JP2019167567A - Production method of directional magnetic steel sheet - Google Patents

Abstract

An object of the present invention is to obtain a higher magnetic flux density in a grain-oriented electrical steel sheet containing Cr without impairing the decarburization property. In the method for manufacturing a grain-oriented electrical steel sheet according to the present invention, the decarburizing annealing step is performed by changing a cold-rolled steel sheet from room temperature to a temperature T1 (° C) that satisfies the equation (1). A first temperature raising step of raising the temperature at a temperature raising rate H1 (° C./second) and a cold-rolled steel sheet having reached the temperature T1 (° C.) are temporarily reduced to a temperature T2 (° C.) satisfying the formula (3). An intermediate cooling step of cooling at a cooling rate C1 (° C./sec) satisfying the formula (4), a second temperature raising step of raising the temperature of the cold-rolled steel sheet from a temperature T2 (° C.), and cold rolling after the temperature is raised. And a soaking step for annealing the steel sheet, so that the oxygen potential P0 in the first heating step and the intermediate cooling step satisfies the equation (5). [Selection diagram] FIG.

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet.

  A grain-oriented electrical steel sheet (also referred to as “unidirectional electrical steel sheet”) is composed of crystal grains that are highly oriented and integrated in {110} <001> orientation (hereinafter also referred to as “Goss orientation”). It is a steel plate containing 7% by mass or less. Oriented electrical steel sheets are mainly used as iron core materials for transformers. When a grain-oriented electrical steel sheet is used as a core material of a transformer (that is, when a grain-oriented electrical steel sheet is laminated as an iron core), it is essential to ensure insulation between layers (between laminated steel sheets). Therefore, from the viewpoint of ensuring insulation, it is necessary to form a primary coating (glass coating) and a secondary coating (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 tension-imparting insulating coating are as follows. First, a steel piece containing 7% by mass or less of silicon (Si) is hot-rolled, and then the steel sheet is finished to a predetermined thickness after cold rolling by one or two cold rolling sandwiching intermediate annealing. Thereafter, decarburization and primary recrystallization treatment are performed by annealing (decarburization annealing) in a wet hydrogen atmosphere to obtain a decarburized annealing plate. In such decarburization annealing, oxide films (Fe ₂ SiO ₄ and SiO ₂ ) are formed on the steel sheet surface. Subsequently, an annealing separator mainly composed of MgO is applied to the decarburized annealing plate and dried, and then finish annealing is performed. By such finish annealing, secondary recrystallization occurs, and the grain structure of the steel sheet accumulates in the {110} <001> orientation. At the same time, on the steel sheet surface, MgO in the annealing separator and the oxide film (Fe ₂ SiO ₄ and SiO ₂ ) formed on the steel sheet surface during decarburization annealing react to form a glass film. The tension-imparting insulating coating is formed by applying and baking a coating solution mainly composed of phosphate on the surface of the finish annealing plate (that is, the surface of the glass coating).

Here, there exists improvement of decarburization as one of the manufacture subjects of a grain-oriented electrical steel sheet.
For example, in the following Patent Document 1, a decarburization improvement technique by increasing the oxygen potential is proposed. However, only increasing the oxygen potential improves decarburization, but produces a large amount of Fe oxide. Fe oxide is a substance that should be avoided because it degrades secondary recrystallization and eventually leads to magnetic degradation.

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

Japanese Patent No. 3392669 Japanese Patent Application Laid-Open No. 07-278668 JP 2002-173715 A JP 2003-003213 A JP 2011-174138 A International Publication No. 2016/056501 International Publication No. 2014/049770 Patent No. 6103281

Here, the carbon contained in the grain-oriented electrical steel sheet has an effect of improving the magnetic flux density by improving the secondary recrystallization, but when decarburization is insufficient, Fe ₃ C (cementite) is steel. There is a possibility that the magnetic properties will deteriorate due to precipitation. In particular, grain oriented electrical steel sheets may contain Cr in an attempt to improve magnetic properties, but in such a case, there has been a problem that decarburization performance is reduced. While the methods proposed in Patent Documents 2 to 8 described above contribute to secondary recrystallization improvement by controlling oxygen potential and heating rate, there is no mention of decarburization improvement.

  This invention is made | formed in view of the said problem, The place made into the objective of this invention is to obtain a higher magnetic flux density, without impairing decarburization property, in the grain-oriented electrical steel sheet containing Cr. An object is to provide a method for producing a grain-oriented electrical steel sheet.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the decrease in decarburization is due to Cr forming a Cr oxide film. However, the formation of a Cr oxide film cannot be avoided under the decarburization annealing conditions for the purpose of improving secondary recrystallization, and as a result, it is difficult to achieve both the magnetic flux density and the decarburization property. Therefore, as a result of further studies, the present inventors have found a decarburization annealing cycle that avoids the formation of a Cr oxide film, and have completed the present invention.
The gist of the present invention completed based on the above findings is as follows.

[1] By mass%, C: 0.01 to 0.20%, Si: 2.5 to 4.0%, Sol. Al: 0.01 to 0.07%, Mn: 0.01 to 0.50%, Cr: 0.01 to 0.50%, N: 0.02% or less, S: 0.005 to 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%, A hot-rolling step of obtaining a hot-rolled steel sheet by hot rolling after heating the steel slab comprising the balance and Fe and impurities, and a hot-rolled sheet annealing step of obtaining the hot-rolled annealed steel sheet by annealing the hot-rolled steel plate The cold-rolled steel sheet is subjected to a single cold-rolling process or a plurality of cold-rolling processes including intermediate annealing to obtain a cold-rolled steel sheet, and the cold-rolled steel sheet is removed. A decarburization annealing step for obtaining a decarburized and annealed steel sheet by performing carbon annealing, and a finish annealing process for applying a final annealing after applying an annealing separator to the decarburized and annealed steel sheet. And an insulating film forming step of forming an insulating film on the surface of the steel sheet after the finish annealing, and the decarburizing annealing step is performed at a temperature T1 (° C.) that satisfies the following formula (1) from room temperature to the cold rolled steel sheet. ) Until the temperature rising rate H1 (° C./second) satisfying the following formula (2) and the cold-rolled steel sheet reaching the temperature T1 (° C.) From the temperature T2 (° C.) to the temperature T2 (° C.) satisfying (3), the cooling step during cooling at the cooling rate C1 (° C./sec) satisfying the following formula (4) A second temperature raising step for raising the temperature, and a soaking step for annealing the cold-rolled steel sheet after the temperature raising, and the oxygen potential P0 in the first temperature raising step and the midway cooling step is as follows: The manufacturing method of a grain-oriented electrical steel sheet which satisfies Formula (5).
200 ≦ T1 ≦ 500 (1)
100 ≦ H1 ≦ 800 (2)
T1-100 ≦ T2 ≦ T1-10 (3)
−40 ≦ C1 <0 Formula (4)
0.0001 ≦ P0 ≦ 0.5 (5)
[2] In the second temperature raising step in the decarburization annealing step, the rate of temperature rise S from the temperature T2 to the decarburization annealing temperature satisfies the following formula (6), the direction according to [1] Method for producing an electrical steel sheet.
400 ≦ S ≦ 2000 (6)
[3] The soaking step in the decarburizing annealing step is a first soaking step in which the temperature is maintained at a temperature T3 (° C.) of 700 ° C. to 900 ° C. for 10 seconds to 1000 seconds in an atmosphere of a predetermined oxygen potential P2. And at the temperature T4 (° C.) satisfying the following formula (8) in the atmosphere of the oxygen potential P3 that satisfies the following formula (7), and is performed for 5 seconds to 500 seconds. The manufacturing method of the grain-oriented electrical steel sheet according to [1] or [2], including a second soaking step that is held below.
P3 <P2 Formula (7)
T3 + 50 ≦ T4 ≦ 1000 (8)
[4] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [3], wherein a thickness of the grain-oriented electrical steel sheet is 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 piece contains 0.001 to 0.020 mass% of Bi.
[6] Any of [1] to [5], wherein the steel slab contains at least one of 0.005 to 0.500% by mass of Sn and 0.01 to 1.00% by mass of Cu. The manufacturing method of the grain-oriented electrical steel sheet as described in any one.

