JPH05195062A - Production of grain-oriented silicon steel sheet having ultralow iron loss - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel sheet reduced in isolated inclusions under the surface by electrostatically applying a specific separation agent at annealing at the time of laminating primarily recrystallized sheets and then performing secondary recrystallization and purification at the time of finish annealing. CONSTITUTION:A strip of a silicon steel has a composition consisting of, by weight, 0.8-4.8% Si, 0.012-0.05% acid-soluble Al, <=0.01% N, and the balance Fe with inevitable impurities. This strip is cold-rolled once or is cold-rolled twice or more while process- annealed between the cold rolling stages so as to be formed to the prescribed sheet thickness, followed by primary recrystallization annealing and finish annealing. At the time of laminating the primarily recrystallized sheets before finish annealing, a powder mixture of Al2O3 and TiO2 is electrostatically applied as a separation agent at annealing, and, at the time of finish annealing secondary recrystallization and purification are done while keeping the surface in a mirror-finished state. By using Al2O3, as an essential component of the separation agent at annealing and also adding TiO2 by 5-30%, the ruggedness in the steel sheet surface causing deterioration in iron loss characteristics can be smoothed.

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 unidirectional silicon steel sheet which is mainly used as an iron core for transformers and other electric devices. In particular, it is intended to improve iron loss characteristics by effectively finishing the surface.

[0002]

2. Description of the Related Art Unidirectional silicon steel sheets are used as magnetic iron cores in many electric devices. Unidirectional silicon steel sheet,
The orientation of the crystal grains of the product is highly integrated in the {110} <001> orientation. The magnetic characteristics are high magnetic flux density (represented by B ₈ value) and low iron loss (W _17/50). Represented by a value) is required. In particular, recently, there is an increasing demand for reduction of power loss from the viewpoint of energy saving.

In response to this demand, a technique for subdividing magnetic domains has been developed as a means for reducing the iron loss of a unidirectional silicon steel sheet. A method of irradiating a laser beam to a steel sheet after finish annealing to locally apply a minute strain to subdivide a magnetic domain to reduce iron loss is disclosed in, for example, JP-A-58-2640.
No. 5 publication. Further, in the case of a wound core, a method in which the magnetic domain refinement effect is not lost even if strain relief annealing (stress relief annealing) is performed after processing the core is disclosed in, for example, JP-A-62-62.
No. 8617 is disclosed. By subdividing the magnetic domains by these technical means, iron loss has been greatly reduced.

However, by observing the movement of these magnetic domains, it is found that some magnetic domains do not move, and in order to further reduce the iron loss value of the unidirectional silicon steel sheet, it is necessary to combine the magnetic domain refinement with the magnetic domain subdivision. It was found that it is important to eliminate the pinning effect from the glass film on the surface of the steel plate that hinders movement. As a means for this, a method of smoothing the surface of the material after finish annealing by chemical polishing or electrolytic polishing is disclosed in, for example, Japanese Patent Laid-Open No. 64-83620.

However, although these chemical polishing / electrolytic polishing methods are capable of processing a small sample material at the laboratory level, in order to carry out on an industrial scale, concentration control of chemical solution, temperature control, There is a big problem in terms of providing pollution equipment. In order to solve this problem, some of the inventors of the present invention, in Japanese Patent Application No. 2-409378, remove the glass film of the product and expose the base steel to a steel sheet in which an atmosphere gas containing a gas containing hydrogen. It proposes a method of smoothing the surface by annealing at a temperature of 1000 ° C. or higher.

[0006]

According to the above method,
It is necessary to newly provide a step of removing the glass film once produced by finish annealing after the finish annealing and a step of smoothing treatment. Therefore, the cost is increased in the process, and there is a problem in industrial application. An object of the present invention is to simultaneously achieve (1) orientation control by secondary recrystallization and (2) surface smoothing during finish annealing.

