JPH0649534A - Production of grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To obtain a grain-oriented silicon steel sheet extremely low in core loss by simultaneously executing mirror finishing and secondary recrystallization to the steel in a finish annealing furnace. CONSTITUTION:A silicon hot rolled steel strip constituted of 2.0 to 4.8% Si, 0.008 to 0.05% acid-soluble Al and <=0.0010% N is annealed and is subjected to cold rolling for one time or >= two times including process annealing to regulate its sheet thickness into a prescribed one. The steel sheet is subjected to primary recrystallization annealing and is coated with alumina having 0.5 to 10.0mum average grain size as a separation agent for annealing. Its temp. is raised to 920 to 1150 deg.C at >=50 deg.C/Hr temp. raising rate in a neutral or reducing atmosphere, and it is held at the same temp. for >=5hr. After the primary recrystallization annealing, by removing an oxidized film formed in the annealing stage, mirror finishing can furthermore be promoted. In this way, the mirror-finished grain-oriented silicon steel sheet having high magnetic flux density can be obtd. This steel sheet is extremely low in core loss, so that electric loss can be reduced, and its social contribution is high.

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 silicon steel sheet (hereinafter referred to as grain-oriented electrical steel sheet) having a high magnetic flux density and an extremely low iron loss. In particular, in the secondary recrystallization process (finish annealing process), do not form a forsterite (hereinafter referred to as glass) coating on the steel plate surface, or complete the process with the steel plate surface mirror-finished by thermal etching. After that, the magnetic domain subdivision, the tension coating and the like are performed to improve the iron loss characteristics.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are frequently used as magnetic iron cores for electric equipment and have been repeatedly improved in order to reduce energy loss. As a means for reducing the iron loss of grain-oriented electrical steel sheets, a method of irradiating a laser beam on the surface of the material after finish annealing to give local strain to thereby subdivide the magnetic domains to reduce the iron loss is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-264
No. 05 publication.

Further, since the local strain is removed by the stress relief annealing (strain relief annealing) after the usual working, the magnetic domain refining effect disappears. For example, Japanese Patent Laid-Open No. 62-8617 discloses a remedy for this, that is, a means for preventing the magnetic domain refining effect from disappearing even when stress relief annealing is performed.

In order to further reduce the iron loss value, it is important to remove (smooth) the irregularities on the surface of the base metal which hinder the movement of magnetic domains near the surface of the steel sheet. The highest level of smoothing is specular. As a method for smoothing (mirror-finishing) the material surface after finish annealing, there is disclosed in JP-A-64-83620.
There are chemical polishing, electrolytic polishing, and the like disclosed in the publication.

[0005]

Conventionally, as a method for mirror-finishing (smoothing) the surface of a steel sheet, there are chemical or physical methods such as brush polishing, sandpaper polishing, and grinding in addition to chemical polishing and electrolytic polishing. is there. However, these methods are suitable for producing small test pieces and small samples, but are accompanied by various difficulties for the surface mirror-finishing (smoothing) of industrially mass-produced metal strips and the like.

In the chemical method that is said to be the most smooth, that is, in chemical polishing, environmental problems such as chemical concentration control and wastewater treatment, and in the physical method, a surface having an industrially large area is used as the same standard. It is extremely difficult to smooth (mirror-finish) with.

An object of the present invention is to eliminate these problems and to provide a method of mirror-finishing or smoothing the surface of a grain-oriented electrical steel sheet on an industrial production scale. Of course, the magnetic properties must not be lost due to mirroring or smoothing. In the present invention, it is intended to simultaneously achieve the object in the finish annealing step. That is, the orientation of secondary recrystallization is controlled to obtain an extremely high magnetic flux density and to obtain a mirror surface or a smooth surface.

[0008]

The feature of the present invention is to obtain a mirror surface or a smooth surface during finish annealing. That is, without using a commonly used annealing separator mainly composed of MgO, SiO mainly composed of Al ₂ O ₃ is used.
Using a substance that does not easily react with ₂ as an annealing separator, finish annealing to obtain a grain-oriented electrical steel sheet with high magnetic flux density and at the same time expose the metal surface without forming a glass (forsterite) coating on the steel sheet surface. Secondary recrystallization is performed in this state, and at the same time, the metal surface is mirror-finished or smoothed by thermal etching.

Here, the term "thermal etching" means that the base iron of the steel sheet is exposed, and there is no substance reacting with the base iron on the surface of the steel sheet (base iron). This is a treatment in which a steel sheet is heated to a temperature equal to or higher than the temperature at which the steel sheet develops and the surface of the steel sheet becomes a mirror surface. The present invention is Si: 2.0-
4.8% by weight, acid-soluble Al: 0.008 to 0.05% by weight, N ≦ 0.010% by weight, after annealing the silicon hot-rolled steel strip consisting of the balance Fe and unavoidable impurities as necessary, In the production of grain-oriented silicon steel sheet, which is subjected to cold rolling once or two or more times with intermediate annealing sandwiched to obtain a predetermined sheet thickness, and then primary recrystallization annealing, followed by applying an annealing separator, and performing final annealing. After the primary recrystallization annealing, the average grain size is 0.5.
˜10.0 μm of an annealing separator containing Al ₂ O ₃ (alumina) as a main component is applied, the finish annealing atmosphere is neutral or reducing atmosphere, and the temperature rising rate is 50 ° C./Hr or more 920 to 920 That is, the temperature is raised to 1150 ° C. and the temperature is maintained for 5 hours or more.

