JPH1180835A - Manufacture of grain oriented silicon steel sheet having high magnetic flux density and extremely low iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silicon steel sheet excellent in formation of forsterite film at finish annealing and stably having extremely low iron loss by incorporating specific amounts of B and N and specific amounts of V and Nb into a slab of steel of specific composition to be heated to a specific temp. or above and hot-rolled and also performing decarburizing annealing under specific conditions. SOLUTION: A steel slab which has a composition containing, by weight, 0.03-0.10% C, 2.5-4.5% Si, 0.05-1.5% Mn, and 0.010-0.040%, in total, of S and/or Se and satisfying Mn/(S+Se)>=2.5, is heated to >=1350 deg.C and hot-rolled, by which a silicon steel sheet is obtained. At this time, 0.0010-0.0060% B and 0.0050-0.0100% N are incorporated into the steel slab and N-(14/10.8)×B>=0.0020% is satisfied, and further, V and/or Nb is incorporated by 0.001 to 0.020%, respectively. Moreover, decarburizing annealing is carried out by performing holding at 800-860 deg.C in a wet hydrogen atmosphere, holding at 860-1050 deg.C in an atmosphere containing >=20% nitrogen, and cooling through the temp. region between 800 and 500 deg.C at >=10 deg.C/sec cooling rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet used for an iron core of a transformer or a generator, and more particularly to a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density and an extremely low iron loss.

[0002]

2. Description of the Related Art Si is contained and the crystal orientation is # 11.
Grain-oriented electrical steel sheets oriented in the 0 ° <001> direction and the {100} <001> direction have excellent soft magnetic properties and are therefore widely used as various core materials in the commercial frequency range. The characteristics required for such an electromagnetic steel sheet include 50H
W which is iron loss when magnetized to 1.7T at the frequency of z
It is important that 17/50 is low. In general, it is effective to reduce the eddy current loss to reduce the iron loss of the material. Therefore, the method of increasing the Si content to increase the electric resistance, the method of reducing the thickness of the steel sheet, the grain size of the product And a method of increasing the degree of integration of the crystal orientation to improve the magnetic flux density. Among them, the method of increasing the Si content is limited because excessively containing Si deteriorates the rollability and workability, and there is a limit, and the method of reducing the steel sheet thickness and the method of reducing the crystal grain size are extremely extreme. It is not preferable because it leads to an increase in production cost.

There have been many studies on methods for increasing the degree of integration of crystal orientations and improving magnetic flux density. For example, Japanese Patent Publication No. 46-23820 discloses a method of adding Al to steel and performing hot rolling. Fine AlN is formed by hot strip annealing at a high temperature of 1000 to 1200 ° C. and a subsequent quenching treatment.
Precipitating, it discloses a technique of further subjecting 80 to 95% of the reduction ratio, whereby ₁₀ value B is the value obtained is very high magnetic flux density of 1.95 T. This method makes use of the fact that AlN finely dispersed and precipitated has a strong effect as an inhibitor for suppressing the growth of primary recrystallized grains. To obtain a product having a high crystal structure. However, in this method, the secondary recrystallized grain size generally becomes coarse,
It is difficult to obtain a low iron loss value, and it is difficult to completely dissolve AlN in hot-rolled sheet annealing.
There is a problem that it is difficult to stably obtain a product having a high magnetic flux density. Further, the content of Al which is easily oxidized makes the formation of subscale in decarburizing annealing and the formation of a forsterite film in finish annealing extremely difficult.

