JP7719342B2 - Grain-oriented electrical steel sheet and its manufacturing method - Google Patents

Description

The present invention relates to grain-oriented electrical steel sheets and their manufacturing methods.

Grain-oriented electrical steel sheets are primarily used in static inductors, such as transformers. The properties that grain-oriented electrical steel sheets must meet include (1) low energy loss (i.e., low iron loss) when excited with AC, (2) high magnetic permeability in the excitation range used by the equipment, allowing for easy excitation, and (3) low magnetostriction, which can cause noise.
In particular, with regard to iron loss, since transformers are continuously excited and continue to generate energy losses over a long period from installation to disposal, iron loss is a major parameter that determines the total owning cost (TOC), which is an index that represents the value of a transformer.

Many developments have been made to reduce the iron loss of grain-oriented electrical steel sheets. These include increasing the concentration of the {110}<001> orientation, known as the Goss orientation, increasing the content of solid solution elements such as Si, which increases electrical resistance, reducing the thickness of the steel sheet, applying a ceramic coating or insulating coating that imparts surface tension to the steel sheet, reducing the size of the crystal grains, and subdividing magnetic domains by introducing linear distortion or grooves.

On the other hand, with regard to magnetic permeability and magnetostriction, it is effective to increase the degree of orientation of crystal grains in the Goss orientation, and _B8 , which is the magnetic flux density at an excitation force of 800 A/m, is used as an index for this.
One typical technique for improving magnetic flux density is the manufacturing method disclosed in Patent Document 1. This manufacturing method involves using AlN and MnS as inhibitors to suppress grain growth, and using a strong rolling reduction of more than 80% in the final cold rolling step. Patent Document 1 discloses that this method increases the degree of grain orientation in the {110}<001> orientation, resulting in a grain-oriented electrical steel sheet with a high magnetic flux density of 1.870 T or more in _B8 .

However, when these Al-based inhibitors are used to increase magnetic flux density, although the steel sheet itself has excellent magnetic properties, the adhesion of the primary coating (hereinafter also referred to as the glass coating) which is primarily composed of forsterite deteriorates, and there has been a demand for improved coating adhesion, particularly in thin grain-oriented electrical steel sheets.

In response to these issues, for example, Patent Document 2 discloses a grain-oriented electrical steel sheet having excellent coating adhesion, and a method for producing the same, which is obtained by adding a compound containing one or more of Ce, La, Pr, Nd, Sc, and Y to an annealing separator mainly composed of MgO, and which contains one or more of oxides, hydroxides, sulfates, or carbonates of Ce, La, Pr, Nd, Sc, and Y having an average particle size of 0.1 to 25 μm in a total amount of 0.001 to 1000 mg/ ^m2 per side in terms of metal, and which has triple frequency iron loss characteristics W17 _/150 of 5.56 W/kg or less and frame peelability of 0.8 mm or less.
Patent Document 3 discloses a grain-oriented electrical steel sheet obtained by adding a compound containing one or more of Ce, La, Pr, Nd, Sc, and Y to an annealing separator mainly composed of MgO, and the primary coating contains one or more of oxides, hydroxides, sulfates, and carbonates of Ce, La, Pr, Nd, Sc, and Y in a total amount of 0.1 to 10 mg/ ^m2 per side in terms of metal basis weight, and also contains 1 to 800 mg/ ^m2 Ti per side in terms of basis weight, and the triple frequency iron loss characteristic W17 _/150 is 5.41 W/kg or less, and the frame peelability is 0.2 mm or less.
Patent Document 4 discloses a grain-oriented electrical steel sheet with excellent coating adhesion, characterized in that the primary coating contains a sulfide compound containing one or more elements selected from Ca, Sr, and Ba, a rare earth metal element, and sulfur, which is obtained by adding, in an annealing separator containing MgO as the main component, one or more of oxides, sulfides, sulfates, silicides, phosphates, hydroxides, carbonates, borides, chlorides, and fluorides of rare earth metals in an amount of 0.1 to 10 mass % calculated as rare earth metals, one or more of oxides, sulfides, sulfates, silicides, phosphates, hydroxides, carbonates, borides, chlorides, and fluorides of one or more alkaline earth metals selected from Ca, Sr, and Ba in an amount of 0.1 to 10 mass % calculated as alkaline earth metals, and 0.01 to 5 mass % calculated as S of a sulfur compound. Patent Document 4 discloses that when a compound (A) composed of one or more elements selected from Ca, Sr, and Ba, a rare earth metal element, and sulfur is present adjacent to a spinel formed at the interface between the coating and the steel sheet and on the steel sheet inner side of the interface, the aforementioned action of the spinel as a starting point for fracture and peeling can be suppressed, and adhesion during strong bending processing can be further improved.

However, as a result of investigations conducted by the present inventors, it was found that for grain-oriented electrical steel sheets with thin sheet thicknesses, particularly those with base steel sheets having a thickness of 0.22 mm or less, when rare earth elements are contained in the annealing separator and these compounds are present in the primary coating, as disclosed in Patent Documents 2 to 4, there is a problem of deterioration in magnetic properties such as core loss.

Special Publication No. 40-15644 Patent No. 5739840 Patent No. 5230194 Patent No. 5419459

The present invention was made in consideration of the above-mentioned problems. It is an object of the present invention to provide a grain-oriented electrical steel sheet and a manufacturing method thereof that exhibit excellent core loss characteristics and coating adhesion, even when manufactured by performing final annealing using an annealing separator containing elements such as Ce, La, Pr, Nd, Ba, Ca, Sr, and Zr.

The present inventors have found that when elements such as Ce, La, Pr, Nd, Ba, Ca, Sr, and Zr are added to an annealing separator, sulfides of these elements remain in the primary coating of the final grain-oriented electrical steel sheet, resulting in deterioration of the iron loss characteristics.
Furthermore, as a result of further investigations, the present inventors have found that the deterioration of iron loss characteristics can be suppressed by controlling the structure and frequency of existence of these sulfides.

The present invention has been made based on the above findings. The gist of the present invention is the following grain-oriented electrical steel sheet and a method for manufacturing the same.
(1) A grain- oriented electrical steel sheet comprising a base steel sheet, a glass coating formed on the surface of the base steel sheet, and a tension-applying insulating coating formed on the surface of the glass coating, wherein the base steel sheet has a chemical composition, in mass%, of C: 0.005% or less, Si: 3.00 to 3.80%, Mn: 0.01 to 0.50%, N: 0.020% or less, Sol-Al: 0.020% or less, S: 0.020% or less, Ce, Ca, Nd, Sr, Pr, Ba, La, Zr the total of: 0.0100% or less, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, Bi: 0 to 0.020%, Mo: 0 to 0.50%, and the balance: Fe and impurities, and the thickness of the base steel plate is 0.18 to 0.22 mm, and cubic type sulfides are present in an amount of 0.001 to 10.00 particles/μm in the glass coating and in a boundary region between the glass coating and the base steel plate. ² , wherein the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the grain-oriented electrical steel sheet is 1.5 to 10.0 times the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the base steel sheet.
(2) The grain-oriented electrical steel sheet according to (1), wherein the chemical composition contains Sn: 0.01 to 0.50%.
(3) The grain-oriented electrical steel sheet according to (1) or (2), wherein the chemical composition contains 0.01 to 0.50% Cr.
(4) The grain-oriented electrical steel sheet according to any one of (1) to (3), wherein the chemical composition contains Cu: 0.01 to 0.50%.
(5) The grain-oriented electrical steel sheet according to any one of (1) to (4), wherein the chemical composition contains Se: 0.001 to 0.020%.
(6) The grain-oriented electrical steel sheet according to any one of (1) to (5), wherein the chemical composition contains Sb: 0.005 to 0.50%.
(7) The grain-oriented electrical steel sheet according to any one of (1) to (6), wherein the chemical composition contains Bi: 0.0001 to 0.020%.
(8) A method for producing a grain-oriented electrical steel sheet according to (1), wherein the chemical composition is, in mass%, C: 0.010 to 0.200%, Si: 3.00 to 3.80%, Sol-Al: 0.010 to 0.050%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.050%, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0. a hot rolling process for hot-rolling the steel slab to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing process for annealing the hot-rolled steel sheet to obtain a hot- rolled annealed steel sheet; a cold rolling process for cold-rolling the hot-rolled annealed steel sheet including a plurality of passes to obtain a cold-rolled steel sheet having a thickness of 0.18 to 0.22 mm; and a cold-rolling process for cold-rolling the cold-rolled annealed steel sheet. a finish annealing step of applying an annealing separator to the decarburization-annealed steel sheet and then finish-annealing the steel sheet to obtain a finish-annealed steel sheet; and an insulating coating formation step of forming an insulating coating on the surface of the finish-annealed steel sheet, wherein the annealing separator contains 90 mass% or more of MgO and one or more oxides, hydroxides, sulfates, and carbonates of one or more elements selected from Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr, and the total content, by mass, of the oxides, hydroxides, sulfates, and carbonates in the annealing separator is 0.5 to 10.0 mass%, and the finish annealing step involves increasing the temperature within a temperature range of 700 to 900°C at an average heating rate of 13°C/hr to 30°C/hr and maintaining the temperature within a temperature range of 1000 to 1300°C for 40 to 100 hours.
(9) The method for producing a grain-oriented electrical steel sheet according to (8), wherein the oxides, hydroxides, sulfates, and carbonates have average particle sizes of 20 μm or less.
(10) The method for producing a grain-oriented electrical steel sheet according to (8) or (9), wherein the annealing separator contains, as the Ti compound, one or more of oxides, carbides, and nitrides of Ti, the total content of the Ti compounds in the annealing separator, in mass%, is 0.5 to 10.0%, and the average particle size of the Ti compounds is 20 μm or less.
(11) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (10), wherein, in the temperature-rising process of the decarburization annealing, the average heating rate in the temperature range of 550 to 750°C is controlled to 500 to 1000°C/s.
(12) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (11), wherein, in the temperature-rising process of the decarburization annealing, the average heating rate in the temperature range of 750 to 800°C is controlled to 1000 to 2000°C/s.
(13) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (12), wherein the dew point of the annealing atmosphere in the temperature range of 550 to 800°C is controlled to 0°C or less during the temperature increase process of the decarburization annealing.
(14) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (13), further comprising a nitriding treatment between the decarburization annealing step and the finish annealing step.
(15) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (14), wherein in the cold rolling step, intermediate annealing is performed between the plurality of passes, and a cumulative reduction rate of passes after the intermediate annealing is set to 80 to 95%.
(16) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (15), wherein the chemical composition of the steel billet contains Sn: 0.01 to 0.50%.
(17) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (16), wherein the chemical composition of the steel billet contains 0.01 to 0.50% Cr.
(18) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (17), wherein the chemical composition of the steel billet contains Cu: 0.01 to 0.50%.
(19) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (18), wherein the chemical composition of the steel billet contains Se: 0.001 to 0.020%.
(20) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (19), wherein the chemical composition of the steel billet contains Sb: 0.005 to 0.50%.
(21) The method for producing a grain-oriented electrical steel sheet according to any one of (8) to (20), wherein the chemical composition of the steel billet contains Bi: 0.0005 to 0.020%.

