JP7188105B2 - Oriented electrical steel sheet - Google Patents

Description

The present invention relates to grain-oriented electrical steel sheets. In particular, it relates to a grain-oriented electrical steel sheet in which iron loss is suitably reduced.

Grain-oriented electrical steel sheets are often used as magnetic iron core materials, and in particular, materials with low iron loss are desired in order to reduce energy loss. Applying tension to the steel sheet is effective in reducing iron loss.

In order to apply tension to the steel sheet, it is effective to form a coating made of a material having a smaller coefficient of thermal expansion and a higher Young's modulus than the steel sheet at a high temperature. That is, tension is applied to the steel sheet using the thermal stress caused by the difference in thermal expansion coefficient between the steel sheet and the coating. On the surface of a normal grain-oriented electrical steel sheet, an oxide film mainly composed of _SiO2 generated in the decarburization annealing process and MgO, which is usually used as an annealing separator, react during finish annealing to form forsterite. There is a coating mainly composed of (Mg ₂ SiO ₄ ) (hereinafter referred to as a final annealing coating). This finish-annealed coating gives a large tension to the steel sheet and is effective in reducing iron loss.

Furthermore, the insulating coating (tensile coating) obtained by applying and baking a coating liquid mainly composed of colloidal silica and phosphate described in Patent Document 1 (Japanese Patent Application Laid-Open No. 48-39338) is It has a great effect of imparting tension to the steel plate, and is effective in reducing iron loss. Therefore, it is a common method of manufacturing a grain-oriented electrical steel sheet to apply an insulating coating after leaving the coating produced in the finish annealing step.

Attempts have also been made to increase the tension applied to the steel sheet by the insulating coating. For example, an Al ₂ O ₃ —B ₂ O ₃ -based film obtained by applying and baking a coating liquid mainly composed of alumina sol and boric acid, which is described in Patent Document 2 (JP-A-6-306628). can obtain a film tension 1.5 to 2 times higher than that of an insulating film mainly composed of colloidal silica and phosphate at the same film thickness.

On the other hand, an attempt has been made to reduce the iron loss by a method different from the improvement of the insulating coating described above. For example, it has been clarified that if the interfacial structure between the finish-annealed coating and the base steel is disturbed by the presence of the forsterite coating, the iron loss improvement effect obtained by the tension applied by the insulating coating is offset to some extent. Therefore, as described in Patent Document 3 (Japanese Patent Laid-Open No. 49-96920) and Patent Document 4 (Japanese Patent Laid-Open No. 4-131326), the finish annealing film generated in the finish annealing process is polished, ground, or the like. Techniques have been developed to try to further reduce iron loss by removing the steel by mechanical means or chemical means such as pickling, then mirror-finishing by chemical polishing or re-annealing, and then forming a tension film. . Alternatively, a technique has been developed to try to further reduce iron loss by preventing the formation of a finish annealing film in the final annealing and forming a tension film after the finish annealing film is substantially absent or mirror-finished.

However, although each of the above-described techniques can obtain an effect of improving iron loss, it has been found that even if the above-described techniques are combined, a combined effect of improving iron loss cannot be obtained. For example, it has been found that even if a boric acid/alumina-based high-tensile coating is formed on a grain-oriented electrical steel sheet that has been mirror-finished, the effect of improving iron loss is small.

JP-A-48-39338 JP-A-6-306628 JP-A-49-96920 JP-A-4-131326

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a grain-oriented electrical steel sheet in which iron loss is suitably reduced.

The gist of the present invention is as follows.
(1) A grain-oriented electrical steel sheet according to an aspect of the present invention comprises a silicon steel sheet as a base material steel sheet, an intermediate layer disposed in contact with the silicon steel sheet, and an insulating coating disposed in contact with the intermediate layer. wherein the intermediate layer is an oxide film, the oxide film contains silicon oxide, the oxide film has an average thickness of 2 nm or more and 500 nm or less, and the insulating film is boric acid It is an aluminum-based coating, the aluminum-borate-based coating contains aluminum/boron oxide, the average thickness of the aluminum borate-based coating is more than 0.5 μm and 8 μm or less, and the cutting direction is parallel to the plate thickness direction. When viewed from the cut surface, the area ratio of voids in the aluminum borate-based coating is 0% or more and 2.3 % or less, and when viewed from the cut surface, the gap between the silicon steel sheet and the oxide film is An oxidized region exists at the interface, and the line segment ratio of the oxidized region extending from the interface toward the silicon steel sheet to a maximum depth of 0.2 μm or more with respect to the interface is 0.1% or more and 12 % or less.
(2) In the grain-oriented electrical steel sheet described in (1) above, at least one of Al ₁₈ B ₄ O ₃₃ and Al ₄ B ₂ O ₉ may be included as the aluminum-boron oxide.
(3) In the grain-oriented electrical steel sheet described in (1) or (2) above, the aluminum borate-based coating may further contain aluminum oxide.
(4) The grain-oriented electrical steel sheet according to any one of (1) to (3) above further includes a phosphoric acid-based coating disposed in contact with the aluminum borate-based coating, The system coating may contain a phosphorous-silicon composite oxide.
(5) In the grain-oriented electrical steel sheet according to any one of (1) to (4) above, the silicon steel sheet contains, as a chemical composition, Si: 0.8% or more and 7.0% or less in mass %. , Mn: 0 to 1.00%, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Sn: 0 to 0.30% , Sb: 0 to 0.30%, Ni: 0 to 1.00%, B: 0 to 0.008%, V: 0 to 0.15%, Nb: 0 to 0.2% , Mo: 0 to 0.10%, Ti: 0 to 0.015%, Bi: 0 to 0.010%, Al: 0 to 0.005%, total of C + N: 0 to 0.005 % or less, and the sum of S + Se: 0 to 0.005%, the balance being Fe and impurities, and the silicon steel sheet may have a texture developed in the {110}<001> orientation. .
(6) In the grain-oriented electrical steel sheet according to any one of (1) to (5) above, the silicon steel sheet has, as a chemical composition, Mn: 0.05% or more and 1.00% or less in mass%. , Cr: 0.02% to 0.30%, Cu: 0.05% to 0.40%, P: 0.005% to 0.50%, Sn: 0.02% to 0.30 % or less, Sb: 0.01% or more and 0.30% or less, Ni: 0.01% or more and 1.00% or less, B: 0.0005% or more and 0.008% or less, V: 0.002% or more and 0 .15% or less, Nb: 0.005% or more and 0.2% or less, Mo: 0.005% or more and 0.10% or less, Ti: 0.002% or more and 0.015% or less, and Bi: 0.001 % or more and 0.010% or less.

According to the above aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet in which iron loss is suitably reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram of the grain-oriented electrical steel sheet which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram which shows the line fraction of the oxidation area|region of the grain-oriented electrical steel sheet which concerns on the same embodiment. It is a cross-sectional photograph of the grain-oriented electrical steel sheet according to the same embodiment.

For example, for the purpose of further reducing iron loss, an intermediate layer (oxide film) containing silica and an insulating coating (aluminum borate-based coating) are laminated on a base material steel plate (silicon steel plate) that does not have a forsterite coating. A grain-oriented electrical steel sheet is manufactured. Since this grain-oriented electrical steel sheet has an oxide film instead of a forsterite film, the interface is smooth, and since it has an aluminum borate-based film, the film tension is increased, so it is expected that the iron loss can be reduced more than ever. be done. However, in practice, iron loss cannot be reduced as much as expected.

The inventors of the present invention have extensively investigated the reason why the iron loss is not reduced. It was observed that voids were present. The reason why the iron loss is not reduced is that the smoothness of the surface of the silicon steel sheet is lost due to the presence of an internal oxide region at the interface between the silicon steel sheet and the oxide film, and the presence of voids in the aluminum borate-based coating. As a result, the effect of applying tension to the silicon steel sheet is reduced, and as a result, it is considered that the iron loss reduction is hindered.

We investigated the cause of the formation of internal oxide regions in the steel sheet and the formation of voids in the coating. It was thought that voids were generated in the film due to partial decomposition, and the steel sheet was internally oxidized by water vapor or oxygen generated during the decomposition.

