JPH0680172B2 - Low-loss grain-oriented silicon steel sheet and method for manufacturing the same - Google Patents

Description

TECHNICAL FIELD The technical contents described in this specification with respect to a grain-oriented silicon steel sheet having a low iron loss and a method for producing the same are the grain size of secondary recrystallized grains after final finish annealing and the distribution thereof. Is related to improving iron loss characteristics without reducing the magnetic flux density of the product.

BACKGROUND ART Grain-oriented silicon steel sheets are mainly used in transformers as iron cores for other electrical equipment, and are required to have excellent magnetizing properties, especially low iron loss (typically W17 / 50). There is.

For this purpose, firstly, the secondary recrystallized grains <001> in the steel sheet
It is necessary to highly align the grain orientation with the rolling direction, and secondly, it is necessary to reduce impurities and precipitates existing in the final product steel as much as possible. The grain-oriented silicon steel sheet manufactured under such consideration has improved its iron loss value year by year through many improvement efforts to date, and recently, the product with a sheet thickness of 0.30 mm has a W17 / 50 A low iron loss value of 1.05 W / kg is obtained.

However, since the energy crisis of several years ago, the tendency to seek electrical equipment with less power loss has become stronger, and as a core material for them, grain-oriented silicon steel sheets with even lower iron loss are required. I'm running.

Conventional technology and its problems By the way, as a method of reducing the iron loss of grain-oriented silicon steel sheets, the Si content is increased, the product sheet thickness is made thinner, the secondary recrystallized grains are made finer, and the impurity content is reduced. , And metallurgical methods are generally known, such as aligning the secondary recrystallized grains in the (110) [001] orientation to a higher degree, but these methods are no longer available from the viewpoint of the current production means. The limit was reached, and further improvement was extremely difficult. Even if some improvement was recognized, the effect of iron loss improvement was small in spite of the efforts.

For example, in the method of aligning the secondary recrystallized grains in the (110) [001] orientation to a high degree, if the integration degree in the (110) [001] orientation is increased as much as possible, the magnetic flux density (magnetization Although the maximum magnetic flux density B ₁₀ at a force of 1000 A / m) is improved), the secondary recrystallized grains are gradually coarsened, and the iron loss is deteriorated.

By the way, various studies have been conducted so far on the optimum grain size of secondary recrystallized grains with respect to iron loss, and the average grain size is
It is known that reducing the grain size to about 1 mm is effective, but further reducing the grain size deteriorates iron loss.

As such a technique for refining secondary recrystallized grains, for example, in Japanese Patent Publication No. Sho 54-23647, a secondary recrystallized block region is formed on the surface of a steel sheet, and the growth of the secondary recrystallized grain is suppressed by the block region. Therefore, a method of substantially refining secondary recrystallized grains has been proposed. In addition, JP-A-54-710
Japanese Unexamined Patent Publication No. 28-28 discloses a method of controlling primary recrystallized texture by cold rolling using a grooved roll and thereby making secondary recrystallized grains fine.

However, all of these methods are methods for simply bringing the secondary recrystallized grains of the entire steel sheet closer to the above-mentioned optimum grain size of about 1 mm. Although it could be achieved, on the other hand, the decrease in the magnetic flux density due to the refinement of particles was unavoidable, which sometimes led to the deterioration of the iron loss itself.

In addition, research has been conducted on the proper grain size of grain-oriented silicon steel product sheets. For example, in Japanese Patent Laid-Open No. 59-23822, a part of the steel sheet surface after secondary recrystallization has been completed. A direction in which iron loss is low by arranging recrystallized grains with a size of about 200 μm or less (when the plate thickness is 0.40 mm or less) in the region subjected to processing strain after applying processing strain and then annealing again A method of obtaining a silicon carbide steel sheet is disclosed.

However, in the above method, in addition to the drawback that the process is complicated, since fine grains of about 200 μm or less that are recrystallized by the introduction of processing strain are essentially primary recrystallized grains,
The preferred orientation for the product is (110) [001]
There was a problem even where the deviation from the magnetic field was large and the decrease in magnetic flux density was unavoidable.

