Specialized metallurgical processes – compositions for use therei – Compositions – Consolidated metal powder compositions
Reexamination Certificate
2002-08-29
2004-03-30
Mai, Ngoclan (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Consolidated metal powder compositions
C075S236000, C075S243000, C075S246000, C419S014000, C419S027000, C419S029000, C419S048000
Reexamination Certificate
active
06712871
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a sintered alloy for valve seat having excellent wear resistance and a method for producing the same. More particularly, it relates to an iron base sintered alloy comprising vanadium carbide(VC) particles, Fe—Co—Ni—Mo alloy particles and Cr—W—Co—C alloy particles in which the composition is dispersed in a structure of sorbite and a method for producing the same, thus being suitable for use as materials of valve seats for automotive engines which requires excellent wear resistance, high-performance, high-rotation-speed and low-fuel-consumption.
BACKGROUND OF THE INVENTION
A valve seat for an automotive engine, which is an engine part to increase thermal efficiency of a combustion chamber, is required to have high heat resistance, high wear resistance and high oxidation resistance at a temperature of from 400° C. to 700° C. to suffer from contact, friction, exposure to exhaust gas during the operation of the internal combustion engine.
Methods for producing valve seats of automotive engines are an infiltration process, a hard metal addition process, a control of alloy composition and the like.
An infiltration is the process of filling pores of a sintered alloy material with infiltrating materials such as Cu, and Cu—Pd, or solid lubricants such as Pb, PbO, B
2
O
3
, ZnO and the like and thus it improves ductility and machinability when valves are rotating.
A hard metal addition is the process of producing a sintered alloy containing hard Fe—Mo, or Co—Ni—W—C carbide complex having about 300 &mgr;m of size. The sintered alloy containing hard carbide complex improves wear resistance by dispersing heavy loading to valve seat through hard carbides having excellent wear resistance when valves are rotating. However, it has several disadvantages such as poor machinability, and use of a large quantity of expensive Co, Ni, W which increases total manufacturing cost.
A control of alloy composition is the process of mixing alloy components as elemental powder, and then melting the powders to form an alloy of a certain composition. It is low in price and easy to produce but difficult to obtain homogeneous structure. Metals such as Co, Ni, Mo, Cr, W and the like are usually used and a large quantity of Co is used to increase thermal stability.
A conventional process of producing sintered alloy includes the steps of mixing each component, compacting the mixture, sintering the compacted mixture, copper infiltration into the sintered mixture, followed by heat treatment. This is a known powder metallurgy manufacturing process. In this process for manufacturing a sintered alloy for a valve seat, Co—Mo—Cr alloy powder or Co—Ni—W—C alloy powder is added to Fe powder to improve wear resistance. However, the sintered alloy produced by this method still has unsatisfied wear resistance to use as materials for valve seats of engines which requires high-performance and high-rotation-speed.
In order to reduce abrasion of valve seat, a gasoline containing 0.2 to 0.8 g/gallon of tetraethyl lead has been used as an anti-knocking agent by increasing octane number. This anti-knocking agent also formed a lubricating film between valve and valve seat by producing lead oxide or lead compound after combustion. However, it is recently a compulsory regulation to use unleaded gasoline containing not higher than 0.004 g/gallon of tetraethyl lead due to serious pollution associated with carbon monoxide, carbon dioxide and lead. It is, therefore, highly desirable to provide novel materials for valve seats of automotive engines having an improved wear resistance compared to the conventional ones.
SUMMARY OF THE INVENTION
The inventors have developed a sintered alloy composition for valve seats having an improved wear resistance to satisfy the requirements for engines to suffer from high output, high rotation and low fuel consumption.
The present invention relates to a sintered alloy composition for valve seats having excellent wear resistance, homogeneous sintered structure and cost effectiveness, in which vanadium carbide particles, Fe—Co—Ni—Mo alloy particles and Cr—W—Co—C alloy particles are dispersed in a structure of sorbite.
