JP4323467B2 - Sintered valve guide and manufacturing method thereof - Google Patents

Description

  The present invention relates to a valve guide for an internal combustion engine, and more particularly to a sintered valve guide formed of a sintered alloy material having excellent wear resistance and machinability and a method for manufacturing the same.

  Conventionally, a cast iron valve guide has been used as a valve guide for an internal combustion engine, but a sintered alloy valve guide has been used in terms of wear resistance and mass productivity. The applicant of the present application has also proposed a valve guide material having excellent wear resistance in, for example, the following publications (see Patent Document 1 and Patent Document 2).

  The valve guide material disclosed in Patent Document 1 has a mass ratio of C: 1.5 to 4%, Cu: 1 to 5%, Sn: 0.1 to 2%, P: 0.1 to 0 Less than 3% and the balance of Fe, a structure in which an iron-phosphorus-carbon compound phase, which is an eutectic compound of Fe-PC, in a mixed base of pearlite and ferrite, a Cu-Sn phase, and free graphite is dispersed. It is an automobile that is highly evaluated for its wear resistance superior to that of cast iron and that it has improved machinability compared to conventional iron-based sintered alloys, although it is harder to cut than cast iron. It has been adopted by manufacturers.

  Further, the valve guide material disclosed in Patent Document 2 is an improvement of the valve guide material disclosed in Patent Document 1, and the magnesium silicate mineral is dispersed among the grains in the metal structure to impair wear resistance. The machinability is improved.

  The valve guide material disclosed in Patent Document 2 shows excellent wear resistance equivalent to the valve guide material disclosed in Patent Document 1 and has improved machinability, but still has the machinability of cast iron. Therefore, further improvement in machinability is desired. Accordingly, the present applicant has developed with a focus on improving machinability at the expense of some wear resistance, and has developed a valve guide material disclosed in the following publication (Patent Document 3).

The valve guide material disclosed in Patent Document 3 has a mass ratio of C: 1.5 to 4%, Cu: 1 to 5%, Sn: 0.1 to 2%, P: 0.01 to 0 Less than 1% and the balance of Fe, exhibiting a structure in which free graphite is dispersed in a matrix mainly composed of pearlite.
Japanese Patent Publication No.55-34858 Japanese Patent No. 2680927 JP 2002-69597 A

  However, along with the need for higher efficiency in product manufacturing, there is an increasing demand for improvement in the workability of the valve guide material, and the need for a valve guide material with better machinability is increasing.

  The present invention solves the problems of the valve guide material as described above, and can efficiently produce a sintered alloy having a good balance between wear resistance and machinability as a valve guide material. Is to provide.

  In order to solve the above problems, in the present invention, paying attention to the metal structure of the valve guide material, designing the structure in consideration of the role of each phase in the structure, the composition and particle size of the raw material powder to be used, etc. This has been achieved by optimizing the manufacturing conditions, and it has become possible to provide a sintered valve guide made of an alloy material with significantly improved machinability without impairing wear resistance.

  According to one aspect of the present invention, the sintered valve guide has a mass ratio of copper: 3.5-5%, tin: 0.3-0.6%, phosphorus: 0.04-0. 15%, carbon: 1.5 to 2.5%, and iron: formed from a sintered alloy composed of the balance, and the sintered alloy includes a pearlite phase, an iron-phosphorus-carbon compound phase, and a copper-tin alloy phase. The graphite phase is dispersed in a mass ratio of 1.2 to 1.7% of the sintered alloy, and the sintered alloy metal. In the structure cross section, the ratio of the pearlite phase to the base is 90% or more in area ratio, and the ratio of the iron-phosphorus-carbon compound phase to the metal structure cross section is 0.1 to 3% in area ratio. In the iron-phosphorus-carbon compound phase, the proportion of the copper-tin alloy phase in the metal structure cross section is 1 to 3% by area ratio. Saga 15μm or more portions wherein the iron - phosphorus - and summarized in that the proportion of carbon compound phase is 10% or less in area ratio.

  According to another aspect of the present invention, the sintered valve guide has a mass composition of copper: 3.5 to 5%, tin: 0.3 to 0.6%, phosphorus: 0.04. -0.15%, carbon: 1.5-2.5%, metal oxide: 0.46-1.41%, and iron: the sintered alloy consisting of the balance, It has a metal structure composed of a pearlite phase, an iron-phosphorus-carbon compound phase, a copper-tin alloy phase and a metal oxide phase, pores, and a graphite phase, and the graphite phase is a sintered alloy in a mass ratio. 1.2 to 1.7% of the above, and in the metallographic cross section of the sintered alloy, the ratio of the pearlite phase to the matrix is 90% or more in area ratio, and the iron-phosphorus-carbon The proportion of the compound phase in the metal structure cross section is 0.1 to 3% in area ratio, and the proportion of the copper-tin alloy phase in the metal structure cross section is area. The ratio of the portion of the iron-phosphorus-carbon compound phase having a thickness of 15 μm or more to the iron-phosphorus-carbon compound phase is 10% or less in terms of area ratio. .

  According to another aspect of the present invention, the sintered valve guide has a mass composition of copper: 3.5 to 5%, tin: 0.3 to 0.6%, phosphorus: 0.04. -0.15%, Carbon: 1.5-2.5%, Solid lubricant selected from at least one of manganese sulfide and magnesium silicate mineral: 1.6% or less, and sintered alloy comprising iron: balance The sintered alloy is a solid having a pearlite phase, an iron-phosphorus-carbon compound phase, and a copper-tin alloy phase, a pore, a graphite phase, and the solid dispersed in the pores or at a powder grain boundary. It has a metal structure composed of a lubricant, and in the metal structure section of the sintered alloy, the ratio of the pearlite phase to the metal structure section is 90% or more in area ratio, and the iron-phosphorus-carbon compound phase is a metal The proportion in the cross section of the structure is 0.1 to 3% by area ratio, and the copper-tin alloy phase The area occupied by the metal structure cross section is 1 to 3% by area ratio, and the graphite phase is dispersed in the pores at an area ratio of 0.8 to 3.2% of the metal structure cross section. The gist is that the ratio of the portion of the carbon compound phase having a thickness of 15 μm or more to the iron-phosphorus-carbon compound phase is 10% or less in terms of area ratio.

According to another aspect of the present invention, the sintered valve guide has a mass composition of copper: 3.5 to 5%, tin: 0.3 to 0.6%, phosphorus: 0.04. -0.15%, carbon: 1.5-2.5%, metal oxide: 0.46-1.41%, solid lubricant selected from at least one selected from manganese sulfide and magnesium silicate mineral: 1.6 %, And a sintered alloy consisting of iron: balance, the sintered alloy comprising a matrix having a pearlite phase, an iron-phosphorus-carbon compound phase, a copper-tin alloy phase and a metal oxide phase, and pores And the graphite phase and the metal structure composed of the solid lubricant dispersed in the pores or at the powder grain boundaries, the ratio of the pearlite phase in the metal structure cross section in the metal structure cross section of the sintered alloy is the area The ratio is 90% or more, and the iron-phosphorus-carbon compound phase occupies a cross section of the metal structure The ratio is 0.1 to 3% by area ratio, the ratio of the copper-tin alloy phase to the metal structure cross section is 1 to 3% by area ratio, and the graphite phase is 0.3% of the metal structure cross section by area ratio. The proportion of the iron-phosphorus-carbon compound phase that is dispersed in the pores at a rate of 8 to 3.2% and the iron-phosphorus-carbon compound phase having a thickness of 15 μm or more occupies the iron-phosphorus-carbon compound phase is 10% by area ratio.
The summary is as follows.

  Moreover, according to one aspect of the present invention, the sintered valve guide manufacturing method includes an iron-phosphorus alloy powder having a phosphorus content of 15 to 21% by mass, the balance being Fe and inevitable impurities, and a tin content of 8 to 8%. Copper-tin alloy powder and graphite powder consisting of 11% by mass and the balance consisting of copper and inevitable impurities are added to iron powder, and iron-phosphorus alloy powder: 0.27 to 0.7% by mass, copper-tin alloy powder: 3.93 to 5.44% by mass, graphite powder: 1.7 to 2.7% by mass, and a step of preparing a mixed powder composed of iron powder in the remainder, and filling the mixed powder into a cylindrical cavity of a mold Pressurizing and compressing to form the mixed powder into a cylindrical green compact; and sintering the green compact at a heating temperature of 950 to 1050 ° C. in a non-oxidizing atmosphere. This is the gist.

  According to the present invention, a highly durable sintered valve guide can be efficiently manufactured by a valve guide material in which wear resistance and machinability are balanced.