  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 decarburization properties.

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 flowchart which showed an example of the flow of the manufacturing method of the grain-oriented electrical steel plate 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.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(Background to the present invention)
In the following, first, prior to describing a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention, the knowledge obtained by the present inventors intensive study and the background to the present invention based on such knowledge. Is briefly described.

  As mentioned earlier, one of the problems in manufacturing grain-oriented electrical steel sheets is to improve decarburization. The present inventors paid attention to the temperature increase cycle in the decarburization annealing process, and conducted investigations such as condition changes. As a result, in the temperature rise from room temperature to a temperature range of 200 to 500 ° C., when the residence time in the temperature range is long, a Cr-based oxide film is generated and causes decarburization deterioration, and It has been found that shortening the residence time in such a temperature range is effective in improving the decarburization property. However, since the Cr-based oxide film is a decarburization inhibiting factor, it has a secondary recrystallization improvement effect. Therefore, even if the decarburization is improved based on the above idea, the magnetic flux density is lowered. there's a possibility that. Therefore, the inventors of the present invention are important to generate an oxide film other than the Cr-based oxide film as an alternative to the Cr-based oxide film, and an Al-based oxide film as an oxide film other than the Cr-based oxide film The idea was that it was useful to use

As a result of further studies based on such an idea, the inventors of the present invention promote the generation of an Al oxide film by controlling the oxygen potential in the temperature raising process from room temperature to a temperature range of 200 to 500 ° C. I found that it was possible. Also, Al oxide film formed in decarburization annealing step, after the finish annealing step follows step, was found to remain in the glass in the coating as MgAl ₂ O _4.

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

<Main configuration of grain-oriented electrical steel sheet>
First, the main structure 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 the present embodiment.

  As schematically shown in FIG. 1A, the grain-oriented electrical steel sheet 10 according to the present embodiment has a base steel plate 11, a glass coating 13 formed on the surface of the base steel plate 11, and a surface of the glass coating 13. And a tension-imparting insulating coating 15 which is an example of the formed insulating coating. The glass coating 13 and the tension-imparting insulating coating 15 may be formed on at least one surface of the base steel plate 11, but usually, as schematically shown in FIG. Formed on both sides.

  Hereinafter, the grain-oriented electrical steel sheet 10 according to the present embodiment will be described focusing on the characteristic configuration. It should be noted that in the following description, detailed descriptions of known configurations and some configurations that can be implemented by those skilled in the art may be omitted.

[About the base steel plate 11]
The base steel plate 11 exhibits excellent magnetic properties by containing chemical components as described in detail below. The chemical components of the base steel plate 11 will be described in detail later.

[Glass coating 13]
The glass coating 13 is an inorganic coating mainly composed of magnesium silicate and located on the surface of the base steel plate 11. In general, the glass coating is formed by a reaction between an annealing separator containing magnesia (MgO) applied to the surface of the base steel plate and a component on the surface of the base steel plate in the finish annealing. It has a composition derived from the components of the agent and the base steel plate. 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, a specific Al-based oxide (MgAl ₂ O ₄ ) is present in the glass coating 13 in place of the Cr-based oxide. Even if it is contained, it becomes possible to express excellent decarburization properties.

In addition, the production amount of MgAl ₂ O ₄ with respect to the adhesion amount of the glass coating can be confirmed from X-ray diffraction (XRD) analysis of the glass coating surface. Here, XRD is a crystal structure analysis technique for specifying 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 database of crystal structure called PDF (Powder Diffraction File, for example, JCPDS card) can be used for collation between the diffraction peak position and the substance.

[Tension imparting insulating coating 15]
The tension-imparting insulating coating 15 is located on the surface of the glass coating 13, reduces the eddy current loss by imparting electrical insulation to the directional electrical steel sheet 10, and reduces the iron loss of the directional electrical steel sheet 10. Improve. Moreover, the tension | tensile_strength imparting insulating film 15 implement | achieves various characteristics, such as corrosion resistance, heat resistance, and slipperiness other than the above electrical insulation.

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

  The tension-imparting insulating coating 15 is formed, for example, by applying a coating liquid mainly composed of metal phosphate and silica on the surface of the glass coating 13 and baking it.

<About the thickness of the grain-oriented electrical steel sheet 10>
The product plate 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 may be, for example, 0.17 mm or more and 0.35 mm or less. In the present embodiment, the effect is remarkable when the thickness after cold rolling is less than 0.22 mm (ie, a thin material), and the decarburization is further improved. The plate thickness after cold rolling is more preferably 0.17 mm or more and 0.20 mm or less, for example.

<About the chemical composition of the base material steel plate 11>
Next, the chemical components of the base steel plate 11 of the grain-oriented electrical steel plate 10 according to this embodiment will be described in detail. Hereinafter, unless otherwise specified, the notation “%” represents “mass%”.

  The chemical composition of the base steel sheet 11 included in the grain-oriented electrical steel sheet 10 according to the present embodiment is mass%, C: 0.01 to 0.20%, Si: 2.5 to 4.0%, Sol. Al: 0.01 to 0.07%, Mn: 0.01 to 0.50%, Cr: 0.01 to 0.50%, N: 0.02% or less, S: 0.005 to 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 balance consists of Fe and impurities.