Therefore, the inventors of the present invention conducted intensive studies and optimally controlled the soaking conditions and cooling conditions in the coating formation process, thereby forming voids in the aluminum borate-based coating and forming an internal oxidation region in the steel sheet. can be suppressed at the same time, and as a result, a grain-oriented electrical steel sheet with further reduced iron loss can be obtained.

Hereinafter, a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the scope of the present invention. Moreover, the lower limit value and the upper limit value are included in the range of numerical limits described below. Any numerical value indicated as "greater than" or "less than" is not included in the numerical range. "%" regarding the content of each element means "% by mass".

The grain-oriented electrical steel sheet according to the present embodiment includes a silicon steel sheet that is a base steel sheet containing Si, an oxide film that is an intermediate layer formed on the silicon steel sheet, and a cross-sectional area of the void formed on the oxide film. and an aluminum borate-based coating that is an insulating coating with a rate of 5.0% or less, and the line rate of the oxidized region present inside the steel sheet is 0.1% or more and 15% or less. FIG. 1 shows a schematic cross-sectional view of a grain-oriented electrical steel sheet according to this embodiment. In FIG. 1, reference numeral 1 is a base material steel plate (silicon steel plate), reference numeral 2 is an intermediate layer (oxide film), reference numeral 3 is an insulating coating (aluminum borate-based coating), reference numeral 4 is an oxidized region (internal oxidized region), and reference numeral Reference numeral 5 denotes a void, and reference numeral 6 denotes an interface between the silicon steel plate and the oxide film. Note that FIG. 1 is a schematic diagram, and the film thickness of each film, the size of the oxidized region, the size of the gap, etc. are not limitedly interpreted by FIG.

(silicon steel plate)
The grain-oriented electrical steel sheet according to this embodiment has a silicon steel sheet as a base material steel sheet. It is preferable that the silicon steel sheet contains, as chemical components, basic elements, optional elements as necessary, and the balance being Fe and impurities.

In the present embodiment, the silicon steel sheet should contain Si as a basic element (main alloying element).

Si: 0.8% or more and 7.0% or less Si (silicon) is an element effective in increasing electrical resistance and reducing iron loss as a chemical component of a silicon steel sheet. If the Si content exceeds 7.0%, the material tends to crack during cold rolling, making rolling difficult. On the other hand, when the Si content is less than 0.8%, the electrical resistance becomes small and the iron loss in the product may increase. Therefore, Si may be contained in the range of 0.8% or more and 7.0% or less. The lower limit of the Si content is preferably 2.0%, more preferably 2.5%, even more preferably 2.8%. The upper limit of the Si content is preferably 5.0%, more preferably 3.5%.

In this embodiment, the silicon steel sheet may contain impurities. The term "impurities" refers to substances mixed from ores and scraps used as raw materials or from the manufacturing environment or the like during the industrial production of steel.

Further, in the present embodiment, the silicon steel sheet may contain selective elements in addition to the basic elements and impurities described above. For example, Mn, Cr, Cu, P, Sn, Sb, Ni, B, V, Nb, Mo, Ti, Bi, Al, C, N , S, and Se. These selective elements may be contained depending on the purpose. Therefore, it is not necessary to limit the lower limit of these selective elements, and the lower limit may be 0%. Moreover, even if these selective elements are contained as impurities, the above effect is not impaired.

Mn: 0 to 1.00% Mn (manganese), like Si, is an element effective in increasing electrical resistance and reducing iron loss. It also functions as an inhibitor by binding with S or Se. Therefore, Mn may be contained in the range of 1.00% or less. The lower limit of the Mn content is preferably 0.05%, more preferably 0.08%, even more preferably 0.09%. The upper limit of the Mn content is preferably 0.50%, more preferably 0.20%.

Cr: 0 to 0.30% Cr (chromium), like Si, is an element effective in increasing electric resistance and reducing iron loss. Therefore, Cr may be contained in the range of 0.30% or less. The lower limit of the Cr content is preferably 0.02%, more preferably 0.05%. The upper limit of the Cr content is preferably 0.20%, more preferably 0.12%.

Cu: 0 to 0.40% Cu (copper) is also an effective element for increasing electrical resistance and reducing iron loss. Therefore, Cu may be contained in the range of 0.40% or less. If the Cu content exceeds 0.40%, the effect of reducing iron loss is saturated and may cause surface defects called "copper scab" during hot rolling. The lower limit of the Cu content is preferably 0.05%, more preferably 0.10%. The upper limit of the Cu content is preferably 0.30%, more preferably 0.20%.

P: 0 to 0.50% P (phosphorus) is also an effective element for increasing electric resistance and reducing iron loss. Therefore, P may be contained in the range of 0.50% or less. If the P content exceeds 0.50%, problems may arise in the rollability of the silicon steel sheet. The lower limit of the P content is preferably 0.005%, more preferably 0.01%. The upper limit of the P content is preferably 0.20%, more preferably 0.15%.

Sn: 0 to 0.30% Sb: 0 to 0.30% Sn (tin) and Sb (antimony) stabilize secondary recrystallization and develop the {110}<001> orientation. It is an effective element. Therefore, Sn may be contained in the range of 0.30% or less, and Sb may be contained in the range of 0.30% or less. If the Sn or Sb content exceeds 0.30%, the magnetic properties may be adversely affected.
The lower limit of the Sn content is preferably 0.02%, more preferably 0.05%. The upper limit of the Sn content is preferably 0.15%, more preferably 0.10%.
The lower limit of the Sb content is preferably 0.01%, more preferably 0.03%. The upper limit of the Sb content is preferably 0.15%, more preferably 0.10%.

Ni: 0 to 1.00% Ni (nickel) is also an effective element for increasing electric resistance and reducing iron loss. Also, Ni is an element effective in controlling the metal structure of the hot-rolled sheet and enhancing the magnetic properties. Therefore, Ni may be contained in the range of 1.00% or less. If the Ni content exceeds 1.00%, secondary recrystallization may become unstable. The lower limit of the Ni content is preferably 0.01%, more preferably 0.02%. The upper limit of the Ni content is preferably 0.20%, more preferably 0.10%.

B: 0 to 0.008% B (boron) is an element effective in exhibiting an inhibitory effect as BN. Therefore, B may be contained in the range of 0.008% or less. If the B content exceeds 0.008%, the magnetic properties may be adversely affected. The lower limit of the B content is preferably 0.0005%, more preferably 0.001%. The upper limit of the B content is preferably 0.005%, more preferably 0.003%.

V: 0 to 0.15% Nb: 0 to 0.2% Ti: 0 to 0.015% V (vanadium), Nb (niobium), and Ti (titanium) combine with N and C. It is an effective element to function as an inhibitor in Therefore, the V content may be 0.15% or less, the Nb content may be 0.2% or less, and the Ti content may be 0.015% or less. If these elements remain in the final product and the V content exceeds 0.15%, the Nb content exceeds 0.2%, or the Ti content exceeds 0.015%, the magnetic properties deteriorate. There is a risk of
The lower limit of the V content is preferably 0.002%, more preferably 0.01%. The upper limit of the V content is preferably 0.10% or less, more preferably 0.05%.
The lower limit of the Nb content is preferably 0.005%, more preferably 0.02%. The upper limit of the Nb content is preferably 0.1%, more preferably 0.08%.
The lower limit of the Ti content is preferably 0.002%, more preferably 0.004%. The upper limit of the Ti content is preferably 0.010%, more preferably 0.008%.

Mo: 0 to 0.10% Mo (molybdenum) is also an effective element for increasing electric resistance and reducing iron loss. Therefore, Mo may be contained in the range of 0.10% or less. If the Mo content exceeds 0.10%, problems may arise in the rollability of the steel sheet. The lower limit of the Mo content is preferably 0.005%, more preferably 0.01%. The upper limit of the Mo content is preferably 0.08%, more preferably 0.05%.

Bi: 0 to 0.010% Bi (bismuth) is an element effective in stabilizing precipitates such as sulfides and strengthening the function as an inhibitor. Therefore, Bi may be contained in the range of 0.010% or less. If the Bi content exceeds 0.010%, the magnetic properties may be adversely affected. The lower limit of the Bi content is preferably 0.001%, more preferably 0.002%. The upper limit of the Bi content is preferably 0.008%, more preferably 0.006%.

