0.0005% or more and 0.005% or less.

V: 0.010% or less V is finely precipitated in the steel as a carbide due to aging in the above-mentioned annealing step or the like, and contributes to the strength increase of the steel sheet by precipitation strengthening, so V is preferably contained at 0.0005% or more. .. On the other hand, if it is added excessively in excess of 0.010%, the precipitated V carbides may prevent relaxation of the tensile residual stress in the annealing step, may become the starting point of fatigue cracks, and may deteriorate fatigue strength. Therefore, the content when V is added is preferably 0.0005% or more and 0.010% or less, and more preferably 0.0005% or more and 0.005% or less.

  Next, a preferred embodiment of the motor core manufacturing method of the present invention (hereinafter, also simply referred to as the “manufacturing method of the present invention”) will be described. Generally, punching for collecting a motor core material from a magnetic steel sheet by punching It is a method of obtaining a motor core having excellent fatigue characteristics by a process, a laminating process of laminating a motor core material, and an annealing process of heat-treating the motor core material or the motor core.

<Electromagnetic steel sheet>
According to the present invention, no matter what kind of electromagnetic steel plate is used as the material of the motor core, it is possible to obtain a motor core having excellent fatigue strength as compared with conventional products. Therefore, the magnetic steel sheet used for manufacturing the motor core of the present invention is not particularly limited, but from the viewpoint of enhancing the performance of the motor core, it is desirable to use a magnetic steel sheet having as high magnetic flux density, low iron loss, and high strength as possible.

<Punching process>
The punching step is a step of punching the motor core material (rotor core material and stator core material) forming the rotor core and the stator core from the electromagnetic steel sheet.
The punching step is not particularly limited as long as a motor core material having a predetermined size can be obtained from the electromagnetic steel sheet, and a conventional punching step can be used.
Further, by combining punching clearances described below, it is possible to obtain a motor core having more excellent fatigue characteristics.

Punching clearance: 3% or more and 15% or less of the plate thickness If the punching clearance when punching the motor core material from the base material is less than 3% of the plate thickness, roughening such as secondary sheared surface and cracks is likely to occur on the punching end surface. The punching clearance is preferably 3% or more of the plate thickness because it may be the starting point of fatigue cracks. On the other hand, if the punching clearance exceeds 15% of the plate thickness, the work hardening of the punching end face due to the punching process is likely to be suppressed, the hardness of the punching end face may be lowered, and the fatigue strength may be lowered. The punching clearance is preferably 15% or less of the plate thickness. Therefore, the punching clearance is preferably 3% or more and 15% or less of the plate thickness. More preferably, it is 5% or more and 12% or less of the plate thickness.

<Lamination process>
The laminating step is a step of laminating motor core materials to manufacture a motor core.
The laminating step is not particularly limited as long as the motor core material can be laminated within a predetermined size range, and a usual laminating step can be used.

<Annealing process>
The annealing step is a step of annealing the motor core material or the motor core in which the motor core material is laminated. More specifically, in the annealing step, the motor core material or the motor core is heated to a temperature T (° C.) of 250 ° C. or higher and 550 ° C. or lower, and the time t (seconds) that holds 3350 ≦ (T + 273) × (2 + logt) ≦ 4650 is maintained. And cooling.

Annealing temperature T (° C.): 250 ° C. or higher and 550 ° C. or lower If the annealing temperature T is lower than 250 ° C., the residual tensile stress of the punched end face due to annealing is not sufficiently released, and the tensile residual stress of the punched end face of the manufactured motor core Does not fall within the desired range. On the other hand, when the annealing temperature T exceeds 550 ° C., the steel sheet structure of the punched end surface, which has been strengthened by punching, is excessively recovered or recrystallized, so that the strength is reduced and the hardness of the punched end surface of the manufactured motor core is desired. It does not fall within the range. Therefore, the annealing temperature T is limited to the range of 250 ° C or higher and 550 ° C or lower. It is preferably in the range of 300 ° C or higher and 500 ° C or lower.

