JP2674927B2 - Method for manufacturing mirror-oriented silicon steel sheet - 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 silicon steel sheet having a high magnetic flux density and extremely low iron loss (hereinafter referred to as a grain-oriented electrical steel sheet). In particular, in the secondary recrystallization step (finish annealing step), no forsterite coating (hereinafter, referred to as glass) is formed on the steel sheet surface, or the steel sheet surface is mirror-finished by thermal etching to complete the same step. Thereafter, treatments such as magnetic domain refinement and tension coating are performed to improve iron loss characteristics.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are frequently used as magnetic iron cores for electrical equipment, and improvements have been repeatedly made to reduce energy loss. As a means for reducing iron loss of grain-oriented electrical steel sheets, a method of irradiating a laser beam to a material surface after finish annealing to impart local strain, thereby subdividing magnetic domains to reduce iron loss is disclosed in, for example, 58-264
No. 05 is disclosed. Further, since the local strain is removed by stress relief annealing (strain relief annealing) after processing which is usually performed, the magnetic domain refining effect disappears.

[0003] This improvement, that is, means for preventing the domain refining effect from disappearing even after stress relieving annealing is disclosed in, for example, Japanese Patent Application Laid-Open No. Sho.
It is disclosed in JP-A-2-8617. In order to further reduce the iron loss value, it is important to remove irregularities (smoothing) on the surface of the base iron that hinder the movement of magnetic domains near the steel sheet surface. The highest level of smoothing is specular. As a method of smoothing (mirror finishing) the material surface after finish annealing,
There are chemical polishing, electrolytic polishing and the like disclosed in JP-A-64-83620.

[0004]

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 the above-mentioned chemical polishing and electrolytic polishing. There is. However, these methods are suitable for producing small specimens and small samples, but have various difficulties for surface mirroring (smoothing) of industrially produced metal strips and the like.

In the chemical method which can be smoothed most, that is, in the chemical polishing, there are environmental problems such as chemical concentration control and wastewater treatment. In the physical method, the surface having an industrially large area is set to the same standard. It is extremely difficult to perform smoothing (mirror finishing) with. An object of the present invention is to eliminate these problems and to provide a method for making the surface of a grain-oriented electrical steel sheet excellent in magnetic properties on an industrial production scale mirror-finished or smooth.

[0006]

SUMMARY OF THE INVENTION In the present invention, the object is to be achieved simultaneously in the finish annealing step. That is, the orientation of the secondary recrystallization is controlled to obtain an extremely high magnetic flux density and to obtain a mirror surface or a smooth surface.

A feature of the present invention is that a mirror surface or a smooth surface is obtained at the time of finish annealing as described above. That is, instead of using the usual annealing separator mainly composed of MgO, Si ₂ mainly composed of Al ₂ O ₃ is used.
Using a substance that does not easily react with O 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, without forming a glass (forsterite) coating on the steel sheet surface, It is characterized in that it is secondarily recrystallized in the exposed state and at the same time, the metal surface is mirror-finished or smoothed by thermal etching.

[0008] The means is to anneal the hot-rolled silicon steel strip as required, and then perform cold rolling once or twice or more with intervening intermediate annealing to obtain a predetermined plate thickness, and then perform primary recrystallization annealing. In the method for producing a grain-oriented silicon steel sheet, which is followed by applying an annealing separating agent and performing finish annealing, after performing the primary recrystallization annealing,
An annealing separator containing l ₂ O ₃ (alumina) as a main component is applied to the steel sheet in a state of being dispersed in an organic solvent, and a neutral or
Finish annealing in a reducing atmosphere.

After the primary recrystallization annealing, the oxide film on the surface of the steel sheet produced in the annealing step is removed to remove Al ₂ O ₃ (alumina).
Is applied to the steel sheet in a state of being dispersed in an organic solvent, and is subjected to finish annealing in a neutral or reducing atmosphere.

Further, after the primary recrystallization annealing, nitriding treatment with ammonia is performed to strengthen the inhibitor, and thereafter, the annealing separator having Al ₂ O ₃ (alumina) as a main component is dispersed in an organic solvent. It is applied to a steel sheet and finish-annealed in a neutral or reducing atmosphere.

