JP2020111813A - Directional electromagnetic steel sheet - Google Patents

Abstract

To provide a directional electromagnetic steel sheet having excellent film adhesion and magnetic characteristics.SOLUTION: A directional electromagnetic steel sheet 1 includes a base material steel plate 10, a tension insulation coating film 30, and an intermediate coating film 20 which is sandwiched between the base material steel plate 10 and the tension insulation coating film 30 and contains silicon oxide. The base material steel plate 10 has a chemical composition comprising, by mass%, 0.100% or less of C, 0.80 to 7.00% of Si, 1.00% or less of Mn, 0.010 to 0.070% of acid soluble Al, 0.080% or less of S, 0.012% or less of N, 0 to 0.010% of B, 0 to 0.20% of Sn, 0 to 0.50% of Cr and 0 to 0.50% of Cu, and the balance Fe with impurities. The intermediate coating film 20 includes a discontinuous region 21 which intermittently exists in an interface direction parallel to an interface 40 between the base material steel plate 10 and the intermediate coating film 20 in a state of being separated from the interface 40, and the discontinuous region 21 contains the same component as the tension insulation coating film 30.SELECTED DRAWING: Figure 1

Description

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

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

The grain-oriented electrical steel sheet is required to have high magnetic flux density in the rolling direction and low iron loss as magnetic characteristics. In recent years, from the viewpoint of energy saving, there is an increasing demand for reduction of power loss, that is, reduction of iron loss. Generally, the B ₈ value is used as an index for evaluating the magnetic flux density, and the W _17/50 value is used as an index for evaluating the iron loss.

It has been conventionally known that applying tension to a base steel sheet is effective in reducing iron loss. As a method for applying tension to the base steel sheet, a method is known in which a coating film having a smaller thermal expansion coefficient than the base steel sheet is formed at a high temperature between the base steel sheet and the insulating coating. For example, in the finish annealing step of the base steel sheet, the forsterite-based coating film generated by the reaction of the oxide present on the surface of the base steel sheet with the annealing separating agent can give tension to the base steel sheet. Since there are irregularities at the interface between the forsterite-based coating and the base steel sheet, the forsterite-based coating also functions as an intermediate coating that enhances the adhesion between the insulating coating and the base steel sheet due to the anchor effect due to this irregularity. To do.

The method disclosed in Patent Document 20 for forming an insulating coating by baking a coating liquid mainly containing colloidal silica and phosphate has a large effect of applying tension to the base steel sheet and is effective in reducing iron loss. Is. Therefore, a general method for producing a grain-oriented electrical steel sheet is to leave the forsterite-based coating film produced in the finish annealing step and then apply an insulating coating mainly containing phosphate. In the specification of the present application, an insulating coating capable of giving not only an insulating property to the base steel sheet but also a tension is referred to as a tension insulating coating.

On the other hand, in recent years, it has been revealed that the forsterite coating hinders the movement of the domain wall and adversely affects the iron loss. In the grain-oriented electrical steel sheet, the magnetic domain changes with the movement of the domain wall under an alternating magnetic field. Smooth movement of this domain wall is effective in improving iron loss, but movement of the domain wall is hindered due to the presence of irregularities at the interface between the forsterite-based coating and the base steel sheet, As a result, it was found that the iron loss improving effect due to the application of tension was canceled and the sufficient iron loss improving effect was not obtained.

In order to prevent the movement of the domain wall from being hindered, it is effective to reduce the anchor effect due to the unevenness present at the interface between the forsterite coating and the base steel sheet. As a matter of course, the anchor effect can be completely eliminated without forming the forsterite coating.

As a method of reducing the anchor effect, for example, in Patent Documents 1 to 19, by controlling the dew point of the decarburization annealing atmosphere, in the oxide layer formed on the surface of the base steel sheet during decarburization annealing, Fe-based oxide It is disclosed that (Fe ₂ SiO ₄ , FeO, etc.) is not produced, and that a material such as alumina that does not react with silica is used as an annealing separator to smooth the surface of the base steel sheet after finish annealing. ing.

When the tension insulation coating is formed on the forsterite coating, the adhesion of the tension insulation coating is improved due to the anchor effect of the forsterite coating. When the forsterite-based coating does not exist on the surface of the base steel sheet, such as when the forsterite-based coating is removed or when the forsterite-based coating is not intentionally formed in the finish annealing step, Since the unevenness that hinders movement disappears from the surface of the base steel sheet, iron loss can be improved. However, in this case, since the tension insulating coating is directly formed on the surface of the base steel sheet, there is a problem that the adhesion of the tension insulating coating is lowered.

The forsterite coating can impart tension to the base steel sheet by itself, but when the forsterite coating is not present, the tension insulating coating alone ensures the required tension to be applied to the base steel sheet. There is a need. Therefore, it is necessary to thicken the tension insulation coating, but as a result, stress is more concentrated at the interface between the base steel sheet and the tension insulation coating, so the adhesion of the tension insulation coating is improved. , It is necessary to raise it further.

With the conventional insulating coating formation method, it is difficult to achieve coating tension that can sufficiently bring out the effect of mirror-finishing the surface of the base steel sheet, and to secure sufficient adhesion of the insulating coating. The iron loss of the magnetic electrical steel sheet could not be reduced sufficiently. Therefore, as a technique for ensuring the adhesion of the tension insulating coating, a method of forming a very thin oxide film on the surface of the base steel sheet after finish annealing before forming the tension insulating coating on the surface of the base steel sheet, For example, it was proposed in Patent Documents 20 to 29.

For example, in Patent Document 22, the base material steel sheet after finish annealing obtained through a step of mirror-finishing the surface of the base material steel sheet, or smoothing to a state close to a mirror surface, in a specific atmosphere for each temperature A technique has been proposed in which an external oxidation type oxide film is formed on the surface of a base material steel sheet by performing annealing and the adhesion between the tension insulating coating and the base material steel sheet is secured by this oxide film.

In Patent Document 23, when the tension insulating coating is crystalline, an amorphous oxide base coating is formed on the surface of the base steel sheet after finish annealing without the inorganic mineral coating (forsterite coating). There has been proposed a technique for preventing the base material steel sheet from being oxidized, that is, a decrease in specularity, which occurs when the crystalline tension insulating film is formed.

Patent Document 25 proposes a technique of forming an oxide film of an external oxidation type on the surface of a base steel sheet and forming a granular oxide inside thereof to improve the adhesion of the tension insulating coating. In Patent Document 26, a silica outer oxide film containing oxides of Fe, Al, Mn, Ti, and Cr in a cross-sectional area ratio of 50% or less is formed on the surface of a base steel sheet, and the adhesion of the tension insulating film is improved. Techniques for improving the are proposed.

It is well known that the iron core of a transformer includes a laminated iron core and a wound iron core, but in recent years, a transformer manufactured by the wound iron core is required to have higher efficiency. Therefore, in addition to reducing iron loss, the grain-oriented electrical steel sheet for wound cores is strongly required to have improved adhesion of the tension insulating coating when the grain-oriented electrical steel sheet is plastically processed into a curved shape during manufacturing of the wound core. Therefore, also in the grain-oriented electrical steel sheet having no forsterite-based coating, similarly, improvement in the adhesion of the tension insulating coating is strongly demanded.

However, it has been found that even if the conventional technique is applied to the grain-oriented electrical steel sheet having no forsterite coating, the adhesion of the tension insulating coating cannot be sufficiently secured at the time of manufacturing the wound core. This is because the manufacturing method of the wound core has changed, the bending diameter becomes smaller in the plastic working (iron core processing) of the grain-oriented electrical steel sheet, and the grain-oriented electrical steel sheet requires severe plastic working. This is due to the peeling of.

