JP2011246810A - Nonoriented magnetic steel sheet and motor core using the same - Google Patents

Abstract

The present invention provides a non-oriented electrical steel sheet with small iron loss deterioration even under a compressive stress to which a high compressive stress of 10 MPa or more is applied.
SOLUTION: In mass%, C: 0.005% or less, Si: 2.0 to 6.0%, Al: 3.0% or less, P: 0.1% or less, Mn: 0.05 to 4.0%, S: 0.005% or less, N: 0.005% Hereinafter, in the non-oriented electrical steel sheet containing O: 0.005% or less and Zr: 0.002% or less and comprising the balance Fe and inevitable impurities, the average crystal grain size is 30 to 120 μm, and it exists in a region within 10 μm from the surface. Diameter: The number density of inclusions of 0.1 to 1 μm is 3 × 10 ⁵ pieces / mm ² or less.
[Selection] Figure 1

Description

  The present invention relates to a non-oriented electrical steel sheet that effectively suppresses deterioration of iron loss due to compressive stress applied to the non-oriented electrical steel sheet without causing a decrease in magnetic flux density, and a motor core using the same. Is.

The compressor motor of a home air conditioner is operated in a variable speed region with a frequency of about 50 to 300 Hz, and in recent years, it is also operated in a state where a carrier frequency of several kHz is superimposed by PWM control or the like.
Recently, a drive motor for a hybrid electric vehicle and a motor for a generator, which are rapidly spreading, are often used at a frequency of several kHz from the viewpoint of high output and miniaturization. As a non-oriented electrical steel sheet for the core material of these motors, an electrical steel sheet with low iron loss at high frequency is desired, and therefore, Si and Al as steel components are about 3 to 4% by mass in total. A high grade electrical steel sheet is used.

  By the way, in the compressor motor, shrink fitting is performed for fastening the core. For this reason, the motor core is always subjected to a compressive stress of about 30 to 100 MPa. In addition, a resin mold or the like is used for the drive motor of the hybrid EV, but a compressive stress is also applied to the motor core. Under the above-described compressive stress, the magnetic properties of the electrical steel sheet are greatly deteriorated. Therefore, there is a demand for an electrical steel sheet with little deterioration of magnetic properties such as iron loss deterioration under the compressive stress.

  Here, as what suppressed the iron loss deterioration of the electromagnetic steel plate under a compressive stress, for example, in patent document 1, Si: 0.1-4.0 mass% and Al: 0.1-4.0 mass% are contained in a steel plate, Furthermore, A non-oriented electrical steel sheet is disclosed in which the X-ray random intensity ratio of the crystal {111} plane in the steel sheet is set to 2.5 or more and 10.0 or less to reduce iron loss deterioration under compressive stress.

  However, in the non-oriented electrical steel sheet described above, the {111} plane texture which is undesirable for the magnetic properties is also developed, so that the iron loss deterioration under compressive stress is reduced, but before the compressive stress is applied. There was a problem that the iron loss of the steel sheet itself was high.

JP 2008-189976 A

The inventors have intensively studied to solve the above-mentioned problems, and by restricting the components of the steel sheet and reducing the crystal grain size of the steel sheet, the iron loss deterioration of the non-oriented electrical steel sheet under compressive stress can be suppressed. It turns out that there is a certain effect.
In addition, as a result of further investigation, by reducing the fine inclusions in the vicinity of the surface of the steel sheet to a predetermined amount or less, it is effective in suppressing iron loss deterioration under compressive stress, especially in high frequency region. I found out that there is.

  The present invention has been made on the basis of the above knowledge, iron loss deterioration without causing a decrease in magnetic flux density even under a compressive stress in which a high compressive stress of 10 MPa or more is applied to a non-oriented electrical steel sheet. An object of the present invention is to provide a non-oriented electrical steel sheet and a motor core using the same.

