JP2910508B2 - Non-oriented electrical steel sheet for high frequency with excellent iron loss characteristics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency non-oriented electrical steel sheet having excellent iron loss characteristics used at a frequency of 200 Hz to 5 kHz.

2. Description of the Related Art Non-oriented electrical steel sheets are used as materials for rotors and stators of electric motors. In recent years, motors have been increasingly used in high frequency ranges as motors have become smaller and more efficient.However, when motors are used in high frequency ranges, an increase in total iron loss due to an increase in eddy current loss has become a problem. For this reason, reduction of eddy current loss is a major issue. In order to reduce the eddy current loss, it is effective to increase the Si + Al amount to increase the specific resistance of the steel sheet or to reduce the thickness of the steel sheet.

[0002]

As a steel sheet having an increased specific resistance, for example, Japanese Patent Application Laid-Open No. 2-267246 discloses that
Although Si steel sheet is disclosed, reduces the cold workability for the material when the Si content is increased becomes brittle, in addition, is represented by magnetic flux density (typically B ₅₀ at high magnetic field with decreasing saturation magnetic flux density ) Also decreases. Further, as a steel sheet having an extremely thin sheet thickness, a thin steel strip manufactured by a so-called ultra-quick solidification method is known. This thin steel strip has extremely low iron loss in a high frequency range, but has a surface property. In addition, there is a problem that the working efficiency is lowered because the number of laminations is increased in order to obtain a predetermined magnetic flux density. In addition, since the shape of a wide one becomes extremely bad, the plate width is also 20 to 3.
The limit is about 0 cm.

[0003] In addition to the specific resistance and the sheet thickness as described above, another factor that affects high-frequency iron loss is the crystal grain size of the steel sheet. Generally, it is said that the optimum particle size for high frequency applications is smaller than that for commercial frequencies.
No. 223445 discloses a high-frequency non-oriented electrical steel sheet having a crystal grain size of 5 to 60 μm for low iron loss at a frequency of 400 Hz or more. However, according to experiments by the present inventors, even with this non-oriented electrical steel sheet, sufficient reduction of iron loss in a high frequency range is not achieved. Also, this non-oriented electrical steel sheet does not optimize the distribution of nitrides and internal oxides in the sheet thickness direction as in the present invention. A similar experiment was conducted by optimizing the distribution of internal oxides. As a result, it was found that the optimum crystal grain size at 700 Hz was about 70 μm, and the optimum grain size was on the coarser side than the above proposal. It has also been found that the high-frequency iron loss in this case is further reduced as compared with the steel plate proposed above.

[0004]

As described above, the conventional high-grade electromagnetic steel sheets are designed to reduce iron loss in the high-frequency magnetization region by reducing the thickness or increasing the specific resistance of the entire steel sheet. Both aim to make it difficult for eddy currents in the steel sheet to flow. On the other hand, in high-frequency magnetization, the distribution of the eddy current density is not uniform in the thickness direction of the steel sheet due to the skin effect, and the eddy current density is high in the surface layer portion of the steel sheet and rapidly decreases inside the steel sheet. Therefore, if the specific resistance of the steel sheet is increased in the surface layer portion of the steel sheet, the eddy current can be effectively reduced without reducing the sheet thickness or increasing the specific resistance of the entire steel sheet as in the related art. The inventor pays attention to this point,
We examined means to reduce iron loss in the high-frequency magnetization region, and as a result, internal oxide in the thickness direction of the steel sheet,
It is possible to optimize the specific resistance in the thickness direction of the steel sheet by appropriately controlling the state of formation of nitride, and furthermore, if the generation state of the internal oxide and nitride in the thickness direction of the steel sheet is optimized, It has been found that the optimum crystal grain size range for reducing iron loss in the magnetized region exists on the coarse grain side. Therefore, by appropriately controlling the state of formation of internal oxides and nitrides and the crystal grain size in the thickness direction of the steel sheet, it is possible to reduce high-frequency iron loss without reducing magnetic flux density in a high magnetic field. Becomes The present invention has been made based on such knowledge, and the characteristic configuration thereof is as follows.

(1) The total amount of Si and Al is 1.7 to
4.5 wt%, C: 0.005 wt% or less, Mn: 0.
1-1 wt%, S: 0.015 wt% or less, P: 0.2
wt% or less, N other than the nitride-containing layer or internal oxide-containing layer or nitride-internal oxide-containing layer defined below: N: 0.005 wt% or less, nitride-containing layer or internal oxide-containing layer or nitride A steel sheet containing 0.005 wt% or less of O: other than the material-internal oxide-containing layer, the balance being Fe and unavoidable impurities, and having a particle diameter of 0.1 μm or more in the surface layer of the steel sheet and / or the inside. When a region where the oxide is present in an area ratio of 0.01% or more in the plane of the steel sheet is defined as a nitride-containing layer or an internal oxide-containing layer or a nitride-internal oxide-containing layer, a nitride-containing layer or An inner oxide-containing layer or a nitride-inner oxide-containing layer is formed from the surface of the steel sheet to a depth x (mm) that satisfies the following equation: 0.05t ≦ x ≦ 0.15t, where t: steel sheet thickness (mm) ) Nitride Yuso or inner oxide containing layer or nitride -
The average particle size of the nitride or / and internal oxide in the internal oxide-containing layer is 3 μm or less, and the particle size in the nitride-containing layer or internal oxide-containing layer or nitride-internal oxide-containing layer is 0.1 μm or more. The area ratio R of the nitride or / and internal oxide in the cross section of the plate thickness is 0.05 to 0.2
0%, and the nitride and internal oxide having a grain size of 0.1 μm or more existing in a region other than the nitride-containing layer, the internal oxide-containing layer, or the nitride-internal oxide-containing layer in the plate thickness cross section. The area ratio is less than 0.01%, and the average crystal grain size D (μm) of the steel sheet satisfies the following expression.
Non-oriented electrical steel sheet for high frequency use with excellent iron loss characteristics used in the frequency range of 5 Hz to 5 kHz.

