RU2772057C1 - Anisotropic electrical steel sheet, a method for forming an insulating coating of anisotropic electrical steel sheet and a method for producing anisotropic electrical steel sheet - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to a sheet of anisotropic electrical steel without a forsterite film. A sheet of anisotropic electrical steel without a forsterite film contains a main steel sheet; an oxide layer located in contact with the main steel sheet, and an insulating coating with tension located in contact with the oxide layer. The main steel sheet includes in its chemical composition, wt. %: 2.5-4.0 Si, 0.05-1.00 Mn, 0.01 or less C, 0-0.005 S+Se, 0-0.01 Al solution, 0-0.005 N, 0-0.03 Bi, 0-0.03 Te, 0-0.03 Pb, 0-0.50 Sb, 0-0.50 Sn, 0-0.50 Cr, 0-1.0 Cu and the rest consisting of iron and impurities. The oxide layer is an iron oxide layer when the iron oxide layer is analyzed using Fourier transform infrared spectroscopy, when A₆₅₀ is the absorption coefficient of the absorption peak detected at 650 cm^-1 in the infrared absorption spectrum, and when A₁₂₅₀ is the absorption coefficient of the absorption peak detected at 1250 cm^-1 in the infrared absorption spectrum, A₆₅₀ and A₁₂₅₀ satisfy the condition 0.2≤A₆₅₀/A₁₂₅₀≤5.0 and the magnetic induction B8 in the direction of rolling a sheet of anisotropic electrical steel is 1.90 T or more.

EFFECT: sheet of anisotropic electrical steel has high adhesion of an insulating coating with tension and without a glass film of forsterite.

7 cl, 13 tbl, 12 ex

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to an anisotropic electrical steel sheet, a method for forming an insulating coating on an anisotropic electrical steel sheet, and a method for producing an anisotropic electrical steel sheet. Priority is claimed from Japanese Patent Application No. 2019-005237, filed January 16, 2019, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The anisotropic electrical steel sheet is a steel sheet that contains silicon (Si) in an amount of about 0.5-7 wt.% and has a crystallographic orientation set to {110}<001> orientation (Goss orientation) by using a phenomenon called secondary recrystallization. Here, the {110}<001> orientation means that the {110} plane of the crystal is aligned parallel to the rolled surface, and the <001> axis of the crystal is aligned parallel to the rolling direction.

[0003] The anisotropic electrical steel sheet is mainly used for the iron core of a transformer and the like. as a soft magnetic material. Since the anisotropic electrical steel sheet significantly affects the characteristics of the transformer, research has been carried out to improve the driving characteristics and the magnetic loss characteristics of the anisotropic electrical steel sheet.

[0004] A typical production method for an anisotropic electrical steel sheet is as follows. A steel billet with a predetermined composition is heated and subjected to hot rolling to obtain a hot-rolled steel sheet. This hot-rolled steel sheet is subjected to hot strip annealing as necessary and then cold-rolled to obtain a cold-rolled steel sheet. This cold rolled steel sheet undergoes decarburization annealing to activate primary recrystallization. The decarburized annealed steel sheet after the decarburization annealing is finally annealed to promote secondary recrystallization.

[0005] After the decarburization annealing and before the final annealing, an aqueous slurry including an annealing separator whose main component is MgO is applied to the surface of the decarburized annealed steel sheet, and then dried. This decarburized annealed steel sheet is coiled and then finally annealed. During the final annealing, the MgO contained in the annealing separator reacts with the SiO ₂ contained in the internally oxidized layer formed on the surface of the steel sheet by decarburization annealing, and thereby a primary layer (called "glass film" or "forsterite film") is formed on the surface of the steel sheet. ”), which includes mainly forsterite (Mg ₂ SiO ₄ ). In addition, after the glass film is formed (that is, after the final annealing), a solution is applied to the surface of the final annealed steel sheet, which mainly includes colloidal silica and phosphate, for example, and is calcined, and thereby a tension insulating coating (called " secondary layer).

[0006] The aforementioned glass film acts as an insulator and also improves the adhesion of the tension insulating coating formed on the glass film. Tension is applied to the base steel sheet by adhering the glass film, the tensioned insulation coating, and the base steel sheet. As a result, the magnetic loss in the anisotropic electrical steel sheet is reduced.

[0007] However, since the glass film is a non-magnetic material, its presence is magnetically unfavorable. In addition, the interface between the base steel sheet and the glass film has a penetrating structure so that the glass film is difficult to intertwine with the sheet, and this penetrating structure tends to suppress the movement of the domain wall when the anisotropic electrical steel sheet is magnetized. Thus, the presence of a glass film can cause an increase in magnetic losses.

[0008] For example, when the formation of a glass film is suppressed, the formation of a penetrating structure can be suppressed, and thus the domain wall can easily move during magnetization. However, in the case where the formation of a glass film is simply suppressed, the adhesion of the insulating coating under tension is not guaranteed, and thus sufficient tension is not applied to the base steel sheet. As a result, it becomes difficult to reduce the magnetic loss.

[0009] As described above, at present, when the glass film is removed from the anisotropic electrical steel sheet, the domain wall can move easily, and therefore the magnetic performance is expected to improve. On the other hand, in the aforementioned case, hardly any tension is applied to the base steel sheet, and therefore deterioration in magnetic characteristics (especially magnetic loss) is inevitable. Therefore, in the case where an anisotropic electrical steel sheet is realized in which the glass film is removed and coating adhesion is guaranteed, the magnetic performance is expected to be improved.

[0010] In the past, the improvement of adhesion of an insulating coating under tension for an anisotropic electrical steel sheet without a glass film has been investigated.

[0011] For example, Patent Document 1 discloses a method for washing a steel sheet by immersing it in an aqueous solution of sulfuric acid or sulfate at a concentration of 2-30% before forming a tension coating. Patent Document 2 discloses a method for carrying out surface pretreatment of a steel sheet using an oxidizing acid before forming an insulating coating under tension. Patent Document 3 discloses an anisotropic electrical silicon steel sheet in which an externally oxidized layer mainly containing silica is included, and in which metallic iron with a sectional area ratio of 30% or less is included in this externally oxidized layer. Patent Document 4 discloses an anisotropic electrical steel sheet in which thin linear grooves are formed directly on the surface of a base steel sheet in the anisotropic electrical steel sheet, and the fine linear grooves have a depth of 0.05-2 µm and a spacing of 0.05-2 µm.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0012] Patent Document 1: Japanese Unexamined Patent Application First Publication No. H05-311453

Patent Document 2: Japanese Unexamined Patent Application First Publication No. 2002-249880

Patent Document 3: Japanese Unexamined Patent Application First Publication No. 2003-313644

Patent Document 4: Japanese Unexamined Patent Application First Publication No. 2001-303215

SUMMARY OF THE INVENTION

SOLVED TECHNICAL PROBLEM

[0013] As described above, the anisotropic electrical steel sheet without the glass film has poor adhesion of the insulating coating under tension. For example, when the aforementioned anisotropic electrical steel sheet is aged for a long time, the tensile insulation coating may peel off. In this case, tension is not applied to the base steel sheet. For anisotropic electrical steel sheet, it is extremely important to improve the adhesion of the insulating coating under tension.

[0014] The methods disclosed in Patent Documents 1-4 are respectively intended to improve the adhesion of the insulating coating under tension. However, in these methods, it is not clear whether adhesion is stably achieved and whether the magnetic loss improvement effect is obtained as a result. The above methods are not enough to get this effect.

[0015] The present invention has been made in view of the above situations. The object of the present invention is to provide an anisotropic electrical steel sheet having excellent insulating coating tension adhesion even without a glass film (forsterite film). In addition, an object of the present invention is to provide a method for forming the aforementioned insulating coating and manufacturing the aforementioned anisotropic electrical steel sheet.

SOLUTION

[0016] Aspects of the present invention are as follows.

[0017] (1) An anisotropic electrical steel sheet according to one aspect of the present invention having no forsterite film includes:

main steel sheet;

an oxide layer located in contact with the base steel sheet; and

tensioned insulating coating in contact with the oxide layer,

moreover, the main steel sheet includes in its chemical composition, in wt.%:

2.5-4.0% Si,

0.05-1.00% Mn,

0-0.01% C,

0-0.005% S+Se,

0-0.01% sol. Al,

0-0.005%N,

0-0.03% Bi,

0-0.03% Those

0-0.03% Pb,

0-0.50% Sb,

0-0.50% Sn,

0-0.50%Cr,

0-1.0% Cu, and

the rest, consisting of iron and impurities,

the oxide layer is an iron oxide layer,

when the iron oxide layer is analyzed by Fourier transform infrared spectroscopy, when A ₆₅₀ is the absorption coefficient of the absorption peak detected at 650 cm ^-1 in the infrared absorption spectrum, and when A ₁₂₅₀ is the absorption coefficient of the absorption peak detected at 1250 cm ^-1 in the infrared absorption spectrum,

A ₆₅₀ and A ₁₂₅₀ satisfy the condition 0.2≤A ₆₅₀ /A ₁₂₅₀ ≤5.0, and

the magnetic induction B8 in the rolling direction of the anisotropic electrical steel sheet is 1.90 T or more.

(2) In the anisotropic electrical steel sheet of (1), the average thickness of the iron oxide layer may be 200-500 nm.

(3) A method for forming an insulating coating of an anisotropic electrical steel sheet without a forsterite film according to one aspect of the present invention includes a process for forming an insulating coating under tension on a steel substrate,

and in the process of forming an insulating coating

the solution is applied to the oxide layer of the steel substrate to form an insulating coating under tension and calcined,

wherein the steel substrate includes a base steel sheet and an oxide layer located in contact with the base steel sheet,

the main steel sheet includes in its chemical composition, in wt.%:

2.5-4.0% Si,

0.05-1.00% Mn,

0-0.01% C,

0-0.005% S+Se,

0-0.01% sol.Al,

0-0.005%N,

0-0.03% Bi,

0-0.03% Those

0-0.03% Pb,

0-0.50% Sb,

0-0.50% Sn,

0-0.50%Cr,

0-1.0% Cu, and

the rest, consisting of iron and impurities,

the oxide layer is an iron oxide layer, and

when the iron oxide layer is analyzed by Fourier transform infrared spectroscopy, when A ₆₅₀ is the absorption coefficient of the absorption peak detected at 650 cm ^-1 in the infrared absorption spectrum, and when A ₁₂₅₀ is the absorption coefficient of the absorption peak detected at 1250 cm ^-1 in the infrared absorption spectrum,

A ₆₅₀ and A ₁₂₅₀ satisfy the condition 0.2≤A ₆₅₀ /A ₁₂₅₀ ≤5.0.

(4) In the method of forming the insulating coating of the anisotropic electrical steel sheet of (3), the average thickness of the iron oxide layer may be 200-500 nm.

(5) A method for producing an anisotropic electrical steel sheet without a forsterite film according to one aspect of the present invention includes

a hot rolling process of heating and then hot rolling a steel billet to obtain a hot rolled steel sheet,

a hot strip annealing process, optionally annealing the hot rolled steel sheet to obtain a hot strip annealed steel sheet;

a cold rolling process with cold rolling of a hot rolled steel sheet or a hot strip annealed steel sheet one or more times with intermediate annealing therebetween to obtain a cold rolled steel sheet,

a decarburization annealing process with decarburization annealing of a cold rolled steel sheet to obtain a decarburized annealed steel sheet;

a final annealing process of applying an annealing separator to the decarburized annealed steel sheet, and then finally annealing the decarburized annealed steel sheet to obtain a final annealed steel sheet;

an oxidation process of sequentially carrying out a washing treatment, a pickling treatment, and a heat treatment of the finally annealed steel sheet to obtain an oxidized steel sheet,

the process of forming an insulating coating with applying a solution for forming an insulating coating with tension on the surface of an oxidized steel sheet and calcining this solution,

and during hot rolling

steel billet includes in its chemical composition, in wt.%:

2.5-4.0% Si,

0.05-1.00% Mn,

0.02-0.10% C,

0.005-0.080% S+Se,

0.010-0.07% sol. Al,

0.005-0.020% N,

0-0.03% Bi,

0-0.03% Those

0-0.03% Pb,

0-0.50% Sb,

0-0.50% Sn,

0-0.50%Cr,

0-1.0% Cu, and

the rest, consisting of iron and impurities, and

while in the process of oxidation

as the washing treatment, the surface of the final annealed steel sheet is washed,

as the pickling treatment, the final annealed steel sheet is pickled using 5 to 20 mass% sulfuric acid, and

as a heat treatment, the finally annealed steel sheet is kept in a temperature range of 700-850°C for 10-50 seconds in an atmosphere with an oxygen concentration of 5-21% by volume and a dew point of -10 to 30°C.

(6) In the production method of the anisotropic electrical steel sheet of (5), in the final annealing process,

the annealing separator may include MgO and Al ₂ O ₃ in a total amount of 85 mass% or more,

MgO:Al ₂ O ₃ , which is the weight ratio of MgO and Al ₂ O ₃ , can be from 3:7 to 7:3, and

the annealing separator may include bismuth chloride in an amount of 0.5-15 wt.% compared to the total amount of MgO and Al ₂ O ₃ .

(7) In the production method of the anisotropic electrical steel sheet of (5), in the final annealing process,

the annealing separator may include MgO in an amount of 60 mass% or more, and

the forsterite film formed on the surface can be removed by grinding or pickling the surface of the finally annealed steel sheet after the final annealing.

(8) In the production method of the anisotropic electrical steel sheet according to any one of (5) to (7), in the decarburization annealing process,

when S1 is the average heating rate in units of °C/second in the temperature range of 500°C or more and less than 600°C during the temperature rise of the cold-rolled steel sheet, and when S2 is the average heating rate in units of °C/second in the temperature range of 600 °C or more and 700°C or less during the temperature rise of the cold rolled steel sheet,

S1 and S2 may satisfy the conditions 300≤S1≤1000, 1000≤S2≤3000 and 1.0<S2/S1≤10.0.

(9) In the method for manufacturing the anisotropic electrical steel sheet according to any one of (5) to (8), in the hot rolling process,

the steel billet may include in its chemical composition, in wt.%, at least one element selected from the group consisting of

0.0005-0.03% Bi,

0.0005-0.03% Te and

0.0005-0.03% Pb.

EFFECTS OF THE INVENTION

[0018] According to the above-described aspects of the present invention, it is possible to provide an anisotropic electrical steel sheet having excellent insulating coating tension adhesion even without a glass film (forsterite film). In addition, it is possible to provide a method for forming the above-mentioned insulating coating and a method for producing the above-mentioned anisotropic electrical steel sheet.

[0019] In particular, according to the above-described aspects of the present invention, the glass film is not included, the formation of the penetrating structure is suppressed, and thus the domain wall can be easily moved. In addition, the morphology of the iron oxide layer is controlled, the adhesion of the insulation coating under tension is guaranteed, and thus sufficient tension can be applied to the base steel sheet. As a result, it is possible to obtain excellent magnetic characteristics of the anisotropic electrical steel sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1A is a sectional illustration showing an anisotropic electrical steel sheet in accordance with one embodiment of the present invention.

Fig. 1B is a sectional illustration showing a modification of an anisotropic electrical steel sheet according to an embodiment.

Fig. 2A is an infrared absorption spectrum from Fourier transform infrared spectroscopy.

