JPH05253602A - Manufacture of cast strip for grain-oriented silicon sheet - Google Patents

Abstract

PURPOSE:To obtain a thin case slab for grain-oriented silicon sheet which is excellent in toughness and improve the coiling and passing characteristics thereof, by reducing the thickness at the specified draft in the temperature range from the completion of solidification to the specified value when the molten steel of grain-oriented silicon sheet is rapidly solidified. CONSTITUTION:In the method where the molten steel containing 2.0-8.0wt.% Si and other components necessary for the grain-oriented silicon sheet is rapidly solidified to make a thin cast slab by the surface of a moving and updating cooling body, when the thin cast slab is rolled in the temperature range from the completion of solidification to 700 deg.C, and the temperature T ( deg.C) to start rolling is set 700-1100 deg.C, the thickness reduction of 45% or less is executed at the draft to be calculated by substituting the temperature T to start rolling into the formula or at the larger draft, while the thickness reduction of 45% or more is executed at the draft of 5% or more but not exceeding 45% when the temperature to start rolling exceeds 1100 deg.C.

Description

Detailed Description of the Invention

[0001]

The present invention relates to S of 2.0-8.0%.
The present invention relates to a method for producing a thin slab for unidirectional electrical steel sheet which contains i and is excellent in toughness.

[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 characteristics such as 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. So recently
A technology has been developed to directly melt molten electromagnetic steel into a ribbon by the 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.

The method for producing a grain-oriented electrical steel sheet by the rapid solidification method is mainly disclosed for improving magnetic properties. For example, in Japanese Examined Patent Publication No. 56-51216 and Japanese Examined Patent Publication No. 56-43295, in both cases, molten steel is cooled so that the solidification cooling rate at the center of the mold is 1 ° C./sec or more, and at least 600 ° C. even after solidification. Up to 0.05
By rapidly cooling at a rate of not less than ° C / sec, a cast piece in which precipitates such as sulfides, nitrides, and carbides are almost solid-solved is obtained, and finely dispersed by precipitation treatment in subsequent steps.

[0004]

As described above, all of the conventionally disclosed methods for producing a grain-oriented electrical steel sheet by the rapid solidification method are aimed at obtaining desirable magnetic properties. However, the inventors of the present invention faced a problem that it is necessary to solve the toughness of the thin slab in the subsequent step when the slab is industrially produced by the rapid solidification method according to the conventional technique. That is, in the rapidly solidified cast slab according to the prior art, the number of times of re-bending is very poor, continuous annealing line, slab cracking occurs during cold rolling, etc. There is.

The present inventors have tackled the problem of solving the brittleness problem of such a thin slab for a grain-oriented electrical steel sheet without imposing too much facility load.

[0006]

In the present invention, as a result of repeated studies to achieve the above object, Si: 2.0 to
Known inhibitors of 8.0% and unidirectional electrical steel,
In the method of rapidly melting and solidifying molten steel, which contains other elements necessary for electromagnetic steel, and the balance of which is substantially Fe, by the moving and renewing cooling body surface to form thin cast pieces, from the completion of solidification of thin cast pieces to 700 ° C When rolling in the temperature range of
When the rolling start temperature T (° C.) is 700 to 1100 ° C., the rolling start temperature is 11% or less when the rolling start temperature T is calculated by substituting the rolling start temperature T into the following formula (1).
It has been found that when the temperature exceeds 00 ° C., a thin cast piece for a grain-oriented electrical steel sheet excellent in toughness can be obtained by reducing the thickness by a rolling reduction of 5% or more and 45% or less.