Further, the wound core is manufactured by bending the grain-oriented electrical steel sheet with a constant radius of curvature and sequentially winding the grain-oriented electrical steel sheet on the outside of the bending portion. It was found that the film peeling occurred due to the superposition of the frictional force between the steel sheets generated in the process of winding the grain-oriented electrical steel sheet, even when there was not. The peeling of the coating film due to the superposition of the frictional force is a peeling phenomenon that could not be found in the conventional adhesion evaluation of the tension insulating coating film, and the necessity of suppressing the peeling of the coating film is increasing. In the present specification, the adhesion of the tension insulating coating to the base steel sheet is abbreviated as coating adhesion.

JP-A-64-062417 JP, 07-118750, A JP, 07-278668, A JP, 07-278669, A JP, 07-278670, A Japanese Unexamined Patent Publication No. 10-046252 JP, 11-106827, A JP-A-11-152517 JP, 2002-060843, A JP 2002-173715 A JP, 2002-348613, A JP, 2002-363646, A JP, 2003-055717, A JP, 2003-003213, A JP, 2003-041320, A JP, 2003-247021, A JP, 2003-247024, A JP, 2008-001980, A Special table 2011-518253 gazette JP 48-039338 A JP-A-60-131976 JP, 06-184762, A JP-A-07-278833 JP, 09-078252, A JP, 2002-322566, A JP-A-2002-348643 JP, 2002-363763, A JP, 2003-293149, A JP, 2003-313644, A

In order to reduce iron loss, the formation of forsterite coatings is intentionally suppressed, the forsterite coatings are removed by means such as grinding or pickling, and the base steel sheet is smoothed to a mirror finish. When a tension insulation coating is formed on the surface of, the tension insulation coating has a high degree of film adhesion in the bending part, which is necessary at the time of manufacturing the wound core, and a high degree of coating in the environment where frictional force is superimposed after bending. Adhesion is required, but it is difficult to realize the high degree of film adhesion required for a grain-oriented electrical steel sheet by the conventional technique.

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

MEANS TO SOLVE THE PROBLEM The present inventors can solve the above-mentioned problems, and as the intermediate film sandwiched between the tension insulating film and the base material steel plate, it is a film other than the forsterite-based film and can improve the film adhesion. The inventors have earnestly studied the chemical composition and structure of a coating that satisfies the condition of coating.

As a result, the present inventors have found that when the external oxide film mainly composed of silicon oxide disclosed in the prior art documents (for example, Patent Documents 22 and 25) is formed on the surface of the base steel sheet, the external oxide film is It was found that the adhesion of the tension insulating film formed on the outer oxide film is significantly improved only when the region containing the same component as the tension insulating film is included so as to satisfy a specific condition. It was Specifically, in the external oxide film, a region containing the same component as the tension insulating film is separated from the interface between the base material steel sheet and the external oxide film in the direction of the interface parallel to the interface. Under the condition that it is present intermittently, the adhesion of the tension insulating coating is remarkably improved.

The present inventors will explain the reason why the adhesion of the tension insulating coating is improved by using the external oxide film satisfying the above specific conditions as an intermediate coating between the base steel sheet and the tension insulating coating. Considered as.
That is, as described above, a region containing the same components as the tension insulating coating and separated from the interface between the base steel sheet and the external oxide film and existing intermittently in the interface direction which is a direction parallel to the interface. When an external oxide film (oxide film mainly composed of silicon oxide) including (discontinuous region) is used as an intermediate film, a structure in which the external oxide film and the tension insulating film are fitted to each other through the discontinuous region appears. By doing so, it is considered that the mechanical coupling force between the external oxide film and the tension insulating coating is strengthened, and as a result, the adhesion of the tension insulating coating is improved.

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

(1) A grain-oriented electrical steel sheet according to an aspect of the present invention includes a base material steel sheet, a tension insulating coating, and an intermediate coating sandwiched between the base material steel sheet and the tension insulating coating and containing silicon oxide. , Is provided. The base steel sheet has a chemical composition of, 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. 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. .About.0.50%, with the balance consisting of Fe and impurities. The intermediate coating, in a state of being separated from the interface between the base steel sheet and the intermediate coating, includes a discontinuous region that is present intermittently in the interface direction that is a direction parallel to the interface, and the discontinuous region is , Containing the same components as the tension insulating coating.

(2) In the grain-oriented electrical steel sheet according to (1) above, when a cross section having a length L in a direction orthogonal to the rolling direction of the base steel sheet is viewed, the discontinuous region appears in the cross section. When the total value of the lengths in the interface direction is ΣLk, the line segment ratio M of the discontinuous region defined by the following equation (1) may be 1 to 50%.
M=(ΣLk/L)×100 (1)

(3) In the grain-oriented electrical steel sheet according to (1) or (2) above, the intermediate coating may have an average thickness of 10 to 200 nm.

(4) In the grain-oriented electrical steel sheet according to any one of (1) to (3) above, the average thickness of the discontinuous region in the thickness direction of the intermediate coating may be 2 to 50 nm. ..

(5) In the grain-oriented electrical steel sheet according to any one of (1) to (4) above, the average distance T _A (nm) between the base material steel sheet and the discontinuous region, and the tension insulation. The average distance T _B (nm) between the coating film and the discontinuous region may satisfy the following formula (2).
T _A ≧T _B (2)

(6) In the grain-oriented electrical steel sheet according to any one of (1) to (5) above, the base steel sheet has a chemical composition of mass% 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%, or one or more of them may be contained.

According to the above aspect of the present invention, a grain-oriented electrical steel sheet having an intermediate coating which is an intermediate coating other than the forsterite-based coating and which can enhance coating adhesion between the tension insulating coating and the base material steel sheet is provided. 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 coating adhesion and magnetic properties.

It is a figure which shows typically the principal part cross section of the grain-oriented electrical steel sheet which concerns on one Embodiment of this invention. It is a figure which shows the outline of the method of forming an intermediate film on the surface of a base material steel plate. It is a figure which shows the outline of the method of forming a discontinuous area|region in an intermediate film while forming an intermediate film on the surface of a base material steel plate. It is a figure which shows the aspect which evaluates the adhesiveness of the tension insulation coating which applied the frictional force.

Hereinafter, an 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 this embodiment. As shown in FIG. 1, the grain-oriented electrical steel sheet 1 according to the present embodiment includes a base material steel sheet 10, an intermediate coating 20, and a tension insulating coating 30. 1 is a view of the grain-oriented electrical steel sheet 1 in a cross section having a length L in a direction orthogonal to the rolling direction of the base steel sheet 10.

[Description of base material steel plate 10]
The base material steel sheet 10 is a steel sheet that is a 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 material steel sheet 10 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. 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. .About.0.50%, with the balance consisting of Fe and impurities.

Hereinafter, the chemical composition of the base material steel sheet 10 will be described in detail. In the following description,% relating to the component composition means mass%.

<C: 0.100% or less>
C is an element effective in controlling primary recrystallization, but since it increases iron loss by magnetic aging, it is an element removed by decarburization annealing before finish 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, so the C content is 0.100% or less.

The lower the C content is, the more preferable it is from the viewpoint of reducing iron loss. Therefore, the C content is preferably 0.045% or less, and more preferably 0.038% or less. Although the lower limit of the C content includes 0%, the detection limit of the C content is about 0.0001%, and if the C content is reduced to less than 0.0001%, the manufacturing cost increases significantly. In practice, 0.0001% is the lower limit of the substantial C content.

<Si: 0.80 to 7.00%>
Si is an element that increases the electrical resistance of the base steel sheet 10 and contributes to the reduction of iron loss. If the Si content is less than 0.80%, 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. The amount is 0.80% or more. A preferable value of Si content is 2.50% or more, and a more preferable value of Si content is 3.00% or more.

On the other hand, if the Si content exceeds 7.00%, the base steel sheet 10 becomes brittle and the stripability in the manufacturing process is significantly deteriorated, so the Si content is set to 7.00% or less. A preferable value of Si content is 4.50% or less, and a more preferable value of 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 finish annealing.

