Method for manufacturing grain-oriented electrical steel sheets, grain-oriented electrical steel sheets, and annealing separating agent

Abstract

To provide a method for producing a directional electromagnetic steel sheet having excellent film adhesion and magnetic characteristics, and a directional electromagnetic steel sheet, and an annealing separation agent.SOLUTION: There is provided a method for producing a directional electromagnetic steel sheet having excellent film adhesion and magnetic characteristics, including the steps of: heating a slab comprising a predetermined component composition and a remainder made up by Fe and an impurity to 1280°C or higher and then subjecting the heated slab to a hot-rolling procedure to produce a hot-rolled steel sheet; subjecting the hot-rolled steel sheet to a hot-rolled sheet annealing procedure and then subjecting the resultant product to one round of cold rolling procedure or two or more rounds of cold-rolling procedures including intermediate annealing to produce a cold-rolled steel sheet; decarburization-annealing the resultant steel sheet; applying an annealing separation agent whose main component is MgO containing a Ti compound, a rare earth metal compound, a B compound, and a predetermined compound onto a surface of the decarburization-annealed cold-rolled steel sheet and then subjecting the resultant steel sheet to a final annealing procedure; and applying an insulation coating film onto the final annealed steel sheet and then subjecting the resultant steel sheet to a flattening annealing procedure.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing grain-oriented electrical steel sheets, grain-oriented electrical steel sheets, and an annealing separating agent. [Background technology]

[0002] Grain-oriented electrical steel sheets contain approximately 2% to 5% by mass of Si, and the orientation of the crystal grains in the steel sheet is called the Goss orientation. <001> This is a steel sheet with a high degree of density concentrated in a specific direction. Grain-oriented electrical steel sheets have excellent magnetic properties and are used in laminated form, for example, as the core material for static inductors such as transformers.

[0003] Various developments have been made to improve the magnetic properties of such grain-oriented electrical steel sheets. In particular, with the recent demand for energy conservation, there is a need for further reduction in iron loss in grain-oriented electrical steel sheets. To reduce iron loss in grain-oriented electrical steel sheets, it is effective to increase the concentration of crystal grains in the Goss orientation, thereby improving the magnetic flux density and reducing hysteresis loss.

[0004] In the manufacturing of grain-oriented electrical steel sheets, the crystal orientation is controlled by utilizing a catastrophic grain growth phenomenon called secondary recrystallization. However, in order to properly control the crystal orientation through secondary recrystallization, it is important to improve the heat resistance of the fine precipitates in the steel called inhibitors.

[0005] As a method for controlling the crystal orientation, for example, one method is to completely dissolve the inhibitor when heating the steel billet before hot rolling, and then finely precipitate it during the hot rolling and subsequent annealing processes. Specifically, this includes a method using MnS and AlN as inhibitors, as exemplified in Patent Document 1 below, and performing rolling with a reduction ratio of more than 80% in the final cold rolling process, or a method using MnS and MnSe as inhibitors and performing two cold rolling processes, as exemplified in Patent Document 2 below.

[0006] As a technique to further improve magnetic flux density, for example, Patent Document 3 below discloses a technique of adding 100 to 5000 g / T of Bi to molten steel. According to Patent Document 3 below, it is disclosed that adding Bi to molten steel improves the magnetic flux density in the final product sheet. Furthermore, when constructing an iron core by laminating grain-oriented electrical steel sheets, in which tension has been applied to the steel sheets to improve their magnetic properties, a coating is formed on the surface of the grain-oriented electrical steel sheets to improve the properties of the iron core by ensuring insulation between the steel sheets. In particular, the primary coating mainly composed of Mg2SiO4 (forsterite) formed in the manufacturing process of grain-oriented electrical steel sheets, along with the insulating coating mainly composed of aluminum phosphate and colloidal silica that is applied on top of it, plays an important role in ensuring adhesion between the steel sheet and the coating. Patent Documents 4 to 6 below disclose a technique to improve the adhesion between the primary coating and the steel sheet by compounding rare earth metal compounds and alkaline earth metal compounds into an annealing separating agent. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 40-15644 [Patent Document 2] Special Publication No. 51-13469 [Patent Document 3] Japanese Patent Application Publication No. 6-88171 [Patent Document 4] International Publication No. 2008 / 62853 [Patent Document 5] International Publication No. 2006 / 126660 [Patent Document 6] Japanese Patent Publication No. 2012-214902 [Overview of the project] [Problems that the invention aims to solve]

[0008] In recent years, there has been a growing demand for miniaturization of transformer cores, driven by the need for space-saving in substation equipment. To meet this demand, particularly in wound cores, the degree of bending of the product sheet has increased, requiring improved adhesion between the primary coating and the steel sheet. Similarly, in stacked cores, the product sheet needs to be processed into elongated shapes, requiring improved adhesion between the primary coating and the steel sheet. Furthermore, the increasing global pressure to regulate transformer efficiency has led to an even greater demand for reduced iron loss in grain-oriented electrical steel sheets. Adding Bicarbonate to molten steel is a promising solution, but it presents the problem of degraded adhesion between the primary coating and the steel sheet.

[0009] However, the technologies disclosed in the above-mentioned Patent Documents 4 to 6 alone could not solve the problem of the primary coating peeling off the steel sheet when the degree of bending or shearing of the product sheet was increased, or when the amount of Bi added to the molten steel was increased. Therefore, there was a need for a technology that could improve the adhesion between the primary coating and the steel sheet.

[0010] Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a method for manufacturing grain-oriented electrical steel sheets, grain-oriented electrical steel sheets, and an annealing release agent that makes it possible to further improve the adhesion between the primary coating and the steel sheet. [Means for solving the problem]

[0011] To solve the above problems, according to one aspect of the present invention, a method for manufacturing grain-oriented electrical steel sheets in which the magnetic flux density B8 value is 1.920T or more when a magnetic field of 800 A / m is applied at a frequency of 50 Hz, wherein the composition is as follows by mass%, C: 0.02% to 0.10%, Si: 2.5% to 4.5%, Mn: 0.01% to 0.15%, one or two of S and Se: total 0.001% to 0.050%, acid-soluble Al: 0.01% to 0.05%. 、N :0.002% or more and 0.015% or less Bi: 0% to 0.0500%, Cu: 0% to 0.30%, Sn: 0% to 0.30%, Ni: 0% to 0.30%, Cr: 0% to 0.30%, and Sb: 0% to 0.30%. It contains, with the remainder being Fe and impurities. Consists ofA hot rolling process in which a slab is heated to 1280°C or higher and hot-rolled to produce a hot-rolled steel sheet; a cold rolling process in which the hot-rolled steel sheet is subjected to hot-rolled sheet annealing, followed by one cold rolling or two or more cold rolling processes with an intermediate annealing in between to produce a cold-rolled steel sheet; a primary recrystallization annealing process in which the cold-rolled steel sheet is subjected to primary recrystallization annealing; and MgO being applied to the surface of the cold-rolled steel sheet after the primary recrystallization annealing process. Main component The process includes a finish annealing step in which a slurry-like annealing separation agent is applied, followed by finish annealing, and a planar annealing step in which an insulating film is applied to the surface of the steel sheet after the finish annealing step, followed by planar annealing, wherein the annealing separation agent contains, by mass%, a Ti compound at 0.3% to 10.0% in terms of Ti content, a rare earth metal compound at 2.0% to 10% in terms of rare earth metal content, a B compound at 0.03% to 1.60% in terms of B content, and Ca, S A method for producing grain-oriented electrical steel sheets is provided, which contains one or more alkaline earth metal compounds comprising one or more alkaline earth metal elements selected from the group consisting of r and Ba, and satisfies the following formula (1) when the content of the alkaline earth metal compound in terms of alkaline earth metal is A (mass%) and the content of compound B in terms of B is B (mass%) relative to the content of MgO, and the annealing separating agent is produced by stirring at a temperature of 0°C to 30°C for a time of 5 minutes to 300 minutes. B ≦A≦(0.8+3×B)...Equation (1)

[0012] Furthermore, in order to solve the above problems, according to another aspect of the present invention, a method for manufacturing grain-oriented electrical steel sheets, wherein the magnetic flux density B8 value is 1.920T or more when a magnetic field of 800 A / m is applied at a frequency of 50 Hz, and the composition is as follows in mass%, C: 0.02% or more and 0.10% or less, Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.15% or less, one or two of S and Se: total of 0.001% or more and 0.050% or less, acid-soluble Al: 0.01% or more and 0.05% or less. 、N :0.002% or more and 0.015% or less Bi: 0% to 0.0500%, Cu: 0% to 0.30%, Sn: 0% to 0.30%, Ni: 0% to 0.30%, Cr: 0% to 0.30%, and Sb: 0% to 0.30%. It contains, with the remainder being Fe and impurities. Consists of A hot rolling process in which a slab is heated to 1280°C or higher and hot rolled to obtain a hot rolled steel sheet, and a cold rolling process in which the hot rolled steel sheet is subjected to hot rolled sheet annealing and then subjected to one cold rolling or two or more cold rollings sandwiching an intermediate annealing to obtain a cold rolled steel sheet, a primary recrystallization annealing process in which the cold rolled steel sheet is subjected to primary recrystallization annealing, and MgO is applied to the surface of the cold rolled steel sheet after the primary recrystallization annealing process Main component After applying a slurry-like annealing release agent containing MgO, a finish annealing process in which finish annealing is performed, and a flattening annealing process in which an insulating film is applied to the surface of the steel sheet after the finish annealing process and then flattening annealing is performed, wherein the annealing release agent contains, in terms of mass%, based on MgO contained in the annealing release agent, a Ti compound in terms of Ti contained therein of 0.3% or more and 10.0% or less, a rare earth metal compound in terms of rare earth metal contained therein of 2.0% or more and 10% or less, a B compound in terms of B contained therein of 0.03% or more and 1.60% or less, one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, and a sulfate, and when the amount of alkaline earth metal in terms of alkaline earth metal compound is A (mass%) with respect to the content of MgO, the content of the B compound in terms of B is B (mass%) Content And the content of sulfate radical (SO4) in terms of sulfate is C (mass%), both of the following formulas (2) and (3) are satisfied, and the annealing release agent is produced by stirring at a temperature of 0°C or higher and 30°C or lower for 5 minutes or more and 300 minutes or less, and a method for producing a grain-oriented electrical steel sheet is provided. 2- 0 < A < B ··· Formula (2) 0 < A < B ··· Formula (2) (3×B) ≤C≤(10×B) ··· Formula (3)

[0013] Preferably, the slab contains Bi: 0.0005% or more and 0.0500% or less in terms of mass%.

[0014] The slab preferably further contains one or more elements selected from the group consisting of Cu: 0.01% to 0.30%, Sn: 0.01% to 0.30%, Ni: 0.01% to 0.30%, Cr: 0.01% to 0.30%, or Sb: 0.01% to 0.30% by mass.

[0015] With the above configuration, by including a Ti compound, a rare earth metal compound, and a B compound in the annealing separating agent, and by appropriately including one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, or such alkaline earth metal compounds and sulfates, it becomes possible to further improve the adhesion between the primary coating and the steel sheet.

[0016] Furthermore, in order to solve the above problems, according to another aspect of the present invention, a grain-oriented electrical steel sheet comprising a base steel sheet and a primary coating formed on the surface of the base steel sheet, wherein the grain-oriented electrical steel sheet comprises an oxide mainly composed of MgAl2O4 bonded to the primary coating, and the base steel sheet has a composition of C: 0.005% or less by mass, Si: 2.5~4.5%, and Mn: 0.01~0.15% by mass. Bi: 0% to 0.0500%, Cu: 0% to 0.30%, Sn: 0% to 0.30%, Ni: 0% to 0.30%, Cr: 0% to 0.30%, and Sb: 0% to 0.30% Includes, The remainder consists of Fe and impurities. The primary coating contains Mg2SiO4 as the main component, and the base steel sheet is inclined and polished at an inclination angle of 5° in the thickness direction, and the amount of oxide present on a line drawn parallel to the surface of the grain-oriented electrical steel sheet after electropolishing is 10% or more in a region within 0.5 μm to 5 μm from the leading edge position of the primary coating on the base steel sheet side, and the magnetic flux density B8 value is 1.920 T or more when a magnetic field of 800 A / m is applied at a frequency of 50 Hz.

[0017] The base steel sheet may contain, by mass%, one or more elements selected from the group consisting of Cu: 0.01% to 0.30%, Sn: 0.01% to 0.30%, Ni: 0.01% to 0.30%, Cr: 0.01% to 0.30%, or Sb: 0.01% to 0.30%.

