Title of invention: grain-oriented electrical steel sheet
Technical field
[0001]
　The present invention relates to grain-oriented electrical steel sheets.
　The present application claims priority based on Japanese Patent Application No. 2018-032552 filed in Japan on February 26, 2018, the contents of which are incorporated herein by reference.
Background technology
[0002]
　There is a grain-oriented electrical steel sheet in which magnetic domains are subdivided by grooves formed on the surface by laser processing (see, for example, Patent Document 1). This grain-oriented electrical steel sheet is used, for example, for a winding iron core of a winding transformer (transformer). In the wound steel core, a plurality of grain-oriented electrical steel sheets are wound in a laminated state.
[0003]
　In the winding transformer manufacturing process, strain removing annealing is performed to remove the deformation strain (bending strain) of the wound iron core. In strain relief annealing, for example, the wound iron core is heated to about 800 ° C.
Prior art literature
Patent documents
[0004]
Patent Document 1: Japanese Patent No. 5234222
Outline of the invention
Problems to be solved by the invention
[0005]
　However, if the wound core formed by the grain-oriented electrical steel sheet having grooves formed on the surface by laser processing is strain-removed and annealed, the iron loss of the electrical steel core (oriented electrical steel sheet) may deteriorate (increase). ..
[0006]
The inventor of the present application studied a wound steel core made of a grain-formed directional electromagnetic steel sheet. When the groove was formed by laser processing, a strain was generated in the steel plate structure at the bottom of the groove, and this strain was finally applied to the wound steel core. It was found that it affects iron loss. Furthermore, the present inventor has found that the iron loss of the wound iron core can be reduced by controlling this strain, and has reached the present invention.
[0007]
In consideration of the above facts, an object of the present invention is to suppress deterioration of iron loss of a wound iron core due to strain relief annealing in a winding transformer manufacturing process.
Means to solve problems
[0008]
The present invention has been completed based on the above findings, and the gist thereof is as follows.
The grain-oriented electrical steel sheet according to the first aspect is a grain-oriented electrical steel sheet having a groove formed on its surface, in a cross section of the grain-oriented electrical steel sheet orthogonal to the groove, in the thickness direction of the grain-oriented electrical steel sheet with respect to the groove. The KAM value in the region on the central side and in the region surrounded by a square having a side in contact with the bottom of the groove and a side length of 50 μm is 0.1 or more and 3.0 or less. It is a feature.
In the grain-oriented electrical steel sheet according to this embodiment, it is preferable that the groove is a laser groove.
　In the grain-oriented electrical steel sheet according to this embodiment, the KAM value is preferably 0.1 or more and 2.0 or less.
Effect of the invention
[0009]
　According to the above aspect, in the manufacturing process of the winding transformer, deterioration of iron loss of the wound iron core due to strain removing annealing can be suppressed.
A brief description of the drawing
[0010]
[Fig. 1] Fig. 1 is a cross-sectional photograph including a grooved portion in a surface layer portion of a grain-oriented electrical steel sheet constituting a strain-removed annealed wound steel core.
FIG. 2 is a graph showing the results of analysis by EBSD (Electron BackScatter Diffraction) regarding the crystal orientation difference at the analysis position of the grain-oriented electrical steel sheet shown in FIG.
FIG. 3 is a cross-sectional view schematically showing the structure of a groove peripheral region in a grain-oriented electrical steel sheet before strain removal and annealing (before SRA).
FIG. 4 is a schematic diagram showing pixels used for EBSD mapping.
[Fig. 5] Fig. 5 shows the KAM value of the area around the groove of the grain-oriented electrical steel sheet before strain annealing, the iron loss improvement rate of the wound steel core after strain annealing, and the simple before strain annealing. It is a graph which shows the relationship with the iron loss improvement rate (SST improvement rate) of a plate.
[Fig. 6] Fig. 6 shows the plate tension in the laser groove forming process, the iron loss improvement rate of the wound iron core after strain removal annealing, and the iron loss improvement rate of the single plate before strain removal annealing (SST improvement rate). ) Is a graph showing the relationship with.
[Fig. 7] Fig. 7 shows the KAM value of the region around the groove of the grain-oriented electrical steel sheet before strain annealing, the iron loss improvement rate of the wound steel core after strain annealing, and the simple before strain annealing. It is a graph which shows the relationship with the iron loss improvement rate (SST improvement rate) of a plate.
[Fig. 8] Fig. 8 shows the cooling rate of the insulating film forming process, the iron loss improvement rate of the wound core after strain annealing, and the iron loss improvement rate of the single plate before strain annealing (SST improvement rate). It is a graph which shows the relationship with.
[Fig. 9] Fig. 9 shows the KAM value of the area around the groove of the grain-oriented electrical steel sheet before strain annealing, the iron loss improvement rate of the wound steel core after strain annealing, and the simple before strain annealing. It is a graph which shows the relationship with the iron loss improvement rate (SST improvement rate) of a plate.
Mode for carrying out the invention
[0011]
Hereinafter, embodiments of the grain-oriented electrical steel sheet according to the present invention will be described. The embodiments described below are described for better understanding of the gist of the present invention, and the grain-oriented electrical steel sheets according to the present invention are not limited to the description of the following embodiments.
