JPH10130726A - Production of low core loss mirror finished grain oriented silicon steel sheet high in magnetic flux density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the magnetic flux density of a steel sheet and to reduce core loss therein by coating the surface of a steel sheet with a separation agent for annealing contg. specified components and thereafter executing secondary recrystallization finish annealing. SOLUTION: Immediately before a sheet subjected to decarburizing annealing is coiled round a coil, the surface of the steel sheet is coated with water slurry obtd. by incorporating the chloride of Bi into a separation agent for annealing, and the surface of the steel sheet is subjected to mirror finishing while secondary recrystallization is secured. The chloride of Bi is incorporated by 0.2 to 15 pts.wt. by chlorine pts.wt. to 100 pts.wt. separation agent for annealing. Concretely, it is suitably added as BiCl, BiOCl or the like. Furthermore, as the separation agent for annealing, a high m.p. compound generating no burning between sheets even at about 1200 deg.C such as MgO is effective, and, in the case the Bi chloride is added, the formation of secondarily recrystallized crystals and the mirror finishing are satisfactorily executed. In this way, the mirror finishing in the high temp. region in the secondary recrystallization finish annealing can realize low core loss as well in the combination with the attainment of high magnetic flux density by the conventional addition of Bi.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet mainly used as an iron core of a transformer or other electric equipment. In particular, {110} <0
01> Orientation, that is, a method for producing a Bi-added high magnetic flux density unidirectional magnetic steel sheet with a highly developed Goss orientation, and a method for effectively introducing a mirror-polishing means and a magnetic domain refining means on the surface thereof, thereby improving iron loss characteristics. It is intended to disclose a production method which achieves the improvement of the production at low cost industrially.

[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. Normally, magnetic flux density B ₈ (magnetic flux density at a magnetic field strength of 800 A / m) is used as an index representing the excitation characteristics, and W _17/50 (magnetization up to 1.7 T at 50 Hz) is used as an index representing iron loss characteristics. (Iron loss per unit weight at the time of the application).

[0003] The grain-oriented electrical steel sheet contains 0.8 to 4.
8%, secondary recrystallization occurs in the final annealing step at a temperature of 900 ° C. or more in the final stage of the manufacturing process, so-called goss having a {110} plane on the steel sheet surface and a <001> axis in the rolling direction. Obtained by developing tissue. Among them, the magnetic flux density B ₈ those with more excellent excitation characteristics 1.88T is called high flux density grain-oriented electrical steel sheet. Representative methods for producing high magnetic flux density electromagnetic steel sheets include Japanese Patent Publication No. 40-15644 and Japanese Patent Publication No. 51-13.
No. 469, and the like. 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 1.88 T to 1.9 at most.
About 5T, for example, the saturation magnetic flux density of 3% Si steel
It only shows a value of about 95% of 03T. 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, there is a tendency that the magnetic flux density B ₈ increases and the crystal grains of the product tend to increase. Even if B ₈ is increased by a high magnetic flux density magnetic steel sheet, the magnetic domain width increases by 180 °, so that eddy current loss And the expectation of further improvement in iron loss is not desired in metallurgy. From this viewpoint, a magnetic domain control technique using laser irradiation or the like as a technique for reducing iron loss is disclosed in Japanese Patent Publication No. 57-2252 and Japanese Patent Publication No. Sho 58-58.
-5968, JP-A-58-26405 and the like. In addition, since the reduction of iron loss by this method is caused by strain introduced by laser irradiation, it cannot be used for a wound core transformer that requires strain relief annealing after forming into a transformer. JP-B-62-53579, JP-B-63-44804
And Japanese Patent Publication No. 04-48847 disclose a method in which grooves are introduced by a gear-type roll after finish annealing, and processing strain is applied to form fine grains to refine magnetic domains. However, the method of forming grooves on the surface of a steel sheet by machining a gear-type roll, etc., requires grinding the surface ceramic layer called the primary film (glass film) of the grain-oriented electrical steel sheet. Large, causing 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 refining treatment 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. That is, it is effective to remove the primary coating or the like of the steel sheet surface, which is a major factor that hinders the movement of the magnetic domain, and to make the surface mirror-finished. For example, Japanese Patent Application Laid-Open No. 64-83620 discloses a method of removing the primary film by pickling or the like after finish annealing and then performing chemical polishing or electrolytic polishing to mirror-finish the surface.
However, methods such as chemical polishing and electrolytic polishing can process a small sample of material at the laboratory level. However, for industrial scale, chemical concentration control, temperature control,
There is a major problem in the provision of pollution equipment and the like, and the addition of such a step increases the production cost, and 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 on an industrial scale at low cost (for example, JP-A-6-346247, JP-A-7-18333, JP-A-7-183). No. 54155). These are generated at about 900 ° C. or more, which does not adversely affect the secondary recrystallization by applying an annealing separator containing Bi chloride to the steel sheet surface after decarburizing annealing and performing secondary recrystallization finish annealing. Cl ₂
This is a method in which a primary film is peeled off by gas phase etching of gas, and the surface is thermally etched by high-temperature annealing to form a surface. In other words, both the mirror finishing of the steel sheet surface and the formation of secondary recrystallization with a high magnetic flux density are achieved. These techniques are suitable mainly for reducing the cost of manufacturing a magnetic domain control material for a wound iron core transformer because abrasion of a gear roll or the like is small when machining is performed on a steel sheet surface for magnetic domain subdivision processing.

