JPH05156362A - Manufacture of high magnetix flux density grain-oriented silicon steel sheet free from forsterite film - Google Patents

Abstract

PURPOSE:To manufacture a grain-oriented silicon steel sheet high in magnetic flux density, having a smoothed surface and excellent in magnetic properties by subjecting a cold rolled silicon steel strip to primary recrystallization annealing, thereafter coating it with an alumina series separation agent for annealing and executing finish annealing. CONSTITUTION:A silicon steel hot rolled sheet contg., by weight, 2.0 to 4.8% Si, 0.008 to 0.05% acid soluble Al and <=0.010% is subjected to cold rolling for one or >=2 times including process annealing and is worked to regulate its sheet thickness into a final one. Next, it is subjected to primary recrystallization annealing and is thereafter electrostatically coated with a separation agent for annealing consisting of Al2O3 or essentially consisting of Al2O3. Its temp. is raised to 920 to 1150 deg.C at a 50 deg.C/hr temp. raising rate of final annealing in a neutral or reducing atmosphere. When its temp. reaches this, the N % in the atmosphere is regulated to about 5% higher than the N % at the time of the temp. raising, and it is held for 5hr and is subjected to finish annealing. The objective silicon steel sheet whose surface is smoothed to form its shape into a mirror like one by thermal etching and low in core loss can be manufactured without forming a forsterite film on the surface of the steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 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. Especially, in the secondary recrystallization process (finish annealing process), the forsterite (hereinafter referred to as glass) film is not formed on the steel plate surface, and at the same time, the same process is completed with the steel plate surface smoothed by thermal etching. After that, the magnetic domain subdivision, tension coating, etc. are performed to improve the iron loss characteristics.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets are frequently used as magnetic 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 the surface of the material after finish annealing with a laser beam to give a local strain and thereby subdividing the magnetic domain to reduce the iron loss is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-264
No. 05 publication.

Further, since the local strain is removed by the stress relief annealing (strain relief annealing) after the usual working, the magnetic domain refining effect disappears. This remedy, that is, means for preventing the magnetic domain refining effect from disappearing even when stress-relief annealing is disclosed, for example, in JP-A-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 a mirror surface, but when used in a low magnetic field, it was found that even if some unevenness was present, iron loss was not significantly affected, so there is no need to make a perfect mirror surface. As a method for smoothing (mirror-finishing) the material surface after finish annealing, there are chemical polishing, electrolytic polishing and the like disclosed in JP-A-64-83620.

[0005]

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

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

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

[0008]

The feature of the present invention resides in that a smooth surface is obtained without a forsterite coating film during finish annealing as described above. That is,
Without using a commonly used annealing separator mainly composed of MgO, a substance that does not react with SiO ₂ such as Al ₂ O ₃ or hardly reacts is used as the annealing separator, and the partial pressure of N _{2 in} the atmosphere is reduced. (%) Is specially annealed to obtain a grain-oriented electrical steel sheet with a high magnetic flux density, and at the same time the glass (forsterite) film is not formed on the surface of the steel sheet, and the secondary metal surface is exposed. It is characterized by being recrystallized and at the same time smoothing the metal surface by thermal etching.

The means are as follows: 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 required, and then cold rolled once or twice or more with intermediate annealing to obtain a predetermined plate thickness. In the production of a grain-oriented silicon steel sheet, which is then subjected to a primary recrystallization annealing, then an annealing separator is applied, and finish annealing is performed, an annealing separator containing Al ₂ O ₃ (alumina) or Al ₂ O ₃ as a main component. Is applied and finish annealing is performed in a neutral or reducing atmosphere at a heating rate of 50 ° C./hr or more of 920 to 1
The temperature is raised to 150 ° C., and when the temperature is reached, N ₂ % of the atmosphere
Is higher than N ₂ % at the time of temperature rise, and is maintained at the temperature for 5 hours or more.

It is effective from the viewpoint of inhibitor strengthening to carry out a nitriding treatment with ammonia before the step of primary recrystallization annealing to the finishing annealing, or to make the atmospheric nitrogen at the time of temperature rise 5% or more. Making the application of the annealing separator electrostatically is also effective from the viewpoint of not forming a glass film and preventing the deterioration of the inhibitor. An oxide of an alkaline earth metal other than MgO can be used as the annealing separator.

The present invention will be described in detail below. The present inventors have conducted a detailed investigation on the rate-determining process of inhibitor deterioration during finish annealing. As a result, the largest factor is the oxidation process of Al at the steel sheet interface, and the oxide layer on the surface of the steel sheet that occurs during primary recrystallization annealing deteriorates the inhibitor. I was found to be heavily involved in.

