Patent Application
20240344467
The present invention relates to a valve seat insert for an internal combustion engine, and particularly to an iron-based sintered alloy valve seat insert having excellent wear resistance.
A valve seat insert is press-fitted into a cylinder head of an internal combustion engine, and plays roles of sealing for a combustion gas and cooling a valve. Conventionally, a valve seat insert has been required to have excellent heat-resistance and wear resistance, and to have low opposite aggressiveness so as not to wear a valve as a mating material, because the valve seat insert is exposed to hitting by a valve, wear due to sliding, heating due to combustion gas, corrosion due to combustion products, and the like.
In response to such a demand, for example, Patent Literature 1 describes a sintered alloy valve seat insert for an internal combustion engine having excellent wear resistance. The sintered alloy valve seat insert described in Patent Literature 1 is an iron-based sintered alloy valve seat insert in which hard particles and solid lubricant particles are dispersed in a base matrix phase, in which the base matrix phase is a fine carbide precipitation phase from which fine carbide having a particle diameter of 10 μm or smaller is precipitated and which has a hardness of 550 HV or more in terms of Vickers hardness, and has a structure in which hard particles having a hardness of 650 to 1200 HV in terms of Vickers hardness are dispersed at 20% to 40% in terms of area ratio and solid phase lubricant particles are dispersed at 0% to 5% in terms of area ratio, and a base matrix part including the base matrix phase, the diffusion phase, the hard particles, and the solid lubricant particles in which a diffusion phase is formed at more than 0% and 5% or less in terms of area ratio and the solid lubricant particles are dispersed at 0% to 5% in terms of area ratio has a composition including C: 0.5% to 2.0%, Si: 0.5% to 2.0%, Mn: 5% or less, Cr: 2% to 15%, Mo: 5% to 20%, and Co: 2% to 30%, in terms of mass %. Accordingly, the wear resistance of the valve seat insert is improved even in a severe wear environment.
Patent Literature 2 describes an iron-based sintered alloy valve seat insert. The valve seat insert described in Patent Literature 2 is a valve seat insert having a double-layer structure in which a valve-contacting face side and a seating face side are integrally sintered. The valve-contacting face side is made of an iron-based sintered alloy material having a porosity of 10% to 25% in terms of volume ratio and a density after sintering of 6.1 g/cm3 to 7.1 g/cm3, in which hard particles are dispersed in a base matrix phase, the hard particles are particles composed of one or two or more elements selected from C, Cr, Mo, Co, Si, Ni, S, and Fe, and are dispersed at 5% to 40% in terms of area ratio, and there is 10.0% to 40.0% in total of one or two or more selected from Ni: 2.0% to 23.0%, Cr: 0.4% to 15.0%, Mo: 3.0% to 15.0%, Cu: 0.2% to 3.0%, Co: 3.0% to 15.0%, V: 0.1% to 0.5%, Mn: 0.1% to 0.5%, W: 0.2% to 6.0%, C: 0.8% to 2.0%, Si: 0.1% to 1.0%, and S: 0.1% to 1.0%, in terms of mass %, in a composition of a base matrix part including the base matrix phase and the hard particles, with a remainder being Fe and inevitable impurities. In Patent Literature 2, as the hard particles, Cr—Mo—Co type intermetallic compound particles, Ni—Cr—Mo—Co type intermetallic compound particles, Fe—Mo alloy particles, Fe—Ni—Mo—S type alloy particles, and Fe—Mo—Si type alloy particles are exemplified.
In the valve seat inserts described in Patent Literature 1 and 2, it is stated that a large amount of Co is preferably contained in the base matrix phase or the hard particles in order to contribute to improvement in high-temperature strength or toughness of the base matrix phase or improvement in wear resistance. However, in recent years, there has been an increasing risk that the price of Co will rise or it will become difficult to obtain Co, due to the political instability of production countries and an increase in the amount of Co used in other fields such as lithium ion batteries. Therefore, it is desired to limit the use of Co.
In response to such a demand, for example, Patent Literature 3 proposes an iron-based sintered alloy valve seat insert. The iron-based sintered alloy valve seat insert described in Patent Literature 3 is an iron-based sintered alloy valve seat insert in which hard particles are dispersed in a base matrix phase, and which has an entire composition including Cr: 5.0% to 20.0%, Si: 0.4% to 2.0%, Ni: 2.0% to 6.0%, Mo: 5.0% to 25.0%, W: 0.1% to 5.0%, V: 0.5% to 5.0%, Nb: 1.0% or less, and C: 0.5% to 1.5%, in terms of mass %, with a remainder being Fe and inevitable impurities. In the iron-based sintered alloy valve seat insert described in Patent Literature 3, it is stated that it is preferable to use, as hard particles, Fe—Mo—Si alloy particles containing Mo: 40.0% to 70.0%, Si: 0.4% to 2.0%, and C: 0.1% or less in terms of mass %, with a remainder being Fe and inevitable impurities.