The present invention provides a grain-oriented electrical steel sheet and a manufacturing method thereof that exhibit excellent core loss characteristics and coating adhesion, even when manufactured by performing final annealing using an annealing separator containing elements such as Ce, La, Pr, Nd, Ba, Ca, Sr, and Zr.

1 is a schematic diagram showing an example of an observation image (magnification: 3000 times) of a cross section of a grain-oriented electrical steel sheet according to an embodiment of the present invention. FIG.

Hereinafter, a grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to this embodiment) will be described.
The grain-oriented electrical steel sheet according to this embodiment is a grain-oriented electrical steel sheet comprising a base steel sheet, a glass coating formed on the surface of the base steel sheet, and a tension-applying insulating coating formed on the surface of the glass coating. The glass coating and the tension-applying insulating coating may be formed on at least one surface of the base steel sheet, but are usually formed on both surfaces of the base steel sheet.
In the electrical steel sheet according to this embodiment, the base steel sheet contains, as a chemical composition, in mass%, C: 0.010% or less, Si: 3.00 to 3.80%, Mn: 0.01 to 0.50%, N: 0.020% or less, Sol-Al: 0.020% or less, S: 0.020% or less, a total of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr: 0.0100% or less, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, Bi: 0 to 0.020%, Mo: 0 to 0.50%, with the balance being Fe and impurities, and the base steel sheet has a thickness of 0.18 to 0.22 mm.
Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, the glass coating and the boundary region between the glass coating and the base steel sheet contain 0.001 to 10.00 cubic-type sulfides per ^μm2 .

<Chemical composition of base steel plate>
C: 0.010% or less C (carbon) is an element effective for controlling the structure of steel sheets in the manufacturing process up to the completion of the decarburization annealing step. However, if the C content exceeds 0.010%, the magnetic properties of the finished grain-oriented electrical steel sheet deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the C content is set to 0.010% or less. The C content is preferably 0.005% or less, more preferably 0.003% or less. In the base steel sheet, the lower the C content, the better. However, even if the C content is reduced to less than 0.0001%, the effect saturates and the manufacturing cost simply increases. Therefore, the C content may be set to 0.0001% or more.

Si: 3.00-3.80%
Silicon (Si) is an element that increases the electrical resistance of grain-oriented electrical steel sheets and improves their iron loss characteristics. If the Si content is less than 3.00%, γ transformation of the structure occurs during finish annealing (secondary recrystallization annealing), impairing the accumulation of the steel sheet in a preferred crystal orientation. Therefore, the Si content is set to 3.00% or more. The Si content is preferably 3.10% or more, and more preferably 3.20% or more.
On the other hand, if the Si content exceeds 3.80%, the grain-oriented electrical steel sheet becomes embrittled and the threading property deteriorates significantly. Furthermore, the workability of the grain-oriented electrical steel sheet deteriorates, and the steel sheet may break during rolling. Therefore, the Si content is set to 3.80% or less. The Si content is preferably 3.60% or less, and more preferably 3.50% or less.

Mn: 0.01-0.50%
Mn (manganese) is an element that combines with S during the manufacturing process to form MnS. This precipitate functions as an inhibitor (a suppressor of normal grain growth) and induces secondary recrystallization in the steel. Mn also improves the hot workability of the steel. If the Mn content is less than 0.01%, the above-mentioned effects cannot be fully obtained. Therefore, the Mn content is set to 0.01% or more. The Mn content is preferably 0.03% or more, and more preferably 0.06% or more.
On the other hand, if the Mn content exceeds 0.50%, secondary recrystallization does not occur, and the magnetic properties of the steel deteriorate. Therefore, the Mn content in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment is set to 0.50% or less. The Mn content is preferably 0.40% or less, and more preferably 0.30% or less.

N: 0.020% or less N (nitrogen) is an element that bonds with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, if the N content exceeds 0.020%, an excessive amount of inhibitor remains in the grain-oriented electrical steel sheet, resulting in a deterioration in magnetic properties. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the N content is set to 0.020% or less. The N content is preferably 0.015% or less, and more preferably 0.010% or less.
If AlN is not utilized as an inhibitor, the lower limit of the N content may be 0%. However, since the detection limit of chemical analysis is 0.0001%, the substantial lower limit of the N content in practical steel sheets is 0.0001%.

Sol-Al: 0.020% or less Sol-Al (acid-soluble aluminum, sometimes referred to as sol.Al) is an element that bonds with N to form AlN, which functions as an inhibitor, during the manufacturing process of grain-oriented electrical steel sheet. However, if the Sol-Al content of the base steel sheet exceeds 0.020%, an excess of inhibitor remains in the base steel sheet, resulting in reduced magnetic properties. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the Sol-Al content is set to 0.020% or less. The Sol-Al content is preferably 0.015% or less, more preferably 0.010% or less. There is no particular lower limit for the Sol-Al content, but reducing it to less than 0.0001% only increases manufacturing costs. Therefore, the Sol-Al content may be set to 0.0001% or more.

S: 0.020% or less S (sulfur) is an element that combines with Mn to form MnS, which functions as an inhibitor, during the manufacturing process of grain-oriented electrical steel sheet. However, if the S content exceeds 0.020% and remains after secondary recrystallization, impurities such as MnS and MgS are formed, resulting in a deterioration in magnetic properties. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the S content is set to 0.020% or less, preferably 0.015% or less, and more preferably 0.010% or less.
The S content in the base steel sheet is preferably as low as possible, and may be 0%. However, reducing the S content of the base steel sheet to less than 0.0001% only increases the manufacturing cost. Therefore, the S content is preferably 0.0001% or more.
The sulfides to be controlled in this embodiment are not those in the base steel sheet, but those present in the glass coating or in the boundary region between the glass coating and the base steel sheet, as will be described later. In the process of removing the primary coating by so-called pickling, which is a preparation stage for subjecting the base steel sheet to analysis for measuring the content of each element, the sulfides present at the interface are removed. Therefore, a base steel sheet having an S content of 0% does not mean that no sulfides are present in the glass coating or in the boundary between the glass coating and the base steel sheet.

Total of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr: 0.0100% or less Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr may be mixed into steel as impurities. These elements bind with S in the steel and suppress the formation of MnS, an important inhibitor of secondary recrystallization, thereby hindering the onset of secondary recrystallization. Since there is no problem if the total content is 0.0100% or less, the total content of the above elements is set to 0.0100% or less.
Although there is no particular lower limit for the total content of the above elements, they may be unintentionally mixed in at a total amount of about 0.0004%, so the lower limit for the total content of the above elements may be set at 0.0004%.

The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment basically contains the above-mentioned elements, with the balance being Fe and impurities. However, for the purpose of improving magnetic properties, Cu, Cr, Sn, Se, Sb, Bi, and Mo may also be contained in the ranges shown below. However, these elements are not essential elements, and the lower limit is 0%.
Here, impurities refer to elements that are mixed in from raw materials such as ore or scrap, or the manufacturing environment, when the base steel sheet is industrially manufactured, and are permissible to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.

Cu: 0-0.50%
Cu (copper) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure. Therefore, it may be contained. To achieve the above effect, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more.
On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, the Cu content of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment is set to 0.50% or less. The Cu content is preferably 0.30% or less, and more preferably 0.10% or less.

Cr: 0-0.50%
Cr (chromium) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure and improves magnetic properties. Therefore, Cr may be added. To achieve the above effect, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
On the other hand, if the Cr content exceeds 0.50%, Cr oxides are formed, resulting in a deterioration in magnetic properties. Therefore, the Cr content is set to 0.50% or less. The Cr content is preferably 0.30% or less, and more preferably 0.10% or less.

