阅读说明：本技术 方向性电磁钢板及其制造方法 (Grain-oriented electromagnetic steel sheet and method for producing same ) 是由 片冈隆史 牛神义行 中村修一 藤井浩康 财前洋一 于 2018-07-13 设计创作，主要内容包括：一种方向性电磁钢板,该方向性电磁钢板以质量％计含有C：0.010％以下、Si：2.50～4.00％、酸可溶性Al：0.0010～0.0100％、N：0.012％以下、Mn：1.00％以下、S：0.02％以下,剩余部分包含Fe及不可避免的杂质,在钢板表面具有张力绝缘皮膜,并且在该张力绝缘皮膜与上述钢板表面的界面具有平均膜厚为1.0nm～1.0μm的SiO_2中间氧化膜层,其中,SiO_2中间氧化膜层的金属元素M(Al)的辉光放电发光分析光谱的时间微分曲线f_M(t)满足规定的条件。(A grain-oriented electrical steel sheet comprising, in mass%, C: 0.010% or less, Si: 2.50-4.00%, acid-soluble Al: 0.0010-0.0100%, N: 0.012% or less, Mn: 1.00% or less, S: 0.02% or less, the balance including Fe and inevitable impurities, a tensile insulating film on the surface of the steel sheet, and the tensile insulating film and the steel sheetThe surface interface has SiO with an average film thickness of 1.0nm to 1.0 μm 2 An intermediate oxide film layer of SiO 2 Time differential curve f of glow discharge luminescence analysis spectrum of metal element M (Al) of intermediate oxide film layer M (t) satisfies a predetermined condition.)

1. A grain-oriented electrical steel sheet, comprising:

a base steel plate;

an intermediate oxide film layer formed on the base steel sheet and containing SiO₂The average film thickness is 1.0 nm-1.0 μm; and

a tensile insulating film formed on the intermediate oxide film layer,

the base steel sheet contains, as chemical components, in mass%:

c: less than 0.010%,

Si：2.50～4.00％、

Acid-soluble Al: 0.0010-0.0100%,

N: less than 0.012 percent,

Mn: less than 1.00 percent,

S: the content of the active ingredients is less than 0.02 percent,

the remainder comprising Fe and impurities,

time differential curve f of glow discharge luminescence analysis spectrum of metal element M of intermediate oxide film layer_M(t) satisfies the following formula (1) wherein M is Al,

T_p: time t (sec) corresponding to the minimum value of the second-order time differential curve of the glow discharge luminescence analysis spectrum of Si;

T_f: the analysis starting point of the glow discharge luminescence analysis spectrum of Si was set to T_sAnd 2T_p-T_sCorresponding to time t (seconds).

2. The grain-oriented electrical steel sheet as claimed in claim 1, further comprising, as the chemical component, in mass%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Ca: 0.001 to 0.05% of one or more kinds,

the SiO₂Time differential curve f of glow discharge luminescence analysis spectrum of metal element M of intermediate oxide film layer_M(t) satisfies one or more of the following formulae (2) to (4), wherein M is Cr, Cu, Ca,

3. the grain-oriented electrical steel sheet according to claim 1 or 2, further comprising, as the chemical components, in mass%: 0.01-0.20%, B: 0.001-0.010% of one or two.

4. A method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3,

which comprises an oxide film forming step of forming an intermediate oxide film layer on the surface of a steel sheet,

in the oxide film forming step, the annealing temperature T1: and (2) annealing at 600-1200 ℃ for: 5 to 1200 seconds, partial pressure of oxygen P_H2O/P_H2: less than 0.15, 600-T1Average heating rate HR2 of temperature region of ° c: annealing is performed under the condition of 5-50 ℃/s, after the annealing, the average cooling speed CR1 of a temperature region of T2-T1 ℃ is set to be below 50 ℃/s, and the average cooling speed CR2 of a temperature region of more than 100 ℃ and less than T2 ℃ is set to be less than CR1, wherein T2 ℃ represents the temperature represented by T1-100 ℃.

Technical Field

The present invention relates to a grain-oriented electrical steel sheet used as an iron core material of a transformer and a method for producing the same, and particularly to a grain-oriented electrical steel sheet excellent in adhesion of a tensile insulating film and a method for producing the same.

Background

Grain-oriented electrical steel sheets are silicon steel sheets containing 7 mass% or less of Si, which are composed of crystal grains having high orientation concentrated in {110} <001> orientation (hereinafter, gaussian (Goss) orientation), and are mainly used as iron core materials of transformers. The high orientation concentration of the gaussian orientation in the grain-oriented electrical steel sheet is achieved by utilizing a grain growth phenomenon called secondary recrystallization.

Grain-oriented electrical steel sheets are required to have high magnetic flux density (represented by B8 value) and low iron loss (represented by W17/50 value) as magnetic properties, but recently, from the viewpoint of energy saving, the demand for reduction in power loss, that is, reduction in iron loss has been further increased.

In a grain-oriented electrical steel sheet, a magnetic domain changes with the movement of a magnetic domain wall under an alternating-current magnetic field. Although the smooth movement of the magnetic domain walls is effective for the reduction of the core loss, if the movement of the magnetic domains is observed, there are also inactive magnetic domains.

In order to further reduce the iron loss of grain-oriented electrical steel sheet, forsterite (Mg) on the surface of the steel sheet, which inhibits the movement of magnetic domains, is removed₂SiO₄) The pinning effect caused by the unevenness of the interface of the coating (hereinafter, sometimes referred to as "glass coating") is importantIn (1). In order to eliminate this pinning effect, it is effective to prevent the formation of a glass coating film on the surface of the steel sheet, which inhibits the movement of magnetic domains.

As means for eliminating the pinning effect, for example, patent documents 1 to 5 disclose the following: controlling the dew point of the decarburization annealing so that Fe-based oxide (Fe) is not formed in the oxide layer formed during the decarburization annealing₂SiO₄FeO, etc.); and, as an annealing separating agent, a substance such as alumina that does not react with silica is used, and the surface is smoothed after the product is annealed.

When grain-oriented electrical steel sheets are used as core materials of transformers, insulation properties of the steel sheets must be ensured, and therefore, an insulating film having tension is formed on the surfaces of the steel sheets. For example, the method disclosed in patent document 6, in which a coating liquid mainly composed of colloidal silica and a phosphate is applied to the surface of a steel sheet and sintered to form an insulating film, is effective not only in ensuring insulation but also in reducing iron loss because of a large effect of imparting tension to the steel sheet.

Forming an insulating film mainly composed of phosphate on a glass film generated in the finish annealing step in this manner is a general method for producing a grain-oriented electrical steel sheet.

When the insulating film is formed on the glass film, a considerable film adhesion can be obtained, but when the glass film is removed or when the glass film is not intentionally formed in the finish annealing step, the film adhesion is insufficient.

When the glass coating is removed, a required coating tension needs to be ensured only by a tension insulating coating formed by applying a coating liquid, and therefore, the thickness inevitably has to be increased, and further coating adhesion is required.