When the acid-soluble Al content is less than 0.010%, secondary recrystallization does not proceed sufficiently and the iron loss characteristics are not improved, so the acid-soluble Al content is set to 0.010% or more. The preferable value of the acid-soluble Al content is 0.015% or more, and the more preferable value of the acid-soluble Al content is 0.020% or more.

On the other hand, when the acid-soluble Al content exceeds 0.070%, the base material steel sheet 10 becomes brittle, and particularly in the grain-oriented electrical steel sheet 1 having a large Si content, embrittlement becomes remarkable, so the acid-soluble Al content is included. The amount is 0.070% or less. The preferable value of the acid-soluble Al content is 0.050% or less, and the 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 is also an element that forms blisters (holes) inside the base steel sheet 10 during cold rolling.

When the N content exceeds 0.012%, blisters (holes) are generated inside the base material steel sheet 10 during cold rolling, and the strength of the base material steel sheet 10 is increased, resulting in poor stripability during manufacturing. Since it deteriorates, the N content is set to 0.012% or less. The preferable value of N content is 0.010% or less, and the more preferable value of N content is 0.009% or less.

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

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

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

MnS can be utilized as an inhibitor during secondary recrystallization, but when AlN is utilized 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 is 0.02% or more. A preferable value of Mn content is 0.05% or more, and a more preferable value of Mn content is 0.07% or more.

<S: 0.080% or less>
S is an element that combines with Mn to form MnS that functions as an inhibitor. If the S content exceeds 0.080%, hot brittleness is caused, and hot rolling becomes extremely difficult. Therefore, the S content is set to 0.080% or less. The preferable value of S content is 0.050% or less, and the more preferable value of S content is 0.030% or less.

When utilizing AlN as an inhibitor, MnS is not essential, so the lower limit of the S content includes 0%, but when utilizing MnS as an inhibitor during secondary recrystallization, the S content is 0.005% or more. And The preferred value of S content is 0.010% or more, and the more preferred value of S content is 0.020% or more.

A part of S may be replaced by Se or Sb. In that case, a formula defined in consideration of the atomic weight ratio, Seq=S+0.406·Se, or a value converted by Seq=S+0.406·Sb To use.

Moreover, in order to improve the characteristic of the grain-oriented electrical steel sheet 1, the base material steel sheet 10 contains B: 0.001 to 0.010%, Sn: 0.01 to 0.20%, in addition to the above elements. One or two or more of Cr: 0.01 to 0.50% and Cu: 0.01 to 0.50% may be contained. Since B, Sn, Cr, and Cu are not essential elements, the lower limit of their contents is 0%.

<B: 0.001 to 0.010%>
B, together with Sn, Cr, and Cu, is an element that contributes to the improvement of coating 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. The preferable value of B content is 0.002% or more, and the more preferable value of 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 increases and the stripability during cold rolling deteriorates, so the B content is set to 0.010% or less. The preferable value of B content is 0.008% or less, and the more preferable value of B content is 0.006% or less.

<Sn: 0.01 to 0.20%>
Sn, together with B, Cr and Cu, is an element that contributes to the improvement of coating adhesion. Although the mechanism for improving the coating adhesion of Sn is not clear, the improvement of the smoothness of the surface of the base steel sheet 10 is recognized by the addition of Sn, and therefore it is considered that Sn contributes to the smoothing of the surface of the base steel sheet 10. ..

If the Sn content is less than 0.01%, the effect of smoothing cannot be sufficiently obtained, so the Sn content is set to 0.01% or more. The preferable value of Sn content is 0.02% or more, and the more preferable value of Sn content is 0.03% or more. On the other hand, when the Sn content exceeds 0.20%, the secondary recrystallization becomes unstable and the magnetic properties deteriorate, so the Sn content is set to 0.20% or less. The preferable value of Sn content is 0.15% or less, and the more preferable value of Sn content is 0.10% or less.

<Cr: 0.01 to 0.50%>
Cr, together with B, Sn, and Cu, is an element that contributes to the improvement of coating adhesion. If the Cr content is less than 0.01%, the effect of improving the coating adhesion cannot be sufficiently obtained, so the Cr content is set to 0.01% or more. The preferable value of Cr content is 0.05% or more, and the more preferable value of 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, it may hinder the formation of the intermediate coating film 20 containing silicon oxide. Therefore, the Cr content is 0.50%. Below. The preferable value of Cr content is 0.30% or less, and the more preferable value of Cr content is 0.20% or less.

<Cu: 0.01 to 0.50%>
Cu is an element that contributes to the improvement of coating adhesion, together with B, Sn, and Cr. If the Cu content is less than 0.01%, the effect of improving the coating adhesion cannot be sufficiently obtained, so the Cu content is set to 0.01% or more. A preferable value of Cu content is 0.05% or more, and a more preferable value of Cu content is 0.10% or more. On the other hand, when the Cu content exceeds 0.50%, the base steel sheet 10 becomes brittle during hot rolling, so the Cu content is set to 0.50% or less. A preferable value of Cu content is 0.40% or less, and a more preferable value of Cu content is 0.30% or less.

In the base material steel plate 10, the balance excluding the above elements is Fe and impurities. Impurities are elements that include at least one of the elements that are inevitably mixed from the steel raw material and the elements that are inevitably mixed in the steelmaking process, and are permitted to be mixed within the range that does not impair the characteristics of the grain-oriented electrical steel sheet 1.

Further, for the purpose of improving magnetic properties, improving properties required for structural members such as strength, corrosion resistance, and fatigue properties, improving castability and stripability, and improving productivity by using scraps, etc. , Mo, W, In, Bi, Sb, Ag, Te, Ce, V, Co, Ni, Se, Ca, Re, Os, Nb, Zr, Hf, Ta, Y, and La, or two or more thereof. May be contained in a total of 5.00% or less, preferably 3.00% or less, more preferably 1.00% or less.

[Description of Intermediate Coating 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 material steel plate 10. The intermediate coating 20 is sandwiched between the base material steel plate 10 and the tension insulating coating 30. Since the intermediate coating 20 is a coating other than the forsterite coating, the interface 40 between the base steel sheet 10 and the intermediate coating 20 has almost no unevenness. In other words, in the grain-oriented electrical steel sheet 1 of the present embodiment, the interface 40 has extremely high flatness, and the domain wall under an AC magnetic field, as compared with the conventional grain-oriented electrical steel sheet using a forsterite-based coating as an intermediate coating. The smooth movement of the iron contributes to the reduction of iron loss. Further, as will be described below, the intermediate coating 20 is an external oxide film having a specific structure, and therefore contributes to improving the adhesion of the tension insulating coating 30.

As shown in FIG. 1, the intermediate coating film 20 is discontinuous from the interface 40 between the base material steel plate 10 and the intermediate coating film 20 and is discontinuously present in the interface direction parallel to the interface 40. To include. Each discontinuous region 21 contains the same components as the tension insulating coating 30 described later. In FIG. 1, the distance between the adjacent discontinuous regions 21 is shown to be constant, but the distance between the adjacent discontinuous regions 21 may be different. Regions inside the intermediate coating 20 other than the discontinuous region 21 contain silicon oxide (eg, SiO ₂ ) as an oxide mainly.

<Chemical composition of the intermediate coating 20>
The intermediate coating 20 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 further preferable from the viewpoint of chemical stability and film adhesion.

The existence and thickness of the intermediate coating 20 can be confirmed by physically polishing the cross section of the grain-oriented electrical steel sheet 1 and observing the polished surface with a transmission electron microscope (TEM). The silicon oxide can be confirmed by elemental analysis such as EDS analysis. The crystallization temperature of silicon oxide is about 1500° C., and in a normal manufacturing process, it does not reach such a high temperature, so crystalline silicon oxide is not formed. In this case, it is difficult to identify the silicon oxide from the crystal diffraction line, and therefore, it is confirmed by the ratio of the elemental analysis values by the EDS analysis, that is, the atomic ratio of Si and O.

