JP3067896B2 - Method of manufacturing thin slab for unidirectional electrical steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing 2.5 to 6.5% of sulfur.
The present invention relates to a method for producing a thin slab for a grain-oriented electrical steel sheet having a thickness of 0.3 to 6.0 mm, including i.

[0002]

2. Description of the Related Art A grain-oriented electrical steel sheet is used as an iron core material of electric equipment such as a transformer, and must have good magnetic properties such as excitation properties and iron loss properties. In recent years, the market demand for low iron loss materials with particularly low energy loss has been increasing.

However, the conventional production method has a problem that the production cost is very high because complicated process treatments such as hot rolling, cold rolling and annealing are required. Therefore, a technique has been recently developed in which molten steel of electromagnetic steel is directly thinned by a rapid solidification method.
According to this method, a product or semi-product can be made directly from molten steel, so that the production cost can be significantly reduced.

A method for producing a thin grain slab by this rapid solidification method and manufacturing a grain-oriented magnetic steel sheet using the thin slab as a starting material is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-11619. here,
It is provided that a molten metal containing Si: 2.5 to 6.5% or the like is supplied and rapidly solidified by a twin roll method to obtain a slab 0.7 to 2.0 mm thick. However, nothing is mentioned about the atmosphere at the time of casting, and it is considered that the casting is carried out in the normal atmosphere.

[0005]

However, according to the findings of the present inventors, the product manufactured from the cast piece for a grain-oriented electrical steel sheet has a low magnetic flux density, which is caused by a problem in controlling the cast structure. I thought there was a point. The present invention is intended to solve such a problem, and focuses on the atmosphere at the time of casting, and controls the casting structure at the time of solidification to reduce the size of the cast iron.
It is an object of the present invention to provide a method of manufacturing a thin slab for obtaining a unidirectional magnetic steel sheet having a high degree of integration of 0｝ <001> orientation and a good magnetic flux density.

[0006]

The present invention has been completed as a result of repeated studies to achieve the above object.
The point is that in twin-roll continuous casting, Si: 2.5 to 6.5% by weight, Mn: 0.02 to
Molten steel containing 0.15%, S: 0.001 to 0.05% as a basic component is continuously supplied and rapidly solidified,
When continuously casting thin cast pieces having a thickness of 0.3 to 3.0 mm, the pool portion of the twin rolls is made to have an argon gas atmosphere, whereby a higher magnetic flux density can be obtained than before.

[0007]

The present invention will be described below in detail. A grain-oriented electrical steel sheet can generally be produced by sufficiently causing secondary recrystallization during the final annealing in the production process to obtain a so-called Goss texture. In order to obtain this Goss texture, the coarse growth of primary recrystallized grains is suppressed, and only recrystallized grains of the {110} <001> orientation are selectively grown in a certain temperature range. That is, it is necessary to make a base material for secondary recrystallization. In contrast, Japanese Patent Application Laid-Open No. 63-11 / 1988
No. 619 has a problem that the presence of a cast structure of {100} <0vw> columnar crystal is inevitable. This {100} <0vw> is {10} even after rolling and recrystallization.
It is well known that the crystal has an orientation close to 0｝ <0vw>. Therefore, if there are many columnar crystals, the secondary recrystallization defective portion increases, so that the magnetic properties of the product deteriorate and a high magnetic flux density cannot be obtained.

Therefore, in order to improve the magnetic flux density of the product, it is necessary to make the cast structure of columnar crystals in thin cast pieces as small as possible to make the cast structure of equiaxed crystals. The present inventors considered that in order to improve the solidification structure morphology during the rapid solidification, the atmosphere in the pool was changed to further increase the solidification speed.

In general, in the twin roll quenching and solidification method, as shown in FIG.
The gas film layer 3 exists between the molten steel 2 and the overall heat transfer resistance including the gas film layer 3 in addition to the roll body 1 needs to be considered as the heat transfer resistance from the surface of the molten steel 2 to the roll 1. The gas film at this time is considered to have a thickness on the order of several μm. Normally, the contact time between the roll 1 and the molten steel 2 in the twin-roll quenching solidification method is on the order of 0.1 second, and it is necessary to form a solidified shell in this short time. The impact seems to be very large. Then, the present inventors paid attention to entrainment of the atmosphere gas 4 in the pool of the twin rolls.

In view of the above, various types of gases were used in place of the conventional atmosphere, and a study was conducted on the form of the casting structure. As a result, when the pool is set to an argon gas atmosphere,
As shown in (a), a thin slab having an equiaxed grain casting structure was obtained, and it was further found that the magnetic flux density was improved by improving the texture to a random orientation. On the other hand, in a nitrogen gas atmosphere, the solidification structure morphology tends to be directional columnar crystals (FIG. 2B).

