CN116060620A

CN116060620A - Valve seat made of iron-based sintered alloy and method for manufacturing same

Info

Publication number: CN116060620A
Application number: CN202211309265.0A
Authority: CN
Inventors: 池见聪史; 鹰木清介
Original assignee: Nippon Piston Ring Co Ltd
Current assignee: Nippon Piston Ring Co Ltd
Priority date: 2021-10-29
Filing date: 2022-10-25
Publication date: 2023-05-05
Also published as: JP2023067801A

Abstract

The invention provides an iron-based sintered alloy valve seat with excellent radial compressive strength. The functional member side layer and the support member side layer are integrally sintered to form a sintered body having a double-layer structure. The mixed powder for the functional member side layer and the mixed powder for the supporting member side layer are sequentially filled in a mold, press-processed to prepare a pressed powder, and the pressed powder is subjected to sintering treatment to prepare the iron-based sintered alloy valve seat with a double-layer structure. In the mixed powder for the functional member side layer, an iron-based powder having a hardness of 170 to 220HV is used as an iron-based powder for forming a matrix phase, and the matrix phase is formed in the form of a fine carbide precipitated phase in which 20 to 40% of Si-Cr-Mo-based Co-based intermetallic compound particles or Si-Cr-Mo-Ni-based Co-based intermetallic compound particles are dispersed in terms of area ratio, and 0 to 5% of solid lubricant particles are also dispersed in terms of area ratio.

Description

Valve seat made of iron-based sintered alloy and method for manufacturing same

Technical Field

The present invention relates to a valve seat for an internal combustion engine and a method for manufacturing the same, and more particularly to an improvement in radial compressive strength (radial crushing strength).

Background

Valve seats are typically pressed into the cylinder head of an internal combustion engine, responsible for the sealing of the combustion gases and the cooling of the valve. Since the valve seat is hit by a valve, worn by sliding, heated by combustion gas, corroded by combustion products, and the like, excellent heat resistance and wear resistance have been demanded.

For such a requirement, for example, patent document 1 describes "an iron-based sintered alloy valve seat for an internal combustion engine having excellent wear resistance". In the technique described in patent document 1, an iron-based sintered alloy valve seat is produced, which has the following structure: the matrix phase is prepared to be precipitated with 10μm or less, and a hard single-phase structure which is a fine carbide precipitated phase having a hardness of 550HV or more, wherein 20 to 40% of hard particles having a hardness of 650 to 1200HV are dispersed in the matrix phase as an area ratio, and 0.5 to 5% of a dispersed phase is formed around the hard particles as an area ratio, or 5% or less of solid lubricant particles are also dispersed as an area ratio. In this way, in an internal combustion engine in a severe wearing environment, that is, in an environment using a special fuel such as a gaseous fuel, even if a valve having high surface hardness is used, the wearing of the valve seat is small, and a combination of the valve and the valve seat excellent in wear resistance can be realized.

Prior art literature

Patent literature

Patent document 1: japanese patent publication No. 6736227.

Disclosure of Invention

Problems to be solved by the invention

However, the iron-based sintered alloy valve seat described in patent document 1 has the following problems: the radial compressive strength is low, cracks are likely to occur when the cylinder head is pressed in, particles are likely to fall off when the cylinder head is in contact with a valve, and abrasion resistance is reduced. In addition, there is a problem that young's modulus is low, deformation is easy, sealability is lowered, and combustion gas leaks.

The invention aims at: the above-mentioned prior art problems are solved, and an iron-based sintered alloy valve seat excellent in radial compressive strength is provided. The term "excellent radial compressive strength" as used herein means that the radial compressive strength obtained in accordance with the regulation of JIS Z2507 is 470MPa or more.

Means for solving the problems

In order to achieve the above object, the present inventors have conducted intensive studies on various factors affecting the radial compressive strength. As a result, it was found that the low "radial compressive strength" was due to the low compressibility of the iron-based powder used. In the technique described in patent document 1, although an iron-based powder in which fine carbides can be precipitated is used as the iron-based powder, carbide precipitation already occurs in the powder, which results in a higher hardness of the powder particles, and plastic deformation (compression) of the powder particles during the powder compacting is insufficient, so that it is also difficult to promote element diffusion during the sintering process, and as a result, it is considered that the inter-particle bonding force is reduced.

Thus, in the present invention, it is contemplated that: the use of an iron-based powder having a low carbon content as an iron-based powder for matrix phase formation enables sufficient compacting during compacting and sufficient plastic deformation of the powder particles. However, if the carbon content of the iron-based powder is excessively reduced, the carbide content is reduced, and the wear resistance of the sintered body is lowered, so that the carbon content of the sintered body is not lowered in consideration of increasing the blending amount of the graphite powder. From this, it follows that: the precipitation amount of fine carbide in the sintered body is significantly increased as compared with the conventional method, and the abrasion resistance and the radial compressive strength are significantly improved.

The present invention has been further studied based on the above findings. Namely, the gist of the present invention is as follows.

[1] An iron-based sintered alloy valve seat having a single-layer structure composed of a functional member side layer, characterized in that:

the functional member side layer is formed by dispersing hard particles and solid lubricant particles in a matrix phase, and has the following structure:

the matrix phase is a fine carbide precipitated phase, wherein the grain size is 10μFine carbide of m or less is 150/(30)μm×30μm) or more, has a hardness of 550HV or more in terms of Vickers hardness,

The hard particles are Si-Cr-Mo Co-based intermetallic compound particle powder having a hardness of 650 to 1200HV in terms of Vickers hardness, and containing 2.20 to 2.70% by mass of Si, 7.5 to 9.5% by mass of Cr, 27.0 to 30.0% by mass of Mo, and the balance being Co and unavoidable impurities; or Si-Cr-Mo-Ni-based Co-based intermetallic compound particles having a hardness of 650 to 1200HV in terms of Vickers hardness, comprising, by mass%, 1.5 to 2.5% of Si, 24.0 to 26.0% of Cr, 23.0 to 26.0% of Mo, 9.5 to 11.0% of Ni, and the balance Co, wherein 20 to 40% of the hard particles are dispersed in terms of area ratio in the matrix phase,

0 to 5% of the solid lubricant particles are also dispersed in terms of area ratio,

density of 6.65g/cm ³ The above is excellent in radial compressive strength.

