JP2019163518A - Method of producing unidirectional magnetic steel sheet - Google Patents

Abstract

To provide a novel and improved method of producing a unidirectional magnetic steel sheet, the method enabling a glass coating film excellent in coating film adhesibility to be formed on a surface of a unidirectional magnetic steel sheet in which a base material steel sheet contains Se or Sb as a chemical component without damaging magnetic properties.SOLUTION: The method of producing a unidirectional magnetic steel sheet includes: a hot rolling step of heating a slab having a predetermined composition at a temperature of 1,200°C or higher and 1,600°C or lower, then hot-rolling the heated slab to obtain a hot-rolled steel sheet; a hot-rolled steel sheet annealing step; a cold rolling step; a decarburization annealing step; a final annealing step of applying an annealing separating agent onto the cold rolled steel sheet; and an insulating coating film forming step, where a temperature-rising rate in a temperature range between 500°C or higher and 600°C or lower, and a temperature-rising rate in a temperature range between 600°C or higher and 700°C or lower when rising a temperature in the decarburization annealing step satisfy formula (1)-formula (3), and an oxygen potential in an atmosphere in a temperature range between 500°C or higher and 700°C or lower when rising the temperature in the decarburization annealing step satisfies formula (4).SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a unidirectional electrical steel sheet.

  The unidirectional 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 integrated in the {110} <001> orientation (hereinafter, Goss orientation). Unidirectional electrical steel sheets are mainly used as iron core materials for transformers. When using a unidirectional electrical steel sheet as an iron core material of a transformer, that is, when the steel sheet is 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 (tensioning insulating coating) on the surface of the unidirectional electrical steel sheet.

A method for forming the glass film and the tension-imparting insulating film and a general method for producing 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 finished to the final thickness by cold rolling once or two times with intermediate annealing. Thereafter, decarburization and primary recrystallization are performed by annealing (decarburization annealing) in a wet hydrogen atmosphere. In the decarburization annealing, an oxide film (Fe ₂ SiO ₄ or SiO ₂ ) is formed on the steel plate surface. Subsequently, an annealing separator mainly composed of MgO is applied to the decarburized annealing plate and dried, and finish annealing is performed. By this finish annealing, secondary recrystallization occurs and the grain structure of the steel sheet accumulates in the {110} <001> orientation. At the same time, on the steel sheet surface, MgO in the annealing separator and decarburization annealing react to form a glass film. A tension-imparting insulating film is formed by applying and baking a coating liquid mainly composed of phosphate on the surface of the finish annealing plate, that is, the glass film surface.

  The glass film is important 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 unidirectional electrical steel sheet is reduced, the iron loss, which is a magnetic property, is improved, but it is difficult to ensure the adhesion of the glass film. For this reason, the manufacturing subject of a unidirectional electrical steel sheet is the improvement of glass film adhesiveness, and its stable control. Since the glass film is caused by an oxide film generated by decarburization annealing, a glass film improvement technique by controlling decarburization annealing conditions has been developed so far.

  For example, in Patent Document 1, before performing decarburization annealing on a grain-oriented electrical steel sheet that has been cold-rolled to the final thickness, the surface layer is pickled to remove surface deposits and the surface iron surface layer, A technique is described in which a charcoal reaction and an oxide formation reaction are allowed to proceed evenly to form a glass film having excellent adhesion.

Patent Documents 2 to 4 disclose a technique in which a glass film reaches the deep part of the steel sheet by imparting fine irregularities to the steel sheet surface in the decarburization annealing so that the film adhesion is improved.
In addition, as described in Patent Documents 5 to 8, techniques for controlling the oxygen potential of a decarburized annealing atmosphere and improving glass film adhesion have been developed. These are technologies that promote oxidation of the decarburized annealed plate and promote glass film formation.

  Furthermore, technical development has progressed, and in Patent Documents 9 to 11, focusing on the temperature raising process of decarburization annealing, a technique for improving not only the atmosphere during temperature raising but also the glass film adhesion and magnetism by temperature rising rate control has been developed. .

  Recently, there is an increasing need for a unidirectional electrical steel sheet having excellent magnetic properties. For example, Patent Documents 12 to 14 disclose techniques of unidirectional electrical steel sheets having excellent magnetic properties by adding Se or Sb.

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

However, each of the methods described in Patent Documents 1 to 4 requires an additional step in the process, so the operation load is large, and further devices have been desired.
Further, when the techniques described in Patent Documents 5 to 8 are adopted, the adhesion of the glass film is improved, but there is a problem that secondary recrystallization becomes unstable and the magnetic properties (magnetism) deteriorate.

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

  Moreover, the film | membrane adhesiveness of the unidirectional electrical steel sheet which added Se or Sb as disclosed by patent documents 12-14 was not enough. In particular, the glass film adhesion of a material having a thickness of less than 0.23 mm (hereinafter referred to as a thin material) tends to be inferior, and it is considered that the technique for improving the film adhesion is still in progress.

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

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a film adhesion to the surface of a unidirectional electrical steel sheet in which the base steel sheet contains Se or Sb as a chemical component. It is an object of the present invention to provide a novel and improved method for producing a unidirectional electrical steel sheet capable of forming a glass film having excellent properties without impairing magnetic properties.

  The inventors of the present invention have intensively studied to solve the above-mentioned problems, and have found that the glass film adhesion is good even if the material uses Sb or Se by controlling the temperature raising process of decarburization annealing. It was.