(Equation 2)

(2) In the non-oriented electrical steel sheet according to (1), the thickness is 0.1 to 0.2 mm and the frequency is 20
High-frequency non-oriented electrical steel sheet with excellent iron loss characteristics used at 0 Hz or more and 5 kHz or less.

[0007]

The details of the present invention will be described below, together with the reasons for its limitation. First, the composition of the steel sheet will be described. Si
And Al are effective elements for increasing the specific resistance of the steel sheet, and the contribution of these elements to the specific resistance is almost the same. Therefore, regarding Si and Al, Si + Al
The amount is limited by the amount. The amount of Si + Al is 1.7wt
%, The iron loss increases because the specific resistance of the steel sheet is small. On the other hand, when the Si + Al content exceeds 4.5 wt%, the steel sheet becomes brittle, so that cold rolling becomes difficult, and the magnetic flux density also decreases. Therefore, the amount of Si + Al is 1.7 to 4.5.
wt%.

C is desirably reduced as much as possible because it causes a problem of magnetic aging. Therefore, the content of C is set to 0.005 wt% or less. Mn is required to be 0.1 wt% or more in order to prevent red-hot brittleness during hot rolling. However, if added in excess of 1%, the magnetic properties deteriorate, so Mn is set to 0.1 to 1 wt%. S is set to 0.015 wt% or less in order to form MnS or the like that deteriorates magnetic properties. P is an element effective for improving the punching property of a steel sheet.
%, The magnetic flux density decreases.
2 wt% or less.

[0009] N is an element useful in the present invention from the viewpoint of forming nitrides such as AlN in the surface layer of the steel sheet. However, the formation of nitride in a part other than the surface layer of the steel sheet deteriorates the magnetic properties. N in the surface layer other than the nitride-containing layer, the internal oxide-containing layer, or the nitride-internal oxide-containing layer is limited to 0.005 wt% or less. O is also an element useful in the present invention from the viewpoint of generating an internal oxide in the surface layer of the steel sheet, but the generation of the internal oxide in a region other than the surface layer of the steel sheet deteriorates the magnetic properties. O other than the material-containing layer or the internal oxide layer or the nitride-internal oxide-containing layer is limited to 0.005 wt% or less. In the present invention, in addition to the above-described component composition, it is possible to add an appropriate amount of one or more of Sb, Sn, B, Cu, Zr, and the like for the purpose of improving magnetic properties.

According to the present invention, the formation state of internal oxides and nitrides in the thickness direction of the steel sheet and the average crystal grain size of the steel sheet are limited to specific ranges under the above-described composition of the steel sheet. Hereinafter, the reasons for these limitations will be described. here,
In the tests described below, the internal oxides and nitrides in the cross section and in the plane of the steel sheet were observed by SEM, and the particle diameters of the internal oxides and nitrides were determined using the internal oxides and nitrides obtained from the SEM images. The diameters of the circles are the particle diameters, and the average value of the particle diameters is the average particle diameter d. Since internal oxides and nitrides having a particle size of less than 0.1 μm could not be identified, internal oxides and nitrides having a particle size of 0.1 μm or more were measured. Therefore, in the following description, when simply referring to nitride or internal oxide,
In any case, the particle diameter is 0.1 μm or more.
The area ratio R of the internal oxide and nitride in the internal oxide-containing layer, the nitride-containing layer, and the nitride-internal oxide-containing layer in the cross section of the plate thickness was SEM magnification of the cross section of the steel plate: 10,000.
By observing at a magnification of 2, the total area of the internal oxides and nitrides in each layer was determined, and the total area was divided by the total viewing area. Also,
The area ratio of the internal oxides and nitrides in the plane of the steel sheet was determined by reducing the steel sheet to a predetermined thickness and then increasing the SEM magnification by 10,000.
The total surface area of the internal oxides and nitrides was determined by observing the steel plate surface randomly at 10 times at a magnification of 2 times, and the total area was determined by dividing the total area by the total view area.

