JP7110642B2 - Method for manufacturing grain-oriented electrical steel sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet.

A grain-oriented electrical steel sheet is a silicon steel sheet containing 7% by mass or less of Si, which is composed of crystal grains highly oriented and accumulated in the {110}<001> orientation (hereinafter referred to as Goss orientation). Grain-oriented electrical steel sheets are mainly used as iron core materials for transformers. When a grain-oriented electrical steel sheet is used as the iron core material of a transformer, that is, when the steel sheets are laminated as an iron core, it is essential to ensure insulation between layers (between laminated steel sheets). Therefore, from the viewpoint of ensuring insulation, it is necessary to form a primary coating (glass coating) and a secondary coating (tension-imparting insulating coating) on the surface of the grain-oriented electrical steel sheet.

The method of forming the glass coating and the tension-applying insulating coating, and the general method of manufacturing the grain-oriented electrical steel sheet are as follows. A silicon steel slab containing 7% by mass or less of Si is hot-rolled and then cold-rolled once or twice with intermediate annealing to finish to the final thickness. Thereafter, decarburization and primary recrystallization are performed by annealing (decarburization annealing) in a moist hydrogen atmosphere. In decarburization annealing, an oxide film (Fe ₂ SiO ₄ or SiO ₂ ) is formed on the surface of the steel sheet. Subsequently, an annealing separating agent mainly composed of MgO is applied to the decarburized annealed sheet and dried, followed by final annealing. Due to this finish annealing, secondary recrystallization occurs and the crystal grain structure of the steel sheet is concentrated in the {110}<001> orientation. At the same time, MgO in the annealing separator reacts with decarburization annealing to form a glass film on the surface of the steel sheet. A tension imparting insulating film is formed by coating and baking a coating solution mainly composed of phosphate on the surface of the finish-annealed plate, that is, the surface of the glass film.

The glass film is an important entity in ensuring insulation, but its adhesion is greatly affected by the constituent elements of the steel sheet and the thickness of the steel sheet. In particular, when the thickness of the grain-oriented electrical steel sheet is reduced, it becomes difficult to secure the adhesion of the glass film while the iron loss, which is a magnetic property, is improved. For this reason, the issues in the production of grain-oriented electrical steel sheets are the improvement and stable control of glass film adhesion. Since the glass film is caused by the oxide film formed by decarburization annealing, techniques for improving the glass film have been developed by controlling decarburization annealing conditions.

For example, in Patent Document 1, a grain-oriented electrical steel sheet that has been cold-rolled to the final thickness is subjected to pickling of the surface layer before decarburization annealing, to remove the surface deposits and the surface layer of the base iron, and then remove the decarburization. A technique is described in which the charcoal reaction and oxide formation reaction proceed evenly to form a glass film with excellent adhesion.

Further, Patent Documents 2 to 4 disclose a technique in which fine unevenness is imparted to the surface of a steel sheet in decarburization annealing so that the glass coating reaches the deep part of the steel sheet and the coating adhesion is improved.
Further, as disclosed in Patent Documents 5 to 8, techniques have been developed to control the oxygen potential of the decarburization annealing atmosphere and improve the glass film adhesion. These are technologies that promote the oxidation of the decarburized annealed sheet and promote the formation of the glass film.

Further technological development progressed, and Patent Documents 9 to 11 focused on the temperature rising process of decarburization annealing, and developed a technology to improve glass film adhesion and magnetism by controlling not only the atmosphere during heating but also the temperature rising rate. .

Recently, there is a growing need for grain-oriented electrical steel sheets with even better magnetic properties. For example, Patent Documents 12 to 14 disclose techniques for producing grain-oriented electrical steel sheets with excellent magnetic properties by adding Se or Sb.

JP-A-50-71526 JP-A-62-133021 JP-A-63-7333 JP-A-63-310917 JP-A-2-240216 JP-A-2-259017 JP-A-6-33142 JP-A-10-212526 JP-A-11-61356 JP-A-2000-204450 Japanese Patent Application Laid-Open No. 2003-27194 JP 2013-47382 A JP 2013-47383 A JP-A-2010-236013

However, the methods described in Patent Literatures 1 to 4 all require additional steps in the process, resulting in a large operational load, and further improvements have been desired.
Further, when the techniques described in Patent Documents 5 to 8 are employed, although the adhesion of the glass film is improved, there is a problem that the secondary recrystallization becomes unstable and the magnetic properties (magnetism) deteriorate.

Furthermore, when the techniques described in Patent Documents 9 to 11 were employed, although these techniques improved magnetism, film improvement was still insufficient.

In addition, the film adhesion of grain-oriented electrical steel sheets to which Se or Sb is added as disclosed in Patent Documents 12 to 14 was not sufficient. In particular, materials with a plate thickness of less than 0.23 mm (hereinafter referred to as thin materials) tend to have poor glass film adhesion, and it is believed that techniques for improving film adhesion are still under development.

As described above, when a grain-oriented electrical steel sheet is used as a core material for a transformer, it is essential to ensure good magnetic properties and insulating properties of the steel sheet. However, it is difficult to achieve both the adhesion of the glass film and good magnetic properties, and in particular, a technique for further improving the adhesion of the glass film is required for materials to which Se or Sb is added.

Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide a film adhesion method on the surface of a grain-oriented electrical steel sheet whose base material steel sheet contains Se or Sb as a chemical composition. To provide a novel and improved method for producing a grain-oriented electrical steel sheet, capable of forming a glass film having excellent properties without impairing magnetic properties.

In order to solve the above-mentioned problems, the present inventors have made extensive studies, and have found conditions under which glass film adhesion is good even for materials using Sb or Se by controlling the temperature rising process of decarburization annealing. rice field.

