JP2012177149A - Grain-oriented silicon steel sheet, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grain-oriented silicon steel sheet obtaining excellent noise characteristics and core loss characteristics when the steel sheets are assembled to an actual transformer.SOLUTION: The average β angle of the secondary recrystallized particle is ≤2°. The average β angle variation range within the secondary recrystallized particle is ≥1° and ≤4°. Surface tension in the rolling direction is ≥10 MPa. Magnetostriction λp-p at the magnetic flux density of 1.7T and the frequency of 50 Hz is ≤1.0×10. Further, the plate thickness t and the core loss Wsatisfy following expression (1): W≤2.1×t +0.3, where t denotes the plate thickness (mm).

Description

  The present invention relates to a grain-oriented electrical steel sheet used for a core material such as a transformer and a method for manufacturing the grain-oriented electrical steel sheet.

The grain-oriented electrical steel sheet is mainly used as an iron core of a transformer, and is required to have excellent magnetization characteristics, particularly low iron loss.
To that end, it is important to align the secondary recrystallized grains in the steel plate with a high degree of (110) [001] orientation (so-called Goth orientation) and to reduce impurities in the product steel plate. There is a limit to the control of the orientation and the reduction of impurities in view of the manufacturing cost. In view of this, Japanese Patent Application Laid-Open No. H10-228561 discloses a technique for reducing the iron loss by introducing strain to the surface of the steel sheet with an electron beam and subdividing the width of the magnetic domain.

Japanese Patent Publication No. 06-072266

  However, when an attempt is made to obtain a good iron loss characteristic in the region shown in FIG. 1 by the above-mentioned magnetic domain subdivision process, the required distortion amount increases, so that the magnetostriction characteristic deteriorates and the noise of the actual transformer is reduced. However, it is difficult to achieve both iron loss and noise.

  The present invention has been developed in view of the above situation, and proposes a grain-oriented electrical steel sheet capable of obtaining excellent noise characteristics and iron loss characteristics when assembled in an actual transformer, and a method of manufacturing the same. Objective.

As described above, the increase in noise generated in an actual transformer using a material having an excellent iron loss characteristic using electron beam irradiation is due to the deterioration of the magnetostriction characteristic due to the introduction of strain. Here, in order to prevent the deterioration of the noise characteristics, it has been found that it is most effective to reduce the strain introduction amount. Therefore, the inventors examined a method for obtaining a sufficient magnetic domain refinement effect with a small amount of strain introduction.
As a result, the magnetic domain width before electron beam irradiation treatment is made as narrow as possible by controlling the crystal orientation (β angle) of the secondary recrystallized grains in the steel sheet, the β angle variation in the grains, and the surface tension in the rolling direction. It was revealed that good iron loss characteristics can be obtained even with a small amount of strain introduction.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. A grain-oriented electrical steel sheet subjected to magnetic domain refinement treatment by introducing thermal strain, wherein the average β angle of secondary recrystallized grains is 2 ° or less, and the average β angle fluctuation range in the grains of secondary recrystallized grains is 1 ° or more and 4 ° or less, surface tension in the rolling direction is 10 MPa or more, magnetic strain λp-p value is 1.0 × 10 ⁻⁶ or less at magnetic flux density: 1.7 T, frequency: 50 Hz, and sheet thickness t A _grain- oriented electrical steel sheet with excellent transformer characteristics, characterized in that the iron loss W _17/50 satisfies the following formula (1).
Record
W _17/50 ≦ 2.1 × t + 0.3 (1)
t: Thickness (mm)

  2. 2. The grain-oriented electrical steel sheet having excellent transformer characteristics as described in 1 above, wherein the introduction of the thermal strain is by electron beam irradiation.