[0019] Furthermore, in order to solve the above problems, according to another aspect of the present invention, an annealing separation agent is provided that contains, in mass%, a Ti compound in terms of contained Ti, 0.3% to 10.0%, a rare earth metal compound in terms of contained rare earth metal, 2.0% to 10%, a B compound in terms of contained B, 0.03% to 1.60%, and one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, and satisfies the following formula (1) when the content of the alkaline earth metal compound in terms of alkaline earth metal is A (mass%) and the content of the B compound in terms of B is B (mass%) relative to the content of MgO. B ≦A≦(0.8+3×B) Formula (1)

[0020] Furthermore, in order to solve the above problems, according to another aspect of the present invention, the present invention contains, in mass%, a Ti compound in an amount of 0.3% to 10.0% in terms of contained Ti, a rare earth metal compound in an amount of 2.0% to 10% in terms of contained rare earth metal, a B compound in an amount of 0.03% to 1.60% in terms of contained B, one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, and a sulfate, wherein the content of the alkaline earth metal compound in terms of alkaline earth metal is A relative to the content of MgO. ( mass% ) The content of compound B in terms of B is B (mass%), and the sulfate (SO4) of the sulfate is 2-An annealing release agent is provided, which is characterized in that when the content in terms of conversion is C (mass %), it satisfies both of the following formulas (2) and (3). 0 < A < B ··· Formula (2) (3×B) ≦ C ≦ (10 × B) ··· Formula (3)

Advantages of the Invention

[0021] As described above, according to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet that is further excellent in the adhesion between the primary film and the steel sheet, and more preferably, has a more excellent magnetic flux density.

Brief Description of the Drawings

[0022] [Figure 1] It is a secondary electron image obtained by observing a grain-oriented electromagnetic steel sheet after final annealing with a tilt angle of 5° applied for tilt polishing, followed by electrolytic polishing, using a scanning electron microscope. [Figure 2] A graph in which the B content in terms of B in the B compound in the annealing release agent is taken on the horizontal axis, and the content in terms of the alkaline earth metal of the alkaline earth metal compound containing an alkaline earth metal element selected from the group consisting of Ca, Sr, and Ba is taken on the vertical axis, and the results of Conditions B1 to B48, B50, and B51 shown in Tables 2A and 2B are plotted.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0024] The inventors of the present invention conducted intensive studies on the manufacturing method of a grain-oriented electromagnetic steel sheet in order to further improve the adhesion between the primary film and the steel sheet of the grain-oriented electromagnetic steel sheet and further improve the magnetic properties, and as a result, found the following findings.

[0025] Specifically, the inventors have found that the adhesion between the primary coating and the steel sheet can be further improved by including a Ti compound, a B compound, and a rare earth metal compound in the annealing separation agent. Furthermore, they confirmed that this adhesion-improving effect is also very favorable to the deterioration of adhesion between the primary coating and the steel sheet that inevitably occurs when molten steel contains Bi in order to strengthen the heat resistance of the inhibitor and improve the magnetic flux density. On the other hand, when none of the Ti compound, B compound, or rare earth metal compound were included in the annealing separation agent, the adhesion between the primary coating and the steel sheet did not improve.

[0026] At the same time, it was found that if the annealing separating agent simply contains Ti compounds, B compounds, and rare earth metal compounds, the magnetic flux density may deteriorate. Therefore, the inventors have found that by appropriately containing, along with Ti compounds, B compounds, and rare earth metal compounds, one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, or such alkaline earth metal compounds and sulfates, it is possible to improve the adhesion between the primary coating and the steel sheet without degrading the magnetic flux density.

[0027] Although the detailed reasons for this phenomenon are not clear, it is presumed that the components of the annealing separation agent affect the behavior of the inhibitor strength during the secondary recrystallization process. Specifically, if the annealing separation agent contains Ti compounds, B compounds, and rare earth metal compounds, the nitriding of the steel sheet by N contained in the annealing atmosphere is promoted during the secondary recrystallization process, leading to overstable secondary recrystallization and a deterioration of the magnetic flux density. However, it is presumed that if the annealing separation agent appropriately contains, in addition to the above-mentioned Ti compounds, B compounds, and rare earth metal compounds, one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, or such alkaline earth metal compounds or sulfates, and the inhibitor strength in the thickness direction of the sheet is properly controlled, the deterioration of the magnetic flux density can be suppressed.

[0028] The inventors of the present invention have come up with this invention by considering the above findings. One embodiment of the present invention is a method for manufacturing grain-oriented electrical steel sheets having the following configuration.

[0029] A slab containing, by mass%, C: 0.02% to 0.10%, Si: 2.5% to 4.5%, Mn: 0.01% to 0.15%, one or two of S and Se: total 0.001% to 0.050%, acid-soluble Al: 0.01% to 0.05%, and N: 0.002% to 0.015%, with the remainder being Fe and impurities, is heated to 1280°C or higher and hot-rolled to produce a hot-rolled steel sheet. A hot rolling process; a cold rolling process in which the hot-rolled steel sheet is subjected to hot-rolled sheet annealing, followed by one cold rolling or two or more cold rolling processes with an intermediate annealing in between, to obtain a cold-rolled steel sheet; a primary recrystallization annealing process in which the cold-rolled steel sheet is subjected to primary recrystallization annealing; a finish annealing process in which a slurry-like annealing separating agent containing MgO is applied to the surface of the cold-rolled steel sheet after the primary recrystallization annealing process, followed by finish annealing; and an insulating coating is applied to the surface of the steel sheet after the finish annealing process, A method for manufacturing grain-oriented electrical steel sheets is provided, comprising a planar annealing step of performing planar annealing, wherein the annealing separating agent contains, in mass%, a Ti compound in the amount of Ti it is equivalent to, 0.3% to 10.0%, a rare earth metal compound in the amount of rare earth metal it is equivalent to, 0.1% to 10%, a B compound in the amount of B it is equivalent to, 0.03% to 1.60%, and one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, and satisfying the following formula (1) when the content of the alkaline earth metal compound in terms of alkaline earth metal is A (mass%) and the content of the B compound in terms of B is B (mass%) relative to the content of MgO, and the annealing separating agent is manufactured by stirring at a temperature of 0°C to 30°C for a time of 5 minutes to 300 minutes. B≦A≦(0.8+3×B) Formula (1)

[0030] [Manufacturing method for grain-oriented electrical steel sheets] The method for manufacturing grain-oriented electrical steel sheets according to this embodiment will be described in detail below.

[0031] (Chemical composition of the slab) First, before describing each step of the manufacturing method for grain-oriented electrical steel sheets according to this embodiment, the component composition of the slab used in the grain-oriented electrical steel sheets according to this embodiment will be described. Unless otherwise specified below, "%" refers to "mass%". The remainder of the slab, other than the elements described below, includes Fe and impurities.

[0032] The carbon (C) content is between 0.02% and 0.10%. While C plays various roles, a C content of less than 0.02% is undesirable because it increases the iron loss value of the final grain-oriented electrical steel sheet due to the excessive increase in grain size during slab heating. On the other hand, a C content exceeding 0.10% is undesirable because it prolongs the decarburization time after cold rolling, increasing manufacturing costs. Furthermore, a C content exceeding 0.10% is undesirable because it tends to result in incomplete decarburization, potentially causing magnetic aging in the final grain-oriented electrical steel sheet. Therefore, the C content should be between 0.02% and 0.10%. Preferably, the C content is between 0.05% and 0.09%.

[0033] The silicon (Si) content is between 2.5% and 4.5%. Si reduces eddy current loss, which is one of the causes of iron loss, by increasing the electrical resistance of the steel sheet. If the Si content is less than 2.5%, it becomes difficult to sufficiently suppress eddy current loss in the final grain-oriented electrical steel sheet, which is undesirable. On the other hand, if the Si content exceeds 4.5%, the workability of the grain-oriented electrical steel sheet decreases, which is also undesirable. Therefore, the Si content should be between 2.5% and 4.5%. Preferably, the Si content is between 2.7% and 4.0%.

[0034] The manganese (Mn) content is between 0.01% and 0.15%. Mn forms inhibitors such as MnS and MnSe, which affect secondary recrystallization. If the Mn content is less than 0.01%, the absolute amount of MnS and MnSe necessary for secondary recrystallization is insufficient, which is undesirable. On the other hand, if the Mn content is greater than 0.15%, solid solution of Mn becomes difficult during slab heating, which is also undesirable. Furthermore, if the Mn content is greater than 0.15%, the precipitate size of the inhibitors MnS and MnSe tends to become coarser, impairing the optimal size distribution as inhibitors, which is also undesirable. Therefore, the Mn content should be between 0.01% and 0.15%. Preferably, the Mn content is between 0.03% and 0.13%.

[0035] The total content of S (sulfur) and Se (selenium) is between 0.001% and 0.050%. S and Se form inhibitors together with Mn as described above. Both S and Se may be present in the slab, but it is sufficient if at least one of them is present. If the total content of S and Se falls outside the above range, a sufficient inhibitory effect cannot be obtained, which is undesirable. Therefore, the total content of S and Se should be between 0.001% and 0.050%. Preferably, the total content of S and Se is between 0.001% and 0.040%.

[0036] The acid-soluble Al (acid-soluble aluminum) content is 0.01% to 0.05%. Acid-soluble Al constitutes the inhibitor necessary for manufacturing high magnetic flux density grain-oriented electrical steel sheets. Furthermore, during the finish annealing process described later, acid-soluble Al reacts with MgO in the primary coating or at or near the interface between the primary coating and the steel sheet to form MgAl2O4 (spinel). If the acid-soluble Al content is less than 0.01%, there will be a quantitative deficiency of acid-soluble Al, resulting in insufficient inhibitor strength, which is undesirable. On the other hand, if the acid-soluble Al content exceeds 0.05%, the AlN precipitated as an inhibitor becomes coarser, reducing the inhibitor strength, which is also undesirable. Therefore, the acid-soluble Al content should be 0.01% to 0.05%. Preferably, the acid-soluble Al content is 0.01% to 0.04%.

[0037] The nitrogen (N) content is between 0.002% and 0.015%. N forms the inhibitor AlN together with the acid-soluble Al mentioned above. If the N content falls outside the above range, a sufficient inhibitory effect cannot be obtained, which is undesirable. Therefore, the N content should be between 0.002% and 0.015%. Preferably, the N content is between 0.002% and 0.012%.

[0038] The effects of the present invention are particularly useful in steel plates manufactured using a method that incorporates Bi (bismuth) into the slab.

[0039] Generally, incorporating Bi into the slab component deteriorates the adhesion between the primary coating and the steel sheet. Although the details of this mechanism are not fully understood, it is presumed that the interface structure between the primary coating and the steel sheet becomes smoother, reducing the anchoring effect and degrading adhesion. However, by applying the present invention, smoothing is suppressed even in Bi-containing steel, resolving the adhesion problem. By incorporating Bi into the slab, the heat resistance of the inhibitor is enhanced, ensuring good adhesion even in steel sheets with increased magnetic flux density.

[0040] In this case, the Bi content is preferably between 0.0005% and 0.0500%. It is presumed that Bi enhances the heat resistance of inhibitors such as MnS and AlN, raising the secondary recrystallization temperature and improving the magnetic flux density. When the Bi content is between 0.0005% and 0.0500%, an even greater inhibitor heat resistance enhancement effect can be obtained. If the Bi content is less than 0.0005%, a sufficient inhibitor heat resistance enhancement effect may not be obtained. If the Bi content exceeds 0.0500%, the brittleness of the steel sheet in hot rolling deteriorates, making sheet feeding difficult and potentially reducing productivity. Therefore, the Bi content is preferably between 0.0005% and 0.0500%. More preferably, the Bi content is between 0.0010% and 0.0200%. Note that since Bi is not necessarily essential in steel materials, the lower limit of the content is 0%.

[0041] Furthermore, the slab used in the manufacture of the grain-oriented electrical steel sheet according to this embodiment may further contain, in addition to the elements mentioned above, one or more of the elements Cu, Sn, Ni, Cr, or Sb as elements that stabilize secondary recrystallization. When the slab contains the above elements, the iron loss value of the manufactured grain-oriented electrical steel sheet can be further reduced.

