HK1183065B - Grain-oriented electrical steel sheet - Google Patents

Description

Grain-oriented electromagnetic steel sheet

Technical Field

The present invention relates to a grain-oriented electrical steel sheet suitable for an iron core of a transformer or the like and a method for manufacturing the same. The present application claims priority based on Japanese application No. 2010-202394, 9/2010, the contents of which are incorporated herein by reference.

Background

As a technique for reducing the iron loss of a grain-oriented electrical steel sheet, a technique of introducing strain into the surface of a base metal to subdivide magnetic domains is known (patent document 3). However, since stress relief annealing is performed in the manufacturing process of the wound core, the introduced strain is relaxed during annealing, and the subdivision of magnetic domains becomes insufficient.

As a method for compensating for this drawback, there is a technique of forming a groove on the surface of a base metal (patent documents 1, 2, 4, and 5). Further, there is a technique of forming a groove on the surface of the base metal and forming a crystal grain boundary from the bottom of the groove to the back surface of the base metal in the plate thickness direction (patent document 6).

The method of forming the grooves and grain boundaries has a good effect of improving the iron loss. However, the technique described in patent document 6 has a significant decrease in productivity. This is because, in order to obtain a desired effect, it is necessary to make the width of the groove about 30 μm to 300 μm, and in order to further form crystal grain boundaries, it is necessary to attach Sn or the like to the groove and anneal, apply strain to the groove, or emit laser light or plasma for heat treatment of the groove. That is, it is difficult to perform treatments such as deposition of Sn, application of strain, and emission of laser light accurately in accordance with a narrow groove, and in order to realize the treatments, at least the steel sheet passing speed needs to be extremely slow. Patent document 6 discloses a method of performing electrolytic etching as a method of forming a groove. However, in order to perform electrolytic etching, it is necessary to perform coating of a resist, etching treatment using an etching solution, removal of the resist, and cleaning. Therefore, the number of man-hours and the processing time are greatly increased.

Documents of the prior art

Patent document

Patent document 1: japanese examined patent publication No. 62-53579

Patent document 2: japanese examined patent publication No. 62-54873

Patent document 3: japanese laid-open patent publication No. 56-51528

Patent document 4: japanese laid-open patent publication No. 6-57335

Patent document 5: japanese patent laid-open publication No. 2003-129135

Patent document 6: japanese laid-open patent publication No. 7-268474

Patent document 7: japanese laid-open patent publication No. 2000-109961

Patent document 8: japanese laid-open patent publication No. 9-49024

Patent document 9: japanese laid-open patent publication No. 9-268322

Disclosure of Invention

Problems to be solved by the invention

The purpose of the present invention is to provide a method for producing a grain-oriented electrical steel sheet, which enables industrial mass production of a grain-oriented electrical steel sheet having low iron loss, and a grain-oriented electrical steel sheet having low iron loss.

Means for solving the problems

In order to solve the above problems and achieve the object, the present invention adopts the following means.

(1) Specifically, a method for manufacturing a grain-oriented electrical steel sheet according to an aspect of the present invention includes: a cold rolling step of cold rolling a silicon steel sheet containing Si while moving the sheet in a steel sheet passing direction; a first continuous annealing process in which decarburization and primary recrystallization of the silicon steel sheet are performed; a winding step of winding the silicon steel sheet to obtain a steel sheet coil; a groove forming step of forming a groove along a trajectory of a laser beam by irradiating the surface of the silicon steel sheet from one end edge of the silicon steel sheet in a sheet width direction to the other end edge thereof a plurality of times at predetermined intervals in the steel sheet passing direction during a period from the cold rolling step to the winding step; a batch annealing step of performing secondary recrystallization on the steel plate curl; a second continuous annealing step of uncoiling the steel sheet coil to flatten the coil; and a continuous coating step of imparting tension and electrical insulation to the surface of the silicon steel sheet; in the batch annealing step, crystal grain boundaries penetrating through the front and back surfaces of the silicon steel sheet are generated along the grooves, and the following expressions 3 and 4 are satisfied when the average intensity of the laser beam is p (w), the focal diameter of the focal spot of the laser beam in the steel sheet passing direction is dl (mm), the focal diameter of the focal spot of the laser beam in the sheet width direction is dc (mm), the scanning speed of the laser beam in the sheet width direction is Vc (mm/sec), the irradiation energy density Up of the laser beam is expression 1, and the instantaneous power density Ip of the laser beam is expression 2.