3. The slab for grain-oriented electrical steel sheet is hot-rolled and subjected to hot-rolled sheet annealing, and then subjected to cold rolling twice or more with intermediate or intermediate annealing, and finished to the final sheet thickness, followed by decarburization. After annealing and then applying an annealing separator mainly composed of MgO to the steel sheet surface, after final finishing annealing, it is subjected to tension coating treatment that also serves as flattening annealing, and after this finishing annealing or the tension In the method for producing grain-oriented electrical steel sheets, which is a series of steps, after the coating treatment, the magnetic domain fragmentation treatment by introducing thermal strain.
(a) In the cooling process during the hot-rolled sheet annealing, the cooling rate in the temperature range of 750 to 350 ° C. is 40 ° C./s or more.
(b) The final finish annealing is performed in a coil shape, and the inner diameter of the coil is 500 mm or more and the outer diameter is 1500 mm or less.
(c) The line tension at 800 ° C. or higher during the flattening annealing is 8 to 12 MPa.
(d) When the thermal strain is introduced, by adjusting the amount of strain introduced, the magnetostriction λp-p at a magnetic flux density of 1.7 T and a frequency of 50 Hz is 1.0 × 10 ⁻⁶ or less, and the thickness t and the iron loss A method for _{producing a grain-} oriented electrical steel sheet having excellent transformer characteristics, wherein W _17/50 is controlled to satisfy the following formula (1).
Record
W _17/50 ≦ 2.1 × t + 0.3 (1)
t: Thickness (mm)

  4). 4. The method for producing a grain-oriented electrical steel sheet having excellent transformer characteristics as described in 3 above, wherein the introduction of the thermal strain is performed by electron beam irradiation.

  According to the present invention, it is possible to achieve both excellent iron loss characteristics and excellent noise characteristics in an actual transformer in which grain-oriented electrical steel sheets that have been subjected to thermal distortion by an electron beam or the like to reduce iron loss are laminated. became.

It is the graph which showed the relationship between the plate | board thickness of a steel plate, and an iron loss value. It is the graph which showed the result of having measured the iron loss before the magnetic domain refinement | purification process of the grain-oriented electrical steel sheet from which an average beta angle and the average beta angle fluctuation in a grain differ. It is the graph which showed the iron loss evaluation result after irradiating an electron beam with the output of 150W, and performing a magnetic domain subdivision process in relation to (beta) angle. It is the graph which showed the result of having investigated the relationship between the output of an electron beam, and a core loss. It is the graph which showed the result of having investigated the relationship between the output of a laser irradiation, and a core loss. It is a graph showing the results of measuring noise and iron loss at 50 Hz, 1.7 T, assembled in a 300 kVA real transformer.

Hereinafter, the present invention will be specifically described.
First, the experimental results that led to the completion of the present invention will be described.
FIG. 2 shows the results of measuring the iron loss before magnetic domain refinement of grain-oriented electrical steel sheets having different average β angles of secondary recrystallized grains (hereinafter also simply referred to as secondary grains) and average β angle fluctuations within the grains. (Results of evaluating samples having an average β angle of 0.5 ° or less and an average β angle of 2.5 to 3.5 °).
The α angle is the deviation angle of the secondary grain orientation from the (110) <001> ideal orientation with respect to the rolling surface normal direction (ND) axis. Further, the β angle is a deviation angle of the secondary grain orientation from the (110) <001> ideal orientation with respect to the rolling perpendicular direction (TD) axis.

All the samples evaluated had an average α angle in the range of 2.8 to 3.2 °, and the α angle was almost the same level.
When the average β angle variation in the secondary grains is small, the iron loss is greatly increased at a β angle of 2 ° or less. On the other hand, when the average β angle variation in the secondary grains was large, the amount of increase in iron loss at a β angle of 2 ° or less was smaller than when the average β angle variation was small.
The above phenomenon is because the deterioration of the iron loss with a β angle of 2 ° or less is due to a sudden increase in the magnetic domain width due to a decrease in the β angle. When the average β angle variation in the grains is large, the iron loss increase is small. This is considered to be because the part where the β angle existing in a part of the grain is large, that is, the part where the magnetic domain width is small also affects the part where the β angle is small, and the increase in the magnetic domain width is suppressed.

  FIG. 3 shows the iron loss evaluation result after irradiation with an electron beam at an output of 150 W and magnetic domain fragmentation treatment, and particularly good iron loss characteristics were exhibited when the β angle was 2 ° or less. From this, it can be said that it is important to make the β angle 2 ° or less in order to improve the iron loss. Next, FIG. 4 shows the results of investigating the relationship between the output of the electron beam and the iron loss for the β = 1 ° sample showing good iron loss characteristics. When the β angle variation in the grains was large, the iron loss characteristics were good even with a low output of the electron beam. As described above, this is considered to be a phenomenon caused by a small magnetic domain width before the electron beam irradiation treatment.

