JP2000160304A - Manufacture of grain oriented silicon steel sheet with high magnetic flux density and low iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the integration degree of crystal orientation and to obtain stabilized high magnetic flux density and low iron loss by subjecting a continuously cast slab containing specific amounts of C, Si, Mn, B, N, S, Se, and Al and having specific columnar crystal ratio, to specific heating and soaking and then applying hot rolling and cold rolling to it. SOLUTION: A continuously cast slab for silicon steel sheet which has a composition containing, by weight, 0.03-0.10% C, 2.5-4.5% Si, 0.05-1.5% Mn, 0.0010-0.0060% B, 0.0030-0.010% N, and 0.010-0.040% of S and/or Se within the range satisfying Mn/(S+Se)>=2.5, further containing 0.0010-0.0080% Al, and further containing, if necessary, 0.005-0.30% each of Cu, Sb, Sn, Bi, and Mn as inhibitor elements, is cast, and its columnar crystal ratio is regulated to >=40%. This cast slab is subjected to temperature-raise and heating from 1250 deg.C up to a temperature T not lower than 1350 deg.C within 1 hr and soaked for (t) min, where 1/5(1450-T)<=t<=2/5(1500-T) is satisfied. Then the cast slab is hot rolled, cold rolled, and subjected to decarburizing annealing and to final finish annealing.

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 particularly high magnetic flux density and extremely low iron loss. About.

[0002]

2. Description of the Related Art Si-containing material having a crystal orientation of # 11
Grain-oriented electrical steel sheets oriented in the 0 ° <001> direction and the {100} <001> direction have been widely used as various iron core materials in the commercial frequency range because of their excellent soft magnetic properties.
The characteristic required for such an electrical steel sheet is W _17/50 (W / k), which is the loss when magnetized to 1.7 T at a frequency of 50 Hz.
It is important that the iron loss represented by g) is low.

[0003] Generally, to reduce the iron loss of an electromagnetic steel sheet,
It is effective to reduce the eddy current loss, so that the method of increasing the Si content to increase the electrical resistance, the method of reducing the steel plate thickness, the method of reducing the crystal grain size of the product, and the degree of crystal integration There is known a method for increasing the magnetic flux density by increasing the magnetic flux density. Among them, about the method of increasing the Si content,
If Si is excessively contained, rollability and workability are deteriorated, so that there is a limit. Further, a method of reducing the thickness of a steel sheet and a method of reducing the crystal grain size are not preferable because they extremely increase manufacturing costs.

[0004] Many studies have been made on a method of improving the magnetic flux density by increasing the degree of integration of the remaining crystal orientations. For example, Japanese Patent Publication No. 46-23820 discloses a method in which Al is added to steel and hot working is performed. after rolling, after precipitating fine AlN by quenching and accompanying hot hot-rolled sheet annealing of 1000 to 1200 ° C., discloses a technique for performing rolling under high pressure rate of 80% to 95%, whereby B ₁₀ As a result, an extremely high magnetic flux density of 1.95 T is obtained. This method makes use of the fact that AlN that has been finely dispersed and precipitated has a strong effect as an inhibitor that suppresses the growth of primary recrystallized grains, and only secondary nuclei with excellent crystallographic orientation are recrystallized, whereby the orientation is improved. An excellent product crystal structure is obtained. However, in this method, since the crystal grain size of the product is generally coarse, it is difficult to reduce the iron loss, and there is a problem that it is difficult to stably obtain a product having a high magnetic flux density and a low iron loss. Furthermore, the inclusion of Al, which is easily oxidized, makes it extremely difficult to form subscales in decarburizing annealing and to form a forsterite film in finish annealing.

In Japanese Patent Publication No. 58-42244 and Japanese Patent Publication No. 60-55570, a steel containing 0.0003% to 0.0035% of B and 0.0030% to 0.0070% of N by weight is used. Mn / S of 1.8 or less or 2.1 respectively
With less, a technique for obtaining a magnetic flux density of 1.92T from 1.85T in B ₈ is disclosed. The method using BN as an inhibitor may provide a high magnetic flux density, but not only leads to an increase in cost due to lowering Mn, but also has a difficulty in industrialization because it causes hot cracking in the hot rolling process.

