RU2776246C1 - 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 that does not have an inorganic coating containing forsterite as the main component used as a material of iron cores of transformers. The electrical 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 an insulating coating with tension 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 has a chemical composition containing, 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 and 0% or more and less than 0.01% Bi, the rest is Fe and impurities. When performing elemental analysis by optical glow discharge emission spectrometry from the surface of an insulating coating with tension in the direction along the thickness of the sheet, there are four or more inflection points on the Si emission intensity profile, in the direction along the thickness of the sheet, the inflection point of the Si emission intensity closest to the side of the main steel sheet is present within the range of 0.3-1.5 mcm in the side of the insulation coating surface with tension from the saturation point at which the Fe emission intensity is maximum, and the peak of the Si emission intensity, the one closest to the side of the main steel sheet has an emission intensity that is multiplied by 1.3 or more and 2.0 or less than the Si emission intensity in the main steel sheet.

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

6 cl, 4 dwg, 2 tbl

Description

FIELD OF TECHNOLOGY

[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. 2019-5239, 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 for 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 calcination 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 of anisotropic electrical steel sheets has become extremely good.

[0003] In this regard, 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 the magnetic loss in a strong magnetic field, studies have been carried out 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 formed on the surfaces of anisotropic electrical steel sheets by reacting oxide layers containing silica (SiO ₂ ) as the main component formed during the decarburization annealing process with oxides magnesium applied 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 final 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 finishing annealing of the surface of the steel sheet, pickling to remove surface formations, and then imparting a mirror finish to the surface of the steel sheet 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 final annealed in the production of an anisotropic electrical steel sheet 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 and then 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 attaching 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 Examined 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 an object of the present invention is to provide an anisotropic electrical steel sheet in which the adhesion of the insulating coating under tension can be improved in a stably manner, and excellent magnetic characteristics can be realized even in case of an anisotropic electrical steel sheet without an inorganic coating, and also propose a method for its production.

REMEDIES FOR SOLVING THE PROBLEM

[0013] In order to solve the above problem, the inventors have conducted extensive research, and as a result, found that after performing pickling treatment using a specific acid and heat treatment of an anisotropic electrical steel sheet not having an inorganic coating containing forsterite as a main component, The tension insulating coating is formed under special conditions, and thus an iron-based oxide layer and a silicon-containing oxide layer in a special state are formed between the tension insulating coating and the base steel sheet, and the adhesion of the tension insulating coating can be stably improved and excellent magnetic performance can be realized. The scope of protection of the present invention, made on the basis of 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 and 0% or more and less than 0.01% Bi, and the rest: Fe and impurities,

wherein, when elemental analysis is performed from the surface of the insulating coating with tension in the thickness direction of the sheet by glow discharge optical emission spectrometry,

(a) there are four or more inflection points in the Si emission intensity profile;

(b) in the thickness direction of the sheet, the inflection point of the Si emission intensity closest to the side of the base steel sheet is present within the range of 0.3-1.5 µm towards the surface of the insulating coating with tension from the saturation point at which the emission intensity of Fe is the maximum, and

(c) the Si emission intensity peak closest to the base steel sheet side has an emission intensity that is 1.3 times or greater and 2.0 or less than the Si emission intensity in the base steel sheet.

[2] The anisotropic electrical steel sheet according to [1],

wherein the silicon-containing oxide layer may contain silica and fayalite as main components, and

while the insulating coating with tension may contain 25-45 wt.% colloidal silica, with the remainder containing one or more selected from the group consisting of aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate and iron phosphate, in as the main components.

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

[4] The anisotropic electrical steel sheet according to any one of [1] to [3], wherein 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;

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

a heat treatment process for heating a sheet of anisotropic electrical steel that has been subjected to a 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; and

a process of forming an insulating tension coating with a thickness of 1-3 µm by applying a treatment solution for forming an insulating tension coating containing phosphate and colloidal silica as main components to the surface of an anisotropic electrical steel sheet after the heat treatment process, and heating is performed at a medium heating rate 20-100°C/s within 1.0-20 seconds after application, and calcination is performed at a temperature of 850-950°C for 10-60 seconds.

[6] The production method of the anisotropic electrical steel sheet of [5] may further include:

before the washing process,

a hot rolling process for subjecting to hot rolling a steel billet which contains, as chemical components, in mass%, 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, and 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 chloride compound into a mixture of MgO and Al ₂ O ₃ , drying the annealing separator, and then performing a final annealing.

EFFECTS OF THE INVENTION

[0015] As described above, according to the present invention, even in an anisotropic electrical steel sheet having no inorganic coating containing forsterite as a main component, the adhesion of the insulating coating under tension can be stably improved and excellent magnetic characteristics can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 is an explanatory drawing schematically showing an example of the 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 same embodiment.

Fig. 3A is a graph showing an example of analysis results of an anisotropic electrical steel sheet according to the same embodiment obtained by glow discharge optical emission spectrometry.

Fig. 3B is a graph showing an example of analysis results of an anisotropic electrical steel sheet having poor adhesion of an insulating coating under tension obtained by glow discharge optical emission spectrometry.

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

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0017] In the following, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In this specification and the drawings, components having essentially the same functional configuration are designated 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 FIG. 2. FIG. 1 is an explanatory drawing schematically showing one example of the structure of an anisotropic electrical steel sheet according to the present embodiment. Fig. 2 is an explanatory drawing for explaining an anisotropic electrical steel sheet according to the present embodiment.

[0019] The inventors have 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 the inorganic coating containing forsterite (Mg ₂ SiO ₄ ) or the like is removed, and that (2) to form an insulating coating with a tension that exhibits a high tension of 1.0 kgf/ ^mm2 or more on the surface of a steel sheet not having an inorganic coating with favorable adhesion , it is required to form a silicon-containing oxide layer and an iron-based oxide layer in this order on the surface of a steel sheet, and good adhesion of the insulating coating under tension and good magnetic loss in a strong magnetic field are ensured by forming such a silicon-containing oxide layer and an iron-based oxide layer. Based on the above findings, the inventors have developed an anisotropic electrical steel sheet according to this embodiment.

[0020] The anisotropic electrical steel sheet 1 according to the present 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 provided on the base steel sheet;

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

a tension insulating coating 13 provided on the iron-based oxide layer having a thickness of 1-3 µm and containing 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 tension insulating coating 13 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 tension insulating coating 13 can be provided only on one surface of the main steel sheet 11.

