JP7110641B2 - 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.
Therefore, as described in Patent Documents 5 to 8, techniques have been developed for controlling the oxygen potential of the decarburization annealing atmosphere and improving 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. .

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

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 particular, materials with a coating thickness of less than 0.23 mm (hereinafter referred to as thin materials) do not have sufficient glass coating adhesion, and it is considered that techniques for improving coating adhesion are still under development.

In addition, since the adhesion of the glass film becomes unstable as the thickness of the product becomes thinner, a technique for further improving the adhesion of the glass film is required.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to apply a glass film having excellent film adhesion to the surface of a grain-oriented electrical steel sheet without impairing the magnetic properties. The object of the present invention is to provide a new and improved method for manufacturing a grain-oriented electrical steel sheet that can be formed into a

In order to solve the above problems, the present inventors focused their attention on the temperature rising process in the decarburization annealing process, and made earnest studies. As a result, it was found that the adhesion of the glass coating is dramatically improved by two-stage control of the temperature rise rate and atmosphere control in the temperature rise in the decarburization annealing process. In addition, the effect of applying this technology was particularly noticeable in thin materials.

When the inventors investigated a decarburized annealed sheet of a material with good film adhesion, SiO ₂ and Mn ₂ SiO ₄ (hereinafter sometimes referred to as tephrite) were observed as surface oxide films. It has been found that controlling the amount of Mn ₂ SiO ₄ produced is effective in improving film adhesion.

The present invention was made based on the above findings, and the gist thereof is as follows.
[1] In mass%, C: 0.010% to 0.20%, Si: 2.50% to 4.0 %, acid-soluble Al: 0.010 % to 0.07%, Mn: 0.010 % or more and 0.50% or less, N: 0.020 % or less, S: 0.005% or more and 0.08% 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% or more and 1.0% or less, and the balance being Fe and unavoidable impurities. A hot-rolling step of obtaining a hot-rolled steel sheet by heating at the following temperature and then hot-rolling;
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 0 Expression (4)
[2] The method for producing a grain-oriented electrical steel sheet according to [1] above, wherein the steel slab contains, by mass %, Bi: 0.001% or more and 0.02% or less.
[3] The steel slab, in mass%, Sn: 0.005% or more and 0.50% or less, Cr: 0.01% or more and 0.50% or less, Cu: 0.01% or more and 1.0% or less The method for producing a grain-oriented electrical steel sheet according to the above [1] or [2], containing one or more of
[4] 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), second-stage annealing is performed for 5 seconds or more and 500 seconds or less, [1] to [3] 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)
[5] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [4], 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 with excellent glass film adhesion can be produced without impairing magnetic properties and their stability.

Preferred embodiments of the present invention are described in detail below. Below, first, 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 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.

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: 0.01% or more and 0.07% % or less, Mn: 0.01% or more and 0.5% or less, N: 0.02% or less, S: 0.005% or more and 0.08% or less, Bi: 0% or more and 0.02% or less, Sn: A steel billet containing 0% or more and 0.50% or less, Cr: 0% or more and 0.50% or less, Cu: 0% or more and 1.0% or less, and the balance being Fe and unavoidable impurities is used.

(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.
From the viewpoint of magnetic flux density, the lower limit of the C content is 0.01%, preferably 0.04%.

(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: 0.01% 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 0.01%, sufficient AlN that functions as an inhibitor is not generated, secondary recrystallization is insufficient, and iron loss characteristics are not improved. The amount should be 0.01% or more. Preferably it is 0.02% 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: 0.02% or less)
N forms AlN, which can be used as an inhibitor. If the N content exceeds 0.02%, blisters (voids) are generated in the steel sheet during cold rolling, and the strength of the steel sheet increases, which deteriorates the threadability during production. The amount should be 0.02% or less. Preferably, it is 0.01% 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 0.005% or more in order to combine with Al to form AlN that functions as an inhibitor.

(Mn 0.01% 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 set to 0.01% or more. Preferably it is 0.05% or more.

