JPH0631397A - Production of thin slab for grain-oriented electrical steel sheet - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for manufacturing a thin slab for unidirectional electrical steel sheet by a rapid solidification method, which can obtain a unidirectional electrical steel sheet having high magnetic flux density by omitting hot rolling. . [Structure] (1) In twin roll type continuous casting, Si: 2.5 to 6.5% and Mn: 0.02 to 0.15 by weight
%, S: 0.001 to 0.05% as a basic component, molten steel is continuously supplied to quench and solidify the steel.
A method for producing a thin slab for a grain-oriented electrical steel sheet, characterized in that, when continuously casting a thin slab with a thickness of 6.0 mm, the molten metal pool of the twin rolls is placed in an argon gas atmosphere. (2)
Acid-soluble Al: 0.01 to 0.04%, N: 0.003
The method of claim 1 containing .about.0.015%.

Description

Detailed Description of the Invention

[0001]

The present invention relates to S of 2.5 to 6.5%.
The present invention relates to a method for manufacturing a thin slab for a grain-oriented electrical steel sheet having a thickness of 0.3 to 6.0 mm containing i.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are used as iron core materials for electrical equipment such as transformers, and must have good magnetic excitation characteristics and iron loss characteristics. Moreover, in recent years, there has been an increasing market demand for low iron loss materials with particularly low energy loss.

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

A method for obtaining a thin slab by this rapid solidification method and producing a unidirectional electrical steel sheet using the thin slab as a starting material is disclosed in, for example, JP-A-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 having a thickness of 0.7 to 2.0 mm. 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 unidirectional electrical steel sheet has a low magnetic flux density, which is a problem in controlling the casting structure. I thought there was a point. The present invention is intended to solve such a problem, and by focusing on the atmosphere during casting and controlling the cast structure during solidification, {11
An object of the present invention is to provide a thin cast product manufacturing method for obtaining a grain-oriented electrical 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 main point is that, in twin roll type continuous casting, Si: 2.5-6.5% and Mn: 0.02-by weight.
Molten steel containing 0.15% and S: 0.001 to 0.05% as a basic component is continuously supplied and rapidly solidified,
When continuously casting thin slabs having a thickness of 0.3 to 3.0 mm, the twin pool rolls have a molten metal pool in an argon gas atmosphere, which makes it possible to obtain a higher magnetic flux density than conventional.

[0007]

The present invention will be described in detail below. Generally, a grain-oriented electrical steel sheet can 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, growth coarsening of the primary recrystallized grains is suppressed, and only the recrystallized grains having the {110} <001> orientation are selectively grown within a certain temperature range. That is, it is necessary to make a base material for secondary recrystallization. On the other hand, JP-A-63-11
The 619 rapid solidification method has a problem that the presence of a cast structure of {100} <0vw> columnar crystals cannot be avoided. This {100} <0vw> is {10} even if rolled and recrystallized.
It is well known that the crystal has an orientation close to 0} <0vw>. Therefore, when there are many columnar crystals, the number of defective secondary recrystallization portions increases, so that the magnetic properties of the product are deteriorated 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 reduce the cast structure of columnar crystals in the thin cast piece as much as possible to obtain a cast structure of equiaxed crystals. The present inventors considered that in order to improve the solidification structure morphology during this rapid solidification, the atmosphere of the pool should be changed to further increase the solidification rate.

Generally, in the twin roll rapid solidification method, as shown in FIG.
/ The gas film layer 3 exists between the molten steels 2, and it is necessary to consider the overall heat transfer resistance including the gas film layer 3 in addition to the roll body 1 as the heat transfer resistance from the surface of the molten steel 2 to the roll 1 side. The gas film at this time is considered to have a thickness on the order of several μm. Usually, the contact time between the roll 1 and the molten steel 2 in the twin roll rapid solidification method is of the order of 0.1 seconds, and it is necessary to form the solidified shell in this short time, and the overall heat transfer resistance due to the gas film layer 3 The impact seems to be very large. Therefore, the present inventors have paid attention to the inclusion of the atmospheric gas 4 in the pool of twin rolls.