Fig. 2B is an infrared absorption spectrum from Fourier transform infrared spectroscopy.

Fig. 3 is a flowchart illustrating a manufacturing method of an anisotropic electrical steel sheet according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The preferred embodiment of the present invention will now be described in detail. However, the present invention is not limited to only the configuration disclosed in this embodiment, and various modifications are possible without departing from the aspect of the present invention. In addition, the limiting range described below includes its lower limit and its upper limit. However, a value expressed as "greater than" or "less than" is not included in this range. Unless otherwise indicated, "%" referring to the chemical composition is "% by weight".

[0022] In addition, in the embodiment and in the drawings, repeated explanations regarding a component that performs essentially the same function are omitted, and the same reference symbol is used for its designation.

[0023] The inventors of the present invention made a thorough study to improve the adhesion of the insulating coating under tension for an anisotropic electrical steel sheet without a glass film (forsterite film). As a result, it has been found that even without a glass film, coating adhesion can be achieved by forming a favorable iron oxide layer through the following treatments. Specifically, the final annealed steel sheet without the glass film after the final annealing is subjected to a washing treatment by washing its surface, a pickling treatment using sulfuric acid, and then a heat treatment under a predetermined atmosphere.

[0024] In addition, it was found that in the anisotropic electrical steel sheet with the aforementioned specific iron oxide layer, the alignment degree of the crystallographic orientation of the base steel sheet significantly affects the magnetic characteristics after the formation of the insulating coating under tension and after the magnetic domain refinement treatment, and that the aforementioned influence is more stronger than expected. The present inventors have also found that it is possible to advantageously improve the magnetic characteristics by controlling the heating rate for decarburization annealing and/or by incorporating an inhibitor intensity increasing element into the steel billet chemistry.

<Anisotropic Electrical Steel Sheet>

[0025] The main features of the anisotropic electrical steel sheet according to the embodiment will be described with reference to FIG. 1A and FIG. 1b. Fig. 1A and FIG. 1B are illustrations schematically showing the structure of an anisotropic electrical steel sheet according to an embodiment.

[0026] As schematically shown in FIG. 1A, an anisotropic electrical steel sheet 10 according to an embodiment includes a base steel sheet 11, an iron oxide layer 13 disposed in contact with the base steel sheet 11, and a tension insulating coating 15 disposed in contact with the iron oxide layer 13. In the sheet 10, the anisotropic In electrical steel, there is no glass film (forsterite film) between the base steel sheet 11 and the insulating coating 15 under tension. In the anisotropic electrical steel sheet 10, the iron oxide layer 13 and the insulating coating 15 can be tension formed on at least one surface of the base steel sheet 11. In general, the iron oxide layer 13 and the insulating coating 15 are tension formed on both surfaces of the base steel sheet 11, as schematically shown in FIG. 1b.

[0027] Next, the anisotropic electrical steel sheet 10 according to the embodiment is explained with emphasis on its characteristic features. The following description may omit a detailed description of known features as well as features that can be implemented by a person skilled in the art.

(Main steel sheet 11)

[0028] The main steel sheet 11 is obtained by using a steel billet with a predetermined chemical composition and applying predetermined production conditions, and thus controlling the chemical composition and texture. The chemical composition of the base steel sheet 11 is described in detail below.

(Iron oxide layer 13)

[0029] The iron oxide layer 13 is an oxide layer that acts as an intermediate layer between the base steel sheet 11 and the insulating coating 15 under tension in the anisotropic electrical steel sheet 10 according to the embodiment. The iron oxide layer 13 mainly includes iron oxides. The constituent phases therein are not specifically limited. In the anisotropic electrical steel sheet 10 according to the embodiment, the iron oxide layer 13 is defined as an oxide layer that satisfies the condition 0.2≤A ₆₅₀ /A ₁₂₅₀ ≤5.0 described later. On the other hand, the forsterite film, the oxide layer excluding the iron oxide layer, and the like. do not satisfy the condition 0.2≤A ₆₅₀ /A ₁₂₅₀ ≤5.0.

[0030] The iron oxide layer 13 mainly includes iron oxides such as magnetite (Fe ₃ O ₄ ), hematite (Fe ₂ O ₃ ), and fayalite (Fe ₂ SiO ₄ ). In addition to the aforementioned iron oxides, it may include silicon oxide (SiO ₂ ) and the like. The presence of the iron oxide layer 13 can be confirmed by performing Fourier transform infrared spectroscopy (FT-IR) on the surface where the tension insulation coating 15 is not formed (on the surface where the tension insulation coating 15 is removed).

[0031] Iron oxides are formed, for example, when oxygen reacts with the surface of the final annealed steel sheet. The iron oxide layer 13 mainly includes iron oxides, and thereby the adhesion to the base steel sheet 11 is improved. In most cases, it is difficult to improve the adhesion between metals and ceramics. However, in the anisotropic electrical steel sheet 10 of the embodiment, the iron oxide layer 13 is located between the base steel sheet 11 and the tension insulating coating 15, which is a kind of ceramic, and thus the adhesion of the tension insulating coating 15 is improved even without the glass film.

[0032] The average thickness of the iron oxide layer 13 (average thickness d ₁ in Fig. 1A and Fig. 1B) is preferably in the range of 200-500 nm, for example. When the average thickness d _{1 of} the iron oxide layer 13 is 200 nm or more, the adhesion can be favorably improved. On the other hand, when the average thickness d _{1 of} the iron oxide layer 13 is more than 500 nm, the iron oxide layer 13 may be excessively thick, and peeling may partially occur. The average thickness d _{1 of} the iron oxide layer 13 is preferably 220 nm or more, and more preferably 250 nm or more. Moreover, the average thickness d _{1 of} the iron oxide layer 13 is preferably 480 nm or less, and more preferably 450 nm or less.

[0033] The above average thickness d _{1 of} the iron oxide layer 13 can be measured by observing the bond distribution between iron and oxygen using, for example, X-ray photoelectron spectroscopy (XPS). In particular, the XPS spectrum is measured by sputtering from the surface, and the average thickness d _{1 of} the iron oxide layer 13 can be considered as the range from the position where the Fe-O peak appears in the spectrum at 712 eV to the position where the above Fe-O peak is replaced by a metallic Fe peak that appears in the spectrum at 708 eV.

[0034] When the sample to be measured has the tension coating 15 as the outermost layer, XPS analysis can be performed after the thickness of the tension coating 15 is reduced. For example, the thickness of the tension coating 15 is preliminarily cross-sectional confirmed along the thickness direction of the anisotropic electrical steel sheet 10, and then the surface of the anisotropic electrical steel sheet 10 is mechanically polished in parallel so that the thickness of the tension coating 15 becomes less than 0.1 μm. Thereafter, XPS analysis can be carried out using the above-described anisotropic electrical steel sheet 10 . The spectrum emanating from the insulating cover 15 with tension can be detected immediately after the start of the XPS analysis (immediately after the start of spraying). Over time, a Fe-O peak is detected that appears at 712 eV and comes from the iron oxide layer 13. After that, a metal Fe peak is detected that appears at 708 eV and comes from the base steel sheet 11. Based on the above Fe-O peak and the above peak of metallic Fe, the average thickness d _{1 of} the iron oxide layer 13 can be measured as described above.

[0035] The constituent phases in the iron oxide layer 13 are not specifically limited. If necessary, the constituent phase can be identified by X-ray crystallography, XPS analysis, and the like.

(Insulating cover 15 with tension)

[0036] An insulating tension coating 15 is disposed on the surface of the iron oxide layer 13. The tension insulating coating 15 guarantees electrical insulation for the anisotropic electrical steel sheet 10, and thereby eddy current losses are reduced. As a result, the magnetic loss characteristics are improved. In addition to electrical insulation, the tensioned insulating coating 15 improves corrosion resistance, heat resistance, slip resistance, and the like. sheet 10 anisotropic electrical steel.

[0037] In addition, the insulating coating 15 exerts tension on the base steel sheet 11 with tension. began to improve.

[0038] The average thickness of the insulating coating 15 with tension is not particularly limited, but may be, for example, 0.1-10 µm.

[0039] In addition, it is possible to irradiate the surface of the insulating coating 15 under tension with a continuous laser beam or an electron beam to refine the magnetic domain.

[0040] For example, the insulating coating 15 is tensionally formed by applying an insulating coating forming solution, which mainly includes metal phosphate and colloidal silica, to the surface of the iron oxide layer 13 located in contact with the base steel sheet 11, and baking the solution.

<Thickness 10 Anisotropic Electrical Steel>

[0041] The average thickness of the anisotropic electrical steel sheet 10 of the embodiment (average thickness t in Fig. 1A and Fig. 1B) is not particularly limited, but may be, for example, 0.17-0.35 mm.

<Chemical composition of base steel sheet 11>

[0042] Next, the chemical composition of the base steel sheet 11 of the anisotropic electrical steel sheet 10 according to the embodiment will be described in detail. The percentages of the respective elements described hereinafter are indicated in mass percent (wt.%), unless expressly indicated otherwise.

[0043] In the anisotropic electrical steel sheet 10 according to the embodiment, the base steel sheet 11 includes basic elements in its chemical composition, optional elements as needed, and the rest consists of Fe and impurities.

[0044] In the embodiment, the base steel sheet 11 includes Si and Mn as base elements (primary alloying elements).

(2.5-4.0% Si)

[0045] Si (silicon) is an element that increases the electrical resistance of steel and reduces eddy current losses. When the Si content is less than 2.5%, the above-mentioned eddy current loss reduction effect is insufficiently obtained. On the other hand, when the Si content is more than 4.0%, the cold workability of the steel deteriorates. Thus, in the embodiment, the Si content in the base steel sheet 11 should be 2.5-4.0%. The Si content is preferably 2.7% or more, and more preferably 2.8% or more. In addition, the Si content is preferably 3.9% or less, and more preferably 3.8% or less.

(0.05-1.0% Mn)

[0046] Mn (manganese) forms MnS and MnSe in the production processes by bonding with S and/or Se, which is explained later. These precipitates act as an inhibitor (inhibitor of normal grain growth) and cause secondary recrystallization in the steel during final annealing. In addition, Mn is an element that improves the hot workability of steel. When the Mn content is less than 0.05%, this effect is insufficiently exhibited. On the other hand, when the Mn content is more than 1.0%, secondary recrystallization does not occur, and the magnetic characteristics of the steel deteriorate. Thus, in the embodiment, the content of Mn in the base steel sheet 11 should be 0.05-1.0%. The manganese content is preferably 0.06% or more. In addition, the Mn content is preferably 0.50% or less.

[0047] In an embodiment, the base steel sheet 11 may include impurities. Impurities correspond to elements that contaminate steel during its industrial production from ores and scrap that are used as raw materials for steel production, or from the environment of the production process.

[0048] In addition, in the embodiment, the main steel sheet 11 may include optional elements in addition to the main elements and impurities. For example, instead of a portion of Fe making up the rest, a silicon steel sheet may include optional elements such as C, S, Se, sol. Al (acid-soluble Al), N, Bi, Te, Pb, Sb, Sn, Cr, and Cu . Optional elements can be included as needed. Thus, the lower limit of the content of the respective optional elements should not be limited, and this lower limit may be 0 mass%. In addition, even if optional elements may be included as impurities, the aforementioned effects are not affected.

(0-0.01% C)

[0049] C (carbon) is an optional element. C is an element effective for controlling the microstructure until the completion of the decarburization annealing process in manufacturing processes, and thereby improving the magnetic performance of the anisotropic electrical steel sheet. However, in the final product, when the C content in the base steel sheet 11 is more than 0.01%, the magnetic characteristics of the anisotropic electrical steel sheet 10 deteriorate. Thus, in the embodiment, the C content in the base steel sheet 11 should be 0.01% or less. The content of C is preferably 0.005 mass% or less. On the other hand, the lower limit of the C content in the base steel sheet 11 is not particularly limited, and may be 0%. Preferably, the C content is as low as possible. However, even when the C content is reduced to less than 0.0001%, the microstructure control effect saturates and the production cost increases. Thus, the C content is preferably 0.0001% or more.

(0-0.005% in S+Se)

[0050] S (sulfur) and Se (selenium) are optional elements. S and Se form MnS and MnSe, which act as an inhibitor by binding to Mn in manufacturing processes. However, when the total amount of S and Se in the base steel sheet 11 is more than 0.005%, the inhibitor remains in the base steel sheet 11, and the magnetic performance deteriorates. Thus, in the embodiment, the total amount of S and Se in the base steel sheet 11 should be 0.005% or less. On the other hand, the lower limit of the total amount of S and Se in the base steel sheet 11 is not particularly limited, and may be 0%. Preferably, the total amount of S and Se is as low as possible. However, even when the total amount of S and Se is reduced to less than 0.0001%, the production cost increases. Thus, the total amount of S and Se is preferably 0.0001% or more.

(0-0.01% sol.Al)

[0051] Solvent Al (acid soluble aluminum Al) is an optional element. Al forms AlN, which acts as an inhibitor by binding to N in manufacturing processes. However, when the content of sol.Al is more than 0.01%, the inhibitor remains excessively in the base steel sheet 11, and the magnetic performance deteriorates. Thus, in the embodiment, the Al solution content in the base steel sheet 11 should be 0.01% or less. The content of sol.Al is preferably 0.005% or less, and more preferably 0.004% or less. The lower limit of the Al solution content in the base steel sheet 11 is not particularly limited, but may be 0%. However, when the content of sol.Al is reduced to less than 0.0001%, production costs increase. Thus, the content of sol.Al is preferably 0.0001% or more.

(0-0.005%N)

[0052] N (nitrogen) is an optional element. N forms AlN, which acts as an inhibitor by binding to Al in manufacturing processes. However, when the N content is more than 0.005%, the inhibitor remains excessively in the base steel sheet 11, and the magnetic performance deteriorates. Thus, in the embodiment, the N content in the base steel sheet 11 should be 0.005% or less. The N content is preferably 0.004 mass% or less. The lower limit of the N content in the base steel sheet 11 is not particularly limited, but may be 0%. However, when the N content is reduced to less than 0.0001%, production costs increase. Thus, the N content is preferably 0.0001% or more.

(0-0.03% Bi)

(0-0.03% Te)

(0-0.03% Pb)

[0053] Bi (bismuth), Te (tellurium), and Pb (lead) are optional elements. When the amount of each of these elements in the base steel sheet 11 is 0.03% or less, it is possible to advantageously improve the magnetic characteristics of the anisotropic electrical steel sheet 10. However, when the amount of each of these elements is more than 0.03%, respectively, the steel sheet may become brittle in the high temperature range. Thus, in the embodiment, the amount of each of these elements in the base steel sheet 11 should be 0.03% or less. The lower limit of the amount of each of these elements in the base steel sheet 11 is not particularly limited, but may be 0%. The lower limit of the amount of each of these elements may be 0.0001%.

(0-0.50%Sb)

(0-0.50% Sn)

(0-0.50%Cr)

(0-1.0% Cu)

[0054] Sb (antimony), Sn (tin), Cr (chromium) and Cu (copper) are optional elements. When these elements are included in the base steel sheet 11, it is possible to advantageously improve the magnetic characteristics of the anisotropic electrical steel sheet 10. Thus, in the embodiment, it is preferable to control the amount of each of these elements in the base steel sheet 11 to be 0.50% or less Sb, 0.50% or less Sn, 0.50% or less Cr, and 1.0 % or less Cu. The lower limit of the amount of each of these elements in the base steel sheet 11 is not particularly limited, but may be 0%. In order to advantageously obtain the above effect, the amount of each of these elements is preferably 0.0005% or more, and more preferably 0.001% or more.

