MIXED POWDER, MGO PARTICLES, METHOD FOR MANUFACTURING GRAIN-ORIENTED ELECTRICAL STEEL SHEET, METHOD FOR MANUFACTURING MGO PARTICLES, AND METHOD FOR MANUFACTURING MIXED POWDER

Abstract

The mixed powder is a mixed powder for an annealing separator containing MgO as a main agent, wherein the mixed powder contains Al and B, an Al content contained in the entire mixed powder is 0.0007 mass % or more and 0.050 mass % or less, a B content contained in the entire mixed powder is 0.005 mass % or more and 0.040 mass % or less, the B contains tri-coordinated boron, an average particle size of the mixed powder is 0.08 m or more and 9.0 m or less, and a formula (1) below is satisfied.

[00001]$\begin{array}{cc}0.06\left[\mathrm{Al}\right]/\left[{\mathrm{BO}}_3\right]<5.& \mathrm{Formula}\left(1\right)\end{array}$

In the formula (1), [Al] is an Al content (mass %) in the mixed powder, and [BO.sub.3] is a content (mass %) of the tri-coordinated boron in the mixed powder.

Claims

1-14. (canceled)

15. A mixed powder for an annealing separator comprising MgO as a main agent, wherein the mixed powder contains Al and B, an Al content contained in the entire mixed powder is 0.0007 mass % or more and 0.050 mass % or less, a B content contained in the entire mixed powder is 0.005 mass % or more and 0.040 mass % or less, the B contains tri-coordinated boron, an average particle size of the mixed powder is 0.08 m or more and 9.0 m or less, and a formula (1) below is satisfied: $\begin{array}{cc}0.06\left[\mathrm{Al}\right]/\left[{\mathrm{BO}}_3\right]<5.& \mathrm{Formula}\left(1\right)\end{array}$ in the formula (1), [Al] is an Al content (mass %) in the mixed powder, and [BO.sub.3] is a content (mass %) of the tri-coordinated boron in the mixed powder.

16. The mixed powder according to claim 15, wherein a proportion of the tri-coordinated boron in the B is 5 mass % or more and less than 70 mass %.

17. The mixed powder according to claim 15, further comprising one or more of Cl: 0.0005 mass % or more and 0.0300 mass % or less and Ti: 0.25 mass % or more and 5.00 mass % or less.

18. The mixed powder according to claim 16, further comprising one or more of Cl: 0.0005 mass % or more and 0.0300 mass % or less and Ti: 0.25 mass % or more and 5.00 mass % or less.

19. The mixed powder according to claim 17, further comprising 0.0005 mass % or more and 0.0300 mass % or less of Cl.

20. The mixed powder according to claim 18, further comprising 0.0005 mass % or more and 0.0300 mass % or less of Cl.

21. The mixed powder according to claim 17, further comprising 0.25 mass % or more and 5.00 mass % or less of Ti.

22. The mixed powder according to claim 18, further comprising 0.25 mass % or more and 5.00 mass % or less of Ti.

23. The mixed powder according to claim 15, wherein the mixed powder contains MgO particles mainly containing MgO, B-containing particles containing B, and Al-containing particles containing Al.

24. The mixed powder according to claim 16, wherein the mixed powder contains MgO particles mainly containing MgO, B-containing particles containing B, and Al-containing particles containing Al.

25. MgO particles comprising Al and B, wherein an Al content is 0.0007 mass % or more and 0.050 mass % or less, a B content is 0.005 mass % or more and 0.040 mass % or less, the B contains tri-coordinated boron, an average particle size is 0.08 m or more and 9.0 m or less, and a formula (1) below is satisfied:
0.06[Al]/[BO.sub.3]<5.00 Formula (1) in the formula (1), [Al] is an Al content (mass %) in the MgO particles, and [BO.sub.3] is a content (mass %) of the tri-coordinated boron in the MgO particles.

26. A method for manufacturing a grain-oriented electrical steel sheet, the method comprising using an annealing separator containing the mixed powder according to claim 15.

27. A method for manufacturing a grain-oriented electrical steel sheet, the method comprising using an annealing separator containing the mixed powder according to claim 16.

28. A method for manufacturing a grain-oriented electrical steel sheet, the method comprising using an annealing separator containing the MgO particles according to claim 21.

29. A method for manufacturing MgO particles, the method comprising baking a raw material powder containing Mg-containing raw material particles containing one or more of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, B-containing raw material particles containing B, and Al-containing raw material particles containing Al at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere.

30. The method for manufacturing MgO particles according to claim 29, wherein a content of tri-coordinated boron with respect to the mass of the raw material powder is 0.005 mass % or more and 0.040 mass % or less.

31. A method for manufacturing MgO particles, the method comprising baking raw material particles containing B and Al and containing one or more of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere.

32. The method for manufacturing MgO particles according to claim 31, wherein a content of tri-coordinated boron with respect to the mass of the raw material particles is 0.005 mass % or more and 0.040 mass % or less.

33. A method for manufacturing a mixed powder, the method comprising baking a raw material powder containing Mg-containing raw material particles containing one or more of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, B-containing raw material particles containing B, and Al-containing raw material particles containing Al at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere.

34. The method for manufacturing a mixed powder according to claim 33, wherein a content of tri-coordinated boron with respect to the mass of the raw material powder is 0.005 mass % or more and 0.040 mass % or less.

Description

DESCRIPTION OF EMBODIMENTS

Mixed Powder

[0034] A mixed powder according to an embodiment of the present invention is a mixed powder for an annealing separator containing MgO as a main agent, in which the mixed powder contains Al and B, an Al content contained in the entire mixed powder is 0.0007 mass % or more and 0.050 mass % or less, a B content contained in the entire mixed powder is 0.005 mass % or more and 0.040 mass % or less, the B contains tri-coordinated boron, an average particle size of the mixed powder is 0.08 m or more and 9.0 m or less, and the following formula (1) is satisfied.

[00004]$\begin{array}{cc}0.06\left[\mathrm{Al}\right]/\left[{\mathrm{BO}}_3\right]<5.& \mathrm{Formula}\left(1\right)\end{array}$

[0035] In the formula (1), [Al] is an Al content (mass %) in the mixed powder, and [BO.sub.3] is a content (mass %) of the tri-coordinated boron in the mixed powder. Details will be described below.

[0036] The mixed powder according to the present embodiment contains MgO as a main agent. The mixed powder contains, for example, 50.0 mass % or more of MgO. A proportion of MgO in the mixed powder is preferably 80.0 mass % or more, and more preferably 90.0 mass % or more.

[0037] The mixed powder contains MgO particles, but the MgO particles contained in the mixed powder are not limited to the MgO particles according to an embodiment of the present invention described later, and for example, MgO particles in which the proportion of MgO in the mixed powder is 50.0 mass % or more can be used.

Al Content is 0.0007 Mass % or More and 0.050 Mass % or Less

[0038] The mixed powder contains Al. When an Al content contained in the entire mixed powder is less than 0.0007 mass %, an amount of Al for fixing nitrogen is reduced, and an external appearance of a coating is deteriorated. On the other hand, when the Al content contained in the entire mixed powder is more than 0.050 mass %, magnetic characteristics are deteriorated. Therefore, the Al content contained in the entire mixed powder is 0.0007 mass % or more and 0.050 mass % or less. The Al content contained in the entire mixed powder may be 0.003 mass % or more, 0.004 mass % or more, or 0.005 mass % or more. In addition, the Al content contained in the entire mixed powder may be 0.045 mass % or less, 0.040 mass % or less, or 0.030 mass % or less.

[0039] The mixed powder contains, for example, Al-containing particles containing Al. The Al-containing particles contain an Al compound, and examples of the Al compound include Al.sub.2O.sub.3, AlN, Al(OH).sub.3, and AlO(OH).

[0040] The mixed powder according to the present embodiment contains boron (B). The mixed powder contains, for example, B-containing particles containing B. The B-containing particles may contain at least one of pure boron and a B compound, and examples of the B compound include Na.sub.2B.sub.4O.sub.7, borax, calcium borate, and magnesium borate.

B Content is 0.005 Mass % or More and 0.040 Mass % or Less

[0041] The mixed powder contains 0.005 mass % or more and 0.040 mass % or less of boron (B). When a B content is less than 0.005 mass %, a structure of a coating is not strengthened due to a shortage of boron, and the coating is broken when gas is released from a steel sheet, so that an external appearance of the grain-oriented electrical steel sheet is deteriorated. In addition, when the B content is less than 0.005 mass %, a thickness of the coating becomes non-uniform due to a shortage of boron, and thus coating tension of the grain-oriented electrical steel sheet is deteriorated. The B content is preferably 0.008 mass % or more, and more preferably 0.010 mass % or more.