Further, after the primary recrystallization annealing, nitriding treatment with ammonia is performed, and thereafter, the oxide film on the surface of the steel sheet generated in the primary recrystallization annealing step is removed, and annealing separation containing Al ₂ O ₃ (alumina) as a main component is carried out. The agent is applied to the steel sheet in a state of being dispersed in an organic solvent, and finish annealing is performed in a neutral or reducing atmosphere.

Further, the component of the silicon hot rolled steel strip is Si: 2.0
-4.8% by weight, acid-soluble Al: 0.008-0.05
It is very effective to make the weight percent, N ≦ 0.010 wt%, balance Fe and inevitable impurities.

It is also effective to use an acid pickling method for removing the oxide film on the surface of the steel sheet, and particularly to pickle with an acid mixed with hydrofluoric acid. When the annealing separator containing Al ₂ O ₃ (alumina) as a main component is dispersed in an organic solvent, it can be applied in the same manner as a normal water slurry containing MgO as a main component.

Alcohols, ketones and esters are particularly effective as the organic solvent, and they may be used in a mixture.

Note that, the inhibitor strengthening with ammonia after the primary recrystallization annealing and the nitrogen partial pressure operation in the finish annealing atmosphere are extremely effective when the cold-rolled steel sheet contains acid-soluble Al, but when it does not contain acid-soluble Al. , Its effect is small. However, nitrogen acts on the unavoidable nitride-forming element, increasing the amount of precipitates and strengthening the inhibitor.

The term "thermal etching" refers to a phenomenon in which when a metal is exposed to a neutral or reducing atmosphere at a high temperature, atoms on the surface of the metal make a thermal motion to reduce and smooth the unevenness.

Hereinafter, the present invention will be described in detail. The present inventors have investigated in detail the rate-limiting process of inhibitor deterioration during finish annealing.When Al is contained in the hot-rolled steel sheet component, the oxidation process of Al at the steel sheet interface is the largest factor, and primary recrystallization annealing is performed. It has been found that the oxidized layer on the surface of the steel sheet, which sometimes occurs, greatly contributes to the deterioration of the inhibitor.

On the other hand, when the hot-rolled steel sheet component does not contain Al but contains MnS, MnSe, MnSb, etc. as an inhibitor, the inhibitor strength increases due to dissolution of the precipitate due to temperature increase or coarsening of the precipitate, so-called Ostwald growth. It turned out to deteriorate. Therefore, the influence of the steel sheet surface (interface) on the secondary recrystallization is not so large, and even if the oxide layer on the steel sheet surface generated during the primary recrystallization annealing is removed or not, there is no great influence.

First, the case where the hot-rolled steel strip component contains Al will be described. The present inventors investigated in detail the rate-limiting process of inhibitor deterioration during finish annealing, and found that the oxidation process of Al at the steel sheet interface was the largest factor, and the oxide layer on the steel sheet surface generated during primary recrystallization annealing caused the deterioration of the inhibitor. Was found to be heavily involved.

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,
1 hot rolled steel strip consisting of the balance Fe and unavoidable impurities
It was annealed at 100 ° C. for 2 minutes and then cold rolled to a thickness of 0.23 mm. These cold-rolled sheets were annealed at 800 ° C. for 2 minutes in an annealing furnace in a humid water atmosphere to serve as decarburization, and primary recrystallized. Next, nitriding treatment is performed in an ammonia atmosphere to stabilize the secondary recrystallization, and the total nitrogen content is 180 ppm.
And strengthened the inhibitor.

Then, Al ₂ O was added to the two materials as they were and after being pickled with a mixed solution of 0.5% hydrofluoric acid and 5% sulfuric acid.
₃ was applied electrostatically, and was subjected to finish annealing in a 100% H ₂ atmosphere while maintaining a heating rate of 15 ° C./Hr.

