Valve seat with superior wear resistance, and combination of valve and valve seat

Abstract

Provided are a valve seat that is made of an iron-based sintered alloy and has superior wear resistance, and a combination of a valve seat and a valve.　This valve seat that is made of an iron-based sintered alloy has a structure in which the base phase is a fine carbide precipitation phase in which an area ratio of 15-40% pearlite and fine carbides of 10 μm or less are precipitated, hard particles with a Vickers hardness of 650-1300 HV are dispersed in the base phase in an area ratio of 20-40%, the structure further has a high alloy phase in an area ratio of 0-5%, and solid lubricant particles are dispersed in an area ratio of 0-5%. Consequently, there is little valve wear even when a Tribaloy-based alloy-metallized valve with a face surface hardness of 550 HV is used, and a combination of a valve and a valve seat that has superior wear resistance can be achieved.

Description

Valve seats and valve / valve seat combinations with excellent wear resistance

[0001] The present invention relates to a valve seat for an internal combustion engine, and more particularly to improving the wear resistance of the valve seat and reducing the valve attack.

[0002] In recent years, the fuels used in internal combustion engines have become more diverse, including gasoline, heavy oil, and special fuels such as gas and ethanol. It is expected that different fuels will result in different combustion conditions, such as different combustion temperatures and generated combustion gases, and that the operating environment of the internal combustion engine will also be different. For example, when gas fuel is used, it is expected that it will be difficult to generate combustion products, creating an environment in which wear due to metal-to-metal contact is more likely to progress.

[0003] Valve seats for internal combustion engines have traditionally been required to have excellent heat resistance and wear resistance. In recent years, there has been an increasing demand for higher performance, improved fuel efficiency, and cleaner exhaust gases from internal combustion engines, and the operating conditions for automotive internal combustion engines have become more severe, resulting in the problem that conventional valve seats do not have the required characteristics.

[0004] To address these issues, for example, Patent Document 1 proposes a valve seat made of an iron-based sintered alloy in which hard particles and solid lubricant particles are dispersed in a matrix phase. In this valve seat, the matrix phase is a fine carbide precipitate phase in which fine carbides with a particle size of 10 μm or less are precipitated, resulting in a Vickers hardness of 550 HV or more. Furthermore, the matrix phase is dispersed with 20 to 40% hard particles with a hardness of 650 to 1200 HV, with an area ratio of 5% or less of a diffusion phase formed around the hard particles, and with an area ratio of 0 to 5% solid lubricant particles dispersed. According to the technology described in Patent Document 1, even when a valve with a high face hardness is used in a harsh environment, the valve seat suffers little wear from the opposing valve seat, resulting in a valve seat with excellent wear resistance.

[0005] JP 2018-90900 A

[0006] However, recently, there has been a demand for alternative fuels such as gas or alcohol-containing fuels in compressed natural gas (CNG) and flexible-fuel vehicles (FFVs). In such environments, the valves used are often made of Tribaloy alloys with a surface hardness (valve face hardness) adjusted to 550 HV or higher.

[0007] It was also discovered that when a triballoy-based alloy-plated valve adjusted to such hardness is used in combination with various valve seats, the triballoy-based alloy-plated valve may be subject to significant wear.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a valve seat which is excellent in wear resistance and which is less likely to attack valves plated with Triballoy alloys, and a combination of a valve seat and a valve which is excellent in wear resistance.

[0009] In order to achieve the above-mentioned objectives, the influence of valve seats on the valve wear of valves plated with Triballoy-based alloys was investigated. As a result, it was discovered that a valve seat structure containing an appropriate amount of soft pearlite in a hard phase is effective in improving the valve wear resistance of valves plated with Triballoy-based alloys.