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

<Regarding base steel sheet 11>

[0022] Generally, an anisotropic electrical steel sheet contains silicon (Si) as a chemical component, but silicon is very easy to oxidize, and an oxidized coating containing silicon (more specifically, an oxidized coating containing silica as the main component) is formed on the surface of the steel sheet after decarburization annealing. component). an annealing separator is applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet is wound into a roll and final annealing is performed. In a conventional method for producing anisotropic electrical steel sheet, when an annealing separator containing MgO as a main component is used, MgO reacts with an oxidized coating on the surface of the steel sheet during final annealing, and an inorganic coating is formed containing forsterite (Mg ₂ SiO ₄ ) as main component. However, in the anisotropic electrical steel sheet 1 according to the present embodiment, as the base steel sheet 11, an anisotropic electrical steel sheet having no inorganic coating containing forsterite as a main component on its surface is used instead of the above-mentioned anisotropic electrical steel sheet having on its surface an inorganic coating 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 the present embodiment, the anisotropic electrical steel sheet used as the base steel sheet 11 is not specifically 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, and 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 wt%, the steel sheet becomes brittle, making production difficult. Therefore, 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 content of Mn in the base steel sheet exceeds 1.00 mass%, the steel undergoes a phase transformation at the time of secondary recrystallization annealing, sufficient secondary recrystallization does not occur, and favorable magnetic induction and magnetic loss characteristics cannot be obtained. Therefore, the content of Mn in the base steel sheet is 1.00 mass% or less.

[0027] The base steel sheet may contain, as chemical components, less than 0.005 mass% each of Al, C, N, S, Se, and Bi in addition to Si and Mn. Since these elements do not have 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 minimize the embrittlement of the steel sheet and improve the magnetic loss performance.

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 favorable 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 0.1 wt.% or less, 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 0.05 wt% or less, 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 0.01 mass% or less, it is possible to realize favorable magnetic induction and magnetic loss characteristics.

[0028] As schematically shown in FIG. 2, on the surface of the base steel sheet 11 according to the present embodiment, a microstructure 21, also referred to as an etch pit, is provided. In the production method of the anisotropic electrical steel sheet according to the present embodiment, which will be described in detail below, the microstructure 21 is formed when a surface treatment liquid using a specific acid is applied to the surface of the anisotropic electrical steel sheet not having an inorganic coating, and subjected to finishing annealing. When the microstructure 21 schematically illustrated in FIG. 2, the silicon-containing oxide layer 17 and the iron-based oxide layer 15 formed on the surface of the base steel sheet 11 further improve adhesion to the base steel sheet 11 due to the so-called anchoring effect.

<Regarding the insulating cover 13 with tension>

[0029] An insulating coating 13 with tension is provided on the surface of the anisotropic electrical steel sheet 1 according to the present embodiment. The tension insulating coating 13 imparts electrical insulation to the anisotropic electrical steel sheet, and thus the eddy current loss is reduced and the magnetic loss in the anisotropic electrical steel sheet is reduced. In addition, the tensioned insulating coating 13 imparts various characteristics such as corrosion resistance, heat resistance, and slipperiness in addition to the above-mentioned electrical insulation.

[0030] In addition, the tension insulating coating 13 has a function of applying tension to the anisotropic electrical steel sheet. The tension insulating coating applies tension to the anisotropic electrical steel sheet, promotes motion of the domain wall in the anisotropic electrical steel sheet, and thus can reduce magnetic loss 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. The tensile insulation coating of such a mixed phosphate-silica system contains, for example, 25-45 wt.% colloidal silica, with the remainder preferably containing one or more selected from the group consisting of aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate and iron phosphate as the main components.

[0032] The thickness (thickness d ₁ in Fig. 1) of the insulation coating 13 with the tension of the mixed phosphate-silica system is in 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 electrical insulation, 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 exceeds 3 μm, this is undesirable because the space filling ratio of the base steel sheet 11 is reduced. When the thickness of the insulating coating 13 with tension is within the range of 1 to 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] The iron-based oxide layer 15 in the anisotropic electrical steel sheet 1 according to the present embodiment functions as an intermediate layer between the base steel sheet 11 and the insulating coating 13 under tension together with the silicon-containing oxide layer 17 described below. 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 ), or 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 when the surface of the base steel sheet 11 reacts with oxygen, the adhesion between the iron-based oxide layer 15 and the base steel sheet 11 is favorable. In addition, as described above and as schematically shown in FIG. 2, a microstructure 21, also referred to as an etch pit, is provided on the surface of the base steel sheet 11. Therefore, the iron-based oxide layer 15 formed on the microstructure 21 can further improve the adhesion to the base steel sheet 11 due to the so-called anchor effect together with the silicon-containing oxide layer 17 described later.

[0035] In general, it is difficult to improve the adhesion between metal and ceramic. On the other hand, in the anisotropic electrical steel sheet 1 according to the present embodiment, since the iron-based oxide layer 15 is provided between the base steel sheet 11 and the tension insulating coating 13, which is a kind of ceramic, it is possible to improve the adhesion of the insulating coating 13 with tension even if no inorganic coating is formed on the surface of the base steel sheet 11.

[0036] In the anisotropic electrical steel sheet 1 according to the present 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 may be dissolved by the acidic treatment solution used in forming the tension insulating coating 13, and there is a high probability of not obtaining sufficient adhesion. On the other hand, when the thickness d _{2 of} the iron-based oxide layer 15 exceeds 500 nm, the iron-based oxide layer 15 becomes too thick, and the possibility of partial peeling increases. In the anisotropic electrical steel sheet 1 according to the present embodiment, the thickness d _{2 of} the iron-based oxide layer 15 is preferably in the range of 150-400 nm, and more preferably in the range of 170-250 nm.

[0037] The thickness d ₂ of the iron-based oxide layer 15 can be determined by observing the distribution of iron-oxygen bonds in a section of the anisotropic electrical steel sheet 1 according to the present embodiment using X-ray photoelectron spectroscopy (XPS). That is, at XPS, focusing on the intensity of the Fe-O peaks appearing at 712 eV and the intensity of the Fe metal peaks appearing at 708 eV, sputtering is performed from the surface side of the anisotropic electrical steel sheet 1 from which the insulating coating 13 has been removed with tension, to the base steel sheet 11, the distance from the outer layer where the measurement starts to the position in the depth direction at which the intensity of the peaks of Fe-O appearing at 712 eV and the intensity of the peaks of Fe metal appearing at 708 eV are reversed can be used as the thickness oxide layer 15 based on iron.