Further, Japanese Patent Publication No. Hei 7-68581 discloses that
By reducing the required B amount to 0.0018% or less, Mn /
Techniques for increasing S to 1.8 or more or 2.5 or more are disclosed, but the magnetic flux density is reduced. Further, JP-A-57-11
In Japanese Patent No. 4615, the remaining amount of N excluding an equivalent amount of N necessary for B to precipitate as BN is defined as the amount of dissolved N, and by setting this to 0.0020% or less, the Mn / S becomes 2.1 or more. However, it is disclosed that a high magnetic flux density can be obtained, but it has not been possible to stably obtain a grain-oriented electrical steel sheet having a good secondary recrystallization structure.

To solve this problem, Japanese Patent Laid-Open Publication No.
No. 3 discloses that by controlling the reduction ratio and the rolling end temperature in hot finish rolling based on the B content, the precipitation of the inhibitor can be made uniform and fine, but in actual operation, It has been difficult to stably obtain a high magnetic flux density throughout the product.

[0008]

The present invention relates to the above BN
Focusing on the superiority in improving the magnetic flux density of grain-oriented electrical steel sheet containing mainly as an inhibitor, further increasing the degree of integration of crystal orientation to obtain a stable magnetic steel sheet with high magnetic flux density and low iron loss The aim is to propose a possible manufacturing method.

[0009]

In order to eliminate the instability of secondary recrystallization which occurs when BN is used as an inhibitor, the inventors of the present invention have studied the use of BN and precipitates containing BN in steel slabs. The influence on secondary recrystallization was studied diligently. As a result, a very small amount and an appropriate amount of Al are contained together with B so as not to be considered effective for secondary recrystallization, and when the steel slab is manufactured by continuous casting, the ratio of columnar crystals is controlled by controlling the cooling rate and the like. After heating at a high temperature of 1350 ° C or more and then controlling the heating time and soaking time, solid solution of precipitates and fine precipitation by subsequent annealing are promoted. Conventionally, it is possible to maintain the effect of suppressing the growth of crystal grains, to obtain an extremely advantageous suppressing force for the growth of secondary recrystallization, and to stably achieve high magnetic properties. The inventors obtained a completely different idea and used it to complete the present invention.

Specifically, C: 0.03 to 0.10 wt%, Si: 2.5 to 4.5 wt%, Mn: 0.05 to 1.5 wt%, B: 0.0010 to 0.0060 wt%, N: 0.0030 to 0.010 wt%, S and 1 or 2 types of Se: 0.010 to 0.040 wt%, and the following formula is satisfied for the amounts of Mn, S, and Se: Mn (wt%) / (S (wt%) + Se (wt%)) ≧ 2.5 After casting a continuous cast slab for electrical steel sheets, and then hot-rolling the continuous cast slab,
Cold rolling is performed once or two or more times with intermediate annealing to obtain a cold-rolled sheet having a final thickness, and the cold-rolled sheet is subjected to decarburizing annealing also serving as primary recrystallization, and then to secondary recrystallization. And in a method for producing a grain-oriented electrical steel sheet which performs a final finish annealing for purifying treatment, further comprising: Al: 0.0010 to 0.00
80% by weight, the columnar crystal ratio in the continuous cast slab is 40% or more, and the slab heating temperature is 1350 ° C or more, and the heating time from 1250 ° C to the heating temperature range Is set within 1 hour, and the subsequent slab soaking time t (min) satisfies the following formula: 1/5 × (1450−T) ≦ t ≦ 2/5 (1500−T) (T: slab heating temperature (° C.)) By setting the range, a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss is manufactured.

The continuous cast slab further contains one or more selected from Cu, Sb, Sn, Bi, and Mo as an inhibitor element in the range of 0.005 to 0.30 wt% each. It is intended to stably produce a high magnetic flux density, low iron loss oriented magnetic steel sheet.

Further, in the present invention, in performing the final cold rolling, at least one or more passes thereof are carried out at 100 to 35
Warm rolling at 0 ° C or 10 to 100 ° C to 350 ° C
By performing the inter-pass aging treatment for 60 minutes, a grain-oriented electrical steel sheet having higher magnetic flux density and lower iron loss can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION With respect to Al present in a trace amount, the following experiment revealed the effect of refining precipitates in a steel slab and the appropriate range of Al.

(Experiment 1) The following experiment was conducted in order to clarify the effect of Al, which is present in a trace amount, on the primary recrystallized grain growth and the slab structure in steel containing BN.

