JP2008127632A - Low core loss grain-oriented magnetic steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low core loss grain-oriented magnetic steel sheet excellent in lower core loss in comparison with the conventional magnetic steel sheet by controlling the stress-condition in the inner part of the grain-oriented magnetic steel sheet into an adequate condition. <P>SOLUTION: The low core loss grain-oriented magnetic steel sheet is characterized in that in one or the plurality of positions in the inner part of the sheet thickness of the steel sheet, the stress in the sheet thickness direction is a tensile stress and the maximum value thereof is 40 MPa or more and not more than the yield stress value of the steel sheet blank. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a unidirectional electrical steel sheet that is used for a transformer core and the like, and is excellent in performance of the unidirectional electrical steel sheet, particularly in low iron loss.

  In recent years, unidirectional electrical steel sheets with an easy axis in the rolling direction of steel sheets are mainly used in the iron cores of transformers and other power converters. Are strongly required to have low iron loss characteristics.

  The iron loss of electrical steel sheets is roughly divided into hysteresis loss and eddy current loss. Hysteresis loss is affected by crystal orientation, defects, grain boundaries, and the like, and eddy current loss is determined by the plate thickness, electrical resistance, 180 ° magnetic domain width, and the like of the material.

  Therefore, until now, from the viewpoint of reducing hysteresis loss, a method of highly aligning the grain structure in the (110) [001] orientation and reducing crystal defects has been used. From the viewpoint of reducing eddy current loss, Reduce the loss of electrical steel sheets by reducing the thickness of the magnetic steel sheet, increasing the resistance value of the material by increasing the Si content, etc., or subdividing the 180 ° magnetic domain width by applying a tensile coating to the steel sheet surface, etc. Has been tried.

  In recent years, in order to dramatically reduce iron loss, from the viewpoint of reducing eddy current loss, which accounts for the majority of iron loss, using means other than the application of tension to the steel sheet surface, artificially applied to the steel sheet. A method has been proposed in which buds of magnetic domain subdivision are generated and a 180 ° magnetic domain is subdivided.

  For example, in Patent Document 1, 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, A method for producing a unidirectional electrical steel sheet is disclosed in which a local high dislocation density region, that is, a micro plastic strain is applied to the steel sheet surface, thereby performing magnetic domain subdivision and reducing iron loss.

  The method of the above-mentioned patent document 1 has a technical idea that a local high dislocation density region (plastic strain region) is generated on the surface of a unidirectional electromagnetic steel sheet, and magnetic domain buds are generated to subdivide the magnetic domain. However, the iron loss (W17 / 50) of the steel sheet obtained by applying these plastic strains was limited to about 0.80 to 0.78 W / Kg. W17 / 50 indicates 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 the above technique defines the iron loss characteristics based on laser irradiation conditions such as a predetermined beam width, energy density, and irradiation interval, and reduces the magnetic domain width (magnetic domain fragmentation). It is considered that the physical phenomenon of eddy current loss reduction due to) has not been studied on the basis of the basic physical quantity such as the strain amount or the stress value converted from the strain. As will be described later, according to the study by the present inventors, when plastic strain or stress in the plastic region is applied, although there is a reduction in eddy current loss due to subdivision of the magnetic domain, conversely, the hysteresis loss increases, It has been confirmed that iron loss is not reduced.

  On the other hand, Patent Document 2 proposes a unidirectional electrical steel sheet that reduces iron loss by defining an elastic tensile stress value and a plastic strain range with respect to the rolling direction of the steel sheet surface. In general, the stress is a value based on the rolling direction, the plate thickness direction, and the plate width direction, and has a value at the surface, inside, and each point of the material. However, the technology of Patent Document 2 focuses on only the strain and tensile stress on the surface of the steel sheet and controls the iron loss characteristics as a technical idea. This is because a tensile film is applied to the surface of the steel sheet to generate a tensile stress in the surface, the lancet magnetic domain generated in the 180-degree magnetic domain disappears (see FIG. 1), and the reconfiguration of the magnetic domain is promoted. This is the same as the technical idea using the phenomenon of subdividing the magnetic domain width (reducing eddy loss). In addition, the technique of Patent Document 2 does not mention any effect on the iron loss characteristics of the internal strain or stress state within the plate thickness, and therefore, the technique of Patent Document 2 alone makes a further leap forward. The reduction in iron loss was not sufficient.