Up = (4/π). times.P/(Dl. times.Vc) (formula 1)

Ip = (4/pi) × P/(Dl × Dc) (formula 2)

1≤Up≤10(J/mm²) (formula 3)

100(kW/mm²)≤Ip≤2000(kW/mm²) (formula 4)

(2) In the aspect (1), in the groove forming step, the gas may be blown to the portion of the silicon steel sheet irradiated with the laser beam at a flow rate of 10L/min or more and 500L/min or less.

(3) A grain-oriented electrical steel sheet according to an aspect of the present invention includes: the laser scanning device comprises a groove formed along the track of a laser beam scanning from one end edge to the other end edge in the width direction of the plate, and a crystal grain boundary extending along the groove and penetrating through the front and the back.

(4) In the embodiment described in (3) above, the crystal grains may have the following sizes: the grain size of the crystal grain in the width direction of the grain-oriented electrical steel sheet is 10mm or more and 10mm or less, and the grain size of the crystal grain in the length direction of the grain-oriented electrical steel sheet exceeds 0mm and is 10mm or less, the crystal grain being present from the groove to the back surface of the grain-oriented electrical steel sheet.

(5) In the aspect (3) or (4), a glass coating may be formed on the groove, and when an average value of characteristic X-ray intensities of Mg in a portion of the grain-oriented electrical steel sheet surface other than the groove portion of the glass coating is 1, an X-ray intensity ratio Ir of the characteristic X-ray intensities of Mg in the groove portion of the glass coating may be in a range of 0 Ir 0.9.

Effects of the invention

According to the aspect of the present invention, a grain-oriented electrical steel sheet with less iron loss can be obtained by a method that enables industrial mass production.

Drawings

Fig. 1 is a view showing a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Fig. 2 is a diagram showing a modification of the embodiment of the present invention.

Fig. 3A is a diagram showing another example of a method of scanning a laser beam in the embodiment of the present invention.

Fig. 3B is a diagram showing still another example of a method of scanning a laser beam in the embodiment of the present invention.

Fig. 4A is a diagram showing a laser beam focusing spot in the embodiment of the present invention.

Fig. 4B is a diagram showing a laser beam focusing spot in the embodiment of the present invention.

Fig. 5 is a diagram showing grooves and crystal grains formed in the embodiment of the present invention.

Fig. 6A is a view showing crystal grain boundaries formed in the embodiment of the present invention.

Fig. 6B is a diagram showing crystal grain boundaries formed in the embodiment of the present invention.

Fig. 7A is a view showing a photograph of the surface of a silicon steel plate in the embodiment of the present invention.

Fig. 7B is a view showing a photograph of the surface of the silicon steel plate in the embodiment of the comparative example.

Fig. 8A is a diagram showing another example of crystal grain boundaries in the embodiment of the present invention.

Fig. 8B is a diagram showing another example of crystal grain boundaries in the embodiment of the present invention.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a view showing a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention.

In the present embodiment, as shown in fig. 1, a silicon steel sheet 1 containing, for example, 2 to 4 mass% of Si is cold-rolled. This silicon steel sheet 1 is manufactured by, for example, continuous casting of molten steel, hot rolling of a slab obtained by the continuous casting, and annealing of a hot-rolled steel sheet obtained by the hot rolling. The temperature of the anneal is, for example, about 1100 ℃. The thickness of the silicon steel sheet 1 after the cold rolling is, for example, about 0.2mm to 0.3mm, and the silicon steel sheet 1 is wound into a coil shape after the cold rolling to form a cold rolled coil.

