Stock material or miscellaneous articles – All metal or with adjacent metals – Having metal particles
Reexamination Certificate
1998-11-05
2001-03-27
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Having metal particles
C428S469000, C428S701000, C428S702000, C075S243000, C075S246000, C384S912000, C420S454000
Reexamination Certificate
active
06207291
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a high-temperature sliding alloy used in an oxidizing atmosphere under a high temperature condition ranging from a room temperature to a high temperature, and also relates to a sliding contact structure comprising a sliding member, made of this sliding alloy, and a mating member disposed in sliding contact with the sliding member.
Conventional high-temperature sliding alloys are disclosed, for example, JP-A-5-17839 and JP-A-7-292430 filed by the Applicant of the present application. These sliding alloys have a structure in which Co—Mo—Cr—Si base hard particles are dispersed in the matrix of Ni base alloy.
The sliding alloy, disclosed in JP-A-5-17839, consists of, by weight, 9 to 30% Cr, 5 to 19% Fe, 0.1 to 1.5% Si, 2 to 22% Co, 1.4 to 11% Mo, and the balance Ni and unavoidable impurities, and has the structure in which 5 to 35% by volume of Co—Mo—Cr—Si base hard particles are dispersed in the matrix. This sliding alloy is suitably used particularly when a mating member is made of a hard material, such as a precipitation hardening-type Ni base heat-resistant alloy, having a hardness of Hv300 to 500, and for example, this sliding alloy is suitably adapted to an exhaust gas control valve of a petrol (gasoline) or a diesel engine, and a variable valve in a gas turbine.
The sliding alloy, disclosed in JP-A-7-292430, consists of, by weight, 2 to 8% Cr, 2 to 10% Fe, 0.1 to 1.5% Si, 2 to 22% Co, 1.4 to 11% Mo, and the balance Ni and unavoidable impurities, and has the structure which comprises 5 to 35% by weight of Co—Mo—Cr—Si base hard particles dispersed in the matrix. Even when a mating member is made of a soft material such as austenitic stainless steel, this sliding alloy alleviates wear of the mating material, and therefore there can be achieved a sliding contact structure, comprising a sliding member (made of this sliding alloy) and the mating member disposed in sliding contact therewith, which sliding contact structure is excellent in durability.
A bearing for use in a carriage for charging a product to be heat treated into a heat treatment furnace, is required to possess excellent bearing properties (such as wear resistance) not only under a high temperature condition in the furnace but also under a room temperature condition.
However, the above conventional sliding members exhibit excellent sliding properties at a high temperature, but the sliding properties and particularly the friction coefficient have been found not entirely satisfactory at a room temperature.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a sliding alloy which exhibits excellent sliding properties and particularly a low friction coefficient and excellent wear resistance at temperatures ranging from room temperature to 900° C.
According to the feature of the present invention, there is provided a high temperature sliding alloy consisting of, by weight, 2 to 8% Cr, 2 to 10% Fe, 0.1 to 1.5% Si, 2 to 22% Co, 1.4 to 11% Mo, and the balance Ni, which comprises 1 to 35% by weight of Co—Mo—Cr—Si base hard particles dispersed in a matrix of the sliding alloy, and each of the hard particles has an oxide phase formed on a surface thereof.
The reason why the Cr content should be 2 to 8 wt. % is that if this content is less than 2 wt. %, the matrix fails to have a sufficient oxidation resistance, and if this content is more than 8 wt. %, the rate of compacting of powder can not be increased, so that a sintered product of a high density can not be obtained. Therefore, the Cr content should be 2 to 8 wt. %, and the content of 5 to 7 wt. % is particularly preferred from the viewpoints of the formability and oxidation resistance.
The reason why the Fe content should be 2 to 10 wt. % is that if this content is less than 2 wt. %, the high temperature strength is inferior, and if this content is more than 10 wt. %, the powder, used to form a compact, becomes hard, and therefore the rate of compacting of the powder can not be increased, so that the sintered product of a high density can not be obtained. Therefore, the Fe content should be 2 to 10 wt. %. The content of 4 to 6 wt. % is particularly preferred since the high temperature strength becomes more excellent, and better oxidation resistance is obtained.