[0055] Meanwhile, at least one of Sb, Sn, Cr, and Cu may be included in the base steel sheet 11. Specifically, the base steel sheet 11 may contain at least one of 0.0005-0.50% Sb, 0.0005-0.50% Sn, 0.0005-0.50% Cr, and 0.0005-1, 0% Cu.

[0056] In the anisotropic electrical steel sheet, the chemical composition is relatively strongly changed (the amount of alloying element is reduced) by decarburization annealing and by refining annealing during secondary recrystallization. Depending on the particular element, it may be reduced by refining annealing to an undetectable level (1 ^ppm or less) using a typical analytical method. The above chemical composition is the chemical composition of the final product (the base steel sheet 11 of the anisotropic electrical steel sheet 10). In general, the chemical composition of the final product is different from that of the steel billet (slab) as the raw material.

[0057] The chemical composition of the base steel sheet 11 of the anisotropic electrical steel sheet 10 can be measured using typical steel analysis methods. For example, the chemical composition can be measured using ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometer: Inductively Coupled Plasma Emission Spectrometry/Emission Spectroscopy). In particular, it is possible to obtain the chemical composition by measuring with a Shimadzu ICPS-8100 meter or the like. under conditions based on a calibration curve prepared in advance using 35 mm square samples taken from the base steel sheet 11. In addition, the C and S content can be measured by the infrared absorption method after combustion, and the N content can be measured using a thermoconductometric method after melting in an inert gas flow.

[0058] The above chemical composition is the composition of the base steel sheet 11 of the anisotropic electrical steel sheet 10 . When the anisotropic electrical steel sheet 10 used as the measurement sample has the tension insulating coating 15 and the iron oxide layer 13 on its surface, the chemical composition is measured after removing the coating and the like. in typical ways.

<Surface Analysis by Fourier Transform Infrared Spectroscopy>

[0059] In the anisotropic electrical steel sheet 10 according to the embodiment, the iron oxide layer 13 is located between the base steel sheet 11 and the insulating coating 15 under tension, and due to this, the iron oxide layer 13, the insulating coating 15 under tension, and the base steel sheet 11 are tightly bonded even without glass film (forsterite film).

[0060] Whether the iron oxide layer 13 is included in the anisotropic electrical steel sheet 10 can be judged by surface analysis using Fourier transform infrared spectroscopy (FT-IR). In particular, FT-IR is carried out, and then the absorption coefficient of a particular peak can be confirmed. Next, surface analysis by FT-IR is explained in detail with reference to FIG. 2A and FIG. 2b. Fig. 2A and FIG. 2B shows an infrared absorption spectrum in Fourier transform infrared (FT-IR) spectroscopy.

[0061] When the tension coating 15 is not included in the anisotropic electrical steel sheet 10 (when the steel sheet is after the oxidation process and before the insulation coating forming process in the anisotropic electrical steel sheet production method of the embodiment), the surface of the iron oxide layer 13 is analyzed with using a well-known commercially available Fourier transform infrared spectrophotometer (for example, Frontier brand manufactured by PERKIN ELMER Frontier, etc.).

[0062] When the insulating cover 15 with tension is present, FT-IR can be carried out with a decrease in the thickness of the sample to be measured. For example, the thickness of the tension coating 15 is preliminarily cross-sectioned along the thickness direction of the anisotropic electrical steel sheet 10, and then the surface of the anisotropic electrical steel sheet 10 is mechanically polished in parallel so that the thickness of the tension coating 15 becomes less than 0.1 µm. FT-IR is carried out using the aforementioned anisotropic electrical steel sheet 10 after polishing. Thereafter, the surface of the sample to be measured is mechanically polished in parallel so that the thickness of the sample to be analyzed is further reduced by approximately 0.05 µm. Then FT-IR is carried out again using the sample after polishing. The above analysis and polishing is repeated until the main steel sheet 11 is exposed in the measurement specimen. In the above procedure, the iron oxide layer 13 is analyzed with an FT-IR spectrophotometer.

[0063] The result of FT-IR is not affected by the presence or absence of the insulating cover 15 under tension. In particular, it is confirmed that the result of FT-IR is equivalent in the case of analysis using the measurement sample, where the insulation coating 15 with tension is absent and where the iron oxide layer 13 is the outermost layer, and in the case of analysis using the measurement sample, where the insulation coating 15 is tensioned and where the iron oxide layer 13 is exposed by the above procedure.

[0064] When conducting FT-IR, for example, it is preferable to measure the infrared absorption spectrum of the iron oxide layer 13 using reflective absorption spectroscopy. Meanwhile, an absorption peak detected at 650 cm ^-1 in the infrared absorption spectrum is observed as an absorption peak originating from iron oxides contained in the iron oxide layer 13. On the other hand, an absorption peak detected at 1250 cm ^-1 in the infrared absorption spectrum, observed as an absorption peak originating from SiO ₂ . In some cases, the position of the wavenumber at which these absorption peaks are found may be shifted by about 1-2 cm ^-1 from the above wavenumbers. However, as shown in FIG. 2A and FIG. 2B, the shape of the spectral curve of the above two absorption peaks is specific, which means that the person skilled in the art can easily identify the above two absorption peaks in the infrared absorption spectrum.

[0065] The absorption coefficient A _k of each absorption peak can be determined as follows (Formula 11) using the intensity I _k (for example, the transmittance T _k (unit: %)) of each absorption peak and the intensity I ⁰ _k (for example, the transmittance T ⁰ _k (unit: %)) of the baseline of each absorption peak, as shown, for example, in FIG. 2A. In addition, if the FT-IR spectrophotometer used for surface analysis is an instrument that can directly output the absorption coefficient, it is also possible to determine the absorption coefficient A _k of each absorption peak (see formula 11') using the absorption coefficient A' _k (dimensionless ) of each absorption peak and the absorption coefficient A ⁰ _k (dimensionless) of the baseline of each absorption peak, as shown, for example, in FIG. 2b.

[0066] A _k =log(I ⁰ _k /I _k ) ... (Formula 11)

A _k =A' _k - A ⁰ _k ... (formula 11')

[0067] Based on the above formula 11 and the above formula 11', A ₆₅₀ is defined as the absorption coefficient of the absorption peak detected at wave number 650 cm ^-1 in the infrared absorption spectrum, and A ₁₂₅₀ is defined as the absorption coefficient of the absorption peak detected at wave number 1250 cm ^-1 in the infrared absorption spectrum.

[0068] The absorption peak found at 650 cm ^-1 comes from iron oxides, and the absorption peak found at 1250 cm ^-1 comes from SiO ₂ . Thus, the value of the above A ₆₅₀ and the value of the above A ₁₂₅₀ correspond to the amount of iron oxides formed and the amount of SiO ₂ formed, respectively.

[0069] In the case of observing the infrared absorption spectrum, which is the ratio between the wave number (cm ^-1 ) and the transmittance T (%), as shown in FIG. 2A, the above baseline can be determined as follows.

Baseline of the absorption peak found at 650 cm ^-1 : the line connecting the maximum transmittance T in the wavenumber range 510-560 cm ^-1 and the maximum transmittance T in the wavenumber range 720-820 cm ^-1 .

Baseline of the absorption peak found at 1250 cm ^-1 : the line connecting the maximum transmittance T in the wavenumber range 1000-1100 cm ^-1 and the maximum transmittance T in the wavenumber range 1280-1350 cm ^-1 .

[0070] In the case of observing the infrared absorption spectrum, which is the ratio between the wave number (cm ^-1 ) and the absorption coefficient A (dimensionless), as shown in FIG. 2B, the above baseline can be determined as follows.

Baseline of the absorption peak found at 650 cm ^-1 : line connecting the minimum of absorption coefficient A in the wavenumber range 510-560 cm ^-1 and the minimum of absorption coefficient A in the wavenumber range 720-820 cm ^-1 .

Baseline of the absorption peak found at 1250 cm ^-1 : line connecting the minimum of absorption coefficient A in the wavenumber range 1000-1100 cm ^-1 and the minimum of absorption coefficient A in the wavenumber range 1280-1350 cm ^-1 .

[0071] In the anisotropic electrical steel sheet 10 according to the embodiment, when the iron oxide layer 13 is analyzed by FT-IR, the following (Formula 101) is satisfied.

[0072] 0.2≤A ₆₅₀ /A ₁₂₅₀ ≤5.0 ... (Formula 101)

[0073] In the anisotropic electrical steel sheet 10 of the embodiment, when the infrared absorption spectrum satisfies the above formula 101, the iron oxide layer 13 is considered to be contained in the anisotropic electrical steel sheet 10. For example, with respect to the anisotropic electrical steel sheet 10 including the tensioned insulating coating 15, when at least one infrared absorption spectrum is observed satisfying the above formula 101 in a plurality of FT-IR analyzes where the above analysis and polishing are repeated, it is considered that the iron oxide the layer 13 is contained in the anisotropic electrical steel sheet 10 . On the other hand, the forsterite film and the oxide layer, except for the iron oxide layer 13, do not satisfy the above formula 101.

[0074] When the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ is less than 0.2, the amount of generated iron oxides is excessively small compared to the amount of generated SiO ₂ , the formation of the iron oxide layer 13 is insufficient, and therefore the adhesion of the insulation coating under tension cannot be improved sufficiently. In addition, when the absorption ratio ratio A ₆₅₀ /A ₁₂₅₀ is more than 5.0, the tensile adhesion of the insulation cover 15 is reduced, which is disadvantageous. The reason why the adhesion decreases when the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ is more than 5.0 is not entirely clear. In the case where, in the heat treatment of the oxidation process to be explained later, the holding time is shorter or the holding temperature is lower, the above-described situation is sometimes observed. Thus, it is assumed that both the amount of iron oxides formed and the amount of SiO ₂ formed are insufficient, and that the formation of iron oxides to ensure adhesion is insufficient.

[0075] In the anisotropic electrical steel sheet 10 according to the embodiment, the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ is preferably 0.4 or more, and more preferably 0.6 or more. In addition, the absorption ratio ratio A ₆₅₀ /A ₁₂₅₀ is preferably 4.5 or less, and more preferably 4.0 or less.

<Forsterite Film>

[0076] The anisotropic electrical steel sheet 10 according to the embodiment does not include a forsterite film. In an embodiment, whether the anisotropic electrical steel sheet 10 includes a forsterite film or not can be determined by the following procedure.

[0077] Whether or not the anisotropic electrical steel sheet includes a forsterite film can be confirmed by an X-ray diffraction method. For example, X-ray diffraction may be performed on the surface after the insulating coating 15 has been removed with tension or the like. from an anisotropic electrical steel sheet 10, and the resulting X-ray diffraction spectrum can be compared to a PDF (Powder Diffraction File). Forsterite (Mg ₂ SiO ₄ ) can be identified by JCPDS Card No. 34-189. In the embodiment, when the main constituent phase in the above X-ray diffraction spectrum is not forsterite, the anisotropic electrical steel sheet 10 is considered to not include the forsterite film.

[0078] In order to remove only the insulating coating 15 under tension from the anisotropic electrical steel sheet 10, the coated anisotropic electrical steel sheet 10 may be immersed in a hot alkaline solution. In particular, it is possible to remove the insulating cover 15 under tension or the like. from an anisotropic electrical steel sheet 10 by immersing the steel sheet in an aqueous sodium hydroxide solution containing 30 wt.% NaOH and 70 wt.% H ₂ O at 80° C. for 20 minutes, washing it with water, and then drying it. In general, only the insulating coating is removed with an alkaline solution, while the forsterite film is removed with an acidic solution such as hydrochloric acid. Thus, in the case where there is a forsterite film, when immersed in the aforementioned alkaline solution, the insulating cover 15 is tensionally removed and the forsterite film is exposed.

<Magnetic characteristics>

[0079] The magnetic characteristics of the anisotropic electrical steel sheet can be measured based on the Epstein test governed by JIS C2550:2011, the Single Sheet Tester (SST) method governed by JIS C 2556:2015, and the like. In the anisotropic electrical steel sheet 10 according to the embodiment, the magnetic characteristics can be evaluated using the Single Sheet Tester (SST) method regulated by JIS C 2556:2015.

[0080] In the anisotropic electrical steel sheet 10 of the embodiment, the magnetic induction B8 in the rolling direction (magnetic induction in a magnetizing field of 800 A/m) may be 1.90 T or more. The upper limit of the magnetic induction is not particularly limited, but may be, for example, 2.02 T.

[0081] As described above, the magnetic characteristics of the anisotropic electrical steel sheet can be measured based on the Epstein test governed by JIS C2550:2011, the Single Sheet Tester (SST) method governed by JIS C 2556:2015, and the like. When a steel ingot is formed in a vacuum furnace, etc. in research and development, it is difficult to obtain a test sample of the same size as in industrial production. In this case, for example, a test piece with a width of 60 mm and a length of 300 mm can be taken, and the measurement can be carried out according to the single-sheet tester method. In addition, the measured value can be multiplied by a correction factor to obtain a measured value equivalent to the value based on the Epstein test. In an embodiment, the measurement is carried out in accordance with the method of a single sheet tester. The test piece can be taken so that the longitudinal direction is the rolling direction, and the magnetic induction B8 in the rolling direction can be measured.

<Method for producing anisotropic electrical steel sheet>

[0082] Next, with reference to FIG. 3, a method for producing an anisotropic electrical steel sheet according to a preferred embodiment of the present invention will be described in detail. Fig. 3 is a flowchart illustrating a manufacturing method of an anisotropic electrical steel sheet according to an embodiment.

[0083] Meanwhile, the production method of the anisotropic electrical steel sheet 10 is not limited to the following method. The following method is just an example of the production of the anisotropic electrical steel sheet 10 .

<Overall process flow of anisotropic electrical steel sheet production process>

[0084] The method for producing an anisotropic electrical steel sheet according to an embodiment is for producing an anisotropic electrical steel sheet without a forsterite film, and its general process sequence is as follows.

[0085] The method for producing an anisotropic electrical steel sheet according to an embodiment includes the following processes, which are shown in FIG. 3.

(S101) A hot rolling process of heating and then hot rolling a steel billet (slab) having a predetermined chemical composition to obtain a hot-rolled steel sheet.

(S103) A hot strip annealing process, optionally annealing the hot rolled steel sheet to obtain a hot strip annealed steel sheet.

(S105) A cold-rolling process with cold rolling of a hot-rolled steel sheet or a hot-strip annealed steel sheet one or more times with intermediate annealing therebetween to obtain a cold-rolled steel sheet.

(S107) Decarburization annealing process with decarburization annealing of a cold-rolled steel sheet to obtain a decarburized annealed steel sheet.

(S109) A final annealing process by applying an annealing separator to the decarburized annealed steel sheet, and then finally annealing the decarburized annealed steel sheet to obtain a final annealed steel sheet.

(S111) An oxidation process of sequentially carrying out a washing treatment, a pickling treatment, and a heat treatment of the finally annealed steel sheet to obtain an oxidized steel sheet.

(S113) A process for forming an insulating coating by applying an insulating coating forming solution by stretching it on the surface of an oxidized steel sheet and baking the solution.

