RU2771766C1 - Grain-oriented electrical steel sheet having excellent insulating coating adhesion without forsterite coating - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, namely to a grain-oriented electrical steel sheet used as a material for iron cores of transformers, in particular transformers with a tape core. The sheet includes a base steel sheet, an intermediate layer that is in contact with the base steel sheet and is mainly silica, and an insulating coating that is in contact with the intermediate layer and is mainly composed of phosphate and colloidal silica. The main steel sheet has a chemical composition containing, wt.%: C: 0.085 or less, Si: 0.80-7.00, Mn: 0.05-1.00, acid-soluble Al: 0.010-0.065, N: 0, 0040 or less, S: 0.0100 or less, B: 0.0005-0.0080, and a residue composed of Fe and impurities, and BN with an average particle size of 50-300 nm present on the surface layer of the intermediate layer, while the ratio of the major axis to the minor axis BN is 1.5 or less.

EFFECT: electrical sheet has excellent insulating coating adhesion and low iron loss.

2 cl, 5 tbl, 3 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0001]

The present invention relates to a grain oriented electrical steel sheet which has an intermediate layer composed primarily of silicon oxide on the surface of a finish annealed grain oriented silicon steel sheet, which is produced under conditions preventing formation of a forsterite coating, or is produced by removing the forsterite coating by means such as grinding or etching, or smoothing the surface until it is mirror-like, and which has on the intermediate layer an insulating coating consisting mainly of phosphate and colloidal silicon dioxide. In particular, the present invention relates to a grain-oriented electrical steel sheet having excellent bending workability and excellent suitability for producing a strip core. Priority is claimed from Japanese Patent Application No. 2019-005395, filed January 16, 2019, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002]

Grain-oriented electrical steel sheet is a soft magnetic material and is used for the metal core of electrical equipment such as a transformer. The grain-oriented electrical steel sheet contains about 7 mass% or less Si, and its crystal grains are highly aligned in the {110}<001> direction in Miller indices.

[0003]

One of the characteristics required of a grain-oriented electrical steel sheet is low energy loss when driven by alternating current, that is, low steel loss. In addition, when a grain-oriented electrical steel sheet is used to produce a transformer core, it is important to ensure the insulating performance of the steel sheet, and thus an insulating coating is formed on the surface of the steel sheet. For example, the method disclosed in Patent Document 1, in which a coating agent mainly composed of colloidal silica and phosphate is applied to the surface of a steel sheet and baked to form an insulating coating, is effective for providing insulation. Thus, this is a conventional grain-oriented electrical steel sheet and a method of producing the same for forming an insulating coating mainly composed of colloidal silicon dioxide and phosphate on a forsterite (Mg ₂ SiO ₄ )-based coating (hereinafter, may be simply referred to as " glass film" or "forsterite coating") formed during the finishing annealing process.

[0004]

Under such circumstances, in recent years, due to the growing awareness of global environmental issues such as global warming, efficiency standards have been put in place for a transformer using grain-oriented electrical steel sheets. Typically, stringent efficiency standards have been applied in applications that use low grade grain oriented electrical steel sheets, especially in the strip core transformer, and there is a growing desire to use higher quality grain oriented electrical steel sheets. For this reason, there is an ever-increasing need to further reduce steel loss in grain-oriented electrical steel sheet.

[0005]

For the above reason, the characteristics required for the grain oriented electrical steel sheet used for the strip core are that (A) the steel loss should be low, and (B) the insulating coating should not be peeled off on a highly curved work portion. Since the strip core is produced by winding an elongated steel sheet into a coil shape, there is a problem that the radius of curvature of the steel sheet on its inner peripheral side becomes small, resulting in strong bending during processing, and thus the insulating coating may peel off.

[0006]

With respect to the above requirement (A), in order to further reduce the loss in steel compared with the conventional grain-oriented electrical steel sheet, it is important to eliminate the fixing effect due to the roughness of the glass film boundary on the surface of the steel sheet, which prevents control of the crystal grain orientation and movement magnetic domains (hereinafter, may be referred to as "mirror processing" and "smoothing").

[0007]

First, the phenomenon of abnormal grain growth, called secondary recrystallization, is used to control the orientation of crystal grains. In order to precisely control the secondary recrystallization, it is important to accurately form the structure (primary recrystallization structure) obtained by primary recrystallization before secondary recrystallization, and appropriately provide fine precipitates or intergranular segregation elements called inhibitors.

[0008]

In secondary recrystallization, since the inhibitor has a function of inhibiting the growth of crystal grains other than the {110}<001> orientation in the primary recrystallization structure and preferably grows crystal grains in the {110}<001> orientation, control of the type and amount of the inhibitor is of particular importance.

[0009]

With respect to inhibitors, many research results have been disclosed. Among them, one of the distinguishing techniques is a technique that uses B as an inhibitor. Patent Documents 2 and 3 disclose that solid solution B acts as an inhibitor and is effective in developing the {110}<001> orientation.

[0010]

Patent Documents 4 and 5 disclose that fine BN formed by nitriding a material to which B is added after cold rolling acts as an inhibitor and is effective for developing the {110}<001> orientation.

[0011]

Patent Document 6 discloses that extremely fine BN obtained by inhibiting BN deposition as much as possible in hot rolling so as to precipitate it in a subsequent annealing heating process acts as an inhibitor. Patent Documents 6 and 7 disclose a method for controlling the emission shape of B in a hot rolling process to exhibit an inhibitor function.

[0012]

Then, in order to eliminate the bonding effect due to the roughness of the glass film boundary on the surface of the steel sheet, which prevents the movement of magnetic domains, for example, Patent Documents 7-9 disclose that the dew point of decarburization annealing is controlled, and iron-based oxides (Fe ₂ SiO ₄ , FeO etc.) are not formed in the oxide layer formed during decarburization annealing, and that a substance such as alumina, which does not react with silica, is used as an annealing separator to achieve surface smoothness after finishing annealing.

[0013]

With regard to the above requirement (B), since a conventional grain-oriented electrical steel sheet having an insulating coating on a finish-annealed glass film has good adhesion of the insulating coating, adhesion of the insulating coating does not become a problem. However, in the case where the glass film is removed or intentionally not formed in the finishing annealing process, it is difficult to obtain good adhesion of the insulation coating, and thus improving the adhesion of the insulation coating is a problem.

[0014]

Therefore, as a technique for ensuring adhesion of an insulating coating to a grain-oriented electrical steel sheet not having a glass film, for example, Patent Documents 10-13 have proposed a method for forming an oxide layer on the surface of a finish-annealed grain-oriented silicon steel sheet before formation of an insulating coating.

[0015]

For example, the technique disclosed in Patent Document 11 is a method in which a finish annealed grain-oriented silicon steel sheet obtained by mirror finishing or produced in a state close to having a mirror surface is annealed in a certain atmosphere at each of the temperatures to form an externally oxidized layer on the surface of the steel sheet, and the adhesion between the insulation coating and the steel sheet is ensured by the oxide layer.

[0016]

The technique disclosed in Patent Document 12 is a technique in which, in the case of a crystalline insulating coating, an amorphous oxide base coat is formed on the surface of a finish annealed grain oriented silicon steel sheet having no inorganic mineral coating to prevent oxidation of the steel sheet upon formation crystalline insulating coating.

[0017]

The technique disclosed in Patent Document 13 is a method for further developing the technology disclosed in Patent Document 11, in which the layered structure of a metal oxide layer containing Al, Mn, Ti, Cr, and Si is controlled at the boundary between the insulation coating and the steel sheet, to improve the adhesion of the insulating coating.

[0018]

However, the grain oriented electrical steel sheets that do not have forsterite coating proposed in Patent Documents 10 to 13 are also based on aluminum-based inhibitors, and do not mention improving the adhesion of the insulating coating in the grain oriented electrical steel sheets with the addition of B disclosed in Patent Documents 2-6. Although the grain-oriented electrical steel sheet without a forsterite coating in which B is added has a low steel loss, there is still a problem with the adhesion of the insulating coating required for the core strip.

BIBLIOGRAPHY

PATENT DOCUMENTS

[0019]

[Patent document 1]

Japanese Unexamined Patent Application, First Publication No. S48-039338

[Patent Document 2]

US Patent No. 3905842

[Patent Document 3]

US Patent No. 3905843

[Patent Document 4]

Japanese Unexamined Patent Application, First Publication No. H01-230721

[Patent Document 5]

Japanese Unexamined Patent Application, First Publication No. H01-283324

[Patent Document 6]

Japanese Unexamined Patent Application, First Publication No. H10-140243

[Patent Document 7]

Japanese Unexamined Patent Application, First Publication No. H07-278670

[Patent Document 8]

Japanese Unexamined Patent Application, First Publication No. H11-106827

[Patent Document 9]

Japanese Unexamined Patent Application, First Publication No. 2002-173715

[Patent Document 10]

Japanese Unexamined Patent Application, First Publication No. S60-131976

[Patent Document 11]

Japanese Unexamined Patent Application, First Publication No. H06-184762

[Patent Document 12]

Japanese Unexamined Patent Application, First Publication No. H07-278833

[Patent Document 13]

Japanese Unexamined Patent Application, First Publication No. 2002-348643

SUMMARY OF THE INVENTION

PROBLEMS SOLVED BY THE INVENTION

[0020]

A grain-oriented electrical steel sheet having low loss in uncoated forsterite steel has been produced as a metal core material using the above-mentioned conventional techniques, but when a transformer, especially a strip-core transformer, is produced, there is a problem in that the insulating coating peels off on a highly curved workpiece on the inner peripheral side of the steel sheet, and this problem has not yet been solved. While high efficiency transformers are required, the aforementioned problem needs to be solved for industrial production of high efficiency transformers.

