Manufacturing method of grain-oriented electrical steel sheet

Abstract

This method for manufacturing a grain-oriented electromagnetic steel sheet includes a tension-applying insulating film forming step made up of an insulating film chemical solution application step for applying an insulating film chemical solution onto a surface of a surface-treated steel sheet the surface of which has been pickled, and a baking step for forming a tension-applying insulating film on the surface of the surface-treated steel sheet by performing a heat treatment on the surface-treated steel sheet on which the insulating film chemical solution has been applied. The heat treatment of the baking step includes a temperature raising stage and an isothermal stage. In the temperature raising stage, the steel sheet average temperature raising speed within a steel sheet temperature range of 100°C to 600°C is set to 10°C / s to 400°C / s in an environment in which the oxygen concentration is 1% to 21% by volume and the dew point is 0°C to 30°C. In the isothermal stage, the holding time of a constant steel sheet temperature in the range of 800°C to 1000°C is 5 seconds to 200 seconds in an isothermal environment of a constant value in a range in which the oxygen concentration is 1% to 15% and the environment dew point is -20°C to +40°C.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet. This application claims priority based on Japanese Patent Application No. 2023-013747, filed on February 1, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets contain silicon (Si) in an amount of 0.5 to 7 mass%, and utilize a phenomenon called secondary recrystallization to change the crystal orientation to {110} <001> It is a steel sheet that has been assembled in a Goss orientation, and is used as a soft magnetic material mainly in the iron cores of transformers, etc. The properties of grain-oriented electrical steel have a significant impact on the performance of transformers, so extensive research has been conducted on grain-oriented electrical steel to achieve good excitation characteristics and low iron loss.

[0003] A typical method for manufacturing grain-oriented electrical steel sheets is as follows. First, a steel slab having a predetermined chemical composition is heated and hot-rolled to produce a hot-rolled steel sheet. The obtained hot-rolled steel sheet is subjected to hot-rolled sheet annealing as necessary, and then the hot-rolled steel sheet is pickled. The pickled hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. The obtained cold-rolled steel sheet is subjected to decarburization annealing to induce primary recrystallization. Then, an aqueous slurry containing an annealing separator mainly composed of MgO is applied to the surface of the cold-rolled steel sheet after decarburization annealing, and the steel sheet is dried. The steel sheet is then wound into a coil and subjected to finish annealing to induce secondary recrystallization. During finish annealing, simultaneously with the induction of secondary recrystallization in the steel sheet, MgO in the annealing separator reacts with SiO2 in the internal oxide layer formed on the surface of the cold-rolled steel sheet during decarburization annealing, and a glass coating mainly composed of forsterite (Mg2SiO4) (hereinafter also referred to as a "primary coating") is formed on the surface of the base steel sheet. After finish annealing (after the formation of the primary coating), a chemical solution containing, for example, silica and phosphate as its main components is applied to the upper layer of the primary coating and baked to form a tension-applying insulating coating (hereinafter also referred to as the "secondary coating").

[0004] The primary coating not only functions as an insulating coating but also improves the adhesion of the secondary coating formed on top of the primary coating. The tension of both the primary and secondary coatings reduces iron loss. However, the primary coating is a non-magnetic phase, which is undesirable from the perspective of magnetic properties. Furthermore, the interface between the base steel sheet and the primary coating has an intricate structure in which the roots of the primary coating are embedded in the base steel sheet, which can sometimes increase iron loss by inhibiting domain wall motion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 8-269560 [Patent Document 2] International Publication No. 2019 / 182149 [Patent Document 3] International Publication No. 2020 / 149345 Summary of the Invention [Problem to be solved by the invention]

[0006] Given the above background, many inventions have been made relating to grain-oriented electrical steel sheets without a primary coating. For example, Patent Document 1 discloses a manufacturing method in which chlorides are added to an annealing separator in an annealing separator application step prior to the secondary recrystallization annealing step, thereby suppressing the formation of a primary coating and promoting its peeling. This manufacturing method is of great industrial value due to its simplicity. However, since no primary coating is formed, the adhesion of the secondary coating is still insufficient. Therefore, for example, in Patent Document 2, unevenness is formed on the surface of the base steel sheet after secondary recrystallization annealing and before the secondary coating is applied and baked. This manufacturing method ensures coating adhesion by the anchor effect that occurs at the interface between the base steel sheet and the secondary coating. However, these unevenness at the interface can hinder domain wall movement when the grain-oriented electrical steel sheet is magnetized, and can be a factor that prevents low iron loss. In Patent Document 3, the base steel sheet is subjected to intermediate annealing prior to application of the secondary coating chemicals. This manufacturing method forms an oxide film on the surface of the base steel sheet, which is used as a buffer layer when adhering the secondary coating, and can achieve both high magnetic properties and high coating adhesion. However, the requirement of an intermediate annealing step in manufacturing poses another problem: a high manufacturing load.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a method for producing grain-oriented electrical steel sheet that can produce grain-oriented electrical steel sheet having high coating adhesion (secondary coating adhesion) without impairing magnetic properties, without performing intermediate annealing. [Means for solving the problem]

[0008] In order to solve the above problems and achieve the above object, the present invention employs the following aspects. (1) A method for producing a grain-oriented electrical steel sheet according to one aspect of the present invention includes: A method for manufacturing a grain-oriented electrical steel sheet having a base steel sheet, an oxide layer containing an Fe-Al-PO compound formed on a surface of the base steel sheet, and a tension-applying insulating coating formed on the surface of the oxide layer, comprising: The chemical composition, in mass%, is: C: 0.020%~0.150%, Si: 3.00% to 4.00% Mn: 0.01% to 0.50%, S: 0.0010%~0.0400%, Acid soluble Al: 0.010%~0.050%, N: 0.002%~0.020%, Bi: 0.0000% to 0.0200%, P: 0.000%~0.100%, Sn: 0.00%~0.50%, Cu: 0.00%~0.50%, Cr: 0.00%~0.50%, Sb: 0.00%~0.20%, Mo: 0.00% to 0.10%, Nb: 0.0000%~0.0200%, B: 0.0000%~0.0200%, Te: 0.0000%~0.0200%, Ni: 0.00%~0.20%, Se: 0.0000%~0.0200%, a hot rolling step of heating and hot rolling the slab, the balance of which is Fe and impurities, to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet to obtain a hot-rolled sheet annealed sheet, and then immersing the hot-rolled sheet annealed sheet in a pickling solution; A cold rolling process in which the hot-rolled annealed sheet is subjected to cold rolling to obtain a cold-rolled steel sheet; a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization annealed sheet; a separator application step of applying an annealing separator containing MgO, Al2O3, and chlorides to the surface of the decarburized annealed steel sheet; a finish annealing step of subjecting the decarburized annealed sheet coated with the annealing separator to finish annealing to obtain a finish annealed sheet; a surface treatment step of pickling the surface of the finish annealed steel sheet to obtain a surface-treated steel sheet; an insulating coating solution application step of applying an insulating coating solution containing 80 mass % or more of aluminum phosphate and silica in total to the surface of the surface-treated steel sheet; and a heat treatment of the surface-treated steel sheet to which the insulating coating solution has been applied, thereby forming a film on the surface of the surface-treated steel sheet. The aforementioned a tensioned insulating coating forming step including a baking step for forming a tensioned insulating coating; and The heat treatment in the baking step includes a temperature rising process and a soaking process, In the temperature-raising process, the average temperature-raising rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C is set to 10°C / second to 400°C / second in an atmosphere having an oxygen concentration of 1% by volume to 21% by volume and a dew point of 0°C to 30°C, In the soaking process, the steel sheet is held at a constant temperature in the range of 800°C to 1000°C for 5 to 200 seconds in a soaking atmosphere with a hydrogen concentration of 1 to 15% by volume and a constant atmospheric dew point in the range of -20 to +40°C. (2) In the method for producing a grain-oriented electrical steel sheet described in (1) above, In the annealing separator, the MgO content may be 0.0 mass % or more and 79.5 mass % or less, the Al2O3 content may be 20.0 mass % or more and 99.5 mass % or less, and the balance may be the chloride. (3) In the method for producing a grain-oriented electrical steel sheet according to (1) or (2), In the surface treatment step, the finish annealed sheet may be immersed for 3 to 60 seconds in a treatment solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, having a total acid concentration of 1% by volume to 20% by volume, and having a solution temperature of 50°C to 90°C. (4) In the method for producing a grain-oriented electrical steel sheet according to any one of (1) to (3), The slab has the following chemical composition in mass%: Bi: more than 0.0000%, less than 0.0200%, P: more than 0.000%, less than 0.100%, Sn: more than 0.00%, less than 0.50%, Cu: more than 0.00%, less than 0.50%, Cr: more than 0.00%, less than 0.50%, Sb: more than 0.00%, less than 0.20%, Mo: more than 0.00%, less than 0.10%, Nb: more than 0.0000%, less than 0.0200%, B: More than 0.0000%, less than 0.0200%, Te: more than 0.0000%, less than 0.0200%, Ni: more than 0.00% and 0.20% or less, and Se: more than 0.0000%, less than 0.0200%, It may contain at least one selected from the group consisting of: [Effects of the Invention]

