JP2012177162A - Method for manufacturing grain-oriented magnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining a grain-oriented magnetic steel sheet that exhibits superior iron loss properties in producing a transformer therewith, in a method for manufacturing a grain-oriented magnetic steel sheet, which applies a magnetic domain subdivision treatment to a material by using electron beam irradiation after flattening annealing.SOLUTION: In subjecting a grain-oriented magnetic steel sheet slab containing 2.0-4.5 mass% of Si, as a material, to the flattening annealing, the method adjusts each condition of a soaking temperature in annealing the material, a cooling rate in a step of cooling the material from the soaking temperature and a plastic elongation amount of the steel sheet, and controls a reduction in coating tension of a forsteritic coating before and after the flattening annealing treatment to be 60% or less.

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent iron loss characteristics used for a core material such as a transformer.

  A grain-oriented electrical steel sheet is a material mainly used as an iron core of a transformer. It is known that the iron loss and magnetostriction of the iron core material have a strong influence on the iron loss and noise of the transformer, and research on reducing the iron loss and magnetostriction of the grain-oriented electrical steel sheet is being actively conducted. Examples of means for achieving low iron loss include magnetic domain fragmentation. These are, for example, methods of introducing a local micro-strain by laser irradiation (see Patent Document 1), plasma irradiation (see Patent Document 2), and electron beam irradiation (see Patent Document 3) to subdivide magnetic domains and reduce iron loss. It is. The present invention uses electron beam irradiation as a magnetic domain subdivision process. Although electron beam irradiation has a handicap that a high vacuum must be used, the beam can be narrowed down, the beam can be scanned easily, the beam penetration depth is deep, and the beam energy efficiency is good It has a number of advantages.

Next, a general method for manufacturing a grain-oriented electrical steel sheet will be described.
A slab containing about 3% Si and an inhibitor component (AlN, MnSe, etc.) is hot-rolled, hot-rolled sheet annealing is performed as necessary, and cold rolling is performed once or two or more times with intermediate annealing. . The obtained cold-rolled sheet is decarburized and annealed, an annealing separator mainly composed of MgO is applied, and finish annealing is performed with coil foam to form a forsterite (Mg ₂ SiO ₄ ) -based film. This forsterite film is formed by reacting SiO ₂ formed on the steel plate surface by decarburization annealing and MgO in the annealing separator during the final annealing. Forsterite has a smaller coefficient of thermal expansion than steel, so when it is formed at a high temperature and then cooled to room temperature, it gives tensile stress to the steel (hereinafter, the tensile stress applied to the steel by the coating) Called). The film tension has an important role of reducing the iron loss of the grain-oriented electrical steel sheet and reducing the magnetostriction.

  On the other hand, since the finish annealing is performed with coil foam, flattening annealing for correcting winding is required. In flattening annealing, it is common to simultaneously bake a glassy coating using phosphate and colloidal silica as raw materials. This glassy coating also has a low coefficient of thermal expansion and has the role of imparting tensile stress to the steel sheet. The purpose of the flattening annealing is to correct the shape by plastically deforming the steel sheet, but it is known that when the plastic deformation is too large, dislocations are introduced into the steel and the iron loss and magnetostriction characteristics deteriorate. For example, Patent Document 4 proposes a technique for improving iron loss by setting the plastic elongation of a steel sheet in flattening annealing to 0.03 to 0.15% and setting the temperature gradient in the cooling process to 1.5 ° C./cm or less.