The present inventors conducted the following experiments to investigate the effects of internal oxides and nitrides on iron loss and magnetic flux density. 0.2mm of 3% Si-0.5% Al steel
A steel sheet, in which Al ₂ O ₃ having an average particle size of 0.3 μm is uniformly distributed in the cross section of the steel sheet and in the plane of the steel sheet,
area ratio of plate thickness within the cross-section of l ₂ O ₃ and the high-frequency iron loss W _12/2000
1 is shown in FIG. FIG. 2 shows the relationship between the area ratio of Al ₂ O _{3 in} the cross section of the plate thickness and the magnetic flux density B ₅₀ . According to these, the area ratio of Al ₂ O _{3 in} the cross section of the plate thickness is 0.01
At ~ 0.20%, the total iron loss decreases due to a decrease in eddy current loss due to an increase in the specific resistance of the steel sheet. On the other hand, when the area ratio is less than 0.01%, there is no change in iron loss because the increase in specific resistance is slight, while when it exceeds 0.20%, eddy current loss is reduced due to increase in specific resistance. However, since the pinning effect of the domain wall by Al ₂ O ₃ is increased, the hysteresis loss is significantly increased, and as a result,
Total iron loss increases sharply. On the other hand, the magnetic flux density B ₅₀ is the area ratio is not changed to 0.01%, which decreased to more than 0.01%. Such a phenomenon was similarly observed in a steel sheet in which AlN having the same average particle size as described above was uniformly distributed in the cross section of the steel sheet and in the plane of the steel sheet. From the above, it can be seen that evenly distributing a certain amount of internal oxides or nitrides in the thickness direction of the steel sheet is effective in reducing the high-frequency iron loss, but at the same time, lowering the magnetic flux density.

As described above, in the high-frequency magnetization, the distribution of the eddy current density is not uniform in the thickness direction of the steel sheet due to the skin effect, but is high in the surface layer portion of the steel sheet and rapidly decreases inside the steel sheet. For this reason, it is not necessary to increase the specific resistance of the steel sheet over the entire thickness of the steel sheet, and it is possible to effectively reduce the eddy current and to minimize the decrease in the magnetic flux density by increasing the specific resistance only at the surface layer of the steel sheet. . Therefore, in the present invention, the distribution of internal oxides and nitrides in the thickness direction of the steel sheet is optimized, specifically, a nitride-containing layer containing a predetermined amount or more of internal oxides and nitrides in the surface layer of the steel sheet. Alternatively, the specific resistance in the thickness direction of the steel sheet is optimized by generating an internal oxide-containing layer or a nitride-internal oxide-containing layer.

In the present invention, in order to define the state of formation of internal oxides and nitrides in the thickness direction, first, nitrides and / or internal oxides having a grain size of 0.1 μm or more are coated on the surface of the steel sheet at the surface layer of the steel sheet. A region having an area ratio of 0.01% or more in the inside was defined as a nitride-containing layer, an internal oxide-containing layer, or a nitride-internal oxide-containing layer. The reason why the area ratio of the nitride and / or the internal oxide is defined as 0.01% as the lower limit is that the area ratio of less than 0.01% has no effect in reducing the iron loss as shown in FIG. That's why. In the present invention, the average particle diameter d of the internal oxide and nitride in the nitride-containing layer or the internal oxide-containing layer or the nitride-internal oxide-containing layer as defined above, The area ratio R of the internal oxide and nitride, the depth x of the nitride-containing layer or the internal oxide-containing layer or the nitride-internal oxide-containing layer from the surface of the steel sheet (thickness of the layer) are used as parameters. The state of formation of internal oxides and nitrides in the directions was specified.

Table 1 shows the component compositions of the samples used in the tests described below and the types of nitrides and internal oxides formed on the surface layer of the steel sheet. And the state of formation of internal oxides, their average particle size, etc., are determined by the annealing temperature, annealing time and annealing atmosphere (N
₍₂ concentration, dew point, etc.). In particular, the particle size of the internal oxide and nitride is mainly changed by changing the annealing temperature and the annealing time, and the depth of formation of the internal oxide-containing layer and the nitride-containing layer is mainly controlled by the annealing time and the annealing atmosphere. By changing the thickness, the area ratios of the internal oxides and nitrides in the cross section of the plate thickness were controlled mainly by changing the annealing atmosphere and the annealing temperature.

FIG. 3 shows the relationship between the operating frequency and the iron loss reducing effect of the present invention using the steel sheets of Samples B and D, which are the materials of the present invention shown in Table 1. Here, the high-frequency iron loss of Samples B and D and the comparative materials having the same component composition and plate thickness as those of the samples but having no nitride-containing layer or internal oxide-containing layer in the surface layer of the samples (Samples H and I) The ratio to the high-frequency iron loss of the steel sheet was determined, and the iron loss reducing effect of the material of the present invention in the frequency range of 50 Hz to 5 kHz was examined. In addition, since the excitation magnetic flux density of most of the devices used in the high-frequency range is about B = 1.2T, here, the evaluation was performed with the iron loss of B = 1.2T. The average crystal grain diameter D of the steel sheets of Samples B and D, the area ratio R of the nitride in the nitride-containing layer in the thickness cross section, the average grain diameter d of the nitride in the nitride-containing layer, and the steel sheet of the nitride-containing layer The depth x from the surface layer and the thickness t of the steel sheet are as follows. The area ratios of the nitrides and internal oxides having a grain size of 0.1 μm or more and existing in the regions other than the nitride-containing layer of each steel plate in the plate thickness cross section were all less than 0.01%. Sample B steel sheet D: 100 μm, R: 0.10%,
d: 0.50 μm x: 0.012 mm, t: 0.10 mm Steel plate of sample D D: 130 μm, R: 0.13%,
d: 0.60 μm x: 0.024 mm, t: 0.20 mm

