JPH0748674A - Production of mirror finished grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To provide a grain-oriented silicon steel sheet extremely low in core loss by simultaneously executing mirror finishing and secondary recrystallization for a steel sheet in a finish annealing furnace. CONSTITUTION:A hot rolled silicon steel strip is subjected to cold rolling for one time ark two times including process annealing to regulate its sheet thickness into a specified one, and thereafter, primary recrystallization annealing is executed. After that, an oxidizing layer on the surface of the steel sheet is removed away into <=0.3g/m<2> per side of the steel sheet, which is coated with a separating agent for annealing essentially consisting of one or >=two kinds among alumina, silica, zirconia, baryta, strontium oxide and forsterite, and finish annealing is executed. The surface of the steel sheet after the finish annealing has a mirror finished face and high in magnetic flux density. This is subjected to laser treatment and applied with a tension film to obtain ultralow core loss. In this way, the mirror finished grain oriented silicon steel sheet having high magnetic flux density can be obtd.

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 the secondary recrystallization process (finishing annealing process), a high magnetic flux density is obtained, and at the same time, the steel plate surface is mirror-finished by thermal etching without forming a forsterite film (hereinafter referred to as a glass film) on the steel plate surface. To complete the process with
It aims to reduce energy loss by providing magnetic materials with extremely low iron loss by performing magnetic domain subdivision, tension coating, and other treatments.

[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) that is usually performed after processing, the magnetic domain refining effect disappears. This remedy, that is, means for preventing the magnetic domain refining effect from disappearing even when stress-relief annealing is disclosed, for example, in Japanese Patent Laid-Open No. 62-8617.

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 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. Further, Japanese Patent Application Laid-Open No. 3-110627 discloses that an annealing separator is made of a substance that does not easily react with silica such as alumina to obtain a mirror-finished surface simultaneously with secondary recrystallization.

[0004]

Conventionally, as a method of mirror-finishing (smoothing) the surface of a steel sheet, chemical or physical methods such as brush polishing, sandpaper polishing and grinding other than the above chemical polishing and electrolytic polishing are used. There is. 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. The chemical method that is said to be the most smooth, that is, chemical polishing, environmental problems such as chemical concentration control and wastewater treatment, and the physical method, the surface with an industrially large area is smoothed by the same standard. It is extremely difficult to make it (mirrored).

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 due to mirroring or smoothing. In the present invention, the finish annealing process is intended to simultaneously achieve the purpose. 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.

[0005]

A feature of the present invention is to obtain a mirror surface or a smooth surface with a high magnetic flux density during finish annealing. S that is formed on the surface of the steel sheet without using an annealing separator mainly composed of MgO that is usually used
A material that does not easily react with iO ₂ is an annealing separator, that is, S
An annealing separator mainly composed of 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 with 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, but secondary recrystallization is performed with the metal surface exposed, and at the same time, thermal etching is performed. The metal surface can be mirror-finished or smoothed.

[0006] The means is to anneal the hot-rolled silicon steel strip as needed, and then cold-roll it once or twice or more with intermediate annealing to obtain a final plate thickness, and then perform primary recrystallization annealing. In the production of a grain-oriented silicon steel sheet, which is subjected to a post-annealing separator coating, followed by drying, and finish annealing, after the primary recrystallization annealing, the oxidized layer on the surface of the steel sheet has an oxygen amount per one surface of the steel sheet: 0.30 g / m.
² or less, Al ₂ O ₃ , SiO ₂ , ZrO ₂ ,
An annealing separator containing BaO, CaO, SrO and forsterite as a main component or a mixture of two or more components is applied to the steel sheet and dried, and finish annealing is performed in a neutral or reducing atmosphere.

In the present invention, Si: 2.0 to 4.8% by weight, acid-soluble Al: 0.008 to 0.05% by weight, N ≦
After annealing a silicon hot-rolled steel strip consisting of 0.010% by weight, the balance Fe and unavoidable impurities as needed, cold rolling is performed once or twice or more with intermediate annealing, to obtain a final plate thickness, Next, in the production of a grain-oriented silicon steel sheet which is then subjected to primary recrystallization annealing and then applied with an annealing separator and then dried and subjected to finish annealing, after the primary recrystallization annealing, an oxide layer on the surface of the steel sheet has an oxygen content of 0. Al removed up to 30 g / m ² or less
₂ O ₃ , SiO ₂ , ZrO ₂ , BaO, CaO, SrO
And an annealing separator containing at least one of forsterite as a main component, applied to the steel sheet and dried, and finish-annealed in a neutral or reducing atmosphere.