Therefore, in the conventional film forming method, it is difficult to secure film tension to such an extent that the effect of mirror surface formation is sufficiently exhibited and also secure film adhesion, and it is not possible to sufficiently reduce iron loss. As a technique for ensuring the film adhesion of the tensile insulating film, for example, patent documents 7 to 10 propose a method of forming an oxide film on the surface of a unidirectional silicon steel sheet subjected to final annealing before forming the tensile insulating film.

For example, the technique disclosed in patent document 8 is a method of: the unidirectional silicon steel sheet, which is prepared in a mirror-finished state or a state close to a mirror-finished state and has been finished with finish annealing, is annealed at each temperature in a specific atmosphere to form an external oxidation-type oxide film on the surface of the steel sheet, and the adhesion between the tensile insulating film and the steel sheet is ensured by the oxide film.

The technique disclosed in patent document 9 is as follows: when the tension insulating film is crystalline, an amorphous oxide base film is formed on the surface of a finished product annealed unidirectional silicon steel sheet having no inorganic mineral film to prevent oxidation of the steel sheet caused by the formation of the crystalline tension insulating film.

The technique disclosed in patent document 10 is a method of: the technique disclosed in patent document 8 is further developed to control the film structure of a metal oxide film containing Al, Mn, Ti, Cr, and Si at the interface between the tensile insulating film and the steel sheet, so as to improve the adhesion of the insulating film. However, the adhesion at the interface between the metal oxide layer and the steel sheet, which is the most problematic in stress sensitivity, is not controlled, and the technique disclosed in patent document 10 is not sufficient as a technique for improving the film adhesion.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. H07-278670

Patent document 2: japanese laid-open patent publication No. 11-106827

Patent document 3: japanese laid-open patent publication No. 11-118750

Patent document 4: japanese laid-open patent publication No. 11-118750

Patent document 5: japanese patent laid-open publication No. 2003-268450

Patent document 6: japanese laid-open patent publication No. Sho 48-039338

Patent document 7: japanese laid-open patent publication No. 60-131976

Patent document 8: japanese laid-open patent publication No. H06-184762

Patent document 9: japanese laid-open patent publication No. H07-278833

Patent document 10: japanese patent laid-open publication No. 2002-348643

Non-patent document

Non-patent document 1: iron and steel, vol99(2013), 40.

Disclosure of Invention

Problems to be solved by the invention

In a unidirectional silicon steel sheet having a tensile insulating film formed on the surface of the steel sheet, when the insulating film is formed on a glass film (forsterite-based film), the film adhesion of the insulating film is good, but when the generation of the glass film is intentionally suppressed, or the glass film is removed by grinding or pickling, and the surface of the steel sheet is further flattened to show a mirror gloss to form the tensile insulating film, the film adhesion of the insulating film is insufficient, and it is difficult to achieve both the film adhesion and the magnetic stability.

Accordingly, an object of the present invention is to form a tensile insulating film having excellent film adhesion without impairing magnetic properties and stability thereof on the surface of a grain-oriented electrical steel sheet subjected to finish annealing until the surface of the steel sheet is flattened to exhibit mirror gloss by intentionally suppressing the formation of a glass film or removing the glass film by means of grinding or pickling, and to provide a grain-oriented electrical steel sheet and a method for producing the same, which solve the above problems.

Means for solving the problems

The present inventors have intensively studied a method for improving the film adhesion of a tensile insulating film in order to solve the above problems. As a result, they found that: before the tensile insulating film is formed, an oxide film (hereinafter sometimes referred to as "intermediate oxide film layer" or "SiO" film) is formed on the surface of a grain-oriented electrical steel sheet subjected to final annealing₂Intermediate oxide film layer "), if the thermal history and oxygen partial pressure are controlled, the film adhesion of the tensile insulating film is dramatically improved.

Further, the inventors of the present invention conducted an intensive investigation on the composition of the intermediate oxide film layer which is considered to have the greatest influence on the film adhesion. The results thereof recognize that: the oxide of the intermediate oxide film layer is Si oxide (SiO)₂) One or more of Al, Cu, Cr and Ca in SiO₂Intermediate oxide film layer or in SiO₂And concentrating the interface of the intermediate oxide film layer and the steel plate.

It is believed that: by using Al, Cr, Cu and Ca in SiO₂Concentrating the interface between the intermediate oxide film layer and the steel plate to generate attractive electron interaction at the interface, and contacting the steel plate with SiO₂The adhesion of the intermediate oxide film layer is improved.

The present invention has been made based on the above-described knowledge, 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; an intermediate oxide film layer formed on the base steel sheet and containing SiO₂The average film thickness is 1.0 nm-1.0 μm; and a tensile insulating film formed on the intermediate oxide film layer.

The base steel sheet contains, as chemical components, in mass%, C: 0.01% or less, Si: 2.50-4.00%, acid-soluble Al: 0.0010-0.0100%, N: 0.012% or less, Mn: 1.00% or less, S: less than 0.02%, and the balance of Fe and impurities.

The above SiO₂Time differential curve f of glow discharge luminescence analysis spectrum of metal element M (M: Al) of intermediate oxide film layer_M(t) satisfies the following formula (1).

[ mathematical formula 1]

T_p: time t (second) corresponding to minimum value of second-order time differential curve of glow discharge luminescence analysis spectrum of Si

T_f: the analysis starting point of the glow discharge luminescence analysis spectrum of Si was set to T_sWhen, with2T_p-T_sCorresponding time t (seconds)

(2) The grain-oriented electrical steel sheet according to the item (1), wherein the base steel sheet may further contain, as the chemical components, in mass%: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Ca: 0.001-0.05% of one or more of the above SiO₂Time differential curve f of glow discharge luminescence analysis spectrum of metal element M (M: Cr, Cu, Ca) of middle oxide film layer_M(t) satisfies one or two or more of the following formulas (2) to (4).

[ mathematical formula 2]

(3) The grain-oriented electrical steel sheet according to the item (1) or (2), wherein the base steel sheet may further contain, as the chemical component, in mass%: 0.01-0.20%, B: 0.001-0.010% of one or two.

(4) A method for producing a grain-oriented electrical steel sheet according to another aspect of the present invention is a method for producing a grain-oriented electrical steel sheet according to any one of the above (1) to (3), including an oxide film forming step of forming an intermediate oxide film layer on a surface of the steel sheet.

In the oxide film forming step, the annealing temperature T1: and (2) annealing at 600-1200 ℃ for: 5 to 1200 seconds, partial pressure of oxygen P_H2O/P_H2: average heating rate HR2 in the temperature range of 600 ℃ to T1 ℃ of 0.15 or less: annealing at 5-50 ℃/sec, and after the annealing, setting the average cooling rate CR1 in the temperature region of T2-T1 ℃ to 50 ℃/secNext, the average cooling rate CR2 in the temperature region of 100 ℃ or higher and lower than T2 ℃ was set to be lower than CR 1. Wherein T2 ℃ represents a temperature represented by T1 ℃ to 100 ℃.

