JP2711614B2 - Manufacturing method of grain-oriented electrical steel sheet with excellent film properties and magnetic properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties by forming a uniform glass film when producing a grain-oriented electrical steel sheet.

[0002]

2. Description of the Related Art Normally, a grain-oriented electrical steel sheet is hot-rolled from a material containing 4% or less of Si, and is subjected to annealing and one or two or more cold-rolling steps including intermediate annealing to obtain a final sheet thickness. Then N ₂ +
Decarburization annealing is performed by controlling P _H2O / P _H2 in an atmosphere such as H ₂ or H ₂ to perform decarburization and form an oxide film mainly composed of SiO ₂ . After that, an annealing separator containing MgO as a main component is applied in the form of a slurry in a coating roll or the like, followed by final finishing annealing, secondary recrystallization, purification, and glass film formation, and, if necessary, insulation film treatment and heat treatment. After flattening, the final product is obtained. Further, in the case of high magnetic flux density grain-oriented electrical steel sheets, depending on the application, before or after the insulating film treatment, magnetic domain refining treatment by applying linear flaws using a laser, a press roll, a rolling roll, a tooth roll, a marking, etc. To improve iron loss.

[0003] This grain-oriented electrical steel sheet utilizes a phenomenon in which (110) <001> crystals having a <001> axis grow preferentially by high-temperature secondary recrystallization. In this secondary recrystallization process, the (110) plane having low surface energy grows preferentially, and the finely dispersed Al as an inhibitor in steel is finely dispersed.
It is considered that the (110) <001> crystal grows preferentially because it erodes other crystals whose growth is suppressed by N, MnS or the like.

[0004] Therefore, in order to produce an excellent grain-oriented electrical steel sheet, it is important to control the dispersion of AlN, MnS, and the like in the steel and the control up to their decomposition. The change of the inhibitor during the final annealing is affected by the oxide film on the steel sheet surface formed by the decarburizing annealing, the annealing separator, the thermal cycle of the finish annealing, and the atmospheric conditions. Among them, the properties of the annealing separator MgO and the effect of additives are particularly large. Annealing separator Mg
O reacts with an oxide film mainly composed of SiO ₂ formed by decarburizing annealing to form a film mainly composed of forsterite, usually called a glass film (2MgO + SiO ₂ → Mg ₂ SiO ₄ ).
In the formation of the glass film, the properties of MgO, in particular, the particle size, purity, and activity, as well as the hydration amount, the amount of coating, and the adhesion of the coating film when coating the steel sheet, have a large effect. The type and amount of the additive added as a component, the state of dispersion on the MgO surface, and the state of dispersion on the surface of the steel sheet affect the formation time, formation speed, formation amount, uniformity, etc. of the glass film. This difference in the reaction of the glass film formation process causes additional oxidation of the steel sheet surface, intrusion of N in the annealing atmosphere gas, and conversely, reduction of N, S, etc. in the steel, and has a great influence on the inhibitor, Secondary recrystallization and, consequently, magnetic properties are also affected.

[0005] As described above, it is important to control the properties of the annealing separator and the state of coating on the steel sheet surface with respect to the glass film and the magnetic properties which are important in determining the commercial value of the grain-oriented electrical steel sheet. Has become an important development issue for those skilled in the production of grain-oriented electrical steel sheets. MgO used as the annealing separator is generally prepared by adjusting a raw material crystal having a mean particle size of several hundred m to several μm from a raw material such as magnesium hydroxide, magnesium carbonate, or basic magnesium carbonate, and It is calcined by a rotary kiln, a batch kiln or the like at a temperature of about ℃ to obtain MgO crystals having an average particle diameter of, for example, 0.2 to 5.0 µm and used. The MgO thus obtained is mixed with various additives as a forsterite formation promoter, and suspended in water to form a slurry. The slurry is provided in a tank provided with a rotor such as a propeller or a shear blade. After stirring, it is applied to the surface of the steel plate with a rubber roll or the like and dried. At that time, the MgO particles and additives are aggregated by sintering at the time of sintering at the manufacturing stage or by agglomeration of particles due to moisture absorption at the time of storage from the sintering stage to the use stage or a strong agglutination reaction of the particles at the stage of suspending with water. At the stage of being applied to the steel sheet surface, it becomes coarse particles of several μm to several tens μm. This is a problem caused by particle surface defects at the stage of MgO production or distortion of the particle surface received at the stage of pulverization and the like.
In order to obtain O, a technique of high-temperature sintering is indispensable, so that the tendency of sintering and agglomeration in such a slurry is further enhanced.