That is, the gist configuration of the present invention is as follows.
1. By mass%, C: 0.005% or less, Si: 2.0 to 6.0%, Al: 3.0% or less, P: 0.1% or less, Mn: 0.05 to 4.0%, S: 0.005% or less, N: 0.005% or less, O: In non-oriented electrical steel sheets used for motor cores containing 0.005% or less and Zr: 0.002% or less, the balance being Fe and inevitable impurities, and applying a compressive stress of 10 MPa or more, the average crystal of the non-oriented electrical steel sheet The grain size is 30 to 120 μm, and the inclusion density of the diameter: 0.1 to 1 μm existing in the region within 10 μm from the surface of the non-oriented electrical steel sheet is 3 × 10 ⁵ pieces / mm ² or less. Non-oriented electrical steel sheet.

  2. 2. The non-oriented electrical steel sheet according to 1 above, wherein the non-oriented electrical steel sheet further contains Cr: 0.05 to 6.0% by mass.

  3. 3. Said 1 or 2 characterized by the said non-oriented electrical steel sheet further containing 1 type or 2 types selected from Sn: 0.002-0.10% and Sb: 0.001-0.05% by the mass%. Non-oriented electrical steel sheet.

4). 4. The non-oriented electrical steel sheet according to any one of 1 to 3, wherein the non-oriented electrical steel sheet has a specific resistance of 64 × 10 ^{−8 to} 85 × 10 ⁻⁸ Ωm.

  5. 5. A motor core comprising a laminate of electromagnetic steel sheets according to any one of 1 to 4, wherein a compressive stress of 10 MPa or more is applied in an inner direction from the outer peripheral surface of the laminate.

According to the non-oriented electrical steel sheet of the present invention and the motor core using the non-oriented electrical steel sheet, the iron loss W _{10 / 3k} caused by the compressive stress applied to the non-oriented electrical steel sheet without causing a decrease in the magnetic flux density B ₅₀ is _achieved . Degradation can be effectively suppressed, and as a result, a small-sized and high-output motor can be obtained.

It is the graph which showed the relationship between the crystal grain size of a steel plate, and the iron loss _{W10 / 3k} . It is the graph which showed the relationship between the number density of inclusions in the area | region within 10 micrometers from a steel plate surface, and the iron loss _{W10 / 3k} under a compressive stress. It is explanatory drawing of the compressive stress provided to a motor core.

Hereinafter, the present invention will be specifically described.
In motors for electric vehicle motors and hybrid electric vehicles, the motor core is shrink-fitted or press-fitted into the housing in order to fix the motor core. The compressive stress imparted to the motor core by shrink fitting or press fitting is said to be about 30 to 150 MPa, and the electrical steel sheet with less iron loss deterioration under such compressive stress is desired as described above. .

  The inventors investigated the fluctuation behavior of the iron loss characteristics under such a compressive stress and found that not only the hysteresis loss but also the eddy current loss increased due to the compressive stress.

Here, hybrid EV motors and electric vehicle motors are not only driven in the high frequency range, but also are controlled by inverters, and because harmonics of several kHz are added, eddy current loss degradation can also be suppressed. is necessary.
Therefore, the cause of the deterioration of the eddy current loss was investigated, and it was found that when compressive stress was applied to the motor core, a phenomenon in which the magnetization vector was directed in the plate surface direction of the steel sheet in order to relieve the compressive stress. In addition, when the steel plate is magnetized in this state, it has been found that eddy current flows in the surface of the steel plate, resulting in deterioration of eddy current loss.

  Next, a method for reducing the direction of the magnetization vector in the direction of the plate surface of the steel plate was studied. As a result, it was found that an increase in eddy current loss during application of compressive stress can be suppressed by reducing the crystal grain size in the steel sheet.