However, with the maturation of peripheral technologies such as magnetic domain control and mirror finishing, it is easy to reduce iron loss using a high magnetic flux density electromagnetic steel sheet, and it is further necessary to aim for an ultra-low iron loss electromagnetic steel sheet. A material having a high magnetic flux density is 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. While ultra-high magnetic flux density grain-oriented electrical steel sheet for the first time the magnetic flux density B ₈ exceeds 1.96T by this method can now be produced at plant scale, repeated plant experiments within the conditional forming a conventional primary coating As a result, it was difficult to stably obtain an ultra-high magnetic flux density over the entire area of the coil. It is generally known that the conditions for forming the primary film greatly affect the magnetic properties.
In the case of the i additive, it was assumed that the effect was remarkable. Therefore, by effectively combining the super-flux density by adding Bi and the mirror finishing technology that does not form a primary film, a super-flux density unidirectional magnetic steel sheet can be more stably manufactured on a factory scale, and the magnetic domain control technology is further improved. It is an object of the present invention to produce a non-conventional ultra-low iron loss unidirectional electrical steel sheet by combining the above.

[0008]

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

[0009]

The features of the present invention are as follows. (1) By weight, C: 0.02 to 0.1%, Si: 2.0
4.8%, acid-soluble Al: 0.012 to 0.050
%, N: 0.0030 to 0.0150%, Bi: 0.0
005-0.03% as a basic component, the remainder is cast molten steel comprising Fe and unavoidable impurities, hot-rolled,
The final sheet thickness is obtained by cold rolling one or more times including intermediate strong annealing of 65 to 95% and intermediate annealing is performed, decarburizing annealing combined with primary recrystallization is performed, and secondary from decarburizing annealing is performed. Nitriding treatment is performed as necessary between the steps of recrystallization finish annealing,
In a method for producing a grain-oriented electrical steel sheet comprising a step of performing a secondary recrystallization finish annealing, an annealing separator 100
Bi chloride is 0.2 to 1 parts by weight of chlorine based on parts by weight.
After applying the annealing separator containing 5 parts by weight, coil winding,
A method for producing a mirror-oriented unidirectional electrical steel sheet having a high magnetic flux density, which is subjected to secondary recrystallization finish annealing.

(2) The main component of the annealing separator is MgO, A
l ₂ O ₃ , SiO ₂ , ZrO, BaO, CaO, SrO
The method for producing a specularly-oriented electrical steel sheet having a low iron loss according to claim 1, characterized in that it is one kind or a mixture of two or more kinds. (3) A method for producing a mirror-oriented unidirectional electrical steel sheet having a low iron loss, which comprises subjecting the steel sheet according to (1) to local distortion to perform magnetic domain refining treatment.