Here, after the primary recrystallization annealing, the oxide film on the surface of the steel sheet generated in the annealing step is removed, and then Al ₂ O ₃ (alumina) having an average grain size of 0.5 to 10.0 μm is formed.
Is applied as an annealing separator, and the finish annealing atmosphere is neutral or reducing atmosphere, and the temperature rising rate is 50 ° C.
/ Hr or more, the temperature is raised to 920 to 1150 ° C, and the temperature is increased to 5
It holds for more than time.

Further, according to the present invention, after the primary recrystallization annealing, nitriding treatment with ammonia is performed to strengthen the inhibitor,
After that, A having an average particle diameter of 0.5 to 10.0 μm
An annealing separator containing l ₂ O ₃ (alumina) as a main component is applied, the finish annealing atmosphere is set to a neutral or reducing atmosphere, and the temperature is raised to 920 to 1150 ° C. at a heating rate of 50 ° C./Hr or more, The temperature is maintained for 5 hours or more.

Further, according to the present invention, after the primary recrystallization annealing, nitriding treatment with ammonia is carried out, and thereafter, the oxide film on the surface of the steel sheet produced in the primary recrystallization annealing step is removed, and the average grain size is 0.5 to 10.0 μm. Consisting of Al ₂ O ₃ (alumina)
Is applied as an annealing separator, and the finish annealing atmosphere is neutral or reducing atmosphere, and the temperature rising rate is 50 ° C.
/ Hr or more, the temperature is raised to 920 to 1150 ° C, and the temperature is increased to 5
Can hold for more than an hour.

The method of removing the oxide film on the surface of the steel sheet is pickling, particularly pickling with an acid mixed with hydrofluoric acid, and the application of the annealing separator is carried out with an average particle size of alumina of 0.5 to 1
By setting the thickness to 0.0 μm, a water slurry can be applied in the same manner as a normal water-based slurry mainly containing MgO.

When a higher magnetic flux density is aimed at, 920
C. to 1150.degree. C. until the completion of holding, the final annealing atmosphere is nitrogen: 5% or more, the final annealing atmosphere is neutral or reducing atmosphere, and the temperature rising rate is 50.degree. C./hr or more to 920 to 1150.degree. During warming, or during temperature rise or upon reaching that temperature, the N ₂ % of the atmosphere can be raised above the previous N ₂ % and held at that temperature for 5 hours or more.

The present invention will be described in detail below. The present inventors have investigated in detail the rate-determining process of inhibitor deterioration during finish annealing, and when Al is contained in the components of the hot-rolled steel sheet, the oxidation process of Al at the steel sheet interface is the largest factor, and the primary recrystallization annealing is performed. It was found that the oxide layer on the surface of the steel sheet, which occurs occasionally, is greatly involved in the deterioration of the inhibitor.

Si: 3.3% by weight, acid-soluble Al: 0.
028% by weight, N: 0.008% by weight, Mn: 0.14
% By weight, S: 0.007% by weight, C: 0.05% by weight,
A hot-rolled silicon steel strip consisting of the balance Fe and unavoidable impurities is annealed at 1100 ° C. for 2 minutes and then cold-rolled to 0.23.
mm thickness. These cold-rolled sheets were annealed at 800 ° C. for 2 minutes in an annealing furnace in a wet water atmosphere in order to also serve as decarburization, and primary recrystallization was performed.

Next, in order to stabilize the secondary recrystallization, nitriding treatment is performed in an ammonia atmosphere, and the total nitrogen content is 180 pp.
m and strengthened the inhibitor.

After that, Al ₂ was added to the two materials that had been pickled as they were and with a 0.5% hydrofluoric acid-5% sulfuric acid mixed solution.
O ₃ is electrostatically applied, 100% H ₂ atmosphere, 15 ℃ / Hr
Finish annealing was performed while maintaining the temperature rising rate of.

Inhibitors (AlN,
(Al, Si) N, etc.), as shown in FIG. 1, the material having an oxide layer formed on the surface of the steel sheet during primary recrystallization annealing has a higher inhibitor strength than the material having no oxide layer. It turns out that it deteriorates quickly.

That is, if the oxide layer formed on the surface of the steel sheet during the primary recrystallization annealing is removed, strong inhibitor strength can be maintained up to a high temperature.

The acid-soluble Al in the steel sheet removes oxygen from the oxide layer composed mainly of SiO ₂ during finish annealing and Al ₂ O ₃
Etc. and precipitate in the oxide layer. Therefore, the acid-soluble Al in the steel sheet decreases.

Although the acid-soluble Al concentration in steel is shown as the inhibitor strength in FIG. 1, Al is AlN,
Since a compound (precipitate) such as (Al, Si) N is formed and acts as an inhibitor, the amount of acid-soluble Al may be considered as an index indicating the inhibitor strength.

