Grain-oriented electrical steel sheet and method for manufacturing same

Abstract

This grain-oriented electrical steel sheet comprises a base material steel sheet, a glass coating film formed on the base material steel sheet so as to be in contact with the base material steel sheet, and an insulating coating film formed on the glass coating film so as to be in contact with the glass coating film, the insulating coating film containing a phosphate and silica. The grain-oriented electromagnetic steel sheet has a thickness of 0.23 mm or less. The glass coating film is present only up to 5.0 μm towards the base material steel sheet in the direction parallel to the sheet thickness direction of the base material steel sheet from the interface between the glass coating film and the insulating coating film. In an analysis space, which is to be subjected to three-dimensional analysis, taking the area of the interface where the base material steel sheet and the glass coating film in contact with and integrally connected to the insulating coating film are in contact with each other to be S1 and the area in a plane perpendicular to the sheet thickness direction to be S0, the ratio of S1 / S0, which is the ratio of S1 to S0, is such that S1 / S0 ≥ 1.30.

Description

Grain-oriented electrical steel sheet and method for manufacturing the same

[0001] This disclosure relates to grain-oriented electrical steel sheets and methods for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2025-030289, filed in Japan on February 27, 2025, the contents of which are incorporated herein by reference.

[0002] Grain-oriented electrical steel (GO) is a soft magnetic material used in the cores of electrical equipment such as transformers. For the cores of transformers, it is necessary to reduce iron loss in order to minimize energy loss. To reduce iron loss, a technique is known in which a glass coating (also called a primary coating or forsterite coating) made of a material with a lower coefficient of thermal expansion than the steel sheet, and an insulating coating on the surface side of the glass coating, are formed at high temperatures on the surface of the steel sheet. In this case, tension is applied to the steel sheet due to the difference in thermal expansion between the steel sheet and the glass coating and insulating coating, thereby reducing iron loss.

[0003] In grain-oriented electrical steel sheets used for the winding cores of transformers, the glass coating must be uniform, defect-free, and have excellent adhesion to the steel sheet to withstand bending and other processes. To increase the magnetic flux density, it is preferable to reduce the thickness of the glass coating, which is a non-magnetic layer. However, when the glass coating is thin, sufficient adhesion to the steel sheet cannot be obtained, and this tends to result in appearance defects.

[0004] In the manufacturing process of grain-oriented electrical steel sheets, SiO is introduced into the steel during the decarburization annealing process performed after cold rolling. ２ A solution is generated, and then an annealing release agent is applied to the surface of the steel plate. Subsequently, in the finish annealing process, the SiO in the steel is removed. ２ The main component of the annealing separating agent, MgO, reacts with the main component Mg ２ SiO ４ A glass coating of (forsterite) is formed. When the glass coating is embedded in the steel (sometimes referred to as an anchored structure), it is thought that the anchoring effect prevents the glass coating from peeling off the steel. In other words, the anchored structure of the glass coating is thought to ensure adhesion to the steel plate.

[0005] Regarding the adhesion of glass coatings, for example, Patent Document 1 states that the adhesion of the primary coating is improved when BN with a particle size of 50 to 300 nm is present inside the glass coating. Although the reason for this is not clear in Patent Document 1, Mg ２ SiO ４ It is stated that the presence of BN inside a glass coating (forsterite coating) mainly composed of BN changes the morphology of the anchor portion of the glass coating (forsterite coating), thereby improving adhesion. Furthermore, Patent Documents 2 to 4 state that by including Ti compounds, B compounds, and rare earth metal compounds in the annealing separating agent, the interface structure between the primary coating and the steel sheet becomes more complex, and the adhesion between the primary coating and the steel sheet is improved by the anchoring effect. In Patent Documents 2 to 4, although the reason is not clear, it is stated 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, and then the Ti compounds and / or B compounds are formed, changing the morphology of the anchor portion and improving adhesion.

[0006] International Publication No. 2019 / 146697 Japanese Patent Publication No. 2021-123768 Japanese Patent Publication No. 2021-123767 Japanese Patent Publication No. 2021-123766

[0007] The technologies disclosed in Patent Documents 1 to 4 can improve the adhesion of glass coatings. However, in recent years, there has been a demand for further improvement in the adhesion of glass coatings. As a result of the inventors' investigations, it was found that even when applying the technologies of Patent Documents 1 to 4, if the glass coating is thin, the adhesion between the glass coating and the steel sheet may not be sufficient to meet the higher demands of recent years, and the resulting grain-oriented electrical steel sheet may have a defective appearance due to the peeling of the glass coating. Therefore, the object of this disclosure is to provide a grain-oriented electrical steel sheet and a method for manufacturing the same that exhibits excellent adhesion between the glass coating and the steel sheet even when the glass coating is thin (when the thickness of the glass coating is 5.0 μm or less from the interface between the insulating coating and the glass coating in the direction of the base steel sheet).

[0008] The present inventors have studied the adhesion of a glass coating. As a result, they have found that excellent adhesion of a glass coating can be obtained by three-dimensionally controlling an anchor structure. Further, for controlling this anchor structure, the temperature during decarburization annealing, the oxygen potential and the soaking time, the hydration amount of slurry applied as an annealing separator, and the H during finish annealing ２ The inventors have found that the gas blowing amount has a great influence.