[2] The iron-based sintered alloy-made valve seat according to item 1, wherein the matrix portion including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: comprises, by mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, and the balance being Fe and unavoidable impurities.

[3] An iron-based sintered alloy valve seat having a double-layer structure in which a functional member side layer and a support member side layer are integrally sintered, characterized in that:

the functional member side layer is formed by a matrix phase and hard particles and solid lubricant particles dispersed in the matrix phase, and has the following structure: the matrix phase is a fine carbide precipitated phase, wherein the grain size is 10μFine carbide of m or less is 150/(30)μm×30μm) density analysis of aboveThe hard particles are Si-Cr-Mo based Co-based intermetallic compound particle powder having a hardness of 550HV or more in terms of Vickers hardness, and have a hardness of 650 to 1200HV in terms of Vickers hardness, and contain 2.20 to 2.70% by mass of Si, 7.5 to 9.5% by mass of Cr, 27.0 to 30.0% by mass of Mo, and the balance being Co and unavoidable impurities; or Si-Cr-Mo-Ni-based Co-based intermetallic compound particles having a hardness of 650 to 1200HV in terms of Vickers hardness, comprising, by mass%, 1.5 to 2.5% of Si, 24.0 to 26.0% of Cr, 23.0 to 26.0% of Mo, 9.5 to 11.0% of Ni, and the balance Co, wherein 20 to 40% of the hard particles are dispersed in terms of area ratio in the matrix phase, and 0 to 5% of the solid lubricant particles are dispersed in terms of area ratio,

The support member side layer has a matrix phase composed of pearlite and a structure formed by dispersing hard particles in the matrix phase in an amount of 0 to 5% by area and solid lubricant particles in an amount of 0 to 5% by area,

density of 6.65g/cm ³ The above is excellent in radial compressive strength.

[4] The iron-based sintered alloy-made valve seat described in [3], characterized in that: the matrix portion of the functional member side layer including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: comprises, by mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, the balance being Fe and unavoidable impurities,

the matrix portion of the support member side layer including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: contains 0.9 to 2.0% by mass of C, or contains 1 or 2 or more selected from Ni of 0.5% or less, mo of 0.8% or less, cu of 5.0% or less, mn of 5.0% or less, S of 2.0% or less, and the balance being Fe and unavoidable impurities.

[5] A method for producing an iron-based sintered alloy valve seat according to [1] or [2], characterized by comprising:

mixing a prescribed amount of iron-based powder, graphite powder, alloy element powder, hard particle powder, or solid lubricant powder, mixing, kneading, and preparing a mixed powder,

filling the mixed powder into a mold of a predetermined shape, pressing the mold to obtain a pressed powder,

when the pressed powder is sintered in a protective environment to form a sintered body, and then cut or further ground to form a valve seat of a predetermined shape,

the iron-based powder was set as follows: has a composition comprising, in mass%, 0.05 to 0.70% of C, 0.70% or less of Si, 0.50% or less of Mn, 4.5% or less of Cr, 10.0% or less of Mo, 4.5% or less of V, 10.0% or less of W, and the balance being Fe and unavoidable impurities, has a particle hardness of 170 to 220HV in Vickers hardness, is blended with 40 to 70% of the iron-based powder in mass% relative to the total amount of the mixed powder,

the hard particle powder was set as: the Si-Cr-Mo Co-based intermetallic compound particle powder has a hardness of 650 to 1200HV in terms of Vickers hardness, contains 2.20 to 2.70% by mass of Si, 7.5 to 9.5% by mass of Cr, 27.0 to 30.0% by mass of Mo, and the balance consisting of Co and unavoidable impurities; or Si-Cr-Mo-Ni-based Co-based intermetallic compound particles having a hardness of 650 to 1200HV in terms of Vickers hardness, comprising 1.5 to 2.5% by mass of Si, 24.0 to 26.0% by mass of Cr, 23.0 to 26.0% by mass of Mo, 9.5 to 11.0% by mass of Ni, the balance being Co, and blending 20 to 40% by mass of the hard particle powder relative to the total mass of the mixed powder,

Blending 0.5 to 2.0% by mass of the graphite powder relative to the total amount of the mixed powder,

the alloy element powder is blended in an amount of 0 to 5.0% by mass based on the total amount of the mixed powder,

the solid lubricant powder is further blended in an amount of 0 to 5% by mass based on the total amount of the mixed powder,

the press working is performed so that the density of the pressed powder is 6.6g/cm ³ The density of the above is such that,

the sintering treatment is performed at a sintering temperature of 1100 to 1200 ℃ to obtain the sintered body.

[6] [5]The manufacturing method of the valve seat made of the iron-based sintered alloy is characterized by comprising the following steps: the sintered body has a particle diameter of 10μFine carbide of m or less is 150/(30)μm×30μm) a matrix phase which is a fine carbide-precipitated phase having a density of 550HV or more in terms of Vickers hardness, and having a structure and a composition as follows: the hard particles are dispersed with 20-40% of the area ratio, and the solid lubricant particles are also dispersed with 0-5% of the area ratio; and, the composition is: the matrix portion including the matrix phase, the diffusion phase, the hard particles, and the solid lubricant particles contains, in mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, and the balance being Fe and unavoidable impurities.

