RU2772720C1 - Anisotropic electrical steel sheet, a method for producing anisotropic electrical steel sheet and annealing separator used for the production of anisotropic electrical steel sheet - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, namely to a sheet of anisotropic electrical steel. Anisotropic electrical steel sheet contains a basic steel sheet having a chemical composition containing, wt. %: C: 0.005 or less, Si: 2.5-4.5, Mn: 0.02-0.2, one or more elements selected from a group consisting of S and Se: in total 0.005 or less, Al solution: 0.01 or less, N: 0.01 or less, the rest is Fe and impurities, and the primary coating formed on the surface of the main steel sheet and containing Mg₂SiO₄ as the main component. The position of the peak intensity of Al emission obtained by performing elemental analysis using optical emission spectrometry of a glow discharge from the surface of the primary coating in the direction along the thickness of the sheet of anisotropic electrical steel is in the range of 2.4-12.0 mcm from the surface of the primary coating in the direction along the thickness. The numerical density of Al oxides at the peak of the intensity of Al emission with a size of 0.2 mcm or more in terms of the diameter of an area-equivalent circle is 0.03-0.18/mcm ². In the set of Al oxides in the observed region of 30 mcm × 50 mcm at the peak of the intensity of Al emission, the total cross-sectional area of the identified Al oxides with cross-sectional areas of 0.4-10.0 mcm² is 75.0% or more of the total cross-sectional area of all Al oxides in the observed region.

EFFECT: sheet of electrical steel has excellent magnetic properties and adhesion of the primary coating to the main steel sheet, as well as resistance to corrosion.

3 cl, 7 tbl

Description

FIELD OF TECHNOLOGY

[0001] The present invention relates to an anisotropic electrical steel sheet, a method for producing an anisotropic electrical steel sheet, and an annealing separator used to produce an anisotropic electrical steel sheet.

BACKGROUND OF THE INVENTION

[0002] The anisotropic electrical steel sheet is a steel sheet containing, in wt.%, approximately 0.5-7% Si and having crystallographic orientations adjusted in the {110}<001> orientation (Goss orientation). To control crystallographic orientations, the phenomenon of catastrophic grain growth, called secondary recrystallization, is used.

[0003] A method for producing an anisotropic electrical steel sheet is as follows: a slab is heated and subjected to hot rolling to obtain a hot-rolled steel sheet. The hot rolled steel sheet is annealed according to need. Hot rolled steel sheet is pickled. The pickled hot-rolled steel sheet is subjected to cold rolling with a reduction of 80% or more to obtain a cold-rolled steel sheet. The cold-rolled steel sheet is subjected to decarburization annealing, causing primary recrystallization. The cold-rolled steel sheet subjected to the decarburization annealing is subjected to final annealing to cause secondary recrystallization. The above process produces an anisotropic electrical steel sheet.

[0004] After the above decarburization annealing and before the final annealing, the surface of the cold rolled steel sheet is coated with an aqueous slurry containing an annealing separator with MgO as a main component, and then dried. The cold-rolled steel sheet with the annealing separator dried thereon is wound into a coil and then subjected to final annealing. During the final annealing, MgO in the annealing separator and SiO ₂ in the inner oxide layer formed on the surface of the cold-rolled steel sheet during the decarburization annealing react with each other, whereby a primary coating having forsterite (Mg ₂ SiO ₄ ) as the main component. After the formation of the primary coating, it is coated, for example, with an insulating coating (also called "secondary coating"), consisting of colloidal silica and phosphate. Primary coating and insulation coating have lower coefficient of thermal expansion than steel sheet. For this reason, the primary coating, together with the insulating coating, applies tension to the steel sheet to reduce magnetic losses. Primary coating further enhances the adhesion of the insulating coating on the steel sheet. Therefore, the adhesion of the Primary Coating on the steel sheet is preferably higher.

[0005] On the other hand, increasing the magnetic flux density and lowering the hysteresis loss are effective for reducing the magnetic loss in the anisotropic electrical steel sheet.

[0006] In order to increase the magnetic induction in the anisotropic electrical steel sheet, the crystallographic orientations of the base steel sheet in the Goss orientation are effectively controlled. Analogues for improving Goss orientation integration are proposed in patent documents PTL 1-3. In these patent documents, the steel sheet contains elements that improve the magnetic properties, which enhance the action of inhibitors (Sn, Sb, Bi, Te, Pb, Se, etc.). Because of this, the integration in the Goss orientation is enhanced and the magnetic induction can be increased.

[0007] However, if the steel sheet contains elements that improve the magnetic properties, parts of the primary coating will be aggregated, so that the interface between the steel sheet and the primary coating becomes easily smoothed. In this case, the adhesion of the primary coating to the steel sheet will deteriorate.

[0008] Analogues for improving the adhesion of the primary coating to steel sheet are described in patent documents PTL 4, 5 and 6.

[0009] In PTL 4, a slab is made with a Ce content of 0.001-0.1%, and the surface of the steel sheet is formed with a primary coating containing Ce in an amount of 0.01-1000 mg/m ² . In PTL 5, in an anisotropic electrical steel sheet containing 1.8-7% Si and having a primary coating with forsterite as the main component, the primary coating is made containing Ce in a specific amount of 0.001-1000 mg/m ² per side.

[0010] In PTL 6, a primary coating, characterized in that it contains one or more types of alkaline earth metal compounds selected from Ca, Sr and Ba, and rare earth elements, is formed from an annealing separator having MgO as a main component, and also containing various compounds, including a rare earth metal compound in an amount of 0.1-10%, one or more types of alkaline earth metal compounds selected from Ca, Sr and Ba in an amount of 0.1-10%, and a sulfur compound in an amount of 0, 01-5%.

[0011] In PTL 7, a primary coating is formed, characterized in that it contains various compounds, including one or more elements selected from Ca, Sr and Ba, rare earth metal compounds in the amount of 0.1-1.0% and sulfur.

LIST OF CITATIONS

PATENT LITERATURE

[0012] PTL 1: Japanese Unexamined Patent Application Publication No. 6-88171

PTL 2: Japanese Patent Pending Publication No. 8-269552

PTL 3: Japanese Patent Application Pending Publication No. 2005-290446

PTL 4: Japanese Patent Application Pending Publication No. 2008-127634

PTL 5: Japanese Patent Pending Publication No. 2012-214902

PTL 6: International Publication WO 2008/062853

PTL 7: Japanese Patent Application Pending Publication No. 2009-270129

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

[0013] However, when the annealing separator is made containing Y, La, Ce or other rare earth compounds to form a primary coating containing Y, La and Ce, the magnetic properties sometimes drop. In addition, if the particle number densities of the compounds of Y, La, Ce or other rare earth elements, or Ca, Sr, Ba, or other additives in the powder of raw materials in the preparation of the annealing separator are insufficient, there will sometimes be areas where the primary coating is not sufficiently developed. , and sometimes the adhesion will drop. In addition, rust resistance is sometimes desirable in an anisotropic electrical steel sheet, but the aforementioned PTL documents 1-4 do not contain any descriptions relating to rust resistance.

[0014] It is an object of the present invention to provide an anisotropic electrical steel sheet having excellent magnetic properties, excellent primary coating adhesion to a base steel sheet, and excellent rust resistance, a method for producing an anisotropic electrical steel sheet, and an annealing separator used to make the sheet. anisotropic electrical steel.

SOLUTION

[0015] The anisotropic electrical steel sheet according to the present invention includes a base steel sheet having a chemical composition containing, in wt %, C: 0.005% or less, Si: 2.5-4.5%, Mn: 0.02-0.2%, one or more elements selected from the group consisting of S and Se: in the amount of 0.005% or less, sol. Al: 0.01% or less, and N: 0.01% or less, with the rest consisting of Fe and impurities, and a primary coating formed on the surface of the base steel sheet and containing Mg ₂ SiO ₄ as a main component, and the position of the Al emission intensity peak obtained by performing elemental analysis using glow discharge optical emission spectrometry from the surface of the primary coating in the direction along the thickness of the anisotropic electrical steel sheet is in the range of 2.4-12.0 μm from the surface of the primary coating in the direction along the thickness , the number density of Al oxides at the Al emission intensity peak position with a size of 0.2 μm or more in terms of the diameter of an area-equivalent circle is 0.03-0.18/μm ² , and in a plurality of Al oxides in the observed region of 30 μm × 50 µm at the peak position of Al emission intensity, the total cross-sectional area of identified Al oxides with cross-sectional areas of 0.4-10.0 µm ² is 75.0% or more of the total cross-sectional area of all Al oxides in the observed region.

[0016] The method for producing an anisotropic electrical steel sheet according to the present invention includes a cold rolling process of a hot-rolled steel sheet containing, in mass%, C: 0.1% or less, Si: 2.5-4.5% , Mn: 0.02-0.2%, one or more elements selected from the group consisting of S and Se: in the amount of 0.005-0.07%, sol. Al: 0.005-0.05%, and N: 0.001-0.030%, with the rest consisting of Fe and impurities, with a cold rolling reduction ratio of 80% or more, for the manufacture of cold-rolled steel sheet, the process of decarburization annealing of cold-rolled steel sheet, a process of coating the surface of a cold-rolled steel sheet after decarburization annealing with an aqueous slurry containing an annealing separator, and drying the aqueous slurry on the surface of the cold-rolled steel sheet in a furnace at 400-1000°C, and a process of performing final annealing of the cold-rolled steel sheet after the aqueous slurry is dried . The annealing separator contains MgO, at least one or more types of metal compounds selected from the group consisting of Y, La and Ce, at least one or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, and at least one or more types of metal compounds selected from the group consisting of Ca, Sr and Ba, wherein when the content of MgO in the annealing separator is taken as 100 wt.%, the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides is 0.8-8.0%, the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 0.5-9.0%, and the total content of metal compounds selected from the group consisting of Ca, Sr and Ba, in terms of sulfates is 0.5-8.0%, the average particle size of metal compounds selected from the group consisting of Ca, Sr and Ba is 12 µm or less, the ratio of the average particle size of the metal compounds selected o from the group consisting of Ca, Sr and Ba to the average particle size of metal compounds selected from the group consisting of Y, La and Ce is 0.1-3.0, the sum of the total content of metal compounds selected from the group, consisting of Y, La and Ce, in terms of oxides and the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 2.0-12.5%, the ratio of the sum of the numbers of Y atoms, La and Ce to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator is 0.18-4.0, in addition, the particle number density of the metal compounds selected from the group consisting of Y, La and Ce, which are particles with a volume-equivalent sphere diameter of 0.1 μm or more is 2000000000/g or more, in addition, the particle number density of metal compounds selected from the group consisting of Ti, Zr and Hf, which are particles with a sphere 0.1 µm or more is 2000000000/g or more, and, in addition, the particle number density of the metal compound particles selected from the group consisting of Ca, Sr and Ba, which are particles with a sphere equivalent in volume diameter of 0.1 μm or more, is 2000000000/g or more.

[0017] The annealing separator used to produce the anisotropic electrical steel sheet according to the present invention contains MgO, at least one or more types of metal compounds selected from the group consisting of Y, La and Ce, at least one or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, and at least one or more types of metal compounds selected from the group consisting of Ca, Sr and Ba, and when the content of MgO in the annealing separator is taken as 100 wt.%, the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides is 0.8-8.0%, the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 0.5-9.0%, and the total content of metal compounds selected from the group consisting of Ca, Sr and Ba, in terms of sulfates is 0.5-8.0%, the average size particles of metal compounds selected from the groups py, consisting of Ca, Sr and Ba, is 12 µm or less, the ratio of the average particle size of the metal compounds selected from the group consisting of Ca, Sr and Ba, to the average particle size of the metal compounds selected from the group consisting of Y, La and Ce is 0.1-3.0, the sum of the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides and the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 2.0-12.5%, the ratio of the sum of the numbers of Y, La and Ce atoms to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator is 0.18-4.0, in addition, the particle number density of the metal compounds selected from the group consisting of Y, La and Ce, which are particles with a sphere equivalent sphere diameter of 0.1 μm or more, is 2000000000/g or more, in addition, the particle number density compounds of a metal selected from the group consisting of Ti, Zr and Hf, which which are particles with a diameter equivalent in volume to a sphere of 0.1 μm or more, is 2000000000/g or more, and, in addition, the particle number density of metal compounds selected from the group consisting of Ca, Sr and Ba, which are particles with a diameter equivalent in volume to a sphere of 0.1 μm or more is 2000000000/g or more.

BENEFICIAL EFFECTS OF THE INVENTION

[0018] The anisotropic electrical steel sheet according to the present invention has excellent magnetic properties and excellent primary coating adhesion to the base steel sheet. The production method according to the present invention makes it possible to produce the aforementioned anisotropic electrical steel sheet. An annealing separator according to the present invention is used in the above production method. Due to this, an anisotropic electrical steel sheet can be produced.

DESCRIPTION OF EMBODIMENTS

[0019] The inventors investigated and studied the magnetic properties of an anisotropic electrical steel sheet containing elements for improving the magnetic properties and adhesion of primary coatings formed by including a Y compound, a La compound, and a Ce compound in an annealing cage. As a result, the inventors obtained the following information.

[0020] Anchor structures are present at the interface between the primary coating and the steel sheet in the anisotropic electrical steel sheet. In particular, near the interface between the Primary Coating and the steel sheet, the roots of the Primary Coating extend downward into the steel sheet. The more the Primary Coating roots penetrate inside the steel sheet, the higher the adhesion of the Primary Coating to the steel sheet. In addition, the more distributed the roots of the primary coating within the steel sheet (the more they spread), the higher the adhesion of the primary coating to the steel sheet.