The composition of the experimental material is as follows. Experimental material a. C: 0.070 wt%, Si: 3.25 wt%, Mn: 0.07
wt%, B: 0.0020 wt%, N: 0.0085 wt%, Se: 0.018 wt
%, Sb: 0.023 wt%, with the balance being a basic component consisting of unavoidable impurities and iron, and this basic component containing Al: 0.0010 wt%
%, 0.0030wt%, 0.0060wt%, 0.0080wt%, 0.0100wt%
And steels which were respectively changed.

When continuously casting steel slabs having the above-mentioned compositions, slabs having columnar crystal ratios of 30% and 60% were produced by changing the temperature of molten steel and controlling cooling during casting. After heating each of the slabs to 1300 ° C and 1400 ° C, hot rolling was performed to form a hot-rolled sheet having a thickness of 2.2 mm, and then 2 mm at 900 ° C.
n hot-rolled sheet, cold-rolled to a thickness of 1.5 mm,
After the intermediate annealing at 1000 ° C for 1 min, final cold rolling was performed.
A 22 mm cold rolled sheet was used.

Each of the above-mentioned materials was subjected to decarburizing annealing at 830 ° C. for 2 minutes, and decarburized to C: 0.002 wt% or less. next,
An annealing separator containing MgO as a main component was applied to each of the decarburized annealing samples, and the temperature was increased from 850 ° C to 1200 ° C.
The final finish annealing was performed by heating at a heating rate of 20 ° C./h. Table 1 shows the magnetic properties and the state of secondary recrystallization of the obtained magnetic steel sheets.
And Table 2 together.

[0018]

[Table 1]

[0019]

[Table 2]

[0020] First, if the columnar crystal ratio is 30%, although some secondary recrystallization has occurred, both B ₈ is less than 1.9 T. Next, even when the columnar crystal ratio becomes 60%, if the heating temperature is 1300 ° C, the secondary recrystallization is not complete,
The magnetic flux density B ₈ is low. When the columnar crystal ratio is 60% and the heating temperature is 1400 ° C., B ₈ is higher than in the case of heating at 1300 ° C. However, although when not containing Al is going secondary recrystallization, B ₈ because some secondary recrystallization becomes incomplete has a low value does not reach the 1.9 T. However, the content of Al is 0.001 to 0.008 wt%
When it is in the range, secondary recrystallization is also complete and B ₈ is 1.
It turned out that 9 T or more was obtained.

Further, by using these decarburized annealing plates, 900
Each was subjected to isothermal annealing at 24 ° C. for 24 hours in an Ar atmosphere. For each of the samples obtained as a result of the above test, (1) primary recrystallized grain size after decarburization annealing (approximately to a circle; the same applies hereinafter); (2) primary recrystallization after isothermal annealing at 900 ° C for 24 hours. The particle size (this corresponds to primary recrystallized grains immediately before the start of secondary recrystallization) was measured and investigated. The result is shown in FIG.

First, for a sample with a columnar crystal ratio of 60%, the primary recrystallized grain size (line c) after decarburization primary recrystallization when heated to 1300 ° C. before hot rolling is based on the basic component. No significant change in crystal grain size was observed even when the Al content was increased. The grain size after holding these decarburized annealed sheets at 900 ° C. for 24 hours, that is, the primary recrystallized grain size (line d) immediately before the start of the secondary recrystallization, was also increased at any Al content. did.

On the other hand, when heating before hot rolling was performed at 1400 ° C., the primary recrystallized grain size after decarburization primary recrystallization (line a)
Decreases as the content of Al increases, and
%, It grew again. When Al is not contained, the particle size after holding at 900 ° C. for 24 hours is coarse, but the Al content is 0.001 wt% to 0.008 wt%.
%, It was found that the coarsening of the particle size was suppressed.

Next, when the columnar crystal ratio is 30%, 14%
Only the sample heated at 00 ° C. is shown in FIG. In these samples, the primary recrystallized grain size became considerably large after annealing for 24 hours, even though the heating temperature was increased to 1400 ° C.

The inventors of the present invention have conducted intensive studies on the causes of the above-mentioned results. As a result, the columnar crystal ratio in which the coarsening of the primary recrystallized grain size immediately before the secondary recrystallization was suppressed was 60% and the Al
It was found that when the content was 0.001 to 0.008 wt%, the solid solution during heating before hot rolling was good. This is described in detail below.