Further, the inventors of the present invention conducted a detailed investigation on the rate-determining process of inhibitor deterioration, and found that the amount of nitrogen in the steel and the amount of nitrogen in the annealing atmosphere were also influenced in addition to the oxidation of Al at the steel sheet interface. It was The amount of nitrogen in the annealing atmosphere increases the amount of nitrogen in the steel through the steel sheet interface, and the effect is the same as nitrogen contained in the steel from the beginning.

The nitrogen in the steel and the nitrogen in the annealing atmosphere are A
Oxidation of Al is suppressed in order to increase the amount of precipitates such as 1N to fix Al and reduce the migration of Al to the steel plate interface. Therefore, acid-soluble Al in steel during finish annealing
The higher the nitrogen partial pressure, the less the amount of deterioration, and the stronger the inhibitor is at high temperatures.

In order to obtain a high magnetic flux density, which is one of the main points of the present invention, it is preferable that the inhibitor is strong, but it is desirable that the inhibitor be maintained strong and constant. This is because only crystals with good orientation (GOSS grains) grow from the start to the end of secondary recrystallization, and if the inhibitor weakens from the start to the end of secondary recrystallization, grains with bad orientation grow and The magnetic flux density of the steel plate decreases.

The solubility of the inhibitor AlN naturally increases as the temperature of the steel sheet rises, and the inhibitor inevitably deteriorates. As a measure for this, as the temperature rises, the partial pressure of nitrogen is increased to increase the amount of nitrogen in the steel sheet,
It is desirable to keep AlN as a precipitate constant.

However, in order to obtain a mirror surface which is one of the main points of the present invention, the nitrogen partial pressure should not be too high. From the viewpoint of secondary recrystallizing the inhibitor with a constant strength, secondary recrystallization at a constant temperature at which the solubility of AlN does not change, that is, the inhibitor strength does not change is extremely effective.

As described above, the solubility of AlN does not change if it is maintained at a constant temperature, but the acid-soluble Al has more oxygen than oxygen in the atmosphere or an oxide of an element having a smaller oxygen affinity than Al on the surface of the steel sheet. Then, it becomes Al ₂ O ₃ and decreases, and the inhibitor deteriorates. Therefore, also in this case, it is necessary to raise the nitrogen partial pressure to suppress the dissolution of AlN and suppress the decrease of the acid-soluble Al.

The higher the rate of temperature rise up to the temperature at which secondary recrystallization is possible in the final annealing, the more convenient the inhibitor is because it is less likely to deteriorate. If the heating rate is less than 15 ° C / Hr, the inhibitor is remarkably deteriorated, and the inhibitor required for secondary recrystallization is not secured, sufficient secondary recrystallization cannot be obtained, and the magnetic flux density (B ₈ ) of the steel sheet is low. Met. From the viewpoint of obtaining a high magnetic flux density, which is one of the main points of the present invention, a temperature rising rate of 50 ° C./Hr or higher is required.

Holding at a constant temperature for secondary recrystallization is effective for obtaining a high magnetic flux density.
This is to prevent deterioration of the inhibitor and carry out secondary recrystallization with an appropriate inhibitor strength. This temperature is
If the temperature is lower than 920 ° C., the time until the completion of secondary recrystallization becomes too long, which is not practical. Also, above 1150 ° C,
Deterioration of the inhibitor becomes so remarkable that the required inhibitor cannot be secured until the secondary recrystallization is completed.

The holding time for secondary recrystallization is required to be 5 hours or more, and if the time is shorter than this, the holding is not completed within the holding time. When the holding temperature is reached or as the temperature rises, deterioration of the inhibitor is suppressed as described above,
To keep the inhibitor strength constant, the nitrogen partial pressure is made higher than that at the time of temperature increase. However, the higher the partial pressure of nitrogen, the better.

If it is too high, the inhibitor becomes too strong and it takes too much time to complete the secondary recrystallization, and the secondary recrystallization does not occur. The nitrogen partial pressure when the temperature is maintained must be increased by linking with the nitrogen partial pressure when the temperature is raised. After the secondary recrystallization is completed, the hydrogen concentration is increased in order to completely purify and mirror-finish the steel plate surface.
Holding at around 1200 ° C. for several hours is extremely effective.

The steel composition in the present invention is Si: 2.0-
4.8% by weight, acid-soluble Al: 0.008 to 0.05% by weight, N ≦ 0.010% by weight, balance Fe and inevitable impurities. As other inhibitor constituent elements,
Mn, S, Se, Sb, P, B, Sn, Bi, Nb, T
There is no problem even if one or more of i, Mo, Cu and the like are added.

Si is important for increasing the electric resistance and decreasing the iron loss, but if it exceeds 4.8%, it tends to crack during cold rolling. On the other hand, if it is less than 2.0%, there is a problem in that the electric resistance is low and the iron loss is lowered.

Next, the inhibitor constituent elements will be described. Acid-soluble Al is important as an inhibitor constituent element, and is combined with nitrogen, silicon, etc. to form AlN, (Al, S
i) It forms a precipitate such as N and plays a role of an inhibitor.
In terms of the inhibitor strength, that is, the range in which the magnetic flux density is high, it is 0.008 to 0.05% by weight.

