Iron-based sintered alloy valve seat for internal combustion engine and method for manufacturing same

Abstract

The invention provides a valve seat made of an iron-based sintered alloy. The sintered body is made of an iron-based sintered alloy and has a double-layer structure in which a functional member-side layer and a support member-side layer are integrally sintered. The functional member-side layer has, dispersed in a matrix phase comprising a fine carbide precipitated phase, 5.0-30.0% by area ratio of a high alloy phase, 10.0-40.0% by area ratio of Si-Cr-Mo or Si-Cr-Mo-Ni Co-based intermetallic compound particles having a Vickers hardness of 600-1200 HV, and 0-4.0% by area ratio of solid lubricant particles. The sintered body made of the iron-based sintered alloy has a composition in which the matrix part contains, in mass%, 0.50 to 2.80% of C, 1.80% or less of Si, 2.50% or less of Mn, 3.00 to 11.00% of Cr, 3.00 to 17.00% of Mo, 1.00 to 8.50% of Ni, 5.00 to 30.00% of Co, 0.50 to 4.00% of V, 4.00 to 10.00% of W, and 0 to 2.00% of S. As a result, it is possible to produce a valve seat having excellent radial compressive strength and excellent wear resistance compared to the prior art.

Description

Technical Field

[0001] The present invention relates to a valve seat made of an iron-based sintered alloy for an internal combustion engine and a method for manufacturing the same, and particularly to an improvement in wear resistance and an improvement in radial compressive strength of a valve seat for an internal combustion engine using gaseous fuels such as LPG, CNG, hydrogen, and special fuels containing ethanol, etc. Background Art

[0002] A valve seat is usually press-fitted into a cylinder head of an internal combustion engine and serves to seal combustion gases and cool the valve. The valve seat is struck by the valve and is faced with wear caused by sliding, heating caused by combustion gases, corrosion caused by combustion products, etc. Therefore, heretofore, the valve seat has been required to have excellent heat resistance and wear resistance, and to have low mating object aggressiveness so as not to wear the valve as the mating object material.

[0003] In response to such requirements, for example, Patent Document 1 describes an "iron-based sintered alloy valve seat for an internal combustion engine having excellent wear resistance". In the technique described in Patent Document 1, the matrix phase is a hard single-phase structure, and the single-phase structure is a fine carbide precipitation phase having a hardness of 550 HV or more and precipitating fine carbides of 10 μm or less. Moreover, an iron-based sintered alloy valve seat having the following structure is formed: in this matrix phase, hard particles having a hardness of 650 to 1200 HV are dispersed at an area ratio of 20 to 40%, and a diffusion phase having an area ratio of 0.5 to 5% is formed around the hard particles, or solid lubricant particles having an area ratio of 5% or less are further dispersed. Thereby, in an internal combustion engine in an environment using a special fuel such as a gaseous fuel, which is a severe wear environment, even when a valve with a high surface hardness is used, the wear of the valve seat is small, and a combination of a valve and a valve seat having excellent wear resistance can be achieved.

[0004] In addition, Patent Document 2 describes an iron-based sintered alloy valve seat. The valve seat described in Patent Document 2 is a valve seat having a double-layer structure in which a valve seating side portion and a cover seating side portion are integrally sintered. The valve seating side portion is made of an iron-based sintered alloy material having a porosity of 10 to 25% by volume and 6.1 to 7.1 g / cm 3The sintered density is such that hard particles are dispersed in the matrix phase. The hard particles are particles composed of one or more elements selected from C, Cr, Mo, Co, Si, Ni, S, and Fe, and are dispersed in the matrix phase at an area ratio of 5 to 40%. The composition of the matrix part containing the matrix phase and the hard particles has a composition in which, in mass%, a total of 10.0 to 40.0% is selected from Ni: 2.0 to 23.0%, Cr: 0.4 to 15.0%, Mo: 3.0 to 15.0%, Cu: 0.2 to 3.0%, Co: 3.0 to 15.0%, V: 0.1 to 0.5%, Mn: 0.1 to 0.5%, W: 0.2 to 6.0%, C: 0.8 to 2.0%, Si: 0.1 to 1.0%, S: 0.1 to 1.0%, and the balance is composed of Fe and unavoidable impurities. It should be noted that in Patent Document 2, as the above hard particles, Cr-Mo-Co-based intermetallic compound particles, Ni-Cr-Mo-Co-based intermetallic compound particles, Fe-Mo alloy particles, Fe-Ni-Mo-S-based alloy particles, and Fe-Mo-Si-based alloy particles are exemplified.

[0005] In addition, a valve seat made of a ferrous sintered alloy is proposed in Patent Document 3. The valve seat made of a ferrous sintered alloy described in Patent Document 3 is such a valve seat made of a ferrous sintered alloy in which hard particles are dispersed in the matrix phase, and the overall composition has, in mass%, Cr: 5.0 to 20.0%, Si: 0.4 to 2.0%, Ni: 2.0 to 6.0%, Mo: 5.0 to 25.0%, W: 0.1 to 5.0%, V: 0.5 to 5.0%, Nb: 1.0% or less, C: 0.5 to 1.5%, and the balance is composed of Fe and unavoidable impurities. In the valve seat made of a ferrous sintered alloy described in Patent Document 3, as the hard particles, Fe-Mo-Si alloy particles containing, in mass%, Mo: 40.0 to 70.0%, Si: 0.4 to 2.0%, C: 0.1% or less, and the balance composed of Fe and unavoidable impurities are preferably used.

[0006] In addition, a hard particle-dispersed iron-based sintered alloy is proposed in Patent Document 4. The hard particle-dispersed iron-based sintered alloy described in Patent Document 4 is an iron-based sintered alloy obtained by dispersing 3 to 20% of hard particles based on the entire alloy in a matrix containing, by weight percentage, Si: 0.4 to 2%, Ni: 2 to 12%, Mo: 3 to 12%, Cr: 0.5 to 5%, V: 0.6 to 4%, Nb: 0.1 to 3%, C: 0.5 to 2%, and the balance being Fe, and then sintering. The dispersed hard particles are hard particles containing Mo: 60 to 70%, B: 0.3 to 1%, C: 0.1% or less, and the balance being Fe. When B is added to the ferromolybdenum-based hard particles, B improves the wettability of ferromolybdenum, prevents the hard particles from detaching from the matrix, improves the adhesion between the matrix and the hard particles, and can improve the thermal strength and mechanical strength of the sintered alloy.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent No. 6736227

[0010] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2004-232088

[0011] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2015-178650

[0012] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2005-325436. Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] In the valve seats described in Patent Documents 1 and 2, in order to contribute to improving the high-temperature strength and toughness of the matrix phase or improving the wear resistance, it is preferable that a large amount of Co is contained in the matrix phase or the hard particles.

[0015] However, the iron-based sintered alloy valve seats described in Patent Documents 1 and 2 have problems such as low radial compressive strength, easy cracking when pressed into the cylinder head, easy detachment of particles when contacting the valve, and reduced wear resistance. In addition, the iron-based sintered alloy valve seats described in Patent Documents 1 and 2 also have problems of low Young's modulus and easy deformation, reduced sealing performance, and leakage of combustion gas.

[0016] In addition, in the technologies described in Patent Documents 3 and 4, since the dispersed iron-based hard particles do not contain Co, cracks and fragmentation are more likely to occur compared with the conventional Co-based hard particles. Therefore, it is found that there is a problem that the hard particles detach from the matrix phase, and particularly in the severe valve seat usage environment in recent years, the desired wear resistance cannot be ensured.

[0017] An object of the present invention is to provide a valve seat made of an iron-based sintered alloy for an internal combustion engine that has excellent wear resistance and excellent radial compressive strength even in the severe valve seat usage environment in recent years. It should be noted that "excellent radial compressive strength" as mentioned here refers to the case where the radial compressive strength obtained according to JIS Z 2507 is 490 MPa or more.