[0038] The main component of the iron-based oxide layer 15 can be determined by performing X-ray crystal structure analysis or XPS analysis. Based on the measurement results, the inventors found that the iron-based oxide layer 15 mainly contains an iron-based oxide as a main component and a small amount of silica.

<Regarding silicon-containing oxide layer 17>

[0039] The silicon-containing oxide layer 17 is a layer functioning as an intermediate layer between the base steel sheet 11 and the insulating coating 13 under tension along with the aforementioned iron-based oxide layer 15 in the anisotropic electrical steel sheet 1 according to the present embodiment. The silicon-containing oxide layer 17 contains silica and fayalite (Fe ₂ SiO ₄ ) as main components.

[0040] As will be described below, when the surface of an anisotropic electrical steel sheet having no inorganic coating is treated using a treatment solution containing at least one of sulfuric acid, nitric acid, and phosphoric acid, a microstructure 21 is formed on the surface of the base steel sheet 11 , also called an etch pit, as shown in FIG. 2, and the adhesion of the insulating coating 13 under tension is ensured. Meanwhile, the inventors conducted a more detailed examination of the adhesion of the insulating coating under tension in an anisotropic electrical steel sheet in which such a microstructure is formed on the surface of the base steel sheet, and found that under certain production conditions, there are some parts with good adhesion and some parts with poor adhesion. .

[0041] As a result of checking the above phenomenon, it was found that in parts with good adhesion, a silicon-containing oxide layer containing silica derived from Si diffused from the base steel sheet and fayalite (Fe ₂ SiO ₄ ) as main components was formed on the side layer (on the side of the base steel sheet) below the iron-based oxide layer, and in parts with poor adhesion, the iron-based oxide layer or the silicon-containing oxide layer is absent. It is believed that one of the reasons why a portion lacking an iron-based oxide layer or a silicon-containing oxide layer is formed is that the present amount of the iron-based oxide layer and the silicon-containing oxide layer is small (in other words, their thickness is small). It is assumed that since the treatment solution used to form the tension insulation coating is acidic, the iron-based thin oxide layer and the silicon-containing oxide layer are dissolved when forming the tension insulation coating, and the adhesion improvement effect is reduced. In addition, as another possibility, the possibility of excessive formation of an iron-based oxide layer is considered. It is assumed that when an excessive amount of an iron-based oxide layer is formed, since an iron-based oxide precipitated from the surface (spot) is formed, the treatment solution for forming the tension insulating coating does not adhere to the surface of the steel sheet.

[0042] From the above findings, it has become clear that in order to realize excellent adhesion of the insulating coating under tension, it is important to form the iron-based oxide layer and the silicon-containing oxide layer in a suitable state.

[0043] From the above findings, it has become clear that when an anisotropic electrical steel sheet with favorable adhesion is analyzed by glow discharge optical emission spectrometry (GDS), a characteristic peak is observed in the obtained GDS diagram. Fig. 3A illustrates an example of results obtained from GDS analysis of an anisotropic electrical steel sheet with good adhesion, and FIG. 3B illustrates an example of results obtained from a GDS analysis of an anisotropic electrical steel sheet with poor adhesion. For each anisotropic electrical steel sheet, a tension insulating coating is formed using a treatment solution containing colloidal silica and aluminum phosphate. On FIG. 3A and FIG. 3B, the horizontal axis indicates the time [seconds] elapsed since the start of the analysis, and the vertical axis indicates the relative GDS intensity [pr.u]. Since GDS is a method of analyzing the surface of a sample in depth in the sheet thickness direction when spraying is performed, a longer elapsed time indicates that a deeper part of the sample is being analyzed. In addition, in FIG. 3A and FIG. 3B for elements other than Fe, the results are magnified by a factor of three and plotted in the figures.

[0044] Referring to FIG. 3A and FIG. 3B, an emission peak originating from Al and an emission peak originating from Si are observed in a region in which the elapsed time is from about 0 seconds to about 50 seconds. In addition, it can be seen that the relative intensity of the GDS originating from P also increases slightly around 5 seconds and then gradually decreases, and there is a smooth and wide-spreading emission peak originating from P. Since these peaks contain Al, Si and P, they come from the insulating cover 13 under tension. In addition, it can be understood that since the number of emission peaks originating from Fe increases as the elapsed time increases, an iron-based oxide layer is formed.

[0045] Focusing on the results of GDS analysis of an anisotropic electrical steel sheet with excellent adhesion shown in FIG. 3A, it can be understood that the Al-derived emission peak and the P-derived emission peak decrease monotonically, but a second Si-derived emission peak is observed in region A surrounded by a dotted line in FIG. 3A, and there are a total of four inflection points in the Si emission intensity profile. These four inflection points are observed in all favorable adhesion anisotropic electrical steel sheets, although the elapsed time corresponding to these inflection points varies. Therefore, it can be understood that the second Si emission peak present between the third inflection point and the fourth inflection point located on the base steel sheet side originates from a silicon-containing oxide layer containing silica and fayalite (Fe ₂ SiO ₄ ) as main components.

[0046] In particular, by focusing on the position of the inflection point (hereinafter, sometimes referred to as the inflection point B) closest to the side of the base steel sheet, it becomes clear that in any one of the favorable adhesion anisotropic electrical steel sheets, the position of the inflection point B is in within the range of 0.3-1.5 µm to the surface of the anisotropic electrical steel sheet (i.e., from the side of the insulating coating under tension) relative to the point at which the intensity of the Fe emission peak is maximum (in Fig. 3A, this is the position at which the elapsed time is approximately 80 seconds; hereinafter sometimes referred to as the saturation point). The distance in the thickness direction of the sheet from the saturation point of the Fe emission intensity to the inflection point (inflection point B) located closest to the side of the base steel sheet corresponds to the distance D in FIG. 3A and is D=0.8 µm in FIG. 3A. In addition, it has become clear that in any one of the favorable adhesion anisotropic electrical steel sheets, the intensity of the Si emission peak (sometimes referred to hereinafter as the B peak) closest to the side of the base steel sheet is equal to times 1.3 or more and 2 0 or less than the emission intensity of Si in the base steel sheet (that is, the emission intensity of the part in which sputtering occurs to the part of the base steel sheet, and the intensity of the emission peak originating from Si becomes constant). On FIG. 3A, the Si emission intensity of peak B is 1.8 times the Si emission intensity in the base steel sheet. On the other hand, it has become clear that when the position of the inflection point B is not within the range of 0.3-1.5 µm relative to the saturation point, or when the Si emission intensity of the B peak is less than 1.5 times or more than 3 times .5 Si emission intensity in the base steel sheet, the tension insulating coating has poor adhesion.

