WO2020013227A1

WO2020013227A1 - Sintered alloy and method for producing same

Info

Publication number: WO2020013227A1
Application number: PCT/JP2019/027344
Authority: WO
Inventors: 大輔深江; 英昭河田
Original assignee: 日立化成株式会社
Priority date: 2018-07-11
Filing date: 2019-07-10
Publication date: 2020-01-16
Also published as: CN112368409A; EP3822379A4; JP7248027B2; EP3822379A1; JPWO2020013227A1; CN112368409B; EP3822379B1

Abstract

Provided is a sintered alloy, which has a total composition comprising, by mass%: 13.86 to 27.72% of Cr; 6.47 to 20.33% of Ni; 0.85 to 11.05% of Cu; 0.46 to 2.77% of Si; 0.15 to 1.95% of P; 0.2 to 1.0% of C; and Fe and inevitable impurities as the balance. The sintered alloy has a density of 6.8 to 7.4 mg/m³, and displays a metal structure having an iron alloy substrate in which pores are dispersed and a carbide dispersed in the iron alloy substrate, the iron alloy substrate having an average crystal particle diameter of 10 to 50 µm.

Description

Sintered alloy and method for producing the same

The present invention relates to a sintered alloy suitable for a turbocharger turbo component or the like and a method for producing the same, and more particularly, to a sintered alloy suitable for a nozzle body or the like which requires heat resistance, corrosion resistance and wear resistance, and a method for producing the same. .

Generally, in a turbocharger attached to an internal combustion engine, a turbine is rotatably supported by a turbine housing connected to an exhaust manifold of the internal combustion engine, and a plurality of nozzle vanes are rotatably supported so as to surround an outer peripheral side of the turbine. Have been. Exhaust gas flowing into the turbine housing flows into the turbine from the outer peripheral side and is discharged in the axial direction, and at that time, rotates the turbine. The air supplied to the internal combustion engine is compressed by rotating a compressor provided on the same shaft on the opposite side of the turbine.

The nozzle vane is rotatably supported by a ring-shaped component called by a name such as a nozzle body or a mount nozzle. The shaft of the nozzle vane passes through the nozzle body and is connected to a link mechanism. When the link mechanism is driven, the nozzle vanes rotate, and the opening degree of the flow path through which the exhaust gas flows into the turbine is adjusted.

Turbo components for a turbocharger as described above, that is, turbo components provided in a turbine housing, such as a nozzle body (mount nozzle) and a plate nozzle attached thereto, are exhaust gas which is a high-temperature corrosive gas. Contact with. Therefore, these parts are required to have heat resistance and corrosion resistance and also wear resistance to cope with sliding contact with the nozzle vanes. For this reason, conventionally, for example, high-chromium cast steel, heat-resistant steel specified as type SCH22 in JIS standards, or heat-resistant alloy which has been subjected to chromium surface treatment for the purpose of improving corrosion resistance has been used as a material constituting a turbo component. Abrasive materials and the like are used.

On the other hand, also in the powder metallurgy method, sintered alloys for application to various machine parts have been developed, and the above-mentioned heat- and wear-resistant sintered alloys for turbo parts have been proposed (see Patent Document 1). In the powder metallurgy method, a sintered alloy having a special metal structure that cannot be formed by molten steel obtained by casting or the like is obtained.

JP 2013-19965 A

However, in a turbocharger component that slides in contact with another member, such as a nozzle body that slides in contact with a nozzle vane, further improvement in wear resistance is desired in order to prevent cohesive wear with another member. . Further, since oxidation is easily progressed by steam contained in high-temperature exhaust gas, further improvement in corrosion resistance is desired. Further, in order to meet the demand for complicated shapes, improvement in machinability (machinability) is desired.

As described above, the present invention provides a sintered alloy having excellent wear resistance, corrosion resistance and machinability, and a method for producing the same, which is suitable for application to turbocharger parts by further improving the iron-based sintered alloy. The task is to provide

According to one embodiment of the present invention, there is provided a sintered alloy having a total composition of 13.86 to 27.72% of Cr and 6.47 to 20.33% of Ni in mass%. %, Cu: 0.85 to 11.05%, Si: 0.46 to 2.77%, P: 0.15 to 1.95%, C: 0.20 to 1.00%, and the balance A metallurgical structure comprising Fe and an unavoidable element and having a density of 6.8 to 7.4 Mg / m ³ , the metal structure having an iron alloy matrix in which pores are dispersed and a carbide dispersed in the iron alloy matrix. The gist is that the iron alloy matrix is composed of crystal grains having an average crystal grain size of 10 to 50 μm.

According to another aspect of the present invention, the sintered alloy has a total composition of 13.86 to 27.72% of Cr, 6.47 to 20.33% of Ni, and 0.85% of Cu in mass%. To 11.05%, Si: 0.46 to 2.77%, P: 0.15 to 1.95%, C: 0.20 to 1.00%, carbide-forming element: 3.23% or less, and A sintered alloy having a balance of Fe and inevitable elements and a density of 6.8 to 7.4 Mg / m ³ , wherein the carbide-forming element is selected from the group consisting of Mo, V, W, Nb and Ti. At least one element selected from the group consisting of an iron alloy matrix in which pores are dispersed and a metal structure having carbides dispersed in the iron alloy matrix, wherein the iron alloy matrix has an average crystal grain size of 10 to 50 μm. The gist of the invention is that it is composed of crystal grains of

According to one embodiment of the present invention, the method for producing a sintered alloy includes, in mass%, Cr: 15 to 30%, Ni: 7 to 24%, Si: 0.5 to 3.0%, and An iron alloy powder comprising the balance of Fe and unavoidable impurities is prepared, and an iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass, a copper-phosphorus alloy powder having a phosphorus content of 5 to 20% by mass, and copper A compounding material for compounding phosphorus and copper, which is composed of one or more kinds selected from powders, is prepared, and the iron alloy powder, the compounding material, and the graphite powder are mixed to form 0.15 to 1.95. By preparing a raw material powder containing phosphorus of 0.8% by mass, 0.85 to 11.05% by mass of copper, and 0.20 to 1.00% by mass of carbon, the raw material powder is compressed to have a density of 6%. From 0.0 to 6.8 Mg / m ³ , and pressing the compact in a non-oxidizing atmosphere at 1050 The essence is to sinter by heating to a temperature of １1160 ° C.

According to another aspect of the present invention, a method for producing a sintered alloy includes: in mass%, 15 to 30% of Cr, 7 to 24% of Ni, 0.5 to 3.0% of Si, : An iron alloy powder comprising 3% by mass or less and the balance of Fe and unavoidable impurities, wherein the carbide-forming element is at least one element selected from the group consisting of Mo, V, W, Nb and Ti The above iron alloy powder is prepared, and is selected from iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass, copper-phosphorus alloy powder having a phosphorus content of 5 to 20% by mass, and copper powder. A compounding material for phosphorus and copper, which is composed of one or more kinds, is prepared, and the iron alloy powder, the compounding material and the graphite powder are mixed, and 0.15 to 1.95 mass% of phosphorus, 0% .85 to 11.05 mass% copper and 0.20 to 1.00 mass% charcoal The raw material powder was prepared containing the raw material powder by compressing a density to form a green compact of ^{6.0 ~ 6.8Mg / m 3, 1050} ~ the green compact in a non-oxidizing atmosphere 1160 The sintering is performed by heating to a temperature of ° C.