An object of the present invention is to solve the above problems advantageously, and to propose a grain-oriented silicon steel sheet and a method for producing the same, which achieves an advantageous improvement in iron loss characteristics without lowering the magnetic flux density. To aim.

SUMMARY OF THE INVENTION The present invention was newly developed after intensive research on the relationship between the magnetic properties and the crystal grain size in order to solve the above problems. Based on the new knowledge that the intended purpose can be advantageously achieved by adding the device to.

Structure of the Invention That is, the present invention relates to a secondary recrystallized grain of a silicon-containing steel sheet that has been subjected to final finish annealing, and its grain size distribution is calculated as follows:
Number ratio of 2.5mm crystal grains is 40-80%, while grain size: 5.0-1
It is a grain-oriented silicon steel sheet with low iron loss characterized by a mixed grain distribution in which the number ratio of 0.0 mm crystal grains is 15% or more.

The present invention also provides a hot-rolled sheet obtained by hot-rolling a silicon steel slab by performing cold rolling once or twice with intermediate annealing to obtain a final sheet thickness and then decarburizing. In a method for producing a grain-oriented silicon steel sheet, which comprises a series of steps in which primary recrystallization annealing is performed, and then an annealing separator containing MgO as a main component is applied to the surface of the steel sheet, followed by final finish annealing and overcoating treatment. After the decarburization / primary recrystallization annealing, the secondary recrystallization development accelerator is discretely adhered to the surface of the steel sheet before the application of the annealing separating agent, so that the particle size distribution of the secondary recrystallized particles becomes 1.0 Number ratio of ~ 2.5mm is 40 ~ 80%, particle size: 5.0 ~ 10.0m
A method for producing a grain-oriented silicon steel sheet having a low iron loss, characterized in that the number ratio of m crystal grains is 15% or more.

In the present invention, the formation region of the crystal grains having a grain size of 1.0 to 2.5 mm is a continuous or discontinuous strip-shaped region having a direction substantially perpendicular to the rolling direction of the steel sheet, and its width is 1.0
~ 4.0mm and 5 ~ 15m repeat interval in rolling direction
Those of m are particularly convenient.

The present invention will be described in detail below based on the experimental results leading to the origin of the present invention.

In the manufacturing process of grain-oriented silicon steel sheet, the steel sheet cold-rolled to the final thickness is usually subjected to decarburization annealing to remove harmful carbon. Due to such annealing, the steel sheet is decarburized and recrystallized at the same time, so it is called a decarburized / first recrystallization annealed sheet. Further, the recrystallized grains obtained at this time have various and various orientations and are called normal grains or primary recrystallized grains. Then, in the subsequent secondary recrystallization annealing, from the normal grains with various orientations (110) [00
The grains in the 1] orientation preferentially and explosively grow, and thus all the crystal grains in the steel sheet become the grains having the (110) [001] orientation or an orientation close thereto. Such abnormal grain growth phenomenon is called secondary recrystallization in the sense that normal grains, that is, primary recrystallized grains are recrystallized. In this secondary recrystallization,
In order to preferentially grow grains close to the (110) [001] orientation, it is necessary to suppress the growth of grains in other orientations, and for that reason, a component called an inhibitor is added to the steel. As such inhibitors, various sulfides, selenides, nitrides, carbides, B, Sb and Te are currently known.

By the way, if S, Se, N, etc. among the components added as a suppressor remain in the final product, the magnetic properties will be significantly adversely affected. Therefore, following the secondary recrystallization treatment, high temperature H ₂ Annealing is performed in the atmosphere to remove the above-mentioned residual impurities from the steel. Therefore, such annealing is referred to as purification annealing. Further, since the secondary recrystallization annealing and the purification annealing are usually performed continuously, they may be collectively referred to as final finish annealing.