[0018] Means for Solving the Problem

[0019] In order to achieve the above object, the inventor of the present invention first conducted in-depth research on various factors affecting the radial compressive strength. As a result, the following insight was obtained: low "radial compressive strength" is caused by low compressibility of the iron-based powder used. In this case, in the iron-based powder used, carbides have precipitated in the powder, the hardness of the powder particles increases, and during powder pressing and molding, plastic deformation (compression) of the powder particles becomes insufficient. Therefore, it is considered that it is also difficult to promote element diffusion during sintering treatment, resulting in a decrease in the bonding force between particles. Therefore, in the present invention, in order to perform sufficient powder pressing and molding during powder pressing and molding and to apply sufficient plastic deformation to the powder particles, it was thought to use an iron-based powder with a low carbon content as the iron-based powder for forming the matrix phase. However, if the carbon content of the iron-based powder is excessively reduced, the amount of carbide will decrease, and the wear resistance of the sintered body will decrease. Therefore, considering increasing the amount of graphite powder added so that the carbon content of the sintered body does not decrease, and in order to increase the amount of carbide, an iron-based powder with an increased amount of carbide-forming elements was used. As a result, it was found that the precipitation amount of fine carbides in the sintered body increased significantly compared with the past, and the wear resistance and radial compressive strength were significantly improved.

[0020] In addition, in the present invention, it was found that by making the matrix contain an appropriate amount of Ni or further containing Co, the progress of sintering is significantly promoted, the wear resistance is not reduced, and the radial compressive strength is improved.

[0021] The present invention was completed through further research based on the above insights. That is, the gist of the present invention is as follows.

[0022] [1] A valve seat made of an iron-based sintered alloy for an internal combustion engine, which is a valve seat pressed into the cylinder head of an internal combustion engine, characterized in that

[0023] the valve seat has a single-layer structure composed of a functional component side layer,

[0024] the functional component side layer has a matrix phase composed of a fine carbide precipitation phase and a structure in which a high-alloy phase of 5.0 to 30.0% and hard particles of 10.0 to 40.0% are dispersed in the matrix phase by area ratio, and further 0 to 4.0% of solid lubricant particles are dispersed,

[0025] The hard particles are Si-Cr-Mo series Co-based intermetallic compound particles with a Vickers hardness of 600 to 1200 HV and a composition containing, by mass%, Si: 2.2 to 2.7%, Cr: 7.5 to 9.5%, Mo: 27.0 to 30.0%, and the balance being composed of Co and inevitable impurities, or Si-Cr-Mo-Ni series Co-based intermetallic compound particles with a composition containing, by mass%, Si: 1.5 to 2.5%, Cr: 24.0 to 26.0%, Mo: 23.0 to 26.0%, Ni: 9.5 to 11.0%, and the balance being composed of Co and inevitable impurities.

[0026] The matrix part containing the matrix phase, the hard particles, and the solid lubricant particles is made of an iron-based sintered alloy material. The iron-based sintered alloy material has a matrix part composition containing, by mass%, C: 0.50 to 2.80%, further containing one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 3.00 to 11.00%, Mo: 3.00 to 17.00%, Ni: 1.00 to 8.50%, Co: 5.00 to 30.00%, V: 0.50 to 4.00%, W: 4.00 to 10.00%, and S: 0 to 2.00%, and the balance being composed of Fe and inevitable impurities.

[0027] The density of the valve seat is 6.6 to 7.4 g / cm 3 。

[0028] [2] An iron-based sintered alloy valve seat for an internal combustion engine, which is a valve seat pressed into the cylinder head of an internal combustion engine, characterized in that

[0029] the valve seat has a double-layer structure formed by integrally sintering a functional component side layer and a support component side layer.

[0030] The functional component side layer has a matrix phase composed of a fine carbide precipitation phase and a structure in which, by area ratio, 5.0 to 30.0% of a high-alloy phase and 10.0 to 40.0% of hard particles are dispersed in the matrix phase, and further 0 to 4.0% of solid lubricant particles are dispersed.

[0031] The hard particles are Si-Cr-Mo series Co-based intermetallic compound particles with a Vickers hardness of 600 to 1200 HV and a composition containing, by mass%, Si: 2.2 to 2.7%, Cr: 7.5 to 9.5%, Mo: 27.0 to 30.0%, and the balance being composed of Co and inevitable impurities, or Si-Cr-Mo-Ni series Co-based intermetallic compound particles with a composition containing, by mass%, Si: 1.5 to 2.5%, Cr: 24.0 to 26.0%, Mo: 23.0 to 26.0%, Ni: 9.5 to 11.0%, and the balance being composed of Co and inevitable impurities.

[0032] The matrix part containing the matrix phase, the hard particles, and the solid lubricant particles has a matrix part composition containing, by mass%, C: 0.50 to 2.80%, further containing one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 3.00 to 11.00%, Mo: 3.00 to 17.00%, Ni: 1.00 to 8.50%, Co: 5.00 to 30.00%, V: 0.50 to 4.00%, W: 4.00 to 10.00%, and S: 0 to 2.00%, and the balance being composed of Fe and inevitable impurities.

[0033] The support member side layer is made of an iron-based sintered alloy material having a matrix phase composed of pearlite, a structure in which 0 to 4.0% of solid lubricant particles and 0 to 5.0% of hardness-improving particles are dispersed in the matrix phase, and a matrix part containing the matrix phase, the solid lubricant particles, and the hardness-improving particles has a composition containing, by mass%, C: 0.30 to 2.00%, further containing Ni: 0 to 2.00%, Mo: 0 to 2.00%, Cu: 0 to 5.00%, Mn: 0 to 5.00%, and S: 0 to 2.00%, and the balance being composed of Fe and inevitable impurities.

[0034] The density of the valve seat is 6.7 to 7.4 g / cm 3 。

[0035] [3] The iron-based sintered alloy valve seat for an internal combustion engine according to [1] or [2], characterized in that the fine carbide precipitation phase is a fine carbide with a precipitation particle size of 10 μm or less and a phase having a Vickers hardness of 450 to 650 HV.

[0036] [4] The iron-based sintered alloy valve seat for an internal combustion engine according to any one of [1] to [3], characterized in that the solid lubricant particles are one or two selected from manganese sulfide MnS and molybdenum disulfide MoS2.

[0037] [5] The valve seat made of an iron-based sintered alloy according to any one of [2] to [4], wherein the hardness-improving particles are iron-molybdenum alloy particles.

[0038] [6] The valve seat made of an iron-based sintered alloy for an internal combustion engine according to any one of [1] to [5], wherein a thermosetting resin or an anaerobic resin is infiltrated into the pores of the iron-based sintered alloy material.

[0039] [7] A method for manufacturing a valve seat made of an iron-based sintered alloy, which is a method for manufacturing a valve seat made of a single-layer iron-based sintered alloy according to [1], and is characterized in that

[0040] after blending a specified amount of iron-based powder, graphite powder, alloy element powder, and hard particle powder, or further blending a specified amount of solid lubricant powder, and performing mixing and kneading to form a mixed powder,

[0041] filling the mixed powder into a mold having a specified shape and performing stamping to form a compacted body, and then,

[0042] when manufacturing a valve seat having a specified shape by performing sintering treatment on the compacted body in a protective atmosphere to form a sintered body and then performing cutting or further performing grinding,

[0043] making the iron-based powder have a composition containing C: 0.2 to 0.8% by mass, Si: 1.0% or less, Mn: 1.0% or less, Cr: 7.0% or less, Mo: 7.0% or less, V: 5.0% or less, W: 12.0% or less, or further containing Co: 12.0% or less, and the balance being composed of Fe and inevitable impurities, and having a particle hardness of 170 to 280 HV as measured by a Vickers hardness tester, and blending 40.0 to 70.0% of this iron-based powder based on the mass% of the total amount of the mixed powder,

[0044] making the hard particle powder have a hardness of 600 to 1200 HV as measured by a Vickers hardness tester, and having a composition containing Si: 2.2 to 2.7% by mass, Cr: 7.5 to 9.5%, Mo: 27.0 to 30.0%, and the balance being composed of Co and inevitable impurities, or having a composition containing Si: 1.5 to 2.5% by mass, Cr: 24.0 to 26.0%, Mo: 23.0 to 26.0%, Ni: 9.5 to 11.0%, and the balance being composed of Co and inevitable impurities, and blending 10.0 to 40.0% of this hard particle powder based on the mass% of the total amount of the mixed powder,

[0045] Combined with 0.5 to 2.0% of the graphite powder based on the mass% of the total amount of the mixed powder,

[0046] Combined with a total of 0 to 7.0% of the alloy element powder based on the mass% of the total amount of the mixed powder, and further combined with 0 to 4.0% of the solid lubricant powder based on the mass% of the total amount of the mixed powder,

[0047] So that the density of the green compact reaches a density of 6.6 / cm 3 The stamping process is carried out in the above manner,

[0048] The sintering treatment is carried out at a sintering temperature of 1100 to 1200 °C to obtain the sintered body.