According to FIG. 3, the material of the present invention has no effect of reducing iron loss in a frequency range of less than 200 Hz, but rather increases the iron loss. This is considered to be because the rate of hysteresis loss is large below 200 Hz, so that the effect of increasing the hysteresis loss by hindering the movement of the domain wall is larger than the effect of reducing the eddy current loss by the nitride-containing layer. On the other hand, at a frequency of 200 Hz or more, the iron loss reducing effect of the present invention is remarkably recognized, and this effect hardly depends on the frequency at 200 Hz or more. At a frequency exceeding 5 kHz, the absolute value of iron loss becomes large. Therefore, in order to obtain a desired low iron loss, it is necessary to further increase the Si + Al amount or make the plate thickness thinner. Therefore, the frequency range used in the non-oriented electrical steel sheet of the present invention is specified to be 200 Hz or more and 5 kHz or less. As described above, the iron loss reduction effect of the present invention hardly depends on the frequency above 200 Hz.
Magnetic properties were evaluated by iron loss at 000 Hz.

FIG. 4 shows the types of internal oxides and nitrides formed on the surface layer of the steel sheet and the iron loss using the steel sheets of Samples B, C, D, E and F which are the materials of the present invention shown in Table 1. It is an examination of the relationship with the reduction effect. Here, samples B, C, D, E,
F of the high-frequency iron loss W _12/2000 with the nitride-containing layer and internal oxide containing layer is not compared material is a plate surface portion having the same component composition and thickness and the samples (Sample H, I, J) obtains the ratio of the high-frequency iron loss W _12/2000, were evaluated samples B, C, D, E, the iron loss of the steel sheet F. Of these samples, Samples B, D, and E have a nitride-containing layer formed of AlN on the surface of the plate, and Samples C and F have internal oxidation of Al ₂ O ₃ , SiO ₂ and Fe-based oxide on the surface of the plate. The substance-containing layer is formed. Average grain size D of each steel sheet, nitride in nitride-containing layer or internal oxide-containing layer, area ratio R of internal oxide in cross section of thickness, nitride in nitride-containing layer or internal oxide-containing layer The average particle diameter d of the internal oxide, the depth x of the nitride-containing layer or the internal oxide-containing layer from the surface of the steel sheet,
And the steel plate thickness t is as follows. The area ratio of the nitride and the internal oxide having a particle size of 0.1 μm or more in the region other than the nitride-containing layer or the internal oxide-containing layer of each steel sheet in the plate thickness cross section was 0.01%. Was less than.

Sample B of steel sheet D: 120 μm, R:
0.12%, d: 1.50 μm, x: 0.010 mm,
t: 0.10 mm Steel plate of sample C D: 115 μm, R: 0.13%,
d: 1.00 μm, x: 0.015 mm, t: 0.15
mm Steel plate of sample D D: 120 μm, R: 0.11%,
d: 0.70 μm, x: 0.010 mm, t: 0.10
mm Steel plate of sample E D: 110 μm, R: 0.15%,
d: 0.30 μm, x: 0.011 mm, t: 0.10
mm Steel plate of sample F D: 150 μm, R: 0.20%,
d: 1.30 μm, x: 0.020 mm, t: 0.20
mm

According to FIG. 4, in a steel sheet in which a nitride-containing layer was formed in the same manner as a steel sheet in which an internal oxide-containing layer was formed in the surface layer of the steel sheet, almost the same effect of reducing iron loss was obtained, And nitrides have almost the same effect on reducing high-frequency iron loss, and therefore the effect of the present invention can be obtained regardless of whether an internal oxide-containing layer or a nitride-containing layer is formed. It turns out that it is possible. In addition, it was confirmed that a steel sheet in which a nitride-internal oxide containing layer in which an internal oxide and a nitride are mixed in the surface layer portion of the steel sheet was generated also had approximately the same iron loss reduction effect as above. .

Next, the depth x of the internal oxide-containing layer, the nitride-containing layer, or the nitride-internal oxide-containing layer from the surface of the steel sheet.
The reason for limiting (layer thickness) will be described. FIGS. 5 and 6 show steel sheets according to the samples shown in Table 1, which have an average crystal grain size D satisfying the conditions of the present invention, and an area ratio of a nitride (AlN) in a nitride-containing layer in a thickness cross section of the steel sheet. R, ratio of depth x (thickness of nitride-containing layer) from the surface of steel plate of nitride-containing layer to thickness t of steel sheet for the following steel sheets having an average grain diameter d of nitride in nitride-containing layer: It illustrates the relationship between the x / t and the high-frequency iron loss W _12/2000. In addition, the particle diameter of 0.1 in the region other than the nitride-containing layer of each steel sheet.
The area ratios of the nitrides and internal oxides of not less than μm in the cross section of the plate thickness were all less than 0.01%.

