Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Reexamination Certificate
1999-06-18
2001-06-12
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
C148S120000, C148S121000, C148S122000, C148S310000, C335S296000, C428S638000, C428S686000, C428S900000, C428S928000
Reexamination Certificate
active
06245441
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite magnetic member combining a ferromagnetic portion and a non-magnetic portion suitable for use in an actuator which treats with automobile fuels and hydraulic operating fluids or the like (hereinafter referred to as an oil controlling device).
2. Description of the Related Art
An oil flow controlling device of an automobile conventionally has a structure in which an effective use of magnetic flux is made by providing a non-magnetic portion in a part of a stator, which stator is ferromagnetic (generally, soft magnetism), to cause magnetic flux to flow to a movable piece. Techniques such as the brazing and laser welding of a ferromagnetic part and a non-magnetic part have been employed to provide a non-magnetic portion in a part of the ferromagnetic portion. In contrast to these techniques of bonding dissimilar materials, the present authors propose the use of a single material as a composite magnetic material which is formed by providing a ferromagnetic portion and a non-magnetic portion by cold working or heat treatment. When such composite magnetic materials made of a single material are used, it is possible to obtain parts superior to those obtained by bonding a ferromagnetic portion and a non-magnetic portion with respect to ensuring airtightness and ensuring reliability, such as prevention of breakage by vibrations, etc.
In Japanese Patent Unexamined Publication No. 9-157802 based on a proposal by the present inventors, for example, a martensitic stainless steel containing 0.5 to 4.0% Ni is disclosed as a composite magnetic member suitable for an oil controlling device of an automobile. This proposal is such that in a martensitic stainless steel composed of ferrite and carbides in an annealed condition, the austenite in a non-magnetic portion having a permeability (&mgr;) of not more than 2, which portion is obtained by cooling a part of the martensitic stainless steel after heating, is stabilized by adding an appropriate amount of Ni to a C-Cr-Fe-base alloy from which ferromagnetic properties with a maximum permeability (&mgr;m) of not less than 200 are obtained, whereby it is possible to lower the Ms point (temperature at which austenite begins to be transformed into martensite) to not more than −30° C.
Also, Japanese Patent Unexamined Publication No. 9-228004 based on a proposal by the present applicant discloses that in a composite magnetic material used in magnetic scales etc., by adding more than 2% but not more than 7% Mn and 0.01 to 0.05% N to a C-Cr-Fe-base alloy containing 10 to 16% Cr and 0.35 to 0.75% C which alloy has ferromagnetic properties with a maximum permeability (&mgr;m) of not less than 200, it is possible to stabilize the retained austenite with a permeability (&mgr;) of not more than 2, which is obtained by cooling after heating, and to thereby lower the Ms point to not more than −10° C. These proposals are excellent in the respect that a ferromagnetic portion with a maximum permeability (&mgr;m) of not less than 200 and a stable non-magnetic portion with a permeability (&mgr;) of not more than 2 and a low Ms point can be obtained in a single material.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a composite magnetic member excellent in corrosion resistance, which combines a ferromagnetic portion and a non-ferromagnetic portion in a single material, in the member the corrosion resistance of the ferromagnetic portion being improved whose structure is mainly composed of ferrite and carbides, and to provide also a method of producing the composite magnetic member.
The composite magnetic members disclosed in the above Japanese Patent Unexamined Publication No. 9-157802 and Japanese Patent Unexamined Publication No. 9-228004 have an advantage in being capable of combining a ferromagnetic portion with a maximum permeability (&mgr;m) of not less than 200 and a stable non-magnetic portion with a permeability (&mgr;)of not more than 2. However, in these composite magnetic members, the corrosion resistance of the ferromagnetic portion mainly composed of ferrite and carbides is inferior to that of the non-magnetic portion mainly composed of austenite, with the result that rust is apt to be formed on the surface of the ferromagnetic portion. Thus, these composite magnetic members had such a serious problem as their surfaces corrode and deteriorate when they are used in oil controlling devices of automobiles, etc.
The present inventors examined the microstructure of a ferromagnetic portion whose structure is mainly composed of ferrite and carbides in a composite magnetic material. As a result, they found out that the carbides are mainly composed of Cr carbides and that the formation of these Cr carbides causes Cr to be concentrated in the carbides, with the result that the Cr concentration is insufficient in the ferrite phase matrix near the carbides.
As a result of a further examination, the present inventors also found out that the corrosion of the ferromagnetic portion starts from a layer of deficient Cr concentration near Cr carbides as the initiation point and that the corrosion resistance of the ferromagnetic portion and hence the corrosion resistance of the composite magnetic material can be substantially improved by increasing the amount of Cr contained in the composite magnetic material to more than 16.0% by weight, thereby increasing the Cr concentration of the ferrite phase matrix to not less than 12.0% by weight.
In addition, the present inventors further examined the disclosure in Japanese Patent Unexamined Publication No. 9-228004 that it is difficult to form the austenite in the non-magnetic portion in a case of Cr concentrations exceeding 16.0% because the ferrite structure becomes stable at such high Cr concentrations.
The present inventors previously considered that because Cr is a ferrite-forming element, the ferrite phase becomes stable when the Cr concentration exceeds 16.0% and, therefore, it is difficult to obtain the non-magnetic phase of austenite even when solution treatment is performed. This time, however, they found out that, surprisingly, an austenite phase with a permeability (&mgr;)of not more than 2 is obtained when a material with a Cr concentration exceeding 16.0% was subjected to solution treatment at 1250° C. for 10 minutes.
As a consequence, the present inventors found out that when water cooling is performed after solution treatment is carried out at the temperature range of from 1050 to 1300° C. in the manufacturing process of a composite magnetic member, austenitizing is possible, in other words, non-magnetic portion can be obtained.
Furthermore, the present inventors found out that, by performing annealing at below the A3 transformation point after hot working, cold working and further annealing at below the A3 transformation point, it is possible to disperse carbides in the ferromagnetic portion having a maximum grain size range of 0.1 to 20 &mgr;m, so that, corrosion resistance can be improved without the deterioration of the conventional magnetic properties even when Cr is added in amounts exceeding 16.0% if they are not more than 25.0%.
In the present invention there is provided a composite magnetic member excellent in corrosion resistance having a chemical composition consisting essentially, by weight, of 0.30 to 0.80% C, more than 16.0% but not more than 25.0% Cr, 0.1 to 4.0% Ni, 0.1 to 0.06% N, at least one kind not more than 2.0% in total selected from the group consisting of Si, Mn and Al, and the balance Fe and impurities, and having a ferromagnetic portion and a non-magnetic portion.
The composite magnetic member of the present invention has such magnetic properties as the maximum permeability (&mgr;m) of the ferromagnetic portion is not less than 200 and the permeability (&mgr;) of the non-magnetic portion is not more than 2.
The composite magnetic member of the present invention has a ferromagnetic portion with a maximum grain size of carbides controlled to the range of
Inui Tsutomu
Tanimura Yoshihiro
Yokoyama Shin-ichiro
Hitachi Metals Ltd.
Jones Deborah
Koehler Robert R.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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