The present invention was made based on the above findings, and the gist thereof is as follows.
[ 1 ] C: 0.010% or more and 0.20% or less, Si: 2.50% or more and 4.00% or less, acid-soluble Al: 0.005 % or more and 0.070 % or less, in mass% , Mn: 0.005% to 0.50%, N: 0.030 % or less, S: 0.0005 % to 0.030 %, Se: 0.0010 % to 0.08% Below, Sb: 0.005% or more and 0.50% or less, Bi: 0 % or more and 0.02% or less, Sn: 0% or more and 0.50% or less, Cr: 0% or more and 0.50% or less, Cu Mo: 0% to 0.5% Ti: 0% to 0.05% V: 0% to 0.05% Nb: 0% to 0.05% a hot rolling step of heating a steel slab containing 05% or less and the balance being Fe and unavoidable impurities at a temperature of 1200 ° C. or higher and 1600 ° C. or lower and then hot rolling to obtain a hot rolled steel plate;
A hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet;
a cold-rolling step of obtaining a cold-rolled steel sheet by subjecting the hot-rolled steel sheet to one cold rolling or a plurality of cold rollings via annealing;
a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing;
A finish annealing step of applying an annealing separator to the cold-rolled steel sheet and subjecting the cold-rolled steel sheet to finish annealing;
and an insulating film forming step of forming a tension-applying insulating film on the cold-rolled steel sheet,
During the temperature increase in the decarburization annealing step, the temperature increase rate S1 (° C./sec) in the temperature range of 500° C. to 600° C. and the temperature increase rate S2 (° C./sec) in the temperature range of 600° C. to 700° C. satisfies the following formulas (1) to (3), and the oxygen potential P1 in the atmosphere in the temperature range of 500 ° C. to 600 ° C. during the temperature rise satisfies the following formula (4). A method of manufacturing a steel plate.
1.0<S2/S1≦10.0 Expression (1)
300≦S1≦2000 Expression (2)
300 < S2≦4000 Expression (3)
0.00001≦P1≦0.5 Expression (4)
[2] The method for producing a grain-oriented electrical steel sheet according to [1], wherein the steel slab contains, by mass %, Bi: 0.001% or more and 0.02% or less.
[3] The steel billet, in mass%, Sn: 0.005% or more and 0.50% or less, Cr: 0.005% or more and 0.50% or less, Cu: 0.01% or more and 1.0% or less and Mo: the method for producing a grain-oriented electrical steel sheet according to [1] or [2], containing one or more selected from the group consisting of 0.005 to 0.5%.
[4] The steel slab is selected from the group consisting of Ti: 0.0005 to 0.05%, V: 0.0005 to 0.05%, and Nb: 0.0005 to 0.05% by mass%. The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [3], containing one or more of the above.
[5] In the decarburization annealing step, following the first stage annealing, the temperature T2° C. of 700° C. or more and 900° C. or less is maintained for 10 seconds or more and 1000 seconds or less in an atmosphere with an oxygen potential P2 of 0.1 or more and 1.0 or less. , in an atmosphere of oxygen potential P3 that satisfies the following formula (5), at a temperature T3 ° C that satisfies the following formula (6), perform second stage annealing for 5 seconds or more and 500 seconds or less, [1] to [4] A method for producing a grain-oriented electrical steel sheet according to any one of .
P3<P2 Expression (5)
T2+50≦T3≦1000 Expression (6)
[6] Any one of [1] to [5], wherein the average temperature increase rate BR1 (° C./h) in the temperature range of 875° C. to 1050° C. satisfies the following formula (7) in the temperature increase in the final annealing step A method for producing a grain-oriented electrical steel sheet according to item 1.
1.0≦BR1≦60.0 Expression (7)
[7] Any one of [1] to [6], wherein the oxygen potential P4 of the finish annealing atmosphere in the temperature range of 875° C. or higher and 1050° C. or lower satisfies the following formula (8) in the temperature rise in the finish annealing step. A method for producing the grain-oriented electrical steel sheet described.
0.00001≦P4≦0.5 Expression (8)
[8] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [7], wherein the grain-oriented electrical steel sheet has a product thickness of 0.18 mm or more and less than 0.22 mm.

As described above, according to the present invention, a grain-oriented electrical steel sheet having excellent glass film adhesion and containing Se or Sb as a chemical composition in the base steel sheet can be manufactured without impairing the magnetic properties and stability thereof. can do.

Preferred embodiments of the present invention are described in detail below. Prior to detailed description of the overall flow of the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, the background to the present invention will be described below.

1. Background to the present invention When a unidirectional electrical steel sheet is used as an iron core material for a transformer, it is essential to ensure the insulation properties of the steel sheet, so a tension insulating film is formed on the steel sheet surface after final annealing. There is a need to. By the way, in order to improve the magnetism of grain-oriented electrical steel sheets, especially to improve the magnetism of thin materials, Sb or Se is sometimes added as a component of billets such as slabs. This aims at improving the texture of the secondary recrystallized steel sheet by precipitating MnSb or MnSe as an inhibitor. However, it is difficult to ensure the adhesion of the glass film to the material to which Sb and Se are applied.

Although the cause of this is not completely clear, the present inventors focused on the possibility that Sb or Se inhibits the growth of the glass film. In the first place, the adhesion between the glass film and the steel sheet largely depends on the morphology of the glass film. The process in which SiO ₂ is formed, ie, the decarburization annealing process, is important for the morphology of the glass film. This is because the glass film is a substance produced by a solid phase reaction between SiO ₂ and MgO, which is the main component of the annealing separator. Since the process in which SiO ₂ is formed is the decarburization annealing process, it is generally possible to ensure excellent film adhesion by controlling the decarburization annealing process. However, when the steel sheet contains Se or Sb, since Se or Sb has a low affinity with _SiO2 , it concentrates at the interface between _SiO2 and the steel sheet during decarburization annealing. In this case, the present inventors considered that the Se or Sb-enriched layer would be the cause of hindering the growth of the glass film.

Faced with such a problem, the inventors of the present invention conducted intensive studies, and as a result, found conditions for good glass film adhesion even with materials using Sb or Se by controlling the temperature rising process of decarburization annealing. rice field. _In response to this result, the inventors conducted a retrospective analysis of the sample after _{decarburization} annealing. Many Se or Sb have been confirmed. On the other hand, in materials with good film adhesion, in addition to SiO ₂ , Mn ₂ SiO ₄ (tephrite) is formed on the surface of the steel sheet, Se or Sb is present in Mn ₂ SiO ₄ , and Mn ₂ SiO ₄ Se or Sb enrichment at the interface between the base iron (base steel plate) and the base iron (base steel plate) could hardly be confirmed.

Since Se or Sb has a low affinity with _SiO2 , it concentrates at the interface between _SiO2 and the steel sheet, but Se or _Sb has a _high affinity with _Mn2SiO4 and is incorporated into _Mn2SiO4 . , do not condense at the interface between Mn ₂ SiO ₄ and the steel sheet. As a result, the glass film could grow and develop, and it was thought that the film adhesion was improved.

Furthermore, the present inventors have found that the film adhesion can be further improved by controlling the heating process of the final annealing. In the decarburization annealing step, part of Se or Sb may not dissolve in Mn ₂ SiO ₄ (tefloite). Undissolved Se or Sb can be dissolved in the tephrite by controlling the heating rate of the final annealing. As a result, the concentration of Se or Sb at the interface (the interface between the glass film and the base iron), which inhibits the growth of the glass film, is thoroughly avoided, and the adhesion of the glass film is improved.

The present inventors arrived at the present invention based on the above studies. Hereinafter, the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described with a focus on control conditions for the decarburization annealing step.

2. Method for Manufacturing Grain-oriented Electrical Steel Sheet Next, the overall flow of the method for manufacturing a grain-oriented electrical steel sheet according to the embodiment of the present invention will be described in detail.

A general method for producing a grain-oriented electrical steel sheet is as follows. A silicon steel slab containing 7% by mass or less of Si is hot-rolled and subjected to hot-rolled sheet annealing. After the hot-rolled annealed sheet is pickled, it is cold-rolled once or twice with intermediate annealing to finish it to the final thickness. Thereafter, decarburization and primary recrystallization are performed by annealing (decarburization annealing) in a moist hydrogen atmosphere. In decarburization annealing, an oxide film (Fe ₂ SiO ₄ or SiO ₂ ) is formed on the surface of the steel sheet. Subsequently, an annealing separating agent mainly composed of MgO is applied to the decarburized annealed sheet and dried, followed by final annealing. Due to this finish annealing, secondary recrystallization occurs and the crystal grain structure of the steel sheet is concentrated in the {110}<001> orientation. At the same time, MgO in the annealing separator reacts with decarburization annealing to form a glass film (Mg ₂ SiO ₄ ) on the surface of the steel sheet. After the finish-annealed sheet is washed with water or pickled to remove powder, a coating solution mainly containing phosphate is applied and baked to form a tension-imparting insulating film.