Sample B of steel plate D: 100 μm, R: 0.10%, d: 0.50 μm, (FIG. 5) t: 0.10 mm Steel plate of sample D: 120 μm, R: 0.11%, d: 0.70 μm, (FIG. 5) t: 0.10 mm Steel plate of sample E D: 110 μm, R: 0.15%, d: 0.30 μm, (FIG. 5) t: 0.10 mm Steel plate of sample D: 130 μm , R: 0.13%, d: 0.60 μm, (FIG. 6) t: 0.20 mm Steel plate of sample E D: 160 μm, R: 0.10%, d: 0.50 μm, (FIG. 6) t: 0.20mm

According to FIGS. 5 and 6, the effect of reducing iron loss is large in the range of 0.05 ≦ x / t ≦ 0.15 for any steel type and plate thickness. Such an iron loss reduction effect is achieved by forming an internal oxide-containing layer or a nitride on the surface layer of the steel sheet.
The same was observed when an internal oxide-containing layer was formed. The reason why the large iron loss reduction effect is obtained only when the nitride-containing layer or the internal oxide-containing layer is generated at a specific thickness in the surface layer portion of the sheet is considered to be as follows. . That is, as is well known, iron loss is composed of hysteresis loss and eddy current loss, and eddy current loss is dominant in the high-frequency magnetization region. The eddy current causing the eddy current loss does not flow uniformly in the thickness direction of the steel sheet, but flows more in the surface layer of the steel sheet than in the central part of the steel sheet thickness. In such a situation, when precipitates and inclusions such as nitrides and internal oxides are generated from the surface of the sheet to a depth of 5 to 15% of the sheet thickness to increase the specific resistance of the surface layer of the steel sheet,
It is considered that the eddy current flowing in the surface layer of the steel sheet is effectively reduced, and as a result, the iron loss is reduced. And when the depth of the formation region of the internal oxide or nitride is less than 5% of the plate thickness,
Since the formation region of the internal oxide or nitride is not sufficient, eddy currents flowing inside the formation region still exist, and the eddy current loss is reduced to some extent, but the reduction effect is not sufficient. On the other hand, a region having a depth exceeding 15% of the plate thickness from the surface layer of the steel plate is a region where the eddy current sharply decreases, and even if an internal oxide or nitride is generated in such a region to increase the specific resistance, It has no effect on reducing iron loss, but rather increases the hysteresis loss due to the pinning action of the domain wall by the internal oxide or nitride, which leads to an increase in total iron loss.

For the above reasons, the present invention requires that a nitride-containing layer, an internal oxide-containing layer, or a nitride-internal oxide-containing layer be formed from a surface layer of a steel sheet to a depth x (mm) satisfying the following expression. Requirements. 0.05 ≦ x / t ≦ 0.15 where t: steel plate thickness (mm)

Next, the reasons for limiting the average particle diameter d of the internal oxide and nitride in the nitride-containing layer, internal oxide-containing layer or nitride-internal oxide-containing layer will be described. FIG. 7 shows a steel sheet according to the sample shown in Table 1, which satisfies the conditions of the present invention, the average crystal grain size D, the area ratio R of the nitride (AlN) in the nitride-containing layer in the thickness cross section, For the following steel sheet having a depth x from the sheet surface layer of the material-containing layer,
Average grain size d of nitride in nitride containing layer and high frequency iron loss W ₁₂
/ ₂₀₀₀ is shown. The area ratio of the nitrides existing in the regions other than the nitride-containing layer of each steel plate was less than 0.01%. Sample B steel sheet D: 120 μm, R: 0.12%, x
/ T: 0.10, t: 0.10 mm Steel plate of sample E D: 125 μm, R: 0.15%, x
/ T: 0.09, t: 0.10 mm

According to FIG. 7, the average grain size of the nitride is 3 μm.
It can be seen that the effect of reducing iron loss is large in the following cases. On the other hand, when the average particle size exceeds 3 μm, the iron loss is reduced even if the area ratio R of the nitride in the nitride-containing layer in the plate thickness section and the depth x of the nitride-containing layer satisfy the conditions of the present invention. Is growing. This is presumably because nitride, which should be finely distributed in the surface layer portion of the steel sheet, agglomerated and coarsened, so that the effect of reducing eddy current loss was reduced and the hysteresis loss was increased. The relationship between the above average particle size and the effect of reducing iron loss is as follows:
The same was observed in the case where an internal oxide-containing layer or a nitride-internal oxide-containing layer was formed on the surface layer of a steel sheet. For the above reasons, in the present invention, the average particle diameter of the internal oxide or nitride in the internal oxide-containing layer or nitride-containing layer or nitride-internal oxide-containing layer in the surface layer portion of the steel sheet is 3 μm.
m or less.