[0009] The present disclosure has been made in view of the above findings. The gist of the present disclosure is as follows. [1] A grain-oriented electrical steel sheet according to one aspect of the present disclosure includes a base steel sheet, a glass coating formed on the base steel sheet in contact with the base steel sheet, and an insulating coating formed on the glass coating in contact with the glass coating and containing phosphate and silica, the sheet thickness is 0.23 mm or less, the glass coating exists only in a range from an interface between the glass coating and the insulating coating to a position 5.0 μm toward the base steel sheet in a direction parallel to the sheet thickness direction of the base steel sheet, in an analysis space which is a space to be subjected to three-dimensional analysis, the area of an interface where the glass coating in contact with and integrally connected to the insulating coating contacts the base steel sheet is S １ , and the area on a plane perpendicular to the sheet thickness direction is S ０ , and the S ０ relative to the S １ which is the ratio of S １ / S ０ satisfies the following formula (1). S １ / S ０ ≧1.30 (1) [2] In the grain-oriented electrical steel sheet according to [1] above, when Y is defined as S １ / S ０ , in a cross section in the sheet thickness direction, the number density per unit number / nm ２ of the glass coating present in the base steel sheet in a state of not being connected to the insulating coating is defined as X Ｄ , the average area per unit nm ２ is defined as X Ａ , X Ａ relative to the X Ｄ which is the ratio of X Ｄ / X Ａ is defined as X, the Y and the X may satisfy the following formula (2). 4.44×10１２ ×X + 0.89 < Y ≤ 1.40 × 10 １３ ×X + 1.30 (2) [3] The grain-oriented electrical steel sheet described in [1] above has a sheet thickness of 0.20 mm or less, and the S １ / S ０ However, the following equation (1') may also be satisfied. S １ / S ０ ≥1.90 (1') [4] The grain-oriented electrical steel sheet described in [1] above is the S １ / S ０ Let Y be the unit number of glass coatings / nm present in the base steel plate in the cross section in the thickness direction, without being connected to the insulating coating. ２ The number density at X Ｄ , unit nm ２ The average area is X Ａ , the X Ａ The X Ｄ X is the ratio of Ｄ / X Ａ When X is denoted by Y, Y and X may satisfy the following equation (4): Y ≤ 4.44 × 10 １２ ×X + 0.89 (4) [5] The grain-oriented electrical steel sheet described in [3] above is the S １ / S ０ Let Y be the unit number of glass coatings / nm present in the base steel plate in the cross section in the thickness direction, without being connected to the insulating coating. ２ The number density at X Ｄ , unit nm ２ The average area is X Ａ , the X Ａ The X Ｄ X is the ratio of Ｄ / X Ａ When X is denoted by Y, Y and X may satisfy the following equation (4): Y ≤ 4.44 × 10 １２×X + 0.89 (4) [6] The grain-oriented electrical steel sheet described in any of [1] to [5] above is the base steel sheet having the following composition in mass%, C: 0.005% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.065% or less, N: 0.012% or less, P: 0 to 0.05%, S: 0.010% or less, Ti: 0 to 0.003% , Nb: 0-0.003%, V: 0-0.002%, Cu: 0-0.1%, Cr: 0-0.1%, Mo: 0-0.03%, Ni: 0-0.1%, B: 0- 0.001%, As: 0-0.1%, Sn: 0-0.1%, Sb: 0-0.05%, Ca: 0-0.001%, Mg: 0-0.0015%, Co: 0-0 .. 1%, Zr: 0-0.003%, W: 0-0.1%, Hf: 0-0.02%, Sc: 0-0.02%, Te: 0-0.005%, Sr: 0-0.02% , Bi: 0-0.1%, Ta: 0-0.02%, Zn: 0-0.02%, Pb: 0-0.1%, Ce: 0-0.0015%, Nd: 0-0.02%, RE The chemical composition may consist of M: 0-0.02%, Ba: 0-0.02%, Cd: 0-0.02%, Pt: 0-0.02%, Au: 0-0.02%, Ga: 0-0.02%, Ge: 0-0.02%, Y: 0-0.02%, La: 0-0.02%, Se: 0-0.02%, and the remainder being Fe and impurities.[7] A method for manufacturing a grain-oriented electrical steel sheet according to another aspect of the present disclosure is a method for manufacturing a grain-oriented electrical steel sheet according to [1] or [2] above, comprising: a hot rolling step of heating a slab and obtaining a hot-rolled steel sheet by hot rolling; a hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet; a cold rolling step of performing cold rolling on the hot-rolled steel sheet after the hot-rolled steel sheet annealing step to obtain a cold-rolled steel sheet; a decarburization annealing step of performing decarburization annealing on the cold-rolled steel sheet; an annealing separating agent application step of applying an annealing separating agent containing magnesia in slurry form to the cold-rolled steel sheet after the decarburization annealing step; a finish annealing step of performing finish annealing on the cold-rolled steel sheet after the annealing separating agent application step to obtain an intermediate steel sheet in which a glass film is formed on the surface of the cold-rolled steel sheet; and the finish annealing step The decarburization annealing process includes an insulating coating forming step, which involves forming an insulating coating on the surface of the intermediate steel sheet to obtain a grain-oriented electrical steel sheet, wherein the decarburization annealing process includes a heating step of raising the temperature of the cold-rolled steel sheet to a soaking temperature and a soaking step of maintaining the temperature at the soaking temperature, wherein the soaking temperature is set to 800 to 870°C, the oxygen potential of the atmosphere is set to 0.70 to 0.95, and the soaking time is set to 80 to 150 seconds, and in the annealing separation agent application step, when adjusting the annealing separation agent into a slurry, the temperature at which the slurry is stirred is set to 15°C or lower, and the finish annealing process includes a heating step of raising the temperature of the cold-rolled steel sheet to a finish annealing temperature and a soaking step of maintaining the temperature at the finish annealing temperature, wherein in the heating step of the finish annealing, H is set at 850 to 900°C. ２ Gas injection rate: 2.5 to 7.0 Nm ３Let / h. [8] A method for manufacturing a grain-oriented electrical steel sheet according to another aspect of the present disclosure is a method for manufacturing a grain-oriented electrical steel sheet according to any one of the above items [3] to [5], comprising: a hot rolling step of heating a slab and obtaining a hot-rolled steel sheet by hot rolling; a hot-rolled steel sheet annealing step of performing annealing on the hot-rolled steel sheet; a cold rolling step of performing cold rolling on the hot-rolled steel sheet after the hot-rolled steel sheet annealing step to obtain a cold-rolled steel sheet; a decarburization annealing step of performing decarburization annealing on the cold-rolled steel sheet; and the decarburization annealing process The decarburization annealing process includes: an annealing separator application step in which an annealing separator containing magnesia is prepared in slurry form and applied to the cold-rolled steel sheet after the decarburization process; a finish annealing step in which the cold-rolled steel sheet after the annealing separator application step is subjected to finish annealing to obtain an intermediate steel sheet in which a glass film is formed on the surface of the cold-rolled steel sheet; and an insulating film formation step in which an insulating film is formed on the surface of the intermediate steel sheet after the finish annealing step to obtain a grain-oriented electrical steel sheet, wherein the decarburization annealing process is performed by annealing the cold-rolled steel sheet to 800°C or higher. The process includes a heating process to raise the temperature to a first soaking temperature in the range of less than 900°C, a first soaking process to maintain the temperature at the first soaking temperature, and a second soaking process to raise the temperature to a second soaking temperature in the range of 900 to 950°C and maintain the temperature thereafter. In the first soaking process, the oxygen potential of the atmosphere is set to 0.40 to 0.60, and in the second soaking process, the oxygen potential of the atmosphere is set to 0.20 or less. The soaking time for the first soaking process is 60 to 150 seconds, and the soaking time for the second soaking process is 10 seconds. The soaking time in the first soaking process and the soaking time in the second soaking process shall be 170 seconds or less, the annealing separating agent coating process shall be performed at a temperature of 15°C or less when the annealing separating agent is prepared into a slurry, the finishing annealing process shall include a heating process to raise the temperature of the cold-rolled steel sheet to the finishing annealing temperature and a soaking process to soak it at the finishing annealing temperature, and in the heating process of the finishing annealing, the temperature shall be 850 to 900°C. ２ Gas injection rate: 2.5 to 7.0 Nm ３ Let's use / h.

[0010] According to the above aspects of this disclosure, it is possible to provide grain-oriented electrical steel sheets and methods for manufacturing the same that exhibit excellent adhesion between the glass coating and the steel sheet.

[0011] This is a schematic diagram showing the steel, glass coating, and insulating coating (the boundary between the glass coating and the insulating coating is not shown) in a cross-section of a grain-oriented electrical steel sheet, including the rolling direction and thickness direction, within a range of 8 μm from the surface of the insulating coating in the thickness direction. This is a schematic diagram of the three-dimensional structure of the interface between the glass coating connected to the insulating coating and the glass coating existing as an isolated structure within the steel and the steel. In this figure, the steel is shown transparently from the same cross-sectional viewpoint as in Figure 1, and the three-dimensional connected structure of the glass coating inside the steel is shown with dashed lines. The three-dimensional area S of the interface between the glass coating connected to the insulating coating and the steel. １ This is a schematic diagram to explain the following: The area S of the plane perpendicular to the thickness direction of the base steel plate in the three-dimensional observation analysis space. ０ This is a schematic diagram to explain [the concept].

[0012] A grain-oriented electrical steel sheet (a grain-oriented electrical steel sheet according to this embodiment) and a method for manufacturing the same, according to one embodiment of this disclosure, will be described.

[0013] <Grain-oriented electrical steel sheet> The grain-oriented electrical steel sheet according to this embodiment comprises a base steel sheet, a glass coating formed on the base steel sheet in contact with the base steel sheet, and an insulating coating formed on the glass coating in contact with the glass coating and containing phosphate and silica, and has a sheet thickness of 0.23 mm or less. Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, the glass coating has a predetermined structure described later.

[0014] (Base Steel Sheet) The base steel sheet of the grain-oriented electrical steel sheet according to this embodiment is not limited, but preferably contains, in terms of mass%, C: 0.005% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.001 to 0.065%, N: 0.012% or less, P: 0 to 0.05%, and S: 0.010% or less. The preferred reasons for limiting the content of each element constituting the chemical composition of the base steel sheet will be explained below.

[0015] C: 0.005% or less. Although carbon (C) is an effective element for controlling the primary recrystallization structure, it adversely affects magnetic properties, so it is removed by decarburization annealing before finish annealing. In grain-oriented electrical steel sheets, the C content of the base steel sheet is reduced by decarburization annealing. When the C content of the base steel sheet of grain-oriented electrical steel sheets is 0.005% or less, the magnetic properties of the grain-oriented electrical steel sheets (products) are particularly good. Therefore, it is preferable to have a C content of 0.005% or less. More preferably, the C content is 0.003% or less. The lower limit of the C content is not particularly limited and may be 0%, but may also be greater than 0%. Considering productivity in industrial production and the magnetic properties of the product, 0.0001% is the effective lower limit of the C content. Considering productivity, the C content may be reduced to less than 0.001%, or it may be 0.001% or more.

[0016] Si: 2.00-4.00% Si is an element that increases the electrical resistance of steel sheets and improves iron loss characteristics. The effect is greater when the Si content is 2.00% or more. For this reason, it is preferable that the Si content be 2.00% or more. More preferably, the Si content is 2.20% or more, and even more preferably 2.50% or more. On the other hand, in terms of workability, it is preferable that the Si content be 4.00% or less. More preferably, the Si content is 3.80% or less, and even more preferably 3.50% or less.

[0017] Mn: 0.05-1.00% Mn is an element that prevents cracking during hot rolling and forms MnS and / or MnSe, which function as inhibitors by bonding with S and / or Se. The effect is greater when the Mn content is 0.05% or more. For this reason, it is preferable that the Mn content be 0.05% or more. The Mn content is more preferably 0.07% or more, and even more preferably 0.09% or more. On the other hand, when the precipitation dispersion of MnS and / or MnSe is made uniform and a desired secondary recrystallized structure is obtained to increase the magnetic flux density, it is preferable that the Mn content be 1.00% or less. The Mn content is more preferably 0.80% or less, and even more preferably 0.60% or less.

[0018] Al: 0.065% or less. Al is an element that combines with N to produce AlN, which functions as an inhibitor. If the Al content is 0.001% or more, the inhibitory effect is fully expressed. Therefore, when using AlN as an inhibitor, it is preferable that the Al content be 0.001% or more. The Al content is more preferably 0.002% or more, and even more preferably 0.003% or more. The Al content may also be 0.005% or more or 0.010% or more. On the other hand, if the Al content is 0.065% or less, the precipitation of AlN becomes uniform, the desired secondary recrystallized structure is formed, and an excellent magnetic flux density can be obtained. Therefore, it is preferable that the Al content be 0.065% or less. The Al content is more preferably 0.050% or less, and even more preferably 0.040% or less. The Al content is the sol. Al (acid-soluble Al) content.

[0019] N: 0.012% or less. N is an element that combines with Al to form AlN, which functions as an inhibitor. When AlN is used as the main inhibitor, a N content of 0.004% or more is sufficient to form AlN. Therefore, when using AlN as an inhibitor, it is preferable that the N content be 0.004% or more. The N content is more preferably 0.006% or more, and even more preferably 0.007% or more. On the other hand, N is also an element that forms blisters (vacancies) in the steel sheet during cold rolling. If the N content is 0.012% or less, there is little concern about the formation of blisters (vacancies) in the steel sheet during cold rolling. Therefore, it is preferable that the N content be 0.012% or less. The N content is more preferably 0.010% or less, and even more preferably 0.009% or less.