[0086] Next, the above processes are described in detail. In the following description, if the conditions of each process are not described, known conditions may be appropriately applied.

<Hot rolling process>

[0087] The hot rolling process (step S101) is a process of heating and then hot rolling a steel billet (for example, a steel ingot such as a slab) having a predetermined chemical composition to obtain a hot-rolled steel sheet. During the hot rolling process, the steel billet is subjected to heat treatment. The heating temperature of the steel billet is preferably in the range of 1200-1400°C. The heating temperature of the steel billet is preferably 1250°C or more, and more preferably 1380°C or more. Thereafter, the heated steel billet is subjected to hot rolling to obtain a hot-rolled steel sheet. The average thickness of the hot rolled steel sheet is preferably in the range of 2.0 to 3.0 mm, for example.

[0088] In the method for manufacturing the anisotropic electrical steel sheet according to the embodiment, the steel billet includes basic elements in its chemical composition, optional elements as needed, and the rest consists of Fe and impurities. In the following, the percentage of the respective elements is indicated in mass percent (wt.%), unless explicitly stated otherwise.

[0089] In the method for producing an anisotropic electrical steel sheet according to an embodiment, a steel billet (slab) includes Si, Mn, C, S+Se, sol. Al, and N as base elements (major alloying elements).

(2.5-4.0% Si)

[0090] Si is an element that increases the electrical resistance of steel and reduces eddy current losses. When the content of Si in the steel billet is less than 2.5%, the above-mentioned eddy current loss reduction effect is insufficiently obtained. On the other hand, when the content of Si in the steel billet is more than 4.0%, the cold workability of the steel deteriorates. Thus, in the embodiment, the content of Si in the steel billet should be 2.5-4.0%. The content of Si in the steel billet is preferably 2.7% or more, and more preferably 2.8% or more. In addition, the content of Si in the steel billet is preferably 3.9% or less, and more preferably 3.8% or less.

(0.05-1.0% Mn)

[0091] Mn forms MnS and MnSe by bonding with S and/or Se during manufacturing processes, which will be explained later. These precipitates act as an inhibitor and cause secondary recrystallization in the steel during final annealing. In addition, Mn is an element that improves the hot workability of steel. When the content of Mn in the steel billet is less than 0.05%, the above effect is insufficiently obtained. On the other hand, when the content of Mn in the steel billet is more than 1.0%, secondary recrystallization does not occur, and the magnetic characteristics of the steel deteriorate. Thus, in the embodiment, the content of Mn in the steel billet should be 0.05-1.0%. The content of Mn in the steel billet is preferably 0.06% or more. In addition, the content of Mn in the steel billet is preferably 0.50% or less.

(0.02-0.10% C)

[0092] C is an element effective for controlling the microstructure to the completion of the decarburization annealing process in manufacturing processes, and thereby improves the magnetic characteristics of the anisotropic electrical steel sheet. When the content of C in the steel billet is less than 0.02% or when the C content in the steel billet is more than 0.10%, the aforementioned magnetic performance improvement effect is insufficiently obtained. The content of C in the steel billet is preferably 0.03% or more. In addition, the content of C in the steel billet is preferably 0.09% or less.

(0.005-0.080% in S+Se)

[0093] S and Se form MnS and MnSe, which act as an inhibitor by binding to Mn in manufacturing processes. When the total amount of S and Se in the steel billet is less than 0.005%, it is difficult to obtain the effect of forming MnS and MnSe. On the other hand, when the total amount of S and Se is more than 0.080%, the magnetic performance deteriorates and the steel sheet may become brittle in the high temperature range. Thus, in the embodiment, the total amount of S and Se in the steel billet should be 0.005-0.080%. The total amount of S and Se in the steel billet is preferably 0.006 mass% or more. In addition, the total amount of S and Se in the steel billet is preferably 0.070% or less.

(0.01-0.07% sol. Al)

[0094] Solvent Al forms AlN, which acts as an inhibitor by binding to N in manufacturing processes. When the Al solution content of the steel billet is less than 0.01%, AlN is not sufficiently formed, and hence the magnetic performance deteriorates. On the other hand, when the Al solution content is more than 0.07%, the magnetic performance deteriorates and cracks may appear during cold rolling. Thus, in the embodiment, the content of sol.Al in the steel billet should be 0.01-0.07%. The content of sol.Al in the steel billet is preferably 0.02% or more. In addition, the Al solution content of the steel billet is preferably 0.05% or less.

(0.005-0.020% N)

[0095] N forms AlN, which acts as an inhibitor by binding to Al in manufacturing processes. When the content of N in the steel billet is less than 0.005%, AlN is not sufficiently formed, and hence the magnetic performance deteriorates. On the other hand, when the content of N in the steel billet is more than 0.020%, AlN practically ceases to act as an inhibitor, and thus secondary recrystallization becomes difficult. In addition, cracks may appear during cold rolling. Thus, in the embodiment, the content of N in the steel billet should be 0.005-0.020%. The N content of the steel billet is preferably 0.012% or less, and more preferably 0.010% or less.

[0096] In the method for manufacturing the anisotropic electrical steel sheet according to the embodiment, the steel billet (slab) may include impurities. Impurities correspond to elements that contaminate steel during its industrial production from ores and scrap that are used as raw materials for steel production, or from the environment of the production process.

[0097] In addition, in the embodiment, the steel billet may include optional elements in addition to the main elements and impurities. For example, instead of a portion of Fe making up the rest, the silicon steel sheet may include optional elements such as Bi, Te, Pb, Sb, Sn, Cr, and Cu. Optional elements can be included as needed. Thus, the lower limit of the content of the respective optional elements should not be limited, and this lower limit may be 0 mass%. In addition, even if optional elements may be included as impurities, the aforementioned effects are not affected.

(0-0.03% Bi)

(0-0.03% Te)

(0-0.03% Pb)

[0098] Bi, Te and Pb are optional elements. When the amount of each of these elements in the steel blank is 0.03% or less, it is possible to advantageously improve the magnetic characteristics of the anisotropic electrical steel sheet. However, when the amount of each of these elements is more than 0.03%, respectively, the steel sheet may become brittle in the high temperature range. Thus, in an embodiment, the amount of each of these elements in the steel billet should be 0.03% or less. The lower limit of the amount of each of these elements in the steel billet is not particularly limited, but may be 0%. In order to advantageously obtain the above effect, the amount of each of these elements is preferably 0.0005% or more, and more preferably 0.001% or more.

[0099] Meanwhile, at least one of Bi, Te, and Pb may be included in the steel billet. In particular, the steel billet may include at least one of 0.0005-0.03% Bi, 0.0005-0.03% Te, and 0.0005-0.03% Pb.

(0-0.50%Sb)

(0-0.50% Sn)

(0-0.50%Cr)

(0-1.0% Cu)

[0100] Sb, Sn, Cr and Cu are optional elements. When these elements are included in the steel billet, it is possible to advantageously improve the magnetic characteristics of the anisotropic electrical steel sheet. Thus, in the embodiment, it is preferable to control the amount of each of these elements in the steel billet so that it is 0.50% or less Sb, 0.50% or less Sn, 0.50% or less Cr, and 1.0% or less less Cu. The lower limit of the amount of each of these elements in the steel billet is not particularly limited, but may be 0%. In order to advantageously obtain the above effect, the amount of each of these elements is preferably 0.0005% or more, and more preferably 0.001% or more.

[0101] At the same time, at least one of Sb, Sn, Cr, and Cu may be included in the composition of the steel billet. In particular, the steel billet may contain at least one of 0.0005-0.50% Sb, 0.0005-0.50% Sn, 0.0005-0.50% Cr, and 0.0005-1.0% Cu.

[0102] The chemical composition of the steel billet can be measured using typical steel analysis methods. For example, the chemical composition can be measured based on the above analytical method.

<Hot Strip State Annealing Process>

[0103] The hot strip annealing process (step S103) is a process of optionally annealing the hot rolled steel sheet after the hot rolling process to obtain a hot strip annealed steel sheet. By carrying out the annealing of the hot-rolled steel sheet, recrystallization occurs in the steel, and as a result, excellent magnetic characteristics can be obtained.

[0104] The heating method is not particularly limited, and a known heating method can be used. In addition, the annealing conditions are not specifically limited. For example, a hot rolled steel sheet may be held in a temperature range of 900-1200°C for 10 seconds to 5 minutes.

[0105] The annealing process in the hot strip state can be omitted if necessary. In addition, after the hot strip state annealing process and before the cold rolling process explained below, the surface of the hot-rolled steel sheet may be pickled.

<Cold rolling process>

[0106] The cold rolling process (step S105) is a process of cold rolling a hot-rolled steel sheet after the hot rolling process or a hot strip state annealed steel sheet after the hot strip state annealing process by performing cold rolling one or more times with intermediate annealing in between for in order to obtain cold rolled steel sheet. Since the shape of the hot strip annealed steel sheet is excellent due to the hot strip annealing, it is possible to reduce the possibility of the steel sheet breaking during the first cold rolling. Cold rolling can be carried out three or more times, but the production costs increase. Thus, it is preferable to carry out cold rolling once or twice.

[0107] In the cold rolling process, a method for cold rolling a steel sheet is not particularly limited, and a known method can be used. For example, final cold rolling reduction (total cold rolling reduction without intermediate annealing or total cold rolling reduction after intermediate annealing) may be in the range of 80-95%.

[0108] Here, the final cold rolling reduction (%) is determined as follows: Final cold rolling reduction (%) = (1 - Steel sheet thickness after final cold rolling/Steel sheet thickness before final cold rolling) × 100.

[0109] When the final cold rolling reduction is less than 80%, Goss cores may not be formed in an advantageous manner. On the other hand, when the final cold rolling reduction is more than 95%, the secondary recrystallization may be unstable in the final annealing process. Thus, it is preferable that the final cold rolling reduction is 80-95%.

[0110] When carrying out multiple cold rolling with intermediate annealing, the reduction in the first cold rolling may be 5-50%, and the intermediate annealing holding may be carried out in the temperature range of 950-1200°C for 30 seconds to 30 minutes.

[0111] The average thickness of the cold rolled steel sheet (thickness after cold rolling) is different from the thickness of the anisotropic electrical steel sheet, which includes the thickness of the insulating coating under tension. For example, the average thickness of a cold rolled steel sheet may be 0.10-0.50 mm. In the embodiment, even when the cold-rolled steel sheet is a thin sheet whose average thickness is less than 0.22 mm, tension adhesion of the insulation coating is advantageously improved. Thus, the average thickness of the cold rolled steel sheet may be 0.20 mm or less.

[0112] In the cold rolling process, an aging treatment may be carried out in order to favorably improve the magnetic characteristics of the anisotropic electrical steel sheet. For example, since the thickness of the steel sheet decreases with multiple passes of cold rolling, the steel sheet can be held in a temperature range of 100° C. or more for 1 minute or more at least once in an interval between multiple passes. Through the aging treatment, the primary recrystallization texture in the decarburization annealing process can be favorably controlled, and as a result, a secondary recrystallized texture in which the {110}<001> orientation favorably develops in the final annealing process can be obtained.

<Decarburization Annealing Process>

[0113] The decarburization annealing process (step S107) is a process for decarburizing annealing a cold rolled steel sheet after a cold rolling process to obtain a decarburized annealed steel sheet. In the decarburization annealing process, a cold-rolled steel sheet is annealed under predetermined conditions to control the primary recrystallized structure.

[0114] In the method for producing an anisotropic electrical steel sheet according to an embodiment, the decarburization annealing process includes two steps, which are a heating step and a holding step, in order to obtain a desired primary recrystallized structure. Conditions in the heating step and the holding step are not particularly limited, and known conditions can be used.

[0115] In the heating step, the heating rate to reach the decarburization annealing temperature may affect the primary recrystallized texture, and thus may affect the degree of Goss alignment after secondary recrystallization. In the anisotropic electrical steel sheet without glass film according to the embodiment, the degree of alignment in the Goss orientation of the base steel sheet greatly affects the magnetic performance after the insulating coating is formed with tension and after the magnetic domain refinement treatment. Thus, it is preferable to appropriately control the heating rate of the decarburization annealing.

[0116] In particular, when the cold-rolled steel sheet is heated in the heating step, it is preferable to control the heating rate in the temperature range of 500-700°C in order to improve the primary recrystallized texture. In particular, it is more preferable to separately control the heating rate in the temperature range of 500°C or more and less than 600°C and the heating speed in the temperature range of 600°C or more and 700°C or less. In terms of the effect on the oxide layer formed by the decarburization annealing, a favorable range is between the average heating rate S1 in the temperature range of 500°C or more and less than 600°C, and the average heating rate S2 in the temperature range of 600°C or more and 700 °C or less. In the temperature range of 500°C or more and less than 600°C, the formation of Mn oxides is affected in addition to the primary recrystallized texture. In the temperature range of 600°C or more and 700°C or less, the formation of SiO ₂ is affected in addition to the primary recrystallized texture.

[0117] In the embodiment, the average heating rate S1 in the temperature range of 500°C or more and less than 600°C is preferably 300°C/second or more and 1000°C/second or less. In addition, in the temperature range of 600°C or more and 700°C or less, where SiO ₂ is generated affecting the reaction of forming a glass film (forsterite film), it is preferable that the holding time of the steel sheet is shortened. Thus, the average heating rate of S2 in the temperature range of 600°C or more and 700°C or less is preferably 1000°C/second or more and 3000°C/second or less.

[0118] Preferably, the average heating rate S2 is higher than the average heating rate S1. For example, it is preferable that the S2/S1 ratio is greater than 1.0 and 10.0 or less.

[0119] In particular, it is preferable that the average heating rate S1 and the average heating rate S2 satisfy all of the following formulas 111-113. When all of the following formulas 111 to 113 are satisfied, it may be more advantageous to improve the magnetic characteristics (magnetic loss characteristics) of the anisotropic electrical steel sheet.

[0120] 300≤S1≤1000... (Formula 111)

1000≤S2≤3000... (Formula 112)

1.0<S2/S1≤10.0... (Formula 113)

[0121] With regard to the above formula 111, when the average heating rate S1 is less than 300°C/second, it may affect the primary recrystallized texture, and hence the magnetic performance may deteriorate. On the other hand, when the average heating rate S1 is more than 1000° C./second, tension adhesion of the insulation coating may be insufficient. The average heating rate S1 in the temperature range of 500°C or more and less than 600°C is more preferably 350°C/second or more. The average heating rate S1 is more preferably 900°C/second or less.

[0122] With regard to the above formula 112, when the average heating rate S2 is less than 1000°C/second, the generation of SiO ₂ affecting the glass film forming reaction may not be sufficiently suppressed. On the other hand, when the average heating rate S2 is more than 3000° C./second, the decarburization annealing temperature may be exceeded. The average heating rate S2 in the temperature range of 600°C or more and 700°C or less is more preferably 1200°C/second or more. The average heating rate S2 is more preferably 2500°C/second or less.

[0123] With regard to the above formula 113, when the ratio S2/S1 of the average heating rates is 1.0 or less, the magnetic characteristics may deteriorate. On the other hand, when the ratio S2/S1 of the average heating rates is more than 10.0, the temperature control may become difficult. The ratio S2/S1 of the average heating rates is more preferably 1.2 or more. The S2/S1 ratio is more preferably 9.0 or less.