[0021]

The present invention has been made in view of the current state of conventional technology, its technical problem is to prevent peeling of an insulating coating formed on a highly curved workpiece portion of a steel sheet serving as the inner peripheral side of a core in a grain-oriented electrical steel sheet having low loss in steel, which uses BN as an inhibitor and does not have forsterite coating, which is used as a metal core material for a transformer, especially a strip-core transformer, and its task is to offer a grain-oriented electrical steel sheet having excellent adhesion of insulating coatings and low losses in steel, which would solve the above problem.

REMEDIES FOR SOLVING THE PROBLEM

[0022]

In a grain-oriented electrical steel sheet having low steel loss, which uses BN as an inhibitor and has no forsterite coating, in order to improve the adhesion of the insulating coating, it is important to strongly align the crystal grains in the {110}<001> orientation when secondary recrystallization to increase the magnetic flux density and control the deposition shape B in the steel sheet.

[0023]

In the case of using BN as an inhibitor, when BN precipitates through the entire thickness of the steel sheet after finish annealing, the hysteresis loss increases and prevents the grain-oriented electrical steel sheet having low steel loss from being obtained, and the adhesion of the insulating coating also becomes insufficient.

[0024]

Based on these facts, the inventors of the present invention carefully studied the method of solving the above problems. As a result, it has been found that the aforementioned problems in a grain-oriented electrical steel sheet having no forsterite coating can be solved by depositing B as fine spherical BN on a surface layer of the steel sheet containing an oxide layer mainly composed of silicon oxide. .

The present invention was made on the basis of the above findings, and its essence is as follows.

[0025]

(1) A grain-oriented electrical steel sheet, including a base steel sheet, an intermediate layer that is in contact with the base steel sheet and is mainly composed of silicon oxide, and an insulating coating that is in contact with the intermediate layer and is mainly from phosphate and colloidal silicon dioxide, containing in its chemical composition, in wt.%: C: 0.085% or less, Si: 0.80-7.00%, Mn: 0.05-1.00%, acid-soluble Al: 0.010-0.065%, N: 0.0040% or less, S: 0.0100% or less, B: 0.0005-0.0080%, with the remainder of Fe and impurities, with BN having an average particle size of 50- 300 nm, present on the surface layer of the intermediate layer, when the total thickness of the base steel sheet and the intermediate layer is determined as d, the time to reach the position of sputtering depth d/100 from the outer surface of the intermediate layer, when the emission intensity B is measured using glow discharge emission spectrometry (GDS ) , is defined as t(d/100), and the time to reach the spray depth position d/10 from the outer surface of the intermediate layer is defined as t(d/10), emission intensity I _{B_t(d/100)} B at time t(d/ 100) and the emission intensity I _{B_t(d/10)} B at time t(d/10) satisfy the following Equation (1), and the ratio of the major axis to the minor axis BN is 1.5 or less.

I _{B_t(d/100)} >I _{B_t(d/10)} Equation (1)

[0026]

(2) The grain-oriented electrical steel sheet according to (1), wherein the number density of BN on the surface layer of the intermediate layer is 2×10 ⁶ pcs/mm ² or more.

BENEFICIAL EFFECTS OF THE INVENTION

[0027]

According to the present invention, in a grain-oriented electrical steel sheet using BN as an inhibitor, peeling of an insulating coating on a strongly curved portion of the steel sheet serving as the inner peripheral side of a metal core can be prevented, and the grain-oriented electrical steel sheet can be stably provided. structure, having excellent adhesion of the insulating coating, low steel loss and excellent suitability for the production of strip core.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0028]

The grain-oriented electrical steel sheet of the present invention having excellent adhesion of the uncoated insulating coating of forsterite (hereinafter, may be simply referred to as the "electrical steel sheet of the present invention") includes a base steel sheet, an intermediate layer, which is located in in contact with the base steel sheet and consists mainly of silicon oxide, and an insulating coating that is in contact with the intermediate layer and consists mainly of phosphate and colloidal silicon dioxide, in which the base steel sheet contains in its chemical composition, in wt%: C : 0.085% or less, Si: 0.80-7.00%, Mn: 0.05-1.00%, acid-soluble Al: 0.010-0.065%, N: 0.0040% or less, S: 0.0100 % or less, B: 0.0005-0.0080%, with the remainder of Fe and impurities, and BN having an average particle size of 50-300 nm is present on the surface layer of the intermediate layer when the total thickness of the base steel sheet and the intermediate layer oa is defined as d, the time to reach the sputter depth position d/100 from the outer surface of the intermediate layer when the emission intensity B is measured using glow discharge emission spectrometry (GDS) is defined as t(d/100), and the time to reach the sputter depth position d /10 from the outer surface of the intermediate layer is defined as t(d/10), emission intensity I _{B_t(d/100)} B at time t(d/100) and emission intensity I _{B_t(d/10)} B at time t (d/10) satisfy the following Equation (1), and the ratio of the major axis to the minor axis BN in the surface layer of the intermediate layer is 1.5 or less.

I _{B_t(d/100)} >I _{B_t(d/10)} Equation (1)

[0029]

In addition, the grain-oriented electrical steel sheet of the present invention is characterized in that the number density of BN on the surface layer of the intermediate layer is 2×10 ⁶ pcs/mm ² or more.

[0030]

First, the reason for limiting the chemical composition of the base steel sheet in the electrical steel sheet of the present invention will be described. Hereinafter, "%" means "wt.%", unless explicitly stated otherwise.

[0031]

<Component composition of base steel sheet (chemical composition)>

C: 0.085% or less

C is an element effective for controlling the primary recrystallization structure, but since it has a negative effect on magnetic characteristics, it is an element removed by decarburization annealing before finishing annealing. When the amount of C exceeds 0.085% in the final product, aging precipitates are generated and hysteresis loss increases, and therefore the amount of C is set to 0.085% or less. The C content is preferably 0.070% or less, and more preferably 0.050% or less.

[0032]

The lower limit of its content includes 0%, but when the amount of C is reduced to less than 0.0001%, the production cost greatly increases, and therefore 0.0001% is a practical lower limit for the actual steel sheet. In addition, in the grain-oriented electrical steel sheet, the amount of C is generally reduced to about 0.001% or less by decarburization annealing.

[0033]

Si: 0.80-7.00%

Si is an element that increases the electrical resistance of the electrical steel sheet and improves the loss characteristics of the steel. When the amount of Si is less than 0.80%, γ-transformation occurs during finish annealing, the crystal orientation of the steel sheet deteriorates, and therefore the amount of Si is set to 0.80% or more. The Si content is preferably 1.50% or more, and more preferably 2.50% or more.

[0034]

On the other hand, when the amount of Si exceeds 7.00%, workability decreases and cracks are generated during rolling, and therefore the amount of Si is set to 7.00% or less. The Si content is preferably 5.50% or less, and more preferably 4.50% or less.

[0035]

Mn: 0.05-1.00%

Mn is an element that prevents cracking during hot rolling and combines with S to form MnS, which functions as an inhibitor. When the amount of Mn is less than 0.05%, the addition effect is insufficiently obtained, and therefore the amount of Mn is set to 0.05% or more. The Mn content is preferably 0.07% or more, and more preferably 0.09% or more.

[0036]

On the other hand, when the amount of Mn exceeds 1.00%, the precipitation and dispersion of MnS become inhomogeneous, the desired secondary recrystallization pattern cannot be obtained, the magnetic flux density decreases, and therefore the amount of Mn is set to 1.00% or less. The Mn content is preferably 0.80% or less, and more preferably 0.60% or less.

[0037]

Acid-soluble Al: 0.010-0.065%

Acid-soluble Al is an element that binds to N to form (Al, Si)N, which functions as an inhibitor. When the amount of acid-soluble Al is less than 0.010%, the effect of addition is insufficiently obtained and the secondary recrystallization is insufficient, and therefore the amount of acid-soluble Al is set to 0.010% or more. The content of acid-soluble Al is preferably 0.015 mass% or more, and more preferably 0.020 mass% or more.

[0038]

On the other hand, when the amount of acid-soluble Al exceeds 0.065%, the precipitation and dispersion of (Al, Si)N become inhomogeneous, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, and therefore the amount of acid-soluble Al is set to 0.065% or less. The acid-soluble Al content is preferably 0.050% or less, and more preferably 0.040% or less.