A method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment comprises a hot rolling step of hot-rolling a billet having a predetermined chemical composition to obtain a hot-rolled steel sheet, and a hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet. a cold rolling step of subjecting the hot-rolled steel sheet to one cold rolling or a plurality of cold rollings via annealing to obtain a cold-rolled steel sheet; and a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing. , a finish annealing step of applying an annealing separator to the cold-rolled steel plate and subjecting the cold-rolled steel plate to finish annealing, and an insulation film forming step of forming a tension imparting insulation film on the cold-rolled steel plate . These steps will be described in detail below. In addition, in the following description, when the conditions of each step are not described, it is possible to perform each step by appropriately adapting known conditions.

2.1. Hot Rolling Process The hot rolling process is a process of hot rolling a billet (for example, a steel ingot such as a slab) having a predetermined chemical composition to form a hot rolled steel sheet. Below, first, the chemical composition of the billet used in the method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be described in detail. In the following description, "%" means "% by mass" unless otherwise specified.

Further, in the present embodiment, in mass %, C: 0.01% or more and 0.20% or less, Si: 2.50% or more and 4.0% or less, acid-soluble Al: 0.005% or more and 0.07% % or less, Mn: 0.005% or more and 0.5% or less, N: 0.03% or less, S: 0.0005% or more and 0.03% or less, Se: 0.001% or more and 0.08% or less, Sb: 0.005% or more and 0.5% or less, Bi: 0% or more and 0.02% or less, Sn: 0% or more and 0.50% or less, Cr: 0% or more and 0.50% or less, Cu: 0% 1.0% or less, Mo: 0% or more and 0.5% or less, Ti: 0% or more and 0.05% or less, V: 0% or more and 0.05% or less, and Nb: 0% or more and 0.02% or less is used, and the balance is Fe and unavoidable impurities.

(C: 0.01% or more and 0.20% or less)
C has the effect of improving the magnetic flux density, but if the content exceeds 0.20%, the steel undergoes a phase transformation in the secondary recrystallization annealing, and the secondary recrystallization does not proceed sufficiently, resulting in a good magnetic flux density. The C content is set to 0.20% or less because the iron loss characteristic cannot be obtained. Since the smaller the amount of C, the more preferable it is for iron loss reduction, the content of C is preferably 0.10% or less from the viewpoint of iron loss reduction.
In this embodiment, Se and Sb are used to improve magnetic properties, so the lower limit of the C content is 0.01%, preferably 0.03%, from the viewpoint of magnetic flux density.

(Si: 2.50% or more and 4.0% or less)
If the Si content is less than 2.50%, the steel undergoes phase transformation during secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss properties cannot be obtained. Therefore, the Si content is set to 2.50% or more. The Si content is preferably 3.00% or more, more preferably 3.20% or more.
On the other hand, if the Si content exceeds 4.0%, the steel sheet becomes embrittled and the threadability in the manufacturing process is significantly deteriorated, so the Si content is made 4.0% or less. The Si content is preferably 3.80% or less, more preferably 3.60% or less.

(Acid-soluble Al: 0.005% or more and 0.07% or less)
In the electrical steel sheet of the present invention, acid-soluble Al (sol. Al) is an essential element from the viewpoint of secondary recrystallization.
If the content of acid-soluble Al is less than 0.005%, sufficient AlN that functions as an inhibitor will not be generated, secondary recrystallization will be insufficient, and iron loss characteristics will not be improved. The amount should be 0.005% or more. Preferably, it is 0.01% or more.
On the other hand, when the content of acid-soluble Al exceeds 0.07%, the steel sheet becomes embrittled. content is 0.07% or less and 0.05% or less.

(N: 0.03% or less)
N forms AlN, which can be used as an inhibitor. However, when Se or Sb is used, if the N content exceeds 0.03%, blisters (voids) are generated in the steel sheet during cold rolling, and the strength of the steel sheet increases. The N content is set to 0.03% or less because it deteriorates plate properties. Preferably, it is 0.02% or less.
The lower limit of the N content includes 0% if AlN is not utilized as an inhibitor. However, since the detection limit of chemical analysis is 0.0001%, the practical lower limit of the steel sheet is 0.0001%. On the other hand, the content of N is preferably 0.001% or more in order to combine with Al to form AlN that functions as an inhibitor.

(Mn 0.005% or more and 0.5% or less)
If Mn exceeds 0.5%, 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. The amount should be 0.5% or less. Preferably, it is 0.10% or less.
Since Mn can be used as an inhibitor of MnS during secondary recrystallization, the Mn content is made 0.005% or more. Preferably, it is 0.01% or more.

(S: 0.0005% or more and 0.03% or less)
When the content of S exceeds 0.03%, MnS causes competitive precipitation with MnSe, so good magnetism cannot be obtained. Therefore, the S content should be 0.03% or less. Preferably, it is 0.015% or less.
When MnS is utilized as an inhibitor during secondary recrystallization, the S content should be 0.0005% or more. Preferably, it is 0.001% or more.

(Se: 0.001% or more and 0.08% or less)
Se is a particularly important element in the present invention. However, if it is added in excess of 0.08%, the glass film will deteriorate significantly. Therefore, the upper limit of the Se content is set to 0.08%. It is preferably 0.03% or less.
If the Se content is less than 0.001%, sufficient magnetism may not be obtained, so the lower limit of the Se content is made 0.001%. Considering compatibility between magnetism and film adhesion, the content is preferably 0.003% or more.

(Sb: 0.005% or more and 0.5% or less)
Sb is a particularly important element in the present invention. However, if it is added in excess of 0.5%, the glass film will deteriorate significantly. Therefore, the upper limit of the Sb content is set to 0.5%. It is preferably 0.1% or less.
If the Sb content is less than 0.005%, sufficient magnetism may not be obtained, so the lower limit of the Sb content is 0.005%. Considering compatibility between magnetism and film adhesion, the content is preferably 0.01% or more.

In the present embodiment, in addition to the above elements, the steel slab contains Bi: 0.001% or more and 0.02% or less in terms of mass% in order to improve the properties of the grain-oriented electrical steel sheet according to the present embodiment. You may Since Bi is an optional element, the lower limit of the Bi content is 0% regardless of the above description.

(Bi: 0.001% or more and 0.02% or less)
Bi, like Cr, Sn, and Cu, which will be described later, is an element that contributes to promoting the improvement of film adhesion. If it is less than 0.001%, the effect of promoting improvement in film adhesion cannot be sufficiently obtained, so the content is made 0.001% or more. Preferably, it is 0.001% or more.
On the other hand, when the Bi content exceeds 0.02%, the threadability during cold rolling deteriorates, so the Bi content is made 0.02% or less. Preferably, it is 0.01% or less.

