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

Abstract

Provided is an iron-based sintered alloy valve seat having excellent wear resistance and radial compressive strength. The sintered body is made of an iron-based sintered alloy having a double-layer structure in which a functional member-side layer and a support member-side layer are integrally sintered. A functional member-side layer of the sintered body made of an iron-based sintered alloy has a structure in which 5.0-30.0% by area of a high alloy phase, 10.0-40.0% by area of Si-Cr-Mo-Ni-based Fe-based intermetallic compound particles having a hardness of 700-1300 HV, and 0-4.0% by area of solid lubricant particles are dispersed in a matrix phase comprising a fine carbide precipitated phase. And a matrix part having a composition containing, in mass%, 0.50 to 2.80% of C, 1.80% or less of Si, 2.50% or less of Mn, 2.00 to 7.00% of Cr, 3.00 to 25.00% of Mo, 2.00 to 8.00% of Ni, 0 to 10.00% of Co, 0.50 to 4.00% of V, 4.00 to 10.00% of W, and 0 to 2.00% of S, with the balance being Fe. As a result, a valve seat having excellent radial compressive strength and excellent wear resistance can be produced.

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 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 and the like. Background Art

[0002] A valve seat is usually press-fitted into a cylinder head of an internal combustion engine and functions to seal combustion gases and cool the valve. The valve seat is struck by the valve and is subject to wear caused by sliding, heating caused by combustion gases, corrosion caused by combustion products, etc. Therefore, conventionally, 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 "a valve seat made of an iron-based sintered alloy for an internal combustion engine having excellent wear resistance". In the technology 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 having 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 realized.

[0004] In addition, Patent Document 2 describes a valve seat made of an iron-based sintered alloy. 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 has a porosity of 10 to 25% by volume and 6.1 to 7.1 g / cm 3The sintered density, and hard particles are dispersed in the matrix phase. The hard particles dispersed in the matrix phase 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%. It is composed of the following iron-based sintered alloy material: the composition of the matrix part containing the matrix phase and hard particles has a total of 10.0 to 40.0% by mass of one or more 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 an iron-based sintered alloy is proposed in Patent Document 3. The valve seat made of an iron-based sintered alloy described in Patent Document 3 is such a valve seat made of an iron-based sintered alloy, in which hard particles are dispersed in the matrix phase, and the overall composition has, by 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 an iron-based sintered alloy described in Patent Document 3, as the hard particles, Fe-Mo-Si alloy particles containing, by 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 was proposed in Patent Document 4. The hard particle-dispersed iron-based sintered alloy described in Patent Document 4 is a matrix containing 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% by weight percentage, with the balance being Fe, in which 3 to 20% of hard particles are dispersed based on the whole alloy and sintered. The hard particles contain Mo: 60 to 70%, B: 0.3 to 1%, C: 0.1% or less, and the balance being Fe hard particle-dispersed iron-based sintered alloy. If B is added to the ferromolybdenum-based hard particles, B improves the wettability of ferromolybdenum, prevents the hard particles from falling off 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 to contain a large amount of Co 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 generation of cracks when pressed into the cylinder head, easy falling off of particles when contacting the valve, and reduction of wear resistance. In addition, the iron-based sintered alloy valve seats described in Patent Documents 1 and 2 also have problems such as low Young's modulus and easy deformation, reduction of 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 likely to occur compared with the conventional Co-based hard particles. Therefore, it has been found that there is a problem that the hard particles fall off 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 an iron-based sintered alloy valve seat 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 the so-called "excellent radial compressive strength" means that 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 inventors 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 compaction 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, and as a result, the bonding force between particles decreases. Therefore, in the present invention, in order to perform sufficient powder compaction during powder compaction molding and to apply sufficient plastic deformation to the powder particles, it was conceived 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 decreases, and the wear resistance of the sintered body decreases. Therefore, considering increasing the amount of graphite powder added so that the carbon content of the sintered body does not decrease, and at the same time, 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 to 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 increased.

[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] 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

[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 is dispersed in the matrix phase at an area ratio of 5.0 to 30.0% and hard particles are dispersed at 10.0 to 40.0%, and further 0 to 4.0% of solid lubricant particles are dispersed.

[0025] The hard particles are Si-Cr-Mo-Ni series Fe-based intermetallic compound particles with a Vickers hardness of 700 to 1300 HV and a composition containing, by mass%, Si: 1.5 to 3.5%, Cr: 7.0 to 9.0%, Mo: 35.0 to 45.0%, Ni: 5.0 to 20.0%, and the balance being composed of Fe and inevitable impurities.

[0026] The matrix part containing the matrix phase, the high-alloy 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 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: 2.00 to 7.00%, Mo: 3.00 to 25.00%, Ni: 2.00 to 8.00%, Co: 0 to 10.00%, 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 dispersed in the functional component side layer are Si-Cr-Mo-Ni series Fe-based intermetallic compound particles with a Vickers hardness of 700 to 1300 HV and a composition containing, by mass%, Si: 1.5 to 3.5%, Cr: 7.0 to 9.0%, Mo: 35.0 to 45.0%, Ni: 5.0 to 20.0%, and the balance being composed of Fe and inevitable impurities.