  Sintered alloys by powder metallurgy can produce alloys with different metallographic structures, even if the overall composition is the same, depending on the manufacturing conditions such as the composition of the raw material powder used, powder particle size, heating temperature and time. Depending on the material characteristics of the sintered alloy, such as mechanical strength, vary greatly. Therefore, in the present invention, in consideration of the contribution to the material characteristics of each phase existing in the sintered alloy, the valve is provided so as to give the sintered alloy the material characteristics required for the material constituting the valve guide. The structure of the guide material is designed, and the raw materials used and production conditions are set based on this design.

  Valve guides are required to have strength and wear resistance, and conventional valve guide alloy materials can meet these requirements. However, since the machinability is still insufficient, Improvement is strongly demanded by consumers. For this reason, in the present invention, based on a base mainly composed of iron, a copper-tin alloy phase that contributes to wear resistance, an iron-phosphorus-carbon compound phase, and an alloy having a free graphite phase, the needs of customers are met. The machinability is improved to fit. Hereinafter, the metallographic structure of the sintered alloy constituting the sintered valve guide of the present invention will be described.

  The base of the sintered alloy has a pearlite structure in order to increase the strength of the base, and the raw iron powder mixed with the graphite powder is sintered so that carbon is diffused into the iron powder. Since metal powder in which carbon is solid-dissolved in metal is hard and has low compressibility, iron powder and graphite powder are used as raw material powder. If the amount of the graphite powder is insufficient, the amount of carbon bonded to the matrix becomes insufficient, and a large amount of ferrite (α-iron) phase is generated in the matrix, so that the strength of the matrix decreases. However, as will be described later, there is a tendency that some ferrite phase is generated around the steadite phase in relation to the generation of the iron-phosphorus-carbon compound phase, but if the area ratio is 90% or more of pearlite Even if ferrite is generated as a residue, the decrease in base strength is slight and acceptable.

  An iron-phosphorus-carbon compound phase is dispersed in the perlite base. The iron-phosphorus-carbon compound is a hard iron-phosphorus-carbon compound that is deposited in a thin layer at the grain boundaries of the pearlite phase by sintering the graphite powder together with the iron-phosphorus alloy powder together with the graphite powder. A phase is generated and contributes to improvement of wear resistance of the sintered alloy. This effect of improving the wear resistance becomes significant when the ratio of the iron-phosphorus-carbon compound phase in the metal structure cross section is 0.1 area% or more. On the other hand, when the amount of iron-phosphorus-carbon compound phase generated increases, the thickness of the layer increases and a plate-like iron-phosphorus-carbon compound phase is formed, and the machinability of the sintered alloy is extremely deteriorated. Therefore, in order not to reduce the machinability of the sintered alloy, it is important to suppress the generation amount of the iron-phosphorus-carbon compound phase and to disperse the iron-phosphorus-carbon compound phase thinly. Specifically, in the cross section of the metal structure, the proportion of the iron-phosphorus-carbon compound phase in the cross section of the metal structure is 3 area% or less, and the portion where the thickness of the iron-phosphorus-carbon compound phase is 15 μm or more is iron. -It needs to be 10 area% or less of the whole phosphorus-carbon compound phase. More specifically, the portion of the iron-phosphorus-carbon compound phase having a thickness of 15 μm or more is 0.1 area% or less of the entire iron-phosphorus-carbon compound phase, and the portion having a thickness of 5 μm or more but less than 15 μm is 10 to 40 area%. And the remaining iron-phosphorus-carbon compound phase preferably has a structure of less than 5 μm in thickness. In addition, since the iron-phosphorus-carbon compound phase tends to take carbon from the pearlite matrix when it is produced, some ferrite can be produced around the iron-phosphorus-carbon compound phase. The ferrite phase has a low strength and is acceptable if it is about 10 area% or less in the base of the sintered alloy, but it is not preferable to disperse in a large amount. That is, if the phosphorus content of the raw material powder is excessive, not only the iron-phosphorus-carbon compound phase that is produced becomes thick, but at the same time, a large amount of ferrite phase with low strength is taken away from the pearlite matrix by depriving the carbon. To be distributed. Therefore, the amount of iron-phosphorus-carbon compound phase must be suppressed so as to prevent them. Specifically, the iron-phosphorus-carbon compound phase has an area of 0.1 to 3 in the metal structure cross section. It is necessary to keep it in the range of%. For this reason, the amount of iron-phosphorus alloy powder used is adjusted so that the phosphorus content in the sintered alloy is 0.04 to 0.15 mass%, and 0 when the strength or wear resistance is important. 0.1 to 0.15% by mass, and when emphasizing machinability, 0.04 to 0.1% by mass is preferable.

  Furthermore, a copper-tin alloy phase is dispersed in the sintered alloy in the present invention. The copper-tin alloy phase is soft and contributes to wear resistance by improving the compatibility with the valve which is the sliding partner. The effect of the copper-tin phase becomes prominent when dispersed in the matrix at a ratio of 1 area% or more of the cross section of the structure. When the area exceeds about 3 area%, dimensional stability during sintering is caused by the expansion of copper during sintering. Therefore, the blending of the raw material powder is adjusted so that the copper-tin alloy phase in the structure cross section is 1 to 3% by area. The copper-tin alloy phase is produced even if plain copper powder and plain tin powder are used as raw material powders, but in that case, the variation in composition and distribution of the alloy phase generated in the sintered alloy becomes large, and the sintered alloy Dimensional stability and wear resistance of the steel deteriorate. For this reason, it is desirable to use copper-tin alloy powder as a raw material. Moreover, in the copper-tin alloy phase dispersed in the pearlite matrix, when the fine particle having a maximum particle size of 20 μm or less is 80% by area or more of the copper-tin alloy phase, the dispersion uniformity of the copper-tin alloy phase is increased. This is particularly effective from the viewpoint of compatibility. However, depending on the bridging state of the powder at the time of compacting, the copper-tin alloy powder may remain undiffused, but a copper-tin alloy of 150 μm or more with such undiffused copper-tin alloy powder. The phase may be 5 area% or less of the entire copper-tin alloy phase in the structure cross section. The copper-tin alloy powder generates a liquid phase during sintering and contributes to the promotion of sintering. Copper and tin each diffuse and dissolve in the matrix to strengthen the matrix. Then, the dimensional stability is significantly lowered due to copper expansion, and the base becomes brittle when excessive tin is dissolved. In order to prevent these and form a copper-tin alloy phase in a dispersed manner, the copper content of the copper-tin alloy powder to be used is preferably 8 to 11% by mass. Accordingly, the composition of the copper-tin alloy phase in the sintered alloy is also in the vicinity of this range. Based on the above, when an appropriate content in the overall alloy composition of copper and tin is derived from the composition of the copper-tin alloy powder and the area ratio of the copper-tin alloy phase in the cross section of the structure, copper is 3.5-5 0.0 mass% and tin will be 0.3-0.6 mass%.

  It is preferable that a trace amount of metal oxide phase is further dispersed in the pearlite matrix. This metal oxide phase is an oxide of at least one metal selected from the group consisting of aluminum, silicon, magnesium, iron, titanium, and calcium. These oxides act as free-cutting components and improve machinability. Contribute. However, since the base becomes brittle when the content of the metal oxide is excessive, it is preferable that 0.46 to 1.41% by mass of the metal oxide in the entire composition is dispersed in the pearlite base. It is important that such a metal oxide phase is uniformly dispersed in the matrix, and it is appropriate to use iron powder containing the metal oxide as a raw material powder. It is preferable that it is an iron powder which contains the said metal oxide in the ratio of 0.5-1.5 mass% in total amount, and there exists an ore reduction iron powder in such an iron powder. Generally used atomized iron powder and mill scale reduced iron powder have a low metal oxide content.

Furthermore, a free graphite phase is dispersed in the metal structure. This originates from the raw graphite powder and acts as a solid lubricant, contributing to the improvement of the machinability and wear resistance of the sintered alloy. It is difficult to accurately know the proportion of the free graphite phase in the sintered alloy from the micrograph of the cross section of the structure because it falls off during sample preparation work, but JIS-G1211 “Method for quantifying carbon in iron and steel” From the mass ratio of free graphite and the specific gravity of graphite determined by the free carbon quantification method stipulated in (1), the effect of the free graphite phase is remarkable when the ratio of the free graphite phase is about 0.8 area% or more. If an attempt is made to generate a free graphite phase exceeding the area%, hard cementite (Fe ₃ C) precipitates in the matrix and impairs the machinability of the sintered alloy. In addition, excessive graphite powder impairs the compressibility of the powder and reduces the proportion of the matrix in the sintered alloy, so that the strength of the sintered alloy is reduced. Therefore, the ratio of the free graphite phase is preferably about 0.8 area% or more and 3.2 area% or less in the structure cross section.