Patent Literature 4 proposes a hard particle-dispersed iron-based sintered alloy. The hard particle-dispersed iron-based sintered alloy described in Patent Literature 4 is a hard particle-dispersed iron-based sintered alloy in which 3% to 20% of hard particles based on the entire alloy are dispersed and sintered in a matrix containing Si: 0.4% to 2%, Ni: 2% to 12%, Mo: 3% to 12%, Cr: 0.5% to 5%, V: 0.6% to 4%, Nb: 0.1% to 3%, C: 0.5% to 2%, and a remainder being Fe in terms of weight percentage, and the hard particles contain Mo: 60% to 70%, B: 0.3% to 1%, C: 0.1% or less, and a remainder being Fe. When B is added to ferromolybdenum-type hard particles, B improves the wettability of ferromolybdenum, prevents the hard particles from falling off from the base matrix, improves adhesion between the base matrix and the hard particles, and can improve the thermal strength and the mechanical strength of the sintered alloy.
However, it has been found that the techniques described in Patent Literature 3 and 4 have problems that iron-based hard particles not containing dispersed Co are more prone to be cracked and chipped than conventional Co-based hard particles, hard particles fall off from the base matrix phase, and in particular, desired wear resistance cannot be secured under a severe environment in which a valve seat insert has been used in recent years. In addition, in a case where common Ni-based hard particles not containing Co are dispersed, there is a problem that hardness is low and adhesion is prone to occur. It was thought that this was because Co contributes to effects of promoting diffusion into a base matrix in a case of being contained in hard particles and promoting a progress of sintering of a base matrix in a case of being contained in the base matrix and plays a major role in improving the strength of the valve seat insert; however, in the techniques described in Patent Literature 3 and 4, since Co is not contained, the effects of promoting the diffusion of alloy elements from hard particles to the base matrix and promoting the sintering of the base matrix are poor, and sufficient strength as a valve seat insert cannot be obtained.
In view of such problems of the prior art, an object of the present invention is to provide an iron-based sintered alloy valve seat insert for an internal combustion engine which has a sintered body composition not containing Co, is excellent in wear resistance, and has sufficient strength as a valve seat insert. The term “excellent in wear resistance” as used herein refers to a case where wear resistance is improved as compared with an iron-based sintered alloy valve seat insert having a conventional Co-containing sintered body composition. The term “sufficient strength as a valve seat insert” as used herein refers to strength at which cracks and cracking do not occur at the time of press-fitting or the like, and can be determined on the basis of radial crushing strength determined in accordance with the provisions of JIS Z 2507.
In order to achieve the object, the present inventors first conducted intensive studies on the influence on wear resistance of hard particles having a composition not containing Co and a base matrix phase having a composition not containing Co. As a result, the present inventors have newly found that even with hard particles having a composition not containing Co, occurrence of cracking or chipping of the hard particles is avoided, hardness is secured, and adhesion of the hard particles and the base matrix is avoided, thereby making it possible to prevent a wear resistance from decreasing and to secure wear resistance equal to or higher than that in a case of using conventional Co-based hard particles.
As a result of further studies, the present inventors have found that it is preferable to use, as hard particles, Si—Cr—Ni—Fe type Mo-based intermetallic compound particles having a composition containing 1.5% to 3.5% of Si, 7.0% to 9.0% of Cr, 35.0% to 45.0% of Mo, and 5.0% to 20.0% of Ni, in terms of mass %, and a remainder being Fe and inevitable impurities.
First, experimental results on which the present invention is based will be described.
Amounts of an iron based powder for forming a base matrix phase, a hard particle powder, an alloy element powder, and a solid lubricant powder were adjusted so as to satisfy the blending amounts shown in Table 1, and mixed to obtain a mixed powder. The used iron based powder for base matrix phase formation was iron based powders No. a and No. b having the compositions shown in Table 2. Also, the used hard particle powder was hard particle powders No. MA and No. MD having the compositions shown in Table 3. The hard particle powder No. MA is a common Co-based intermetallic compound particle powder, and the hard particle powder No. MD is a Mo-based intermetallic compound particle powder not containing Co. The Vickers hardness HV of each particle powder is also shown in Table 3. As the solid lubricant particle powder, a MnS particle powder was used. In addition, into the mixed powder, 0.75 parts by mass of zinc stearate was blended as a lubricant with respect to 100 parts by mass of the mixed powder.
A die was then filled with the resulting mixed powder, and the mixed powder was formed into a green compact having a predetermined valve seat insert shape by a powder forming machine. The green compact was further subjected to a dewaxing step, and subjected to sintering at 1100° C. to 1200° C. for 0.5 hr in a reducing atmosphere to obtain a sintered body. The obtained sintered body was further subjected to processing such as cutting and polishing to obtain an iron-based sintered alloy valve seat insert having a predetermined dimensional shape (outer diameter: 32.1 mmφ×inner diameter: 26.1 mm×thickness: 5.5 mm).
The obtained valve seat insert (sintered body) was subjected to a hard particle crack resistance test and a wear test. A test method was as follows.
