JP2000119823A - Electrical steel sheet with low iron loss - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To further improve iron loss characteristics by appropriately controlling the crystal grain structure of an electrical steel sheet. SOLUTION: In an electromagnetic steel sheet containing Si: 1.0 to 8.0 wt%, an average crystal grain size calculated by excluding fine crystal grains having a circle equivalent diameter of 1 mm or less is 3 mm or more in circle equivalent diameter,
And in the cross section in the thickness direction of the steel sheet, the grain size is 0.03 mm or more,
The crystal grain structure is such that the frequency of ultra-fine crystal grains of 30 mm or less satisfies 3 / mm ² or more and 200 / mm ² or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic steel sheet having a low iron loss and suitable for use as an iron core material of a power transformer or a rotating machine.

[0002]

2. Description of the Related Art In the production of grain-oriented electrical steel sheets, it is a general method to use a precipitate called an inhibitor to cause secondary recrystallization during final finish annealing. For example, as a representative technology,
Japanese Patent Publication No. 15644 discloses a method using AlN and MnS, and Japanese Patent Publication No. 51-13469 discloses a method using MnS and MnSe, both of which are industrially practically used.
Apart from these, the technology of adding CuSe and BN is disclosed in
A number of other techniques are known, for example, a method using a nitride such as Ti, Zr, V, etc. is proposed in Japanese Patent Publication No. 46-40855.

[0003] The method using these inhibitors is a useful method for stably developing secondary recrystallized grains. However, since it is necessary to finely disperse the precipitates, the slab heating temperature before hot rolling is required. Must be set to a high temperature of 1300 ° C. or higher. However, high-temperature heating of the slab not only increases the equipment cost, but also increases the amount of scale generated at the time of hot rolling, so that not only the yield is reduced but also the maintenance of the equipment becomes complicated, which causes many problems.

[0004] Another problem with the technique using inhibitors is that if these components remain after the final finish annealing, the magnetic properties are degraded. Therefore, in order to remove Al, B, Se, S, and the like, which are inhibitor components, from the steel, it is necessary to purify the steel for several hours in a hydrogen atmosphere at 1100 ° C. or higher following the completion of the secondary recrystallization. However, due to such high temperature purification annealing,
There is a problem that the mechanical strength of the steel sheet is reduced, the lower part of the coil buckles, and the yield of the product is significantly reduced. Therefore, a technique that does not use an inhibitor as described above is a means for solving such a problem.

A method for producing a grain-oriented electrical steel sheet without using an inhibitor is disclosed, for example, in JP-A-64-55339.
The techniques disclosed in Japanese Patent Application Laid-Open Nos. Hei 2-57635, Hei 7-76732 and Hei 7-197126 are known.
What is common to these techniques is that the {110} plane is preferentially grown using surface energy as a driving force. In order to effectively utilize the surface energy difference, it is inevitably required to reduce the plate thickness in order to increase the contribution of the surface.
In the technology disclosed in Japanese Patent Publication No. 339, the thickness is limited to 0.2 mm or less, and in the technology disclosed in Japanese Patent Application Laid-Open No. 2-57635, the thickness is limited to 0.15 mm or less. In this regard, the thickness disclosed in Japanese Patent Application Laid-Open No. 7-76732 is not particularly limited. However, according to the first embodiment, when the thickness is 0.30 mm, the magnetic flux density is B _8.
At 1.700T or less, the degree of azimuth integration is extremely poor. Further, in the examples, the plate thickness at which a good magnetic flux density is obtained is limited to 0.10 mm. Similarly, the thickness disclosed in Japanese Patent Application Laid-Open No. 7-197126 is not limited, but since this technology is a technology of performing tertiary cold rolling of 50 to 75%, the thickness is necessarily thin. In the embodiment, the thickness is 0.10 mm. Since the thickness of the grain-oriented electrical steel sheet currently used is almost 0.20 mm or more, it is difficult to obtain a normal product by the method using surface energy as described above.

