JPH07278668A - Manufacture of grain-oriented silicon steel sheet with low iron loss - Google Patents

Abstract

PURPOSE:To stably manufacture the grain-oriented silicon steel sheet with low iron loss at a low cost by performing the decarburization annealing of the silicon steel strip containing Si and C of a specific amount in the specific atmospheric gas at the specific temperature raising speed and annealing temperature. CONSTITUTION:The silicon steel coil containing, by weight, 0.8-4.8% Si and 0.03-0.1% C is cold rolled, and decarburization annealed, and then, the separating agent for annealing is coated thereon to perform the finish annealing to obtain the silicon steel sheet. In the decarburization annealing, the temperature is risen to the temperature range of 770-860 deg.C at the temperature raising speed of >=9 deg.C/sec, and the degree of oxidation (PH20/PH2) of the atmospheric gas in this temperature range is set to 0.01-0.15 to execute the annealing. The separating agent for annealing which is mainly composed of Al2O3 or MgO is preferable. This constitution performs the decarburization where the carbon content of the silicon steel coil is approximately <=0.003% to effectively improve the iron loss property.

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,
It is a steel sheet containing 0.8 to 4.8% of Si and having the crystal grains of the product highly integrated in the {110} <001> orientation. 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. 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.

In the case of a laminated iron core, a method of irradiating a steel plate after finish annealing with a laser beam to give a local minute strain to subdivide a magnetic domain to reduce iron loss is disclosed, for example, in Japanese Patent Laid-Open No. 58-26505. It is disclosed in the publication. However, by observing the movement of these magnetic domains, it was found that some magnetic domains were pinned due to the unevenness of the glass film on the surface of the steel sheet and did not move. Therefore, in order to further reduce the iron loss value of grain-oriented electrical steel sheet, it is important to eliminate the pinning effect due to the unevenness of the glass film on the surface of the steel sheet that inhibits the movement of the magnetic domain together with the subdivision of the magnetic domain. To be

For that purpose, it is considered 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 forming it, a glass film is formed by using coarse high pure alumina as an annealing separator. A method that does not prevent it is, for example, U.S.P. S. Patent 3785882. However, this method cannot eliminate the inclusions just below the surface, and due to the pinning effect due to the inclusions, the iron loss improving _margin is only 2% at W _15/60 .

As a method for controlling the inclusions just below the surface and achieving a mirror-finished surface, a method of performing chemical polishing or electrolytic polishing after finish annealing is disclosed in, for example, JP-A-64-
No. 83620. 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. The present inventors have conducted various experiments in order to solve the above problems, controlled the dew point of decarburization annealing, and in the oxide layer formed during decarburization annealing, Fe-based oxides (Fe ₂ SiO ₄ ,
It was found that not forming FeO or the like is effective in eliminating inclusions on the surface (Japanese Patent Application No. 5-267).
546).

[0006]

However, in the removal of carbon, which is an important issue in decarburization annealing, there arises a problem that it may not reach 0.003% or less, which is necessary for reducing iron loss. It was An object of the present invention is to provide a method for performing stable decarburization without increasing the manufacturing cost.

[0007]

Means for Solving the Problems The present inventors have conducted various experiments in order to solve the above-mentioned problems, and decarburization is characterized by the temperature rising rate of decarburization annealing, the annealing temperature and the atmosphere gas being important controlling factors. And the temperature was raised to a temperature range of 770 to 860 ° C. at a temperature rising rate of 9 ° C./sec or less, and the Fe-based oxide (Fe ₂ SiO ₄ , F
The degree of oxidation of the atmospheric gas (P H ₂ O
/ P H _2): decarburization by performing annealing at from 0.01 to 0.15 were found to be stably performed.

The details will be described below. The present inventors consider that the decarburization behavior of silicon steel sheets is greatly affected by the oxide layer formed in the initial stage of decarburization annealing (heating process), and various decarburization behaviors related thereto are considered. The experiment was done. By weight, Si: 3.3%, Mn: 0.14%, C: 0.0
5%, S: 0.007%, acid-soluble Al: 0.028
%, N: 0.008% of a silicon steel slab was heated at 1150 ° C. and then hot-rolled to a plate thickness of 1.6 mm. This hot rolled sheet 11
After annealing at 00 ° C. for 2 minutes, it was cold-rolled to a final plate thickness of 0.15 mm. This cold-rolled sheet is subjected to an atmospheric gas oxidation degree (PH ₂ O / PH
₂ ): Decarburization annealing was performed at 830 ° C. in a wet gas of 0.01. Here, as the temperature rising time for decarburization annealing, (1) 30 seconds (28 ° C / second), (2) 60 seconds (14 ° C / second), (3)
90 seconds (9 ° C / second), (4) 120 seconds (7 ° C / second),
(5) Annealing was performed under the condition of 180 seconds (5 ° C./second).