Further, JP-B-58-42244 and JP-B-60-55570 disclose 0.0003 to 0.0.
Using 035% B and steel containing from 0.0030 to 0.0070% of N, ₈ value B by the Mn / S and 1.8 or 2.1 or less each from 1.85 to 1.9
A technique for obtaining a magnetic flux density of 2T is disclosed. This BN
Is an inhibitor, there is a high possibility that a high magnetic flux density can be obtained, but it not only leads to an increase in cost due to the reduction of Mn, but also has a problem that it is difficult to industrialize because it causes hot cracking in the hot rolling process. Was. Furthermore, Japanese Patent Publication No. 60-54371 and Japanese Patent Publication No. 7-68581 disclose an improvement technique in which the Mn / S exceeds 1.8 or 2.5 by reducing the B content to 0.0018% or less, respectively. Is disclosed. Furthermore, Japanese Patent Laid-Open No. 57
In JP-A-114615, the remaining amount of N excluding the equivalent amount of N required for B to precipitate as BN is defined as the amount of dissolved N, and by setting this to 0.0020% or less, M
It is disclosed that a high magnetic flux density can be obtained even when n / S is 2.1 or more, but a grain-oriented electrical steel sheet having good secondary recrystallization has not yet been industrially stably obtained. .

[0005]

SUMMARY OF THE INVENTION The present invention focuses on the superiority in improving the magnetic flux density of a grain-oriented electrical steel sheet containing BN as an inhibitor, and further increases the degree of integration of the crystal orientation to provide a steel sheet having a high magnetic flux density. To obtain a grain-oriented electrical steel sheet having excellent production of a forsterite film in finish annealing by solving the above-mentioned problems in the production of a grain-oriented electrical steel sheet, and having a stable and extremely low iron loss value. It is an object to provide a method that can be used.

In order to effectively control the growth of normal grains, it is essential to properly control the size, morphology, and dispersion state of precipitates.
It is also known to use nitrides of b and V. However, steel containing these elements has a problem in that although secondary recrystallization occurs stably, the magnetic flux density is low. According to the study of the present inventors, when these elements are added, the amount of their precipitation increases remarkably.
The secondary recrystallized grains are extremely fine, so that the driving force for grain growth of the secondary recrystallized grains becomes too large (110) [001].
The degree of integration in the direction decreases, and the magnetic flux density decreases. In order to solve such a problem, it is conceivable to increase the particle size of the primary recrystallized grains to some extent. To that end, it is necessary to reduce the amount of precipitates or to perform hot-rolled sheet annealing or intermediate annealing at a high temperature. It is conceivable to adjust the dispersion state of the object.
However, good magnetic flux density cannot be obtained by such means. 1 depending on the nitride element that should be used
This is because the suppressing power of the next grain growth is negated.
Therefore, the present invention solves the problem that the particle size of the primary particles becomes too small when using nitrides of B, Nb, and V as an inhibitor, and uses these elements to increase the degree of integration. This makes it possible to manufacture electrical steel sheets.

[0007]

Means for Solving the Problems The present inventors have proposed B, N
(b) In order to solve the problem that the degree of integration of secondary recrystallization in the goss orientation is reduced when the nitride of VN is used as an inhibitor, the precipitation behavior of these nitrides and the growth of secondary recrystallized grains are further reduced. As a result of earnestly studying the effects, the present inventor has found a completely different use method from the prior art, and has effectively utilized the method to complete the present invention. That is, in addition to using BN, nitrides of V and Nb having excellent high-temperature stability are used as inhibitors, and NbC or VN of BN or Si ₃ N ₄ is obtained by optimizing decarburization annealing conditions.
In addition to increasing the primary recrystallized grain size, the grain growth suppressing force is enhanced while increasing the primary recrystallized grain size, whereby secondary recrystallized grains having a high degree of integration in the Goss orientation are obtained.

