BR102018006453A2 - method for producing a wear-resistant iron-based sintered alloy - Google Patents

Abstract

A wear-resistant iron-based sintered alloy made of a mixed powder is produced which includes the first hard particles, the second hard particles, the graphite particles and the iron particles. the first hard particles are fe-mo-ni-co-mn-si-c alloy particles. the second hard particles are fe-mo-si alloy particles. the blended powder includes the first 5 wt.% to 50 wt.% hard particles, the second 1 wt.% to 8 wt.% hard particles, and the 0.5 wt.% to 1.5 wt. Mass% when a total amount of the above particles is defined as 100% mass. In a sintering process, sintering is performed so that the hardness of the first hard particles becomes from 400 to 600 hv and the hardness of the second hard particles exceeds 600 hv. then an oxidation treatment is performed such that a density difference between before and after oxidation treatment in a sintered product becomes 0.05 g / cm3 or more.

Description

(54) Title: METHOD FOR THE PRODUCTION OF A WEAR RESISTANT IRON BASE SINTERIZED ALLOY (51) Int. Cl .: B22F 1/00; B22F 7/00; C22C 33/02; C22C 38/00; C22C 38/02; (...)

(30) Unionist Priority: 04/04/2017 JP 2017-074255.

(71) Depositor (s): TOYOTA JIDOSHA KABUSHIKI KAISHA; FINE SINTER CO., LTD ..

(72) Inventor (s): NOBUYUKI SHINOHARA; YUKI KAMO; YOSHIHISA UEDA; TAKANORI YONEDA; TAKESHI NAKAMURA.

(57) Abstract: A sintered wear-resistant iron-based alloy made of a mixed powder is produced that includes the first hard particles, the second hard particles, the graphite particles and the iron particles. The first hard particles are Fe-Mo-Ni-Co-Mn-Si-C alloy particles. The second hard particles are Fe-Mo-Si alloy particles. The mixed powder includes the first hard particles from 5% by mass to 50% by mass, the second hard particles from 1% by mass to 8% by mass, and graphite particles from 0.5% by mass to 1.5% % by mass when a total amount of the above particles is defined as 100% by mass. In a sintering process, sintering is performed so that the hardness of the first hard particles becomes 400 to 600 Hv and the hardness of the second hard particles exceeds 600 Hv. Then, an oxidation treatment is performed so that a difference in density between the before and after oxidation treatment in a sintered product becomes 0.05 g / cm3 or more.

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Descriptive Report of the Patent of Invention for METHOD FOR THE PRODUCTION OF A SINTERIZED ALLOY BASED ON WEAR RESISTANT IRON.

Background of the Invention

1. Field of the invention [001] The present invention relates to a method of producing a wear-resistant sintered iron-based alloy, including hard particles suitable for improving the wear resistance of a sintered alloy.

2. Description of Related Art [002] An iron-based sintered alloy can be applied to a valve seat and the like. Hard particles can be included in the sintered alloy in order to further improve wear resistance. When hard particles are included, graphite particles and iron particles are mixed into hard particles to form a powder, and the mixed powder is compactly molded into a product molded to a sintered alloy. Then, in general, the molded product for a sintered alloy is heated and, in this way, it is sintered and becomes a sintered alloy.

[003] As a method to produce such a sintered alloy, a method of producing a wear-resistant iron-based sintered alloy, in which a mixed powder in which hard particles, graphite particles and iron particles are blended is compactly molded into a molded product for a sintered alloy, and the molded product for a sintered alloy is sintered while the C of the graphite particles of the molded product for a sintered alloy diffuses into the hard particles and the iron particles have been proposals (for example, referenced in Japanese Unexamined Patent Application Publication No. 2004-156101 (JP 200 4-156101 A).

[004] Here, rigid particles include Mo: 20% by mass at

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70% by mass, C: 0.2% by mass at 3% by mass, and Mn: 1% by mass at 15% by mass, with the balance including unavoidable impurities and Co. The mixed powder includes the hard particles at 10 % by mass to 60% by mass and graphite particles to 0.2% by mass to 2% by mass when the total amount of hard particles, graphite particles and iron particles are defined as 100% by mass. Since the hard particles are dispersed in such a sintered alloy, abrasive wear can be avoided.

SUMMARY OF THE INVENTION [005] However, a matrix material that connects the hard particles of a wear-resistant iron-based sintered alloy produced in the production method described in JP 2004156101 A is soft because it is a Fe-C material where the C of the graphite particles diffused into the iron particles. Therefore, when the wear-resistant iron-based sintered alloy and a metallic material of a sliding counterpart component that comes into contact with them are in metal contact with each other, it is likely that a contact surface of the sintered alloy based on wear-resistant iron is plastically deformed and adhesive wear easily occurs on the contact surface. In order to avoid such problems, it is desirable to increase the hardness of the wear-resistant iron-based sintered alloy. However, there is a risk that the machinability of wear-resistant sintered iron alloys deteriorates accordingly and it is difficult to obtain adhesive wear resistance and machinability.