Further, according to the present invention, the hot-rolled silicon steel sheet is annealed as required, and then cold rolled once or twice or more with intermediate annealing to obtain a final sheet thickness, and then primary recrystallization annealing. In the production of a grain-oriented silicon steel sheet, which is applied with a post-annealing separator and dried, and subjected to finish annealing, after primary recrystallization annealing, a nitriding treatment with ammonia is performed, and thereafter, an oxide layer on the steel sheet surface is provided with an oxygen amount per one surface of the steel sheet: Removed to 0.30 g / m ² or less, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , BaO,
One or two of CaO, SrO and forsterite
An annealing separator containing at least one kind of component as a main component is applied to the steel sheet and dried, and finish annealing is performed in a neutral or reducing atmosphere.

Further, in the present invention, Si: 2.0 to 4.8% by weight, acid-soluble Al: 0.008 to 0.05% by weight, N ≦
A silicon hot-rolled steel strip consisting of 0.010% by weight, balance Fe and unavoidable impurities is annealed as necessary, and then cold rolled once or twice or more with intermediate annealing to obtain a final plate thickness, and then In the production of a grain-oriented silicon steel sheet, which is subjected to a primary recrystallization annealing and then an annealing separator is applied and dried, and subjected to finish annealing, after the primary recrystallization annealing, a nitriding treatment with ammonia is performed, and thereafter, an oxide layer on the steel sheet surface is removed. Oxygen amount per surface of steel sheet: Removed to 0.30 g / m ² or less, Al ₂ O ₃ ,
By applying an annealing separator containing one or more of SiO ₂ , ZrO ₂ , BaO, CaO, SrO and forsterite as a main component to the steel sheet and drying it, and finish annealing in a neutral or reducing atmosphere. is there. Here, the method of removing the oxide layer on the surface of the steel sheet is pickling, and particularly pickling with an acid mixed with hydrofluoric acid is extremely effective. or,
From the viewpoint of improving the magnetic flux density, it is also effective to set N ₂ in the atmosphere at the time of temperature rise to 5% or more.

The state of the surface, which is referred to as a mirror surface, satisfies the following conditions. That is, it has a metallic luster in appearance, has little irregular reflection of light and has no cloudiness, and when magnetically specific, when the magnetic flux density (B ₈ ) is high, when a magnetic domain is subdivided and a tensile tension is applied, a low iron content is obtained. It means that there is no loss and that the surface of the steel sheet is free of foreign substances other than metals such as oxides and nitrides. Furthermore, what is called a smooth surface (mirror surface) is a so-called dull surface which has a metallic color but has a dull gloss. When the surface profile is measured with a surface roughness meter, the profile of the surface referred to as a mirror surface is smooth, the profile of the surface referred to as a smooth surface becomes rough, and the surface having a loss of metallic luster further increases the roughness.

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.
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 deteriorates due to dissolution of the precipitate due to temperature rise or coarsening of the precipitate, so-called Ostwald growth. I understood. 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 have investigated the rate-determining process of inhibitor deterioration during finish annealing in detail, and the oxidation process of Al at the steel plate interface is the largest factor, and the oxide layer on the surface of the steel plate that occurs during primary recrystallization annealing causes inhibitor deterioration. We found that they were very involved. Si: 3.3% by weight, acid-soluble Al: 0.028% by weight, N: 0.008
After annealing a silicon hot-rolled steel strip consisting of 1 wt%, Mn: 0.14 wt%, S: 0.007 wt%, C: 0.05 wt%, the balance Fe and unavoidable impurities at 1100 ° C. for 2 minutes, It was cold rolled to a thickness of 0.23 mm. These cold-rolled sheets were placed in an annealing furnace in a wet water atmosphere for double decarburization.
It was annealed at 00 ° 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 p.
pm to enhance the inhibitor. Then, as it is (oxygen amount per one side 0.85 g / m ² ), and pickled with a 0.5% hydrofluoric acid-5% sulfuric acid mixed solution (oxygen amount per one side 0.04 g / m ² ), two kinds of Al ₂ O as the material
₃ by electrostatic coating, 100% H ₂ atmosphere, 15 ° C./Hr
Finish annealing was performed while maintaining the temperature rising rate.