The reason may be that the argon gas has a relatively good thermal conductivity and tends to increase the cooling rate. That is, argon gas has almost the same thermal conductivity as nitrogen gas, but in the case of nitrogen gas, a small amount of nitrogen absorption is performed on the surface of the molten steel, so that the apparent thermal conductivity decreases, and as a result, It is conceivable that the thermal conductivity of argon gas is higher than that of nitrogen gas.

As described above, the inventors of the present invention focused on the entrainment of the atmosphere gas in the pool portion of the twin rolls and examined various gases. It was found that thin slabs having a grain structure and a random texture were obtained, and the magnetic flux density was improved.

Next, the reason why the steel composition and the production conditions are limited as described above in the present invention will be described in detail. The reasons for limiting the steel components are as follows.

Si has a lower limit of 2.5 to improve iron loss.
However, if the content is too large, it tends to crack during cold rolling, making it difficult to work. Therefore, the upper limit is set to 6.5%. Mn is an element necessary for forming MnS. The lower limit of 0.02% is less than this, the absolute amount of MnS is insufficient, and the upper limit is 0.15%.
Exceeds this range, an appropriate dispersion state of MnS cannot be obtained. S is MnS, (Mn · F
e) Element necessary for forming S, with a lower limit of 0.001
% Is less than this, the absolute amounts of MnS and (Mn.Fe) S are insufficient, and the upper limit of 0.05% is limited to the above range, because if it exceeds this, desulfurization becomes difficult by finish high-temperature annealing.

When AlN is used in addition to sulfide, acid-soluble Al and N are added. Acid soluble Al is an element necessary for forming AlN, and the lower limit is 0.01%
Is less than this, the absolute amount of AlN is insufficient, and the upper limit is 0.0
If it exceeds 4%, an appropriate dispersion state of AlN cannot be obtained, so the content is limited. N is an element necessary for forming AlN. The lower limit of 0.03% is less than the lower limit, the absolute amount of AlN is insufficient, and the upper limit of 0.015% is over, secondary recrystallization is unstable. , And blisters are likely to be generated.

In addition, at least one of Cu, Sn and Sb may be added at 1.0% or less for the purpose of strengthening the inhibitor. For C, 0.03 to 0.
10% is desirable. If the lower limit of 0.03% is less than this, the secondary recrystallization becomes unstable, and if the upper limit of 0.10% is more than this, the decarburization time becomes longer, which is economically disadvantageous.

Next, the molten steel is rapidly solidified by a twin roll method or the like to produce a thin slab having a thickness of 0.3 to 6.0 mm. A product having a final thickness of 0.05 to 0.40 mm is assumed. At times, in order to obtain good secondary recrystallization, the cold rolling reduction is insufficient when the diameter is less than 0.3 mm, and the cold rolling reduction is excessive when the distance exceeds 6.0 mm. In the present invention, in order to have an equiaxed cast structure and a random texture, the casting atmosphere gas is limited to argon gas. The degree of supercooling of the molten steel during solidification is desirably 10 ° C or less. Further, after the solidification is completed, 600 ° C.
It is preferable to rapidly cool the temperature range up to 10 ° C./sec. Here, the inhibitor was not precipitated at a temperature of 600 ° C. or less, so the temperature range was limited to a temperature range of 600 ° C. or more. Also, the lower limit of 10 ° C./sec is because below this, the inhibitor grows, agglomerates and coarsens, and the crystal grains grow and coarsen. Furthermore, there is a method in which a slight reduction is applied to the thin slab in order to obtain the toughness of the slab. Here, when a nitride is also required as an inhibitor, 950 is required for precipitation of AlN or the like.
It is desirable to perform intermediate annealing at a temperature of 1200 ° C. for 30 seconds to 30 minutes.

Next, cold rolling is performed once or twice or more including intermediate annealing. The final cold rolling reduction at this time is 60% to 90% in order to obtain a product having a high degree of Goss accumulation.
Is required. Thereafter, decarburization annealing is performed in a wet hydrogen atmosphere, an annealing separator such as MgO is applied, and finish annealing at 1100 ° C. or more is performed for secondary recrystallization and purification, so that magnetic properties are good. A simple grain-oriented electrical steel sheet is manufactured. Next, an example of the present invention will be described.

