Grain-oriented electromagnetic steel sheet and method for manufacturing grain-oriented electromagnetic steel sheet

Abstract

Provided is a grain-oriented electromagnetic steel sheet that enables reduction of iron loss and improvement of adhesiveness of a secondary coating film. In the grain-oriented electromagnetic steel sheet according to the present embodiment, when a glow discharge emission spectrometric analysis is carried out from the surface of the secondary coating film in a thickness direction of a base material steel sheet, a glow emission spectrum indicating relationships between a sputtering time and emission intensity of Mg and between a sputtering time and emission intensity of Sn is obtained, wherein when the maximum emission intensity of Mg is defined as IMg / Mg and the emission intensity of Sn at the sputtering time at which Mg reaches the maximum emission intensity is defined as ISn / Mg in the glow emission spectrum, the intensity ratio Iref defined by formula (1) is between 0.0000 and 0.0006, and the iron loss W17 / 50 is less than 0.90 W / kg.　(1): Iref=ISn / Mg / IMg / Mg

Description

Grain-oriented electrical steel sheet and method for manufacturing grain-oriented electrical steel sheet

[0001] The present disclosure relates to a grain-oriented electrical steel sheet and a method for manufacturing the grain-oriented electrical steel sheet.

[0002] Grain-oriented electrical steel sheets are steel sheets with a crystal orientation concentrated in the {110}<001> (Goss) direction. Grain-oriented electrical steel sheets are used as soft magnetic materials in the iron cores of transformers and other electrical equipment.

[0003] The method for producing grain-oriented electrical steel sheet is as follows: A slab is heated and hot-rolled to produce a hot-rolled steel sheet; The produced hot-rolled steel sheet is annealed; The hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet; The cold-rolled steel sheet is decarburization annealed to induce primary recrystallization; The cold-rolled steel sheet after decarburization annealing is finish annealed to induce secondary recrystallization. Grain-oriented electrical steel sheet is produced by the above steps.

[0004] As mentioned above, grain-oriented electrical steel sheets are used as iron core materials, so they are required to have high magnetic properties, specifically low core loss.

[0005] Increasing the density of Goss orientation is known as a technique for improving iron loss. Means for improving the density of Goss orientation are proposed in Japanese Patent Laid-Open Publication Nos. 6-049543 (Patent Document 1), 7-62436 (Patent Document 2), 10-280040 (Patent Document 3), and 2003-096520 (Patent Document 4).

[0006] In these documents, rapid heating is performed during the temperature rise process of decarburization annealing to induce primary recrystallization. Rapid heating enriches Goss-oriented grains, which act as nuclei for secondary recrystallization, in the primary recrystallized structure. As a result, the iron loss of grain-oriented electrical steel sheets is improved.

[0007] JP 6-049543, JP 7-62436, JP 10-280040, JP 2003-096520

[0008] Grain-oriented electrical steel sheets typically comprise a base steel sheet, a primary coating, and a secondary coating. The primary coating is formed on the base steel sheet. The secondary coating is formed on the primary coating. By providing the grain-oriented electrical steel sheet with the primary coating and the secondary coating, the insulation between the steel sheets is improved when the grain-oriented electrical steel sheet is used as an iron core.

[0009] The primary coating is forsterite (Mg ２ SiO ４ The primary coating contributes to tensioning the steel sheet and improving its insulation. The primary coating also plays a role in improving the adhesion of the secondary coating to the base steel sheet.

[0010] Therefore, in grain-oriented electrical steel sheets, it is necessary to reduce iron loss and improve the adhesion of the secondary coating. Patent Documents 1 to 4 do not consider achieving both a reduction in iron loss and an improvement in the adhesion of the secondary coating.

[0011] An object of the present disclosure is to provide a grain-oriented electrical steel sheet that can reduce iron loss and improve the adhesion of a secondary coating.

[0012] The grain-oriented electrical steel sheet according to the present disclosure has the following configuration.

[0013] A grain-oriented electrical steel sheet comprising: a base steel sheet; a primary coating formed on the base steel sheet; and a secondary coating formed on the primary coating, wherein the chemical composition of the base steel sheet is, in mass%, Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, Sn: 0.05 to 0.30%, N: 0.010% or less, C: 0.010% or less, sol. Al: 0.010% or less, one or more elements selected from the group consisting of S and Se: 0.020% or less in total, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance being Fe and impurities, wherein glow discharge optical emission spectroscopy is carried out from the surface of the secondary coating in the thickness direction of the base steel sheet to obtain a glow emission spectroscopy spectrum showing the relationship between sputtering time and the emission intensity of Mg and the emission intensity of Sn, and in the glow emission spectroscopy spectrum, Ｍｇ／Ｍｇ The emission intensity of Sn at the sputtering time when the emission intensity of Mg reaches the maximum is defined as I Ｓｎ／Ｍｇ When the intensity ratio I is defined as ｒｅｆ is 0.0000 to 0.0006, and the iron loss W １７／５０ A grain-oriented electrical steel sheet having a strength of less than 0.90 W / kg. ｒｅｆ =I Ｓｎ／Ｍｇ / I Ｍｇ／Ｍｇ (1)

[0014] The method for producing a grain-oriented electrical steel sheet according to the present disclosure includes the following steps.

[0015] The method for producing the grain-oriented electrical steel sheet described above is characterized in that the composition of the steel sheet is selected from the group consisting of Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, Sn: 0.05 to 0.30%, N: 0.002 to 0.020%, C: 0.020 to 0.100%, sol. a hot rolling process for producing a hot rolled steel sheet by hot rolling a slab having a chemical composition consisting of Al: 0.010 to 0.050%, one or more elements selected from the group consisting of S and Se: 0.010 to 0.050% in total, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance being Fe and impurities; a hot rolled steel sheet annealing process for annealing the hot rolled steel sheet; a pickling process for performing a pickling treatment on the hot rolled steel sheet after the hot rolled steel sheet annealing process; and a cold rolling process for cold rolling the hot rolled steel sheet after the pickling process to produce a cold rolled steel sheet. the cold-rolled steel sheet is subjected to decarburization annealing to produce a decarburization-annealed steel sheet; a finish annealing process in which an annealing separator is applied to the decarburization-annealed steel sheet and the decarburization-annealed steel sheet coated with the annealing separator is subjected to finish annealing to produce a finish annealed steel sheet on which the primary coating is formed; and a secondary coating forming process in which a secondary coating forming liquid is applied to the finish annealed steel sheet and the finish annealed steel sheet coated with the secondary coating forming liquid is subjected to heat treatment to form the secondary coating on the finish annealed steel sheet, wherein in the pickling process, the hydrochloric acid concentration in the pickling bath is set to 5 to 20% by mass and the bath temperature is set to 80 to 100°C, and the immersion time in the pickling bath is set to 30 to 120 seconds, and in the decarburization-annealing process, the rapid heating ultimate temperature Ta is set to 800 to 900°C, an average heating rate V1 during which the temperature of the cold-rolled steel sheet is increased from 550°C to the rapid heating temperature Ta is set to 100°C / sec or more, after which the temperature of the cold-rolled steel sheet is increased to the rapid heating temperature Ta, the cold-rolled steel sheet is held at a decarburization annealing temperature of 800 to 950°C for 60 seconds or more, and an average oxygen partial pressure ratio PO4 during the period of holding at the decarburization annealing temperature is set to 0.60 or less, and in the finish annealing step,a method for producing a grain-oriented electrical steel sheet, wherein an average heating rate V3 (°C / hour) during the temperature rise of the decarburization annealed steel sheet from 900°C to 1100°C and an average oxygen partial pressure ratio PO3 satisfy formulas (3) and (4), and the purity of hydrogen gas introduced into the furnace atmosphere of a finish annealing furnace used for the finish annealing is more than 99.9%: 31×Sn+5≦V3≦30 (3) 0.000≦PO3≦-0.020×Sn+0.015 (4) where Sn in formulas (3) and (4) is substituted with the Sn content in mass% in the slab.

[0016] The grain-oriented electrical steel sheet according to the present disclosure can reduce iron loss and improve adhesion of the secondary coating. The method for manufacturing a grain-oriented electrical steel sheet according to the present disclosure can manufacture the above-mentioned grain-oriented electrical steel sheet.

[0017] Fig. 1 is a perspective view of a grain-oriented electrical steel sheet according to the present embodiment. Fig. 2 is a diagram showing glow discharge optical emission spectroscopy spectra of Mg and Sn (GDS spectrum of Mg, GDS spectrum of Sn) obtained by performing glow discharge optical emission spectroscopy from the surface of the secondary coating of the grain-oriented electrical steel sheet in the sheet thickness direction.

[0018] The present inventors first investigated chemical compositions as a means for reducing iron loss in grain-oriented electrical steel sheets having a primary coating and a secondary coating, and concluded that iron loss can be reduced to a certain extent if the base steel sheet of the grain-oriented electrical steel sheet has a chemical composition, by mass%, of Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, N: 0.010% or less, C: 0.010% or less, sol. Al: 0.010% or less, S: 0.010% or less, Se: 0.010% or less, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance being Fe and impurities.

[0019] However, the above-mentioned chemical composition did not result in a sufficient reduction in iron loss. Therefore, the inventors conducted further studies and obtained the following findings.

[0020] In the above-described chemical composition, if 0.05 to 0.30% Sn is further added in place of a portion of the Fe, the degree of integration in the Goss orientation can be increased. As a result, iron loss can be sufficiently reduced. Specifically, the grain-oriented electrical steel sheet of this embodiment can increase the degree of integration in the Goss orientation and reduce iron loss by satisfying the following feature 1. (Feature 1) The chemical composition of the base steel sheet is, in mass %, Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, Sn: 0.05 to 0.30%, N: 0.010% or less, C: 0.010% or less, sol. Al: 0.010% or less, one or more elements selected from the group consisting of S and Se: 0.020% or less in total, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance being Fe and impurities.

[0021] However, it has been newly discovered that even if a grain-oriented electrical steel sheet satisfies Feature 1, that is, even if the chemical composition of the base steel sheet contains the above-mentioned amount of Sn, it may not be possible to sufficiently improve the adhesion of the secondary coating. Therefore, the inventors further investigated means for achieving both a reduction in iron loss and an improvement in the adhesion of the secondary coating. As a result, the inventors have obtained the following findings.

[0022] As described above, Sn reduces the iron loss of grain-oriented electrical steel sheets. However, because Sn is a segregation element, Sn tends to segregate in the surface layer of the base steel sheet. Therefore, during the manufacturing process of grain-oriented electrical steel sheets, Sn segregated in the surface layer of the base steel sheet tends to diffuse into the primary coating. If Sn diffuses excessively into the primary coating, the region of the primary coating where the excess Sn has penetrated will not have a dense structure compared to other regions, but will have a porous structure. Such a porous region of the primary coating is referred to as a "porous region."

[0023] The secondary coating is formed on the surface of the primary coating. If the primary coating contains an excessive amount of porous regions, the portion of the secondary coating formed on the porous regions is susceptible to the effects of Sn segregated in the surface layer of the base steel sheet. Specifically, the adhesion of the portion of the secondary coating formed on the porous regions is reduced due to Sn segregated in the surface layer of the base steel sheet.

[0024] Therefore, in order to simultaneously reduce the iron loss of grain-oriented electrical steel sheets and improve the adhesion of the secondary coating, it is effective to suppress the porous regions in the primary coating, and in order to reduce the porous regions in the primary coating, it is effective to reduce the Sn content of the primary coating.

[0025] Therefore, in the grain-oriented electrical steel sheet of this embodiment, the glow emission spectroscopy spectrum from the surface of the grain-oriented electrical steel sheet in the sheet thickness direction is used as an index of the Sn content in the primary coating. Specifically, glow discharge optical emission spectroscopy is performed from the surface of the secondary coating of the grain-oriented electrical steel sheet in the sheet thickness direction of the base steel sheet to obtain a glow emission spectroscopy spectrum that shows the relationship between sputtering time and the emission intensity of Mg and the emission intensity of Sn. In the glow emission spectroscopy spectrum, the following items are defined: The maximum emission intensity of Mg is I Ｍｇ／Ｍｇ The emission intensity of Sn at the sputtering time when the emission intensity of Mg is maximum is defined as I Ｓｎ／Ｍｇ It is defined as:

[0026] As mentioned above, the primary coating is forsterite (Mg ２ SiO ４ ) is the main focus. Ｍｇ／Ｍｇ The position where I is detected means that it is the primary coating. Ｓｎ／Ｍｇ I Ｍｇ／Ｍｇ Therefore, I Ｓｎ／Ｍｇ can be used as an index of the Sn content in the primary coating. Ｍｇ／Ｍｇ and I Ｓｎ／ＭｇThe inventors further investigated the relationship between the strength ratio I defined by the formula (1) and the adhesion of the secondary coating. As a result, they found that if a grain-oriented electrical steel sheet satisfying the characteristic 1 also has the following characteristics 2 and 3, it is possible to sufficiently reduce iron loss and also sufficiently improve the adhesion of the secondary coating. (Characteristic 2) ｒｅｆ is 0.0000 to 0.0006. ｒｅｆ =I Ｓｎ／Ｍｇ / I Ｍｇ／Ｍｇ (1) (Feature 3) Iron loss W conforming to JIS C2556:2015 １７／５０ is less than 0.90 W / kg.

[0027] The grain-oriented electrical steel sheet of this embodiment has been completed based on the above findings. The grain-oriented electrical steel sheet of this embodiment has the following configuration, and the method for manufacturing the grain-oriented electrical steel sheet of this embodiment includes the following steps.