Time t (second) held at annealing temperature T (° C.): 3350 ≦ (T + 273) × (2 + logt) ≦ 4650
If the time t held at the annealing temperature T is too short, the tensile residual stress due to annealing is not sufficiently released, and the tensile residual stress of the punched end surface of the manufactured motor core does not fall within the desired range. On the other hand, when the time t held at the annealing temperature T is excessively long, the steel sheet structure of the punched end face, which has been strengthened by punching, is excessively recovered, so that the strength of the punched end face is reduced and the manufactured motor core The hardness of the punched end face does not fall within the desired range. Therefore, the time t held at the annealing temperature T needs to be controlled within an appropriate range.
Further, the behavior of releasing the tensile residual stress and reducing the strength of the punched end face depends on the annealing temperature T, and thus the holding time t changes depending on the annealing temperature T.
However, according to the investigation by the inventors, the time t (second) held at the annealing temperature T (° C.) is calculated by the following formula;
3350 ≦ (T + 273) × (2 + logt) ≦ 4650
It has been found that the tensile residual stress and hardness of the punched end surface of the manufactured motor core fall within the desired range if the above condition is satisfied. That is, as shown in FIG. 3A, when the value of (T + 273) × (2 + logt) exceeds 4650, the punching end face hardness becomes less than 1.10 of the hardness of the base material. On the other hand, as shown in FIG. 3B, when the value of (T + 273) × (2 + logt) is less than 3350, the tensile residual stress exceeds 250 MPa. Therefore, in the present invention, the time t held at the annealing temperature T is limited to a range satisfying 3350 ≦ (T + 273) × (2 + logt) ≦ 4650. The preferable range of the time t held at the annealing temperature T is a range satisfying 3650 ≦ (T + 273) × (2 + logt) ≦ 4250.

  The motor core obtained as described above has excellent fatigue strength, but when a high strength steel plate is used as the motor core material, more excellent fatigue strength can be obtained. In this case, when it is feared that the iron loss of the stator core is deteriorated by using the high strength steel plate, the stress relief annealing may be performed only for the stator core to improve the iron loss.

<Manufacture of motor core>
A stator core material and a rotor core material were sampled from a magnetic steel sheet having a plate thickness and a component composition shown in the following Table 1 by a commonly known punching process and laminated to manufacture a stator core and a rotor core from the same material. Further, the rotor core was heat-treated under the conditions shown in Table 2 below (annealing step).

<Evaluation>
A test piece was sampled from the obtained rotor core, and residual stress measurement and hardness measurement were performed. For the fatigue strength measurement, the same electromagnetic steel plate as the rotor core was used, punched under the same conditions, and heat-treated under the same conditions to prepare tensile fatigue test pieces. Furthermore, for magnetic property evaluation, a test piece for magnetic measurement was prepared from a steel sheet obtained by heat-treating the same electromagnetic steel sheet as the rotor core under the same conditions. Using these test pieces, magnetic property evaluation and tensile fatigue test were performed. The test method was as follows.

(Measurement of residual stress)
A test piece for residual stress measurement is cut out from the rotor core bridge part of the rotor core, and the tensile residual stress of the punched end face, specifically, perpendicular to the plate surface normal direction at the half thickness of the punched end face and the punched end face The tensile residual stress in the parallel direction was measured by the X-ray method (2θ · sin ² ψ method). The incident X-ray was a CoKα ray and the collimator diameter was 300 μm.

(Hardness measurement)
The rotor core was cut in the direction perpendicular to the punched end face from the rotor core bridge portion of the rotor core, and the hardness of the punched end face was measured by a micro-Vickers test according to JIS Z2244: 2009. However, the diagonal length of the depression was sometimes less than 0.020 mm, but it was used for hardness conversion as it was. The measurement position was 1/2 the plate thickness and 50 μm away from the punched end face, and the measurement load was 0.025 kgf (0.245 N). In the above hardness measurement, in order to reduce the variation in measurement, after the first hardness measurement, 3 times or more of the diagonal length of the indentation is removed by polishing, and the measurement is performed again at the same position. The measurement was repeated 5 times, and the average value was used.
As for the hardness of the base metal, the hardness of the sample taken from an arbitrary position of the rotor core was measured at a plate thickness of 1/2 and at a position separated from the punched end face by 3 times or more of the plate thickness. The load was 0.025 kgf (0. 245 N) was measured at 5 points, and the average value was used.

(Tensile test)
After subjecting the same magnetic steel sheet from which the rotor core material was sampled to heat treatment under the same conditions as the rotor core, a JIS No. 5 tensile test piece with the rolling direction as the tensile direction was sampled and subjected to a tensile test in accordance with JIS Z2241: 2011. The tensile strength (TS) was measured.