Al: 0 to 0.005% Al (aluminum) is an element effective in exhibiting an inhibitory effect by bonding with N. Therefore, Al may be contained in the range of 0.01 to 0.065% before finish annealing, for example, at the slab stage. However, if Al remains as an impurity in the final product (magnetic steel sheet) and the Al content exceeds 0.005%, the magnetic properties may be adversely affected. Therefore, the Al content of the final product is preferably 0.005% or less. The upper limit of the Al content in the final product is preferably 0.004%, more preferably 0.003%. The Al content of the final product is an impurity, and the lower limit is not particularly limited, and the lower the better. However, since it is industrially difficult to reduce the Al content of the final product to 0%, the lower limit of the Al content of the final product may be set to 0.0005%. In addition, Al content shows content of acid-soluble Al.

Total of C+N: 0 to 0.005% C (carbon) is an effective element for adjusting the primary recrystallization texture and improving the magnetic properties. Also, N (nitrogen) is an element effective in exhibiting an inhibitor effect by bonding with Al, B, and the like. Therefore, C may be contained in the range of 0.02 to 0.10% before decarburization annealing, for example, in the slab stage. Also, N may be contained in the range of 0.01 to 0.05% before finish annealing, for example, after nitriding annealing. However, if these elements remain as impurities in the final product and the total content of C and N exceeds 0.005%, the magnetic properties may be adversely affected. Therefore, the total content of C and N in the final product is preferably 0.005% or less. The upper limit of the total C+N content in the final product is preferably 0.004%, more preferably 0.003%. The lower limit of the total content of C and N in the final product is an impurity and is not particularly limited, and the lower the better. However, since it is industrially difficult to make the total content of C and N in the final product 0%, the lower limit of the total content of C and N in the final product may be 0.0005%.

Total of S+Se: 0 to 0.005% S (sulfur) and Se (selenium) are elements effective in exhibiting an inhibitory effect by bonding with Mn or the like. Therefore, S and Se may be contained in a total range of 0.005 to 0.050% before finish annealing, for example, at the slab stage. However, if these elements remain as impurities in the final product and the total content of S and Se exceeds 0.005%, the magnetic properties may be adversely affected. Therefore, the total content of S and Se in the final product is preferably 0.005% or less. The upper limit of the total S+Se content in the final product is preferably 0.004%, more preferably 0.003%. In addition, the lower limit of the total content of S and Se in the final product is an impurity and is not particularly limited, and the lower the better. However, since it is industrially difficult to make the total content of S and Se in the final product 0%, the lower limit of the total content of S and Se in the final product may be 0.0005%.

In the present embodiment, the silicon steel sheet contains, as selected elements, Mn: 0.05% or more and 1.00% or less, Cr: 0.02% or more and 0.30% or less, and Cu: 0.05% or more by mass%. 0.40% or less, P: 0.005% or more and 0.50% or less, Sn: 0.02% or more and 0.30% or less, Sb: 0.01% or more and 0.30% or less, Ni: 0.01 % or more and 1.00% or less, B: 0.0005% or more and 0.008% or less, V: 0.002% or more and 0.15% or less, Nb: 0.005% or more and 0.2% or less, Mo: 0 .005% or more and 0.10% or less, Ti: 0.002% or more and 0.015% or less, and Bi: 0.001% or more and 0.010% or less. may

The chemical composition of the silicon steel sheet described above may be measured by a general analytical method. For example, the steel composition may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Incidentally, C and S can be measured using a combustion-infrared absorption method, N can be measured using an inert gas fusion-thermal conductivity method, and O can be measured using an inert gas fusion-nondispersive infrared absorption method.

Moreover, the silicon steel sheet of the grain-oriented electrical steel sheet according to the present embodiment preferably has a texture developed in the {110}<001> orientation. The {110}<001> orientation means a crystal orientation (Goss orientation) in which {110} planes are aligned parallel to the steel sheet surface and <100> axes are aligned in the rolling direction. Magnetic properties are preferably improved by controlling the silicon steel sheet to have a Goss orientation.

The texture of the silicon steel sheet described above may be measured by a general analytical method. For example, it may be measured by an X-ray diffraction method (Laue method). The Laue method is a method of irradiating a steel plate with an X-ray beam perpendicularly and analyzing the transmitted or reflected diffraction spots. By analyzing the diffraction spots, it is possible to identify the crystal orientation of the location irradiated with the X-ray beam. By changing the irradiation position and analyzing the diffraction spots at a plurality of positions, the crystal orientation distribution at each irradiation position can be measured. The Laue method is a technique suitable for measuring the crystal orientation of metal structures having coarse grains.

(Oxide film)
The grain-oriented electrical steel sheet according to the present embodiment has an oxide film as an intermediate layer disposed in contact with the silicon steel sheet.

This oxide film contains silicon oxide as a main component and has a film thickness of 2 nm or more and 500 nm or less. This oxide film continuously spreads along the surface of the silicon steel sheet. By forming the oxide film between the silicon steel sheet and the aluminum borate-based coating, the adhesion between the silicon steel sheet and the aluminum borate-based coating is improved, and stress can be applied to the silicon steel sheet. In this embodiment, the oxide film is not a forsterite film but an oxide film mainly composed of silicon oxide.

The oxide film is formed by heat-treating the silicon steel sheet from which the forsterite coating is suppressed during final annealing or from which the forsterite coating is removed after final annealing in an atmosphere gas adjusted to a predetermined degree of oxidation. . In this embodiment, the oxide film is preferably an external oxide film formed by external oxidation.

Here, the external oxide film is an oxide film formed in a low oxidation atmosphere gas, and after the alloying element (Si) in the steel plate diffuses to the steel plate surface, the oxide film formed on the steel plate surface. Say things.

The oxide film contains silica (silicon oxide) as a main component. The oxide film may contain oxides of alloying elements contained in the silicon steel sheet in addition to silicon oxide. That is, it may contain any oxide of Fe, Mn, Cr, Cu, Sn, Sb, Ni, V, Nb, Mo, Ti, Bi, Al, or a composite oxide thereof. In addition, it may contain metal grains such as Fe. Also, impurities may be contained within a range that does not impair the effect.

The average thickness of the oxide film is preferably 2 nm or more and 500 nm or less. If the average thickness is less than 2 nm or more than 500 nm, the adhesion between the silicon steel sheet and the aluminum borate-based coating is lowered, and sufficient stress cannot be applied to the silicon steel sheet, resulting in increased core loss. The lower limit of the average film thickness of the oxide film is preferably 5 nm. The upper limit of the average thickness of the oxide film is preferably 300 nm, more preferably 100 nm, and even more preferably 50 nm.

The crystal structure of the oxide film is not particularly limited. However, the oxide film preferably has an amorphous mother phase. When the parent phase of the oxide film is amorphous, the adhesion between the silicon steel sheet and the aluminum borate-based coating can be preferably improved.

(oxidized area)
The grain-oriented electrical steel sheet according to the present embodiment has an oxidized region (internal oxidized region) at the interface between the silicon steel sheet and the oxide film.

This oxidized region has a shape that extends from the interface between the silicon steel plate and the oxide film toward the silicon steel plate side when viewed from a cut surface in which the cutting direction is parallel to the plate thickness direction. This oxidized region is formed by growing from the oxide film in the depth direction of the silicon steel sheet, and is in contact with the oxide film at the interface.

When this oxidized region is formed, the smoothness of the surface of the silicon steel sheet is impaired and iron loss increases. Therefore, the fewer the oxidized regions, the better. In particular, the oxidized region having a maximum depth of 0.2 μm or more from the interface toward the silicon steel sheet greatly impairs the smoothness of the surface of the silicon steel sheet, thereby aggravating iron loss. Therefore, it is preferable to reduce the oxidized region with a maximum depth of 0.2 μm or more. In this embodiment, an oxidized region having a maximum depth of 0.2 μm or more is controlled. Note that the oxidized region may grow up to a maximum depth of about 0.5 μm depending on manufacturing conditions. Therefore, the maximum depth of the oxidized region may have an upper limit of 0.5 μm.