In such a case, the contact area of the MgO particles on the steel sheet surface after coating and drying is reduced, and the adhesion and uniformity of the coating film are reduced. Further, in such a case, the viscosity of the slurry is lowered, and the coating property in high-speed operation is deteriorated, so that a uniform coating film cannot be obtained. As a result, the properties of the glass film are deteriorated. In addition, when an additive is used in combination with MgO,
As with MgO, the additive itself becomes coarse particles due to sintering at the time of production and agglomeration in the slurry, and is present unevenly on the coating film or the steel plate oxide film. A uniform reaction occurs, which causes a problem in obtaining a uniform glass film. Naturally, it may affect the inhibitor control and affect the magnetic properties.

As a means for solving such a problem due to a decrease in reactivity and a decrease in adhesion due to sintering and agglomeration of the annealing separator, conventionally, the physical properties of MgO are controlled at the production stage to suppress the agglomeration, By giving MgO itself hydration,
Methods have been used in which forsterite formation is assisted by moisture or an additive for a reaction accelerator is added more than necessary. Japanese Patent Application Laid-Open No. Sho 62-156226 has proposed a method of activating the outermost surface layer of MgO particles by the present inventors. In this method, MgO obtained by firing at a high temperature is used.
Hydrate layer (Mg
It forms (OH) ₂ ), which improves the uniformity of the glass film and improves the magnetic properties. In Japanese Patent Application Laid-Open No. Hei 2-26278, calcined MgO is
Treated in a steam-containing atmosphere of at least
The chemisorbed phase is converted to 0.8 based on MgO weight in terms of H ₂ O.
A method for obtaining a grain-oriented electrical steel sheet having a uniform glass film and excellent magnetic properties by applying an annealing separator containing MgO formed to about 2.5% to a steel sheet after decarburization annealing and finish annealing. Is disclosed.

[0008] In any of these techniques, as a solution to the problem of agglomeration of MgO particles during the application of an annealing separator, the surface of the MgO particles after firing is modified by performing a special surface treatment at a high temperature to reduce the surface energy. Thus, the compatibility with water is improved, and at the same time, the forsterite forming reaction is improved by a certain amount of OH formed on the surface layer of the MgO particles. Due to this effect, the MgO particles are applied to the steel sheet surface in a state of better dispersion than before, and a considerable effect is obtained.

[0009] However, there are problems of sintering due to MgO production conditions, stability of the chemisorbed phase, and agglomeration due to aging change from MgO production to use. Technology development is desired.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a method for preparing a sintered body, agglomerate, and slurry produced during the production of MgO and additives when applying an annealing separator to the surface of a decarburized plate in the production of grain-oriented electrical steel sheets. The problem of agglomeration at the stage is to be improved by a new slurry preparation method which has not been tried in the conventional grain-oriented electrical steel sheet manufacturing process.
The use of inert fine-grained MgO as a material significantly suppresses the amount of hydration, improves the reactivity by the dispersing effect and the surface activating effect, forms a uniform high-quality glass film, and at the same time has excellent magnetic properties. It aims to provide a grain-oriented electrical steel sheet.

[0011]

Means for Solving the Problems The present inventors have a uniform glass film in a glass film forming step from decarburizing annealing to application of an annealing separating agent to finish annealing step of grain-oriented electrical steel sheet, The manufacturing method of products with excellent magnetic properties was studied. In this study, the main component of the annealing separator, Mg
The study was carried out by focusing on the properties of O and the dispersion method of the MgO and the additives during slurry production.

As a method for adjusting the slurry of the annealing separating agent, usually, a method of automatically stirring and dispersing by a device provided with a rotating body such as a propeller or a shear blade in a stirring vessel (a cylindrical tank or the like) is used. It is done in. When the slurry is dispersed with such a stirring device, high-speed stirring and long-time stirring are required to perform fine particle dispersion of the annealing separating agent, and sufficient particles can be obtained even if the treatment is performed under considerably strong stirring conditions. Dispersion cannot be obtained. In particular, with such stirring, it is difficult to obtain the effect of disintegrating the sintered body or aggregate during the production of MgO or the like, or obtaining the surface activation effect of the particles.