The carbon content after annealing is shown in FIG. It can be seen from FIG. 1 that the carbon content in the steel stably decreases to 0.003% or less at the temperature rising rate of 9 ° C./second or more. Based on this result, the effect of decarburization annealing temperature was investigated. That is, the above cold-rolled sheet was heated at a heating rate of 28 ° C./sec (1) 740 ° C. in a wet gas having an atmospheric gas oxidation degree (P H ₂ O / P H ₂ ) of 0.06,
(2) 770 ° C, (3) 800 ° C, (4) 830 ° C,
Annealing was performed at temperatures of (5) 860 ° C and (6) 890 ° C. The amount of carbon after annealing is shown in FIG. From FIG. 2, it can be seen that the carbon content in the steel stably decreases to 0.003% or less in the annealing temperature range of 770 to 860 ° C.

From the above results, it was found that carbon is stably reduced to 0.003% or less by heating at a temperature rising rate of 9 ° C./sec or more and annealing in the range of 770 to 860 ° C. The cause of this is not clear, but it is considered that it depends on the form of silica formed on the surface of the steel sheet during the temperature rising process. That is, on the surface of decarburization annealing, (1) decarburization reaction and (2) silica formation (oxidation) reaction are performed in competition with the moisture content of the atmosphere. At low oxidation degree like this condition, silica generally forms a dense film and inhibits decarburization, but the decarburization reaction is carried out by raising the temperature at a high rate of temperature, and once the decarburization reaction occurs on the surface. It is considered that if a site of is secured, a dense silica film cannot be formed, and the decarburization reaction subsequently occurs.

As described above, at the time of soaking at 770 to 860 ° C. after controlling the morphology of initially formed silica, the atmospheric gas has an oxidation degree (PH ₂ O / PH ₂ ) of 0.01 or more and 0 or more. Annealing may be performed at 0.15 or less. When the degree of oxidation exceeds 0.15, inclusions are formed under the surface of the product, which becomes an obstacle to lower iron loss. Further, if the degree of oxidation is lower than 0.01, the decarburization rate becomes slow, which is an industrial problem.

Embodiments will be described below. As a basic manufacturing method, a manufacturing method using AlN and MnS as main inhibitors by Taguchi, Sakakura, etc. capable of manufacturing a product having a high magnetic flux density B ₈ (for example, Japanese Patent Publication No. 40-15644), or Komatsu et al. (Al, Si ) A production method using N as a main inhibitor (for example, JP-B-62-45285) may be applied. Si is an important element for increasing electric resistance and reducing iron loss. If the content exceeds 4.8%,
During cold rolling, the material becomes fragile and cannot be rolled.
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.

When C remains, it causes deterioration of product characteristics (iron loss), so it is necessary to keep C to 0.003% or less. However, if the C content is lowered in the steelmaking stage, coarse {100} elongated grains are present in the crystal structure of the hot rolled sheet, which adversely affects secondary recrystallization. Further, from the viewpoint of controlling precipitates and primary recrystallization texture, it is necessary to add C to some extent in the steelmaking stage. Therefore, at the steelmaking stage, 0.003% or more, preferably α / γ transformation occurs at a level of 0.
It is desirable to add 02% or more. Even if more than 0.1% is added, the above-mentioned influence on the crystal structure, precipitates, etc. is almost saturated and the time required for decarburization becomes long, so 0.1% is made the upper limit.

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 ribbon is immediately or cold-rolled after annealing for a short time. The above annealing is 750
The annealing is performed in a temperature range of ~ 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 to accept or reject the product considering the characteristic level and cost of the desired product.

Cold rolling is basically carried out in Japanese Examined Patent Publication No. 40-15.
As disclosed in Japanese Patent No. 644, the final cold rolling reduction rate is 8
It may be 0% or more. The material after cold rolling is subjected to decarburization annealing in a wet hydrogen atmosphere in order to remove carbon contained in steel. In this decarburization annealing, the degree of oxidation (P H ₂ O / P H ₂ ) of the atmosphere gas was 0.01 or more and 0.15 or less F.
The point of the present invention is to perform decarburization stably during annealing at a low degree of oxidation that does not form an e-based oxide (Fe ₂ SiO ₄ , FeO, etc.). The present invention discloses that the rate of temperature rise is limited to 9 ° C / sec or more and the decarburization temperature is limited to 770 to 860 ° C.

After completion of decarburization in this temperature range, there is a case where annealing is performed at a temperature of 900 ° C., for example, in order to adjust the grain size.
In some cases, a manufacturing method using (Al, Si) N as a main inhibitor for this decarburized annealed sheet (see, for example, Japanese Examined Patent Publication No. 62-4
No. 5285), a nitriding treatment 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. Quantitatively, 0.005% or more, preferably, the total nitrogen content may be nitrided by Al equivalent or more in the steel. When laminating these decarburized and annealed plates, the surface after finishing annealing is mirror-finished by dry-coating an annealing separating agent whose main component is alumina, which is difficult to react with silica, with water slurry or electrostatic coating method. It is possible to greatly reduce the iron loss by finishing it into a shape.