Japanese Patent Publication No.57-2252 JP-A 62-96617 JP-A 63-186826 JP-A-7-305115

Maruyama / Nakajima, P170, High-temperature strength material science, Uchida Otsukuru

However, the material that is irradiated with an electron beam by the conventional method and magnetically subdivided exhibits the same iron loss as the magnetically subdivided material with a laser or the like, but has characteristics that are expected to actually produce a transformer. There was a problem that it could not be obtained. That is, there is a problem that a material obtained by irradiating an electron beam and subdividing a magnetic domain has a large value obtained by dividing an equipment iron loss by a material iron loss, a so-called building factor.
Moreover, if the furnace tension is lowered in order to reduce the plastic elongation of the steel sheet, there is a problem that the steel sheet becomes easy to meander and stable plate passing is difficult. Furthermore, if the annealing temperature is lowered in order to reduce the plastic elongation, there is a problem that the properties of the glassy coating deteriorate, and in fact, the plastic elongation of the steel sheet is adjusted by adjusting the flattening annealing conditions. It was difficult to adjust.
That is, the prior art related to flattening annealing places importance on the magnetic properties of the obtained material, and no particular consideration is given to the deterioration of other properties, particularly the iron loss properties when a transformer is manufactured. It was. In addition, the combination with the magnetic domain fragmentation has not been studied.

  The present invention has been developed in view of the above-described situation, and is an excellent iron when a transformer is manufactured in a method of manufacturing a grain-oriented electrical steel sheet that is subjected to magnetic domain subdivision treatment after flattening annealing using electron beam irradiation. It aims at providing the method of obtaining the grain-oriented electrical steel sheet which has a loss characteristic.

Hereinafter, the experiment that led to the completion of the present invention will be described.
The inventors produced grain-oriented electrical steel sheets under various production conditions in a factory production line, and subjected the obtained steel sheets to magnetic domain fragmentation treatment by electron beam irradiation. A transformer was made using steel plates that had been subjected to magnetic domain subdivision treatment, the iron loss and noise of the transformer were investigated, and the correlation with the iron loss characteristics of the material steel plate was investigated. As a result, it has been clarified that transformer core materials having poor iron loss and noise characteristics tend to have low film tension of forsterite film.

なお、Eは圧延方向のヤング率、dは板厚、aは片面被膜による反り量、νは圧延方向に応力を加えた場合のポアソン比、lは固定端と反り量を測定する位置の長さを意味する。本発明では、Eとして純鉄の弾性定数：132GPa、νとして0.37の値を用いた。 Here, a method for measuring the film tension: σ _F of the forsterite film in the present invention will be described. A specimen having a rolling direction of 280 mm and a perpendicular direction of rolling of 30 mm is prepared, and first, the glassy coating on both sides is removed with a boiling alkaline aqueous solution. Next, etching is performed using an acid to remove the forsterite film on one side. Finally, the warpage amount of the steel sheet is measured, and the warpage amount is converted into the film tension by the following equation (1).

E is the Young's modulus in the rolling direction, d is the plate thickness, a is the amount of warpage due to the single-sided coating, ν is the Poisson's ratio when stress is applied in the rolling direction, and l is the length of the position where the fixed end and the amount of warpage are measured. Means. In the present invention, E is an elastic constant of pure iron: 132 GPa, and ν is 0.37.

  First, the forsterite film coating of the steel sheet having inferior transformer characteristics was investigated in detail by combining the above forsterite film tension measurement with SEM observation, corrosion test and the like. As a result, it has been found that the forsterite film of the steel sheet with inferior transformer characteristics has many extremely fine cracks. In addition, some transformers obtained excellent iron loss characteristics despite the low film tension of the forsterite film, but the above-mentioned cracks were hardly observed in such steel sheets. There wasn't.

Therefore, it was found that the transformer characteristics of the electron beam irradiation material are more strongly influenced by the damage of the forsterite film rather than the film tension.
The reason why the characteristics of the transformer deteriorate due to cracks in the film is not clear, but the forsterite film breaks down due to various stresses applied during transformer production. Is presumed to be almost lost. In addition, when the magnetic domain fragmentation process is performed by electron beam irradiation, the forsterite film is particularly damaged and is considered to be a factor that promotes such destruction.