Sn: 0-0.50%
Sn (tin) is an element that contributes to improving magnetic properties through crystal structure control. Therefore, it may be contained. In order to obtain the effect of improving magnetic properties, the Sn content is preferably 0.01% or more. In consideration of achieving both magnetic properties and coating adhesion, the Sn content is more preferably 0.02% or more, and even more preferably 0.03% or more.
On the other hand, if the Sn content exceeds 0.50%, the glass coating deteriorates, and sufficient tension for magnetic domain refinement cannot be obtained, resulting in poor core loss characteristics. Therefore, the Sn content is set to 0.50% or less. The Sn content is preferably 0.30% or less, and more preferably 0.10% or less.

Se: 0-0.020%
Se (selenium) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. If it is contained, the Se content is preferably 0.001% or more to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Se content is more preferably 0.003% or more, and even more preferably 0.006% or more.
On the other hand, if the Se content exceeds 0.020%, the adhesion of the glass coating deteriorates. Therefore, the Se content is set to 0.020% or less. The Se content is preferably 0.015% or less, and more preferably 0.010% or less.

Sb: 0-0.50%
Sb (antimony) is an element that has a magnetic property improving effect. Therefore, it may be contained. When Sb is contained, the Sb content is preferably 0.005% or more in order to effectively exhibit the magnetic property improving effect. The Sb content is more preferably 0.01% or more, and even more preferably 0.02% or more.
On the other hand, if the Sb content exceeds 0.50%, the adhesion of the glass coating significantly deteriorates. Therefore, the Sb content is set to 0.50% or less. The Sb content is preferably 0.30% or less, and more preferably 0.10% or less.

Bi: 0~0.020%
Bi (bismuth) is an element that can further increase the magnetic flux density of grain-oriented electrical steel sheets. Therefore, Bi may be added. To obtain this effect, the Bi content is preferably 0.001% or more.
On the other hand, if the Bi content in the base steel sheet exceeds 0.020%, the magnetic properties deteriorate. Therefore, the Bi content in the base steel sheet is set to 0.020% or less. The Bi content is preferably 0.010% or less, more preferably 0.005% or less, even more preferably 0.002% or less, and even more preferably less than 0.001%.

Mo: 0~0.50%
Mo (molybdenum) is an element that has a magnetic property improving effect. Therefore, it may be contained. When Mo is contained, the Mo content is preferably 0.01% or more in order to effectively exhibit the magnetic property improving effect. The Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more.
On the other hand, if the Mo content exceeds 0.50%, the cold rolling property deteriorates and there is a possibility of fracture. Therefore, the Mo content is set to 0.50% or less. The Mo content is preferably 0.30% or less, and more preferably 0.10% or less.

As described above, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment contains the essential elements described above, with the balance being Fe and impurities, or contains the essential elements described above and one or more optional elements, with the balance being Fe and impurities.

To obtain the chemical composition of a base steel sheet from a grain-oriented electrical steel sheet having a glass coating and a tension-imparting insulating coating on the base steel sheet, the grain-oriented electrical steel sheet is washed with an alkaline solution to remove the tension-imparting insulating coating, and then the glass coating is removed by pickling to obtain a base steel sheet. A drill is used to generate chips from the obtained base steel sheet, and the chips are collected. The collected chips are dissolved in acid to obtain a solution. The solution can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry).
In this case, C and S may be measured using the combustion-infrared absorption method, N may be measured using the inert gas fusion-thermal conductivity method, and O may be measured using the inert gas fusion-non-dispersive infrared absorption method.

Specifically, the tension-imparting insulating coating can be removed by immersing the grain-oriented electrical steel sheet having the coating in an aqueous sodium hydroxide solution containing 30-50% by mass of NaOH and 50-70% by mass of H ₂ O at 80-90°C for 5-10 minutes, followed by rinsing with water and drying. This allows the tension-imparting insulating coating to be removed from the grain-oriented electrical steel sheet. The time for immersion in the aqueous sodium hydroxide solution can be adjusted depending on the thickness of the tension-imparting insulating coating.
After removing the tension-applying insulating coating, the glass coating can be removed by immersing the wire in 30 to 40% hydrochloric acid at 80 to 90°C for 1 to 10 minutes, followed by rinsing with water and drying.
As mentioned above, the insulating coating is removed with an alkaline solution, the glass coating with hydrochloric acid, etc. By removing the insulating coating and the glass coating, the steel sheet is exposed, allowing the chemical composition of the base steel sheet to be measured.

<Glass coating>
In the grain-oriented electrical steel sheet according to this embodiment, a glass coating is formed on the surface of the base steel sheet.
The glass coating is an inorganic coating primarily composed of magnesium silicate. The glass coating is formed during finish annealing by a reaction between an annealing separator containing magnesia (MgO) applied to the surface of the base steel sheet and the components on the surface of the base steel sheet, and has a composition derived from the components of the annealing separator and the base steel sheet (more specifically, a composition primarily composed _{of Mg2SiO4} ).

<Tension-applying insulating coating>
In the grain-oriented electrical steel sheet according to this embodiment, a tension-applying insulating coating is formed on the surface of the glass coating.
The tension-imparting insulating coating imparts electrical insulation to the grain-oriented electrical steel sheet, thereby reducing eddy current loss and improving the iron loss characteristics of the grain-oriented electrical steel sheet. In addition to the electrical insulation properties described above, the tension-imparting insulating coating also provides various other properties such as corrosion resistance, heat resistance, and slip resistance.
Furthermore, the tension-imparting insulating coating has the function of imparting tension to the grain-oriented electrical steel sheet. By applying tension to the grain-oriented electrical steel sheet, it is possible to facilitate domain wall motion in the grain-oriented electrical steel sheet, thereby improving the iron loss characteristics of the grain-oriented electrical steel sheet.
The tension-imparting insulating coating is formed, for example, by applying a coating liquid containing metal phosphate and silica as its main components to the surface of the glass coating and baking it.

<Base steel plate thickness: 0.18 to 0.22 mm>
As described above, the grain-oriented electrical steel sheet according to this embodiment is a grain-oriented electrical steel sheet that can achieve both good coating adhesion and low iron loss (good iron loss characteristics) in a grain-oriented electrical steel sheet having a base steel sheet thickness of 0.18 to 0.22 mm, which has traditionally been difficult to achieve both good coating adhesion and low iron loss (good iron loss characteristics).

<Cubic-type sulfides are contained in the glass coating and in the boundary region between the glass coating and the base steel sheet at 0.001 to 10.00 particles/ ^μm2 >
The present inventors investigated the cause of deterioration in iron loss characteristics when elements such as Ce, La, Pr, Nd, Ba, Ca, Sr, and Zr are contained in an annealing separator in order to improve coating adhesion. As a result, they found that in the final product, grain-oriented electrical steel sheet, sulfides such as SrS, BaS, CaS, NdS, CeS, LaS, PrS, and ZrS present in the glass coating or in the boundary region between the glass coating and the base steel sheet pin the domain walls, thereby deteriorating the iron loss characteristics. Furthermore, they found that this adverse effect is particularly pronounced when the base steel sheet is thin, i.e., when the glass coating or the boundary region between the glass coating and the base steel sheet accounts for a large proportion of the grain-oriented electrical steel sheet.

As a result of further investigation, the inventors have found that the adverse effect on iron loss can be reduced depending on the crystal structure and frequency of sulfides. In other words, they have found that the deterioration of iron loss characteristics can be suppressed by controlling the crystal structure and frequency of sulfides.
Specifically, they found that when cubic-type sulfides are contained in the glass coating and in the boundary region between the glass coating and the base steel sheet at a number density of 0.001 to 10.00 particles/ ^μm2 , deterioration of iron loss characteristics is suppressed, and good coating adhesion and low iron loss can both be achieved.
Cubic-type sulfides refer to sulfides in which metal elements (M) and sulfur (S) are arranged three-dimensionally with periodicity, and the smallest unit (unit cell) of the bonding period between M and S is a cube (cubic). The reason that cubic-type sulfides have little adverse effect on iron loss is thought to be because they have a crystal structure that is well-matched with the base steel.
If the number density of cubic-type sulfides in the glass coating and in the boundary region between the glass coating and the base steel sheet is less than 0.001/ ^μm2 , non-cubic-type sulfides will be present in the composition system of this embodiment, and the iron loss characteristics will deteriorate. On the other hand, if the number density of cubic-type sulfides exceeds 10.00/ ^μm2 , the iron loss characteristics will also deteriorate. In the grain-oriented electrical steel sheet according to this embodiment, the adverse effects of precipitates are minimized by controlling the crystal structure of the precipitates, but if the number density of cubic-type sulfides exceeds 10.00/ ^μm2 , the magnetic properties will deteriorate regardless of crystal structure control. A preferred range is 0.003 to 5.00/ ^μm2 , and a more preferred range is 0.005 to 1.00/ ^μm2 .
Cubic type sulfides are produced by changing the crystal structure of sulfides by controlling the heat cycle of the final annealing, as will be described later.

