JPH07118750A - Production of mirror finished grain oriented silicon steel sheet with low iron loss - Google Patents

Abstract

PURPOSE:To obviate the necessity of an acid pickling stage for removing an oxide layer from a decarburized sheet and to obtain the silicon steel sheet at a low cost by using alumina as a separation agent at annealing at the time of laminating steel sheets, limiting the degree of oxidation at the time of decarburizing annealing, and controlling a surface oxide layer. CONSTITUTION:A steel, having 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, is refined. This silicon steel is cold-rolled to the final sheet thickness, followed by decarburizing annealing and nitrogen enriching treatment. Then, alumina is used as a separation agent at annealing, between sheets at the time of laminating the steel sheets, to form the surface after finish annealing into mirror finished state. In this manufacturing method, decarburizing annealing is clone in an atmosphere of wet hydrogen, etc., not forming Fe oxides.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a unidirectional silicon steel sheet mainly used as an iron core of a transformer or other electric equipment. In particular, it is intended to improve the iron loss characteristics by effectively finishing the surface.

[0002]

2. Description of the Related Art Unidirectional silicon steel sheets are used as magnetic cores in many electric devices. Unidirectional silicon steel sheet is S
The crystal grain orientation of the product is {1
10} <001> orientation is a highly integrated steel sheet.
The magnetic properties are required to have a high magnetic flux density (represented by a B ₈ value) and low iron loss (represented by a W _17/50 value). In particular, recently, there is an increasing demand for reduction of power loss from the viewpoint of energy saving. As a means for responding to this demand and reducing the iron loss of the unidirectional silicon steel sheet,
A technique for subdividing magnetic domains has been developed.

In the case of a laminated iron core, a method of irradiating a steel sheet after finish annealing with a laser beam to give a local minute strain to subdivide a magnetic domain to reduce iron loss is disclosed in, for example, JP-A-58-26405. It is disclosed in the official gazette. or,
In the case of a wound iron core, a method in which the magnetic domain refinement effect does not disappear even after stress relief annealing (Stress Release Annealing) after processing the iron core is disclosed in, for example, Japanese Patent Laid-Open No.
No. 2-8617. By subdividing the magnetic domains by these technical means, iron loss has been greatly reduced. However, observing the movement of these magnetic domains reveals that some magnetic domains do not move, and in order to further reduce the iron loss value of the grain-oriented electrical steel sheet, the movement of the magnetic domains is obstructed together with the magnetic domain subdivision. It was found that it is important to eliminate the pinning effect from the glass film on the steel plate surface.

For that purpose, it is effective not to form a glass film on the surface of the steel sheet which hinders the movement of magnetic domains. As a means for this, a method of forming a glass film by using coarse and highly pure alumina as an annealing separator is disclosed in U.S. Pat. S. Patent 3785882. However, with this method, it is not possible to eliminate inclusions just below the surface, and the improvement _margin of iron loss is W _15/60 of only 2% at most.

As a method of controlling the inclusions just below the surface and achieving a mirror surface of the surface, a method of performing chemical polishing or electrolytic polishing after finish annealing is disclosed in, for example, Japanese Patent Laid-Open No. 64-8.
It is disclosed in Japanese Patent No. 3620. However, chemical polishing, electrolytic polishing, etc. can process a small amount of material at the laboratory level, but for industrial scale processing, chemical concentration control, temperature control, and provision of pollution equipment are required. There is a big problem in terms of such things, and it has not yet been put to practical use. As a measure to solve this problem, the present inventors have disclosed that it is effective to remove the oxide layer of the decarburized annealed plate by pickling or the like, and use a substance that does not react with silica as an annealing separator. (For example, Japanese Patent Application No. 5-43810)
issue).

[0006]

However, when pickling is performed after decarburization annealing, the steps of performing pickling and chemical polishing after finish annealing are technically easy.
Since the pickling process is added to the conventional process, the cost increases. Therefore, an object of the present invention is to disclose a manufacturing method capable of reducing the cost, specifically, a measure for eliminating the pickling step.

[0007]

Means for Solving the Problems The present inventors have conducted various experiments in order to solve the above problems by controlling the dew point of decarburization annealing so that the Fe-based oxide is formed in the oxide layer formed during decarburization annealing. It was found that the step of removing the oxide layer by pickling the decarburized plate can be omitted by not forming (Fe ₂ SiO ₄ , FeO, etc.).

The details will be described below. The present inventors investigated the inclusions formed when the oxide layer of the decarburized plate was not removed, and as shown in FIG. 3, these inclusions showed Al-Si-
It was found to be an oxide of Fe. Al-Si-Fe
As shown in FIG. 4, the ternary phase diagram of the oxide has a region having a melting point of 1150 ° C. or lower. Therefore, due to the presence of the Fe-based oxide, SiO ₂ which is the main component of the oxide layer formed by decarburization annealing and A applied as the annealing separator.
inclusions reaction to inhibit the movement of the magnetic domains in the subsurface is promoted in _{l 2 O 3 (Al-Si} -Fe oxide) is estimated to have been formed.