Each slab having each composition of the experimental material a described above was heated to 1300 ° C. and 1400 ° C., respectively, and then water-quenched. The slab before and after the heating was examined in detail with an optical microscope and an electron microscope, and as a result, a large number of precipitates were confirmed. When the components of these precipitates were analyzed, B and N as inhibitor components were detected. Table 1,
FIG. 2 also shows the results of observing the presence of precipitates after heating when the slab heating conditions before hot rolling and the amount of Al added to the material were changed.

From these results, when the heating temperature was 1300 ° C. and when the columnar crystal ratio was 30% and the heating temperature was 1400 ° C.,
Residual precipitates were confirmed also in the Al content. When the columnar crystal ratio was 60% and the heating temperature was 1400 ° C., residual precipitates were confirmed when Al was not contained. However, when Al was contained at 0.001 to 0.008 wt%, residual precipitates were observed. Nothing was observed.

Next, among the slabs having the composition a, the precipitates observed before heating of the raw material containing no Al and the raw material containing 0.006 wt% of Al were subjected to particle size analysis by an image analyzer. Measurement was performed to determine the distribution of the precipitate particle size and the average particle size of the precipitate. This is shown in FIG. First, the columnar crystal ratio
For 60% of the material, the steel without Al (Fig. 2a)
The distribution of the precipitate particle size is wide, and there are many coarse precipitates exceeding 10 μm, and the average particle size is as large as 7.74 μm. On the other hand, the steel containing Al (FIG. 2b) is 10 μm
The average particle size was 5.65 μm, indicating that the precipitates were relatively fine.

Next, in the case of a material having a columnar crystal ratio of 30%, Al is added in an amount of 0.1%.
Even when it contains 006% (FIG. 2c), there are many coarse precipitates exceeding 10 μm, and the average particle size is as large as 7.16 μm. Regarding the precipitated particles in this slab, a large number of particles of 10 μm or less occupy in the columnar crystal part, but more particles of 10 μm or more in the equiaxed crystal part, thereby increasing the average particle diameter value. .

Therefore, in the samples of Nos. 20 to 23 in Table 1, the columnar crystal ratio was increased, that is, the cooling was strengthened and the quenching was performed.
The inhibitor component was finely precipitated for the first time by containing 0.001 to 0.008 wt% of, and the heating temperature was increased to 1400 ° C to promote the solid solution of the precipitate. As a result, the remaining precipitate was observed. Probably not.

As described above, the inhibitor component precipitated relatively finely forms a complete solid solution once and re-precipitates more finely in a later step, thereby suppressing the coarsening of the primary recrystallized grains immediately before the secondary recrystallization. It is considered that the effect of strong grain growth suppression was exhibited.

(Experiment 2) In Experiment 1, by adding Al to the steel containing B and N, stabilization of secondary recrystallization and good magnetic properties were obtained. Therefore, the magnetic properties when Al was contained in the same range as in Experiment 1 without adding B were investigated.

The composition of the experimental material is as follows. Experimental material b. C: 0.070 wt%, Si: 3.23 wt%, Mn: 0.07
wt%, N: 0.0080 wt%, Se: 0.020 wt%, Sb: 0.025 wt
%, The balance being a basic component consisting of unavoidable impurities and iron, and this basic component containing Al: 0.0010 wt%, 0.0030 wt%
%, 0.0060 wt%, 0.0080 wt%, and 0.0100 wt%, respectively.

When manufacturing a continuous cast slab having each of the above compositions, the columnar crystal ratio was set to 60%, and after heating this to 1400 ° C.
Hot rolled sheet with a thickness of 2.6 mm by hot rolling, 2 mi at 950 ° C
n, and then cold rolled to a thickness of 1.8 mm.
After the intermediate annealing at 1050 ° C for 1 min, the final cold rolling was performed.
A 34 mm cold-rolled sheet was used. For this cold rolled sheet at 840 ° C
After decarburizing annealing for min, C: 0.002% or less.
Each of the samples was coated with an annealing separator mainly composed of MgO and heated at a rate of 15 ° C./h from 850 ° C. to 1200 ° C. for finish annealing. Table 3 shows the magnetic properties and coating appearance of the obtained magnetic steel sheets.

[0035]

[Table 3]

From the above results, it was confirmed that secondary recrystallization did not occur and the magnetic characteristics were deteriorated only by adding Al. Further, it was found that when the Al content was increased, the appearance of the coating film changed to whitish and deteriorated.