  After that, we continued to search for conditions under which the magnetic domain fragmentation effect can be obtained even when the electron beam irradiation is low. As a result, it was found that it is important that the average β angle variation in the secondary grains is in the range of 1 ° to 4 °. FIG. 5 shows the result of a similar experiment performed by laser irradiation. The same tendency was observed with the laser irradiated material although the effect was somewhat low.

Here, the reason why the effect is slightly different between the laser and the electron beam is considered as follows. The electron beam has a higher penetration ability into the steel plate than the laser and can introduce strain more effectively. It is thought that this difference in penetration ability led to different results due to the condition that the magnetic domain width before irradiation was narrow.
Conventionally, sufficient distortion is introduced under high output conditions, so that it is difficult to make a difference between a laser and an electron beam. In addition, when the magnetic domain width before processing is wide even at low output, the influence of the wide magnetic domain width is larger, and even with an electron beam with excellent penetration ability, the iron loss is not sufficiently reduced, and the difference between the electron beam and the laser is difficult to appear. I think.
From the above results, it is important to make the magnetic domain width as small as possible before the magnetic domain subdivision treatment is an important point for obtaining a good iron loss when the electron beam irradiation is performed under a low output condition. found.

  Next, the surface tension (hereinafter also simply referred to as tension) in the rolling direction, which has an influence on the magnetic domain width, was investigated. As a result, it was found that the above-described phenomenon does not occur unless the surface tension is 10 MPa or more. Here, the surface tension of the sample of the above experiment was measured and found to be 14 MPa. In addition, the tension | tensile_strength of the steel plate surface was calculated | required by the method shown below.

In addition, with the sample irradiated with the electron beam under each irradiation condition in FIG. 4 and subjected to magnetic domain subdivision processing, a 300 kVA actual transformer was assembled, and the results of measuring noise and iron loss at 50 Hz and 1.7 T are shown in FIG. ) And (b). The design values of this transformer are iron loss: 0.82 W / kg and noise: 46 dB. There is a condition that transformer iron loss and noise are good only under the condition of large β angle fluctuation.
Therefore, the material magnetostriction under conditions with good noise was measured. As a result, λp-p was 1.0 × 10 ⁻⁶ or less, and noisy noises were all over 1.0 × 10 ⁻⁶ .
Therefore, the magnetostriction characteristic λp-p in the present invention is 1.0 × 10 ⁻⁶ or less. Among them, the region condition with the best iron loss / noise balance is preferably 0.8 × 10 ⁻⁶ or less because λp-p is 0.8 × 10 ⁻⁶ or less.

From the above, in order to satisfy the iron loss characteristic and noise characteristic of the transformer, the average β angle of β angle secondary grains is 2 ° or less, the average β angle variation in the grains is 1 ° or more and 4 ° or less, and rolling Even if the surface tension with respect to the direction is 10 MPa or more, and the λp-p of magnetostriction at a magnetic flux density of 1.7 T and a frequency of 50 Hz is 1.0 × 10 ⁻⁶ or less, the iron loss characteristic at each thickness t (mm) is W _{17 /} It has been found that it is necessary to introduce thermal distortion of the electron beam under conditions that satisfy ₅₀ ≦ 2.1 × t + 0.3.

  In the present invention, the X-ray Laue method is used, the measurement interval is set to 1 mm pitch, the fluctuation width in the secondary grain and the average crystal orientation of the crystal grain at all measurement points in one grain ( α angle and β angle) were obtained. Here, 50 crystal grains were randomly measured, and the average value was taken as the crystal orientation of the entire sample.

When measuring the tension in the rolling direction as described above from the product (tension coating coating material), a sample with a perpendicular direction of rolling: 280 mm x rolling direction: 30 mm is cut out, and then a forsterite film and tension coating on one side are cut out. The amount of warpage obtained by measuring the amount of warpage of the steel sheet before and after the removal is converted into tension by the following conversion formula (2).
The tension obtained by this method is the tension applied to the surface from which the forsterite film and the tension coating have not been removed. Since the tension is applied to both sides of the sample, the tension for each side is obtained by the above method, and the tension on the opposite side is obtained by a similar method using another sample of the same product. The tension applied to the sample was used.