[0039]

N: 0.0040% or less

N is an element that combines with Al to form AlN, which functions as an inhibitor, but when its amount in the final product is 0.0040% or more, it precipitates as AlN in the steel sheet and increases the hysteresis loss, and therefore the amount of N is set to 0.0040% or less. The lower limit of its content includes 0%, but when the amount of N is reduced to less than 0.0001%, the production cost increases significantly, and therefore 0.0001% is a practical lower limit for the actual steel sheet. In addition, in the grain-oriented electrical steel sheet, the amount of N is generally reduced to about 0.0001% or less by finishing annealing.

[0040]

S: 0.0100% or less

S combines with Mn and functions as an inhibitor, but when the amount of S exceeds 0.0100% in the final product, it is released as MnS in the steel sheet, and the hysteresis loss increases, and therefore the amount of S is set to 0.0100% or less. The lower limit of the S content includes 0%, but when the amount of S is reduced to less than 0.0001%, the production cost greatly increases, and therefore 0.0001% is a practical lower limit for an actual steel sheet. In addition, in the grain-oriented electrical steel sheet, the amount of S is generally reduced to about 0.005% or less by finishing annealing.

[0041]

B: 0.0005-0.0080%

B is an element that combines with N and is complexed with MnS to form BN, which functions as an inhibitor.

[0042]

When the amount of B is less than 0.0005%, the effect of the addition is insufficiently obtained, and therefore the amount of B is set to 0.0005% or more. The B content is preferably 0.0010% or more, and more preferably 0.0015% or more. On the other hand, when the amount of B exceeds 0.0080%, the separation and dispersion of BN become inhomogeneous, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, and therefore the amount of B is set to 0.0080% or less. The Si content is preferably 0.0060% or less, and more preferably 0.0040% or less.

[0043]

In the base steel sheet components, the remainder is Fe and impurities. The impurities include elements that are inevitably introduced from the steel raw material and/or during the steel production process and are acceptable elements as long as they do not degrade the performance of the electrical steel sheet of the present invention.

[0044]

In addition, instead of the Fe part, the base steel sheet may contain at least one element selected from the group consisting of Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, and Bi: 0.01% or less, in the range that it does not degrade the magnetic performance and can improve other characteristics.

[0045]

The chemical composition of the above-described base steel sheet can be measured by a conventional steel analytical method. For example, the chemical composition can be measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). In addition, acid-soluble Al can be measured with ICP-AES using the filtrate after heating and dissolving the sample in acid. In addition, the content of C and S can be measured by using the method of absorption of infrared light by a flame, and the content of N can be measured by using the method of determining the thermal conductivity by melting in an inert gas.

[0046]

<Intermediate Layer>

The electrical steel sheet of the present invention includes an intermediate layer mainly composed of silicon oxide in contact with the base steel sheet. In the electrical steel sheet of the present invention, the intermediate layer has the function of adhering the base steel sheet and the insulating coating.

[0047]

The silicon oxide which is the main component of the intermediate layer is preferably SiO _α (α = 1.0 to 2.0). When α=1.5-2.0, silica becomes more stable, which is more preferable. If sufficient oxidation annealing is performed to form silicon oxide on the surface of the steel sheet, SiO ₂ having α≈2.0 can be formed.

[0048]

The thickness of the intermediate layer (length in the sheet thickness direction) is not particularly limited, and may be, for example, 1 nm or more and 1 μm or less. The thickness of the intermediate layer is preferably 10 nm or more and 500 nm or less.

[0049]

The surface layer of the intermediate layer (near the boundary between the intermediate layer and the insulation coating) means the range from the outer surface of the intermediate layer to A×1/4 nm when the thickness of the intermediate layer is A nm.

[0050]

<Insulating coating>

The electrical steel sheet of the present invention is in contact with an intermediate layer and includes an insulating coating mainly composed of phosphate and colloidal silicon dioxide. The electrical steel sheet of the present invention includes an insulating coating so that a high surface tension can be applied to the electrical steel sheet of the present invention.

[0051]

<BN Presence Form>

The average particle size of BN present in the surface layer of the intermediate layer (hereinafter may be referred to simply as the surface layer of the intermediate layer): 50 nm or more and 300 nm or less.

If BN having an average particle size (major axis length) of 50 nm or more and 300 nm or less is present in the surface layer of the intermediate layer (near the boundary between the intermediate layer and the insulation coating), adhesion of the insulation coating (adhesion between the base steel sheet and the insulation coating) is improved. The reason for this is not clear, but it is believed that BN having the above average particle size is present in the oxide layer (intermediate layer) after finish annealing or in the oxide layer (intermediate layer) formed by heat treatment to form the intermediate layer, whereby it functions as anchor for the oxide layer and improve the adhesion of the insulation coating.

[0052]

Because BN is re-precipitated from solid solution, it is often spherical to reduce surface energy. Therefore, the shape BN is preferably spherical. In addition, in the present embodiment, "spherical BN" is a BN having a (major axis)/(minor axis) ratio of 1.5 or less.

[0053]

The average particle size of BN is 50 nm or more and 300 nm or less. If the average particle size of BN is less than 50 nm, when the average particle size is determined by the major axis of BN precipitation, the frequency of BN precipitation increases and steel loss increases, and thus the average particle size of BN is 50 nm or more. The average particle size of BN is preferably 80 nm or more.

[0054]

If the average particle size of BN exceeds 300 nm, the emission frequency of BN decreases, and the effect of improving the adhesion of the insulation coating cannot be sufficiently obtained, and thus the average particle size of BN is 300 nm or less. The average particle size of BN is preferably 280 nm or less.

[0055]

The average particle size is obtained by visually observing 10 fields of view measuring 4 µm in the sheet width direction × 2 µm in the sheet thickness direction using an energy dispersive X-ray spectroscope (EDS) attached to a scanning electron microscope (SEM) or a transmission electron microscope (TEM), measuring the lengths of the main axes of inclusions in the observed fields of view, identified as BN using EDS, and taking their average value as the average particle size.

[0056]

BN number density: 2×10 ⁶ pcs/mm ² or more

The number density of BN having an average particle size of 50 nm or more and 300 nm or less is preferably 2×10 ⁶ pcs/mm ² or more. If the number density of BN is less than 2×10 ⁶ pcs/mm ² , the dispersion of BN functioning as an anchor becomes insufficient, and the adhesion improvement effect of the insulation coating cannot be sufficiently obtained. For this reason, the number density of BN is preferably 2×10 ⁶ pieces/mm ² or more. The number density of BN is preferably 3×10 ⁶ pieces/mm ² or more. Since the number density of BN varies depending on the amount of B in the steel sheet, no particular upper limit is set.

[0057]

The number density BN is measured by washing the grain oriented electrical steel sheet (product) with sodium hydroxide, removing the insulating coating from the surface of the steel sheet, and observing the surface of the steel sheet (i.e., the surface layer of the intermediate layer) using a field emission scanning electron microscope (FE- SEM). The number density of the surface layer of the intermediate layer can be measured in its cross section perpendicular to the rolling direction of the steel sheet by visualizing 10 fields of view of 4 µm in the sheet width direction × 2 µm in the sheet thickness direction using an EDS attached to the FE-SEM, and counting the number of BNs identified by the EDS.

[0058]

In the distribution of B in the thickness direction of the steel sheet, in the case where the concentration (strength) of B in the surface layer of the steel sheet, including the oxide layer (intermediate layer) located on the base steel sheet of the steel sheet after finish annealing, or the oxide layer (intermediate layer ) formed by thermal oxidation is lower than the concentration (strength) of B in the base steel sheet, BN is not deposited on the surface layer of the steel sheet, or even if it is deposited in a small amount, and the adhesion of the insulation coating becomes insufficient. In addition, the surface layer of the steel sheet means a portion within the outer surface of the intermediate layer to a position separated from the boundary between the surface of the base iron and the intermediate layer by 1/100 of the thickness of the base iron. Therefore, the surface layer of the steel sheet includes an intermediate layer and a portion of the base steel sheet.

[0059]

I _{B_t(d/100)} >I _{B_t(d/10)}

In the grain-oriented electrical steel sheet according to the present embodiment, when the thickness of the sheet excluding the insulating coating is determined as d, the measurement is performed using glow discharge emission spectrometry (GDS), the time to reach the spray depth position d/100 from the outer surface layer steel sheet (outer surface of the intermediate layer) excluding the insulating coating is defined as t(d/100), and the time to reach the spray depth position d/10 from the outer surface of the intermediate layer is defined as t(d/10), emission intensity I _B B satisfies the following Equation (1). The position d/100 from the outer surface of the intermediate layer is located on the surface layer of the steel sheet, and the position d/10 from the outer surface of the intermediate layer is located on the side of the base steel sheet relative to the surface layer of the steel sheet. Therefore, if the intensity I _B of the emission B satisfies the following Equation (1), a sufficient amount of BN is deposited on the surface layer of the steel sheet, and thus the steel loss is not degraded, and the adhesion of the insulation coating is further improved.