Specifically, as a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density and an extremely low iron loss, C:
0.03 to 0.10%, Si: 2.5 to 4.5%, M
n: 0.05 to 1.5%, S and / or Se: 0.010 to 0.040% in total, and Mn / (S
+ Se) 1350 for steel slabs satisfying ≧ 2.5
After hot-rolling after heating to ℃ or more, hot-rolled sheet annealing is performed as necessary, and then cold rolling is performed once or twice or more with intermediate annealing sandwiched to obtain a final sheet thickness and primary recrystallization. The method for producing a grain-oriented electrical steel sheet according to the present invention comprises a series of steps of performing a final finish annealing for applying an annealing separator containing MgO as a main component, performing a secondary recrystallization and purifying after applying a decarburizing annealing also serving as B: 0.0010 to 0.0
060%, N: 0.0050 to 0.0100%, and N− (14 / 10.8) × B ≧ 0.0020
% And further contain 0.001 to 0.020% of V and / or Nb, respectively, and the decarburizing annealing is performed in a wet hydrogen atmosphere at 8%.
After the temperature is maintained at 00 to 860 ° C, the temperature is maintained at 860 to 1050 ° C in an atmosphere containing 20% or more of nitrogen, and then the temperature is cooled between 800 to 500 ° C at a cooling rate of 10 ° C / s or more. It is. Further, in the above invention, one or more selected from Cu, Sb, Sn, Bi, and Mo as inhibitors may be used in a total amount of 0.005 to 0.005.
0.30% is contained, and it is preferable to perform aging treatment in the cold rolling process or to subject the steel sheet after the secondary recrystallization to magnetic domain refining treatment.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the experimental results on which the present invention is based will be described, and then specific embodiments will be described together with examples.

(Basic Experiment) A steel ingot containing the components shown in Table 1 was prepared, heated at 1430 ° C. for 60 minutes, and then heated to 2.6 mm.
Hot rolled sheet. After the hot-rolled sheet was annealed at 1100 ° C. for 60 seconds, it was finished into a cold-rolled sheet having a final thickness of 0.23 mm. The obtained cold-rolled sheet was first subjected to a temperature of 825 ° C. for 100 seconds, 50% of hydrogen, 50% of nitrogen, and a dew point of 60%.
C., and then soaked in a nitrogen atmosphere with a dew point of 40 ° C. at a temperature of 830 to 1100 ° C. for 60 seconds.
Decarburization annealing was performed to cool between 800 and 500 ° C at 25 ° C / s. That is, the annealing temperature and the annealing atmosphere are changed in the first half and the second half of the decarburizing annealing. To the decarburized annealed steel sheet, MgO is applied as an annealing separator, and first heated to 1200 ° C. at a heating rate of 25 ° C./hr in nitrogen.
Finish annealing was performed at that temperature for 5 hours soaking in hydrogen for purification. The obtained steel sheet was subjected to strain relief annealing at 800 ° C. for 2 hours, and then the magnetic flux density was measured. In addition, the crystal grain size and texture of the steel sheet after the decarburizing annealing were examined.

[0011]

[Table 1]

FIG. 1 is a graph showing the relationship between the temperature and the magnetic flux density in the latter half of the decarburization annealing obtained by the above experiment. As shown here, steels B and C to which Nb or V was added together with B showed remarkable improvement in magnetic properties when the temperature in the latter half of the decarburization annealing was in the range of 860 to 1040 ° C.
In steel A containing no, a phenomenon in which the magnetic flux density decreases when the temperature exceeds 860 ° C. is observed.

The reason why the magnetic flux density of steels B and C to which Nb or V is added together with B is not necessarily clear, but if the temperature in the latter half of the decarburizing annealing is sufficiently high, 1% in the soaking process. It is presumed that the increase in the particle size of the secondary grains and the conversion of nitrides such as BN or Si ₃ N ₄ into NbN or VN, which are more stable at high temperatures, re-precipitated and strengthened the suppressing power. In fact, as a result of electron microscopic observation, if the temperature in the latter half of the decarburizing annealing is high, N
The amount of nitride precipitation of bN or VN is increasing, supporting the above estimation.

The present inventors further conducted an experiment similar to the above-mentioned basic experiment by fixing Nb and V at 0.01%, while changing the addition amounts of B and N widely, and increasing the soaking temperature in the latter half to 90%.
As a result of fixing at 0 ° C., the relationship shown in FIG. 2 was obtained. That is, in order to obtain a high magnetic flux density, the surplus N (denoted as N ^* ) of N that is not fixed by B is 0.002.
It became clear that 0% (20 ppm) or more was necessary. In other words, when the condition of N ^* = N− (14 / 10.8) × B ≧ 0.0020% is satisfied, nitride such as BN or Si ₃ N ₄ is converted into nitride of NbN or VN. Redeposited,
It is presumed that despite the increase in the primary crystal grain size, the suppressing force is strengthened, and thereby a high magnetic flux density is obtained.