The number density of cubic type sulfides can be determined by investigating the presence or absence of cubic type sulfides in the glass coating and the boundary region between the glass coating and the base steel sheet by electron beam diffraction using a transmission electron microscope (TEM), and then counting the number density of cubic type sulfides contained in the image observed by the TEM. The method for calculating the number density is described below.
The observation magnification is not specified, but the number of sulfides is counted at, for example, 3000x. As shown in Figure 1 , the measurement range is a cross section in the sheet thickness direction, extending from the sample surface to the boundary region B between the glass coating 2 and the base steel sheet (base metal) 1. The "boundary region" B refers to the region including the interface between the glass coating 2 and the base steel sheet 1, and is the region sandwiched between the outermost end 21 of the glass coating 2, which has an inlaid structure into the base steel sheet 1, on the base steel sheet 1 side and the outermost end 22 of the tension-applying insulating coating 3 side. Specifically, at the above magnification, 10 or more fields are randomly observed, and the number density of sulfides 4 observed in each field is calculated as the average. Any number of fields can be observed, as long as it is 10 or more. The greater the number of fields, the higher the evaluation accuracy. However, observing more than 20 fields does not significantly improve evaluation accuracy. Therefore, the number density of cubic-type sulfides 4 is evaluated as the average of the observation results of 10 to 20 fields. The number density is the number of sulfides per unit area. Therefore, it is necessary to divide the number of sulfides by the area. However, the area referred to here does not refer to the entire field of view, but rather to the coating/base steel interface area, as shown below. The derivation of the coating/base steel interface area will now be described. In the observation field of view, the outermost edge 21 of the glass coating located at the deepest position (the base steel sheet side) is identified. As shown in Figure 1, the interface position is defined as a 4 μm distance from the bottom of the outermost edge 21 to the sample surface side (the tension-applying insulating coating side). Next, the lengths of the left and right edges of the observation field of view are measured. For example, in Figure 1, the length of the left and right edges is 40 μm. Therefore, in this example, the interface area is 160 ^μm² . If five cubic-type sulfides are observed in this field of view, the number density is 0.03/ ^μm² . If the measurement results are for 10 fields of view, this calculation is repeated 10 times in different fields of view, and the average of the obtained number densities is calculated.
Whether or not a part is a glass coating can be determined by electron microscope observation, as the color tone differs from that of the base steel, and so visual inspection is possible, but it can also be determined by electron diffraction. Since glass coatings contain Mg ₂ SiO ₄ and MgAl ₂ O ₄ , if electron diffraction that can be analyzed using JCPDS card numbers 074-1678, 034-189, or 021-1152, for example, is obtained, the part can be determined to be a glass coating. Since electron diffraction is performed for the purpose of material identification, there are no limitations on the observation magnification during electron diffraction.

<The total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the grain-oriented electrical steel sheet is 1.5 to 10.0 times the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the base steel sheet>
In the grain-oriented electrical steel sheet according to this embodiment, the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the grain-oriented electrical steel sheet is at least 1.5 times the total content of Ce, Ca, Nd, Sr, Pr, Ba, and La in the base steel sheet, which means that the primary coating contains more Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr than the base steel sheet. In other words, this is preferable because it further improves coating adhesion.
On the other hand, if the content exceeds 10.0 times, there is a concern that the magnetic flux density may decrease. Although the reason for this is unknown, it is thought that these elements have the effect of reducing the thermal stability of the inhibitors MnS and AlN, making secondary recrystallization unstable. Therefore, it is preferable that the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the grain-oriented electrical steel sheet is 10.0 times or less the total content of Ce, Ca, Nd, Sr, Pr, Ba, and La in the base steel sheet.

The total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the base steel sheet and the grain-oriented electrical steel sheet can be determined by the following method.
As described above, the total content of the above elements in the base steel sheet can be obtained by first removing the tension-applying insulating coating and then removing the glass coating from the grain-oriented electrical steel sheet (base steel sheet), and then performing ICP-AES to perform elemental analysis of the chemical composition.
On the other hand, the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in grain-oriented electrical steel sheet (comprising a base steel (base steel sheet), a primary coating (glass coating), and a secondary coating (tension-applying insulating coating)) is determined by using a drill to generate chips from the entire thickness of the grain-oriented electrical steel sheet, without carrying out the coating removal process described above, and then collecting the chips. The collected chips are dissolved in acid to obtain a solution, which is then subjected to ICP-AES to perform elemental analysis of the chemical composition.

<Manufacturing method>
The grain-oriented electrical steel sheet according to this embodiment can be manufactured by a manufacturing method including the following steps.
(i) a heating step of heating a steel slab containing, in mass%, C: 0.010 to 0.200%, Si: 3.00 to 3.80%, Sol-Al: 0.010 to 0.050%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.050%, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, Bi: 0 to 0.020%, Mo: 0 to 0.50%, and the balance: Fe and impurities; (ii) a hot rolling step of hot rolling the steel slab to obtain a hot-rolled steel sheet; (iv) a cold rolling process in which the hot-rolled annealed steel sheet is subjected to a single cold rolling or multiple cold rolling processes with intermediate annealing in between to obtain a cold-rolled steel sheet having a thickness of 0.18 to 0.22 mm; (v) a decarburization annealing process in which the cold-rolled steel sheet is subjected to decarburization annealing to obtain a decarburization annealed steel sheet; (vi) a finish annealing process in which an annealing separator is applied to the decarburization annealed steel sheet and then finish annealed to obtain a finish annealed steel sheet; and (vii) an insulating coating formation process in which an insulating coating is formed on the surface of the finish annealed steel sheet. These processes will be described in detail below. In the following description, unless certain conditions for each process are described, each process can be performed by appropriately applying known conditions.

<Heating process>
In the heating process, a steel billet (slab, etc.) having a predetermined chemical composition is heated prior to the subsequent hot rolling process. The heating temperature is preferably within the range of 1100 to 1450°C. If the heating temperature is below 1100°C, the subsequent hot rolling becomes difficult, adversely affecting production. On the other hand, if the heating temperature exceeds 1450°C, the slab, etc., melts, making hot rolling difficult. A more preferable heating temperature for obtaining a good magnetic flux density is 1300°C or higher and 1400°C or lower. By controlling the temperature within this range, the inhibitor can be uniformly dispersed in the steel.

<Chemical composition of steel billets>
The chemical composition of the steel slab to be subjected to the heating step will be briefly described below. In the following description, unless otherwise specified, the notation "%" represents "mass %".

C: 0.010-0.200%
C (carbon) is an element that has an effect of improving magnetic flux density. However, if the C content of a steel slab exceeds 0.200%, the steel undergoes a phase transformation during secondary recrystallization annealing (i.e., finish annealing), and secondary recrystallization does not proceed sufficiently, making it impossible to obtain good magnetic flux density and low iron loss. Therefore, the C content of the steel slab is set to 0.200% or less. The lower the C content, the better for reducing iron loss. From the viewpoint of reducing iron loss, the C content is preferably 0.150% or less, and more preferably 0.100% or less.
On the other hand, if the C content of the steel bloom is less than 0.010%, the effect of improving the magnetic flux density cannot be obtained. Therefore, the C content of the steel bloom is set to 0.010% or more. The C content is preferably 0.040% or more, and more preferably 0.060% or more.

Si: 3.00-3.80%
Silicon (Si) is an extremely effective element for increasing the electrical resistance (resistivity) of steel and reducing eddy current loss, which constitutes part of iron loss. If the Si content of a steel slab is less than 3.00%, the steel undergoes phase transformation during secondary recrystallization annealing, preventing sufficient secondary recrystallization, and preventing good magnetic flux density and low iron loss from being obtained. Therefore, the Si content of the steel slab is set to 3.00% or more. The Si content of the steel slab is preferably 3.10% or more, and more preferably 3.20% or more.
On the other hand, if the Si content exceeds 3.80%, the steel sheet becomes embrittled and the sheet threadability in the manufacturing process deteriorates significantly. Therefore, the Si content of the steel billet is set to 3.80% or less. The Si content of the steel billet is preferably 3.60% or less, and more preferably 3.50% or less.

Sol-Al: 0.010-0.050%
Acid-soluble aluminum (Sol-Al) is a constituent element of a major inhibitor among compounds called inhibitors that affect secondary recrystallization in grain-oriented electrical steel sheets, and is an essential element in the base steel sheet according to this embodiment from the viewpoint of secondary recrystallization occurrence. If the Sol-Al content of the steel slab is less than 0.010%, AlN, which functions as an inhibitor, is not sufficiently generated, secondary recrystallization becomes insufficient, and iron loss characteristics do not improve. Therefore, the Sol-Al content of the steel slab is set to 0.010% or more. The Sol-Al content is preferably 0.015% or more, and more preferably 0.020%.
On the other hand, if the Sol-Al content exceeds 0.050%, the embrittlement of the steel sheet becomes significant. Therefore, the Sol-Al content of the steel slab is set to 0.050% or less. The Sol-Al content is preferably 0.040% or less, and more preferably 0.030% or less.

Mn: 0.01-0.50%
Mn (manganese) is an important element that forms MnS, one of the main inhibitors. If the Mn content of a steel slab is less than 0.01%, the absolute amount of MnS necessary to cause secondary recrystallization is insufficient. Therefore, the Mn content of a steel slab is set to 0.01% or more. The Mn content is preferably 0.03% or more, and more preferably 0.06% or more.
On the other hand, if the Mn content of the steel slab exceeds 0.50%, the steel undergoes a phase transformation during secondary recrystallization annealing, and secondary recrystallization does not proceed sufficiently, making it difficult to obtain good magnetic flux density and low iron loss. Therefore, the Mn content of the steel slab is set to 0.50% or less. The Mn content is preferably 0.40% or less, and more preferably 0.30% or less.

