JP2005248291A - Low core loss grain oriented silicon steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low core loss grain oriented silicon steel sheet having core loss more excellent than that of a conventional one by controlling its plastic strain and elastic strain to proper conditions. <P>SOLUTION: In the low core loss grain oriented silicon steel sheet, among the strain regions composed of tensile elastic stress and plastic strain formed on the surface of a steel sheet, the maximum value of the tensile residual stress in the rolling direction is 70 to 150 MPa, and also, the range in the rolling direction of the plastic strain is ≤0.6 mm. Further, the spacing in the rolling direction between the strain regions is ≤7.0 mm, and also, the strain regions are formed continuously or at prescribed intervals in a direction of 60 to 120° to the rolling direction of the steel sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a low iron loss unidirectional electrical steel sheet used for a transformer core and the like.

  In recent years, unidirectional electrical steel sheets that have an easy axis in the rolling direction of steel sheets have been put to practical use mainly in applications such as electrical equipment such as transformers, and magnetics for further reducing energy loss in terms of energy environment. Reduction of iron loss is required as a characteristic improvement.

Iron loss in unidirectional electrical steel sheets is generally divided into hysteresis loss and eddy current loss. Hysteresis loss is affected by crystal orientation, impurities, etc., and eddy current loss is affected by plate thickness and magnetic domain width. It has been. Since there are limits to the crystal orientation control method for reducing hysteresis loss, in recent years, many techniques have been proposed to reduce the magnetic domain width, that is, to subdivide the magnetic domain for the purpose of reducing eddy current loss, which accounts for the majority of iron loss. Yes.
Application of such a magnetic domain refinement method suppresses generation of eddy currents in the cross-sectional direction of the steel sheet and thermal energy thereby, and as a result, iron loss of the unidirectional electrical steel sheet can be reduced.

  For example, in Patent Document 1 or the like, for the purpose of improving iron loss, by irradiating a laser at a predetermined beam width, energy density, and irradiation interval with respect to a direction perpendicular to the rolling direction of the unidirectional steel sheet surface, By adding a local high dislocation density region, that is, a small plastic strain to the steel sheet surface (see page 15, left lower column, line 15), magnetic domain buds are generated to subdivide the magnetic domain (page 2, lower right column 18). -20th line), the manufacturing method of the unidirectional electrical steel sheet which reduces an iron loss is disclosed.

  Further, in Patent Document 2 and the like, for the purpose of improving iron loss, a groove is formed by applying a predetermined load in a range of 45 ° from a direction perpendicular to the rolling direction of the unidirectional steel sheet surface, and then at a predetermined temperature. By carrying out strain relief annealing, fine crystal grains are formed in the strain-introduced part, and buds of magnetic domain subdivision are generated from the interface between the grains and secondary recrystallized grains (see the lower left column, lines 9 to 19 on page 2). ) A method is disclosed.

Although the methods of Patent Document 1 and Patent Document 2 are different from each other, both generate a local plastic strain region (high dislocation density region) on the surface of the unidirectional electrical steel sheet, generate magnetic domain buds, and generate magnetic domains. However, the iron loss (W17 / 50) of the steel sheet obtained by applying these plastic strains is limited to about 0.80 to 0.78 W / Kg. there were. W17 / 50 represents the iron loss at a magnetic flux density of 1.7 T and a frequency of 50 Hz.
The reason why the iron loss becomes insufficient is that, according to the examination results of the present inventors, the eddy current loss is reduced among the iron losses by reducing the magnetic domain width (magnetic domain fragmentation) by applying plastic strain. However, it has been found that the hysteresis loss increases.

  On the other hand, Non-Patent Document 1 and the like have proposed and put to practical use a method of applying elastic strain by coating a unidirectional electrical steel sheet surface with a tensile film to reduce iron loss. However, the tension generated by the formation of a tensile film on the steel sheet surface is limited to about 20 MPa at most, and the iron loss W17 / 50 obtained by this method is only about 1.03 W / Kg. Based on the current state of the prior art, further improvement in iron loss is desired.

As described above, in recent years, there has been a demand for further reduction of iron loss of unidirectional electrical steel sheets in order to reduce energy loss when used in electrical equipment. Thus, a method of improving stably is desired.
Japanese Patent Laid-Open No. 55-18566 JP 61-117218 A T. Yamamoto and T. Nozawa: J. Appl. Phys., 57 (1970) 2981.