[C: 0.01% or more and 0.20% or less]
C (carbon) is an element showing an effect of improving the magnetic flux density, but when its content exceeds 0.20%, the steel undergoes phase transformation in secondary recrystallization annealing (that is, finish annealing), 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 this embodiment, the C content is set to 0.20% or less. Since the lower the C content, the better the iron loss reduction. From the viewpoint of reducing the iron loss, the C content is preferably 0.15% or less, more preferably 0.10% or less. On the other hand, from the viewpoint of magnetic flux density, the C content is 0.01% or more. The content of C is preferably 0.04% or more, more preferably 0.06% or more.

[Si: 2.5% to 4.0%]
Si (silicon) is an extremely effective element for increasing the electric resistance (specific resistance) of steel and reducing eddy current loss that constitutes a part of iron loss. When the Si content is less than 2.5%, the steel undergoes phase transformation in the secondary recrystallization annealing, and the secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics are obtained. Rena. Therefore, in the base material steel plate 11 according to the present embodiment, the Si content is set to 2.5% or more. The content of Si is preferably 3.0% or more, more preferably 3.2% or more. On the other hand, when the Si content exceeds 4.0%, the steel plate becomes brittle, and the plate-passability in the manufacturing process is significantly deteriorated. Therefore, in the base material steel plate 11 according to the present embodiment, the Si content is 4.0% or less. The content of Si is preferably 3.8% or less, and 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 constituent element of a major inhibitor among compounds called inhibitors that influence secondary recrystallization in grain-oriented electrical steel sheets. In the base steel sheet 11 according to the present embodiment, It is an essential element from the viewpoint of subsequent recrystallization. sol. When the Al content is less than 0.01%, AlN functioning as an inhibitor is not sufficiently generated, secondary recrystallization is insufficient, and iron loss characteristics are not improved. Therefore, in the base material steel plate 11 according to the present embodiment, sol. The Al content is 0.01% or more. sol. The Al content is preferably 0.015% or more, and more preferably 0.020% or more. On the other hand, sol. When 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 Al content is 0.07% or less. sol. The Al content is preferably 0.05% or less, and more preferably 0.030% or less.

[Mn: 0.01% to 0.50%]
Mn (manganese) is an important element that forms MnS, which is one of the main inhibitors. When the Mn content is less than 0.01%, the absolute amount of MnS necessary for causing secondary recrystallization is insufficient. Therefore, in the base material steel plate 11 according to the present embodiment, the Mn content is set to 0.01% or more. The Mn content is preferably 0.03% or more, and more preferably 0.06% or more. On the other hand, when the Mn content exceeds 0.50%, the steel undergoes phase transformation in the secondary recrystallization annealing, the secondary recrystallization does not proceed sufficiently, and good magnetic flux density and iron loss characteristics are obtained. I can't. Therefore, in the base material steel plate 11 according to the present embodiment, the Mn content 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% to 0.50%]
Cr is an element that improves the magnetic properties and improves the adhesion of the glass coating. When the Cr content is less than 0.01%, it is impossible to obtain the effect of improving the magnetic properties as described above and the effect of improving the adhesion of the glass coating. Therefore, in the base material steel plate 11 according to the present embodiment, the Cr content is 0.01% or more. The content of Cr is preferably 0.03% or more, and more preferably 0.05% or more. On the other hand, when the content of Cr exceeds 0.50%, the decarburization performance decreases even when the manufacturing method according to this embodiment is applied. Therefore, in the base material steel plate 11 according to the present embodiment, the Cr content is 0.50% or less. The content of Cr is preferably 0.20% or less, and 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. When the N content exceeds 0.02%, blisters (voids) are generated in the steel sheet during cold rolling, and the strength of the steel sheet is increased, and the plate-passability during production is deteriorated. 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 used as an inhibitor, the lower limit of the N content may include 0%. However, since the detection limit value of chemical analysis is 0.0001%, the practical lower limit of the N content in a practical steel sheet is 0.0001%. On the other hand, in order to form AlN that functions as an inhibitor by combining with Al, the N content is preferably 0.001% or more, and 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 Mn. When the S content is less than 0.005%, a sufficient inhibitor effect cannot be obtained. Therefore, in the base material steel plate 11 according to the present embodiment, the S content is set to 0.005% or more. The S content is preferably 0.010% or more, and more preferably 0.020% or more. On the other hand, if the S content exceeds 0.080%, it becomes a cause of hot brittleness and hot rolling becomes 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, and more preferably 0.030% or less.

[Bi: 0% to 0.02%]
Since Bi (bismuth) is an arbitrary element in the base steel plate 11 according to this embodiment, the lower limit of the content thereof is 0%. On the other hand, by containing Bi in place of a part of the remaining Fe, as with Sn and Cu described later, it contributes to promoting the improvement of glass film adhesion, and the properties of the grain-oriented electrical steel sheet according to this embodiment are improved. Improve. In order to obtain the effect of promoting the improvement of the glass film adhesion, the Bi content is preferably 0.001% or more. On the other hand, if the Bi content exceeds 0.02%, the plate-passability during cold rolling deteriorates. Therefore, the Bi content is 0.02% or less. The Bi content is preferably 0.01% or less, and more preferably 0.007% or less.

  In the base material steel plate 11 according to this embodiment, in order to improve the characteristics of the grain-oriented electrical steel plate according to this embodiment, in addition to the various elements described above, Se, Sb, You may further contain at least 1 type of Sn and Cu. Since Se, Sb, Sn, and Cu are arbitrary elements in the base material steel plate 11 according to this embodiment, the lower limit of the content thereof is 0%.

[Se: 0% to 0.080%]
Se (selenium) is an element having an effect of improving magnetic properties, and therefore can be selectively contained. However, if it exceeds 0.080%, the glass film is remarkably deteriorated. Therefore, the upper limit of the Se content is 0.080%. Preferably it is 0.050% or less. More preferably, it is 0.020% or less. Considering the compatibility between magnetism and film adhesion, it is preferably 0.003% or more, more preferably 0.006% or more. In addition, since Se is an arbitrary element in the base material steel plate 11 according to the present embodiment, the lower limit value of the content thereof is 0%. However, when Se is selectively contained, the magnetic improvement effect is good. Therefore, the content is preferably 0.001% or more.

[Sb: 0% to 0.50%]
Sb (antimony), like Se, is an element having a magnetic improvement effect, and therefore can be selectively contained. However, if Sb is contained in excess of 0.50%, the glass coating is significantly deteriorated. Therefore, the upper limit of the Sb content is set to 0.50%. The Sb content is preferably 0.30% or less, and more preferably 0.10% or less. In consideration of compatibility between magnetism and film adhesion, the Sb content is preferably 0.01% or more, more preferably 0.02% or more. In addition, since Sb is an arbitrary element in the base material steel plate 11 according to the present embodiment, the lower limit value of the content is 0%. However, when Sb is selectively contained, the magnetic improvement effect is good. Therefore, the content is preferably 0.005% or more.

