RU2790283C1 - Electrical steel sheet with oriented grain structure - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: the invention relates to metallurgy, namely to an electrical steel sheet with oriented grain structure, and can be used in the production of transformer cores. The electrical steel sheet with oriented grain structure contains a main steel sheet and a glass coating formed on the surface of the main steel sheet and having a covering part and a fixing structure included in the main steel sheet. The main steel sheet includes as a chemical composition in wt.%: 0.010 or less C, from 2.00 to 4.00 Si, from 0.05 to 1.00 Mn, from 0.010 to 0.065 or less Al, 0.004 or less N and 0.010 or less S with a residue of Fe and impurities. The oxygen concentration in the glass coating and the main steel sheet is 2500 parts per million or less. The Al concentration profile obtained by glow discharge optical emission spectroscopy (GDS) has at least two peaks, while the first peak having the intensity I_{Al_1} of the first peak of Al is obtained from Al inclusions in the coating part of the glass coating, and the second peak having the intensity I_{Al_2} of the second peak of Al is obtained from Al inclusions in the fixing structure of the glass coating, and the intensity of each of the peaks is defined as the maximum intensity of the peak of Al in the covering part and in the fixing structure when the following ratio is fulfilled: I_{Al_1}<I_{Al_2}.

EFFECT: improvement of magnetic losses before magnetic domain control, while achieving a sufficient effect of improving magnetic losses even with heat-resistant magnetic domain control.

2 cl, 5 dwg, 3 tbl, 2 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0001]

The present invention relates to grain oriented electrical steel sheets.

BACKGROUND OF THE INVENTION

[0002]

Since grain-oriented electrical steel sheets are mainly used as iron cores of transformers, it is desirable that their magnetization characteristics be good, and in particular, the magnetic loss be low. For this purpose, it is important to accurately align the crystal grains accumulated in the {110} <001> orientation, provide Si content to increase the intrinsic resistance, and reduce the amount of impurities.

[0003]

However, there is a limit to the reduction of magnetic loss by controlling the crystal orientation and components of the steel sheet, and therefore, a technique for dividing magnetic domains in width to reduce magnetic loss (hereinafter also referred to as "magnetic domain control technique") has been developed. The magnetic domain control technology can be conditionally divided into non-heat-resistant and heat-resistant technologies.

[0004]

As a non-temperature-resistant magnetic domain driving technology, such as described in Patent Documents 1 and 2, a method of forming a linear thermal deformation region in a surface layer of a steel sheet by irradiating the steel sheet with a laser beam is known. In this method, the width of the magnetic domain is narrowed by the thermal deformation region, so that the magnetic loss is reduced. However, since the stress in the thermal deformation region is relieved by heat treatment, the grain-oriented electrical steel sheet to which the non-heat-resistant magnetic domain control technology is applied cannot be used for a transformer that requires stress-removal annealing after processing such as iron core winding. Therefore, there is a problem that the use of a grain-oriented electrical steel sheet is limited.

[0005]

On the other hand, grain-oriented electrical steel sheets to which the heat-resistant magnetic domain driving technology is applied have the advantage that their application is not limited. As such a heat-resistant magnetic domain driving technology, for example, the electrolytic etching groove forming method disclosed in Patent Document 3 is known. In this method, for example, first a glass coating is formed on the surface of a steel sheet after secondary recrystallization. Then, the glass coating on the surface of the steel sheet is linearly removed by laser or mechanical means, and a groove is formed on the exposed area of the base iron by etching. Therefore, this method complicates the process steps and increases the production cost. In addition, there is a limitation on the processing speed.

[0006]

In addition, as disclosed in Patent Document 4, a method for forming a groove on the surface of a steel sheet using a mechanical gear press is known. However, Si is often added to the electrical steel sheet in an amount of about 3% by mass in order to increase the electrical resistance. Since such an electrical steel sheet is very hard, the method disclosed in Patent Document 4 may cause wear and damage to the tooth profile. In addition, the depth of the groove may vary, and as a result, the magnetic loss improvement effect may become uneven.

[0007]

In addition, there is also a problem that the above-described heat-resistant magnetic domain driving technology cannot have a sufficient effect of reducing magnetic loss compared to a non-heat-resistant magnetic domain driving technology that introduces a thermal deformation region into the surface layer of a steel sheet by irradiating it with a laser. beam. Patent Documents 5 and 6 disclose a technique for developing a steel sheet surface shape and a groove shape as a heat-resistant magnetic domain driving technology, but a fundamental solution to each of the aforementioned problems associated with a heat-resistant magnetic domain driving technology has not been achieved.

[0008]

Incidentally, in order to sufficiently obtain the effect of reducing magnetic loss by separating magnetic domains as described above, the tension applied to the steel sheet by the insulating coating or the glass coating (hereinafter also referred to as "coating tension") is extremely important. . As an insulating coating, for example, a coating formed by coating a steel sheet with an aqueous film-forming solution containing a phosphate salt and colloidal silica is known. As a glass coating to be described in detail below, for example, a glass coating containing an oxide containing forsterite as a main component is known.

[0009]

Patent Documents 7 and 8 disclose a technique for increasing the tension of a glass coating. Specifically, Patent Document 7 discloses an electrical steel sheet in which 5% or more of spinel (eg, MgAl ₂ O ₄ ) is contained in forsterite (ie, glass coating). In addition, Patent Document 8 discloses an electrical steel sheet in which the light intensities of Al and Fe obtained by glow discharge analysis satisfy a predetermined condition. In addition, Patent Document 9 discloses a technique for improving the adhesion of a glass coating (preventing peeling by bending in the manufacture of a transformer). Specifically, Patent Document 9 discloses an electrical steel sheet in which the light intensity B obtained by glow discharge analysis satisfies a predetermined condition. However, although the techniques disclosed in Patent Documents 7-9 can be expected to improve the tension or adhesion of the glass coating, these techniques alone cannot provide the magnetic domain separation effect. Thus, the techniques disclosed in Patent Documents 7-9 are based on the heat-resistant magnetic domain driving technology as described above. Therefore, even with these techniques, it is not possible to adequately solve the problem that the magnetic loss reduction effect cannot be sufficiently obtained.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0010]

Patent Document 1: Japanese Unexamined Patent Application (Kokai) No. 6-57335

Patent Document 2: Japanese Unexamined Patent Application (Kokai) No. 2003-129135

Patent Document 3: Japanese Unexamined Patent Application (Kokai) No. 61-117284

Patent Document 4: Japanese Unexamined Patent Application (Kokai) No. 61-117218

Patent Document 5: International Patent Application WO 2010/147009

Patent Document 6: Japanese Unexamined Patent Application (Kohyo) No. 2013-510239

Patent Document 7: Japanese Unexamined Patent Application (Kokai) No. 8-134660

Patent Document 8: Japanese Unexamined Patent Application (Kokai) No. 2000-204450

Patent Document 9: International Patent Application WO 2019/146697

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

[0011]

As described above, a problem with the heat-resistant magnetic domain driving technology is that the magnetic loss reduction effect cannot be sufficiently obtained. On the other hand, although the non-temperature-resistant magnetic domain driving technology can improve the magnetic loss reduction effect compared to the temperature-resistant magnetic domain driving technology, further improvement in the magnetic loss reduction effect is required.

[0012]

The present invention has been made in view of the foregoing, and it is an object of the present invention to provide a grain-oriented electrical steel sheet in which the magnetic loss before magnetic domain driving is further improved, and in which, even with heat-resistant magnetic domain driving, which is unlikely to achieve sufficient effect reduce the magnetic loss, the magnetic loss is improved sufficiently.

SOLUTION

[0013]

The inventors of the present invention have made extensive studies to solve the above problems. In particular, the present inventors repeated experiments in which heat-resistant magnetic domain driving was performed on grain-oriented electrical steel sheets having the same magnetic flux density and different magnetic loss characteristics before magnetic domain driving. As a result, the present inventors found that the better the magnetic loss in the state before magnetic domain driving, the better the magnetic loss after magnetic domain driving. Then, as a result of examining the characteristics of a steel sheet having good magnetic loss before driving the magnetic domains, the present inventors found that such a steel sheet has a structure in which a glass coating is embedded in the surface layer of the base steel sheet (which is hereinafter referred to as "fixing structure glass cover). Based on such discoveries, the inventor of the present invention developed the present invention. The essence of the present invention is as follows.

[0014]

According to a certain point of view of the present invention, there is provided a grain-oriented electrical steel sheet which comprises a base steel sheet and a glass coating which is formed on the surface of the base steel sheet, and is characterized in that: the base steel sheet contains, in its chemical composition, wt. %, 0.010% or less C, 2.00% to 4.00% Si, 0.05% to 1.00% Mn, 0.010% to 0.065% or less Al, 0.004% or less N, and 0.010% or less than S, with the remainder of Fe and impurities; the oxygen concentration in the glass coating and the base steel sheet is 2500 ppm or less; and the Al concentration profile obtained by glow discharge optical emission spectrometry (GDS) has at least two peaks in which each Al peak is set as the first peak and the second peak in order from the surface of the glass coating, and when I _{Al_1} is the intensity of the first peak of Al, and I _{Al_2} is the intensity of the second peak of Al, expression (1) is satisfied.

I _{Al_1} < I _{AL_2} expression (1)

[0015]

Here, in a vertical section of a part of the surface layer of the base steel sheet parallel to the rolling direction, the area within the range from the surface of the glass coating to a depth of 10 µm in the direction towards the thickness center of the sheet may contain aluminum-containing inclusions having an area-equivalent circle diameter of 1 µm or more and scattered in rolling direction with an average frequency of 50 pcs/mm or more. Unless explicitly stated otherwise in the present specification, a vertical section refers to a section parallel to the direction of the normal to the surface of the steel sheet.