[0010] The present invention was completed based on these findings and through further investigation. That is, the gist of the present invention is as follows: [1] An iron-based sintered alloy valve seat for internal combustion engines having a single-layer structure consisting of a functional component-side layer, wherein the functional component-side layer is formed by dispersing hard particles and solid lubricant particles in a matrix phase, the matrix phase being composed of 15 to 40% pearlite in area ratio and a fine carbide precipitate phase having a Vickers hardness of 400 HV or more and in which 15 to 55% by area of ​​fine carbides having a particle size of 10 μm or less are precipitated, the hard particles having a Vickers hardness of 650 to 1300 HV, the hard particles being dispersed in the matrix phase in an area ratio of 20 to 40%, and the iron-based sintered alloy valve seat having excellent wear resistance and low valve attacking properties, characterized in that it has a structure in which 0 to 5% of a high alloy phase and 0 to 5% of the solid lubricant particles are dispersed. [2] A valve seat made of an iron-based sintered alloy having a two-layer structure in which a functional member-side layer and a support member-side layer are sintered together, wherein the functional member-side layer is formed by dispersing hard particles and solid lubricant particles in a matrix phase, the matrix phase being composed of 15 to 40% pearlite in area ratio and 15 to 55% fine carbide precipitate phase having a Vickers hardness of 400 HV or more in which fine carbides having a particle size of 10 μm or less are precipitated, and the hard particles are hard particles having a Vickers hardness of 650 to 1300 HV. and wherein the support member side layer has a structure in which the hard particles are dispersed in the matrix phase at an area ratio of 20 to 40%, and further has a high alloy phase at an area ratio of 0 to 5%, and the solid lubricant particles are dispersed at an area ratio of 0 to 5%, and the support member side layer has a structure in which the matrix phase has dispersed therein 0 to 4% of solid lubricant particles and 0 to 5% of hardness improving particles at an area ratio of 0 to 5%.[3] A valve seat made of an iron-based sintered alloy for an internal combustion engine according to [1] or [2], characterized in that the matrix portion of the functional component side layer, which includes the matrix phase, the hard particles, the high alloy phase, and the solid lubricant particles, contains, by mass%, C: 0.5 to 2.0%, Si: 0.5 to 2.0%, Mn: 5% or less, Cr: 2 to 15%, Mo: 5 to 20%, Co: 2 to 30%, and further contains one or more elements selected from V: 0 to 5%, Ni: 0 to 5%, S: 0 to 2%, and Cu: 0 to 5%, with the balance being Fe and unavoidable impurities. [4] The iron-based sintered alloy valve seat for an internal combustion engine according to [2], characterized in that the matrix portion of the support member side layer, which includes the matrix phase, the solid lubricant particles, and the hardness improver particles, contains, in mass %, C: 0.3 to 1.3%, and further contains Ni: 0 to 2%, Mo: 0 to 2%, Cu: 0 to 5%, Mn: 0 to 5%, and S: 0 to 2%, with the remainder being Fe and unavoidable impurities. [5] The valve seat made of an iron-based sintered alloy for an internal combustion engine according to [1] or [2], wherein the hard particles are Cr-Mo-Co intermetallic compound particles containing, by mass, 20-40% Mo, 3.5-15% Cr, 0-3% Si, and 0-3% Fe, with the balance being Co and unavoidable impurities, or Cr-Mo-Ni-Fe intermetallic compound particles containing, by mass, 35-45% Mo, 7-9% Cr, 5-20% Ni, and 1.5-3.5% Si, with the balance being Fe and unavoidable impurities. [6] The valve seat made of an iron-based sintered alloy for an internal combustion engine according to [1] or [2], wherein the solid lubricant particles are either manganese sulfide (MnS) or molybdenum disulfide (MoS2). [7] The valve seat made of an iron-based sintered alloy for an internal combustion engine according to [2], wherein the hardness-improving particles are iron-molybdenum alloy particles. [8] A combination of a valve and a valve seat, wherein the valve is a Triballoy alloy overlaid valve having a surface hardness of 550 HV or more on the contact surface with the valve seat, and the valve seat is a valve seat made of an iron-based sintered alloy for an internal combustion engine as described in [1] or [2].

[0011] According to the present invention, even when Tribaloy alloy-plated valves are used as valves in internal combustion engines in environments using special fuels, valve wear is not increased and wear on the valve seat is also reduced, making it possible to realize a combination of valve and valve seat with excellent wear resistance, which has significant industrial benefits.

[0012] FIG. 1 is an explanatory diagram showing an overview of a rig testing machine.

[0013] The functional component-side layer of the iron-based sintered alloy valve seat of the present invention has a structure in which hard particles, or further solid lubricant particles, are dispersed in a matrix phase, and the matrix phase is made up of a hard fine carbide precipitate phase having a Vickers hardness of 400 HV or more and pearlite having a Vickers hardness of 200 HV or more but less than 400 HV.

[0014] If the hardness of the hard fine carbide precipitate phase of the matrix phase is less than 400 HV, adhesion is likely to occur upon contact with valves, especially valves with high surface hardness, making it impossible to ensure the desired wear resistance. On the other hand, if the hardness exceeds 700 HV, the toughness of the sintered body decreases. For this reason, the hardness of the hard fine carbide precipitate phase of the matrix phase is limited to a Vickers hardness of 400 HV or more, preferably 700 HV or less. The Vickers hardness is preferably 500 to 650 HV. Furthermore, pearlite is softer than the fine carbide precipitate phase, and preferably has a Vickers hardness of 200 HV or more but less than 400 HV.

