JP7368688B2 - grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a grain-oriented electrical steel sheet suitable as a core material for a transformer, and in particular, an intermediate coating other than a forsterite coating between a tension insulation coating and a base steel plate, and which improves the adhesion of the tension insulation coating. The present invention relates to a grain-oriented electrical steel sheet having an intermediate coating that can be enhanced.

A grain-oriented electrical steel sheet suitable as a core material for a transformer generally contains 7% by mass or less of Si and is made so that the crystal orientation of each crystal grain matches the {110}<001> orientation called the Goss orientation. The base steel plate has a controlled texture, and an insulating coating for imparting insulation to the base steel plate. In such grain-oriented electrical steel sheets, the orientation of crystal grains is generally controlled using a grain growth phenomenon called secondary recrystallization so that the crystal orientation matches the Goss orientation.

The magnetic properties of grain-oriented electrical steel sheets require high magnetic flux density in the rolling direction and low iron loss. In recent years, from the viewpoint of energy conservation, there has been an increasing demand for reducing power loss, that is, reducing iron loss. Generally, the B ₈ value is used as an index for evaluating magnetic flux density, and the W _17/50 value is used as an index for evaluating iron loss.

It has been known that applying tension to a base steel plate is effective in reducing iron loss. As a method for imparting tension to a base steel plate, a method is known in which a coating having a coefficient of thermal expansion smaller than that of the base steel plate is formed between the base steel plate and an insulating coating at a high temperature. For example, in the final annealing process of the base steel plate, a forsterite film produced when oxides present on the surface of the base steel plate react with an annealing separator can impart tension to the base steel plate. Since there are irregularities at the interface between this forsterite-based coating and the base steel plate, the anchor effect caused by these irregularities allows the forsterite-based coating to also function as an intermediate coating that increases the adhesion between the insulating coating and the base steel plate. do.

The method disclosed in Patent Document 20, in which an insulating film is formed by baking a coating liquid mainly composed of colloidal silica and phosphate, has a large effect of applying tension to the base steel plate and is effective in reducing iron loss. It is. Therefore, a common method for manufacturing grain-oriented electrical steel sheets is to leave the forsterite-based film produced in the final annealing step and then apply an insulating coating mainly composed of phosphate. In this specification, an insulating coating that can provide not only insulation but also tension to the base steel plate is referred to as a tension insulating coating.

On the other hand, in recent years, it has become clear that forsterite-based coatings inhibit the movement of domain walls and have an adverse effect on iron loss. In grain-oriented electrical steel sheets, magnetic domains change with movement of domain walls under an alternating magnetic field. Smooth movement of this domain wall is effective in improving iron loss, but the presence of unevenness at the interface between the forsterite coating and the base steel plate prevents the movement of the domain wall. As a result, it was found that the effect of improving iron loss by applying tension was canceled and a sufficient effect of improving iron loss could not be obtained.

In order to prevent the movement of the domain wall from being inhibited, it is effective to reduce the anchoring effect due to the unevenness existing at the interface between the forsterite coating and the base steel plate. Naturally, unless a forsterite film is formed, the anchor effect can be completely eliminated.

As a method for reducing the anchor effect, for example, Patent Documents 1 to 19 disclose that by controlling the dew point of the decarburization annealing atmosphere, Fe-based oxidation is It is disclosed that the surface of the base steel sheet after finish annealing is smoothed by not producing any substances (Fe ₂ SiO ₄ , FeO, etc.) and by using a substance such as alumina that does not react with silica as an annealing separator. ing.

When a tension insulation coating is formed on a forsterite coating, the adhesion of the tension insulation coating is improved due to the anchor effect of the forsterite coating. When a forsterite-based film is not present on the surface of the base steel sheet, such as when a forsterite-based film is removed or a forsterite-based film is not intentionally formed in the final annealing process, the domain wall Since the unevenness that inhibits movement disappears from the surface of the base steel plate, iron loss can be improved. However, in this case, since the tension insulation coating is directly formed on the surface of the base steel plate, there is a problem that the adhesion of the tension insulation coating decreases.

The forsterite-based coating itself can apply tension to the base steel sheet, but in the absence of the forsterite-based coating, the required tension to be applied to the base steel sheet can be secured with only the tension insulating coating. There is a need. Therefore, it is necessary to thicken the tension insulation coating, but as a result, stress will be concentrated at the interface between the base steel plate and the tension insulation coating, so the adhesion of the tension insulation coating must be improved. , there is a need to further improve this.

With conventional insulation coating formation methods, it is difficult to achieve coating tension that can fully bring out the effect of mirror-finishing the surface of the base steel plate, and to ensure sufficient adhesion of the insulation coating. However, it has not been possible to sufficiently reduce the iron loss of magnetic steel sheets. Therefore, as a technique to ensure the adhesion of the tension insulation coating, there is a method of forming a very thin oxide film on the surface of the base steel plate after finish annealing before forming the tension insulation coating on the surface of the base steel plate. For example, it was proposed in Patent Documents 20 to 29.

For example, in Patent Document 22, a base steel plate is annealed in a specific atmosphere at each temperature after finish annealing, which is obtained through a process of mirror-finishing the surface of the base steel plate or preparing it to a state close to a mirror surface. A technique has been proposed in which an external oxidation-type oxide film is formed on the surface of the base steel plate by applying this process, and this oxide film ensures adhesion between the tension insulation coating and the base steel plate.

Patent Document 23 discloses that when the tension insulation coating is crystalline, a base coating of an amorphous oxide is applied to the surface of the base steel plate after finish annealing where no inorganic mineral coating (forsterite coating) is present. A technique has been proposed to prevent oxidation of the base steel sheet, that is, a decrease in specularity, which occurs when forming a crystalline tensile insulating film.

Patent Document 25 proposes a technique in which an external oxidation type oxide film is formed on the surface of a base steel plate, and granular oxides are formed inside the oxide film to improve the adhesion of a tension insulation coating. Patent Document 26 discloses that a silica external oxide film containing oxides of Fe, Al, Mn, Ti, and Cr with a cross-sectional area ratio of 50% or less is formed on the surface of a base steel plate, and the adhesion of the tension insulation coating is improved. Techniques have been proposed to improve this.

It is well known that there are laminated cores and wound cores as transformer cores, but in recent years, there has been a demand for even higher efficiency, particularly in transformers manufactured using wound cores. Therefore, in addition to reducing core loss, grain-oriented electrical steel sheets for wound cores are strongly required to improve the adhesion of the tension insulation coating when plastically working grain-oriented electrical steel sheets into curved shapes during the manufacturing of wound cores. Therefore, there is a strong demand for improving the adhesion of the tension insulation coating in grain-oriented electrical steel sheets that do not have a forsterite coating.

However, it has been found that even if the conventional technology is applied to a grain-oriented electrical steel sheet that does not have a forsterite coating, sufficient adhesion of the tension insulating coating cannot be ensured during the manufacture of the wound core. This is due to changes in the manufacturing method of wound cores, which have resulted in smaller bending diameters in the plastic working (core processing) of grain-oriented electrical steel sheets, which require severe plastic working for grain-oriented electrical steel sheets. This is because peeling occurs.