Hereinafter, the test contents that led to limiting the crystal grain size and the reasons for limitation will be described. In the following, “%” in relation to steel plate components means mass% unless otherwise specified.
First, C: 0.0012%, Si: 3.1%, Mn: 1.5%, Al: 1.2%, P: 0.01%, S: 0.0007% and N: 0.0020% to investigate the effect of crystal grain size on magnetic properties The steel which consists of remainder and Fe which consists of inevitable impurities was melt | dissolved in the laboratory, and it hot-rolled. Subsequently, the hot-rolled sheet was pickled, subjected to hot-rolled sheet annealing at 1000 ° C. for 30 s in a 100% N ₂ atmosphere, cold-rolled to a thickness of 0.30 mm, and then 30% H ₂ -70. % N at ₂ atmosphere, temperature range of from 850 to 1,050 ° C., was significantly changing the crystal grain size by performing the 10s of finish annealing.

From this material, two types of single-sheet test pieces with a length of 180 mm and a width of 30 mm were cut out so that the rolling direction and the direction perpendicular to the rolling direction were the longitudinal directions, respectively, and a compressive force of 50 MPa was applied to each longitudinal direction. The iron loss (W _{10 / 3k} ) was measured.
In FIG. 1, the result of having investigated about the relationship between the crystal grain diameter of a steel plate and _{W10 / 3k} is shown. In addition, the value in a figure has shown the average value of the measured value of a rolling direction and a rolling orthogonal direction. The crystal grain size of the steel sheet was determined by polishing the steel sheet from the surface by 50 μm and measuring it according to JIS G 0551. Here, during the test, the iron loss at a frequency of 3 kHz was evaluated in the case of an electric vehicle motor or a hybrid electric vehicle motor with a fundamental wave having a frequency of about 400 to 1 kHz and a harmonic of a frequency of 3 to 7 kHz. This is because since the waves are superimposed, the correlation between iron loss and motor efficiency at a frequency of about 3 kHz is strong.

  As shown in FIG. 1, when there is no compressive stress, the iron grain loss is less dependent on the crystal grain size, whereas when compressive stress is applied, the steel grain has a crystal grain size of 30 to 120 μm. It was found that the loss was reduced. Here, it has been found that the reason why the iron loss of the steel sheet increases on the coarse grain side where the crystal grain size exceeds 120 μm is that the eddy current loss significantly increases.

The cause of the increase in the eddy current loss is considered as follows.
In a steel plate with a large crystal grain having positive magnetostriction like a normal high-grade electromagnetic steel plate, the magnetization vector of the steel plate is directed in the plate surface direction of the steel plate due to the application of compressive stress. Therefore, an eddy current flows in the steel plate surface due to the magnetization of the steel plate, and the eddy current loss greatly increases as compared with the case of no stress.

On the other hand, when the crystal grain size of the electrical steel sheet is reduced, the change of the magnetization vector is suppressed by the adjacent crystal, so that the magnetization vector directed in the plate surface direction is small, and therefore in the plate surface. It is thought that the eddy current has decreased.
On the other hand, in a small particle size region having a particle size of less than 30 μm, the hysteresis loss is increased under compressive stress, so that the iron loss is deteriorated.
From the above, in the present invention, the crystal grain size of the non-oriented electrical steel sheet is limited to the range of 30 to 120 μm. Preferably it is 40-90 micrometers.

As described above, it was found that iron loss deterioration of the steel sheet is suppressed by setting the crystal grain size of the steel sheet to a predetermined size. However, in some steel sheets, iron loss deterioration of the steel sheet may not necessarily be suppressed. there were.
When this cause was examined, under the compressive stress, the magnetization vector is magnetized in the state of facing the steel plate surface, and therefore, if there are precipitates, such as oxides, that hinder the domain wall movement near the surface of the steel plate, It was thought that the iron loss could increase due to the significant inhibition of movement.