[0020] P: 0-0.05% P may be included as it has the effect of improving the texture and magnetic properties of the steel sheet. To obtain the above effect, it is preferable that the P content be 0.01% or more. If the P content is 0.05% or less, the steel sheet will have excellent workability. For this reason, it is preferable that the P content be 0.05% or less. The P content is more preferably 0.03% or less, and even more preferably 0.02% or less.

[0021] S: 0.010% or less. S is an element that, during the manufacturing process, combines with Mn to form MnS, which functions as an inhibitor. When MnS is used as an inhibitor, it is preferable that the S content be 0.001% or more. More preferably, the S content is 0.003% or more or 0.005% or more. On the other hand, in order to obtain excellent magnetic properties, it is preferable that the S content be 0.010% or less in the base steel sheet of the grain-oriented electrical steel sheet. More preferably, the S content is 0.005% or less. When MnS is not used as an inhibitor, the S content may be less than 0.001% or less than 0.0005%.

[0022] Remainder: Fe and impurities. In the chemical composition of the base steel sheet, the remainder excluding the above elements may contain Fe and impurities. Preferably, the remainder consists of Fe and impurities. Impurities are elements that are inevitably mixed in from the steel raw materials and / or during the steelmaking process. On the other hand, the above chemical composition, for the purpose of improving magnetic properties, includes, in addition to C, Si, Mn, Al, P, and S, Ti: 0.003% or less, Nb: 0.003% or less, V: 0.002% or less, Cu: 0.1% or less, Cr: 0.1% or less, Mo: 0.03% or less, Ni: 0.1% or less, B: 0.001% or less, As: 0.1% or less, Sn: 0.1% or less, Sb: 0.05% or less, Ca: 0.001% or less, Mg: 0.0015% or less, Co: 0.1% or less, Zr: 0.003% or less, W: 0.1% or less, Hf: 0.02% or less, Sc: 0 It may contain one or more elements selected from the following: 0.02% or less, Te: 0.005% or less, Sr: 0.02% or less, Bi: 0.1% or less, Ta: 0.02% or less, Zn: 0.02% or less, Pb: 0.1% or less, Ce: 0.0015% or less, Nd: 0.02% or less, REM: 0.02% or less, Ba: 0.02% or less, Cd: 0.02% or less, Pt: 0.02% or less, Au: 0.02% or less, Ga: 0.02% or less, Ge: 0.02% or less, Y: 0.02% or less, La: 0.02% or less, and Se: 0.02% or less. These elements are optional and do not need to be included, so the lower limit is 0%.In other words, the chemical composition of the base steel sheet is, in mass%, C: 0.005% or less, Si: 2.00-4.00%, Mn: 0.05-1.00%, Al: 0.065% or less, N: 0.012% or less, P: 0-0.05%, S: 0.010% or less, Ti: 0-0.003%, Nb: 0-0.003%, V: 0-0.002%, Cu: 0-0.1%, Cr: 0-0.1%, Mo: 0-0.03%, Ni: 0-0.1%, B: 0-0.001%, As: 0 ~0.1%, Sn: 0-0.1%, Sb: 0-0.05%, Ca: 0-0.001%, Mg: 0-0.0015%, Co: 0-0.1%, Zr: 0-0.003%, W: 0-0.1%, Hf: 0-0.02%, Sc: 0-0.02%, Te: 0-0.005%, Sr: 0-0.02%, Bi : 0-0.1%, Ta: 0-0.02%, Zn: 0-0.02%, Pb: 0-0.1%, Ce: 0-0.0015%, Nd: 0-0.02%, R The composition may consist of EM: 0-0.02%, Ba: 0-0.02%, Cd: 0-0.02%, Pt: 0-0.02%, Au: 0-0.02%, Ga: 0-0.02%, Ge: 0-0.02%, Y: 0-0.02%, La: 0-0.02%, Se: 0-0.02%, with the remainder being Fe and impurities. Any of the above-mentioned elements may be included as impurities within the above ranges.

[0023] The chemical composition of the base steel sheet can be measured using general analytical methods. For example, it can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Acid-soluble Al can be measured by ICP-AES using the filtrate obtained after heating and decomposing a sample of the base steel sheet cut into small pieces with acid. C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas fusion-thermal conductivity method. When analyzing, the glass coating and insulating coating formed on the surface of the base steel sheet should be removed before measuring the components. Specifically, for grain-oriented electrical steel sheets with an insulating coating, NaOH: 30-50% by mass and H ２The insulating coating is removed by immersing the sheet in an aqueous sodium hydroxide solution containing 50-70% by mass of O at 80-90°C for 7-10 minutes. The grain-oriented electrical steel sheet from which the insulating coating has been removed is washed with water, and after washing, it is dried with a hot air blower for slightly less than 1 minute. Alternatively, grain-oriented electrical steel sheets with a glass coating after the insulating coating has been removed are immersed in an aqueous hydrochloric acid solution containing 30-40% by mass of HCl at 80-90°C for 1-10 minutes to remove the glass coating. The base steel sheet after immersion is washed with water, and after washing, it is dried with a hot air blower for slightly less than 1 minute. Through these steps, the base steel sheet can be extracted from the grain-oriented electrical steel sheet from which the glass coating and insulating coating have been formed.

[0024] (Glass Coating) In the grain-oriented electrical steel sheet according to this embodiment, the glass coating is formed on the base steel sheet in contact with the base steel sheet. Furthermore, the glass coating exists only in the range from the interface between the glass coating and the insulating coating to a position of 5.0 μm toward the base steel sheet in a direction parallel to the thickness direction of the base steel sheet. In order to achieve excellent magnetic properties, the glass coating does not exist beyond a position of 5.0 μm toward the base steel sheet in a direction parallel to the thickness direction of the base steel sheet from the interface. In other words, if the maximum thickness of the glass coating is defined as the distance from the interface between the glass coating and the insulating coating to the furthest glass coating location in a direction parallel to the thickness direction of the base steel sheet toward the base steel sheet, then the maximum thickness of the glass coating is 5.0 μm or less. The glass coating is formed in the finishing annealing treatment described later by the reaction of an oxide layer mainly containing silica with an annealing separating agent mainly containing magnesia (MgO). Therefore, the glass coating is formed by forsterite (Mg ２ SiO ４) is the main component and contains 50% by mass or more. The glass coating may also contain 95% by mass or more forsterite. The grain-oriented electrical steel sheet according to this embodiment has a glass coating and an insulating coating formed thereon (for example, 1 and 2 in Figure 1). Figure 2 shows the glass coating inside the base steel sheet with a dashed line and illustrates the three-dimensional structure of the glass coating. The glass coating has a structure (anchored structure) 4 in which a part of the glass coating in contact with the insulating coating is integrally connected to the inside of the base steel sheet, as shown by the dashed line portion 5 in Figure 2 (the dashed line portion is at the back of the observation surface), and an isolated structure (isolated structure) 6 that is not included in the anchored structure. As shown in Figure 1, when the cross-section of the electrical steel sheet is observed (when two-dimensional observation is performed), this anchored structure appears to exist in isolation inside the base steel sheet (it is observed in the same way as the isolated structure). By performing three-dimensional observation, it is made clear that the structure that appeared isolated is an integrally connected structure inside the base steel sheet. When such anchoring structures are formed frequently, the adhesion of the glass coating is excellent. Similarly, when such anchoring structures are observed frequently, isolated glass coating structures are also observed frequently.

[0025] Furthermore, as shown in Figures 3 and 4, the glass coating provided in the grain-oriented electrical steel sheet according to this embodiment is in contact with and integrally connected to the insulating coating identified by three-dimensional observation in the analysis space that is the target of three-dimensional observation. The area of ​​the interface between the glass coating and the base steel sheet is S. １ The area of ​​the base steel plate in a plane perpendicular to the thickness direction is S. ０ When this is the case, S ０ S for １ S is the ratio of １ / S ０ However, it is formed such that the following equation (1) is satisfied. １ / S ０ ≥1.30 (1) In the evaluation of formula (1), the S of the glass coating １ Only the interface is targeted. In Figure 3, the interface formed by the dashed line 7, which represents the field of view of the three-dimensional observation, is excluded from the analysis, while the solid line portion is the interface being targeted.

[0026] The glass coating is formed in the steel during the decarburization annealing process that follows the cold rolling process. ２Using [the aforementioned] as a precursor, MgO, which is the main component of the annealing separator applied to the surface of the steel sheet prior to finish annealing, reacts with SiO in the steel generated in the decarburization annealing step ２ to form the product with Mg ２ SiO ４ as the main component. The SiO generated in the steel in this decarburization annealing step ２ includes two existing structures: one is a connected structure (hereinafter referred to as connected structure) where SiO formed on the steel sheet surface and SiO in the steel are connected ２ and SiO in the steel are connected ２ , and the other is an isolated structure (isolated structure) where SiO is isolated in the steel. The SiO with this connected structure ２ becomes a precursor of a glass coating having a structure (anchoring structure) where the glass coating penetrates (embeds) into the steel in a more complex manner. SiO with an isolated structure ２ is consumed in the formation reaction of Mg formed on the surface depending on the finish annealing conditions ２ SiO ４ , which may result in a decrease in the number and size of individual isolated SiO. On the other hand, isolated SiO coarsens via Ostwald ripening, and when Mg ２ is incorporated to form Mg ２ SiO ４ is formed, the interface shape of Mg ２ SiO ４ may be flattened (the anchoring structure is reduced). A glass coating with a flattened interface shape has insufficient adhesion to the steel sheet, so it is prone to peeling and causes appearance defects resulting from coating defects of grain-oriented electrical steel sheets.