[0007]

[Equation 2] The present invention will be described in detail below. As a result of observing the fracture surface after the repeated bending test, the present inventors have found that all of them are intragranular fractures. From this, as a cause of embrittlement of the thin cast piece for unidirectional electrical steel sheet, in addition to the large crystal grain size in the thin cast piece as compared with the hot rolled sheet of the conventional hot rolling process, Si addition As a result, it was found that the toughness of the ferrite material itself deteriorates, making it difficult to cross-slip during the bending and bending of thin cast pieces. Furthermore, in the thin slab that is rapidly solidified,
It was also found that there are more defects in the casting that are introduced due to the large shrinkage ratio of the molten metal or the thermal stress during cooling, as compared with ordinary continuous cast materials. This is considered to be due to the fact that solidification occurs instantaneously on the order of 0.1 seconds in the rapid solidification method. Therefore, as a result of repeated measures, it was found that the toughness is improved by imparting a working strain at a predetermined temperature to facilitate cross-slip and reduce defects contained in the slab, and thus completed the present invention. . The present invention will be described in detail below.

[0008]

Next, the reason why the steel composition and manufacturing conditions are limited as described above in the present invention will be described in detail. The reasons for limiting the steel composition are as follows. Si has a lower limit of 2.0% in order to improve iron loss, but if it is too much, it easily cracks during cold rolling, which makes working difficult, so the upper limit is 8.0.
%.

Further, in order to manufacture the grain-oriented electrical steel sheet, it is preferable to add the following constituent elements. Mn is an element necessary for forming MnS, and is preferably 0.02 to 0.15% in order to obtain an appropriate dispersed state. S is Mn
An element necessary to form S, (Mn · Fe) S,
In order to obtain a proper dispersion state, 0.001 to 0.05% is desirable. Further, when AlN is used in addition to the sulfide, acid-soluble Al and N are added. In order to obtain a suitable dispersed state of AlN, Al is preferably 0.01 to 0.04% and N is preferably 0.003 to 0.02%. Others, Cu, S
n, Sb, and Se are 1.0 to strengthen the inhibitor.
% Or less, at least one kind may be added. As for C, 0.10% or less is desirable. Upper limit 0.10%
The reason is that if the amount is larger than this, 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 obtain a thin cast piece, and the plate thickness at that time is 0.5 to 3.5.
mm is preferred. The upper limit of 3.5 mm is limited because the solidified shell becomes unstable due to the weight of the slab above this. The lower limit of 0.5 mm is limited because production efficiency is poor below this range.

The reason why hot rolling is performed at a predetermined rolling reduction in a temperature range from immediately after solidification to 700 ° C. is as follows. The lower limit of 700 ° C. of the rolling temperature is limited because if it is lower than this, the hot deformation resistance becomes high and hot rolling becomes difficult. Figure 1
Indicates the relationship between the hot rolling rate at the rolling start temperature of 1100 ° C. and the number of times of bending. This shows the number of times until breaking with a 90 ° bending tester having a radius of 8 mm. The number of turns shall be one when turning 90 °. From this figure, in order to improve the toughness, a rolling reduction of 5% or more is required. Further, the effect of improving the toughness is saturated at 45% or more. This tendency is 700 ℃
This tendency is commonly seen in the above temperature range.
Therefore, since the equipment becomes huge and industrialization is difficult, the upper limit was limited to 45%. Further, FIG. 2 shows changes in the number of times of rolling and bending at each rolling start temperature and rolling reduction. From this figure, when rolling in the temperature range from completion of solidification of the thin slab to 700 ° C, when the rolling start temperature T (° C) is 700 to 1100 ° C, the rolling start temperature T is substituted into the following formula (1). When the rolling start temperature exceeds 1100 ° C., the reduction is performed at a rolling reduction of not less than 5% and not more than 45%.

[0012]

[Equation 3] By performing hot rolling under the above conditions, it is possible to obtain a thin slab for unidirectional electrical steel sheets having excellent toughness. Further, in order to obtain the required magnetic characteristics, it is desirable that the rapidly solidified cast piece be cooled by steam cooling or the like immediately after solidification.