As described above, there is a limit to the effect of improving the iron loss value (W17 / 50) achieved by the method of imparting plastic strain or elastic strain to the surface of the conventional unidirectional electrical steel sheet.
In view of the current state of the prior art, the present invention divides the iron loss of a unidirectional electrical steel sheet into hysteresis loss and eddy current loss, and controls plastic strain and elastic strain to appropriate conditions from each viewpoint. Accordingly, it is an object of the present invention to provide a low iron loss unidirectional electrical steel sheet that is superior in iron loss as compared with the prior art.

The present invention solves the above-mentioned problems, and the gist thereof is as follows. (1) Of the strain region consisting of tensile elastic stress and plastic strain formed on the steel sheet surface, the maximum value of tensile residual stress in the rolling direction is 70 to 150 MPa, and the range of the plastic strain in the rolling direction is 0. A low iron loss unidirectional electrical steel sheet characterized by being 6 mm or less.
(2) The low iron loss unidirectional electrical steel sheet according to (1), wherein an interval in the rolling direction between the strain regions is 7.0 mm or less.
(3) The low iron according to (1) or (2), wherein the strain region is formed continuously or at a predetermined interval in a direction of 60 to 120 ° with respect to a rolling direction of the steel sheet. Loss-oriented magnetic steel sheet.

  According to the present invention, the iron loss of the unidirectional electrical steel sheet is divided into hysteresis loss and eddy current loss, and the plastic strain and elastic strain are controlled to appropriate conditions from the respective viewpoints, thereby reducing the iron loss (W17 / 50). Can be improved to 0.7 W / Kg or less, and a low iron loss unidirectional electrical steel sheet excellent in iron loss as compared with the prior art can be provided. By applying the unidirectional electrical steel sheet excellent in iron loss of the present invention to electrical equipment such as a transformer, it is expected that energy loss will be significantly reduced compared to the conventional case. The above utility value is very high.

The present invention is described in detail below.
The present inventors conducted a confirmation test of a method of irradiating a laser on the surface of a unidirectional electrical steel sheet disclosed in Patent Document 1 and the like to form a local high dislocation density region, that is, a microplastic strain, on the steel sheet surface. The effect on iron loss improvement was examined in detail. As a result, when a laser is irradiated on the surface of a unidirectional electrical steel sheet, a plastic strain due to the thermal history is locally formed on the steel sheet surface, and at the same time, a tensile residual stress that is an elastic strain is formed. It was confirmed that the iron loss was affected.

  In addition, the tensile residual stress, which is elastic strain, increases the magnetic anisotropy in the direction of the easy axis of the unidirectional electrical steel sheet in the rolling direction and causes magnetic domain fragmentation, thereby causing vortices that are part of iron loss. Although it has an effect of reducing current loss, particularly abnormal eddy current loss, it has been found that plastic strain increases hysteresis loss as a part of iron loss by acting as a pinning site to prevent the domain wall from moving.

  In the conventional methods proposed in Patent Document 1 and Patent Document 2 and the like, magnetic buds are generated by actively generating a local plastic strain region (high dislocation density region) on the surface of the unidirectional electrical steel sheet. The technical idea was to subdivide the magnetic domains. However, based on the above examination results, the present inventors have found that the increase in the plastic strain region is counterproductive to reduce the iron loss of the unidirectional electrical steel sheet, and forms a tensile residual stress that is an elastic strain. Is considered effective for reducing iron loss.

  The present invention divides the iron loss of a unidirectional electrical steel sheet into hysteresis loss and eddy current loss, limits the plastic strain region formed on the steel sheet surface to reduce the hysteresis loss, and achieves an appropriate tensile residual on the steel sheet surface. The technical idea is to significantly reduce iron loss compared to conventional unidirectional electrical steel sheets by forming stress (elastic strain) and reducing eddy current loss.

  First, the low iron loss unidirectional electrical steel sheet of the present invention has a maximum tensile residual stress in the rolling direction of 70 to 150 MPa in a strain region composed of tensile elastic stress and plastic strain, and plastic strain. The range in the rolling direction is 0.6 mm or less.