　Hereinafter, one embodiment will be described with reference to the drawings.
[0012]
(Directional Magnetic Steel Sheet)
　The grain-oriented electrical steel sheet of this embodiment is an electrical steel sheet in which the easy axes of magnetization of crystal grains (<100> direction of body-centered cubic crystals) are substantially aligned in the rolling direction described later. Further, the grain-oriented electrical steel sheet has a plurality of magnetic domains whose magnetization is oriented in the rolling direction.
[0013]
　A plurality of grooves are formed on the surface of the grain-oriented electrical steel sheet of this embodiment by laser processing. The plurality of grooves extend in the width direction of the grain-oriented electrical steel sheet and are arranged at intervals in the rolling direction. The magnetic domains of the grain-oriented electrical steel sheet are subdivided by these grooves. This grain-oriented electrical steel sheet tends to be magnetized in the rolling direction described later. Therefore, it is suitable for the winding iron core (iron core material) of the winding transformer in which the direction in which the magnetic field lines flow is substantially constant. In the wound steel core, for example, a plurality of grain-oriented electrical steel sheets are wound in a laminated state.
[0014]
　The steel plate body of the grain-oriented electrical steel sheet of this embodiment is made of an iron alloy containing Si.
As an example, the composition of the steel plate body is Si; 2.0% by mass or more and 4.0% by mass or less, C; 0.003% by mass or less, Mn; 0.05% by mass or more and 0.15% by mass or less, and acid soluble. Al; 0.003% by mass or more and 0.040% by mass or less, N; 0.002% by mass or less, S; 0.020% by mass or less, and the balance is Fe and impurities. The thickness of the steel plate body is, for example, 0.15 mm or more and 0.35 mm or less.
[0015]
　The surface of the steel sheet body is coated with a glass coating. The glass coating is composed of composite oxides such as forsterite (Mg 2 SiO 4 ), spinel (Mg Al 2 O 4 ) and cordierite (Mg 2 Al 4 Si 5 O 18 ). The thickness of this glass coating is, for example, 1 μm.
[0016]
　The glass coating is further coated with an insulating coating. The insulating coating is, for example, an insulating coating agent (coating liquid) mainly composed of colloidal silica and phosphate (magnesium phosphate, aluminum phosphate, etc.), or an insulating coating agent (coating liquid) in which alumina sol and boric acid are mixed. It is composed of.
[0017]
(Method of manufacturing grain-oriented electrical steel sheet)
　Next, an example of a method of manufacturing grain-oriented electrical steel sheet will be described. The manufacturing method of the directional electromagnetic steel sheet is, for example, a casting process, a hot rolling process, an annealing process, a cold rolling process, a decarburization annealing process, an annealing separator coating process, a final finish annealing process, an insulating coating agent coating process, and a flat surface. It includes a chemical annealing step, a laser groove forming step, a heat treatment step, and a reinsulating film forming step.
[0018]
(Casting process-annealing process)
　First, in the casting process (continuous casting process), slabs are formed by continuous casting.
Next, in the hot rolling step, the slab is hot rolled to form a hot rolled steel sheet having a predetermined thickness. Next, in the annealing step, the hot-rolled steel sheet is annealed at a predetermined temperature, for example, 1100 ° C.
[0019]
(Cold Rolling Step)
　Next, in the cold rolling step, the hot rolled steel sheet is stretched in a predetermined direction (hereinafter referred to as "rolling direction") to form a steel sheet having a predetermined thickness (cold rolled steel sheet). Will be done. The rolling direction coincides with the longitudinal direction of the cold-rolled steel sheet (oriented electrical steel sheet).
[0020]
(Decarburization Annealing Step)
　Next, in the decarburization annealing step, the cold-rolled steel sheet is decarburized and annealed (continuous annealing) at a predetermined temperature (for example, 700 ° C. to 900 ° C.). As a result, the cold-rolled steel sheet is decarburized, and primary recrystallization (crystal grain size: 10 to 30 μm) occurs in the cold-rolled steel sheet. Further, if necessary, the steel sheet can be nitrided by heat treatment in an ammonia-containing atmosphere during decarburization annealing or after decarburization annealing (for example, 150 to 300 ppm).
[0021]
(Annealing Separant Coating Step)
　Next, in the annealing separating agent coating step, an annealing separator containing MgO as a main component is applied to the surface of the cold-rolled steel sheet. After that, the cold-rolled steel sheet is wound into a coil.
[0022]
(Final Finish Annealing Step)
　Next, in the final finishing annealing step, the cold-rolled steel sheet wound in a coil shape is annealed at a predetermined temperature (for example, about 1200 ° C.) and for a predetermined time (for example, about 20 hours). (Batch annealing). As a result, secondary recrystallization occurs in the cold-rolled steel sheet, a crystal orientation in which the easily magnetized axes are substantially aligned in the rolling direction is generated, and a glass film is formed on the surface of the cold-rolled steel sheet. As a result, a grain-oriented electrical steel sheet is formed. After that, the coiled grain-oriented electrical steel sheet is unwound.