[006] The present invention provides a method of producing a sintered, wear-resistant iron-based alloy through which it is possible to ensure machinability while preventing adhesive wear.

[007] The inventors expected that the adhesive wear of a

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3/36 the contact surface would accelerate when the iron matrix of a wear-resistant sintered iron base was plastically deformed as described above. In this regard, the inventors have studied the addition of other hard particles through which it is possible to avoid plastic deformation of an iron matrix in addition to the hard particles through which abrasive wear has so far been prevented. For this reason, the inventors focused on molybdenum as the main component of hard particles and found that when an iron-molybdenum intermetallic compound and a molybdenum carbide precipitated during sintering are interspersed in an iron matrix, it is possible to control the plastic deformation of the iron matrix. In addition, the inventors have acquired a new discovery that by oxidizing a part of the iron in the iron matrix derived from the iron particles to triferro tetroxide, it is possible to improve its wear resistance without deteriorating the machinability of the sintered alloy.

[008] One aspect of the present invention relates to a method of producing a wear-resistant sintered iron-based alloy, which includes a molding process in which a mixed powder including hard particles, graphite particles and iron particles it is compactly molded into a molded product for a sintered alloy; and a sintering process in which the molded product for the sintered alloy is sintered while the C of the graphite particles of the molded product for the sintered alloy diffuses into the hard particles and the iron particles, where the hard particles include the first particles hard and the second hard particles, where the first hard particles include Mo: 20% by mass to 70% by mass, Ni: 5% by mass to 40% by mass, Co: 5% by mass to 40% by mass, Mn: 1 wt% to 20 wt%, Si: 0.5 wt% to 4.0 wt%, and C: 0.5 wt% to 3.0 wt%,

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4/36 with the balance including Fe and unavoidable impurities when an amount of the first hard particles is defined as 100% by mass, where the second hard particles include Mo: 60% by mass to 70% by mass, and Si: 2, 0% by mass or less, with the balance including Fe and unavoidable impurities when an amount of the second hard particles is defined as 100% by mass, where the mixed powder includes the first hard particles at 5% by mass at 50% by mass , the second hard particles at 1 mass% to 5% by mass and the graphite particles at 0.5% by mass at 1.5% by mass when a total quantity of the first hard particles, the second hard particles, the particles of graphite and iron particles are defined as 100% by mass, and where, in the sintering process, sintering is performed so that the hardness of the first hard particles becomes 400 to 600 Hv and the hardness of the second particles exceeds 600 Hv, after the sintering process, it is carried out an oxidation treatment over a sintered product, sintered from the molded product to the sintered alloy, so that a part of the iron contained in an iron matrix derived from the iron particles becomes triferro tetroxide, and the oxidation treatment is performed so that a difference between a density of the sintered product before the oxidation treatment and a density of the sintered product after the oxidation treatment becomes 0.05 g / cm3 or more.

[009] According to the present invention, it is possible to ensure machinability while avoiding adhesive wear.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] The characteristics, advantages and technical and industrial significance of the exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which similar numbers indicate similar elements, and in which:

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5/36 [0011] FIG. 1 is a schematic conceptual view of a wear test used in examples and comparative examples;

[0012] FIG. 2 is a conceptual schematic view of a machinability test used in examples and comparative examples;

[0013] FIG. 3A is a graph showing the results of the proportions of the amount of wear from the wear test in relation to the quantities of the first hard particles added in Examples 1 to 3 and in Comparative Examples 1 and 9;

[0014] FIG. 3B is a graph showing the results of the proportions of the amount of tool wear in relation to the quantities of the first hard particles added in Examples 1 to 3 and Comparative Examples 1 and 9;

[0015] FIG. 4A is a graph showing the results of the proportions of the amount of wear from the wear test in relation to the amounts of the second hard particles added in Examples 1.4 and 5 and in Comparative Examples 3, 4 and 9;

[0016] FIG. 4B is a graph showing the results of the proportions of the amount of tool wear to the amounts of the second hard particles added in the Examples

1.4 and 5 and in Comparative Examples 3, 4 and 9;

[0017] FIG. 5A is a graph showing the results of the proportions of the amount of wear from the wear test in relation to the amounts of graphite particles added in Examples 1, 6 and 7 and in Comparative Examples 5, 6 and 9;