Now, the grain size of the primary recrystallized grains of the decarburization / primary recrystallization annealing liquid is
Usually about 20 μm, but when the inhibitory effect of the above-mentioned inhibitor is insufficient in the subsequent secondary recrystallization annealing, normal grains cause grain growth, and as a result, the desired secondary recrystallization can be induced. Therefore, the steel sheet after the final finish annealing is composed of so-called normal grains with a size of up to about several hundreds of μm, and the magnetic properties of the product are significantly deteriorated.

In order to quantitatively grasp the situation as described above, the inventors of the present invention have variously changed the production conditions of grain-oriented silicon steel sheet containing 3.2% by weight of Si (hereinafter referred to simply as%) to obtain a plate. The crystal grain size of the product with a thickness of 0.30 mm was intentionally changed, and the relationship between the average grain size of the obtained crystal grains and the magnetic properties (magnetic flux density B ₁₀ and iron loss W 17/50) was investigated. As a result, the first
It is indicated by a circle in Figures a and b.

As is clear from FIG. 1, the B ₁₀ value simply increases with an increase in the average crystal grain size, but the iron loss value W17 / 50 gradually decreases, and after reaching a minimum value at a grain size of 1 to 3 mm. It tends to increase again. Therefore, for the iron loss, the average value of 1 to 3 mm is the optimum value as conventionally known in terms of the average particle size.

Meanwhile, according to FIG. 1, in the range of average particle size of 0.5 to 1.0 mm, although changing rapidly with B ₁₀ value and W17 / 50 value, this phenomenon, per crystal grains constituting the steel sheet, the average With a grain size of 0.5 to 1.0 mm as a boundary, fine grains on the finer side have normal grains,
On the other hand, it is shown that the secondary recrystallized grains are mainly contained on the coarse grain side. That is, when the average grain size is 1.0 mm or more, the degree of accumulation in the (110) [001] orientation of the product is increased due to the appearance of secondary recrystallized grains, and the B ₁₀ value and the iron loss are rapidly reduced. It will be brought.

Next, the inventors examined the grain size distribution of the crystal grains in the steel sheet and the arrangement thereof. The experiment is 3.2% S listed above.
The i-containing grain-oriented silicon steel sheet was used. One was locally distorted on the product sheet indicated by a circle in FIG. 1 according to the method disclosed in JP-A-56-130454. Then, re-annealing is performed to arrange recrystallized grains having an average grain size of about 0.1 mm in a direction perpendicular to the rolling direction on the surface of the steel sheet.
Repeated at mm intervals. The obtained results are shown by Δ in FIG. The other one is to attach fine SrO powder to the surface of the decarburized / primary recrystallization annealed plate, so that the secondary recrystallization structure of the product plate has a grain size of 1.0 to 2.5 mm. A region composed of secondary recrystallized grains was provided. This region has a width of about 3 mm and is a strip-shaped region which is continuous or intermittently continuous in the direction perpendicular to the rolling direction, and has repetitive pitches spaced at 12 mm in the rolling direction. The obtained results are indicated by a double circle in FIG. The reason why fine SrO powder is attached to the surface of the decarburized / primary recrystallization annealed plate to form fine secondary recrystallized grains with a grain size of 1.0 to 2.5 mm on the product sheet is SrO. Since the appearance of secondary recrystallized grains in the secondary recrystallization annealing is accelerated and the growth rate is not high at the parts attached to the powder, they should remain as fine secondary recrystallized grains in the steel sheet. It is thought to be because. It is speculated that the reason why the growth rate of the secondary recrystallized grains is slow is that the orientation thereof is slightly deviated from the (110) [001] orientation.

As is clear from the results shown in Fig. 1, in the example where the recrystallized grains having a size of about 100 µm are arranged on the surface of the steel sheet according to the conventional method (marked with △), the average grain size is certainly in the range of 7 to 20 mm. Although a large iron loss reduction effect was observed in, the value was only about the same as the product with the optimum crystal grain size indicated by ○, while the magnetic flux density (B ₁₀ value) showed a considerable decrease. .