[0009] According to the above-described aspects of the present invention, grain-oriented electrical steel sheets having high coating adhesion (secondary coating adhesion) without impairing magnetic properties can be produced without intermediate annealing. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional schematic view showing a grain-oriented electrical steel sheet obtained by a method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention. [Figure 2] 3 is a flowchart showing a method for manufacturing a grain-oriented electrical steel sheet according to the embodiment. [Figure 3] 1 is a diagram illustrating the baking step in the manufacturing method, in which the horizontal axis indicates time and the vertical axis indicates the base steel sheet temperature. DETAILED DESCRIPTION OF THE INVENTION

[0011] A method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention is described below. However, the present invention is not limited to the configurations and processes disclosed in this embodiment, and various modifications are possible without departing from the spirit of the present invention. Furthermore, the numerical ranges described below include the lower and upper limits. On the other hand, values ​​indicated as "greater than" or "less than" do not include the numerical range. Furthermore, % regarding chemical components means % by mass unless otherwise specified.

[0012] Fig. 1 is a cross-sectional schematic diagram showing a grain-oriented electrical steel sheet (grain-oriented electrical steel sheet according to the present embodiment) obtained by the manufacturing method of grain-oriented electrical steel sheet according to the present embodiment. As shown in Fig. 1, the grain-oriented electrical steel sheet 1 according to the present embodiment, when viewed on a cross section whose cutting direction is parallel to the sheet thickness direction, has a base steel sheet 2 and a secondary coating 3 which is an insulating coating disposed on the surface of the base steel sheet 2. At the interface between the base steel sheet 2 and the secondary coating 3, only an oxide layer 4 containing an Fe-Al-PO compound is formed, and a glass coating (hereinafter also referred to as a "primary coating") is substantially not present. The average thickness of the base steel plate 2 can be, for example, 0.17 mm to 0.29 mm, and the average film thickness of the secondary coating 3 can be, for example, 1.0 μm to 6.0 μm.

[0013] To improve the iron loss characteristics, it is effective to smooth the surface of the base steel sheet 2 to facilitate domain wall motion. It is also effective to bring the base steel sheet 2 and the secondary coating 3 into close contact with each other, thereby applying tension to the base steel sheet 2 and ensuring electrical insulation between the overlapping grain-oriented electrical steel sheets 1. In the grain-oriented electrical steel sheet 1 according to this embodiment, the secondary coating 3 is disposed in contact with the base steel sheet 2 (no primary coating is present), thereby ensuring the surface smoothness of the base steel sheet 2. Furthermore, as will be explained in the manufacturing method described later, by controlling the atmospheric conditions, the average heating rate of the steel sheet, the soaking temperature holding time, and the like in the baking step of the secondary coating 3, Fe—Al—PO compounds are formed at the interface between the base steel sheet 2 and the secondary coating 3, thereby ensuring adhesion. Therefore, the grain-oriented electrical steel sheet 1 according to this embodiment has excellent iron loss characteristics and coating adhesion.

[0014] In the Fe-Al-PO compound, Fe originates from the steel substrate components of the base steel sheet 2, while Al and P originate from the insulating coating formation liquid (insulating coating chemical solution). Fe ions diffuse from the steel substrate side to the coating side, while Al and P ions diffuse and concentrate from the coating side to the steel substrate side. Chemical bonds are formed when Fe ions meet with Al or P ions, resulting in the formation of Fe-Al-PO compounds. In other words, as a result of chemical bonding between the ions in the coating and the steel substrate (resulting in the coating adhering to the steel substrate), Fe-Al-PO compounds are observed at the interface between the coating and the steel substrate.

[0015] Next, a method for producing a grain-oriented electrical steel sheet according to this embodiment will be described with reference to Figures 2 and 3. The following production method is an example, and appropriate modifications may be made as long as they do not affect the formation of Fe-Al-PO compounds. Figure 2 is a flowchart showing the method for producing a grain-oriented electrical steel sheet according to this embodiment. Figure 3 is a diagram explaining the baking step in this production method, with the horizontal axis representing time and the vertical axis representing the base steel sheet temperature.

[0016] The method for producing a grain-oriented electrical steel sheet according to this embodiment includes a hot rolling process in which a slab (steel billet) having a predetermined chemical composition is heated and hot rolled to obtain a hot rolled steel sheet, a hot rolled annealing process in which the hot rolled steel sheet is annealed to obtain a hot rolled annealed sheet, and then the hot rolled annealed sheet is immersed in a pickling solution for pickling, a cold rolling process in which the hot rolled annealed sheet is cold rolled to obtain a cold rolled steel sheet, a decarburization annealing process in which the cold rolled steel sheet is decarburized to obtain a decarburization annealed sheet, and an annealing separator is applied to the surface of the decarburization annealed sheet. a finish annealing process in which the decarburized annealed sheet to which the annealing separator has been applied is subjected to finish annealing to obtain a finish annealed sheet; a surface treatment process in which the surface of the finish annealed sheet is pickled to obtain a surface-treated steel sheet; an insulating coating solution application process in which an insulating coating forming solution is applied, a temperature rise process, and a soaking process performed after the temperature rise process, and a tensioned insulating coating formation process in which a tensioned insulating coating containing aluminum phosphate and silica is formed on the surface of the surface-treated steel sheet.

[0017] In the temperature-raising process, the average temperature-raising rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C is set to 10°C / sec to 400°C / sec in an atmosphere with an oxygen concentration of 1% by volume to 21% by volume and a dew point of 0°C to 30°C. Furthermore, in the soaking process, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C is set to 5 seconds to 200 seconds in a soaking atmosphere with a hydrogen concentration of 1 to 15% by volume and a constant atmospheric dew point in the range of -20 to +40°C.