Therefore, an experiment was carried out by changing the dew point during decarburization annealing to change the oxide formed. By weight, Si: 3.
3%, Mn: 0.14%, C: 0.05%, S: 0.0
07%, acid-soluble Al: 0.028%, N: 0.008
% Silicon steel slab after heating at 1150 ° C.
Hot rolled to 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 annealed at 830 ° C. for 70 seconds in wet gas for decarburization to perform primary recrystallization. The atmosphere gas dew point of decarburization annealing is the degree of oxidation (PH ₂
O / P H ₂ ) as (1) 0.016, (2) 0.0
6, (3) 0.105, (4) 0.185, (5) 0.
Annealing was performed under the condition of 327. As will be demonstrated later, the oxide formed forms Si under the conditions (1) to (3).
O ₂ , under the conditions (4) and (5) SiO ₂ and Fe ₂ SiO
_{Is 4} .

After that, the amount of nitrogen was increased to 0.02% by ammonia nitriding to strengthen the inhibitor. This decarburized annealed plate was applied with an annealing separator containing alumina as a main component in the form of a water slurry, and then subjected to finish annealing. Finish annealing is performed up to 1200 ° C. in an atmosphere gas of N ₂ : 100% for 15
Performed at a temperature rising rate of ℃ / hr, H ₂ at 1200 ℃: 100%
After that, purification annealing was performed for 20 hours.

FIG. 1 shows the magnetic properties of these samples after the tension coating treatment and the magnetic domain refinement treatment by laser irradiation. The composition of these surface oxides after decarburization annealing was identified by infrared reflection spectrum. The result is shown in FIG. From these results, Fe-based oxide (F
e ₂ SiO ₄ ) is not generated in the oxidation range (Experimental condition (1)
It is understood that in (3)), inclusions are not generated and a good iron loss value can be obtained.

Embodiments will be described below. As a basic manufacturing method, a manufacturing method using AlN and MnS as a main inhibitor by Taguchi, Sakakura et al.
5644), or a production method using (Al, Si) N as a main inhibitor by Komatsu et al.
No. 45285) may be applied. Si is an important element for increasing electric resistance and reducing iron loss. Content is 4.
If it exceeds 8%, the material tends 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, and the crystal orientation is impaired. Therefore, the lower limit is 0.8%, which does not substantially affect the crystal orientation.

Acid-soluble Al is an essential element for binding N and functioning as AlN or (Al, Si) N as an inhibitor. Higher magnetic flux density 0.012
˜0.050% is the limited range. N is 0.0 during steelmaking
If 1% or more is added, voids in the steel sheet called blister are generated, so 0.01% is made the upper limit. As other inhibitor constituent elements, B, Bi, Se, Pb, Sn, Ti
Etc. can also be added.

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 the continuously cast strip is cold-rolled immediately or after a short time annealing. The above annealing is 750 to 1
The annealing is performed in the temperature range of 200 ° C. for 30 seconds to 30 minutes, and this annealing is effective to enhance the magnetic properties of the product. It is advisable to decide whether to accept or reject the product considering the characteristic level and cost of the desired product.
The cold rolling may be basically carried out at a final cold rolling reduction of 80% or more as disclosed in Japanese Patent Publication No. 40-15644.

The material after cold rolling is 750 to 900 ° C. in a wet hydrogen atmosphere in order to remove carbon contained in steel.
Decarburization annealing is performed in the temperature range of. In this decarburization annealing, F
The point of the present invention is to perform annealing at an oxidation degree that does not form an e-based oxide (Fe ₂ SiO ₄ , FeO, etc.). For example, 800 to 850 ° C. where decarburization annealing is usually performed
In the temperature range of, the degree of oxidation of the atmospheric gas (P H ₂ O /
By adjusting P H ₂ ) <0.15, generation of Fe-based oxide can be suppressed. However, if the degree of oxidation is lowered too much, the decarburization rate will become slow. Considering both of them, in this temperature range, the degree of oxidation of the atmospheric gas (PH ₂ O / PH ₂ ): 0.01 to 0.15 is preferable.

A manufacturing method using (Al, Si) N as a main inhibitor for this decarburized annealed plate (see, for example, Japanese Patent Publication No. 62-4).
At 5285), a nitriding process is performed. The method of this nitriding treatment is not particularly limited, and there is a method of performing it in an atmosphere gas having a nitriding ability such as ammonia. Amount of 0.005% or more, preferably A in steel as total nitrogen content
It is sufficient to nitride at least 1 equivalent. When laminating these decarburized annealed plates, alumina is dry-coated as an annealing separator by a water slurry or an electrostatic coating method. This laminated plate is finish annealed to carry out secondary recrystallization and purification of nitride. It is effective to increase the magnetic flux density by carrying out the secondary recrystallization in a predetermined temperature range by means such as holding at a constant temperature as disclosed in JP-A-2-258929.
After completion of the 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. After finish annealing, the surface is already smoothed,
Tension coating treatment may be performed, and if necessary, magnetic domain subdivision treatment such as laser irradiation may be performed.

