JP7119474B2 - Manufacturing method of 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 (also referred to as a "unidirectional electrical steel sheet") is composed of crystal grains highly oriented and accumulated in the {110} <001> orientation (hereinafter also referred to as a "Goss orientation"), and contains Si. It is a steel sheet containing 7% by mass or less. Grain-oriented electrical steel sheets are mainly used as iron core materials for transformers. When grain-oriented electrical steel sheets are used as the iron core material of a transformer (that is, when the grain-oriented electrical steel sheets are laminated as the 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.

A general method for producing a grain-oriented electrical steel sheet and a method for forming a glass coating and a tensile insulating coating are as follows. First, a steel billet containing 7% by mass or less of silicon (Si) is hot-rolled, and then cold-rolled once or twice with intermediate annealing to finish the steel sheet to a predetermined thickness after cold-rolling. After that, decarburization and primary recrystallization are performed by annealing (decarburization annealing) in a moist hydrogen atmosphere to obtain a decarburization annealed sheet. In such decarburization annealing, oxide films (Fe ₂ SiO ₄ and SiO ₂ ) are formed on the surface of the steel sheet. Subsequently, an annealing separator mainly composed of MgO is applied to the decarburized annealed sheet, dried, and then finish annealed. Due to such finish annealing, secondary recrystallization occurs, and the crystal grain structure of the steel sheet is accumulated in the {110}<001> orientation. At the same time, on the steel sheet surface, MgO in the annealing separator reacts with oxide films (Fe ₂ SiO ₄ and SiO ₂ ) formed on the steel sheet surface during decarburization annealing to form a glass coating. A tension-imparting insulating coating is formed by applying a coating solution mainly containing phosphate to the surface of the finish-annealed sheet (that is, the surface of the glass coating) and baking the coated solution.

Here, one of the problems in producing grain-oriented electrical steel sheets is the improvement of decarburization.
For example, Patent Literature 1 below proposes a technique for improving decarburization by increasing the oxygen potential. However, although the decarburization property is improved only by increasing the oxygen potential, a large amount of Fe oxide is generated. Fe oxide is a substance that should be avoided because it deteriorates secondary recrystallization and eventually leads to deterioration of magnetism.

Therefore, in addition to oxygen potential control, a technique for controlling the rate of temperature increase in decarburization annealing has been devised as a technique for improving secondary recrystallization. For example, Patent Documents 2 to 8 below propose techniques for improving the texture of the crystal orientation of a steel sheet by controlling the oxygen potential and heating rate during decarburization annealing, leading to improvement in magnetic properties. .

Japanese Patent No. 3392669 JP-A-07-278668 JP-A-2002-173715 Japanese Patent Application Laid-Open No. 2003-003213 Japanese Unexamined Patent Application Publication No. 2011-174138 WO2016/056501 WO2014/049770 Patent No. 6103281

Here, the carbon contained in the grain _- oriented electrical steel sheet has the effect of improving the magnetic flux density by improving the secondary recrystallization. There is a possibility that it will precipitate inside and the magnetic properties will deteriorate. In particular, grain-oriented electrical steel sheets sometimes contain Cr for the purpose of improving magnetic properties, but in such cases, there is a problem that the decarburization property is lowered. The methods proposed in Patent Documents 2 to 8 contribute to improving the secondary recrystallization by controlling the oxygen potential and controlling the heating rate, but do not mention the improvement of the decarburization property.

The present invention has been made in view of the above problems, and an object of the present invention is to obtain a higher magnetic flux density without impairing the decarburization property in a grain-oriented electrical steel sheet containing Cr. To provide a possible method for manufacturing a grain-oriented electrical steel sheet.

As a result of intensive studies to solve the above problems, the present inventors have found that the deterioration of decarburization is caused by Cr forming a Cr oxide film. However, under decarburization annealing conditions aimed at improving secondary recrystallization, the formation of a Cr oxide film cannot be avoided, and as a result, it is difficult to achieve both magnetic flux density and decarburization properties. As a result of further studies, the inventors of the present invention found a decarburization annealing cycle that avoids the formation of a Cr oxide film, and completed the present invention.
The gist of the present invention completed based on the above knowledge is as follows.

[1] % by mass, C: 0.01 to 0.20%, Si: 2.5 to 4.0%, Sol. Al: 0.010-0.07 %, Mn: 0.010-0.50 %, Cr: 0.01-0.50%, N: 0.020% or less, S: 0.005- 0.080%, Se: 0-0.080%, Sb: 0-0.50%, Bi: 0-0.02%, Sn: 0-0.50%, Cu: 0-1.0% A hot-rolling step of obtaining a hot-rolled steel sheet by heating a steel billet containing Fe and the remainder consisting of Fe and impurities, followed by hot-rolling to obtain a hot-rolled steel sheet, and annealing the hot-rolled steel sheet to obtain a hot-rolled annealed steel sheet. An annealing step, a cold rolling step of obtaining a cold-rolled steel sheet by performing one cold rolling or a plurality of cold rollings with intermediate annealing on the hot-rolled and annealed steel sheet, and the cold-rolled steel sheet A decarburization annealing step of applying decarburization annealing to obtain a decarburization annealed steel plate, a finish annealing step of applying an annealing separator to the decarburization annealing steel plate and then performing finish annealing, and after finish annealing and an insulating coating forming step of forming an insulating coating on the surface of the steel sheet, wherein the decarburization annealing step heats the cold-rolled steel sheet from room temperature to a temperature T1 (° C.) that satisfies the following formula (1) by the following formula ( 2) in which the temperature is increased at a temperature increase rate H1 (°C/sec), and the cold-rolled steel sheet that has reached the temperature T1 (°C) is once subjected to the following formula (3): An intermediate cooling step of cooling to a temperature T2 (°C) at a cooling rate C1 (°C/sec) that satisfies the following formula (4); and a soaking step of annealing the cold-rolled steel sheet after heating, and the oxygen potential P0 in the first heating step and the intermediate cooling step satisfies the following formula (5). A method for producing a grain-oriented electrical steel sheet.
200 ≤ T1 ≤ 500 Expression (1)
100≦H1≦800 Expression (2)
T1-100 ≤ T2 ≤ T1-10 Expression (3)
−40≦C1<0 Expression (4)
0.0001 0 ≤ P0 ≤ 0.5 Expression (5)
[2] In the second temperature raising step in the decarburization annealing step, the temperature increase rate S (° C./sec) from the temperature T2 to the decarburization annealing temperature satisfies the following formula (6), [1 ] The method for producing a grain-oriented electrical steel sheet according to .
400≦S≦2000 Expression (6)
[3] The soaking step in the decarburization annealing step is performed at a temperature T3 (° C.) of 700° C. to 900° C. for 10 seconds to 1000 seconds in an atmosphere with an oxygen potential P2 of 0.1 to 1.0 . A first soaking step held below, and a temperature T4 (° C.) that satisfies the following formula (8) in an atmosphere of an oxygen potential P3 that satisfies the following formula (7) following the first soaking process: and a second soaking step of holding for 5 seconds or more and 500 seconds or less.
P3<P2 Expression (7)
T3+50≦T4≦1000 Expression (8)
[4] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [3], wherein the grain-oriented electrical steel sheet has a thickness of 0.17 mm or more and less than 0.22 mm.
[5] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [4], wherein the steel billet contains 0.001 to 0.020% by mass of Bi.
[6] Any one of [1] to [5], wherein the steel billet contains at least one of 0.005 to 0.500% by mass of Sn and 0.01 to 1.00% by mass of Cu. A method for producing a grain-oriented electrical steel sheet according to claim 1.

