JPH10130727A - 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 by coating the surface of a steel sheet with a separation agent for annealing added with specified components and executing secondary recrystallization finish annealing. SOLUTION: As for MgO used for a separation agent for annealing, for obtaining a uniform mirror finished face, the grain size is limited in such a manner that the ratio of the ones having <=10μm grain diameter is regulated to >=30%. Furthermore, its CAA value is prescribed to 50 to 300sec. Moreover, the content of hydrated water is prescribed to <=5%. Then, as for the added substance to MgO, one or more kinds among the chlorides, carbonates, nitrates, sulfates and sulfides are blended by 2 to 30 pts.wt. to 100 pts.wt. MgO. In this way, suitably thin primary coating is formed on the surface of the steel sheet in a stage prior to finish annealing, primary coating is decomposed by etching reaction of Fe in a coating layer in the poststage of temp. rising, and, by the subsequent high temp. annealing, the surface is subjected to thermal etching and is mirror-finished. Thus, this mirror finishin is combined with the conventional addition of Bi, its magnetic flux density can furthermore be increased.

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 having 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 higher 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. As a typical manufacturing method of high magnetic flux density electromagnetic steel sheet,
JP-B-40-15644, JP-B-51-1346
No. 9 publication. 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 base Nuisance product in Patent at most from 1.88T 1.95 T
For example, the saturation magnetic flux density of 3% Si steel is 2.03.
It only shows a value of about 95% of T. And
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 magnetization properties of unidirectional magnetic 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 the eddy current loss increases. Therefore, the expectation of iron loss improvement is not desired because it is more than metallurgical. 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 5
8-5968, 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-63-4480
No. 4, Japanese Patent Publication No. 04-48847, etc.
For example, a method is disclosed in which grooves are introduced by, for example, 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 small sample materials at the laboratory level,
On an industrial scale, there are major problems in terms of chemical solution concentration control, temperature control, and provision of pollution equipment, and the addition of such a step increases the manufacturing cost. Has not been converted.

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, Japanese Patent Application Laid-Open Nos. 5-222489, 5-299228, 5-5-228). No. 320770). These are made of Li, K, Na, Ba, Ca, M on the steel sheet surface after decarburizing annealing.
chlorides such as g, Zn, Fe, Zr, Sn, Sr, and Al;
Secondary recrystallization by applying an annealing separator containing 2 to 30 parts by weight of one or more selected from carbonates, nitrates, sulfates, and sulfides and performing a secondary recrystallization finish annealing An appropriate thin primary film is formed on the surface of the steel sheet before the finish annealing to prevent the deterioration of the inhibitor necessary for the secondary recrystallization. Next, the formation of the primary film and the additional oxidation are prevented,
In this method, the primary film is decomposed by the etching reaction of Fe in the film layer after the temperature is raised, and the surface is thermally etched by high-temperature annealing to form the 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 low 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 surface technology, it is possible to stably manufacture ultra-high magnetic flux density unidirectional mirror-surface electromagnetic steel 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 produce an ultra-low iron loss-specular grain oriented electrical steel sheet having extremely low iron loss at a low cost.

[0009]

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: 0.0030 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 the method for producing a grain-oriented electrical steel sheet comprising a step of performing a secondary recrystallization finish annealing, the steel sheet surface is coated with Li, K, Na, Ba, Ca, Mg, Zn, Zn, and 100 parts by weight of MgO.
Apply an annealing separator containing 2 to 30 parts by weight of one or more selected from chlorides, carbonates, nitrates, sulfates, and sulfides such as Fe, Zr, Sn, Sr, and Al. ,
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) A mirror surface having a high magnetic flux density according to (1), wherein an oxygen basis weight of the steel sheet in the decarburizing annealing is 900 ppm or less, and FeO / SiO ₂ in the oxide film is 0.20 or less. Manufacturing method of unidirectional electrical steel sheet. (3) The physical properties of MgO used as an annealing separator include 30% or more of particles having a particle size of 10 μm or less, a citric acid activity CAA value of 50 to 300 seconds (measured at 30 ° C.), and a hydration moisture of 5%. (1) The method for producing a mirror-oriented unidirectional electromagnetic steel sheet having a high magnetic flux density according to (1).