[0047] Here, the above-described position of the inflection point on the Si emission intensity profile can be determined by doubly differentiating the Si emission intensity profile using any known numerical calculation application and determining the position at which the intensity becomes zero on the second derivative profile.

[0048] Thus, it became clear that when the part 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 the present embodiment, and the Si element in the part (Regions A in Fig. 3A ) corresponding to the silicon-containing oxide layer 17 has a specific concentration (equal to times 1.3 times or more and 2.0 times or less of the Si emission intensity in the steel), favorable adhesion is exhibited. Since the Si segregated element part is obtained from Si diffused from the base steel sheet, this Si segregated element part is present at a position close to the base steel sheet.

[0049] On the other hand, as shown in FIG. 3B, in the GDS analysis results of anisotropic electrical steel sheets with poor adhesion, although the second peak originating from Si as described above is slightly observed, the position (distance D in FIG. 3B) of the inflection point closest to the side of the base steel sheet , is 0.4 μm, which is outside the above range, and the Si emission intensity is 1.2 of the Si emission intensity in steel, which is also outside the above range. In addition, it has become clear that when other poor adhesion anisotropic electrical steel sheets are analyzed by GDS, the second peak originating from Si is not observed, and as a result, there are no four inflection points.

[0050] Here, since GDS is an analysis method when spraying a zone with a diameter of about 5 mm, it can be considered that in the results of the GDS analysis shown in FIG. 3A, the average behavior of each element in the sample is observed in a zone 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 zone at a position remote from the coil head by an arbitrary distance is considered to show the behavior shown in FIG. 3A, parts of the roll at the same distance from its head show the same results of the GDS analysis as in FIG. 3A. In addition, it can be considered that if the results of the GDS analysis show that shown in FIG. 3A both at the head and at the tail of the coil, the results of the GDS analysis show that shown in FIG. 3A behavior throughout the roll.

[0051] As described above, in the anisotropic electrical steel sheet 1 according to the present embodiment, when elemental analysis is performed from the surface of the anisotropic electrical steel sheet 1 in the thickness direction of the anisotropic electrical steel sheet 1 by glow discharge optical emission spectrometry (GDS), there is a silicon-containing oxide layer 17 which satisfies all of the following conditions (a) to (c).

[0052] (a) There are four or more inflection points in the Si emission intensity profile.

(b) In the thickness direction of the sheet, the inflection point of the Si emission intensity closest to the base steel sheet side is present within the range of 0.3-1.5 µm towards the surface of the insulation coating with tension from the saturation point at which the Fe emission intensity is the maximum.

(c) The Si emission intensity peak closest to the side of the base steel sheet has an emission intensity that is 1.3 times or greater and 2.0 less than the Si emission intensity in the base steel sheet.

[0053] In the above condition (a), the reason why the number of inflection points in the Si emission intensity profile is four or more is as follows. When an anisotropic electrical steel sheet is analyzed by GDS, depending on the state of the insulating coating under tension, shoulders (overlapping peaks) occur at the Si emission peak originating from the insulating coating under tension, and in FIG. 3A, there may be two or more emission peaks appearing as a single peak. In addition, in the anisotropic electrical steel sheet, in order to apply a stronger tension, an insulating coating with tension can be repeatedly formed by changing the concentration of Si in the treatment solution. In this case, at the left end portion of those shown in FIG. 3A of the GDS analysis results (short elapsed time=surface layer side of the anisotropic electrical steel sheet), there are many emission peaks originating from the insulating coating under tension. As a result, four or more inflection points can be observed in the Si emission intensity profile. However, when the number of Si emission intensity inflection points is five or more, since the Si segregated portion to focus on is obtained from Si diffused from the base steel sheet, among the plurality of observed inflection points, it is possible to focus on the closest inflection point B to the side of the main steel sheet.

[0054] In the above condition (b), the position of the inflection point B of the Si emission intensity closest to the side of the base steel sheet can be calculated using the time difference between the saturation point and the inflection point B and the sputtering rate at GDS.

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

[0056] The conditions for performing depth direction analysis with GDS from the surface of the anisotropic electrical steel sheet are as follows. When the depth direction analysis is performed by GDS under the following conditions, the GDS analysis results shown in FIG. 3A. That is, in the high frequency mode of a conventional glow discharge optical emission spectrometer (for example, GDA 750 manufactured by Rigaku Corporation), measurement is performed under the conditions: output power: 30 W, Ar pressure: 3 hPa, measurement area: 4 mm in diameter, measurement time: 100 seconds, and thus the GDS analysis results shown in FIG. 3A.

[0057] The thickness (thickness d ₃ in Fig. 1) of the silicon-containing oxide layer 17 is 100 nm or less in many cases, and may be about 20-30 nm. Meanwhile, 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 peak originating from Si is observed, as shown in region A in FIG. 3A.

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

<Regarding the thickness of the base steel sheet 11>

[0059] In the anisotropic electrical steel sheet 1 according to the present embodiment, the thickness (thickness d in FIG. 1) of the base steel sheet 11 is not particularly limited, and may be 0.27 mm or less, for example. Generally, in an anisotropic electrical steel sheet, as the thickness of the steel sheet decreases, the tension adhesion of the insulation coating decreases in many cases. However, in the anisotropic electrical steel sheet 1 according to the present embodiment, when the iron-based oxide layer 15 and the silicon-containing oxide layer 17 are provided, excellent tension adhesion of the insulating coating 13 can be obtained even if the thickness d is 0.27 mm or less.

[0060] In the present embodiment, even when the thickness d of the base steel sheet 11 is as small as 0.23 mm or less, excellent tension adhesion of the insulation coating 13 can be obtained. In the anisotropic electrical steel sheet 1 according to the present embodiment, the thickness d of the base steel sheet 11 is more preferably in the range of 0.17 to 0.23 mm. Meanwhile, in the anisotropic electrical steel sheet 1 according to the present embodiment, the thickness d of the base steel sheet 11 is not limited to the above range.

[0061] The anisotropic electrical steel sheet according to the present embodiment does not have an inorganic coating containing forsterite as a main component. The state in which "an inorganic coating containing forsterite as a main component is not formed" is determined by the following analysis.