(Experiment 3) C: 0.068 wt%, Si: 3.24 wt%
%, Mn: 0.07 wt%, B: 0.0040 wt%, N: 0.0075 wt%,
A slab containing 0.019 wt% of Se, 0.025 wt% of Sb, and 0.0060 wt% of Al and the balance consisting of unavoidable impurities and iron was prepared by continuous casting to have a columnar crystal ratio of 45%. . 80min in the range of 1300 ~ 1425 ℃
After the slab was heated for various heating times up to 2.2 mm, a hot-rolled sheet with a thickness of 2.2 mm was formed by hot rolling, annealed at 900 ° C for 2 min, cold-rolled to a thickness of 1.5 mm, 1 in ° C
After the intermediate annealing of min, final cold rolling was performed to obtain a cold-rolled sheet of 0.22 mm. These cold rolled sheets were subjected to decarburizing annealing at 830 ° C. for 2 minutes to decarbonize C: 0.002% or less. Each sample was coated with an annealing separator containing MgO as a main component, and was subjected to finish annealing by heating from 850 ° C. to 1200 ° C. at a rate of 20 ° C./h. FIG. 3 shows the quality of the magnetic properties of the obtained magnetic steel sheet. ○ marks in FIG. 3 is a magnetic flux density B ₈ is 1.9 T
In the above, the crosses indicate those where the magnetic flux density was less than 1.9 T.

From this figure, the following equation, in which the slab heating time t (min) is determined by the heating temperature T (° C.), is given by: 1/5 × (1450−T) ≦ t ≦ 2/5 × (1500−T) It was found that a material having a high magnetic flux density can be obtained within a satisfactory range.

Although the important points relating to the present invention have been invented above, the embodiments of the present invention will be specifically described below. (Chemical component) C: 0.03 to 0.10 wt% When the C content exceeds 0.10 wt%, the amount of γ transformation becomes excessive, the distribution of B during hot rolling becomes uneven, and the uniformity of the distribution of BN is hindered. It is harmful. Further, the load of decarburization annealing also increases, and decarburization failure easily occurs. On the other hand, 0.03wt%
If it is less than 2, the secondary recrystallization is incomplete, and the magnetic properties are similarly deteriorated. Therefore, C is limited to the range of 0.03 to 0.10 wt%.

Si: 2.5-4.5 wt% Si is an essential component for increasing electric resistance and reducing iron loss. Therefore, it is necessary to contain 2.5 wt% or more, but it exceeds 4.5 wt%. And workability deteriorates, making rolling and product processing extremely difficult.
Range.

Mn: 0.05 to 1.5 wt% Mn is also a necessary component for increasing electric resistance and improving hot workability at the time of production. 0.05 for this purpose
It is necessary that the content is not less than 1.5% by weight. However, if the content exceeds 1.5% by weight, γ transformation is induced to deteriorate magnetic properties.

B and N: In the present invention, BN is used as a main inhibitor component for the stable generation of sub-scale and the formation of a good undercoat film thereby. In particular, when the final cold rolling reduction is 80% or more, the secondary recrystallization temperature becomes extremely high. Therefore, it is essential to include B and N as high-temperature and stable inhibitor components in steel. Of these, B is contained in the range of 0.0010 to 0.0060 wt%. If the B content is less than 0.0010 wt%, B
Insufficient amount of N could not obtain good secondary recrystallization,
If the content exceeds 0.0060 wt%, the solid solution temperature increases, and it is impossible to completely dissolve BN before hot rolling by ordinary heating. The content of N must be 0.0030 wt% or more, and if the N content is less than 0.0030 wt%, the amount of precipitated BN becomes insufficient. If the N content exceeds 0.010 wt%, gasification occurs in the steel and defects such as blisters occur.
% Range.

Auxiliary inhibitor component: It is necessary to contain Se or S alone or in combination as an inhibitor component for supporting B and N. Since these components precipitate as Mn compounds or Cu compounds in steel, a total of 0.010 wt% or more is required to maintain the suppression effect. However, if it exceeds 0.040 wt%, the slab heating temperature becomes extremely high. However, they cannot be completely dissolved and remain as coarse precipitates, which is rather harmful. Therefore,
The range is 0.010 to 0.040 wt%. If the value of Mn (wt%) / (S (wt%) + Se (wt%)) is smaller than 2.5 in relation to the amount of Mn, grain boundary cracks and edge cracks increase significantly during hot rolling. It is practically necessary that Mn / (S + Se) ≧ 2.5.