(4) After forming a tension film by coating on the steel sheet as described in (1), a magnetic domain refinement treatment is performed by introducing local strain, whereby a mirror surface with low iron loss is characterized. Manufacturing method of grain-oriented electrical steel sheet. (5) The steel sheet described in (1) is perpendicular to the rolling direction or within a range of 45 degrees from the perpendicular to the rolling direction at an interval of 2 to 10 mm and a width of 10 to 10 mm.
A continuous, discontinuous or point-like groove or a local groove is formed in a range of 300 μm and a depth of 5 to 50 μm, and the magnetic domain is subdivided by forming a tension film by a coating process. A method for manufacturing mirror-oriented unidirectional electrical steel sheets with low iron loss.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The present inventors have disclosed JP-A-6-8814 and JP-A-6-8814.
As shown in the publication 88173 and the like, 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 electromagnetic material is obtained. B _{8 of} steel plate
= 1.95T or more, far exceeding 1.93T, 2
An ultra-high magnetic flux density unidirectional magnetic steel sheet was obtained. The mechanism for obtaining an ultra-high magnetic flux density is not yet clear, but it is presumed that Bi has a very small diffusion constant in steel and thus functions as a thermally stable inhibitor-enhancing element. That is, while achieving a very high magnetic flux density requires a Bi content in the steel of a certain amount or more, it is necessary to moderately reduce the inhibitor strength during the progress of the secondary recrystallization.
It is necessary to gradually evaporate and remove i from the steel sheet surface. In this regard, it is easy to remove Bi during the secondary recrystallization finish annealing in the case of a laboratory-scale plate-shaped small test piece because the gas permeability between the plates is good. However, in the case of manufacturing on a factory scale, it is premised that the steel sheet wound in a coil shape is annealed in a box-type annealing furnace. In particular, since gas permeability is poor inside the coil, Bi vapor is generated between the steel sheets. It becomes difficult to remove Bi from the steel. Therefore, it is presumed that it is difficult to obtain an ultra-high magnetic flux density, and that Bi is concentrated at the interface between the primary film and the ground iron to form BiCl ₃ or the like, and the primary film is peeled off by etching. Conversely, since the gas permeability is relatively good at the coil end, Bi vapor is not concentrated, and it is estimated that an ultra-high magnetic flux density is easily obtained. That is, in the case of annealing with a coil form on a factory scale, it is difficult to control gas permeability particularly at the center and the edge of the coil, and there is a possibility that an ultra-high magnetic flux density cannot be stably obtained over the entire coil. Therefore, the present inventors conducted the following experiment in order to quantitatively grasp the effect of gas permeability between the plates during the secondary recrystallization finishing 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: Silicon steel containing 0.12% is melted, and the Bi content is set to 0, 0.007%, 0.013%, and 0.025%. Heating,
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 quenched in 80 ° C. water. Then, pickling was carried out.
Cold rolling was performed five times with aging treatment at 250 ° C. halfway to 23 mm. Subsequently, the introduced steam was adjusted so that the degree of oxidation was 0.40 (PH ₂ O / PH ₂ ) in the mixed gas of nitrogen and hydrogen, decarburization and primary recrystallization annealing were performed, and subsequently N ₂ was introduced in an NH ₃ atmosphere. Nitriding annealing was performed so that the content became 200 ppm. After applying an ordinary annealing separator containing MgO as a main component, secondary recrystallization finish annealing was performed. In order to see the effect of gas permeability between the plates, a sample in which about 50 100 mm x 500 mm steel plates were stacked was packed in an iron thin film and inserted into the furnace, and then a gas in a wet hydrogen atmosphere with a nitrogen partial pressure of 25% was removed. The temperature was increased to 1200 ° C. at 15 ° C./hr while the flow rate was set to 1, 5, 10, 15 Nm ³ / min, followed by purification annealing at 1200 ° C. for 20 hours in a dry hydrogen atmosphere. . At this time, the inner volume of the annealing furnace was 0.06 m ³ . FIG. 1 shows the relationship between the flow rate of the gas introduced into the furnace and the oxygen content and the magnetic flux density B ₈ of the obtained steel sheet. The oxygen content of the steel sheet basically indicates the amount of the primary film formed, and when the oxygen content was low, peeling or weakening of the primary film was observed.

As a result, the ultra-high magnetic flux density unidirectional magnetic steel sheet to which Bi is added is compared with the conventional high magnetic flux density unidirectional magnetic steel sheet mainly using aluminum nitride.
When the gas permeability during the secondary recrystallization finishing annealing is poor, the magnetic flux density varies, and the conclusion suggesting the above-mentioned assumption that stable high magnetic flux density is difficult to obtain is obtained. In order to solve this problem in factory production, for example, the flow rate of gas introduced into the annealing furnace in the factory may be increased, but the furnace volume of a box-scale annealing facility on a factory scale is usually about 30 m ³ , Even if the calculation is performed as described above, an introduction gas of 500 times the introduction gas flow rate of the laboratory annealing furnace for steam is required. This puts pressure on equipment costs and is difficult from the viewpoint of cost per unit, etc. Therefore, in order to stably produce ultra-high magnetic flux density unidirectional magnetic steel sheets on an industrial scale by adding Bi, it is necessary to form a primary film. It is found that the application of mirroring technology that does not rely on the image is effective.