[Sn: 0% to 0.50%]
Sn (tin) is an element that contributes to magnetic improvement through primary crystal structure control. In order to obtain a 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%, 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 0.50% or less. The Sn content is preferably 0.30% or less, more preferably 0.15% or less.

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

  The balance of the chemical components of the base steel plate 11 according to the present embodiment is Fe and impurities. However, for the purpose of improving the characteristics required of structural members such as improvement of magnetic characteristics, strength, corrosion resistance, fatigue characteristics, etc., improvement of castability and sheeting property, and productivity by using scraps, the base steel plate 11 is In place of part of the remaining Fe, 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 ones to be lost. In addition, since these elements are elements which can be included arbitrarily, the lower limit of the total content of these elements is 0%.

  Further, the impurities are present in the base steel plate 11 regardless of the intention of addition, and are components that do not need to exist originally in the obtained grain-oriented electrical steel plate. The term “impurities” is a concept that includes impurities mixed from ores, scraps, or production environments as raw materials when industrially producing steel materials. Such impurities may be included in an amount that does not adversely affect the effects of the present invention.

  Heretofore, the chemical components of the base steel plate 11 according to the present embodiment have been described in detail.

  In addition, the various magnetic characteristics which the grain-oriented electrical steel sheet which concerns on this embodiment show are based on the Epstein method prescribed | regulated to JISC2550, and the single plate magnetic property measuring method (Single Sheet Tester: SST) prescribed | regulated to JISC2556. And can be measured.

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

<Overall flow of manufacturing method of grain-oriented electrical steel sheet>
Below, the general flow of the manufacturing method of the grain-oriented electrical steel sheet which concerns on this embodiment is demonstrated, referring FIG.
The overall flow of the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment is as follows.
First, after hot-rolling the steel piece (slab) which has the above chemical components, it anneals and obtains a hot rolling annealing process. Next, after the pickling, the obtained hot-rolled annealed steel sheet is cold-rolled to the final sheet thickness by performing cold rolling once or two times with intermediate annealing. obtain. Then, about the obtained cold-rolled steel plate, decarburization and primary recrystallization are performed by annealing (decarburization annealing) in a wet hydrogen atmosphere to obtain a decarburized annealed steel plate. In such decarburization annealing, a predetermined Mn-based oxide film is formed on the surface of the steel plate. Subsequently, an annealing separator mainly composed of MgO is applied to the surface of the decarburized and annealed steel sheet and then dried to perform finish annealing. By such finish annealing, secondary recrystallization occurs, and the grain structure of the steel sheet accumulates in the {110} <001> orientation. At the same time, on the steel sheet surface, MgO in the annealing separator and the oxide film (Fe ₂ SiO ₄ and SiO ₂ ) formed on the steel sheet surface during decarburization annealing react to form a glass film. After the finish annealed plate is powdered by washing or pickling, a tension-imparting insulating coating is formed by applying and baking a coating solution mainly composed of phosphate.

  That is, in the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, as shown in FIG. 2, a steel slab having the above chemical components is hot-rolled at a predetermined temperature to obtain a hot-rolled steel sheet. For the hot rolling process (step S101), the hot rolled sheet annealing process (step S103) to obtain the hot rolled annealed steel sheet by annealing the obtained hot rolled steel sheet, and the obtained hot rolled annealed steel sheet once. Cold rolling, or a plurality of cold rolling sandwiching intermediate annealing, cold rolling step (step S105) to obtain a cold-rolled steel sheet, and decarburization annealing to the obtained cold-rolled steel sheet, A decarburization annealing step (step S107) for obtaining a decarburized annealing steel plate, a finish annealing step (step S109) for applying a final annealing after applying an annealing separator to the obtained decarburized annealing steel plate, and after the finish annealing Insulating coating on steel plate surface (more specifically, with tension Comprising an insulating film forming step of forming a sexual insulating film) (step S 111), the.

  Hereinafter, these steps will be described in detail. In the following description, when any condition in each step is not described, each step can be performed by appropriately applying known conditions.

<Hot rolling process>
The hot rolling step (step S101) is a step of hot rolling a steel slab having a predetermined chemical component (for example, a steel ingot such as a slab) to form a hot rolled steel plate. The component of the billet is the same as the component of the base steel plate 11 as described above. In such a hot rolling process, a steel piece of silicon steel having the above chemical components is first heat-treated. Here, the heating temperature is preferably in the range of 1100 to 1450 ° C. The heating temperature is more preferably 1300 ° C. or higher and 1400 ° C. or lower. Next, the steel slab heated to the above temperature is processed into a hot-rolled steel sheet by subsequent hot rolling. It is preferable that the plate | board thickness of the processed hot-rolled steel plate exists in the range of 2.0 mm or more and 3.0 mm or less, for example.

<Hot rolled sheet annealing process>
A hot-rolled sheet annealing process (step S103) is a process which anneals the hot-rolled steel plate manufactured through the hot rolling process, and makes it a hot-rolled annealed steel sheet. By performing such annealing treatment, recrystallization occurs in the steel sheet structure, and it becomes possible to realize good magnetic properties.

  In the hot-rolled sheet annealing step according to the present embodiment, the hot-rolled steel plate manufactured through the hot rolling step may be annealed to obtain a hot-rolled annealed steel plate according to a known method. The means for heating the hot-rolled steel sheet during annealing is not particularly limited, and a known heating method can be employed. Moreover, although it does not specifically limit about annealing conditions, For example, annealing for 10 second-5 minutes can be performed with respect to a hot-rolled steel plate in a 900-1200 degreeC temperature range.

In addition, this hot-rolled sheet annealing process can be skipped as needed.
Moreover, you may perform pickling with respect to the surface of a hot-rolled steel plate after the hot-rolled-sheet annealing process and before the cold rolling process explained in full detail below.

<Cold rolling process>
The cold rolling step (step S105) is a step of forming a cold rolled steel sheet by performing cold rolling twice or more with respect to the hot rolled annealed steel sheet once or with intermediate annealing. Moreover, since the steel plate shape becomes favorable when the above hot-rolled sheet annealing is performed, the possibility of the steel plate breakage in the first rolling can be reduced. Moreover, although cold rolling may be implemented in 3 times or more, since manufacturing cost increases, it is preferable to carry out 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 into a cold-rolled steel sheet according to a known method. For example, the final cold rolling reduction can be in the range of 80% to 95%. If the final rolling reduction is less than 80%, it is likely that the {110} <001> orientation cannot obtain Goss nuclei having a high degree of accumulation in the rolling direction, which is not preferable. On the other hand, if the final rolling reduction exceeds 95%, it is not preferable because secondary recrystallization is likely to be unstable in the subsequent final annealing step. By setting the final cold rolling reduction in the above range, it is possible to obtain Goss nuclei having a high degree of integration in the rolling direction in the {110} <001> orientation and to suppress instability of secondary recrystallization. .