In the present embodiment, the steel billet contains, in addition to the above elements, Sn: 0.005 to 0.50% and Cr: 0% by mass in order to improve the properties of the grain-oriented electrical steel sheet according to the present embodiment. 0.005 to 0.50%, Cu: 0.01 to 1.0%, and Mo: 0.005 to 0.5%. Since Sn, Cr, Cu and Mo are optional elements, the lower limit of the content of Sn, Cr, Cu and Mo is 0% regardless of the above description.

(Sn: 0.005% or more and 0.50% or less)
Sn is an element that contributes to the improvement of film adhesion. Although the mechanism by which Sn improves film adhesion is not clear, it is believed that Sn promotes the growth of the glass film and contributes to the formation of an intrusion structure with respect to the base iron (base steel plate).
If the Sn content is less than 0.005%, the effect of improving film adhesion due to the addition of Sn cannot be sufficiently obtained, so the Sn content can be made 0.005% or more. Preferably, it is 0.01% or more.
On the other hand, if the Sn content exceeds 0.50%, the secondary recrystallization becomes unstable and the magnetic properties deteriorate, so the Sn content is made 0.50% or less. Preferably, it is 0.30% or less.

(Cr: 0.005% or more and 0.50% or less)
Cr, like Bi and Cu, is an element that contributes to improving film adhesion. If the Cr content is less than 0.005%, a sufficient effect of improving film adhesion cannot be obtained, so the Cr content can be made 0.005% or more. Preferably, it is 0.01% or more.
On the other hand, if the Cr content exceeds 0.50%, Cr oxide is formed and there is a concern that the magnetism may be deteriorated, so the Cr content is made 0.50% or less. Preferably, it is 0.30% or less.

(Cu: 0.01% or more and 1.0% or less)
Cu, like Bi, Cr, and Sn, is an element that contributes to improving film adhesion. If the Cu content is less than 0.01%, a sufficient effect of improving film adhesion cannot be obtained, so the Cu content can be made 0.01% or more. Preferably it is 0.03% or more.
On the other hand, if the Cu content exceeds 1.0%, the steel sheet becomes embrittled during hot rolling, so the Cu content is made 1.0% or less. Preferably, it is 0.50% or less.

(Mo: 0.005% or more and 0.5% or less)
Mo, like Bi, Cr, Sn, and Cu, is an element that contributes to improving film adhesion. If it is less than 0.005%, a sufficient effect of improving film adhesion cannot be obtained, so Mo is made 0.005% or more. Preferably, it is 0.01% or more.
On the other hand, if the Mo content exceeds 0.5%, the steel sheet may become brittle and break during cold rolling, so Mo should be 0.5% or less. Preferably, it is 0.30% or less.

In the present embodiment, in addition to the elements described above, the steel billet contains, in terms of mass %, Ti: 0.0005% or more and 0.05% or less, V : 0.0005% or more and 0.05% or less, and Nb: 0.0005% or more and 0.05% or less. Since Ti, V and Nb are optional elements, the lower limit of the content of Ti, V and Nb is 0% regardless of the above description.

(Ti: 0.0005% or more and 0.05% or less)
Ti has the effect of promoting the magnetic improvement effect of Se and Sb. Therefore, in the present invention, by adding Ti, it can be expected that even better magnetism can be obtained without impairing film adhesion. However, when Ti is added in excess of 0.05%, TiN is formed. TiN causes poor secondary recrystallization, and the desired magnetism cannot be obtained. Therefore, the upper limit of the Ti content is set to 0.05%.
On the other hand, if the Ti content is less than 0.0005%, the effect of improving the magnetic properties of Ti cannot be expected. Therefore, when Ti is added in anticipation of a magnetic improvement effect, the lower limit of its content is made 0.0005%. A preferable range of Ti content is 0.001% or more and 0.02% or less.

(V: 0.0005% or more and 0.05% or less)
Like Ti, V also has the effect of promoting the effect of improving the magnetism of Se and Sb. Therefore, in the present invention, by adding V, it can be expected that even better magnetism can be obtained without impairing film adhesion. However, when V is added in excess of 0.05%, VN is formed. VN causes secondary recrystallization defects, and the desired magnetism cannot be obtained. Therefore, the upper limit of the V content is set to 0.05%.
On the other hand, if the V content is less than 0.0005%, the magnetic improvement effect of V cannot be expected. Therefore, when V is added in anticipation of a magnetic improvement effect, the lower limit of its content is made 0.0005%. A preferable range of the V content is 0.001% or more and 0.02% or less.

(Nb: 0.0005% or more and 0.05% or less)
Like Ti and V, Nb also has the effect of promoting the magnetic improvement effect of Se and Sb. Therefore, in the present invention, by adding Nb, it can be expected that even better magnetism can be obtained without impairing film adhesion. However, when Nb is added in excess of 0.05%, NbN is formed. NbN causes poor secondary recrystallization, and the desired magnetism cannot be obtained. Therefore, the upper limit of the Nb content is set to 0.05%.
On the other hand, if the Nb content is less than 0.0005%, the magnetic improvement effect of Nb cannot be expected. Therefore, when Nb is added in anticipation of the magnetic improvement effect, the lower limit of its content is made 0.0005%. The preferred range of Nb content is 0.001% or more and 0.02% or less.

The remainder of the component composition of the steel billet used in this embodiment is Fe and unavoidable impurities. However, for the purpose of improving magnetic properties, improving properties required for structural members such as strength, corrosion resistance and fatigue properties, improving castability and plate threadability, and improving productivity by using scrap etc., Fe 1 selected from In, B, Au, Ag, Te, Ce, Co, Ni, Ca, Re, Os, Zr, Hf, Ta, Y, La, Cd, Pb, As, etc. instead of a part of A total of 5.00% or less, preferably 3.00% or less, and more preferably 1.00% or less of the species or two or more of them may be contained. In addition, since these elements are elements that can be included arbitrarily, the lower limit of the total content of these elements is 0%.

Unavoidable impurities are components that exist in steel slabs regardless of the intention of their addition and do not need to exist in the obtained grain-oriented electrical steel sheet. The term "inevitable impurities" is a concept that includes impurities mixed in from ores, scraps, or manufacturing environments used as raw materials during the industrial production of steel materials. Such unavoidable impurities can be contained in amounts that do not adversely affect the effects of the present invention.

In this step, the steel slab having the above components is first heat-treated. The heating temperature is, for example, 1200° C. or higher and 1600° C. or lower, preferably 1280° C. or higher and 1500° C. or lower. The heated billet is then processed into a hot rolled steel sheet by subsequent hot rolling. The plate thickness of the processed hot-rolled steel sheet is preferably in the range of, for example, 2.0 mm or more and 3.0 mm or less.

2.2. Hot Rolled Steel Sheet Annealing Step Next, the obtained hot rolled steel sheet is annealed. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties.
The annealing conditions are not particularly limited, but for example, the steel sheet can be annealed in a temperature range of 900 to 1200° C. for 10 seconds to 5 minutes.
After this step and before the cold-rolling step, the surface of the hot-rolled steel sheet may be pickled.