Further, in order to utilize surface energy, high-temperature final finish annealing must be performed in a state where formation of surface oxides is suppressed. For example, JP-A-64-5553
The technique disclosed in Japanese Patent Application Publication No. 9 describes that a vacuum or an inert gas, or a mixed gas of a hydrogen gas and a nitrogen gas is used as an annealing atmosphere at a temperature of 1180 ° C. or more. In the technique disclosed in Japanese Patent Application Laid-Open No. 2-57635, it is recommended to reduce the pressure in an inert gas atmosphere or a mixed gas of hydrogen gas and inert gas at a temperature of 950 to 1100 ° C. Have been. Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 7-197126, it is described that the final finish annealing is performed in a non-oxidizing atmosphere or a vacuum at a temperature of 1000 to 1300 ° C. and an oxygen partial pressure of 0.5 Pa or less. .

As described above, in order to obtain good magnetic properties by utilizing surface energy, the atmosphere of the final finish annealing requires an inert gas or hydrogen, and it is recommended that a vacuum be used as a recommended condition. Although required, compatibility between high temperature and vacuum is extremely difficult in terms of equipment, and costs are high.

Further, when the surface energy is used, only the {110} plane can be selected in principle, and the growth of goss grains having the <001> direction aligned with the rolling direction is selected. Not necessarily. Since the magnetic properties of a grain-oriented electrical steel sheet are improved only when the easy axis <001> is aligned in the rolling direction, good magnetic properties cannot be obtained in principle only by selecting the {110} plane. Therefore, rolling conditions and annealing conditions that can obtain good magnetic properties by a method utilizing surface energy are extremely limited, and as a result, the obtained magnetic properties must be unstable.

In addition, in the method utilizing surface energy, the final finish annealing must be performed while suppressing the formation of a surface oxide layer. For example, an annealing separator such as MgO cannot be applied and annealed. After finish annealing, an oxide film similar to that of a normal grain-oriented electrical steel sheet cannot be formed. For example, a forsterite film is a film formed when MgO is mainly used as an annealing separator, and this film not only gives tension to the steel sheet surface,
It has the function of ensuring the adhesion of the insulating tension coating mainly composed of phosphate, which is further applied and baked on the forsterite film. Therefore, when there is no forsterite film, the iron loss is significantly deteriorated.

Furthermore, even if the orientation of secondary recrystallization is adjusted to the Goss orientation by the method using an inhibitor or the method not using an inhibitor as described above, the iron loss of a product is not necessarily sufficiently reduced. . This is because the secondary recrystallized grains are coarse. In order to solve this problem, Japanese Patent Publication No. 20720/1984 discloses a technique for improving the core loss by reducing the average grain size of the secondary recrystallized grains. A technique for controlling the distribution to reduce iron loss has been proposed in Japanese Patent Publication No. Hei 4-19296. However, in these secondary recrystallized grain refinement techniques, the degree of orientation accumulation of the secondary recrystallized grains is reduced, so that the obtained iron loss is not sufficient.

It is known that high magnetic flux density and low iron loss can be obtained in a state where fine crystal grains exist inside coarse secondary recrystallized grains having a high degree of orientation integration. For example, Japanese Unexamined Patent Publication No. Hei 10-17931 discloses a technique in which heat treatment is locally performed to produce 0.25 to 5 fine crystal grains having a diameter of 2 mm or less per 100 mm ² . Japanese Patent Application Laid-Open No. 8-213225 discloses that coarse crystal grains having a particle size of 5 to 50 mm have a diameter of 0.05 to 50 mm.
A grain-oriented electrical steel sheet having a secondary recrystallized structure having fine crystal grains of 2 mm is disclosed. Regarding the size of the fine crystal grains produced by the above technique, the size is often 1 mm or more in the case of secondary recrystallized grains having a Goss orientation, and almost Thickness or more, that is, particle size: 0.30 mm or more. Fine primary recrystallized grains with a grain size of 0.30 mm or less are almost completely eaten by secondary recrystallized grains during high-temperature finish annealing, especially during purification annealing performed in a temperature range exceeding 1100 ° C .

