JPH07278669A - Manufacture of mirror surface oriented silicon steel sheet with low iron loss - Google Patents

Abstract

PURPOSE:To stably manufacture the mirror surface oriented silicon steel sheet with low iron loss by performing the decarburization annealing of the silicon steel strip having the prescribed composition consisting of Si, Al, N and Fe in a specific atmospheric gas, and coating the MgO separation agent for annealing with the chloride added to perform the finish annealing. CONSTITUTION:The silicon steel strip having the 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 is cold rolled to the final thickness in one or two or more cold rolling including the intermediate annealing. This cold-rolled steel sheet is decarburization annealed in the atmospheric gas where the degree of oxidation (PH2O/PH2) is 0.01-0.15, and the inhibitor is reinforced through the nitrogen increasing process. Then, the separation agent for annealing which is mainly composed of MgO and is added with the chloride is coated and laminated on this steel sheet to perform the finish annealing, and the blunting annealing in the atmosphere of H2 gas. The chloride is preferably BiOCl or Bi2O3+FeCl2. The mirror surface is achieved in the whose zone of the coil to stably obtain the grain-oriented silicon steel sheet with low iron loss.

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, from the viewpoint of energy saving, there is an increasing demand for reduction of electric power iron loss. 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 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-58-265405. It is disclosed in the publication. Further, in the case of a wound core, a method in which the magnetic domain refining effect is not lost even if strain relief annealing is performed after processing the core is also disclosed in, for example, Japanese Patent Application Laid-Open No. 62-8617. 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 grain-oriented electrical steel sheet, the movement of the magnetic domains should be combined with the magnetic domain subdivision. It was found that 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 For that purpose, it is effective not to form a glass film on the surface of the steel sheet that 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 already proposed a method of adding chloride to the annealing separator (for example, Japanese Patent Application Nos. 5-204393 and 5-323).
059).

[0006]

However, when industrially carried out on a coil scale, the decomposition gas of chloride varies because the atmosphere gas at the time of finish annealing temperature rise varies depending on the coil portion, and the entire surface of the coil has a uniform mirror surface. It turned out that the realization could not be realized. In order to solve this problem, when the amount of chloride added was increased and the mirror surface was made uniform, the grain boundaries were partially etched. It is an object of the present invention to provide a method for producing a mirror-oriented grain-oriented electrical steel sheet having a low iron loss, which is uniformly mirror-finished on a coil scale.

[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 has been found that by not forming (Fe ₂ SiO ₄ , FeO, etc.), it is possible to obtain a stable mirror finish under the condition that the amount of chloride added in the annealing separator is reduced.

The details will be described below. By weight, Si:
3.3%, Mn: 0.14%, C: 0.05%, S:
0.007%, acid-soluble Al: 0.028%, N: 0.
A 008% silicon steel slab was 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 annealed at 830 ° C. for 70 seconds in wet gas for decarburization to perform primary recrystallization. Atmospheric gas dew point of decarburization annealing is as oxidation degree (PH ₂ O / PH ₂ ) of (1) 0.016, (2)
0.06, (3) 0.105, (4) 0.185,
(5) Annealing was performed under the condition of 0.327. The composition of these surface oxides after decarburization annealing was identified by infrared reflection spectrum. The result is shown in FIG. As shown in FIG. 2, the formed oxide is 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 separating agent containing magnesia as a main component to which BiOCl was added in an amount of 0 to 8%, followed by finish annealing. Finish annealing is N ₂ : 50% + up to 1200 ℃
H ₂ was performed at a temperature rising rate of 15 ° C./hr in an atmosphere gas of 50%, and at 1200 ° C., H _{2 was changed to} 100%, and purification annealing was performed for 20 hours. The specularity of these samples is shown in FIG. From these results, the Fe-based oxide (Fe ₂
Oxidation degree range in which SiO ₄ ) is not generated (experimental condition (1)-
It can be seen that in (3)), uniform mirroring is achieved in a wide range of chloride addition.

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 by Komatsu et al. (Al, Si)
A production method using N as a main inhibitor (for example, Japanese Patent Publication No. 62-45285) may be applied. 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, 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 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. 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 in a wet hydrogen atmosphere in order to remove carbon contained in steel.
Decarburization annealing is performed in the temperature range of ℃.