[0049] [8] A method for manufacturing a valve seat made of a ferrous sintered alloy, which is a method for manufacturing a valve seat made of a ferrous sintered alloy having a double-layer structure according to [2], characterized in that,

[0050] A specified amount of iron-based powder, graphite powder, alloy element powder, and hard particle powder are combined, or a specified amount of solid lubricant powder is further combined, and then mixed and kneaded to prepare a mixed powder for the functional component side layer,

[0051] A specified amount of iron-based powder and graphite powder are combined, or a specified amount of alloy element powder, hardness-improving particles, and solid lubricant powder are further combined, and then mixed and kneaded to prepare a mixed powder for the support component side layer,

[0052] When the mixed powder for the functional component side layer and the mixed powder for the support component side layer are sequentially filled into a mold with a specified shape, and stamping is carried out to form a green compact, and then the green compact is sintered in a protective atmosphere to form a sintered body with a double-layer structure in which the functional component side layer and the support component side layer are integrally sintered, and then machining is carried out, or further grinding is carried out to manufacture a valve seat with a double-layer structure of a specified shape,

[0053] In the mixed powder for the functional component side layer, the iron-based powder has a composition containing C: 0.2 to 0.8%, Si: 1.0% or less, Mn: 1.0% or less, Cr: 7.0% or less, Mo: 7.0% or less, V: 5.0% or less, W: 12.0% or less, or further contains Co: 12.0% or less, and the balance is composed of Fe and unavoidable impurities, and has a particle hardness of 170 to 280 HV as measured by a Vickers hardness tester. 40.0 to 70.0% of this iron-based powder is combined based on the mass% of the total amount of the mixed powder,

[0054] The hard particle powder has a hardness of 600 to 1200 HV measured by a Vickers hardness tester, and in terms of mass percentage, is a Si-Cr-Mo-based Co-based intermetallic compound particle having a composition containing Si: 2.2 to 2.7%, Cr: 7.5 to 9.5%, Mo: 27.0 to 30.0%, and the balance being composed of Co and inevitable impurities, or a Si-Cr-Mo-Ni-based Co-based intermetallic compound particle having a composition containing Si: 1.5 to 2.5%, Cr: 24.0 to 26.0%, Mo: 23.0 to 26.0%, Ni: 9.5 to 11.0%, and the balance being composed of Co and inevitable impurities. 10 to 40% of this hard particle powder is compounded based on the mass percentage of the total amount of the mixed powder.

[0055] 0.5 to 2.0% of the graphite powder is compounded based on the mass percentage of the total amount of the mixed powder, 0 to 7.0% in total of the alloy element powder is compounded based on the mass percentage of the total amount of the mixed powder, and further 0 to 4.0% of the solid lubricant particle powder is compounded based on the mass percentage of the total amount of the mixed powder.

[0056] In the mixed powder for the support member side layer, the iron-based powder is pure iron powder, 0.5 to 2.0% of the graphite powder is compounded based on the mass percentage of the total amount of the mixed powder for the support member side layer, 0 to 5.0% in total of the alloy element powder is compounded based on the mass percentage of the total amount of the mixed powder for the support member side layer, the hardness improvement particle powder is iron-molybdenum alloy particle powder, 0 to 5.0% of this hardness improvement particle powder is compounded based on the mass percentage of the total amount of the mixed powder for the support member side layer, and 0 to 4.0% of the solid lubricant powder is compounded based on the mass percentage of the total amount of the mixed powder for the support member side layer.

[0057] The compact is processed by pressing in such a way that the density of the compact reaches a density of 6.6 g / cm 3 or more.

[0058] The sintering treatment is a treatment carried out at a sintering temperature of 1100 to 1200 °C.

[0059] A sintered body having the double-layer structure is produced.

[0060] [9] The method for manufacturing an iron-based sintered alloy valve seat according to [7] or [8], characterized in that a resin impregnation treatment of impregnating a thermosetting resin or an anaerobic resin is further carried out after the sintering treatment.

[0061] Effects of the invention

[0062] According to the present invention, a valve seat made of an iron-based sintered alloy for an internal combustion engine can be manufactured, which not only has excellent abrasion resistance but also excellent radial compressive strength, and exhibits a remarkable effect industrially. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 An explanatory diagram showing an outline of a bench test machine. DETAILED DESCRIPTION OF THE INVENTION

[0064] The valve seat of the present invention is a single-layer iron-based sintered alloy valve seat having only a functional component side layer, or a double-layer iron-based sintered alloy valve seat in which a functional component side layer and a support component side layer are integrally sintered.

[0065] First, the functional component side layer will be described.

[0066] The functional component side layer has a matrix phase composed of a fine carbide precipitation phase, and a structure in which a high-alloy phase, 10.0 to 40.0% hard particles, and 0 to 4.0% solid lubricant particles are respectively dispersed in the matrix phase at an area ratio with respect to the entire structure. It should be noted that the balance other than the high-alloy phase, hard particles, and solid lubricant particles is the matrix phase and pores. It should be noted that it is preferable to infiltrate a thermosetting resin or an anaerobic resin into the pores. By sealing the pores by infiltrating a thermosetting resin or an anaerobic resin, the abrasion resistance is not reduced, the machinability and workability are improved, and an improvement in corrosion resistance can also be expected.

[0067] The pores can also be obtained by calculation based on the true density and the density of the functional component side layer.

[0068] The matrix phase is a fine carbide precipitation phase.

[0069] The fine carbide precipitation phase is a phase in which fine carbides with a precipitation particle size of 10 μm or less are precipitated, and is a hard phase having a hardness of 450 HV or more, preferably 650 HV or less, as measured by a Vickers hardness tester. Due to the presence of such hard fine carbide precipitation phases, the matrix can be strengthened and the abrasion resistance can be further improved. If the particle size of the carbides precipitated in the matrix phase increases and exceeds 10 μm, the hardness and toughness of the matrix phase decrease, the aggressiveness of the mating object increases, and the radial compressive strength decreases.

[0070] ​The high-alloy phase dispersed in the matrix phase is a region where the alloying elements diffuse from the hard particles or added elements during sintering, resulting in an increase in the alloy content. The high-alloy phase particularly has the effect of preventing the hard particles from falling off, and preferably has a hardness of 170 HV or more and preferably 280 HV or less as measured by a Vickers hardness tester. In order to obtain the above effect, it is necessary to contain 5.0% or more of the high-alloy phase based on the area ratio of the entire structure. On the other hand, if the content of the high-alloy phase exceeds 30.0%, the strength of the valve seat decreases. Therefore, the high-alloy phase is in the range of 5.0 to 30.0% in terms of area ratio. It should be noted that it is preferably 10.0 to 20.0%.

[0071] The dispersed hard particles are hard particles having a hardness of 600 to 1200 HV as measured by a Vickers hardness tester. If the hardness of the hard particles is lower than 600 HV, the effect of improving wear resistance is small. On the other hand, if it increases and exceeds 1200 HV, the machinability decreases. Therefore, the hardness of the hard particles dispersed in the matrix phase is limited to the range of 600 to 1200 HV as measured by a Vickers hardness tester.

[0072] In the present invention, 10.0 to 40.0% of the hard particles having the above hardness are dispersed in the matrix phase based on the area ratio of the entire structure (including the matrix phase, hard particles, solid lubricant particles, and pores). If the dispersion amount of the hard particles is less than 10.0%, the desired wear resistance cannot be ensured. On the other hand, if it exceeds 40.0%, the bonding strength with the matrix phase decreases and the wear resistance decreases. Therefore, the dispersion amount of the hard particles dispersed in the matrix phase is limited to the range of 10.0 to 40.0% in terms of area ratio.

[0073] It should be noted that the hard particles are preferably particles having the above hardness and an average particle diameter of 10 to 150 μm. If the average particle diameter of the hard particles is less than 10 μm, over-diffusion easily occurs during sintering. On the other hand, if it increases and exceeds 150 μm, the bonding strength with the matrix decreases and the wear resistance decreases. Therefore, the average particle diameter of the hard particles dispersed in the matrix phase is preferably limited to the range of 10 to 150 μm. It should be noted that the "average particle diameter" referred to here is the particle diameter D50 at which the cumulative distribution measured by the laser scattering method reaches 50%.