Hereinafter, the results of the experiment which led to the present invention will be described. The present inventors have, for the case of applying the mirror technique to Bi doping techniques, in order to quantitatively assess the effect of furnace Flow rate of introduced gas in the secondary recrystallization finish annealing on mirror surface state and the magnetic flux density B ₈ The following experiment was performed. That is, a material having the same components as in the above-described experiment was treated under the same process conditions until nitriding annealing, and then Bi was added to 100 parts by weight of MgO.
After applying an annealing separator containing 5 parts by weight of OCl, secondary recrystallization finishing annealing was performed. And like the above experiment,
A sample in which about 50 steel plates of 100 mm × 500 mm are stacked is packed with an iron thin film and inserted into a furnace. Then, a gas in a wet hydrogen atmosphere having a nitrogen partial pressure of 25% is introduced, and the flow rate is set to 1,5,1.
Up to 11200 ° C with 15/15 Nm ³ / min.
The temperature was raised in hr, followed by purification annealing 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. The oxygen content of the steel sheet was 200 ppm or less in all cases, and the steel sheet exhibited a good mirror surface without a primary film.

As is apparent from FIG. 2, by applying the mirror finishing technique, the magnetic flux density is not affected by the gas flow rate during the secondary recrystallization finishing annealing, and the effect of improving the magnetic flux density by adding Bi is stabilized. Obtained. As described above, since the secondary recrystallization process is not affected by the gas flow rate during the secondary recrystallization finishing annealing, the secondary recrystallization process is hardly affected by the variation in gas permeability at the position in the coil. This shows that it is advantageous for production by recrystallization finish annealing. 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 have studied the sample obtained in FIG.
Was subjected to strain relief annealing at a temperature of 850 ° C. for 2 hours.
And laser irradiation at 5mm intervals in the direction perpendicular to the rolling direction
And tried to control the magnetic domain. The element of the obtained sample
Magnetic flux density B (before magnetic domain control) ₈And 1.0kgf / mm^Twoof
Iron loss W after domain control measured under tension_17/50Diagram of the relationship
3 is shown.

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 A super-iron-loss magnetic steel sheet can be obtained in combination with the above. Also, B ₈ and W
_The straight line indicating the _17/50 relationship decreases with the addition of Bi, indicating that the iron loss of the Bi-added material is further improved from the iron loss expected from the improvement in magnetic flux density. this is,
As described with reference to FIG. 2, Bi addition is presumed to be due to the effect of promoting mirror finishing. The present invention is not merely a combination of a conventional method of manufacturing a high magnetic flux density unidirectional magnetic steel sheet by a Bi addition method and a method of manufacturing a low iron loss unidirectional magnetic steel sheet by a mirror finishing technique, but also the drawbacks in the former industrialization and the latter. It is intended to provide a method for solving the enhancement of stability 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:
2.0-4.8%, acid-soluble Al: 0.012-0.0
50%, N: 0.0030 to 0.0150%, Bi:
0.0005 to 0.03%, the balance being Fe and unavoidable impurities, and these are essential components and the other components 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 Patent Publication No. 62-45285) or a main inhibitor using AlN and MnS by Taguchi / Sakakura et al. (For example, Japanese Patent Publication No. 40-15644)
Should be applied. C is a γ-region open type element, and is an important element that forms a texture advantageous for secondary recrystallization due to the α → γ transformation or the presence of solid solution C in the steps from hot rolling to decarburizing annealing. If C is 0.02% or less, α → γ transformation does not occur, which is not preferable. On the other hand, if it exceeds 0.1%, a load is applied to the decarburization annealing step, which increases the 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 combines with N to form AlN and is a main inhibitor constituent element for producing a high magnetic flux density unidirectional magnetic 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
%, AlN becomes coarse, and as a result, the inhibitor strength is reduced, so that secondary recrystallization does not occur.

N contained in the material forms a nitride such as Si, Al, etc., and has an effect particularly as an inhibitor of primary recrystallization when low-temperature slab heating is assumed. The N content is determined from the heat history of the process and the necessary primary recrystallization annealing temperature from the viewpoint of controlling the primary recrystallization particle size. On the other hand, in the case where AlN is finely dispersed in a previous stage by high-temperature slab heating, it is necessary to consider the atmosphere conditions of secondary recrystallization annealing and the like. 0.0
If it is less than 030%, the cost of the smelting step is increased due to denitrification, and if it exceeds 0.0150%, a defect called a blister is generated.

