Metal treatment – Stock – Magnetic
Reexamination Certificate
2001-07-24
2002-08-06
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C420S117000
Reexamination Certificate
active
06428632
ABSTRACT:
TECHNICAL FIELD
This invention relates to a nonoriented electromagnetic steel sheet suitable for use in mostly rotating machines such as motor or the like and small-size power transducer and so on.
Particularly, the invention is intended to reduce a magnetic anisotropy in a high frequency zone to improve magnetic properties and to decrease a hardness at an iron loss equal to the conventional products to advantageously improve a blanking property in the pressing.
BACKGROUND ART
Recently, it is increasingly intended to increase the efficiency of electrical equipments accompanied with the increase in the demand for energy saving. In order to cope with such a demand, steel sheet makers make efforts for improving iron loss properties of electromagnetic steel sheets for electrical equipments by various means as mentioned later.
The addition of Si to the electromagnetic steel sheet is a most effective means for enhancing a specific resistance of the steel sheet to reduce the iron loss. This technique of reducing the iron loss by the Si addition is widely used in the field of the electromagnetic steel sheets. And also, Al is known to have the effect similar to Si as an additional element.
For example, JP-A-53-66816 proposes a positive addition of Al for enhancing the specific resistance of the steel sheet and avoiding the function of suppressing the grain growth through the precipitation of fine AlN.
And also, JP-A-55-73819 attains good magnetic properties at high magnetic field by adding Al and adjusting an annealing atmosphere to decrease an internal oxide layer on a surface of a steel sheet.
Furthermore, JP-A-54-68716 and JP-A-58-25427 reduce the iron loss by adding Al and co-adding REM and Sb or purifying to improve a texture.
Besides, JP-A-61-87823 attains the improvement of magnetic properties by adding Al and controlling a cooling rate of steel sheet in the final annealing. JP-A-3-274247 attains the improvement of magnetic properties by adding Al and co-adding B, Sb and Sn to prevent oxidation and nitriding. JP-A-3-294422 attains the improvement of magnetic properties by adding Al and controlling cold rolling to reduce a ratio of L, C characteristics of the steel sheet. JP-A-4-63252 attains the improvement of magnetic properties by co-adding Mn and Al. JP-A-4-136138 attains the improvement of magnetic properties by adding Al and extremely reducing Si and adding P, Sb to improve a texture.
All of the aforementioned techniques improve the properties of the electromagnetic steel sheet itself to bring about the improvement of the efficiency of the electrical equipments using such an electromagnetic steel sheet.
On the other hand, a technique of controlling a small-size rotating machine is recently and rapidly advanced by remarkable improvement of techniques surrounding semiconductors with the improvement of performances of the semiconductor and the lowering of cost thereof, and rotation control is carried out through an inverter. And also, it is possible to manufacture a high-efficiency rotating machine such as DC brushless motor or the like with the improvement of permanent magnet materials.
However, the driving conditions of the motor are complicated with the advance of the technique of controlling the small-size rotating machine or the improvement of the permanent magnet materials, and hence an exciting condition at not only high rotating zone but also low rotating zone becomes contain a great amount of high frequency components based on strain or the like. Since a great amount of the high frequency components is contained, it is difficult to reduce the iron loss to a certain level in an iron core of a motor using the above conventional materials, and the improvement of the efficiency in the motor is reaching the ceiling.
In addition, when a content of a specific resistance element such as Si, Al or the like is increased for reducing the iron loss, the hardness of the steel sheet rises, which has problems that the life of the mold in the press forming of motor or transformer is lowered and defective blanking is increased.
DISCLOSURE OF THE INVENTION
It is an object of the invention to propose a nonoriented electromagnetic steel sheet for a rotating machine capable of more enhancing an efficiency of a high-efficiency rotating machine and having a small magnetic anisotropy in a high frequency zone.
It is another object of the invention to propose a nonoriented electromagnetic steel sheet also improving a press formability to have a small magnetic anisotropy in a high frequency zone and an excellent press formability.
The inventors have not only examined the magnetic properties of various electromagnetic steel sheets in detail, but also actually prepared rotating machines (motors) by using these electromagnetic steel sheets and made various studies with respect to a relation between actual properties and material properties in these motors. As a result, the inventors have found that it is very important to make small a magnetic anisotropy of a raw material in a high frequency zone rather than a commercial frequency for enhancing the efficiency of the actual motor.
And also, the inventors have found that it is effective to restrict the hardness of the steel sheet to an adequate range in accordance with the value of iron loss in order to prevent the degradation of the magnetic properties feared in the press forming such as blanking or the like.
The invention is based on the above knowledge.
The gist and construction of the invention are as follows.
1. A nonoriented electromagnetic steel sheet having a small magnetic anisotropy in a high frequency zone and an excellent press formability, characterized in that it has a composition containing C: not more than 0.0050 mass %, Si: 0.5-4.5 mass %, Mn: 0.1-2.5 mass % and Al: 0.2-2.5 mass % and controlling S: not more than 0.01 mass %, and that as to magnetic properties in rolling direction (L-direction), direction perpendicular to the rolling direction (C-direction) and direction inclined at an angle of 45° with respect to the rolling direction (D-direction) using an Epstein test piece, L, C average iron loss W
15/50
(L+C)[W/kg] at 1.5 T and 50 Hz and L, C average magnetic flux density B
50
(L+C)[T] at 5000 A/m satisfy a relation of the following equation (1):
B
50
(
L+C
)≧0.03
·W
15/50
(
L+C
)+1.63 (1)
and a ratio of D iron loss W
10/400
(D)[W/kg] to L, C average iron loss W
10/400
(L+C)[W/kg] at 1.0 T and 400 Hz satisfies a relation of the following equation (2):
W
10/400
(
D
)/
W
10/400
(
L+C
)≦1.2 (2)
and that a hardness of the steel sheet is defined in accordance with a sheet thickness and W
15/50
(L+C).
2. A nonoriented electromagnetic steel sheet having a small magnetic anisotropy in a high frequency zone and an excellent press formability according to the above item 1, wherein the hardness of the steel sheet is defined in accordance with a sheet thickness and W
15/50
(L+C).
3. A nonoriented electromagnetic steel sheet having a small magnetic anisotropy in a high frequency zone and an excellent press formability according to the above item 2, wherein the hardness of the steel sheet Hv
1
(JIS Z2244, test load: 9.807 N) satisfies a relation of the following equation (3):
Hv
1
≦−83.3·
W
15/50
(
L+C
)+380 (3)
within a range of iron loss of W
15/50
(L+C)≦5.0 W/kg and at a sheet thickness of 0.35 mm±0.02 mm.
4. A nonoriented electromagnetic steel sheet having a small magnetic anisotropy in a high frequency zone and an excellent press formability according to the above item 2, wherein the hardness of the steel sheet Hv
1
(JIS Z2244, test load: 9.807 N) satisfies a relation of the following equation (4):
Hv
1
≦−63.6·
W
15/50
(
L+C
)+360 (4)
within a range of iron loss of W
15/50
(L+C)≦5.0 W/kg and at a sheet thickness of 0.50 mm±0.02 mm.
5. A nonoriented electromagnetic steel sheet having a small magnetic anisotropy in a high frequency zone
Fujiyama Toshiro
Sakai Keiji
Kawasaki Steel Corporation
Schnader Harrison Segal & Lewis LLP
Sheehan John
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