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 silicon steel strip consisting of the balance Fe and unavoidable impurities
0.23mm after cold-rolling after annealing at 100 ℃ for 2 minutes
Made thick These cold-rolled sheets were annealed at 830 ° C. for 2 minutes in an annealing furnace in a wet water atmosphere for double decarburization, and primary recrystallization was performed. Next, nitriding treatment is performed in an ammonia atmosphere to stabilize the secondary recrystallization, and the total nitrogen content is 180 pp.
m and strengthened the inhibitor.

After that, Al ₂ O ₃ is electrostatically applied to 100
Finish annealing was performed in a% H ₂ atmosphere while maintaining a temperature rising rate of 15 ° C./hr and 150 ° C./hr. When the inhibitors (AlN, (Al, Si) N, etc.) during the finish annealing were examined, as shown in FIG. 1, the material having a slower heating rate had the same temperature as the material having a faster heating rate. It was found that the inhibitor strength was weak.

That is, if the temperature rising rate is increased, a strong inhibitor strength can be maintained up to a high temperature. The acid-soluble Al in the steel sheet removes oxygen from the oxide layer mainly composed of SiO ₂ during finish annealing to become Al ₂ O ₃ or the like and precipitates in the oxide layer. Therefore, the acid-soluble Al in the steel sheet decreases.

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

FIG. 1 shows changes in the inhibitor (acid-soluble Al) of the steel sheet during finish annealing. After primary recrystallization annealing, alumina was applied and nitrogen: 25% -hydrogen: 7.
Temperature rising rate 15 ° C / h in finish annealing furnace with 5% atmosphere
The temperature was raised at r and 150 ° C./hr.

Further, the inventors of the present invention have conducted a detailed investigation of 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 steel and nitrogen in the annealing atmosphere are Al
Oxidation of Al is suppressed in order to increase the amount of precipitates such as N and fix Al to reduce the migration of Al to the steel plate interface.

Therefore, acid-soluble Al in steel during finish annealing
The higher the nitrogen partial pressure, the less the amount of deterioration, and the stronger the inhibitor is at high temperatures. In order to obtain a high magnetic flux density, which is one of the gist of the present invention, it is preferable that the inhibitor be strong, but it is desirable that the inhibitor be strongly and constantly maintained.

This is for growing only the crystals (GOSS grains) having a good orientation 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, the grains with bad orientation grow. However, 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 rises, and the inhibitor inevitably deteriorates. As a measure for this, 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 keep AlN as a precipitate constant.
However, in order to obtain a smooth surface, which is one of the main points of the present invention, the nitrogen partial pressure must not be too high.

The 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.
l is oxygen in the atmosphere or oxygen from an oxide of an element having a lower oxygen affinity than Al on the surface of the steel sheet, Al ₂ O 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.

The implementation conditions will be described below. 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 the nitrogen partial pressure during finish annealing is increased to strengthen the inhibitor or prevent deterioration even if secondary recrystallization is performed. Sometimes we can't get enough inhibitors.
Therefore, strengthening the inhibitor by treating with ammonia generally improves the magnetic properties.

In order to secure an inhibitor necessary for the progress of secondary recrystallization, nitrogen gas is added to the annealing atmosphere at a temperature rise of 5%.
% Or more and 95% or less is desirable, but hydrogen gas 10
0% is fine. If the nitrogen gas content is less than 5%, the effect of strengthening the inhibitor or preventing deterioration is small.

The neutral or reducing atmosphere refers to one or a mixture of two or more gases selected from inert gases such as nitrogen, oxygen, water, hydrogen, argon, etc. for oxidation and reduction of silicon. A gas composition that is neutral or reducing.

Since nitrogen and hydrogen gases are generally used in finish annealing of electromagnetic steel sheets, 0% to 1% of both gases are used.
The combination is up to 00%. 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 the steel and to oxidize silicon in the steel so as not to produce or increase SiO ₂ on the surface.

When MgO is present, a forsterite film (glass film) is formed.
A substance that does not react with or is difficult to react with iO ₂ is required. Al ₂ O ₃ is suitable for this purpose.
(Alumina) is the best.

From the viewpoint of obtaining a smooth surface, which is the gist of the present invention, oxides of alkaline earth metals such as BaO, CaO and SrO were effective. Also,
In order to prevent the formation of a coating on the surface of the steel sheet, it was effective to use a material state having low reactivity, for example, to increase the particle size of the powder or to apply it to the surface of the steel sheet without forming a hydrate. Electrostatic coating was extremely effective as a method for coating the annealing separator on the surface of the steel sheet without forming a hydrate.

The higher the rate of temperature rise up to the temperature at which secondary recrystallization is possible in the finish annealing, the more convenient the inhibitor is. If the heating rate is less than 15 ° C./hr, the inhibitor is remarkably deteriorated, the inhibitor required for secondary recrystallization is not secured, sufficient secondary recrystallization is not obtained, and the magnetic flux density (B ₈ ) of the steel sheet is low. .. In terms of obtaining a high magnetic flux density, which is one of the main points of the present invention, it is 5
A heating rate of 0 ° C./hr or more was required.

