Sintered alloy having superior wear resistance

Details Sintered alloy having superior wear resistance Sintered alloy having superior wear resistance

1999-11-29

2001-10-16

Mai, Ngoclan (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Compositions

Consolidated metal powder compositions

C075S240000, C075S246000

Reexamination Certificate

active

06302937

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a sintered alloy which exhibits superior wear resistance and to a process of manufacture therefor, and more particularly, relates to a technique suitable for use for valve seats in internal combustion engines.
Recently, with the increasing performance of automobile engines, operating conditions have become much more severe. The valve seats used for such engines are also inevitably required to withstand more severe environments than before. To meet such requirements, the present applicant previously proposed several sintered alloys having superior wear resistance as disclosed in, for example, Japanese Examined Patent Publications (KOKOKU) Nos. 17968/74, 36242/80, 56547/82, 55593/93, and 98985/95.
Of all the proposed sintered alloys having superior wear resistance, the sintered alloy disclosed in Japanese Examined Patent Publication (KOKOKU) No. 55593/9395 is particularly improved in wear resistance. The sintering alloy exhibits a metallographic structure in which diffusing phase diffused Co is surrounded by a hard phase consisting of Mo silicide in a matrix structure, and superior wear resistance is obtained by the presence of the hard phase. A matrix is disclosed in Japanese Examined Patent Publication (KOKOKU) No. 36242/80. A sintered alloy having superior wear resistance disclosed in Japanese Examined Patent Publication (KOKOKU) No. 98985/95 is an improvement of the alloy disclosed in Japanese Patent Examined Publication (KOKOKU) No. 55593/93. By including Ni in an amount of 5 to 27% by weight in the alloy of Publication (KOKOKU) No. 55593/93, the matrix structure is strengthened, thereby further improving wear resistance.
However, since these alloys use expensive materials such as Co, they may not meet the demands for recent cost-performance. That is to say, the development of automobiles is recently directed not only to higher performance but also to lower cost from an economic point of view. Therefore, the present applicant proposed a sintered alloy having superior wear resistance which can yield the required wear resistance using inexpensive materials in Japanese Examined Patent Publication (KOKOKU) No. 195012/97. In this proposal, by using a powder which partially diffuses each powder of Ni, Cu, and Mo into Fe powder, as a matrix forming powder, the matrix is strengthened, and by dispersing the hard phase primarily consisting of Cr carbide into this matrix structure, the required wear resistance and mechanical strength are obtained without using expensive materials such as Co.
However, the demands on cost-performance become more severe every year, and a sintered alloy having superior wear resistance for the valve seat, which is less expensive than the above-proposed sintered alloy having superior wear resistance, is further demanded. Therefore, since expensive materials such as Mo are used in the above-proposed sintered alloy having superior wear resistance, it seems that there is room for further improvement concerning the use of materials.
At present, the conditions for operation are even further increased in severity as the performance of automobile engines continues to improve, and a material, which is superior in wear resistance and in strength to the above-mentioned sintered alloys, is demanded.
SUMMARY OF INVENTION
The present invention has been made in view of the above situation. It is therefore an object of the present invention to provide a sintered material which can further improve mechanical strength and wear resistance without using expensive materials, and to provide a process of manufacture therefor.
The first sintered alloy having superior wear resistance according to the present invention relates to an improvement of a sintered alloy having superior wear resistance which was previously disclosed in Japanese Unexamined Patent Application Publication No. 195012/97 by the present applicant. In this sintered alloy, Mo is removed from components forming a matrix structure and the Ni content therein is increased, whereby austenite is adjusted to a suitable ratio, so that an object of the present invention is attained.
Therefore, the first sintered alloy having superior wear resistance according to the present invention has an overall composition consisting of, in percent by weight, Ni in an amount of 6.0 to 25.0%, Cr in an amount of 0.6 to 8.75%, C in an amount of 0.54 to 2.24%, and the balance consisting of Fe and inevitable impurity, the sintered alloy exhibiting a metallographic structure in which a hard phase is dispersed in a mixed structure of martensite and austenite, the hard phase comprising a core consisting of Cr carbide and a ferrite phase diffused Cr or a mixed phase of ferrite and austenite diffused Cr surrounding the core, and the area ratio of austenite in the mixed structure in the metallographic structure ranges from 5 to 30%.
Effects of the sintered alloy having superior wear resistance thus formed, as well as the basis for the numerical limitations, will now be described with reference to FIG.
1
.
{circle around (1)} Matrix
FIG. 1
is a schematic view showing a metallographic structure of the sintered alloy having superior wear resistance, whose surface is subjected to corrosion treatment by nital or the like. As shown in
FIG. 1
, the matrix for this sintered alloy has a mixed structure of martensite and austenite. The martensite has high hardness and high mechanical strength, so that it is capable of contributing to the improvement of wear resistance. However, because of the hardness, the wear on a valve as counterpart component element is made worse. Grains worn from the counterpart component element function as abrasive grains, and the wear on the valve seat is consequentially increased. Therefore, by dispersing austenite having a high toughness, the counterpart component element is less damaged, without decreasing the wear resistance of the matrix. According to research by the inventors, when the area ratio of austenite is less than 5%, the martensite content is too high, whereby abrasion of the counterpart component element is increased, while when the area ratio of austenite is more than 30%, the wear resistance and the mechanical strength are decreased.
Although not shown in
FIG. 1
, sorbite or bainite is often formed, depending on the component constituent and the cooling conditions after sintering. In the present invention, such a formation is also included. For example, such a formation is a structure in which bainite surrounds a core consisting of sorbite and/or the bainite. A mixed structure includes bainite having high hardness and high strength in proximity to martensite, whereby adjustment to suitable hardness can maintain the wear resistance and can suppress the abrasion of the counterpart component element. Whether to produce the martensite or the bainite may be decided by the below-described dispersing concentration of elements which improve the hardenability of Ni, Cr, or the like, and the cooling rate thereof. That is, in a portion in which such element is enriched (high concentration), the structure thereof transforms into martensite, and then in a portion in which such element is enriched, the structure thereof is transformed into bainite. When the cooling is rapid, the structure thereof is transformed into martensite, and then when the cooling continues rapidly, the structure thereof is transformed into bainite. In contrast, in portions in which the above-described elements which improve hardenability are scarce, or in the case in which cooling rate is low, the structure is transformed into sorbite and/or the bainite.
{circle around (2)} Hard Phase
As shown in
FIG. 1
, a hard phase, in which ferrite phase or mixed phase of ferrite and austenite surrouds a core consisting of Cr carbide, is dispersed in the matrix. The core of Cr carbide has higher hardness than martensite, whereby wear resistance is further improved. The ferrite phase or the mixed phase of ferrite and austenite has high toughness because the Cr content is high, and is bound to the cor

Affiliated with

Also associated with

Rating

Sintered alloy having superior wear resistance does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Sintered alloy having superior wear resistance, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sintered alloy having superior wear resistance will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2563418