BENEFICIAL EFFECTS OF THE INVENTION

[0016]

According to the above point of view of the present invention, when I _{Al_1} is the intensity of the first Al peak and I _{Al_2} is the intensity of the second Al peak, relation (1) is satisfied. Although details will be described later, when the condition of the mathematical formula (1) is satisfied, the anchoring structure of the glass coating is highly developed, and a large amount of Al inclusions are formed in the surface layer part of the base steel sheet. Since these Al inclusions form magnetic poles, the magnetic domain separation effect can be sufficiently improved by these Al inclusions. Additional control of magnetic domains can be applied to the grain oriented electrical steel sheet according to the present invention. Therefore, according to the present invention, the magnetic loss before magnetic domain driving is further improved, and the magnetic loss improvement effect can be sufficiently obtained even with high-temperature magnetic domain driving in which a sufficient magnetic loss reducing effect is unlikely.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]

[Fig. 1]

Fig. 1 is a graph showing one example of an Al concentration profile obtained using glow discharge optical emission spectrometry (GDS) for a grain-oriented electrical steel sheet according to the present embodiment.

[Fig. 2]

Fig. 2 is a schematic sectional view parallel to the rolling direction of a grain-oriented electrical steel sheet according to the present embodiment.

[Fig. 3]

Fig. 3 is an example of an optical microscope photograph of a section parallel to the rolling direction of a grain-oriented electrical steel sheet according to the present embodiment.

[Fig. 4]

Fig. 4 is a schematic vertical section parallel to the rolling direction of a grain-oriented electrical steel sheet in which a glass coating anchoring structure has not been developed.

[Fig. 5]

Fig. 5 is a graph illustrating an example of a temperature rise profile during decarburization annealing of the present embodiment.

DESCRIPTION OF EMBODIMENTS

[0018]

<1. Brief description of the present invention>

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail. First, the scheme of the present invention will be described. The inventors of the present invention have carefully studied the method of promoting the separation of magnetic domains in order to further reduce magnetic losses. When the magnetic domains separate, the width of the magnetic domains becomes narrow. When the width of the magnetic domain narrows, the travel distance of the domain wall when magnetizing the steel sheet is reduced, and thus the energy loss when moving the domain wall is reduced. This means that the magnetic losses are reduced.

[0019]

Here, separation of the magnetic domains can be realized by creating new magnetic poles in a part of the surface layer of the base steel sheet. More specifically, such magnetic poles increase the magnetostatic energy of a portion of the surface layer of the base steel sheet. Then, a new 180-degree domain wall is created in the surface layer part of the main steel sheet to reduce the magnetostatic energy. As a result, the magnetic domains are subdivided. In other words, the width of the magnetic domain becomes narrower.

[0020]

As mentioned above, to separate the magnetic domains, it is necessary to create new magnetic poles. Specifically, in a part of the surface layer of the base steel sheet, it is necessary to build a boundary made of a substance having a magnetic permeability different from that of the base steel sheet.

[0021]

Therefore, the present inventors studied the incorporation of a glass coating into a part of the surface layer of the base steel sheet. The reason for this is that the fixing structure of the glass coating forms magnetic poles in a portion of the surface layer of the base steel sheet, so that magnetic domain separation can be realized. Although details will be described later, the anchoring structure of the glass coating contains Al inclusions from which the magnetic poles are formed.

[0022]

The inventors of the present invention repeated studies to maximize the magnetic domain separation effect by the anchoring structure of the glass coating, and found that the anchoring structure is controlled by forming a satisfying glass coating on the surface of the base steel sheet, and that the magnetic domain separation effect can be maximized.

[0023]

In particular, the concentration of oxygen contained in the glass cover and the base steel sheet is set to 2500 ppm or less. In addition, in the concentration profile of Al obtained by performing optical emission analysis (GDS) of a glow discharge on a grain-oriented electrical steel sheet as shown in FIG. 1, when the intensity of the first peak 1 Al (the intensity of the first peak) is I _{Al_1} and the intensity of the second peak 2 Al (the intensity of the second peak) is I _{Al_2} , the structure of the glass coating is controlled so that the relationship I _{Al_1} <I _{AL_2} (mathematical formula (1)). As shown in FIG. 2 and 3, in a vertical section parallel to the rolling direction of part of the surface layer of the base steel sheet c), the area within the range from the surface of the glass coating a) to a depth of 10 µm in the direction towards the center of the thickness of the sheet contains aluminum-containing inclusions b) having a diameter equivalent to circle area of 1 μm or more, which preferably scatter in the rolling direction at an average frequency of 50 pcs/mm or more. Next, the present embodiment will be described in detail.

[0024]

<2. Grain-Oriented Electrical Steel Sheet Configuration>

(2-1. General configuration)

The grain-oriented electrical steel sheet according to the present embodiment includes a base steel sheet and a glass coating formed on the surface of the base steel sheet. An insulating film may be further formed on the surface of the glass coating. The glass cover has a fixing structure which is included in the main steel sheet, and this fixing structure is very well developed. Thus, the anchoring structure has a complicated three-dimensional network structure. Therefore, the glass coating is classified into a cover part that covers a large part of the surface layer of the base steel sheet, and a fixing structure that penetrates into the surface layer part of the base steel sheet from the cover part. In addition, the anchoring structure contains a large number of inclusions containing aluminum.

[0025]

Fig. 2 and 3 show an example of a vertical section parallel to the rolling direction of the grain-oriented electrical steel sheet according to the present embodiment. Fig. 2 is a schematic view, and FIG. 3 - micrograph. ND means the sheet thickness direction (direction of the normal to the surface of the steel sheet), and RD means the rolling direction.

[0026]

In these examples, the grain-oriented electrical steel sheet includes a base steel sheet c) and a glass coating a) formed on the surface of the base steel sheet c). The glass cover a) has a fixing structure which is included in the main steel sheet c), and this fixing structure is highly developed. The anchoring structure contains Al inclusions b). Although Al inclusions appear scattered in FIG. 2 and 3, Al inclusions are present not only in the plane of the drawing (ie, in a section parallel to the rolling direction of the steel sheet) as shown in FIG. 2 and 3, but also actually extend in a direction intersecting the plane of the drawing in FIG. 2 and 3 (for example, perpendicular to it) (ie, in the width direction of the steel sheet), and have a three-dimensional network structure connected to the cover portion. In addition, in FIG. 2 and 3, the anchor structure generally appears to extend from the cover portion to the surface layer portion of the base steel sheet (that is, extends in the sheet thickness direction), but the anchor structure may extend in the rolling direction and the sheet width direction. When observing the vertical section of this portion, a long anchoring structure is observed from the left side to the right side (in the rolling direction and the sheet width direction). Details of the anchoring structure and Al inclusions will be described later. The covering part in the glass coating is the part that covers the majority of the surface layer of the base steel sheet, and is the part that is connected to the fixing structure that penetrates the inside of the surface layer part of the base steel sheet. The cover portion and anchoring structure can be classified according to the Al concentration profile, as will be described later.

[0027]

(2-2. Component composition of the base steel sheet)

The main steel sheet includes in its chemical composition, in wt. %, C: 0.010% or less, Si: 2.00-4.00%, Mn: 0.05-1.00%, Al: 0.010-0.65% or less, N: 0.004% or less, S : 0.010% or less, with the remainder consisting of Fe and impurities. In the future, %, referring to the component composition, will mean wt. % relative to the total weight of the base steel sheet.

[0028]

(C: 0.010% or less)

C is an element effective for controlling primary recrystallization structures, but has a negative effect on the magnetic properties. Thus, C must be removed by decarburization annealing before the final annealing. If the concentration of C in the final product exceeds 0.010%, then C will be released during aging, and the hysteresis loss will worsen. Therefore, the C concentration should be 0.010% or less. The C concentration is preferably 0.007% or less, and more preferably 0.005% or less. The lower limit of the C concentration may be 0%, but if the C concentration is less than 0.0001%, the production cost will increase significantly. Therefore, 0.0001% is a practical lower limit in a real steel sheet. In grain-oriented electrical steel sheets, the C concentration is generally reduced to about 0.001% or less by decarburization annealing.

[0029]

(Si: 2.00-4.00%)

Si is an element that increases the electrical resistance of the steel sheet and improves the magnetic loss characteristics. If the Si concentration is less than 2.00%, a γ-transformation occurs at the time of final annealing, and the crystal orientation of the grain-oriented electrical steel sheet deteriorates. Therefore, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, and more preferably 3.00% or more. On the other hand, if the Si concentration exceeds 4.00%, the workability of the grain-oriented electrical steel sheet deteriorates and cracks are generated during rolling. Therefore, the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.

[0030]

(Mn: 0.05-1.00%)

Mn is an element that prevents cracking during hot rolling and combines with S to form MnS, which functions as an inhibitor. If the concentration of Mn is less than 0.05%, the effect of adding Mn is insufficient. Therefore, the Mn concentration is set to 0.05% or more. The Mn concentration is preferably 0.07% or more, and more preferably 0.09% or more. On the other hand, if the concentration of Mn exceeds 1.00%, the precipitation and dispersion of MnS become inhomogeneous, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Mn concentration is set to 1.00% or less. The Mn concentration is preferably 0.80% or less, and more preferably 0.60% or less.

[0031]

(Al: 0.010-0.065%)

Al is an element that binds to N to form (Al, Si)N or AlN, which functions as an inhibitor. If the Al concentration is less than 0.010%, the effect of adding Al is insufficient, and secondary recrystallization does not proceed sufficiently. Therefore, the Al concentration is set to 0.010% or more. The Al concentration is preferably 0.015% or more, and more preferably 0.020% or more. On the other hand, if the Al concentration exceeds 0.065%, the release and dispersion of the inhibitor become inhomogeneous, the desired secondary recrystallization pattern cannot be obtained, and the magnetic flux density decreases. Therefore, the Al concentration is set to 0.065% or less. The Al concentration is preferably 0.050% or less, and more preferably 0.040% or less. Although details will be described later, the Al in the base steel sheet also has the function of interacting with a glass coating having an advanced anchoring structure to form Al inclusions.