[0032] Further, the matrix part including the matrix phase, the high-alloy phase, the hard particles, and the solid lubricant particles is made of an iron-based sintered alloy material, and the iron-based sintered alloy material contains C: 0.50 to 2.80% by mass, further contains one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 2.00 to 7.00%, Mo: 3.00 to 25.00%, Ni: 2.00 to 8.00%, Co: 0 to 10.00%, V: 0.50 to 4.00%, W: 4.00 to 10.00%, and S: 0 to 2.00%, and the balance is composed of Fe and inevitable impurities,

[0033] The support member side layer is made of an iron-based sintered alloy material, and the iron-based sintered alloy material has: a matrix phase, a structure in which solid lubricant particles with an area ratio of 0 to 4.0% and hardness improvement particles with an area ratio of 0 to 5.0% are dispersed in the matrix phase, and a matrix part including the matrix phase, the solid lubricant particles, and the hardness improvement particles contains C: 0.30 to 2.00% by mass, further contains 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 is 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 has a hardness of 450 to 650 HV measured by a Vickers hardness tester.

[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 iron-based sintered alloy valve seat according to any one of [2] to [4], characterized in that the hardness improvement particles are iron-molybdenum alloy particles.

[0038] [6] The iron-based sintered alloy valve seat for an internal combustion engine according to any one of [1] to [5], characterized in that 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 a ferrous sintered alloy, which is a method for manufacturing a valve seat made of a ferrous sintered alloy having a single-layer structure as described in [1], characterized in that,

[0040] After blending a specified amount of ferrous 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] The mixed powder is filled into a mold having a specified shape and subjected to stamping to form a compact body. Then,

[0042] After sintering the compact body in a reducing atmosphere to form a sintered body, cutting is performed, or further grinding is performed to manufacture a valve seat having a specified shape,

[0043] The ferrous powder is a ferrous powder having 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. The ferrous powder is blended in an amount of 40.0 to 70.0% by mass based on the total amount of the mixed powder,

[0044] The hard particle powder is Si-Cr-Mo-Ni-based Fe-based intermetallic compound particles having a hardness of 700 to 1300 HV as measured by a Vickers hardness tester, and having a composition containing Si: 1.5 to 3.5% by mass, Cr: 7.0 to 9.0% by mass, Mo: 35.0 to 45.0% by mass, Ni: 5.0 to 20.0% by mass, and the balance being composed of Fe and inevitable impurities. The hard particle powder is blended in an amount of 10.0 to 40.0% by mass based on the total amount of the mixed powder,

[0045] The graphite powder is blended in an amount of 0.5 to 2.0% by mass based on the total amount of the mixed powder,

[0046] The alloy element powder is blended in a total amount of 0 to 7.0% by mass based on the total amount of the mixed powder. Further,

[0047] The solid lubricant powder is blended in an amount of 0 to 4.0% by mass based on the total amount of the mixed powder,

[0048] The stamping is performed in such a manner that the density of the compact body reaches a density of 6.6 g / cm 3 or more.

[0049] The sintering treatment is carried out at a sintering temperature of 1100 to 1200 °C to obtain the sintered body.

[0050] [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

[0051] After mixing and kneading a specified amount of iron-based powder, graphite powder, alloy element powder, and hard particle powder, or further mixing and kneading a specified amount of solid lubricant powder, a mixed powder for the functional component side layer is prepared.

[0052] After mixing and kneading a specified amount of iron-based powder and graphite powder, or further mixing and kneading a specified amount of alloy element powder, hardness improvement particle powder, and solid lubricant particle powder, a mixed powder for the support component side layer is prepared.

[0053] When manufacturing a valve seat having a double-layer structure with a specified shape by sequentially filling the mixed powder for the functional component side layer and the mixed powder for the support component side layer into a mold with a specified shape, performing stamping to form a green compact, and then performing a sintering treatment on the green compact in a reducing atmosphere to form a sintered body in which the functional component side layer and the support component side layer are integrally sintered, and then performing cutting or further performing grinding,

[0054] In the mixed powder for the functional component side layer, the iron-based powder has 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 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% by mass of this iron-based powder is added based on the total amount of the mixed powder.

[0055] The hard particle powder has a hardness of 700 to 1300 HV as measured by a Vickers hardness tester and has a composition containing Si: 1.5 to 3.5% by mass, Cr: 7.0 to 9.0% by mass, Mo: 35.0 to 45.0% by mass, Ni: 5.0 to 20.0% by mass, and the balance is composed of Fe and unavoidable impurities, which is a Si-Cr-Mo-Ni-based Fe-based intermetallic compound particle. 10.0 to 40.0% by mass of this hard particle powder is added based on the total amount of the mixed powder.

[0056] 0.5 to 2.0% by mass of the graphite powder is added based on the total amount of the mixed powder.