Therefore, in order to investigate the influence of precipitates on the steel sheet, C: 0.0012%, Si: 3.1%, Mn: 1.0%, Al: 1.4%, P: 0.01%, S: 0.0007% and N: 0.0020% are contained. The steel consisting of the remaining Fe and inevitable impurities was melted in the laboratory, and the amount of inclusions in the steel was changed by variously changing the deoxidation time, and hot rolling was performed as an ingot. Subsequently, the hot-rolled sheet was pickled by changing the pickling time in the range of 10 to 100 s, and then subjected to hot-rolled sheet annealing at 1000 ° C. for 30 s in a 100% N ₂ atmosphere until the sheet thickness: 0.30 mm Cold rolling was performed, followed by finish annealing at 950 ° C. for 10 s in a 30% H ₂ -70% N ₂ atmosphere.
Here, when the Si content is 2.0% or more, ridging occurs on the surface of the product unless hot-rolled sheet annealing is performed. On the other hand, the scale layer of the steel sheet surface layer acts as a kind of catalyst to promote internal oxidation and nitriding during hot-rolled sheet annealing, so that the amount of inclusions in the steel sheet in the final product varies depending on the surface condition after hot rolling. Became clear. Therefore, the effect of changing the pickling time after hot rolling was investigated.

FIG. 2 shows the relationship between the number of inclusions in the region within 10 μm from the steel sheet surface and the iron loss under compressive stress.
FIG. 2 shows that in order to reduce the iron loss under compressive stress, the inclusion number density in the region within 10 μm from the steel plate surface needs to be 3 × 10 ⁵ pieces / mm ² or less.
Here, the iron loss measurement under the compressive stress was performed by applying a compressive stress of 50 MPa in the longitudinal direction of the sample as in FIG. For the observation of inclusions, the energy dispersive X-ray fluorescence spectrometer (EDX) is used to identify whether the inclusions are oxides, nitrides or sulfides, and using a scanning electron microscope (SEM). The area near the surface was observed at a magnification of 5000, and the number (number density) of inclusions per unit area having a diameter corresponding to a circle of 0.1 to 1 μm was determined. The inclusion number density was measured by embedding a steel plate in a resin mold, polishing the cross section, and observing inclusions in the vicinity of the surface layer of the steel plate.
Further, the inclusions of the present invention may be Al ₂ O ₃ , SiO ₂ , AlN, MnS and the like.

  The inclusions with a diameter of 0.1 μm to 1 μm were targeted because it is difficult to observe with SEM below 0.1 μm and the influence on the magnetic properties is small. On the other hand, when the thickness exceeds 1 μm, the influence of the magnetic field on the domain wall movement is small.

  Furthermore, the investigation of the inclusion number density in the region within 10 μm from the steel sheet surface (hereinafter also simply referred to as the surface layer part) was performed under the compressive stress to the magnetic properties of the inclusion number density of the steel sheet surface layer part. This is because the influence is great, and oxides, nitrides and the like generated during hot-rolled sheet annealing and finish annealing are mainly generated in the surface layer portion.

Further, the number density of inclusions in the entire steel plate was measured in a steel plate in which many oxides generated during casting were observed in a region of about 70 μm from the surface. That is, for the cross section of the steel sheet, the depth from the surface to 150 μm was 4 × 10 ⁵ pieces / mm ² , while the surface layer portion was 2 × 10 ⁵ pieces / mm ² . Although the test which gives a compressive stress was implemented with respect to this steel plate, iron loss deterioration was not recognized. This also shows that it is most important to reduce the inclusions in the surface layer.

  In the present invention, the inclusions in the surface layer portion are pickled before hot-rolled sheet annealing, and the hydrogen partial pressure during finish annealing is 20% by volume or more, more preferably 30% by volume or more, It can adjust within the predetermined range by performing pickling after annealing and adjusting the time of pickling at that time.

Next, the reason why the component composition of the steel sheet is limited to the above range in the present invention will be described.
C: 0.005% or less When C exceeds 0.005%, the iron loss increases due to magnetic aging, so the content is made 0.005% or less.

Si: 2.0-6.0%
Si is an effective element for increasing the specific resistance, but if it exceeds 6.0%, not only does the magnetic flux density decrease as the saturation magnetic flux density decreases, but rolling becomes difficult, so the upper limit was made 6.0%. On the other hand, if Si is less than 2.0%, the specific resistance decreases and the iron loss increases, so the lower limit was set to 2.0%.

Al: 3.0% or less
Al is an effective element for increasing the specific resistance of the steel sheet. However, if it exceeds 3.0%, the magnetic flux density decreases, so the upper limit was made 3.0%.

