JP3489945B2 - Method for manufacturing mirror-oriented unidirectional electrical steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a method for producing a grain-oriented electrical steel sheet used as an iron core of a transformer or other electric equipment. In particular, {110} <0
01> orientation, that is, the Goss orientation is highly developed, by effectively introducing a method for producing a Bi-added high magnetic flux density unidirectional electrical steel sheet and a means for mirroring the surface thereof, and a magnetic domain subdividing means, Disclosed is a manufacturing method that achieves industrial improvement at low cost.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are mainly used as a soft magnetic material for iron core materials of transformers and other electric equipment, and their magnetic characteristics must be good in excitation characteristics and iron loss characteristics. I won't. A magnetic flux density B ₈ (magnetic flux density at a magnetic field strength of 800 A / m) is usually used as an index _showing this excitation characteristic, and W _17/50 (magnetization up to 1.7 T at 50 Hz is used as an index _showing iron loss characteristics. The iron loss per unit weight when made) is used.

The unidirectional electrical steel sheet contains Si in an amount of 0.8-4.
A so-called goss containing 8% and causing secondary recrystallization in the final annealing step at a temperature of 900 ° C. or higher in the final stage of the manufacturing process, having a {110} plane on the steel plate surface and a <001> axis in the rolling direction. Obtained by developing tissue. Among them, a magnetic flux density B ₈ having an excellent excitation characteristic of 1.88 T or more is called a high magnetic flux density unidirectional electrical steel sheet. As a typical manufacturing method of high magnetic flux density electrical steel sheet,
Japanese Patent Publication No. 40-15644, Japanese Patent Publication No. 51-1346
No. 9 publication is cited. It can be said that the high magnetic flux density unidirectional electrical steel sheets currently produced on a global scale are produced based on the above two patents. However, the magnetic flux density B _{8 of the} product based on the above patent is from 1.88T to 1.95T at most.
And 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 saving and resource saving have become more and more strict, and demands for reducing iron loss and improving magnetization characteristics of unidirectional electrical steel sheets have also become fierce.

By the way, in general, the magnetic flux density B ₈ tends to increase and the crystal grains of the product tend to increase. Even if B ₈ is increased by a high magnetic flux density electromagnetic steel sheet, the 180 ° magnetic domain width increases, so that eddy current loss occurs. The metallurgical value is higher than this, so expectations for iron loss improvement are not desired. From this point of view, as a technical iron loss reduction method, a magnetic domain control technology using laser irradiation or the like is disclosed in Japanese Patent Publication No. 57-2252 and Japanese Patent Publication No. 5252.
It was established by Japanese Patent Application Laid-Open No. 8-5968, Japanese Patent Application Laid-Open No. 58-26405, and the like. Further, since the reduction of the iron loss by the method is caused by the strain introduced by the laser irradiation, it cannot be used for a wound iron core transformer which requires strain relief annealing after forming into a transformer. Japanese Patent Publication No. 62-53579, Japanese Patent Publication No. 63-4480.
In Japanese Patent No. 4 and Japanese Patent Publication No. 04-48847,
A method is disclosed in which, after finish annealing, a groove is introduced by, for example, a gear type roll, and processing strain is applied to form fine grains to subdivide magnetic domains. However, the method of forming a groove on the surface of a steel sheet by machining such as a gear-type roll requires crushing the surface ceramics layer called the primary coating (glass coating) of grain-oriented electrical steel sheet, which causes wear of the gear roll and the like. It is large and causes a problem in manufacturing cost.

On the other hand, when the movement of the magnetic domains of the steel sheet subjected to the magnetic domain subdivision processing was observed in detail, it was found that some of the statically subdivided magnetic domains did not move. In order to further reduce the iron loss value of grain-oriented electrical steel sheet, a technology to eliminate the factors that obstruct the movement of the magnetic domain together with the magnetic domain subdivision technology by the above method (magnetic domain activation technology)
Need to be introduced. That is, it is effective to remove the primary coating or the like on the surface of the steel sheet, which is a major factor that obstructs the movement of magnetic domains, to make the surface mirror-finished. As a means for this, a method of removing the primary coating by pickling after finishing annealing and then performing chemical polishing or electrolytic polishing to make the surface mirror-finished is disclosed in, for example, JP-A-64-83620. However, chemical polishing, electrolytic polishing, etc. can process a small amount of material at the laboratory level,
There are major problems in terms of concentration control of chemicals, temperature control, provision of pollution equipment, etc. when carried out on an industrial scale.Addition of such steps further increases the manufacturing cost, so it is still practical. It hasn't been realized.

On the other hand, the present applicant has developed a method of mirror-finishing the surface of a steel sheet at a low cost on an industrial scale (for example, JP-A-5-222489, JP-A-5-299228, and JP-A-5-229228). No. 320770). These are Li, K, Na, Ba, Ca, M on the steel plate surface after decarburization 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 secondary recrystallization finish annealing. A moderately 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 secondary recrystallization. Next, suppression of primary film formation and additional oxidation are prevented,
This is a method in which the primary coating is decomposed by an etching reaction of Fe in the coating layer after the temperature is raised, and then the surface is subjected to thermal etching by high temperature annealing to make the surface. That is, the mirror surface of the steel sheet and the secondary recrystallization of high magnetic flux density are formed at the same time. These techniques are suitable for low cost mainly for manufacturing a magnetic domain control material for a wound core transformer because wear of a gear roll or the like is small when machining a steel plate surface for magnetic domain subdivision processing.

