JPH0733549B2 - Method for manufacturing bidirectional silicon steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] Iron-based materials are characterized in that the energy state of electrons that bear magnetism differs depending on the direction with respect to the crystal axis, and that they are easily magnetized in the direction of the Miller index <100> axis. By utilizing this crystalline magnetic anisotropy, in the grain-oriented electrical steel sheet used for the magnetic core of a transformer or the like, only the crystal grains expressed as {110} <001> in the Miller index (called the Goss orientation) are selectively selected. The magnetic permeability in one direction in the plane of the steel sheet was dramatically improved.

For this unidirectional electrical steel sheet ({110} <100>), a bidirectional electrical steel sheet (Mirror index {100} <001>) in which the <100> axis is oriented in two orthogonal directions within the steel sheet plane. Is a more ideal soft magnetic material. However, since the industrial process is complicated, but sufficient magnetic properties cannot be obtained,
Bidirectional electrical steel sheets have not been widely used as magnetic core materials.

The conventional bi-directional electrical steel sheet manufacturing methods are roughly classified into the following 3
There are two ways.

1) A method using a directional ingot composed of columnar grains.

This method is disclosed in JP-B-33-7509 or JP-B-33-7952.
As disclosed in the publication, an ingot with developed columnar grains is manufactured while maintaining a temperature gradient, and cold rolling is performed in a direction satisfying a certain angular relationship with the extending direction of the columnar grains to perform recrystallization. Is the way. The point of this method is
If the deviation from the {100} <001> orientation of the material is within a certain allowable range as described in −7953 publication, the crystal grains may have {100} <001> orientation again after cold rolling and recrystallization. .

2) Method using surface energy.

This method is disclosed in JP-B-36-8554, JP-B-37-7110 or JP-B-38-16212, in which the heat treatment atmosphere is used when cold-rolling and recrystallizing a thin material. Is controlled to recrystallize only the crystal grains having the {100} plane on the plate surface.

3) Cross cold rolling method.

As disclosed in Japanese Examined Patent Publication No. 35-2657, this method involves cold rolling a silicon steel material in one direction, then further cold rolling in a cross direction with this cold rolling, followed by short-time annealing and 900 ~ 130
This is a method of performing high temperature annealing at 0 ° C. The principle of this method is
Cross-cold rolling develops a texture that makes it easy to grow {100} <001> oriented grains, and develops {100} <001> oriented grains by secondary recrystallization using an inhibitor of grain growth such as AlN. It is what makes me.

On the other hand, a method of directly obtaining a thin steel sheet from molten steel without going through a hot rolling step has been invented, and is greatly expected as a new process capable of cost reduction.

[Problems to be solved by the invention]

As described above, the bi-directional electrical steel sheet is an ideal magnetic material in which two of the three easy axes of magnetization are oriented in the plane of the steel sheet, but has been used almost industrially to date. Absent. This is because it is extremely difficult to industrially carry out the manufacturing methods devised up to the present and the cost is high, but the expected degree of integration of crystal orientation cannot be obtained.

For example, in the method of 1) using a directional ingot, in order to sufficiently develop the columnar grains, it is necessary to cool the bottom surface while heating the side surface of the mold to give a temperature gradient to the molten steel, which is a large amount of industrial process. It was extremely difficult to produce.

Moreover, in the method of using the surface energy of 2),
Strictly controlling the heat treatment atmosphere so that only {100} oriented grains grow is industrially difficult, and in principle, the <100> axial directions in the plate surface cannot be aligned.

The method using the cross cold rolling of 3) can obtain a considerably high degree of crystal orientation accumulation and can be expected to have a considerably high magnetic permeability in two directions within the plate surface, but in the sense of producing a magnetic material that is suitable for the manufacturing cost, it is more advantageous. It is desired to improve the degree of integration and further reduce costs.

[Means for Solving the Problems]

As mentioned above, it is possible to obtain a grain-oriented electrical steel sheet having a considerably high degree of crystal orientation integration by expressing secondary recrystallization using a grain growth inhibitor in a cross cold rolled material. The present inventors have invented a method for obtaining a bidirectional electrical steel sheet which can be sufficiently put into practical use, by improving the method using the cross cold rolling.