[0007]

Means for Solving the Problems The present inventors first conducted various studies on the interface, and as a result, when laminating a primary recrystallized plate before finish annealing, reaction with an oxide layer (silica) existing on the surface of a steel plate such as alumina Do not use, or use a substance that does not react easily as an annealing separator, and apply this annealing separator instead of water slurry as in the past, so that the surface can be smoothed. I found it.

However, it has been found that when such an annealing separator is used, the inhibitor in the steel sheet weakens quickly as the temperature rises, and it is difficult to sufficiently control the orientation by secondary recrystallization. As a countermeasure against this, it has been found that by adding TiO ₂ to alumina, the weakening of the inhibitor can be delayed and a product having a high magnetic flux density can be obtained.

The present invention will be described in detail below. Currently, ordinary grain-oriented silicon steel sheets are subjected to finish annealing by applying a annealing separating agent containing magnesia as a main component in a slurry form after primary recrystallization annealing. In this manufacturing method, an oxide layer containing SiO ₂ as a main component present on the surface of the steel sheet after primary recrystallization annealing reacts with MgO applied in a slurry form as an annealing separator to form a glass (forsterite) film. Or
It was found that the surface of aluminum does not become smooth because aluminum existing in the steel as an inhibitor constituent element reacts with the water introduced by magnesia to form inclusions in the steel. That is, these glass films and inclusions become pinning sites for magnetic domains.

In order to prevent the formation of forsterite,
Does it react with silica such as alumina as an annealing separator?
Alternatively, it is effective to use a substance that does not easily react.
It was also found that it is important to keep the oxygen partial pressure of the finish annealing low in order to prevent precipitation of aluminum added as an inhibitor constituent element in the steel as inclusions in the steel. An electrostatic coating method that does not bring in moisture is effective as a means for performing this.

It has been found that the secondary recrystallization is stabilized and the magnetic density is improved by adding TiO ₂ when the primary recrystallized sheets are laminated and finish annealing is performed by using such an annealing separator. By weight, Si: 3.3%, Mn: 0.14%,
C: 0.05%, S: 0.007%, acid-soluble Al:
A silicon steel slab consisting of 0.028%, N: 0.008%, the balance Fe and unavoidable impurities was heated at 1150 ° C., and then hot-rolled to a plate thickness of 1.6 mm. This hot rolled sheet is
After annealing at 0 ° C for 2 minutes, it was cold-rolled to a final plate thickness of 0.15 mm. This cold-rolled sheet also serves as decarburization in wet gas, and (1) 8
It was annealed at 30 ° C. and (2) 850 ° C. for 70 seconds to carry out primary recrystallization.

Thereafter, the amount of nitrogen was increased to 0.02% by ammonia nitriding to strengthen the inhibitor. Part of this sample was electrostatically coated with (A) alumina, and partly with (B)
20% of TiO ₂ was added to alumina, electrostatically applied and laminated, and then finish annealed. The finish annealing is performed at a temperature rising rate of 15 ° C./hr in an atmosphere gas of N ₂ : 100% up to 1200 ° C., and switched to H ₂ : 100% at 1200 ° C.
Purification annealing was performed for 20 hours.

Table 1 shows the magnetic characteristics of these samples after the tension coating treatment and the magnetic domain refinement treatment by laser irradiation. 85% if TiO ₂ is not added
It can be seen that when the primary recrystallization annealing is performed at 0 ° C., the secondary recrystallization does not proceed well and the magnetic flux density remains low.

[0014]

[Table 1]

From Table 1, it can be seen that the addition of TiO ₂ improves the magnetic flux density and stabilizes the secondary recrystallization. This is because the inhibitor (AlN, (Al, Si) N) is used when the slurry is not used as the annealing separator.
This is because the deterioration of (), etc. occurs by denitrification from the surface, not by the oxidation of Al as in the conventional case. Therefore, by forming a concentrated layer of silica on the surface of the steel sheet, the rate at which nitrogen passes through becomes slow. it is conceivable that. The above sample is shown in FIG.
The results of chemical analysis of the amounts of inhibitors (nitrogen, acid-soluble aluminum) after annealing at 75 ° C. for 20 hours are shown. From FIG. 1, it can be seen that the weakening of the inhibitor is delayed by adding TiO ₂ .