Holding at a constant temperature for secondary recrystallization is particularly effective for obtaining a high magnetic flux density. This is to prevent deterioration of the inhibitor and carry out secondary recrystallization with an appropriate inhibitor strength.

If this temperature is lower than 920 ° C., the time until the completion of secondary recrystallization becomes too long and it becomes impractical.
Further, if it exceeds 1150 ° C., the inhibitor deterioration becomes so remarkable that the required inhibitor cannot be secured until the completion of secondary recrystallization.

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

However, the higher the nitrogen partial pressure, the higher the better. If it is too high, the inhibitor becomes too strong and it takes too much time to complete the secondary recrystallization, and the secondary recrystallization does not occur. The nitrogen partial pressure when the temperature is maintained must be increased by linking with the nitrogen partial pressure when the temperature is raised. After the completion of the secondary recrystallization, increasing the hydrogen concentration in order to complete the purification and the smoothing of the steel plate surface and maintaining the temperature at around 1200 ° C. for several hours
It is extremely effective.

The steel composition in the present invention is Si: 2.0-
4.8% by weight, acid-soluble Al: 0.008 to 0.05% by weight, N ≦ 0.010% by weight, balance Fe and unavoidable impurities, and other elements are not particularly limited.

Si is important in increasing the electric resistance and reducing the iron loss, but if it exceeds 4.8%, it is likely 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.

Acid-soluble Al is an important constituent element of the inhibitor, and is combined with nitrogen, silicon, etc. to form AlN, (A
l, Si) N, etc. are formed to serve as an inhibitor. In terms of the inhibitor strength, that is, the range in which the magnetic flux density is high, it is 0.008 to 0.05% by weight.

When nitrogen exceeds 0.010% by weight, vacancies called blisters are formed in the steel sheet, so this range is optimal. Further, as an inhibitor constituent element, M
n, S, Se, Sn, B, Bi, Nb, Ti, P, Cu
Etc. can be added.

The embodiments of the present invention will be described below. Si:
2.0-4.8% by weight, acid-soluble Al: 0.008-
Molten steel consisting of 0.05% by weight, N ≦ 0.010% by weight, the balance Fe and unavoidable impurities is cast into a hot-rolled steel sheet or a hot-rolled steel strip in a usual process or continuously cast. This hot rolled steel sheet or hot rolled steel strip has a temperature of 750 ° C to 1200 ° C.
Annealing for improving the magnetic flux density is performed in the temperature range of 30 seconds to 30 minutes.

Subsequently, these hot rolled steel sheets or hot rolled steel strips are cold rolled. Cold rolling is conducted in Japanese Patent Publication No. 40-15
As disclosed in Japanese Patent No. 644, the final cold rolling rate 8
0% or more. The material after cold rolling is usually 750 ° C. to 900 ° C. in a wet water atmosphere to remove carbon in steel.
Primary recrystallization annealing is performed in the temperature range of.

Then, nitriding treatment with ammonia for strengthening the inhibitor is extremely effective for improving the magnetic flux density. The primary recrystallized plate is coated with the annealing separator and enters the finish annealing furnace. The temperature rising rate of finish annealing is as large as possible and preferably 50 ° C./hr or more in order to prevent inhibitor deterioration.

The atmosphere at the time of raising the temperature of the finish annealing is 5% nitrogen.
As described above, the balance consists of hydrogen and / or an inert gas.
When the temperature reaches 20 ° C. to 1150 ° C., the partial pressure of nitrogen is made higher than that at the time of raising the temperature and maintained for 5 hours or more. It should be noted that mixing an inert gas such as argon or helium for adjusting the nitrogen partial pressure does not matter at all.

After the secondary recrystallization is completed, the product is kept at a high temperature (about 1200 ° C.) with 100% hydrogen for purification. In addition, unlike the commonly used annealing separator (mainly MgO),
Since it is possible to prevent moisture or hydrated water from being brought into the annealing separator, a step for removal is not required during the final annealing, and the final annealing can be shortened accordingly. ◎ After finishing annealing, magnetic domain subdivision such as laser beam irradiation is performed, and then tension coating is performed.

[0043]

【Example】

Example 1 Si: 3.2 wt%, acid-soluble Al: 0.029 wt%, N: 0.008 wt%, Mn: 0.13 wt%,
S: 0.007% by weight, C: 0.05% by weight, 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 0.23 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 to reduce the total nitrogen amount to 160.
ppm to strengthen the inhibitor. After that, Al ₂ O
₃ : Electrostatically apply an annealing separator consisting of 100% to 110
Up to 0 ℃, 150 ℃ in 10% N ₂ -90% H ₂ atmosphere
The temperature was raised to 1100 ° C. while maintaining the heating rate of / hr.