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

[0063] That region of the layered structure which is at the deepest position in the sheet thickness direction and which is the region having an Fe content of 80 at.% or more and an O content of less than 30 at.%, excluding the measurement noise, is defined as the main steel sheet.

[0064] As for the region excluding the base steel sheet defined above, that region in which 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, excluding measurement noise, defined as the insulating coating under tension.

[0065] A region excluding the base steel sheet and the tension insulating coating defined above is defined as an intermediate layer composed of a silicon-containing oxide layer and an iron-based oxide layer. The intermediate layer can satisfy, in total average, an Fe content of less than 80 at.% on average, a P content of less than 5 at.% on average, a Si content of 20 at.% or more on average, and an O content of 30 at.% or more in average. In addition, in the present embodiment, since the intermediate layer is not a forsterite coating, the intermediate layer can satisfy the Mg content of less than 20 at.% on average. 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, when the anisotropic electrical steel sheet according to the present embodiment includes an iron-based oxide layer 15 and a silicon-containing oxide layer 17 that are provided between the base steel sheet 11 and the tension insulating coating 13, it is possible to further improve adhesion of the insulating coating 13 under tension, and the magnetic loss in a strong magnetic field can also be greatly reduced, for example, from 1.7 T to 1.9 T.

[0067] Various magnetic characteristics of the anisotropic electrical steel sheet according to the present embodiment, such as magnetic induction and magnetic loss, can be measured according to the Epstein method specified in JIS C 2550 or the single sheet magnetic measurement method (single sheet tester: SST) as defined in JIS C 2556.

[0068] The anisotropic electrical steel sheet according to the present 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 manufacturing method of the anisotropic electrical steel sheet according to the present 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 the present embodiment as described above, the anisotropic electrical steel sheet having no inorganic coating containing forsterite as a main component on its surface (more specifically, the finally annealed anisotropic electrical steel sheet having no inorganic coating containing forsterite as the main component on its surface) is used as the main steel sheet 11.

[0071] A method for producing an anisotropic electrical steel sheet having no inorganic coating is not particularly limited. For example, as an example, a method including a hot rolling process in which a steel billet containing, 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 and less than 0.01% Bi, and the rest is Fe and impurities, an optional annealing process, a cold rolling process in which one cold rolling pass or two or more cold rolling passes with intermediate annealing in between, a decarburization annealing process, and a final annealing process are performed. Meanwhile, in order to prevent the formation of an inorganic coating, for example, a method in which an annealing separator which does not form an inorganic coating is applied and a final annealing is performed, and a method in which the final annealing is performed using a commonly used annealing separator, and then the resulting inorganic coating is removed by a known method such as grinding or pickling.

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

[0073] Examples of bismuth chlorides include bismuth oxychloride (BiOCl) and bismuth trichloride (BiCl ₃ ). Examples of bismuth compounds include bismuth oxide, bismuth hydroxide, bismuth sulfide, bismuth sulfate, bismuth phosphate, bismuth carbonate, bismuth nitrate, bismuth organic acid salt, and bismuth halide. Examples of metal chloride compounds include iron chloride, cobalt chloride and nickel chloride. The amount of bismuth chloride or bismuth compound and metal chloride 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 an anisotropic electrical steel sheet, the excess annealing separator remaining after the final annealing is removed by cleaning, and then the alignment annealing is performed. On the other hand, as shown in FIG. 4, in the production method of the anisotropic electrical steel sheet according to the present embodiment using the finally annealed anisotropic electrical steel sheet having no inorganic coating, the excess annealing separator is removed by cleaning (step S101, washing process), and then an acid with a specific concentration ( surface treatment liquid) is applied to the surface of the steel sheet to perform surface treatment (step S103, surface treatment process), heat treatment is performed at a specific temperature in an oxidizing atmosphere (step S105, heat treatment process), and a tensile insulation coating is formed with favorable adhesion under specific conditions (Step S107, Insulation Coating Tension Forming Process). Thereby, on the surface of the finally annealed anisotropic electrical steel sheet having no inorganic coating, an intermediate layer mainly composed of the iron-based oxide layer and the silicon-containing oxide layer described above can be formed, and the adhesion of the insulating coating under tension can also be improved.

<Regarding the surface treatment process>

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

[0076] When the temperature of the surface treatment liquid is less than 70°C, the solubility in the surface treatment liquid decreases, and not only can the possibility of precipitation be increased, but effective etch pits cannot be obtained. On the other hand, when the temperature of the surface treatment liquid exceeds 90°C, this is not preferable because the reactivity of the surface treatment liquid becomes too high and the surface of the steel sheet is excessively pickled during the surface treatment process. The temperature of the surface treatment liquid is preferably in the range of 75-87°C, and more preferably in the range of 80-85°C.

[0077] When the total concentration of acids in the surface treatment liquid is less than 2 mass%, it is industrially disadvantageous because etch pits cannot be suitably formed on the surface of the steel sheet and the treatment time becomes long. When the total concentration of acids in the surface treatment liquid exceeds 20 mass%, this is not preferable because the surface of the steel sheet is excessively pickled during the surface treatment process. The total concentration of acids in the surface treatment liquid is preferably in the range of 2-17% by weight, and even more preferably in the range of 2-10% by weight.

[0078] The duration of the surface treatment process is not particularly limited. The surface treatment process is in many cases performed by continuously dipping steel sheets into a treatment bath containing a surface treatment liquid. When this method is used, the time the steel sheet passes through the treatment bath is the treatment time in the surface treatment process. When the steel sheets are immersed in the treatment bath and passed through at a normal sheet 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 after the surface treatment process, heating is performed in an atmosphere having an oxygen concentration of 1-21 vol.% and a dew point of -20 to 30° C, for 10-60 seconds so that the temperature of the steel sheet reaches 700-900°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, and the productivity is lowered. On the other hand, when the oxygen concentration in the atmosphere exceeds 21 vol%, this is not preferable because the formed iron-based oxide layer tends to be uneven. The oxygen concentration in the atmosphere is preferably in the range of 2-21% by volume, and more preferably in the range of 15-21% by volume.