In addition, wound cores are manufactured by bending a grain-oriented electrical steel sheet with a fixed radius of curvature and sequentially winding the grain-oriented electrical steel sheet around the outside of the bent portion, but simply bending the sheet may cause the coating to peel off. It has been found that even in cases where there is no coating, peeling occurs due to the superposition of frictional forces between the steel plates that occur during the process of winding the grain-oriented electrical steel sheets. The peeling of the coating due to the superimposition of the frictional force is a peeling phenomenon that could not be detected in conventional evaluations of the adhesion of tension insulation coatings, and there is an increasing need to suppress the peeling of the coating. In this specification, the adhesion of the tension insulation coating to the base steel plate is abbreviated as coating adhesion.

Japanese Unexamined Patent Publication No. 64-062417 Japanese Patent Application Publication No. 07-118750 Japanese Patent Application Publication No. 07-278668 Japanese Patent Application Publication No. 07-278669 Japanese Patent Application Publication No. 07-278670 Japanese Patent Application Publication No. 10-046252 Japanese Patent Application Publication No. 11-106827 Japanese Patent Application Publication No. 11-152517 Japanese Patent Application Publication No. 2002-060843 Japanese Patent Application Publication No. 2002-173715 Japanese Patent Application Publication No. 2002-348613 Japanese Patent Application Publication No. 2002-363646 Japanese Patent Application Publication No. 2003-055717 JP2003-003213A JP2003-041320A Japanese Patent Application Publication No. 2003-247021 Japanese Patent Application Publication No. 2003-247024 Japanese Patent Application Publication No. 2008-001980 Special Publication No. 2011-518253 Japanese Unexamined Patent Publication No. 48-039338 Japanese Unexamined Patent Publication No. 1983-131976 Japanese Patent Application Publication No. 06-184762 Japanese Patent Application Publication No. 07-278833 Japanese Patent Application Publication No. 09-078252 Japanese Patent Application Publication No. 2002-322566 Japanese Patent Application Publication No. 2002-348643 Japanese Patent Application Publication No. 2002-363763 Japanese Patent Application Publication No. 2003-293149 Japanese Patent Application Publication No. 2003-313644

In order to reduce iron loss, the formation of a forsterite film is intentionally suppressed, the forsterite film is removed by grinding, pickling, etc., and the base material steel sheet is smoothed to a mirror-like surface. When a tension insulating film is formed on the surface of the wound core, the tension insulating film has a high degree of film adhesion at the bending part, which is necessary when manufacturing the wound core, and a high level of film adhesion in the environment where frictional forces are superimposed after the bending process. Although adhesion is required, it is difficult to achieve the high degree of film adhesion required for grain-oriented electrical steel sheets using conventional techniques.

The present invention has been made in view of the above circumstances, and includes an intermediate coating other than a forsterite coating between the tension insulating coating and the base steel plate, which is capable of increasing coating adhesion. The purpose is to provide grain-oriented electrical steel sheets. That is, an object of the present invention is to provide a grain-oriented electrical steel sheet having excellent film adhesion and magnetic properties.

In order to solve the above-mentioned problems, the present inventors have proposed that the intermediate coating sandwiched between the tension insulation coating and the base steel plate be a coating other than a forsterite coating and that can improve coating adhesion. We conducted extensive research on the chemical composition and structure of films that meet the requirements of being a film.

As a result, the present inventors found that when the external oxide film mainly composed of silicon oxide disclosed in prior art documents (for example, Patent Documents 22, 25, etc.) is formed on the surface of the base steel sheet, the external oxide film is Only when a region containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ is included to meet specific conditions, the adhesion of the tensile insulation film formed on the external oxide film will be significantly improved. I found out what to do. Specifically, in the external oxide film, regions containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ exist intermittently in contact with the interface between the base steel plate and the external oxide film, and Under the condition that the region is included in a region containing silicon oxide, the adhesion of the tension insulation coating is significantly improved.

The present inventors have explained the reason why the adhesion of the tension insulation coating is improved by using an external oxide film that satisfies the above specific conditions as an intermediate coating between the base steel plate and the tension insulation coating as follows. I considered it as follows.
That is, when an external oxide film (oxide film mainly composed of silicon oxide) that does not have a region containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ as described above is used as an intermediate film, the external oxide film Since the lattice matching between the steel plate and the base steel plate is good, it is considered that the adhesion of the tension insulation coating is good. However, since silicon oxide has a high elastic modulus, during the manufacturing process of the wound core or other excessive plastic working processes, the frictional force applied to the tension insulation coating is concentrated at the interface between the base steel plate and the external oxide film. Conceivable. As a result, the above-mentioned lattice matching is inhibited, and it is thought that the adhesion of the tension insulating film is reduced.
On the other hand, a region containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ exists inside the external oxide film in a form that is intermittently in contact with the surface of the base steel sheet (the interface between the external oxide film and the base steel sheet). In this case, this region, that is, the iron-based oxide containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ functions as a buffer to alleviate the frictional force, thereby reducing the tension insulating coating caused by the frictional force. It is thought that the peeling of the tensile insulation coating is suppressed, and as a result, the adhesion of the tension insulation coating is improved.

The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) A grain-oriented electrical steel sheet according to one aspect of the present invention includes a base steel plate, a tension insulation coating, and an intermediate coating sandwiched between the base steel plate and the tension insulation coating. The base steel plate has a chemical composition, in mass %, of C: 0.100% or less, Si: 0.80 to 7.00%, Mn: 1.00% or less, and acid-soluble Al: 0.010 to 0. .070%, S: 0.080% or less, N: 0.012% or less, B: 0 to 0.010%, Sn: 0 to 0.20%, Cr: 0 to 0.50%, Cu: 0 ~0.50%, with the remainder consisting of Fe and impurities. The intermediate coating is a coating other than a forsterite coating, and has a first region that is intermittently in contact with the interface between the base steel plate and the intermediate coating, and a second region that includes the first region. . The first region contains at least one of Fe ₂ SiO ₄ and FeSiO ₃ , and the second region contains silicon oxide, and has a cross section having a length Lsum in a direction perpendicular to the rolling direction of the base steel plate. If ΣL is the total length of the first region that appears in the cross section and touches the interface, then the abundance ratio R of the first region defined by the following equation (1) is 1%. The average thickness of the intermediate coating is 10 to 100 nm, and the average thickness of the first region in the thickness direction of the intermediate coating is 1 to 20 nm.

( 2 ) In the grain-oriented electrical steel sheet according to (1) above, at least one of the Fe ₂ SiO ₄ and the FeSiO ₃ may be crystalline.

( 3 ) In the grain-oriented electrical steel sheet according to (1) or (2) above, the base steel sheet has the chemical composition, in mass %, of B: 0.001 to 0.010%, Sn: 0. 01 to 0.20%, Cr: 0.01 to 0.50%, and Cu: 0.01 to 0.50%.

According to the above aspect of the present invention, a grain-oriented electrical steel sheet is provided which has an intermediate coating other than a forsterite coating between the tension insulating coating and the base steel sheet and which is capable of increasing coating adhesion. can be provided. That is, according to the above aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet having excellent film adhesion and magnetic properties.