  When further improvement of machinability is desired, as a solid lubricant, at least one of manganese sulfide (MnS) powder and magnesium silicate mineral powder is blended in a ratio of 1% by mass or less of the raw material powder in total amount. These components may be dispersed in pores and powder grain boundaries of the sintered alloy. Although the MnS phase and the magnesium silicate phase contribute to the improvement of wear resistance, the effect of improving the machinability is particularly great. Further, the MnS phase protects the cutting edge of the cutting tool and contributes to the extension of the tool life, and the magnesium silicate mineral is cleaved and is cleaved during the cutting process, so it is effective in reducing the force required for cutting. Further, both components have a chip breaking action, and have the effect of extending tool life by preventing the accumulation of heat on the cutting edge of the tool by finely shearing the chips.

  A sintered alloy in which a free graphite phase, an iron-phosphorus-carbon compound phase, a copper-tin alloy phase, a metal oxide phase and, if necessary, a solid lubricant phase are dispersed in a metal structure as described above is as follows. A sintered valve guide can be obtained by molding in a shape corresponding to the valve guide in the molding step. As a result, the overall composition of the sintered alloy and the sintered valve guide to be produced is as follows: copper: 3.5 to 5% by mass, tin: 0.3 to 0.6% by mass, phosphorus: 0.04 to 0.15 Mass%, carbon: 1.5 to 2.5 mass%, metal oxide: 0.5 to 1.5 mass%, and the balance iron. When a solid lubricant is used, 1% by mass or less of the total alloy composition is a solid lubricant.

The valve guide generally has a density of 6.3 to 6.9 g / cm ³ and includes pores of about 4 to 15% in density ratio. The above-described sintered valve guide of the present invention is the same in this respect.

  In the method for manufacturing a sintered alloy and a sintered valve guide, first, a mixed powder is prepared. As the raw material, graphite powder, iron-phosphorus alloy powder, copper-tin alloy powder, ore-reduced iron powder, and solid lubricant powder as necessary are mixed uniformly to obtain a mixed powder. Details of each raw material powder are as follows.

  As the raw iron powder for generating the pearlite base, atomized iron powder having a particle size of about −150 to −65 mesh (maximum particle size of 104 to 200 μm) can be used. In addition, when using iron-reduced iron powder having a metal oxide content of 0.5 to 1.5 mass% and a particle size of about -150 to -65 mesh, It is preferable because the property can be improved. Ore-reduced iron powder is a powder having a high content of metal oxide due to its production method, and this metal oxide is effective in improving machinability. When content of a metal oxide is less than the said range, the effect of machinability improvement will reduce. If the content of the metal oxide exceeds the above range, the powder is hard and the compressibility is lowered, which is not preferable. Since the ore-reduced iron powder is porous, the copper-tin alloy liquid phase generated during sintering is easily absorbed by capillary force, and has an effect of homogenizing the component distribution of the sintered alloy. When the particle size of the ore-reduced iron powder is coarse, the density of the powder is difficult to increase, and when it is fine, the fluidity of the powder decreases. Therefore, a powder of about −150 to −65 mesh is suitable. However, ore-reduced iron powder has a property that it is slightly harder and less compressible than atomized iron powder because of its high content of metal oxides. Is slightly lower than that due to atomized iron powder. Therefore, the raw material powder for the sintered valve guide may be selected according to the required characteristics of strength or machinability. Moreover, when 10 mass% or more of the ore reduced iron powder is used as a mixed powder of the ore reduced iron powder and the atomized iron powder instead of the atomized iron powder, the compressibility is improved and the strength of the obtained sintered alloy is improved. In this case, if the replacement ratio of the atomized iron powder exceeds 30% by mass, the distribution of the metal oxide becomes non-uniform or the effect of improving the machinability cannot be obtained, so the atomized iron powder and the ore reduced iron powder are used in combination. In that case, it is desirable that the replacement ratio of the atomized iron powder is 10 to 30% by mass. The particle size of the atomized iron powder is the same as or smaller than that of the ore reduced iron powder.

  The iron-phosphorus alloy powder is a raw material for blending phosphorus, and is used as an iron-phosphorus alloy in order to safely handle phosphorus that is unstable and ignitable alone. Phosphorus diffuses into the iron base to increase the strength of the pearlite base, and forms an iron-phosphorus-carbon compound phase to contribute to the improvement of wear resistance. An iron-phosphorus alloy having a phosphorus content of about 10 to 13% by mass generates a liquid phase of an iron-phosphorus alloy in the temperature range of 950 to 1050 ° C., and a large amount of the liquid phase impairs the dimensional stability of the sintered alloy. Therefore, although an appropriate amount of the liquid phase promotes neck growth and improves the strength of the sintered alloy, an iron-phosphorus alloy having a phosphorus content of 15% by mass or more in order to moderately suppress the formation of the liquid phase. Use powder. Phosphorus in the iron-phosphorus alloy powder having a phosphorus content of 15% by mass or more diffuses into the iron powder during sintering, and a part of the phosphorus content falls within the above range to generate a liquid phase. This liquid phase wets and covers the surface of the iron powder, but phosphorus diffuses rapidly from the covered liquid phase into the iron powder, and becomes a solid phase when the phosphorus content in the liquid phase falls below the above range. Therefore, the growth of the neck between the iron powders is promoted, contributing to the improvement of the strength, and the formation of the liquid phase is partially suppressed and the solid phase is formed in a short time. Is prevented. If the phosphorus content of the iron-phosphorus alloy powder to be used is less than 15% by mass, the composition of the iron-phosphorus alloy becomes the above-mentioned liquid phase generation range due to the diffusion of phosphorus during sintering, and the generation of the liquid phase becomes intense. Therefore, the dimensional stability is impaired, and phosphorus is diffused and thinned throughout the base, resulting in an insufficient amount of iron-phosphorus-carbon compound phase. On the other hand, when the phosphorus content of the iron-phosphorus alloy powder exceeds 21% by mass, the iron-phosphorus alloy powder becomes hard, so the compressibility of the mixed powder is impaired, and the density of the green compact and the sintered alloy decreases. As a result, the strength of the sintered valve guide is insufficient, and the iron-phosphorus-carbon compound phase to be formed becomes thick and the machinability of the sintered alloy decreases. Therefore, an iron-phosphorus alloy powder having a phosphorus content of 15 to 21% by mass is used, and the amount used is about 0.27 to 0.7% by mass of the total amount of the mixed powder. From the viewpoint of compressibility of the mixed powder, it is preferable to use an iron-phosphorus alloy powder having a particle size of about −250 to −150 mesh (maximum particle size of 61 to 104 μm). The iron-phosphorus alloy powder to be used is allowed to contain an unavoidable amount of impurities, and may contain, for example, carbon, silicon, manganese or the like in a total amount of 1.5% by mass or less.

  The copper-tin alloy powder is used to increase the fineness and dispersion uniformity of the copper-tin alloy phase in the sintered alloy, and is preferably a copper-tin alloy powder finer than the particle size of the iron powder. In order to prevent deterioration of dimensional stability due to copper expansion and embrittlement of the base due to excessive solid solution of tin, it is preferable to use a copper-tin alloy powder having a tin content of 8 to 11% by mass. And about 3.93 to 5.44% by mass of the total amount of the mixed powder. Thereby, copper content in mixed powder will be about 3.5-5.0 mass%, and tin content will be 0.3-0.6 mass%. In order that the copper-tin alloy powder is uniformly dispersed in the mixed powder and the copper-tin alloy phase is finely and uniformly dispersed in the sintered alloy, a copper-tin alloy powder having a particle size smaller than that of the iron powder is used. Preferably, a copper-tin alloy powder having a particle size of about −250 to −400 mesh (maximum particle size of 35 to 61 μm) is used. The copper-tin alloy powder is allowed to contain unavoidable impurities.

  The graphite powder combines with the iron powder and the iron-phosphorus alloy powder during sintering to produce a pearlite structure and an iron-phosphorus-carbon compound, and the remaining graphite forms a free graphite phase. The appropriate carbon content in the sintered alloy is 1.5 to 2.5% by mass, but it is necessary to consider the loss due to reduction of metal oxides in iron powder and bonding with moisture in the atmospheric gas Therefore, the amount of graphite powder used is about 1.7 to 2.7% by mass of the total amount of the mixed powder. However, excessive graphite not only precipitates cementite in the pearlite matrix, but also reduces the compressibility of the mixed powder, so that the density of the green compact and the sintered alloy is lowered, and the strength of the valve guide is insufficient. If the particle size of the graphite powder used is too small, the free graphite phase remaining after sintering will be insufficient, and if the particle size is too large, the compressibility of the mixed powder will deteriorate drastically, and the component distribution in the sintered alloy will be extremely poor. It becomes uniform and a ferrite phase is likely to occur around the iron-phosphorus-carbon compound phase.