JP-A-55-18586 JP 2005-248291 A Japanese Patent Laid-Open No. 7-320921

  The present invention divides the iron loss of a unidirectional electrical steel sheet into hysteresis loss and eddy current loss. In particular, from the viewpoint of eddy current loss due to magnetic domain subdivision, strain and stress distributions are not only within the surface but also within the plate thickness. In addition, the present invention provides a unidirectional electrical steel sheet that is superior to conventional ones by controlling under quantitatively appropriate conditions.

The present invention solves the above problems, and the gist of the invention is as follows.
(1) The stress in the plate thickness direction is tensile stress at one or a plurality of locations inside the plate thickness of the steel plate, and the maximum value is 40 MPa or more and below the yield stress value of the steel plate material. Item 1. The low iron loss unidirectional electrical steel sheet according to Item 1.
(2) The distribution width in the rolling direction in the region where the tensile stress exists is 0.8 mm or less, and the distribution width in the plate thickness direction is 80% or less of the plate thickness (1). ) Low iron loss unidirectional electrical steel sheet.
(3) The low iron loss unidirectional electrical steel sheet according to (1) or (2), wherein the region where the tensile stress exists has an interval of 7.0 mm or less in the rolling direction of the steel sheet.
(4) The region where the tensile stress exists is formed continuously or at a predetermined interval in a direction of 60 to 120 ° with respect to the rolling direction of the steel sheet. A low iron loss unidirectional electrical steel sheet according to claim 1.

  According to the present invention, it is possible to provide a unidirectional electrical steel sheet with very excellent iron loss characteristics, and the effects on industrial effects and improvement of global environmental problems are extremely large, such as the energy loss of the transformer being extremely small.

  The present invention is described in detail below.

  The present inventors formed a local strain inside the thickness of the unidirectional electromagnetic steel sheet, and conducted a test to investigate the correlation between the stress value converted from the strain and the iron loss, and the stress state inside the thickness The effect of iron on iron loss improvement was examined in detail. As a result, the strain or stress state that has a dramatic effect on the promotion of 180 degree magnetic domain subdivision, that is, the reduction of vortex loss, is not the stress or strain on the steel sheet surface proposed in Patent Document 2, but the thickness of the steel sheet. It was found that the stress state, particularly the tensile stress in the thickness direction, is the bud that generates the reflux magnetic domain, and promotes 180-degree magnetic domain subdivision. It was also found that when the value of the tensile stress exceeds the stress in the plastic region, that is, the yield stress, the plastic region inside the plate thickness acts as a pinning site for the domain wall, and the hysteresis loss, which is part of the iron loss, increases. .

  The present invention effectively controls the reflux magnetic domain by controlling the strain formed in the thickness of the unidirectional electrical steel sheet or the stress converted from the strain so that a tensile stress is introduced in the thickness direction. To reduce the eddy current loss and to quantitatively limit the stress value inside the plate thickness to below the yield stress, thereby suppressing the increase in hysteresis loss. The technical idea is to significantly reduce iron loss compared to grain-oriented electrical steel sheets.

  First, the technical idea of the present invention will be described.

  As shown in the conceptual diagram of FIG. 2, since the easy magnetization axis of the unidirectional electrical steel sheet is generally oriented in the rolling direction, the magnetic domain is composed of magnetization parallel and antiparallel to the rolling direction and forms a 180 ° magnetic domain width. To do. As proposed in Patent Document 2, in this state, simply by applying a tensile stress to the surface of the steel sheet in the rolling direction, the magnetization constituting the magnetic domain should be oriented in a direction parallel and antiparallel to the rolling direction. Since it becomes more stable in terms of energy, the magnetic domain structure remains in the state shown in FIG.

When tensile stress is applied in the rolling direction, the magnetization is more stable in the rolling direction for the following reason. In general, when magnetization and stress are present, the interaction energy of magnetization and stress of the electrical steel sheet = −C × M × σ × cos ² θ (where C: positive constant, M: magnitude of magnetization, σ: stress) , Θ: angle between magnetization and stress). As proposed in Patent Document 2, even when a tensile stress is present in the rolling direction, the magnetization has the lowest energy when the angle formed by the stress is θ = 0 or 180 degrees. That is, the stress and magnetization are stable in terms of energy when they are parallel or antiparallel. Therefore, even if a tensile stress is introduced in the rolling direction of the steel sheet surface in the state of FIG. 2, a large change cannot be given to the current magnetic domain structure, and a reduction in the 180-degree magnetic domain width cannot be expected so much.