As another inhibitor constituent element, M
n, S, Se, V, N, B, Nb, Sn, Cu, Ti,
Zr, Ta, Mo, Sn and the like can be added in combination. Bi is an essential element for obtaining an ultra-high-speed density,
The effective content of the additive is in the range of 0.0005 to 0.03%. Less than 0.0005% has little effect,
If it exceeds 0.03%, the effect of improving the magnetic flux density is saturated and cracks occur at the end of the hot-rolled sheet.
Limited to 3%.

Next, the manufacturing process conditions will be described. The material for an ultra-high magnetic flux density unidirectional electrical steel sheet whose components are adjusted as described above can be used as the material of the present invention regardless of any ordinary melting method or ingot making method. Next, the magnetic steel sheet material is rolled into a hot-rolled coil by ordinary hot rolling. Production method using (Al, Si) N as main inhibitor by Komatsu et al. (For example, JP-B-62-45)
No. 285), in view of securing the temperature during hot rolling, the temperature is 1100 ° C. or higher, and AlN is not completely encapsulated.
After performing heating at a temperature of 0 ° C. or lower, hot rolling is performed. A production method using AlN and MnS as main inhibitors by Taguchi and Sakakura (for example, Japanese Patent Publication No. 40-15644).
In Japanese Patent Application Laid-Open No. H10-260, it is only necessary to perform hot rolling after heating at a temperature of 1300 ° C. or higher for complete volumeization.

Subsequently, the final sheet thickness is obtained by one-stage cold rolling or a plurality of stages of cold rolling including intermediate annealing. However, since a unidirectional magnetic steel sheet having a high magnetic flux density is obtained, the final cold rolling rate ( In the case of one-stage cold rolling, the rolling reduction is preferably from 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 is subjected to primary recrystallization annealing and 750 to 900 in wet hydrogen or a mixed atmosphere of hydrogen and nitrogen for the purpose of removing carbon contained in steel.
Decarburization annealing is performed in a temperature range of 30C for 30 seconds to 30 minutes. For this decarburization annealing, a known technique for forming a good primary film can be applied. Further, it is necessary to apply appropriate conditions according to the annealing separator used. For example, MgO
When using as an annealing separator, excessive Fe-based oxide (Fe
₍₂ SiO ₄ , FeO, etc.) facilitates additional oxidation and nitrogen permeation, and makes inhibitors such as AlN thermally unstable. Therefore, it is desirable to perform annealing at a degree of oxidation that does not cause excessive formation of Fe-based oxides. Normally 800 ~
In the temperature range of 900 ° C., the generation of Fe-based oxides can be suppressed by adjusting the degree of oxidation of the atmospheric gas. When Al ₂ O ₃ is used as an annealing separator, it is desirable to perform annealing in an atmosphere having a low oxidation degree, since the oxide of only SiO ₂ without FeO has less seizure of Al ₂ O _{3 to} a steel sheet. On the other hand, the decarburization annealing temperature is determined mainly from the viewpoint of obtaining an optimum primary recrystallized grain size.

When it is necessary to strengthen the (Al, Si) N inhibitor of the decarburized annealed sheet, or when (Al, S
i) In a production method using N as a main inhibitor (for example, Japanese Patent Publication No. 62-45285), a nitriding treatment is performed between the steps of decarburizing annealing and secondary recrystallization finishing annealing. 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.

These decarburized annealed sheets are wound into a coil form.
Immediately before, a water slurry containing Bi chloride in the annealing separator
Is applied to the surface of the steel plate to secure the secondary recrystallization.
The point of the present invention is to make the plate surface mirror-finished.
The mechanism of secondary recrystallization and surface mirroring is not yet clear
However, in the process of secondary recrystallization finish annealing of the coil at 1000 ° C.
Until the primary film is formed, AlN etc. necessary for secondary recrystallization
Inhibits the deterioration of inhibitors. And annealing separator
Bi and Cl contained in BiOCl react with water during annealing.
And furthermore, BiCl_ThreeMin while generating steam
Understand. BiCl _ThreeHas a very high equilibrium dissociated chlorine partial pressure
Generates Cl gas between coil plates compared to other chlorides
Easy to make. The generated Cl gas spreads the oxide layer on the steel sheet surface.
Scattered, and when it reaches the ground iron, Fe + 2Cl → FeCl_Tworeaction
According to FeCl_TwoOf gas. Oxide film and ground iron
Some FeCl at the interface_TwoWhen the gas is generated
Since the surface is separated from the oxide layer, the movement of surface Fe atoms is easy
It is assumed that the surface becomes a mirror surface at a high temperature of 1000 ° C or higher.
Is determined. In this way, the mirror is used in the high temperature region of the secondary recrystallization finish annealing.
Surface area is a call-for-
Production of Bi-added ultra high magnetic flux density unidirectional electrical steel sheet
It is very effective to make up for the disadvantages of the method. FIG.
A small amount adhered to the mirror-finished steel sheet surface with the amount of Bi added
Bi addition promotes specularization as oxygen is reduced
It is expected to have the effect of causing About this cause
Although not yet clear, Bi in the steel added during the steelmaking stage
When the gas is vaporized from the steel sheet surface, the primary coating peels off and
Has a favorable effect on the subsequent thermal etching
It is estimated that. That is, the present invention uses the conventional Bi addition
Of high magnetic flux density by using the method and low iron loss by using mirror surface finishing technology
Are very effectively combined.