The compounding material is a powder material containing phosphorus in one or both forms of iron-phosphorus alloy powder and copper-phosphorus alloy powder, and containing copper in one or both forms of copper powder and copper-phosphorus alloy powder. Good to be. Any of the following (1) to (5) can be used as the compounding material. (1) a combination of an iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass and a copper powder; (2) an iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass; (3) an iron-phosphorus alloy powder having a phosphorus content of 10 to 30 mass%, and a copper-phosphorus alloy powder having a phosphorus content of 5 to 20 mass%. (4) a combination of a copper-phosphorus alloy powder having a phosphorus content of 5 to 20% by mass and a copper powder, (5) a copper-phosphorus alloy powder having a phosphorus content of 5 to 20% by mass . The non-oxidizing atmosphere may be a mixed gas of nitrogen and hydrogen containing 10% by mass or more of nitrogen, or a normal-pressure atmosphere composed of nitrogen gas, and may be a surface of the sintered alloy and an inner surface of the pore. Thus, the above sintered alloy in which a nitride is formed is obtained.

Based on the composition design of the iron-based alloy, it is possible to improve the machinability of the sintered alloy while suppressing the influence on other material properties, thereby providing excellent wear resistance, corrosion resistance and machinability, and It is possible to provide a sintered alloy suitable for application to a charger component and a method of manufacturing the same.

炭化 Carbide particles dispersed in the metal structure of the sintered alloy tend to hinder cutting during machining, and as the amount of carbide particles increases, the machinability of the sintered alloy decreases. Therefore, in order to improve the machinability of the sintered alloy, it is considered effective to suppress the generation of carbide particles. In accordance with this policy, a study was conducted on sintered alloys having a composition with a low proportion of carbides.While weight reduction of carbides was effective in improving machinability, the pinning effect of carbides was reduced and crystal grains of the iron alloy base were reduced. It was found that the grains became coarse, which led to a decrease in oxidation resistance.

For this reason, a study was made of a method for compensating for the above-mentioned drawbacks, and it was found that when copper forms a solid solution in the iron alloy matrix, the oxidation resistance of the matrix in a steam environment is improved, and the corrosion resistance can be improved. It has also been found that the solid solution of copper in the matrix hardens soft austenite and suppresses adhesion between the matrix and other members, thereby improving machinability. Furthermore, it has been clarified that by lowering the sintering temperature, it is possible to suppress the growth of crystal grains and increase the oxidation resistance. In this regard, since the copper-phosphorus alloy powder can generate a liquid phase at a low temperature, if it is used as a raw material for introducing copper, it is an effective means for setting the sintering temperature low.

In consideration of the above points, in the present invention, by designing the alloy composition so that the functions of the components constituting the sintered alloy are exhibited in a good balance, oxidation resistance, corrosion resistance, and machining Provided is a sintered alloy having improved properties. Hereinafter, the component compositions of the sintered alloy and the raw material powder of the present invention will be described.

<Component composition of sintered alloy and raw material powder>
In the present invention, the matrix of the sintered alloy is an iron alloy matrix having an austenitic stainless steel composition, and has a metal structure in which pores are dispersed in the matrix and carbide particles are precipitated and dispersed. Austenitic stainless steel is an iron alloy in which chromium and nickel are dissolved in γ-iron, has high corrosion resistance and heat resistance, and has the same thermal expansion coefficient as a general austenitic heat-resistant material.

Austenitic stainless steel improves oxidation resistance in a steam environment by suppressing the growth of crystal grains. In the present invention, the austenitic stainless steel constituting the base of the sintered alloy is composed of crystal grains having an average crystal grain size of 10 to 50 μm. It is possible to suppress the growth of crystal grains in such a particle size range by sintering at a temperature lower than the conventional sintering temperature, and the sintering temperature is set in the range of 1050 to 1160 ° C. To enable sintering at low temperatures, it is useful to use components that generate a liquid phase at low temperatures. In this regard, the copper-phosphorus alloy powder can proceed with sintering at relatively low temperatures of 1050-1130 ° C. Therefore, the use of the copper-phosphorus alloy powder effectively acts to lower the sintering temperature and is useful in suppressing the growth of crystal grains. With the appropriate sintering proceeding at such a temperature setting, the density of the sintered alloy becomes about 6.8 to 7.4 Mg / m ³ .

オー Austenite constituting the base of the sintered alloy can be produced using iron alloy powder in which chromium or nickel is dissolved in iron as a main material. That is, the austenitizing elements (chromium and nickel) are introduced into the raw material powder by alloying with iron to prepare an iron alloy powder. Thereby, the austenitizing element is uniformly distributed in the iron alloy matrix, and exhibits corrosion resistance and heat resistance. Another component that alloys with iron is silicon, which acts as an antioxidant to chromium during the preparation of the iron-chromium alloy powder.

When the iron alloy base contains chromium (Cr) in an amount of 12% by mass or more, it exhibits corrosion resistance to oxidizing acids. Considering that a part of chromium contained in the iron alloy powder used as a raw material precipitates as carbides during sintering, the chromium content of the iron alloy powder is set to 15 mass so that sufficient chromium remains in the iron alloy base. %. However, if the chromium content of the iron alloy powder exceeds 30% by mass, a brittle σ phase is formed, and the compressibility of the iron alloy powder is significantly impaired. Therefore, the iron alloy powder as a raw material preferably has a chromium content of about 15 to 30% by mass. In a preferred sintered alloy obtained using such a powder, the proportion of chromium in the entire composition is about 13.86 to 27.72% by mass. It is more preferably at least 16.88% by mass and at most 23.10% by mass, most preferably at least 18.48% by mass and at most 20.33% by mass.

If the iron alloy base contains 3.5% by mass or more of nickel (Ni), it exhibits corrosion resistance to non-oxidizing acids. Further, when the nickel content of the iron alloy powder is 7% by mass or more, such an effect is suitably exhibited, and oxidation resistance is imparted to the obtained sintered alloy. However, when an iron alloy powder having a nickel content of more than 24% by mass is used, the effects on corrosion resistance and oxidation resistance do not change much. Since nickel is also an expensive material, considering the production cost, the nickel content of the iron alloy powder used as a raw material is preferably 7 to 24% by mass, preferably 10 to 22% by mass. Is used. The nickel content in the overall composition of a suitable sintered alloy obtained using such a raw material is 6.47 to 20.33% by mass. The oxidation resistance is preferably 7.39% by mass or more, and the economical efficiency is preferably 18.48% by mass or less.

鋼 Steel exhibiting an austenitic structure has a higher atomic density crystallographically, so its corrosion resistance is better than that of a ferritic structure. For this reason, it is preferable to use as a raw material an iron alloy powder whose chromium content and nickel content are appropriately adjusted so that the iron alloy matrix obtained after sintering suitably exhibits an austenite structure. Specifically, in the annealed structure diagram of the Fe—Cr—Ni-based alloy in which the abscissa represents the amount of chromium (% by mass) and the ordinate represents the amount of nickel (% by mass), point A (Cr: 15, Ni: 7. 5) An austenite structure is formed in a region where the amount of nickel is larger than a broken line connecting point B (Cr: 18, Ni: 6.5) and point C (Cr: 24, Ni: 18). Therefore, it is preferable to adjust the composition of the iron alloy powder used as a raw material so that the chromium amount and the nickel amount in such a region are obtained.

