RU2776385C1 - Anisotropic electrical steel sheet and its production method - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, namely to a sheet of anisotropic electrical steel used as a material for iron cores of transformers. An electrical steel sheet contains a main steel sheet, a silicon-containing oxide layer provided on the main steel sheet, an iron-based oxide layer provided on a silicon-containing oxide layer, and a tension insulation coating provided on an iron-based oxide layer having a thickness of 1-3 mcm and containing phosphate and colloidal silica as the main components. The main steel sheet contains as chemical components, wt. %: 2.5-4.5% Si, 0.05-1.00% Mn, 0% or more and less than 0.05% Al, less than 0.1% C, 0% or more and less than 0.05% N, 0% or more and less than 0.1% S, 0% or more and less than 0.05% Se, 0% or more and less than 0.01% Bi, and the rest is Fe and impurities. When an insulating coating is subjected to elemental analysis using optical glow discharge emission spectrometry in the direction along the thickness of the sheet from the surface of the insulating coating with tension, there are two or more peaks of Si emission intensity, peak A, which is the peak of Si emission intensity, present furthest towards the main steel sheet in the direction along the thickness of the sheet, is present between the point of inflection, in which the rate of increase in the intensity of Fe emission changes in the direction along the thickness of the sheet from the surface of the insulation coating with tension, and the saturation point at which the intensity of Fe emission becomes saturated, and when the length of the perpendicular line drawn from the peak vertex to the baseline connecting the troughs closest to the peak is defined as the peak height, the peak height A is equal to the Si emission intensity in the main steel sheet multiplied by 0.30 or more and 2.5 or less.

EFFECT: sheet has excellent magnetic characteristics and adhesion of the insulating coating.

6 cl, 4 dwg, 1 tbl

Description

[0001] The present invention relates to an anisotropic electrical steel sheet and a method for producing the same. Priority is claimed from Japanese Patent Application No. 2019-5238, filed January 16, 2019, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] Generally, anisotropic electrical steel sheets are used as iron cores for transformers and the like, and the magnetic characteristics of the anisotropic electrical steel sheets have a significant effect on the performance of transformers. Therefore, various research and development activities have been carried out to improve the magnetic performance. As a means for reducing magnetic loss in anisotropic electrical steel sheets, for example, Patent Document 1 describes a method of forming a tension-applying coating by applying a solution containing colloidal silica and phosphate as main components to the surface of a steel sheet that has been finished annealed, and calcining them to reduce magnetic losses. In addition, Patent Document 2 describes a method for irradiating the surface of a material that has been finished annealed with a laser beam to create local deformations in a steel sheet to separate magnetic domains and reduce magnetic loss. With these methods, the magnetic loss in anisotropic electrical steel sheets has become extremely good.

[0003] At the same time, in recent years, there has been a growing need to reduce the size and improve the performance of transformers. In addition, in order to reduce the size of transformers, anisotropic electrical steel sheets with excellent magnetic loss in a strong magnetic field are required so that excellent magnetic loss is ensured even at high magnetic induction. As a means for improving magnetic loss in a strong magnetic field, studies have been made to eliminate the inorganic coating present on a conventional anisotropic electrical steel sheet in order to apply more tension. Since the tension-applying coating is formed later, in some cases the inorganic coating may be referred to as a "primary coating" and the tension-applied coating may be referred to as a "secondary coating".

[0004] Inorganic coatings containing forsterite (Mg ₂ SiO ₄ ) as the main component are created on the surfaces of anisotropic electrical steel sheets by causing the formation of oxide layers containing silica (SiO ₂ ) as the main component in the process of decarburization annealing and deposition of oxides magnesium to the surface to prevent sticking during final annealing. The inorganic coatings have a weak tension effect and also have the effect of improving magnetic loss in anisotropic electrical steel sheets. However, as a result of the studies carried out, it became clear that since inorganic coatings are non-magnetic layers, they adversely affect the magnetic characteristics (in particular, the characteristics of magnetic losses in a strong magnetic field). Therefore, studies have been carried out regarding methods for producing anisotropic electrical steel sheets in which no inorganic coatings are provided, or methods for providing mirror surfaces of steel sheets (methods of magnetically smoothing the surfaces of steel sheets) by removing inorganic coatings using mechanical means such as polishing, or chemical means such as etching, or preventing the formation of inorganic coatings during high temperature finishing annealing.

[0005] As methods for preventing the formation of such inorganic coatings or smoothing the surfaces of steel sheets, for example, Patent Document 3 describes a method for carrying out conventional final annealing of the surface of the steel sheet, pickling to remove surface formations, and then making the surface of the steel sheet mirror by chemical or electrolytic polishing . In recent years, for example, the one described in Patent Document 4 and the like has been developed. a method for preventing the formation of an inorganic coating by introducing bismuth (Bi) or a bismuth compound into the annealing separator used during the final annealing. It has been found that an excellent magnetic loss reducing effect can be obtained by forming tension-applying coatings on the surfaces of anisotropic electrical steel sheets which are produced by these known methods and which do not contain inorganic coatings or which have excellent magnetic smoothness.

[0006] However, the inorganic coatings should have the effect of exhibiting insulating properties, serve as interlayers to provide adhesion in the application of insulating coatings under tension, and serve as intermediate layers of inorganic coatings when tension-applying secondary coatings are formed on anisotropic electrical steel sheets. , in which inorganic coatings are not provided.

[0007] That is, although an inorganic coating is formed on the surface of a steel sheet that has been finished annealed, when the anisotropic electrical steel sheet is produced by a conventional manufacturing process, such an inorganic coating is formed in a state of deep penetration into the steel sheet. Thus, the inorganic coating has good adhesion to the metal steel sheet. For this reason, a tensile insulating coating containing colloidal silica, phosphate, and the like can be formed on the surface of the inorganic coating. as the main component. At the same time, in most cases, the metal does not bond well with oxides. Thus, in the absence of an inorganic coating, it is not easy to ensure sufficient adhesion between the tension insulating coating and the surface of the electrical steel sheet.

[0008] As the method described above for improving the adhesion between a steel sheet and an insulating coating under tension, for example, Patent Document 5 describes a method for forming an iron-based oxide by annealing an anisotropic electrical steel sheet containing no inorganic coating in an acidic atmosphere, forming a coating of SiO ₂ on the surface of a steel sheet by further annealing the anisotropic electrical steel sheet in a weakly reducing atmosphere, followed by forming an insulating coating under tension.

[0009] In addition, as a method for reducing magnetic loss in an anisotropic electrical steel sheet having no inorganic coating, for example, Patent Document 6 describes a method for forming a nitride/oxide layer that contains Si as a ground layer for an insulating coating under tension by adhering active Si to a surface of an anisotropic electrical steel sheet having no inorganic coating, and then forming an insulating coating under tension.

BIBLIOGRAPHY

PATENT DOCUMENTS

[0010] Patent Document 1: Japanese Patent Application Pending, First Publication No. S48-39338

Patent Document 2: Japanese Unexamined Patent Application Second Publication No. S58-26405

Patent Document 3: Japanese Unexamined Patent Application First Publication No. S49-96920

Patent Document 4: Japanese Unexamined Patent Application First Publication No. H7-54155

Patent Document 5: Japanese Patent No. 4041289

Patent Document 6: Japanese Patent No. 4300604

SUMMARY OF THE INVENTION

PROBLEMS SOLVED BY THE INVENTION

[0011] However, even with the methods disclosed in the above-mentioned Patent Document 5 and Patent Document 6, there remain opportunities for improving adhesion and magnetic loss in an anisotropic electrical steel sheet that does not have an inorganic coating.

[0012] Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an anisotropic electrical steel sheet and a production method thereof, in which the adhesion of the insulating coating under tension is stably improved and excellent magnetic characteristics can be realized, even when this anisotropic electrical sheet has no inorganic coating.

REMEDIES FOR SOLVING THE PROBLEM

[0013] In order to solve the above problem, as a result of painstaking research, the inventors of the present invention have found that the adhesion of the insulating coating under tension is stably improved and excellent magnetic characteristics can be realized by subjecting an anisotropic electrical steel sheet having no inorganic coating to a pickling treatment using a particular acid. and heat treatment, and then further subjecting the anisotropic electrical steel sheet to a pickling treatment to form an iron-based oxide layer and a silicon-containing oxide layer in a special state between the tension insulating coating and the base steel sheet. The gist of the present invention, based on the above findings, is as follows.