[0032]

(N: 0.004% or less)

N is an element that binds to Al to form AlN, which functions as an inhibitor. However, if the concentration of N in the final product exceeds 0.004%, N in the steel sheet precipitates as AlN, which worsens the hysteresis loss. Therefore, the N concentration is set to 0.004% or less. The lower limit of the N concentration may be 0%, but if the N concentration is less than 0.0001%, the production cost will increase significantly. Therefore, 0.001% is a practical lower limit in a real steel sheet. In grain-oriented electrical steel sheets, the N concentration is generally reduced to about 0.001% or less by finishing annealing.

[0033]

(S: 0.010% or less)

S is an element that binds to Mn to form MnS, which functions as an inhibitor. However, if the concentration of S in the final product exceeds 0.010%, S in the steel sheet precipitates as MnS, which worsens the hysteresis loss. Therefore, the concentration S is set to 0.010% or less. The lower limit of the S concentration may be 0%, but if the S concentration is less than 0.0001%, the production cost will increase significantly. Therefore, 0.0001% is a practical lower limit in a real steel sheet. In grain-oriented electrical steel sheets, the S concentration is generally reduced to about 0.005% or less by finishing annealing.

[0034]

In the base steel sheet, the remainder of the chemical composition is Fe and impurities. The impurities are basically unavoidable impurities, but when the base steel sheet contains the optional additives described below, the impurities are composed of these optional additives in addition to the inevitable impurities. The unavoidable impurity is an element that inevitably enters from the steel raw material and/or during the steel production process, and is an element tolerable in the range that does not degrade the characteristics of the grain-oriented electrical steel sheet according to the present embodiment.

[0035]

In addition, in the base steel sheet, one or more of Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, B: 0.0100% or less, Mo: 0.1% or less, and Bi: 0.01% or less can be added as optional elements in order to improve other characteristics without degrading the magnetic characteristics. Since these elements are optional additives, the lower limit of their concentration can be 0%.

[0036]

(Cr: 0.30% or less)

Cr is an element that improves the oxide layer in decarburization annealing and is effective for forming a glass coating. Therefore, Cr may be added to the base steel sheet in an amount of 0.30% or less. If the Cr concentration exceeds 0.30%, the decarburization property is greatly reduced. Therefore, the upper limit of the Cr concentration is preferably 0.30%.

[0037]

(Cu: 0.40% or less)

Cu is an element that effectively increases the resistivity of the base steel sheet and reduces its magnetic loss. If the Cu concentration exceeds 0.40%, the magnetic loss reduction effect saturates, and surface defects such as "copper scab" may occur during hot rolling. Therefore, the upper limit of Cu concentration is preferably 0.40%.

[0038]

(P: 0.50% or less)

P is an element that effectively increases the resistivity of the base steel sheet and reduces its magnetic loss. If the P concentration exceeds 0.50%, rolling problems will occur. Therefore, the upper limit of the concentration P is preferably 0.50%.

[0039]

(Ni: 1.00% or less)

Ni is an element that effectively increases the resistivity of the base steel sheet and reduces its magnetic loss. Ni is also an element that effectively regulates the structure of iron in a hot-rolled sheet and improves its magnetic properties. However, if the Ni concentration exceeds 1.00%, the secondary recrystallization becomes unstable. Therefore, the upper limit of Ni concentration is preferably 1.00%.

[0040]

(Sn: 0.30% or less, Sb: 0.30% or less)

Sn and Sb are well known elements of grain boundary segregation. Since the base steel sheet according to the present embodiment contains Al, this Al may be oxidized by the moisture released from the annealing separator depending on the final annealing conditions, and the strength of the inhibitor may fluctuate depending on the coil position. As a result, the magnetic properties may fluctuate depending on the position in the roll. As one of the countermeasures, there is a method for preventing Al oxidation by adding these grain boundary segregation elements, and to this end, Sn and Sb can be added to the base steel sheet at a concentration of 0.30% or less, respectively. On the other hand, if the concentration of these elements exceeds 0.30%, Si is less likely to be oxidized during decarburization annealing, glass film formation becomes insufficient, and decarburization annealing deteriorates significantly. Therefore, the upper limit of the concentration of these elements is preferably 0.30%.

[0041]

(B: 0.0100% or less)

B is an element that binds to N in the base steel sheet and is complexed with MnS to form BN, which acts as an inhibitor. The lower limit of the B concentration is not particularly limited, and may be 0% as described above. However, in order to fully exhibit the effect of adding B, the lower limit of the concentration of B is preferably 0.0005%. The B concentration is preferably 0.001% or more, and more preferably 0.0015% or more. On the other hand, if the concentration of B exceeds 0.0100%, the precipitation and dispersion of BN become inhomogeneous, it is not possible to obtain the desired texture of the secondary recrystallized grain, and the magnetic flux density decreases. Therefore, the concentration of B is preferably 0.0100% or less. The B concentration is preferably 0.0080% or less, more preferably 0.0060% or less, and even more preferably 0.0040% or less.

[0042]

(Mo: 0.1% or less)

Mo is an element that effectively improves the surface texture during hot rolling. However, if the concentration of Mo exceeds 0.1%, the effect of adding Mo is saturated. Therefore, the upper limit of the Mo concentration is preferably 0.1%.

[0043]

(Bi: 0.01% or less)

Bi has the effect of stabilizing inclusions such as sulfides and enhances the inhibitor function. However, if the Bi concentration exceeds 0.01%, Bi has a negative effect on the formation of the glass coating. Therefore, the upper limit of the Bi concentration is preferably 0.01%.

[0044]

(2-3. Oxygen concentration in glass coating and base steel sheet)

The total oxygen concentration in the glass coating and the base steel sheet is 2500 ppm or less. Most of the oxygen is contained in the glass coating, and the oxygen content in the steel sheet is about 10 to 100 ppm. When the grain-oriented electrical steel sheet contains an insulating film to be described later, the oxygen concentration is measured after the insulating film is removed from the grain-oriented electrical steel sheet. Thus, the insulating film is not included in the purpose of measuring the oxygen concentration. The insulating film is removed, for example, with an aqueous solution of sodium hydroxide.

[0045]

The oxygen analysis method uses a gas analysis method in which a sample is placed in a graphite crucible, melted and heated, and CO and CO ₂ are measured by an infrared absorption method.

[0046]

When the oxygen concentration exceeds 2500 ppm, the magnetic flux density of the base steel sheet decreases (more specifically, the amount of magnetic iron decreases), and the magnetic loss deteriorates. Therefore, the upper limit of oxygen concentration is 2500 ppm. The lower limit of the oxygen concentration is not particularly limited, but when the oxygen concentration is extremely low, such as 500 ppm or less, no glass coating is actually formed on the surface of the base steel sheet, and the glass coating fixing structure is not developed. Therefore, the magnetic loss worsens. In addition, the adhesion of the insulating film may decrease. Therefore, the oxygen concentration is preferably more than 500 ppm, and more preferably 1000 ppm or more. The oxygen concentration is measured using a gas analyzer based on the inert gas melting method. In the examples described below, this value is measured in this way. Examples of the method for setting the oxygen concentration to 2500 ppm or less include decarburization annealing conditions, in particular, the dew point control method. For example, an oxygen concentration of 2500 ppm or less can be achieved by adjusting the dew point in consideration of the annealing time and the annealing temperature.

[0047]

(2-4. Al Concentration Profile from GDS)

When the grain-oriented electrical steel sheet according to the present embodiment is subjected to glow discharge optical emission analysis (GDS), Al luminous intensity distribution (Al concentration profile) is observed in the thickness direction of the sheet. When the grain-oriented electrical steel sheet contains an insulating film to be described later, the Al concentration profile is measured after the insulating film is removed from the grain-oriented electrical steel sheet. Thus, the insulating film is not included in the purpose of measuring the concentration profile of Al. The measurement with the GDS is taken from the surface of the glass coating.

[0048]

GDS analysis requires appropriate adjustment of the conditions depending on the sample, and this adjustment is within the normal practice of specialists in this field of technology. Therefore, the GDS measurement conditions are not limited. However, the power was set to 35 W and data was taken, for example, at intervals of 0.01 to 0.10 s.

[0049]

The Al concentration profile has at least two peaks. The Al peaks are referred to as the first peak, the second peak, and so on. in order from the surface of the glass coating. Fig. 1 shows one example of an Al concentration profile. The Al concentration profile shown in FIG. 1 has two peaks, ie the first peak 1 and the second peak 2. The number of peaks is preferably two. The peaks may partially overlap or may be separated from each other.

[0050]

The first peak is obtained from Al inclusions in the capping portion of the glass coating, and the second peak is obtained from Al inclusions in the anchoring structure of the glass coating. The Al inclusions from which each peak is obtained are, for example, Mg ₂ Al ₂ O ₄ in which the Si of the forsterite (Mg ₂ SiO ₄ ) constituting the glass coating is replaced by Al. MgAl ₂ O ₄ has a composition of constituent elements similar to forsterite (Mg ₂ SiO ₄ ), has a polymorphic relationship and is easily produced. However, Al inclusions are not necessarily limited to Mg ₂ Al ₂ O ₄ if they form a magnetic pole in a portion of the surface layer of the base steel sheet. Examples of other Al inclusions contemplated in the present embodiment include those in which MgAl ₂ O ₄ is substituted with other elements and is in solid solution, Al ₂ O ₃ inclusions, and the like.

[0051]

In addition, when the intensity of the first Al peak is I _{Al_1} and the intensity of the second Al peak is I _{Al_2} , relation (1) is satisfied.

I _{Al_1} < I _{Al_2} (1)

Thus, the intensity of the second peak is greater than the intensity of the first peak. Here, the intensity of each peak is defined as the maximum luminous intensity Al at each peak (in other words, the maximum peak height).