Other inhibitor elements: Cu, Sb, Sn,
Since Bi and Mo have an auxiliary role of enhancing the inhibitory power as inhibitors, they can be added as needed. The preferred range of these addition amounts is 0.005 to 0.30 wt%. In addition, the addition of Ni or Co also improves the surface properties of the steel sheet, and thus may be appropriately added.

Al: 0.0010 to 0.0080 wt% In the present invention, secondary recrystallization is stabilized by adding a small amount of Al, and good magnetic properties are obtained. Al is Al
Although it is known as an inhibitor element for forming N, it is presumed from the above experimental results that effects on the stability of secondary recrystallization and the improvement of magnetic properties were recognized. It is considered that the precipitation behavior of BN or Mn (Se + S) was changed by adding Al in the range. One is that the precipitation temperature was lowered due to the presence of Al during continuous casting, and uniform precipitation was achieved. .

By adding Al, the precipitates are refined before heating the slab, so that the solid solution becomes easy. As a result, the inhibitor is re-precipitated more finely after hot rolling, and as a result, the ability to suppress the growth of the primary recrystallized grains is reduced. Thus, it is considered that good magnetic properties were finally obtained. If the amount of Al is less than 0.0010 wt%, the above effect cannot be obtained, and
When the content exceeds 0080 wt%, the secondary recrystallized grain size becomes coarse, and iron loss deteriorates. For the above reasons, the addition amount of Al is 0.0010 to 0.00
It must be in the range of 80 wt%.

In addition, when Al is added in a large amount, it is difficult to form subscales in decarburizing annealing and forsterite in finishing annealing. Such deterioration of the coating deteriorates not only the appearance of the coating but also the magnetic properties. In order to prevent such deterioration, it is necessary to limit Al to 0.0080 wt% or less. It is not clear why such an appropriate range exists, but as the amount of solute Al increases, oxides are more likely to form near the surface of the steel sheet, producing subscale during decarburization annealing and forsterite coating during finish annealing. It is thought that an adverse effect such as inhibiting the production of is produced.

(Rolling conditions) The steel adjusted to the above components is continuously cast into a slab. At this time, it is necessary to increase the ratio of columnar crystals in the structure in the slab.
The precipitated particles in the columnar crystal are finer than the equiaxed crystal part, and by increasing this ratio, the solid solution in the subsequent slab heating is improved. Therefore, the ratio of columnar crystals must be 40% or more.

In the subsequent slab heating, it is necessary to set the heating temperature to 1350 ° C. or higher. In the present invention, after adding the above-mentioned predetermined amount of Al, the columnar crystal ratio in the slab in continuous casting is set to 40% or more, and the slab heating temperature is set to 1350 ° C.
For the first time, BN, Mn (Se + S)
Can be once completely dissolved in a solid solution, and a uniform finely dispersed state of the inhibitor can be obtained by subsequent reprecipitation.

Also, in slab heating, there is a problem that the deposited BN becomes coarse. This seems to be due to the large diffusion coefficient of B. Therefore, the time required to raise the temperature from 1250 ° C. to the target heating temperature should be within one hour,
Further, according to the above-mentioned experiment, the soaking time t (min) is changed to the soaking temperature T
The following equation determined by (° C.): 1/5 × (1450−T) ≦ t ≦ 2/5 (1500−T) (T: slab heating temperature) needs to be in the range.

In the subsequent hot rolling, a known technique such as a thickness reduction treatment or a width reduction treatment for uniformizing the structure can be added before and after the slab heating, as needed. The hot-rolled sheet obtained by hot rolling is subjected to hot-rolled sheet annealing after hot-rolled sheet annealing as necessary, and one-time cold-rolling to make the final sheet thickness by one cold rolling, or hot-rolled sheet annealing as necessary. After the application, a cold rolling twice method in which a first cold rolling and further a second cold rolling with an intermediate annealing interposed therebetween can be adopted. Further, cold rolling can be performed three times or more with a plurality of intermediate annealings interposed therebetween.

With respect to the rolling reduction of the cold rolling, the rolling of the first rolling is performed at a rolling reduction of 15 to 60% in the case of the cold rolling twice method as conventionally known. If the rolling reduction is less than 15%, the mechanism of rolling recrystallization does not work, so that the crystal structure cannot be made uniform. If it exceeds 60%, the crystal structure is integrated and the effect of the second rolling is obtained. This is because it will not be possible. The rolling reduction of the final rolling is set to 80 to 90%. If the rolling reduction exceeds 90%, secondary recrystallization becomes difficult, and if it is less than 80%, good orientation of secondary recrystallized grains cannot be obtained and the magnetic flux density of the product deteriorates.