Next, the reason why the area ratio R of the internal oxide or nitride in the internal oxide-containing layer or nitride-containing layer or nitride-internal oxide-containing layer in the surface layer of the steel sheet in the cross section of the plate thickness is limited. explain. FIG. 8 shows a steel sheet according to the sample shown in Table 1, which satisfies the conditions of the present invention, the average grain size D, the depth x of the nitride-containing layer from the steel sheet surface, and the nitride content of the nitride in the nitride-containing layer. the steel sheet below having an average particle diameter d, shows the relationship between the area ratio R and the high-frequency iron loss W _12/2000 in a thickness cross section of the nitride in the nitride-containing layer of the steel sheet surface layer portion. In addition, the area ratio of the nitride and the internal oxide existing in the region other than the nitride-containing layer of each steel plate was less than 0.01%. Sample D steel plate D: 120 μm, d: 0.70 μm, x
/ T: 0.10, t: 0.10 mm Steel plate of sample E D: 110 μm, d = 0.30 μm, x
/T=0.11, t: 0.10 mm

According to FIG. 8, the core loss is such that the area ratio R of the nitride in the nitride-containing layer in the thickness cross section of the nitride is 0.05 to 0.2.
It is greatly reduced in the range of 0%. On the other hand, the area ratio R
Is less than 0.05%, the effect of reducing iron loss is not sufficient,
If it exceeds 0.20%, the iron loss increases sharply. this is,
If the area ratio R is less than 0.05%, the specific resistance of the surface layer of the steel sheet does not become sufficiently high, so that the effect of reducing the eddy current loss is not sufficient. This is because, although the suppression effect of the above becomes large, the hysteresis loss is further increased due to the pinning of the domain wall movement. The relationship between the area ratio R in the sheet thickness section and the iron loss reducing effect is based on the internal oxidation of a steel sheet having an internal oxide-containing layer or a nitride-internal oxide-containing layer formed on the surface layer of the steel sheet. The same applies to the area ratio R of the nitride and the nitride. For the above reasons, in the present invention, the area ratio of the internal oxide or / and nitride in the internal oxide-containing layer or the nitride-containing layer or the nitride-internal oxide-containing layer in the surface layer portion of the steel sheet in the plate thickness cross section is determined. 0.05-0.20
%.

Next, nitrides and internal oxides existing in a region other than the nitride-containing layer or the internal oxide-containing layer or the nitride-internal oxide-containing layer on the surface of the steel sheet (region on the plate thickness center portion side) It is necessary to regulate the generation amount from the viewpoint of not lowering the magnetic flux density, and based on the relationship between the area ratio and the magnetic flux density in the thickness cross section of the internal oxide or the like shown in FIG. The area ratio of the nitride and internal oxide having a grain size of 0.1 μm or more existing in the region other than the nitride-containing layer or the internal oxide-containing layer or the nitride-internal oxide-containing layer does not lower the magnetic flux density 0.
Defined as less than 01%.

Next, the reason for limiting the average crystal grain size of the steel sheet will be described. Here, the average crystal grain size is obtained by measuring the crystal grain size in the thickness direction (total thickness) of the steel sheet and taking the average. FIG. 9 shows a steel sheet (R: 0.10%, d: 0.50 μm, x / t:
0.13, plate thickness t: 0.10 mm), and a steel plate of sample J having the same component composition and plate thickness but having no internal oxide-containing layer or nitride-containing layer in the surface layer of the steel plate (comparative material). for shows the relationship between their mean crystal grain size and the iron loss W _12/2000. According to this, in the comparative material having no internal oxide-containing layer or nitride-containing layer in the surface layer of the steel sheet, the optimum particle size for iron loss is about 50 μm, whereas the steel sheet has a nitride-containing layer in the surface layer. The optimum particle size of the material of the present invention is about 1
It is found that the optimum grain size of the steel sheet having a nitride-containing layer on the surface layer of the steel sheet is shifted to the coarser side than that of the steel sheet having no internal oxide-containing layer or nitride-containing layer. Further, in the material of the present invention, the iron loss is lower than that of the comparative material in the range of the particle size of 60 to 160 μm.

Therefore, samples A, B, D, E, and
F, the nitride ratio in the nitride-containing layer or the internal oxide-containing layer that satisfies the conditions of the present invention, the area ratio R of the internal oxide in the plate thickness cross section, the content of the nitride-containing layer or the internal oxide The following steel sheets having a depth x from the surface of the steel sheet and the average particle diameter d of the nitride and the internal oxide in the nitride-containing layer or the internal oxide layer have the average crystal grain size D and iron loss W We examined the relationship between the _12/2000. In addition, the area ratio of the nitride and the internal oxide present in a region other than the nitride-containing layer or the internal oxide-containing layer of each steel sheet in the plate thickness cross section was less than 0.01%.