[0042] Furthermore, if the slab contains one or more of these elements, it is preferable that the content of each element be between 0.01% and 0.30%. When the slab contains one or more of Cu, Sn, Ni, Cr, or Sb, having the content of each element within the above range further enhances the effect of stabilizing secondary recrystallization. If the content of each of these elements is less than 0.01%, it becomes difficult to obtain a sufficient effect of stabilizing secondary recrystallization, which is undesirable. On the other hand, if the content of each of these elements exceeds 0.30%, the effect of stabilizing secondary recrystallization saturates, which is undesirable from the viewpoint of suppressing an increase in manufacturing costs. Since these elements are not necessarily essential in steel, the lower limit of their content is 0%.

[0043] A slab is formed by casting molten steel adjusted to the component composition described above. The casting method for the slab is not particularly limited. Furthermore, in research and development, even if a steel ingot is formed in a vacuum melting furnace, the same effects as when a slab is formed can be confirmed for the above components.

[0044] (Hot rolling process) Next, the slab having the above composition is heated to 1280°C or higher, causing the inhibitor components in the slab to be dissolved. If the heating temperature of the slab is below 1280°C, it becomes difficult to sufficiently dissolve the inhibitor components such as MnS, MnSe, and AlN, which is undesirable. There is no particular upper limit for the heating temperature of the slab at this time, but from the viewpoint of protecting the equipment, 1450°C is preferred, and for example, the heating temperature of the slab is preferably between 1300°C and 1450°C.

[0045] Next, the heated slab is hot-rolled to form a hot-rolled steel sheet. Hot rolling can be carried out by known methods. The thickness of the hot-rolled steel sheet after processing is preferably, for example, 1.8 mm or more and 3.5 mm or less. By setting the thickness of the hot-rolled steel sheet to 1.8 mm or more and 3.5 mm or less, secondary recrystallization can be stabilized, and it is possible to maintain excellent magnetic properties in the final grain-oriented electrical steel sheet. On the other hand, if the thickness of the hot-rolled steel sheet is less than 1.8 mm, the temperature of the steel sheet after hot rolling will be lower, and the amount of AlN precipitated in the steel sheet will increase, which may make secondary recrystallization unstable and reduce the magnetic properties. If the thickness of the hot-rolled steel sheet is greater than 3.5 mm, the rolling load in the cold-rolling process may be increased.

[0046] (Cold rolling process) Next, the processed hot-rolled steel sheet is subjected to hot-rolled sheet annealing, followed by a single cold-rolling or multiple cold-rollings with an intermediate annealing in between, to be processed into a cold-rolled steel sheet. Hot-rolled sheet annealing, cold-rolling, and intermediate annealing can each be carried out by known methods. In the case of multiple cold-rollings with an intermediate annealing in between, the preceding hot-rolled sheet annealing can be omitted. However, when hot-rolled sheet annealing is performed, the shape of the steel sheet is improved, which reduces the possibility of the steel sheet fracturing during cold-rolling.

[0047] Furthermore, the steel sheet may be heat-treated at approximately 300°C or lower between cold rolling passes, between rolling roll stands, or during rolling. In such cases, the magnetic properties of the final grain-oriented electrical steel sheet can be improved. Although hot-rolled steel sheets may be rolled by cold rolling three or more times, multiple cold rolling passes increase manufacturing costs, so it is preferable that hot-rolled steel sheets be rolled by cold rolling once or twice. When cold rolling is performed using a reverse rolling mill such as a Zenzimir mill, the number of passes in each cold rolling step is not particularly limited, but from the viewpoint of manufacturing costs, it is preferable to have nine passes or less.

[0048] (Primary recrystallization annealing process) Next, the cold-rolled steel sheet is decarburized and annealed. Rapid heating during the heating process is also effective in improving magnetic properties. This process is also called primary recrystallization annealing, and when rapid heating is performed, it is preferable to perform it in succession with decarburization annealing. Decarburization annealing can be performed by known methods, but it is preferable to perform it in a humid atmosphere containing hydrogen and nitrogen at a temperature of, for example, 900°C or lower. In addition, in the primary recrystallization annealing step, the cold-rolled steel sheet may be subjected to reduction annealing following decarburization annealing for the purpose of improving magnetic properties and coating properties.

[0049] (Finishing annealing process) Subsequently, an annealing separation agent mainly composed of MgO is applied to the cold-rolled steel sheet after primary recrystallization annealing for the purposes of preventing sticking between steel sheets during subsequent finish annealing, forming a primary film, and controlling secondary recrystallization behavior. Here, "main component" refers to a component that is present in a certain substance at a concentration of 50% by mass or more. For example, MgO is present at a concentration of 50.0% by mass or more relative to the solid content of the annealing separation agent. Preferably, the MgO content is 50.0% by mass or more and 99.3% by mass or less relative to the solid content of the annealing separation agent, and more preferably 70.0% by mass or more and 99.0% by mass or less. In addition to MgO, Ti compounds, rare earth metal compounds, alkaline earth metal compounds may be contained, and further sulfates, Al compounds, Fe compounds, Si compounds, etc., may also be contained. The annealing separation agent is prepared by containing the above compounds in water, applying it to the surface of the steel sheet in a slurry state, and drying it. Here, the components of the annealing separation agent have a significant impact, particularly on the adhesion between the primary coating and the steel sheet, and on the secondary recrystallization behavior. The content and effects of the components of the annealing separation agent are described below. Here, unless otherwise specified, the content of each compound contained in the annealing separation agent is given as the mass % of the component relative to 100% MgO, the main component of the annealing separation agent.

[0050] The annealing separation agent according to this embodiment contains at least MgO, a Ti compound, a rare earth metal compound, and a B compound. Furthermore, the annealing separation agent according to this embodiment may also contain one or more alkaline earth metal compounds (hereinafter simply referred to as "alkaline earth metal compounds") containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba.

[0051] In the method for manufacturing grain-oriented electrical steel sheets according to this embodiment, the content of the Ti compound in the annealing separating agent is 0.3% to 10.0% in terms of Ti. The Ti compound has a significant effect on the adhesion between the primary coating and the steel sheet. If the Ti compound content is less than 0.3% in terms of Ti, the effect of improving adhesion is insufficient. If the Ti compound content is more than 10.0% in terms of Ti, Ti may dissolve into the steel sheet during the finish annealing process, and later form fine precipitates such as TiC in the steel, degrading the magnetism (magnetic aging), which is undesirable. Therefore, the Ti compound content is set to 0.3% to 10.0% in terms of Ti. Preferably, the Ti compound content is 0.5% to 8.5%.

[0052] In the above annealing separation agent, the content of rare earth metal compounds is 0.1% to 10% in terms of rare earth metals. The rare earth metal compounds contained in the annealing separation agent include one or more elements selected from the group consisting of rare earth elements. It is presumed that the rare earth metal compounds release oxygen during finish annealing, promoting the formation of an embedded structure between the primary coating and the steel sheet, thereby improving the adhesion between the primary coating and the steel sheet. However, if the content of rare earth metal compounds is less than 0.1%, the effect of improving adhesion is insufficient, and if the content of rare earth metal compounds exceeds 10%, the coatability of the annealing separation agent slurry deteriorates, which is undesirable. Therefore, the content of rare earth metal compounds is set to 0.1% to 10% in terms of rare earth metals. Preferably, the content of rare earth metal compounds is 0.2% to 8% in terms of rare earth metals. The rare earth metal compound is not particularly limited and may be a mixture of one or more oxides, sulfides, sulfates, silicides, phosphates, hydroxides, carbonates, borides, chlorides, or fluorides of various rare earth metal elements. From the standpoint of availability and cost, the use of compounds of La, Ce, and Y is more preferable.

[0053] In the above annealing separating agent, the content of compound B is 0.0.03% or more and 1.60% or less in terms of B equivalent. If the content of compound B is less than 0.03% in terms of B equivalent, the effect of improving adhesion is insufficient, and if the content of compound B is greater than 1.60% in terms of B equivalent, the effect of improving adhesion saturates and costs increase, which is undesirable. Therefore, the content of compound B is set to 0.0.03% or more and 1.60% or less in terms of B equivalent. Preferably, the content of compound B is 0.05% or more and 1.60% or less in terms of B equivalent.

[0054] By including Ti compounds, rare earth metal compounds, and B compounds in the annealing release agent, the adhesion between the primary coating and the steel sheet is improved. Although the details of this mechanism are not clear, it is presumed that during the finish annealing process, Ti compounds, rare earth metal compounds, and B compounds are formed in the primary coating or at or near the interface between the primary coating and the steel sheet. This causes the oxide, mainly composed of MgAl2O4 (spinel), to be bonded to the primary coating on the base steel sheet side of the primary coating, which is mainly composed of Mg2SiO4. In other words, a portion of the oxide is fixed to the primary coating, thereby exhibiting an anchoring effect. In the following, the oxide mainly composed of MgAl2O4 may simply be referred to as "Al oxide".

[0055] In the above-mentioned annealing separating agent, the total content of one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba is such that it satisfies the following formula (1).

[0056] B≦A≦(0.8+3×B) Formula (1)

[0057] Here, in formula (1) above, A(%) is the alkaline earth metal equivalent value of the alkaline earth metal compound relative to 100% MgO, and B(%) is the B equivalent value of compound B relative to 100% MgO. If the annealing separating agent contains two or more alkaline earth metal compounds, A(%) above is the sum of the equivalent values ​​of each alkaline earth metal element contained. In addition, the alkaline earth metal compound may contain one or more selected from the group consisting of sulfates, carbonates, hydroxides, chlorides, and oxides. If the alkaline earth metal compound is one or more of sulfates, carbonates, hydroxides, chlorides, and oxides, it is the alkaline earth metal equivalent value of the total content. Here, the species of compound may be defined by its chemical formula, and different chemical formulas may indicate different types of compounds. The converted amount of alkaline earth metals can be calculated by determining the proportion of alkaline earth metal elements contained in the compound using the atomic weights of each element from the chemical formula of the alkaline earth metal compound contained in the annealing separation agent, and multiplying this by the content of the compound in the annealing separation agent. If two or more alkaline earth metal compounds are contained, the values ​​calculated from each compound may be added together. If the stoichiometric ratio of each element in the chemical formula is not determined, the content of alkaline earth metals may be measured using a component analysis device such as inductively coupled plasma mass spectrometry (ICP-MS) of the annealing separation agent. The converted values ​​of Ti, B, and rare earth metals may also be calculated or measured in a similar manner. Furthermore, the identification of compound species may be performed using general instruments such as X-ray diffractometers or transmission electron microscopes.

[0058] The alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba are not particularly limited, but examples include sulfates, carbonates, hydroxides, chlorides, and oxides. Specifically, examples include CaSO4·0.5H2O, CaCO3, SrSO4, Sr(OH)2, BaSO4, SrCO3, etc.

[0059] When A < B, it is not preferable because the magnetic flux density (B8) value of the steel sheet deteriorates when the grain-oriented electrical steel sheet is excited at 50 Hz and 800 A / m. On the other hand, when (0.8 + 3×B) < A, secondary recrystallization becomes unstable and the B8 value deteriorates, so it is not preferable.

[0060] In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, in order to more surely exhibit the above effects, the total content of the alkaline earth metal compound in the annealing separating agent is preferably B ≤ A ≤ (0.6 + 3×B).

[0061] The inventors of the present invention have found that when the annealing separating agent contains a Ti compound, a B compound, and a rare earth metal compound, the adhesion between the primary coating and the steel sheet is remarkably improved, and at the same time, the B8 value deteriorates. This mechanism is not necessarily clear, but it is presumed that in the secondary recrystallization process, nitridation of the steel sheet by N contained in the atmosphere gas of the final annealing progresses, and the secondary recrystallization becomes overstable and the B8 value deteriorates. Here, when one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba are contained in an appropriate amount in the annealing separating agent, it is presumed that a barrier layer is formed in the vicinity of the interface between the primary coating and the steel sheet during the secondary recrystallization process, suppressing the nitridation of the steel sheet by the atmosphere gas of the final annealing and preventing the deterioration of the B8 value.

[0062] Note that MgO, which is the main component of the annealing separating agent, is also an alkaline earth metal compound, but Mg 2+ ions are presumed to have no effect of suppressing the nitridation from the atmosphere gas of the final annealing to the steel sheet during the secondary recrystallization process because the diffusion in silica, which is the main component of the decarburized oxide film, is slow. Therefore, in the total content of the alkaline earth metal compound defined by the above B, Mg compounds are not considered.