<Average film thickness T _D of the intermediate coating 20: 10 to 200 nm>
Thickness of the intermediate coating 20 is dependent on the annealing conditions of the base material steel plate, the average thickness T _D is not limited to a particular value, in order to ensure a high degree of coating adhesion, is 10~200nm preferable.

When the average film thickness T _D of the intermediate coating film 20 is less than 10 nm, the adhesiveness of the interface 40 between the base steel sheet 10 and the intermediate coating film 20 becomes insufficient, and during winding core production or other excessive plastic working, and In the environment in which the frictional force is superposed between the steel plates, the tensile insulating coating 30 is easily peeled off, so the average thickness T _D of the intermediate coating 20 is preferably 10 nm or more. A more preferable value of the average film thickness T _D of the intermediate coating 20 is 15 nm or more, and a further preferable value thereof is 25 nm or more.

On the other hand, when the average film thickness T _D of the intermediate coating film 20 exceeds 200 nm, the cohesive force of the intermediate coating film 20 itself becomes large, and the frictional force is superposed during the manufacturing of the wound core or other excessive plastic working and between the steel sheets. In such an environment, the tensile insulating coating 30 is easily separated from the inside of the intermediate coating 20 as a starting point, so that the average thickness T _D of the intermediate coating 20 is preferably 200 nm or less. The more preferable value of the average film thickness T _D of the intermediate coating 20 is 150 nm or less, and the more preferable value thereof is 100 nm or less.

The method of specifying the average film thickness T _D of the intermediate coating 20 is as follows.

First, a sample is taken from the grain-oriented electrical steel sheet 1 so that the cross section of the base steel sheet 10 orthogonal to the rolling direction is exposed. After polishing the cross section of the sample to expose a cross section in which the length of the interface 40 between the base material steel plate 10 and the intermediate coating film 20 is about 10 μm, as shown in FIG. The average film thickness T _D of the intermediate coating 20 between the surface and the tension insulating coating 30 is measured as follows.

The interface 40 between the base steel sheet 10 and the intermediate coating 20 does not have unevenness as in the case of using a forsterite-based coating, but the shape of the interface 40 has a wavy shape in which peaks and valleys appear at long periods. In many cases Similarly, the interface 50 between the tension insulating coating 30 and the intermediate coating 20 often has a wavy shape in which peaks and valleys appear at long intervals.
Therefore, a wave center line is drawn for each of the interface 40 and the interface 50 having a wavy shape. Here, when a straight line parallel to the average line of the wave curve is drawn, a straight line in which the areas surrounded by this straight line and the wave curve are equal on both sides of this straight line is the wave center line. The distance between these two wave center lines is defined as the film thickness of the intermediate coating 20.
Then, inside the intermediate film 20, 10 or more lines perpendicular to the interface 40 are drawn so as not to overlap with the first region 21, and the film thickness according to the above definition is measured on the line. Then, the average is defined as the average film thickness T _D of the intermediate coating 20.

Next, the discontinuous area 21 included in the intermediate coating 20 will be described.

<Chemical composition of discontinuous region 21>
As shown in FIG. 1, the discontinuous region 21 is partially formed in the intermediate coating 20, and is present inside the intermediate coating 20 in a discontinuous form. The discontinuous region 21 is formed at the same time when the intermediate coating 20 and the tension insulating coating 30 are formed, and therefore contains the same components as the tension insulating coating 30.

For example, the discontinuous region 21 is composed of the same component as the tension insulating coating 30, such as magnesium phosphate or aluminum phosphate and chromic acid, and an insulating coating component made of colloidal silica, or crystalline boric acid and alumina oxide. Insulating coating components are included. The composition can be confirmed by EDS elemental analysis of the cross-sectional TEM image. A method of forming the discontinuous area 21 will be described later.

<Line segment ratio M of the discontinuous region 21: 1 to 50%>
The existence mode of the discontinuous region 21 is defined by the line segment ratio M defined by the following equation (1). Specifically, as shown in FIG. 1, when a cross section having a length L in the direction orthogonal to the rolling direction of the base material steel sheet 10 is viewed, the interface direction (interface 40) of the discontinuous region 21 appearing in the cross section. It is preferable that the line segment ratio M of the discontinuous region 21 defined by the following equation (1) is 1 to 50%, where ΣLk is the total value of the lengths in the direction parallel to.
M=(ΣLk/L)×100 (1)

In the above equation (1), ΣLk is defined by the following equation (1a). In the formula (1a), Li is the length in the interface direction of the i-th discontinuous region 21 that appears in the cross section having the length L (see FIG. 1). The length L needs to be at least about 10 μm.
ΣLk=L ₁ +L ₂ +L ₃ +...+Li+...+L _k (1a)

If the line segment ratio M is less than 1%, it will be difficult to obtain the required film adhesion at the time of manufacturing a wound core or at the time of other excessive plastic working, and in an environment where frictional force is superimposed between steel sheets. Therefore, the line segment ratio M is preferably 1% or more. A more preferable value of the line segment ratio M is 3% or more, and a further preferable value is 5% or more.

On the other hand, when the line segment ratio M exceeds 50%, stress is concentrated inside the discontinuous region 21 during manufacturing of the wound core or other excessive plastic working, and in an environment where frictional force is superimposed between the steel plates. Then, the tension insulating coating 30 is easily peeled off, so that the line segment ratio M is preferably 50% or less. A more preferable value of the line segment ratio M is 40% or less, and a further preferable value is 30% or less.

Next, the average thickness of the discontinuous region 21 in the thickness direction of the intermediate coating 20 will be described.

<Average thickness of the discontinuous area 21 _T C: 2~50nm>
The average thickness _{T C} of the discrete regions 21 in the thickness direction of the intermediate coating 20 is preferably 2 to 50 nm.
The method of specifying the average thickness T _C of the discontinuous region 21 is the same as the method of specifying the average film thickness T _D of the intermediate coating 20. However, since the discontinuous region 21 exists in a discontinuous form in the intermediate coating film 20, the interval for measuring the average thickness T _C of the discontinuous region 21 is approximately 2 times the thickness of the discontinuous region 21. A spacing of twice or more is preferable.

When the average thickness T _C of the discontinuous region 21 is less than 2 nm, the coating adhesion required in the winding core production or other excessive plastic working and in the environment where the frictional force is superimposed between the steel plates is obtained. Therefore, the average thickness T _C of the discontinuous region 21 is preferably 2 nm or more. A more preferable value of the average thickness T _C of the discontinuous region 21 is 5 nm or more, and a further preferable value is 8 nm or more.

On the other hand, when the average thickness T _C of the discontinuous region 21 exceeds 50 nm, the discontinuous region 21 has a discontinuous region 21 at the time of manufacturing the wound core or during other excessive plastic working, and in an environment where frictional force is superimposed between the steel plates. Since the stress is concentrated inside and the tensile insulating coating 30 is easily peeled off, the average thickness T _C of the discontinuous region 21 is preferably 50 nm or less. A more preferable value of the average thickness T _C of the discontinuous region 21 is 40 nm or less, and a further preferable value is 35 nm or less.

Then, the average distance _T A between base steel sheet 10 and the discrete regions 21 (nm), the average distance _T relationship between B (nm) between the tension insulating film 30 and the discontinuous area 21 described To do.

<Relationship between T _A and T _B >
It is preferable that T _A and T _B satisfy the following formula (2).
T _A ≧T _B (2)

As shown in FIG. 1, the existence position of the discontinuous region 21 in the film thickness direction of the intermediate coating 20 can be understood from the magnitude relation between T _A and T _B. When T _A ≧T _B , the coating adhesion required during manufacturing of a wound core or other excessive plastic working and in an environment where frictional force is superposed between steel sheets is further improved.