Next, the rolled silicon steel sheet 1 is fed into a decarburization annealing furnace 3 while being unwound, and a first continuous annealing, so-called decarburization annealing, is performed in the decarburization annealing furnace 3. The temperature of this annealing is, for example, 700 ℃ to 900 ℃. During this annealing, decarburization and primary recrystallization occur. As a result, gaussian-oriented crystal grains having an axis of easy magnetization aligned with the rolling direction are formed with a certain degree of probability. Then, the silicon steel sheet 1 discharged from the decarburization annealing furnace 3 is cooled by the cooling device 4. Next, coating 5 of an annealing separator containing MgO as a main component on the surface of the silicon steel sheet 1 is performed. Then, the silicon steel sheet 1 coated with the annealing separator is wound up in a coil shape to form a steel sheet coil 31.

In the present embodiment, a groove is formed on the surface of the silicon steel sheet 1 by using the laser beam irradiation apparatus 2 during the period from when the rolled silicon steel sheet 1 is unwound to when it is supplied to the decarburization annealing furnace 3. At this time, the silicon steel sheet 1 is irradiated with the laser beam from one end edge to the other end edge in the sheet width direction at a predetermined interval in the steel sheet passing direction at a predetermined focused power density Ip and a predetermined focused energy density Up. As shown in fig. 2, the laser beam irradiation device 2 may be disposed on the downstream side of the cooling device 4 in the steel sheet passing direction, and the laser beam may be irradiated to the surface of the silicon steel sheet 1 between the cooling by the cooling device 4 and the application 5 of the annealing separator. The laser beam irradiation device 2 may be disposed at two positions, i.e., the upstream side of the annealing furnace 3 in the steel sheet passing direction and the downstream side of the cooling device 4 in the steel sheet passing direction, and may irradiate the laser beam at the two positions. The laser beam may be irradiated between the annealing furnace 3 and the cooling device 4, or may be irradiated in the annealing furnace 3 or the cooling device 4. In the formation of the groove by the laser beam, a molten layer described later is generated, unlike the groove formation in the machining. Since this molten layer does not disappear during decarburization annealing or the like, the effect can be obtained by irradiating the laser beam in any step before the secondary recrystallization.

The irradiation of the laser beam is performed by scanning the laser beam 9 emitted from a laser device as a light source in a C direction, which is a sheet width direction substantially perpendicular to the L direction, which is a rolling direction of the silicon steel sheet 1, at a predetermined interval PL by a scanning device 10, as shown in fig. 3A, for example. At this time, an auxiliary gas 25 such as air or an inert gas is blown to the portion of the silicon steel sheet 1 irradiated with the laser beam 9. As a result, the grooves 23 are formed in the portions of the surface of the silicon steel plate 1 irradiated with the laser beam 9. The rolling direction is consistent with the steel plate passing direction.

The scanning of the laser beam over the entire width of the silicon steel sheet 1 may be performed by using 1 scanner 10, or may be performed by using a plurality of scanners 20 as shown in fig. 3B. When a plurality of scanning devices 20 are used, only 1 laser device may be provided as a light source of the laser beam 19 incident on each scanning device 20, or 1 laser device may be provided for each scanning device 20. When the number of light sources is 1, the laser beam emitted from the light source may be divided into laser beams 19. By using the plurality of scanning devices 20, the irradiation region can be divided into a plurality of regions in the plate width direction, and thus the time required for scanning and irradiation per 1 laser beam can be shortened. Therefore, the steel plate passing device is particularly suitable for high-speed steel plate passing equipment.

The laser beam 9 or 19 is focused by a prism in the scanning device 10 or 20. As shown in fig. 4A and 4B, the shape of the laser beam focusing spot 24 of the laser beam 9 or 19 on the surface of the silicon steel plate 1 is, for example, a circle or an ellipse having a diameter Dc in the plate width direction, i.e., C direction, and a diameter Dl in the rolling direction, i.e., L direction. The scanning of the laser beam 9 or 19 is performed at a speed Vc using, for example, a polygon mirror or the like within the scanning device 10 or 20. For example, the C-direction diameter Dc, which is the diameter in the plate width direction, may be set to 0.4mm, and the L-direction diameter Dl, which is the diameter in the rolling direction, may be set to 0.05 mm.

As the laser device of the light source, for example, CO can be used₂A laser. A high power laser generally used in industry, such as a YAG laser, a semiconductor laser, and a fiber laser, may be used. The laser used may be any of a pulse laser and a continuous wave laser as long as it can stably form the groove 23 and the crystal grain 26.