[0063] As described above, for one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, when there is a relationship of A < B between the total content A (%) in terms of Ca, Sr, and Ba contained and the B conversion value B (%) of the B compound contained, secondary recrystallization becomes overstable and the B8 value deteriorates, which is not preferable. However, the inventors of the present invention have found that by containing a predetermined amount of sulfate in the annealing separator, even when there is a relationship of A < B between the total content A (%) and the B conversion value B (%) of the B compound contained, a grain-oriented electrical steel sheet excellent in both magnetic properties and adhesion between the primary coating and the steel sheet can be manufactured.

[0064] That is, in detail, the inventors of the present invention, in the above annealing separator, set the content of one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba as A% in terms of alkaline earth metal, and the B conversion value of the B compound contained as B%. Even when the relationship between A and B is A < B, when the sulfate content is C% in terms of sulfate radical (SO4) 2- and the relationship of (3×B) ≦ C ≦ (10×B) holds, it has been found that a grain-oriented electrical steel sheet excellent in both magnetic properties and adhesion between the primary coating and the steel sheet can be manufactured. In this case, the total content of the alkaline earth metal compounds defined by the above B satisfies both relationships represented by the following formulas (2) and (3).

[0065] 0 ≦ A < B ··· Formula (2) (3×B) ≦ C ≦ (10×B) ··· Formula (3)

[0066] In the above formula (2), the case where the value of A becomes zero is also included. However, as shown in the following examples, even when the value of A is zero (that is, no alkaline earth metal compound is contained), if the sulfate content C satisfies the relationship of the above formula (3), a grain-oriented electrical steel sheet excellent in both magnetic properties and adhesion between the primary coating and the steel sheet can be manufactured.

[0067] Also, regarding the content C of the sulfate in the above formula (3), for the counter ion of the SO4 2- ion, it is not particularly limited, and a compound that can generate SO4 2- ions present in the annealing separating agent is targeted when considering the content C.

[0068] In the above formula (3), when C < (3 × B), the B8 value deteriorates, which is not preferable. On the other hand, when (10 × B) < C, secondary recrystallization becomes unstable and the B8 value may deteriorate, so it is not preferable.

[0069] In addition, one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba contained in the annealing separating agent so as to satisfy the above formula (2) and the above formula (3) are the same as one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba contained in the annealing separating agent so as to satisfy the above formula (1). That is, one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba contained in the annealing separating agent so as to satisfy the above formula (2) and the above formula (3) are not particularly limited, but examples include sulfates, carbonates, hydroxides, chlorides, oxides, etc. Specifically, CaSO4·0.5H2O, CaCO3, SrSO4, Sr(OH)2, BaSO4, SrCO3, etc. can be mentioned.

[0070] When the annealing separator contains an appropriate amount of sulfate, it is presumed that during the secondary recrystallization process, the sulfate decomposes, sulfur penetrates into the steel sheet, and sulfides such as MnS are formed in the steel, thereby obtaining the effect of improving the inhibitor strength near the surface layer. Even if nitridation of the steel sheet by the atmosphere gas in the finish annealing progresses with A < B, by appropriately controlling the penetration of sulfur from the annealing separator into the steel sheet and forming MnS near the surface layer, it is presumed that the balance of the inhibitor strength in the thickness direction during the secondary recrystallization process is appropriately maintained, preventing the deterioration of the B8 value. Even when (10 × B) < C, when the above formula (1) is satisfied, good magnetic properties may be obtained. Although the mechanism is not necessarily clear, when the annealing separator contains an appropriate amount of alkaline earth metal, the amount of sulfur penetration may be reduced. When the alkaline earth metal diffuses as a cation through silica, which is the main component of the decarburized film, it is presumed that oxygen ions are more likely to be selected as counter ions than SO4 2- ions, which is one of the reasons.

[0071] The annealing separation agent according to this embodiment contains at least MgO, a Ti compound, a rare earth metal compound, and a B compound, and is a slurry in which these are dispersed in water. However, the rare earth metal compound has a high specific gravity, while the B compound has a low specific gravity. Therefore, when preparing a slurry-type annealing separation agent, it is necessary to stir the mixture to suppress precipitation and suspension and ensure uniform mixing. To prepare a slurry-type annealing separation agent, stirring is performed at a temperature of 0°C to 30°C for a time of 5 minutes to 300 minutes. If the slurry temperature is below 0°C, ice will form, making uniform mixing difficult, and it is undesirable because a slurry in which the compounds contained in the annealing separation agent are uniformly dispersed cannot be obtained. If the slurry temperature is above 30°C, the viscosity of the slurry will be high, and the compounds contained in the slurry will not be uniformly mixed, and it is undesirable because a slurry in which the compounds contained in the annealing separation agent are uniformly dispersed cannot be obtained. If the stirring time is less than 5 minutes, the compounds contained in the slurry will not be sufficiently mixed, and it is undesirable because a slurry in which the compounds contained in the annealing separation agent are uniformly dispersed cannot be obtained. If the stirring time exceeds 300 minutes, it will reduce productivity and is therefore undesirable. Thus, stirring in the preparation of a slurry-like annealing separation agent in which the above compound is dispersed in water should be carried out at a temperature between 0°C and 30°C for a time between 5 minutes and 300 minutes.

[0072] The total mass of MgO, Ti compounds, rare earth metal compounds, and B compounds contained in the slurry-like annealing separation agent is preferably 3% to 50% of the total mass of the slurry-like annealing separation agent. If the total mass of MgO, Ti compounds, rare earth metal compounds, and B compounds contained in the annealing separation agent is 3% to 50% of the total mass of the annealing separation agent, the above compounds will be uniformly dispersed in water by stirring, and a uniformly dispersed annealing separation agent will be obtained.

[0073] Furthermore, the particle sizes of the MgO, Ti compounds, rare earth metal compounds, and B compounds contained in the annealing separation agent are not particularly limited as long as they can be uniformly dispersed in water, for example, 0.1 μm to 50 μm. Preferably, the particle sizes of the MgO, Ti compounds, rare earth metal compounds, and B compounds contained in the annealing separation agent are 0.5 μm to 25 μm. The particle size is, for example, the average particle size measured using a volume-based distribution with a laser diffraction particle size distribution analyzer.

[0074] Furthermore, the agitator used to stir the slurry is not particularly limited as long as it enables uniform mixing, and various shapes of agitators and impellers can be appropriately combined. Needless to say, baffles may be included inside the agitator to achieve uniform mixing.

[0075] Next, finish annealing is performed for the purpose of primary film formation, Al oxide generation, and secondary recrystallization. For example, in finish annealing, it is preferable to heat the coiled steel sheet to a temperature of 800°C to 1000°C over a period of 10 hours or more using a batch-type heating furnace. Alternatively, it may be held at a specific temperature. Furthermore, in order to further reduce the iron loss value of the final grain-oriented electrical steel sheet, a purification treatment may be performed in which the coiled steel sheet is heated to a temperature of approximately 1200°C and then held.

[0076] The average heating rate during the heating process of finish annealing is not particularly limited, and general finish annealing conditions can be used. For example, the average heating rate during the heating process of finish annealing, including secondary recrystallization annealing, is preferably 5°C / h to 100°C / h from the viewpoint of productivity and general equipment constraints. Furthermore, the heating process of finish annealing may be carried out using other known heat patterns.

[0077] The atmospheric gas composition in finish annealing is not particularly limited. During the secondary recrystallization process, a mixture of nitrogen and hydrogen gas may be used. The atmosphere may be dry or wet. The atmospheric gas composition for purification annealing may be dry hydrogen gas.

[0078] In the above finish annealing process, an oxide mainly composed of MgAl2O4 is formed in a range of 0.5 μm to 5 μm from the leading edge of the primary film on the base steel sheet side, connected to a primary film mainly containing Mg2SiO4, in the thickness direction of the base steel sheet.

[0079] (Planarization annealing process) Next, after finish annealing, an insulating coating, mainly composed of aluminum phosphate or colloidal silica, is applied to the surface of the steel sheet to impart insulation and tension to the steel sheet. Subsequently, planar annealing is performed to bake the insulating coating and to flatten the shape of the steel sheet through finish annealing. The composition of the insulating coating is not particularly limited as long as it imparts insulation and tension to the steel sheet. Furthermore, planar annealing can be carried out by known methods. Needless to say, in this embodiment, depending on the customer's purpose, magnetic domain control treatment may be applied to the grain-oriented electrical steel sheet.

[0080] Through the above process, the final grain-oriented electrical steel sheet can be manufactured. According to the manufacturing method of this embodiment, a grain-oriented electrical steel sheet with excellent magnetic properties and excellent adhesion between the primary coating and the steel sheet can be manufactured.

[0081] The resulting grain-oriented electrical steel sheet is then processed into a transformer. For example, in a wound core transformer, it is wound to a predetermined size and then shaped using a die or the like. In this process, the inner circumference of the core is particularly subjected to processing with a very small radius of curvature. To sufficiently prevent delamination between the primary coating and the steel sheet even with such processing, the delamination area ratio in a 10mmφ bending adhesion test is preferably 10% or less, and more preferably 5% or less.

[0082] The 10mmφ bending adhesion test (10mmφ bending test) is performed by using a cylindrical mandrel bending tester to place a sample steel plate in the tester and perform a bending test, then observing the surface of the sample steel plate after the bending test. The coating delamination area ratio is the ratio of the area where the primary coating has peeled off to the total area of ​​the sample steel plate.

[0083] [Grain-oriented electrical steel sheet] The grain-oriented electrical steel sheet according to this embodiment comprises a base steel sheet containing predetermined components and a primary coating formed on the surface of the base steel sheet, the primary coating containing Mg2SiO4 as the main component.

[0084] [Component composition of the base steel sheet] In the grain-oriented electrical steel sheet according to this embodiment, in order to increase magnetic flux density and reduce iron loss, it is important to control the content of the following elements in the component composition of the base steel sheet of the grain-oriented electrical steel sheet. Unless otherwise specified, the notation "%" represents "mass%".

[0085] Carbon (C) is an effective element for controlling the microstructure until the completion of the decarburization annealing process in the manufacturing process. However, if the C content exceeds 0.0050%, it causes magnetic aging and reduces the magnetic properties. Therefore, the C content should be 0.0050% or less. On the other hand, while a lower C content is preferable, reducing the C content to less than 0.0001% will saturate the effect of microstructure control and only increase manufacturing costs. Therefore, the C content may be 0.0001% or more. More preferably, the C content is between 0.0001% and 0.0030%.

[0086] Si reduces eddy current loss, which constitutes part of iron loss, by increasing the electrical resistance of the steel sheet. Si is contained in the base steel sheet in a range of 2.5% to 4.5% by mass. If the Si content is less than 2.5%, it becomes difficult to suppress eddy current loss in the grain-oriented electrical steel sheet, which is undesirable. If the Si content exceeds 4.5%, the workability of the grain-oriented electrical steel sheet deteriorates, which is also undesirable. The Si content is more preferably 2.7% to 4.0%.

[0087] Mn forms MnS and MnSe, which are inhibitors that influence secondary recrystallization. Mn is contained in the base steel sheet in a mass percentage range of 0.01% to 0.15%. If the Mn content is less than 0.01%, it is undesirable because the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient. If the Mn content is greater than 0.15%, it is undesirable because solid solution of Mn becomes difficult when the slab is heated, and the size of the precipitated inhibitors becomes coarser, impairing the optimal size distribution of the inhibitors. The Mn content is more preferably 0.03% to 0.13%.

[0088] The remainder of the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to the present invention includes Fe and impurities. Here, impurities refer to elements such as those introduced from raw materials such as ore, scrap, or the manufacturing environment during the industrial production of the base steel sheet, or elements that remain in the steel without being completely purified during the purification annealing process, and which are acceptable within a range that does not adversely affect the grain-oriented electrical steel sheet of the present invention.

[0089] Furthermore, the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may contain one or more of the elements Cu, Sn, Ni, Cr, or Sb as elements that stabilize secondary recrystallization. When the base steel sheet contains the above elements, the iron loss value can be further reduced, thereby obtaining better magnetic properties.

[0090] When the base steel sheet contains one or more of these elements, the content of each element may be between 0.01% and 0.30% by mass. When the base steel sheet contains one or more of Cu, Sn, Ni, Cr, or Sb, the effect of stabilizing secondary recrystallization can be further enhanced if the content of each element is within the above range. If the content of each of these elements is less than 0.01%, it may be difficult to obtain a sufficient effect of stabilizing secondary recrystallization. If the content of each of these elements exceeds 0.30%, the effect of stabilizing secondary recrystallization may saturate, which is undesirable from the viewpoint of suppressing an increase in the manufacturing cost of grain-oriented electrical steel sheets. Note that these elements are not necessarily essential in steel materials, so the lower limit of their content is 0%.