[0028] [1] A grain-oriented electrical steel sheet comprising: a base steel sheet; a primary coating formed on the base steel sheet; and a secondary coating formed on the primary coating, wherein the chemical composition of the base steel sheet is, in mass%, Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, Sn: 0.05 to 0.30%, N: 0.010% or less, C: 0.010% or less, sol. Al: 0.010% or less, one or more elements selected from the group consisting of S and Se: 0.020% or less in total, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance being Fe and impurities, wherein glow discharge optical emission spectroscopy is carried out from the surface of the secondary coating in the thickness direction of the base steel sheet to obtain a glow emission spectroscopy spectrum showing the relationship between sputtering time and the emission intensity of Mg and the emission intensity of Sn, and in the glow emission spectroscopy spectrum, Ｍｇ／Ｍｇ The emission intensity of Sn at the sputtering time when the emission intensity of Mg reaches the maximum is defined as I Ｓｎ／Ｍｇ When the intensity ratio I is defined as ｒｅｆis 0.0000 to 0.0006, and the iron loss W １７／５０ A grain-oriented electrical steel sheet having a strength of less than 0.90 W / kg. ｒｅｆ =I Ｓｎ／Ｍｇ / I Ｍｇ／Ｍｇ (1)

[0029] [2] The grain-oriented electrical steel sheet according to [1], Ｓｎ／Ｍｇ A grain-oriented electrical steel sheet, wherein the σ is 0.0021 or less.

[0030] [3] The grain-oriented electrical steel sheet according to [1] or [2], wherein in the glow emission spectrum, Ｓｎ／Ｍｇ The emission intensity of Sn at the time when 20.0 seconds have elapsed since the sputtering time when the value of Ｓｎ／Ｍｇ＋２０ When the Sn concentration gradient ΔI is defined as Ｓｎ Grain-oriented electrical steel sheet ΔI is 0.0000 to 0.0004 / sec. Ｓｎ = (I Ｓｎ／Ｍｇ＋２０ -I Ｓｎ／Ｍｇ ) / 20 (2)

[0031] [4] The grain-oriented electrical steel sheet according to any one of [1] to [3], wherein the chemical composition of the base steel sheet contains one or more elements selected from the group consisting of P: 0.01 to 0.05%, Sb: 0.01 to 0.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, and Bi: 0.0001 to 0.0100%.

[0032] [5] A method for producing a grain-oriented electrical steel sheet according to [1], wherein Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, Sn: 0.05 to 0.30%, N: 0.002 to 0.020%, C: 0.020 to 0.100%, sol. a hot rolling process for producing a hot rolled steel sheet by hot rolling a slab having a chemical composition consisting of Al: 0.010 to 0.050%, one or more elements selected from the group consisting of S and Se: 0.010 to 0.050% in total, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance being Fe and impurities; a hot rolled steel sheet annealing process for annealing the hot rolled steel sheet; a pickling process for performing a pickling treatment on the hot rolled steel sheet after the hot rolled steel sheet annealing process; and a cold rolling process for cold rolling the hot rolled steel sheet after the pickling process to produce a cold rolled steel sheet. the cold-rolled steel sheet is subjected to decarburization annealing to produce a decarburization-annealed steel sheet; a finish annealing process in which an annealing separator is applied to the decarburization-annealed steel sheet and the decarburization-annealed steel sheet coated with the annealing separator is subjected to finish annealing to produce a finish annealed steel sheet on which the primary coating is formed; and a secondary coating forming process in which a secondary coating forming liquid is applied to the finish annealed steel sheet and the finish annealed steel sheet coated with the secondary coating forming liquid is subjected to heat treatment to form the secondary coating on the finish annealed steel sheet, wherein in the pickling process, the hydrochloric acid concentration in the pickling bath is set to 5 to 20% by mass and the bath temperature is set to 80 to 100°C, and the immersion time in the pickling bath is set to 30 to 120 seconds, and in the decarburization-annealing process, the rapid heating ultimate temperature Ta is set to 800 to 900°C, an average heating rate V1 during which the temperature of the cold-rolled steel sheet is increased from 550°C to the rapid heating temperature Ta is set to 100°C / sec or more, after which the temperature of the cold-rolled steel sheet is increased to the rapid heating temperature Ta, the cold-rolled steel sheet is held at a decarburization annealing temperature of 800 to 950°C for 60 seconds or more, and an average oxygen partial pressure ratio PO4 during the period of holding at the decarburization annealing temperature is set to 0.60 or less, and in the finish annealing step,a method for producing a grain-oriented electrical steel sheet, wherein an average heating rate V3 (°C / hour) during the temperature rise of the decarburization annealed steel sheet from 900°C to 1100°C and an average oxygen partial pressure ratio PO3 satisfy formulas (3) and (4), and the purity of hydrogen gas introduced into the furnace atmosphere of a finish annealing furnace used for the finish annealing is more than 99.9%: 31×Sn+5≦V3≦30 (3) 0.000≦PO3≦-0.020×Sn+0.015 (4) where Sn in formulas (3) and (4) is substituted with the Sn content in mass% in the slab.

[0033] [6] The method for producing a grain-oriented electrical steel sheet according to [5], wherein in the decarburization annealing step, the average oxygen partial pressure ratio PO4 further satisfies the following formula (5): 0.88×Sn+0.19≦PO4≦0.60 (5) where Sn in formula (5) is substituted with the Sn content in mass% in the slab.

[0034] [7] The method for producing a grain-oriented electrical steel sheet according to [5] or [6], wherein the chemical composition of the slab contains one or more elements selected from the group consisting of P: 0.01 to 0.05%, Sb: 0.01 to 0.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, and Bi: 0.0001 to 0.0100%.

[0035] The grain-oriented electrical steel sheet and the method for manufacturing the grain-oriented electrical steel sheet according to this embodiment will be described in detail below. Note that "%" relating to elements means mass % unless otherwise specified.

[0036] [Configuration of Grain-Oriented Electrical Steel Sheet] Fig. 1 is a perspective view of a grain-oriented electrical steel sheet according to this embodiment. In the figure, direction L means the rolling direction of the grain-oriented electrical steel sheet. Direction W means the sheet width direction of the grain-oriented electrical steel sheet. Direction T means the sheet thickness direction of the grain-oriented electrical steel sheet.

[0037] Referring to Fig. 1 , a grain-oriented electrical steel sheet 1 according to this embodiment includes a base steel sheet 10, a primary coating 11, and a secondary coating 12. The primary coating 11 is formed on the base steel sheet 10. In Fig. 1 , the primary coating 11 is formed on the surface of the base steel sheet 10 in direct contact with the surface of the base steel sheet 10. The secondary coating 12 is formed on the primary coating 11. As shown in Fig. 1 , the primary coating 11 and the secondary coating 12 are formed on a pair of surfaces of the base steel sheet 10 (i.e., the front and back surfaces of the base steel sheet 10).

[0038] The grain-oriented electrical steel sheet 1 of this embodiment satisfies the following Features 1 to 3. (Feature 1) The chemical composition of the base steel sheet 10 is, in mass%, Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, Sn: 0.05 to 0.30%, N: 0.010% or less, C: 0.010% or less, sol. Al: 0.010% or less, one or more elements selected from the group consisting of S and Se: 0.020% or less in total, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance being Fe and impurities. (Feature 2) Glow discharge optical emission spectroscopy is performed from the surface of the secondary coating 12 in the thickness direction of the base steel sheet 10 to obtain a glow emission spectrum showing the relationship between the sputtering time and the optical emission intensity of Mg and the optical emission intensity of Sn. In the glow emission spectrum, the maximum optical emission intensity of Mg is determined as I Ｍｇ／Ｍｇ The emission intensity of Sn at the sputtering time when the emission intensity of Mg is maximum is defined as I Ｓｎ／Ｍｇ When the intensity ratio I is defined as ｒｅｆ is 0.0000 to 0.0006. ｒｅｆ =I Ｓｎ／Ｍｇ / I Ｍｇ／Ｍｇ (1)

[0039] (Feature 3) Iron loss W conforming to JIS C2556:2015 １７／５０ is less than 0.90 W / kg.

[0040] Hereinafter, features 1 to 3 of the grain-oriented electrical steel sheet 1 of this embodiment will be described.

[0041] [(Feature 1) Chemical Composition of Base Steel Plate 10] The chemical composition of the base steel plate 10 contains the following elements.

[0042] Si: 2.50 to 4.50% Silicon (Si) increases the electrical resistance (specific resistance) of the steel material and reduces the iron loss of the grain-oriented electrical steel sheet 1. If the Si content is less than 2.50%, even if the contents of other elements are within the ranges of this embodiment, the steel undergoes phase transformation during the finish annealing process, and secondary recrystallization does not proceed sufficiently. As a result, the above-mentioned effect is not fully achieved. On the other hand, if the Si content exceeds 4.50%, the steel sheet becomes embrittled even if the contents of other elements are within the ranges of this embodiment. Therefore, the Si content is 2.50 to 4.50%. A preferred lower limit of the Si content is 2.80%, more preferably 3.00%, and even more preferably 3.20%. A preferred upper limit of the Si content is 4.20%, more preferably 4.00%, even more preferably 3.70%, even more preferably 3.60%, and even more preferably 3.50%.

[0043] Mn: 0.01 to 1.00% Manganese (Mn) increases the resistivity of the grain-oriented electrical steel sheet 1 and reduces iron loss. Mn also improves hot workability and suppresses cracking during hot rolling. Mn further combines with S and / or Se to form fine MnS and / or fine MnSe. Fine MnS and fine MnSe serve as precipitation nuclei for fine AlN, which acts as an inhibitor. Therefore, a sufficient amount of fine AlN can be obtained if the precipitation amounts of fine MnS and fine MnSe are large. If the Mn content is less than 0.01%, sufficient amounts of fine MnS and fine MnSe will not precipitate, even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mn content exceeds 1.00%, the magnetic flux density of the grain-oriented electrical steel sheet 1 will decrease and iron loss will also deteriorate, even if the contents of other elements are within the ranges of this embodiment. Therefore, the Mn content is 0.01 to 1.00%. The lower limit of the Mn content is preferably 0.02%, more preferably 0.03%, and even more preferably 0.05%. The upper limit of the Mn content is preferably 0.70%, more preferably 0.50%, even more preferably 0.30%, and even more preferably 0.10%.

[0044] Sn: 0.05 to 0.30% Tin (Sn) improves the primary recrystallization texture by applying rapid heating during the temperature rise process in the decarburization annealing step. Specifically, it enriches the steel sheet with the Goss orientation, which serves as the nucleus for secondary recrystallization. This reduces the iron loss of the grain-oriented electrical steel sheet 1. If the Sn content is less than 0.05%, the above effects cannot be fully achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Sn content exceeds 0.30%, the steel sheet becomes embrittled or secondary recrystallization becomes unstable during the manufacturing process of the grain-oriented electrical steel sheet 1, even if the contents of other elements are within the ranges of this embodiment. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 deteriorate. Therefore, the Sn content is 0.05 to 0.30%. The preferred lower limit of the Sn content is 0.07%, more preferably 0.09%, and even more preferably 0.11%. The upper limit of the Sn content is preferably 0.28%, more preferably 0.25%, even more preferably 0.22%, and still more preferably 0.20%.

[0045] N: 0.010% or less Nitrogen (N) combines with Al to form AlN during the manufacturing process of the grain-oriented electrical steel sheet 1, functioning as an inhibitor. Therefore, N is an essential element for the slab, which is the raw material for the grain-oriented electrical steel sheet 1. However, N is lost from the steel sheet during the manufacturing process of the grain-oriented electrical steel sheet 1. If the N content in the grain-oriented electrical steel sheet 1 exceeds 0.010%, nitrides that cause magnetic aging are likely to form. Therefore, the N content is 0.010% or less. The preferred lower limit of the N content is 0.001%, more preferably 0.002%. The preferred upper limit of the N content is 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0046] C: 0.010% or less Carbon (C) is an essential element in slabs to improve magnetic flux density. However, C is lost from the steel sheet during the manufacturing process of the grain-oriented electrical steel sheet 1. If the C content in the grain-oriented electrical steel sheet 1 exceeds 0.010%, C will not form cementite (Fe) even if the contents of other elements are within the range of this embodiment.３ In this case, the iron loss of the grain-oriented electrical steel sheet 1 deteriorates. Therefore, the C content is 0.010% or less. A preferred lower limit of the C content is 0.001%, and more preferably 0.002%. A preferred upper limit of the C content is 0.009%, and more preferably 0.008%, and even more preferably 0.007%.

[0047] Sol. Al: 0.010% or less Acid-soluble aluminum (sol. Al) combines with N to form AlN during the manufacturing process of the grain-oriented electrical steel sheet 1, functioning as an inhibitor. However, if the sol. Al content exceeds 0.010%, Al-based inclusions remain in the steel sheet even if the contents of other elements are within the ranges of this embodiment. In this case, the iron loss of the grain-oriented electrical steel sheet 1 deteriorates. Therefore, the sol. Al content is 0.010% or less. The preferred lower limit of the sol. Al content is 0.001%, more preferably 0.002%. The preferred upper limit of the sol. Al content is 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0048] One or more elements selected from the group consisting of S and Se: 0.020% or less in total. Sulfur (S) and selenium (Se) combine with Mn during the manufacturing process to form fine MnS or MnSe, which act as inhibitors. Therefore, S and Se are essential elements in slabs. However, S and Se are lost from the steel sheet during the manufacturing process of the grain-oriented electrical steel sheet 1. If the total content of one or more elements selected from the group consisting of S and Se in the grain-oriented electrical steel sheet 1 exceeds 0.020%, MnS or MnSe will remain in the base steel sheet 10 even if the contents of other elements are within the ranges of this embodiment. In this case, the iron loss of the grain-oriented electrical steel sheet 1 will deteriorate. Therefore, the total content of one or more elements selected from the group consisting of S and Se is 0.020% or less. The preferred lower limit of the total content of one or more elements selected from the group consisting of S and Se is 0.001%, and more preferably 0.002%. The upper limit of the total content of one or more elements selected from the group consisting of S and Se is preferably 0.018%, more preferably 0.016%, and even more preferably 0.014%. Preferably, the S content or the total content of S and Se is 0.020% or less. The Se content may be 0%.

[0049] The balance of the chemical composition of the base steel sheet 10 is made up of Fe and impurities. Here, the term "impurities" refers to substances that are mixed in from raw materials such as ore, scrap, or the manufacturing environment when industrially manufacturing the base steel sheet 10, which is the material for the grain-oriented electrical steel sheet 1, and are not intentionally contained but are allowed to the extent that they do not adversely affect the grain-oriented electrical steel sheet 1 of this embodiment.