As the annealing separating agent, a known high melting point compound which is applied between coil plates and does not cause seizure between the plates even at a temperature of about 1200 ° C., for example, MgO, Al ₂ O
₃ , SiO ₂ , ZrO, BaO, CaO, SrO are effective, and one kind or a mixture of two or more kinds is used. When Bi chloride is added to these oxides, secondary recrystallization formation and mirror finishing can be satisfied in any case.

In order to form Bi chloride in the annealing separator, it is appropriate to add BiCl, BiOCl and BiCl ₂ . Further, as described in JP-A-7-54155, the same effect can be obtained even when a unit of Bi or a compound of Bi and a chlorine compound of a metal are added in combination. If the Bi chloride contained in the annealing separator is less than 0.2 parts by weight of chlorine relative to 100 parts by weight of the annealing separator, the etching effect is insufficient and the oxide film is removed over the entire area in the coil width direction. Can not do. On the other hand, even if the amount of addition is increased, the volume of Cl gas that can be present between the plates is constant, so that the Bi chloride added extra flows out from between the coil plates and has no effect. Further, in order to prevent the steel sheet from burning during the secondary recrystallization annealing, it is necessary that the separating agent remains after the Bi chloride evaporates. Therefore, the upper limit of the amount of Bi chloride added was 15 parts by weight as chlorine.

Regarding the secondary recrystallization finish annealing conditions, as disclosed in Japanese Patent Application Laid-Open No. 7-18333, a method of stabilizing the (Al, Si) N inhibitor by controlling the partial pressure of nitrogen during temperature rise, As disclosed in Japanese Patent Application Laid-Open No. 2-258929, performing secondary recrystallization in a predetermined temperature range by maintaining a constant temperature or controlling a heating rate is effective in increasing the magnetic flux density. is there. After the completion of the secondary recrystallization, 100% hydrogen is applied in order to purify impurities such as nitrides and smoothen the surface by thermal etching.
Anneal at a temperature of 0 or more.

After the secondary recrystallization finish annealing, the excess annealing separating agent is continuously removed, followed by continuous tension annealing for correcting coil winding and the like, and at the same time, an insulating 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. Since the present invention increases the secondary recrystallized grain size at the same time as increasing the magnetic flux density by adding Bi, the magnetic domain refining treatment is effective from the viewpoint of improving iron loss characteristics. There is no particular limitation on the method of magnetic domain subdivision.

In the case of performing magnetic domain subdivision by introducing local distortion, for example, a method of irradiating a laser beam described in Japanese Patent Publication No. 57-2252 or the like,
A method for performing plasma flame irradiation described in Japanese Patent No. 51511 and Japanese Patent Publication No. 6-45824 may be used.
In the case of performing magnetic domain subdivision by forming local grooves, mechanical plasticity such as a gear roll method (for example, Japanese Patent Publication No. 4-48847) and a die pressing method (for example, Japanese Patent Publication No. 6-63037). Processing method, photo etching method (for example, Japanese Patent Publication No. 5-69284) and resist ink etching method (for example, Japanese Patent Publication No. 2-46673, Japanese Patent Publication
No. 69968), a method using chemical etching or electrolytic etching, or the like may be employed. The groove formed in the steel plate is perpendicular to the rolling direction or within a range of 45 degrees from the perpendicular, and the interval is preferably 2 to 10 mm from the viewpoint of reducing iron loss. The shape of the groove may be continuous, discontinuous or point-like. The width and depth of the groove are each 10 to 300μ
m, the range of 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. Further, the step of forming such a local groove may be any step after the cold rolling.

As the tension coating, for example, a coating solution mainly composed of colloidal silica and aluminum phosphate disclosed in JP-A-48-39338;
A method of baking a coating solution mainly containing colloidal silica and magnesium phosphate according to Japanese Patent Application Laid-Open No. 0-79442 or a coating solution mainly containing alumina sol and boric acid according to Japanese Patent Application No. 4-22849 is adopted. I just need.