(S: 0.005% or more and 0.08% or less)
If the S content exceeds 0.08%, it causes hot shortness and makes hot rolling extremely difficult, so the S content is made 0.08% or less. Preferably, it is 0.04% or less.
When MnS is used as an inhibitor during secondary recrystallization, the S content should be 0.005% or more. Preferably, it is 0.01% or more.

In the present embodiment, the billet contains, in mass%, Bi: 0.001% or more and 0.02% or less in order to improve the properties of the grain-oriented electrical steel sheet according to the present embodiment, in addition to the above elements. 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 billet contains, in mass %, Sn: 0.005 to 0.50%, Cr: 0.5%, in addition to the above elements, in order to improve the properties of the grain-oriented electrical steel sheet according to the present embodiment. 01 to 0.50% and Cu: 0.01 to 1.0%. Since Sn, Cr and Cu are optional elements, the lower limit of the content of Sn, Cr and Cu 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: 0.01% 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 0.01%, a sufficient effect of improving film adhesion cannot be obtained, so the Cr content can be made 0.01% or more. Preferably it is 0.03% 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 and Cr, 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.

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 Mo, W, In, B, Sb, Au, Ag, Te, Ce, V, Co, Ni, Se, Ca, Re, Os, Nb, Zr, Hf, Ta, Y, La , Cd, Pb, As, etc. may be contained in a total amount of 5.00% or less, preferably 3.00% or less, more preferably 1.00% or less. 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. 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.
Annealing conditions are not particularly limited, but, for example, the steel sheet can be annealed in a temperature range of 900 to 1250° 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.

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.

4. Decarburization Annealing Step Next, in the decarburization annealing step, the obtained cold-rolled steel sheet is decarburized and annealed.

4.1 Overview of Decarburization Annealing Decarburization annealing, which plays a particularly important role in the present invention, will now be described.
When using a unidirectional electrical steel sheet as a core material for a transformer, it is essential to ensure the insulation properties of the steel sheet, so it is necessary to form a glass coating and a tension-imparting insulating coating on the surface of the steel sheet after final annealing. . However, it is difficult to ensure the film adhesion of the glass film. Although the reason for this is not completely clear, we believe that the oxide film formation behavior during decarburization annealing may be peculiar to thin materials.

In the first place, the adhesion between the glass film and the steel sheet largely depends on the morphology of the glass film. This morphology is largely determined by the decarburization annealing process in which _SiO2 is formed. This is because the glass film is a substance produced by a solid phase reaction between MgO and _SiO2 . Since the grain-oriented electrical steel sheet contains a large amount of Si, various forms of SiO ₂ should be formed on the surface of the grain-oriented electrical steel sheet during the decarburization annealing process. Therefore, it is considered that excellent film adhesion can be secured by controlling the decarburization annealing process.

Having received the idea, the inventors focused on the heating process of decarburization annealing and searched for the optimum conditions of the heating rate and the oxygen potential during heating. As a result, the inventors have found the conditions under which the adhesion between the glass film and the steel plate is significantly improved. In response to this result, the inventors conducted a retrospective analysis of the sample after decarburization annealing, and as a result, in the material with good film adhesion, Mn ₂ SiO ₄ was formed on the surface of the steel sheet in addition to SiO ₂ . I found out. It is believed that this Mn ₂ SiO ₄ reacts with MgO, which is an annealing separator, to form Mg(Si, Mn)O ₄ , thereby forming a strong glass film with excellent adhesion. Since Mg(Si, Mn) _O4 is a thermodynamically unstable substance, in the second half of the final annealing process, only the composition of Mg(Si, Mn) _O4 is changed while maintaining the morphology of the glass film. It is thought that it changes to Mg ₂ SiO ₄ . A method for effectively forming Mn ₂ SiO ₄ in the decarburization annealing process and improving the glass film adhesion will be described below in detail.

4.2 Temperature rising conditions The temperature rising 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 Mn ₂ SiO ₄ can be sufficiently formed by adopting the temperature elevation conditions as described above under the oxygen potential conditions described later.