  In addition, when two or more cold rollings with intermediate annealing are performed, the first cold rolling has a rolling reduction of about 5 to 50% and a temperature of 950 ° C. to 1200 ° C. for about 30 seconds to 30 minutes. It is preferable to perform the intermediate annealing.

  Here, the thickness of the cold-rolled cold-rolled steel sheet (thickness after cold-rolling) is usually the thickness of the directional electrical steel sheet finally produced (the thickness of the tension-imparting insulating coating). It is different from the product thickness. The product thickness of the grain-oriented electrical steel sheet is as described above.

  In the cold rolling process as described above, an aging treatment can be applied in order to further improve the magnetic properties. Each of the plate thickness stages passes through multiple passes during cold rolling, but at least once in the intermediate plate thickness stage, the steel plate is given a thermal effect of holding at a temperature range of 100 ° C. or higher for a time of 1 minute or longer. It is preferable. This thermal effect makes it possible to form a more excellent primary recrystallization texture in the subsequent decarburization annealing process, and in the subsequent final annealing process, the {110} <001> orientation is aligned in the rolling direction. It is possible to sufficiently develop a good secondary recrystallization.

<Decarburization annealing process>
A decarburization annealing process (step S107) is a process of performing a decarburization annealing with respect to the obtained cold-rolled steel plate, and making it a decarburization annealing steel plate. In the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment, the decarburization is improved by forming a specific Al-based oxide film in the steel sheet in the decarburization annealing process.

  In the decarburization annealing process according to the present embodiment, in order to form an Al-based oxide film having a specific Al-based oxide, the decarburization annealing process according to the present embodiment is performed as shown in FIG. The temperature raising step (step S131), the midway cooling step (step S133), the second temperature raising step (step S135), and the soaking step (step S137) are comprised of four steps.

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

  In the midway cooling step (step S133), the cold rolled steel sheet that has reached the temperature T1 (° C.) through the first temperature raising step is temporarily reduced to a temperature T2 (° C.) that satisfies the following equation (103): This is a step of cooling at a cooling rate C1 (° C./second) satisfying In addition, the oxygen potential P0 in the midway 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 the temperature T2 (° C.).

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

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

Hereinafter, these steps will be described in detail with reference to FIGS. 4 and 5.
In the explanatory diagrams of the heat treatment pattern 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. Is something.

[First heating step]
As mentioned earlier, one of the problems with grain-oriented electrical steel sheets is improving decarburization. The inventors focused on the temperature increase cycle in the decarburization annealing process and performed various verifications such as condition changes. As a result, it has been found that shortening the residence time in a low temperature range of 200 to 500 ° C. is effective for improving the decarburization property when raising the temperature from room temperature. When the residence time in a low temperature region of 200 to 500 ° C. is long, a Cr-based oxide film is generated, which is considered to cause decarburization deterioration. However, while the Cr-based oxide film is a decarburization inhibiting factor, it is also an oxide film having a magnetic improvement effect, so even if the decarburization is improved by the above policy, the magnetic flux density may be lowered. There is. Therefore, the present inventors mainly controlled a specific Al-based oxide film (MgAlO ₄ as an alternative to the 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 has been found that the formation of an oxide film as a component is promoted. Thereby, in the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment, an Al-based oxide film is generated without forming a Cr-based oxide film, thereby improving decarburization.

Therefore, in the first temperature raising step (step S131) according to this embodiment, as shown in FIG. 4, the temperature is raised from room temperature to a temperature range of temperature T1 (° C.) defined by the above equation (101). The speed H1 is controlled so as to satisfy the above formula (102), and heating is performed to the temperature T1. Here, when the temperature T1 is less than 200 ° C. and exceeds 500 ° C., even when the oxygen potential P0 is controlled as described below, a specific Al-based oxide (MgAl ₂ O ₄ ) Cannot be generated. Moreover, when the temperature rising rate H1 is less than 100 ° C./second, the residence time in a temperature range where an Fe-based oxide film is likely to be generated becomes long, and the amount of specific Al-based oxide (MgAl ₂ O ₄ ) generated Is not preferable because of a decrease. On the other hand, when the heating rate H1 exceeds 800 ° C./second, overshooting may occur, which is not preferable.

  In addition, temperature T1 (degreeC) becomes like this. Preferably it is 200-400 degreeC, More preferably, it is 250-350. Moreover, the temperature rising rate H1 (° C./second) is preferably 200 to 600 ° C./second, and more preferably 300 to 500 ° C./second.

In the first temperature raising step according to this embodiment, the oxygen potential (ratio of the water vapor partial pressure P _H2O to the hydrogen partial pressure P _{H2 in the} atmosphere, that is, P _H2O / P _H2 ) P0 is expressed by the above formula (105). Control to satisfy. Thus, it is possible to promote the formation of advantageous specific Al oxide (MgAl ₂ O ₄₎ for decarburizing. When the value of the oxygen potential P0 is less than 0.0001 and more than 0.5, the generation of Al-based oxide (MgAl ₂ O ₄ ) cannot be promoted. The oxygen potential P0 in the first temperature raising step is preferably 0.0001 to 0.03, and more preferably 0.0001 to 0.01.

[Cooling process]
In the midway cooling step (step S133) according to the present embodiment, an Al-based oxide that is advantageous for decarburization is generated. Specifically, in the midway cooling process according to the present embodiment, in order to ensure a residence time in the temperature range of T1 to T2 ° C, the temperature is gradually cooled from T1 ° C to T2 ° C. Here, the cooling rate C1 of the 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./second (in other words, when the absolute value of the cooling rate C1 is larger than 40), a sufficient residence time in the temperature range of T1 to T2 ° C. is secured. Therefore, an Al-based oxide (MgAl ₂ O ₄ ) advantageous for decarburization cannot be generated sufficiently. The cooling rate C1 is preferably −40 to −5 ° C./second, more preferably −30 to −5 ° C./second, and further preferably −15 to −10 ° C./second. Moreover, it is preferable that temperature T2 is (T1-75) degreeC or more and (T1-10) degreeC or less, and it is more preferable that it is (T1-50) degreeC or more and (T1-10) degreeC or less.

