Grain-oriented electrical steel sheet, method for manufacturing grain-oriented electrical steel sheet, 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, 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 1

Description

Technical Field

[0001] The present invention relates to a grain-oriented electrical steel sheet, a method for manufacturing the grain-oriented electrical steel sheet, and an annealing separating agent.

Background Art

[0002] The grain-oriented electrical steel sheet contains about 2% to 5% by mass of Si, and is a steel sheet in which the orientation of crystal grains of the steel sheet is highly concentrated in the {110}<001> orientation called the Goss orientation. The grain-oriented electrical steel sheet has excellent magnetic properties and is used, for example, by being laminated as a core material of a static inductor such as a transformer.

[0003] In such a grain-oriented electrical steel sheet, various developments have been made to improve the magnetic properties. In particular, with the recent demand for energy conservation, further reduction of iron loss is required for the grain-oriented electrical steel sheet. To reduce the iron loss of the grain-oriented electrical steel sheet, it is effective to increase the degree of aggregation in the Goss orientation of the orientation of crystal grains of the steel sheet to improve the magnetic flux density and reduce the hysteresis loss.

[0004] Here, in the manufacture of the grain-oriented electrical steel sheet, control of the crystal orientation is performed by utilizing a catastrophic grain growth phenomenon called secondary recrystallization. However, in order to appropriately control the crystal orientation by secondary recrystallization, it is important to improve the heat resistance of fine precipitates in the steel called inhibitors.

[0005] As a method for controlling the crystal orientation, for example, a method in which an inhibitor is completely dissolved during heating of a steel slab before hot rolling, and then finely precipitated during hot rolling and a subsequent annealing process can be mentioned. Specifically, a method in which MnS and AlN as exemplified in Patent Document 1 below are used as inhibitors and rolling is performed with a rolling reduction rate exceeding 80% in the final cold rolling process, or a method in which MnS and MnSe as exemplified in Patent Document 2 below are used as inhibitors and two cold rolling processes are performed can be mentioned.

[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 plate. Since improved magnetic flux density also reduces iron loss, the practical application of Bi-added steel is expected.

[0007] Furthermore, when constructing an iron core by laminating grain-oriented electrical steel sheets, which have their magnetic properties improved by applying tension to the steel sheets, 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 during 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 technology 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. Patent document 7 below discloses a technology to achieve both magnetic properties and coating adhesion by precipitating BN during hot rolling. [Prior art documents] [Patent Documents]

[0008] [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 [Patent Document 7] International Publication No. 2012 / 096350 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] 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.

[0010] However, the technologies disclosed in the above-mentioned Patent Documents 4 to 6 alone are insufficient to resolve the problem of the primary coating peeling off the steel sheet when the degree of bending or shearing of the product sheet is increased, or when the amount of Bi added to the molten steel is increased. Therefore, there has been a need for technologies that can improve the adhesion between the primary coating and the steel sheet. Furthermore, although the technology disclosed in Patent Document 7 forms BN precipitates in the base steel sheet, the conditions for the finish annealing process are not specified. As a result, there is a concern that the BN precipitates may remain in a fine state in the grain-oriented electrical steel sheet after the final process, degrading the hysteresis loss.

[0011] Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide grain-oriented electrical steel sheets, a method for manufacturing grain-oriented electrical steel sheets, and an annealing separating agent that can improve the adhesion between the primary coating and the base steel sheet and further suppress hysteresis loss degradation. [Means for solving the problem]

[0012] To solve the above problems, according to one aspect of the present invention, the composition by mass is as follows: C: 0.0050% or less, Si: 2.5~4.5%, Mn: 0.01~0.15%, B: 0.0005~0.0200%, N: 0.0005~0.0100% 、T i: 0.0010~0.0050%, Bi:0~0.0500%, Cu:0~0.30%, Sn:0~0.30%, Ni:0~0.30%, Cr:0~0.30%, and Sb:0~0.30%, It contains, with the remainder being Fe and impurities. Consists of The device comprises a base steel sheet, a primary coating formed on the surface of the base steel sheet and containing Mg2SiO4 as the main component, and an insulating coating formed on the surface of the primary coating. Hysteresis loss W when the base steel plate on which the primary coating and the insulating coating are formed is excited to 1.7T h A grain-oriented electrical steel sheet is provided that satisfies the following formula (1) in terms of (W / kg), and has a coating peeling area ratio of 10% or less in a bending adhesion test of 10 mmφ. W h ≤ (-V B8 ×2.5+5.3) ··· Formula (1) Here, V B8 This is the magnetic flux density when a magnetic field of 800 A / m is applied at 50 Hz to the base steel plate on which the primary coating and the insulating coating are formed.

[0013] In the aforementioned grain-oriented electrical steel sheet, the base steel sheet may contain BN precipitates in the steel, and the average particle size of the BN precipitates may be 0.8 μm or more.

[0014] In the grain-oriented electrical steel sheet, the base steel sheet may further contain 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%, and Sb: 0.01% to 0.30% by mass.

[0015] Furthermore, according to another aspect of the present invention, an annealing separating agent applicable to the manufacture of the grain-oriented electrical steel sheet described above, wherein MgO As a main componentIt contains, and with respect to the MgO content, the Ti compound is present in mass %, equivalent to 0.3% to 10.0% of the contained Ti, the B compound is present in mass %, equivalent to 0.03% to 1.60% of the contained B, and the rare earth metal compound is present in mass %, equivalent to 0.1% to 10% of the rare earth metal, and when the Ti content of the Ti compound is A (mass %) and the B content of the B compound is B (mass %), the following formula (2) 0.33 ≦ (A+B) ≦ 10.30 ··· Formula (2) An annealing separating agent that satisfies the requirements is provided.

[0016] Furthermore, according to another aspect of the present invention, a method for manufacturing grain-oriented electrical steel sheet as described above, comprising 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, heated to 1280°C or higher. The process includes: heating and hot rolling to produce a hot-rolled steel sheet; hot-rolled annealing of the hot-rolled steel sheet, followed by one cold-rolling or two or more cold-rollings with an intermediate annealing in between to produce a cold-rolled steel sheet; primary recrystallization annealing of the cold-rolled steel sheet; applying an annealing separation agent containing MgO to the surface of the cold-rolled steel sheet after primary recrystallization annealing, followed by finish annealing; and applying an insulating coating to the steel sheet after finish annealing, followed by planarization annealing, wherein the annealing separation agent contains MgO. As a main component It contains, in terms of mass%, a Ti compound at 0.3% to 10.0% of the total Ti content, a B compound at 0.03% to 1.60% of the total B content, and a rare earth metal compound at 0.1% to 10% of the total rare earth metal content, where A (mass%) is the Ti content of the Ti compound and B (mass%) is the B content of the B compound, then the following formula (2) 0.33≦ (A+B) ≦ 10.30 ··· Formula (2) The following equation satisfies the conditions, and the residence time T(h) in the finish annealing at a temperature of 1100°C or higher and with a nitrogen concentration of 10 vol% or less in the atmosphere is given by the following formula (3) (5+9×B) ≦ T ≦ 100 ··· Formula (3) A method for manufacturing grain-oriented electrical steel sheets is provided, characterized in that the conditions are met and the stirring in the preparation of the aqueous slurry of the annealing separating agent is carried out at a temperature of 0°C to 30°C for a period of 5 minutes to 300 minutes.

[0017] The annealing separating agent further contains one or more alkaline earth metal compounds comprising one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, The content of the alkaline earth metal compound may be 0.3% by mass or more and 5.8% by mass or less in terms of the alkaline earth metal, relative to the content of MgO.

[0018] The slab may further contain Bi: 0.0005% or more and 0.0500% or less.

[0019] The slab may further contain 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%, and Sb: 0.01% to 0.30%, in mass%.

[0020] With the above configuration, by including a Ti compound, a rare earth metal compound, and a B compound in the annealing separation agent, the adhesion between the primary coating and the base steel sheet is improved. Furthermore, by controlling the high-temperature holding conditions during finish annealing, it is possible to suppress the deterioration of hysteresis loss. [Effects of the Invention]

[0021] As described above, according to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet that has even better adhesion between the primary coating and the steel sheet, suppresses deterioration of hysteresis loss, and has an even better magnetic flux density. [Brief explanation of the drawing]

[0022] [Figure 1] Tables 1 and 2 are graphs plotting the results shown, with the B (percentage) content of the B compound in the annealing separation agent plotted on the horizontal axis and the Ti (percentage) content of the Ti compound plotted on the vertical axis. [Modes for carrying out the invention]

[0023] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0024] The inventors of the present invention have diligently studied methods for manufacturing grain-oriented electrical steel sheets in order to further improve the adhesion between the primary coating and the steel sheet, while also improving the magnetic properties, and have found the following findings.

[0025] Specifically, the inventors have found that in grain-oriented electrical steel sheets, while the inclusion of Bi in the molten steel is expected to improve the heat resistance of the inhibitor and thus the magnetic flux density, the adhesion between the primary coating and the steel sheet deteriorates. However, by including Ti compounds, B compounds, and rare earth metal compounds in the annealing release agent, the adhesion between the primary coating and the steel sheet can be further improved. On the other hand, when none of the Ti compounds, B compounds, or rare earth metal compounds were included in the annealing release agent, the adhesion between the primary coating and the steel sheet did not improve.

