JP2007023383A - Sintered valve seat and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered valve seat which exhibits excellent high-temperature abrasion resistance in a high-load engine environment such as in a CNG engine or a heavy-duty diesel engine and to provide a method for producing the same. <P>SOLUTION: The sintered valve seat is composed of a Co-based alloy having a composition of 48 to 60 mass% Mo, 3 to 12 mass% Cr, 1 to 5 mass% Si, and the balance being Co and inevitable impurities, and having a structure comprising 5 to 40 mass% of hard phase mainly formed of molybdenum silicides and integrally precipitated and dispersed in the Co-based alloy matrix and a Cr sulfide dispersing around the hard phase. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sintered valve seat for an automobile engine, a manufacturing method thereof, and the like, and more particularly, to a technology for developing a sintered alloy valve seat suitable for use in a high load engine such as a CNG engine or a heavy duty diesel engine.

  In recent years, the operating conditions of automobile engines have become more severe due to higher performance, and the valve seats used in engines are also required to withstand more severe use environment conditions than ever before. For example, in an LPG engine that is often mounted in a taxi automobile, the sliding contact surfaces of the valve and the valve seat are used in a dry state, and therefore wear is faster than that of a gasoline engine valve seat. Also, in an environment where sludge adheres, such as a highly leaded gasoline engine, wear is promoted by sludge when the surface pressure against the valve seat is high, or when the temperature and compression ratio are high, such as a diesel engine. . When used in such a harsh environment, high wear resistance is required, and high strength that does not cause a sag phenomenon is required.

  On the other hand, a valve mechanism equipped with a lash adjuster device that can automatically adjust the valve position and valve drive timing even when the valve seat is worn has been put into practical use, but the problem of engine life due to wear of the valve seat has been solved. However, development of a valve seat material having excellent wear resistance is desired. Also, in recent years, not only aiming at high performance, but also the development of inexpensive automobiles with an emphasis on economy has been emphasized. Therefore, as a sintered alloy for valve seats in the future, such as the above lash adjuster device There is a growing demand for high-temperature wear resistance and high strength that do not require additional mechanisms.

  As such a sintered alloy for a valve seat, a technique in which Co—Mo—Si hard particles are dispersed in a patchy base of Fe—Co and Fe—Cr (see Patent Document 1) is disclosed. ). In addition, a technique in which Co—Mo—Si hard particles are dispersed in an Fe—Co base is also disclosed (see Patent Document 2). And the technique which disperse | distributed Co-Mo-Si type hard particles in the base which added Ni to Fe-Co type is also indicated (refer to patent documents 3). Furthermore, an Fe-based alloy in which Co—Mo—Si hard particles are dispersed is also disclosed (see Patent Document 4).

Japanese Examined Patent Publication No. 59-037343 Japanese Patent Publication No. 05-055593 Japanese Patent Publication No. 07-098985 Japanese Patent Laid-Open No. 02-163351

  The hard particles in the alloys described in these Patent Documents 1 to 4 have an Mo amount of 40% by mass or less, but the sintered alloy containing these hard particles has considerable high temperature wear resistance and high strength. It is what has. However, in recent years, a sintered alloy having high temperature wear resistance and high strength has been desired. In particular, in CNG engines that have been put into practical use in recent years and heavy-duty diesel engines for high output, the load on the valve seat material due to metal contact is even higher, so even in such an environment high resistance Development of a material that exhibits wear is desired.

  Accordingly, an object of the present invention is to provide a sintered valve seat that exhibits excellent high-temperature wear resistance and a method for manufacturing the same, particularly in a high-load engine environment such as a CNG engine or a heavy-duty diesel engine.

  The sintered valve seat of the present invention includes the sintered valve seats of the first to third inventions from the state of the metal structure. Hereinafter, these sintered valve seats and their manufacturing methods will be described.

[1] Sintered valve seat of the first invention The sintered valve seat of the first invention can be said to be a basic structure of the present invention, and the composition is Mo: 48-60 mass%, Cr: 3-12 in the base. Mass%, Si: 1 to 5% by mass, and the balance: Co and inevitable impurities, and a hard phase in which precipitates mainly composed of molybdenum silicide precipitate in a lump in a Co base alloy matrix are 5 to 40 It is characterized by being dispersed by mass% and exhibiting a structure in which Cr sulfide is dispersed around the hard phase. FIG. 1 schematically shows the metal structure of the sintered valve seat of the first invention. Hereinafter, the metal structure and contained elements of the valve seat of the present invention will be described individually.

<Cr sulfide formed around hard phase and hard phase>
As described above, the hard phase is composed of Mo: 48 to 60% by mass, Cr: 3 to 12% by mass, Si: 1 to 5% by mass, and the balance: Co and inevitable impurities. This shows a structure in which precipitates mainly composed of are precipitated in a lump. As shown in FIG. 1, Cr sulfide is precipitated and dispersed around the hard phase.

  The hard phase of the present invention increases the molybdenum silicide precipitated as the amount of Mo increases and is integrated and precipitated, and at the same time, produces the necessary molybdenum silicide with the Si amount. Optimized to the required amount, the increase in the hardness of the powder accompanying the increase in the Mo amount is minimized.

  FIG. 4 is a diagram schematically showing a metal structure of a valve seat made of a conventional wear-resistant sintered alloy. According to this figure, the hard phase of the conventional valve seat is an alloy in which molybdenum silicide is a hard phase. Deposited in groups in the base, and according to such a metal structure, in an environment where metal contact occurs, the base of the alloy base of the hard phase other than molybdenum silicide functioning as hard particles, Plastic flow and adhesion occurred, and wear was likely to occur.