  Furthermore, the inventors conducted various experiments with a small laboratory facility, and investigated under what conditions the cracks in the forsterite film were formed. However, almost no cracks occurred in the forsterite film of the grain-oriented electrical steel sheet produced in the laboratory. Therefore, the inventors considered the difference in the manufacturing process between the laboratory and the factory, and paid attention to the presence or absence of flattening annealing. That is, the idea that the forsterite film is destroyed by the flattening annealing was obtained.

  Therefore, a 300mm x 30mm sample of grain-oriented electrical steel sheet with forsterite coating was prepared and annealed at 820 ° C for 1 min while applying tensile stress in a small experimental furnace. As a result, the film tension was greatly reduced. Moreover, when the film of the sample after annealing was investigated, it confirmed that many cracks were formed. The inventors who have obtained the above knowledge have re-examined and found that excellent transformer characteristics can be obtained by keeping the amount of decrease in film tension of the forsterite film in the flattening annealing low (FIG. 1). As can be seen from FIG. 1, the amount of decrease in the film tension of the forsterite film is extremely useful as a parameter representing the degree of damage to the film.

Furthermore, the inventors examined conditions for suppressing the decrease in the film tension of the forsterite film by changing the conditions for the flattening annealing.
As a result, it was found that as the plastic elongation of the ground iron is smaller, the decrease in the film tension is suppressed (see FIG. 2). This is presumably because the forsterite film is ceramic, so that cracks are introduced without following the plastic deformation of the steel sheet. Moreover, when the plastic elongation was the same, it turned out that the fall of a film tension | tensile_strength is suppressed, so that the temperature of planarization annealing is high (refer FIG. 3). This is presumably because cracks are difficult to be introduced because the forsterite film is more easily plastically deformed at higher temperatures. Further, it was found that the decrease in the film tension can be suppressed by lowering the cooling rate of the flattening annealing (see FIG. 4). This is considered to be because the thermal shock generated during cooling is alleviated.

The inventors conducted further detailed studies based on the above findings. However, it has been found that when the tension of the flattening annealing is lowered in order to suppress the plastic elongation of the base iron, the steel plate becomes easy to meander and stable plate passing is difficult. Therefore, the inventors paid attention to the high-temperature strength of the steel sheet in order to suppress plastic elongation. In other words, it was thought that by increasing the high-temperature strength of the steel sheet, the plastic elongation of the steel sheet could be suppressed while increasing the flattening annealing tension. As a result of the study, as shown in FIG. 5, it was found that the plastic elongation of the steel sheet in the flattening annealing is significantly suppressed by adding a small amount of Sn. Sb, Mo and W were also found to have the same effect. That is, the forsterite film can be effectively prevented from being destroyed by adding a small amount of any of the above elements.
The superior point of the above technique is that even if the flattening annealing temperature is increased or the tension in the furnace is increased, the plastic deformation of the steel sheet can be suppressed and the forsterite film can be prevented from being broken.

  Said element is an element with a big misfit parameter in iron, and it is known that the effect of especially increasing high temperature strength is large (nonpatent literature 1). These elements are considered to be dissolved in iron, forming a Cottrell atmosphere, and being resistant to dislocation motion. However, since these elements have a great influence on the high-temperature strength, if they are added at the steelmaking stage, they tend to cause surface defects during casting or hot rolling. Therefore, in order to avoid the occurrence of surface defects, Sn, Sb, Mo and W compounds are added to the annealing separator without adding a large amount in the steelmaking stage, and diffused from the annealing separator to the steel during the final annealing. It is preferable to adjust the content.