[0018] FIG. 5B is a graph showing the results of the proportions of the amount of wear of the tool in relation to the quantities of the graphite particles added in Examples 1, 6 and 7 and in Comparative Examples 5, 6 and 9;

[0019] FIG. 6A is a graph showing the results of the proportions of the amount of wear from the wear test in relation to the

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6/36 hardness of the first hard particles in Examples 1, 3, 5 and 8 and in Comparative Examples 8 and 9;

[0020] FIG. 6B is a graph showing the results of the proportions of the amount of tool wear in relation to the hardness of the first hard particles in Examples 1, 3, 5 and 8 and in Comparative Examples 8 and 9;

[0021] FIG. 7A is a graph showing the results of the proportions of the amount of wear from the wear test in relation to the density difference in the sintered products in Examples 1 to 8 and in Comparative Examples 7 and 9;

[0022] FIG. 7B is a graph showing the results of the proportions of the amount of tool wear in relation to the difference in density in the sintered products in Examples 1 to 8 and in Comparative Examples 7 and 9;

[0023] FIG. 8A is an image of a test piece surface according to Example 1 after a wear test;

[0024] FIG. 8B is an image of a test piece surface according to Comparative Example 7 after a wear test;

[0025] FIG. 9A is an image of a test piece structure according to Example 1;

[0026] FIG. 9B is an image of a test piece structure according to Comparative Example 5;

[0027] FIG. 9C is an image of a test piece structure according to Comparative Example 6;

[0028] FIG. 10A is a graph showing the results of the proportions of the amount of wear from the wear test in Examples 1 and 9 and in Comparative Example 10; and [0029] FIG. 10B is a graph showing the results of the proportions of the amount of tool wear in Examples 1 and 9

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7/36 and Comparative Example 10.

DETAILED DESCRIPTION OF THE MODALITIES [0030] One embodiment of the present invention will be described in detail below. A molded product for a sintered alloy (hereinafter referred to as a molded product) according to the present embodiment is obtained by compactly molding a mixed powder which includes first and second hard particles, graphite particles and iron particles to be described below. A wear-resistant iron-based sintered alloy (hereinafter referred to as a sintered alloy) is obtained by sintering the molded product while the C of the graphite particles diffuses into the hard particles and the iron particles. The hard particles, the molded product obtained by compactly molding a mixed powder into which the hard particles are mixed, and the sintered alloy obtained by sintering the molded product will be described below.

[0031] 1. First hard particles [0032] The first hard particles are particles that are mixed as raw material in the sintered alloy and have high hardness in relation to the iron particles and an iron matrix of the sintered alloy and, in this way prevent the abrasive wear of the sintered alloy.

[0033] The first hard particles are particles made of an alloy of Co-Mo-Ni-Fe-Mn-Si-C. Specifically, the first hard particles include Mo: 20 wt% to 70 wt%, Ni: 5 wt% to 40 wt%, Co: 5 wt% to 40 wt%, Mn: 1 wt% to 20% by mass, Si: 0.5% by mass at 4.0% by mass, and C: 0.5% by mass at 3.0% by mass, with the balance including Fe and unavoidable impurities when the quantity of first hard particles is defined as 100% by mass. In addition, Cr can be added to the first hard particles in a range of 10% by mass or less as needed. The hardness of the first hard particles an

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8/36 days of sintering is preferably between 400 and 600 Hv.

[0034] The first hard particles can be produced by preparing molten metal in which the above composition is mixed together in the above proportions and performing an atomization treatment in which the molten metal is atomized. In addition, as another method, a solidified body in which the molten metal has solidified can be transformed into a powder by mechanical grinding. Like the atomization treatment, a gas atomization treatment or a water atomization treatment can be carried out. However, in view of sinterability and the like, a gas atomization treatment is more preferable because round particles are obtained.

[0035] Here, the lower limit values and upper limit values of the hard particle composition above can be appropriately changed according to the degree of importance of the characteristics of the application components in consideration of the limitation reasons to be described below and hardness, solid lubrication, adhesiveness and cost at such intervals.

[0036] 1-1. Mo: 20% by mass to 70% by mass [0037] In the composition of the first hard particles, Mo can generate Mo carbide together with C of a carbon powder during sintering and improve hardness and wear resistance of the first hard particles. In addition, in relation to Mo, since under a high temperature environment, Mo in a solid solution state and Mo carbide are oxidized to form a Mo oxide film, it is possible to obtain solid lubrication favorable for a sintered alloy.