As described above, according to the present invention, a grain-oriented electrical steel sheet having a high magnetic flux density can be produced without impairing the decarburization property.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which showed typically the structure of the grain-oriented electrical steel plate which concerns on embodiment of this invention. It is explanatory drawing which showed typically the structure of the grain-oriented electrical steel plate which concerns on the same embodiment. It is the flow chart which showed an example of the flow of the manufacturing method of the grain-oriented electrical steel sheet which concerns on the same embodiment. It is the flowchart which showed an example of the flow of the decarburization annealing process which concerns on the same embodiment. It is explanatory drawing which showed an example of the heat processing pattern of the decarburization annealing process which concerns on the same embodiment. It is explanatory drawing which showed an example of the heat processing pattern of the decarburization annealing process which concerns on the same embodiment.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

(Regarding the background to the present invention)
Below, first, prior to explaining the method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, the knowledge obtained through intensive studies by the present inventors and the background to the present invention based on such knowledge will be described. will be briefly explained.

As mentioned above, one of the problems in producing grain-oriented electrical steel sheets is the improvement of decarburization. The present inventors paid attention to the temperature rise cycle in the decarburization annealing process and conducted investigations such as changing the conditions. As a result, when the temperature is raised from room temperature to a temperature range of 200 to 500 ° C., if the residence time in this temperature range is long, a Cr-based oxide film is formed and causes deterioration of the decarburization property. It has been found that shortening the residence time in such a temperature range is effective for improving decarburization. However, while the Cr-based oxide film is a decarburization inhibitor, it has an effect of improving secondary recrystallization, so even if the decarburization property is improved based on the above idea, the magnetic flux density will decrease there's a possibility that. Therefore, the present inventors have found that it is important to generate an oxide film other than a Cr-based oxide film as a substitute for a Cr-based oxide film, and that an Al-based oxide film is an oxide film other than a Cr-based oxide film. Each conceived that it is useful to use

As a result of further studies based on this idea, the present inventors have found that controlling the oxygen potential in the temperature rising process from room temperature to a temperature range of 200 to 500 ° C. promotes the formation of an Al oxide film. I found that it is possible. It was also found that the Al oxide film formed in the decarburization annealing step remains in the glass coating as MgAl ₂ O ₄ through the subsequent finish annealing step.

(Regarding grain-oriented electrical steel sheets)
Next, grain-oriented electrical steel sheets according to embodiments of the present invention will be described in detail.

<Main composition of grain-oriented electrical steel sheet>
First, the main configuration of the grain-oriented electrical steel sheet according to the present embodiment will be described with reference to FIGS. 1A and 1B. 1A and 1B are explanatory diagrams schematically showing the structure of a grain-oriented electrical steel sheet according to this embodiment.

A grain-oriented electrical steel sheet 10 according to the present embodiment includes a base steel plate 11, a glass coating 13 formed on the surface of the base steel plate 11, and a and a tension-applying insulating coating 15, which is an example of the formed insulating coating. The glass coating 13 and the tension-applying insulating coating 15 may be formed on at least one surface of the base steel plate 11. Usually, as schematically shown in FIG. Formed on both sides.

Below, the grain-oriented electrical steel sheet 10 according to the present embodiment will be described with a focus on its characteristic configuration. In the following description, detailed descriptions of known configurations and some configurations that can be implemented by those skilled in the art are omitted.

[Regarding the base material steel plate 11]
The base material steel plate 11 exhibits excellent magnetic properties by containing chemical components as detailed below. The chemical composition of the base material steel plate 11 will be described in detail again below.

[Regarding the glass coating 13]
The glass coating 13 is an inorganic coating containing magnesium silicate as a main component and located on the surface of the base steel plate 11 . A glass coating is generally formed by reaction between an annealing separating agent containing magnesia (MgO) applied to the surface of the base steel sheet and components on the surface of the base steel sheet during finish annealing. It has a composition derived from the ingredients of the agent and the base steel sheet. As described above, MgAl ₂ O ₄ is present in the glass coating 13 in the grain-oriented electrical steel sheet 10 according to the present embodiment. _In the grain _- oriented electrical steel sheet 10 according to the present embodiment, Cr Even if it contains, it is possible to express excellent decarburization.

The amount of MgAl ₂ O ₄ produced relative to the amount of glass coating deposited can be confirmed by X-Ray Diffraction (XRD) analysis of the surface of the glass coating. Here, XRD is a crystal structure analysis method for identifying a compound from the position of a diffraction peak appearing at a specific diffraction angle 2θ with respect to the crystal structure of a substance. A crystal structure database called PDF (Powder Diffraction File, for example, JCPDS card) can be used to collate the diffraction peak position and the substance.

[Regarding tension-applying insulating coating 15]
The tension-applying insulating coating 15 is located on the surface of the glass coating 13 and provides electrical insulation to the grain-oriented electrical steel sheet 10 to reduce eddy current loss and reduce iron loss of the grain-oriented electrical steel sheet 10. Improve. Moreover, the tension-applying insulating coating 15 realizes various properties such as corrosion resistance, heat resistance, and slipperiness in addition to the electrical insulation described above.

Furthermore, the tension-applying insulating coating 15 has the function of applying tension to the grain-oriented electrical steel sheet 10 . By applying tension to the grain-oriented electrical steel sheet 10 to facilitate domain wall movement in the grain-oriented electrical steel sheet 10, iron loss of the grain-oriented electrical steel sheet 10 can be improved.

Such a tension-applying insulating coating 15 is formed, for example, by coating the surface of the glass coating 13 with a coating liquid containing metal phosphate and silica as main components and baking the coating.

<Regarding the thickness of the grain-oriented electrical steel sheet 10>
The product thickness (thickness t in FIGS. 1A and 1B) of the grain-oriented electrical steel sheet 10 according to the present embodiment is not particularly limited, and can be, for example, 0.17 mm or more and 0.35 mm or less. In addition, in the present embodiment, the effect becomes remarkable when the sheet thickness after cold rolling is as thin as less than 0.22 mm (that is, thin material), and the decarburization property becomes even more excellent. More preferably, the plate thickness after cold rolling is, for example, 0.17 mm or more and 0.20 mm or less.

<Chemical Composition of Base Material Steel Plate 11>
Next, the chemical composition of the base material steel sheet 11 of the grain-oriented electrical steel sheet 10 according to this embodiment will be described in detail. In addition, below, the notation of "%" shall represent "mass %" unless otherwise specified.

The chemical composition of the base material steel sheet 11 of the grain-oriented electrical steel sheet 10 according to the present embodiment is C: 0.01 to 0.20%, Si: 2.5 to 4.0%, Sol. Al: 0.01-0.07%, Mn: 0.01-0.50%, Cr: 0.01-0.50%, N: 0.02% or less, S: 0.005-0.080 %, Se: 0 to 0.080%, Sb: 0 to 0.50%, Bi: 0 to 0.02%, Sn: 0 to 0.50%, Cu: 0 to 1.0%, The remainder consists of Fe and impurities.

[C: 0.01% or more and 0.20% or less]
C (carbon) is an element that exhibits the effect of improving the magnetic flux density. Secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics cannot be obtained. Therefore, in the base material steel plate 11 according to the present embodiment, the C content is set to 0.20% or less. Since the lower the C content is, the more preferable it is for iron loss reduction, the C content is preferably 0.15% or less, more preferably 0.10% or less, from the viewpoint of iron loss reduction. On the other hand, from the viewpoint of magnetic flux density, the content of C is set to 0.01% or more. The content of C is preferably 0.04% or more, more preferably 0.06% or more.

[Si: 2.5% or more and 4.0% or less]
Si (silicon) is an extremely effective element for increasing the electrical resistance (specific resistance) of steel and reducing eddy current loss that constitutes a part of iron loss. If the Si content is less than 2.5%, the steel undergoes phase transformation during secondary recrystallization annealing, and secondary recrystallization does not proceed sufficiently, resulting in good magnetic flux density and core loss characteristics. can't Therefore, in the base material steel plate 11 according to this embodiment, the Si content is set to 2.5% or more. The Si content is preferably 3.0% or more, more preferably 3.2% 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. Therefore, in the base material steel plate 11 according to the present embodiment, the Si content is set to 4.0% or less. The Si content is preferably 3.8% or less, more preferably 3.6% or less.