By the way, since fine crystal grains of 0.30 mm or more that penetrate the plate inevitably cause a reduction in magnetic flux density, as disclosed in Japanese Patent Application Laid-Open No. 10-17931, Good iron loss cannot be obtained unless the number of generation of fine crystal grains is limited and the generation place is artificially controlled within a narrow range. Further, in the electromagnetic steel sheet disclosed in Japanese Patent Application Laid-Open No. 8-213225, Al is contained in its component in an amount of 0.005 to 0.06.
Although it is an essential condition to contain wt%, good iron loss cannot be obtained because Al as a steel sheet component is precipitated by bonding with nitrogen as a trace impurity.

[0013]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and achieves a further improvement in iron loss characteristics by appropriately controlling the grain structure of a steel sheet. The purpose is to propose an electrical steel sheet.

[0014]

Means for Solving the Problems Now, the inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have used a steel slab containing no inhibitor component as a material and minimized impurities in the steel slab. By appropriately controlling the heat treatment conditions while reducing the amount, it is possible to generate an appropriate amount of ultrafine crystal grains in the coarse secondary recrystallized grains, and as a result, the intended purpose is advantageously achieved. Obtained knowledge. The present invention is based on the above findings.

That is, according to the present invention, Si: 1.0 to 8.0 wt%
And the grain structure is equivalent to a circle with a particle size of 1 mm
Existence of ultra-fine crystal grains whose average crystal grain diameter calculated excluding the following fine crystal grains is 3 mm or more in circle equivalent diameter and 0.03 mm or more and 0.30 mm or less in the cross section in the thickness direction of the steel sheet An electromagnetic steel sheet having a low iron loss, wherein the frequency is 3 pieces / mm ² or more and 200 pieces / mm ² or less.

In the present invention, C, O,
Impurity components such as Al, B, V, Nb, Se, and S are desirably reduced to 50 ppm or less, preferably 30 ppm or less.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the invention will be described below. By the way, the present inventors have tried to improve iron loss by performing the following experiment using a material containing no inhibitor component. C: 0.070 wt%, Si: 3.22 wt%, Mn 0.070 wt
%, Especially for Al, N and O, respectively:
A steel slab with the composition controlled to 10 ppm, N: 10 ppm, O: 15 ppm and other impurities to 30 ppm or less is manufactured by continuous casting, then heated to 1100 ° C, It was finished to a thickness of 2.6 mm by rolling. Then, after annealing the hot-rolled sheet at 1000 ° C. for 1 minute in a nitrogen atmosphere, it was quenched and then cold-rolled to a final slope thickness of 0.35 mm. Then, decarburizing annealing was performed at 840 ° C for 120 seconds in an atmosphere of hydrogen: 75%, nitrogen: 25% and dew point: 65 ° C to reduce the C content in the steel to 0.0020 wt.
%. Thereafter, an annealing separator containing MgO as a main component was applied, followed by final finish annealing. The final finish annealing was performed in nitrogen, and an experiment was performed in which the heating rate and the ultimate temperature were changed.

FIG. 1 shows the results of a study on the relationship between the iron loss of a product sheet and the maximum temperature reached in the final finish annealing.
As is apparent from the figure, when the maximum temperature is 1100 ° C. or lower, good iron loss is obtained.

Further, the inventors have found that, in the course of the above experiment, the iron loss of the product sheet is determined by the particle size existing in the secondary recrystallized grains.
It has been found that there is a remarkable relationship with the frequency of ultrafine crystal grains of 0.03 mm or more and 0.30 mm or less. Figure 2 shows the result.
As shown in the figure, the particle size existing in the coarse secondary recrystallized grains is 0.03
The number of ultra-fine crystal grains of not less than mm and not more than 0.30 mm is 3 / mm ²
It has been found that good iron loss can be obtained in the range of from 200 pieces / mm ^2, particularly from 5 pieces / mm ² to 100 pieces / mm ² .