[7] A method for producing an iron-based sintered alloy valve seat according to [3] or [4], characterized by comprising:

mixing a prescribed amount of iron-based powder, graphite powder, alloy element powder, hard particle powder, or solid lubricant powder, and mixing and kneading to prepare a mixed powder for a functional member side layer,

mixing a prescribed amount of iron-based powder, graphite powder, or alloy element powder, hard particle powder, and solid lubricant powder, mixing, kneading, and making a mixed powder for a support member side layer,

when the powder mixture for the functional member side layer and the powder mixture for the support member side layer are sequentially filled in a mold having a predetermined shape, and press-processed to form a pressed powder, then the pressed powder is sintered in a protective environment to form a sintered body having a double-layer structure, and thereafter cutting or further grinding is performed to manufacture a valve seat having a double-layer structure having a predetermined shape,

in the above-described mixed powder for a functional member side layer, the above-described iron-based powder is set to be the following iron-based powder: has a composition comprising, in mass%, 0.05 to 0.70% of C, 0.70% or less of Si, 0.50% or less of Mn, 4.5% or less of Cr, 10.0% or less of Mo, 4.5% or less of V, 10.0% or less of W, and the balance being Fe and unavoidable impurities, and has a particle hardness of 170 to 220HV in terms of Vickers hardness, and is blended with 40 to 70% of the iron-based powder in mass% relative to the total amount of the mixed powder,

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 for the functional member side layer,

in the mixed powder for a support member side layer, the iron-based powder is a pure iron powder, the graphite powder is blended in an amount of 0.5 to 2.0% by mass relative to the total amount of the mixed powder for a support member side layer, the alloy element powder is blended in an amount of 0 to 5.0% by mass relative to the total amount of the mixed powder for a support member side layer, the hard particle powder is an Fe-Mo alloy powder, the hard particle powder is blended in an amount of 0 to 5% by mass relative to the total amount of the mixed powder for a support member side layer, the solid lubricant powder is blended in an amount of 0 to 5% by mass relative to the total amount of the mixed powder for a support member side layer,

the sintering treatment is carried out at a sintering temperature of 1100-1200 ℃,

the above sintered body was produced into a sintered body having a double layer structure.

[8] [7]The method for manufacturing the iron-based sintered alloy valve seat is characterized in that the sintered body having a double layer structure is a sintered body having a double layer structure, and the functional member side layer has: particle size of 10μFine carbide of m or less is 150/(30)μm×30μm) a matrix phase which is a fine carbide-precipitated phase having a density of not less than 550HV in terms of Vickers hardness; a matrix phase containing 20 to 40% by area of hard particles and 0 to 5% by area of solid lubricant particles; and a composition comprising, in mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, and the balance being Fe and unavoidable impurities in a matrix portion comprising the matrix phase, the hard particles and the solid lubricant particles,

The support member side layer includes: a matrix phase composed of pearlite; a structure formed by dispersing 0 to 5% by area of hard particles and 0 to 5% by area of solid lubricant particles in the matrix phase; and a composition comprising, in mass%, 0.9 to 2.0% of C, or 1 or 2 or more selected from the group consisting of 0.5% or less of Ni, 0.8% or less of Mo, 5.0% or less of Cu, 5.0% or less of Mn, 2.0% or less of S, and the balance being Fe and unavoidable impurities, in a matrix portion comprising the matrix phase, the hard particles, and the solid lubricant particles.

Effects of the invention

According to the present invention, an iron-based sintered alloy valve seat excellent in wear resistance and radial compressive strength can be produced, and a remarkable industrial effect can be achieved.

Drawings

FIG. 1 is an explanatory diagram showing an outline of a drilling (rig) test machine.

Detailed Description

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

First, the functional member side layer will be described.

The functional member side layer has a matrix phase and a structure in which hard particles and solid lubricant particles are dispersed in the matrix phase.

The matrix phase is a single phase composed of a fine carbide-precipitated phase having a hardness of 550HV or more in terms of Vickers hardness, and having a particle size of 10μFine carbide of m or less is 150/(30)μm×30μm) or more. The term "single phase" as used herein means that the phase occupies 95% or more of the area ratio. If the amount of the metal is less than 5% by area, the effect on the abrasion resistance is small even if the hardness of the metal is less than 550HV in the matrix phase. When the hardness of the matrix phase is less than 550HV, the matrix phase tends to be coagulated when in contact with a valve, and abrasion resistance is reduced. On the other hand, if the hardness exceeds 700HV, toughness as a sintered body decreases. Therefore, the hardness of the matrix phase is set to 550HV or more, preferably 700HV or less in terms of vickers hardness. It is preferable that the voltage is 560 to 660HV.

If the grain size of carbide precipitated in the matrix phase exceeds 10μm, the hardness and toughness of the matrix phase decrease, the aggressiveness to hands increases, and the radial compressive strength decreases. In the present invention, the carbide content in the matrix phase is 150/(30) μm×30μm) or more. The precipitation density is less than 150/(30)μm×30μm), the precipitation density is too low to ensure the desired radial compressive strength or abrasion resistance. Therefore, the matrix phase is a fine carbide precipitated phase having a Vickers hardness of 550HV or moreHardness of 10 particle sizeμFine carbide of m or less is 150/(30)μm×30μm) or more.

The matrix phase having the above-described hardness and texture preferably has the following composition: contains, in mass%, 0.05 to 0.70% C, 0.70% or less Si, 0.50% or less Mn, 4.5% or less Cr, 10.0% or less Mo, 4.5% or less V, 10.0% or less W, or further contains 5.0% or less Co, with the balance being Fe and unavoidable impurities.