[0014] [1] The anisotropic electrical steel sheet according to one aspect of the present invention is an anisotropic electrical steel sheet having no inorganic coating containing forsterite as a main component, including:

main steel sheet;

a silicon-containing oxide layer provided on the base steel sheet;

an iron-based oxide layer provided on the silicon-containing oxide layer; and

a tension insulating coating provided on an iron-based oxide layer having a thickness of 1-3 µm and containing phosphate and colloidal silica as main components,

moreover, the main steel sheet contains as chemical components, in wt.%, 2.5-4.5% Si, 0.05-1.00% Mn, 0% or more and less than 0.05% Al, 0% or more and less than 0.1% C, 0% or more and less than 0.05% N, 0% or more and less than 0.1% S, 0% or more and less than 0.05% Se, 0% or more and less than 0.01% Bi, and the rest is Fe and impurities, and

when the tensioned insulation coating is subjected to elemental analysis using glow discharge optical emission spectrometry in the thickness direction of the sheet from the surface of the tensioned insulation coating,

(a) there are two or more Si emission intensity peaks;

(b) peak A, which is the Si emission intensity peak present farthest towards the base steel sheet in the thickness direction of the sheet, is present between the inflection point at which the rate of increase in the intensity of Fe emission in the thickness direction from the surface of the insulating coating changes with tension, and a saturation point at which the Fe emission intensity becomes saturated; and

(c) when the length of a perpendicular line drawn from the top of the peak to the base line connecting the troughs closest to the peak is defined as the height of the peak, the peak height A is equal to times 0.30 or more and 2.5 or less of the Si emission intensity in the main steel sheet.

[2] In the anisotropic electrical steel sheet according to [1], the silicon-containing oxide layer may contain silica and fayalite as main components, and the tension insulating coating may contain 25 to 45 mass% of colloidal silica, and the balance may be one or more, selected from the group consisting of aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate and iron phosphate.

[3] In the anisotropic electrical steel sheet of [1] or [2], the iron-based oxide layer may contain magnetite, hematite, and fayalite as main components.

[4] In the anisotropic electrical steel sheet according to any one of [1] to [3], the thickness of the base steel sheet may be 0.27 mm or less.

[5] A method for producing an anisotropic electrical steel sheet according to another aspect of the present invention is a method for producing an anisotropic electrical steel sheet that includes a base steel sheet and a tension insulating coating, and does not have an inorganic coating containing forsterite as a main component, including :

washing process with surface cleaning of anisotropic electrical steel sheet;

first surface treatment process for treating the surface of an anisotropic electrical steel sheet that has been subjected to a washing process using a first treatment liquid containing one or more of sulfuric acid, phosphoric acid and nitric acid and having a total acid concentration of 2-20% and a liquid temperature of 70 -90°C;

a heat treatment process for heating an anisotropic electrical steel sheet that has been subjected to a first surface treatment process at a temperature of 700-900°C for 10-60 seconds in an atmosphere having an oxygen concentration of 1-21% by volume and a dew point of -20 to 30° C;

a second surface treatment process of treating the surface of an anisotropic electrical steel sheet that has been subjected to a heat treatment process for 1 to 10 seconds using a second treatment liquid containing one or more of sulfuric acid, phosphoric acid and nitric acid and having a total acid concentration of 1- ten%; and

a process of forming an insulating coating with tension, which has a thickness of 1-3 μm and contains phosphate and colloidal silica as main components, on the surface of an anisotropic electrical steel sheet that has been subjected to a second surface treatment process.

[6] In the manufacturing method of the anisotropic electrical steel sheet of [5], the manufacturing method of the anisotropic electrical steel sheet may further include, before the washing process,

a hot rolling process of subjecting a steel billet to hot rolling, which contains, as chemical components, in mass%, 2.5-4.5% Si, 0.05-1.00% Mn, 0.05% or less Al, 0.1% or less C, 0.05% or less N, 0.1% or less S, 0.05% or less Se, 0.01% or less Bi, and the rest is Fe and impurities;

an optional annealing process;

a cold rolling process of performing cold rolling one, two or more times with intermediate annealing performed therebetween;

decarburizing annealing process; and

a final annealing process by applying an annealing separator obtained by introducing bismuth chloride into a mixture of MgO and Al ₂ O ₃ , or an annealing separator obtained by introducing a bismuth compound and a metal compound and chlorine into a mixture of MgO and Al ₂ O ₃ , drying the annealing separator, and then performing the final annealing.

EFFECTS OF THE INVENTION

[0015] As described above, according to the present invention, it is possible to stably improve the adhesion of the insulating coating under tension and realize excellent magnetic characteristics even when the anisotropic electrical steel sheet does not have an inorganic coating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is a schematic explanatory drawing of an example structure of an anisotropic electrical steel sheet according to one embodiment of the present invention.

Fig. 2 is an explanatory drawing for explaining an anisotropic electrical steel sheet according to the embodiment.

Fig. 3A is a graph illustrating an example of analysis results using glow discharge optical emission spectrometry of an anisotropic electrical steel sheet according to an embodiment.

Fig. 3B is a graph illustrating an example of the results of a glow discharge optical emission spectroscopy analysis of an anisotropic electrical steel sheet having poor insulating coating adhesion under tension.

Fig. 4 is a flowchart showing an example of a process flow of a method for manufacturing an anisotropic electrical steel sheet according to the embodiment.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0017] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present description and the drawings, constituent elements having essentially the same functional structure are denoted by the same reference numerals, and their repeated description is omitted.

(Relative to anisotropic electrical steel sheet)

[0018] First, an anisotropic electrical steel sheet according to one embodiment of the present invention will be described in detail with reference to FIG. 1 and 2. FIG. 1 is a schematic explanatory drawing of one example of the structure of an anisotropic electrical steel sheet according to this embodiment. Fig. 2 is an explanatory drawing for explaining an anisotropic electrical steel sheet according to this embodiment.

[0019] The present inventors found that (1), for example, for magnetic loss in a strong magnetic field such as 1.7 T to 1.9 T, the magnetic loss is greatly reduced when an inorganic coating such as forsterite is removed ( Mg ₂ SiO ₄ ), and that (2) in order to form a tension insulating coating which exhibits a high tension of 1.0 kgf/mm ² or more and which has high adhesion on the surface of a steel sheet not having an inorganic coating, the formation of silicon-containing oxide layer and iron-based oxide layer in this order on the surface of the steel sheet, and good adhesion of the insulating coating under tension and magnetic loss in a strong magnetic field are ensured by forming such a silicon-containing oxide layer and iron-based oxide layer. Based on the above-described findings, the present inventors have developed an anisotropic electrical steel sheet according to this embodiment.

[0020] The anisotropic electrical steel sheet 1 according to this embodiment is an anisotropic electrical steel sheet having no inorganic coating containing forsterite as a main component, and as schematically illustrated in FIG. 1, includes:

base steel sheet 11;

a silicon-containing oxide layer 17 which is provided on the base steel sheet;

an iron-based oxide layer 15 which is provided on the silicon-containing oxide layer; and

the tension insulating coating 13, which is provided on the iron-based oxide layer, has a thickness of 1-3 µm and contains phosphate and colloidal silica as main components.

As schematically illustrated in FIG. 1, a silicon-containing oxide layer 17, an iron-based oxide layer 15, and a tension insulating coating 13 are provided on both surfaces of the base steel sheet 11. Although FIG. 1 illustrates a case in which the silicon-containing oxide layer 17, the iron-based oxide layer 15, and the insulating coating 13 under tension are provided on both surfaces of the base steel sheet 11, the silicon-containing oxide layer 17, the iron-based oxide layer 15, and the insulating coating 13 under tension some cases may be provided only on one surface of the main steel sheet 11.

[0021] Next, the base steel sheet 11, the tension insulating coating 13 (which may be referred to simply as "insulating coating" in some cases hereinafter), the iron-based oxide layer 15, and the silicon-containing oxide layer 17 constituting the sheet will be described in detail. anisotropic electrical steel 1 according to this embodiment.

<Regarding base steel sheet 11>

[0022] Generally, although the anisotropic electrical steel sheet contains silicon (Si) as a chemical component, the silicon is extremely easy to oxidize. Thus, a silicon-containing oxide coating (more specifically, an oxide coating containing silica as a main component) is formed on the surface of the steel sheet that has been subjected to decarburization annealing. After applying the annealing separator to the surface of the steel sheet that has been subjected to decarburization annealing, the steel sheet is coiled and subjected to final annealing. In the conventional production method of anisotropic electrical steel sheet, an inorganic coating containing forsterite (Mg ₂ SiO ₄ ) as a main component is formed by reacting MgO and the oxide coating of the surface of the steel sheet with each other during final annealing using an annealing separator containing MgO as main component. However, the anisotropic electrical steel sheet 1 according to this embodiment is not an anisotropic electrical steel sheet that has an inorganic coating formed on its surface containing forsterite as a main component as described above, and an anisotropic electrical steel sheet is used as the base steel sheet 11, not having an inorganic coating formed on its surface containing forsterite as the main component.