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 the primary recrystallization annealing shows that the inhibitor strength deteriorates faster than the material having no oxide layer. I found out that That is, if the oxide layer formed on the surface of the steel sheet during the primary recrystallization annealing is removed, the strong inhibitor strength can be maintained up to a high temperature. During the finish annealing, the acid-soluble Al in the steel sheet removes oxygen from the oxide layer mainly composed of SiO ₂ 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 addition, 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 l, Si) N is formed to serve as an inhibitor, the amount of acid-soluble Al can be considered as an index indicating the inhibitor strength.

Further, the inventors of the present invention have 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 are 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. Nitrogen in the steel and nitrogen in the annealing atmosphere increase the amount of precipitates such as AlN to fix Al and reduce the migration of Al to the steel plate interface, so that the oxidation of Al is suppressed.

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 gist of the present invention, it is preferable that the inhibitor be strong, but it is desirable that the inhibitor be kept strong and constant. This is a crystal (GO) having a good orientation from the start to the end of secondary recrystallization.
This is to grow only SS grains), 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 product steel sheet decreases.

The solubility of the inhibitor AlN naturally increases as the temperature of the steel sheet increases, 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, the nitrogen partial pressure must not be too high in order to obtain a mirror surface, which is one of the gist of the present invention.

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 if it is maintained at a constant temperature, but
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 raise the nitrogen partial pressure to suppress the dissolution of AlN and suppress the decrease of the acid-soluble Al.

Next, the case where the hot rolled steel sheet component does not contain Al will be described. As described above, Al is added to the components of the hot rolled steel sheet.
In the case of a silicon steel sheet containing no MnS, MnS, etc., S, Se, Te, Sb, etc. are added as inhibitors.
It is common to precipitate e, MnTe, MnSb, etc. and use them as inhibitors. Unlike Al, the inhibitor does not deteriorate due to desorption from the steel plate interface like Al, and the decrease in the precipitate due to the increase in the solubility due to the increase in the steel plate temperature, or the average particle size of the precipitate due to Ostwald growth of the precipitate As a result, the inhibitor effect strength deteriorates. Therefore, after the primary recrystallization annealing, the behavior of the inhibitor is almost constant regardless of the presence of the oxide film on the surface of the steel sheet formed by the annealing.

Si: 3.2% by weight, N: 0.008% by weight, Mn: 0.08% by weight, S: 0.002% by weight,
C: 0.05% by weight of silicon, the hot-rolled silicon steel strip consisting of the balance Fe and unavoidable impurities was cold-rolled to 0.23 mm, and in the same manner as above, it was heated in an annealing furnace in a wet water atmosphere to also serve as decarburization.
It was annealed at 00 ° C. for 2 minutes for primary recrystallization. afterwards,
Al ₂ O ₃ was electrostatically applied to the _two materials that had been pickled as they were and with a 0.5% hydrofluoric acid-5% sulfuric acid mixed solution, and 10
Finish annealing was performed in a 0% H ₂ atmosphere while maintaining a temperature rising rate of 15 ° C./Hr. Figure 2 shows an analysis of S during finish annealing.
Got

With or without pickling, even up to relatively high temperatures
It turns out that does not decrease. However, this does not mean that both inhibitor strengths are strong up to high temperatures. The reason is, as described above, the dissolution of the precipitate and the coarsening of the precipitate due to Ostwald growth.