  In the present invention, the method for forming the tensile residual stress (elastic strain) or plastic strain on the surface of the unidirectional electrical steel sheet is not particularly limited. For example, pulse laser or continuous laser irradiation as shown in Patent Document 1 or the like is used. By adjusting the irradiation conditions using the method, it can be realized by controlling the tensile residual stress (elastic strain) or plastic strain on the surface of the steel sheet to be in the above range. Other methods for introducing the strain on the surface of the steel sheet include an ion implantation method, an electric discharge machining method, and a local plating method, and any method may be used.

FIG. 1 is a schematic view showing a strain region formed on the surface of a steel sheet when a unidirectional electrical steel sheet is irradiated with a pulse laser.
As shown in FIG. 1, a strain region 2 composed of tensile residual stress (elastic strain) and plastic strain is applied to a steel sheet surface by irradiating a unidirectional electrical steel sheet with a pulse laser whose laser irradiation spot shape 1 and laser output are adjusted. Is formed.

  The maximum value of the tensile residual stress (elastic strain) in the rolling direction formed on the surface of the steel sheet can be controlled by adjusting the laser output without changing the optical conditions such as the focal length of the condenser lens. As a result, the maximum value of the tensile residual stress (elastic strain) in the rolling direction increases. The range of the plastic strain formed on the surface of the steel sheet in the rolling direction is, for example, by adjusting the optical system without changing the laser output, and by adjusting the laser spot area under a certain condition, the major axis is the rolling direction (L direction). By changing the minor axis to an elliptical shape in the width direction (C direction) and adjusting the axial ratio (L / C), the range of the plastic strain in the rolling direction can be controlled.

FIG. 2 shows the maximum tensile residual stress in the rolling direction formed on the surface of the unidirectional electrical steel sheet by laser irradiation, the range of the plastic strain in the rolling direction (maximum length), and the iron loss (W17 / 50). Show the relationship.
Here, W17 / 50 represents an iron loss value measured under the condition of magnetic flux density (B) 1.7T when excited at a frequency of 50 Hz using a normal magnetometer. Further, the thickness of the unidirectional electrical steel sheet is 0.23 mm, the pulse laser irradiation conditions are 5.0 mm in the rolling direction (L direction) of the steel sheet, and the direction perpendicular to the rolling direction (L direction) of the steel sheet (C direction). ) At an irradiation interval (pitch) of 0.3 mm.

  As described above, the iron loss value (W17 / 50) of the unidirectional electrical steel sheet obtained by the prior art is limited to about 0.80 to 0.78 W / Kg. In the present invention, these iron loss values (W17 / 50) are limited. The aim is to obtain a unidirectional electrical steel sheet with excellent low iron loss characteristics that is less than 50).

  As is apparent from FIG. 2, in order to obtain a unidirectional electrical steel sheet having an excellent iron loss value (W17 / 50) of 0.70 W / Kg or less, the maximum tensile residual stress in the rolling direction is obtained. At the same time as the value of 70 to 150 MPa, the range of the plastic strain in the rolling direction needs to be 0.6 mm or less. For this reason, in the present invention, the maximum tensile residual stress in the rolling direction is set to 70 to 150 MPa in the strain region consisting of tensile elastic stress and plastic strain formed on the steel sheet surface, and the rolling direction of plastic strain. Was set to 0.6 mm or less.

  In the present invention, the maximum value of the tensile residual stress in the rolling direction formed on the surface of the steel plate is, for example, a single crystal X-ray stress analysis method (see, for example, Suyama, Otani, Yoshioka: Materials, 48 (1999), p. 372). It can be used to measure the residual stress (elastic strain) in the rolling direction and determine the maximum value. In the present invention, the range (maximum length) in the rolling direction of the plastic strain formed on the surface of the steel sheet is determined by measuring the hardness of the steel sheet surface using, for example, a micro Vickers hardness tester, and the amount of increase in hardness due to work hardening is The range of 5% or more is defined as the range of plastic strain, and is determined from the range (maximum length) of the plastic strain in the rolling direction.

  The present invention can achieve a unidirectional electrical steel sheet having lower iron loss and superior low iron loss characteristics than the conventional ones according to the first embodiment, but in addition to these invention embodiments, the following By defining the conditions, the low iron loss characteristics can be stably improved, which is preferable.