[0060]

I _{B_t(d/100)} >I _{B_t(d/10)} Equation (1)

where I _{B_t(d/100)} : emission intensity B at time t(d/100)

I _{B_t(d/10)} : emission intensity B at time t(d/10)

[0061]

In addition, as described above, in order to precisely control the particle size, emission rate, and presence position of BN, the rate of temperature decrease after finish annealing must be appropriately controlled.

[0062]

<Identification of Layers Constituting Grain-Oriented Electrical Steel Sheet>

In order to identify each layer in the cross-sectional structure of the present electrical steel sheet, a linear analysis is performed in the thickness direction of the sheet using an EDS connected to SEM or TEM, and a quantitative analysis of the chemical composition of each layer is performed. The elements to be quantified are the six elements Fe, P, Si, O, Mg and Al.

[0063]

The layered region present at the deepest position in the sheet thickness direction in which the Fe content is 80 at.% or more and the O content is less than 30 at.%, excluding measurement noise, is defined as the base steel sheet.

[0064]

A region not including the base steel sheet as defined above, having an Fe content of less than 80 at.%, a P content of 5 at.% or more, and an O content of 30 at.% or more, excluding measurement noise, is defined as an insulating coating.

[0065]

The area excluding the silicon steel sheet and the insulation coating identified above is defined as the intermediate layer. In the intermediate layer, preferably, the average content of Fe is less than 80 at.%, the average content of P is less than 5 at.%, the average content of Si is 20 at.% or more, and the average content of O is 30 at.% or more. Further, in the present embodiment, since the intermediate layer is not a forsterite coating but an oxide layer containing mainly silicon oxide, the intermediate layer may have an average Mg content of less than 20 at.%.

[0066]

Next, the production method of the electrical steel sheet of the present invention will be described.

[0067]

<Silicon Steel Slab Components>

The silicon steel slab, which is the material of the electrical steel sheet of the present invention, contains in its chemical composition, in mass%: C: 0.085% or less, Si: 0.80-7.00%, Mn: 0.05- 1.00%, acid-soluble Al: 0.010-0.065%, N: 0.0040-0.0120%, S: 0.0100% or less, and B: 0.0005-0.0080%.

[0068]

C: 0.085% or less

C is an element effective for controlling the primary recrystallization structure, but since it has a negative effect on magnetic characteristics, it is an element removed by decarburization annealing before finishing annealing. If the C amount exceeds 0.085%, the decarburization annealing time becomes longer and the productivity decreases, and therefore the C amount is set to 0.085% or less. The C content is preferably 0.070% or less, and more preferably 0.050% or less.

[0069]

The lower limit of its content includes 0%, but when the amount of C is reduced to less than 0.0001%, the production cost greatly increases, and therefore 0.0001% is a practical lower limit for an actual steel sheet. In addition, in the grain-oriented electrical steel sheet, the amount of C is generally reduced to about 0.001% or less by decarburization annealing.

[0070]

Si: 0.80-7.00%

Si is an element that increases the electrical resistance of the steel sheet and improves the loss characteristics of the steel. When the amount of Si is less than 0.80%, γ-transformation occurs during finish annealing, the crystal orientation of the steel sheet deteriorates, and therefore the amount of Si is set to 0.80% or more. The Si content is preferably 1.50% or more, and more preferably 2.50% or more.

[0071]

On the other hand, when the amount of Si exceeds 7.00%, workability decreases and cracks are generated during rolling, and therefore the amount of Si is set to 7.00% or less. The Si content is preferably 5.50% or less, and more preferably 4.50% or less.

[0072]

Mn: 0.05-1.00%

Mn is an element that prevents cracking during hot rolling and combines with S and/or Se to form MnS, which functions as an inhibitor. When the amount of Mn is less than 0.05%, the addition effect is insufficiently obtained, and therefore the amount of Mn is set to 0.05% or more. The Mn content is preferably 0.07% or more, and more preferably 0.09% or more.

[0073]

On the other hand, when the amount of Mn exceeds 1.00%, the precipitation and dispersion of MnS become inhomogeneous, the desired secondary recrystallization pattern cannot be obtained, the magnetic flux density decreases, and therefore the amount of Mn is set to 1.00% or less. The Mn content is preferably 0.80% or less, and more preferably 0.60% or less.

[0074]

Acid-soluble Al: 0.010-0.065%

Acid-soluble Al is an element that binds to N to form (Al, Si)N, which functions as an inhibitor. When the amount of acid-soluble Al is less than 0.010%, the effect of addition is insufficiently obtained and the secondary recrystallization is insufficient, and therefore the amount of acid-soluble Al is set to 0.010% or more. The acid-soluble Al content is preferably 0.015 mass% or more, and more preferably 0.020 mass% or more.

[0075]

On the other hand, when the amount of acid-soluble Al exceeds 0.065%, the precipitation and dispersion of (Al, Si)N become inhomogeneous, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, and therefore the amount of acid-soluble Al is set to 0.065% or less. The acid-soluble Al content is preferably 0.050% or less, and more preferably 0.040% or less.

[0076]

N: 0.0040-0.0120%

N is an element that binds with Al to form AlN, which functions as an inhibitor, but on the other hand, it is also an element that forms bubbles (voids) in the steel sheet during cold rolling. When the amount of N is less than 0.004%, the formation of AlN is insufficient, and therefore the amount of N is set to 0.004% or more. The N content is preferably 0.006% or more, and more preferably 0.007% or more.

[0077]

On the other hand, when the N amount exceeds 0.012%, bubbles (voids) may be generated in the steel sheet during cold rolling, and therefore the N amount is set to 0.012% or less. The N content is preferably 0.010% or less, and more preferably 0.009% or less.

[0078]

S: 0.0100% or less

S is an element that combines with Mn to form MnS, which functions as an inhibitor.

[0079]

If the S content is 0.0100% or more, the precipitation dispersion of MnS becomes non-uniform after purification, and the desired secondary recrystallization pattern cannot be obtained, and thus the magnetic flux density decreases, MnS remains after purification, and hysteresis loss increases.

No particular lower limit is provided, but it is preferably 0.0030% or more. More preferably, this amount is 0.0070% or more.

[0080]

B: 0.0005-0.0080%

B is an element that combines with N and is complexed with MnS to form BN, which functions as an inhibitor.

[0081]

When the amount of B is less than 0.0005%, the effect of adding is insufficiently obtained, and therefore the amount of B is set to 0.0005% or more. The B content is preferably 0.0010% or more, and more preferably 0.0015% or more. On the other hand, when the amount of B exceeds 0.0080%, the separation and dispersion of BN become inhomogeneous, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, and therefore the amount of B is set to 0.0080% or less. The B content is preferably 0.0060% or less, and more preferably 0.0040% or less.

[0082]

In the silicon steel slab, the remainder of the chemical composition is Fe and impurities. The impurities include elements that are inevitably introduced from the steel raw material and/or during the steel production process and are acceptable elements as long as they do not degrade the performance of the electrical steel sheet of the present invention.

[0083]

In addition, instead of the Fe part, the silicon steel slab may contain at least one element selected from the group consisting of Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less , Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, and Bi: 0.01% or less, in the range in which the magnetic characteristics of the electrical steel sheet are really the invention is not degraded, and other characteristics can be improved.

[0084]

<Silicon Steel Slab Production>

Silicon steel slab is obtained by continuously casting or casting ingots and rolling slabs from molten steel having a desired composition, which has been melted in a converter or an electric furnace and subjected to vacuum degassing if necessary. The silicon steel slab is usually a slab having a thickness of 150-350 mm, preferably 220-280 mm, but may be a thin slab with a thickness of 30-70 mm. In the case of a thin slab, there is an advantage that no intermediate thickness is required during the production of the hot rolled sheet.

[0085]

<Heating Temperature of Silicon Steel Slab>

The silicon steel slab is preferably heated to 1250° C. or lower and subjected to hot rolling. If the heating temperature exceeds 1250°C, the amount of molten dross increases, and MnS and/or MnSe are completely solid-dissolved and finely precipitated in subsequent processes, and thus it is necessary to set the decarburization annealing temperature to 900°C or higher to obtain the desired primary recrystallization particle size. For this reason, the heating temperature is preferably 1250°C or lower. The heating temperature is more preferably 1200°C or lower.

[0086]

The lower limit of the heating temperature is not particularly limited, but the heating temperature is preferably 1100° C. or higher from the viewpoint of ensuring the workability of the silicon steel slab.

[0087]

<Hot rolling and hot annealing>

The silicon steel slab heated to 1250°C or less is hot rolled to obtain a hot rolled sheet. In hot strip annealing, the hot rolled sheet is heated at 1000-1150°C (first stage temperature) to recrystallize, and then heated to 850-1100°C (second stage temperature), lower than the first stage temperature, and annealed to homogenize the inhomogeneous structure formed during hot rolling. The hot annealing is preferably performed one or more times in order to homogenize the hot rolling history of the hot rolled sheet before it is subjected to final cold rolling.