The steel composition in the present invention is Si: 2.0-
4.8% by weight, acid-soluble Al, Mn, S, Se, Sb, P, B, Sn, Bi, N as an inhibitor constituent element
One or more of b, Ti, Mo and Cu are added. Si is important in increasing the electric resistance and reducing 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 inhibitor strength, that is, the range in which the magnetic flux density is high, 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: 0.0
1 to 0.10% by weight, Sb: 0.01 to 0.10% by weight
One or two or more kinds are added within the range. Furthermore S
n, Bi, Nb, Ti, P, Mo, Cu, etc. are used as an inhibitor or as an auxiliary element. The carbon content is preferably 0.085% by weight or less.

The present inventors have examined in detail the relationship between the amount of surface layer removed after the primary recrystallization annealing and the magnetic properties. Generally, the primary recrystallization annealing is performed in a wet atmosphere for decarburizing the steel sheet, so that an oxide layer is formed on the steel sheet surface. Since hydrogen is added to the wet atmosphere at this time so as not to oxidize iron, only elements having a higher oxygen affinity (larger) than iron in steel are oxidized. In silicon steel, since the amount of Si is extremely large compared to other additive elements, the main 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 plate, 90% or more was silica.

When the distribution in the depth direction was analyzed by a technique such as polishing, an X-ray microanalyzer, and an electron microscope, it was found that the depth of 1 to 3 μm from the surface was reached. Here, it seems that Si in the 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. After that, an annealing separator having Al ₂ O ₃ as a main component is applied to the steel sheet and dried, and the temperature is set to 15 ° C. in a 100% nitrogen atmosphere.
At a heating rate of / Hr up to 1200 ° C., 120
After reaching 0 ° C., the finish annealing was performed by switching to hydrogen: 100% and holding for 20 hours. After finishing annealing, the magnetic domain was subdivided by laser beam irradiation, and then tension coating was performed to observe the surface and examine the magnetic properties. The results are shown in Table 1.

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: A material consisting of 0.05% by weight, the balance being Fe and inevitable impurities. Further, for pickling, a mixed solution of sulfuric acid-hydrofluoric acid was used, and pickling was performed at normal temperature for different pickling times, and the oxygen content of the pickled steel sheet was analyzed. This was expressed as the amount of oxygen per steel plate surface area (one side).

[0028]

[Table 1]

The oxygen content of the steel sheet is 0.30 g / m ² (one side)
It can be seen below that the surface is mirror-finished and the magnetic properties are improved. However, if the oxygen content of the steel sheet exceeds 0.30 g / m ² (one side), the improvement of magnetic properties is insufficient. Further, 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 optimum amount of oxygen in the steel sheet is 0.30 g / m ² (one side) or less, and the range in which the magnetic properties are most favorable is less than 0.30 and 0.04 g / m ² (one side) or more.

When the oxygen content of the steel sheet is less than 0.03 g / m ² (one side), the magnetic properties deteriorate because the pickling is excessive and the surface of the steel plate becomes rough (roughness increases), that is, the degree of the mirror property I understand that it will deteriorate. Excessive pickling is also not good from the viewpoint of production, that is, the product weight is reduced.

The optimum values for the oxygen content and magnetic properties of the steel sheet are due to the reaction between SiO ₂ which is the main component of oxygen in the steel sheet and the annealing separator. For example, when alumina is used as the annealing separator, the steel sheet If there is a large amount of oxygen, a large amount of mullite (Al
_{This is because 2} O ₃ · SiO ₂ ) or the like is generated on the surface of the steel sheet to hinder the mirror finish. In Table 1, the oxygen content of the steel sheet is 0.30 g / m
^For materials with more than ² (one side), 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. 3 and 4.
Fig. 3 shows that the amount of oxygen in the steel sheet is 0.72 g / m by pickling.
² is a result of observing the surface of the grain-oriented electrical steel sheet, which was subjected to finish annealing by applying alumina as an annealing separating agent to the material set to ² (one side) and using SEM.

FIG. 4 shows that the amount of oxygen is 0.17 g /
The surface of the grain-oriented electrical steel sheet, which was obtained by applying alumina as an annealing separator to the material with m ² (one side) and finish annealing, was SEM.
It is the result of observation. The oxygen content of the steel sheet is 0.72 g / m
² (one side), the oxygen content of the steel sheet is 0.17 g / m ²
It was found that a large number of fine particles were present on the surface of the steel sheet as compared with the (single-sided) material, and elemental analysis of this with a microanalyzer or the like reveals elements such as Al and Si.