  In the present invention, the total mass ratio of Si and Al in the steel plate components is not particularly defined, but is preferably 4.1% or more from the viewpoint of preventing increase in specific resistance.

P: 0.1% or less When P exceeds 0.1%, the steel sheet becomes brittle and rolling becomes difficult.

Mn: 0.05-4.0%
Mn is required to be 0.05% or more, preferably 1.5% or more for suppressing red heat brittleness. On the other hand, if it exceeds 4.0%, the magnetic flux density decreases, so the upper limit was made 4.0%.

S: 0.005% or less S is 0.005% or less because the amount of sulfide increases and the iron loss increases when the content is large.

N: 0.005% or less N is 0.005% or less because the amount of nitride increases and the iron loss increases when the content is large.

O: 0.005% or less O contains 0.005% or less because the amount of oxide increases and the iron loss increases when the content is large.

Zr: 0.002% or less
Zr is an element having a strong nitride forming ability. When Zr is high, the amount of nitride in the surface layer portion increases and the iron loss under compressive stress increases, so the content is made 0.002% or less.

Cr: 0.05-6.0%
Cr, like Mn, is an element effective for increasing the specific resistance of a steel sheet. Therefore, when adding Cr, the lower limit is made 0.05%. On the other hand, if it exceeds 6.0%, the magnetic flux density decreases, so the upper limit is made 6.0%.

Sn: 0.002 to 0.10%
Sn is an element effective in suppressing nitriding of the steel sheet in the surface layer portion and reducing iron loss. The effect is obtained by adding 0.002% or more. On the other hand, if it exceeds 0.10%, the steel sheet becomes brittle and difficult to manufacture, so the upper limit is made 0.10%.

Sb: 0.001 to 0.05%
Sb, like Sn, is an element effective for suppressing surface nitriding of the steel sheet, and its additive effect is stronger than Sn. For this reason, the lower limit is set to 0.001%. On the other hand, if it exceeds 0.05%, the steel sheet becomes brittle and difficult to manufacture, so the upper limit is made 0.05%.

  In the present invention, Ni, Cu or the like can be further added within a range in which the magnetic characteristics are not deteriorated. When added, the preferred range is 0.03% to 5% for Ni and 0.05% to 3% for Cu.

In the present invention, the specific resistance of the steel sheet is preferably about 64 × 10 ^{−8 to} 85 × 10 ⁻⁸ Ωm. This is because when the specific resistance is less than 64 × 10 ⁻⁸ Ωm, the high-frequency iron loss increases due to the increase in eddy current loss. On the other hand, when producing a material with a specific resistance exceeding 85 × 10 ^-8 Ωm, it is necessary to add a large amount of various alloys, which not only significantly increases the cost, but also makes the material hard and brittle. This is because manufacturing becomes very difficult.

In the present invention, the manufacturing conditions for the above-mentioned specific resistance of the steel sheet to be about 64 × 10 ^{−8 to} 85 × 10 ⁻⁸ Ωm are the contents of Si, Al, Mn, Cr [Si], [Al], [ Mn] and [Cr] (%) are exemplified as [Si] + [Al] + ([Mn] + [Cr]) / 2 = 5.0 to 7.5. Follow it.

In the present invention, it is assumed that the compression stress during shrink fitting of the motor core is 10 MPa or more. This is because the motor core cannot be satisfactorily fixed to the housing when the compressive stress is less than 10 MPa. On the other hand, the upper limit of the compressive stress is not particularly defined, but as the compressive stress increases, the iron loss deterioration increases accordingly, so the upper limit is set to about 250 MPa. The pressure is preferably 20 MPa or more, more preferably 50 MPa or more.
In the present invention, the compressive stress means a force directed from the outer peripheral surface of the motor core (a laminated body of steel plates) toward the inside as shown in FIG. Moreover, in this invention, the plate | board surface direction of a steel plate means the up-down direction of Fig.3 (a). In the figure, reference numeral 1 is a back yoke portion, 2 is a ring, 3 is a teeth portion, and 4 is a shrink-fitted ring (housing).

