JP7031364B2 - Manufacturing method of grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet.

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.

In the winding transformer manufacturing process, strain removing annealing is performed to remove the deformation strain (bending strain) of the winding core. In strain-removing annealing, for example, the wound core is heated to about 800 ° C.

Japanese Patent No. 5234222

However, if the wound core formed by the grain-oriented electrical steel sheet having grooves formed on the surface by laser machining is strain-removed and annealed, the iron loss of the grain core (oriented electrical steel sheet) may deteriorate (increase). be.

In consideration of the above facts, it is an object of the present invention to suppress deterioration of iron loss of the wound iron core due to strain removal annealing in the manufacturing process of the winding transformer.

The method for manufacturing a grain-oriented electrical steel sheet according to the first aspect includes a laser groove forming step of forming a groove on the surface of the final finish-baked grain-oriented electrical steel sheet by laser processing, and the grain-oriented electrical steel sheet having the groove formed therein. It is provided with a heat treatment step of heating to 900 ° C. or higher.

According to the method for manufacturing grain-oriented electrical steel sheets according to the first aspect, a laser groove forming step and a heat treatment step are provided. In the laser groove forming step, grooves are formed on the surface of the final finish annealed grain-oriented electrical steel sheet by laser machining. As a result, the magnetic domain of the grain-oriented electrical steel sheet is divided, and the iron loss of the grain-oriented electrical steel sheet is reduced.

Next, in the heat treatment step, the grain-oriented electrical steel sheet having grooves formed on its surface is heated to 900 ° C. or higher. Here, for example, when a wound steel core formed of a grain-oriented electrical steel sheet that has not undergone the heat treatment step according to the first aspect is strain-removed and annealed at about 800 ° C. in the winding transformer manufacturing process, the directionality with respect to the groove is obtained. Subgrain boundaries occur on the center side of the magnetic steel sheet in the thickness direction. As a result, the iron loss of the wound steel core (oriented electrical steel sheet) deteriorates. The subgrain boundary means a low-angle grain boundary having an orientation difference (crystal orientation difference) of 15 ° or less.

On the other hand, in the first aspect, the grain-oriented electrical steel sheet is heated to 900 ° C. or higher in the heat treatment step. As a result, even if the wound steel core formed by the grain-oriented electrical steel sheet is strain-removed and annealed at about 800 ° C. in the winding transformer manufacturing process, subgrain boundaries are generated on the central side of the grain-oriented electrical steel sheet in the thickness direction with respect to the groove. Is suppressed. As a result, deterioration of iron loss of the wound steel core (oriented electrical steel sheet) is suppressed.

In the method for manufacturing grain-oriented electrical steel sheets according to the second aspect, the grain-oriented electrical steel sheets are heated to 950 ° C. or higher in the heat treatment step of the method for manufacturing grain-oriented electrical steel sheets according to the first aspect.

According to the method for manufacturing grain-oriented electrical steel sheets according to the second aspect, the grain-oriented electrical steel sheets are heated to 950 ° C. or higher in the heat treatment step. As a result, when the wound steel core formed by the grain-oriented electrical steel sheet is strain-removed and annealed at about 800 ° C. in the winding transformer manufacturing process, subgrain boundaries are formed on the center side of the grain-oriented electrical steel sheet in the thickness direction with respect to the groove. Occurrence is further suppressed. Therefore, deterioration of iron loss of the wound iron core is suppressed.

Further, in the heat treatment step, the grain-oriented electrical steel sheet heated to 950 ° C. or higher has a reduced iron loss as compared with the grain-oriented electrical steel sheet having no groove formed on the surface by laser processing. Therefore, the performance of the grain-oriented electrical steel sheet is improved.

In the method for manufacturing a directional electromagnetic steel sheet according to the third aspect, the directional electromagnetic steel sheet is heated to 1000 ° C. or higher in the heat treatment step of the directional electromagnetic steel sheet according to the first aspect or the second aspect.