[Acid-soluble Al: 0.01% or more and 0.07% or less]
Acid-soluble aluminum (sol.Al) is a major constituent element of inhibitors among compounds called inhibitors that influence secondary recrystallization in grain-oriented electrical steel sheets. It is an essential element from the viewpoint of occurrence of subsequent recrystallization. sol. If the Al content is less than 0.01%, sufficient AlN, which functions as an inhibitor, is not generated, resulting in insufficient secondary recrystallization and no improvement in iron loss properties. Therefore, in the base material steel plate 11 according to the present embodiment, sol. The content of Al is set to 0.01% or more. sol. The Al content is preferably 0.015% or more, more preferably 0.020% or more. On the other hand, sol. If the Al content exceeds 0.07%, embrittlement of the steel sheet becomes significant. Therefore, in the base material steel plate 11 according to the present embodiment, sol. The content of Al is set to 0.07% or less. sol. The Al content is preferably 0.05% or less, more preferably 0.030% or less.

[Mn: 0.01% or more and 0.50% or less]
Mn (manganese) is an important element forming MnS, which is one of the main inhibitors. If the Mn content is less than 0.01%, the absolute amount of MnS required to cause secondary recrystallization is insufficient. Therefore, in the base material steel plate 11 according to the present embodiment, the content of Mn is set to 0.01% or more. The Mn content is preferably 0.03% or more, more preferably 0.06% or more. On the other hand, when the Mn content exceeds 0.50%, the steel undergoes phase transformation during secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic flux density and core loss properties are obtained. can't Therefore, in the base material steel plate 11 according to the present embodiment, the content of Mn is set to 0.50% or less. The Mn content is preferably 0.30% or less, more preferably 0.10% or less.

[Cr: 0.01% or more and 0.50% or less]
Cr is an element that improves the magnetic properties and the adhesion of the glass coating. If the Cr content is less than 0.01%, the effect of improving the magnetic properties and the effect of improving the glass coating adhesion cannot be obtained. Therefore, in the base material steel plate 11 according to this embodiment, the Cr content is set to 0.01% or more. The Cr content is preferably 0.03% or more, more preferably 0.05% or more. On the other hand, when the Cr content exceeds 0.50%, the decarburization performance is lowered even if the manufacturing method according to the present embodiment is applied. Therefore, in the base material steel plate 11 according to the present embodiment, the Cr content is set to 0.50% or less. The Cr content is preferably 0.20% or less, more preferably 0.10% or more.

[N: 0.02% or less]
N (nitrogen) is an element that reacts with the acid-soluble Al to form AlN. If the N content exceeds 0.02%, blisters (voids) are generated in the steel sheet during cold rolling, the strength of the steel sheet increases, and the threadability during production deteriorates. Therefore, in the base material steel plate 11 according to the present embodiment, the N content is set to 0.02% or less. The N content is preferably 0.015% or less, more preferably 0.010% or less. On the other hand, if AlN is not utilized as an inhibitor, the lower limit of the N content may include 0%. However, since the detection limit of chemical analysis is 0.0001%, the substantial lower limit of the N content in practical steel sheets is 0.0001%. On the other hand, in order to combine with Al to form AlN that functions as an inhibitor, the N content is preferably 0.001% or more, more preferably 0.005% or more.

[S: 0.005% or more and 0.080% or less]
S (sulfur) is an important element that forms MnS, which is an inhibitor, by reacting with the Mn. If the S content is less than 0.005%, a sufficient inhibitory effect cannot be obtained. Therefore, in the base material steel plate 11 according to this embodiment, the S content is set to 0.005% or more. The S content is preferably 0.010% or more, more preferably 0.020% or more. On the other hand, if the S content exceeds 0.080%, it causes hot brittleness and makes hot rolling extremely difficult. Therefore, in the base material steel plate 11 according to the present embodiment, the S content is set to 0.080% or less. The S content is preferably 0.040% or less, more preferably 0.030% or less.

[Bi: 0% or more and 0.02% or less]
Since Bi (bismuth) is an optional element in the base material steel sheet 11 according to the present embodiment, the lower limit of its content is 0%. On the other hand, by containing Bi instead of part of the remaining Fe, it contributes to promoting the improvement of glass coating adhesion in the same manner as Sn and Cu, which will be described later, and improves the characteristics of the grain-oriented electrical steel sheet according to the present embodiment. Improve. In order to obtain the effect of promoting the improvement of glass coating adhesion, the Bi content is preferably 0.001% or more. On the other hand, when the Bi content exceeds 0.02%, the threadability during cold rolling deteriorates. Therefore, the content of Bi is set to 0.02% or less. The Bi content is preferably 0.01% or less, more preferably 0.007% or less.

In the base material steel sheet 11 according to the present embodiment, in order to improve the characteristics of the grain-oriented electrical steel sheet according to the present embodiment, in addition to the various elements described above, Se, Sb, At least one of Sn and Cu may be further contained. Since Se, Sb, Sn and Cu are optional elements in the base material steel sheet 11 according to the present embodiment, the lower limit of their content is 0%.

[Se: 0% or more and 0.080% or less]
Se (selenium) is an element having an effect of improving magnetism, and thus can be selectively contained. However, adding more than 0.080% significantly deteriorates the glass coating. Therefore, the upper limit of the Se content is set to 0.080%. It is preferably 0.050% or less. More preferably, it is 0.020% or less. Considering compatibility between magnetism and film adhesion, the content is preferably 0.003% or more, more preferably 0.006% or more. Since Se is an arbitrary element in the base material steel sheet 11 according to the present embodiment, the lower limit of its content is 0%. It is preferable that the content is 0.001% or more in order to achieve the desired performance.

[Sb: 0% or more and 0.50% or less]
Sb (antimony), like Se, is an element having an effect of improving magnetism, and thus can be selectively contained. However, if the Sb content exceeds 0.50%, the glass coating is remarkably deteriorated. Therefore, the upper limit of the Sb content is set to 0.50%. The Sb content is preferably 0.30% or less, more preferably 0.10% or less. Considering compatibility between magnetism and film adhesion, the Sb content is preferably 0.01% or more, more preferably 0.02% or more. Since Sb is an arbitrary element in the base material steel sheet 11 according to the present embodiment, the lower limit of its content is 0%. It is preferable that the content is 0.005% or more in order to achieve the desired performance.

[Sn: 0% or more and 0.50% or less]
Sn (tin) is an element that contributes to the improvement of magnetism through primary crystal structure control. In order to obtain the magnetic improvement effect, the Sn content is preferably 0.005% or more. The Sn content is more preferably 0.009% or more. On the other hand, when the Sn content exceeds 0.50%, the secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, in the base material steel plate 11 according to the present embodiment, the Sn content is set to 0.50% or less. The Sn content is preferably 0.30% or less, more preferably 0.15% or less.

[Cu: 0% or more and 1.0% or less]
Cu (copper), like Bi and Cr, is an element that contributes to the improvement of glass film adhesion. In order to obtain the effect of improving glass film adhesion by Cu, the content of Cu is preferably 0.01% or more. The Cu content is more preferably 0.03% or more. On the other hand, when the Cu content exceeds 1.0%, the steel sheet becomes embrittled during hot rolling. Therefore, the content of Cu is set to 1.0% or less in the base material steel plate 11 according to the present embodiment. The Cu content is preferably 0.50% or less, more preferably 0.10% or less.

The remainder of the chemical composition of the base material steel plate 11 according to this embodiment is Fe and impurities. However, the base material steel plate 11 is used for the purpose of improving the properties required for structural members such as improving magnetic properties, strength, corrosion resistance, and fatigue properties, improving castability and threadability, and improving productivity through the use of scrap and the like. , Mo (molybdenum), W (tungsten), In (indium), B (boron), Au (gold), Ag (silver), Te (tellurium), Ce (cerium) , V (vanadium), Co (cobalt), Ni (nickel), Ca (calcium), Re (rhenium), Os (osmium), Nb (niobium), Zr (zirconium), Hf (hafnium), Ta (tantalum) , Y (yttrium), La (lanthanum), Cd (cadmium), Pb (lead), As (arsenic), etc. not a thing In addition, since these elements are elements that can be included arbitrarily, the lower limit of the total content of these elements is 0%.