[0027] In the grain-oriented electrical steel sheet according to the present embodiment, the area ratio of interfaces having an anchoring structure in the glass coating is controlled using a new index to improve the adhesion of the glass coating. Specifically, in the grain-oriented electrical steel sheet according to the present embodiment, as described above, the glass coating is formed such that S １ / S ０ satisfies the following formula (1). S １ / S ０ ≧1.30 (1) When S １ / S ０ is less than 1.30, sufficient adhesion cannot be obtained. S １ / S ０is preferably 1.40 or more, and more preferably 1.90 or more. Particularly when the plate thickness is 0.20 mm or less, S １ / S ０ is more preferably 1.90 or more. The upper limit of S １ / S ０ is not limited, but may be 3.00 or less from the viewpoint of productivity. By controlling the complicated three-dimensional shape such as the anchor structure at the interface of the glass coating as a new index, compared with the conventional control by two-dimensional indexes, the present invention is less susceptible to disturbance of data including glass coatings other than the anchor structure that have no direct correlation with adhesion, and can control glass coatings excellent in adhesion with high accuracy, so that the effect of improving adhesion can be stably obtained.

[0028] The extent of the glass coating from the interface between the glass coating and the insulating coating (maximum thickness) is measured using a scanning electron microscope (SEM) in the following manner. Specifically, test pieces measuring 10 mm in the rolling direction and 10 mm in the width direction (plate width direction: perpendicular to the rolling direction) are taken from 10 locations in the width direction of the steel sheet, separated from each other (if the width direction of the oriented electrical steel sheet is less than 100 mm, test pieces may be taken from 5 locations separated from each other in the width direction, and 2 locations separated in a direction perpendicular to the width direction, for a total of 10 (5 × 2) locations). The cross section of the collected test piece, including the rolling direction and the thickness direction, is used as the observation surface (observation cross section), and the observation range (observation field of view) is set to 25 μm in the rolling direction and 15 μm in the thickness direction, arbitrarily selected from a 10 mm × 10 mm range, and the SEM imaging conditions are set so that the pixel size is 30 nm. The acceleration voltage for acquiring backscattered electron images is set to 2-10 kV, and the irradiation current is set to 50-1000 pA. The depth to which the glass coating exists (existence depth) is measured from the interface between the glass coating and the insulating coating in the backscattered electron image. At that time, the distance in the thickness direction of the base steel plate to the glass coating at the position furthest from the interface between the glass coating and the insulating coating within the field of view is defined as the existence range (maximum thickness) of the glass coating. The above measurement is performed on each of the 10 test pieces taken from 10 locations, for a total of 10 fields of view. The maximum existence range measured in the 10 fields of view is defined as the existence range (maximum thickness) of the glass coating from the interface between the glass coating and the insulating coating. The base steel plate, glass coating, and insulating coating can be distinguished by the difference in brightness of the backscattered electron image. Since the difference in brightness between the base steel plate, glass coating, and insulating coating is large, the interface between the base steel plate and the glass coating, and the interface between the glass coating and the insulating coating can also be clearly determined. However, the location of the interface between the glass coating and the insulating coating may be determined using an EDS (Energy Dispersive X-ray Spectroscopy) mounted on the SEM. In this case, the area near the interface between the glass coating and the insulating coating may be analyzed with the EDS, and after removing measurement noise, the region where the Fe content is less than 80 atomic%, the P content is 5 atomic% or more, and the O content is 30 atomic% or more may be determined to be the insulating coating (phosphate-based coating), and the rest may be determined to be the glass coating.The settings for EDS analysis are as follows: acceleration voltage: 15 keV, irradiation current: 1 nA, measurement pitch: 0.5 μm.

[0029] S １ / S ０This is confirmed using a three-dimensional observation method in the following manner. Using a Focused Ion Beam-Scanning Electric Microscope (hereinafter referred to as FIB-SEM) and a SEM, the three-dimensional structure of the region including the base steel sheet and glass coating on the surface of the grain-oriented electrical steel sheet is observed using the serial sectioning method. Specifically, it is as follows. In this embodiment, portions of the predetermined regions to be observed are cut from multiple positions on the grain-oriented electrical steel sheet, and the cut fragments are obtained as test pieces for observation. For example, to ensure that the cross-section including the rolling direction and the thickness direction becomes the observation surface (observation cross-section), test specimens measuring 10 mm in the rolling direction and 10 mm in the width direction (perpendicular to the rolling direction) and thickness are taken from 10 locations that are isolated from each other in the width direction of the steel sheet (if the grain-oriented electrical steel sheet is less than 100 mm in the width direction, specimens may be taken from 5 locations that are isolated from each other in the width direction, and 2 locations that are isolated in a direction perpendicular to the width direction, for a total of 10 (5 x 2) locations). The observation surface of the collected test specimens is imaged using a SEM to obtain a two-dimensional image. Then, the surface of the test specimen (observation surface) is ground to a predetermined depth using a FIB, and the ground surface of the test specimen is photographed with a SEM as the next surface. By repeating this process, multiple consecutive two-dimensional images are obtained toward the interior of the test specimen. By classifying the glass coating and the base steel sheet in each two-dimensional image based on their brightness difference, and then combining multiple two-dimensional images to create a three-dimensional model, a three-dimensional image of the glass coating and a three-dimensional image of the base steel sheet can be obtained. Since the observation surface is a cross-section that includes the rolling direction and the thickness direction, the direction in which the observation surface moves during grinding is the width direction of the steel sheet. Therefore, the distance in the width direction between the surface before grinding and the surface after grinding is called the "grinding width." When measuring, the smaller the grinding width per pass, the higher the resolution of the resulting three-dimensional image. However, the resolution of the three-dimensional image is also determined by the resolution of each two-dimensional image, so the grinding width per pass (the distance in the width direction between the surface before grinding and the surface after grinding) should be determined based on the resolution of the two-dimensional images.When acquiring two-dimensional images, the SEM imaging conditions should be set so that the field of view (observation range) is 25 μm in the rolling direction and 15 μm in the plate thickness direction, the spatial resolution is 10 nm, the pixel size is 30 nm, the acceleration voltage for acquiring backscattered electron images is 10 kV, and the irradiation current is 1000 pA. In this case, the FIB processing conditions should be set so that grinding and imaging are repeatedly performed with a grinding width of 100 nm per pass, for a total grinding width of 25 μm. By setting the field of view of the two-dimensional image to the above size, it is possible to observe even fine glass coatings and a sufficient range of glass coating characteristics. To improve image quality by preventing static charge on the test piece during SEM observation, a protective film containing one or more of the following components—gold, tungsten, carbon, or platinum—is deposited on surfaces other than the observation surface from which the two-dimensional image is acquired. Furthermore, the three-dimensional image generated by superimposing multiple images is constructed in voxel format, which is three-dimensional pixels. In this embodiment, the determination of whether a region of each voxel is base metal (base steel sheet), a glass coating, or an oxide is made based on the brightness of each voxel. For example, if the brightness is below a predetermined threshold, the region of the corresponding voxel is determined to be a glass coating or an oxide; if the brightness is equal to or greater than a predetermined threshold, the region of the corresponding voxel is determined to be base metal. Alternatively, for example, if the brightness is within a predetermined range, the region of the corresponding voxel may be determined to be a glass coating or an oxide; if the brightness is within another predetermined range, the region of the corresponding voxel may be determined to be base metal. When using the method of identifying each phase by brightness as described above, the imaging time per pixel when capturing a two-dimensional image is set to 30 μs. Furthermore, the reconstruction of a three-dimensional image from a two-dimensional image can be performed using commercially available image analysis software (Avizo, manufactured by Thremo Fisher Scientific). In this process, the glass coatings are classified according to their connectivity state in a three-dimensional image of the constructed glass coating, such that adjacent pixels in the front, back, left, right, top, and bottom directions are of the same material (i.e., within the same brightness range). For example, regions connected to the glass coating formed on the surface are classified as anchored structures, and other glass coatings are classified as isolated structures.Using the three-dimensional image converted from this voxel-formatted three-dimensional image to a mesh format such as triangles, the area of ​​the interface where the glass coating, which is in contact with and integrally connected to the insulating coating, and the base steel plate are in contact, within the entire construction range (analysis space) of the three-dimensional image, is calculated and defined as S. １ (nm ２ ) is set as follows. In addition, the area of ​​a plane that is parallel to both the rolling direction and the plate width direction of the entire construction range of the three-dimensional image as shown in Figure 4, and that includes both directions (a plane perpendicular to the plate thickness direction) is calculated and set to S ０ (nm ２ ) This S １ and S ０ tokara S １ / S ０ The following is calculated. When the two-dimensional image observation area is set to 25 μm in the rolling direction and 15 μm in the plate thickness direction, and grinding and imaging are repeated so that the total grinding width in the plate width direction is 25 μm, the construction area of ​​the three-dimensional image (analysis space) will be a rectangular parallelepiped area of ​​25 μm in the rolling direction, 15 μm in the plate thickness direction, and 25 μm in the plate width direction. In this embodiment, S obtained from 10 sampled test pieces １ / S ０ The eight S values ​​obtained by excluding the minimum and maximum values ​​are... １ / S ０ The evaluation is based on the average value of the factors.