[0124] Preferably, the cold rolled steel sheet is heated to a decarburization annealing temperature of 750-950°C at the above-mentioned average heating rates.

[0125] Other conditions in the heating step (eg, heating atmosphere, etc.) are not particularly limited. The cold rolled steel sheet may be heated in a known humid atmosphere including hydrogen and nitrogen according to a conventional procedure.

[0126] In the decarburization annealing process, after the above-mentioned heating process, the cold-rolled steel sheet is held at the decarburization annealing temperature as a holding step. Conditions in the holding step are not specifically limited. For example, a cold rolled steel sheet can be kept in a temperature range of 750-950°C for 1-5 minutes. In addition, the atmosphere in the soaking step is not specifically limited. The holding step can be carried out in a known humid atmosphere, including hydrogen and nitrogen, in accordance with the usual procedure.

<Final annealing process>

[0127] The final annealing process (step S109) is a process of applying an annealing separator to the decarburized annealed steel sheet after the decarburization annealing process, and then finally annealing the decarburized annealed steel sheet so as to obtain a finally annealed steel sheet. In the final annealing, the coiled steel sheet can be kept at a higher temperature for a long time, as a rule. Thus, in order to suppress adhesion between the inside and outside of the coiled steel sheet, the annealing separator is applied to the decarburized annealed sheet and dried before final annealing.

[0128] In the final annealing process, the annealing separator applied to the decarburized annealed steel sheet is not particularly limited, and a known annealing separator may be used. The method for producing the anisotropic electrical steel sheet according to the embodiment is a method for producing an anisotropic electrical steel sheet without a glass film (forsterite film), which means that an annealing separator that does not form a forsterite film can be used. In the case where an annealing separator is used which forms a forsterite film, this forsterite film can be removed by grinding or pickling after the final annealing.

(Annealing separator that does not form forsterite film)

[0129] As an annealing separator that does not form a glass film (forsterite film), an annealing separator that mainly includes MgO and Al ₂ O ₃ can be used. For example, it is preferable that the annealing separator includes MgO and Al ₂ O ₃ in a total solid content of 85 mass% or more, MgO:Al ₂ O ₃ , which is the mass ratio of MgO and Al ₂ O ₃ , ranged from 3 :7 to 7:3, and that the annealing separator includes bismuth chloride in an amount of 0.5-15 wt.% compared with the total amount of MgO and Al ₂ O ₃ as a solid content. The range of the above weight ratio of MgO and Al ₂ O ₃ and the amount of the above bismuth chloride are determined from the viewpoint of obtaining a base steel sheet having excellent surface smoothness without a glass film.

[0130] With regard to the above weight ratio of MgO and Al ₂ O ₃ , when the amount of MgO exceeds the above range, a glass film may form and remain on the surface of the steel sheet, which means that the surface of the base steel sheet cannot be smoothed. In addition, with regard to the above weight ratio of MgO and Al ₂ O ₃ , when the amount of Al ₂ O ₃ exceeds the above range, sticking of Al ₂ O ₃ may occur, and therefore the surface of the base steel sheet cannot be smoothed. More preferably, MgO:Al ₂ O ₃ , which is the weight ratio of MgO and Al ₂ O ₃ , satisfies the condition from 3.5:6.5 to 6.5:3.5.

[0131] In the case where bismuth chloride is included in the annealing separator, the glass film is easily removed from the surface of the steel sheet even when it is formed in the final annealing. When the amount of bismuth chloride is less than 0.5 wt% compared to the total amount of MgO and Al ₂ O ₃ , a glass film may remain. On the other hand, when the amount of bismuth chloride is more than 15 mass% compared to the total amount of MgO and Al ₂ O ₃ , the effect of suppressing adhesion between steel sheets by the annealing separator cannot be obtained. The amount of bismuth chloride is more preferably 3 wt.% or more and 7 wt.% or less compared to the total amount of MgO and Al ₂ O ₃ .

[0132] The type of bismuth chloride is not particularly limited, and known bismuth chloride can be used. For example, bismuth oxychloride (BiOCl), bismuth trichloride (BiCl ₃ ) and the like can be used. In addition, compounds that can form bismuth oxychloride by reaction in the annealing separator during the final annealing process can be used. For example, as compounds that can form bismuth oxychloride during final annealing, a mixture of a bismuth compound and a metal chloride can be used. For example, as the bismuth compound, bismuth oxide, bismuth hydroxide, bismuth sulfide, bismuth sulfate, bismuth phosphate, bismuth carbonate, bismuth nitrate, organic bismuth compound, bismuth halide, and the like can be used. For example, iron chloride, cobalt chloride, nickel chloride, and the like can be used as the metal chloride.

[0133] After applying the above-mentioned annealing separator not forming a forsterite film on the surface of the steel sheet subjected to decarburization annealing, and drying the annealing separator, final annealing is carried out. The annealing conditions in the final annealing process are not particularly limited, and known conditions may be used. For example, a steel sheet may be kept in a temperature range of 1100-1300°C for 10-30 hours. In addition, the furnace atmosphere may be a known nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen. After the final annealing, it is preferable that the excess annealing separator is removed from the surface of the steel sheet by water washing or pickling.

(Annealing separator forming forsterite film)

[0134] As an annealing separator forming a glass film (forsterite film), an annealing separator that mainly includes MgO can be used. For example, it is preferable that the annealing separator includes MgO in an amount of 60 mass% or more as a solid content.

[0135] After applying the annealing separator to the surface of the decarburized annealed steel sheet and drying the annealing separator, final annealing is performed. The annealing conditions in the final annealing process are not particularly limited, and known conditions may be used. For example, a steel sheet may be kept in a temperature range of 1100-1300°C for 10-30 hours. In addition, the furnace atmosphere may be a known nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0136] When an annealing separator forming a forsterite film is used, the MgO in the annealing separator reacts with the SiO _{2 of} the surface of the steel sheet during final annealing to form forsterite (Mg ₂ SiO ₄ ). Thus, it is preferable that the forsterite film formed on the surface be removed by grinding or pickling the surface of the finally annealed steel sheet after the final annealing. The method for removing the forsterite film from the surface of the final annealed steel sheet is not particularly limited, and known grinding or known pickling may be used.

[0137] For example, in order to remove the forsterite film by pickling, the final annealed steel sheet may be immersed in 20-40 wt% hydrochloric acid at 50-90°C for 1-5 minutes, washed with water, and then dried. In addition, the finished annealed steel sheet can be pickled in a mixed solution of ammonium fluorinated and sulfuric acid, chemically polished in a mixed solution of hydrofluoric acid and hydrogen peroxide, washed with water, and then dried.

<Oxidation process>

[0138] The oxidizing process (step S111) is a process of carrying out washing treatment, pickling treatment, and heat treatment in turn on the final annealed steel sheet after the final annealing process (finally annealed steel sheet without forsterite film) to obtain an oxidized steel sheet. Specifically, the surface of the finally annealed steel sheet is washed as a washing treatment, then the finally annealed steel sheet is pickled using 5 to 20 wt% sulfuric acid as a pickling treatment, and the finally annealed steel sheet is held in a temperature range of 700 to 850° C. for 10-50 seconds in an atmosphere having an oxygen concentration of 5-21 vol.% and a dew point of -10 to 30°C, as a heat treatment.

(Wash treatment)

[0139] The surface of the final annealed steel sheet after the final annealing process is washed. The method for washing the surface of the final annealed steel sheet is not particularly limited, and a known washing method may be used. For example, the surface of the finished annealed steel sheet may be washed with water.

(Etching treatment)

[0140] The final annealed steel sheet after washing is pickled using 5-20% by weight sulfuric acid. When the sulfuric acid is less than 5 mass%, an iron oxide layer satisfying the above formula 101 is not formed. In addition, when the sulfuric acid is more than 20% by mass, an iron oxide layer satisfying the above formula 101 is not formed. The concentration of sulfuric acid is preferably 6 mass% or more. The concentration of sulfuric acid is preferably 15 mass% or less. In addition, the temperature of sulfuric acid used for pickling is not particularly limited, but may be, for example, 70°C or higher.

[0141] The duration of the etching treatment is not particularly limited. For example, the final annealed steel sheet may be passed at a normal linear speed through a pickling bath containing the aforementioned sulfuric acid.

(Heat treatment)

[0142] The final annealed steel sheet after pickling is held in a temperature range of 700-850°C for 10-50 seconds in an atmosphere with an oxygen concentration of 5-21% by volume and a dew point of -10 to 30°C. In heat treatment, the surface of the finally annealed steel sheet after pickling is oxidized, and thereby an iron oxide layer is formed. The oxidized steel sheet after undergoing the washing treatment, the pickling treatment, and the heat treatment satisfies the above formula 101.

[0143] When the oxygen concentration is less than 5%, when the dew point is below -10°C, or when the holding temperature is less than 700°C, the iron oxide layer satisfying the above formula 101 is not formed. In addition, when the oxygen concentration is more than 21% or when the dew point exceeds 30°C, the iron oxide layer satisfying the above formula 101 is not formed. When the holding temperature is over 850°C, the effect becomes saturated and the heating cost increases.

[0144] When the holding time is less than 10 seconds, the iron oxide layer satisfying the above formula 101 is not formed. On the other hand, when the holding time is more than 50 seconds, the effect becomes saturated and the heating cost increases.

[0145] The oxygen concentration is preferably 6 vol.% or more, and preferably 21 vol.% or less. The dew point is preferably 0°C or more, and preferably 30°C or less. The holding temperature is preferably 720°C or more, and preferably 850°C or less. The holding time is preferably 15 seconds or more, and preferably 50 seconds or less.

<Insulating coating forming process>

[0146] The insulating coating forming process (step S113) is a process of applying an insulating coating solution under tension to the surface of the oxidized steel sheet after the oxidizing process and calcining the solution to obtain an anisotropic electrical steel sheet. In the process of forming the insulating coating, the tensioned insulating coating may be formed on one surface of the sheet or on both surfaces of the oxidized steel sheet.

[0147] Before applying the solution, the surface of the oxidized steel sheet on which the insulating coating is formed may be subjected to optional pre-treatment such as alkali degreasing treatment, hydrochloric acid, sulfuric acid, phosphoric acid pickling treatment, and the like. Pre-processing may not be carried out.

[0148] The conditions for forming the tensile insulation coating are not particularly limited, and known conditions can be used. In addition, the tensile insulation coating may include mainly inorganic substances and may additionally include organic substances. For example, the tensile insulation coating may mainly include at least one of a metal chromate, a metal phosphate, colloidal silica, a Zr compound, a Ti compound, and the like. as inorganic substances, and fine particles of organic resin can be dispersed in the insulating coating under tension. From the point of view of reducing the environmental load during production, the tensioned insulation coating can be produced from raw materials such as metal phosphate, binders with Zr or Ti, their carbonates, their ammonium salts.

<Other Processes>

(Leveling annealing process)

[0149] After the process of forming the insulating coating to straighten the sheet, a leveling annealing may be carried out. By performing the leveling annealing of the anisotropic electrical steel sheet after the insulating coating forming process, the magnetic loss characteristics can be advantageously reduced.

(Magnetic domain grinding process)

[0150] The magnetic domain refinement treatment can be carried out on the produced anisotropic electrical steel sheet. Meanwhile, the magnetic domain refinement treatment is a treatment in which a laser beam that refines the magnetic domain is irradiated on the surface of the anisotropic electrical steel sheet or a groove is formed on the surface of the anisotropic electrical steel sheet. By carrying out the magnetic domain refinement treatment, the magnetic characteristics can be advantageously improved.

<Method for Forming Insulating Coating of Anisotropic Electrical Steel Sheet>

[0151] The following describes a method for forming an insulating coating on an anisotropic electrical steel sheet according to a preferred embodiment of the present invention. The method for forming an insulating coating of an anisotropic electrical steel sheet according to the embodiment includes a process for forming an insulating coating. In the process of forming an insulating coating, a solution for forming an insulating coating under tension is applied to a steel substrate, and the solution is calcined to form a tension insulation.

[0152] The above steel substrate includes a base steel sheet and an oxide layer located in contact with the base steel sheet.

[0153] The main steel sheet includes in its chemical composition, in wt.%:

2.5-4.0% Si,

0.05-1.0% Mn,

0-0.01% C,

0-0.005% S+Se,

0-0.01% sol. Al,

0-0.005%N,

0-0.03% Bi,

0-0.03% Those

0-0.03% Pb,

0-0.50% Sb,

0-0.50% Sn,

0-0.50%Cr,

0-1.0% Cu, and

the rest, consisting of iron and impurities.

[0154] The oxide layer is an iron oxide layer. When the iron oxide layer is analyzed by Fourier transform infrared spectroscopy, when A ₆₅₀ is the absorption coefficient of the absorption peak detected at 650 cm ^-1 in the infrared absorption spectrum, and when A ₁₂₅₀ is the absorption coefficient of the absorption peak detected at 1250 cm ^-1 in the infrared absorption spectrum, A ₆₅₀ and A ₁₂₅₀ satisfy the condition 0.2≤A ₆₅₀ /A ₁₂₅₀ ≤5.0.

[0155] In the process of forming an insulating coating, a solution for forming an insulating coating with tension is applied to an iron oxide layer of a steel substrate, and the solution is calcined.

[0156] Preferably, the average thickness of the iron oxide layer is 200-500 nm.

[0157] The method for forming the insulating coating of the anisotropic electrical steel sheet according to the embodiment is essentially the same as the process for forming the insulating coating in the method for producing the anisotropic electrical steel sheet described above. For example, the steel substrate in the method for forming an insulating coating of the anisotropic electrical steel sheet according to the embodiment corresponds to the oxidized steel sheet in the above-described method for producing the anisotropic electrical steel sheet. In addition, the steel substrate in the method for forming an insulating coating of an anisotropic electrical steel sheet according to the embodiment is as shown in FIG. 1A and FIG. 1B to the base steel sheet 11 and the iron oxide layer 13 of the above-described anisotropic electrical steel sheet. Thus, a detailed explanation of the method for forming the insulating coating of the anisotropic electrical steel sheet according to the embodiment is omitted.

Examples

[0158] Next, the effects of one aspect of the present invention are described in detail with reference to the following examples. However, the conditions in the examples are exemplary conditions used to confirm the operation and effects of the present invention, so the present invention is not limited to these exemplary conditions. The present invention may use various types of conditions, as long as these conditions do not depart from the scope of protection of the present invention and achieve the object of the present invention.

(Example 1)

[0159] Steel slab A (steel billet A) and steel slab B (steel billet B) were heated to 1350°C and then hot rolled to obtain hot-rolled steel sheets having an average thickness of 2.3 mm, and steel slab A contained 0.082 wt.% C, 3.3 wt.% Si, 0.082 wt.% Mn, 0.023 wt.% S, 0.025 wt.% sol. Al, 0.008 wt.% N and the rest, consisting of Fe and impurities, and steel slab B contained 0.081 wt% C, 3.3 wt% Si, 0.083 wt% Mn, 0.022 wt% S, 0.025 wt% sol. Al, 0.008 wt% N, 0.0025 wt% Bi and the rest, consisting of Fe and impurities.

[0160] The obtained hot-rolled steel sheets were annealed at 1100°C for 120 seconds and then pickled. The steel sheets after pickling were subjected to cold rolling to obtain cold-rolled steel sheets having an average thickness of 0.23 mm.