[0042] On the other hand, when the B content contained in the mixed powder is more than 0.040 mass %, heat resistance of an internal oxide layer is excessively increased, and transmission of a gas element, such as nitrogen in the steel sheet, which becomes a gas at a temperature at the time of final annealing, into an atmosphere is excessively inhibited, so that gas pressure is excessively increased, and then the gas is released in association with breakage of the coating, whereby the external appearance of the grain-oriented electrical steel sheet is deteriorated. Therefore, the B content in the mixed powder is set to 0.040 mass % or less. The B content is preferably 0.035 mass % or less, and more preferably 0.030 mass % or less.

[0043] The Al content and the B content in the mixed powder are determined by performing quantitative analysis using inductively coupled plasma mass spectrometry (ICP-MS). For quantitative analysis by ICP-MS, the mixed powder is dissolved in a mixed acid of hydrochloric acid and nitric acid. At this time, if there is any undissolved residue, the residue is recovered and dissolved in an alkaline solution to perform analysis.

[00005]$0.06\left[\mathrm{Al}\right]/\left[{\mathrm{BO}}_3\right]<5.$

[0044] Boron contained in the mixed powder is present in a form of tri-coordinated boron (BO.sub.3) and tetra-coordinated boron (BO.sub.4). Tri-coordinated boron is boron having a tri-coordinated structure in which three oxygen atoms are coordinated around a boron atom, and tetra-coordinated boron is boron having a tetra-coordinated structure in which four oxygen atoms are coordinated around a boron atom. Boron other than tri-coordinated boron is present as tetra-coordinated boron.

[0045] As a result of investigating reactions of tri-coordinated boron and tetra-coordinated boron, it has been found that tri-coordinated boron and tetra-coordinated boron have different influences on coating defects and external appearance characteristics. Specifically, tri-coordinated boron has a greater influence on decomposition of precipitates while promoting coating formation than tetra-coordinated boron. In addition, it has been found that when an amount of tri-coordinated boron is too large, reactions of coating formation and decomposition of precipitates occur too intensively at a low temperature, and coating breakage occurs due to gas release. Therefore, it has been found that by shifting the timing of decomposition of precipitates, it is possible to form a good coating while preventing coating breakage. The smaller the particle size, or the higher the tri-coordinated boron ratio, the more promoted the decomposition of precipitates due to the formation of a coating at a low temperature.

[0046] When a tri-coordinated boron content contained in the mixed powder and an Al content contained in the mixed powder satisfy the following formula (1), it is possible to suppress an adverse effect on purification while improving secondary recrystallization of the grain-oriented electrical steel sheet.

[00006]$\begin{array}{cc}0.06\left[\mathrm{Al}\right]/\left[{\mathrm{BO}}_3\right]<5.& \mathrm{Formula}\left(1\right)\end{array}$

[0047] In the formula (1), [Al] is an Al content (mass %) in the mixed powder, and [BO.sub.3] is a content (mass %) of the tri-coordinated boron in the mixed powder.

[0048] If [Al]/[BO.sub.3] is less than 0.06, an amount of Al for fixing nitrogen is insufficient at a relatively low temperature stage during secondary recrystallization, so that a gas release suppressing effect of a coating by BO.sub.3 becomes too strong, and the coating is easily broken in association with gas release at a low temperature stage, so that an oxide film on a surface of the steel sheet exhibits a non-uniform external appearance, and the external appearance of the grain-oriented electrical steel sheet is deteriorated. [Al]/[BO.sub.3] is preferably 0.08 or more, and more preferably 0.15 or more.

[0049] On the other hand, when [Al]/[BO.sub.3] is 5.00 or more, formation of BN is small, so that a large amount of Al nitride is formed, and the Al nitrides are maintained until reaching a relatively high temperature stage during secondary recrystallization. These nitrides decompose at a high temperature, and nitrogen generated by decomposition of the nitrides breaks a coating having low strength due to a small amount of BO.sub.3 and is released, so that the external appearance of the grain-oriented electrical steel sheet is deteriorated. [Al]/[BO.sub.3] is preferably 4.5 or less, and more preferably 4.0 or less.

[0050] The content [BO.sub.3] of tri-coordinated boron in the mixed powder is determined by multiplying the B content determined by ICP-MS by a proportion of tri-coordinated boron in B determined by the method described later.

Proportion of Tri-Coordinated Boron in B is 5 Mass % or More and Less than 70 Mass %

[0051] The mixed powder preferably contains 5 mass % or more and less than 70 mass % of tri-coordinated boron with respect to the content of B in the mixed powder. When the proportion of tri-coordinated boron in B is 5 mass % or more, magnetic characteristics and coating characteristics can be improved. The proportion of tri-coordinated boron in B is more preferably 8 mass % or more.

[0052] On the other hand, when the proportion of tri-coordinated boron in B is 70 mass % or more, reactivity may become too high, decomposition of precipitates may be promoted, and grains may be likely to grow in an orientation other than the Goss orientation. As a result, magnetic characteristics may be deteriorated. The proportion of tri-coordinated boron in B is more preferably 50 mass % or less. Incidentally, tri-coordinated boron is mainly contained in the above-described B-containing particles, but may be contained in MgO particles or Al-containing particles.

[0053] The proportion of tri-coordinated boron in B contained in the mixed powder is determined by the following method. Measurement is performed by nuclear magnetic resonance (NMR), and in the obtained spectrum, a peak within a range of 27 ppm or less and 6 ppm or more is defined as a peak of tri-coordinated boron, a peak within a range of less than 6 ppm and 6 ppm or more is defined as a peak of tetra-coordinated boron, and a value obtained by dividing an integration area of the peak of tri-coordinated boron by a total integration area of the integration area of the peak of tri-coordinated boron and an integration area of the peak of tetra-coordinated boron is defined as the proportion of tri-coordinated boron in B.

[0054] The Al content in the mixed powder is quantitatively analyzed by ICP-MS by the method described above.

Cl: 0.0005 Mass % or More and 0.0300 Mass % or Less

[0055] Cl (chlorine) is an element that enhances reactivity with SiO.sub.2 formed on a surface of a steel sheet after decarburization annealing. When the mixed powder according to the present embodiment contains 0.0005 mass % or more of Cl, coating characteristics are further improved, which is preferable. A Cl content is more preferably 0.0008 mass % or more.

[0056] On the other hand, when the Cl content is more than 0.0300 mass %, there is a possibility that desulfurization is excessively suppressed due to the strength of the effect of dissolving an oxide. When the Cl content is 0.0300 mass % or less, desulfurization can be sufficiently suppressed. Therefore, the Cl content is preferably 0.0300 mass % or less. The Cl content is more preferably 0.0250 mass % or less.

0.02 Mass % or More and 4.00 Mass % or Less in Total of One or More Selected from the Group Consisting of Ca, Sr, and Ba

[0057] Ca (calcium), Sr (strontium), and Ba (barium) are elements that enhance reactivity with SiO.sub.2, similarly to Cl. Therefore, it is preferable that 0.02 mass % or more in total of one or more selected from the group consisting of Ca, Sr, and Ba be contained because adhesion is further improved.

[0058] On the other hand, when a content in total of one or more selected from the group consisting of Ca, Sr, and Ba is more than 4.00 mass %, desulfurization of a steel sheet may be caused due to the strength of the sulfurization tendency. When the content in total of one or more selected from the group consisting of Ca, Sr, and Ba is 4.00 mass % or less, desulfurization can be sufficiently suppressed. Therefore, the content in total of one or more selected from the group consisting of Ca, Sr, and Ba is preferably 4.00 mass % or less.

[0059] Ca may be contained in the mixed powder as a Ca compound. Examples of the Ca compound include calcium sulfate, hemihydrate gypsum, calcined gypsum, and gypsum. Sr may be contained in the mixed powder as a Sr compound. Examples of the Sr compound include strontium sulfate. Ba may be contained in the mixed powder as a Ba compound. Examples of the Ba compound include barium sulfate. Cl, Sr, and Ba may be contained in the mixed powder as particles mainly containing each of Cl, Sr, and Ba, or may be contained in the above-described particles constituting the mixed powder.