In addition, the ratio of the intensity of the first peak to the intensity of the second peak may be less than 1, which follows from the mathematical formula (1). Thus, relation (1)' is satisfied.

I _{Al_1} /I _{Al_2} <1 (1)'

The intensity of the first peak may be 0, and the lower limit of the peak ratio may be 0. The lower limit of the peak ratio is 0.1 or more, or more than 0.1, 0.2 or more, or more than 0.2, 0 .3 or greater, or greater than 0.3, 0.4 or greater, or greater than 0.4, 0.5 or greater, or greater than 0.5, 0.6 or greater, or greater than 0.6 , 0.7 or more, or more than 0.7, 0.8 or more, or more than 0.8, 0.9 or more, or more than 0.9.

On the other hand, as a rule, the stronger the intensity of the second peak, the closer the peak ratio is to 1, which is preferable. Therefore, the upper limit of the peak ratio is 0.9 or less or less than 0.9, 0.8 or less or less than 0.8, 0.7 or less or less than 0.7, 0.6 or less or less than 0.6, 0.5 or less or less than 0.5, 0.4 or less or less than 0.4.

[0052]

(2-5. Structure of part of the surface layer of the base steel sheet)

As described above, the intensity of the second peak is greater than the intensity of the first peak. The reason for this is that the fixing structure of the glass coating is formed on a part of the surface layer of the base steel sheet, and a large amount of Al inclusions are distributed in the fixing structure, as described in detail below. The fixing structure of the glass cover will be described with reference to FIG. 2 and 3. As described above, FIG. 2 and 3 show an example of a surface state of a grain-oriented electrical steel sheet according to the present embodiment. In these examples, the grain-oriented electrical steel sheet includes a base steel sheet c) and a glass coating a) formed on the surface of the base steel sheet c). The glass cover a) has a fixing structure which is included in the main steel sheet c), and this fixing structure is highly developed. The anchoring structure contains Al inclusions b).

[0053]

As shown in these examples, in the grain-oriented electrical steel sheet according to the present embodiment, a glass coating reinforcing structure is formed in a portion of the surface layer of the base steel sheet. In addition, the anchoring structure has a very complex three-dimensional network structure. Although Al inclusions appear scattered in FIG. 2 and 3, Al inclusions are present not only in the plane of the drawing (ie, in a section parallel to the rolling direction of the steel sheet) as shown in FIG. 2 and 3, but also actually extend in a direction intersecting the plane of the drawing in FIG. 2 and 3 (for example, perpendicular to it) (ie, in the width direction of the steel sheet), and have a three-dimensional network structure connected to the cover portion. In addition, in FIG. 2 and 3, the anchor structure generally appears to extend from the cover portion to the surface layer portion of the base steel sheet (that is, extends in the sheet thickness direction), but the anchor structure may extend in the rolling direction and the sheet width direction. When observing the vertical section of this portion, a long anchoring structure is observed from the left side to the right side (in the rolling direction and the sheet width direction).

[0054]

The term "part of the surface layer of the base steel sheet" in the present embodiment means the area from the surface of the base steel sheet (the boundary between the cover portion of the glass cover and the base steel sheet) to a predetermined depth in the base steel sheet. For example, the part on which the fixing structure of the glass coating is formed may be referred to as part of the surface layer of the base steel sheet. Here, the surface of the base steel sheet (the boundary between the glass cover and the base steel sheet) generally corresponds to the boundary between the glass cover and the anchoring structure, and this boundary is determined by the Al concentration profile. In addition, the predetermined depth may be 10 μm from the surface of the glass coating towards the center of the thickness of the sheet, considering the thickness of the glass coating on a conventional grain-oriented electrical steel sheet.

[0055]

In addition, part of the anchoring structure consists of Al inclusions. Al inclusions are abundantly distributed in the end part of the anchoring structure. Here, the end part of the anchoring structure means an end part extending in the depth direction on the inside of the steel sheet when viewed in two-dimensional section, as shown, for example, in FIG. 3. In FIG. 2 and 3, it can be seen that a large number of Al inclusions are formed at the end of the anchoring structure. In addition, in FIG. 2 and 3, Al inclusions appearing to be dispersed substantially spherically in the base steel sheet are formed at the end portion of the anchoring structure extending in the direction intersecting the plane of the drawing (ie, in the width direction of the steel sheet). Because the anchor structure may further develop at a later stage, Al inclusions may be present in a portion other than the end portion of the anchor structure. The specific three-dimensional network structure of the anchor structure is not particularly limited, but the more complex it is, the more Al inclusions are formed in the anchor structure and retained therein. In the grain-oriented electrical steel sheet according to the present embodiment, since the anchor structure forms a very complex three-dimensional network structure, a large amount of Al inclusions are present in the anchor structure. On the other hand, most of the Al inclusions are formed in and retained by the anchoring structure, thereby reducing the number of inclusions in the coating portion of the glass coating. In addition, as described above, in the Al concentration profile, the first peak is obtained from Al inclusions in the coating portion of the glass coating, and the second peak is obtained from Al inclusions in the anchoring structure of the glass coating. Therefore, in the grain-oriented electrical steel sheet according to the present embodiment, the intensity of the second peak is larger than the intensity of the first peak, and the mathematical formula (1) is satisfied. Based on this, the interface between the glass coating cap and the anchoring structure can be classified according to the Al concentration profile.

[0056]

Al inclusions form a boundary in a part of the surface layer of the base steel sheet, which has a magnetic permeability different from that of the steel sheet. Thus, the Al inclusions having a fixing structure embedded in the surface layer portion of the base steel sheet form a magnetic pole. In the grain-oriented electrical steel sheet according to the present embodiment, a plurality of Al inclusions, that is, magnetic poles, are formed in a portion of the surface layer of the base steel sheet, so that the magnetic domains are further separated.

[0057]

An example where the mathematical formula (1) is not satisfied includes, for example, the case where the anchoring structure is not developed and the number of Al inclusions is small. An example of such a grain oriented electrical steel sheet is shown in FIG. 4. The meaning of the reference numbers in FIG. 4 is similar to FIG. 2 and 3. In the example shown in FIG. 4, the fixing structure is practically not developed, and therefore Al inclusions are present practically only in the glass coating (in the part corresponding to the covering part). In this case, the fixing structure is not developed, and Al inclusions serving as magnetic poles are practically not formed in the surface layer portion of the base steel sheet. Therefore, the effect of separation of magnetic domains cannot be achieved.

[0058]

(2-6. Method for observing Al inclusions)

The fixing structure of the glass coating is a part included in the surface layer part of the base steel sheet, and Al inclusions contained in the fixing structure are present in a large amount in the surface layer part of the base steel sheet from the surface of the glass coating to a depth of 10 µm. Therefore, Al inclusions can be observed in the following way. Parallel to the rolling direction, a vertical section of a part of the surface layer of the base steel sheet from the surface of the glass coating to a depth of 10 µm (hereinafter also referred to as "observation area") is observed with an optical microscope or FE-SEM (Field Emission Scanning Electron Microscope), etc. . Then, the composition of the observation area is analyzed using EDS (Energy Dispersive X-ray Spectroscopy), EPMA (Electron Probe Microanalyzer), and the like. This makes it possible to identify Al inclusions in the observation area. For example, the size and frequency of Al inclusions can be measured, which will be described later. With regard to the frequency of inclusions, for example, a plurality of photographs of the area of interest can be taken, and the frequency of inclusions measured in each photograph can be arithmetically averaged.

[0059]

(2-7. Size and frequency of Al inclusions)

Preferably, Al inclusions having an area-equivalent circle diameter of 1 µm or more are scattered in the observation area at an average frequency of 50 pcs/mm or more in the rolling direction. In this case, the magnetic domain separation effect can be further improved.

[0060]

Although the presence of Al inclusions having an area-equivalent circle diameter of less than 1 μm does not adversely affect the performance of the base steel sheet, it is believed that such Al inclusions are unlikely to contribute to the magnetic domain separation effect. The upper limit of the diameter of the area-equivalent circle of Al inclusions is not particularly limited. However, if the size of the Al inclusions is too large, the numerical density of the Al inclusions is relatively reduced, and the magnetic loss improvement effect can be reduced. Therefore, for example, the diameter of the area-equivalent circle is preferably 10 µm or less.

[0061]

If the frequency of inclusions of Al is less than 50 pieces/mm, the frequency of formation of magnetic poles decreases, and thus the separation effect of magnetic domains can be slightly reduced. The upper limit of the turn-on frequency is not particularly limited, but if the turn-on frequency is too high, the Al inclusions may hinder the motion of the domain walls itself. In this case, the magnetic losses may worsen. Therefore, the switching frequency is preferably 100 pieces/mm or less.

[0062]

As described above, in the grain-oriented electrical steel sheet according to the present embodiment, when the intensity of the first Al peak is I _{Al_1} and the intensity of the second Al peak is I _{Al_2} , relationship (1) is satisfied. When condition (1) is satisfied, the anchoring structure of the glass coating is greatly developed, and many Al inclusions are formed in the anchoring structure, in other words, in the surface layer part of the base steel sheet. Since these Al inclusions form magnetic poles, the magnetic domain separation effect can be sufficiently improved by these Al inclusions. The magnetic domain control described below can be further applied to the grain-oriented electrical steel sheet according to the present embodiment. Therefore, according to the present embodiment, the magnetic loss prior to magnetic domain driving is further improved, and even with high-temperature magnetic domain driving that is unlikely to achieve a sufficient magnetic loss reduction effect, the magnetic loss reduction effect can be sufficiently obtained.

[0063]

<3. Production Method of Grain-Oriented Electrical Steel Sheet>

Next, one example of a method for producing a grain-oriented electrical steel sheet according to the present embodiment will be described. The production method of the grain-oriented electrical steel sheet according to the present embodiment is not limited to the production method described below, and any production method can be used as long as it can produce the grain-oriented electrical steel sheet according to the present embodiment.