Therefore, the amount of oxygen in the steel sheet is reduced in order to prevent the formation of a reaction product with SiO ₂ , but this also suppresses the deterioration of the inhibitor as described above. Therefore, if the smaller the better, the better, as described above, another problem occurs, that is, the surface of the steel sheet becomes rough, and the optimum value exists.

The annealing separator is Al ₂ O ₃ or SiO.
₂ , ZrO ₂ , BaO, CaO, SrO and forsterite are used as the main components, but these may be used alone or
Further, two or more kinds may be mixed and used. Furthermore, it does not hurt to add a little rust preventive agent to these main components. The method for applying the annealing separator to the steel sheet may be any of electrostatic coating, water slurry coating, organic solvent slurry coating, powder spray coating and the like, but in the case of water slurry coating, substances that react with water, that is, CaO, BaO, SrO is inconvenient.

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 and a sufficient magnetic flux density cannot be obtained.
The smoothness of the surface of the product is insufficient, which adversely affects the magnetic properties and makes 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 surface of the steel sheet during the primary recrystallization annealing. As a method for removing, there are mechanical polishing, for example, brush polishing, sand pepper polishing, grinding and the like. Although effective for this purpose, various industrial difficulties are involved. The present invention has found that the method by pickling is extremely easy and 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), hydrochloric acid,
Although mineral acids such as sulfuric acid and nitric acid are effective, the oxide layer formed on the surface of the steel sheet is an oxide mainly composed of SiO ₂ , and therefore pickling with only mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid. Hard to do. When hydrofluoric acid is mixed with these acids, the oxide layer can be removed very efficiently, that is, at high speed. In addition,
It is also effective to combine physical methods such as pickling and mechanical polishing such as brush polishing.

When a nitride is used as an inhibitor,
It is effective to strengthen the inhibitor by performing a nitriding treatment with ammonia after the primary recrystallization annealing and before the finish annealing. This is because the inhibitor strength at the time of completion of primary recrystallization is not sufficient 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, strengthening the inhibitor by treating with ammonia generally 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 to add more than 95% but not more than 100% hydrogen gas
% Is also acceptable. 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 means nitrogen, oxygen,
It refers to a gas composition which is neutral or reductive with respect to oxidation-reduction of silicon, which is a gas of one kind or a mixture of two or more kinds of inert gases such as water, hydrogen and argon. Generally, in the finish annealing of the electromagnetic steel sheet, nitrogen and hydrogen gases are used, so 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 atmosphere of neutral or reducing atmosphere is
This is because the reduction of Al in the steel is prevented and the silicon in the steel is not oxidized to form SiO ₂ on the surface or increase SiO ₂ . After the completion of secondary recrystallization, it is extremely effective to increase the hydrogen concentration and maintain the temperature at around 1200 ° C. for several hours in order to completely purify and mirror-finish the surface of the steel sheet. The higher the heating temperature to the temperature at which secondary recrystallization is possible in the finish annealing, the more convenient the less the deterioration of the inhibitor. When the temperature rising rate was less than 15 ° C./Hr, the inhibitor was remarkably deteriorated, and sufficient inhibitor required for secondary recrystallization was not secured, and sufficient secondary recrystallization was not 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, as an inhibitor constituent element,
Acid-soluble Al, Mn, S, Se, Sb, P, B, Sn,
Molten steel to which one or more kinds of Bi, Nb, Ti, Mo, Cu, etc. have been added is formed into a hot rolled steel sheet or a hot rolled steel strip by an ordinary process or continuous casting. This hot rolled steel sheet or hot rolled steel strip is annealed in the temperature range of 750 ° C. to 1200 ° C. for 30 seconds to 3 minutes to improve the magnetic flux density. Then, 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 along with decarburization and primary recrystallization. This oxide layer is
A so-called internal oxide layer is formed, depending on the degree of water content (usually represented by dew point) in a wet water atmosphere, that is, an atmosphere containing water, and SiO ₂ mainly exists as an oxide here. Note that 80 to 90% or more of the oxygen amount 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 characteristics. The oxide film can be removed by a physical or chemical method as described above, but is generally pickled. When a nitride inhibitor is used, it is extremely effective to improve the magnetic flux density by performing nitriding treatment with ammonia for strengthening the inhibitor prior to 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 the above-mentioned annealing separator and placed in a finish annealing furnace. The atmosphere at the time of raising the temperature of the finish annealing is neutral or reducing, and it is no problem to mix an inert gas such as argon or helium for adjusting the partial pressure of nitrogen. After the completion of the secondary recrystallization, 100% hydrogen for high temperature (about 1200
℃) is held. After finishing annealing, magnetic domain subdivision processing such as laser beam irradiation is performed, and further tension coating processing is performed.