Since iron alloy powder contains chromium which is easily oxidized, silicon is added as a deoxidizing agent to the molten metal for preparing iron alloy powder. For this reason, the iron alloy base contains silicon (Si). Further, when silicon forms a solid solution in the iron alloy matrix, it has an effect of improving the oxidation resistance and heat resistance of the matrix, and the effect is remarkable at 0.46% by mass or more. However, since the iron alloy powder having a silicon content exceeding 3.0% by mass is hard, the compressibility is significantly impaired. When the amount of oxides generated from silicon increases, the progress of sintering is hindered, and the strength of the sintered alloy is reduced. Therefore, the silicon content of the iron alloy powder used as a raw material is preferably 0.5 to 3.0% by mass. The silicon content in the overall composition of the sintered alloy produced using such an iron alloy powder is 0.46 to 2.77% by mass. From the viewpoint of oxidation resistance, the silicon content in the entire composition is preferably 0.74% by mass or more and 1.85% by mass or less.

鉄 Sintering of iron alloy powder with high chromium content is difficult to progress. Therefore, phosphorus (P), which generates a eutectic liquid phase of iron-phosphorus-carbon, is used to promote sintering and is blended in the form of a phosphorus alloy powder. In the present invention, one or both of an iron-phosphorus alloy powder and a copper-phosphorus alloy powder can be used as the phosphorus alloy powder. When an iron-phosphorus alloy powder is used, if the phosphorus content is less than 10% by mass, the amount of liquid phase generated is small, and sintering does not proceed sufficiently. On the other hand, if the phosphorus content exceeds 30% by mass, the iron-phosphorus alloy powder becomes hard, so that the compressibility of the raw material powder is significantly impaired. Accordingly, the iron-phosphorus alloy powder used preferably has a phosphorus content of 10 to 30% by mass. When a copper-phosphorus alloy powder is used, if the phosphorus content is less than 5% by mass, the amount of liquid phase generated is small, and sintering does not proceed sufficiently. On the other hand, when the phosphorus content exceeds 25% by mass, the copper-phosphorus alloy powder becomes hard, and the compressibility of the raw material powder is significantly impaired. Further, the generated liquid phase may easily flow out of the sintered body before being sufficiently diffused. Therefore, the copper-phosphorus alloy powder used preferably has a phosphorus content of 5 to 25% by mass. When the proportion of phosphorus is less than 0.15% by mass in the entire composition of the sintered alloy, the amount of generated liquid phase is insufficient, and the sintering promoting effect is poor. On the other hand, when the proportion of phosphorus exceeds 1.95% by mass, sintering proceeds excessively and densifies, and when the density exceeds the upper limit of the density of the sintered alloy, pores are reduced. Thereby, it becomes difficult to suppress the plastic flow of the matrix, and the wear resistance is reduced. In addition, the excess phosphorus alloy powder is likely to flow out as a liquid phase to the outside, and when the liquid phase flows out, the portion where the phosphorus alloy powder was present becomes pores (so-called Kirkendall voids), and the iron alloy base is coarse. Since the pores are formed, the corrosion resistance is reduced. Further, when sintering proceeds excessively due to the increase in the generation of the eutectic liquid phase, the growth of chromium carbide is promoted, and the precipitated chromium carbide becomes coarse. Therefore, the phosphorus alloy powder is preferably blended with the raw material powder such that the proportion of phosphorus in the entire composition of the sintered alloy is 0.15 to 1.95% by mass. More preferably, the phosphorus content is 0.60% by mass or more and 1.50% by mass or less, and the more appropriate phosphorus content is 0.60% by mass or more and 1.05% by mass or less.

酸化 In the sintered alloy of the present invention, oxidation resistance and corrosion resistance are improved by the solid solution of copper (Cu) in the matrix. At the same time, copper hardens soft austenite and suppresses adhesion of matrix, thereby improving machinability. Copper can be blended with the raw material powder as copper powder or copper-phosphorus alloy powder. When the total amount of phosphorus to promote sintering is formulated as iron-phosphorus alloy powder, copper is formulated in the form of copper powder. When part or all of phosphorus is not blended in the form of an iron-phosphorus alloy powder, a copper-phosphorus alloy powder is used so that the phosphorus content of the raw material powder becomes the above-mentioned proper phosphorus composition ratio. . When the amount of copper introduced by the copper-phosphorus alloy powder is insufficient, or when the copper-phosphorus alloy powder is not used, copper powder is used. When the copper content in the entire composition of the sintered alloy is 0.85 to 11.05% by mass, the oxidation resistance and the corrosion resistance are favorable, so that it is preferable. More preferably, the copper content is 3.40% by mass or more and 8.50% by mass or less, and a more appropriate copper content is 3.40% by mass or more and 5.95% by mass or less.

Therefore, one kind of powder or a combination of plural kinds of powders as shown in the following five forms can be used as the compounding material for compounding phosphorus and copper. In the case of using copper-phosphorus alloy powder (P: 5 to 25% by mass) as the form of (5), when the copper-phosphorus alloy powder is blended at a ratio of 1.0 to 13% by mass of the raw material powder, In the composition, the amount of copper can be adjusted in the range of 0.75 to 12.35% by mass, and the amount of phosphorus can be adjusted in the range of 0.05 to 3.25% by mass. The copper-phosphorus alloy powder generates a eutectic liquid phase at a lower temperature than the iron-phosphorus alloy powder, so that the sintering temperature can be lowered and is suitable for suppressing the growth of crystal grains. The copper-phosphorus alloy powder used preferably has a phosphorus content of 5% by mass or more and 25% by mass or less, more preferably 10% by mass or more and 20% by mass or less, from the viewpoint of generating a liquid phase well. It becomes. The copper-phosphorus alloy powder uses copper-phosphorus alloy powder since the machinability of the obtained sintered alloy tends to be improved as compared with the use of iron-phosphorus alloy powder. The form (5) is preferable. Further, in the embodiments (1) and (5), the amount of the compounding material can be easily determined based on the composition ratio of phosphorus and copper.
(1) Combination of iron-phosphorus alloy powder and copper powder (2) Combination of iron-phosphorus alloy powder and copper-phosphorus alloy powder (3) Iron-phosphorus alloy powder and copper-phosphorus alloy powder Combination with copper powder (4) Combination with copper-phosphorus alloy powder and copper powder (5) Copper-phosphorus alloy powder

Carbon is mixed with raw material powder as graphite powder, and generates a eutectic liquid phase of iron-phosphorus-carbon upon heating to promote sintering. When carbon diffused from the iron-phosphorus-carbon eutectic liquid phase to the iron alloy matrix is combined with chromium, the carbon is dispersed and precipitated as chromium carbide in the matrix. If the amount of carbide precipitation is large, the machinability decreases, so in the present invention, the precipitation of carbide is controlled by appropriately adjusting the blending amount of the graphite powder. Specifically, graphite powder is blended so that the ratio of carbon to the entire composition is 0.20 to 1.00% by mass. If the proportion of carbon exceeds 1.00% by mass of the entire composition, even if sintering proceeds due to the generation of an iron-phosphorus-carbon eutectic liquid phase, a large amount of carbides will be formed, resulting in reduced machinability. I do. In addition, the amount of chromium dissolved in the matrix decreases, and heat resistance and corrosion resistance decrease. When the proportion of carbon is less than 0.20% by mass of the entire composition, the effect of promoting sintering and the wear resistance due to carbides cannot be obtained. Preferably, the carbon content is 0.20% by mass or more and 1.00% by mass or less, more preferably 0.4% by mass or more and 0.80% by mass or less of the whole composition.

