JPH09202924A - Production of mirror-finished grain-oriented silicon steel sheet with high magnetic flux density and low iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably obtain a mirror-finished grain-oriented silicon steel sheet with high magnetic flux density on an industrial scale by effectively combining the attainment of ultrahigh magnetic flux density by means of conventional Bi addition with the reduction of iron loss by means of mirror finishing technique by application of alumina. SOLUTION: A molten steel, having a composition consisting of, by weight, 0.02-0.1% C, 2.0-4.8% Si, 0.012-0.050% acid soluble Al, 0.030-0.150% N, 0.0005-0.03% Bi, and the balance Fe, is cast, hot-rolled, and subjected to cold rolling including final heavy cold rolling at 65-95%, while process-annealed between cold rolling stages, to the final sheet thickness. After decarburizing annealing, the resultant sheet is nitrided and subjected to secondary recrystallization finish annealing, by which a grain-oriented silicon steel sheet is produced. At this time, decarburizing annealing is performed in the atmospheric gas of a degree of oxidation free from formation of Fe oxides, or, the oxides resultant from decarburizing annealing are removed by acid pickling, and then, alumina is applied as a separation agent at annealing, by which the steel sheet surface after finish annealing is formed into mirror-finished state. By this method, the mirror-finished grain-oriented silicon steel sheet, having a magnetic flux density as high as >=1.95T B8 , can be obtained.

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 mainly used as an iron core of a transformer or other electric equipment. In particular, {110}
<001> azimuth, that is, Goss azimuth highly developed B
Manufacturing that achieves improvement of iron loss characteristics at an industrially low cost by effectively introducing a method for manufacturing an i-added high magnetic flux density unidirectional electrical steel sheet, a means for mirroring the surface thereof, and a means for subdividing magnetic domains It relates to the method.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is mainly used as a soft magnetic material for core materials of transformers and other electric equipment, and must have good magnetic properties such as excitation properties and iron loss properties. No. A magnetic flux density B ₈ (magnetic flux density at a magnetic field strength of 800 A / m) is usually used as an index representing this excitation characteristic.
W _17/50 (iron loss per unit weight when magnetized to 1.7 T at 50 Hz) is used.

[0003] The grain-oriented electrical steel sheet contains 0.8 to 4.
A so-called Goss containing 8% and causing secondary recrystallization in the final annealing step at a temperature of 900 ° C. or higher in the final stage of the manufacturing process, having a {110} plane on the steel plate surface and a <001> axis in the rolling direction. It is obtained by developing the organization. Among them, a magnetic flux density B ₈ having an excellent excitation characteristic of 1.88 T or more is called a high magnetic flux density unidirectional electrical steel sheet.

As a typical method for producing a high magnetic flux density electromagnetic steel sheet, Japanese Patent Publication No. 40-15644 and Japanese Patent Publication No. 51-1 are available.
3469 publication etc. are mentioned. It can be said that the high magnetic flux density unidirectional electrical steel sheet currently produced on a worldwide scale is produced based on the above two patents. However, the magnetic flux density B _{8 of the} product based on the above patent is from 1.88 T to at most 1.
The value is about 95T, and shows only a value of about 95% of the saturation magnetic flux density of 2.03T of 3% Si steel, for example.
In recent years, social demands for energy savings and resource savings have become increasingly severe, and demands for reduction of iron loss and improvement of magnetic properties of the grain-oriented electrical steel sheets have also become fierce.

By the way, in general, the magnetic flux density B ₈ tends to increase and the crystal grains of the product tend to increase. Even if B ₈ is increased by a high magnetic flux density electromagnetic steel sheet, the 180 ° magnetic domain width increases, so that eddy current loss occurs. Therefore, metallurgically, further improvement of iron loss is not expected. From this viewpoint, magnetic domain control technology such as laser irradiation is a technical technique for reducing iron loss, which is disclosed in Japanese Patent Publication No. 57-2252 and Japanese Patent Publication No. 58-59.
68, JP-A-58-26405 and the like. Further, since the reduction of the iron loss by the method is caused by the strain introduced by the laser irradiation, it cannot be used for a wound iron core transformer that requires strain relief annealing after forming into a transformer, and therefore, for example, Kosho 6
No. 2-53579, Japanese Patent Publication No. 63-44804, Japanese Patent Publication No. 04-48847, etc., a groove is introduced by, for example, a gear type roll after finish annealing, and
A method is disclosed in which a processing strain is applied to form fine grains to subdivide magnetic domains.

However, the method of forming a groove on the surface of a steel sheet by machining such as a gear type roll requires crushing a surface ceramics layer called a primary coating (glass coating) of a grain-oriented electrical steel sheet, so that a gear roll, etc. Wears out and causes a problem in manufacturing cost.

On the other hand, when the movement of the magnetic domains of the steel sheet subjected to the magnetic domain subdivision processing was observed in detail, it was found that some of the statically subdivided magnetic domains did not move. In order to further reduce the iron loss value of grain-oriented electrical steel sheets, in addition to the magnetic domain refining technology according to the above method, a technology that eliminates factors that hinder the movement of magnetic domains (magnetic domain activation technology)
Need to be introduced. In other words, it is effective to remove the glass coating on the surface of the steel sheet, which is a major factor that hinders the movement of magnetic domains, to make the surface mirror-finished.