However, with the maturation of peripheral technologies such as magnetic domain control and mirror finishing, it becomes easier to reduce iron loss using a high magnetic flux density electromagnetic steel sheet, and it is further necessary to aim at an ultra-low iron loss electromagnetic steel sheet. A material having a high magnetic flux density has been expected as an essential condition. On the other hand, the inventors of the present invention include Bi in the molten steel of the unidirectional electrical steel sheet to increase the magnetic flux density from the conventional high magnetic flux density unidirectional electrical steel sheet level to ultrahigh magnetic flux density by industrial means. A method of increasing the grain size of the grain-oriented electrical steel sheet is disclosed in JP-A-6-8814 and JP-A-6-
It was proposed in Japanese Patent No. 88173. With this method, it became possible for the first time to produce ultra-high magnetic flux density grain-oriented electrical steel sheets with a magnetic flux density B ₈ exceeding 1.96 T on a factory scale. However, factory experiments were repeated under the conventional conditions for forming a primary coating. As a result, it was difficult to stably obtain an ultrahigh magnetic flux density over the entire area of the coil. It is generally known that the conditions for forming the primary coating have a great influence on the magnetic properties.
It was assumed that the effect was significant in the case of the i-added material. Therefore, by effectively combining the super-flux density increasing by adding Bi with the mirror-finishing technology that does not form the primary coating, the super-flux density unidirectional electrical steel sheet can be manufactured more stably at the factory scale and the magnetic domain control technology It is an object of the present invention to produce an unprecedented ultra-low iron loss unidirectional electrical steel sheet by combining the above.

[0008]

The present invention is based on the conventional Bi method.
By organically combining the addition technology and the mirroring technology, it is possible to stably manufacture ultra-high magnetic flux density unidirectional specular electromagnetic steel sheet material with extremely high magnetic flux density on a factory scale, and combine magnetic domain control technology. Thus, an object is to manufacture an ultra-low iron loss-mirror-oriented electrical steel sheet with extremely low iron loss at low cost.

[0009]

The features of the present invention are as follows. (1) C: 0.02 to 0.1% by weight, Si: 2.
0-4.8%, acid-soluble Al: 0.012-0.050
%, N: 0.0030 to 0.0150%, Bi: 0.0
Casting molten steel consisting of 005 to 0.03% as a basic component and the balance Fe and unavoidable impurities, hot rolling,
A final strip thickness is obtained by cold rolling at least once, including final strong cold rolling of 65 to 95%, or by intervening intermediate annealing, and then subjected to decarburization annealing that also serves as primary recrystallization, and secondary recrystallization finish annealing. In the method for producing a grain-oriented electrical steel sheet, which comprises the steps of:
K, Na, Ba, Ca, Mg, Zn, Fe, Zr, S
Secondary recrystallization by applying an annealing separator containing 2 to 30 parts by weight of one or more selected from chlorides, carbonates, nitrates, sulfates, and sulfides of n, Sr, Al. Manufacturing method of mirror-oriented unidirectional electrical steel sheet characterized by finish annealing
Law .

(2) The oxygen basis weight of the steel sheet in decarburization annealing is 900 ppm or less, and FeO / SiO ₂ in the oxide film
Is 0.20 or less, the mirror described in (1).
Method for manufacturing plane-oriented electrical steel sheet . (3) The physical properties of MgO used for the annealing separator include 30% or more of particles having a particle diameter of 10 μm or less, a citric acid activity CAA value of 50 to 300 seconds (measured at 30 ° C.), and a hydrated water content of 5%. One of the mirror surface described in (1), characterized in that
Method for manufacturing tropic electrical steel sheet .

(4) As a condition of the secondary recrystallization finish annealing, the atmosphere during the temperature rise until the completion of the secondary recrystallization is N ₂
Is a N ₂ + H ₂ atmosphere having a ratio of 30% or more. (1) The method for producing a specular grain-oriented electrical steel sheet having a high magnetic flux density according to (1). (5) A mirror surface characterized by performing a magnetic domain refining process by introducing a local strain to the steel sheet described in (1).
Method for manufacturing grain-oriented electrical steel sheet .