[0021] On the other hand, if the roots of the Primary Coating penetrate too much into the steel sheet, they will make secondary recrystallization in the Goss orientation more difficult. Because of this, crystal grains with random orientations will grow in the surface layer. In addition, the roots of the primary coating become factors preventing the motion of the domain walls, and the magnetic properties deteriorate. Similarly, if the roots of the Primary Coating are excessively distributed within the steel sheet, they will impede secondary recrystallization in the Goss orientation, and crystal grains with random orientations will increase in the surface layer. In addition, the roots of the primary coating become factors preventing the motion of the domain walls, and the magnetic properties deteriorate.

[0022] Based on the above knowledge, the inventors further investigated the condition of the roots of the Primary Coating, the magnetic properties of the anisotropic electrical steel sheet, and the adhesion of the Primary Coating.

[0023] If the annealing separator is made containing Y, La and Ce compounds to form the primary coating as explained above, the magnetic properties fall. The reason for this is believed to be that the roots of the Primary Coating penetrate the steel sheet too deeply and impede the movement of the domain walls.

[0024] Therefore, the inventors experimented with lowering the contents of Y, La, and Ce compounds in the annealing separator containing MgO as the main component, and incorporating Ti, Zr, and Hf compounds instead to form the primary coating, and also experimented with a higher number density compound particles in an annealing separator before preparing an aqueous suspension (powder of raw materials). As a result, they found that sometimes the magnetic properties of the anisotropic electrical steel sheet are improved, and the adhesion of the primary coating is also improved.

[0025] The inventors further studied the Y, La and Ce compounds and the Ti, Zr and Hf compounds in the annealing separator. As a result, the inventors have learned the following: It is difficult for the unreacted Y, La, and Ce compounds and the Ti, Zr, and Hf compounds to form a Primary Coating, so that the Primary Coating does not become dense. In this case, the Primary Coating cannot cover the entire surface of the steel sheet, and part of the surface of the steel sheet remains exposed. If the amount of exposed surface of the steel sheet increases, the rust resistance decreases.

[0026] Therefore, the inventors further investigated the annealing separator containing mainly MgO. As a result, the inventors have found that by making the annealing separator including Y, La and Ce compounds and Ti, Zr and Hf compounds, as well as Ca, Sr and Ba compounds to control the content of Y, La and Ce compounds in terms of oxides, the content of compounds Ti, Zr and Hf in terms of oxides and the contents of Ca, Sr and Ba compounds in terms of sulfates in the annealing separator, the depth and state of dispersion of the roots of the primary coating can be controlled. This will be explained in detail below.

[0027] The main component of the primary coating roots is Al oxide, such as spinel (MgAl ₂ O ₄ ). It is considered that the depth position from the surface at the Al emission intensity peak obtained by performing elemental analysis by glow discharge optical emission spectrometry (GDS method) from the surface of the anisotropic electrical steel sheet in the thickness direction (hereinafter referred to as the “D _{Al position of the Al} peak ”), shows the position of the presence of the spinel, i.e. the position of the roots of the primary coating. In addition, the number density of Al oxides represented by a spinel with a size of 0.2 μm or more in diameter equivalent in area to the circle at the D _{Al position of the Al} peak (hereinafter referred to as "number density ND of Al oxides") is considered to indicate the dispersion state of the roots. primary coverage.

[0028] If the following conditions (1)-(3) are satisfied, the Primary Coating roots have a suitable length and a suitable state of dispersion, and therefore excellent magnetic properties and Primary Coating adhesion are obtained. In addition, the primary coating becomes dense and acquires excellent rust resistance.

(1) The D _{Al position of the Al} peak is 2.4-12.0 µm.

(2) The number density ND of Al oxides is 0.03-0.18/μm ² .

(3) In a plurality of Al oxides in the observed region at the peak position of the Al emission intensity, the ratio of the total cross-sectional area of identified Al oxides with cross-sectional areas of 0.4-10.0 μm ² to the total cross-sectional area of all Al oxides in the observed region (hereinafter referred to as " the area ratio of the identified oxides Al RA _AREA ") is 75% or more.

[0029] The aforementioned suitable ranges of the position D _Al of the Al peak, the numerical density ND of the Al oxides, and the area fraction of the identified Al oxides RA _AREA can be obtained by adjusting the average particle size of the Y, La, and Ce compounds in the annealing separator, the content of the Y compounds to suitable ranges. , La and Ce in terms of oxides, content of Ca, Sr and Ba compounds in terms of sulfates, average particle size of Ca, Sr and Ba compounds and content of Ti, Zr and Hf compounds in terms of oxides and, in raw material powder before preparation an aqueous suspension annealing separator, the number density of metal compounds selected from the groups Y, La and Ce, the number density of particles of metal compounds selected from the groups Ti, Zr and Hf, and the number density of particles of metal compounds selected from the groups Ca, Sr and Ba.

[0030] The inventors studied the ratio of the C _RE content of Y, La and Ce compounds in terms of oxides (explained later) and the C _G4 content of Ti, Zr and Hf compounds in terms of oxides (explained later) in an annealing separator mainly composed of MgO, images showing the distribution of Al obtained by EDS analysis in the region of the glow discharge mark at the position D _{Al of the Al} peak, and the number density ND of Al oxides (/μm ² ) in each image. As a result, it was found that the number density ND of Al oxides is changed by adjusting the contents of Y, La and Ce compounds and the contents of Ti, Zr and Hf compounds in the annealing separator.

[0031] In addition, by adjusting the contents of the annealing separator of Y, La and Ce compounds in terms of oxides and the contents of Ti, Zr and Hf compounds in terms of oxides, the sizes of Al oxides dispersed in the observed area also change.

[0032] In addition, at the D _Al position of the Al peak, Al oxides with cross-sectional areas of less than 0.4 μm ² (hereinafter referred to as "fine Al oxides") are either extremely shallow coating roots or coating roots that do not reach the peak depth. Small oxides of Al almost do not contribute to improving the adhesion of the primary coating. Even with such fine Al oxides, as the number density increases, the adhesion of the coating improves. However, if the number density of fine Al oxides is increased, the primary coating will not become denser. In this case, not only will the rust resistance of the anisotropic electrical steel sheet deteriorate, but the motion of the domain wall will also be inhibited, and the magnetic loss will drop. On the other hand, Al oxides with cross-sectional areas of more than 10.0 μm ² (hereinafter referred to as "coarse Al oxides") are aggregated, and adhesion is promoted inefficiently. Even with such coarse Al oxides, as the number density increases, the adhesion of the coating improves. However, the higher the number density of large Al oxides, the more the magnetic induction decreases.

[0033] In the observed area, if Al oxides are dispersed with a number of 0.03-0.18/μm ² , and the total area of Al oxides with an area of 0.4-10.0 μm ² , which is a size that can help improve adhesion ( hereinafter referred to as "identified Al oxides"), is 75% or more of the total area of all Al oxides, which means that those depth positions where identified Al oxides are present are aligned. This means that in the Primary Coating, the sizes of the Al oxides are uniform (ie, there are many identified Al oxides) and the Primary Coating is dense. For this reason, the rust resistance of the anisotropic electrical steel sheet is improved, and excellent magnetic properties and excellent coating adhesion are also obtained.

[0034] The above primary coating can be formed using the following annealing separator. An annealing separator suitable for the anisotropic electrical steel sheet of the present invention contains MgO, Y, La, and Ce compounds, Ti, Zr, and Hf compounds, and Ca, Sr, and Ba compounds. When the content of MgO in the annealing separator is taken as 100 mass%, the total content of Y, La and Ce compounds in terms of oxides is 0.8-8.0%, the total content of Ti, Zr and Hf compounds in terms of oxides is 0, 5-9.0%, and the total content of Ca, Sr and Ba compounds in terms of oxides is 0.5-8.0%. In the annealing separator, the average particle size of Ca, Sr and Ba compounds is 12 µm or less, the ratio of the average particle size of Ca, Sr and Ba compounds to the average particle size of Y, La and Ce compounds is 0.1-3.0, the sum of the total content compounds of Y, La and Ce in terms of oxides and the total content of compounds of Ti, Zr and Hf in terms of oxides is 2.0-12.5%, the ratio of the sum of the numbers of Y, La and Ce atoms to the sum of the numbers of Ti, Zr and Hf contained in the annealing separator is 0.18-4.0, and in the powder of raw materials before preparing the annealing separator in the form of an aqueous suspension, the particle number density of the metal compounds selected from the group consisting of Y, La and Ce, and having a size particles of 0.1 µm or more, the number density of particles of metal compounds selected from the group consisting of Ti, Zr and Hf, and having a particle size of 0.1 µm or more, and the number density of particles of metal compounds selected from the group consisting of Ca, Sr and Ba, and having dimensions particles of 0.1 μm or more are 2000000000/g (2 billion particles/g) or more. By using this annealing separator, even in an anisotropic electrical steel sheet made from a hot-rolled steel sheet containing magnetic induction improving elements (Sn, Sb, Bi, Te, Pb, etc.), in the primary coating, the D _{Al position of the Al} peak becomes 2.4-12.0 µm, the number density ND of Al oxides with a size of 0.2 µm or more in diameter of the area-equivalent circle becomes 0.03-0.18/µm ² , and in the observed region 30 µm × 50 µm at the Al emission intensity peak position, the area ratio of the identified Al oxides RA _AREA becomes 75.0% or more. The result is excellent magnetic properties and primer adhesion, as well as excellent rust resistance.

[0035] The anisotropic electrical steel sheet according to the present invention, based on the above knowledge, includes a base steel sheet having a chemical composition containing, in mass%, C: 0.005% or less, Si: 2.5- 4.5%, Mn: 0.02-0.2%, one or more elements selected from the group consisting of S and Se: 0.005% or less in total, sol. Al: 0.01% or less, and N: 0.01% or less, with the rest consisting of Fe and impurities, and a primary coating formed on the surface of the base steel sheet and containing Mg ₂ SiO ₄ as the main component. The position of the peak intensity of Al emission obtained by performing elemental analysis using glow discharge optical emission spectrometry from the surface of the primary coating in the direction along the thickness of the anisotropic electrical steel sheet is in the range of 2.4-12.0 μm from the surface of the primary coating in the direction along the thickness , the numerical density of Al oxides at the peak position of the Al emission intensity is 0.03-0.18/μm ² , and in the set of Al oxides in the observed region of 30 μm × 50 μm at the peak position of the Al emission intensity, the total cross-sectional area of the identified Al oxides with areas section 0.4-10.0 μm ² is 75.0% or more of the total cross-sectional area of all Al oxides in the observed region.

[0036] The method for producing an anisotropic electrical steel sheet according to the present invention includes a cold rolling process of a hot-rolled steel sheet containing, in mass%, C: 0.1% or less, Si: 2.5-4.5%, Mn : 0.02-0.2%, one or more elements selected from the group consisting of S and Se: in the amount of 0.005-0.07%, sol. Al: 0.005-0.05%, and N: 0.001-0.030%, and with the rest consisting of Fe and impurities, with a cold rolling reduction ratio of 80% or more, for the manufacture of cold-rolled steel sheet, used as the main steel sheet , a process for decarburizing annealing a cold-rolled steel sheet, a process for coating the surface of a cold-rolled steel sheet after decarburization annealing with an aqueous slurry containing an annealing separator, and drying this aqueous slurry on the surface of the cold-rolled steel sheet in a furnace at 400-1000°C, and a process for performing final annealing of the cold-rolled steel leaf after the aqueous suspension is dried. The annealing separator contains MgO, at least one or more types of metal compounds selected from the group consisting of Y, La and Ce, at least one or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, and at least one or more types of metal compounds selected from the group consisting of Ca, Sr and Ba, wherein when the content of MgO in the annealing separator is taken as 100 wt.%, the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides is 0.8-8.0%, the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 0.5-9.0%, and the total content of metal compounds selected from the group consisting of Ca, Sr and Ba, in terms of oxides is 0.5-8.0%, the average particle size of metal compounds selected from the group consisting of Ca, Sr and Ba is 12 µm or less, the ratio of the average particle size of the metal compounds selected from the group consisting of Ca, Sr and Ba to the average particle size of metal compounds selected from the group consisting of Y, La and Ce is 0.1-3.0, the sum of the total content of metal compounds selected from the group consisting of of Y, La and Ce, in terms of oxides and the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 2.0-12.5%, the ratio of the sum of the numbers of Y, La atoms and Ce to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator is 0.18-4.0, and furthermore, the particle number density of the metal compounds selected from the group consisting of Y, La and Ce having particle sizes of 0.1 µm or more, a particle number density of metal compounds selected from the group consisting of Ti, Zr and Hf having particle sizes of 0.1 µm or more, and a particle number density of metal compounds selected from the group consisting of Ca, Sr and Ba having a particle size of 0.1 µm or more in the raw material powder before by preparing the aqueous suspension annealing separator, respectively, 2000000000/g or more. However, these particle sizes are diameters of spheres equivalent in volume.

[0037] In the above method for producing an anisotropic electrical steel sheet, the chemical composition of the hot-rolled steel sheet may further contain, instead of a portion of Fe, one or more elements selected from the group consisting of Cu, Sb, and Sn in a total amount of 0.6% or less .

[0038] In the above method for producing an anisotropic electrical steel sheet, the chemical composition of the hot-rolled steel sheet further contains, instead of a portion of Fe, one or more elements selected from the group consisting of Bi, Te, and Pb in a total amount of 0.03% or less.