N: 0.020% or less N (nitrogen) is an element that reacts with the acid-soluble Al to form AlN, which functions as an inhibitor. If the N content of a steel slab exceeds 0.020%, blisters (voids) are formed in the steel sheet during cold rolling, and the strength of the steel sheet increases, resulting in poor sheet threadability during production. Therefore, the N content of the steel slab is set to 0.020% or less. The N content is preferably 0.015% or less, and more preferably 0.010% or less. If AlN is not utilized as an inhibitor, the lower limit of the N content may include 0%. However, since the detection limit of chemical analysis is 0.0001%, the lower limit of the N content in practical steel sheets is essentially 0.0001%. On the other hand, in order to bond with Al to form AlN, which functions as an inhibitor, the N content of the steel slab is preferably 0.001% or more, and more preferably 0.005% or more.

S: 0.005-0.050%
S (sulfur) is an important element that reacts with the above-mentioned Mn to form MnS, an inhibitor. If the S content of the steel slab is less than 0.005%, a sufficient inhibitor effect cannot be obtained. Therefore, the S content of the steel slab is set to 0.005% or more. The S content is preferably 0.010% or more, and more preferably 0.020% or more.
On the other hand, if the S content of the steel slab exceeds 0.050%, it causes hot embrittlement, making hot rolling extremely difficult. Therefore, the S content of the steel slab is set to 0.050% or less. The S content is preferably 0.040% or less, and more preferably 0.030% or less.

The chemical composition of the steel billet used to manufacture the grain-oriented electrical steel sheet according to this embodiment basically contains the above-mentioned elements, with the balance being Fe and impurities. However, for the purpose of improving magnetic properties, the steel billet may further contain Cu, Cr, Sn, Se, Sb, Bi, and Mo in the ranges shown below.
Here, impurities refer to elements that are mixed in from raw materials such as ore or scrap, or the manufacturing environment, and are permissible to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.

Cu: 0-0.50%
Cu (copper) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallization structure and also contributes to improving the adhesion of the glass coating. Therefore, it may be added. To obtain the above effects, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more.
On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, the Cu content of the steel slab is set to 0.50% or less. The Cu content is preferably 0.30% or less, and more preferably 0.10% or less.

Cr: 0-0.50%
Like Sn and Cu described below, Cr (chromium) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure, thereby improving magnetic properties, and also contributes to improving the adhesion of the glass coating. Therefore, Cr may be added. To achieve the above effects, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.
On the other hand, if the Cr content exceeds 0.50%, Cr oxides are formed, resulting in a deterioration in magnetic properties. Therefore, the Cr content is set to 0.50% or less. The Cr content is preferably 0.30% or less, and more preferably 0.10% or less.

Sn: 0-0.50%
Sn (tin) is an element that has a magnetic property improving effect. Therefore, it may be contained. When Sn is contained, the Sn content is preferably 0.01% or more in order to effectively exhibit the magnetic property improving effect. In consideration of achieving both magnetic properties and coating adhesion, the Sn content is preferably 0.02% or more, and more preferably 0.03% or more.
On the other hand, if the Sn content exceeds 0.50%, the glass coating deteriorates significantly, and sufficient tension for magnetic domain refinement is not obtained, resulting in poor core loss characteristics. Therefore, the Sn content is set to 0.50% or less. The Sn content is preferably 0.30% or less, and more preferably 0.10% or less.

Se: 0-0.020%
Se (selenium) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Se is contained, the Se content is preferably 0.001% or more in order to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Se content is more preferably 0.003% or more, and even more preferably 0.006% or more.
On the other hand, if the Se content exceeds 0.020%, the glass coating will deteriorate significantly. Therefore, the Se content is set to 0.020% or less. The Se content is preferably 0.015% or less, and more preferably 0.010% or less.

Sb: 0-0.50%
Sb (antimony) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sb is contained, the Sb content is preferably 0.005% or more in order to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Sb content is preferably 0.005% or more, and more preferably 0.01% or more.
On the other hand, if the Sb content exceeds 0.50%, the glass coating deteriorates significantly. Therefore, the Sb content is set to 0.50% or less. The Sb content is preferably 0.30% or less, and more preferably 0.10% or less.

Bi: 0~0.020%
Bi (bismuth) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. Bi is an optional element. When Bi is contained, in order to effectively exhibit the effect of improving magnetic properties, the Bi content is preferably 0.0005% or more, and more preferably 0.001% or more.
On the other hand, if the Bi content exceeds 0.020%, the sheet threadability during cold rolling may deteriorate. Therefore, the Bi content is set to 0.020% or less. Furthermore, if the purification during finish annealing is insufficient and excessive Bi remains as an impurity in the final product, it may adversely affect the magnetic properties. Therefore, the Bi content is preferably 0.015% or less, more preferably 0.010% or less.

Mo: 0~0.50%
Mo (molybdenum) is an element that has a magnetic property improving effect. Therefore, it may be contained. When Mo is contained, the Mo content is preferably 0.01% or more in order to effectively exhibit the magnetic property improving effect. The Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more.
On the other hand, if the Mo content exceeds 0.50%, the cold rolling property may deteriorate, leading to fracture. Therefore, the Mo content is set to 0.50% or less. The Mo content is preferably 0.30% or less, and more preferably 0.10% or less.

When a steel slab having the above chemical composition is made into grain-oriented electrical steel sheet through the processes detailed below, the contents of all elements other than carbon (C), acid-soluble aluminum (Sol-Al), nitrogen (N), sulfur (S), and Bi (bismuth) are generally maintained at the same levels as in the steel slab. However, the contents of carbon (C), acid-soluble aluminum (Sol-Al), nitrogen (N), sulfur (S), and Bi (bismuth) may change as a result of the processes detailed below.

<Hot rolling process>
The hot rolling process is a process in which the heated steel slab is hot-rolled to produce a hot-rolled steel sheet. The hot-rolling conditions are not particularly limited and may be appropriately set based on the desired properties. The thickness of the hot-rolled steel sheet is preferably in the range of 2.0 mm to 3.0 mm, for example.

<Hot-rolled sheet annealing process>
The hot-rolled steel sheet annealing process is a process in which a hot-rolled steel sheet manufactured through a hot-rolling process is annealed to produce a hot-rolled annealed steel sheet. By performing such annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties.

In the hot-rolled sheet annealing step in the method for manufacturing grain-oriented electrical steel sheet according to this embodiment, the hot-rolled steel sheet manufactured through the hot rolling step is annealed according to a known method to produce a hot-rolled annealed steel sheet. The means for heating the hot-rolled steel sheet during annealing is not particularly limited, and any known heating method can be used. The annealing conditions are also not particularly limited, but for example, the hot-rolled steel sheet can be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes.

<Cold rolling process>
The cold rolling process is a process in which the hot-rolled and annealed steel sheet after hot-rolled sheet annealing is subjected to cold rolling including multiple passes to obtain a cold-rolled steel sheet with a sheet thickness of 0.18 to 0.22 mm. When the hot-rolled sheet annealing as described above is performed, the steel sheet shape is improved, thereby reducing the possibility of the steel sheet breaking in the first rolling pass. In addition, in the cold rolling process, cold rolling may be interrupted between multiple passes, for example, before the final pass, and one or more intermediate annealing steps may be performed.
When intermediate annealing is performed, it is preferable to perform annealing for 5 seconds or more and 180 seconds or less at a temperature of 1000 to 1200° C., and the atmosphere is not particularly limited. In consideration of manufacturing costs, the number of times intermediate annealing is performed is preferably three or less.
A cold rolling method without intermediate annealing is sometimes called a single-stage cold rolling method, and a cold rolling method with one intermediate annealing is sometimes called a double-stage cold rolling method.
Furthermore, before the cold rolling step, the surface of the hot-rolled steel sheet may be subjected to pickling.

In the cold rolling step of this embodiment, the hot-rolled annealed steel sheet may be cold-rolled according to a known method to obtain a cold-rolled steel sheet. For example, the cumulative reduction is preferably set within a range of 80% to 95%. If the cumulative reduction is less than 80%, it is highly likely that Goss nuclei having a high concentration of the {110}<001> orientation in the rolling direction cannot be obtained, which is undesirable. On the other hand, if the cumulative reduction is more than 95%, it is highly likely that secondary recrystallization will become unstable in the subsequent finish annealing step, which is undesirable. By setting the cumulative reduction within the above range, it is possible to obtain Goss nuclei having a high concentration of the {110}<001> orientation in the rolling direction and to suppress instability of secondary recrystallization.
In this embodiment, the cumulative reduction is the cumulative reduction of cold rolling when no intermediate annealing is performed, and is the cumulative reduction in the pass after the final intermediate annealing is performed when one or more intermediate annealings are performed.

Here, the thickness of the cold-rolled steel sheet (thickness after cold rolling) is usually different from the thickness of the grain-oriented electrical steel sheet that is finally manufactured (product thickness including the thickness of the tension-applying insulating coating). The product thickness of grain-oriented electrical steel sheet is as mentioned above.

During the cold rolling process described above, an aging treatment can also be applied to further improve magnetic properties. If the cold rolling process includes multiple passes, it is preferable to apply a thermal effect by holding the steel sheet at a temperature of 100°C or higher for one minute or longer at any intermediate stage before the final pass. This thermal effect makes it possible to form a better primary recrystallization texture in the subsequent decarburization annealing process, and ultimately makes it possible to fully develop a good secondary recrystallization texture in which the {110}<001> orientation is aligned in the rolling direction in the subsequent finish annealing process.