  As described above, the solid lubricant is a MnS powder and / or a magnesium silicate mineral powder, and the magnesium silicate mineral includes a magnesium metasilicate mineral and a magnesium orthosilicate mineral. Examples of the magnesium magnesium silicate mineral include enstatite, clinoenstatite, enstenite, hypersten, and the like. Examples of the magnesium orthosilicate mineral include forsterite and chrysolite. When a solid lubricant is used, the amount used is 1.6% by mass or less of the mixed powder in order to prevent a decrease in strength of the sintered alloy.

The mixed powder obtained by uniformly mixing the raw material powders according to the above is compression-molded into a green compact using a molding die. At this time, a mold having a shape corresponding to the product is used, and the mold used in the case of the valve guide has a vertically long cylindrical cavity. As a specific example, a die having a cylindrical hole, a cylindrical core rod disposed in the center of the die and forming a vertically long tubular cavity between the die, and a cross-sectional circle inserted into the cavity Using an annular upper and lower punch, the lower punch is fitted into the bottom of the cavity, the mixed powder is filled into the cavity, the upper punch is inserted into the cavity, and the mixed powder is pressed in the axial direction between the upper and lower punches. Compress. At this time, it is preferable to appropriately adjust the molding pressure so that the green compact has a molding density of about 6.5 to 7.1 g / cm ³ .

  In the above molding, since the molding shape is vertically long, it is difficult for the molding pressure to propagate to the axial central part of the tube shape, so the compacting density of the green compact is higher at the central part than at both axial end parts. hard. As a result, the strength of the obtained sintered valve guide is lowered at the central portion in the axial direction. In order to improve this, it is effective to incline the radial surface in at least one of the die hole portion and the core rod peripheral portion so that the cavity is slightly tapered in the punching direction. If the taper is slightly inclined, the effect on the green compact size is eliminated by the springback effect of the powder particles, so the molding pressure can be reduced to the center in the axial direction without substantially affecting the product size. By acting, the molding density can be made uniform. The taper ratio is preferably about 1/5000 to 1/1000, and if it is smaller than 1/5000, the improvement of the molding density in the center is insufficient, and if it exceeds 1/1000, it is apparent between both ends of the green compact. Dimensional difference occurs.

  The green compact thus formed is heated and sintered at a temperature of 950 to 1050 ° C. in a non-oxidizing atmosphere and then cooled. Sintering is maintained by heating in this range, and graphite combines with iron powder to form a pearlite structure. The iron-phosphorus alloy powder partly forms a liquid phase and contributes to the sintering bond by diffusion between the powders, and phosphorus diffuses in the iron powder and combines with the graphite to form an iron-phosphorus-carbon compound. A phase is formed, and an iron-phosphorus-carbon compound phase is precipitated in the cooling process after sintering. The copper-tin alloy powder promotes sintering by generating a liquid phase in the temperature rising process during sintering, and copper and tin are diffused and dissolved in the iron base. In a sintered alloy cooled through sintering, the iron-phosphorus-carbon compound phase formed in the pearlite structure is dispersed and precipitated in a thin layer, and a fine copper-tin alloy phase is dispersed and precipitated from liquefied and diffused copper and tin. To do. The above metal structure is formed with a sintering holding time of about 5 minutes, but if the sintering holding time is lengthened, the strength is improved by the growth of the neck between the iron powders. The sintering holding time is preferably 20 minutes or more, more preferably 45 minutes or more. However, when the sintering temperature exceeds 1050 ° C. or the sintering time exceeds 90 minutes, the amount of free graphite remaining due to the diffusion of graphite to the matrix decreases and the iron-phosphorus-carbon compound that precipitates. Since the amount of iron increases and the thickness of the iron-phosphorus-carbon compound phase also increases, the machinability is significantly reduced. On the other hand, if the sintering temperature is less than 950 ° C., the sintering does not proceed sufficiently, the desired metal structure cannot be obtained, and the strength is significantly reduced. Since the liquid phase generation rate and diffusion / dispersion rate change depending on the heating temperature during sintering, in order to obtain a suitable metal structure, the sintering time should be shorter and lower when sintering at higher temperatures. When sintering at temperature, it is preferable to lengthen the sintering time. When the cooling rate is slow, the amount of iron-phosphorus-carbon compound phase and ferrite phase deposited increases and the thickness also increases. Therefore, it is preferably about 8 ° C./min or more, preferably about 10 ° C./min or more.

  The sintered product of the sintered valve guide is obtained by the above-described sintering, and the inner diameter of the sintered valve guide is further precisely machined by a reamer to be the final product of the sintered valve guide. In the present invention, since the machinability of the sintered alloy constituting the sintered valve guide is improved, the time required for machining by the reamer is shortened, and defective machining is also reduced.

  When the crude product of the sintered valve guide is immersed in oil, the oil is absorbed into the pores by the capillary force, which is effective because the hermeticity of the sintered valve guide is enhanced. It also has the effect of improving machinability by acting as a lubricating oil during machining. At the time of immersion, the pores of the sintered valve guide crude product may be forcibly impregnated by vacuuming and degassing. In addition, it is preferable to disperse molybdenum disulfide or the like in the oil because machinability is improved and wear resistance is also improved.

  FIG. 1 is a schematic representation of the cross section of the metal structure of the sintered valve guide of the present invention obtained as described above. The metal structure includes a matrix, pores, and a graphite phase dispersed in the pores. The matrix includes a pearlite phase that may include a metal oxide phase, a copper-tin alloy phase, and an iron-phosphorus-carbon compound phase. Have The iron-phosphorus-carbon compound phase is thinly dispersed, and a very slight ferrite phase is formed around it.

  FIG. 2 is a diagram schematically showing a cross-section of a metal structure of a conventional sintered alloy described in Patent Document 1 and the like in which the content of phosphorus is increased. In the iron-phosphorus-carbon compound phase, the thickness is There are many portions of 15 μm or more, and a large amount of ferrite phase is generated around the iron-phosphorus-carbon compound phase by carbon deprivation. In the case of such a metal structure, the machinability is inferior and the strength is low as compared with the case of FIG. The sintered alloy shown in Patent Document 1 has a thick iron-phosphorus-carbon compound phase as shown in FIG.

  Hereinafter, the present invention will be described in more detail with reference to examples.

(Samples 1 to 27)
Using iron-reduced iron powder (containing 0.1% by mass of metal oxide) or atomized iron powder (containing 0.2% by mass of metal oxide) as iron powder, iron powder, iron according to the compounding ratio shown in Table 1 -Phosphor alloy powder, copper-tin alloy powder, and graphite powder were mixed to prepare mixed powders of Samples 1 to 27, respectively. Table 2 shows the component composition of the entire mixed powder for each sample. The particle size of each powder used was ore reduced iron powder (150 μm or more: 5%, 45 to 150 μm: 75%, less than 45 μm: 20%), atomized iron powder (150 μm or more: 17%, 45 to 150 μm: 58%, less than 45 μm: 25%), iron-phosphorus alloy powder (63 μm or more: 3%, 45-63 μm: 10%, less than 45 μm: 87%), copper-tin alloy powder (150 μm or more: 7%, 45%) 150 μm: 73%, less than 45 μm: 20%) and graphite powder (average particle size: 0.6 to 0.8).

  For each sample, the mixed powder was pressed and compressed at a pressure of 550 MPa to obtain a cylindrical compact having an outer diameter of 11 mm, an inner diameter of 6 mm, and a length of 40 mm (for wear test and machinability test) and an outer diameter of 18 mm. , Molded into an annular green compact (for pressure ring test) with an inner diameter of 10 mm and a length of 10 mm, sintered in a non-oxidizing atmosphere at a temperature of 1000 ° C. for 60 minutes, and from 1000 ° C. to 600 ° C. at 12 ° The sample was cooled at a cooling rate of 1 minute, and then returned to room temperature to obtain sintered bodies of Samples 1 to 27.

  About the sintered compact of samples 1-27, the metal structure cross section (x340) of a sintered compact is observed using a microscope, and the ratio of the iron-phosphorus-carbon compound phase and copper-tin alloy phase which occupy in a metal structure cross section (Area%), ratio of ferrite phase in the base (area%), ratio of free graphite (mass%), thickness in the iron-phosphorus-carbon compound phase is less than 5 μm, 5 μm or more and less than 15 μm, 15 μm or more The proportion (area%) of the part was determined. The results are shown in Table 3.