Inhibitors during finish annealing (AlN,
When (Al, Si) N, etc. were examined, as shown in FIG. 1, the material having an oxide layer generated on the steel sheet surface during the primary recrystallization annealing had a lower inhibitor strength than the material having no oxide layer. It was found that it deteriorated quickly. That is, if the oxide layer generated on the steel sheet surface during the primary recrystallization annealing is removed,
High inhibitor strength can be maintained up to high temperatures.

The acid-soluble Al in the steel sheet removes oxygen from the oxide layer mainly composed of SiO ₂ during finish annealing and Al ₂ O ₃
And so on and precipitates in the oxide layer. Therefore, the acid-soluble Al in the steel sheet decreases. In addition, in FIG. 1, the acid-soluble Al concentration in steel is shown as the inhibitor strength.
Since a compound (precipitate) such as AlN or (Al, Si) N is formed to serve as an inhibitor, the amount of acid-soluble Al may be considered as an index indicating inhibitor strength.

Further, the present inventors have conducted a detailed investigation on the rate-determining process of inhibitor deterioration. As a result, it has been found that, besides the above-mentioned oxidation of Al at the steel sheet interface, it is influenced by the nitrogen content in the steel and the nitrogen content in the annealing atmosphere. 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 that of nitrogen contained in the steel from the beginning.

The nitrogen in the steel and the nitrogen in the annealing atmosphere are Al
Oxidation of Al is suppressed in order to increase the number of precipitates such as N to fix Al and reduce the movement of Al to the steel sheet interface.

Therefore, acid-soluble Al in steel during finish annealing
As for the quantity, the higher the nitrogen partial pressure, the less the deterioration, and the higher the temperature, the stronger the inhibitor.

In order to obtain a high magnetic flux density, which is one of the gist of the present invention, it is preferable that the inhibitor is strong, but it is desirable that the inhibitor be kept strong and constant. This is because only crystals with good orientation (GOSS grains) are grown from the start to the end of the secondary recrystallization, and if the inhibitor is weakened from the start to the end of the secondary recrystallization, it grows to grains with a poor orientation. The magnetic flux density of the steel sheet decreases.

The solubility of AlN, which is an inhibitor, naturally increases with an increase in the temperature of the steel sheet, and the inhibitor naturally deteriorates. As this measure, it is desirable to increase the partial pressure of nitrogen as the temperature rises to increase the amount of nitrogen in the steel sheet and to keep AlN as a precipitate constant.
However, in order to obtain a mirror surface, which is one of the gist of the present invention, the nitrogen partial pressure must not be too high.

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 in that the inhibitor is secondarily recrystallized at a constant strength. As described above, the solubility of AlN does not change when kept at a constant temperature, but the acid-soluble Al
Oxygen or in the atmosphere takes oxygen from the oxide of oxygen affinity smaller element than Al of the steel sheet surface, Al ₂ O ₃
And the inhibitor deteriorates. Therefore, also in this case, it is necessary to suppress the dissolution of AlN by increasing the nitrogen partial pressure, and to suppress the decrease in acid-soluble Al.

Next, the case where the hot-rolled steel sheet does not contain Al will be described. As described above, in a silicon steel sheet in which the hot-rolled steel sheet component does not contain Al, MnS, MnS is added by adding S, Se, Te, Sb, etc. as an inhibitor.
Usually, e, MnTe, MnSb, and the like are precipitated and used as an inhibitor.

These precipitates do not deteriorate the inhibitor due to desorption from the steel plate interface unlike Al.
The inhibitor effect strength is degraded by a decrease in precipitates due to an increase in solubility due to an increase in the temperature of the steel sheet, or an increase in the average particle size of the precipitates due to Ostwald growth of the precipitates. Therefore, after the primary recrystallization annealing, the behavior of the inhibitor is almost constant irrespective of the presence of the oxide film on the steel sheet surface generated by the annealing.

Si: 3.2% by weight, N: 0.008% by weight, Mn: 0.08% by weight, S: 0.027% by weight,
C: A silicon hot rolled steel strip composed of 0.05% by weight, the balance of Fe and unavoidable impurities was cold-rolled to 0.23 mm and, similarly to the above, 80% in an annealing furnace in a wet water atmosphere for decarburization.
Annealed at 0 ° C. for 2 minutes for primary recrystallization.

