JPH0631394A - Production of thin cast slab for non-oriented silicon steel sheet - Google Patents

Abstract

PURPOSE:To provide a producing method of a thin cast slab for non-oriented silicon steel sheet by a quench-solidifying method which the non-oriented silicon steel sheet having good iron loss characteristic can be obtd. by saving hot- rolling. CONSTITUTION:At the time of casting thin cast slab by continuously supplying molten steel 2 containing 0.01-8.0wt.% Si and the other necessary components to the electrical steel and the balance substantially Fe and executing quench- solidifying in the twin roll type continuous casting method, a pouring basin in the twin rolls 1 is made to be nitrogen gas atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin slab for a non-oriented electrical steel sheet containing 0.01 to 8.0% Si.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are widely used as iron core materials for rotating machines, small and medium-sized transformers, etc., and they 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 of obtaining a thin slab by a rapid solidification method and using it as a starting material is disclosed in, for example, Japanese Patent Laid-Open No. 2-194123, in which a molten metal containing Si: 0.1 to 4.0% by weight is used. Characterized by rapidly quenching and solidifying, hot rolling at a rolling reduction temperature of 600 to 1000 ° C. without reheating, and then cold rolling and finish annealing the obtained hot rolled steel strip. A method for manufacturing a non-oriented electrical steel sheet having excellent magnetic properties is disclosed. 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.

Further, some have focused on improving the crystal grain size of thin cast pieces. In JP-A-62-240714, the average particle size of the continuous body is set to 0.05 mm or more by selecting the condition of the surface gap of the cooling body during rapid solidification and the cooling condition of the slab after rapid solidification. Is disclosed, which discloses a method for producing a non-oriented electrical steel sheet having excellent magnetic properties. 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]

When the non-oriented electrical steel sheet is industrially produced by such a rapid solidification method according to the prior art, the iron loss characteristic is insufficient, and the cause is the control of the casting structure. There seems to be a problem. The present inventors aimed to improve the iron loss characteristics in the final product of the non-oriented electrical steel sheet by focusing on the atmosphere during this casting and controlling the casting structure of the molten steel during rapid solidification. .

[0006]

The present invention has been completed as a result of repeated studies for achieving the above object, and the gist thereof is in twin roll type continuous casting, in which Si: 0. When a thin slab is cast by continuously supplying and rapidly quenching and solidifying molten steel containing 01 to 8.0% and other component elements necessary for electromagnetic steel, and the balance being substantially Fe, There is a nitrogen gas atmosphere in the molten metal pool of the roll, which makes it possible to obtain better iron loss characteristics than before.

[0007]

The present invention will be described in detail below. Applications of electromagnetic steel sheets can be broadly divided into two categories: rotating machines and stationary machines. In these two applications, electromagnetic characteristics suitable for each are required. That is, isotropic electromagnetic characteristics in the plate plane are desired for materials for rotating machines, and materials having a non-oriented texture in the {100} plane are suitable for this purpose. On the other hand, it is desired that the static material has good electromagnetic characteristics in the L direction or the C direction. For this, a material having a {110} <001> texture or a {100} <001> texture is suitable is there. In general, it is well known that {100} <0vw> becomes a crystal having an orientation close to {100} <0vw> even if rolled and recrystallized. In the present invention, this idea is applied to the rapid solidification method. It was considered necessary to increase the cast structure of columnar crystals in thin cast pieces as much as possible. Therefore, the present inventors have focused on changing the atmosphere of the molten metal pool portion in order to improve the solidification structure morphology during the rapid solidification.

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 inventors of the present invention focused on the inclusion of the atmospheric gas 4 in the pool of the twin rolls, and used various gases in place of the conventional atmosphere, and examined the casting structure morphology. . As a result, it was found that when the molten metal pool was made to have a nitrogen gas atmosphere, a thin cast piece having a columnar grain cast structure was obtained as shown in FIG. 2 (a), thereby improving the magnetic characteristics. On the other hand, in an argon gas or helium gas atmosphere, the solidified structure morphology tends to be equiaxed grains.
FIG. 2B shows the solidification structure in the helium gas atmosphere.
The reason for this is that in the case of nitrogen gas, a slight amount of nitrogen is absorbed on the surface of the molten steel, so that the apparent thermal conductivity becomes small, and as a result, the thermal conductivity of nitrogen gas becomes small.