Although the cause of the formation of the oxidized region is not clear, when forming the aluminum borate-based film, part of the aluminum-boron oxide contained in the film decomposes, and the water vapor generated during the decomposition or It is presumed that oxygen is generated by internal oxidation of the steel sheet. That is, the oxidized regions are considered to be internal oxidized regions.

Here, the internal oxidized region is an oxidized region formed in a gas atmosphere with a relatively high degree of oxidation. , an oxidized region that is dispersed in islands inside the steel plate.

The oxidized region contains silica (silicon oxide) as a main component, similar to the oxide film. The oxidized region may contain oxides of alloying elements contained in the silicon steel sheet in addition to silicon oxide. That is, it may contain any oxide of Fe, Mn, Cr, Cu, Sn, Sb, Ni, V, Nb, Mo, Ti, Bi, Al, or a composite oxide thereof. In addition, it may contain metal grains such as Fe. Also, impurities may be contained within a range that does not impair the effect.

Note that the oxide film and the oxide region may or may not have the same chemical components and constituent phases. In the present embodiment, there is no particular limitation as to whether or not the oxide film and the oxide region have the same chemical components, constituent phases, and the like.

As noted above, fewer oxidized regions are preferred. However, it is industrially difficult to make the oxidized region zero. The inventors of the present invention have found that if the oxidized region intruded to a maximum depth of 0.2 μm or more is controlled to a linear fraction of 15% or less with respect to the interface, the decrease in iron loss can be preferably suppressed. . Therefore, in the present embodiment, the oxidized region is limited to 15% or less in terms of line fraction with respect to the interface as viewed from the cut surface. Since it is not industrially easy to control the linear fraction of the oxidized region to less than 0.1% with respect to the interface, the lower limit of the linear fraction may be set to 0.1%.

FIG. 2 shows a schematic cross-sectional view illustrating the line fraction of the oxidized region of the grain-oriented electrical steel sheet according to the present embodiment. As shown in FIG. 2, the line segment ratio of the oxidized region is defined as the ratio of the total length of the oxidized region 4 to the length of the interface 6 when viewed in cross section. Specifically, the linear segment ratio of the oxidized region is defined as the percentage of the value obtained by dividing the total value Σd of the length d of the oxidized region 4 by the length L of the interface 6 . That is, linear segment rate (%)=Σd/L×100. The length d of the oxidized region 4 is the length of the oxidized region 4 on a line that is equally spaced apart from the interface 6 by 0.02 μm in the depth direction. Also, the oxidized region to be measured is an oxidized region with a maximum depth of 0.2 μm or more from the interface.

(Aluminum borate coating)
The grain-oriented electrical steel sheet according to the present embodiment has an aluminum borate-based coating disposed in contact with the oxide film as an insulating coating.

This aluminum borate-based coating contains aluminum-boron oxide. This aluminum-boron oxide is considered to have a large Young's modulus, and therefore, it is considered that a large tension can be applied to the silicon steel sheet as an aluminum borate-based coating.

The crystal structure of the aluminum-boron oxide contained in the aluminum borate-based coating is not particularly limited. The aluminum-boron oxide may be amorphous or crystalline. In this embodiment, the aluminum-boron oxide is predominantly amorphous. However, the aluminum-boron oxide preferably contains at least one of Al ₁₈ B ₄ O ₃₃ and Al ₄ B ₂ O ₉ which are crystalline. By including these crystalline Al ₁₈ B ₄ O ₃₃ or Al ₄ B ₂ O ₉ in the aluminum borate-based coating, the tension applied to the silicon steel sheet is further increased.

Further, the aluminum borate-based coating may contain crystalline aluminum oxide in addition to aluminum-boron oxide. Aluminum oxide does not have a large difference in thermal expansion coefficient (approximately 4×10 ⁻⁶ K ⁻¹ ) from that of a silicon steel plate, but has a large Young's modulus (3 to 4×10 ⁴ kgf·mm ⁻² ). Therefore, as an aluminum borate-based coating, a large tension can be applied to the silicon steel sheet. For example, the aluminum borate-based coating may contain aluminum oxide in an area ratio of 0.01% or more and 1% or less.

Further, the aluminum borate-based coating may contain crystalline boron oxide (B ₂ O ₃ ) in addition to aluminum oxide and aluminum-boron oxide. Boron oxide has a large difference in thermal expansion coefficient from that of a silicon steel plate. Therefore, the tension applied to the silicon steel sheet is increased as the aluminum borate-based coating. In addition, boron oxide has the function of lowering the baking temperature of aluminum oxide during baking of the coating, facilitating the baking, and further enhancing the adhesion of the coating. However, when boron oxide is excessively present alone, it may deteriorate the water resistance and the like. For example, the area ratio of boron oxide contained in the aluminum borate-based coating may be 20% or less, and may be 5% or less.

The smaller the number of voids in the aluminum borate-based coating, the better. The present inventors have found that if the voids in the aluminum borate-based coating are controlled to 5.0 area % or less when viewed on a cut surface in which the cutting direction is parallel to the plate thickness direction, the iron loss is preferably reduced. I have found that it can be suppressed. For example, if the voids in the aluminum borate-based coating exceed 5.0 area %, the tension applied to the silicon steel sheet is reduced, and the formation of an internal oxidized region is promoted, resulting in an increase in iron loss. . The upper limit of this void is preferably 4.0%, more preferably 3.0%. Moreover, since the smaller the voids in the aluminum borate-based coating, the better, so the lower limit is not particularly limited, and the lower limit may be 0 area %. However, since it is not easy to control the voids to 0 area %, the lower limit of the voids may be 0.1% or 0.5%.

The average thickness of the aluminum borate-based coating is preferably more than 0.5 μm and 8 μm or less. If the coating is too thick, the effect of improving iron loss by applying tension is saturated and the space factor is significantly reduced. Therefore, the upper limit of the average thickness of the aluminum borate-based coating is preferably 8 μm, more preferably 6 μm, and even more preferably 4 μm. On the other hand, if the coating is too thin, it will not be possible to apply sufficient tension to the silicon steel sheet. Therefore, the lower limit of the average thickness of the aluminum borate-based coating is preferably over 0.5 μm, more preferably 1 μm, and even more preferably 2 μm.

The aluminum borate-based coating is formed by forming an oxide film on a silicon steel sheet from which the formation of a forsterite coating is suppressed during final annealing or from which the forsterite coating is removed after final annealing, and then fine particles containing alumina sol and boric acid are dispersed. It is formed by applying a liquid and heat-treating it. The aluminum borate-based coating thus formed contains aluminum-boron oxide, and optionally aluminum oxide or boron oxide. Also, impurities may be contained within a range that does not impair the effect.

(Phosphate coating)
The grain-oriented electrical steel sheet according to the present embodiment may further have a phosphoric acid-based coating disposed in contact with the aluminum borate-based coating.

This phosphoric acid-based coating contains a phosphorous-silicon composite oxide (composite oxide containing phosphorus and silicon). The phosphoric acid-based coating is formed by coating and baking an insulating coating-forming composition containing a mixture of colloidal silica, a phosphate such as a metal phosphate, and water on the aluminum borate-based coating. be done. The insulating film-forming composition may contain 25 to 75% by mass of phosphate and 75 to 25% by mass of colloidal silica on a dry basis. The phosphate may be an aluminum salt, magnesium salt, nickel salt, manganese salt, or the like of phosphoric acid. By forming the phosphoric acid-based coating, the iron loss can be preferably reduced by applying further tension to the grain-oriented electrical steel sheet.

The average thickness of the phosphoric acid-based coating is preferably 0.1 μm or more and 10 μm or less. The upper limit of the average thickness of the phosphoric acid-based coating is preferably 5 μm, more preferably 3 μm. The lower limit of the average thickness of the phosphoric acid-based coating is preferably 0.5 µm, more preferably 1 µm.

The grain-oriented electrical steel sheet according to the present embodiment described above is observed and measured as follows.

A test piece is cut out from the grain-oriented electrical steel sheet on which each layer is formed, and the layer structure of the test piece is observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). For example, a layer with a thickness of 300 nm or more may be observed with an SEM, and a layer with a thickness of less than 300 nm may be observed with a TEM.