It has also been found that such an arrangement of fine grains is realized when the ultimate temperature in the final finish annealing is 1120 ° C. or less. This is because the final annealing temperature is 1120
It is considered that when the temperature exceeds ℃, ultrafine crystal grains having a particle size of 0.03 mm or more and 0.30 mm or less are eaten by coarse secondary recrystallized grains.

In the case where MgO is applied as an annealing separator, an oxide base coat mainly composed of forsterite is formed on the steel sheet surface after the final finish annealing. However, in general, by forming a phosphate-based tension coating containing colloidal silica on the undercoat, iron loss can be further reduced.

[0022]

The reason why low iron loss can be obtained by the present invention has not always been clearly elucidated, but the inventors consider as follows. That is, when the fine crystal grains are left inside the coarse secondary recrystallized grains, a magnetic pole is generated at the grain boundary between the coarse secondary recrystallized grains and the fine crystal grains, and the magnetic domain is subdivided by this effect, and iron It is considered that the loss is reduced. In particular, the ultra-fine crystal grains having a grain size in the range of 0.03 to 0.30 mm, which are noted in the present invention, can generate magnetic poles without breaking the flow of magnetic flux, as compared with grains having a grain size exceeding 0.30 mm. Therefore, it is considered that iron loss can be improved without lowering the magnetic flux density.

For the production of such an electromagnetic steel sheet, it is preferable to complete the high-temperature finish annealing at a temperature of 1120 ° C. or less using a high-purity material without using an inhibitor. In the case where an inhibitor is used, when the annealing is completed in this temperature range, the removal of the inhibitor component from the steel becomes incomplete, and it becomes difficult to arrange suitable fine crystal grains in the coarse secondary recrystallized grains.

As described above, when an inhibitor is used, its properties are somewhat inferior to those when no inhibitor is used. However, when an inhibitor is used, secondary recrystallization can be performed by short-time continuous annealing. Therefore, it is extremely advantageous in terms of manufacturing cost, and in that case, in order to improve iron loss, it is extremely effective to form fine crystal grains within the range specified in the present invention.

Next, the reasons for limiting the configuration requirements of the present invention will be described. It is necessary to contain Si as a component of the magnetic steel sheet of the present invention to increase electric resistance and reduce iron loss. For this purpose, at least 1.0 wt% must be added, but if it exceeds 8.0 wt%, not only does the magnetic flux density decrease, but also the secondary workability of the product deteriorates significantly. %. A particularly preferable range of the amount of Si is 2.0 to 4.5 wt%.

The crystal grain size of the product plate is equivalent to a circle, and the grain size is 1
It is necessary that the average crystal grain diameter calculated excluding crystal grains of less than mm is 3 mm or more in circle equivalent diameter. This is because if the crystal grain size is less than 3 mm, the magnetic flux density decreases. The upper limit of the particle size is not particularly defined because it does not affect the iron loss characteristics. Here, the equivalent circle diameter (D) is given by the following formula D = 2 (S / nπ) ^1/2, where n is the number of crystal grains per unit area (S). In defining the crystal grain size, crystal grains having a grain size of 1 mm or less were excluded because the number of such fine grains was larger than that of secondary recrystallized grains of 1 mm or more. This is because the value of the average particle diameter greatly changes when the average particle size is included.

In the cross section in the thickness direction, the grain size is 0.03
3 ultra-fine crystal grains of not less than 0.30 mm and not less than 3 mm / mm ^{2 and not} less than 20
It is the most important point in the present technology that there are 0 or less pieces / mm ² . Here, when the particle size of the fine particles is less than 0.03 mm, the effect of forming the magnetic pole is poor, so that the iron loss is not improved, while the particle size is 0.
When the diameter exceeds 30 mm, the magnetic flux density decreases. Therefore, the particle diameter of the fine particles is limited to 0.03 mm or more and 0.30 mm or less. Also, FIG.
As shown in FIG.
Is not sufficient improvement of iron loss for small production amount of the magnetic poles is less than ^2, whereas since 200 / mm ² by weight, the magnetic flux density decreases, the occurrence frequency is 3 / mm ² or more, 200 / m ² It was limited to the following range. A particularly preferred presence frequency is 5 / mm ²
As mentioned above, it is 100 pieces / m ² or less.