That is, since the discontinuous region 21 exists in the intermediate coating film 20 on the tension insulating coating film 30 side, the adhesion of the tension insulating coating film 30 is further improved. Although the reason for this has not been confirmed, when T _A ≧T _B , the tension insulating coating 30 has a layered structure in which the tension insulating coating 30 is integrated with the intermediate coating 20 via the discontinuous region 21, and thus the intermediate coating 20. It is considered that the mechanical coupling force with the tension insulating coating 30 becomes stronger and the adhesion of the tension insulating coating 30 is improved.

[Explanation of Tension Insulation Coating 30]
Next, the tension insulating coating 30 formed on the surface of the intermediate coating 20 will be described.

<Chemical composition of tension insulating coating 30>
As the tensile insulating coating 30, an insulating coating made of magnesium phosphate or aluminum phosphate, chromic acid and colloidal silica (see Patent Document 20), or crystalline boric acid and alumina oxide that can obtain higher tension than the insulating coating. An insulating coating made of a material (see Patent Document 23) or the like can be used.

<Average film thickness T _E of the tension insulating coating 30: 0.5 to 10 μm>
The film thickness of the tension insulating coating 30 is set in consideration of the tension required for improving the magnetic properties, the space factor of the grain-oriented electrical steel sheet 1 in the iron core, etc., but the average film thickness T _E is 0.5. It is preferably 10 μm.

If the average film thickness T _E of the tension insulating coating 30 is less than 0.5 μm, the effect of reducing iron loss by applying tension cannot be sufficiently obtained. Therefore, the average film thickness T _E of the tension insulating coating 30 is 0.5 μm or more. preferable. A more preferable value of the average film thickness T _E of the tension insulating coating 30 is 0.8 μm or more, and a further preferable value is 1.5 μm or more.

On the other hand, if the average film thickness T _E of the tension insulating coating 30 exceeds 10 μm, sufficient coating adhesion may not be obtained even if the intermediate coating 20 and the discontinuous region 21 are properly formed, and Since the space factor decreases, the average film thickness T _E of the tension insulating coating 30 is preferably 10 μm or less. A more preferable value of the average film thickness T _E of the tension insulating coating 30 is 8 μm or less, and a further preferable value is 5 μm or less.

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

<Manufacturing method>
(I) (a) A steel sheet obtained by removing the coating of inorganic mineral substances such as forsterite formed on the surface of the steel sheet by finish annealing by means such as pickling and grinding, and (b) coating of the above inorganic mineral substance by finish annealing. Steel sheet that intentionally suppresses the formation of the steel sheet, or (c) a steel sheet that is a steel sheet surface that is smoothed until it exhibits specular gloss, that is, a steel sheet that does not substantially have a forsterite coating on the steel sheet surface (base material Steel plate 10),
(Ii) When the forming liquid for the tension insulating coating 30 is applied to the surface of the base material and baked to form the tension insulating coating 30, the heating and the atmosphere during the baking are appropriately controlled,
(Ii-1) The surface of the steel sheet is oxidized to form an intermediate coating 20 containing silicon oxide as a main oxide, and a discontinuous region 21 containing the same components as the tension insulating coating 30 is formed in the intermediate coating 20. And then
(Ii-2) The tension insulating coating 30 is formed on the intermediate coating 20.

A steel sheet in which a film of an inorganic mineral substance such as forsterite is removed by a method such as pickling and grinding, and a steel plate in which the formation of the inorganic mineral substance film is intentionally suppressed are produced, for example, as follows.

A silicon steel piece containing about 2.0 to 4.0 mass% of Si is subjected to hot rolling to form a hot-rolled steel sheet, and if necessary, the hot-rolled steel sheet is annealed, and thereafter, the hot-rolled steel sheet or the annealed hot-rolled steel sheet. The steel sheet is cold-rolled once or twice or more with intervening intermediate annealing to finish the steel sheet to the final thickness, and then the steel sheet is decarburized and annealed, and primary recrystallization proceeds. The decarburization annealing forms an oxide layer on the surface of the steel sheet.

An annealing separator having magnesia (MgO) as a main component is applied to the surface of a steel sheet having an oxide layer, dried, and then dried, wound into a coil, and subjected to finish annealing (secondary recrystallization). The film of the inorganic mineral substance mainly composed of forsterite (Mg ₂ SiO ₄ ) formed on the surface of the steel sheet by the finish annealing is removed by means such as pickling and grinding. After removing the coating, the surface of the steel sheet is preferably finished by chemical polishing or electrolytic polishing.

Instead of the annealing separating agent containing magnesia (MgO) as a main component, an annealing separating agent containing alumina as a main component is applied and dried, and after drying, it is wound into a coil and finish annealing (secondary recrystallization). To serve. By finish annealing, it is possible to obtain a steel sheet in which the formation of an inorganic mineral coating such as forsterite is intentionally suppressed. After the finish annealing, preferably, the surface of the steel sheet is finished smooth by chemical polishing or electrolytic polishing.

The tension insulating coating 30 is formed by applying a forming liquid for the tension insulating coating 30 onto the surface of the steel sheet (base material) of the above (a) to (c) where the forsterite coating is not substantially present on the surface of the steel sheet, and baking it. When forming, properly control the heating and atmosphere during baking,
(Ii-1) The surface of the steel sheet is oxidized to form an intermediate coating 20 containing silicon oxide as a main oxide, and a discontinuous region 21 containing the same components as the tension insulating coating 30 is formed in the intermediate coating 20. And then
(Ii-2) The tension insulating coating 30 is formed on the intermediate coating 20.

First, a method of forming the intermediate coating 20 on the surface of the steel sheet will be described.

<Formation of Intermediate Coating 20>
FIG. 2 schematically shows a method for forming the intermediate coating 20 on the surface of the steel sheet. An oxide layer (mainly Fe type) is formed on the steel sheet surface by annealing a base steel sheet (process x1: base material production) in which a forsterite coating is not substantially present on the steel sheet surface to oxidize the steel sheet surface in a high dew point atmosphere. Are formed (step x2: high dew point annealing).

A steel sheet having an oxide layer (mainly Fe-based) on the surface of the steel sheet is annealed in a low dew point atmosphere to reduce the oxide layer (mainly Fe-based) and form a silicon oxide layer on the steel sheet side having a low oxygen concentration, An "oxide layer (mainly Fe-based)+reduced Fe layer" is formed on the surface side (step x3: low dew point annealing).

A high-dew-point annealing (step x2) and then a low-dew-point annealing (step x3) surface of the steel sheet are coated with a forming liquid for the tension insulating coating 30 and baked to form a tension insulating coating 30 on the silicon oxide layer. (Step x4: Insulating film forming liquid application/baking).

In step x4, the “oxide layer (mainly Fe-based)+reduced Fe layer” generated in step x3 is dissolved and taken in by the tension insulating coating 30, so that the layer structure of the steel sheet surface is silicon oxide from the steel sheet side. It comprises a layer (ie, intermediate coating 20) and a tension insulating coating 30 thereon.

Next, a method of forming the intermediate coating 20 on the surface of the steel sheet and forming the discontinuous region 21 in the intermediate coating 20 will be described.

<Formation of Intermediate Coating 20 and Discontinuous Region 21>
FIG. 3 schematically shows a method of forming the intermediate coating 20 on the surface of the steel sheet and forming the discontinuous region 21 in the silicon oxide layer intermediate coating 20.

A base steel sheet (process y1: base material preparation) in which the forsterite-based coating is not substantially present on the steel sheet surface is annealed in a high dew point atmosphere to oxidize the steel sheet surface, and an oxide layer (mainly Fe-based) on the steel sheet surface. Are formed (step y2: high dew point annealing). Up to this point, the steps are the same as the steps (x1 and x2) shown in FIG. 2, but the subsequent step y3 and subsequent steps are characteristic steps in the production of the grain-oriented electrical steel sheet 1.