[0023] A method for producing an anisotropic electrical steel sheet having no inorganic coating containing forsterite as a main component on its surface will again be described below.

[0024] In the anisotropic electrical steel sheet 1 according to this embodiment, the anisotropic electrical steel sheet used as the base steel sheet 11 is not particularly limited, and an anisotropic electrical steel sheet containing known chemical components can be used. Examples of such an anisotropic electrical steel sheet include an anisotropic electrical steel sheet containing as chemical components, in mass%, 2.5-4.5% Si, 0.05-1.00% Mn, 0% or more and less than 0 .05% Al, 0% or more and less 0.1% C, 0% or more and less 0.05% N, 0% or more and less 0.1% S, 0% or more and less 0.05 % Se, 0% or more and less than 0.01% Bi, and the rest is Fe and impurities.

[0025] When the Si content in the base steel sheet is 2.5 mass% or more, desired magnetic characteristics can be obtained. On the other hand, when the content of Si in the base steel sheet exceeds 4.5 mass%, a brittle steel sheet is obtained, which makes production difficult. For this reason, the content of Si in the base steel sheet is 4.5 mass% or less.

[0026] When the content of Mn in the base steel sheet is 0.05 mass% or more, it is possible to provide the absolute amount of MnS, which is an inhibitor, required for secondary recrystallization to proceed. On the other hand, when the Mn content in the base steel sheet is more than 1.00 wt%, the steel undergoes a phase transformation in the secondary recrystallization annealing, sufficient secondary recrystallization does not occur, and good magnetic induction and magnetic loss characteristics cannot be obtained. For this reason, the content of Mn in the base steel sheet is 1.00 mass% or less.

[0027] In addition to Si and Mn, the base steel sheet may contain as chemical components less than 0.05 mass% Al, less than 0.1 mass% C, less than 0.05 mass% N, less than 0.1 wt.% S, less than 0.05 wt.% Se and less than 0.01 wt.% Bi. Since these elements do not need to be contained, the lower limit of their content is 0 wt.%.

When the Al content in the base steel sheet is more than 0 mass% and less than 0.05 mass%, it is possible to improve the magnetic loss characteristics while minimizing the embrittlement of the steel sheet.

When the content of C in the base steel sheet is more than 0 wt% and less than 0.1 wt%, it is possible to realize good magnetic induction and magnetic loss characteristics.

When the N content in the base steel sheet is more than 0 wt.% and less than 0.05 wt.%, it is possible to minimize the decrease in permeability during production.

When the content of S in the base steel sheet is more than 0 wt.% and less than 0.1 wt.%, it is possible to minimize the embrittlement of the steel sheet.

When the Se content in the base steel sheet is 0 wt% or more and less than 0.05 wt%, it is possible to realize a magnetic enhancement effect.

When the content of Bi in the base steel sheet is 0 mass% or more and less than 0.01 mass%, it is possible to realize good magnetic induction and magnetic loss characteristics.

[0028] The microstructure 21 schematically illustrated in FIG. 2, which is also called an etch pit, is provided on the surface of the base steel sheet 11 according to this embodiment. In the production method of the anisotropic electrical steel sheet according to this embodiment, which will be described later, the microstructure 21 is formed by subjecting the first treatment liquid containing a specific acid to the surface of the anisotropic electrical steel sheet, which has no inorganic coating and has been final annealed, to react . When the microstructure 21 schematically illustrated in FIG. 2 is provided on the surface of the base steel sheet 11, the adhesion between the silicon-containing oxide layer 17 and the iron-based oxide layer 15 formed on the surface of the base steel sheet 11 and the base steel sheet 11 is further improved due to the so-called anchoring effect.

<Regarding the insulating cover 13 with tension>

[0029] A tensile insulating coating 13 is provided on the surface of the anisotropic electrical steel sheet 1 according to this embodiment. The tensile insulating coating 13 reduces eddy current losses by imparting electrical insulating properties to the anisotropic electrical steel sheet, and reduces magnetic losses in the anisotropic electrical steel sheet. In addition, the tensioned insulating coating 13 exhibits various characteristics such as corrosion resistance, heat resistance, and slipperiness in addition to the electrical insulating properties described above.

[0030] In addition, the tension insulating coating 13 has a function of applying tension to the anisotropic electrical steel sheet. The tension insulating coating 13 can reduce magnetic loss in the anisotropic electrical steel sheet by applying tension to the anisotropic electrical steel sheet to promote movement of the domain wall in the anisotropic electrical steel sheet.

[0031] The tension insulating coating 13 is a tension insulating coating of a mixed phosphate-silica system containing phosphate and colloidal silica as main components. Desirably, such a mixed phosphate-silica system tension insulation coating contains, for example, 25-45 wt.% colloidal silica, and the balance consists mainly of one or more selected from the group consisting of aluminum phosphate, magnesium phosphate, zinc phosphate , manganese phosphate, cobalt phosphate and iron phosphate.

[0032] The thickness (thickness d ₁ in Fig. 1) of the insulation coating 13 with the tension of the mixed phosphate-silica system is within the range of 1-3 µm. When the thickness of the tension coating 13 is less than 1 µm, it is not possible to sufficiently improve various characteristics such as insulation properties, corrosion resistance, heat resistance, slipperiness, and tension application properties as described above. On the other hand, when the tensioned thickness of the insulating coating 13 is more than 3 µm, the space filling ratio of the base steel sheet 11 decreases, which is not preferable. When the thickness of the insulating coating 13 with tension is within the range of 1-3 µm, a high tension of 1.0 kgf/mm ² or more can be realized. The thickness d ₁ of the tensioned insulating coating 13 is preferably within the range of 2.5-3.0 µm.

<Regarding iron-based oxide layer 15>

[0033] In the anisotropic electrical steel sheet 1 according to this embodiment, the iron-based oxide layer 15 functions as an intermediate layer between the base steel sheet 11 and the tension insulating coating 13 together with the silicon-containing oxide layer 17, which will be described later. The iron-based oxide layer 15 contains, for example, an iron-based oxide such as magnetite (Fe ₃ O ₄ ), hematite (Fe ₂ O ₃ ), and fayalite (Fe ₂ SiO ₄ ) as a main component.

[0034] Since the iron-based oxide, which is the main component of the iron-based oxide layer 15, is formed by reacting the surface of the base steel sheet 11 and oxygen with each other, good adhesion between the iron-based oxide layer 15 and the base steel sheet 11 is ensured. Further, as described above, a microstructure 21, also referred to as an etch pit, is provided on the surface of the base steel sheet 11, schematically illustrated in FIG. 2. For this reason, the iron-based oxide layer 15 formed in the microstructure 21 can further improve the adhesion between the iron-based oxide layer 15 and the base steel sheet 11 due to the so-called anchoring effect together with the silicon-containing oxide layer 17, which will be described later.

[0035] In general, improving adhesion between metal and ceramic can be difficult in many cases. On the other hand, when the anisotropic electrical steel sheet 1 according to this embodiment is provided with an iron-based oxide layer 15 between the base steel sheet 11 and the tension insulating coating 13, which is a kind of ceramic, even though the inorganic coating is not formed on the surface of the base steel sheet 11, the tension adhesion of the insulating coating 13 can be improved.

[0036] In addition, in the production method of the anisotropic electrical steel sheet according to this embodiment, the surface of the iron-based oxide layer 15 has the microstructure illustrated in FIG. 2 formed by etching processing using a second processing liquid. For this reason, it is possible to further improve the adhesion between the iron-based oxide layer 15 and the tension insulating coating 13 .

[0037] In the anisotropic electrical steel sheet 1 according to this embodiment, the thickness (thickness d ₂ in FIG. 1) of the iron-based oxide layer 15 is preferably within the range of 100-500 nm. When the thickness d _{2 of} the iron-based oxide layer 15 is less than 100 nm, the iron-based oxide layer 15 and the silicon-containing oxide layer 17 will be dissolved by the acidic processing liquid used in forming the tension insulating coating 13, which is unlikely to obtain sufficient adhesion. On the other hand, when the thickness d _{2 of} the iron-based oxide layer 15 is more than 500 nm, the iron-based oxide layer 15 is too thick, which is likely to increase partial peeling. In the anisotropic electrical steel sheet 1 according to this embodiment, the thickness d _{2 of} the iron-based oxide layer 15 is preferably within the range of 150-400 nm, and more preferably within the range of 170-250 nm.