Impurities exist in the base material steel sheet 11 regardless of the intention of their addition, and are components that do not need to exist in the resulting grain-oriented electrical steel sheet. The term "impurities" is a concept that includes impurities mixed in from raw materials such as ores, scraps, or the manufacturing environment when steel materials are industrially manufactured. Such impurities may be contained in amounts that do not adversely affect the effects of the present invention.

The chemical composition of the base material steel plate 11 according to the present embodiment has been described above in detail.

Various magnetic properties exhibited by the grain-oriented electrical steel sheet according to the present embodiment are determined 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 measure

(Method for manufacturing grain-oriented electrical steel sheet)
Next, a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment will be described in detail with reference to FIGS. 2 to 5. FIG. FIG. 2 is a flow chart showing an example of the flow of the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment. FIG. 3 is a flow chart showing an example of the flow of the decarburization annealing process according to this embodiment. 4 and 5 are explanatory diagrams showing an example of the heat treatment pattern of the decarburization annealing process according to the present embodiment.

<Overall Flow of Manufacturing Method of Grain-Oriented Electrical Steel Sheet>
Hereinafter, the overall flow of the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment will be described with reference to FIG. 2 .
The overall flow of the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment is as follows.
First, a steel billet (slab) having the chemical components as described above is hot rolled and then annealed to obtain a hot rolling annealing step. Next, the obtained hot-rolled and annealed steel sheet is cold-rolled once or twice with intermediate annealing after pickling to obtain a cold-rolled steel sheet that has been cold-rolled to the final thickness. obtain. Thereafter, the obtained cold-rolled steel sheet is subjected to decarburization and primary recrystallization by annealing (decarburization annealing) in a moist hydrogen atmosphere to obtain a decarburized annealed steel sheet. In such decarburization annealing, a predetermined Mn-based oxide film is formed on the surface of the steel sheet. Subsequently, an annealing separator mainly composed of MgO is applied to the surface of the decarburized annealed steel sheet, dried, and then subjected to finish annealing. Due to such finish annealing, secondary recrystallization occurs, and the crystal grain structure of the steel sheet is accumulated in the {110}<001> orientation. At the same time, on the steel sheet surface, MgO in the annealing separator reacts with oxide films (Fe ₂ SiO ₄ and SiO ₂ ) formed on the steel sheet surface during decarburization annealing to form a glass coating. 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 coating.

That is, in the method for producing a grain-oriented electrical steel sheet according to the present embodiment, as shown in FIG. 2, a steel billet having the chemical composition as described above is hot-rolled at a predetermined temperature to obtain a hot-rolled steel sheet. A hot-rolling step (step S101), a hot-rolled sheet annealing step (step S103) of annealing the obtained hot-rolled steel sheet to obtain a hot-rolled annealed steel sheet, and performing one-time A cold rolling step (step S105) of obtaining a cold-rolled steel sheet by performing cold rolling or a plurality of cold rollings with intermediate annealing, and decarburizing annealing the obtained cold-rolled steel sheet, A decarburization annealing step (step S107) of obtaining a decarburized annealed steel sheet, a finish annealing step (step S109) of applying an annealing separator to the obtained decarburized annealed steel sheet and then performing finish annealing, and after finish annealing and an insulating coating forming step (step S111) of forming an insulating coating (more specifically, a tension-applying insulating coating) on the surface of the steel plate.

These steps will be described in detail below. In addition, in the following description, when some conditions in each step are not described, each step can be performed by appropriately adapting known conditions.

<Hot rolling process>
The hot-rolling step (step S101) is a step of hot-rolling a steel billet (for example, a steel ingot such as a slab) having a predetermined chemical composition into a hot-rolled steel sheet. The components of the steel slab are the same as those of the base material steel plate 11 as described above. In such a hot rolling process, a silicon steel slab having the chemical composition as described above is first heat-treated. Here, the heating temperature is preferably within the range of 1100 to 1450.degree. The heating temperature is more preferably 1300° C. or higher and 1400° C. or lower. The billet heated to the temperature as described above 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, for example, within the range of 2.0 mm or more and 3.0 mm or less.

<Hot-rolled sheet annealing process>
The hot-rolled steel sheet annealing step (step S103) is a step of annealing the hot-rolled steel sheet manufactured through the hot rolling process to obtain a hot-rolled annealed steel sheet. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties.

In the hot-rolled sheet annealing process according to the present embodiment, the hot-rolled steel sheet manufactured through the hot rolling process may be annealed according to a known method to form a hot-rolled annealed steel sheet. The means for heating the hot-rolled steel sheet during annealing is not particularly limited, and a known heating method can be employed. The annealing conditions are also not particularly limited, but for example, the hot-rolled steel sheet can be annealed in the temperature range of 900 to 1200° C. for 10 seconds to 5 minutes.

Note that the hot-rolled sheet annealing step can be omitted as necessary.
After the hot-rolled steel sheet annealing process, the surface of the hot-rolled steel sheet may be pickled before the cold rolling process described in detail below.

<Cold rolling process>
The cold-rolling step (step S105) is a step of cold-rolling the hot-rolled and annealed steel sheet once or two or more times with intermediate annealing to obtain a cold-rolled steel sheet. Further, when the hot-rolled sheet is annealed as described above, the shape of the steel sheet is improved, so the possibility of the steel sheet breaking in the first rolling can be reduced. Also, 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.

In the cold-rolling process according to the present embodiment, the hot-rolled annealed steel sheet manufactured through the hot-rolled sheet annealing process may be cold-rolled to obtain a cold-rolled steel sheet according to a known method. For example, the final cold rolling reduction can be in the range of 80% or more and 95% or less. If the final rolling reduction is less than 80%, there is a high possibility that Goss nuclei with a high degree of accumulation of the {110}<001> orientation in the rolling direction cannot be obtained, which is undesirable. On the other hand, if the final rolling reduction exceeds 95%, secondary recrystallization is likely to become unstable in the subsequent finish annealing step, which is not preferable. By setting the final cold rolling reduction within the above range, it is possible to obtain Goss nuclei with {110}<001> orientations having a high degree of accumulation in the rolling direction, and to suppress destabilization of secondary recrystallization. .

In addition, when cold rolling is performed twice or more with intermediate annealing, the first cold rolling is performed at a rolling reduction of about 5 to 50% at a temperature of 950 ° C to 1200 ° C for about 30 seconds to 30 minutes. It is preferable to carry out an intermediate annealing of

Here, the thickness of the cold-rolled steel sheet (thickness after cold rolling) usually corresponds to the thickness of the finally produced grain-oriented electrical steel sheet (the thickness of the tension-applying insulating coating). product plate thickness including). The product thickness of the grain-oriented electrical steel sheet is as mentioned above.

In order to further improve the magnetic properties during the cold rolling process as described above, it is possible to apply an aging treatment. During cold rolling, each thickness stage is passed through multiple passes, but at least one intermediate thickness stage gives the steel sheet a thermal effect of holding at a temperature range of 100 ° C or higher for a time of 1 minute or longer. is preferred. Due to such a thermal effect, it is possible to form a more excellent primary recrystallization texture in the subsequent decarburization annealing step, and by extension, in the subsequent finish annealing step, the {110} <001> orientation is aligned in the rolling direction. It becomes possible to sufficiently develop good secondary recrystallization.

<Decarburization annealing process>
The decarburization annealing step (step S107) is a step of performing decarburization annealing on the obtained cold-rolled steel sheet to obtain a decarburization-annealed steel sheet. In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, the decarburization property is improved by forming a specific Al-based oxide film in the steel sheet in the decarburization annealing process.

In the decarburization annealing step according to the present embodiment, in order to form an Al-based oxide film having a specific Al-based oxide, the decarburization annealing step according to the present embodiment is performed as shown in FIG. It consists of four steps: a heating step (step S131), an intermediate cooling step (step S133), a second heating step (step S135), and a soaking step (step S137).