[0050] [Optional Elements] The chemical composition of the base steel plate 10 may further contain one or more elements selected from the group consisting of P, Sb, Cr, Cu, Ni, and Bi in place of a portion of Fe.

[0051] P: 0.00 to 0.05% Phosphorus (P) is an optional element and does not necessarily need to be contained. In other words, the P content may be 0.00%. P improves the primary recrystallization texture during the manufacturing process of the grain-oriented electrical steel sheet 1 and reduces the iron loss of the grain-oriented electrical steel sheet 1. Even if even a small amount of P is contained, the above effects can be obtained to some extent. However, P reduces the workability of the steel sheet. If the P content exceeds 0.05%, the workability of the steel sheet will significantly decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the P content is 0.00 to 0.05%. The preferred lower limit of the P content is 0.01%, and more preferably 0.02%. The preferred upper limit of the P content is 0.04%, and more preferably 0.03%.

[0052] Sb: 0.00 to 0.50% Antimony (Sb) is an optional element and does not necessarily need to be contained. That is, the Sb content may be 0.00%. When contained, Sb functions as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the grain-oriented electrical steel sheet 1. As a result, iron loss of the grain-oriented electrical steel sheet 1 is reduced. Even if even a small amount of Sb is contained, the above effect can be achieved to some extent. However, if the Sb content exceeds 0.50%, the adhesion of the primary coating to the base steel sheet 10 decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Sb content is 0.00 to 0.50%. The preferred lower limit of the Sb content is 0.01%, more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Sb content is 0.40%, more preferably 0.30%, even more preferably 0.20%, and even more preferably 0.10%.

[0053] Cr: 0.00 to 0.50% Chromium (Cr) is an optional element and does not necessarily need to be contained. In other words, the Cr content may be 0.00%. When contained, Cr increases the concentration of Goss-oriented grains during secondary recrystallization in the manufacturing process of the grain-oriented electrical steel sheet 1. Even if a small amount of Cr is contained, the above effect can be achieved to some extent. However, if the Cr content exceeds 0.50%, Cr oxides will form even if the contents of other elements are within the ranges of this embodiment. In this case, the iron loss of the grain-oriented electrical steel sheet 1 will deteriorate. Therefore, the Cr content is 0.00 to 0.50%. The preferred lower limit of the Cr content is 0.01%, more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Cr content is 0.40%, more preferably 0.30%, even more preferably 0.20%, and even more preferably 0.10%.

[0054] Cu: 0.00 to 0.50% Copper (Cu) is an optional element and does not necessarily need to be contained. That is, the Cu content may be 0.00%. When contained, Cu improves the adhesion of the primary coating 11 to the base steel sheet 10. Even if even a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content exceeds 0.50%, the hot workability during the manufacturing process of the grain-oriented electrical steel sheet 1 deteriorates even if the contents of other elements are within the ranges of this embodiment. Therefore, the Cu content is 0.00 to 0.50%. The preferred lower limit of the Cu content is 0.01%, more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Cu content is 0.40%, more preferably 0.30%, even more preferably 0.20%, and even more preferably 0.10%.

[0055] Ni: 0.00 to 0.50% Nickel (Ni) is an optional element and does not necessarily need to be contained. In other words, the Ni content may be 0.00%. When contained, Ni increases the concentration of Goss-oriented grains during secondary recrystallization in the manufacturing process of the grain-oriented electrical steel sheet 1. Even if even a small amount of Ni is contained, the above effect can be achieved to some extent. However, if the Ni content exceeds 0.50%, secondary recrystallization becomes unstable even if the contents of other elements are within the ranges of this embodiment. In this case, the iron loss of the grain-oriented electrical steel sheet 1 deteriorates. Therefore, the Ni content is 0.00 to 0.50%. The preferred lower limit of the Ni content is 0.01%, more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Ni content is 0.40%, more preferably 0.30%, even more preferably 0.20%, and even more preferably 0.10%.

[0056] Bi: 0.0000 to 0.0100% Bi (bismuth) is an optional element and does not necessarily need to be contained. That is, the Bi content may be 0.0000%. When contained, Bi functions as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the grain-oriented electrical steel sheet 1. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. Even if even a small amount of Bi is contained, the above effect can be achieved to some extent. However, if the Bi content exceeds 0.0100%, the adhesion of the primary coating 11 to the base steel sheet 10 decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Bi content is 0.0000 to 0.0100%. The preferred lower limit of the Bi content is 0.0001%, more preferably 0.0005%, even more preferably 0.0010%, and even more preferably 0.0020%. The upper limit of the Bi content is preferably 0.0090%, more preferably 0.0070%, and even more preferably 0.0050%.

[0057] [Method for measuring the chemical composition of the base steel sheet 10] The chemical composition of the base steel sheet of this embodiment can be measured by a known elemental analysis method. First, the primary coating 11 and the secondary coating 12 are removed from the base steel sheet 10 by the following method. Specifically, the grain-oriented electrical steel sheet 1 with the secondary coating 12 is immersed in a high-temperature alkaline solution to remove the coating. The composition, temperature, and immersion time of the alkaline solution may be adjusted as appropriate. For example, the grain-oriented electrical steel sheet 1 with the secondary coating 12 is immersed in a high-temperature alkaline solution containing 30 to 50% by mass of NaOH + H ２ O: The steel sheet is immersed in a 50 to 70 mass % aqueous sodium hydroxide solution at 80 to 90°C for 5 to 10 minutes. After immersion, the steel sheet is rinsed with water and then dried. This process removes the secondary coating 12 from the grain-oriented electrical steel sheet 1.

[0058] Furthermore, the grain-oriented electrical steel sheet 1 from which the secondary coating 12 has been removed and from which the primary coating 11 remains is immersed in high-temperature hydrochloric acid to remove the coating. The concentration, temperature, and immersion time of the hydrochloric acid may be adjusted as appropriate. For example, the grain-oriented electrical steel sheet 1 from which the secondary coating 12 has been removed and from which the primary coating 11 remains is immersed in 30 to 40 mass % hydrochloric acid at 80 to 90°C for 1 to 5 minutes. After immersion, the steel sheet is rinsed with water and then dried. Through the above steps, a base steel sheet 10 from which the secondary coating 12 and primary coating 11 have been removed is obtained.

[0059] Chips are collected from the obtained base steel plate 10. The collected chips are dissolved in acid to obtain a solution. ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) is performed on the solution to perform elemental analysis of the chemical composition. The C content and S content are determined by the well-known high-frequency combustion method (combustion-infrared absorption method). The N content is determined using the well-known inert gas fusion-thermal conductivity method. Specifically, the analysis can be performed using, for example, a component analyzer manufactured by Shimadzu Corporation (product name: ICPS-8000).

[0060] The content of each element is determined by rounding off the measured value to the nearest significant digit based on the significant digits specified in this embodiment. For example, the C content of the base steel plate in this embodiment is determined to be a value up to three decimal places. Therefore, the C content is determined to be a value up to three decimal places obtained by rounding off the measured value to the fourth decimal place.

[0061] Similarly, the contents of other elements other than the C content of the base steel plate of this embodiment are also determined by rounding off the measured value to the smallest digit specified in this embodiment, and the value obtained is the content of the element.

[0062] Rounding off means rounding down if the fraction is less than 5, and rounding up if the fraction is 5 or more.

[0063] [Regarding the Primary Coating 11] The primary coating 11 is made of forsterite (Mg ２ SiO ４ Specifically, the primary coating 11 contains forsterite in a mass % of 50% or more. The primary coating 11 is formed by separating the annealing separator containing magnesia and the SiO 2 on the surface of the base steel sheet 10 during the final annealing. ２ The primary coating 11 is formed by a reaction between the oxide film of the annealing separator and the elements contained in the base steel sheet 10, such as forsterite, and spinel (MgAl ２ O ４ ) and sulfides. The sulfides contain one or more of Mn, Ca, and Ti.

[0064] [Regarding the Secondary Coating 12] The secondary coating 12 is formed on the primary coating 11. When multiple grain-oriented electrical steel sheets 1 are stacked together, the secondary coating 12 ensures insulation between the stacked grain-oriented electrical steel sheets 1. The secondary coating 12 has a well-known configuration. Specifically, the secondary coating 12 contains at least one inorganic substance, such as a metal chromate, a metal phosphate, colloidal silica, a Zr compound, or a Ti compound. Preferably, the secondary coating 12 is a coating mainly containing a phosphate compound. In other words, the secondary coating 12 contains a phosphate compound.

[0065] The secondary coating 12 may contain, for example, one or more selected from the group consisting of colloidal silica and polytetrafluoroethylene together with a phosphate compound. Examples of the phosphate compound include sodium phosphate, aluminum phosphate, and magnesium phosphate.

[0066] [(Feature 2) Intensity ratio I ｒｅｆ Regarding the grain-oriented electrical steel sheet 1 of this embodiment, the ratio of the Sn concentration to the Mg concentration in the primary coating is further sufficiently low. Specifically, glow discharge optical emission spectroscopy is performed from the surface of the secondary coating 12 in the thickness direction T of the base steel sheet 10, and a glow emission spectrum is obtained that shows the relationship between the sputtering time and the emission intensity of Mg and the emission intensity of Sn. In the obtained glow emission spectrum, the maximum emission intensity of Mg is expressed as I Ｍｇ／Ｍｇ The emission intensity of Sn at the sputtering time when the emission intensity of Mg is maximum is defined as I Ｓｎ／Ｍｇ In this case, the intensity ratio I defined by equation (1) ｒｅｆ is 0.0000 to 0.0006. ｒｅｆ =I Ｓｎ／Ｍｇ / I Ｍｇ／Ｍｇ (1) Below, intensity ratio I ｒｅｆ This article explains:

[0067] Sn in the base steel sheet 10 promotes the enrichment of fine Goss-oriented grains during primary recrystallization. Therefore, Sn increases the concentration of Goss-oriented grains in the grain-oriented electrical steel sheet 1, thereby reducing the iron loss of the grain-oriented electrical steel sheet 1.

[0068] On the other hand, Sn is a segregation element and therefore tends to segregate in the surface layer of the base steel sheet 10. Therefore, in the manufacturing process of the grain-oriented electrical steel sheet 1, the Sn segregated in the surface layer of the base steel sheet 10 diffuses into the primary coating 11. If Sn diffuses excessively into the primary coating 11, the region in the primary coating 11 into which the excess Sn has penetrated will not have a dense structure compared to other regions, but will become a porous region.

[0069] The secondary coating 12 is formed on the surface of the primary coating 11. If the primary coating 11 contains an excessive number of porous regions, the portion of the secondary coating 12 formed on the porous regions is susceptible to the influence of Sn segregated in the surface layer of the base steel sheet 10. Specifically, the adhesion of the portion of the secondary coating 12 formed on the porous regions is reduced due to Sn segregated in the surface layer of the base steel sheet 10.

[0070] Therefore, in order to achieve both a reduction in iron loss of the directional electrical steel sheet 1 and an improvement in the adhesion of the secondary coating 12, it is effective to give the base steel sheet 10 a chemical composition that satisfies Feature 1 and to suppress the generation of porous regions within the primary coating 11.

[0071] Fig. 2 is a diagram showing glow emission spectroscopy spectra of Mg and Sn (GDS spectrum of Mg, GDS spectrum of Sn) obtained by glow discharge optical emission spectroscopy in the sheet thickness direction T from the surface of the secondary coating 12 of the grain-oriented electrical steel sheet 1. The horizontal axis of Fig. 2 represents the sputtering time in the glow discharge optical emission spectroscopy analysis, and the vertical axis represents the emission intensity of Mg and the emission intensity of Sn. Referring to Fig. 2, I Ｍｇ , I Ｓｎ , I Ｍｇ／Ｍｇ , I Ｓｎ／Ｍｇ , I ｒｅｆ is defined as follows:

[0072] I ＭｇGlow discharge optical emission spectroscopy is performed from the surface of the grain-oriented electrical steel sheet 1, i.e., the surface of the secondary coating 12, in the sheet thickness direction T of the grain-oriented electrical steel sheet 1. A glow discharge optical emission spectroscopy spectrum of Mg (GDS spectrum of Mg) is obtained by the glow discharge optical emission spectroscopy. The GDS spectrum of Mg shows the relationship between sputtering time and the emission intensity of Mg, with the surface of the secondary coating 12 being the measurement start time (i.e., sputtering time = 0). The obtained GDS spectrum of Mg is Ｍｇ It is defined as:

[0073] I Ｓｎ The glow discharge optical emission spectrum of Sn (GDS spectrum of Sn) is obtained by the above-mentioned glow discharge optical emission spectroscopy. The obtained GDS spectrum of Sn is Ｓｎ When the emission intensity is 0.01 or less, the GDS spectrum is smoothed to remove noise. For smoothing, a 50-section moving average is used as an approximation. One section represents the measurement interval, which is 0.025 seconds.

[0074] For the purpose of zero-point correction of the Sn emission intensity, the offset value is the Sn emission intensity in each section of the GDS spectrum of a reference steel sheet having a chemical composition with an Sn content of 0% and containing elements other than Sn as described in Feature 1, with the balance consisting of Fe and impurities, and with the content of each element falling within the content range of the corresponding element as described in Feature 1. The value obtained by subtracting the Sn offset value of the reference steel sheet from each section of the Sn GDS spectrum obtained above is taken as the Sn emission intensity in each section.

[0075] I Ｍｇ／Ｍｇ : The maximum emission intensity in the GDS spectrum of Mg is I Ｍｇ／Ｍｇ It is defined as:

[0076] I Ｓｎ／Ｍｇ : I in the GDS spectrum of Mg Ｍｇ／Ｍｇ The sputtering time at T Ｍｇ In the GDS spectrum of Sn, the sputtering time T Ｍｇ The emission intensity of Sn at I Ｓｎ／Ｍｇ It is defined as:

[0077] I ｒｅｆ : I Ｓｎ／Ｍｇ No, IＭｇ／Ｍｇ The ratio to the intensity ratio I ｒｅｆ That is, the intensity ratio I ｒｅｆ is defined by equation (1). ｒｅｆ =I Ｓｎ／Ｍｇ / I Ｍｇ／Ｍｇ (1)

[0078] As described above, the primary coating 11 is made of forsterite (Mg ２ SiO ４ ) and has the highest Mg content compared to the secondary coating 12 and the base steel sheet 10. Therefore, in FIG. 2, the GDS spectrum I of Mg Ｍｇ I in Ｍｇ／Ｍｇ The region 11 including the Sn GDS spectrum I corresponds to the primary coating 11. Ｓｎ The region 10 where the Sn intensity is almost constant even with the passage of sputtering time corresponds to the base steel sheet 10. The region 10 where the sputtering time is shorter than that of the primary coating 11 and the Mg GDS spectrum I Ｍｇ The region 12 where the Mg intensity remains almost constant even with the passage of sputtering time corresponds to the secondary coating 12.