[0017]

【Example】

Example 1 By weight, Si: 3.3%, Mn: 0.1%, C: 0.0
5%, S: 0.007%, acid-soluble Al: 0.03%,
A 1.8 mm thick silicon steel hot-rolled steel sheet having N: 0.008% and Sn: 0.05% was pickled and cold-rolled to 1.4 mm. Then 11
After annealing at 00 ° C for 2 minutes, the product was cold-rolled to a final plate thickness of 0.14 mm. The cold-rolled sheet was subjected to a mixed gas of nitrogen and hydrogen in an oxidation degree of (1) 0.005, (2) 0.06, (3) 0.44.
At 830 ° C. for 70 seconds for primary recrystallization. Then, by annealing in an ammonia atmosphere, the amount of nitrogen was increased to 0.025% to strengthen the inhibitor. Some of these steel plates were then (1) Alumina (A
The l ₂ O _3), after some of the magnesia (MgO) as in (2) prior to coating with water slurry was subjected to a finish annealing.

Finish annealing is N ₂ : 10 up to 1200 ° C.
Performed at a temperature rising rate of 10 ° C / hr in 0% atmosphere gas, 1
It was annealed at 200 ° C. for 20 hours while switching to H ₂ : 100%. After subjecting these samples to tension coating, laser irradiation was performed to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 1. When the degree of oxidation was 0.005, decarburization was not performed well in the decarburization annealing, and the secondary recrystallization structure did not develop.

[0019]

[Table 1]

Example 2 By weight, Si: 3.3%, Mn: 0.07%, C: 0.
07%, S: 0.025%, acid-soluble Al: 0.026
%, N: 0.008%, Sn: 0.1%, plate thickness 2.0 mm
The hot-rolled silicon steel sheet was annealed at 1120 ° C. for 2 minutes and then cold-rolled to a final sheet thickness of 0.23 mm. This cold-rolled sheet was oxidized in a mixed gas of nitrogen and hydrogen at an oxidation degree of (1) 0.005, (2) 0.0
6, (3) 0.44 was annealed at a temperature of 850 ° C. for 90 seconds for primary recrystallization.

Then, these steel sheets were partially coated with (1) alumina (Al ₂ O ₃ ) and partially (2) magnesia (MgO) as a conventional water slurry, and then subjected to finish annealing. did.

Finish annealing is N ₂ : 15 up to 1200 ° C.
% + H ₂ 85% in an atmosphere gas at a temperature rising rate of 15 ° C./hr, and switched to H ₂ : 100% at 1200 ° C. and annealed for 20 hours. After subjecting these samples to tension coating, laser irradiation was performed to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 2.

[0023]

[Table 2]

[0024]

According to the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having a low iron loss, which has never been seen before, without increasing the cost.

[Brief description of drawings]

[Fig. 1] Oxidation degree of atmosphere gas (P H ₂ O /
3 is a chart showing the relationship between P H ₂ ) and the magnetic properties of products (iron loss: W _17/50 ).

FIG. 2 is a chart in which an oxide formed when the degree of oxidation of an atmospheric gas during decarburization annealing is changed is examined by an infrared reflection spectrum.

3A is a photograph showing the texture of inclusions formed under the surface, FIG. 3B is a reflection spectrum of photograph 24, and FIG. 3C is a reflection spectrum of photograph 25.

FIG. 4 is a chart showing a ternary phase diagram of an oxide of Al—Si—Fe.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C22C 38/06 H01F 1/16 (72) Inventor Takeo Nagashima 20-1 Shintomi, Futtsu-shi Nippon Steel Technology Development Co., Ltd.

Claims (3)

[Claims] 1. By weight, Si: 0.8 to 4.8%, acid-soluble Al: 0.012 to 0.05%, N ≤ 0.01%, balance balance silicon consisting essentially of Fe and unavoidable impurities. A steel strip is made into a final thickness by cold rolling once or twice or more with intermediate annealing, and then decarburization annealing / nitrogen-enhancing treatment is performed, followed by an annealing separator between the sheets when laminating the steel sheets. In the method for producing a mirror-oriented electrical steel sheet in which the surface is mirror-finished after finish annealing by using alumina as the material, decarburization annealing is performed in an atmosphere gas with an oxidation degree that does not form Fe-based oxides. Of low specular grain oriented electrical steel sheet. 2. By weight, Si: 0.8 to 4.8%, acid-soluble Al: 0.012 to 0.05%, N ≤ 0.01%, Mn: 0.02 to 0.3%, S: 0.005-0.040% A silicon steel strip consisting essentially of Fe and unavoidable impurities in the balance is cold-rolled once or twice or more with intermediate annealing to a final plate thickness, and then decarburized and annealed. In the method for producing a mirror-oriented electrical steel sheet having a mirror-finished surface after finish annealing by using alumina as an annealing separator between the sheets when laminating the steel sheets, decarburization annealing is performed using Fe-based oxide. A method for producing a mirror-oriented electrical steel sheet with low iron loss, which is performed in an atmosphere gas having an oxidation degree that does not form. 3. The degree of oxidation (P H ₂
O / P H ₂₎ of claim 1 or 2 method for producing a low specular oriented electrical steel sheet iron loss according to, characterized in that less than 0.01 to 0.15.