With respect to the obtained valve seat insert (sintered body), a cross section was polished, an impression was imparted using a Vickers hardness meter (test force: 0.98 N) so as to fit within hard particles (20 particles respectively) dispersed in a base matrix phase, and the presence or absence of occurrence of cracking in each particle imparted with the impression was observed with an optical microscope. In a case where a crack was generated outside from the impression, it was determined that cracking occurred, and the number of particles in which cracking occurred (the number of cracking occurrences) was investigated. Using the number of cracking occurrences of the valve seat insert No. S1 as a reference (=1.0), a ratio of the number of occurrences of cracking of the hard particles of the valve seat insert to the reference (cracking occurrence ratio) was calculated.
The obtained valve seat insert was subjected to a wear test under the following test conditions using a single rig wear testing machine shown in
After the test, a wear amount of the test piece (valve seat insert) was measured. From the obtained wear amount, a wear ratio of the valve seat insert was calculated with the valve seat insert No. S1 as a reference (=1.00).
With respect to the obtained valve seat insert (only a valve contacting face material side layer), the radial crushing strength was determined in accordance with the provisions of JIS Z 2507.
The obtained results are shown in Table 4.
In a case of the valve seat insert (No. S4) using the hard particle powder No. MD, which is a Mo-based intermetallic compound particle powder having a composition not containing Co, there is no occurrence of cracking or the like of the hard particles, and it is possible to obtain a valve seat insert having a wear resistance equal to or higher than that in a case of using Co-based intermetallic compound particles as the hard particles (valve seat insert No. S1). That is, it was found that by dispersing Si—Cr—Ni—Fe type Mo-based intermetallic compound particles having a composition not containing Co as hard particles in a base matrix phase, a decrease in wear resistance can be prevented.
In addition, the present inventors have found that in order to further improve the wear resistance, when increasing a proportion of the fine carbide precipitation phase in the base matrix phase in addition to dispersing the hard particles having the above-described composition, the wear resistance can be improved.
The present invention has been completed by further conducting studies based on such findings. That is, the gist of the present invention is as follows.
According to the present invention, it is possible to obtain a valve seat insert having excellent wear resistance with less occurrence of cracking or chipping of hard particles and no occurrence of adhesion even under a severe wear environment, and it is possible to obtain an industrially remarkable effect.
The valve seat insert of the present invention is made of an iron-based sintered alloy, and has a double-layer structure in which a valve contacting face material side layer on which a valve is seated and a supporting material side layer that is seated on a cylinder head and supports the valve contacting face material side layer are integrally sintered, or has a single-layer structure of only the valve contacting face material side layer.
An iron-based sintered alloy material constituting the valve contacting face material side layer of the valve seat insert of the present invention has a structure in which hard particles and optionally solid lubricant particles are dispersed in a base matrix phase, and has characteristics excellent in wear resistance. The term “excellent in wear resistance” as used herein refers to a case where wear resistance is improved to be equal to or higher than that of an iron-based sintered alloy material having a conventional Co-containing sintered body composition.
In the valve contacting face material side layer of the valve seat insert of the present invention, the hard particles dispersed in the base matrix phase are Si—Cr—Ni—Fe type Mo-based intermetallic compound particles having a hardness of 700 to 1300 HV in terms of Vickers hardness.
When the hardness of the hard particles is less than 700 HV, adhesion occurs in the hard particles themselves and the effect of improving the wear resistance is small, and when the hardness exceeds 1300 HV, toughness of the hard particles is reduced and machinability is reduced. For this reason, the hardness of the hard particles dispersed in the base matrix phase was limited to the range of 700 to 1300 HV in terms of Vickers hardness.
The hard particles dispersed in the base matrix phase in the present invention preferably have the hardness described above and have an average particle diameter of 10 to 150 μm. When the average particle diameter is smaller than 10 μm, the particles are prone to be diffused during sintering. On the other hand, when the average particle diameter is larger than 150 μm, the bonding force with the base matrix decreases and the wear resistance decreases. Therefore, the average particle diameter of the hard particles dispersed in the base matrix phase is preferably limited to the range of 10 to 150 μm. The term “average particle diameter” as used herein means a particle diameter D50 at which a cumulated distribution measured by a laser diffraction method is 50%.
In addition, in the present invention, the hard particles having the hardness described above are dispersed in the base matrix phase by 10% to 40% in terms of area ratio. When a dispersed amount of the hard particles is less than 10%, desired wear resistance cannot be secured. On the other hand, when the dispersed amount is more than 40%, the bonding force with the base matrix phase decreases, and the wear resistance decreases. Therefore, the dispersed amount of the hard particles dispersed in the base matrix phase was limited to the range of 10% to 40% in terms of area ratio with respect to the entire base matrix phase.
In the present invention, the Si—Cr—Ni—Fe type Mo-based intermetallic compound particles to be dispersed in the base matrix phase are Mo-based intermetallic compound particles having a composition (hard particle composition) containing Si: 1.5% to 3.5%, Cr: 7.0% to 9.0%, Mo: 35.0% to 45.0%, and Ni: 5.0% to 20.0% in terms of mass %, with a remainder being Fe and inevitable impurities.