  Moreover, about the sintered compact of samples 1-27, the abrasion test, the machinability test, and the crushing test were done according to the following, and the wear amount, the machinability index | exponent, and the crushing strength were measured. The results are shown in Table 3.

(Abrasion test)
A wear test was performed by attaching a circular tube-shaped sintered body to a vertical valve guide wear tester. In the wear test, the valve stem was attached to the lower end of the piston with the axis set in the vertical direction, the valve was inserted into the sintered body, a 3 MPa lateral load was applied to the piston, and the valve was placed in an exhaust gas atmosphere at 500 ° C. Was reciprocated. In this case, the stroke speed was 3000 times / minute, and the stroke length was 8 mm. After 30 hours of reciprocation, the amount of wear (μm) on the inner peripheral surface of the sintered body was measured.

(Machinability test)
Using a cemented carbide reamer, the reaming time was applied to the inner diameter of the circular tube-shaped sintered body and the time required for cutting 10 mm in the axial direction was determined. The required time in each sample was converted into an index with the required time in Sample 13 (corresponding to the alloy composition described in Japanese Patent Publication No. 55-034858, hereinafter referred to as conventional alloy) being 100. The smaller the index, the easier it is to cut the sintered body and the shorter the processing time, that is, the better the machinability.

(Pressure test)
In accordance with the method specified in JIS Z2507 “Sintered bearing-crushing strength test method”, the maximum load when the sintered body is destroyed by pressing the annular shaped sintered body in the radial direction and increasing the pressing load. The crushing strength (N / mm ² ) was calculated by the following formula 1 (where F: maximum weight at break (N), L: length of the ring (mm), D: circle) (Outer diameter of the ring (mm), e: wall thickness of the ring (mm).)

(Equation 1)
K = F (D−e) / (L * e ² )

Samples 1 to 9 are obtained by changing the amount of phosphorus in the entire composition. Samples 1 to 7 have a constant phosphorus content in the iron-phosphorus alloy powder. Samples 8 and 9 are the amount of phosphorus in the entire composition. Both the phosphorus contents of the iron-phosphorus alloy powder are changed. Regarding these and Sample 10 (sintered alloy disclosed in Japanese Patent Publication No. 55-034858, labeled as a conventional alloy), the relationship between the amount of phosphorus in the overall composition and the proportion of each phase is shown in FIG. FIG. 4 shows the relationship between the thickness of the phosphorus-carbon compound phase and material properties (amount of wear, machinability index, and crushing strength).

  The proportion of the copper-tin alloy phase does not vary depending on the amount of phosphorus (FIG. 3B), but the proportion and thickness of the iron-phosphorus-carbon compound phase increase rapidly with an increase in the amount of phosphorus, and the amount of phosphorus is 0.1. It can be seen from FIGS. 3 (a), (c), (d) and FIG. 4 (a) that the amount of free graphite phase decreases and the ferrite phase increases in the region exceeding 15% by mass. This is because the formation of iron-phosphorus-carbon compound is promoted by increasing the amount of phosphorus, but free graphite and carbon dissolved in the matrix are consumed for the formation of this iron-phosphorus-carbon compound, As a result, it means that the ferrite phase increases. Further, according to FIGS. 4B, 4C, and 4D, when the phosphorus amount is less than 0.04 mass%, the machinability is good, but the wear amount is large, and the crushing strength is high. Indicates a low value. When the phosphorus amount is 0.04% by mass or more, the crushing strength increases and the wear amount decreases as the phosphorus amount increases, but the machinability index increases and the machinability deteriorates. In particular, when the amount of phosphorus is 0.15% by mass or more, the machinability index is remarkably increased.

  From FIG. 3 (d) and FIGS. 4 (a) and 4 (c), it is recognized that the change in the machinability index is related to the generation ratio of the iron-phosphorus-carbon compound phase and the ratio of the thickness of 15 μm or more. In the region where the amount of phosphorus is 0.15% by mass or less, the ratio of the iron-phosphorus-carbon compound phase having a thickness of 15 μm or more is 10% by area or less, and the machinability index is suppressed to 35 or less. That is, it can be said that the machinability is improved when the iron-phosphorus-carbon compound phase is refined.

  On the other hand, the fluctuation of the crushing strength is recognized to be related to the ratio of the iron-phosphorus-carbon compound phase, and the crushing strength increases as the ratio of the iron-phosphorus-carbon compound phase increases, A sufficient crushing strength of about 500 MPa or more is obtained in a region where the amount of phosphorus is 0.1 area% or more and the phosphorus amount is 0.04 mass% or more, and the phosphorus amount is 0.1 mass% or more, which is higher than the conventional alloy Although the crushing strength is shown, the ratio of the ferrite phase having low strength increases with an increase in the amount of phosphorus. Therefore, when the amount of phosphorus is 0.2% by mass or more, the strength is reduced.

  In addition, the variation in the amount of wear is recognized to be related to the generation ratio of the iron-phosphorus-carbon compound phase, the phosphorus amount is 0.04% by mass or more, and the ratio of the iron-phosphorus-carbon compound phase is 0.1 area%. In this region, the amount of wear decreases rapidly, and the amount of wear decreases as the amount of phosphorus increases and the rate of formation of the iron-phosphorus-carbon compound phase increases.

  From the above, the amount of phosphorus in the overall composition is 0.04 to 0.15 mass%, the ratio of the iron-phosphorus-carbon compound phase is 0.1 to 3 area%, and the iron-phosphorus- When the proportion of the carbon compound phase having a thickness of 15 μm or more is 10% or less in terms of area ratio, it becomes an appropriate valve guide in all of the crushing strength, machinability and wear resistance.

  Samples 4 and 11-23 were obtained by changing the amount of tin or copper in the overall composition. Samples 4, 11-14 had a constant amount of copper, and samples 4, 15-19 were copper-tin used. The composition of the alloy powder is constant, and Samples 20 to 23 have different amounts of tin, copper, and copper-tin alloy powder in the overall composition. For these and sample 13, the relationship between the amount of tin in the overall composition and the proportion of each phase is shown in FIG. 5. The amount of tin, the thickness of the iron-phosphorus-carbon compound phase, and the material properties (wear amount, machinability index and FIG. 6 shows the relationship with the crushing strength. Moreover, the relationship between the copper content in the overall composition and the ratio of each phase is shown in FIG. 7. The copper content, the thickness of the iron-phosphorus-carbon compound phase, and material properties (amount of wear, machinability index, and crushing strength) FIG. 8 shows the relationship.

  The change in the proportion of the copper-tin alloy phase in FIG. 5 (b) varies greatly depending on the addition form of tin, and when this is combined with FIG. 7 (b), the proportion of the copper-tin alloy phase is determined by the amount of tin. Rather, it is thought to change depending on the amount of copper. Further, FIGS. 5 (a), (c), (d) and FIG. 6 (a) also show that the influence of the amount of tin on the phase structure of the metal structure is small.

  On the other hand, wear resistance and crushing strength are improved by increasing the amount of tin, and machinability is lowered. This is due to an increase in tin dissolved in the base. When the amount of tin is 0.3% by mass or more of the total composition, the wear amount is 70 μm or less and the crushing strength is 500 MPa or more, which shows good wear resistance and crushing strength. In terms of machinability, the tin content is preferably 0.6% by mass or less.

  According to FIGS. 7 (a) and 8 (a), the increase in the amount of copper decreases the ratio and thickness of the iron-phosphorus-carbon compound phase, and therefore the machinability is reduced as shown in FIG. 8 (c). Improve. This is because the hardenability of the base is improved by copper and the apparent cooling rate is increased (details of the influence of the cooling rate will be described later). Moreover, according to FIG.7 (b), the increase in the amount of copper increases the ratio of a copper-tin alloy phase. The presence of a soft and adaptable copper-tin alloy phase improves wear resistance and facilitates processing, and a good value with a machinability index of 35 or less in a region where the amount of copper is 3.5% by mass or more. (FIG. 8C). The copper-tin alloy phase also improves the crushing strength (FIG. 8 (d)), but at 5.0% by mass or more, the softness of the copper-tin alloy phase acts excessively and decreases the strength. From these results, the range of the appropriate amount of tin is 0.3 to 0.6% by mass, and the range of the appropriate amount of copper is 3.5 to 5.0% by mass.

  Samples 4 and 24 to 27 were obtained by changing the carbon amount in the entire composition. Regarding these and sample 13, the relationship between the carbon amount in the entire composition and the ratio of each phase is shown in FIG. FIG. 10 shows the relationship between the thickness of the phosphorus-carbon compound phase and material properties (amount of wear, machinability index, and crushing strength).