2.3. Cold rolling process Next, the processed hot-rolled steel sheet is rolled by one cold rolling after hot-rolled sheet annealing, or by cold rolling multiple times with intermediate annealing in between. Rolled. Further, when the hot-rolled sheet is annealed, the shape of the steel sheet is improved, so the possibility of the steel sheet breaking in the first rolling can be reduced. In this case, the method of heating the steel plate is not particularly limited. The cold rolling may be performed three times or more, but since the manufacturing cost increases, it is preferable to perform the cold rolling once or twice.
Also, the final cold rolling reduction can be, for example, in the range of 80% or more and 95% or less. By setting the final cold rolling reduction within the above range, obtaining Goss nuclei with {110} <001> orientation having a high degree of accumulation in the rolling direction and suppressing destabilization of secondary recrystallization. can be done.
The thickness of the cold-rolled steel sheet that has undergone cold rolling is usually the thickness (final thickness) of the grain-oriented electrical steel sheet that is finally manufactured.

2.4. Decarburization Annealing Step Next, in the decarburization annealing step, the obtained cold-rolled steel sheet is decarburized and annealed. In the present embodiment, the decarburization annealing is performed by heating under the specific conditions described below.

(i) Temperature raising conditions First, the temperature raising conditions in this step will be described in detail.
In this step, the temperature increase rate S1 (° C./sec) in the temperature range of 500° C. or higher and 600° C. or lower and the temperature increase rate S2 (° C./sec) in the temperature range of 600° C. or higher and 700° C. or lower are expressed by the following formula (1). The temperature is raised so as to satisfy the following formula (3).
1.0<S2/S1≦10.0 Expression (1)
300≦S1≦2000 Expression (2)
300≦S2≦4000 Expression (3)
The present inventors have found that by adopting the above temperature elevation conditions under the oxygen potential conditions described later, tephrite (Mn ₂ SiO ₄ ) can be sufficiently formed on the surface layer of the steel sheet, and the Se or Sb interface It has been found that thickening can be avoided.

Explain why. The SiO ₂ oxide film is most easily formed in the temperature range of 600-700°C. It is considered that the Si diffusion rate and the O diffusion rate in the steel in this temperature range are balanced on the steel plate surface. On the other hand, in the temperature range of 500 to 600° C., tephrite is likely to be formed as an oxide film. In the present invention, since it is necessary to generate tephrite, the residence time at 500 to 600° C., which is the formation temperature range of tefloite, is reduced compared to the residence time at 600 to 700° C., which is the formation temperature range of SiO ₂ . Earning more is the first priority.

Therefore, it is necessary that the ratio S2/S1 between the temperature increase rate S1 in the temperature range of 500 to 600° C. and the temperature increase rate S2 in the temperature range of 600 to 700° C. is greater than 1.0. The residence time in the temperature range of 500 to 600°C corresponds to the amount of tephrite produced, and the residence time in the temperature range of 600 to 700°C corresponds to the amount of _SiO2 produced. However, the amount of SiO ₂ produced may exceed the above, and the effects of the present invention may not be obtained. On the other hand, the upper limit of the ratio S2/S1 is determined to be 10.0 from the lower limit of S1 and the upper limit of S2. However, when the amount of SiO ₂ produced is extremely small, the glass film formation behavior becomes unstable, which may cause film defects such as holes in the film. Therefore, the preferred range of the ratio S2/S1 is more than 1.0 and 5.0 or less, and a more preferred range is 1.2 or more and 3.5 or less.

The lower limit of S1 is 300° C./sec or more, and the upper limit is 2000° C./sec. Good magnetism cannot be obtained at 300° C./sec or less, and teflonite is not formed at over 2000° C./sec. S1 is preferably 400° C./sec or more. Also, S1 is preferably 1700° C./sec or less.
Furthermore, control of the heating rate S2 in the temperature range of 600 to 700° C. is also important. The range of S2 is from 300° C./sec to 4000° C./sec. Since the effect of the present invention can be enjoyed as the value of S2 increases, S2 is preferably 500° C./second or more. However, if the heating rate is too high, there is a concern of overshoot, so the upper limit is set to 4000° C./second or less. S2 is preferably 3000° C./sec or less.

Note that if an isothermal holding cycle at 600° C. or a heating cycle including cooling after reaching 600° C. is employed, the residence time corresponding to each of S1 and S2 becomes unclear. Therefore, in this embodiment, when a 600° C. isothermal holding cycle is adopted, the residence time corresponding to S1 is from the time when 500° C. is reached until the end of isothermal holding at 600° C. In the case of a heating cycle including cooling after reaching 600° C. is the time required to reach 600° C. again by reheating. Therefore, the residence time corresponding to S2 is defined as the time from the end of isothermal holding at 600°C or the time when 600°C is reached again by reheating to the time of reaching 700°C.

Further, in the present embodiment, the oxygen potential P1 in the atmosphere in the temperature range of 500° C. or higher and 600° C. or lower when the temperature is raised satisfies the following formula (4).
0.00001≦P1≦0.5 Expression (4)

The thermodynamic stability of the oxide film is also affected by the oxygen potential P1 of the atmosphere in the temperature range of 500° C. to 600° C. where Mn ₂ SiO ₄ is produced. _The oxygen potential can be defined by the ratio of the water vapor partial pressure _PH2O and the hydrogen partial pressure PH2 in the atmosphere, that is, _PH2O / _PH2 . If P1 exceeds 0.5, Fe ₂ SiO ₄ is produced and inhibits the formation of tephrite, so the upper limit of P1 is 0.5. The smaller P1 is, the easier it is to form tefloite, but the industrial limit is considered to be P1=0.00001. That is, P1 is 0.00001 or more and 0.5 or less, preferably 0.0001 or more and 0.3 or less.

When a 600° C. isothermal holding cycle is employed, the atmosphere corresponding to P1 is defined as the atmosphere from the time when 500° C. is reached until the end of the 600° C. isothermal holding.

(ii) Holding conditions In addition, the annealing conditions (holding conditions) in this step are not particularly limited as long as the above temperature elevation conditions are satisfied. It is carried out by holding for seconds to 10 minutes. Also, multistage annealing may be performed. For example, a two-step anneal as described below can be performed.

For example, in this step, following the first-stage annealing in which the temperature T2° C. of 700° C. or higher and 900° C. or lower is maintained for 10 seconds or longer and 1000 seconds or shorter in an atmosphere of oxygen potential P2, oxygen potential P3 satisfying the following formula (5) is performed. Second-stage annealing can be performed in an atmosphere at a temperature of T3° C. that satisfies the following formula (6) for 5 seconds or more and 500 seconds or less.
P3<P2 Expression (5)
T2+50≦T3≦1000 Expression (6)

As mentioned above, the formation of tephrite during decarburization annealing is important, but the decarburization annealing process may be carried out by two-stage annealing in which the former stage is low temperature and the latter stage is high temperature annealing. At this time, it is necessary to control the high-temperature annealing temperatures of the first stage and the second stage. Under the conditions described above, it is possible to sufficiently form tephrite on the surface layer of the steel sheet in the decarburization annealing step, and to more reliably avoid the concentration of Se or Sb at the interface.