In the final cold rolling, warm rolling at 100 to 350 ° C. or aging treatment between passes at 100 to 350 ° C. for 10 to 60 minutes can further improve the texture of primary recrystallization. It is preferable to employ the present invention. Further, after the final cold rolling, it is also possible to perform a known domain refining process, for example, a process of providing a linear groove on the surface of the steel sheet.

The steel sheet having the final thickness obtained through the above steps is
The steel sheet is subjected to decarburization and primary recrystallization annealing by a known method, and an annealing separator containing MgO as a main component is applied to the surface of the steel sheet and subjected to final finish annealing. At that time, adding a Ti compound or adding Ca or B to the annealing separator has the effect of further improving magnetic properties.

In the final finish annealing, it is necessary to raise the temperature in an atmosphere containing H ₂ from at least 900 ° C. during the temperature rise. That is, if annealing is performed in an atmosphere of only N ₂ up to a high temperature, nitridation occurs during the final finish annealing, and crystal grains having inferior orientation undergo secondary recrystallization, leading to deterioration of the magnetic flux density. The atmosphere during annealing requires H ₂ to pass at least at 900 ° C. or higher. In addition, the H ₂ atmosphere plays an important role in the formation of oxides and nitrides in the above film, and it is considered necessary to enhance the reducibility especially in the middle to late stages of annealing at 900 ° C or higher. Can be

After the final finish annealing, after removing the unreacted annealing separating agent, an insulating coating is applied to the steel sheet surface to form a product. If necessary, the steel sheet surface may be mirror-finished before coating. Also, the coating baking process of the coating can also be used as the flattening process.
Further, for the steel sheet after the secondary recrystallization, known domain refining treatment, that is, performing plasma jet or laser irradiation on the linear region, or performing a process of providing a linear concave region by a projection roll, Iron loss reduction effect can also be obtained.

[0057]

EXAMPLE A continuously cast slab was prepared in which the components shown in Table 4 and the balance consisted of iron and unavoidable impurities.

[0058]

[Table 4]

With respect to these continuous cast slabs, two slabs each having a columnar crystal ratio of 25% and 70% by controlling the cooling rate were heated from 1250 ° C. to 1420 ° C. for 50 minutes and soaked for 15 minutes. mm and rolled into a coil at 550 ° C to form a hot-rolled sheet. The hot-rolled sheet was annealed at 1000 ° C. for 60 s, rapidly cooled at 20 ° C./s, and finished with a first cold-rolling to a thickness of 1.6 mm. The temperature of this steel sheet is raised to 1050 ° C and
s Holding intermediate annealing, quenching at 40 ° C / s, aging treatment between passes at 300 ° C for 30min during cold rolling, each finished to 0.22mm thickness. The obtained cold-rolled sheet was subjected to degreasing treatment and decarburizing annealing at 840 ° C for 2 minutes, and then SrSO4 was added to MgO.
An annealing separator containing 2% of ₄ and 8% of TiO ₂ was applied and then subjected to final finish annealing. The conditions for this final finish annealing are as follows:
After heating up to 850 ° C at 30 ° C / h in N ₂ ,
Up to 1200 ℃ in 50% N ₂・ 50% H ₂ at 20 ℃ / h
H ₂ and 8 h holding in, then up to 600 ° C. in H _2, 600
And it shall be cooled in an atmosphere of N ₂ from ° C.. After the final finish annealing, the unreacted annealing separating agent was removed, and magnesium phosphate containing 60% colloidal silica was applied as a tension coating and baked at 840 ° C. to obtain a product. Table 5 shows the magnetic properties of the obtained product.

[0060]

[Table 5]

As is clear from Table 5, when manufacturing a grain-oriented electrical steel sheet using BN as an inhibitor, when a small amount of Al is contained in the material slab and the columnar crystal ratio in the slab is increased, Extremely high magnetic flux density and low iron loss characteristics are obtained.

(Example 2) A continuous casting slab composed of the components shown in Table 6 and the balance being iron and unavoidable impurities was prepared.

[0063]

[Table 6]

With respect to these continuously cast slabs, the columnar crystal ratio was adjusted to 83% by controlling the cooling rate, and the temperature was changed from 1250 ° C. to 1400 ° C.
After heating for 40 min and soaking for 35 min, it was hot-rolled to a thickness of 2.6 mm and wound into a coil at 550 ° C to form a hot-rolled sheet.
The hot-rolled sheet was subjected to hot-rolled sheet annealing at 900 ° C. for 60 s, followed by rapid cooling at 20 ° C./s, pickling, and first cold rolling at 1.
Finished to 8 mm.