[0038] Here, when a Mo content is less than 20% by mass, not only does the amount of Mo carbide generated be reduced, but it also increases the oxidation initiation temperature of the first hard particles, and the generation of oxide of Mo under an environment of

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9/36 use of high temperature is prevented. In this way, the solid lubrication of the obtained sintered alloy is insufficient and the abrasive wear resistance of it decreases. On the other hand, when a Mo content exceeds 70% by mass, it is not only difficult to produce the first hard particles using an atomization method, but also the adhesiveness between the hard particles and the iron matrix decreases. More preferably, a Mo content is from 30% by weight to 50% by weight.

[0039] 1-2. Ni: 5% by mass to 40% by mass [0040] In the composition of the first hard particles, Ni can expand an austenitic structure of the matrix of the first hard particles and improve their resistance. In addition, Ni can increase an amount of Mo in a solid solution state of the first hard particles and improve the wear resistance of the first hard particles.

[0041] In addition, the Ni that diffuses in the iron matrix of the sintered alloy during sintering, can enlarge the austenitic structure of the iron matrix, increase the strength of the sintered alloy, increase an amount of Mo in a state of solid solution in the iron matrix, and improve wear resistance.

[0042] Here, when a Ni content is less than 5% by mass, the previous effects of Ni are expected to be unlikely. On the other hand, when a Ni content exceeds 40% by mass, although the aforementioned effects of Ni are maximized, the cost of the first hard particles increases. More preferably, a Ni content is 20 wt% to 40 wt%.

[0043] 1-3. Co: 5 wt% to 40 wt% [0044] In the composition of the first hard particles, similar to Ni, Co can enlarge the austenitic structure in the matrix of the first hard particles and the iron matrix of the sintered alloy and

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10/36 improve the hardness of the first hard particles.

[0045] Here, when a Co content is less than 5% by mass, the above mentioned effects of Ni are expected to be unlikely. On the other hand, when a Co content exceeds 40% by mass, although the aforementioned effects of Co are maximized, the cost of the first hard particles increases. Most preferably, a Co content is 10 wt% to 30 wt%.

[0046] 1-4. Mn: 1% by mass to 20% by mass [0047] In the composition of the first hard particles, since Mn diffuses efficiently from the first hard particles to the iron matrix of the sintered alloy during sintering, it is possible to improve the adhesiveness between the first hard particles and the iron matrix. In addition, Mn can expand the austenitic structure in the matrix of the first hard particles and in the iron matrix of the sintered alloy.

[0048] Here, when an Mn content is less than 1% by mass, since the amount of Mn that diffuses in the iron matrix is small, the adhesion between the hard particles and the iron matrix decreases. In this way, the mechanical strength of the obtained sintered alloy decreases. On the other hand, when an Mn content exceeds 20% by mass, the effects above Mn are maximized. Most preferably, an Mn content is 2 wt% to 8 wt%.

[0049] 1-5. Si: 0.5 mass% to 4.0 mass% [0050] In the composition of the first hard particles, Si can improve the adhesion between the first hard particles and a Mo oxide film. Here, when a Si content is less than 0.5% by mass, the previous effects of Si are expected to be unlikely. On the other hand, when a Si content exceeds 4.0% by mass, the moldability of the molded product deteriorates and the density of the sintered alloy decreases. More preferably, a Si content is 0.5% in

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11/36 mass at 2% by mass.

[0051] 1-6. C: 0.5 wt% to 3.0 wt% [0052] In the composition of the first hard particles, C combines with Mo to form a Mo carbide and can improve the hardness and wear resistance of the first hard particles . Here, when a C content is less than 0.5% by mass, the wear resistance effect is not sufficient. On the other hand, when a C content exceeds 3.0% by mass, the moldability of the molded product deteriorates and the density of the sintered alloy decreases. Most preferably, a C content is 0.5% by mass to 2% by mass.

[0053] 1-7. Cr: 10% by mass [0054] From this point on, in the composition of the first hard particles, Cr can prevent excessive oxidation of Mo during use. For example, the addition of Cr is effective when the temperature of the sintered alloy usage environment is high, an amount of the Mo oxide film generated in the first hard particles increases, and the Mo oxide film disappears from the first hard particles.

[0055] Here, when a Cr content exceeds 10% by mass, the formation of the Mo oxide film in the first hard particles is too much prevented. Here, under a corrosive environment, such as an alcohol fuel environment, in order to improve corrosion resistance, it is desirable to add Cr. On the other hand, under an environment where adhesive wear is likely to occur, in order to accelerate oxidation, it is desirable to reduce the Cr content.

[0056] 1-8. Particle size of the first hard particles [0057] The particle size of the first hard particles can be appropriately selected according to an application, a type, and the like of the sintered alloy. However, the particle size of the first hard particles is preferably between 44 pm to 250 pm, and more preferably in a range from 44 pm to 105 pm

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12/36 pm.