Effects of the invention

According to the present invention, it is possible to form a tensile insulating film having excellent film adhesion without impairing the magnetic properties and stability of the film, on the surface of a grain-oriented electrical steel sheet subjected to finish annealing, in which the formation of a glass film is intentionally suppressed, the glass film is removed by means of grinding, pickling, or the like, and the surface of the steel sheet is further flattened to exhibit a mirror surface gloss.

Drawings

Fig. 1 is a graph showing a differential curve of a spectrum derived from Si obtained by glow discharge luminescence analysis (GDS).

Detailed Description

The grain-oriented electrical steel sheet of the present invention (hereinafter, sometimes referred to as "electrical steel sheet of the present invention") includes: a base steel plate; an intermediate oxide film layer formed on the base steel sheet and containing SiO₂The average film thickness is 1.0 nm-1.0 μm; and a tensile insulating film formed on the intermediate oxide film layer.

The base steel sheet contains, as chemical components, in mass%:

c: less than 0.010%,

Si：2.50～4.00％、

Acid-soluble Al: 0.0010-0.0100%,

N: less than 0.012 percent,

Mn: less than 1.00 percent,

S: the content of the active ingredients is less than 0.02 percent,

the rest part contains Fe and impurities, and the time differential curve f of glow discharge luminescence analysis spectrum of metal element M (M: Al) of the intermediate oxide film layer_M(t) satisfies the following formula (1).

[ mathematical formula 3]

T_p: time t (seconds) corresponding to the minimum of the 2 nd order time differential curve of glow discharge luminescence analysis spectrum of Si

T_f: the analysis starting point of the glow discharge luminescence analysis spectrum of Si was set to T_sAnd 2T_p-T_sCorresponding time t (seconds)

The electrical steel sheet of the present invention may further contain, in mass%, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Ca: 0.001-0.05% of one or more of the above SiO₂Time differential curve f of glow discharge luminescence analysis spectrum of metal element M (M: Cr, Cu, Ca) of middle oxide film layer_M(t) satisfies one or two or more of the following formulas (2) to (4).

[ mathematical formula 4]

The electrical steel sheet of the present invention may further contain, in mass%, Sn: 0.01-0.20%, B: 0.001-0.010% of one or two.

The method for producing a grain-oriented electrical steel sheet according to the present invention (hereinafter, sometimes referred to as "the method for producing the present invention") includes an oxide film forming step of forming an intermediate oxide film layer on the surface of the steel sheet, wherein in the oxide film forming step, the annealing temperature T1: and (2) annealing at 600-1200 ℃ for: 5 to 1200 seconds, partial pressure of oxygen P_H2O/P_H2: average heating rate HR2 in the temperature range of 600 ℃ to T1 ℃ of 0.15 or less: annealing at a temperature of 5 to 50 ℃/sec, and averaging the average temperature of the temperature region of T2 to T1 ℃ after the annealingThe cooling rate CR1 was set to 50 ℃/sec or less, and the average cooling rate CR2 in the temperature range of 100 ℃ or more and less than T2 ℃ was set to be less than CR 1. Wherein T2 ℃ represents a temperature represented by T1 ℃ to 100 ℃.

The electrical steel sheet of the present invention and the production method of the present invention will be described below.

[ base Steel sheet ]

< composition of ingredients >

First, the reasons for limiting the composition of the base steel sheet will be described. Hereinafter, "%" relating to the component composition means "% by mass".

C: 0.010% or less

If C exceeds 0.010%, C inhibits SiO₂And Al or other element concentration layer at the interface between the intermediate oxide film layer and the steel plate. Therefore, C is set to 0.010% or less. From the viewpoint of improvement of the iron loss characteristics, it is preferably 0.008% or less.

The lower limit of C includes 0%, but since the detection limit of C is about 0.0001%, 0.0001% is a substantial lower limit in the case of practical steel sheets.

Si：2.50～4.00％

If Si is less than 2.50%, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained, so Si is set to 2.50% or more. Preferably 2.75% or more, more preferably 3.00% or more.

On the other hand, if Si exceeds 4.00%, the steel sheet becomes brittle and the sheet passing property in the production process deteriorates significantly, so Si is set to 4.00% or less. Preferably 3.75% or less, more preferably 3.50% or less.

Acid-soluble Al: 0.0010 to 0.0100 percent

In the electrical steel sheet of the present invention, acid-soluble Al (sol.al) is an essential element from the viewpoint of improving the coating adhesion. That is, the acid-soluble Al is in SiO₂An element which forms a concentrated layer by concentrating the interface between the intermediate oxide film layer and the steel sheet and remarkably improves the adhesion of the film.

If the acid-soluble Al content is less than 0.0010%, the concentrated layer is not formed, and therefore the acid-soluble Al content is set to 0.0010% or more. Preferably 0.0030% or more.

On the other hand, the acid-soluble Al is contained in the slab composition at an upper limit of 0.07% from the viewpoint of the pass-through property of cold rolling. In this sense, the upper limit of the acid-soluble Al is 0.07%, but actually, Al is discharged to the outside of the steel sheet by the secondary recrystallization annealing. As a result, the acid-soluble Al contained in the base steel sheet may be 0.0100% or less. Although the pass-through properties are not problematic if Al is 0.07% or less, the less acid-soluble Al contained in the base steel sheet, the better the iron loss characteristics, and preferably 0.006% or less.

N: 0.012% or less

If N exceeds 0.012%, then blisters (voids) will form in the steel sheet during cold rolling, the strength of the steel sheet will increase, and the sheet passing properties during manufacture will deteriorate, so N is set to 0.012% or less. Preferably 0.010% or less, and more preferably 0.009% or less.

The lower limit includes 0%, but since the detection limit of N is about 0.0001%, 0.0001% is a substantial lower limit in practical steel sheets.

Mn: 1.00% or less

If Mn exceeds 1.00%, the steel undergoes phase transformation during secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained, so Mn is set to 1.00% or less. Preferably 0.50% or less, more preferably 0.20% or less.

Although MnS may be used as an inhibitor in the secondary recrystallization, MnS is not essential in the case of AlN as an inhibitor, and therefore the lower limit of Mn includes 0%. When MnS is used as the inhibitor, Mn is set to 0.02% or more. Preferably 0.05% or more, more preferably 0.07% or more.

S: less than 0.02%

If S exceeds 0.02%, SiO is suppressed in the same manner as C₂And Al or other element concentration layer at the interface between the intermediate oxide film layer and the steel plate. Therefore, S is set to 0.02% or less. Preferably 0.01 percentThe following.

The lower limit includes 0%, but since the detection limit of S is about 0.0001%, 0.0001% is a substantial lower limit for practical steel sheets.

In addition, a part of S may be replaced with Se or Sb, and in this case, a value obtained by conversion from Seq ═ S +0.406Se or Seq ═ S +0.406Sb may be used.

The electrical steel sheet of the present invention may contain one or two or more of the following elements in addition to the above elements in order to improve the properties of the electrical steel sheet of the present invention.