Next, a method for controlling the β angle will be described.
The point of control of the β angle can be controlled within the optimum range of the present invention by adjusting the curvature per secondary grain during coil annealing. Here, the factor that has the greatest influence on the curvature per secondary grain is the coil diameter during annealing. That is, when the coil diameter is large, the curvature decreases, and the β-angle variation in the grains becomes small. On the other hand, when the coil diameter is small, the curvature increases, and the β angle variation in the grains increases.
Therefore, in order to control the total coil length within the target range of the present invention, it is necessary to set the coil inner diameter to 500 mm or more and the coil outer shape to 1500 mm or less.

Hereinafter, a method for controlling the β angle to 2 ° or less will be described.
For this control, it is extremely effective to improve the primary recrystallization texture by adjusting the cooling rate during hot-rolled sheet annealing. That is, it is a means for changing the primary recrystallization texture formed after rolling by increasing the cooling rate during hot-rolled sheet annealing and finely depositing carbides that precipitate during cooling. Specifically, in the cooling process during hot-rolled sheet annealing, the temperature range of 750 to 350 ° C. is cooled at a rate of 40 ° C./s or more.

Hereinafter, a method for setting the surface tension in the rolling direction to 10 MPa or more will be described.
The rolling direction tension is applied by the forsterite film and the tension coating applied thereon. In order to increase the tension by the tension coating, it is effective to increase the line tension and stretch the steel sheet particularly in the temperature range of 800 ° C. or higher in the tension coating process that also serves as flattening annealing. However, if the line tension is too high, the forsterite film is destroyed and the tension of the forsterite film is greatly reduced, so that the desired surface tension cannot be obtained. Therefore, in order not to destroy the forsterite film, the line tension is limited to 12 MPa or less. On the other hand, when the line tension is low, the tension applied by the tension coating is low, and the flattening effect is reduced to cause a shape defect. Therefore, the lower limit of the line tension is 8 MPa.

Hereinafter, the thermal strain introduction method will be described.
As the thermal strain introduction method in the present invention, a known thermal strain introduction method such as an electron beam or a laser may be applied, but it is preferable to use an electron beam that has a high penetration ability into a steel plate and has a higher effect. Here, in order to obtain the grain-oriented electrical steel sheet of the present invention, parameters for changing the amount of strain introduced include beam output, irradiation interval, scanning speed, degree of vacuum, and the like. These parameters may be combined so that the iron loss characteristics and magnetostriction characteristics of the steel sheet satisfy the present invention. The parameters to be controlled are not particularly limited, but it is relatively easy to change the beam output and irradiation interval. The irradiation direction is a direction crossing the rolling direction, preferably 60 ° to 90 °, and preferably 3 to 15 mm apart.

  As other conditions, the electron beam preferably has an acceleration voltage of 10 to 200 kV, a beam current of 0.1 to 100 mA, and a beam diameter of 0.01 to 0.3 mm. The laser preferably has a heat amount per unit length of about 5 to 100 J / m and a spot diameter of about 0.1 to 0.5 mm.

For samples in which the β angle and β angle fluctuation are controlled within the scope of the present invention under the above-described thermal strain introduction conditions, the magnetostriction λp-p at a magnetic flux density of 1.7 T and a frequency of 50 Hz is 1.0 × 10 ⁻⁶ or less, and The iron loss characteristic of the steel sheet can satisfy the following formula (1).
W _17/50 ≦ 2.1 × t + 0.3 (1)
On the other hand, when the β angle and β angle fluctuation are not controlled within the scope of the present invention, even if the thermal strain introduction condition is adjusted, if the desired iron loss is aimed, the magnetostriction becomes too large, and an attempt is made to optimize the magnetostriction. Then, since the iron loss becomes insufficient, it becomes difficult to achieve both good iron loss characteristics and good magnetostriction characteristics.