析出 Furthermore, if necessary, the precipitation of chromium carbide can be suppressed by mixing an element having a higher ability to generate carbide than chromium (hereinafter referred to as a carbide-forming element) into the raw material powder. The carbide-forming element reacts with graphite preferentially over chromium during sintering to form carbide, and at least a part of the carbide-forming element exists as a carbide in the sintered alloy. This suppresses a decrease in the chromium concentration in the iron alloy base, and thus has an effect of improving the heat resistance and corrosion resistance of the base. Further, when the carbide-forming element reacts with carbon to form an alloy carbide, it contributes to an improvement in wear resistance. The carbide-forming element can be selected from the group consisting of molybdenum, vanadium, tungsten, niobium, and titanium, and may be used alone or in combination of two or more. However, if the carbide-forming element is added in excess of 3.23% by mass of the entire composition, the compressibility of the raw material powder is reduced, so that it is arbitrarily added within the range of 3.23% by mass or less of the entire composition of the sintered alloy. do it. Preferably, the content of the carbide-forming element is 0.46% by mass or more and 2.77% by mass or less of the whole composition. When a plurality of types of elements are used in combination, the total amount may be the above composition ratio.

Therefore, as a first embodiment of the present invention, the sintered alloy has a total composition of 13.86 to 27.72% of Cr, 6.47 to 20.33% of Ni, and Cu: 0 by mass%. 0.85 to 11.05%, Si: 0.46 to 2.77%, P: 0.15 to 1.95%, C: 0.20 to 1.00%, and the balance of Fe and unavoidable elements Preferably. As a second embodiment, the sintered alloy has a total composition of 13.86 to 27.72% of Cr, 6.47 to 20.33% of Ni, and 0.85 to 0.8% of Cu in mass%. 11.05%, Si: 0.46 to 2.77%, P: 0.15 to 1.95%, C: 0.20 to 1.00%, carbide forming element: 3.23% or less, and It is preferable that the balance consists of Fe and unavoidable elements. The carbide-forming element is at least one selected from the group consisting of molybdenum, vanadium, tungsten, niobium, and titanium, and may be one or more of these.

In the sintered alloy prepared based on the above composition ratio, carbides are precipitated and dispersed in the iron alloy matrix in which pores are dispersed, and the carbides can be formed from iron, chromium, and the above-mentioned carbide-forming elements. It can be suitably produced as a sintered alloy having a density of about 6.8 to 7.4 Mg / m ³ . The carbide reduces the contact between the ferrous alloy base and the mating member when the sintered alloy slides with the mating member and suppresses the plastic flow of the matrix, thereby contributing to wear resistance. In the present invention, in order to improve the machinability, the alloy composition is designed so that the ratio of carbide is equal to or less than a predetermined amount. For this reason, it is preferable that the carbide be dispersed and deposited as a large number of particles without coarsening so that the function of the carbide is efficiently exhibited. Specifically, when the carbide is coarsened to exceed 10 μm, the ubiquitous carbide increases the region where the carbide is absent, that is, the region where the plastic flow is not suppressed, and the wear resistance is significantly reduced. It also has an adverse effect on the machinability of the sintered alloy. However, if the dispersed carbide has a size of less than 1 μm, it cannot substantially have the function of suppressing the flow of the matrix. For these reasons, carbide particles having a maximum diameter (maximum particle size) in the range of 1 to 10 μm are preferable. In the microstructure section of the sintered alloy, the ratio (area ratio) of the area of the carbide particles having the maximum diameter in the range of 1 to 10 μm to the area of all the carbide particles is preferably 90% or more. In the present invention, by promoting the sintering of the phosphorus alloy (particularly, the copper-phosphorus alloy), the heating temperature at the time of sintering can be set low, and the coarsening of the carbide particles is suppressed.

Note that the maximum value of the particle size of the carbide particles is determined by image analysis software when measuring the particle size from the image of the particle cross section by image analysis of the metal structure cross section using image analysis software (WinROOF manufactured by Mitani Corporation). The long length of the particle portion determined to be the maximum in the image shall be applied. The average grain size of the crystal grains of the iron alloy matrix is obtained by measuring the area of the austenite matrix and the number of crystal grains in the cross section by image analysis of the metal structure cross section, and from these values, the average area of the crystal grains (number average). Is calculated, and a value converted as an area circle equivalent diameter by an approximate calculation is applied.

<Production method of sintered alloy>
A mixed powder is prepared by mixing the raw materials so that the ratio of each component becomes the composition ratio of the sintered alloy, and the mixed powder is used as a raw material powder for molding. A green compact is obtained by compression molding this, and a sintered body obtained by heating the green compact to a sintering temperature is the above-mentioned sintered alloy.

In the first embodiment, the iron alloy powder containing nickel, chromium, and silicon (first raw material) as described above is mixed with phosphorus and copper in any of the above-described forms (1) to (5). (The second raw material) and the graphite powder are uniformly mixed to prepare a mixed powder. At this time, the mixed powder contains 0.15 to 1.95% by mass of phosphorus, 0.85 to 11.05% by mass of copper, and 0.20 to 1.00% by mass of carbon. Adjust the mixing ratio. The obtained mixed powder can be used as a raw material powder for molding. When a combination of a plurality of powders (forms (1) to (4)) is used as the second raw material, the plurality of powders may be individually charged in the preparation of a mixed powder, or they may be uniformly mixed in advance. You may throw in after mixing.

{Circle around (2)} In the second embodiment, a raw material powder further containing a carbide-forming element so as to be 3.23% by mass or less of the whole composition is used. The carbide-forming element is selected from molybdenum, vanadium, tungsten, niobium, and titanium, and may be used alone or in combination of two or more. The carbide-forming element can be used in a state of being alloyed with the iron alloy as the first raw material. That is, in the second embodiment, an iron alloy powder containing nickel, chromium, silicon, and a carbide-forming element may be used as the first raw material. If the ratio of the carbide-forming element exceeds 3.23% by mass of the entire composition, the compressibility of the iron alloy powder decreases, and it becomes difficult to form the raw material powder to a desired green density. Therefore, the ratio of the carbide forming element is preferably not more than 3.23% by mass of the entire composition. Since the effect of the addition of the carbide-forming element becomes apparent at about 0.92% by mass, it is preferable to use it in the range of 0.92 to 3.23% by mass. However, this is an optional component, and can be used in the range of 0 to 3.23% by mass depending on the design of the alloy composition, particularly the composition ratio of chromium and carbon.