This invention was made | formed based on the said knowledge, and the summary is as follows.
[1] By mass%, C: 0.01% to 0.20%, Si: 2.50% to 4.0%, acid-soluble Al: 0.005% to 0.07%, 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 %: 0.5% to 0.5%, Bi: 0% to 0.02%, Sn: 0% to 0.50%, Cr: 0% to 0.50%, Cu: 0% to 1.0% Hereinafter, Mo: 0% or more and 0.50% 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, and the balance Hot rolling to obtain a hot-rolled steel sheet by heating a steel slab comprising Fe and inevitable impurities at a temperature of 1200 ° C. or higher and 1600 ° C. or lower and hot rolling. About
A hot-rolled steel sheet annealing step for 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 a plurality of cold rolling via a single cold rolling or annealing;
A decarburization annealing step for subjecting the cold-rolled steel sheet to decarburization annealing;
Applying a annealing separator to the cold-rolled steel sheet, and performing a final annealing step on the cold-rolled steel sheet;
An insulating film forming step of forming a tension-imparting insulating film on the cold-rolled steel sheet,
At the time of temperature increase in the decarburization annealing step, the temperature increase rate S1 (° C./second) in the temperature range of 500 ° C. to 600 ° C. and the temperature increase rate S2 (° C./second) 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. at the time of the temperature rise satisfies the following formula (4). A method of manufacturing a steel sheet.
1.0 <S2 / S1 ≦ 10.0 (1)
300 ≦ S1 ≦ 2000 (2)
300 ≦ S2 ≦ 4000 Formula (3)
0.00001 ≦ P1 ≦ 0.5 (4)
[2] The method for producing a unidirectional electrical steel sheet according to [1], wherein the steel piece contains, by mass%, Bi: 0.001% or more and 0.02% or less.
[3] The steel slab is mass%, Sn: 0.005% to 0.50%, Cr: 0.005% to 0.50%, Cu: 0.01% to 1.0% And Mo: The manufacturing method of the unidirectional electrical steel sheet as described in [1] or [2] containing 1 type, or 2 or more types selected from the group which consists of 0.005-0.5%.
[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 manufacturing method of the unidirectional electrical steel sheet as described in any one of [1]-[3] containing 1 type or 2 types or more.
[5] In the decarburization annealing step, oxygen satisfying the following formula (5) following the first-stage annealing that is 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 of oxygen potential P2. One of the methods according to any one of [1] to [4], wherein second-stage annealing is performed at a temperature T3 ° C. satisfying the following formula (6) in an atmosphere of potential P3, and held for 5 seconds or more and 500 seconds or less. A method for producing grain-oriented electrical steel sheets.
P3 <P2 Formula (5)
T2 + 50 ≦ T3 ≦ 1000 (6)
[6] In any one of [1] to [5], in the temperature increase in the finish annealing step, an average temperature increase rate BR1 (° C./h) in a temperature range of 875 ° C. to 1050 ° C. satisfies the following formula (7). The method for producing a unidirectional electrical steel sheet according to one item.
1.0 ≦ BR1 ≦ 60.0 (7)
[7] In any one of [1] to [6], in the temperature increase in the finish annealing step, the oxygen potential P4 of the finish annealing atmosphere in the temperature range of 875 ° C. or more and 1050 ° C. or less satisfies the following formula (8). The manufacturing method of the unidirectional electrical steel sheet of description.
0.00001 ≦ P4 ≦ 0.5 (8)
[8] The method for producing a unidirectional electrical steel sheet according to any one of [1] to [7], wherein a product plate thickness of the unidirectional electrical steel sheet is 0.18 mm or more and less than 0.22 mm.

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

  Hereinafter, preferred embodiments of the present invention will be described in detail. In the following, first, prior to the detailed description of the overall flow of the method for manufacturing a unidirectional electrical steel sheet according to the embodiment of the present invention, the background leading to the present invention will be described.

1. Background to the present invention When a unidirectional electrical steel sheet is used as the iron core material of a transformer, it is essential to ensure the insulation of the steel sheet, so a tension insulating film is formed on the steel sheet surface after finish annealing. There is a need to. By the way, Sb or Se may be added as a component of a steel slab such as a slab in order to improve the magnetic properties of the unidirectional electrical steel sheet, particularly the thin materials. This is intended to improve the texture of the secondary recrystallized steel sheet by precipitating MnSb or MnSe as an inhibitor. However, in the material to which Sb and Se are applied, it is difficult to ensure the adhesion of the glass film.

Although the cause of this is not completely clear, the present inventors have focused on the possibility that Sb or Se suppresses the development 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. As for the morphology of the glass film, a process in which SiO ₂ is formed, that is, a decarburization annealing process is important. This is because the glass film is a substance generated by a solid phase reaction between SiO ₂ and MgO which is a main component of the annealing separator. Since the process of forming SiO ₂ is a decarburization annealing process, generally excellent film adhesion can be secured by controlling the decarburization annealing process. However, when the steel sheet contains Se or Sb, Se or Sb has a low affinity with SiO _2, and thus concentrates at the interface between SiO ₂ and the steel sheet during decarburization annealing. In this case, the present inventors considered that the Se or Sb enriched layer would inhibit glass film growth.

As a result of intensive studies, the present inventors who have faced such a problem have found that the glass film adhesiveness is good even for materials using Sb or Se by controlling the temperature raising step of decarburization annealing. It was. In response to this result, the inventors went back to the sample after decarburization annealing, and as a result, in the material with poor film adhesion, SiO ₂ was generated on the steel plate surface, and at the interface between SiO ₂ and the steel plate, A large number of Se or Sb could be confirmed. In contrast, in the good material film adhesion, in addition to SiO _2, Mn ₂ SiO ₄ (Tefuroito) is formed on the surface of the steel sheet, Se or Sb is present in _{Mn 2 SiO 4, Mn 2 SiO} 4 Concentration of Se or Sb at the interface between iron and ground iron (base steel plate) could hardly be confirmed.

Since Se or Sb has a low affinity with SiO _2, although concentrated in the interface between the SiO ₂ and the steel plate, Se or Sb has a high affinity for _Mn 2 SiO _4, incorporated into the Mn 2 SiO ₄ , Mn ₂ SiO ₄ and the steel plate is considered not to be concentrated at the interface. As a result, it was considered that the glass film could grow and develop, and the film adhesion improved.