  On the other hand, in the present invention, as shown in the conceptual diagram of FIG. 3, a tensile stress or a strain corresponding thereto is locally introduced into the thickness direction inside the thickness. As a result, the interaction energy between magnetization and stress of the above-described electrical steel sheet is positive because the stress σ is tension, and the magnetization is more stable in the direction of the stress, that is, in the thickness direction. As a result, as shown in FIG. 4, the magnetic domain structure obtained has a magnetization distribution perpendicular to the rolling direction, that is, a reflux magnetic domain is formed, and as a result, reconfiguration of the magnetic domain of the entire steel sheet is promoted, and 180 degrees Magnetic domain width subdivision, that is, eddy current loss is reduced. Based on the magnetic domain analysis results described above, the present invention significantly increases the iron loss of a unidirectional electrical steel sheet by locally introducing a tensile stress or a strain corresponding to the thickness direction inside the sheet thickness of the steel sheet. It is based on a technical idea different from the conventional one.

  In other words, the technical idea proposed in Patent Document 2 for regulating the amount of stress in the steel sheet surface and improving iron loss is based on the technical idea of improving iron loss characteristics by applying a tension film to the steel sheet surface. is there. On the other hand, in the present invention, the stress generated at each point of the steel sheet, that is, the stress in the plate thickness direction inside the plate thickness among the stresses defined for the rolling direction, the plate thickness direction, and the plate width direction. However, by controlling the maximum value of the stress by focusing on the buds of the occurrence of magnetic domain fragmentation, the technical idea of promoting the magnetic domain fragmentation more efficiently and reducing the iron loss of the unidirectional electrical steel sheet Is based. In the present invention, the technical idea of reducing iron loss is completely different from the conventional one.

  The low iron loss unidirectional electrical steel sheet of the present invention is characterized in that, firstly, the stress in the thickness direction is a tensile stress, and the maximum value is 40 MPa or more and less than the yield stress value of the material. To do.

  In the present invention, the method for introducing tensile stress in the thickness direction into the thickness of the unidirectional electrical steel sheet is not particularly limited, but for example, laser irradiation method, shot peening, ultrasonic vibration method, steel sheet surface There are a machining method for marking with a metal such as a knife or a ceramic piece, an ion implantation method for a steel sheet surface, a doping method, an electric discharge machining method, a method in which plating and heat treatment are combined, and any method may be used.

  FIG. 5 shows a sample in which the surface of a unidirectional electrical steel sheet is irradiated with a laser to generate stress in the thickness of the steel sheet. Among the generated stress, the maximum value of tensile stress in the thickness direction It is the graph which showed the correlation with an iron loss (W17 / 50). 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 single plate magnetometer. The thickness of the unidirectional electrical steel sheet was about 0.23 mm, and a pulse YAG laser with an irradiation beam diameter of 150 μm was used as the laser. Irradiation conditions were as follows: a steel plate was placed in water, and irradiation pulses (pitch) of 5.0 mm in the rolling direction of the steel plate were irradiated so that the irradiation pulse overlapped in a direction perpendicular to the rolling direction of the steel plate, as shown in FIG. .

  The stress value inside the plate thickness is the stress in each of the rolling direction, plate thickness direction, plate width direction by measuring the distortion of the crystal lattice in three directions by X-ray diffraction method and using the material property values such as elastic modulus. The value was determined. The crystal strain in the three directions can be obtained by irradiating the steel sheet with X-rays as shown in FIG. For the conversion from strain to stress value, for example, the strain scanning method using the elastic modulus and Poisson's ratio is used (reference: The Japan Society of Mechanical Engineers, Vol. 71, No. 711, 2005, pp. 1530). Is possible.

  The maximum value of tensile stress in the thickness direction formed inside the steel plate can be controlled by adjusting the laser output without changing the optical conditions such as the focal length of the condenser lens. The maximum value of tensile stress with respect to the direction increases.