Thereafter, Al ₂ O was added to the two materials as they were and after pickling with a mixed solution of 0.5% hydrofluoric acid and 5% sulfuric acid.
₃ was applied electrostatically, and was subjected to finish annealing in a 100% H ₂ atmosphere while maintaining a heating rate of 15 ° C./Hr. FIG. 2 was obtained by analyzing S during the finish annealing. It can be seen that S does not decrease up to a relatively high temperature with or without pickling.

However, this does not mean that the inhibitor strengths are both strong up to high temperatures. The reason is as described above.
It is coarsening due to dissolution of the precipitate and Ostwald growth of the precipitate.

The steel component in the present invention is Si: 2.0 to
4.8% by weight, acid-soluble Al, Mn, S, Se, Sb, P, B, Sn, Bi, N
One or more of b, Ti, Mo, Cu and the like are added.

[0036] Si is important in increasing electric resistance and reducing iron loss, but if it exceeds 4.8%, it is liable to crack during cold rolling. On the other hand, if it is less than 2.0%, there is a problem in lowering electric resistance and lowering iron loss.

Next, the constituent elements of the inhibitor will be described. Acid-soluble Al is important as an inhibitor constituent element and combines with nitrogen, silicon, etc. to form AlN, (Al, S
i) It forms precipitates such as N and plays a role of an inhibitor.
In terms of inhibitor strength, that is, the range in which the magnetic flux density is increased, it is 0.008 to 0.06% 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
One type or two or more types are added in the range of 1 to 0.10% by weight. Further, Sn, Bi, Nb, Ti, P, Mo,
Cu or the like is used as an inhibitor constituent or an auxiliary element. In addition, carbon is desirably 0.085% by weight or less. The inventors have investigated in detail the relationship between the steel sheet surface state from the application of the annealing separator to the start of the temperature rise of the finish annealing and the steel sheet surface state after the completion of the finish annealing and found the following results. That is, if rust is generated on the steel sheet surface from the application of the annealing separator to the start of the temperature rise of the finish annealing, the smoothness (mirror surface) of the steel sheet after the finish annealing is deteriorated. This rust is generally so-called red rust, which is reddish with trivalent iron hydroxide.
In particular, it tends to appear in the case of water slurry application.

The rust on the surface of the steel sheet is
It is presumed that it is reduced on the surface of the steel sheet and scattered on the surface of the steel sheet in the form of dots, and the smoothing is insufficient in the normal finish annealing time, and the surface smoothness of the product (after the finish annealing) is deteriorated.

FIG. 3 shows the results obtained by finish-annealing a steel sheet having rust on the surface of the steel sheet before finish annealing and a steel sheet having no rust, and measuring the surface of the steel sheet after annealing with a stylus roughness meter. . The steel sheet without rust before finish annealing is extremely smooth. As described above, the improvement in the smoothness improves the magnetic characteristics, that is, the iron loss characteristics.

The inventors examined a method in which rust did not occur on the surface of the steel sheet from the application of the annealing separator to the start of the temperature rise in the final annealing, and the annealing separator mainly composed of Al ₂ O ₃ (alumina) was used as an organic solvent. It has been found that it is effective to disperse and apply it to This is because the annealing separator can be applied without contacting the steel sheet with water that causes rust, and the organic solvent used here must have as little water as possible. In addition, if an organic solvent having a low boiling point is used, drying can be performed quickly.

Powder coating, for example, electrostatic coating is also excellent as a method for applying an annealing separating agent without generating rust, but it is not necessary to apply a commonly used annealing separating agent mainly composed of MgO. In comparison, there are inconveniences such as complexity of the coating device, equipment cost, and deterioration of working environment due to powder scattering. The present invention has been achieved by studying the application of the same method as the MgO aqueous slurry application which is usually performed.