Further, it is also effective to apply an annealing separating agent containing magnesia as a main component in a water slurry or dry-coat by an electrostatic coating method as in the prior art. In this case, the surface does not become a mirror surface as in the case where alumina is used as the annealing separator, but the unevenness of the surface glass film can be reduced and the iron loss can be reduced as compared with the conventional product.
This laminated decarburized annealed plate is finish annealed to perform secondary recrystallization and purification of the nitride. Secondary recrystallization is described in JP-A-2-258.
As disclosed in Japanese Patent No. 929, it is effective to increase the magnetic flux density by carrying out in a predetermined temperature range by means such as holding at a constant temperature. 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. After finish annealing, the surface may be subjected to tension coating treatment and, if necessary, magnetic domain subdivision treatment such as laser irradiation.

[0019]

【Example】

Example 1 By weight, Si: 3.3%, Mn: 0.1%, C: 0.05
%, S: 0.007%, acid-soluble Al: 0.03%, N:
A hot-rolled silicon steel sheet of 0.008% and Sn: 0.05% with a thickness of 1.8 mm was pickled and cold-rolled to 1.4 mm. Then 1100
After annealing at 0 ° C for 2 minutes, it was cold rolled to a final plate thickness of 0.14 mm.
The cold rolled sheet was subjected to an oxidation degree (P H ₂ O / P H ₂ ) (1) of 0.0
6 and (2) in a mixed gas of nitrogen and hydrogen adjusted to 0.33 (conventional method), the heating rate (1) 42 ° C./second,
(2) 28 ° C./sec, (3) 14 ° C./sec, and (4) 5 ° C./sec, the temperature was raised to 830 ° C., and annealing was performed for 70 seconds to perform decarburization annealing. Then, by annealing in an ammonia atmosphere, the amount of nitrogen was increased to 0.025% to strengthen the inhibitor.

These steel sheets were then 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 : 75 up to 1200 ° C
% + H _2: performed in 25% of the ambient gas at a heating rate of 10 ° C. / hr, at 1200 ° C. H _2: switch 20 to 100%
Annealed for a period of time. These samples were subjected to tension coating treatment and then laser-irradiated to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 1.

[0021]

[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: 0.06%, plate thickness 2.0
mm 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 subjected to an oxidation degree (P H ₂
O ₂ / P H ₂ ) In a mixed gas of nitrogen and hydrogen adjusted to 0.1, the temperature was raised to 800 ° C. at a heating rate of 30 ° C./sec, and 90
After second annealing and decarburization, it was annealed at 900 ° C. for 60 seconds to adjust the grain size. These steel sheets are then partly (1) alumina (Al ₂ O ₃ ) and partly (2) magnesia (Mg).
O) was applied as a water slurry and then subjected to finish annealing.

On the other hand, as a comparative material, the cold-rolled sheet was heated to 800 ° C. at a heating rate of 30 ° C./sec in a mixed gas of nitrogen and hydrogen in which the degree of oxidation (P H ₂ O / P H ₂ ) was adjusted to 0.4. After the temperature was raised, annealing was performed for 90 seconds to decarburize, annealing was performed at 900 ° C. for 60 seconds to adjust the particle size, and magnesia (MgO) was applied with a water slurry, and then final annealing was performed. Finish annealing is 120
Up to 0 ° C., in an atmosphere gas of N ₂ : 15% + H ₂ : 85% at a temperature rising rate of 15 ° C./hr, H ₂ : 1 at 1200 ° C.
It switched to 00% 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.

[0024]

[Table 2]

[0025]

Industrial Applicability According to the present invention, decarburization can be stably decarburized in an atmosphere having a lower oxidation degree than conventional ones, and by effectively finishing the surface of the product, the iron content is lower than that of the conventional product. The loss-oriented electrical steel sheet can be manufactured without increasing the cost.

[Brief description of drawings]

FIG. 1 is a chart showing the relationship between the temperature rising rate during decarburization annealing and the residual carbon amount after decarburization annealing.

FIG. 2 is a chart showing the relationship between the annealing temperature during decarburization annealing and the residual carbon amount after decarburization annealing.

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

Claims (3)

[Claims] 1. A cold rolling / decarburizing annealing of a silicon steel strip containing Si: 0.8 to 4.8% and C: 0.03 to 0.1% by weight, and then applying an annealing separator. In the decarburizing annealing of the grain-oriented silicon steel sheet subjected to the finishing annealing, the temperature is raised to a temperature range of 770 to 860 ° C. at a temperature rising rate of 9 ° C./sec or more, and the degree of oxidation (P H
_A method of manufacturing a grain-oriented silicon steel sheet having a low iron loss, which comprises annealing at a rate of ₂ O / PH ₂ of 0.01 or more and 0.15 or less. 2. The method according to claim 1, wherein alumina is used as a main component as the annealing separator. 3. The method according to claim 1, wherein magnesia is used as a main component as the annealing separator.