Further, in the midway cooling step according to the present embodiment, the oxygen potential (ratio of the water vapor partial pressure P _H2O to the hydrogen partial pressure P _{H2 in the} atmosphere, that is, P _H2O / P _H2 ) P0 satisfies the above formula (105). Control to do. Thus, it is possible to promote the formation of advantageous specific Al oxide (MgAl ₂ O ₄₎ for decarburizing. When the value of the oxygen potential P0 is less than 0.0001 and more than 0.5, the generation of Al-based oxide (MgAl ₂ O ₄ ) cannot be promoted. The oxygen potential P0 in the midway 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 temperature raising step and the oxygen potential P0 in the midway cooling step are not necessarily set to the same value, and are preferably set within a range of 0.0001 to 0.5, respectively. Different values may be used.

[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 the temperature T2 (° C.). The second temperature raising step is not particularly limited, and a temperature raising condition may be set as appropriate. The temperature raising rate S from the temperature T2 to the decarburization annealing temperature satisfies the following formula (106). It is preferable to control so as to. A specific Al-based oxide (MgAl ₂ O ₄ ) produced in the first temperature raising step and the midway cooling step by raising the temperature of the cold-rolled steel sheet at a temperature raising rate S that satisfies the following formula (106) It is possible to quickly raise the temperature up to the decarburization annealing temperature while remaining. The temperature rising rate S is preferably 700 to 2000 ° C./second, more preferably 1000 to 2000 ° C./second. Although the detailed reason is still unclear, the effect of improving magnetism has been confirmed by increasing the heating rate. It is presumed that the recrystallization texture is probably controlled in a favorable state for secondary recrystallization.

      400 ≦ S ≦ 2000 (Formula (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 may be appropriately controlled to an appropriate value. 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, similarly to the oxygen potential P0 in the first temperature raising step. In particular, by setting the first temperature raising step and the second temperature raising step in the same atmosphere, there is an advantage in that the furnace atmosphere control for each step becomes unnecessary, and a complicated equipment configuration can be avoided.

[Soaking process]
The soaking process according to the present embodiment is not particularly limited as long as each condition of the first temperature raising process, the midway cooling process, and the second temperature raising process is satisfied. For example, 700 This is a step of maintaining a temperature range of not less than 1000 ° C. and not more than 1000 ° C. for not less than 10 seconds and not more than 10 minutes.

  Moreover, the soaking process according to the present embodiment may include a plurality of processes. For example, as shown in FIG. 5, the soaking process may be composed of two processes.

  That is, as shown in the heat treatment pattern 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. The first soaking step to be held below and the first soaking step are performed at a temperature T4 (° C.) satisfying the following formula (108) in the atmosphere of the oxygen potential P3 satisfying the following formula (107). A second soaking step of holding for 5 seconds or more and 500 seconds or less. Hereinafter, the annealing process including a plurality of soaking processes is also referred to as multi-stage annealing.

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

  When performing such two-stage annealing, it is important to control the annealing temperature and holding time of 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. The holding time of the annealing temperature T3 is preferably 10 seconds or more and 1000 seconds or less. An annealing temperature T3 of less than 700 ° C. is not preferable because decarburization does not proceed and poor decarburization occurs. On the other hand, when the annealing temperature T3 exceeds 900 ° C., the grain structure becomes coarse and secondary recrystallization failure (magnetic failure) is caused. Further, even when the holding time is less than 10 seconds, decarburization does not proceed and decarburization is poor, which is not preferable. Note that increasing the holding time itself is not a problem from the viewpoint of decarburization, but the holding time is preferably set to 1000 seconds or less from the viewpoint of productivity. The annealing temperature T3 is more preferably 780 ° C. or higher and 860 ° C. or lower. The holding time is more preferably 50 seconds or more and 300 seconds or less in the production of a practical steel sheet.

From the viewpoint of securing the amount of Al-based oxide formed, it is preferable that the oxygen potential P2 at the time of annealing in the first soaking step is higher than the oxygen potential P0 in the midway cooling step. By obtaining a sufficient oxygen potential, the decarburization reaction can proceed sufficiently. However, when the oxygen potential P2 during annealing in the first soaking step is too large, Al-based oxides (MgAl ₂ O ₄₎ is may become substituted to _{Fe 2 SiO 4, Fe 2 SiO} 4 , the magnetic Degrading properties. Therefore, it is preferable to control the oxygen potential P2 during annealing in the first soaking step within a range of 0.1 to 1.0. The oxygen potential P2 during annealing in the first soaking process is more preferably 0.2 or more and 0.8 or less.

Even if the above control 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 is performed following the first soaking step, it is preferable that the annealing temperature T4 (plate temperature) be 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 SiO ₂ . MgAl ₂ O ₄ does not change to another oxide in the second soaking step and continues to remain. In addition, the temperature range of the more preferable annealing temperature T4 is (T2 + 100) degreeC or more and 1000 degrees C or less.

Moreover, the holding time of the said annealing temperature T4 in a 2nd soaking process shall be 5 to 500 second. When the holding time is less than 5 seconds, there is a possibility that Fe ₂ SiO ₄ generated in the first soaking step cannot be reduced to SiO ₂ even when the annealing temperature is in the above range. There is. On the other hand, when the holding time exceeds 500 seconds, the grain growth of the steel sheet proceeds, which may cause a magnetic failure. The holding time of the annealing temperature T4 in the second soaking step is more preferably 10 seconds or longer and 100 seconds or shorter.

  In order to make the second soaking step a reducing atmosphere, the oxygen potential P3 in the second soaking step is set smaller than the oxygen potential P2 in the first soaking step as shown in the above formula (107). It is preferable to do. 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 is preferably as short as possible, and the first soaking step and the second soaking step are continued. It is preferable to carry out. In the case where the first soaking step and the second soaking step are continuously performed, two continuous annealing furnaces controlled so as to satisfy the conditions of each soaking step may be provided in succession.

<Finishing 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 performing the finish annealing after applying a predetermined annealing separating agent to the decarburized and annealed steel sheet obtained in the decarburization annealing step. Here, the finish annealing is generally performed for a long time in a state where the steel sheet is wound in a coil shape. Therefore, prior to finish annealing, an annealing separator is applied to the decarburized annealed steel sheet and dried for the purpose of preventing seizure between the inside and outside of the steel sheet. As the annealing separator, for example, an annealing separator containing magnesia (MgO) as a main component can be used.

  The heat treatment conditions in finish annealing are not particularly limited, and known conditions can be appropriately employed. For example, finish annealing can be performed by holding in a temperature range of 1100 ° C. to 1300 ° C. for 10 hours to 60 hours. Moreover, the atmosphere at the time of final annealing can be made into, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen. In the case of a mixed atmosphere of nitrogen and hydrogen, the oxygen potential of the atmosphere is preferably 0.5 or less.

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

<Insulating film formation process>
The insulating coating forming step (step S111) is a step of forming a tension-imparting insulating coating 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 treatment liquid may be applied and dried by a known method using the following known insulating film treatment liquid. 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 or the like before applying the treatment liquid. And the surface as it is after finishing annealing without performing these pretreatments may be sufficient.

