Metal treatment – Stock – Ferrous
Reexamination Certificate
2001-12-04
2004-02-17
Yee, Deborah (Department: 1742)
Metal treatment
Stock
Ferrous
C148S325000
Reexamination Certificate
active
06692585
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ferritic Fe—Ni—Cr—Al alloy having both of excellent oxidation resistance and high-strength, which is suitable for use mainly in the atmospheric environment around room temperature after formation of an oxide film on the surface of the alloy under exposure to a high-temperature oxidation atmosphere, and a plate made of the alloy.
2. Description of the Related Art
Conventionally, the electrothermic alloys of Fe—Cr and Ni—Cr as defined in JIS C2520 have been well known as those having excellent oxidation resistance used in the atmospheric environment at a temperature range of from room temperature to a high temperature. Those alloys are excellent in oxidation resistance, and widely used for high-temperature heating elements.
On the other hand, JP-A-9-263906 discloses a ferritic Fe—Ni—Cr—Al alloy and a method for manufacturing the same, the ferritic Fe—Ni—Cr—Al alloy having excellent properties of corrosion resistance to molten metal and wear resistance.
While, with regard to the electrothermic Fe—Cr alloys and Ni—Cr alloys defined in JIS C2520, the electric resistance thereof is an important factor because of those use, taking their use, around room temperature, into consideration, any particular attentions have not been paid to the strength thereof. Therefore, when the alloys are used for structural members or parts for which oxidation resistance and strength at room temperature are required, the members or parts can not help having an increased size, so that it is difficult to make the members or parts compact and light.
Further, the ferritic Fe—Ni—Cr—Al alloy of JP-A-9-263906 is a material which is improved in properties of oxidation resistance, corrosion resistance to molten metal, wear resistance and so on by forming a film primarily comprising aluminum oxides on the surface of the alloy by heating the alloy in an oxidizing atmosphere at a temperature in the range of 800 to 1300° C. As will be understood from embodiments of JP′906, the inner metal structure of the alloy has a very high Vickers hardness of not less than 413 HV.
However, since the alloy of JP′906 is directed to a tool material on which the film is formed primarily comprising aluminum oxides to improve properties of oxidation resistance, corrosion resistance to molten metal, wear resistance and so on, any particular attentions are not paid to tensile properties including 0.2% yield strength and elongation determined by a tensile test, such properties being required for structural members and parts.
An object of the present invention is to provide an Fe—Cr—Ni—Al alloy which can possess both of excellent oxidation resistance and good mechanical properties especially at room temperature and which can be applied to structural members and parts, and to provide an alloy plate made of the same alloy and a material for a substrate made of the same alloy.
With regard to the ferritic Fe—Cr—Ni—Al alloy, the present inventors made every effort to realize a balance among chemical components according to which the tensile strength is adjustable at a proper level while keeping good oxidation resistance. As a result, it has been found that, when the amounts of Ni, Cr and Al in the Fe—Ni—Cr—Al alloy are adjusted in proper ranges, it is possible to keep the matrix to have a single phase structure of ferrite, and to finely precipitate an intermetallic compound of Ni—Al, which greatly contributes to precipitation strengthening of the alloy, in the ferrite matrix, whereby a high strength can be realized without deterioration of good oxidation resistance, cold workability and ductility.
It has been also found that, when the alloy contains small amounts of C and Zr, carbides are formed to keep ferrite crystal grains of the Fe—Ni—Cr—Al fine, thereby enabling to improve the alloy in 0.2% yield strength while keeping ductility and toughness at proper levels.
Further, it has been found that, when optionally one or more elements selected from the group of Hf, V, Nb, Ta, Y and REM (rare earth metals) are added, an adhesiveness of an oxide film to the alloy base is improved, the oxide film being primarily composed of aluminum oxides and formed on the surface of the alloy when exposed to a high temperature.
Moreover, it has been found that it is necessary to adjust a Cr equivalent, which has been defined by an F value determined on the basis of a result of experimental investigation by the present inventors, to a specific value as well as adjustment of the amount of the respective alloying elements, and that it is necessary to adjust the amount of solute elements defined by an S value to a specific value in order to obtain good cold workability of the alloy, resulting in the present invention.
Thus, according to a first aspect of the invention, there is provided a ferritic Fe—Cr—Ni—Al alloy having excellent oxidation resistance and high strength, which consists essentially of, by mass, 0.003 to 0.08% C, 0.03 to 2.0% Si, not more than 2.0% Mn, from more than 1.0% to not more than 8.0% Ni, from not less than 10.0% to less than 19.0% Cr, 1.5 to 8.0% Al, 0.05 to 1.0% Zr, and the balance of Fe and incidental impurities, wherein an F value is not less than 12% and an S value is not more than 25%, where the F value is defined by the following equation (1) and the S value is defined by the following equation (2):
F
=−34.3C+0.48Si−0.012Mn−1.4Ni+Cr+2.48Al, (1)
and
S=Ni+Cr+Al,
(2)
and wherein
the Fe—Cr—Ni—Al alloy, after an annealing heat treatment at 600 to 1050° C., has 0.2% yield strength of 550 to 1,000 MPa by a tensile test at room temperature.
According to a second aspect of the invention, there is provided a ferritic Fe—Cr—Ni—Al alloy having excellent oxidation resistance and high strength, which consists essentially of, by mass, 0.003 to 0.06% C, 0.03 to 1.0% Si, not more than 2.0% Mn, from more than 1.0% to less than 5.0% Ni, 10.0 to 17.0% Cr, from not less than 1.5% to less than 4.0% Al, 0.05 to 0.8% Zr, and the balance of Fe and incidental impurities, wherein the F value is not less than 12% and the S value is not more than 25%, and wherein
the Fe—Cr—Ni—Al alloy, after an annealing heat treatment at 600 to 1050° C., has 0.2% yield strength of 550 to 1,000 MPa by a tensile test at room temperature.
In the above ferritic Fe—Cr—Ni—Al alloys having excellent oxidation resistance and high strength, preferably 0.05 to 1.0% in total of one or more elements selected from the group of Hf, V, Nb and Ta are added. It is also preferred to add 0.05 to 1.0% in total of one or more elements selected from the group of Hf, V, Nb and Ta, and/or 0.05 to 1.0% in total of at least one element selected from Y and REM to the ferritic Fe—Cr—Ni—Al alloys.
Preferably, the Fe—Cr—Ni—Al alloy, after an annealing heat treatment at 600 to 1050° C. of temperature, has a Vickers hardness of 250 to 410 HV.
Preferably, the Fe—Cr—Ni—Al alloy has a mean coefficient of thermal expansion 11×10
−6
to 14×10
−6
/° C. in a temperature range of 20 to 800° C.
The invention alloy is excellent in cold workability, so that a ferritic alloy plate and a plate for substrates can be produced.
It should be also noted that such a plate can be produced by the powder metallurgical method from a powder of the invention alloy.
DETAILED DESCRIPTION OF THE INVENTION
Herein below, there will be described functions of the alloying elements in the invention alloy.
C (carbon) forms carbides with Cr and Zr in the invention alloy to deteriorate effects of the additive alloying elements. Thus, the carbon amount is preferably low. Further, a much amount of carbon makes the ferrite phase unstable, since carbon is an austenite forming element. On the other hand, in the case where the carbon amount is small, ferrite grains of the alloy can be maintained fine since carbides restrain grain boundaries of the ferrite not to move while maintaining the ferrite structure. If the carbon amount is less than 0.003%, t
Inoue Ken-ichi
Minagi Yoshihiro
Uehara Toshihiro
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