[0015] The matrix phase with this hardness has a structure consisting of 15-40% pearlite by area and 15-55% fine carbide precipitate phase, in which fine carbides of 10 μm or less are precipitated. If the pearlite content is less than 15%, the fine carbide precipitate phase becomes too large, resulting in excessive attack on the valve. On the other hand, if it exceeds 40%, the wear resistance of the valve seat decreases. The pearlite content is preferably 20-30%.

[0016] If the particle size of the carbides precipitated in the fine carbide precipitate phase exceeds 10 μm, the hardness and toughness of the matrix phase decrease, the valve attack increases, and the radial crushing strength decreases. For these reasons, the fine carbide precipitate phase is preferably a fine carbide precipitate phase in which fine carbides of 10 μm or less are precipitated.

[0017] The matrix phase having the above-described hardness and structure preferably has a composition containing, in mass%, C: 0.5 to 2.0%, Si: 0 to 1.0%, Mn: 0.5 to 5.0%, Cr: 0 to 5.0%, Mo: 0 to 8.0%, V: 0 to 5.0%, W: 0 to 10.0%, Co: 0 to 5.0%, with the balance being Fe and unavoidable impurities.

[0018] The functional component-side layer of the valve seat of the present invention has a structure in which hard particles, or further solid lubricant particles, are dispersed in a matrix phase having the above-mentioned hardness, composition, and structure. The dispersed hard particles have a Vickers hardness of 650 to 1300 HV. If the hardness of the hard particles is less than 650 HV, the effect of improving wear resistance is small, while if it exceeds 1300 HV, machinability is reduced. For these reasons, the hardness of the hard particles dispersed in the matrix phase is limited to the range of 650 to 1300 HV Vickers hardness.

[0019] In addition, the hard particles dispersed in the matrix phase of the functional component-side layer of the valve seat of the present invention preferably have the above hardness and an average particle size of 10 to 150 μm. If the average particle size is less than 10 μm, they tend to diffuse during sintering, making it impossible to ensure the desired improvement in wear resistance. On the other hand, if the particle size exceeds 150 μm, the bonding strength with the matrix decreases. For this reason, it is preferable to limit the average particle size of the hard particles dispersed in the matrix phase to the range of 10 to 150 μm. Note that the "average particle size" here refers to the particle size D50 at which the cumulative distribution measured by the laser scattering method reaches 50%.

[0020] In the functional component-side layer of the valve seat of the present invention, hard particles having the above-mentioned hardness are dispersed in the matrix at an area ratio of 20 to 40%. If the amount of dispersed hard particles is less than 20%, the desired wear resistance cannot be ensured under severe environments. On the other hand, if the amount exceeds 40%, the bonding strength between the matrix and the hard particles decreases, resulting in a decrease in wear resistance.

[0021] The hard particles used in the functional component side layer of the valve seat of the present invention are Mo-Cr-Co based intermetallic compound particles or Mo-Cr-Ni-Fe based intermetallic compound particles.

[0022] The Mo-Cr-Co intermetallic compound particles contain, by mass, 3-15% Cr, 20-40% Mo, the balance being Co and unavoidable impurities, and have a hardness of 650-850 HV after sintering.The Mo-Cr-Ni-Fe intermetallic compound particles contain, by mass, 35-45% Mo, 7-9% Cr, 5-20% Ni, and 1.5-3.5% Si, the balance being Fe and unavoidable impurities, and have a hardness of 700-1300 HV.

[0023] The functional component-side layer of the valve seat of the present invention has a structure in which a high alloy phase exists at an area ratio of 0 to 5%. This high alloy phase is formed by the diffusion of alloying elements from the hard particles into the matrix phase during sintering, and has the effect of preventing the hard particles from falling out of the matrix phase. Therefore, even if a large amount of hard particles are dispersed, it is believed that the hard particles can be prevented from falling out of the matrix phase, and the high alloy phase can suppress a decrease in radial crushing strength.

[0024] To achieve this effect, the high alloy phase is preferably present in an amount of about 0 to 5% by area. If the amount of high alloy phase exceeds 5%, the hardness decreases and the desired wear resistance cannot be ensured. The formation of the high alloy phase depends on the sintering temperature and sintering time, and it is preferable to adjust the sintering temperature and time so that the amount present is within the above range (5% or less by area).