  On the other hand, in the hard phase of the present invention, the molybdenum silicide is integrated and formed into a lump, thereby suppressing the plastic flow and adhesion of the alloy base portion of the hard phase by the pinning effect. Therefore, the wear resistance can be improved.

  Further, in the present invention, Cr sulfide having excellent lubricity is precipitated and dispersed around the hard phase, so that the hard phase itself is prevented from plastic flow, and as a result, further wear resistance is achieved. Improves sex.

  When the hard phase of the present invention is dispersed in an amount of 5 to 40% by mass in the base of the sintered valve seat, it exhibits extremely good wear resistance. If the amount is less than 5% by mass, the effect of improving the wear resistance is not remarkable. If the amount exceeds 40% by mass, the compressibility of the mixed powder is reduced, so that the strength of the sintered body is reduced and the attack of the other party is increased. The amount of wear will increase.

<Reason for numerical limitation of the above component composition (containing elements)>
The hard phase can be applied to an alloy base that has been conventionally used as a base for sintered valve seats, such as base-forming steel powders (A) to (E) described later, and the steel powder that forms the base. Or the following hard phase formation powder (F) is added and mixed with mixed powder, and it forms suitably.
(F) Co-based alloy powder comprising Mo: 48 to 60% by mass, Cr: 3 to 12% by mass, Si: 1 to 5% by mass, and the balance: Co and inevitable impurities.
The grounds for limiting the numerical values of these component compositions are as follows.

・ Mo: 48-60 mass%
Mo mainly bonds with Si to form molybdenum silicide excellent in wear resistance and lubricity, and contributes to improvement in wear resistance of the sintered alloy. A part of Mo combines with hard phase Co and Cr to form molybdenum composite silicide. When the Mo content is less than 48% by mass, the molybdenum silicide is not integrated and deposited, and the conventional granular molybdenum silicide is dispersed in the Co-based hard phase, and the wear resistance is about the same as before. Stop on. On the other hand, when the Mo content exceeds 60% by mass, the hardness of the powder increases and the compressibility during molding is impaired. Moreover, since the hard phase to be formed becomes brittle, part of the hard phase is lost due to impact, and the wear resistance is reduced by the action of the abrasive powder. Therefore, the Mo content is set to 48 to 60% by mass.

・ Cr: 3-12% by mass
Cr contributes to strengthening the hard-phase Co base. Further, it diffuses to the Fe base and fixes the hard phase to the Fe base, and contributes to the improvement of the wear resistance by solid solution in the Fe base and strengthening the base. Further, Cr diffused in the Fe base is combined with S to form Cr sulfide having excellent lubricity around the hard phase, thereby contributing to improvement of wear resistance. If the Cr content is less than 3% by mass, these effects are poor. On the other hand, if the Cr content exceeds 12% by mass, the amount of oxygen in the powder increases and an oxide film is formed on the surface of the powder. Decrease. For this reason, since the intensity | strength of a sintered alloy falls and causes a fall of abrasion resistance, the upper limit of Cr content was 12 mass%. As described above, the Cr content was set to 3 to 12% by mass.

・ Si: 1 to 5% by mass
Si mainly combines with Mo to form molybdenum silicide excellent in wear resistance and lubricity, and contributes to improvement in wear resistance of the sintered alloy. When the Si content is less than 1% by mass, a sufficient molybdenum silicide cannot be obtained, so that a sufficient wear resistance improvement effect cannot be obtained. On the other hand, if the Si content is excessive, Si that diffuses into the base without reacting with Mo increases. Si hardens the Fe base, but also makes it brittle. For this reason, a certain amount of Si diffusion to the base is effective in terms of fixing the hard phase to the base. However, excessive diffusion of Si is not preferable because it reduces the wear resistance of the Fe base and increases the partner's aggression. Here, if the amount of Si that does not react with Mo is reduced, an appropriate amount of Mo can be provided without increasing the hardness of the powder. Therefore, the upper limit of the Si content is set to 5 mass% where Si diffused to the base without reacting with the Mo amount starts to increase. As described above, the Si content is set to 1 to 5% by mass.

<About sulfide powder as S supply source>
S required for precipitation of Cr sulfide formed around the hard phase is supplied by the decomposition of any of the following sulfides (G) to (J).
(G) Molybdenum disulfide powder (H) Tungsten disulfide powder (I) Iron sulfide powder (J) Copper sulfide powder

  Metal sulfides are not all stable, some metal sulfides are prone to decomposition during sintering, and molybdenum disulfide, tungsten sulfide, iron sulfide, and copper sulfide can easily decompose under certain conditions. , And a reference (issued on March 15, 1964, Kyoritsu Publishing Co., Ltd.). Also, in the actual sintering process, moisture, oxygen, hydrogen, and moisture adsorbed on the surface of the iron powder may be decomposed due to desorption of moisture and oxygen, and sulfides may be decomposed at high temperatures. It is fully conceivable that the metal surface activated at the high temperature reacts or the metal surface activated at a high temperature acts as a catalyst to promote the decomposition of the sulfide. On the other hand, it is found that manganese sulfide and chromium sulfide are metal sulfides that are hardly decomposed even by the above-mentioned references.

The ability to form sulfides has a correlation with electronegativity, and S tends to form sulfides by binding to elements having low electronegativity. Here, the electronegativity of each element is
Mn (1.5) <Cr (1.6) <Fe, Ni, Co, Mo (1.8) <Cu (1.9)
Since Mn is most easily bonded, manganese sulfide can be selectively deposited. This order is consistent with the description in the above reference.

  In order to deposit and disperse a sufficient amount of Cr sulfide particles around the hard phase using the above sulfide powder, the amount of sulfide powder added is required to be 0.04% by mass or more as S content. . On the other hand, the addition of excess sulfide powder causes a decrease in the strength of the valve seat due to an increase in the amount of pores remaining after decomposition, and this results in a decrease in wear resistance. The amount of S content should be 5% by mass. The metal component decomposed by the above-mentioned sulfide powder diffuses to the base. However, when molybdenum disulfide powder, tungsten sulfide powder, or copper sulfide powder is selected as the sulfide powder, Mo, W, Cu diffuses into the base and works to strengthen the solid solution of the base, thereby contributing to improvement of the wear resistance of the base.

<About the base>
As the base of the valve seat of the present invention, conventional bases shown in the following (a) to (e) can be used.

(A) Mo: 1.5 to 5% by mass, C: 0.4 to 1.2% by mass, the balance is Fe and inevitable impurities, and the base is bainite.
(B) Cr: 2-4% by mass, Mo: 0.2-0.4% by mass, V: 0.2-0.4% by mass, C: 0.4-1.2% by mass and the balance: Fe A base that consists of unavoidable impurities and has a bainite structure.
(C) Co: 5.5 to 7.5% by mass, Mo: 0.5 to 3% by mass, Ni: 0.1 to 3% by mass, C: 0.4 to 1.2% by mass, and the balance: Fe A base that consists of inevitable impurities and the organization is sorbite.
(D) Mo: 0.4-4 mass%, Ni: 0.6-5 mass%, Cu: 0.5-5 mass%, Cr: 0.05-2 mass%, and V: 0.05- 0.6% by mass, C: 0.4 to 1.2% by mass, and balance: Fe and inevitable impurities, and the base is a bainite single phase structure or a mixed structure of bainite and martensite.
(E) Ni: 1 to 10%, Cu: 1 to 3%, Mo: 0.4 to 1.0%, C: 0.4 to 1.2% by mass, and the balance consisting of Fe and inevitable impurities. Base that is a mixed structure of site, austenite, bainite, and perlite.

  The present invention is selected from at least one of the above base structures (a) to (e), and can be appropriately selected and combined depending on the required degree of wear resistance and cost.

  For the single phase structure or mixed structure of (a) to (e) above, the following (A) to (E) steel powder and C: 0.4 to 1.2 mass% graphite powder are used as the base forming powder. Can be formed.

(A) Mo: Steel powder consisting of 1.5 to 5% by mass and the balance being Fe and inevitable impurities.
(B) Cr: 2-4% by mass, Mo: 0.2-0.4% by mass, V: 0.2-0.4% by mass and the balance: steel powder comprising Fe and inevitable impurities.
(C) Steel powder comprising Co: 5.5 to 7.5% by mass, Mo: 0.5 to 3% by mass, Ni: 0.1 to 3% by mass, and the balance: Fe and inevitable impurities.
(D) Mo: 0.4-4 mass%, Ni: 0.6-5 mass%, Cu: 0.5-5 mass%, Cr: 0.05-2 mass%, and V: 0.05- 0.6% by mass and the balance: steel powder composed of Fe and inevitable impurities.
(E) Partially diffused steel powder consisting of Ni: 1 to 10%, Cu: 1 to 3%, Mo: 0.4 to 1.0%, and the balance of Fe and inevitable impurities.

  C is added by adding graphite powder to the above steel powder from the viewpoint of compressibility of the raw material powder. However, if the amount of C (addition amount of graphite powder) is less than 0.4% by mass, a ferrite structure having low strength and wear resistance is mixed in the base structure. On the other hand, when the amount of C (addition amount of graphite powder) exceeds 1.2% by mass, hard but brittle cementite is precipitated, and the opponent attack property becomes high, and wear resistance and strength are lowered. Therefore, the C amount (graphite powder addition amount) needs to be 0.4 to 1.2% by mass.

  Further, the base structure may be a mixed phase of martensite, austenite, and bainite by adding 5 mass% or less of nickel powder and / or copper powder to the base. In this case, the base is strengthened by Ni of 5% by mass or less and / or Cu by 5% by mass or less, and the base strength is improved. However, in the case of nickel powder addition, the amount of soft austenite increases when the addition amount exceeds 5% by mass. In the case of copper powder, if the addition amount exceeds 5% by mass, the soft free copper phase is in the base structure. Therefore, it is necessary to limit the upper limit of the amount added to 5% by mass.

  The method for producing the sintered valve seat of the first invention exhibiting the metal structure shown in FIG. 1 is one of the present inventions based on the above technique, that is, the base-forming steel powder (A) to In at least one of (E), 5-40% by mass of the hard phase-forming powder (F), graphite powder: 0.4-1.2% by mass, and the sulfide powders (G)-( The raw material powder composed of at least one of J) and added in such an amount that the amount of S in the raw material powder is 0.04 to 5% by mass is compacted into a desired shape and then sintered. It is characterized by that.

  In the method of the present invention, as described above, for the purpose of adding Ni and / or Cu to the base, it is included that the raw material powder contains 5% by mass or less of nickel powder and / or 5% by mass or less of copper powder.

[2] Sintered valve seat of the second invention The sintered valve seat of the second invention comprises a lubricating phase in which Cr sulfide particles are further precipitated in groups in the base of the sintered valve seat of the first invention. 20% by mass is dispersed. FIG. 2 schematically shows the metal structure of the sintered valve seat according to the second aspect of the present invention. Cr sulfide excellent in lubricity is added around the hard phase. By dispersing the spots in groups, the lubricity of the base is improved and the wear resistance is improved.

  When cutting the valve seat, if the sulfide is uniformly dispersed in the base, the cutting edge uniformly hits the sulfide. For this reason, the effect of reducing cutting resistance is acquired. In addition, the chip breaking action facilitates removal of cutting powder, prevents heat from being accumulated on the blade edge, and provides an effect that the blade edge temperature is lowered. These effects further improve machinability. On the other hand, since the sulfide particles themselves are small, in order to improve the lubricity of the matrix structure and improve the wear resistance, a large amount of sulfide is required, but if a large amount of sulfide is dispersed in the matrix, The strength of the base will be reduced.

  For this reason, in the present invention, the Cr sulfide having excellent lubricity is dispersed in the base in a spot-like manner in the base, and the wear resistance of the base is reduced by a small amount of Cr sulfide that does not cause a reduction in the base strength. It is intended to realize improvement. In such a lubricating phase, if the amount of dispersion in the base is less than 5% by mass, the effect of improving the wear resistance by improving the lubricity of the base is poor. On the other hand, when the content exceeds 20% by mass, the strength of the base is significantly reduced. For this reason, the dispersion of the lubricating phase in the base needs to be 5 to 20% by mass.

  The lubricating phase in which the above-mentioned Cr sulfide particles are precipitated in a group can be formed by adding chromium-containing steel powder containing 4 to 25% by mass of Cr to the raw material powder. That is, S generated by the decomposition of the sulfide powder in the sintering process is combined with Cr in the chromium-containing steel powder, and Cr sulfide is deposited on the original chromium-containing steel powder portion. It becomes a dispersed substructure in groups. For this reason, the composition of the lubricating phase substantially matches the composition of the original chromium-containing steel powder, that is, contains Cr: 4 to 25% by mass. Further, the alloy base where Cr sulfide precipitates in a group is an Fe-Cr alloy base.

  If the amount of Cr in this lubricating phase is less than 4% by mass, Cr sulfide does not precipitate and does not contribute to improvement of wear resistance. On the other hand, if the Cr content exceeds 25% by mass, the chromium-containing steel powder becomes hard and the compressibility is impaired, and the σ phase is generated and embrittles, so the upper limit needs to be 25% by mass.

  The lubricating phase can be formed from chromium-containing steel powder containing 4 to 25% by mass of Cr as described above. Specifically, the chromium-containing steel powder is the following (L) to (Q) It is selected from at least one of them.

(L) Cr: 4 to 25% by mass, and the balance: chromium-containing steel powder composed of Fe and inevitable impurities (M) Cr: 4 to 25% by mass, Ni: 3.5 to 22% by mass, and the balance: Fe Chrome-containing steel powder consisting of inevitable impurities.
(N) Cr: 4 to 25% by mass, Mo: 0.3 to 7% by mass, Cu: 1 to 4% by mass, Al: 0.1 to 5% by mass, N: 0.3% by mass or less, Mn : 5.5-10 mass%, Si: 0.15-5 mass%, Nb: 0.45 mass% or less, P: 0.2 mass% or less, S: 0.15 mass% or less, and Se: 0 A chromium-containing steel powder composed of at least one of 15% or less and the balance: Fe and inevitable impurities.
(O) Cr: 4 to 25% by mass, Ni: 3.5 to 22% by mass, Mo: 0.3 to 7% by mass, Cu: 1 to 4% by mass, Al: 0.1 to 5% by mass N: 0.3 mass% or less, Mn: 5.5-10 mass%, Si: 0.15-5 mass%, Nb: 0.45 mass% or less, P: 0.2 mass% or less, S: A chromium-containing steel powder comprising at least one of 0.15% by mass or less and Se: 0.15% or less, and the balance: Fe and inevitable impurities.
(P) Cr: 7.5-25 mass%, Mo: 0.3-3.0 mass%, C: 0.25-2.4 mass%, and V: 0.2-2.2 mass% W: One or more of 1.0 to 5.0% by mass of chromium-containing steel powder, the balance being Fe and inevitable impurities.
(Q) Cr, 4-6 mass%, Mo: 4-8 mass%, V: 0.5-3 mass%, W: 4-8%, C: 0.6-1.2%, and the balance: A chromium-containing steel powder consisting of Fe and inevitable impurities.

  The above (L) is an Fe—Cr alloy, and those in which Cr exceeds 12 mass% are known as ferritic stainless steel powders. Also, ferritic stainless steel powder whose characteristics are improved with other elements as in (N) above can be used.

  The above (M) is an Fe—Ni—Cr alloy, and the one in which Cr exceeds 12 mass% is known as an austenitic stainless steel powder. In addition, austenitic stainless steel powder having improved characteristics with other elements such as (O) can also be used.

  The above (P) is known as die steel powder, and originally contained Cr precipitates as chromium carbide, but when coexisting with S as in the present invention, most of the precipitated Cr is Cr sulfide. It precipitates as a product. In addition, a lubricating phase in which chromium carbide remains in part, or molybdenum carbide, vanadium carbide, tungsten carbide, and composite carbides thereof precipitate and coexist with Cr sulfide is obtained.

  (Q) is known as high-speed tool steel powder. Like (P), in addition to depositing Cr sulfide together with S, chromium carbide remains in part, molybdenum carbide, A lubricating phase in which vanadium carbide, tungsten carbide, and composite carbides thereof precipitate and coexist with Cr sulfide is obtained.

  The method for producing the sintered valve seat of the second invention exhibiting the metal structure shown in FIG. 2 is one of the present inventions based on the above technique, that is, the sintered valve seat of the first invention. In this manufacturing method, the raw material powder further contains 5 to 20% by mass of chromium-containing steel powder containing 4 to 25% by mass of Cr as a lubricating phase forming powder. In this case, it is further included that the chromium-containing steel powder is composed of at least one of the above (L) to (Q).

[3] Sintered valve seat of the third invention In the case of the above (P) and (Q), it becomes a structure in which carbide is precipitated together with Cr sulfide in the lubricating phase. This is the sintered valve seat of the third invention. is there. FIG. 3 schematically shows the metal structure of the sintered valve seat of the third invention. According to this sintered valve seat, carbides precipitate in the lubricating phase, so that the plasticity of the alloy base portion of the lubricating phase is increased. The wear resistance can be further improved by preventing the flow. When (P) and (Q) are compared, a lubricating phase in which (P) has less carbide and (Q) precipitates more carbide is obtained, and can be appropriately selected according to desired characteristics.

  Now, the sintered valve seats of the first to third inventions can be manufactured by using a conventional machinability improving substance addition method. As the method, manganese sulfide particles, calcium fluoride particles, boron nitride particles, magnesium silicate mineral particles, bismuth particles, and bismuth oxide particles are placed in the pores of the wear-resistant sintered member or in the powder grain boundaries. This is a method of dispersing at least one kind.

  These machinability improving materials are stable even at high temperatures, and even when added to the raw powder in the form of powder, they do not decompose during the sintering process, and are dispersed in the above locations as machinability improving materials to improve machinability. Can improve. By using this machinability improving substance addition method in combination, the machinability of the wear-resistant sintered member can be further improved. In addition, the amount of the machinability improving substance powder added when the machinability improving substance addition method is used in combination with the upper limit because excessive addition will impair the strength of the wear resistant sintered member and cause a decrease in wear resistance. Should be kept at 2.0% by weight.

  Furthermore, in the sintered valve seat of the present invention, as described in Patent Document 2 and the like, the pores of the wear-resistant sintered member are made of lead or lead alloy, copper or copper alloy, or acrylic resin. In any case, it is possible to use a technique that fills with an impregnation or infiltration method and thereby improves machinability.

  That is, when lead or lead alloy, copper or copper alloy, and acrylic resin are present in the pores, the cutting mode changes from intermittent cutting to continuous cutting during cutting. For this reason, it is effective in reducing the impact given to a tool, preventing damage to a tool edge, and improving machinability. Also, since lead or lead alloy, copper or copper alloy is soft, it adheres to the tool blade surface and protects the cutting edge of the tool, improving machinability and tool life, and at the time of use, the valve seat and valve It acts as a solid lubricant with the face surface and functions to reduce wear on both sides. Furthermore, copper or a copper alloy has a high thermal conductivity, and has the effect of releasing heat generated at the cutting edge during cutting to the outside, preventing heat accumulation at the cutting edge and reducing damage to the cutting edge.

  According to the present invention, in the matrix, the composition is Mo: 48 to 60 mass%, Cr: 3 to 12 mass%, Si: 1 to 5 mass%, and the balance: Co and inevitable impurities. A hard phase in which precipitates mainly composed of molybdenum silicide are integrally precipitated in a lump is dispersed in an amount of 5 to 40% by mass, and a structure in which Cr sulfide is dispersed around the hard phase is provided. Thus, the load associated with the metal contact is reduced, and a sintered valve seat that exhibits even higher wear resistance under such an environment is obtained. Therefore, it is possible to provide a valve seat that exhibits excellent high temperature wear resistance in a high load engine environment such as a CNG engine or a heavy duty diesel engine.

  Various powders having the following composition were mixed as raw material powders, and a molding lubricant (zinc stearate 0.8% by mass) was further blended to prepare raw material powders. The number before the element symbol indicates the mass% of the element contained in the powder. For example, “Fe-5Mo” indicates that 5 mass% of Mo is contained and the balance is composed of Fe and inevitable impurities.

・ Base forming powder: Fe-5Mo (remainder)
・ Hard phase forming powder: Component composition is as shown in Table 1 (25% by mass; constant)
・ Sulfide powder: MoS ₂ (2% by mass)
Graphite powder: (1.1% by mass)

  This mixed powder was molded into a ring of outer diameter: φ30 (mm) × inner diameter: φ20 (mm) × height: h10 (mm) at a molding pressure of 650 MPa.

  Next, these compacts were heated and sintered in an ammonia decomposition gas atmosphere at 1180 ° C. for 60 minutes to prepare samples 01 to 16 having the compositions shown in Table 1. These samples were subjected to a simple wear test in the following manner.

  The simple wear test was performed in a state in which tapping and sliding input were applied at a high temperature. Specifically, the sample was processed into a valve seat shape having a 45 ° tapered surface on the inner diameter surface, and the sample was press-fitted and fitted into an aluminum alloy housing. Then, a disk-shaped mating material (corresponding to a valve) made of SUH-36 material and having a tapered surface with a part of 45 ° on the outer surface is moved up and down by a motor-driven eccentric cam to move the sample. And the taper surfaces of the mating material repeatedly collided.

That is, the operation of the valve repeats the opening operation of separating from the valve seat by the eccentric cam rotated by the motor drive and the seating operation on the valve seat by the valve spring, thereby realizing the vertical piston motion. In this test, the partner material was heated with a burner and the temperature was set so that the sample reached 300 ° C., the number of hits of the simple wear test was 2800 times / minute, and the repetition time was 15 hours. In this way, the wear amount of the sample after test and the counterpart material (indicated in Table 1 as a valve seat and a valve, respectively) was measured and evaluated.
The test results of Example 1 are also shown in Table 1.

  Looking at the sample numbers 01 to 06 in Table 1, the sample in which the amount of Mo in the hard phase forming powder is in the range of 48 to 60% by mass (sample numbers 02 to 05) has a stable valve seat and valve wear amount. It can be seen that it shows a good wear resistance. On the other hand, in the sample (sample number 01, 06) in which the Mo amount deviates from the range of 48 to 60% by mass, the wear amount of the valve seat is particularly high, and the wear amount of the valve is relatively high. Therefore, it was confirmed that if the amount of Mo in the hard phase forming powder is in the range of 48 to 60% by mass, excellent wear resistance is realized.

  Moreover, when the sample numbers 03 and 07 to 11 in Table 1 are viewed, the samples (sample numbers 03 and 08 to 10) in which the Cr amount in the hard phase forming powder is in the range of 3 to 12% by mass are the valve seat and the valve. It can be seen that the amount of wear is stable and low and exhibits good wear resistance. On the other hand, in the samples (sample numbers 07 and 11) in which the Cr amount deviates from the range of 3 to 12% by mass, the wear amount of the valve seat is particularly high. Therefore, it was confirmed that excellent wear resistance was achieved when the Cr content in the hard phase forming powder was in the range of 3 to 12 mass%.

  Next, when looking at sample numbers 03 and 12 to 16 in Table 1, samples (sample numbers 03, 13, and 14) in which the Si amount in the hard phase forming powder is in the range of 1 to 5% by mass are valve seats and It can be seen that the amount of wear of the valve is stable and low, and shows good wear resistance. On the other hand, in the samples (sample numbers 12 and 15) in which the Si amount deviates from the range of 1 to 5% by mass, the wear amount of the valve seat is particularly high. Therefore, it was confirmed that if the Si content in the hard phase forming powder is in the range of 1 to 5% by mass, excellent wear resistance is realized.

Moreover, it was confirmed that the sample of the said range of this invention shows much higher abrasion resistance compared with a prior art example (sample number 16).
Further, when the metal structure of the sample No. 03 was observed, it was confirmed that chromium sulfide was dispersed around the hard phase as shown in the schematic diagram of FIG.

  Using the following raw material powder, the raw material powder was mixed, molded and sintered in the same manner as in Example 1 to prepare a ring-shaped sample. And about these samples, the simple abrasion test was done on the conditions similar to Example 1. FIG. The results are shown in Table 2.

・ Base forming powder: Fe-5Mo (remainder)
・ Hard phase forming powder: Co-50Mo-10Cr-3Si (addition amount is as shown in Table 2)
・ Sulfide powder: MoS ₂ (2% by mass)
Graphite powder: (1.1% by mass)

  As shown in Table 2, the samples (sample numbers 03 and 18-22) in which the amount of the hard phase forming alloy powder added to the mass of the mixed powder is in the range of 5 to 40% by mass are the wear of the valve seat and the valve. It can be seen that the amount is stable and low and exhibits good wear resistance. On the other hand, in the sintered alloy (sample numbers 17 and 23) in which the addition amount of the alloy powder for forming the hard phase deviates from the range of 5 to 40% by mass, the wear amount of the valve seat is particularly high. Therefore, it was confirmed that if the addition amount of the alloy powder for forming the hard phase with respect to the total mass of the mixed powder is in the range of 5 to 40% by mass, excellent wear resistance is realized.

  Using the following raw material powder, the raw material powder was mixed, molded and sintered in the same manner as in Example 1 to prepare a ring-shaped sample. And about these samples, the simple abrasion test was done on the conditions similar to Example 1. FIG. The results are shown in Table 3.

・ Base forming powder: Fe-5Mo steel powder (remainder)
Fe-6.5Co-1.5Mo-1.5Ni steel powder (remainder)
Fe-3Cr-0.3Mo-0.3V steel powder (remainder)
Half of Fe-6.5Co-1.5Mo-1.5Ni steel powder and Fe-3Cr-0.3Mo-0.3V steel powder (remainder)
Fe-4Ni-1.5Cu-0.5Mo partially diffused steel powder (remainder)
・ Hard phase forming powder: Co-50Mo-10Cr-3Si (25% by mass)
Co-28Mo-8Cr-2.5Si (conventional example) (25% by mass)
・ Sulfide powder: MoS ₂ (2% by mass)
・ Graphite powder: (1.1% by mass)

  Example 3 shown in Table 3 compares the wear resistance when the hard phase and sulfide of the present invention are applied to various bases and when the conventional hard phase is applied. According to this, when the hard phase and sulfide of the present invention are applied to various bases conventionally used for sintered valve seats, the wear resistance is much better than when the conventional hard phase is applied. It was confirmed to show. In addition, it was confirmed that the hard phase of the present invention can be applied to a base of a sintered valve seat that has been used conventionally.

  Using the following raw material powder, the raw material powder was mixed, molded and sintered in the same manner as in Example 1 to prepare a ring-shaped sample. And about these samples, the simple abrasion test was done on the conditions similar to Example 1. FIG. The results are shown in Table 4.

・ Base forming powder: Fe-5Mo (remainder)
・ Hard phase forming powder: Co-50Mo-10Cr-3Si (25% by mass)
・ Sulphide powder: Types are as shown in Table 4 (2% by mass)
Graphite powder: (1.1% by mass)

  The metal structures of the samples Nos. 32-35 in Table 4 were observed and the presence of chromium sulfide was confirmed. Samples added with tungsten disulfide, iron sulfide, and copper sulfide, which were easily decomposed (Sample Nos. 32-34). Then, like the sample to which molybdenum disulfide was added (sample number 03), it was observed that chromium sulfide particles were precipitated around the hard phase. On the other hand, in the sample (Sample No. 35) to which manganese sulfide, which is a stable sulfide, was added, the sulfide was dispersed in pores and powder grain boundaries in the form of manganese sulfide, and precipitated sulfide was present in the matrix around the hard phase. Things were not recognized. From these facts, by adding a sulfide that is easily decomposed to the raw material powder, S generated by the decomposition of the sulfide during sintering combines with Cr diffused to the base from the hard phase, and forms chromium sulfide It was confirmed that it was precipitated. Moreover, as shown in Table 4, the samples (sample numbers 03, 32 to 34) in which chromium sulfide was deposited around the hard phase showed improved wear resistance and values, and excellent wear resistance. It was confirmed to show.

  Using the following raw material powder, the raw material powder was mixed, molded and sintered in the same manner as in Example 1 to prepare a ring-shaped sample. And about these samples, the simple abrasion test was done on the conditions similar to Example 1. FIG. The results are shown in Table 5.

・ Base forming powder: Fe-5Mo (remainder)
・ Hard phase forming powder: Co-50Mo-10Cr-3Si (25% by mass)
・ Sulfide powder: MoS ₂ (2% by mass)
Graphite powder: (1.1% by mass)
-Lubricating phase forming powder: Fe-12Cr-1Mo-0.5V-1.4C (addition amount is as shown in Table 5)

  According to Table 5, it is confirmed that when 5% by mass of the lubricating phase forming powder is added (Sample No. 36), the wear amount is reduced and the wear resistance is improved as compared with the case where it is not added (Sample No. 03). It was. Moreover, when the addition amount of the lubricating phase forming powder is 10% by mass (sample number 37), the effect of improving the wear resistance is maximized. On the other hand, when the added amount exceeds 10% by mass, the effect of improving the wear resistance is diminished, and when the added amount exceeds 20% by mass, the influence of the strength of the base is increased, and the wear amount is increased. is doing. Therefore, it was confirmed that the addition amount of the lubricating phase forming powder has an effect of improving the wear resistance in the range of 5 to 20% by mass.

  Further, when the metal structure of the sample to which the lubricating phase forming powder was added (Sample No. 37) was observed, chromium sulfide was precipitated around the hard phase, and further, chromium sulfide particles were found in the original lubricating phase forming powder. It was confirmed that was deposited in groups. Further, it was confirmed that some carbide particles were precipitated together with the lubricating phase in which the chromium sulfide particles were precipitated in groups.

  Using the following raw material powder, the raw material powder was mixed, molded and sintered in the same manner as in Example 1 to prepare a ring-shaped sample. And about these samples, the simple abrasion test was done on the conditions similar to Example 1. FIG. The results are shown in Table 6.

・ Base forming powder: Fe-5Mo (remainder)
・ Hard phase forming powder: Co-50Mo-10Cr-3Si (25% by mass)
・ Sulfide powder: MoS ₂ (2% by mass)
Graphite powder: (1.1% by mass)
-Lubricating phase forming powder: The types are as shown in Table 6 (10% by mass)

  According to Table 6, it was confirmed that even if the type of the lubricating phase forming powder was changed, the effect of improving the wear resistance was similarly obtained. Further, when the metallographic structure of these samples was observed, in the samples of sample numbers 41 and 42, precipitation of chromium sulfide was observed around the hard phase, and a lubricating phase in which chromium sulfide particles precipitated in groups was found. It was confirmed that they were dispersed throughout the base. In addition, in the sample of Sample No. 43, precipitation of chromium sulfide was observed around the hard phase, and it was confirmed that the lubricating phase in which chromium sulfide particles and carbide particles were precipitated in groups was dispersed in the base. It was done.

It is a figure which represents typically the metal structure of the sintered valve seat of 1st invention in this invention. It is a figure which represents typically the metal structure of the sintered valve seat of 2nd invention in this invention. It is a figure which represents typically the metal structure of the sintered valve seat of 3rd invention in this invention. It is a figure which shows typically the metal structure of the conventional valve seat.