When nitrogen exceeds 0.010% by weight, vacancies called blisters are generated in the steel sheet, so this range is optimal.

Other inhibitor components include Mn:
0.03 to 0.40% by weight, S: 0.01 to 0.05% by weight, Se: 0.01 to 0.10% by weight, Sb: 0.0
You may add in 1 to 0.10 weight% of range.

Further, Sn, Bi, Nb, Ti, P, M
o, Cu, etc. are used as an inhibitor or as an auxiliary element. The carbon content is preferably 0.085% by weight or less.

The inventors examined a method of applying alumina (Al ₂ O ₃ ) as an annealing separator. Electrostatic coating is excellent as a method that does not bring moisture into the finish annealing furnace, but compared to the commonly used coating method for annealing separating agent mainly composed of MgO, the complexity of coating equipment, equipment cost, powder There are inconveniences such as deterioration of the work environment due to scattering.

The inventors of the present invention have examined the same method as the method of applying the annealing separator mainly composed of MgO, that is, the application with an aqueous slurry, and it is possible that the average particle diameter of alumina is within a certain range. I found it.

That is, the average particle size of alumina is 0.5 to 1
It was found that good results were obtained when the thickness was 0.0 μm. If the powder is less than 0.5 μm, it can be effectively applied as a water slurry, but since alumina itself is activated because the average particle size is small, it sinters to form a film and does not reveal a metal surface. .

On the other hand, if it exceeds 10.0 μm, the water slurry is unstable and precipitates immediately when stirring is stopped, making it difficult to apply. Since the particles are coarse, the surface of the steel sheet becomes difficult to obtain, and not only a smooth surface cannot be obtained. However, there is a problem that the magnetic characteristics are deteriorated.

This phenomenon is not limited to the case of water slurry,
The same happens with powder coating, for example electrostatic coating as described above.

That is, when the average particle size of alumina is small,
Although it is easy to apply, if the average particle size is less than 0.5 μm as described above,
If the average particle size exceeds 10.0 μm, it will be difficult to supply the powder to the coating device, and it will be difficult to apply the powder, and the weight of the particle will be reduced. Due to the amount of electrification, it is difficult to adhere, and even if it adheres, it quickly desorbs, and because the particles are coarse, the surface of the steel plate becomes difficult to obtain, and not only a smooth surface cannot be obtained, but also magnetic properties deteriorate. .

Also in the case of coating methods other than the water slurry coating, the average particle size of alumina (Al ₂ O ₃ ) is 0.5 to 10.0 μm.
m is good. The average particle size is 50% by weight.
It is the particle size when passing. It should be noted that there is no problem even if a slight amount of a substance such as CaO or the like which hardly reacts with silica, an anticorrosive agent, or the like is added to the annealing separator containing alumina as a main component.

The implementation conditions will be described below. The oxide layer formed on the surface of the steel sheet during the primary recrystallization annealing affects the following two during the finish annealing. That is, as described above, the inhibitor strength is weakened, a sufficient magnetic flux density cannot be obtained, the surface smoothness of the product is insufficient, and the magnetic characteristics are adversely affected.
It is difficult to obtain the ultimate magnetic characteristics. Therefore, in order to obtain the ultimate magnetic properties, it is desirable to remove the oxide layer formed on the surface of the steel sheet during the primary recrystallization annealing.

As a method for removing, there are mechanical polishing, for example, brush polishing, sandpaper polishing, grinding, etc.
Although it is effective for this purpose, it is not very practical due to various industrial difficulties. The present inventors have found that the method of pickling is extremely effective. This is because a continuous pickling line for hot-rolled steel strips or steel plates has already been put to practical use.

As the pickling solution (pickling solution), mineral acids such as hydrochloric acid, sulfuric acid and nitric acid are effective, but the oxide layer formed on the surface of the steel sheet is an oxide mainly composed of SiO _2. Therefore, it is difficult to pickle with only mineral acids such as hydrochloric acid, sulfuric acid and nitric acid. When hydrofluoric acid is mixed with these acids, the oxide layer can be removed very efficiently, that is, at high speed.

When the nitride is used as an inhibitor, it is effective to perform a nitriding treatment with ammonia after the primary recrystallization annealing and before the finish annealing to strengthen the inhibitor. This is because the inhibitor strength at the time of completion of primary recrystallization is not sufficient for secondary recrystallization, and the nitrogen partial pressure during finish annealing is increased to strengthen the inhibitor or prevent deterioration even during secondary recrystallization. We cannot secure enough inhibitors.

Therefore, strengthening the inhibitor by treating with ammonia generally improves the magnetic properties. In order to secure an inhibitor required during the progress of secondary recrystallization, it is desirable to add 5% or more and 95% or less of nitrogen gas into the annealing atmosphere at the time of temperature rise, but hydrogen gas may be 100%.

If the nitrogen gas content is less than 5%, the effect of strengthening the inhibitor or preventing deterioration is small. If nitride is not the inhibitor, the effect of nitrogen partial pressure is weak.

The neutral or reducing atmosphere is one or a mixture of two or more gases selected from inert gases such as nitrogen, oxygen, water, hydrogen, argon, etc., and is neutral to the redox of silicon. Gas composition that is neutral or reductive.
Nitrogen and hydrogen gases are generally used in finish annealing of electromagnetic steel sheets, so that the combination of both gases is 0% to 100%.

There is no problem even if an inert gas such as argon or helium is mixed with the combination of both gases in order to adjust the nitrogen partial pressure. The neutral or reducing atmosphere prevents the reduction of Al in the steel and oxidizes silicon in the steel so that SiO ₂ is not formed on the surface. Alternatively, it is not to increase.

After the completion of the secondary recrystallization, the hydrogen concentration was raised to complete the purification and the mirror-finishing of the steel sheet surface.
Holding for several hours at around 00 ° C is extremely effective.

The higher the rate of temperature rise up to the temperature at which secondary recrystallization is possible in the finish annealing, the more convenient the inhibitor is. When the temperature rising rate is less than 15 ° C./Hr, the inhibitor was remarkably deteriorated, and the inhibitor required for the secondary recrystallization was not sufficiently secured, and sufficient secondary recrystallization was not obtained. From the viewpoint of obtaining a high magnetic flux density, which is one of the main points of the present invention, a heating rate of 50 ° C./Hr or more is desirable.

The embodiments of the present invention will be described below. Si: 2.0 to 4.8% by weight, acid-soluble Al: 0.00
8 to 0.05% by weight, N ≦ 0.010% by weight, balance Fe
And molten steel consisting of unavoidable impurities in the usual process,
Alternatively, it is continuously cast into a hot rolled steel sheet or a hot rolled steel strip.

This hot-rolled steel sheet or hot-rolled steel strip is 75
Annealing for improving the magnetic flux density is performed in a temperature range of 0 ° C to 1200 ° C for 30 seconds to 30 minutes. Subsequently, these hot rolled steel sheets or hot rolled steel strips are cold rolled.

The cold rolling is carried out at a final cold rolling rate of 80% or more as disclosed in Japanese Patent Publication No. 40-15644. The material after cold rolling is usually subjected to primary recrystallization annealing in a temperature range of 750 ° C. to 900 ° C. in a wet water atmosphere to remove carbon in steel.

At this time, an oxide layer is formed on the surface of the steel sheet together with decarburization and primary recrystallization. This oxide layer forms a so-called internal oxide layer and has a thickness of 0.1 to 6.0 μm from the steel sheet surface, depending on the degree of water content (usually represented by dew point) in a wet water atmosphere, that is, an atmosphere containing water. Therefore, SiO ₂ mainly exists as an oxide here. Note that 80 to 90% or more of the oxygen content of the oxide formed during the primary recrystallization annealing is in the form of SiO ₂ .

The steel sheet or steel strip after primary recrystallization is
When pursuing the ultimate magnetic properties, the surface oxide layer is removed. If the magnetic properties may be slightly worse as described above, this step is omitted. This choice is made in terms of cost and characteristics.

The oxide film can be removed by a physical or chemical method as described above, but it is generally carried out by pickling.
It is extremely effective to improve the magnetic flux density by nitriding with ammonia for strengthening the inhibitor before removing the oxide layer on the surface of the steel sheet.

Next, the primary recrystallized plate is coated with an annealing separator mainly composed of alumina as a water slurry and then enters the finish annealing furnace. Change the annealing atmosphere to neutral or reducing 15
It is heated to 1200 ° C. at a temperature rising rate of ℃ / Hr or more, and at that temperature, it is switched to 100% hydrogen for purification and mirroring, and kept for about 20 hours.

The following measures can be taken to obtain the ultimate magnetic flux density. From the viewpoint of preventing inhibitor deterioration, the temperature increase rate of the finish annealing is set as high as possible, preferably 50 ° C./Hr or more, and the atmosphere during temperature increase is made neutral or reducing so that the temperature during temperature increase or 920 ° C. to 1150 ° C. When it reaches, the nitrogen partial pressure is made higher than that at the time of temperature rise and the temperature is maintained for 5 hours or more.

It should be noted that there is no problem in mixing an inert gas such as argon or helium for adjusting the nitrogen partial pressure. After the completion of the secondary recrystallization, it is kept at a high temperature (about 1200 ° C.) with 100% hydrogen for purification. After the completion of the secondary recrystallization, it is kept at a high temperature (about 1200 ° C.) with 100% hydrogen for purification. After finishing annealing, magnetic domain subdivision processing such as laser beam irradiation is performed, and tension coating processing is further performed.

[0065]

【Example】

Example 1 Si: 3.2 wt%, acid-soluble Al: 0.028 wt%, N: 0.008 wt%, Mn: 0.13 wt%,
S: 0.008 wt%, C: 0.05 wt%, balance Fe
And a hot-rolled silicon steel strip consisting of inevitable impurities
After annealing at 0 ° C for 2 minutes, it was cold rolled to a thickness of 0.18 mm. These cold-rolled sheets were annealed at 820 ° C. for 2 minutes in an annealing furnace in a wet water atmosphere for double decarburization, and primary recrystallization was performed.

Next, in order to stabilize the secondary recrystallization, a nitriding treatment is performed in an ammonia atmosphere to reduce the total nitrogen amount to 190.
ppm to enhance the inhibitor.

After that, the oxide layer formed on the surface of the steel sheet was removed with sulfuric acid mixed with hydrofluoric acid to obtain an average particle size of 2.0 μm.
Al ₂ O _{3 in the form} of an aqueous slurry was applied as an annealing separator, and as it was, Al ₂ O ₃ having an average particle size of 2.0 μm was applied in the form of an aqueous slurry as an annealing separator. The separating agent was applied as a water slurry.

These three kinds of materials were heated to 1200 ° C., and 2
In a 5% N ₂ -75% H ₂ atmosphere, the temperature was raised while maintaining the temperature rising rate of 50 ° C./Hr, the temperature was raised to 1050 ° C., and the temperature was maintained for 10 hours. The temperature was raised to 1200 ° C. at a heating rate. 100% after reaching 1200 ° C
It was hydrogen and kept at that temperature for 20 hours.

After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are as shown in Table 1.

[0070]

[Table 1]

Example 2 Si: 3.2% by weight, acid-soluble Al: 0.027% by weight, N: 0.008% by weight, Mn: 0.13% by weight,
S: 0.007 wt%, C: 0.05 wt%, balance Fe
And a hot-rolled silicon steel strip consisting of inevitable impurities
After being annealed at 0 ° C. for 2 minutes, it was cold rolled to a thickness of 0.15 mm.

These cold-rolled sheets were annealed at 820 ° C. for 2 minutes in an annealing furnace in a wet water atmosphere in order to also serve as decarburization, and primary recrystallization was performed. Next, in order to stabilize the secondary recrystallization, nitriding treatment is performed in an ammonia atmosphere to reduce the total nitrogen amount to 170
ppm to enhance the inhibitor.

After that, the oxide layer formed on the surface of the steel sheet was removed with sulfuric acid mixed with hydrofluoric acid, and the average particle size was 2.0 μm.
Al ₂ O ₃ as an annealing separator in a water slurry state,
Up to 00 ° C, 100% H ₂ atmosphere, average particle size 2.0
μm Al ₂ O ₃ as an annealing separator in a water slurry state,
To 1200 ° C., in 5% N ₂ -95% H ₂ atmosphere, the Al ₂ O ₃ having an average particle size of 2.0μm and annealing separator in water slurry, to _{1200 ℃, 75% N 2 -25} % H 2
In an atmosphere, for comparison, MgO was used as an annealing separator in a water slurry state, and up to 1200 ° C., 5% N ₂ -95%
In an H ₂ atmosphere, the temperature is raised while maintaining the temperature rising rate of 50 ° C./Hr, the temperature is raised to 1050 ° C., the temperature is held for 10 hours, and the temperature rising rate of 50 ° C./Hr is increased to 1200 ° C. The temperature was raised.

After reaching 1200 ° C., the temperature was set to 100% hydrogen and the temperature was maintained for 20 hours. After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are as shown in Table 2.

[0075]

[Table 2] The material using the MgO water slurry as an annealing separator had a small amount of glass coating formed on the surface. Therefore, smoothing was insufficient and magnetic properties were poor.

Example 3 Si: 3.2% by weight, acid-soluble Al: 0.030% by weight, N: 0.007% by weight, Mn: 0.16% by weight,
S: 0.008 wt%, C: 0.05 wt%, balance Fe
And a hot-rolled silicon steel strip consisting of inevitable impurities
After being annealed at 0 ° C. for 2 minutes, it was cold rolled to a thickness of 0.15 mm.

These cold-rolled sheets were annealed at 850 ° C. for 2 minutes in an annealing furnace in a wet water atmosphere in order to also serve as decarburization, and primary recrystallization was performed. Next, in order to stabilize the secondary recrystallization, nitriding treatment is performed in an ammonia atmosphere, and the total nitrogen amount is reduced to 200
ppm to enhance the inhibitor.

After that, the oxide layer formed on the surface of the steel sheet was removed with sulfuric acid mixed with hydrofluoric acid, and the average particle size was 0.3 μm.
Alumina (Al ₂ O ₃ ), average particle size 0.5 μm alumina (Al ₂ O ₃ ), average particle size 3.0 μm alumina (Al ₂ O ₃ ), average particle size 10.0 μm alumina (Al ₂ O ₃ ), alumina having an average particle size of 14.9 μm (Al ₂ O ₃ ), alumina having an average particle size of 35 μm (Al
₂ O ₃ ) was applied as an annealing separator in a water slurry state.

The temperature of this material was raised in a 75% N ₂ -25% H ₂ atmosphere while maintaining the temperature rising rate of 50 ° C./Hr, and the temperature was raised to 10
The temperature was raised to 50 ° C., the temperature was maintained for 10 hours, and further the temperature was raised to 1200 ° C. at a heating rate of 50 ° C./Hr.
After reaching 1200 ° C., the temperature was set to 100% hydrogen and the temperature was maintained for 20 hours. After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are as shown in Table 3.

[0080]

[Table 3] When alumina having an average particle size of less than 0.5 μm was used as the annealing separator, the alumina sintered body adhered to the surface of the steel sheet. When alumina having an average particle size of more than 10.0 μm is used as the annealing separator, the alumina particles bite into the steel plate and the roughness can be confirmed with a finger, and the alumina on the steel plate surface can be confirmed with an electron microscope. did it.

Example 4 The primary recrystallized plate of Example 3 was subjected to a nitriding treatment in an ammonia atmosphere in order to stabilize the secondary recrystallization,
The total nitrogen content was 210 ppm and the inhibitor was strengthened.

After that, the oxide layer formed on the surface of the steel sheet was removed with sulfuric acid mixed with hydrofluoric acid, and as an annealing separator,
The average particle diameter 2.0μm of alumina (Al ₂ O ₃₎ electrostatically coating, with 100% H ₂ atmosphere, annealing the separating agent, the average particle diameter 2.0μm of alumina (Al ₂ O ₃₎ electrostatically coating the and, in 5% N ₂ -95% H ₂ atmosphere, the annealing as a separating agent, the average particle diameter 2.0μm of alumina (Al ₂ O ₃₎ electrostatically coating, with 75% N ₂ -25% H ₂ atmosphere Further, for comparison, MgO in a water slurry state as an annealing separator is heated in a 75% N ₂ -25% H ₂ atmosphere while maintaining a temperature rising rate of 50 ° C./Hr to 1050 ° C. The temperature was maintained for 10 hours, and then the temperature was raised to 1200 ° C. at a heating rate of 50 ° C./Hr.

After reaching 1200 ° C., the temperature was set to 100% hydrogen and the temperature was maintained for 20 hours. After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are shown in Table 4.

[0084]

[Table 4] The material using the MgO water slurry as an annealing separator had a small amount of glass coating formed on the surface. Therefore, smoothing was insufficient and magnetic properties were poor.

Example 5 Si: 3.2% by weight, acid-soluble Al: 0.031% by weight, N: 0.008% by weight, Mn: 0.14% by weight,
S: 0.008 wt%, C: 0.05 wt%, balance Fe
And a hot-rolled silicon steel strip consisting of inevitable impurities
After being annealed at 0 ° C. for 2 minutes, it was cold rolled to a thickness of 0.15 mm.

These cold-rolled sheets were annealed at 820 ° C. for 2 minutes in an annealing furnace in a wet water atmosphere in order to also serve as decarburization, and primary recrystallization was performed. Next, in order to stabilize the secondary recrystallization, nitriding treatment is performed in an ammonia atmosphere, and the total nitrogen amount is adjusted to 160
ppm to enhance the inhibitor.

Then, the oxide layer formed on the surface of the steel sheet was removed with sulfuric acid mixed with hydrofluoric acid, and Al ₂ O ₃ having an average particle diameter of 2.0 μm was applied to this material as an annealing separator in a water slurry state. Then, in a 25% N ₂ -75% H ₂ atmosphere, 3
Heated to 1200 ° C at a heating rate of 0 ° C / Hr, 1200
After reaching 0 ° C, the temperature was adjusted to 100% hydrogen and the temperature was maintained for 20 hours. Al ₂ O ₃ having an average particle size of 2.0 μm was applied as an annealing separator in a water slurry state, and 25% N ₂ -75% H ₂
In the atmosphere, the temperature is raised to 1075 ° C. at a heating rate of 50 ° C./Hr, held at the temperature for 10 hours, further heated to 1200 ° C. at a heating rate of 50 ° C./Hr, and after reaching 1200 ° C., 1
It was set to 00% hydrogen and kept at this temperature for 20 hours.

Al ₂ O ₃ having an average particle size of 2.0 μm was applied as an annealing separator in a water slurry state, and 25% N ₂ -7
1075 ° C at a heating rate of 50 ° C / Hr in a 5% H ₂ atmosphere
Up to 75% N ₂ − when the temperature is reached.
25% H ₂ and hold at that temperature for 10 hours, then 50
The mixture was heated to 1200 ° C. at a temperature rising rate of ° C./Hr, reached 1200 ° C., adjusted to 100% hydrogen, and kept at that temperature for 20 hours.
Further, for comparison, MgO was applied as an annealing separator in a water slurry state, and was applied in an atmosphere of 25% N ₂ -75% H ₂ for 5 minutes.
The temperature was raised to 1075 ° C. at a heating rate of 0 ° C./Hr, and when the temperature was reached, the annealing atmosphere was set to 75% N ₂ -25% H ₂ , held at that temperature for 10 hours, and further raised to 50 ° C./Hr. 1 at temperature rate
After heating to 200 ° C. and reaching 1200 ° C., the temperature was adjusted to 100% hydrogen and the temperature was maintained for 20 hours.

After completion of the finish annealing, the products produced by the four finish annealing methods were irradiated with a laser beam to perform phosphoric acid-chromic acid tension coating. The characteristics of the obtained product are as shown in Table 5.

[0090]

[Table 5] By holding at 1075 ° C for 10 hours, the magnetic flux density,
It can be seen that the iron loss is further improved. Note that a small amount of glass film was formed on the surface of the material using the MgO water slurry as the annealing separator. Therefore, smoothing was insufficient and magnetic properties were poor.

[0091]

According to the present invention, a grain-oriented electrical steel sheet having a high magnetic flux density and small irregularities on the surface of the steel sheet (which is a mirror surface) which is a factor that obstructs magnetic properties can be easily obtained, and magnetic domains for laser beam irradiation treatment or the like can be obtained. The subdivided, tension-coated treatment provided a magnetic material with extremely low iron loss. In the production of this grain-oriented electrical steel sheet, mirror finishing of the steel sheet is carried out in a normal finish annealing furnace, so that it is extremely easy and its industrial value is enormous.

[Brief description of drawings]

FIG. 1 is a diagram of acid-soluble Al-finish annealing temperature showing a change in inhibitor (acid-soluble Al) of a steel sheet during finish annealing, in which the surface oxide layer is removed after the primary recrystallization annealing. .

Continuation of front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location C22C 38/06 (72) Inventor Yoshiyuki Ushigami 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technical Development Division Within

Claims (9)

[Claims] 1. By weight ratio, Si: 2.0 to 4.8%, acid-soluble Al: 0.008 to 0.05%, N ≤ 0.010%, balance: heat composed of Fe and unavoidable impurities Rolled steel strip,
In the manufacturing process of the grain-oriented silicon steel sheet, which has a final plate pressure by cold rolling once or twice or more with an intervening intermediate annealing, and then is subjected to primary recrystallization annealing, is applied with an annealing separator, and is subjected to finish annealing. After the primary recrystallization annealing, an annealing separator having Al ₂ O ₃ having an average particle size of 0.5 to 10.0 μm as a main component was applied, and then, in a neutral or reducing atmosphere, 5
A method for producing a grain-oriented silicon steel sheet, which comprises performing finish annealing including heating to 920 to 1150 ° C. at a temperature rising rate of 0 ° C./Hr or more and holding the temperature for 5 hours or more. 2. After the primary recrystallization annealing, the oxide film on the surface of the steel sheet produced in the annealing step is removed, and then the average grain size is reduced to 0.
After applying an annealing separator containing Al ₂ O _{3 of 5} to 10.0 μm as a main component, in a neutral or reducing atmosphere at 50 ° C.
/ Hr or more at a heating rate of 920 to 1150 ° C,
The method for producing a grain-oriented silicon steel sheet according to claim 1, wherein a finish annealing is performed, which has a process of holding at that temperature for 5 hours or more. 3. After the primary recrystallization annealing, the steel sheet is subjected to a nitriding treatment in an atmosphere containing ammonia gas, and then an annealing separation containing Al ₂ O ₃ having an average grain size of 0.5 to 10.0 μm as a main component. After applying the agent, in a neutral or reducing atmosphere, 5
2. The method for producing a grain-oriented silicon steel sheet according to claim 1, wherein the finish annealing is performed by heating to 920 to 1150 [deg.] C. at a temperature rising rate of 0 [deg.] C./Hr or more and holding the temperature for 5 hours or more. . 4. After the primary recrystallization annealing, the steel sheet is subjected to a nitriding treatment in an atmosphere containing ammonia and gas, and then the oxide film on the surface of the steel sheet produced in the annealing step is removed to obtain an average grain size of 0.5. After applying an annealing separator having Al ₂ O _{3 of up} to 10.0 μm as a main component, in a neutral or reducing atmosphere,
A method for producing a grain-oriented silicon steel sheet, which comprises performing finish annealing including a process of heating to 920 to 1150 ° C. at a temperature rising rate of 50 ° C./Hr or more and holding at that temperature for 5 hours or more. 5. The method for producing a grain-oriented silicon steel sheet according to claim 2, wherein the means for removing the oxide film on the surface of the steel sheet produced in the primary recrystallization annealing step comprises pickling the steel sheet. 6. The method for removing an oxide film on the surface of a steel sheet produced in the primary recrystallization annealing step, wherein the steel sheet is pickled with a pickling solution containing hydrofluoric acid.
The method for manufacturing the grain-oriented silicon steel sheet according to claim 1. 7. The directional silicon according to claim 1, wherein a water slurry of an annealing separator containing Al ₂ O _{3 of} 0.5 to 10.0 μm as a main component is applied. Steel plate manufacturing method. 8. The process of heating a steel sheet to 920 to 1150 ° C. at a temperature rising rate of 50 ° C./hr or more in the finish annealing step is performed in an atmosphere containing 5% or more of N _2. A method for manufacturing a grain-oriented silicon steel sheet according to claim 1. 9. A steel sheet is heated to 920 to 1150 ° C. at a temperature rising rate of 50 ° C./Hr or more at a temperature of 920 to 1150 ° C., and the atmosphere in the finish annealing step is a neutral or reducing atmosphere. When reaching the area, the atmosphere N
_The method for producing a grain-oriented silicon steel sheet according to any one of claims 1 to 8, wherein the content of ₂ is made higher than the content of N ₂ before that, and the reached temperature is maintained for 5 hours or more.