[0161] The obtained cold-rolled steel sheets were subjected to decarburization annealing. In the decarburization annealing, cold-rolled steel sheets were heated under such conditions that the average heating rate S1 in the heating step to 500°C or more and less than 600°C was 400°C/second, and the average heating rate S2 in the heating step to 600°C or more and 700°C or less was 1100°C/second (S2÷S1=2.75), and then held at 850°C for 120 seconds.

[0162] Thereafter, the annealing separator was applied and dried. The annealing separator contained MgO and Al ₂ O ₃ in a total solid content of 95 wt.%, and the ratio of miscible MgO and Al ₂ O ₃ was 50%:50% by mass (mass ratio 1:1), and also contained BiOCl in amount of 5 wt.% compared with the total amount of MgO and Al ₂ O ₃ . After that, the final annealing was carried out at 1200°C for 20 hours.

[0163] The excess annealing separator was removed from the resulting final annealed steel sheet by washing with water. In all steel sheets, no glass film (forsterite film) was formed, which was confirmed by the X-ray diffraction method.

[0164] The steel sheets, after removing the excess water-wash annealing separator, were pickled using sulfuric acid at a temperature of 70°C and the concentration shown in the following Table 1. Thereafter, a heat treatment was carried out with changes in oxygen concentration, dew point, temperature, and time.

[0165] [Table 1]

Production conditions Oxidation process flushing Etching Heat treatment No. Washing method sulfuric acid concentration,
wt% Temperature,
°C oxygen concentration,
about.% Dew point,
°C Temperature, °C Time,
with 1-1 flushing with water 5 70 20 ten 800 5 1-2 flushing with water 5 70 20 ten 800 fifteen 1-3 flushing with water 5 70 20 ten 800 40 1-4 flushing with water fifteen 70 20 ten 680 20 1-5 flushing with water fifteen 70 20 ten 800 20 1-6 flushing with water fifteen 70 20 ten 840 20 1-7 flushing with water 3 70 20 ten 720 fifteen 1-8 flushing with water fifteen 70 20 ten 800 thirty 1-9 flushing with water fifteen 70 27 ten 800 thirty 1-10 flushing with water fifteen 70 20 -fifteen 800 thirty 1-11 flushing with water fifteen 70 one ten 800 thirty 1-12 flushing with water fifteen 70 20 35 800 thirty 1-13 flushing with water 25 70 20 ten 680 20 1-14 flushing with water 5 70 20 ten 800 5 1-15 flushing with water 5 70 20 ten 800 fifteen 1-16 flushing with water 5 70 20 ten 800 40 1-17 flushing with water fifteen 70 20 ten 680 20 1-18 flushing with water fifteen 70 20 ten 800 20 1-19 flushing with water fifteen 70 20 ten 840 20 1-20 flushing with water 3 70 20 ten 720 fifteen 1-21 flushing with water fifteen 70 20 ten 800 thirty 1-22 flushing with water fifteen 70 25 ten 800 thirty 1-23 flushing with water fifteen 70 20 -fifteen 800 thirty 1-24 flushing with water fifteen 70 one ten 800 thirty 1-25 flushing with water fifteen 70 20 35 800 thirty 1-26 flushing with water 25 70 20 ten 680 20

[0166] After the oxidation process, an aqueous solution was applied to the steel sheets, which mainly included aluminum phosphate and colloidal silica, this solution was calcined at 850°C for 1 minute, and thereby a tension insulating coating was formed, the specific gravity of which was 4, 5 g/m ² on the surface of the test piece. The test sample was then irradiated with a laser beam to refine the magnetic domain.

[0167] The base steel sheets of the anisotropic electrical steel sheets were chemically analyzed based on the method described above. The steel sheets made from the steel slab A contained in its chemical composition, in mass%, 0.002% or less C, 3.30% Si, 0.082% Mn, 0.005% or less S (0.005% or less S+Se) , 0.005% or less sol. Al, 0.005% or less N, and the rest consisted of Fe and impurities. The steel sheets made from the steel slab B contained in its chemical composition, in mass%, 0.002% or less C, 3.30% Si, 0.083% Mn, 0.005% or less S (0.005% or less S+Se) , 0.005% or less sol. Al, 0.005% or less N, 0.0001 wt.% Bi, and the rest consisted of Fe and impurities.

<Score>

[0168] Fourier transform infrared spectroscopy, average thickness of the iron oxide layer, magnetic characteristics, and adhesion of the insulating coating under tension were evaluated. The evaluation methods were as follows.

(Magnetic characteristics)

[0169] Magnetic induction B8 in the rolling direction (in T) (magnetic induction at 800 A/m) and magnetic loss W17/50 (in W/kg) (magnetic loss when driven up to 1.7 T at 50 Hz) were evaluated at based on the method governed by JIS C 2556:2015 using a single test piece with a length of 300 mm and a width of 60 mm. When the magnetic induction of B8 was 1.90 T or more, it was considered acceptable.

(Infrared spectroscopy with Fourier transform)

[0170] The surface of the steel sheet after oxidization and before forming the insulating tension coating was analyzed by Fourier transform reflective absorption infrared spectroscopy using a Frontier spectrometer manufactured by PERKIN ELMER Frontier. From the obtained infrared absorption spectrum based on the above method, the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ was calculated. When the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ was 0.2-5.0, this was considered acceptable.

(Adhesion of insulation coating with tension)

[0171] From the obtained anisotropic electrical steel sheets, a test specimen was taken, the longitudinal direction of which corresponded to the rolling direction, and bending tests were carried out with a diameter of ∅ 10 and a diameter of ∅ 20 using a bending tester with a cylindrical mandrel. The surface of the test piece after bending tests was observed, the proportion of the area where the insulating coating remained unpeeled in the area of the bent portion (the remaining coating fraction) was calculated, and thus the adhesion of the insulating coating under tension was evaluated. When the share of remaining coverage received an A rating, it was considered acceptable.

[0172] Grade A: 90% or more coverage remaining.

Grade B: The proportion of remaining coverage is 70% or more and less than 90%.

Grade C: less than 70% coverage remaining.

(Average iron oxide layer thickness)

[0173] The XPS test sample was taken from the obtained anisotropic electrical steel sheets, and the average thickness of the iron oxide layer was measured based on the above method.

[0174] The results obtained are shown in the following Table 2.

[0175] [Table 2]

No. Production results Assessment results Notes The ratio of absorption coefficients at
FT-IR Presence or absence of forsterite Thickness of the iron oxide layer, nm Magnetic characteristics Adhesion _B8 ,
Tl W _17/50 , W/kg Share of the remaining
coatings after bending with Ø20 Share of the remaining
coatings after bending with Ø10 1-1 12.5 is absent 125 1.925 0.736 C C comparative example 1-2 3.2 is absent 190 1,930 0.701 A A example according to the invention 1-3 2.5 is absent 355 1.931 0.702 A A example according to the invention 1-4 14.5 is absent 135 1.929 0.725 C C comparative example 1-5 2.3 is absent 380 1.931 0.702 A A example according to the invention 1-6 2.1 is absent 260 1.932 0.702 A A example according to the invention 1-7 6.1 is absent 140 1.920 0.748 B B comparative example 1-8 2.8 is absent 250 1.932 0.711 A A example according to the invention 1-9 6.1 is absent 145 1.915 0.762 B B comparative example 1-10 9.5 is absent 125 1.921 0.746 C C comparative example 1-11 0.1 is absent 105 1.921 0.748 C C comparative example 1-12 6.2 is absent 130 1.922 0.744 B B comparative example 1-13 8.5 is absent 160 1.921 0.746 C C comparative example 1-14 12.3 is absent 150 1.951 0.679 C C comparative example 1-15 3.3 is absent 190 1,970 0.631 A A example according to the invention 1-16 2.4 is absent 510 1.971 0.630 A A example according to the invention 1-17 14.2 is absent 160 1.956 0.651 C C comparative example 1-18 2.5 is absent 400 1.971 0.632 A A example according to the invention 1-19 2.3 is absent 290 1.973 0.633 A A example according to the invention 1-20 6.4 is absent 130 1.953 0.662 B B comparative example 1-21 2.6 is absent 330 1.973 0.631 A A example according to the invention 1-22 6.5 is absent 120 1.943 0.689 B B comparative example 1-23 10.2 is absent 150 1.944 0.686 C C comparative example 1-24 0.1 is absent 110 1.949 0.673 C C comparative example 1-25 6.1 is absent 150 1.951 0.668 B B comparative example 1-26 9.2 is absent 160 1.948 0.675 C C comparative example

[0176] As clearly shown in Tables 1 and 2, since the oxidation conditions were satisfied in Test Nos. 1-2, 1-3, 1-5, 1-6, 1-8, 1-15, 1-16, 1- 18, 1-19 and 1-21, the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ was satisfied, and both the magnetic characteristics and the adhesion of the insulating coating under tension were excellent. In addition, since the chemical compositions of the steel slabs in Test Nos. 1-15, 1-16, 1-18, 1-19, and 1-21 among the above tests were favorable, the magnetic characteristics were even more excellent.

[0177] On the other hand, since the holding time for oxidation was shorter in Test No. 1-1 and the holding temperature for oxidation was lower in Test No. 1-4, the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ was not satisfied, and adhesion of the insulation coating tension was bad.

Because the concentration of sulfuric acid was lower in Test No. 1-7 and the concentration of oxygen for oxidation was higher in Test No. 1-9, the tension adhesion of the insulation coating was poor.

Because the oxidation dew point was lower in Test No. 1-10 and the oxygen concentration for oxidation was lower in Test No. 1-11, the tension adhesion of the insulation coating was poor.

Because the dew point for oxidation was higher in test No. 1-12, the tension adhesion of the insulation coating was poor.

Since the concentration for etching was higher and the temperature for oxidizing was lower in test No. 1-13, the tension adhesion of the insulation coating was poor.

Because the oxidation holding time was shorter in Test No. 1-14 and the oxidation holding temperature was lower in Test No. 1-17, the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ was not satisfied, and the adhesion of the insulation coating under tension was poor.

Since the concentration of sulfuric acid was lower in Test No. 1-20 and the concentration of oxygen for oxidation was higher in Test No. 1-22, the tension adhesion of the insulation coating was poor.

Because the dew point for oxidation was lower in Test No. 1-23 and the oxygen concentration for oxidation was lower in Test No. 1-24, the tension adhesion of the insulation coating was poor.

Since the dew point for oxidation was higher in test No. 1-25, the tension adhesion of the insulation coating was poor.

Since the concentration for etching was higher and the temperature for oxidizing was lower in test No. 1-26, the tension adhesion of the insulation coating was poor.

(Example 2)

[0178] Steel slabs (steel billets) with the chemical compositions shown in the following Table 3 were heated to 1380° C. and then subjected to hot rolling to obtain hot-rolled steel sheets having an average thickness of 2.3 mm. Some samples cracked and therefore could not be subjected to subsequent processes.

[0179] [Table 3]

Steel type Production conditions The chemical composition of the slab (steel billet) (unit: mass%, the rest consists of Fe and impurities) C Si Mn S Se S+Se Solvent Al N Bi Those Pb A-1 0.079 3.31 0.080 0.022 0.001 0.023 0.025 0.008 A-2 0.078 3.51 0.077 0.002 0.051 0.053 0.024 0.008 A-3 0.082 3.31 0.080 0.001 0.023 0.024 0.025 0.008 0.0025 A-4 0.082 3.31 0.080 0.020 0.006 0.026 0.025 0.008 0.0025 A-5 0.081 3.22 0.075 0.021 0.002 0.023 0.025 0.009 0.0015 A-6 0.080 3.32 0.080 0.019 0.003 0.022 0.026 0.008 0.0015 A-7 0.079 3.31 0.080 0.022 0.001 0.023 0.025 0.009 0.0026 0.0005 A-8 0.078 3.51 0.077 0.001 0.018 0.019 0.024 0.008 0.0018 0.0011 A-9 0.079 3.22 0.080 0.019 0.003 0.022 0.025 0.009 0.0021 0.0015 A-10 0.080 3.31 0.080 0.001 0.022 0.023 0.025 0.008 0.0018 0.0018 0.0018 A-11 0.085 3.31 0.080 0.022 0.001 0.023 0.025 0.008 0.0141 0.0018 0.0012 A-12 0.071 4.05 0.081 0.019 0.051 0.070 0.025 0.008 A-13 0.071 2.41 0.081 0.019 0.001 0.020 0.025 0.008 A-14 0.008 3.28 0.075 0.022 0.006 0.028 0.021 0.008 A-15 0.209 3.15 0.051 0.021 0.006 0.027 0.031 0.006 A-16 0.061 3.31 0.081 0.012 0.003 0.015 0.009 0.009 A-17 0.061 3.29 0.082 0.015 0.003 0.018 0.075 0.009 A-18 0.072 3.19 0.008 0.051 0.001 0.052 0.018 0.008 A-19 0.073 3.18 1.010 0.051 0.001 0.052 0.015 0.009 A-20 0.071 3.25 0.081 0.003 0.001 0.004 0.025 0.008 A-21 0.071 3.19 0.051 0.095 0.001 0.096 0.019 0.008 A-22 0.085 3.31 0.082 0.052 0.002 0.054 0.023 0.023 A-23 0.085 3.31 0.052 0.052 0.002 0.054 0.023 0.002

[0180] Hot rolled steel sheets that could be subjected to subsequent processes were annealed at 1120° C. for 120 seconds and then pickled. The steel sheets after pickling were subjected to cold rolling to obtain cold-rolled steel sheets having an average thickness of 0.23 mm. Some steels cracked during cold rolling and therefore could not be further processed.

[0181] Steel sheets that could be subjected to subsequent processes were subjected to decarburization annealing. In the decarburization annealing, cold-rolled steel sheets were heated under such conditions that the average heating rate S1 in the heating step to 500°C or more and less than 600°C was 900°C/second, and the average heating rate S2 in the heating step to 600°C or more and 700°C or less was 1600°C/second (S2÷S1=1.78), and then kept at 850°C for 150 seconds.

[0182] After that, an annealing separator was applied and dried. The annealing separator contained MgO and Al ₂ O ₃ in a total solid content of 94 wt.%, and the ratio of miscible MgO and Al ₂ O ₃ was 50%:50% by mass (mass ratio 1:1), and also contained BiOCl in amount of 6 wt.% compared with the total amount of MgO and Al ₂ O ₃ . After that, the final annealing was carried out at 1200°C for 20 hours.

[0183] The excess annealing separator was removed from the resulting final annealed steel sheet by washing with water. In all steel sheets, no glass film (forsterite film) was formed, which was confirmed by the X-ray diffraction method.

[0184] The steel sheets after removal of the excess annealing separator by water washing were subjected to a pickling treatment using sulfuric acid at a temperature of 70°C and a concentration of 10%. Thereafter, heat treatment was carried out by soaking under conditions such as an oxygen concentration of 21%, a dew point of 10°C, a temperature of 800°C, and a time of 20 seconds. Meanwhile, in Test No. 2-24 shown below, no heat treatment was performed, and Test No. 2-24 had a state after pickling.

[0185] Thereafter, an aqueous solution was applied, which mainly included aluminum phosphate and colloidal silica, and the solution was calcined at 850°C for 1 minute, and thereby formed a tensile insulation coating whose specific gravity was 4.5 g/m ² on the surface of the test piece.