[0038] The thickness d _{2 of} the iron-based oxide layer 15 can be specifically identified, for example, by observing the distribution of iron-oxygen bonds over the cross section of the anisotropic electrical steel sheet 1 according to this embodiment using X-ray photoelectron spectroscopy (XPS). That is, spraying is performed from the surface of the anisotropic electrical steel sheet 1 from which the insulating coating 13 has been removed under tension towards the base steel sheet 11, paying attention to the intensity of the peaks of Fe-O appearing at 712 eV and the intensity of the peaks of metallic Fe appearing at 708 eV. when using XPS, and the distance from the outer layer at which the measurement begins to the position in the depth direction at which the intensity of the Fe-O peaks appearing at 712 eV and the intensity of the metallic Fe peaks appearing at 708 eV are reversed can be defined as the thickness oxide layer 15 based on iron.

[0039] The main component of the iron-based oxide layer 15 can be specifically identified by performing an analysis using an X-ray crystal structure analysis or XPS method. Based on the measurement results, the inventors of the present invention found that the iron-based oxide layer 15 mainly contains iron oxide as a main component, as well as a small amount of silica.

<Regarding the silicon-containing oxide layer 17>

[0040] In the anisotropic electrical steel sheet 1 according to this embodiment, the silicon-containing oxide layer 17 is a layer designed to function as an intermediate layer between the base steel sheet 11 and the tension insulating coating 13 together with the iron-based oxide layer 15 described above. The silicon-containing oxide layer 17 contains silica and fayalite (Fe ₂ SiO ₄ ) as main components.

[0041] As will be described in detail later, the microstructure 21, also referred to as the etch pit, illustrated in FIG. 2 is formed on the surface of the base steel sheet 11 by treating the surface of the anisotropic electrical steel sheet having no inorganic coating using a treatment liquid containing at least one of sulfuric acid, nitric acid, and phosphoric acid, so that adhesion of the insulation coating 13 is ensured. with tension. The present inventors have found that when the adhesion of the tension coating in an anisotropic electrical steel sheet in which a microstructure has been formed on the surface of the base steel sheet is subjected to more detailed examination, under some production conditions, there are good adhesion parts and poor adhesion parts.

[0042] As a result of checking the above phenomenon, it was found that in parts with good adhesion, a silicon-containing oxide layer mainly composed of silica derived from Si diffused from the base steel sheet and fayalite (Fe ₂ SiO ₄ ) is formed on the side of the sublayer (side of the main steel sheet) of the iron-based oxide layer, and in parts with poor adhesion, the iron-based oxide layer or the silicon-containing oxide layer is absent. The fact that small amounts of the iron-based oxide layer and the silicon-containing oxide layer are provided (in other words, small thicknesses are provided) can be considered as one of the reasons why the iron-based oxide layer and the silicon-containing oxide layer are not present. It is assumed that since an acidic treatment liquid is used to form the tension coating, the adhesion improvement effect is reduced by dissolving the thin iron-based oxide layer and the silicon-containing oxide layer during the formation of the tension insulation coating. In addition, the fact that an excessive amount of an iron-based oxide layer is likely to be formed can be considered as another possible reason. It is assumed that when an excessive amount of the iron-based oxide layer is formed, an iron oxide isolated from the surface (stain) is formed, and therefore the treatment liquid used to form the tension insulating coating does not adhere to the surface of the steel sheet.

[0043] From the above results, it is clear that the formation of an iron-based oxide layer and a silicon-containing oxide layer in a suitable state is important for realizing good tension adhesion of the insulation coating.

[0044] Based on the above results, it is clear that when the anisotropic electrical steel sheet with good adhesion is analyzed using Glow Discharge Optical Emission Spectrometry (GDS), characteristic peaks are observed in the resulting GDS diagram.

[0045] FIG. 3A illustrates an example of an analysis result using GDS of an anisotropic electrical steel sheet with good adhesion, and FIG. 3B illustrates an example result of an analysis using GDS of an anisotropic electrical steel sheet with poor adhesion. For each anisotropic electrical steel sheet, a tension insulating coating is formed using a treatment fluid containing colloidal silica and aluminum phosphate. On FIG. 3A and 3B, the horizontal axis indicates the time [seconds] elapsed since the start of the analysis, and the vertical axis indicates the relative intensity of the GDS [prev]. Since GDS is a method of analyzing the surface of a sample in depth in the thickness direction when sputtering is performed, an increase in the elapsed time means that a deeper part of the sample is being analyzed. In addition, in FIG. 3A and 3B for elements other than Fe, the diagrams show three times the results obtained.

[0046] Referring to FIG. 3A and 3B, emission peaks originating from Al and emission peaks originating from Si are confirmed in a region in which the elapsed time is about 0 seconds to 40 seconds. In addition, it appears that the relative intensity of the GDS originating from P also increases slightly around 5 seconds and then gradually falls off, and there are smooth and broadly spreading emission peaks originating from P. Since these peaks contain Al, Si and P, they are obtained from the insulating cover 13 under tension. In addition, since the emission peaks originating from Fe increase with increasing elapsed time, it can be seen that an iron-based oxide layer is formed.

[0047] When considering the result of the GDS analysis of the good adhesion anisotropic electrical steel sheet illustrated in FIG. 3A, it can be seen that the emission peaks originating from Al and the emission peaks originating from P decrease monotonically, while the second emission peak originating from Si (which may hereinafter be referred to as "peak A") is observed in the A region. , surrounded by a dotted line in FIG. 3A. The second emission peak (peak A) is present between the inflection point at which the rate of increase in the intensity of the emission peak originating from Fe changes (in the case of Fig. 3A, this is the point at which the elapsed time is about 40 seconds) and the point at which the intensity saturates an emission peak originating from Fe (in the case of Fig. 3A, this is the position at which the elapsed time is about 70 seconds; hereinafter may be referred to as the "saturation point"). Although the second emission peak originating from Si (peak A) has a different elapsed time at which peaks are observed, this second emission peak originating from Si (peak A) is observed in all good adhesion anisotropic electrical steel sheets. Therefore, it can be seen that the second emission peak (peak A) is obtained from a silicon-containing oxide layer containing silica and fayalite (Fe ₂ SiO ₄ ) as main components.

[0048] In addition, as illustrated in the enlarged portion of FIG. 3A, when the line segment connecting the troughs close to the second Si-derived peak (peak A) is defined as the base line, the length of the perpendicular line drawn from the top of the second Si-derived peak (peak A) to the base line is defined as the height of the peak A. It was found that the peak height A is equal to times 0.30 or more and 2.5 or less of the emission intensity of Si in the steel (that is, the intensity of the emission of the part in which the sputtering reaches the part of the base steel sheet, and the intensity of the Si-derived peaks emission becomes constant) in all sheets of anisotropic electrical steel with good adhesion. On the other hand, it has been found that when the peak height A is less than 0.30 times or more than 2.5 times the Si emission intensity in the base steel sheet, the tension insulating coating has insufficient adhesion.

[0049] As described above, it has been found that good adhesion is ensured when the portion in which the Si element is segregated at a certain position along the depth of the anisotropic electrical steel sheet is the silicon-containing oxide layer 17 in this embodiment, and the Si element in the portion corresponding to the silicon-containing oxide layer 17 (region A in Fig. 3A) has a specific concentration (equal to or less than 0.30 times the emission intensity of Si in steel). Since the Si segregated element portion is internally obtained from Si diffusing from the base steel sheet, the Si segregated element portion exists at a position close to the base steel sheet.

[0050] On the other hand, it can be seen that although the second peaks originating from Si as described above are weakly observed as a result of the GDS analysis of the poor adhesion anisotropic electrical steel sheet illustrated in FIG. 3B, the height of such peaks is not equal to times 0.30 or more and 2.5 or less than the Si emission intensity in the steel. It has also been found that when other poor adhesion anisotropic electrical steel sheets are analyzed using GDS, Si-derived second peaks may not be observed.

[0051] Since GDS is a method for performing analysis by spraying an area having a diameter of about 5 mm, it can be assumed that as a result of the GDS analysis shown in FIG. 3A, the average behavior of each element is observed in a region of the sample having a diameter of approximately 5 mm. Therefore, in a coil in which an anisotropic electrical steel sheet is wound, when the GDS analysis result of the optional area at a position remote from the coil head by an optional distance shows the behavior shown in FIG. 3A, the part of the roll at the same distance from its head is considered to show the same GDS analysis result as shown in FIG. 3A. In addition, if the result of the GDS analysis shows the behavior shown in FIG. 3A, both at the head and at the tail of the roll, the depicted in FIG. 3A, the result of the GDS analysis shows behavior throughout the roll.