(6) A mirror surface unidirectional electromagnetic steel sheet characterized by performing a magnetic domain refinement treatment by forming a tension film by a coating treatment on the steel sheet according to (1) and then introducing a local strain. Manufacturing method . (7) The steel sheet according to (1) has a width of 10 to 10 mm at an interval of 2 to 10 mm within a range perpendicular to the rolling direction or within 45 degrees from the right angle.
Characterized by forming continuous, discontinuous or dot-like grooves or local grooves in a range of 300 μm and a depth of 5 to 50 μm, and forming a tension film by a coating process to subdivide magnetic domains. Mirror surface unidirectional electrical steel sheet
Manufacturing method . (8) Nitriding between the steps of decarburization annealing and secondary recrystallization finish annealing
Any one of (1) to (7) characterized by performing processing
The method for producing a mirror-oriented unidirectional electrical steel sheet according to.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The inventors of the present invention have disclosed that Japanese Patent Laid-Open Nos. 6-8814 and 6-
As shown in Japanese Patent No. 88173, etc., a high magnetic flux density which is commercially available at present is obtained by adding Bi to a material for unidirectional electrical steel sheet having aluminum nitride as a main inhibitor by experiment in a laboratory. Magnetic steel sheet B
₈ = 1.93T or more, far exceeding 1.93T,
Ultra-high magnetic flux density unidirectional electrical 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, in order to realize an ultra-high magnetic flux density, a certain amount of Bi content in steel is necessary, while it is necessary to appropriately weaken the inhibitor strength during the progress of secondary recrystallization.
It is necessary to gradually vaporize and remove i from the steel plate surface. In this regard, it is easy to remove Bi during the secondary recrystallization finish annealing because the gas permeability between the plates is good in the case of a laboratory-scale plate-shaped small test piece. However, in the case of manufacturing on a factory scale, since it is premised that a coiled steel sheet is annealed in a box-type annealing furnace, gas vapor permeability is particularly poor inside the coil. It becomes difficult to remove Bi in steel by staying. Therefore, it is presumed that it is difficult to obtain an ultra-high magnetic flux density, and Bi is concentrated at the interface between the primary coating and the base metal to form BiCl _3, etc., and the primary coating is peeled off. On the contrary, since it is relatively good in gas permeability at the coil end, it is presumed that the Bi vapor is not concentrated and the 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 a stable ultra-high magnetic flux density cannot be obtained throughout the coil. Therefore, the present inventors conducted the following experiment in order to quantitatively understand the influence of gas permeability between the plates during the secondary recrystallization finish annealing by adding Bi.

C: 0.05%, Si: 3.25%, M
n: 0.10%, S: 0.007%, P: 0.025
%, Acid-soluble Al: 0.029%, N: 0.007%,
Cr: 0.12% containing silicon steel was melted and the Bi content was set to 0, 0.007%, 0.013%, 0.025%, and the temperature was adjusted to 1150 ° C. after dispensing casting into slabs. Heat
Immediately after extraction, hot-rolled to a thickness of 2.3 mm, hot-rolled and water-cooled 5
It was held at 50 ° C. Thereafter, the hot-rolled sheet was annealed at a temperature of 1120 ° C. for 30 seconds and subsequently at 900 ° C. for 90 seconds, air-cooled to 750 ° C., and then quenched in water at 80 ° C. Then, it is pickled.
The product was cold rolled by aging treatment at 250 ° C for 5 times with a gap of 23 mm. Subsequently, in a mixed gas of nitrogen and hydrogen, the introduced steam was adjusted so that the degree of oxidation would be 0.40 (PH ₂ O / PH ₂ ), decarburization and primary recrystallization annealing were performed, and then N ₃ atmosphere was applied. Nitriding annealing was performed so that the content was 200 ppm. After applying an ordinary annealing separator containing MgO as a main component, secondary recrystallization finish annealing was performed. In order to check 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 N ₂ was set to 50% in a N ₂ + H ₂ wet atmosphere. A gas was introduced and the flow rate was increased to 1,5,10,15 Nm ³ / min, and the temperature was raised up to 1200 ° C. at 15 ° C./hr, followed by purification annealing at 1200 ° C. for 20 hours in a dry hydrogen atmosphere. went. At this time, the internal volume of the annealing furnace was 0.06 m ³ . FIG. 1 shows the relationship between the flow rate of gas introduced into the furnace and the oxygen content and magnetic flux density B ₈ of the obtained steel sheet. The amount of oxygen in the steel sheet uniquely indicates the amount of the primary coating formed, and in the case where the amount of oxygen was low, peeling or weakening of the primary coating was observed.

As a result, the Bi-added ultra-high magnetic flux density unidirectional electrical steel sheet is superior to the conventional high magnetic flux density unidirectional electrical steel sheet in which aluminum nitride is the main inhibitor.
It was concluded that when the gas permeability during finish annealing is poor, the magnetic flux density varies and it is difficult to obtain a stable high magnetic flux density. In order to solve this factory production problem, for example, the flow rate of gas introduced into the factory annealing furnace may be increased, but the furnace volume of a factory-scale box annealing equipment is usually about 30 m ³ , Even if the calculation is performed, the introduction gas flow rate of 500 times the introduction gas flow rate of the steam laboratory annealing furnace is required. This imposes pressure on equipment costs and is difficult from the viewpoint of costs such as unit consumption. Therefore, in order to stably manufacture an ultra-high magnetic flux density unidirectional electrical steel sheet on an industrial scale by adding Bi, the primary film formation is required. It has been found that the application of mirror finishing technology that does not rely on is effective.

The experimental results of the present invention will be described below. In order to quantitatively understand the influence of the flow rate of the gas introduced into the furnace during the secondary recrystallization finish annealing on the magnetic flux density B ₈ and the mirror-finished state when the mirror-finishing technique is applied to the Bi addition technique. , The following experiment was conducted. That is, after the material having the same composition as in the above-mentioned experiment was processed under the same process conditions until nitriding annealing, 100 parts by weight of MgO was added to Ca.
After applying an annealing separator containing 10 parts by weight of Cl ₂ , secondary recrystallization finish annealing was performed. Then, similar to the above experiment, a sample in which about 50 sheets of 100 mm × 500 mm steel sheets were laminated was packed with an iron thin film and inserted into the furnace, and N ₂ was set to 50%.
₂ + H ₂ Wet atmosphere was introduced into the furnace and its flow rate was set to 1, 5,
15 ℃ / up to 1200 ℃ with 10,15Nm ³ / min
The temperature is raised for 1 hour, and subsequently at 1200 ° C. for 2 in a hydrogen atmosphere.
Purification annealing was performed for 0 hours. FIG. 2 shows the relationship between the flow rate of gas introduced into the furnace and the oxygen content and magnetic flux density B ₈ of the obtained steel sheet. The oxygen content of all the steel sheets was 200 ppm or less, and a good mirror-like state without a primary coating was exhibited.