[0088]

During hot annealing, the temperature of the first stage strongly affects the release of the inhibitor in subsequent processes. If the temperature of the first stage exceeds 1150°C, the inhibitor is finely precipitated in subsequent processes, and the temperature of decarburization annealing to obtain the desired primary recrystallization particle size should be 900°C or higher. For this reason, the temperature of the first stage is preferably 1150° C. or lower. The temperature of the first stage is more preferably 1120°C or lower.

[0089]

On the other hand, if the temperature of the first stage is less than 1000°C, recrystallization is insufficient and homogenization of the structure of the hot-rolled sheet is not achieved, and thus the temperature of the first stage is preferably 1000°C or higher. The temperature of the first stage is more preferably 1030°C or higher.

[0090]

If the second stage temperature exceeds 1100°C, the inhibitor is thinly released in subsequent processes, as in the case of the first stage temperature, and thus the second stage temperature is preferably 1100°C or lower. The temperature of the second stage is more preferably 1070°C or lower. On the other hand, if the temperature of the second stage is less than 850°C, the γ phase is not formed and homogenization of the structure of the hot-rolled sheet is not achieved, and thus the temperature of the second stage is preferably 850°C or higher. The temperature of the second stage is more preferably 880°C or higher.

[0091]

<Cold rolling>

The steel sheet that has been hot annealed is cold rolled one or more times with intermediate annealing in between to obtain a steel sheet with a final thickness. Cold rolling may be carried out at room temperature (10-30°C), or the steel sheet may be heated to above room temperature, for example up to about 200°C for warm rolling.

[0092]

<Decarburizing Annealing>

In order to remove C from the steel sheet and control the primary recrystallization grain size to a desired size in the steel sheet having a final thickness, decarburization annealing is performed in a humid atmosphere with an oxidation state of less than 0.15. For example, it is preferable to perform decarburization annealing at a temperature of 770-950°C for such a time until the primary recrystallization particle size becomes 15 μm or more. Here, the oxidation state is obtained by dividing the partial pressure (P _H2O ) of water vapor in atmospheric gas by the partial pressure (P _H2 ) of hydrogen, i.e. P _H2O /P _H2 .

[0093]

If the decarburization annealing temperature is less than 770°C, the desired crystal grain size cannot be obtained, and thus the decarburization annealing temperature is preferably 770°C or higher. The decarburization annealing temperature is more preferably 800° C. or higher. On the other hand, if the decarburization annealing temperature exceeds 950°C, the crystal grain size is larger than desired, and thus the decarburization annealing temperature is preferably 950°C or lower. The decarburization annealing temperature is more preferably 920° C. or lower.

[0094]

<Nitriding Treatment>

Before finishing annealing, the decarburized annealed steel sheet is subjected to a nitriding treatment so that the N content of the steel sheet is 40-1000 ppm. The nitriding treatment method is not particularly limited, and, for example, the decarburized annealed steel sheet may be treated with ammonia gas. If the N content of the steel sheet after the nitriding treatment is less than 40 ppm, AlN is not sufficiently released and does not function as an inhibitor, and thus the N content of the steel sheet after the nitriding treatment is preferably 40 ppm or more. The N content in the steel sheet after the nitriding treatment is more preferably 80 ppm or more.

[0095]

On the other hand, if the N content of the steel sheet exceeds 1000 ppm, AlN is excessively present even after completion of the secondary recrystallization in the subsequent finish annealing, and steel loss increases, and thus the N content is preferably 1000 ppm or less. The N content in the steel sheet after the nitriding treatment is more preferably 970 ppm or less.

[0096]

<Applying the annealing separator>

Then, an annealing separator containing magnesium oxide as the main component is applied to the nitrided steel sheet and finished annealed. A forsterite glass film is formed on the surface of the steel sheet during finish annealing, and this coating is removed by means such as pickling and grinding. After removing the glass film, the surface of the steel sheet is preferably smoothed by chemical or electrolytic polishing.

[0097]

Alternatively, an annealing separator containing alumina as the main component can be used instead of an annealing separator containing magnesium oxide, and the nitrided steel sheet is coated with this separator, dried, rolled up after drying, and subjected to finishing annealing (secondary recrystallization and/or cleaning annealing). ). By finishing annealing, it is possible to prevent the formation of a coating of an inorganic mineral substance such as forsterite to produce a grain-oriented electrical steel sheet. After production, the surface of the steel sheet is preferably smoothed by chemical or electrolytic polishing.

[0098]

<Finish annealing>

[Secondary recrystallization annealing]

In the secondary recrystallization annealing of the finish annealing, crystal grains in the preferred {110}<001> orientation are grown due to the function of the BN inhibitor. Secondary recrystallization annealing is a process of annealing a steel sheet coated with an annealing cage at a heating rate of 15°C/hour or less in a temperature range of 1000-1100°C during heating up to a cleaning annealing temperature. The heating rate in the temperature range of 1000 to 1100°C is more preferably 10°C/hour or less. In the secondary recrystallization annealing, instead of controlling the heating rate, the steel sheet coated with the annealing cage can be kept in the temperature range of 1000-1100° C. for 10 hours or more.

[0099]

[Purifying annealing]

The steel sheet which has been subjected to the secondary recrystallization annealing may be subjected to a purification annealing after the secondary recrystallization annealing. When the steel sheet is subjected to cleaning annealing after completion of secondary recrystallization, the precipitates used as an inhibitor are eliminated and the hysteresis loss in the final magnetic characteristics is reduced. The cleaning annealing is preferably carried out by holding at 1200°C for 10-30 hours, for example, in a hydrogen atmosphere.

[0100]

In order to provide an average particle size of BN in the range of 50-300 nm, the rate of temperature decrease in the temperature range of 1200-1000°C should be less than 50°C/hour. In addition, the rate of temperature decrease in the temperature range of 1000-600°C is less than 30°C/hour.

[0101]

The reason for setting such a rate of temperature decrease is as follows.

BN becomes B solid solution and N solid solution in the high temperature range, and N, which cannot be solid dissolved, is released into the atmosphere at the time of temperature decrease, but during temperature decrease, B, which cannot be solid solution, is not released into the atmosphere, but is released as compounds B, for example, BN, Fe ₂ B and Fe ₃ B, on the surface layer of the steel sheet, including the intermediate layer consisting mainly of silicon oxide, or inside the steel sheet. If the N solid solution is not sufficiently present inside the steel sheet, BN is not released, but Fe ₂ B or Fe ₃ B are released.

[0102]

During the temperature decrease from the high temperature range, if the temperature decrease rate is suitable, the solid solution N is discharged outside the system, Fe ₂ B or Fe ₃ B is precipitated in the steel sheet, and the precipitated Fe ₂ B or Fe ₃ B grows Ostwald and becomes coarse . Solid dissolved B in the surface layer of the steel sheet combines with N from the atmosphere and is released as thin BN in the oxide layer present on the surface layer or outer layer of the steel sheet.

[0103]

If the rate of temperature decrease is high, the N solid solution is not released outside the system, and BN is finely precipitated in the steel sheet, or Fe ₂ B or Fe ₃ B is finely precipitated without Ostwald growth. BN subtly exuding in the steel sheet increases the hysteresis loss and causes an increase in steel loss in the final product.

[0104]

The lower limit of the temperature lowering rate is not particularly limited, but if the temperature lowering rate is less than 10°C/hour, the productivity is strongly affected, and thus the temperature lowering rate is preferably 10°C/hour or more. Therefore, the temperature decrease rate in the temperature range of 1200-1000°C is preferably 10-50°C/hour, and the temperature decrease rate in the temperature range of 1000-600°C is preferably 10-30°C/hour.

[0105]

<Heat treatment to form an intermediate layer>

A grain oriented electrical steel sheet with an inorganic mineral material such as forsterite (forsterite film) removed or a grain oriented electrical steel sheet in which the formation of a coating of an inorganic mineral material such as forsterite is inhibited is annealed to form on the surface of the base steel sheet of the intermediate layer, consisting mainly of silicon oxide.

[0106]

The annealing atmosphere is preferably a reducing atmosphere so that the inside of the steel sheet is not oxidized, and is particularly preferably a nitrogen atmosphere mixed with hydrogen. For example, an atmosphere in which the hydrogen:nitrogen ratio is 75:25% by volume and the dew point is -20 to 0°C is preferred.

[0107]

The heat treatment process for forming the intermediate layer can be omitted for the grain oriented electrical steel sheet from which the coating of inorganic mineral material such as forsterite has been removed, or for the grain oriented electrical steel sheet in which formation of the coating of inorganic mineral is inhibited. a mineral substance such as forsterite.

[0108]

<Formation of the insulating coating>

After applying an aqueous film-forming solution (insulation coating solution) mainly composed of phosphate and colloidal silica to an intermediate layer mainly composed of silicon oxide, the insulation coating solution is subjected to heat treatment to form an insulation coating.