With the above knowledge, the present invention has been completed.
That is, in order to suppress forsterite damage, it is a finding that it is important to suppress the plastic elongation of the steel sheet in the flattening annealing, to increase the soaking temperature, and to lower the cooling rate.
In addition, forsterite damage can be suppressed by adding at least one of Sn, Sb, Mo, and W to the steel, and it is not necessary to excessively reduce the tension of flattening annealing. As described above, Sn, Sb, Mo, and W are preferably supplied from the auxiliary agent for final annealing.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. Si: Hot rolling using slabs for grain-oriented electrical steel sheets containing 2.0-4.5% by mass, and performing hot-rolled sheet annealing as necessary, then cold once or twice with intermediate annealing in between After cold rolling, followed by primary recrystallization annealing, an annealing separator mainly composed of MgO is applied, and then final finish annealing is performed to form a forsterite film, followed by planarization annealing, and further electron beam A series of grain-oriented electrical steel sheet manufacturing methods for performing magnetic domain subdivision treatment by irradiation,
When performing the above planarization annealing,
(A) Soaking temperature during annealing,
(B) Adjusting each condition of the cooling rate in the cooling process from the soaking temperature and (c) the plastic elongation amount of the base iron, respectively, the amount of decrease in the coating tension of the forsterite coating before and after the flattening annealing treatment A method for producing a grain-oriented electrical steel sheet, characterized by being controlled to 60% or less.

2. (A) The soaking temperature at the time of annealing is in the range of 820 to 950 ° C, and the cooling rate in the cooling process from the (b) soaking temperature is at least 800 to 600 ° C and not more than 100 ° C / s. Further, (c) the method for producing a grain-oriented electrical steel sheet according to 1 above, wherein the amount of plastic elongation of the ground iron is in the range of 0.03 to 0.15%.

3. In the above 1 or 2, characterized in that one or more selected from Sn, Sb, Mo and W are contained in a total amount of 0.02 to 0.5% by mass in the steel before the flattening annealing treatment The manufacturing method of the grain-oriented electrical steel sheet of description.

4). 4. The grain-oriented electrical steel sheet according to 3 above, wherein one or more selected from Sn compound, Sb compound, Mo compound and W compound are added to the annealing separator and contained in the base iron. Manufacturing method.

  According to the present invention, the iron loss reduction effect by magnetic domain subdivision using an electron beam is effectively maintained even when a transformer is manufactured. ) And noise-oriented electrical steel sheets that exhibit noise characteristics can be obtained.

It is the graph which showed the relationship between the amount of film tension reduction | decrease of a forsterite film, and a transformer iron loss. It is the graph which showed the relationship between the amount of plastic elongation of a base iron, and the amount of film tension reduction of a forsterite film. It is the graph which showed the relationship between the soaking | uniform-heating temperature of flattening annealing, and the film tension decreasing amount of a forsterite film. It is the graph which showed the relationship between the cooling rate from the soaking | uniform-heating temperature of flattening annealing, and the coating-tension reduction amount of a forsterite film. It is the graph which showed the relationship between Sn amount and the amount of plastic elongation of a ground iron.

Hereinafter, the present invention will be specifically described.
First, the component composition of the slab for grain-oriented electrical steel sheets used in the present invention may be any component composition that causes secondary recrystallization.
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. In this case, the preferred contents of Al, N, S and Se are, respectively, by mass, Al: 0.01 to 0.065%, N: 0.005 to 0.012%, S: 0.005 to 0.03%, Se: 0.005 to 0.03%. .

Furthermore, the present invention can be applied to a so-called inhibitorless grain-oriented electrical steel sheet in which the contents of Al, N, S, and Se are limited.
In this case, the amounts of Al, N, S, and Se are preferably suppressed to mass ppm, and Al: 100 ppm or less, N: 50 ppm or less, S: 50 ppm or less, and Se: 50 ppm or less.

The basic components and optional added components of the slab for grain-oriented electrical steel sheets suitable for the present invention will be specifically described as follows. Hereinafter, “%” and “ppm” in steel sheet components mean “% by mass” and “ppm by mass” unless otherwise specified.
C: 0.08% or less C is added to improve the hot-rolled sheet structure in the α-γ transformation, but if it exceeds 0.08%, C may be reduced to 50 ppm or less at which no magnetic aging occurs during the manufacturing process. Since it becomes difficult, 0.08% or less is preferable. 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: 2.0-4.5%
Si is an important component for increasing the specific resistance of steel and reducing eddy current loss. If the content is less than 2.0%, the crystal orientation is damaged by α-γ transformation during the final finish annealing, and if it exceeds 4.5%, cold rolling becomes difficult, so 2.0 to 4.5 wt%. More preferably, it is 2.5 to 3.5%.