Further, in the present invention, in order to effectively reduce iron loss, it is preferable to reduce trace components in the steel sheet as much as possible. That is, it is desirable that the content of C, O, B, V, Nb, Se, S, etc. in the steel not containing the oxide film be 50 ppm or less, respectively.

Next, the range of components suitable for producing the magnetic steel sheet of the present invention will be described. First, components in the case where no inhibitor is used will be described. When an inhibitor is not used, a relatively long final finish annealing is required, but a good iron loss can be obtained without performing high-temperature purification annealing, so that it is suitable as a material of the present invention.

C is a useful element for improving magnetic properties by improving the structure. However, if the content exceeds 0.12 wt%, it becomes difficult to remove it by decarburizing annealing. Therefore, the upper limit is set to about 0.12 wt%. . The lower limit is not particularly set, since secondary recrystallization is possible even with a material containing no C. In particular, if C is reduced to 30 ppm or less from the material stage, decarburization annealing can be omitted, which is advantageous in terms of production cost. Therefore, when manufacturing low-grade products, use a material with reduced C. Is advantageous.

O greatly inhibits the appearance of secondary recrystallization,
Since it is difficult to remove in the post-process, it is desirable to reduce it to 30 ppm or less in the molten steel stage. It is desirable to reduce other elements as much as possible. In particular, B, V, Nb, S, and Se that are not only harmful to the generation of secondary recrystallized grains but also remain in the base iron and deteriorate iron loss. Since it may be difficult to remove each element such as in the subsequent steps, it is desirable to reduce the content to 30 ppm or less at the raw material stage and to 70 ppm or less for Al.

Next, the case where an inhibitor is used will be described. When an inhibitor is used, secondary recrystallization can be performed by continuous annealing for a short time, so that there is an advantage that the production cost can be reduced. However, since purification cannot be sufficiently performed, characteristics are somewhat inferior. The inhibitor is not particularly limited, but MnSe, which is usually used,
MnS, AlN and the like are preferred.

When MnSe or MnS is used as an inhibitor If the amount of Mn is less than 0.05% by weight, the amount of precipitate formed is insufficient,
If too much, the dispersion state deteriorates, so the Mn content is 0.05 to 0.15
It is preferred to be about wt%. S and Se are Mn
In order to precipitate S or MnSe, it is preferable to contain about 0.01 to 0.04% by weight in both cases of single use and combined use.

When AlN is used as an inhibitor Acid-soluble Al and N are finely dispersed as AlN before secondary recrystallization and exert a strong inhibitory effect on the growth of primary recrystallized grains. For this purpose, Al is 0.0050-0.040 wt%, and N is 0.
It is preferred to be about 0010 to 0.0150 wt%. If the amount exceeds this range, the precipitates become coarse and the suppressing power decreases. If the amount is less than this, the amount of AlN becomes insufficient. In addition, Al is Nb, B,
It can be used in place of or in combination with another nitride forming element such as V or Ti. In order to realize a suitable dispersion state and obtain good magnetic characteristics, Nb is 0.01 to 0.40 wt%, and B is 0.002 to 0.2%.
It is preferable to add 02 wt%, V in the range of 0.01 to 0.03 wt%, and Ti in the range of about 0.01 to 0.04 wt%.

Further, by adding Sb, which is an inhibitor reinforcing component, a material having better magnetic properties can be obtained. It is considered that the addition causes Sb to segregate at the grain boundaries and further improve the magnetic properties by compensating for the suppression of primary grain growth during finish annealing. However, if it is too large, processing becomes difficult, so it is preferable to set the content to about 0.005 to 0.20 wt%. In addition to Sb, Cu: 0.02 to 0.20 wt%, Sn: 0.02 to 0.
30wt%, Ni: 0.02-0.50wt% and Mo: 0.01-0.05wt%
Is also advantageous in improving magnetic properties.