[0074] Moreover, in the present invention, the hard particles dispersed in the matrix phase are Si-Cr-Mo based Co-based intermetallic compound particles having a composition containing Si: 2.2 to 2.7%, Cr: 7.5 to 9.5%, Mo: 27.0 to 30.0%, and the balance being composed of Co and inevitable impurities, or Si-Cr-Mo-Ni based Co-based intermetallic compound particles having a composition containing Si: 1.5 to 2.5%, Cr: 24.0 to 26.0%, Mo: 23.0 to 26.0%, Ni: 9.5 to 11.0%, and the balance being composed of Co and inevitable impurities. By making the dispersed hard particles be Co-based intermetallic compound particles having the above composition, the diffusion of alloy elements becomes significant during sintering, and it is easy to form a high-alloy phase around the hard particles.

[0075] In addition, in the functional component side layer of the valve seat of the present invention, solid lubricant particles of 4.0% or less can be further dispersed in the matrix phase. By dispersing solid lubricant particles in the matrix phase, the machinability and lubricity are improved. However, if the dispersion exceeds 4.0% in terms of area ratio, the mechanical properties are significantly reduced. Therefore, in terms of area ratio, the solid lubricant particles are limited to the range of 0 to 4.0%. It should be noted that the solid lubricant particles are preferably one or two selected from manganese sulfide MnS and molybdenum disulfide MoS2.

[0076] In addition, the matrix part of the functional component side layer of the valve seat of the present invention, which includes the matrix phase, the high-alloy phase, the hard particles, and the solid lubricant particles, has a composition (matrix part composition) containing C: 0.50 to 2.80% by mass, further containing one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 3.00 to 11.00%, Mo: 3.00 to 17.00%, Ni: 1.00 to 8.50%, Co: 5.00 to 30.00%, V: 0.50 to 4.00%, W: 4.00 to 10.00%, and S: 0 to 2.00%, and the balance being composed of Fe and inevitable impurities.

[0077] Next, the reasons for limiting the matrix part composition of the functional component side layer will be described. It should be noted that hereinafter, the mass% in the composition is only expressed as %.

[0078] C: 0.50 to 2.80%

[0079] C is an element necessary for adjusting the matrix phase to a specified hardness or structure or for forming carbides, and it contains 0.50% or more. On the other hand, if the content exceeds 2.80%, the melting point decreases and the sintering treatment becomes liquid-phase sintering. If it becomes liquid-phase sintering, the amount of precipitated carbides is excessive, and in addition, the number of pores increases, and the elongation characteristics and dimensional accuracy decrease. Therefore, C is limited to the range of 0.50 to 2.80%. It should be noted that it is preferably 0.90 to 1.70%. When the pores are infiltrated with resin, C is preferably 2.30 to 2.60%.

[0080] Si: 1.80% or less

[0081] Si is mainly contained in the hard particles and is an element that constitutes the intermetallic compound. While increasing the hardness of the hard particles, it also increases the matrix strength, thereby improving the wear resistance. Therefore, Si is preferably contained in an amount of 0.20% or more. On the other hand, if Si contains more than 1.80%, the aggressiveness of the mating object increases. Therefore, Si is preferably limited to 1.80% or less. It should be noted that it is more preferably 0.50 to 1.00%.

[0082] Mn: 2.50% or less

[0083] Mn is an element that increases the hardness of the matrix phase. In addition, a part of Mn is contained in the matrix part due to the solid lubricant particles and is an element that helps to improve the machinability, and it is preferably contained in an amount of 0.05% or more. On the other hand, if Mn contains more than 2.50%, the hardness, toughness, and ductility of the matrix phase decrease. Therefore, Mn is preferably limited to 2.50% or less. It should be noted that it is more preferably 0.20 to 1.60%.

[0084] Cr: 3.00 to 11.00%

[0085] Cr is dissolved in the matrix phase. In addition, it forms carbides to increase the hardness of the matrix phase. At the same time, Cr is an element that contributes to increasing the hardness of the hard particles as a constituent element of the intermetallic compound and is contained in the matrix part in an amount of 3.00% or more. On the other hand, if Cr contains more than 11.00%, the precipitation of Cr carbides in the matrix phase becomes excessive, and it is difficult to make the carbides in the matrix phase into fine carbides. Therefore, Cr is preferably limited to the range of 3.00 to 11.00%. It should be noted that it is more preferably 4.00 to 6.00%.

[0086] Mo: 3.00 to 17.00%

[0087] Mo is dissolved in the matrix phase. In addition, it precipitates as carbides to increase the hardness of the matrix phase. Moreover, Mo is an element that contributes to increasing the hardness of hard particles as a constituent element of intermetallic compounds, and is preferably contained in the matrix part at 3.00% or more. On the other hand, if Mo exceeds 17.00%, it is difficult to increase the density during powder molding, and the moldability decreases. Therefore, Mo is preferably limited within the range of 3.00 - 17.00%. It should be noted that it is more preferably 9.00 - 15.00%.

[0088] Ni: 1.00 - 8.50%

[0089] Ni is an element that contributes to the improvement of the strength and toughness of the matrix phase and the formation of high-alloy phases. In addition, Ni is an element that contributes to increasing the toughness of hard particles as a constituent element of intermetallic compounds, and is preferably contained at 1.00% or more. On the other hand, if Ni exceeds 8.50%, it is difficult to increase the density during powder molding, and the moldability decreases. Therefore, Ni is preferably limited within the range of 1.00 - 8.50%. It should be noted that it is more preferably 1.00 - 3.00%.

[0090] Co: 5.00 - 30.00%

[0091] Co is mainly contained in hard particles, forms intermetallic compounds, increases the hardness of hard particles, diffuses in the matrix during sintering, contributes to the formation of high-alloy phases, is further contained in the matrix phase, increases the strength of the matrix phase, especially the high-temperature strength, and further contributes to improving the toughness of the matrix phase. As the matrix part, it is preferably contained at 5.00% or more. On the other hand, if Co exceeds 30.00%, the wear resistance decreases. Therefore, Co is preferably limited within 5.00 - 30.00%. It should be noted that it is more preferably 9.00 - 27.00%.

[0092] V: 0.50 - 4.00%

[0093] V is precipitated as fine carbides to increase the hardness of the matrix phase, thereby improving the wear resistance, and is preferably contained at 0.50% or more. On the other hand, if V exceeds 4.00%, the moldability decreases. Therefore, V is preferably limited within the range of 0.50 - 4.00%. It should be noted that it is more preferably 1.00 - 3.00%.

[0094] W: 4.00 - 10.00%

[0095] W precipitates as fine carbides, increasing the hardness of the matrix phase and thus improving the wear resistance. It is preferably contained at 4.00% or more. On the other hand, if the content of W exceeds 10.00%, the formability will decrease. Therefore, the content of W is preferably limited within the range of 4.00 - 10.00%. It should be noted that a more preferable range is 3.00 - 7.00%.

[0096] In the matrix part, one or more of the above components can be contained. In addition, in the matrix part, in addition to the above components, S: 0 - 2.0% can be contained.

[0097] S: 0 - 2.00%

[0098] S is contained in the solid lubricant particles and included in the matrix part, which is an element that helps improve the machinability and can be contained as needed. If the content of S exceeds 2.00%, the toughness and ductility will decrease. Therefore, the content of S is preferably limited within the range of 0 - 2.00%.

[0099] The balance except for the above components is composed of Fe and inevitable impurities. It should be noted that as the inevitable impurities, P: 0.10% or less is allowable.

[0100] Next, the support member side layer when the valve seat of the present invention is made into a double-layer structure will be described. It should be noted that the functional member side layer of the double-layer structure is the same as the functional member side layer in the above single-layer structure. Moreover, the support member side layer when made into a double-layer structure only needs to be able to hold the functional member side layer and does not need to be particularly limited.

[0101] It should be noted that as the support member side layer, it is preferably composed of an iron-based sintered alloy material having: a matrix phase, in which solid lubricant particles with an area ratio of 0 - 4.0% and hardness-improving particles with an area ratio of 0 - 5.0% are dispersed, and a matrix part containing the matrix phase, solid lubricant particles, and hardness-improving particles, containing C: 0.30 - 2.00% by mass, further containing Ni: 0 - 2.00%, Mo: 0 - 2.00%, Cu: 0 - 5.00%, Mn: 0 - 5.00%, and S: 0 - 2.00%, and the balance is composed of Fe and inevitable impurities.