<Green density and sintered alloy density>
Pores between the powder particles in the green compact obtained by compression molding remain in the sintered alloy after sintering, and when the amount of the pores is large, the strength and wear resistance are reduced. However, in a sintered alloy used as a turbocharger component, a passivation film of chromium is formed on the surface of the sintered alloy and on the inner surface of the pores due to oxygen contained in the high-temperature exhaust gas, which results in abrasion resistance and corrosion resistance. Is improved. The passivation film of chromium is hard and firmly fixed to the surface of the sintered alloy, and has an effect of preventing the iron alloy base from adhering to the mating member. Therefore, when an appropriate amount of pores are dispersed in the sintered alloy, the pores covered with the passivation film of chromium have an effect of preventing plastic flow of the iron alloy matrix, and the wear resistance of the sintered alloy is improved. . In consideration of this point, the density of the sintered alloy is preferably about 6.80 to 7.40 Mg / m ³ , and when the density exceeds 7.40 Mg / m ³ , the passivation film has No effect is obtained and wear resistance is reduced. If it is less than 6.80 Mg / m ³ , the strength as a sintered alloy is reduced, and the wear resistance is reduced. Preferably may When it is 7.00 mg / ^{m 3} or more and 7.40Mg / ^{m 3} or less, it is more appropriate when there in sintered density of 7.20Mg / ^{m 3} or more and 7.40Mg / ^{m 3} or less.

<Molding and sintering>
In order to obtain a sintered alloy having the above density, the compression molding of the raw material powder is preferably performed so that the green compact has a density of about 6.00 to 6.80 Mg / m ³ . Since the sintering proceeds due to the generation of a liquid phase at a low temperature due to the use of the phosphorus alloy powder, sintering proceeds by heating a green compact having such a density to 1050 to 1160 ° C., and the density becomes 6. A sintered alloy of about 80 to 7.40 Mg / m ³ is obtained. By setting the heating temperature during sintering to the above temperature range, the growth of crystal grains in the iron alloy matrix is suppressed, and the average crystal grain size of the iron alloy matrix becomes about 10 to 50 μm. If the heating temperature is lower than 1050 ° C., sintering hardly proceeds, and if it exceeds 1160 ° C., it becomes easy to grow into coarse crystal grains having a grain size exceeding 50 μm in the iron alloy base after sintering. More preferably, the sintering temperature is 1100 ° C or higher and 1140 ° C or lower.

Generally, in the production of a sintered alloy having a high chromium content, a chromium-containing alloy powder from which a passivation film on the surface has been removed is used as a raw material so that sintering proceeds actively, and sintering is performed in a vacuum atmosphere or This is performed in a reduced pressure atmosphere. In this regard, in the present invention, the sintering proceeds satisfactorily at a relatively low temperature due to the generation of the liquid phase by the phosphorus alloy powder, so that the activity during sintering can be maintained in a non-oxidizing atmosphere, and Sintering is possible even in a pressure environment. Therefore, there is no need to adjust the pressure environment to vacuum or reduced pressure, and a turbocharger component can be manufactured at low cost in a non-oxidizing environment similar to that for manufacturing a general sintered component.

When a gas containing about 10% by volume or more of nitrogen is used as a sintering atmosphere, hard nitride (mainly chromium nitride) is formed on the surface of the sintered alloy and the inner surface of the pores, and the wear resistance of the sintered alloy is reduced. Is preferred because the Examples of the atmosphere gas containing nitrogen include a nitrogen gas, a mixed gas of nitrogen and hydrogen, an ammonia decomposition gas, a mixed gas obtained by mixing nitrogen with an ammonia decomposition gas, and a mixed gas obtained by mixing hydrogen with an ammonia decomposition gas. In this case, the amount of nitrogen introduced into the sintered alloy from the atmosphere is extremely small, and is substantially the same as the amount of unavoidable impurities contained in the sintered alloy.

As described above, a sintered alloy having a density of 6.8 to 7.4 Mg / m ³ is obtained, and the obtained sintered alloy has pores and carbide precipitate particles dispersed in an iron alloy matrix having an austenitic stainless steel composition. Presents an organized tissue structure. The austenite structure is hardened by the solid solution of copper, and the wear resistance and corrosion resistance of the iron alloy base are improved. The structure of the iron alloy matrix becomes fine crystal grains having an average crystal grain size of about 10 to 50 μm due to the low sintering temperature, and the corrosion resistance and oxidation resistance of the matrix are improved. Further, the size of the carbide particles is about 1 to 10 μm in size, and the carbide having a particle size exceeding 10 μm is less than 10% of the area occupied by carbide in the structure cross section. Since it is manufactured based on the composition ratio determined so that the amount of carbide precipitation is suppressed, the ratio of carbide particles occupying the metal structure cross section is 10 area% or less, and the machinability of the sintered alloy is improved. Moreover, even if the amount of carbide precipitation itself decreases, the carbide particles are finely dispersed, so that the adhesion wear of the matrix can be prevented, and the suppression of the crystal grain growth of the matrix by the pinning effect of the carbide is also effective. is there.

(Sample Nos. 1 to 39)
As an iron alloy powder, an alloy powder containing chromium, nickel, and silicon at the composition ratios shown in Table 1 (average particle diameter: 70 μm) was prepared. Further, as the copper-phosphorus alloy powder, a copper-phosphorus alloy powder having a phosphorus content shown in Table 1 (average particle diameter: 40 μm, containing copper and unavoidable impurities as the balance) was prepared. In addition, the median diameter based on the particle size distribution measurement was applied to the average particle diameter of the powder. These alloy powder and graphite powder (average particle diameter: 10 μm) were uniformly mixed at the mixing ratio shown in Table 1 to obtain a mixed powder having the overall composition shown in Table 2. This was used as a raw material powder for molding by the following operation.

The raw material powder was filled in a mold hole, and compression-molded at a pressure of 600 MPa using a punch, thereby forming two types of compacts, a columnar shape and a disc-like shape. The dimensions of the cylindrical green compact were: outer diameter: 10 mm, height: 10 mm, and the dimensions of the disc-shaped green compact were: outer diameter: 24 mm, height: 8 mm. For sample numbers 4, 9 to 39, the amount of the raw material powder at which the density of the green compact was 6.4 Mg / m ³ was calculated in advance, and for sample numbers 1 to 3, 5 to 8, the density of the green compact was calculated. The amount of the raw material powder having the value shown in Table 2 was calculated, and the amount of the raw material powder filled in the mold cavity was adjusted by weighing. The density of the obtained green compact was confirmed according to the Archimedes method.

The obtained two types of green compacts were heated to 1130 ° C. in a mixed gas atmosphere of hydrogen and nitrogen, sintered at the same temperature for 60 minutes, and then cooled to room temperature. At this time, the average cooling rate from the sintering temperature to 300 ° C. was 12 ° C./min. In this way, sintered bodies of sample numbers 1 to 39 were produced.

密度 Using the obtained sintered body as a sintered alloy sample, the density, the wear amount, the crystal grain size of the iron alloy base, and the thickness of the oxide film were measured by the following operations. Table 3 shows the measurement results.