[0081] When the dew point in the atmosphere is less than -20°C, it takes too long for the iron-based oxide layer to form, and the productivity is lowered. On the other hand, when the atmospheric dew point exceeds 30° C., this is not preferable because the formed iron-based oxide layer tends to be uneven. The atmospheric dew point is preferably in the range of -10 to 25°C, and more preferably in 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, this is not preferable because it is difficult to form the iron-based oxide layer and the silicon-containing oxide layer in a suitable state even if the heating time is 60 seconds. On the other hand, when the heating temperature of the steel sheet exceeds 900°C, this is not preferable because the iron-based oxide layer tends to be uneven, and the silicon-containing oxide layer in the desired state cannot be formed. The heating temperature of the steel sheet during the heat treatment is preferably in the range of 750-800°C.

[0083] When the heating time is less than 10 seconds, this is not preferable because the resulting iron-based oxide layer and the silicon-containing oxide layer tend to be uneven. On the other hand, when the heating time exceeds 60 seconds, this is not preferable because high costs are required in production. The heating time is preferably in the range of 20-30 seconds.

[0084] When the heat treatment process is performed after the surface treatment process, the activated surface of the anisotropic electrical steel sheet having no inorganic coating is oxidized, an iron-based oxide layer is formed, the thermal expansion coefficient of which is intermediate between the thermal expansion coefficients of the metal and the insulation coating, and a silicon-containing oxide layer with Si diffused from the base steel sheet. Etching pits are formed on the surface of the 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, relieving stress, and thus further improvement of the tension coating adhesion can be realized, and an effect of improving magnetic loss in a strong magnetic field can be exhibited.

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

[0085] In the method for producing an anisotropic electrical steel sheet according to the present embodiment, in the process of forming the tension coating, using the following treatment solution for forming the tension coating of the mixed phosphate-silica system, the treatment solution is applied and dried under the following conditions. When the insulating coating is tensionally formed on the surface of the steel sheet, it is possible to further improve the magnetic characteristics of the anisotropic electrical steel sheet.

[0086] Before applying the treatment solution for forming the tension coating, the surface of the steel sheet on which the tension coating is formed may be subjected to optional pre-treatment such as an alkali degreasing treatment or the like, or the surface may be left without such pre-processing.

[0087] 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 insulating tension coating of the known mixed phosphate-silica can be 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. In the method for producing an anisotropic electrical steel sheet according to the present embodiment, a treatment solution for forming an insulating coating under tension is applied to the surface of the anisotropic electrical steel sheet after the heat treatment process, and within 1.0 to 20 seconds after application, the anisotropic electrical steel sheet is heated at an average heating rate of 20-100°C/s and calcined at a steel sheet temperature of 850-950°C for 10-60 seconds.

[0088] In actual operation, since it is often difficult to set the time to start heating after application of the treatment solution for forming an insulating coating with a tension of less than 1.0 seconds, the time to start heating is 1.0 seconds or more after application. On the other hand, when the time to start of heating exceeds 20 seconds, the reaction between the surface of the anisotropic electrical steel sheet subjected to the heat treatment process and the treatment solution for forming the tension insulating coating takes too long, and the iron-based oxide layer and the silicon-containing oxide layer , formed during heat treatment, can dissolve with a high probability. Therefore, the time to start heating after applying the treatment solution is from 1.0 seconds to 20 seconds. The shorter the time before heating starts, the better.

[0089] When the average heating rate is less than 20°C/s, the reaction between the surface of the anisotropic electrical steel sheet subjected to the heat treatment process and the treatment solution for forming the tension insulating coating takes too long, and the iron-based oxide layer and the silicon-containing the oxide layer formed during heat treatment is highly likely to dissolve. On the other hand, when the average heating rate exceeds 100°C/s, this is not preferable because the desired temperature of the steel sheet at the time of calcination is highly likely to be exceeded. Therefore, in the present embodiment, the average heating rate is in the range of 20-100°C/s. The average heating rate is preferably in the range of 25-50°C/s.

[0090] In the process of forming the insulating coating under tension, the treatment solution is calcined at a steel sheet temperature of 850-950°C for 10-60 seconds. When the temperature of the steel sheet is less than 850°C, even if the holding time is 60 seconds, the tension-formed insulating coating cannot achieve the desired performance. On the other hand, when the temperature of the steel sheet exceeds 950°C, even if the holding time is 10 seconds, the tension insulation coating is excessively calcined, and the tension insulation coating formed cannot achieve the desired performance. In addition, when the holding time is less than 10 seconds, the tension coating treatment solution cannot be sufficiently dried, and when the holding time exceeds 60 seconds, the tension coating formed cannot achieve the desired characteristics. The temperature of the steel sheet is preferably in the range of 870-900°C, and the holding time is preferably in the range of 25-45 seconds.

[0091] Thereby, a tension insulating coating with a thickness of 1-3 µm is formed on the surface of the iron-based oxide layer.

[0092] The time between the surface treatment process and the heat treatment process is preferably as short as possible, and for example, preferably a few minutes.

[0093] After the process of forming the insulating coating under tension, an alignment annealing may be performed to correct the shape. When the alignment annealing of the steel sheet is performed, the magnetic loss can be further reduced.

[0094] The production method of the anisotropic electrical steel sheet according to the present embodiment has been described in detail above.

Examples

[0095] 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. Here, the following examples are merely examples of the anisotropic electrical steel sheet and the production method of the anisotropic electrical steel sheet according to the present invention. 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)

[0096] A steel billet (silicon steel slab) was cast, containing, in mass%, C: 0.08%, Si: 3.24%, Mn: 0.08%, Al: 0.028%, N: 0.008%, S: 0.03%, Se: 0.01% and Bi: 0.004%, and the rest is Fe and impurities, and the resulting steel billet was heated and then hot rolled to obtain a hot-rolled strip with a thickness of 2.2 mm. After annealing at a steel sheet temperature of 1100°C for 60 seconds, cold rolling was performed until the thickness of the sheet became 0.22 mm, and decarburization annealing was performed at a steel sheet temperature of 830°C. Then, an annealing separator containing MgO and Al ₂ O ₃ as main components and 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 (final annealing at such also referred to as "refining annealing"). When the excess annealing separator was removed by water washing after the final annealing, no inorganic coating was formed on the surface of the steel sheet. In addition, as a result of such final annealing, the Al content was 0% or more and less than 0.05%, the C content was 0% or more and less than 0.1%, the N content was 0% or more and less than 0.05%, the S content was 0% or more and less than 0.1%, the Se content was 0% or more and less than 0.05%, and the Bi content was 0% or more and less than 0.01%.