[0039] An annealing separator according to the present invention is used to manufacture an anisotropic electrical steel sheet. The annealing separator contains MgO, at least one or more types of metal compounds selected from the group consisting of Y, La and Ce, at least one or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, and at least one or more types of metal compounds selected from the group consisting of Ca, Sr and Ba, wherein when the content of MgO in the annealing separator is taken as 100 wt.%, the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides is 0.8-8.0%, the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 0.5-9.0%, and the total content of metal compounds selected from the group consisting of Ca, Sr and Ba, in terms of sulfates is 0.5-8.0%, the average particle size of metal compounds selected from the group consisting of Ca, Sr and Ba is 12 µm or less, the ratio of the average particle size of the metal compounds selected o from the group consisting of Ca, Sr and Ba to the average particle size of metal compounds selected from the group consisting of Y, La and Ce is 0.1-3.0, the sum of the total content of metal compounds selected from the group, consisting of Y, La and Ce, in terms of oxides and the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 2.0-12.5%, the ratio of the sum of the numbers of Y atoms, La and Ce to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator is 0.18-4.0, and furthermore, the particle number density of the metal compounds selected from the group consisting of Y, La and Ce, having particle sizes of 0.1 µm or more, the particle number density of metal compounds selected from the group consisting of Ti, Zr and Hf having particle sizes of 0.1 µm or more, and the particle number density of metal compounds selected from the group consisting of of Ca, Sr and Ba having a particle size of 0.1 µm or more in raw material powder before preparation of the annealing separator in the form of an aqueous suspension are respectively 2000000000/g or more.

[0040] Next, the anisotropic electrical steel sheet, the production method of the anisotropic electrical steel sheet, and the annealing separator used to manufacture the anisotropic electrical steel sheet according to the present invention will be described in detail. In the following description, percentages referring to elemental contents will mean percentages by mass (wt%). In addition, in relation to the numerical values of A and B, the expression "A-B" will mean "A or more and B or less". In this expression, when the unit is specified only after value B, the same unit applies to value A.

Composition of anisotropic electrical steel sheet

[0041] The anisotropic electrical steel sheet according to the present invention is provided with a base steel sheet and a primary coating formed on the surface of the base steel sheet.

Chemical composition of base steel sheet

[0042] The chemical composition of the base steel sheet constituting the aforementioned anisotropic electrical steel sheet contains the following elements. It should be noted that, as explained in the following production method, a base steel sheet is produced by cold rolling using a hot-rolled steel sheet having a chemical composition explained below.

C: 0.005 mass% or less

[0043] Carbon (C) is an element effective for controlling the microstructure until the completion of the decarburization annealing in the manufacturing process, but if the content of C is more than 0.005%, the magnetic properties of the final product anisotropic electrical steel sheet deteriorate. Therefore, the C content is 0.005% or less. The C content is preferably as low as possible. However, if the C content is lowered to less than 0.0001%, the production cost simply increases. The above effect practically does not change. Therefore, the preferred lower limit of the C content is 0.0001%.

Si: 2.5-4.5%

[0044] Silicon (Si) increases the electrical resistance of steel, reducing eddy current losses. If the Si content is less than 2.5%, the above effect is insufficiently obtained. On the other hand, if the Si content is more than 4.5%, the cold workability of the steel falls. Therefore, the Si content is 2.5 to 4.5%. The preferred lower limit of the Si content is 2.6%, and more preferably 2.8%. The preferred upper limit of the Si content is 4.0%, and more preferably 3.8%.

Mn: 0.02-0.2%

[0045] Manganese (Mn) binds to S and Se explained below in the manufacturing process to form MnS and MnSe. These precipitates act as inhibitors (inhibitors of the normal growth of crystal grains) and cause secondary recrystallization in the steel. Mn further enhances the hot workability of the steel. If the Mn content is less than 0.02%, the above effect is insufficiently obtained. On the other hand, if the Mn content is more than 0.2%, secondary recrystallization does not occur, and the magnetic characteristics of the steel fall. Therefore, the Mn content is 0.02 to 0.2%. The preferred lower limit of the Mn content is 0.03%, and more preferably 0.04%. The preferred upper limit of the Mn content is 0.13%, and more preferably 0.10%.

One or more elements selected from the group consisting of S and Se: 0.005% or less in total

[0046] Sulfur (S) and selenium (Se) bind to Mn in the manufacturing process to form MnS and MnSe, which act as inhibitors. However, if the content of these elements in total exceeds 0.005%, the magnetic properties drop due to the remaining inhibitors. In addition, due to the segregation of S and Se in the anisotropic electrical steel sheet, surface defects sometimes occur. Therefore, in the anisotropic electrical steel sheet, the total content of one or more elements selected from the group consisting of S and Se is 0.005% or less. The sum of the contents of S and Se in the anisotropic electrical steel sheet is preferably as low as possible. However, if the sum of the S content and the Se content in the anisotropic electrical steel sheet is reduced to less than 0.0005%, the production cost simply increases. The above effect practically does not change. Therefore, the preferred lower limit for the total content of one or more elements selected from the group consisting of S and Se in the anisotropic electrical steel sheet is 0.0005%.

Solv. Al: 0.01 mass% or less

[0047] Aluminum (Al) binds to N during production to form AlN, which acts as an inhibitor. However, if the content of sol. Al in the anisotropic electrical steel sheet is more than 0.01%, the inhibitor is left excessively in the base steel sheet, and the magnetic properties are degraded. Therefore, the content of sol. Al is 0.01% or less. The preferred upper limit of the content of sol. Al is 0.004%, and more preferably 0.003%. The content of sol. Al is preferably as low as possible. However, if you lower the content of sol. Al in the anisotropic electrical steel sheet to less than 0.0001%, the production cost simply increases. The above effect practically does not change. Therefore, the preferred lower limit of the content of sol. The Al in the anisotropic electrical steel sheet is 0.0001%. It should be noted that in this description sol. Al means "acid soluble Al". Therefore, the content of sol. Al is the content of acid-soluble Al.

N: 0.01 mass% or less

[0048] Nitrogen (N) binds to Al during manufacture to form AlN, which acts as an inhibitor. However, if the N content in the anisotropic electrical steel sheet is more than 0.01%, the inhibitor remains excessively in the anisotropic electrical steel sheet, and the magnetic properties fall. Therefore, the N content is 0.01% or less. The preferred upper limit of the N content is 0.004%, and more preferably 0.003%. The N content is preferably as low as possible. However, if the total N content in the anisotropic electrical steel sheet is reduced to less than 0.0001%, the production cost simply increases. The above effect practically does not change. Therefore, the preferred lower limit of the N content in the anisotropic electrical steel sheet is 0.0001%.

[0049] The rest of the chemical composition of the base steel sheet (base sheet) of the anisotropic electrical steel sheet according to the present invention consists of Fe and impurities. Here, "impurities" means the following elements that come from the ore used as raw material, scrap or production environment, etc. in industrial production of the base steel sheet, or remain in the steel without being completely removed by refining annealing, and which are acceptable in an amount that does not adversely affect the performance of the anisotropic electrical steel sheet according to the present invention.

Regarding impurities

[0050] In the impurities in the base steel sheet of the anisotropic electrical steel sheet according to the present invention, the total content of one or more elements selected from the group consisting of Cu, Sn, Sb, Bi, Te, and Pb is 0.30% or less .

[0051] With regard to copper (Cu), tin (Sn), antimony (Sb), bismuth (Bi), tellurium (Te) and lead (Pb), the part of Cu, Sn, Sb, Bi, Te and Pb is mainly steel sheet is removed from the system by high temperature heat treatment, also known as "refining annealing", one final annealing process. These elements increase the secondary recrystallization orientation selectivity in final annealing, showing magnetic induction improvement action, but if left in the anisotropic electrical steel sheet after completion of final annealing, cause deterioration in magnetic loss as simple impurities. Therefore, the total content of one or more elements selected from the group containing Cu, Sn, Sb, Bi, Te, and Pb is 0.30% or less. As explained above, these elements are impurities, so it is preferable to have as low a total content of these elements as possible.

Primary Coating

[0052] The anisotropic electrical steel sheet according to the present invention is also provided with a primary coating as explained above. The primary coating is formed on the surface of the base steel sheet. The main component of the primary coating is forsterite (Mg ₂ SiO ₄ ). More specifically, the primary coating contains 50-90 wt.% Mg ₂ SiO ₄ .

[0053] It should be noted that the main component of the Primary Coating, as explained above, is Mg ₄ SiO ₄ , but the Primary Coating also contains Ce, Zr and Ca. The Ce content in the primary coating is 0.001-8.0%. The content of Zr in the primary coating is 0.0005-4.0%. The content of Ca in the primary coating is 0.0005-4.0 wt.%.

[0054] As explained above, in the present invention, an annealing separator containing the aforementioned Y, La, and Ce compounds, Ti, Zr, and Hf compounds, and Ca, Sr, and Ba compounds is used in the method for producing an anisotropic electrical steel sheet. Because of this, the magnetic properties of the anisotropic electrical steel sheet can be improved, and the adhesion of the coating and the rust resistance of the primary coating can also be improved. Due to Y, La and Ce compounds, Ti, Zr and Hf compounds and Ca, Sr and Ba compounds contained in the annealing separator, the Primary Coating also has the aforementioned contents of Y, La, Ce, Ti, Zr, Hf, Ca, Sr and Ba.

[0055] The content of Mg ₂ SiO ₄ in the primary coating can be measured in the following way. The anisotropic electrical steel sheet is subjected to electrolysis to separate the primary coating from the surface of the base metal sheet. Mg in the separated primary coating is quantified by inductively coupled plasma mass spectrometry (ICP-MS). The product of the obtained quantitative value (wt.%) and the molecular weight of Mg ₂ SiO ₄ is divided by the atomic mass of Mg, finding the equivalent content of Mg ₂ SiO ₄ .

[0056] The contents of Y, La, Ce, Ti, Zr, Hf, Ca, Sr and Ba in the primary coating can be measured by the following method. The anisotropic electrical steel sheet is subjected to electrolysis to separate the primary coating from the surface of the base metal sheet. The contents of Y, La and Ce (wt.%), the contents of Ti, Zr and Hf (wt.%) and the contents of Ca, Sr and Ba (wt.%) in the separated primary coating are quantitatively analyzed by ICP-MS.

Al emission intensity peak position at GDS

[0057] In addition, in the anisotropic electrical steel sheet according to the present invention, the peak position of the Al emission intensity obtained by performing elemental analysis by glow discharge optical emission spectrometry from the surface of the primary coating in the thickness direction of the anisotropic electrical steel sheet is in the range 2.4-12.0 µm from the surface of the primary coating in the thickness direction.

[0058] In the anisotropic electrical steel sheet, there are engaging structures at the interface between the primary coating and the steel sheet (base metal, base sheet). In particular, parts of the primary coating penetrate into the steel sheet from the surface of the steel sheet. Parts of the Primary Coating which penetrate inside the steel sheet from the surface of the steel sheet exhibit a so-called anchoring effect and increase the adhesion of the Primary Coating to the steel sheet. Hereinafter in the present description, parts of the primary coating penetrating into the steel sheet from the surface of the steel sheet will be referred to as "primary coating roots".

[0059] In areas where Primary Coating roots penetrate deep into the steel sheet, the primary component of Primary Coating roots is spinel (MgAl ₂ O ₄ ), one of the oxides of Al. The Al emission intensity peak obtained by performing elemental analysis using glow discharge optical emission spectrometry indicates the position where the spinel is present.

[0060] The depth position of the Al emission intensity peak from the Primary Coating surface is defined as "D _{Al position of Al} peak" (μm). The position D _Al of the Al peak less than 2.4 μm means that the spinel is formed at a shallow position from the surface of the steel sheet, that is, the primary coating roots are shallow (small). That is, it means that the roots of the primary coating are shallow. In this case, the adhesion of the primary coating is low. On the other hand, the D _Al position of the Al peak above 12.0 µm means that the roots of the primary coating have developed excessively. The roots of the Primary Coating penetrate down into deep parts within the steel sheet. In this case, the roots of the primary coating prevent the motion of the domain walls, and the magnetic properties decrease.

[0061] If the D _Al position of the Al peak is 2.4-12.0 µm, it is possible to maintain excellent magnetic properties, and the adhesion of the coating can be improved. The preferred lower limit of the D _Al position of the Al peak is 3.0 µm, more preferably 4.0 µm. The preferred upper limit of the D _Al position of the Al peak is 11.0 µm, more preferably 10.0 µm.

[0062] The position D _Al of the Al peak can be measured by the following method. For elemental analysis, the well-known glow discharge optical emission spectrometry (GDS) is used. In particular, an argon (Ar) atmosphere is created in the space above the surface of the anisotropic electrical steel sheet. An electrical voltage is applied to the anisotropic electrical steel sheet to generate a glow discharge plasma, which is used to sputter the surface layer of the steel sheet as it is analyzed in the thickness direction.

[0063] Al contained in the surface layer of the steel sheet is identified based on the wavelength of the emission spectrum characteristic of this element and generated by excitation of atoms in the glow discharge plasma. In addition, the identified Al emission intensity is plotted as a function of depth. Based on this Al emission intensity plot, the D _{Al position of the Al} peak is found.

[0064] The position in depth from the surface of the primary coating in elemental analysis is calculated based on the sputtering time. In particular, in a standard sample, the relationship between spray time and spray depth in (hereinafter referred to as calibration results) is predetermined. The calibration results are used to convert spray time to spray depth. The converted spray depth is defined as the depth position found by elemental analysis (Al analysis) (depth position from the Primary Coating surface). In the GDS of the present invention, a commercially available high frequency glow discharge optical emission spectrometry analyzer can be used.

Number density ND of Al oxides with a size of 0.2 µm or more at the discharge mark

[0065] In addition, in the anisotropic electrical steel sheet according to the present invention, the number density ND of Al oxides with a size of 0.2 µm or more in terms of the diameter of the area-equivalent circle at the D _{Al position of the Al} peak is 0.03-0.18 / µm ² .

[0066] As explained above, the D _Al position of the Al peak corresponds to parts of the roots of the primary coating. In the roots of the primary coating there is a large amount of alumina spinel (MgAl ₂ O ₄ ). Therefore, when determining the number density of Al oxides in any region at the position D _Al of the Al peak (for example, in the lower parts of the glow discharge marks) as the number density ND of Al oxides, the number density ND of Al oxides becomes an indicator showing the dispersed state of the roots of the primary coating (spinels ) in the surface layer of the steel sheet.