(4) The conditions for the secondary recrystallization finish annealing include:
(1) Manufacturing the mirror-oriented unidirectional electrical steel sheet having a high magnetic flux density according to (1), wherein the atmosphere at the time of raising the temperature until the completion of the secondary recrystallization is an N ₂ + H ₂ atmosphere in which the ratio of N ₂ is 30% or more Method. (5) A method for producing a mirror-oriented unidirectional magnetic steel sheet having a low iron loss, which comprises subjecting the steel sheet according to (1) to local distortion to perform a magnetic domain refining treatment.

(6) After forming a tension film by coating on the steel sheet according to (1), a magnetic domain refining treatment is performed by introducing local distortion, whereby a mirror surface with low iron loss is characterized. Manufacturing method of grain-oriented electrical steel sheet. (7) The steel sheet according to (1) is perpendicular to the rolling direction or within a range of 45 degrees from the perpendicular to 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.

[0013]

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 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 = 1.95T or more, far exceeding 1.93T,
An ultra-high magnetic flux density unidirectional magnetic steel sheet of 2T was obtained. Although the mechanism for obtaining the super magnetic flux density is not yet clear, it is presumed that Bi functions as a thermally stable inhibitor strengthening element because the diffusion constant in steel is extremely small. 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 base iron to form BiCl ₃ or the like, and the primary film is peeled off. 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 × 500 mm steel plates were stacked was packed in an iron thin film and inserted into the furnace, and then a N ₂ + H ₂ wet atmosphere with N _{2 set} to 50% was used. The gas was introduced, the temperature was raised to 1200 ° C. at 15 ° C./hr while the flow rate was set to 1, 5, 10, 15 Nm ³ / min, followed by purifying annealing at 1200 ° C. for 20 hours in a dry hydrogen atmosphere. went. 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 using aluminum nitride as a main inhibitor.
When the gas permeability during the finish annealing is poor, the magnetic flux density fluctuates, and the conclusion suggesting the above-mentioned assumption that stable high magnetic flux density is difficult to obtain was 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 experiments which have 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, after a material having the same components as in the above-described experiment was treated under the same process conditions until nitriding annealing, Ca was added to 100 parts by weight of MgO.
After applying an annealing separator containing 10 parts by weight of Cl ₂ , secondary recrystallization finish annealing was performed. Then, in the same manner as in the above experiment, a sample in which about 50 100 mm × 500 mm steel plates were stacked was packed in an iron thin film, inserted into a furnace, and N ₂ was set to 50%.
_{A 2} + H ₂ humid atmosphere was introduced into the furnace, and the flow rate was set at 1, 5,
15 ° C / 1200 ° C with 10,15 Nm ³ / minute
hr, followed by 2 hours at 1200 ° C in a hydrogen atmosphere.
A zero-hour purification annealing was performed. 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 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. As described above, being not affected by the gas flow rate during the finish annealing, the secondary recrystallization process is hardly affected by the variation in gas permeability at the position in the coil.
It shows that it is advantageous for production by secondary recrystallization finish annealing in a coil scale on a factory scale. Also, in FIG.
Since a small amount of oxygen attached to the surface of the mirror-finished steel sheet decreases along with the amount of i added, it is expected that the addition of Bi has an effect of promoting mirror finishing.