[0102] It should be noted that the matrix phase of the support member side layer is preferably pearlite.

[0103] In addition, in the matrix phase, solid lubricant particles for improving machinability may be dispersed as needed. Examples of the solid lubricant particles include MnS, MoS2, etc. In the case of dispersion, the solid lubricant particles are preferably 0.3% or more in terms of the area ratio with respect to the entire structure of the support member side layer. If the dispersion amount of the solid lubricant particles is less than 0.3%, it is difficult to achieve the purpose of improving machinability. On the other hand, even if more than 4.0% of the solid lubricant particles are dispersed, the effect saturates and an effect commensurate with the dispersion amount cannot be expected. Therefore, the solid lubricant particles are preferably in the range of 0 to 4.0% in terms of the area ratio.

[0104] In addition, in the matrix phase of the support member side layer, in order to increase the strength of the matrix phase, hardness improvement particles of 0 to 5.0% may be dispersed in terms of the area ratio. Examples of the hardness improvement particles dispersed in the support member side layer include iron-molybdenum (Fe-Mo) alloys. Since even if more than 5.0% of the hardness improvement particles are dispersed in terms of the area ratio, the effect saturates, the upper limit is 5.0% when contained.

[0105] In the support member side layer, there is a structure in which solid lubricant particles and hardness improvement particles are dispersed in the matrix phase as needed. The remainder other than the matrix phase, solid lubricant particles, and hardness improvement particles is pores. It should be noted that, similar to the functional member side layer, it is preferable to impregnate the pores with a thermosetting resin or an anaerobic resin. By sealing the pores by impregnating the thermosetting resin or the anaerobic resin, there will be no significant reduction in wear resistance, and the cutting performance and machinability are improved. In addition, by sealing the pores, an improvement in corrosion resistance can be expected.

[0106] The reasons for limiting the composition of the matrix part of the support member side layer are described.

[0107] C contains 0.30% or more to ensure the desired strength. On the other hand, if the content exceeds 2.00%, the strength is too high and the toughness is reduced. Therefore, C is preferably limited to the range of 0.30 to 2.00%. C is preferably 0.30 to 1.20%. In the case where the pores are impregnated with a resin, C is preferably 1.40 to 1.80%. It should be noted that in addition to the above C, the matrix part of the support member side layer may further contain Ni: 0 to 2.00%, Mo: 0 to 2.00%, Cu: 0 to 5.00%, Mn: 0 to 5.00%, and S: 0 to 2.00%.

[0108] Ni, Mo, and Cu are elements that increase the matrix phase strength (hardness) of the support member side layer and can be contained as needed. Although Ni, Mo, and Cu are contained according to the desired strength, if the content exceeds Ni: 2.00%, Mo: 2.00%, and Cu: 5.00% respectively, the strength becomes too high. Therefore, when contained, it is preferably limited to the range of Ni: 2.00% or less, Mo: 2.00% or less, and Cu: 5.00% or less. In addition, a part of Mo and Mn, S are contained in the matrix part due to the dispersion of solid lubricant particles, but even if a large amount of solid lubricant particles are dispersed, the effect saturates and the ductility decreases. Therefore, when contained, it is preferably limited to Mn: 5.00% or less and S: 2.00% or less.

[0109] The balance other than the above components consists of Fe and inevitable impurities. As inevitable impurities, P: 0.10% or less is allowable.

[0110] Next, a method for manufacturing the iron-based sintered alloy valve seat of the present invention will be described.

[0111] In the method for manufacturing the single-layer structure iron-based sintered alloy valve seat of the present invention, first, a prescribed amount of iron-based powder, graphite powder, alloy element powder, and hard particle powder are mixed in such a manner as to form the above matrix part composition, or further, a prescribed amount of solid lubricant particle powder is mixed, and they are mixed and kneaded to form a mixed powder (mixed powder for the functional component side layer).

[0112] The iron-based powder mixed in the mixed powder (mixed powder for the functional component side layer) is a powder mixed to form the matrix phase, and in the present invention, it is an alloy steel powder capable of making the matrix phase a structure composed of fine carbide precipitation phases. As such an alloy steel powder, powders having a composition conforming to the high-speed tool steel composition specified in JIS G 4403 can be exemplified, but of course, it is not limited thereto.

[0113] The iron-based powder to be mixed has a composition containing C: 0.2 to 0.8%, Si: 1.0% or less, Mn: 1.0% or less, Cr: 7.0% or less, Mo: 7.0% or less, V: 5.0% or less, W: 12.0% or less, Co: 0 to 12.0% by mass, and the balance consists of Fe and inevitable impurities, and has a particle hardness of 170 to 280 HV as measured by a Vickers hardness tester. The iron-based powder mixed in the present invention is a powder having a high-speed steel composition with reduced C.

[0114] First, the reasons for limiting the composition of the iron-based powder will be described. Hereinafter, the mass% in the composition is represented only by %.

[0115] C: 0.2 to 0.8%

[0116] If C is less than 0.2%, no further reduction in the hardness of the powder particles can be observed. On the other hand, if C exceeds 0.8%, the hardness of the powder particles becomes too high and the compressibility of the powder particles decreases. Therefore, the C content of the iron-based powder is preferably limited to the range of 0.2 to 0.8%. It should be noted that more preferably it is 0.4 to 0.6%.

[0117] Si: 1.0% or less

[0118] Si is an element that affects the fluid flow during powder production (atomized powder production). In order to obtain such an effect, it becomes significant when Si is contained at 0.3% or more. On the other hand, if Si is contained in excess of 1.0%, the compressibility decreases. Therefore, Si is preferably limited to 1.0% or less. It should be noted that more preferably it is 0.5% or less.

[0119] Mn: 1.0% or less

[0120] Mn acts as a deoxidizer and at the same time contributes to an increase in strength (hardness). Such an effect becomes significant when it contains 0.10% or more. On the other hand, if it contains more than 1.0% of Mn, the oxygen concentration of the powder increases and the diffusivity during sintering decreases. In addition, the hardness increases while the compressibility decreases. Therefore, Mn is preferably limited to 1.0% or less.

[0121] Cr: 7.0% or less

[0122] Cr is an element that forms carbides and has the effect of improving wear resistance. Such an effect becomes significant when it contains 0.1% or more of Cr, but if the content exceeds 7.0%, the toughness decreases. Therefore, Cr is preferably limited to 7.0% or less.

[0123] Mo: 7.0% or less

[0124] Mo is an element that forms fine carbides and has the effect of improving wear resistance. Such an effect becomes significant when it contains 2.0% or more of Mo, but if the content exceeds 7.0%, the formability decreases. Therefore, Mo is preferably limited to 7.0% or less. It should be noted that more preferably it is 2.0 to 5.0%.

[0125] V: 5.0% or less

[0126] V is an element that forms fine carbides and has the effect of improving wear resistance. Such an effect becomes significant when it contains 2.0% or more of V, but if the content exceeds 5.0%, the formability decreases. Therefore, V is preferably limited to 5.0% or less. It should be noted that more preferably it is 2.0 to 4.0%.

[0127] W: 12.0% or less

[0128] W is an element that forms fine carbides and has the effect of improving wear resistance. Such an effect becomes significant when the content of W is 5.0% or more, but if the content exceeds 12.0%, the formability decreases. Therefore, the content of W is preferably limited to 12.0% or less.

[0129] In addition to the above components, Co may be contained as needed: 12.0% or less.

[0130] Co: 0 to 12.0%

[0131] Co is an element that increases strength, especially high-temperature strength, further contributes to the improvement of toughness, and also contributes to the formation of high-alloy phases. It is preferably contained in an amount of 10.0% or more as needed. On the other hand, if the content of Co exceeds 12.0%, the strength decreases. Therefore, when Co is contained, it is preferably limited to 12.0% or less.

[0132] The balance other than the above components consists of Fe and inevitable impurities. As inevitable impurities, P: 0.03% or less and S: 0.02% or less are allowable. Since P segregates at the austenite grain boundaries and promotes grain boundary brittleness, it is preferably reduced as much as possible. It should be noted that it is more preferably 0.010% or less. In addition, since S exists as sulfide-based inclusions in the steel and impairs hot workability, it is desirable to reduce it as much as possible. It should be noted that it is more preferably 0.005% or less.