As the annealing separator, Al ₂ O ₃ is considered to be desirable as a substance that does not easily react with silica, but other substances such as SiO ₂ , ZrO ₂ , BaO and Ca are considered.
O, SrO, etc. can also be used. Next, constituent elements and embodiments will be described. As the steel component in the present invention, Si: 0.8 to 4.8% by weight and acid-soluble Al:
0.012-0.050%, N ≦ 0.01%, balance Fe
And unavoidable impurities, and these are essential components with no particular limitation.

Si is an important element for increasing electric resistance and reducing iron loss. If the content exceeds 4.8%, the material is likely to crack during cold rolling, making rolling impossible. On the other hand, if the amount of Si is reduced, α → γ transformation occurs during finish annealing,
Since the crystal orientation is impaired, the lower limit is 0.8%, which does not substantially affect the crystal orientation. Acid soluble A
l is an essential element for binding to N and functioning as an inhibitor as AlN or (Al, Si) N.
The range of 0.012 to 0.050% at which the magnetic flux density becomes high is set as the limited range.

If N is added in excess of 0.01% during steel making, holes called blisters are generated in the steel sheet, so 0.01% is added.
Is the upper limit. As another inhibitor constituent element, M
It is also possible to add n, S, Se, B, Bi, Pb, Sn, Ti and the like. The molten steel having the above components is formed into a hot-rolled sheet by a usual process, or the molten steel is continuously cast into a ribbon.

The hot-rolled sheet or continuously cast ribbon is immediately
Alternatively, it is annealed for a short time and cold rolled. The annealing is performed in the temperature range of 750 to 1200 ° C. for 30 seconds to 30 minutes, and this annealing is effective for enhancing the magnetic properties of the product. It is advisable to decide whether or not to accept the product, taking into consideration the characteristic level and cost of the desired product.

Cold rolling is basically carried out in Japanese Examined Patent Publication No. 40-15.
Final cold rolling reduction of 8 as disclosed in Japanese Patent No. 644
It may be 0% or more. The material after cold rolling is usually subjected to primary recrystallization annealing in a temperature range of 750 to 900 ° C. in a wet hydrogen atmosphere in order to remove carbon contained in steel. This primary recrystallized plate is subjected to a nitriding treatment to strengthen the inhibitor. The method of nitriding is not particularly limited, and there is a method of performing it in an atmosphere gas having a nitriding ability such as ammonia. The amount of nitriding should be 0.005% or more, preferably Al equivalent or more in steel.

As an annealing separator for laminating the primary recrystallized sheet for finish annealing, a substance such as alumina which does not react with the surface oxide of the steel sheet is used, and in order to reduce the oxygen potential during finish annealing, It is important that no water is brought in when using the annealing separator. As a means for this, a method of electrostatically applying the above substances in powder is effective. Ti in the annealing separator
The addition of O ₂ is a feature of the present invention.

Further, it is effective to remove the oxide on the surface before laminating the primary recrystallized plate in order to smooth the surface of the product. This laminated plate is finish annealed to carry out secondary recrystallization and purification of nitride. Secondary recrystallization is described in JP-A-2-
As disclosed in Japanese Patent No. 258929, it is effective to increase the magnetic flux density by using a means such as holding at a constant temperature in a predetermined temperature range.

After the completion of secondary recrystallization, annealing is performed at a temperature of 1100 ° C. or higher with 100% hydrogen in order to purify the nitride and smooth the surface. Since the surface has already been smoothed after the finish annealing, tension coating treatment may be performed and, if necessary, magnetic domain subdivision treatment such as laser irradiation may be performed.

