Metal treatment – Stock – Nickel base
Patent
1980-10-24
1983-09-13
Dean, R.
Metal treatment
Stock
Nickel base
148442, C22C 1905
Patent
active
044040490
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to nickel-base alloy for hard facing, and more particularly to a hard facing nickel-base alloy which has high toughness, high wear resistance and high corrosion resistance and which is used for hard facing of various kinds of structures, machine parts, instruments, etc.
BACKGROUND ART
Among various methods of hard facing various kinds of structures, machine parts, instruments, etc. for prevention of wear, corrosion, high temperature oxidation, errosion etc., there is known a method of hard facing through use of what is called the self-fluxing alloy by means of spraying or build up welding.
Self-fluxing alloys comprise a base of nickel (Ni), nickel-chromium (Ni-Cr) or cobalt-chromium (Co-Cr) and additives of boron (B) and silicon (Si). Among such self-fluxing alloys nickel-base alloys containing 1 to 3% by weight of boron and 2.3 to 5% by weight of silicon are widely used because of their relatively good wear resistance, corrosion resistance and workability for hard facing.
However, the above-mentioned conventional self-fluxing nickel-base alloys have a disadvantage that when they have been applied onto a large piece of base metal or a base of a metal which has a thermal expansion coefficient greatly different from those of the alloys, craks or fissures will occur in the hard facing alloy layer under certain conditions of employment.
This disadvantage is caused by the presence of a quasi-binary eutectic structure of a Ni-solid solution+Ni.sub.3 B in the structure constituting the matrix of the conventional self-fluxing nickel-base alloys.
Since the Ni.sub.3 B in the quasi-binary eutectic structure of Ni-solid solution+Ni.sub.3 B is so brittle that this binary eutectic structure is the least tough and ductile in the matrix, cracks or fissures occur in the hard facing layer of the alloy under certain conditions of employment as mentioned above.
Moreover, although the above-mentioned self-fluxing nickel-base alloys have relatively high wear resistance and corrosion resistance, these characteristics have been found not sufficiently satisfactory under certain conditions of employment with much room left for improvement.
Besides the self-fluxing nickel-base alloys there are known cobalt-base alloys available for hard facing. These alloys are composed of 0.9 to 1.6% by weight of carbon, less than 0.5% by weight of manganese, 0.8 to 1.5% by weight of silicon, 26 to 29% by weight of chromium, 4 to 6% by weight of tungsten, and less than 3% by weight of iron, the balance being cobalt. The alloys have a hardness of 35 to 45 in Rockwell C scale and a Charpy impact value of 0.9 to 1.4 kgm/cm.sup.2. Even under such conditions as would cause cracks or fissures in the hard facing layer of the conventional self-fluxing nickel-base alloys, the cobalt-base alloys are less susceptible to cracks or fissures and have relatively high wear resistance.
However, when the cobalt-base alloys are used at the places such as nuclear plants, where they are exposed to radioactivity, Co.sup.60 that is an isotope having a long half-life is produced with a resulting danger of environmental pollution. Therefore, it is undesirable to use a cobalt-base alloy for hard facing of the seat of a valve used in, e.g., an atomic power plant, and there has been a demand for hard facing alloys which can replace the cobalt-base alloys.
In an effort to solve the above technical problems, the present inventors have studied the compositions of self-fluxing nickel-base alloys and conducted various experiments, with the following three conditions having been set as the basic conditions the alloys of this invention are to satisfy: exceed 45. (This value will be referred to as the HI value hereinafter).
The hard facing nickel-base alloys which satisfy the above conditions sufficiently satisfy the usual conditions under which the cobalt-base alloys are actually used in various applications.
One object of this invention is to provide hard facing nickel-base alloys which satisfy the above three conditions and which are toug
REFERENCES:
patent: 2755183 (1956-07-01), Cape
patent: 2864696 (1958-12-01), Foreman
patent: 2899302 (1959-08-01), Cape et al.
patent: 3428442 (1969-02-01), Yurasko, Jr.
patent: 4188209 (1980-02-01), Kruske
Hidaka Kensuke
Tanaka Kanichi
Dean R.
Fukuda Metal Foil & Powder Co., Ltd.
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