Ti: 0.25 Mass % or More and 5 Mass % or Less

[0060] Ti (titanium) is an element that serves as an oxide or becomes an oxide at an initial stage of final annealing, and then adjusts an oxygen partial pressure in an annealing atmosphere at a high temperature to about a decomposed oxygen partial pressure of TiO.sub.2 to help increase a formation amount of a coating. When the mixed powder according to the present embodiment contains 0.25 mass % or more of Ti, the above effect can be obtained. A Ti content is more preferably 0.5 mass % or more.

[0061] On the other hand, when the Ti content is 5 mass % or less, deterioration of magnetic characteristics due to excessive oxygen release can be suppressed. Therefore, the Ti content is preferably 5 mass % or less. The Ti content is more preferably 4 mass % or less.

[0062] Ti may be contained in the mixed powder as, for example, TiO.sub.2, titanate, titanium boride, titanium nitride, or BaTiO.sub.3. Ti may be contained in the mixed powder as particles mainly containing each compound, or may be contained in the above-described particles constituting the mixed powder.

[0063] The contents of Cl, Ca, Sr, Ba, and Ti are quantitatively analyzed by ICP-MS by the method described above.

Impurities

[0064] Components other than the above in the mixed powder according to the present embodiment are MgO and impurities. Examples of the impurities include Fe and Si. When a content of each impurity element is 0.5 mass % or less, or 1.0 mass % or less in total, an influence on magnetic characteristics or coating characteristics of the grain-oriented electrical steel sheet is small.

Average Particle Size of Mixed Powder

[0065] An average particle size of the mixed powder is 0.08 m or more and 9.0 m or less in terms of a volume-based equivalent circle average particle size. When the average particle size of the mixed powder is less than 0.08 m, seizure between steel sheets cannot be prevented as an annealing separator, so that formation of a coating becomes incomplete and magnetic characteristics are deteriorated. In addition, when the average particle size of the mixed powder is less than 0.08 m, formation of a coating becomes incomplete, and the external appearance is deteriorated. In addition, when the average particle size of the mixed powder is less than 0.08 m, formation of a coating becomes incomplete, and coating tension is deteriorated. The average particle size of the mixed powder is preferably 0.2 m or more. On the other hand, when the average particle size of the mixed powder is more than 9.0 m, reactivity with a steel sheet is low, so that formation of a coating becomes insufficient. The average particle size of the mixed powder is preferably 7.0 m or less, and more preferably 6.0 m or less.

[0066] For the average particle size of the mixed powder, a particle size distribution of a volume frequency is measured with a laser diffraction particle size distribution measuring apparatus ((apparatus name) LA-920 manufactured by HORIBA, Ltd.), and an average particle size in an equivalent circle diameter is defined as the average particle size of the mixed powder. A refractive index is set to 1.74, and dispersion treatment by ultrasonic waves is performed in pure water to measure the average particle size of the mixed powder.

Method for Manufacturing Mixed Powder

[0067] The mixed powder according to the present embodiment described above is manufactured by baking a raw material powder containing Mg-containing raw material particles containing one or two or more selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, B-containing raw material particles containing B, and Al-containing raw material particles containing Al at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere.

[0068] The B-containing raw material particles contain Mg-containing raw material particles, boron, boric acid, magnesium boride, sodium borate, borax, and the like. The B-containing raw material particles contain, for example, 0.01 mass % or more of B.

[0069] The Al-containing raw material particles contain Mg-containing raw material particles, Al.sub.2O.sub.3, AlN, KAl(SO.sub.4).sub.2.12H.sub.2O, Al(OH).sub.3, AlO(OH), and the like. The Al-containing raw material particles contain, for example, 0.01 mass % or more of Al.

[0070] Respective particle sizes of the Mg-containing raw material particles, the Al-containing raw material particles, and the B-containing raw material particles constituting the raw material powder may be, for example, a particle size at which the average particle size of the mixed powder described above is obtained, or a particle size larger than the average particle size. When the particle size of the raw material powder is larger than the average particle size of the mixed powder, a mixed powder obtained by baking by a known method may be pulverized or classified. The respective particle sizes of the Mg-containing raw material particles, the Al-containing raw material particles, and the B-containing raw material particles may be, for example, 0.08 m or more, or 0.10 m or more. In addition, the respective particle sizes of the Mg-containing raw material particles, the Al-containing raw material particles, and the B-containing raw material particles may be, for example, 15 m or less, or 10 m or less.

[0071] In addition, the raw material powder may appropriately contain Cl, Ca, Sr, Ba, and Ti. When these elements are contained in the raw material powder, one or more of these elements may be contained in one particle.

[0072] The Al content in the raw material powder is preferably 0.0007 mass % or more and 0.050 mass % or less. When the Al content in the raw material particles is 0.0007 mass % or more and 0.050 mass % or less, the Al content in the mixed powder manufactured can be set to 0.0007 mass % or more and 0.050 mass % or less. The Al content in the raw material powder may be 0.003 mass % or more, 0.004 mass % or more, or 0.005 mass % or more. In addition, the Al content in the raw material powder may be 0.045 mass % or less, 0.040 mass % or less, or 0.030 mass % or less. However, when the raw material powder contains a component that volatilizes by baking, the Al content in the raw material powder is adjusted in consideration of the component amount.

[0073] Al is mainly contained in the Al-containing raw material particles described above, but may be contained in other particles constituting the raw material powder, for example, Mg-containing raw material particles, B-containing raw material particles, Ti-containing particles, and the like.

[0074] The B content in the raw material powder is preferably 0.005 mass % or more and 0.040 mass % or less. When the B content in the raw material particles is 0.005 mass % or more and 0.040 mass % or less, the B content in the mixed powder manufactured can be set to 0.005 mass % or more and 0.040 mass % or less. The B content is more preferably 0.006 mass % or more, and still more preferably 0.008 mass % or more. In addition, the B content is more preferably 0.036 mass % or less, and still more preferably 0.032 mass % or less. However, when the raw material powder contains a component that volatilizes by baking, the B content in the raw material powder is adjusted in consideration of the component amount.

[0075] B is mainly contained in the B-containing raw material particles described above, but may be contained in other particles constituting the raw material powder, for example, Mg-containing raw material particles, Al-containing raw material particles, Ti-containing particles, and the like.

[0076] The Al content and the B content in the raw material powder are quantitatively analyzed by ICP-MS by the method described above.

[0077] A content of tri-coordinated boron with respect to the mass of the raw material powder is preferably 0.005 mass % or more and 0.040 mass % or less, and more preferably 0.010 mass % or more and 0.030 mass % or less. In addition, a content of tri-coordinated boron with respect to the B content in the raw material powder is preferably 5% or more and 70% or less. When the content of tri-coordinated boron with respect to the mass of the raw material powder or the content of tri-coordinated boron with respect to the B content is within the above range, tri-coordinated boron in the mixed powder after baking more reliably satisfies the formula (1).

[0078] The content [BO.sub.3] of tri-coordinated boron in the raw material powder is determined by multiplying the B content determined by ICP-MS by the proportion of tri-coordinated boron in B determined by the method described above.

[0079] The raw material powder is baked at a temperature of 700 C. or higher and 1100 C. or lower in an air atmosphere or a nitrogen atmosphere.

[0080] It is not preferable that a baking atmosphere be other than an air atmosphere or a nitrogen atmosphere because it is economically disadvantageous.

[0081] In addition, when a baking temperature is lower than 700 C., baking becomes insufficient. Therefore, the baking temperature is set to 700 C. or higher. The baking temperature is preferably 720 C. or higher, and more preferably 750 C. or higher. On the other hand, by setting the baking temperature to 1100 C. or lower, a proportion of tri-coordinated boron in the mixed powder can be increased without significantly changing the particle size while the chemical structure of the baked tri-coordinated boron is stabilized. Therefore, the baking temperature is set to 1100 C. or lower. The baking temperature is preferably 1080 C. or lower, and more preferably 1040 C. or lower.

[0082] A baking time can be set to, for example, 5 minutes or more and 120 minutes or less. From the viewpoint of eliminating baking unevenness, the baking time is preferably 8 minutes or more, and more preferably 10 minutes or more. On the other hand, from the viewpoint of economic efficiency, the baking time is preferably 80 minutes or less, and more preferably 60 minutes or less.

[0083] The method for manufacturing a mixed powder has been described so far.