[0026] On the other hand, it was found that hysteresis loss may deteriorate if the annealing separating agent contains Ti compounds, B compounds, and rare earth metal compounds. Therefore, the inventors investigated how to suppress the deterioration of hysteresis loss and found that by controlling the content of Ti compounds and B compounds in the annealing separating agent, as well as controlling the high-temperature holding conditions in finish annealing, it is possible to suppress the deterioration of hysteresis loss and improve the adhesion between the primary coating and the steel sheet.

[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 inhibitors during the secondary recrystallization process. Specifically, if the annealing separation agent contains compound B, the compound B contained in the annealing separation agent decomposes during the secondary recrystallization process while the temperature is being raised during finish annealing, causing B (boron) to penetrate into the steel. At the same time, nitrogen contained in the annealing atmosphere causes nitriding of the steel sheet, forming precipitates of BN in the steel, and degrading the hysteresis loss. However, it is presumed that by controlling the high-temperature holding conditions during finish annealing, the BN undergoes Ostwald growth to reach a size of 0.8 μm or larger, thereby suppressing the degradation of the hysteresis loss.

[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%, total of one or two of S and Se: 0.001% to 0.050%, acid-soluble Al: 0.01% to 0.05%, N: 0.002% to 0.015%, with the remainder being Fe and impurities, is subjected to heating at 1280°C or higher. The process involves heating and hot-rolling to produce a hot-rolled steel sheet, hot-rolled steel 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, primary recrystallization annealing of the cold-rolled steel sheet, applying a predetermined annealing release agent containing MgO to the surface of the cold-rolled steel sheet after primary recrystallization annealing, and then performing finish annealing, and after finish annealing... A method for producing grain-oriented electrical steel sheets with good coating adhesion and magnetic properties, comprising the steps of applying an insulating film to a steel sheet and then performing planar annealing, wherein the annealing separating agent contains MgO, and with respect to the MgO content, contains a Ti compound in mass %, equivalent to 0.3% to 10.0% of the contained Ti, a B compound in mass %, equivalent to 0.03% to 1.60%, and a rare earth metal compound in mass %, equivalent to 0.1% to 10%, and when the Ti content of the Ti compound is A (%) and the B content of the B compound is B (%), the following formula (2) is satisfied, and the residence time T (h) in the finish annealing at 1100°C or higher and with a nitrogen concentration of 10 vol% or less in the atmosphere satisfies the following formula (3). 0.33 ≦ (A+B) ≦ 10.30 ··· Formula (2) (5+9×B) ≦ T ≦ 100 ··· Formula (3)

[0030] 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%". In addition, the remainder of the slab, other than the elements described below, contains 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. 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 will become 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 sheets manufactured using a method that incorporates Bi (bismuth) into the slab.

[0039] Generally, when Bi is included in the slab component, the adhesion between the primary coating and the steel sheet deteriorates. Although the details of this mechanism are not clear, 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, and the adhesion problem can be resolved. By applying the present invention, good adhesion can be ensured even in steel sheets where the heat resistance of the inhibitor is strengthened by the Bi content of the slab, thereby improving the magnetic flux density.

[0040] In this case, the Bi content is preferably 0.0005% to 0.0500%. Bi is thought to enhance the heat resistance of inhibitors such as MnS and AlN, thereby raising the secondary recrystallization temperature and improving the magnetic flux density. When the Bi content is 0.0005% to 0.05%, 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 0.0005% to 0.0500%. More preferably, the Bi content is 0.0010% to 0.0200%. Note that since Bi is not necessarily essential in the slab used in the grain-oriented electrical steel sheet according to this embodiment, 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%. If the content of each of these elements is less than 0.01%, it becomes difficult to obtain a sufficient effect in stabilizing secondary recrystallization, which is undesirable. On the other hand, if the content of each of these elements exceeds 0.30%, the effect in stabilizing secondary recrystallization becomes saturated, which is undesirable from the viewpoint of suppressing an increase in manufacturing costs. Since these elements are not necessarily essential in the slab used in the grain-oriented electrical steel sheet according to this embodiment, 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 solid-solve. If the heating temperature of the slab is below 1280°C, it becomes difficult to sufficiently dissolve inhibitor components such as MnS, MnSe, and AlN. There is no specific 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. This process is also called primary recrystallization annealing. Rapid heating during the heating process in decarburization annealing is also effective in improving magnetic properties. When rapid heating is used, it is preferable from the viewpoint of manufacturing costs to perform the rapid heating and decarburization annealing consecutively. Decarburization annealing can be carried out by known methods, but it is preferable to carry it out at a temperature of 900°C or lower in a humid atmosphere containing hydrogen and nitrogen, for example. In this process, 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] (Annealing separating agent application 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 50.0% by mass or more. For example, MgO is present at a concentration of 50.0% by mass or more relative to the total mass of the materials constituting the annealing separation agent. The MgO content is 50.0% by mass or more and 99.57% by mass or less, preferably 70.0% by mass or more and 99.0% by mass or less, relative to the total mass of the materials constituting the annealing separation agent. In addition to MgO, Ti compounds and rare earth metal compounds are also contained, and alkaline earth metal compounds, Al compounds, Fe compounds, Si compounds, etc., may also be contained. The annealing separation agent is contained in water and applied to the surface of the steel sheet in slurry form and dried, but it may also be applied using electrostatic coating or the like. 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 the following compounds contained in the annealing separation agent is given as mass % relative to 100% MgO, the main component of the annealing separation agent.

[0050] In the method for manufacturing grain-oriented electrical steel sheets according to this embodiment, the content of rare earth metal compounds in the annealing separation agent is 0.1% to 10.0% 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 and promote the formation of an embedded structure between the primary film and the steel sheet, thereby improving the adhesion between the primary film and the steel sheet. However, if the content of the rare earth metal compounds is less than 0.1%, the effect of improving adhesion is insufficient, and if the content of the rare earth metal compounds exceeds 10.0%, the coatability of the annealing separation agent slurry deteriorates, which is undesirable. Therefore, the content of the rare earth metal compounds is set to 0.1% to 10.0% in terms of rare earth metals. Preferably, the content of the rare earth metal compounds is 0.2% to 8.0% in terms of rare earth metals. The rare earth metal compound may be a mixture of one or more compounds selected from the group consisting of oxides, sulfides, sulfates, silicides, phosphates, hydroxides, carbonates, borides, chlorides, and fluorides. From the viewpoint of availability and cost, compounds of La, Ce, and Y are preferred.

[0051] In the above annealing separation agent, the content of compound B is between 0.03% and 1.60% 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 the adhesion of the primary film 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. Furthermore, by setting the content of compound B to between 0.03% and 1.60% in terms of B equivalent, it is possible to suppress the excessive diffusion of B contained in the annealing separation agent into the steel during finish annealing. Therefore, the content of compound B shall be 0.03% to 1.60% in terms of B equivalent. Preferably, the content of compound B shall be 0.05% to 1.60% in terms of B equivalent. Compound B is not particularly limited, but is preferably BN, H3BO3, B2O3, Na2B4O7·10H2O, or TiB2.

[0052] In the above annealing separating agent, the Ti compound content is 0.3% to 10.0% in terms of Ti equivalent. 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 equivalent, the effect of improving adhesion is insufficient. If the Ti compound content is more than 10.0% in terms of Ti equivalent, 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 hysteresis loss (magnetic aging), which is undesirable. Therefore, the Ti compound content should be 0.3% to 10.0% in terms of Ti equivalent. Preferably, the Ti compound content is 0.3% to 8.0% in terms of Ti equivalent. The Ti compound is not particularly limited, but is preferably TiN, TiO2, Ti2O3, or Ti3O5.

[0053] By including Ti compounds, B compounds, and rare earth metal 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, the Ti compounds and B compounds decompose and penetrate into the primary coating or the interface between the primary coating and the steel sheet or its vicinity, forming Ti compounds and / or B compounds. This contributes to the complexity of the interface structure between the primary coating and the steel sheet, thereby exhibiting an anchoring effect. Furthermore, as mentioned above, the rare earth metal compounds are presumed to improve the adhesion between the primary coating and the steel sheet by releasing oxygen during the finish annealing and promoting the formation of an embedded structure between the primary coating and the steel sheet.