It is an essential point of the present invention that the above-mentioned conditions of the amount of N ^* (excess nitrogen) and the soaking temperature in the latter half of the decarburization annealing are satisfied.
The heat treatment and the like will be specifically described.

C: 0.03 to 0.10% The content of C is 0.03 to 0.10%. C is 0.
If it exceeds 10%, the amount of γ transformation becomes excessive, the distribution of B during hot rolling becomes uneven, and the uniformity of BN distribution is impaired, which is harmful. In addition, the load of decarburization annealing also increases, and poor decarburization is likely to occur. On the other hand, if it is less than 0.03%, the effect of improving the structure cannot be obtained, and the secondary recrystallization becomes incomplete, and the magnetic properties also deteriorate. Therefore, C is 0.03-0.1.
It is limited to the range of 0%.

Si: 2.5 to 4.5% Si is an essential element for increasing electric resistance and reducing iron loss. For this purpose, it is necessary to contain 2.5% or more. If it exceeds 4.5%, the workability is deteriorated, and it becomes extremely difficult to perform cold rolling and product processing.
The range is 4.5%.

Mn: 0.05 to 1.5% Mn is also an element necessary for increasing electric resistance and improving hot workability during production. For this purpose, the content of 0.05% or more is necessary. However, if the content exceeds 1.5%, γ transformation is induced to deteriorate magnetic properties. Range.

Se and / or S: 0.010 in total
０．０0.040% It is necessary to contain Se or S alone or in combination as an inhibitor component. These components are present in the steel in M
It precipitates as an n-compound or a Cu compound, but a total amount of 0.010% or more is required to maintain the suppression effect. However, if it exceeds 0.040%, a complete solid solution can be obtained even by high-temperature slab heating. It is rather harmful because it becomes coarse precipitates. Therefore, a total of 0.010 to 0.04
The range is 0%. At this time, Mn / (Se + S)
Is smaller than 2.5, grain boundary cracks and edge roughness increase significantly during hot rolling, so that Mn / (Se + S) ≧ 2.5 is practically necessary.

B: 0.0010 to 0.0060% B needs to be contained in an amount of 0.0010 to 0.0060%. If B is less than 0.0010%, the precipitation amount of BN is insufficient, and a good secondary recrystallized structure cannot be obtained. On the other hand, if B exceeds 0.0060%, N ^* becomes insufficient and NbN or This is because generation of VN becomes difficult.

N: 0.0050 to 0.100% N must be contained in an amount of 0.0050 to 0.100%. If less than 0.0050%, BN or even N
This is because the amount of bN and VN generated is insufficient.
If the content exceeds 010%, N is gasified in the steel, causing defects such as so-called "swelling". Further, as described above, N ^* needs to be 0.020% or more.

Nb, V: 0.001 to 0.020% Nb and / or V are 0.001 to 0.02, respectively.
0% is contained. If the content is less than 0.001%, the precipitation amount of NbN or VN becomes too small, and the suppressing power becomes insufficient. On the other hand, 0.020%
If the content exceeds 0.1%, recrystallization in the hot rolling process or the cold rolling process is significantly inhibited.
It is limited to the range of 001 to 0.020%. These are added alone or in combination within the above range.

Cu, Sb, Sn, Bi, Mo, Ni, C
o Cu, Sb, Sn, Bi, and Mo have an auxiliary function as an inhibitor to reinforce the inhibitory force, and thus are preferably added to steel at any time. Suitable values for this are 0.005 to 0.30% in total. Also, Ni or Co
Is effective for improving the surface properties of the steel sheet, so that it is preferable to appropriately add it.