[0084] In the method for manufacturing a mixed powder described above, the aspect has been described in which the raw material powder contains the Mg-containing raw material particles, the B-containing raw material particles, and the Al-containing raw material particles on the premise that particles serving as an Mg source, particles serving as a B source, and particles serving as an Al source are different from one another. However, the present invention is not limited to such an aspect, and the Mg-containing raw material particles serving as the Mg source may contain B and/or Al so that the Mg-containing raw material particles serve as the B source and/or the Al source, or may contain other elements. The B-containing raw material particles may contain Al or may contain other elements.

[0085] In addition, the mixed powder according to the present embodiment described above may be manufactured by mixing MgO particles, Al-containing particles, and B-containing particles containing tri-coordinated boron so that MgO is a main agent, the B content is 0.005 mass % or more and 0.040 mass % or less, the average particle size is 0.08 m or more and 9.0 m or less, and the above formula (1) is satisfied.

MgO Particles

[0086] MgO particles according to an embodiment of the present invention contain Al and B, in which an Al content is 0.0007 mass % or more and 0.050 mass % or less, a B content is 0.005 mass % or more and 0.040 mass % or less, the B contains tri-coordinated boron, an average particle size is 0.08 m or more and 9.0 m or less, and the following formula (1) is satisfied.

[00007]$\begin{array}{cc}0.06\left[\mathrm{Al}\right]/\left[{\mathrm{BO}}_3\right]<5.& \mathrm{Formula}\left(1\right)\end{array}$

[0087] In the formula (1), [Al] is an Al content (mass %) in the MgO particles, and [BO.sub.3] is a content (mass %) of the tri-coordinated boron in the MgO particles.

[0088] The above characteristics of the MgO particles according to the present embodiment are similar to the characteristics of the mixed powder described above, and thus detailed description thereof will be omitted here. In addition, in the MgO particles according to the present embodiment, similarly to the mixed powder, a proportion of the tri-coordinated boron in B is preferably 5 mass % or more and less than 70 mass %. In addition, similarly to the mixed powder, the MgO particles preferably contain 0.0005 mass % or more and 0.0300 mass % or less of Cl. In addition, similarly to the mixed powder, the MgO particles preferably contain 0.25 mass % or more and 5.0 mass % or less of Ti. However, the fact that the MgO particles contain the above components means that MgO particles constituting an MgO powder contain the above components, and that particles other than the MgO particles do not exist alone.

Method for Manufacturing MgO Particles

[0089] The MgO particles described above are manufactured by the following manufacturing method (I) or (II). [0090] (I)

[0091] A raw material powder containing Mg-containing raw material particles containing one or two or more selected from the group consisting of magnesium hydroxide (Mg(OH).sub.2), basic magnesium carbonate (mMgCO.sub.3.Mg(OH).sub.2.nH.sub.2O), and magnesium carbonate (Mg(CO.sub.3)), B-containing raw material particles containing B, and Al-containing raw material particles containing Al is baked at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere. [0092] (II)

[0093] Raw material particles containing B and Al and containing one or two or more selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate are baked at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere.

[0094] Each manufacturing method will be described below.

Manufacturing Method (I)

[0095] Manufacturing method (1) is a method for manufacturing MgO particles by baking a raw material powder containing Mg-containing raw material particles containing one or two or more selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate, B-containing raw material particles containing B, and Al-containing raw material particles containing Al at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere. When the raw material powder contains a component that volatilizes by baking, the Al content and the B content are adjusted in consideration of the component amount. The present manufacturing method is basically the same as the method for manufacturing a mixed powder described above. However, the method for manufacturing a mixed powder described above is different from the present manufacturing method in that there is a case where an oxide or the like other than B and Al, which is not solid-dissolved or contained as an impurity in the MgO particles, is mixed and baked in the method for manufacturing a mixed powder described above.

Manufacturing Method (II)

[0096] In manufacturing method (II), raw material particles containing B and Al and containing one or two or more selected from the group consisting of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate are baked at a temperature of 700 C. or higher and 1100 C. or lower in an air or nitrogen atmosphere. When the raw material powder contains a component that volatilizes by baking, the Al content and the B content are adjusted in consideration of the component amount.

[0097] The raw material particles containing at least one of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate contain B and Al. The Al content is 0.0007 mass % or more and 0.050 mass % or less. When the Al content in the raw material particles is 0.0007 mass % or more and 0.050 mass % or less, the Al content in the MgO particles manufactured can be set to 0.001 mass % or more and 0.050 mass % or less. The Al content in the raw material particles may be 0.003 mass % or more, 0.004 mass % or more, or 0.005 mass % or more. In addition, the Al content in the raw material particles may be 0.045 mass % or less, 0.040 mass % or less, or 0.030 mass % or less.

[0098] The B content is preferably 0.005 mass % or more and 0.040 mass % or less. When the B content in the raw material particles is 0.005 mass % or more and 0.040 mass % or less, the B content in the MgO particles manufactured can be set to 0.005 mass % or more and 0.040 mass % or less. The B content is more preferably 0.008 mass % or more, and still more preferably 0.010 mass % or more. In addition, the B content is more preferably 0.035 mass % or less, and still more preferably 0.030 mass % or less.

[0099] A content of tri-coordinated boron with respect to the B content in the raw material particles is preferably 5% or more and 70% or less. When the content of tri-coordinated boron with respect to the B content is within the above range, tri-coordinated boron in the MgO particles after baking under the baking conditions described later satisfies the formula (1).

[0100] Regarding the raw material particles, respective particle sizes of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate may be, for example, a particle size at which the average particle size of the MgO particles described above is obtained, or a particle size larger than the average particle size. When the particle size of the raw material particles is larger than the average particle size of the MgO particles, MgO particles obtained by baking by a known method may be pulverized. The respective particle sizes of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate may be, for example, 0.05 m or more, or 0.08 m or more. In addition, the respective particle sizes of magnesium hydroxide, basic magnesium carbonate, and magnesium carbonate may be, for example, 12 m or less, or 10 m or less.

[0101] The raw material particles are baked at a temperature of 700 C. or higher and 1100 C. or lower in an air atmosphere or a nitrogen atmosphere. The baking atmosphere, the baking temperature, and the baking time are the same as the baking conditions of the raw material powder described above, and thus the detailed description thereof will be omitted here.

Method for Manufacturing Grain-Oriented Electrical Steel Sheet

[0102] In a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, a grain-oriented electrical steel sheet is manufactured using the MgO particles or mixed powder as an annealing separator. In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, it is possible to manufacture a grain-oriented electrical steel sheet according to a manufacturing method including, for example, a hot rolling step of hot-rolling a steel slab to obtain a hot band; a hot-band annealing step of annealing the hot band; a cold rolling step of cold-rolling the hot band after the hot-band annealing step to obtain a cold rolled sheet; a decarburization annealing step of performing decarburization annealing on the cold rolled sheet; and a final annealing step of applying an annealing separator containing the MgO particles or mixed powder to the cold rolled sheet after the decarburization annealing step, drying the cold rolled sheet, and then performing final annealing.

[0103] In the present embodiment, as the annealing separator applied before final annealing, an annealing separator obtained by mixing the mixed powder according to the present embodiment described above with water to form a slurry is used. When Ti is not contained in the mixed powder, Ti may be further mixed. By using this annealing separator, it is possible to manufacture a grain-oriented electrical steel sheet having an excellent external appearance of a coating and excellent coating adhesion.

[0104] In the above manufacturing method, as for the chemical composition of the steel slab and the conditions of each step, known manufacturing conditions of a grain-oriented electrical steel sheet can be applied except for the annealing separator to be used.

[0105] Regarding the annealing separator, when a mixed powder obtained by mixing MgO particles and TiO.sub.2 particles is mixed with water to form a slurry (when an aqueous slurry is formed), it is preferable that the mixing be performed so that a proportion of TiO.sub.2 is 0.25 to 5.0 mass % in terms of Ti content when the mass of the mixed powder is 100%.