[0018] The details of each of the above steps are explained below. In the following explanation, when the conditions for each step are not described, known conditions may be appropriately applied. [Hot rolling process] In the hot rolling process, a steel billet (for example, a steel ingot such as a slab) having a predetermined chemical composition is hot rolled. For example, the slab (steel billet) to be subjected to the hot rolling process has a chemical composition, in mass %, of: C: 0.020%~0.150%, Si: 3.00% to 4.00% Mn: 0.01% to 0.50%, S: 0.0010%~0.0400%, Acid soluble Al: 0.010%~0.050%, N: 0.002%~0.020%, Bi: 0.0000% to 0.0200%, P: 0.000%~0.100%, Sn: 0.00%~0.50%, Cu: 0.00%~0.50%, Cr: 0.00%~0.50%, Sb: 0.00%~0.20%, Mo: 0.00% to 0.10%, Nb: 0.0000%~0.0200%, B: 0.0000%~0.0200%, Te: 0.0000%~0.0200%, Ni: 0.00%~0.20%, Se: 0.0000% to 0.0200% and the remainder may be Fe and impurities.

[0019] The chemical composition of the above-mentioned slab (steel billet) is, in mass %, Bi: more than 0.0000%, less than 0.0200%, P: more than 0.000%, less than 0.100%, Sn: more than 0.00%, less than 0.50%, Cu: more than 0.00%, less than 0.50%, Cr: more than 0.00%, less than 0.50%, Sb: more than 0.00%, less than 0.20%, Mo: more than 0.00%, less than 0.10%, Nb: more than 0.0000%, less than 0.0200%, B: More than 0.0000%, less than 0.0200%, Te: more than 0.0000%, less than 0.0200%, Ni: more than 0.00%, less than 0.20%, Se: more than 0.0000%, less than 0.0200%, It may contain at least one selected from the group consisting of:

[0020] C: 0.020% to 0.150% Carbon (C) is a basic element in steel slabs. It is included to enhance the density of Goss orientation during secondary recrystallization. The C content required to improve magnetic properties is 0.020% or more, preferably 0.040% or more, and more preferably 0.050% or more, for the slab. However, excessive C remaining in the final product can cause deterioration in iron loss. Therefore, decarburization treatment is required in a decarburization annealing process. If the C content of the slab exceeds 0.150%, decarburization becomes difficult. Therefore, the C content of the slab is 0.150% or less, preferably 0.120% or less, and more preferably 0.100% or less.

[0021] Si: 3.00% to 4.00% Silicon (Si) is a basic element for steel slabs. If the Si content is less than 3.00%, eddy current loss cannot be sufficiently reduced, and good magnetic properties cannot be obtained. 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 4.00%, the steel sheet becomes embrittled and threading properties during production deteriorate significantly. Therefore, the Si content is set to 4.00% or less. The Si content is preferably 3.80% or less, and more preferably 3.60% or less.

[0022] Mn: 0.01% to 0.50% Manganese (Mn) is a basic element for steel slabs. If the Mn content is less than 0.01%, MnS (or MnSe when Se is used as part of S) that functions as an inhibitor is difficult to form, secondary recrystallization does not proceed sufficiently, and good magnetic properties cannot be 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%, the steel undergoes phase transformation during finish annealing, secondary recrystallization does not proceed sufficiently, and good magnetic properties cannot be obtained. Therefore, the Mn content is set to 0.50% or less. The Mn content is preferably 0.30% or less, and more preferably 0.20% or less.

[0023] S: 0.0010% to 0.0400% Se: 0.0000 to 0.0200% S (sulfur) is a basic element for steel slabs. S forms MnS, an inhibitor. The S content is 0.0010% or more, preferably 0.0100% or more, and more preferably 0.0150% or more, for the slab. On the other hand, if the S content exceeds 0.0400%, it can cause hot embrittlement, making hot rolling difficult. The S content is 0.0400% or less, preferably 0.0350% or less, and more preferably 0.0300% or less, for the slab. If excessive S remains in the final product, it can also cause magnetic degradation. Therefore, S must also be removed (purified) from the base steel sheet during finish annealing. Since Se (selenium) is also an element that forms MnSe, Se may be used as part of S (Se content may exceed 0.0000%). Excessive Se may destabilize secondary recrystallization, potentially causing magnetic deterioration. Therefore, the Se content must be 0.0000% or more and 0.0200% or less. The Se content is preferably 0.0000% or more and 0.0150% or less, more preferably 0.0000% or more and 0.0100% or less.

[0024] Acid soluble Al: 0.010%~0.050% Acid-soluble aluminum (sol. Al) is a basic element for steel slabs. Acid-soluble Al forms the inhibitor AlN and is an element necessary for improving magnetic properties. The acid-soluble Al content is 0.010% or more, preferably 0.015% or more, and more preferably 0.020% or more, based on the slab. On the other hand, if the slab contains excessive acid-soluble Al, embrittlement may become significant. The acid-soluble Al content is 0.050% or less, preferably 0.040% or less, and more preferably 0.030% or less, based on the slab. Like N, acid-soluble Al needs to be removed (purified) from the base steel sheet during final annealing.

[0025] N: 0.002% to 0.020% N (nitrogen) is a fundamental element for steel slabs. N is an element necessary for forming the inhibitor AlN and increasing the concentration of Goss orientation during secondary recrystallization. The N content necessary for inhibitor formation is 0.002% or more, preferably 0.004% or more, and more preferably 0.006% or more, for the slab. On the other hand, if the N content of the slab exceeds 0.020%, blisters (voids) may occur in the steel sheet during cold rolling, and the strength of the steel sheet may increase, resulting in poor sheet threadability during production. The N content of the slab is 0.020% or less, preferably 0.015% or less, and more preferably 0.010% or less. Like C, excessive N remaining in the final product can cause magnetic degradation. Therefore, N must be removed (purified) during final annealing.

[0026] P: 0.000% to 0.100% P (phosphorus) is an optional element for steel slabs. If the P content exceeds 0.100%, the workability of the steel sheet may be significantly reduced. Therefore, the P content should be 0.100% or less. The P content is preferably 0.070% or less, and more preferably 0.030% or less. On the other hand, the lower limit of the P content is not particularly limited and may be 0.000%. However, since P has the effect of improving the texture and the magnetic properties of the steel sheet, the P content may be more than 0.000% or may be 0.005% or more.

[0027] Bi: 0.0000% to 0.0200% Bi (bismuth) is an optional element for steel slabs. If the Bi content exceeds 0.0200%, threadability during cold rolling may deteriorate. Furthermore, if purification during finish annealing is insufficient and excessive Bi remains, it may adversely affect magnetic properties. Therefore, the Bi content should be 0.0200% or less. The Bi content is preferably 0.0150% or less, and more preferably 0.0100% or less. On the other hand, the lower limit of the Bi content is not particularly limited and may be 0.0000%. However, because Bi has the effect of improving magnetic properties, the Bi content may be more than 0.0000% or may be 0.0005% or more.

[0028] Sn: 0.00% to 0.50% Sn (tin) is an optional element for steel slabs. If the Sn content exceeds 0.50%, secondary recrystallization becomes unstable, which may adversely affect magnetic properties. Therefore, the Sn content should be 0.50% or less. The Sn content is preferably 0.40% or less, and more preferably 0.30% or less. On the other hand, the lower limit of the Sn content is not particularly limited and may be 0.00%. However, since Sn has the effect of increasing the concentration of Goss orientation and improving magnetic properties, the Sn content may be more than 0.00%, may be 0.01% or more, or may even be 0.03% or more.

[0029] Cu: 0.00% to 0.50% Copper (Cu) is an optional element for steel slabs. If the Cu content exceeds 0.50%, the steel sheet may become embrittled during hot rolling. Therefore, the Cu content should be 0.50% or less. The Cu content is preferably 0.40% or less, more preferably 0.30% or less. On the other hand, the lower limit of the Cu content is not particularly limited and may be 0.00%. However, since Cu has the effect of increasing the concentration of Goss orientation and improving magnetic properties, the Cu content may be more than 0.00%, may be 0.01% or more, or may even be 0.03% or more.