A major problem with such a method is that the slurry temperature rises due to friction between the particles in the slurry due to high-speed or long-time stirring or between the particles and the rotating body of the stirring device, and the hydrated water increases. . As a result, there arises a problem that the glass film characteristics and the magnetic characteristics are deteriorated. Therefore, the present inventors have conducted a huge amount of experiments on a dispersion technique that can reliably disintegrate the sintered body and agglomerates of the annealing separator by a slurry dispersing process in a short time and do not increase the hydration moisture generated in the conventional technique. And conducted a study.

As a result, as a method of applying an annealing separating agent capable of solving the above-mentioned problems, a technique for improving a glass film and a magnetic property by a new method of controlling the dispersion of ultrafine particles of a slurry using a physical and mechanical method was developed. In this way, by applying MgO whose physical property value is controlled to a specific range at the MgO production stage, coarsening of particles due to sintered bodies and aggregates of the annealing separator, non-uniformity of components such as additives, coating The problems caused by non-uniformity of the film, poor adhesion of the coating film and increase in hydration moisture have been solved at once.

Hereinafter, the present invention will be described in detail based on experimental results. In this experiment, C by weight; 0.068
%, Si; 3.23%, Mn: 0.060%, S;
024%, Al: 0.027%, N: 0.0077%,
Cu: 0.06%, Sn: 0.07% High magnetic flux density grain-oriented electrical steel sheet slab comprising the balance of Fe and unavoidable impurities is hot-rolled, annealed and cold-rolled by a known method to a final sheet thickness of 0.225 m.
m. Then, N ₂ 25% + H ₂ 75%, dew point 65
Decarburization annealing was performed at 850 ° C. for 120 seconds in an atmosphere of ° C. Then MgO100 parts by weight of TiO ₂ 5 parts by weight of a change CAA value when MgO prepared as shown in Table 1, Na ₂
B ₄ O ₇ 0.3 parts by weight of an annealing separator was mixed with a stirrer equipped with a shear blade at a liquid temperature of 5 ° C. and 1500 RPM × 30.
After stirring for one minute, the dispersion was carried out with a dispersing apparatus equipped with an ultrasonic vibrator while changing the flow rate of the slurry, the number of vibrators, and the processing time, and each was decarburized and annealed as an annealed separating agent slurry having an average particle diameter of 2 μm. And subjected to finish annealing at 1200 ° C. for 20 hours. After this, 20% colloidal silica 10
An insulating coating agent consisting of 0 ml + 50% Al phosphate 50 ml + 6 kg of CrO ₃ was applied and baked at 850 ° C. for 30 seconds to obtain a product.

In this experiment, the results of the observation of the application state of the annealing separator, the glass film of the product, and the magnetic properties are shown in Table 2.
Shown in

[0017]

[Table 1]

[0018]

[Table 2]

As a result of this experiment, the present inventions 1, 2, and 3 in which the CAA value of MgO was within the range of the present invention and the slurry dispersion treatment was performed by ultrasonic stirring and dispersion, the surface after slurry application and drying was very low. Fine and uniform application, uniform glass film, and very good magnetic properties were obtained. On the other hand, in Comparative Examples 1 and 2 in which ultrasonic stirring and dispersion were not performed as the slurry dispersion method, the surface after application had many roughness and was applied unevenly. As a result, the glass film was thin and non-uniform, and the magnetic properties were somewhat poor. Further, even if ultrasonic stirring and dispersion is performed as a slurry dispersion method, Mg
When the CAA value of O was out of the range of the present invention, Comparative Examples 3 and 4
As described above, a uniform application state of the slurry was obtained, but the formation state of the glass film was poor, and the magnetic properties were considerably worse than those of the present invention.

Here, the contents of the processing will be briefly described.
The dispersion treatment is a treatment for once again aggregating MgO particles once aggregated, and includes physical means and mechanical means as described later. On the other hand, crushing refers to a process of not only separating MgO particles from each other but also crushing each particle. Next, the reasons for limitation of the present invention will be described.