EXAMPLES

[0106] Next, Examples of the present invention will be described, but conditions in Examples are examples of conditions adopted to confirm the feasibility and effect of the present invention, but the present invention is not limited to the conditions used in the following Examples. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1

[0107] Grain-oriented electrical steel sheets were produced using MgO particles shown in Table 1 or mixed powders of MgO particles and TiO.sub.2 particles shown in Table 2. Specifically, an aqueous slurry of an annealing separator containing MgO particles of Table 1 or a mixed powder shown in Table 2 was applied to a cold-rolled steel sheet after primary recrystallization annealing. The aqueous slurry was prepared by mixing an MgO powder or a mixed powder with water. The content of the solid content (MgO particles or mixed powder) in the aqueous slurry was set to 20 mass %. The cold-rolled steel sheet having a surface coated with the aqueous slurry was subjected to baking treatment at 300 C. for 30 seconds in any test number, and the aqueous slurry was dried to bake the solid content. After baking, final annealing treatment was performed. In the final annealing treatment, the steel sheet was held at 1200 C. for 20 hours in any test number. By the above manufacturing steps, a grain-oriented electrical steel sheet having a longitudinal direction length of 300 mm, a sheet width direction length of 60 mm, and a sheet thickness of 0.23 mm and including a base steel sheet and a glass coating containing a composite oxide such as forsterite (Mg.sub.2SiO.sub.4) was manufactured. The BO.sub.3 ratio shown in Table 1 indicates the proportion of tri-coordinated boron in B.

[0108] The B content, the Al content, and the Cl content in the MgO particles and the mixed powder were measured using inductively coupled plasma mass spectrometry (ICP-MS). Specifically, a solution obtained by dissolving the MgO particles or the mixed powder in a mixed acid of hydrochloric acid and nitric acid was used. When a residue remained, the residue was recovered and dissolved in an alkaline solution to perform analysis. In addition, the proportion of tri-coordinated boron in B was determined by the following method. Measurement was performed by NMR, and in the obtained spectrum, a peak within a range of 27 ppm or less and 6 ppm or more was defined as tri-coordinated boron, a peak within a range of less than 6 ppm and 6 ppm or more was defined as tetra-coordinated boron, and a value obtained by dividing an integration area of the peak of tri-coordinated boron by a total integration area of the integration area of the peak of tri-coordinated boron and an integration area of the peak of tetra-coordinated boron was defined as the proportion of tri-coordinated boron in B. The BO.sub.3 content [BO.sub.3] in the MgO particles and the mixed powder was determined by multiplying the B content determined by ICP-MS by the proportion of tri-coordinated boron in B.

[0109] Magnetic characteristics (B8), external appearance, and coating tension of the obtained grain-oriented electrical steel sheets were evaluated in the following manner.

Magnetic Characteristics

[0110] Magnetic characteristics of each grain-oriented electrical steel sheet were evaluated by the following method.

[0111] Specifically, a magnetic field of 800 A/m was applied to a sample having a rolling direction length of 300 mma width of 60 mm to obtain a magnetic flux density B8. When B8 was 1.92 T or more, it was determined that the magnetic characteristics were good.

External Appearance

[0112] A color tone was evaluated for a sample having a rolling direction length of 50 mma width of 60 mm cut out from the position of the center of the rolling direction length of each grain-oriented electrical steel sheet, and then a known insulating coating was formed to evaluate coating defects. When the color tone of a primary layer of each grain-oriented electrical steel sheet before formation of the insulating coating was uniform and there was no coating defect (hole and rusting) after formation of the insulating coating, it was determined that the external appearance was excellent. Specifically, evaluation was performed as follows.

[0113] A: The color tone before formation of the insulating coating was uniform, and the maximum area of coating defects after formation of the insulating coating was less than 2 mm.sup.2.

[0114] B: The color tone before formation of the insulating coating was uniform, and the maximum area of coating defects after formation of the insulating coating was 2 mm.sup.2 or more and less than 4 mm.sup.2.

[0115] C: The color tone before formation of the insulating coating was uniform, and the maximum area of coating defects after formation of the insulating coating was 4 mm.sup.2 or more and less than 6 mm.sup.2.

[0116] D: Color unevenness was observed in the color tone before formation of the insulating coating, or the maximum area of coating defects after formation of the insulating coating was 6 mm.sup.2 or more.

[0117] A or B was determined to be acceptable in the evaluation.

Coating Tension

[0118] For a sample having a rolling direction length of 300 mma width of 60 mm, the primary layer was removed only on one surface by pickling, and then coating tension was determined from the radius of curvature of the curvature of the steel sheet. The method for determining the coating tension from the radius of curvature may be a known method, and for example, a method disclosed in Report on Post-Evaluation of Development of Innovative Magnetic Materials for Reduction of Power Loss in Transformers (February 2006) of Research Evaluation Committee of New Energy and Industrial Technology Development Organization was used.

[0119] When the coating tension was 350 g/mm.sup.2 or more, it was determined that the coating tension was excellent. The results are shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 MgO particles Grain-oriented Chemical component (remainder Average electrical steel sheet is Mg, O, and impurities) particle Coating B BO.sub.3 ratio Al Cl [Al]/ size B8 External tension No. mass % mass % mass % mass % [BO.sub.3] [m] [T] appearance [g/mm.sup.2] Remarks 1 0.020 72 0.0300 0.0005 2.08 0.05 1.91 D 290 Comparative Example 2 0.020 72 0.0300 0.0005 2.08 9.80 1.90 D 321 Comparative Example 3 0.020 72 0.0300 0.0005 2.08 0.20 1.92 A 376 Inventive Example 4 0.020 72 0.0300 0.0005 2.08 1.50 1.94 A 470 Inventive Example 5 0.020 72 0.0300 0.0005 2.08 3.80 1.93 A 365 Inventive Example 6 0.004 72 0.0100 0.0005 3.47 1.50 1.91 C 345 Comparative Example 7 0.045 85 0.0050 0.0005 0.13 1.50 1.92 C 370 Comparative Example 8 0.008 4 0.0007 0.0005 2.19 1.50 1.94 A 398 Inventive Example 9 0.038 75 0.0110 0.0005 0.39 4.50 1.93 A 372 Inventive Example 10 0.035 4 0.0090 0.0005 6.43 1.50 1.91 C 388 Comparative Example 11 0.033 88 0.0010 0.0005 0.03 1.50 1.91 C 372 Comparative Example 12 0.005 72 0.0170 0.0005 4.72 6.00 1.93 B 389 Inventive Example 13 0.035 88 0.0020 0.0005 0.06 6.00 1.93 B 361 Inventive Example 14 0.020 66 0.0170 0.0005 1.29 7.00 1.94 A 420 Inventive Example 15 0.040 66 0.0480 0.0005 1.82 6.70 1.94 A 414 Inventive Example 16 0.040 66 0.0520 0.0005 1.97 6.40 1.91 A 411 Comparative Example

TABLE-US-00002 TABLE 2 MgO particles Chemical component (remainder TiO.sub.2 Mixed powder is Mg, O, and impurities) particles Average Chemical component (remainder Blending BO.sub.3 Blending particle is Mg, O, and impurities) ratio B ratio Al Cl ratio size B No. mass % mass % mass % mass % mass % mass % [m] mass % 17 97.00 0.021 44 0.0180 0.0005 3.00 2.00 0.020 18 96.00 0.021 8 0.0050 0.0005 4.00 2.00 0.020 19 95.00 0.021 44 0.0180 0.0295 5.00 2.00 0.020 20 94.00 0.021 44 0.0180 0.0160 6.00 2.00 0.020 21 93.00 0.022 44 0.0180 0.0022 7.00 2.00 0.020 22 92.00 0.022 44 0.0050 0.0163 8.00 2.00 0.020 23 99.50 0.020 44 0.0050 0.0133 0.50 2.00 0.020 24 99.50 0.039 95 0.0020 0.0168 0.50 2.00 0.039 25 99.50 0.035 88 0.0020 0.0189 0.50 2.00 0.035 26 99.50 0.020 15 0.0141 0.0223 0.50 2.00 0.020 27 99.50 0.020 14 0.0161 0.0125 0.50 2.00 0.020 28 99.50 0.022 60 0.0006 0.0168 0.50 2.00 0.022 29 99.50 0.039 95 0.0533 0.0168 0.50 2.00 0.039 Mixed powder Chemical component (remainder Grain-oriented is Mg, O, and impurities) electrical steel sheet BO.sub.3 Coating Al Ti Cl ratio [Al]/ B8 External tension No. mass % mass % mass % mass % [BO.sub.3] [T] appearance [g/mm.sup.2] Remarks 17 0.0170 1.78 0.0005 44 1.93 1.94 A 400 Inventive Example 18 0.0050 2.38 0.0005 8 3.13 1.94 A 411 Inventive Example 19 0.0170 2.97 0.0280 44 1.93 1.96 A 358 Inventive Example 20 0.0170 3.57 0.0150 44 1.93 1.95 A 372 Inventive Example 21 0.0170 4.16 0.0020 44 1.93 1.96 A 399 Inventive Example 22 0.0050 4.76 0.0150 44 0.57 1.93 A 488 Inventive Example 23 0.0050 0.30 0.0132 44 0.57 1.93 A 488 Inventive Example 24 0.0020 0.30 0.0167 95 0.05 1.91 C 322 Comparative Example 25 0.0020 0.30 0.0188 88 0.06 1.91 B 405 Inventive Example 26 0.0140 0.30 0.0222 15 4.67 1.93 B 411 Inventive Example 27 0.0160 0.30 0.0124 14 5.71 1.91 C 428 Comparative Example 28 0.0006 0.30 0.0167 60 0.08 1.91 C 355 Comparative Example 29 0.0530 0.30 0.0167 95 1.43 1.89 A 395 Comparative Example

[0120] In the example of No. 1, since the average particle size was too small, coating formation was non-uniform, and B8, the external appearance, and the coating tension of the grain-oriented electrical steel sheet were all poor.