[0052] As described above, in the anisotropic electrical steel sheet 1 according to this embodiment, when the anisotropic electrical steel sheet 1 is subjected to elemental analysis using glow discharge optical emission spectrometry (GDS) in the thickness direction of the sheet from the surface of the anisotropic electrical steel sheet 1, there is a silicon-containing oxide layer 17 in which all of the following conditions (a) to (c) are satisfied.

[0053] (a) There are two or more Si emission intensity peaks.

(b) Peak A, which is the Si emission intensity peak present furthest towards the base steel sheet in the thickness direction of the sheet, is present between the inflection point at which the rate of increase in the intensity of Fe emission in the thickness direction from the surface of the insulating coating changes with tension, and the saturation point at which the Fe emission intensity saturates.

(c) When the length of a perpendicular line drawn from the top of the peak to the base line connecting the troughs closest to the peak is determined as the height of the peak, the peak height A is equal to times 0.30 or more and 2.5 or less of the Si emission intensity in the main steel sheet.

[0054] The reason why the number of Si emission intensity peaks is two or more in the above condition (1) is as follows. When an anisotropic electrical steel sheet is analyzed using GDS, shoulders (peak overlap) may occur in the Si emission peak obtained from the insulating coating under tension according to its condition, and in FIG. 3A, there may be a case in which emission peaks that are considered as one peak appear as two or more peaks. In addition, in the anisotropic electrical steel sheet, in order to apply a stronger tension, a tension insulating coating may be repeatedly formed by changing the Si concentration in the treatment liquid in some cases. In this case, a plurality of emission peaks obtained from the tensile insulation coating are observed at the left end of the GDS analysis result, as illustrated in FIG. 3A (short elapsed time=surface layer side of anisotropic electrical steel sheet). However, even when the number of Si emission intensity peaks is 3 or more, the Si segregated portion to be taken into account is from Si diffusing from the inside of the base steel sheet. Thus, it is possible to pay attention to a peak (peak A) which is present farthest towards the base steel sheet among the plurality of observed peaks.

[0055] The silicon-containing oxide layer 17 is formed when the surface of the base steel sheet 11 is subjected to the pickling treatment used to form the microstructure 21 using the first treatment liquid, and then heat treatment is performed at a predetermined temperature.

[0056] The conditions for performing depth direction analysis using GDS from the surface of an anisotropic electrical steel sheet are as follows. When the depth direction analysis using GDS is performed under the following conditions, in the anisotropic electrical steel sheet with good adhesion, the GDS analysis result illustrated in FIG. 3A. That is, in the high frequency mode of a conventional glow discharge optical emission spectrometer (eg, GDA 750 manufactured by Rigaku Co., Ltd.), when measurement is performed under conditions such as output power: 30 W; Ar pressure: 3 hPa; measurement zone: 4 mm in diameter; and measurement time: 100 seconds, it is possible to obtain the GDS analysis result illustrated in FIG. 3A.

[0057] The thickness of the silicon-containing oxide layer 17 (thickness d ₃ in Fig. 1) may be 100 nm or less, and in some cases may often be about 20-30 nm. The thickness of the silicon-containing oxide layer 17 can be calculated from the sputtering rate at GDS and the elapsed time at which the second Si-derived peak is observed, as shown in region A of FIG. 3A.

[0058] The main component of the silicon-containing oxide layer 17 can be specifically identified by analysis using X-ray crystal structure analysis or XPS.

<Regarding the thickness of the base steel sheet 11>

[0059] In the anisotropic electrical steel sheet 1 according to this embodiment, the thickness of the base steel sheet 11 (thickness d in Fig. 1) is not particularly limited, and may be 0.27 mm or less, for example. Generally, when a thin thickness of the steel sheet is provided in the anisotropic electrical steel sheet, poor adhesion of the insulating coating under tension can be caused in many cases. However, in the anisotropic electrical steel sheet 1 according to this embodiment, when the iron-based oxide layer 15 and the silicon-containing oxide layer 17 are provided, even when the thickness d is 0.27 mm or less, good tension adhesion of the insulating coating 13 can be obtained.

[0060] In this embodiment, even when the thickness d of the base steel sheet 11 is as small as 0.23 mm or less, the tension coating 13 can obtain good adhesion. In the anisotropic electrical steel sheet 1 according to this embodiment, the thickness d of the base steel sheet 11 is more preferably within the range of 0.17 to 0.23 mm. The thickness d of the base steel sheet 11 in the anisotropic electrical steel sheet 1 according to this embodiment is not limited to the above-described range.

[0061] The anisotropic electrical steel sheet according to this embodiment does not have an inorganic coating containing forsterite as a main component. The fact that "an inorganic coating containing forsterite as a main component is not formed" is determined using an analysis to be illustrated later.

[0062] In order to specifically identify each layer in the cross-sectional structure, a linear analysis is performed in the thickness direction of the sheet, and a quantitative analysis of the chemical components of each layer is performed using an energy dispersive X-ray spectroscope (EDS) attached to a scanning electron microscope (SEM) or transmission electron microscope (TEM). The elements to be quantified are the 6 elements Fe, P, Si, O, Mg and Al.

[0063] It is determined that the area of the layered structure present at the deepest position in the thickness direction of the sheet, after removing the measurement noise, in which the Fe content is 80 at.% or more and the O content is less than 30 at.%, is the area that is the main steel sheet.

[0064] With regard to the area excluding the main steel sheet that was specifically identified as described above, it is determined that the area in which, after eliminating measurement noise, the Fe content is less than 80 at.%, the P content is 5 at.% or more , and the O content is 30 at.% or more, is a tension insulating coating.

[0065] It is determined that the region excluding the base steel sheet and the tension insulating coating, which were specifically identified as described above, is an intermediate layer composed of a silicon-containing oxide layer and an iron-based oxide layer. The intermediate layer can be recognized as long as the intermediate layer has an average Fe content of less than 80 at.%, an average P content of less than 5 at.%, an average Si content of 20 at.% or more, and an average O content of 30 at.% or more as a general average. In addition, since the intermediate layer is not a forsterite coating in this embodiment, the average Mg content in the intermediate layer can satisfy the condition of less than 20 at.%. The Mg content of the intermediate layer is preferably 10 at.% or less, more preferably 5 at.% or less, and even more preferably 3 at.% or less.

[0066] As described above, in the anisotropic electrical steel sheet according to this embodiment, it is possible to further improve the adhesion of the tension coating 13 by providing an iron-based oxide layer 15 and a silicon-containing oxide layer 17 between the base steel sheet 11 and the tension coating 13 and, for example, it is possible to greatly reduce the magnetic loss in a strong magnetic field such as 1.7 T to 1.9 T.

[0067] Various magnetic characteristics such as magnetic induction and magnetic loss of the anisotropic electrical steel sheet according to this embodiment can be measured in accordance with the Epstein method provided in JIS C2550 or the single sheet magnetic measurement method (single sheet tester: SST ) specified in JIS C2556.

[0068] The anisotropic electrical steel sheet according to this embodiment has been described in detail above.

(Concerning the production method of the anisotropic electrical steel sheet)

[0069] Next, with reference to FIG. 4, the production method of the anisotropic electrical steel sheet according to this embodiment will be described in detail. Fig. 4 is a flowchart showing one example of a process flow of a method for producing an anisotropic electrical steel sheet according to the present embodiment.

[0070] In the production method of the anisotropic electrical steel sheet according to this embodiment as described above, as the base steel sheet 11, an anisotropic electrical steel sheet is used that does not have an inorganic coating containing forsterite as a main component on its surface (more specifically, anisotropic electrical steel sheet which has been finished annealed and which does not have on its surface an inorganic coating containing forsterite as the main component).

[0071] A method for producing an anisotropic electrical steel sheet having no inorganic coating is not particularly limited. For example, a method can be used, including: a hot rolling process of hot rolling a steel billet containing as chemical components, in wt%, 2.5-4.5% Si, 0.05-1.00% Mn, 0 .05% or less Al, 0.1% or less C, 0.05% or less N, 0.1% or less S, 0.05% or less Se, 0.01% or less Bi, and the rest is Fe and impurities; random annealing process; a cold rolling process of performing cold rolling one or two or more times, with intermediate annealing performed between two or more cold rollings; decarburizing annealing process; and the final annealing process. Meanwhile, in order not to form an inorganic coating, examples include, for example, a method of applying an annealing separator that does not form an inorganic coating and performing final annealing, a method of performing final annealing using a commonly used annealing separator, and then removing the generated inorganic coating using a known method such as grinding or etching, and the like.