[0035]

【Example】

(Example 1) By weight%, 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) B
i: Two levels of 0% silicon steel were melted, each was cast into a slab, heated to 1200 ° C., and immediately extracted to 2.3 mm.
It was hot rolled to the sheet thickness. Thereafter, it was pickled and cold rolled to 0.23 mm. This cold rolled sheet was annealed at a temperature of 830 ° C. for 100 seconds at a degree of oxidation of 0.1 (C) and 0.4 (D) in a mixed gas of nitrogen and hydrogen for primary recrystallization. Then, by annealing in an ammonia atmosphere, the nitrogen amount is reduced to 0.02.
% To increase the inhibitor.

These steel sheets were then (C: mirror-finished)
After applying a water slurry of l ₂ O ₃ + BiOCl (5 parts by weight) and (D: conventional method) MgO, the steel sheets are laminated, and the steel sheets are laminated under a low gas flow rate in a humid hydrogen atmosphere having a nitrogen partial pressure of 25%. Next, recrystallization finishing annealing was performed. These samples were rolled with a gear roll in a direction of 10 degrees from a direction perpendicular to the rolling direction and a width of 50 μm.
m, a groove having a depth of 50 μm is formed, and then a coating liquid containing colloidal silica and phosphate as main components is applied to form a groove.
Bake at 50 ° 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.

[0037]

[Table 1]

Example 2 Si: 3.3% by weight
Mn: 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 which had been pickled and rolled to 1.4 mm was annealed at a temperature of 1120 ° C. for 30 seconds at 900 ° C. for 90 seconds, then air-cooled to 750 ° C. and quenched into 80 ° C. water to a final thickness of 0.15 mm Cold rolled. This cold-rolled sheet was annealed in a mixed gas of nitrogen and hydrogen at a temperature of 830 ° C. with a degree of oxidation of 0.3 for 70 seconds to perform 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) Z
rO + BiCl (10 parts by weight) and (D: conventional method) M
After applying the gO water slurry, the steel sheets were laminated and subjected to secondary recrystallization finish annealing under a low gas flow rate in a wet hydrogen atmosphere with a nitrogen partial pressure of 25%. A groove having a width of 30 μm and a depth of 10 μm is formed on the sample after the finish annealing in a direction perpendicular to the rolling direction by a photoetching method, and then a coating solution containing alumina sol and boric acid as main components is applied 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.

[0040]

[Table 2]

(Example 3) Si: 3.3% by weight
Mn: 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 is oxidized in a mixed gas of
8 at 850 ° C. for 120 seconds for primary recrystallization.

These steel sheets were then (C: mirror-finished) M
After applying a water slurry of gO + BiCl ₃ and (D: conventional method) MgO, a steel sheet is laminated and 20 kg / mm in a thickness direction.
After pressurizing with ^2, nitrogen partial pressure is subjected to secondary recrystallization finish annealing under a low gas flow rate in a hydrogen atmosphere humidity 25%. A coating solution 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.

[0043]

[Table 3]

(Example 4) By volume%, C: 0.05%,
Si: 3.25%, Mn: 0.10%, S: 0.007
%, P: 0.025%, acid-soluble Al: 0.029%,
N: 0.007% Bi: 0.007%, Cr: 0.12
% Is melted and cast into a slab.
Heated to 0 ° C and immediately hot rolled to a 2.3mm plate thickness after extraction,
After hot rolling, it was cooled with water and wound up at 550 ° C. Then hot-rolled sheet
Anneal at a temperature of 120 ° C. for 30 seconds, 900 ° C. for 90 seconds, 75
After air cooling to 0 ° C, it was quenched into 80 ° C water. Next, after pickling, rolling was performed in 5 passes to 0.23 mm, and 200 ° C.
Thus, the aging treatment was performed for 5 minutes or more. Subsequently, decarburization / primary recrystallization annealing is performed in a mixed gas of nitrogen and hydrogen in an atmosphere having an oxidation degree of 0.49, at a temperature of 850 ° C. for 100 seconds, and subsequently in an NH ₃ atmosphere with an N content of 200 ppm.
Nitriding annealing was performed to obtain. 6. As an annealing separator containing MgO as a main component, BiOCl is added to 100 parts by weight of MgO.
A 5 T coil wound by applying 5 parts by weight of added water slurry to the surface of the steel sheet was subjected to secondary recrystallization finish annealing in a box type annealing furnace. The temperature was raised to 1200 ° C. at a rate of 15 ° C./hr while flowing a mixed gas of 50% nitrogen and hydrogen in the furnace, and subsequently, purification annealing was performed at 1200 ° C. for 75 hours while flowing hydrogen. Then, while developing the coil in a continuous annealing line, a groove is formed by pressing a tooth mold having a groove having a width of 50 μm and a depth of 11 μm, which is inclined by 10 degrees from the rolling direction and a direction perpendicular to the rolling direction. 86 by applying a coating liquid containing silica and phosphate as main components
Bake for 2 minutes at 0 ° C. The Epstein value after annealing at 800 ° C. for 2 hours, sampled at five points of the obtained coil, was 1.9 on average with the magnetic flux density B ₈ before the magnetic domain control.
7T, was 0.68W / kg in iron loss W _17/50.