On the other hand, the one in which the band-shaped region composed of the fine secondary recrystallization group of 1.0 to 2.5 mm is arranged (marked with ⊚) has an extremely large effect of improving the iron loss, and the result exceeding the conventional best value can be obtained. Moreover, the decrease in magnetic flux density (B ₁₀ value) was almost negligible as shown in the figure.

That is, by arranging the secondary recrystallized grains having different grain sizes alternately in the rolling direction, the grain-oriented silicon steel sheet having a lower iron loss than the conventional one without causing deterioration of the magnetic flux density. It was found that The reason why the magnetic flux density is not deteriorated here is that although the crystal grains that make up the steel sheet are fine grains, since they are secondary recrystallized grains, the deviation from the (110) [001] orientation is small. Is considered to be.

2a and 2b show the frequency distribution of the crystal grain size and the macrostructure of the products indicated by the double circles in FIG. 1 having an average grain size of 3.98 mm, respectively. The area indicated by A in Fig. 2b (width
3 mm), the number of crystal grains of 1.0 to 2.5 mm accounts for about 90%, while the grain size in the other area B (9 mm wide)
The number of crystal grains of 5.0 to 7.5 mm accounted for about 60%. When the areas A and B are not distinguished, the number ratio of crystal grains with a grain size of 1.0 to 2.5 mm is about 60%, that of crystal grains with a grain size of 5.0 to 7.5 mm is about 17%.
It was in%.

On the other hand, among the conventional materials indicated by ◯ in FIG. 1, the same investigation was conducted on the products having an average grain size of 3.89 mm, and the frequency distribution of the crystal grain size was as shown in FIG. 3a. The largest number of crystal grains with a grain size of 2.5-5.0 mm occupies about 70% of the total, and as a result, the finer grain side becomes,
Moreover, the numbers tended to decrease as the particles became coarser.

As described above, in the conventional product, the particle size distribution of the secondary recrystallized particles exhibited a uniform particle size distribution, whereas in the product according to the present invention, the particle size distribution of the secondary recrystallized particles exhibited a mixed particle distribution. Has a big feature.

Here, the calculation method of the crystal grain size and the average grain size will be described. In FIGS.
Since it is the next recrystallized grain, the crystal grain penetrates the plate thickness in the product with the plate thickness of 0.30 mm. Therefore, it is sufficient to calculate only on one side of the steel sheet. Now, assuming that the area of one crystal grain is Scm ² , this crystal grain size Dmm is Can be calculated by Next, the average grain size of polycrystalline grains is
When m ² and the number of crystal grains contained therein is N, the average grain size mm is Calculated by

Note that the method of calculating the particle size distribution in the area shown in FIG. 2b is such that the particles completely contained in the areas A and B are the areas A and B, respectively.
For a grain that spans regions A and B, on the other hand, of the two areas of the grain divided into two by the boundary line, it belongs to the region having the larger area,
I counted.

Next, regarding the iron loss improving effect, which one is better is that the grain size distribution of the secondary recrystallized grains is a mixed grain type and that the secondary recrystallized grains with a grain size of 1.0 to 2.5 mm are arranged in a strip shape. In order to determine what is essential, the following experiments were conducted.

That is, when applying fine SrO powder to obtain fine particles on the surface of the decarburized / primary recrystallization annealed plate, the SrO powder is scattered in spots, and the subsequent treatment is performed in the same manner as in the above example. It was a done product. The frequency distribution of secondary recrystallized grains and the macrostructure of the obtained product are shown in FIGS. 4a and 4b, respectively.

As is clear from Fig. 4b, this product plate has a particle size of 1.0.
Areas of secondary recrystallized grains of ~ 2.5 mm are scattered in spots, and the grain size distribution is about 64 with the largest number of grains of 1.0 ~ 2.5 mm.
%, On the other hand, the number of particles with a particle size of 5.0 to 7.5 mm is the second largest and is about 20.
%, And all others were 10% or less, and almost the same mixed grain type product as the example shown in FIG. 2 was obtained.

Now, the three types of frequency distributions shown in FIGS. 2 to 4 and the magnetic properties of the product sheet having a macrostructure are shown in Table 1 below.