A steel sheet having an oxide layer (mainly Fe-based) on the steel sheet surface is annealed in a low dew point atmosphere for a short time (step y3: low dew point annealing (short time)). In the low dew point annealing (short time) of step y3, since the annealing time is short, diffusion of oxides (mainly Fe-based) and reduced Fe contained in the oxide layer (mainly Fe-based) on the steel sheet side is not possible. This is sufficient, and a "discontinuous interposing layer containing an oxide (mainly Fe-based) and reduced Fe" is formed inside the silicon oxide layer.

At this time, Fe contained in the surface layer of the oxide layer (mainly Fe-based) is partially reduced, and “oxidation is performed on the outermost surface layer of the oxide layer (mainly Fe-based) as in the method shown in FIG. Object layer (mainly Fe-based)+reduced Fe layer" is formed.

On the surface of the steel sheet that has been subjected to high dew point annealing (step y2) and then low dew point annealing (short time) (step y3), a forming liquid for the tension insulating coating 30 is applied and baked to form a layer on the silicon oxide layer. Then, the tension insulating coating 30 is formed (step y4: coating/baking of insulating coating forming liquid).

At this time, the above “oxide layer (mainly Fe-based)+reduced Fe layer” is dissolved and incorporated in the tension insulating coating film 30 as in the step x4 of FIG. Further, the forming liquid for the tensile insulating coating 30 permeates into the “discontinuous interposing layer containing oxide (mainly Fe-based) and reduced Fe” formed inside the silicon oxide layer, and the silicon oxide layer ( That is, inside the intermediate coating 20), a "discontinuous interposing layer containing an insulating coating component (that is, a discontinuous region 21 containing the same component as the tension insulating coating 30)" is formed.

The "discontinuous interposing layer containing oxide (mainly Fe-based)+reduced Fe" exists independently in the silicon oxide layer, but "discontinuous interposing layer containing oxide (mainly Fe-based)+reduced Fe". Considering the phenomenon that the forming liquid for the tensile insulating coating 30 permeates into the "intercalation layer", a part of the "discontinuous intercalation layer containing oxide (mainly Fe-based)+reduced Fe" is "oxidized" on the surface. There is also a possibility that the material layer (mainly Fe-based)+reduced Fe layer” is connected in a minute region.

As shown in FIG. 3, the formation of the "discontinuous interposition layer containing the insulating coating component" inside the silicon oxide layer is performed by discontinuous interposition of "oxide (mainly Fe-based) and +reduced Fe" on the surface of the steel sheet. After forming the silicon oxide layer including the "intercalation layer", the forming liquid for the tension insulating coating 30 may be applied and baked, or the forming liquid for the tension insulating coating 30 may be applied to the steel plate surface. After that, high dew point annealing (step y2) may be performed, and then low dew point annealing (short time) (step y3) may be performed.

The surface of the steel sheet is coated with a forming liquid for the tensile insulating coating 30, followed by high dew point annealing and then low dew point annealing (short time) to discontinue the inside of the silicon oxide layer as a "discontinuous intermediate containing insulating coating components". In the case of forming the "insertion layer", each annealing also serves as a step of drying and baking the forming liquid for the tension insulating coating 30. The baking temperature and time are preferably 650 to 950° C. and 1 to 300 seconds in order to suppress thermal decomposition of the insulating coating component.

Here, the high dew point annealing in step y2 (hereinafter sometimes referred to as "first stage annealing") and the low dew point annealing in step y3 (short time) (hereinafter sometimes referred to as "second stage annealing"). Will be described.

<Process y2: High dew point annealing (first stage annealing)>
Heat retention temperature: 650-950°C
Heating time: 1 to 300 seconds Annealing Atmosphere: nitrogen, or nitrogen and hydrogen atmosphere dew point (T _1): 30~50 ℃

A base steel sheet having substantially no forsterite coating on the steel sheet surface is heated and maintained at 650 to 950° C. in a high dew point nitrogen atmosphere or a nitrogen+hydrogen mixed atmosphere, and an oxide is formed on the steel sheet surface. A layer (mainly Fe-based) is formed. The heating and holding time is preferably 1 to 300 seconds, but is preferably 5 seconds or more from the viewpoint of ensuring uniform heating in the width direction of the steel sheet. The heating rate up to the heating and holding temperature is not particularly limited, but is preferably 5° C./sec or more, more preferably 10° C./sec or more.

As the annealing atmosphere, a nitrogen atmosphere or a nitrogen+hydrogen mixed atmosphere is used in order to suppress excessive formation of an oxide layer (mainly Fe-based). The nitrogen+hydrogen mixed atmosphere is preferably an atmosphere of 25% nitrogen:75% hydrogen.

The atmosphere dew point is preferably 30 to 50° C., though it depends on the annealing atmosphere and the annealing temperature. When the atmospheric dew point exceeds this range, the amount of the oxide layer (mainly Fe-based) formed or the layer thickness increases, and the amount of oxygen that diffuses in the oxide layer (mainly Fe-based) and reaches the surface of the steel sheet is increased. In the next step y3 (low dew point annealing (short time) [second step annealing]), the discontinuous insertion layer containing "oxide (mainly Fe-based) and reduced Fe" inside the silicon oxide layer. Is less likely to be formed, and even if it is formed, the line segment ratio M thereof may exceed 50%.

As for the atmosphere dew point, the nitrogen+hydrogen mixed atmosphere is an atmosphere of 25% nitrogen:75% hydrogen, 30 to 50° C. is preferable if the annealing temperature is 650 to 800° C., and the annealing temperature is 750 to 950° C. 40-50 degreeC is preferable.

<Process y3: Low dew point annealing (short time) (second stage annealing)>
Heat retention temperature: 800-1100°C
Heating holding time: 1 to 60 seconds Temperature rising rate: 10 to 400°C/second Annealing atmosphere: Nitrogen or nitrogen + hydrogen Atmosphere dew point (T ₂ ): -20 to 30°C

In step y3, the steel sheet that has been subjected to step y2 is heated to preferably 800 to 1100° C. in a nitrogen atmosphere with a low dew point or a mixed atmosphere of nitrogen and hydrogen and held for a short time to form the silicon oxide layer formed in step y2. A discontinuous insertion layer containing "oxide (mainly Fe-based) and reduced Fe" is formed inside, and a silicon oxide layer including the discontinuous insertion layer is formed on the surface of the steel sheet.

The heating and holding time is 1 second or more, but 5 seconds or more is preferable from the viewpoint of ensuring uniform heating in the width direction of the steel sheet and the thickness of 2 nm or more of the discontinuous interposing layer. From the viewpoint of suppressing diffusion and making the layer thickness of the discontinuous interposing layer 50 nm or less, 60 seconds or less is preferable, and 30 seconds or less is more preferable.

The rate of temperature increase up to the heating and holding temperature is preferably 10° C./sec or more in order to control the line segment ratio M of the discontinuous interposing layer to 1 to 50%. If the rate of temperature increase is less than 10° C./sec, the difference in relative diffusion rate between Fe and Si becomes small, making it difficult to form a discontinuous interposition layer, and the above line segment ratio does not reach 1%. .. It is more preferably 15° C./second or more.

When the temperature rising rate is high, the diffusion/oxidation rate of Si contained in the steel sheet is relatively high with respect to the diffusion/oxidation rate of Fe and oxide contained in the oxide layer (mainly Fe-based) to the surface. As a result, diffusion of Fe is delayed, and a discontinuous interposing layer containing oxide (mainly Fe-based) and reduced Fe is efficiently formed. However, if the heating rate is too fast, a denser silicon oxide layer is formed, and the layer thickness becomes thinner. The rate of temperature increase is preferably 400° C./sec or less in consideration of ensuring uniform heating in the width direction of the steel sheet.

As the annealing atmosphere, a nitrogen atmosphere or a nitrogen+hydrogen mixed atmosphere is used in order to suppress the excessive formation of the oxide layer (mainly Fe-based)+reduced Fe layer. The nitrogen+hydrogen mixed atmosphere is preferably an atmosphere of 25% nitrogen:75% hydrogen.