[0091] [Primary coating] Furthermore, the inventors have found that there is a close relationship between the adhesion between the primary coating, which mainly consists of Mg2SiO4, and the steel sheet, and the state of the Al oxide bonded to the primary coating. Specifically, in the grain-oriented electrical steel sheet according to the present invention, Al oxide mainly composed of MgAl2O4 (spinel) is arranged on the base steel sheet side of the primary coating, which mainly contains Mg2SiO4, in a state of being bonded to the primary coating, in a range of 0.5 μm to 5 μm.

[0092] In grain-oriented electrical steel sheets, the interface between the primary coating and the steel sheet (base metal) has an embedded structure. Specifically, a portion of the primary coating penetrates from the surface into the interior of the steel sheet. This portion of the primary coating that penetrates from the surface into the interior of the steel sheet exerts a so-called anchoring effect, enhancing the adhesion of the primary coating to the steel sheet. Oxides penetrate further into the steel sheet than the primary coating, which is mainly composed of Mg2SiO4. In the region where oxides penetrate deeper into the steel sheet than the primary coating, which is mainly composed of Mg2SiO4, the main component of the oxide is MgAl2O4 (spinel), a type of Al oxide. It is presumed that the peak of Al emission intensity obtained when elemental analysis is performed by glow discharge emission spectrometry reflects the location of the above-mentioned MgAl2O4.

[0093] However, under conditions in which the annealing separating agent of the present invention contained a Ti compound, a rare earth metal compound, and a B compound, although the adhesion between the primary film and the steel sheet was significantly improved, the depth position of the Al emission intensity peak from the surface of the primary film (Al peak position) did not change much. The inventors conducted a detailed investigation of the vicinity of the interface between the primary film and the base metal and revealed for the first time that under conditions in which the annealing separating agent contained a Ti compound, a rare earth metal compound, and a B compound, Al oxides mainly composed of MgAl2O4, which are present on the base steel sheet side of the primary film, are strongly bound to the primary film. It is presumed that the presence of these Al oxides bound to the primary film, like spikes, further enhances the anchoring effect.

[0094] To investigate the state of Al oxide in detail, for example, it is effective to observe a minute area by slightly tilting and polishing a steel plate with a primary coating (inclined polishing). The inventors succeeded in observing the vicinity of the interface between the primary coating and the base metal in detail by applying an angle of about 4° from the surface of the steel plate, with a magnification of about 15 times. Furthermore, the sample after inclined polishing was subjected to a pressure of approximately 0.33 C / mm on the polished surface where the base metal was exposed. 2 Electropolishing with the specified charge successfully enabled selective electrolytic removal of the base metal on the base steel sheet side from the primary coating, which mainly contains Mg2SiO4. The electrolytic removal depth of the base metal on the base steel sheet side from the primary coating was confirmed to be approximately 5 μm by confocal laser microscopy observation. The electrolyte used was condition No. 6 in Table 2 of the following known reference 1, namely 4% MS + 5% TET: 4% methyl salicylate + 1% salicylic acid + 1% TMAC + 5% TET + Methanol. Here, TMAC is tetramethyl ammonium chloride, TET is triethylene tetramine, and MS is methyl salicylate.

[0095] Publicly available document 1: Iron and Steel Tetsu-to-Hagane Vol.104(2018) No.11, P634

[0096] Here, when the region where the base metal on the base steel sheet side of the primary coating was selectively removed was observed in detail using a scanning electron microscope, it was found that under conditions where the annealing separating agent did not simultaneously contain Ti compounds, rare earth metal compounds, and B compounds, almost only base metal was observed. In contrast, under conditions where Ti compounds, rare earth metal compounds, and B compounds were present, a large amount of Al oxide, mainly composed of MgAl2O4 (spinel), was observed. Figure 1 shows the scanning electron microscope image. Figure 1 is a secondary electron image observed with a scanning electron microscope after finishing annealing, inclined polishing at an inclination angle of 5°, and electrolytic polishing of a grain-oriented electrical steel sheet. Under conditions where the annealing separating agent contained Ti compounds, rare earth metal compounds, and B compounds, the observation of Al oxide despite electrolytic removal of the base metal to a depth of approximately 5 μm is presumed to be because the Al oxide is strongly bound to the primary coating. On the other hand, the fact that Al oxide was hardly observed under conditions where Ti compounds, rare earth metal compounds, and B compounds were not simultaneously present suggests that the Al oxide was either not bonded to the primary film or its bond was weak, and therefore it was washed away or blown off during the electrolysis and subsequent cleaning and drying processes. It is presumed that Al oxide present bonded to the primary film exerts a spike effect, further improving the adhesion between the primary film and the base metal. The oxide components were investigated using an energy-dispersive X-ray analyzer attached to a scanning electron microscope.

[0097] The range of Al oxide, mainly composed of MgAl2O4, that exists on the base steel sheet side of the primary coating, which mainly contains Mg2SiO4, in the thickness direction of the base steel sheet is between 0.5 μm and 5.0 μm from the boundary (tip position) of the primary coating on the base steel sheet side. If the range of Al oxide in the thickness direction of the base steel sheet is less than 0.5 μm from the boundary of the primary coating on the base steel sheet side, the spike effect is insufficient, and a sufficient improvement in coating adhesion cannot be obtained, which is undesirable. If the range of Al oxide in the thickness direction of the base steel sheet extends beyond 5.0 μm from the boundary of the primary coating on the base steel sheet side, not only is the improvement in coating adhesion saturated, but the amount of Ti compound, rare earth metal compound, and B compound added to the annealing separation agent is increased, which is undesirable because the cost is high. The range of Al oxide presence is preferably in the thickness direction of the base steel sheet, from 0.5 μm to 4.5 μm from the boundary of the primary coating on the base steel sheet side, and more preferably from 0.5 μm to 4.0 μm.

[0098] Here, the boundary (tip position) of the primary coating containing Mg2SiO4 as the main component on the base steel sheet side was defined as the position where the amount of primary coating present on a line drawn parallel to the surface in the secondary electron image obtained by observing the sample after inclined polishing and electrolytic polishing with a scanning electron microscope was 50%. Similarly, the location of Al oxide was defined as the region where the amount of Al oxide present on a line drawn parallel to the surface was 10% or more in the secondary electron image obtained by observing the sample after inclined polishing and electrolytic polishing with a scanning electron microscope, and the position where the amount of Al oxide was 10% was defined as the boundary of Al oxide on the base steel sheet side. Since the amount of Al oxide is 10% or more at the position where the amount of primary coating is 50%, the range of Al oxide was defined as the depth value calculated from the inclined polishing angle, which is the length from the base steel sheet side boundary of the primary coating to the base steel sheet side boundary of Al oxide measured in the above secondary electron image.

[0099] As described above, the primary coating is formed on the surface of the base steel sheet and contains Mg2SiO4 as a main component. The content of Mg2SiO4 in the primary coating is preferably 50% by mass or more, more preferably 70% by mass or more, based on the oxides forming the primary coating. From the viewpoints of adhesion and insulation of the primary coating, it is preferable that the content of Mg2SiO4 formed on the surface of the base steel sheet is large, and thus the upper limit is not particularly defined.

[0100] Incidentally, the primary coating may contain, for example, an Al compound, a sulfide, an Fe compound, or the like.

[0101] The main component of the primary coating can be measured, for example, in a grain-oriented electrical steel sheet after the final process, by using an energy dispersive X-ray analyzer attached to a scanning electron microscope or a fluorescent X-ray analyzer after mirror-polishing the cross section. Specifically, after washing the steel sheet after finish annealing with water, gold is vapor-deposited on the surface, and about 0.005 mm 2 of the area is quantitatively analyzed to measure the main component of the primary coating. When the quantitative analysis result shows that the Mg concentration is 17% by mass or more and the Si concentration is 11% by mass or more, it can be determined that the primary coating contains 50% by mass or more of Mg2SiO4.

[0102] [Insulating Coating] As described above, the insulating coating contains aluminum phosphate or colloidal silica or the like as a main component. However, as described above, the components of the insulating coating are not particularly limited as long as insulation and / or a predetermined tension are imparted to the steel sheet.

[0103] The coating amount of the insulating coating is not particularly limited as long as insulation and / or a predetermined tension are imparted to the steel sheet, and can be adjusted appropriately.

[0104] In the grain-oriented electrical steel sheet according to this embodiment, it is preferable to further control the magnetic flux density B8 value. Specifically, in the grain-oriented electrical steel sheet according to this embodiment, the magnetic flux density B8 value is preferably 1.920T or higher, and more preferably 1.930T or higher. Here, the magnetic flux density B8 value is the magnetic flux density when a magnetic field of 800 A / m is applied to the grain-oriented electrical steel sheet at 50 Hz. If the magnetic flux density B8 value is less than 1.920T, the iron loss value (especially hysteresis loss) of the grain-oriented electrical steel sheet may become large. The upper limit of the magnetic flux density B8 value is not particularly limited, but in practice, it may be, for example, 2.0T. The magnetic properties of the grain-oriented electrical steel sheet, such as magnetic flux density, can be measured by known methods. For example, the magnetic properties of grain-oriented electrical steel sheets can be measured using a method based on the Epstein test specified in JIS C2550:2011, or the Single Sheet Tester (SST) method specified in JIS C2556:2015. In research and development, if steel ingots are formed in a vacuum melting furnace, it becomes difficult to take test pieces of the same size as those used in actual manufacturing. In this case, for example, a test piece measuring 60 mm in width and 300 mm in length may be taken, and measurements may be performed in accordance with the Single Sheet Tester method. Furthermore, a correction factor may be applied to the obtained results so that the measured values ​​are equivalent to those obtained using the method based on the Epstein test. In this embodiment, measurements are performed using a measurement method in accordance with the Single Sheet Tester method.

[0105] The grain-oriented electrical steel sheet according to this embodiment has been described above. While the present invention does not specifically specify the thickness of the steel sheet, it goes without saying that thinner sheets are preferable as they reduce eddy current losses. The grain-oriented electrical steel sheet according to this embodiment can be manufactured by the manufacturing method of the grain-oriented electrical steel sheet of this embodiment described above. However, the invention is not limited to this method. [Examples]

[0106] The following describes in more detail the method for manufacturing grain-oriented electrical steel sheets, grain-oriented electrical steel sheets, and annealing separation agent according to one embodiment of the present invention, with reference to examples. Note that the following examples are merely examples of the method for manufacturing grain-oriented electrical steel sheets, grain-oriented electrical steel sheets, and annealing separation agent according to this embodiment, and the method for manufacturing grain-oriented electrical steel sheets, grain-oriented electrical steel sheets, and annealing separation agent according to this embodiment are not limited to the following examples.

[0107] (Example 1) First, steel ingot A was prepared, containing, by mass%, C:0.08%, Si:3.2%, Mn:0.08%, S:0.025%, acid-soluble Al:0.03%, N:0.008%, and Bi:0.02%, with the remainder being Fe and impurities. Steel ingot R was prepared, containing, by mass%, C:0.08%, Si:3.2%, Mn:0.08%, S:0.025%, acid-soluble Al:0.03%, and N:0.008%, with the remainder being Fe and impurities. After annealing the steel ingots at 1350°C for 1 hour, hot rolling was performed to obtain a hot-rolled steel sheet with a thickness of 2.3 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0108] Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and then finish annealing was performed using a batch heating furnace, with the temperature raised at a rate of 15°C / h and held at 1200°C for 30 hours. After that, the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 2% CeO2 (calculated as Ce), and the remainder consisted of unavoidable impurities and compounds under the conditions shown in Tables 1A and 1B. The stirring conditions for the annealing separation agent were 30 minutes at 5°C after adding the compounds under the conditions shown in Tables 1A and 1B. After that, an insulating film mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel sheet, and then planarization annealing was performed for the purpose of baking the insulating film and planarizing the steel sheet. This planarization annealing was performed at 850°C for 40 seconds.