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, Mn ₂ SiO ₄ is easily formed in the temperature range of 500 to 600°C. Since the present invention is a technique for generating Mn ₂ SiO ₄ and improving film adhesion, the residence time in the Mn ₂ SiO ₄ formation temperature range of 500 to 600° C. is changed to that of the SiO ₂ formation temperature range of 600 to 700° C. It is first important to earn more than the residence time.

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. Since the residence time in the temperature range of 500 to 600°C corresponds to the amount of Mn ₂ SiO ₄ produced, and the residence time in the temperature range of 600 to 700°C corresponds to the amount of SiO ₂ produced, when S2/S1 is 1.0 or less, The amount of SiO ₂ produced exceeds the amount of Mn ₂ SiO ₄ produced, and the effect 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 Mn ₂ SiO ₄ is not formed at 2000° C./sec or more. 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.

It should be noted that if an isothermal holding cycle of 600° C. is employed, the residence time corresponding to each of S1 and S2 becomes unclear. Therefore, in the present embodiment, when a 600° C. isothermal holding cycle is adopted, the residence time corresponding to S1 is from when 500° C. is reached to the start of isothermal holding at 600° C., and the residence time corresponding to S2 is isothermal holding at 600° C. is defined as the time from the end of

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 production of Mn ₂ SiO ₄ , so the upper limit of P1 is 0.5. Mn ₂ SiO ₄ is more easily generated as P1 is smaller, but P1=0.00001 is considered to be the industrial 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 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.

4.3 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 Mn ₂ SiO ₄ 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.

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 formation amount of Mn ₂ SiO ₄ , the oxygen potential P2 during the first stage annealing can be made higher than the oxygen potential P1 during the temperature rise. When sufficient oxygen potential is obtained, Mn ₂ SiO ₄ can be prevented from replacing with SiO ₂ . Moreover, the decarburization reaction can be sufficiently advanced. However, if P2 is too large, Mn ₂ SiO ₄ may be replaced with 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 Mn ₂ SiO ₄ . If the annealing time exceeds 500 seconds, Mn ₂ SiO ₄ is reduced to SiO ₂ , so the upper limit of the annealing time is 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.

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.

Next, the conditions for the finish annealing are not particularly limited, and known conditions can be appropriately employed. For example, finish annealing can be performed by heating to a temperature range of 900° C. or more and 1400° C. or less and maintaining the same temperature for 10 hours or more and 100 hours or less. In addition, the atmosphere during finish annealing can have an oxygen potential of, for example, 0.0002 or more and 0.2 or less.

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, MgO in the annealing separator reacts with decarburization annealing to form a glass film on the surface of the steel sheet.
After the completion of this step, the surface of the cold-rolled steel sheet may be washed with water or pickled to remove powder.

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.

7. Grain-oriented Electrical Steel Sheet Finally, the grain-oriented electrical steel sheet obtained by the method described above will be described.
In the grain-oriented electrical steel sheet manufactured by the method described above, Mn ₂ SiO ₄ is formed on the surface of the steel sheet in addition to SiO ₂ in the decarburization annealing process. Then, this Mn ₂ SiO ₄ reacts with MgO, which is an annealing separator, to form Mg(Si, Mn)O ₄ , thereby forming a strong glass film with excellent adhesion. 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. Furthermore, the method described above does not impair the magnetic properties particularly as compared with the conventional method. That is, the obtained grain-oriented electrical steel sheet has sufficiently excellent magnetic properties.

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, it is necessary to generate Mn ₂ SiO ₄ in the decarburization annealing in the present invention. The formation of Mn ₂ SiO ₄ 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 it is possible to efficiently generate Mn ₂ SiO ₄ in thin materials 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 Table 1 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. After that, cold rolling was performed once or multiple times of cold rolling with intermediate annealing was performed to obtain a cold-rolled steel sheet having a final thickness of 0.22 mm. For each silicon steel, the balance other than the components listed in Table 1 is iron and impurities.