In one embodiment, the invention relates to a sintered alloy comprising:
between about 0.7 to about 1.3 weight % of vanadium carbide particles;
between about 84 to about 86 weight % of Fe—Co—Ni—Mo alloy particles; and
between about 12.5 to about 13.5 weight % of Cr—W—Co—C alloy particles.
The sintered alloy may further include between about 0.6 to about 1.3 weight % of added carbon, wherein the particles are dispersed in a structure of sorbite. The Fe—Co—Ni—Mo alloy powder advantageously comprises about 86 to about 93 weight % of Fe; about 5 to about 8 weight % of Co; about 1 to about 3 weight % of Ni; and about 1 to about 3 weight % of Mo. The Cr—W—Co—C alloy powder advantageously comprises about 48 to about 80 weight % of Cr; about 8 to about 25 weight % of W; about 10 to about 25 weight % of Co; and about 1 to about 3 weight % of C. The sintered alloy advantageously further includes between about 11 to about 18 weight % of added infiltrating material. The infiltrating material advantageously includes copper. The infiltrating material may in one embodiment be selected from the group consisting of Cu, a Cu—Pd alloy, Pb, PbO, B
2
O
3
, ZnO, or mixtures thereof. The sintered alloy advantageously further includes added carbon, for example added in the form of graphite particles. Advantageously, the Fe—Co—Ni—Mo alloy powder consists essentially of about 86 to about 93 weight % of Fe; about 5 to about 8 weight % of Co; about 1 to about 3 weight % of Ni; and about 1 to about 3 weight % of Mo; and the Cr—W—Co—C alloy powder consists essentially of about 48 to about 80 weight % of Cr; about 8 to about 25 weight % of W; about 10 to about 25 weight % of Co; and about 1 to about 3 weight % of C. The sintered alloy composition is:
between about 1 to about 1.5 weight % of C;
between about 1 to about 3 weight % of Ni;
between about 6 to about 11 weight % of Cr;
between about 1 to about 3 weight % of Mo;
between about 5 to about 11 weight % of Co;
between about 1 to about 3 weight % of W;
between about 0.5 to about 1.0 weight % of V;
between about 11 to about 18 weight % of Cu; and
the balance Fe.
Advantageously, a valve seat for automotive engines is machined from the sintered alloy.
In another embodiment, the sintered alloy includes:
at least about 0.7 weight % of metal-carbide particles;
Fe—Co—Ni—Mo alloy particles, wherein the Fe—Co—Ni—Mo alloy particles contain an alloy comprising about 86 to about 93 weight % of Fe, about 5 to about 8 weight % of Co, about 1 to about 3 weight % of Ni, and about 1 to about 3 weight % of Mo;
at least 11.5 weight % of Cr—W—Co—C alloy particles, wherein the Cr—W—Co—C alloy particles contain an alloy comprising about 48 to about 80 weight % of Cr, about 8 to about 25 weight % of W, about 10 to about 25 weight % of Co, and about 1 to about 3 weight % of C, wherein the metal-carbide particles, Fe—Co—Ni—Mo alloy particles, and Cr—W—Co—C alloy particles are mixed and then are sintered into a substantially homogeneous porous structure; and
an infiltrating material disposed in the porous structure.
The sintered alloy advantageously further includes between about 0.6 to about 1.3 weight % of added carbon. The sintered particles are dispersed in a structure of sorbite, and the infiltrating material is advantageously Cu. The infiltrating material in one embodiment is selected from the group consisting of Cu, a Cu—Pd alloy, Pb, PbO, B
2
O
3
, ZnO, or mixtures thereof. Advantageously, the metal-carbide comprises vanadium carbide. In one embodiment, the sintered alloy had added carbon that was added in the form of graphite particles which were sintered into the sorbite structure, and the sintered alloy includes between about 11 to about 18 weight % of infiltrating material.
The invention also relates to a method for producing the sintered alloy for valve seat comprising the steps of:
mixing 84 to 86 weight % of Fe—Co—Ni—Mo alloy po
Hyundai Motor Company
Mai Ngoclan
Morgan & Lewis & Bockius, LLP
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