[0024]

【Example】

Example 1 By weight, Si: 3.3%, Mn: 0.14%, C: 0.
05%, S: 0.007%, acid-soluble Al: 0.028
%, N: 0.008%, the balance Fe and unavoidable impurities were heated at 1150 ° C. and then hot rolled to a plate thickness of 1.6 mm. The hot rolled sheet was annealed at 1100 ° C. for 2 minutes and then cold rolled to a final sheet thickness of 0.15 mm. This cold-rolled sheet was also decarburized in a wet gas, annealed at 850 ° C. for 70 seconds, and primary recrystallized. Then, by annealing at 750 ° C. in an ammonia atmosphere, the amount of nitrogen was increased to 0.02% to strengthen the inhibitor.

On these steel sheets, 0% TiO ₂ was added to alumina.
The annealing separator added by ˜50% was electrostatically applied, laminated, and then finish annealed. Finish annealing is N up to 1200 ℃
₂ : 50% + H ₂ : 50% in ambient gas at 15 ° C / h
The heating was carried out at a heating rate of r and the temperature was switched to H ₂ : 100% at 1200 ° C. for 10 hours for purification annealing.

These samples were subjected to tension coating treatment and then irradiated with laser to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 2. When the amount of TiO ₂ added is increased, the magnetic flux density is gradually increased and the iron loss is also reduced.
On the contrary, it can be seen that when it exceeds%, it gets worse. It is considered that this is because the oxygen potential on the surface of the steel sheet becomes too high and, conversely, it reacts with aluminum to weaken the inhibitor.

[0027]

[Table 2]

Example 2 The same nitrided plate as in Example 1 was pickled and then Ti
An annealing separator containing alumina as a main component and containing 20% of O ₂ was electrostatically applied and laminated, and then finish annealing was performed. The finish annealing is performed up to 1200 ° C. in an atmosphere gas of N ₂ : 50% + H ₂ : 50% at a temperature rising rate of 15 ° C./hr and is 120
Purification annealing was carried out for 10 hours by switching to H ₂ : 100% at 0 ° C.

These samples were subjected to tension coating treatment and then laser-irradiated to subdivide the magnetic domains. Table 3 shows the magnetic properties of the obtained product.

[0030]

[Table 3]

This iron loss value is better than the result of Example 1. This indicates that the smoothness of the surface is further improved by removing the oxide layer of several μm of the primary recrystallized plate.

[0032]

According to the present invention, a unidirectional silicon steel sheet can be manufactured at low cost, in which unevenness on the surface of the steel sheet, which is a factor that deteriorates iron loss characteristics, is smoothed and isolated inclusions under the surface are reduced. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the amount of TiO ₂ added to an annealing separator on the deterioration behavior of an inhibitor.

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[Procedure amendment]

[Submission date] April 3, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

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Claims (4)

[Claims] 1. By weight, Si: 0.8 to 4.8%, acid-soluble Al: 0.012 to 0.050%, N ≦ 0.01.
%, The balance Fe and unavoidable impurities, and a unidirectional silicon steel sheet that is subjected to primary recrystallization annealing / finish annealing to a predetermined thickness by cold rolling once or twice or more with intermediate annealing. In the manufacturing method of No. 1, when a primary recrystallized sheet before finish annealing is laminated, A1 _{2 is} used as an annealing separator.
By electrostatically applying a mixed powder of O ₃ and TiO ₂ ,
Secondary recrystallization with the surface mirror-finished during finish annealing.
A method for producing an ultra-low iron loss unidirectional silicon steel sheet, characterized by performing purification. 2. The main component of the annealing separator is Al ₂ O ₃ ,
The method for producing an ultra-low iron loss unidirectional silicon steel sheet according to claim 1, wherein TiO ₂ is added in an amount of 5 to 30%. Method. 3. Al ₂ O ₃ as a main component of the annealing separator.
Instead of SiO ₂ , ZrO ₂ , BaO, CaO, Sr
The method for producing an ultra-low iron loss unidirectional silicon steel sheet according to claim 1 or 2, wherein a powder of a substance that does not react with or is difficult to react with SiO ₂ such as O is used. 4. The method for producing an ultra-low iron loss unidirectional silicon steel sheet according to claim 1, wherein the surface oxide layer of the primary recrystallized plate is removed. Method.