[0057] Combined with the alloy element powder in an amount of 0 to 7.0% in total by mass based on the total amount of the mixed powder, and further combined with the solid lubricant particle powder in an amount of 0 to 4.0% in total by mass based on the total amount of the mixed powder,

[0058] In the mixed powder for the support member side layer, the iron-based powder is pure iron powder,

[0059] Combined with the graphite powder in an amount of 0.5 to 2.0% in total by mass based on the total amount of the mixed powder for the support member side layer,

[0060] Combined with the alloy element powder in an amount of 0 to 5.0% in total by mass based on the total amount of the mixed powder for the support member side layer,

[0061] The hardness improvement particle powder is Fe-Mo alloy powder, and combined with this hardness improvement particle powder in an amount of 0 to 5.0% in total by mass based on the total amount of the mixed powder for the support member side layer,

[0062] Combined with the solid lubricant particle powder in an amount of 0 to 4.0% in total by mass based on the total amount of the mixed powder for the support member side layer,

[0063] So that the density of the green compact reaches a density of 6.6 g / cm 3 or more, the stamping process is carried out in such a manner,

[0064] The sintering treatment is a treatment carried out at a sintering temperature of 1100 to 1200 °C,

[0065] A sintered body having a double-layer structure in which the functional member side layer and the support member side layer are integrally sintered is formed.

[0066] [9] The method for manufacturing an iron-based sintered alloy valve seat according to [7] or [8], characterized in that, after the sintering treatment, an impregnation treatment with a thermosetting resin or an anaerobic resin is further carried out.

[0067] Effects of the Invention

[0068] According to the present invention, an iron-based sintered alloy valve seat for an internal combustion engine having not only excellent wear resistance but also excellent radial compressive strength can be manufactured, and remarkable effects are exerted in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 An explanatory diagram showing the outline of a bench test machine. DETAILED DESCRIPTION

[0070] ​The valve seat of the present invention is a valve seat made of an iron-based sintered alloy having a single-layer structure with only a functional component side layer, or a valve seat made of an iron-based sintered alloy having a double-layer structure in which the functional component side layer and the support component side layer are integrally sintered.

[0071] First, the functional component side layer will be described.

[0072] 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, there is no reduction in wear resistance, the machinability and workability are improved, and at the same time an improvement in corrosion resistance can be expected.

[0073] It should be noted that the pores can also be obtained by calculation based on the true density and the density of the functional component side layer.

[0074] The matrix phase is a fine carbide precipitation phase.

[0075] 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, with a Vickers hardness tester. Due to the presence of such hard fine carbide precipitation phases, the matrix can be strengthened and the wear resistance is 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.

[0076] The high alloy phase dispersed in the matrix phase is a region where the alloy amount increases due to the diffusion of alloy elements from hard particles or additive elements during sintering. 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, preferably 280 HV or less, with 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 at an area ratio with respect to the entire structure. On the other hand, if the high alloy phase contains more than 30.0%, the strength of the valve seat decreases. Therefore, the high alloy phase is in the range of 5.0 to 30.0% by area ratio. It should be noted that it is preferably 10.0 to 20.0%.

[0077] In addition, the hard particles are hard particles having a Vickers hardness of 700 to 1300 HV. If the hardness of the hard particles is lower than 700 HV, the effect of improving the wear resistance is small. On the other hand, if it increases and exceeds 1300 HV, the machinability is reduced. Therefore, with a Vickers hardness tester, the hardness of the hard particles dispersed in the matrix phase is limited to the range of 700 to 1300 HV.

[0078] It should be noted that the hard particles are preferably particles having the above hardness and an average particle size of 10 to 150 μm. If the average particle size of the hard particles is less than 10 μm, over-diffusion is likely to occur during sintering. On the other hand, if it increases and exceeds 150 μm, the bonding force with the matrix is reduced and the wear resistance is reduced. Therefore, the average particle size 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 size" mentioned here refers to the particle size D50 at which the cumulative distribution measured by the laser scattering method reaches 50%.

[0079] In the present invention, based on the area ratio with respect to the entire structure, 10.0 to 40.0% of the hard particles having the above hardness are dispersed in the matrix phase. 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 the dispersion amount of the hard particles exceeds 40.0%, the bonding force with the matrix phase is reduced and the wear resistance is reduced. Therefore, based on the area ratio, the dispersion amount of the hard particles dispersed in the matrix phase is limited to the range of 10.0 to 40.0%.

[0080] Moreover, the hard particles are Si-Cr-Mo-Ni-based Fe-based intermetallic compound particles having a composition containing, by mass%, Si: 1.5 to 3.5%, Cr: 7.0 to 9.0%, Mo: 35.0 to 45.0%, Ni: 5.0 to 20.0%, and the balance being composed of Fe and inevitable impurities. By making the hard particles Fe-based intermetallic compound particles, the oxidation characteristics are significantly improved.

[0081] In addition, on 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 based on the area ratio with respect to the entire structure. By dispersing solid lubricant particles in the matrix phase, the machinability and lubricity are improved. However, if the solid lubricant particles are dispersed in an amount exceeding 4.0% based on the area ratio, the mechanical properties are significantly reduced. Therefore, based on the area ratio equivalent to the entire structure, 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.