[0054] Here, it was found that if the Ti compound content in the annealing separation agent is too high, the decomposition of the Ti compound into the steel sheet progresses during the finish annealing process, and later forms fine precipitates such as TiC in the steel, which can degrade the hysteresis loss (magnetic aging). Therefore, the Ti equivalent content of the Ti compound in the annealing separation agent is set to A%, and the B equivalent content of the B compound is set to B%, and the sum of the Ti equivalent content of the Ti compound and the B equivalent content of the B compound (A+B) is set to be between 0.33% and 10.30%. If the sum of the Ti equivalent content of the Ti compound and the B equivalent content of the B compound (A+B) is less than 0.33%, the effect of improving adhesion is insufficient. If the sum of the Ti equivalent content of the Ti compound and the B equivalent content of the B compound (A+B) is greater than 10.30%, Ti and / or B may solid dissolve into the steel sheet during the finish annealing process, later forming precipitates such as TiC, TiN, and BN in the steel, or nitrogen may penetrate from the atmosphere into the steel during finish annealing, forming nitrides in the steel and degrading hysteresis loss (magnetic aging), which is undesirable. Therefore, the sum of the Ti equivalent content of the Ti compound and the B equivalent content of the B compound (A+B) should be between 0.33% and 10%. Preferably, the sum of the Ti equivalent content of the Ti compound and the B equivalent content of the B compound (A+B) is between 0.35% and 8.30%.

[0055] The above annealing separating agent may further contain 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, wherein the content of the alkaline earth metal compounds may be 0.3% to 5.8% by mass relative to the content of MgO in terms of alkaline earth metal. The alkaline earth metal compounds are effective in further improving magnetic properties and coating adhesion. By having a total content of 0.3% to 5.8% relative to the content of MgO in terms of alkaline earth metal, the magnetic property improvement effect and coating adhesion improvement effect can be obtained more effectively. If the total content of 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, is less than 0.3% relative to the content of MgO in terms of alkaline earth metal, the magnetic property improvement effect and coating adhesion improvement effect may not be sufficiently obtained. If 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 exceeds 5.8% in terms of alkaline earth metal content relative to the MgO content, secondary recrystallization becomes unstable, and V B8 The values ​​may deteriorate. Furthermore, since 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 not necessarily essential in annealing separation agents, the lower limit of their content is 0%. If the annealing separating agent contains two or more alkaline earth metal compounds, the content of the alkaline earth metal compounds is the sum of the converted values ​​of each of the contained alkaline earth metal elements.

[0056] 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. 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 contained 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 types of 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 in the annealing separation agent may be measured using a component analysis device such as inductively coupled plasma mass spectrometry (ICP-MS). 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.

[0057] The annealing separation agent according to this embodiment contains at least MgO, a Ti compound, a rare earth metal compound, and a B compound. However, the rare earth metal compound has a high specific gravity, while the B compound has a low specific gravity. Therefore, when preparing an aqueous slurry, it is necessary to stir the mixture to suppress precipitation and suspension and ensure uniform mixing. The stirring in the preparation of the aqueous slurry of the annealing separation agent is carried out at a temperature of 0°C to 30°C for a time of 5 minutes to 300 minutes. If the temperature of the aqueous slurry 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 temperature of the aqueous slurry is above 30°C, the viscosity of the slurry will be high, and the materials constituting the annealing separation agent 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 mixing of the compounds contained in the slurry will be insufficient, 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. Stirring in the preparation of the aqueous slurry for annealing separation agents should be carried out at a temperature between 0°C and 30°C for a time between 5 minutes and 300 minutes.

[0058] For example, the total mass of the materials constituting the annealing separator in the aqueous slurry state is not particularly limited as long as it does not affect the workability of the coating process, and can be, for example, 5% by mass or more and 30% by mass or less of the total mass of the aqueous slurry.

[0059] 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.

[0060] 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.

[0061] (Finishing annealing process) Next, finish annealing is performed for the purpose of primary film formation and secondary recrystallization. In finish annealing, a primary film mainly composed of Mg2SiO4 is formed on the surface of the base steel sheet. Finish annealing is preferably performed by heating the coiled steel sheet at a temperature of 800°C to 1000°C for 10 hours or more, for example, using a batch-type heating furnace. Alternatively, it may be held at a specific temperature. Furthermore, in order to further reduce the iron loss of the final grain-oriented electrical steel sheet, purification annealing may be performed, in which the coiled steel sheet is heated to a temperature of approximately 1200°C and then held.

[0062] 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.

[0063] Here, it was found that the hysteresis loss of the steel sheet can deteriorate significantly depending on the high-temperature holding conditions during the finish annealing process. As a result of a detailed investigation of the steel sheet with deteriorated hysteresis loss, the inventors discovered for the first time that many fine BN precipitates were formed in the steel. These fine BN precipitates were not present in the steel at the time of hot-rolling, but rather, during the finish annealing process, B (boron) penetrated into the steel from the annealing separating agent and N (nitrogen) penetrated from the annealing atmosphere, forming BN precipitates in the steel, and it is believed that these fine BN precipitates are the cause of the deterioration of hysteresis loss.

[0064] The inventors conducted detailed studies on the conditions of the finish annealing process, but were unable to remove the BN precipitates formed in the steel from the steel again by purification annealing or the like. Therefore, as a result of further investigation, they found that the deterioration of hysteresis loss could be suppressed by coarsening the fine BN precipitates formed in the steel through grain growth. In other words, by strictly controlling the high-temperature holding conditions in the finish annealing process according to the B equivalent value of the amount of B compound contained in the annealing separation agent, they succeeded in coarsening the BN precipitates formed in the steel.

[0065] The high-temperature holding temperature in the finish annealing process should be 1100°C or higher. Below 1100°C, grain growth of BN precipitates is slow, making it difficult to coarse them. There is no specific upper limit, but from the viewpoint of equipment maintenance, 1250°C or lower is preferable. The high-temperature holding temperature in the finish annealing process is preferably 1120°C or higher. The atmosphere during high-temperature holding should have a nitrogen concentration of 10 vol% or less. If the nitrogen concentration exceeds 10 vol%, nitrogen will penetrate into the steel from the atmosphere, increasing not only the amount of BN and TiN precipitates in the steel, but also leaving AlN precipitates, thus degrading the hysteresis loss. The nitrogen concentration during high-temperature holding is preferably 8 vol% or less. Since a lower nitrogen concentration during high-temperature holding is preferable, there is no specific lower limit.

[0066] The residence time T(h) during high-temperature holding is strictly controlled according to the B equivalent value B(%) of the amount of B compound in the annealing separation agent. The more boron that penetrates into the steel from the annealing separation agent, the greater the amount of BN precipitates formed in the steel. Therefore, to suppress hysteresis loss degradation, it is necessary to further grow the grain size of the BN precipitates to make them coarser. Thus, the residence time T during high-temperature holding should be between (5+9×B)h and 100h. If it is less than (5+9×B)h, the grain growth of the BN precipitates is insufficient, and the suppression of the hysteresis loss effect of the BN precipitates in the steel is insufficient, which is undesirable. If it exceeds 100h, the annealing takes a long time, which increases production costs, and is therefore undesirable. Based on the above, the residence time T(h) during the finish annealing process should be between (5+9×B)h and 100h at a temperature of 1100°C or higher and a nitrogen concentration of 10 vol% or less in the atmosphere. The residence time T is preferably (6 + 9 × B) hours or more and 80 hours or less.

[0067] The high-temperature holding in the finish annealing process may also serve as part or all of the purification annealing described above. Furthermore, the atmospheric gas composition in processes other than the high-temperature holding is not particularly limited. In 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.

[0068] (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 / or 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.

[0069] 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.

[0070] 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, in particular, is 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, it is preferable that the coating delamination area ratio in a 10mmφ bending adhesion test is 10% or less.

[0071] 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.

[0072] [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. Furthermore, an insulating coating is provided on the surface of the primary coating.

[0073] (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 composition of the base steel sheet of the grain-oriented electrical steel sheet. Unless otherwise specified, the notation "%" for the chemical composition of the steel sheet represents "mass%". The notation "%" for the gas composition represents "vol%".

[0074] 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%.

[0075] 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%.

[0076] 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%.

[0077] B is an element that forms BN precipitates in the base steel sheet, and may be contained in the slab in a range of 0.0080% or less, for example. If the B content of the slab exceeds 0.0080%, secondary recrystallization becomes unstable, which is undesirable. The B content of the slab is more preferably 0.0050% or less, and even more preferably 0.0020% or less. There is no lower limit, but the B content of the slab may be 0.0001% or more. In addition to what was contained in the slab, B compounds and impurities contained in the annealing separating agent decompose in the finish annealing process and penetrate into the steel, thereby becoming contained in the base steel sheet. The more B compounds contained in the annealing separating agent, the more B is contained in the base steel sheet. In the grain-oriented electrical steel sheet according to this embodiment, B is contained in the base steel sheet in a range of 0.0005% to 0.0200% by mass. It is preferable that B be contained in the base steel sheet in a range of 0.0010% to 0.0150%. If the B content of the base steel sheet is less than 0.0005%, it is undesirable because a sufficient improvement in coating adhesion cannot be obtained. If the B content of the base steel sheet exceeds 0.0200%, it is undesirable because not only does the improvement in coating adhesion saturate, but the amount of BN precipitates formed in the steel increases, raising concerns about deterioration of hysteresis loss.