As a means therefor, there is a method of removing the glass coating by pickling after finishing annealing and then chemically polishing or electrolytically polishing the surface to make the surface mirror-finished.
No. 83620. However, chemical polishing, electrolytic polishing, etc. can process a small amount of sample material at the laboratory level, but for industrial scale, chemical solution concentration control, temperature control, and provision of pollution equipment. However, since the manufacturing cost is increased by adding such a step, it has not yet been put to practical use.

On the other hand, the present applicant has developed a method for mirror-finishing the surface of a steel sheet at a low cost on an industrial scale (for example, JP-A-5-033052 and JP-A-6-093335). These remove oxygen generated on the steel sheet surface during decarburizing annealing, or after controlling the oxygen amount by controlling the atmosphere of decarburizing annealing, by applying alumina as a annealing separating agent to the steel sheet surface and performing finish annealing, This is to make the surface of the steel sheet mirror-like and to form secondary recrystallization with high magnetic flux density.

These techniques are suitable for reducing the cost of manufacturing the magnetic domain control material mainly for the winding core transformer, because the gear rolls are less worn when machining the steel plate surface for the magnetic domain subdivision processing. ing. For example, JP-A-7-2589
Japanese Patent Laid-Open No. 45-45 discloses that the life of a gear roll is extended five times or more when a ceramic coating is not present on the surface of a steel sheet after finish annealing as in the conventional case.

However, with the maturation of peripheral technologies such as magnetic domain control and mirror finishing, it becomes easy to reduce the iron loss using a high magnetic flux density electromagnetic steel sheet, and it is further necessary to aim at an ultra-low iron loss electromagnetic steel sheet. A material having a high magnetic flux density has been expected as an essential condition. On the other hand, the present inventors have found that by including Bi in the molten steel of the grain-oriented electrical steel sheet, the magnetic flux density can be reduced by industrial means from the level of the conventional high magnetic flux density unidirectional magnetic steel sheet to the ultra-high magnetic flux density. JP-A-6-8814 and JP-A-6-8814 disclose a method for increasing the level of grain-oriented electrical steel sheets.
88173.

With this method, the magnetic flux density B ₈ is 1.
Ultra-high magnetic flux density grain-oriented electrical steel sheets exceeding 96T can now be produced relatively stably on a factory scale. The present invention is not a simple combination of the conventional method for producing an ultra-high magnetic flux density unidirectional electrical steel sheet by the Bi addition method and the low iron loss unidirectional electrical steel sheet production method by the mirror finishing technology, and the former is a drawback in industrialization and the latter is stable. It is intended to provide a method of solving acceleration very effectively.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a conventional Bi
By organically combining the addition technology and the mirroring technology, it is possible to stably manufacture ultra-high magnetic flux density unidirectional mirror-finished electromagnetic steel sheet material with extremely high magnetic flux density on a factory scale, and further develop magnetic domain control technology. By combining,
The purpose of the present invention is to manufacture an ultra-low iron loss-oriented mirror-oriented electrical steel sheet with extremely low iron loss at low cost.

[0014]

The features of the present invention are as follows. (1) By weight, C: 0.02 to 0.1%, Si: 2.
0 to 4.8%, acid-soluble Al: 0.012 to 0.050
%, N: 0.030 to 0.0150%, Bi: 0.00
Cast molten steel containing 0.05 to 0.03% with the balance Fe and unavoidable impurities, hot rolled, then 6
5 to 95% final cold rolling, including one final cold rolling, or two or more cold rollings with intermediate annealing, to obtain the final sheet thickness, and decarburization annealing followed by nitriding or not In a method for producing a grain-oriented electrical steel sheet comprising a step of performing recrystallization finish annealing, decarburization annealing is performed in an atmosphere gas having an oxidation degree that does not form Fe-based oxides, or an oxide produced by decarburization annealing is treated with an acid. A method for producing a specular unidirectional electrical steel sheet having a high magnetic flux density, which comprises removing the surface by washing and then applying alumina as an annealing separator to make the surface of the steel sheet after finish annealing into a mirror surface state.

(2) A method for producing a specular grain-oriented electrical steel sheet having a low iron loss, which comprises subjecting the steel sheet according to (1) above to local distortion to perform a magnetic domain refining treatment. (3) A grain-oriented electrical steel sheet with low iron loss, characterized by performing a magnetic domain refinement treatment by introducing a local strain after forming a tension film by the coating treatment on the steel sheet according to (1) above. Manufacturing method.