From the viewpoint of improving decarburization, for example, in the first stage annealing, the annealing temperature T2 (plate temperature) is 700° C. or higher and 900° C. or lower, preferably 780° C. or higher and 860° C. or lower, and is held for 10 seconds or more. A longer annealing time itself poses no problem from the viewpoint of decarburization, but from the viewpoint of productivity, the upper limit of the annealing time is 1000 seconds or less. In the production of practical steel sheets, the time is preferably 50 seconds or more and 300 seconds or less.

From the viewpoint of ensuring the amount of tephrite formed, it is preferable that the oxygen potential P2 during the first stage annealing be higher than the oxygen potential P1 during the temperature rise. When sufficient oxygen potential is obtained, tephrite can be prevented from being replaced by _SiO2 . Moreover, the decarburization reaction can be sufficiently advanced. However, if P2 is too large, tephrite may be replaced by Fe ₂ SiO ₄ . Fe ₂ SiO ₄ deteriorates the adhesion of the glass film. Therefore, P2 can be controlled within the range of 0.1 or more and 1.0 or less. It is preferably 0.2 or more and 0.8 or less.

The generation of Fe ₂ SiO ₄ cannot be completely suppressed in the first stage annealing. Therefore, in the second stage annealing, the annealing temperature T3 (sheet temperature) is preferably T2 + 50°C or higher and 1000°C or lower, preferably T2 + 100°C or higher and 1000°C or lower, and is held for 5 seconds or longer. This is because within this temperature range, even if Fe ₂ SiO ₄ is produced during the first stage of annealing, it is reduced to tephrite. If the annealing time exceeds 500 seconds, tephrite will be reduced to SiO ₂ , so the upper limit of the annealing time is made 500 seconds. It is preferably 10 seconds or more and 100 seconds or less.

In order to create a reducing atmosphere, the oxygen potential P3 in the second stage annealing can be set smaller than P2. For example, if the oxygen potential of P3 itself can be controlled to 0.00001 or more and 0.1 or less, better adhesion can be obtained.

2.5. Finish Annealing Step Next, finish annealing is performed on the obtained cold-rolled steel sheet after decarburization annealing (decarburization annealing steel sheet). Here, the finish annealing is generally performed for a long time while the steel sheet is coiled. Therefore, prior to final annealing, an annealing separating agent is applied to the decarburized annealed steel sheet for the purpose of preventing seizure between the inside and the outside of the winding of the steel sheet, and dried. As the annealing separator, an annealing separator containing magnesia (MgO) as a main component can be used. In this case, the annealing separator may contain magnesia as a main component.

Then, finish annealing is performed. Secondary recrystallization accumulates in the {110}<001> orientation during the final annealing, forming coarse crystal grains with easy magnetization axes aligned in the rolling direction, resulting in excellent magnetic properties. At the same time, on the surface of the steel sheet, MgO in the annealing separator reacts with an oxide film formed by decarburization annealing to form a glass film.

The conditions for the finish annealing are not particularly limited, and known conditions can be appropriately adopted. However, in order to avoid the concentration of Se or Sb at the interface and further improve the film adhesion of the grain-oriented electrical steel sheet, it is preferable to raise the temperature under the following conditions.

First, in the temperature increase in the final annealing step, it is preferable that the average temperature increase rate BR1 (°C/hour) in the temperature range of 875°C to 1050°C satisfies the following formula (7).
1.0≦BR1≦60.0 Expression (7)

Explain why. As described above, the oxide film formed by decarburization annealing changes into a glass film in finish annealing. The glass film continues to grow toward the base iron and has an intrusive structure. At this time, if Se or Sb is concentrated at the growth front of the glass film, that is, at the interface between the glass film and the base iron, the growth of the glass film is suppressed, and good film adhesion cannot be obtained. As described above, it is important in the present invention to generate teflite in the decarburization annealing process, incorporate Se or Sb into the teflite, and render Se or Sb harmless. A solid solution of Se or Sb into teflite mainly occurs in the decarburization annealing process, but a part of Se or Sb may not be incorporated into teflite.

Therefore, the film adhesion can be further improved by controlling the heating conditions so that the rate of temperature rise during the final annealing is reduced to promote the dissolution of Se or Sb into the teflonite. The temperature range for controlling the heating rate is 875-1050°C. This is because diffusion of Se or Sb progresses most in this temperature range, and solid solution in tephrite is promoted. If the heating rate exceeds 60.0° C./h, the above effects may not be obtained. Although there is no particular lower limit, the lower limit can be set at 1.0° C./h from the viewpoint of productivity. A preferable range of BR1 is 1.0° C./h or more and 30.0° C./h or less. It is more preferably 1.0° C./h or more and 20.0° C./h or less.

Further, in the temperature rise in the final annealing step, it is preferable that the oxygen potential P4 of the finish annealing atmosphere in the temperature range of 875° C. or higher and 1050° C. or lower satisfies the following formula (8). As a result, further improvement in film adhesion can be expected.
0.00001≦P4≦0.5 Expression (8)

If the annealing atmosphere has a high oxygen potential, the teflite will change into a glass film before Se or Sb dissolves into the tefloite, and depending on the conditions, the film adhesion cannot be further improved. Sometimes. Therefore, in the above temperature range, it is important to control the conditions so that the rate of change of the teflon into the glass film is small in the range of 875°C to 1050°C. Therefore, it is preferable to control the atmosphere P4 in the temperature range within the range of 0.00001 to 0.5. If the oxygen potential exceeds 0.2, depending on the heating conditions and the composition of the steel billet, the teflite may change into a glass film before Se or Sb dissolves into the teflite. Therefore, the upper limit of P4 can be 0.5, preferably 0.2, more preferably 0.1. Although there is no particular lower limit, it is considered practically difficult to control to 0.00001 or less, so the lower limit of P4 can be 0.00001, preferably 0.0001, more preferably 0.0005. .

In the final annealing process, even if the purification treatment is performed at a high temperature of 1050° C. or higher, the Se and Sb once solid-dissolved in the teflonite are not separated, and the film adhesion is not lowered. In the final annealing step, after the temperature is raised under the above conditions, the temperature range of 1100° C. or higher and 1300° C. or lower may be maintained for 10 hours or longer and 60 hours or shorter.
After the completion of this step, the surface of the cold-rolled steel sheet may be washed with water or pickled to remove powder.

2.6. Insulating Coating Forming Step In the insulating coating forming step, tension imparting insulating coatings are formed on both surfaces of the cold-rolled steel sheet after the finish annealing step. For example, by applying an insulating coating liquid containing a mixture of a resin such as acrylic and an inorganic substance such as a phosphate, or an insulating coating liquid containing colloidal silica and a phosphate, to the surface of the steel sheet and performing heat treatment, the steel sheet A tension-imparting insulating coating can be formed on the surface of the The heat treatment may be performed in a temperature range of, for example, 250° C. to 400° C. when the insulating coating liquid contains an organic substance, and in a temperature range of, for example, 840° C. to 920° C. when the insulating coating liquid contains only inorganic substances. do it.
A grain-oriented electrical steel sheet can be manufactured by the above steps.