[0030] Cr: 0.00% to 0.50% Cr (chromium) is an optional element for steel slabs. If the Cr content exceeds 0.50%, Cr oxides may be formed, which may adversely affect magnetic properties. Therefore, the Cr content should be 0.50% or less. The Cr content is preferably 0.40% or less, and more preferably 0.30% or less. On the other hand, the lower limit of the Cr content is not particularly limited and may be 0.00%. However, since Cr has the effect of increasing the concentration of Goss orientation and improving magnetic properties, the Cr content may be more than 0.00%, may be 0.01% or more, or may even be 0.03% or more.

[0031] Sb: 0.00% to 0.20% Sb (antimony) is an optional element for steel slabs. If the Sb content exceeds 0.20%, it may adversely affect magnetic properties. Therefore, the Sb content should be 0.20% or less. The Sb content is preferably 0.15% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Sb content is not particularly limited and may be 0.00%. However, since Sb functions as an inhibitor and has the effect of stabilizing secondary recrystallization, the Sb content may be more than 0.00% or may be 0.01% or more.

[0032] Mo: 0.00% to 0.10% Mo (molybdenum) is an optional element for steel slabs. If the Mo content exceeds 0.10%, problems may occur with the rollability of the steel sheet. Therefore, the Mo content should be 0.10% or less. The Mo content is preferably 0.05% or less, and more preferably 0.03% or less. On the other hand, the lower limit of the Mo content is not particularly limited and may be 0.00%. However, since Mo has the effect of increasing the concentration of Goss orientation and improving magnetic properties, the Mo content may be more than 0.00% or may be 0.01% or more.

[0033] Nb: 0.0000% to 0.0200% Nb (niobium) is an optional element for steel slabs. If the Nb content exceeds 0.0200%, secondary recrystallization may become unstable. Therefore, the Nb content may be 0.0200% or less. The Nb content is preferably 0.0100% or less, and more preferably 0.0050% or less. On the other hand, the lower limit of the Nb content is not particularly limited and may be 0.0000%. However, since Nb has the effect of stabilizing secondary recrystallization, the Nb content may be more than 0.0000% or may be 0.0005% or more.

[0034] B: 0.0000% to 0.0200% B (boron) is an optional element for steel slabs. If the B content exceeds 0.0200%, secondary recrystallization may become unstable. Therefore, the B content should be 0.0200% or less. The B content is preferably 0.0100% or less, and more preferably 0.0050% or less. On the other hand, the lower limit of the B content is not particularly limited and may be 0.0000%. However, since B has the effect of stabilizing secondary recrystallization, the B content may be more than 0.0000% or may be 0.0005% or more.

[0035] Te: 0.0000% to 0.0200% Te (tellurium) is an optional element for steel slabs. If the Te content exceeds 0.0200%, fracture may occur during hot rolling or cold rolling. Therefore, the Te content should be 0.0200% or less. The Te content is preferably 0.0150% or less, and more preferably 0.0100% or less. On the other hand, the lower limit of the Te content is not particularly limited and may be 0.0000%. However, since Te has the effect of stabilizing secondary recrystallization, the Te content may be more than 0.0000% or may be 0.0005% or more.

[0036] Ni: 0.00% to 0.20% Ni (nickel) is an optional element for steel slabs. Ni influences the crystal orientation rotation that occurs during cold rolling and is an effective element for obtaining a texture favorable for secondary recrystallization. Ni is also an effective element for increasing resistivity and reducing iron loss. Therefore, Ni may be added. When Ni is added, in order to obtain these effects, the Ni content is preferably more than 0.00%, and more preferably 0.01% or more. On the other hand, if the Ni content exceeds 0.20%, secondary recrystallization may become unstable. Therefore, if Ni is contained, the Ni content is set to 0.20% or less. The Ni content is preferably 0.15% or less, and more preferably 0.10% or less.

[0037] The steel slabs to be subjected to the hot rolling process may contain impurities. "Impurities" refer to substances that are mixed in from raw materials such as ore and scrap, or from the manufacturing environment, during the industrial production of steel. The chemical composition of steel slabs used in the hot rolling process can be measured using standard analytical methods. For example, ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) can be used. Acid-soluble Al can be measured by ICP-AES using the filtrate obtained after thermal decomposition of the sample in acid. C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas fusion-thermal conductivity method.

[0038] In the hot rolling process, first, the slab (steel billet) is heat-treated. The heating temperature may be, for example, 1200°C or higher and 1600°C or lower. The heating temperature is preferably 1280°C or higher and 1500°C or lower. Next, the heated slab is hot-rolled. The thickness of the hot-rolled steel sheet after hot rolling is preferably, for example, in the range of 2.0mm or higher and 3.0mm or lower.

[0039] [Hot-rolled sheet annealing process] In the hot-rolled sheet annealing process, the hot-rolled steel sheet obtained in the hot rolling process is annealed. This hot-rolled sheet annealing causes recrystallization in the steel sheet, ultimately making it possible to achieve good magnetic properties. The conditions for the hot-rolled sheet annealing are not particularly limited, but for example, the hot-rolled steel sheet may be annealed in a temperature range of 900°C to 1200°C for 10 seconds to 5 minutes. After this hot-rolled sheet annealing step, pickling is subsequently performed by immersing the surface of the hot-rolled steel sheet after the hot-rolled sheet annealing in a pickling solution to obtain an annealed hot-rolled sheet.

[0040] [Cold rolling process] In the cold rolling process, the hot-rolled annealed sheet after the hot-rolled sheet annealing process is subjected to one cold rolling or multiple cold rollings with intermediate annealing in between. Here, "one time" means one pass or multiple passes of cold rolling or intermediate annealing is performed once. When intermediate annealing is performed between cold rollings, the heating method for the intermediate annealing is not particularly limited. Furthermore, cold rolling may be performed three or more times with intermediate annealing in between, but since this increases production costs, it is preferable to perform cold rolling once or twice.

[0041] The final cold rolling reduction in cold rolling (the cumulative cold rolling reduction without intermediate annealing, or the cumulative cold rolling reduction after the final intermediate annealing if intermediate annealing is performed) may be, for example, in the range of 80% to 95%. By setting the final cold rolling reduction within the above range, the {110} <001> This can increase the degree of concentration in the orientation and suppress the instability of secondary recrystallization. The thickness of the cold-rolled steel sheet after cold rolling is usually the thickness (final thickness) of the base steel sheet of the grain-oriented electrical steel sheet that is finally manufactured. The thickness of the cold-rolled steel sheet after cold rolling is preferably in the range of 0.15 mm or more and 0.30 mm or less, for example.

[0042] [Decarburization annealing process] In the decarburization annealing step, the cold-rolled steel sheet obtained in the cold rolling step is decarburized and annealed. This decarburization annealing removes C contained in the cold-rolled steel sheet, causing primary recrystallization. Decarburization annealing is preferably performed in a humid atmosphere to remove C contained in the cold-rolled steel sheet. For example, annealing may be performed in a humid atmosphere at a temperature range of 700°C to 1000°C for 10 seconds to 10 minutes. Furthermore, from the viewpoint of improving magnetic properties, the temperature-raising step may be performed at a temperature range of 500°C to 800°C at a rate of 100°C / second or more and 3000°C / second or less.

[0043] Alternatively, nitriding may be performed after decarburization annealing and before applying the annealing separator. In the nitriding treatment, the decarburization annealed sheet after decarburization annealing is subjected to nitriding treatment to produce a nitrided steel sheet. For example, annealing may be performed in an atmosphere containing a gas having nitriding ability, such as hydrogen, nitrogen, or ammonia, at a temperature range of 700°C to 850°C for 10 to 60 seconds.