[0121] In the example of No. 2, since the average particle size was too large, the coating formation amount was excessively small, and B8, the external appearance, and the coating tension of the grain-oriented electrical steel sheet were all poor.

[0122] In the example of No. 6, since the B content was excessively low, B8, the external appearance, and the coating tension were poor.

[0123] In the example of No. 7, since the B content was excessive, the external appearance of the grain-oriented electrical steel sheet was poor.

[0124] In the examples of Nos. 10, 11, 24, and 27, the [Al]/[BO.sub.3] value was out of the range of the above formula (1), and B8 and the external appearance of the grain-oriented electrical steel sheet were poor.

[0125] In the examples of Nos. 16 and 29, Al was more than 0.050 mass %, and B8 of the grain-oriented electrical steel sheet was poor.

[0126] In the example of No. 28, Al was less than 0.001 mass %, and B8 and the external appearance of the grain-oriented electrical steel sheet were poor.

[0127] In the examples of Nos. 3 to 5, 8, 9, 12 to 15, 17 to 23, 25, and 26, the average particle size was within a range of 0.08 m or more and 9.0 m or less, the Al content was 0.0007 mass % or more and 0.050 mass % or less, the B content was 0.005 mass % or more and 0.040 mass % or less, the [Al]/[BO.sub.3] value was within the range of the above formula (1), and a grain-oriented electrical steel sheet having excellent magnetic characteristics, external appearance, and coating tension was obtained. In Nos. 3 to 5, 8, 9, 14, 15, and 17 to 23, the [Al]/[BO.sub.3] value was within 0.15 to 4.00, and therefore the external appearance characteristics were particularly excellent.

Example 2

[0128] Grain-oriented electrical steel sheets were manufactured using a mixed powder containing MgO particles, TiO.sub.2 particles, and at least one of B compound particles or Al compound particles at blending ratios shown in Table 3. Specifically, an aqueous slurry of an annealing separator containing a mixed powder of Table 3 was applied to a cold-rolled steel sheet after primary recrystallization annealing. The aqueous slurry was prepared by mixing a mixed powder of Table 3 with water. The content of the solid content (mixed powder) in the aqueous slurry was set to 20 mass %. The cold-rolled steel sheet having a surface coated with the aqueous slurry was subjected to baking treatment at 300 C. for 30 seconds in any example, and the aqueous slurry was dried to bake the solid content. After baking, final annealing treatment was performed. In the final annealing treatment, the steel sheet was held at 1200 C. for 20 hours in any example. By the above manufacturing steps, a grain-oriented electrical steel sheet having a longitudinal direction length of 300 mm, a sheet width direction length of 60 mm, and a sheet thickness of 0.23 mm and including a base steel sheet and a glass coating containing a composite oxide such as forsterite (Mg.sub.2SiO.sub.4) shown in Table 3 was manufactured.

TABLE-US-00003 TABLE 3 MgO particles Chemical component (remainder TiO.sub.2 is Mg, O, and impurities) particles B compound particles Blending BO.sub.3 Blending Blending BO.sub.3 ratio B ratio Al Cl ratio ratio B ratio No. mass % mass % mass % mass % mass % mass % Type mass % mass % mass % 30 97.920 0.005 72.000 0.0200 0.0005 2.000 Na.sub.2B.sub.4O.sub.7 0.080 21.49 50 31 97.920 0.005 72.000 0.0200 0.0005 2.000 Na.sub.2B.sub.4O.sub.7 0.080 21.49 50 32 97.920 0.010 72.000 0.0200 0.0005 2.000 Na.sub.2B.sub.4O.sub.7 0.080 21.49 50 33 97.940 0.010 72.000 0.0200 0.0005 2.000 BN 0.060 43.55 50 34 97.992 0.001 72.000 0.0200 0.0005 2.000 BN 0.008 43.55 95 35 96.950 0.020 72.000 0.0103 0.0005 3.000 BN 0.050 43.55 50 36 96.950 0.010 60.000 0.1500 0.0005 3.000 BN 0.050 43.55 90 37 96.950 0.010 4.000 0.0007 0.0005 3.000 BN 0.050 43.55 80 38 96.998 0.040 75.000 0.0003 0.0005 3.000 39 95.920 0.030 4.000 0.0200 0.0005 4.000 40 92.980 0.020 44.000 0.0183 0.0301 7.000 Na.sub.2B.sub.4O.sub.7 0.060 21.49 50 Mixed powder Chemical component (remainder Al compound particles Average is Mg, O, and impurities) Blending particle BO.sub.3 ratio Al size B Al Ti Cl ratio [Al]/ No. Type mass % mass % [m] mass % mass % mass % mass % mass % [BO.sub.3] 30 0.06 0.022 0.0196 1.19 0.0005 55 1.62 31 9.70 0.022 0.0196 1.19 0.0005 55 1.62 32 0.20 0.027 0.0196 1.19 0.0005 58 1.25 33 1.50 0.036 0.0196 1.19 0.0005 56 0.97 34 3.80 0.004 0.0196 1.19 0.0005 90 4.88 35 1.50 0.041 0.0100 1.78 0.0005 60 0.40 36 1.50 0.031 0.1454 1.78 0.0005 81 5.72 37 1.50 0.031 0.0007 1.78 0.0005 57 0.04 38 AlN 0.002 65.85 1.50 0.039 0.0016 1.78 0.0005 95 0.04 39 AlN 0.080 65.85 1.50 0.029 0.0719 2.38 0.0005 45 5.55 40 Al.sub.2O.sub.2 0.020 52.94 2.00 0.031 0.0276 4.16 0.0280 46 1.89

[0129] The B content, the Al content, the Cl content, and the BO.sub.3 content, and the proportion of tri-coordinated boron in B (BO.sub.3 ratio) in the mixed powder were measured in the same manner as in Example 1. In addition, magnetic characteristics (B8), external appearance, and coating tension of the obtained grain-oriented electrical steel sheets were evaluated in the same manner as in Example 1. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Grain-oriented electrical steel sheet B8 External Coating tension No. [T] appearance [g/mm.sup.2] Remarks 30 1.90 D 277 Comparative Example 31 1.90 D 311 Comparative Example 32 1.92 A 376 Inventive Example 33 1.94 A 470 Inventive Example 34 1.91 C 345 Comparative Example 35 1.93 C 370 Comparative Example 36 1.91 C 388 Comparative Example 37 1.91 C 372 Comparative Example 38 1.91 C 372 Comparative Example 39 1.91 C 388 Comparative Example 40 1.96 A 358 Inventive Example

[0130] In the example of No. 30, since the average particle size of the mixed powder was too small, coating formation was non-uniform, and B8, the external appearance, and the coating tension of the grain-oriented electrical steel sheet were all poor.

[0131] In the example of No. 31, since the average particle size of the mixed powder was too large, coating formation was non-uniform, and B8, the external appearance, and the coating tension of the grain-oriented electrical steel sheet were all poor.

[0132] In the example of No. 34, since the B content in the mixed powder was excessively low, B8, the external appearance, and the coating tension of the grain-oriented electrical steel sheet were poor.

[0133] In the example of No. 35, since the B content in the mixed powder was excessive, the external appearance of the grain-oriented electrical steel sheet was poor.