[0186] The base steel sheets of the anisotropic electrical steel sheets were chemically analyzed based on the method described above. The chemical compositions are shown in Table 4. In Tables 3 and 4, an element whose value is not indicated means an element whose amount was not purposefully controlled during production.

[0187] [Table 4]

No. Steel type Production results Chemical composition of the base steel sheet in the anisotropic electrical steel sheet (unit: wt%, the rest consists of Fe and impurities) C Si Mn S Se S+Se Solvent Al N Bi Those Pb 2-1 A-1 ≤0.002 3.31 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-2 A-2 ≤0.002 3.51 0.077 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-3 A-3 ≤0.002 3.31 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0001 2-4 A-4 ≤0.002 3.31 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0001 2-5 A-5 ≤0.002 3.22 0.075 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0001 2-6 A-6 ≤0.002 3.32 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0015 2-7 A-7 ≤0.002 3.31 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0001 0.0001 2-8 A-8 ≤0.002 3.51 0.077 ≤0.005 <0.001 ≤0.005 <0.005 ≤0.005 0.0001 0.0011 2-9 A-9 ≤0.002 3.22 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0001 0.0015 2-10 A-10 ≤0.002 3.31 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0001 0.0001 0.0018 2-11 A-11 ≤0.002 3.31 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 0.0001 0.0001 0.0012 2-12 A-12 - - - - - - - - - - - 2-13 A-13 ≤0.002 2.41 0.081 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-14 A-14 ≤0.002 3.28 0.075 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-15 A-15 <0.002 3.15 0.051 ≤0.005 <0.001 ≤0.005 <0.005 ≤0.005 2-16 A-16 ≤0.002 3.31 0.081 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-17 A-17 - - - - - - - - - - - 2-18 A-18 ≤0.002 3.19 0.008 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-19 A-19 ≤0.002 3.18 1.010 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-20 A-20 ≤0.002 3.25 0.081 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-21 A-21 - - - - - - - - - - - 2-22 A-22 - - - - - - - - - - - 2-23 A-23 ≤0.002 3.31 0.052 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005 2-24 A-1 ≤0.002 3.31 0.080 ≤0.005 ≤0.001 ≤0.005 ≤0.005 ≤0.005

<Score>

[0188] Fourier transform infrared spectroscopy, average thickness of the iron oxide layer, magnetic characteristics, and adhesion of the insulating coating under tension were evaluated. The evaluation methods for FT-IR, the average thickness of the iron oxide layer, and the adhesion of the insulating coating under tension were the same as in the above Example 1. The magnetic characteristics were evaluated as follows.

(Magnetic characteristics)

[0189] The magnetic characteristics in the rolling direction were evaluated based on the method regulated by JIS C 2556:2015 using a single test piece with a length of 300 mm and a width of 60 mm. When the magnetic induction of B8 was 1.90 T or more, it was considered acceptable. Steel sheets whose magnetic induction B8 was acceptable were irradiated with a laser beam to refine the magnetic domain. Then, the magnetic loss W17/50 of the steel sheets irradiated with the laser beam was evaluated.

[0190] The results obtained are shown in the following Table 5.

[0191] [Table 5]

No. Steel type Production results Assessment results Notes FT-IR absorbance ratio The presence or absence of forsterite The thickness of the iron oxide layer,
nm Magnetic characteristics Adhesion _B8 ,
Tl W _17/50 , W/kg Percentage of remaining coverage after bending with
Ø20 share
remaining coating after bending with
Ø10 2-1 A-1 1.8 is absent 310 1.944 0.704 A A example according to the invention 2-2 A-2 1.7 is absent 305 1.946 0.705 A A example according to the invention 2-3 A-3 1.8 is absent 330 1.985 0.621 A A example according to the invention 2-4 A-4 1.6 is absent 320 1.985 0.625 A A example according to the invention 2-5 A-5 1.8 is absent 340 1.985 0.625 A A example according to the invention 2-6 A-6 1.9 is absent 350 1.981 0.631 A A example according to the invention 2-7 A-7 1.7 is absent 380 1.982 0.632 A A example according to the invention 2-8 A-8 1.8 is absent 305 1.982 0.631 A A example according to the invention 2-9 A-9 1.8 is absent 360 1.986 0.618 A A example according to the invention 2-10 A-10 1.8 is absent 370 1.987 0.613 A A example according to the invention 2-11 A-11 1.8 is absent 350 1.988 0.611 A A example according to the invention 2-12 A-12 - - - - - - - comparative example 2-13 A-13 1.7 is absent 360 1.681 - A A comparative example 2-14 A-14 1.6 is absent 370 1.661 - A A comparative example 2-15 A-15 1.5 is absent 350 1.721 - A A comparative example 2-16 A-16 1.5 is absent 330 1.691 - A A comparative example 2-17 A-17 - - - - - - - comparative example 2-18 A-18 1.6 is absent 340 1.722 - A A comparative example 2-19 A-19 1.7 is absent 320 1.701 - A A comparative example 2-20 A-20 1.8 is absent 350 1.725 - A A comparative example 2-21 A-21 - - - - - - - comparative example 2-22 A-22 - - - - - - - comparative example 2-23 A-23 1.8 is absent 305 1.741 - A A comparative example 2-24 A-1 0.1 is absent 20 1.941 0.711 C C comparative example

[0192] As clearly shown in Tables 3-5, since the chemical compositions of the base steel sheets were satisfied in Test Nos. 2-1 to 2-11, the ratio of absorption coefficients A ₆₅₀ /A ₁₂₅₀ was satisfied, and both magnetic characteristics and adhesion insulating cover with tension were excellent. In addition, since the chemical compositions of the steel slabs in Tests Nos. 2-3 to 2-11 among the above tests were favorable, the magnetic characteristics were even more excellent.

[0193] On the other hand, since the Si content was excessive in Test No. 2-12, the steel sheet broke during cold rolling.

Because the Si content was insufficient in Test No. 2-13, the magnetic performance was poor.

Because the C content was insufficient in Test No. 2-14 and the C content was excessive in Test No. 2-15, the magnetic performance was poor.

Since the content of sol.Al was insufficient in test No. 2-16, the magnetic performance was poor.

Because the content of sol.Al was excessive in Test No. 2-17, the steel sheet broke during cold rolling.

Because the Mn content was insufficient in Test No. 2-18 and the Mn content was excessive in Test No. 2-19, the magnetic performance was poor.

Because the total amount of S and Se was insufficient in test No. 2-20, the magnetic performance was poor.

Because the total amount of S and Se was excessive in Test No. 2-21, the steel sheet broke during hot rolling.

Because the N content was excessive in Test No. 2-22, the steel sheet broke during cold rolling.

Because the N content was insufficient in Test No. 2-23, the magnetic performance was poor.

Because the heat treatment during the oxidation process was not carried out in test No. 2-24, the tension adhesion of the insulation coating was poor. In Test No. 2-24, the coating peeled off immediately after annealing even in the flat part in addition to the curved part.

(Example 3)

[0194] Steel slabs (steel billets) with the chemical compositions shown in the following Table 6 were heated to 1380° C. and then subjected to hot rolling to obtain hot-rolled steel sheets having an average thickness of 2.3 mm.

[0195] [Table 6]

Steel type Production conditions The chemical composition of the slab (steel billet) (unit: mass%, the rest consists of Fe and impurities) C Si Mn S S+Se Solvent Al N Bi Those Pb B-1 0.079 3.34 0.080 0.022 0.022 0.025 0.008 B-2 0.079 3.32 0.080 0.022 0.022 0.025 0.008 0.0015 B-3 0.078 3.31 0.081 0.023 0.023 0.024 0.008 0.002 B-4 0.078 3.34 0.082 0.022 0.022 0.025 0.008 0.001 B-5 0.078 3.34 0.081 0.021 0.021 0.025 0.008 0.0012 0.001 B-6 0.079 3.31 0.082 0.022 0.022 0.025 0.008 0.002 0.002 B-7 0.078 3.32 0.082 0.023 0.023 0.025 0.008 0.0012 0.001 0.002

[0196] The hot rolled steel sheets were annealed at 1120° C. for 120 seconds and then pickled. The steel sheets after pickling were subjected to cold rolling to obtain cold-rolled steel sheets having an average thickness of 0.23 mm.

[0197] The obtained cold-rolled steel sheets were subjected to decarburization annealing. In the decarburization annealing, cold-rolled steel sheets were heated by changing the average heating rate S1 (°C/second) in the heating step to 500°C or more and less than 600°C and the average heating rate S2 (°C/second) in the heating stage to 600°C. C or more and 700°C or less, as shown in Table 7, and then kept at 850°C for 150 seconds.

[0198] [Table 7]

No. Steel type Production conditions Decarburizing annealing S1,
°C/s S2,
°C/s S2/S1 Temperature,
°C Time,
with 3-1 B-1 280 950 3.39 850 150 3-2 B-1 400 950 2.38 850 150 3-3 B-1 280 1600 5.71 850 150 3-4 B-2 280 950 3.39 850 150 3-5 B-2 400 950 2.38 850 150 3-6 B-2 400 2000 5.00 850 150 3-7 B-2 700 2000 2.86 850 150 3-8 B-3 700 2000 2.86 850 150 3-9 B-4 700 1600 2.29 850 150 3-10 B-5 700 1600 2.29 850 150 3-11 B-6 700 1600 2.29 850 150 3-12 B-7 700 1600 2.29 850 150 3-13 B-1 280 950 3.39 850 150 3-14 B-1 400 950 2.38 850 150 3-15 B-1 280 1600 5.71 850 150 3-16 B-1 600 350 0.58 850 150

[0199] After that, the annealing separator was applied and dried. The annealing separator contained MgO and Al ₂ O ₃ in a total solid content of 94 wt.%, and the ratio of miscible MgO and Al ₂ O ₃ was 50%:50% by mass (mass ratio 1:1), and also contained BiOCl in amount of 6 wt.% compared with the total amount of MgO and Al ₂ O ₃ . After that, the final annealing was carried out at 1200°C for 20 hours.

[0200] The excess annealing separator was removed from the obtained final annealed steel sheet by washing with water. In all of the steel sheets, no glass film (forsterite film) was formed, which was confirmed by the X-ray diffraction method.

[0201] The steel sheets after removal of the excess annealing separator by water washing were subjected to a pickling treatment using sulfuric acid at a temperature of 85°C and a concentration of 8%. Thereafter, for Tests Nos. 3-1 to 3-12 and 3-16, heat treatment was carried out by soaking under conditions such as oxygen concentration 21%, dew point 10°C, temperature 800°C, and time 30 seconds. In addition, for Test No. 3-13, heat treatment was carried out by soaking under conditions such as oxygen concentration 1%, dew point 10°C, temperature 700°C, and time 5 seconds. In addition, for Test Nos. 3-14 and 3-15, heat treatment was carried out by soaking under conditions such as oxygen concentration 21%, dew point 10°C, temperature 650°C, and time 5 seconds.

[0202] After the oxidation process, an aqueous solution was applied to the steel sheets, which mainly included aluminum phosphate and colloidal silica, the solution was calcined at 850°C for 1 minute, and thereby formed a tension insulating coating whose specific gravity was 4.5 g/m ² on the surface of the test sample. The test sample was then irradiated with a laser beam to refine the magnetic domain.

[0203] The base steel sheets of the anisotropic electrical steel sheets were chemically analyzed based on the method described above. All steel sheets contained in their chemical composition, in wt%, 0.002% or less C, 0.005% or less S (0.005% or less S+Se), 0.005% or less sol. Al, and 0.005% or less N. Except Moreover, the Si content, the Mn content and the Pb content in all steel sheets were the same as in the steel slabs (steel billets). Further, in all steel sheets including Bi or Te, the Bi content was 0.0001% and the Te content was 0.0001%. In addition, in all steel sheets, the rest of the composition consisted of Fe and impurities.

<Score>

[0204] Fourier transform infrared spectroscopy, average thickness of the iron oxide layer, magnetic characteristics, and adhesion of the insulating coating under tension were evaluated. The evaluation methods were the same as in Example 1 above.

[0205] The results obtained are shown in the following Table 8.

[0206] [Table 8]

No. Steel type Production results Assessment results Notes Ratio of absorption coefficients
with FT-IR Presence or absence of forsterite The thickness of the iron oxide layer,
nm Magnetic characteristics Adhesion _B8 ,
Tl W _17/50 , W/kg Percentage of remaining coating after bending with Ø20 Percentage of remaining coating after bending with Ø10 3-1 B-1 1.8 is absent 350 1.925 0.718 A A example according to the invention 3-2 B-1 1.7 is absent 340 1.928 0.729 A A example according to the invention 3-3 B-1 1.6 is absent 330 1.935 0.705 A A example according to the invention 3-4 B-2 1.5 is absent 320 1.958 0.639 A A example according to the invention 3-5 B-2 1.8 is absent 310 1.956 0.642 A A example according to the invention 3-6 B-2 1.7 is absent 330 1.978 0.605 A A example according to the invention 3-7 B-2 1.9 is absent 350 1.978 0.601 A A example according to the invention 3-8 B-3 2.1 is absent 290 1.978 0.601 A A example according to the invention 3-9 B-4 1.8 is absent 280 1.977 0.607 A A example according to the invention 3-10 B-5 1.9 is absent 290 1.976 0.611 A A example according to the invention 3-11 B-6 1.7 is absent 330 1.977 0.609 A A example according to the invention 3-12 B-7 1.6 is absent 320 1.976 0.605 A A example according to the invention 3-13 B-1 0.1 is absent 110 1.911 0.745 C C comparative example 3-14 B-1 16.5 is absent 120 1.915 0.751 C C comparative example 3-15 B-1 15.1 is absent 130 1.921 0.738 C C comparative example 3-16 B-1 1.6 is absent 330 1.922 0.731 A A example according to the invention

[0207] As clearly shown in Tables 6-8, since the chemical compositions of the base steel sheets were satisfied and the production conditions in Tests Nos. 3-1 to 3-12 and 3-16 were satisfied, the magnetic performance and adhesion of the insulation coating under tension were excellent. .

In addition, since among the above tests, the oxidation conditions were favorable in Tests Nos. 3-1 to 3-3, although the steel number and the heating rate in decarburization annealing in Tests Nos. 3-1 to 3-3 were the same, As in Tests Nos. 3-13 to 3-15, the magnetic performance and adhesion of the insulating coating under tension were excellent compared to Tests Nos. 3-13 to 3-15.

In addition, since the chemical compositions of the steel slabs in Tests Nos. 3-4 to 3-12 among the above tests were favorable, the magnetic characteristics were even more excellent.

In particular, since among the above tests, the average heating rate S1 and the average heating rate S2 in the heating step of decarburization annealing were favorable in addition to the favorable chemical compositions of the steel slabs in Test Nos. 3-6 to 3-12, the magnetic performance was even more excellent.

[0208] On the other hand, since the conditions for the oxidation process were not favorable in Test Nos. 3-13 to 3-15, the tension adhesion of the insulation coating was poor. In these tests, the coating peeled off prior to the bend test.

(Example 4)

[0209] Steel slabs (steel billets) with the chemical compositions shown in the following Table 9 were heated to 1350° C. and then subjected to hot rolling to obtain hot-rolled steel sheets having an average thickness of 2.3 mm.

