Metal treatment – Stock – Magnetic
Reexamination Certificate
2000-04-13
2002-07-30
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C148S306000
Reexamination Certificate
active
06425962
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-oriented electrical steel sheet having a high permeability and excellent electrical properties that is usable as iron core material of electrical, equipment and to a method of producing the non-oriented electrical steel sheet.
2. Description of the Related Art
Against a backdrop of worldwide moves to protect the global environment by conserving electric power and other forms of energy, restricting use of Freon gas and other measures, there has arisen a rapidly spreading drive to enhance the efficiency of electrical equipment, particularly in the rotating machine, small transformer and other sectors that use non-oriented electrical steel sheet as a material for magnetic iron cores. This has also made non-oriented electrical steel sheet a target of calls for property improvement, i.e., demands for non-oriented electrical steel sheets with high magnetic permeability.
Conventionally, the effort to lower the core loss of non-oriented electrical steel sheet has generally relied on the method of increasing the content of Si or of Al or the like. This is based on the principle that increasing electrical resistance reduces eddy-current loss. This method has the disadvantage that it inevitably lowers permeability. To overcome this problem, the method of coarsening the crystal grain diameter of the hot-rolled sheet to enhance both permeability and core loss property is used.
On the other hand, in non-oriented electrical steel sheet that has a transformation, one conventional practice has been to terminate hot-rolling near the upper limit of the a region, thereby securing the required crystal grain diameter before cold rolling and, as a result, elevating the permeability of the product. It is from this standpoint that Japanese Unexamined Patent Publication No. 56(1981)-38420 teaches a method for increasing coarseness of the hot-rolled crystalline texture by finishing hot-rolling at a temperature at or below a temperature midway between the Ar
3
point and the Ar
1
point and carrying out coiling at a temperature of 680° C. or higher. The improvement in the permeability of a non-oriented electrical steel sheet that can be achieved solely by controlling the hot-rolling conditions is, however, limited.
As methods for enhancing the permeability of non-oriented electrical steel sheet by improving the primary recrystallized texture, Japanese Unexamined Patent Publication No. 55(1980)-158252 teaches Sn addition, Japanese Unexamined Patent Publication No. 62(1987)-180014 teaches addition of Sn and Cu and Japanese Unexamined Patent Publication No. 59(1984)-100217 teaches addition of Sb as methods for enhancing crystalline texture so as to produce non-oriented electrical steel sheet excellent in electrical properties. The expense of adding a crystalline texture controlling element such as Sn, Cu or Sb is, however, by no means negligible. It has therefore been difficult to provide a non-oriented electrical steel sheet at low cost.
Measures implemented during the production process, such as innovations to the finish annealing cycle as taught by Japanese Unexamined Patent Publication No. 57(1982)-35626, have achieved core loss reduction but have not had much effect toward improving permeability.
SUMMARY OF THE INVENTION
The inventors conducted an in-depth analysis in search of means for overcoming the aforesaid limitations of the prior art. Through this study they discovered that a non-oriented electrical steel sheet excellent in both permeability and core loss can be produced using a low-alloy composition system, effecting controlled hot rolling, and controlling the electrical resistivity of the steel to within a definite range.
One object of the present invention is to overcome the problems of the prior art by providing a non-oriented electrical steel sheet excellent in permeability and a method of producing the non-oriented electrical steel sheet.
The gist of the present invention is as follows:
(1) A non-oriented electrical steel sheet excellent in permeability whose steel contains, in percentage by weight,
0.1%≦Si≦1.0%
0.1%≦Mn≦0.8%
0.4%≦Al≦1.0%, and
the balance of Fe and unavoidable impurities,
and which has an ay transformation, an electrical resistivity of not less than 10×10
−8
&OHgr;m and not greater than 32×10
−8
&OHgr;m, and a permeability &mgr;15/60 of not less than 1500 (Gauss/Oe).
(2) A hot-rolled sheet for a non-oriented electrical steel sheet whose steel contains, in percentage by weight,
0.1%≦Si≦1.0%
0.1%≦Mn≦0.8%
0.4%≦Al≦1.0%, and
the balance of Fe and unavoidable impurities,
and which has an ay transformation, an electrical resistivity of not less than 10×10
−8
&OHgr;m and not greater than 32×10
−8
&OHgr;m, a recrystallized texture of a grain diameter viewed in a hot-rolled sheet cross-section of not less than 5 &mgr;m and less than 50 &mgr;m, and a worked texture of an area ratio viewed in a hot-rolled sheet cross-section of not greater than 80%.
(3) A hot-rolled sheet for a non-oriented electrical steel sheet whose steel contains, in percentage by weight,
0.1%≦Si≦1.0%
0.1%≦Mn≦0.8%
0.4%≦Al≦1.0%, and
the balance of Fe and unavoidable impurities,
and which has an ay transformation, an electrical resistivity of not less than 10×10
−8
&OHgr;m and not greater than 32×10
−8
&OHgr;m, and a crystal grain diameter of not less than 50 &mgr;m and not greater than 500 &mgr;m.
(4) A method of producing a non-oriented electrical steel sheet excellent in permeability comprising the steps of subjecting a steel containing, in percentage by weight,
0.1%≦Si—1.0%
0.1%≦Mn≦0.8%
0.4%≦Al≦1.0%, and
the balance of Fe and unavoidable impurities,
and having an at transformation and an electrical resistivity of not less than 10×10
−8
&OHgr;m and not greater than 32×10
−8
&OHgr;m to hot rolling at a hot-rolling finishing temperature in finish hot rolling of not less than 850° C. and not greater than 1050° C. and also not greater than (Ar
3
+Ar
1
)/2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be explained in detail.
The inventors conducted an intensive study to overcome the drawbacks of the prior art and enable simultaneous achievement of low core loss and high flux density. As a result, they discovered that, in the case of a non-oriented electrical steel sheet having a transformation, when a steel containing 0.1%-1.0% of Si, 0.4%-1.0% of Al and 0.1%-0.8% of Mn is designed in composition to have an &agr;&lgr; transformation, the result is subjected to controlled hot rolling under specified conditions to form a distinctive hot-rolled texture, and the hot-rolled sheet is used as a starting material, a non-oriented electrical steel sheet excellent in both permeability and core loss property can be produced.
The conventional method used to improve the permeability of a non-oriented electrical steel sheet has been to coarsen the crystalline texture before cold rolling. In research leading to the present invention, the inventors confirmed that an additional improvement in permeability,can be obtained by conducting hot-rolled sheet annealing to coarsen the crystalline texture before cold rolling but they further discovered that non-oriented electrical steel sheet with permeability comparable to that of a material subjected to hot-rolled sheet annealing can be obtained by the present invention even if hot-rolled annealing is not conducted.
The steel composition will be explained first. Silicon (Si) is added to increase the specific resistance of the steel sheet and thereby lower eddy-current loss and improve core loss value. Si must be added to a content of not less than 0.1% because sufficient specific resistance cannot be obtained at less than 0.1%. The Si content is further limited to not greater than 1.0% because permeability decreases at a content in excess of 1%.
Manganese (Mn), like Si, also works to lower eddy-curren
Arita Yoshihiro
Hanzawa Kazufumi
Kanao Shinichi
Kawamata Ryutaro
Kubota Takeshi
Nippon Steel Corporation
Sheehan John
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