[0058] Here, when hard particles with a particle size less than 44 pm are included as the first hard particles, since the particle size is very small, the wear resistance of the wear-resistant sintered iron-based alloy may decrease. On the other hand, when hard particles with a particle size greater than 250 pm are included as the first hard particles, since the particle size is very large, the machinability of the wear-resistant sintered iron-based alloy can be deteriorate.

[0059] 2. Second hard particles [0060] Similar to the first hard particles, the second hard particles are particles that are mixed as raw material in the sintered alloy and have high hardness in relation to the iron particles and a matrix of sintered alloy iron. Second hard particles are particles that significantly increase the hardness of the sintered alloy when added in a small amount, prevent plastic deformation of the iron matrix of the sintered alloy and, as a result, decrease the adhesive wear of the sintered alloy.

[0061] The second hard particles are particles made from an Fe-Mo alloy, and include Mo: 60% by mass to 70% by mass, and Si: 2.0% by mass or less, with the balance including Fe and unavoidable impurities when the quantity of the second hard particles is defined as 100% by mass. The hardness of the second hard particles before sintering is preferably in the range of 600 to 1600 Hv.

[0062] A solidified body in which the molten metal has solidified is transformed into a powder by means of mechanical grinding to produce the second hard particles. Furthermore, like the first hard particles, the second hard particles can be produced through

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13/36 through a gas atomization treatment, a water atomization treatment or the like.

[0063] 2-1. Mo: 60% by mass to 70% by mass [0064] In the composition of the second hard particles, Mo can generate a carbide of Mo together with C of a carbon powder during sintering and improve hardness and wear resistance of the second hard particles. In addition, in relation to Mo, since under a high temperature environment, Mo in a solid solution state and Mo carbide are oxidized to form a Mo oxide film, it is possible to obtain solid lubrication favorable for a sintered alloy. In addition, when molybdenum carbide precipitates on a grain boundary of the iron matrix during sintering, it is possible to avoid plastic deformation of the iron matrix and adhesive wear during use.

[0065] Here, when a Mo content is less than 60% by weight, it is difficult to avoid plastic deformation of the iron matrix according to the molybdenum carbide described above and the resistance to adhesive wear decreases. On the other hand, when a Mo content exceeds 70% by mass, it is difficult to produce second hard particles using a grinding method, and its yield decreases. [0066] 2-2. Si: 2.0% by mass or less [0067] When Si is contained in the composition of the second hard particles, it is easy to produce the second hard particles using a grinding method. Here, when a Si content exceeds 2.0% by mass, the hardness of the second hard particles increases, the moldability of the molded product deteriorates, the density of the sintered alloy decreases and also the machinability of the sintered alloy deteriorates.

[0068] 2-3. Particle size of the second hard particles [0069] The particle size of the second hard particles poPetition 870180025516, from 29/03/2018, p. 103/141

14/36 to be appropriately selected according to an application, a type and the like of the sintered alloy. However, the particle size (maximum particle size) of the second hard particles is preferably in the range of 100 pm or less, and more preferably, 75 pm or less. In this way, the second hard particles can be uniformly dispersed in the matrix and it is possible to increase the hardness of the sintered alloy. Here, when hard particles with a particle size greater than 100 pm are included as the second hard particles, since the particle size is very large, the machinability of the sintered alloy can deteriorate. Here, the particle size of the second hard particles is preferably 1 pm or more in consideration of production. [0070] 3. Graphite particles [0071] Graphite particles can be either natural graphite particles, or artificial graphite particles or a mixture of them, as long as the C of the graphite particles can diffuse in the iron matrix and hard particles in a solid solution state during sintering. The particle size of the graphite particles is preferably in the range of 1 pm to 45 pm. As a powder that includes preferred graphite particles, a graphite powder (CPB-S commercially available from the Nippon Kokuen Group) can be exemplified.

[0072] 4. Iron particles [0073] The iron particles that serve as the matrix of the sintered alloy are iron particles that contain Fe as the main component. As a powder, which includes iron particles, a pure iron powder is preferable. However, a low-alloy steel powder can be used as long as the moldability during compact molding does not deteriorate and the diffusion of elements such as the Mn of the first hard particles above does not decrease. Like a low-alloy steel powder, a powder of

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15/36

Fe-C can be used. For example, a powder with a composition that includes C: 0.2% by mass to 5% by mass, the balance including unavoidable impurities and Fe when the amount of low alloy steel powder is defined as 100% by mass. In addition, such a powder can be a gas atomized powder, a water atomized powder or a reduced powder. The particle size of the iron particles is preferably in the range of 150 μm or less.