A cold-rolled steel sheet with a final thickness of 0.22 mm is subjected to decarburization annealing, then coated with an annealing separator mainly composed of magnesia (MgO), subjected to finish annealing at 1200 ° C., and then finished annealed. made. In addition, in the temperature rise in the decarburization annealing step of this experiment, the heating rate in the temperature range of 500 to 700° C. and the oxygen potential were controlled (S1=800° C./sec, S2=1000° C./sec, P1=0. 20). In the decarburization annealing, the steel was held at 850° C. for about 150 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.5.
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.

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 2 shows a series of evaluation results.

All of the invention steels B1 to B24 exhibited excellent film adhesion and magnetic properties. In particular, invention steels B18 to B24 contain one or more of the selective elements Sn, Cr, Cu, and Bi, and exhibit better film adhesion than invention steels B1 to B11. On the other hand, in the comparative steels b1 to b11 in which the content of any of the essential elements is outside the scope of the present invention, sufficient magnetic properties were not obtained or breakage occurred during rolling.

<Example 2>
A silicon steel having the chemical composition shown in Table 1 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. After that, cold rolling was performed once or cold rolling was performed multiple times with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.19 to 0.22 mm.

The above cold-rolled steel sheet was decarburized and annealed under the conditions shown in Table 3, then coated with an annealing separator mainly composed of MgO, subjected to finish annealing at 1200°C, and then insulated on the surface of the finish-annealed steel sheet. A coating solution for film formation 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). In the decarburization annealing, the steel was held at 830° C. for about 180 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.4.

Table 3 shows evaluation results of film adhesion and magnetic properties. All measurement methods and evaluation methods were performed according to Example 1.

The invention steels C1 to C7 exhibited good film adhesion because the heating rates S1, S2, S2/S1 and P1 were all controlled within the ranges of the invention. Inventive steels C8 to C14 also exhibited good film adhesion because the heating rates S1, S2, and S2/S1 were controlled within preferable ranges. In particular, since C10, C12 and C13 had thin plate thicknesses, they exhibited better film adhesion than C8, C9, C11 and C14. For the invention steels C15 to C19, the heating rates S1, S2, S2/S1 and P1 were controlled within preferable ranges, and the plate thickness was thin, so the film adhesion was particularly good. On the other hand, in Comparative Steel c1, S2/S1 was out of the range of the present invention, and the film adhesion was poor. Comparative steels c2 to c4 were inferior in film adhesion because either S1 or S2 was out of the scope of the present invention. As for Comparative Steel c5, the oxygen potential at the time of temperature rise in decarburization annealing was outside the range of the present invention, so the film adhesion was poor.

<Example 3>
A silicon steel having the chemical composition shown in Table 1 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. After that, cold rolling was performed once or cold rolling was performed multiple times with intermediate annealing to obtain a cold-rolled steel sheet having a final thickness of 0.19 to 0.22 mm.

The cold-rolled steel sheet was subjected to two-stage decarburization annealing under the conditions shown in Table 4, then coated with an annealing separator mainly composed of MgO, subjected to finish annealing at 1200 ° C., and then finished annealed. A coating solution for forming an insulating film was applied to the surface and baked to form a tension-applying insulating film.

In the decarburization annealing step of this experiment, S1 was controlled to 1700° C./sec, S2=2500° C./sec, and P1=0.10. Table 4 shows evaluation results of film adhesion and magnetic properties. All measurement methods and evaluation methods were performed according to Example 1.

For invention steels D11 to D16, the film adhesion was better than for invention steels D1 to D10 because the conditions for the first stage annealing were controlled. In addition, D17 to D22 had better film adhesion than the invention steels D1 to D10 because the conditions of the second stage annealing were controlled. Inventive steels D23 to D26 exhibit particularly good film adhesion because both the first-stage annealing and second-stage annealing conditions were controlled to favorable conditions.