[0133] Particle hardness: 170 - 280 HV

[0134] The iron-based powder used in the present invention is a powder having a particle hardness of 170 - 280 HV. If the particle hardness is lower than 170 HV, the hardness of the iron-based powder is too low, and the wear resistance of the sintered body decreases. On the other hand, if the particle hardness increases and exceeds 280 HV, the compressibility decreases, and the radial compressive strength of the sintered body decreases. Therefore, the particle hardness of the iron-based powder to be incorporated is limited to 170 - 280 HV.

[0135] In addition, the hard particle powder incorporated in the mixed powder is Si-Cr-Mo series Co-based intermetallic compound particle powder or Si-Cr-Mo-Ni series Co-based intermetallic compound particle powder having the above-mentioned hardness and composition. In the present invention, such hard particle powder is incorporated in an amount of 10.0 to 40.0% by mass based on the total amount of the mixed powder. It should be noted that the incorporated hard particle powder is preferably particle powder having an average particle diameter of 10 to 150 μm. If the average particle diameter of the hard particles is less than 10 μm, it is likely to diffuse during sintering and the desired abrasion resistance cannot be ensured. On the other hand, if the average particle diameter of the hard particles exceeds 150 μm, the bonding force with the matrix decreases. It should be noted that the "average particle diameter" as mentioned herein means the particle diameter D50 at which the cumulative distribution measured by the laser scattering method reaches 50%.

[0136] In addition, solid lubricant particles are incorporated as needed to improve machinability, workability, and lubricity. As the solid lubricant particles, MnS, MoS2, etc. are preferably used. The incorporation amount of the solid lubricant particle powder is preferably 0 to 4.0% by mass based on the total amount of the mixed powder.

[0137] It should be noted that in the mixed powder, it goes without saying that a prescribed amount of the above-mentioned iron-based powder, hard particle powder, or further solid lubricant particle powder is incorporated, and graphite powder and alloy element powder are further incorporated so as to form the composition of the matrix part. As the incorporated alloy element powder, Ni powder can be exemplified, or Co powder can be further exemplified. It should be noted that lubricants such as zinc stearate can also be incorporated in the mixed powder.

[0138] As described above, a prescribed amount of graphite powder, alloy element powder, and hard particle powder is further incorporated in the iron-based powder, or a prescribed amount of solid lubricant particle powder is further incorporated, and they are mixed and kneaded to produce a mixed powder.

[0139] Next, the obtained mixed powder is filled into a mold having a prescribed valve seat shape.

[0140] After the mixed powder is filled into the mold, stamping is performed using a stamping machine or the like to produce a compact having a valve seat shape. It should be noted that the stamping is preferably adjusted in such a way that the density of the compact reaches 6.6 g / cm 3 in the above manner.

[0141] Next, the obtained compact is subjected to a sintering treatment to produce a sintered body.

[0142] The sintering treatment is preferably carried out in a reducing atmosphere such as nitrogen, hydrogen, or ammonia-decomposed gas, and maintained at a heating temperature in the range of 1100 to 1200 °C for 0.5 hours or more. If the heating temperature is lower than 1100 °C, sintering diffusion is insufficient. On the other hand, if it exceeds 1200 °C, over-diffusion occurs and the wear resistance decreases. It should be noted that the stamping process P - sintering process S can be a process repeated multiple times (such as 2P2S, etc.).

[0143] The obtained sintered body is subjected to machining such as grinding and cutting to form a valve seat (single-layer structure) with a desired size and shape.

[0144] It should be noted that after the above sintering treatment, it is preferable to perform a resin impregnation treatment on the valve seat (product) obtained by machining such as grinding and cutting. The resin impregnation treatment is preferably carried out in a vacuum atmosphere. The valve seat is immersed in a liquid of a thermosetting resin or an anaerobic resin, and then further pressurized starting from atmospheric pressure to allow the resin to fully impregnate the pores, and then heated to cure the resin in the pores for hole sealing. It should be noted that any of the known (commercially available) resins can be used as the thermosetting resin and anaerobic resin used.

[0145] Next, in the method for manufacturing a valve seat made of a double-layer iron-based sintered alloy of the present invention, in addition to the above-mentioned mixed powder (mixed powder for the functional component side layer), a mixed powder for the support component side layer is also prepared.

[0146] The mixed powder for the support component side layer is formulated by mixing a specified amount of iron-based powder and graphite powder in such a way as to form the above-mentioned matrix part composition, or further mixing a specified amount of alloy element powder, hardness improvement particle powder, and solid lubricant powder, and then mixing and kneading to form a mixed powder (mixed powder for the support component side layer). In the mixed powder for the support component side layer, the iron-based powder is pure iron powder. 0.5 to 2.0% of graphite powder is formulated based on the total mass% of the mixed powder for the support component side layer. A total of 0 to 5.0% of alloy element powder is formulated based on the total mass% of the mixed powder for the support component side layer. As the alloy element powder to be formulated, Mo powder, Ni powder, and Cu powder are preferably used. The hardness improvement particle powder is iron-molybdenum (Fe-Mo) alloy particle powder, and 0 to 5.0% of this hardness improvement particle powder is formulated based on the total mass% of the mixed powder for the support component side layer. 0 to 4.0% of solid lubricant powder is formulated based on the total mass% of the mixed powder for the support component side layer. In addition, lubricants such as zinc stearate can also be formulated in the mixed powder.

[0147] Then, the functional component side layer mixed powder and the support component side layer mixed powder are successively filled into a mold with a specified shape at a desired ratio. After being filled into the mold, stamping is performed in the same manner as in the case of the above single-layer structure to form a compacted powder body. Then, sintering treatment is performed on the compacted powder body in the same manner as in the case of the above single-layer structure to obtain a sintered body with a double-layer structure. The sintering treatment is the same as in the case of the single-layer structure, and is preferably a treatment of maintaining for 0.5 hours or more in a reducing atmosphere within a temperature range of a heating temperature of 1100 to 1200 °C. If the heating temperature is lower than 1100 °C, sintering diffusion is insufficient. On the other hand, if it exceeds 1200 °C, over-diffusion occurs and wear resistance decreases. It should be noted that the stamping process P - sintering process S can be a process repeated multiple times (such as 2P2S, etc.).

[0148] The obtained sintered body with a double-layer structure is subjected to processing such as grinding and cutting to form a valve seat (product) with a double-layer structure having a desired size and shape.

[0149] It should be noted that after the above sintering treatment, it is preferable to perform a resin impregnation treatment on the valve seat (product) with a double-layer structure obtained by processing such as grinding and cutting. The resin impregnation treatment is preferably a treatment in which, in a vacuum atmosphere, the valve seat is immersed in a liquid of a thermosetting resin or an anaerobic resin, then pressurized starting from atmospheric pressure to allow the resin to fully impregnate the pores, and then heated to cure the resin in the pores for sealing. Through the resin impregnation treatment, a thermosetting resin or an anaerobic resin is impregnated into the pores of the iron-based sintered alloy material (functional component side layer and support member side layer, or functional component side layer).

[0150] Hereinafter, the present invention will be further described based on examples.

[0151] Examples

[0152] First, a functional component side layer mixed powder and a support component side layer mixed powder are prepared.

[0153] The functional component side layer mixed powder (mixed powders No. A to No. N) is prepared by adjusting graphite powder, alloy element powder, hard particle powder, and solid lubricant particle powder (MnS powder) in an iron-based powder used for forming a matrix phase to the blending amounts shown in Table 1, and then mixing and kneading them. It should be noted that the iron-based powder used is a high-speed tool steel-based powder having the composition and hardness shown in Table 2. In addition, the hard particle powder used is a particle powder having the composition, hardness, and average particle diameter shown in Table 3. It should be noted that in the mixed powder, as a lubricant, 1 part by mass of zinc stearate is blended with respect to 100 parts by mass of the mixed powder.