As is clear from Table 1, even when fine secondary recrystallized groups are scattered in spots, even if they do not reach the example shown in FIG. 2 in which they are distributed in strips in the direction perpendicular to the rolling. , It was found that there is a considerable effect on reducing iron loss.

Regarding the improvement of iron loss that is not accompanied by the deterioration of magnetic flux density, the arrangement of fine secondary recrystallization groups is not an essential factor, but the particle size distribution has a great significance. It has been clarified that it is important to make the mixed grain type as shown in FIG.

Now, regarding the composition of the grain-oriented silicon steel sheet in this invention, it is essential to contain Si, but the amount is 2.0
If it is less than 4.0%, the iron loss is significantly deteriorated, while if it exceeds 4.0%, the cold workability tends to be deteriorated, so the Si content is 2.
It is desirable to set it to 0 to 4.0%. As for other components, any conventionally known component can be used as long as it is a component usually used for grain-oriented silicon steel sheets.

The plate thickness of the steel plate is preferably about 0.15 to 0.5 mm. Because, if it is less than 0.15 mm, secondary recrystallization is difficult, while
This is because if it exceeds 0.5 mm, the effect of improving iron loss is poor and it is not practical.

Most of the crystal grains that make up the steel sheet have a grain size of 1.
It is necessary that the secondary recrystallized grains have a size of 0 mm or more and a small size from the (110) [001] orientation. Particle size is 1.
If it is less than 0 mm, the deviation from the (110) [001] orientation is large, and in an extreme case, it remains as normal grains and seriously damages the magnetic flux density of the steel sheet and thus the iron loss.

Here, the grain size distribution of the crystal grains forming the steel sheet is a mixed grain type, that is, in the number ratio, 1.0 to
Secondary recrystallized grains having a grain size of 2.5 mm are 40 to 80%, preferably 60 to 7
It is required that the secondary recrystallized grains having a grain size of 0 to 10 mm and a grain size of 5.0 to 10.0 mm be 15% or more.

This is because the number ratio of secondary recrystallized grains with a grain size of 1.0 to 2.5 mm
If it is less than 40%, the effect of reducing iron loss is poor. On the other hand, if it exceeds 80%, or if the number ratio of crystal grains with a grain size of 5.0 to 10.0 mm is less than 15%, the number ratio on the coarse grain side becomes small. This causes deterioration of the magnetic flux density.

The number ratio of crystal grains having a grain size of more than 2.5 mm and less than 5.0 mm is preferably smaller than that of crystal grains of 5.0 to 10.0 mm.

By having a mixed-grain type particle size distribution in this way,
It is possible to reduce iron loss without reducing the magnetic flux density of the product.
In order to obtain the secondary recrystallization structure, it is sufficient to attach a material that promotes the development of secondary recrystallization to the decarburized / primary recrystallization annealed plate prior to the secondary recrystallization annealing. In addition to SrO powder, MgO ₃ , SnO, and SnO ₂ powders are particularly advantageous as secondary secondary crystallization promoters.

The reason why these agents promote the development of secondary recrystallization is that these agents change the existing form of the SiO ₂ particles dispersed in the steel sheet surface base metal during secondary recrystallization annealing. This is because the time required to develop the secondary recrystallized grains (called the latency) is shortened. With these agents, the growth rate of the secondary recrystallized grains that appeared early was smaller than the growth rate of normal secondary recrystallized grains.
It remains on the steel sheet as fine particles of mm. It is speculated that the reason for this slow growth rate is that the orientation is slightly deviated from the (110) [001] orientation.

The region to which the secondary recrystallization development accelerator is attached brings about secondary recrystallization of about 1.0 to 2.5 mm to the steel sheet after the final thickness, as a result of the accelerated development of the secondary recrystallization, while the secondary recrystallization is promoted. Since crystal grains of 5.0 to 10.0 mm are mainly expressed in the region where the recrystallization promoting agent is not attached, a desired mixed grain type secondary recrystallization structure can be obtained.

