Metal treatment – Stock – Magnetic
Reexamination Certificate
2000-01-04
2001-11-27
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C148S306000, C148S111000, C148S120000
Reexamination Certificate
active
06322639
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic steel sheet used for an alternating-current magnetic core and having excellent magnetic properties in two directions including a rolling direction (referred to as “the L direction” hereinafter) and the direction perpendicular thereto (referred to as “the C direction” hereinafter), and a method of producing the same.
BACKGROUND ART
Core materials of a transformer and an electric motor are required to have a high magnetic flux density and low iron loss in order to increase the efficiency of these devices and miniaturize the devices.
As magnetic alloys supplied as such core materials, Fe-Si alloys and the like are known, and widely brought into practical use as non-oriented magnetic steel sheets. Namely, the method of increasing the amount of Si or Al added is known as a method having the effect of increasing resistivity to decrease an eddy current loss, and widely used. However, addition of an alloy component such as Si, Al, or the like decreases the saturation magnetic flux density. The method of increasing the amount of Si or Al added is difficult to satisfy both a low iron loss and high magnetic flux density.
An example of methods of improving an iron loss without adding an alloy component such as Si, Al, or the like is a method comprised of applying several % skin pass rolling to a cold rolled and annealed sheet, stamping by a user, and then applying stress relief annealing. However, this method requires a finish hot rolling temperature of 800° C. or more, 75% or more of cold rolling, and high-temperature annealing for a shot time, as well as several % skin pass rolling. When a coiling temperature after hot rolling is low and recrystallization is insufficient, this method also requires a hot-rolled sheet annealing. Therefore, the method has disadvantages in which the production process is significantly complicated, and the production cost is increased.
Japanese Examined Patent Publication No. 7-23509 discloses a method of improving magnetic properties without complicating the production process. This publication discloses that the Si amount is decreased to 1% or less, and ferrite coarse particles are rolled in a hot rolling step between rough hot rolling and finish hot rolling, improving both an iron loss and a magnetic flux density. However, this method increases less resistivity because the Si content is as low as 1% or less, and thus it cannot sufficiently decrease an iron loss. As a result of investigation, the inventors found that even when this method is applied to steel containing over 1% or Si, the sufficient effect on improving magnetic properties cannot be obtained.
Various attempts have been made to improve a texture. Japanese Unexamined Patent Publication No. 54-110121 discloses that an iron loss is decreased, and particularly, a magnetic flux density is increased when crystal grains in the {011}<100> orientation, i.e., the Goss orientation, are enriched. The Goss orientation generally improves magnetic properties in the L direction, and consequently improves average magnetic properties including those in the C direction. However, the magnetic properties in the C direction are improved only to some extent, and thus improvement in average magnetic properties is limited.
On the other hand, {100}<001> orientation, i.e., regular cubic orientation, is known to simultaneously improve magnetic properties in the two directions including the L direction and the C direction. However, in order to obtain a structure integrated only in the regular cubic orientation, a complicated, long-term and high-cost process is required, such as the high-temperature region intermediate annealing method disclosed in Japanese Examined Patent Publication No. 46-23814, the bidirectional rolling method disclosed in Japanese Unexamined Patent Publication No. 5-271883, the quenched ribbon method disclosed in Japanese Unexamined Patent Publication No. 5-306438, the method of &ggr;→&agr; transformation accompanied by decarbonization disclosed in Japanese Unexamined Patent Publication No. 1-108345, etc., thereby failing to establish industrial practicability.
Furthermore, as means for improving magnetic properties, it is useful to accelerate the production of crystal gains in the orientation in which magnetic properties are improved, and suppress the production of crystal grains in the orientation in which magnetic properties are deteriorated. Particularly, crystal grains in the orientation in which magnetic properties are deteriorated include crystal grains in the <111>//ND (the direction perpendicular to a steel sheet plane) orientation. It is preferable to suppress the crystal grains in this orientation, but the above-described special means and high-cost process are required. Therefore, the conventional process for producing a non-oriented magnetic steel sheet is difficult to decrease the grains in the <111>//ND orientation.
Namely, magnetic steel sheets produced in these methods cannot satisfy a low iron loss which is required from the viewpoint of global environment and energy environment at present.
DISCLOSURE OF INVENTION
An object of the present invention is to make an appropriate texture by hot rolling under appropriate conditions to achieve a low iron loss and a high magnetic flux density, and decrease cost by simplifying the production process.
The present invention relates to a magnetic steel sheet having excellent magnetic properties in the L direction and the C direction, wherein the structure of a recrystallized cold-rolled sheet has a ratio of {100}<001> orientation intensity to random orientation intensity ratio of 2.0 or more, and a ratio of {011}<100> orientation intensity to random orientation intensity of 2.0 to 10.0. The structure of a recrystallized cold-rolled sheet preferably has a ratio of <111>//ND orientation intensity to random orientation intensity of 2.0 or less. The present invention also relates to a method of producing a magnetic steel sheet having excellent magnetic properties in the L direction and the C direction, the method comprising hot-rolling silicon steel slab so that the structure of a recrystallized hot-rolled sheet has a ratio of (015)[100] orientation intensity to random orientation intensity of 3.0 or more, wherein the structure of a recrystallized cold-rolled sheet has a ratio of {100}<001> orientation intensity to random orientation intensity of 2.0 or more, and a ratio of {011}<100> orientation intensity to random orientation intensity of 2.0 to 10.0. In order that the structure of a recrystallized hot-rolled sheet has a ratio of (015)[100] orientation intensity to random orientation intensity of 3.0 or more, the structure after hot rough rolling, hot finish rolling conditions, the structure of a steel sheet on the delivery side of a final stand of a finish hot rolling mill, and the amount of effective accumulated stress (Q) of a steel sheet at the entrance side of the final stand of the finish hot rolling mill are optimized.
The inventors extensively studied means for practically improving magnetic properties of a non-oriented magnetic steel sheet. As a result, it was found that when a rolling reduction of one pass of hot rolling is set to a sufficiently large value, the degree of integration in the regular cubic orientation is increased. This was proposed in Japanese Application No. 9-244216. In advancing this study, a production method was extensively studied, in which a practical texture can be selected, and the existing process for producing a magnetic steel sheet can be used.
In study of the selection of a practical texture, it was found that a magnetic steel sheet having excellent average magnetic properties in the L direction and C direction can be obtained by increasing the degrees of integration in both the Goss orientation ({011}<100> orientation) and the regular cubic orientation ({100}<001> orientation). It
Kondo Osamu
Matsuzaki Akihiro
Takajo Shigeaki
Yamashita Takako
Kawasaki Steel Corporation
Schnader Harrison Segal & Lewis LLP
Sheehan John
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