  It can be seen from FIGS. 9A and 10A that the ratio of the iron-phosphorus-carbon compound phase and the thickness of the phase increase as the amount of carbon increases. The proportion of free graphite phase also increases (FIG. 9 (c)). However, FIG. 9 (d) shows that when the carbon content exceeds 2.5% by mass, the proportion of the ferrite phase increases abruptly, and carbon capture occurs from the base with the formation of the iron-phosphorus-carbon compound phase. Represents.

  The machinability index in FIG. 10C is influenced by the ratio of the free graphite phase in addition to the influence of the thickness of the iron-phosphorus-carbon compound phase. In other words, the sum of the decrease in the machinability index due to the increase in the free graphite phase (improving machinability) and the increase in the machinability index due to the increase and coarsening of the iron-phosphorus-carbon compound phase (deterioration in machinability). As a result, the machinability index is minimized in the range of carbon content of 1.5 to 2.5 mass%. The amount of wear is thought to decrease with increasing proportion of the iron-phosphorus-carbon compound phase. However, the crushing strength should be improved by increasing the ratio of the iron-phosphorus-carbon compound phase, but it decreases according to FIG. 10 (d), and in particular, the carbon content exceeds 2.5 mass%. And the decrease in crushing strength is remarkable. This is because the compressibility of the mixed powder decreases due to an increase in the amount of carbon powder, and the strength of the green compact and the sintered body decreases. From these results, the appropriate carbon amount range in all of the crushing strength, machinability and wear resistance is 1.5 to 2.5 mass%.

(Samples 28-38)
The blending ratio of the mixed powder in each sample was set to the same blending ratio as that of sample 4 in Example 1, and as shown in Table 4, sintering temperatures were 900 ° C. (sample 28), 950 ° C. (sample 29), 1050 ° C. (sample 30). ) The same operations as in Sample 4 were repeated except that the temperature was changed to 1100 ° C. (Sample 31), and mixed powder was prepared, green compact was formed, sintered, and cooled. Obtained. In addition, Table 5 shows the component composition of the entire mixed powder in each sample.

  The same as sample 4 except that the sintering time was changed to 10 minutes (sample 32), 20 minutes (sample 33), 45 minutes (sample 34), 90 minutes (sample 35), and 120 minutes (sample 36). The above operations were repeated to prepare mixed powder, compact green compact, sinter, and cool to obtain sintered bodies of Samples 32-36.

  Further, the same procedure as in Sample 4 was repeated except that the cooling rate after sintering was changed to 8 ° C./min (Sample 37) and 4 ° C./min (Sample 38). Molding, sintering, and cooling were performed to obtain sintered bodies of Samples 37 to 38.

For the sintered bodies of Samples 28 to 38, as in Samples 1 to 27, determination of the proportion of each phase in the metal structure cross section of the sintered body by observation of the structure cross section, wear test, machinability test, and pressure ring test are performed. It was. These results are shown in Table 6.

FIG. 11 shows the relationship between the sintering temperature and the ratio of each phase in the overall composition of Sample 4 and Samples 28 to 31, and the sintering temperature, the thickness of the iron-phosphorus-carbon compound phase, and the material properties (amount of wear, The relationship between the machinability index and the crushing strength is shown in FIG.

  According to FIG. 11 (b), the proportion of the copper-tin alloy phase does not depend on the sintering temperature, but the iron-phosphorus-carbon compound phase is formed when the temperature exceeds 900 ° C., and the proportion and thickness are determined by firing. It increases with the increase of the setting temperature (FIGS. 11A and 12A), and the proportion of the free graphite phase decreases on the contrary (FIG. 11C). This is because the higher the sintering temperature is, the more the solid solution diffusion of the graphite proceeds. The lower the sintering temperature, the higher the ratio of the ferrite phase is because the graphite particles are difficult to diffuse. However, when the sintering temperature exceeds 1100 ° C., the ratio of the ferrite phase increases due to the lack of carbon due to the excessive formation of the iron-phosphorus-carbon compound phase (FIG. 11 (d)).

  The correlation between the thickness of the iron-phosphorus-carbon compound phase and the ratio of the free graphite phase and the machinability index can also be confirmed in FIGS. 11 and 12, and when the range where the machinability index is 35 or less is obtained, In this range, the ratio of the iron-phosphorus-carbon compound phase is about 3 area% or less, and the ratio of the iron-phosphorus-carbon compound phase having a thickness of 15 μm or more is 10% or less.

  Further, the crushing strength has not only a correlation with the ratio of the iron-phosphorus-carbon compound phase but also a correlation with the ratio of the ferrite phase, and the crushing strength decreases when the ratio of the ferrite phase is large. When the range of the crushing strength is 500 MPa or more, the sintering temperature is 950 to 1050 ° C. In this range, the ratio of the iron-phosphorus-carbon compound phase is about 0.2 to 3 area%, and the ferrite phase is about 9 area% or less.

  Thus, even if the composition is the same, the metal structure formed and the material properties to be exhibited are greatly different depending on the sintering temperature, and the material properties obtained at the sintering temperatures to be exhibited are 950 ° C. to 1050 ° C. The valve guide has an iron-phosphorus-carbon compound phase ratio of about 0.2 to 3 area%, an iron-phosphorus-carbon compound phase ratio of 15 μm or more in thickness of 10% or less, and a ferrite phase of about 9 area% or less. It becomes.

  For Sample 4 and Samples 32-36, the relationship between the sintering time and the proportion of each phase in the overall composition is shown in FIG. 13, and the sintering time, the thickness of the iron-phosphorus-carbon compound phase, and the material properties (amount of wear, The relationship between the machinability index and the crushing strength is shown in FIG.

  13 (a), (c), and (d), carbon solid solution diffusion and formation of an iron-phosphorus-carbon compound phase proceed as the sintering time increases, and carbon diffusion is insufficient and iron -When the phosphorus-carbon compound phase is excessively formed, the ferrite phase increases. This is similar to the effect of sintering temperature.

  Therefore, the correlation between the ratio of the iron-phosphorus-carbon compound phase, the thickness, the ratio of the free graphite phase, and the machinability index can also be confirmed in FIGS. 13 and 14, and the machinability index is 35 or less. In this range, the ratio of the iron-phosphorus-carbon compound phase is about 3 area% or less, and the ratio of the iron-phosphorus-carbon compound phase having a thickness of 15 μm or more is about 10%. %, The ratio of the free graphite phase is 1 area% or more.

  Moreover, about the crushing strength, when the range which becomes 500 Mpa or more is calculated | required, sintering time will be 20 minutes or more. The iron-phosphorus-carbon compound phase is generated in a sufficient amount to exhibit strength even when the sintering time is 20 minutes or less, and the metal structure itself is formed. The strength improved by maintaining the sintering is obtained by growing the neck between the iron particles, so that the sintering is properly maintained according to the required crushing strength and wear resistance. Set the sintering time.

  For sample 4 and samples 37 and 38, the relationship between the cooling rate and the proportion of each phase in the overall composition is shown in FIG. 15, and the cooling rate, the thickness of the iron-phosphorus-carbon compound phase, and the material properties (amount of wear, machining) The relationship between the sex index and the crushing strength is shown in FIG.

  From FIG. 15 and FIG. 16 (a), the amount of the copper-tin alloy phase and the free graphite phase does not change depending on the cooling rate, but the iron-phosphorus-carbon compound phase and the ferrite phase decrease as the cooling rate increases. The thickness of the iron-phosphorus-carbon compound phase is also reduced.

  On the other hand, the machinability is affected by the cooling rate in the material properties. In general, the precipitation when the liquid solidifies as the cooling rate increases, and in the sintered valve guide, the precipitated iron-phosphorus-carbon compound phase becomes thinner, and the amount produced is also reduced. The proportion of phases also decreases. As a result, machinability is improved. The copper-tin alloy phase is also finely precipitated from the liquid phase. When the range of the cooling rate at which the machinability index is 35 or less is obtained, it is 8 ° C./min or more. At this time, the ratio of the iron-phosphorus-carbon compound phase is 3 area% or less and the thickness is 15 μm or more. -The proportion of the carbon compound phase is 10% or less and the proportion of the ferrite phase is 5% or less.

(Samples 39-49)
According to Table 7 which shows the mixing | blending of the mixed powder in each sample, the oxide amount in raw material iron powder is 0.2 mass% (mill scale reduced iron powder, sample 39), 0.5 mass% (sample 40), 1.5 Except for changing to mass% (sample 41) and 2.0 mass% (sample 42), the same operations as in sample 4 were repeated to prepare a mixed powder, mold a green compact, sinter, and cool the sample. 39-42 sintered bodies were obtained. The component composition of the entire mixed powder in each sample is shown in Table 8.