[0097] An aqueous solution was prepared containing aluminum phosphate and colloidal silica as the main components shown in Table 1. A commercially available ultra pure reagent was used as the various phosphates shown in Table 1, and a commercially available commercially available silica was used as colloidal silica. high purity reagent. Here, all average particle sizes of colloidal silica shown in Table 1 are catalog values.

[0098] After the surface treatment process and the heat treatment process of the steel sheet after final annealing under the conditions shown in Table 2-1 were carried out, an aqueous solution containing aluminum phosphate and colloidal silica as the main components shown in Table 2-1 was applied and calcined. 1, and a 2.5 µm thick insulating tension coating was formed on the surface of the steel sheet.

[0099] With the anisotropic electrical steel sheets thus produced using the XPS (PHI 5600 instrument manufactured by ULVAC-PHI), the thickness d ₂ of the iron-based oxide layer was measured according to the above method, and the main components of the iron-based oxide layer were determined method of x-ray analysis of the crystal structure. In addition, the obtained anisotropic electrical steel sheet was analyzed by GDS (Glow Discharge Optical Emission Spectrometer GDA 750 manufactured by Rigaku Corporation) according to the following analysis conditions.

[0100] 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, 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

[0101] 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, Fe

[0102] In addition, magnetic loss in a strong magnetic field (magnetic loss at a frequency of 50 Hz when the maximum magnetic induction was 1.7 T or 1.9 T) after laser irradiation and performing magnetic domain refinement processing was measured by the magnetic characteristics of a single sheet (single sheet tester: SST) in accordance with JIS C 2556. In addition, adhesion and tension of the insulation coating with tension were evaluated in accordance with the following evaluation method. The results obtained are summarized in Table 2-2.

[0103] The number of Si emission intensity profile inflection points in the GDS analysis was calculated from the second derivative plot obtained by doubly differentiating the Si emission intensity profile using a commercially available numerical calculation application. In addition, in the following Table 2-2, the column "Distance from saturation point" in the column "Si emission intensity at GDS" shows the distance between the position of the inflection point closest to the side of the base steel plate and the saturation point at which the Fe emission intensity was maximum.

<Evaluation of adhesion of insulating coating under tension>

[0104] The tension adhesion of the insulation coating was evaluated as follows. First, a specimen with a width of 30 mm and a length of 300 mm was taken from each of the anisotropic electrical steel sheets and subjected to stress relief annealing at 800°C in nitrogen flow for 2 hours, and then subjected to a bending adhesion test using a cylinder with a diameter of ∅ 10 mm, and the adhesion was evaluated according to the degree of peeling of the insulating coating under tension. The evaluation criteria were as follows, and the A grade and B grade were satisfactory.

Grade A: no flaking

B: Almost no flaking

C: several mm of peeling observed

D: 1/3-1/2 surface peeling observed

E: The entire surface has peeled off

<Evaluation of the tension of the insulating coating with tension>

[0105] In addition, the tension of the tensile insulation coating was calculated by inverse calculation from the bending state when one side of the tensile insulation coating was peeled off. That is, the coating tension σ was calculated using the following Formula (1).

[0106] σ≈{E/(1-µ)}×(T ² /3t)×(2H/L ² ) ... Formula (1)

where

σ: coating tension [Pa]

E: Young's modulus [Pa]

µ: Poisson's ratio [-]

T: sample thickness [m]

t: thickness [m] of steel sheet

H: bending [m] of the sample

L: length [m] of the sample.

[0107] Then, the resulting coating tension was evaluated according to the following evaluation criteria. Evaluation criteria were as follows, and grades from A to C were considered satisfactory.

Grade A: 8 MPa or more

B: 7MPa or more and less than 8MPa

C: 6MPa or more and less than 7MPa

D: 5MPa or more and less than 6MPa

E: less than 5MPa

[0108] [Table 1]

No. Phosphate Solid Content Concentration (wt%) colloidal silica Solid Content Concentration (wt%) one aluminum phosphate 65 Average particle size 15 nm, alkaline type 35 2 Aluminum Phosphate + Magnesium Phosphate 60 Average particle size 8 nm, aluminum coated type 40 3 Aluminum Phosphate + Zinc Phosphate 70 Average particle size 30 nm, alkaline type thirty four aluminum phosphate 58 Average particle size 8 nm, alkaline type 42 5 manganese phosphate 34 Average particle size 15 nm, acid type 66 6 cobalt phosphate 72 Average particle size 15 nm, alkaline type 28 7 Aluminum Phosphate + Zinc Phosphate + Iron Phosphate 72 Average particle size 15 nm, alkaline type 28

[0109] [Table 2-1]

No. surface treatment process heat treatment process The process of forming an insulating coating with tension Acid Liquid temperature (°C) Processing time (seconds) Atmosphere (vol.%) Dew point (°C) Steel sheet temperature (°C) Processing time (seconds) processing solution Time to heat up (seconds) Heating rate (°C/s) Steel sheet temperature (°C) Holding time (seconds) one 10% sulfuric acid 80 ten 20% _O2 28 800 ten one four fifty 900 thirty 2 5% sulfuric acid 80 12 20% _O2 -eighteen 800 twenty 2 eight fifty 900 thirty 3 5% sulfuric acid 80 12 ₁ %O2 28 850 ten 3 eight 25 860 60 four 7% nitric acid 70 twenty 20% _O2 twenty 800 ten four 16 85 950 12 5 15% phosphoric acid 85 fourteen 20% _O2 5 800 ten 5 16 fifty 900 twenty 6 5% sulfuric acid 80 12 20% _O2 -eighteen 850 ten 6 four fifty 900 twenty 7 5% sulfuric acid 80 12 20% _O2 -eighteen 850 ten 7 four fifty 900 twenty eight 25% sulfuric acid 60 ten 20% _O2 5 850 ten one four 25 830 55 9 1% sulfuric acid 80 60 20% _O2 0 800 ten one four fifty 900 twenty ten 10% sulfuric acid 60 ten 20% _O2 0 800 thirty 2 eight fifty 900 twenty eleven 5% sulfuric acid 95 ten 20% _O2 0 800 ten 2 eight fifty 900 twenty 12 10% sulfuric acid 75 ten 20% _O2 5 600 thirty 3 eight fifty 900 twenty 13 15% phosphoric acid 80 fourteen 20% _O2 0 1,000 ten 3 four fifty 900 twenty fourteen 10% sulfuric acid 80 ten ₃ %O2 25 800 four one eight fifty 900 twenty fifteen 10% sulfuric acid 80 ten 20% _O2 -fifteen 800 80 one four fifty 900 twenty 16 10% sulfuric acid 80 ten 20% _O2 25 750 ten 2 0.5 fifty 900 twenty 17 10% sulfuric acid 80 ten 20% _O2 5 880 thirty 2 thirty fifty 900 twenty eighteen 10% sulfuric acid 80 ten 20% _O2 25 800 ten 3 four 13 830 60 19 10% sulfuric acid 80 ten 20% _O2 5 800 thirty 3 four 160 950 12 twenty 10% sulfuric acid 80 fifteen 20% _O2 25 800 ten one eight fifty 800 60 21 10% sulfuric acid 80 12 20% _O2 5 800 thirty 2 eight 85 980 12 22 10% sulfuric acid 80 12 20% _O2 25 800 ten 3 eight 85 950 6 23 10% sulfuric acid 80 12 20% _O2 5 800 thirty four eight 25 830 90 24 10% sulfuric acid 80 12 Without heat treatment four four 160 830 6