Next, the manufacturing process of the present invention will be described. First, a slab is manufactured from molten steel adjusted to the above preferable component composition, and such a slab may be manufactured by a normal ingot-bulking method, a continuous casting method, or may have a thickness of 100 mm or less. A thin cast piece may be manufactured by a direct casting method. The slab is usually hot-rolled by heating, but may be hot-rolled immediately after casting without heating. In the case of a thin cast slab, the hot rolling may be omitted and supplied directly to the subsequent steps.

Next, after hot-rolled sheet annealing is performed, if necessary, cold rolling is performed once or twice or more with intermediate annealing, then decarburization annealing is performed as necessary, and further, if necessary. After applying an annealing separator mainly composed of MgO,
A final finish annealing is performed. Here, the magnetic properties can be improved by performing hot-rolled sheet annealing. Further, sandwiching the intermediate annealing between the cold rolling is also useful for stabilizing the magnetic properties. However, since all of them increase production costs, it is determined from the economical point of view whether hot rolled sheet annealing or intermediate annealing is to be selected. The preferred temperature range for hot-rolled sheet annealing and intermediate annealing is 700 ° C or more and 1200 ° C.
It is as follows. This is because if the annealing temperature is lower than 700 ° C, recrystallization during annealing does not progress, and the effect is weak.
If the temperature exceeds 00 ° C., the mechanical strength of the steel sheet decreases, and it becomes difficult to pass through the line.

The decarburization annealing is not particularly necessary when a material containing no C is used. In addition, since oxidation of the steel sheet surface is performed by oxides and hydroxides in the annealing separator at the time of final finish annealing, it is not always necessary to oxidize before the final finish annealing. Further, prior to the final finish annealing, a technique of increasing the amount of Si after cold rolling by a siliconizing method may be used in combination.

Next, the final finish annealing is performed. In order to obtain the desired magnetic steel sheet according to the present invention, it is important that the maximum temperature is 1120 ° C. or lower. That is, if the ultimate temperature exceeds 1120 ° C, the particle size is 0.03 mm or more and 0.30 mm
This is because the following fine crystal grains are reduced by being eaten by the coarse secondary recrystallized grains, and the improvement of iron loss becomes insufficient. The annealing atmosphere is not particularly limited, but is preferably a non-oxidizing atmosphere such as nitrogen or hydrogen to prevent excessive oxidation of the steel sheet.

In order to further improve iron loss, it is effective to form a tension coating on the surface of the steel sheet. For this purpose, a multilayer structure composed of two or more kinds of films may be used. Further, depending on the application, a coating in which a resin or the like is mixed may be applied. Furthermore, a magnetic domain refinement technique can be used to obtain good iron loss. Here, as a method for refining magnetic domains, a method of irradiating a product plate with a pulse laser described in JP-B-57-2252,
The method of irradiating a product plate with a plasma flame described in Japanese Patent Application No. 9-96617 and the method of providing grooves by etching before decarburizing annealing disclosed in Japanese Patent Publication No. 3-69968 are effective.

[0041]

EXAMPLES Example 1 C: 0.005 wt%, Si: 3.45 wt%, Mn: 0.15 wt%, Ni: 0.
A steel slab containing 30 wt%, Al: 50 ppm, N: 15 ppm and O: 10 ppm, with the balance being substantially Fe, was manufactured by continuous casting and then heated at 1050 ° C for 20 minutes. Then, a hot-rolled sheet having a thickness of 2.5 mm was formed by hot rolling. Then 1000 ℃, 6
After annealing the hot-rolled sheet for 0 seconds, the sheet was finished to a final sheet thickness of 0.34 mm by cold rolling. Then, hydrogen: 75%, nitrogen: 25%,
Dew point: Decarburizing annealing at 900 ° C for 10 seconds in an atmosphere of 40 ° C to reduce C in steel to 0.0020wt%, then apply an annealing separator mainly composed of MgO, and then finish Annealed. The final finish annealing was performed under the conditions shown in Table 1.

