JPH04367353A - Production of cast thin sheet for grain-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel having high magnetic flux density by making pouring basin part helium gas atmosphere at the time of rapidly solidifying the specific molten steel in twin roll type continuous casting. CONSTITUTION:In the twin roll type continuous casting, the molten metal 2 basically containing 2.5-6.5wt.% Si, 0.02-0.155 Mn, 0.01-0.05% S is continuously supplied and rapidly solidified to continuously cast the cast thin sheet having 0.3-6.0mm thickness. At this time, the pouring basin part in the twin rolls 1 is made to the helium atmosphere 4. In this result, the cast thin sheet having equiaxed grain casting structure is obtd. and further, by improving texture to random orientation, too, the magnetic flux density can be improved. Therefore, the silicon steel cast thin sheet obtd. with rapid solidifying method is used as stock and hot-rolling is saved, and the grain-oriented silicon steel sheet having high magnetic flux density can be produced in low cost and energy saving.

Description

[Detailed description of the invention]

0001

[Industrial field of application] The present invention is directed to
The present invention relates to a method for producing thin slabs for unidirectional electrical steel sheets having a thickness of 0.3 to 6.0 mm, including the method.

0002

2. Description of the Related Art Unidirectional electrical steel sheets are used as core materials for electrical equipment such as transformers, and must have good magnetic properties such as excitation properties and iron loss properties. Moreover, in recent years, there has been an increasing demand in the market for low core loss materials with particularly low energy loss. However, conventional manufacturing methods require complicated process treatments such as hot rolling, cold rolling, and annealing, resulting in a problem of extremely high manufacturing costs. Recently, a technology has been developed to directly turn molten electrical steel into a thin ribbon using a rapid solidification method. According to this method, a finished product or a semi-finished product can be produced directly from molten steel, making it possible to significantly reduce manufacturing costs.

[0003] As a method for manufacturing grain-oriented electrical steel sheets by this rapid solidification method, there is a method described, for example, in Japanese Patent Application Laid-open No. 11619/1983. Here, Si: 2.5 to 6.5
It has been proposed to supply a molten metal containing 0.7 to 2.0 mm thick and rapidly solidify it using a twin roll system to obtain a slab with a thickness of 0.7 to 2.0 mm.

0004

[Problem to be Solved by the Invention] However, according to the findings of the present inventors, products manufactured from this cast slab for unidirectional electrical steel sheets have the problem of low magnetic flux density even if the iron loss is good. be. Therefore, the present inventors {110}<001>
We have been working on a method for manufacturing thin slabs to obtain unidirectional electrical steel sheets with high orientational integration and good magnetic flux density.

[0005]

[Means for Solving the Problems] As a result of repeated studies to solve the above problems, the present inventors have developed a twin-roll continuous casting method in which Si: 2.5 to 6.5% by weight and Mn: 0. .0
Molten steel containing 2 to 0.15% and S: 0.01 to 0.05% as basic components is continuously supplied and rapidly solidified to form a thin slab with a thickness of 0.3 to 6.0 mm. It was discovered that during continuous casting, by creating a helium gas atmosphere in the pool of twin rolls, a higher magnetic flux density than before can be obtained.

The present invention will be explained in detail below. Generally, grain-oriented electrical steel sheets can be manufactured by sufficiently causing secondary recrystallization during the final annealing of the manufacturing process to obtain a so-called Goss texture. In order to obtain this Goss texture, the coarsening of the primary recrystallized grains is suppressed, and {110}<001
> recrystallized grains are selectively grown in a certain temperature range. In other words, it is necessary to create a base that will allow secondary recrystallization. On the other hand, JP-A-63-1
In the rapid solidification method described in Publication No. 1619, {100}<0v
w〉There is a problem that the presence of a columnar crystal casting structure is unavoidable. It is well known that this {100}<0vw> becomes a crystal with an orientation close to {100}<0vw> even if rolled and recrystallized. Therefore, if there are many columnar crystals, the number of secondary recrystallization defects increases, which deteriorates the magnetic properties of the product and makes it impossible to obtain a high magnetic flux density. Therefore, in order to improve the magnetic flux density of the finished product, it is necessary to reduce the columnar crystal casting structure in a thin slab as much as possible to create an equiaxed crystal casting structure. As a result, the present inventors believed that in order to improve the solidified structure morphology during rapid solidification, it was necessary to further increase the solidification rate.

Generally, in the twin roll rapid solidification method, as shown in FIG.
A gas film layer 3 exists between the molten steel 2 and the molten steel 2, and as a heat transfer resistance from the surface of the molten steel 2 to the roll 1 side, it is necessary to consider the overall heat transfer resistance including the gas film layer 3 in addition to the roll body 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 rapid solidification method is on the order of 0.1 seconds, and it is necessary to form a solidified shell in this short time. The impact is likely to be very large. Therefore, the present inventors have focused on the entrainment of the atmospheric gas 4 in the pool of twin rolls, and have investigated the casting structure morphology using various gases. As a result, when the molten metal pool was placed in a helium gas atmosphere, a thin slab with an equiaxed grain casting structure was obtained (Fig. 2(a)), and the texture was further improved to have a random orientation (Fig. 3(a)). It has been found that magnetic flux density is improved by a)).