As the phosphate, for example, phosphate of Ca, Al, Sr, etc. is preferable, and among them, aluminum phosphate is more preferable. The type of colloidal silica is not particularly limited, and its particle size (average particle size) can be suitably selected, but if it exceeds 200 nm, the particles can be classified in the processing agent, and thus the particle size (number average particle size) of the colloidal dioxide silicon is preferably 200 nm or less. The particle size of the colloidal silica is more preferably 170 nm.

[0109]

If the particle size of the colloidal silica is less than 100 nm, there is no difficulty in dispersion, but the production cost increases, and thus a size of 100 nm or more is economically preferable. The particle size of the colloidal silica is more preferably 150 nm or more.

[0110]

The method for applying the solution for forming an insulating coating is not particularly limited, and, for example, a wet coating method using a roller coater and the like can be used.

[0111]

The baking atmosphere can be formed, for example, by baking in air at 800-900° C. for 10-60 seconds, but the baking atmosphere is not particularly limited.

[0112]

<Magnetic Domain Management>

Magnetic domain control is performed on a grain-oriented electrical steel sheet on which an insulating coating is formed in order to reduce steel losses. The magnetic domain driving method is not limited to a particular method, and it may be performed using, for example, laser irradiation, electron beam irradiation, etching, or a groove forming method using gears (knurling). As a result, a grain-oriented electrical steel sheet having a lower steel loss can be obtained. The magnetic domain control processing may be performed on the steel sheet after cold rolling.

[Examples]

[0113]

<Example 1>

Steel slabs A1 to A15 having compositions shown in Table 1-1 were heated to 1150° C. and subjected to hot rolling to obtain hot-rolled steel sheets with a thickness of 2.6 mm, these hot-rolled steel sheets were subjected to hot annealing at temperature of 1100°C and then 900°C, and then subjected to cold rolling one or more times with intermediate annealing at 30°C in between, to obtain cold rolled steel sheets having a final sheet thickness of 0.22 mm.

The steel slabs a1 to a13 having the compositions shown in Table 1-1 were heated to 1150° C. and subjected to hot rolling to obtain hot-rolled steel sheets with a thickness of 2.6 mm, these hot-rolled steel sheets were subjected to hot annealing at temperature of 1100°C and then 900°C, and then subjected to cold rolling one or more times with intermediate annealing at 30°C in between, to obtain cold rolled steel sheets having a final sheet thickness of 0.22 mm.

[0114]

[Table 1-1]

Slab No. Chemical composition of steel slab (wt.%) (with balance of Fe and impurities) C Si Mn Al N S B A1 0.085 3.45 0.10 0.028 0.0040 0.008 0.0015 A2 0.031 1.21 0.10 0.029 0.0100 0.009 0.0020 A3 0.033 6.52 0.10 0.029 0.0100 0.007 0.0018 A4 0.041 3.45 0.08 0.028 0.0070 0.005 0.0019 A5 0.044 3.33 0.80 0.029 0.0060 0.004 0.0021 A6 0.052 4.52 0.12 0.020 0.0050 0.003 0.0016 A7 0.055 3.12 0.09 0.055 0.0017 0.001 0.0017 A8 0.061 2.81 0.09 0.030 0.0120 0.009 0.0018 A9 0.062 3.12 0.11 0.030 0.0040 0.001 0.0019 A10 0.071 2.92 0.13 0.030 0.0050 0.001 0.0021 A11 0.078 3.45 0.12 0.028 0.0110 0.010 0.0022 A12 0.055 3.44 0.10 0.027 0.0090 0.007 0.0006 A13 0.085 4.21 0.10 0.027 0.0080 0.006 0.0078 A14 0.082 3.45 0.11 0.031 0.0100 0.008 0.0025 A15 0.045 3.35 0.12 0.030 0.0060 0.009 0.0017 a1 0.092 3.45 0.12 0.029 0.0019 0.007 0.0002 a2 0.076 0.50 0.08 0.028 0.0028 0.007 0.0004 a3 0.065 8.00 0.09 0.028 0.0031 0.007 0.0004 a4 0.045 3.45 0.04 0.029 0.0021 0.009 0.0002 a5 0.061 3.35 1.21 0.029 0.0035 0.009 0.0006 a6 0.032 3.25 0.08 0.005 0.0038 0.006 0.0007 a7 0.012 3.12 0.07 0.082 0.0032 0.006 0.0009 a8 0.072 3.23 0.08 0.030 0.0051 0.009 0.0061 a9 0.043 3.45 0.10 0.027 0.0152 0.009 0.0003 a10 0.033 3.55 0.09 0.026 0.0012 0.012 0.0055 a11 0.039 3.15 0.08 0.026 0.0022 0.030 0.0002 a12 0.058 3.28 0.10 0.027 0.0019 0.007 0.0003 a13 0.021 3.19 0.13 0.028 0.0036 0.007 0.0152

[0115]

Grain-oriented electrical steel sheets Nos. B1 to B15 shown in Table 2 were produced as follows. Cold-rolled steel sheets having a final sheet thickness of 0.22 mm were subjected to decarburization annealing in which a uniform heat treatment is performed at 860°C in a humid atmosphere with an oxidation state of 0.10, and then a nitriding treatment (annealing that increases the amount of nitrogen in steel sheets) with ammonia gas. Then, an annealing separator containing alumina as a main component was applied to the nitrided steel sheets, and finish annealing was performed at 1200° C. for 20 hours under a hydrogen gas atmosphere. When the temperature was raised during finishing annealing, the heating rate in the range of 1000–1100°C was set to 5°C/hour. Further, after holding at 1200°C for 20 hours, the temperature decrease rate in the range of 1200-1000°C was set to 45°C/hour, and the temperature decrease rate in the range of 1000-600°C was set to 25°C/hour. After finishing annealing, the excess alumina was removed from the steel sheets, and a heat treatment to form an intermediate layer was performed on the steel sheets with the excess alumina removed in a 75:25 vol% hydrogen:nitrogen atmosphere and a dew point of -5°C. An aqueous film-forming solution comprising mainly colloidal silica and phosphate was applied to steel sheets after heat treatment to form an intermediate layer, and insulating coatings were formed by baking at a temperature of −5°C for 30 seconds in a hydrogen:nitrogen atmosphere with a ratio of 75:25 vol .% to get products. The number average particle size of colloidal silicon dioxide in an aqueous film-forming solution was 100 nm.

Table 1-2 shows the chemical compositions of the main steel sheets in the products. The compositions of the base steel sheets were measured using ICP-AES. Acid-soluble Al was measured by ICP-AES using the filtrate after heating and dissolving the sample in acid. In addition, the content of C and S was measured using an infrared ray flame absorption method, and the N content was measured using an inert gas melting thermal conductivity method.

[0116]

Grain-oriented electrical steel sheets Nos. b1 to b13 shown in Table 1-2 were produced as follows. Cold-rolled steel sheets having a final sheet thickness of 0.22 mm were subjected to decarburization annealing in which a uniform heat treatment is performed at 860°C in a humid atmosphere with an oxidation state of 0.10, and then a nitriding treatment (annealing that increases the amount of nitrogen in steel sheets) with ammonia gas. Then, an annealing separator containing alumina as a main component was applied to the nitrided steel sheets, and finish annealing was performed at 1200° C. for 20 hours under a hydrogen gas atmosphere. When the temperature was raised during finishing annealing, the heating rate in the range of 1000–1100°C was set to 5°C/hour. Further, after holding at 1200°C for 20 hours, the temperature decrease rate in the range of 1200-1000°C was set to 100°C/hour, and the temperature decrease rate in the range of 1000-600°C was set to 100°C/hour. After finishing annealing, the excess alumina was removed from the steel sheets, and a heat treatment to form an intermediate layer was performed on the steel sheets with the excess alumina removed in a hydrogen:nitrogen atmosphere with a ratio of 75:25 vol.% and a dew point of -5°C. An aqueous film-forming solution comprising mainly colloidal silica and phosphate was applied to steel sheets after heat treatment to form an intermediate layer, and insulating coatings were formed by baking at a temperature of −5°C for 30 seconds in a hydrogen:nitrogen atmosphere with a ratio of 75:25 vol .% to get products. The number average particle size of colloidal silicon dioxide in an aqueous film-forming solution was 100 nm.

Table 1-2 shows the chemical compositions of the main steel sheets in the products. The compositions of the base steel sheets were measured using the same method as for steel Nos. B1 to B15.