As is apparent from FIG. 2, by applying the mirror finishing technique, the magnetic flux density was not affected by the gas flow rate during the finish annealing, and the effect of improving the magnetic flux density by adding Bi was stably obtained. In this way, not being affected by the gas flow rate during finish annealing, since the secondary recrystallization process is less likely to be affected by the variation in gas permeability at the position inside the coil,
It is shown to be advantageous for manufacturing by secondary recrystallization finish annealing in factory-scale coil foam. Also, in FIG.
Since a small amount of oxygen attached to the surface of the mirror-finished steel sheet decreases with the amount of i added, it is expected that the addition of Bi has an action of promoting mirror finish.

Furthermore, the present inventors have found that the sample obtained in FIG.
Was subjected to strain relief annealing at a temperature of 850 ° C. for 2 hours
Then, laser irradiation processing at 5 mm intervals in the direction perpendicular to the rolling direction
Then, the magnetic domain control was tried. Element of the obtained sample
Material (before domain control) magnetic flux density B ₈And 1.0 kgf / mm²of
Iron loss W after magnetic domain control measured under tension_17/50Diagram of the relationship
3 shows.

The following can be seen from FIG. First, by adding Bi and adjusting the Bi content from 0.007% to 0.025%, an ultrahigh magnetic flux density unidirectional electrical steel sheet having a magnetic flux density B ₈ of 1.96 T or more is developed, and magnetic domain control is performed. Ultra low iron loss electrical steel sheet can be obtained in combination with. Also, B ₈ and W
_The straight line showing the relationship of _17/50 decreases with Bi addition, and it can be seen that the iron loss of the Bi-added material is further improved than the iron loss expected from the improvement of the magnetic flux density. this is,
As described with reference to FIG. 2, it is presumed that the addition of Bi is due to the action of promoting the mirroring. The present invention is not a simple combination of the conventional method for producing an ultra-high magnetic flux density unidirectional electrical steel sheet by the Bi addition method and the low iron loss unidirectional electrical steel sheet production method by the mirroring technique. It is intended to provide a method for solving stabilization promotion extremely 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 raw material are C: 0.02 to 0.1% and Si: 2.
0-4.8%, acid-soluble Al: 0.012-0.050
%, 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 others are not limited.

As a basic manufacturing method, a manufacturing method using (Al, Si) N as a main inhibitor by Komatsu et al. (For example, Japanese Patent Publication No. 62-45285) or AlN and MnS by Taguchi / Sakakura etc. Manufacturing method used as (for example, Japanese Patent Publication No. 40-15644)
Should be applied. C is an element that is open to the γ region, and is an important element that forms an texture that is advantageous for secondary recrystallization due to the α → γ transformation or the presence of solute C in the steps from hot rolling to decarburization annealing. When 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%, the decarburization annealing process is burdened with an increase in cost, which is not preferable.

Si is an important element for increasing electric resistance and reducing iron loss. If the content exceeds 4.8%, the material is likely to crack during cold rolling, making rolling impossible. On the other hand, if it is less than 2.0%, the eddy current loss of the product increases, and at the time of finish annealing, the α → γ transformation occurs and the crystal orientation 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 electrical steel sheet. If it is less than 0.012%, the amount is insufficient and the inhibitor strength is insufficient. On the other hand, 0.05
If it exceeds 0%, AlN is coarsened and, as a result, the inhibitor strength is lowered, so that secondary recrystallization does not occur.

N contained in the material forms nitrides of Si, Al, etc., and particularly acts as an inhibitor of primary recrystallization when low temperature slab heating is assumed. The N content is determined from the thermal history of the process and the required primary recrystallization annealing temperature from the viewpoint of controlling the primary recrystallization grain size. On the other hand, when AlN is finely dispersed in the previous stage by high temperature slab heating, it is necessary to consider the atmospheric conditions of the secondary recrystallization annealing. 0.0
If it is less than 030%, the cost at the melting stage increases due to denitrification, and if it exceeds 0.0150%, defects called blisters occur, so the range was made 0.0030 to 0.0150%.

As other inhibitor constituent elements, M
n, S, Se, V, N, B, Nb, Sn, Cu, Ti,
Zr, Ta, Mo, Sn, etc. can be added in combination. Bi is an essential element for obtaining ultra-high-speed density,
The effective addition content is 0.0005 to 0.03%. If less than 0.0005%, the effect is slight,
On the other hand, if it exceeds 0.03%, the effect of improving the magnetic flux density is saturated and cracks occur at the ends of the hot-rolled sheet, so the upper limit is 0.0.
Limited to 3%.