The steel adjusted to the above components is usually subjected to slab heating and then hot-rolled to form a hot-rolled coil. At this time, it is important that the slab heating temperature be 1350 ° C. or higher. When the slab heating temperature is lower than 1350 ° C., the solid solution of the inhibitor is not sufficient, and Mn (Se,
S) Fine and uniform dispersion and precipitation of BN cannot be obtained. At the time of hot rolling, a known technique such as a thickness reduction process or a width reduction process for uniformizing the structure can be added before and after the slab heating as needed.

In the cold rolling step, the cold rolling process is performed once to obtain a final sheet thickness by one cold rolling after the hot rolling sheet annealing, and, if necessary, the first cold rolling is performed after the hot rolling sheet annealing is performed. A cold rolling twice method in which cold rolling and intermediate annealing are performed and a second cold rolling is performed can be employed. The rolling reduction of the cold rolling is not particularly limited, and may be performed in a conventionally known range. In general, the first rolling in the cold rolling twice method is preferably performed at a rolling reduction of 15 to 60%, and the rolling reduction at the final rolling is preferably 80 to 90%. In addition, cold rolling is performed as warm rolling at 100 to 350 ° C as is known, or 10 to 10 at 350 to 350 ° C between passes.
By performing the aging treatment for 60 minutes, the texture of the primary recrystallization can be further improved. Furthermore, after the final cold rolling, it is also possible to perform a process of providing a linear groove on the surface of the steel sheet for magnetic domain refining, whereby an electromagnetic steel sheet with lower iron loss can be obtained.

The steel sheet having the final thickness is subjected to primary recrystallization annealing also serving as decarburization by a method unique to the present invention. First, in the first stage, under a wet hydrogen atmosphere, at 800 to 860 ° C
In the above temperature range, the treatment mainly for decarburization is performed.
The moist atmosphere is used to quickly perform decarburization, and a hydrogen atmosphere having a dew point of about 50 ° C. is generally used.
The heating temperature at this stage is set to 800 ° C. or higher because at a lower temperature, the decarburization rate is too low.
The reason for setting the temperature to 60 ° C. or lower is that if the temperature is higher than that, an oxide film is formed on the surface of the steel sheet during the decarburization process, and the decarburization is hindered. The temperature after the decarburizing annealing is 860 to 1050 ° C
Range. If the temperature is lower than 860 ° C., the conversion and reprecipitation of Si ₃ N ₄ into NbN or VN is insufficient, so that the improvement of the magnetic properties is insufficient.
This is because the precipitates such as are coarsened, the suppressing power is reduced, and the magnetic properties are deteriorated. The atmosphere after the above decarburization annealing is nitrogen 2
The atmosphere contains 0% or more. If the nitrogen content is less than 20%, the precipitation of NbN or VN becomes insufficient. Cooling after completion of decarburization is performed at a cooling rate of 800C to 500C of 10C / s or more. If the cooling rate is slow, N
This is because bN or VN becomes coarse and deteriorates magnetic characteristics.

On the steel sheet after decarburizing annealing, an annealing separator containing MgO as a main component is applied to the surface and subjected to final finish annealing. At this time, a Ti compound is added or Ca or B is annealed. The inclusion in the separating agent has the effect of further improving the magnetic properties, and can provide favorable results. The conditions for the final finish annealing may be those generally used and are not particularly limited. After the final finish annealing, after removing the unreacted separating agent, an insulating coating is applied to the steel sheet surface to form a product, but if necessary, the steel sheet surface may be mirror-finished before coating, or as an insulating coating. A tension coating may be used. Further, the coating baking process of the coating may also serve as the flattening process. Further, in order to obtain an iron loss reducing effect on the steel sheet after the secondary recrystallization, a known magnetic domain refining treatment, that is, plasma jet or laser irradiation is applied to a linear area, or a linear dent area is provided by a projection roll. Or other processing can be performed.