Cr：0.01～0.50％

Cr is in SiO₂An element that concentrates at the interface between the intermediate oxide film layer and the steel sheet to form a concentrated layer and contributes to the improvement of the film adhesion. When Cr is less than 0.01%, the effect of improving the film adhesion cannot be sufficiently obtained, and therefore Cr is set to 0.01% or more. Preferably 0.03% or more, more preferably 0.05% or more.

On the other hand, if Cr exceeds 0.50%, Cr bonds with Si and O, and SiO may be inhibited₂Since the intermediate oxide layer is formed, Cr is set to 0.50% or less. Preferably 0.30% or less, more preferably 0.20% or less.

Cu：0.01～0.50％

Cu is in SiO as in Al and Cr₂An element that concentrates at the interface between the intermediate oxide film layer and the steel sheet to form a concentrated layer and contributes to the improvement of the film adhesion. When Cu is less than 0.01%, the effect of improving the film adhesion cannot be sufficiently obtained, and therefore Cu is set to 0.01% or more. Preferably 0.03% or more, more preferably 0.05% or more.

On the other hand, if Cu exceeds 0.50%, the steel sheet becomes brittle during hot rolling, so Cu is set to 0.50% or less. Preferably 0.20% or less, more preferably 0.10% or less.

Ca：0.001～0.05％

Ca is in SiO in the same way as Al, Cr and Cu₂An element that concentrates at the interface between the intermediate oxide film layer and the steel sheet to form a concentrated layer and contributes to the improvement of the film adhesion. When Ca content is less than 0.001%, a sufficient coating density cannot be obtainedSince the effect of improving the compatibility is high, Ca is set to 0.001% or more. Preferably 0.005% or more, and more preferably 0.010 or more.

On the other hand, if Ca exceeds 0.05%, fine CaS is generated in the steel, and the magnetic properties deteriorate, so Ca is set to 0.05% or less. Preferably 0.04% or less, more preferably 0.03% or less.

Sn：0.01～0.20％

Although Sn is not in SiO₂An element that concentrates at the interface between the intermediate oxide film layer and the steel sheet, but contributes to the improvement of the film adhesion. Although the mechanism of improvement in the coating adhesion of Sn is not clear, the smoothness of the steel sheet after secondary recrystallization is examined and the improvement in the smoothness of the steel sheet is confirmed, and therefore it is considered that: sn reduces and smoothes irregularities on the surface of the steel sheet, and contributes to the formation of SiO having few irregularities₂The interface between the intermediate oxide film layer and the steel plate.

If Sn is less than 0.01%, the effect of smoothing the steel sheet surface cannot be sufficiently obtained, so Sn is set to 0.01% or more. Preferably 0.02% or more, more preferably 0.03% or more.

On the other hand, if Sn exceeds 0.20%, secondary recrystallization becomes unstable and magnetic properties deteriorate, so Sn is set to 0.20% or less. Preferably 0.15% or less, more preferably 0.10% or less.

B：0.001～0.010％

B is in SiO in the same way as Al, Cr, Cu and Ca₂The interface between the intermediate oxide film layer and the steel sheet is concentrated to form a concentrated layer (the inventors of the present invention confirmed that the concentrated layer is formed by GDS), and the element contributes to the improvement of the film adhesion. When B is less than 0.001%, the effect of improving the film adhesion cannot be sufficiently obtained, so B is set to 0.001% or more. Preferably 0.002% or more, more preferably 0.003% or more.

On the other hand, if B exceeds 0.010%, the steel sheet strength increases and the pass-through property in cold rolling deteriorates, so B is set to 0.010% or less. Preferably 0.008% or less, more preferably 0.006% or less.

The remainder of the composition of the base steel sheet is Fe and impurities (inevitable impurities), but may contain one or two or more of Mo, W, In, Sn, Bi, Sb, Ag, Te, Ce, V, Co, Ni, Se, Re, Os, Nb, Zr, Hf, Ta, Pb, Y, La, and the like In total In an amount of 5.00% or less, preferably 3.00% or less, more preferably 1.00% or less, for the purpose of improving the magnetic properties, the properties required for the structural member such as strength, corrosion resistance, fatigue properties, and the like, the castability and the throughput, and the productivity due to the use of scrap and the like.

[ intermediate oxide film layer ]

Next, an intermediate oxide film layer (hereinafter, sometimes referred to as SiO) which plays an important role in improving the adhesion of the film₂Intermediate oxide film layer). The electrical steel sheet of the present invention is manufactured by removing a glass coating by grinding, pickling, or the like, or intentionally preventing the formation of a glass coating. In order to sufficiently ensure the film adhesion of the tension insulating film, SiO having a desired film thickness at the interface between the tension insulating film and the steel sheet₂An intermediate oxide film layer.

SiO₂Average film thickness of intermediate oxide film layer: 1.0 nm-1.0 mu m

If SiO₂If the average thickness of the intermediate oxide film layer is less than 1.0nm, the film adhesion cannot be sufficiently ensured, and therefore, SiO is not sufficient₂The average thickness of the intermediate oxide film layer is set to 1.0nm or more. Preferably 5.0nm or more, more preferably 9.0nm or more.

On the other hand, if SiO₂If the average thickness of the intermediate oxide film layer exceeds 1.0 μm, the thickness of the intermediate oxide film layer is larger than that of the SiO₂Cracks that become starting points of fracture occur in the intermediate oxide film layer, and the film adhesion is deteriorated, so SiO₂The average thickness of the intermediate oxide film layer is set to 1.0 μm or less. Preferably 0.7 μm (═ 700nm) or less, and more preferably 0.4 μm (═ 400nm) or less.

SiO₂The thickness of the intermediate oxide film layer was measured by observing the cross section of the sample with a Transmission Electron Microscope (TEM) or a Scanning Electron Microscope (SEM).

The oxide forming the intermediate oxide film layer is' SiO₂"this fact can be passed throughElemental analysis by Energy Dispersive Spectroscopy (EDS) attached to TEM or SEM was used for confirmation. Further, since the chemical bond ratio of Si to O is not necessarily limited to 2, even if SiOx (x is an arbitrary number) is analyzed as a result of the stoichiometric ratio, the properties of the electrical steel sheet of the present invention are not impaired.

In particular, in SiO₂In the EDS spectrum of the intermediate oxide film layer, "SiO" was confirmed by detecting Si-Ka rays at a position of energy of 1.8. + -. 0.3kev and O-Ka rays at a position of 0.5. + -. 0.3kev on the horizontal axis₂"is present. Identification of elements can be performed by using L α rays and K γ rays in addition to K α rays.

However, since the EDS spectrum of Si may include a spectrum derived from Si in the steel sheet, it is precisely determined whether Si is derived from the steel sheet or SiO by analyzing the cross section of the steel sheet with an Electron Probe Microanalyzer (EPMA)₂The intermediate oxide film layer is from.

Further, to SiO₂The intermediate oxide film layer was measured by Fourier transform infrared spectrophotometer (FT-IR), and it was confirmed that the wave number was 1250cm^-1In the presence of SiO₂Peaks of origin, which are identified as constituting SiO₂The compound aspect of the intermediate oxide film layer is preferable.