Furthermore, the present inventors have found that the film adhesion is further improved by controlling the temperature raising step of finish annealing. In the decarburization annealing process, part of Se or Sb may not be dissolved in Mn ₂ SiO ₄ (Tefroit). By controlling the temperature increase rate of the finish annealing, undissolved Se or Sb can be dissolved in the tephroite. Thereby, avoidance of interfacial concentration of Se or Sb that inhibits the development of the glass film (interface between the glass film and the ground iron) is more thorough and the glass film adhesion is improved.

  Based on the above studies, the present inventors have reached the present invention. Below, the manufacturing method of the unidirectional electrical steel sheet which concerns on embodiment of this invention is demonstrated centering on the control conditions of a decarburization annealing process.

2. Next, the overall flow of the method for manufacturing a unidirectional electrical steel sheet according to an embodiment of the present invention will be described in detail.

The general manufacturing method of a unidirectional electrical steel sheet is as follows. A silicon steel slab containing 7% by mass or less of Si is hot-rolled and hot-rolled sheet annealing is performed. After pickling the hot-rolled sheet annealed sheet, it is finished to the final sheet thickness by cold rolling once or two times with intermediate annealing. Thereafter, decarburization and primary recrystallization are performed by annealing (decarburization annealing) in a wet hydrogen atmosphere. In the decarburization annealing, an oxide film (Fe ₂ SiO ₄ or SiO ₂ ) is formed on the steel plate surface. Subsequently, an annealing separator mainly composed of MgO is applied to the decarburized annealing plate and dried, and finish annealing is performed. By this finish annealing, secondary recrystallization occurs and the grain structure of the steel sheet accumulates in the {110} <001> orientation. At the same time, on the steel sheet surface, MgO in the annealing separator and decarburization annealing react to form a glass film (Mg ₂ SiO ₄ ). After the finish-annealed plate is powdered by washing or pickling, a tension-imparting insulating film is formed by applying and baking a coating solution mainly composed of phosphate.

  The method for producing a unidirectional electrical steel sheet according to the present embodiment includes a hot rolling process for hot rolling a steel piece having a predetermined chemical component to obtain a hot rolled steel sheet, and a hot rolled steel sheet annealing process for 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 a plurality of cold rollings through a single cold rolling or annealing, and a decarburizing annealing process of subjecting the cold rolled steel sheet to decarburization annealing. And a annealing process for 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 process for forming a tension-imparting insulating film on the cold-rolled steel sheet. . Hereinafter, these steps will be described in detail. In addition, in the following description, when conditions for each process are not described, it is possible to perform each process by appropriately applying known conditions.

2.1. Hot-rolling step The hot-rolling step is a step of hot rolling a steel piece (for example, a steel ingot such as a slab) having a predetermined chemical component to obtain a hot-rolled steel plate. Below, the chemical composition of the billet used for the manufacturing method of the grain-oriented electrical steel sheet which concerns on this embodiment is demonstrated in detail first. Hereinafter, unless otherwise specified, the notation “%” represents “mass%”.

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

(C: 0.01% or more and 0.20% or less)
C has an effect of improving the magnetic flux density, but if its content exceeds 0.20%, the steel undergoes phase transformation in the secondary recrystallization annealing, and the secondary recrystallization does not proceed sufficiently, and the good magnetic flux density. Therefore, the C content is set to 0.20% or less. The smaller C is, the more preferable for reducing iron loss. From the viewpoint of reducing iron loss, the C content is preferably 0.10% or less.
In the present embodiment, Se and Sb are used to improve the magnetic properties, so that the lower limit of the C content is 0.01%, preferably 0.03%, from the viewpoint of magnetic flux density.

(Si: 2.50% to 4.0%)
If the Si content is less than 2.50%, the steel undergoes phase transformation in the secondary recrystallization annealing, the secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics 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 plate becomes brittle, and the plate-passability in the manufacturing process is significantly deteriorated, so the Si content is 4.0% or less. The Si content is preferably 3.80% or less, more preferably 3.60% or less.

(Acid-soluble Al: 0.005% to 0.07%)
In the electromagnetic steel sheet of the present invention, acid-soluble Al (sol. Al) is an essential element from the viewpoint of secondary recrystallization.
When the content of acid-soluble Al is less than 0.005%, AlN that functions as an inhibitor is not sufficiently generated, secondary recrystallization becomes insufficient, and iron loss characteristics are not improved. The amount is 0.005% or more. Preferably it is 0.01% or more.
On the other hand, if the content of acid-soluble Al exceeds 0.07%, the steel sheet becomes brittle, and in particular, in the unidirectional electrical steel sheet according to the present embodiment with a large amount of Si, embrittlement becomes significant. The content of is 0.07% or less and 0.05% or less.

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

(Mn 0.005% to 0.5%)
If Mn exceeds 0.5%, the steel undergoes phase transformation in secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained. The amount is 0.5% or less. Preferably it is 0.10% or less.
Since Mn can be used as an inhibitor during secondary recrystallization, Mn content is set to 0.005% or more. Preferably it is 0.01% or more.

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

(Se: 0.001% to 0.08%)
Se is a particularly important element in the present invention. However, if it exceeds 0.08%, the glass film is remarkably deteriorated. Therefore, the upper limit of the Se content is 0.08%. Preferably it is 0.03% or less.
If the Se content is less than 0.001%, sufficient magnetism may not be obtained. Therefore, the Se content is 0.001%. Considering compatibility between magnetism and film adhesion, the content is preferably 0.003% or more.

(Sb: 0.005% to 0.5%)
Sb is an especially important element in the present invention. However, if added over 0.5%, the glass film deteriorates significantly. Therefore, the upper limit of the Sb content is 0.5%. Preferably, the content is 0.1% or less.
If the Sb content is less than 0.005%, sufficient magnetism may not be obtained, so the Sb content is 0.005% as the lower limit. Considering compatibility between magnetism and film adhesion, it is preferably 0.01% or more.