[0064]

(3-1. Diagram of production method)

Further, the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment includes a steel slab preparation step, a reheating step, a hot rolling step, a hot annealing step, a cold rolling step, a decarburization annealing step, a nitriding treatment step. , an annealing separator application step, a final annealing step, a cleaning annealing step, and a cooling step. Next, each stage will be described in detail.

[0065]

(3-2. Steel slab preparation stage)

At this stage, the steel slab will be prepared. In particular, steel is melted, for example, using a converter or an electric furnace. The molten steel thus obtained is optionally degassed under vacuum and then cast continuously or into ingots followed by bloom rolling. The result is a steel slab. The thickness of the steel slab is not particularly limited, but is usually in the range of 150-350 mm, preferably 220-280 mm. However, the steel slab may be a so-called thin slab having a thickness range of 30-70 mm. The advantage of using a thin slab is that it does not need to be roughed to an intermediate thickness when making hot rolled sheet.

[0066]

Here, the component composition of the steel slab is the same as that of the base steel sheet described above, except for the N content. In the following, only the N content will be described.

[0067]

(N: 0.004-0.012%)

N is an element that binds to Al to form AlN, which functions as an inhibitor. However, N is also an element that forms bubbles (flakes) in the steel sheet during cold rolling. If the N content is less than 0.004%, AlN formation is insufficient. Therefore, the N concentration is set to 0.004% or more. Preferably, this concentration is 0.006% or more, and more preferably 0.007% or more. If the N concentration exceeds 0.012%, many bubbles may form in the steel sheet during cold rolling. Therefore, the N concentration is set to 0.012% or less.

[0068]

(3-3. Reheating step)

At this stage, the steel slab is reheated. The reheating temperature of the steel slab is preferably 1280° C. or lower. If the reheat temperature exceeds 1280°C, the amount of molten scale increases. In addition, since MnS is completely dissolved in the steel slab and finely precipitated in subsequent steps, it is necessary to set the decarburization annealing temperature above 900° C. in order to obtain a desired primary recrystallized grain size. Therefore, in the present embodiment, it is preferable to reheat the steel slab to 1280° C. or lower. The lower limit of the reheating temperature is not particularly limited, but may be, for example, 1100°C.

[0069]

(3-4. Hot rolling stage, hot annealing stage)

In the hot rolling step, the steel slab is subjected to hot rolling after reheating. In the hot annealing step, the iron structure is recrystallized by heating the hot-rolled sheet obtained in the hot rolling step as described above to a first step temperature of 1000 to 1150°C. Then, the hot-rolled sheet is annealed at a second stage temperature of 850 to 1100° C., which is lower than the first stage temperature. This hot annealing step is mainly carried out for the purpose of homogenizing the inhomogeneous structure formed during hot rolling.

[0070]

Thus, in order to homogenize the inhomogeneous structure of iron formed during hot rolling before final cold rolling, it is important in the present embodiment to perform annealing one or more times. The upper temperature limit of the first stage in this case has a great influence on the inhibitor. For example, if the temperature of the first stage exceeds 1150°C, the inhibitor is thinly released in subsequent stages. Therefore, the upper limit temperature of the first stage is set to 1150°C. On the other hand, if the temperature of the first stage is less than 1000° C., recrystallization becomes insufficient and the iron structure after hot rolling becomes inhomogeneous. Therefore, the lower limit temperature of the first stage is set to 1000°C. The upper temperature limit of the second stage also has a great influence on the inhibitor. For example, if the temperature of the second stage exceeds 1100°C, the inhibitor is thinly released in subsequent stages. Therefore, the upper limit temperature of the second stage is set to 1100°C. If the temperature of the second stage is less than 850°C, the γ phase is not formed, and thus the iron structure cannot be made uniform. Therefore, the lower temperature limit of the second stage is set to 850°C. In addition, it is necessary to control the temperature of the second stage so that it is lower than the temperature of the first stage.

[0071]

(3-5. Cold rolling stage)

After the hot annealing step is performed, the hot rolled sheet is subjected to one cold rolling or two or more cold rollings with an intermediate annealing in between. The result is the final cold rolled sheet. Each cold rolling may be performed at room temperature, or may be a warm rolling in which the temperature of the steel sheet is raised to a temperature above room temperature, for example, up to about 200°C.

[0072]

(3-6. Decarburization annealing step)

The decarburization annealing step first includes a step of heating the steel sheet after the cold rolling step (cold rolled sheet) from an inlet temperature of t0°C to a holding temperature t2°C higher than the inlet temperature, and a holding step, i. maintaining the temperature of the cold rolled sheet at a holding temperature of t2°C for a predetermined time. The decarburization annealing step is carried out in a humid atmosphere. Here, the inlet temperature t0°C is the temperature at which the cold-rolled sheet is introduced into the annealing furnace, and is usually 600°C or lower. The holding temperature is a temperature in the range of 700 to 900°C.

[0073]

The holding step (the process of maintaining a temperature between 700 and 900° C. for a predetermined time) of decarburization annealing is performed to remove carbon from the steel and adjust the primary recrystallized grain size to a desired size. The holding step is preferably performed at a holding temperature of t2°C in the temperature range of 700°C to 900°C for a period of time so that the primary recrystallized grain size is 15 µm or more. If the holding temperature t2°C is less than 700°C, the desired primary recrystallized grain size cannot be achieved, and if the holding temperature t2°C exceeds 900°C, the primary recrystallized grain exceeds the desired grain size.

[0074]

In the decarburization annealing step, the primary recrystallized texture (in particular, the crystal orientation in the texture) can be controlled by controlling the heating rate during the heating process. In the primary recrystallized texture, it is preferable to decrease the {111} azimuth grains and increase the {411} azimuth grains and Goss azimuth grains. The ease of recrystallization differs depending on the orientation of the crystals, and {411} azimuth grains are likely to recrystallize at a heating rate of about 100°C/sec, while Goss azimuth grains are likely to recrystallize in proportion to the heating rate. Therefore, in the present embodiment, it is preferable to heat at a heating rate HR1 of 40°C/s or more, preferably 75°C/s or more, more preferably 75-125°C/s, from t0°C where the temperature of the steel sheet is 600 °C or lower, up to t2°C (temperature in the metal holding zone in the furnace) in the range of 700-900°C. This makes it possible to reduce the {111} azimuth grains and increase the {411} azimuth grains and the Goss azimuth grains. Although details will be described later, SiO ₂ can be generated and developed on a part of the surface layer of the steel sheet by adjusting the heating rate HR1 to be 40°C/s or more in the temperature range t0 to t2. Thus, an inner oxide layer containing a large amount of SiO ₂ can be formed in a portion of the surface layer of the steel sheet. HR1 is the average heating rate from t0°C to t2°C, and this rate may fluctuate in part of the heating process and temporarily become less than 40°C/s.

[0075]

In addition, in the heating step, the heating rate may be changed between the first half and the second half.

In one embodiment, the decarburization annealing step includes a step of heating the cold rolled sheet from an inlet temperature of t0°C of 600°C or lower to a holding temperature t2°C higher than the inlet temperature of t0°C, and a holding step, i.e. . maintaining the temperature of the cold-rolled sheet at the holding temperature of t2°C. In the heating step of decarburization annealing, the heating rate hr1 is set to 40°C/s or more, while the temperature of the cold-rolled sheet is in the inlet temperature range t0°C of 700 to 900°C until it reaches the desired temperature t1°C which is lower than holding temperature t2°C. The heating rate hr2 can be 15°C/s - 30°C/s until the temperature of the cold rolled sheet reaches the holding temperature t2°C from the desired temperature t1°C.

[0076]

In particular, as shown in FIG. 5, the heating rate hr1 in the temperature range in which the temperature of the cold rolled sheet is within the inlet temperature range t0°C of 700 to 900°C and until it reaches the desired temperature t1°C, which is lower than the holding temperature t2°C (that is, in the rapid heating temperature range) is set to 40°C/s or more, and the heating rate hr2 in that temperature range until the temperature of the cold-rolled sheet reaches the holding temperature t2°C from the desired temperature t1°C, set to 15°C/s - 30°C/s. The desired temperature t1°C can be arbitrarily set within a range in which the above conditions are satisfied, but by setting the desired temperature t1°C to be equal to or lower than the Curie point (750°C) of the steel sheet, the heating is in the temperature range from the inlet temperature t0°C to the desired temperature t1°C (in the temperature range of rapid heating) can be carried out by an induction heating device.

[0077]

Here, the heating rate hr1 may be 40°C/s or more, and preferably 75-125°C/s.

In the present embodiment, the heating rate hr1 from the inlet temperature t0°C to the holding temperature t1°C is set to 40°C/s or more. This makes it possible to reduce the {111} azimuth grains and increase the {411} azimuth grains and the Goss azimuth grains. The heating rate hr1 is preferably 75°C/s or higher, and more preferably 75-125°C/s.

[0078]

In addition, in the present embodiment, the heating rate hr2 in the temperature range from the desired temperature t1°C to the holding temperature t2°C can be set to 15°C/s to 30°C/s. The lower limit of the heating rate hr2 is preferably 16°C/s. As such, in the present embodiment, the heating rate hr2 after the temperature of the cold rolled sheet reaches the desired temperature t1°C can be set to a relatively high value of more than 15°C/s to 30°C/s. As a result, a primary recrystallized grain texture can be obtained in which the frequencies of the {411} azimuth grains and the Goss azimuth grains are high, and the size of the Goss azimuth crystal grains is increased. As a result, the size of the secondarily recrystallized grain decreases during the second recrystallization due to subsequent final annealing. Therefore, a grain-oriented electrical steel sheet having good magnetic loss can be obtained.