[0079] The intensity ratio I defined by equation (1) ｒｅｆ is an index of the Sn concentration relative to the Mg concentration in the primary coating 11. ｒｅｆ If the Sn concentration exceeds 0.0006, the Sn concentration in the primary coating 11 is excessively high. In this case, the primary coating 11 has an excessively large number of porous regions. Therefore, even if the grain-oriented electrical steel sheet 1 satisfies Feature 1 and has excellent iron loss properties, the adhesion of the secondary coating 12 decreases.

[0080] intensity ratio I ｒｅｆ If the strength ratio I is 0.0006 or less, the grain-oriented electrical steel sheet 1 satisfying Feature 1 can achieve both excellent iron loss and excellent adhesion of the secondary coating 12. Therefore, in the grain-oriented electrical steel sheet 1 of this embodiment, ｒｅｆ is 0.0000 to 0.0006.

[0081] intensity ratio I ｒｅｆ The upper limit of the intensity ratio I is preferably 0.0005, and more preferably 0.0004. ｒｅｆThe lower limit is preferably as low as possible.

[0082] In addition, I Ｓｎ／Ｍｇ The upper limit of I is preferably 0.0021 or less, more preferably 0.0020, even more preferably 0.0018, even more preferably 0.0016, and even more preferably 0.0014. Ｓｎ／Ｍｇ The lower limit of is preferably 0.0001, more preferably 0.0000.

[0083] [Intensity ratio I ｒｅｆ Determination method of intensity ratio I ｒｅｆ can be determined by the following method: First, a sample is taken from the center of the grain-oriented electrical steel sheet 1 in the sheet width direction W, measuring 30 mm in the rolling direction L and 40 mm in the sheet width direction W, and having the same thickness as the sheet thickness of the grain-oriented electrical steel sheet 1.

[0084] Glow discharge optical emission spectroscopy is performed in the thickness direction T of the base steel sheet 10 from the surface of the secondary coating 12 of the sample or from the surface of the primary coating 11 after removing the secondary coating 12 by the above-mentioned method, to measure the glow emission spectroscopy spectra (GDS spectra) of Mg and Sn. Specifically, using a high-frequency glow emission spectroscopy device (GD-OES, manufactured by Rigaku Corporation, GDA750), the sample is used as the cathode in an argon atmosphere (Ar pressure: 3 hPa) and a power output of 30 W is applied to measure the GDS spectrum of Mg and the GDS spectrum of Sn. The measurement area is 4 mmφ, the measurement time is 200 seconds, and the measurement interval is 0.025 seconds.

[0085] In the obtained GDS spectrum of Mg, I Ｍｇ／Ｍｇ Furthermore, the sputtering time T Ｍｇ Intensity I of Sn in the GDS spectrum of Sn Ｓｎ／Ｍｇ The obtained I Ｍｇ／Ｍｇ and I Ｓｎ／Ｍｇ Using the above, the intensity ratio I is calculated based on the formula (1). ｒｅｆ Ask for.

[0086] I Ｍｇ／Ｍｇ The significant figure of is the first decimal place. Ｍｇ／Ｍｇ is the value obtained by rounding off the number to the second decimal place. Ｓｎ／ＭｇThe significant figures of are four decimal places. Ｓｎ／Ｍｇ is the value obtained by rounding off the number to the fifth decimal place. ｒｅｆ The significant figure of is four decimal places. In other words, the intensity ratio I ｒｅｆ is the value obtained by rounding off the number to the fifth decimal place.

[0087] In the grain-oriented electrical steel sheet 1 of this embodiment, the intensity I of Sn in the GDS spectrum Ｓｎ／Ｍｇ is less than or equal to 0.0021. Ｓｎ／Ｍｇ The upper limit of the intensity I is preferably 0.0020, more preferably 0.0019, and even more preferably 0.0018. Ｓｎ／Ｍｇ The lower limit of is preferably 0.0005, more preferably 0.0003, even more preferably 0.0001, and even more preferably 0.0000.

[0088] [(Feature 3) Regarding Iron Loss] The grain-oriented electrical steel sheet 1 of this embodiment, which satisfies the above-described features 1 and 2, further has an iron loss W １７／５０ The iron loss W of the grain-oriented electrical steel sheet 1 of this embodiment is less than 0.90 W / kg. １７／５０ The upper limit of the power consumption is preferably 0.88 W / kg, and more preferably 0.85 W / kg.

[0089] [Preferred Sn concentration gradient ΔI Ｓｎ Preferably, the grain-oriented electrical steel sheet 1 of the present embodiment further satisfies the following feature 4: (Feature 4) In the glow emission spectrum, Ｓｎ／Ｍｇ The emission intensity of Sn at 20.0 seconds after the sputtering time at which the value of Ｓｎ／Ｍｇ＋２０ When the Sn concentration gradient ΔI is defined as Ｓｎ is 0.0000 to 0.0004 / sec. Ｓｎ = (I Ｓｎ／Ｍｇ＋２０ -I Ｓｎ／Ｍｇ ) / 20 (2)

[0090] The grain-oriented electrical steel sheet 1 of this embodiment does not necessarily have to satisfy the above-mentioned characteristic 4. If the grain-oriented electrical steel sheet 1 satisfies characteristic 4, the adhesion of the secondary coating 12 will be further improved. Feature 4 will be described below.

[0091] ΔI Ｓｎ is defined as follows: Ｓｎ : Referring to FIG. 2, the sputtering time T Ｍｇ The point in time when 20.0 seconds have passed since the sputtering time T Ｍｇ＋２０ In the GDS spectrum of Sn, the sputtering time T Ｍｇ＋２０ The emission intensity of Sn at I Ｓｎ／Ｍｇ＋２０ At this time, the Sn concentration gradient ΔI Ｓｎ is defined by the above equation (2).

[0092] Sn concentration gradient ΔI Ｓｎ is an index of the gradient of the Sn concentration in the primary coating 11. In the grain-oriented electrical steel sheet 1 that satisfies the characteristics 1 and 2, the Sn concentration gradient ΔI Ｓｎ is 0.0004 / sec or less, the gradient of the Sn concentration in the primary coating 11 is not steep but gentle. Therefore, the Sn concentration in the primary coating 11 is more effectively suppressed. Therefore, the porous region in the primary coating 11 is more effectively suppressed. As a result, the adhesion of the secondary coating 12 in the grain-oriented electrical steel sheet 1 is further improved. Therefore, the Sn concentration gradient ΔI Ｓｎ is 0.0000 to 0.0004 / second.

[0093] Sn concentration gradient ΔI Ｓｎ The upper limit of the Sn concentration gradient ΔI is preferably 0.0003, and more preferably 0.0002. Ｓｎ is preferably as low as possible.

[0094] [Sn concentration gradient ΔI Ｓｎ Determination method of Sn concentration gradient ΔI Ｓｎ can be obtained by the following method. ｒｅｆ In the GDS spectrum of Sn obtained by glow discharge optical emission spectroscopy performed under the conditions described in [Method for determining I Ｓｎ／Ｍｇ and I Ｓｎ／Ｍｇ＋２０ The obtained I Ｓｎ／Ｍｇ and IＳｎ／Ｍｇ＋２０ Using the above formula, the Sn concentration gradient ΔI is calculated based on the formula (2). Ｓｎ Ask for.

[0095] I Ｓｎ／Ｍｇ and I Ｓｎ／Ｍｇ＋２０ The significant figures of are four decimal places. Ｓｎ／Ｍｇ and I Ｓｎ／Ｍｇ＋２０ is the value obtained by rounding off the value to the fifth decimal place. Ｓｎ The significant figure of is four decimal places. That is, the Sn concentration gradient ΔI Ｓｎ is the value obtained by rounding off the number to the fifth decimal place.

[0096] The grain-oriented electrical steel sheet 1 according to this embodiment satisfies Features 1 to 3. Therefore, it is possible to achieve both excellent core loss and excellent adhesion of the secondary coating 12. Preferably, the grain-oriented electrical steel sheet 1 according to this embodiment also satisfies Feature 4. In this case, the adhesion of the secondary coating 12 is further improved.

[0097] [Manufacturing Method] An example of a manufacturing method for the grain-oriented electrical steel sheet 1 of this embodiment will be described below. Note that the manufacturing method for the grain-oriented electrical steel sheet 1 of this embodiment is not particularly limited as long as it has the configuration described above. However, the manufacturing method for the grain-oriented electrical steel sheet 1 described below is a suitable example of the manufacturing method for the grain-oriented electrical steel sheet 1 of this embodiment.

[0098] [Manufacturing Process Flow] The manufacturing method of the grain-oriented electrical steel sheet 1 of this embodiment includes the following processes: (Step 1) Hot rolling process (Step 2) Hot-rolled sheet annealing process (Step 3) Pickling process (Step 4) Cold rolling process (Step 5) Decarburization annealing process (Step 6) Finish annealing process (Step 7) Secondary coating formation process

[0099] The method for producing the grain-oriented electrical steel sheet 1 of this embodiment is characterized in that the following production conditions are satisfied in the pickling step, the decarburization annealing step, and the finish annealing step.

[0100] (Step 3: Manufacturing conditions in the pickling step) Condition 1: The hydrochloric acid concentration in the pickling bath is 5 to 20% by mass, the bath temperature is 80 to 100°C, and the immersion time in the pickling bath is 30 to 120 seconds. (Step 5: Manufacturing conditions in the decarburization annealing step) Condition 2: The rapid heating target temperature Ta is 800 to 900°C. Condition 3: The average heating rate V1 during the period in which the temperature of the cold-rolled steel sheet is raised from 550°C to the rapid heating target temperature Ta is 100°C / second or more. Condition 4: After the temperature of the cold-rolled steel sheet is raised to the rapid heating target temperature Ta, the cold-rolled steel sheet is held at a decarburization annealing temperature of 800 to 950°C for 60 seconds or more, and the average oxygen partial pressure ratio PO4 during the period in which it is held at the decarburization annealing temperature is 0.60 or less. (Step 6: Manufacturing conditions in the finish annealing step) Condition 5: The average heating rate V3 and the average oxygen partial pressure ratio PO3 during the period when the temperature of the decarburization annealed steel sheet rises from 900°C to 1100°C satisfy the following formulas (3) and (4): 31×Sn+5≦V3≦30 (3) 0.000≦PO3≦−0.020×Sn+0.015 (4) Here, the Sn content in mass% in the slab is substituted for Sn in formulas (3) and (4). Condition 6: The purity of the hydrogen gas in the atmosphere at the finish annealing temperature in the finish annealing furnace is greater than 99.9% (i.e., greater than 3N (4N or greater)). Hereinafter, each of Steps 1 to 7 and Conditions 1 to 6 will be explained.

[0101] [(Step 1) Hot Rolling Step] In the hot rolling step, a prepared slab is hot rolled to produce a hot-rolled steel sheet.

[0102] [Chemical composition of slab] The chemical composition of the slab is, in mass%, Si: 2.50 to 4.50%, Mn: 0.01 to 1.00%, Sn: 0.05 to 0.30%, N: 0.002 to 0.020%, C: 0.020 to 0.100%, sol.Al: 0.010 to 0.050%, one or more selected from the group consisting of S and Se: 0.010 to 0.050% in total, P: 0.00 to 0.05%, Sb: 0.00 to 0.50%, Cr: 0.00 to 0.50%, Cu: 0.00 to 0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and the balance is Fe and impurities. The chemical composition of the slab may contain one or more elements selected from the group consisting of P: 0.01 to 0.05%, Sb: 0.01 to 0.50%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, and Bi: 0.0001 to 0.0100%.

[0103] The chemical composition of the slab has higher contents of N, C, sol. Al, S, and Se compared to the chemical composition of the base steel sheet 10. These elements act as inhibitors during the manufacturing process. However, many of these elements are removed from the steel sheet in the final annealing process. As a result of the removal, the chemical composition of the base steel sheet 10 is obtained. The function of each element is the same as the function of the corresponding element described above in [(Feature 1) Regarding the Chemical Composition of the Base Steel Sheet 10].

[0104] Slabs are produced by a known method, for example, by producing (smelting) molten steel and then using the molten steel to produce slabs by a continuous casting method.

[0105] The prepared slab is hot-rolled using a hot rolling mill to produce a steel plate (hot-rolled steel plate). First, the steel material is heated. For example, the slab is charged into a known heating furnace or a known soaking furnace and heated. The preferred heating temperature of the slab is 1100 to 1450°C.

[0106] The heated slab is hot-rolled using a hot rolling mill to produce a hot-rolled steel sheet. The hot rolling mill includes a roughing mill and a finishing mill arranged downstream of the roughing mill. The roughing mill includes one roughing stand or multiple roughing stands arranged in a row. Each roughing stand includes a pair of work rolls arranged above and below. When there is one roughing stand, the roughing mill is of a reverse type. When there are multiple roughing stands arranged, the roughing mills may be of a tandem type or a reverse type. The finishing mill includes finishing stands arranged in a row. Each finishing stand includes a pair of work rolls arranged above and below. After the heated slab is rolled by the roughing mill, it is further rolled by the finishing mill to produce a hot-rolled steel sheet.

[0107] The thickness of the hot-rolled steel sheet produced by hot rolling is not particularly limited and may be any known thickness, for example, 1.5 mm to 3.0 mm.

[0108] [(Step 2) Hot-rolled sheet annealing step] In the hot-rolled sheet annealing step, the hot-rolled steel sheet produced in the hot rolling step is subjected to an annealing treatment. By performing the hot-rolled sheet annealing step, recrystallization occurs in the steel sheet structure, and magnetic properties are improved.

[0109] The hot-rolled steel sheet annealing step may be performed by a known method. The method for heating the hot-rolled steel sheet is not particularly limited, and any known heating method may be used. The annealing temperature is, for example, 900 to 1200°C, and the holding time at the annealing temperature is, for example, 10 to 300 seconds.

[0110] [(Step 3) Pickling Step] In the pickling step, the hot-rolled steel sheet is subjected to pickling treatment after the hot-rolled steel sheet annealing step and before the cold-rolling step. The pickling treatment satisfies the following condition 1.

[0111] [Condition 1: Pickling Time] The hydrochloric acid concentration in the pickling bath is 5 to 20% by mass. The temperature of the pickling bath (bath temperature) is 80 to 100°C. The immersion time in the pickling bath (pickling time) is 30 to 120 seconds (Condition 1). If the pickling time in the pickling bath exceeds 120 seconds, not only is the scale layer of the hot-rolled steel sheet removed, but also the desiliconized layer present in the surface layer of the hot-rolled steel sheet. In this case, a strong Si oxide layer is formed on the surface layer of the steel sheet in the subsequent decarburization annealing process, and the formation of an internal Si oxide layer in the surface layer of the steel sheet is insufficient. As a result, the amount of primary coating formed in the finish annealing process after the decarburization annealing process is insufficient. As a result, the secondary coating does not have sufficient adhesion to the steel sheet in the manufactured steel sheet.

[0112] If the pickling time is 120 seconds or less, the scale layer of the hot-rolled steel sheet is removed, but the desiliconized layer present on the surface of the hot-rolled steel sheet remains sufficiently. Therefore, sufficient adhesion of the secondary coating to the steel sheet can be obtained. Although there is no particular limitation on the lower limit of the pickling time, if the pickling time is 30 seconds or more, the scale layer of the hot-rolled steel sheet is sufficiently removed. Therefore, the lower limit of the pickling time is 30 seconds.

[0113] [(Step 4) Cold Rolling Step] In the cold rolling step, the hot-rolled steel sheet after the hot-rolled sheet annealing step is subjected to one or more cold rolling passes. The cold rolling is performed using a cold rolling mill. The cold rolling mill is, for example, a tandem rolling mill having a plurality of cold rolling stands arranged in a row, each of which includes a pair of work rolls. The cold rolling mill may also be a single reverse cold rolling stand.

[0114] In the cold rolling step, only one cold rolling may be performed, or multiple cold rolling may be performed. When multiple cold rolling is performed, an intermediate annealing treatment may be performed for the purpose of softening the steel sheet after cold rolling using the above-mentioned cold rolling mill. In this case, the next cold rolling is performed after the intermediate annealing treatment. In other words, the intermediate annealing treatment may be performed between cold rollings.

[0115] Well-known conditions are sufficient for the intermediate annealing treatment performed between cold rolling and the next cold rolling. The annealing temperature in the intermediate annealing treatment is, for example, 900 to 1200°C, and the holding time at the annealing temperature is 30 to 1800 seconds. After the intermediate annealing treatment reduces the strain introduced into the steel sheet by the previous cold rolling (softens the steel sheet), the next cold rolling is performed.

[0116] In the cold rolling step, as described above, only one cold rolling may be performed. The thickness of the cold-rolled steel sheet produced by cold rolling is not particularly limited and may be a known thickness. The thickness of the cold-rolled steel sheet is, for example, 0.17 mm to 0.22 mm.

[0117] [(Step 5) Decarburization Annealing Step] In the decarburization annealing step, the cold-rolled steel sheet after the cold rolling step is subjected to decarburization annealing to induce primary recrystallization.

[0118] The decarburization annealing step includes the following steps: (Step 51) Temperature increase step (Step 52) Decarburization step (Step 53) Cooling step Each of steps 51 to 53 will be explained below.

[0119] [(Step 51) Heating Step] In the heating step, first, the cold-rolled steel sheet after the cold rolling step is loaded into a heat treatment furnace. In the heat treatment furnace (continuous annealing furnace) for decarburization annealing in this embodiment, the cold-rolled steel sheet is heated at an average heating rate V1 to a rapid heating temperature Ta of 800 to 900°C, for example, by electrical heating or high-frequency induction heating. After reaching the rapid heating temperature Ta, the cold-rolled steel sheet is heated or cooled to the decarburization annealing temperature. The decarburization annealing temperature is 800 to 950°C.

[0120] [(Step 52) Decarburization Step] In the decarburization step, the cold-rolled steel sheet after the heating step is held at a decarburization annealing temperature to perform decarburization annealing. This causes primary recrystallization to occur in the steel sheet. By performing decarburization annealing, carbon in the steel sheet is removed from the steel sheet, causing primary recrystallization. As described above, the decarburization annealing temperature is 800 to 950°C.

[0121] [(Step 53) Cooling Step] In the cooling step, the cold-rolled steel sheet after the decarburization step is cooled to room temperature by a well-known method to obtain a decarburization-annealed steel sheet. The cooling method may be natural cooling or water cooling. Preferably, the cold-rolled steel sheet after the decarburization step is natural cooling. Through the above steps, in the decarburization-annealing step, the cold-rolled steel sheet is subjected to decarburization annealing treatment to obtain a decarburization-annealed steel sheet.

[0122] [Manufacturing Conditions in Decarburization Annealing Step] In the decarburization annealing step, the following conditions 2 to 4 are satisfied.

[0123] [Condition 2: Rapid heating temperature Ta] The rapid heating temperature Ta is set to 800 to 900°C. The rapid heating temperature Ta corresponds to the temperature of the steel sheet. If the rapid heating temperature Ta is less than 800°C, the rapid heating effect may not be sufficient. On the other hand, if it exceeds 900°C, a strong oxide film may be formed, and decarburization during decarburization annealing may be poor. If the rapid heating temperature Ta is 800 to 900°C, the crystal grains of the steel sheet after primary recrystallization will be of an appropriate size. Therefore, secondary recrystallization will be sufficiently achieved in the finish annealing process.

[0124] After reaching the rapid heating temperature Ta, the steel sheet is heated or cooled to a decarburization annealing temperature of 800 to 950°C, and then held at the decarburization annealing temperature for 60 seconds or more to perform decarburization annealing. The upper limit of the holding time at the decarburization annealing temperature is, for example, 300 seconds. The preferred upper limit of the holding time at the decarburization annealing temperature is 290 seconds, more preferably 280 seconds, and even more preferably 270 seconds. The preferred lower limit of the holding time at the decarburization annealing temperature is 65 seconds, more preferably 70 seconds, and even more preferably 75 seconds.

[0125] [Condition 3: Average heating rate V1] The average heating rate V1 during the time when the temperature of the cold-rolled steel sheet rises from 550°C to the rapid heating temperature Ta is set to 100°C / sec or more.

[0126] Strain accumulates in the cold-rolled steel sheet. If the average heating rate V1 for the cold-rolled steel sheet is less than 100°C / s, the strain energy that serves as the driving force for recrystallization is released before the recrystallization begins. In this case, a sufficient amount of fine Goss-oriented grains cannot be generated in the cold-rolled steel sheet after primary recrystallization (i.e., the cold-rolled steel sheet after the decarburization annealing process). In addition, the effect of containing Sn is also difficult to achieve.

[0127] If the average heating rate V1 is 100°C / sec or higher, primary recrystallization occurs in a state where sufficient strain energy is accumulated in the cold-rolled steel sheet. Therefore, a sufficient amount of fine Goss orientation grains can be generated in the cold-rolled steel sheet after primary recrystallization. Therefore, in the subsequent finish annealing process, the concentration of Goss orientation grains after secondary recrystallization can be increased. As a result, the iron loss of the grain-oriented electrical steel sheet 1 can be sufficiently reduced.

[0128] The upper limit of the average heating rate V1 is not particularly limited. Even if the average heating rate V1 is set to be faster than 3000° C. / sec, the above effect is almost saturated. Therefore, the upper limit of the average heating rate V1 is, for example, 3000° C. / sec.

[0129] The lower limit of the average heating rate V1 is preferably 150°C / sec, more preferably 200°C / sec, even more preferably 300°C / sec, even more preferably 400°C / sec, even more preferably 500°C / sec, even more preferably 600°C / sec, even more preferably 700°C / sec, even more preferably 800°C / sec, and even more preferably 900°C / sec.

[0130] In addition, when the Sn content is the same, if the average heating rate V1 is 400 ° C. / sec or more, the iron loss W of the grain-oriented electrical steel sheet is lower than when the average heating rate V1 is less than 400 ° C. / sec. １７／５０ can be further reduced.

[0131] The average heating rate V1 is measured by the following method. A plurality of thermometers are installed in a heat treatment furnace to measure the surface temperature of the steel sheet. The thermometers are arranged from upstream to downstream of the heat treatment furnace. The average heating rate V1 is calculated based on the temperature of the steel sheet measured by the thermometers and the time it takes for the steel sheet temperature to rise from 550°C to the rapid heating target temperature Ta.

[0132] [Condition 4: Average oxygen partial pressure ratio PO4] After the temperature of the cold-rolled steel sheet is raised to the rapid heating ultimate temperature Ta, the cold-rolled steel sheet is held at a decarburization annealing temperature of 800 to 950°C for 60 seconds or more, and the average oxygen partial pressure ratio PO4 in the heat treatment furnace during the holding period at the decarburization annealing temperature is set to 0.60 or less. The upper limit of the holding time at the decarburization annealing temperature is not particularly limited, but is, for example, 300 seconds.

[0133] If the average oxygen partial pressure ratio PO4 exceeds 0.60, the iron loss W of the grain-oriented electrical steel sheet １７／５０ When the average oxygen partial pressure ratio PO4 is 0.60 or less, a grain-oriented electrical steel sheet satisfying Features 1 to 3 can be manufactured, provided that other conditions are met.

[0134] The average oxygen partial pressure ratio PO4 can be measured by the following method. The atmospheric gas at the decarburization annealing temperature in the soaking zone of a heat treatment furnace through which coils for decarburization annealing are continuously passed is sampled once. The dew point and hydrogen concentration of each sampled atmospheric gas are measured. Based on the obtained dew point and hydrogen concentration, the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) to calculate the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) based on PH ２ O / PH ２ The arithmetic mean value of the oxygen partial pressure ratios of the sampled atmospheric gases is defined as the average oxygen partial pressure ratio PO4.

[0135] [Other Conditions: Average Oxygen Partial Pressure Ratio PO1] The average oxygen partial pressure ratio PO1 is set to 0.10 or less during the period in which the temperature of the cold-rolled steel sheet is increased from 550°C to the rapid heating temperature Ta. The average oxygen partial pressure ratio PO1 is a known condition.

[0136] If the average oxygen partial pressure ratio PO1 is 0.10 or less, SiO ２ Therefore, sufficient decarburization is achieved in the decarburization step. Furthermore, in the subsequent finish annealing step, a primary coating can be formed sufficiently. Therefore, the average oxygen partial pressure ratio PO1 is 0.10 or less.

[0137] The upper limit of the average oxygen partial pressure ratio PO1 is preferably 0.09, and more preferably 0.08. The lower limit of the average oxygen partial pressure ratio PO1 is not particularly limited.

[0138] The average oxygen partial pressure ratio PO1 can be measured by the following method. The atmospheric gas is sampled once from 550°C in the temperature rising zone of the heat treatment furnace where decarburization annealing is performed until the rapid heating temperature Ta is reached. The dew point and hydrogen concentration of each sampled atmospheric gas are measured. Based on the obtained dew point and hydrogen concentration, the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) to calculate the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) based on PH ２ O / PH ２ is the oxygen partial pressure ratio. The arithmetic mean value of the oxygen partial pressure ratios of the sampled atmospheric gases is defined as the average oxygen partial pressure ratio PO1. Note that an electric heating device or an induction heating device is arranged in the temperature rising zone.

[0139] [(Step 6) Finish Annealing Step] In the finish annealing step, an annealing separator is applied to a decarburization-annealed steel sheet, and the decarburization-annealed steel sheet coated with the annealing separator is subjected to finish annealing to produce a finish annealed steel sheet. In the finish annealing step, a primary coating 11 is formed on a base steel sheet 10. The finish annealing step includes the following steps: (Step 61) Annealing Separator Application Step (Step 62) Annealing Step Each step will be described below.

[0140] [(Step 61) Annealing Separator Application Step] In the annealing separator application step, an annealing separator is applied to a decarburized annealed steel sheet. Specifically, an aqueous slurry containing the annealing separator is applied to the decarburized annealed steel sheet. The aqueous slurry is prepared by adding water to the annealing separator and stirring. The annealing separator has a well-known composition. The annealing separator contains magnesium oxide (MgO). Preferably, MgO is the main component of the annealing separator. Here, "main component" means that the MgO content in the annealing separator is 60.0% or more by mass. The annealing separator may contain well-known additives in addition to MgO.

[0141] In the annealing separator application process, an aqueous slurry of annealing separator is applied to the surface of the decarburized annealed steel sheet. The steel sheet with the annealing separator applied to its surface is dried in an annealing furnace, and then wound up into a coil. After the steel sheet is coiled, the annealing process is carried out.

[0142] [(Step 62) Annealing Step] In the annealing step, the steel sheet after the annealing separator application step is subjected to finish annealing to induce secondary recrystallization. In the annealing step, the coiled steel sheet is loaded into an annealing furnace and finish annealing is performed. The annealing step includes a temperature-raising step and a purification step. In the temperature-raising step, the coiled steel sheet is heated to the finish annealing temperature in the annealing furnace. The finish annealing temperature is 1100 to 1250°C. In this temperature-raising step, the primary coating 11 is formed. After the temperature-raising step, the steel sheet is held at the finish annealing temperature for 5 to 50 hours to perform purification (purification step). In the purification step, each element in the chemical composition of the steel sheet is removed to a certain extent from the steel sheet. In particular, S, Al, N, etc., which function as inhibitors, are largely removed. A primary coating containing forsterite is formed on the surface of the grain-oriented electrical steel sheet 1 after the annealing step.