[0023]
　Here, the cold-rolled steel sheet contains, for example, an inhibitor such as MnS or AlN. As a result, in the final finish annealing step, crystal grains in the Goth orientation in which the axes of easy magnetization are substantially aligned in the rolling direction are preferentially grown. As a result, a grain-oriented electrical steel sheet having high crystal orientation (crystal orientation) is formed.
[0024]
(Insulating coating agent coating step)
　Next, in the insulating coating agent coating step, an insulating coating agent (coating liquid) having electrical insulation and capable of applying a predetermined tension to the surface of the directional electromagnetic steel plate is directional electromagnetic. It is applied to the surface of the steel plate.
[0025]
(Flatration Annealing Step)
　Next, in the flattening annealing step, the directional electromagnetic steel sheet is conveyed at a predetermined temperature (for example, 800 ° C. to 850 ° C.) and for a predetermined time (for example, 10 seconds or more) while being conveyed by the conveying device. It is annealed (flattened and annealed) in 120 seconds or less). At this time, tension (passing tension) is applied to the grain-oriented electrical steel sheet in the rolling direction (longitudinal direction) of the grain-oriented electrical steel sheet from the transport device. As a result, curl and strain of the cold-rolled steel sheet during final finish annealing are removed, and the grain-oriented electrical steel sheet is flattened.
[0026]
　Further, in the flattening annealing step, when the grain-oriented electrical steel sheet is annealed, the insulating coating agent is baked on the surface of the grain-oriented electrical steel sheet, and the surface of the grain-oriented electrical steel sheet is coated with the insulating coating agent. After that, the grain-oriented electrical steel sheet is cooled.
[0027]
(Laser Groove Forming Step)
　Next, in the laser groove forming step, a plurality of grooves (laser grooves) are formed on the surface of the grain-oriented electrical steel sheet conveyed by the conveying device by laser processing. Specifically, the grain-oriented electrical steel sheet is transported to the laser irradiation device by the transport device.
At this time, a tension (plate tension) of 2 MPa or more and 15 MPa or less is applied to the grain-oriented electrical steel sheet in the rolling direction (longitudinal direction) of the grain-oriented electrical steel sheet from the transport device. In this state, the laser beam emitted from the laser irradiation device irradiates (scans) the surface of the grain-oriented electrical steel sheet along the width direction of the grain-oriented electrical steel sheet. The plate tension is more preferably in the range of 2 MPa or more and 9 MPa or less.
[0028]
　Further, the laser grooves are formed at predetermined intervals (pitch) in the rolling direction of the grain-oriented electrical steel sheet. As a result, the magnetic domains of the grain-oriented electrical steel sheet are subdivided by the plurality of laser grooves, and the iron loss of the grain-oriented electrical steel sheet is reduced.
[0029]
　The type of laser beam is, for example, a fiber laser, a YAG laser, or a CO 2 laser. The wavelength of the laser beam is, for example, 1070 to 1090 nm or 10.6 μm. Further, the depth of each groove is set to, for example, 20 μm. The width of the groove is, for example, 50 μm. Further, the groove spacing (pitch) is set to, for example, 3 mm.
[0030]
(Reinsulating film forming step) In
　the laser groove forming step described above, the insulating film covering the surface of the grain-oriented electrical steel sheet is partially removed. Therefore, in the reinsulation coating forming step, the surface of the grain-oriented electrical steel sheet is again insulated.
[0031]
　Specifically, an insulating coating agent (coating liquid) having electrical insulating properties and capable of applying a predetermined tension to the surface of the steel sheet is applied to the surface of the grain-oriented electrical steel sheet. The grain-oriented electrical steel sheet coated with the insulating coating agent is heated to a predetermined temperature (for example, 800 ° C. to 850 ° C.) and then cooled. As a result, the insulating coating agent is baked onto the surface of the grain-oriented electrical steel sheet, and the surface of the grain-oriented electrical steel sheet is coated with the insulating coating agent. As a result, a grain-oriented electrical steel sheet is manufactured. The reinsulating film forming step is an example of the insulating film forming step.
[0032]
　After that, the grain-oriented electrical steel sheet is cooled at, for example, 20 ° C./s or more and 100 ° C./s or less. As a result, the grain-oriented electrical steel sheet is manufactured.
　In this reinsulation film forming step, by cooling at 20 ° C./s or more and 100 ° C./s or less, the grain-oriented electrical steel sheet having a KAM value of 0.1 or more and 0.3 or less in the above-mentioned groove peripheral region can be obtained. can get.
[0033]
　The cooling rate of the grain-oriented electrical steel sheet is adjusted by, for example, the amount of coolant or cooling air injected onto the grain-oriented electrical steel sheet, or the transport speed of the grain-oriented electrical steel sheet. The reinsulating film forming step is an example of the insulating film forming step.
[0034]
(Effect)
　Next, the effect of the present embodiment will be described.
　The grain-oriented electrical steel sheet manufactured by the method for manufacturing grain-oriented electrical steel sheet according to the present embodiment is used, for example, as a winding iron core of a winding transformer. In the wound steel core, a plurality of grain-oriented electrical steel sheets are wound in a laminated state.
[0035]
　In the winding transformer manufacturing process, strain relief annealing (SRA: Stress Relief Anealing) is performed to remove the deformation strain (bending strain) of the wound iron core. In strain relief annealing, for example, the wound iron core is heated to about 800 ° C.
However, when the wound steel core formed by the grain-oriented electrical steel sheet having grooves formed on the surface by laser processing is strain-removed and annealed, the iron loss of the electrical steel core (oriented electrical steel sheet) deteriorates (increases).
[0036]
　Specifically, FIG. 1 shows the cross-sectional structure of the wound iron core 20 that has been strain-removed and annealed at 800 ° C. for 2 hours in the winding transformer manufacturing process. The wound iron core 20 is formed of a grain-oriented electrical steel plate 10 having a groove 12 formed on the surface 10A in the laser groove forming step. Note that FIG. 1 shows a microstructure photograph of a cross section orthogonal to a groove 12 formed on the surface 10A of the grain-oriented electrical steel sheet 10 constituting the wound steel core 20.
[0037]
　As shown in FIG. 1, when the wound iron core 20 formed by the directional electromagnetic steel plate 10 having the groove 12 formed on the surface 10A by laser processing is strain-removed and annealed, the thickness direction of the directional electromagnetic steel plate 10 with respect to the groove 12 Subgrain boundaries 14 are generated on the central side (arrow X side). The subgrain boundary means a low-angle grain boundary having an orientation difference (crystal orientation difference) of 15 ° or less.
[0038]
　Further, FIG. 2 shows the analysis result of the crystal orientation difference on the central side in the thickness direction of the grain-oriented electrical steel sheet 10 with respect to the groove 12. In this analysis, the cross section perpendicular to the steel plate surface including the rolling direction of the directional electromagnetic steel plate 10 shown in FIG. 1 is polished with colloidal silica or colloidal alumina almost without strain, and at a plurality of analysis points on the analysis position P, the cross section is polished. The crystal orientation difference was analyzed by EBSD (Electron BackScatter Diffraction).
[0039]
　The horizontal axis of the graph shown in FIG. 2 is the measurement point number from the left side of the measurement points of the crystal orientation arranged at equal intervals on the analysis position P of FIG. The vertical axis of the graph shown in FIG. 2 is the crystal orientation difference (deg) at each analysis point. The crystal orientation difference was an integral value from a reference point (origin) where the subgrain boundary 14 does not exist.
　The measurement points for which these integral values ​​were obtained are located at a depth position 5 μm away from the concave groove 12 shown in FIG. 1 in the X direction (direction toward the center in the thickness direction of the grain-oriented electrical steel sheet). I set it. Further, at this depth position, 29 measurement points were set at equal intervals (2 μm intervals) with respect to the range corresponding to the groove width along the direction parallel to the surface of the steel sheet.
As shown in FIG. 1, since regions having different hues from the surroundings, which are considered to be subgrain boundaries 14, are generated below the groove 12, the measurement points on the leftmost side of these measurement points are subgrain boundaries. It is determined that 14 does not exist as a reference point.
[0040]
　As shown in FIG. 2, in the region R surrounded by the alternate long and short dash line, the crystal orientation difference is 3 to 5 (deg). From this, it can be seen that the subgrain boundaries 14 (see FIG. 1) were generated on the central side (arrow X side) of the grain-oriented electrical steel sheet 10 with respect to the groove 12 in the thickness direction.
Then, when the subgrain boundaries 14 are generated on the central side of the grain-oriented electrical steel sheet 10 with respect to the groove 12 in the thickness direction, the iron loss of the wound steel core 20 (oriented electrical steel sheet 10) deteriorates as can be seen from the test results described later. ..
[0041]
On the other hand, FIG. 3 schematically shows a cross section of the grain-oriented electrical steel sheet 10 before being strain-removed and annealed. Grooves 12 are formed on the surface 10A of the grain-oriented electrical steel sheet 10 by laser processing. In the grain-oriented electrical steel sheet 10, the KAM value in the region (hereinafter, referred to as “groove peripheral region”) 16 on the center side (arrow X side) in the thickness direction of the grain-oriented electrical steel sheet 10 with respect to the groove 12 increases.
[0042]
Note that FIG. 1 is a cross section orthogonal to the groove 12 on the surface 10A of the grain-oriented electrical steel sheet 10. That is, FIG. 1 is a cross section of the grain-oriented electrical steel sheet 10 cut along the width direction. Further, the groove peripheral region 16 is, for example, a region on the central side (arrow X side) in the thickness direction of the grain-oriented electrical steel sheet 10 with respect to the groove 12 in the cross section of the grain-oriented electrical steel sheet 10 shown in FIG. Means a region in contact with the groove bottom 12A of the groove 12 and surrounded by a square having a side length of 50 μm.
[0043]
　Further, the groove bottom 12A of the groove 12 referred to here means the deepest portion (deepest portion) of the groove 12. Further, when one side of the square is in contact with the groove bottom 12A of the groove 12, the one side of the square is parallel to the surface 10A of the grain-oriented electrical steel sheet 10, and the one side is the groove bottom 12A (deepest part) of the groove 12. It means the state of contact.
[0044]
　For the measurement of the KAM (Kernel Average Misorientation) value, as an example, the above-mentioned cross section of the directional electromagnetic steel plate 10 is subjected to strain-free cross-sectional processing by ion milling or the like, and the FE-SEM (Field Emission-Scanning Electron Microscope) EBSD ( The crystal orientation difference can be analyzed and obtained by Electron BackScatter Diffraction).
At this time, for example, as shown in FIG. 4, it can be obtained by using the hexagonal pixel C and mapping the groove peripheral region 16 shown in FIG.
For example, a particular pixel C A and six pixels C adjacent to the pixel B to calculate the average value of the azimuth difference between the average value given pixel C A may be a KAM value. Then, a step size of, for example, about 0.1 to 1 μm is defined in the groove peripheral region 16, the probe diameter is set to 10 nm, and a considerable number, for example, 10,000 KAM values ​​are calculated in the groove peripheral region 16. The KAM value of the groove peripheral region 16 can be determined by adopting the maximum value among them.
When determining the KAM value in this way, the pixels used are not limited to the hexagonal pixel C shown in FIG. 4, and pixels of other shapes such as a square may be used.
[0045]
　Here, as can be seen from the test results described later, the wound steel core formed by the grain-oriented electrical steel sheet 10 in which the KAM value of the groove peripheral region 16 exceeds 3.0 is strain-removed and annealed in the winding transformer manufacturing process. Then, a subgrain boundary 14 is generated on the central side in the thickness direction of the grain-oriented electrical steel sheet 10 with respect to the groove 12, and the iron loss of the wound steel core may be deteriorated.
[0046]
　On the other hand, even if the wound steel core formed by the grain-oriented electrical steel sheet 10 having a KAM value of 0.1 or more and 3.0 or less in the groove peripheral region 16 is strain-removed and annealed in the winding transformer manufacturing process, the direction with respect to the groove 12 Subgrain boundaries generated on the central side of the electrical steel sheet 10 in the thickness direction are reduced, and the iron loss of the wound steel core is not deteriorated.
[0047]
　Therefore, in the present embodiment, in the laser groove forming step, 2 MPa or more is applied to the grain-oriented electrical steel sheet 10 so that the KAM value in the groove peripheral region 16 of the grain-oriented electrical steel sheet 10 is 0.1 or more and 3.0 or less. , Apply a plate tension of 15 MPa or less.
[0048]
　Further, in the present embodiment, the cooling rate of the grain-oriented electrical steel sheet 10 in the flattening annealing step is such that the KAM value in the groove peripheral region 16 of the grain-oriented electrical steel sheet 10 is 0.1 or more and 3.0 or less. Is adjusted to 20 ° C./s or higher and 100 ° C./s or lower.
[0049]
　As a result, even if the wound core is strain-removed and annealed in the winding transformer manufacturing process, deterioration of iron loss in the wound core (oriented electrical steel sheet 10) can be suppressed.
Example
[0050]
　Next, an embodiment will be described.
　In this example, the KAM value of the groove peripheral region of the grain-oriented electrical steel sheet in which the groove was formed on the surface by laser processing was measured.
[0051]
　Next, a 25 KVA single-layer wound steel core was prepared from the grain-oriented electrical steel sheet whose KAM value was measured. Then, the produced core was strained and annealed, and the iron loss of the wound core (oriented electrical steel sheet) was measured. When a similar wound steel core was made of a grain-oriented electrical steel sheet having no groove formed on the surface, the transformer iron loss was 36 W. The iron loss of the wound iron core due to the grain-oriented electrical steel sheet that does not form this groove is used as a reference value, and the KAM value is compared with the iron loss of the wound steel core due to the measured grain-oriented electrical steel sheet. %) Was asked.
[0052]
　Next, the cross section of the wound core that was strain-removed and annealed was analyzed, and the presence or absence of subgrain boundaries was confirmed.
(Directional Electromagnetic Steel Sheet) The
　grain-oriented electrical steel sheet was manufactured by the same manufacturing method as in the above embodiment. In the reinsulation film forming step, the heating temperature (baking temperature) of the grain-oriented electrical steel sheet was set to 800 ° C. to 850 ° C., and the cooling rate of the grain-oriented electrical steel sheet was set to 20 ° C./s or more and 100 ° C./s or less.
[0053]
　The grain-oriented electrical steel sheet has a Si amount of 3.3%, a plate thickness of 0.23 mm, a B8 of 1.930 T, and W17 / 50 = 0.860 w / kg. Note that B8 means the magnetic flux density [T] generated in the grain-oriented electrical steel sheet when the grain-oriented electrical steel sheet is magnetized in the rolling direction by a magnetization force of 800 A / m.
[0054]
(Laser Groove Machining Conditions) Further
　, in the laser groove forming step, the machining conditions of the grooves (laser grooves) formed on the surface of the grain-oriented electrical steel sheet are as follows.
　Laser beam type: Fiber laser
　Laser beam wavelength: 1080 nm
　Laser beam output: 1000 W
　Laser beam diameter: 0.1 x 0.3 mm
　Laser beam scanning speed: 30 m / s
　Groove spacing (pitch): 3 mm
　Groove Depth: 20 μm
　Groove width: 50 μm
　Passing tension of directional electromagnetic steel plate: 2 MPa or more, 15 MPa or less
[0055]
(Measurement of KAM Value)
　As described above, FIG. 3 shows a cross section of a grain-oriented electrical steel sheet 10 in which a groove 12 is formed on the surface 10A by laser processing. In the cross section of the grain-oriented electrical steel sheet 10, the KAM value in the groove peripheral region 16 on the center side (arrow X side) in the thickness direction of the grain-oriented electrical steel sheet 10 with respect to the groove 12 was measured. The KAM value is an index showing the degree of relative difference in the orientations of adjacent crystal grains in a predetermined cross section of a grain-oriented electrical steel sheet.
[0056]
　In the measurement of KAM (Kernel Average Misorientation) value, the cross section of the directional electromagnetic steel plate 10 is subjected to strain-free cross-sectional processing by ion milling or the like, and is subjected to EBSD (Electron BackScatter Diffraction) of FE-SEM (Field Emission-Scanning Electron Microscope). The crystal orientation difference was analyzed. At this time, as shown in FIG. 4, the hexagonal pixel C was used to map the groove peripheral region 16.
Then, a given pixel C A and, the pixel C A 6 a pixel C adjacent to B an average value of the azimuth difference between the calculated and the average value given pixel C A was KAM values. Then, the maximum value of the KAM value of the pixel C in the groove peripheral region 16 was set as the KAM value of the groove peripheral region 16.
[0057]
　The step size S of the pixel C is, for example, 0.1 to 1 μm. The probe diameter was 10 nm. In this example, the step size was set to 0.5 μm. Therefore, KAM values ​​at 10,000 locations were calculated for the above-mentioned groove peripheral region 16, and the maximum values ​​thereof were used as the KAM values ​​of the groove peripheral region 16.
[0058]
(Iron loss improvement rate of
　wound steel core ) The iron loss improvement rate η of the wound iron core is the iron loss W0 of the wound steel core formed by the grain-oriented electrical steel sheet without grooves and the direction in which the grooves are formed by laser processing. The iron loss Wg of the wound iron core formed of the electrical steel sheet was obtained and calculated from the following formula (1).
　η = (W0-Wg) / W0 × 100 ・ ・ ・ Equation (1)
[0059]
　The iron loss W0 and Wg of the wound iron core were measured by winding a primary winding (excited winding) and a secondary winding (search coil) around the wound iron core, respectively, and measuring with a wattmeter.
[0060]
(Test Results)
　Fig. 5 shows the KAM value of the region around the groove of the grain-oriented electrical steel sheet before strain-removal annealing and the iron loss improvement rate η of the wound steel core (oriented electrical steel sheet) after strain-removal annealing. , The relationship with the iron loss improvement rate of a single plate before strain removal annealing (SST improvement rate: improvement rate based on the iron loss value measured by the Single Sheet Test (JIS C2556 regulation)) is shown.
[0061]
　The plot indicated by reference numeral D1 in FIG. 5 (◇ in the symbol) is the iron loss improvement rate η of the wound steel core formed by laser processing and having grooves formed on the surface of the wound steel core. is there. Further, the plot shown by reference numeral D2 in FIG. 5 shows the iron loss improvement rate η of the wound iron core in which grooves are formed on the surface by an etching method described later and strain is removed and annealed.
[0062]
　Further, the plot indicated by reference numeral D0 (□ in the symbol) in FIG. 5 is the iron loss improvement rate (SST improvement rate) of the single plate before strain removal annealing. The iron loss improvement rate η of the grain-oriented electrical steel sheet is a well-known iron loss measurement of the iron loss W0 of the grain-oriented electrical steel sheet without grooves and the iron loss Wg of the grain-oriented electrical steel sheet with grooves formed by laser processing. It was measured by the SST (Single Sheet Tester) method, which is a method, and calculated from the formula (1). Therefore, when the iron loss improvement rate η of the wound iron core is lower than the iron loss improvement rate of the single plate before the strain removing annealing, it means that the iron loss has deteriorated due to the strain removing annealing.
[0063]
　As shown in FIG. 5, in the wound steel core formed by the grain-oriented electrical steel sheet having a KAM value of more than 3.0 in the groove peripheral region and annealed by strain removal, the iron loss improvement rate η is the iron loss improvement of the single plate. Since it is lower than the rate, it can be judged that the iron loss of the wound steel core has deteriorated.
[0064]
　Further, as shown in FIG. 1, for example, as shown in FIG. 1, the directional electromagnetic steel plate 10 with respect to the groove 12 is formed on the wound iron core formed of the directional electromagnetic steel plate having a KAM value of more than 3.0 in the groove peripheral region and annealed by strain removal. A subgrain boundary 14 was generated on the central side (arrow X side) in the thickness direction of.
[0065]
　On the other hand, as shown in FIG. 5, in a wound steel core formed of grain-oriented electrical steel sheets having a KAM value of 0.1 or more and 3.0 or less in the region around the groove and annealed by strain removal, the iron loss improvement rate η is high. The iron loss improvement rate of the single plate was equal to or higher than that of the single plate, and the iron loss of the wound steel core was reduced.
[0066]
　Further, in a wound iron core formed of a directional electromagnetic steel sheet having a KAM value of 0.1 or more and 3.0 or less in the groove peripheral region and annealed by strain removal, it is located on the center side in the thickness direction of the directional electromagnetic steel sheet with respect to the groove 12. Subgrain boundaries did not occur or were reduced.
[0067]
　From the above, in the wound steel core formed by the grain-oriented electrical steel sheet having a KAM value of more than 3.0 in the groove peripheral region and annealed by strain removal, the region on the center side in the thickness direction of the grain-oriented electrical steel sheet with respect to the groove 12. It was found that subgrain boundaries occur in the steel and the iron loss of the wound core deteriorates.
[0068]
　On the other hand, the wound steel core formed of the grain-oriented electrical steel sheet having a KAM value of 0.1 or more and 3.0 or less in the groove peripheral region is centered in the thickness direction of the grain-oriented electrical steel sheet with respect to the groove 12 even if it is strain-removed and annealed. It was found that the occurrence of subgrain boundaries on the side was suppressed and the iron loss of the wound core did not deteriorate.
[0069]
　Here, it is considered that the cause of the deterioration of the iron loss of the strain-annealed wound core is the subgrain boundaries generated on the central side in the thickness direction of the grain-oriented electrical steel sheet with respect to the groove in the strain-annealed wound core. The amount of this subgrain boundary generated correlates with the KAM value in the groove peripheral region of the grain-oriented electrical steel sheet before it is strain-removed and annealed.
[0070]
　That is, when the KAM value in the region around the groove of the directional electromagnetic steel sheet before being strain-removed and annealed becomes large, it occurs on the center side of the directional electromagnetic steel sheet in the thickness direction with respect to the groove in the wound iron core after the strain-removing annealing. The amount of subgrain boundaries generated increases. On the other hand, when the KAM value in the region around the groove of the directional electromagnetic steel sheet before being strain-removed and annealed becomes small, it occurs on the center side of the directional electromagnetic steel sheet in the thickness direction with respect to the groove in the wound iron core after the strain-removing annealing. The amount of subgrain boundaries generated is reduced.
[0071]
　Therefore, based on the KAM value in the region around the groove of the grain-oriented electrical steel sheet before it is strain-removed and annealed, it is estimated (evaluated) whether or not the iron loss of the wound steel core deteriorates in the strain-removing annealing of the winding transformer. be able to. Then, in the manufacturing process of the grain-oriented electrical steel sheet, by reducing the KAM value in the region around the groove of the grain-oriented electrical steel sheet, the iron loss of the wound steel core that has been strain-removed and annealed can be efficiently reduced.
[0072]
　Here, supplementing the lower limit of the KAM value, as the KAM value in the groove peripheral region of the grain-oriented electrical steel sheet decreases, the subgrain boundaries generated in the strain-annealed wound core decrease, and the iron loss of the wound core decreases. Is reduced. Therefore, it is preferable that the KAM value in the region around the groove is as small as possible. However, laser processing can produce a KAM value of at least 0.1 due to its characteristics. Therefore, in this embodiment, the lower limit of the KAM value is set to 0.1.
[0073]
　When a groove is formed on the surface of the grain-oriented electrical steel sheet by the etching method, it is assumed that the KAM value in the region around the groove is approximately 0 [deg], but in the etching method, the manufacturing cost and productivity are improved. There is a problem in. Therefore, the laser processing method is superior to the etching method in consideration of manufacturing cost, productivity, and the like.
[0074]
(Relationship between the plate tension in the laser groove forming process and the iron loss improvement rate of the wound iron core)
　Next, the plate tension of the grain-oriented electrical steel sheet in the laser groove forming process and the iron loss improvement of the strain-removed annealed wound iron core. The relationship with the rate will be explained.
[0075]
　In this test, in the laser groove forming step, as shown in Table 1 below, the threading tension applied to the grain-oriented electrical steel sheet is changed, the KAM value in the groove peripheral region of the grain-oriented electrical steel sheet is measured, and the strain is strained. The iron loss improvement rate η of the wound steel core that was annealed was obtained.
[0076]
[table 1]

[0077]
　FIG. 6 shows a graph showing the relationship between the threading tension of the grain-oriented electrical steel sheet in the laser groove forming process and the iron loss improvement rate η of the strain-annealed wound steel core. As can be seen from FIG. 6, when the through-plate tension of the grain-oriented electrical steel sheet exceeds 15 MPa, the iron loss improvement rate η of the wound steel core that has been annealed by strain removal becomes lower than the iron loss improvement rate (SST improvement rate) of the single plate. , The iron loss of the wound core has deteriorated.
[0078]
　On the other hand, when the threading tension of the grain-oriented electrical steel sheet was 9 MPa or less, the iron loss improvement rate η of the wound steel core was higher than the iron loss improvement rate (SST improvement rate) of the single plate, and the iron loss of the wound steel core was reduced. Therefore, the threading tension of the grain-oriented electrical steel sheet is more preferably 9 MPa or less.
[0079]
　The plate tension in the laser groove forming step is preferably 2 MPa or more. This is because when the sheet tension is less than 2 MPa, the grain-oriented electrical steel sheet during transportation tends to vibrate, and processing defects in laser processing are likely to occur.
[0080]
　Further, FIG. 7 shows a graph showing the relationship between the KAM value in the groove peripheral region of the grain-oriented electrical steel sheet before strain annealing and the iron loss improvement rate η of the wound steel core after strain annealing. As can be seen from FIG. 7, when the KAM value in the region around the groove is 3.0 or less, the iron loss improvement rate η of the wound iron core is equal to or higher than the iron loss improvement rate (SST improvement rate) of the single plate, and in particular, the groove. When the KAM value in the peripheral region was 2.0 or less, the iron loss improvement rate η of the wound iron core was higher than the iron loss improvement rate of the single plate, and it was confirmed that the iron loss was reduced. Therefore, the KAM value in the groove peripheral region is more preferably 2.0 or less.
[0081]
(Relationship between
　the cooling rate of the reinsulating film forming process after laser groove formation and the iron loss improvement rate of the wound iron core) Next, the cooling rate of the electrical steel sheet and the strain of the reinsulating film forming process performed after the laser groove formation. The relationship with the iron loss improvement rate η of the wound steel core that has been annealed will be described.
[0082]
　In this embodiment, in the reinsulation coating forming step performed after the laser groove formation, the cooling rate of the grain-oriented electrical steel sheet is changed and the KAM value in the groove peripheral region of the grain-oriented electrical steel sheet is measured as shown in Table 2 below. At the same time, the iron loss improvement rate η of the wound steel core that was strain-removed and annealed was determined.
[0083]
[Table 2]

[0084]
　FIG. 8 shows a graph showing the relationship between the cooling rate of the grain-oriented electrical steel sheet in the reinsulation film forming step performed after the laser groove formation and the iron loss improvement rate η of the strain-annealed wound steel core. As can be seen from FIG. 8, when the cooling rate of the grain-oriented electrical steel sheet is in the range of 20 ° C./s to 100 ° C./s, the iron loss improvement rate η of the wound steel core is the iron loss improvement rate of the single plate (SST improvement rate). Equivalent to or higher than. However, when the cooling rate exceeds 100 ° C./s, the iron loss improvement rate η of the wound iron core becomes lower than the iron loss improvement rate of the single plate, and the iron loss of the wound iron core deteriorates.
[0085]
　On the other hand, when the cooling rate of the grain-oriented electrical steel sheet was 75 ° C./s or less, the iron loss improvement rate η of the wound steel core was definitely higher than the iron loss improvement rate of the single plate, and the iron loss of the wound steel core was reduced. Therefore, the cooling rate of the grain-oriented electrical steel sheet is more preferably 75 ° C./s or less.
[0086]
　The cooling rate of the grain-oriented electrical steel sheet in the reinsulation film forming step performed after the laser groove formation is preferably 20 ° C./s or more. This is because if the cooling rate is less than 20 ° C./s, the manufacturability (cooling efficiency) of the grain-oriented electrical steel sheet decreases.
[0087]
　Further, FIG. 9 shows a graph showing the relationship between the KAM value in the groove peripheral region of the grain-oriented electrical steel sheet before strain annealing and the iron loss improvement rate η of the wound steel core after strain annealing. As can be seen from FIG. 9, when the KAM value in the groove peripheral region is 3.0 or less, the iron loss improvement rate η of the wound iron core is higher than the iron loss improvement rate (SST improvement rate) of the single plate, and the iron loss is reduced. I was able to confirm that.
[0088]
(Modification Example)
　Next, a modification of the embodiment will be described.
[0089]
　The method for measuring the KAM value in the region around the groove of the grain-oriented electrical steel sheet can be changed as appropriate. Further, for example, the size of the pixel C (see FIG. 4) when mapping the groove peripheral region can be appropriately changed.
[0090]
　Further, in the above embodiment, an insulating coating agent coating step and a flattening annealing step are performed between the final finish annealing step and the laser groove forming step. However, the insulating coating agent coating step and the flattening annealing step may be performed after the laser groove forming step. That is, the final finish annealing step, the laser groove forming step, the heat treatment step, the insulating coating agent coating step, and the flattening annealing step may be performed in this order. In this case, since the reinsulation film forming step is not required, the number of steps in the manufacturing step of the grain-oriented electrical steel sheet is reduced.
[0091]
　Although one embodiment of the present invention has been described above, the present invention is not limited to these embodiments, and one embodiment and various modifications may be used in combination as appropriate, and the gist of the present invention Of course, it can be carried out in various modes as long as it does not deviate from the above.
Description of the sign
[0092]
10 oriented electrical steel sheet
10A surface (direction surface of the electrical steel
sheet) 12 Groove
12A groove bottom (groove bottom of the
groove) 14 sub-grain boundaries
16 groove peripheral region
(region) 20 vol core C,
C A , C B　　　pixels
The scope of the claims
[Claim 1]
　In a grain-oriented electrical steel sheet having a groove formed on its surface, in
　the cross section of the grain-oriented electrical steel sheet orthogonal to the groove, the region on the center side in the thickness direction of the grain-oriented electrical steel sheet with respect to the groove and one side thereof A grain-oriented electrical steel sheet having a KAM value of 0.1 or more and 3.0 or less in a region surrounded by a square having a side length of 50 μm and in contact with the groove bottom of the groove.
[Claim 2]
　The grain-oriented electrical steel sheet according to claim 1, wherein the groove is a laser groove.
[Claim 3]
　The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the KAM value is 0.1 or more and 2.0 or less.