The organic solvent used includes alkanes such as hexane, heptane and octane, those having a benzene ring such as benzene, xylene and toluene, alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol and butyl alcohol, acetone, There are ketones such as methyl ethyl ketone and methyl butyl ketone, ethers such as methyl ethyl ether and diethyl ether, esters such as methyl acetate and ethyl acetate, and halogen derivatives thereof can also be used. Further, there is no problem even if these are mixed and used.

Among them, alcohols, ketones and esters were better in dispersion of the annealing separator alumina than other solvents. It should be noted that there is no problem even if a small amount of a substance that hardly reacts with silica, such as CaO, is added to the annealing separator mainly containing alumina.

The implementation conditions will be described below. The oxide layer formed on the steel sheet surface during primary recrystallization annealing affects the following two factors during finish annealing. That is, as described above, the inhibitor strength is weakened, and a sufficient magnetic flux density cannot be obtained.
Insufficient smoothness of the surface of the product adversely affects the magnetic properties, making it difficult to obtain the ultimate magnetic properties. Therefore, in order to obtain the ultimate magnetic properties, it is desirable to remove the oxide layer formed on the steel sheet surface during the primary recrystallization annealing. As a method for removing, mechanical polishing, for example, brush polishing, sandpaper polishing, grinding, etc. are effective for this purpose, but they are not practical due to various industrial difficulties.

The present inventors have found that the pickling method is extremely effective. This is because a continuous pickling line for hot-rolled steel strips or steel sheets has already been put to practical use. The pickling solution (pickling solution) includes hydrochloric acid, sulfuric acid,
Although a mineral acid such as nitric acid is effective, since the oxide layer formed on the surface of the steel sheet is an oxide mainly composed of SiO ₂ , it is difficult to pickle it with only a mineral acid such as hydrochloric acid, sulfuric acid or nitric acid. When hydrofluoric acid is mixed with these acids, the oxide layer can be removed very efficiently, that is, at a high speed.

When a nitride is used as the inhibitor, it is necessary to strengthen the inhibitor by performing a nitriding treatment with ammonia after the primary recrystallization annealing and before the finish annealing.
It is valid. This is because the inhibitor strength at the time of completion of primary recrystallization is insufficient for secondary recrystallization, and even if the inhibitor is strengthened or deterioration is prevented by increasing the partial pressure of nitrogen during finish annealing. Sometimes we can't get enough inhibitors. Therefore, generally, the reinforcement of the inhibitor by the ammonia treatment improves the magnetic properties.

Nitrogen gas was added at 5% in the annealing atmosphere at the time of temperature increase in order to secure an inhibitor necessary for the progress of secondary recrystallization.
It is desirable that the hydrogen gas be contained in an amount of at least
% May be used. If the nitrogen gas content is less than 5%, the effect is not strong for strengthening the inhibitor or preventing deterioration. If nitride is not used as the inhibitor, the effect of nitrogen partial pressure is weak. Note that the neutral or reducing atmosphere is a neutral or reducing atmosphere for the oxidation and reduction of silicon with one or a mixture of two or more of inert gases such as nitrogen, oxygen, moisture, hydrogen, and argon. Gas composition. In general, nitrogen and hydrogen gas are used in the finish annealing of the magnetic steel sheet, so that the combination of these two 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 is used to prevent reduction of Al in steel and to oxidize silicon in steel so as not to produce or increase SiO ₂ on the surface. After the completion of the secondary recrystallization, the hydrogen concentration was increased to complete the purification and the mirror finishing of the steel plate surface.
It is extremely effective to keep the temperature at around ° C for several hours.

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. At a heating rate of less than 15 ° C./Hr, the deterioration of the inhibitor was remarkable, and the inhibitor required at the time of secondary recrystallization was not sufficiently secured, so that sufficient secondary recrystallization could not be obtained. From the viewpoint of obtaining a high magnetic flux density, which is one of the gist 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, Mn, S, Se, Sb, P, B,
Molten steel to which one or more kinds of Sn, Bi, Nb, Ti, Mo, Cu, etc. are added is subjected to a normal process or continuous casting to obtain a hot rolled steel sheet or a hot rolled steel strip. This hot-rolled steel sheet or hot-rolled steel strip is annealed in a temperature range of 750 to 1200 ° C. for 30 seconds to 30 minutes to improve the magnetic flux density. Subsequently, these hot-rolled steel sheets or strips are cold-rolled.