The functional member side layer of the valve seat of the present invention has: a matrix phase having the above hardness, texture, and composition is a texture in which hard particles or solid lubricant particles are dispersed. The dispersed hard particles are hard particles having a hardness of 650 to 1200HV in Vickers hardness. When the hardness of the hard particles is less than 650HV, the effect of improving the abrasion resistance is small. On the other hand, if the cutting performance is increased by exceeding 1200HV, the machinability is lowered. Therefore, the hardness of the hard particles dispersed in the matrix phase is limited to the range of 650 to 1200HV in vickers hardness.

The hard particles dispersed in the matrix phase are preferably formed to have an average particle diameter of 10 to 150μm. Average particle diameter of less than 10μm is liable to spread during sintering, and the desired effect of improving the abrasion resistance cannot be ensured. On the other hand, if it exceeds 150μm increases, the binding force with the matrix decreases. Therefore, the average particle diameter of the hard particles dispersed in the matrix phase is preferably set to 10 to 150μm. The "average particle diameter" as used herein means a particle diameter D50 having a cumulative distribution of 50% as measured by a laser light scattering method.

In the functional member side layer of the valve seat of the present invention, hard particles of the hardness described above are dispersed in the matrix phase at an area ratio of 20 to 40%. When the dispersion amount of the hard particles is less than 20%, the desired abrasion resistance cannot be ensured. On the other hand, if it exceeds 40%, the binding force of the matrix phase with the hard particles decreases and the abrasion resistance decreases.

The hard particle powder used in the functional member side layer of the valve seat of the present invention is preferably a si—cr—mo-based Co-based intermetallic compound particle powder or a si—cr—mo—ni-based Co-based intermetallic compound particle. The Si-Cr-Mo Co-based intermetallic compound particle powder comprises: a composition comprising, in mass%, 2.20 to 2.70% of Si, 7.5 to 9.5% of Cr, 27.0 to 30.0% of Mo, and the balance being Co and unavoidable impurities; and has a hardness of 650 to 1200HV in Vickers hardness. The Si-Cr-Mo-Ni based Co-based intermetallic compound particles comprise: comprises, in mass%, 1.5 to 2.5% of Si, 24.0 to 26.0% of Cr, 23.0 to 26.0% of Mo, 9.5 to 11.0% of Ni, and the balance being Co; and has a hardness of 650 to 1200HV in Vickers hardness.

In the functional member side layer of the valve seat of the present invention, although a diffusion phase may be formed around the hard particles, the amount thereof is small, and is at most about 0.5% by area ratio. The diffusion phase is formed by diffusing an alloy element from hard particles into a matrix phase during sintering, but in the functional member side layer of the valve seat of the present invention, the carbide is stabilized, so that the formation amount of the diffusion phase is small.

In the functional member side layer of the valve seat of the present invention, 0 to 5% of solid lubricant particles can be dispersed in the matrix phase in terms of area ratio. By dispersing the solid lubricant particles in the matrix phase, machinability, workability, lubricity are improved. However, if it exceeds 5%, progress of the sintering reaction is hindered, resulting in deterioration of mechanical properties. Therefore, the solid lubricant particles are limited to a range of 0 to 5% in terms of area ratio. As the solid lubricant, there may be exemplified: manganese sulfide MnS and molybdenum disulfide MoS ₂ Etc.

In the functional member side layer of the valve seat of the present invention, the matrix portion including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: comprises, by mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, and the balance being Fe and unavoidable impurities.

The reason why the composition of the matrix portion in the functional member side layer is limited will be described below. Hereinafter, mass% in the composition is expressed as% only.

C：1.0～2.0%

C is an essential element for adjusting the matrix phase to a predetermined hardness and texture to form a predetermined fine carbide, and is contained at 1.0% or more. On the other hand, if the content exceeds 2.0%, liquid phase sintering is performed during sintering, the amount of precipitated carbide becomes excessive, the number of voids increases, and the dimensional accuracy decreases. Therefore, C is preferably limited to a range of 1.0 to 2.0%. It is more preferable that the content is 1.0 to 1.5%.

Si：0.5～1.5%

Si is an element for increasing hardness, and preferably contains 0.5% or more. On the other hand, when the content exceeds 1.5%, the toughness is lowered. Therefore, si is preferably limited to a range of 0.5 to 1.5%. It is more preferable that the content is 0.5 to 1.3%.

Mn: less than 2.0%

Mn is an element that increases the hardness of the matrix phase, and Mn is contained in the matrix portion by containing solid lubricant particles, contributing to improvement of machinability. This effect becomes remarkable when it is 0.05% or more, but when it is 2.0% or more, the hardness, toughness and ductility of the matrix phase are lowered. Therefore, mn is preferably limited to less than 2.0%. It is more preferable that the content is 0.05 to 1.5%.

Cr：2.0～10.0%

Cr is an element that is solid-dissolved in the matrix phase, forms carbide to increase the hardness of the matrix phase, increases the hardness of hard particles, and improves heat resistance and abrasion resistance, and preferably contains 2.0% or more. On the other hand, if the content exceeds 10.0%, the formation of Cr carbide becomes excessive, and it is difficult to form fine carbide, and the hardness of hard particles becomes excessively high. Therefore, cr is preferably limited to a range of 2.0 to 10.0%. It is more preferable that the content is 4.0 to 6.0%.

Mo：5.0～15.0%

Mo is an element that is solid-dissolved in the matrix phase, forms fine carbides, increases the hardness of the matrix phase, and contributes to improvement of wear resistance. In addition, it increases the hardness of the hard particles. Such an effect becomes remarkable when the content is 5.0% or more, but when the content exceeds 15.0%, moldability is lowered. Therefore, mo is preferably limited to 5.0 to 15.0%. It is more preferable that the content is 10.0 to 14.0%.