In the first temperature raising step (step S131), the cold-rolled steel sheet obtained in the cold rolling step is heated from room temperature to a temperature T1 (° C.) that satisfies the following expression (101) and satisfies the following expression (102): In this step, the temperature is increased at a temperature increase rate H1 (°C/sec). Here, the oxygen potential P0 in the first temperature raising step satisfies the following formula (105).

In the intermediate cooling step (step S133), the cold-rolled steel sheet that has reached the temperature T1 (°C) through the first heating step is once cooled to the temperature T2 (°C) that satisfies the following formula (103): ) is cooled at a cooling rate C1 (°C/sec). Also, the oxygen potential P0 in the intermediate cooling step also satisfies the following formula (105).

The second temperature raising step (step S135) is a step of raising the temperature of the cold-rolled steel sheet that has undergone the intermediate cooling step from temperature T2 (°C).

The soaking step (step S137) is a step of annealing the cold-rolled steel sheet that has undergone the second heating step under predetermined conditions.

200 ≤ T1 ≤ 500 Expression (101)
100≦H1≦800 Expression (102)
T1-100 ≤ T2 ≤ T1-10 Expression (103)
−40≦C1<0 Expression (104)
0.0001≦P0≦0.5 Expression (105)

These steps will be described in detail below with reference to FIGS. 4 and 5. FIG.
In the explanatory diagrams of the heat treatment patterns shown in FIGS. 4 and 5, the scale intervals on the vertical axis and the horizontal axis are not accurate, and the heat treatment patterns shown in FIGS. 4 and 5 are only schematic. It is typical.

[First temperature rising step]
As mentioned earlier, one of the problems with grain-oriented electrical steel sheets is the improvement of decarburization. The present inventors focused on the temperature rise cycle in the decarburization annealing process, and conducted various verifications such as changing the conditions. As a result, it was found that shortening the residence time in the low temperature range of 200 to 500° C. is effective for improving the decarburization property when the temperature is raised from room temperature. If the residence time in the low temperature range of 200 to 500° C. is long, a Cr-based oxide film is formed, which is considered to cause deterioration of the decarburization property. However, while the Cr-based oxide film is a factor that inhibits decarburization, it is also an oxide film that has an effect of improving magnetic properties. There is Therefore, the present inventors have developed a specific Al-based oxide film (mainly _MgAlO4 ) as a substitute for Cr-based oxide film by controlling the oxygen potential in the temperature rising process from room temperature to a low temperature range of 200 to 500 °C. It was found that the formation of the component oxide film) was promoted. As a result, in the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, an Al-based oxide film is formed without forming a Cr-based oxide film, thereby improving decarburization.

Therefore, in the first temperature raising step (step S131) according to the present embodiment, as shown in FIG. The speed H1 is controlled to satisfy the above formula (102) and heated to the temperature T1. Here, when the temperature T1 is less than 200° C. or exceeds 500° C., a specific Al-based oxide (MgAl ₂ O ₄ ) cannot be generated. Further, when the heating rate H1 is less than 100° C./sec, the retention time in the temperature range where the Fe-based oxide film is likely to form increases, and the amount of specific Al-based oxide (MgAl ₂ O ₄ ) produced decreases. is not preferred because it reduces On the other hand, if the heating rate H1 exceeds 800° C./sec, overshoot may occur, which is not preferable.

The temperature T1 (°C) is preferably 200-400°C, more preferably 250-350°C. Also, the temperature increase rate H1 (°C/sec) is preferably 200 to 600°C/sec, more preferably 300 to 500°C/sec.

Further, in the first temperature raising step according to the present embodiment, the oxygen potential (the ratio of the water vapor partial pressure _PH2O and the hydrogen partial pressure _PH2 in the atmosphere, that is, _PH2O / _PH2 ) P0 is expressed by the above formula (105) controlled to satisfy This can promote the formation of a specific Al-based oxide (MgAl ₂ O ₄ ) that is advantageous for decarburization. If the value of oxygen potential P0 is less than 0.0001 or exceeds 0.5, the formation of Al-based oxide (MgAl ₂ O ₄ ) cannot be promoted. The oxygen potential P0 in the first heating step is preferably 0.0001 to 0.03, more preferably 0.0001 to 0.01.

[Mid-way cooling process]
In the intermediate cooling step (step S133) according to the present embodiment, Al-based oxides are produced which are advantageous for decarburization. Specifically, in the intermediate cooling step according to the present embodiment, the temperature is gradually cooled from T1°C to T2°C in order to secure a residence time in the temperature range of T1°C to T2°C. Here, the cooling rate C1 for slow cooling from the temperature T1 to the temperature T2 as shown in FIG. 4 is a cooling rate that satisfies the above formula (104). When the cooling rate C1 is less than −40° C./sec (in other words, when the absolute value of the cooling rate C1 is greater than 40), ensure a sufficient residence time in the temperature range of T1 to T2° C. Al-based oxide (MgAl ₂ O ₄ ), which is advantageous for decarburization, cannot be sufficiently generated. The cooling rate C1 is preferably -40 to -5°C/sec, more preferably -30 to -5°C/sec, still more preferably -15 to -10°C/sec. The temperature T2 is preferably (T1-75)° C. or higher and (T1-10)° C. or lower, and more preferably (T1-50)° C. or higher and (T1-10)° C. or lower.

Further, in the intermediate cooling step according to the present embodiment, the oxygen potential (the ratio of the water vapor partial pressure _PH2O and the hydrogen partial pressure _PH2 in the atmosphere, that is, _PH2O / _PH2 ) P0 satisfies the above formula (105). control to This can promote the formation of a specific Al-based oxide (MgAl ₂ O ₄ ) that is advantageous for decarburization. If the value of oxygen potential P0 is less than 0.0001 or exceeds 0.5, the formation of Al-based oxide (MgAl ₂ O ₄ ) cannot be promoted. The oxygen potential P0 in the intermediate cooling step is preferably 0.0001 to 0.1, more preferably 0.0001 to 0.05. It should be noted that the oxygen potential P0 in the first heating step and the oxygen potential P0 in the intermediate cooling step do not necessarily have to be the same value, and each value is preferably within the range of 0.0001 to 0.5. , may have different values.

[Second heating step]
The second temperature raising step (step S135) is a step of raising the temperature of the cold-rolled steel sheet that has undergone the intermediate cooling step from temperature T2 (°C). The second temperature raising step is not particularly limited, and the temperature raising conditions may be appropriately set. It is preferable to control to By heating the cold-rolled steel sheet at a heating rate S that satisfies the following formula (106), a specific Al-based oxide (MgAl ₂ O ₄ ) generated in the first heating step and the intermediate cooling step It is possible to quickly raise the temperature to the decarburization annealing temperature while leaving the The heating rate S is preferably 700-2000° C./sec, more preferably 1000-2000° C./sec. Although the detailed reason is still unknown, it has been confirmed that increasing the rate of temperature increase has the effect of improving the magnetism. This is probably because the recrystallized texture is well controlled for secondary recrystallization.

400≦S≦2000 Expression (106)

Further, in the second temperature raising step according to the present embodiment, the value of the oxygen potential in the temperature range from the temperature T2 to the decarburization annealing temperature is not particularly limited, and can be appropriately controlled to an appropriate value. It is possible. For example, the oxygen potential in the temperature range from the temperature T2 to the decarburization annealing temperature is preferably 0.0001 to 0.5, like the oxygen potential P0 in the first heating step. In particular, by setting the same atmosphere in the first temperature raising process and the second temperature raising process, there is an advantage that the atmosphere control in the furnace for each process becomes unnecessary, and a complicated equipment configuration can be avoided.

[Soaking process]
The soaking step according to the present embodiment is not particularly limited as long as it satisfies the conditions of the first temperature rising step, the midway cooling step and the second temperature rising step as described above. C. to 1000.degree. C. for 10 seconds to 10 minutes.