Then, various gases were used in place of the conventional atmosphere, and the cast microstructure was examined. As a result, when the molten metal pool is placed in an argon gas atmosphere, the
As shown in (a), it has been found that a thin slab having an equiaxed grain cast structure is obtained, and the texture is also improved in a random orientation to improve the magnetic flux density. On the other hand, in the nitrogen gas atmosphere, the solidified morphology tends to be columnar crystals having a directionality (FIG. 2 (b)).

The reason for this is that argon gas has a relatively high thermal conductivity and tends to increase the cooling rate. That is, although the argon gas has substantially the same thermal conductivity as the nitrogen gas, in the case of the nitrogen gas, a slight amount of nitrogen absorption is performed on the surface of the molten steel, so that the apparent thermal conductivity becomes small, and as a result, It is considered that the thermal conductivity of argon gas is higher than that of nitrogen gas.

As described above, the inventors of the present invention have studied various gases by paying attention to the entrainment of the atmospheric gas in the pool of twin rolls. It was found that a thin cast piece having a grain casting structure and a random texture was obtained, and the magnetic flux density was improved.

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

Si has a lower limit of 2.5 in order to improve iron loss.
%, But if it is too large, it easily cracks during cold rolling and processing becomes difficult, so the upper limit is made 6.5%. Mn is an element necessary for forming MnS, and if the lower limit is 0.02%, the absolute amount of MnS is insufficient if it is less than this, and the upper limit is 0.15%.
When MnS exceeds this value, an appropriate dispersed state of MnS cannot be obtained, so the above range was limited. S is MnS, (Mn · F
e) an element necessary for forming S, with a lower limit of 0.001
%, If it is less than this range, the absolute amounts of MnS and (Mn.Fe) S are insufficient, and if the upper limit is more than 0.05%, desulfurization is difficult in finish high temperature annealing, so the range is limited to the above range.

Furthermore, when AlN is used in addition to the 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
4% was limited because if it exceeds this, a proper dispersed state of AlN cannot be obtained. N is an element necessary for forming AlN, and if the lower limit is 0.03%, the absolute amount of AlN is insufficient below this range, and the upper limit is 0.015%, and secondary recrystallization is unstable above this range. In addition, blisters are likely to occur, so the content is limited to the above range.

In addition, at least one of Cu, Sn and Sb may be added in an amount of 1.0% or less for the purpose of strengthening the inhibitor. Regarding C, 0.03 to 0.
10% is desirable. This is because if the lower limit is 0.03%, if it is less than this range, the secondary recrystallization becomes unstable, and if the upper limit is more than 0.10%, the time required for decarburization becomes long, which is economically disadvantageous.

Next, this 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, and a product having a final plate thickness of 0.05 to 0.40 mm is assumed. At this time, in order to obtain good secondary recrystallization, the cold rolling reduction is insufficient if it is less than 0.3 mm, and the cold rolling reduction is excessive if it is more than 6.0 mm. In the present invention, the casting atmosphere gas is limited to argon gas in order to have an equiaxed cast structure and a random texture. The degree of supercooling of the molten steel when solidifying is preferably 10 ° C or lower. After completion of solidification, 600 ° C to prevent inhibitor growth, coarsening of aggregates, and growth of crystal grains.
It is preferable to rapidly cool the temperature range up to 10 ° C./second or more. Here, since the inhibitor does not precipitate at 600 ° C or lower, the temperature range is limited to 600 ° C or higher. Further, the lower limit of 10 ° C./sec is that the inhibitor grows and the aggregate coarsens and the crystal grains grow coarser below this. Further, in order to obtain the toughness of the slab, there is also a method of adding a slight reduction to the thin 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 ˜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 goss accumulation degree.
Is required. After that, decarburization annealing is performed in a wet hydrogen atmosphere, an annealing separator such as MgO is applied, and final annealing is performed at 1100 ° C. or higher for secondary recrystallization and purification. Unidirectional electrical steel sheet is manufactured. Next, examples of the present invention will be described.