Next, when a nitride is also required as an inhibitor, it is necessary to deposit 950 to 1200 for the precipitation of AlN or the like.
It is desirable to perform intermediate annealing at 30 ° 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 requires a reduction of 50% or more in order to obtain a product having a high Goss integration degree. After this, decarburization annealing is performed in a wet hydrogen atmosphere, and further Mg
By applying an annealing separator such as O and performing final annealing at 1100 ° C. or higher for secondary recrystallization and purification, a unidirectional electrical steel sheet having good magnetic properties is manufactured. Next, examples of the present invention will be described.

[0014]

【Example】

(Example 1) A molten steel containing the composition shown in Table 1 was (A) 2.7 mm, (B) 2.3 m by a twin roll rapid solidification method.
m, (C) 2.0 mm thick cast pieces were cast. As for the casting conditions, the roll diameter is 300 mmφ and the molten steel roll contact time is about 0.3 seconds. Immediately after casting, water-cooling was performed immediately below the twin rolls, and (A) and (B) were hot-rolled at 1100 ° C. to have a thickness of 2.0 mm. Table 2 shows the respective rolling reductions. Table 2 shows the number of times of bending of the obtained steel strip. This shows the number of times until breaking with a 90 ° bending tester having a radius of 8 mm. Good toughness was obtained under the conditions (A) and (B).

Then, the obtained steel strip is annealed at 1120 ° C. for 5 minutes, further pickled, and then cold-rolled to 0.
29mm thick. Then decarburize and anneal in moist hydrogen to remove MgO
After applying the powder, high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. At this time, the magnetic properties of the obtained product are also shown in Table 2.

[0016]

[Table 1]

[0017]

[Table 2]

(Example 2) Molten steel having the composition shown in Table 3 was subjected to a twin roll rapid solidification method to obtain (D) 3.0 mm,
(E) 2.5 mm, (F) 2.2 mm thick cast pieces were cast. As for the casting conditions, the roll diameter is 300 mmφ and the molten steel roll contact time is about 0.3 seconds. For (D) and (E), hot rolling was performed at 1050 ° C. to obtain a thickness of 2.2 mm. The rolling reduction at this time is shown in Table 4. Table 4 shows the number of times of bending of the obtained steel strip. Good toughness was obtained under the conditions (D) and (E). Then, the obtained steel strip 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 0.29 mm. Next, decarburization annealing was performed in wet hydrogen, MgO powder was applied, and then high temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere. The magnetic properties of the obtained product were as shown in Table 4.

[0019]

[Table 3]

[0020]

[Table 4]

[0021]

According to the present invention, it is possible to obtain a silicon steel thin slab having good toughness and excellent sheet passing property by the rapid solidification method, and to make the unidirectional electrical steel sheet inexpensive and energy saving. Since it can be manufactured, its industrial contribution is extremely large.

[Brief description of drawings]

FIG. 1 shows the relationship between the thickness reduction rate of thin cast pieces and the number of times of bending of the obtained steel strip.

FIG. 2 shows changes in the number of times of repeated bending at each rolling start temperature and rolling reduction.

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Claims (2)

[Claims] 1. A molten steel containing Si: 2.0 to 8.0% by weight, a known inhibitor of unidirectional electromagnetic steel, and other element elements necessary for the electromagnetic steel, and the balance being substantially Fe. In the method of rapidly cooling and solidifying by the surface of a cooling body to be renewed to form a thin cast piece,
When rolling in the temperature range up to 0 ° C, the rolling start temperature T
When (° C) is 700 to 1100 ° C, the rolling start temperature T is substituted into the following formula (1) to obtain a rolling reduction of 45% or more.
A thin cast piece for unidirectional electrical steel sheet having excellent toughness, which is characterized by performing a thickness reduction of 5% or more and 45% or less when the rolling start temperature exceeds 1100 ° C. Production method. [Equation 1] 2. The method according to claim 1, wherein when the molten steel is rapidly solidified into a thin cast piece, the plate thickness is set to 0.5 to 3.5 mm.