Specifically, first, a test piece is cut so that the cutting direction is parallel to the plate thickness direction (more specifically, the test piece is cut so that the cut surface is parallel to the plate thickness direction and perpendicular to the rolling direction. cutting), and the cross-sectional structure of this cut surface is observed with an SEM at a magnification that allows each layer to be included in the observation field. For example, by observing a backscattered electron composition image (COMPO image), it is possible to infer how many layers the cross-sectional structure is composed of. For example, in a COMPO image, a silicon steel sheet can be identified as a light color, an oxide film and an oxidized region as a dark color, and an aluminum borate-based coating and a phosphoric acid-based coating as a neutral color.

In order to identify each layer in the cross-sectional structure, SEM-EDS (Energy Dispersive X-ray Spectroscopy) is used to perform line analysis along the plate thickness direction and quantitatively analyze the chemical components of each layer. Six elements of Fe, P, Si, O, Mg and Al are to be quantitatively analyzed. Although the device to be used is not particularly limited, in this embodiment, for example, SEM (NB5000 manufactured by Hitachi High-Technologies Corporation), EDS (XFlash (r) 6 | 30 manufactured by Bruker AXS), EDS analysis software ( ESPRIT 1.9) manufactured by Bruker AXS may be used.

From the observation result of the COMPO image and the quantitative analysis result of SEM-EDS, it is a layered region existing at the deepest position in the plate thickness direction, and the Fe content is 80 atomic% or more excluding measurement noise. and O content is less than 30 atomic%, and if the line segment (thickness) on the scanning line of line analysis corresponding to this region is 300 nm or more, this region is judged to be a silicon steel plate Then, the area excluding this silicon steel sheet is judged to be an oxide film, an oxidized area, an aluminum borate-based coating, and a phosphoric acid-based coating.

Regarding the region excluding the silicon steel sheet specified above, from the observation results of the COMPO image and the quantitative analysis results of SEM-EDS, excluding measurement noise, the Fe content is less than 80 atomic% and the P content is 5 atomic% or more. , O content is 30 atomic % or more, and if the line segment (thickness) on the scanning line of the line analysis corresponding to this region is 300 nm or more, this region is a phosphoric acid coating I judge. In addition to the above three elements which are the determining elements for specifying the phosphoric acid-based coating, the phosphoric acid-based coating may contain aluminum, magnesium, nickel, manganese, etc. derived from phosphates. Silicon derived from colloidal silica may also be contained. Further, in this embodiment, the phosphoric acid-based coating may not be present.

Regarding the region excluding the silicon steel sheet and the phosphoric acid coating specified above, from the observation results of the COMPO image and the quantitative analysis results of SEM-EDS, excluding measurement noise, the Fe content is less than 80 atomic%, and the P content is less than 5 atomic%, the Si content is less than 20 atomic%, the O content is 20 atomic% or more, and the Al content is 10 atomic% or more, and on the scanning line of the line analysis corresponding to this region If the line segment (thickness) is 300 nm or more, this area is determined to be an aluminum borate-based coating. In addition to the above-described five elements that are judgment elements for specifying the aluminum borate-based coating, the aluminum borate-based coating contains boron. However, it may be difficult to accurately analyze the content of boron by EDS quantitative analysis due to the influence of carbon and the like. Therefore, if necessary, EDS qualitative analysis may be performed to determine whether or not the aluminum borate-based coating contains boron.

When judging the region that is the aluminum borate-based coating or the phosphoric acid-based coating, the precipitates, inclusions, and pores contained in each coating are not included in the determination target, and the above-mentioned matrix is used as the matrix. A region that satisfies the quantitative analysis result of is judged to be an aluminum borate-based coating or a phosphoric acid-based coating. For example, if it is confirmed from the COMPO image and line analysis results that there are precipitates, inclusions, and vacancies on the scanning line of the line analysis, the result of quantitative analysis as the mother phase without including this region Judging by Precipitates, inclusions, and vacancies can be distinguished from the matrix phase by the contrast in the COMPO image, and can be distinguished from the matrix phase by the abundance of constituent elements in the quantitative analysis results. When specifying the aluminum borate-based coating or the phosphoric acid-based coating, it is preferable to specify at a position where no precipitates, inclusions, or voids are included on the scanning line of line analysis.

If the silicon steel sheet, the aluminum borate-based coating, and the phosphoric acid-based coating specified above are excluded, and the line segment (thickness) on the scanning line of the line analysis corresponding to this region is 300 nm or more, This region is determined to be an oxide film and an oxide region. The oxide film and the oxidized region have an average Fe content of less than 80 atomic percent, an average P content of less than 5 atomic percent, an average Si content of 20 atomic percent or more, and an O content of What is necessary is just to satisfy 30 atomic % or more on average. Further, in the present embodiment, the oxide film is not a forsterite film but an oxide film mainly composed of silicon oxide. Therefore, the average Mg content in the oxide film and the oxidized region should be less than 20 atomic %. The quantitative analysis results of the oxide film and the oxidized region are the results of the quantitative analysis of the parent phase without including the analysis results of the precipitates, inclusions, pores, etc. contained in the oxide film and the oxidized region. When specifying the oxide film and the oxidized region, it is preferable to specify at a position where no precipitates, inclusions, or holes are included on the scanning line of the line analysis.

The COMPO image observation and the measurement of the thickness of each layer by the above COMPO image observation and SEM-EDS quantitative analysis are carried out at five or more locations with different observation fields. For the thickness of each layer determined at a total of five or more locations, the average value is determined from the values excluding the maximum value and the minimum value, and this average value is taken as the average thickness of each layer. However, the thickness of the oxide film is obtained by measuring the thickness at locations where it can be judged that it is an externally oxidized region and not an internally oxidized region while observing the structure morphology, and obtains an average value.

If a layer having a line segment (thickness) of less than 300 nm on the line analysis scanning line exists in at least one of the five or more observation fields described above, the corresponding layer is observed in detail with a TEM. Then, a TEM is used to identify and measure the thickness of the layer in question.

A test piece containing a layer to be observed in detail using a TEM is cut out by FIB (Focused Ion Beam) processing so that the cutting direction is parallel to the thickness direction (in detail, the cutting surface is in the thickness direction and A test piece is cut out so that it is parallel and perpendicular to the rolling direction), and the cross-sectional structure of this cut surface is observed with STEM (Scanning-TEM) at a magnification in which the corresponding layer is included in the observation field (bright field image). . If each layer does not fall within the observation field of view, the cross-sectional structure is observed in a plurality of continuous fields of view.

In order to identify each layer in the cross-sectional structure, TEM-EDS is used to perform line analysis along the sheet thickness direction, and quantitative analysis of the chemical components of each layer is performed. Six elements of Fe, P, Si, O, Mg and Al are to be quantitatively analyzed. The device to be used is not particularly limited, but in this embodiment, for example, TEM (JEM-2100F manufactured by JEOL Ltd.), EDS (JED-2300T manufactured by JEOL Ltd.), EDS analysis software (manufactured by JEOL Ltd. Analysis Station) may be used.

From the results of bright-field image observation by TEM and quantitative analysis results of TEM-EDS, each layer is specified and the thickness of each layer is measured. The method for specifying each layer and the method for measuring the thickness of each layer using TEM may be carried out according to the above-described method using SEM.

When the thickness of each layer specified by TEM is 5 nm or less, it is preferable to use a TEM having a spherical aberration correction function from the viewpoint of spatial resolution. Further, when the thickness of each layer is 5 nm or less, point analysis is performed at intervals of, for example, 2 nm or less along the plate thickness direction, the line segment (thickness) of each layer is measured, and the line segment is the thickness of each layer. It may be adopted as For example, if a TEM having a spherical aberration correction function is used, EDS analysis can be performed with a spatial resolution of about 0.2 nm.

In the method for specifying each layer described above, first, the silicon steel sheet is specified in the entire region, then the phosphoric acid coating in the remainder is specified, the aluminum borate coating in the remainder is specified, and finally Since the remaining part is determined to be an oxide film and an oxide region, in the case of the grain-oriented electrical steel sheet that satisfies the configuration of this embodiment, there is no unspecified region other than the above layers in the entire region.

The quantitative analysis results of the chemical components of the aluminum borate-based coating specified by the above method show that the Fe content is less than 80 atomic%, the P content is less than 5 atomic%, the Si content is less than 20 atomic%, and O is contained. If the amount is 20 atomic % or more, the Al content is 10 atomic % or more, and boron is detected by qualitative analysis, it is determined that the aluminum borate-based coating mainly contains aluminum-boron oxide.