  In this embodiment, the steel slab contains Bi: 0.001% or more and 0.02% or less in mass% in order to improve the characteristics of the unidirectional electrical steel sheet according to this embodiment in addition to the elements described above. May be. Since Bi is an optional element, the lower limit of the Bi content is 0% regardless of the above description.

(Bi: 0.001% to 0.02%)
Bi, like Cr, Sn, and Cu 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 the improvement of film adhesion cannot be obtained sufficiently, so the content is made 0.001% or more. Preferably it is 0.001% or more.
On the other hand, if it exceeds 0.02%, the plateability during cold rolling deteriorates, so the Bi content is 0.02% or less. Preferably it is 0.01% or less.

  In this embodiment, in addition to the elements described above, the steel slab is mass% in order to improve the characteristics of the unidirectional electrical steel sheet according to this embodiment, Sn: 0.005 to 0.50%, Cr: 0. You may contain 1 type (s) or 2 or more types selected from the group which consists of 0.005-0.50%, Cu: 0.01-1.0%, and Mo: 0.005-0.5%. In addition, since Sn, Cr, Cu, and Mo are arbitrary elements, the lower limit of content of Sn, Cr, Cu, and Mo is 0% irrespective of the above-mentioned description.

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

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

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

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

  In this embodiment, in addition to the elements described above, the steel slab improves the characteristics of the unidirectional electrical steel sheet according to this embodiment, so that the mass percentage is Ti: 0.0005% or more and 0.05% or less, V : 0.0005% or more and 0.05% or less, Nb: One or more selected from the group consisting of 0.0005% or more and 0.05% or less may be contained. In addition, since Ti, V, and Nb are arbitrary elements, the lower limit of content of Ti, V, and Nb is 0% irrespective of the above-mentioned description.

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

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

  The balance of the component composition of the steel slab used in this embodiment is Fe and inevitable impurities. However, in order to improve magnetic properties, strength, corrosion resistance, fatigue properties, and other characteristics required for structural members, castability and plateability, and productivity by using scraps, steel slabs are made of Fe. 1 selected from In, B, Au, Ag, Te, Ce, Co, Ni, Ca, Re, Os, Zr, Hf, Ta, Y, La, Cd, Pb, As, etc. You may contain a seed | species or 2 or more types in total 5.00% or less, Preferably it is 3.00% or less, More preferably, you may contain 1.00% or less. Since these elements can be included arbitrarily, the lower limit of the total content of these elements is 0%.

  Inevitable impurities are components that are present in the steel slab regardless of the intention of addition, and need not be present in the obtained unidirectional electrical steel sheet. The term “inevitable impurities” is a concept that includes impurities mixed from ores, scraps, or production environments as raw materials when industrially producing steel materials. Such inevitable impurities can be included in an amount that does not adversely affect the effects of the present invention.

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

2.2. Hot-rolled steel sheet annealing step Next, the obtained hot-rolled steel sheet is annealed. By performing such annealing treatment, recrystallization occurs in the steel sheet structure, and it becomes possible to realize good magnetic properties.
Although it does not specifically limit as annealing conditions, For example, annealing for 10 second-5 minutes can be performed at a temperature range of 900-1200 degreeC with respect to a steel plate.
In addition, after this step, before the cold rolling step, the surface of the hot rolled steel sheet may be pickled.

2.3. Cold-rolling step Next, the processed hot-rolled steel sheet is subjected to hot-rolled sheet annealing and then rolled by one cold rolling, or by multiple cold rollings with intermediate annealing in between Rolled. In addition, when hot-rolled sheet annealing is performed, the shape of the steel sheet is improved, so that the possibility of steel sheet breakage in the first rolling can be reduced. In this case, the heating method of the steel plate is not particularly limited. The cold rolling may be performed three times or more, but is preferably performed once or twice because the manufacturing cost increases.
Moreover, the final cold rolling reduction ratio can be in the range of 80% to 95%, for example. By setting the final cold rolling reduction within the above range, the {110} <001> orientation can obtain Goss nuclei having a high degree of integration in the rolling direction, and can suppress secondary recrystallization from becoming unstable. Can do.
In addition, the plate | board thickness of the cold rolled steel plate in which cold rolling was given becomes normally the plate | board thickness (final plate | board thickness) of the unidirectional electrical steel plate finally manufactured.

2.4. Decarburization annealing process Next, in the decarburization annealing process, the obtained cold-rolled steel sheet is decarburized and annealed. In this embodiment, in decarburization annealing, the temperature is increased under specific conditions described below.

(I) Temperature raising conditions First, the temperature raising conditions in this step will be described in detail.
In this step, a temperature increase rate S1 (° C./second) in a temperature range of 500 ° C. or higher and 600 ° C. or lower and a temperature increase rate S2 (° C./second) in a temperature range of 600 ° C. or higher and 700 ° C. or lower are expressed by the following formula (1). -Temperature rise is performed to satisfy Equation (3).
1.0 <S2 / S1 ≦ 10.0 (1)
300 ≦ S1 ≦ 2000 (2)
300 ≦ S2 ≦ 4000 Formula (3)
The present inventors can sufficiently generate tephroite (Mn ₂ SiO ₄ ) on the surface of the steel sheet by adopting the above temperature rising conditions under the oxygen potential condition described later, and the interface of Se or Sb. It has been found that thickening can be avoided.

The reason will be explained. The SiO ₂ oxide film is most easily formed in the temperature range of 600 to 700 ° C. This is probably because the Si diffusion rate in the steel and the O diffusion rate in this temperature range are balanced on the steel plate surface. On the other hand, in the temperature range of 500 to 600 ° C., tephroite is easily formed as an oxide film. In the present invention, since it is necessary to generate tephroit, the residence time of 500 to 600 ° C., which is the formation temperature region of tephrite, is compared with the residence time of 600 to 700 ° C., which is the formation temperature region of SiO _2. It ’s important to earn a lot.