  In addition to the above conditions, it is also effective to reduce the particle size of the secondary grains in order to make the magnetic domain width before the magnetic domain refinement treatment as small as possible. As described above, it is possible to obtain the effect of the present invention by controlling the coil diameter and the surface tension. However, since the stability is improved by adding the control of the secondary particle size, the secondary particle It is preferable to control the diameter simultaneously. Specifically, the secondary particle size is preferably 15 mm or less, and the method is to increase the temperature rising rate during decarburization annealing to 50 ° C./s or more so that goth grains in the primary recrystallization texture It is extremely effective to increase the frequency of the presence of. More preferably, the rate of temperature rise is set to 100 ° C./s or more.

In the present invention, the component composition of the slab for grain-oriented electrical steel sheet may be any component composition that produces secondary recrystallization with a large magnetic domain refinement effect.
Further, when using an inhibitor, for example, when using an AlN-based inhibitor, Al and N, and when using an MnS / MnSe-based inhibitor, an appropriate amount of Mn and Se and / or S should be contained. Good. Of course, both inhibitors may be used in combination. The preferred contents of Al, N, S and Se in this case are Al: 0.01 to 0.065 mass%, N: 0.005 to 0.012 mass%, S: 0.005 to 0.03 mass%, and Se: 0.005 to 0.03 mass%, respectively. .

Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets in which the contents of Al, N, S, and Se are limited and no inhibitor is used.
In this case, the amounts of Al, N, S and Se are preferably suppressed to Al: 100 mass ppm or less, N: 50 mass ppm or less, S: 50 mass ppm or less, and Se: 50 mass ppm or less.

The basic components and optional components of the slab for grain-oriented electrical steel sheets according to the present invention are specifically described as follows.
C: 0.08 mass% or less C is added to improve the hot-rolled sheet structure, but if it exceeds 0.08 mass%, it is difficult to reduce C to 50 mass ppm or less where no magnetic aging occurs during the manufacturing process. Therefore, the content is preferably 0.08% by mass or less. In addition, regarding the lower limit, since a secondary recrystallization is possible even for a material not containing C, it is not particularly necessary to provide it.

Si: 2.0 to 8.0 mass%
Si is an element effective in increasing the electrical resistance of steel and improving iron loss. However, if the content is less than 2.0% by mass, a sufficient iron loss reduction effect cannot be achieved, while 8.0% by mass. If it exceeds 1, the workability is remarkably lowered and the magnetic flux density is also lowered. Therefore, the Si content is preferably in the range of 2.0 to 8.0% by mass.

Mn: 0.005 to 1.0 mass%
Mn is an element necessary for improving the hot workability. However, if the content is less than 0.005% by mass, the effect of addition is poor, whereas if it exceeds 1.0% by mass, the magnetic flux density of the product plate decreases. The amount of Mn is preferably in the range of 0.005 to 1.0 mass%.

In addition to the above basic components, the following elements known as magnetic property improving components can be appropriately contained.
Ni: 0.03-1.50% by mass, Sn: 0.01-1.50% by mass, Sb: 0.005-1.50% by mass, Cu: 0.03-3.0% by mass, P: 0.03-0.50% by mass, Mo: 0.005-0.10% by mass and Cr: At least one selected from 0.03 to 1.50 mass%
Ni is an element useful for improving the magnetic properties by improving the hot-rolled sheet structure. However, if the content is less than 0.03% by mass, the effect of improving the magnetic properties is small. On the other hand, if the content exceeds 1.5% by mass, the secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, the amount of Ni is preferably in the range of 0.03 to 1.5 mass%.

Sn, Sb, Cu, P, Mo and Cr are elements useful for improving the magnetic properties, respectively, but if any of them is less than the lower limit of each component described above, the effect of improving the magnetic properties is small, When the upper limit amount of each component described above is exceeded, the development of secondary grains is inhibited.
The balance other than the above components is inevitable impurities and Fe mixed in the manufacturing process.

  Next, the slab having the above-described component composition is heated and subjected to hot rolling according to a conventional method, but may be immediately hot rolled after casting without being heated. In the case of a thin slab, hot rolling may be performed, or the hot rolling may be omitted and the process may proceed as it is.