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

In the present invention, in addition to the above basic components, it is possible to add one or more selected from Sn, Sb, Mo and W as a high-temperature strengthening element in a total range of 0.02 to 0.5%. As described above, it is advantageous to suppress damage to the coating.
If the content is less than 0.02%, the effect of increasing the high-temperature strength cannot be obtained. On the other hand, if the content exceeds 0.5%, the cost increases and the steel sheet becomes brittle and easily cracks. Therefore, in this invention, content of the said element shall be 0.02-0.5% of the total of 1 type or 2 types or more. More preferably, it is 0.04 to 0.3% of range. More preferably, it is 0.06 to 0.2% of range.

Furthermore, in the present invention, the following elements can be appropriately contained as the magnetic property improving component.
At least one selected from Ni: 0.03-1.50%, Cu: 0.03-3.0%, P: 0.03-0.50% and Cr: 0.03-1.50%
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%, the effect of improving the magnetic properties is small. On the other hand, if it exceeds 1.5%, the secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, the Ni content is preferably in the range of 0.03 to 1.5%.

Cu, P, and Cr are elements that are useful for improving the magnetic properties. However, if any of them is less than the lower limit of each component, the effect of improving the magnetic properties is small. When the amount exceeds the limit, the development of secondary recrystallized grains is hindered. Cu can also be used as the inhibitor component described above.
The balance other than the above components is inevitable impurities and Fe mixed in the manufacturing process.

  Next, the manufacturing conditions of the grain-oriented electrical steel sheet targeted by the present invention will be described. The molten steel adjusted to the above component composition by a known steelmaking process is cast by a continuous casting method or an ingot-making method, and a slab is obtained with a lump step as necessary. Subsequently, hot rolling is performed, and hot-rolled sheet annealing is performed as necessary, and then a cold-rolled sheet having a final thickness is obtained by cold rolling at least once and sandwiching intermediate annealing. The obtained cold-rolled sheet is subjected to primary recrystallization annealing, and then secondary recrystallization and forsterite film are formed. Here, when forming the film, an annealing separator mainly composed of MgO is applied, and annealing is performed with coil foam.

  At this time, as described above, one or more selected from the Sn compound, Sb compound, Mo compound and W compound are added to the steel making stage or the annealing separator, and the base iron is Sn, It is advantageous from the viewpoint of suppressing damage to the forsterite film to adjust the total of one or more selected from Sb, Mo and W to 0.02 to 0.5%.

After the finish annealing, flattening annealing is performed to correct the coil winding. In the present invention, it is important that this flattening annealing is performed under the following conditions.
That is,
(A) Soaking temperature during annealing,
(B) Adjusting each condition of the cooling rate in the cooling process from the soaking temperature and (c) the plastic elongation amount of the base iron, respectively, the amount of decrease in the coating tension of the forsterite coating before and after the flattening annealing treatment It is to suppress to 60% or less.

Moreover, the suitable range of each above-mentioned conditions is as follows.
Soaking temperature: 820-950 ° C
By increasing the soaking temperature of the flattening annealing, damage to the coating can be prevented. If it is less than 820 ° C., damage to the film cannot be prevented. On the other hand, if it exceeds 950 ° C., it becomes difficult to control the plastic deformation of the steel sheet. More preferably, it is 840-930 degreeC. More preferably, it is 860-910 degreeC.

Cooling rate: 100 ° C./s or less In the present invention, it is important to control the cooling rate in the cooling process from the soaking temperature. That is, even in the cooling process from the soaking temperature, damage to the coating can be prevented by slowing the cooling rate between 800 ° C. and 600 ° C. in particular. Here, if it exceeds 100 ° C./s, it becomes difficult to prevent film damage. More preferably, it is 80 ° C./s or less. More preferably, it is 60 degrees C / s or less.