However, since FT-IR is a method for selectively analyzing the compound on the outermost surface of the sample, the analysis is performed after (a) the sample having no tensile insulating film or (b) the sample having a tensile insulating film on the surface of the steel sheet has been completely removed by alkali cleaning or the like.

The infrared spectroscopy (IR) includes a reflection method and an absorption method, but the absorption method overlaps information on the outermost surface of the sample with information on the inside of the steel sheet, and thus the absorption method is applied to SiO constituting the sample₂The identification of the compound of the intermediate oxide film layer is preferably a reflection method.

In addition, the absorption method is derived from SiO₂The wave number of the intermediate oxide film layer does not become 1250cm^-1According to SiO₂The formation state of (3) is subjected to peak shift. But only by mixingSiO₂When the average thickness of the intermediate oxide film layer is controlled to 1.0nm to 1.0 μm, the adhesion of the film is not sufficiently ensured.

By controlling SiO₂The thickness of the intermediate oxide film layer can ensure the tensile insulating film and SiO₂The adhesiveness (coating adhesiveness) of the intermediate oxide film layer. However, SiO₂The interface between the intermediate oxide film layer and the steel plate is the interface between metal and oxide, namely the interface between different atoms, and is the interface with weak interaction between atoms. Therefore, SiO is often used₂The interface between the intermediate oxide film layer and the steel sheet causes peeling as a starting point.

It is therefore assumed that: if Al is in SiO₂The interface between the intermediate oxide film layer and the steel plate is concentrated on SiO₂The intermediate oxide film layer and the steel sheet exert an interaction between electrons as an attractive force, and the film adhesion is improved. For example, it is known that: since the interaction between C and Fe is an attractive force, if C segregates at grain boundaries, the grain boundary strength increases. If this is assumed, then: in the electromagnetic steel sheet of the present invention, Al is similarly in SiO₂And the magnetic iron generates attractive electron interaction with Fe.

Although it is difficult to directly detect the degree of interaction between electrons by experiment, it is difficult to detect the degree of interaction between electrons in SiO₂The Al concentration at the interface between the intermediate oxide film layer and the steel sheet can be determined by glow discharge luminescence analysis (GDS)₂The surface of the steel sheet in the state of the intermediate oxide film layer was analyzed.

In the electromagnetic steel sheet of the present invention, Al is made to be SiO₂The interface of the intermediate oxide film layer and the steel plate is concentrated to form a concentrated layer. Thus, SiO₂The relationship between the depth position of the intermediate oxide film layer and the depth position of the Al concentrated layer is important. SiO 2₂The position where the intermediate oxide film layer is present may be derived from the GDS spectrum derived from Si (hereinafter sometimes referred to as "F_Si(t) ") was analyzed.

In the analysis, the obtained spectrum may be subjected to smoothing processing using peak analysis software or the like. In addition, the interval Δ t of the measurement time is preferably small, and preferably 0.05 seconds or less, in order to improve the accuracy of peak analysis.

Hereinafter, t is a time (second) corresponding to the depth position of the sample, and is a parameter when the GDS spectrum is set as a function of time.

If SiO is present on the surface of a sample taken from a steel sheet₂The intermediate oxide film layer is observed in the GDS spectrum derived from Si in a region corresponding to the surface of the sample, wherein (a) the position of the peak rising from the background, (B) the position of the peak apex, and (C) the position of the peak ending to the background are observed.

Here, T corresponding to the peak-up position is set to T_sT corresponding to the peak top position is set to T_pT corresponding to the peak terminal position is set to T_f。SiO₂The intermediate oxide film layer corresponds to the outermost surface of the measurement sample. That is, T at the measurement start point of the GDS spectrum is associated with the peak rising position, and the measurement start point of the GDS spectrum is defined as T_sIt is preferable. In addition, the peak is bilaterally symmetric according to the normal distribution and can be defined as T_f＝2T_p-T_s。

Since the measurement time interval Δ T of the GDS spectrum is as small as 0.05 second or less, T can be approximated as_sIs set to be T by being approximately equal to 0_f＝2×T_p. In any event, in determining T_fAspect (2) determining T_p. As follows for T_pThe method of determining (2) will be explained.

Fig. 1 shows a differential curve of a spectrum of a Si source obtained by glow discharge luminescence analysis (GDS).

T_pCorresponding to the peak top position of the GDS spectrum from Si. To determine the peak position, F is simply added_Si(t) second order differentiation with time, finding a curve corresponding to the second order differentiation (in FIG. 1, refer to "d²F(t)/dT²") may be used. However, the minimum value is limited to a value found in a range of t 0 seconds to Δ t × 100 seconds. The reason for this is that: SiO 2₂The intermediate oxide film layer is present only on the surface of the sample and not inside the steel sheet, and therefore t has a relatively small value.

Then, F is added_Si(t) in timeCurve f obtained by first order differentiation_Si(t)(＝dF_Si(T)/dt) (in FIG. 1, refer to "dF (T)/dt"), if T is T_s～T_pIs always f in the range of_Si(T) is greater than or equal to 0, then T_pCorrespondence to the peak-top location is more deterministic.

In addition, as for the derivation method of the differential curve, the derivative function may be obtained, or f (t) may be approximated by the difference method_n)＝[F(t_n)-F(t_n-1)]/[t_n-t_n-1]. Wherein the nth measurement point (time) is set to t_nThe spectral intensity at this time was set to F (t)_n)。

When the Si-derived peak is unclear, the GDS spectrum [ F below ] derived from Fe may be used_Fe(t)]And (6) carrying out analysis. In this case, at F_FeFirst order differential curve of (t) (hereinafter, f is set to_Fe(T)), the T corresponding to the maximum value is set to the above-mentioned T_fIn the case of (1), the above-mentioned T_pIs denoted by T_p＝0.5×(T_f+T_s) But may also be approximated by T_sIs set to be T by being approximately equal to 0_p＝0.5×T_f. This is due to: f. of_FeMaximum value of (t) corresponds to SiO₂Interface with the base metal.

The maximum value is limited to a value found in a range of t 0 seconds to Δ t × 100 seconds. The reason for this is that: SiO 2₂The intermediate oxide film layer is present only on the surface of the sample and not inside the steel sheet, and therefore t has a relatively small value.

In the electrical steel sheet of the present invention, it is necessary to use Al in SiO for improving the coating adhesion₂T is T which is the position of the interface between the intermediate oxide film layer and the steel plate_fAnd (4) concentrating. However, Al is retained only at T ═ T_fIs not possible, in practice, at a position T ═ T_fAs a starting point, when T is T_p～T_fIs distributed over the entire range of (a). This region is hereinafter referred to as an interface concentrated layer.

In addition to Al, it was also confirmed that Cr, Cu, and Ca contribute to the improvement of film adhesion by forming an interface concentrated layer. That is to say that the first and second electrodes,in the electromagnetic steel sheet of the present invention, SiO corresponds to₂T ═ T at the interface between the intermediate oxide film layer and the steel sheet_p～T_fIn the range of (1), the metal element M (M ═ Al, Cr, Cu, Ca) forms an interface concentrated layer.