[0074] 5. Mixing ratio of the mixed powder [0075] A mixed powder that includes the first hard particles, the second hard particles, the graphite particles and the iron particles is prepared. The mixed powder includes the first hard particles from 5% by mass to 50% by mass, the second hard particles from 1% by mass to 5% by mass, and graphite particles from 0.5% by mass to 1.5% % by mass when the total amount of the first hard particles, the second hard particles, the graphite particles and the iron particles is defined as 100% by mass.

[0076] The mixed powder can include only the first hard particles, the second hard particles, the graphite particles and the iron particles, but they can include about several mass% of other particles, as long as the mechanical strength and strength wear of the sintered alloy obtained does not decrease. In this case, when the total amount of the first and second hard particles, graphite particles and iron particles is 95% by weight or more in relation to the mixed powder, sufficient effects can be expected. For example, at least one type of particles to improve machinability, selected from the group consisting of sulfides (for example, MnS), oxides (for example, CaCO3), fluorides (for example, CaF), nitrides (for example, BN ) and oxisulfides can be included in the mixed powder.

[0077] Since the first hard particles are included

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16/36 by 5% by weight to 50% by weight in relation to the total amount of the first hard particles, the second hard particles, graphite particles and iron particles, it is possible to improve both mechanical strength and wear resistance abrasive of the sintered alloy.

[0078] Here, when the first hard particles are included at less than 5% by weight in relation to the total quantity, as can be clearly understood from experiments carried out by the inventors to be described below, a sufficient effect of the abrasive wear resistance according to the first hard particles it cannot be displayed.

[0079] On the other hand, when the quantity of the first hard particles exceeds 50% by weight in relation to the total quantity, since the quantity of the first hard particles is very large, when the molded product is molded from the mixed powder, it is difficult to shape the molded product. In addition, since there is greater contact between the first hard particles and a part where the iron particles are sintered becomes less, the abrasive wear resistance of the sintered alloy decreases.

[0080] Since the second hard particles are included in 1% by mass to 5% by weight in relation to the total amount of the first hard particles, second hard particles, graphite particles and iron particles, as described above , it is possible to prevent plastic deformation of the iron matrix during use and reduce the adhesive wear of the sintered alloy.

[0081] Here, when the content of the second hard particles is less than 1% by weight in relation to the total amount, as can be clearly understood from experiments carried out by the inventors to be described below, the resistance to adhesive wear of the sintered alloy decreases. On the other hand, when a content of

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17/36 second hard particles exceed 5% by mass in relation to the total quantity, the machinability of the sintered alloy deteriorates.

[0082] Since graphite particles are included in 0.5% by mass to 1.5% by weight in relation to the total amount of the first hard particles, second hard particles, graphite particles and iron particles , after sintering, without melting the first and second hard particles, the C of the graphite particles can diffuse into a solid solution state in the first and second hard particles and, in addition, a perlite structure can be held in the matrix of iron. For this reason, it is possible to improve the mechanical strength and wear resistance of the sintered alloy.

[0083] Here, when a content of the graphite particles is less than 0.5% by weight in relation to the total amount, since the ferrite structure of the iron matrix is likely to increase, the strength of the alloy iron matrix itself sintered decreases. On the other hand, when the content of the graphite particles exceeds 1.5% by weight in relation to the total amount, a cementite structure precipitates and the machinability of the sintered alloy deteriorates.

[0084] 6. Production method of sintered alloy based on wear-resistant iron [0085] In this way, the mixed powder obtained is compactly molded into a product molded to a sintered alloy (molding process). In the product molded to a sintered alloy, the first hard particles, the second hard particles, the graphite particles and the iron particles are included in the same proportion as in the mixed powder.

[0086] While the C of the graphite particles of the molded product for a sintered alloy diffuses to the first and second hard particles and to the iron particles, the molded product to

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18/36 a sintered alloy that is compactly molded is sintered to produce a sintered product (sintering process). In this case, not only is there a greater diffusion of iron from the iron matrix (iron particles) in the first and second hard particles, but also the second hard particles do not contain carbon. For this reason, the carbon of the graphite particles diffuses easily into the second hard particles, the Mo carbide is generated at a grain boundary between the second hard particles, and the hardness of the sintered alloy can increase.