Sample A Steel Sheet Si + Al: 1.75 wt%, R:
0.05%, d: 0.20 μm, x / t: 0.09,
t: 0.17 mm Steel plate of sample B Si + Al: 2.36 wt%, R:
0.17%, d: 0.50 μm, x / t: 0.10,
t: 0.10 m Steel sheet of sample D Si + Al: 2.93 wt%, R:
0.13%, d: 0.60 μm, x / t: 0.12,
t: 0.20 m Steel sheet of sample E Si + Al: 3.49 wt%, R:
0.15%, d: 0.30 μm, x / t: 0.11,
t: 0.10 m Steel sheet of sample F Si + Al: 3.49 wt%, R:
0.20%, d: 1.30 μm, x / t: 0.10,
t: 0.20m

FIG. 10 shows the high-frequency iron loss W ₁₂ /
The lower and upper limits of the average crystal grain size D when ₂₀₀₀ is 5 W / kg or more lower than the minimum iron loss of the steel sheets of Samples G, H, I, and J, which are comparative materials having the same component composition and thickness. The ratio (x / t) × 100 (%) of the depth x of the internal oxide-containing layer and the nitride-containing layer to the thickness t of the steel sheet, and the internal oxide and nitride in the internal oxide-containing layer and the nitride-containing layer The relationship between the area ratio R (%) and the square root of the product of the amount of Si + Al (wt%) in the cross section of the sheet thickness is shown. According to this,
In the material of the present invention in which the distribution of internal oxides and nitrides in the thickness direction is optimized, the average crystal grain size D (μ
It is understood that the range of m) can be defined by the following equation.

(Equation 3) Therefore, in the present invention, it is a requirement that the average crystal grain size D (μm) of the steel sheet satisfies the above expression.

In this equation, the term in the square root indicates the specific resistance of the surface layer portion of the steel sheet and its area, and the larger the specific resistance, the closer the appropriate grain size becomes to the coarse grain side. It is considered that the reason why the appropriate particle size shifts to the coarse particle side is as follows. In other words, when eddy current loss is reduced by forming a layer having a high specific resistance due to internal oxides and nitrides on the surface layer of the steel sheet, the ratio of hysteresis loss in high-frequency iron loss becomes higher than that of conventional materials. . For example, in a 0.1 mm material of 3% Si-0.4% Al steel, the ratio of the hysteresis loss to the total iron loss at 2 kHz is about 50%. In such a situation, it is necessary to reduce the hysteresis loss even for a high frequency. In order to reduce the hysteresis loss, it is better that the crystal grains are large. In the steel sheet of the present invention, it is considered that the optimum grain size has shifted to the coarse grain side from the balance between the hysteresis loss and the eddy current loss.

Next, the thickness of the steel sheet will be described. Reducing the thickness of a steel sheet is very effective in reducing eddy current loss in a high frequency range. However, a sheet thickness of less than 0.1 mm not only makes cold rolling difficult, but also leads to an increase in the number of stacked steel sheets at the time of assembling the rotor and the stator of the motor, thereby lowering production efficiency. On the other hand, when the plate thickness exceeds 0.2 mm, iron loss starts to increase due to an increase in eddy current loss. Therefore, the thickness of the steel sheet is preferably set to 0.1 to 0.2 mm.

Next, the method for producing a non-oriented electrical steel sheet according to the present invention will be described. The control of the formation state of the internal oxides and nitrides and the adjustment of the average crystal grain size of the steel sheet of the present invention are generally performed by adjusting the final annealing conditions. Therefore, the steps before the final annealing can adopt the usual manufacturing process. That is, molten steel blown in a converter is degassed, adjusted to a predetermined component, cast, and then subjected to normal hot rolling. Hot-rolled sheet annealing may be performed after pickling this steel sheet, but this is not essential. Next, after a predetermined thickness is obtained by one cold rolling or two or more cold rollings sandwiching intermediate annealing, final annealing is performed. In this final annealing, by controlling the annealing atmosphere, the dew point, the annealing temperature, and the annealing time, it is possible to obtain the state of formation of internal oxides and nitrides in the thickness direction of the steel sheet required by the present invention, and the crystal grain size. . For example, 0.1m of 3% Si-0.5% Al steel
In the case of the m material, the nitrogen content of the annealing atmosphere is set to 100% for about 10 to 20 seconds immediately before the end of the final annealing, and the annealing temperature is raised about 30 to 60 ° C. higher than usual, thereby producing AlN in the steel sheet. The state can be as desired. Further, the internal oxide may be generated in a desired state by adjusting the dew point. Further, the nitride-internal oxide-containing layer can be formed by setting the atmosphere to a nitriding atmosphere during the secondary annealing and increasing the dew point. Further, the control of the formation state of the internal oxides and nitrides by the heat treatment as described above may be performed during annealing of the hot-rolled sheet.

[0036]

EXAMPLE Steels of the steel types a to h shown in Table 2 were hot-rolled to a thickness of 2.0 mm, pickled and then pickled.
After cold rolling to 1 mm to 0.2 mm, the obtained cold rolled sheet was annealed under the annealing conditions shown in Tables 3 and 4. In addition, the steel sheet of the present invention can be manufactured by a single annealing treatment,
In this embodiment, the nitride of the surface layer of the steel sheet, the depth of the internal oxide, the particle size, in order to easily control the area ratio, etc.
After performing the primary annealing corresponding to the finish annealing of the normal electromagnetic steel sheet, the secondary annealing was performed for the purpose of generating internal oxides and nitrides on the surface layer of the steel sheet. The magnetic properties of each steel sheet were determined by punching a ring test piece having an outer diameter of 45 mm and an inner diameter of 33 mm from each steel sheet,
The magnetic properties at Hz were measured. Tables 5 and 6 show the formation state and average crystal grain size of nitrides and internal oxides in the thickness direction of each steel sheet, and Table 7 shows the magnetic properties. According to these, it is understood that the high-frequency iron loss of the steel sheet of the present invention is reduced by about 10% as compared with the comparative example without lowering the magnetic flux density.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

[0042]

[Table 6]

[0043]

[Table 7]

[0044]

As described above, the non-oriented electrical steel sheet of the present invention has an excellent property that the iron loss is effectively reduced without lowering the magnetic flux density in the high-frequency magnetization region.