Next, the temperature was raised to 1050 ° C., an intermediate annealing was performed for 60 seconds, and quenched at 25 ° C./s. One of the two steel sheets obtained above was subjected to warm rolling at 250 ° C., and further, Sr was added to MgO containing 0.5% Ca and 0.09% B.
An annealing separator made by adding 4% of SO ₄ and 7% of TiO ₂ was applied, and final finish annealing was performed. The condition of final finish annealing is 85
0 ℃ until the temperature was raised at 30 ° C. / h in N _2, was heated at 15 ° C. / h in a mixed atmosphere of from 850 ° C. to 1050 ℃ 25% N ₂ and 75% H _2, further the temperature was raised to 1200 ° C. at 25 ° C. / h in H _2, the 12
After 8 h holding at 00 ° C., after cooling in H ₂ to 600 ° C., 600
And it shall be cooled in an atmosphere of N ₂ from ° C.. After the finish annealing, the unreacted annealing separator was removed, magnesium phosphate containing 50% colloidal silica was applied as a tension coating, and baked at 840 ° C. to obtain a product. Table 7 shows the magnetic properties of these products.

[0066]

[Table 7]

As is apparent from Table 7, when manufacturing a grain-oriented electrical steel sheet using BN as an inhibitor, the invention example in which a small amount of Al is contained in the material slab has extremely high magnetic flux density and low iron loss characteristics. Obtained and the coating appearance is good. Further, when warm rolling is performed during cold rolling, the magnetic properties are further improved.

[0068]

As described above, according to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss while using BN as a main inhibitor. This makes it possible to achieve both densities and reduce the iron loss value even more than before.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Al content and the primary recrystallized grain size in a basic experiment leading to the present invention.

FIG. 2 is a graph showing the difference in the distribution of precipitates depending on the presence or absence of Al in a basic experiment leading to the present invention.

FIG. 3 is a graph showing the quality of magnetic characteristics with respect to a slab heating temperature and a heating time in a basic experiment leading to the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K033 AA02 BA01 BA02 CA01 CA03 CA04 CA06 CA09 DA01 FA01 HA03 HA05 JA01 JA04 RA04 RA09 SA01

Claims (3)

[Claims] 1. C: 0.03 to 0.10 wt%, Si: 2.5 to 4.5 wt%, Mn: 0.05 to 1.5 wt%, B: 0.0010 to 0.0060 wt%, N: 0.0030 to 0.010 wt%, one of S and Se Species or 2 types: For electromagnetic steel sheets containing 0.010 to 0.040 wt%, and satisfying the following formula for the amounts of Mn, S, and Se: Mn (wt%) / (S (wt%) + Se (wt%)) ≧ 2.5 A continuous cast slab is cast, the continuous cast slab is heated and soaked, then hot-rolled, and then cold-rolled to a final thickness of one or two or more times with intermediate annealing to obtain a cold-rolled sheet having a final thickness. The method for producing a grain-oriented electrical steel sheet obtained by subjecting the cold-rolled sheet to decarburizing annealing also serving as primary recrystallization, and then performing final finish annealing for secondary recrystallization and purification treatment, wherein the continuous cast slab is cast. By further, Al: 0.0010-0.
0080 wt%, the columnar crystal ratio in the continuous cast slab is 40% or more, and the slab heating temperature is 1350 ° C or more.
The heating time from the temperature to the heating temperature range is set within one hour, and the subsequent slab soaking time t (min) is expressed by the following formula: 1/5 × (1450−T) ≦ t ≦ 2/5 (1500−T) ( (T: slab heating temperature (° C.)). 2. The continuous casting slab further contains one or more selected from Cu, Sb, Sn, Bi, and Mo as an inhibitor element.
2. The method for producing a magnetic steel sheet having a high magnetic flux density and a low iron loss according to claim 1, wherein each of the seeds contains at least 0.005 to 0.30 wt%. 3. The final cold rolling is characterized in that at least one or more passes are warm-rolled at 100 to 350 ° C. or an inter-pass aging treatment is performed at 100 to 350 ° C. for 10 to 60 minutes. The method for producing a high magnetic flux density and low iron loss grain-oriented electrical steel sheet according to claim 1 or 2.