[0078] In conventional technology, nitrogen (N) is preferably discharged from the steel during the purification process of the finish annealing stage to suppress the degradation of hysteresis loss. In this technology, Ti and B compounds contained in the annealing release agent for the purpose of improving film adhesion decompose during the finish annealing stage, and B and Ti penetrate into the steel. At this time, N in the finish annealing atmosphere also penetrates into the steel, and AlN, which is a precipitate in the steel, decomposes to form solid-solution N in the steel, forming BN precipitates and TiN precipitates in the steel, so N is contained in the base steel sheet. The more Ti and B compounds contained in the annealing release agent, the more N is contained in the base steel sheet. The N content of the base steel sheet is between 0.0005% and 0.0100%. If the N content of the base steel sheet exceeds 0.0100%, not only does the coating adhesion improvement effect saturate, but the amount of BN precipitates and TiN precipitates formed in the steel increases, raising concerns about deterioration of hysteresis loss, which is undesirable. On the other hand, a lower N content is preferable, but even if it is less than 0.0005%, the hysteresis reduction effect saturates, and long-term, high-temperature purification annealing is required, which only increases manufacturing costs. Therefore, the N content is 0.0005% or more. The N content of the steel sheet is preferably 0.0005% to 0.0085%, and more preferably 0.0005% to 0.0080%.

[0079] Ti is an element that is preferable to have in small amounts in the base steel sheet because it may form fine precipitates in the steel and degrade hysteresis loss. For example, Ti may be contained in the slab in a range of 0.0050% or less. If the Ti content of the slab exceeds 0.0050%, it is undesirable because it degrades hysteresis loss. The Ti content of the slab is preferably 0.0040% or less, and more preferably 0.0030% or less. There is no particular lower limit for the Ti content of the slab, but it may be 0.0005% or more. In this technology, the Ti compound contained in the annealing release agent for the purpose of improving film adhesion decomposes in the finish annealing process, and Ti penetrates into the steel. The more Ti compound contained in the annealing release agent, the more Ti the base steel sheet will contain. In the grain-oriented electrical steel sheet according to this embodiment, Ti is contained in the base steel sheet in a range of 0.0010% to 0.0050% by mass. It is more preferable that the base steel sheet contains Ti in the range of 0.0010% to 0.0040%. If the Ti content of the base steel sheet is less than 0.0010%, it is undesirable because a sufficient improvement in coating adhesion cannot be obtained. If the Ti content of the base steel sheet exceeds 0.0050%, it is undesirable because not only does the improvement in coating adhesion saturate, but the formation of TiN precipitates and TiC precipitates in the steel increases, raising concerns about deterioration of hysteresis loss.

[0080] The remainder of the chemical composition of the base steel sheet in 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 the raw materials (ore, scrap, or manufacturing environment) or the following elements that remain in the steel without being completely purified during the purification annealing process, and which are acceptable as long as they do not adversely affect the grain-oriented electrical steel sheet of the present invention.

[0081] The base steel sheet in the grain-oriented electrical steel sheet according to the present invention may contain Bi. In this case, the Bi content is preferably 0.0005% or more and 0.0500% or less. Bi is thought to have the effect of strengthening 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 0.0005% or more and 0.05% or less, an even greater inhibitor heat resistance strengthening effect can be obtained. If the Bi content is less than 0.0005%, a sufficient inhibitor heat resistance strengthening effect may not be obtained. If the Bi content is greater than 0.0500%, the brittleness of the steel sheet in hot rolling may deteriorate. Therefore, the Bi content is preferably 0.0005% or more and 0.0500% or less. The Bi content is more preferably 0.0010% or more and 0.0200% or less. Since Bi is not necessarily essential in the grain-oriented electrical steel sheet according to this embodiment, the lower limit of its content is 0%.

[0082] The base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may further contain one or more elements selected from the group consisting of Cu, Sn, Ni, Cr, and 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.

[0083] 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 becomes saturated, 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 the grain-oriented electrical steel sheets according to this embodiment, so the lower limit of their content is 0%.

[0084] As previously explained, the primary coating is formed on the surface of the base steel sheet and contains Mg2SiO4 as its main component. The Mg2SiO4 content of the primary coating is preferably 50% by mass or more, and more preferably 70% by mass or more, relative to the oxides forming the primary coating. From the viewpoint of primary coating adhesion and insulation, a higher Mg2SiO4 content formed on the surface of the base steel sheet is preferable, so no upper limit is particularly set.

[0085] The primary coating may contain, for example, Al compounds, sulfides, and Fe compounds. The presence or absence of an insulating coating and a primary coating can be confirmed, for example, in a grain-oriented electrical steel sheet after the sampling process, by mirror-polishing the cross-section, applying gold deposition to the mirror-polished surface, and using an energy-dispersive X-ray analyzer attached to a scanning electron microscope.

[0086] The main component of the primary coating can be measured, for example, in the grain-oriented electrical steel sheet after the final process, using an energy-dispersive X-ray analyzer attached to a scanning electron microscope or a fluorescent X-ray analyzer. Specifically, in the grain-oriented electrical steel sheet after the final process, after immersion in a hot alkaline aqueous solution, it is washed with water and dried to remove the insulating coating on the grain-oriented electrical steel sheet. Next, gold is vapor-deposited on the surface, and measurement using an energy-dispersive X-ray analyzer attached to a scanning electron microscope is performed to quantify an area of about 0.005 mm 2 and the main component of the primary coating can be measured. 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. Note that the analysis of the main component of the above primary coating may be performed after washing the steel sheet after finish annealing with water.

[0087] As described above, the insulating coating contains, as a main component, aluminum phosphate, colloidal silica, or the like. However, 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.

[0088] 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 as appropriate.

[0089] In the grain-oriented electrical steel sheet thus obtained, the hysteresis loss W h (W / kg) is set to (-V B8 ×2.5 + 5.3) W / kg or less. Here, V B8 is the magnetic flux density when a magnetic field of 800 A / m at 50 Hz is applied to the grain-oriented electrical steel sheet having the primary coating and the insulating coating on the surface of the base steel sheet. The hysteresis loss W h when excited up to 1.7 T is (-V B8If the value exceeds (×2.5 + 5.3), the hysteresis loss will be large and the iron loss will be inferior, which is undesirable. Since a lower hysteresis loss is preferable, no lower limit is specifically set. Reducing or coarsening precipitates in the steel, removing residual strain in the steel sheet, and improving orientation concentration are effective in reducing hysteresis loss. Note that since hysteresis loss is not affected by the steel sheet thickness as much as eddy current loss, the steel sheet thickness is not specifically specified in this invention, but it goes without saying that it is preferable for the eddy current loss to decrease as the thickness decreases. Note that the magnetic properties of grain-oriented electrical steel sheets, 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 the method based on the Epstein test specified in JIS C 2550:2011, or the Single Sheet Tester (SST) specified in JIS C 2556:2015. In research and development, if steel ingots are formed in a vacuum melting furnace or the like, it becomes difficult to take test pieces of the same size as those used in actual machine 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 magnetic properties test method. Furthermore, a correction factor may be applied to the obtained results so that measurements equivalent to those obtained using the Epstein test method can be obtained. In this embodiment, measurements are performed using a measurement method in accordance with the single-sheet magnetic properties test method.

[0090] For single-plate measurements, JIS C 2556:2015 can be used as a reference for measuring hysteresis loss, while JIS C 2550-1:2011 can be used as a reference for Epstein measurements. By sufficiently increasing the excitation time compared to normal commercial frequency measurements, eddy current losses can be suppressed, allowing for the measurement of hysteresis loss.

[0091] When the slab contains B and N, the B and N content decreases during finish annealing, so hysteresis loss is not degraded due to BN precipitates in the steel. On the other hand, when the annealing release agent contains B compound, although the adhesion of the primary film is improved, the amount of BN precipitates in the steel increases during finish annealing. Therefore, it was found that hysteresis loss may be slightly degraded compared to steel sheets obtained by finish annealing without applying an annealing release agent containing B compound.

[0092] Therefore, a detailed investigation of the base steel sheet revealed that in samples where the deterioration of hysteresis loss was suppressed, the BN precipitates in the steel were coarser. Thus, it is possible to suppress the increase in hysteresis loss by including BN precipitates with larger particle sizes in the steel. The average particle size of the BN precipitates in the steel is preferably 0.8 μm or larger, and more preferably 1.0 μm or larger. The average particle size can be adjusted by appropriately adjusting the B content in the slab, the B compound content in the annealing separating agent, or the finish annealing conditions within the above range.

[0093] The grain-oriented electrical steel sheet according to this embodiment has been described above. 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, it is not limited to that method. [Examples]

[0094] 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.

[0095] (Example 1) First, steel ingot A was prepared, containing, by mass%, C:0.08%, Si:3.2%, Mn:0.08%, S:0.024%, 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 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. The steel ingots were 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.