[0082] In addition, the matrix part of the functional component side layer of the valve seat of the present invention, which contains a matrix phase, a high-alloy phase, hard particles, and 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: 2.00 to 7.00%, Mo: 3.00 to 25.00%, Co: 0 to 10.00%, Ni: 2.00 to 8.00%, V: 0.50 to 4.00%, W: 4.00 to 10.00%, further containing S: 0 to 2.00%, and the balance being composed of Fe and inevitable impurities.

[0083] Next, the reasons for limiting the composition of the matrix part of the functional component side layer will be described. It should be noted that hereinafter, mass% in the composition is only expressed as %.

[0084] C: 0.50 to 2.80%

[0085] C is an element necessary to adjust the matrix phase to a specified hardness or structure or to form 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 C is preferably 0.90 to 1.70%. When the pores are infiltrated with resin, C is preferably 2.30 to 2.60%.

[0086] Si: 1.80% or less

[0087] Si is an element mainly contained in the hard particles and constitutes an intermetallic compound. It increases the hardness of the hard particles and at the same time increases the matrix strength, thereby improving the wear resistance. Therefore, Si preferably contains 0.20% or more. On the other hand, if Si containing more than 1.80% is contained, the aggressiveness of the mating object increases. Therefore, Si is limited to 1.80% or less. It should be noted that it is preferably 0.50 to 1.00%.

[0088] Mn: 2.50% or less

[0089] 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 0.05% or more. On the other hand, if Mn containing more than 2.50% is contained, the hardness, toughness, and ductility of the matrix phase decrease. Therefore, Mn is limited to 2.50% or less. It should be noted that it is preferably 0.20 to 1.60%.

[0090] Cr: 2.00 to 7.00%

[0091] Cr is dissolved in the matrix phase. Additionally, carbides are formed, increasing the hardness of the matrix phase. At the same time, Cr is an element that contributes to increasing the hardness of hard particles as a constituent element of intermetallic compounds and is contained in the matrix part at 2.00% or more. On the other hand, if the content of Cr exceeds 7.00%, the precipitation of Cr carbides in the matrix phase becomes excessive, making it difficult to form fine carbides in the matrix phase. Therefore, the content of Cr is limited to the range of 2.00 - 7.00%. It should be noted that the preferred range is 3.00 - 6.00%.

[0092] Mo: 3.00 - 25.00%

[0093] Mo is dissolved in the matrix phase. Additionally, it precipitates as carbides, increasing 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 the content of Mo exceeds 25.00%, it is difficult to increase the density during powder molding, and the formability decreases. Therefore, the content of Mo is limited to the range of 3.00 - 25.00%. It should be noted that the preferred range is 7.00 - 23.00%.

[0094] Co: 0 - 10.00%

[0095] Co is an element that increases the strength of the matrix phase, especially the high-temperature strength, further improves the toughness of the matrix phase, and contributes to the formation of high-alloy phases. It can be contained as needed. When Co is contained, it is preferably contained at 1.00% or more. On the other hand, if the content of Co exceeds 10.00%, no improvement in the effect can be expected. Therefore, when Co is contained, it is limited to 10.00% or less. It should be noted that the preferred range is 1.00 - 5.00%.

[0096] Ni: 2.00 - 8.00%

[0097] 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. Additionally, Ni is an element that contributes to increasing the toughness of hard particles as a constituent element of intermetallic compounds and is contained at 2.00% or more. On the other hand, if the content of Ni exceeds 8.00%, it is difficult to increase the density during powder molding, reducing the formability. Therefore, the content of Ni is limited to the range of 2.00 - 8.00%. It should be noted that the preferred range is 3.00 - 7.00%.

[0098] V: 0.50 - 4.00%

[0099] V precipitates as fine carbides, increasing the hardness of the matrix phase and thus improving wear resistance. It is required to contain 0.50% or more. On the other hand, if the content of V exceeds 4.00%, the formability will decrease. Therefore, V is limited to the range of 0.50 - 4.00%. It should be noted that the preferred range is 1.00 - 3.00%.

[0100] W: 4.00 - 10.00%

[0101] W precipitates as fine carbides, increasing the hardness of the matrix phase and thus improving wear resistance. It is required to contain 4.00% or more. On the other hand, if the content of W exceeds 10.00%, the formability will decrease. Therefore, W is limited to the range of 4.00 - 10.00%. It should be noted that the preferred range is 3.00 - 7.00%.

[0102] 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 - 2.00% can be contained.

[0103] S: 0 - 2.00%

[0104] S is contained in the solid lubricant particles and included in the matrix part, which helps to improve machinability and can be contained as needed. If the content of S exceeds 2.00%, the toughness and ductility will decrease. Therefore, S is preferably limited to the range of 0 - 2.00%.

[0105] The balance except for the above components is composed of Fe and inevitable impurities. It should be noted that as inevitable impurities, P of 0.10% or less is allowable.