<Decarburization annealing process>
The decarburization annealing step is a step in which the obtained cold-rolled steel sheet is subjected to decarburization annealing to obtain a decarburization annealed steel sheet. In the decarburization annealing step, the cold-rolled steel sheet is subjected to primary recrystallization and C, which adversely affects magnetic properties, is removed from the steel sheet.
The decarburization annealing conditions are not limited, but examples include an oxidation degree (PH ₂ O/PH ₂ ) in the annealing atmosphere (furnace atmosphere) of 0.3 to 0.6, an annealing temperature of 800 to 900° C., and holding for 10 to 600 seconds.

In addition, during the heating process in decarburization annealing, it is preferable to control the average heating rate between 550 and 750°C to 500 to 1000°C/s. Increasing the heating rate in this temperature range increases the Goss orientation, which is advantageous for magnetic properties, leading to improved iron loss. Although a higher heating rate tends to increase the Goss orientation, there is an optimal heating rate depending on the combination with other processes, so even if a certain heating rate is exceeded, significant improvement in magnetic properties may not be expected. The heating rate is more preferably 700 to 1000°C/s, and even more preferably 800 to 1000°C/s.

In addition, in the temperature rising process in decarburization annealing, when the annealing temperature is 800° C. or higher, it is preferable to control the average temperature rising rate from 750 to 800° C. to 1000 to 2000° C./s.
Controlling the heating rate within this temperature range suppresses the excessive formation of _SiO2 oxide film, which is a decarburization inhibitor layer. As a result, decarburization is promoted and good iron loss characteristics are obtained. From the perspective of preventing excessive _SiO2 oxide film formation, the higher the heating rate, the better. An average heating rate of 1000°C/s or higher significantly improves the effect. On the other hand, if the average heating rate exceeds 2000°C/s, not only will the effect of preventing excessive _SiO2 oxide film formation saturate, but there is also a risk of overshoot, where the steel sheet temperature rises excessively even temporarily, resulting in partial saturation of the inhibitors within the steel sheet. This can cause secondary recrystallization instability. Therefore, the average heating rate is set to 2000°C/s or less. The average heating rate is more preferably 1200 to 1800°C/s, and even more preferably 1300 to 1600°C/s.
Furthermore, during the temperature rise process in decarburization annealing, when the annealing temperature is 800°C or higher, it is preferable to control the annealing atmosphere dew point at 550 to 800°C to 0°C _or lower. By controlling the annealing atmosphere dew point at 0°C or lower in this temperature range, the formation of oxide films other than _SiO2 , such as _Fe2SiO4 and FeO, is suppressed. Since Fe-based oxides other than _SiO2 adversely affect magnetic properties, it is preferable to set the annealing atmosphere dew point at 550 to 800°C to 0°C or lower. As long as the annealing atmosphere dew point is 0°C or lower, there are no particular limitations on the atmosphere, but examples include nitrogen or hydrogen, or a mixed gas of nitrogen and hydrogen. The lower the dew point, the greater the decarburization improvement effect, but at -50°C or lower, the decarburization improvement effect may plateau. Therefore, the atmosphere dew point is more preferably -30 to 0°C, and even more preferably -50 to 0°C.

Furthermore, after the decarburization annealing, a second decarburization annealing may be performed at an annealing temperature of 900°C or higher, with the oxidation degree ( _PH2O / _PH2 ) in the annealing atmosphere (furnace atmosphere) controlled to 0.1 or less. By performing the second decarburization annealing, compounds of Fe and Si that inhibit the formation of the primary coating are reduced, and improvement in coating adhesion can be expected. When the second decarburization annealing is performed, the second decarburization annealing may be performed after cooling to room temperature after the first decarburization annealing, or the second decarburization annealing may be performed without cooling after the first decarburization annealing.

<Nitriding process>
Nitriding may be performed between the decarburization annealing step and the finish annealing step described below. In the nitriding step, for example, the decarburization annealed steel sheet is maintained at approximately 700 to 850°C in a nitriding atmosphere (an atmosphere containing hydrogen, nitrogen, and a nitriding gas such as ammonia). Here, it is preferable to perform nitriding on the steel sheet so that the N content of the decarburization annealed steel sheet is 40 ppm or more and 1000 ppm or less. If the N content of the decarburization annealed steel sheet after nitriding is less than 40 ppm, AlN may not precipitate sufficiently in the decarburization annealed steel sheet, and AlN may not function as an inhibitor. Therefore, when AlN is used as an inhibitor, the N content of the decarburization annealed steel sheet is preferably 40 ppm or more. On the other hand, if the N content of the decarburization annealed steel sheet exceeds 1000 ppm, excess AlN remains in the steel sheet even after secondary recrystallization is completed during finish annealing. Such AlN may cause deterioration of iron loss characteristics. For this reason, the N content is preferably 1000 ppm or less.
The nitriding treatment step may be performed between the first decarburization annealing step and the second decarburization annealing step, and then the finish annealing step may be performed. Alternatively, the nitriding treatment step may be performed after the first decarburization annealing step, and the finish annealing may be performed without the second decarburization annealing step. Alternatively, the nitriding treatment step may be performed after the second decarburization annealing step that follows the first decarburization annealing step, and then the finish annealing step may be performed.

<Finish annealing process>
The final annealing process is a process in which a predetermined annealing separator is applied to a decarburized annealed steel sheet obtained in the decarburization annealing process or that has been further subjected to nitriding treatment, and then the steel sheet is subjected to final annealing to obtain a final annealed steel sheet. Final annealing is generally performed for a long period of time while the steel sheet is wound into a coil. Therefore, prior to final annealing, an annealing separator is applied to the decarburized annealed steel sheet and dried in order to prevent seizure between the inside and outside of the coil winding.
The annealing separator to be applied is an annealing separator containing MgO as a main component (e.g., containing 80% or more by weight), in which the total content of any one or more of oxides, hydroxides, sulfates, and carbonates of Ce, Ca, Nd, Sr, Pr, Ba, La, and/or Zr in the annealing separator is 0.5 to 10.0% by mass.
By using an annealing separator containing MgO as the main component (containing 80% or more), a glass coating can be formed on the surface of the base steel sheet. If MgO is not the main component, a primary coating (glass coating) will not be formed. This is because the glass coating is a compound of _Mg2SiO4 or _MgAl2O4 , and there is a deficiency of Mg _{, which} is necessary for the formation reaction.
Furthermore, if the total content ratio of any one or more of oxides, hydroxides, sulfates, or carbonates of Ce, Ca, Nd, Sr, Pr, Ba, La, and/or Zr in the annealing separator is less than 0.5% by mass, the effect of improving coating adhesion cannot be obtained. On the other hand, if it exceeds 10.0% by mass, these elements will remove the S from MnS, lowering the melting temperature of MnS. As a result, the secondary recrystallization onset temperature will decrease, which will be a factor in poor magnetic properties. From the viewpoint of improving coating adhesion, the preferred range is 3.0 to 8.0%.

The average particle size of the oxides, hydroxides, sulfates, and/or carbonates of Ce, Ca, Nd, Sr, Pr, Ba, La, and/or Zr in the annealing separator described above is preferably 20 μm or less. If the average particle size exceeds 20 μm, the surface area of the particles will be small, resulting in insufficient reactivity for forming a glass coating, and there is a concern that the effects of including the oxides, hydroxides, sulfates, and/or carbonates of Ce, Ca, Nd, Sr, Pr, Ba, Zr, and/or Zr will not be achieved.

The annealing separator further contains, as a Ti compound, one or more of oxides, carbides, and nitrides of Ti, and the total content of the Ti compounds in the annealing separator is preferably 0.5 to 10.0% by mass, and the average particle size of the Ti compounds is preferably 20 μm or less.
By using an annealing separator containing a Ti compound having the above average particle size in the above range, the glass film forming reaction is promoted and good film adhesion can be ensured.

The decarburized annealed steel sheet coated with the annealing separator is subjected to finish annealing. In finish annealing, the decarburized annealed steel sheet is heated to an average heating rate of 13 to 30°C/hr in the temperature range of 700 to 900°C during heating, and held at a temperature of 1000 to 1300°C for 40 hours or more. If the temperature exceeds 1300°C during finish annealing, the weight of the steel sheet coil will cause shape defects. On the other hand, if the holding temperature is less than 1000°C, there is insufficient thermal energy required for crystal structure transformation to a thermally stable cubic structure, resulting in insufficient structural control. Furthermore, N, which should be discharged from the system, remains in the steel, resulting in deterioration of magnetic properties. Here, holding at a temperature of 1000 to 1300°C for 40 hours or more does not necessarily mean isothermal holding; even if there is a temperature change, the steel sheet may remain in the temperature range of 1000 to 1300°C for 40 hours or more. Preferably, it is 100 hours or less.
Furthermore, if the average heating rate in the temperature range of 700 to 900°C is less than 13°C/hr, the MgAl ₂ O ₄ production reaction and the Mg ₂ SiO ₄ production reaction compete with each other. As a result of this competition, the amount of Mg ₂ SiO ₄ produced decreases, the Mg ₂ SiO ₄ intercalation structure with the base steel is underdeveloped, and coating adhesion deteriorates. If coating adhesion deteriorates, the steel sheet does not have sufficient coating tension, resulting in deterioration of magnetic properties. If the heating rate is too high, the thermal decomposition of the inhibitor at temperatures above 900°C is inhibited, causing grain refinement, which is a secondary recrystallization defect. If grain refinement occurs, preferential growth of the Goss orientation cannot be achieved, resulting in deterioration of both magnetic flux density and iron loss characteristics. For this reason, the upper limit of the average heating rate is set to 30°C/hr.