[0096] 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, a slurry of an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and after drying, it was heated to 1200°C in a batch-type heating furnace at a heating rate of 15°C / h and a nitrogen concentration of 50 vol% in the atmosphere. At 1200°C, the atmosphere was switched to a dry hydrogen atmosphere (nitrogen concentration 0 vol%) and held for 20 hours for finish annealing, and the steel sheet after finish annealing was washed with water. Here, the annealing separation agent contained 100% MgO, 0.55% CaSO4·0.5H2O (calculated as Ca), 2.0% CeO2 (calculated as Ce), and the remainder consisted of unavoidable impurities and compounds under the conditions shown in Tables 1-3. The stirring conditions for the annealing separation agent were 30 minutes at 10°C after adding the above compounds. The amount of annealing release agent applied after drying is 8 g / m² per side of the steel plate. 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.

[0097] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density V of the grain-oriented electrical steel sheet (sample after stress-relieving annealing) for each example of the present invention and comparative example was measured in accordance with the single-sheet measurement method described in JIS C2556:2015 for a sample with a sample size of 60 mm × 300 mm. B8Value, hysteresis loss W h and iron loss W 17 / 50 V was measured. B8 The value is the magnetic flux density of a grain-oriented electrical steel sheet when it is excited at 50 Hz with 800 A / m. h This is the hysteresis loss when a grain-oriented electrical steel sheet is excited to 1.7T. 17 / 50 This refers to the iron loss when grain-oriented electrical steel sheets are excited to 1.7T at 50Hz. In the present invention example, V was measured from 5 samples. B8 Value, W h and W 17 / 50 The average values ​​were calculated from each. The above samples were cut from grain-oriented electrical steel sheets after stress-relieving annealing so that the longitudinal direction of the grain-oriented electrical steel sheet before shearing matched the longitudinal direction of the sample.

[0098] 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 portion where the primary coating peeled off was measured for each. For each sample, the ratio of the area of ​​the peeled portion to the total area was defined as the coating peeling area ratio, and the average value was calculated from the coating peeling area ratios of the three test pieces.

[0099] Furthermore, in the grain-oriented electrical steel sheet after the final process, the presence or absence of a primary coating and an insulating coating was confirmed by component analysis using SEM-EDS measurement of the cross-section. In addition, the Mg2SiO4 content was measured by the following method: After washing the steel sheet with water after finish annealing, gold deposition was applied to the surface, and approximately 0.005 mm was measured using SEM-EDS. 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.

[0100] Furthermore, after the final processing stage, the insulating and primary coatings of the grain-oriented electrical steel sheets were removed, and the composition of the base steel sheet was analyzed using inductively coupled plasma atomic emission spectroscopy. The carbon (C) content was measured using a carbon-sulfur analyzer. The nitrogen (N) content was measured using an oxygen-nitrogen analyzer.

[0101] Here, the hysteresis loss W of the grain-oriented electrical steel sheet. h However, (-V B8 The condition was judged as good if the ratio was less than or equal to (×2.5 + 5.3) W / kg and the coating peeling area ratio in the 10 mmφ bending test was 10% or less.

[0102] Tables 1-3 show the manufacturing conditions and measurement results for the above-mentioned examples and comparative examples of the present invention. In Tables 1-3, a "○" indicates a good evaluation result, and a "×" indicates a poor result. Conditions A1-A30 in Table 1 are examples using steel ingot A, and conditions R1-R12 are examples using steel ingot R. In addition, in Tables 1-3, when compound B is TiB2, the "Ti compound equivalent content A [%]" is a value that also takes into account the Ti in TiB2.

[0103] [Table 1]

[0104] [Table 2]

[0105] [Table 3]

[0106] 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.

[0107] Referring to Tables 1-3, it was found that grain-oriented electrical steel sheets that satisfy the conditions of this embodiment yield a good result.

[0108] Here, Figure 1 shows a graph plotting the results for conditions A1 to A30 in Tables 1 and 2, with the B equivalent value B(%) of the B compound content in the annealing separation agent on the horizontal axis and the T equivalent value A(%) of the Ti compound content on the vertical axis. As shown in Figure 1, when the present invention example is plotted as a circle and the comparative example is plotted at the intersection, it was found that the following relationships (101), (102), and (103), defined by the conditions of this embodiment, hold between the B equivalent value B(%) of the B compound content in the annealing separation agent and the Ti equivalent value A(%) of the T compound content.

[0109] 0.3≦A≦10.0 ···Formula (101) 0.03≦B≦1.60 ···Formula (102) 0.33≦(A+B)≦10.30 ···Formula (103)

[0110] Thus, it was found that by containing a rare earth metal compound at an amount of 2.0% (in terms of the rare earth metal equivalent), and controlling the content of the Ti compound and the B compound to satisfy formulas (101), (102), and (103), it is possible to manufacture grain-oriented electrical steel sheets that suppress hysteresis loss degradation and have excellent adhesion between the primary coating and the steel sheet.

[0111] Furthermore, the B, N, and Ti content of the base steel sheet is shown in Tables 1 to 3. The component ranges that satisfy the conditions of this embodiment were B: 0.0005 to 0.0200%, N: 0.0005 to 0.0100%, and Ti: 0.0010 to 0.0050%. The C content of the base steel sheet was 0.0018%, the Si content was 3.1%, the Mn content was 0.08%, and the remainder was Fe and impurities, which remained the same regardless of the annealing separation agent conditions.

[0112] (Example 2) First, a steel ingot was prepared containing, by mass%, C:0.08%, Si:3.3%, Mn:0.09%, S:0.003%, Se:0.018%, acid-soluble Al:0.03%, N:0.008%, and Bi:0.02%, with the remainder being Fe and impurities. This 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.

[0113] Next, the obtained cold-rolled steel sheets were subjected to primary recrystallization annealing in a humid hydrogen atmosphere at 850°C for 180 seconds. Then, a slurry of an annealing separation agent containing MgO was applied to the surface of the steel sheets after primary recrystallization annealing, and after drying, the temperature was raised using a batch heating furnace at a heating rate of 15°C / h and a nitrogen concentration of 50 vol% in the atmosphere to the high-temperature holding temperatures shown in Tables 4 and 5. At each high-temperature holding temperature, finish annealing was performed in a dry atmosphere with the nitrogen concentration and the remainder being hydrogen as shown in Tables 4 and 5, and held for the time shown in Tables 4 and 5. After finish annealing, the steel sheets were washed with water. Here, the annealing separation agent contained 100% MgO, 0.55% CaCO3 (calculated equivalent), 2.0% Ce(OH)4 (Cecal equivalent), and the remainder being unavoidable impurities and compounds under the conditions shown in Tables 4 and 5. The stirring conditions for the annealing separation agent were 60 minutes at 5°C after adding the above compounds. The amount of annealing release agent applied after drying is 8 g / m² per side of the steel plate. 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.

[0114] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density V of the grain-oriented electrical steel sheet (sample after stress-relieving annealing) for each example of the present invention and comparative example was measured in accordance with the single-sheet measurement method described in JIS C2556:2015 for a sample with a sample size of 60 mm × 300 mm. B8 Value, hysteresis loss W h and iron loss W 17 / 50The following measurements were taken. The above sample was cut from a 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. Here, V B8 The value is the magnetic flux density of a grain-oriented electrical steel sheet when it is excited at 50 Hz with 800 A / m. h This is the hysteresis loss when a grain-oriented electrical steel sheet is excited to 1.7T. 17 / 50 This refers to the iron loss when grain-oriented electrical steel sheets are excited to 1.7T at 50Hz. In the present invention example, V was measured from 5 samples. B8 Value, W h and W 17 / 50 The average values ​​were calculated from these values.

[0115] 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 portion where the primary coating peeled off was measured for each. For each sample, the ratio of the area of ​​the peeled portion to the total area was defined as the coating peeling area ratio, and the average value was calculated from the coating peeling area ratios of the three test pieces.

[0116] Furthermore, in the grain-oriented electrical steel sheet after the final process, the presence or absence of a primary coating and an insulating coating, as well as the Mg2SiO4 content, were confirmed using the same method as in Example 1.

[0117] Furthermore, in the grain-oriented electrical steel sheet after the final processing, the cross-section was mirror-polished, and then BN precipitates in the steel were identified using wavelength-dispersive X-ray analysis attached to an electron beam microanalyzer. The rolling direction length was then measured by backscattered electron imaging. The average of the rolling direction lengths of five BN precipitates measured here was taken as the average grain size of the BN precipitates in the steel. Furthermore, after removing the insulating and primary coatings, the composition of the base steel sheet was analyzed using inductively coupled plasma atomic emission spectroscopy. The carbon (C) content was measured using a carbon-sulfur analyzer. The nitrogen (N) content was measured using an oxygen-nitrogen analyzer.

[0118] Here, the hysteresis loss W of the grain-oriented electrical steel sheet. h However, (-V B8The condition was judged as good if the ratio was less than or equal to (×2.5 + 5.3) W / kg and the coating peeling area ratio in the 10 mmφ bending test was 10% or less.

[0119] The manufacturing conditions for the above-mentioned examples of the present invention and comparative examples are shown in Tables 4 and 5, and the evaluation results are shown in Tables 6 and 7. In Tables 6 and 7, a "○" indicates a good evaluation result, and a "×" indicates a poor result.

[0120] [Table 4]

[0121] [Table 5]

[0122] [Table 6]

[0123] [Table 7]

[0124] 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.

