Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
1998-12-01
2001-02-20
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C148S120000, C148S101000
Reexamination Certificate
active
06190463
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing Fe—Co based magnetic alloys having excellent mechanical characteristics, and particularly, to a process for producing an Fe—Co based magnetic alloy having a Co content which is in a range of 30% by weight≦Co≦65% by weight.
2. Description of the Related Art
In the course of producing an Fe—Co based magnetic alloy having a composition as described above, it is conventional practice to subject the material to a magnetic softening treatment for the purpose of improving magnetic properties after processing of the alloy. In this magnetic softening treatment, the material is maintained, for example, at 1,123° K for 3 hours, whereby the metallographic structure is converted into a ferrite structure (which will be referred to as &agr; structure hereinafter). Then, the resulting material is gradually cooled at a cooling rate of 100 to 200 K°/hr, and at such a cooling rate, an order-disorder transition is produced to provide an &agr; structure of CuZn-type (L2
0
type) ordered lattice.
However, while the Fe—Co based magnetic alloy has good magnetic properties because it has the &agr;′ structure, it suffers from a problem that it has poor mechanical characteristics, particularly, a decreased toughness, resulting in a narrower available range.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a production process of the above-described type, which is capable of producing an Fe—Co based magnetic alloy having not only good magnetic properties but also excellent mechanical characteristics and particularly, an increased toughness.
To achieve the above object, according to the present invention, there is provided a process for producing an Fe—Co based magnetic alloy, comprising a first step of heating an Fe—Co based magnetic alloy material having a Co content which is in a range of 30% by weight≦Co≦65% by weight to convert the metallographic structure into a &ggr; single-phase structure, a second step of gradually cooling the material to an a single-phase range at a cooling rate C
1
set in a range of 20 K°/hr <C, <0.5 K°/sec (i.e., 20 K°/hr <C
1
<1,800 K°/hr), and a third step of subjecting the material to a magnetic softening treatment, wherein the first to third steps are carried out in the mentioned order.
In the above production process, if the homogeneous &ggr; single-phase structure produced in the first step is gradually cooled to the a single-phase range at the cooling rate C
1
in the second step, a mixed structure comprising an a phase and an intermediate phase can be produced. An integrated heat energy in the magnetic softening treatment in the third step participates in the growing of grains. A portion of the integrated heat energy is consumed as the energy required for the subsequent order-disorder transition, whereby the a phase is converted into the &agr;′ phase. The intermediate phase cannot receive sufficient order-disorder transition, because the heat energy of the intermediate phase is consumed in the transformation to the a phase and growing of the grains in the magnetic softening treatment, and thus, a portion of the intermediate phase is left as the a phase. As a result, a mixed structure comprising the &agr; phase and the &agr;′ phase is produced.
In this way, the Fe—Co based magnetic alloy has the &agr; structure in addition to the &agr;′ phase required for enhancing magnetic properties. This &agr; structure contributes to the enhancement in the mechanical properties and particularly, the toughness of the magnetic alloy. The mixed &agr;-&agr;′ structure is a structure having a uniform grain size and is obtained by the transformation from the homogeneous &ggr; phase and the growing of grains. This is also effective for enhancing the mechanical characteristics of the Fe—Co based magnetic alloy.
According to the present invention, it is possible to produce the Fe—Co based magnetic alloy having not only good magnetic properties but also excellent mechanical characteristics and hence, it is possible to provide an increase in performance of and a reduction in size of an actuator or the like. In addition, the production process can be continuously carried out from the first step to the third step, whereby the treatment time can be shortened. Further, at completion of the second step, the material has a high elongation and a high Charpy impact value and hence, at this stage, a process utilizing the high mechanical property can be carried out.
However, if the cooling rate C
1
in the second step is set in a range of C
1
>0.5 K°/sec, a martensite transformation is produced and for this reason, the desired mixed &agr;-&agr;′ structure cannot be obtained. On the other hand, if C
1
<20 K°/hr, the a single-phase structure is provided before completion of the second step and for this reason, the desired mixed &agr;-&agr;′ structure cannot be obtained even by the subsequent thermal treatment.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3891475 (1975-06-01), Tomita et al.
patent: 4008105 (1977-02-01), Yuda et al.
patent: 4075437 (1978-02-01), Chin et al.
patent: 4366007 (1982-12-01), Inoue
Itami Hitoshi
Kondo Tetsuya
Mukaibo Nagatsugu
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Sheehan John
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