[0028]

【Example】

Example 1 C: 0.06%, Si: 3.43%, M
n: 0.065%, Se: 0.018%, Sb: 0.0
20%, B: 0.0032%, N: 0.0083%,
V: 0.007%, Nb: 0.012%, Mo: 0.0
1. 11 steel slabs comprising 21%, balance Fe and inevitable impurities were produced, heated to 1420 ° C., and then hot-rolled.
The sheet was made 6 mm thick and wound into a coil at 600 ° C. to obtain a hot-rolled sheet. This hot-rolled sheet was heated to 1000 ° C., subjected to hot-rolled sheet annealing maintained at that temperature for 70 seconds, and rapidly cooled at 25 ° C./s. The hot-rolled sheet is pickled and warm-rolled at 200 ° C. to a temperature of 0.1 mm.
It was finished to a cold-rolled sheet by rolling once to a thickness of 34 mm. The obtained cold-rolled sheet was subjected to degreasing treatment, decarburization annealing under the conditions shown in Table 2, and further, Sr (OH) ₂ was added to MgO containing 0.5% Ca and 0.09% B. 2%, TiO ₂ 3%
The added annealing separator was applied, and final finishing annealing was performed. Final finish annealing in nitrogen up to 850 ° C at 20 ° C / h
, The temperature is raised from 850 ° C to 1050 ° C at a rate of 12.5 ° C / h in a mixed atmosphere of 25% nitrogen and 75% hydrogen, and further increased to 1200 ° C at a rate of 20 ° C / h in hydrogen. After the temperature was raised, the temperature was held at 1200 ° C. for 8 hours, and then the temperature was lowered to 600 ° C. in hydrogen. After the final finish annealing, the unreacted annealing separating agent was removed, magnesium phosphate containing 50% colloidal silica was applied as a tension coating, and baked at 850 ° C. to obtain a product. Table 2 also shows the magnetic properties of these products.

[0029]

[Table 2]

[0030]

Example 2 C: 0.052%, Si: 3.41%, M
n: 0.062%, S: 0.020%, Cu: 0.10
%, Sn: 0.15%, B: 0.0040%, N: 0.
0090%, V: 0.010%, Mo: 0.015%,
Eight steel slabs consisting of the remainder Fe and unavoidable impurities were produced, heated to 1400 ° C., hot rolled to a sheet thickness of 2.6 mm, and coiled at 550 ° C. to form a hot rolled sheet.
This hot-rolled sheet was heated to 950 ° C., subjected to hot-rolled sheet annealing for 60 seconds, and rapidly cooled at 20 ° C./s. The hot-rolled sheet was pickled, finished to 1.8 mm by the first cold rolling, heated to 1100 ° C., held at that temperature for 60 seconds, and then subjected to intermediate annealing in which it was rapidly cooled at 25 ° C./s. The second cold rolling was performed while performing the aging treatment at 300 ° C. at a final thickness of 0.23 mm. Thereafter, a degreasing treatment is performed, a decarburizing annealing is performed under the conditions shown in Table 3, and a Mg containing 0.5% Ca and 0.09% B is further added.
An annealing separator made by adding 2% of SrSO ₄ and 7% of TiO ₂ to O was applied, and final finish annealing was performed. After the final finish annealing, the temperature is raised to 850 ° C in nitrogen at 30 ° C / h,
The temperature was raised from 850 ° C. to 1050 ° C. at a rate of 12.5 ° C./h in a mixed atmosphere of 25% nitrogen and 75% hydrogen, and further raised to 1200 ° C. at a rate of 25 ° C./h in hydrogen for 8 hours. After the temperature was maintained, the temperature was lowered to 600 ° C. in hydrogen and then to nitrogen. After the final finish annealing, the unreacted annealing separating agent is removed, and magnesium phosphate containing 50% colloidal silica is applied as a tension coating,
It was baked at 850 ° C. to obtain a product. Table 3 also shows the magnetic properties of these products.