W：0.5～10.0%

W is an element that forms fine carbides, has an effect of increasing hardness of a matrix phase, and improves wear resistance. Such an effect becomes remarkable when the content is 0.5% or more, and if the content exceeds 10.0%, the moldability is lowered. Therefore, W is preferably limited to 0.5 to 10.0%. It is more preferable that the content is 2.0 to 5.0%.

V：0.5～5.0%

V is an element that forms fine carbides, has an effect of increasing hardness of the matrix phase, and improves wear resistance. Such an effect becomes remarkable when the content is 0.5% or more, but if the content exceeds 5.0%, the moldability is lowered. Accordingly, V is preferably limited to a range of 0.5 to 5.0%. It is more preferable that the content is 0.5 to 2.0%.

Co：10.0～35.0%

Co is an element that increases the strength of the matrix phase, particularly the high-temperature strength, and improves the abrasion resistance, or an element that improves the toughness of the matrix phase, and increases the hardness of the hard particles. This effect becomes remarkable when it is 10.0% or more. On the other hand, if the content exceeds 35.0%, the matrix phase hardness is lowered. Therefore, co is preferably limited to a range of 10.0 to 35.0%. It is more preferable that the content is 10.0 to 25.0% or less.

Ni：0～5.0%

Ni is an element that contributes to the improvement of hardness and toughness of the matrix phase, and also contributes to the increase of hardness of the hard particles, and may be contained as needed. When Ni is contained, it is preferably 0.3% or more, and when Ni is contained in an amount exceeding 5.0%, the formability of the matrix phase is lowered. Therefore, in the case of Ni, it is preferably limited to 5.0% or less. It is more preferable that the content is 1.0% or less.

S：0～2.0%

S is an element that is contained in the matrix portion due to the inclusion of the solid lubricant particles and contributes to improvement of machinability, and may be contained as needed. However, if the content of S exceeds 2.0%, the toughness and ductility are reduced. Therefore, when S is contained, S is preferably limited to 2.0% or less.

The balance other than the above components is composed of Fe and unavoidable impurities. As an unavoidable impurity, P of 0.03% or less is allowable.

Next, a description will be given of a support member side layer in the case where the valve seat of the present invention is made into a double-layer structure. The functional member side layer having the double-layer structure is the same as the functional member side layer in the case of the single-layer structure described above.

The substrate phase of the support member side layer of the valve seat of the present invention is a pearlite-based structure, and the support member side layer has a structure in which hard particles in an area ratio of 0 to 5% are dispersed in the substrate phase and solid lubricant particles in an area ratio of 0 to 5% are formed.

In the matrix phase of the support member side layer, solid lubricant particles that improve machinability can be dispersed as needed. As the solid lubricant particles, mnS, moS can be exemplified ₂ Etc. In the case of dispersion, the solid lubricant particles are preferably set to 0.3% or more in terms of area ratio. When the content is less than 0.3%, it is difficult to achieve the object of improving the machinability. On the other hand, even if the dispersion exceeds 5%, the effect is saturated, and an effect commensurate with the amount of dispersion cannot be expected. Therefore, in the case of dispersion, the solid lubricant particles are preferably limited to 5% or less.

In addition, in the matrix phase of the support member side layer, in order to increase the strength of the matrix phase, 0 to 5% of hard particles may be dispersed in terms of area ratio. As the hard particles dispersed in the support member side layer, iron-molybdenum (fe—mo) alloy iron can be exemplified. Even if hard particles are dispersed at an area ratio exceeding 5%, the effect is saturated, and therefore, the upper limit is 5%.

In the support member side layer of the valve seat of the present invention, the matrix portion including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: contains 0.9 to 2.0% by mass of C, or contains 1 or 2 or more selected from Ni of 0.5% or less, mo of 0.8% or less, cu of 5.0% or less, mn of 5.0% or less, S of 2.0% or less, and the balance being Fe and unavoidable impurities.

C. Ni, mo, cu are elements that increase the matrix phase strength (hardness) of the support member side layer. To ensure the desired strength, 0.9% or more of C is contained. On the other hand, if the content exceeds 2.0%, the strength is too high and the toughness is lowered. Therefore, C is limited to a range of 0.9 to 2.0%. Although Ni, mo, and Cu are contained according to the desired strength, if Ni, mo, and Cu are contained in an amount exceeding 0.5%, mo exceeding 0.8%, and Cu exceeding 5.0%, the strength becomes too high, and thus the range of Ni of 0.5% or less, mo of 0.8% or less, and Cu of 5.0% or less is preferably limited. In addition, a part of Mn, S, and Mo is contained by dispersing the solid lubricant particles, and even if the solid lubricant particles are dispersed in a large amount, the effect is saturated. Therefore, the Mn is limited to 5.0% or less and the S is limited to 2.0% or less.

Next, a method for manufacturing the iron-based sintered alloy valve seat according to the present invention will be described.

In the method for producing a valve seat made of an iron-based sintered alloy having a single-layer structure of the present invention, first, a prescribed amount of iron-based powder, graphite powder, alloy element powder, hard particle powder, or solid lubricant powder is blended to form the above-described matrix composition, and the mixture is mixed and kneaded to prepare a mixed powder (mixed powder for a functional member side layer).

The iron-based powder to be blended in the mixed powder (mixed powder for functional member side layer) is a powder to be blended for forming a matrix phase, and in the present invention, an alloy steel powder capable of forming the matrix phase into a fine carbide precipitated phase is used. As such alloy steel powder, powder based on the composition of the high-speed tool steel composition specified in JIS G4403 can be exemplified, but of course, it is not limited thereto.