The temperature of the silicon steel sheet 1 when the laser beam is irradiated is not particularly limited. For example, the irradiation of the laser beam may be performed to the silicon steel plate 1 at about room temperature. The direction of the scanning laser beam does not need to coincide with the plate width direction, i.e., the C direction. However, from the viewpoint of work efficiency and the like, and from the viewpoint of subdividing the magnetic domains into long stripes in the rolling direction, the angle formed by the scanning direction and the C direction, which is the sheet width direction, is preferably within 45 °. More preferably within 20 °, and still more preferably within 10 °.

The instantaneous power density Ip and the irradiation energy density Up of the laser beam suitable for forming the groove 23 will be described. In the present embodiment, for the reasons described below, it is preferable that the instantaneous power density Ip, which is the peak power density of the laser beam defined by equation 2, satisfy equation 4, and that the irradiation energy density Up of the laser beam defined by equation 1 satisfy equation 3.

Up = (4/π). times.P/(Dl. times.Vc) (formula 1)

Ip = (4/pi) × P/(Dl × Dc) (formula 2)

1≤Up≤10(J/mm²) (formula 3)

100kW/mm²≤Ip≤2000kW/mm²(formula 4)

Here, P represents the average intensity of the laser beam, i.e., the power (W), Dl represents the diameter (mm) of the focused spot of the laser beam in the rolling direction, Dc represents the diameter (mm) of the focused spot of the laser beam in the sheet width direction, and Vc represents the scanning speed (mm/sec) of the laser beam in the sheet width direction.

When the silicon steel sheet 1 is irradiated with the laser beam 9, the irradiated portion is melted, and a part of the melted portion is scattered or evaporated. As a result, the groove 23 is formed. The melted portion remains without being scattered or evaporated, and solidifies after the irradiation with the laser beam 9 is completed. During this solidification, as shown in fig. 5, columnar crystals extending long from the bottom of the groove toward the inside of the silicon steel sheet and/or crystal grains having a larger grain size than the grain size of the non-laser-irradiated portion, that is, crystal grains 26 having a shape different from that of crystal grains 27 obtained by primary recrystallization are formed. The crystal grains 26 serve as starting points of crystal grain boundary growth at the time of secondary recrystallization.

The instantaneous power density Ip is less than 100kW/mm²In this case, it is difficult to sufficiently melt, scatter, or evaporate the silicon steel sheet 1. That is, it is difficult to form the groove 23. On the other hand, the instantaneous power density Ip exceeds 2000kW/mm²In this case, most of the molten steel is scattered or evaporated, and the crystal grains 26 are hard to be formed. The irradiation energy density Up exceeds 10J/mm²In this case, the molten portion of the silicon steel sheet 1 increases, and the silicon steel sheet 1 is easily deformed. On the other hand, the irradiation energy density is less than 1J/mm²When the magnetic properties were not improved, the magnetic properties were not observed. For these reasons, the above-described formulas 3 and 4 are preferably satisfied.

When the laser beam is irradiated, the assist gas 25 is blown to remove components scattered or evaporated from the silicon steel sheet 1 from the irradiation path of the laser beam 9. By this blowing, the laser beam 9 stably reaches the silicon steel sheet 1, and thus the grooves 23 are stably formed. Further, by blowing the auxiliary gas 25, the reattachment of the components to the silicon steel sheet 1 can be suppressed. In order to sufficiently obtain these effects, the flow rate of the assist gas 25 is preferably set to 10L (liters) per minute or more. On the other hand, when the flow rate exceeds 500L/min, the effect is saturated and the cost is increased. Therefore, the upper limit is preferably set to 500L/min.

The above-described preferable conditions are also the same in the case where the laser beam is irradiated between the decarburization annealing and the finish annealing and in the case where the laser beam is irradiated before and after the decarburization annealing.

The explanation returns to the explanation using fig. 1. After the application 5 and winding of the annealing separator, the steel sheet coil 31 is conveyed into the annealing furnace 6, and the central axis of the steel sheet coil 31 is placed in a substantially vertical direction, as shown in fig. 1. Then, batch annealing, so-called finish annealing, of the steel sheet coil 31 is performed by batch processing. The maximum attainment temperature of the batch annealing is set to, for example, about 1200 deg.c, and the holding time is set to, for example, about 20 hours. In the batch annealing, secondary recrystallization occurs, and a glass coating film is formed on the surface of the silicon steel sheet 1. Then, the steel sheet coil 31 is taken out of the annealing furnace 6.

In the glass coating film obtained by the above-described means, when the average value of the characteristic X-ray intensities of Mg in the portions of the grain-oriented electrical steel sheet surface other than the grooves is 1, the X-ray intensity ratio Ir of the characteristic X-ray intensities of Mg in the grooves is preferably in the range of 0 Ir 0.9. Within this range, good iron loss characteristics are obtained.

The X-ray intensity ratio is obtained by measurement using EPMA (Electron Probe microanalyzer), or the like.

Subsequently, the steel sheet coil 31 is fed to the annealing furnace 7 while being unwound, and a second continuous annealing, so-called temper annealing, is performed in the annealing furnace 7. In the second continuous annealing, the curling and strain deformation generated in the final annealing are removed to flatten the silicon steel sheet 1. The annealing conditions may be set to a temperature of 700 ℃ to 900 ℃ for 10 seconds to 120 seconds, for example. Next, coating 8 on the surface of the silicon steel sheet 1 is performed. In coating 8, a material capable of achieving the effects of securing electrical insulation and reducing the tension of iron loss is coated. After this series of processes, grain-oriented electrical steel sheet 32 is manufactured. After the coating is formed by the coating 8, the grain-oriented electrical steel sheet 32 is wound into a roll shape for convenience of storage, transportation, and the like.

In the case of producing grain-oriented electrical steel sheet 32 by the above-described method, crystal grain boundaries 41 penetrating the front and back surfaces of silicon steel sheet 1 along grooves 23 are generated during secondary recrystallization, as shown in fig. 6A and 6B. This is because the crystal grains 26 are less likely to be eroded by the gaussian-oriented crystal grains and remain at the end of the secondary recrystallization, and the crystal grains grown largely from both sides of the groove 23 at this time cannot be eroded each other although they are finally absorbed by the gaussian-oriented crystal grains.

In the grain-oriented electrical steel sheet manufactured according to the above embodiment, the crystal grain boundaries shown in fig. 7A are observed. These crystal grain boundaries include crystal grain boundaries 41 formed along the grooves. In addition, in the grain-oriented electrical steel sheet manufactured in the above-described embodiment except that the irradiation with the laser beam is omitted, the crystal grain boundaries shown in fig. 7B are observed.

Fig. 7A and 7B are photographs taken by removing a glass coating or the like from the surface of a grain-oriented electrical steel sheet to expose a base metal and then pickling the surface. In these photographs, crystal grains and crystal grain boundaries obtained by secondary recrystallization appear.

In the grain-oriented electrical steel sheet manufactured by the above-described method, the grooves 23 formed on the surface of the base metal provide an effect of finely dividing magnetic domains. Further, the effect of finely dividing the magnetic domains can be obtained by the crystal grain boundaries 41 penetrating the front and back surfaces of the silicon steel sheet 1 along the grooves 23. The iron loss can be further reduced by the synergistic effect of these.

Since the groove 23 is formed by irradiating a predetermined laser beam, the crystal grain boundary 41 is formed extremely easily. That is, after the grooves 23 are formed, it is not necessary to perform alignment or the like with reference to the positions of the grooves 23 for forming the crystal grain boundaries 41. Therefore, it is not necessary to significantly reduce the steel sheet passing speed, and the grain-oriented electrical steel sheet can be industrially mass-produced.

The irradiation with the laser beam can be performed at high speed, and the laser beam can be focused on a minute space to obtain high energy density. Therefore, the increase in the time required for the treatment is small as compared with the case where the irradiation with the laser beam is not performed. That is, the steel sheet passing speed at the time of performing the treatment such as decarburization annealing while unwinding the cold rolled coil is hardly changed regardless of the presence or absence of the irradiation of the laser beam. Further, since the temperature at which the laser beam is irradiated is not limited, a heat insulating mechanism of the laser irradiation device or the like is not necessary. Therefore, the configuration of the apparatus can be simplified as compared with the case where the treatment needs to be performed in the high-temperature furnace.