[Brief description of the drawings]

[1] the area ratio and the high-frequency core loss in thickness in cross section of the Al ₂ O ₃ of 3% Si-0.5% Al steel sheet was uniformly distributed steel section and in the plate plane Al ₂ O ₃ Graph showing the relationship with

[Figure 2] and the area ratio and the magnetic flux density in a thickness cross section of the Al ₂ O ₃ the steel cross-section and in 3 of% Si-0.5% Al steel sheet Al ₂ O ₃ were uniformly distributed in the plate plane Graph showing the relationship

FIG. 3 is a graph showing the relationship between the working frequency of the steel sheet of the present invention and the iron loss reducing effect.

FIG. 4 is a graph showing the iron loss reducing effect of the steel sheet of the present invention having an internal oxide-containing layer on the surface layer of the steel sheet and the steel sheet of the present invention also having a nitride-containing layer.

FIG. 5 is a graph showing the relationship between the ratio x / t of the depth x of the nitride-containing layer from the surface of the steel sheet to the steel sheet thickness t and the high-frequency iron loss.

FIG. 6 is a graph showing a relationship between a ratio x / t of a depth x of a nitride-containing layer from a surface layer of a steel sheet to a steel sheet thickness t and high-frequency iron loss.

FIG. 7 is a graph showing the relationship between the average particle diameter d of nitride in a nitride-containing layer in the surface layer of a steel sheet and high-frequency iron loss.

FIG. 8 is a graph showing the relationship between the area ratio R and the high-frequency iron loss of a nitride-containing layer in the surface layer portion of a steel sheet in a cross section of the thickness of nitride.

FIG. 9 is a graph showing the relationship between the average crystal grain size and the high-frequency iron loss of a steel sheet in which the nitride-containing layer in the surface layer portion of the steel sheet satisfies the conditions of the present invention and a steel sheet having no nitride-containing layer in the surface layer portion of the steel sheet.

FIG. 10 is a graph showing an optimum average crystal grain size range with respect to iron loss of a steel sheet in which an internal oxide-containing layer and a nitride-containing layer in the surface layer of the steel sheet satisfy the conditions of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoyoshi Ohkita 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) References JP-A-3-223445 (JP, A) JP-A Heihei 5-59441 (JP, A) JP-A-4-63252 (JP, A) JP-A-3-274247 (JP, A) JP-A-59-74258 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C22C 38/00 303 C22C 38/06 H01F 1/16

Claims (2)

(57) [Claims] 1. The total amount of Si and Al is 1.7 to 4.5 w.
t%, C: 0.005 wt% or less, Mn: 0.1 to 1 w
t: S: 0.015 wt% or less, P: 0.2 wt% or less, N other than a nitride-containing layer or an internal oxide-containing layer or a nitride-internal oxide-containing layer defined as follows:
0.005 wt% or less, O other than the nitride-containing layer or the internal oxide-containing layer or the nitride-internal oxide-containing layer:
A steel sheet containing 0.005 wt% or less, the balance being Fe and unavoidable impurities, wherein the nitride or / and internal oxide having a particle size of 0.1 μm or more in the surface layer of the steel sheet has an area ratio in the plane of the steel sheet. In the region containing 0.01% or more of the nitride-containing layer or internal oxide-containing layer or nitride-
When defined as an internal oxide-containing layer, a nitride-containing layer or an internal oxide-containing layer or a nitride-internal oxide-containing layer is formed from a surface layer of a steel sheet to a depth x (mm) satisfying the following expression. 05t ≦ x ≦ 0.15t where t: steel plate thickness (mm) nitride-containing layer or internal oxide-containing layer or nitride
The average particle size of the nitride or / and internal oxide in the internal oxide-containing layer is 3 μm or less, and the particle size in the nitride-containing layer or internal oxide-containing layer or nitride-internal oxide-containing layer is 0.1 μm or more. The area ratio R of the nitride or / and internal oxide in the cross section of the plate thickness is 0.05 to 0.2
0%, and the nitride and internal oxide having a grain size of 0.1 μm or more existing in a region other than the nitride-containing layer, the internal oxide-containing layer, or the nitride-internal oxide-containing layer in the plate thickness cross section. The area ratio is less than 0.01%, and the average crystal grain size D (μm) of the steel sheet satisfies the following expression.
Non-oriented electrical steel sheet for high frequency use with excellent iron loss characteristics used in the frequency range of 5 Hz to 5 kHz. (Equation 1) 2. The high-frequency non-oriented electrical steel sheet according to claim 1, which has a thickness of 0.1 to 0.2 mm and has excellent iron loss characteristics used at a frequency of 200 Hz or more and 5 kHz or less.