Further, the present inventors have prepared 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 In combination with the above, an ultra-low iron loss electromagnetic steel sheet can be obtained. 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:
0 to 4.8%, acid-soluble Al: 0.012 to 0.050
%, N: 0.0030 to 0.0150%, Bi: 0.0
005 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 or the like (for example, Japanese Patent Publication No. Sho 62-45285), or a main inhibitor using AlN and MnS by Taguchi / Sakakura or the like. (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%, eddy current loss of the product increases, and at the time of finish annealing, α → γ transformation occurs, 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, 0.05
If it exceeds 0%, 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 nitrides such as Si and Al, and particularly when used for low-temperature slab heating, has an effect as an inhibitor of primary recrystallization. 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), from the viewpoint of securing the temperature during hot rolling, the temperature is 1100 ° C. or higher, and AlN is not completely dissolved.
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 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, 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. In the decarburization annealing in the present invention, the oxygen basis weight of the steel sheet is 900 ppm or less, and FeO / SiO
₂ is limited to 0.20 or less. Here, FeO is FeO in firelite (Fe ₂ SiO ₄ ). If the basis weight of oxygen exceeds 900 ppm, SiO 2 in the oxide film layer is inevitably contained.
₂ and the amount of FeO increases and the thickness of the oxide film also increases, which is disadvantageous when performing a temporary film decomposition reaction during the secondary recrystallization finish annealing. That is, SiO ₂ remains immediately below the surface, and not only a completely mirror-like surface state cannot be obtained, but also magnetic deterioration. Furthermore, since the formation of excessive SiO ₂ promotes the decomposition of the (Al, Si) N inhibitor in the steel before the start of the secondary recrystallization, there is a problem that it becomes difficult to obtain an ultra-high magnetic flux density. However, if the amount of oxidation is extremely suppressed, there is a problem that the decarburization time is prolonged and productivity is impaired. The preferred range is 400-700 ppm. If the amount of FeO / SiO ₂ in the oxidized amount exceeds 0.20, the primary film forming reaction in the first half of the secondary recrystallization finish annealing increases extremely, and the amount of the primary film formed increases. The reaction does not proceed sufficiently at the stage. FeO / S
If iO ₂ ≦ 0.20, the primary film is almost completely decomposed by the secondary recrystallization finish annealing due to the effects of additives and the like to MgO. 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 (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.

Next, the particle size, CAA value, hydration moisture and the like of MgO used for the annealing separator are limited. In the technique of the present invention, mirror finishing is performed by decomposing and removing a moderate primary film formed before the temperature rise in the secondary recrystallization finish annealing by a chemical reaction after the temperature rise. That is, in order to stabilize the inhibitor until the start of the secondary recrystallization in the pre-annealing stage of the secondary recrystallization, it is necessary to use the effect of suppressing the additional oxidation and nitridation by a moderate amount of the primary film at this time, It is commonly used to obtain mirror products with excellent magnetic properties. For this purpose, it is important that MgO itself, which is the base of the annealing separator, has an appropriate reactivity. That is, Mg
If the reactivity of O is extremely poor, the primary film forming reaction before the secondary recrystallization finish annealing does not proceed, and the atmosphere sealing effect by the film cannot be obtained. In such a case, even if secondary recrystallization occurs, the crystal orientation becomes extremely poor, or additional oxidation causes residual SiO ₂ , Al ₂ O ₃ or their spinels to be generated immediately below the steel sheet surface, thereby deteriorating iron loss. Bring. For this reason,
The particle size of MgO is limited so that those having a particle size of 10 μm or less are 30% or more. If it is less than 30%, the reactivity becomes extremely poor, and the effect of the first period cannot be exhibited. MgO C
The AA value is defined as 50 to 300 seconds. If this value is less than 50 seconds, the progress of hydration becomes extremely short in industrial use, and it becomes difficult to control the hydrated water. If it exceeds 300 seconds, the reactivity of MgO particles is extremely reduced. As a result, the formation of the primary swelling before the secondary recrystallization finishing annealing does not occur. Also M
The hydration moisture of gO is limited to 5% or less. If it exceeds 5%, the dew point between the steel sheets will increase, and additional oxidation will occur in the first stage of the temperature rise, making it difficult to obtain a uniform mirror surface condition. Recrystallization failure occurs.

As an additive to the annealing separator MgO, L
i, K, Na, Ba, Ca, Mg, Zn, Fe, Zr,
One or more selected from chlorides, carbonates, nitrates, sulfates, and sulfides such as Sn, Sr, and Al are Mg.
2 to 30 parts by weight are blended with respect to 100 parts by weight of O. By the addition of these compounds, a moderately thin primary film is formed on the steel sheet surface before the temperature rise of the secondary recrystallization finish annealing,
Next, formation of the primary film is suppressed and additional oxidation is prevented, and the primary film is decomposed by the etching reaction of Fe in the film layer after the temperature is raised, and the surface is thermally etched by high-temperature annealing to form a surface. When the addition amount of these compounds is less than 2 parts by weight, the decomposition reaction of the primary film formed in the former stage does not sufficiently proceed, and the primary film remains, which is not preferable. On the other hand, when the amount exceeds 30 parts by weight, the component elements in the additive diffuse into the steel sheet to cause grain boundary etching, affect an inhibitor, and affect a subsequent purification treatment. The most preferred range is from 5 to 15 parts by weight.