<Insulating film formation process>
The insulating coating formation step is a step of forming a tension-imparting insulating coating on one or both sides of the finish-annealed steel sheet after finish annealing. The insulating coating formation step is not particularly limited, and a known insulating coating treatment liquid such as that described below may be used, and the treatment liquid may be applied and dried by a known method. Forming a tension-imparting insulating coating on the steel sheet surface can further improve the magnetic properties of the grain-oriented electrical steel sheet.
The surface of the steel sheet on which the insulating coating is formed may be a surface that has been subjected to any pretreatment, such as a degreasing treatment with an alkali or the like, or an acid pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, or the like, before the treatment liquid is applied, or the surface may be the same as it is after finish annealing without being subjected to these pretreatments.
The insulating coating formed on the surface of the steel sheet is not particularly limited as long as it is suitable for use as an insulating coating for grain-oriented electrical steel sheets, and known insulating coatings can be used. Examples of such insulating coatings include composite insulating coatings that are primarily made of an inorganic material and further contain an organic material. Here, a composite insulating coating is an insulating coating that is primarily made of at least one inorganic material, such as a metal chromate salt, a metal phosphate salt, colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during manufacturing, which has become increasingly necessary in recent years, insulating coatings that use metal phosphate salts, Zr or Ti coupling agents, or their carbonates or ammonium salts as starting materials are preferably used.

Following the above-described insulating coating formation process, flattening annealing may be performed to correct the shape. By performing flattening annealing on the steel sheet, it is possible to further reduce iron loss.

In the manufacturing method of grain-oriented electrical steel sheet according to this embodiment, a magnetic domain refinement process may be performed after the finish annealing process or the insulating coating formation process. The magnetic domain refinement process involves irradiating the surface of the grain-oriented electrical steel sheet with laser light, which has a magnetic domain refinement effect, or forming grooves in the surface. Such a magnetic domain refinement process makes it possible to manufacture grain-oriented electrical steel sheet with even better magnetic properties.

By going through the steps described above, the grain-oriented electrical steel sheet according to this embodiment can be manufactured.

Next, we will explain an example of the present invention.

Example 1
Steel billets with different chemical compositions were prepared for each steel number (A1 to A33) in Table 1.
Next, grain-oriented electrical steel sheets (test numbers B1 to B42, b1 to b23) were manufactured using each steel billet.
Specifically, each steel billet was heated to a temperature in the range of 1350±100°C, and then hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.3±0.3 mm. In this case, the steel billet of test number b11 broke during hot rolling. Therefore, the subsequent steps and tests were not performed on test number b11, and the magnetic property evaluation was NG.
Next, the obtained hot-rolled steel sheets other than b11 were subjected to hot-rolled sheet annealing. Specifically, the hot-rolled steel sheets were annealed at an annealing temperature of 1100±100°C for a holding time of 10 to 200 seconds. In this way, hot-rolled and annealed steel sheets were produced.
Next, the hot-rolled annealed steel sheets were subjected to a cold rolling process to produce cold-rolled steel sheets with a base material thickness of 0.18 to 0.22 mm. Here, for B1 to B29, B37 to B42, and b1 to b23, cold rolling without intermediate annealing was performed (single-stage cold rolling method), and for B30 to B33, the hot-rolled annealed steel sheets were cold-rolled to 1.5 mm, then intermediate annealed at 1100 ± 100 ° C for 30 seconds, and further cold-rolled after the intermediate annealing to obtain the final thickness. For B34 and B35, the hot-rolled annealed steel sheets were cold-rolled to 2.0 mm, then intermediate annealed at 1100 ± 100 ° C for 30 seconds, and then subjected to a second cold rolling to obtain the final thickness. For B36 and B37, the hot-rolled and annealed steel sheets were cold-rolled to 1.0 mm, followed by intermediate annealing at 1200±100°C for 20 seconds, and then subjected to a second cold rolling to obtain the final thickness. For Comparative Examples b4, b7, and b9, the hot-rolled and annealed steel sheets fractured during cold rolling. For this reason, the subsequent processes and tests were not performed on Comparative Examples b4, b7, and b9, and the magnetic property evaluation was NG.

Next, the cold-rolled steel sheet was subjected to a decarburization annealing process to obtain a decarburization annealed steel sheet. The temperature rise rate and annealing atmosphere dew point in the heating process of this decarburization annealing process were controlled to the conditions in Tables 3-1 to 3-6. The soaking process of the decarburization annealing was carried out at a temperature of 820±20°C for 120±20 seconds. The oxidation degree (PH ₂ O/PH ₂ ) was controlled to 0.4±0.1.
Next, the decarburization-annealed steel sheets were subjected to a finish annealing process. Specifically, an annealing separator containing magnesium oxide (MgO) as a main component (weight fraction of 80% or more) was applied to the surface of the decarburization-annealed steel sheets. The annealing separator contained the additives listed in Tables 3-1 to 3-6.
Next, the decarburization annealed steel sheets coated with the annealing separator were subjected to a residence time in the temperature range of 1000 to 1300°C under the conditions shown in Tables 3-1 to 3-6, to prepare finish annealed steel sheets.

Next, the finish-annealed steel sheet was subjected to an insulating coating formation step. Specifically, an insulating coating formation liquid containing colloidal silica and phosphate as the main components was applied to the surface of the finish-annealed steel sheet (more specifically, the surface of the glass coating, which is the primary coating), and then heat-treated (baked).
Grain-oriented electrical steel sheets with each test number were produced using the above process. Their chemical compositions are shown in Tables 2-1 to 2-3. (The chemical compositions of b4, b7, b9, and b11 were not analyzed.)

The magnetic properties of the grain-oriented electrical steel sheets of each test number obtained were evaluated. Specifically, a sample measuring 60 mm in width and 300 mm in length was first taken from each grain-oriented electrical steel sheet of each test number, including the center position of the sheet width of the grain-oriented electrical steel sheet. The length direction of the sample was parallel to the rolling direction. The taken sample was held at 800°C for 2 hours in a nitrogen atmosphere with a dew point of 0°C or less. This removed any strain introduced during sample taking.
Next, using the samples after strain removal, the magnetic flux density (T) was determined by a single sheet magnetic property test (SST test) in accordance with JIS C2556:2011. Specifically, a magnetic field of 800 A/m was applied to the samples to determine the magnetic flux density B ₈ (T). The measurement results are shown in Tables 3-1 to 3-6.
It was determined that secondary recrystallization had occurred in samples with a magnetic flux density of 1.88 T or higher when a magnetic field of 800 A/m was applied (more specifically, a secondary recrystallization structure with highly aligned Goss-oriented grains had been formed). The iron loss of the samples with secondary recrystallization was evaluated using the following method. For samples with a magnetic flux density of less than 1.88 T, W _17/50 was also evaluated as NG.

Furthermore, using the above samples, iron loss W _17/50 (W/kg) was measured in accordance with JIS C2556:2011 when the frequency was 50 Hz and the maximum magnetic flux density was 1.7 T, and was evaluated as follows.
VG (Excellent): Less than 0.85 G (Slightly better): 0.85 to less than 0.90 F (Effective): 0.90 to 0.95
NG (no effect): over 0.95 The measurement results are shown in Tables 3-1 to 3-6.

Furthermore, an evaluation test of coating adhesion was conducted as follows. A sample of 80 mm in the rolling direction and 30 mm in the sheet width direction was taken from the center of the sheet width of each grain-oriented electrical steel sheet of test number. The taken sample was wrapped around a cylinder with a diameter of 10 mm and bent 180°. After that, the bent sample was returned to its original flat state, and the total area of the glass coating that remained without peeling was calculated. The calculated total area of the glass coating was used to calculate the glass coating remaining rate (%) according to the following formula.
Glass coating remaining rate (%) = total area of glass coating remaining without peeling / total area of sample (80 mm x 30 mm) x 100
The adhesion of the glass film was evaluated according to the obtained glass film remaining rate as follows. The evaluation results are shown in Tables 3-1 to 3-6.
VG (Excellent): The remaining coating area rate is 90% or more. G (Fairly excellent): The remaining coating area rate is 85% or more and less than 90%. F (Effective): The remaining coating area rate is 80% or more and less than 85%. NG (Ineffective): The remaining coating area rate is less than 80%. The measurement results are shown in Tables 3-1 to 3-6.

As can be seen from Tables 1 to 3-6, inventive examples B1 to B42 achieved excellent glass coating adhesion, high magnetic flux density, and low iron loss. On the other hand, in comparative examples b1 to b23, grain-oriented electrical steel sheets could not be produced, or the glass coating adhesion and/or iron loss characteristics were inferior.

Among the inventive examples B1 to B42, the chemical compositions of the steel pieces B13 to B16 and B23 were within the preferred ranges, and as a result, the magnetic properties were evaluated as "G".
In addition to the chemical composition of the steel billets B17 to B22, B24 to B29, and B31 to B36 being within the preferred range, they also contained one or more selected elements that contribute to improving magnetic properties. As a result, the magnetic property evaluation was "VG."
B30 is an example in which intermediate annealing was carried out in the cold rolling process, although the selected elements were not contained, and the magnetic properties were evaluated as "VG."