That is, the present inventors, when casting a thin slab using a pair of rotating cooling rolls, by raising the temperature of the molten steel immediately above the cooling rolls by 30 ° C. or more above the solidification start temperature, the development of columnar crystal structure The obtained thin slab can be obtained by subjecting the thin slab to cold rolling of 40 to 80%, and further cold rolling of 30 to 70% in the direction perpendicular to this cold rolling for the purpose of primary recrystallization. It was found that by performing the annealing, the secondary recrystallization, and the annealing for the purpose of purification, it is possible to obtain a grain-oriented electrical steel sheet having a very good orientation in the {100} <001> orientation.

The present invention will be described in detail below.

When casting a thin slab using a casting method of supplying molten steel between a pair of rotating cooling rolls, immediately above the cooling roll, that is, if the temperature of the molten steel in the molten steel reservoir is higher than the solidification start temperature by 30 ° C. or more. The columnar crystal structure develops, and the texture of the thin cast piece has a strong {100} <Ovw> orientation (Fig. 1 (a)). On the other hand, when the temperature of the molten steel is less than the solidification start temperature + 30 ° C, the texture of the thin cast pieces becomes almost random (Fig. 1 (b)).

The inventors of the present invention have used, as a starting material, a material having a developed {100} <OVW> texture obtained by adjusting the temperature of molten steel, and a {100} <001> oriented grain oriented steel sheet. Invented a method of manufacturing.

As a component of this thin slab, the lower limit of the Si component is 1.8% in order to suppress the destruction of the crystal structure due to the α-γ transformation. Moreover, 6.8% was set as an effective upper limit for reducing eddy current loss in an alternating magnetic field. When Si is 4.8% or more, cracks are likely to occur during cold rolling, but since rolling is possible by warm rolling, the above upper limit value was set.

This other component is one or more selected from AlN, MnS, Cu2S, MnSe, Nb (C, N), Sn, Sb, etc., which are necessary for stable secondary recrystallization. If it is included within a known range, {100} <001> oriented grains with a high degree of integration can be obtained.

The thickness of the thin slab is 0 because it is easy to handle during processing.
The thickness is preferably 4 to 3.0 mm, but is not particularly limited to this range.

Next, this thin slab material can be annealed in the temperature range of 700 to 1200 ° C. at the same time as disclosed in Japanese Patent Publication No. 388213, if necessary, but some magnetic It is also possible to sacrifice the deterioration of characteristics and omit it. Then
Cold rolling is carried out at a reduction rate of 40 to 80%, and further cold rolling is carried out at a rate of 30 to 70% in the direction perpendicular to this cold rolling. This cold rolling is equivalent to that disclosed in Japanese Examined Patent Publication No. 35-2657. Further, this steel sheet is annealed for the purpose of primary recrystallization. This annealing is more preferably performed in the temperature range of 750 to 1000 ° C. for a short time, but it is not particularly limited to this condition.

Then, final annealing for the purpose of secondary recrystallization and purification is performed. This final annealing is preferably carried out for a long time in the temperature range of 900 to 1300 ° C. in order to completely carry out the secondary recrystallization, but it is not particularly limited to this condition. Further, in order to stabilize the secondary recrystallization, it is possible to nitride the steel sheet after the completion of the primary recrystallization and before the start of the secondary recrystallization. As the nitriding method, a method of mixing a gas having a nitriding ability such as N2 and NH3 into the atmosphere of the final annealing, a method of adding a substance having a nitriding ability such as ferromanganese nitride to the annealing material during the final annealing, and After the soaking process of crystal annealing, any method such as a method of treating in an atmosphere containing a gas having a nitriding ability such as NH3 or a method of ion nitriding may be used.

It has been found that the grain-oriented electrical steel sheet having excellent grain orientation can be obtained by performing the above-mentioned steps.

[Work]

In the present invention, the temperature of molten steel is
{100} <OVW obtained by adjusting higher than ℃
> A high degree of integration has been obtained by cross cold rolling using a thin slab with a developed texture as a starting material {100} <001
> Oriented grains can be developed, but the reason is that when a material with developed {100} <OVW> texture is used as a material for cross cold rolling, the texture obtained after cold / primary recrystallization is {100} It is considered that this is because it is advantageous for growing the <001> orientation. This texture is, for example,
It is considered to have a specific azimuth relationship with the {100} <001> azimuth as described by Harase in the Japan Institute of Metals, 53 (1989) 858. On the other hand, if the temperature of the molten steel is less than the solidification start temperature + 30 ° C and a random texture develops, the texture after cross cold rolling and primary recrystallization is {100} <001.
It is considered that the azimuth can be grown from <>.