In the first embodiment of the present invention, the distance in the steel plate width direction (C direction) of the strain region consisting of tensile elastic stress and plastic strain is not particularly limited, but the interval in the rolling direction (L direction) of the strain region is not limited. Affects the subdivision of the magnetic domain due to the interaction between the adjacent strain regions. Therefore, if the interval is too large, the effect of reducing the iron loss is reduced.
According to the experimental results of the present inventors, even if the maximum value of the tensile residual stress in the rolling direction and the range of the plastic strain in the rolling direction of the present invention are optimal, the tensile elastic stress and the plastic strain are included. When the interval in the rolling direction of the strain region exceeds 7.0 mm, it was confirmed that the magnetic domain refinement action of the steel sheet is reduced and the iron loss value cannot be sufficiently reduced as compared with the conventional case.

  For these reasons, in the present invention, in addition to the requirements defined in the first embodiment, as the second embodiment, the interval in the rolling direction of the strain region composed of tensile elastic stress and plastic strain is further set to 7.0 mm. The following is preferable. More preferably, the interval in the rolling direction between the strain regions including the tensile elastic stress and the plastic strain is 0 mm, that is, it is more desirable to form the strain regions continuously in the rolling direction.

  As described above, the unidirectional electrical steel sheet is ideally composed of crystal grains with (110) [001] orientation having an easy axis of magnetization in the rolling direction (L direction) in order to reduce iron loss. A textured steel sheet is desirable. However, the easy magnetization axis in a unidirectional electrical steel sheet that can be actually produced industrially is not completely parallel to the rolling direction, and the easy magnetization axis has a deviation angle with respect to the rolling direction. Moreover, in order to reduce iron loss by subdividing the magnetic domain of a unidirectional electrical steel sheet, it is possible to reduce the tensile elastic stress on the steel sheet surface continuously or at a predetermined interval in the magnetization direction of the steel sheet, that is, in the direction perpendicular to the easy axis of magnetization. It is considered effective to form a strain region composed of plastic strain.

  According to the experimental results of the present inventors, due to the deviation angle of the easy axis with respect to the rolling direction, the tensile elastic stress is applied to the surface of the steel sheet continuously or at predetermined intervals in the direction of 60 to 120 ° with respect to the rolling direction. In addition, when forming a strain region composed of plastic strain, it was confirmed that a sufficient reduction in iron loss due to the effect of magnetic domain refinement can be obtained. The above angle range corresponds to an ideal range of easy axis of magnetization, that is, a range within 30 ° in deviation angle from a direction (C direction) perpendicular to the rolling direction (L direction) of the steel sheet. If this is not the case, even if the maximum value of the tensile residual stress in the rolling direction and the range of the plastic strain in the rolling direction of the present invention are under optimum conditions, the magnetic domain refinement action of the steel sheet is reduced, which is sufficiently higher than in the past. The iron loss value cannot be reduced.

Therefore, in addition to the requirements defined in the first embodiment or the second embodiment, the present invention further includes a strain region composed of the tensile elastic stress and the plastic strain in the rolling direction of the steel plate. On the other hand, it is preferable to form continuously or at predetermined intervals in the direction of 60 to 120 ° in order to further reduce iron loss.
Hereinafter, the present invention will be described based on examples.

  By irradiating the surface of this steel sheet with a pulse laser using a unidirectional electrical steel sheet having a thickness of 0.23 mm, the maximum value of the tensile residual stress (elastic strain) as shown in Table 1 and the plastic strain in the rolling direction are shown. Manufactures unidirectional electrical steel sheets with a range (maximum length), an angle with respect to the rolling direction in the direction of the strain region (strain region consisting of tensile elastic stress and plastic strain), and an interval in the rolling direction (L direction) of the strain region. Thereafter, the iron loss (W17 / 50) of each unidirectional electrical steel sheet was measured (see Table 1).

  In addition, the maximum value of the tensile residual stress in the rolling direction in Table 1 was determined from the maximum value obtained by measuring the residual stress (elastic strain) in the rolling direction using a single crystal X-ray stress analysis method. The range (maximum length) of the plastic strain in the rolling direction is determined by measuring the hardness of the steel sheet surface using a micro Vickers hardness tester, and setting the range of increase in hardness by work hardening to 5% or more as the range of plastic strain. It was determined from the range (maximum length) in the rolling direction of the plastic strain.