After reaching 1100 ° C., 50% N ₂ -50%
The atmosphere was changed to H ₂ atmosphere, and the temperature was maintained for 10 hours without changing the atmosphere. After that, 100% hydrogen,
The temperature was further raised to 1200 ° C., and the temperature was maintained for 10 hours. After finishing annealing, a laser beam was irradiated to perform a phosphoric acid-chromic acid tension coating process. The characteristics of the obtained product are as shown in Table 1.

[0046]

[Table 1] Example 2 The hot-rolled silicon steel strip of Example 1 was annealed at 1100 ° C. for 2 minutes and then cold-rolled to a thickness of 0.20 mm. These cold-rolled sheets were placed in an annealing furnace in a wet water atmosphere to also serve as decarburizer.
It was annealed at 0 ° C. for 2 minutes to carry out primary recrystallization. Next, in order to stabilize the secondary recrystallization, nitriding treatment was performed in an ammonia atmosphere to set the total nitrogen amount to 170 ppm and strengthen the inhibitor.

After that, Al ₂ O ₃ (alumina): 100
%, An annealing separator consisting of 10% is applied electrostatically,
In a 10% N ₂ -90% H ₂ atmosphere, the temperature was raised to 1100 ° C. while maintaining the temperature rising rate of 150 ° C./hr.

After reaching 1100 ° C., 75% N ₂ -25%
The atmosphere was changed to H ₂ atmosphere, and the temperature was maintained for 10 hours without changing the atmosphere. After that, 100% hydrogen,
The temperature was further raised to 1200 ° C., and the temperature was maintained for 10 hours. After finishing annealing, a laser beam was irradiated to perform tension coating of phosphoric acid-chromic acid system. The characteristics of the obtained product are shown in Table 2.

[0049]

[Table 2]

[0050]

According to the present invention, it is possible to easily obtain 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 factor that obstructs the magnetic characteristics. The process provided a magnetic material with extremely low iron loss. In the production of this grain-oriented electrical steel sheet, the smoothing treatment of the steel sheet is carried out in an ordinary finish annealing furnace, so that it is extremely easy and its industrial value is enormous.

[Brief description of drawings]

FIG. 1 is a table showing changes in finish annealing temperature and inhibitor (acid-soluble Al) of steel sheet.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyasu Fujii 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technical Development Division

Claims (5)

[Claims] 1. A weight ratio of: Si: 2.0 to 4.8%, acid-soluble Al: 0.008 to 0.05%, N ≦ 0.010%, balance: Fe and inevitable impurities Insert one or intermediate annealing between rolled steel strips 2
In the method for producing a grain-oriented silicon steel sheet, which is subjected to cold rolling more than once to obtain a final plate thickness, and then subjected to primary recrystallization annealing and then applying an annealing separating agent and then finish annealing, After applying an annealing separator containing ₂ O ₃ or Al ₂ O ₃ as a main component, in a neutral or reducing atmosphere,
After heating to a temperature range of 920 to 1150 ° C. at a heating rate of 50 ° C./hr or more and reaching the temperature range, N ₂ % in the atmosphere
Is higher than N ₂ % at the time of the temperature rise and is subjected to finish annealing in which the reached temperature range is maintained for 5 hours or more, a method for producing a high magnetic flux density grain-oriented silicon steel sheet having no forsterite coating. 2. By weight ratio, Si: 2.0 to 4.8%, acid-soluble Al: 0.008 to 0.05%, N ≦ 0.010%, balance: heat composed of Fe and unavoidable impurities Insert one or intermediate annealing between rolled steel strips 2
In the method for producing a grain-oriented silicon steel sheet, which is cold-rolled more than once to obtain the final plate thickness, and then is subjected to primary recrystallization annealing, then an annealing separator is applied, and then finish annealing is performed. Nitriding the material in an atmosphere containing gas, and then Al ₂ O ₃ or Al ₂ O ₃
After applying the annealing separating agent whose main component is 920-1 in a neutral or reducing atmosphere at a temperature rising rate of 50 ° C / hr or more.
After heating to a temperature range of 150 ° C., after reaching this temperature range, N ₂ % in the atmosphere is made higher than N ₂ % at the time of the temperature rise, and finish annealing is carried out for maintaining at the reaching temperature range for 5 hours or more. A method for producing a high magnetic flux density grain-oriented silicon steel sheet having no forsterite coating, comprising: 3. The N ₂ content in the atmosphere during the temperature rising process of the material in the finish annealing process is 5% or more.
Alternatively, the method described in 2. 4. The method according to claim 1, wherein an oxide of an alkaline earth metal other than MgO or an annealing separator containing them as a main component is applied. 5. The method according to claim 1, wherein the application of the annealing separator is electrostatic application.