Although the exact reason for this is not certain, the following may be considered. Since helium has high thermal conductivity, the growth rate of the solidified phase is fast and the temperature gradient at the solid-liquid interface is large. Therefore, the solidified structure tends to be equiaxed (FIG. 2(a)). On the other hand, since air, nitrogen, and argon have low thermal conductivity, the growth rate of the solidified phase is relatively slow, and the temperature gradient at the solid-liquid interface is also small. Therefore, the solidified structure tends to become directional columnar crystals (FIG. 2(b)). It is generally said that the solidified shell grows in the <100> direction, and it is believed that the above-mentioned difference in the morphology of the cast structure affected the texture of the thin slab. In other words, when the molten pool during rapid solidification is placed in a helium gas atmosphere, as shown in Figure 3(a), the structure of the resulting thin slab has a significant decrease in {100}<0vw> columnar crystals and almost random orientation. becomes. On the other hand, nitrogen (Fig. 3(b)), argon and air have {100}<0vw
〉Columnar crystals are on the increase.

As described above, the present inventors focused on the entrainment of atmospheric gas in the pool of twin rolls and investigated various gases. As a result, when the pool is made into a helium gas atmosphere, equiaxed It was found that a thin cast slab with a grain casting structure and a random texture was obtained, and the magnetic flux density was improved.

0010

[Operation] Next, the reason why the steel composition and manufacturing conditions are limited as described above in the present invention will be explained in detail. The reasons for limiting the steel composition are as follows. The lower limit of Si is set to 2.5% in order to improve iron loss, but if it is too large, it tends to break during cold rolling and processing becomes difficult, so the upper limit is set to 6.5%.

[0011] Mn is an element necessary to form MnS, and the lower limit of 0.02% means that if it is less than this, the absolute amount of MnS is insufficient, and the upper limit of 0.15% means that if it exceeds this, MnS will not be present.
Since it is not possible to obtain an appropriate dispersion state, the amount is limited to the above range. S is an element necessary to form MnS, (Mn・Fe)S, and the lower limit of 0.01% is less than MnS, (
The absolute amount of Mn/Fe)S is insufficient, and the upper limit of 0.05% is
If it exceeds this range, desulfurization becomes difficult during final high-temperature annealing, so it was limited to the above range.

Furthermore, when AlN is used in addition to sulfide, acid-soluble Al and N are added. Acid-soluble Al is an element necessary to form 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
The content was limited to 4% because if it exceeds this, a proper dispersion state of AlN cannot be obtained. N is an element necessary to form AlN. If the lower limit is 0.003%, the absolute amount of AlN will be insufficient, and if the upper limit is 0.015%, secondary recrystallization will be unstable. As a result, blisters are likely to occur, so it was limited to the above range.

[0013] In addition, at least one of Cu, Sn, and Sb may be added in an amount of 1.0% or less in order to strengthen the inhibitor. For C, 0.03-0.10%
is desirable. If the lower limit is 0.03%, secondary recrystallization will become unstable, and if the upper limit is 0.10%, the time required for decarburization will become longer, which is economically disadvantageous.

[0014] Next, this molten steel is rapidly solidified by a twin roll method to produce a thin slab with a thickness of 0.3 to 6.0 mm, but assuming a product with a final plate thickness of 0.05 to 0.40 mm. ,
In order to obtain good secondary recrystallization, a cold rolling reduction of less than 0.3 mm is insufficient, and a cold rolling reduction of more than 6.0 mm is excessive. In the present invention, the casting atmosphere gas is limited to helium in order to obtain an equiaxed crystal casting structure and a random texture. At this time, it is desirable that the helium gas content be 90% or more. Furthermore, after solidification is completed, the temperature range up to 600°C is increased by 10°C in order to suppress the growth of inhibitors, coarsening of agglomerations, and growth of crystal grains.
It is preferable to perform rapid cooling at a speed of 1/sec or more. Here, since the inhibitor does not precipitate when the lower limit of the quenching temperature range is less than 600°C, the temperature range was limited to 600°C or higher. Further, the lower limit of the cooling rate is 10° C./sec because if the cooling rate is less than this, the inhibitor will grow, aggregate and become coarse, and the crystal grains will grow and become coarse.

[0015] This thin slab material proceeds to the next process without performing a hot rolling process. Here, if nitride is also required as an inhibitor, 950
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 needs to be 60 to 90% in order to obtain a product with a high degree of goss accumulation.