The cold rolling is carried out at a final cold rolling rate of 80% or more as disclosed in JP-B-40-15644. The material after cold rolling is usually subjected to primary recrystallization annealing in a humid water atmosphere in a temperature range of 750 to 900 ° C. in order to remove carbon in steel. At this time, an oxide layer is formed on the steel sheet surface together with decarburization and primary recrystallization.

This oxide layer forms a so-called internal oxide layer, which depends on the degree of water content (usually expressed as a dew point) in a wet water atmosphere, that is, an atmosphere containing water.
The thickness is up to 6.0 μm, and SiO ₂ is mainly present 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 oxide layer on the surface of the steel sheet or steel strip after primary recrystallization is removed when pursuing the ultimate magnetic properties.

If the magnetic properties may be slightly deteriorated as described above, this step is omitted. This choice is made in terms of cost and characteristics. The method of removing the oxide film includes physical and chemical methods as described above, but is generally performed by pickling. When a nitride inhibitor is used, it is extremely effective to improve the magnetic flux density by performing a nitriding treatment with ammonia for strengthening the inhibitor before removing the oxide layer on the surface of the steel sheet.

The primary recrystallized plate from which the oxide layer on the surface has been removed is coated with an annealing separator containing alumina as a main component as an organic solvent slurry and placed in a finishing annealing furnace. The atmosphere at the time of raising the temperature of the finish annealing is neutral or reducing. Mixing an inert gas such as argon or helium for adjusting the partial pressure of nitrogen does not cause any problem. After the completion of the secondary recrystallization, it is kept at high temperature (about 1200 ° C.) with 100% hydrogen for purification. After finishing annealing, a magnetic domain refinement treatment such as laser beam irradiation is performed, and a tension coating treatment is further performed.

[0056]

【Example】

Example 1 Si: 3.25% by weight, acid-soluble Al: 0.023% by weight, N: 0.009% by weight, Mn: 0.07% by weight,
S: 0.015% by weight, C: 0.08% by weight, Se:
0.015% by weight, Sn: 0.13% by weight, Cu: 0.
A hot-rolled silicon steel strip consisting of 0.7% by weight, the balance being Fe and unavoidable impurities was annealed at 1120 ° C. for 2 minutes and then cold-rolled to a thickness of 0.20 mm. These cold-rolled sheets were annealed at 850 ° C. for 2 minutes in an annealing furnace in a wet water atmosphere (dew point: 65 ° C.) for the purpose of decarburization, and subjected to primary recrystallization. afterwards,
The product was pickled with a mixed solution of 0.5% hydrofluoric acid and 5% sulfuric acid.

An annealing separator: Al ₂ O ₃ (alumina) was suspended in this material in acetone and applied to the steel sheet with a roll coater. For comparison, an Al ₂ O ₃ (alumina): 100% annealing separator was applied in a water slurry state.

These two kinds of materials were heated to 1200 ° C.
The temperature was raised in a 5% N ₂ -75% H ₂ atmosphere while maintaining the temperature rising rate of 15 ° C./Hr, and after reaching 1200 ° C., 100% hydrogen was obtained and the temperature was maintained for 20 hours. After finishing annealing,
Irradiation with a laser beam was performed for phosphoric acid-chromic acid-based tension coating treatment. The characteristics of the obtained product are shown in Table 1.
It is as follows. The surface of the product according to the present invention has improved smoothness and reduced iron loss.

[0059]

[Table 1]

The surface condition after the finish annealing of the comparative example is shown in the table as a smooth surface (mirror surface). The surface shows a metallic color but has a dull luster and is a so-called dull surface. It was

Example 2 Si: 3.22% by weight, acid-soluble Al: 0.029% by weight, N: 0.008% by weight, Mn: 0.13% by weight,
S: 0.007% by weight, C: 0.05% by weight, balance Fe
And hot rolled steel strip consisting of unavoidable impurities at 1100 ° C
And then 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, nitriding treatment was performed in an ammonia atmosphere to make the total nitrogen amount 190 ppm, and the inhibitor was strengthened.