[0134] In the examples of Nos. 36 to 39, the [Al]/[BO.sub.3] value was out of the range of the above formula (1), and B8 and the external appearance of the grain-oriented electrical steel sheet were poor.

[0135] In the examples of Nos. 32, 33, and 40, the average particle size was within a range of 0.08 m or more and 9.0 m or less, the Al content contained in the entire mixed powder was 0.0007 mass % or more and 0.050 mass % or less, the B content was 0.005 mass % or more and 0.040 mass % or less, the [Al]/[BO.sub.3] value was within the range of the above formula (1), and a grain-oriented electrical steel sheet having excellent magnetic characteristics, external appearance, and coating tension of the grain-oriented electrical steel sheet was obtained. In addition, in Nos. 32, 33, and 40, the [Al]/[BO.sub.3] value was within 0.15 to 4.00, and therefore the external appearance characteristics were particularly excellent.

Example 3

[0136] Raw material powders shown in Table 5 and TiO.sub.2 particles were mixed and baked under conditions shown in Table 5 to produce mixed powders shown in Table 6. Using the produced mixed powders, grain-oriented electrical steel sheets were manufactured in the same manner as in Example 1. Hereinafter, a powder obtained by baking without mixing TiO.sub.2 particles may be referred to as MgO particles.

[0137] The B content, the Al content, the Cl content, and the BO.sub.3 content, and the proportion of tri-coordinated boron in B (BO.sub.3 ratio) in the raw material powder, the MgO particles, and the mixed powder were measured in the same manner as in Example 1. In addition, the BO.sub.3 content with respect to the mass of the raw material powder was determined by multiplying the B content determined by ICP-MS by the proportion of tri-coordinated boron in B. Magnetic characteristics (B8), external appearance, and coating tension of each of the manufactured grain-oriented electrical steel sheets were evaluated in the same manner as in Example 1. The results are shown in Table 6.

TABLE-US-00005 TABLE 5 Raw material particles Mg-containing raw material particles Chemical component (remainder Raw material is Mg, O, and impurities) particle size B Al BO.sub.3 ratio [Al]/ No. Raw material type m mass % mass % mass % [BO.sub.3] 41 MgCO.sub.3 2.8 0.003 0.0030 50 2.00 42 MgCO.sub.3 2.8 0.042 0.0420 50 2.00 43 MgCO.sub.3 2.8 0.008 0.0220 50 5.50 44 MgCO.sub.3 2.5 0.038 0.0004 50 0.02 45 MgCO.sub.3 2.5 0.020 0.0040 50 0.40 46 MgCO.sub.3 2.5 0.020 0.0040 50 0.40 47 MgCO.sub.3 2.5 0.006 0.0040 85 0.78 48 MgCO.sub.3 2.5 0.020 0.0010 50 0.10 49 MgCO.sub.3 2.2 0.020 0.0020 50 0.20 50 MgCO.sub.3 2.2 0.020 0.0010 50 0.10 51 MgCO.sub.3 2.2 0.020 0.0020 50 0.20 52 MgCO.sub.3 2.2 0.020 0.0010 50 0.10 53 MgCO.sub.3 2.2 0.020 0.0020 50 0.20 54 MgCO.sub.3 2.2 0.018 0.0040 66 0.34 55 mMgCO.sub.3Mg(OH).sub.2nH.sub.2O 2.4 0.006 0.0040 35 1.90 56 Mg(OH).sub.2 2.5 0.025 0.0010 35 0.11 57 MgCO.sub.3 + 2.2 0.011 0.0020 15 1.21 mMgCO.sub.3Mg(OH).sub.2nH.sub.2O + Mg(OH).sub.2 Raw material particles Mg-containing raw material particles BO.sub.3 content with respect TiO.sub.2 to mass of particles raw material Blending Blending Baking condition powder ratio ratio Temperature Time No. mass % mass % mass % Atmosphere C. min 41 0.002 100 0 Air 800 10 42 0.021 100 0 Air 800 10 43 0.004 100 0 Air 800 10 44 0.019 100 0 Air 800 10 45 0.010 100 0 Air 800 10 46 0.010 95 5 Air 800 10 47 0.005 95 5 Air 800 10 48 0.010 95 5 Air 800 10 49 0.010 95 5 Air 800 10 50 0.010 95 5 Air 700 10 51 0.010 95 5 Air 1100 10 52 0.010 95 5 Air 680 10 53 0.010 95 5 Air 1120 10 54 0.012 95 5 Nitrogen 800 10 atmosphere 55 0.012 95 5 Air 800 10 56 0.009 95 5 Air 800 10 57 0.005 95 5 Air 800 10

TABLE-US-00006 TABLE 6 MgO particles or mixed powder Chemical component (remainder Grain-oriented Average is Mg, O, and impurities) electrical steel sheet particle BO.sub.3 Coating size B Al ratio [Al]/ Cl Ti B8 External tension No. [m] mass % mass % mass % [BO.sub.3] mass % mass % [T] appearance [g/mm.sup.2] Remarks 41 3.40 0.003 0.0030 50 2.00 0.0005 0.00 1.93 C 345 Comparative Example 42 3.40 0.042 0.0420 50 2.00 0.0005 0.00 1.92 C 370 Comparative Example 43 3.40 0.008 0.0220 50 5.50 0.0005 0.00 1.91 C 410 Comparative Example 44 3.40 0.038 0.0004 50 0.02 0.0005 0.00 1.91 C 372 Comparative Example 45 3.40 0.020 0.0040 50 0.40 0.0005 0.00 1.94 A 398 Inventive Example 46 3.40 0.019 0.0038 50 0.40 0.0005 2.97 1.94 A 352 Inventive Example 47 3.40 0.006 0.0038 50 1.33 0.0005 2.97 1.92 A 362 Inventive Example 48 3.40 0.019 0.0010 50 0.10 0.0005 2.97 1.93 B 405 Inventive Example 49 3.40 0.019 0.0019 50 0.20 0.0005 2.97 1.95 A 392 Inventive Example 50 3.40 0.019 0.0010 66 0.08 0.0005 2.97 1.92 B 372 Inventive Example 51 3.40 0.019 0.0019 20 0.50 0.0005 2.97 1.93 A 352 Inventive Example 52 3.40 0.019 0.0010 MgO as a main agent was not obtained Comparative Example 53 9.60 0.019 0.0019 50 0.20 0.0005 2.97 1.94 C 344 Comparative Example 54 3.40 0.017 0.0038 66 0.34 0.0005 2.97 1.93 A 380 Inventive Example 55 3.40 0.006 0.0040 35 1.90 0.0005 2.97 1.94 A 365 Inventive Example 56 3.40 0.024 0.0010 35 0.11 0.0005 2.97 1.92 B 373 Inventive Example 57 3.40 0.010 0.0019 15 1.21 0.0005 2.97 1.94 A 388 Inventive Example

[0138] In the example of No. 41, the B content in the obtained MgO particles was less than 0.005 mass %, and the external appearance and the coating tension of the grain-oriented electrical steel sheet manufactured using the MgO particles were poor.

[0139] In the example of No. 42, the B content in the obtained MgO particles was more than 0.040 mass %, and the external appearance of the grain-oriented electrical steel sheet manufactured using the MgO particles was poor.

[0140] In the examples of Nos. 43 and 44, the [Al]/[BO.sub.3] value of the obtained MgO particles was out of the range of the above formula (1), and B8 and the external appearance of the grain-oriented electrical steel sheet were poor.

[0141] In the examples of Nos. 45 to 51 and 54 to 57, the Al content contained in the MgO particles or the entire mixed powder was 0.0007 mass % or more and 0.050 mass % or less, the B content was 0.005 mass % or more and 0.040 mass % or less, the average particle size of the MgO particles or the mixed powder was 0.08 m or more and 9.0 m or less, the [Al]/[BO.sub.3] value of the MgO particles or the mixed powder was within the range of the above formula (1), and a grain-oriented electrical steel sheet having excellent magnetic characteristics, external appearance, and coating tension of the grain-oriented electrical steel sheet was obtained. In addition, in Nos. 45 to 47, 49, 51, 54, 55, and 57, the [Al]/[BO.sub.3] value was within 0.15 to 4.00, and therefore the external appearance characteristics were particularly excellent.

[0142] In the example of No. 52, since the baking temperature was too low, baking of the raw material powder was insufficient, and MgO as a main agent was not obtained.

[0143] In the example of No. 53, since the baking temperature was too high, the particle size of the mixed powder was too large, and the external appearance and the coating tension of the grain-oriented electrical steel sheet were poor.