The interface concentration layer may be present by using a GDS spectrum derived from the metal element M (hereinafter sometimes referred to as "F_M(t) ") for confirmation. Specifically, F is_MTime differential curve f of (t)_M(T) integration (integration range: T ═ T)_p～T_f) When the integral value is larger than 0, it can be judged that the metal element M exists as an interface concentrated layer.

Further, inside the steel sheet, the metal element M is uniformly distributed, and therefore f inside the steel sheet_MThe integrated value of (t) becomes 0 or a value infinitely close to 0.

In addition, T in the measurement of GDS is not continuous, and T is T_p～T_fIn, f_M(t) is a set of discontinuous points. Thus, f will be_MThe points (t) are connected by straight lines to form a continuous function, and are approximated and integrated. In addition, an integration value obtained using Σ may be set.

According to the above discussion, to make Al in SiO₂The interface between the intermediate oxide film layer and the steel sheet is concentrated and exists as a concentrated layer, and the following formula (1) needs to be satisfied.

[ math figure 5]

Further, by satisfying one or more of the following expressions (2) to (4), the film adhesion is further improved.

[ mathematical formula 6]

In the electrical steel sheet of the present invention, the metal element M (Al, Cr, Cu, Ca) can also be detected by chemical analysis. The steel sheet portion of the sample in the state before the formation of the tensile insulating film or in the state where the tensile insulating film was removed was dissolved by the iodomethanol method, and SiO was extracted₂An intermediate oxide film layer. Then, the extracted SiO₂The intermediate oxide film layer is chemically analyzed using ICP or the like. Thereby, SiO can be trapped₂And a metal element M contained in the intermediate oxide film layer.

The metal element M (Al, Cr, Cu, Ca) is only in SiO₂The total amount of the intermediate oxide film layer may be 0.05 to 2.00% by mass. When the metal element M is less than 0.05%, the coating adhesion is not improved, and therefore the total amount of the metal element M is preferably 0.05% or more. More preferably 0.10% or more.

On the other hand, if the metal element M exceeds 2.00%, SiO is caused by the influence of segregation₂In SiO₂Since a large number of lattice defects are introduced into the interface between the intermediate oxide film layer and the steel sheet and the film adhesion is deteriorated, the total amount of the metal elements M is preferably 2.00% or less. More preferably 1.50% or less.

Verification of the effect of improving the film adhesion by GDS, chemical analysis, or the like revealed that SiO was formed on the surface of the steel sheet₂The steel sheet sample in a state after the intermediate oxide film layer and before the tensile insulating film is formed is most suitable, but the steel sheet sample having the tensile insulating film formed on the surface thereof may be subjected to analysis by completely removing only the tensile insulating film after alkali washing by acid washing or ultrasonic washing with alcohol, water, or the like.

After acid washing or ultrasonic washing with alcohol, water, or the like, 8 may be performed in an atmosphere of 100% hydrogen for the purpose of further surface cleaningAnnealing at 00-1100 deg.C for 1-5 hours for analysis. SiO 2₂SiO is a stable compound in the above annealing₂Can not be reduced to make SiO₂The intermediate oxide film layer disappears.

The electrical steel sheet of the present invention is produced by subjecting a steel slab melted in a converter and continuously cast to hot rolling, hot-rolled sheet annealing, cold rolling, primary recrystallization annealing, secondary recrystallization annealing to form SiO, in the same manner as in the production of a normal electrical steel sheet₂Annealing the intermediate oxide film layer and annealing the insulating film layer.

The hot rolling may be direct hot rolling or continuous hot rolling, and the slab heating temperature is not limited. The cold rolling may be cold rolling or warm rolling performed twice or more, and the reduction ratio is not limited. The secondary recrystallization annealing may be either batch annealing or continuous line annealing using a box furnace, and is not dependent on the annealing method.

The annealing separator may contain an oxide such as alumina, magnesia or silica, and is not limited to the kind thereof.

In the case of producing a grain-oriented electrical steel sheet, SiO is used₂When the intermediate oxide film layer is formed, SiO is generated₂The intermediate oxide film layer is simultaneously used for leading metal elements M (Al, Cr, Cu and Ca) to be in SiO₂The heat treatment condition for the interface concentration of the intermediate oxide film layer and the steel sheet is important. That is, the presence of Al, Cr, Cu and Ca in SiO is ensured₂The concentration time of the interface concentration of the intermediate oxide film layer and the steel plate is important.

In the electromagnetic steel sheet of the present invention, SiO₂The intermediate oxide film layer is formed by annealing the steel sheet after the secondary recrystallization at a temperature T1 (DEG C) of 600-1200 ℃ for 5-1200 seconds.

If the annealing temperature is lower than 600 ℃, SiO is not generated₂Without formation of SiO₂The annealing temperature is set to 600 ℃ or higher because of the intermediate oxide film layer. On the other hand, if the annealing temperature exceeds 1200 ℃, SiO₂Non-uniform reaction of formation of intermediate oxide film layer, SiO₂The intermediate oxide film layer and the base steel plate have severe unevenness and are densely covered with the filmThe compatibility is deteriorated. Therefore, the annealing temperature is set to 1200 ℃ or lower. Preferably SiO₂The precipitation temperature is 700-1100 ℃.

To make SiO₂The intermediate oxide film layer is grown to ensure a layer thickness necessary for ensuring excellent film adhesion, and the annealing time is set to 5 seconds or more. Preferably 20 seconds or more. The annealing time may be long from the viewpoint of ensuring excellent film adhesion, but 200 seconds is set as the upper limit from the viewpoint of productivity. Preferably 100 seconds or less.

The annealing atmosphere is set to form external oxidation type silicon dioxide (SiO)₂Intermediate oxide film layer) and avoids the generation of lower oxides such as fayalite, wustite, magnetite, and the like. Therefore, the oxygen partial pressure P, which is the ratio of the water vapor pressure to the hydrogen pressure in the annealing atmosphere_H2O/P_H2The oxygen partial pressure is set to satisfy the following formula (5). Preferably 0.05 or less.

P_H2O/P_H2≤0.15 (5)

Partial pressure of oxygen P_H2O/P_H2The lower the content, the external oxidation type of Silica (SiO)₂Intermediate oxide film layer) is more easily formed and the effect of the present invention is more easily exhibited, but it is difficult to control the oxygen partial pressure P_H2O/P_H2Controlled to be lower than 5.0 x 10^-4Therefore, 5.0X 10 is industrially used^-4The lower limit is substantially the same.

In order to make the metal element M (Al, Cr, Cu, Ca) in SiO₂The interface between the intermediate oxide film layer and the steel plate is effectively concentrated, and the segregation temperature of the metal element M needs to be ensured. Thus, SiO is formed₂In the cooling after annealing of the intermediate oxide film layer, a temperature region from T2 (DEG C) to T1 (DEG C), which is a segregation temperature region defined by the following formula (6), is cooled at an average cooling rate of 50 ℃/sec or less. This average cooling rate was designated as CR1 (. degree.C./sec).

The electrical steel sheet of the present invention is not deteriorated in properties by cooling at the average cooling rate CR1, but CR1 is preferably 0.1 ℃/sec or more from the viewpoint of productivity. After cooling to T2 (deg.c), since thermal strain is introduced and the film adhesiveness and magnetic properties are degraded if the cooling rate is increased, the average cooling rate CR2 in the temperature range of 100 to T2 (deg.c) is set to an average cooling rate satisfying the following expression (7).

T2＝T1-100 (6)

CR1>CR2 (7)

In SiO₂In the formation of the intermediate oxide film, a heating rate at which the steel sheet is heated during annealing is also important. Due to SiO₂The other oxides not only reduce the adhesion of the tensile insulating film but also inhibit the surface smoothness of the steel sheet to reduce the iron loss characteristics, and therefore it is necessary to use an oxide which does not generate SiO as much as possible₂Other than the heating rate of the oxide.

SiO₂The formation temperature range of (A) is 600 to T1 ℃. Therefore, to generate more SiO₂The average heating rate HR2 in this temperature range is set to 50 ℃/sec or less. However, if the heating rate is slow, SiO is generated₂Compared with more thermally stable Fe₂SiO₄Therefore, the average heating rate HR2 is set to 5 ℃/sec or more. Preferably, HR2 is 10-40 ℃/sec, more preferably 15-30 ℃/sec.

Examples

Hereinafter, the technical contents of the present invention will be further described while exemplifying the embodiments of the present invention. The conditions in the examples shown below are one example of conditions adopted for confirming the feasibility and the effect of the present invention, and the present invention is not limited to this example of conditions. In addition, as long as the object of the present invention is achieved without departing from the gist of the present invention, various conditions can be adopted in the present invention.

< example 1>

Silicon steel having a composition shown in Table 1-1 was soaked at 1100 ℃ for 60 minutes, then subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.6mm, annealed at 1100 ℃, pickled, and subjected to one cold rolling or multiple cold rolling with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.23 mm.

[ tables 1-1]

A cold rolled steel sheet having a final thickness of 0.23mm was subjected to decarburization annealing and nitriding annealing. Thereafter, the coating of an aqueous slurry of an annealing separator mainly composed of alumina was performed, and the final annealing was performed at 1200 ℃ for 20 hours. Then, the finished annealed plate is placed at an oxygen partial pressure P_H2O/P_H2: 0.06, annealing temperature T1: annealing time at 1000 ℃: average heating rate HR2 in the temperature region of 600 to T1 ℃ for 30 seconds: annealing is carried out under the condition of 30 ℃/second to form SiO on the surface of the steel plate₂An intermediate oxide film layer.

In addition, the average cooling rate CR1 in the temperature region of T2 ℃ (900 ℃) to T1 ℃ (1000 ℃) is set to 40 ℃/s, and the average cooling rate CR2 of more than 100 ℃ and less than T2 ℃ (900 ℃) is set to 5 ℃/s.

Then, the coating liquid for forming an insulating film is applied to the surface of the steel sheet and sintered to form a tensile insulating film. Chemical compositions of base steel sheets of the produced grain-oriented electrical steel sheets are shown in tables 1 to 2. The coating adhesion of the insulating coating was evaluated, and the magnetic properties (magnetic flux density) were also evaluated.

[ tables 1-2]

The film adhesion of the tensile insulating film was evaluated by winding the test specimen for evaluation around a cylinder having a diameter of 20mm and bending the test specimen at 180 ° to obtain a film remaining area ratio. For the evaluation, VG (very excellent) was set for the case where the film remaining area ratio was 95% or more without peeling from the steel sheet, G (excellent) was set for the case where the film remaining area ratio was 90% or more and less than 95%, F was set for the case where the film remaining area ratio was 80% or more and less than 90% (effective), and B was set for the case where the film remaining area ratio was less than 80% (ineffective).

The magnetic properties were evaluated in accordance with JIS C2550. The magnetic flux density was evaluated by using B8. B8 is the magnetic flux density at a magnetic field strength of 800A/m, and is the criterion for determining the quality of the secondary recrystallization. A sample in which secondary recrystallization was performed was judged as B8 equal to or greater than 1.89T.

In addition, SiO was formed on a part of the samples₂After the intermediate oxidation film layer, no tensile insulating film is formed for SiO₂Film thickness investigation of the intermediate oxide film layer and investigation of interface concentration elements. SiO 2₂The thickness of the intermediate oxide film layer was determined by TEM observation according to the method described in patent document 10. The interface concentration elements were investigated by GDS. The measurement time of GDS was set to 100 seconds, and the time interval was set to 0.05 seconds. A series of evaluation results are shown in table 2. The case where the expression (1) is satisfied is set to "OK", and the case where it is not satisfied is set to "NG".

[ Table 2]

B1 to B14 are examples of the invention and all show good film adhesion, but the S content of B1 is out of the preferred range, the N content of B2 is out of the preferred range, and the Mn contents of B3 and B14 are out of the preferred ranges. The Si contents of the invention steels B10 and B11 were out of the preferable range, and the acid-soluble Al contents of the invention steels B12 and B13 were out of the preferable range.

On the other hand, B4 contains no optional element, but since any element is controlled to be in a preferred range or a more preferred range, B4 has more favorable film adhesion such as "G" compared with effect "F" of B1 to B3 and B10 to B14. B5 to B7 were also evaluated as "G" because they contained 1 or more of Cr, Cu, Ca, Sn, and B as optional elements. B8 and B9 contained 5 kinds of Cr, Cu, Ca, Sn, and B as optional elements, and therefore the film adhesion was particularly good, and evaluated to be "VG".

On the other hand, b1 to b8 are comparative examples. b3, b5, and b6 contain large amounts of Si, acid-soluble Al, and N in steel a3, steel a5, and steel a6, respectively, and therefore embrittlement at room temperature is significant, and cold rolling is not possible. Therefore, none of b3, b5, and b6 achieved evaluation of film adhesion.

The Si content of b2 is outside the scope of the invention, and the Mn content of b7 is outside the scope of the invention. Therefore, b2 and b7 were not recrystallized twice. In addition, the samples not subjected to the secondary recrystallization had poor film adhesion. This is believed to be due to: in the case where secondary recrystallization is not performed, the crystal grain size of the steel sheet is fine, the surface unevenness is severe, and SiO is₂The intermediate oxide film layer cannot be properly grown. B1 was evaluated as "B" because C was present in excess and thus secondary recrystallization was not performed at all, and C inhibited the formation of an Al interface concentrated layer that is advantageous for film adhesion. B4 was evaluated as "B" in the same manner, since the acid-soluble Al content did not satisfy the range of the present invention, no interface concentrated layer was formed. B8 was evaluated as "B" because S contained excessively inhibited the formation of an Al interface concentrated layer advantageous for film adhesion.

< example 2>

Silicon steel having a composition shown in Table 1-1 was soaked at 1100 ℃ for 60 minutes, then subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.6mm, annealed at 1100 ℃, pickled, and subjected to one cold rolling or multiple cold rolling with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.23 mm.