[0044] [Separation material application process] In the separator application process, in order to prevent the coiled steel sheet from seizing during the subsequent finish annealing process, an annealing separator is applied to the decarburized annealed sheet obtained in the decarburization annealing process (which has been further subjected to nitriding treatment as necessary) and then dried before the finish annealing process. The annealing separator contains magnesia (MgO), alumina (Al2O3), and chlorides. The total content of MgO and Al2O3 in the annealing separator is preferably 80.0 mass% or more and 99.5 mass% or less, in terms of solid content, with the remainder being chlorides. That is, the chloride content in the annealing separator is the value obtained by subtracting the total content of MgO and Al2O3 from 100 mass%, and is preferably 0.5 mass% or more and 20.0 mass% or less. The remainder may contain impurities. In the annealing separator, the content of MgO alone is preferably 0.0% by mass or more and 79.5% by mass or less, and the content of Al2O3 alone is preferably 20.0% by mass or more and 99.5% by mass or less. The total content of MgO and Al2O3 is more preferably 85.0% by mass or more, and even more preferably 90.0% by mass or more. The total content of MgO and Al2O3 is more preferably 99.0% by mass or less, and even more preferably 95.0% by mass or less. On the other hand, the content of the remainder, ie, chloride, is more preferably 1.0 mass% or more, and even more preferably 5.0 mass% or more.The chloride content is more preferably 15.0 mass% or less, and even more preferably 10.0 mass% or less. Although no specific chloride is specified, examples of chlorides that may be considered include bismuth oxychloride (BiOCl), bismuth trichloride (BiCl3), calcium chloride, iron chloride, cobalt chloride, and nickel chloride.

[0045] [Finishing annealing process] In the final annealing step following the separator application step, the decarburized annealed sheet to which the annealing separator has been applied is subjected to final annealing for a long period of time while the steel sheet is wound into a coil. The annealing conditions for the finish annealing are not particularly limited, and known conditions may be appropriately adopted. For example, in the finish annealing, a decarburized annealed sheet that has been coated with an annealing separator and dried may be held at a temperature range of 1000°C to 1300°C for 10 hours to 60 hours. The atmosphere during the finish annealing may be, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen. After the finish annealing, the surface of the finish annealed sheet may be washed with water to remove powder.

[0046] This final annealing causes secondary recrystallization in the steel sheet, resulting in a crystal orientation of {110} <001> The secondary recrystallized structure has an easy axis of magnetization aligned in the rolling direction, and the crystal grains are coarse. This secondary recrystallized structure results in excellent magnetic properties. In this embodiment, the annealing separator contains chloride, which suppresses the formation of a primary coating and results in a smooth surface of the finish-annealed sheet. Alternatively, the atmosphere during the finish annealing may be changed to a hydrogen atmosphere for purification treatment, which purifies the steel sheet by removing elements such as Al, N, and S (including Se when Se is used as part of S) contained in the steel sheet as a steel composition. After the finish-annealed sheet is obtained by this finish-annealing step, the surface treatment step is carried out successively without intermediate annealing.

[0047] [Surface treatment process] In this step, the surface of the finish-annealed sheet obtained in the finish-annealing step is pickled to obtain a surface-treated steel sheet. The pickling conditions at this time are not particularly specified, but for example, the finish-annealed sheet may be immersed in an acid (treatment solution) of a specific concentration. The treatment solution preferably contains at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, with a total acid concentration of 1% by volume to 20% by volume, and a solution temperature of 50°C to 90°C. The finish-annealed sheet is preferably surface-treated using this treatment solution for 3 to 60 seconds.

[0048] In this process, the annealing separator adhering to the surface of the finish-annealed sheet is removed. It is preferable to perform the surface treatment under conditions that do not create etch pits on the surface of the finish-annealed sheet. To achieve this, the above conditions can be controlled in a combined and inseparable manner. For example, if the pickling strength is increased for one of the above conditions, the other conditions can be changed to weaken the pickling strength, thereby ensuring a smooth surface. Those skilled in the art can perform surface control, including the pickling behavior, and can control the surface condition by combining the above conditions, taking into account the effect of each of the above conditions on the pickling strength.

[0049] If the total acid concentration of the treatment solution is less than 1% by volume, it is difficult to remove the annealing separator from the surface of the finish-annealed sheet. The residual annealing separator on the surface makes it difficult to form internal oxide SiO2 in the subsequent tension-applying insulating coating formation process. On the other hand, if the total acid concentration of the treatment solution exceeds 20% by volume, etch pits are likely to form on the surface of the finish-annealed sheet. Similarly, if the temperature of the treatment solution is less than 50°C, an active surface state cannot be obtained, and if the temperature of the treatment solution is more than 90°C, etch pits are likely to form. Similarly, if the surface treatment time is less than 3 seconds, an active surface state cannot be obtained, and if the surface treatment time is more than 60 seconds, etch pits are likely to form.

[0050] [Tensioned insulating film forming process] The tensioned insulating coating formation process is carried out following the surface treatment process and involves forming a tensioned insulating coating containing aluminum phosphate and silica on the surface of the surface-treated steel sheet. This process includes an insulating coating chemical application process and a baking process. In the insulating coating chemical application step, an insulating coating forming liquid containing aluminum phosphate and silica (hereinafter also referred to as "insulating coating chemical") is applied to the surface of the surface-treated steel sheet. The total content of aluminum phosphate and silica is 80 mass % or more. The total content of aluminum phosphate and silica is preferably 90 mass % or more, and more preferably 95 mass % or more. It is preferable that the insulating coating chemical does not contain chromium. The silica is not limited to silica with a specific property. The particle size is also not limited to a specific particle size, but is preferably 200 nm (number average particle size) or less. For example, it may be 5 nm to 30 nm. If the particle size exceeds 200 nm, it may settle in the coating liquid.

[0051] In the baking process following the insulating coating chemical application process, the coated steel sheet is heat treated to form an insulating coating (secondary coating 3) on the surface of the coated steel sheet. This insulating coating (tensioned insulating coating) applies tension to the grain-oriented electrical steel sheet, thereby reducing the iron loss of the individual steel sheets, and also ensures electrical insulation between the steel sheets when grain-oriented electrical steel sheets are stacked together, thereby reducing the iron loss of the iron core.

[0052] The heat treatment carried out in the baking step will be described with reference to Fig. 3. Fig. 3 is a diagram for explaining the baking step, in which the horizontal axis represents time and the vertical axis represents the base steel sheet temperature. The baking process includes a temperature-raising process P1 in which the surface-treated steel sheet is heated to raise its temperature, and a soaking process P2 that is carried out after the temperature-raising process P1.

[0053] <Temperature rising process P1> The temperature-raising process P1 is an important step for controlling the interaction between the surface of the coated steel sheet and the insulating coating chemical solution in contact with this surface at the interface. In the temperature-raising process P1, the average temperature-raising rate of the steel sheet in the temperature range of 100°C to 600°C is set to 10°C / s to 400°C / s in an atmosphere with an oxygen concentration of 1% to 21% by volume and a dew point of 0°C to 30°C. In the temperature rising process P1, by setting the atmosphere during the temperature rise within the above range, reduction of Al(PO)4 and SiO2 in the insulating coating chemical solution is suppressed, and high coating adhesion can be obtained.