After this, decarburization annealing is performed in a wet hydrogen atmosphere, and an annealing separator such as MgO is applied, followed by final annealing at 1100°C or higher for secondary recrystallization and purification. A unidirectional electrical steel sheet with good properties is produced. Next, examples of the present invention will be described.

[0017]

【Example】

(Example 1) Molten steel having the composition shown in Table 1 was made into a thin slab with a thickness of 2.4 mm by a twin roll rapid solidification method. The casting conditions are a roll diameter of 300mmφ and a roll circumferential speed of 440mm.
mm/sec, and the roll contact time of the molten steel was about 0.3 seconds. As shown in Table 2, the casting atmosphere consisted of He, N2, A
r, 4 levels of air. Immediately after casting, air-water cooling was performed from directly below the twin rolls. The secondary cooling rate from 1400°C to 600°C is 100°C/sec.

FIG. 2 shows the casting structure in the casting atmospheres of He and N2. In the He casting atmosphere, the crystals were equiaxed (FIG. 2(a)), and in the N2 atmosphere, they were columnar crystals (FIG. 2(b)). Moreover, the texture of the thin slab at this time is shown in FIG. In the casting atmosphere He, random texture (Fig. 3(a)),
In N2, {100}〈0vw〉 texture (Fig. 3(b)
)Met.

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 at 1200° C. for 10 hours in a hydrogen gas atmosphere. Table 2 shows the magnetic properties of the obtained product. Regarding the magnetism of the product, a higher magnetic flux density was obtained in the He casting atmosphere than in other casting atmospheres.

[0020]

[Table 1]

[0021]

[Table 2]

(Example 2) Molten steel having the composition shown in Table 3 was made into a thin slab with a thickness of 2.3 mm by a twin roll rapid solidification method. The casting conditions were as follows: roll diameter was 300 mmφ, roll peripheral speed was 450 mm/sec, and roll contact time of molten steel was approximately 0.
It was 3 seconds. The casting atmosphere was He as shown in Table 4.
, N2, Ar, and air. Immediately after casting, air-water cooling was performed from directly below the twin rolls. 6 from 1400℃
The secondary cooling rate to 00°C is 100°C/sec in both cases.

[0023] Next, the obtained slab was annealed at 1120°C for 5 minutes, further pickled, and then cold rolled.
．． The thickness was set to 30 mm. Next, decarburization annealing is performed in wet hydrogen, and M
After applying the gO powder, high temperature annealing was performed at 1200° C. for 10 hours in a hydrogen gas atmosphere. The magnetism of the obtained product is
As shown in Table 4, when the casting atmosphere was He, the magnetic flux density was higher and the iron loss was better than when using other casting atmospheres.

[0024]

[Table 3]

[0025]

[Table 4]

(Example 3) Molten steel having the composition shown in Table 5 was made into a thin slab with a thickness of 2.0 mm by a twin roll rapid solidification method. The casting conditions were as follows: roll diameter was 300 mmφ, roll circumferential speed was 550 mm/sec, and roll contact time of molten steel was approximately 0.
It was 3 seconds. The casting atmosphere was He. The secondary cooling conditions after casting were air-water cooling from directly below the twin rolls. The secondary cooling rate was 145°C/sec up to 600°C.

Next, the obtained slab was annealed at 1120°C for 5 minutes, further pickled, and then cold rolled.
The thickness was set to 23 mm. Next, decarburization annealing is performed in wet hydrogen, and Mg
After applying O powder, high temperature annealing was performed at 1200° C. for 10 hours in a hydrogen gas atmosphere. The magnetism of the obtained product is as follows: magnetic flux density is B8 = 1.94 (T), iron loss W17/50 =
Good magnetic properties were obtained at 0.87 (W/kg).

[0028]

[Table 5]

[0029]

[Effects of the Invention] According to the present invention, a unidirectional electrical steel sheet having a high magnetic flux density can be produced at low cost and with energy savings by using a silicon steel thin slab obtained by a rapid solidification method as a raw material and omitting hot rolling. Therefore, the contribution to industry is extremely large.

[Brief explanation of drawings]

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

[Figure 2] A photograph of the casting metallographic structure of a thin slab with a thickness of 1/4.
The casting atmosphere in a) is He, and in (b) is N2.

FIG. 3 is a {100} pole figure showing the crystal orientation of a thin slab.
In (a), the casting atmosphere is He, and in (b), it is N2.

Claims (2)

[Claims] Claim 1: In twin-roll continuous casting, Si: 2.5 to 6.5%, Mn: 0.02 to 0.15% by weight.
, S: 0.3-6.
A method for producing a thin slab for unidirectional electrical steel sheets, which comprises creating a helium gas atmosphere in a pool of twin rolls when continuously casting a thin slab having a thickness of 0 mm. [Claim 2] Acid-soluble Al: 0.01 to 0.04%
, N: 0.003 to 0.015%. The method for producing a thin slab for grain-oriented electrical steel sheet according to claim 1.