The conditions for the secondary recrystallization finishing annealing are important when the primary film is appropriately formed and decomposed during the annealing process as in the present invention. Usually, N ₂ , H _2, or a mixed gas thereof is used as the atmosphere gas in the secondary recrystallization finishing annealing, but N ₂ + H ₂ is advantageous from the viewpoint of controlling the oxidation of the surface. For the present invention, for controlling the strength of the inhibitor during the course of the decomposition reaction of the primary coating, an atmosphere composed of at least N ₂ 30% or more N _2, H ₂ and other inert gas as the atmosphere gas NoboriAtsushichu Used. N ₂ partial pressure of 30%
If it is less than 5, the weakening of (Al, Si) N does not occur in the process of mirror finishing, and an ultra-high magnetic flux density material can be stably obtained. Especially N
For ₂ to 20% results in a deterioration of the magnetic properties. However, in the case of N ₂ 100%, the degree of oxidation between the steel sheets increases depending on the physical properties of MgO, and the surface of the steel sheet may become uneven due to oxidation. Preferably N ₂ 30~90%
Range. When using a gas of N ₂ 30% or more, the entire temperature rise may be annealed in this atmosphere. However, depending on the conditions of MgO, additional oxidation may occur, and (Al,
It is preferable to switch the temperature to 700 ° C. or higher, which is the most effective temperature for stabilizing Si) N. It is advantageous to set the soaking temperature in the secondary recrystallization finishing annealing to 1180 to 1200 ° C. In the present invention, the decomposition of the primary film has been completed when the soaking of the secondary recrystallization finish annealing is reached, and the surface of the steel sheet can be mirror-finished by thermal etching during the purification annealing. If the soaking temperature is less than 1180 ° C., this effect is weak and disadvantageous to purification. On the other hand, when the temperature exceeds 1250 ° C., the coil shape may be deteriorated, or burn-in of the edge portion may occur. As disclosed in JP-A-2-258929, performing secondary recrystallization in a predetermined temperature range by maintaining the temperature at a constant value or controlling the rate of temperature rise is effective in increasing the magnetic flux density. It is.

On the other hand, as shown in FIG. 2, the amount of oxygen added to the surface of the mirror-finished steel sheet in a small amount decreases with the addition amount of Bi.
It is expected that i-addition will have the effect of promoting mirror finishing. Although the cause is not clear yet, it is presumed that when Bi in the steel added at the steelmaking stage is vaporized from the steel sheet surface, it has an advantageous effect on the peeling of the primary film and the subsequent thermal etching. ing. In addition, Bi finely precipitated in the steel complementarily brings about thermal stabilization of the inhibitor.
i) If there is a concern about instability of N, it is presumed that this has an advantageous effect on the appearance of secondary recrystallization. On the other hand, in order to stably bring out the effect of increasing the super magnetic flux density of Bi in factory production of a coil form, there is a limit in a technique for forming a primary coating, and a mirror finishing technique is most suitable.
Furthermore, the Bi addition technology presupposes magnetic domain refinement because the crystal grain size becomes coarse with the increase in super magnetic flux density. In particular, when a method of mechanically forming a local groove is used, a mirror surface is required from the viewpoint of mold cost. The material is appropriate. That is, the present invention is an extremely effective combination of the ultra-high magnetic flux density by the conventional Bi addition method, the mirror finishing, and the low iron loss by the magnetic domain segmentation technology.

After the secondary recrystallization finish annealing, the excess annealing separating agent is continuously removed, and continuous tension annealing for correcting coil winding and the like is performed, 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 preferred 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.

Examples of the tension coating include 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 JP-A-79442 or a coating solution mainly comprising alumina sol and boric acid according to JP-A-4-22849 is adopted. Good.