Furthermore, hot-rolled sheet annealing is performed as necessary. At this time, in order to develop a goth structure at a high level in the product plate, a range of 800 to 1100 ° C. is preferable as the hot-rolled sheet annealing temperature. When the hot-rolled sheet annealing temperature is less than 800 ° C, the band structure in hot rolling remains, making it difficult to achieve a sized primary recrystallization structure and inhibiting the development of secondary recrystallization. . On the other hand, when the hot-rolled sheet annealing temperature exceeds 1100 ° C., the grain size after the hot-rolled sheet annealing is excessively coarsened, so that it is very difficult to realize a sized primary recrystallized structure.
Further, as described above, the cooling rate during the hot-rolled sheet annealing needs to be 40 ° C./s or more in average in a temperature range of at least 750 to 350 ° C.

After hot-rolled sheet annealing, cold rolling is performed once or two or more times with intermediate annealing between them to finish the final sheet thickness, and after decarburization annealing, an annealing separator is applied. After applying the annealing separator, it is wound around a coil and subjected to final finish annealing for the purpose of secondary recrystallization and forsterite film formation.
Here, as described above, the rate of temperature increase during this decarburization annealing is preferably 50 ° C./s or more, more preferably 100 ° C./s or more.
Further, as described above, the final finish annealing is performed in a coil shape, and at that time, the inner diameter of the coil needs to be 500 mm or more and the outer diameter needs to be 1500 mm or less.

After the final finish annealing, it is effective to correct the shape by performing flattening annealing. In the present invention, an insulating coating is applied to the steel sheet surface before or after planarization annealing. Here, in the present invention, this insulating coating means a coating (hereinafter referred to as tension coating) that can apply tension to a steel sheet in order to reduce iron loss. Examples of the tension coating include silica-containing inorganic coating, physical vapor deposition, and ceramic coating by chemical vapor deposition.
As described above, it is necessary to set the line tension at 800 ° C. or higher during the flattening annealing to 8 to 12 MPa.

Next, in the present invention, magnetic domain subdivision processing is performed by introducing strain. The strain introduction method is a known method such as an electron beam or a laser, and each parameter and other conditions relating to strain introduction are as described above. In this case, as described above, it is necessary to control the magnetostriction λp-p to 1.0 × 10 ⁻⁶ or less by adjusting the amount of strain introduced in the strain introduction.

  In the present invention, except for the above-described steps and manufacturing conditions, a conventionally known method for manufacturing a grain-oriented electrical steel sheet that introduces thermal strain and performs magnetic domain refinement can be used as appropriate.

C: 0.055 mass%, Si: 3.05 mass%, Mn: 0.08 mass%, Ni: 0.02 mass%, Al: 190 mass ppm, N: 65 mass ppm, Se: 150 mass ppm, S: 10 mass ppm and O: A steel slab containing 15 ppm by mass, the balance being made of Fe and inevitable impurities, manufactured by continuous casting, heated to 1450 ° C, and hot rolled into a sheet thickness: 2.4 mm, Hot-rolled sheet annealing was performed at 1025 ° C. for 300 seconds. At this time, the cooling rate in the temperature range of 350 to 750 ° C. in the cooling process of hot-rolled sheet annealing was changed in the range of 20 to 60 ° C./s. Subsequently, intermediate annealing was performed by cold rolling to an intermediate plate thickness of 1.6 mm, an oxidation degree of PH ₂ O / PH ₂ = 0.42, a temperature of 1075 ° C., and a time of 20 seconds. Then, after removing the subscale on the surface by hydrochloric acid pickling, cold rolling was performed again to obtain a cold-rolled sheet having a sheet thickness of 0.215 mm.

Next, after decarburization annealing was performed at an oxidation degree of PH ₂ O / PH ₂ = 0.52 and a soaking temperature of 825 ° C. for 300 seconds, an annealing separator containing MgO as a main component was applied, and secondary recrystallization Final finish annealing for the purpose of stellite film formation and purification was performed at 1220 ° C. for 50 hours. The heating rate during decarburization annealing was changed to 20 to 100 ° C./s, the inner diameter during final finish annealing was set to 300 mm to 700 mm, and the outer diameter was set to 1200 to 1800 mm.