[0125] Referring to Tables 4-7, it was found that grain-oriented electrical steel sheets that satisfy the conditions of this embodiment yield a good result.

[0126] Here, it was found that the following relationship, defined by formula (104) under the conditions of this embodiment, holds between the content B (%) of compound B in the annealing separating agent and the residence time T (h) in finish annealing at a temperature of 1100°C or higher and a nitrogen concentration in the atmosphere of 10 vol% or less.

[0127] (5+9×B) ≦ T ≦ 100 ··· Formula (104)

[0128] Thus, in the method for manufacturing grain-oriented electrical steel sheets according to this embodiment, it has been found that by controlling the B equivalent value of the B compound content in the annealing separating agent and the temperature, time, and atmosphere conditions during high-temperature holding so as to satisfy formula (104), it is possible to suppress hysteresis loss degradation and manufacture grain-oriented electrical steel sheets with excellent adhesion between the primary coating and the steel sheet.

[0129] Furthermore, the B, N, and Ti content of the base steel sheet is shown in Tables 6 and 7. The component ranges that satisfy the conditions of this embodiment were B: 0.0005 to 0.0200%, N: 0.0005 to 0.0100%, and Ti: 0.0010 to 0.0050%. The C content of the base steel sheet was 0.0019%, the Si content was 3.2%, the Mn content was 0.09%, and the remainder was Fe and impurities, which remained the same regardless of the annealing separation agent conditions. Tables 6 and 7 show the average particle size of BN precipitates in the steel. The average particle size range that satisfies the conditions of this embodiment was 0.8 μm or larger.

[0130] (Example 3) First, a steel ingot was prepared containing, by mass%, C:0.08%, Si:3.3%, Mn:0.09%, S:0.026%, acid-soluble Al:0.03%, N:0.009%, and Bi:0.02%, 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.

[0131] 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, a slurry of an annealing separator containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and after drying, it was heated to 1200°C in a batch heating furnace at a heating rate of 15°C / h and a nitrogen concentration of 50 vol% in the atmosphere. At 1200°C, the atmosphere was switched to a dry hydrogen atmosphere (nitrogen concentration 0 vol%) and held for 20 hours for finish annealing, after which the steel sheet was washed with water. Here, the annealing separator contained 100% MgO, 2.0% La2O3 (in terms of La), and the remainder consisted of unavoidable impurities and compounds under the conditions shown in Table 8. The stirring conditions for the annealing separator were 20°C for 100 minutes after adding the above compounds. The amount of annealing separator applied after drying was 8 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.

[0132] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density V of the grain-oriented electrical steel sheet (sample after stress-relieving annealing) for each example of the present invention and comparative example was measured in accordance with the single-sheet measurement method described in JIS C2556:2015 for a sample with a sample size of 60 mm × 300 mm. B8 Value, hysteresis loss W h and iron loss W 17 / 50 The following measurements were taken. The above sample was cut from a 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. Here, V B8 The value is the magnetic flux density of a grain-oriented electrical steel sheet when it is excited at 50 Hz with 800 A / m. h This is the hysteresis loss when a grain-oriented electrical steel sheet is excited to 1.7T. 17 / 50 This refers to the iron loss when grain-oriented electrical steel sheets are excited to 1.7T at 50Hz. In the present invention example, V was measured from 5 samples. B8 Value, W h and W 17 / 50 The average values ​​were calculated from these values.

[0133] 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 portion where the primary coating peeled off was measured for each. For each sample, the ratio of the area of ​​the peeled portion to the total area was defined as the coating peeling area ratio, and the average value was calculated from the coating peeling area ratios of the three test pieces.

[0134] Furthermore, in the grain-oriented electrical steel sheet after the final process, the presence or absence of a primary coating and an insulating coating, as well as the Mg2SiO4 content, were confirmed using the same method as in Example 1.

[0135] Furthermore, in the grain-oriented electrical steel sheet after the final processing stage, the cross-section was mirror-polished, and then BN precipitates in the steel were identified using wavelength-dispersive X-ray analysis attached to an electron beam microanalyzer. The rolling direction length of the BN precipitates was then measured by backscattered electron imaging. The average of the rolling direction lengths of five BN precipitates measured here was taken as the average grain size of the BN precipitates in the steel. Furthermore, after removing the insulating and primary coatings, the composition of the base steel sheet was analyzed using inductively coupled plasma atomic emission spectroscopy. The carbon (C) content was measured using a carbon-sulfur analyzer. The nitrogen (N) content was measured using an oxygen-nitrogen analyzer.

[0136] Here, the hysteresis loss W of the grain-oriented electrical steel sheet. h However, (-V B8 The conditions of having a hysteresis loss of (×2.5 + 5.3) W / kg or less, and a coating delamination area ratio of 10 mmφ bending test of 10% or less, were judged to be good. In addition, the hysteresis loss W of grain-oriented electrical steel sheets was judged to be less than 10%. h However, (-V B8 The magnetic flux density is less than or equal to (2.5 + 5.3) W / kg, the coating peeling area ratio in the 10mmφ bending test is 10% or less, and the magnetic flux density is V B8 The condition of having a value of 1.900T or higher was judged to be even better.

[0137] The manufacturing conditions for the above-mentioned examples of the present invention and comparative examples are shown in Table 8, and the evaluation results are shown in Table 9. In Table 9, a good evaluation result is indicated by "○", an even better result by "◎", and a poor result by "×".

[0138] [Table 8]

[0139] [Table 9]

[0140] 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.

[0141] Referring to Tables 8 and 9, it was found that grain-oriented electrical steel sheets that satisfy the conditions of this embodiment yield a good result.

[0142] Here, it was found that by controlling the amount 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 in the annealing separation agent to 0.3% to 5.8% in terms of alkaline earth metal equivalent, hysteresis loss degradation is suppressed, and it is possible to manufacture grain-oriented electrical steel sheets with excellent adhesion between the primary coating and the steel sheet, as well as good magnetic flux density.

[0143] Furthermore, the B, N, and Ti components of the base steel sheet are shown in Table 9. The component ranges that satisfy the conditions of this embodiment were B: 0.0005 to 0.0200%, N: 0.0005 to 0.0100%, and Ti: 0.0010 to 0.0050%. The C content of the base steel sheet was 0.0015%, the Si content was 3.2%, the Mn content was 0.09%, and the remainder was Fe and impurities, which remained the same regardless of the annealing separation agent conditions. Table 9 also shows the average particle size of BN precipitates in the steel. The average particle size range that satisfies the conditions of this embodiment was 0.8 μm or larger.

[0144] (Example 4) First, a steel ingot was prepared containing, by mass%, C: 0.08%, S: 0.025%, acid-soluble Al: 0.03%, N: 0.009%, and Bi: 0.02%, with the remainder being Si and Mn in the amounts shown in Table 10, along with 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 1100°C for 140 seconds, pickled, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.23 mm.

[0145] 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, a slurry of an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and after drying, it was heated to 1200°C in a batch heating furnace at a heating rate of 15°C / h and a nitrogen concentration of 50 vol% in the atmosphere. At 1200°C, the atmosphere was switched to a dry hydrogen atmosphere (nitrogen concentration 0 vol%) and held for 20 hours for finish annealing, and the steel sheet after finish annealing was washed with water. Here, the annealing separation agent contained 1.10% Ca equivalent of CaSO4·0.5H2O, 2.0% Y2O3 equivalent of Y, with the remainder being unavoidable impurities and compounds under the conditions shown in Table 10, relative to 100% MgO. The stirring conditions for the annealing separation agent were 10°C for 200 minutes after adding the above compounds. The amount of annealing release agent applied after drying is 7 g / m² per side of the steel plate. 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.

[0146] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density V of the grain-oriented electrical steel sheet (sample after stress-relieving annealing) for each example of the present invention and comparative example was measured in accordance with the single-sheet measurement method described in JIS C2556:2015 for a sample with a sample size of 60 mm × 300 mm. B8 Value, hysteresis loss W h and iron loss W 17 / 50 The following measurements were taken. The above sample was cut from a 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. Here, V B8 The value is the magnetic flux density of a grain-oriented electrical steel sheet when it is excited at 50 Hz with 800 A / m. h This is the hysteresis loss when a grain-oriented electrical steel sheet is excited to 1.7T. 17 / 50 This refers to the iron loss when grain-oriented electrical steel sheets are excited to 1.7T at 50Hz. In the present invention example, V was measured from 5 samples. B8 Value, W h and W 17 / 50 The average values ​​were calculated from these values.

[0147] 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 portion where the primary coating peeled off was measured for each. For each sample, the ratio of the area of ​​the peeled portion to the total area was defined as the coating peeling area ratio, and the average value was calculated from the coating peeling area ratios of the three test pieces.

[0148] Furthermore, in the grain-oriented electrical steel sheet after the final process, the presence or absence of a primary coating and an insulating coating, as well as the Mg2SiO4 content, were confirmed using the same method as in Example 1.