<Density and wear of sintered alloy>
The density of the sintered alloy was measured using a cylindrical sintered alloy sample according to a method for testing the sintered density of a metal sintered material specified in Japanese Industrial Standards (JIS) Z2505.
The wear amount of the sintered alloy was measured as a wear amount in a roll-on-disc friction wear test using a disc-shaped sintered alloy sample. In the roll-on-disk friction and wear test, a sintered alloy sample was used as a disk material, and reciprocal sliding with respect to a mating member was performed at 700 ° C. for 15 minutes to measure the amount of wear of the disk material. As a mating member, a roll (outer diameter: 15 mm, length: 22 mm) obtained by subjecting JIS SUS316L equivalent material to chromizing treatment was used.

<Grit of iron alloy base>
Further, the columnar sintered alloy sample was cut, the cross section of the sample was mirror-polished, and the cross section was corroded with aqua regia (nitric acid: hydrochloric acid = 1: 3). The tissue at the base was observed at a magnification of × 2. At this time, using a WinROOF manufactured by Mitani Shoji Co., Ltd. as image analysis software, image analysis of the tissue cross section is performed to binarize the image, the area of the austenite matrix is measured, and the number of crystal grains in the matrix is determined. The average area of the crystal grains was calculated by the measurement. The average crystal grain size of the crystal grains was determined by converting this value to the area circle equivalent diameter.

<Thickness of oxide film>
A strip-shaped sintered alloy sample having a major axis of 20 mm, a minor axis of 10 mm, and a height of 3 mm was cut out from a cylindrical sintered body having an outer diameter of 24 mm and a length of 8 mm by machining. The sintered alloy sample was left in an atmosphere containing steam (temperature: 860 ° C., test atmosphere: 8% steam / air) for 100 hours, then collected and cut. The cross section was processed and the metal structure of the cross section was observed under a microscope. In this cross-sectional observation, the thickness of the oxide film was measured. In this measurement, three points are arbitrarily selected in the oxide film portion of the cross-sectional image, the thickness is measured, and the measured value is displayed as an average value.

焼結 The sintered alloys of sample numbers 1 to 8 have different chromium contents. In each sample, the crystal grains of the iron alloy matrix are small, and the growth of the crystal grains of the matrix is suitably suppressed. As the chromium content increases, the crystal grain size, the amount of wear, and the thickness of the oxide film tend to decrease. When the chromium content is 18.48% by mass or more of the whole composition, the size of the crystal grains becomes large. It becomes substantially constant, and the amount of wear also becomes substantially constant. Even if the chromium content exceeds 30% by mass, the wear amount does not increase. This is considered to be due to the fact that the amount of graphite added is small, so that the generation of chromium carbide and the particle growth are suppressed, and the amount of chromium in the matrix is maintained to prevent a decrease in the strength of the matrix, resulting in wear. Seems to be suppressed. However, when the chromium content exceeds 20% by mass, the thickness of the oxide film increases. This is considered to be because the compressibility of the iron alloy powder having an excessively high chromium content is reduced, so that the densities of the green compact and the sintered body are reduced, whereby oxidation from the surface is apt to proceed. From these results, the preferable chromium content for achieving both abrasion resistance and oxidation resistance can be considered to be in the range of 13.86% by mass or more and 27.72% by mass or less, and more preferably 16.88% by mass. % And 23.10% by mass or less, most preferably 18.48% by mass and 20.33% by mass or less.

焼結 The sintered alloys of Sample Nos. 4 and 9 to 15 have different nickel contents, and in each sample, the crystal grains of the iron alloy matrix are small, and the growth of the crystal grains of the matrix is suitably suppressed. The addition of nickel sharply reduces the thickness of the oxide film, indicating that nickel improves the oxidation resistance of the sintered alloy. The increase in the density of the sintered body is considered to be due to the large specific gravity of nickel. From the results in Table 3, it can be expected that even if the nickel content is 22.18% by mass (sample No. 15) or more, there is no inconvenience in the material properties. At a nickel content of 6.47% by mass or more, It is understood that a sintered alloy having wear resistance and oxidation resistance can be obtained. It can be said that a nickel content of 7.39% by mass or more is more preferable in terms of oxidation resistance.

焼結 The sintered alloys of sample numbers 4, 16 to 21 have different silicon contents. Since the thickness of the oxide film sharply decreases as the silicon content increases, it is understood that silicon is effective for improving the oxidation resistance. However, when the silicon content exceeds 2.77% by mass, the thickness of the oxide film rapidly increases. The reason for this is considered to be a decrease in the density of the sintered alloy due to a decrease in the compressibility of the raw material powder, and a decrease in the oxidation resistance due to the coarsening of the crystal grains. And it can be understood from the tendency seen in the crystal grain size of the iron alloy matrix. The density of the green compact and the sintered body decreases as the silicon content increases, which is considered to be due to the decrease in the compressibility of the iron alloy powder. Also, the crystal grain size of the iron alloy matrix increases as the silicon content increases. From these results, it is considered that the oxidation resistance is lowered due to insufficient density of the sintered body and coarsening of the crystal grains. Therefore, the silicon content is preferably 0.46% by mass or more and 2.77% by mass or less, and more preferably 0.74% by mass or more and 1.85% by mass or less.

焼結 The sintered alloys of sample numbers 4, 22 to 27 have different mixing ratios of the copper-phosphorus alloy powder, and accordingly, the contents of copper and phosphorus in the alloy composition change with the mixing ratio. It is understood that the addition of the copper-phosphorus alloy powder and the increase in the proportion thereof increase the density of the obtained sintered alloy, and promote the sintering of the matrix by the copper-phosphorus alloy powder. In addition, it is understood that the oxidation resistance is improved because the thickness of the oxide film is significantly reduced. Further, when the compounding ratio of the copper-phosphorus alloy powder exceeds 4% by mass, the wear amount is reduced, and the wear resistance is improved. However, when the compounding ratio of the copper-phosphorus alloy powder exceeds 13% by mass, the sintering density decreases, which is due to the excessive generation of the liquid phase during sintering. Therefore, in Sample No. 27, the measurement of the crystal grain size and the material properties were omitted. The results in Table 3 show that the sintered alloys of Sample Nos. 4 and 23 to 26 in which the mixing ratio of the copper-phosphorus alloy powder is 1.00 to 13.00% by mass have good wear resistance and oxidation resistance. is there. The copper content of these sintered alloys is 0.85 to 11.05% by mass, and the phosphorus content is 0.15 to 1.95%. Can be considered. More preferably, the copper content is 3.40% by mass or more and 8.50% by mass or less, and the phosphorus content is 0.60% by mass or more and 1.50% by mass or less. It is 40% by mass or more and 5.95% by mass or less, and a more appropriate phosphorus content is 0.60% by mass or more and 1.05% by mass or less.