The depth of the groove 23 is not particularly limited, but is preferably 1 μm or more and 30 μm or less. If the depth of the groove 23 is less than 1 μm, the domain subdivision may become insufficient. When the depth of the groove 23 exceeds 30 μm, the amount of the base metal, which is a silicon steel plate as a magnetic material, is reduced, and the magnetic flux density is reduced. More preferably 10 μm or more and 20 μm or less. The grooves 23 may be formed only on one surface of the silicon steel sheet, or may be formed on both surfaces.

The interval PL of the grooves 23 is not particularly limited, but is preferably 2mm or more and 10mm or less. When the interval PL is less than 2mm, the slots significantly inhibit the formation of magnetic flux, and it is difficult to form sufficiently high magnetic flux density required for a transformer. On the other hand, when the interval PL exceeds 10mm, the effect of improving the magnetic properties by the grooves and the grain boundaries is greatly reduced.

In the above embodiment, 1 crystal grain boundary 41 is formed along 1 groove 23. However, for example, when the width of the groove 23 is wide and the crystal grains 26 are formed in a wide range in the rolling direction, some of the crystal grains 26 may grow faster than other crystal grains 26 at the time of secondary recrystallization. In this case, as shown in fig. 8A and 8B, a plurality of crystal grains 53 along the groove 23 are formed with a certain width below the thickness direction of the groove 23. The grain size Wcl of the crystal grains 53 in the rolling direction may be more than 0mm, for example, 1mm or more, but is easily 10mm or less. The reason why the particle diameter Wcl is easily 10mm or less is that the crystal grain which is most preferentially grown at the time of secondary recrystallization is the crystal grain 54 having the gaussian orientation, and the growth of the crystal grain 53 is hindered by the crystal grain 54. Crystal grain boundaries 51 substantially parallel to the grooves 23 exist between the crystal grains 53 and the crystal grains 54. Crystal grain boundaries 52 exist between adjacent crystal grains 53. The grain size Wcc of the crystal grains 53 in the plate width direction is easily 10mm or more, for example. The crystal grains 53 may exist in the form of one crystal grain in the width direction across the entire plate width, and in this case, the crystal grain boundary 52 may not exist. The particle size can be measured, for example, by the following method. After removing the glass coating and pickling to expose the base metal, the field of view of 100mm was observed in the rolling direction along the width direction of 300mm, and the dimensions of the crystal grains in the rolling direction and the thickness direction were measured by visual observation or image processing to obtain the average value.

The crystal grains 53 extending along the grooves 23 do not necessarily have to be crystal grains of gaussian orientation. However, since the size is limited, the influence on the magnetic characteristics is extremely small.

Patent documents 1 to 9 do not describe a technique of forming a groove by irradiating a laser beam as in the above-described embodiment, and generating a crystal grain boundary extending along the groove at the time of secondary recrystallization. That is, even though the laser beam irradiation is described, the timing of the irradiation is not appropriate, and thus the effects obtained in the above-described embodiments cannot be obtained.

Examples

(first experiment)

In the first experiment, hot rolling, annealing, and cold rolling of a steel material for grain-oriented electrical steel were performed so that the thickness of the silicon steel sheet was 0.23mm, and the silicon steel sheet was wound to form a cold rolled coil. 5 cold rolled coils were made. Next, 3 cold rolled coils corresponding to examples nos. 1, 2 and 3 were subjected to the formation of a groove by irradiation with a laser beam, and then subjected to decarburization annealing to cause primary recrystallization. The irradiation of the laser beam is performed using a fiber laser. The power P was 2000W, and the focal shape was 0.05mm in the L-direction diameter Dl and 0.4mm in the C-direction diameter Dc for examples No.1 and No. 2. In example No.3, the L-direction diameter Dl was 0.04mm and the C-direction diameter Dc was 0.04 mm. The scanning speed Vc was set to 10 m/sec for example Nos. 1 and 3 and to 50 m/sec for example No. 2. Therefore, the temperature of the molten metal is controlled,the instantaneous power density Ip is 127kW/mm for the examples No.1, No.2²1600kW/mm for example No.3². The irradiation energy density Up was 5.1J/mm for example No.1²1.0J/mm for example No.2²6.4J/mm for example No.3². The irradiation pitch PL was set to 4mm, and air was blown as an assist gas at a flow rate of 15L/min. As a result, the width of the groove formed was about 0.06mm, i.e., 60 μm, for example Nos. 1 and 3, and 0.05mm, i.e., 50 μm, for example No. 2. The depth of the grooves was about 0.02mm, i.e., 20 μm for example No.1, 3 μm for example No.2, and 30 μm for example No. 3. The variation in width is within + -5 μm and the variation in depth is within + -2 μm.