  In this test, water was selected as the laser absorption layer, but any of plastic tape, black paint, metal foil, etc. may be used. The underwater laser irradiation method used in this test is called laser peening and is known as a method for improving fatigue characteristics of welded structures such as bridge girders and undercarriage parts of automobiles. However, the laser irradiation condition in this case is characterized in that the entire surface of the steel sheet is irradiated. On the other hand, in this test, as shown in FIG. 7, irradiation is performed so that irradiation pulses overlap in a direction perpendicular to the rolling direction of the steel sheet at an irradiation interval (pitch) of 5.0 mm in the rolling direction of the steel sheet. It is different from the irradiation conditions used for improving the characteristics.

  As is clear from FIG. 5, in order to obtain a unidirectional electromagnetic steel sheet having an excellent iron loss value (W17 / 50), the maximum value of the tensile stress in the thickness direction in the steel sheet must be 40 MPa or more. I understand. Here, the stress in the rolling direction and the stress in the sheet width direction are about several Mpa, which is smaller than the tensile stress in the sheet thickness direction, and no correlation with the iron loss characteristics was obtained.

  The Δ values in FIG. 5 indicate the conventional laser irradiation conditions, that is, pulse laser is irradiated in the air, the pulse interval is 0.3 mm in the rolling direction of the steel plate, 5.0 mm in the direction perpendicular to the rolling direction of the steel plate. The iron loss value of the steel plate irradiated on pitch conditions is shown. At this time, the tensile stress value in the plate thickness direction inside the steel plate was about 6 Mpa, which was smaller than the tensile stress value in the plate thickness direction inside the steel plate introduced according to the present invention, and there was no correlation with iron loss. Further, the stress in the rolling direction is compression, the magnitude is 35 MPa, the stress in the sheet width direction is several MPa, and the stress state in the present invention and the conventional steel sheet is different.

  As shown in FIG. 5, the iron loss increases from the vicinity where the maximum value of the tensile stress exceeds 300 MPa. This is presumably because when the maximum value of the tensile stress increases, the plastic region increases, so that the domain wall is pinned to the plastic region and the hysteresis loss increases. Therefore, by introducing tensile stress in the thickness direction inside the steel sheet, magnetic domain subdivision, that is, eddy current loss is reduced, but hysteresis loss increases, so total loss including eddy current loss and hysteresis loss is reduced. do not do. In general, the point at which the stress state changes greatly from the elastic region to the plastic region can be defined by the yield stress of the material. Although the yield stress of the material depends on the composition, for example, the yield stress of the unidirectional electrical steel sheet having the composition of Fe-3% Si is about 350 MPa, so that the stress value with the increased iron loss in FIG. Trends agree.

  For the above reasons, in the present invention, the maximum value of the tensile stress in the thickness direction inside the thickness is required to be 40 MPa or more and not more than the yield stress value of the material.

  The present invention can achieve a unidirectional electrical steel sheet excellent in low iron loss characteristics according to the above-described embodiment. However, in addition to these invention embodiments, the present invention can be stabilized by further defining the following conditions. Can improve low iron loss characteristics.

  FIG. 8 shows the distribution width extending in the plate thickness direction (plate width) with respect to the stress distribution defined above, that is, the stress distribution in which the maximum value of the tensile stress in the plate thickness direction is 40 MPa or more and less than the yield stress value of the material. It is a graph showing the relationship between the ratio to the thickness (see FIG. 7) and the distribution width (see FIG. 7) extending in the rolling direction and the iron loss (W17 / 50). From FIG. 8, in order to achieve a unidirectional electrical steel sheet with more excellent iron loss characteristics, the distribution width in the rolling direction is 0.8 mm or less, and the distribution width in the sheet thickness direction (ratio to the sheet thickness) is It is necessary to be 80% or less. As described above, the upper limit of the width of the stress distribution is required because the stress distribution of the stress value defined in the present invention increases, so that the number of strains, defects, etc. increases, which hinders the domain wall movement, and the hysteresis loss. This is because of the increase.

  From the above, in the present invention, in addition to the requirements stipulated in the above embodiment, the region where tensile stress is present has a distribution width in the rolling direction of 0.8 mm or less, and a distribution in the plate thickness direction. The width (ratio to the plate thickness) is preferably 80% or less.

