Wear resistant sintered member

Details Wear resistant sintered member Wear resistant sintered member

2002-08-05

2003-05-13

Mai, Ngoclan (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Compositions

Consolidated metal powder compositions

C075S246000

Reexamination Certificate

active

06562098

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wear resistant sintered member which is superior in wear resistance at high temperatures, and in particular, relates to a technique suited to be used for a valve seat insert of internal combustion engines.
2. Description of the Related Art
In order to deal with performance enhancement and power increase of engines for automobiles, a sintered alloy for a valve seat insert having high wear resistance and high strength at high temperature has been required, and the present applicants have also developed a wear resistant sintered alloy (Japanese Patent Publication No. 55-36242) manufactured by a method disclosed in Japanese Patent No. 1043124. In addition, the applicants further developed wear resistant sintered alloys which are superior in high wear resistance and high strength at high temperature, as disclosed in Japanese Patent Publication No. 5-55593, Japanese Patent Application Laid-open No. 7-233454, and the like, in order to deal with recent even greater performance enhancement, power increase, and in particular, increase in combustion temperature due to lean combustion. However, the above conventional materials were disadvantageous in cost because expensive Co-based materials were employed as a hard phase in order to improve the performance at high temperature.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a wear resistant sintered member which can exhibit superior wear resistance at the same level as those of the conventional materials without using a hard phase consisting of Co-based materials.
First Embodiment of Wear Resistant Sintered Member of the Present Invention
In order to solve the above problems, a first embodiment of a wear resistant sintered member according to the present invention exhibits a metallographic structure comprising a first hard phase and a second hard phase diffused in an Fe-based alloy matrix, wherein the first hard phase comprises Mo silicide particles dispersed in an Fe-based alloy matrix of the first hard phase, the second hard phase comprises a ferrite phase or a mixed phase of ferrite and austenite having a higher Cr concentration than the Fe-based alloy matrix surrounding a core consisting of Cr carbide particles, the Mo silicide particles in the first hard phase are contained in an amount of 3 to 25% by area in the member, and the Cr carbide particles in the second hard phase are contained in an amount of 3 to 30% by area in the member.
FIG. 1
shows a schematic drawing of the metallographic structure.
{circle around (1)} First Hard Phase
As shown in
FIG. 1
, in the first hard phase, Mo silicide is dispersed in an Fe-based alloy matrix of the first hard phase, and moreover, composite silicide composed of Mo, Fe, Cr, or Ni, or intermetallic compounds of these elements, may be partially dispersed instead of the Mo silicide. Mo silicide is hard so as to have an effect which improves wear resistance of the wear resistant sintered member, and it has solid lubricity so that action (facing member interaction) which wears or attacks a facing material is low.
In addition, it is preferable that the alloy matrix of the first hard phase for dispersing Mo silicide, etc., be composed of an alloy consisting of Fe and at least one of Ni and Cr. Wear resistance of the first hard phase can be further improved by strengthening the alloy matrix of the first hard phase. Furthermore, Ni or Cr in the alloy matrix of the first hard phase has an effect in which adhesion to the alloy matrix is further strengthened by diffusing into the surrounding matrix.
The Mo silicide particles must be dispersed in the matrix of the first hard phase of the wear resistant sintered member in an amount of 3 to 25% by area. Here, the “area” of the Mo silicide particles refers as an inside area of an outline of the Mo silicide particles. When it is under 3% by area, an improvement effect is poor, and in contrast, when it exceeds 25% by area, facing member interaction increases, and the facing member is thereby worn.
{circle around (2)} Second Hard Phase
As shown in
FIG. 1
, the second hard phase is a phase in which a ferrite phase or a mixed phase of ferrite and austenite, having a higher Cr concentration than the matrix, surrounds a core consisting of Cr carbide particles. Since Cr carbide as a core receives impacts in a valve seating and the surrounding mixed phase of austenite and ferrite has a buffering effect, wear resistance is improved. In addition, Cr which further diffuses contributes to improvement of wear resistance of the overall sintered alloy by acting to strengthen the matrix or the second hard phase as described below. Furthermore, when carbide particles of Mo, V, or W, are dispersed in addition to Cr carbide particles in the second hard phase, it is effective to further improve wear resistance.
The Cr carbide particles must be dispersed in the matrix of the second hard phase in an amount of 3 to 30% by area. Here, an area of the Cr carbide particles refers as an inside area of an outline of the Cr carbide particles. When it is under 3% by area, the above effect is poor and does not contribute to wear resistance, and in contrast, when it exceeds 30% by area, wear of a facing material is enhanced by hard Cr carbide, etc., and worn powder of a facing material acts as grinding particles, so that the sintered member also is worn.
Component composition and metallographic structure of the matrix in a wear resistant sintered member of the present invention are not limited, and conventional alloys can be employed.
Second Embodiment of Wear Resistant Sintered Member of the Present Invention
In order to solve the above problem, a second embodiment of a wear resistant sintered member according to the present invention has an overall composition comprising, by mass, Mo: 1.25 to 17.93%, Si: 0.025 to 3.0%, C: 0.35 to 0.95%, at least one of Cr: 0.025 to 3.0% and Ni: 0.025 to 3.0%, and a balance of Fe and unavoidable impurities, and exhibits a metallographic structure comprising a matrix which consists of bainite or a mixture of bainite and martensite, and a first hard phase comprising Mo silicide particles dispersed in an alloy matrix which consists of Fe and at least one of Ni and Cr, wherein the Mo silicide particles are contained in the alloy matrix of the first hard phase in an amount of 3 to 30% by area.
FIG. 2
shows a schematic drawing of a metallographic structure of the second embodiment of a wear resistant sintered member according to the present invention. As shown in
FIG. 2
, in the second embodiment of a wear resistant sintered member of the present invention, the above first hard phase is strengthened by Ni and/or Cr, the composition of the matrix comprises, by mass, Mo: 0.8 to 4.2%, C: 0.35 to 0.95%, and a balance of Fe and unavoidable impurities, and the matrix consists of bainite or a mixture of bainite and martensite, and therefore, strength and wear resistance of the matrix are improved and superior wear resistance is exhibited by only the first hard phase.
In the first hard phase, Mo silicide is dispersed in an alloy matrix consisting of Fe and at least one of Ni and Cr. When the Mo silicide particles are dispersed in the alloy matrix of the first hard phase in an amount of less than 3% by area, the improvement effect of the wear resistance is insufficient. In contrast, the upper limit of the content of the Mo silicide particles in the first hard phase is higher than that of the above embodiment of a wear resistant sintered member since the second embodiment has no second hard phase; however, when it exceeds 30% by area, the facing member interaction increases and a facing member is thereby worn.
The matrix has a single phase structure consisting of bainite which has high strength, which is hardest after martensite, and which is superior in wear resistance, or has a mixed structure of the above bainite and martensite which is the hardest structure and which has a high facing member interaction. In the mixed structure, by mixing martensite

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