The reason why the content of the Co—Mo—Cr—Si base hard particles should be 1 to 35 wt. % is that if this content is less than 1 wt. %, the effect of enhancing the sliding properties at high temperatures is not satisfactory, and if this content is more than 35 wt. %, the formability of the powder becomes poor, and the alloy becomes hard, so that the amount of wear of the mating member increases when the sliding member and the mating member slide relative to each other. It is particularly preferred that the Co—Mo—Cr—Si base hard particles having a particle size of 100 to 200 &mgr;m, are uniformly dispersed in the matrix.
The Co—Mo—Cr—Si base hard particles have a close-packed hexagonal crystal structure consisting of, by weight, 26 to 30% Mo, 7.5 to 9.5% Cr, 2.4 to 2.6% Si, and the balance Co.
In order to form the Co—Mo—Cr—Si base hard particles having the close-packed hexagonal structure, the sliding alloy consists of, by weight, 0.1 to 1.5% Si, 2 to 22% Co and 1.4 to 11% Mo.
When the sintered product is heated in an oxidizing atmosphere at a temperature of 600 to 900° C., the surface of each of the Co—Mo—Cr—Si base hard particles, exposed to the surface of the sintered product, is oxidized. As a result, that portion of each of the Co—Mo—Cr—Si base hard particles
2
(dispersed in the Ni—Cr—Fe matrix
1
), exposed to the surface of the sintered product, is oxidized to form a phase
2
a
of a Co—Mo—Cr—Si oxide, as shown in FIG.
1
. Then, this phase is further oxidized, and a phase
2
b
of a Co—Cr oxide is formed, and then an molybdenum oxide phase
2
c
is formed on the surface of the Co—Cr oxide phase
2
b.
When the sliding member, made of this sliding alloy, slides relative to the mating member, the molybdenum oxide phase
2
c
, having a lubrication property, is transferred and adhered to the mating member, thereby performing a lubrication effect. Also, the Co—Cr oxide phase
2
b
, which is brittle and hard, is broken into fine pieces or grains which roll between the sliding member and the mating member, and these grains achieve a kind of rolling frictional effect. It is thought that with the synergistic effect, achieved by the lubrication effect and the rolling effect, a stick-slip phenomenon is eliminated, so that a low friction coefficient is obtained.
According to another feature of the present invention, there is provided a sliding contact structure comprising a sliding member, made of the above sliding alloy, and a mating member having a sliding contact surface disposed in sliding contact with the sliding member, wherein the sliding contact surface of the mating member is subjected to a nitriding treatment. With this nitriding treatment, the friction coefficient can be reduced in the temperature range from room temperature to a high temperature, and also the wear resistance of the sliding member and the mating member is enhanced, so that there can be provided the sliding contact structure having more excellent durability.
The sliding member may have a bimetal construction, in which case, for example, the sliding alloy is bonded to a stainless steel material. Further, in order to enhance initial conformability, a coating layer, made of a solid lubricant (e.g. BN or MoS
2
), may be coated on the sliding contact surface of the sliding member.
Preferably, the mating member is made of a heat-resistant material such as stainless steel and heat-resistant steel.
In one aspect of the invention of the high temperature sliding alloy consists of, by weight, 2 to 8% Cr, 2 to 10% Fe, 0.1 to 1.5% Si, 2 to 22% Co, 1.4 to 11% Mo, and the balance Ni, which comprises 1 to 35% by weight of Co—Mo—Cr—Si base hard particles dispersed in the matrix of the sliding alloy, and each of the hard particles has an oxide phase formed on a surface thereof.
Matsumura Hideyumi
Ozaki Kouki
Shibayama Takayuki
Browdy and Neimark
Daido Metal Company Ltd.
Jones Deborah
McNeil Jennifer
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