The most characteristic feature of the present invention is a method for preparing an annealing separator slurry. In the present invention, the method for dispersing the ultrafine particles of the slurry is performed using physical and mechanical means. The physical means is a stirring tank provided with an ultrasonic vibrator,
This is performed by changing the vibration width of the vibrator, clearance, slurry flow rate, slurry concentration, and the like. The mechanical means is a stirrer provided with a rotating body such as a shear blade, and is performed by changing the number of rotations, the slurry concentration, and the like. In the present invention, these physical and mechanical means are used in combination.

That is, it is efficient that the raw material supplied for the ultra-fine atomization of the slurry is previously dispersed in water. For this reason, first, the annealing separator is provided with a shear blade-shaped rotor. It is preferable that the slurry dispersed in the stirred tank is finely dispersed by a stirring device provided with an ultrasonic vibrator. Further, the atomization and pulverization processing is performed by these devices by continuous, intermittent or circulation processing. In the treatment by these methods, when the particles of the annealing separator are crushed, friction between the crushing tool and the particles, friction between the particles, collision, and the like increase the slurry temperature and increase the hydration moisture. Preferably,
It is preferable to carry out while continuously cooling the slurry. In the slurry that has been crushed in this way and subjected to ultra-fine atomization, Mg
As the O particles are finely dispersed, a new extremely lightly hydrated layer is formed on the surface layer of the particles, and the surface energy of the particles is reduced and stabilized. The treatment for forming the hydrated layer on the surface layer is the activation treatment. For this reason, reaggregation hardly occurs even if the mixture is stirred for a long time by ordinary stirring. Needless to say, the particle surface is activated by such a crushing treatment.

Further, when titanium oxide, an S compound, and a B compound are added to the annealing separator as glass film formation promoters, these are similarly finely dispersed and uniformly dispersed on the MgO surface. Next, the particle diameter by the pulverization treatment in the present invention is 10 μm or less in average particle diameter. Usually, since MgO for grain-oriented electrical steel sheets is fired at a high temperature, it has many sintered grains, and when mixed with water to form a slurry, agglomeration reaction occurs and coarse grains having an average grain size of 20 to 40 μm are formed. Become. For this reason, the surface where coarse particles of about 100 μm are mixed is present in a rough coating state, and the forsterite formation reaction of the steel sheet oxide film is reduced due to coarsening. The present inventors have conducted enormous research and experiments and found that the average particle size was 10 μm.
It has been found that if it can be ground to not more than m, a remarkable effect of improving the film formation reaction can be obtained. If it exceeds 10 μm, the effect of improving the reactivity is not sufficient. On the other hand, if it is 10 μm or less, the effect of the film forming reaction is gradually improved, but if it is less than 1 μm, it becomes difficult to control the hydration moisture. The most preferable range of the particle size by the pulverization treatment is 7 to 1 μm.

The MgO of the annealing separator used in the present invention has a CAA value of 50 to 150 seconds. This is important for maintaining the hydration characteristics of MgO and the reactivity of forming a glass film within an appropriate range together with the ultrafine atomization treatment.
When the CAA value is less than 50 seconds, the hydration of MgO is high.
The increase of hydration moisture in the ultra-fine atomization treatment increases,
It is not preferable because the film becomes unstable, and pinholes, shimofuri, gas marks, etc. peculiar to the peroxidation phenomenon are generated as film defects, thereby affecting the stability of the inhibitor and deteriorating the magnetic characteristics. On the other hand, if it exceeds 150 seconds, even though the outermost layer of the particles can be modified, the particles themselves are too inert and the glass film reactivity is poor, resulting in an uneven glass film.
In particular, since the reaction shifts to the high temperature side, a sealing effect on the surface of the steel sheet cannot be obtained, and the magnetic characteristics as well as the film characteristics deteriorate, which is not preferable. When the CAA value is 50 to 150 seconds, these problems do not occur, and a product excellent in both the glass film and the magnetic properties can be obtained.

Next, the reason why the present invention makes the glass film uniform and improves the magnetic properties will be described. In the present invention, M
As a method for dispersing MgO in an ultrafine particle state, in which the CAA value is appropriately controlled as a physical property value in the production of gO, a crushing treatment is performed by a physical or mechanical means to a particle diameter of 10 μm or less in the slurry. Thereby, fine dispersion and surface activation of the particles are performed. At this time, the additive compound that is added as required is also refined and activated, and uniformly adheres to the MgO surface. When the slurry thus obtained is applied to a steel sheet, the slurry adheres to the surface of the steel sheet ultra-finely, uniformly and with good adhesion.