[0044]

【Example】

Example 1 Si: 3.25 wt%, acid-soluble Al: 0.024 wt%, N: 0.009 wt%, Mn: 0.07 wt%,
S: 0.015% by weight, C: 0.08% by weight, Se:
0.15 wt%, Sn: 0.15 wt%, Cu: 0.0
A hot-rolled silicon steel strip consisting of 7% by weight, the balance Fe and unavoidable 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 decarburization in a wet water atmosphere (dew point: 65 ° C) in an annealing furnace at 85
It was annealed at 0 ° C. for 2 minutes for primary recrystallization. After that, 0.
It was pickled with a 5% hydrofluoric acid-5% sulfuric acid mixed solution.

The oxygen content of the steel sheet after the pickling was 0.66.
It was g / m ² (one side) and 0.17 g / m ² (one side). Al ₂ O ₃ (alumina) was electrostatically applied to these two materials, and the temperature was raised to 1200 ° C. in a 25% N ₂ -75% H ₂ atmosphere while maintaining a temperature rising rate of 15 ° 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 2. The surface of the product according to the invention has improved smoothness and reduced iron loss. In addition, the surface state after finish annealing of the comparative example is described in the table as a smooth surface (mirror surface), but the surface shows a metallic color but has a dull gloss, which is a so-called dull surface.

[0046]

[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 wt%, C: 0.05 wt%, balance Fe
And hot-rolled silicon steel strip consisting of inevitable impurities at 1100 ° C
After annealing for 2 minutes, it was 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 wet water atmosphere for double 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 200 ppm.
And strengthened the inhibitor. Then, it was pickled with a 0.5% hydrofluoric acid-5% sulfuric acid mixed solution.

The oxygen content of the steel sheet after the pickling was 0.67.
It was 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 raised up to 1200 ° C. in a 75% N ₂ -25% H ₂ atmosphere while maintaining a temperature rising rate of 15 ° 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. The surface of the product according to the invention has improved smoothness and reduced iron loss. In addition, the surface state after finish annealing of the comparative example is described in the table as a smooth surface (mirror surface), but the surface shows a metallic color but has a dull gloss, which is a so-called dull surface.

[0049]

[Table 3]

Example 3 The primary recrystallized plate of Example 2 was subjected to a nitriding treatment in an ammonia atmosphere to stabilize the secondary recrystallization so that the total nitrogen content was 220 ppm and the inhibitor was strengthened.
Then, the oxide layer formed on the surface of the steel sheet was removed with a mixed solution of sulfuric acid-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 preventive agent, coated with a roll coater and dried,
ZrO ₂ was suspended in ion-exchanged water containing a rust preventive agent, coated and dried with a roll coater, and for comparison,
MgO was suspended in ion-exchanged water, coated on the steel sheet with a roll coater and dried, and these three materials were treated with 75% N ₂
The temperature was raised in a -25% H ₂ atmosphere while maintaining the temperature rising rate of 15 ° C./Hr, and after reaching 1200 ° C., 100% hydrogen was added 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. In addition, what is called a glass is a forsterite film.