  Moreover, a part or all of the ore reduced iron powder is replaced with atomized iron powder (amount of oxide: 0.2 mass%), and the ratio in the total composition of the mixed powder is 5 mass% (sample 43), 10 mass% (sample 44), 15% by mass (Sample 45), 20% by mass (Sample 46), 30% by mass (Sample 47), 40% by mass (Sample 48), and 92.2% by mass (Sample 49) The same operations as in Sample 4 were repeated to prepare a mixed powder, to form a green compact, to sinter and to cool, and to obtain sintered bodies of Samples 43 to 49.

For the sintered bodies of Samples 39 to 49, as in Samples 1 to 27, determination of the proportion of each phase in the metal structure cross section of the sintered body by observation of the structure cross section, wear test, machinability test, and pressure ring test are performed. It was. These results are shown in Table 9.

For Samples 4 and 10 and Samples 39 to 42, the relationship between the amount of oxide in the iron powder and the proportion of each phase in the overall composition is shown in FIG. 17, and the amount of oxide in the iron powder and the thickness of the iron-phosphorus-carbon compound phase are shown in FIG. FIG. 18 shows the relationship between the thickness and material characteristics (amount of wear, machinability index, and crushing strength).

  According to FIGS. 17 and 18 (a), the amount of oxide in the iron powder hardly affects the formation of other phases such as an iron-phosphorus-carbon compound phase and a copper-tin alloy phase, and the oxide is independent. It exists in the metal structure. On the other hand, the machinability index (FIG. 18C) decreases as the amount of oxide increases. However, at the same time, the crushing strength (FIG. 18 (d)) also decreases and the amount of wear increases. Therefore, from FIGS. 18B to 18D, when the machinability index is 35 or less, the crushing strength is 500 MPa or more, and the wear amount is 60 μm or less, the amount of oxide in the iron powder is about 0.5. It becomes -1.5 mass%.

  For Samples 4 and 10 and Samples 43 to 49, the relationship between the amount of atomized iron powder blended and the proportion of each phase in the overall composition is shown in FIG. 19. The amount of atomized iron powder blended and the thickness of the iron-phosphorus-carbon compound phase FIG. 20 shows the relationship between the thickness and material properties (amount of wear, machinability index, and crushing strength).

  Also in FIG.19 and FIG.20 (a), the influence with respect to formation of the other phase by the compounding quantity of atomized iron powder is not seen. According to FIGS. 20 (b) to (d), the material properties are slightly affected, and the crushing strength increases as the added amount of atomized iron powder increases, and only the atomized iron powder is used. The highest strength. Further, the machinability index decreases as the amount of atomized iron powder added decreases, and the effect of improving the machinability is particularly remarkable when the amount of atomized iron powder added is 30% by mass or less. When mill scale reduced iron powder is used, the machinability index is the same as when atomized iron powder is used, which is higher than when using ore reduced iron powder, and the crushing strength is when using atomized iron powder. It is slightly lower than. Therefore, the use of atomized iron powder is recommended when emphasizing strength as a sintered valve guide, and the use of ore reduced iron powder is recommended when emphasizing machinability. Moreover, when mixing and using atomized iron powder with ore reduced iron powder, it can be said that the mixing ratio of atomized iron powder is about 30 mass% or less from which the effect of a machinability improvement becomes remarkable.

(Samples 50-66)
According to Table 10 showing the blended powder composition of each sample, manganese sulfide powder 0.2 to 2.0 mass% (samples 50 to 55, samples 62 to 66), magnesium silicate powder 0. Except for blending 2 to 2.0 mass% (Samples 56 to 61, Samples 62 to 66), the same operation as Sample 4 was repeated to prepare a mixed powder, mold a green compact, sinter, and cool. The sintered bodies of Samples 50 to 66 were obtained. The component composition of the entire mixed powder in each sample is shown in Table 11.

For the sintered bodies of Samples 50 to 66, similarly to Samples 1 to 27, determination of the proportion of each phase in the metal structure cross section of the sintered body by observation of the structure cross section, wear test, machinability test, and pressure ring test are performed. It was. These results are shown in Table 12.

For Samples 4 and 10 and Samples 50 to 66, the relationship between the addition of the machinability improving powder in the mixed powder and the ratio of each phase in the overall composition is shown in FIG. 21, and the addition of the machinability improving powder in the mixed powder. The relationship between the amount, the thickness of the iron-phosphorus-carbon compound phase, and the material properties (wear amount, machinability index, and crushing strength) is shown in FIG.

  According to FIG. 21 (c) and FIG. 22 (c), as the machinability improving powder in the mixed powder increases, the ratio of the free graphite phase gradually increases and the machinability index also gradually decreases. However, the effect of the machinability improving powder is relatively mild, and the crushing strength gradually decreases as the amount added increases. If the amount exceeds 1.6% by mass, sintering inhibition (diffusion) occurs. Since the amount of wear increases rapidly due to the embrittlement of the base due to (suppression), it is difficult to dramatically improve the machinability using only the machinability improving powder. Therefore, it is important to optimize the influence on the machinability by the ratio and thickness of the iron-phosphorus-carbon compound phase and the ratio of the free graphite phase, and in that case, the crushing strength and the wear resistance Therefore, it is necessary to determine the composition and manufacturing conditions in consideration of the balance of the above.

It is the schematic diagram showing the metal structure cross section of the sintering valve guide in this invention. It is the schematic diagram showing the metal structure cross section of the sintering valve guide with many ratios of an iron-phosphorus-carbon compound phase. Relationship between the amount of phosphorus in the overall composition and the proportion of iron-phosphorus-carbon compound phase (a), the proportion of copper-tin alloy phase (b), the amount of free graphite phase (c), the proportion of ferrite phase (d) It is a graph which shows. It is a graph which shows the relationship between the amount of phosphorus in the whole composition, the thickness (a) of the iron-phosphorus-carbon compound phase, the wear amount (b), the machinability index (c), and the crushing strength (d). Relationship between the amount of tin in the overall composition and the proportion of iron-phosphorus-carbon compound phase (a), the proportion of copper-tin alloy phase (b), the amount of free graphite phase (c), and the proportion of ferrite phase (d) It is a graph which shows. It is a graph which shows the relationship between the amount of tin in the whole composition, the thickness (a) of the iron-phosphorus-carbon compound phase, the wear amount (b), the machinability index (c), and the crushing strength (d). Relationship between the amount of copper in the overall composition and the proportion of iron-phosphorus-carbon compound phase (a), the proportion of copper-tin alloy phase (b), the amount of free graphite phase (c), and the proportion of ferrite phase (d) It is a graph which shows. It is a graph which shows the relationship between the amount of copper in a whole composition, the thickness (a) of an iron-phosphorus-carbon compound phase, the amount of wear (b), the machinability index (c), and the crushing strength (d). Relationship between the amount of carbon in the total composition and the proportion of iron-phosphorus-carbon compound phase (a), the proportion of copper-tin alloy phase (b), the amount of free graphite phase (c), and the proportion of ferrite phase (d) It is a graph which shows. It is a graph which shows the relationship between the amount of carbon in a whole composition, the thickness (a) of an iron-phosphorus-carbon compound phase, the amount of wear (b), the machinability index (c), and the crushing strength (d). Graph showing the relationship between the sintering temperature and the ratio of iron-phosphorus-carbon compound phase (a), the ratio of copper-tin alloy phase (b), the amount of free graphite phase (c), and the ratio of ferrite phase (d) It is. It is a graph which shows the relationship between sintering temperature and the thickness (a) of an iron- phosphorus-carbon compound phase, the amount of wear (b), the machinability index (c), and the crushing strength (d). Graph showing the relationship between the sintering time and the ratio of iron-phosphorus-carbon compound phase (a), the ratio of copper-tin alloy phase (b), the amount of free graphite phase (c), and the ratio of ferrite phase (d) It is. It is a graph which shows the relationship between sintering time and the thickness (a), wear amount (b), machinability index (c), and crushing strength (d) of an iron-phosphorus-carbon compound phase. A graph showing the relationship between the cooling rate and the ratio of iron-phosphorus-carbon compound phase (a), the ratio of copper-tin alloy phase (b), the amount of free graphite phase (c), and the ratio of ferrite phase (d). is there. It is a graph which shows the relationship between a cooling rate, the thickness (a) of an iron-phosphorus-carbon compound phase, the amount of wear (b), the machinability index (c), and the crushing strength (d). Relationship between the amount of oxide in the iron powder and the proportion of iron-phosphorus-carbon compound phase (a), the proportion of copper-tin alloy phase (b), the amount of free graphite phase (c), the proportion of ferrite phase (d) It is a graph which shows. It is a graph which shows the relationship between the oxide amount in iron powder, the thickness (a) of an iron- phosphorus-carbon compound phase, the amount of wear (b), the machinability index (c), and the crushing strength (d). The relationship between the amount of atomized iron powder and the proportion of iron-phosphorus-carbon compound phase (a), the proportion of copper-tin alloy phase (b), the amount of free graphite phase (c), the proportion of ferrite phase (d) It is a graph to show. It is a graph which shows the relationship between the quantity of atomized iron powder, the thickness (a) of an iron-phosphorus-carbon compound phase, the amount of wear (b), the machinability index (c), and the crushing strength (d). The amount of machinability improving powder and the ratio of iron-phosphorus-carbon compound phase (a), the ratio of copper-tin alloy phase (b), the amount of free graphite phase (c), and the ratio of ferrite phase (d) It is a graph which shows a relationship. It is a graph which shows the relationship between the quantity of machinability improvement powder, the thickness (a) of an iron-phosphorus-carbon compound phase, the amount of wear (b), the machinability index (c), and the crushing strength (d). .