[0025] In the functional component-side layer of the valve seat of the present invention, solid lubricant particles may be further dispersed in the matrix phase at an area ratio of 0 to 5%. Dispersing solid lubricant particles in the matrix phase improves machinability, processability, and lubrication. However, if the dispersion exceeds 5%, it hinders the progress of the sintering reaction, resulting in a decrease in mechanical properties. For this reason, it is preferable to limit the solid lubricant particles to an area ratio of 0 to 5%. Examples of solid lubricants include manganese sulfide (MnS) and molybdenum disulfide (MoS). ２ Examples include:

[0026] As described above, the functional component side layer of the valve seat of the present invention has a structure in which a predetermined amount of hard particles having the above-mentioned hardness and solid lubricant particles having the above-mentioned composition are dispersed in a matrix phase having the above-mentioned structure and hardness, or a high alloy phase is further formed.

[0027] The matrix portion of the functional component side layer, which includes a matrix phase, hard particles, and solid lubricant particles, contains, by mass%, 0.5-2.0% C, 0.5-2.0% Si, 0.5-5% Mn, 2-15% Cr, 5-20% Mo, 2-30% Co, and one or more elements selected from 0-5% V, 0-10% W, 0-5% Ni, 0-2% S, and 0-5% Cu, with the balance being Fe and unavoidable impurities. Note that mass% in the composition is simply expressed as %.

[0028] The reasons for limiting the composition of the matrix in the functional component-side layer will be explained below. Note that mass % is the % relative to the total amount of the matrix in the functional component-side layer.

[0029] C: 0.5-2.0% C is an element necessary for adjusting the matrix phase to a specified hardness and structure, or for forming carbides, and should be contained in an amount of 0.5% or more. On the other hand, if the content exceeds 2.0%, the melting point drops and liquid phase sintering occurs. When liquid phase sintering occurs, the amount of precipitated carbides becomes excessive, the number of voids increases, elongation properties deteriorate, and dimensional accuracy decreases. For this reason, it is preferable to limit C to the range of 0.5-2.0%. A range of 0.5-1.75% is more preferable.

[0030] Si: 0.5-2.0% Si is an element that is mainly contained in hard particles and forms silicide, increasing hardness. A content of 0.5% or more is preferable. On the other hand, if the content exceeds 2.0%, toughness decreases. For this reason, it is preferable to limit the Si content to the range of 0.5-2.0%, and more preferably 0.5-1.5%.

[0031] Mn: 0.5 to 5% Mn is an element that increases the hardness of the matrix phase, and a content of 0.5% or more is preferable. On the other hand, if the content exceeds 5%, the radial crushing strength decreases. For this reason, it is preferable to limit the Mn content to the range of 0.5 to 5%.

[0032] Cr: 2-15% Cr is an element that dissolves in the matrix phase and forms carbides, increasing the hardness of the matrix phase and the hard particles, improving heat resistance and wear resistance. A Cr content of 2% or more is preferable. On the other hand, a Cr content of more than 15% results in excessive precipitation of Cr carbides, making it difficult to form fine carbides. For this reason, it is preferable to limit the Cr content to the range of 2-15%. A Cr content of 2.5-12.5% ​​is more preferable.

[0033] Mo: 5-20% Mo is an element that dissolves in the matrix phase and precipitates as carbides, increasing the hardness of the matrix phase and further contributing to an increase in the hardness of the hard particles, improving wear resistance. A content of 5% or more is preferable. Less than 5% results in an insufficient amount of precipitates, making it impossible to ensure the desired wear resistance. On the other hand, a content of more than 20% results in a decrease in formability. For this reason, the Mo content is limited to the range of 5-20%. A more preferable range is 7.5-17.5%.

[0034] Co: 2-30% Co is an element that increases the strength of the matrix phase, especially its high-temperature strength, contributing to improved wear resistance, and also improves the toughness of the matrix phase. It also contributes to increasing the hardness of the hard particles, and should be contained in an amount of 2% or more. On the other hand, if it is contained in a large amount exceeding 30%, the hardness of the matrix phase decreases, making it impossible to ensure the desired properties. For this reason, the Co content is limited to the range of 2-30%.

[0035] The above-mentioned components are the basic components, but in addition to the basic components, one or more optional elements selected from V: 0-5%, W: 0-10%, Ni: 0-5%, S: 0-2%, and Cu: 0-5% can be included.