The magnetic flux density B ₈ and iron loss W _17/50 of the product plate thus obtained were measured. Further, the average grain size of the secondary recrystallized grains calculated by excluding the grain size of 1 mm or less, and the grain size present in the cross section in the thickness direction is 0.03 mm or more,
The existence frequency of ultra-fine crystal grains of 0.30 mm or less was also investigated. Table 1 also shows the obtained results.

[0043]

[Table 1]

As is clear from the table, the average crystal grain size of the secondary recrystallized grains is 3 mm or more in circle equivalent diameter, and the grain size in the cross section in the thickness direction is 0.03 mm or more and 0.30 mm or less. Good iron loss characteristics are obtained when the presence frequency of the grains is in the range of 5 / mm ² or more and 100 / mm ² or less.

Example 2 C: 0.08 wt%, Si: 3.4 wt%, N: 59 ppm, O: 10 pp
m, Al: 200 ppm, B: 30 ppm, V: 10 ppm, Nb: 10 pp
A thin slab containing m, Se: 180 ppm, S: 10 ppm and P: 20 ppm, and the balance being substantially Fe, was produced by a continuous thin casting method with a thickness of 2.5 mm. Then, in cold rolling
After finishing to a final thickness of 0.34 mm, hydrogen: 75%, nitrogen:
Decarburization annealing was performed at 830 ° C for 120 seconds in an atmosphere with a dew point of 60 ° C at 25% to reduce C in steel to 0.0020 wt%. Then, final finish annealing was performed by short-time continuous annealing under the conditions shown in Table 2.

With respect to the product plate thus obtained, the magnetic characteristics, the average crystal grain size of the secondary recrystallized grains calculated by excluding the crystal grains having a grain size of 1 mm or less and the grain size in the cross section in the thickness direction are 0.03 mm or more. Table 2 also shows the results of the determination of the frequency of existence of ultra-fine crystal grains of 0.30 mm or less in the cross section.

[0047]

[Table 2]

As shown in the table, even when an inhibitor was used, a product having good iron loss could be obtained by satisfying the requirements of the present invention. Moreover, in this case, short-time continuous annealing could be used as the final finish annealing.

[0049]

Thus, according to the present invention, the average grain size of the grain structure of the electrical steel sheet calculated by excluding the grain having a circle equivalent diameter of 1 mm or less is 3 mm or more in circle equivalent diameter. In addition, the presence frequency of ultra-fine crystal grains having a grain size of 0.03 mm or more and 0.30 mm or less in the cross section in the thickness direction is 3 grains / mm ² or more, and 200 grains /
By setting it to not more than mm ² , good iron loss characteristics can be obtained. In particular, when a high-purity material containing no inhibitor component is used as a material, more excellent iron loss characteristics can be obtained.On the other hand, when a material containing an inhibitor component is used as a material, characteristics Although is somewhat inferior to the case of using a high-purity material, the production cost can be significantly reduced by utilizing short-time continuous annealing at the time of final finish annealing.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the highest attained temperature in final finish annealing and iron loss of a product sheet.

[Fig. 2] The particle size present in the secondary recrystallized grains is 0.03 mm or more,
4 is a graph showing the relationship between the frequency of ultra-fine crystal grains of 0.30 mm or less and iron loss of a product sheet.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsumasa Kurosawa 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. Chome (without address) Kawasaki Steel Corporation Mizushima Works F-term (reference) 5E041 AA02 AA11 CA02 CA04 NN01 NN06 NN17

Claims (1)

[Claims] An average crystal grain size calculated by excluding fine crystal grains having a diameter of a circle and a grain diameter of 1 mm or less, which is 1.0 to 8.0 wt% of Si: The presence frequency of ultra-fine crystal grains having a grain size of 0.03 mm or more and 0.30 mm or less in the cross section in the thickness direction of the steel sheet of 3 mm or more is 3 /
An electromagnetic steel sheet with low iron loss, characterized in that the thickness is not less than mm ^{2 and not} more than 200 pieces / mm ² .