[0067] If the number density ND of Al oxides is less than 0.03/μm ² , the primary coating roots are not sufficiently formed. For this reason, the adhesion of the primary coating to the steel sheet is poor. On the other hand, if the number density ND of the Al oxides exceeds 0.18/μm ² , the primary coating roots develop excessively and penetrate downward into deep portions within the steel sheet. In this case, the roots of the primary coating impede secondary recrystallization and impede the movement of domain walls, and the magnetic properties decrease. Therefore, the numerical density ND of Al oxides is 0.03-0.18/μm ² . The preferred lower limit of the number density ND of Al oxides is 0.035/µm ² , and more preferably 0.04/µm ² . The preferred upper limit of the number density ND of Al oxides is 0.15/µm ² , and more preferably 0.1/µm ² .

[0068] The number density ND of Al oxides can be found by the following method: A glow discharge optical emission analyzer is used for glow discharge up to the D _{Al position of the Al} peak. Any 30 µm × 50 µm area (observed area) in the discharge marks at the D _Al position of the Al peak is analyzed for elements using an energy dispersive X-ray spectroscope (EDS) to obtain a map showing the characteristic X-ray intensity distribution in the observed area and identify Al oxides. . Specifically, the region in which the intensity of the characteristic X-ray emission of oxygen (O) is 50% or more of the maximum intensity of the characteristic X-ray emission of O in the observed region is identified as an oxide. In the identified oxide regions, the region in which the Al characteristic X-ray intensity is 30% or more of the maximum Al characteristic X-ray intensity is identified as alumina. The identified Al oxide is mainly spinel. In addition, there is a possibility that these are silicates containing various alkaline earth metals and Al in high concentrations. Among the identified Al oxides, count the number of Al oxides with a size of 0.2 μm or more in diameter of an area-equivalent circle, and find the numerical density ND of Al oxides (/μm ² ) using the following formulas:

Equivalent circle diameter = √(4/p⋅(area of regions identified as Al oxides (area of each analysis point on a map showing the characteristic X-ray intensity distribution) × number of analysis points corresponding to regions identified as Al oxides))

The area of each analysis point on a map showing the intensity distribution of the characteristic X-ray radiation = the area of the observed area × the number of analysis points

ND = number of identified Al oxides with an equivalent circle diameter of 0.2 μm or more / area of the observed area.

[0069] If the Ce content of the Primary Coating is 0.001-8.0%, the Zr content of the Primary Coating is 0.0005-4.0%, and the Ca content of the Primary Coating is 0.0005-4.0%, Position D The Al of the _Al peak becomes 2.4-12.0 µm, and the number density ND of the Al oxides at the D _{Al position of the Al} peak becomes 0.03-0.18/µm ² .

Area fraction of identified oxides Al RA _AREA

[0070] In addition, in the anisotropic electrical steel sheet according to the present invention, in the observed region of 30 μm × 50 μm at the D _{Al position of the Al} peak, among the plurality of Al oxides, the proportion of the total area of identified Al oxides with an area of 0.4-10, 0 μm ² in the total area of all Al oxides in the observed area (area ratio of identified Al oxides RA _AREA ) is 75.0% or more. The area of the observed area may, for example, be equal to the area of any area of 30 μm×50 μm. It can be freely selected at the D _{Al position of the Al} peak.

[0071] As explained above, the D _Al position of the Al peak corresponds to part of the roots of the primary coating. In the roots of the primary coating there is a large amount of alumina spinel (MgAl ₂ O ₄ ). Therefore, the area fraction of the identified Al oxides RA _AREA shows the dispersed state of the primary coating roots (Al oxides) in the same way as the numerical density ND of the Al oxides.

[0072] In the observed region of 30 μm×50 μm, if among a plurality of Al oxides, the total area of Al oxides with an area of 0.4-10.0 μm ² is 75% or more of the total area of all Al oxides in the observed region, this means that the depth positions of the identified Al oxides that help improve adhesion are aligned. This means that the grain sizes of the Al oxides in the resulting Primary Coating are substantially uniform and the Primary Coating is dense.

[0073] If the area ratio of the identified oxides Al RA _AREA is too low, the Primary Coating does not become dense and the rust resistance drops. Therefore, the area ratio of identified oxides Al RA _AREA is 75.0% or more. The preferred area ratio of the identified oxides Al RA _AREA is 84.0% or more, more preferably 90.0% or more.

[0074] It should be noted that in the above observed area, if the area of the Al oxides is less than 0.4 μm ² , they do not grow sufficiently as the roots of the primary coating. On the other hand, if the area of Al oxides exceeds 10.0 μm ² , primary coating roots develop excessively in number. As a result, the primary coating does not become dense and the rust resistance decreases.

[0075] The area fraction of identified oxides Al RA _AREA can be found in the following way: an optical glow discharge analyzer is used for glow discharge up to the D _{Al position of the Al} peak. Any 30 μm×50 μm region (observed region) in the discharge marks at the D _Al position of the Al peak is analyzed for elements by an energy dispersive X-ray spectroscope (EDS) to identify Al oxides in the observed region. Specifically, a region in which the intensity of the characteristic X-ray emission of oxygen (O) is 50% or more of the maximum intensity of the characteristic X-ray emission of O in the observed region is identified as an oxide. In the identified oxide regions, the region in which the Al characteristic X-ray intensity is 30% or more of the maximum Al characteristic X-ray intensity is identified as alumina. The identified Al oxide is mainly spinel. In addition, there is a possibility that these are silicates containing various alkaline earth metals and Al in high concentrations. Based on the measurement results, a diagram of the distribution of Al oxides in the observed region is constructed. The area of the observed region may, for example, have dimensions of 30 μm×50 μm. It can be freely selected at any position D _{Al of the Al} peak.

[0076] In the constructed distribution diagram (observed area), the areas of Al oxides are calculated. Based on the results of the calculations in the distribution diagram, Al oxides with an area of 0.4-10.0 μm ² are considered "identified Al oxides". Then the total area of the identified Al oxides is found. In addition, the total area of all Al oxides is found on the distribution diagram. Based on the following formula, the area fraction of the identified oxides Al RA _AREA is found.

[0077] Area fraction of identified Al oxides RA _AREA =total area of identified Al oxides in the observed area/total area of all Al oxides in the observed area×100.

Mode of production

[0078] Next, one example of the production method of the anisotropic electrical steel sheet according to the present invention will be explained. One example of a method for producing an anisotropic electrical steel sheet includes a cold rolling process, a decarburization annealing process, and a finishing annealing process. These processes will be explained next.

cold rolling process

[0079] In the cold rolling process, a hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. Hot rolled steel sheet has the following chemical composition.

C: 0.1 mass% or less

[0080] If the content of C in the hot-rolled steel sheet is more than 0.1%, the time required for decarburization annealing becomes longer. In this case, production costs increase and productivity falls. Therefore, the C content in the hot-rolled steel sheet is 0.1% or less. The preferred upper limit of the C content in the hot rolled steel sheet is 0.092%, and more preferably 0.085%. The lower limit of the C content in the hot rolled steel sheet is 0.005%, more preferably 0.02%, even more preferably 0.04%.

Si: 2.5-4.5%

[0081] As explained in the section on the chemical composition of the final product anisotropic electrical steel sheet, Si increases the electrical resistance of the steel, but if it is present excessively, cold workability deteriorates. If the Si content of the hot rolled steel sheet is 2.5% to 4.5%, the Si content of the anisotropic electrical steel sheet after the final annealing process becomes 2.5% to 4.5%. The preferred upper limit of the Si content in the hot rolled steel sheet is 4.0%, more preferably 3.8%. The preferred lower limit of the Si content in the hot rolled steel sheet is 2.6%, more preferably 2.8%.

Mn: 0.02-0.2%

[0082] As explained in the section on the chemical composition of the final product, anisotropic electrical steel sheet, during the manufacturing process, Mn binds with S and Se, forming precipitates that act as inhibitors. Mn further improves the hot workability of the steel. If the Mn content of the hot-rolled steel sheet is 0.02-0.2%, the Mn content of the anisotropic electrical steel sheet after the final annealing process becomes 0.02-0.2%. The preferred upper limit of the Mn content in the hot rolled steel sheet is 0.13%, more preferably 0.1%. The preferred lower limit of the Mn content in the hot rolled steel sheet is 0.03%, more preferably 0.04%.

One or more elements selected from the group consisting of S and Se: in the amount of 0.005-0.07%

[0083] In the manufacturing process, sulfur (S) and selenium (Se) bind to Mn to form MnS and MnSe. MnS and MnSe act as inhibitors required to suppress the growth of crystal grains during secondary recrystallization. If the total content of one or more elements selected from the group consisting of S and Se is less than 0.005%, the above effect is difficult to obtain. On the other hand, if the total content of one or more elements selected from the group consisting of S and Se is more than 0.070%, secondary recrystallization does not occur in the production process, and the magnetic properties of the steel fall. Therefore, in the hot-rolled steel sheet, the total content of one or more elements selected from the group consisting of S and Se is 0.005-0.07%. The preferred lower limit for the total content of one or more elements selected from the group consisting of S and Se is 0.008%, more preferably 0.016%. The preferred upper limit for the total content of one or more elements selected from the group consisting of S and Se is 0.06%, more preferably 0.05%.

Solv. Al: 0.005-0.05%

[0084] In the manufacturing process, aluminum (Al) bonds with N to form AlN. AlN acts as an inhibitor. If the content of sol. Al in the hot rolled steel sheet is less than 0.01%, the above effect is not obtained. On the other hand, if the content of sol. Al in hot-rolled steel sheet exceeds 0.05%, AlN is coarsened. In this case, it becomes difficult for AlN to act as an inhibitor, and sometimes secondary recrystallization is not caused. Therefore, the content of sol. Al in hot rolled steel sheet is 0.005-0.05%. The preferred upper limit of the content of sol. The Al in the hot rolled steel sheet is 0.04%, more preferably 0.035%. The preferred lower limit of the content of sol. The Al in the hot rolled steel sheet is 0.01%, more preferably 0.015%.

N: 0.001-0.030%

[0085] In the manufacturing process, nitrogen (N) binds to Al to form AlN, which acts as an inhibitor. If the N content in the hot-rolled steel sheet is less than 0.001%, the above effect is not obtained. On the other hand, if the content of N in the hot-rolled steel sheet exceeds 0.030%, AlN coarsens. In this case, it becomes difficult for AlN to act as an inhibitor, and sometimes secondary recrystallization is not caused. Therefore, the N content in the hot-rolled steel sheet is 0.001-0.030%. The preferred upper limit of the N content in the hot rolled steel sheet is 0.012%, more preferably 0.010%. The preferred lower limit of the N content in the hot rolled steel sheet is 0.005%, more preferably 0.006%.

[0086] The rest of the chemical composition in the hot-rolled steel sheet of the present invention consists of Fe and impurities. Here, "impurities" means elements that come from the ore used as raw material, scrap or production environment, etc. industrial production of hot-rolled steel sheet, and which are acceptable in an amount that does not adversely affect the hot-rolled steel sheet of the present embodiment.

Regarding optional elements

[0087] The hot-rolled steel sheet according to the present invention may further contain, instead of a portion of Fe, one or more elements selected from the group consisting of Cu, Sn, and Sb in a total amount of 0.6% or less. All of these elements are optional elements.

One or more elements selected from the group consisting of Cu, Sn and Sb: 0-0.6% in total

[0088] Copper (Cu), tin (Sn) and antimony (Sb) are optional elements, and should not be required. If they are included, Cu, Sn and Sb increase the magnetic induction of the anisotropic electrical steel sheet. If Cu, Sn, and Sb are contained even in a small amount, the above effect is obtained to some extent. However, if the content of Cu, Sn and Sb in total exceeds 0.6%, it becomes difficult for an inner oxide layer to form during the decarburization annealing. In this case, during the final annealing, the formation of the primary coating, which occurs due to the reaction of the MgO of the annealing separator and the SiO _{2 of} the inner oxide layer, is delayed. As a result, the adhesion of the formed primary coating falls. In addition, after refining annealing, Cu, Sn, and Sb easily remain as impurity elements. As a result, the magnetic properties deteriorate. Therefore, the content of one or more elements selected from the group consisting of Cu, Sn and Sb is 0-0.6% in total. The preferred lower limit for the total content of one or more elements selected from the group consisting of Cu, Sn and Sb is 0.005%, more preferably 0.007%. The preferred upper limit for the total content of one or more elements selected from the group consisting of Sn and Sb is 0.5%, more preferably 0.45%.

[0089] The hot-rolled steel sheet according to the present invention may further contain, instead of a portion of Fe, one or more elements selected from the group consisting of Bi, Te, and Pb in a total amount of 0.03% or less. All of these elements are optional elements.

One or more elements selected from the group consisting of Bi, Te and Pb: 0-0.03% in total

[0090] Bismuth (Bi), tellurium (Te) and lead (Pb) are optional elements, and should not be required. If they are included, Bi, Te, and Pb increase the magnetic induction of the anisotropic electrical steel sheet. If these elements are contained even in a small amount, the above effect is obtained to some extent. However, if the total content of these elements is more than 0.03%, during the final annealing, these elements are segregated at the surface and interface of the primary coating, and the steel sheet becomes smooth. In this case, the adhesion of the primary coating falls. Therefore, the total content of one or more elements selected from the group containing Bi, Te and Pb is 0-0.03%. The preferred lower limit for the total content of one or more elements selected from the group consisting of Bi, Te and Pb is 0.0005%, more preferably 0.001%. The preferred upper limit for the total content of one or more elements selected from the group consisting of Bi, Te and Pb is 0.02%, more preferably 0.015%.

[0091] A hot-rolled steel sheet having the above chemical composition is produced by a known method. One example of a method for producing a hot rolled steel sheet is as follows. A slab having the same chemical composition as the above-mentioned hot-rolled steel sheet is prepared. The slab is produced by known refining and casting processes. The slab is heated. The heating temperature of the slab is, for example, over 1280°C to 1350°C. The heated slab is subjected to hot rolling to produce a hot-rolled steel sheet.