[0143] [Condition 5 in the Finish Annealing Process: Average Temperature Rise Rate V3 and Average Oxygen Partial Pressure PO3] The finish annealing process satisfies the following condition 5.

[0144] [(Condition 5) Regarding Equations (3) and (4)] In the temperature-raising step during the annealing process in which the above-mentioned finish annealing is carried out, the average temperature-raising rate V3 (°C / hour) during which the temperature of the decarburization annealed steel sheet rises from 900°C to 1100°C and the average oxygen partial pressure ratio PO3 satisfy Equations (3) and (4): 31 × Sn + 5 ≦ V3 ≦ 30 (3) 0.000 ≦ PO3 ≦ -0.020 × Sn + 0.015 (4) Here, Sn in Equations (3) and (4) is substituted with the Sn content in mass% in the slab.

[0145] [Regarding Formula (3)] If the average heating rate V3 is less than the lower limit of Formula (3), the SiO formed in the surface layer of the steel sheet in the decarburization annealing step is ２ The internal oxide layer grows further. In this case, the primary coating is not sufficiently formed, resulting in the formation of an excessively large number of porous regions. As a result, the grain-oriented electrical steel sheet 1 does not satisfy Feature 2. As a result, the adhesion of the secondary coating 12 of the grain-oriented electrical steel sheet 1 decreases. On the other hand, if the average heating rate V3 exceeds the upper limit of formula (3), the start temperature of secondary recrystallization increases. In this case, the inhibitor is rapidly removed. This causes poor secondary recrystallization. As a result, the iron loss of the grain-oriented electrical steel sheet 1 deteriorates. Therefore, the average heating rate V3 satisfies formula (3).

[0146] The average heating rate V3 is measured by the following method. Since the finish annealing is performed in a coiled state, a thermocouple is installed on the outer surface of the coil and used for measurement. The temperature inside the coil is calculated from the outer surface temperature using a general heat conduction calculation.

[0147] [Regarding Formula (4)] If the average oxygen partial pressure ratio PO3 exceeds the upper limit of Formula (4), the formation of the primary coating becomes insufficient, resulting in the formation of an excessively large number of porous regions. In this case, the grain-oriented electrical steel sheet 1 no longer satisfies Feature 2. As a result, the adhesion of the secondary coating 12 of the grain-oriented electrical steel sheet 1 decreases. Therefore, the average oxygen partial pressure ratio PO3 satisfies Formula (4). Note that the average oxygen partial pressure PO3 refers to the average oxygen concentration in the atmospheric gas in the annealing furnace from 900°C to 1100°C.

[0148] The average oxygen partial pressure ratio PO3 can be measured by the following method. The atmospheric gas in an annealing furnace containing a coil for finish annealing is sampled multiple times from 900°C to 1100°C. The sampling interval is 1 minute. The dew point and hydrogen concentration are measured for each sampled atmospheric gas. Based on the obtained dew point and hydrogen concentration, the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) to calculate the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) based on PH ２ O / PH ２ The arithmetic mean value of the oxygen partial pressure ratios of the sampled atmospheric gases is defined as the average oxygen partial pressure ratio PO3.

[0149] [Other Condition 1: Average Temperature Rise Rate V2] The average temperature rise rate V2 during the temperature rise of the decarburization annealed steel sheet from 650°C to 900°C is set to 5 to 50°C / hour. The average temperature rise rate V2 is a known condition.

[0150] If the average temperature rise rate V2 is 5°C / hour or more, the SiO formed on the surface layer of the steel sheet in the decarburization annealing process is ２ The growth of the internal oxide layer is suppressed. In this case, the primary coating 11 is sufficiently formed, and the porous region in the primary coating can be sufficiently suppressed.

[0151] Furthermore, if the average temperature rise rate V2 is 50°C / hour or less, the temperature deviation within the coil can be sufficiently suppressed. In this case, secondary recrystallization defects are suppressed. Therefore, the average temperature rise rate V2 is 5 to 50°C / hour.

[0152] The lower limit of the average temperature increase rate V2 is preferably 7° C. / hour, more preferably 10° C. / hour. The upper limit of the average temperature increase rate V2 is preferably 45° C. / hour, more preferably 40° C. / hour.

[0153] The average heating rate V2 is measured by the following method. Since the finish annealing is performed in a coiled state, a thermocouple is installed on the outer surface of the coil and used for measurement. The temperature inside the coil is calculated from the outer surface temperature of the coil using a general heat conduction calculation.

[0154] [(Condition 6) Purity of hydrogen gas in the atmosphere inside the annealing furnace in the finish annealing step] In the finish annealing step, the atmosphere gas inside the finish annealing furnace during the temperature rise process is a mixed atmosphere gas of hydrogen gas and nitrogen gas. Then, after the finish annealing temperature is reached, the atmosphere gas is switched from a mixed atmosphere of hydrogen gas and nitrogen gas to a hydrogen gas atmosphere alone. In this embodiment, the purity of the hydrogen gas introduced into the atmosphere inside the finish annealing furnace at the finish annealing temperature is set to more than 3N (i.e., 4N or more: 99.99% or more). When the purity of hydrogen gas is 3N or less (i.e., 99.9% or less), the purity of I in the formed primary coating is set to be 1. ｒｅｆ If the purity of the hydrogen gas exceeds 3N (i.e., 4N or more), the I content in the primary coating film is ｒｅｆ is 0.0006 or less.

[0155] [Other Condition 2: Average Oxygen Partial Pressure Ratio PO2] The average oxygen partial pressure ratio PO2 is set to 0.020 or less when the temperature of the decarburization annealed steel sheet is in the range from 650° C. to 900° C. The average oxygen partial pressure ratio PO2 is a known condition.

[0156] If the average oxygen partial pressure ratio PO2 is 0.020 or less, the primary coating is sufficiently formed. Therefore, the average oxygen partial pressure ratio PO2 is 0.020 or less.

[0157] The upper limit of the average oxygen partial pressure ratio PO2 is preferably 0.018, more preferably 0.016, and even more preferably 0.014. The lower limit of the average oxygen partial pressure ratio PO2 is not particularly limited.

[0158] The average oxygen partial pressure ratio PO2 can be measured by the following method. The atmospheric gas in the heat treatment furnace containing the coil for finish annealing is sampled multiple times from 650°C to 900°C. The sampling interval is 1 minute. The dew point and hydrogen concentration are measured for each sampled atmospheric gas. Based on the obtained dew point and hydrogen concentration, the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) to calculate the water vapor partial pressure (PH ２ O) and hydrogen partial pressure (PH ２ ) based on PH ２ O / PH２ The arithmetic mean value of the oxygen partial pressure ratios of the sampled atmospheric gases is defined as the average oxygen partial pressure ratio PO2.

[0159] [(Step 7) Secondary Coating Formation Step] In the secondary coating formation step, an insulating coating agent mainly containing colloidal silica and phosphate is applied to the primary coating 11 of the steel sheet after the finish annealing step, and then baked. As a result, a secondary coating 12 is formed on the primary coating 11.

[0160] By the above manufacturing process, the grain-oriented electrical steel sheet 1 satisfying Features 1 to 3 can be manufactured.

[0161] [Preferred Manufacturing Process] Preferably, the decarburization annealing step of step 5 further satisfies the following condition 7: (Condition 7) The cold-rolled steel sheet is held at the decarburization annealing temperature for 60 seconds or more, and the average oxygen partial pressure ratio PO4 during the period of holding at the decarburization annealing temperature satisfies formula (5): 0.88×Sn+0.19≦PO4≦0.60 (5) Here, the Sn content in mass% in the slab is substituted for Sn in formula (5).

[0162] [Condition 7: Regarding Formula (5)] If the average oxygen partial pressure ratio PO4 is equal to or greater than the lower limit of Formula (5), the SiO ２ An internal oxide layer is appropriately formed. In this case, the primary coating formed in the finish annealing step is stably formed. Therefore, the grain-oriented electrical steel sheet 1 satisfies not only Features 1 to 3 but also Feature 4. As a result, the adhesion of the secondary coating 12 of the grain-oriented electrical steel sheet 1 is further improved. Therefore, preferably, the average oxygen partial pressure ratio PO4 satisfies formula (5).

[0163] [Other Manufacturing Steps] The manufacturing method of the grain-oriented electrical steel sheet 1 according to this embodiment may further include a magnetic domain refinement step after the finish annealing step or the secondary coating formation step, as necessary. In the magnetic domain refinement step, the surface of the grain-oriented electrical steel sheet 1 is irradiated with a laser beam or the like that has a magnetic domain refinement effect, or grooves are formed in the surface. In this case, a grain-oriented electrical steel sheet 1 with even better magnetic properties can be manufactured. The magnetic domain refinement step does not have to be performed.

[0164] The method for producing the grain-oriented electrical steel sheet 1 according to this embodiment may further include, if necessary, performing a nitriding treatment after the decarburization annealing step and before the finish annealing step. The nitriding treatment may be performed under well-known conditions. Preferred nitriding conditions are, for example, as follows: Nitriding temperature: 700 to 850°C Atmosphere in the nitriding furnace (nitriding atmosphere): an atmosphere containing hydrogen, nitrogen, and a gas having nitriding ability such as ammonia

[0165] If the nitriding temperature is 700 to 850°C, nitrogen easily penetrates into the steel sheet during the nitriding treatment. If the nitriding treatment is performed within this temperature range, the amount of nitrogen inside the steel sheet can be preferably secured. Therefore, fine AlN is preferably formed in the steel sheet before secondary recrystallization. As a result, secondary recrystallization is preferably exhibited during finish annealing. The time for which the steel sheet is held at the nitriding treatment temperature is not particularly limited, but may be, for example, 10 to 60 seconds.

[0166] The present invention will be described in more detail below with reference to examples. These examples are provided to confirm the effects of the present invention and are not intended to limit the scope of the present invention.

[0167] In Example 1, the manufacturing conditions of the finish annealing step were changed to manufacture grain-oriented electrical steel sheet 1. Specifically, slabs containing Si, Mn, N, C, sol. Al, and S in the amounts shown in Table 1-1 and further containing Sn in the amount shown in Table 1-2 were prepared.

[0168]

[0169] The slab was subjected to a hot rolling process. Specifically, the slab was heated to 1350°C and then hot rolled to produce a hot-rolled steel sheet having a thickness of 2.3 mm.

[0170] The hot-rolled steel sheet after the hot rolling process was subjected to a hot-rolled sheet annealing process at an annealing temperature of 900 to 1200°C for a holding time of 10 to 300 seconds. After the hot-rolled sheet annealing process, a pickling process was carried out. In the pickling process, a pickling bath with a hydrochloric acid concentration of 10% and a bath temperature of 90°C was used. For test numbers other than test number 61, the pickling time was 120 seconds. For test number 61, the pickling time was 180 seconds. Thereafter, a cold-rolling process was carried out to produce a cold-rolled steel sheet (base steel sheet) with a thickness of 0.22 mm.

[0171] The cold-rolled steel sheet was subjected to a decarburization annealing process. In the decarburization annealing process, the rapid heating temperature Ta was set to 850°C, and the decarburization annealing temperature was set to 830°C. The average heating rate V1 from 550°C to the rapid heating temperature Ta (850°C) was set to 800°C / sec, and the average oxygen partial pressure ratio PO1 was set to 0.03. The holding time at the decarburization annealing temperature (830°C) was set to 60 seconds. The average oxygen partial pressure ratio PO4 at the decarburization annealing temperature was set to 0.50.

[0172] The decarburization-annealed steel sheet after the decarburization annealing process was coated with an annealing separator (water slurry) mainly composed of MgO, and then wound into a coil. The coiled steel sheet was subjected to a finish annealing process. In the finish annealing process, the average temperature rise rate V2 during the steel sheet temperature rise from 650°C to 900°C was 20°C / hour, and the average oxygen partial pressure ratio PO2 was 0.008. Furthermore, the average temperature rise rate V3 and the average oxygen partial pressure ratio PO3 during the temperature rise from 900°C to 1100°C were as shown in Table 1-2. After heating to 1100°C or higher, soaking was performed for 5 hours or more. For test numbers other than test number 62, the purity of the hydrogen gas used as the atmosphere gas for finish annealing was 6N (99.9999%). On the other hand, for test number 62, the purity of the hydrogen gas used as the atmosphere gas for finish annealing was 3N (99.9%).

[0173]

[0174] The steel sheets after the final annealing process were subjected to a secondary coating process. In the secondary coating process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface of the steel sheets after the final annealing process (on the primary coating), and then baked under well-known conditions to form a secondary coating. Grain-oriented electrical steel sheets of each test number were manufactured by the above manufacturing process.

[0175] [Evaluation Tests] The following evaluation tests were carried out on the grain-oriented electrical steel sheets with each test number: (Test 1) Chemical composition measurement test of base steel sheet (Test 2) Strength ratio I ｒｅｆ Decision test (Test 3) Sn concentration gradient ΔI Ｓｎ Decision test (Test 4) Secondary coating adhesion evaluation test (Test 5) Iron loss measurement test

[0176] [(Test 1) Test for measuring the chemical composition of the base steel sheet] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet of each test number was measured by the following method. First, the primary coating and secondary coating of the grain-oriented electrical steel sheet were removed by the method described above, and the base steel sheet was extracted. Using the base steel sheet, the chemical composition of the base steel sheet was analyzed based on the above-mentioned [Method for measuring the chemical composition of the base steel sheet 10]. As a result of the analysis, the chemical composition of the base steel sheet in Example 1 was as shown in Table 1-3.

[0177]

[0178] [(Test 2) Intensity Ratio I ｒｅｆ Determination test] Strength ratio I of grain-oriented electrical steel sheet of each test number ｒｅｆ is calculated by the above-mentioned [intensity ratio I ｒｅｆ The glow discharge optical emission spectrometer (GD-OES) used was a GDA750 manufactured by Rigaku Corporation. Ｍｇ／Ｍｇ , I Ｓｎ／Ｍｇ , intensity ratio I ｒｅｆ is shown in Table 1-2.