  In the embodiment of the present invention, the interval in the rolling direction of the region where the tensile stress in the plate thickness direction inside the plate thickness exists affects the magnetic domain fragmentation due to the interaction between the adjacent regions. If it is too large, the effect of reducing iron loss is reduced. That is, when the space between adjacent regions in which tensile stress exists increases, the surface area of the 180-degree domain wall shown in the conceptual diagram of FIG. 9 increases, leading to an increase in domain wall energy. Generally, since the domain wall energy is inversely proportional to the size of the 180-degree domain width, an increase in the surface area of the domain wall blunts the subdivision of the 180-degree domain.

  FIG. 10 shows that the maximum value of the tensile stress in the plate thickness direction within the plate thickness is 40 Mpa, and the iron loss (W17) when the interval between adjacent regions in the rolling direction in which the stress exists is changed. / 50) is a graph showing a change. As shown in FIG. 10, the eddy current loss is reduced at 7.0 mm or less, and the iron loss characteristic is stably reduced.

  As described above, even when the maximum value of the tensile stress in the thickness direction inside the thickness of the present invention is under the optimum condition, the interval in the rolling direction in the region where the tensile stress exists exceeds 7.0 mm. Therefore, it was confirmed that the magnetic domain fragmentation effect 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 above embodiment, it is preferable that the interval where the tensile stress exists is 7.0 mm or less.

  In the embodiment of the present invention, the belt-like range where the stress state in the thickness direction exists in the thickness is preferably substantially perpendicular to the rolling direction of the steel plate as shown in FIG. However, at the time of actual production, since the stress inside the steel sheet is formed while being wound around the coil, it is confirmed that the direction of the belt-shaped range to which the stress is applied is displaced with respect to the rolling direction of the steel sheet. did.

  As described above, the unidirectional electrical steel sheet before the magnetic domain control is ideally made of (110) [001] oriented grains having an easy axis of magnetization in the rolling direction in order to reduce iron loss. It is desirable that the textured steel plate is configured. 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. As described above, in order to reduce the iron loss by subdividing the magnetic domain of the unidirectional electrical steel sheet, it is effective to form a belt-shaped range in the magnetization direction of the steel sheet, that is, in the direction perpendicular to the easy axis of magnetization. Conceivable.

  FIG. 11 shows a unidirectional electrical steel sheet in which the stress value and distribution defined by the present invention are formed using the above-described laser irradiation method in water, and the interval between the regions where the stress state exists is 5 mm. Is a graph showing the correlation with the iron loss when the angle with respect to the rolling direction of the strip-shaped range where the tensile stress in the thickness direction in the thickness of the sheet exists. In FIG. 12, the conceptual diagram for demonstrating the angle with respect to the said strip | belt-shaped range and a rolling direction is shown. FIG. 11 shows that when the band-shaped range is formed in the direction of 60 to 120 ° with respect to the rolling direction, the iron loss can be sufficiently reduced by the effect of magnetic domain subdivision. The above-mentioned angle range corresponds to an ideal easy axis direction, that is, a range within 30 ° in deviation angle from a direction perpendicular to the rolling direction of the steel sheet. Beyond this angle range, the magnetic domain subdivision action of the steel sheet is reduced, so there is a tensile stress in the sheet thickness direction inside the sheet thickness in order to improve the iron loss value more stably than before. It is preferable that the direction of the belt-shaped range to be made is a direction of 60 to 120 ° with respect to the rolling direction.

  Therefore, in this invention, it is preferable that the strip | belt-shaped range where the tensile stress with respect to the plate | board thickness direction inside a plate | board thickness exists exists in the direction which makes an angle of 60-120 degrees with respect to a steel plate rolling direction.

  In addition, regarding the space | interval between stress area | regions shown above and the angle of the introduction | transduction area | region, patent document 3 has description regarding the space | interval and angle about the groove | channel processed into the steel plate surface. However, the present invention achieves low iron loss by applying strain or stress to the inside of the plate thickness and controlling the tensile stress in the plate thickness direction. It is completely different from the technology to do.