The iron-based powder to be blended was set as follows: has a composition containing, in mass%, 0.05 to 0.70% of C, 0.70% or less of Si, 0.50% or less of Mn, 4.5% or less of Cr, 10.0% or less of Mo, 4.5% or less of V, 10.0% or less of W, and the balance being Fe and unavoidable impurities, and has a particle hardness of 170 to 220HV in Vickers hardness. The reason why the composition of the iron-based powder is limited will be described first. Hereinafter, mass% in the composition is abbreviated as%.

The reason why the composition of the blended iron-based powder is limited will be described below.

C：0.05～0.70%

The iron-based powder blended in the present invention is a powder of a high-speed steel composition reduced in C. When C is less than 0.05%, the hardness of the powder particles is not decreased. On the other hand, if C exceeds 0.70%, the hardness of the powder particles becomes too high, and the compressibility of the powder particles decreases. Therefore, the C content of the iron-based powder is preferably limited to a range of 0.05 to 0.70%. It is more preferable that the content is 0.3 to 0.6%.

Si: less than 0.70%

Si is an element that functions as a deoxidizer, and is remarkable when it is contained in an amount of 0.05% or more in order to obtain such an effect. On the other hand, if the content exceeds 0.70%, the compressibility decreases. Therefore, si is preferably limited to 0.70% or less. It is more preferable that the content is 0.40% or less.

Mn: less than 0.50%

Mn acts as a deoxidizer while contributing to an increase in strength (hardness). This effect becomes remarkable when it is 0.10% or more. On the other hand, if the content exceeds 0.50%, the hardness becomes high and the compressibility decreases. Therefore, mn is preferably limited to 0.50% or less.

Cr:4.5% or less

Cr is an element that forms carbide and has an effect of improving wear resistance. Such an effect becomes remarkable when the content is 2.0% or more, but if the content exceeds 4.5%, toughness is lowered. Therefore, cr is preferably limited to 4.5% or less.

Mo:10.0% or less

Mo is an element that forms fine carbide and has an effect of improving wear resistance. Such an effect becomes remarkable when it is contained at 3.0% or more, but if it exceeds 10.0%, moldability is lowered. Therefore, mo is preferably limited to 10.0% or less. It is more preferable that the content is 4.0 to 6.0%.

V:4.5% or less

V is an element that forms fine carbide and has an effect of improving wear resistance. Such an effect becomes remarkable when the content is 1.5% or more, but when the content exceeds 4.5%, the moldability is lowered. Therefore, V is preferably limited to 4.5% or less.

W:10.0% or less

W is a fine carbide forming agent an element having an effect of improving abrasion resistance. Such an effect becomes remarkable when the content is 5.0% or more, but if the content exceeds 10.0%, the moldability is lowered. Therefore, W is preferably limited to 10.0% or less.

The balance other than the above components is composed of Fe and unavoidable impurities. As unavoidable impurities, P of 0.03% or less and S of 0.02% or less are allowed. Since P segregates at austenite grain boundaries to promote grain boundary brittleness, it is preferable to reduce P as much as possible. It is more preferable that the content is 0.010% or less. In addition, S exists as sulfide-based inclusions in steel, which hampers hot workability, and therefore it is desirable to reduce S as much as possible. It is more preferable that the content is 0.005% or less.

Particle hardness: 170-220 HV

The iron-based powder used in the present invention is a powder having a particle hardness of 170 to 220HV. When the particle hardness is less than 170HV, the hardness of the iron-based powder is too low, and the wear resistance as a sintered body is lowered. On the other hand, if the particle hardness is increased beyond 220HV, the compressibility decreases and the radial compressive strength as a sintered body decreases. Therefore, the particle hardness of the blended iron-based powder is limited to 170 to 220HV.

In addition, in the case of the optical fiber, the hard particle powder to be blended is preferably a Si-Cr-Mo system having the above-mentioned hardness and composition Co-based intermetallic compound particle powder or Si-Cr-Mo-Ni-based Co-based intermetallic compound particles. In the present invention, hard particle powder having such hardness is blended in an amount of 20 to 40% by mass relative to the total amount of the mixed powder.

The hard particle powder to be blended in the mixed powder is preferably one having the above hardness and an average particle diameter of 10 to 150μm. Average particle diameter of less than 10μm is liable to spread during sintering, and the desired abrasion resistance cannot be ensured. On the other hand, over 150μIn m, the bonding force with the substrate is reduced. Therefore, the average particle diameter of the hard particle powder is preferably 10 to 150 μm. The "average particle diameter" refers to the cumulative value measured by the laser light scattering methodThe cloth had a particle size D50 of 50%.

In addition, solid lubricant particles are dispersed in a matrix phase to improve machinability, workability, lubricity. The solid lubricant particles are preferably MnS, moS ₂ Etc. The blending amount of the solid lubricant particle powder is preferably set to 0 to 5% by mass relative to the total amount of the mixed powder.

The above-mentioned iron-based powder, hard particle powder, or solid lubricant powder may be blended in a prescribed amount in the mixed powder, and of course, graphite powder and alloy element powder may be blended so as to have the above-mentioned matrix phase composition and matrix portion composition. The mixed powder may be blended with a lubricant such as zinc stearate.

As described above, a prescribed amount of graphite powder, alloy element powder, hard particle powder, or solid lubricant powder is mixed with the iron-based powder, followed by mixing and kneading to prepare a mixed powder.

Next, the obtained mixed powder was filled in a mold having a predetermined valve seat shape.