(4) The steel plate described in (1) above is spaced at an interval of 2 at right angles to the rolling direction or within a range of 45 degrees from the right angles.
To form a continuous, discontinuous or dot-shaped local groove within a range of 10 mm to a width of 10 to 300 μm and a depth of 5 to 50 μm, and also to form a tension film by a coating process to subdivide magnetic domains. A method for producing a specular grain-oriented electrical steel sheet having low iron loss.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The present inventors have disclosed JP-A-6-8814 and JP-A-6-8814.
As disclosed in Japanese Patent No. 88173, etc., by conducting experiments in a laboratory, Bi is added to and contained in a material for a grain-oriented electrical steel sheet having aluminum nitride as a main inhibitor, so that a commercially available high magnetic flux density is obtained. B of electrical steel sheet
₈ = 1.93T or more, far exceeding 1.93T,
An ultra-high magnetic flux density unidirectional magnetic steel sheet of 2T was obtained. After that, in order to stably manufacture a so-called ultra-high magnetic flux density unidirectional electrical steel sheet with a magnetic flux density B ₈ of 1.95 T or more on a steel sheet, a factory test was conducted using coil form. A close examination of the properties and properties of the primary coating revealed that in some cases there were problems.

That is, there was a variation in the magnetization characteristics depending on the coil position and a peeled portion of the primary coating was found inside the coil. In order to solve this problem, we developed a coil that had been subjected to finish annealing and investigated the positional relationship between the secondary recrystallized structure and the state of formation of the primary film in detail. while recrystallization structure hardly ultra-high magnetic flux density equiaxed grains manner is obtained, the secondary recrystallized grains has good primary coating also exhibited stretch particle is characteristic of Bi additive in the portion of the coil end portion, B ₈ It was found that 1.95T or more was stably obtained.

By the way, in order to realize an ultra-high magnetic flux density, a certain amount of Bi content in the steel is required, while it is necessary to vaporize and remove Bi in the steel from the surface of the steel sheet during finishing / purification annealing. is there. For example, in the case of a laboratory-scale plate-shaped small test piece, it is easy to remove Bi during finish annealing. However, in the case of manufacturing on a factory scale, since it is premised that the coiled steel sheet is annealed in a box-shaped finishing annealing furnace, gas permeability is particularly poor inside the coil,
It is difficult to remove Bi in steel, and it is difficult to obtain an ultrahigh magnetic flux density.

Further, it was estimated that it was difficult to obtain a good primary coating because the Bi vapor concentrated between the steel sheets adversely affected the formation of the primary coating. On the contrary, since the gas permeability is relatively good at the coil end, it is easy to obtain an ultra-high magnetic flux density.
It is presumed that the primary coating is good because the vapor also does not thicken. That is, it is presumed that it is difficult to remove Bi particularly in the center of the coil by annealing in a coil form on a factory scale, and Bi remaining between the steel sheets is harmful to the primary film formation. Conducted the following experiment in order to quantitatively understand the influence of gas permeability between the plates during the secondary recrystallization finish annealing by adding Bi.

C: 0.05%, Si: 3.25%, M
n: 0.10%, S: 0.007%, P: 0.025
%, Acid-soluble Al: 0.029%, N: 0.007%,
Cr: 0.12% containing silicon steel was melted, Bi content was set to 0, 0.007%, 0.013%, 0.025%, and after casting by casting into slabs, respectively, to 1150 ° C. Heat
Immediately after extraction, hot-rolled to a thickness of 2.3 mm, and water-cooled after hot-rolling.
It was kept at 50 ° C. Thereafter, the hot-rolled sheet was annealed at a temperature of 1120 ° C. for 30 seconds and subsequently at 900 ° C. for 90 seconds, air-cooled to 750 ° C. and then rapidly cooled to 80 ° C. in water.

Next, pickling is carried out to 250 mm on the way to 0.23 mm.
Cold rolling was performed by sandwiching the aging treatment at ℃ 5 times. Subsequently, in a mixed gas of nitrogen and hydrogen, the degree of oxidation is 0.40 (PH ₂ O
/ PH ₂ ) Adjust the introduced steam to decarburize.
Next, recrystallization annealing was performed, and then nitriding annealing was performed in an NH ₃ atmosphere so that the N content was 200 ppm. After applying an annealing separator containing MgO as a main component, secondary recrystallization finish annealing was performed.

To check the effect of gas permeability between the plates, 10
A sample in which about 50 sheets of 0 mm x 500 mm steel sheets were laminated was packed with an iron thin film and inserted into the furnace. Then, a gas in a wet hydrogen atmosphere with a nitrogen partial pressure of 25% was introduced, and the flow rate was 1, 5, 10, 1
The temperature was raised up to 1200 ° C. at 15 ° C./hr at 5 Nm ³ / min, and subsequently at 1200 ° C. in a dry hydrogen atmosphere at 2 ° C.
A zero-hour purification annealing was performed. At this time, the furnace internal volume of the annealing furnace was 0.06 m ³ . FIG. 1 shows the relationship between the flow rate of gas introduced into the furnace, the condition of the obtained steel sheet primary coating, and the magnetic flux density B ₈ .

As a result, the ultra-high magnetic flux density unidirectional electrical steel sheet containing Bi is compared with the conventional high magnetic flux density unidirectional electrical steel sheet using aluminum nitride as the main inhibitor.
It was found that when the gas permeability during finish annealing was poor, the primary coating was adversely affected and it was difficult to obtain a high magnetic flux density. Although the inventors have not yet explained the mechanism of primary film peeling and B ₈ deterioration, when Bi in steel diffuses to the surface during finish / purification annealing and then evaporates from the surface, Bi vapor forms It is presumed that the primary coating peels from the base iron due to expansion at the interface of the primary coating.