[0106] Next, the support component 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 component side layer of the double-layer structure is the same as that of the above single-layer structure. Moreover, the support component side layer when made into a double-layer structure only needs to be able to hold the functional component side layer and does not need to be particularly limited. It should be noted that in the matrix phase, solid lubricant particles that improve machinability can also 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 component 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 the solid lubricant particles are dispersed in an area ratio exceeding 4.0%, the effect is saturated and the effect commensurate with the dispersion amount cannot be expected. Therefore, in the case of dispersion, the solid lubricant particles are preferably limited to 4.0% or less in terms of the area ratio. It should be noted that the matrix phase of the support component side layer is pearlite.

[0107] Further, in the matrix phase of the support member side layer, in order to increase the strength of the matrix phase, hardness improving particles may be dispersed in an area ratio of 0 to 5.0%. Examples of the hardness improving particles dispersed in the support member side layer include iron-molybdenum (Fe-Mo) based alloys. Since the effect saturates even when the hardness improving particles are dispersed in an area ratio exceeding 5.0%, the upper limit is 5.0%.

[0108] The support member side layer has a structure in which solid lubricant particles and hardness improving particles are dispersed in the matrix phase as needed. The balance other than the matrix phase, solid lubricant particles, and hardness improving particles is pores. 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 them with a thermosetting resin or an anaerobic resin, a significant reduction in wear resistance is not accompanied, the cutting performance and machinability are improved, and an improvement in corrosion resistance can be expected.

[0109] Moreover, it is further preferable that the matrix portion of the support member side layer of the valve seat of the present invention, which contains the matrix phase, solid lubricant particles, and hardness improving particles, has a composition containing C: 0.30 to 2.00% by mass, 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 unavoidable impurities.

[0110] The reasons for limiting the composition of the matrix portion of the support member side layer will be described.

[0111] C is contained in an amount of 0.30% or more to ensure the desired strength. On the other hand, if the content exceeds 2.00%, the strength becomes too high and the toughness decreases. Therefore, C is preferably limited to the range of 0.30 to 2.00%. C is preferably 0.30 to 1.20%. When the pores are impregnated with a resin, C is preferably 1.40 to 1.80%. It should be noted that the matrix portion 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% in addition to the above C.

[0112] 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, Mn, and 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.

[0113] The balance other than the above components consists of Fe and unavoidable impurities. As unavoidable impurities, P: 0.10% or less is allowable.

[0114] Next, a method for manufacturing the iron-based sintered alloy valve seat of the present invention will be described.

[0115] 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 blended in such a way as to form the above matrix part composition, or further a prescribed amount of solid lubricant particle powder is blended, and then they are mixed and kneaded to form a mixed powder (mixed powder for the functional component side layer).

[0116] The iron-based powder blended in the mixed powder (mixed powder for the functional component side layer) is a powder blended to form the matrix phase, and in the present invention, it is an alloy steel powder that can make the matrix phase a structure composed of fine carbide precipitation phases. As such an alloy steel powder, powders whose composition conforms to the high-speed tool steel composition specified in JIS G 4403 can be exemplified, but of course it is not limited thereto.

[0117] The blended 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, in mass%, or further contains Co: 12.0% or less, and the balance consists of Fe and unavoidable impurities, and has a particle hardness of 170 to 280 HV as measured by a Vickers hardness tester. The iron-based powder blended in the present invention is a powder of a high-speed steel composition with reduced C.

[0118] First, the reasons for limiting the composition of the iron-based powder will be described. Hereinafter, mass% in the composition is only expressed as %.

[0119] C: 0.2 to 0.8%

[0120] If C is less than 0.2%, the melting point increases, making it difficult to manufacture the powder. 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 within the range of 0.2 to 0.8%. It should be noted that it is more preferably 0.4 to 0.6%.

[0121] Si: 1.0% or less

[0122] Si is an element that affects the fluid flow during powder manufacturing (manufacturing atomized powder). In order to obtain such an effect, it becomes significant when Si is contained in an amount of 0.3% or more. On the other hand, if Si is contained in an amount exceeding 1.0%, the compressibility decreases. Therefore, Si is preferably limited to 1.0% or less. It should be noted that it is more preferably 0.5% or less.

[0123] Mn: 1.0% or less

[0124] Mn acts as a deoxidizer and at the same time contributes to an increase in strength (hardness). Such an effect becomes significant when the content is 0.10% or more. On the other hand, if the content exceeds 1.0%, the oxygen concentration of the powder increases and the diffusivity during sintering decreases. In addition, if Mn is contained in an amount exceeding 1.0%, the hardness increases and the compressibility decreases. Therefore, Mn is preferably limited to 1.0% or less.

[0125] Cr: 7.0% or less

[0126] Cr is an element that forms carbides and has the effect of improving wear resistance. Such an effect becomes significant when Cr is contained in an amount of 0.1% or more, but if the content exceeds 7.0%, the toughness decreases. Therefore, Cr is preferably limited to 7.0% or less.