Next, the manufacturing process conditions will be described. The material for ultra-high magnetic flux density unidirectional electrical steel sheet having the components adjusted as described above can be used as the material of the present invention even when any ordinary melting method or ingot making method is used. Next, this raw material for electromagnetic steel sheets is rolled into a hot rolled coil by ordinary hot rolling. A production method using (Al, Si) N as a main inhibitor by Komatsu et al.
No. 285), from the viewpoint of ensuring the temperature during hot rolling, the temperature is 1100 ° C. or higher, and AlN is not completely dissolved 128.
After heating at a temperature of 0 ° C. or less, hot rolling is performed. Further, a production method using AlN and MnS as main inhibitors by Taguchi, Sakakura, etc. (see, for example, Japanese Patent Publication No. 40-15644).
In Japanese Patent Laid-Open Publication No. JP-A-2003-187, hot rolling may be performed after heating at a temperature of 1300 ° C. or higher at which a complete solution is formed.

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

The cold-rolled sheet rolled to the final product thickness has a thickness of 750 to 900 in wet hydrogen or a mixed atmosphere of hydrogen and nitrogen for the purpose of primary recrystallization annealing and removal of carbon contained in steel.
Decarburization annealing is performed for 30 seconds to 30 minutes in the temperature range of ° C. For this decarburization annealing, known techniques for forming a good primary coating can be applied. In the decarburization annealing of 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 oxygen basis weight exceeds 900ppm, the SiO in the oxide film layer will inevitably occur.
₂ and the amount of FeO increase and the thickness of the oxide film increases, which is disadvantageous in performing the temporary film decomposition reaction during the secondary recrystallization finish annealing. That is, SiO ₂ remains just below the surface, and not only a perfect mirror-like surface state cannot be obtained, but it also causes deterioration of magnetism. Furthermore, the formation of excessive SiO ₂ accelerates the decomposition of the (Al, Si) N inhibitor in the steel before the start of secondary recrystallization, which makes it difficult to obtain an ultrahigh magnetic flux density. However, if the amount of oxidation is extremely suppressed, there is a problem that the decarburization time becomes long, which hinders productivity. The preferred range is 400 to 700 ppm. Further, when FeO / SiO ₂ in the amount of oxidation exceeds 0.20, the reaction of forming the primary film in the first half of the secondary recrystallization finish annealing extremely increases, and the amount of forming the primary film increases. Reaction does not proceed sufficiently in stages. FeO / S
If iO ₂ ≦ 0.20, the primary coating is almost completely decomposed by the secondary recrystallization finish annealing due to the effect of the additive to MgO. On the other hand, the decarburization annealing temperature is mainly determined from the viewpoint of obtaining the optimum primary recrystallized grain size.

When it is necessary to strengthen the (Al, Si) N inhibitor of this decarburized annealed plate, or (Al, S)
i) In the manufacturing method using N as a main inhibitor (for example, Japanese Patent Publication No. 62-45285), a nitriding treatment is performed between the steps of decarburization annealing and secondary recrystallization finish annealing. The method of this nitriding treatment is not particularly limited, and there is a method of performing it in an atmosphere gas having a nitriding ability such as ammonia.
Quantitatively, 0.005% or more, preferably, the total nitrogen content may be nitrided by Al equivalent or more in the steel.

Next, the particle size, CAA value, hydration water content, etc. of MgO used as an annealing separator are limited. In the technique of the present invention, the mirror-finishing is performed by decomposing and removing an appropriate primary coating film formed before the temperature rise of 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 secondary recrystallization before the secondary recrystallization finish annealing, it is necessary to utilize the effect of suppressing the additional oxidation, nitriding, etc. by the appropriate amount of the primary coating at this time, It is commonly used to obtain mirror-finished 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. Ie Mg
If the reactivity of O is extremely poor, the reaction of forming the primary film in the stage before the secondary recrystallization finish annealing does not proceed, and the atmosphere sealing effect of the film cannot be obtained. In such a case, even if secondary recrystallization occurs, the crystal orientation is extremely deteriorated, and additional oxidation causes residual SiO ₂ , Al ₂ O ₃ or a spinel of these to occur immediately below the surface of the steel sheet to deteriorate iron loss. Bring For this reason,
The grain size of MgO is limited so that the grain size of 10 μm or less is 30% or more. If it is less than 30%, the reactivity is extremely deteriorated and the previous period effect cannot be exhibited. C of MgO
The AA value is specified to be 50 to 300 seconds. If this value is less than 50 seconds, the hydration progresses extremely rapidly for industrial use, and it becomes difficult to control the water content of hydration. If it exceeds 300 seconds, the reactivity of MgO particles is extremely lowered. As a result, the formation of the primary re-formation before the secondary recrystallization finish annealing does not occur. Also M
The hydrated water content of gO is limited to 5% or less. If it exceeds 5%, the dew point between the steel sheets becomes high, making it difficult to obtain a uniform mirror-like state due to additional oxidation in the former stage during temperature rise. 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 such as Sn, Sr and Al, carbonates, nitrates, sulfates and sulfides are Mg.
2 to 30 parts by weight is mixed with 100 parts by weight of O. By the addition of these compounds, firstly a moderately thin primary coating is formed on the surface of the steel sheet before the temperature rise of the secondary recrystallization finish annealing,
Then, the formation of the primary coating is suppressed and additional oxidation is prevented, the primary coating is decomposed by the etching reaction of Fe in the coating layer after the temperature is raised, and then the surface is thermally etched and surfaced by high temperature annealing. If the addition amount of these compounds is less than 2 parts by weight, the decomposition reaction of the primary coating formed in the previous stage does not proceed sufficiently and the primary coating remains, which is not desirable. On the other hand, if it exceeds 30 parts by weight, the component elements in the additive diffuse and penetrate into the steel sheet to cause grain boundary etching, affect the inhibitor, and affect the subsequent purification treatment, which is not preferable. The most preferred range is 5 to 15 parts by weight.