Then, an insulating coat composed of 60% colloidal silica and aluminum phosphate was applied and baked at 850 ° C. This coating application treatment also serves as flattening annealing. During flattening annealing, the line tension of 800 ° C. or more was changed in the range of 6 to 14 MPa. Thereafter, a magnetic domain fragmentation treatment in which an electron beam or a laser was irradiated at right angles to the rolling direction was performed on one side.
The electron beam / laser irradiation conditions were performed under a plurality of conditions as shown in Table 1 for the irradiation interval and beam output.

Next, each product was sheared at an oblique angle, a 1000 kVA three-phase transformer was assembled, and iron loss and noise were measured in an excited state at 60 Hz and 1.7 T. The design values of iron loss and noise in this transformer are 0.94W / kg and 70dB. Separately, samples were taken at intervals of 500 m from the obtained coil, and the secondary grain diameter, average β angle, average β angle fluctuation, and surface tension in the rolling direction were evaluated. For the material characteristics, the maximum value of the sample in each coil is shown.
Each evaluation result is shown in Table 1.

As shown in the table, when a directional electrical steel sheet that satisfies the scope of the present invention is used over the entire length of the coil, the condition that the amount of strain introduced into the steel sheet is small (the beam output is low or the irradiation interval is increased). However, both the iron loss and noise satisfy the design values.
Also, the iron loss of the steel plate is from the above formula (1),
W _17/50 ≦ 2.1 × 0.215 + 0.3 ＝ 0.7515
W _17/50 ≦ 0.7515 (W / kg)
From the iron loss W _17/50 It can be seen that 0.7515 (W / kg) or less is satisfied.
On the other hand, when the grain-oriented electrical steel sheet that deviates from the scope of the present invention is present in a part of the coil, an actual transformer using the coil as an iron core material cannot obtain various characteristics as designed.

Claims (4)

A grain-oriented electrical steel sheet subjected to magnetic domain refinement treatment by introducing thermal strain, wherein the average β angle of secondary recrystallized grains is 2 ° or less, and the average β angle fluctuation range in the grains of secondary recrystallized grains is 1 ° or more and 4 ° or less, surface tension in the rolling direction is 10 MPa or more, magnetic strain λp-p value is 1.0 × 10 ⁻⁶ or less at magnetic flux density: 1.7 T, frequency: 50 Hz, and sheet thickness t A _grain- oriented electrical steel sheet with excellent transformer characteristics, characterized in that the iron loss W _17/50 satisfies the following formula (1).
Record
W _17/50 ≦ 2.1 × t + 0.3 (1)
t: Thickness (mm)   The grain-oriented electrical steel sheet having excellent transformer characteristics according to claim 1, wherein the introduction of the thermal strain is caused by electron beam irradiation. The slab for grain-oriented electrical steel sheet is hot-rolled and subjected to hot-rolled sheet annealing, and then subjected to cold rolling twice or more with intermediate or intermediate annealing, and finished to the final sheet thickness, followed by decarburization. After annealing and then applying an annealing separator mainly composed of MgO to the steel sheet surface, after final finishing annealing, it is subjected to tension coating treatment that also serves as flattening annealing, and after this finishing annealing or the tension In the method for producing grain-oriented electrical steel sheets, which is a series of steps, after the coating treatment, the magnetic domain fragmentation treatment by introducing thermal strain.
(a) In the cooling process during the hot-rolled sheet annealing, the cooling rate in the temperature range of 750 to 350 ° C. is 40 ° C./s or more.
(b) The final finish annealing is performed in a coil shape, and the inner diameter of the coil is 500 mm or more and the outer diameter is 1500 mm or less.
(c) The line tension at 800 ° C. or higher during the flattening annealing is 8 to 12 MPa.
(d) When the thermal strain is introduced, by adjusting the amount of strain introduced, the magnetostriction λp-p at a magnetic flux density of 1.7 T and a frequency of 50 Hz is 1.0 × 10 ⁻⁶ or less, and the thickness t and the iron loss A method for _{producing a grain-} oriented electrical steel sheet having excellent transformer characteristics, wherein W _17/50 is controlled to satisfy the following formula (1).
Record
W _17/50 ≦ 2.1 × t + 0.3 (1)
t: Thickness (mm)   4. The method for producing a grain-oriented electrical steel sheet having excellent transformer characteristics according to claim 3, wherein the introduction of the thermal strain is performed by electron beam irradiation.

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