[0030] In the grain-oriented electrical steel sheet according to this embodiment, S １ / S ０ In addition to satisfying ≥ 1.30, it is preferable that the glass coating is in a predetermined state when observed in a cross-section in the rolling direction and a cross-section in the thickness direction (a cross-section including both the rolling direction and the thickness direction). Specifically, S １ / S ０ Let Y be the value of Y, and in the cross-section in the thickness direction (in a two-dimensional evaluation), the number of glass coatings present in the base steel sheet without being connected to the insulating coating is [number of pieces / nm]. ２ The number density in ] is X Ｄ , unit [nm ２ The average area in ] is X Ａ , X Ａ X Ｄ X is the ratio of Ｄ / XＡ Let X be X. Then Y and X are such that Y ≤ 1.40 × 10 １３ It is preferable that ×X + 1.30 is satisfied. In this case, the adhesion of the coating is further improved by having a complex shape in three dimensions and by having an appropriate frequency of glass coating formation.

[0031] Furthermore, to further reduce iron loss, it is preferable that Y satisfies the following equation (4): Y ≤ 4.44 × 10 １２ ×X + 0.89 (4) In terms of productivity, it may be within the range that satisfies the following equation (4'): 2.75 × 10 １２ ×X + 0.86 < Y ≤ 4.44 × 10 １２ ×X + 0.89 (4')

[0032] On the other hand, lowering Y reduces productivity, so if productivity is prioritized over iron loss, Y may be within the range that satisfies the following equation (2): 4.44 × 10 １２ ×X + 0.89 < Y ≤ 1.40 × 10 １３ ×X + 1.30 (2) In addition, in order to reduce iron loss while ensuring productivity, Y may be set to a range that satisfies the following equation (3): 1.54 × 10 １３ ×X + 0.62 < Y ≤ 1.40 × 10 １３ ×X + 1.30 (3) The range of X is not limited, but 1.00 × 10 －１４ ~5.00 x 10 ―１３ That's fine.

[0033] The number density X of glass coatings present in the base steel sheet in an isolated structure (not connected to the insulating coating). Ｄ , average area X ＡThe following method can be used for measurement. Although the glass coating, which exists as an isolated structure, is distributed more like "particles" than a "coating" that covers something because it is isolated, here we will use the term "glass coating" consistently, assuming that it is simply the same phase as the glass coating in isolation. A test piece of 10 mm in the rolling direction and 10 mm in the width direction (perpendicular to the rolling direction) is taken from the grain-oriented electrical steel sheet so that the cross section including the rolling direction and the thickness direction becomes the observation surface. The observation surface of the test piece is finished for SEM observation using wet polishing and Ar ion beam irradiation. On the observation surface, an image is acquired using the backscattered electron detector of the SEM, with one observation field of view extending 15 to 50 μm in the rolling direction and 8 μm (0.008 mm) or more from the surface of the insulating coating toward the interior of the steel sheet (i.e., the thickness direction). Multiple images are acquired in the rolling direction, and in total, the area is 1.0 mm or more in the rolling direction and 0.008 mm or more in the thickness direction. ２ The above range is used as the field of view. After identifying the glass coating from the acquired image using brightness as a threshold based on the phase contrast between the glass coating and the base steel plate, the glass coating is classified by image processing for each region where pixels are adjacent and connected in the extracted region of glass coating. From the classified image, it is confirmed that the glass coating with the largest area is the glass coating formed on the surface, and the others are glass coatings that were dispersed in the steel, as far as can be determined from the cross-sectional image. Next, the number and area of ​​the glass coatings dispersed in the steel other than the glass coating formed on the surface are measured, and the number density (number / field of view area) and the average area are calculated. When acquiring images with SEM, it is preferable for clear observation of the glass coating if the spatial resolution is 10 nm, the pixel size is less than 30 nm, for example 10 nm, the acceleration voltage when acquiring backscattered electron images is 2 to 10 kV or less, and the irradiation current is 50 to 1000 pA. Figure 1 shows a schematic diagram of a cross-section of a grain-oriented electrical steel sheet, including the rolling direction and thickness direction, specifically a cross-section within 8 μm from the surface of the insulating coating in the thickness direction, showing the steel, the glass coating, and insulating coating 1 (the boundary between the glass coating and the insulating coating is not shown) and glass coating 2.

[0034] (Insulating Coating) In the grain-oriented electrical steel sheet according to this embodiment, an insulating coating mainly composed of phosphate and silica (for example, 60% by mass or more in total) is formed in contact with the glass coating. The insulating coating may be any known insulating coating. The phosphate-based coating may contain aluminum, magnesium, nickel, etc. derived from phosphate. It may also contain silicon derived from colloidal silica. The thickness of the insulating coating is preferably 2 to 5 μm. The thickness of the insulating coating can be measured using an SEM. Specifically, test pieces measuring 10 mm in the rolling direction and 10 mm in the width direction (perpendicular to the rolling direction) are taken from the grain-oriented electrical steel sheet from 10 locations that are separated from each other in the width direction of the steel sheet (if the grain-oriented electrical steel sheet is less than 100 mm in the width direction, test pieces may be taken from 5 locations that are separated from each other in the width direction, and 2 locations that are separated in a direction perpendicular to the width direction, for a total of 10 (5 × 2) locations). The cross-section of the collected test specimen, including both the rolling direction and the thickness direction, is used as the observation plane. The SEM imaging conditions are set so that the field of view is 25 μm in the rolling direction and 15 μm in the thickness direction, and the pixel size is 30 nm. The acceleration voltage for acquiring the backscattered electron image is set to 10 kV and the irradiation current to 1000 pA. The distance from the interface between the glass coating and the insulating coating in the backscattered electron image to the surface of the insulating coating (surface of the grain-oriented electrical steel sheet) is measured and defined as the thickness of the insulating coating. The above measurement is performed for one field of view at each of the 10 collected locations, for a total of 10 fields of view. The thickness measured in each field of view is averaged to determine the thickness of the insulating coating. An EDS mounted on the SEM may be used to identify the insulating coating. That is, by performing analysis with the EDS and removing measurement noise, the region where the Fe content is less than 80 atomic%, the P content is 5 atomic% or more, and the O content is 30 atomic% or more may be determined to be an insulating coating (phosphate-based coating). The settings for EDS analysis are as follows: acceleration voltage: 15 keV, irradiation current: 1 nA, measurement pitch: 0.5 μm.

[0035] (Sheet Thickness) The grain-oriented electrical steel sheet according to this embodiment has a sheet thickness (thickness of the base steel sheet, glass coating, and insulating coating) of 0.23 mm or less. Preferably, the sheet thickness is 0.20 mm or less. The lower limit of the sheet thickness is not limited, but it may be 0.18 mm or more in order to improve the magnetic properties. The sheet thickness can be measured using a micrometer at any position.

[0036] <Manufacturing Method> The grain-oriented electrical steel sheet according to this embodiment can achieve the above-mentioned effects regardless of the manufacturing method, but it is preferable to use a manufacturing method that includes the following steps because it can be manufactured stably. (I) A hot rolling step of heating a slab and obtaining a hot-rolled steel sheet by hot rolling; (II) A hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet; (III) A cold rolling step of cold rolling the hot-rolled steel sheet after the hot-rolled steel sheet annealing step to obtain a cold-rolled steel sheet; (IV) A decarburization annealing step of decarburizing the cold-rolled steel sheet; (V) An annealing separating agent application step of applying an annealing separating agent containing magnesia in slurry form to the cold-rolled steel sheet after the decarburization annealing step; (VI) A finish annealing step of performing finish annealing on the cold-rolled steel sheet after the annealing separating agent application step to obtain an intermediate steel sheet in which a glass film is formed on the surface of the cold-rolled steel sheet; (VII) An insulating film forming step of forming an insulating film on the surface of the intermediate steel sheet after the finish annealing step to obtain a grain-oriented electrical steel sheet. For each of these, we will explain the preferred conditions.

[0037] (Hot Rolling Process) In the hot rolling process, a slab having a predetermined chemical composition is heated to 1000°C or higher, and a hot-rolled steel sheet is obtained by hot rolling. The hot rolling conditions are not limited, but for example, conditions under which hot rolling is performed so that the finishing temperature is 1000°C or higher are given as examples. Regarding the chemical composition of the slab to be subjected to hot rolling, the content of elements other than C, Mn, Al, N, and S does not change significantly during the manufacturing process, so it is sufficient to have the same content as the base steel sheet of the grain-oriented electrical steel sheet to be obtained. In mass%, the C content should be 0.060 to 0.090%, the Mn content 0.07 to 0.20%, the Al content 0.010 to 0.065%, the N content 0.005 to 0.015%, and the S content 0.030% or less.