The secondary recrystallization finish annealing conditions are important when proper formation and decomposition of the primary coating are carried out in the annealing process as in the present invention. Usually, the atmosphere gas in the secondary recrystallization finish annealing is N _2, H ₂ or is a mixed gas is used, from the viewpoint of the oxidation control of the surface is advantageously N ₂ + H _2. 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 is 30%
When it is less than the above value, weakening of (Al, Si) N does not occur in the process of mirror-finishing, and an ultrahigh 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 steel sheets may increase depending on the physical property value of MgO, and unevenness may occur on the surface of the steel sheet due to oxidation. Preferably N ₂ 30 to 90%
Is the range. The entire temperature rise may be annealed in this atmosphere when using a gas of N _{2 of} 30% or more, but additional oxidation may occur depending on the conditions of MgO (Al,
It is preferable to switch to 700 ° C. or higher, which is the most effective temperature for stabilizing Si) N. It is advantageous that the soaking temperature in the secondary recrystallization finish annealing is 1180 to 1200 ° C. In the present invention, the decomposition of the primary coating is completed when the soaking of the secondary recrystallization finish annealing is reached, and the steel sheet surface is mirror-finished by thermal etching during the purification annealing. If the soaking temperature is lower than 1180 ° C., this effect is weak and it is disadvantageous for purification. On the other hand, if the temperature exceeds 1250 ° C., the coil shape may be deteriorated or seizure of the edge portion may occur. Further, as disclosed in JP-A-2-258929, it is effective to increase the magnetic flux density by carrying out secondary recrystallization within a predetermined temperature range by maintaining a constant temperature or controlling the temperature rising rate. Is.

On the other hand, as shown in FIG. 2, the amount of oxygen adhering to the surface of the mirror-finished steel sheet decreases with the addition amount of Bi.
It is expected that the addition of i will have the effect of promoting the mirroring. The reason for this is not clear yet, but it is presumed that when Bi in the steel added in the steelmaking stage is vaporized from the steel sheet surface, it has an advantageous effect on the peeling of the primary coating and the subsequent thermal etching. ing. In addition, Bi finely precipitated in steel complementarily thermally stabilizes the inhibitor, so that Bi (Al, S
i) When there is a concern about destabilization of N, it is presumed to bring about a beneficial effect on the expression of secondary recrystallization. On the other hand, in order to stably bring out the effect of increasing the super-flux density of Bi in the factory manufacturing of coil foam, the conventional technique for forming a primary coating has a limit, and the mirror-finishing technique is most suitable.
In addition, the Bi addition technology is premised on the magnetic domain refinement processing because the crystal grain size becomes coarse with the super-flux density increase. Especially, when the method of mechanically forming the local groove is used, the mirror surface is taken into consideration from the viewpoint of the die cost. The material is appropriate. That is, the present invention is an extremely effective combination of the ultra-high magnetic flux density achieved by the conventional Bi addition method, the mirror finish, and the low iron loss achieved by the domain refinement technique.

After the secondary recrystallization finish annealing, the excess annealing separating agent is subsequently removed, and then continuous tension annealing for correcting coil winding and the like is performed, and at the same time, an insulating film coating is applied and baked. At this time, if necessary, the steel sheet is subjected to magnetic domain subdivision processing such as laser irradiation, mechanical groove formation, and tension film coating. In the present invention, the addition of Bi increases the magnetic flux density and simultaneously increases the secondary recrystallized grain size. Therefore, the magnetic domain refining treatment is effective from the viewpoint of improving the iron loss characteristics. The method of subdividing the magnetic domains is not particularly limited.

When the magnetic domain is subdivided by introducing a local strain, for example, a method of irradiating a laser beam described in Japanese Patent Publication No. 57-2252, or JP-A-62-1 is used.
The method of performing plasma flame irradiation described in Japanese Patent Publication No. 51511, Japanese Patent Publication No. 6-45824, etc. may be used.
When magnetic domains are subdivided by forming local grooves, mechanical plasticity such as a gear roll method (for example, Japanese Patent Publication No. 4-48847) or a die pressing method (for example, Japanese Patent Publication No. 6-63037) A processing method, a photo-etching method (for example, Japanese Patent Publication No. 5-69284) and a resist ink etching method (Japanese Patent Publication No. 2-46673, Japanese Patent Publication 3-).
69968), a method using chemical etching or electrolytic etching, or the like may be adopted. The grooves formed in the steel sheet are preferably at right angles to the rolling direction or within a range of 45 degrees from the right angles, and the intervals are preferably 2 to 10 mm from the viewpoint of reducing iron loss. The shape of the groove may be continuous, discontinuous, or dot-shaped. The width and depth of the groove are 10 to 300μ, respectively
The range of m and 5 to 50 μm is preferable from the viewpoint of reducing iron loss. If the width of the groove is narrowed, it tends to be a starting point of bending when performing bending with a small radius of curvature. If the width of the groove is widened, the magnetic flux density will decrease. Similarly, if the depth of the groove is too deep, the magnetic flux density will decrease. The step of forming such a local groove may be any step as long as it is a step after cold rolling.