3. Grain-oriented Electrical Steel Sheet Finally, the grain-oriented electrical steel sheet obtained by the method described above will be described.
The grain-oriented electrical steel sheet produced by the above method has improved magnetic properties due to the inclusion of Se and Sb. On the other hand, in the decarburization annealing process, in addition to SiO ₂ , tephrite (Mn ₂ SiO ₄ ) is sufficiently formed on the steel sheet surface. As a result of solid solution of Se and Sb in this teflonite, deterioration of film adhesion due to Se and Sb is prevented. Therefore, the grain-oriented electrical steel sheet manufactured by the method according to the present embodiment described above has excellent adhesion to the glass coating.

The grain-oriented electrical steel sheet according to the present embodiment can have a product thickness of, for example, 0.18 mm or more and 0.35 mm or less. Moreover, in the present invention, the effect is remarkable when the grain-oriented electrical steel sheet is a material having a small final thickness (hereinafter referred to as a thin material). Specifically, the effect is remarkable when the product thickness of the grain-oriented electrical steel sheet is 0.18 mm or more and less than 0.22 mm, particularly 0.18 mm or more and 0.20 mm or less.

That is, in the present invention, it is necessary to generate a sufficient amount of tephrite in the decarburization annealing. The formation of tephrite is controlled by the diffusion of Mn in the steel to the plate thickness surface. Since the ratio of the surface area occupied by the thin material is larger than that of the thick material, the diffusion distance of Mn from the inside of the steel sheet to the surface of the steel sheet can be short. That is, the thin material has a high substantial diffusion rate of Mn. This is believed to be the reason why thin materials can efficiently produce tephrite even at a low temperature range of 500 to 600°C.

Various magnetic properties exhibited by grain-oriented electrical steel sheets are measured according to the Epstein method specified in JIS C2550 and the single sheet magnetic property measurement method (Single Sheet Tester: SST) specified in JIS C2556. It is possible to

Hereinafter, the technical content of the present invention will be further described with reference to examples of the present invention. It should be noted that the conditions in the examples shown below are an example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is not limited to this example of conditions. Moreover, the present invention can adopt various conditions without departing from the gist of the present invention and as long as the objects of the present invention are achieved.

<Example 1>
A silicon steel having the chemical composition shown in Tables 1 and 2 is heated to 1280° C. or more and 1450° C. or less and subjected to hot rolling to obtain a hot rolled steel sheet having a thickness of 2.3 to 2.8 mm. It was annealed at 1200° C. and then cold-rolled once or cold-rolled a plurality of times with intervening annealing to obtain a cold-rolled steel sheet with a final thickness of 0.22 mm. In each silicon steel, the balance other than the components listed in Tables 1 and 2 is iron and impurities.

A cold-rolled steel sheet having a final thickness of 0.22 mm was decarburized and annealed, then coated with an annealing separating agent and subjected to finish annealing at 1200° C., and then a finish-annealed steel sheet was produced. In the decarburization annealing step of this experiment, the heating rate in the temperature range of 500 to 700 ° C. and the oxygen potential in the temperature range of 500 to 600 ° C. were controlled (S1 = 700 ° C./sec, S2 = 950 ° C./sec, P1 = 0.15). After that, the surface of the steel sheet was coated with the coating solution for forming an insulating film and baked to form a tension-imparting insulating film. The decarburization annealing was performed at 830° C. for 150 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.4.

Magnetic properties were evaluated according to JIS C 2550. Magnetic flux density was evaluated using B8. B8 is the magnetic flux density at a magnetic field strength of 800 A/m, and serves as a criterion for determining the quality of secondary recrystallization. B8=1.89 T or more was judged to have undergone secondary recrystallization. The comparative steel b4 was broken in the cold rolling process, and the comparative steel b11 was broken in the hot rolling process, so the magnetic properties were not evaluated.

The film adhesion of the tension-applying insulating film was evaluated by winding the evaluation sample around a cylinder with a diameter of 20 mm and bending it 180° to evaluate the residual film area ratio. The evaluation is VG (very excellent) when the film does not peel off from the steel plate and the residual film area ratio is 95% or more, G (excellent) when it is 90% or more and less than 95%, and 80% or more and less than 90%. F (effective), less than 80% B (no effect). Film adhesion was not evaluated for those that fractured during rolling and those with poor secondary recrystallization. Table 3 shows a series of evaluation results.

All of the invention steels B1-38 exhibited excellent film adhesion and magnetic properties. In particular, in invention steels B32 to B36, one or more of the selective elements Bi, Sn, Cr, Cu, Mo, Ti, V, and Nb are added in an appropriate amount. Exhibits good film adhesion. On the other hand, comparative steels b14 and b16 were poor in film adhesion due to excessive addition of Se and Sb. In all other comparative steels, the amount of added elements was not within the above range, so the desired magnetic properties could not be obtained, or the steel was broken during the test and was not evaluated.

<Example 2>
A silicon steel having the chemical composition shown in Tables 1 and 2 is heated to 1280° C. or higher and 1450° C. or lower and subjected to hot rolling to obtain a hot rolled steel sheet having a thickness of 2.3 to 2.8 mm. It was annealed at 1200° C. and then cold-rolled once or cold-rolled multiple times with intermediate annealing to obtain a cold-rolled steel sheet with a final thickness of 0.19 to 0.22 mm.

The cold-rolled steel sheet was decarburized and annealed under the conditions shown in Table 4, then coated with an annealing separator, subjected to finish annealing at 1200 ° C., and then coated on the surface of the finish-annealed steel sheet for forming an insulating film. was applied and baked to form a tension-applying insulating film, and the adhesion of the insulating film was evaluated, as well as the magnetic properties (magnetic flux density). The decarburization annealing was carried out at 830° C. for 120 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.5.

Table 4 shows the evaluation results of film adhesion and magnetism. All measurement methods and evaluation methods were performed according to Example 1.

All of the invention steels C1 to C24 exhibited excellent film adhesion and magnetic properties. For the invention steels C13 to C19, since the heating rates S1, S2 and S2/S1 were controlled within preferable ranges, the adhesion was particularly good. For C21 to C23, since the heating rates S1, S2 and S2/S1 and P1 were controlled within preferable ranges, the film adhesion was particularly good. On the other hand, in comparative steel c1, S2/S1 is out of the range defined in the present invention, in c2 and c3 S1 is out of the range defined in the present invention, and in c4, S2 is out of the range of the present invention. Since it was detached, the film adhesion was poor. Moreover, the comparative steel c2 was inferior in magnetic properties.

<Example 3>
A silicon steel having the chemical composition shown in Tables 1 and 2 is heated to 1280° C. or higher and 1450° C. or lower and subjected to hot rolling to obtain a hot rolled steel sheet having a thickness of 2.3 to 2.8 mm. It was annealed at 1200° C. and then cold rolled once or cold rolled multiple times with intervening annealing to obtain a cold rolled steel sheet with a final thickness of 0.18 to 0.22 mm.

The above cold-rolled steel sheets were subjected to two-step decarburization annealing under the conditions shown in Tables 5 and 6, and then coated with an annealing separating agent, and heated to 1200°C under the conditions shown in Tables 5 and 6 in the heating rate and atmosphere. Then, the surface of the finish-annealed sheet is coated with a coating liquid for forming an insulating film and baked to form a tension-applying insulating film, and the adhesion of the insulating film is evaluated, and the magnetic properties (magnetic flux density) was evaluated.
In addition, in the temperature rising step of the decarburization annealing, S1=700° C./sec, S2=1200° C./sec, and P1=0.15.

Tables 5 and 6 show evaluation results of film adhesion and magnetism. All measurement methods and evaluation methods were performed according to Example 1.

<Example 4>
A silicon steel having the chemical composition shown in Tables 1 and 2 is heated to 1280° C. or higher and 1450° C. or lower and subjected to hot rolling to obtain a hot rolled steel sheet having a thickness of 2.3 to 2.8 mm. It was annealed at 1200° C. and then cold-rolled once or cold-rolled multiple times with intermediate annealing to obtain a cold-rolled steel sheet with a final thickness of 0.19 mm.

A cold-rolled steel sheet having a final thickness of 0.19 mm was decarburized and annealed, then coated with an annealing separating agent and subjected to finish annealing at 1200° C., and then a finish-annealed steel sheet was produced. In the decarburization annealing step of this experiment, the heating rate in the temperature range of 500 to 700 ° C. and the oxygen potential in the temperature range of 500 to 600 ° C. were controlled (S1 = 800 ° C./sec, S2 = 1600 ° C./sec, P1 = 0.07). After that, the surface of the steel sheet was coated with the coating solution for forming an insulating film and baked to form a tension-imparting insulating film. The decarburization annealing was carried out at 800° C. for 160 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.4.

Table 7 shows the evaluation results of film adhesion and magnetism.
All of the invention steels E1 to E38 exhibited excellent film adhesion and magnetic properties. In particular, in invention steels E32 to E36, one or more of the selective elements Bi, Sn, Cr, Cu, Mo, Ti, V, and Nb are added in an appropriate amount. Exhibits good film adhesion. Since the plate thickness was thin, compared with the results in Table 3 of Example 1, good film adhesion was obtained as a whole.

On the other hand, comparative steels e14 and e16 had too much added amount of Se and Sb, so the film adhesion was poor. In all other comparative steels, the amount of added elements was not within the above range, so the desired magnetic properties could not be obtained, or the steel was broken during the test and was not evaluated.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also naturally belong to the technical scope of the present invention.

As described above, according to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties and film adhesion can be produced. In particular, the present technology exhibits its effect even in a grain-oriented electrical steel sheet to which Se or Sb is added. In the case of a grain-oriented electrical steel sheet having a product thickness of less than 0.22 mm, the effect is further exhibited. As described above, the present invention has high applicability in the electromagnetic steel sheet manufacturing industry and the electromagnetic steel sheet utilization industry.

Claims (8)

% by mass, C: 0.010 % or more and 0.20% or less, Si: 2.50% or more and 4.00% or less, acid-soluble Al: 0.005 % or more and 0.070 % or less, Mn: 0.005% or more and 0.50 % or less, N: 0.030 % or less, S: 0.0005% or more and 0.030 % or less, Se: 0.0010 % or more and 0.08% or less, Sb : 0.005% to 0.50%, Bi: 0 % to 0.02%, Sn: 0% to 0.50%, Cr: 0% to 0.50%, Cu: 0% 1.0% or less, Mo: 0% or more and 0.5% or less, Ti: 0% or more and 0.05% or less, V: 0% or more and 0.05% or less, and Nb: 0% or more and 0.05% or less A hot rolling step of obtaining a hot rolled steel sheet by heating a steel billet containing the balance Fe and unavoidable impurities at a temperature of 1200 ° C. or higher and 1600 ° C. or lower and then hot rolling it;
A hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet;
a cold-rolling step of obtaining a cold-rolled steel sheet by subjecting the hot-rolled steel sheet to one cold rolling or a plurality of cold rollings via annealing;
a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing;
A finish annealing step of applying an annealing separator to the cold-rolled steel sheet and subjecting the cold-rolled steel sheet to finish annealing;
and an insulating film forming step of forming a tension-applying insulating film on the cold-rolled steel sheet,
During the temperature increase in the decarburization annealing step, the temperature increase rate S1 (° C./sec) in the temperature range of 500° C. to 600° C. and the temperature increase rate S2 (° C./sec) in the temperature range of 600° C. to 700° C. satisfies the following formulas (1) to (3), and the oxygen potential P1 in the atmosphere in the temperature range of 500 ° C. to 600 ° C. during the temperature rise satisfies the following formula (4). A method of manufacturing a steel plate.
1.0<S2/S1≦10.0 Expression (1)
300≦S1≦2000 Expression (2)
300 < S2≦4000 Expression (3)
0.00001≦P1≦0.5 Expression (4) 2. The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein the steel slab contains, by mass %, Bi: 0.001% or more and 0.02% or less. The steel billet contains, in mass%, Sn: 0.005% or more and 0.50% or less, Cr: 0.005% or more and 0.50% or less, Cu: 0.01% or more and 1.0% or less, and Mo: The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, containing one or more selected from the group consisting of 0.005 to 0.5%. The steel slab is one selected from the group consisting of Ti: 0.0005 to 0.05%, V: 0.0005 to 0.05%, and Nb: 0.0005 to 0.05% in mass%. Or the method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, containing two or more. In the decarburization annealing step, following the first stage annealing held at a temperature T2° C. of 700° C. or more and 900° C. or less for 10 seconds or more and 1000 seconds or less in an atmosphere with an oxygen potential P2 of 0.1 or more and 1.0 or less , Any one of claims 1 to 4, wherein the second stage annealing is performed in an atmosphere of oxygen potential P3 that satisfies (5), at a temperature T3° C. that satisfies the following formula (6), and held for 5 seconds or more and 500 seconds or less. The method for producing a grain-oriented electrical steel sheet according to 1.
P3<P2 Expression (5)
T2+50≦T3≦1000 Expression (6) The average temperature increase rate BR1 (° C./h) in the temperature range of 875° C. or higher and 1050° C. or lower in the temperature increase in the final annealing step satisfies the following formula (7), according to any one of claims 1 to 5. A method for producing a grain-oriented electrical steel sheet.
1.0≦BR1≦60.0 Expression (7) Unidirectional according to any one of claims 1 to 6, wherein the oxygen potential P4 of the finish annealing atmosphere in the temperature range of 875 ° C. to 1050 ° C. satisfies the following formula (8) in the temperature rise in the finish annealing step. A method for manufacturing an electromagnetic steel sheet.
0.00001≦P4≦0.5 Expression (8) The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 7, wherein the grain-oriented electrical steel sheet has a product thickness of 0.18 mm or more and less than 0.22 mm.