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

  Moreover, you may perform the planarization annealing for shape correction following the above insulating film formation processes. It is possible to further reduce the iron loss by performing the flattening annealing on the steel plate.

  Through the steps as 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 film. Furthermore, the above-described manufacturing method does not impair the particular magnetic characteristics as compared with the conventional manufacturing method. That is, the obtained grain-oriented electrical steel sheet has sufficiently excellent magnetic properties.

  As mentioned above, the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment has been described in detail.

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

(Experimental example 1)
A steel slab containing the components shown in Table 1 below was prepared, heated to 1350 ° C. and subjected to hot rolling to obtain a hot-rolled steel plate having a thickness of 2.3 mm. Thereafter, 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 subjected to decarburization annealing, and then an annealing separator mainly composed of magnesia (MgO) was applied, and finish annealing was performed at 1200 ° C. to produce a finish annealing plate. In addition, about each steel slab, the remainder other than the component described in Table 1 is Fe and impurities.

Here, in the first temperature raising step and the midway cooling step in the decarburization annealing process of this experimental example, the temperature T1 = 320 ° C., the temperature raising rate H1 = 350 ° C./second, the temperature T2 = 280 ° C., and the cooling rate C1. = −20 ° C./sec. In the second heating step in the decarburization annealing step of this experimental example, the heating rate S was set to 500 ° C./second. Further, the oxygen potential (P _H2O / P _H2 ) P0 in the first temperature raising 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, the oxygen potential was set to 0.4 in a wet hydrogen atmosphere, and holding was performed at an annealing temperature of 830 ° C. for 150 seconds. These conditions are all within the scope of the present invention.

  Thereafter, a coating solution for forming an insulating film mainly composed of a metal phosphate was applied to the surface of the steel sheet and baked to form a tension-imparting insulating film to obtain a grain-oriented electrical steel sheet.

  Each grain-oriented electrical steel sheet was evaluated for decarburization and magnetic properties (magnetic flux density).

<Magnetic flux density>
The magnetic flux density was evaluated using B8. B8 is the magnetic flux density at a magnetic field strength of 800 A / m, which is a criterion for determining the quality of secondary recrystallization. B8 = 1.89T or more was judged as having been recrystallized, and it was accepted, and less than B8 = 1.89T was judged as having not been recrystallized, and was rejected. In addition, the magnetic property (magnetic flux density) was not evaluated for those in which breakage occurred in the hot rolling process or the cold rolling process (indicated in Table 2 below, “−”). .

<Decarburization>
Decarburization was evaluated by measuring iron loss after the magnetic aging test. If decarburization is inadequate, iron loss should show a negative value after magnetic aging treatment. A magnetic aging test was performed on each of the obtained grain-oriented electrical steel sheets under a 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. The 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. According to the value of the obtained iron loss W17 / 50, evaluation was performed as in the following evaluation criteria.

[Evaluation criteria]
EX (Excellent), particularly good effect is recognized: less than 0.85 VG (Very Good), good effect is recognized: 0.85 or more and less than 0.90 G (Good), relatively good effect is recognized : 0.90 or more and less than 0.95 F (Fine), effect is recognized: 0.95 or more and less than 1.00 B (Bad), no effect is 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 adjustment method was performed according to JIS G 0417. At this time, those having a residual carbon amount of 20 ppm or less were determined as “A: Pass”, and those having a residual carbon amount exceeding 20 ppm were determined as “B: Fail”.

  In addition, about the thing fractured | ruptured during rolling and the thing with a secondary recrystallization defect, the decarburization property was not evaluated (it shows with "-" in Table 2 shown below).

  The obtained results are summarized in Table 2 below.

  As apparent from Table 2 above, the inventive 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 and favorable conditions for decarburization, and, for some steel types, include a selective element as a chemical component of the steel slab, Compared with invention steel B1-B16, the better decarburization property was shown. On the other hand, in the comparative steels b1 to b11 in which the content of any essential element is 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 cold-rolled steel sheet was decarburized and annealed under the conditions shown in Table 3 below. In addition, the 1st temperature rising process in the decarburization annealing process and the middle cooling process were implemented on the conditions shown in Table 3. In the second temperature raising step of the decarburization annealing step, S = 1500 ° C./s, and in the soaking step of the decarburization annealing step, the annealing temperature 830 is performed in a wet hydrogen atmosphere with an oxygen potential = 0.4. Holding at 150 ° C. for 150 seconds was performed. Thereafter, an annealing separator mainly composed of MgO was applied, and finish annealing was performed at 1200 ° C. to produce a finish annealed plate. Next, a coating solution for forming an insulating film mainly composed of a metal phosphate was applied to the surface of the finish annealed plate and baked to form a tension-imparting insulating film to obtain a grain-oriented electrical steel sheet.

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

  As apparent from Table 3 above, the inventive steels C9 to C24 are controlled under preferable conditions in which the first temperature raising step and the midway cooling step in the decarburization annealing step are within the scope of the present invention, and the inventive steel C1. Compared with -C8, the iron loss evaluation result after the aging treatment showed better "G". Since the comparative steels c1 to c10 were conditions under which the first temperature raising step and the intermediate cooling step were outside the scope of the present invention, 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 sheet was decarburized and annealed under the conditions shown in Table 4 below. In the soaking step in the decarburization annealing step, holding was performed at an annealing temperature of 810 ° C. for 160 seconds in a wet hydrogen atmosphere with an oxygen potential of 0.5. Thereafter, an annealing separator mainly composed of MgO was applied, and finish annealing was performed at 1200 ° C. to produce a finish annealed plate. Next, a coating solution for forming an insulating film mainly composed of a metal phosphate was applied to the surface of the finish annealed plate and baked to form a tension-imparting insulating film to obtain a grain-oriented electrical steel sheet.

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

  Inventive steels D8 to 29 are controlled to have preferable conditions for the first temperature raising step and the intermediate cooling step in the decarburization annealing step, and the second temperature raising step in the decarburization annealing step is controlled within the scope of the present invention. Therefore, compared with invention steel D1-D7, the favorable magnetic characteristic was shown. In particular, since D14 to D29 are controlled under more preferable conditions for the first temperature raising step and the mid-step cooling step in the decarburization annealing step, the magnetic characteristics are “EX”, indicating a very good result. Inventive steels D31 to D33 are irons after aging treatment from the viewpoint of the second temperature raising step in the decarburization annealing step, although the first temperature raising step and the midway cooling step in the decarburization annealing step are controlled within a preferable range. The loss assessment result remained “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 cold-rolled steel sheet was decarburized and annealed, and then an annealing separator mainly composed of MgO was applied and subjected to finish annealing at 1200 ° C. to produce a finished annealed sheet.