[0036]

【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 in a mixed gas of nitrogen and hydrogen at a temperature of 840 ° C. with an oxidation degree of 0.4 for 100 seconds to perform 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 subjected to (C: mirror finishing) M
gO + K ₂ S (7 parts by weight) and (D: conventional method) MgO
After applying the water slurry, the steel sheets were laminated, and subjected to secondary recrystallization finish annealing at a partial pressure of N of 40% under a low gas flow rate.
These samples were placed on a gear roll in a direction perpendicular to the rolling direction.
After forming a groove having a width of 50 μm and a depth of 15 μm in the direction of 0 °, a coating liquid containing colloidal silica and phosphate as main components was applied and baked at 850 ° C. for 2 minutes. After the magnetic properties of these samples were measured,
Time annealing was performed. Table 1 shows the magnetic properties of the obtained products.

[0038]

[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 was pickled and cold rolled to 1.4 mm was annealed at a temperature of 1120 ° C. for 30 seconds at 900 ° C. for 90 seconds, air-cooled to 750 ° C., quenched into 80 ° C. water, and finally finished to a 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 an oxidation degree of 0.5 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) M
gO + SnCl ₂ (10 parts by weight), and (D: conventional method)
After applying the MgO water slurry, the steel sheets were laminated and subjected to secondary recrystallization finish annealing at a 50% partial pressure of N ₂ under a low gas flow rate. 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, an additional 80
The strain relief annealing was performed at 0 ° C. for 4 hours. Table 2 shows the magnetic properties of the obtained products.

[0041]

[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., hot-rolled to a thickness of 2.3 mm immediately after extraction, 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 nitrogen and hydrogen to a degree of oxidation of 0.6.
At 850 ° C. for 120 seconds for primary recrystallization.

These steel sheets were then subjected to (C: mirror finishing) M
gO + K ₂ CO ₃ (15 parts by weight) and (D: conventional method) M
After applying a water slurry of gO, a steel plate is laminated and pressurized at 20 kg / mm ² in the thickness direction.
_{A second} recrystallization finish annealing was performed at 75% partial pressure of 2. 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.

[0044]

[Table 3]

Example 4 C: 0.05% by weight
Si: 3.25%, Mn: 0.10%, S: 0.007
%, P: 0.025%, acid-soluble Al: 0.029%,
N: 0.007%, Bi: 0.007%, Cr: 0.1
After smelting silicon steel containing 2% and casting it into a slab, 11
It was heated to 50 ° C., immediately after the extraction, hot-rolled to a thickness of 2.3 mm, water-cooled after hot rolling, and wound at 550 ° C. Thereafter, the hot rolled sheet was annealed at a temperature of 1120 ° C. for 30 seconds and 900 ° C. for 90 seconds,
After air cooling to 750 ° C, it was quenched into 80 ° C water. Next, after pickling, rolling was performed for 5 passes to 0.23 mm, and 200
Aging treatment was performed at a temperature of not less than 5 ° C. for not less than 5 minutes. Continue decarburization
Primary recrystallization annealing is performed in a mixed gas of nitrogen and hydrogen in an atmosphere having an oxidation degree of 0.5, at a temperature of 850 ° C. for 100 seconds, and subsequently, in a NH ₃ atmosphere, nitriding annealing is performed so that the N content becomes 200 ppm. Was. A water slurry obtained by adding 5 parts by weight of CaCl ₂ to 100 parts by weight of MgO to an annealing separator containing MgO as a main component was applied to the surface of the steel sheet and wound.
The coil of T 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 hydrogen mixed gas with a nitrogen partial pressure of 50% into the furnace, followed by a purification annealing at 1200 ° C. for 75 hours while flowing hydrogen. Then, while developing the coil in a continuous annealing line, a groove of a tooth mold having a width of 50 μm and a depth of 11 μm, which is inclined by 10 degrees from the direction perpendicular to the rolling direction, is formed by pressing, and then the colloid is formed. 860 by applying a coating liquid containing silica and phosphate as main components.
Bake at 2 ° C. for 2 minutes. The Epstein value after annealing at 800 ° C. for 2 hours, which was sampled and measured at five points of the obtained coil, was 1.96 on average with the magnetic flux density B ₈ before the magnetic domain control.
T and the iron loss W _17/50 were 0.69 W / kg.