[0019]

【Example】

[Example 1] A molten steel containing the composition shown in Table 1 was formed into a thin cast piece having a thickness of 2.4 mm by a twin roll rapid solidification method. The casting conditions are roll diameter 300 mmφ and roll peripheral speed 440.
mm / sec, the roll contact time of molten steel was about 0.3 sec.
The molten steel temperature in the pool was 1495 ° C. As shown in Table 2, the casting atmosphere was at two levels of Ar and N ₂ . Immediately after casting, water / water cooling was performed immediately below the twin rolls. The secondary cooling rate from 1400 ° C. to 600 ° C. is 100 ° C./sec in all cases. FIG. 2 shows a casting structure in which the casting atmosphere is Ar and N ₂ at this time. Casting atmosphere is A
equiaxed with r (FIG. 2 (a)), the N ₂ columnar crystals (Fig. 2
(B)). Then, the obtained slab was pickled and 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. Further, after decarburizing annealing in wet hydrogen and applying MgO powder, high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. Table 2 shows the magnetic properties of the obtained products. The magnetism of the product was such that the casting atmosphere was Ar and the magnetic flux density was higher than that of the other casting atmospheres.

[0020]

[Table 1]

[0021]

[Table 2]

Example 2 A molten steel containing the composition shown in Table 3 was formed into a thin cast piece having a thickness of 2.3 mm by a twin roll rapid solidification method. The casting conditions are: roll diameter 300 mmφ, roll peripheral speed 450 mm / sec, roll contact time of molten steel is about 0.3
It was seconds. The molten steel temperature in the pool was 1495 ° C. As shown in Table 4, the casting atmosphere was set to two levels of Ar and N ₂ . Immediately after casting, water / water cooling was performed immediately below the twin rolls. The secondary cooling rate from 1400 ° C. to 600 ° C. is 100 ° C./sec in all cases. Then, the obtained slab was annealed at 1120 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.30 mm. Next, decarburize and anneal in wet hydrogen, apply MgO powder to the coated cloth, then 1200 ° C
For 10 hours, decarburization annealing was performed in a hydrogen gas atmosphere. Regarding the magnetism of the obtained product, as shown in Table 4, 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 A molten steel containing the composition shown in Table 5 was made into a thin cast piece having a thickness of 2.0 mm by a twin roll rapid solidification method. The casting conditions are: roll diameter 300 mmφ, roll peripheral speed 550 mm / sec, molten steel roll contact time about 0.3.
It was seconds. The molten steel temperature in the pool was 1495 ° C. The casting atmosphere is He. The secondary cooling condition after casting was water-cooling immediately below the twin rolls. The secondary cooling rate was 145 ° C / sec up to 600 ° C.

Then, the obtained slab is annealed at 1120 ° C. for 5 minutes, further pickled, and then cold-rolled to 0.
It was 23mm thick. Next, decarburization annealing is performed in wet hydrogen to obtain MgO.
After coating the powder with a cloth, high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. The magnetism of the obtained product is such that the magnetic flux density is B ₈ = 1.92 (T) and the iron loss is W _17/50 = 0.8.
At 7 (kg / W), good magnetic properties were obtained.

[0027]

[Table 5]

[0028]

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

[Brief description of drawings]

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

FIG. 2 is a photograph of a cast metal structure of a thin slab with a thickness of ¼, (a) using Ar gas as a casting atmosphere, (b)
Is N ₂ gas.

[Explanation of symbols]

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

Claims (2)

[Claims] 1. In twin roll continuous casting, S by weight is used.
i: 2.5 to 6.5%, Mn: 0.02 to 0.15%,
Molten steel containing S: 0.001 to 0.05% as a basic component is continuously supplied to quench and solidify, and 0.3 to 6.
A method for producing a thin slab of unidirectional electrical steel sheet, characterized in that, when continuously casting a thin slab with a thickness of 0 mm, the molten metal pool of the twin rolls is placed in an argon gas atmosphere. 2. Acid-soluble Al: 0.01 to 0.04%,
N: 0.003 to 0.015% is contained, The manufacturing method of the thin cast piece for unidirectional electrical steel sheets of Claim 1 characterized by the above-mentioned.