[0054] During the heating stage P1, Fe dissolves from the surface-treated steel sheet into the insulating coating solution, and Fe atoms diffuse into the insulating coating solution. The Fe dissolves in Al(PO)4, and nuclei of Fe-Al-PO compounds are formed on the surface of the base steel sheet. If the average heating rate of the steel sheet during the heating stage P1 exceeds 400°C / s, Fe-Al-PO compounds will not be formed, so the average heating rate of the steel sheet must be 400°C / s or less. Conversely, if the temperature-raising process P1 is performed by slow heating and the average temperature-raising rate of the steel sheet is less than 10°C / sec, FeO and Fe3O4 are formed at the interface between the insulating coating solution and the surface of the base steel sheet. These FeO and Fe3O4 become the starting points for coating peeling, which hinders improvement of coating adhesion. Therefore, the average temperature-raising rate of the steel sheet is set to 10°C / sec or more. The average temperature-raising rate of the steel sheet is preferably 20°C / sec or more, and more preferably 50°C / sec or more.

[0055] The steel sheet temperature at which FeO and Fe3O4 precipitate is 400°C to 600°C. Therefore, it is conceivable to control the average heating rate of the steel sheet within at least the temperature range of 400°C to 600°C to within a range of 10°C / sec to 400°C / sec. However, since special equipment is required to control the average heating rate of the steel sheet only within the narrow temperature range of 400°C to 600°C, the start of control of the average heating rate of the steel sheet may be set to a relatively low temperature range of around 100°C. However, even in this case, the average heating rate of the steel sheet within the temperature range of 400°C to 600°C is controlled to within a range of 10°C / sec to 400°C / sec.

[0056] Furthermore, if the oxygen concentration in the atmosphere is less than 1% by volume, an oxide film of Fe2SiO4 or SiO2 will form at the interface between the insulating coating solution and the steel sheet. These oxide films have the effect of suppressing the formation of Fe-Al-PO, resulting in poor coating adhesion. On the other hand, if the oxygen concentration is more than 21% by volume, FeO and Fe3O4 will form at the interface between the insulating coating solution and the steel sheet, resulting in poor coating adhesion. Furthermore, if the dew point of the atmosphere is below 0°C, an oxide film of Fe2SiO4 or SiO2 will form at the interface, resulting in poor coating adhesion. On the other hand, if the dew point is above 30°C, FeO or Fe3O4 will form at the interface, resulting in poor coating adhesion.

[0057] When the steel sheet temperature reaches 600°C, a sufficient number of nuclei of Fe-Al-PO compounds have been formed on the surface of the base steel sheet. The heat cycle from when the steel sheet temperature reaches 600°C until the start of the soaking step P2 does not significantly affect the nuclei of Fe-Al-PO compounds. Therefore, when the steel sheet temperature reaches 600°C, the steel sheet may be temporarily cooled to room temperature and then reheated to perform the soaking step P2. Alternatively, as shown in FIG. 3 , the steel sheet may be heated continuously after reaching 600°C to the soaking temperature T1 (a constant steel sheet temperature within the range of 800°C to 1000°C), and then the soaking step P2 may be performed. In either case, the nuclei of Fe-Al-PO compounds that were once formed remain on the surface of the base steel sheet.

[0058] <Soaking process P2> In the subsequent soaking step P2, the steel sheet temperature is maintained at the soaking temperature T1 in Fig. 3. Specifically, the soaking temperature T1 is a constant steel sheet temperature selected from the range of 800°C to 1000°C. In the soaking step P2, the soaking atmosphere is, for example, a mixed gas of an inert gas (nitrogen or argon), hydrogen, and water vapor. At this time, the hydrogen concentration in the soaking atmosphere is set to 1 to 15% by volume, and the dew point is set to -20 to +40°C. The temperature maintenance time in the soaking step P2 is set to a range of 5 to 200 seconds. If the holding time is less than 5 seconds, the time required for nucleation of the Fe-Al-PO compound formed in the temperature rise step P1 cannot be secured, resulting in poor coating adhesion.On the other hand, if the holding time is more than 200 seconds, the secondary coating will crystallize, resulting in poor coating adhesion.

[0059] This soaking step P2 is an important step for growing the nuclei of the Fe-Al-PO compound formed in the temperature-raising step P1, and it is particularly important to control both the soaking temperature and the soaking atmosphere. If the soaking temperature T1 is less than 800°C, the nuclei of the Fe-Al-PO compound cannot grow sufficiently, and as a result, sufficient coating adhesion cannot be ensured. Therefore, the soaking temperature T1 is set to 800°C or higher. The soaking temperature T1 is preferably 820°C or higher, and more preferably 840°C or higher.

[0060] Conversely, if the soaking temperature T1 exceeds 1000°C, the secondary coating formed may crystallize, potentially leading to coating peeling. Therefore, from the viewpoint of preventing deterioration of coating adhesion, the soaking temperature T1 is set to 1000°C or less. The soaking temperature T1 is preferably 950°C or less, and more preferably 900°C or less. For the above reasons, it is necessary to control the soaking temperature T1 in the soaking process P2 to a constant steel sheet temperature within the range of 800°C to 1000°C.

[0061] Furthermore, in the soaking step P2, controlling the soaking atmosphere is also important. Specifically, the hydrogen concentration in the annealing atmosphere is set to 1 to 15% by volume, and the atmospheric dew point is controlled to be approximately constant (for example, ±5°C) in the range of -20 to +40°C. This control allows the nuclei of the Fe-Al-PO compound formed in the heating step P1 to grow most stably. If the soaking step P2 is performed with a hydrogen concentration below 1%, there is a risk of generating Fe-based oxides such as FeO, which are a factor in degrading coating adhesion. Therefore, the hydrogen concentration is set to 1% by volume or more. The hydrogen concentration is preferably 2% by volume or more, and more preferably 3% by volume or more. Furthermore, if the atmospheric dew point is below -20°C, the nuclei of the Fe-Al-PO compound formed in the temperature-raising step P1 will be reduced, resulting in a deterioration in coating adhesion. The atmospheric dew point is set to -20°C or higher. The atmospheric dew point is preferably 0°C or higher, and more preferably 15°C or higher.

[0062] On the other hand, if the hydrogen concentration in the atmosphere exceeds 15% by volume, FeP may be generated from the Fe-Al-PO compound. FeP causes voids to form in the secondary coating. If many voids occur in the secondary coating, this can cause the coating to peel off and significantly reduce the coating adhesion. Therefore, the hydrogen concentration is set to 15% by volume or less. The hydrogen concentration is preferably 10% by volume or less, and more preferably 5% by volume or less. Furthermore, if the atmospheric dew point exceeds +40°C, there is a risk of generating Fe-based oxides such as FeO, which are a factor in deteriorating the adhesion of the coating. Therefore, the atmospheric dew point is +40°C or lower. The atmospheric dew point is preferably +35°C or lower, and more preferably +30°C or lower.

[0063] Through the above steps, the grain-oriented electrical steel sheet 1 shown in FIG. 1 is manufactured. After the secondary coating is formed, flattening annealing may be performed for shape correction, if necessary. By performing flattening annealing on the steel sheet, it becomes possible to further reduce iron loss. Furthermore, a magnetic domain control treatment may be carried out before or after the secondary coating formation step, as necessary. By carrying out the magnetic domain control treatment, the iron loss of the grain-oriented electrical steel sheet can be further reduced. When the magnetic domain control treatment is performed before the secondary coating formation step, linear or dot-like grooves extending in a direction intersecting the rolling direction may be formed at predetermined intervals along the rolling direction. When the magnetic domain control treatment is performed after the secondary coating formation step, linear or dot-like stress-strain portions extending in a direction intersecting the rolling direction may be formed at predetermined intervals along the rolling direction. The magnetic domain control treatment narrows the width of the 180° magnetic domains (subdivides the 180° magnetic domains). The grooves can be formed by mechanical groove formation using gears or the like, chemical groove formation using electrolytic etching, or thermal groove formation using laser irradiation, etc. The stress-strained portions can be formed by laser beam irradiation, electron beam irradiation, etc.