By using the hard particles having the hard particle composition described above, it is possible to obtain a valve seat insert including hard particles having a structure from which an intermetallic compound is precipitated after sintering. In addition, in order to obtain hard particles having a hardness of 700 HV or more in terms of Vickers hardness in which occurrence of cracking, chipping, and the like is suppressed and from which an intermetallic compound having high resistance to hard particle cracking is precipitated, it is important to maintain the Mo content as high as 35.0% to 45.0%. Further, in order to obtain hard particles which further have toughness and maintain desired hardness, it is important to set the Ni content in the range of 5.0% to 20.0%.
In the valve contacting face material side layer of the valve seat insert of the present invention, solid lubricant particles may be further dispersed in the base matrix phase. By dispersing the solid lubricant particles in the base matrix phase, machinability and lubricity are improved. However, when more than 5% thereof in terms of area ratio are dispersed, deterioration of mechanical properties is significant. Therefore, the solid lubricant particles were limited to the range of 0% to 5% in terms of area ratio. The solid lubricant particles are preferably one or two selected from manganese sulfide MnS and molybdenum disulfide MOS2.
The base matrix phase of the valve contacting face material side layer of the valve seat insert of the present invention preferably has a structure including 10% to 90% and more preferably 10% to 85% of a fine carbide precipitation phase and 0% to 30% of a high-alloy phase, with a remainder being pearlite, a structure including 0% to 15% of a high-alloy phase with a remainder being a fine carbide precipitation phase, or a structure including 0% to 25% of a high-alloy phase with a remainder being a bainite phase in terms of area ratio where an area of the base matrix phase excluding hard particles and solid lubricant particles is 100%. The fine carbide precipitation phase is a hard phase from which fine carbide having a particle diameter of 10 μm or smaller is precipitated and which has a hardness of 400 to 600 HV in terms of Vickers hardness. Due to the presence of such a hard fine carbide precipitation phase, the base matrix can be strengthened, and the wear resistance is further improved. In the valve contacting face material side layer of the valve seat insert of the present invention, the base matrix phase excluding the hard particles and the solid lubricant particles may have a structure including 0% to 30% of the high-alloy phase and a remainder being pearlite. Even in the base matrix phase having such a structure, as long as the sintered body has a composition not containing Co, the wear resistance is improved as compared with the sintered body having a composition containing Co at the same hardness level.
The high-alloy phase is a region where the alloy element diffuses from the hard particles during sintering and the alloy amount increases, and has an action of preventing the hard particles from falling off. In the valve contacting face material side layer, the high-alloy phase can be allowed up to 30% in terms of area ratio when an area of the base matrix phase excluding the hard particles and the solid lubricant particles is 100%.
As described above, the valve contacting face material side layer of the valve seat insert of the present invention has a structure in which a predetermined amount of the hard particles having the composition, the structure, and the hardness described above and the solid lubricant particles having the composition described above are dispersed in the base matrix phase having the structure described above.
In the valve contacting face material side layer of the valve seat insert of the present invention, the base matrix part containing the base matrix phase, the hard particles, and the solid lubricant particles has a base matrix part composition containing, in terms of mass %, C: 0.5% to 2.0%, Si: 0.2% to 2.0%, Mn: 5% or less, Cr: 0.5% to 15%, Mo: 3% to 20%, and Ni: 1% to 10%, and further containing V: 0% to 5%, W: 0% to 10%, S: 0% to 2%, and Cu: 0% to 5%, with a remainder being Fe and inevitable impurities.
Next, the reason for limitation in the base matrix part composition of the valve contacting face material side layer will be described. Hereinafter, mass % in the composition is simply expressed as %.
C is an element necessary for adjusting the base matrix phase to have a predetermined hardness and structure or for forming carbide, and is contained in an amount of 0.5% or more. On the other hand, when the content is more than 2.0%, a melting point decreases, and sintering becomes liquid phase sintering. In the case of the liquid phase sintering, the amount of precipitated carbide is excessively large, the number of pores is increased, and elongation characteristics and dimensional accuracy deteriorate. Therefore, C was limited to the range of 0.5% to 2.0%. The content is preferably 0.50% to 2.00%, and more preferably 1.00% to 1.50%.
Si is an element mainly contained in the hard particles and constituting an intermetallic compound, and increases the hardness of the hard particles and also increases the base matrix strength to improve the wear resistance. For this purpose, the content is preferably 0.2% or more. On the other hand, when the content is more than 2.0%, the opposite aggressiveness increases. For this reason, Si was limited to the range of 0.2% to 2.0%. The content is preferably 0.20% to 2.00%. The content is more preferably 0.20% to 1.40%.
Mn is an element that increases the hardness of the base matrix phase, and Mn is an element that is contained in the base matrix part due to the solid lubricant particles and contributes to improvement in machinability, and is preferably contained at 0.05% or more. On the other hand, when the content is more than 58, the base matrix phase hardness, toughness, and ductility decrease. Therefore, Mn was limited to the range of 5% or less. The content is preferably 5.00% or less, and more preferably 0.20% to 3.00%.
Cr is an element that forms a solid solution in the base matrix phase and forms carbide to increase the hardness of the base matrix phase, and Cr is an element that contributes to an increase in the hardness of hard particles as a constituent element of an intermetallic compound, and is preferably contained in an amount of 0.5% or more as a base matrix part. On the other hand, when the content is more than 15%, the precipitation of Cr carbide in the base matrix phase becomes excessive, and it becomes difficult to form carbide in the base matrix phase into fine carbide. Therefore, Cr was limited to the range of 0.5% to 15%. The content is preferably 1.00% to 15.00%, and more preferably 0.70% to 6.00%.
Mo is an element that forms a solid solution in the base matrix phase and precipitates as carbide to increase the base matrix phase hardness, and Mo is an element that contributes to an increase in the hardness of hard particles as a constituent element of the intermetallic compound, and is preferably contained in an amount of 3% or more as a base matrix part. On the other hand, when the content is more than 20%, a density during powder forming is less prone to increase, and formability deteriorates. Therefore, Mo is limited to the range of 3% to 20%. The content is preferably 4.00% to 20.00%, and more preferably 4.00% to 19.00%.
Ni is an element that contributes to improvement in strength and toughness of the base matrix phase, and Ni is an element that contributes to increase in hardness of hard particles as a constituent element of the intermetallic compound, and is contained in an amount of 1% or more. On the other hand, when the content is more than 10%, the density during powder forming is less prone to increase, and formability deteriorates. Therefore, Ni is limited to the range of 1% to 10%. The content is preferably 1.00% to 10.00%, and more preferably 2.00% to 9.00%.
The above components are basic components, and it is possible to further contain V: 0% to 5%, W: 0% to 10%, S: 0% to 2%, and Cu: 0% to 5% as selective elements.
V is an element that precipitates as fine carbide, increases the hardness of the base matrix phase, and improves the wear resistance, and can be contained as necessary. When contained, the content is preferably 0.5% or more. On the other hand, when the content is more than 5%, formability deteriorates. Therefore, V is preferably limited to the range of 0% to 5%. The content is more preferably 5.00% or less, and still more preferably 2.00% or less.
W is an element that precipitates as fine carbide, increases the hardness of the base matrix phase, and improves the wear resistance, and can be contained as necessary. When contained, it is preferably contained at 0.5% or more. On the other hand, when the content is more than 108, formability deteriorates. Therefore, W is preferably limited to the range of 0% to 10%. The content is more preferably 10.00% or less, and still more preferably 5.00% or less.
S is an element that is contained in the solid lubricant particles, is contained in the base matrix part, and contributes to improvement in the machinability, and can be contained as necessary. When S is contained in an amount more than 2%, toughness and ductility deteriorate. Therefore, S is preferably limited to the range of 0% to 2%. The content is more preferably 2.00% or less.
Cu is an element that contributes to improvement in the strength and toughness of the base matrix phase, and can be contained as necessary. When Cu is contained in an amount more than 5%, adhesion resistance is reduced. Therefore, Cu is preferably limited to the range of 0% to 5%. The content is more preferably 5.00% or less.
The remainder other than the above components is composed of Fe and inevitable impurities. As the inevitable impurities, P: 0.1% or less is acceptable.
In addition, the iron-based sintered alloy material constituting the supporting material side layer of the valve seat insert of the present invention has a structure including a base matrix phase, and 0% to 5% of solid lubricant particles in terms of area ratio and 0% to 5% of hardness improving particles in terms of area ratio dispersed in the base matrix phase. The base matrix phase of the supporting material side layer of the valve seat insert of the present invention preferably has a structure including 100% of pearlite or 100% of a bainite phase, in terms of area ratio when an area of the base matrix phase excluding the solid lubricant particles and the hardness improving particles is 100%. In the base matrix phase, a high-alloy phase up to 5% in terms of area ratio when an area of the base matrix phase excluding the solid lubricant particles is 100% is acceptable. The hardness improving particles are preferably iron-molybdenum alloy (also referred to as Fe—Mo alloy and ferromolybdenum alloy) particles. The Fe—Mo alloy particles preferably have a composition containing, for example, 60 mass % of Mo and a remainder being Fe and inevitable impurities.
In the supporting material side layer of the valve seat insert of the present invention, the base matrix part including the base matrix phase, the solid lubricant particles, and the hardness improving particles has a composition containing C: 0.3% to 1.3% in terms of mass %, and further containing Ni: 0% to 2.0%, Mo: 0% to 2.0%, Cu: 0% to 5.0%, Cr: 0% to 5.0%, Mn: 0% to 5.0%, and S: 0% to 2.0%, with a remainder being Fe and inevitable impurities. The reason for limiting the base matrix part composition of the supporting material side layer is as follows.