On the other hand, when the primary coating peels off, A
It is presumed that this is because it affects the formation of l ₂ O ₃ and the behavior of nitrogen, affects the behavior of the inhibitor mainly containing AlN, and changes the secondary recrystallization process. In order to solve these problems, for example, the flow rate of gas introduced into the annealing furnace of the factory may be increased, but the furnace internal volume of the factory-scale box-type annealing equipment is usually about 30 m ³ and can be calculated simply. However, the introduction gas flow rate of 500 times the introduction gas flow rate of the laboratory annealing furnace for steam is required.

This is because the equipment cost is pressed down and it is difficult from the viewpoint of the cost of the basic unit etc., that is, in order to stably manufacture the super high magnetic flux density unidirectional electrical steel sheet on an industrial scale by adding Bi. Found that the application of a mirror finishing technology that does not rely on the formation of a primary film may be effective.

The results of the experiments that led to the present invention will be described below. The present inventors conducted the following experiment in order to quantitatively understand the influence of the temperature gradient during the secondary recrystallization finish annealing due to the addition of Bi. C: 0.05%, Si: 3.25%, M
n: 0.10%, S: 0.007%, P: 0.025
%, Acid-soluble Al: 0.029%, N: 0.007%,
Cr: 0.12% containing silicon steel is melted, and Bi content is 0%, 0.007%, 0.013%, 0.025%
Each of them was dispensed and cast into a slab, heated to 1150 ° C., hot-rolled immediately after extraction to a plate thickness of 2.3 mm, hot-rolled and then water-cooled and held at 550 ° C.

Thereafter, the hot-rolled sheet was annealed at a temperature of 1120 ° C. for 30 seconds and subsequently at 900 ° C. for 90 seconds, air-cooled to 750 ° C. and then rapidly cooled in water of 80 ° C. Next, it was pickled and cold rolled by aging treatment at 250 ° C. 5 times to reach 0.23 mm. Subsequently, the degree of oxidation is 0.0 in a mixed gas of nitrogen and hydrogen.
Introduced water vapor so that the steel plate oxygen content is 20
Perform decarburization and primary recrystallization annealing so that the concentration becomes 0 ppm or less,
Subsequently, nitriding annealing was performed in an NH ₃ atmosphere so that the N content was 200 ppm.

Then, after applying an annealing separator containing Al ₂ O ₃ as a main component, secondary recrystallization finish annealing was performed. Then, similarly to the above experiment, a sample in which about 50 sheets of 100 mm × 500 mm steel sheets were laminated was packed with an iron thin film, inserted into the furnace, and a dry nitrogen atmosphere was introduced into the furnace, and the flow rate was set to 1, 5, 10 , 15,
The temperature was raised to 1200 ° C. at 15 ° C./hr at Nm ³ / min, and then purification annealing was performed at 1200 ° C. for 20 hours. Oxygen of the steel sheet obtained as furnace Flow rate of introduced gas and shows the relationship between the magnetic flux density B ₈ in FIG.

As is apparent from FIG. 2, by applying the mirror finishing technique, the magnetic flux density was not affected by the gas flow rate during the finish annealing, and the effect of improving the magnetic flux density by adding Bi was stably obtained. In this way, the fact that the gas flow rate during finish annealing is not affected is advantageous for manufacturing by finish annealing in factory-scale coil form because the secondary recrystallization process is less affected by the variation in gas permeability in the coil. It indicates that there is. In addition, in FIG. 2, since the amount of oxygen adhering to the mirror-finished steel sheet in a small amount decreases along with the amount of Bi added, it is expected that the addition of Bi has an effect of promoting mirror polishing.

Further, the present inventors performed strain relief annealing of the sample obtained in FIG. 2 at a temperature of 850 ° C. for 2 hours, and then performed laser irradiation treatment in the direction perpendicular to the rolling direction at intervals of 5 mm to obtain magnetic domains. Tried to control. Magnetic flux density B ₈ of the material (before magnetic domain control) and iron loss W after magnetic domain control for the obtained sample
The relationship of _17/50 is shown in FIG.

The following can be seen from FIG. First, by adjusting the Bi content of 0.007% or perform Bi added to 0.025%, the magnetic flux density B ₈ is expressed more ultra-high magnetic flux density grain-oriented electrical steel sheet 1.96T, also the magnetic domain control In combination with the above, an ultra-low iron loss electromagnetic steel sheet can be obtained. Also, B ₈ and W
_The straight line showing the relationship of _17/50 decreases with Bi addition, and it can be seen that the iron loss of the Bi-added material is further improved than the iron loss expected from the improvement of the magnetic flux density.