  As for the laser beam shape, the spot shape at the irradiation position on the surface of the steel plate was a circle having a diameter of 150 μm, and the laser output was changed from 1 to 10 mJ with energy per pulse as shown in Table 1. The irradiation direction is 70 ° to 135 ° with respect to the rolling direction of the steel plate, the irradiation interval is fixed to 0.3 mm in the steel plate width direction (C direction), and 3.0 mm to the steel plate rolling direction (L direction). It was changed to 9.0 mm.

  As is apparent from Table 1, test no. In the unidirectional electrical steel sheets shown in 1 to 9 (examples of the present invention), the maximum value of the tensile residual stress in the rolling direction and the range of the plastic strain in the rolling direction are both within the range defined by the present invention. The iron loss value (W17 / 50) can be reduced to 0.70 W / Kg or less, and these conditions are not met. A unidirectional electrical steel sheet excellent in low iron loss characteristics as compared with 10-13 (comparative example) was obtained.

  In addition, the above test No. 1 to 9 (examples of the present invention), in addition to the maximum value of the tensile residual stress in the rolling direction and the range of the plastic strain in the rolling direction, the strain region (tensile elastic stress and plastic strain in the rolling direction of the steel sheet) Test No. in which the angle in the direction of the strain region) and the rolling direction interval of the strain region are within the preferred range. 1 to 7 (examples of the present invention) are test No. Compared with 8 and 9 (examples of the present invention), the iron loss could be further reduced.

By irradiating the surface of this steel sheet with a pulse laser using a unidirectional electrical steel sheet having a thickness of 0.23 mm, the maximum value of the tensile residual stress (elastic strain) as shown in Table 2 and the plastic strain in the rolling direction are shown. After manufacturing each unidirectional electrical steel sheet in the range (maximum length), the iron loss (W17 / 50) of each unidirectional electrical steel sheet was measured (see Table 2).
The laser output is constant at 5 mJ in energy per pulse, and the laser beam shape is an elliptical spot shape at the irradiation position on the steel sheet surface, and its axial ratio (L / C, where L: in the rolling direction) The major axis length, C: the minor axis length in the width direction, was changed from 0.5 to 2.0 as shown in Table 2.

  In addition, the spacing in the rolling direction (L direction) of the strain region (strain region consisting of tensile elastic stress and plastic strain) formed on the steel plate surface is 5.0 mm, and the steel plate width perpendicular to the rolling direction (L direction) of the strain region Laser was irradiated so that the interval between the directions (C direction) was 0.3 mm, and the angle of the strain region direction with respect to the rolling direction was constant at 90 °. The maximum tensile residual stress in the rolling direction and the range of the plastic strain in the rolling direction (maximum length) in Table 2 were measured in the same manner as in Example 1.

  Test No. 1 and 2 (examples of the present invention) were tested because both the maximum tensile residual stress in the rolling direction formed on the steel sheet surface and the range of the plastic strain in the rolling direction range satisfy the range specified in the present invention. No. Compared with 3-5 (comparative example), the iron loss was able to be reduced more.

The conceptual diagram of the laser irradiation spot shape and the rolling direction range of distortion is shown. The figure which shows the relationship between the maximum tensile residual stress of a rolling direction, the plastic strain range of a rolling direction, and an iron loss (W17 / 50).

Explanation of symbols

1: Laser irradiation spot shape 2: Strain area

Claims (3)

Of the strain region consisting of tensile elastic stress and plastic strain formed on the steel plate surface, the maximum value of the tensile residual stress in the rolling direction is 70 to 150 MPa, and the range of the plastic strain in the rolling direction is 0.6 mm or less. A low iron loss unidirectional electrical steel sheet characterized by being. The low iron loss unidirectional electrical steel sheet according to claim 1, wherein an interval in the rolling direction between the strain regions is 7.0 mm or less. 3. The low iron loss unidirectional electrical steel sheet according to claim 1, wherein the strain region is formed continuously or at a predetermined interval in a direction of 60 to 120 ° with respect to a rolling direction of the steel sheet. .

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