Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
2000-11-27
2003-05-13
Koehler, Robert R. (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C148S306000, C148S307000, C148S308000, C148S310000, C148S100000, C148S110000, C148S111000, C148S112000, C148S120000, C148S121000, C427S409000, C427S419500, C427S419600, C428S432000, C428S900000, C428S928000
Reexamination Certificate
active
06562473
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrical steel sheets having superior magnetic properties, anti-noise properties, and workability, which are suitably used as compact iron core materials primarily for use in compact transformers, motors, electric-generators, and the like. The invention also relates to methods for manufacturing such electrical steel sheets.
2. Description of the Related Art
Compact iron core materials in electric apparatuses are mainly required to have superior magnetic properties. In addition, superior anti-noise properties or superior workabilities are desired.
Magnetic properties will first be described. Magnetic properties are greatly influenced by the orientations of crystalline grains constituting steel sheets. Among the directions mentioned above, it has been well known that, in order to obtain superior magnetic properties, the <001> axes, i.e., the axes of easy magnetization of crystalline grains, should be parallel with the surface of the steel sheet.
The following types of steel sheet are conventionally used for iron cores in compact electric apparatus: (1) a general-purpose cold-rolled steel sheet or a decarburized steel thereof, (2) a non-oriented silicon steel sheet in which the iron loss is decreased by adding silicon (Si) and by decreasing impurities; (3) a singly oriented silicon steel sheet in which crystalline grains are preferentially grown having the Goss orientations, i.e., the {110}<001> orientation, by using secondary recrystallization; and (4) a doubly oriented silicon steel sheet in which crystalline grains are preferentially grown having the cube orientations, i.e., the {100}<001> orientation.
Among the steel sheets described above, the general-purpose cold-rolled steel sheet, the decarburized steel sheet thereof, and the non-oriented silicon steel sheet have a smaller number of crystalline grains in the surface thereof having the <001> axes in parallel with each other since the evolution of the texture is insufficient. Accordingly, compared to the singly oriented silicon steel sheet, superior magnetic properties cannot be obtained.
The singly oriented silicon steel sheet is most generally used for iron core materials for transformers. In the singly oriented silicon steel sheet composed of crystalline grains integrated in the Goss orientations, the <001> axes, which are easily magnetized, are highly integrated in a rolling direction. Consequently, in particular, when magnetization is performed in the rolling direction, superior magnetic properties can be obtained. However, the <111> axes, which are most difficult to magnetize, are present in the surface of the steel sheet. As a result, when magnetization is performed in the direction of the axes described above, the magnetic properties are extremely inferior. That is, singly oriented silicon steel sheets are advantageously used for applications, such as for transformers, which require superior magnetic properties only in one direction. On the other hand, singly oriented silicon steel sheets are not advantageously used for applications, such as for iron core materials for motors and electric generators or the like, which require superior magnetic properties in multiple directions on the surface of the steel sheet.
Methods for manufacturing doubly oriented silicon steel sheets have been researched for many years, in which the cube-oriented texture is grown by secondary recrystallization. For example, a method is disclosed in Japanese Examined Patent Application Publication No. 35-2657, in which the cube-oriented grains are recrystallized by so-called “cross rolling” while using an inhibitor. In the method described above, secondary recrystallization is performed by cross rolling in which cold rolling is performed in one direction followed by cold rolling in the direction perpendicular thereto, annealing for a short period, and annealing at a higher temperature of 900 to 1,300° C. In addition, a method is disclosed in Japanese Unexamined Patent Application Publication No. 4-362132, in which the cube-oriented grains are recrystallized using aluminum nitride (AlN) after cold rolling is performed at a reduction rate of 50 to 90% in the direction perpendicular to hot rolling direction. In the method described above, after cold rolling, annealing is conducted so as to perform primary recrystallization, and final finish annealing is then conducted so as to perform secondary recrystallization and purification.
In the methods performed using recrystallization, steel sheets having cube-oriented texture are obtained in which the <100> axes in the surface thereof are highly integrated in the rolling direction. Accordingly, magnetic properties in the rolling direction and the direction perpendicular thereto are superior. However, as the direction 45° with respect to the rolling direction is the <110> axes orientation, which is difficult to magnetize, the magnetic properties in this direction are inferior.
In the steel sheets having the {100} orientations in the rolling surfaces thereof, a number of the easily magnetized axes <100> are present in the rolling surface, and the difficult magnetization axes <111> are not present. Accordingly, compared to the steel sheets conventionally used, the steel sheets having the {100} orientations in the rolling surfaces can be advantageously used for applications which require superior magnetic properties in every direction in the surfaces thereof. In particular, in the steel sheet composed of crystals having the {100}<uvw> orientations in which the rolling surface is in parallel with the {100}orientation, and the <001> axes are randomly aligned in the rolling surface, ansiotropic magnetic properties are not present at all in the rolling surface direction. Therefore, the steel sheets described above are ideal materials for use in motors.
Based on the understanding described above, methods for growing the {100} texture have been attempted. In the present invention, “to grow the {100} texture” means “to increase the number of crystals having the {100} orientations forming a rolling surface.”
For example, a method is disclosed in Japanese Examined Patent Application Publication No. 51-942, in which cold rolling is performed at a reduction rate of 85% or more, and more preferably, 90% or more, and after that, prolonged annealing is performed at 700 to 1,2000° C. for 1 minute to 1 hour. However, in the method described above, even though the {100} texture is grown immediately after rolling is complete, the {111} texture is also grown after prolonged annealing for recrystallization is performed. As a result, the product thus formed cannot is have superior magnetic properties.
In addition, a method is disclosed in Japanese Examined Patent Application Publication No. 57-14411, in which, after cold rolling is complete, a cooling rate is controlled in the phase transition region from a &ggr; phase to an &agr; phase during recrystallization. However, in the method described above, since a &ggr; transformation must occur during recrystallization, the content of Si, which stabilizes the &agr; phase, cannot be increased. For example, when carbon (C) and manganese (Mn) are not contained, the &ggr; transformation will not occur when the content of Si is approximately 2 wt % or more, whereby the method cannot be used. That is, the method described above is a disadvantageous method since the content of Si cannot be increased, which also advantageously works to decrease an iron loss.
Furthermore, a method is disclosed in Japanese Unexamined Patent Application Publication No 5-5126, in which a steel containing 0.006 to 0.020 wt % C is cold rolled, is recrystallized by heating to 900 to 1,000° C., and is subsequently processed by recrystallization annealing. The steel sheet thus obtained according to Example 1 in the same publication described above
Hayakawa Yasuyuki
Imamura Takeshi
Kurosawa Mitsumasa
Okabe Seiji
Kawasaki Steel Corporation
Koehler Robert R.
Young & Thompson
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