[0038] (Hot-rolled steel sheet annealing process) In the hot-rolled steel sheet annealing process, the hot-rolled steel sheet is annealed. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties. In the hot-rolled steel sheet annealing process of this embodiment, the hot-rolled steel sheet manufactured through the hot-rolling process can be annealed according to a known method. The means for heating the hot-rolled steel sheet during annealing are not particularly limited, and a known heating method can be adopted. For example, so-called continuous annealing may be used, or the hot-rolled steel sheet may be coiled and batch annealed. The annealing conditions are also not particularly limited, but for example, the hot-rolled steel sheet can be annealed at a temperature range of 900 to 1200°C for 10 seconds to 5 minutes. The atmosphere is not particularly limited, but it is preferable to suppress oxidation of the steel sheet, and it is preferable to perform the process in a non-oxidizing atmosphere mainly containing nitrogen, argon, hydrogen, etc. (or one or more of these). Alternatively, the hot-rolled steel sheet may be heated to 1000-1150°C (first stage temperature) to recrystallize it, and then subsequently annealed at a lower temperature of 850-1100°C (second stage temperature). This is preferable because it allows for the homogenization of the non-uniform structure that occurred during hot rolling.

[0039] (Cold Rolling Process) In the cold rolling process, the hot-rolled steel sheet, after the hot-rolled steel sheet annealing process, is cold-rolled to obtain a cold-rolled steel sheet. The cold rolling may be a single cold rolling process (a series of cold rolling processes without intermediate annealing), or it may be two or more cold rolling processes with intermediate annealing in between. The thickness of the sheet after cold rolling becomes the final thickness of the base steel sheet. Cold rolling may be carried out at room temperature, or the steel sheet may be heated to a temperature higher than room temperature, for example, around 200°C.

[0040] (Decarburization Annealing Process) In the decarburization annealing process, decarburization annealing is performed on the cold-rolled steel sheet. The purpose of a general decarburization annealing process is to remove carbon from the steel sheet and to control the primary recrystallized grain size to a desired grain size. However, in the manufacturing method of grain-oriented electrical steel sheet according to this embodiment, in the decarburization annealing process, in order to control the glass coating formed in the finish annealing process, the precursor SiO ２ It controls S. １ / S ０If the ratio is 1.30 or higher, the decarburization annealing process includes a heating process to raise the temperature to a soaking temperature and a soaking process to maintain the temperature at the soaking temperature. In the soaking process, the soaking temperature is set to 800-870°C, the oxygen potential of the atmosphere to 0.70-0.95, and the soaking time to 80-150 seconds. By using the above conditions, SiO that can grow Ostwald during finish annealing can be achieved. ２ The source of the generation of the material can be reduced. As a result, the flattening of the interface between the glass coating and the base steel sheet can be suppressed. Below a soaking temperature of 800°C, decarburization may not be sufficient under any oxygen potential. Above a soaking temperature of 870°C, the coarsening of precipitates is significant, and the magnetism may be inferior. Also, the oxygen potential (P Ｈ２Ｏ / P Ｈ２ If the oxygen potential is less than 0.70, decarburization will be insufficient, and the carbon remaining in the final product will degrade the magnetic properties. On the other hand, if the oxygen potential is greater than 0.95, Fe ２ SiO ４ Excessive generation of this substance inhibits the formation of a glass coating with an anchoring structure in the subsequent finish annealing process. Furthermore, if the soaking time is less than 80 seconds, decarburization may be insufficient, and if it exceeds 150 seconds, the magnetic flux density may decrease.

[0041] Also, S １ / S ０ If the ratio is set to 1.90 or higher, productivity will be lower than under the above conditions, but it is preferable to use a two-stage soaking decarburization annealing process which includes a heating process to raise the temperature to a first soaking temperature in the range of 800°C to less than 900°C, a first soaking process to maintain the temperature at the first soaking temperature, and a second soaking process to raise the temperature to a second soaking temperature in the range of 900 to 950°C and maintain the temperature thereafter, and to set the oxygen potential of the atmosphere to 0.40 to 0.60 in the first soaking process and to set the oxygen potential of the atmosphere to 0.20 or lower in the second soaking process, and to set the total soaking time of the first soaking process and the soaking time of the second soaking process to 70 to 170 seconds. In this case, in order to suppress the formation of the glass film which is a non-magnetic layer, the precursor SiO ２The amount of SiO generated can be significantly reduced, and a glass coating with excellent adhesion can be formed. Below 800°C in the first soaking temperature, decarburization may not be sufficient under any oxygen potential. On the other hand, above 900°C, when the oxygen potential is reduced in the subsequent second soaking process, the required SiO ２ It cannot produce a sufficient quantity. Also, if the second soaking temperature is below 900°C, S １ / S ０ If the oxygen potential is less than 1.90, a dense interfacial structure glass coating cannot be formed, and above 950°C, the coarsening of precipitates is significant, and the magnetism may be inferior. Also, if the oxygen potential in the first soaking process is less than 0.40, decarburization is insufficient, and the magnetic properties deteriorate due to the carbon remaining in the final product. On the other hand, if the oxygen potential in the first soaking process is greater than 0.60, when the oxygen potential is lowered in the subsequent second soaking process, the required SiO ２ It cannot produce a sufficient quantity. Also, if the oxygen potential in the second sonication process is greater than 0.20, S １ / S ０ It is not possible to form a glass coating with a dense interface structure where S is 1.90 or higher. Preferably, the soaking time for the first soaking process is 60 to 150 seconds, and the soaking time for the second soaking process is 10 to 20 seconds. If the first soaking time is less than 60 seconds, decarburization may be insufficient, and if the second soaking time is less than 10 seconds, S １ / S ０ It is not possible to form a glass coating with a dense interface structure where the ratio is 1.90 or higher. If the total time of the first and second soaking times exceeds 170 seconds, there is a concern that the magnetic flux density will decrease.

[0042] (Annealing Separating Agent Coating Process) In the annealing separating agent coating process, an annealing separating agent containing magnesia (MgO) (for example, 80% by mass or more) is prepared into a slurry and applied to the cold-rolled steel sheet after the decarburization annealing process. Furthermore, when preparing the annealing separating agent into a slurry, the temperature at which the slurry is stirred is kept below 15°C. The temperature at which the slurry is stirred is the temperature of the tank in which the slurry is stirred. The tank temperature can be controlled by known methods. When MgO is prepared into a slurry, some of the MgO becomes Mg(OH) ２A hydration reaction occurs as follows. When a slurry containing a large amount of hydrated water is applied to a steel sheet, the hydrated water in the slurry evaporates during the finish annealing of the coiled steel sheet, and the atmosphere between the sheets in the coil becomes a high oxygen potential. This high oxygen potential of the atmosphere is SiO ２ This is one of the causes of coarsening due to Ostwald growth. Therefore, in the manufacturing method of grain-oriented electrical steel sheet according to this embodiment, the amount of hydrated water in the MgO slurry is reduced in order to reduce the introduction of hydrated water into the coil. As a means to do this, the stirring temperature of the slurry is set to 15°C or lower. The stirring temperature may be 0°C or higher to prevent the slurry from freezing. It may also be 4°C or higher to avoid reducing productivity. If the amount of hydrated water in the slurry is reduced, SiO will be reduced during finish annealing due to Ostwald growth. ２ Before the material becomes coarse, the hydrated water evaporates early, allowing the inter-plate atmosphere within the coil to be controlled to an oxygen potential suitable for the development of the anchoring structure. If the slurry stirring temperature exceeds 15°C, the amount of hydrated water in the annealing separating agent becomes excessive, resulting in SiO ２ This will promote the growth of Ostwald.

[0043] (Finish Annealing Process) In the finish annealing process, the cold-rolled steel sheet, after the annealing release agent application process, is coiled after the applied annealing release agent has dried, and then the finish annealing is performed. This process adds Mg to the surface of the cold-rolled steel sheet. ２ SiO ４ An intermediate steel sheet (a steel sheet having a cold-rolled steel sheet as the base material and a glass coating formed on the surface of the base material steel sheet) is obtained, on which a glass coating mainly composed of is formed. The finish annealing process includes a heating process to raise the temperature to the finish annealing temperature and a soaking process to soak the temperature at the finish annealing temperature, and in the heating process, H in 850 to 900°C ２ Gas injection rate: 2.5 to 7.0 Nm ３ Let / h. During the heating process of the finish annealing process, especially in the temperature range of 850-900°C, SiO ２ Ostwald growth is easily achieved. Therefore, in the manufacturing method of grain-oriented electrical steel sheet according to this embodiment, by controlling the furnace atmosphere to be dry, Ostwald growth is suppressed and MgO is reduced (i.e., SiO in the linkage structure in the steel) ２(Supply of Mg to) SiO in isolated structures in steel ２ SiO on the surface ２ or Mg ２ SiO ４ To promote fusion, H in this temperature range is used to create a dry atmosphere. ２ The amount of gas injected is controlled. Assuming a typical box-type annealing furnace, the injection amount is 2.5 Nm³. ３ If the rate is less than / h, the furnace atmosphere cannot be sufficiently dried, and the above effects cannot be fully obtained. Also, for stable operation, the blowing rate should be 7.0 Nm³. ３ The amount should not exceed / h. Therefore, the blowing rate should be 2.5 to 7.0 Nm ３ Set to / h. This will, for example, create a dry atmosphere inside the furnace with a dew point of -10°C or lower. Preferably, the blowing rate is 4.0 to 5.0 Nm ３ / h. H ２ If the gas injection rate is within the above range, you may add nitrogen gas.