[0046]

According to the present invention, Li, K, Na, Ba, Ca, Mg, Z
One or more selected from chlorides, carbonates, nitrates, sulfates, and sulfides such as n, Fe, Zr, Sn, Sr, and Al are blended in an amount of 2 to 30 parts by weight based on 100 parts by weight of MgO. By combining the mirror finishing technology of applying the MgO slurry to be applied very effectively, inexpensive super magnetic flux density low unidirectional electrical steel sheets can be obtained extremely stably in industrial production, and the iron loss after the magnetic domain refining treatment is obtained. The characteristics are also extremely excellent, and it can be said that it is very valuable industrially.

[Brief description of the drawings]

[1] Primary film forming method in the (conventional magnesia annealing separator), a diagram showing a relationship between amount of oxygen gas introduction amount and the magnetic flux density B ₈ and the steel sheet during finish annealing at each Bi content [A ] 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] of the amount of oxygen gas introduction amount and the steel sheet during finish annealing at each Bi content The figure which shows a relationship.

FIG. 2 is a diagram showing a relationship between a gas introduction amount, a magnetic flux density B ₈ and an oxygen amount of a steel sheet during finish annealing at each Bi content in a mirror polishing method (magnesia annealing separator containing calcium chloride). [A] is a diagram showing the relationship between the amount of gas introduced during finish annealing and the magnetic flux density B ₈ at each Bi content, [B]
The figure which shows the relationship between the gas introduction amount during the finish annealing in each Bi content, and the oxygen amount of a steel plate.

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 (7)

[Claims] C .: 0.02 to 0.1% by weight, Si: 2.0 to 4.8%, acid-soluble Al: 0.012 to 0.050%, N: 0.0030% by weight. 0.0150%, Bi: 0.0005 to 0.03% as a basic component, and the balance is cast molten steel including Fe and unavoidable impurities.
After hot rolling, the final sheet thickness is obtained by cold rolling one or more times, including final strong cold rolling of 65 to 95%, or intermediate annealing, and decarburizing annealing combined with primary recrystallization is performed. In a method for producing a unidirectional electrical steel sheet, which comprises performing a nitriding treatment as needed between the steps of charcoal annealing and secondary recrystallization finish annealing, and performing a secondary recrystallization finish annealing, wherein the surface of the steel sheet contains Mg.
O, 100 parts by weight, Li, K, Na, Ba, Ca,
Annealing separation in which one or more selected from chlorides, carbonates, nitrates, sulfates, and sulfides such as Mg, Zn, Fe, Zr, Sn, Sr, and Al are added at 2 to 30 parts by weight. A method for producing a mirror-oriented unidirectional electrical steel sheet having a high magnetic flux density, characterized by applying a refining agent and performing a secondary recrystallization finish annealing. 2. A steel sheet having an oxygen basis weight of 90 in decarburizing annealing.
0 ppm or less and FeO / SiO ₂ in the oxide film is 0.1 ppm or less.
2. The method for producing a mirror-oriented unidirectional electrical steel sheet having a high magnetic flux density according to claim 1, wherein the number is 20 or less. 3. The physical properties of MgO used for the annealing separator are as follows:
2. The magnetic flux according to claim 1, wherein a particle having a particle diameter of 10 [mu] m or less contains 30% or more, a citric acid activity CAA value is 50 to 300 seconds (measured at 30 [deg.] C.), and a hydration moisture is 5% or less. Manufacturing method of high density mirror-oriented unidirectional electrical steel sheet. As wherein conditions of the secondary recrystallization finish annealing, wherein, wherein the atmosphere at the time of heating up the secondary recrystallization completion ratio of N ₂ is N ₂ + H ₂ atmosphere at 30% or more Item 1. A method for producing a mirror-oriented unidirectional electrical steel sheet having a high magnetic flux density according to Item 1. 5. 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. 6. A mirror surface unidirectional with low iron loss, characterized in that after forming a tension film by a coating process on the steel sheet according to claim 1, a magnetic domain refinement process is performed by introducing local strain. Manufacturing method of conductive electrical steel sheet. 7. The steel sheet according to claim 1, which is at right angles to the rolling direction or at an interval of 2 to 10 mm within a range of 45 degrees from the right angle.
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: