JP2000064002A - Iron-base sintered valve seat and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve high temperature wear resistance, strength, and machinability by dispersing, through a matrix, a compound phase which consists of a mixed-grain group of Cr carbide grains and Cr sulfide grains and a ferritic phase or a mixed phase of ferrite and austenite, each of the phases surrounding the above mixed-grain group in the iron-base. SOLUTION: Mixed-grain groups, where Cr carbide grains and Cr sulfide grains are present as a mixture, are allowed to exist mixedly in the matrix of an iron-base sintered valve seat. The periphery of each grain group is surrounded by a ferritic phase or a mixed phase of ferrite and austenite to form a compound phase having the grain group as a nucleus. By dispersing the Cr sulfide grains having self-lubricity together with the hard Cr carbide grains, improved machinability as well as high wear resistance can be provided. Owing to high Cr concentration, the ferritic phase or the mixed phase of ferrite and austenite can provide excellent toughness and increased material strength and also can act as a buffer against mating parts. It is preferable that the grain groups comprise, by area ratio, 3 to 25% of the metallic structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based sintered valve seat suitable for use in, for example, an internal combustion engine and a method for manufacturing the same, and more particularly to a technique for improving high temperature wear resistance and machinability.

[0002]

2. Description of the Related Art In recent years, operating conditions of automobile engines have become more severe due to higher power performance, and valve seats are required to withstand more severe operating environment conditions than ever. The applicant of the present invention has also previously disclosed Japanese Patent Publication No. 49-17968, Japanese Patent Publication No. 55-36242, Japanese Patent Publication No. 57-56547, and Japanese Patent Publication No. 5-55.
In 593, JP-A-9-195012, JP-A-9-195013, JP-A-9-195014, etc., sintered alloys having excellent wear resistance have been disclosed. Also, Japanese Patent Application No. 9-34449 and Japanese Patent Application No. 10-14.
No. 1976 proposes a wear resistant sintered alloy having improved wear resistance and machinability.

Among the wear-resistant sintered alloys previously disclosed by the applicant, the wear-resistant sintered alloy disclosed in Japanese Patent Publication No. 57-56547 is used in order to form a matrix as a valve seat. The alloys disclosed in JP-B-49-17968 and JP-B-55-36242 are alloyed with the components except for graphite to form two kinds of alloy powders, which are used as a mixed powder with graphite powder, and have a mottled matrix structure. Is a sintered alloy having improved wear resistance. That is, by weight ratio, Cr: 2 to 4%, Mo: 0.2 to 0.4%,
V: 0.2 to 0.4% and Fe: A alloy powder consisting of the balance, and Ni: 0.5 to 3% and Mo: 0.5 by weight.
When graphite is added to a mixed powder of B alloy powder consisting of ˜3%, Co: 5.5 to 7.5% and Fe: balance, the ratio of A alloy powder to B alloy powder is 25:75 to 75:25. It has been disclosed that the wear resistance is improved between the two.

The wear-resistant sintered alloy disclosed in Japanese Examined Patent Publication No. 5-55593 is similar to the alloy disclosed in Japanese Examined Patent Publication No. 55-36242, in which Mo: 26-30% and Cr: 7-
9%, Si: 1.5 to 2.5%, and Co: the remaining hard phase is present in a dispersed structure. The above B alloy powder, Mo: 26 to 30%, Cr: 7 to 9%, Si: 1.
5 to 2.5% and Co: The rest can be produced by using a mixed powder of C alloy powder and graphite powder.

The wear-resistant sintered alloy disclosed in JP-A-9-195012 has a total composition of Ni: 0.736 to
9.65%, Cu: 0.736 to 2.895%, Mo:
0.294 to 0.965%, Cr: 0.12 to 6.25
%, C: 0.508 to 2.0%, having martensite, sorbite and / or upper bainite nuclei, and surrounding bainite, austenite with high Ni concentration, and ferrite with high Cr concentration. It exhibits a structure composed of a hard phase mainly composed of Cr carbide, Ni: 1 to 10%, Cu: 1 to 3
%, Mo: 0.4 to 1% to a powder obtained by partially diffusing and adhering Fe powder to Cr: 4 to 25%, C: 0.25 to 2.4%,
The essence is to use a powder obtained by mixing 3 to 25% of Fe-Cr alloy powder of the balance Fe and 0.5 to 1.4% of graphite powder.

The wear-resistant sintered alloy disclosed in JP-A-9-195013 has an overall composition of Ni: 0.736 to
5.79%, Cr: 0.12 to 6.25%, Mo: 0.
294 to 0.965%, C: 0.508 to 2.0%,
In the matrix of bainite or a mixed structure of bainite and sorbite, a structure having a hard phase core mainly composed of Cr carbide, in which a ferrite with a high Cr concentration surrounding the core and a martensite phase further surrounding the core are dispersed, Present: Ni: 1 to 6%, Mo: 0.4
~ 1% alloy powder, Cr: 4-25%, C: 0.25
~ 2.4%, the balance of Fe Fe-Cr alloy powder 3 ~ 2
The main point is to use a powder in which 5% and graphite powder of 0.5 to 1.4% are mixed.

The wear-resistant sintered alloy disclosed in JP-A-9-195014 has an overall composition of Ni: 0.736 to
5.79%, Cr: 0.12 to 6.25%, Mo: 0.
368 to 1.93%, C: 0.508 to 2.0%,
Bainite or bainite, sorbite, martensite, and austenite have a hard phase core composed mainly of Cr carbide in the mixed structure of ferrite, which has a high Cr concentration surrounding the core and a martensite phase which further surrounds the ferrite. Is present in the alloy powder of Mo: 0.5 to 2% with the balance being Fe.
i: 1 to 6% by partial diffusion adhesion to the powder, Cr: 4 to
25%, C: 0.25-2.4%, balance Fe-C
3-25% r-alloy powder, 0.5-1.4% graphite powder
The main point is to use a powder in which

Further, the wear-resistant sintered alloy filed in Japanese Patent Application No. 9-34449 is based on the alloy having the mottled structure disclosed in Japanese Patent Publication No. 57-56547, and Ni is added to strengthen the matrix. In addition to the above
Co-based alloy powder used in Japanese Patent No.
F used in Japanese Patent Laid-Open No. 195012, Japanese Patent Laid-Open No. 9-195013 and Japanese Patent Laid-Open No. 9-195014
e-Cr alloy powder was added to form a hard phase, and the overall composition was Ni: 1.35 to 19.61%, C
r: 0.9 to 11.05%, Mo: 1.44 to 9.09
%, Co: 3.6 to 20.05%, V: 0.018 to
0.26%, Si: 0.1 to 0.75%, C: 0.35
In the mixed structure of martensite, sorbite, and austenite, the first hard phase, which is surrounded by the diffusion phase in which Co is diffused around the hard phase mainly composed of Mo silicide, is mainly used as Cr. The essence is to have a structure in which a hard phase made of carbide is used as a nucleus and a second hard phase surrounded by a mixed phase of ferrite and austenite is dispersed around the core.

The wear-resistant sintered alloy filed in Japanese Patent Application No. 10-141976 is applied to the base strengthened by adding Ni powder to Fe powder to the above-mentioned Japanese Patent Laid-Open Nos. 9-195012 and 9- Japanese Patent Laid-Open No. 195013 and Japanese Patent Laid-Open No. 9-1
To optimize the amount of austenite in the structure by adding the Fe-Cr alloy powder used in Japanese Patent Publication No. 95014 for the formation of a hard phase and subjecting the formed-sintered sintered body to deep-chill treatment in some cases. Is the main point.

[0010]

As described above, the applicant of the present invention has also provided sintered alloys having more excellent wear resistance in accordance with the demands of the times. However, due to the further improvement in performance of automobile engines, the operating conditions become more severe. Is the current situation,
Wear resistance at higher temperature than the above-mentioned sintered alloy,
A valve seat having excellent strength and machinability is desired.

[0011]

The iron-based sintered valve seat of the present invention comprises a particle group in which Cr carbide particles and Cr sulfide particles are mixed, and a ferrite phase or ferrite and austenite surrounding the particle group as a core. The composite phase consisting of the mixed phase of is dispersed in the matrix. Hereinafter, the operation of the iron-based sintered valve seat having the above structure will be described with reference to FIG.

FIG. 1 is a schematic view showing a metal structure when the surface of an iron-based sintered valve seat is corroded by Nital or the like. As shown in FIG. 1, a group of particles in which Cr carbide particles and Cr sulfide particles are mixed are dispersed in the matrix of the iron-based sintered valve seat. Further, the particle group is surrounded by a ferrite phase or a mixed phase of ferrite and austenite, thus forming a composite phase having the particle group as a nucleus. As described above, in the iron-based sintered valve seat of the present invention, hard Cr carbide particles and self-lubricating C
By further dispersing r sulfide, it is possible to impart high wear resistance to the matrix and at the same time improve machinability. Further, since the ferrite phase or the mixed phase of austenite and ferrite has a high Cr concentration, it is rich in toughness and enhances the material strength, and also plays a role of a cushioning material for the valve which is a counterpart component. Therefore, the wear resistance is further enhanced by suppressing the wear of the mating component. As the matrix structure, a generally used single structure of pearlite, sorbite, bainite, martensite, or a mixed structure selected from the group of austenite added to these can be used, and the above-mentioned single structure A matrix structure in which hard particles, a lubricant, etc. are dispersed in the structure or mixed structure can also be used.

Here, the ratio of the particle group in the metal structure is preferably 3 to 25% in area ratio. When the area ratio of the particle group is less than 3%, it becomes difficult to obtain the wear resistance and machinability as described above. On the other hand, if the area ratio exceeds 25%, the hardness becomes too high to accelerate the wear of the mating component, and the abrasion powder acts as abrasive grains to reduce the wear resistance. In addition,
The area of the particle group is obtained by measuring the area inside the contour line of the particle group.

In the iron-based sintered valve seat, it is preferable that at least one kind of carbide particles of Mo, W and V be mixed in the particle group. As a result, in addition to Cr carbide and Cr sulfide, Mo carbide,
The V carbide or W carbide and the intermetallic compound of Cr and Mo, V or W are contained, and the wear resistance is further improved. That is, in the schematic diagram of FIG.
A metal structure is obtained by replacing the “particle group in which r carbide and Cr sulfide are mixed” with “a particle group in which Cr carbide and Cr sulfide are mainly mixed”. Further, V and W are C
And forming a fine carbide to contribute to the improvement of wear resistance, and these intermetallic compounds and carbides have the effect of preventing Cr carbide from coarsening. Coarse Cr
Since the carbide promotes the wear of the mating component, the wear of the valve, which is the mating component, is suppressed by the prevention of coarsening, and the wear resistance is also improved.

The iron-based sintered valve seat as described above is C
a particle group forming powder containing 4 to 25% by weight of r, M
oS ₂ powder, WS ₂ powder, FeS powder, and sulfide powder consisting of at least one of CuS powder are added to the iron-based mixed powder or the iron-based alloy powder not containing Cr, and the mixed powder is used, It can be produced by adding sulfide powder so that the S content in the entire composition is 0.3 to 1.5% by weight.

In particular, by using MoS ₂ powder or WS ₂ powder, Mo carbide or W carbide is dispersed in the matrix,
The wear resistance can be further improved. Also, Cu
By using S, Cu is dispersed in the matrix to promote the strengthening of the matrix, and at the same time, the hardenability is improved and the wear resistance can be further improved.

Here, the iron-based mixed powder or the iron-based alloy powder not containing Cr is a matrix-forming powder, and if only the Fe-Cr-based alloy powder is used as the matrix-forming powder, the Fe-Cr-based powder is also used for forming the particle group. Since the alloy powder is used, a high chromium ferrite phase (mixed phase of ferrite and austenite) is not formed around the particle group, and improvement in wear resistance due to improvement in strength cannot be achieved. However, Fe-
When an iron-based alloy powder that does not contain Cr is used together with the Cr-based alloy powder, a high chromium ferrite phase (mixed phase of ferrite and austenite) is formed around the particle group to improve wear resistance.

In the above manufacturing method, the ratio of Cr in the particle group forming powder is set to 4 to 25% by weight is 4% by weight.
If the amount is less than the above, the amount of Cr carbide and Cr sulfide to be formed is insufficient and it does not contribute to improvement of wear resistance and machinability.
On the other hand, if it exceeds 25% by weight, on the contrary, the amount of Cr carbide becomes too large to promote the wear of the mating component, and the hardness of the powder increases to impair the compressibility. As described above, in order to set the area ratio of the particle group in the metal structure to 3 to 25%, the particle group forming powder is added to the powder in an amount of 5 to 25% by weight.

The amount of S in the overall composition is 0.3 to 1.5.
Addition of sulfide powder so that the weight% is 0.3
If it is less than 1.5% by weight, the formation of Cr sulfide or the like will be insufficient and the wear resistance and machinability will be insufficiently improved. If it exceeds 1.5% by weight, the precipitation of Cr sulfide will be excessive and the strength will be poor. Because it will decrease.

Further, Mo, V, W is contained in the particle group forming powder.
It is preferable that at least one kind of Mo, W, and V carbide particles can be mixed in the particle group by including at least one kind of the above.

[0021]

EXAMPLES Examples of the present invention will be described below. Alloy powders A to E for forming a matrix shown in Table 1, Fe powder, Ni powder, graphite powder,
A hard phase forming powder F, a particle group forming alloy powder G and a sulfide powder were prepared. The alloy powder C for forming the matrix is
Partial diffusion alloy powder in which Ni and Mo are partially diffused and adhered to Fe powder, alloy powder E is a partial diffusion alloy powder in which Ni is partially diffused and adhered to Fe-Mo perfect alloy powder, and other A,
The B, D, F and G powders are perfect alloy powders. These powders were mixed at the compounding ratios shown in Tables 2 and 3, and then molded into a valve seat shape of φ30 × φ25 × t10 at a molding pressure of 6.5 ton / cm ² , and the mixture was molded in an atmosphere of ammonia decomposition gas 1
Sintering was performed at 180 ° C. for 60 minutes to obtain alloys (Sample Nos. 1 to 54) having the component compositions shown in Table 4. The examples of the present invention are obtained by adding sulfide powder in Tables 2 and 3, and the others are comparative examples.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

A simple wear test and a machinability test were conducted on the above alloys. The results are shown in Table 5 and FIGS.
Shown in. In the simple wear test, a sintered alloy processed into a valve seat shape is press-fitted into an aluminum alloy housing, and the valve is moved up and down by the rotation of an eccentric cam driven by a motor. This is a test in which a sheet repeatedly collides with the sheet surface. In addition, the temperature setting in this test was performed by heating the umbrella of the valve with a burner, and the test was performed simply by using the environment in the engine room. In this test,
The rotation speed of the eccentric cam was set to 2700 rpm, the test temperature of the valve seat portion was set to 250 ° C., and the repetition time was set to 15 hours, and the abrasion amount of the valve seat and the valve after the test was measured and evaluated. In addition, the machinability test is a test in which a sample is drilled with a constant load using a table-top drilling machine and the possible number of machining is compared. In this test, the load is 1.0 kg and the drill used is A φ3 carbide drill was used, and the thickness of the sample was set to 3 mm.

[0027]

[Table 5]

First, comparing sample Nos. 1 to 16 in Table 2, Nos. 1, 3, 5, 7, 9, 9, 11, 13 and 15 are conventional sintered alloys, and Nos. 2, 4, 6 are. The mixed powder of these conventional sintered alloys is manufactured by mixing the particle group forming powder G and the sulfide powder, and the numbers 8, 10, 12, 14, and 16 are manufactured by mixing the sulfide powder. The number 17
54 are all examples of the present invention. As is clear from FIG. 2, it was confirmed that in the example of the present invention in which the sulfide powder was mixed and the particle group containing Cr sulfide was included, both the valve seat and the valve had less wear than the conventional example. . Further, as is clear from FIG. 3, it was confirmed that in the example of the present invention, the number of processed holes was large and the machinability was good as compared with the conventional example.

Next, FIG. 4 is a diagram showing the relationship between the proportion of particles in the metal structure, the amount of wear, and the number of processed holes.
As is clear from FIG. 4, as the area ratio of the particle group increases, the hardness of the sintered alloy increases and the number of processed holes decreases.
However, the wear amount of the valve seat decreases when the area ratio of the particle group is in the range of 3 to 25%. On the other hand, if the area ratio exceeds 25%, the aggression of the valve seat on the valve is increased, and the valve is worn, so that the valve seat is also worn.

Next, FIG. 5 is a diagram showing the relationship between the ratio of the particle group forming powder to the entire mixed powder, the amount of wear and the number of processed holes. As is clear from FIG. 5, the hardness of the sintered alloy increases and the number of processed holes decreases as the addition amount of the particle group forming powder increases. However, the wear amount of the valve seat decreases in the range of 5 to 25% by weight of the particle group forming powder added. Also in this case, when the addition amount of the particle group forming powder exceeds 25% by weight, the aggressiveness of the valve seat with respect to the valve is increased and the valve is worn, so that the wear of the valve seat is also increased.

Next, FIG. 6 is a diagram showing the relationship between the S content, the wear amount and the number of processed holes in the sintered alloy to which FeS was added as the sulfide powder. As is clear from FIG. 6, as the content of S increases, the machinability improves and the number of machined holes increases. Further, the wear amount of the valve seat is small when the S content is in the range of 0.3 to 1.5% by weight. On the other hand, when the S content exceeds 1.5% by weight, the precipitation of Cr sulfide becomes excessive and the strength decreases, and the wear of the valve seat and the valve increases. As can be seen from FIGS. 7 to 9, MoS ₂ , WS ₂ or CuS was used as the sulfide powder.
The same result is obtained with the added sintered alloy.

Next, FIG. 10 is a diagram showing the relationship between the Cr content in the particle group forming powder, the amount of wear and the number of processed holes.
As is clear from FIG. 10, as the Cr content increases, the amount of Cr carbide increases and the number of processed holes decreases. However, the wear amount of the valve seat is such that the Cr content is 4
If the Cr content exceeds 25% by weight, the hardness of the powder increases and the compressibility is impaired.
The amount of carbide becomes too large, which accelerates the wear of the mating parts,
As a result, valve seat and valve wear increases.

Next, FIG. 11 shows a sintered alloy (No. 15) of Japanese Patent Application No. 10-141976 previously proposed by the present applicant.
And Mo, V and W in the particle group forming powder of this sintered alloy.
The wear amount of the sintered alloy containing one or more of the above (Nos. 48 to 54) is shown, and FIG. 12 shows the number of processed holes. As can be seen from FIG. 12, the number of holes machined in each sintered alloy was almost unchanged, but the amount of wear of the valve seat of the present invention was greatly reduced, and excellent wear resistance was exhibited. For comparison, the wear amount and the number of processed holes of the present invention example (No. 16) in which the particle group forming powder did not contain Mo or the like are also shown.

[0034]

As described above, the iron-based sintered valve seat and the manufacturing method thereof according to the present invention can impart higher wear resistance and machinability as compared with the prior art. Further, by defining the area ratio of the particle group and the like, wear resistance and machinability can be more reliably improved.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a metal structure of a wear resistant sintered alloy of the present invention.

FIG. 2 is a diagram showing the amount of wear in sample numbers 1 to 16.

FIG. 3 is a diagram showing the number of processed holes in sample numbers 1 to 16.

FIG. 4 is a diagram showing the relationship between the area ratio of particle groups in the metal structure, the amount of wear, and the number of processed holes.

FIG. 5 is a diagram showing the relationship between the amount of particle group forming powder added, the amount of wear, and the number of processed holes.

FIG. 6 is a diagram showing the relationship between the S content in a sintered alloy, the amount of wear, and the number of processed holes when FeS powder was added.

FIG. 7: S in a sintered alloy when MoS ₂ powder was added
It is a diagram showing the relationship between the content, the amount of wear and the number of processed holes.

FIG. 8 is a diagram showing the relationship between the S content in the sintered alloy, the amount of wear, and the number of processed holes when WS ₂ powder was added.

FIG. 9 is a diagram showing the relationship between the S content in the sintered alloy, the amount of wear, and the number of processed holes when CuS powder was added.

FIG. 10 is a diagram showing the relationship between the Cr content in the particle group forming powder, the wear amount, and the number of processed holes.

11 is a diagram showing the amount of wear in sample numbers 15, 16, and 48 to 54. FIG.

FIG. 12 is a diagram showing the number of processed holes in sample numbers 15, 16, and 48 to 54.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koichi Aonuma             1018-2 Minorita, Matsudo City, Chiba Prefecture Seiwa Dormitory No. 613             Room (72) Inventor Toru Tsuboi             4-5-7 Minami-Hatsutomi, Kamagaya City, Chiba Prefecture F-term (reference) 4K018 AA34 AB05 AB07 AC01 BA16                       BC20 DA12

Claims (6)

[Claims] 1. A particle group in which Cr carbide particles and Cr sulfide particles are mixed, and a ferrite phase surrounding the periphery with the particle group as a core or a composite phase composed of a mixed phase of ferrite and austenite is dispersed in a matrix. A characteristic iron-based sintered valve seat. 2. The iron-based sintered valve seat according to claim 1, wherein the proportion of the particle group in the metal structure is 3 to 25% in area ratio. 3. The iron-based sintered valve seat according to claim 1, wherein the group of particles has a metal structure in which at least one kind of carbide particles of Mo, W, and V are further mixed. . 4. A particle group forming powder containing 4 to 25% by weight of Cr, and a sulfide powder composed of at least one of MoS ₂ powder, WS ₂ powder, FeS powder, CuS powder, and an iron base. A mixed powder or an iron-based alloy powder that does not contain Cr is used as a mixed powder, and the sulfide powder has an S content of 0.3 to 1.
A method for producing an iron-based sintered valve seat, which is characterized by adding 5%. 5. The method for producing an iron-based sintered valve seat according to claim 4, wherein the amount of the Cr-containing particle group forming powder added is 5 to 25%. 6. The iron-based baking according to claim 4, wherein a powder containing at least one of Mo, V and W in the particle group forming powder containing Cr is used. A method for manufacturing a valve seat.