Therefore, it is necessary that the ratio S2 / S1 between the temperature increase rate S1 in the temperature range 500 to 600 ° C. and the temperature increase rate S2 in the temperature range 600 to 700 ° C. is larger than 1.0. The residence time in the temperature range of 500 to 600 ° C. corresponds to the amount of tephroite produced, and the residence time in the temperature range of 600 to 700 ° C. corresponds to the amount of SiO ₂ produced, so when S2 / S1 is 1.0 or less, the amount of tephroite produced There is a possibility that the amount of SiO ₂ generation exceeds the amount and the effect of the present invention cannot be enjoyed. On the other hand, the upper limit of the ratio S2 / S1 is determined to be 10.0 from the lower limit value of S1 and the S2 upper limit value. However, when the generation amount of SiO ₂ is extremely small, the glass film formation behavior becomes unstable, which may cause film defects such as holes in the film. Therefore, a preferable range of the ratio S2 / S1 is more than 1.0 and 5.0 or less, and a more preferable range is 1.2 or more and 3.5 or less.

The lower limit of S1 is 300 ° C./second or more, and the upper limit is 2000 ° C./second. Good magnetic properties cannot be obtained at 300 ° C./second or less, and no tephroite is formed when it exceeds 2000 ° C./second. S1 is preferably 400 ° C./second or more. Further, S1 is preferably 1700 ° C./second or less.
Furthermore, it is important to control the temperature increase rate S2 in the temperature range of 600 to 700 ° C. The range of S2 is set to 300 ° C./second or more and 4000 ° C./second or less. Since the effect of the present invention can be enjoyed as the value of S2 is larger, S2 is preferably 500 ° C./second or more. However, if the rate of temperature increase is too high, overshoot may occur, so the upper limit is set to 4000 ° C./second or less. S2 is preferably 3000 ° C./second or less.

  If a 600 ° C. isothermal holding cycle or a heating cycle including cooling after reaching 600 ° C. is employed, the residence time corresponding to each of S 1 and S 2 becomes unclear. Therefore, in this embodiment, when an isothermal holding cycle of 600 ° C. is adopted, the residence time corresponding to S 1 is a heating cycle including cooling after reaching 600 ° C. from the time of reaching 500 ° C. until the end of the isothermal holding of 600 ° C. Is the time to reach 600 ° C. again by reheating. Therefore, the residence time corresponding to S2 is defined as the time from the end of the 600 ° C. isothermal holding, or the time from reaching 600 ° C. again by reheating to reaching 700 ° C.

In the present embodiment, the oxygen potential P1 in the atmosphere in the temperature range of 500 ° C. or more and 600 ° C. or less at the time of temperature rise satisfies the following formula (4).
0.00001 ≦ P1 ≦ 0.5 (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. generated by Mn ₂ SiO ₄ . The oxygen potential can be defined by the ratio between the water vapor partial pressure PH ₂ O and the hydrogen partial pressure PH _{2 in the} atmosphere, that is, PH ₂ O / PH ₂ . When P1 exceeds 0.5, Fe ₂ SiO ₄ is generated and inhibits the generation of tephroite, so the upper limit of P1 is 0.5. The smaller P1, the easier it is to produce tephroit, but industrially P1 = 0.00001 is considered the limit. That is, P1 is 0.00001 or more and 0.5 or less, preferably 0.0001 or more and 0.3 or less.

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

(Ii) Holding conditions The annealing conditions (holding conditions) in this step are not particularly limited as long as the above temperature rising conditions are satisfied. For example, annealing is performed in a temperature range of 700 ° C. or higher and 1000 ° C. or lower. It is carried out by holding for not less than 10 seconds. Further, multi-stage annealing may be performed. For example, two-stage annealing as described below can be performed.

For example, in this step, oxygen atmosphere P3 satisfying the following formula (5) is satisfied following the first-stage annealing that is held at a temperature T2 ° C. of 700 ° C. to 900 ° C. for 10 seconds to 1000 seconds in an atmosphere of oxygen potential P2. In the atmosphere, second-stage annealing can be performed at a temperature T3 ° C. satisfying the following formula (6) and maintained for 5 seconds or more and 500 seconds or less.
P3 <P2 Formula (5)
T2 + 50 ≦ T3 ≦ 1000 (6)

  As described above, the generation of tephroite during decarburization annealing is important, but the decarburization annealing process may be performed in two-stage annealing in which the former stage is annealed at a low temperature and the latter stage is annealed at a high temperature. At this time, it is necessary to control the high-temperature annealing temperature in the first stage and the second stage. Under the conditions described above, the tephroit can be sufficiently generated on the surface of the steel sheet in the decarburization annealing step, and Se or Sb interfacial concentration can be avoided more reliably.

  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 longer. In addition, although the annealing time itself has no problem from the viewpoint of decarburization, the upper limit of the annealing time is 1000 seconds or less from the viewpoint of productivity. In the production of a practical steel sheet, it is preferably 50 seconds or longer and 300 seconds or shorter.

From the viewpoint of securing the amount of tephroite formed, it is preferable that the oxygen potential P2 during the first-stage annealing is higher than the oxygen potential P1 during the temperature increase. When sufficient oxygen potential is obtained, it is possible to prevent the Tefuroito is replaced by SiO _2. Further, the decarburization reaction can be sufficiently advanced. However, if P2 is too large, the 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 in the range of 0.1 to 1.0. Preferably they are 0.2 or more and 0.8 or less.

In the first stage annealing, the formation of Fe ₂ SiO ₄ cannot be completely suppressed. Therefore, preferably, in the second stage annealing, the annealing temperature T3 (plate temperature) is 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 generated during the first stage annealing, it is reduced to tephroite. When the annealing time exceeds 500 seconds, the tephroite is reduced to SiO ₂ , so the upper limit of the annealing time is 500 seconds. Preferably, it is 10 seconds or more and 100 seconds or less.