[0092] The produced hot-rolled steel sheet is subjected to cold rolling to obtain a cold-rolled steel sheet as the main steel sheet. Cold rolling may be performed only once or may be performed several times. If cold rolling is performed several times, intermediate annealing is performed between cold rolling passes to soften the steel, and then cold rolling is performed again. By performing cold rolling one or more times, a cold-rolled steel sheet having a final product thickness (final thickness) is produced.

[0093] The cold rolling reduction ratio for one or more cold rolling passes is 80% or more. Here, the cold rolling reduction ratio (%) is defined as follows: Cold rolling reduction ratio (%) = {1-(cold-rolled steel plate thickness after final cold rolling)/(hot-rolled steel plate thickness before initial cold rolling starts)}×100 .

[0094] It should be noted that the preferred upper limit of the cold rolling reduction ratio is 95%. In addition, before cold rolling, the hot rolled steel sheet may be heat treated or may be pickled.

Decarburizing Annealing Process

[0095] The steel sheet produced by the cold rolling process is subjected to a decarburization annealing and, if necessary, treated with a nitriding annealing. The decarburization annealing is carried out in a known humid atmosphere containing hydrogen-nitrogen. Due to the decarburization annealing, the C concentration in the anisotropic electrical steel sheet is reduced to 50 ^ppm or less, that is, to a level that can suppress deterioration due to magnetic aging. In the process of decarburization annealing, in addition, primary recrystallization occurs in the steel sheet and the work hardening introduced due to the cold rolling process is removed. In addition, during the decarburization annealing process, an inner oxide layer with SiO ₂ as its main component is formed on a part of the surface layer of the steel sheet. The heating temperature during decarburization annealing is known. For example, it is 750-950°C. The holding time at this annealing temperature is, for example, 1-5 minutes.

Final annealing process

[0096] The steel sheet after the decarburization annealing process is subjected to a final annealing process. In the final annealing process, the surface of the steel sheet is first coated with an aqueous slurry containing an annealing separator. The steel sheet to which the aqueous slurry has been applied is annealed (final annealing).

Regarding aqueous suspension

[0097] An aqueous slurry is obtained by adding pure industrial grade water to an annealing separator, which will be explained later, and mixing them. The ratio of the annealing separator to industrial clean water can be determined to provide the required amount of coating when using a roller coater. For example, this ratio is preferably 2 or more and 20 or less. If the ratio of water to annealing separator is less than 2, then the viscosity of the aqueous slurry becomes too high and the annealing separator cannot be evenly applied to the surface of the steel sheet, so this is not preferable. If the ratio of water to annealing separator exceeds 20, the subsequent drying process will not dry the aqueous slurry sufficiently, and the remaining moisture in the final annealing will cause further oxidation of the steel sheet, resulting in deterioration of the appearance of the primary coating, so this is not preferable.

Concerning the annealing separator

[0098] In the present invention, the annealing separator used in the final annealing process contains magnesium oxide (MgO) and additives. MgO is the main component of the annealing separator. "Main component" means a component contained in a certain substance in the amount of 50 wt.% or more, preferably 70 wt.% or more, more preferably 90 wt.% or more. The amount of the annealing separator applied to one side of the steel sheet is preferably 2 g/m ² or more and 10 g/m ² or less, for example. If the amount of the annealing separator applied to the steel sheet is less than 2 g/m ² , the steel sheets will stick to each other in the final annealing, so this is not preferable. If the amount of the annealing separator to be applied to the steel sheet is more than 10 g/m ² , the production cost will increase, so this is not preferable. The annealing separator may be applied by electrostatic coating or the like instead of being applied as an aqueous suspension. The additives include at least one or more types of metal compounds selected from the group consisting of Y, La and Ce, at least one or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, and at least one or more types of metal compounds selected from the group consisting of Ca, Sr and Ba, wherein when the content of MgO in the annealing separator is taken as 100 wt%, the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides is 0.8-8.0%, the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 0.5-9.0%, and the total the content of metal compounds selected from the group consisting of Ca, Sr and Ba, in terms of oxides is 0.5-8.0%. In the annealing separator, the average particle size of the metal compounds selected from the group consisting of Ca, Sr and Ba is 12 µm or less, and the ratio of the average particle size of the metal compounds selected from the group consisting of Ca, Sr and Ba to the average particle size particles of metal compounds selected from the group consisting of Y, La and Ce is 0.1-3.0, and the sum of the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides and the total the content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 2.0-12.5%. The ratio of the sum of the numbers of Y, La and Ce atoms to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator is 0.18-4.0.

Additives

[0099] Additives include Y, La and Ce compounds, Ti, Zr and Hf compounds, and Ca, Sr and Ba compounds. The contents of Y, La and Ce compounds, Ti, Zr and Hf compounds and Ca, Sr and Ba compounds are as follows.

Compounds of a metal selected from the group consisting of Y, La and Ce

[0100] Compounds of a metal selected from the group consisting of Y, La and Ce (“Y, La and Ce compounds”) are contained, in terms of oxides, in a total amount of 0.8-8.0%, when taking the content MgO in the annealing separator for 100 wt.%. Here, some single type of Y, La and Ce compound contained in the annealing separator is defined as M _RE . The content of W _RE (wt.%) M _RE in the annealing separator in terms of oxides is as follows:

W _RE =(amount of M _RE added (wt%))/(molecular weight M _RE )×((molecular weight Y ₂ O ₃ )×(number of Y atoms per molecule M _RE /2)+(molecular weight La ₂ O ₃ )×(number of La atoms in the molecule M _RE /2)+(molecular weight of CeO ₂ )×(number of Ce atoms in the molecule M _RE )).

In addition, with regard to M _RE , the ratio x _RE of the sum of the numbers of Y, La and Ce atoms to the number of Mg atoms contained in the annealing separator is as follows:

x _RE =((number of Y atoms in the M _RE molecule)+(number of La atoms in the M _RE molecule)+(number of Ce atoms in the M _RE molecule))×(amount of M _RE added (wt%)/molecular weight of M _RE )×(molecular weight MgO/100).

Therefore, the total C _RE content of Y, La, and Ce compounds in terms of oxides, taken as 100 mass% of the MgO content in the annealing separator to which one, two or more Y, La, and Ce compounds have been added (hereinafter referred to as "C content _RE compounds of Y, La and Ce in terms of oxides”), and the ratio X _RE of the sum of the numbers of Y, La and Ce atoms to the number of Mg atoms in the annealing separator (hereinafter referred to as the “occurrence X _RE of Y, La and Ce atoms”) represent is respectively the sum of W _RE and the sum x _RE of metal compounds selected from the group consisting of Y, La and Ce contained in the annealing separator.

[0101] "Compounds Y, La and Ce", for example, are oxides or hydroxides, carbonates, sulfates, etc., which are partially or completely converted into oxides during drying and final annealing explained later. Compounds Y, La and Ce suppress the aggregation of the primary coating. The Y, La and Ce compounds additionally function as sources of oxygen evolution. This promotes the growth of the roots of the primary coating formed during the final annealing, and the coating oxides become denser. As a result, the adhesion of the primary coating to the steel sheet is improved. In addition, resistance to rust is increased. If the content of C _RE in terms of oxides is less than 0.8%, the above effect is insufficiently obtained. On the other hand, if the content of C _RE in terms of oxides exceeds 8.0%, the primary coating roots develop excessively. In this case, the roots of the primary coating prevent the motion of the domain walls, and the magnetic properties decrease. In addition, if the content of C _RE in terms of oxides exceeds 8.0%, the content of MgO in the annealing separator becomes lower, so that the generation of forsterite is suppressed. That is, the reactivity decreases. Therefore, the content of C _RE in terms of oxides is 0.8-8.0%. The preferred lower limit of the content of C _RE in terms of oxides is 1.0%, more preferably 2.0%. The preferred upper limit of the content of C _RE in terms of oxides is 6.0%, more preferably 4.5%.

Compounds of a metal selected from the group consisting of Ti, Zr and Hf

[0102] Compounds of a metal selected from the group consisting of Ti, Zr and Hf (“Ti, Zr and Hf compounds”) are contained, in terms of oxides, in a total amount of 0.5-9.0% when taking the content of MgO in the annealing separator for 100 wt.%. Here, some single type of Ti, Zr and Hf compound contained in the annealing separator is defined as M _G4 . The content of W _G4 (wt.%) M _G4 in the annealing separator in terms of oxides is as follows:

W _G4 =(amount of M _G4 added (wt%))/(molecular weight of M _G4 )×((molecular weight of TiO ₂ )×(number of Ti atoms in M _G4 molecule)+(molecular weight of ZrO ₂ )×(number of atoms Zr in the M _G4 molecule)+(molecular weight of HfO ₂ )×(number of Hf atoms in the M _G4 molecule)).

In addition, with regard to M _G4 , the ratio x _G4 of the sum of the numbers of Ti, Zr and Hf atoms to the number of Mg atoms contained in the annealing separator is as follows:

x _G4 =((number of Ti atoms in molecule M _G4 )+(number of Zr atoms in molecule M _G4 )+(number of Hf atoms in molecule M _G4E ))×(amount of added M _G4 (wt%)/molecular weight of M _G4 )×(molecular weight MgO/100).

Therefore, the total C _G4 content of Ti, Zr and Hf compounds in terms of oxides, taken as 100 wt. _G4 compounds of Ti, Zr and Hf in terms of oxides”), and the ratio X _G4 of the sum of the numbers of Ti, Zr and Hf atoms to the number of Mg atoms in the annealing separator (hereinafter referred to as the “occurrence X _G4 of Ti, Zr and Hf atoms”) represent is respectively the sum W _G4 and the sum x _G4 of metal compounds selected from the group consisting of Ti, Zr and Hf contained in the annealing separator.

[0103] "Ti, Zr and Hf compounds", for example, are oxides and hydroxides, carbonates, sulfates, etc., which are partially or completely converted into oxides during drying and final annealing explained later. The Ti, Zr and Hf compounds, when included in the annealing separator along with the Y, La and Ce compounds, react with a portion of the Y, La and Ce compounds during the final annealing to form complex oxides. If complex oxides are formed, compared to when only Y, La, and Ce compounds are contained, the capacity of the annealing separator to release oxygen can be increased. For this reason, by incorporating Ti, Zr, and Hf compounds instead of Y, La, and Ce compounds, the drop in magnetic properties accompanying the incorporation of excess Y, La, and Ce compounds can be suppressed while promoting Primary Coating root growth and enhancing Primary Coating adhesion to steel sheet. . If the content of C _G4 in terms of oxides is less than 0.5%, the above effect is insufficiently obtained. On the other hand, if the content of C _G4 in terms of oxides exceeds 9.0%, the content of MgO in the annealing separator becomes lower, so that the generation of forsterite is suppressed. That is, the reactivity drops and the amount of surface oxides decreases. As a result, rust resistance deteriorates. In addition, if the content of C _G4 in terms of oxides exceeds 9.0%, the magnetic properties sometimes fall. If the content of C _G4 in terms of oxides is 0.5-9.0%, the drop in rust resistance and the drop in magnetic properties can be suppressed, while the adhesion of the primary coating to the base steel sheet can be improved.

[0104] The preferred lower limit of the content of C _G4 in terms of oxides is 1.0%, more preferably 2.0%. The preferred upper limit of the C _G4 content is 8.0%, more preferably 7.5%.

Amount of content C _RE Y, La and Ce compounds in terms of oxides and C contents _G4 Ti, Zr and Hf compounds in terms of oxides

[0105] The sum of the C _RE content of Y, La and Ce compounds in terms of oxides and the content of C _G4 compounds of Ti, Zr and Hf in terms of oxides is 2.0-12.5%. If this sum of contents is less than 2.0%, the Primary Coating roots do not grow enough, and the adhesion of the Primary Coating to the steel sheet falls. On the other hand, if this sum of contents exceeds 12.5%, the roots of the primary coating develop excessively and the magnetic properties fall. Therefore, the sum of the C _RE content of Y, La and Ce compounds in terms of oxides and the C _G4 contents of Ti, Zr and Hf compounds in terms of oxides is 2.0-12.5%. The preferred lower limit for this amount of contents is 3.0%, while the preferred upper limit is 11.0%.

Compounds of a metal selected from the group consisting of Ca, Sr and Ba

[0106] Compounds of a metal selected from the group consisting of Ca, Sr and Ba (referred to as "Ca, Sr and Ba compounds") are contained, in terms of sulfates, in a total amount of 0.5-8.0% when taking the content MgO in the annealing separator for 100 wt.%. Here, when defining some single type of compound Ca, Sr and Ba contained in the annealing separator as M _AE , the content of WC _AE M _AE , in terms of sulfates, when the content of MgO in the annealing separator is taken as 100 wt.%, is found by the following formula:

W _AE =wt% M _AE /molecular weight M _AE ×((number of Ca atoms per molecule M _AE )×(molecular weight CaSO ₄ )+(number of Sr atoms per molecule M _AE )×(molecular weight SrSO ₄ )+( the number of Ba atoms in the molecule M _AE )×(molecular weight of BaSO ₄ )).

Therefore, the total C _AE content of Ca, Sr and Ba compounds in terms of sulfates, when the MgO content in the annealing separator to which one or two or more Ca, Sr and Ba compounds are added, is taken as 100 wt.% (hereinafter referred to as "content C _AE compounds of Ca, Sr and Ba in terms of oxides”), is the sum of W _G4 .