[0072] Among the above methods, a method for performing final annealing using an annealing separator that does not form an inorganic coating is preferable because it is easier to control and also provides a good surface of the steel sheet. As such an annealing separator, for example, it is desirable to use an annealing separator in which bismuth chloride is provided in a mixture with MgO and Al ₂ O ₃ or an annealing separator in which a bismuth compound and a metal-chlorine compound are provided in a mixture with MgO and Al ₂ O ₃ .

[0073] Examples of the above-described bismuth chloride include bismuth oxychloride (BiOCl), bismuth trichloride (BiCl ₃ ), and the like. Examples of the above-described bismuth compound include bismuth oxides, bismuth hydroxides, bismuth sulfides, bismuth sulfates, bismuth phosphates, bismuth carbonates, bismuth nitrates, bismuth organic acid salts, bismuth halides, and the like. In addition, examples of the metal-chlorine compound include iron chloride, cobalt chloride, nickel chloride, and the like. The amount of bismuth chloride or chlorinated bismuth metal compound product is not particularly limited, but is preferably about 3-15 mass parts per 100 mass parts of the mixture of MgO and Al ₂ O ₃ .

[0074] Generally, in the production of anisotropic electrical steel sheet remaining after final annealing, the excess annealing separator is removed by cleaning, and then straightening and annealing are performed. On the other hand, as illustrated in FIG. 4, the method for producing an anisotropic electrical steel sheet according to this embodiment includes: removing an excess annealing separator by cleaning an anisotropic electrical steel sheet that has been final annealed and has no inorganic coating (step S101; washing process); then performing a surface treatment by reacting the surface of the steel sheet and the specific concentration acid (of the first treatment liquid) (step S103; first surface treatment process); performing heat treatment at a specific temperature in an oxidizing atmosphere (step S105; heat treatment process); and performing a surface treatment by reacting the surface of the steel sheet that has been heat treated and the specific concentration acid (second treatment liquid) (step S107; second surface treatment process). Thus, an intermediate layer mainly composed of an iron-based oxide layer and a silicon-containing oxide layer as described above is formed on the surface of the anisotropic electrical steel sheet that has been finished annealed and has no inorganic coating. Thereafter, a tension insulating coating is formed with good adhesion to an anisotropic electrical steel sheet having an iron-based oxide layer and a silicon-containing oxide layer formed thereon (step S109; tension insulating coating forming process).

<Concerning the first surface treatment process>

[0075] The first treatment liquid used in the first surface treatment process of process S103 contains one or more of sulfuric acid, nitric acid, and phosphoric acid, and has a total acid concentration of 2-20 mass% and a liquid temperature of 70-90°C. When the surface of the steel sheet is etched using the first treatment liquid, etch pits are formed on the surface of the steel sheet, and it is possible to create an active surface state which cannot be obtained normally. The microstructure 21 illustrated in FIG. 2 schematically represents etch pits formed in the surface of a steel sheet.

[0076] When the temperature of the first treatment liquid is lower than 70°C, the solubility of the first treatment liquid decreases, a precipitate is likely to form, and effective etch pits cannot be obtained. On the other hand, when the temperature of the first treatment liquid exceeds 90°C, the reactivity of the first treatment liquid becomes too high, which is not desirable because the surface of the steel sheet is excessively etched during the first surface treatment. The temperature of the first treatment liquid is preferably within the range of 75-87°C, and more preferably within the range of 80-85°C.

[0077] When the total concentration of acids in the first treatment liquid is less than 2 mass%, pickling pits cannot be suitably formed on the surface of the steel sheet, and the treatment time is long, which is industrially disadvantageous. When the total concentration of acids in the first treatment liquid exceeds 20 mass%, the surface of the steel sheet is excessively etched during the first surface treatment, which is not preferable. The total concentration of acids in the first treatment liquid is preferably within the range of 2-17 wt.%, and more preferably within the range of 2-10 wt.%.

[0078] The duration of the first surface treatment is not specifically limited. The first surface treatment process can in many cases be carried out by continuously immersing the steel sheet in a treatment bath containing the first treatment liquid. When this method is used, the time the steel sheet passes through the treatment bath is the treatment time during the first surface treatment process. When the steel sheet is dipped and passed through the treatment bath at a normal sheet passing speed, the above-described active surface state can be realized.

<Regarding the heat treatment process>

[0079] In order to form an iron-based oxide layer and a silicon-containing oxide layer on the anisotropic electrical steel sheet that has undergone the first surface treatment process, in an atmosphere in which the oxygen concentration is 1-21 vol% and the dew point is from − 20 to 30°C, heating is performed for 10 to 60 seconds so that the temperature of the steel sheet reaches 700 to 900°C (heat treatment process).

[0080] When the oxygen concentration in the atmosphere is less than 1% by volume, it takes too long for the iron-based oxide layer to form, which degrades performance. On the other hand, when the oxygen concentration in the atmosphere exceeds 21 vol%, the formed iron-based oxide layer easily becomes uneven, which is undesirable. The oxygen concentration in the atmosphere is preferably within the range of 2-21% by volume, and more preferably within the range of 15-21% by volume.

[0081] When the atmospheric dew point is less than −20°C, it takes too long for the iron-based oxide layer to form, which degrades performance. On the other hand, when the atmospheric dew point exceeds 30° C., the formed iron-based oxide layer easily becomes uneven, which is undesirable. The atmospheric dew point is preferably within the range of -10 to 25°C, and more preferably within the range of -10 to 20°C.

[0082] When the heating temperature of the steel sheet in the heat treatment process is less than 700°C, even if the heating time is 60 seconds, it is difficult to form an iron-based oxide layer and a silicon-containing oxide layer in a suitable state, which is not preferable. On the other hand, when the heating temperature of the steel sheet exceeds 900°C, the iron-based oxide layer easily becomes uneven, and a silicon-containing oxide layer in a desired state cannot be formed, which is not preferable. The heating temperature of the steel sheet during the heat treatment is preferably within the range of 750-800°C.

[0083] When the heating time is less than 10 seconds, the iron-based oxide layer and the silicon-containing oxide layer easily become uneven, which is not preferable. On the other hand, when the heating time exceeds 60 seconds, the industrial production cost increases, which is not preferable. The heating time is preferably within the range of 20-30 seconds.

[0084] When the heat treatment process is performed after the first surface treatment process, the activated surface of the anisotropic electrical steel sheet having no inorganic coating is oxidized to form an iron-based oxide layer whose thermal expansion coefficient is intermediate between that of the metal and the insulation coating, and a silicon-containing oxide layer is formed of Si diffusing from the inside of the base steel sheet. When etch pits are formed in the surface of an anisotropic electrical steel sheet and an iron-based oxide layer having a preferable thermal expansion coefficient and a silicon-containing oxide layer in a preferential segregation state are formed, by relieving the stress, further improvement in the adhesion of the insulating coating under tension and the effect of improving magnetic loss can be realized. in a strong magnetic field.

<Regarding the second surface treatment process>

[0085] The second treatment liquid used in the second surface treatment process of step S107 contains one or more of sulfuric acid, nitric acid, and phosphoric acid, and has a total acid concentration of 1-10% by weight. When the surface of the iron-based oxide layer is lightly etched using the second treatment liquid, etch pits are formed on the surface of the iron-based oxide layer, and an active surface state that cannot be obtained normally can be created.

[0086] The temperature of the second treatment liquid is preferably 50°C or higher and 90°C or lower. When the temperature of the second treatment liquid is less than 50°C, the solubility of the second treatment liquid decreases, it is likely to precipitate, and effective etch pits cannot be obtained. On the other hand, when the temperature of the second treatment liquid exceeds 90° C., the reactivity of the second treatment liquid becomes too high, and the iron-based oxide layer and the silicon-containing oxide layer can easily dissolve with a high probability. The temperature of the second treatment liquid is preferably within the range of 70-85°C, and more preferably within the range of 80-85°C.

[0087] When the total concentration of acids in the second treatment liquid is less than 1 wt%, etch pits cannot be properly formed on the surface of the iron-based oxide layer, and the treatment time increases, which is industrially unfavorable. When the total concentration of acids in the second treatment liquid exceeds 10 mass%, the surface of the steel sheet is excessively etched during the second surface treatment process, which is not preferable. The total concentration of acids in the second treatment liquid is preferably within the range of 1-5 wt.%, and more preferably within the range of 1-3 wt.%.

[0088] The duration of the second surface treatment process is 1 second or more and 10 seconds or less. When the treatment time is less than 1 second, etch pits cannot be properly formed on the surface of the iron-based oxide layer. On the other hand, when the treatment time exceeds 10 seconds, the surface of the steel sheet is excessively etched during the second surface treatment process, which is not preferable. The duration of the second surface treatment process is preferably within the range of 2-8 seconds, and more preferably within the range of 2-5 seconds.