[0064] According to the method for producing a grain-oriented electrical steel sheet described above, it is possible to produce a grain-oriented electrical steel sheet having high magnetic properties and high coating adhesion without the intermediate annealing step that was previously required. [Example]

[0065] Next, the effects of one embodiment of the present invention will be explained in more detail using examples, but the various conditions in these examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0066] First, in the hot rolling process, slabs (steel billets) Nos. a to 1 having the chemical compositions shown in Table 1 below were prepared.

[0067] [Table 1]

[0068] Specifically, in all of the slabs No. a to 1, the chemical composition is as follows, in mass%: C: 0.020%~0.150%, Si: 3.00% to 4.00% Mn: 0.01% to 0.50%, S: 0.0010%~0.0400%, Acid soluble Al: 0.010%~0.050%, N: 0.002%~0.020%, and the balance being Fe and impurities. In addition, for slabs No. c to l, the chemical composition is, in mass%, Bi:0.0200% or less, P: 0.100% or less, Sn: 0.50% or less, Cu: 0.50% or less, Cr: 0.50% or less, Sb: 0.20% or less, Mo: 0.10% or less Nb: 0.0200% or less, B: 0.0200% or less, Te: 0.0200% or less, Ni: 0.20% or less, Se: 0.0200% or less, At least one selected from the group consisting of: Then, these slabs Nos. a to 1 were heated to 1350°C and subjected to hot rolling to produce hot-rolled steel sheets with a thickness of 2.3 mm.

[0069] Subsequently, in the hot-rolled sheet annealing step, the hot-rolled steel sheet obtained in the hot-rolling step was subjected to hot-rolled sheet annealing at 1100°C for 120 seconds, and the surface thereof was further pickled by immersing it in a pickling solution. In this way, a hot-rolled sheet annealed sheet was obtained. Subsequently, in the cold rolling process, the hot-rolled annealed sheet after the hot-rolled sheet annealing process was subjected to one cold rolling or multiple cold rollings with intermediate annealing in between to obtain cold-rolled steel sheets having final thicknesses shown in Tables 2A to 2C and Tables 3A to 3C.

[0070] Subsequently, in the decarburization annealing step, the cold-rolled steel sheet obtained in the cold rolling step was subjected to decarburization annealing at 830°C for 100 seconds in a wet hydrogen atmosphere. Subsequently, in the separator application step, an annealing separator containing the components shown in Tables 2A to 2C and Tables 3A to 3C was applied to the surface of the decarburized annealed steel sheet, and then dried. Subsequently, in the final annealing step, the decarburized annealed sheet to which the annealing separator had been applied in advance was subjected to final annealing.

[0071] After the finish-annealed sheet was obtained by this finish-annealing step, the surface treatment step was carried out immediately without intermediate annealing. In the surface treatment step, the finish-annealed steel sheet was immersed in a treatment solution for 3 to 60 seconds to perform surface treatment, thereby obtaining a surface-treated steel sheet. The treatment solution used here contained sulfuric acid, had a total acid concentration of 3 to 5% by volume, and a solution temperature of 70 to 90°C. However, for Test No. 35, the surface treatment step was performed under conditions of an acid concentration of 5% by volume and a solution temperature of 30°C. The subsequent tension-applying insulating coating formation process included an insulating coating solution application process and a baking process. In the insulating coating solution application process, an insulating coating solution containing 100 mass% of silica and aluminum phosphate in terms of solid content was applied to the surface of the surface-treated steel sheet.

[0072] In the baking process following the insulating coating solution application process, the surface-treated steel sheet to which the insulating coating solution had been applied was subjected to a heat treatment to form an insulating coating (secondary coating 3) on the surface of the surface-treated steel sheet. This baking process included a temperature-raising process P1 in which the surface-treated steel sheet was heated to increase its temperature, and a soaking process P2 which was carried out after the temperature-raising process P1. In the temperature rising process P1, the average temperature rising rate of the steel sheet, the dew point, and the oxygen concentration were set to the conditions shown in Tables 2A to 2C and Tables 3A to 3C described later. Similarly, in the soaking step P2, the annealing temperature, annealing time, hydrogen concentration, and atmospheric dew point were set to the conditions shown in Tables 2A to 2C and Tables 3A to 3C described later.

[0073] The test pieces obtained through the above tensioned insulating coating formation process were evaluated for coating adhesion, core loss, and magnetic flux density. In all examples, the average thickness of the secondary coating was 1.0 to 5.0 μm. Specifically, coating adhesion was evaluated by wrapping a test piece around a cylinder with a diameter of 20 mm and bending it 180°, and then measuring the remaining coating area ratio. The area ratio of the remaining coating surface to the steel sheet area in contact with the cylinder was calculated. The steel sheet area in contact with the roll was determined by calculation. The remaining surface area was determined by taking a photograph of the steel sheet after the test and performing image analysis on the photograph. When the remaining coating area ratio was 90% or more, it was rated as Very Good (VG), when it was 85% or more but less than 90%, it was rated as Good (G), when it was 80% or more but less than 85%, it was rated as Fair (F), and when it was less than 80%, it was rated as Poor (P).When the remaining coating area ratio was 80% or more, it was determined that the coating adhesion was excellent.

[0074] Next, the iron loss characteristics of the test specimens were evaluated in accordance with the Single Sheet Tester (SST) method. Iron loss W17 / 50 (W / kg), defined as the power loss per unit weight (1 kg) of the steel sheet, was measured under conditions of an AC frequency of 50 Hz and an excitation magnetic flux density of 1.7 T. When the iron loss W17 / 50 was less than 0.75 W / kg, it was determined that the iron loss characteristics were excellent. The magnetic flux density B8 (T) was measured in the rolling direction by applying a magnetic field of 800 A / m to the test piece.

[0075] The results are shown in Tables 2A to 2C and Tables 3A to 3C.

[0076] [Table 2A]

[0077] [Table 2B]

[0078] [Table 2C]

[0079] [Table 3A]

[0080] [Table 3B]

[0081] [Table 3C]

[0082] First, in the results of Tables 2A to 2C, in all of Test Nos. 1 to 12, which are invention examples, the manufacturing conditions in the heating process P1 and the soaking process P2 were within the ranges described in the above embodiment. That is, in the heating process P1, the average heating rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C was 10°C / s to 400°C / s in an atmosphere with an oxygen concentration of 1 vol% to 21 vol% and a dew point of 0°C to 30°C. Furthermore, in the soaking process P2, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C was 5 seconds to 200 seconds in a soaking atmosphere with a hydrogen concentration of 1 to 15 vol% and a constant atmospheric dew point of -20 to +40°C. In the examples shown in Tables 2A to 2C, various changes were made to the steel compositions, but the manufacturing conditions were within the above ranges, resulting in relatively good coating adhesion. However, the average heating rate of the steel sheet in the heating step P1, and the annealing temperature and annealing atmosphere (hydrogen concentration, atmospheric dew point) in the soaking step P2 were outside the preferred ranges, so the evaluation remained at "F." On the other hand, as shown in Tables 2A to 2C, the iron loss W17 / 50 was less than 0.75 W / kg in all of Test Nos. 1 to 12. Furthermore, as shown in Tables 2A to 2C, no significant decrease in magnetic flux density was observed in any of Test Nos. 1 to 12. Therefore, the results satisfied the pass criteria for both coating adhesion and core loss without compromising magnetic flux density.