After filling the mixed powder into a mold, press working is performed by a press working machine or the like to prepare a pressed powder having a valve seat shape. The press working is preferably performed so that the density of the pressed powder is 6.6g/cm ³ The adjustment is performed in the above manner.

Then, the obtained pressed powder is subjected to a sintering treatment to prepare a sintered body.

The sintering treatment is preferably performed in a temperature range of 1100 to 1200 ℃ which is a heating temperature in a protective environment. When the heating temperature is lower than 1100 ℃, sintering diffusion is insufficient, while when it exceeds 1200 ℃, excessive diffusion occurs, and abrasion resistance is lowered. The press P-sintering step S may be repeated a plurality of times (e.g., 2P 2S).

The obtained sintered body is subjected to grinding, cutting, etc., to produce a valve seat of a desired size and shape.

Next, in the method for manufacturing the iron-based sintered alloy valve seat having the double-layer structure according to the present invention, the above-described mixed powder (mixed powder for the functional member side layer) is prepared, and the mixed powder for the support member side layer is also prepared.

The mixed powder for the support member side layer is prepared by mixing a predetermined amount of iron-based powder, graphite powder, or alloy element powder, hard particle powder, and solid lubricant powder, and mixing and kneading the mixture. In the mixed powder for the support member side layer, the iron-based powder is a pure iron powder, 0.5 to 2.0% of graphite powder is blended in mass% with respect to the total amount of the mixed powder for the support member side layer, 0 to 5.0% of alloy element powder is blended in mass% with respect to the total amount of the mixed powder for the support member side layer, the hard particle powder is an iron-molybdenum (Fe-Mo) alloy powder, 0 to 5% of the hard particle powder is blended in mass% with respect to the total amount of the mixed powder for the support member side layer, and 0 to 5% of solid lubricant powder is blended in mass% with respect to the total amount of the mixed powder for the support member side layer.

Then, the mixed powder for the functional member side layer and the mixed powder for the support member side layer are sequentially filled in a mold of a predetermined shape at a desired ratio.

After filling the powder into the mold, press working was performed in the same manner as in the case of the above-described single-layer structure to prepare a green compact, and then sintering treatment was performed on the green compact in the same manner as in the case of the above-described single-layer structure to obtain a sintered compact of a double-layer structure.

The obtained sintered body of the double-layer structure is subjected to processing such as grinding and cutting, and a valve seat of a double-layer structure having a desired size and shape is produced.

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

Examples

First, a mixed powder for a functional member side layer and a mixed powder for a support member side layer are prepared.

The powder mixture for the functional member side layer was prepared by adjusting the blending amounts of graphite powder, alloy element powder, hard particle powder, and solid lubricant powder (MnS powder) to those shown in table 1 in the iron-based powder for matrix phase formation, and mixing and kneading the powders to prepare powder mixtures (nos. a to k). The iron-based powder used was a high-speed tool steel-based powder (nos. a to d) having the composition and hardness shown in table 2. The hard particle powder used was a particle powder having the composition, hardness, and average particle diameter shown in Table 3 (Nos. h1 to H2).

The mixed powder for the support member side layer was prepared by mixing and kneading iron-based powder, graphite powder, or alloy element powder, hard particle powder, and solid lubricant particle powder for matrix phase formation in amounts shown in table 1, and then preparing mixed powders (nos. 1a to 1 b). The iron-based powder used was a powder (No. e) having a composition and hardness shown in table 2. The iron-based powder No. e is pure iron powder. The hard particle powder used was a particle powder (No. h 3) having the composition, hardness, and average particle diameter shown in table 3. Hard particle powder No. h3 is iron ferromolybdenum. In the mixed powder, 1 part by mass of zinc stearate was blended as a lubricant with respect to 100 parts by mass of the mixed powder. In a part of the valve seat, a single-layer structure having only the functional member side layer is produced.

TABLE 1

TABLE 2

TABLE 3

The obtained mixed powder was filled in a mold, and a press-molded powder having a predetermined valve seat shape was produced by using a press-molding machine. The density of the obtained compact was measured by the archimedes method.

Then, the obtained green compact was subjected to a sintering treatment. The sintering treatment was carried out in a sintering furnace (holding time: 6 hours) at a heating temperature of 1150 ℃ in a protective atmosphere to prepare a sintered body.

The obtained sintered body was further subjected to machining such as cutting and polishing, to thereby obtain an iron-based sintered alloy valve seat having a predetermined shape (outer diameter: 27mm ϕ. Times.inner diameter: 22mm ϕ. Times.6 mm in thickness).

The obtained valve seat was subjected to chemical analysis, tissue observation, hardness test, density test, abrasion test, and radial compressive strength test. The test method is as follows.

(1) Chemical analysis

The analysis samples were collected from the respective parts of the obtained valve seat, and the contents of the respective components of the respective parts were analyzed by a luminescence analysis method to obtain the composition of the sintered body matrix portion.

(2) Tissue observation

The obtained valve seat was polished in a cross section perpendicular to the axial direction, and etched (etching solution: nitric acid-ethanol solution) to give a structure, and the type of matrix phase structure was determined by observation under an optical microscope (magnification: 200 times). Further, the particle size of the carbide precipitated in the matrix phase was measured using a scanning electron microscope (magnification: 2000 times), and it was confirmed that the maximum particle size of the carbide was 10μm or less, wherein the matrix phase is a fine carbide precipitated phase. The maximum diameter of the carbide grain diameter (length of long side) exceeds 10μm, only a carbide precipitated phase is formed. Further, an observation field of view (30) was measured for carbide precipitated in the matrix phase by using a scanning electron microscope (magnification: 2000) μm×30μm), the carbide precipitation density (individual/(30)μm×30μm))。

(3) Hardness test

The obtained valve seat was polished in a cross section perpendicular to the axial direction, and etched (etching solution: nitric acid ethanol solution) to give a structure, and the vickers hardness HV of the matrix phase was measured using a vickers hardness tester (test force: 0.98N (100 gf)).