<Regarding the process of forming the insulating coating under tension>

[0089] In the production method of the anisotropic electrical steel sheet according to this embodiment, the process of forming the insulating coating under tension is not particularly limited, and the insulating coating liquid can be applied and dried by a known method using the insulating coating liquid of the mixed phosphate-silica system , as will be described later. When the tension coating is formed on the surface of the steel sheet, it is possible to further improve the magnetic characteristics of the anisotropic electrical steel sheet.

[0090] The surface of the steel sheet with the insulating coating under tension formed thereon may be subjected to any pretreatment, such as an alkali degreasing treatment or the like, before applying the insulating coating liquid, or may be the surface without these pretreatments.

[0091] The insulating tension coating formed on the surface of the steel sheet is not particularly limited as long as it is used as the tension insulating coating of the mixed phosphate-silica system of the anisotropic electrical steel sheet, and the known insulating tension coating of the mixed phosphate-silica is used. systems. Examples of such a tension insulating coating include a coating containing phosphate and colloidal silica as main components. As another example, a composite insulation coating containing phosphate and colloidal silica as main components and having fine organic resin particles dispersed therein can be given.

[0092] When forming an insulating coating with tension, first, a liquid for forming an insulating coating is prepared, which contains colloidal silica in an amount of 25-45 wt.%, based on the total mass of the solid content, and the remainder of the solid content contains one or more phosphates selected from the group, consisting of aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate and iron phosphate as main components.

[0093] Desirably, the pH of the coating fluid is in the range of 1.2-3.4. When the pH value of this liquid is within the specified range, it is possible to form an insulating coating under tension in a more suitable state.

[0094] The prepared insulating coating liquid is applied to the surface of the anisotropic electrical steel sheet that has been subjected to the second surface treatment process by a known method so that the thickness after drying is 1-3 µm, dried, and calcined.

[0095] The time intervals between the first surface treatment process and the heat treatment process and between the second surface treatment process and the tension coating forming process are preferably as short as possible, for example, within a few minutes.

[0096] After the process of forming the insulating coating under tension, straightening and annealing can be performed to correct the shape. When straightening and annealing of the steel sheet are performed, the magnetic loss can be further reduced.

[0097] The production method of the anisotropic electrical steel sheet according to the present embodiment has been described in detail above.

Example

[0098] With reference to Examples and Comparative Examples, the anisotropic electrical steel sheet and the production method of the anisotropic electrical steel sheet according to the present invention will be described in detail. The examples to be illustrated below are merely examples of the anisotropic electrical steel sheet and the production method of the anisotropic electrical steel sheet according to the present invention, and the anisotropic electrical steel sheet and the production method of the anisotropic electrical steel sheet according to the present invention are not limited to the following examples.

(Experimental example)

[0099] A hot-rolled strip with a thickness of 2.2 mm was obtained by casting a steel billet (silicon steel slab) containing, in wt.%; C: 0.08%; Si: 3.24%; Mn: 0.08%; Al: 0.028%; N: 0.008%; S: 0.03%; Se: 0.01%; Bi: 0.004%, and the rest is Fe and impurities, and heating the resulting steel billet, followed by subjecting the steel billet to hot rolling. The steel billet was annealed at a steel sheet temperature of 1100°C for 60 seconds, cold rolled to a sheet thickness of 0.22 mm, and subjected to decarburization annealing at a steel sheet temperature of 830°C. Thereafter, an annealing separator containing MgO and Al ₂ O ₃ as the main components and also containing 10 wt% BiOCl, which is bismuth chloride, was applied and dried, and final annealing was performed at a steel sheet temperature of 1200°C for 20 hours ( the final annealing under these conditions is also referred to as "refining annealing"). When the excess of the annealing separator was removed by washing with water after the final annealing, no inorganic coating was formed on the surface of the steel sheet. In addition, as a result of this final annealing, the Al content was less than 0.05%, the C content was less than 0.1%, the N content was less than 0.05%, the S content was less than 0.1%, the Se content was less than 0. 05%, and the content of Bi was less than 0.01%.

[0100] The steel sheet that was finished annealed was subjected to a first surface treatment process under the conditions illustrated in Table 1, subjected to a heat treatment process under the conditions illustrated in Table 1, and then subjected to a second surface treatment process under the conditions illustrated in Table 1 After that, an insulating coating liquid containing aluminum phosphate (content: 60 wt.% on total solids) and silica (colloidal silica, i.e. silicon dioxide; average particle size 20 nm (catalog value) was applied and calcined ); content: 40 wt.% on the total mass of solids) as the main components, with the formation of an insulating coating with a tension of 2.5 μm.

[0101] The chemicals used for the first treatment fluid and the second treatment fluid were both commercially available high purity conventional reagents and commercially available high purity conventional reagents that were used for aluminum phosphate and colloidal silica.

[0102] For each of the anisotropic electrical steel sheets thus produced, the thickness d ₂ of the iron-based oxide layer was measured according to the above method using XPS (PHI5600 instrument manufactured by ULVAC-PHI), and the main components of the iron-based oxide layer were specifically identified using the method of X-ray analysis of the crystal structure. In addition, the obtained anisotropic electrical steel sheets were analyzed according to the following analysis conditions using a GDS (Glow Discharge Emission Analyzer GDA750 manufactured by Rigaku).

[0103] XPS measurement conditions

X-ray source: MgKα

Analytical area: approximately 800 µm in diameter

Depth direction analysis (sputtering rate: 2 nm/min in terms of SiO ₂ )

Measured elements: C, O, Al, Si and Fe

Measurement surface: outermost surface, after spraying for 0.1, 0.5, 1, 2, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 minutes

[0104] GDS measurement conditions

High frequency mode

Output power: 30W

Ar pressure: 3 hPa

Measurement area: 4 mm in diameter

Measurement time: 100 seconds

Measured elements: O, Al, Si, P and Fe

[0105] In addition, magnetic loss in a strong magnetic field was measured after performing laser beam irradiation and performing magnetic domain refinement processing (magnetic loss at a frequency of 50 Hz and a maximum magnetic induction of 1.7 T or 1.9 T) using the measurement method magnetic characteristics of a single sheet (single sheet tester: SST) in accordance with JIS C2556. In addition, the tension adhesion of the insulation coating was evaluated according to the following evaluation method. The results obtained are summarized in Table 1.

[0106] In Table 1, the column "peak position" in the column "Si emission intensity at GDS" indicates whether there is a Si emission intensity peak present in the part closest to the side of the base steel sheet between the position of the inflection point at which the speed changes increasing the Fe emission intensity in the thickness direction of the sheet from the surface of the anisotropic electrical steel sheet, and a saturation point at which the Fe emission intensity saturates. The grade "A" means that the Si emission intensity peak present in the part closest to the side of the base steel sheet is present between the position of the inflection point and the saturation point, and the grade "B" means that the Si emission intensity peak present in the part closest to the side of the main steel sheet, is not present between the position of the inflection point and the saturation point.

<Evaluation of adhesion of insulating coating under tension>

[0107] Tensile insulation coating adhesion was evaluated as follows. First, a sample with a width of 30 mm × a length of 300 mm was taken from each of the anisotropic electrical steel sheets, subjected to stress relief and annealing in nitrogen flow at 800°C for 2 hours, then subjected to a bending adhesion test using a cylindrical rod with a diameter of ∅10 mm, and evaluated according to the degree of peeling of the insulating coating under tension. Evaluation criteria were as follows, and A and B grades were acceptable.