焼結 The sintered alloys of sample numbers 4, 28 to 33 have different alloy compositions in the used copper-phosphorus alloy powder. In these samples, the copper content decreases as the phosphorus content increases, but in any of the samples, the copper content of the obtained sintered alloy is in the above-mentioned preferred range. It is considered that the density of the sintered body in Sample No. 28 was relatively low and the thickness of the oxide film was large, so that the phosphorus content was insufficient and the sintering promotion effect was small. Further, the decrease in the sintering density in Sample No. 33 is due to the excessive generation of the liquid phase during sintering. For this reason, the measurement of the crystal grain size and the material properties of sample No. 33 was omitted. From these results, the copper-phosphorus alloy powder used preferably has a phosphorus content of 5% by mass or more and 25% by mass or less, more preferably 10% by mass or more and 20% by mass or less.

The sintered alloys of sample numbers 4, 34 to 39 have different carbon contents, and the carbon content is designed to be as low as 0.10 to 1.50 mass% in order to enhance the machinability of the sintered alloy. Have been. In this range, when the carbon content decreases, the density of the sintered body decreases, and the crystal grain size of the iron alloy matrix tends to increase. However, even if the carbon content is reduced to 0.20% by mass, the wear amount and The thickness of the oxide film is kept low. That is, it is understood that the wear resistance and the oxidation resistance are maintained. In sample No. 39, it is considered that the oxidation resistance of the matrix decreased because the amount of chromium dissolved in the matrix during the formation of the iron-phosphorus-carbon eutectic liquid phase decreased. Therefore, the preferable carbon content is 0.20% by mass or more and 1.00% by mass or less, and more preferably 0.4% by mass or more and 0.80% by mass or less.

(Sample numbers 40 to 46)
In the sample No. 4 of Example 1, instead of the copper-phosphorus alloy powder, 3.00% by mass of an iron-phosphorus alloy powder (phosphorus content: 35.00% by mass, average particle size: 40 μm) and 0 to 13 A mixed powder as shown in Table 4 was prepared in the same manner except that 0.000% by mass of copper powder (average particle diameter: 30 μm) was blended. This was used as a raw material powder for molding, and was molded into disk-shaped and column-shaped green compacts as shown in Table 5 by the same operation as in Example 1 (density of the green compact: 6.4 Mg / m ³ ). These were sintered under the same conditions as in Example 1 to produce a sintered alloy sample, and the density, the wear amount, the crystal grain size of the iron alloy base, and the thickness of the oxide film were measured. Table 6 shows the results.

In sample No. 43 of Table 6, the density of the sintered alloy was 7.1 Mg / m ³ , the average crystal grain size of the iron alloy matrix was 22 μm, the wear amount was 23 μm, and the thickness of the oxide film was 6 μm. Was. The overall composition of Sample No. 43 is almost the same as that of Sample No. 4, and when these samples are compared, it is understood that the properties of the sintered alloy are also the same. Accordingly, it can be seen that a sintered alloy having the same wear resistance and oxidation resistance can be obtained even when the iron-phosphorus alloy powder and the copper powder are used in combination instead of the copper-phosphorus alloy powder.

In Table 6, there is a tendency that the crystal grain size, the amount of wear, and the thickness of the oxide film of the alloy matrix tend to decrease as the composition ratio of copper increases. This is considered to be due to the fact that the solid solution of copper in the matrix protects the passivation film on the surface layer and improves oxidation resistance. However, when the proportion of copper further increases, the crystal grain size of the matrix, the amount of wear and the thickness of the oxide film all begin to increase, so that the proportion of copper is in the range of 0.85 to 11.05% by mass. It is good to set.

において In sample numbers 40 to 46, the density of the sintered alloy decreases as the composition ratio of copper increases. Such a tendency is not observed in Sample Nos. 22 to 25 using the copper-phosphorus alloy powder, and is considered to be related to the balance between the generation of the liquid phase and the progress of sintering. In this regard, the use of copper-phosphorus alloy powder is considered to be more preferable than the combined use of iron-phosphorus alloy powder and copper powder.

(Sample numbers 47 to 52)
A mixed powder similar to that of Sample No. 4 of Example 1 was prepared. This was used as a raw material powder for molding, and the same operation as in Example 1 was performed except that the amount of the raw material powder filled into the mold cavity was changed so that the green density of the green compact became the value shown in Table 7. Was repeated to form a disc-shaped and column-shaped green compact. These were sintered under the same conditions to produce a sintered alloy sample. The density of the sample, the amount of wear, the crystal grain size of the iron alloy matrix, and the thickness of the oxide film were measured. Table 7 shows the results.

(Sample numbers 53 to 58)
The same operation as in Sample No. 4 of Example 1 was repeated to prepare a mixed powder. This was used as a raw material powder for molding, and was molded into a disc-shaped and column-shaped green compact in the same manner as in Example 1. Using these, sintered alloy samples were produced under the same conditions as in Example 1 except that the sintering temperature was changed to the temperature shown in Table 7. The density of the sample, the amount of wear, the crystal grain size of the iron alloy matrix, and the thickness of the oxide film were measured. Table 7 shows the results.

From the results of sample numbers 4, 47 to 52, the sintered alloy obtained by sintering the green compact having a density of 6.00 to 6.80 Mg / m ³ has good wear resistance and oxidation resistance. I understand. When the density of the green compact is low, the oxidation resistance is reduced due to insufficient density of the sintered alloy. In sample 52, it was difficult to form a green compact, and a green compact having a density exceeding 6.80 Mg / m ³ was not obtained. The results in Table 7, the density of the sintered body, 6.90Mg / ^{m 3} or more and 7.40Mg / ^{m 3} or less are preferred, preferably 7.00 mg / ^{m 3} or more and 7.40Mg / ^{m 3} or less It is good to adjust so that it becomes. It is more appropriate that the sintered density is not less than 7.20 Mg / m ³ and not more than 7.40 Mg / m ³ .

から From the results of Sample Nos. 4, 53 to 58, it is understood that as the sintering temperature increases, the average crystal grain size of the iron alloy matrix increases, and the increase in the sintering temperature promotes the progress of sintering. A sintered alloy sintered at a temperature of 1050 ° C. or more and 1160 ° C. or less has excellent wear resistance and oxidation resistance. Sample No. 53 having a sintering temperature of less than 1050 ° C. has low wear resistance and oxidation resistance. This can be considered to be because the eutectic liquid phase was not sufficiently generated and the strength of the iron alloy matrix could not be obtained. In sample No. 58 having a sintering temperature of more than 1160 ° C., the liquid density was excessively generated during sintering, and the sintering density was reduced. Therefore, the measurement of the crystal grain size and the material properties were omitted. . A more preferred sintering temperature can be considered to be 1100 ° C or higher and 1140 ° C or lower.

(Sample numbers 59 to 65)
A mixed powder was prepared in the same manner except that the iron alloy powder in Sample No. 4 of Example 1 was changed to an iron alloy powder obtained by alloying molybdenum so as to have an overall composition shown in Table 8 (average particle diameter: 70 μm). Prepared. This was used as a raw material powder for molding, and the same operation as in Example 1 was repeated to form a disc-shaped and a column-shaped compact (molding pressure: 600 MPa). These were sintered under the same conditions as in Sample No. 4 to prepare a sintered alloy sample, and the density, wear amount, crystal grain size of the iron alloy matrix, and thickness of the oxide film were measured. Table 8 shows the results.