[0079]

Here, the reason why the above-described effect is achieved when the heating rate hr2 is maintained in the range of more than 15°C/s to 30°C/s is not clear, but the present inventors consider it as follows. In the temperature range from the desired temperature t1°C to the holding temperature t2°C (the holding temperature is 700-900°C), recrystallization of unrecrystallized grains and growth of crystal grains that have already been recrystallized will occur for rapid heating. At a holding temperature of t2°C, all non-recrystallized grains become recrystallized grains. After that, at the exposure stage (annealing with exposure) at a holding temperature of t2°C, the recrystallized grains go into the grain growth mode, while azimuthal grains with a small crystal grain size are captured, and azimuth grains with a large crystal grain size increase their size. Here, the Goss azimuth grains have already completed recrystallization at the desired temperature of t1°C or lower. The growth of the Goss azimuth grain, which has already completed recrystallization, will be facilitated by adjusting the heating rate hr2 from the desired temperature t1°C to the holding temperature t2°C in the range from more than 15°C/s to 30°C/s, and preferably 16°C/ s or more and 30°C/s or less. Thus, since the Goss azimuth grains are already large diameter crystal grains at the beginning of the soaking stage, they can exist without the intrusion of other azimuth grains in the soaking stage.

[0080]

Here, if the heating rate hr2 is 15°C/s or less, the growth of crystal grains along the recrystallization azimuth after the desired temperature t1°C competes with the growth of Goss azimuth grains, and the Goss azimuth grains cannot grow sufficiently. As a result, the frequency of Goss azimuth grains in the primary recrystallized grain texture decreases, and an electrical steel sheet having good magnetic loss characteristics cannot be obtained. On the other hand, if the heating rate hr2 is more than 30° C./s, the frequency and size of the Goss azimuth crystal grains in the primary recrystallized grain texture become extremely large, and the dimensional property (uniformity) of the entire texture deteriorates significantly. Therefore, stable secondary recrystallized grains cannot be obtained, and as a result, the magnetic loss performance deteriorates.

In addition, the upper limit hr2 may not be higher than 25°C, or lower than 25°C. The hr2 range can be achieved by heating using various heating devices, as detailed below. However, if hr2 becomes too large and goes beyond the holding temperature t2, this may lead to the impossibility of subsequent secondary recrystallization. Therefore, by setting the upper limit hr2 to not higher than 25°C or lower than 25°C, the holding temperature t2 can be prevented from exceeding, which is preferable.

[0081]

(3-6-1. Heating method in the decarburization annealing step)

The heating during the decarburization annealing step may be performed by induction heating. In this case, the flexibility of the heating rate is high, the steel sheet can be heated in a non-contact manner, and the effect of a relatively simple installation in a decarburization annealing furnace can be obtained.

[0082]

In particular, if the heating rate changes between the first half and the second half, and the desired temperature t1°C does not exceed 750°C, which is the Curie point of the steel sheet, the cold rolled sheet can be quickly heated from the inlet temperature t0°C to the desired temperature t1 °C only with induction heating device.

[0083]

On the other hand, heating from the desired temperature t1°C to the holding temperature t2°C and the subsequent holding step can be performed using a heating device using a radiant heat source such as a radiant tube. It is difficult to heat with an induction heating device beyond the Curie point, but a heating device using a radiant heat source can stably heat a cold-rolled sheet even in such a temperature range. In addition, radiant heat heating has the advantage that it can be easily controlled in the heating rate range hr2 (lower range than the heating rate hr1).

[0084]

Of course, the heating method is not particularly limited. In addition to the above method, the heating method may be a method using a high-energy heat source such as a new laser or plasma, a method using a direct-powered heating device, and the like. They can also be combined as needed. However, using an induction heating device or a heating device using a radiant heat source has the advantage that the cold-rolled sheet can be heated without the heating device directly contacting the cold-rolled sheet.

[0085]

Here is a way to measure the heating rate HR1, HR2 (which will be described later), hr1, hr2, etc. is not particularly limited, and can be calculated by measuring the temperature of the steel sheet with, for example, a radiation thermometer or the like. However, if it is difficult to measure the steel sheet temperatures t0, t1, t2, etc., and it is difficult to accurately estimate the start and end points HR1, HR2, hr1, hr2, etc., these points can be estimated by comparing each thermal profile. during the temperature increase.

[0086]

(3-7. Nitriding treatment step)

After the decarburization annealing, the steel sheet is subjected to a nitriding treatment so that the nitrogen concentration in the steel sheet is 40 ppm or more and 1000 ppm or less. If the nitrogen concentration in the steel sheet after the nitriding treatment is less than 40 ppm, AlN is not sufficiently released in the steel sheet, and AlN does not function as an inhibitor. Therefore, the nitrogen concentration in the steel sheet is set to 40 ppm or more. On the other hand, if the nitrogen concentration in the steel sheet exceeds 1000 ppm, excess AlN is present in the steel sheet even after completion of the secondary recrystallization in the final annealing. Such AlN causes degradation of the magnetic loss. Therefore, the nitrogen concentration in the steel sheet is set to 1000 ppm or less.

[0087]

(3-8. Annealing separator application step)

After the nitriding treatment step, the annealing separator is applied to the surface of the steel sheet. The final annealing described later may be performed in a state where the steel sheet is coiled. If the final annealing is performed in such a state, the roll may be baked to jam and it may be difficult to unwind the roll. Therefore, in the present embodiment, an annealing separator is used so that the roll can be unwound after the final annealing. Here, the main component of the annealing separator is MgO, and the MgO in the annealing separator solid-state reacts with SiO ₂ in the inner oxide layer during final annealing to form forsterite (Mg ₂ SiO ₄ ) and a glass coating.

[0088]

(3-9. Final annealing step)

The final annealing step is an annealing, which is also called a secondary recrystallization annealing step, and is a process for promoting secondary recrystallization of an iron structure. In the final annealing step, the steel sheet is heated to approximately 1200° C., as will be described later. Here, in the heating process, it is preferable that the heating rate of HR2 is 15°C/hour or less in the temperature range of at least 1000°C to 1100°C. In addition, instead of adjusting the heating rate, it is also effective to maintain the temperature in the range of 1000°C to 1100°C for 10 hours or more. Thus, the heating rate in this temperature range is extremely slow. As a result, the preferred growth (secondary recrystallization) of the Goss azimuth grains can be maintained. If the heating rate HR2 is too high (greater than 15°C/hour), crystal grains will grow having a crystal azimuth different from the Goss azimuth. The heating rate in other temperature ranges is not particularly limited, and may be about the same as in conventional finishing annealing.

[0089]

The final annealing step is carried out in a mixed atmosphere of nitrogen and hydrogen. In addition, in the present embodiment, the nitrogen concentration (nitrogen partial pressure) is controlled so that it is gradually lowered during the heating process. Specifically, when the temperature range of 700-900°C is referred to as T2, the temperature range of 800-1000°C is referred to as T3, and the temperature range of 900-1200°C is referred to as T4, the nitrogen partial pressure P0 from room temperature to T2 (T2 or less) is 60-90%, the nitrogen partial pressure P1 from T2 to T3 (greater than T2 and T3 or less) is 40-60%, and the nitrogen partial pressure P2 from T3 to T4 (greater than T3 and T4 or less) is 10-40%. In this case, T2 < T3 < T4 and P0 > P1 > P2. Details will be described later, but by gradually lowering the nitrogen partial pressure in this way, the fixing structure of the glass coating can be developed to a great extent. When T4 is set below 1200°C, the nitrogen partial pressure in the range from T4 to 1200°C is 0% (hydrogen partial pressure is 100%).

[0090]

(3-10. Cleaning annealing step)

In the cleaning annealing step after the final annealing step, the inclusions (AlN, MnS, etc.) used as an inhibitor are neutralized by cleaning after completion of the secondary recrystallization. This makes it possible to reduce hysteresis losses in the final magnetic characteristics. In the cleaning annealing step, for example, it is preferable to hold the steel sheet at 1200° C. for 10 hours or more in a hydrogen atmosphere.

[0091]

(3-11. Cooling stage)

After the cleaning annealing step, the steel sheet is cooled. Here, it is preferable that the cooling rate (rate of temperature decrease) CR in the temperature range (T5) of 1200 to 1000°C is 30 to 100°C/hour. The cooling rate of the CR is more preferably 30-50°C/hour. Although details will be described later, the anchoring structure can be further developed by reducing the cooling rate of the CR.

[0092]

With the above step, a grain-oriented electrical steel sheet according to the present embodiment can be produced. The reason why the grain-oriented electrical steel sheet according to the present embodiment can be produced by each of the above steps is not clear, but the present inventors generally consider the reason as follows.

[0093]

First, during the heating process in the decarburization annealing step, by adjusting the heating rate HR1 in the temperature range t0 to t2 to be 40°C/s or more, an inner oxide layer containing a large amount of SiO ₂ can be formed in parts of the surface layer of the steel sheet before final annealing.

[0094]

Then, in the final annealing step, forsterite (Mg ₂ SiO ₄ ) is formed by solid phase reaction between SiO ₂ in the inner oxide layer and MgO in the annealing separator. The forsterite then accumulates on the surface of the steel sheet, forming a glass coating. As a result, a glass coating is formed on the surface of the steel sheet (base steel sheet). Here, as described above, at the stage of final annealing, the partial pressure of nitrogen is gradually reduced from high partial pressure to low in the temperature range of 700-1200°C. As a result, the MgO in the annealing separator also stably reacts with SiO ₂ present at a deeper position in the inner oxide layer to form forsterite. Thus, the glass coating is embedded in a part of the surface layer of the base steel sheet, and a reinforcing structure is formed. In addition, the anchoring structure develops as the resulting forsterite undergoes Ostwald growth. In particular, the three-dimensional network structure of the anchoring structure becomes more complex, and the branches constituting the anchoring structure become thicker.

