Metal treatment – Stock – Magnetic
Reexamination Certificate
1999-12-08
2001-10-02
Sheehan, John (Department: 1742)
Metal treatment
Stock
Magnetic
C075S244000, C420S083000, C420S121000
Reexamination Certificate
active
06296720
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a novel rare earth/iron/boron-based permanent magnet alloy composition capable of giving permanent magnets having greatly improved magnetic properties.
As is well known, the demand for rare earth-based permanent magnets is rapidly growing in recent years by virtue of their very excellent magnetic properties enabling a compact design of electric and electronic instruments with a permanent magnet built therein as well as the relative economical merits obtained by using such a high-performance permanent magnet. In order to further increase these advantages, it is now desired to upgrade the magnetic properties of rare earth-based permanent magnets more and more. Among various types of rare earth-based permanents magnets, rare earth/iron/boron-based magnets, referred to as the R/Fe/B-based magnets hereinafter, or, in particular, neodymium/iron/boron-based magnets are highlighted as compared with earlier developed samarium/cobalt-based magnets in respect of lower material costs because of the much greater abundance in nature of neodymium as the principal rare earth element constituting than samarium and saving of expensive cobalt in addition to the much better magnetic properties than samarium/cobalt-based magnets.
A great variety of proposals and attempts have been made heretofore with an object to improve the magnetic properties of the R/Fe/B-based permanent magnets. For example, Japanese Patent Kokai 59-64733 and 59-132104 teach a R/Fe/B-based magnet alloy composition with admixture of titanium, nickel, bismuth, vanadium and others as additive elements with an object to obtain a stabilized coercive force of the magnets. Japanese Patent Kokai 1-219143 proposes addition of 0.02 to 0.5 atomic % of copper to the R/Fe/B-based magnet alloy so as to improve the magnetic properties of the magnets along with an advantage in the productivity of the magnet products due to broadened tolerance for the range of temperatures in which the magnet body is to be subjected to a heat treatment. Further, Japanese Patent Kokai 1-219143 reports an increase in the corrosion resistance of R/Fe/B-based magnets by the addition of 0.2 to 0.5 atomic % of chromium to the magnet alloy.
Starting from the above mentioned copper-admixed R/Fe/B-based magnet alloys, the inventors conducted extensive investigations for further improving the magnetic properties of the magnets by the addition of various kinds of other additive elements. The attempts in this direction, however, were not very fruitful because the improvement in the coercive force of the magnet obtained by the addition of most of other additive elements is accompanied by a decrease in the residual magnetic flux density practically to cancel the improvement in the coercive force.
SUMMARY OF THE INVENTION
The present invention accordingly has an object to provide a novel R/Fe/B-based permanent magnet alloy composition obtained by the addition of unique additive elements to the basic R/Fe/B-based magnet alloy composition to exhibit excellent coercive force and residual magnetic flux density.
Thus, the present invention provides a rare earth/iron/boron-based permanent magnet alloy composition which consists of:
(a) from 28 to 35% by weight of a rare earth element selected from the group consisting of neodymium, praseodymium, dysprosium, terbium and holmium;
(b) from 0.1 to 3.6% by weight of cobalt;
(c) from 0.9 to 1.3% by weight of boron;
(d) from 0.05 to 1.0% by weight of aluminum;
(e) from 0.02 to 0.25% by weight of copper;
(f) from 0.02 to 0.3% by weight of zirconium or chromium;
(g) from 0.03 to 0.1% by weight of carbon;
(h) from 0.1 to 0.8% by weight of oxygen;
(i) from 0.002 to 0.2% by weight of nitrogen; and
(j) the balance to 100% by weight of iron and unavoidable impurity elements.
REFERENCES:
patent: 5162064 (1992-11-01), Kim et al.
patent: 5589009 (1996-12-01), Kim et al.
patent: 5968289 (1999-10-01), Sakurada et al.
patent: 0 106 948 (1984-05-01), None
patent: 0 477 810 (1992-04-01), None
patent: 0 994 483 (2000-04-01), None
Patent Abstracts of Japan, 018 (No. 590)(E-1628), Nov. 10, 1994—Abstract of JP 224018.
Minowa Takehisa
Tatami Koro
Yamamoto Kenji
Sheehan John
Shin-Etsu Chemical Co. , Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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