Similarly, the quantitative analysis results of the chemical components of the oxide film and the oxidized region specified by the above method show that the average Fe content is less than 80 atomic percent, the average P content is less than 5 atomic percent, and the average Si content is If the O content is 20 atomic % or more, the average O content is 30 atomic % or more, and the average Mg content is less than 20 atomic %, it is determined that the oxide film and the oxidized region mainly contain silicon oxide.

Similarly, if the quantitative analysis results of the chemical components of the phosphoric acid-based coating identified by the above method show that the Fe content is less than 80 atomic percent, the P content is 5 atomic percent or more, and the O content is 30 atomic percent or more, It is determined that the phosphoric acid-based coating mainly contains a phosphorous-silicon composite oxide.

Among the oxide films and oxidized regions specified by the above method, the oxidized regions having a maximum depth of 0.2 μm or more are specified by the following method. When the average thickness of the oxide film measured above is _Dave , the line segment (thickness) along the thickness direction of the oxide film and the oxidized region specified by the above method is 2 × _Dave or more. It is determined that an oxidized region exists in the region. The oxidized regions exist discretely (island-like) along the interface between the silicon oxide and the oxide film. In each discrete oxidized region, the maximum thickness, specifically, the maximum value of the line segment in the plate thickness direction including the oxide film and the oxidized region is measured. If this maximum value is greater than or equal to _Dave + 0.2 µm, the oxidized region is determined to have a maximum depth of greater than or equal to 0.2 µm.

The line fraction of the oxidized region with a maximum depth of 0.2 μm or more is specified by the following method. First, the interface between the silicon steel plate and the oxide film is specified except for the region having a thickness of 2× _Dave or more among the oxide films and the oxide regions specified by the above method. This specified interface is a broken-line interface in which a region of 2× _Dave or more is missing in the observation field of view. The missing areas are connected by straight lines to specify one continuous interface (estimated interface) on the observation field. Lines are drawn on the observation field at regular intervals of 0.02 μm from this estimated interface in the depth direction, and these lines are used as reference lines for measuring the line fraction of the oxidized region. An oxidized region having a maximum depth of 0.2 μm or more existing on this reference line is specified, and its line segment ratio is obtained. Specifically, the total value Σd of the length d on the estimated interface of the oxidized regions having a maximum depth of 0.2 μm or more is divided by the estimated interface length L. rate. The linear fraction of the oxidized region is obtained from at least the region where the estimated total length L of the interface is 50 μm or more.

The area ratio of voids in the aluminum borate-based coating is specified by the following method. The aluminum borate-based coating identified by the above method is observed with a TEM (bright field image). In this bright-field image, the white regions are voids. Since the TEM test piece is a thin film, the voids in the aluminum borate-based coating are completely voids on the TEM test piece. Therefore, whether or not the white region in the bright-field image is a void can be clearly determined by EDS analysis of the white region. Void regions and non-void regions in the aluminum borate-based coating are binarized in the observation field, and the area ratio of the voids is determined by image analysis. The area ratio of voids is obtained from at least a region where the total area of the aluminum borate-based coating is 4 μm ² or more. In the binarization of the image for image analysis, the image may be binarized by manually coloring the voids in the tissue photograph based on the above-described determination result of the voids.

Whether or not the aluminum borate-based coating contains crystalline aluminum oxide, Al ₁₈ B ₄ O ₃₃ , Al ₄ B ₂ O ₉ , boron oxide, or the like is determined by the following method. A sample is cut out from the grain-oriented electrical steel sheet, polished as necessary so that the surface parallel to the sheet surface becomes the measurement surface, and the aluminum borate-based coating is exposed, and X-ray diffraction measurement is performed. For example, X-ray diffraction may be performed using CoKα rays (Kα1) as incident X-rays. X-ray diffraction patterns identify whether aluminum oxide, Al ₁₈ B ₄ O ₃₃ , Al ₄ B ₂ O ₉ , boron oxide, etc. are present. This identification may be performed using a PDF (Powder Diffraction File) of ICDD (International Center for Diffraction Data). Identification of aluminum oxide can be found in PDF: No. 00-047-1770, or 00-056-1186. The identity of Al ₁₈ B ₄ O ₃₃ is given in PDF: No. 00-029-0009, 00-053-1233, or 00-032-0003. The identification of Al ₄ B ₂ O ₉ is given in PDF: No. 00-029-0010. The identity of boron oxide can be found in PDF:No. 00-044-1085, 00-024-0160, or 00-006-0634.

Next, a method for manufacturing the grain-oriented electrical steel sheet according to this embodiment will be described.

In addition, the method of manufacturing the grain-oriented electrical steel sheet according to the present embodiment is not limited to the following method. The following manufacturing method is an example for manufacturing the grain-oriented electrical steel sheet according to this embodiment.

The grain-oriented electrical steel sheet according to the present embodiment is obtained by forming an oxide film on a silicon steel sheet from which the forsterite coating is suppressed during finish annealing or from which the forsterite coating is removed after finish annealing, followed by boric acid. It may be produced by forming an aluminum-based coating.

Specifically, the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment includes:
A silicon steel sheet having a texture developed in the {110} <001> direction and having a forsterite coating suppressed from forming or having a forsterite coating removed as a starting material,
an oxide film forming step of forming an oxide film on the silicon steel sheet;
a film forming step of forming an aluminum borate-based film on the silicon steel sheet on which the oxide film is formed,
In the oxide film forming process,
A silicon steel sheet is heated to 100° C. for 10 seconds or more in a temperature range of 600° C. or more and 1150° C. or less in an atmosphere gas containing hydrogen and having an oxidation degree PH ₂ O/PH ₂ adjusted to 0.00008 or more and 0.012 or less. Soaking for seconds or less,
In the film formation process,
A fine particle dispersion liquid containing alumina sol and boric acid is applied to a silicon steel sheet on which an oxide film is formed, and dried,
A silicon steel sheet coated with a fine particle dispersion and dried is heated to 750° C. or more and 1350° C. or less in an atmosphere gas containing hydrogen and having an oxidation degree PH ₂ O/PH ₂ adjusted to 0.0002 or more and 0.04 or less. Soaking for 10 seconds or more and 100 seconds or less in the temperature range of
The silicon steel sheet that has been soaked in the above temperature range is treated to contain hydrogen and have an oxidation degree PH ₂ O/PH ₂ in the range of 0.00002 or more and 0.02 or less, which is lower than the oxidation degree during soaking. It may be cooled to 600° C. or lower in an atmosphere gas whose degree of oxidation has been changed.

The method of manufacturing the silicon steel sheet to be subjected to the oxide film forming step is not particularly limited. A silicon steel sheet having a texture developed in the {110}<001> orientation may be produced by applying the usual conditions for producing a grain-oriented electrical steel sheet. In addition, in order to manufacture a silicon steel sheet in which the formation of the forsterite coating is suppressed, for example, the silicon steel sheet is manufactured by performing finish annealing using an annealing separator containing alumina (Al ₂ O ₃ ) as a main component. good. In order to manufacture a silicon steel sheet from which the forsterite coating has been removed, for example, finish annealing is performed using an annealing separator containing magnesia (MgO) as a main component, and the forsterite coating is removed mechanically or chemically after the finish annealing. A silicon steel sheet can be manufactured by removing the silicon steel sheet. In the case of either the silicon steel sheet in which the formation of the forsterite coating is suppressed or the silicon steel sheet from which the forsterite coating has been removed, the surface of the silicon steel sheet may be mirror-finished before the oxide film forming step.

(Oxide film forming step)
In the oxide film forming step, a silicon steel sheet having a controlled texture and having no forsterite coating is annealed to form an oxide film disposed in contact with the silicon steel sheet.