Claims (13)

  In the matrix, the composition is Mo: 48-60 mass%, Cr: 3-12 mass%, Si: 1-5 mass%, and the balance: Co and inevitable impurities. A sintered valve seat characterized by exhibiting a structure in which a hard phase in which main precipitates are integrally formed in a lump is dispersed in an amount of 5 to 40% by mass and Cr sulfide is dispersed around the hard phase. .   2. The sintered valve seat according to claim 1, wherein an amount of S in the sintered valve seat is 0.04 to 5 mass%.   The base contains Cr: 4 to 25% by mass, and 5 to 20% by mass of a lubricating phase in which Cr sulfide particles are precipitated in a group is dispersed in the Fe—Cr alloy base. The sintered valve seat according to claim 1.   The sintered valve seat according to claim 3, wherein carbides are dispersed in the lubricating phase.   A metal structure in which at least one of manganese sulfide particles, calcium fluoride particles, boron nitride particles, magnesium silicate-based mineral particles, bismuth particles, and bismuth oxide particles is dispersed in an amount of 2% by mass or less in the powder grain boundaries and pores. It exhibits, The sintered valve seat | sheet in any one of Claims 1-4 characterized by the above-mentioned.   The sintered valve seat according to any one of claims 1 to 5, wherein the pores are filled with one of lead, lead alloy, copper, copper alloy and acrylic resin. In at least one of the following base-forming steel powders (A) to (E), 5 to 40% by mass of the following hard phase forming powder (F) and graphite powder: 0.4 to 1.2% by mass And a raw material powder comprising at least one of the following sulfide powders (G) to (J) and added and mixed in an amount such that the amount of S in the raw material powder is 0.04 to 5% by mass. A method for producing a sintered valve seat, comprising: compacting into a green shape and then sintering.
"Base forming steel powder"
(A) Mo: Steel powder consisting of 1.5 to 5% by mass and the balance being Fe and inevitable impurities.
(B) Cr: 2-4% by mass, Mo: 0.2-0.4% by mass, V: 0.2-0.4% by mass and the balance: steel powder comprising Fe and inevitable impurities.
(C) Steel powder comprising Co: 5.5 to 7.5% by mass, Mo: 0.5 to 3% by mass, Ni: 0.1 to 3% by mass, and the balance: Fe and inevitable impurities.
(D) Mo: 0.4-4 mass%, Ni: 0.6-5 mass%, Cu: 0.5-5 mass%, Cr: 0.05-2 mass%, and V: 0.05- 0.6% by mass and the balance: steel powder composed of Fe and inevitable impurities.
(E) Partially diffused steel powder consisting of Ni: 1 to 10%, Cu: 1 to 3%, Mo: 0.4 to 1.0%, and the balance of Fe and inevitable impurities.
"Hard phase forming powder"
(F) Co-based alloy powder comprising Mo: 48 to 60% by mass, Cr: 3 to 12% by mass, Si: 1 to 5% by mass, and the balance: Co and inevitable impurities.
"Sulfide powder"
(G) Molybdenum disulfide powder (H) Tungsten disulfide powder (I) Iron sulfide powder (J) Copper sulfide powder   The method for producing a sintered valve seat according to claim 7, wherein the raw material powder further contains 5% by mass or less of nickel powder.   The method for producing a sintered valve seat according to claim 7 or 8, wherein the raw material powder further contains 5% by mass or less of copper powder.   The said raw material powder further contains 5-20 mass% of chromium containing steel powder containing 4-25 mass% Cr as lubrication phase formation powder, The any one of Claims 7-9 characterized by the above-mentioned. A method for manufacturing a sintered valve seat. The said chromium containing steel powder consists of at least 1 sort (s) of following (L)-(Q), The manufacturing method of the sintered valve seat | sheet of Claim 10 characterized by the above-mentioned.
(L) Cr: 4 to 25% by mass, and balance: chromium-containing steel powder composed of Fe and inevitable impurities.
(M) Cr: 4 to 25% by mass, Ni: 3.5 to 22% by mass, and the balance: chromium-containing steel powder composed of Fe and inevitable impurities.
(N) Cr: 4 to 25% by mass, Mo: 0.3 to 7% by mass, Cu: 1 to 4% by mass, Al: 0.1 to 5% by mass, N: 0.3% by mass or less, Mn : 5.5-10 mass%, Si: 0.15-5 mass%, Nb: 0.45 mass% or less, P: 0.2 mass% or less, S: 0.15 mass% or less, and Se: 0 A chromium-containing steel powder composed of at least one of 15% or less and the balance: Fe and inevitable impurities.
(O) Cr: 4 to 25% by mass, Ni: 3.5 to 22% by mass, Mo: 0.3 to 7% by mass, Cu: 1 to 4% by mass, Al: 0.1 to 5% by mass N: 0.3 mass% or less, Mn: 5.5-10 mass%, Si: 0.15-5 mass%, Nb: 0.45 mass% or less, P: 0.2 mass% or less, S: A chromium-containing steel powder comprising at least one of 0.15% by mass or less and Se: 0.15% or less, and the balance: Fe and inevitable impurities.
(P) Cr: 7.5-25 mass%, Mo: 0.3-3.0 mass%, C: 0.25-2.4 mass%, and V: 0.2-2.2 mass% W: One or more of 1.0 to 5.0% by mass of chromium-containing steel powder, the balance being Fe and inevitable impurities.
(Q) Cr, 4-6 mass%, Mo: 4-8 mass%, V: 0.5-3 mass%, W: 4-8%, C: 0.6-1.2%, and the balance: A chromium-containing steel powder consisting of Fe and inevitable impurities.   The raw material powder contains 2% by mass or less of at least one of manganese sulfide powder, calcium fluoride powder, boron nitride powder, magnesium silicate mineral powder, bismuth powder, and bismuth oxide powder. The manufacturing method of the sintered valve seat | sheet in any one of 7-11.   After sintering, the pores of the sintered body are impregnated or infiltrated with any one of lead, lead alloy, copper, copper alloy, and acrylic resin. A manufacturing method for a valve seat.

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