[0087] In the present modality, sintering is carried out by adjusting a sintering temperature and a sintering time in such a way that the hardness of the first hard particles becomes 400 to 600 Hv and the hardness of the second hard particles exceeds 600 Hv . Regarding the hardness of the first and second hard particles in the obtained sintered alloy, these hardnesses are values measured using a micro Vickers hardness tester with a measuring load of 0.1 kgf. When the hardness of the first hard particles is adjusted to be within this range, it is possible to guarantee wear resistance and machinability for the sintered alloy. Here, when the hardness of the first hard particles is less than 400 Hv, a difference in the hardness of the iron matrix in which the carbon is in a solid solution state is small, and the wear resistance of the sintered alloy decreases. On the other hand, when the hardness of the sintered alloy exceeds 600 Hv, the machinability of the sintered alloy may deteriorate.

[0088] In addition, when the hardness of the second hard particles is adjusted to be within this range, it is possible to improve the wear resistance of the soft iron matrix. Here, when the hardness of the second hard particles is less than 600 Hv, the wear resistance of the sintered alloy can decrease.

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19/36 [0089] The hardness of the first and second hard particles can be adjusted by properly defining the proportions of the components in the above content range, the content of the graphite particles, the sintering temperature and the sintering time. The sintering temperature can be from about 1050Ό to 1250Ό, and in particular, about 1100X3 to 1150X3. The sintering time at the above sintering temperature can be from 30 minutes to 120 minutes, and more preferably from 45 minutes to 90 minutes. The sintering atmosphere can be a non-oxidizing atmosphere such as an inert gas atmosphere. As a non-oxidizing atmosphere, a nitrogen gas atmosphere, an argon gas atmosphere, a vacuum atmosphere and the like can be used.

[0090] The matrix of the sintered iron-based alloy obtained by sintering preferably includes a structure containing perlite in order to ensure its hardness. The perlite-containing structure can be a perlite structure, a mixed perlite-austenitic structure, or a mixed perlite-ferrite structure. In order to guarantee wear resistance, low hardness ferrite is preferably contained in a small amount.

[0091] After the sintered product is prepared, an oxidation treatment is carried out on the sintered product, so that part of the iron contained in the iron matrix derived from the iron particles becomes a triferro tetroxide (Fe ₃ O ₄ ). The oxidation treatment is carried out in such a way that a difference in density between the before and after the oxidation treatment in the sintered product becomes 0.05 g / cm ³ or more. In the oxidation treatment, oxides are generated, which mainly include triferro tetroxide. For this reason, the mass of the sintered product after the oxidation treatment increases. For this reason, a difference in greater density indicates a greater amount of triferro tetroxide generated.

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20/36 [0092] When a difference in density between the before and after the oxidation treatment in the sintered product is adjusted to 0.05 g / cm ³ or more, it is possible to improve the wear resistance of the sintered alloy. Here, when a density difference between the before and after oxidation treatment in the sintered product is less than 0.05 g / cm ³ , since a proportion of triferro tetroxide in the sintered alloy is small, the adhesive wear is accelerated due to metal contact with a counterpart member. As a result, the wear resistance of the sintered alloy decreases.

[0093] In such an oxidation treatment, for example, under a water vapor atmosphere, the sintered product is heated under temperature conditions of 500Ό to 600Ό for 30 minutes to 90 minutes. For this reason, in the range above the difference in density, iron (Fe), which is a matrix of the sintered product, can be oxidized to triferro tetroxide (Fe ₃ O ₄ ).

[0094] 7. Application of wear-resistant iron-based sintered alloy [0095] The sintered alloy obtained in the above production method has greater mechanical strength and wear resistance under a high temperature usage environment than those in technology related. For example, it can be used properly for a valve system (for example, a valve seat and a valve guide) and a discharge valve for a turbocharger for an internal combustion engine in which a compressed natural gas or a liquefied petroleum gas is used as a fuel under a high temperature usage environment.

[0096] For example, when a valve seat of an exhaust valve of an internal combustion engine is made of a sintered alloy, even if a wear pattern in which the adhesive wear when the valve seat and the valve come into contact contact and

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21/36 the abrasive wear when the two slide, one over the other, are combined, the wear resistance of such a valve seat improves compared to the related technology. In particular, under a usage environment in which a compressed natural gas or a liquefied petroleum gas is used as a fuel, although it is unlikely that a Mo oxide film will form in such an environment, it is possible to reduce adhesive wear.

[0097] Examples in which the present invention is carried out in practice will be described below in conjunction with comparative examples. Example 1: ideal amount of first hard particles added [0098] An alloy sintered according to Example 1 was produced according to the following production method. Like the first hard particles, the hard particles (commercially available from Daido Steel Co., Ltd) produced from an alloy including Mo: 40% by mass, Ni: 30% by mass, Co: 20% by mass, Mn: 5% by mass, Si: 0.8% by mass and C: 1.2% by mass, with the balance including Fe and unavoidable impurities (ie Fe-40Mo-30Ni-20Co-5Mn-0.8Si1.2C ) using a gas atomization method. The first hard particles were classified in a range from 44 pm to 250 pm using a sieve according to the JIS Z8801 standard. Here, particle granularity in this specification is a value obtained by classification according to this method.