The degree of oxidation (PH ₂ O/PH ₂ ) during soaking in the oxide film forming step is preferably in the range of 0.00008 to 0.012. When the degree of oxidation (PH ₂ O/PH ₂ ) of the atmosphere containing hydrogen exceeds 0.012 during soaking, internal oxidation is likely to occur on the surface of the silicon steel sheet, forming many oxidized regions, and the surface of the steel sheet The smoothness of the core is reduced and the iron loss is increased. On the other hand, if the oxidation degree (PH ₂ O/PH ₂ ) of this atmosphere is less than 0.00008, annealing for forming an oxide film will take a long time. PH ₂ O is the partial pressure of H ₂ O in the atmosphere, and PH ₂ is the partial pressure of hydrogen.

Also, the soaking temperature in the oxide film forming process is preferably in the range of 600 to 1150.degree. If the soaking temperature is less than 600° C., an oxide film cannot be formed, which is not preferable. On the other hand, if the soaking temperature exceeds 1150° C., the oxidized region increases and the thickness of the oxide film increases, which is not preferable.

The soaking time in the oxide film forming process is preferably in the range of 10 to 100 seconds. If the soaking time is 10 seconds or more, the oxide film can be stably formed, and if the soaking time is 100 seconds or less, the productivity is good, and the film thickness of the oxide film is set to a preferable thickness. You can control it.

(Coating process)
In the film forming step, the silicon steel sheet on which the oxide film is formed is coated with a fine particle dispersion and annealed to form an aluminum borate-based film on and in contact with the oxide film.

The fine particle dispersion liquid to be applied to the silicon steel sheet on which the oxide film is formed may contain alumina sol and boric acid. This fine particle dispersion preferably uses water as a solvent. If an organic solvent is contained in part of the fine particle dispersion, the voids in the aluminum borate-based coating may increase, and the oxidized regions may also increase.

In order to apply the fine particle dispersion containing alumina sol and boric acid to the silicon steel sheet, it is preferable to cool the silicon steel sheet to 50° C. or less after the soaking for forming the oxide film is completed.

As for the composition ratio of alumina sol and boric acid in the fine particle dispersion, the atomic ratio (Al/B) of aluminum to boron is preferably 1.25 to 1.81. Any sol can be used as the alumina sol as long as it is composed of uniform alumina fine particles with good dispersibility. The alumina fine particles are preferably fine fine particles in order to uniformly coat the silicon steel sheet, and preferably have a particle size of several nanometers to several tens of nanometers. If the particle size significantly exceeds 100 nm, the coating may become non-uniform after baking.

The degree of oxidation (PH ₂ O/PH ₂ ) during soaking in the film forming step is preferably in the range of 0.0002 to 0.04. When the degree of oxidation (PH ₂ O/PH ₂ ) of the atmosphere containing hydrogen exceeds 0.04 during soaking, internal oxidation progresses on the surface of the silicon steel sheet, many oxidized regions are formed, and the surface of the steel sheet becomes smooth. iron loss increases. On the other hand, if the oxidation degree (PH ₂ O/PH ₂ ) of this atmosphere is less than 0.0002, it may take a long time for annealing to form a coating. PH ₂ O is the partial pressure of H ₂ O in the atmosphere, and PH ₂ is the partial pressure of hydrogen.

Also, the soaking temperature in the film forming step is preferably in the range of 750 to 1350°C. If the soaking temperature is less than 750°C, the aluminum borate-based film cannot be formed, which is not preferable. On the other hand, if the soaking temperature exceeds 1350° C., the oxidized region increases and the thickness of the oxide film increases, which is not preferable.

In the coating formation step, when the soaking temperature reaches 1000° C. or higher, crystalline Al ₁₈ B ₄ O ₃₃ or Al ₄ B ₂ O ₉ is added to the aluminum borate-based coating, which is mainly amorphous. At least one will be included. Aluminum oxide and boron oxide that may be contained in the aluminum borate-based coating are affected by the component ratio of alumina sol and boric acid in the fine particle dispersion. When the proportion of alumina sol in the fine particle dispersion is high, aluminum oxide is likely to be produced, and when the proportion of boric acid in the fine particle dispersion is high, boron oxide is likely to be produced.

The soaking time in the film forming step is preferably in the range of 10 to 100 seconds. If the soaking time is 10 seconds or more, the aluminum borate-based coating can be stably formed, and if the soaking time is 100 seconds or less, the productivity is good, and the thickness of the oxide film can be reduced. Desirable thickness can be controlled.

The silicon steel sheet soaked under the above conditions is cooled to 600° C. or less in an atmospheric gas whose oxidation degree has been changed to a lower oxidation degree than that during soaking.

In the grain-oriented electrical steel sheet according to the present embodiment, the line fraction of the oxidized region, the thickness of the oxide film, and the porosity of the aluminum borate-based coating are controlled by controlling the soaking conditions and cooling conditions in the coating forming process. , can be stably built in the range defined in this embodiment.

Specifically, by controlling the soaking conditions in the coating formation step and controlling the cooling conditions after soaking, the decomposition of the aluminum/boron oxide contained in the aluminum borate-based coating is suppressed, It is possible to suppress the internal oxidation of the silicon steel sheet that accompanies this. Unless both the soaking and cooling conditions are controlled, the linear fraction of the oxidized region and the porosity of the aluminum borate-based coating cannot be satisfied.

The degree of oxidation (PH ₂ O/PH ₂ ) during cooling in the coating forming step is changed to a degree of oxidation lower than that during soaking, and is in the range of 0.00002 to 0.02. preferable. If the degree of oxidation is not changed during cooling to a degree lower than that during soaking, internal oxidation of the silicon steel sheet proceeds, forming many oxidized regions, reducing the smoothness of the surface of the steel sheet, and increasing iron loss. put away. In addition, when the degree of oxidation (PH ₂ O/PH ₂ ) of the atmosphere gas containing hydrogen exceeds 0.02 during cooling, internal oxidation of the silicon steel sheet progresses, forming many oxidized regions and smoothing the surface of the steel sheet. This is not preferable because the iron loss is increased due to the decrease in strength. Although the lower limit of the degree of oxidation (PH ₂ O/PH ₂ ) is not particularly limited, it may be 0.00002.

In the film forming step, it is preferable to cool to 600° C. or lower in the above atmosphere. If the cooling end temperature exceeds 600°C, the oxidized region may increase.

(Phosphate-based film forming step)
When manufacturing the grain-oriented electrical steel sheet according to the present embodiment, a phosphoric acid-based film forming step may be further included after the film forming step.

In the phosphoric acid-based coating forming step, an insulating coating-forming composition containing a mixture of colloidal silica, a phosphate such as a metal phosphate, and water is applied onto the aluminum borate-based coating and baked. can be formed by The insulating film-forming composition may contain 25 to 75% by mass of phosphate and 75 to 25% by mass of colloidal silica on a dry basis. The phosphate may be an aluminum salt, magnesium salt, nickel salt, manganese salt, or the like of phosphoric acid.

Baking conditions in the phosphoric acid-based coating formation step are preferably conditions that can suppress an increase in oxidized regions and an increase in voids in the aluminum borate-based coating. For example, in an atmosphere composed of hydrogen, nitrogen, and water vapor, the degree of oxidation (PH ₂ O/PH ₂ ) is 0.15 or less, and heated to 350 to 900° C. at a rate of temperature increase of 5° C./second or more. Soaking for 100 seconds is good.

Next, the effects of one aspect of the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to this one conditional example. Various conditions can be adopted in the present invention as long as the objects of the present invention are achieved without departing from the gist of the present invention.

Using the silicon steel sheets of steel A to steel N shown in Tables 1 and 2 as starting materials, the oxide film forming process and the film forming process were carried out. In addition, a phosphoric acid-based film forming step was carried out as necessary. Further, the produced grain-oriented electrical steel sheet was subjected to magnetic domain refining treatment by irradiating laser. In the table, "-" in the chemical composition of the silicon steel sheet indicates that the alloying element was not intentionally added or the content was below the detection limit of measurement.

The silicon steel sheets of steel A to steel N shown in Tables 1 and 2 were prepared by heating a slab with the adjusted composition to 1150°C, hot-rolling it to a thickness of 2.6 mm, and then The hot-rolled sheet is annealed in stages, quenched after hot-rolled sheet annealing, pickled, cold-rolled to a sheet thickness of 0.23 mm, and decarburized at a soaking temperature of 820°C in an atmosphere containing hydrogen-nitrogen-steam. Annealed, nitrided and annealed in an atmosphere containing hydrogen-nitrogen-ammonia so that the nitrogen content is 200 ppm, coated with an annealing separator mainly composed of alumina (Al ₂ O ₃ ) or magnesia (MgO), and hydrogen - Heated to 1200°C in an atmosphere containing nitrogen, switched to a hydrogen atmosphere after heating, performed final annealing at 1200°C for 20 hours, and removed the forsterite coating as necessary.