1 is a diagram schematically showing a cross section of a main part of a grain-oriented electrical steel sheet 1 according to an embodiment of the present invention. It is a figure which shows the aspect which evaluates the adhesion of the tension insulation coating which loaded the frictional force.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing a cross section of a main part of a grain-oriented electrical steel sheet 1 according to the present embodiment. As shown in FIG. 1, the grain-oriented electrical steel sheet 1 according to the present embodiment includes a base steel sheet 10, an intermediate coating 20, and a tension insulation coating 30. Note that FIG. 1 is a view of the grain-oriented electrical steel sheet 1 in a cross section having a length Lsum in a direction orthogonal to the rolling direction of the base steel sheet 10.

[Description of base material steel plate 10]
The base steel plate 10 is a steel plate that serves as the base material of the grain-oriented electrical steel sheet 1, and has a texture controlled so that the crystal orientation of each crystal grain matches the {110}<001> orientation called the Goss orientation. . The base steel plate 10 has a chemical composition in mass %: C: 0.100% or less, Si: 0.80 to 7.00%, Mn: 1.00% or less, acid-soluble Al: 0.010 to 0. .070%, S: 0.080% or less, N: 0.012% or less, B: 0 to 0.010%, Sn: 0 to 0.20%, Cr: 0 to 0.50%, Cu: 0 ~0.50%, with the remainder consisting of Fe and impurities.

Hereinafter, the chemical composition of the base steel plate 10 will be explained in detail. In the following description, % in the component composition means mass %.

<C: 0.100% or less>
C is an element effective in controlling primary recrystallization, but because it increases core loss due to magnetic aging, it is an element that is removed by decarburization annealing before final annealing. If the C content exceeds 0.100%, the steel undergoes phase transformation during finish annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained. 0.100% or less.

Since the smaller the C content, the better from the viewpoint of reducing iron loss, the C content is preferably 0.045% or less, more preferably 0.038% or less. The lower limit of C content includes 0%, but the detection limit of C content is about 0.0001%, and if the C content is reduced to less than 0.0001%, the manufacturing cost will increase significantly. In practice, 0.0001% is the lower limit of the substantial C content.

<Si: 0.80-7.00%>
Si is an element that increases the electrical resistance of the base steel plate 10 and contributes to reducing iron loss. If the Si content is less than 0.80%, the steel undergoes phase transformation during final annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained. The amount shall be 0.80% or more. A preferable value of the Si content is 2.50% or more, and a more preferable value of the Si content is 3.00% or more.

On the other hand, if the Si content exceeds 7.00%, the base steel plate 10 will become brittle and the passability in the manufacturing process will be significantly deteriorated, so the Si content should be 7.00% or less. A preferable value of the Si content is 4.50% or less, and a more preferable value of the Si content is 4.00% or less.

<Acid-soluble Al: 0.010 to 0.070%>
Acid-soluble Al (sol.Al) is an element that combines with N to generate (Al, Si)N that functions as an inhibitor and contributes to the progress of secondary recrystallization in final annealing.

If the acid-soluble Al content is less than 0.010%, the addition effect will not be sufficiently expressed, secondary recrystallization will not proceed sufficiently, and iron loss characteristics will not improve, so the acid-soluble Al content will be 0. .010% or more. A preferable value of the acid-soluble Al content is 0.015% or more, and a more preferable value of the acid-soluble Al content is 0.020% or more.

On the other hand, if the acid-soluble Al content exceeds 0.070%, the base steel plate 10 becomes embrittled, and the embrittlement of the base steel plate 10 becomes particularly noticeable in the grain-oriented electrical steel sheet 1 with a high Si content. , the acid-soluble Al content is 0.070% or less. A preferable value of the acid-soluble Al content is 0.050% or less, and a more preferable value of the acid-soluble Al content is 0.040% or less.

<N: 0.012% or less>
N is an element that combines with Al to form AlN that functions as an inhibitor, but on the other hand, it is also an element that forms blisters (holes) inside the base steel sheet 10 during cold rolling.

If the N content exceeds 0.012%, blisters (holes) will occur inside the base steel sheet 10 during cold rolling, and the strength of the base steel sheet 10 will increase, resulting in poor threadability during manufacturing. Since this causes deterioration, the N content is set to 0.012% or less. A preferable value of the N content is 0.010% or less, and a more preferable value of the N content is 0.009% or less.

On the other hand, in order for N and Al to combine to form AlN that functions as an inhibitor, the N content is preferably 0.004% or more. A more preferable value of the N content is 0.006% or more.

<Mn: 1.00% or less>
Mn is an austenite-forming element that prevents cracking during hot rolling and combines with at least one of S and Se to form MnS, which functions as an inhibitor.

If the Mn content exceeds 1.00%, the steel undergoes phase transformation during secondary recrystallization during finish annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained. , the Mn content is 1.00% or less. A preferable value of the Mn content is 0.70% or less, and a more preferable value of the Mn content is 0.40% or less.

MnS can be used as an inhibitor during secondary recrystallization, but when AlN is used as an inhibitor, MnS is not essential, so the lower limit of the Mn content includes 0%. When utilizing MnS as an inhibitor, the Mn content should be 0.02% or more. A preferable value of the Mn content is 0.05% or more, and a more preferable value of the Mn content is 0.07% or more.

<S: 0.080% or less>
S is an element that combines with Mn to form MnS, which functions as an inhibitor. If the S content exceeds 0.080%, it causes hot brittleness and makes hot rolling extremely difficult, so the S content is set to 0.080% or less. A preferable value of the S content is 0.050% or less, and a more preferable value of the S content is 0.030% or less.

When using AlN as an inhibitor, MnS is not essential, so the lower limit of the S content includes 0%, but when using MnS as an inhibitor during secondary recrystallization, the S content is 0.005% or more. shall be. A preferable value of the S content is 0.010% or more, and a more preferable value of the S content is 0.020% or more.

A part of S may be replaced with Se or Sb, and in that case, the value converted by the formula specified by considering the atomic weight ratio, Seq = S + 0.406 · Se, or Seq = S + 0.406 · Sb. Use.

In addition, in order to improve the properties of the grain-oriented electrical steel sheet 1, the base steel sheet 10 contains, in addition to the above elements, B: 0.001 to 0.010%, Sn: 0.01 to 0.20%, It may contain one or more of Cr: 0.01 to 0.50% and Cu: 0.01 to 0.50%. Since B, Sn, Cr, and Cu are not essential elements, the lower limit of their content is 0%.

<B: 0.001-0.010%>
B, along with Sn, Cr, and Cu, is an element that contributes to improving film adhesion. If the B content is less than 0.001%, the improvement effect cannot be sufficiently obtained, so the B content is set to 0.001% or more. A preferable value of the B content is 0.002% or more, and a more preferable value of the B content is 0.004% or more.

On the other hand, if the B content exceeds 0.010%, the strength of the base steel sheet 10 will increase and the threadability during cold rolling will deteriorate, so the B content is set to 0.010% or less. A preferable value of the B content is 0.008% or less, and a more preferable value of the B content is 0.006% or less.