[0095]

On the other hand, at a temperature of about 1000° C. or higher, N is separated while AlN, which is an inhibitor in the base steel sheet, floats towards the glass cover. Thereafter, Al reaching the end of the anchor structure reacts with forsterite in the anchor structure to form Al inclusions (MgAl ₂ O ₄ etc.). These Al inclusions are captured by the anchoring structure and held there. In addition, in the cooling step, by adjusting the cooling rate of CR in the temperature range (T5) of 1200 to 1000°C in the range of 30 to 100°C/hour, Ostwald growth of Al inclusions constituting the anchoring structure is promoted, and the anchoring structure is further developed. In this case, the branches of Al inclusions become more complicated and thicker. Al inclusions abundantly distributed in this anchoring structure correspond to the second peak of the Al concentration profile. A large part of the Al separated from AlN, which is an inhibitor in the base steel sheet, forms Al inclusions in the anchor structure, but a portion of the separated Al reaches the portion of the glass coating other than the anchor structure, that is, the cap portion, and Al inclusions are formed in the cap portion of the glass coatings. The Al inclusions present in this glass coating correspond to the first peak of the Al concentration profile. Therefore, the second peak corresponding to the Al inclusions of the anchor structure is larger than the first peak corresponding to the Al inclusions of the glass coating. Thus, the Al inclusions grow in the fixing structure and develop in the surface layer part of the base steel sheet, so that the mathematical formula (1) is satisfied. Fig. 2 and 3 show an example in which the anchoring structure is developed (that is, the mathematical formula (1) is satisfied), and FIG. 4 shows an example in which the anchoring structure is not developed (that is, the mathematical formula (1) is not satisfied).

[0096]

The lower the cooling rate CR, the more the anchoring structure develops. Thus, the lower the cooling rate of CR, the higher the frequency of inclusions of Al, and as a result, it reaches 50 pieces/mm or more.

[0097]

After performing each of the above steps, an insulating film coating step and a magnetic domain driving step can be further performed.

[0098]

(3-12. Coating with insulating film)

The surface of the steel sheet after the cooling step is covered with an insulating film, which is then baked. The type of the insulating film is not particularly limited, and any conventionally known insulating film is suitable for the grain oriented electrical steel sheet of the present embodiment. Examples of the insulating film include a film formed by applying an aqueous film-forming solution containing a phosphate salt and colloidal silica. In this case, examples of the phosphate salt include phosphates such as Ca, Al, and Sr phosphates. Of these, aluminum phosphate is more preferred. The colloidal silica is not particularly limited, and its particle size can be suitably determined. A particularly preferred particle size (average particle size) is 200 nm or less. Even if the particle size is less than 100 nm, there is no difficulty in dispersion, but the production costs increase, which may not be realistic. If the particle size exceeds 200 nm, they may settle in the coating liquid.

[0099]

It is preferable to apply the insulating film coating liquid to the surface of the steel sheet by a wet coating method such as using a roller coater, and bake it in an air atmosphere at 800-900°C for 10-60 seconds to form an insulating film. tension film.

[0100]

(3-13. Magnetic domain control stage)

The specific processing method for the magnetic domain driving step is not particularly limited, and lower magnetic loss can be obtained by magnetic domain driving such as laser irradiation, electron beam, etching, or a groove forming method using gears (knurling). As described above, the magnetic loss is greatly improved in the grain-oriented electrical steel sheet according to the present embodiment even before the magnetic domains are controlled. Therefore, even if heat-resistant magnetic domain driving is performed in which a sufficient magnetic loss reduction effect is unlikely to be achieved, the magnetic loss reduction effect can be sufficiently obtained.

EXAMPLES

[0101]

Next, examples of the present invention will be described. The conditions in the following examples are examples of conditions used to confirm the feasibility and effects of the present invention, and the present invention is not limited to these example conditions. The present invention may use various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

[0102]

<1. Example 1>

In Example 1, a steel slab having the component composition shown in Table 1 was heated to 1150°C and then hot rolled to obtain a hot rolled sheet with a thickness of 2.6 mm. Then, the hot rolled sheet was subjected to hot annealing at a first stage temperature of 1100°C and a second stage temperature of 900°C. Then, the hot-rolled sheet was cold-rolled one or more times with intermediate annealing in between to obtain a cold-rolled sheet having a final thickness of 0.23 mm.

[0103]

[Table 1] Steel No. Chemical components (wt.%) C Si Mn Al N S Other Example according to the invention A1 0.0021 3.45 0.080 0.010 0.0031 0.0012 A2 0.0032 3.33 0.150 0.012 0.0020 0.0013 Cu 0.02 A3 0.0034 2.55 0.190 0.011 0.0016 0.0008 Cr 0.1 A4 0.0022 2.90 0.090 0.011 0.0017 0.0009 P 0.0125 A5 0.0028 3.50 0.090 0.060 0.0018 0.0011 Ni 0.1 A6 0.0076 3.95 0.080 0.041 0.0018 0.0019 A7 0.0034 3.30 0.080 0.020 0.0021 0.0012 Bi 0.001 A8 0.0021 3.10 0.120 0.028 0.0009 0.0017 A9 0.0019 3.12 0.100 0.018 0.0011 0.0012 B 0.001 A10 0.0023 3.30 0.250 0.011 0.0019 0.0013 A11 0.0025 3.45 0.150 0.051 0.0021 0.0011 A12 0.0023 3.40 0.120 0.045 0.0032 0.0012 Mo 0.05 A13 0.0022 3.80 0.500 0.035 0.0031 0.0011 A14 0.0020 3.40 0.150 0.038 0.0039 0.0031 A15 0.0030 3.40 0.180 0.021 0.0012 0.0095 Cu 0.2 A16 0.0031 3.30 0.190 0.011 0.0011 0.0028 A17 0.0023 3.60 0.100 0.010 0.0011 0.0027 Comparative Example a1 0.1200 3.35 0.12 0.021 0.0022 0.0023 a2 0.0022 3.35 2.50 0.011 0.0018 0.0032 Bi 0.001 a3 0.0012 3.00 0.03 0.011 0.0018 0.0031 a4 0.0013 3.25 0.15 0.125 0.0015 0.0030 a5 0.0021 3.10 0.07 0.001 0.0022 0.0045 a6 0.0021 3.20 0.08 0.021 0.0150 0.0065 Cu 0.2 a7 0.0015 3.34 0.12 0.025 0.0021 0.0200 a8 0.0031 6.50 0.09 0.023 0.0022 0.0021 P0.025 a9 0.0032 1.20 0.12 0.033 0.0017 0.0032

[0104]

Then, the cold-rolled sheet having a final thickness of 0.23 mm was subjected to decarburization annealing and nitriding (annealing to increase the amount of nitrogen in the steel sheet). The heating rate HR1 during decarburization annealing was set to 100°C/s. A radiant tube was used for heating. The t0 value was 550°C and the t2 value was 840°C. In the holding temperature range, temperature t2 was maintained for 100 s. The nitrogen concentration was 200-2500 ppm, and the analysis was performed by the method described in JIS G 1228.

[0105]

Thereafter, an annealing separator containing magnesium oxide (MgO) as a main component was deposited on the surface of the steel sheet, and final annealing was performed. In the final annealing step, the steel sheet was heated to 1200°C. The heating rate in the temperature range 1000-1100°C was set to 10°C/hour. In addition, with regard to the annealing atmosphere, the nitrogen partial pressure P0 up to 800°C (up to T2) was 80%, the nitrogen partial pressure P1 up to 1000°C (up to T3) was 50%, and the nitrogen partial pressure P2 up to 1200°C ( to T4) was set at 20%. However, the annealing atmosphere of Comparative Examples b10 and b11 was an atmosphere to be described later. Purification was carried out at 1200°C for 10 hours.

[0106]

In the subsequent cooling step, the steel sheet was cooled at a cooling rate CR of 60°C/hour in a temperature range (T5) of 1200°C to 1000°C. However, the cooling rate CR of Comparative Examples b12 and b13 was set to a value to be described later. A grain-oriented electrical steel sheet was produced by the steps described above.

[0107]

Then, the oxygen concentration in the grain-oriented electrical steel sheet was measured, and the Al concentration profile was further measured by GDS. The oxygen concentration was analyzed by the method described in JIS G 1239. The output power of the GDS was set to 35 W and data was acquired at 0.01 second intervals. The results are shown in Table 2.

[0108]

Then, an aqueous coating liquid composed of a phosphate salt and colloidal silica was applied to this steel sheet, and the steel sheet was baked in air at 800°C for 60 seconds. As a result, a tension insulating film was formed on the surface of the steel sheet (more specifically, on the surface of the glass cover). Then, magnetic loss W _17/50 (energy loss measured under excitation conditions of 1.7 T and 50 Hz) was measured in a grain-oriented electrical steel sheet on which an insulating film was applied under tension. The measurements were performed in accordance with JIS C 2550. The results are shown in Table 2.

[0109]

[Table 2] No. Steel No. Oxygen concentration of glass coating film and base steel sheet (ppm) Al peak intensity ratio determined by GDS
I _{Al_1} /I _{Al_2} Magnetic properties Comments Magnetic loss W17/50 (W/kg) Example according to the invention B1 A1 2102 0.8 0.82 B2 A2 2322 0.5 0.81 B3 A3 1988 0.6 0.79 B4 A4 1978 0.9 0.81 B5 A5 1965 0.7 0.82 B6 A6 1988 0.5 0.80 B7 A7 1899 0.4 0.81 B8 A8 1789 0.7 0.78 B9 A9 2103 0.9 0.79 B10 A10 2122 0.7 0.80 B11 A11 2133 0.8 0.82 B12 A12 2100 0.5 0.83 B13 A13 2187 0.6 0.82 B14 A14 1999 0.5 0.79 B15 A15 1989 0.5 0.78 B16 A16 2102 0.5 0.82 B17 A17 2018 0.6 0.78 Comparative Example b1 a1 2009 0.5 1.85 Without secondary recrystallization b2 a2 2678 1.1 2.02 Without secondary recrystallization b3 a3 1798 0.7 0.95 Magnetic losses X b4 a4 1980 0.9 1.35 Without secondary recrystallization b5 a5 1887 5 1.65 Without secondary recrystallization b6 a6 1909 2 0.98 Magnetic losses X b7 a7 2198 0.6 0.99 Magnetic losses X b8 a8 - - - Rolling termination b9 a9 2878 1.1 0.96 Magnetic losses X b10 A1 2872 0.9 0.88 b11 A5 2677 1.1 0.89 b12 A7 2532 1.2 0.88 b13 A8 1899 1.3 0.87

[0110]

In Inventive Examples B1 to B17 of the grain-oriented electrical steel sheet according to the present embodiment, which satisfies all requirements (component composition, oxygen concentration, and formula (1) regarding Al concentration profile), a magnetic loss of 0.85 W/kg or less, indicating good magnetic properties.