[0110] [Table 2-2]

No. Iron based oxide layer Si emission intensity at GDS Adhesion Coating tension Magnetic loss in strong magnetic field (W/kg) Note Thickness (nm) Number of inflection points Distance from saturation point (µm) The proportion of Si in steel W17/50 W19/50 one 240 four 1.5 1.4 A A 0.64 1.01 Example 2 140 four 1.2 1.8 A A 0.62 0.93 Example 3 140 four 0.6 1.8 B C 0.68 1.03 Example four 340 four 1.0 1.7 B A 0.65 0.97 Example 5 260 four 1.0 1.6 A A 0.61 0.89 Example 6 120 four 0.7 1.8 A A 0.61 0.87 Example 7 120 four 0.9 1.6 B A 0.66 0.99 Example eight 220 four 1.5 2.3 B B 0.71 1.21 Comparative Example 9 40 3 - - D A 0.68 1.18 Comparative Example ten 420 four 0.2 1.2 D B 0.67 1.08 Comparative Example eleven 80 four 0.4 1.2 D A 0.65 1.10 Comparative Example 12 60 3 - - E B 0.69 1.17 Comparative Example 13 560 four 1.5 2.1 C A 0.73 1.21 Comparative Example fourteen 80 four 0.3 0.8 E A 0.71 1.15 Comparative Example fifteen 460 four 2.1 3.3 B B 0.70 1.18 Comparative Example 16 100 3 - - C B 0.66 1.14 Comparative Example 17 300 four 0.4 0.4 D A 0.69 1.13 Comparative Example eighteen 140 four 0.3 0.8 D B 0.69 1.08 Comparative Example 19 240 four 0.4 0.5 B D 0.66 1.08 Comparative Example twenty 140 four 0.5 0.7 B E 0.71 1.17 Comparative Example 21 220 four 1.8 1.9 C B 0.72 1.17 Comparative Example 22 160 four 2.3 1.5 C D 0.69 1.09 Comparative Example 23 240 four 2.4 2.1 B E 0.68 1.09 Comparative Example 24 160 four 0.6 0.9 D D 0.70 1.09 Comparative Example

[0111] According to the results of X-ray analysis of the crystal structure in the samples corresponding to the examples of the present invention, the iron-based oxide layer contained magnetite, hematite and fayalite as the main components, and the silicon-containing oxide layer contained silica and fayalite as the main components. On the other hand, in the Comparative Examples not falling within the protection scope of the present invention, an iron-based oxide layer containing magnetite, hematite, and fayalite as main components was formed, but a silicon-containing oxide layer having a predetermined number of inflection points and a distance was not formed. from the saturation point and exhibiting a given Si emission intensity.

[0112] As can be clearly seen from Table 2-2, it is clear that the samples corresponding to the examples of the present invention had excellent adhesion, and the magnetic loss in a strong magnetic field was improved. On the other hand, it can be seen that the samples corresponding to the comparative examples of the present invention were inferior at least either in adhesion or in magnetic loss in a strong magnetic field.

[0113] 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 these examples. It is clear that those skilled in the art will be able to make various changes or modifications within the technical ideas described in the scope of the claims, and, of course, all of them fall within the technical scope of the present invention.

BRIEF DESCRIPTION OF REFERENCE SYMBOLS

[0114] 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 (etch pit)

Claims (27)

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, 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 and 0% or more and less than 0.01% Bi , and the rest - Fe and impurities, wherein, when elemental analysis is performed from the surface of the insulating coating with tension in the sheet thickness direction by glow discharge optical emission spectrometry, (a) there are four or more inflection points in the Si emission intensity profile; (b) in the thickness direction of the sheet, the inflection point of the Si emission intensity closest to the side of the base steel sheet is present within the range of 0.3-1.5 µm towards the surface of the insulating coating with tension from the saturation point at which the emission intensity of Fe is the maximum; and (c) the Si emission intensity peak closest to the base steel sheet side has an emission intensity that is 1.3 times or greater and 2.0 or less than the Si emission intensity in the base steel sheet. 2. A sheet of anisotropic electrical steel according to claim 1, wherein the silicon-containing oxide layer contains silica and fayalite as main components, and wherein the tensile insulating coating contains 25-45 wt. % colloidal silica with a balance containing one or more selected from the group consisting of aluminum phosphate, magnesium phosphate, zinc phosphate, manganese phosphate, cobalt phosphate and iron phosphate as the main components. 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, wherein 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; a surface treatment process for treating the surface of an anisotropic electrical steel sheet that has been subjected to a washing process using a surface treatment liquid that contains one or more of sulfuric acid, phosphoric acid, and nitric acid and has a total acid concentration of 2-20% and a liquid temperature 70-90°C; a heat treatment process for heating a sheet of anisotropic electrical steel that has been subjected to a 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; and a process of forming an insulating tension coating with a thickness of 1-3 µm by applying a treatment solution for forming an insulating tension coating containing phosphate and colloidal silica as main components to the surface of an anisotropic electrical steel sheet after the heat treatment process, and heating is performed at a medium heating rate 20-100°C/s within 1.0-20 s after application, and calcination is performed at a temperature of 850-950°C for 10-60 s. 6. A method for producing an anisotropic electrical steel sheet according to claim 5, further comprising: before the washing process, hot rolling process with subjecting to hot rolling a steel billet, which contains as chemical components, 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 and 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 chloride compound into a mixture of MgO and Al ₂ O ₃ , drying the annealing separator, and then performing a final annealing.

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