Thereafter, the oxide layer formed on the surface of the steel sheet was removed with sulfuric acid mixed with hydrofluoric acid, and the annealing separator: Al ₂
O ₃ (alumina) was suspended in ethyl alcohol and applied to the steel sheet with a roll coater. The annealing separator: Al ₂ O ₃ (alumina) was suspended in ethyl alcohol and the steel sheet was rolled with a roll coater. Al ₂ O ₃ (alumina): 100% annealing separator was applied in the state of water slurry.

These three kinds of materials are heated to 1200 ° C., and 2
The temperature was raised in a 5% N ₂ -75% H ₂ atmosphere while maintaining the temperature rising rate of 30 ° C./Hr, and after reaching 1200 ° C., 100% hydrogen was obtained and the temperature was maintained for 20 hours. After finishing annealing,
Irradiation with a laser beam was performed for phosphoric acid-chromic acid-based tension coating treatment. The characteristics of the obtained product are shown in Table 2.
It is as follows.

[0064]

[Table 2]

The surface condition after the finish annealing of the comparative example is shown in the table as a smooth surface (mirror surface). The surface shows a metallic color but has a dull gloss, which is a so-called dull surface. It was

Example 3 The primary recrystallized plate of Example 2 was subjected to a nitriding treatment in an ammonia atmosphere in order to stabilize the secondary recrystallization,
The total nitrogen content was set to 210 ppm, and the inhibitor was strengthened.

Thereafter, the oxide layer formed on the surface of the steel sheet was removed with hydrochloric acid, and an annealing separator: Al ₂ O ₃ (alumina) was used.
Suspended in methyl alcohol and applied to the steel sheet with a roll coater, and heated to 1200 ° C. in a 100% H ₂ atmosphere,
Annealing Separator: Al ₂ O ₃ (alumina) is suspended in methyl alcohol and applied to the steel sheet with a roll coater,
In a 75% N ₂ -25% H ₂ atmosphere up to 1200 ° C., and for comparison, an Al ₂ O ₃ (alumina): 100% annealing separator is applied in a water slurry state, and up to 1200 ° C. in a 100% H ₂ atmosphere. Then, the temperature was raised while maintaining the temperature rising rate of 30 ° C./Hr, and after reaching 1200 ° C., hydrogen was set to 100%, and the temperature was maintained for 20 hours.

After the finish annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The properties of the obtained product are as shown in Table 3.

[0069]

[Table 3]

The surface condition after finish annealing of the comparative example is shown in the table as a smooth surface (mirror surface). The surface shows a metallic color but has a dull gloss, which is a so-called dull surface. It was

[0071]

According to the present invention, a grain-oriented electrical steel sheet having a high magnetic flux density and a small irregularity (a mirror surface) on the steel sheet surface, which is a factor inhibiting magnetic properties, can be easily obtained. The subdivision and tension coating treatment provided a magnetic material with extremely low iron loss. In the production of the grain-oriented electrical steel sheet, the mirror finishing treatment of the steel sheet is performed in a normal finish annealing furnace, so that it is extremely easy and has great industrial value.

[Brief description of the drawings]

FIG. 1 is a chart showing a change in an inhibitor (acid-soluble Al) of a steel sheet during finish annealing.

FIG. 2 is a chart showing a change in S of a steel sheet during finish annealing of a steel sheet containing S without containing acid-soluble Al.

FIGS. 3 (a) and 3 (b) are measurement diagrams of an optical stylus type roughness meter on the surface of a steel plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Ushigami 20-1 Shintomi, Futtsu City Within Nippon Steel Co., Ltd. Technology Development Division (56) References JP-A-55-89423 (JP, A) JP-A-SHO 54-106009 (JP, A) JP 63-286584 (JP, A) JP 2-107722 (JP, A) JP 2-77525 (JP, A)

Claims (8)

(57) [Claims] 1. A silicon hot rolled steel strip is annealed or annealed.
Without blunting, cold rolling is performed once or twice or more with an intermediate anneal sandwiched to obtain a predetermined plate thickness, then primary recrystallization anneal, then an annealing separator is applied, and final anneal is performed. In the method for producing a grain-oriented silicon steel sheet, after primary recrystallization annealing,
The oxide film on the surface of the steel sheet generated in the annealing step is removed, and Al ₂
A method for producing a mirror-oriented silicon steel sheet, characterized in that an annealing separator containing O ₃ (alumina) as a main component is applied to the steel sheet in a state of being dispersed in an organic solvent, and finish annealing is performed in a neutral or reducing atmosphere. . 2. Si: 2.0 to 4.8% by weight, acid-soluble Al: 0.008 to 0.05% by weight, N ≦ 0.010% by weight, silicon hot rolling consisting of balance Fe and unavoidable impurities the steel strip,
After annealing or without annealing, cold rolling is performed once or two or more times with intermediate annealing sandwiched to obtain a predetermined plate thickness,
Then after primary recrystallization annealing, the annealing separator was applied, in the method of manufacturing grain-oriented silicon steel sheet subjected to finish annealing, the oxide film is removed in the primary after recrystallization annealing, the steel sheet surface occurring in said annealing step, An annealing separator having Al ₂ O ₃ (alumina) as a main component is applied to the steel sheet in a state of being dispersed in an organic solvent, and finish annealing is performed in a neutral or reducing atmosphere. Production method. 3. A silicon hot rolled steel strip is annealed or annealed.
Without blunting, cold rolling is performed once or twice or more with an intermediate anneal sandwiched to obtain a predetermined plate thickness, then primary recrystallization anneal, then an annealing separator is applied, and final anneal is performed. In the method for producing a grain-oriented silicon steel sheet, after primary recrystallization annealing,
A nitridation treatment with ammonia is performed, and thereafter, an oxide film on the steel sheet surface generated in the primary recrystallization annealing step is removed, and Al ₂
A method for producing a mirror-oriented silicon steel sheet, characterized in that an annealing separator containing O ₃ (alumina) as a main component is applied to the steel sheet in a state of being dispersed in an organic solvent, and finish annealing is performed in a neutral or reducing atmosphere. . 4. Hot-rolled silicon comprising Si: 2.0 to 4.8% by weight, acid-soluble Al: 0.008 to 0.05% by weight, N ≦ 0.010% by weight, balance Fe and unavoidable impurities Steel strip ,
After annealing or without annealing, cold rolling is performed once or two or more times with intermediate annealing sandwiched to obtain a predetermined plate thickness,
Then, after performing the primary recrystallization annealing, in the method for producing a grain-oriented silicon steel sheet, which is applied with an annealing separator and is subjected to finish annealing, after the primary recrystallization annealing, a nitriding treatment with ammonia is performed, and then the primary recrystallization annealing is performed. The oxide film on the surface of the steel sheet generated in the process is removed, and an annealing separator containing Al ₂ O ₃ (alumina) as a main component is applied to the steel sheet in a state of being dispersed in an organic solvent, and finish annealing is performed in a neutral or reducing atmosphere. A method for manufacturing a mirror-oriented grain-oriented silicon steel sheet. 5. The steel surface preparation method of claims 1 to mirror oriented silicon steel sheet <br/> according to any one of the four methods of removing the oxide film, characterized in that the pickling. 6. A method for removing the oxide film on the steel sheet surface of claim 1, characterized in that the pickling with an acid mixed with hydrofluoric acid
The method for producing a mirror-oriented silicon steel sheet according to any one of Ishishi. 7. The organic Solvent alcohols, mirror oriented silicon steel sheet according to any one of claims 1, characterized in that with one or a mixture of two or more ketones and esters 6 Manufacturing method. 8. The process for producing a mirror oriented silicon steel sheet according to any one of claims 1 to 7, characterized in that the atmosphere in N ₂ at Atsushi Nobori of 5% or more.