Plastic steel elongation: 0.03-0.15%
By reducing the amount of plastic elongation of the base iron, damage to the coating can be prevented. If it is less than 0.03%, shape correction cannot be performed, and if it exceeds 0.15%, film damage becomes remarkable, so 0.03 to 0.15% is preferable. More preferably, it is 0.03 to 0.12%. More preferably, it is 0.03 to 0.08%.

Film tension reduction amount of forsterite film: 60% or less In the present invention, the decrease amount of film tension is an index representing the degree of damage of the forsterite film, and the above-described flattening annealing (a) to ( The most important point of the present invention is to combine the three conditions of c) so that the index is 60% or less.
This is because when the amount of decrease in the film tension exceeds 60%, the characteristics of the transformer are greatly deteriorated. Preferably it is 40% or less. More preferably, it is 20% or less. In the prior art as described above, attempts have been made to reduce plastic elongation in order to reduce dislocations introduced into steel. However, simply reducing the plastic elongation cannot effectively prevent the forsterite film from being destroyed as in the present invention. Therefore, simply reducing the plastic elongation cannot improve the iron loss characteristics and the like of a transformer made of an electron beam irradiation material.

  In addition, in this invention, except the process and manufacturing conditions mentioned above, the conventionally well-known manufacturing method of a grain-oriented electrical steel sheet which performs a magnetic domain refinement | purification process using an electron beam after planarization annealing is applicable.

Example 1
C: 0.05 to 0.07%, Si: 3.1 to 3.3%, Mn: 0.06 to 0.09%, Se: 0.012 to 0.016%, sol. Al: 0.025 to 0.027%, N: 0.0075 to 0.0090%, and Table 1 The slab was composed of Fe and unavoidable impurities as the raw material, and the slab was heated at 1380 ° C. for 1 hour and hot-rolled to obtain a hot-rolled sheet having a thickness of 2.4 mm. The hot-rolled sheet was subjected to hot-rolled sheet annealing at 1000 ° C. for 1 minute, pickled, and subjected to intermediate annealing at a temperature of 1050 ° C. after the first cold rolling. Next, the second cold rolling was warm rolling at a temperature of 220 ° C. and finished to a thickness of 0.26 mm. This cold-rolled sheet is subjected to decarburization annealing at 830 ° C. in a wet hydrogen atmosphere, and then applied with an annealing separator mixed at a mass ratio of MgO: TiO ₂ = 95: 5, and then 1180 ° C. Finish annealing for 5 hours was performed.
Next, flattening annealing is performed under the conditions shown in Table 1, and then the electron beam is scanned linearly in the direction orthogonal to the rolling direction at intervals of 7 mm in the rolling direction while moving the sample in the rolling direction (running direction). And magnetic domain refinement treatment was performed. The acceleration voltage of the electron gun was 38 kV, the current density was 3.5 mA, and the distance from the polarizing coil to the sample was 300 mm. A 1200 kVA three-phase three-leg transformer was produced from the product plate thus obtained.
For each flattening annealing condition, the forsterite film tension and the reduction rate thereof, and the iron loss W _17/50 of the material and the transformer were measured. The results are also shown in Table 1. The film tension was determined using the above equation (1).

  As shown in the table, Nos. 6 to 8 in which the rate of decrease in the film tension of the forsterite coating is out of the range of the present invention is poor in transformer iron loss and inferior in building factor. On the other hand, Nos. 1 to 5 and 9 to 14 according to the conditions of the present invention all have excellent transformer iron loss and a good building factor.