[0154] In addition, the mixed powder for the support member side layer (mixed powders No. 1A and No. 1B) is prepared by adjusting the iron-based powder and graphite powder used for forming the matrix phase, or further adjusting the alloy element powder, hardness improvement particle powder, and solid lubricant particle powder to achieve the blending amounts shown in Table 1, and then mixing and kneading them. It should be noted that the iron-based powder used is the powder with the composition and hardness shown in Table 2. Iron-based powder No. c is pure iron powder. In addition, the hard particle powder used is the particle powder with the composition, hardness, and average particle diameter shown in Table 3. Hard particle powder No. h3 is a hardness improvement particle powder and is an iron-molybdenum alloy particle powder. It should be noted that in the mixed powder, as a lubricant, 1 part by mass of zinc stearate is blended relative to 100 parts by mass of the mixed powder. In addition, a part of the valve seat has a single-layer structure with only the functional member side layer.

[0155] [Table 1]

[0156]

[0157] *) Refer to Table 2

[0158] **) Refer to Table 3

[0159] [Table 2]

[0160]

[0161] [Table 3]

[0162]

[0163] The obtained mixed powder is filled into a mold and formed into a green compact with a specified valve seat shape by a stamping processing machine. For the obtained green compact, the density is measured by the Archimedes method and is 6.6 g / cm 3 The above.

[0164] Next, the obtained green compact is subjected to a sintering treatment. The sintering treatment is carried out in a reducing atmosphere and loaded into a sintering furnace set at a heating temperature of 1160 °C (holding time: 6 h) to form a sintered body.

[0165] The obtained sintered body is further processed by cutting, grinding, etc. to form an iron-based sintered alloy valve seat with a specified shape (outer diameter: 27 mm Φ × inner diameter 22 mm Φ × thickness 6 mm).

[0166] It should be noted that for a part of the obtained valve seat, resin impregnation treatment is further carried out using anaerobic resin. The resin impregnation treatment is carried out in a vacuum atmosphere. The valve seat is immersed in the liquid of the resin, and then further pressurized starting from atmospheric pressure to allow the resin to fully impregnate the pores. Then, the resin in the pores is cured by heating to seal the pores. It should be noted that the anaerobic resin used is a commercially available anaerobic resin.

[0167] Next, for the obtained valve seat, chemical analysis, microstructure observation, hardness test, density test, wear test, and radial compressive strength test are carried out. The test methods are as follows.

[0168] (1) Chemical analysis

[0169] Analysis specimens are collected from each part of the obtained valve seat, and the content of each component in each part is analyzed by emission spectrometry to determine the composition of the sintered body matrix part.

[0170] (2) Microstructure observation

[0171] For the obtained valve seat, the cross-section perpendicular to the axis is ground, corroded (corrosion solution: nitric acid ethanol solution) to reveal the microstructure, and observed with an optical microscope (magnification: 200 times). Using the obtained microstructure photos, the type of the matrix phase microstructure is determined, and the area ratio is obtained by image analysis. In addition, a scanning electron microscope (magnification: 2000 times) is used to observe the carbides precipitated in the matrix phase, and the particle size of the carbides is measured. It is confirmed that the maximum diameter of the carbide particle size is 10 μm or less, and the matrix phase is a fine carbide precipitation phase. In the case where the maximum diameter of the carbide particle size (long side length) exceeds 10 μm, it is only regarded as a carbide precipitation phase.

[0172] In addition, alloy diffusion occurs around the hard particles to form a high-alloy phase. The cross-section perpendicular to the axis is ground, corroded (corrosion solution: Marble solution) to reveal the microstructure, observed with an optical microscope (magnification: 200 times), and the tissue fraction (area ratio) is measured by image analysis.

[0173] (3) Hardness test

[0174] For the obtained valve seat, the cross-section perpendicular to the axis is ground, corroded (corrosion solution: nitric acid ethanol solution) to reveal the microstructure, and the Vickers hardness HV of the matrix phase is measured using a Vickers hardness tester (test force: 0.98 N (100 gf)).

[0175] (4) Density test

[0176] For the obtained valve seat (only the functional component side layer, only the support component side layer, and the double-layer structure), the density (sintered body density) is measured by the Archimedes method.

[0177] (5) Wear test

[0178] For the obtained valve seat, use Figure 1 the bench test machine shown in the figure to conduct a wear test under the test conditions shown below.

[0179] Test temperature: 150 °C, 250 °C (temperature on the seating side)

[0180] Test time: 12 hr

[0181] Cam rotation speed: 3000 rpm

[0182] Valve rotation speed: 20 rpm

[0183] Impact load: 700 N

[0184] Valve material: Heat-resistant steel with a nitride film (surface hardness of SUH35 is 1150 HV)

[0185] After the test, measure the wear amount of the test piece (valve seat). Based on the obtained wear amount, with valve seat No. 1 (existing example) as the reference (1.00), calculate the wear ratio of this valve seat.

[0186] (6) Radial compressive strength test

[0187] For the obtained valve seat (only the functional component side layer), according to the provisions of JIS Z 2507, obtain the radial compressive strength. Based on the obtained radial compressive strength, with valve seat No. 1 (existing example) as the reference (1.00), calculate the radial compressive strength ratio of this valve seat (functional component side layer). It should be noted that the radial compressive strength of valve seat No. 1 (existing example) is 490 MPa.

[0188] The obtained results are shown in Tables 4 and 5.

[0189]

[0190]

[0191]

[0192] Compared with the existing example (valve seat No. 1), for any one of the examples of the present invention, the sintered body density of the functional component side layer is increased, and further, the radial compressive strength ratio is high, the radial compressive strength (functional component side layer) is increased, and in addition, the wear ratio is low and the wear resistance is improved. It should be noted that the valve seat material for internal combustion engines (iron-based sintered alloy material) of the present invention can be expected to contribute to improving the wear resistance of valve seats for internal combustion engines using gas fuels such as LPG, CNG, hydrogen, and special fuels containing ethanol.

[0193] In addition, in the inventive examples (valve seats No. 17 and No. 18) where the pores were subjected to resin impregnation treatment, the radial compressive strength and wear resistance were improved compared to the conventional example (valve seat No. 1). The inventive example (valve seat No. 17) subjected to resin impregnation treatment showed the same radial compressive strength and wear resistance as the inventive example (valve seat No. 6) without resin impregnation treatment. By sealing the pores using resin impregnation treatment, a decrease in radial compressive strength and wear resistance is not accompanied, and an improvement in corrosion resistance can be expected.

[0194] Symbol Explanation

[0195] 1 Valve seat,

[0196] 2 Material equivalent to the cylinder block,

[0197] 3 Heating mechanism,

[0198] 4 Valve.

Claims

1. An iron-based sintered alloy valve seat for an internal combustion engine, which is a valve seat pressed into a cylinder head of an internal combustion engine, characterized in that: The valve seat has a single-layer structure consisting of a functional component side layer. The functional component side layer has a matrix phase composed of a fine carbide precipitation phase, and a structure in which 5.0 to 30.0% of a high alloy phase and 10.0 to 40.0% of hard particles are dispersed in the matrix phase, and 0 to 4.0% of solid lubricant particles are further dispersed. The hard particles have a hardness of 600 to 1200 HV in terms of Vickers hardness, and are Si-Cr-Mo series Co-based intermetallic compound particles having a composition, in mass %, of 2.2 to 2.7% Si, 7.5 to 9.5% Cr, 27.0 to 30.0% Mo, and the remainder of Co and inevitable impurities, or Si-Cr-Mo-Ni series Co-based intermetallic compound particles having a composition of 1.5 to 2.5% Si, 24.0 to 26.0% Cr, 23.0 to 26.0% Mo, 9.5 to 11.0% Ni, and the remainder of Co and inevitable impurities, The matrix portion including the matrix phase, the hard particles and the solid lubricant particles is composed of an iron-based sintered alloy material, the iron-based sintered alloy material comprising, in mass%, 0.50 to 2.80% C, further containing one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 3.00 to 11.00%, Mo: 3.00 to 17.00%, Ni: 1.00 to 8.50%, Co: 5.00 to 30.00%, V: 0.50 to 4.00%, W: 4.00 to 10.00%, and S: 0 to 2.00%, with the remainder being Fe and inevitable impurities. The density of the valve seat is 6.6-7.4 g / cm 3 .