C is an element necessary for adjusting the base matrix phase of the supporting material side layer to have a predetermined hardness and structure or for forming carbide, and is contained in an amount of 0.3% or more. On the other hand, when the content is more than 1.3%, a melting point decreases, and sintering becomes liquid phase sintering. In the case of the liquid phase sintering, the amount of precipitated carbide is excessively large, and elongation characteristics and dimensional accuracy deteriorate. Therefore, C was limited to the range of 0.3% to 1.3%. The content is preferably 0.30% to 1.30%, and more preferably 0.80% to 1.20%.
Ni, Mo, Cu, and Cr are all elements that increase the hardness of the base matrix phase, and can be contained as necessary. In order to obtain such an effect, it is desirable to contain Ni: 0.1% or more, Mo: 0.1% or more, Cu: 0.1% or more, and Cr: 0.1% or more. On the other hand, when the contents are respectively more than Ni: 2.0%, Mo: 2.0%, Cu: 5.0%, and Cr: 5.0%, the formability of the base matrix phase deteriorates. Therefore, it is preferable to limit the contents to the ranges of Ni: 0% to 2.0%, Mo: 0% to 2.0%, Cu: 0% to 5.0%, and Cr: 0% to 5.0%. The contents are more preferably Ni: 2.00% or less, Mo: 2.00% or less, Cu: 5.00% or less, and Cr: 5.00% or less.
Mn and S are both elements that are contained in the base matrix part due to the content of the solid lubricant particles and contribute to improvement in the machinability, and can be contained as necessary. Mn also contributes to an increase in hardness of the base matrix phase. When S is more than 2.0% and Mn is more than 5.0%, ductility is significantly reduced. Therefore, it is preferable to limit to S: 0% to 2.0% and Mn: 0% to 5.0%. The contents are more preferably S: 2.00% or less, and Mn: 5.00% or less.
In the supporting material side layer, the remainder other than the above components is composed of Fe and inevitable impurities. As the inevitable impurities, P: 0.1% or less is acceptable.
Next, a preferred method of producing the valve seat insert of the present invention will be described.
First, a raw-material powder for the valve contacting face material side layer and a raw-material powder for the supporting material side layer are blended and mixed so as to have the composition and the structure of the base matrix phase and the composition and the structure of the base matrix part to obtain a mixed powder for the valve contacting face material side layer and a mixed powder for the supporting material side layer. As the raw-material powder for the valve contacting face material side layer, an alloy element powder, a hard particle powder, and a solid lubricant particle powder are blended into an iron based powder for base matrix phase formation so as to have the predetermined composition and structure described above. In addition, as the raw-material powder for the supporting material side layer, a graphite powder, or further an alloy element powder, a solid lubricant particle powder, and a hardness improving particle powder are blended into the iron based powder for base matrix phase formation so as to have the predetermined composition and structure described above. As the hard particle powder to be blended into the mixed powder as the raw-material powder, it is preferable that a molten metal having the above-described hard particle composition is melted by a common smelting method, and a powder (powder for hard particles) is obtained using a common atomizing method.
The iron based powder to be blended into the mixed powder is preferably any one of an atomized pure iron powder, a reduced iron powder, and an alloy steel powder, or a mixture thereof. The alloy steel powder is preferably a powder having a high speed tool steel composition defined in JIS G 4403 such that a fine carbide precipitation phase having the hardness described above can be formed as the base matrix phase. The high speed tool steel is preferably a Mo type such as SKH 51. In addition to the high speed tool steel composition, there is no problem even if an alloy steel having the above-described hardness and having a composition capable of forming a fine carbide precipitation phase or a bainite phase is used. As the mixed powder, it is needless to say that the graphite powder or further the alloy element powder is blended into the pure iron powder, into the pure iron powder and the alloy steel powder having the above-described composition, or into the alloy steel powder having the above-described composition so as to have the above-described base matrix phase composition. A lubricant such as zinc stearate may be blended into the mixed powder.
Subsequently, a die is filled with the resulting mixed powder and the mixed powder is subjected to forming processing with a powder forming machine or the like to form a valve seat insert-shaped green compact having a predetermined dimension. In a case of the double-layer structure, the die is sequentially filled with the raw-material powder for a supporting material side layer and the raw-material powder for a valve contacting face material side layer so as to form two layers. On the other hand, in the case of the single-layer structure, the die is filled with the raw-material powder for a valve contacting face material side layer.
Then, the obtained green compact is subjected to a sintering to obtain a sintered body.
The sintering is preferably a treatment of holding for 0.5 hours or longer in a heating temperature range of 1100° C. to 1200° C. in a reducing atmosphere such as an ammonia cracking gas or vacuum. It is needless to say that a step of performing powder forming-sintering once (1P1S) or a step of repeating the powder forming-sintering a plurality of times (2P2S or the like) may be performed.
The obtained sintered body is processed by cutting, grinding, or the like to obtain a valve seat insert having a desired dimensional shape.
Hereinafter, the present invention will be further described with reference to Examples.
First, the mixed powder for a valve contacting face material side layer and the mixed powder for a supporting material side layer were prepared.