[0109] After shearing and stress-relieving annealing the grain-oriented electrical steel sheets obtained above, the magnetic flux density B8 value of the grain-oriented electrical steel (samples after stress-relieving annealing) according to each of the present invention examples and comparative examples was measured for samples with a sample size of 60 mm × 300 mm in accordance with the single-sheet measurement method described in JIS C2556:2015. Here, the B8 value is the magnetic flux density of the steel sheet when the grain-oriented electrical steel sheet is excited at 50 Hz with 800 A / m. In the present invention examples, the average value of 5 samples was used as the B8 value. The above samples were cut from the grain-oriented electrical steel sheet after stress-relieving annealing so that the longitudinal direction of the sample coincided with the longitudinal direction of the grain-oriented electrical steel sheet before shearing.

[0110] Furthermore, the above samples were sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the area of ​​the delaminate portion was measured for each. For each sample, the ratio of the area of ​​the delaminate portion to the total area was defined as the delamination area ratio, and the average value of the delamination area ratios among the samples was calculated.

[0111] Here, when the steel ingot contains Bi, the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the peeling area ratio in the 10mmφ bending test is 10% or less was judged as good, and the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T or the peeling area ratio in the 10mmφ bending test is greater than 10% was judged as unacceptable. Furthermore, when the steel ingot does not contain Bi, the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.910T or higher and the peeling area ratio in the 10mmφ bending test is 5% or less was judged as good, and the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.910T or the peeling area ratio in the 10mmφ bending test is greater than 5% was judged as unacceptable.

[0112] Furthermore, after the final processing of the grain-oriented electrical steel sheet, the cross-section was mirror-polished, and the presence or absence of the primary coating was confirmed using an energy-dispersive X-ray analyzer attached to a scanning electron microscope. The composition of the primary coating was also analyzed by the following method: After washing the steel sheet with water following finish annealing, gold deposition was applied to the surface, and the presence or absence of the primary coating was measured using an energy-dispersive X-ray analyzer attached to a scanning electron microscope. 2 The area was quantitatively analyzed, and if the Mg concentration was 17% by mass or more and the Si concentration was 11% by mass or more, it was determined that the main component of the primary coating was Mg2SiO4. This method has concerns such as detecting Fe beneath the primary coating and large measurement errors, but it is sufficient for determining the main component. Alternatively, the insulating coating can be removed by immersing the steel plate, after coating and baking, in a high-temperature alkaline solution, and then the analysis can be performed after rinsing with water. Furthermore, the method for analyzing the primary coating is not limited to the above method; for example, X-ray fluorescence analysis may also be used.

[0113] The manufacturing conditions and measurement results for the above-mentioned examples and comparative examples of the present invention are shown in Tables 1A and 1B. Conditions A1 to A31 shown in Tables 1A and 1B are examples using steel ingot A, and conditions R1 to R16 are examples using steel ingot R.

[0114] [Table 1A]

[0115] [Table 1B]

[0116] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0117] Referring to the results in Tables 1A and 1B, it was found that grain-oriented electrical steel sheets that satisfy the conditions of this embodiment receive a good rating.

[0118] (Example 2) First, a steel ingot was prepared containing, by mass%, C:0.08%, Si:3.3%, Mn:0.08%, S:0.004%, Se:0.018%, acid-soluble Al:0.03%, N:0.009%, and Bi:0.03%, with the remainder consisting of the components shown in Tables 2A and 2B below, along with Fe and impurities. The steel ingot was annealed at 1380°C for 1 hour, and then hot-rolled to obtain a hot-rolled steel sheet with a thickness of 2.3 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0119] Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and then finish annealing was performed using a batch heating furnace, with the temperature raised at a rate of 15°C / h and held at 1200°C for 30 hours. After that, the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 2% Ce(OH)4 (calculated as Ce), and the remainder consisted of unavoidable impurities and compounds under the conditions shown in Tables 2A and 2B. The stirring conditions for the annealing separation agent were 10°C for 20 minutes after adding the compounds under the conditions shown in Tables 2A and 2B. Subsequently, an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel plate, and then a planar annealing process was performed at 850°C for 40 seconds to bake the insulating coating and flatten the steel plate.

[0120] The grain-oriented electrical steel sheets obtained above were sheared and then annealed to relieve stress. The magnetic flux density B8 value of each grain-oriented electrical steel sheet according to the present invention example and comparative example was measured for a sample size of 60 mm × 300 mm, in accordance with the single-sheet measurement method described in JIS C2556:2015. The above samples were cut from the grain-oriented electrical steel sheet after stress relief annealing so that the longitudinal direction of the sample coincided with the longitudinal direction of the grain-oriented electrical steel sheet before shearing. In this example, as in Example 1, the average value of five samples was used as the B8 value. Furthermore, the magnetic aging characteristics were evaluated by the following method: Magnetic domain control processing was applied to the sample after shearing and stress relief annealing, and the iron loss W of the grain-oriented electrical steel sheet was measured in accordance with the single-sheet measurement method described in JIS C2556:2015. 17 / 50 The (W / kg) was measured, and if the following relationship (A) held, it was determined to be magnetic aging. Here, T is the thickness (mm) of the grain-oriented electrical steel sheet sample. 17 / 50 This refers to the iron loss obtained by exciting grain-oriented electrical steel sheets to 1.7T at 50Hz, and, as in Example 1, the average value of 5 samples is W 17 / 50 The magnetic domain control process was performed by laser irradiation. The direction of laser irradiation was perpendicular to the longitudinal direction of the grain-oriented electrical steel sheet (i.e., perpendicular to the longitudinal direction of the sample), and the laser irradiation interval P was 4 mm. The laser irradiation energy density Ua was 2.0 mJ / mm². 2 That's what I decided. W 17 / 50 >(-2.5×B8)+(1.25×T)+5.4 ···Formula (A)

[0121] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the average value of the peeling area ratio was determined. The peeling area ratio was calculated using the same method as in Example 1.

[0122] The presence or absence of a primary coating and the analysis of the primary coating's components in the grain-oriented electrical steel sheet after the final process were performed using the same method as in Example 1.

[0123] Here, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the delamination area ratio in the 10mmφ bending test is 10% or less were judged as good. Conversely, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T, the delamination area ratio in the 10mmφ bending test is greater than 10%, or the relationship given by equation (A) holds true regarding the magnetic aging characteristics were judged as unacceptable (aged).

[0124] The manufacturing conditions and measurement results for the above-mentioned examples of the present invention and comparative examples are shown in Tables 2A and 2B.

[0125] [Table 2A]

[0126] [Table 2B]

[0127] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0128] Referring to the results in Tables 2A and 2B, it was found that grain-oriented electrical steel sheets that satisfy the conditions of this embodiment receive a good rating.

[0129] Here, focusing on the amount of B compound and alkaline earth metal compound in the annealing separating agent, the B equivalent value B(%) of the B compound content was plotted on the horizontal axis, and the content of alkaline earth metal compounds containing alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba was plotted on the vertical axis as A% based on the Ca, Sr, and Ba content. The content of these compounds was plotted for conditions B1 to B48, B50, and B51. The resulting graph is shown in Figure 2. In Figure 2, examples with a magnetic flux density of 1.920T or higher are plotted as circles, and examples with a magnetic flux density of less than 1.920T are indicated by ×. Note that conditions B49 and B52 are not shown in Figure 2 because their Ti compound equivalent content does not meet the conditions of this embodiment.

[0130] As shown in Figure 2, it was found that the following relationship, expressed by formula (101) defined under the conditions of this embodiment, holds between the B-equivalent value B(%) of the B compound content in the annealing separation agent for electrical steel sheets with a magnetic flux density of 1.920T or higher, and the A(%) equivalent value based on the content of a compound containing at least one of Ca, Sr, and Ba in the annealing separation agent.

[0131] B ≤ A ≤ (0.8 + 3 × B) (where 0.03 ≤ B ≤ 1.60) ··Equation (101)

[0132] (Example 3) First, steel ingot C was prepared, containing, by mass%, C:0.08%, Si:3.4%, Mn:0.08%, S:0.027%, acid-soluble Al:0.03%, N:0.008%, and Bi:0.01%, with the remainder being Fe and impurities. Steel ingot S was prepared, containing, by mass%, C:0.08%, Si:3.4%, Mn:0.08%, S:0.027%, acid-soluble Al:0.03%, and N:0.008%, with the remainder being Fe and impurities. After annealing these steel ingots at 1350°C for 1 hour, hot rolling was performed to obtain a hot-rolled steel sheet with a thickness of 2.3 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0133] Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and then finish annealing was performed using a batch heating furnace, with the temperature raised at a rate of 15°C / h and held at 1200°C for 30 hours. After that, the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 2% La2O3 (in terms of La), and the remainder consisted of unavoidable impurities and compounds under the conditions shown in Tables 3A and 3B. The stirring conditions for the annealing separation agent were 200 minutes at 5°C after adding the compounds under the conditions shown in Tables 3A and 3B. Subsequently, an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel plate, and then a planar annealing process was performed at 850°C for 40 seconds to bake the insulating coating and flatten the steel plate.

[0134] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density B8 value of the grain-oriented electrical steel sheet according to each example of the present invention and comparative example was measured for a sample size of 60 mm × 300 mm in accordance with the single-sheet measurement method described in JIS C2556:2015. In this example, as in Example 1, the average value of five samples was used as the B8 value. The above samples were cut from the grain-oriented electrical steel sheet after stress-relieving annealing so that the longitudinal direction of the grain-oriented electrical steel sheet before shearing coincided with the longitudinal direction of the sample.

[0135] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the average value of the peeling area ratio was determined. The peeling area ratio was calculated using the same method as in Example 1.

[0136] The presence or absence of a primary coating and the analysis of the primary coating's components in the grain-oriented electrical steel sheet after the final process were performed using the same method as in Example 1.

[0137] Here, when the steel ingot contains Bi, the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the peeling area ratio in the 10mmφ bending test is 10% or less was judged as good, and the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T or the peeling area ratio in the 10mmφ bending test is greater than 10% was judged as unacceptable. Furthermore, when the steel ingot does not contain Bi, the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.910T or higher and the peeling area ratio in the 10mmφ bending test is 5% or less was judged as good, and the condition that the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.910T or the peeling area ratio in the 10mmφ bending test is greater than 5% was judged as unacceptable.

[0138] The manufacturing conditions and measurement results for the above-mentioned examples and comparative examples of the present invention are shown in Tables 3A and 3B. Conditions C1 to C24 shown in Table 1 are examples using steel ingot C, and conditions S1 to S8 are examples using steel ingot S.

[0139] [Table 3A]

[0140] [Table 3B]

[0141] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0142] Referring to the results in Tables 3A and 3B, it was found that grain-oriented electrical steel sheets that satisfy the conditions of this embodiment receive a better rating.

[0143] Here, the B equivalent value B(%) of the B compound content in the annealing separation agent, the A(%) equivalent value of Ca, Sr, and Ba contained in the annealing separation agent as the content of one or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, and the sulfate content in the annealing separation agent as sulfate (SO4) 2- It was found that the following relationships, formulas (102) and (103), defined by the conditions of this embodiment, exist between the converted C(%) and the converted C(%).

[0144] 0 ≤ A (3 × B) ≤ C ≤ (10 × B) (where 0.03 ≤ B ≤ 1.60) ··Equation (103) Thus, it has been found that the method for manufacturing grain-oriented electrical steel sheets according to this embodiment, which satisfies equations (102) and (103), makes it possible to manufacture grain-oriented electrical steel sheets with higher magnetic flux density and superior adhesion between the primary coating and the steel sheet.

[0145] (Example 4) First, a steel ingot was prepared containing, by mass%, C:0.08%, Si:3.3%, Mn:0.08%, S:0.025%, acid-soluble Al:0.03%, N:0.008%, and Bi:0.02%, with the remainder consisting of the components shown in Table 4, along with Fe and impurities. This steel ingot was annealed at 1350°C for 1 hour, and then hot-rolled to obtain a hot-rolled steel sheet with a thickness of 2.3 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0146] ​Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, after primary recrystallization annealing, an annealing separation agent containing MgO was applied to the surface of the steel sheet, and then finish annealing was performed using a batch heating furnace, raising the temperature at a rate of 15°C / h and holding it at 1200°C for 30 hours. After that, the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 2.0% Y2O3 (calculated as Y), 1.66% CaSO4·0.5H2O (calculated as Ca), and the remainder consisted of unavoidable impurities and compounds under the conditions shown in Table 4. The stirring conditions for the annealing separation agent were 30°C for 200 minutes after adding the compounds under the conditions shown in Table 4. Subsequently, an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel plate, and then a planar annealing process was performed at 850°C for 40 seconds to bake the insulating coating and flatten the steel plate.