  The present invention provides a non-oriented electrical steel sheet having low iron loss in a high frequency range, and is particularly preferably applied to a motor used at a frequency of 1 kHz or more. The frequency referred to in the present invention is also effective when the carrier frequency is 1 kHz or more in addition to the fundamental frequency.

In the present invention, the component, the crystal grain size, and the amount of inclusions in the surface layer portion may be within the above-described range of the present invention. Examples of the manufacturing process therefor include the following. The manufacturing conditions for controlling the amount of inclusions in the surface layer part and the specific resistance of the steel sheet are as described above.
Predetermined component raw materials are blown in a converter, degassed as molten steel, adjusted to have predetermined component / inclusion amounts, cast, and made into a slab. Thereafter, the slab is hot-rolled by a conventional method.
Next, hot-rolled sheet annealing for preventing ridging is performed as essential, but as described above, pickling must be performed prior to hot-rolled sheet annealing in order to suppress the formation of inclusions in the surface layer portion. Thereafter, finish annealing is performed with a predetermined plate thickness by two or more cold or warm rolling sandwiched by one cold or warm rolling or intermediate annealing.
Here, the finishing temperature and the coiling temperature at the time of hot rolling do not need to be specified in particular, and may be in accordance with ordinary methods.

  After finish annealing, perform pickling to remove inclusions on the surface layer, or to suppress inclusion formation during finish annealing, as described above, perform annealing in a hydrogen partial pressure atmosphere of 20% by volume or more. Is desirable.

  In addition, the thickness of the steel sheet in the present invention is not particularly limited, but is preferably 0.35 mm or less, more preferably 0.3 mm or less from the viewpoint of reducing high-frequency iron loss. On the other hand, the lower limit is preferably about 0.05 mm from the viewpoint of productivity.

  Furthermore, using the steel plate, a motor core to which a compressive stress of 10 MPa or more is applied in the inner direction from the outer peripheral surface of the laminate of steel plates is produced. In addition, the manufacturing method of the motor core in this invention can use a conventional method for manufacturing conditions other than using the steel plate according to this invention, and providing the said compressive stress to a steel plate.

In the vacuum melting furnace, the molten steel prepared to the component composition shown in Table 1-1 and Table 1-2 was cast into a small slab. The slab was heated at 1100 ° C. for 1 h, and then hot-rolled to a thickness of 1.6 mm. The hot rolling finishing temperature was 800 ° C. The coiling temperature was 500 ° C., and after the coiling, pickling was performed at various times shown in Table 1-1 and Table 1-2. Thereafter, in a 100% by volume N ₂ atmosphere, hot strip annealing at 1000 ° C. for 30 s was performed, and the plate thicknesses shown in Table 1-1 and Table 1-2 at a temperature of 150 ° C. in order to prevent plate breakage. Until hot rolling. After rolling, finish annealing was performed in a 30% by volume H ₂ -70% by volume N ₂ atmosphere under the conditions shown in Table 1-1 and Table 1-2. When the surface of the steel sheet after finish annealing was visually confirmed, generation of ridging was not recognized in any case. Other production conditions were in accordance with ordinary methods.

The crystal grain size of the steel plate was determined by polishing the steel plate from the surface by 50 μm and measuring it according to JIS G 0551. In addition, the number density of inclusions on the surface layer of the steel sheet is determined by observing a region within 10 μm from the surface at 5000 times using SEM and counting the number of inclusions with a circle equivalent diameter of 0.1 to 1 μm per unit area. Asked.
Furthermore, the magnetic properties were measured by cutting out two types of single-sheet test pieces having a length of 180 mm and a width of 30 mm so that the rolling direction and the direction perpendicular to the rolling direction are the longitudinal directions, respectively, while applying a compressive force in the longitudinal direction. The magnetic properties (iron loss W _{10 / 3k} and magnetic flux density B ₅₀ ) of the steel sheet in the compressive force application direction were measured. The results are shown in Table 1-1 and Table 1-2. The magnetic characteristics shown in Table 1-1 and Table 1-2 are average values in the rolling direction and the direction perpendicular to the rolling direction.