[0111]

On the other hand, in Comparative Examples b1, b2, b4 and b5, since steel slabs in which the content of some components was outside the range of the present embodiment were used, secondary recrystallization did not occur and their magnetic loss exceeded 1.0 W/kg, t .e. were bad. In Comparative Examples b3 and b9, since steel slabs in which the content of some components was below the range of the present embodiment were used, their intrinsic resistance was small and their magnetic loss was 0.9 W/kg or more, i. were bad. In Comparative Examples b6 and b7, since steel slabs in which the content of some components exceeded the range of the present embodiment were used, impurities remained in the slabs and their magnetic loss was 0.9 W/kg or more, i. were bad. In Comparative Example b8, since a steel slab in which the content of some components was outside the range of the present embodiment was used, the steel sheet became brittle after reheating, and rolling had to be stopped. In Comparative Examples b10 and b11, the nitrogen partial pressure P0 to 800°C (to T2) was 50%, the nitrogen partial pressure P1 to 1000°C (to T3) was 50%, and the nitrogen partial pressure P2 to 1200°C (to T4 ) was 50% relative to the final annealing atmosphere. Thus, the partial pressure of nitrogen was kept constant. Therefore, the fixing structure of the glass coating did not develop, and the magnetic loss exceeded 0.85 W/kg, i.e. were bad. In Comparative Examples b12 and b13, the cooling rate of CR in the temperature range (T5) from 1200°C to 1000°C was set to 150°C/hour in the cooling step after the final annealing. Therefore, the anchoring structure of the glass coating, in particular the Al inclusion, did not develop, and the magnetic loss exceeded 0.85 W/kg, i.e. were bad.

[0112]

<2. Example 2>

In Example 2, a steel slab having a composition shown in Table 1 was heated to 1150°C and then hot rolled to obtain a hot-rolled steel sheet with a thickness of 2.6 mm. Then, the hot rolled sheet was subjected to hot annealing at a first stage temperature of 1100°C and a second stage temperature of 900°C. Then, the hot-rolled sheet was cold-rolled one or more times with intermediate annealing in between to obtain a cold-rolled sheet having a final thickness of 0.23 mm.

[0113]

Then, the cold-rolled steel sheet having a final thickness of 0.23 mm was subjected to decarburization annealing and nitriding (annealing to increase the amount of nitrogen in the steel sheet). The heating rate HR during decarburization annealing was 100°C/s. A radiant tube was used for heating. The t0 value was 580°C and the t2 value was 860°C. In the holding temperature range, temperature t2 was maintained for 120 s. The nitrogen concentration was 220-260 ppm, and the analysis was performed by the method described in JIS G 1228.

[0114]

Thereafter, an annealing separator containing magnesium oxide (MgO) as a main component was deposited on the surface of the steel sheet, and final annealing was performed. In the final annealing step, the steel sheet was heated to 1200°C. The heating rate in the temperature range 1000-1100°C was set to 10°C/hour. Here, the annealing atmosphere and the cooling rate of CR in the subsequent cooling step were different for each of the examples of the present invention. In particular, with regard to the annealing atmosphere of Examples of the present invention C1 to C3 (see Table 3), the nitrogen partial pressure P0 up to 800°C (up to T2) was set to 90%, the nitrogen partial pressure P1 up to 1000°C (up to T3 ) was set to 60% and the nitrogen partial pressure P2 up to 1200° C. (up to T4) was set to 30%. In the subsequent cooling step, the cooling rate of CR in the temperature range (T5) from 1200°C to 1000°C was set to 100°C/hour.

[0115]

On the other hand, with regard to the annealing atmosphere of Examples of the present invention C4 to C17 (see Table 3), the nitrogen partial pressure P0 up to 800°C (up to T2) was set to 75%, the nitrogen partial pressure P1 up to 1000°C (up to T3) was set to 50% and the nitrogen partial pressure P2 up to 1200° C. (up to T4) was set to 30%. In addition, the cooling rate of the CR in the temperature range (T5) from 1200°C to 1000°C was set to 40°C/hour.

[0116]

Thereafter, the oxygen concentration in the grain-oriented electrical steel sheet was measured in the same manner as in Example 1, and the Al concentration profile was further measured by GDS. The oxygen concentration was analyzed by the method described in JIS G 1239. In addition, in Example 2, a section of a grain-oriented electrical steel sheet was also observed. Specifically, in a vertical section parallel to the rolling direction of a part of the surface layer of the base steel sheet, the area from the surface of the glass coating to a depth of 10 µm, i. e. the observation area was photographed using an optical microscope. The magnification at the time of photography was 400x and 10 images were taken for each sample. Then, the composition of the region of interest in each image was analyzed using SEM-EDS. By measuring the frequency of Al inclusions (frequency of inclusions in the rolling direction) having an area-equivalent circle diameter of 1 μm or more in each of these 10 images and arithmetic averaging them, the frequency of Al inclusions (numerical frequency) in each sample was calculated. The results are shown in Table 3.

[0117]

Then, an aqueous coating liquid composed of a phosphate salt and colloidal silica was applied to this steel sheet, and the steel sheet was baked in air at 800°C for 60 seconds. As a result, a tension insulating film was formed on the surface of the steel sheet (more specifically, on the surface of the glass cover). Then, magnetic loss W _17/50 (energy loss measured under excitation conditions of 1.7 T and 50 Hz) was measured in a grain-oriented electrical steel sheet on which an insulating film was applied under tension. The measurement was performed in accordance with JIS C 2550. The results are shown in Table 3.

[0118]

[Table 3] No. Steel No. Oxygen concentration of glass coating film and base steel sheet (ppm) Al peak intensity ratio determined by GDS
I _{Al_1} /I _{Al_2} Inclusions Magnetic properties Presence of Al yes/no Numerical frequency (pcs/mm) Magnetic loss W17/50 (W/kg) Example according to the invention C1 A1 2201 0.8 Yes 38 0.83 C2 A2 2098 0.4 Yes 49 0.84 C3 A3 2187 0.6 Yes 48 0.83 C4 A4 1998 0.8 Yes 70 0.79 C5 A5 1987 0.7 Yes 52 0.80 C6 A6 2019 0.5 Yes 65 0.78 C7 A7 2032 0.5 Yes 88 0.79 C8 A8 1887 0.7 Yes 91 0.76 C9 A9 1987 0.9 Yes 89 0.77 C10 A10 1987 0.8 Yes 89 0.78 C11 A11 2298 0.8 Yes 98 0.80 C12 A12 2090 0.9 Yes 56 0.80 C13 A13 2187 0.6 Yes 67 0.80 C14 A14 2301 0.7 Yes 76 0.77 G15 A15 1898 0.5 Yes 77 0.76 C16 A16 1898 0.8 Yes 71 0.80 C17 A17 1798 0.6 Yes 77 0.76

[0119]

The magnetic loss of Examples C4 to C17 of the present invention, satisfying the condition of Al inclusion frequency of 50 pcs/mm or more, was 0.80 W/kg or less, which is better than Examples C1 to C3 of the present invention having Al inclusion frequency less than 50 pcs/mm. Since the cooling rates in Examples C4 to C17 of the present invention were lower than the cooling rates in Examples C1 to C3, this result is believed to have been obtained.

[0120]

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to these examples. A person skilled in the art will easily be able to make various changes or corrections within the technical ideas described in the claims. It should be understood that these changes or corrections are naturally also within the technical scope of the present invention.

EXPLANATION OF REFERENCE NUMBERS

[0121]

1: First Al peak

2: Al second peak

a: Glass coating (Mg ₂ SiO ₄ )

b: Al inclusions

c: Main steel sheet

Claims (9)

1. Grain-oriented electrical steel sheet, comprising: main steel sheet; And a glass coating formed on the surface of the base steel sheet and having a cover portion and a fixing structure included in the base steel sheet, characterized in that the main steel sheet includes as a chemical composition in wt%: 0.010 or less C, 2.00 to 4.00 Si, 0.05 to 1.00 Mn, 0.010 to 0.065 or less Al, 0.004 or less N and 0.010 or less S, with the remainder of Fe and impurities; the oxygen concentration in the glass coating and the base steel sheet is 2500 ppm or less; And the Al concentration profile obtained by glow discharge optical emission spectrometry (GDS) has at least two peaks, wherein the first peak having intensity I _{Al_1} of the first Al peak is obtained from Al inclusions in the capping portion of the glass coating, and the second peak having intensity I _{Al_2} of the second Al peak is obtained from Al inclusions in the fixing structure of the glass coating, wherein the intensity of each of the peaks defined as the maximum intensity of the Al peak in the coating part and in the fixing structure when the relation is fulfilled: I _{Al_1} <I _{Al_2} expression (1). 2. The grain-oriented electrical steel sheet according to Claim. 1, characterized in that in the vertical section of a part of the surface layer of the base steel sheet, parallel to the rolling direction, the area within the range from the surface of the glass coating to a depth of 10 μm in the direction to the center of the thickness of the sheet contains aluminum-containing inclusions having an area-equivalent circle diameter of 1 μm or more and scattered in the rolling direction at an average frequency of 50 pcs/mm or more.

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