(Example 1) Si: 3.5%, C: 0.040%, Mn: 0.18%, P: 0.020%, A by weight
L: 0.030%, N: 0.0080%, S: 0.0050%, Cr: 0.10%, and the slab A cast at a temperature of 20 ℃ above the solidification start temperature of molten steel consisting of the balance Fe and unavoidable impurities, 30 ℃ A cast slab B cast at a high temperature, a cast slab C cast at a high temperature of 50 ° C., and a cast slab D cast at a temperature of 70 ° C. were obtained. The thickness of all the cast pieces was 2.0 mm. These slabs were annealed at 1000 ° C. for 5 minutes, then cold-rolled to a thickness of 1.0 mm, and further cold-rolled in the direction perpendicular to the cold rolling to a thickness of 0.5 mm. This material was annealed at 820 ° C. for 400 seconds in wet hydrogen, coated with magnesia oxide containing 5% ferro-manganese nitride, and then finally annealed at 1200 ° C. for 30 hours. The atmosphere of this final annealing is a mixture of nitrogen 50% and hydrogen 50% up to 1200 ° C, and a dry atmosphere of hydrogen 100% after holding at 1200 ° C. The characteristics of the obtained material are shown in FIG. As shown in this figure, it was confirmed that the magnetic flux density B8 of the obtained material becomes 1.9 (T) or more when the temperature of the molten steel in the molten steel reservoir is cast higher than the solidification start temperature of this molten steel by 30 ° C or more. Was done.

(Example 2) Si: 3.02%, C: 0.055%, Mn: 0.075%, P: 0.006 by weight
%, S: 0.024%, Al: 0.024%, N: 0.090%, Cu: 0.10%, S
Molten steel containing n: 0.09% and the balance Fe and unavoidable impurities is cast at a temperature 20 ° C higher than the solidification start temperature to obtain a slab A, 50
A slab B was produced by casting at a temperature higher by ℃. The thickness of the slab is 0.
It was 8 mm. These slabs were annealed at 1100 ° C. for 2 minutes, cold rolled to a thickness of 0.4 mm, and further cold rolled in the direction perpendicular to the cold rolling to a thickness of 0.2 mm. This material was annealed at 850 ° C. for 90 seconds in wet hydrogen and further subjected to a final annealing at 1200 ° C. for 20 hours. The final annealing atmosphere is up to 1200 ° C with 25% nitrogen,
A mixture of 75% hydrogen and 100% hydrogen after being kept at 1200 ° C were in a dry atmosphere. The magnetic properties of the obtained materials are shown in the table below.

[Advantages of the Invention] As described above, the present invention defines the casting temperature as {100} <OVW.
> Because a material with a developed texture is used as a starting material, it is possible to manufacture a bidirectional electrical steel sheet having a magnetic flux density of 1.9 (T) or more. Therefore, since such an electromagnetic steel sheet can be widely used as a magnetic core material, its industrial effect is extremely large.

[Brief description of drawings]

Figures 1 (a) and (b) show the crystal orientation of thin cast pieces (20
0) It is a pole figure, and FIG. 2 is a diagram showing the relationship between the temperature difference from the solidification start temperature of molten steel and the magnetic flux density of the material.

Claims (1)

[Claims] 1. A columnar crystal in which molten steel containing Si: 1.8 to 6.8% by weight is supplied between a pair of rotating cooling rolls, and the temperature of the molten steel immediately above this cooling roll is set to a solidification start temperature + 30 ° C. or more. A thin slab with a well-developed structure is manufactured, and then this thin slab is cold-rolled at a reduction rate of 40 to 80%, and further cooled at a reduction rate of 30 to 70% in the direction perpendicular to the cold rolling direction. Manufacture of bi-directional electrical steel sheet with excellent grain orientation, characterized by performing annealing for the purpose of primary recrystallization after performing hot rolling, and then performing final annealing for the purpose of secondary recrystallization and purification. Method.