  In order to obtain 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 process Next, finish annealing is performed to the obtained cold rolled steel sheet (decarburized annealed steel sheet) after decarburization annealing. Here, finish annealing is generally performed for a long time in a state where a steel sheet is wound in a coil shape. Therefore, prior to finish annealing, an annealing separator is applied to the decarburized annealed steel sheet and dried for the purpose of preventing seizure between the inside and outside of the steel sheet. 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.

  Next, finish annealing is performed. During re-annealing, secondary recrystallization accumulates in the {110} <001> orientation, producing coarse crystal grains with easy magnetization axes in the rolling direction, resulting in excellent magnetic properties. At the same time, on the steel sheet surface, MgO in the annealing separator and the oxide film generated by decarburization annealing react to form a glass film.

  The conditions for finish annealing are not particularly limited, and known conditions can be adopted as appropriate. However, in order to avoid Se or Sb interfacial concentration and further improve the film adhesion of the unidirectional 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. or higher and 1050 ° C. or lower satisfies the following formula (7).
1.0 ≦ BR1 ≦ 60.0 (7)

  The reason will be explained. As described above, the oxide film formed by decarburization annealing changes to a glass film in finish annealing. The glass film continues to grow toward the ground iron and has a fitting structure. At this time, if Se or Sb is concentrated at the growth front of the glass film, that is, the interface between the glass film and the ground iron, the growth of the glass film is suppressed, so that good film adhesion cannot be obtained. As described above, in the present invention, it is important in the present invention that tephroit is generated in the decarburization annealing step, Se or Sb is taken into the tephrite, and Se or Sb is made harmless. Although the solid solution of Se or Sb in the tephroite mainly occurs in the decarburization annealing step, some Se or Sb may not be taken into the tephroit.

  Therefore, the film adhesion can be further improved by controlling the heating conditions so as to reduce the rate of temperature increase during finish annealing and promoting the solid solution of Se or Sb into the tephrite. The temperature range for controlling the heating rate is 875 to 1050 ° C. This is because, in this temperature range, the diffusion of Se or Sb is most advanced, and the solid solution in the tephrite is promoted. When the rate of temperature rise exceeds 60.0 ° C./h, the above effect may not be enjoyed. Although a lower limit is not particularly provided, 1.0 ° C./h can be set as the lower limit from the viewpoint of productivity. A preferable range of BR1 is 1.0 ° C./h or more and 30.0 ° C./h or less. More preferably, it is 1.0 ° C./h or more and 20.0 ° C./h or less.

Further, in the temperature increase 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). Thereby, further improvement in film adhesion can be expected.
0.00001 ≦ P4 ≦ 0.5 (8)

  When the annealing atmosphere has a high oxygen potential, before Se or Sb dissolves in the tephroite, the tephroite changes to a glass film, and depending on the conditions, the film adhesion cannot be further improved. There is a case. Therefore, in the above temperature range, it is important to control the conditions so that the rate of change of the tephroite into the glass film becomes small at 875 ° C. to 1050 ° C. Therefore, the atmosphere P4 in the temperature range is preferably controlled in the range of 0.00001 to 0.5. If the oxygen potential exceeds 0.2, depending on the temperature rise conditions and the composition of the steel slab, the tephroite may change into a glass film before Se or Sb dissolves in the tephrite. Therefore, the upper limit of P4 can be 0.5, preferably 0.2, and more preferably 0.1. Although there is no particular lower limit value, it is considered practically difficult to control to 0.00001 or less, so the lower limit value of P4 can be set to 0.00001, preferably 0.0001, more preferably 0.0005. .

In the finish annealing step, even if the purification treatment is performed at a high temperature of 1050 ° C. or higher, Se and Sb once dissolved in the tephroite do not leave and the film adhesion does not decrease. In the finish annealing step, the temperature can be maintained for 10 hours or more and 60 hours or less in a temperature range of 1100 ° C. or more and 1300 ° C. or less after the temperature rise based on the above conditions.
In addition, after the completion of this step, the surface of the cold-rolled steel sheet may be washed with water or pickled to perform powder removal.

2.6. Insulating film forming process In the insulating film forming process, a tension-imparting insulating film is formed on both surfaces of the cold-rolled steel sheet after the finish annealing process. For example, an insulating coating solution in which a resin such as acrylic and an inorganic substance such as phosphate are mixed, or an insulating coating solution containing colloidal silica and phosphate is applied to the surface of the steel plate, and heat treatment is performed. A tension-imparting insulating film can be formed on the surface. When the insulating coating liquid contains an organic material, the heat treatment may be performed, for example, in a temperature range of 250 ° C. to 400 ° C., and when the insulating coating liquid contains only an inorganic material, for example, it is performed in a temperature range of 840 ° C. to 920 ° C. do it.
A unidirectional electrical steel sheet can be manufactured by the above process.

3. Unidirectional electrical steel sheet Finally, the unidirectional electrical steel sheet obtained by the above-described method will be described.
The unidirectional electrical steel sheet manufactured by the above-described method has improved magnetic properties by containing Se and Sb. On the other hand, in addition to SiO ₂ in the decarburization annealing process, tephroite (Mn ₂ SiO ₄ ) is sufficiently generated on the steel sheet surface. As a result of Se and Sb being dissolved in this tephroite, a decrease in film adhesion due to Se and Sb is prevented. Therefore, the unidirectional electrical steel sheet manufactured by the method according to this embodiment described above has excellent glass film adhesion.

  In the unidirectional electrical steel sheet according to the present embodiment, for example, the product plate thickness can be 0.18 mm or more and 0.35 mm or less. In the present invention, the effect is remarkable when the unidirectional electrical steel sheet is a material having a thin final thickness (hereinafter referred to as a thin material). Specifically, the effect is significant when the product thickness of the unidirectional 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 sufficiently generate tephroit in the decarburization annealing. Note that the formation of tephroit is limited by the diffusion of Mn in the steel to the surface of the plate thickness. Since the proportion of the surface area of the thin material is larger than that of the thick material, the diffusion distance of Mn from the inside of the steel plate to the steel plate surface can be short. That is, in the thin material, the substantial diffusion rate of Mn is fast. Accordingly, it is considered that the thin material can efficiently generate tephroit even in a low temperature range of 500 to 600 ° C.