[0107] Ca, Sr, and Ba compounds are, for example, sulfates, hydroxides, carbonates, etc., whose Ca, Sr, and Ba ions rapidly diffuse into the coating, so that when Ca, Sr, and Ba compounds are added, the rate of formation of primary coating is increased, the coating becomes denser, and the rust resistance is improved. If the content of C _AE in terms of sulfates is less than 0.5%, the above effect is not sufficiently obtained. On the other hand, if the content of _CAE in terms of sulfates exceeds 8.0%, the roots of the primary coating develop excessively, and sometimes the magnetic properties fall. In addition, if the content of _CAE in terms of sulfates exceeds 8.0%, the oxides in the steel sheet become too dense, fine defects are generated in the coating due to the outgassing of the steel sheet in the late stage of final annealing, and rust resistance deteriorates. If the content of CAE in terms of sulfates is _0.5-8.0 %, the drop in magnetic properties can be suppressed by improving the adhesion of the primary coating to the base steel sheet, and the rust resistance of the anisotropic electrical steel sheet can be improved.

[0108] The average PS _AE particle size of the Ca, Sr and Ba compounds is 12 µm or less. If the average particle size PS _AE of the Ca, Sr and Ba compounds exceeds 12 µm, the coating formation will not become faster, and even if the adhesion of the coating is improved due to the effect of adding Y, La and Ce compounds and Ti, Zr and Hf compounds together, then the coating will not become denser and it will be difficult to improve the rust resistance. Therefore, the average PS _AE particle size is 12 µm or less. The preferred upper limit of the average PS _AE particle size is 8 µm, more preferably 6 µm. The lower limit of the average particle size PS _AE of the particles is not particularly prescribed, but becomes, for example, 0.01 µm or more in industrial production.

[0109] The average particle size PS _RE of the particles is found by measuring the powder of Y, La and Ce compounds by laser diffraction/scattering based on JIS Z8825 (2013) using a laser diffraction/scattering type device to measure the particle size distribution. This makes it possible to determine the average size PS _RE of the particles. In addition, the average particle size PS _AE of the particles is found by measuring the powder of Ca, Sr and Ba compounds by laser diffraction/scattering based on JIS Z8825 (2013) using a laser diffraction/scattering type device to measure the particle size distribution. This makes it possible to determine the average particle size PS _AE .

[0110] As explained above, the Ca, Sr, and Ba ions rapidly diffuse into the Primary Coating, so that when Ca, Sr, and Ba compounds are added, the rate of formation of the Primary Coating increases. In addition, as the size of the Ca, Sr, and Ba compounds decreases, the rate of formation of the primary coating further increases. By controlling the particle size ratio of Y, La and Ce compounds having the function of oxygen evolution and Ca, Sr and Ba compounds in specific ranges, the formation of the primary coating is further accelerated compared to simply reducing the size of the Ca, Sr and Ba compounds, the sizes of the single components of the primary coatings, i.e. oxide particles, become uniform and finer, and a dense coating is obtained. As a result, the surface exposure of the steel sheet is reduced, and the rust resistance of the anisotropic electrical steel sheet is improved. From this point of view, the ratio of the average particle size of the Ca, Sr and Ba compounds to the average particle size of the Y, La and Ce compounds (average particle size ratio RA _AE/RE ) is 0.1-3.0. If the average particle size ratio RA _AE/RE is less than 0.1, the oxygen release capacity for decomposing Ca, Sr and Ba compounds becomes insufficient, the diffusion flux of Ca, Sr and Ba into the coating becomes smaller, and the aforementioned effect is not obtained. In addition, if the ratio of the average particle size of Ca, Sr, and Ba compounds to the average particle size of Y, La, and Ce compounds (average particle size ratio RA _AE/RE ) exceeds 3.0, since the diffusion sites of Ca, Sr, and Ba are limited, diffusion the flow of Ca, Sr and Ba into the coating becomes smaller, and therefore the above effect cannot be obtained.

[0111] The ratio of the average particle sizes RA _AE/RE is found in the following way. The same measurement method as for the average particle size PS _RE is used to find the average particle size PS _AE . The obtained average particle sizes PS _RE and PS _AE are used to find the ratio of average particle sizes RA _AE/RE using the following formula.

Ratio of average particle sizes RA _AE/RE = average particle size PS _AE / average particle size PS _RE

The ratio of the number of atoms (Y+La+Ce)/(Ti, Zr, Hf) in the annealing separator

[0112] The ratio of the sum of the numbers of Y, La and Ce atoms to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator (X _RE /X _G4 ) is 0.18-4.0. If X _RE /X _G4 is less than 0.18, at the time of final annealing, the number of Ti, Zr and Hf atoms that do not react with Y, La and Ce atoms increases too much, and as a result, the coating does not become dense. For this reason, the rust resistance deteriorates. On the other hand, if X _RE /X _G4 exceeds 4.0, the growth of the coating is not accelerated and the adhesion drops. If X _RE /X _G4 is 0.18-4.0, the adhesion of the primary coating to the steel sheet is enhanced. The preferred lower limit of X _RE /X _G4 is 0.3, more preferably 0.5. The preferred upper limit of X _RE /X _G4 is 3.0, more preferably 2.0.

N _RE and N _G4 and N _AE in the annealing separator

[0113] If, in the preparation of the annealing separator, the particle number densities in the raw material powder of Y, La, Ce and other rare earth compounds, or Ti, Zr, Hf and other metal compounds, and Ca, Sr, Ba, and other additives are insufficient , there will be areas of insufficient development of the primary coating, and adhesion and rust resistance will sometimes fall. In the raw material powder contained in the annealing separator, the number density N _RE of particles of 0.1 µm or more of metal compounds selected from the group consisting of Y, La, and Ce, the number density N _G4 of particles of 0.1 µm or more of compounds of a metal selected from the group consisting of Ti, Zr and Hf, and the number density N _AE of particles having a size of 0.1 μm or more of the compounds of the metal selected from the group consisting of Ca, Sr and Ba, respectively, is 2000000000/g or more. The particle sizes of these metal compounds are found as the diameter of a volume-equivalent sphere and are found from the particle size distribution based on the number of particles obtained by measuring raw material powder with a diffraction-type laser particle size distribution measuring device.

Here, "particle size distribution based on number of particles" shows the frequency of presence (%) relative to the total number of particles in various sections after dividing into 30 or more sections with equal width in the logarithmic scale of the particle size range having any value in the range 0.1-0.15 µm as the minimum size and any value in the range of 2000-4000 µm as the maximum size. Here, the representative particle size D in each section is found as

D=10^((LogD _MAX +LogD _MIN )/2)

using the value of the upper limit D _MAX [µm] and the value of the lower limit D _MIN [µm] of the respective sections.

In addition, the weight w [g] of particles of each section in 100 particles of raw material powder is found as

w=f⋅d⋅(D^3⋅p)/6

using the presence frequency "f" relative to all particles, the representative particle size D [μm] and the density "d" [g/μm ³ ] of the metal compound.

The sum W [g] of the "w" weights of all sections is the average weight of 100 particles of raw material powder, so that the number of particles "n" [/g] in 1 g of metal compound powder is found as

n=100/W.

When finding the number density N _RE of particles with a size of 0.1 μm or more of metal compounds selected from the group consisting of Y, La and Ce, calculate the number "n" of particles in 1 g of powders of metal compounds in the powder of raw materials, and the content of "c" (%) of the corresponding metal compounds in suspension and the sum C (%) of all the contents of "c" is used in order to find it as:

N _RE =∑(n⋅c/C).

The number densities of N _G4 and N _AE are found in a similar way.

If N _RE or N _G4 is less than 2000000000/g, at the time of final annealing, the root growth effect of the Primary Coating becomes uneven, and there are areas where root growth is not sufficiently stimulated. As a result, the adhesion of the Primary Coating to the steel sheet is insufficient. Not only that, the diffusion routes of the alkaline earth metals cannot be secured, leading to deterioration in rust resistance. If N _RE and N _G4 are 2000000000/g or more, the adhesion of the Primary Coating is improved. Compounds Y, La, Ce, Ti, Zr, Hf, etc. have the effect of releasing oxygen during final annealing. Y, La and Ce compounds release oxygen smoothly from low temperature to high temperature. On the other hand, Ti, Zr, and Hf compounds can release oxygen for relatively short periods of time, but have the effect of enhancing the oxygen release effect of Y, La, and Ce compounds, and can continue to inhibit the aggregation of the inner oxide layer necessary for coating development. For this reason, by increasing the number densities to increase the state of dispersion in the separator layer, this interaction can be efficiently obtained.

[0114] If RA _AE/RE is within the preferred range and N _RE , N _G4 , and N _AE are 2000000000/g or more, the coating becomes more markedly developed and rust resistance becomes excellent. The reason seems to be that when the particle sizes of the Y, La and Ce compounds and the Ca, Sr and Ba compounds are the same when preparing the slurry, if X _RE /X _G4 is in the above preferred range, the Ti, Zr and Hf are located near the Y, La and Ce compounds, and the areas where oxygen evolution is enhanced can be provided on the surface of the sheet without unevenness, and the diffusion paths of alkaline earth metals, which diffuse rapidly, are maintained even at a constant annealing temperature, which contributes to a more uniform coverage development.

[0115] On the other hand, if RA _AE/RE is outside the preferred range or N _RE , N _G4 and N _AE are insufficient (less than 2000000000/g), there are areas where the primary coating has not developed enough. In this case, the rust resistance drops.

Production conditions of the final annealing process

[0116] The final annealing process is performed, for example, under the following conditions: drying is performed before the final annealing. First, the surface of the steel sheet is coated with an aqueous suspension annealing separator. The steel sheet coated on the surface with an anneal separator is loaded into a furnace maintained at a temperature of 400-1000° C. and kept there (dried). As a result, the annealing separator applied to the surface of the steel sheet is dried. The holding time is, for example, 10-90 seconds.

[0117] After drying the annealing separator, a final annealing is performed. In the final annealing, the annealing temperature is set to 1150-1250°C, for example, and the base steel sheet (cold-rolled steel sheet) is held. The holding time is, for example, 15-30 hours. The atmosphere inside the final annealing furnace is a known atmosphere.

[0118] In the anisotropic electrical steel sheet obtained by the above-described manufacturing process, a primary coating containing Mg ₂ SiO ₄ as a main component is formed. In addition, the position D _Al of the Al peak is located in the range of 2.4-12.0 μm from the surface of the primary coating. In addition, the number density ND of Al oxides becomes 0.03-0.18/μm ² . In addition, among the plurality of Al oxides in the observed area at the peak position of the Al emission intensity, the ratio of the total area of the identified Al oxides with cross-sectional areas of 0.4-10.0 μm ² to the total area of the cross section of all Al oxides in the observed area (hereinafter referred to as the area of identified oxides Al RA _AREA ") becomes 75.0% or more.

[0119] It should be noted that, due to the decarburization annealing process and the final annealing process, chemical composition elements of the hot-rolled steel sheet are removed to some extent from the steel components. The change in composition (and the process itself) during the final annealing process is sometimes referred to as "refining (refining annealing)". In addition to the Sn, Sb, Bi, Te, and Pb used to control the crystallographic orientation, S, Al, N, etc., acting as inhibitors, are largely removed. For this reason, compared with the chemical composition of the hot-rolled steel sheet, the aforementioned element contents in the chemical composition of the base steel sheet in the anisotropic electrical steel sheet become lower, as explained above. By using a hot-rolled steel sheet with the above-described chemical composition to carry out the above-described production method, an anisotropic electrical steel sheet having a base steel sheet with the above-described chemical composition can be produced.

Secondary Coating Process

[0120] In one example of the production method of the anisotropic electrical steel sheet according to the present invention, furthermore, after the final annealing process, a secondary coating forming process may be further carried out. In the secondary coating process, the surface of the anisotropic electrical steel sheet after the final annealing temperature is lowered is coated with an insulating coating agent mainly composed of colloidal silicon dioxide (silica) and phosphate, and then calcined. As a result, a secondary coating is formed on the primary coating, which is a high-strength insulating coating.

Process for separating magnetic domains

[0121] The anisotropic electrical steel sheet according to the present invention may be further subjected to a magnetic domain separation treatment after a final annealing process or a secondary coating process. In a magnetic domain separation processing, a surface of an anisotropic electrical steel sheet is scanned with a laser beam having a magnetic domain separation effect, or grooves are formed on the surface. In this case, an anisotropic electrical steel sheet with more excellent magnetic properties can be produced.

EXAMPLES

[0122] In the following, aspects of the present invention will be more specifically explained with examples. These examples are merely illustrations to confirm the effects of the present invention and do not limit the present invention.

Production of anisotropic electrical steel sheet

[0123] Molten steel having the chemical compositions shown in Table 1 was produced using a vacuum melting furnace. The resulting molten steel was used to make a slab by continuous casting.

[0124] [Table 1]

Table 1

Steel type Chemical composition (wt.%, the rest - Fe and impurities) C Si Mn S Se S+Se Solv. Al N sn Sb Bi Those Pb A 0.077 3.3 0.080 0.025 - 0.025 0.029 0.008 - - - - - B 0.077 3.3 0.082 - 0.033 0.033 0.032 0.008 - - - - - C 0.076 3.3 0.080 0.024 0.010 0.034 0.031 0.008 0.08 - - - - D 0.076 3.3 0.080 0.018 0.006 0.024 0.032 0.008 - 0.04 - - - E 0.077 3.3 0.080 0.025 0.006 0.031 0.032 0.008 - - 0.004 - - F 0.076 3.3 0.081 0.018 0.004 0.022 0.032 0.008 - - - 0.002 - G 0.076 3.3 0.080 0.019 0.003 0.022 0.032 0.008 - - - - 0.0018

[0125] The slab was heated at 1350°C. The heated slab was subjected to hot rolling to produce a hot-rolled steel sheet having a thickness of 2.3 mm. The chemical composition of the hot rolled steel sheet was the same as that of the molten steel, and is shown in Table 1.

[0126] The hot-rolled steel sheet was annealed, and then the hot-rolled steel sheet was pickled. The annealing processing conditions of the hot-rolled steel sheet and the pickling conditions of the hot-rolled steel sheet were the same in all of the above tests.

[0127] The pickled hot-rolled steel sheet was subjected to cold rolling to obtain a cold-rolled steel sheet having a thickness of 0.22 mm. In each of these tests, the cold rolling reduction ratio was 90.4%.