[0083] Next, in the results shown in Tables 3A to 3C, where both the manufacturing conditions and the steel components were changed, the results varied depending on the manufacturing conditions. First, in all of Test Nos. 21 to 26 and 35, which are inventive examples, in the heating process P1, the average heating rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C was set to a range of 10°C / sec to 400°C / sec in an atmosphere with an oxygen concentration of 1% by volume to 21% by volume and a dew point of 0°C to 30°C. Additionally, in all of Test Nos. 21 to 26 and 35, in the soaking process P2, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C was set to a range of 5 seconds to 200 seconds in a soaking atmosphere with a constant hydrogen concentration of 1 to 15% and an atmospheric dew point of -20 to +40°C. As a result, the pass criteria were met for both coating adhesion and iron loss in all of Test Nos. 21 to 26 and 35. Test Nos. 23 to 26 in particular showed high coating adhesion, with Test Nos. 25 and 26 demonstrating the highest coating adhesion. In addition, as shown in Tables 3A to 3C, no significant decrease in magnetic flux density was observed in any of Test Nos. 21 to 26. Therefore, both coating adhesion and core loss were excellent without compromising magnetic flux density.

[0084] On the other hand, in Test No. 27, which is a comparative example, the average temperature rise rate of the steel sheet in the temperature rise process P1 was 5°C / sec, which was below the lower limit of 10°C / sec of the range of the present invention. As a result, both the coating adhesion and the iron loss were insufficient. In Test No. 28, which is a comparative example, the average heating rate of the steel sheet in the heating process P1 was 450°C / sec, which exceeded the upper limit of the range of 400°C / sec according to the present invention. As a result, both the coating adhesion and the iron loss were insufficient. In Test No. 29, which is a comparative example, the dew point during the temperature rise process P1 was −22° C., which was below the lower limit of −20° C. within the range of the present invention. As a result, although the iron loss met the pass standard, the coating adhesion was insufficient. In Test No. 30, which is a comparative example, the dew point during the temperature rise process P1 was 32° C., which exceeded the upper limit of the range of the present invention, 30° C. As a result, both the coating adhesion and the iron loss were insufficient.

[0085] In Test No. 31, which is a comparative example, the annealing temperature in the soaking step P2 was 780° C., which was below the lower limit of the range of 800° C. according to the present invention. As a result, both the coating adhesion and the iron loss were insufficient. In Test No. 32, which is a comparative example, the annealing temperature in the soaking step P2 was 1020°C, which exceeded the upper limit of the range of the present invention, 1000°C. As a result, although the iron loss satisfied the pass criteria, the coating adhesion was insufficient. In Test No. 33, which is a comparative example, the atmospheric dew point in the soaking step P2 was −30° C., which was below the lower limit of the range of −20° C. according to the present invention. As a result, although the iron loss satisfied the pass criteria, the coating adhesion was insufficient. In Test No. 34, which is a comparative example, the atmospheric dew point in the soaking step P2 was +45° C., which exceeded the upper limit of the range of the present invention, +40° C. As a result, although the iron loss met the pass standard, the coating adhesion was insufficient.

[0086] From the above results, it was confirmed that in order to achieve both excellent coating adhesion and iron loss, the conditions of both the heating process P1 and the soaking process P2 must be appropriately controlled. Specifically, in the heating process P1, the average heating rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C must be 10°C / s to 400°C / s in an atmosphere with an oxygen concentration of 1% to 21% by volume and a dew point of 0°C to 30°C. Furthermore, in the soaking process P2, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C must be 5 seconds to 200 seconds in a soaking atmosphere with a constant hydrogen concentration of 1% to 15% and a dew point of -20 to +40°C. [Industrial Applicability]

[0087] According to the present invention, a grain-oriented electrical steel sheet having high coating adhesion (secondary coating adhesion) without impairing magnetic properties can be produced without intermediate annealing, and therefore has high industrial applicability. [Explanation of symbols]

[0088] 1 Grain-oriented electrical steel sheet 2 Base steel plate 3 Secondary coating (tensioned insulating coating) 4. Oxide layer P1 Temperature rise process P2 Soaking process

Claims

1. A method for manufacturing a grain-oriented electrical steel sheet having a base steel sheet, an oxide layer containing an Fe-Al-P-O compound formed on the surface of the base steel sheet, and a tension-imparting insulating coating formed on the surface of the oxide layer, comprising: The chemical composition, in mass%, is: C: 0.020% to 0.150%, Si: 3.00% to 4.00%, Mn: 0.01% to 0.50%, S: 0.0010% to 0.0400%, Acid-soluble Al: 0.010% to 0.050%, N: 0.002% to 0.020%, Bi: 0.0000% to 0.0200%, P: 0.000% to 0.100%, Sn: 0.00% to 0.50%, Cu: 0.00% to 0.50%, Cr: 0.00% to 0.50%, Sb: 0.00% to 0.20%, Mo: 0.00% to 0.10%, Nb: 0.0000% to 0.0200%, B: 0.0000% to 0.0200%, Te: 0.0000% to 0.0200%, Ni: 0.00% to 0.20%, Se: 0.0000% to 0.0200%, a hot rolling step of heating and hot rolling the slab, the balance of which is Fe and impurities, to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet to obtain a hot-rolled sheet annealed sheet, and then immersing the hot-rolled sheet annealed sheet in a pickling solution; A cold rolling process in which the hot-rolled annealed sheet is subjected to cold rolling to obtain a cold-rolled steel sheet; a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization annealed sheet; The surface of the decarburized annealed sheet is coated with MgO and Al. ２ O ３ a separator application step of applying an annealing separator containing a chloride; a finish annealing step of subjecting the decarburized annealed sheet coated with the annealing separator to finish annealing to obtain a finish annealed sheet; a surface treatment step of pickling the surface of the finish annealed steel sheet to obtain a surface-treated steel sheet; a tensioned insulating coating forming process including an insulating coating solution applying process for applying an insulating coating solution containing aluminum phosphate and silica in a total amount of 80 mass % or more to the surface of the surface-treated steel sheet, and a baking process for forming the tensioned insulating coating on the surface of the surface-treated steel sheet by heat treating the surface-treated steel sheet to which the insulating coating solution has been applied; and The heat treatment in the baking step includes a temperature rising process and a soaking process, In the temperature-raising process, the average temperature-raising rate of the steel sheet in the steel sheet temperature range of 100°C to 600°C is set to 10°C / sec to 400°C / sec in an atmosphere having an oxygen concentration of 1% by volume to 21% by volume and a dew point of 0°C to 30°C, In the soaking process, the holding time at a constant steel sheet temperature in the range of 800°C to 1000°C is 5 seconds to 200 seconds in a soaking atmosphere having a hydrogen concentration of 1 to 15 volume% and an atmospheric dew point of a constant value in the range of -20 to +40°C. A method for producing a grain-oriented electrical steel sheet.

2. In the annealing separator, the content of the MgO is 0.0 mass % or more and 79.5 mass % or less, and the Al ２ O ３ The content of is 20.0 mass% or more and 99.5 mass% or less, and the remainder is the chloride. The method for producing a grain-oriented electrical steel sheet according to claim 1 .

3. In the surface treatment step, the finish annealed sheet is immersed for 3 to 60 seconds in a treatment solution containing at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, having a total acid concentration of 1% by volume to 20% by volume, and having a solution temperature of 50°C to 90°C. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2.

4. The slab has the following chemical composition in mass%: Bi: more than 0.0000%, less than 0.0200%, P: more than 0.000%, less than 0.100%, Sn: more than 0.00%, less than 0.50%, Cu: more than 0.00%, less than 0.50%, Cr: more than 0.00%, less than 0.50%, Sb: more than 0.00%, less than 0.20%, Mo: more than 0.00%, less than 0.10%, Nb: more than 0.0000%, less than 0.0200%, B: more than 0.0000%, less than 0.0200%, Te: more than 0.0000%, less than 0.0200%, Ni: more than 0.00% and 0.20% or less; and Se: more than 0.0000%, less than 0.0200%, 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet contains at least one selected from the group consisting of:

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