Example 4

[0144] Raw material powders shown in Table 7 were baked under conditions shown in Table 7 to produce mixed powders shown in Table 8. Using the produced mixed powders, grain-oriented electrical steel sheets were manufactured in the same manner as in Example 2.

[0145] The B content, the Al content, the Cl content, and the BO.sub.3 content, and the proportion of tri-coordinated boron in B (BO.sub.3 ratio) in the raw material powder and the mixed powder were measured in the same manner as in Example 1. In addition, the BO.sub.3 content with respect to the mass of the raw material powder was determined by multiplying the B content determined by ICP-MS by the proportion of tri-coordinated boron in B. In addition, magnetic characteristics (B8), external appearance, and coating tension of each of the manufactured grain-oriented electrical steel sheets were evaluated in the same manner as in Example 1. The results are shown in Table 8.

TABLE-US-00007 TABLE 7 Raw material powder B-containing raw Mg-containing raw material particles material particles Raw material Blending Blending particle size B Al ratio B ratio B No. Raw material type m mass % mass % mass % compound mass % mass % 58 Mg(OH).sub.2 2.5 0.0010 0.005 99.950 Na.sub.2B.sub.4O.sub.7 0.050 21.49 59 Mg(OH).sub.2 2.5 0.0010 0.005 94.930 Na.sub.2B.sub.4O.sub.7 0.050 21.49 60 Mg(OH).sub.2 2.5 0.0080 0.005 94.990 61 Mg(OH).sub.2 2.5 0.0008 0.001 99.820 Na.sub.2B.sub.4O.sub.7 0.180 21.49 62 Mg(OH).sub.2 2.5 0.0010 0.005 99.990 63 Mg(OH).sub.2 2.5 0.0010 0.005 99.950 Na.sub.2B.sub.4O.sub.7 0.050 21.49 64 Mg(OH).sub.2 2.5 0.0010 0.005 99.950 Na.sub.2B.sub.4O.sub.7 0.005 21.49 65 Mg(OH).sub.2 2.5 0.0010 0.005 99.950 Na.sub.2B.sub.4O.sub.7 0.050 21.49 66 Mg(OH).sub.2 2.5 0.0010 0.005 99.950 Na.sub.2B.sub.4O.sub.7 0.050 21.49 67 Mg(OH).sub.2 2.5 0.0110 0.005 99.990 21.49 68 MgCO.sub.3 2.5 0.0080 0.004 99.980 21.49 69 mMgCO.sub.3Mg(OH).sub.2nH.sub.2O 2.5 0.0130 0.005 99.970 21.49 70 Mg(OH).sub.2 2.5 0.0010 0.005 99.970 B.sub.2O.sub.3 0.030 31.03 71 Mg(OH).sub.2 2.5 0.0010 0.005 99.996 B 0.004 100.00 72 Mg(OH).sub.2 2.5 0.0010 0.005 99.940 Na.sub.2B.sub.4O.sub.7 0.050 21.49 73 Mg(OH).sub.2 2.5 0.0010 0.005 99.942 Na.sub.2B.sub.4O.sub.7 0.050 21.49 74 MgCO.sub.3 + 2.5 0.0140 0.004 99.950 Na.sub.2B.sub.4O.sub.7 0.050 21.49 mMgCO.sub.3Mg(OH).sub.2nH.sub.2O + Mg(OH).sub.2 Raw material powder BO.sub.3 content Al-containing raw TiO.sub.2 with respect material particles particles to mass of Baking condition Blending Blending raw material B Temperature Time Al ratio Al ratio powder content Atmosphere C. min No. compound mass % mass % mass % mass % mass % Air 900 10 58 0.000 0.006 0.012 Air 900 10 59 Al.sub.2O.sub.3 0.020 52.9 5.000 0.006 0.012 Air 900 10 60 Al.sub.2O.sub.3 0.010 52.9 5.000 0.005 0.008 Air 900 10 61 0.000 0.026 0.039 Air 900 10 62 Al.sub.2O.sub.3 0.010 52.9 0.000 0.001 0.001 Air 900 10 63 0.000 0.006 0.012 Air 700 10 64 0.000 0.006 0.012 Air 1100 10 65 0.000 0.006 0.012 Air 650 10 66 0.000 0.006 0.012 Air 1150 10 67 Al.sub.2O.sub.3 0.010 52.9 0.000 0.005 0.011 Nitrogen 900 10 atmosphere 68 Al.sub.2O.sub.3 0.020 52.9 0.000 0.006 0.008 Air 900 10 69 Al.sub.2O.sub.3 0.030 52.9 0.000 0.006 0.013 Air 900 10 70 0.000 0.005 0.010 Air 900 10 71 0.000 0.008 0.005 Air 900 10 72 Al(OH).sub.3 0.010 34.6 0.000 0.006 0.012 Air 900 10 73 AlO(OH) 0.008 45.0 0.000 0.006 0.012 Air 900 10 74 0.000 0.012 0.025 Air 900 10

TABLE-US-00008 TABLE 8 Mixed powder Chemical component (remainder Grain-oriented Average is Mg, O, and impurities) electrical steel sheet particle BO.sub.3 Coating size B Al ratio [Al]/ Cl Ti B8 External tension No. [m] mass % mass % mass % [BO.sub.3] mass % mass % [T] appearance [g/mm.sup.2] Remarks 58 2.8 0.012 0.005 50 0.85 0.0005 0.00 1.94 A 398 Inventive Example 59 2.8 0.012 0.015 50 2.62 0.0005 2.97 1.93 A 405 Inventive Example 60 2.8 0.008 0.010 50 2.64 0.0005 2.97 1.95 A 392 Inventive Example 61 2.8 0.039 0.001 66 0.04 0.0005 0.00 1.91 C 355 Comparative Example 62 2.8 0.001 0.010 50 20.59 0.0005 0.00 1.91 C 366 Comparative Example 63 2.5 0.012 0.005 50 0.85 0.0005 0.00 1.92 A 372 Inventive Example 64 5.5 0.012 0.005 50 0.85 0.0005 0.00 1.93 A 355 Inventive Example 65 2.2 0.012 0.005 MgO as a main agent was not obtained Comparative Example 66 9.2 0.012 0.005 50 0.85 0.0005 0.00 1.92 C 342 Comparative Example 67 4.2 0.011 0.010 50 1.87 0.0005 0.00 1.94 A 392 Inventive Example 68 4.2 0.008 0.015 50 3.65 0.0005 0.00 1.93 A 388 Inventive Example 69 4.2 0.013 0.021 50 3.21 0.0005 0.00 1.94 A 372 Inventive Example 70 4.2 0.010 0.005 50 0.97 0.0005 0.00 1.94 A 362 Inventive Example 71 4.2 0.005 0.005 50 2.00 0.0005 0.00 1.94 A 365 Inventive Example 72 4.2 0.012 0.008 50 1.44 0.0005 0.00 1.94 A 370 Inventive Example 73 4.2 0.012 0.009 50 1.46 0.0005 0.00 1.93 A 399 Inventive Example 74 4.2 0.025 0.004 50 0.32 0.0005 0.00 1.92 A 382 Inventive Example

[0146] As shown in Nos. 58 to 60, 63, 64, and 67 to 74, in the mixed powder manufactured using a raw material powder containing B and Al, the Al content contained in the entire mixed powder was 0.0007 mass % or more and 0.050 mass % or less, the B content was 0.005 mass % or more and 0.040 mass % or less, and MgO particles satisfying the above formula (1) were obtained. As a result, a grain-oriented electrical steel sheet having excellent magnetic characteristics, external appearance, and coating tension of the grain-oriented electrical steel sheet was obtained. In addition, in Nos. 58 to 60, 63, 64, and 67 to 74, the [Al]/[BO.sub.3] value was within 0.15 to 4.00, and therefore the external appearance characteristics were particularly excellent.

[0147] In the examples of Nos. 61 and 62, the [Al]/[BO.sub.3] value of the obtained mixed powder was out of the range of the above formula (1), and B8 and the external appearance of the grain-oriented electrical steel sheet were poor.

[0148] In the example of No. 65, since the baking temperature was too low, baking of the raw material powder was insufficient, and MgO as a main agent was not obtained.

[0149] In the example of No. 66, since the baking temperature was too high, the particle size of the mixed powder was too large, and the external appearance and the coating tension of the grain-oriented electrical steel sheet were poor.