Also, the soaking step according to the present embodiment may have a plurality of steps. For example, as shown in FIG. 5, the soaking step may consist of two steps.

That is, as the heat treatment pattern is shown in FIG. 5, the soaking process according to the present embodiment is performed at a temperature T3 (° C.) of 700° C. or more and 900° C. or less in an atmosphere of a predetermined oxygen potential P2 for 10 seconds or more and 1000 seconds. A first soaking step held below, and a temperature T4 (° C.) that satisfies the following formula (108) in an atmosphere of an oxygen potential P3 that satisfies the following formula (107) following the first soaking process: and a second soaking step of holding for 5 seconds or more and 500 seconds or less. Hereinafter, such annealing treatment including a plurality of soaking steps is also referred to as multistage annealing.

P3<P2 Expression (107)
T3+50≦T4≦1000 Expression (108)

When performing such two-stage annealing, it is important to control the annealing temperature and holding time in the first and second stages.

From the viewpoint of improving decarburization, for example, in the first soaking step, the annealing temperature T3 (plate temperature) is preferably 700° C. or higher and 900° C. or lower. Also, the holding time at the annealing temperature T3 is preferably 10 seconds or more and 1000 seconds or less. If the annealing temperature T3 is less than 700° C., decarburization does not proceed and decarburization is defective, which is not preferable. On the other hand, if the annealing temperature T3 exceeds 900° C., the grain structure becomes coarse, which causes poor secondary recrystallization (poor magnetic properties), which is not preferable. Moreover, even if the holding time is less than 10 seconds, the decarburization does not progress and decarburization failure occurs, which is not preferable. A longer holding time itself does not pose a problem from the viewpoint of decarburization, but from the viewpoint of productivity, the holding time is preferably 1000 seconds or less. The annealing temperature T3 is more preferably 780°C or higher and 860°C or lower. Further, the holding time is more preferably 50 seconds or more and 300 seconds or less in the production of practical steel sheets.

From the viewpoint of ensuring the amount of Al-based oxides formed, it is preferable that the oxygen potential P2 during annealing in the first soaking step is higher than the oxygen potential P0 in the intermediate cooling step. Obtaining a sufficient oxygen potential allows the decarburization reaction to proceed sufficiently. However, if the oxygen potential P2 during annealing in the first soaking step is too large, the Al-based oxide (MgAl ₂ O ₄ ) may be replaced with Fe ₂ SiO ₄ , and Fe ₂ SiO ₄ is a magnetic deteriorate the characteristics. Therefore, it is preferable to control the oxygen potential P2 during annealing in the first soaking step within a range of 0.1 or more and 1.0 or less. The oxygen potential P2 during annealing in the first soaking step is more preferably 0.2 or more and 0.8 or less.

Even if the control as described above is performed, the generation of Fe ₂ SiO ₄ cannot be completely suppressed in the first soaking step. Therefore, in the second soaking step that follows the first soaking step, it is preferable to set the annealing temperature T4 (plate temperature) within the range defined by the above formula (108). By setting the annealing temperature T4 within the range defined by the above formula (108), even if Fe ₂ SiO ₄ is generated in the first soaking step, the generated Fe ₂ SiO ₄ is harmless to the film adhesion. This is because it is reduced to _SiO2 . MgAl ₂ O ₄ continues to remain without changing to another oxide in the second soaking step. A more preferable temperature range of the annealing temperature T4 is (T2+100)°C or higher and 1000°C or lower.

In addition, the holding time of the annealing temperature T4 in the second soaking step is 5 seconds or more and 500 seconds or less. If the holding time is less than 5 seconds, even if the annealing temperature is within the above range, the Fe ₂ SiO ₄ generated in the first soaking step may not be reduced to SiO ₂ . There is On the other hand, when the holding time exceeds 500 seconds, the grain growth of the steel sheet proceeds, possibly causing poor magnetism. The holding time of the annealing temperature T4 in the second soaking step is more preferably 10 seconds or more and 100 seconds or less.

In order to set the second soaking process to a reducing atmosphere, the oxygen potential P3 in the second soaking process is set smaller than the oxygen potential P2 in the first soaking process, as shown in the above formula (107). preferably. For example, better decarburization and magnetic properties can be obtained by controlling the oxygen potential P3 in the second soaking step to 0.00001 or more and 0.1 or less.

The time interval between the first soaking step and the second soaking step is not particularly specified, but it is preferably as short as possible, and the first soaking step and the second soaking step are continuous. It is preferable to carry out When the first soaking step and the second soaking step are performed continuously, two continuous annealing furnaces controlled to meet the conditions of each soaking step may be provided in succession.

<Finish annealing process>
Returning to FIG. 3 again, the finish annealing step in the method of manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be described.
The finish annealing step (step S109) is a step of applying a predetermined annealing separator to the decarburized annealed steel sheet obtained in the decarburization annealing step, and then performing finish annealing. Here, the finish annealing is generally performed for a long time while the steel sheet is coiled. Therefore, prior to final annealing, an annealing separator 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, for example, an annealing separator containing magnesia (MgO) as a main component can be used.

The heat treatment conditions in the finish annealing are not particularly limited, and known conditions can be appropriately adopted. For example, the finish annealing can be performed by holding in a temperature range of 1100° C. or higher and 1300° C. or lower for 10 hours or longer and 60 hours or shorter. Also, the atmosphere during the finish annealing can be, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen. Further, when a mixed atmosphere of nitrogen and hydrogen is used, it is preferable to set the oxygen potential of the atmosphere to 0.5 or less.

During the finish annealing as described above, secondary recrystallization is accumulated in the {110}<001> orientation, and coarse crystal grains with easy magnetization axes aligned in the rolling direction are generated. As a result, excellent magnetic properties are realized. At the same time, on the surface of the steel sheet, MgO in the annealing separator reacts with oxides generated by decarburization annealing to form a glass coating.

<Insulating film forming process>
The insulating coating forming step (step S111) is a step of forming tension-applying insulating coatings on both surfaces of the cold-rolled steel sheet after the finish annealing step. Here, the insulating film forming step is not particularly limited, and the following known insulating film treatment liquid may be used and the treatment liquid may be applied and dried by a known method. By further forming a tension-imparting insulating coating on the surface of the steel sheet, it is possible to further improve the magnetic properties of the grain-oriented electrical steel sheet.

In addition, the surface of the steel sheet on which the insulating coating is formed may be subjected to any pretreatment such as degreasing treatment with alkali or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, etc. before applying the treatment liquid. However, the surface may be as it is after finish annealing without performing these pretreatments.

Here, the insulating coating formed on the surface of the steel sheet is not particularly limited as long as it is used as an insulating coating for grain-oriented electrical steel sheets, and known insulating coatings can be used. As such an insulating coating, for example, a composite insulating coating containing an inorganic substance as a main component and an organic substance can be cited. Here, the composite insulating coating is mainly composed of, for example, at least one of inorganic substances such as metal chromate, metal phosphate, colloidal silica, Zr compound, Ti compound, etc., and fine organic resin particles are dispersed. It is an insulating film that has In particular, from the viewpoint of reducing the environmental impact during production, which has been in increasing demand in recent years, insulating coatings using metal phosphates, Zr or Ti coupling agents, or their carbonates or ammonium salts as starting materials. It is preferably used.

Further, flattening annealing for shape correction may be performed following the insulating coating forming process as described above. By flattening the steel sheet, the iron loss can be further reduced.

Through the steps described above, the grain-oriented electrical steel sheet according to the present embodiment can be manufactured. In the grain-oriented electrical steel sheet manufactured by the manufacturing method described above, MnS is generated in the glass coating. Furthermore, the manufacturing method described above does not particularly impair the magnetic properties as compared with the conventional manufacturing method. That is, the obtained grain-oriented electrical steel sheet has sufficiently excellent magnetic properties.

The method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment has been described in detail above.

Hereinafter, the technical content of the present invention will be further described with reference to examples and comparative examples. The conditions of the examples shown below are examples of conditions adopted for confirming the feasibility and effect 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.

