Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2003-03-10
2004-10-12
Mai, Ngoclan T. (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S231000, C075S244000, C075S246000, C419S012000, C419S014000, C419S036000
Reexamination Certificate
active
06802883
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to an iron-based sintered alloy with high performance and low cost for use as a valve seat of all internal combustion engine. The present invention also relates to a production method of the iron-based sintered alloy.
2. Description of Related Art
There is a tendency of increasing thermal load and mechanical load, to which the valve seat of an engine is subjected, along with the performance increase of an internal combustion engine as increasing the fuel efficiency and reducing an exhaust emission. In order to cope with this tendency, the sintered alloy to be used as valve seats has been strengthened by means of high alloying, forging, or copper infiltration. For example, chromium (Cr), cobalt (Co) and tungsten (W), which are added in the raw material powder for producing the iron-based sintered alloy, enhance the high-temperature strength of the alloy. Copper infiltration enhances the thermal conductivity of the sintered compact and hence indirectly enhances the high-temperature strength. Meanwhile, the strengthening of the sintered alloy by means of high-pressure compacting, powder forging, cold forging and high-temperature sintering are effective for increasing the mechanical strength of the sintered compact.
The present applicant proposed the iron-based sintered alloy, which consists of an iron base matrix with nickel (Ni)-molybdenum (Mo)-chromium (Cr)-carbon (C) and hard particles dispersed in the matrix, in Japanese Unexamined Patent Publication (kokai) No. 09-053158 (hereinafter referred to as “prior application”). However the proposed alloy is expensive since the matrix contains a large amount of expensive alloying elements. In the prior application, the performance of a valve seat is evaluated in terms of valve clearance between a cam and a cam follower. The valve clearance is mainly the total wear of the valve seat and the valve which are subject to hammering and sliding wear. The present inventors paid attention to the respective parts subject to the hammering and sliding wear and made further researches and discovered that high-alloying can be avoided.
Copper infiltration into the internal poles of the sintered compact enhances the thermal conductivity, so that the temperature of the material is not liable to rise even when the combustion temperature becomes high. Wear-resistance at high temperature is thus enhanced and the usable temperature of the iron-based alloy is increased. However, the copper-infiltrated sintered alloy needs secondary sintering, which increases the production cost.
SUMMARY OF INVENTION
It is, therefore, an object of the present invention to provide an iron-based sintered alloy, in which the alloying elements are reduced to the minimum level, for use as a valve seat of an internal combustion engine.
It is also an object of the present invention to provide a method for producing an iron-based sintered alloy for use as a valve seat of an internal combustion engine without secondary treatment such as copper infiltration.
In accordance with the objects of the present invention, there is provided an iron-based sintered alloy, which consists, by weight %, of from 0.5 to 5% of nickel (Ni), from 0.5 to 4% of chromium (Cr), from 0.5 to 2% of carbon (C), the balance being iron (Fe) and unavoidable impurities, and which has a microstructure comprising an iron-based matrix containing the nickel (Ni) and a part of the chromium (Cr) as solutes and carbides containing the other part of the chromium (Cr) and dispersed in the iron-based matrix. This alloy is hereinafter referred to as the Fe—Ni—Cr—C alloy.
The iron-based sintered alloy according to the present invention may additionally contain one or more of the following hard particles.
(1) Hard particles which consist, by weight %, of from 50 to 57% of chromium (Cr), from 18 to 22% of molybdenum (Mo), from 8 to 12% of cobalt (Co), from 0.1 to 1.4% of carbon (C), from 0.8 to 1.3% of silicon (Si) and the balance being iron (Fe).
(2) Hard particles which consist, by weight %, of from 27 to 33% of chromium (Cr), from 22 to 28% of tungsten (W), from 8 to 12% of cobalt (Co), from 1.7 to 2.3% of carbon (C), from 1.0 to 2.0% of silicon (Si) and the balance being iron (Fe).
(3) Hard particles which consist, by weight %, of from 60 to 70% of molybdenum (Mo), 0.0% less of carbon and the balance being iron (Fe).