[0044] The conditions during the soaking process are not limited, but examples include heating the steel plate to 1150-1250°C in an atmosphere containing hydrogen and nitrogen, and holding it at that temperature for 15-30 hours.

[0045] (Insulating Coating Formation Process) In the insulating coating formation process, an insulating coating is formed on the surface of the intermediate steel sheet after the finish annealing process to obtain a grain-oriented electrical steel sheet (including a base steel sheet, a glass coating formed on the base steel sheet in contact with the base steel sheet, and an insulating coating formed on the glass coating in contact with the glass coating). The method of forming the insulating coating is not limited, but an insulating coating containing phosphate and silica can be formed by applying an aqueous coating solution containing phosphate and colloidal silica and baking it.

[0046] In the manufacturing method of grain-oriented electrical steel sheets according to this embodiment, the following nitriding treatment step and magnetic domain subdivision step may be further performed. These steps are not required.

[0047] <Nitriding Treatment Process> The nitriding treatment process is optional, but may be performed to increase the nitrogen content in the base steel sheet. If performed, the nitriding treatment is carried out on the decarburized annealed steel sheet before the finish annealing, so that the nitrogen content of the steel sheet is 40 to 1000 ppm (0.0040 to 0.1000 mass%) by mass. If the nitrogen content of the steel sheet after nitriding is less than 40 ppm, AlN will not precipitate sufficiently, and AlN will not function as an inhibitor, which is undesirable. The nitrogen content of the steel sheet after nitriding is more preferably 80 ppm or more. On the other hand, if the nitrogen content of the steel sheet after the nitriding treatment exceeds 1000 ppm, excess AlN will remain even after secondary recrystallization is completed in the next finish annealing, increasing iron loss, which is undesirable. The nitrogen content of the steel sheet after nitriding is more preferably 970 ppm or less.

[0048] <Magnetic Domain Refinement Process> In the magnetic domain refinement process, the grain-oriented electrical steel sheet is subjected to magnetic domain refinement after finish annealing. This process is preferable because it forms grooves on the surface of the steel sheet, reducing the magnetic domain width and consequently reducing iron loss. The specific method of magnetic domain refinement is not particularly limited, but examples include laser irradiation, electron beam irradiation, etching, or groove formation using gears. The magnetic domain refinement process is preferably performed after the finish annealing process, but it may also be performed before the finish annealing process or after the insulating film formation process.

[0049] The grain-oriented electrical steel sheets of this disclosure will be described in more detail using examples. However, the conditions in the examples are a set of example conditions adopted to confirm the feasibility and effectiveness of this disclosure, and this disclosure is not limited to this one example condition. This disclosure may adopt various conditions insofar as they do not depart from the gist of this disclosure and achieve the objectives of this disclosure.

[0050] Slabs having the chemical composition shown in Table 1 (total impurities of 0.10% or less) were heated to 1150°C and subjected to hot rolling to obtain hot-rolled steel sheets with a thickness of 2.0 mm. The hot-rolled steel sheets were annealed by holding at 1200°C for 5 minutes (hot-rolled steel sheet annealing). Subsequently, the hot-rolled steel sheets were cold-rolled to obtain cold-rolled steel sheets with a thickness of 0.20 to 0.23 mm. These cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Table 3. In Table 3, examples where the column for the later stage of the soaking process is marked with "-" indicate that only one stage of annealing was performed. Subsequently, nitriding treatment was performed to adjust the N content of the cold-rolled steel sheets to 40 to 1000 ppm. Then, an annealing separating agent containing MgO was made into a slurry, applied to the cold-rolled steel sheets, and dried. The stirring temperature of the slurry was as shown in Table 4. Finally, finish annealing was performed. In the finish annealing process, the temperature was raised to 1200°C and held at that temperature for 30 hours. In addition, during the heating process, H was used at 850-900°C. ２ The amount of gas injected should be as shown in Table 4. ２ I injected gas.

[0051] The appearance of the steel sheets after finish annealing was evaluated before forming the insulating coating. The appearance was evaluated visually according to the following criteria. The results are shown in Table 5. • If the glass coating is uniformly gray and no defects with metallic luster are observed: Very good (Ex) • If the glass coating is almost uniformly gray and almost no defects with metallic luster are observed: Good (G) • If the glass coating is generally uniformly gray, with some unevenness and defects with metallic luster are observed: Poor (P) • If the glass coating is thin gray, with unevenness and prominent defects with metallic luster are observed: Very poor (B)

[0052] A grain-oriented electrical steel sheet with an insulating coating containing phosphate and silica was obtained by applying an aqueous coating solution containing phosphate and colloidal silica to a steel sheet whose appearance had been evaluated and then baking it. Furthermore, the surface of the steel sheet was subjected to magnetic domain refinement treatment by irradiating it with a laser under known conditions.

[0053] For the obtained grain-oriented electrical steel sheet, the chemical composition of the base steel sheet, S １ / S ０ , X Ｄ , X Ａ, was determined by the method described above. Table 2 shows the chemical composition of the base steel sheet, and Table 4 shows S １ / S ０ And, X Ｄ and X Ａ The value of X calculated from the above is shown. However, S １ / S ０ Table 4 shows the S values ​​of eight test specimens, excluding the smallest and largest of the ten specimens taken. １ / S ０ This is the average value over S. １ / S ０ The structure of the glass coating, expressed by the relationship between X and X, was evaluated to determine whether it satisfied equation (2) or equation (4). Examples not described did not satisfy either relationship.

[0054] Furthermore, the magnetic properties and coating adhesion of the obtained grain-oriented electrical steel sheets were evaluated in the following manner.

[0055] <Coating Adhesion> A test piece (plate) measuring 60 mm in the rolling direction and 15 mm in the plate width direction was taken from a grain-oriented electrical steel sheet. This test piece was wrapped around a round bar with a diameter of 20 mm to 50 mm, and after bending the plate, the peeling area of ​​the surface coating was visually evaluated. The evaluation criteria were as follows. - If no peeling is observed in the test using a φ20 mm round bar: Adhesion B - If less than 30% peeling is observed in the test using a φ20 mm round bar, and no peeling is observed with a φ30 mm round bar: Adhesion C - If 30% or more peeling is observed in the test using a φ20 mm round bar, and no peeling is observed with a φ30 mm round bar: Adhesion D - If less than 30% peeling is observed in the test using a φ30 mm round bar, and no peeling is observed with a φ50 mm round bar: Adhesion E - If 30% or more peeling is observed in the test using a φ30 mm round bar, and no peeling is observed with a φ50 mm round bar: Adhesion F - If peeling is observed in the test using a φ50 mm round bar: Adhesion G Adhesion is judged to be good if it is B to F.

[0056] <Magnetic Properties> As a measure of magnetic properties, the magnetic flux density B8 was measured by single-plate magnetic testing (SST) in accordance with JIS C2556 (2015) (magnetic flux density when magnetized at 800 A / m). A magnetic flux density of 1.88 T or higher was judged to indicate excellent magnetic properties.

[0057]

[0058]

[0059]

[0060]

[0061]

[0062] As can be seen from the results in Tables 1 to 5, the plate thickness is 0.23 mm or less, and the glass coating exists in a range from the interface between the glass coating and the insulating coating to a position of 5.0 μm in the direction of the base steel plate in a direction parallel to the thickness direction of the base steel plate, S １ / S ０ However, in cases with a value of 1.30 or higher (Test Nos. 1-5, 12, 13, 16-26), the appearance, adhesion, and magnetic properties were all excellent. １ / S ０ However, in cases with a value of 1.90 or higher (Test Nos. 12 and 13), the magnetic properties were particularly excellent.

[0063] On the other hand, in comparative examples, Tests No. 6-11, 14, and 15, one or more of the following were inferior: appearance, adhesion, and magnetic properties. In Tests No. 6-7, the oxygen potential exceeded 0.95 during the soaking process of the decarburization annealing process. Consequently, Fe ２ SiO ４ It is thought that an excessive amount of was generated, which inhibited the formation of the glass coating in the subsequent finishing annealing process, and therefore the structure of the glass coating was S １ / S ０ The result was below 1.30. As a result, the appearance, adhesion, and magnetic flux density were inferior. In tests No. 8-9, the slurry stirring temperature exceeded 15°C during the annealing separation agent coating process. Consequently, the hydrated water content of the annealing separation agent became excessive, resulting in the SiO2 in the finish annealing process. ２It is thought that this promoted Ostwald growth, and therefore the structure of the glass coating was S １ / S ０ The value fell below 1.30. As a result, the appearance, adhesion, and magnetic flux density were inferior. In tests No. 10-11, the H value at 850-900°C during the heating process of the finish annealing step was... ２ Gas injection volume: 2.5 Nm ３ The rate fell below / h. Consequently, the furnace atmosphere could not be sufficiently dried, resulting in SiO ２ It is thought that this promoted Ostwald growth, and therefore the structure of the glass coating was S １ / S ０ The value fell below 1.30. As a result, the appearance, adhesion, and magnetic flux density were inferior. In Test No. 14, the oxygen potential fell below 0.40 in the pre-soaking stage (first soaking stage) of the decarburization annealing process. Consequently, decarburization was insufficient, and S １ / S ０ The value fell below 1.30. As a result, the appearance, adhesion, and magnetic flux density were inferior. In Test No. 15, the oxygen potential exceeded 0.20 in the latter stage of the soaking process (second soaking process) of the decarburization annealing process. Consequently, it is thought that a glass coating with a dense interface structure could not be formed, so S １ / S ０ The value fell below 1.30. As a result, the appearance, adhesion, and magnetic flux density were inferior.