Claims (16)

The total composition is by mass: copper: 3.5-5%, tin: 0.3-0.6%, phosphorus: 0.04-0.15%, carbon: 1.5-2.5%, and , Iron: formed of a sintered alloy consisting of the balance,
The sintered alloy has a metal structure composed of a matrix having a pearlite phase, an iron-phosphorus-carbon compound phase, and a copper-tin alloy phase, pores, and a graphite phase, and the graphite phase is bonded by mass ratio. Dispersed at a rate of 1.2-1.7% of gold,
In the metal structure cross section of the sintered alloy, the ratio of the pearlite phase to the matrix is 90% or more in area ratio, and the ratio of the iron-phosphorus-carbon compound phase to the metal structure cross section is 0.00. 1 to 3%, the proportion of the copper-tin alloy phase in the cross section of the metal structure is 1 to 3% by area ratio, and the iron-phosphorus-carbon compound phase has a thickness of 15 μm or more in the iron- A sintered valve guide characterized in that the proportion of the phosphorus-carbon compound phase is 10% or less in terms of area ratio. Total composition is mass ratio, copper: 3.5-5%, tin: 0.3-0.6%, phosphorus: 0.04-0.15%, carbon: 1.5-2.5%, metal Oxide: 0.46 to 1.41%, and iron: formed of a sintered alloy consisting of the balance,
The sintered alloy has a metal structure composed of a matrix having a pearlite phase, an iron-phosphorus-carbon compound phase, a copper-tin alloy phase and a metal oxide phase, pores, and a graphite phase, Dispersed in a mass ratio of 1.2 to 1.7% of the sintered alloy,
In the metal structure cross section of the sintered alloy, the ratio of the pearlite phase to the matrix is 90% or more in area ratio, and the ratio of the iron-phosphorus-carbon compound phase to the metal structure cross section is 0.00. 1 to 3%, and the proportion of the copper-tin alloy phase in the metal structure cross section is 1 to 3% in terms of area ratio. In the iron-phosphorus-carbon compound phase, the portion having a thickness of 15 μm or more is the iron- A sintered valve guide characterized in that the proportion of the phosphorus-carbon compound phase is 10% or less in terms of area ratio. Total composition is mass ratio, copper: 3.5-5%, tin: 0.3-0.6%, phosphorus: 0.04-0.15%, carbon: 1.5-2.5%, sulfide Solid lubricant selected from at least one of manganese and magnesium silicate minerals: 1.6% or less, and iron: formed of a sintered alloy consisting of the balance,
The sintered alloy comprises a matrix having a pearlite phase, an iron-phosphorus-carbon compound phase, and a copper-tin alloy phase, pores, a graphite phase, and the solid lubricant dispersed in the pores or at the powder grain boundaries. Has a metallographic structure,
In the metal structure section of the sintered alloy, the ratio of the pearlite phase to the metal structure section is 90% or more by area ratio, and the ratio of the iron-phosphorus-carbon compound phase to the metal structure section is 0 by area ratio. The proportion of the copper-tin alloy phase in the metal structure section is 1 to 3% by area ratio, and the graphite phase is 0.8 to 3.2% of the metal structure section by area ratio. The ratio of the portion of the iron-phosphorus-carbon compound phase in which the thickness is 15 μm or more occupies the iron-phosphorus-carbon compound phase is 10% or less in terms of area ratio. Sintered valve guide. Total composition is mass ratio, copper: 3.5-5%, tin: 0.3-0.6%, phosphorus: 0.04-0.15%, carbon: 1.5-2.5%, metal Oxide: 0.46 to 1.41%, solid lubricant selected from at least one selected from manganese sulfide and magnesium silicate mineral: 1.6% or less, and iron: formed of a sintered alloy consisting of the balance,
The sintered alloy includes a matrix having a pearlite phase, an iron-phosphorus-carbon compound phase, a copper-tin alloy phase, and a metal oxide phase, pores, a graphite phase, and the pores dispersed in the pores or powder grain boundaries. It has a metal structure consisting of a solid lubricant,
In the metal structure section of the sintered alloy, the ratio of the pearlite phase to the metal structure section is 90% or more by area ratio, and the ratio of the iron-phosphorus-carbon compound phase to the metal structure section is 0 by area ratio. The proportion of the copper-tin alloy phase in the metal structure cross section is 1 to 3% by area ratio, and the graphite phase is 0.8 to 3.2% of the metal structure cross section by area ratio. The ratio of the portion of the iron-phosphorus-carbon compound phase in which the thickness is 15 μm or more occupies the iron-phosphorus-carbon compound phase is 10% or less in terms of area ratio. Sintered valve guide.   The sintered valve guide according to claim 2 or 4, wherein the metal oxide is an oxide of at least one metal selected from the group consisting of aluminum, silicon, magnesium, iron, calcium, and titanium.   In the iron-phosphorus-carbon compound phase, in the metal structure cross section, a portion having a thickness of 5 μm or more and less than 15 μm is 10 to 40% in area ratio, and the remaining iron-phosphorus-carbon compound phase is less than 5 μm in thickness. The sintered valve guide according to any one of claims 1 to 5, wherein Iron-phosphorus alloy powder having a phosphorus content of 15 to 21% by mass and the balance being Fe and unavoidable impurities, copper-tin alloy powder and graphite powder having a tin content of 8 to 11% by mass and the balance being copper and unavoidable impurities Is added to the iron powder, iron-phosphorus alloy powder: 0.27 to 0.7 mass%, copper-tin alloy powder: 3.93 to 5.44 mass%, graphite powder: 1.7 to 2.7 A step of preparing a mixed powder composed of iron powder by mass% and the balance,
Filling the powder mixture into a tubular cavity of a mold and pressurizing and compressing the mixed powder into a powder compact in a tubular shape; and
And sintering the green compact at a heating temperature of 950 to 1050 ° C. in a non-oxidizing atmosphere.   The method for manufacturing a sintered valve guide according to claim 7, wherein the iron powder is ore reduced iron powder containing 0.5 to 1.5 mass% of a metal oxide.   The method for producing a sintered valve guide according to claim 7, wherein the iron powder is a mixed powder of ore reduced iron powder and atomized iron powder containing 10 to 30% by mass of atomized iron powder.   The method for producing a sintered valve guide according to any one of claims 7 to 9, wherein the iron powder has a maximum particle size of 104 to 200 µm.   11. The iron-phosphorus alloy powder has a maximum particle size of 61 to 104 [mu] m, and the copper-tin alloy powder has a maximum particle size of 35 to 61 [mu] m. A method for manufacturing a sintered valve guide.   The method for producing a sintered valve guide according to any one of claims 7 to 11, wherein in the sintering step, a sintering holding time is 15 to 90 minutes.   In the mixed powder preparation step, at least one powder selected from manganese sulfide powder and magnesium silicate mineral powder is further added so as to be 1.6% by mass or less of the mixed powder. Item 13. A method for producing a sintered valve guide according to any one of Items 7 to 12.   14. The surface of at least one of the hole portion of the die and the outer periphery of the core rod is inclined so that the cavity is tapered at a ratio of 1/5000 to 1/1000. The manufacturing method of the sintered valve guide in any one of.   Furthermore, it has the process of immersing the sintered compact obtained by the said sintering process in oil, The manufacturing method of the sintered valve guide in any one of Claims 7-14 characterized by the above-mentioned.   The method for producing a sintered valve guide according to any one of claims 7 to 15, further comprising a step of cooling the sintered body obtained by the sintering step at a cooling rate of 8 ° C / min or more.