[0128] The cold rolled steel sheet was annealed with a dual function of primary recrystallization annealing and decarburization annealing. The temperature of the primary recrystallization annealing in each of the above tests was 750-950°C. The exposure time at the annealing temperature was 2 minutes.

[0129] The cold-rolled steel sheet after the primary recrystallization annealing was coated with an aqueous slurry and dried to obtain an annealing separator coating with a specific gravity of 5 g/m ² per surface. It should be noted that an aqueous slurry was prepared by mixing an annealing separator (raw material powder) and industrial grade pure water at a ratio of 1:5. The annealing separator contained MgO and additives shown in Table 2 and Table 3. It should be noted that the content of C _RE (wt%) of Y, La and Ce compounds in the annealing separator shown in Tables 2 and 3 means the total content of Y compounds, La and Ce in terms of oxides, taking the content of MgO in the annealing separator as 100 wt.% (content of C _RE compounds of Y, La and Ce in terms of oxides). Similarly, the occurrence of X _RE Y, La and Ce shown in Tables 2 and 3 means the ratio of the sum of the numbers of Y, La and Ce atoms to the number of Mg atoms contained in the annealing separator. Similarly, the content of C _G4 (wt.%) compounds of Ti, Zr and Hf in the annealing separator, shown in Tables 2 and 3, means the total content of the compounds of Ti, Zr and Hf in terms of oxides, taking the content of MgO in the annealing separator as 100 wt.% (content of C _G4 compounds of Ti, Zr and Hf in terms of oxides). Similarly, the occurrence of X _G4 Ti, Zr and Hf shown in Tables 2 and 3 means the ratio of the sum of the numbers of Ti, Zr and Hf atoms to the number of Mg atoms contained in the annealing separator. Similarly, the content of C _AE (wt.%) of Ca, Sr and Ba compounds in the annealing separator shown in Tables 2 and 3 means the total content of Ca, Sr and Ba compounds in terms of sulfates, taking the content of MgO in the annealing separator as 100 wt.% (content of C _AE compounds of Ca, Sr and Ba in terms of sulfates). Similarly, the number density N _RE Y, La and Ce shown in Tables 2 and 3 means the number density in the raw material powder of particles with a size of 0.1 μm or more of metal compounds selected from Y, La and Ce in the annealing separator before preparing an aqueous suspension therefrom. Similarly, the number density of N _G4 Ti, Zr and Hf shown in Tables 2 and 3 means the number density in the raw material powder of particles with a size of 0.1 μm or more of metal compounds selected from Ti, Zr and Hf in the annealing separator before preparing an aqueous suspension therefrom. Similarly, the number density N _AE of Ca, Sr and Ba shown in Tables 2 and 3 means the number density in the raw material powder of particles with a size of 0.1 μm or more of metal compounds selected from Ca, Sr and Ba in the annealing separator before preparing an aqueous suspension therefrom. It should be noted that the particle sizes are the diameters of spheres equivalent in volume.

[0130] [Table 2]

[0131] [Table 3]

[0132] The average particle size PS _AE (μm) in Table 2 and Table 3 means the average particle size of the Ca, Sr and Ba compounds measured by the above measurement method. The average particle size PS _RE (μm) in Table 2 and Table 3 means the average particle size of the Y, La and Ce compounds measured by the above measurement method. The RA _AE/RE value in Table 2 and Table 3 means the ratio of the average particle size of the Ca, Sr and Ba compounds to the average particle size of the Y, La and Ce compounds measured by the above measurement method.

[0133] The cold-rolled steel sheet coated on the surface with an aqueous slurry was dried at 900° C. for 10 seconds in each of the above tests in order to dry the aqueous slurry. After drying, the sheet was subjected to final annealing. In the final annealing in each of the above tests, the sheet was kept at 1200°C for 20 hours. Due to the above-described production process, an anisotropic electrical steel sheet having a base steel sheet and a primary coating was produced.

Analysis of the chemical composition of the base steel sheet in an anisotropic electrical steel sheet

[0134] The base steel sheets of the produced anisotropic electrical steel sheets of Test Nos. 1-100 were examined by spark discharge optical emission spectrometry and atomic absorption spectrometry in order to find the chemical compositions of the base steel sheets. The found chemical compositions are shown in Table 4 and Table 5.

[0135] [Table 4]

TABLE 4

Test No. Chemical composition (wt.%, the rest - Fe and impurities) C Si Mn S Se S+Se Solv. Al N sn Sb Bi Those Pb one 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 2 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.001 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 3 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 four 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 5 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.001 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 6 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.001 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 7 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.001 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 eight 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.001 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 9 0.0005 3.3 0.078 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 ten 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 eleven 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 12 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 13 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 fourteen 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 fifteen 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 16 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 17 0.0005 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 eighteen 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 19 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 twenty 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 21 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 22 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 23 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 24 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 25 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 26 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 27 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 28 0.0005 3.3 0.079 0.001 <0.0005 <0.0015 0.002 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 29 0.0005 3.3 0.075 0.001 <0.0005 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 thirty 0.0005 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 31 0.0005 3.3 0.074 0.001 <0.0005 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 32 0.0005 3.3 0.073 0.001 <0.0005 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 33 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 34 0.0005 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 35 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 36 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 37 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 38 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 39 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 40 0.0005 3.3 0.081 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 41 0.0005 3.3 0.081 <0.0005 0.001 <0.0015 0.004 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 42 0.0005 3.3 0.082 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 43 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.001 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 44 0.0005 3.3 0.081 <0.0005 0.001 <0.0015 0.002 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 45 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 46 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 47 0.0005 3.3 0.079 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 48 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 49 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 fifty 0.0005 3.3 0.081 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 51 0.0005 3.3 0.077 0.001 0.001 0.002 0.002 0.001 0.0200 <0.0005 <0.0005 <0.0005 <0.0005 52 0.0005 3.3 0.080 0.001 0.001 0.002 0.002 0.001 <0.0005 0.0010 <0.0005 <0.0005 <0.0005 53 0.0005 3.3 0.079 0.001 0.001 0.002 0.002 0.001 <0.0005 <0.0005 0.0008 <0.0005 <0.0005 54 0.0005 3.3 0.081 0.001 0.001 0.002 0.003 0.001 <0.0005 <0.0005 <0.0005 0.0005 <0.0005 55 0.0005 3.3 0.080 0.001 0.001 0.002 0.003 0.003 <0.0005 <0.0005 <0.0005 <0.0005 0.0005 56 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 57 0.0005 3.3 0.080 0.001 <0.0005 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 58 0.0005 3.3 0.077 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 59 0.0005 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 60 0.0005 3.3 0.079 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 61 0.0005 3.3 0.077 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 62 0.0005 3.3 0.077 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 63 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 64 0.0005 3.3 0.077 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 65 0.0005 3.3 0.077 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 66 0.0005 3.3 0.078 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 67 0.0005 3.3 0.077 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 68 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 69 0.0005 3.3 0.078 <0.0005 0.001 <0.0015 0.001 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 70 0.0005 3.3 0.079 <0.0005 0.001 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 71 0.0005 3.3 0.076 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 72 0.0005 3.3 0.076 <0.0005 0.001 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 73 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 74 0.0005 3.3 0.078 <0.0005 0.001 <0.0015 0.003 0.003 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 75 0.0005 3.3 0.077 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 76 0.0005 3.3 0.079 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 77 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 78 0.0005 3.3 0.080 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 79 0.0005 3.3 0.079 <0.0005 0.001 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 80 0.0005 3.3 0.079 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 81 0.0005 3.3 0.079 <0.0005 0.001 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 82 0.0005 3.3 0.076 <0.0005 0.001 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005

[0136] [Table 5]

TABLE 5

Test No. Chemical composition (wt.%, the rest - Fe and impurities) C Si Mn S Se S+Se Solv. Al N sn Sb Bi Those Pb 83 A 3.3 0.077 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 84 A 3.3 0.077 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 85 B 3.3 0.078 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 86 B 3.3 0.077 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 87 A 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 88 B 3.3 0.078 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 89 A 3.3 0.077 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 90 A 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 91 B 3.3 0.078 <0.0005 0.001 <0.0015 0.003 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 92 B 3.3 0.077 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 93 A 3.3 0.077 0.001 <0.0005 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 94 B 3.3 0.079 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 95 A 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.001 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 96 A 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 97 B 3.3 0.079 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 98 B 3.3 0.076 <0.0005 0.001 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 99 A 3.3 0.076 0.001 <0.0005 <0.0015 0.002 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005 100 B 3.3 0.079 <0.0005 0.001 <0.0015 0.003 0.002 <0.0005 <0.0005 <0.0005 <0.0005 <0.0005

Evaluation tests

Position measurement test D _Al peak Al

[0137] For each sheet of anisotropic electrical steel in all of the above tests, the following measurement method was used in order to find the position D _{Al of the Al} peak. In particular, the surface layer of an anisotropic electrical steel sheet was examined by elemental analysis using the GDS method. Elemental analysis was carried out in the range of 100 μm in the direction in depth from the surface of the sheet of anisotropic electrical steel (in the surface layer). Al contained in various depth positions in the surface layer was identified. The emission intensity of identified Al was plotted as a function of distance from the surface in the depth direction. Based on this Al emission intensity plot, the D _{Al position of the Al} peak was found. The found position D _Al of the Al peak is shown in Table 6 and Table 7.

[0138] [Table 6]

[0139] [Table 7]

Numerical Density Measurement Test ND of Al Oxides

[0140] For each of the anisotropic electrical steel sheets of the listed tests, the number density ND of Al oxides (/µm ² ) at the D _{Al position of the Al} peak was found by the following method. A glow discharge was carried out using a glow discharge optical emission analyzer up to the D _{Al position of the Al} peak. Any 52×39 μm region (observed region) in the discharge marks at the D _{Al position of the Al} peak was analyzed for elements using an energy dispersive X-ray spectroscope (EDS). Al oxides were identified in the observed area. The precipitates containing Al and O in the observed area were identified as Al oxides. The number of identified Al oxides was counted, and the number density ND of Al oxides (/µm ² ) was found using the following formula: ND = number of Al oxides identified/surface area observed. The number density ND of Al oxides found is shown in Table 6 and Table 7.

Test for measuring the area fraction of identified Al RA oxides _AREA

[0141] The area fraction of the identified Al oxides RA _AREA was found by the following method. A glow discharge optical emission analyzer was used for glow discharge up to the D _{Al position of the Al} peak. Any 30 µm×50 µm region (observed region) in the discharge marks at the D _Al position of the Al peak was analyzed for elements using an energy dispersive X-ray spectroscope (EDS) to identify Al oxides in the observed region. Specifically, a region in which the characteristic X-ray intensity O is 50% or more of the maximum intensity of the characteristic X-ray O in the observed area was identified as an oxide. In the identified oxide regions, the region in which the Al characteristic X-ray intensity is 30% or more of the maximum Al characteristic X-ray intensity was identified as alumina. Based on the measurement results, a distribution diagram of Al oxides was plotted in the observed region.

[0142] On the constructed distribution diagram (observed area), the areas of Al oxides were calculated. Based on the calculation results on the distribution diagram, Al oxides with an area of 0.4-10.0 μm ² were considered "identified Al oxides". Then the total cross-sectional area of the identified Al oxides was found. In addition, the total cross-sectional area of all Al oxides in the distribution diagram was found, and the area ratio of the identified Al oxides RA _AREA was found by the following formula.

[0143] Area fraction of identified Al oxides RA _AREA =total cross-sectional area of identified Al oxides in the observed region/total cross-sectional area of all Al oxides in the observed region×100.

Y, La, Ce, Ti, Zr, Hf, Ca, Sr and Ba measurement test in primary coating

[0144] Each of the anisotropic electrical steel sheets of the listed tests was measured by the following method for the contents of Y, La and Ce (wt.%), the contents of Ti, Zr and Hf (wt.%) and the contents of Ca, Sr and Ba (wt.%) in primary coverage. Specifically, the anisotropic electrical steel sheet was subjected to electrolysis to separate the primary coating from the surface of the base metal sheet. The Mg in the separated Primary Coating was quantified by ICP-MS. The product of the obtained quantitative value (wt.%) and the molecular weight of Mg ₂ SiO ₄ was divided by the atomic mass of Mg in order to find the equivalent content of Mg ₂ SiO ₄ . Y, La, Ce, Ti, Zr, Hf, Ca, Sr and Ba in the primary coating were measured by the following method. The anisotropic electrical steel sheet was subjected to electrolysis to separate the primary coating from the surface of the base metal sheet. The contents of Y, La and Ce (wt.%), the contents of Ti, Zr and Hf (wt.%) and the contents of Ca, Sr and Ba (wt.%) in the separated primary coating were quantitatively analyzed by ICP-MS. The contents of Y, La and Ce (wt%), the contents of Ti, Zr and Hf (wt%) and the contents of Ca, Sr and Ba (wt%) obtained from the measurement are shown in Table 6 and Table 7.

Magnetic evaluation test

[0145] Using the following method, the magnetic properties of each of the anisotropic electrical steel sheets of the listed tests were evaluated. Specifically, from each of the anisotropic electrical steel sheets of the above tests, a sample with a length in the rolling direction of 300 mm x a width of 60 mm was taken. This sample was subjected to a magnetic field of 800 A/m in order to find the magnetic induction B8. Table 6 and Table 7 show the test results. If the magnetic induction of B8 was 1.92 T or more, the magnetic properties were considered to be excellent.