[0149] Furthermore, in the grain-oriented electrical steel sheet after the final processing, the cross-section was mirror-polished, and then BN precipitates in the steel were identified using wavelength-dispersive X-ray analysis attached to an electron beam microanalyzer. The rolling direction length was then measured by backscattered electron imaging. The average of the rolling direction lengths of five BN precipitates measured here was taken as the average grain size of the BN precipitates in the steel. In addition, after removing the insulating film and primary film, the composition of the base steel sheet was analyzed. The content of Si, Mn, B, and Ti was analyzed by inductively coupled plasma atomic emission spectroscopy. The content of C was measured using a carbon-sulfur analyzer. The content of N was measured using an oxygen-nitrogen analyzer.

[0150] Here, the hysteresis loss W of the grain-oriented electrical steel sheet. h However, (-V B8 The condition was judged as good if the ratio was less than or equal to (×2.5 + 5.3) W / kg and the coating peeling area ratio in the 10 mmφ bending test was 10% or less.

[0151] The manufacturing conditions for the above-mentioned examples of the present invention and comparative examples are shown in Table 10, and the evaluation results are shown in Table 11. In Table 11, a "○" indicates a good evaluation result, and a "×" indicates a poor result.

[0152] [Table 10]

[0153] [Table 11]

[0154] 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.

[0155] Referring to Tables 10 and 11, it was found that grain-oriented electrical steel sheets that satisfy the conditions of this embodiment yield a good result.

[0156] Table 11 shows the C, Si, Mn, B, N, and Ti content of the base steel sheet. The component ranges that satisfy the conditions of this embodiment were C: 0.0050% or less, Si: 2.5-4.5%, Mn: 0.01-0.15%, B: 0.0005-0.0200%, N: 0.0005-0.0100%, and Ti: 0.0010-0.0050%. The remainder consisted of Fe and impurities. Table 11 also shows the average particle size of BN precipitates in the steel. The range of average particle size that satisfies the conditions of this embodiment was 0.8 μm or larger.

[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:0.009%, and Bi:0.03%, with the remainder consisting of the components shown in Table 12, along with 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 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, a slurry of an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and after drying, it was heated to 1200°C in a batch heating furnace at a heating rate of 15°C / h and a nitrogen concentration of 75 vol% in the atmosphere. At 1200°C, the atmosphere was switched to a dry hydrogen atmosphere (nitrogen concentration 0 vol%) and held for 20 hours for finish annealing, and the steel sheet after finish annealing was washed with water. The annealing separation agent contained 1.10% Ca equivalent of CaSO4·0.5H2O, 2.0% Ce(OH)4 equivalent of Ce, and the remainder being unavoidable impurities and compounds under the conditions shown in Table 12, relative to 100% MgO. The stirring conditions for the annealing separation agent were 20°C for 100 minutes after adding the compounds under the conditions shown in Table 12. The amount of annealing release agent applied after drying is 7 g / m² per side of the steel plate. 2Subsequently, 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.

[0159] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density V of the grain-oriented electrical steel sheet (sample after stress-relieving annealing) for each example of the present invention and comparative example was measured in accordance with the single-sheet measurement method described in JIS C2556:2015 for a sample with a sample size of 60 mm × 300 mm. B8 Value, hysteresis loss W h and iron loss W 17 / 50 The following measurements were taken. The above sample was cut from a 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. Here, V B8 The value is the magnetic flux density of a grain-oriented electrical steel sheet when it is excited at 50 Hz with 800 A / m. h This is the hysteresis loss when a grain-oriented electrical steel sheet is excited to 1.7T. 17 / 50 This refers to the iron loss when grain-oriented electrical steel sheets are excited to 1.7T at 50Hz. In the present invention example, V was measured from 5 samples. B8 Value, W h and W 17 / 50 The average values ​​were calculated from these values.

[0160] 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 portion where the primary coating peeled off was measured for each. For each sample, the ratio of the area of ​​the peeled portion to the total area was defined as the coating peeling area ratio, and the average value was calculated from the coating peeling area ratios of the three test pieces.

[0161] Furthermore, in the grain-oriented electrical steel sheet after the final process, the presence or absence of a primary coating and an insulating coating, as well as the Mg2SiO4 content, were confirmed using the same method as in Example 1.

[0162] Furthermore, in the grain-oriented electrical steel sheet after the final processing, the cross-section was mirror-polished, and then BN precipitates in the steel were identified using wavelength-dispersive X-ray analysis attached to an electron beam microanalyzer. The rolling direction length was then measured by backscattered electron imaging. The average of the rolling direction lengths of five BN precipitates measured here was taken as the average grain size of the BN precipitates in the steel. Furthermore, after removing the insulating and primary coatings, the composition of the base steel sheet was analyzed using inductively coupled plasma atomic emission spectroscopy. The carbon (C) content was measured using a carbon-sulfur analyzer. The nitrogen (N) content was measured using an oxygen-nitrogen analyzer.

[0163] Here, the hysteresis loss W of the grain-oriented electrical steel sheet. h However, (-V B8 The conditions of having a hysteresis loss of (×2.5 + 5.3) W / kg or less, and a coating delamination area ratio of 10 mmφ bending test of 10% or less, were judged to be good. In addition, the hysteresis loss W of grain-oriented electrical steel sheets was judged to be less than 10%. h However, (-V B8 The magnetic flux density is less than or equal to (2.5 + 5.3) W / kg, the coating peeling area ratio in the 10mmφ bending test is 10% or less, and the magnetic flux density is V B8 The condition of having a value of 1.930T or higher was judged to be even better.

[0164] The base steel sheet components of the above-mentioned examples and comparative examples are shown in Table 13, and the evaluation results are shown in Table 14. In Table 14, a good evaluation result is indicated by "〇", an even better result by "◎", and a poor result by "×".

[0165] [Table 12]

[0166] [Table 13]

[0167] [Table 14]

[0168] 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.

[0169] Referring to Tables 12-14, it was found that grain-oriented electrical steel sheets that meet the conditions of this embodiment yield even better results.

[0170] Furthermore, as shown in Table 13, the component range that satisfies the conditions of this embodiment is C: 0.0050% or less, B: 0.0005 to 0.0200%, N: 0.0005 to 0.0100%, Ti: 0.0010 to 0.0050%, and also contains one or more of the following: 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 Si content of the base steel sheet was 3.2%, and the Mn content was 0.08%, which remained the same regardless of the annealing separation agent conditions. Table 14 shows the average particle size of BN precipitates in the steel. The range of average particle size that satisfies the conditions of this embodiment was 0.8 μm or larger.

[0171] (Example 6) 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.

[0172] 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, a slurry of an annealing separation agent containing MgO was applied to the surface of the steel sheet after primary recrystallization annealing, and after drying, it was heated to 1200°C in a batch-type heating furnace at a heating rate of 15°C / h and a nitrogen concentration of 50 vol% in the atmosphere. At 1200°C, the atmosphere was switched to a dry hydrogen atmosphere (nitrogen concentration 0 vol%) and held for 20 hours for finish annealing, and the steel sheet after finish annealing was washed with water. Here, the annealing separation agent contained 100% MgO, 0.55% Ca (cal equivalent) of CaSO4·0.5H2O, 5.0% CeO2 (cere equivalent), and the remainder being unavoidable impurities and compounds under the conditions shown in Table 15. The stirring conditions for the annealing separation agent were 10°C for 20 minutes after adding the above compounds. The amount of annealing release agent applied after drying is 8 g / m² per side of the steel plate. 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.

[0173] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density V of the grain-oriented electrical steel sheet (sample after stress-relieving annealing) for each example of the present invention and comparative example was measured in accordance with the single-sheet measurement method described in JIS C2556:2015 for a sample with a sample size of 60 mm × 300 mm. B8 Value, hysteresis loss W h and iron loss W 17 / 50 The following measurements were taken. The above sample was cut from a 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. Here, V B8 The value is the magnetic flux density of a grain-oriented electrical steel sheet when it is excited at 50 Hz with 800 A / m. h This is the hysteresis loss when a grain-oriented electrical steel sheet is excited to 1.7T. 17 / 50 This refers to the iron loss when grain-oriented electrical steel sheets are excited to 1.7T at 50Hz. In the present invention example, V was measured from 5 samples. B8 Value, W h and W17 / 50 The average value was calculated from each of them.

[0174] Furthermore, the above sample was sheared to a width of 30 mm and subjected to a bending test with a diameter of 10 mm. Here, three test pieces were subjected to the bending test, the area of the portion where the primary coating was peeled off was measured for each, and for each sample, the ratio of the area of the peeled portion to the total area was defined as the coating peeling area ratio, and the average value was obtained from the coating peeling area ratios of the three test pieces.

[0175] Furthermore, in the grain-oriented electrical steel sheet after the final step, confirmation of the presence or absence of the primary coating and the insulating coating, and measurement of the content of Mg2SiO4 were carried out in the same manner as in Example 1.

[0176] Furthermore, in the grain-oriented electrical steel sheet after the final step, after removing the insulating coating and the primary coating, the components of the base steel sheet were analyzed using inductively coupled plasma optical emission spectrometry. The content of C was measured using a carbon-sulfur analyzer. The content of N was measured using an oxygen-nitrogen analyzer.