[0045]

The present invention provides an extremely effective combination of ultra-high magnetic flux density by the conventional Bi addition method and low iron loss by the mirror finishing technique of applying an annealing separator containing Bi chloride. In addition to being able to obtain inexpensively super-flux density low unidirectional electrical steel sheets in an extremely stable manner in industrial production, the iron loss properties after magnetic domain refinement are extremely excellent.
It can be said that it is very valuable industrially.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a gas introduction amount, a magnetic flux density B ₈ and a steel sheet oxygen amount during finish annealing at each Bi content in a primary film forming method (conventional magnesia annealing separating agent); ] is a diagram showing the relationship between the gas introduction amount and the magnetic flux density B ₈ in finish annealing at the Bi content, [B] the relationship of the gas introduction amount in finish annealing and a steel sheet oxygen amount in each Bi content FIG.

Fig. 2 Mirroring method (magnesium containing bismuth chloride)
Finish annealing at each Bi content in (A annealing separator)
Amount of gas introduced and magnetic flux density B₈Between steel and oxygen content
[A] shows the results during the finish annealing at each Bi content.
Gas introduction amount and magnetic flux density B ₈[B] is a diagram showing the relationship of
Gas introduction amount and acid of steel sheet during finish annealing for each Bi content
The figure which shows the relationship of an elementary quantity.

FIG. 3 shows the relationship between the magnetic flux density (before magnetic domain refining) B ₈ and the iron loss W _17/50 after the magnetic domain refining when the sample obtained in FIG. 2 is subjected to magnetic domain refining treatment by laser irradiation. FIG.

Claims (5)

[Claims] 1. Weight%, C: 0.02-0.1% Si: 2.0-4.8%, Acid-soluble Al: 0.012-0.050%, N: 0.0030-0 0.0150%, Bi: 0.0005 to 0.03% as a basic component, the remainder being cast molten steel composed of Fe and unavoidable impurities, hot-rolled, and including 65-95% final strong cold rolling. The final thickness is obtained by cold rolling once or twice or more with intermediate annealing, decarburizing annealing combined with primary recrystallization, and between decarburizing annealing and secondary recrystallization finishing annealing as necessary A unidirectional electrical steel sheet comprising a step of performing a secondary recrystallization finish annealing by performing a nitriding treatment and performing a secondary recrystallization finish annealing.
A method for producing a mirror-oriented unidirectional electrical steel sheet having a high magnetic flux density, comprising applying an annealing separator containing 0.2 to 15 parts by weight of a chloride in parts by weight of chlorine and then performing secondary recrystallization finish annealing. 2. The main component of the annealing separator is MgO, Al ₂
1 of O ₃ , SiO ₂ , ZrO, BaO, CaO, SrO
The method for producing a mirror-oriented unidirectional magnetic steel sheet having a low iron loss according to claim 1, which is a kind or a mixture of two or more kinds. 3. A method for producing a mirror-oriented unidirectional magnetic steel sheet having a low iron loss, wherein a magnetic domain refinement treatment is performed by introducing local strain into the steel sheet according to claim 1. 4. A mirror surface unidirectional having a low iron loss, wherein a magnetic domain refinement treatment is performed by introducing a local strain after forming a tension film by a coating treatment on the steel sheet according to claim 1. Manufacturing method of conductive electrical steel sheet. 5. The steel sheet according to claim 1, which is perpendicular to the rolling direction or at an interval of 2 to 10 mm within a range of 45 degrees from the perpendicular.
Forming a continuous, discontinuous or point-like groove or a local groove in the range of 10 to 300 μm in width and 5 to 50 μm in depth, and forming a tension film by a coating process to further subdivide the magnetic domains. A method for producing a mirror-oriented unidirectional magnetic steel sheet having a low iron loss, characterized by comprising: