JP2706039B2 - 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 the secondary recrystallization step (finish annealing step), a high magnetic flux density is obtained, and at the same time, the steel sheet surface is mirror-finished by thermal etching without forming a forsterite film (hereinafter, referred to as a glass film) on the steel sheet surface. To complete the process, then
The purpose of the present invention is to provide a magnetic material having extremely low iron loss by performing processes such as magnetic domain segmentation and tension coating to reduce energy loss.

[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. A means for improving this, that is, means for preventing the domain refining effect from disappearing even by stress relief annealing, is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-8617.

In order to further reduce the iron loss value, it is important to remove unevenness (smoothing) on the surface of the ground iron that hinders the movement of magnetic domains near the steel sheet surface. The highest level of smoothing is specular. As a method for smoothing (mirror finishing) the material surface after the finish annealing, there are chemical polishing, electrolytic polishing and the like disclosed in JP-A-64-83620. Further, Japanese Patent Application Laid-Open No. 3-110627 and the like disclose that a mirror-finished surface can be obtained at the same time as secondary recrystallization by using an annealing separating agent such as alumina which is difficult to react with silica.

[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 that can be smoothed most, that is, in chemical polishing, environmental problems such as chemical concentration control and wastewater treatment, and in the physical method, industrially large surfaces are smoothed on the same basis. (Mirroring) is extremely difficult.

[0005] An object of the present invention is to eliminate these problems and to provide a method for 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 for mirroring or smoothing. In the present invention, the purpose 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.

[0006]

A feature of the present invention is that a mirror surface or a smooth surface is obtained with a high magnetic flux density at the time of finish annealing. Without using the usual annealing separator mainly composed of MgO, the S
The substance which hardly reacts with iO ₂ is converted into an annealing separator, that is, S
An annealing separator mainly containing one or more of iO ₂ , ZrO ₂ , BaO, CaO, SrO and forsterite (Mg ₂ SiO ₄ ) is applied and finish annealing is performed. As a result, a grain-oriented electrical steel sheet having a high magnetic flux density is obtained, and at the same time, the glass (forsterite) film is not formed on the surface of the steel sheet, and the metal surface is secondarily recrystallized while the metal surface is exposed. Thereby, the metal surface can be mirror-finished or smoothed.

[0007] The means, after annealing the hot rolled silicon steel strip,
Alternatively, without annealing, cold rolling is performed once or twice or more with intermediate annealing in between to obtain a final sheet thickness, then primary recrystallization annealing is performed, an annealing separator is applied and dried, and final annealing is performed. In the method for producing a grain-oriented silicon steel sheet to be applied, after the primary recrystallization annealing, the oxide layer on the surface of the steel sheet
From 0.03 g / m ² to 0.30 g / m ² , and Al ₂ O ₃ , SiO ₂ , ZrO ₂ , BaO, Ca
An annealing separator containing one or more of O, SrO and forsterite as a main component is applied to the steel sheet, dried and finish-annealed in a neutral or reducing atmosphere.

Further, the present invention relates to a composition comprising: 2.0 to 4.8% by weight of Si; 0.008 to 0.05% by weight of acid-soluble Al;
After annealing or not annealing a silicon hot rolled steel strip consisting of 0.010% by weight, balance Fe and unavoidable impurities
Then, cold rolling is performed l times or two or more times with intermediate annealing therebetween to obtain the final sheet thickness, and then, after performing primary recrystallization annealing,
In a method for producing a grain-oriented silicon steel sheet to which an annealing separator is applied, dried and subjected to finish annealing, after primary recrystallization annealing, an oxide layer on the surface of the steel sheet has an oxygen content of 0.03 g / m ² per steel sheet piece surface.
Above, it was removed to 0.30 g / m ² or less, and Al ₂ O ₃ ,
An annealing separator containing one or more of SiO ₂ , ZrO ₂ , BaO, CaO, SrO and forsterite as a main component is applied to the steel sheet, dried and finish-annealed in a neutral or reducing atmosphere. .

Further, the present invention relates to a method in which a silicon hot-rolled steel strip is subjected to 1 or intermediate annealing after annealing or without annealing.
Cold rolling more than once, to the final sheet thickness, then after performing the primary recrystallization annealing, applying and drying an annealing separator, and performing a finish annealing in the method for producing a directional silicon steel sheet, after the primary recrystallization annealing Then, nitriding treatment with ammonia is performed, and thereafter, an oxidized layer on the surface of the steel sheet is reduced to an oxygen amount of 0.
Removed to not less than 03 g / m ^{2 and not} more than 0.30 g / m ² ,
Al ₂ O ₃ , SiO ₂ , ZrO ₂ , BaO, CaO, S
An annealing separator containing at least one of rO and forsterite as a main component is applied to the steel sheet, dried and finish-annealed in a neutral or reducing atmosphere.

Further, the present invention relates to Si: 2.0 to 4.8 weight.
%, Acid-soluble Al: 0.008 to 0.05% by weight, N ≦
0.010% by weight, the balance being Fe and unavoidable impurities.
After annealing the hot rolled silicon steel stripOr without annealing
ToCold rolling for 1 or 2 times or two or more times with intermediate annealing
After the final sheet thickness, and after performing the primary recrystallization annealing,
Directional silicon coated with an annealing separator, dried and finish-annealed
Manufacture of steel sheetMethodAfter the primary recrystallization annealing,
A nitriding treatment, followed by an oxide layer on the steel sheet surface.
The amount of oxygen per steel sheet surfaceIs 0.03 g / m ^Two that's all,
0.30 g / m^TwoRemoved to below_TwoO_Three, SiO
_Two, ZrO_Two, BaO, CaO, SrO and forster
Annealing separation with one or more types of light as main components
The agent is applied to the steel sheet and dried, and in a neutral or reducing atmosphere.
This is finish annealing. Here, the oxide layer on the steel sheet surface
Pickling should be used as a method for removing
It is extremely effective to pickle with acid. Also, magnetic flux density
From the point of improvement, N_Two5% or more
It is also effective.

The surface condition referred to as a mirror surface here satisfies the following conditions. That is, when it has a metallic luster in appearance, it has little irregular reflection of light and no haze, and when it is magnetism specific, the magnetic flux density (B ₈ ) is high. In other words, it means that there is no foreign matter other than metals such as oxides and nitrides on the steel sheet surface. Further, what is referred to as a smooth surface (mirror surface) is a surface which shows a metallic color but has a dull luster and is so-called dull. When the surface profile is measured with a surface roughness meter, the profile of the surface, called the mirror surface, is smooth, the profile of the surface, called the smooth surface, becomes rougher, and the roughness is further increased on the surface that has lost metallic luster. .

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. oxide layer of the resulting steel sheet surface when it was found that they are largely responsible for the degradation of the inhibitor. On the other hand, when the hot-rolled steel sheet component does not contain Al and contains MnS, MnSe, MnSb, etc. as inhibitors,
It was found that the inhibitor strength was deteriorated due to the dissolution of the precipitate due to the temperature rise or the coarsening of the precipitate, so-called Ostwald growth. Thus, not so large impact surface of the steel sheet for secondary recrystallization (interface), no significant effect or may not remove the oxide layer of the steel sheet produced during the primary recrystallization annealing.

First, the case where the hot-rolled steel strip component contains Al will be described. The present inventors have was investigate the rate-determining step of the inhibitor degradation during finish annealing, the largest factor oxidation process of Al in the steel sheet surface oxide layer is an inhibitor deterioration of the steel sheet surface occurring during the primary recrystallization annealing Was found to be heavily involved. Si: 3.3% by weight, acid-soluble Al: 0.028% by weight, N: 0.008
After annealing a hot-rolled silicon steel strip composed of 0.1% by weight, Mn: 0.14% by weight, S: 0.007% by weight, C: 0.05% by weight, balance Fe and inevitable impurities at 1100 ° C. for 2 minutes, Cold-rolled to a thickness of 0.23 mm. These cold-rolled sheets were subjected to an annealing furnace in a wet water atmosphere for decarburization.
Annealed at 0 ° C. for 2 minutes for primary recrystallization.

Next, in order to stabilize the secondary recrystallization, a nitriding treatment is performed in an ammonia atmosphere to reduce the total nitrogen amount to 180 pp.
m and strengthened the inhibitor. Thereafter, as it is (0.85 g / m ² per oxygen content per side),
Al ₂ O ₃ was electrostatically applied to two kinds of materials pickled with a mixed solution of 5% hydrofluoric acid and 5% sulfuric acid (0.04 g / m ² per one surface of oxygen), and 15% in a 100% H ₂ atmosphere. Finish annealing was performed while maintaining the heating rate of ° C / Hr.

Inhibitor (AlN,
(Al, Si) N, etc.), as shown in FIG. 1, as shown in FIG. 1, a material having an oxide layer formed on the steel sheet surface during primary recrystallization annealing has a faster inhibitor strength than a material having no oxide layer. I found out. That is, if the oxide layer generated on the steel sheet surface during the primary recrystallization annealing is removed, strong 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 the finish annealing and becomes Al ₂ O ₃ or the like and precipitates in the oxide layer. Therefore, the acid-soluble Al in the steel sheet decreases. In FIG. 1, the acid-soluble Al concentration in steel is shown as the inhibitor strength, but Al is AlN, (A
Since a compound (precipitate) such as (1, Si) N is formed to serve as an inhibitor, the amount of acid-soluble Al may be considered as an index indicating the 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 in addition to the above-mentioned oxidation of Al at the steel sheet interface, it is influenced by nitrogen in steel and the amount of nitrogen in an 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 the nitrogen contained in the steel from the beginning. Nitrogen in steel and nitrogen in the annealing atmosphere increase the amount of precipitates such as AlN to fix Al and reduce the movement of Al to the steel plate interface, thereby suppressing the oxidation of Al.

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,
Crystal with good orientation from the start to the end of secondary recrystallization (GOSS
This is for growing only the grains), and if the inhibitor is weakened from the beginning to the end of the secondary recrystallization, the grains grow to have poor orientation and the magnetic flux density of the product 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 inevitably deteriorates. As a measure, 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 the AlN as a precipitate constant. However, in order to obtain a mirror surface which is one of the gist of the present invention, the partial pressure of nitrogen must not be too high.

The secondary recrystallization at a constant temperature where the solubility of AlN does not change, that is, the inhibitor strength does not change, in terms of secondary recrystallization of the inhibitor with a constant strength is extremely effective. As described above, the solubility of AlN does not change when maintained at a constant temperature,
l is oxygen in the atmosphere or, taking the oxygen from the oxide of the less elements than Al of the steel sheet surface oxygen affinity, Al ₂ O
It decreases to _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 contains no Al will be described. As described above, Al is added to the hot-rolled steel sheet component.
In a silicon steel sheet containing no MnS, MnS, MnS is added by adding S, Se, Te, Sb or the like as an inhibitor.
Usually, e, MnTe, MnSb, and the like are precipitated and used as an inhibitor. These precipitates do not cause deterioration of the inhibitor due to desorption from the steel sheet interface unlike Al, and decrease in precipitates due to an increase in solubility due to an increase in the temperature of the steel sheet, or average precipitates due to Ostwald growth of the precipitates. As the diameter increases, the inhibitor effect strength decreases. 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: 0.002% 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. Then, Al ₂ O ₃ was electrostatically applied to the _two materials as they were, and to the two materials pickled with a mixed solution of 0.5% hydrofluoric acid and 5% sulfuric acid, and then 100
Finish annealing was performed in a% H ₂ atmosphere while maintaining a heating rate of 15 ° C./Hr. Fig. 2 was obtained by analyzing S during the finish annealing.

[0022] Regardless of the presence or absence of pickling, S
Does not decrease. However, this does not mean that the inhibitor strengths are both strong up to high temperatures. As described above, the reason is that the precipitate is dissolved and the precipitate is coarsened by Ostwald ripening.

In the present invention, the steel component 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. Si is important in increasing electric resistance and reducing iron loss, but if it exceeds 4.8%, it is easily cracked 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. If the nitrogen content exceeds 0.010% by weight, voids called blisters are formed in the steel sheet, so this range is optimal. As other inhibitor components, Mn: 0.03 to 0.4
0% by weight, S: 0.01 to 0.05% by weight, Se: 0.
One type or two or more types are added in the range of 0.01 to 0.10% by weight and Sb: 0.01 to 0.10% by weight. Further S
n, Bi, Nb, Ti, P, Mo, Cu, etc. are used as an inhibitor component or an auxiliary element. In addition, carbon is desirably 0.085% by weight or less.

The present inventors have examined in detail the relationship between the removal amount of the surface layer after the primary recrystallization annealing and the magnetic properties. Generally, the primary recrystallization annealing is performed in a humid atmosphere to decarburize the steel sheet, so that an oxide layer is formed on the surface of the steel sheet. At this time, since the hydrogen is added to the wet atmosphere so as not to oxidize the iron, only the elements having higher (greater) oxygen affinity than iron in the steel are oxidized. In silicon steel, since the amount of Si is extremely large as compared with other additive elements, the main component of the oxide layer formed on the surface is silica (SiO ₂ ). When the inventors analyzed the composition of the oxide on the surface of the primary recrystallization annealed sheet, 90% or more was silica.

When the distribution in the depth direction was analyzed by means of polishing, an X-ray microanalyzer, an electron microscope or the like, it was found that the distribution reached a depth of 1 to 3 μm from the surface. Here, it seems that Si in steel becomes SiO ₂ and is dispersed in iron. That is, according to the analysis result of the X-ray microanalyzer, the presence of Si, O, and Fe is recognized in this region.

The inventors changed the removal amount of the surface layer by pickling after nitriding such a primary recrystallized steel sheet with ammonia. Thereafter, an annealing separator containing Al ₂ O ₃ as a main component is applied to the steel sheet and dried.
/ Hr at a heating rate of 1200 ° C.
After reaching ° C., hydrogen was switched to 100% and finish annealing was performed for 20 hours. After finishing annealing, a magnetic domain refinement treatment by laser beam irradiation was performed, and a tension coating treatment was further performed, and the surface observation and magnetic properties were examined.
Table 1 shows the results.

The steel components are Si: 3.25% 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:
The material is composed of 0.05% by weight, the balance being Fe and unavoidable impurities. Further, in the pickling, a mixed solution of sulfuric acid and hydrofluoric acid was used, the pickling was performed at room temperature for different pickling times, and the oxygen content of the pickled steel sheet was analyzed. This was indicated by the amount of oxygen per steel sheet surface area (one side).

[0029]

[Table 1]

The oxygen content of the steel sheet is 0.30 g / m ² (one side)
In the following, it can be seen that the surface is mirror-finished and the magnetic properties are improved. However, when the oxygen content of the steel sheet exceeds 0.30 g / m ² (one side), the magnetic properties are not sufficiently improved. When the oxygen content of the steel sheet is less than 0.03 g / m ² (one side), the magnetic properties seem to be slightly inferior. Therefore, the optimal amount of oxygen for the steel sheet is
It is 0.03 g / m ² or more and 0.30 g / m ² (one side) or less, and the range with the best magnetic properties is 0.04 g / m 2.
² or more and less than 0.30 g / m ² (one side) .

When the oxygen content of the steel sheet is less than 0.03 g / m ² (one side), the magnetic properties are deteriorated because the pickling is excessive and the steel sheet surface is roughened (roughness is increased). I understand that it is to deteriorate. Excessive pickling is also not good from the viewpoint of manufacturing that the weight of the product is reduced.

The optimum values of the oxygen content and the magnetic properties of the steel sheet are due to the reaction between SiO ₂ , which is the main oxygen component of the steel sheet, and the annealing separator. For example, when alumina is used as the annealing separator, A large amount of oxygen in the mullite (Al
_{This is because 2} O ₃ · SiO ₂ ) or the like is generated on the surface of the steel sheet and hinders mirror finishing. In Table 1, the oxygen content of the steel sheet is 0.30 g / m.
^{2 With} more than (one side) material, the material after finish annealing is smooth but milky white and not a perfect mirror surface. The results of observing this with an electron microscope (SEM) are shown in FIGS.
FIG. 3 shows that the oxygen content of the steel sheet was reduced to 0.72 g / m by pickling.
² shows the results of SEM observation of the surface of a grain-oriented electrical steel sheet that was coated with alumina as an annealing separator on the (single-sided) material and finish-annealed.

FIG. 4 shows that the amount of oxygen was 0.17 g /
m ² coated with alumina materials (the one side) as annealing separator, SEM surface finish annealed grain-oriented electrical steel sheet
This is the result of observation. The oxygen content of the steel sheet is 0.72 g / m
² The material of (one side) has an oxygen content of 0.17 g / m ²
It can be seen that there are very many fine particles on the steel sheet surface as compared with the (one-sided) material, and when this is subjected to elemental analysis with a microanalyzer or the like, elements such as Al and Si are recognized.

Therefore, in order not to generate a reaction product with SiO ₂ , it is necessary to reduce the amount of oxygen in the steel sheet, but this also suppresses the deterioration of the inhibitor as described above. As described above, the smaller the better, the better the problem is, as described above, that is, the problem that the surface of the steel sheet is roughened, and an optimum value exists.

The annealing separator is Al ₂ O ₃ , SiO.
₂ , ZrO ₂ , BaO, CaO, SrO and forsterite are used as main components, but these are used alone or
Also, two or more kinds may be used as a mixture. Further, it does not matter if a small amount of a rust inhibitor or the like is added to these main components. The method of applying the annealing separating agent to the steel sheet may be any of electrostatic coating, water slurry coating, organic solvent slurry coating, powder spray coating, etc. In the case of water slurry coating, a substance that reacts with water, that is, CaO, BaO, SrO is disadvantageous.

Hereinafter, the working conditions will be described. 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 of removing the mechanical polishing, for example brushing, Sandope over par polishing, there is a grinding or the like, is effective for this purpose involves industrial various difficulties. The present inventors have noticed that the pickling method is extremely easy and effective. This is because a continuous pickling line for a hot-rolled steel strip or a steel plate has already been put into practical use.

As the pickling solution (pickling solution), hydrochloric acid,
Mineral acids such as sulfuric acid and nitric acid are effective, but the oxide layer formed on the steel sheet surface is an oxide mainly composed of SiO ₂ , so 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 a high speed. It is also effective to combine physical methods such as pickling and mechanical polishing such as brush polishing.

When nitride is used as the 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 completion of primary recrystallization is not enough for secondary recrystallization, and even if the inhibitor is strengthened or prevented from deteriorating by increasing the nitrogen partial pressure during finish annealing, secondary recrystallization is not possible. Sometimes we can't get enough inhibitors. Therefore, generally, the reinforcement of the inhibitor by the ammonia treatment improves the magnetic properties.

In order to secure a necessary inhibitor during the progress of the secondary recrystallization, nitrogen gas is introduced into the annealing atmosphere at the time of temperature increase.
% Or more and 95% or less is preferable.
It may be 0%. If the nitrogen gas content is less than 5%, the effect is weak for strengthening the inhibitor or preventing deterioration. If nitride is not used as the inhibitor, the effect of nitrogen partial pressure is weak. The neutral or reducing atmosphere is a mixture of one or more of inert gases such as nitrogen, oxygen, moisture, hydrogen, argon, etc. A gas composition that is reducing. In general, nitrogen and hydrogen gas are used in the finish annealing of an electromagnetic steel sheet, so that the combination of these two gases is 0% to 100%. Even if an inert gas such as argon or helium is mixed with the combination of these two gases in order to adjust the nitrogen partial pressure, there is no problem at all.

The neutral or reducing atmosphere is set as follows.
This is to prevent the reduction of Al in the steel and to prevent the silicon in the steel from being oxidized to form or increase SiO ₂ on the surface. After completion of the secondary recrystallization, it is extremely effective to increase the hydrogen concentration and keep it at around 1200 ° C. for several hours in order to complete the purification and the mirror finishing of the steel sheet surface. As for the heating temperature up to the temperature at which the secondary recrystallization can be performed in the finish annealing, the higher the speed, the less the inhibitor deterioration and the more favorable. 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.

Hereinafter, embodiments of the present invention will be described. Si:
2.0 to 4.8% by weight, as an inhibitor constituent element,
Acid-soluble Al, Mn, S, Se, Sb, P, B, Sn,
A molten steel to which one or more of Bi, Nb, Ti, Mo, Cu and the like are added is formed into a hot-rolled steel sheet or a hot-rolled steel strip in a usual process or by continuous casting. This hot-rolled steel sheet or hot-rolled steel strip is annealed in a temperature range of 750 ° C. to 1200 ° C. for 30 seconds to 3 minutes to improve the magnetic flux density. Subsequently, these hot-rolled steel sheets or strips are cold-rolled.

The cold rolling is performed at a final cold rolling reduction 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 humid water atmosphere 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
A so-called internal oxide layer is formed depending on the degree of moisture content (usually expressed by a dew point) in a wet water atmosphere, that is, an atmosphere containing moisture, in which SiO ₂ is mainly present as an oxide. Incidentally least 80-90% of the oxygen amount of the oxide formed during the primary recrystallization annealing takes the SiO ₂ forms.

The oxide layer on the surface of the steel sheet or the steel strip after the primary recrystallization is removed when the ultimate magnetic properties are pursued. 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, nitriding treatment with ammonia to strengthen the inhibitor prior to removal of the oxide layer on the surface of the steel sheet is extremely effective in improving the magnetic flux density.

The primary recrystallized plate from which the oxide layer on the surface has been removed is coated with the above-mentioned annealing separating agent 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 secondary recrystallization is completed, 100% hydrogen and high temperature (about 1200
° C) is maintained. After finishing annealing, a magnetic domain refinement treatment such as laser beam irradiation is performed, and a tension coating treatment is further performed.

[0045]

EXAMPLES Example 1 Si: 3.25% by weight, acid-soluble Al: 0.024% by weight, N: 0.009% by weight, Mn: 0.07% by weight,
S: 0.015% by weight, C: 0.08% by weight, Se:
0.15% by weight, Sn: 0.15% by weight, Cu: 0.0
7% by weight, a steel hot-rolled steel strip consisting of the balance Fe and inevitable impurities was annealed at 1120 ° C. for 2 minutes, and then cold-rolled.
The thickness was 0.23 mm. These cold rolled sheets were subjected to 850 in an annealing furnace in a wet water atmosphere (dew point: 65 ° C.) for decarburization.
Annealed at 2 ° C. for 2 minutes for primary recrystallization. Then 0.5
The solution was pickled with a mixed solution of 5% hydrofluoric acid and 5% sulfuric acid.

The oxygen content of the steel sheet by the pickling was 0.66.
g / m ² (one side) and 0.17 g / m ² (one side). Al ₂ O ₃ (alumina) is electrostatically applied to these two materials, and the temperature is increased to 1200 ° C. in a 25% N ₂ -75% H ₂ atmosphere while maintaining a rate of 15 ° C./Hr, 1
After reaching 200 ° C., it was made 100% hydrogen and kept at that temperature for 20 hours. After the finish annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid-based tension coating treatment. Table 2 shows the properties of the obtained product. The surface of the product according to the present invention has improved smoothness and reduced iron loss. The surface state of the comparative example after the finish annealing was described in the table as "smooth surface (mirror surface)". The surface showed a metallic color but had a dull luster and was a so-called dull surface.

[0047]

[Table 2]

Example 2 Si: 3.25% 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 0.155 mm. These cold-rolled sheets were annealed at 820 ° C. for 2 minutes in an annealing furnace in a humid water atmosphere in order to perform decarburization, and were subjected to primary recrystallization. Next, in order to stabilize the secondary recrystallization, nitriding treatment was performed in an ammonia atmosphere to make the total nitrogen amount 200 ppm, and the inhibitor was strengthened. Thereafter, the resultant was pickled with a mixed solution of 0.5% hydrofluoric acid and 5% sulfuric acid.

The oxygen content of the steel sheet by the pickling was 0.67
g / m ² (one side) and 0.24 g / m ² (one side). Al ₂ O ₃ (alumina) is electrostatically applied to these two materials, and the temperature is increased to 1200 ° C. in a 75% N ₂ -25% H ₂ atmosphere while maintaining a temperature increasing rate of 15 ° C./Hr. 1
After reaching 200 ° C., it was made 100% hydrogen and kept at that temperature for 20 hours. After the finish annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid-based tension coating treatment. The properties of the obtained product are as shown in Table 3. The surface of the product according to the present invention has improved smoothness and reduced iron loss. The surface state of the comparative example after the finish annealing was described in the table as "smooth surface (mirror surface)". The surface showed a metallic color but had a dull luster and was a so-called dull surface.

[0050]

[Table 3]

Example 3 In order to stabilize the secondary recrystallization, the primary recrystallized plate in Example 2 was subjected to a nitriding treatment in an ammonia atmosphere, the total nitrogen content was set to 220 ppm, and the inhibitor was strengthened. Thereafter, an oxide layer formed on the surface of the steel sheet was removed with a mixed solution of sulfuric acid and hydrofluoric acid. The amount of oxygen was 0.13 g / m ² (one side).

Al ₂ O ₃ was suspended in ion-exchanged water containing a rust inhibitor, applied with a roll coater and dried.
ZrO ₂ is suspended in ion-exchanged water containing a rust inhibitor, applied with a roll coater and dried.
MgO is suspended in ion-exchanged water, applied to the steel sheet by a roll coater and dried, and these three materials are mixed with 75% N _2.
In a -25% H ₂ atmosphere, the temperature was raised while maintaining a temperature rising rate of 15 ° C./Hr. After reaching 1200 ° C., the temperature was changed to 100% hydrogen and maintained at that temperature for 20 hours. After the finish annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid-based tension coating treatment. The properties of the obtained product are as shown in Table 4. In addition, what is called a glass is a forsterite film.

[0053]

[Table 4]

Example 4 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 amount of nitrogen was set to 220 ppm, and the inhibitor was strengthened.
Thereafter, an oxide layer formed on the surface of the steel sheet was removed with a mixed solution of sulfuric acid and hydrofluoric acid. The amount of oxygen was 0.13 g / m ² (one side). Al ₂ O ₃ , SiO ₂ , Zr
Six types of O ₂ , BaO, CaO, and SrO were each electrostatically applied to the steel sheet, and for comparison, MgO was suspended in water by ion exchange for comparison and applied to the steel sheet with a roll coater and dried.

A total of seven kinds of these materials were heated to 1200 ° C.
In a 5% N ₂ -5% H ₂ atmosphere, the temperature was raised while maintaining a temperature rising rate of 20 ° C./Hr. After reaching 1200 ° C., the temperature was changed to 100% hydrogen, and the temperature was maintained for 20 hours. After the finish annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid-based tension coating treatment. Table 5 shows the properties of the obtained product. In addition, what is called a glass is a forsterite film.