[0064] This disclosure provides a grain-oriented electrical steel sheet and a method for manufacturing the same, which exhibits excellent adhesion between the glass coating and the steel sheet. Therefore, it has high industrial applicability.

[0065] 1. Glass coating and insulating coating 2. Glass coating 3. Base steel plate 4. A structure in which the glass coating is in contact with and integrally connected to the insulating coating, and a part of the glass coating is embedded in the base steel plate at the point where the glass coating and the base steel plate are in contact, i.e., an anchoring structure 5. A location where the anchoring structure is connected three-dimensionally inside the base steel plate (the dashed line is at the back of the observation surface) 6. Isolated structure 7. S １ / S ０ Interface S that is excluded from the analysis １　The area S of the interface where the glass coating, which is in contact with and integrally connected to the insulating coating, and the base steel plate are in contact within the constructed range (analysis space) of the three-dimensional observation. ０　 Area of ​​the plane perpendicular to the thickness direction of the base steel sheet within the construction range (analysis space) of the three-dimensional observation. 8. Construction range (analysis space) of the three-dimensional observation: RD: Rolling direction TD: Width direction ND: Thickness direction (normal direction)

Claims

1. The material comprises a base steel sheet, a glass coating formed on the base steel sheet in contact with the base steel sheet, and an insulating coating formed on the glass coating in contact with the glass coating, containing phosphate and silica, wherein the sheet thickness is 0.23 mm or less, the glass coating exists only in a range from the interface between the glass coating and the insulating coating to a position of 5.0 μm toward the base steel sheet in a direction parallel to the thickness direction of the base steel sheet, and in the analysis space which is the space to be analyzed in three dimensions, the area of ​​the interface where the glass coating, which is in contact with and integrally connected to the insulating coating, and the base steel sheet are in contact is S １ , the area in the plane perpendicular to the thickness direction of the plate is S ０ And the above S ０ The S for １ S is the ratio of １ / S ０ However, a grain-oriented electrical steel sheet characterized by satisfying the following formula (1). １ / S ０ ≥ 1.30 (1) 2. wherein S １ / S ０ is defined as Y, and in the cross-section in the sheet thickness direction, with respect to said glass coating that exists in said base steel sheet in a state not connected to said insulating coating, the number density per unit number / nm ２ is X Ｄ , the average area in unit nm ２ is X Ａ , wherein X Ａ relative to X Ｄ the ratio of which is X Ｄ / X Ａ is defined as X, said Y and said X satisfy the following formula (2), the grain-oriented electrical steel sheet according to claim 1, characterized in that: 4.44×10 １２ ×X+0.89<Y≤1.40×10 １３ ×X+1.30 (2) 3. The plate thickness is 0.20 mm or less, and the S １ / S ０ The grain-oriented electrical steel sheet according to claim 1, characterized in that it satisfies the following formula (1'). １ / S ０ ≥ 1.90 (1') 4. The above S １ / S ０ Let Y be the unit number of glass coatings / nm present in the base steel plate in the cross section in the thickness direction, without being connected to the insulating coating. ２ The number density at X Ｄ , unit nm ２ The average area is X Ａ , the X Ａ The X Ｄ X is the ratio of Ｄ / X Ａ The grain-oriented electrical steel sheet according to claim 1, characterized in that when X is denoted by Y, Y and X satisfy the following equation (4): Y ≤ 4.44 × 10 １２ ×X + 0.89 (4) 5. The above S １ / S ０ Let Y be the unit number of glass coatings / nm present in the base steel plate in the cross section in the thickness direction, without being connected to the insulating coating. ２ The number density at X Ｄ , unit nm ２ The average area is X Ａ , the X Ａ The X Ｄ X is the ratio of Ｄ / X Ａ The grain-oriented electrical steel sheet according to claim 3, characterized in that when X is denoted by Y, Y and X satisfy the following formula (4): Y ≤ 4.44 × 10 １２ ×X + 0.89 (4) 6. The base steel sheet has the following composition in mass%, C: 0.005% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.065% or less, N: 0.012% or less, P: 0 to 0.05%, S: 0.010% or less, Ti: 0 to 0.003%, Nb: 0 to 0.003%, V: 0 to 0.002%, Cu: 0 to 0.1%, Cr: 0 to 0.1%, Mo: 0 to 0.03%, Ni: 0 to 0.1%, B: 0 to 0.001%, As: 0 to 0.1%, Sn: 0 to 0.1%, Sb: 0 to 0.05%, Ca: 0 to 0.001% Mg: 0-0.0015%, Co: 0-0.1%, Zr: 0-0.003%, W: 0-0.1%, Hf: 0-0.02%, Sc: 0-0.02%, Te: 0-0.005%, Sr: 0-0.02%, Bi: 0-0.1%, Ta: 0-0.02%, Zn: 0-0.02%, Pb: 0-0.1%, Ce: 0-0.0015%, Nd: 0-0.02%, REM: 0-0.02%, Ba: 0-0.02%, Cd: 0-0.02%, Pt: 0-0.02%, Au: 0 to 0.02%, Ga: 0 to 0.02%, A grain-oriented electrical steel sheet according to any one of claims 1 to 5, characterized in that it has a chemical composition consisting of Ge: 0 to 0.02%, Y: 0 to 0.02%, La: 0 to 0.02%, Se: 0 to 0.02%, and the remainder being Fe and impurities.

7. A method for manufacturing a grain-oriented electrical steel sheet according to claim 1 or 2, comprising: a hot rolling step of heating a slab and obtaining a hot-rolled steel sheet by hot rolling; a hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet; a cold rolling step of cold rolling the hot-rolled steel sheet after the hot-rolled steel sheet annealing step to obtain a cold-rolled steel sheet; a decarburization annealing step of decarburizing the cold-rolled steel sheet; an annealing separating agent application step of applying an annealing separating agent containing magnesia in slurry form to the cold-rolled steel sheet after the decarburization annealing step; a finish annealing step of performing finish annealing on the cold-rolled steel sheet after the annealing separating agent application step to obtain an intermediate steel sheet in which a glass film is formed on the surface of the cold-rolled steel sheet; and an insulating film forming step of forming an insulating film on the surface of the intermediate steel sheet after the finish annealing step to obtain a grain-oriented electrical steel sheet. The decarburization annealing process includes a heating process to raise the temperature of the cold-rolled steel sheet to a soaking temperature and a soaking process to maintain the temperature at the soaking temperature, wherein the soaking temperature is set to 800 to 870°C, the oxygen potential of the atmosphere is set to 0.70 to 0.95, and the soaking time is set to 80 to 150 seconds; the annealing separation agent application process includes a heating process to adjust the annealing separation agent into a slurry, with the temperature at which the slurry is stirred being 15°C or lower; the finish annealing process includes a heating process to raise the temperature of the cold-rolled steel sheet to a finish annealing temperature and a soaking process to maintain the temperature at the finish annealing temperature, wherein the heating process of the finish annealing includes an H2C at 850 to 900°C. ２ Gas injection rate: 2.5 to 7.0 Nm ３ A method for manufacturing grain-oriented electrical steel sheets, characterized by setting / h.

8. A method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 3 to 5, comprising: a hot rolling step of heating a slab and obtaining a hot-rolled steel sheet by hot rolling; a hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet; a cold rolling step of cold rolling the hot-rolled steel sheet after the hot-rolled steel sheet annealing step to obtain a cold-rolled steel sheet; a decarburization annealing step of decarburizing the cold-rolled steel sheet; an annealing separating agent application step of applying an annealing separating agent containing magnesia in slurry form to the cold-rolled steel sheet after the decarburization annealing step; a finish annealing step of performing finish annealing on the cold-rolled steel sheet after the annealing separating agent application step to obtain an intermediate steel sheet in which a glass film is formed on the surface of the cold-rolled steel sheet; and an insulating film forming step of forming an insulating film on the surface of the intermediate steel sheet after the finish annealing step to obtain a grain-oriented electrical steel sheet. The decarburization annealing process includes a heating process of raising the temperature of the cold-rolled steel sheet to a first soaking temperature in the range of 800°C to less than 900°C, a first soaking process of maintaining the temperature at the first soaking temperature, and a second soaking process of raising the temperature to a second soaking temperature in the range of 900 to 950°C and maintaining the temperature thereafter, wherein in the first soaking process the oxygen potential of the atmosphere is set to 0.40 to 0.60, in the second soaking process the oxygen potential of the atmosphere is set to 0.20 or less, the soaking time of the first soaking process is set to 60 to 150 seconds, the soaking time of the second soaking process is set to 10 seconds or more, and the sum of the soaking time of the first soaking process and the soaking time of the second soaking process is set to 170 seconds or less, and in the annealing separation agent coating process, when adjusting the annealing separation agent into a slurry, the temperature at which the slurry is stirred is set to 15°C or less. The finish annealing process includes a heating process to raise the temperature of the cold-rolled steel sheet to the finish annealing temperature and a soaking process to soak it at the finish annealing temperature, wherein the heating process of the finish annealing includes heating at 850 to 900°C. ２ Gas injection rate: 2.5 to 7.0 Nm ３ A method for manufacturing grain-oriented electrical steel sheets, characterized by setting / h.

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