(Example 2)
C: 0.053%, Si: 3.16%, Mn: 0.06%, Se: 0.015%, sol. Al: 0.025%, N: 0.0078%, and the minor components shown in Table 2, with the remainder from Fe and inevitable impurities Using this slab as a raw material, the slab was heated at 1380 ° C. for 1 hour and hot-rolled to obtain a hot-rolled sheet having a thickness of 2.4 mm. The hot-rolled sheet is subjected to hot-rolled sheet annealing at 1000 ° C. for 1 minute, pickled, subjected to the first cold rolling, subjected to intermediate annealing at a temperature of 1050 ° C., and then subjected to the second cold rolling. The plate thickness was 0.26 mm as warm rolling at a temperature of ° C. The cold-rolled sheet was subjected to decarburization annealing at 830 ° C. in a wet hydrogen atmosphere. Further, after applying an annealing separator having the components shown in Table 2, finish annealing was performed at 1180 ° C. for 5 hours.
After finishing annealing, one sample of 200 mm × 30 mm was collected per 1000 m ² and analyzed for trace components by wet analysis.
Subsequently, planarization annealing was performed at 850 ° C. for 1 minute. At that time, annealing was performed with the furnace tension (line tension) set to 12 MPa, and the cooling rate of 800 to 600 ° C. was set to 80 ° C./s. In addition, as for the plastic elongation amount of the base iron in that case, No. 1 was 0.21% and others were 0.10% or less.
Thereafter, while moving the sample in the rolling direction (running direction), scanning with an electron beam was performed linearly in a direction perpendicular to the rolling direction at intervals of 5 mm in the rolling direction, and a magnetic domain refinement process was performed. The acceleration voltage of the electron gun was 40 kV, the current density was 3 mA, and the distance from the polarizing coil to the sample was 400 mm. A 1200 kVA three-phase three-leg transformer was produced from the product plate thus obtained.
For each flattening annealing condition, the forsterite film tension and its reduction rate, the iron loss W _17/50 of the material and the transformer, and the noise characteristics were measured. The results are also shown in Table 2. The measuring procedure for the film tension was the same as in Example 1.

  As shown in the table, No. 1, which is outside the scope of the present invention, has poor transformer iron loss and inferior building factor. On the other hand, Nos. 2 to 9 according to the conditions of the present invention all have excellent transformer iron loss and a good building factor. Excellent noise characteristics are also obtained.

Claims (4)

Si: Hot rolling using slabs for grain-oriented electrical steel sheets containing 2.0-4.5% by mass, and performing hot-rolled sheet annealing as necessary, then cold once or twice with intermediate annealing in between After cold rolling, followed by primary recrystallization annealing, an annealing separator mainly composed of MgO is applied, and then final finish annealing is performed to form a forsterite film, followed by planarization annealing, and further electron beam A series of grain-oriented electrical steel sheet manufacturing methods for performing magnetic domain subdivision treatment by irradiation,
When performing the above planarization annealing,
(A) Soaking temperature during annealing,
(B) Adjusting each condition of the cooling rate in the cooling process from the soaking temperature and (c) the plastic elongation amount of the base iron, respectively, the amount of decrease in the coating tension of the forsterite coating before and after the flattening annealing treatment A method for producing a grain-oriented electrical steel sheet, characterized by being controlled to 60% or less.   (A) The soaking temperature at the time of annealing is in the range of 820 to 950 ° C, and the cooling rate in the cooling process from the (b) soaking temperature is at least 800 to 600 ° C and not more than 100 ° C / s. Furthermore, the amount of plastic elongation of said (c) ground iron is made into 0.03 to 0.15% of range, The manufacturing method of the grain-oriented electrical steel sheet of Claim 1 characterized by the above-mentioned.   The total amount of one or more selected from Sn, Sb, Mo and W is 0.02 to 0.5% by mass in the base iron before the flattening annealing. The manufacturing method of the grain-oriented electrical steel sheet described in 1.   4. The directional electromagnetic according to claim 3, wherein one or more selected from an Sn compound, an Sb compound, an Mo compound, and a W compound are added to the annealing separator and contained in the ground iron. 5. A method of manufacturing a steel sheet.

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