[0019]

【Example】

[Example 1] Molten steel containing the component compositions shown in Table 1 was formed into a thin slab 2.4 mm thick by twin-roll rapid solidification. As for the casting conditions, the roll diameter was 300 mmφ and the roll peripheral speed was 440.
mm / sec, the molten steel roll contact time was about 0.3 seconds.
The molten steel temperature at the pool was 1495 ° C. As shown in Table 2, the casting atmosphere had two levels of Ar and N ₂ . Immediately after casting, steam-water cooling was performed immediately below the twin rolls. The secondary cooling rate from 1400 ° C. to 600 ° C. is 100 ° C./sec. FIG. 2 shows a casting structure in which the casting atmosphere is Ar and N ₂ . Casting atmosphere is A
r is an equiaxed crystal (FIG. 2A), and N ₂ is a columnar crystal (FIG. 2A).
(B)). Next, the obtained slab was pickled and then cold-rolled to a thickness of 0.8 mm. Next, it was annealed in wet hydrogen and cold rolled again to a thickness of 0.30 mm. Furthermore, after decarburizing annealing in wet hydrogen and applying MgO powder, high temperature annealing was performed in a hydrogen gas atmosphere at 1200 ° C. for 10 hours. Table 2 shows the magnetic properties of the obtained products. Regarding the magnetism of the product, the casting atmosphere was Ar having a higher magnetic flux density than other casting atmospheres.

[0020]

[Table 1]

[0021]

[Table 2]

Example 2 Molten steel containing the component compositions shown in Table 3 was formed into a 2.3 mm thick thin slab by a twin roll rapid solidification method. The casting conditions were as follows: a roll diameter of 300 mmφ, a roll peripheral speed of 450 mm / sec, and a molten steel roll contact time of about 0.3 mm.
Seconds. The molten steel temperature at the pool was 1495 ° C. As shown in Table 4, the casting atmosphere was set at two levels of Ar and N ₂ . Immediately after casting, steam-water cooling was performed immediately below the twin rolls. The secondary cooling rate from 1400 ° C. to 600 ° C. is 100 ° C./sec. Then, the obtained slab was annealed at 1120 ° C. for 5 minutes, pickled, and then cold rolled to a thickness of 0.30 mm. Next, after decarburizing annealing in wet hydrogen and applying MgO powder as a coating cloth, 1200 ° C.
For 10 hours in a hydrogen gas atmosphere. As shown in Table 4, the magnetism of the obtained product was such that the casting atmosphere was Ar, the magnetic flux density was higher than the other casting atmospheres, and the iron loss was good.

[0023]

[Table 3]

[0024]

[Table 4]

Example 3 Molten steel containing the component composition shown in Table 5 was formed into a 2.0 mm thick thin slab by a twin-roll rapid solidification method. The casting conditions were a roll diameter of 300 mmφ, a roll peripheral speed of 550 mm / sec, and a molten steel roll contact time of about 0.3 seconds. The molten steel temperature at the pool was 1495 ° C. The casting atmosphere is Ar . Regarding the secondary cooling conditions after casting, steam-water cooling was performed immediately below the twin rolls. Secondary cooling rate is 145 ° C up to 600 ° C
/ Sec.

Next, the obtained slab was annealed at 1120 ° C. for 5 minutes, pickled, and then cold rolled.
The thickness was 23 mm. Next, decarburization annealing is performed in wet hydrogen, and MgO
After the powder was coated with a cloth, high-temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. _Regarding the magnetism of the obtained product, the magnetic flux density is B ₈ = 1.92 (T), and the iron loss W _17/50 = 0.8.
At 7 (kg / W), good magnetic properties were obtained.

[0027]

[Table 5]

[0028]

According to the present invention, a unidirectional electrical steel sheet having a high magnetic flux density by using a thin cast slab of silicon steel obtained by a rapid solidification method as a raw material and omitting hot rolling can be obtained at low cost and energy saving. Because it can be manufactured, the industrial contribution is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a gas film layer on a roll surface in a pool portion of a twin roll.

FIGS. 2A and 2B are photographs of a metal structure of a thin cast slab at a thickness of １ ／, wherein FIG.
Is N ₂ gas.

[Explanation of symbols]

 1 roll 2 molten steel 3 gas film layer 4 casting atmosphere gas

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01F 1/16 H01F 1/16 B (56) References JP-A-2-258149 (JP, A) JP-A-4-4953 ( JP, A) JP-A-62-267448 (JP, A) JP-A-2-258922 (JP, A) JP-A-56-163235 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , (DB name) B22D 11/00 B22D 11/06 330 C22C 33/04 C22C 38/00 303 H01F 1/16

Claims (2)

(57) [Claims] In a twin-roll continuous casting, S is expressed by weight.
i: 2.5 to 6.5%, Mn: 0.02 to 0.15%,
S: Molten steel containing 0.001 to 0.05% as a basic component is continuously supplied and rapidly solidified, and 0.3 to 6.
A method for producing a thin slab for a grain-oriented electrical steel sheet, wherein a continuous pool of a thin slab having a thickness of 0 mm is subjected to an argon gas atmosphere in a pool portion of a twin roll. 2. Acid-soluble Al: 0.01 to 0.04%,
The method for producing a thin slab for a grain-oriented electrical steel sheet according to claim 1, wherein N: 0.003 to 0.015% is contained.