(Tensile fatigue test)
From the same magnetic steel sheet from which the above rotor core material was sampled, a tensile fatigue test piece having the rolling direction as the longitudinal direction was punched (the same shape as No. 1 test piece according to JIS Z2275: 1978, b: 15 mm, R: 100 mm). Was sampled, heat-treated under the same conditions as the rotor core, and then subjected to a fatigue test. The fatigue test, tensile - tensile (pulsating), stress ratio (= Min stress / maximum stress): 0.1 and Frequency: conducted under the condition of 20 Hz, the maximum stress that does not cause a fatigue fracture at repeated several 10 ⁷ times The fatigue limit was set. In the evaluation of the test results, those having a fatigue limit satisfying the conditions of the following formula were evaluated as having excellent fatigue properties (◯), and those not satisfying the fatigue limit were evaluated as having poor fatigue properties (x).
Fatigue limit ≥ 0.4 x tensile strength (TS) + 70 (MPa)

(Magnetic property measurement)
From the same magnetic steel sheet from which the rotor core material was sampled, a test piece for magnetic measurement having a width direction of 30 mm and a length of 180 mm, where the length direction was the rolling direction and the direction orthogonal to the rolling direction, was sampled, and after heat treatment under the same conditions as the rotor core, According to JIS C2550-1: 2011, the iron loss W _10/400 was measured by the Epstein method.

  The results of the above evaluation tests are also shown in Table 2. Further, in the case where the tensile residual stress of the punched end face is 250 MPa or less, the influence of the hardness of the punched end face on the fatigue limit is shown in FIG. 1, and the influence of the ratio of the end face hardness to the matrix phase hardness on the fatigue limit of 1. FIG. 2 shows the effect of the tensile residual stress for the samples having a hardness of 10 or more and 2.0 or less. FIG. 3 shows the effect of the annealing time t (seconds) on the characteristics of the motor core when the annealing temperature T is in the range of 250 to 550 ° C. In FIGS. 3A and 3B, the horizontal axis represents (T + 273) × (2 + logt). In FIG. 3 (a), the vertical axis represents the ratio of the end face hardness to the base material hardness, and those with a hardness ratio of 1.10 or more are plotted with ◯, and those with a hardness ratio of less than 1.10 are plotted with x. In FIG. 3B, the vertical axis represents the tensile residual stress, and those having a tensile residual stress of 250 MPa or less are plotted with ◯, and those with a tensile residual stress exceeding 250 MPa are plotted with x.

  From the results of Table 1, Table 2, FIG. 1 and FIG. 2, all the motor cores of the invention examples not only have excellent iron loss characteristics, but also excellent fatigue characteristics of fatigue limit ≧ 0.4 × TS + 70 (MPa). You can see that it has.

  Since the technology of the present invention is effective in improving the fatigue strength of the motor core, it is not limited to the case where the rotor core material and the stator core material are simultaneously extracted from the same material steel sheet, and the rotor core material and the stator core material are obtained from different material steel sheets. It can also be applied when collecting separately.

Claims (6)

A motor core formed by laminating electromagnetic steel sheets, wherein the punching end face of the motor core has a tensile residual stress of 250 MPa or less, and the punching end face has a hardness of 1.10 times or more the base metal hardness. Motor core. The magnetic steel sheet, in mass%, is C: 0.0050% or less, Si: 2.0% or more, 7.0% or less, Mn: 0.05% or more, 3.0% or less, Al: 3.0%. Hereinafter, P: 0.2% or less, S: 0.005% or less and N: 0.0050% or less, and the balance has a component composition of Fe and inevitable impurities. Motor core described. The electromagnetic steel sheet is, in mass%, one or two selected from Cu: 0.10% or less, Ti: 0.010% or less, Nb: 0.010% or less, and V: 0.010% or less. The motor core according to claim 2, containing the above. It is a manufacturing method of the motor core according to any one of claims 1 to 3,
A punching process of punching a motor core material from a magnetic steel sheet as a base material,
A laminating step of laminating the motor core material,
An annealing process in which the laminated motor cores are heated to a temperature T of 250 ° C. or higher and 550 ° C. or lower and the temperature is maintained for 3 t ≦ (T + 273) × (2 + logt) ≦ 4650 for t (seconds). Motor core manufacturing method. It is a manufacturing method of the motor core according to any one of claims 1 to 3,
A punching process of punching a motor core material from a magnetic steel sheet as a base material,
An annealing step of heating the motor core material to a temperature T of 250 ° C. or higher and 550 ° C. or lower and maintaining the temperature for 3 t ≦ (T + 273) × (2 + logt) ≦ 4650 for a time t (seconds);
A method of manufacturing a motor core, comprising a step of laminating annealed motor core materials. The method of manufacturing a motor core according to claim 4 or 5, wherein the punching clearance in the punching step is 3% or more and 15% or less of the plate thickness.

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