In the mixed powder for a valve contacting face material side layer, an iron based powder for base matrix phase formation, a graphite powder, an alloy element powder, a hard particle powder, and a solid lubricant particle powder (MnS powder) were adjusted so as to have blending amounts shown in Table 7, and mixed to obtain a mixed powder. The iron based powder used was a pure iron powder (atomized pure iron powder or reduced iron powder), a high-speed steel powder, or an alloy steel powder having the compositions shown in Table 5. Also, the used hard particle powder was a hard particle powder having the composition shown in Table 6. Note that a hard particle powder No. A was a common Co-based intermetallic compound particle powder, which was Conventional Example. In addition, in Table 6, a Vickers hardness HV and an average particle diameter D50 of respective hard particles before sintering are shown.
In the mixed powder for a supporting material side layer, an iron based powder for base matrix phase formation, a graphite powder, an alloy element powder, a hardness improving particle powder, and a solid lubricant particle powder (MnS powder) were adjusted so as to have blending amounts shown in Table 8, and mixed to obtain a mixed powder. The iron based powder used was a pure iron powder (atomized pure iron powder or reduced iron powder) having the compositions shown in Table 5. In addition, the hardness improving particle powder used was an iron-molybdenum alloy particle powder having a composition containing Mo: 60 mass % with a remainder being Fe and inevitable impurities.
Note that, into the mixed powder, 0.75 parts by mass of zinc stearate was blended as a lubricant with respect to 100 parts by mass of the mixed powder.
Subsequently, a die was filled with the obtained mixed powder for a valve contacting face material side layer and the obtained mixed powder for a supporting material side layer sequentially so as to form two layers, and a green compact having a predetermined valve seat insert shape was formed by a powder forming machine. A valve seat insert No. 17A was a single layer including only the valve contacting face material side layer.
Then, the obtained green compact was subjected to a degreasing step of further removing the lubricant and a sintering at 1100° C. to 1200° C. for 0.5 hr in an ammonia cracking gas to obtain a sintered body.
In some cases, the step (2P2S) was performed by performing the powder forming-sintering twice.
The obtained sintered body was further subjected to processing such as cutting and polishing to obtain an iron-based sintered alloy valve seat insert having a predetermined dimensional shape (outer diameter: 32.1 mmφ×inner diameter: 26.1 mmφ×thickness: 5.5 mm).
For the obtained valve seat insert (sintered body), the base matrix part composition of each part of the sintered body was analyzed, and a structure observation, a hardness measurement, a density measurement, a hard particle crack resistance test, a wear test, and a radial crushing strength test were further performed. A test method was as follows.
For the obtained valve seat insert, a cross section perpendicular to an axial direction was polished and etched (etching liquid: Nital liquid, Marble liquid) to reveal a structure, and the structure of the base matrix phase was specified with an optical microscope (magnification: 200 times). In addition, the particle diameter of the carbide precipitated in the base matrix phase was measured using a scanning electron microscope (magnification: 2000 times), and it was confirmed that the particle diameter (long side length) of the carbide was 10 μm or smaller at the maximum, and that the phase where the carbide was precipitated was a fine carbide precipitation phase. In a case where the particle diameter (long side length) of the carbide was larger than 10 μm at the maximum, it was defined as a carbide precipitation phase.
For the obtained valve seat insert, a cross section is polished and etched (etching liquid: Nital liquid, and Marble liquid) to reveal a structure, and the hardness of the base matrix phase was measured using a Vickers hardness meter (test force: 0.98 N). In a case where the base matrix phase was double phases, measurement was performed separately.
For the obtained valve seat insert, the density of the valve seat insert was measured using the Archimedes method.
With respect to the obtained valve seat insert, a cross section was polished, an impression was imparted using a Vickers hardness meter (test force: 0.98 N) to hard particles (20 particles respectively) dispersed in a base matrix phase, and the presence or absence of occurrence of cracking in each particle imparted with the impression was observed and the number of cracking occurrences was investigated. When a crack observed at a magnification of 500 times was developed outside the imparted impression, it was determined that cracking occurred. Using the number of cracking occurrences of the valve seat insert No. 1A which is a conventional example as a reference (=1.0), a ratio of the number of occurrences of cracking of the hard particles of the valve seat insert to the reference (cracking occurrence ratio) was calculated. From the obtained results, a case where the cracking occurrence ratio was less than 1.0 was evaluated as ∘ (having cracking resistance), and a case where the cracking occurrence ratio was 1.0 or more was evaluated as x (not having cracking resistance).
The obtained valve seat insert was subjected to a wear test under the following test conditions using a single rig wear testing machine shown in
After the test, a wear amount of the test piece (valve seat insert) was measured. From the obtained wear amount, a wear ratio of the valve seat insert was calculated with the valve seat insert No. 1A as a reference (=1.00).
With respect to the obtained valve seat insert (only a valve contacting face material side layer), the radial crushing strength (kg/mm2) was determined in accordance with the provisions of JIS Z 2507. It has been confirmed that when the radial crushing strength is 40 kg/mm2 or more, there is no occurrence of cracking or chipping at the time of press-fitting the valve seat insert, and the valve seat insert has sufficient strength as a valve seat insert.