<Sn: 0.01-0.20%>
Sn, along with B, Cr, and Cu, is an element that contributes to improving film adhesion. Although the mechanism by which Sn improves film adhesion is not clear, since it was observed that the smoothness of the surface of the base steel plate 10 was improved by the addition of Sn, it is thought that Sn contributes to smoothing the surface of the base steel plate 10. It will be done.

If the Sn content is less than 0.01%, a sufficient smoothing effect cannot be obtained, so the Sn content is set to 0.01% or more. A preferable value of Sn content is 0.02% or more, and a more preferable value of Sn content is 0.03% or more.

On the other hand, if the Sn content exceeds 0.20%, secondary recrystallization becomes unstable and magnetic properties deteriorate, so the Sn content is set to 0.20% or less. A preferable value of Sn content is 0.15% or less, and a more preferable value of Sn content is 0.10% or less.

<Cr:0.01~0.50%>
Cr, along with B, Sn, and Cu, is an element that contributes to improving film adhesion. If the Cr content is less than 0.01%, a sufficient effect of improving film adhesion cannot be obtained, so the Cr content is set to 0.01% or more. A preferable value of the Cr content is 0.05% or more, and a more preferable value of the Cr content is 0.10% or more.

On the other hand, if the Cr content exceeds 0.50%, since Cr is an easily oxidizable element, an intermediate film 20 containing an iron-based oxide (Fe-Si-O oxide) and silicon oxide, which will be described later, is formed. Since Cr content may be inhibited, the Cr content is set to 0.50% or less. A preferable value of the Cr content is 0.30% or less, and a more preferable value of the Cr content is 0.20% or less.

<Cu: 0.01 to 0.50%>
Cu, along with B, Sn, and Cr, is an element that contributes to improving film adhesion. If the Cu content is less than 0.01%, the effect of improving film adhesion cannot be sufficiently obtained, so the Cu content is set to 0.01% or more. A preferable value of the Cu content is 0.05% or more, and a more preferable value of the Cu content is 0.10% or more.

On the other hand, if the Cu content exceeds 0.50%, the base steel plate 10 becomes brittle during hot rolling, so the Cu content is set to 0.50% or less. A preferable value of the Cu content is 0.40% or less, and a more preferable value of the Cu content is 0.30% or less.

In the base material steel plate 10, the remainder other than the above elements is Fe and impurities. Impurities include at least one of elements that are unavoidably mixed in from steel raw materials and elements that are unavoidably mixed in during the steel manufacturing process, and are elements that are allowed to be mixed in as long as they do not impede the properties of grain-oriented electrical steel sheet 1.

Furthermore, the base steel plate 10 is used to improve magnetic properties, improve properties required for structural members such as strength, corrosion resistance, and fatigue properties, improve castability and threadability, and improve productivity by using scrap. , Mo, W, In, Bi, Sb, Ag, Te, Ce, V, Co, Ni, Se, Ca, Re, Os, Nb, Zr, Hf, Ta, Y, and one or more of La. may be contained in a total amount of 5.00% or less, preferably 3.00% or less, more preferably 1.00% or less.

[Description of intermediate film 20]
The intermediate coating 20 is an external oxide film mainly composed of silicon oxide (for example, SiO ₂ ) provided on the surface of the base steel plate 10 . This intermediate coating 20 is sandwiched between the base steel plate 10 and the tension insulation coating 30. Since the intermediate coating 20 is a coating other than a forsterite coating, there are almost no irregularities at the interface 40 between the base steel plate 10 and the intermediate coating 20. That is, compared to the conventional grain-oriented electrical steel sheet that uses a forsterite-based film as an intermediate film, in the grain-oriented electrical steel sheet 1 of this embodiment, the flatness of the interface 40 is extremely high, and the flatness of the domain wall under an alternating magnetic field is Since the movement of the iron is carried out smoothly, it contributes to reducing iron loss. Further, as explained below, since the intermediate coating 20 is an external oxide film having a specific structure, it also contributes to improving the adhesion of the tension insulation coating 30.

As shown in FIG. 1, the intermediate coating 20 has a first region 21 that is intermittently in contact with an interface 40 between the base steel plate 10 and the intermediate coating 20, and a second region 22 that includes the first region 21. Each first region 21 contains at least one of Fe ₂ SiO ₄ and FeSiO ₃ . In FIG. 1, the distance between adjacent first regions 21 is shown to be constant, but the distance between adjacent first regions 21 may be different. The second region 22 is a region inside the intermediate film 20 other than the first region 21, and contains silicon oxide (for example, SiO ₂ ) as a main oxide.

As shown in FIG. 1, the film thickness T1 of the intermediate film 20 is the film thickness between the surface (interface 40) of the base material steel plate 10 and the tension insulation film 30, and is not particularly limited to a specific film thickness, The average thickness of the intermediate film 20 is preferably 10 to 100 nm.

<Average film thickness of intermediate film 20: 10 to 100 nm>
If the average film thickness of the intermediate coating 20 is less than 10 nm, the adhesion force at the interface 40 between the base steel plate 10 and the intermediate coating 20 will be insufficient, and the steel plate may be damaged during the manufacturing of the wound core or other excessive plastic working. The average thickness of the intermediate coating 20 is preferably 10 nm or more because the tension insulation coating 30 is likely to peel off in an environment where frictional force is superimposed between the two. A more preferable average thickness of the intermediate film 20 is 20 nm or more.

On the other hand, if the average film thickness of the intermediate coating 20 exceeds 100 nm, the cohesive force of the intermediate coating 20 itself becomes large, which may occur during the manufacturing of the wound core or other excessive plastic working, and in environments where frictional force is superimposed between steel plates. The tension insulating film 30 is likely to peel off starting from the second region 22 containing SiO ₂ as the main oxide, and if the film adhesion is sufficient, the thinner the nonmagnetic layer is, the better. Therefore, the average thickness of the intermediate film 20 is preferably 100 nm or less. A more preferable average thickness of the intermediate film 20 is 80 nm or less.

The method for determining the average thickness of the intermediate film 20 is as follows.

First, a sample is taken from the grain-oriented electrical steel sheet 1 so that a cross section perpendicular to the rolling direction of the base steel sheet 10 is exposed. By polishing the cross section of the sample, a cross section including the length of the interface 40 between the base steel plate 10 and the intermediate coating 20 of about 10 μm is created, and then the base steel plate 10 is polished as shown in FIG. The average film thickness between the surface and the tensile insulation coating 30 is measured as follows.
Although there is no unevenness at the interface 40 between the base steel plate 10 and the intermediate coating 20 as in the case where a forsterite coating is used, the shape of the interface 40 is a wave shape in which peaks and valleys appear over a long period. In many cases, it is. Similarly, the shape of the interface 50 between the tension insulating film 30 and the intermediate film 20 is often a wave shape in which peaks and valleys appear over a long period.
Therefore, a wave center line is drawn for each of the interface 40 and the interface 50 having a wave shape. Here, when a straight line parallel to the average line of the wave curve is drawn, the straight line in which the area surrounded by this straight line and the wave curve is equal on both sides of this straight line is defined as the wave center line. The distance between these two wave center lines is defined as the film thickness.
Then, inside the intermediate coating 20, draw 10 or more lines perpendicular to the interface 40 in a direction parallel to the interface 40 so as not to overlap the first region 21, and measure the film thickness according to the above definition on the line. The average thereof is defined as the average film thickness of the intermediate film 20.