[0147] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density B8 value of the grain-oriented electrical steel sheet according to each example of the present invention and comparative example was measured for a sample size of 60 mm × 300 mm in accordance with the single-sheet measurement method described in JIS C2556:2015. In this example, as in Example 1, the average value of five samples was used as the B8 value. The above samples were cut from the grain-oriented electrical steel sheet after stress-relieving annealing so that the longitudinal direction of the grain-oriented electrical steel sheet before shearing coincided with the longitudinal direction of the sample.

[0148] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the average value of the peeling area ratio was determined. The peeling area ratio was calculated using the same method as in Example 1.

[0149] The presence or absence of a primary coating and the analysis of the primary coating's components in the grain-oriented electrical steel sheet after the final process were performed using the same method as in Example 1.

[0150] Furthermore, after the final processing of the grain-oriented electrical steel sheet, the insulating and primary coatings were removed, and the composition of the base steel sheet was analyzed. The content of Si, Mn, Cu, Sn, Ni, Cr, and Sb was analyzed by inductively coupled plasma atomic emission spectrometry. The content of C was measured using a carbon-sulfur analyzer. The content of N was measured using an oxygen-nitrogen analyzer.

[0151] Here, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the delamination area ratio in the 10mmφ bending test is 10% or less were judged as good. Conversely, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T or the delamination area ratio in the 10mmφ bending test is greater than 10% were judged as unacceptable.

[0152] Table 4 shows the manufacturing conditions and measurement results for the above-mentioned examples and comparative examples of the present invention, and Table 5 shows the base steel sheet composition of the grain-oriented electrical steel sheet after the final process.

[0153] [Table 4]

[0154] [Table 5]

[0155] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0156] Referring to the results in Tables 4 and 5, it was found that if formula (101) is satisfied, even if the sheet further contains one or more of the following materials in mass%, in the following amounts: Cu: 0.01% to 0.30%, Sn: 0.01% to 0.30%, Ni: 0.01% to 0.30%, Cr: 0.01% to 0.30%, or Sb: 0.01% to 0.30%, the grain-oriented electrical steel sheet that satisfies the conditions of this embodiment will be judged favorably.

[0157] (Example 5) First, a steel ingot was prepared containing, by mass%, C:0.08%, Si:3.3%, Mn:0.08%, S:0.025%, acid-soluble Al:0.03%, N:0.008%, and Bi:0.02%, with the remainder consisting of the components shown in Table 6, plus Fe and impurities. This steel ingot was annealed at 1350°C for 1 hour, and then hot-rolled to obtain a hot-rolled steel sheet with a thickness of 2.3 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0158] Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, after primary recrystallization annealing, an annealing separation agent containing MgO was applied to the surface of the steel sheet. Finally, finish annealing was performed using a batch-type heating furnace, increasing the temperature at a rate of 15°C / h and holding it at 1200°C for 30 hours. Afterward, the steel sheet was washed with water. Here, the annealing separation agent contained 100% MgO, 4% CeO2 (in Ce equivalent), and MgSO4 (SO4). 2- The composition was calculated as 4.0%, with the remainder consisting of unavoidable impurities and compounds under the conditions shown in Table 6. The stirring conditions for the annealing separator were 50 minutes at 10°C after adding the compounds under the conditions shown in Table 6. Subsequently, an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel plate, and then a planar annealing process was performed at 850°C for 40 seconds to bake the insulating coating and flatten the steel plate.

[0159] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density B8 value of the grain-oriented electrical steel sheet according to each example of the present invention and comparative example was measured for a sample size of 60 mm × 300 mm in accordance with the single-sheet measurement method described in JIS C2556:2015. In this example, as in Example 1, the average value of five samples was used as the B8 value. The above samples were cut from the grain-oriented electrical steel sheet after stress-relieving annealing so that the longitudinal direction of the grain-oriented electrical steel sheet before shearing coincided with the longitudinal direction of the sample.

[0160] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the average value of the peeling area ratio was determined. The peeling area ratio was calculated using the same method as in Example 1.

[0161] The presence or absence of a primary coating and the analysis of the primary coating's components in the grain-oriented electrical steel sheet after the final process were performed using the same method as in Example 1.

[0162] Furthermore, the composition of the steel ingot and the composition of the base steel sheet after the removal of the insulating and primary coatings in the grain-oriented electrical steel sheet following the final process were analyzed. The content of Si, Mn, Cu, Sn, Ni, Cr, and Sb was analyzed by inductively coupled plasma atomic emission spectrometry. The content of C was measured using a carbon-sulfur analyzer. The content of N was measured using an oxygen-nitrogen analyzer.

[0163] Here, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the delamination area ratio in the 10mmφ bending test is 10% or less were judged as good. Conversely, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T or the delamination area ratio in the 10mmφ bending test is greater than 10% were judged as unacceptable.

[0164] Table 6 shows the manufacturing conditions and measurement results for the above-mentioned examples and comparative examples of the present invention, and Table 7 shows the base steel sheet composition of the grain-oriented electrical steel sheet after the final process.

[0165] [Table 6]

[0166] [Table 7]

[0167] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0168] Referring to the results in Tables 6 and 7, it was found that if formulas (102) and (103) are satisfied, even if the sheet further contains one or more of the following materials in mass%, in amounts of Cu: 0.01% to 0.30%, Sn: 0.01% to 0.30%, Ni: 0.01% to 0.30%, Cr: 0.01% to 0.30%, or Sb: 0.01% to 0.30%, the grain-oriented electrical steel sheet that satisfies the conditions of this embodiment will be judged more favorably.

[0169] (Example 6) Samples shown in Table 8 were selected from Examples 1, 3, 4, and 5 to investigate the extent of Al oxides mainly composed of MgAl2O4 that are connected to the base steel sheet side of the primary coating mainly containing Mg2SiO4. The sample was inclined and polished at an angle of approximately 4° from the steel sheet surface, and the area near the interface between the primary coating and the base metal was observed in detail at approximately 15x magnification. Furthermore, the sample after inclined polishing was subjected to a pressure test of approximately 0.33C / mm² against the polished surface where the base metal was exposed. 2 Electropolishing was performed with the following charge level. The electrolyte used was 4% MS + 5% TET: 4% methyl salicylate + 1% salicylic acid + 1% TMAC + 5% TET + Methanol. Here, TMAC is tetramethyl ammonium chloride and TET is triethylene tetramine. Here, the electrolytic removal depth of the base metal on the base steel plate side from the primary coating containing Mg2SiO4 as the main component was confirmed to be approximately 5 μm by confocal laser microscopy observation.

[0170] Next, the region where the base metal on the base steel sheet side of the primary coating was selectively removed was observed in detail using a scanning electron microscope. Here, the base steel sheet side boundary of the primary coating, which mainly contains Mg2SiO4, was defined as the position where the amount of primary coating present on a line drawn parallel to the surface was less than 50% in the secondary electron image obtained by observing the sample after tilt polishing and electrolysis with a scanning electron microscope. Similarly, the location of Al oxide was defined as the region where the amount of Al oxide present on a line drawn parallel to the surface was 10% or more in the secondary electron image obtained by observing the sample after tilt polishing and electrolysis with a scanning electron microscope, and the position where the amount of Al oxide was 10% was defined as the base steel sheet side boundary of Al oxide. The range of Al oxide was defined as the depth value calculated from the tilt polishing angle, which is the length from the base steel sheet side boundary of the primary coating to the base steel sheet side boundary of Al oxide measured in the above secondary electron image. The oxide components were investigated using an energy-dispersive X-ray analyzer attached to the scanning electron microscope.

[0171] Table 8 shows the range of presence of Al oxides mainly composed of MgAl2O4 (spinel), which are connected to the base steel sheet side of the primary coating containing Mg2SiO4 as the main component. It was found that good coating adhesion is achieved when the range of Al oxides is from 0.5 μm to 5.0 μm from the boundary of the primary coating on the base steel sheet side toward the base steel sheet.

[0172] [Table 8]

[0173] (Example 7) First, a steel ingot was prepared containing, by mass%, C: 0.08%, S: 0.025%, acid-soluble Al: 0.03%, N: 0.008%, and Bi: 0.02%, with the remainder being Si and Mn in the amounts shown in Table 9, as well as Fe and impurities. The steel ingot was annealed at 1350°C for 1 hour, and then hot-rolled to obtain a hot-rolled steel sheet with a thickness of 23 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0174] Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, after primary recrystallization annealing, an annealing separation agent containing MgO was applied to the surface of the steel sheet, and then finish annealing was performed using a batch heating furnace, raising the temperature at a rate of 15°C / h and holding it at 1200°C for 30 hours. After that, the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 1.10% or 1.66% Ca equivalent of CaSO4·0.5H2O, 2.0% CeO2 equivalent of Ce, and the remainder being unavoidable impurities and compounds under the conditions shown in Table 9. The stirring conditions for the annealing separation agent were 20 minutes at 5°C after adding the compounds under the conditions shown in Table 9. The amount of annealing separation agent applied after drying was 7 g / m² per side of the steel sheet. 2 Subsequently, an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel plate, and then planar annealing was performed for the purpose of baking the insulating coating and flattening the steel plate. This planar annealing was carried out at 850°C for 40 seconds.

[0175] After shearing and stress-relieving annealing the grain-oriented electrical steel sheets obtained above, the magnetic flux density B8 values ​​of the grain-oriented electrical steel sheets according to each example of the present invention and comparative example were measured for samples with a sample size of 60 mm × 300 mm in accordance with the single-sheet measurement method described in JIS C2556:2015. In this example, as in Example 1, the average value of five samples was used as the B8 value.

[0176] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the average value of the peeling area ratio was determined. The peeling area ratio was calculated using the same method as in Example 1.

[0177] The presence or absence of a primary coating and the analysis of the primary coating's components in the grain-oriented electrical steel sheet after the final process were performed using the same method as in Example 1.

[0178] Furthermore, after the final processing of the grain-oriented electrical steel sheet, the insulating film and primary film were removed, and the composition of the base steel sheet was analyzed. The Si and Mn content was analyzed by inductively coupled plasma atomic emission spectroscopy. The C content was measured using a carbon-sulfur analyzer. The range of Al oxide mainly composed of MgAl2O4, which is present in a linked state on the base steel sheet side of the primary film mainly composed of Mg2SiO4, was investigated using the same method as described in Example 6.

[0179] Here, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the delamination area ratio in the 10mmφ bending test is 10% or less were judged as good. Conversely, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T or the delamination area ratio in the 10mmφ bending test is greater than 10% were judged as unacceptable.

[0180] Table 9 shows the manufacturing conditions and measurement results for the above-mentioned examples of the present invention and comparative examples.

[0181] [Table 9]

[0182] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0183] Table 9 shows the range of Al oxides mainly composed of MgAl2O4 (spinel) that are connected to the base steel sheet side of the primary coating which mainly contains Mg2SiO4. It was found that when the range of Al oxides is 0.5 μm to 5.0 μm from the boundary of the primary coating on the base steel sheet side, the coating adhesion is good, and grain-oriented electrical steel sheets that satisfy the conditions of this embodiment are judged to be good.

[0184] (Example 8) First, a steel ingot was prepared containing, by mass%, C:0.08%, Si:3.3%, Mn:0.08%, S:0.025%, acid-soluble Al:0.03%, N:0.008%, and Bi:0.02%, with the remainder being Fe and impurities. The steel ingot was annealed at 1350°C for 1 hour, and then hot-rolled to obtain a hot-rolled steel sheet with a thickness of 2.3 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1050°C for 140 seconds, pickled, and then subjected to primary cold rolling to obtain a primary cold-rolled sheet with a thickness of 1.8 mm. The obtained primary cold-rolled sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then subjected to secondary cold rolling to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0185] Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and then finish annealing was performed using a batch heating furnace, with the temperature raised at a rate of 15°C / h and held at 1200°C for 30 hours. After that, the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 5.0% CeO2 (calculated as Ce), and the remainder consisted of unavoidable impurities and compounds under the conditions shown in Table 10. The stirring conditions for the annealing separation agent were 15°C for 30 minutes after adding the compounds under the conditions shown in Table 10. Subsequently, an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel plate, and then a planar annealing process was performed at 850°C for 40 seconds to bake the insulating coating and flatten the steel plate.

[0186] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density B8 value of the grain-oriented electrical steel sheet according to each example of the present invention and comparative example was measured for a sample size of 60 mm × 300 mm in accordance with the single-sheet measurement method described in JIS C2556:2015. In this example, as in Example 1, the average value of five samples was used as the B8 value. The above samples were cut from the grain-oriented electrical steel sheet after stress-relieving annealing so that the longitudinal direction of the grain-oriented electrical steel sheet before shearing coincided with the longitudinal direction of the sample.