  Various magnetic properties of the unidirectional electrical steel sheet are measured in accordance with the Epstein method defined in JIS C2550 and the single plate magnetic property measurement method (Single Sheet Tester: SST) defined in JIS C2556. Is possible.

  The technical contents of the present invention will be further described below with reference to examples of the present invention. In addition, the conditions in the Example shown below are one example of conditions used in order to confirm the feasibility and effect of this invention, and this invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

<Example 1>
Silicon steel having the 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 plate having a thickness of 2.3 to 2.8 mm. Annealing was performed at 1200 ° C., and then a single cold rolling or a plurality of cold rolling sandwiching the intermediate annealing was performed to obtain a cold rolled steel sheet having a final thickness of 0.22 mm. In addition, about each silicon steel, the remainders other than the components described in Tables 1 and 2 are iron and impurities.

  A cold-rolled steel sheet having a final thickness of 0.22 mm was subjected to decarburization annealing, and then an annealing separator was applied to perform final annealing at 1200 ° C., and then a final annealed sheet was produced. In the decarburization annealing process of this experiment, the heating rate in the temperature range 500 to 700 ° C. and the oxygen potential in the temperature range 500 to 600 ° C. were controlled (S1 = 700 ° C./second, S2 = 950 ° C./second, P1 = 0.15). Then, the coating liquid for insulating film formation was apply | coated and baked on the steel plate surface, the tension | tensile_strength insulating film was formed, and while evaluating the film | membrane adhesiveness of this insulating film, the magnetic characteristic (magnetic flux density) was evaluated. The decarburization annealing was held at 830 ° C. for 150 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.4.

  The magnetic properties were evaluated according to JIS C 2550. The magnetic flux density was evaluated using B8. B8 is a magnetic flux density at a magnetic field strength of 800 A / m, which is a criterion for determining the quality of secondary recrystallization. It was judged that B8 = 1.89T or more was secondary recrystallized. In addition, since the comparative steel b4 was a cold rolling process and the comparative steel b11 was a hot rolling process, the magnetic characteristics were not evaluated because fracture occurred.

  The film adhesion of the tension-imparting insulating film was evaluated by the film remaining area ratio when the sample for evaluation was wound around a cylinder having a diameter of 20 mm and bent 180 °. The evaluation is VG (very good) when the film remaining area ratio is 95% or more without peeling from the steel sheet, G (excellent) when 90% or more and less than 95%, and 80% or more and less than 90%. F (effective) and less than 80% were defined as B (ineffective). The film adhesion was not evaluated for those that were broken during rolling and those that had poor secondary recrystallization. Table 3 shows a series of evaluation results.

  Inventive steels B1 to B38 all exhibited excellent film adhesion and magnetic properties. In particular, in the invention steels B32 to 36, one or more of the selective elements Bi, Sn, Cr, Cu, Mo, Ti, V, and Nb are appropriately added. Good film adhesion. On the other hand, the comparative steels b14 and b16 were inferior in film adhesion because the amount of Se and Sb added was too large. None of the other comparative steels had element addition amounts within the above-mentioned range, so that the desired magnetic properties could not be obtained, or they broke during the test and were not evaluated.

<Example 2>
Silicon steel having the 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 plate having a thickness of 2.3 to 2.8 mm. Annealing was performed at 1200 ° C., and then a single cold rolling or a plurality of cold rolling sandwiching the intermediate annealing was performed to obtain a cold rolled steel sheet having a final thickness of 0.19 to 0.22 mm.

  The cold-rolled steel sheet is decarburized and annealed under the conditions shown in Table 4, and after that, an annealing separator is applied, finish annealing is performed at 1200 ° C., and then a coating solution for forming an insulating film is formed on the surface of the finish annealing plate. Was applied and baked to form a tension-providing insulating film, and the adhesion of the insulating film was evaluated, and the magnetic properties (magnetic flux density) were evaluated. The decarburization annealing was performed for 120 seconds at 830 ° C. in a wet hydrogen atmosphere having an oxygen potential of 0.5.

  Table 4 shows the evaluation results of film adhesion and magnetism. Any measurement method and evaluation method were carried out in accordance with Example 1.

  Inventive steels C1 to 24 all showed excellent film adhesion and magnetic properties. For the inventive steels C13 to C19, the heating rates S1, S2 and S2 / S1 were controlled within a preferable range, so that the adhesion was particularly good. As for C21 to C23, the heating rates S1, S2, S2 / S1, and P1 were controlled within a preferable range, so that the film adhesion was particularly good. On the other hand, the comparative steel c1 is out of the range where S2 / S1 is defined in the present invention, c2 and c3 are out of the range defined in the present invention, and c4 is out of the range of the present invention. C5 was inferior in film adhesion because P1 was outside the range defined in the present invention. Further, the comparative steel c2 was inferior in magnetic properties.

<Example 3>
Silicon steel having the 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 plate having a thickness of 2.3 to 2.8 mm. Annealing was performed at 1200 ° C., and then a single cold rolling or a plurality of cold rolling sandwiching the intermediate annealing was performed to obtain a cold rolled steel sheet having a final thickness of 0.18 to 0.22 mm.

The cold-rolled steel sheet is subjected to two-stage decarburization annealing under the conditions shown in Tables 5 and 6, and then coated with an annealing separator, and the temperature rise rate and atmosphere under the conditions shown in Tables 5 and 6 are 1200 ° C. Next, the insulating film forming coating solution is applied to the surface of the finish annealed plate and baked to form a tension-imparting insulating film. The adhesion of the insulating film is evaluated, and the magnetic properties (magnetic flux) Density).
In the decarburization annealing, the temperature was controlled to S1 = 700 ° C./second, S2 = 1200 ° C./second, and P1 = 0.15.

  Tables 5 and 6 show the evaluation results of film adhesion and magnetism. Any measurement method and evaluation method were carried out in accordance with Example 1.

<Example 4>
Silicon steel having the 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 plate having a thickness of 2.3 to 2.8 mm. Annealing was performed at 1200 ° C., and then a single cold rolling or a plurality of cold rolling sandwiching the intermediate annealing was performed to obtain a cold rolled steel sheet having a final thickness of 0.19 mm.

  A cold rolled steel sheet having a final thickness of 0.19 mm was subjected to decarburization annealing, and then an annealing separator was applied to perform final annealing at 1200 ° C., and then a final annealed sheet was produced. In the decarburization annealing process of this experiment, the heating rate in the temperature range 500 to 700 ° C. and the oxygen potential in the temperature range 500 to 600 ° C. were controlled (S1 = 800 ° C./second, S2 = 1600 ° C./second, P1 = 0.07). Then, the coating liquid for insulating film formation was apply | coated and baked on the steel plate surface, the tension | tensile_strength insulating film was formed, and while evaluating the film | membrane adhesiveness of this insulating film, the magnetic characteristic (magnetic flux density) was evaluated. 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.
Inventive steels E1 to E38 exhibited excellent film adhesion and magnetic properties. In particular, in the inventive steels E32 to 36, one or more of the selective elements Bi, Sn, Cr, Cu, Mo, Ti, V, and Nb are appropriately added. Good film adhesion. Since the plate thickness was thin, compared to the results shown in Table 3 of Example 1, good film adhesion was obtained as a whole.

  On the other hand, the comparative steels e14 and e16 were inferior in film adhesion because the amount of Se and Sb added was too large. None of the other comparative steels had element addition amounts within the above-mentioned range, so that the desired magnetic properties could not be obtained, or they broke during the test and were not evaluated.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

As described above, according to the present invention, a unidirectional electrical steel sheet excellent in magnetic properties and film adhesion can be produced. In particular, the present technology is also effective in a unidirectional electrical steel sheet to which Se or Sb is added. The effect is further exhibited in the case of a unidirectional electrical steel sheet having a product plate thickness of less than 0.22 mm. From the above, the present invention has high applicability in the electrical steel sheet manufacturing industry and the electrical steel sheet utilization industry.

Claims (8)

In mass%, C: 0.01% to 0.20%, Si: 2.50% to 4.0%, acid-soluble Al: 0.005% to 0.07%, Mn: 0.005 %: 0.5% or less, N: 0.03% or less, S: 0.0005% or more, 0.03% or less, Se: 0.001% or more, 0.08% or less, Sb: 0.005% or more, 0 0.5% or less, Bi: 0% to 0.02%, Sn: 0% to 0.50%, Cr: 0% to 0.50%, Cu: 0% to 1.0%, Mo : 0% to 0.5%, Ti: 0% to 0.05%, V: 0% to 0.05%, and Nb: 0% to 0.05%, with the remainder Fe and inevitable A hot-rolling step of obtaining a hot-rolled steel sheet by hot-rolling a steel slab composed of mechanical impurities at a temperature of 1200 ° C or higher and 1600 ° C or lower
A hot-rolled steel sheet annealing step for 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 a plurality of cold rolling via a single cold rolling or annealing;
A decarburization annealing step for subjecting the cold-rolled steel sheet to decarburization annealing;
Applying a annealing separator to the cold-rolled steel sheet, and performing a final annealing step on the cold-rolled steel sheet;
An insulating film forming step of forming a tension-imparting insulating film on the cold-rolled steel sheet,
At the time of temperature increase in the decarburization annealing step, the temperature increase rate S1 (° C./second) in the temperature range of 500 ° C. to 600 ° C. and the temperature increase rate S2 (° C./second) 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. at the time of the temperature rise satisfies the following formula (4). A method of manufacturing a steel sheet.
1.0 <S2 / S1 ≦ 10.0 (1)
300 ≦ S1 ≦ 2000 (2)
300 ≦ S2 ≦ 4000 Formula (3)
0.00001 ≦ P1 ≦ 0.5 (4)   The method for producing a unidirectional 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 slab is in mass%, Sn: 0.005% to 0.50%, Cr: 0.005% to 0.50%, Cu: 0.01% to 1.0% and Mo: The method for producing a unidirectional electrical steel sheet according to claim 1 or 2, comprising one or more selected from the group consisting of 0.005 to 0.5%.   The steel slab is one type 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%. Or the manufacturing method of the unidirectional electrical steel sheet as described in any one of Claims 1-3 containing 2 or more types. In the decarburization annealing step, in the atmosphere of oxygen potential P2, following the first-stage annealing that is held at a temperature T2 ° C. of 700 ° C. or higher and 900 ° C. or lower for 10 seconds or longer and 1000 seconds or shorter, The unidirectional electrical steel sheet according to any one of claims 1 to 4, wherein second-stage annealing is performed at a temperature T3 ° C satisfying the following formula (6) in an atmosphere, and held for 5 seconds or more and 500 seconds or less. Production method.
P3 <P2 Formula (5)
T2 + 50 ≦ T3 ≦ 1000 (6) In the temperature increase in the finish annealing step, the average temperature increase rate BR1 (° C / h) in the temperature range of 875 ° C or more and 1050 ° C or less satisfies the following formula (7). A method for producing a unidirectional electrical steel sheet.
1.0 ≦ BR1 ≦ 60.0 (7) The one-way property as described in any one of Claims 1-6 in which the oxygen potential P4 of the finish annealing atmosphere in the temperature range 875 degreeC or more and 1050 degrees C or less satisfy | fills following formula (8) in the temperature increase of the said finish annealing process. A method for producing electrical steel sheets.
0.00001 ≦ P4 ≦ 0.5 (8) The manufacturing method of the unidirectional electrical steel plate as described in any one of Claims 1-7 whose product board thickness of the said unidirectional electrical steel plate is 0.18 mm or more and less than 0.22 mm.