(Experimental example 1)
Steel slabs containing the components shown in Table 1 below were produced, heated to 1350° C. and subjected to hot rolling to obtain hot-rolled steel sheets having a thickness of 2.3 mm. After that, the hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 900 to 1200° C., and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.19 to 0.22 mm. The cold-rolled steel sheet was decarburized and annealed, then coated with an annealing separator mainly composed of magnesia (MgO), and subjected to finish annealing at 1200°C to produce a finish-annealed steel sheet. In each steel piece, the balance other than the components listed in Table 1 is Fe and impurities.

Here, in the first heating step and the intermediate cooling step in the decarburization annealing step of this experimental example, the temperature T1 = 320 ° C., the heating rate H1 = 350 ° C./sec, the temperature T2 = 280 ° C., and the cooling rate C1 =-20°C/sec. Further, in the second heating step in the decarburization annealing step of this experimental example, the heating rate S was set to 500° C./sec. Further, the oxygen potential (P _H2O /P _H2 ) P0 in the first heating step in the decarburization annealing step is set to P0=0.01, and the oxygen potential (P _H2O /P _H2 ) in the intermediate cooling step in the decarburization annealing step. P0 was set to P0=0.04, and in the soaking step in the decarburization annealing step, a wet hydrogen atmosphere with an oxygen potential of 0.4 was used, and the annealing temperature was maintained at 830° C. for 150 seconds. All of these conditions are within the scope of the present invention.

After that, the surface of the steel sheet was coated with a coating solution for forming an insulating film mainly composed of a metal phosphate and baked to form a tension-imparting insulating film, thereby obtaining a grain-oriented electrical steel sheet.

Decarburization and magnetic properties (magnetic flux density) were evaluated for each grain-oriented electrical steel sheet.

<Magnetic flux density>
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. Those with B8 of 1.89 T or more were judged to have undergone secondary recrystallization and were accepted, and those with B8 of less than 1.89 T were judged to have not undergone secondary recrystallization and were judged to be unacceptable. In addition, the magnetic properties (magnetic flux density) of those that fractured in the hot rolling process or cold rolling process were not evaluated (indicated as "-" in Table 2 below). .

<Decarburization>
Decarburization was evaluated by measuring iron loss after the magnetic aging test. If the decarburization is insufficient, the iron loss should show a bad value after magnetic aging treatment. Each of the obtained grain-oriented electrical steel sheets was subjected to a magnetic aging test under the condition that it was held at 150° C. for 100 hours in a nitriding atmosphere, and then the iron loss W17/50 was measured by SST. Iron loss W17/50 represents the iron loss that occurs when the maximum magnetic flux density is 1.7 T and the frequency is 50 Hz. Evaluation was performed according to the following evaluation criteria according to the value of iron loss W17/50 obtained.

[Evaluation criteria]
EX (Excellent), particularly good effect observed: less than 0.85 VG (Very Good), good effect observed: 0.85 or more and less than 0.90 G (Good), relatively good effect observed 0.90 or more and less than 0.95 F (Fine), effect observed: 0.95 or more and less than 1.00 B (Bad), effect not observed: 1.00 or more

In addition to the measurement of the iron loss W17/50, the amount of residual carbon was also analyzed. The amount of residual carbon was measured with a carbon-sulfur simultaneous analyzer (Leco, CS600). The sample preparation method was performed according to JIS G 0417. At this time, those with a residual carbon amount of 20 ppm or less were judged as "A: Acceptable", and those with a residual carbon amount exceeding 20 ppm were judged as "B: Unacceptable".

The decarburization property was not evaluated for those that fractured during rolling and those that failed in secondary recrystallization (indicated by "-" in Table 2 below).

The results obtained are summarized in Table 2 below.

As is clear from Table 2 above, the invention steels B1 to B32 all exhibited excellent decarburization and magnetic properties. In addition, the invention steels B17 to B32 have a final plate thickness of 0.19 mm, which is a favorable condition for decarburization. They exhibited better decarburization properties than the invention steels B1 to B16. On the other hand, in the comparative steels b1 to b11 in which the content of any of the essential elements was outside the range of the present invention, sufficient magnetic properties were not obtained or breakage occurred during rolling.

(Experimental example 2)
A steel slab having the chemical composition shown in Table 1 was heated to 1350° C. and subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.3 mm. The hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 900 to 1200° C., and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.19 to 0.22 mm.

The above cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Table 3 below. The first heating step and the intermediate cooling step in the decarburization annealing step were performed under the conditions shown in Table 3. Further, in the second temperature rising step of the decarburization annealing step, S = 1500 ° C./s, and in the soaking step of the decarburization annealing step, the annealing temperature was 830 in a wet hydrogen atmosphere with oxygen potential = 0.4. C. for 150 seconds. After that, an annealing separator mainly composed of MgO was applied, and finish annealing was performed at 1200° C. to produce a finish-annealed sheet. Next, the surface of the finish-annealed steel sheet was coated with a coating solution for forming an insulating film mainly composed of a metal phosphate and baked to form a tension-imparting insulating film, thereby obtaining a grain-oriented electrical steel sheet.

Decarburization and magnetic properties (magnetic flux density) were evaluated for each grain-oriented electrical steel sheet. The evaluation content and evaluation method are the same as in Experimental Example 1. The results obtained are summarized in Table 3 below.

As is clear from Table 3 above, in the invention steels C9 to C24, the first heating step and the intermediate cooling step in the decarburization annealing step are controlled to preferable conditions within the scope of the present invention, and the invention steel C1 Compared to ~C8, the iron loss evaluation results after aging showed better "G". In the comparative steels c1 to c10, the conditions of the first heating step and the intermediate cooling step were outside the scope of the present invention, so the iron loss evaluation results after the aging treatment were all "B".

(Experimental example 3)
A steel slab having the chemical composition shown in Table 1 was heated to 1350° C. and subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.3 mm. The hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 900 to 1200° C., and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.19 to 0.22 mm.

The cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Table 4 below. In the soaking step in the decarburization annealing step, the annealing temperature was maintained at 810° C. for 160 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.5. After that, an annealing separator mainly composed of MgO was applied, and finish annealing was performed at 1200° C. to produce a finish-annealed sheet. Next, the surface of the finish-annealed steel sheet was coated with a coating solution for forming an insulating film mainly composed of a metal phosphate and baked to form a tension-imparting insulating film, thereby obtaining a grain-oriented electrical steel sheet.

Decarburization and magnetic properties (magnetic flux density) were evaluated for each grain-oriented electrical steel sheet. The evaluation content and evaluation method are the same as in Experimental Example 1. The results obtained are summarized in Table 4 below.

In invention steels D8 to D29, the first heating step and the intermediate cooling step in the decarburization annealing step are controlled to preferable conditions, and the second heating step in the decarburization annealing step is controlled within the scope of the present invention. Therefore, compared with the invention steels D1 to D7, good magnetic properties were exhibited. In particular, in D14 to D29, the first heating step and the intermediate cooling step in the decarburization annealing step were controlled to more favorable conditions, so the magnetic properties were "EX", showing very good results. In the invention steels D31 to D33, although the first heating step and the intermediate cooling step in the decarburization annealing step are controlled within a preferable range, from the viewpoint of the second heating step in the decarburization annealing step, the iron after aging treatment The loss evaluation result remained at "G".

(Experimental example 4)
A steel slab having the chemical composition shown in Table 1 was heated to 1350° C. and subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.3 mm. The hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 900 to 1200° C., and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.19 to 0.22 mm. The above cold-rolled steel sheet was decarburized and annealed, then coated with an annealing separator mainly composed of MgO, and subjected to finish annealing at 1200° C. to produce a finish-annealed steel sheet.

Here, in the first heating step and the intermediate cooling step in the decarburization annealing step of this experimental example, the temperature T1 = 320 ° C., the heating rate H1 = 340 ° C./sec, the temperature T2 = 280 ° C., and the cooling rate C1 = -20°C/sec and oxygen potential P0 = 0.01. All of these conditions are within the scope of the present invention. Table 5 shows various conditions of the temperature rising step and the soaking step in the decarburization annealing step.