[0187] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the average value of the peeling area ratio was determined. The peeling area ratio was calculated using the same method as in Example 1.

[0188] The presence or absence of a primary coating and the analysis of the primary coating's components in the grain-oriented electrical steel sheet after the final process were performed using the same method as in Example 1.

[0189] Here, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the delamination area ratio in the 10mmφ bending test is 10% or less were judged as good. Conversely, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T or the delamination area ratio in the 10mmφ bending test is greater than 10% were judged as unacceptable.

[0190] Table 10 shows the manufacturing conditions and measurement results for the above-mentioned examples of the present invention and comparative examples.

[0191] [Table 10]

[0192] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0193] Referring to the results in Table 10, it was found that grain-oriented electrical steel sheets that meet the conditions of this embodiment and are manufactured by performing cold rolling twice during the manufacturing process receive a good rating.

[0194] (Example 9) First, a steel ingot was prepared containing, by mass%, C:0.08%, Si:3.2%, Mn:0.08%, S:0.023%, acid-soluble Al:0.03%, N:0.008%, and Bi:0.03%, with the remainder being Fe and impurities. This steel ingot was annealed at 1350°C for 1 hour, and then hot-rolled to obtain a hot-rolled steel sheet with a thickness of 2.3 mm. The obtained hot-rolled steel sheet was annealed at a maximum temperature of 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0195] Next, the obtained cold-rolled steel sheet was subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and then finish annealing was performed using a batch heating furnace, with the temperature raised at a rate of 15°C / h and held at 1200°C for 30 hours. After that, the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 3.0% TiO2 (Ti equivalent), 5.0% CeO2 (Ce equivalent), 0.61% H3BO3 (B equivalent), 1.1% CaSO4·0.5H2O (Ca equivalent), with the remainder being unavoidable impurities. The stirring conditions for the annealing separation agent were as shown in Table 11. Subsequently, an insulating coating mainly composed of aluminum phosphate and colloidal silica was applied to the surface of the steel plate, and then a planar annealing process was performed at 850°C for 40 seconds to bake the insulating coating and flatten the steel plate.

[0196] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density B8 value of the grain-oriented electrical steel sheet according to each example of the present invention and comparative example was measured for a sample size of 60 mm × 300 mm in accordance with the single-sheet measurement method described in JIS C2556:2015. In this example, as in Example 1, the average value of five samples was used as the B8 value. The above samples were cut from the grain-oriented electrical steel sheet after stress-relieving annealing so that the longitudinal direction of the grain-oriented electrical steel sheet before shearing coincided with the longitudinal direction of the sample.

[0197] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a 10 mmφ bending test. Here, three test pieces were subjected to the bending test, and the average value of the peeling area ratio was determined. The peeling area ratio was calculated using the same method as in Example 1.

[0198] The presence or absence of a primary coating and the analysis of the primary coating's components in the grain-oriented electrical steel sheet after the final process were performed using the same method as in Example 1.

[0199] Here, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is 1.920T or higher and the delamination area ratio in the 10mmφ bending test is 10% or less were judged as good. Conversely, the conditions in which the magnetic flux density B8 value of the grain-oriented electrical steel sheet is less than 1.920T or the delamination area ratio in the 10mmφ bending test is greater than 10% were judged as unacceptable.

[0200] Table 11 shows the manufacturing conditions and measurement results for the above-mentioned examples of the present invention and comparative examples.

[0201] [Table 11]

[0202] The grain-oriented electrical steel sheets that satisfy the conditions of this embodiment have a primary coating, and analysis of the Mg2SiO4 in the primary coating revealed that the Mg concentration was 35% by mass or more and the Si concentration was 13% by mass in all cases, indicating that the primary coating mainly contains Mg2SiO4.

[0203] Referring to the results in Table 11, it was found that grain-oriented electrical steel sheets that meet the conditions of this embodiment, manufactured by stirring the annealing separating agent at a temperature of 0°C to 30°C for a period of 5 minutes to 300 minutes during production, yielded a good result.

[0204] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

Claims

1. A method for manufacturing grain-oriented electrical steel sheets, wherein the magnetic flux density B8 value is 1.920T or more when a magnetic field of 800 A / m is applied at a frequency of 50 Hz, In mass percent, C: 0.02% or more and 0.10% or less. Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.15% or less, One or two of S and Se: total of 0.001% or more and 0.050% or less. Acid-soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.015% or less, Bi: 0% or more and 0.0500% or less, Cu: 0% or more and 0.30% or less, Sn: 0% or more and 0.30% or less, Ni: 0% or more and 0.30% or less, Cr: 0% or more and 0.30% or less, Sb: 0% or more and 0.30% or less, A hot rolling process is performed to obtain a hot-rolled steel sheet by heating a slab containing [a certain substance] with the remainder being Fe and impurities to 1280°C or higher and hot rolling it, The process involves a cold rolling step in which the hot-rolled steel sheet is subjected to hot-rolled sheet annealing, followed by one cold rolling or two or more cold rolling steps with an intermediate annealing step in between, to obtain a cold-rolled steel sheet. A primary recrystallization annealing step is performed on the cold-rolled steel sheet, A finish annealing step is performed in which a slurry-like annealing separating agent mainly composed of MgO is applied to the surface of the cold-rolled steel sheet after the primary recrystallization annealing step, and then a finish annealing step is performed. The process includes a planar annealing step in which an insulating coating is applied to the surface of the steel sheet after the finish annealing step, followed by planar annealing. The annealing separating agent is, in mass % relative to the MgO contained in the annealing separating agent, The Ti compound is included in an amount of 0.3% to 10.0% in terms of total Ti content. The rare earth metal compound is contained in an amount of 2.0% to 10% in terms of the total rare earth metal content. Compound B is included in an amount of 0.03% to 1.60% in terms of the total amount of B contained, and It contains one or more alkaline earth metal compounds, each containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba. When the content of the alkaline earth metal compound in terms of alkaline earth metal is A (mass%) and the content of compound B in terms of B is B (mass%) relative to the MgO content, the following formula (1) is satisfied, The annealing separating agent is produced by stirring at a temperature of 0°C to 30°C for a period of 5 minutes to 300 minutes, in a method for producing grain-oriented electrical steel sheets. B≦A≦(0.8+3×B) ...Formula (1)

2. A method for manufacturing grain-oriented electrical steel sheets, wherein the magnetic flux density B8 value is 1.920T or more when a magnetic field of 800 A / m is applied at a frequency of 50 Hz, In mass percent, C: 0.02% or more and 0.10% or less. Si: 2.5% or more and 4.5% or less, Mn: 0.01% or more and 0.15% or less, One or two of S and Se: total of 0.001% or more and 0.050% or less. Acid-soluble Al: 0.01% or more and 0.05% or less, N: 0.002% or more and 0.015% or less, Bi: 0% or more and 0.0500% or less, Cu: 0% or more and 0.30% or less, Sn: 0% or more and 0.30% or less, Ni: 0% or more and 0.30% or less, Cr: 0% or more and 0.30% or less, Sb: 0% or more and 0.30% or less, A hot rolling process is performed to obtain a hot-rolled steel sheet by heating a slab containing [a certain substance] with the remainder being Fe and impurities to 1280°C or higher and hot rolling it, The process involves a cold rolling step in which the hot-rolled steel sheet is subjected to hot-rolled sheet annealing, followed by one cold rolling or two or more cold rolling steps with an intermediate annealing step in between, to obtain a cold-rolled steel sheet. A primary recrystallization annealing step is performed on the cold-rolled steel sheet, A finish annealing step is performed in which a slurry-like annealing separating agent mainly composed of MgO is applied to the surface of the cold-rolled steel sheet after the primary recrystallization annealing step, and then a finish annealing step is performed. The process includes a planar annealing step in which an insulating coating is applied to the surface of the steel sheet after the finish annealing step, followed by planar annealing. The annealing separating agent is, in mass % relative to the MgO contained in the annealing separating agent, The Ti compound is included in an amount of 0.3% to 10.0% in terms of total Ti content. The rare earth metal compound is contained in an amount of 2.0% to 10% in terms of the total rare earth metal content. Compound B is included in an amount of 0.03% to 1.60% in terms of the amount of B contained. One or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, and It contains sulfates, With respect to the MgO content, A (mass%) is the content of the alkaline earth metal compound in terms of alkaline earth metal, B (mass%) is the content of compound B in terms of B, and the sulfate rhizate (SO4) of the sulfate. ４ ) ２－ When the converted content is denoted as C (mass%), both equations (2) and (3) below must be satisfied. The annealing separating agent is produced by stirring at a temperature of 0°C to 30°C for a period of 5 minutes to 300 minutes, in a method for producing grain-oriented electrical steel sheets. 0<A<B...Formula (2) (3×B)≦C≦(10×B) ...Formula (3)

3. The method for producing grain-oriented electrical steel sheets according to claim 1 or 2, wherein the slab contains Bi: 0.0005% or more and 0.0500% or less by mass.

4. The aforementioned slab is, by mass%, Cu: 0.01% or more and 0.30% or less, Sn: 0.01% or more and 0.30% or less, Ni: 0.01% or more and 0.30% or less, Cr: 0.01% or more and 0.30% or less, A method for producing grain-oriented electrical steel sheets according to any one of claims 1 to 3, comprising one or more selected from the group consisting of Sb: 0.01% to 0.30%.

5. A grain-oriented electrical steel sheet comprising a base steel sheet and a primary coating formed on the surface of the base steel sheet, The aforementioned grain-oriented electrical steel sheet has MgAl bonded to the primary coating. ２ O ４ It comprises an oxide having as its main component, The aforementioned base steel plate is In mass%, C: 0.005% or less, Si: 2.5-4.5%, Mn: 0.01 to 0.15%, Bi: 0% or more and 0.0500% or less, Cu: 0% or more and 0.30% or less, Sn: 0% or more and 0.30% or less, Ni: 0% or more and 0.30% or less, Cr: 0% or more and 0.30% or less, Sb: Contains 0% to 0.30%, The remainder consists of Fe and impurities. The primary coating is Mg ２ SiO ４ It contains as its main component, In the thickness direction of the base steel sheet, the amount of oxide present on a line drawn parallel to the surface of the grain-oriented electrical steel sheet after inclined polishing with an inclination angle of 5° is 10% or more in the region from 0.5 μm to 5 μm from the leading edge position of the primary coating on the base steel sheet side. A grain-oriented electrical steel sheet having a magnetic flux density B8 value of 1.920T or higher when a magnetic field of 800 A / m is applied at a frequency of 50 Hz.

6. The aforementioned base steel sheet has a mass percentage of Cu: 0.01% or more and 0.30% or less. Sn: 0.01% or more and 0.30% or less, Ni: 0.01% or more and 0.30% or less, Cr: 0.01% or more and 0.30% or less, The grain-oriented electrical steel sheet according to claim 5, containing one or more selected from the group consisting of Sb: 0.01% to 0.30%.

7. In terms of mass percent relative to MgO, The Ti compound is included in an amount of 0.3% to 10.0% in terms of total Ti content. The rare earth metal compound is contained in an amount of 2.0% to 10% in terms of the total rare earth metal content. Compound B is included in an amount of 0.03% to 1.60% in terms of the total amount of B contained, and It contains one or more alkaline earth metal compounds, which include one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba. An annealing separating agent that satisfies the following formula (1), where A (mass%) is the content of the alkaline earth metal compound in terms of alkaline earth metal relative to the MgO content, and B (mass%) is the content of compound B in terms of B. B≦A≦(0.8+3×B) ...Formula (1)

8. In terms of mass percent relative to MgO, The Ti compound is included in an amount of 0.3% to 10.0% in terms of total Ti content. The rare earth metal compound is contained in an amount of 2.0% to 10% in terms of the total rare earth metal content. Compound B is included in an amount of 0.03% to 1.60% in terms of the amount of B contained. One or more alkaline earth metal compounds containing one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, and It contains sulfates, With respect to the MgO content, A (mass%) is the content of the alkaline earth metal compound in terms of alkaline earth metal, B (mass%) is the content of compound B in terms of B, and the sulfate rhizate (SO4) of the sulfate. ４ ) ２－ An annealing separating agent characterized by satisfying both of the following equations (2) and (3) when the converted content is C (mass%). 0<A<B...Formula (2) (3×B)≦C≦(10×B) ...Formula (3)

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