Dew point T ₂ ° C., depending on the heating temperature, preferably -20 to 30 ° C.. In relation to the atmosphere dew point T ₁ °C in the process y2, T ₂ ≤T ₁ -20 is preferable.

The average layer thickness (average distance T _A between the base material steel sheet 10 and the discontinuous region 21) of the silicon oxide layer sandwiched between the “discontinuous interposing layer containing the insulating coating component” and the steel sheet, and the tension insulating coating 30. And the average thickness of the silicon oxide layers sandwiched between the “discontinuous interposing layers containing insulating coating components” (the average distance T _B between the tension insulating coating 30 and the discontinuous region 21), T _A ≧ From the viewpoint of ensuring T _B in a stable manner, the atmosphere dew point is preferably low, and -20 to +15°C is preferable.

After annealing, the degree of oxidation (dew point) of the atmosphere is controlled so that the silicon oxide layer and the discontinuous insertion layer containing the “oxide (mainly Fe-based) part+reduced Fe” do not deteriorate, and the steel sheet is Cooling. Cooling to 500° C. that affects the oxidation of the steel sheet should be 75%:25% of hydrogen:nitrogen, and a dew point of −20 to 30° C. (similar to the atmosphere of the process y3 (second annealing)). Therefore, the deterioration of the silicon oxide layer can be suppressed).

A higher cooling rate is preferable from the viewpoint of suppressing the oxidation of the steel sheet, but if the cooling rate is excessively high, the distortion amount of the steel sheet increases and the magnetic properties deteriorate, so the cooling rate is 5 to 100°C/sec. Is preferred.

<Process y4: Insulating film forming liquid application/baking>
Liquid pH: 0.5-4.0
Coating amount: 0.5-10 μm in dry film thickness
Baking atmosphere: Hydrogen: 75% nitrogen: 25%
Atmospheric dew point: -20 to 40°C
Baking temperature/time: 650-950°C, 5-300 seconds,

In step y3, the forming liquid for the tensile insulating coating film 30 is applied to the steel sheet on which a silicon oxide layer including a discontinuous interposing layer containing "oxide (mainly Fe-based) portion+reduced Fe" is formed on the steel sheet surface. Then, the tension insulating coating 30 is formed by baking.

As the forming liquid for the tension insulating coating 30, for example, a liquid mainly containing phosphate and colloidal silica is preferable. The pH of the forming liquid for the tension insulating coating 30 is preferably 4.0 or less. When the pH is 4.0 or less, the reaction between the discontinuous intercalation layer containing the "oxide (mainly Fe-based) portion+reduced Fe" in the silicon oxide layer and the forming liquid for the tension insulating coating 30 is better. proceed. It is more preferably 3.0 or less.

However, if the pH of the forming liquid for the tension insulating coating 30 becomes too low, the silicon oxide layer and the base steel sheet are corroded, so the pH of the forming liquid for the tensile insulating coating 30 is preferably 0.5 or more. The forming liquid for the tension insulating coating 30 is applied to the surface of the steel sheet and baked so that the dry film thickness becomes 0.5 to 10 μm, and the tension insulating coating 30 is formed.

The baking after applying the forming liquid for the tension insulating coating 30 is preferably 650 to 950° C. in a nitrogen-hydrogen mixed atmosphere having a hydrogen:nitrogen content of 75%:25% and a dew point of −20 to 20° C. Heating is performed for 5 to 300 seconds.

In the first-stage annealing (high dew point annealing) and the second-stage annealing (low dew point annealing (short time)), formation of a discontinuous insertion layer containing an oxide (mainly Fe-based) portion+reduced Fe and a tension insulating coating 30. In the case where the formation is simultaneously performed, for example, it is necessary to heat in an atmosphere of hydrogen:nitrogen of 75%:25% and a dew point of −20 to 40° C. for 650 to 950° C. for 5 to 300 seconds. The heating rate up to the heating and holding temperature is not particularly limited, but is preferably 5° C./sec or more, more preferably 10° C./sec or more.

The upper limit of the rate of temperature increase is not particularly limited, but the rate of temperature increase is preferably 100° C./sec or less from the viewpoint of sufficiently hardening the coating film and ensuring the heat uniformity in the width direction of the steel sheet.

Similarly, the cooling of the steel sheet after the application and baking is performed in an atmosphere of hydrogen:nitrogen 75%:25% and dew point of -20 to 20°C, which affects the oxidation of the steel sheet to 500°C. Is preferred. A higher cooling rate is preferable in terms of suppressing surface oxidation of the steel sheet, but if the cooling rate is excessively high, the strain amount of the steel sheet increases and the magnetic properties deteriorate, so 5° C./sec or more is preferable. ..

Next, an example of the present invention will be described. The condition in the example is one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is based on this one condition example. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

<Example 1>
A silicon steel piece having the composition shown in Table 1 is heated at 1200° C. for 60 minutes and subjected to hot rolling to obtain a hot-rolled steel sheet having a plate thickness of 2.30 mm. The hot-rolled steel sheet is hot-rolled at 1080° C. for 180 seconds. The plate was annealed and then cold-rolled to obtain a cold-rolled steel plate having a plate thickness of 0.23 mm. The cold-rolled steel sheet is subjected to decarburization annealing and nitriding annealing, and then an annealing separating agent containing alumina as a main component is applied, finish annealing is performed at 1200° C. in a hydrogen atmosphere, and natural cooling is performed to obtain a smooth surface. The steel plate of

The above steel sheet was subjected to a first stage annealing (high dew point annealing) in an atmosphere of hydrogen:nitrogen of 75%:25% and a dew point of 40° C., the temperature was raised to 700° C. and held for 30 seconds. After that, the atmosphere dew point was switched to 0° C., the temperature was raised to 1000° C. at 15° C./sec, and the temperature was held for 15 seconds to perform the second stage annealing (low dew point/short time annealing). Then, it was cooled to room temperature at 50° C./sec in the same atmosphere as the second annealing.

After that, a forming liquid for a tension insulating film made of aluminum phosphate and colloidal silica is applied on the surface of the steel sheet so that the dry film thickness is 3 μm, and hydrogen:nitrogen is 75%:25% and dew point is 10° C. In the above atmosphere, the temperature was raised to 800° C. at a temperature rising rate of 10° C./sec and held for 30 seconds, and then cooled to room temperature at 50° C./sec.

<Layer structure>
The chemical composition and layer structure of the intermediate coating containing the discontinuous region containing the same components as the tension insulating coating were investigated as follows. The cross section of the micro test piece produced by the focused ion beam method was observed with a transmission electron microscope (TEM) from the cross section of the steel sheet orthogonal to the rolling direction of the grain-oriented electrical steel sheet. The observation was performed over the interface direction (width) of 10 μm, and the line segment ratio M of the discontinuous region was calculated.

Further, with an energy dispersive spectroscopic analyzer (EDS) attached to the TEM, oxygen (O) and silicon (Si) derived from silicon oxide, iron (Fe) derived from a steel plate, and phosphorus (P ) Elemental analysis and quantitative analysis were performed to identify the compound. Further, _α of SiO _α responsible for silicon oxide was determined from the element ratio of silicon and oxygen. α was about 2.0 in all the samples.

Table 2 shows the survey results.

<Film adhesion bending>
The film adhesion of the tension insulating film was evaluated by the film remaining area ratio when the evaluation sample was wound around a cylinder having a diameter of 20 mm and bent 180°.

The evaluation criteria are as follows.
⊚: The residual film area ratio is 95% or more (very excellent)
◯: The residual film area ratio is 90% or more and less than 95% (excellent)
Δ: coating residual area ratio is 80% or more and less than 90% (effective)
X: The residual film area ratio is less than 80% (no effect)

Table 2 also shows the evaluation results.