<Example 4>
A silicon steel having the chemical composition shown in Table 1 is heated at 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. After that, cold rolling was performed once or multiple times of cold rolling with intermediate annealing was performed to obtain a cold-rolled steel sheet having a final thickness of 0.19 mm.

The cold-rolled steel sheets were decarburized and annealed, then coated with an annealing separator mainly composed of MgO, and subjected to finish annealing at 1200° C., and then finish-annealed sheets were 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 P1 in the temperature range of 500 to 600 ° C. were controlled (S1 = 900 ° C./sec, S2 = 1200 ° C./sec. , P1=0.03). 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-applying insulating film. In the decarburization annealing, the steel was held at 850° C. for about 150 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.3.

Table 5 shows evaluation results of film adhesion and magnetic properties. All measurement methods and evaluation methods were performed according to Example 1. 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.
All of the invention steels E1 to E24 exhibited excellent film adhesion and magnetic properties. In particular, invention steels E12 to E24 contain one or more of the selective elements Sn, Cr, Cu, and Bi, and thus exhibit better film adhesion than invention steels E1 to E11. On the other hand, in the comparative steels e1 to e11 in which the content of any of the essential elements is outside the scope of the present invention, sufficient magnetic properties were not obtained or breakage occurred during rolling.

<Example 5>
A silicon steel having the chemical composition shown in Table 1 is heated at 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. After that, cold rolling was performed once or multiple times of cold rolling with intermediate annealing was performed to obtain a cold-rolled steel sheet having a final thickness of 0.22 mm.

The cold-rolled steel sheets were decarburized and annealed under the conditions shown in Table 6, then coated with an annealing separator mainly composed of MgO, and subjected to finish annealing at 1200°C, and then finish-annealed sheets were produced.

The decarburization annealing in this experiment is two-step annealing, the first step is held at 850 ° C. for 150 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.3, and the second step is with an oxygen potential of 0.01. It was held at 950° C. for 20 seconds in a dry hydrogen atmosphere. Thereafter, the surface of the finish-annealed sheet was coated with a coating solution for forming an insulating film and baked to form a tension-applying insulating film. Table 6 shows the results.

As shown in Table 6, the invention steels F1 to F16 exhibited good film adhesion because the two-step annealing conditions were all controlled within the preferred ranges of the present invention. On the other hand, in Comparative Steel f1, the ratio of S2/S1 was outside the range of the present invention, so the film adhesion was inferior. Comparative steels f2 to f4 were inferior in film adhesion because either S1 or S2 was out of the scope of the present invention. As for Comparative Steel f5, the oxygen potential during the temperature rise in the decarburization annealing was out of the range of the present invention, so the film adhesion was poor.

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 glass film having excellent film adhesion can be formed without impairing magnetic properties and stability thereof. In particular, the present technology is particularly effective in grain-oriented electrical steel sheets with a product thickness of less than 0.22 mm. As described above, the present invention has high applicability in the electromagnetic steel sheet manufacturing industry and the electromagnetic steel sheet utilization industry.

Claims (5)

% by mass, C: 0.010% or more and 0.20% or less, Si: 2.50% or more and 4.0 % or less, acid-soluble Al: 0.010% or more and 0.07% or less, Mn: 0 .010% or more and 0.50% or less, N: 0.020 % or less, S: 0.005% or more and 0.08% or less, Bi: 0 % or more and 0.02% or less, Sn: 0 % or more A steel billet containing 0.50% or less, Cr: 0% or more and 0.50% or less, Cu: 0% or more and 1.0% or less, and the balance being Fe and inevitable impurities, is heated at a temperature of 1200°C or more and 1600°C or less. A hot rolling step of obtaining a hot rolled steel sheet by hot rolling after heating with
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 0 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, in mass%, is one of Sn: 0.005% to 0.50%, Cr: 0.01% to 0.50%, and Cu: 0.01% to 1.0%. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, which contains two or more kinds. 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 3, wherein 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 method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the grain-oriented electrical steel sheet has a product thickness of 0.18 mm or more and less than 0.22 mm.