The other cold rolled coil corresponding to comparative example No.1 was subjected to primary recrystallization by forming a groove by etching and then decarburization annealing. The shape of the groove was set to the same shape as that of the groove of example No.1 formed by the irradiation of the laser beam described above. The remaining 1 cold rolled coil corresponding to comparative example No.2 was subjected to decarburization annealing without forming a groove, and primary recrystallization was caused.

In each of examples 1, 2, 3, 1 and 2, the coating of the annealing separating agent, the final annealing, the leveling annealing and the coating were performed on the silicon steel sheets after the decarburization annealing. Thus, 5 kinds of grain-oriented electrical steel sheets were produced.

The structure of these grain-oriented electrical steel sheets was observed, and it was found that secondary recrystallized grains formed by secondary recrystallization were present in all of example nos. 1, 2, 3, 1 and 2. In example nos. 1, 2, and 3, the same crystal grain boundaries along the grooves as the crystal grain boundaries 41 shown in fig. 6A or 6B exist, while in comparative example nos. 1 and 2, such crystal grain boundaries do not exist.

30 pieces of each sample were rolled from each of the above-mentioned oriented electrical steel sheetsThe average value of the magnetic properties of a Single plate having a length in the direction of 300mm and a length in the width direction of the plate of 60mm was measured by Single plate magnetic Test (SST). The measurement method was carried out according to IEC60404-3: 1982. As the magnetic properties, the magnetic flux density B was measured₈(T) and iron loss W_17/50(W/kg). Magnetic flux density B₈Is the magnetic flux density generated in the grain-oriented electrical steel sheet under a magnetizing force of 800A/m. Magnetic flux density B₈The grain-oriented electrical steel sheet having a larger value of (a) is suitable for a small-sized transformer having excellent efficiency because the magnetic flux density generated by the grain-oriented electrical steel sheet under a constant magnetizing force is larger. Iron loss W_17/50The iron loss is the iron loss when the grain-oriented electrical steel sheet is subjected to alternating current excitation under the conditions that the maximum magnetic flux density is 1.7T and the frequency is 50 Hz. Iron loss W_17/50The smaller the value of (b), the smaller the energy loss of the grain-oriented electrical steel sheet, and is suitable for a transformer. Magnetic flux density B₈(T) and iron loss W_17/50The average values (W/kg) are shown in Table 1 below. The single-plate sample was measured for the X-ray intensity ratio Ir using EMPA. The average values are shown in table 1 below.

TABLE 1

	B8Average value of (T)	W17/50Average value of (W/kg)	Average value of Ir
				Example No.1	1.89	0.74	0.5
Example No.2	1.90	0.76	0.9
				Example No.3	1.87	0.75	0.1
Comparative example No.1	1.88	0.77	1.0
				Comparative example No.2	1.91	0.83	1.0

As shown in Table 1, in examples Nos. 1, 2, and 3, the magnetic flux density B was increased by forming the grooves as compared with comparative example No.2₈However, the iron loss is significantly small because of the presence of the grooves and the crystal grain boundaries along the grooves. In examples 1, 2 and 3, since crystal grain boundaries along the grooves were present, the iron loss was also small as compared with comparative example 1.

(second experiment)

In the second experiment, verification was performed with respect to the irradiation condition of the laser beam. Here, the irradiation with the laser beam was performed under the following 4 conditions.

Under a first condition, a continuous wave fiber laser is used. The power P was set to 2000W, the L-direction diameter Dl was set to 0.05mm, and the C-direction diameter Dc was set0.4mm, and the scanning speed Vc is set to 5 m/sec. Thus, the instantaneous power density Ip is 127kW/mm²The irradiation energy density Up is 10.2J/mm². That is, the scanning speed was halved and the irradiation energy density Up was 2 times as high as the conditions in the first experiment. Therefore, the first condition does not satisfy equation 3. As a result, warping deformation of the steel sheet occurs with the irradiated portion as a starting point. The warping angle is 3 to 10 degrees, so that the winding is difficult.

Under the second condition, a continuous wave fiber laser is also used. The power P was set to 2000W, the L-direction diameter Dl was set to 0.10mm, the C-direction diameter Dc was set to 0.3mm, and the scanning speed Vc was set to 10 m/sec. Thus, the instantaneous power density Ip is 85kW/mm²The irradiation energy density Up is 2.5J/mm². That is, the L-direction diameter Dl and the C-direction diameter Dc are changed to reduce the instantaneous power density Ip as compared with the conditions of the first experiment. The second condition does not satisfy formula 4. As a result, it is difficult to form a penetrating grain boundary.

Under a third condition, a continuous wave fiber laser is also used. The power P was set to 2000W, the L-direction diameter Dl was set to 0.03mm, the C-direction diameter Dc was set to 0.03mm, and the scanning speed Vc was set to 10 m/sec. Thus, the instantaneous power density Ip is 2800kW/mm²The irradiation energy density Up is 8.5J/mm². That is, the L-direction diameter Dl is reduced and the instantaneous power density Ip is increased as compared with the conditions of the first experiment. Therefore, the third condition also does not satisfy formula 4. As a result, it is difficult to form crystal grain boundaries sufficiently along the grooves.

Under the fourth condition, a continuous wave fiber laser is also used. The power P was set to 2000W, the L-direction diameter Dl was set to 0.05mm, the C-direction diameter Dc was set to 0.4mm, and the scanning speed Vc was set to 60 m/sec. Thus, the instantaneous power density Ip is 127kW/mm²The irradiation energy density Up is 0.8J/mm². That is, the irradiation energy density Up is decreased while the scanning speed is increased as compared with the conditions of the first experiment. The fourth condition does not satisfy formula 3. As a result, it is difficult to form a groove having a depth of 1 μm or more in the fourth condition.

(third experiment)

In the third experiment, the irradiation with the laser beam was performed under both the condition of making the flow rate of the assist gas less than 10L/min and the condition of not supplying the assist gas. As a result, it is difficult to stabilize the depth of the grooves, and the variation in the width of the grooves is + -10 μm or more and the variation in the depth is + -5 μm or more. Therefore, the variation in magnetic characteristics was large as compared with the examples.

Industrial applicability

According to the aspect of the present invention, a grain-oriented electrical steel sheet with less iron loss can be obtained by a method that enables industrial mass production.

Description of the reference symbols

1 silicon steel sheet

2 laser beam irradiation apparatus

3. 6, 7 annealing furnace

31 steel plate coil

32-oriented electrical steel sheet

9. 19 laser beam

10. 20 scanning device

23 groove

24 laser beam focusing spot

25 assist gas

26. 27, 53, 54 crystal grains

41. 51, 52 crystal grain boundaries

Claims (2)

1. A grain-oriented electrical steel sheet, comprising: a groove formed along a track of the laser beam scanned from one end edge to the other end edge in the width direction, and a crystal grain boundary extending along the groove and penetrating the front and back,

and forming a glass coating film on the groove, wherein when an average value of characteristic X-ray intensities of Mg in portions of the surface of the grain-oriented electrical steel sheet other than the groove of the glass coating film is 1, an X-ray intensity ratio Ir of the characteristic X-ray intensities of Mg in the groove of the glass coating film is in a range of 0 Ir 0.9.

2. The grain-oriented electrical steel sheet according to claim 1, having the following crystal grains: the grain size of the crystal grain in the width direction of the grain-oriented electrical steel sheet is 10mm or more and 10mm or less, and the grain size of the crystal grain in the length direction of the grain-oriented electrical steel sheet exceeds 0mm and is 10mm or less, the crystal grain being present from the groove to the back surface of the grain-oriented electrical steel sheet.