By the way, in the above-mentioned mixed grain type, 1.0 to 2.5 mm of 2
If the secondary recrystallized grain group is also repeatedly distributed in the form of a strip in the direction perpendicular to the rolling direction, it is possible to obtain a further effect in reducing the iron loss. At this time, the band-shaped region of the crystal grain group having a grain size of 1.0 to 2.5 mm preferably has a width of 1.0 to 4.0 mm and a repeating interval of 5 to 15 mm.

And the surface of such steel sheet is forsterite (MgO ₂ Si
In some cases, it has a glass coating made of O ₄ ), and on top of that, an overcoating coating may be provided if necessary due to requirements such as interlayer resistance. For the top coating film,
In addition to the usual insulating coating, it also includes a coating film that gives tension to the steel sheet.

Examples Example 1 A silicon steel sheet material containing Si: 3.2% was made into a cold-rolled steel sheet having a thickness of 0.30 mm according to a conventional method, then decarburized and subjected to primary recrystallization annealing, and then the steel sheet was divided into two. Is applied as it is with an annealing resolving agent containing MgO as the main component, followed by secondary recrystallization annealing and 1200 ° C, 5
A final finish annealing consisting of time-purified annealing was given as a comparative example. The other one has an average grain size of 500 on the steel plate surface.
Å SrO powder was applied in a strip shape with an attachment width of 2 mm in the direction perpendicular to the rolling direction, and with an interval of 7 mm repeatedly in the rolling direction, and then an annealing separator was applied over it, following the same procedure as in the comparative example. Final finishing annealing was performed to obtain a product.

As a result, in the latter example, fine secondary recrystallized grains having a grain size of 1.0 to 2.5 mm appeared in a band-like shape in the region where the SrO powder was adhered, but in the comparative example, a grain size of 2.5 to 5.0 mm was obtained. The number of secondary recrystallized grains was the highest. As shown in FIG. 5, the results of the measurement of the particle size distributions show that the comparative examples have a uniform particle size distribution, but the examples show a mixed particle size distribution with a particle size of 1.0.
The ratio of the number of crystal grains of ~ 2.5mm is 72.8%, while that of 5.0 to 10.0
The number ratio of the particle size of mm was 15.6%.

And, regarding these magnetic characteristics, the example is B ₁₀ = 1.902T; W17 /
While 50 = 0.985 W / kg, the comparative example has B ₁₀ = 1.908.
It was T; W17 / 50 = 1.073 W / kg.

Example 2 A silicon steel material containing Si: 3.2% was thickened according to a conventional method.
After making 0.23 mm cold-rolled steel sheet, decarburization / primary recrystallization annealing is performed, and then when applying the annealing separator, before application,
MoO ₃ powder with an average particle size of 1000Å was scattered on the surface of the steel sheet in spots with a diameter of 3 mm, and then an annealing separator was applied.

After that, secondary recrystallization annealing and then purification annealing at 1200 ° C. for 5 hours were performed.

For comparison, only an annealing separator containing MoO as a main component was applied according to a conventional method, secondary recrystallization annealing was performed, and then purification annealing was performed at 1200 ° C. for 5 hours, which was used as a comparative example.

As a result, in the example, a group of fine secondary recrystallized grains of 1.0 to 2.5 mm appeared in spots in the region to which the MoO ₃ powder was attached, but in the comparative example, a secondary recrystallized grain of 2.5 to 5.0 mm was observed. The largest number of crystal grains. As a result of measuring these particle size distributions, as shown in FIG. 6, a particle size distribution was obtained in the comparative example, but a mixed particle size distribution was shown in the example, and the number ratio of particle sizes of 1.0 to 2.5 mm was 71.4. %; The ratio of the number of particles with particle size of 5.0 to 10.0 mm is 19.7%
It was.

The magnetic characteristics of these examples are as follows: B ₁₀ = 1.885T; W17 / 50
= 0.856 W / kg, whereas the comparative example has B ₁₀ = 1.889T, W17
/50=0.937W/kg.