A cold-rolled steel sheet having a final thickness of 0.23mm was subjected to decarburization annealing and nitriding annealing, and then subjected to water slurry coating of an annealing separator mainly composed of alumina, followed by finish annealing at 1200 ℃ for 20 hours. Then, the finished annealed plate is placed at an oxygen partial pressure P_H2O/P_H2: 0.005, annealing temperature: annealing time at 800 ℃: average heating rate HR2 in the temperature region of 600 to T1 ℃ for 60 seconds: annealing at 20 deg.C/sec to form SiO on the surface of the steel plate₂An intermediate oxide film layer.

Further, the average cooling rate CR1 in the temperature region of T2 ℃ (900 ℃) to 1100 ℃ was set to 20 ℃/sec, and the average cooling rate CR2 of 100 ℃ or higher and lower than T2 ℃ (900 ℃) was set to 10 ℃/sec.

After that, the surface of the steel sheet was coated with an insulating film-forming coating liquid and sintered to form a tensile insulating film, and the adhesiveness of the insulating film and the magnetic properties (magnetic flux density) were evaluated.

SiO is shown in Table 3₂The film thickness of the intermediate oxide film layer, the concentration of interface concentration elements obtained by GDS analysis, and the evaluation result of the film adhesion. The measurement and evaluation were carried out in accordance with the measurement and evaluation in example 1. In addition, "SiO" in Table 3₂In the column of "concentration elements at the interface between the intermediate oxide film layer and the steel sheet", elements whose concentration is confirmed by GDS spectroscopy are described. The case where the expressions (1) to (4) are satisfied is set to "OK", and the case where the expressions are not satisfied is set to "NG".

The chemical compositions of the base steel sheets of the produced grain-oriented electrical steel sheets are shown in tables 1 to 2.

[ Table 3]

C1-C7 are examples of the invention. The inventive steels C1 to C5 contain any 1 or more of Cr, Ca, Cu and Sn as optional elements. Therefore, in the invention steels C1 to C5, concentration (segregation) of any 1 or more of Cr, Cu, Ca, and Sn was confirmed, and "G" as a good film adhesion was obtained. The inventive steels C6 and C7 contained optional elements Cr, Ca, Cu, Sn, B. Concentrations of Cr, Cu, and Ca were confirmed, and "VG" was obtained as a more favorable evaluation result of film adhesion than those of C1 to C5.

< example 3>

Silicon steel having a composition shown in Table 1-1 was soaked at 1100 ℃ for 60 minutes, then subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.6mm, annealed at 1100 ℃, pickled, and subjected to one cold rolling or multiple cold rolling with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.23 mm.

A cold rolled steel sheet having a final thickness of 0.23mm was subjected to decarburization annealing and nitriding annealing. Then, water slurry coating of an annealing separating agent mainly composed of alumina is performedAnd final product annealing at 1200 ℃ for 20 hours is carried out. Next, the finished annealed sheets were annealed under the conditions shown in tables 4-1 and 4-2 to form SiO on the surfaces of the steel sheets₂An intermediate oxide film layer. After that, the coating liquid for forming an insulating film was applied to the surface of the steel sheet and sintered to form a tensile insulating film, and the film adhesion of the insulating film and the magnetic properties (magnetic flux density) were evaluated.

The chemical compositions of the base steel sheets of the produced grain-oriented electrical steel sheets are shown in tables 1 to 2.

SiO is shown in Table 4-1 and Table 4-2₂The film thickness of the intermediate oxide film layer, the concentration of interface concentration elements by GDS spectroscopy, and the evaluation result of the film adhesion. The measurement and evaluation were carried out in accordance with the measurement and evaluation in example 1. The case where the expression (1) is satisfied is set to "OK", and the case where it is not satisfied is set to "NG".

[ Table 4-1]

[ tables 4-2]

D1-D33 are examples of the invention. In the inventive steels D1 to D4, SiO was formed₂The annealing time in the intermediate oxide film layer and the average heating rate HR2 in the temperature range of 600 to T1 ℃ were out of the preferable ranges, and therefore the evaluation of the film adhesion was retained at "F", but the inventive steels D5 to D11 did not contain any optional elements, but formed SiO₂Since the annealing time and HR2 in the case of the intermediate oxide film layer were controlled to be in more preferable ranges, the evaluation of the film adhesion was a good result of "G".

As for the invention steels D12-D22, the invention steels D16-D18 formed SiO₂The annealing temperature, annealing time and oxygen partial pressure in the intermediate oxide film layer are controlled to be in the preferable ranges, and the temperature is raisedSince the speed is controlled to be in a more preferable range, the film adhesion is particularly good, and is "VG". The temperature increase rates of D12 to D15 were controlled to fall within the preferable ranges, but the annealing temperatures deviated from the preferable ranges and were evaluated as "G". Further, the annealing temperatures and annealing times were controlled to be within the preferable ranges and the temperature increase rates were controlled to be within the more preferable ranges for D19 to D22, but the oxygen partial pressure was out of the preferable ranges, and therefore, the evaluation was "G".

The inventive steels D23 to D33 contained Cr, Ca, Cu, Sn, and B as optional elements. Therefore, the coating showed good film adhesion compared to the other invention steels D1 to D22. For example, the annealing temperatures of D23 to D26 deviate from the preferable ranges, but the evaluation results are particularly good evaluation results of "VG". The inventive steels D30 to D33 had oxygen partial pressures outside the preferable range, but the evaluation was particularly favorable evaluation results of "VG".

On the other hand, d1 to d9 are comparative examples. In d1 to d3 and d5, SiO was formed₂Any one of the annealing temperature, the annealing time and the oxygen partial pressure at the time of the intermediate oxide film layer is out of the range of the present invention, and therefore SiO is not formed₂The intermediate oxide film layer cannot ensure the film adhesion. In d1 to d3, SiO was not observed by GDS₂Peaks of origin, therefore T cannot be defined_pAnd T_f. Therefore, the column of "surface GDS analytical formula (1) Al" in table 4 is set to "-".

In d4, d8 and d9, SiO was formed₂An intermediate oxide film layer, but the cooling rate is high, so that Al can not be ensured to be in SiO₂The time at which the interface between the intermediate oxide film layer and the steel sheet was concentrated was B (no effect).

HR2 exceeds the upper limit for d6 and HR2 is below the lower limit for d7, thus forming SiO in large amounts₂And other oxides. Therefore, the evaluation of the film adhesion was B.

Industrial applicability

As described above, according to the present invention, it is possible to form a tensile insulating film having excellent film adhesion without impairing magnetic properties and stability of the film on the surface of a grain-oriented electrical steel sheet subjected to finish annealing until the surface of the steel sheet is flattened to have a mirror-like gloss by intentionally suppressing the formation of a glass film or removing a glass film by means of grinding, pickling, or the like. Therefore, the present invention is highly applicable to the electrical steel sheet manufacturing industry and the electrical steel sheet utilization industry.