As the tension coating, for example, a coating liquid mainly composed of colloidal silica and aluminum phosphate according to Japanese Patent Laid-Open No. 48-39338, Japanese Patent Laid-Open Publication No.
If a method of baking a coating solution mainly composed of colloidal silica and magnesium phosphate according to JP-A 0-79442 or a coating solution mainly composed of alumina sol and boric acid according to JP-A-4-222849 is adopted, Good.

[0036]

【Example】

(Example 1) C: 0.05% and Si: 3.3 by weight%
%, 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: 2% silicon steel of 0% was melted, dispensed and cast into slabs, respectively, and heated to 1200 ° C., and 2.3 mm immediately after extraction
It was hot rolled to the plate thickness. Then, 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. for 100 seconds at an oxidation degree of 0.4 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 plates were then (C: mirror-finished) M
gO + K ₂ S (7 parts by weight), and (D: conventional method) MgO
After applying the water slurry of No. 2, the steel sheets were laminated and subjected to secondary recrystallization finish annealing at a N partial pressure of 40% under a low gas flow rate.
Apply 1 to each of these samples with a gear roll from the 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 a main component was applied and baked at 850 ° C. for 2 minutes. After measuring the magnetic properties of these samples,
Strain relief annealing was performed for a period of time. The magnetic properties of the obtained product are shown in Table 1.

[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:
0.01% and (B: conventional method) Bi: 0%, two levels of silicon steel are melted, dispensed and cast into slabs, respectively, and heated to 1200 ° C. Immediately after extraction, up to 2.3 mm plate thickness It was hot rolled.
The cold-rolled sheet, which has been pickled and cold-rolled to 1.4 mm, is annealed at a temperature of 1120 ° C. for 30 seconds at 900 ° C. for 90 seconds, air-cooled to 750 ° C., and then rapidly cooled in water at 80 ° C. to obtain a final sheet thickness of 0.15 mm. Cold rolled. This cold-rolled sheet was annealed at a temperature of 830 ° C. for 70 seconds at a degree of oxidation of 0.5 in a mixed gas of nitrogen and hydrogen for primary recrystallization. Then, by annealing in an ammonia atmosphere, the amount of nitrogen was increased to 0.025% to strengthen the inhibitor.

These steel sheets were then subjected to (C: mirror surface) M
gO + SnCl ₂ (10 parts by weight), and (D: conventional method)
After applying a water slurry of MgO, steel sheets were laminated and subjected to secondary recrystallization finish annealing at a low gas flow rate at a partial pressure of N ₂ of 50%. Grooves having a width of 30 μm and a depth of 10 μm were formed in the sample after the finish annealing in a direction perpendicular to the rolling direction by a photoetching method, and then a coating liquid containing alumina sol and boric acid as a main component was applied to the sample at 870 ° C. Baked for 2 minutes. After measuring the magnetic properties of these samples, an additional 80
Strain relief annealing was performed at 0 ° C. for 4 hours. The magnetic properties of the obtained product are shown in Table 2.

[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: 0%, two levels of silicon steel were melted, and each was cast by casting into a slab and then cast at 1350.
Immediately after extraction, the product was hot-rolled to a plate thickness of 2.3 mm, and immediately cooled to room temperature with water. This hot rolled sheet is 1100 ° C
It was annealed for 2 minutes at 0.25 ° C., then pickled, and then cold rolled by aging treatment at 250 ° C. five times until it reached a final plate thickness of 0.27 mm. This cold-rolled sheet was oxidized to a degree of oxidation of 0.6 in a mixed gas of nitrogen and hydrogen.
At 120 ° C. for 120 seconds for primary recrystallization.

These steel sheets are then (C: mirror-finished) M
gO + K ₂ CO ₃ (15 parts by weight) and (D: conventional method) M
After applying gO water slurry, steel plates were laminated and pressed in the thickness direction at 20 kg / mm ² , and then N was applied under a low gas flow rate.
It was subjected to secondary recrystallization finish annealing at ₂ 75% partial pressure. A coating liquid containing colloidal silica and phosphate as main components was applied to these samples and baked at 850 ° C. for 2 minutes. After that, laser irradiation was performed on the surface of the steel sheet at intervals of 5 mm in the direction perpendicular to the rolling direction. Table 3 shows the magnetic properties of the obtained product.

[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 melting silicon steel containing 2% and casting into slab,
It was heated to 50 ° C., hot-rolled immediately after extraction to a plate thickness of 2.3 mm, hot-rolled and then water-cooled and wound at 550 ° C. Then, the hot rolled sheet is annealed at a temperature of 1120 ° C. for 30 seconds and 900 ° C. for 90 seconds,
After air cooling to 750 ° C., it was rapidly cooled to 80 ° C. in water. Then, after pickling, rolling 5 passes up to 0.23 mm, 200
The aging treatment was performed at 5 ° C. or higher for 5 minutes or longer. Continue to decarburize
The primary recrystallization annealing is performed in a mixed gas of nitrogen and hydrogen in an atmosphere with an oxidation degree of 0.5, at a temperature of 850 ° C. for 100 seconds, and then in a NH ₃ atmosphere, nitriding annealing is performed so that the N content becomes 200 ppm. It was An annealing slurry containing MgO as a main component was added with 5 parts by weight of CaCl ₂ with respect to 100 parts by weight of MgO, and the resulting water slurry was applied to the surface of the steel sheet and rolled.
The T coil was subjected to secondary recrystallization finish annealing in a box type annealing furnace. The temperature was raised to 1200 ° C. at 15 ° C./hr while flowing a hydrogen mixed gas with a nitrogen partial pressure of 50% in the furnace, and subsequently, purification annealing was performed at 1200 ° C. for 75 hours while flowing hydrogen. Then, while rolling the coil on a continuous annealing line, a tooth mold having a groove with a width of 50 μm and a depth of 11 μm, which is tilted 10 degrees from the direction perpendicular to the rolling direction, was formed with a press, and then colloidal. 860 by applying a coating liquid containing silica and phosphate as main components
Bake for 2 minutes at ° C. The Epstein value after annealing at 800 ° C. for 2 hours, which was sampled at 5 points of the obtained coil, was 1.96 on average in the magnetic flux density B ₈ before domain control.
The T and iron loss were W _17/50 and 0.69 W / kg.