Next, the surface of the finish-annealed steel sheet was coated with a coating solution for forming an insulating film mainly composed of a metal phosphate and baked to form a tension-imparting insulating film, thereby obtaining a grain-oriented electrical steel sheet.

Decarburization and magnetic properties (magnetic flux density) were evaluated for each grain-oriented electrical steel sheet. The evaluation content and evaluation method are the same as in Experimental Example 1. The results obtained are summarized in Table 5 below.

As is clear from Table 5 above, invented steels E11 to E18 did not have more favorable conditions for the second heating step of the decarburization annealing step, but the first heating step and the midway cooling step were within the scope of the present invention. Therefore, the iron loss evaluation after aging was "G", which was a good result. In the invention steels E19 to E22, both the conditions of the second heating step in the decarburization annealing step and the two-stage annealing performed in the soaking step of the decarburization annealing step are controlled within a preferable range or a more preferable range. Therefore, the iron loss evaluation after aging was "EX", indicating particularly good magnetic properties. In invention steels E23 to E26, the two-stage annealing conditions in the soaking process are all controlled within a preferable range, but from the viewpoint of the second heating process in the decarburization annealing process, the iron loss evaluation after aging is " I stayed at VG.

(Experimental example 5)
A steel slab having the chemical composition shown in Table 1 was heated to 1350° C. and subjected to hot rolling to obtain a hot-rolled steel sheet having a thickness of 2.3 mm. The hot-rolled steel sheet was subjected to hot-rolled sheet annealing at 900 to 1200° C., and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.19 to 0.22 mm. The above cold-rolled steel sheet was decarburized and annealed, then coated with an annealing separator mainly composed of MgO, and subjected to finish annealing at 1200° C. to produce a finish-annealed steel sheet.

Here, in the first heating step and the intermediate cooling step in the decarburization annealing step of this experimental example, the temperature T1 = 330 ° C., the heating rate H1 = 370 ° C./sec, the temperature T2 = 300 ° C., and the cooling rate C1 = -20°C/sec and oxygen potential P0 = 0.005. All of these conditions are within the scope of the present invention. Table 6 shows the conditions of the second heating step and the soaking step in the decarburization annealing step.

Next, the surface of the finish-annealed steel sheet was coated with a coating solution for forming an insulating film mainly composed of a metal phosphate and baked to form a tension-imparting insulating film, thereby obtaining a grain-oriented electrical steel sheet.

Decarburization and magnetic properties (magnetic flux density) were evaluated for each grain-oriented electrical steel sheet. The evaluation content and evaluation method are the same as in Experimental Example 1. The results obtained are summarized in Table 6 below.

As is clear from Table 6 above, the invention steels F2, F7, F12, F17, F22, F27, F32, F37, and F42 were subjected to two-step annealing in the soaking step in the decarburization annealing step. Although the control range was within the preferred invention range, the iron loss evaluation after aging remained at "G" from the viewpoint of the second heating step in the decarburization annealing step.

Inventive steels F4, F9, F14, F19, F24, F29, F34, F39, and F44 are within the preferred range of the present invention with respect to the second heating step of the decarburization annealing step. However, the two-stage annealing was not performed in the soaking process, and the iron loss evaluation after aging remained at "G".

In the invention steels F1, F6, F11, F16, F21, F26, F31, F36, and F41, the intermediate cooling conditions (H1, T2, C1) in the decarburization annealing step are controlled within a preferable range, but the decarburization annealing Regarding the second heating step in the process, the two-step annealing was not performed in the soaking step, which is not within a preferable range. However, since the final sheet thickness of invention steels F11, F26, and F41 was 0.19 mm, compared with the iron loss evaluation "F" after aging in invention steels F1, F6, F16, F21, F31, and F36, A good evaluation result of "G" was obtained.

In the invention steels F3, F5, F8, F10, F13, F15, F18, F20, F23, F25, F28, F30, F33, F35, F38, F40, F43, and F45, the second heating step in the decarburization annealing step is , is within the preferred range of the present invention, and in the subsequent soaking step, two-stage annealing is performed, so compared to other invention steels, good results are obtained in the iron loss evaluation after aging. was taken. In particular, in invention steels F5, F10, F15, F20, F25, F30, F35, F40, and F45, the second heating step in the decarburization annealing step was controlled within a more preferable range, so the iron loss evaluation after aging was It was very good with "EX".

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, 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.

REFERENCE SIGNS LIST 10 Grain-oriented electrical steel sheet 11 Base material steel sheet 13 Glass coating 15 Tensioning insulating coating

Claims (6)

in % by mass,
C: 0.01-0.20%
Si: 2.5-4.0%
Sol. Al: 0.010 to 0.07%
Mn: 0.010-0.50 %
Cr: 0.01-0.50%
N: 0.020 % or less S: 0.005 to 0.080%
Se: 0-0.080%
Sb: 0-0.50%
Bi: 0-0.02%
Sn: 0-0.50%
Cu: 0-1.0%
A hot rolling step of heating a steel billet containing Fe and impurities and then hot rolling to obtain a hot rolled steel sheet;
A hot-rolled sheet annealing step of annealing the hot-rolled steel sheet to obtain a hot-rolled annealed steel sheet;
A cold-rolling step of obtaining a cold-rolled steel sheet by subjecting the hot-rolled and annealed steel sheet to one cold-rolling or a plurality of cold-rollings with intermediate annealing;
a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization-annealed steel sheet;
A finish annealing step of applying an annealing separator to the decarburized annealed steel sheet and then performing finish annealing;
an insulating coating forming step of forming an insulating coating on the surface of the steel sheet after finish annealing;
including
The decarburization annealing step is
a first heating step of raising the temperature of the cold-rolled steel sheet from room temperature to a temperature T1 (°C) that satisfies the following formula (1) at a heating rate H1 (°C/sec) that satisfies the following formula (2): ,
The cold-rolled steel sheet that has reached the temperature T1 (°C) is once cooled to a temperature T2 (°C) that satisfies the following formula (3) at a cooling rate C1 (°C/sec) that satisfies the following formula (4): A cooling process in the middle of
A second temperature raising step of raising the temperature of the cold-rolled steel sheet from the temperature T2 (° C.);
a soaking step of annealing the cold-rolled steel sheet after the temperature rise;
and
A method for producing a grain-oriented electrical steel sheet, wherein the oxygen potential P0 in the first heating step and the intermediate cooling step satisfies the following formula (5).
200 ≤ T1 ≤ 500 Expression (1)
100≦H1≦800 Expression (2)
T1-100 ≤ T2 ≤ T1-10 Expression (3)
−40≦C1<0 Expression (4)
0.0001 0 ≤ P0 ≤ 0.5 Expression (5) 2. The method according to claim 1, wherein in the second temperature raising step in the decarburization annealing step, a temperature elevation rate S (° C./sec) from the temperature T2 to the decarburization annealing temperature satisfies the following formula (6): A method for producing a grain-oriented electrical steel sheet.
400≦S≦2000 Expression (6) The soaking step in the decarburization annealing step is
a first soaking step of holding at a temperature T3 (° 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 ;
Following the first soaking step, in an atmosphere of oxygen potential P3 that satisfies the following formula (7), the temperature T4 (° C.) that satisfies the following formula (8) is maintained for 5 seconds or more and 500 seconds or less. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, comprising a second soaking step.
P3<P2 Expression (7)
T3+50≦T4≦1000 Expression (8) The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 3, wherein the grain-oriented electrical steel sheet has a thickness of 0.17 mm or more and less than 0.22 mm. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the steel billet contains 0.001 to 0.020% by mass of Bi. The steel billet according to any one of claims 1 to 5, containing at least one of 0.005 to 0.500% by mass of Sn and 0.01 to 1.00% by mass of Cu. A method for producing a grain-oriented electrical steel sheet.

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