Adhesion quality test

[0146] Using the following method, the primary coating adhesion of each of the anisotropic electrical steel sheets of all the above tests was evaluated. Specifically, a sample with a length in the rolling direction of 60 mm x a width of 15 mm was taken from each of the anisotropic electrical steel sheets of the listed tests. This sample was subjected to a bending test with a diameter of 10 mm. The bending test was carried out using a cylindrical mandrel bending tester (manufactured by TP Giken) by setting the specimen so that the axial direction of the cylindrical mandrel matches the width direction of the specimen. The surface of the sample after the bending test was investigated and the total area of the areas where the primary coating remained undelaminated was determined. The following formula was used to find the proportion of Primary Coating remaining: Fraction of Primary Coating remaining=total area of areas in which the Primary Coating remained unpeeled/sample surface area×100.

[0147] Table 6 and Table 7 show the test results. If the proportion of the remaining Primary Coating is 90% or more, the adhesion of the Primary Coating to the base steel sheet is said to be excellent.

Rust resistance test

[0148] The following method was used to evaluate the rust resistance of the coating of each of the anisotropic electrical steel sheets of the listed tests. Specifically, each of the anisotropic electrical steel sheets of the above tests was coated with a predetermined insulating coating and kept at a temperature of 80° C. in a humid (98% relative humidity) atmosphere for 48 hours. The following formula was used to find the proportion of red rust formation: Proportion of red rust formation=total area of the area where red rust was confirmed/area of the test piece.

[0149] Table 6 and Table 7 show the test results. In the absence of red rust, the rust resistance was rated as "Good", when the proportion of red rust formation was less than 5%, the rust resistance was rated as "Intermediate", and if the proportion of red rust formation was more than 5%, the rust resistance was rated as "Poor". If no red rust was generated (ie, "Good" in Table 6 and Table 7), the Primary Coating was considered to have excellent rust resistance of the base steel sheet.

Test results

[0150] Table 6 and Table 7 show the test results. As shown in Table 6 and Table 7, in Test Nos. 25-27, 35, 36, 40, 43, 44, 51-55, 59, 60, 69, 70 and 76-78, the chemical composition of the base steel sheet was suitable. In addition, the production conditions, in particular the additives in the annealing separator, were also suitable. For this reason, the D _Al position of the Al peak was in the range of 2.4-12.0 µm, and the numerical density ND of the Al oxides was in the range of 0.03-0.18/µm ² . In addition, the area ratio of the identified Al oxides RA _AREA was 75.0% or more. In addition, the Ce content in the primary coating was in the range of 0.001-8.0%, the Zr content was in the range of 0.0005-4.0%, and the Ca content was in the range of 0.0005-4.0%.

[0151] In addition, in particular in Test Nos. 26, 27 and 51-55, contained at least two or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, the primary coating showed very excellent adhesion, and excellent magnetic properties have been demonstrated.

[0152] On the other hand, in Test Nos. 1, 2, and 6-8, the chemical composition was appropriate, but the content of C _RE compounds of Y, La, and Ce in terms of oxides in the annealing separator was too low. In addition, the C _G4 content of Ti, Zr and Hf compounds in terms of oxides in the annealing separator was too low, and furthermore, the C _AE content of Ca, Sr and Ba compounds in terms of sulfates in the annealing separator was too low. For this reason, the position D _Al of the Al peak or the numerical density ND of Al oxides were too low. In addition, the area fraction of the identified oxides Al RA _AREA was less than 75.0%. As a result, the percentage of the remaining primary coating was less than 90%, and the adhesion was low. In addition, the rust resistance was low.

[0153] On the other hand, in Test Nos. 3-5, 9-19, 21, 22, 33, 34, and 38, the chemistry was appropriate, but the _CRE content of Y, La, and Ce compounds in terms of oxides in the annealing separator was too low. As a result, in each of the anisotropic electrical steel sheets of these listed tests, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was poor.

[0154] In Tests Nos. 23, 24, 57, and 58, the chemistry was appropriate, but the _CAE content in terms of sulfates in the annealing separator was too low. For this reason, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was low.

[0155] In Tests Nos. 28 and 61, the chemistry was appropriate, but the _CAE content in terms of sulfates in the annealing separator was too high. For this reason, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was low.

[0156] In Test Nos. 29, 62, 79, 80, and 82, the chemistry was appropriate, but the average particle size PS _AE of the Ca, Sr, and Ba compounds in the annealing separator was too high. For this reason, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was low.

[0157] In Tests Nos. 30, 56, and 63, the chemistry was appropriate, but the average particle size ratio RA _AE/RE in the annealing separator was too high. For this reason, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was low.

[0158] In Test No. 31, the chemistry was appropriate, but the average particle size ratio RA _AE/RE in the annealing separator was too low. For this reason, RA _AREA was too low. As a result, the proportion of remaining primary coating was less than 75%, and the rust resistance was low.

[0159] In Test Nos. 20, 32, 37, 42, and 48, the chemistry was appropriate, but the C _G4 content of the Ti, Zr, and Hf compounds in terms of oxides in the annealing separator was too low. For this reason, the position D _Al of the Al peak or the numerical density ND of Al oxides were too low. As a result, the percentage of the remaining primary coating was less than 90%, and the adhesion was low.

[0160] In Test Nos. 39, 47, and 75, the chemistry was appropriate, but the C _G4 content of the Ti, Zr, and Hf compounds in terms of oxides in the annealing separator was too high. For this reason, the magnetic properties have deteriorated. In addition, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was low.

[0161] In Test No. 41, the chemical composition was suitable, but the ratio of the sum of the numbers of Y, La, and Ce atoms to the sum of the numbers of Ti, Zr, and Hf atoms contained in the annealing separator was too high. The number density ND of Al oxides was too low. As a result, the percentage of the remaining primary coating was less than 90%, and the adhesion was low.

[0162] In Test No. 45, the chemical composition was suitable, but the sum of the C _RE content of Y, La, and Ce compounds in terms of oxides and the content of C _{4 G} in terms of oxides in the annealing separator was too high. For this reason, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was low.

[0163] In Test No. 46, the chemical composition was suitable, but the content of C _RE compounds of Y, La and Ce in terms of oxides in the annealing separator was too high. For this reason, the magnetic induction of B8 became less than 1.92 T, and the magnetic properties were low.

[0164] In Test No. 49, the chemical composition was suitable, but the ratio of the sum of the numbers of Y, La, and Ce atoms to the sum of the numbers of Ti, Zr, and Hf atoms contained in the annealing separator was too low. For this reason, the area ratio of the identified oxides Al RA _AREA became lower than 75.0%, and the rust resistance was low.

[0165] In Test No. 50, the chemical composition was suitable, but the sum of the content of C _RE in terms of oxides and the content of C _4G in terms of oxides in the annealing separator was too low. For this reason, the position D _Al of the Al peak and the number density ND of Al oxides were too low. As a result, the percentage of the remaining primary coating was less than 90%, and the adhesion was low.

[0166] In Test Nos. 64-68, 71-74, and 81, the chemistry was appropriate, but the average particle size ratio RA _AE/RE in the annealing separator was too low. For this reason, the RA _AREA value was too low. As a result, the proportion of remaining primary coating was less than 75%, and the rust resistance was poor.

[0167] In Test Nos. 83-88, the particle number density in the raw material powder of Y, La, and Ce compounds was too low. For this reason, the number density ND of the Al oxides was too low, and the area ratio of the identified Al oxides RA _AREA was less than 75.0%. As a result, the proportion of the remaining primary coating became less than 90%, the adhesion was poor, and the rust resistance was poor.

[0168] In Test Nos. 89-94, the particle number density in the raw material powder of the Ti, Zr, and Hf compounds was too low. For this reason, the D _Al position of the Al peak was too low, and the area fraction of identified Al oxides RA _AREA was less than 75.0%. As a result, the proportion of the remaining primary coating became less than 90%, the adhesion was poor, and the rust resistance was poor.

[0169] In Test Nos. 95-100, the number density of particles in the raw material powder of Ca, Sr, and Ba compounds was too low. For this reason, the area fraction of the identified oxides Al RA _AREA was less than 75.0%. As a result, the proportion of remaining primary coating was 90% or more, but the rust resistance was poor.

[0170] Embodiments of the present invention have been explained above. However, the embodiments explained above are merely illustrative of the implementation of the present invention. Therefore, the present invention is not limited to the above-explained embodiments, and can be implemented by making suitable modifications to the above-explained embodiments without departing from the spirit and scope of the present invention.

Claims (53)

1. Sheet of anisotropic electrical steel, including: the main steel sheet having a chemical composition containing, wt.%: C: 0.005 mass% or less Si: 2.5-4.5%, Mn: 0.02-0.2%, one or more elements selected from the group consisting of S and Se: in the amount of 0.005% or less, sol. Al: 0.01% or less, and N: 0.01% or less, and with the rest, consisting of Fe and impurities, and primary coating formed on the surface of the base steel sheet and containing Mg ₂ SiO ₄ as the main component, and the position of the Al emission intensity peak obtained by performing elemental analysis using glow discharge optical emission spectrometry from the surface of the primary coating in the direction along the thickness of the anisotropic electrical steel sheet is in the range of 2.4-12.0 μm from the surface of the primary coating in the direction along the thickness , the numerical density of Al oxides at the Al emission intensity peak position with a size of 0.2 µm or more in terms of the diameter of an area-equivalent circle is 0.03-0.18/µm ² , and in a plurality of Al oxides in the observed region of 30 μm × 50 μm at the peak position of the Al emission intensity, the total cross-sectional area of identified Al oxides with cross-sectional areas of 0.4-10.0 μm ² is 75.0% or more of the total cross-sectional area of all Al oxides in the observed area. 2. A method for producing an anisotropic electrical steel sheet according to claim 1, including: cold rolling process of hot rolled steel sheet containing, wt.%, C: 0.1 mass% or less Si: 2.5-4.5%, Mn: 0.02-0.2%, one or more elements selected from the group consisting of S and Se: in the amount of 0.005-0.07%, sol. Al: 0.005-0.05%, and N: 0.001-0.030%, and, optionally, one or more elements selected from the group consisting of Cu, Sb and Sn, in a total amount of 0.6% or less, and, optionally, one or more elements selected from the group consisting of Bi, Te, and Pb in a total amount of 0.03% or less, and with the rest consisting of Fe and impurities, with a cold rolling reduction ratio of 80% or more to produce a cold rolled steel sheet, decarburization annealing process of cold rolled steel sheet, a process of coating the surface of the cold-rolled steel sheet after the decarburization annealing with an aqueous slurry containing an annealing separator, and drying the aqueous slurry on the surface of the cold-rolled steel sheet in a 400-1000°C furnace, and a process for performing final annealing of a cold-rolled steel sheet after the aqueous slurry is dried, wherein annealing separator contains MgO at least one or more types of metal compounds selected from the group consisting of Y, La and Ce, at least one or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, and at least one or more types of metal compounds selected from the group consisting of Ca, Sr and Ba, when the content of MgO in the annealing separator is 100 mass parts, the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides is 0.8 to 8.0 mass parts, the total content of metal compounds selected from of the group consisting of Ti, Zr and Hf, in terms of oxides is 0.5-9.0 mass parts and the total content of metal compounds selected from the group consisting of Ca, Sr and Ba, in terms of sulfates is 0.5 -8.0 mass parts, the average particle size of metal compounds selected from the group consisting of Ca, Sr and Ba is 12 µm or less, the ratio of the average particle size of metal compounds selected from the group Ca, Sr and Ba to the average particle size of metal compounds selected from the group consisting of Y, La and Ce is 0.1-3.0, the sum of the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides and the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 2.0-12 .5 mass parts, the ratio of the sum of the numbers of Y, La and Ce atoms to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator is 0.18-4.0, in addition, the particle number density of metal compounds selected from the group consisting of Y, La and Ce, which are particles with a diameter equivalent in sphere volume of 0.1 μm or more, is 2000000000/g or more, in addition, the particle number density of the metal compound particles selected from the group consisting of Ti, Zr and Hf, which are particles with a sphere equivalent sphere diameter of 0.1 µm or more, is 2000000000/g or more, and, in addition, the particle number density of the metal compound particles selected from the group consisting of Ca, Sr and Ba, which are particles with a sphere equivalent in volume diameter of 0.1 μm or more, is 2000000000/g or more. 3. The annealing separator used to produce the anisotropic electrical steel sheet according to claim 1, comprising: MgO at least one or more types of metal compounds selected from the group consisting of Y, La and Ce, at least one or more types of metal compounds selected from the group consisting of Ti, Zr and Hf, and at least one or more types of metal compounds selected from the group consisting of Ca, Sr and Ba, when the content of MgO in the annealing separator is 100 mass parts, the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides is 0.8 to 8.0 mass parts, the total content of metal compounds selected from of the group consisting of Ti, Zr and Hf, in terms of oxides is 0.5-9.0 mass parts and the total content of metal compounds selected from the group consisting of Ca, Sr and Ba, in terms of sulfates is 0.5 -8.0 mass parts, the average particle size of metal compounds selected from the group consisting of Ca, Sr and Ba is 12 µm or less, the ratio of the average particle size of metal compounds selected from the group Ca, Sr and Ba to the average particle size of metal compounds selected from the group consisting of Y, La and Ce is 0.1-3.0, the sum of the total content of metal compounds selected from the group consisting of Y, La and Ce, in terms of oxides and the total content of metal compounds selected from the group consisting of Ti, Zr and Hf, in terms of oxides is 2.0-12 .5 mass parts, the ratio of the sum of the numbers of Y, La and Ce atoms to the sum of the numbers of Ti, Zr and Hf atoms contained in the annealing separator is 0.18-4.0, in addition, the particle number density of metal compounds selected from the group consisting of Y, La and Ce, which are particles with a diameter equivalent in sphere volume of 0.1 μm or more, is 2000000000/g or more, in addition, the particle number density of the metal compound particles selected from the group consisting of Ti, Zr and Hf, which are particles with a sphere equivalent sphere diameter of 0.1 µm or more, is 2000000000/g or more, and, in addition, the particle number density of the metal compound particles selected from the group consisting of Ca, Sr and Ba, which are particles with a sphere equivalent in volume diameter of 0.1 μm or more, is 2000000000/g or more.