[0031]

[Table 3]

[0032]

Example 3 A steel slab having the composition shown in Table 4 was heated at 1420 ° C.
After hot-rolling, the sheet was rolled to a thickness of 2.2 mm and wound into a coil at 550 ° C. to form a hot-rolled sheet. This hot rolled sheet is
The temperature was raised to 0 ° C., the sheet was annealed at a temperature of 60 ° C. for 60 seconds, and rapidly cooled at 20 ° C./s. After pickling the hot-rolled sheet and finishing it to 1.5 mm by the first cold rolling, 1010
℃ and maintained at that temperature for 60 seconds.
After the intermediate annealing of rapid cooling in s,
Aging treatment was performed at 00 ° C. to perform a second cold rolling.
Finished to a final thickness of 23 mm. After degreasing,
Decarburization annealing was performed. The first half was held at 840 ° C. for 60 seconds in an atmosphere of 55% hydrogen, 45% nitrogen and a dew point of 60 ° C., and the second half was an atmosphere of 100% nitrogen and a dew point of 35 ° C.
The temperature was kept at 00 ° C. for 30 seconds. The decarburized annealed plate was subjected to a final finish annealing by applying an annealing separator made by adding 2% of SrSO ₄ and 8% of TiO ₂ to MgO. In the final finish annealing, the temperature is raised to 850 ° C. in nitrogen at 30 ° C./h, and then from 850 ° C. to 1050 ° C. with 25% nitrogen and 75%.
% Hydrogen in a mixed atmosphere of 12.5 ° C./h, and further heated up to 1200 ° C. in hydrogen at a rate of 25 ° C./h and kept for 8 hours. Then, the temperature was lowered in nitrogen. After final annealing,
The unreacted annealing separator was removed, magnesium phosphate containing 50% colloidal silica was applied as a tension coating, and baked at 850 ° C. to obtain a product. Table 5 shows the magnetic properties of these products.

[0033]

[Table 4]

[0034]

[Table 5]

[0035]

According to the present invention, since the above-mentioned structure is employed as the inhibitor, a grain-oriented electrical steel sheet having a higher magnetic flux density and an extremely low iron loss can be stably manufactured. Further, since AlN is not used, the formation of sub-scale in decarburizing annealing and the formation of forsterite film in finishing annealing are performed stably.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the decarburizing annealing temperature and the magnetic flux density when Nb or B is added to steel containing B and N.

FIG. 2 shows N ^* (excess N) in the component system according to the present invention.
FIG. 3 is a relationship diagram between the magnetic flux density and the magnetic flux density.

Claims (4)

[Claims] C: 0.03 to 0.10% by weight,
Si: 2.5 to 4.5%, Mn: 0.05 to 1.5%,
S and / or Se: 0.010 to 0.040% in total
, And hot-rolled after heating to 1350 ° C or higher, and if necessary, after hot-rolled sheet annealing, once or Cold rolling is performed two or more times with the intermediate annealing interposed therebetween to obtain the final thickness, and after decarburizing annealing also serving as primary recrystallization, MgO
A method for producing a grain-oriented electrical steel sheet comprising a series of steps of performing a final finish annealing in which an annealing separating agent containing as a main component is applied and subjected to a secondary recrystallization and a purification treatment. ~ 0.0060
%, N: 0.0050 to 0.0100%, and the relationship of N− (14 / 10.8) × B ≧ 0.0020% is satisfied, and further, V and / or Nb
, Respectively, and the decarburization annealing is performed in a wet hydrogen atmosphere at 800
After maintaining the temperature at 860 ° C. to 860 ° C., the temperature is maintained at 860 to 1050 ° C. in an atmosphere containing 20% or more of nitrogen.
A method for producing a grain-oriented electrical steel sheet having a high magnetic flux density and an extremely low iron loss, wherein cooling is performed at a cooling rate of 10 ° C / s or more between 00 and 500 ° C. 2. As an inhibitor, Cu, Sb, Sn,
2. A directional electromagnetic element having a high magnetic flux density and an extremely low iron loss according to claim 1, wherein one or more elements selected from Bi and Mo are contained in a total amount of 0.005 to 0.30%. Steel plate manufacturing method. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the aging treatment is performed in a cold rolling process. 4. A grain-oriented magnetic steel sheet having a high magnetic flux density and an extremely low iron loss according to claim 1, wherein the steel sheet after the secondary recrystallization is subjected to a magnetic domain refining treatment. Method.