(4) Hard particles which consist of Stellite alloy
The hard particles are in an amount of from 3 to 20% by weight based on the iron-based sintered alloy, i.e., total of the Fe—Ni—Cr—C alloy and the hard particles. The hard particles are preferably of less than 150 &mgr;m of particle size.
In the iron-based sintered alloys mentioned above, solid lubricant such as fluoride (LiF
2
, CaF
2
, BaF
2
and the like), boride (BN and the like) and the sulfide (MnS and the like) may be uniformly dispersed. The amount of the solid lubricant is from 1 to 20% by weight based on the iron-based sintered alloy, i.e., the total of the Fe—Ni—Cr—C alloy and the solid lubricant, and occasionally the hard particles. The solid lubricant is preferably of less than 45 &mgr;m of particle size.
A preferred method for producing the iron-based sintered alloy according to the present invention comprises the steps of:
preparing the raw material powder, which consists, by weight %, of from 0.5 to 5% of nickel (Ni), from 0.5 to 4% of chromium (Cr), from 0.5 to 2% of carbon (C) and the balance being iron (Fe) and unavoidable impurities by using at least an iron (Fe)-chromium (Cr) powder capable of supplying the total amount of chromium (Cr);
mixing zinc stearate and said raw material powder to prepare a green mixture;
pressing the green mixture to form a green compact;
heating the green compact to dewax; and,
sintering the green compact followed by cooling and then, annealing if necessary.
Preferably, the raw material powder consists of pure-iron (Fe) powder having average particle size of 75~150 &mgr;m, iron (Fe)-chromium (Cr) alloy powder containing chromium (Cr) of from (10) to (14)% having average particle size of 75~106 &mgr;m, nickel (Ni) powder having particle size less than 45 &mgr;m and fine graphite (C) powder. The nickel powder is preferably pure nickel powder. The method may further comprise a step of mixing the raw material powder with from 3 to 20% of one or more hard particles selected from (1) hard particles which consist of from 50 to 57% of chromium (Cr), from 18 to 22% of molybdenum (Mo), from 8 to 12% of cobalt (Co), from 0.1 to 1.4% of carbon (C), from 0.8 to 1.3 of silicon (Si) and the balance being iron (Fe), (2) hard particles which consist of from 27 to 33% of chromium (Cr), from 22 to 28% of tungsten (W) from 8 to 12% of cobalt (Co), from 1.7 to 2.3% of carbon (C), from 1.0 to 2.0% of silicon (Si) and the balance being iron (Fe), (3) hard particles which consist of from 60 to 70% of molybdenum (Mo), 0.01% or less of carbon and the balance being iron (Fe), and (4) hard particles which consist of Stellite alloy, and/or with from 1 to 20% of solid lubricant, as well as with the zinc stearate, thereby preparing green mixture.
DESCRIPTION OF PREFERRED EMBODIMENTS
The composition of the iron-based sintered alloy according to the present invention is hereinafter described.
Nickel (Ni) is dissolved in the iron (Fe) matrix and enhances its strength and heat resistance. Wear resistance of the iron-based sintered alloy at the operation temperature of the valve is thus enhanced. The addition amount of nickel (Ni) is from 0.5 to 5%. When the addition amount of nickel (Ni) is less than 0.5%, the wear resistance is not satisfactorily improved. On the other hand, when the nickel (Ni) content is more than 5%, although the mechanical properties of the iron-based sintered alloy are excellent, the opposite material (valve) is seriously worn out (see examples No. 28 and No. 29), probably because the high Ni content of the valve seat results in disadvantageous adhesive wear condition with the valve which has high nickel (Ni) content to enhance the heat resistance.
Henmi Hiroji
Ishibashi Akiyoshi
Kabushiki Kaisha Riken
Kubovcik & Kubovcik
Mai Ngoclan T.
LandOfFree
Iron-based sintered alloy for use as valve seat and its... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Iron-based sintered alloy for use as valve seat and its..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Iron-based sintered alloy for use as valve seat and its... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3273280