[0056]

[Table 5]

Example 5 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 230 ppm, and the inhibitor was strengthened.
Thereafter, an oxidized layer formed on the steel sheet surface was removed with a hydrochloric acid aqueous solution. The oxygen content was 0.70 g / m ² (one side) and 0.20 g / m ² (one side). Al ₂
O ₃ was suspended in ion-exchanged water containing a rust inhibitor, applied with a roll coater and dried.

These two materials are combined with 75% N ₂ -25%
In an H ₂ atmosphere, the temperature was increased while maintaining a temperature increase rate of 15 ° C./Hr.
Hold for hours. After the finish annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid-based tension coating treatment. The properties of the obtained product are as shown in Table 6. The surface state of the comparative example after the finish annealing was described in the table as "smooth surface (mirror surface)". The surface showed a metallic color but had a dull luster and was a so-called dull surface.

[0059]

[Table 6]

[0060]

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 this grain-oriented electrical steel sheet, since the mirror finishing treatment of the steel sheet is performed in a normal finish annealing furnace, it is extremely easy,
The industrial value is enormous.

[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. After primary recrystallization annealing,
Represents the surface oxide layer removed as it is.

[Figure 2] of the steel sheet containing S not contain acid-soluble Al,
It is a chart which shows the change of S of the steel plate during finish annealing. After the primary recrystallization annealing, the surface oxide layer was removed as it was.

[FIG. 3] Alumina is applied as an annealing separating agent to a material having an oxygen content of 0.72 g / m ² (one side) by pickling,
It is a photograph of the metallographic structure which observed the surface of the grain-oriented electrical steel sheet which performed the finish annealing by SEM.

FIG. 4 is a diagram showing an example in which alumina is applied as an annealing separating agent to a material having an oxygen content of 0.17 g / m ² (one side) by pickling;
It is a photograph of the metallographic structure which observed the surface of the grain-oriented electrical steel sheet which performed the finish annealing by SEM.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiyuki Ushigami 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Hiroyasu Fujii 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (56) References JP-A-5-179354 (JP, A)

Claims (6)

(57) [Claims] 1. The method of claim 1 wherein the hot-rolled silicon steel strip is annealed or annealed.
Without annealing, cold rolling is performed once or twice or more with intermediate annealing in between to make the final sheet thickness, then primary recrystallization annealing is performed, then an annealing separator is applied and dried, and finish annealing is performed. In the method for producing a grain-oriented silicon steel sheet, after primary recrystallization annealing,
The oxide layer on the steel sheet surface has an oxygen content of 0.03 per steel sheet surface.
g / m ² or more and 0.30 g / m ² or less, and Al
₂ O ₃ , SiO ₂ , ZrO ₂ , BaO, CaO, SrO
A method for producing a mirror-oriented silicon steel sheet, comprising applying an annealing separator containing one or more of forsterite as a main component to the steel sheet, drying and applying finish annealing in a neutral or reducing atmosphere. 2. Hot-rolled silicon comprising 2.0 to 4.8% by weight of Si, 0.008 to 0.05% by weight of acid-soluble Al, N ≦ 0.010% by weight, the balance being Fe and unavoidable impurities. The method for producing a mirror-oriented silicon steel sheet according to claim 1, wherein the steel sheet is a steel strip. 3. After the primary recrystallization annealing, a nitriding treatment with ammonia is performed. Thereafter, an oxide layer on the surface of the steel sheet has an oxygen content of at least 0.03 g / m ² and 0.30 g /
^{3. The method according} to claim 1 , wherein the material is removed up to m ² or less.
The method for producing a mirror-oriented silicon steel sheet according to the above. 4. A steel plate manufacturing method of the mirror surface oriented silicon steel sheet <br/> according to any one of claims 1 to 3 for the method for removing the oxide layer, characterized in that the pickling of the surface. 5. A method of pickling with an acid mixed with hydrofluoric acid.
A method for producing a mirror-oriented silicon steel sheet according to claim 4. 6. The N ₂ in the atmosphere at the time of raising the temperature of the finish annealing is set to 5%.
Claim 1, characterized in that a higher%
2. The method for producing a mirror-oriented silicon steel sheet according to item 1 .