<Film adhesion and friction>
In order to evaluate the film adhesion of the tension insulating film when a frictional force was applied, a sample was wound around a cylinder having a diameter of 30 mm, once bent inward at 180°, bent, and then bent and stretched. As shown in FIG. 4, the sample was fixed on a surface plate, a steel ball having a diameter of 10 mm was pressed against the sample surface with 1 kgf, and the sample was slid (30 mm) at a speed of 1 mm/sec for 30 seconds to obtain a steel plate surface. A friction mark was added to the (see above figure). The maximum peeling width of the coating peeled off at the friction marks was evaluated (see the figure below).

The evaluation criteria are as follows.
⊚: Maximum peeling width is 1 mm or less (very excellent)
◯: Maximum peeling width is 2 mm or less (excellent)
Δ: Maximum peeling width is 4 mm or less (effective)
X: Maximum peeling width exceeds 4 mm (no effect)

Table 2 also shows the evaluation results.

<Magnetic characteristics>
The magnetic characteristics were evaluated according to JIS C 2550. The magnetic flux density was evaluated using B ₈ . B ₈ is a magnetic flux density at a magnetic field strength of 800 A/m, which serves as a criterion for determining the quality of secondary recrystallization. It was judged that B ₈ =1.80 T or more was secondary recrystallized.

Table 2 also shows the evaluation results.

In Table 2, sample No. The invention examples of B1 to B18 all show good film adhesion. Sample No. In the invention examples of B12 and B17, the effect of adding B, Cr, Cu, and Sn is sufficiently exhibited, and particularly good film adhesion is exhibited.

Sample No. Since the comparative examples of b3, b5, and b6 respectively contained a large amount of Si, Al, and N, the ductility at room temperature was poor and cold rolling was impossible. Sample No. In the comparative example of b8, the S content was large, the hot ductility was poor, and hot rolling was impossible. Therefore, the sample No. In the comparative examples of b3, b5, b6, and b8, the film adhesion was not evaluated.

Sample No. In the comparative examples of b1, b2, b4, and b7, the elemental amounts of the base steel sheet were out of the range of the present invention, so that none of the secondary recrystallization occurred and the magnetic flux density was very low. The samples that did not undergo secondary recrystallization had low coating adhesion. When the secondary recrystallization was not performed, it is considered that the crystal grain size of the steel sheet was fine and the formation of the oxide layer (intermediate coating) was not appropriately performed.

<Example 2>
Among the silicon steel pieces having the composition shown in Table 1, Steel No. The silicon steel piece of A6 is heated at 1200° C. for 60 minutes and subjected to hot rolling to obtain a hot rolled steel sheet having a plate thickness of 2.30 mm, and the hot rolled steel sheet is annealed at 1080° C. for 180 seconds. Then, cold rolling was performed to obtain a cold rolled steel sheet having a thickness of 0.23 mm. The cold-rolled steel sheet was subjected to decarburization annealing and nitriding annealing, and then an annealing separating agent containing magnesia as a main component was applied, finish annealing was performed at 1200° C. in a hydrogen atmosphere, and it was naturally cooled as it was.

After the inorganic coating film formed on the steel sheet surface is dissolved and removed with a 10% hydrochloric acid aqueous solution, the steel sheet is immersed in an aqueous solution consisting of 10% hydrofluoric acid and 10% hydrogen peroxide, and the steel sheet surface is chemically polished and smoothed. Turned into

A steel sheet with a smoothed surface was heated to 800°C for 30 seconds in an atmosphere of hydrogen: nitrogen of 75%: 25% and a dew point of -20 to 60°C and held for 30 seconds to perform first-stage annealing (high dew point). Annealing), then the atmosphere dew point was switched to 0 to 40° C., the temperature was raised to 1050° C. at 15° C./sec and held for 20 seconds, and the second stage annealing (low dew point/short time annealing) was performed. Then, in the same atmosphere, it was cooled to room temperature at 50° C./sec to prepare a sample.

After that, a forming liquid for a tension insulating film composed of aluminum phosphate and colloidal silica was applied to the surface of the steel sheet so that the dry film thickness was 3 μm, and hydrogen:nitrogen was 75%:25% and dew point was 10%. In an atmosphere of °C, the temperature was raised to 820°C at a rate of 10°C/sec, held for 30 seconds, and then cooled at 10°C/sec. The evaluation of the adhesion of the tensile insulating coating was performed by the same method as in Example 1.

The results are shown in Table 3.

Sample No. The invention examples of C4 to C9 all show good film adhesion. In particular, the sample No. In the invention examples of C4 to C8, the formation of the discontinuous insertion layer (discontinuous region) is appropriately controlled, and good film adhesion is exhibited.

Sample No. In the comparative examples of C1, C2, C3, c1, c2, and c3, the dew point of the high dew point annealing was too low, the discontinuous insertion layer was not formed, and the film adhesion was poor. Sample No. In the comparative example of c4, the line segment ratio M of the discontinuous interposing layer is too large, and the coating adhesion when the frictional force is applied is poor. Sample No. In the comparative example of c5, the line segment ratio M of the discontinuous insertion layer is too large, and the layer thickness of the discontinuous insertion layer becomes too large, resulting in poor film adhesion. Sample No. In the comparative example of c6, the line segment ratio M and the layer thickness of the discontinuous interposing layer are appropriate, but the layer thickness of the silicon oxide layer (intermediate coating) is too thick and the coating adhesion is poor.

According to the present invention, a grain-oriented electrical steel sheet having an intermediate coating which is an intermediate coating other than the forsterite coating between the tension insulating coating and the base material steel sheet and which can enhance coating adhesion, that is, excellent It is possible to provide a grain-oriented electrical steel sheet having excellent coating adhesion and magnetic properties. Therefore, the present invention is highly applicable in the electromagnetic steel sheet manufacturing industry and the electromagnetic steel sheet utilizing industry.

DESCRIPTION OF SYMBOLS 1... Grain-oriented electrical steel sheet, 10... Base material steel sheet, 20... Intermediate film, 21... Discontinuous area, 30... Tension insulating film, 40... Interface between base material steel plate and intermediate film, 50... Intermediate film and tension insulating film Interface with

Claims (6)

Base material steel plate,
Tension insulation coating,
An intermediate film sandwiched between the base steel plate and the tension insulating film and containing silicon oxide,
Equipped with
The base material steel sheet, as 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 to 0.50%,
And the balance consists of Fe and impurities,
The intermediate coating, in a state away from the interface between the base material steel sheet and the intermediate coating, includes a discontinuous region that is intermittently present in the interface direction that is a direction parallel to the interface,
The grain-oriented electrical steel sheet, wherein the discontinuous region contains the same component as the tension insulating coating. When a cross section having a length L in a direction orthogonal to the rolling direction of the base steel sheet is viewed, when the total value of the lengths in the interface direction of the discontinuous regions appearing in the cross section is ΣLk, the following ( The line segment ratio M of the discontinuous region defined by the formula (1) is 1 to 50%, and the grain-oriented electrical steel sheet according to claim 1.
M=(ΣLk/L)×100 (1) The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the intermediate coating has an average thickness of 10 to 200 nm. The grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein an average thickness of the discontinuous region in the thickness direction of the intermediate coating is 2 to 50 nm. Wherein the average distance T _A between base steel sheet and the discontinuous region _(nm), and the average distance T _B between the tension insulating film and said discontinuous region _(nm), but the following equation (2) The grain-oriented electrical steel sheet according to any one of claims 1 to 4, characterized by satisfying the following.
T _A ≧T _B (2) The base material steel sheet has, as the chemical composition, by mass% B: 0.001 to 0.010%, Sn: 0.01 to 0.20%, Cr: 0.01 to 0.50%, and Cu: 0.01-0.50% of 1 type(s) or 2 or more types is contained, The grain-oriented electrical steel sheet as described in any one of Claims 1-5 characterized by the above-mentioned.

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