As a result, high reactivity and uniformity of the reaction, which were not seen in the prior art, can be obtained, and the glass film is formed uniformly and at an early stage of the finish annealing under the condition that the atmosphere between the steel plates is relatively dry. . It is considered that the effect of improving the sealing property of the surface by the film stabilizes the inhibitor such as AlN and MnS, and the effect of improving the magnetic properties is obtained.

[0027]

【Example】

Example 1 C; 0.075% by weight, Si; 3.30%, Mn;
0.060%, S; 0.025%, Al; 0.028
%, N; 0.0078%, Cu; 0.070%, Sn;
A raw material for a high magnetic flux density grain-oriented electrical steel sheet comprising 0.070%, balance Fe and inevitable impurities, was treated by a known method to obtain a cold-rolled coil having a final sheet thickness of 0.29 mm.

This steel sheet was subjected to 25% N ₂ + 75% H ₂ ,
Decarburization annealing was performed at 850 ° C. × 150 seconds in P65 ° C.
Next, MgO100 having a CAA value of 75 seconds was used as an annealing separator.
Parts, TiO ₂ 5 parts by weight, Sb ₂ (SO _{4) 3} A slurry having a composition of 0.3 parts by weight was applied by changing the stirring conditions as shown in Table 3, after winding the coil, 1200 ° C. × 20
Final finishing annealing was performed for a time. After that, 100 ml of 20% colloidal silica + 50% phosphoric acid A as an insulating film agent
A coating solution consisting of 150 ml + 6 kg of CrO ₃ was applied and baked at 850 ° C. for 30 seconds to obtain a product. Table 4 shows the results of investigating the application state of the annealing separator and the product characteristics in this manufacturing process.

[0029]

[Table 3]

[0030]

[Table 4]

As a result, the ultrasonic dispersion according to the present invention is utilized.
As for the slurry , the slurry was ultrafine and applied with good adhesion. Further, the glass film after the finish annealing formed a uniformly glossy film, and very good results were obtained in the magnetic properties. On the other hand, when the stirring of the comparative example was performed only with the apparatus equipped with the shear blade rotating body, there were many agglomerated particles and the like, there was roughness, a nonuniform coating film was obtained, and the adhesion to the steel sheet was very poor. In this case, the glass film after the finish annealing was thin and non-uniform, and the magnetic properties were considerably worse than those of the present invention.

[0032]

According to the present invention, the sintered layer and the aggregate of the annealing separator slurry are disintegrated into ultrafine particles, and the surface of the particles is activated. A coating film can be formed finely, uniformly and with good adhesion on the top, and at this time, an additive added as a reaction accelerator for forming a glass film is also finely and uniformly dispersed,
The formation reactivity of the film can be significantly increased, thus accelerating the time of forming the glass film at the time of raising the finish annealing temperature,
A glass film can be formed uniformly and a glass film without film defects can be formed. By early formation and uniformization of this film, the inhibitor in the steel is kept stable, and at the same time, the effect of improving the magnetic properties is exhibited. You.

Continued on the front page (72) Inventor Hiroshi Sato 59 Nippon Steel Plant Design Co., Ltd., 46-46 Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Prefecture (72) Keisuke Yamochi 1-1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (56) References JP-A-5-295423 (JP, A) JP-A-6-158339 (JP, A)

Claims (3)

(57) [Claims] Claims 1. A material for a grain-oriented electrical steel sheet which is made of Mg after decarburizing annealing.
In a method for producing a grain-oriented electrical steel sheet, which comprises applying an annealing separator containing O as a main component and performing finish annealing, the annealing separator slurry is supplied to a rotating blade such as an ultrasonic vibrator and a shear blade.
A method for producing a grain-oriented electrical steel sheet having excellent film properties and magnetic properties, which comprises crushing and dispersing using a device provided with , activating the particle surface , and then applying the resultant to a steel sheet. 2. A crushing / dispersing treatment and activation of the particle surface.
Grain measured by laser diffraction method of MgO after performing
2. The method for producing a grain- oriented electrical steel sheet according to claim 1 , wherein the average diameter is 10 [mu] m or less . 3. A disintegration / dispersion treatment and a particle surface activation treatment.
As the MgO to be treated, the CAA value at a liquid temperature of 30 ° C.
2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein MgO for 50 to 150 seconds is used .