[0052]

[Table 4]

Example 4 In order to stabilize the secondary recrystallization, the primary recrystallized plate of Example 2 was subjected to a nitriding treatment in an ammonia atmosphere so that the total nitrogen content was 220 ppm and the inhibitor was strengthened.
Then, the oxide layer formed on the steel sheet surface was removed with a sulfuric acid-hydrofluoric acid mixture. The amount of oxygen was 0.13 g / m ² (one side). Al ₂ O ₃ , SiO ₂ , Zr
Six kinds of O ₂ , BaO, CaO, and SrO were electrostatically applied to the steel plate, and MgO was suspended in water by ion exchange for comparison, and the steel plate was applied and dried with a roll coater.

These total 7 kinds of materials are heated to 1200 ° C.
The temperature was raised in a 5% N ₂ -5% H ₂ atmosphere while maintaining a temperature rising rate of 20 ° 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 5.
Is the street. In addition, what is called a glass is a forsterite film.

[0055]

[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 amount of nitrogen was set to 230 ppm to strengthen the inhibitor. After that, the oxide layer formed on the surface of the steel sheet was removed with a hydrochloric acid aqueous solution. The oxygen amount 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 preventive agent, and the suspension was applied and dried with a roll coater.

75% N ₂ -25%
In the H ₂ atmosphere, the temperature was raised while maintaining the temperature rising rate of 15 ° C./Hr, and after reaching 1200 ° C., 100% hydrogen was added and the temperature was adjusted to 2
Hold for 0 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 6. The surface condition after finish annealing of the comparative example is described as a smooth surface (mirror surface) in the table, but the surface shows a metallic color but has a dull gloss, which is a so-called dull surface.

[0058]

[Table 6]

[0059]

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 chart showing changes in an inhibitor (acid-soluble Al) of a steel sheet during finish annealing. After primary recrystallization annealing,
Indicates that the surface oxide layer was removed as is.

FIG. 2 is a chart showing changes in S of a steel sheet during finish annealing of a steel sheet that does not contain oxide-soluble Al and contains S. After the primary recrystallization annealing, the is the same as is, but the surface oxide layer is removed.

FIG. 3 Alumina was applied as an annealing separator to a material having an oxygen content of 0.72 g / m ² (one side) by pickling,
It is the photograph of the metal structure which observed the surface of the grain-oriented electrical steel sheet which carried out finish annealing by SEM.

FIG. 4 Alumina is applied as an annealing separator on a material having an oxygen content of 0.17 g / m ² (one side) by pickling,
It is the photograph of the metal structure which observed the surface of the grain-oriented electrical steel sheet which carried out finish annealing by SEM.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Ushigami 20-1 Shintomi, Futtsu-shi Nippon Steel Corporation Technical Development Division (72) Inventor Hiroyasu Fujii 20-1 Shintomi, Futtsu Nippon Steel Co., Ltd. Company Technology Development Division

Claims (6)

[Claims] 1. A silicon hot rolled steel strip is annealed as required, and then cold rolled once or twice or more with intermediate annealing to obtain a final plate thickness, and then primary recrystallization annealing. In the method for producing a grain-oriented silicon steel sheet, which is applied with an annealing separator and dried, and subjected to finish annealing, after the primary recrystallization annealing, the oxide layer on the steel sheet surface is removed to an oxygen amount per steel sheet piece surface: 0.30 g / m ² or less. , Al ₂ O ₃ , SiO ₂ , ZrO ₂ , Ba
Specular surface orientation characterized by applying an annealing separator containing at least one of O, CaO, SrO and forsterite as a main component to the steel sheet and drying it, and finish annealing in a neutral or reducing atmosphere. Manufacturing method of silicon steel sheet. 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 method for manufacturing a mirror-oriented silicon steel sheet according to claim 1, which is a steel strip. 3. The method according to claim 1, wherein after the primary recrystallization annealing, nitriding treatment with ammonia is carried out, and thereafter, the oxide layer on the surface of the steel sheet is removed to an oxygen amount per surface of the steel sheet of 0.30 g / m ² or less. 1. A method for manufacturing a mirror-oriented silicon steel sheet. 4. The method according to claim 1, wherein the method for removing the oxide layer on the surface of the steel sheet is pickling. 5. The pickling with an acid containing hydrofluoric acid.
The method described. 6. N ₂ in the atmosphere at the time of temperature rise during finish annealing
The method according to claim 1, wherein the content is at least%.