[0036] V: 0-5% V is an element that precipitates as carbides, increases the hardness of the matrix phase, and improves wear resistance, and can be added as needed. If added, it is preferable to add 0.5% or more. If it is less than 0.5%, the amount of precipitates is insufficient and the desired wear resistance cannot be ensured. On the other hand, if it is added in excess of 5%, formability decreases. For this reason, the V content is limited to the range of 0-5%. A more preferable range is 0.5-2.5%.

[0037] W: 0-10% W is an element that precipitates as fine carbides, increasing the hardness of the matrix phase and improving wear resistance, and can be added as needed. If added, it is preferable to set it at 0.5% or more. If it is less than 0.5%, the amount of precipitates is insufficient and the desired wear resistance cannot be ensured. On the other hand, if it is added in excess of 10%, formability decreases. For this reason, W is limited to the range of 0-10%. If added, it is more preferably 0.5-7.5%.

[0038] Ni: 0-5% Ni is an element that contributes to improving the strength and toughness of the matrix phase and also contributes to increasing the hardness of the hard particles, and can be contained as needed. If contained, it is preferable that it be 2% or more. On the other hand, a content of more than 5% reduces the formability of the matrix phase. For this reason, it is preferable to limit Ni to the range of 0-5%. If contained, it is more preferably 1-4%.

[0039] S: 0-2% S is an element contained in the matrix due to the inclusion of solid lubricant particles and contributes to improving machinability, and can be included as needed. If S is included in excess of 2%, it leads to a decrease in toughness and ductility. For this reason, if S is included, it is preferable to limit it to 2% or less.

[0040] Cu: 0-5% Cu is an element that contributes to improving the strength and toughness of the matrix phase and can be added as needed. If Cu is added in excess of 5%, it can lead to a decrease in adhesion. Therefore, if Cu is added, it is preferable to limit it to 5% or less.

[0041] The balance other than the above components is Fe and unavoidable impurities, of which P: 0.1% or less is permissible.

[0042] The valve seat of the present invention may have a single layer of the functional component side layer as described above, or may have a two-layer structure in which the support component side layer is sintered integrally with the functional component side layer. The support component side layer used in the two-layer structure is made of an iron-based sintered alloy, like the functional component side layer, and is integrated with the functional component side layer via the boundary surface by sintering.

[0043] The support member-side layer contacts the cylinder head via the seating surface, supports the functional material-side layer, and also improves thermal conductivity, contributing to a decrease in the temperature of the valve seat. Therefore, it is preferable that the support member-side layer in the valve seat of the present invention has a configuration that can ensure the desired strength and thermal conductivity.

[0044] The matrix composition of the support member side layer of the valve seat of the present invention preferably contains, in mass % relative to the total amount of the matrix of the support member side layer, 0.3 to 1.3% C, 0 to 2% Ni, 0 to 2% or less Mo, 0 to 5% Cu, 0 to 5% Mn, and 0 to 2% S, with the remainder being Fe and unavoidable impurities.

[0045] The reasons for limiting the composition of the matrix portion of the support member side layer will be explained below.

[0046] To ensure the desired strength, the C content is set to 0.30% or more. On the other hand, if the C content exceeds 1.3%, the strength becomes too high and the toughness decreases. For this reason, it is preferable to limit the C content to the range of 0.3 to 1.3%. In addition to the C content described above, the matrix of the support member side layer may contain Ni: 0-2%, Mo: 0-2%, Cu: 0-5%, Mn: 0-5%, and S: 0-2%.

[0047] Ni, Mo, and Cu are elements that increase the matrix strength (hardness) of the support member-side layer and can be included as needed. Ni, Mo, and Cu are included according to the desired strength, but if the content exceeds Ni: 2%, Mo: 2%, and Cu: 5%, respectively, the strength becomes too high. Therefore, if these elements are included, it is preferable to limit the content to Ni: 2% or less, Mo: 2% or less, and Cu: 5% or less. Furthermore, a portion of Mo, as well as Mn and S, are included in the matrix due to the dispersion of solid lubricant particles. However, even if the solid lubricant particles are dispersed in large amounts, the effect saturates and ductility decreases. Therefore, if these elements are included, it is preferable to limit Mn: 5% or less and S: 2% or less.

[0048] The balance other than the above components consists of Fe and unavoidable impurities, of which P: 0.10% or less is permissible.