[0179] [(Test 3) Sn concentration gradient ΔI Ｓｎ Determination test] Sn concentration gradient ΔI of grain-oriented electrical steel sheet of each test number Ｓｎ is calculated by the above-mentioned [Sn concentration gradient ΔI ＳｎIn this case, a moving average line of 50 sections was used as an approximate value. In addition, as an offset of the Sn emission intensity, a value obtained by subtracting 0.0070 from the Sn emission intensity of each section was used as the Sn emission intensity I Ｓｎ The obtained I Ｓｎ／Ｍｇ＋２０ , Sn concentration gradient ΔI Ｓｎ is shown in Table 1-2.

[0180] [(Test 4) Secondary Coating Adhesion Evaluation Test] The adhesion of the secondary coating of each grain-oriented electrical steel sheet was evaluated by the following method: Specifically, a sample measuring 60 mm in the rolling direction and 15 mm in the width direction was taken from the widthwise center of each grain-oriented electrical steel sheet.

[0181] A bending test was performed on the sample using a cylindrical mandrel bending tester. Specifically, a bending resistance test described in JIS K 5600-5-1 (1999) was performed. A cylindrical mandrel (i.e., a mandrel round bar) was installed in the tester. The sample was placed on the cylindrical mandrel so that the axial direction of the cylindrical mandrel coincided with the sheet width direction of the sample. After fixing the sample with a clamp, the sample was bent 180° around the cylindrical mandrel as a fulcrum.

[0182] The above-mentioned bending process was performed using a cylindrical mandrel with a diameter of 10 mm, and then the diameter of the cylindrical mandrel was increased in 10 mm increments, and the above-mentioned bending process was performed again. The smallest diameter at which the secondary coating remained at a rate of 40% or more was defined as the "bending peel diameter" (mm). If the bending peel diameter was 30 mm or less, the adhesion of the secondary coating was judged to be excellent. If the bending peel diameter was 20 mm or less, the adhesion of the secondary coating was judged to be significantly excellent. If the bending peel diameter was 40 mm or more, the adhesion of the secondary coating was judged to be low. The obtained bending peel diameters are shown in Table 1-2.

[0183] [(Test 5) Iron Loss Measurement Test] The magnetic properties (iron loss W １７／５０ ) was evaluated in accordance with JIS C2556:2015. １７／５０ is shown in Table 1-2.

[0184] [Evaluation Results] Referring to Tables 1-1 to 1-3, the chemical compositions and manufacturing conditions were all appropriate for test numbers 7 to 9, 11 to 13, 15 to 17, 20 to 22, 24 to 26, 28 to 30, 37 to 39, 41 to 43, 50, 51, 54, and 55. As a result, the intensity ratio I defined by formula (1) was 0.01 for all test numbers. ｒｅｆ Furthermore, the Sn concentration gradient ΔI Ｓｎ was 0.0004 / sec or less. １７／５０ The iron loss was low at less than 0.90 W / kg, and the bending peeling diameter was 30 mm or less, and the adhesion of the secondary coating was also excellent.

[0185] On the other hand, in test numbers 1 and 2, the Sn content of the base steel sheet was low. １７／５０ was 0.90 W / kg or more.

[0186] In Test No. 59, the Sn content of the slab was high. As a result, cracks occurred in the steel sheet during the cold rolling process. Therefore, the subsequent manufacturing process and Tests 2 to 5 were discontinued.

[0187] In test number 60, the Sn content of the base steel sheet was high. １７／５０ was 0.90 W / kg or more.

[0188] In test numbers 3 to 6, 33 to 36, and 46 to 49, the average heating rate V3 during the final annealing process from 900°C to 1100°C was too slow. Furthermore, in test numbers 6, 36, 48, and 49, the average oxygen partial pressure ratio PO3 during the final annealing process was too high. Therefore, the strength ratio I ｒｅｆ As a result, the bending peeling diameter was 40 mm or more, and the adhesion of the secondary coating was low.

[0189] In all of the test numbers 19, 32, 45 and 58, the average temperature rise rate V3 was too high. １７／５０ was 0.90 W / kg or more.

[0190] In all of the test numbers 10, 14, 18, 23, 27, 31, 40, 44, 52, 53, 56 and 57, the average oxygen partial pressure ratio PO3 in the final annealing process was too high.ｒｅｆ As a result, the bending peeling diameter was 40 mm or more, and the adhesion of the secondary coating was low.

[0191] In test number 61, the pickling time in the pickling process was too long. ｒｅｆ As a result, the bending peeling diameter was 40 mm or more, and the adhesion of the secondary coating was low.

[0192] In test number 62, the purity of hydrogen gas in the final annealing process was too low. ｒｅｆ As a result, the bending peeling diameter was 40 mm or more, and the adhesion of the secondary coating was low.

[0193] In Example 2, a plurality of grain-oriented electrical steel sheets having different base metal chemical compositions were manufactured. Specifically, slabs having the chemical compositions shown in Table 2 were prepared.

[0194]

[0195] The slab was subjected to a hot rolling process. Specifically, the slab was heated to 1350°C and then hot rolled to produce a hot-rolled steel sheet having a thickness of 2.3 mm.

[0196] The hot-rolled steel sheet after the hot rolling process was subjected to a hot-rolled sheet annealing process at an annealing temperature of 900 to 1200°C for a holding time of 10 to 300 seconds. After the hot-rolled sheet annealing process, a pickling process was carried out. In the pickling process, a pickling bath with a hydrochloric acid concentration of 10% and a bath temperature of 90°C was used, and the pickling time was 120 seconds. Thereafter, a cold-rolling process was carried out to produce a cold-rolled steel sheet (base steel sheet) with a thickness of 0.22 mm.

[0197] The cold-rolled steel sheet was subjected to a decarburization annealing process. In the decarburization annealing process, the rapid heating temperature Ta was set to 870°C, and the decarburization annealing temperature was set to 830°C. The average heating rate V1 from 550°C to the rapid heating temperature Ta (870°C) was set to 1000°C / sec, and the average oxygen partial pressure ratio PO1 was set to 0.03. The holding time at the decarburization annealing temperature (830°C) was set to 80 seconds. The average oxygen partial pressure ratio PO4 at the decarburization annealing temperature was set to 0.40.

[0198] The decarburization annealed steel sheet after the decarburization annealing process was coated with an annealing separator (water slurry) mainly composed of MgO, and then wound into a coil. The coiled steel sheet was subjected to a finish annealing process. In the finish annealing process, the average temperature increase rate V2 during the steel sheet temperature increase from 650°C to 900°C was 15°C / hour, and the average oxygen partial pressure ratio PO2 was 0.008. Furthermore, the average temperature increase rate V3 during the temperature increase from 900°C to 1100°C was 15°C / hour, and the average oxygen partial pressure ratio PO3 was 0.005. After heating to 1100°C or higher, soaking was performed for 5 hours or more. The purity of the hydrogen gas used as the atmospheric gas in the finish annealing process was 6N (99.9999%).

[0199] The steel sheets after the final annealing process were subjected to a secondary coating process. In the secondary coating process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface of the steel sheets after the final annealing process (on the primary coating), and then baked under well-known conditions to form a secondary coating. Grain-oriented electrical steel sheets of each test number were manufactured by the above manufacturing process.

[0200] [Evaluation Tests] Tests 1 to 5 were carried out on the grain-oriented electrical steel sheets with each test number. In Example 2, the chemical composition of the base steel sheet obtained in Test 1 is shown in Table 3.

[0201]

[0202] The results of tests 2 to 5 are shown in Table 4.

[0203]

[0204] [Evaluation Results] Referring to Table 4, the chemical composition of the base steel sheet was appropriate and the manufacturing conditions were also appropriate for all of the test numbers 1 to 17. As a result, the strength ratio I defined by the formula (1) was ｒｅｆ Furthermore, the Sn concentration gradient ΔI Ｓｎ was 0.0004 / sec or less. １７／５０ The iron loss was low at less than 0.90 W / kg, and the bending peeling diameter was 20 mm or less, and the adhesion of the secondary coating was also excellent.

[0205] In Example 3, grain-oriented electrical steel sheets were manufactured by changing the average oxygen partial pressure ratio PO4 in the decarburization annealing step. Specifically, slabs containing Si, Mn, N, C, sol. Al, and S in the amounts shown in Table 5-1 and further containing Sn in the amount shown in Table 5-2 were prepared.

[0206]

[0207] The slab was subjected to a hot rolling process. Specifically, the slab was heated to 1350°C and then hot rolled to produce a hot-rolled steel sheet having a thickness of 2.3 mm.

[0208] The hot-rolled steel sheet after the hot rolling process was subjected to a hot-rolled sheet annealing process at an annealing temperature of 900 to 1200°C for a holding time of 10 to 300 seconds. After the hot-rolled sheet annealing process, a pickling process was carried out. In the pickling process, a pickling bath with a hydrochloric acid concentration of 10% and a bath temperature of 90°C was used, and the pickling time was 120 seconds. Thereafter, a cold-rolling process was carried out to produce a cold-rolled steel sheet (base steel sheet) with a thickness of 0.22 mm.

[0209] The cold-rolled steel sheet was subjected to a decarburization annealing process. In the decarburization annealing process, the rapid heating temperature Ta was set to 870°C, and the decarburization annealing temperature was set to 830°C. The average heating rate V1 from 550°C to the rapid heating temperature Ta (870°C) was set to 1600°C / sec, and the average oxygen partial pressure ratio PO1 was set to 0.03. The holding time at the decarburization annealing temperature (830°C) was set to 80 seconds. The average oxygen partial pressure ratio PO4 at the decarburization annealing temperature is shown in Table 5-2.

[0210]

[0211] The decarburization annealed steel sheet after the decarburization annealing process was coated with an annealing separator (water slurry) mainly composed of MgO, and then wound into a coil. The coiled steel sheet was subjected to a finish annealing process. In the finish annealing process, the average temperature increase rate V2 during the steel sheet temperature increase from 650°C to 900°C was 20°C / hour, and the average oxygen partial pressure ratio PO2 was 0.008. Furthermore, the average temperature increase rate V3 during the temperature increase from 900°C to 1100°C was 15°C / hour, and the average oxygen partial pressure ratio PO3 was 0.005. After heating to 1100°C or higher, soaking was performed for 5 hours or more. The purity of the hydrogen gas used as the atmospheric gas in the finish annealing process was 6N (99.9999%).

[0212] The steel sheets after the final annealing process were subjected to a secondary coating process. In the secondary coating process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface of the steel sheets after the final annealing process (on the primary coating), and then baked under well-known conditions to form a secondary coating. Grain-oriented electrical steel sheets of each test number were manufactured by the above manufacturing process.

[0213] [Evaluation Tests] Tests 1 to 5 were carried out on the grain-oriented electrical steel sheets with each test number.

[0214] As a result of the analysis in Test 1, in Example 3, the chemical composition of the base steel plate was as shown in Table 5-3.

[0215]

[0216] [Evaluation Results] Referring to Tables 5-1 to 5-3, in test numbers 1 to 5, 7 to 11, 13 to 16, and 18 to 21, the chemical compositions of the slabs and the base steel plates were appropriate, and the manufacturing conditions were also appropriate. As a result, in all test numbers, the strength ratio I ｒｅｆ was 0.0006 or less. １７／５０ The iron loss was low at less than 0.90 W / kg, and the bending peeling diameter was 30 mm or less, and the adhesion of the secondary coating was also excellent.

[0217] Furthermore, in test numbers 2 to 5, 8 to 11, 14 to 16, 20, and 21, the average oxygen partial pressure ratio PO4 was equal to or greater than the lower limit of formula (5).Ｓｎ Therefore, the bending peeling diameter was 20 mm or less, and the adhesion of the secondary coating was further improved.

[0218] On the other hand, in test numbers 6, 12, 17, and 22, PO4 was high. １７／５０ was 0.90 W / kg or more.

[0219] In Example 4, a slab containing Si, Mn, N, C, sol. Al, and S in the amounts shown in Table 6-1 and further containing Sn in the amount shown in Table 6-2 was prepared.

[0220]

[0221] The slab was subjected to a hot rolling process. Specifically, the slab was heated to 1350°C and then hot rolled to produce a hot-rolled steel sheet having a thickness of 2.3 mm.

[0222] The hot-rolled steel sheet after the hot rolling process was subjected to a hot-rolled sheet annealing process at an annealing temperature of 900 to 1200°C for a holding time of 10 to 300 seconds. After the hot-rolled sheet annealing process, a pickling process was carried out. In the pickling process, a pickling bath with a hydrochloric acid concentration of 10% and a bath temperature of 90°C was used, and the pickling time was 120 seconds. Thereafter, a cold-rolling process was carried out to produce a cold-rolled steel sheet (base steel sheet) with a thickness of 0.22 mm.

[0223] The cold-rolled steel sheet was subjected to a decarburization annealing process. In the decarburization annealing process, the rapid heating temperature Ta was set to 860°C, and the decarburization annealing temperature was set to 830°C. The average heating rate V1 from 550°C to the rapid heating temperature Ta (860°C) was set to 800°C / sec, and the average oxygen partial pressure ratio PO1 was set to 0.03. The holding time at the decarburization annealing temperature (830°C) was set to 60 seconds. The average oxygen partial pressure ratio PO4 at the decarburization annealing temperature was set to 0.30.

[0224] After the decarburization annealing process, the decarburization annealed steel sheet was coated with an annealing separator (water slurry) mainly composed of MgO and then wound into a coil. The coiled steel sheet was then subjected to a finish annealing process. In the finish annealing process, the average heating rate V2 during the temperature rise from 650°C to 900°C was 20°C / hour, and the average oxygen partial pressure ratio PO2 was 0.008. Furthermore, the average heating rate V3 and the average oxygen partial pressure ratio PO3 during the temperature rise from 900°C to 1100°C were as shown in Table 6-2. After heating to 1100°C or higher, soaking was performed for 5 hours or more. The purity of the hydrogen gas used as the atmospheric gas in the finish annealing process was 6N (99.9999%).

[0225]

[0226] The steel sheets after the final annealing process were subjected to a secondary coating process. In the secondary coating process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface of the steel sheets after the final annealing process (on the primary coating), and then baked under well-known conditions to form a secondary coating. Grain-oriented electrical steel sheets of each test number were manufactured by the above manufacturing process.