The above slab contained, in mass %, acid-soluble Al: 0.03%, C: 0.056%, N: 0.008%, and S+Se total: 0.005%.

Moreover, the above silicon steel sheet had a texture developed in the {110}<001> orientation, but did not have a forsterite coating.

As the oxide film forming step, the silicon steel sheet was subjected to the conditions shown in Tables 3 and 4 in an atmosphere gas containing hydrogen and adjusted to the degree of oxidation (PH ₂ O/PH ₂ ) shown in Tables 3 and 4. It was annealed under the indicated temperature and soaking conditions.

As a coating forming step, a fine particle dispersion containing alumina sol and boric acid was applied to the silicon steel sheet after forming the oxide film. This silicon steel sheet was soaked in an atmosphere gas containing hydrogen and adjusted to the degree of oxidation (PH ₂ O/PH ₂ ) shown in Tables 3 and 4 at the temperature and time shown in Tables 3 and 4. Annealed under conditions. Further, the soaked silicon steel sheet was cooled as shown in Tables 3 and 4 in an atmosphere gas containing hydrogen and adjusted to the degree of oxidation (PH ₂ O/PH ₂ ) shown in Tables 3 and 4. Cooled in conditions. In addition, test No. The fine particle dispersion of test No. 37 has a high proportion of alumina sol. No. 38 microparticle dispersion had a high proportion of boric acid.

The silicon steel sheets of Steel B to Steel N were subjected to the phosphoric acid-based film forming process after the oxide film forming process and the film forming process. In the phosphoric acid-based coating forming step, a composition for forming an insulating coating containing a mixture of colloidal silica, a phosphate of aluminum salt or magnesium salt, and water is applied to the produced grain-oriented electrical steel sheet, and the composition is applied under normal conditions. annealed at The formed phosphoric acid-based coating contained a phosphorous-silicon composite oxide (a composite oxide containing phosphorus and silicon). The average thickness of the phosphoric acid-based coating was 1 μm.

Tables 5 and 6 show the production results. Regarding the constituent phases of the aluminum borate-based coating in the table, "a" indicates aluminum/boron oxide, "b1" indicates Al ₁₈ B ₄ O ₃₃ , and "b2" indicates Al ₄ B ₂ O ₉ , “c” indicates aluminum oxide, and “d” indicates boron oxide. In addition, the constituent phases of the oxide film, the average thickness of the oxide film, the linear fraction of the oxidized region, the constituent phases of the aluminum borate-based coating, the average thickness of the aluminum borate-based coating, and the void area of the aluminum borate-based coating The rate was measured according to the method described above.

Tables 5 and 6 show the evaluation results. Adhesion was evaluated by a 180 degree bending test. The manufactured directional magnet was wound around a roll with a diameter of 20 mm, and the area ratio of the peeled surface of the film to the steel plate area in contact with the roll was calculated. The steel plate area in contact with the roll was obtained by calculation. The area of the peeled surface was obtained by taking a photograph of the steel plate after the test and performing image analysis on the photographed image. The ratio of the peeled area to the steel plate area in contact with the roll was defined as the peeled area ratio (%). In the table, "good" when the peeled area ratio is 10% or less, "no good" when the peeled area ratio is more than 10% and less than 50%, and "bad" when the peeled area ratio is 50% or more. show. When the peeled area ratio was "good", it was judged that the adhesion was good.

Iron loss was evaluated by Single Sheet Tester (SST). A sample of width 60 mm×length 300 mm was taken from the produced grain-oriented electrical steel sheet, and W17/50 (iron loss when the steel sheet was magnetized at 50 Hz to a magnetic flux density of 1.7 T) was measured. When W17/50 was 0.68 W/kg or less, it was determined that the core loss was good.

As shown in Tables 1 to 6, the inventive examples had excellent adhesion and iron loss characteristics as grain-oriented electrical steel sheets because the oxide film and the aluminum borate-based coating were preferably controlled.

On the other hand, in the comparative example, since at least one of the oxide film and the aluminum borate-based coating was not controlled favorably, the adhesion as a grain-oriented electrical steel sheet was not satisfactory, and the iron loss characteristics were not satisfactory. The underlined values in the table are outside the scope of the present invention.

According to the above aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet with suitably reduced core loss and a method for manufacturing the same. Therefore, industrial applicability is high.

1 base material steel plate (silicon steel plate),
2 intermediate layer (oxide film),
3 insulating coating (aluminum borate-based coating),
4 oxidized regions (internal oxidized regions),
5 voids,
6 Interface between silicon steel sheet and oxide film L Length of interface d Length of oxidized region

Claims (6)

A grain-oriented electrical steel sheet having a silicon steel sheet as a base material steel sheet, an intermediate layer arranged in contact with the silicon steel sheet, and an insulating coating arranged in contact with the intermediate layer,
The intermediate layer is an oxide film, the oxide film contains silicon oxide, and the oxide film has an average thickness of 2 nm or more and 500 nm or less, and the insulating coating is an aluminum borate-based coating, and the aluminum borate-based coating The coating contains aluminum/boron oxide, and the average thickness of the aluminum borate-based coating is more than 0.5 μm and 8 μm or less,
The area ratio of voids in the aluminum borate-based coating is 0% or more and 2.3 % or less when viewed on a cut surface in which the cutting direction is parallel to the plate thickness direction,
When viewed from the cut surface, an oxidized region exists at the interface between the silicon steel plate and the oxide film, and the oxidized region extends from the interface toward the silicon steel plate to a maximum depth of 0.2 μm or more. The line fraction to the interface is 0.1% or more and 12 % or less,
A grain-oriented electrical steel sheet characterized by: The _grain -oriented electrical steel sheet according to claim ₁ , wherein at least _one of _Al18B4O33 and _Al4B2O9 is included as the aluminum _- boron oxide. 3. The grain-oriented electrical steel sheet according to claim 1, wherein the aluminum borate-based coating further contains aluminum oxide. further comprising a phosphoric acid-based coating disposed in contact with the aluminum borate-based coating;
The grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the phosphoric acid-based coating contains a phosphor-silicon composite oxide. The silicon steel sheet, as a chemical component, is mass%,
Si: 0.8% or more and 7.0% or less,
Mn: 0 or more and 1.00% or less,
Cr: 0 or more and 0.30% or less,
Cu: 0 or more and 0.40% or less,
P: 0 or more and 0.50% or less,
Sn: 0 or more and 0.30% or less,
Sb: 0 or more and 0.30% or less,
Ni: 0 or more and 1.00% or less,
B: 0 or more and 0.008% or less,
V: 0 or more and 0.15% or less,
Nb: 0 or more and 0.2% or less,
Mo: 0 or more and 0.10% or less,
Ti: 0 or more and 0.015% or less,
Bi: 0 or more and 0.010% or less,
Al: 0 or more and 0.005% or less,
Total of C + N: 0 to 0.005%, and Total of S + Se: 0 to 0.005%,
and the balance consists of Fe and impurities,
The grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the silicon steel sheet has a texture developed in {110} <001> orientation. The silicon steel sheet, as a chemical component, is mass%,
Mn: 0.05% or more and 1.00% or less,
Cr: 0.02% or more and 0.30% or less,
Cu: 0.05% or more and 0.40% or less,
P: 0.005% or more and 0.50% or less,
Sn: 0.02% or more and 0.30% or less,
Sb: 0.01% or more and 0.30% or less,
Ni: 0.01% or more and 1.00% or less,
B: 0.0005% or more and 0.008% or less,
V: 0.002% or more and 0.15% or less,
Nb: 0.005% or more and 0.2% or less,
Mo: 0.005% or more and 0.10% or less,
Ti: 0.002% or more and 0.015% or less, and Bi: 0.001% or more and 0.010% or less,
The grain-oriented electrical steel sheet according to claim 5, containing at least one selected from the group consisting of:

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