In B13 and B14, the annealing separator contained one or more of oxides, hydroxides, sulfates, and carbonates of Ce, La, Pr, Nd, Ba, Ca, Sr, and Zr, as well as a Ti compound. As a result, the coating adhesion was rated "G".
In the annealing separators B15 to B36, in addition to containing a Ti compound, the total amount of oxides, hydroxides, sulfates, and carbonates of Ce, La, Pr, Nd, Ba, Ca, Sr, and Zr was controlled within a preferred range. As a result, the coating adhesion was rated "VG."

Example 2
Of the steel billets used in Example 1, steel billets with steel numbers A13 to A16 were used to produce grain-oriented electrical steel sheets (C1 to C16). Specifically, each steel billet was heated to a temperature in the range of 1100±100°C, and then hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.3±0.3 mm. The obtained hot-rolled steel sheet was then annealed at an annealing temperature of 1100±100°C for a holding time of 10 to 200 seconds. In this way, a hot-rolled and annealed steel sheet was produced.
Next, the hot-rolled annealed steel sheets were subjected to multiple passes of cold rolling without intermediate annealing to produce cold-rolled steel sheets with a base sheet thickness of 0.19 mm or 0.20 mm.
Next, the cold-rolled steel sheet was subjected to a decarburization annealing process to obtain a decarburization annealed steel sheet. The temperature rise rate and annealing atmosphere in the heating step of this decarburization annealing process were performed under the conditions shown in Tables 4-1 to 4-3. The soaking step of the decarburization annealing was performed at a temperature of 830±20°C for 140±20 seconds. The oxidation degree (PH ₂ O/PH ₂ ) was controlled to 0.5±0.1.
Next, for C5 to C16, the decarburization-annealed steel sheets were subjected to nitriding treatment. For C9 to C12, the first decarburization annealing step was followed by a second decarburization annealing step without cooling, followed by nitriding treatment. For C13 to C16, the steel sheets were cooled to room temperature after the first decarburization annealing step, then subjected to nitriding treatment, followed by a second decarburization annealing step. For the nitriding treatment, the steel sheets after decarburization annealing were held in an ammonia gas atmosphere at a temperature of 700 to 800°C for 30 seconds. The N content in the base steel sheet after the nitriding treatment was 200 to 400 ppm. The N content was determined by cutting the steel sheets into chips and using the well-known inert gas fusion-thermal conductivity method.

Next, the decarburization-annealed steel sheets after decarburization annealing or nitriding treatment were subjected to finish annealing. Specifically, an annealing separator containing magnesium oxide (MgO) as a main component (weight fraction of 80% or more) was applied to the surface of the decarburization-annealed steel sheets. The annealing separator contained the additives listed in Tables 4-1 to 4-3.
Next, the decarburization annealed steel sheets coated with the annealing separator were subjected to a residence time in the temperature range of 1000 to 1300°C under the conditions shown in Tables 4-1 to 4-3, to prepare finish annealed steel sheets.
Next, the finish-annealed steel sheet was subjected to an insulating coating formation step. Specifically, an insulating coating formation liquid containing colloidal silica and phosphate as the main components was applied to the surface of the finish-annealed steel sheet (more specifically, the surface of the glass coating, which is the primary coating), and then heat-treated (baked).
Grain-oriented electrical steel sheets of each test number were produced by the above steps.
The magnetic properties and coating adhesion of the obtained samples were evaluated in the same manner as in Example 1.
The results are shown in Tables 4-1 to 4-3.

As can be seen from Tables 1, 2-1 to 2-3, and 4-1 to 4-3, all grain-oriented electrical steel sheets had excellent magnetic properties and coating adhesion.

1. Base steel plate (base steel)
2 Glass coating 3 Tension-imparting insulating coating 4 Sulfide 21 End of glass coating (base steel sheet side)
22 End of glass coating (tension-applying insulating coating side)
B Boundary area

Claims (21)

A base steel plate;
a glass coating formed on the surface of the base steel sheet;
a tension- applying insulating coating formed on the surface of the glass coating,
The base steel plate has a chemical composition, in mass%,
C: 0.005% or less,
Si: 3.00-3.80%,
Mn: 0.01 to 0.50%,
N: 0.020% or less,
Sol-Al: 0.020% or less,
S: 0.020% or less,
The total of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr: 0.0100% or less,
Cu: 0 to 0.50%,
Cr: 0 to 0.50%,
Sn: 0 to 0.50%,
Se: 0 to 0.020%,
Sb: 0 to 0.50%,
Bi: 0 to 0.020%,
Mo: 0 to 0.50%,
The balance is Fe and impurities.
The thickness of the base steel plate is 0.18 to 0.22 mm,
Cubic-type sulfides are contained in the glass coating and in the boundary region between the glass coating and the base steel sheet at 0.001 to 10.00 particles/ ^μm2 ,
A grain-oriented electrical steel sheet in which the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the grain-oriented electrical steel sheet is 1.5 to 10.0 times the total content of Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr in the base steel sheet. The chemical composition is
Sn: 0.01 to 0.50%;
The grain-oriented electrical steel sheet according to claim 1. The chemical composition is
Cr: 0.01 to 0.50%;
The grain-oriented electrical steel sheet according to claim 1 or 2. The chemical composition is
Cu: Contains 0.01 to 0.50%;
The grain-oriented electrical steel sheet according to any one of claims 1 to 3. The chemical composition is
Se: 0.001 to 0.020%;
The grain-oriented electrical steel sheet according to any one of claims 1 to 4. The chemical composition is
Sb: 0.005 to 0.50%;
The grain-oriented electrical steel sheet according to any one of claims 1 to 5. The chemical composition is
Bi: 0.0001 to 0.020%;
The grain-oriented electrical steel sheet according to any one of claims 1 to 6. A method for producing the grain-oriented electrical steel sheet according to claim 1,
a heating step of heating a steel slab having a chemical composition, in mass%, of C: 0.010 to 0.200%, Si: 3.00 to 3.80%, Sol-Al: 0.010 to 0.050%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.050%, Cu: 0 to 0.50%, Cr: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, Bi: 0 to 0.020%, Mo: 0 to 0.50%, and the balance: Fe and impurities;
a hot rolling step of hot rolling the steel slab to obtain a hot-rolled steel plate;
a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet to obtain a hot-rolled annealed steel sheet;
A cold rolling process in which the hot-rolled annealed steel sheet is subjected to cold rolling including a plurality of passes to obtain a cold-rolled steel sheet having a thickness of 0.18 to 0.22 mm;
a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization annealed steel sheet;
a finish annealing step of applying an annealing separator to the decarburized annealed steel sheet and then performing finish annealing to obtain a finish annealed steel sheet;
and an insulating coating forming step of forming an insulating coating on the surface of the finish-annealed steel sheet,
The annealing separator contains 90 mass% or more of MgO and one or more oxides, hydroxides, sulfates, and carbonates of one or more elements selected from Ce, Ca, Nd, Sr, Pr, Ba, La, and Zr,
the total content of the oxide, the hydroxide, the sulfate, and the carbonate in the annealing separator is 0.5 to 10.0 mass%,
In the finish annealing step,
The temperature is increased in the range of 700 to 900°C at an average heating rate of 13°C/hr to 30°C/hr, and the temperature is maintained in the range of 1000 to 1300°C for 40 to 100 hours.
Manufacturing method for grain-oriented electrical steel sheets. The method for manufacturing grain-oriented electrical steel sheet according to claim 8, wherein the average particle size of the oxides, hydroxides, sulfates, and carbonates is 20 μm or less. The annealing separator contains, as a Ti compound, one or more of oxides, carbides, and nitrides of Ti, the total content of the Ti compounds in the annealing separator in mass% is 0.5 to 10.0%, and the average particle size of the Ti compounds is 20 μm or less.
The method for producing a grain-oriented electrical steel sheet according to claim 8 or 9. In the temperature rising process of the decarburization annealing, the average temperature rising rate in the temperature range of 550 to 750 ° C. is controlled to 500 to 1000 ° C./s.
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 10. In the temperature rising process of the decarburization annealing, the average temperature rising rate in the temperature range of 750 to 800 ° C. is controlled to 1000 to 2000 ° C./s.
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 11. During the temperature rise process of the decarburization annealing, the dew point of the annealing atmosphere in the temperature range of 550 to 800 ° C. is controlled to 0 ° C. or less.
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 12. A nitriding treatment is included between the decarburization annealing step and the finish annealing step.
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 13. In the cold rolling step, intermediate annealing is performed between the plurality of passes, and the cumulative reduction rate of the passes after the intermediate annealing is set to 80 to 95%.
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 14. The chemical composition of the steel billet is
Sn: 0.01 to 0.50%;
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 15. The chemical composition of the steel billet is
Cr: 0.01 to 0.50%;
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 16. The chemical composition of the steel billet is
Cu: Contains 0.01 to 0.50%;
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 17. The chemical composition of the steel billet is
Se: 0.001 to 0.020%;
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 18. The chemical composition of the steel billet is
Sb: 0.005 to 0.50%;
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 19. The chemical composition of the steel billet is
Bi: 0.0005 to 0.020%
The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 20.