Next, the first region 21 and the second region 22 that constitute the intermediate film 20 will be explained in detail.

<First area 21>
The first region 21 that exists inside the intermediate coating 20 and is intermittently in contact with the surface (interface 40) of the base steel plate 10 may be a region made of an oxide containing Fe and Si; The material is mainly at least one of Fe ₂ SiO ₄ and FeSiO ₃ .

The function of the first region 21 inside the intermediate coating 20 is not clear, but when a frictional force is applied to the tension insulation coating 30 during the core manufacturing process or other excessive plastic working process, it is used to absorb the applied frictional force. It is thought that it functions as a relaxing buffer.

If the first region 21 does not exist, the lattice matching between the base steel plate 10 and the external oxide film mainly composed of silicon oxide is good, so the adhesion of the tension insulation coating 30 is good, but the oxidation Since silicon has a high elastic modulus, all of the frictional force, that is, shear stress, applied to the tension insulation coating 30 is transferred to the interface between the base steel plate 10 and the external oxide film where the first region 21 is not present. It is thought that the above-mentioned lattice matching is inhibited in a concentrated manner, and the adhesion of the tension insulation coating 30 becomes unstable.

That is, as in the present embodiment, inside the intermediate coating 20, the first region 21 containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ is intermittently in contact with the surface (interface 40) of the base steel plate 10. When the first region 21, that is, the iron-based oxide containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ , relieves stress when frictional force is applied to the tensile insulating coating 30. It is thought that it functions as a buffer, maintains good lattice matching between base steel plate 10 and intermediate coating 20, and maintains good adhesion of tension insulation coating 30.

The presence of the first region 21 and the thickness T2 (see FIG. 1) of the first region 21 in the film thickness direction of the intermediate coating 20 can be determined by physically polishing the cross section of the grain-oriented electrical steel sheet 1, and then using a transmission electron microscope. It can be confirmed by observing with TEM). A cross section of the grain-oriented electrical steel sheet 1 is polished, for example, with a focused ion beam using Ga as an ion source, and then photographed with a TEM at a magnification of 10,000 times or more.

That the first region 21 is a region made of an oxide containing Fe and Si can be confirmed by elemental analysis such as EDS analysis. It is also possible to confirm by electron diffraction method. The electron diffraction method is mainly used to confirm Fe ₂ SiO ₄ and FeSiO ₃ , and it can also confirm that at least one of Fe ₂ SiO ₄ and FeSiO ₃ is crystalline.

Because at least one of Fe ₂ SiO ₄ and FeSiO ₃ is crystalline, it provides the necessary film adhesion during the production of wound cores or other excessive plastic working, and in environments where frictional forces are superimposed between steel plates. can be increased. This is considered to be due to an increase in the lattice matching between the first region 21 and the base steel plate 10, or to an increase in the density of the intermediate coating 20 itself.

The average thickness of the first region 21 in the thickness direction of the intermediate coating 20 is preferably 1 to 20 nm. Further, as will be described later, the abundance ratio R of the first region 21 is preferably 1% or more.

<Average thickness of first region 21: 1 to 20 nm>
If the average thickness of the first region 21 is less than 1 nm, the stress relaxation function of the first region 21 will not function sufficiently, and frictional force between the steel plates will occur during the manufacturing of the wound core or other excessive plastic working. The average thickness of the first region 21 is preferably 1 nm or more, since it becomes difficult to ensure the necessary film adhesion in an environment where there is overlap. A more preferable average thickness of the first region 21 is 5 nm or more.

On the other hand, if the average thickness of the first region 21 exceeds 20 nm, the cohesive force of the first region 21 itself becomes large, and similarly, friction between the steel plates occurs during the manufacturing of the wound core or other excessive plastic working. Since it becomes difficult to ensure necessary film adhesion in an environment where forces are superimposed, the average thickness of the first region 21 is preferably 20 nm or less. A more preferable average thickness of the first region 21 is 15 nm or less.

The method for determining the average thickness of the first region 21 is as follows.

First, a sample is taken from the grain-oriented electrical steel sheet 1 so that a cross section perpendicular to the rolling direction of the base steel sheet 10 is exposed. By polishing the cross section of the sample, a cross section including a length of the interface 40 between the base steel plate 10 and the intermediate coating 20 of about 10 μm is revealed.
The shape of the interface between the base steel plate 10 and the first region 21 is often a wavy shape in which peaks and valleys appear over a long period. Similarly, the shape of the interface between the first region 21 and the second region 22 is often a wave shape in which peaks and valleys appear in long periods.
Therefore, wave center lines are drawn for each of the interface between the base steel plate 10 and the first region 21 and the interface between the first region 21 and the second region 22. Here, when a straight line parallel to the average line of the wave curve is drawn, the straight line in which the area surrounded by this straight line and the wave curve is equal on both sides of this straight line is defined as the wave center line. The distance between these two wave center lines is defined as thickness.

Then, inside the intermediate coating 20, ten or more lines perpendicular to the interface 40 are drawn in a direction parallel to the interface 40 so as to overlap the first region 21, and the thickness according to the above definition is measured on the lines. , the average thereof is taken as the average thickness of the first region 21.

<Existence ratio of first region 21: 1% or more per total length of interface>
As shown in FIG. 1, first regions 21 are formed intermittently on the surface of the base steel plate 10, and the first regions 21 are formed on the surface of the base steel plate 10 where the first regions 21 are not formed. A second region 22 is formed to cover and wrap the first region 21 .

As shown in FIG. 1, when looking at a cross section having a length Lsum in the direction perpendicular to the rolling direction of the base steel plate 10, the total length of the first region 21 appearing within the cross section touching the interface 40 is calculated as follows: When ΣL, the abundance ratio R of the first region 21 is defined by the following equation (1).
R=(ΣL×100)/Lsum…(1)

In the above equation (1), ΣL is defined by the following equation (2). In equation (2), Li is the length at which the i-th first region 21 appearing in the cross section having length Lsum contacts the interface 40 (see FIG. 1). The length Lsum is required to be at least about 10 μm.
ΣL=L ₁ +L ₂ +L ₃ +...+Li+...+L _n ...(2)

The abundance ratio R of the first region 21 is preferably 1% or more. If the abundance ratio R is less than 1%, it will be difficult to ensure the necessary film adhesion during the production of wound cores or other excessive plastic working, and in environments where frictional forces are superimposed between steel plates. Therefore, the abundance ratio R is preferably 1% or more. A more preferable value of the abundance ratio R is 5% or more.

Since the abundance ratio R depends on the film formation conditions, its upper limit cannot be set in particular, but if it exceeds approximately 50%, the effect of improving film adhesion will be saturated, and domain wall movement under AC excitation will be difficult to proceed smoothly. The abundance ratio R is preferably 50% or less, since the magnetic properties are lowered and, in particular, the iron loss is increased. From the viewpoint of ensuring stable film adhesion and excellent magnetic properties, the abundance ratio R is more preferably 40% or less.