This is presumed to be due to the action of Bi addition for promoting the mirroring, as explained in FIG.
The present invention is not a simple combination of the conventional method for producing an ultra-high magnetic flux density unidirectional electrical steel sheet by the Bi addition method and the low iron loss unidirectional electrical steel sheet production method by the mirror finishing technology, and the former is a drawback in industrialization and the latter is stable. It is intended to provide a method of solving acceleration very effectively.

Next, the components necessary for the present invention and the reasons for limiting them will be described. In the present invention, the components contained in the material are, by weight, C: 0.02 to 0.1%, Si:
0 to 4.8%, acid-soluble Al: 0.012 to 0.050
%, N: 0.030 to 0.0150%, Bi: 0.00
05 to 0.03%, the balance being Fe and unavoidable impurities, and these are essential components, and the others are not limited.

As a basic production method, a production method using (Al, Si) N as a main inhibitor by Komatsu et al. (For example, Japanese Examined Patent Publication No. 62-45285) or AlN and MnS by Taguchi / Sakakura etc. as main inhibitors. Manufacturing method used as (for example, Japanese Patent Publication No. 40-15644)
Should be applied.

C is an element of the γ region open type, which is an important element that forms an advantageous texture for secondary recrystallization due to α → γ transformation or the presence of solute C in the steps from hot rolling to decarburization annealing. Is. If C is less than 0.02%, α → γ transformation does not occur, which is not preferable. On the other hand, if it exceeds 0.1%, the decarburization annealing process is burdened with an increase in cost, which is not preferable.

Si is an important element for increasing electric resistance and reducing iron loss. If the content exceeds 4.8%, the material is easily cracked during cold rolling, and cannot be rolled. On the other hand, if it is less than 2.0%, the eddy current loss of the product increases, and the α → γ transformation occurs at the time of finish annealing, and the directionality of the crystal is impaired.

Acid-soluble Al is combined with N to form AlN, and is a main inhibitor constituent element for producing a high magnetic flux density unidirectional electrical steel sheet. If it is less than 0.012%, the amount is insufficient, and the inhibitor strength is insufficient. On the other hand, 0.050
If it exceeds%, AlN becomes coarse and, as a result, the inhibitor strength is lowered, so that secondary recrystallization does not occur.

N contained in the material forms nitrides of Si, Al, etc., and acts as an inhibitor of primary recrystallization especially when low temperature slab heating is premised. The N content is determined from the thermal history of the process and the required primary annealing temperature from the viewpoint of controlling the primary recrystallized grain size. On the other hand, when AlN is finely dispersed in the previous stage by high temperature slab heating, it is necessary to consider the atmospheric conditions of the secondary recrystallization annealing. 0.030%
If the amount is less than the above, denitrification will increase the cost in the melting stage,
If it exceeds 0.0150%, defects called blisters occur, so the range was made 0.030% to 0.0150%. Other inhibitor constituent elements include Mn, S,
Se, V, N, B, Nb, Sn, Cu, Ti, Zr, T
It is possible to add a, Mo, Sn and the like in combination.

Bi is a necessary element for obtaining an ultra-high speed density, and it is effective that the content of addition is 0.0005 to 0.03%. If it is less than 0.0005%, the effect is slight, and if it exceeds 0.03%, the effect of improving the magnetic flux density saturates and cracks occur at the ends of the hot-rolled sheet, so the upper limit is limited to 0.03%.

Next, the manufacturing process conditions will be described. The material for ultra-high magnetic flux density unidirectional electrical steel sheet whose components have been adjusted as described above can be used as the material of the present invention even when any ordinary melting method or ingot making method is used. Next, the magnetic steel sheet material is rolled into a hot-rolled coil by ordinary hot rolling.

A production method using (Al, Si) N as a main inhibitor by Komatsu et al. (Eg Japanese Patent Publication No. 62-452).
No. 85), from the viewpoint of ensuring the temperature during hot rolling, 1
100 ° C or higher, and 1280 without complete solution of AlN
Hot rolling is performed after heating at a temperature of ℃ or less. A production method using AlN and MnS as main inhibitors by Taguchi and Sakakura (for example, Japanese Patent Publication No. 40-15644).
In Japanese Unexamined Patent Publication (Kokai) No. H11-260, hot rolling may be performed after heating at a temperature of 1300 ° C. or higher at which complete solution is formed.

Subsequently, final sheet thickness is obtained by one-stage cold rolling or multiple-stage cold rolling including intermediate annealing, but since a unidirectional electrical steel sheet having a high magnetic flux density is obtained, the final cold rolling reduction rate is set. (The rolling ratio in the case of one-stage cold rolling) is preferably a strong reduction of 65 to 95%. The rolling rates of stages other than the final rolling need not be particularly defined. Further, in order to strengthen AlN, annealing and cooling may be performed before final cold rolling. Annealing is performed in a temperature range of 750 to 1200 ° C. for 30 seconds to 30 minutes, and this annealing is effective for enhancing the magnetic properties of the product. It is advisable to decide whether or not to take into account the desired product characteristic level and cost.