In the decarburization annealing, the point of the present invention is to perform the annealing at a degree of oxidation that does not form Fe-based oxides (Fe ₂ SiO ₄ , FeO, etc.). For example,
In the temperature range of 800 to 850 ° C. where decarburization annealing is usually performed, the Fe-based oxide is produced by adjusting the degree of oxidation (P H ₂ O / P H ₂ ) of the atmospheric gas to 0.15 or less. Can be suppressed. However, if the degree of oxidation is lowered too much, the decarburization rate will become slow. Taking these two factors into consideration, the degree of oxidation (P H
₂ O / PH ₂ ): The range of 0.01 to 0.15 is preferable.

A production method using (Al, Si) N as a main inhibitor (for example, Japanese Patent Publication No. 62-45285).
In the above, the decarburized annealed plate is subjected to nitriding treatment. 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 annealing plates, chloride is added to the annealing separator having magnesia as a main component. As the chloride, it is effective to add a complex of a bismuth chloride or a bismuth compound and a chlorine compound for mirroring.

This laminated plate is finish annealed to carry out secondary recrystallization and purification of nitride. Secondary recrystallization is described in JP-A-2-2.
As disclosed in Japanese Patent No. 58929, it is effective to increase the magnetic flux density by using a means such as holding at a constant temperature. After the 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. Since the surface has already been smoothed after the finish annealing, tension coating treatment may be performed, and magnetic domain subdivision treatment such as laser irradiation may be performed as necessary.

[0016]

EXAMPLES Si: 3.2% by weight, Mn: 0.13
%, C: 0.05%, S: 0.007%, acid-soluble A
1: 0.027%, N: 0.008%, the balance of Fe and unavoidable impurities hot-rolled silicon steel sheet 2 at 1100 ℃
After annealing for a minute, the product was cold rolled to a final plate thickness of 0.23 mm. This cold-rolled sheet also serves as decarburization and has an oxidation degree of (1) 0.06, (2) 0.
It was annealed at 44 at a temperature of 830 ° C. for 120 seconds for primary recrystallization. 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 subjected to magnesia (Mg
O) was applied as a water slurry and then subjected to finish annealing.
Bi ₂ O ₃ and FeCl ₂ as annealing separators (1)
1%, (2) 3%, (3) 5% and (4) 7% were added.
These samples were subjected to phosphoric acid-chromic acid-based tension coating treatment and then laser-irradiated to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 1. In the case of decarburization annealing conditions with an oxidation degree of 0.06, mirror-finishing is achieved with a wide range of additive amounts.

[0018]

[Table 1]

[0019]

According to the present invention, it is possible to stably produce a grain-oriented electrical steel sheet having a low iron loss, which has never been seen before, on an industrial scale.

[Brief description of drawings]

[Fig. 1] Oxidation degree of atmosphere gas (P H ₂ O /
3 is a table showing the influence of the addition amounts of P H ₂ ) and chloride (BiOCl) on the surface specularity of the product.

FIG. 2 is an infrared reflection spectrum of an oxide formed when the degree of oxidation of atmospheric gas during decarburization annealing is changed.

Claims (3)

[Claims] 1. By weight, Si: 0.8 to 4.8%, acid-soluble Al: 0.012 to 0.05%, N ≤ 0.01%, the balance consisting essentially of Fe and inevitable impurities. A direction in which a silicon steel strip is subjected to a final thickness by cold rolling once or twice or more with intermediate annealing, followed by decarburizing annealing / nitrogen-enhancing treatment, and then applying an annealing separator to perform final annealing. (1) Decarburization annealing with a degree of oxidation (PH ₂ O / PH ₂ ) of 0.0
It is performed in an atmosphere gas of 1 or more and 0.15 or less, and (2) the surface is mirror-finished after finish annealing by adding chloride to the annealing separating agent having magnesia as a main component between the sheets when laminating the steel sheets. A method of manufacturing a mirror-oriented grain-oriented electrical steel sheet having low iron loss. 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 to 0.040%, the balance being a silicon steel strip consisting essentially of Fe and unavoidable impurities to a final thickness by cold rolling once or twice or more with intermediate annealing, and then decarburization In the method of manufacturing a grain-oriented electrical steel sheet, which comprises performing annealing and then applying an annealing separating agent and performing final annealing, (1) decarburization annealing is performed with an oxidation degree (P H ₂ O / P H ₂ ) of 0.0.
It is performed in an atmosphere gas of 1 or more and 0.15 or less, and (2) the surface is mirror-finished after finish annealing by adding chloride to the annealing separating agent having magnesia as a main component between the sheets when laminating the steel sheets. A method of manufacturing a mirror-oriented grain-oriented electrical steel sheet having low iron loss. 3. The production method according to claim 1, wherein a chloride of bismuth or a compound of bismuth and a chlorine compound are compounded and added as a chloride to be added to the annealing separator.