[0117]

Grain-oriented electrical steel sheet No. b14 shown in Table 1-2 was produced as follows. A cold-rolled steel sheet having a final sheet thickness of 0.22 mm was subjected to decarburization annealing in which a uniform heat treatment is performed at 850°C in a humid atmosphere with an oxidation state of 0.10, and then a nitriding treatment (annealing that increases the amount of nitrogen in steel sheet) with ammonia gas. Then, an annealing separator containing alumina as a main component was applied to the nitrided steel sheet, and finish annealing was performed at 1200° C. for 20 hours under a hydrogen gas atmosphere. When the temperature was raised during finishing annealing, the heating rate in the range of 1000–1100°C was set to 5°C/hour. Further, after holding at 1200°C for 20 hours, the temperature decrease rate in the range of 1200-1000°C was set to 200°C/hour, and the temperature decrease rate in the range of 1000-600°C was set to 100°C/hour. After finishing annealing, the excess alumina was removed from the steel sheet, and a heat treatment to form an intermediate layer was performed on the steel sheet with the excess alumina removed in a hydrogen:nitrogen atmosphere of 75:25 vol.% and a dew point of -5°C. An aqueous film-forming solution mainly comprising colloidal silica and phosphate was applied to a steel sheet after heat treatment to form an intermediate layer, and an insulating coating was formed by baking at a temperature of 800°C for 30 seconds in a hydrogen:nitrogen atmosphere with a ratio of 75:25 vol. % to get the product. The number average particle size of colloidal silicon dioxide in an aqueous film-forming solution was 100 nm.

[0118]

Grain-oriented electrical steel sheet No. b15 shown in Table 1-2 was produced as follows. A cold-rolled steel sheet having a final sheet thickness of 0.22 mm was subjected to decarburization annealing in which a uniform heat treatment is performed at 860°C in a humid atmosphere with an oxidation state of 0.10, and then a nitriding treatment (annealing that increases the amount of nitrogen in steel sheet) with ammonia gas. Then, an annealing separator containing alumina as a main component was applied to the nitrided steel sheet, and finish annealing was performed at 1200° C. for 20 hours under a hydrogen gas atmosphere. When the temperature was raised during finishing annealing, the heating rate in the range of 1000–1100°C was set to 5°C/hour. Further, after holding at 1200°C for 20 hours, the temperature-lowering rate in the range of 1200-1000°C was set to 30°C/hour, the temperature was held at 1000°C for 1 hour or more, and the temperature-lowering rate in the range of 1000 -600°C was set to 50°C/hour. After finish annealing, the excess alumina was removed from the steel sheet, and heat treatment to form the intermediate layer was performed on the steel sheet with the excess alumina removed in a hydrogen:nitrogen atmosphere with a ratio of 75:25 vol.% and dew point
-5°C. An aqueous film-forming solution mainly comprising colloidal silica and phosphate was applied to a steel sheet after heat treatment to form an intermediate layer, and an insulating coating was formed by baking at a temperature of 800°C for 30 seconds in a hydrogen:nitrogen atmosphere with a ratio of 75:25 vol. % to get the product. The number average particle size of colloidal silicon dioxide in an aqueous film-forming solution was 100 nm.

[0119]

[Table 1-2]

Steel No. Slab No. Chemical composition (wt.%, with the remainder of Fe and impurities) C Si Mn Al N S B Examples B1 A1 0.080 3.45 0.10 0.028 0.0021 0.0021 0.0015 B2 A2 0.031 1.21 0.10 0.029 0.0031 0.0032 0.0020 B3 A3 0.001 6.52 0.10 0.029 0.0012 0.0012 0.0018 B4 A4 0.003 3.45 0.08 0.028 0.0010 0.0007 0.0019 B5 A5 0.005 3.33 0.80 0.029 0.0021 0.0005 0.0021 B6 A6 0.001 4.52 0.12 0.020 0.0019 0.0007 0.0016 B7 A7 0.002 3.12 0.09 0.055 0.0017 0.0008 0.0017 B8 A8 0.003 2.81 0.09 0.030 0.0006 0.0009 0.0018 B9 A9 0.007 3.12 0.11 0.030 0.0039 0.0051 0.0019 B10 A10 0.006 2.92 0.13 0.030 0.0022 0.0004 0.0021 B11 A11 0.012 3.45 0.12 0.028 0.0018 0.0092 0.0022 B12 A12 0.011 3.44 0.10 0.027 0.0019 0.0007 0.0006 B13 A13 0.002 4.21 0.10 0.027 0.0010 0.0081 0.0078 B14 A14 0.003 3.45 0.11 0.031 0.0009 0.0005 0.0025 B15 A15 0.001 3.35 0.12 0.030 0.0008 0.0005 0.0017 Comparative examples b1 a1 0.090 3.45 0.12 0.029 0.0008 0.0012 0.0002 b2 a2 0.008 0.50 0.08 0.028 0.0010 0.0014 0.0004 b3 a3 0.001 8.00 0.09 0.028 0.0009 0.0018 0.0004 b4 a4 0.002 3.45 0.04 0.029 0.0011 0.0022 0.0002 b5 a5 0.001 3.35 1.21 0.029 0.0019 0.0009 0.0006 b6 a6 0.012 3.25 0.08 0.005 0.0018 0.0010 0.0007 b7 a7 0.011 3.12 0.07 0.082 0.0018 0.0022 0.0009 b8 a8 0.001 3.23 0.08 0.030 0.0018 0.0018 0.0061 b9 a9 0.002 3.45 0.10 0.027 0.0018 0.0011 0.0003 b10 a10 0.001 3.55 0.09 0.026 0.0009 0.0025 0.0055 b11 a11 0.020 3.15 0.08 0.026 0.0018 0.0021 0.0002 b12 a12 0.010 3.28 0.10 0.027 0.0007 0.0012 0.0003 b13 (a13) 0.002 3.19 0.13 0.028 0.0018 0.0011 0.0152 b14 a14 0.002 3.28 0.12 0.028 0.0019 0.0012 0.0029 b15 a15 0.001 3.32 0.11 0.019 0.0009 0.0018 0.0112

[0120]

<Magnetic Domain Management>

Magnetic domain control was performed on the product on which the insulating coating was formed using a mechanical method, a laser, or an electron beam. For some products, grooves have been applied to cold rolled sheets by etching or laser irradiation to manipulate the magnetic domains.

[0121]

<Highlights>

With regard to precipitation, Compound B observed up to 5 µm from the outer surface of the intermediate layer perpendicular to the rolling direction of the steel sheet was analyzed using SEM-EDS in order to identify particle size and composition of BN. In addition, in the "presence or absence of BN highlights" column in Table 2, the "○" sign indicates that one or more spherical BNs (BNs having a major axis to minor axis ratio of 1.5 or less) were present in the observed field of view. , and the "x" sign means that there were no spherical BNs in the observed field of view.

[0122]

<Emission intensity B>

The intensity I _B of the B emission was measured using glow discharge emission spectrometry (GDS). The value of I _{B_t(d/100)} , which is the emission intensity of B at time t(d/100), and the value of I _{B_t(d/10)} , which is the emission intensity of B at time t(d/10), were obtained when the time to reach the spray depth position d/100 from the outer surface layer of the steel sheet, excluding the insulating coating, was determined as t(d/100), and the time to reach the spray depth position d/10 from the outer surface of the steel sheet, excluding the insulating coating, was defined as t(d/10), and the value of I _{B_t(d/100)} /I _{B_t(d/10)} , which is their ratio, was recorded in a table.

[0123]

<Coating Adhesion>

The adhesion of the coating was evaluated by the peel area fraction for each diameter by forming an insulating coating on the steel sheet after finish annealing and then winding the steel sheet around mandrels of various diameters (20 mm, 10 mm and 5 mm). The peel area ratio is a ratio obtained by dividing the area actually peeled off by the area of the treated part (the contact area of the steel sheet with the mandrel, which corresponds to the product of the width of the sample sheet×the diameter of the mandrel×π). If peeling does not develop and the peeling area ratio is small even when the insulating coating peels off when strongly bent, it can be considered that the deterioration of the transformer performance is small.

[0124]

The adhesion of the coating was evaluated on a seven-point scale from A to G: when the peel area ratio was 0%, the adhesion was evaluated as A, greater than 0% and less than 20% as B, 20% or more and less than 40% as C, 40% or more and less than 60% as D, 60% or more and less than 80% as E, 80% or more and less than 100% as F, and when the peel area ratio was 100%, the adhesion was evaluated as G. Coating adhesion with a rating of B or higher was considered good.

[0125]

<Magnetic characteristics>

<Magnetic flux density B8>

Magnetic flux density B8 (magnetic flux density when magnetized by a field of 800 A/m) was measured on a grain-oriented electrical steel sheet obtained using the above-mentioned production method using a single-sheet magnetic tester (SST).

[0126]

<Steel loss W17/50>

A test sample (for example, 100×500 mm in size) was prepared from a grain-oriented electrical steel sheet before and after magnetic domain control, and the steel loss W17/50 (W/kg), which is the energy loss per unit mass, was measured. when excited with a magnetic flux density of 1.7 T and a frequency of 50 Hz.

[0127]

Table 2 shows the BN emission state of the grain-oriented electrical steel sheet (product), GDS results, coating adhesion evaluation, and magnetic characteristics. In Examples C1 to C15 of the present invention, grain-oriented electrical steel sheets having excellent coating adhesion and excellent magnetic characteristics were obtained. In Comparative Examples c1 to c15 not in accordance with the present invention, either the adhesion of the coating or the magnetic characteristics were unsatisfactory.