[0049] The support member side layer of the valve seat of the present invention may have a structure in which a pearlite matrix phase is formed, and solid lubricant particles are dispersed in the matrix phase at an area ratio of 0 to 4% relative to the total amount of the support member side layer, and hardness-improving particles are dispersed at an area ratio of 0 to 5%. If the amount of dispersed solid lubricant particles exceeds 4%, the machinability improvement effect saturates and strength decreases. If the amount of dispersed hardness-improving particles exceeds 5%, the hardness becomes too high. Therefore, when dispersed, it is preferable to limit the area ratio of the solid lubricant particles to 0 to 4% and the hardness-improving particles to 0 to 5%. Examples of solid lubricant particles include MnS and MoS2, and examples of hardness-improving particles include Fe-Mo alloy particles.

[0050] Next, a preferred method for manufacturing the valve seat of the present invention will be described.

[0051] First, an iron-based powder for forming the matrix phase, an alloying element powder, a hard particle powder, and a solid lubricant particle powder are blended, mixed, and kneaded to obtain a mixed powder so as to obtain the above-mentioned predetermined functional component-side layer composition. Note that, from the viewpoint of uniformity, the iron-based powder to be blended in the mixed powder is preferably an alloy steel powder having a composition close to the above-mentioned fine carbide precipitate phase composition, and a pure iron powder for forming a desired amount of pearlite.

[0052] The alloy steel powder is preferably a powder having a high-speed tool steel composition as specified in JIS G 4403. The high-speed tool steel is preferably a Mo-based one. From the viewpoint of formability, the above-mentioned high-speed tool steel composition preferably contains 0.03 to 0.70 mass% C. It should be noted that, in addition to the above-mentioned high-speed tool steel composition, there is no problem in using an alloy steel having a composition capable of forming the above-mentioned fine carbide precipitate phase in the functional component-side layer of the valve seat of the present invention. It goes without saying that, in addition to the above-mentioned alloy steel powder, graphite powder and further alloy element powder can be blended into the mixed powder so as to form the above-mentioned matrix phase composition.

[0053] When a valve seat having a two-layer structure is produced, the iron-based powder forming the matrix phase, the alloying element powder, the solid lubricant particle powder, and the hardness improving particles are blended, mixed, and kneaded to obtain a mixed powder so as to obtain the predetermined composition of the support member-side layer. The iron-based powder may be pure iron powder or a steel-based powder of a specific composition. The iron-based powder used is preferably an atomized powder. A lubricant such as zinc stearate may be blended into the mixed powder.

[0054] To produce a two-layer valve seat, a filling space (mold) capable of forming a support member side layer of a predetermined shape is first formed in a press molding machine, and the filling space is filled with a mixed powder for the support member side layer. Then, a filling space (mold) capable of forming a functional component side layer of a predetermined shape as an upper layer of the support member side layer is further formed, and the mixed powder for the functional component side layer is then filled into the filling space. The support member side layer and the functional component side layer are then integrally pressure-molded in a conventional press molding machine to produce a green compact (valve seat). The green compact has a density of 6.6 g / cm. ２ It is preferable to adjust the density so as to achieve the above conditions before pressure molding. Furthermore, in order to ensure uniformity of density, temporary pressing may be performed after filling the raw material powder (mixed powder) for the support member side layer. When a valve seat having a single-layer structure is to be formed, only the mixed powder for the functional member side layer is filled into the filling space.

[0055] The press molding machine used in the present invention does not need to be particularly limited, and any press molding machine capable of molding a two-layer valve seat can be used. For example, a press molding machine capable of molding a two-layer valve seat can be exemplified by a press molding machine having two types of feeders that can be driven independently of each other, a die, a core rod, an upper punch, and a lower punch.

[0056] The obtained green compact is then sintered to form a sintered body, which is then machined or otherwise processed to form a valve seat (product) for an internal combustion engine. The sintering temperature is preferably in the range of 1100-1200°C, and the temperature is maintained for 0.5 hours or more. Sintering temperatures below 1100°C result in insufficient sintering diffusion. Temperatures above 1200°C result in excessive diffusion of the hard particles and matrix, resulting in reduced wear resistance.

[0057] In addition, in the present invention, the product is manufactured by a 1P1S process that combines pressure molding (P) and sintering treatment (S). However, from the viewpoint of ensuring strength, it is preferable to use a 2P2S process that repeats pressure molding (P) and sintering treatment (S) twice in order to further improve density.

[0058] The obtained sintered body is processed by grinding, cutting, etc. to form a valve seat (product) of the desired size and shape.