<Second area 22>
The second region 22 contains silicon oxide as a main oxide. The chemical composition of silicon oxide is SiO _α . From the viewpoint of chemical stability, α=1.0 to 2.0 is preferable. α=1.5 to 2.0 is more preferable, and α≈2.0 is even more preferable from the viewpoint of film adhesion as well as chemical stability.

The presence of the silicon oxide region (second region 22) is confirmed by physically polishing the cross section of the grain-oriented electrical steel sheet 1 and then observing it with a transmission electron microscope (TEM), similarly to the first region 21. be able to. Confirmation that it is silicon oxide can be performed by elemental analysis such as EDS analysis. Note that if silicon oxide is, for example, silicon oxide with a β-cristobalite structure, its crystallization temperature is as high as about 1470°C, and it is not formed in normal manufacturing processes, so its identification is performed by elemental analysis such as EDS analysis. This is done based on the atomic ratio of Si and O.

[Description of tension insulation coating 30]
Next, the tension insulation coating 30 formed on the intermediate coating 20 will be explained.

The tension insulation coating 30 may be an insulation coating made of magnesium phosphate or aluminum phosphate, chromic acid, and colloidal silica (see Patent Document 20), or crystalline boric acid and alumina oxide, which can provide higher tension than the insulation coating. An insulating coating made of a material (see Patent Document 23) or the like can be used.

The thickness T3 of the tension insulation coating 30 is set in consideration of the tension required to improve the magnetic properties, the space factor of the steel plate in the iron core, etc., and is preferably 0.5 to 10 μm. If the thickness T3 of the tension insulating coating 30 is less than 0.5 μm, the effect of reducing iron loss by applying tension is poor, so the thickness T3 is preferably 0.5 μm or more. More preferably, it is 0.8 μm or more.

On the other hand, if the thickness T3 of the tension insulating coating 30 exceeds 10 μm, sufficient coating adhesion may not be obtained even if the intermediate coating 20 is properly formed, and the above-mentioned space factor may decrease. Therefore, the film thickness T3 is preferably 10 μm or less. More preferably, it is 8 μm or less.

[Method for manufacturing grain-oriented electrical steel sheet 1]
Next, a method for manufacturing the grain-oriented electrical steel sheet 1 will be explained.

<Manufacturing method>
(i) (a) A steel plate from which a coating of inorganic minerals such as forsterite formed on the surface of the steel plate during final annealing has been removed by means such as pickling or grinding; (b) A coating of the above-mentioned inorganic minerals during final annealing. The base material (base material steel sheet 10) is a steel sheet in which the formation of .
(ii) When coating the surface of the base material with a forming liquid for the tension insulation coating 30 and baking it to form the tension insulation coating 30, the heating and atmosphere during baking are appropriately controlled, and the tension insulation coating 30 and the tension insulation coating 30 are formed. An intermediate film 20 that is oxidized at the interface with the base material and has a first region 21 containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ and a second region 22 containing silicon oxide as a main oxide is applied to the base material. At the same time, a tension insulation coating 30 is formed on the intermediate coating 20.

A steel plate from which a film of inorganic mineral such as forsterite has been removed by means such as pickling or grinding, and a steel plate from which the formation of the film of inorganic mineral is suppressed are produced, for example, as follows.

A silicon steel slab containing about 2.0 to 4.0 mass% of Si is hot rolled to obtain a hot rolled steel sheet, and if necessary, the hot rolled steel sheet is annealed, and then hot rolled steel sheet or annealed hot rolled The steel plate is subjected to cold rolling once or twice or more with intermediate annealing in between to finish the steel plate to the final thickness, and then the steel plate is subjected to decarburization annealing and primary recrystallization is advanced. An oxidized layer is formed on the surface of the steel sheet due to decarburization annealing.

An annealing separator containing magnesia (MgO) as a main component is applied to the surface of a steel sheet having an oxidized layer and dried. After drying, the steel sheet is wound into a coil shape and subjected to final annealing (secondary recrystallization). As a result of final annealing, a film of an inorganic mineral substance mainly composed of forsterite (Mg ₂ SiO ₄ ) is formed on the surface of the steel sheet, and this film is removed by means such as pickling and grinding. After the coating is removed, the surface of the steel plate is preferably smoothed by chemical polishing or electropolishing.

Instead of an annealing separator whose main ingredient is magnesia (MgO), an annealing separator whose main ingredient is alumina is applied and dried. After drying, it is wound up into a coil shape and subjected to final annealing (secondary recrystallization). Serve. Finish annealing makes it possible to obtain a steel sheet in which the formation of a film of inorganic minerals such as forsterite is intentionally suppressed. After final annealing, the surface of the steel plate is preferably finished smooth by chemical polishing or electric field polishing.

(a) Steel sheet from which a film of inorganic minerals such as forsterite has been removed, (b) Steel sheet from which the formation of a film of inorganic minerals such as forsterite has been suppressed, or (c) Steel sheet surface smoothed to a specular luster. A forming liquid for the tension insulation coating 30 is applied to the surface of the steel plate and baked.

For example, in the case of a liquid mainly composed of phosphate and colloidal silica, which is typically used as a forming liquid for the tensile insulation coating 30, apply the liquid to the steel sheet in an amount that gives a dry coating thickness of 0.5 to 10 μm. The tensile insulation coating 30 is formed by applying it to the surface and baking it.

The baking is performed, for example, in a nitrogen-hydrogen mixed atmosphere of 75%:25% hydrogen:nitrogen and a dew point of 5 to 50°C, by heating to 650 to 950°C for 5 to 300 seconds. By appropriately controlling the heating temperature, heating rate, and atmosphere (composition, dew point) during the baking process, at least one of oxygen and moisture in the atmosphere diffuses into the tensile insulation coating 30 and oxidizes the steel plate surface. As a result, an intermediate film 20 having a first region 21 containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ and a second region 22 containing silicon oxide is formed, and a tension insulating film is formed on the intermediate film 20. 30 is formed.

The heating temperature and heating time during baking and cooling after baking in the above forming method will be explained.

Heating temperature: 650-950℃
Heating time: 5 to 300 seconds The heating temperature and heating time are appropriately set in order to promote and complete the baking hardening of the tension insulating coating 30 and obtain the tension imparting effect. 5 seconds or more is preferable.

Considering the efficient formation of the intermediate film 20, the heating temperature is preferably 700° C. or higher and the heating time is preferably 10 seconds or longer, and more preferably 800° C. or higher and 10 seconds or longer.

The upper limit of the heating temperature is not particularly limited, but if it exceeds 950°C, the tension imparting effect of the tension insulation coating 30 will be saturated, and some of the chemical bonds in the tension insulation coating 30 will be broken, causing the tension to decrease instead. The heating temperature is preferably 950° C. or lower because the magnetic properties deteriorate. More preferably it is 920°C or lower.

The upper limit of the heating time is not particularly limited, but if it exceeds 300 seconds, the tension imparting effect of the tension insulation coating 30 will be saturated, and some of the chemical bonds in the tension insulation coating 30 will be broken, causing the tension to decrease instead. The heating time is preferably 300 seconds or less because the magnetic properties deteriorate. More preferably, it is 280 seconds or less.