[0127] Mo: 7.0% or less

[0128] Mo is an element that forms fine carbides and has the effect of improving wear resistance. Such an effect becomes significant when Mo is contained in an amount of 2.0% or more, 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 it is more preferably 2.0 to 5.0%.

[0129] V: 5.0% or less

[0130] V is an element that forms fine carbides and has the effect of improving wear resistance. Such an effect becomes significant when V is contained in an amount of 2.0% or more, 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 it is more preferably 2.0 to 4.0%.

[0131] W: 12.0% or less

[0132] 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, W is preferably limited to 12.0% or less.

[0133] In addition to the above components, Co may be contained as needed: 12.0% or less.

[0134] Co: 0 - 12.0%

[0135] 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.

[0136] 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.

[0137] Particle hardness: 170 - 280 HV

[0138] 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.

[0139] In addition, the hard particle powder incorporated in the mixed powder is an Si-Cr-Mo-Ni-based Fe-based intermetallic compound particle powder having the above hardness and composition. In the present invention, such a hard particle powder is incorporated in an amount of 10.0 - 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 a particle powder having an average particle size of 10 - 150 μm. If the average particle size of the particles is less than 10 μm, over-diffusion easily occurs during sintering, and the desired wear resistance cannot be ensured. On the other hand, if the average particle size of the particles exceeds 150 μm, the bonding force with the matrix decreases. It should be noted that the "average particle size" mentioned here means the particle size D50 at which the cumulative distribution measured by the laser scattering method reaches 50%.

[0140] In addition, solid lubricant particles are incorporated to improve machinability, workability, and lubricity. As the solid lubricant particles, MnS, MoS2, etc. are preferably used. The blending amount of the solid lubricant particle powder is preferably 0 to 4.0% by mass based on the total amount of the mixed powder.

[0141] It should be noted that in the mixed powder, it goes without saying that a specified 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 alloy element powder to be incorporated, Ni powder and Co powder can be exemplified. It should be noted that lubricants such as zinc stearate can also be incorporated in the mixed powder.

[0142] As described above, a specified amount of graphite powder, alloy element powder, and hard particle powder is further incorporated into the iron-based powder, or a specified amount of solid lubricant particle powder is further incorporated, and they are mixed and kneaded to produce a mixed powder.

[0143] Next, the obtained mixed powder is filled into a mold having a specified valve seat shape.

[0144] After the mixed powder is filled into the mold, it is subjected to stamping by a stamping machine or the like to produce a compact in the shape of a valve seat. It should be noted that the stamping is preferably adjusted so that the density of the compact reaches 6.6 g / cm 3 or more.

[0145] Next, the obtained compact is sintered to produce a sintered body.

[0146] The sintering treatment is preferably a treatment of maintaining for 0.5 hours or more in a reducing atmosphere such as nitrogen, hydrogen, or ammonia-decomposed gas at a heating temperature in the range 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 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.).

[0147] The obtained sintered body is subjected to machining such as grinding and cutting to produce a valve seat (single-layer structure) having a desired size and shape.

[0148] It should be noted that it is preferable to perform a resin impregnation treatment on the valve seat (product) obtained through the above-mentioned processes. The resin impregnation treatment is preferably a treatment of impregnating the valve seat in a liquid of a thermosetting resin or an anaerobic resin in a vacuum atmosphere, then further pressurizing from atmospheric pressure to allow the resin to fully penetrate into the pores, and then heating to cure the resin in the pores for sealing.

[0149] Next, in the method for manufacturing the valve seat made of the double-layered iron-based sintered alloy of the present invention, in addition to the above-mentioned mixed powder (the mixed powder for the functional component side layer), a mixed powder for the support component side layer is also prepared.

[0150] The mixed powder for the support component side layer is made by mixing and kneading a prescribed amount of iron-based powder and graphite powder, or further mixing a prescribed amount of alloy element powder, hardness improvement particle powder, and solid lubricant powder. In the mixed powder for the support component side layer, the iron-based powder is pure iron powder. Graphite powder is mixed in an amount of 0.5 to 2.0% by mass based on the total amount of the mixed powder for the support component side layer. Alloy element powder is mixed in a total amount of 0 to 5.0% by mass based on the total amount of the mixed powder for the support component side layer. It should be noted that as the alloy element powder to be mixed, Mo powder, Ni powder, and Cu powder are preferably used. In addition, the hardness improvement particle powder is iron-molybdenum (Fe-Mo) alloy particle powder, and this hardness improvement particle powder is mixed in an amount of 0 to 5.0% by mass based on the total amount of the mixed powder for the support component side layer. Solid lubricant powder is mixed in an amount of 0 to 4.0% by mass based on the total amount of the mixed powder for the support component side layer.

[0151] Then, 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 having a prescribed shape at a desired ratio.

[0152] After filling into the mold, stamping is performed in the same manner as in the case of the above-mentioned single-layer structure to form a green compact, and then sintering treatment is performed on the green compact in the same manner as in the case of the above-mentioned single-layer structure to obtain a double-layered sintered body.