[0059] The valve seat of the present invention is preferably used in combination with a valve plated with a Triballoy alloy, which has a surface hardness of 550 HV or more on the contact surface with the valve seat. This combination of valve and valve seat can prevent valve wear from increasing and keep valve seat wear to an acceptable level, achieving a combination of valve and valve seat that achieves a balanced wear suppression.

[0060] The present invention will be further described below with reference to examples.

[0061] An iron-based powder for forming the matrix phase, a hard particle powder, an alloying element powder, and a solid lubricant powder were mixed and kneaded to obtain a mixed powder in the amounts shown in Table 1. The iron-based powder used had the composition shown in Table 2. Pure iron powder was partially mixed into the iron-based powder. The hard particle powder used had the composition shown in Table 3. The solid lubricant powder used was MnS powder. The mixed powder contained 1 part by mass of zinc stearate as a lubricant per 100 parts by mass of the mixed powder.

[0062] Next, the resulting mixed powder for the support member side layer was filled into a mold, and then the mixed powder for the functional component side layer was filled into the mold as an upper layer of the support member side layer, and a green compact of a predetermined shape was formed using a press. The green compact was then sintered at 1150°C for 30 minutes in a protective atmosphere to form a two-layer sintered compact. Some of the sintered compacts were formed into a single-layer sintered compact.

[0063] The obtained sintered body was further subjected to machining, polishing, etc. to obtain an iron-based sintered alloy valve seat having a predetermined size and shape (outer diameter: 27 mmφ×inner diameter: 22 mmφ×thickness: 6 mm).

[0064] The obtained valve seat inserts were subjected to chemical analysis, microstructural observation, hardness testing, abrasion testing, and radial crushing strength testing under the following test conditions. Valve seat insert No. 1 was used as the reference valve seat insert, as it had excellent abrasion resistance and had a fine carbide precipitate phase as the matrix.

[0065] (1) Chemical Analysis: Analytical samples were collected from the resulting sintered compacts, and the content of each element was determined by optical emission spectroscopy to determine the matrix composition. The results are shown in Table 4. (2) Microstructural Observation: A cross section perpendicular to the axial direction of the resulting valve seat was polished and etched (etchant: nital solution) to reveal the microstructure. The microstructure was then observed under an optical microscope (magnification: 200x) to identify the type of matrix microstructure. Additionally, the particle size of carbides precipitated in the matrix was measured using a scanning electron microscope (magnification: 2000x). When the maximum diameter of the carbide particle size (long side length) exceeded 10 μm, the matrix was simply considered a carbide precipitate phase. In the compositions shown in Table 5, phases other than those listed in the table were present in small amounts and therefore were omitted from the table as the remainder. (3) Hardness Test The cross section of the obtained valve seat was polished and etched (etchant: nital solution) to reveal the structure, and the hardness of the matrix (Vickers hardness HV) was measured using a Vickers hardness tester (test force: 0.98 N (100 gf)). When the matrix was two-phase, each phase was measured separately. (4) Wear Test The obtained valve seat was subjected to a wear test using the rig tester shown in Figure 1 under the following test conditions: Test temperature: 270°C (seat seating); Test time: 8 hours; Cam rotation speed: 3000 rpm; Valve rotation speed: 20 rpm; Impact load: 700 N; Burner: LPG. The valve used was a Tribaloy-based alloy clad valve (valve contact surface hardness: 600 HV). After the test, the wear amount of the valve seat and valve was measured. From the obtained wear amount, the wear ratio of the valve seat and the wear ratio of the valve were calculated, with the case of valve seat No. 1 set as the standard (1.00). (5) Radial Crushing Strength Test For the obtained valve seats, the radial crushing strength of only the functional component side layer was determined in accordance with the provisions of JIS Z 2507. The density was measured using the Archimedes method. The obtained results are shown in Table 5.

[0066]

[0067]

[0068]

[0069]

[0070]

[0071] The valve seats of the present invention have a lower valve wear ratio and less valve attack compared to valve seat No. 1 (standard). In particular, valve seats Nos. 3 and 4 have low valve attack and no significant decrease in wear resistance.

[0072] Thus, even when the valve seat of the present invention is a valve with a Triballoy-based alloy cladding on the valve seat contact surface with a hardness of 550 HV or more, the valve has a valve wear resistance ratio of 0.37 to 0.67 compared to the reference material (No. 1) (reference 1.00), which is less aggressive to the valve. Moreover, when Valve Seat No. 1 is used as the reference (1.00), the valve seat wear resistance ratio is approximately 1.12 to 1.60, which is 2.0 or less, so the valve seat shows relatively little decline in wear resistance.