Grade A: no flaking

Grade B: almost no flaking

Grade C: several mm of flaking visible

Grade D: noticeable 1/3 to 1/2 peeling

Grade E: Complete Peel

[0108] [Table 1]

No. First surface treatment heat treatment process Second surface treatment process Iron based oxide layer Si emission intensity at GDS Adhesion Magnetic loss in strong magnetic field (W/kg) Notes Acid Liquid temperature
(°C) Processing time (s) Atmosphere (vol.%) Dew point (°C) Steel sheet temperature (°C) Processing time (s) Acid Liquid temperature (°C) Processing time (s) Thickness (nm) Number of peaks Peak position The proportion of Si in steel W17/50 W19/50 one 5% sulfuric acid 80 ten 20% _O2 25 850 thirty 1% sulfuric acid 60 ten 360 2 A 0.50 B 0.65 0.96 Example 2 2% sulfuric acid 85 ten 20% _O2 -eighteen 800 40 5% sulfuric acid 70 5 200 2 A 0.36 A 0.66 0.99 Example 3 10% sulfuric acid 70 2 20% _O2 fifteen 880 ten 5% sulfuric acid 80 5 160 2 A 1.20 A 0.67 1.00 Example four 5% nitric acid 70 ten 20% _O2 28 750 55 1% nitric acid 55 3 180 2 A 0.70 B 0.63 1.04 Example 5 20% phosphoric acid 80 twenty ₂ %O2 -ten 850 thirty 7% phosphoric acid 70 3 200 2 A 2.20 B 0.62 0.91 Example 6 25% sulfuric acid 60 ten 20% _O2 fifteen 850 thirty 5% sulfuric acid 60 ten 180 2 A 0.21 C 0.66 1.01 Comparative Example 7 0.5% sulfuric acid 80 60 20% _O2 fifteen 850 thirty 1% sulfuric acid 80 60 80 0 − − E 0.68 1.07 Comparative Example eight 10% sulfuric acid 60 ten 20% _O2 fifteen 850 thirty 5% sulfuric acid 60 ten 410 0 − − E 0.71 1.08 Comparative Example 9 5% sulfuric acid 95 ten 20% _O2 fifteen 850 thirty 5% sulfuric acid 95 ten 80 2 A 0.26 D 0.67 1.15 Comparative Example ten 10% sulfuric acid 75 ten 20% _O2 twenty 600 thirty 5% sulfuric acid 75 ten 40 0 − − E 0.72 1.09 Comparative Example eleven 15% phosphoric acid 75 ten 20% _O2 twenty 1000 ten 7% phosphoric acid 80 fourteen 440 2 A 2.80 C 0.69 1.13 Comparative Example 12 5% sulfuric acid 85 ten 20% _O2 ten 800 four 5% sulfuric acid 80 ten 120 2 A 0.12 E 0.74 1.10 Comparative Example 13 5% sulfuric acid 85 ten 20% _O2 -eight 850 80 1% sulfuric acid 80 ten 320 2 A 0.08 D 0.64 1.18 Comparative Example fourteen 5% sulfuric acid 85 ten 20% _O2 fifteen 800 thirty 0.5% sulfuric acid 80 ten 240 2 A 0.21 E 0.67 1.03 Comparative Example fifteen 5% sulfuric acid 85 fifteen 20% _O2 25 750 thirty 15% sulfuric acid 80 ten 60 0 − − E 0.65 1.12 Comparative Example 16 5% sulfuric acid 85 fifteen ₂ %O2 25 850 thirty 5% sulfuric acid 80 0.5 160 2 A 0.22 E 0.63 1.08 Comparative Example 17 5% sulfuric acid 85 fifteen 20% _O2 twenty 850 fifteen 5% sulfuric acid 80 12 120 0 − − E 0.63 0.99 Comparative Example eighteen 5% sulfuric acid 80 ten Without heat treatment 1% sulfuric acid 60 ten 100 one A 0.25 E 0.72 1.21 Comparative Example 19 5% sulfuric acid 80 ten 20% _O2 fifteen 850 fifteen 7% phosphoric acid 80 5 200 2 A 0.6 B 0.64 0.97 Example

[0109] As a result of the analysis using the above-described X-ray crystal structure analysis method, the iron-based oxide layers of the samples corresponding to the examples of the present invention contained magnetite, hematite and fayalite as the main components, and silicon-containing oxide layers contained silica and fayalite as the main components . On the other hand, although iron-based oxide layers containing magnetite, hematite, and fayalite as main components were formed in the Comparative Examples outside the protection scope of the present invention, silicon-containing oxide layers showing the prescribed number of peaks and prescribed peak heights did not were formed. Samples were prepared from anisotropic electrical steel sheets according to the examples and analyzed using SEM-EDS. As a result, in the intermediate layers in the anisotropic electrical steel sheets according to the examples, the Mg content was 20 at.% or less in each case, and an inorganic coating containing forsterite as a main component was not formed.

[0110] As is clear from the above Table 1, it can be seen that the samples corresponding to the examples of the present invention have very excellent adhesion, and the magnetic loss in a strong magnetic field is improved. On the other hand, it can be seen that the samples corresponding to the comparative examples of the present invention are inferior at least either in adhesion or in magnetic loss in a strong magnetic field.

[0111] Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to such examples. Obviously, a person of ordinary skill in the technical field to which the present invention pertains will be able to develop various examples of changes or examples of modifications within the technical ideas described in the attached claims, and it should be understood that such examples also belong to the technical scope of this inventions.

LIST OF REFERENCES

[0112] 1 - Anisotropic Electrical Steel Sheet

11 - Main steel sheet

13 - Insulating coating with tension

15 - Iron-based oxide layer

17 - Silicon-containing oxide layer

21 - Microstructure (pit etching).

Claims (26)

1. Sheet of anisotropic electrical steel, not having an inorganic coating containing forsterite as a main component, including: main steel sheet; a silicon-containing oxide layer provided on the base steel sheet; an iron-based oxide layer provided on the silicon-containing oxide layer; and a tension insulating coating provided on an iron-based oxide layer having a thickness of 1-3 µm and containing phosphate and colloidal silica as main components, moreover, the main steel sheet contains as chemical components, in wt.%: 2.5-4.5% Si, 0.05-1.00% Mn, 0% or more and less than 0.05% Al, less than 0, 1% C, 0% or more and less 0.05% N, 0% or more and less 0.1% S, 0% or more and less 0.05% Se, 0% or more and less 0.01% Bi, and the rest - Fe and impurities, and when the tensioned insulation coating is subjected to elemental analysis using glow discharge optical emission spectrometry in the thickness direction of the sheet from the surface of the tensioned insulation coating, (a) there are two or more Si emission intensity peaks; (b) peak A, which is the Si emission intensity peak present farthest towards the base steel sheet in the thickness direction of the sheet, is present between the inflection point at which the rate of increase in the intensity of Fe emission in the thickness direction from the surface of the insulating coating changes with tension, and a saturation point at which the Fe emission intensity becomes saturated; and (c) when the length of a perpendicular line drawn from the top of the peak to the base line connecting the troughs closest to the peak is defined as the height of the peak, the peak height A is equal to times 0.30 or more and 2.5 or less of the Si emission intensity in the main steel sheet. 2. The anisotropic electrical steel sheet according to claim 1, wherein the silicon-containing oxide layer contains silica and fayalite as main components, and the tensile insulating coating contains 25-45 wt % colloidal silica and the balance is one or more selected from the group consisting of aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate and iron phosphate. 3. The anisotropic electrical steel sheet according to claim 1 or 2, wherein the iron-based oxide layer contains magnetite, hematite, and fayalite as main components. 4. Sheet of anisotropic electrical steel according to any one of paragraphs. 1-3, in which the thickness of the base steel sheet is 0.27 mm or less. 5. A method for producing an anisotropic electrical steel sheet including a base steel sheet and an insulating coating under tension and not having an inorganic coating containing forsterite as a main component, comprising: washing process with surface cleaning of anisotropic electrical steel sheet; first surface treatment process for treating the surface of an anisotropic electrical steel sheet that has been subjected to a washing process using a first treatment liquid containing one or more of sulfuric acid, phosphoric acid and nitric acid and having a total acid concentration of 2-20% and a liquid temperature of 70 -90°C; a heat treatment process for heating an anisotropic electrical steel sheet which has been subjected to a first surface treatment process at a temperature of 700-900°C for 10-60 seconds in an atmosphere having an oxygen concentration of 1-21 vol% and a dew point of -20 to 30 °C; a second surface treatment process of treating the surface of an anisotropic electrical steel sheet that has been subjected to a heat treatment process for 1 to 10 seconds using a second treatment liquid containing one or more of sulfuric acid, phosphoric acid and nitric acid and having a total acid concentration of 1- ten%; and a process of forming an insulating coating with tension, which has a thickness of 1-3 μm and contains phosphate and colloidal silica as main components, on the surface of an anisotropic electrical steel sheet that has been subjected to a second surface treatment process. 6. The method for producing an anisotropic electrical steel sheet according to claim 5, further comprising: before the washing process, a hot rolling process for subjecting a steel billet to hot rolling, which contains as chemical components, in wt%: 2.5-4.5% Si, 0.05-1.00% Mn, less than 0.05% Al, less than 0.1% C, less than 0.05% N, less than 0.1% S, less than 0.05% Se, less than 0.01% Bi, and the rest is Fe and impurities; an optional annealing process; a cold rolling process of performing cold rolling one or two or more times with intermediate annealing performed therebetween; decarburizing annealing process; and a final annealing process by applying an annealing separator obtained by introducing bismuth chloride into a mixture of MgO and Al ₂ O ₃ , or an annealing separator obtained by introducing a bismuth compound and a metal compound and chlorine into a mixture of MgO and Al ₂ O ₃ , drying the annealing separator, and then performing the final annealing.

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