[0153] The obtained sintered body is subjected to processing such as grinding and cutting to form a valve seat having a double-layered structure with a desired size and shape.

[0154] In the obtained valve seat having a double-layered structure, it is also preferable to perform a resin impregnation treatment of impregnating a thermosetting resin or an anaerobic resin into the pores in the same manner as in the case of the above-mentioned single-layered valve seat. The pores of the single-layered and double-layered valve seats (iron-based sintered alloy materials) subjected to the resin impregnation treatment are impregnated with a thermosetting resin or an anaerobic resin.

[0155] Hereinafter, the present invention will be further described based on examples.

[0156] Examples

[0157] First, a mixed powder for the functional component side layer and a mixed powder for the support component side layer are prepared.

[0158] The mixed powder for the functional component side layer is prepared by adjusting the graphite powder, alloy element powder, hard particle powder, and solid lubricant particle powder (MnS powder) in the iron-based powder used to form the matrix phase to achieve the compounding amounts shown in Table 1, and then mixing and kneading them. It should be noted that the iron-based powder used is the high-speed tool steel-based powder with the composition and hardness shown in Table 2. In addition, the hard particle powder used is the particle powder with the composition, hardness, and average particle diameter shown in Table 3.

[0159] The mixed powder for the support component side layer is prepared by adjusting the iron-based powder and graphite powder used to form the matrix phase, or further adjusting the alloy element powder, hard particle powder, and solid lubricant particle powder to achieve the compounding 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.d 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. Here, hard particle powder No.h3 is a hardness-improving particle powder, which is an iron-molybdenum (ferromolybdenum) alloy particle powder. It should be noted that in the mixed powder, as a lubricant, 1 part by mass of zinc stearate is compounded relative to 100 parts by mass of the mixed powder. A part of the valve seat has a single-layer structure with only the functional component side layer.

[0160] [Table 1]

[0161]

[0162] *) Refer to Table 2

[0163] **) Refer to Table 3

[0164] [Table 2]

[0165]

[0166] [Table 3]

[0167]

[0168] 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. The density of the obtained green compact is 6.6 g / cm 3 or more.

[0169] Next, the obtained green compact is subjected to a sintering treatment. The sintering treatment is carried out in a reducing atmosphere by loading it into a sintering furnace set at a heating temperature of 1160 °C (holding time: 6 h) to form a sintered body.

[0170] The obtained sintered body is further processed by cutting, grinding, etc. to produce an iron-based sintered alloy valve seat with a specified shape (outer diameter: 27 mm Φ × inner diameter 22 mm Φ × thickness 6 mm).

[0171] It should be noted that for a part of the obtained valve seat, a resin impregnation treatment is further carried out using an anaerobic resin. The resin impregnation treatment is carried out by immersing the valve seat in the liquid of the resin in a vacuum atmosphere, then further pressurizing from atmospheric pressure to allow the resin to fully infiltrate into the pores, and then heating to cure the resin in the pores for hole sealing. It should be noted that the resin used is a commercially available anaerobic resin.

[0172] 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.

[0173] (1) Chemical analysis

[0174] Analysis samples 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.

[0175] (2) Microstructure observation

[0176] 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 observed microstructure photos, the type of the matrix phase microstructure is determined, and the area ratio relative to the whole microstructure is measured. 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.

[0177] 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 relative to the whole microstructure) is measured by image analysis.

[0178] (3) Hardness test

[0179] 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)).

[0180] (4) Density test

[0181] For the obtained valve seats (only the functional component side layer, only the support component side layer, and the double-layer structure), the density (sintered body density) was measured using the Archimedes method.

[0182] (5) Wear test

[0183] For the obtained valve seats, the Figure 1 shown bench test machine was used to conduct a wear test under the test conditions shown below.

[0184] Test temperature: 150 °C, 250 °C (seating side temperature)

[0185] Test time: 12 hr

[0186] Cam rotation speed: 3000 rpm

[0187] Valve rotation speed: 20 rpm

[0188] Impact load: 700 N

[0189] Valve material: Heat-resistant steel with a nitride film (SUH35 surface hardness 1150 HV)

[0190] After the test, the wear amount of the test piece (valve seat) was measured. Based on the obtained wear amount, with valve seat No. 1 (existing example) as the reference (1.00), the wear ratio of this valve seat was calculated.

[0191] (6) Radial compressive strength test

[0192] For the functional component side layer of the obtained valve seat, according to the provisions of JIS Z 2507, the radial compressive strength was obtained. Based on the obtained radial compressive strength, with valve seat No. 1 (existing example) as the reference (1.00), the radial compressive strength ratio of the functional component side layer of this valve seat was calculated. It should be noted that the radial compressive strength of the functional component side layer of valve seat No. 1 (existing example) is 490 MPa.

[0193] The obtained results are shown in Tables 4 and 5.