[0073] 1 Valve seat 2 Cylinder block equivalent material 3 Heating means 4 Valve

Claims

1. An iron-based sintered alloy valve seat having a single-layer structure consisting of a functional component-side layer, wherein the functional component-side layer is formed by dispersing hard particles and solid lubricant particles in a matrix phase, the matrix phase being composed of 15 to 40% pearlite in area ratio and a fine carbide precipitate phase having a Vickers hardness of 400 HV or more in which fine carbides having a particle size of 10 μm or less are precipitated in an area ratio of 15 to 55%, the hard particles having a Vickers hardness of 650 to 1300 HV, the hard particles being dispersed in the matrix phase in an area ratio of 20 to 40%, and the iron-based sintered alloy valve seat for internal combustion engines having excellent wear resistance and low valve attack, characterized in that it has a structure in which a high alloy phase is dispersed in an area ratio of 0 to 5%, and the solid lubricant particles are dispersed in an area ratio of 0 to 5%.

2. A valve seat made of an iron-based sintered alloy having a two-layer structure in which a functional component-side layer and a support component-side layer are sintered together, wherein the functional component-side layer is formed by dispersing hard particles and solid lubricant particles in a matrix phase, a matrix phase comprising 15 to 40% by area of ​​pearlite and a fine carbide precipitate phase in which fine carbides having a particle size of 10 μm or less are precipitated at an area ratio of 15 to 55% and having a Vickers hardness of 400 HV or more; the hard particles have a Vickers hardness of 650 to 1300 HV; the hard particles are dispersed in the matrix phase at an area ratio of 20 to 40%; and the support member side layer has a structure in which a high alloy phase and the solid lubricant particles are dispersed at an area ratio of 0 to 5%; and the support member side layer has a structure in which a matrix phase and 0 to 4% by area of ​​solid lubricant particles and 0 to 5% by area of ​​hardness improving particles are dispersed in the matrix phase.

3. An iron-based sintered alloy valve seat for an internal combustion engine according to claim 1 or 2, characterized in that the matrix portion of the functional component side layer, which includes the matrix phase, the hard particles, the high alloy phase, and the solid lubricant particles, contains, by mass%, C: 0.5-2.0%, Si: 0.5-2.0%, Mn: 5% or less, Cr: 2-15%, Mo: 5-20%, Co: 2-30%, and further contains one or more elements selected from V: 0-5%, Ni: 0-5%, S: 0-2%, and Cu: 0-5%, with the balance being Fe and unavoidable impurities.

4. An iron-based sintered alloy valve seat for an internal combustion engine as set forth in claim 2, characterized in that the matrix portion of the support member side layer, which includes the matrix phase, the solid lubricant particles, and the hardness improving particles, contains, by mass%, C: 0.3 to 1.3%, Ni: 0 to 2%, Mo: 0 to 2%, Cu: 0 to 5%, Mn: 0 to 5%, and S: 0 to 2%, with the remainder being Fe and unavoidable impurities.

5. A valve seat made of an iron-based sintered alloy for an internal combustion engine as set forth in claim 1 or 2, characterized in that the hard particles are Cr-Mo-Co intermetallic compound particles containing, by mass%, C: 0.5 to 2.0%, Si: 0.5 to 2.0%, Mn: 5% or less, Cr: 2 to 15%, Mo: 5 to 20%, Co: 2 to 30%, and further containing one or more elements selected from V: 0 to 5%, Ni: 0 to 5%, S: 0 to 2%, and Cu: 0 to 5%, with the balance being Co and unavoidable impurities, or Cr-Mo-Ni-Fe intermetallic compound particles containing Mo: 35 to 45%, Cr: 7 to 9%, Ni: 5 to 20%, and further containing Si: 1.5 to 3.5%, with the balance being Fe and unavoidable impurities.

6. An iron-based sintered alloy valve seat for an internal combustion engine according to claim 1 or 2, characterized in that the solid lubricant particles are either manganese sulfide (MnS) or molybdenum disulfide (MoS2).

7. The iron-based sintered alloy valve seat for an internal combustion engine according to claim 2, wherein the hardness improving particles are iron-molybdenum alloy particles.

8. A combination of a valve and a valve seat with excellent wear resistance, characterized in that the valve is a Triballoy alloy overlaid valve having a surface hardness of 550 HV or more on the contact surface with the valve seat, and the valve seat is a valve seat made of an iron-based sintered alloy for internal combustion engines as set forth in claim 1 or 2.

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