[0210] [Table 9]

Steel type Production conditions The chemical composition of the slab (steel billet) (unit: mass%, the rest consists of Fe and impurities) C Si Mn S S+Se Solvent Al N Bi Sb sn Cr Cu C-1 0.081 3.35 0.081 0.022 0.022 0.025 0.008 C-2 0.083 3.25 0.082 0.023 0.023 0.025 0.008 0.0031 C-3 0.082 3.30 0.082 0.023 0.023 0.025 0.008 C-4 0.081 3.30 0.083 0.022 0.022 0.025 0.008 0.0025 C-5 0.082 3.30 0.082 0.023 0.023 0.025 0.008 0.021 C-6 0.081 3.30 0.083 0.022 0.022 0.025 0.008 0.0025 0.031 C-7 0.082 3.30 0.082 0.023 0.023 0.025 0.008 0.052 C-8 0.081 3.30 0.083 0.022 0.022 0.025 0.008 0.0025 0.051 C-9 0.082 3.30 0.082 0.023 0.023 0.025 0.008 0.021 C-10 0.081 3.30 0.083 0.022 0.022 0.025 0.008 0.0025 0.031 C-11 0.082 3.30 0.082 0.023 0.023 0.025 0.008 0.052 C-12 0.081 3.30 0.083 0.022 0.022 0.025 0.008 0.0025 0.051

[0211] The obtained hot-rolled steel sheets were annealed at 1100°C for 120 seconds and then pickled. The steel sheets after pickling were subjected to cold rolling to obtain cold-rolled steel sheets having an average thickness of 0.23 mm.

[0212] The obtained cold-rolled steel sheets were subjected to decarburization annealing. In the decarburization annealing, cold-rolled steel sheets were heated under such conditions that the average heating rate S1 in the heating step to 500°C or more and less than 600°C was 400°C/second, and the average heating rate S2 in the heating step to 600°C or more and 700°C or less - 1100°C/second (S2÷S1=2.75), and then kept at 850°C for 120 seconds.

[0213] Thereafter, final annealing was carried out under the conditions shown in the following Table 10. In Table 10, the amount of main materials in the annealing separator is shown as a percentage of solid content. In addition, the amount of bismuth chloride is shown as an amount compared to the total amount of MgO and Al ₂ O ₃ .

[0214] [Table 10]

No. Steel type Production conditions final annealing Annealing separator Temperature,
°C Time,
h Film removal Main material bismuth chloride Type I or II Quantity (total),
wt% Mass ratio
MgO/Al ₂ O ₃ Type Quantity, wt.% 4-1 C-1 I 93 1:1 BiOCl 7 1200 20 did not 4-2 C-2 I 93 1:1 BiOCl 7 1200 20 did not 4-3 C-3 II 100 1:0 Not - 1200 20 carried out 4-4 C-4 II 100 1:0 Not - 1200 20 carried out 4-5 C-5 I 95 1:1 BiOCl 5 1200 20 did not 4-6 C-6 I 95 1:1 BiOCl 5 1200 20 did not 4-7 C-7 I 95 1:1 BiOCl 5 1200 20 did not 4-8 C-8 I 95 1:1 BiOCl 5 1200 20 did not 4-9 C-3 I 89 4:6 BiOCl 12 1200 20 did not 4-10 C-4 I 96 4:6 _BiCl3 4 1200 20 did not 4-11 C-9 I 93 6:4 BiOCl eight 1200 20 did not 4-12 C-10 I 97 6:4 BiOCl 3 1200 20 did not 4-13 C-11 I 98 3:7 BiOCl 2 1200 20 did not 4-14 C-12 I 93 7:3 BiOCl 7 1200 20 did not

Note: In the table above, "I" means "MgO/Al ₂ O ₃ " and "II" means "MgO".

[0215] The excess annealing separator was removed from the resulting final annealed steel sheet by washing with water. In any of the steel sheets except for Test Nos. 4-3 and 4-4, no glass film (forsterite film) was formed, which was confirmed by X-ray diffraction. In the steel sheets of Tests Nos. 4-3 and 4-4, the forsterite film formed on the surface was removed by grinding or pickling the surface of the finally annealed steel sheet after the final annealing. Thereafter, the absence of a glass film (forsterite film) in all of the steel sheets was confirmed by an X-ray diffraction method.

[0216] The steel sheets after removing the excess annealing separator by water washing (the steel sheets after removing the glass film in Tests Nos. 4-3 and 4-4) were pickled under the conditions shown in the following Table 11. Here, in Tests Nos. 4 -1 and 4-2 shown in Table 11, the etching treatment in the oxidation process was not performed, and the oxygen concentration in the atmosphere during the heat treatment was 0 vol.% (25 vol.% nitrogen and 75 vol.% hydrogen).

[0217] [Table 11]

No. Steel type Production conditions Oxidation process flushing Etching Heat treatment Washing method sulfuric acid concentration,
wt% Temperature,
°C oxygen concentration,
about.% Dew point,
°C Temperature,
°C Time,
with 4-1 C-1 flushing with water did not did not Note 1 -2 800 fifteen 4-2 C-2 flushing with water did not did not Note 1 -ten 800 fifteen 4-3 C-3 flushing with water fifteen 75 20 ten 800 20 4-4 C-4 flushing with water fifteen 75 20 ten 800 20 4-5 C-5 flushing with water fifteen 75 20 ten 800 20 4-6 C-6 flushing with water fifteen 75 20 ten 800 20 4-7 C-7 flushing with water fifteen 75 20 ten 800 20 4-8 C-8 flushing with water fifteen 75 20 fifteen 800 20 4-9 C-3 flushing with water fifteen 75 ten eight 800 20 4-10 C-4 flushing with water fifteen 75 fifteen fifteen 800 20 4-11 C-9 flushing with water fifteen 75 ten 5 800 20 4-12 C-10 flushing with water fifteen 75 fifteen fifteen 800 20 4-13 C-11 flushing with water fifteen 75 ten fifteen 800 20 4-14 C-12 flushing with water fifteen 75 fifteen 20 800 20

Note 1: The oxygen concentration was 0% (25% nitrogen and 75% hydrogen).

[0218] After the oxidation process, an aqueous solution was applied to the steel sheets, which mainly included aluminum phosphate and colloidal silica, the solution was calcined at 850°C for 1 minute except for tests Nos. 4-1 and 4-2, the solution was calcined at 850 °C for 30 minutes in Tests Nos. 4-1 and 4-2, and thereby formed a tension insulating coating whose specific gravity was 4.5 g/m ² on the surface of the test piece. The test sample was then irradiated with a laser beam to refine the magnetic domain.

[0219] The base steel sheets of the anisotropic electrical steel sheets were chemically analyzed based on the method described above. The chemical compositions are shown in Table 12. In Tables 9 and 12, an element whose value is not indicated means an element that was not purposefully controlled during manufacture.

[0220] [Table 12]

No. Steel type Production results Chemical composition of the base steel sheet in the anisotropic electrical steel sheet (unit: wt%, the rest consists of Fe and impurities) C Si Mn S S+Se Solvent Al N Bi Sb sn Cr Cu 4-1 C-1 ≤0.002 3.35 0.081 ≤0.005 ≤0.005 ≤0.005 ≤0.005 4-2 C-2 ≤0.002 3.25 0.082 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.0001 4-3 C-3 ≤0.002 3.30 0.082 ≤0.005 ≤0.005 ≤0.005 ≤0.005 4-4 C-4 ≤0.002 3.30 0.083 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.0001 4-5 C-5 ≤0.002 3.30 0.082 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.021 4-6 C-6 ≤0.002 3.30 0.083 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.0001 0.031 4-7 C-7 ≤0.002 3.30 0.082 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.052 4-8 C-8 ≤0.002 3.30 0.083 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.0001 0.051 4-9 C-3 ≤0.002 3.30 0.082 ≤0.005 ≤0.005 ≤0.005 ≤0.005 4-10 C-4 ≤0.002 3.30 0.083 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.0001 4-11 C-9 ≤0.002 3.30 0.082 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.021 4-12 C-10 ≤0.002 3.30 0.083 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.0001 0.031 4-13 C-11 ≤0.002 3.30 0.082 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.052 4-14 C-12 ≤0.002 3.30 0.083 ≤0.005 ≤0.005 ≤0.005 ≤0.005 0.0001 0.051

<Score>

[0221] Fourier transform infrared spectroscopy, average thickness of the iron oxide layer, magnetic characteristics, and adhesion of the insulating coating under tension were evaluated. The evaluation methods were the same as in Example 1 above.

[0222] The results obtained are shown in the following Table 13.

[0223] [Table 13]

No. Steel type Production results Assessment results Notes FT-IR absorbance ratio Presence or absence of forsterite Thickness
iron oxide layer
nm Magnetic characteristics Adhesion _B8 ,
Tl W _17/50 , W/kg share
remaining coverage
after bending with Ø20 Share of the remaining
coatings after bending with Ø10 4-1 C-1 0.1 is absent 20 1.925 0.741 C C comparative example 4-2 C-2 0.1 is absent 20 1.969 0.735 C C comparative example 4-3 C-3 2.3 is absent 370 1.931 0.702 A A example according to the invention 4-4 C-4 2.5 is absent 405 1.971 0.632 A A example according to the invention 4-5 C-5 2.3 is absent 385 1.933 0.701 A A example according to the invention 4-6 C-6 2.5 is absent 405 1.973 0.631 A A example according to the invention 4-7 C-7 2.3 is absent 375 1.933 0.701 A A example according to the invention 4-8 C-8 2.5 is absent 405 1.973 0.630 A A example according to the invention 4-9 C-3 2.8 is absent 390 1,930 0.703 A A example according to the invention 4-10 C-4 2.8 is absent 410 1,970 0.634 A A example according to the invention 4-11 C-9 2.7 is absent 395 1.932 0.703 A A example according to the invention 4-12 C-10 3.1 is absent 415 1.972 0.637 A A example according to the invention 4-13 C-11 3.2 is absent 385 1.934 0.712 A A example according to the invention 4-14 C-12 3.1 is absent 410 1.974 0.639 A A example according to the invention

[0224] As clearly shown in Tables 9-13, since the chemical compositions of the base steel sheets were satisfied and the production conditions in Tests Nos. 4-3 to 4-14 were satisfied, both the magnetic performance and the adhesion of the insulating coating under tension were excellent. On the other hand, since the production conditions were not favorable in Test Nos. 4-1 and 4-2, the tension adhesion of the insulation coating was poor.

LIST OF REFERENCES

[0225] 10 - Anisotropic Electrical Steel Sheet

11 - Main steel sheet

13 - Iron oxide layer

15 - Insulating coating with tension

Claims (67)

1. An anisotropic electrical steel sheet without a forsterite film, characterized in that anisotropic electrical steel sheet contains: main steel sheet; an oxide layer located in contact with the base steel sheet; and tensioned insulating coating in contact with the oxide layer, moreover, the main steel sheet includes in its chemical composition, wt.%: 2.5-4.0 Si, 0.05-1.00 Mn, 0.01 or less C, 0-0.005 S+Se, 0-0.01 sol. Al, 0-0.005N, 0-0.03 Bi, 0-0.03 Those 0-0.03Pb, 0-0.50 Sb, 0-0.50 Sn, 0-0.50Cr, 0-1.0 Cu and the rest, consisting of iron and impurities, the oxide layer is an iron oxide layer, when the iron oxide layer is analyzed by Fourier transform infrared spectroscopy, when A ₆₅₀ is the absorption coefficient of the absorption peak detected at 650 cm ^-1 in the infrared absorption spectrum, and when A ₁₂₅₀ is the absorption coefficient of the absorption peak detected at 1250 cm ^-1 in the infrared absorption spectrum, A ₆₅₀ and A ₁₂₅₀ satisfy the condition 0.2≤A ₆₅₀ /A ₁₂₅₀ ≤5.0 and the magnetic induction B8 in the rolling direction of the anisotropic electrical steel sheet is 1.90 T or more. 2. Sheet according to claim. 1, in which the average thickness of the iron oxide layer is 200-500 nm. 3. A method for producing an anisotropic electrical steel sheet without a forsterite film according to claim 1 or 2, characterized in that the method includes: a hot rolling process of heating and then hot rolling a steel billet to obtain a hot rolled steel sheet, a hot strip annealing process, optionally annealing the hot rolled steel sheet to obtain a hot strip annealed steel sheet; a cold rolling process with cold rolling of a hot rolled steel sheet or a hot strip annealed steel sheet once or a plurality of times with intermediate annealing therebetween to obtain a cold rolled steel sheet, a decarburization annealing process with decarburization annealing of a cold rolled steel sheet to obtain a decarburized annealed steel sheet; a final annealing process of applying the annealing separator to the decarburized annealed steel sheet, and then finally annealing the decarburized annealed steel sheet to obtain a final annealed steel sheet, an oxidation process of sequentially carrying out a washing treatment, a pickling treatment, and a heat treatment of the finally annealed steel sheet to obtain an oxidized steel sheet, the process of forming an insulating coating with applying a solution for forming an insulating coating with tension on the surface of an oxidized steel sheet and calcining this solution, and during hot rolling steel billet includes in its chemical composition, wt.%: 2.5-4.0 Si, 0.05-1.00 Mn, 0.02-0.10 C, 0.005-0.080 S + Se, 0.010-0.07 sol. Al, 0.005-0.020 N, 0-0.03 Bi, 0-0.03 Those 0-0.03Pb, 0-0.50 Sb, 0-0.50 Sn, 0-0.50Cr, 0-1.0 Cu and the rest, consisting of iron and impurities, and while in the process of oxidation as the washing treatment, the surface of the final annealed steel sheet is washed, as the pickling treatment, the final annealed steel sheet is pickled using 5 to 20 mass% sulfuric acid and as a heat treatment, the finally annealed steel sheet is kept in a temperature range of 700-850°C for 10-50 seconds in an atmosphere with an oxygen concentration of 5-21% by volume and a dew point of -10 to 30°C. 4. The method according to p. 3, in which during the final annealing the annealing separator includes MgO and Al ₂ O ₃ in a total amount of 85 mass% or more, MgO:Al ₂ O ₃ , which is the mass ratio of MgO and Al ₂ O ₃ , satisfies the condition from 3:7 to 7:3 and the annealing separator includes bismuth chloride in an amount of 0.5-15 wt.% compared with the total amount of MgO and Al ₂ O ₃ . 5. The method according to p. 3, in which during the final annealing the annealing separator includes MgO in an amount of 60% by mass or more, and the forsterite film formed on the surface is removed by grinding or pickling the surface of the finally annealed steel sheet after the final annealing. 6. The method according to any one of paragraphs. 3-5, in which during the decarburization annealing process, when S1 is the average heating rate in units of °C/second in the temperature range of 500°C or more and less than 600°C at the time of temperature rise of the cold-rolled steel sheet, and when S2 is the average heating rate in units of °C/second in the temperature range of 600° C or more and 700°C or less during the temperature rise of the cold rolled steel sheet, S1 and S2 satisfy the conditions 300≤S1≤1000, 1000≤S2≤3000 and 1.0<S2/S1≤10.0. 7. The method according to any one of paragraphs. 3-6, in which during the hot rolling process, the steel billet includes in its chemical composition, wt.%, at least one element selected from the group consisting of 0.0005-0.03 Bi, 0.0005-0.03 Those and 0.0005-0.03 Pb.

Images