[0194]

[0195]

[0196]

[0197] In any of the examples of the present invention, compared with the existing example (valve seat No. 1), the sintered body density of the functional component side layer is increased. Further, the ratio of the radial compressive strength is high, the radial compressive strength is increased, the wear is relatively low, and the wear resistance is improved. It should be noted that the valve seat material for an internal combustion engine of the present invention can be expected to contribute to improving the wear resistance of the valve seat for an internal combustion engine using gaseous fuels such as LPG, CNG, and hydrogen, as well as special fuels containing ethanol and the like.

[0198] In addition, compared with the existing example (valve seat No. 1), the example of the present invention (valve seat No. 17) in which the pores are subjected to resin impregnation treatment has an increased radial compressive strength and an improved wear resistance. Further, the example of the present invention (valve seat No. 17) in which the resin impregnation treatment is performed exhibits the same radial compressive strength and wear resistance as the example of the present invention (valve seat No. 6) in which the resin impregnation treatment is not performed. By sealing the pores by using the resin impregnation treatment, a decrease in the radial compressive strength or the wear resistance is not accompanied, and an improvement in the corrosion resistance can be expected.

[0199] Symbol Explanation

[0200] 1 Valve seat,

[0201] 2 Material equivalent to the cylinder block,

[0202] 3 Heating mechanism,

[0203] 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 are Si-Cr-Mo-Ni based Fe-based intermetallic compound particles having a hardness of 700 to 1300 HV in terms of Vickers hardness and containing, by mass%, 1.5 to 3.5% Si, 7.0 to 9.0% Cr, 35.0 to 45.0% Mo, 5.0 to 20.0% Ni, and the balance being Fe and unavoidable impurities. The matrix portion including the matrix phase, the high alloy phase, the hard particles and the solid lubricant particles is composed of an iron-based sintered alloy material, the iron-based sintered alloy material having a matrix portion consisting of 0.50-2.80% C, further containing one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 2.00-7.00%, Mo: 3.00-25.00%, Ni: 2.00-8.00%, Co: 0-10.00%, V: 0.50-4.00%, W: 4.00-10.00% and S: 0-2.00%, and the balance is Fe and inevitable impurities, The 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 dispersed in the functional component side layer are Si-Cr-Mo-Ni based Fe-based intermetallic compound particles having a hardness of 700 to 1300 HV in terms of Vickers hardness and containing, by mass%, Si: 1.5 to 3.5%, Cr: 7.0 to 9.0%, Mo: 35.0 to 45.0%, Ni: 5.0 to 20.0%, and the balance being Fe and unavoidable impurities, Furthermore, the matrix portion including the matrix phase, the high alloy phase, the hard particles and the solid lubricant particles is composed of an iron-based sintered alloy material, the iron-based sintered alloy material having a matrix portion consisting of 0.50-2.80% C, further containing one or more selected from Si: 1.80% or less, Mn: 2.50% or less, Cr: 2.00-7.00%, Mo: 3.00-25.00%, Ni: 2.00-8.00%, Co: 0-10.00%, 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, a structure in which solid lubricant particles with an area ratio of 0 to 4.0% and hardness improving particles with an area ratio of 0 to 5.0% 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 to 2.00%, further contains 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 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 700 to 1300 HV in Vickers hardness, and has Si-Cr-Mo-Ni system Fe-based intermetallic compound particles having a composition of 1.5 to 3.5% Si, 7.0 to 9.0% Cr, 35.0 to 45.0% Mo, 5.0 to 20.0% Ni, and the balance Fe and inevitable impurities, and the hard particle powder is added in an amount of 10.0 to 40.0% by 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 further The solid lubricant powder is added in an amount of 0 to 4.0% by mass relative to the total amount of the mixed powder. The density of the powder compact reaches 6.6 g / 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 is Si-Cr-Mo system Fe-based intermetallic compound particles having a hardness of 700 to 1300 HV in Vickers hardness and having a composition consisting of Si: 1.5 to 3.5%, Cr: 7.0 to 9.0%, Mo: 35.0 to 45.0% by mass, and the balance consisting of Fe and inevitable impurities, or Si-Cr-Mo-Ni system Fe-based intermetallic compound particles having a composition consisting of Si: 1.5 to 3.5%, Cr: 7.0 to 9.0%, Mo: 35.0 to 45.0%, Ni: 5.0 to 20.0% by mass, and the balance consisting of Fe and inevitable impurities, and the hard particle powder is added in an amount of 10.0 to 40.0% by 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. In the mixed powder for the supporting member side layer, the iron-based powder is pure iron 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 for the supporting member side layer. The alloy element powder is added in an amount of 0 to 5.0% by mass relative to the total amount of the mixed powder for the supporting member side layer. The hardness-improving particle powder is an iron-molybdenum alloy powder, and the hardness-improving particle powder is mixed in an amount of 0 to 5.0% by mass relative to the total amount of the mixed powder for the supporting member side layer. The solid lubricant powder is added in an amount of 0 to 4.0% by mass relative to the total amount of the mixed powder for the supporting member side layer. The density of the powder compact reaches 6.6 g / 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. A sintered body having a double-layer structure is produced by integrally sintering the functional component side layer and the supporting component side layer.

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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