According to the results of Sample Nos. 4, 59 to 65, all of the samples exhibited stable wear resistance and excellent oxidation resistance. However, the densities of the green compact and the sintered body tend to decrease as the molybdenum content increases. This is considered to be due to the fact that the compressibility of the iron alloy powder is slightly reduced due to alloying of molybdenum. Therefore, it is preferable to add molybdenum, that is, a carbide-forming element in a range of 3.23% by mass or less. Can be More preferably, the molybdenum content is 0.46% by mass or more and 2.77% by mass or less.

In order to examine the machinability of the sintered alloys of Sample Nos. 4, 22 to 27, and 34 to 46, a turning tool made of cemented carbide was prepared, and a cylindrical sintered alloy sample was used as follows. Turning. That is, lathe processing (cutting speed: 50 m / min, cutting depth: 0.2 mm, feed speed: 0.05 mm / rotation) is performed on the end face of the sample from the outer peripheral side to the inner peripheral side with a cutting tool, and the total cutting distance is reduced. At the stage when the height reached 1000 m, the wear amount of the flank of the cutting tool (tool wear amount) was measured. The measured values are shown in Table 9 as a guide for evaluating the machinability.

れば According to the results of Sample Nos. 4, 22 to 27, and 40 to 46, it is understood that the addition of copper reduces the tool wear and improves machinability. When the copper content is 0.85% by mass or more, the machinability is good. However, when the addition amount of copper further increases, the wear amount of the tool starts to increase, and this is considered to be due to excessive hardening of the matrix due to solid solution of copper. In the results of Table 9, it can be considered that the machinability of the sintered alloy is improved when the content of copper is in the range of 0.85 to 11.05% by mass.

Also, according to the results of Sample Nos. 4, 34 to 39, there is a tendency that the tool wear amount tends to increase as the carbon content increases. In other words, it is clear that setting the blending amount of graphite lower than before is effective in improving machinability, and the carbon content of the sintered alloy is set so as to be 1.00% by mass or less. Thus, it is understood that the machinability can be improved and tool wear can be suppressed.

The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2018-131364 filed on Jul. 11, 2018, the entire disclosures of which are incorporated herein by reference.
It should be noted that various modifications and alterations may be made to the above-described embodiments without departing from the novel and advantageous features of the invention, other than those already described. Accordingly, all such modifications and changes are intended to be included within the scope of the appended claims.

A sintered alloy with excellent oxidation resistance, heat resistance and wear resistance and improved machinability is provided, so it can be applied to turbo parts for turbochargers, and it is highly corrosive at high temperatures such as nozzle bodies. The present invention can be advantageously applied to parts requiring durability against gas.

Claims

The overall composition is, in mass%, Cr: 13.86 to 27.72%, Ni: 6.47 to 20.33%, Cu: 0.85 to 11.05%, Si: 0.46 to 2.77. %, P: 0.15 to 1.95%, C: 0.20 to 1.00%, and the balance consisting of Fe and unavoidable elements and having a density of 6.8 to 7.4 Mg / m 3. Binding gold,
A sintered alloy, comprising: a metal structure having an iron alloy matrix in which pores are dispersed and a carbide dispersed in the iron alloy matrix, wherein the iron alloy matrix is composed of crystal grains having an average crystal grain size of 10 to 50 μm. .
The overall composition is, in mass%, Cr: 13.86 to 27.72%, Ni: 6.47 to 20.33%, Cu: 0.85 to 11.05%, Si: 0.46 to 2.77. %, P: 0.15 to 1.95%, C: 0.20 to 1.00%, carbide forming element: 3.23% or less, and the balance of Fe and unavoidable elements, and the density is 6.8. A sintered alloy of up to 7.4 Mg / m 3 ,
The carbide-forming element is at least one element selected from the group consisting of Mo, V, W, Nb, and Ti;
A sintered alloy, comprising: a metal structure having an iron alloy matrix in which pores are dispersed and a carbide dispersed in the iron alloy matrix, wherein the iron alloy matrix is composed of crystal grains having an average crystal grain size of 10 to 50 μm. .
The sintered alloy according to claim 1 or 2, wherein a nitride is formed on a surface of the sintered alloy and an inner surface of the pore.
In mass%, Cr: 15 to 30%, Ni: 7 to 24%, Si: 0.5 to 3.0%, and an iron alloy powder comprising the balance of Fe and unavoidable impurities is prepared.
The iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass, the copper-phosphorus alloy powder having a phosphorus content of 5 to 25% by mass, and one or more combinations selected from copper powders; Prepare compounding materials for phosphorus and copper compounding,
The iron alloy powder, the compounding material and the graphite powder are mixed to form 0.15 to 1.95% by mass of phosphorus, 0.85 to 11.05% by mass of copper, and 0.20 to 1.00% by mass. % Raw material powder containing carbon,
Compressing the raw material powder to form a green compact having a density of 6.0 to 6.8 Mg / m 3 ;
A method for producing a sintered alloy, wherein the green compact is heated to a temperature of 1050 to 1160 ° C. in a non-oxidizing atmosphere and sintered.
Fe: 15 to 30% by mass, Ni: 7 to 24%, Si: 0.5 to 3.0%, carbide-forming element: 3% by mass or less, and the balance of Fe and iron and inevitable impurities A powder, wherein the carbide-forming element is at least one element selected from the group consisting of Mo, V, W, Nb, and Ti;
The iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass, the copper-phosphorus alloy powder having a phosphorus content of 5 to 25% by mass, and one or more combinations selected from copper powders; Prepare compounding materials for phosphorus and copper compounding,
The iron alloy powder, the compounding material and the graphite powder are mixed to form 0.15 to 1.95% by mass of phosphorus, 0.85 to 11.05% by mass of copper, and 0.20 to 1.00% by mass. % Raw material powder containing carbon,
Compressing the raw material powder to form a green compact having a density of 6.0 to 6.8 Mg / m 3 ;
A method for producing a sintered alloy, wherein the green compact is heated to a temperature of 1050 to 1160 ° C. in a non-oxidizing atmosphere and sintered.
The compounding material is a powder containing phosphorus in one or both forms of iron-phosphorus alloy powder and copper-phosphorus alloy powder, and a powder containing copper in one or both forms of copper powder and copper-phosphorus alloy powder. The method for producing a sintered alloy according to claim 4.
The method for producing a sintered alloy according to any one of claims 4 to 6, wherein the compounding material is any of the following (1) to (5).
(1) Combination of an iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass and a copper powder (2) An iron-phosphorus alloy powder having a phosphorus content of 10 to 30% by mass and a phosphorus content of 5 to 30% Combination with 25 mass% copper-phosphorus alloy powder (3) Iron-phosphorus alloy powder having a phosphorus content of 10 to 30 mass%, copper-phosphorus alloy powder having a phosphorus content of 5 to 25 mass%, copper Combination with powder (4) Combination of copper-phosphorus alloy powder having a phosphorus content of 5 to 25% by mass and copper powder (5) Copper-phosphorus alloy powder having a phosphorus content of 5 to 25% by mass
The sinter bonding according to any one of claims 4 to 7, wherein the non-oxidizing atmosphere is a mixed gas of nitrogen and hydrogen containing 10% by mass or more of nitrogen, or a normal pressure atmosphere made of nitrogen gas. Gold manufacturing method.