In the valve seat insert No. 1A (conventional example) used as a reference in the hard particle crack resistance test and the wear test, the valve contacting face material side layer is an iron-based sintered alloy material having a structure in which hard particles and solid lubricant particles are dispersed in a base matrix phase and a Co-containing composition, and is a material used for valve seat insert for exhaust side in a wide range from a general gasoline engine to a high-performance gasoline engine. In the valve seat insert, a degree of influence of items (for example, a design value of a heat load/valve train) that affects the wear resistance differs between the exhaust side and an intake side. In general, the exhaust side is more severe as the use environment, and the valve seat insert is required to have a wear resistance higher than that of the intake side.
The obtained results are shown in Tables 9 and 10.
All of invention examples do not contain Co, and are valve seat inserts having excellent wear resistance equal to or higher than that of the conventional example (valve seat insert No. 1A) and having a sufficient radial crushing strength as a valve seat insert. On the other hand, the wear ratio of the comparative example departing the scope of the present invention is higher than that of the conventional example (valve seat insert No. 1A).
First, the mixed powder for a valve contacting face material side layer and the mixed powder for a supporting material side layer were prepared.
In the mixed powder for a valve contacting face material side layer, an iron based powder for base matrix phase formation, a graphite powder, an alloy element powder, a hard particle powder, and a solid lubricant particle powder (MnS powder) were adjusted so as to have blending amounts shown in Table 13, and mixed to obtain a mixed powder. The iron based powder used was a pure iron powder (atomized pure iron powder or reduced iron powder) or an alloy iron powder (pre-alloy powder) having the compositions shown in Table 11. Also, the used hard particle powder was a hard particle powder having the composition shown in Table 12. Note that a hard particle powder No. A was a common Co-based intermetallic compound particle powder, and a mixed powder DI to which the hard particle powder No. A was blended was a conventional example. In addition, in Table 12, a Vickers hardness HV and an average particle diameter D50 of respective hard particles before sintering are shown.
In the mixed powder for a supporting material side layer, an iron based powder for base matrix phase formation, a graphite powder, an alloy element powder, and a hardness improving particle powder were adjusted so as to have blending amounts shown in Table 14, and mixed to obtain a mixed powder. The iron based powder used was a pure iron powder (atomized pure iron powder) No. a having the compositions shown in Table 11. In addition, the hardness improving particle powder used was an iron-molybdenum alloy particle powder Fe—Mo having a composition containing Mo: 60 mass % with a remainder being Fe and inevitable impurities. In addition, the solid lubricant particle powder (MnS powder) was not added.
Note that, into the mixed powder, 0.75 parts by mass of zinc stearate was blended as a lubricant with respect to 100 parts by mass of the mixed powder.
Subsequently, a die was filled with the obtained mixed powder for a valve contacting face material side layer and the obtained mixed powder for a supporting material side layer sequentially so as to form two layers, and a green compact having a predetermined valve seat insert shape was formed by a powder forming machine. Then, the obtained green compact was subjected to a step (1P1S) of performing a degreasing step of further removing the lubricant and sintering at 1100° C. to 1200° C. for 0.5 hr in an ammonia cracking gas to obtain a sintered body.
The obtained sintered body was further subjected to processing such as cutting and polishing to obtain an iron-based sintered alloy valve seat insert having a predetermined dimensional shape (outer diameter: 32.1 mmφ×inner diameter: 26.1 mmφ×thickness: 5.5 mm).
For the obtained valve seat insert (sintered body), the base matrix part composition of each part of the sintered body was analyzed, and a structure observation, a hardness measurement, a density measurement, a hard particle crack resistance test, a wear test, and a radial crushing strength test were further performed. The test method was the same as that in Example 1. In the hard particle crack resistance test, using the number of cracking occurrences of the valve seat insert No. 1B as a reference (=1.0), a cracking occurrence number ratio (cracking occurrence ratio) of the hard particles of the valve seat insert to the reference was calculated. In addition, in the wear test, a wear ratio of the valve seat insert was calculated with the valve seat insert No. 1B as a reference (=1.00).
The valve seat insert No. 1B (conventional example) used as a reference in the hard particle crack resistance test and the wear test is a material used for valve seat insert for intake side of a general gasoline engine, and the valve contacting face material side layer is an iron-based sintered alloy material having a Co-containing composition. In the valve seat insert used on the intake side, required wear resistance is lower than that of the valve seat insert used on the exhaust side.
The obtained results are shown in Tables 15 and 16.
In invention examples, although the structure of the base matrix phase is a structure including the high-alloy phase and pearlite, a valve seat insert having excellent wear resistance equivalent to or higher than that of a sintered body (Conventional Example No. 1B) having a composition containing Co at the same hardness level, and having sufficient radial crushing strength is obtained. For example, it can be said that requirement for wear resistance is relatively low, and it is fully applicable to intake-side valve seat insert.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-119738 | Jul 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/028064 | 7/19/2022 | WO |