Example 3 A silicon steel material containing Si: 3.0% was formed in a thickness according to a conventional method.
After making 0.30 mm cold-rolled steel sheet, decarburization and primary recrystallization annealing are applied, and then when applying the annealing separator, before applying,
SnO powder was scattered on the surface of the steel sheet in spots having a diameter of 2 mm, and then an annealing separator was applied.

After that, secondary recrystallization annealing and then purification annealing at 1200 ° C. for 5 hours were performed.

For comparison, only an annealing separator containing MgO as a main component was applied according to a conventional method, secondary recrystallization annealing was performed, and then purification annealing was performed at 1200 ° C. for 5 hours, which was used as a comparative example.

As a result, in the example, a group of fine secondary recrystallized grains of 1.0 to 2.5 mm appeared in spots in the region to which the SnO powder was attached, but in the comparative example, a secondary recrystallized grain of 2.5 to 5.0 mm was formed. It had the most grains. When the number ratio of particle size distribution was calculated, in the example, the number ratio of particle sizes of 1.0 to 2.5 mm was 63.0.
%; The number ratio of particle diameters of 5.0 to 10.0 mm was 16.3%. On the other hand, in the comparative example, the number ratios were 9.3% and 18.5%, respectively, and the number ratio of the particle diameters of 2.5 to 5.0 mm was 65%.

The magnetic properties of these examples are B ₁₀ = 1.915T; W17 /
50 = 0.997 W / kg, whereas the comparative example has B ₁₀ = 1.920T; W
It was 17/50 = 1.062 W / kg.

EFFECTS OF THE INVENTION Thus, according to the present invention, it is possible to obtain a grain-oriented silicon steel sheet having significantly excellent iron loss characteristics as compared with the prior art without deteriorating the magnetic flux density.

[Brief description of drawings]

1 a and b are graphs showing the relationship between the average grain size and B ₁₀ and W 17/50, respectively, and FIGS. 2 a and b are the grain size distribution and macrostructure of the grain-oriented silicon steel sheet according to the present invention, respectively. 3A and 3B are schematic diagrams of the grain size distribution and macrostructure of the conventional grain-oriented silicon steel sheet, and FIGS. 4A and 4B are grain sizes of other embodiments of the present invention. Schematic diagrams showing the distribution and macrostructure, FIG. 5 and FIG. 6 are graphs showing the comparison of the particle size distributions of the present invention and the conventional example, respectively.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yo Ito 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.

Claims (3)

[Claims] 1. The particle size distribution of secondary recrystallized grains of a silicon-containing steel sheet that has been subjected to final finish annealing, the ratio of the number of crystal grains having a grain size of 1.0 to 2.5 mm is 40 to 80%, while the grain size is 5.0 to 10.0. A grain-oriented silicon steel sheet with low iron loss characterized by a mixed grain distribution in which the number ratio of mm crystal grains is 15% or more. 2. A grain formation region of grain size: 1.0 to 2.5 mm,
A continuous or discontinuous strip-shaped region that is oriented almost at right angles to the rolling direction of the steel sheet, and the width of such strip-shaped region is 1.
0 ~ 4.0mm and the repeat interval in rolling direction is 5 ~ 15
The grain-oriented silicon steel sheet according to claim 1, which is in the range of mm. 3. A hot-rolled sheet obtained by hot-rolling a silicon steel slab is cold-rolled once or twice with intermediate annealing to obtain a final thickness, and then decarburized. In a method for producing a grain-oriented silicon steel sheet, which comprises a series of steps in which primary recrystallization annealing is performed, and then an annealing separator containing MgO as a main component is applied to the surface of the steel sheet, followed by final finish annealing and overcoating treatment. After the decarburization / primary recrystallization annealing, the secondary recrystallization development accelerator is discretely adhered to the surface of the steel sheet before the application of the annealing separating agent, so that the particle size distribution of the secondary recrystallized particles becomes 1.0
A method for producing a grain-oriented silicon steel sheet having a low iron loss, characterized in that the number ratio of ~ 2.5 mm is 40 to 80%, and the number ratio of crystal grains of grain size: 5.0 to 10.0 mm is 15% or more.