Atmosphere dew point: -20~40℃
Cooling rate: 5 to 100°C/sec After the baking hardening of the tension insulation coating 30 is completed, the oxidation degree (dew point) of the atmosphere during cooling is adjusted to prevent the surface of the steel plate from oxidizing and the intermediate coating 20 from deteriorating. It is necessary to properly control the cooling rate.

For example, cooling to 500°C, which affects the surface oxidation of the steel plate, is preferably carried out in an atmosphere of 75%:25% hydrogen:nitrogen and a dew point of -20 to 40°C. Normally, a faster cooling rate is preferable in order to suppress oxidation of the steel plate, but if it is too fast, the amount of distortion in the steel plate will increase and the magnetic properties will deteriorate, so the cooling rate should be 5 to 100°C/sec. preferable. More preferably it is 10 to 90°C/sec.

The degree of oxidation of the cooling atmosphere is preferably lower than the degree of oxidation of the baking atmosphere in which the forming liquid for the tension insulation coating 30 is baked, in terms of suppressing surface oxidation of the steel plate and suppressing the amount of distortion of the steel plate.

Alternatively, the intermediate coating 20 is formed by annealing without applying a forming liquid for the tension insulation coating 30 on the surface of the steel plate, and after cooling, the forming liquid for the tension insulation coating 30 is applied and baked to form the tension insulation coating 30. may be formed.

Heating temperature: 600-1150℃
Atmosphere dew point: -20~20℃
In annealing to form the intermediate coating 20, the heating temperature is preferably 600 to 1150° C., and the atmosphere is preferably a nitrogen atmosphere mixed with hydrogen from the viewpoint of preventing excessive oxidation. For example, an atmosphere with hydrogen:nitrogen ratio of 75%:25% and a dew point of -20 to 20°C is preferable.

In order to form iron-based oxides, which become the source of the first region 21, on the surface of the steel sheet, the dew point of the atmosphere is controlled at 0 to 40°C in the initial stage of annealing, and then the first region 21 and the second region 22 are formed. In order to form the intermediate film 20 having the following properties, it is preferable to control the dew point to -20 to 20°C and to lower the oxidizing nature of the atmosphere.

In this way, when forming the intermediate coating 20, the oxidation degree of the atmosphere is controlled from the high side to the low side from the early stage to the late stage of annealing, thereby forming the intermediate film 20 having the first region 21 and the second region 22. It can be formed efficiently and reliably.

After forming the intermediate coating 20, a forming liquid for the tension insulation coating 30, which is mainly composed of phosphate and colloidal silica, is applied to the surface of the steel plate and baked to form the tension insulation coating 30.

Heating temperature: 650-950℃
Heating time: 5 to 300 seconds Atmosphere dew point: -20 to 20℃
Since the formation of the intermediate coating 20 is almost completed, the atmosphere is preferably an atmosphere with a low degree of oxidation so that the steel plate is not further oxidized when baking the forming liquid for the tension insulation coating 30. For example, an atmosphere with hydrogen:nitrogen ratio of 75%:25% and a dew point of -20 to 20°C is preferable.

If the dew point is less than -20°C, Fe in the first region 21 containing Fe-Si-O oxide will be reduced and impede the insulation properties of the tensile insulation coating 30, so the dew point should be -20°C or higher. is preferred. More preferably it is -10°C or higher.

On the other hand, if the dew point exceeds 20°C, oxidation of the surface of the steel plate will progress, the intermediate coating 20 will become too thick, and the adhesion of the tension insulation coating 30 will decrease, so the dew point is preferably 20°C or less. More preferably it is 10°C or lower. The heating temperature is preferably 650 to 950°C, and the heating time is preferably 5 to 300 seconds.

The steel plate after baking is preferably cooled in an atmosphere with a dew point of -20 to 20°C at a cooling rate of 5 to 100°C/sec.

Atmosphere dew point: -20~20℃
Cooling rate: 5 to 100°C/sec The same applies to cooling the steel plate after baking. Cooling to 500°C, which affects the oxidation of the steel plate, requires hydrogen: nitrogen of 75%: 25%, dew point of -20 to -20°C. It is carried out in an atmosphere of 20°C. A fast cooling rate is preferable in order to suppress surface oxidation of the steel plate, but if it is too fast, the amount of distortion in the steel plate will increase and the magnetic properties will decrease, so the cooling rate is preferably 5 to 100°C/sec. .

Next, an example of the present invention will be described. The conditions in the example are examples of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is based on this example of conditions. It is not limited. The present invention can adopt various conditions as long as the purpose of the present invention is achieved without departing from the gist of the present invention.

<Example 1>
A silicon steel slab having the composition shown in Table 1 was heated at 1200°C for 60 minutes and subjected to hot rolling to obtain a hot rolled steel plate with a thickness of 2.30mm. The plate was annealed and then cold rolled to obtain a cold rolled steel plate with a thickness of 0.23 mm.

After decarburization annealing and nitriding annealing, the cold-rolled steel sheet was coated with an annealing separator mainly composed of alumina, finished annealed at 1200°C in a hydrogen atmosphere, and then naturally cooled to smooth it. A steel plate with a smooth surface was obtained.

The above steel plate was heated to 1000°C at a heating rate of 10°C/sec in an atmosphere of 25% N ₂ + 75% H ₂ and a dew point of +10°C, held for 5 seconds, and then the dew point was reduced to -10°C. Similarly, the temperature was changed to 1000°C for 25 seconds, and then the temperature was cooled at 10°C/second to form an intermediate film on the surface of the steel plate.

Thereafter, a forming solution for a tensile insulation film consisting of aluminum phosphate and colloidal silica was applied to the surface of the steel plate so that the dry film thickness was 3 μm, and the temperature was 25% N ₂ + 75% H ₂ and the dew point was +10°C. In this atmosphere, the temperature was raised to 800°C at a rate of 10°C/second, held for 30 seconds, and then cooled at 10°C/second.

(layer structure)
The chemical composition of the intermediate coating was investigated as follows. A cross section of a micro test piece produced by a focused ion beam method was observed using a transmission electron microscope (TEM) from a steel plate cross section perpendicular to the rolling direction of a grain-oriented electrical steel sheet. The observation was performed over a 10 μm area in the interface direction (width). In addition, elemental and quantitative analyzes of oxygen (O), silicon (Si), iron (Fe), etc. were performed using an energy dispersive spectrometer (EDS) attached to the TEM, and compounds were identified.

In the observed interface direction of 10 μm, the average film thickness of the intermediate film, the average thickness of the first region containing at least one of Fe ₂ SiO ₄ and FeSiO ₃ , and the abundance ratio of the first region per interface length Lsum R was measured. Furthermore, crystallinity investigation and crystal identification were performed using electron beam diffraction patterns for silicon oxide contained in the second region of the intermediate film and at least one of Fe ₂ SiO ₄ and FeSiO ₃ contained in the first region. Note that the composition of silicon oxide contained in the second region of the intermediate film was SiO ₂ in all samples.

Table 2 shows the identification and measurement results of the intermediate film.

(Film adhesion bending)
The film adhesion of the tension insulation film was evaluated by the remaining area ratio of the film when the evaluation sample was wound around a cylinder with a diameter of 20 mm and bent by 180°.