(4) Density test

The density (sintered body density) of the obtained valve seat was measured by an archimedes method.

(5) Abrasion test

The obtained valve seat was subjected to a wear test under the test conditions shown below using a drilling tester shown in fig. 1.

Test temperature: 300 ℃ (valve seat surface);

test time: 12 hours;

cam rotational speed: 3000rpm;

valve rotational speed: 20rpm;

impact load: 700N.

Valve material: heat-resistant steel with nitride film (SUH 35 surface hardness 1150 HV).

After the test, the abrasion loss of the test piece (valve seat) was measured. The wear ratio of the valve seat was calculated from the obtained wear amount based on valve seat No.1 (conventional example) (1.00).

(6) Radial compressive Strength test

The radial compressive strength of the obtained valve seat was obtained in accordance with the regulation of JIS Z2507. The radial compressive strength ratio of the valve seat was calculated from the radial compressive strength obtained based on the valve seat No.1 (conventional example) (1.00). The radial compressive strength of the valve seat No.1 (conventional example) was 470MPa.

The results obtained are shown in tables 4 and 5.

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In the present invention, the precipitation density of carbide in the matrix phase was significantly improved as compared with the conventional example (valve seat No. 1), and carbide was finely dispersed as compared with the conventional example. Thus, the sintered compact density is increased, and the radial compressive strength is increased, the wear ratio is decreased, and the wear resistance is improved.

Symbol description

1: a valve seat;

2: cylinder block equivalent material;

3: a heating device;

4: and (3) a valve.

Claims

1. An iron-based sintered alloy valve seat having a single-layer structure composed of a functional member side layer, characterized in that:

density of 6.65g/cm ³ The above is excellent in radial compressive strength.

2. The iron-based sintered alloy-made valve seat according to claim 1, wherein a matrix portion including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: comprises, by mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, and the balance being Fe and unavoidable impurities.

3. An iron-based sintered alloy valve seat having a double-layer structure in which a functional member side layer and a support member side layer are integrally sintered, characterized in that:

the functional member side layer is formed by a matrix phase and hard particles and solid lubricant particles dispersed in the matrix phase, and has the following structure:

The hard particles are Si-Cr-Mo Co-based intermetallic compound particle powder having a hardness of 650 to 1200HV in terms of Vickers hardness, and containing 2.20 to 2.70% by mass of Si, 7.5 to 9.5% by mass of Cr, 27.0 to 30.0% by mass of Mo, and the balance being Co and unavoidable impurities; or Si-Cr-Mo-Ni-based Co-based intermetallic compound particles having a hardness of 650 to 1200HV in terms of Vickers hardness, comprising, by mass%, 1.5 to 2.5% of Si, 24.0 to 26.0% of Cr, 23.0 to 26.0% of Mo, 9.5 to 11.0% of Ni, and the balance Co, wherein 20 to 40% of the hard particles are dispersed in terms of area ratio in the matrix phase, and 0 to 5% of the solid lubricant particles are dispersed in terms of area ratio,

density of 6.65g/cm ³ The above is excellent in radial compressive strength.

4. The iron-based sintered alloy valve seat according to claim 3, wherein:

the matrix portion of the functional member side layer including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: comprises, by mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, the balance being Fe and unavoidable impurities,

The matrix portion of the support member side layer including the matrix phase, the hard particles, and the solid lubricant particles has the following composition: contains 0.9 to 2.0% by mass of C, or contains 1 or more than 2 selected from Ni of 0.5% or less, mo of 0.4 to 0.8% or less, cu of 5.0% or less, mn of 5.0% or less, S of 2.0% or less, and the balance being Fe and unavoidable impurities.

5. A method for producing an iron-based sintered alloy valve seat according to claim 1 or 2, characterized by comprising:

6. The method for manufacturing an iron-based sintered alloy valve seat according to claim 5, wherein:

The sintered body has a particle diameter of 10μFine carbide of m or less is 150/(30)μm×30μm) a matrix phase which is a fine carbide-precipitated phase having a density of not less than 550HV in terms of Vickers hardness, and having the following structure and composition:

the organization is as follows: the hard particles are dispersed with 20-40% of the area ratio, and the solid lubricant particles are also dispersed with 0-5% of the area ratio; and, the composition is: the matrix portion including the matrix phase, the diffusion phase, the hard particles, and the solid lubricant particles contains, in mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, and the balance being Fe and unavoidable impurities.

7. A method for manufacturing an iron-based sintered alloy valve seat according to claim 3 or 4, characterized by comprising:

8. The method for manufacturing an iron-based sintered alloy valve seat according to claim 7, wherein the sintered body having a double layer structure is a sintered body having a double layer structure, and the functional member side layer has: particle size of 10μFine carbide of m or less is 150/(30)μm×30μm) a matrix phase which is a fine carbide-precipitated phase having a density of not less than 550HV in terms of Vickers hardness; a matrix phase containing 20 to 40% by area of hard particles and 0 to 5% by area of solid lubricant particles; comprising the matrix phase, the hard particles and the solid lubricantThe matrix part of the agent particles comprises, in mass%, 1.0 to 2.0% of C, 0.5 to 1.5% of Si, less than 2.0% of Mn, 2.0 to 10.0% of Cr, 5.0 to 15.0% of Mo, 0.5 to 10.0% of W, 0.5 to 5.0% of V, 10.0 to 35.0% of Co, 0 to 5.0% of Ni, 0 to 2.0% of S, and the balance of Fe and unavoidable impurities,