2. An iron-based sintered alloy valve seat for an internal combustion engine, which is a valve seat pressed into a cylinder head of an internal combustion engine, characterized in that: The valve seat has a double-layer structure formed by integrally sintering a functional component side layer and a supporting component side layer. The functional component side layer has a matrix phase composed of a fine carbide precipitation phase, and a structure in which 5.0 to 30.0% of a high alloy phase and 10.0 to 40.0% of hard particles are dispersed in the matrix phase, and 0 to 4.0% of solid lubricant particles are further dispersed. The hard particles have a hardness of 600 to 1200 HV in terms of Vickers hardness, and are Si-Cr-Mo series Co-based intermetallic compound particles having a composition, in mass %, of 2.2 to 2.7% Si, 7.5 to 9.5% Cr, 27.0 to 30.0% Mo, and the remainder of Co and inevitable impurities, or Si-Cr-Mo-Ni series Co-based intermetallic compound particles having a composition of 1.5 to 2.5% Si, 24.0 to 26.0% Cr, 23.0 to 26.0% Mo, 9.5 to 11.0% Ni, and the remainder of Co and inevitable impurities, The matrix part including the matrix phase, the hard particles and the solid lubricant particles has a matrix part composition containing, in mass%, C: 0.50-2.80%, further containing one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 3.00-11.00%, Mo: 3.00-17.00%, Ni: 1.00-8.50%, Co: 5.00-30.00%, V: 0.50-4.00%, W: 4.00-10.00%, and S: 0-2.00%, and the balance is Fe and inevitable impurities, The supporting member side layer is composed of an iron-based sintered alloy material, the iron-based sintered alloy material having: a matrix phase composed of pearlite, a structure in which 0-4.0% of solid lubricant particles and 0-5.0% of hardness improving particles are dispersed in the matrix phase, and a matrix portion including the matrix phase, the solid lubricant particles and the hardness improving particles contains, by mass%, C: 0.30-2.00%, further contains Ni: 0-2.00%, Mo: 0-2.00%, Cu: 0-5.00%, Mn: 0-5.00% and S: 0-2.00%, and the balance is Fe and inevitable impurities, The density of the valve seat is 6.7-7.4 g / cm 3 .

3. The iron-based sintered alloy valve seat for internal combustion engines according to claim 1 or 2, characterized in that: The fine carbide precipitation phase is a phase of fine carbides having a precipitation particle size of 10 μm or less and having a hardness of 450 to 650 HV in terms of Vickers hardness.

4. The iron-based sintered alloy valve seat for internal combustion engines according to any one of claims 1 to 3, characterized in that: The solid lubricant particles are one or two selected from manganese sulfide MnS and molybdenum disulfide MoS2.

5. The iron-based sintered alloy valve seat according to any one of claims 2 to 4, characterized in that: The hardness improving particles are iron-molybdenum alloy particles.

6. The iron-based sintered alloy valve seat for internal combustion engines according to any one of claims 1 to 5, characterized in that: The pores of the iron-based sintered alloy material are impregnated with a thermosetting resin or an anaerobic resin.

7. A method for manufacturing an iron-based sintered alloy valve seat, which is a method for manufacturing an iron-based sintered alloy valve seat with a single-layer structure according to claim 1, characterized in that: After mixing and kneading a predetermined amount of iron-based powder, graphite powder, alloy element powder and hard particle powder, or further mixing a predetermined amount of solid lubricant powder to prepare a mixed powder, The mixed powder is filled into a mold of a predetermined shape and pressed to form a powder compact. After the powder compact is sintered in a protective atmosphere to obtain a sintered body, cutting or grinding is performed to produce a valve seat of a predetermined shape. The iron-based powder has a composition containing, by mass%, C: 0.2-0.8%, Si: 1.0% or less, Mn: 1.0% or less, Cr: 7.0% or less, Mo: 7.0% or less, V: 5.0% or less, W: 12.0% or less, or further contains Co: 12.0% or less, and the balance is Fe and inevitable impurities, and has a particle hardness of 170-280 HV in Vickers hardness, and the iron-based powder is added in an amount of 40.0-70.0% by mass relative to the total amount of the mixed powder, The hard particle powder has a hardness of 600 to 1200 HV in Vickers hardness, and has, in mass%, Si: 2.2 to 2.7%, Cr: 7.5 to 9.5%, Mo: 27.0 to 30.0%, and the balance is Co and inevitable impurities, or has a composition of Si: 1.5 to 2.5%, Cr: 24.0 to 26.0%, Mo: 23.0 to 26.0%, Ni: 9.5 to 11.0%, and the balance is Co and inevitable impurities, and the hard particle powder is added in an amount of 10.0 to 40.0% in mass % relative to the total amount of the mixed powder, The graphite powder is added in an amount of 0.5 to 2.0% by mass relative to the total amount of the mixed powder. The alloy element powder is added in an amount of 0 to 7.0% by mass relative to the total amount of the mixed powder, and the solid lubricant powder is further added in an amount of 0 to 4.0% by mass relative to the total amount of the mixed powder. So that the density of the powder compact reaches a density of 6.6 / cm 3 The stamping process is carried out in the above manner. The sintering process is performed at a sintering temperature of 1100 to 1200° C. to obtain the sintered body.

8. A method for manufacturing an iron-based sintered alloy valve seat, which is a method for manufacturing an iron-based sintered alloy valve seat with a double-layer structure according to claim 2, characterized in that: A specified amount of iron-based powder, graphite powder, alloy element powder and hard particle powder is added, or a specified amount of solid lubricant powder is further added, and mixed and kneaded to prepare a mixed powder for the side layer of the functional component. A predetermined amount of iron-based powder and graphite powder, or a predetermined amount of alloy element powder, hardness-improving particles and solid lubricant powder, is mixed and kneaded to prepare a mixed powder for the side layer of the supporting member. The mixed powder for the functional component side layer and the mixed powder for the supporting component side layer are sequentially filled into a mold of a specified shape, and a press process is performed to form a powder compact. Subsequently, the powder compact is sintered in a protective atmosphere to form a sintered body with a double-layer structure in which the functional component side layer and the supporting component side layer are sintered as a whole. Then, a cutting process or a grinding process is performed to manufacture a double-layer structure valve seat of a specified shape. In the mixed powder for the functional component side layer, the iron-based powder is a powder having a composition containing, by mass%, C: 0.2-0.8%, Si: 1.0% or less, Mn: 1.0% or less, Cr: 7.0% or less, Mo: 7.0% or less, V: 5.0% or less, and W: 12.0% or less, or further containing Co: 12.0% or less, and the balance being Fe and inevitable impurities, and having a particle hardness of 170-280 HV in Vickers hardness, and the iron-based powder is added in an amount of 40.0-70.0% by mass relative to the total amount of the mixed powder, The hard particle powder has a hardness of 600 to 1200 HV in Vickers hardness, and has, in mass%, Si: 2.2 to 2.7%, Cr: 7.5 to 9.5%, Mo: 27.0 to 30.0%, and the balance is Co and inevitable impurities, or has a composition of Si: 1.5 to 2.5%, Cr: 24.0 to 26.0%, Mo: 23.0 to 26.0%, Ni: 9.5 to 11.0%, and the balance is Co and inevitable impurities, and the hard particle powder is added in an amount of 10 to 40% by mass relative to the total amount of the mixed powder, 0.5 to 2.0% of the graphite powder is added in terms of mass % relative to the total amount of the mixed powder, 0 to 7.0% of the alloy element powder is added in terms of mass % relative to the total amount of the mixed powder, and 0 to 4.0% of the solid lubricant powder is added in terms of mass % relative to the total amount of the mixed powder. In the mixed powder for the supporting component side layer, the iron-based powder is pure iron powder, and is mixed with 0.5 to 2.0% of the graphite powder in terms of mass % relative to the total amount of the mixed powder for the supporting component side layer, and is mixed with 0 to 5.0% of the alloy element powder in terms of mass % relative to the total amount of the mixed powder for the supporting component side layer; the hardness-improving particle powder is iron-molybdenum alloy particle powder, and is mixed with 0 to 5.0% of the hardness-improving particle powder in terms of mass % relative to the total amount of the mixed powder for the supporting component side layer, and is mixed with 0 to 4.0% of the solid lubricant powder in terms of mass % relative to the total amount of the mixed powder for the supporting component side layer, The density of the powder compact reaches 6.6 g / cm 3 The above-mentioned stamping process is implemented in the above-mentioned manner. The sintering process is performed at a sintering temperature of 1100 to 1200° C. A sintered body with the double-layer structure is produced.

9. The method for manufacturing an iron-based sintered alloy valve seat according to claim 7 or 8, characterized in that: After the sintering treatment, a resin impregnation treatment of impregnating with a thermosetting resin or an anaerobic resin is further performed.

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