The evaluation criteria are as follows.
◎: Film remaining area ratio is 95% or more (excellent)
○: Film remaining area ratio is 90% or more and less than 95% (excellent)
△: Film remaining area ratio is 80% or more and less than 90% (effective)
×: Film remaining area ratio is less than 80% (no effect)

Table 2 also shows the evaluation results.

(Film adhesion friction)
In order to evaluate the film adhesion of the tension insulating film when a frictional force is applied, a sample was prepared by wrapping it around a cylinder with a diameter of 30 mm, bending it inward at 180°, and then bending and stretching it. As shown in Figure 2, this sample was fixed on a surface plate, a steel ball with a diameter of 10 mm was pressed against the sample surface at 1 kgf, and the steel ball was slid (30 mm) at a speed of 1 mm/sec for 30 seconds to remove the surface of the steel plate. Friction marks were added to the surface (see figure above). The maximum peeling width of the film peeled off from this friction trace was evaluated (see the figure below).

The evaluation criteria are as follows.
◎: Maximum peeling width is 1 mm or less (excellent)
○: Maximum peeling width is 2 mm or less (excellent)
△: Maximum peeling width is 4 mm or less (effective)
×: Maximum peeling width exceeds 4 mm (no effect)

Table 2 also shows the evaluation results.

(Magnetic properties)
The magnetic properties were evaluated according to JIS C 2550. The magnetic flux density was evaluated using _B8 . B ₈ is the magnetic flux density at a magnetic field strength of 800 A/m, and is a criterion for determining the quality of secondary recrystallization. B ₈ =1.80T or more was judged to have undergone secondary recrystallization.

Table 2 also shows the evaluation results.

In Table 2, sample No. Invention examples B1 to B18 all exhibit good film adhesion and magnetic properties. Sample No. Inventive examples B12 and B17 fully exhibit the effects of adding B, Cr, Cu, and Sn, and exhibit particularly good film adhesion.

On the other hand, sample No. Comparative examples b3, b5, and b6 each contained large amounts of Si, Al, and N, and therefore had poor brittleness at room temperature, making cold rolling impossible. In addition, sample No. Comparative example b8 had a high S content and poor hot brittleness, making hot rolling impossible. For this reason, sample no. In the comparative examples b3, b5, b6, and b8, the film adhesion could not be evaluated in any of them.

Sample No. In Comparative Examples b1, b2, b4, and b7, the content of the additive element was outside the range of the present invention, so secondary recrystallization did not occur in any of them, and the magnetic flux density became very small. Incidentally, all of the samples that were not subjected to secondary recrystallization had poor film adhesion. When secondary recrystallization did not occur, it is considered that the crystal grain size of the steel sheet was so fine that the intermediate coating was not formed properly.

<Example 2>
A silicon steel slab having the composition shown in Table 1 was heated at 1200°C for 60 minutes and subjected to hot rolling to obtain a hot rolled steel plate with a thickness of 2.30mm. The plate was annealed and then cold rolled to obtain a cold rolled steel plate with a thickness of 0.23 mm. After decarburization annealing and nitriding annealing, the cold-rolled steel sheet is coated with an annealing separator containing alumina as a main component, finish annealed at 1200°C in a hydrogen atmosphere, and then naturally cooled to create a smooth surface. steel plate was obtained.

The above steel plate was heated to 1000°C (previous stage temperature) at a heating rate of 10°C/sec in an atmosphere of 25% N ₂ + 75% H ₂ and a dew point of 15°C (first stage dew point) for 10 seconds. After holding, the dew point was adjusted to -20 to 10°C (second stage dew point) and the temperature was adjusted to 1000 to 1200°C (second stage temperature), held for 40 seconds, and then cooled at 10°C/second to form a steel plate. An intermediate film was formed on the surface. Note that the composition of silicon oxide contained in the second region of the intermediate film was SiO ₂ in all samples.

A forming solution for a tensile insulation film consisting of aluminum phosphate and colloidal silica was applied to the surface of the steel plate so that the dry film thickness was 3 μm, and the film was coated in an atmosphere of 25% N ₂ +75% H ₂ and a dew point of +10°C. The temperature was raised to 800°C at a heating rate of 10°C/sec, held for 30 seconds, and then cooled at a rate of 10°C/sec. Evaluation of the adhesion between the intermediate film and the tension insulation film was performed in the same manner as in Example 1.

The results are shown in Table 3.

Sample No. D1 to D9 are invention examples, and all exhibit good film adhesion. In particular, when the latter stage dew point is high, the abundance ratio R of the first region is high, the first region is appropriately formed, and good film adhesion is obtained. Moreover, when the subsequent stage temperature is 1150° C. or higher, the iron-based oxide contained in the first region is crystallized, and even better film adhesion is obtained.

According to the present invention, a grain-oriented electrical steel sheet having an intermediate coating other than a forsterite-based coating between a tension insulating coating and a base steel sheet and capable of improving coating adhesion, that is, an excellent A grain-oriented electrical steel sheet having excellent film adhesion and magnetic properties can be provided. Therefore, the present invention has high applicability in the electrical steel sheet manufacturing industry and the electrical steel sheet utilization industry.

DESCRIPTION OF SYMBOLS 1... Grain-oriented electrical steel plate, 10... Base material steel plate, 20... Intermediate coating, 21... First region, 22... Second region, 30... Tension insulation coating, 40... Interface between base material steel plate and intermediate coating, 50... Interface between intermediate coating and tension insulation coating

Claims (3)

base material steel plate,
a tensile insulation coating;
an intermediate coating sandwiched between the base steel plate and the tension insulation coating;
Equipped with
The base steel plate has a chemical composition in mass%,
C: 0.100% or less,
Si: 0.80-7.00%,
Mn: 1.00% or less,
Acid-soluble Al: 0.010 to 0.070%,
S: 0.080% or less,
N: 0.012% or less,
B: 0 to 0.010%,
Sn: 0-0.20%,
Cr: 0 to 0.50%,
Cu: 0 to 0.50%,
, with the remainder consisting of Fe and impurities,
The intermediate coating is a coating other than a forsterite coating, and has a first region intermittently in contact with an interface between the base steel plate and the intermediate coating, and a second region containing the first region. death,
The first region includes at least one of Fe ₂ SiO ₄ and FeSiO ₃ ,
The second region includes silicon oxide,
When looking at a cross section having a length Lsum in the direction perpendicular to the rolling direction of the base steel plate, and assuming that the total length of the first region appearing in the cross section is in contact with the interface is ΣL, the following ( 1) The abundance ratio R of the first region defined by the formula is 1% or more and 50% or less,
The average thickness of the intermediate film is 10 to 100 nm,
The average thickness of the first region in the thickness direction of the intermediate coating is 1 to 20 nm.
A grain-oriented electrical steel sheet characterized by: The grain-oriented electrical steel sheet according to claim 1, wherein at least one of the Fe ₂ SiO ₄ and the FeSiO ₃ is crystalline. The base steel plate has the chemical composition, in mass %, of B: 0.001 to 0.010%, Sn: 0.01 to 0.20%, Cr: 0.01 to 0.50%, and The grain-oriented electrical steel sheet according to claim 1 or 2, containing one or more kinds of Cu: 0.01 to 0.50%.

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