The cold-rolled sheet rolled to the final product thickness has a thickness of 750 to 900 in wet hydrogen or a mixed atmosphere of hydrogen and nitrogen for the purpose of primary recrystallization annealing and removal of carbon contained in the steel.
Decarburization annealing is performed in a temperature range of 30C for 30 seconds to 30 minutes. In this decarburization annealing, Fe-based oxides (Fe ₂ SiO ₄ ,
One point of the present invention is to perform annealing at an oxidation degree that does not form (FeO etc.) and apply alumina as an annealing separator. For example, 80 where decarburization annealing is usually performed
In the temperature range of 0 ° C. to 850 ° C., the generation of Fe-based oxide can be suppressed by adjusting the degree of oxidation of the atmospheric gas (PH ₂ O / PH ₂ ) <0.15.

However, if the degree of oxidation is lowered too much, the decarburization rate becomes slow, which is not desirable from an industrial viewpoint. Taking both of these into consideration, in the temperature range of 750 to 900 ° C., the degree of oxidation of the atmospheric gas (PH ₂ O / PH ₂ ): 0.0
It is preferable to anneal in the range of 1 to 0.15. The annealing temperature is determined mainly from the viewpoint of obtaining the optimum primary recrystallized grain size.

When it is necessary to strengthen the (Al, Si) N inhibitor in the decarburized and annealed sheet, or (Al, S)
i) In the production method using N as a main inhibitor (for example, Japanese Patent Publication No. 62-45285), a nitriding treatment is performed. The method of the nitriding treatment is not particularly limited, and there is a method of performing the nitriding treatment in an atmosphere gas having a nitriding ability such as ammonia. Nitrogen may be nitrided in an amount of 0.005% or more, desirably the equivalent of Al in steel as a total nitrogen amount.

When these decarburized and annealed plates are wound on the coil form, alumina is dry-coated as an annealing and separating agent by a water slurry or an electrostatic coating method. When coating with a water slurry, it is preferable to employ the method disclosed in, for example, JP-A-7-62427.

The alumina annealing separator is extremely effective in the production method of Bi-added ultra-high magnetic flux density unidirectional electrical steel sheet by Colefoam on a factory scale, and the present invention is an ultra-high magnetic flux density by the conventional Bi-added method. This is an extremely effective combination of the reduction of iron loss by the mirror finishing technology by applying alumina and the application of alumina. This coil is finish annealed to carry out secondary recrystallization and purification of nitride. Secondary recrystallization is described in JP-A-2-2.
As disclosed in Japanese Patent No. 58929, it is effective to increase the magnetic flux density by using a means such as maintaining a constant temperature.

After the secondary recrystallization is completed, 110% 100% hydrogen is used to purify impurities such as nitrides and smooth the surface.
Anneal at a temperature of 0 ° C. or higher. After the finish annealing, the excess annealing separator is subsequently removed, and then continuous tension annealing is performed to correct coil winding and the like, and at the same time, an insulating film coating is applied and baked. At this time, if necessary, the steel sheet is subjected to magnetic domain refining treatment such as laser irradiation, mechanical groove formation, and tension film coating. In the present invention, the addition of Bi makes the magnetic flux density extremely high and at the same time greatly controls the secondary recrystallized grain size. Therefore, the magnetic domain refining treatment is effective from the viewpoint of improving the iron loss characteristics. There is no particular limitation on the method of magnetic domain subdivision.

When the magnetic domain is subdivided by introducing a local strain, for example, a method of irradiating a laser beam described in Japanese Patent Publication No. 57-2252, or JP-A-62-1 is used.
A method for performing plasma flame irradiation described in Japanese Patent No. 51511 and Japanese Patent Publication No. 6-45824 may be used.

When the magnetic domains are subdivided by forming local grooves, a gear roll method (for example, Japanese Patent Publication No. 4-48847) is used.
Publication) and die pressing method (for example, Japanese Patent Publication No. 6-63037).
Such as a photo-etching method (for example, Japanese Patent Publication No. 5-69284), a resist ink etching method (Japanese Patent Publication No. 2-46673, Japanese Patent Publication No. 3-69968), and the like. A method using chemical etching or electrolytic etching may be adopted.
The grooves formed in the steel sheet are at right angles to the rolling direction or within a range of 45 degrees from the right angles, and the intervals are preferably 2 to 10 mm from the viewpoint of reducing iron loss.

The shape of the groove may be continuous, discontinuous or dot-shaped. The groove width and depth are 10 to 30 respectively.
The range of 0 μm and 5 to 50 μm is preferable from the viewpoint of reducing iron loss. When the width of the groove is reduced, the groove tends to be a starting point when bending with a small radius of curvature. In addition, if the width of the groove is increased, the magnetic flux density decreases. Similarly, if the depth of the groove is too large, the magnetic flux density will decrease.

As the tension coating, for example, a coating liquid mainly composed of colloidal silica and aluminum phosphate according to JP-A-48-39338, JP-A-5-58 is disclosed.
If the coating liquid mainly composed of colloidal silica and magnesium phosphate according to JP-A-0-79442 or the coating liquid mainly composed of alumina sol and boric acid according to JP-A-6-65754 is adopted, Good.