[0227] [Evaluation Tests] Tests 1 to 5 were carried out on the grain-oriented electrical steel sheets with each test number.

[0228] As a result of the analysis in Test 1, in Example 4, the chemical composition of the base steel plate was as shown in Table 6-3.

[0229]

[0230] [Evaluation Results] Referring to Tables 6-1 to 6-3, the chemical compositions and manufacturing conditions were all appropriate for test numbers 7 to 9, 11 to 13, 15 to 17, 20 to 22, 24 to 26, 28 to 30, 37 to 39, 41 to 43, 50, 51, 54, and 55. As a result, the intensity ratio I defined by formula (1) was 0.01 for all test numbers. ｒｅｆ was 0.0006 or less. １７／５０ The iron loss was low at less than 0.90 W / kg, and the bending peeling diameter was 30 mm or less, and the adhesion of the secondary coating was also excellent.

[0231] Furthermore, test numbers 7 to 9, 11 to 13, 15 to 17, 20 to 22, 24 to 26, and 28 to 30 satisfied formula (5). Ｓｎ Therefore, the bending peeling diameter was 20 mm or less, and the adhesion of the secondary coating was further improved.

[0232] On the other hand, in test numbers 1 and 2, the Sn content of the base steel sheet was low. １７／５０ was 0.90 W / kg or more.

[0233] In Test No. 59, the base steel sheet had a high Sn content. As a result, cracks occurred in the steel sheet during the cold rolling process. Therefore, the subsequent manufacturing process and Tests 2 to 5 were discontinued.

[0234] In test number 60, the Sn content of the base steel sheet was high. １７／５０ was 0.90 W / kg or more.

[0235] In test numbers 3 to 6, 33 to 36, and 46 to 49, the average heating rate V3 during the final annealing process from 900°C to 1100°C was too slow. Furthermore, in test numbers 6, 36, 48, and 49, the average oxygen partial pressure ratio PO3 during the final annealing process was too high. Therefore, the strength ratio I ｒｅｆ As a result, the bending peeling diameter was 40 mm or more, and the adhesion of the secondary coating was low.

[0236] In all of the test numbers 19, 32, 45 and 58, the average temperature rise rate V3 was too high. １７／５０ was 0.90 W / kg or more.

[0237] In all of the test numbers 10, 14, 18, 23, 27, 31, 40, 44, 52, 53, 56 and 57, the average oxygen partial pressure ratio PO3 in the final annealing process was too high. ｒｅｆ As a result, the bending peeling diameter was 40 mm or more, and the adhesion of the secondary coating was low.

[0238] In Example 5, grain-oriented electrical steel sheets were produced by changing the production conditions in the temperature-raising step of the decarburization annealing step. Specifically, slabs containing Si, Mn, N, C, sol. Al, and S in the amounts shown in Table 7-1 and further containing Sn in the amount shown in Table 7-2 were prepared.

[0239]

[0240] The slab was subjected to a hot rolling process. Specifically, the slab was heated to 1350°C and then hot rolled to produce a hot-rolled steel sheet having a thickness of 2.3 mm.

[0241] The hot-rolled steel sheet after the hot rolling process was subjected to a hot-rolled sheet annealing process at an annealing temperature of 900 to 1200°C for a holding time of 10 to 300 seconds. After the hot-rolled sheet annealing process, a pickling process was carried out. In the pickling process, a pickling bath with a hydrochloric acid concentration of 10% and a bath temperature of 90°C was used, and the pickling time was 120 seconds. Thereafter, a cold-rolling process was carried out to produce a cold-rolled steel sheet (base steel sheet) with a thickness of 0.22 mm.

[0242] The cold-rolled steel sheet was subjected to a decarburization annealing process. In the decarburization annealing process, the rapid heating temperature Ta was set to 850°C, and the decarburization annealing temperature was set to 830°C. The average heating rate V1 for the temperature of the cold-rolled steel sheet from 550°C to the rapid heating temperature Ta (850°C) was set as shown in Table 7-2, and the average oxygen partial pressure ratio PO1 was set to 0.03. The holding time at the decarburization annealing temperature (830°C) was set to 60 seconds. The average oxygen partial pressure ratio PO4 at the decarburization annealing temperature was set to 0.40.

[0243]

[0244] An annealing separator (water slurry) mainly composed of MgO was applied to the decarburized annealed steel sheet after the decarburization annealing process, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. In the finish annealing process, the average temperature increase rate V2 during the steel sheet temperature increase from 650°C to 900°C was 15°C / hour, and the average oxygen partial pressure ratio PO2 was 0.008. Furthermore, the average temperature increase rate V3 during the steel sheet temperature increase from 900°C to 1100°C was 15°C / hour, and the average oxygen partial pressure ratio PO3 was 0.005. After the temperature increase to 1100°C or higher, soaking was performed for 5 hours or more. The purity of the hydrogen gas used as the atmospheric gas in the finish annealing process was 6N (99.9999%).

[0245] The steel sheets after the final annealing process were subjected to a secondary coating process. In the secondary coating process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface of the steel sheets after the final annealing process (on the primary coating), and then baked under well-known conditions to form a secondary coating. Grain-oriented electrical steel sheets of each test number were manufactured by the above manufacturing process.

[0246] [Evaluation Tests] Tests 1 to 5 were carried out on the grain-oriented electrical steel sheets with each test number.

[0247] As a result of the analysis in Test 1, in Example 5, the chemical composition of the base steel plate was as shown in Table 7-3.

[0248]

[0249] [Evaluation Results] Referring to Tables 7-1 to 7-3, in test numbers 2 to 8, 10 to 16, 18 to 24, and 26 to 32, the chemical composition was appropriate, V1 was 100°C / sec or more, and other manufacturing conditions were also appropriate. As a result, in all test numbers, the intensity ratio I defined by formula (1) ｒｅｆ was 0.0006 or less. １７／５０ The iron loss was low at less than 0.90 W / kg, and the bending peeling diameter was 30 mm or less, and the adhesion of the secondary coating was also excellent.

[0250] Furthermore, in test numbers 2 to 8, 10 to 16, and 18 to 24, the average oxygen concentration PO4 satisfied the lower limit of formula (5).Ｓｎ Therefore, the bending peeling diameter was 20 mm or less, and the adhesion of the secondary coating was also excellent.

[0251] Furthermore, in the test numbers of the examples of the present invention, the higher the Sn content and the faster the temperature rise rate V1, the lower the iron loss W １７／５０ Specifically, in test numbers 2 to 8, which had similar Sn contents, the iron loss W １７／５０ In test numbers 10 to 16, which have similar Sn contents, the iron loss W １７／５０ In test numbers 18 to 24, which have similar Sn contents, the iron loss W １７／５０ In test numbers 26 to 32, which have similar Sn contents, the iron loss W １７／５０ When the Sn content is 0.10% or more and the heating rate V1 is 100°C / sec or more, the iron loss W １７／５０ was 0.85 W / kg or less, which was very good.

[0252] On the other hand, in test numbers 1, 9, 17, and 25, V1 was less than 100°C / sec. １７／５０ was 0.90 W / kg or more.

[0253] The embodiments of the present invention have been described above. However, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be appropriately modified and carried out without departing from the spirit of the present invention.

[0254] 1 Grain-oriented electrical steel sheet 10 Base steel sheet 11 Primary coating 12 Secondary coating

Claims

1. A grain-oriented electrical steel sheet, A base steel plate; A primary coating formed on the base steel sheet; a secondary coating formed on the primary coating, The chemical composition of the base steel sheet is, in mass%, Si: 2.50-4.50%, Mn: 0.01-1.00%, Sn: 0.05-0.30%, N: 0.010% or less, C: 0.010% or less, sol. Al: 0.010% or less, One or more selected from the group consisting of S and Se: 0.020% or less in total; P: 0.00-0.05%, Sb: 0.00 to 0.50%, Cr: 0.00-0.50%, Cu: 0.00-0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and The balance is Fe and impurities, A glow discharge optical emission spectroscopy analysis is carried out from the surface of the secondary coating in the sheet thickness direction of the base steel sheet to obtain a glow optical emission spectrum showing the relationship between the sputtering time, the optical emission intensity of Mg, and the optical emission intensity of Sn. In the glow optical emission spectrum, The maximum emission intensity of Mg is I Ｍｇ／Ｍｇ Define it as: The emission intensity of Sn at the sputtering time when the emission intensity of Mg becomes the maximum is defined as I Ｓｎ／Ｍｇ When we define The intensity ratio I defined by the formula (1) ｒｅｆ is 0.0000 to 0.0006, Iron loss W according to JIS C2556:2015 １７／５０ is less than 0.90 W / kg; Grain-oriented electrical steel sheet. I ｒｅｆ =I Ｓｎ／Ｍｇ / I Ｍｇ／Ｍｇ (1)

2. The grain-oriented electrical steel sheet according to claim 1, I Ｓｎ／Ｍｇ is less than or equal to 0.0021; Grain-oriented electrical steel sheet.

3. The grain-oriented electrical steel sheet according to claim 1, In the glow emission spectrum, I Ｓｎ／Ｍｇ The emission intensity of Sn at the time when 20.0 seconds have elapsed from the sputtering time at which the above value was obtained was I Ｓｎ／Ｍｇ＋２０ When the Sn concentration gradient ΔI is defined as Ｓｎ is 0.0000 to 0.0004 / sec. Grain-oriented electrical steel sheet. ΔI Ｓｎ =(I Ｓｎ／Ｍｇ＋２０ -I Ｓｎ／Ｍｇ ) / 20 (2)

4. A grain-oriented electrical steel sheet according to claim 2, In the glow emission spectrum, When the emission intensity of Sn at a point in time when 20.0 seconds have elapsed from the sputtering time at which the I Sn / Mg was obtained is defined as I Sn / Mg+20 , the Sn concentration gradient ΔI Sn defined by the formula (2) is 0.0000 to 0.0004 / second. Grain-oriented electrical steel sheet. ΔI Sn = (I Sn / Mg+20 - I Sn / Mg) / 20 (2)

5. The grain-oriented electrical steel sheet according to any one of claims 1 to 4, The chemical composition of the base steel plate is P: 0.01-0.05%, Sb: 0.01 to 0.50%, Cr: 0.01-0.50%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, and Bi: 0.0001-0.0100%, Contains one or more elements selected from the group consisting of Grain-oriented electrical steel sheet.

6. A method for producing the grain-oriented electrical steel sheet according to claim 1, Si: 2.50-4.50%, Mn: 0.01-1.00%, Sn: 0.05-0.30%, N: 0.002-0.020%, C: 0.020-0.100%, sol. Al: 0.010 to 0.050%, One or more selected from the group consisting of S and Se: 0.010 to 0.050% in total, P: 0.00-0.05%, Sb: 0.00 to 0.50%, Cr: 0.00-0.50%, Cu: 0.00-0.50%, Ni: 0.00 to 0.50%, Bi: 0.0000 to 0.0100%, and A hot rolling process for producing a hot rolled steel sheet by hot rolling a slab having a chemical composition with the balance being Fe and impurities; A hot-rolled steel sheet annealing process for annealing the hot-rolled steel sheet; A pickling process in which a pickling treatment is performed on the hot-rolled steel sheet after the hot-rolled sheet annealing process; A cold rolling process in which the hot-rolled steel sheet after the pickling process is cold-rolled to produce a cold-rolled steel sheet; a decarburization annealing step of performing decarburization annealing on the cold-rolled steel sheet to manufacture a decarburization annealed steel sheet; a finish annealing step of applying an annealing separator to the decarburization annealed steel sheet and performing finish annealing on the decarburization annealed steel sheet to which the annealing separator has been applied, thereby manufacturing a finish annealed steel sheet having the primary coating formed thereon; A secondary coating forming process includes applying a secondary coating forming liquid to the finish annealed steel sheet and performing a heat treatment on the finish annealed steel sheet to which the secondary coating forming liquid has been applied, thereby forming the secondary coating on the finish annealed steel sheet. In the pickling process, The hydrochloric acid concentration of the pickling bath is set to 5 to 20% by mass, and the bath temperature is set to 80 to 100°C. The immersion time in the acid pickling bath is 30 to 120 seconds, In the decarburization annealing step, The rapid heating temperature Ta is set to 800 to 900°C. The average heating rate V1 during the period in which the temperature of the cold-rolled steel sheet is increased from 550 ° C. to the rapid heating end temperature Ta is set to 100 ° C. / sec or more; After the temperature of the cold-rolled steel sheet is raised to the rapid heating attainment temperature Ta, the cold-rolled steel sheet is held at a decarburization annealing temperature of 800 to 950° C. for 60 seconds or more, and an average oxygen partial pressure ratio PO4 during the period of holding at the decarburization annealing temperature is set to 0.60 or less; In the finish annealing step, The average heating rate V3 (°C / hour) during the temperature of the decarburization annealed steel sheet from 900°C to 1100°C and the average oxygen partial pressure ratio PO3 satisfy formulas (3) and (4), The purity of hydrogen gas introduced into the furnace atmosphere of the finish annealing furnace used for the finish annealing is more than 99.9%. Manufacturing method of grain-oriented electrical steel sheet. 31×Sn+5≦V3≦30 (3) 0.000≦PO3≦−0.020×Sn+0.015 (4) Here, the Sn content in mass % in the slab is substituted for Sn in the formulas (3) and (4).

7. A method for producing the grain-oriented electrical steel sheet according to claim 6, The decarburization annealing step further comprises: The average oxygen partial pressure ratio PO4 satisfies formula (5), Manufacturing method of grain-oriented electrical steel sheet. 0.88×Sn+0.19≦PO4≦0.60 (5) Here, the Sn content in mass % in the slab is substituted for Sn in formula (5).

8. A method for producing the grain-oriented electrical steel sheet according to claim 6 or 7, The chemical composition of the slab is P: 0.01-0.05%, Sb: 0.01 to 0.50%, Cr: 0.01-0.50%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, and Bi: 0.0001-0.0100%, Contains one or more elements selected from the group consisting of Manufacturing method of grain-oriented electrical steel sheet.