  In addition, in order to confirm the magnetic characteristics of the motor core, a 12-slot stator core was manufactured by punching using the non-oriented electrical steel sheets having the components and thicknesses shown in Table 1-1 and Table 1-2. Here, the outer diameter of the stator was 100 mm, the back yoke width was 20 mm, the stacking thickness was 25 mm, and the shrinkage of the motor core was 0 to 100 μm. Further, the stress in the circumferential direction at the center of the back yoke was measured using a strain gauge. Furthermore, the iron loss in the circumferential direction of the motor core was measured by winding an excitation coil and a pickup coil around the back yoke portion. At that time, the magnetic flux density was 1 T, and the frequency was 3 kHz. The results are shown in Table 1-1 and Table 1-2.

According to the table, when the component, crystal grain size, and inclusion number density in the surface layer are within the scope of the present invention, the magnetic properties under compressive stress, that is, iron loss under good magnetic flux density, respectively. It can be seen that the degradation of is suppressed. The content of Al is No. 28 out of the upper limit of the range of the present invention, the content of Mn is out of the upper limit of the range of the present invention, and the content of Si and No. 32 of the present invention. No. 47 out of the lower limit of the range had a low iron loss value but was inferior in magnetic flux density.
Further, No. 23 whose specific resistance is out of the upper limit of the range of the present invention and No. 25 whose Si content is out of the upper limit of the range of the present invention are cracked during cold rolling. It was.

  Furthermore, from the same table, when using a steel sheet that satisfies all of the components, crystal grain size, and surface layer inclusions within the scope of the present invention, during shrink fitting, that is, from the outer peripheral surface of the laminate of steel sheets to the inner direction. It can be seen that a motor core having excellent iron loss characteristics is obtained even when compressive stress is applied.

  According to the present invention, a non-oriented electrical steel sheet having low iron loss in a high frequency region under compressive stress can be obtained. Therefore, when a motor core is manufactured using such a non-oriented electrical steel sheet, in particular, a compressor motor for an air conditioner, a hybrid EV drive motor, an EV drive motor, an FCEV drive motor, and a high-speed motor that apply a compressive force to the core material. In the high-frequency rotating machine for generators, the iron loss is reduced, contributing to energy saving of various facilities.

1 Back yoke part 2 Ring 3 Teeth part 4 Shrink fit ring (housing)

Claims (5)

By mass%, C: 0.005% or less, Si: 2.0 to 6.0%, Al: 3.0% or less, P: 0.1% or less, Mn: 0.05 to 4.0%, S: 0.005% or less, N: 0.005% or less, O: In non-oriented electrical steel sheets used for motor cores containing 0.005% or less and Zr: 0.002% or less, the balance being Fe and inevitable impurities, and applying a compressive stress of 10 MPa or more, the average crystal of the non-oriented electrical steel sheet The grain size is 30 to 120 μm, and the inclusion density of the diameter: 0.1 to 1 μm existing in the region within 10 μm from the surface of the non-oriented electrical steel sheet is 3 × 10 ⁵ pieces / mm ² or less. Non-oriented electrical steel sheet.   The non-oriented electrical steel sheet according to claim 1, wherein the non-oriented electrical steel sheet further contains Cr: 0.05 to 6.0% by mass.   The non-oriented electrical steel sheet further contains one or two kinds selected from Sn: 0.002 to 0.10% and Sb: 0.001 to 0.05% in mass%. Non-oriented electrical steel sheet. The non-oriented electrical steel sheet according to claim 1, wherein a specific resistance of the non-oriented electrical steel sheet is 64 × 10 ^{−8 to} 85 × 10 ⁻⁸ Ωm. A motor core comprising a laminate of electromagnetic steel sheets according to any one of claims 1 to 4, wherein a compressive stress of 10 MPa or more is applied in an inner direction from an outer peripheral surface of the laminate.