[0054]

【Example】

(Example 1) C: 0.05%, Si: 3.3%, Mn:
0.1%, S: 0.01%, acid-soluble Al: 0.03
%, N: 0.008%, as a basic component, (A: Bi added) Bi: 0.01% and (B: conventional method) Bi: 0% 2
After melting standard level of silicon steel and dispensing casting into slabs, 1
It was heated to 200 ° C., and immediately after extraction, it was hot rolled to a plate thickness of 2.3 mm. Then, it was pickled and cold rolled to 0.23 mm. This cold-rolled sheet was annealed for 100 seconds at a temperature of 830 ° C. in a mixed gas of nitrogen and hydrogen at an oxidation degree (C: mirror surface) of 0.1 and (D: conventional method) of 0.44 for primary recrystallization. . Then, by annealing in an ammonia atmosphere, the amount of nitrogen was increased to 0.02% to strengthen the inhibitor.

These steel sheets were then coated with (C: mirror-finished) alumina (Al ₂ O ₃ ) and (D: conventional) magnesia (MgO) in a water slurry, and then the steel sheets were laminated to obtain a low gas flow rate. Originally, finish annealing was applied. A groove having a width of 50 μm and a depth of 15 μm was formed on each of these samples by a gear roll in a direction of 10 ° from the direction perpendicular to the rolling direction, and then a coating liquid containing colloidal silica and phosphate as a main component was applied. It was baked at 850 ° C. for 2 minutes. After measuring the magnetic properties of these samples, strain relief annealing was further performed at 800 ° C. for 4 hours. Table 1 shows the magnetic properties of the obtained products.

[0056]

[Table 1]

(Example 2) Si: 3.3% by weight, M
n: 0.1%, C: 0.05%, S: 0.007%, acid-soluble Al: 0.03%, N: 0.008%, Sn:
0.05% as a basic component, (A: Bi added) Bi:
Melting two levels of silicon steel of 0.01% and (B: conventional method) Bi: 0%, dispensing and casting each to a slab, heating to 1200 ° C., and immediately after extraction to 2.3 mm sheet thickness. Hot rolled.
The cold-rolled sheet that has been pickled and cold-rolled to 1.4 mm is annealed at a temperature of 1120 ° C. for 30 seconds and 900 ° C. for 90 seconds, air-cooled to 750 ° C., and then rapidly cooled in water at 80 ° C. Cold rolled to 15 mm. This cold-rolled sheet was subjected to a mixed gas of nitrogen and hydrogen with an oxidation degree (C: mirror-finishing method) of 0.06, and (D: conventional method).
It was annealed at 0.44 at 830 ° C. for 70 seconds for primary recrystallization. Then, by annealing in an ammonia atmosphere, the amount of nitrogen was increased to 0.025% to strengthen the inhibitor.

These steel sheets were then subjected to (C: mirror-finishing method).
Alumina (Al ₂ O ₃ ) and (D: conventional method) magnesia (MgO) were applied with a water slurry, and then steel sheets were laminated,
Finish annealing was performed under a low gas flow rate. Grooves having a width of 30 μm and a depth of 10 μm were formed in the samples after the finish annealing in a direction perpendicular to the rolling direction by a photoetching method, and then a coating liquid containing alumina sol and boric acid as main components was applied. Baking at 870 ° C. for 2 minutes. After measuring the magnetic properties of these samples, strain relief annealing was further performed at 800 ° C. for 4 hours. Table 2 shows the magnetic properties of the obtained products.

[0059]

[Table 2]

(Example 3) Si: 3.3% by weight, M
n: 0.07%, C: 0.07%, Se: 0.025
%, Acid-soluble Al: 0.028%, N: 0.008%,
Sb: 0.1% as a basic component, (A: Bi added) B
i: 0.01% and (B: conventional method) Bi-level silicon steels of 2% were melted, each of which was dispensed and cast into a slab, and then 1350
C., immediately after the extraction, hot-rolled to a thickness of 2.3 mm, and immediately cooled with water to room temperature. 1100 ° C
And then pickled, and cold rolled with aging treatment at 250 ° C. five times on the way to a final sheet thickness of 0.27 mm. This cold-rolled sheet was subjected to a degree of oxidation (A:
Inventive method) 0.06 and (B: Conventional method) 0.44 8
It was annealed at a temperature of 50 ° C. for 120 seconds for primary recrystallization.

These steel sheets were then subjected to (A: method of the present invention).
Alumina (Al ₂ O ₃ ) and (B: conventional method) magnesia (MgO) were applied in a water slurry, steel plates were laminated, pressed at 20 kg / mm ² in the thickness direction, and then subjected to finish annealing. A coating liquid containing colloidal silica and phosphate as main components was applied to these samples and baked at 850 ° C. for 2 minutes. Thereafter, the surface of the steel sheet was irradiated with laser at intervals of 5 mm in a direction perpendicular to the rolling direction. Table 3 shows the magnetic properties of the obtained products.