  Here, in the first temperature raising step and the midway cooling step in the decarburization annealing process of this experimental example, the temperature T1 = 320 ° C., the temperature raising rate H1 = 340 ° C./second, the temperature T2 = 280 ° C., and the cooling rate C1. = −20 ° C./second and oxygen potential P0 = 0.01. These conditions are all within the scope of the present invention. The conditions of the temperature raising step and the soaking step in the decarburization annealing step are as shown in Table 5.

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

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

  As apparent from Table 5 above, the invention steels E11 to 18 were not more preferable conditions for the second heating step in the decarburization annealing step, but the first heating step and the midway cooling step were within the scope of the present invention. Since the iron loss evaluation after aging was “G”, a good result was obtained. Inventive steels E19 to E22 are controlled in a preferable range or a more preferable range in both the second temperature raising step in the decarburization annealing step and the two-stage annealing conditions performed in the soaking step of the decarburization annealing step. Therefore, the evaluation of iron loss after aging was “EX”, and particularly good magnetic properties were exhibited. Inventive steels E23 to E26 are controlled in the preferable range for the two-stage annealing conditions in the soaking process. From the viewpoint of the second temperature raising process in the decarburization annealing process, the iron loss evaluation after aging is “ 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 cold-rolled steel sheet was decarburized and annealed, and then an annealing separator mainly composed of MgO was applied and subjected to finish annealing at 1200 ° C. to produce a finished annealed sheet.

  Here, in the first temperature raising step and the midway cooling step in the decarburization annealing process of this experimental example, the temperature T1 = 330 ° C., the temperature raising rate H1 = 370 ° C./second, the temperature T2 = 300 ° C., and the cooling rate C1. = −20 ° C./second and oxygen potential P0 = 0.005. These conditions are all within the scope of the present invention. The conditions of the second temperature raising step and the soaking step in the decarburization annealing step are as shown in Table 6.

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

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

  As apparent from Table 6 above, the invention steels F2, F7, F12, F17, F22, F27, F32, F37, and F42 are subjected to two-stage annealing in the soaking process in the decarburization annealing process. Although the control range is included in the preferred invention range, the iron loss evaluation after aging was only “G” from the viewpoint of the second temperature raising 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 for the second temperature raising step of the decarburization annealing step. However, the two-step annealing was not performed in the soaking process, and the iron loss evaluation after aging remained at “G”.

  Inventive steels F1, F6, F11, F16, F21, F26, F31, F36, and F41 are decarburized and annealed, although the intermediate cooling conditions (H1, T2, and C1) in the decarburizing and annealing process are controlled within a preferred range. About the 2nd temperature rising process in a process, it is not a preferable range, and the two-step annealing is not implemented in the soaking process. However, the invention steels F11, F26, F41 had a final plate thickness of 0.19 mm, so compared with the iron loss evaluation “F” after aging in the invention steels F1, F6, F16, F21, F31, F36, A favorable evaluation result “G” was obtained.

  Inventive steels F3, F5, F8, F10, F13, F15, F18, F20, F23, F25, F28, F30, F33, F35, F38, F40, F43, F45 are the second heating step in the decarburization annealing step. In the subsequent soaking process, two-stage annealing is performed, and therefore, the iron loss evaluation after aging has obtained good results compared to other invention steels. It was. In particular, the invention steel F5, F10, F15, F20, F25, F30, F35, F40, F45, the second temperature raising step in the decarburization annealing process was controlled in a more preferable range, so the iron loss evaluation after aging is “EX” was very good.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but 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 pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Directional electrical steel sheet 11 Base material steel plate 13 Glass coating 15 Tension imparting insulating coating

Claims (6)

% By mass
C: 0.01 to 0.20%
Si: 2.5-4.0%
Sol. Al: 0.01 to 0.07%
Mn: 0.01 to 0.50%
Cr: 0.01 to 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%
A hot-rolling step of obtaining a hot-rolled steel sheet by hot rolling after heating a steel slab comprising Fe and impurities,
Annealing the hot-rolled steel sheet to obtain a hot-rolled annealed steel sheet,
For the hot-rolled annealed steel sheet, a single cold rolling, or a cold rolling process for obtaining a cold-rolled steel sheet by performing a plurality of cold rolling sandwiching intermediate annealing,
Decarburization annealing is performed on the cold-rolled steel sheet to obtain a decarburized annealing steel sheet,
After applying an annealing separator to the decarburized and annealed steel sheet, a final annealing step for performing final annealing,
An insulating film forming step for forming an insulating film on the surface of the steel sheet after finish annealing;
Including
The decarburization annealing step,
A first temperature raising step for raising the temperature of the cold-rolled steel sheet from room temperature to a temperature T1 (° C.) satisfying the following formula (1) at a temperature rising rate H1 (° C./second) satisfying 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 equation (3) at a cooling rate C1 (° C / second) that satisfies the following equation (4). A cooling process on the way,
A second temperature raising step for raising the temperature of the cold-rolled steel sheet from the temperature T2 (° C);
A soaking step for annealing the cold-rolled steel sheet after the temperature rise;
Have
A method for producing a grain-oriented electrical steel sheet, wherein an oxygen potential P0 in the first temperature raising step and the midway cooling step satisfies the following formula (5).
200 ≦ T1 ≦ 500 (1)
100 ≦ H1 ≦ 800 (2)
T1-100 ≦ T2 ≦ T1-10 (3)
−40 ≦ C1 <0 Formula (4)
0.0001 ≦ P0 ≦ 0.5 (5) The grain-oriented electrical steel sheet according to claim 1, wherein, in the second temperature raising step in the decarburizing annealing step, a temperature raising rate S from the temperature T2 to the decarburizing annealing temperature satisfies the following formula (6). Manufacturing method.
400 ≦ S ≦ 2000 (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 of a predetermined oxygen potential P2,
Following the first soaking step, the temperature is maintained for 5 seconds or more and 500 seconds or less at a temperature T4 (° C.) satisfying the following formula (8) in an atmosphere of an oxygen potential P3 satisfying the following formula (7). The manufacturing method of the grain-oriented electrical steel sheet according to claim 1 or 2, comprising a second soaking step.
P3 <P2 Formula (7)
T3 + 50 ≦ T4 ≦ 1000 (8)   The plate | board thickness of the said grain-oriented electrical steel sheet is a manufacturing method of the grain-oriented electrical steel sheet of any one of Claims 1-3 which are 0.17 mm or more and less than 0.22 mm.   The said steel piece is a manufacturing method of the grain-oriented electrical steel sheet of any one of Claims 1-4 which contains Bi 0.001-0.020 mass%. The said steel piece contains 0.005-0.500 mass% Sn and at least any one of 0.01-1.00 mass% Cu, The any one of Claims 1-5. Method for producing a grain-oriented electrical steel sheet.

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