[0128]

[Table 2]

No. Steel No. Presence or absence of BN secretions Average particle size BN (nm) I _{B_t(d/100)}
/I _{B_t(d/10)} Coating adhesion Magnetic characteristics Other Fraction of peel area at φ 20 mm Fraction of peel area at φ 10 mm Fraction of peel area at φ 5 mm Magnetic flux density B8 (Tl) Steel loss W _17/50 (W/kg) Steel loss W _17/50 with magnetic domain control (W/kg) Examples C1 B1 ○ 120 1.3 A A B 1.946 0.87 0.62 C2 B2 ○ fifty 1.1 A B B 1.947 0.86 0.64 C3 B3 ○ 80 1.6 A A B 1.953 0.87 0.66 C4 B4 ○ 150 2.0 A A B 1.952 0.88 0.64 C5 B5 ○ 300 4.5 A B B 1.944 0.85 0.63 C6 B6 ○ 280 2.8 A A B 1.948 0.89 0.62 C7 B7 ○ 200 1.9 A B B 1.956 0.87 0.63 C8 B8 ○ 150 2.3 A A B 1.951 0.86 0.60 C9 B9 ○ 130 1.9 A B B 1.951 0.87 0.61 C10 B10 ○ 70 2.2 A B B 1.947 0.87 0.62 C11 B11 ○ 90 2.3 A A B 1.945 0.85 0.64 C12 B12 ○ 110 4.3 A A B 1.949 0.89 0.65 C13 B13 ○ 250 5.5 A B B 1.956 0.86 0.64 C14 B14 ○ 200 3.5 A A B 1.944 0.84 0.64 C15 B15 ○ 100 1.5 A A B 1.954 0.85 0.60 Comparative examples c1 b1 x - 0.8 E E G 1.945 0.95 0.69 No allocation of BN c2 b2 x - 0.7 G G G 1.944 0.97 0.71 No allocation of BN c3 b3 x - 0.9 E F G 1.945 0.99 0.72 No allocation of BN c4 b4 x - 0.5 G G G 1.948 0.97 0.71 No allocation of BN c5 b5 x - 0.9 D G G 1.945 0.99 0.72 No allocation of BN c6 b6 x - 0.9 D G G 1.947 0.96 0.70 No allocation of BN c7 b7 x - 0.9 C D G 1.946 0.94 0.68 No allocation of BN c8 b8 x - 15.0 C D G 1.945 0.93 0.68 No allocation of BN c9 b9 x - 0.5 D E G 1.944 0.94 0.68 No allocation of BN c10 b10 x - 1.3 D E G 1.943 1.03 0.75 No allocation of BN c11 b11 x - 0.9 C E G 1.942 1.04 0.76 No allocation of BN c12 b12 x - 0.9 B C G 1.922 1.06 0.77 No allocation of BN c13 b13 x - 5.0 E F G 1.946 0.96 0.70 No allocation of BN c14 b14 ○ thirty 1.2 A A B 1.946 0.92 0.73 c15 b15 ○ 500 1.3 E F G 1.921 0.96 0.78

[0129]

<Example 2>

First, a grain-oriented electrical steel sheet (product) was produced using the same method as in Example 1. Then, magnetic domain control was performed on the product using a mechanical method, a laser, and an electron beam.

[0130]

When the BN number density was measured, the insulating coating was removed using sodium hydroxide from the grain-oriented electrical steel sheet obtained using the above-mentioned production method. Then, 10 fields of view of 4 μm in the sheet width direction × 2 μm in the sheet thickness direction were observed from the outer surface of the intermediate layer having a cross section perpendicular to the rolling direction of the steel sheet to 5 μm using SEM, and the number of BN having a particle size of from 50 to 300 nm.

In addition, using SEM-EDS, the average particle size was observed in 10 fields of view measuring 4 µm in the leaf width direction × 2 µm in the sheet thickness direction, the lengths of the principal axes of precipitates in the observed areas identified as BN using EDS were measured, and their average the value was taken as the average particle size.

In addition, the value of I _{B_t (d/100)} /I _{B_t (d/10)} was measured using the method described above.

[0131]

Table 3 shows the BN emission state of the grain-oriented electrical steel sheet (product), GDS results, coating adhesion evaluation, and magnetic characteristics. In examples D1 to D5 according to the present invention, the adhesion of the coating was more excellent, and the magnetic characteristics were also excellent.

[0132]

[Table 3]

No. Steel No. BN I _{B_t(d/100)}
/I _{B_t(d/10)} Coating adhesion Magnetic characteristics Magnetic domain control method Numerical density (pcs/mm ³ ) Average particle size (nm) Fraction of peel area at φ 20 mm Fraction of peel area at φ 10 mm Fraction of peel area at φ 5 mm Magnetic flux density B8 (Tl) Steel loss W _17/50 (W/kg) Steel loss W _17/50 with magnetic domain control (W/kg) Examples D1 B1 2×10 ⁶ 80 1.3 A A B 1.947 0.88 0.63 Laser irradiation D2 B2 4×10 ⁶ 120 1.5 A A B 1,950 0.86 0.62 Laser irradiation D3 B3 3×10 ⁶ 130 3.0 A A B 1.951 0.85 0.61 knurling D4 B4 2×10 ⁶ 90 1.1 A A B 1.949 0.89 0.59 Etching D5 B5 3×10 ⁶ 100 5.1 A A B 1.945 0.88 0.65 electron beam

[0133]

<Example 3>

Grain-oriented electrical steel sheets (products) were produced using the same method as in Examples 1 and 2. Then, magnetic domain control was performed on these products using a mechanical method, a laser, and an electron beam.

[0134]

For these grain-oriented electrical steel sheets (products), BN precipitation state, I _{B_t (d/100)} /I _{B_t (d/10)} value, coating adhesion, and magnetic characteristics were measured. The results are shown in Table 4.

[0135]

[Table 4]

No. Steel No. Presence or absence of BN secretions Average particle size BN (nm) GDS Coating adhesion Magnetic characteristics Magnetic domain control method Emission intensity B
I _{B_t(d/100)}
/I _{B_t(d/10)} Fraction of peel area at φ 20 mm Fraction of peel area at φ 10 mm Fraction of peel area at φ 5 mm Magnetic flux density B8 (Tl) Steel loss W _17/50 (W/kg) Steel loss W _17/50 with magnetic domain control (W/kg) Examples E1 B1 ○ 70 eighteen A A B 1.951 0.87 0.61 Laser irradiation E2 B2 ○ 120 12 A B B 1.952 0.86 0.62 Etching E3 B3 ○ 300 sixteen A A B 1.949 0.87 0.63 knurling E4 B4 ○ 250 fifteen A A B 1.952 0.88 0.62 electron beam E5 B5 ○ 200 17 A B B 1.948 0.86 0.60 electron beam

[0136]

In examples E1 to E5, in which the ratio of I _{B_t(d/100)} /I _{B_t(d/10)} of the emission intensity B on the surface layer of the steel sheet to the emission intensity B at the center of the steel sheet (on the side closest to the base steel sheet, than to the surface layer of steel sheet) satisfies the above Equation (1), coating adhesion and magnetic performance were more excellent.

INDUSTRIAL APPLICABILITY

[0137]

As described above, according to the present invention, peeling of the insulating coating generated at the strong bend portion of the steel sheet serving as the inner peripheral side of the metal core can be prevented in the grain-oriented electrical steel sheet using BN as an inhibitor, and can be stably to obtain a grain-oriented electrical steel sheet having excellent insulation adhesion, low steel loss, and excellent suitability for the production of a strip core. Therefore, the present invention has high applicability in the production of electrical steel sheets and industries using them.

Claims (19)

1. Grain-oriented electrical steel sheet, comprising: main steel sheet; an intermediate layer which is placed in contact with the base steel sheet and includes mainly silicon oxide; and an insulating coating that contacts the intermediate layer and includes mainly phosphate and colloidal silica, while the main steel sheet includes as a chemical composition, wt.%: C: 0.085 or less; Si: 0.80-7.00; Mn: 0.05-1.00; acid-soluble Al: 0.010-0.065; N: 0.0040 or less; S: 0.0100 or less; B: 0.0005-0.0080; and residue consisting of Fe and impurities, BN having an average particle size of 50-300 nm is present on the surface layer of the intermediate layer, when the total thickness of the base steel sheet and the intermediate layer is defined as d, the time to reach the sputter depth position d/100 from the outer surface of the intermediate layer when the emission intensity B is measured using glow discharge emission spectrometry (GDS) is defined as t(d/100) , and the time to reach the spray depth position d/10 from the outer surface of the intermediate layer is defined as t(d/10), the emission intensity I _{B_t(d/100)} B at time t(d/100) and the emission intensity I _{B_t(d/10)} B at time t(d/10) satisfy the following Equation (1), and the ratio of the major axis to the minor axis BN is 1.5 or less, I _{B_t(d/100)} >I _{B_t(d/10)} Equation (1). 2. The grain-oriented electrical steel sheet according to claim 1, wherein the BN number density on the surface layer of the intermediate layer is 2×10 ⁶ pcs/mm ² or more.