[0062]

[Table 3]

Example 4 C: 0.05%, Si: 3.
25%, Mn: 0.10%, S: 0.007%, P:
0.025%, acid-soluble Al: 0.029%, N: 0.
Silicon steel containing 007%, Bi: 0.007%, Cr: 0.12% is melted, cast into a slab, heated to 1150 ° C., and immediately after extraction, hot rolled to a thickness of 2.3 mm, After hot rolling, it was cooled with water and wound at 550 ° C. After that, 1120 the hot rolled sheet
Annealed at ℃ for 30 seconds, 900 ℃ for 90 seconds, 750 ℃
After air cooling, it was rapidly cooled in water at 80 ° C. Then after pickling,
Rolling was performed for 5 passes to 0.23 mm, and aging treatment was performed at 200 ° C or higher for 5 minutes or longer. Subsequently, decarburization / primary recrystallization annealing was performed in a mixed gas of nitrogen and hydrogen to an oxidation degree of 0.
The atmosphere was set to 06 and the temperature was set to 850 ° C. for 100 seconds, followed by nitriding annealing in an NH ₃ atmosphere so that the N content was 200 ppm.

The 5T coil coated with the annealing separator containing alumina (Al ₂ O ₃ ) as a main component was subjected to secondary recrystallization finish annealing in a box type annealing furnace. While flowing nitrogen into the furnace, the temperature was raised to 1200 ° C. at 15 ° C./hr, and subsequently purifying annealing was performed at 1200 ° C. for 75 hours while flowing hydrogen. After that, while expanding the coil on the continuous annealing line, the width of 50
After forming a groove of a tooth mold having a groove of μm and a depth of 11 μm by a press, a coating liquid containing colloidal silica and a phosphate as main components was applied and baked at 860 ° C. for 2 minutes. Sampling at 5 points on the obtained coil,
The measured Epstein value after annealing at 800 ° C. for 2 hours is
Magnetic flux density B ₈ is 1.97T on average, iron loss W _17/50 is 0.6
It was 1 W / kg.

[0065]

INDUSTRIAL APPLICABILITY The present invention combines extremely high magnetic flux density by the conventional Bi addition method and low iron loss by the mirror-finishing technique by alumina coating, which is extremely stable and inexpensive in industrial production. It can be said that it is very valuable industrially because it has excellent super-flux density and low unidirectional electrical steel sheet, and the iron loss characteristics after magnetic domain refinement treatment are also very excellent.

[Brief description of drawings]

FIG. 1 is a chart showing the relationship among the flow rate of introduced finish annealing gas, magnetic flux density B ₈ and primary coating peeling area at each Bi content in the primary coating forming method (magnesia annealing separator).

FIG. 2 is a flow diagram of the final annealing introduction gas and the magnetic flux density B _{8 for} each Bi content in the mirror-finishing method (alumina annealing separator).
And a chart showing the relationship between the steel plate oxygen content.

FIG. 3 shows the relationship between the material magnetic flux density (before magnetic domain subdivision) B ₈ and the iron loss W _17/50 after magnetic domain subdivision when the sample obtained in FIG. 2 was subjected to magnetic domain subdivision processing by laser irradiation. Chart showing.

Front page continuation (72) Inventor Shuichi Yamazaki 20-1 Shintomi, Futtsu City Technical Development Division, Nippon Steel Corporation (72) Inventor Kento Abe 1 Fuji-machi, Hirohata-ku, Himeji City Nippon Steel Co., Ltd. Hirohata Works

Claims (4)

[Claims] 1. By weight, C: 0.02-0.1% Si: 2.0-4.8%, acid-soluble Al: 0.012-0.050%, N: 0.030-0. 0150%, Bi: 0.0005 to 0.03%, the balance Fe and inevitable impurities cast molten steel, hot-rolled, then including 65-95% final strong cold rolling 1 Unidirectionality consisting of two or more cold rolling steps with intermediate or intermediate annealing to obtain the final plate thickness, decarburization annealing, and then nitriding or not, and secondary recrystallization finish annealing. In the method for producing an electromagnetic steel sheet, decarburization annealing is performed in an atmosphere gas having an oxidation degree that does not form Fe-based oxides, or oxides produced by decarburization annealing are removed by pickling, and then alumina is used as an annealing separator. By coating, the steel plate surface after finish annealing is mirror-like Method for producing a high specular grain-oriented electrical steel sheet magnetic flux density, characterized by a. 2. A method for producing a specular unidirectional electrical steel sheet with low iron loss, which comprises subjecting the steel sheet according to claim 1 to local strain to perform a magnetic domain refining treatment. 3. A mirror surface unidirectional direction with low iron loss, characterized in that the steel sheet according to claim 1 is subjected to a coating treatment to form a tension film, and then a local strain is introduced to perform a magnetic domain refinement treatment. For manufacturing high-performance electrical steel sheet. 4. The steel sheet according to claim 1 having a distance of 2 to 10 m at right angles to the rolling direction or within a range of 45 degrees from right angles.
It is possible to subdivide the magnetic domains by forming continuous, discontinuous or dot-shaped local grooves in the range of 10 to 300 μm in width and 5 to 50 μm in depth, and forming a tension film by coating treatment. A method for producing a specular grain-oriented electrical steel sheet having low iron loss.