[0046]

According to the present invention, Li, K, Na, Ba, Ca, Mg, Z can be used to obtain an ultrahigh magnetic flux density by the conventional Bi addition method.
2 to 30 parts by weight of one or more selected from chlorides, carbonates, nitrates, sulfates, sulfides of n, Fe, Zr, Sn, Sr, Al, etc., based on 100 parts by weight of MgO. It is possible to obtain a very stable and inexpensive superflux density low unidirectional electrical steel sheet that is extremely stable in industrial production by using a very effective combination of the mirror-finishing technology for applying the MgO slurry described above, and also to the iron loss after the magnetic domain refinement treatment. It has extremely excellent characteristics and can be said to be very valuable industrially.

[Brief description of drawings]

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

FIG. 2 is a diagram showing the relationship between the amount of gas introduced during finish annealing and the magnetic flux density B ₈ and the amount of oxygen of a steel sheet during mirror annealing (magnesia annealing separator containing calcium chloride) at each Bi content. [A] is a diagram showing the relationship between the gas introduction amount and the magnetic flux density B ₈ during finish annealing at each Bi content.
FIG. 4 is a diagram showing the relationship between the amount of gas introduced during finish annealing and the amount of oxygen in a steel sheet at each Bi content.

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

Continuation of the front page (56) Reference JP-A-5-222489 (JP, A) JP-A-5-299228 (JP, A) JP-A-5-320770 (JP, A) JP-A-6-8814 (JP , A) JP-A-6-88173 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 C22C 38/00 303 C22C 38/06 H01F 1 / 16

Claims (8)

(57) [Claims] 1. C: 0.02 to 0.1% by weight, S
i: 2.0 to 4.8%, acid-soluble Al: 0.012
0.050%, N: 0.0030 to 0.0150%, B
i: 0.0005 to 0.03% as a basic component, the balance being a molten steel consisting of Fe and unavoidable impurities, hot-rolled, and once or in the middle including 65 to 95% final strong cold rolling. In a method for producing a unidirectional electrical steel sheet, which comprises a step of performing decarburization annealing that also serves as primary recrystallization to a final sheet thickness by cold rolling two or more times with an intervention of annealing, and performing secondary recrystallization finish annealing, On the surface of the steel sheet, Li, K, Na, Ba, Ca, Mg, Zn, Fe,
One or more selected from Zr, Sn, Sr, and Al chlorides, carbonates, nitrates, sulfates, and sulfides.
The annealing separating agent was added to 30 parts by weight was coated, mirror-oriented electrical steel sheet characterized by annealing finishing secondary recrystallization
Manufacturing method . 2. The oxygen basis weight of the steel sheet during decarburization annealing is 90.
FeO / SiO ₂ in the oxide film is less than 0 ppm.
The mirror surface according to claim 1, wherein the mirror surface is 20 or less.
Method for manufacturing grain-oriented electrical steel sheet . 3. The physical properties of MgO used as an annealing separator are
The mirror surface according to claim 1, which comprises 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 hydrated water content of 5% or less. Manufacturing method of unidirectional electrical steel sheet . 4. The condition for the secondary recrystallization finish annealing is that the atmosphere during the temperature rise until the secondary recrystallization is completed is an N ₂ + H ₂ atmosphere in which the ratio of N ₂ is 30% or more. Item 1. A method for producing a mirror-oriented unidirectional electrical steel sheet according to Item 1. 5. A method for producing a mirror-oriented unidirectional electrical steel sheet, which comprises subjecting the steel sheet according to claim 1 to local strain to carry out a magnetic domain refining treatment. 6. A mirror characterized in that after forming a tension film on the steel sheet according to claim 1 by a coating process, a local strain is introduced to perform a magnetic domain refining process.
Method for manufacturing plane-oriented electrical steel sheet . 7. The steel sheet according to claim 1 having a distance of 2 to 10 mm at right angles to the rolling direction or within a range of 45 degrees from right angles.
To form continuous, discontinuous or dot-like grooves or local grooves in the range of 10 to 300 μm in width and 5 to 50 μm in depth, and to form a tension film by coating treatment to subdivide magnetic domains. Mirror surface characterized by
Method for manufacturing tropic electrical steel sheet . 8. A process from decarburization annealing to secondary recrystallization finish annealing.
Nitriding treatment is performed between the two.
A method for manufacturing a mirror-oriented unidirectional electrical steel sheet according to any one of 1.