According to the method for manufacturing grain-oriented electrical steel sheets according to the third aspect, the grain-oriented electrical steel sheets are heated to 1000 ° C. or higher in the heat treatment step. As a result, when the wound steel core formed by the grain-oriented electrical steel sheet is strain-removed and annealed at about 800 ° C. in the winding transformer manufacturing process, the subgrain boundaries are located on the center side of the grain-oriented electrical steel sheet in the thickness direction with respect to the groove. Is further suppressed. Therefore, deterioration of iron loss of the wound iron core is suppressed.

Further, when the grain-oriented electrical steel sheet is heated to 1000 ° C. or higher in the heat treatment step, the effect of reducing the iron loss of the wound steel core by the heat treatment step is maximized. Therefore, the performance of the winding core is improved.

The method for manufacturing grain-oriented electrical steel sheets according to the fourth aspect is such that the grain-oriented electrical steel sheets are at least 1100 ° C. in the heat treatment step of the method for manufacturing grain-oriented electrical steel sheets according to any one of the first to third aspects. Heat to.

According to the method for manufacturing grain-oriented electrical steel sheets according to the fourth aspect, the grain-oriented electrical steel sheets are heated to 1100 ° C. or lower in the heat treatment step. As a result, thermal deformation of the grain-oriented electrical steel sheet is suppressed.

The method for manufacturing a grain-oriented electrical steel sheet according to a fifth aspect is the method for manufacturing a grain-oriented electrical steel sheet according to any one of the first to fourth aspects, in which the grained grain-oriented electrical steel sheet is heated. The flattening annealing step is provided, and the heat treatment step is a part of the flattening annealing step.

According to the method for manufacturing grain-oriented electrical steel sheets according to the fifth aspect, a flattening annealing step is provided. In the flattening annealing step, the grain-oriented electrical steel sheet in which the grooves are formed in the laser groove forming step is flattened while being heated. A heat treatment step is performed as part of this flattening annealing step. That is, in the flattening treatment step, the grain-oriented electrical steel sheet having grooves formed by laser processing is flattened while being heated to 900 ° C. or higher.

Thereby, in the fifth aspect, energy saving can be achieved as compared with the case where the flattening annealing step and the heat treatment step are performed separately.

The method for manufacturing grain-oriented electrical steel sheets according to the sixth aspect is the method for manufacturing grain-oriented electrical steel sheets according to any one of the first to fourth aspects, wherein the grain-oriented electrical steel sheets having the grooves are insulated. The heat treatment step is performed before the insulating film forming step.

According to the method for manufacturing grain-oriented electrical steel sheets according to the sixth aspect, an insulating film forming step is provided. In the insulating film forming step, the grain-oriented electrical steel sheet is insulated. In this sixth aspect, a heat treatment step is performed before the insulating film forming step.

Here, if the heat treatment step is performed after the insulating film forming step, the insulating film formed on the grain-oriented electrical steel sheet may be thermally deteriorated.

On the other hand, in the sixth aspect, as described above, the heat treatment step is performed before the insulating film forming step. As a result, thermal deterioration of the insulating film formed on the grain-oriented electrical steel sheet is suppressed.

As described above, according to the method for manufacturing grain-oriented electrical steel sheets according to the present invention, it is possible to suppress deterioration of iron loss of the wound steel core due to strain removal annealing in the manufacturing process of the winding transformer.

FIG. 1 is a cross section of 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 an analysis result obtained by analyzing the crystal orientation difference of the grain-oriented electrical steel sheet shown in FIG. 1 by EBSD. It is a graph which shows the relationship between the iron loss improvement rate η of the grain-oriented electrical steel sheet and the winding iron core, and the heat treatment temperature of a heat treatment process. FIG. 4A is a cross section of a grain-oriented electrical steel sheet constituting a wound steel core that has been strain-removed and annealed at 800 ° C. FIG. 4B is a cross section of a grain-oriented electrical steel sheet constituting a wound steel core that has been strain-removed and annealed at 850 ° C. FIG. 4C is a cross section of a grain-oriented electrical steel sheet constituting a wound steel core that has been strain-removed and annealed at 900 ° C.

Hereinafter, one embodiment will be described with reference to the drawings.

(Directional magnetic steel sheet)
The grain-oriented electrical steel sheet is an electrical steel sheet in which the easy-to-magnetize axes of crystal grains (the <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.

A plurality of grooves are formed on the surface of the grain-oriented electrical steel sheet 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 sheets 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 a winding iron core (iron core material) of a winding transformer in which the direction in which magnetic lines of force 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.

The main body of the grain-oriented electrical steel sheet is made of an iron alloy containing Si. As an example, the composition of the steel plate body is Si; 2.5% by mass or more and 4.0% by mass or less, C; 0.001% by mass or more and 0.10% by mass or less, Mn; 0.05% by mass or more and 0.20. Mass% or less, acid-soluble Al; 0.001% by mass or more and 0.040% by mass or less, N; 0.0002% by mass or more and 0.012% by mass or less, S; 0.0001% by mass or more and 0.030% by mass or less , P; 0.01% by mass or more and 0.04% by mass or less, and the balance is Fe and unavoidable impurities. The thickness of the steel plate body is, for example, 0.15 mm or more and 0.35 mm or less.

The surface of the steel sheet body is coated with a glass film. The glass coating is composed of composite oxides such as forsterite (Mg ₂ SiO ₄ ), spinel (Mg Al ₂ O ₄ ) and cozilite (Mg ₂ Al ₄ Si ₅ O ₁₈ ). The thickness of this glass coating is, for example, 1 μm.

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.

(Manufacturing method of grain-oriented electrical steel sheet)
Next, an example of a method for manufacturing a 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 application process, a final finish annealing process, an insulating coating agent application 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.

(Casting process-annealing process)
First, in the casting process (continuous casting process), a slab is 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.

(Cold rolling process)
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). The rolling direction coincides with the longitudinal direction of the cold rolled steel sheet (oriented electrical steel sheet).

(Decarburization annealing process)
Next, in the decarburization annealing step, the cold-rolled steel sheet is decarburized and annealed (continuously annealed) 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).

(Annealing separator application process)
Next, in the annealing separation agent application step, an annealing separation agent 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.

(Final finish annealing process)
Next, in the final finish annealing step, the cold-rolled steel sheet wound in a coil shape is annealed (batch annealing) at a predetermined temperature (for example, about 1200 ° C.) and for a predetermined time (for example, about 20 hours). .. 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.

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 direction 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.

(Insulation coating agent application process)
Next, in the insulating coating agent coating step, an insulating coating agent (coating liquid) having electrical insulating properties and capable of applying a predetermined tension to the surface of the grain-oriented electrical steel sheet is applied to the surface of the grain-oriented electrical steel sheet. ..

(Flatration annealing process)
Next, in the flattening annealing step, the grain-oriented electrical steel sheet is annealed at a predetermined temperature (for example, 800 ° C. to 850 ° C.) and for a predetermined time (for example, 10 seconds or more and 120 seconds or less) while being conveyed by the conveying device. (Flattening and annealing). 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, the curl and strain of the cold-rolled steel sheet at the time of final finish annealing are removed, and the grain-oriented electrical steel sheet is flattened.

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 film. After that, the grain-oriented electrical steel sheet is cooled.

(Laser groove forming process)
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, 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. 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. As a result, a groove extending in the width direction of the grain-oriented electrical steel sheet is formed on the surface of the grain-oriented electrical steel sheet.

Further, the 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 grooves, and the iron loss of the grain-oriented electrical steel sheet is reduced.

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.

(Heat treatment process)
Next, in the heat treatment step, the grain-oriented electrical steel sheet is heated at 900 ° C. or higher and 1100 ° C. or lower and for a predetermined time (for example, 30 seconds to 300 seconds). As a result, when the wound core formed of the grain-oriented electrical steel sheet is strain-removed and annealed at about 800 ° C. in the winding transformer manufacturing process described later, deterioration (increase) of iron loss of the wound core is suppressed.

(Re-insulating film forming process)
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 step of forming the insulating film, the surface of the grain-oriented electrical steel sheet is again coated with the insulating film.

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 directional electromagnetic steel plate 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, grain-oriented electrical steel sheets are manufactured. The reinsulating film forming step is an example of the insulating film forming step.

(effect)
Next, the effect of this embodiment will be described.

According to the method for manufacturing grain-oriented electrical steel sheets according to the present embodiment, a heat treatment step is performed after the laser groove forming step. In this heat treatment step, in the laser groove forming step, the grain-oriented electrical steel sheet having grooves formed on the surface is heated to 900 ° C. or higher.

Here, for example, when a winding transformer formed of a grain-oriented electrical steel sheet which has not experienced the heat treatment step according to the present embodiment is strain-removed and annealed at about 800 ° C. in the winding transformer manufacturing process, the directionality with respect to the groove is obtained. Subgrain boundaries occur on the center side of the magnetic steel sheet in the thickness direction. As a result, the iron loss of the wound core deteriorates.

More specifically, FIG. 1 shows a wound iron core 20 that has been strain-removed and annealed at 800 ° C. to 900 ° C. in the winding transformer manufacturing process. The wound steel core 20 is formed of a grain-oriented electrical steel sheet 10 that has not experienced the heat treatment step according to the present embodiment. 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 constituting the wound steel core 20.

As shown in FIG. 1, when the wound steel core 20 formed by the grain-oriented electrical steel sheet 10 which has not experienced the heat treatment step according to the present embodiment is strain-removed and annealed, the thickness of the grain-oriented electrical steel sheet 10 with respect to the groove 12 is thickened. The subgrain boundary 14 was generated on the central side (arrow X side) of the direction. The subgrain boundary means a low-angle grain boundary having an orientation difference (crystal orientation difference) of 15 ° or less.

Further, FIG. 2 shows the analysis result of the crystal orientation difference on the center 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).

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. Further, 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 the reference point (origin) where the subgrain boundary 14 does not exist.

As shown in FIG. 2, in the region R surrounded by the two-dot chain 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 in the thickness direction with respect to the groove 12. 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 heat treatment experiment described later. ..

On the other hand, in the present embodiment, as described above, the grain-oriented electrical steel sheet 10 is heated to 900 ° C. or higher in the heat treatment step. As a result, even if the grain-oriented electrical steel sheet forming the winding iron core 20 is strain-removed and annealed in the winding transformer manufacturing process, subgrain boundaries are generated on the center side of the grain-oriented electrical steel sheet 10 with respect to the groove 12 in the thickness direction. Is suppressed. As a result, deterioration of iron loss of the wound steel core 20 (oriented electrical steel sheet 10) is suppressed.

Further, in the present embodiment, the heat treatment step is performed before the reinsulation film forming step. Here, it is possible to perform a heat treatment step after the reinsulation film forming step, but in this case, the insulating film formed on the grain-oriented electrical steel sheet may be thermally deteriorated in the reinsulation film forming step.

On the other hand, in the present embodiment, as described above, the heat treatment step is performed before the reinsulation film forming step. This makes it possible to suppress thermal deterioration of the insulating film formed on the grain-oriented electrical steel sheet in the reinsulating film forming step.

(Heat treatment experiment)
Next, the heat treatment experiment of the grain-oriented electrical steel sheet will be described.

In this experiment, a grain-oriented electrical steel sheet having a plurality of grooves formed on its surface by laser processing was heated at a predetermined temperature in a heat treatment step, and the iron loss improvement rate of the grain-oriented electrical steel sheet was determined. Further, as a comparative example, the iron loss improvement rate of the grain-oriented electrical steel sheet, which has a plurality of grooves formed on the surface by laser processing but has not experienced the heat treatment process, was also obtained. The heating time of the grain-oriented electrical steel sheet was 60 seconds.

Next, a 20 kVA single-layer wound steel core was manufactured from a grain-oriented electrical steel sheet heated to a predetermined temperature in the heat treatment step. Then, the produced wound steel core was strained and annealed, and the iron loss improvement rate of the wound steel core (oriented electrical steel sheet) was obtained. Further, as a comparative example, the wound steel core formed by the grain-oriented electrical steel sheet which had not undergone the above-mentioned heat treatment process was strain-removed and annealed, and the iron loss improvement rate of the grain-oriented electrical steel sheet (oriented electrical steel sheet) was also obtained. In the strain-removing annealing, the wound steel core (oriented electrical steel sheet) was annealed at 800 ° C. for 3 hours in an atmosphere of 100% nitrogen.

(Directional magnetic steel sheet)
The grain-oriented electrical steel sheet was manufactured by the same manufacturing method as in the above embodiment. In this grain-oriented electrical steel sheet, B8 is 1.91T and W17 / 50 = 0.9w / kg. 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 0.8 A / m.

(Laser groove processing conditions)
Further, in the laser groove forming step, the processing conditions of the groove (laser groove) 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: 1000W
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

(Iron loss improvement rate)
The iron loss improvement rate η of the grain-oriented electrical steel sheet is the iron loss WO 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. Calculated from (1).
η = (W0-Wg) / W0 × 100 ... (1)

The iron loss WO and Wg of the grain-oriented electrical steel sheet were measured by the SST (Single Sheet Tester) method, which is a well-known iron loss measuring method. The iron loss W0 and Wg of the grain-oriented electrical steel sheet are iron loss values under exciting conditions with a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T.

Similar to the grain-oriented electrical steel sheet, the iron loss improvement rate η of the rolled iron core is the iron loss WO of the rolled iron core formed by the grain-free electrical steel sheet and the directionality in which the groove is formed by laser machining. The iron loss Wg of the wound steel core formed by the electromagnetic steel sheet was obtained and calculated from the above formula (1).

The iron loss WO and Wg of the wound core were measured by winding a primary winding (excited winding) and a secondary winding (search coil) around the wound core, respectively, and measuring with a power meter.

(Experimental result)
Next, the experimental results will be described.

(Relationship between heat treatment temperature in heat treatment process and iron loss improvement rate)
First, the relationship between the heat treatment temperature in the heat treatment step and the iron loss improvement rate η of the grain-oriented electrical steel sheet and the wound steel core will be described.

FIG. 3 shows a graph G1 showing the relationship between the heat treatment temperature in the heat treatment step and the iron loss improvement rate η of the grain-oriented electrical steel sheet. Further, FIG. 3 also shows a graph G2 showing the relationship between the heat treatment temperature in the heat treatment step and the iron loss improvement rate η of the wound core that has been strain-removed and annealed.

The heat treatment temperature of 0 ° C. means a grain-oriented electrical steel sheet that has not undergone a heat treatment process and a wound core formed by the grain-oriented electrical steel sheet and that has been strain-removed and annealed.

As shown in FIG. 3, when the heat treatment temperature in the heat treatment step was 0 ° C., the iron loss improvement rate η of the grain-oriented electrical steel sheet was 18%, and the iron loss improvement rate η of the wound steel core was 13%. That is, when the heat treatment temperature in the heat treatment step was 0 ° C., the iron loss improvement rate η of the wound steel core was lower than the iron loss improvement rate η of the grain-oriented electrical steel sheet. This is considered to be the effect of straining and annealing the wound core.

On the other hand, when the heat treatment temperature in the heat treatment step was 900 ° C. or higher, the iron loss improvement rate η of the wound iron core became 18% or higher. That is, it was confirmed that when the heat treatment temperature in the heat treatment step was 900 ° C. or higher, the iron loss did not deteriorate even if the wound core was strained and annealed. When the heat treatment temperature in the heat treatment step was 900 ° C. or higher, the iron loss improvement rate η of the grain-oriented electrical steel sheet was 18% or more, as in the case of the wound steel core, and it was confirmed that the iron loss was reduced.

Further, when the heat treatment temperature in the heat treatment step was 950 ° C., the iron loss improvement rate η of the wound iron core was 19%. Further, at the heat treatment temperatures of 1000 ° C. and 1100 ° C. in the heat treatment step, the iron loss improvement rate η of the wound iron core was 20%. That is, the heat treatment temperature in the heat treatment step is preferably 950 ° C. or higher, more preferably 1000 ° C. or higher.

When the heat treatment temperature in the heat treatment step was 1000 ° C. or higher, the iron loss improvement rate η of the wound iron core was substantially constant. Therefore, from the viewpoint of energy saving, the heat treatment temperature in the heat treatment step is preferably 900 ° C. or higher and 1000 ° C. or lower.

Further, if the heat treatment temperature in the heat treatment step exceeds 1100 ° C., the grain-oriented electrical steel sheet may be thermally deformed. Therefore, from the viewpoint of suppressing thermal deformation of the grain-oriented electrical steel sheet, the heat treatment temperature in the heat treatment step is preferably 900 ° C. or higher and 1100 or lower.

(Relationship between heat treatment temperature in heat treatment process and subgrain boundaries)
Next, the relationship between the heat treatment temperature in the heat treatment step and the subgrain boundaries generated in the rolled core (oriented electrical steel sheet) will be described.

4A, 4B, and 4C show the strain-annealed wound core 20. 4A to 4C are cross sections orthogonal to the groove 12 on the surface 10A of the grain-oriented electrical steel sheet 10 constituting the wound steel core 20.

The cross section of the grain-oriented electrical steel sheet 10 shown in FIGS. 4A to 4C was observed with a microscope in a state where the cross section was diamond-polished and corroded with a 10% nital solution. In diamond polishing, the particle size was gradually reduced in the order of 3 μm → 1 μm → 1/4 μm.

FIG. 4A is a wound steel core 20 formed of a grain-oriented electrical steel sheet 10 having a heat treatment temperature of 800 ° C. in the heat treatment step and strain-removed and annealed. In FIG. 4A, the subgrain boundary 14 was confirmed in the region K surrounded by the dotted line on the center side of the grain-oriented electrical steel sheet 10 with respect to the groove 12.

Next, FIG. 4B is a wound steel core 20 formed by a grain-oriented electrical steel sheet 10 having a heat treatment temperature of 850 ° C. in the heat treatment step and strain-removed and annealed. Also in FIG. 4B, the subgrain boundary 14 was confirmed in the region K surrounded by the dotted line on the center side of the grain-oriented electrical steel sheet 10 with respect to the groove 12.

Further, as shown in FIG. 3, the iron loss improvement rate η of the wound steel core formed by the grain-oriented electrical steel sheet having a heat treatment temperature of less than 900 ° C. (800 ° C., 850 ° C.) in the heat treatment step and annealed by strain removal is 18. It became less than%, and the iron loss of the grain-oriented electrical steel sheet deteriorated.

From this, when the wound steel core 20 formed by the grain-oriented electrical steel sheet 10 having a heat treatment temperature of less than 900 ° C. (800 ° C., 850 ° C.) in the heat treatment step is strain-removed and annealed, the central side of the grain-oriented electrical steel sheet 10 with respect to the groove 12 is obtained. It can be seen that the subgrain boundaries 14 are generated in the core and the iron loss of the winding core 20 is deteriorated.

On the other hand, FIG. 4C is a wound steel core 20 formed by a grain-oriented electrical steel sheet 10 having a heat treatment temperature of 900 ° C. in the heat treatment step and strain-removed and annealed. In FIG. 4C, no subgrain boundaries were confirmed in the central region of the grain-oriented electrical steel sheet 10 with respect to the groove 12.

Further, as shown in FIG. 3, the iron loss improvement rate η of the wound steel core formed by the grain-oriented electrical steel sheet having a heat treatment temperature of 900 ° C. or higher in the heat treatment step and annealed by strain removal is 18% or more, which is directional. The iron loss of electrical steel sheets has been reduced.

From this, the wound steel core 20 formed of the grain-oriented electrical steel sheet 10 having a heat treatment temperature of 900 ° C. or higher (900 ° C., 950 ° C., 100 ° C., 1100 ° C.) in the heat treatment step has a groove 12 even if it is strain-removed and annealed. It can be seen that the subgrain boundary does not occur on the central side of the grain-oriented electrical steel sheet 10 and the deterioration of the iron loss of the grain-oriented electrical steel sheet 10 is suppressed. That is, the iron loss of the wound steel core 20 that has been strain-removed and annealed can be evaluated by the presence or absence of subgrain boundaries on the central side of the grain-oriented electrical steel sheet 10 with respect to the groove 12.

(Modification example)
Next, a modified example of the above embodiment will be described.

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 application 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 becomes unnecessary, the number of steps in the manufacturing step of the grain-oriented electrical steel sheet is reduced.

Further, when the flattening annealing step is performed after the laser groove forming step, the heat treatment step may be performed as a part of the flattening annealing step. That is, in the flattening and annealing step, the directional electromagnetic steel plate may be flattened while being heated to 900 ° C. or higher. As a result, energy saving can be achieved as compared with the case where the flattening annealing step and the heat treatment step are performed separately.

Further, the heat treatment step may be carried out after the laser groove forming step, and the execution order of each step can be changed as appropriate.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment, and one embodiment and various modifications may be used in combination as appropriate. Of course, it can be carried out in various embodiments as long as it does not deviate.

10 Electrical steel sheet 10A surface (surface of electrical steel sheet)
12 grooves

Claims (3)

A method for manufacturing grain-oriented electrical steel sheets used for winding transformers.
A laser groove forming process in which a groove is formed on the surface of a grain-oriented electrical steel sheet that has been annealed by laser machining.
A heat treatment step of heating the grained grained steel sheet to 1000 ° C. or higher and 1100 ° C. or lower .
A method for manufacturing grain-oriented electrical steel sheets. A method for manufacturing grain-oriented electrical steel sheets used for winding transformers.
The final finish annealing process to form grain-oriented electrical steel sheets by causing secondary recrystallization in cold-rolled steel sheets.
An insulating coating agent coating step of applying an insulating coating agent capable of imparting electrical insulation and tension to the surface of the grain-oriented electrical steel sheet, and
By annealing the grain-oriented electrical steel sheet at 850 ° C. or lower, strain is removed to flatten the grain-oriented electrical steel sheet, and the insulating coating agent is baked on the surface of the grain-oriented electrical steel sheet to obtain the grain-oriented electrical steel sheet. A flattening annealing step of applying tension to the surface of the grain steel to insulate the surface of the grain-oriented electrical steel sheet.
A laser groove forming step of forming a groove on the surface of the grain-oriented electrical steel sheet by laser processing,
A heat treatment step of heating the grained grained steel sheet to 1000 ° C. or higher and 1100 ° C. or lower.
To prepare
Manufacturing method of grain-oriented electrical steel sheet. A method for manufacturing grain-oriented electrical steel sheets used for winding transformers.
The final finish annealing process to form grain-oriented electrical steel sheets by causing secondary recrystallization in cold-rolled steel sheets.
A laser groove forming step of forming a groove on the surface of the grain-oriented electrical steel sheet by laser processing,
A heat treatment step of heating the grained grained steel sheet to 1000 ° C. or higher and 1100 ° C. or lower.
An insulating coating agent coating step of applying an insulating coating agent capable of imparting electrical insulation and tension to the surface of the grain-oriented electrical steel sheet, and
By annealing the grain-oriented electrical steel sheet at 850 ° C. or lower, strain is removed to flatten the grain-oriented electrical steel sheet, and the insulating coating agent is baked on the surface of the grain-oriented electrical steel sheet to obtain the grain-oriented electrical steel sheet. A flattening annealing step of applying tension to the surface of the grain steel to insulate the surface of the grain-oriented electrical steel sheet.
To prepare
Manufacturing method of grain-oriented electrical steel sheet.

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