[0177] Here, the hysteresis loss W h of the grain-oriented electrical steel sheet is B8 (-V × 2.5 + 5.3) W / kg or less, and when the coating peeling area ratio in the 10 mmφ bending test is 10% or less, the condition is determined to be good.

[0178] The manufacturing conditions and measurement results of the above examples of the present invention and comparative examples are shown in Table 15. In Table 15, when the evaluation result is good, it is indicated by "〇", and when it is bad, it is indicated by "×".

[0179]

Table 15

[0180] The grain-oriented electrical steel sheet satisfying the conditions of the present embodiment has a primary coating. As a result of analyzing Mg2SiO4 in the primary coating, in all cases, the Mg concentration was 35 mass% or more and the Si concentration was 13 mass%, and the primary coating contained Mg2SiO4 as a main component.

[0181] Referring to Table 15, 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.

[0182] Furthermore, the B, N, and Ti components of the base steel sheet are shown in Table 15. The component ranges that satisfy the conditions of this embodiment were B: 0.0005 to 0.0200%, N: 0.0005 to 0.0100%, and Ti: 0.0010 to 0.0050%. The C content of the base steel sheet was 0.0018%, the Si content was 3.2%, the Mn content was 0.08%, and the remainder was Fe and impurities, which remained the same regardless of the annealing separation agent conditions.

[0183] (Example 7) 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:0.009%, 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.

[0184] 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 the temperature was raised to 1200°C using a batch heating furnace at a heating rate of 15°C / h and a nitrogen concentration of 50 vol% in the atmosphere. At 1200°C, the atmosphere was switched to a dry hydrogen atmosphere (nitrogen concentration 0 vol%) and held for 20 hours for finish annealing, after which the steel sheet was washed with water. The annealing separation agent contained 100% MgO, 3.3% Ti2O3 (Ti equivalent), 5.0% CeO2 (Ce equivalent), 0.68% Na2B4O7·10H2O (B equivalent), 0.95% SrSO4 (Sr equivalent), with the remainder being unavoidable impurities. The stirring conditions for the annealing separation agent were as shown in Table 16. 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.

[0185] After shearing and stress-relieving annealing the grain-oriented electrical steel sheet samples obtained above, the magnetic flux density V of the grain-oriented electrical steel sheet (sample after stress-relieving annealing) for each example of the present invention and comparative example was measured in accordance with the single-sheet measurement method described in JIS C2556:2015 for a sample with a sample size of 60 mm × 300 mm. B8 The values ​​were measured. The above samples were cut from grain-oriented electrical steel sheets after stress-relieving annealing so that the longitudinal direction of the grain-oriented electrical steel sheet before shearing matched the longitudinal direction of the sample. In this example, as in Example 1, the average value of 5 samples was V B8 It was set as the value.

[0186] 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 coating peeling area ratio was determined. The coating peeling area ratio was calculated using the same method as in Example 1.

[0187] 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.

[0188] Here, the magnetic flux density V of the grain-oriented electrical steel sheet B8 The conditions were judged as good if the value was 1.920T or higher and the coating delamination area ratio in the 10mmφ bending test was 10% or less. In addition, the magnetic flux density V of the grain-oriented electrical steel sheet was B8 A product was judged to be defective if it did not meet at least one of the following conditions: a value of 1.920T or higher, or a coating delamination area ratio of 10mmφ in the bending test was 10% or less.

[0189] Table 16 shows the stirring conditions and evaluation results for the annealing separating agents in the above-mentioned examples and comparative examples of the present invention. In Table 16, a "○" indicates a good evaluation result, and a "×" indicates a poor evaluation result.

[0190] [Table 16]

[0191] 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.

[0192] Referring to Table 16, it was found that grain-oriented electrical steel sheets that meet the conditions of this embodiment, manufactured by stirring the aqueous slurry of the annealing separating agent at a temperature of 0°C to 30°C for a period of 5 minutes to 300 minutes during manufacturing, yielded a good result.

[0193] 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. In mass%, C: 0.0050% or less, Si: 2.5-4.5%, Mn: 0.01 to 0.15%, B: 0.0005-0.0200%, N: 0.0005-0.0100%, Ti: 0.0010 to 0.0050%, Bi: 0-0.0500%, Cu: 0 to 0.30%, Sn: 0 to 0.30%, Ni: 0 to 0.30%, Cr: 0-0.30%, and, Sb: 0 to 0.30%, A base steel sheet containing, with the remainder being Fe and impurities, Formed on the surface of the base steel plate, Mg ２ SiO ４ A primary coating containing as its main component, An insulating film formed on the surface of the primary film, Equipped with, Hysteresis loss W when the base steel plate on which the primary coating and the insulating coating are formed is excited to 1.7T ｈ (W / kg) satisfies the following equation (1), A grain-oriented electrical steel sheet characterized by having a coating peeling area ratio of 10% or less in a bending adhesion test of 10 mm diameter. W ｈ ≦(-V) Ｂ８ ×2.5+5.3) ・・・ Equation (1) Here, V Ｂ８ This is the magnetic flux density when a magnetic field of 800 A / m is applied at 50 Hz to the base steel plate on which the primary coating and the insulating coating are formed.

2. The grain-oriented electrical steel sheet according to claim 1, characterized in that the base steel sheet contains BN precipitates in the steel, and the average particle size of the BN precipitates is 0.8 μm or more.

3. The aforementioned base steel plate 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, The grain-oriented electrical steel sheet according to claim 1 or 2, further characterized by containing one or more types selected from the group consisting of Sb: 0.01% to 0.30%.

4. An annealing separating agent applicable to the manufacture of grain-oriented electrical steel sheet as described in claim 1, It contains MgO as its main component, and in terms of mass %, relative to the MgO content, Ti compounds are included in an amount of 0.3% to 10.0% in terms of total Ti content. The amount of compound B is 0.03% to 1.60% in terms of the total amount of B contained. The product contains rare earth metal compounds in an amount of 0.1% to 10.0% in terms of the total amount of rare earth metals contained. When the Ti content of the Ti compound is A (mass%) and the B content of the B compound is B (mass%), the following formula (2) 0.33≦(A+B)≦10.30... Formula (2) An annealing separating agent that satisfies the requirements.

5. It further 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. The annealing separation agent according to claim 4, characterized in that the content of the alkaline earth metal compound is 0.3% by mass or more and 5.8% by mass or less in terms of the alkaline earth metal content relative to the content of MgO.

6. A method for manufacturing grain-oriented electrical steel sheets according to claim 1, 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 to 0.30%, Sn: 0 to 0.30%, Ni: 0 to 0.30%, Cr: 0-0.30%, and, Sb: 0 to 0.30%, A process 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 subjecting it to hot rolling, The process involves hot-rolled steel sheet being subjected to hot-rolled sheet annealing, followed by one cold-rolling or two or more cold-rolling processes with intermediate annealing in between, to obtain a cold-rolled steel sheet. The process involves subjecting the cold-rolled steel sheet to primary recrystallization annealing, The process involves applying an annealing separating agent containing MgO to the surface of the cold-rolled steel sheet after primary recrystallization annealing, followed by finish annealing. The process includes applying an insulating coating to the steel sheet after finish annealing, followed by a flattening annealing step. The aforementioned annealing separating agent contains MgO as its main component, and in terms of mass%, relative to the MgO content, Ti compounds are included in an amount of 0.3% to 10.0% in terms of total Ti content. Compound B is included in an amount of 0.03% to 1.60% in terms of the total amount of B contained, and The product contains rare earth metal compounds in an amount of 0.1% to 10.0% in terms of the total amount of rare earth metals contained. When the Ti content of the Ti compound is A (mass%) and the B content of the B compound is B (mass%), the following formula (2) 0.33≦(A+B)≦10.30... Formula (2) Satisfying the conditions, The stirring in the preparation of the aqueous slurry of the annealing separating agent is carried out at a temperature of 0°C to 30°C for a time of 5 minutes to 300 minutes. The residence time T (h) in the finish annealing process at a temperature of 1100°C or higher and a nitrogen concentration in the atmosphere of 10 vol% or less is given by the following formula (3): (5+9×B)≦T≦100... Formula (3) A method for manufacturing grain-oriented electrical steel sheets, characterized by satisfying the following conditions.

7. The annealing separating agent further contains one or more alkaline earth metal compounds comprising one or more alkaline earth metal elements selected from the group consisting of Ca, Sr, and Ba, The method for manufacturing grain-oriented electrical steel sheets according to claim 6, characterized in that the content of the alkaline earth metal compound is 0.3% by mass or more and 5.8% by mass or less in terms of the alkaline earth metal content relative to the content of MgO.

8. The method for manufacturing grain-oriented electrical steel sheets according to claim 6 or 7, characterized in that the slab further contains Bi: 0.0005% or more and 0.0500% or less.

9. The slab 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, A method for producing grain-oriented electrical steel sheets according to any one of claims 6 to 8, characterized in that it further contains one or more selected from the group consisting of Sb: 0.01% to 0.30%.

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