Using a unidirectional electrical steel sheet having a thickness of 0.23 mm, this steel sheet was placed in water and irradiated with a pulse YAG laser having a beam diameter of 150 μm so that the irradiation pulses overlapped. By adjusting the output of this laser, as shown in Table 1, the maximum value of the tensile stress in the plate thickness direction within the plate thickness, the distribution width in the rolling direction and the distribution in the plate thickness direction within the plate thickness of this stress distribution. Measurement of iron loss W17 / 50 of each steel sheet after manufacturing unidirectional electrical steel sheets with different width (against plate thickness ratio), spacing in the rolling direction in the region where the stress is present, and angle in the rolling direction in the region. Went. The tensile stress in the thickness direction within the thickness in Table 1 is an applied value obtained by measuring the strain of the crystal lattice in the three directions by the X-ray diffraction method and using the physical properties such as the elastic modulus as described above. Converted to Moreover, the iron loss value measured the iron loss W17 / 50 at the time of frequency 50Hz and magnetic flux density 1.7T using the single plate magnetic apparatus.

  As is apparent from Table 1, test no. In any of the unidirectional electrical steel sheets shown in 1 to 7 (examples of the present invention), the maximum value of the tensile stress in the sheet thickness direction within the sheet thickness is within the range defined by the present invention. No. A unidirectional electromagnetic steel plate excellent in low iron loss characteristics as compared with 8 to 10 (comparative example) was obtained.

  In addition, the above test No. Among 1 to 7 (examples of the present invention), in addition to the maximum value of the tensile stress in the plate thickness direction inside the plate thickness, the distribution width in the rolling direction and the distribution in the plate thickness direction inside the plate thickness of this stress distribution The width (against the plate thickness ratio), the stress-existing region with respect to the rolling direction of the steel plate (the region in which the tensile stress with respect to the plate thickness direction within the plate thickness exists), the angle in the rolling direction, and the angle of the same region with respect to the rolling direction are within the preferred ranges. Test No. 1-3 (invention example) was able to reduce iron loss more compared with test No. 4-7 (invention example).

The conceptual diagram which shows the lancet magnetic domain which arises in a steel plate. The conceptual diagram which shows the magnetic domain structure which arises in a steel plate. The conceptual diagram which shows the stress state introduce | transduced into the steel plate of this invention. The conceptual diagram which shows distribution of the magnetization changed with the stress introduce | transduced according to this invention. The graph which shows the relationship between the maximum value of the tensile stress with respect to the plate | board thickness direction formed in the steel plate inside, and an iron loss. The conceptual diagram which shows arrangement | positioning of the steel plate sample in the case of measuring the stress value of 3 directions inside a plate | board thickness using a X-ray diffraction method. The conceptual diagram which shows one Embodiment in which the tensile stress with respect to the plate | board thickness direction formed in the steel plate of this invention was formed. The graph which shows the relationship between the distribution width | variety of the rolling direction of the tensile stress of the plate | board thickness direction in a plate | board thickness direction, the distribution width | variety (plate thickness ratio) in a plate | board thickness direction, and an iron loss. The conceptual diagram which shows the surface area of the 180 degree | times domain wall which exists in the space | interval which each adjoins the area | region where tensile stress exists. The graph which shows the relationship between each adjacent space | interval of the area | region where tensile stress exists, and an iron loss. The graph which shows the relationship between the angle with respect to the rolling direction of a strip | belt-shaped range where the tensile stress of a plate | board thickness direction exists, and an iron loss. The conceptual diagram for demonstrating the angle which the area | region where tensile stress exists, and the rolling direction make.

Claims (4)

  The low iron loss is characterized in that the stress in the thickness direction is tensile stress at one or a plurality of locations inside the thickness of the steel plate, and the maximum value is 40 MPa or more and less than the yield stress value of the steel plate material. Oriented electrical steel sheet.   The distribution width in the rolling direction in the region where the tensile stress exists is 0.8 mm or less, and the distribution width in the plate thickness direction is 80% or less of the plate thickness. Low iron loss unidirectional electrical steel sheet.   The low iron loss unidirectional electrical steel sheet according to claim 1 or 2, wherein the region where the tensile stress exists has an interval of 7.0 mm or less in a rolling direction of the steel sheet.   The region in which the tensile stress exists is formed continuously or at a predetermined interval in a direction of 60 to 120 ° with respect to the rolling direction of the steel sheet. Iron loss unidirectional electrical steel sheet.

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