As described above, the present inventors have studied various gases by paying attention to the entrainment of the atmospheric gas in the pool of twin rolls. It has been found that a thin slab having a cast structure can be obtained and the magnetic properties are improved.

Next, in the present invention, the reason why the steel composition and the 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 0.01% in order to improve iron loss, but if it is too much, it is easily cracked during cold rolling and working becomes difficult, so the upper limit is made 8.0%. In the present invention, steel components other than Si may be Al, Mn, P, B, N for the purpose of improving magnetic properties, mechanical properties, rust resistance, and the like.
One or two or more of i, Cr, Sb, Sn and Cu may be contained in an amount of 0.01 to 10%.

Next, this molten steel is rapidly solidified by a twin roll method or the like, and the obtained thin cast piece has a plate thickness of 0.3 to 4.0 mm.
Thickness is preferred. This is the final plate thickness 0.03-1.00mm
In order to obtain good magnetic properties, the cold rolling reduction is insufficient if it is less than 0.3 mm, and the cold rolling reduction is excessive if it exceeds 4.0 mm. In the present invention,
The casting atmosphere gas was limited to nitrogen gas in order to obtain a columnar crystal casting structure. At this time, after completion of solidification, there is a method of gradually cooling as much as possible in order to promote growth of inhibitors, coarsening of aggregation and growth of crystal grains. Furthermore, in order to obtain the toughness of the slab, there is also a method of adding a slight reduction to the thin slab.

Next, examples of the present invention will be described.

[0014]

【Example】

[Example 1] Molten steel containing the composition shown in Table 1 was cast into a thin cast piece having a thickness of 1.7 mm by a twin roll rapid solidification method.
The casting condition is that the molten steel roll contact time is about 0.3 seconds. The molten steel temperature in the pool was 1495 ° C. As shown in Table 2, the casting atmosphere was set to three levels of N ₂ , Ar and He. At this time, the casting structure is the casting atmosphere Ar,
He was an equiaxed crystal, and N ₂ was a columnar crystal.

Then, the obtained thin cast piece was pickled and cold-rolled to a thickness of 0.35 mm. Next, continuous finish annealing was performed at 1000 ° C. for 30 seconds, and the magnetic characteristics were measured. Table 2 shows the magnetic properties of the obtained products. Regarding the magnetism of the product, when the casting atmosphere was nitrogen, magnetic properties were better than those of other casting atmospheres.

[0016]

[Table 1]

[0017]

[Table 2]

Example 2 Molten steel having the composition shown in Table 3 was cast into a thin cast piece having a thickness of 1.5 mm by a twin roll rapid solidification method. As for the casting conditions, the molten steel roll contact time is about 0.3 seconds. The molten steel temperature in the pool was 1505 ° C. As shown in Table 2, the casting atmosphere is N ₂ , A
It was set to 3 levels of r and He.

Then, the obtained thin cast piece was pickled and cold-rolled to a thickness of 0.50 mm. Then 2 at 950 ° C
Continuous finish annealing was performed for 0 seconds, and the magnetic properties were measured.
Regarding the magnetism of the obtained product, as shown in Table 4, when the casting atmosphere was set to nitrogen, the magnetic characteristics were better than those of the other casting atmospheres.

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

According to the present invention, a non-oriented electrical steel sheet having a good iron loss characteristic can be manufactured at low cost and with low energy consumption, which makes a great industrial contribution.

[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.

2A and 2B are micrographs showing a cast metal structure of a thin cast piece at a thickness of 1/4, in which (a) is a casting atmosphere of N ₂ and (b) is He.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. In twin roll continuous casting, S by weight is used.
i: 0.01 to 8.0% is included, and the other component elements necessary for electromagnetic steel are included, and the balance is a molten steel consisting essentially of Fe and is rapidly supplied for rapid solidification to cast a thin slab. In this case, a method for producing a thin cast piece for a non-oriented electrical steel sheet is characterized in that the molten metal pool of the twin rolls is placed in a nitrogen gas atmosphere.