[0099] As the second hard particles, second hard particles (commercially available from Kinsay Matec Co., Ltd) produced from an Fe-65 alloy including Mo: 65% by mass, the balance including Fe and impurities inevitable with the use of a grinding method. The second hard particles were classified in a range of 75 pm or less.

[00100] Next, a graphite powder (CPB-S commercially available from the Nippon Kokuen Group) was prepared which includes

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22/36 graphite gouges and a reduced iron powder (JIP255M-90 commercially available from JFE Steel Corporation) that includes pure iron particles. The first hard particles above, the second hard particles and graphite particles in proportions of 40% by mass, 3% by mass and 1.1% by mass, respectively, with the remaining iron particles (specifically 55.9% in mass) were mixed together with the use of a type V mixer for 30 minutes. In this way, a mixed powder was obtained.

[00101] Then, using a molding matrix, the mixed powder obtained was compacted into a ring-shaped test piece with a pressurizing force of 588 MPa in order to form a molded product for a sintered alloy (compact molded product). The compact molded product was sintered in an inert atmosphere (nitrogen gas atmosphere) at 1120Ό for 60 minutes to obtain a sintered product. The sintered product was oxidized by heating under a water vapor atmosphere under heating conditions of 550Ό for 50 minutes. In this way, a sintered alloy test piece (valve seat) was formed according to Example 1.

Examples 2 and 3: ideal amount of first hard particles added [00102] In the same way as in Example 1, sintered alloy test pieces were prepared. Examples 2 and 3 were examples to evaluate an ideal amount of first hard particles added. Examples 2 and 3 differed from Example 1 in that, as shown in Table 1, the first hard particles were added in a proportion of 5% by weight and 50% by weight, respectively, with respect to all the mixed powder.

Examples 4 and 5: optimized amount of second hard particles added

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23/36 [00103] In the same way as in Example 1, sintered alloy test pieces were prepared. Examples 4 and 5 were examples to assess an ideal amount of second hard particles added. Examples 4 and 5 differed from Example 1 in that, as shown in Table 1, the second hard particles were added in a proportion of 1% by weight and 5% by weight, respectively, with respect to all the mixed powder.

Examples 6 and 7: ideal amount of graphite particles added [00104] In the same way as in Example 1, sintered alloy test pieces were prepared. Examples 6 and 7 were examples to evaluate an ideal amount of graphite particles added. Examples 6 and 7 differed from Example 2 in that, as shown in Table 1, the graphite particles were added in a proportion of 0.5% by weight and 1.5% by weight, respectively, with respect to all the mixed powder .

Example 8: hardness of the first hard particles [00105] As in Example 1, a sintered alloy test piece was prepared. Example 8 differed from Example 1 in that the sintering temperature was lower than in Example 1 and the hardness of the first hard particles of the sintered product after sintering was reduced (see Table 1, 545 Hv).

[00106] Comparative Examples 1 and 2: Comparative examples for the ideal amount of first hard particles added [00107] In the same way as in Example 1, sintered alloy test pieces were prepared. Comparative Examples 1 and 2 were comparative examples for evaluating an ideal amount of first hard particles added. Comparative Examples 1 and 2 differed from Example 1 in that, as shown in Table 1, the first hard particles were added in a proportion of 0%

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24/36 by weight (that is, not added) and 60% by weight, respectively, in relation to all the mixed powder. Here, in Comparative Example 2, it was not possible to mold a molded product from the mixed powder.

[00108] Comparative Examples 3 and 4: Comparative examples for the ideal amount of the second hard particles added [00109] In the same way as in Example 1, sintered alloy test pieces were prepared. Comparative Examples 3 and 4 were comparative examples to evaluate an ideal amount of second hard particles added. Comparative Examples 3 and 4 differed from Example 1 in that, as shown in Table 1, the second hard particles were added in a proportion of 0 wt% and 10 wt%, respectively, with respect to all the mixed powder. In addition, in Comparative Example 3, the graphite particles were added in a proportion of 0.8% by weight.

[00110] Comparative Examples 5 and 6: Comparative examples for the ideal amount of graphite particles added [00111] In the same way as in Example 1, sintered alloy test pieces were prepared. Comparative Examples 5 and 6 were comparative examples for evaluating an ideal amount of graphite particles added. Comparative Examples 5 and 6 differed from Example 1 in that, as shown in Table 1, the graphite particles were added in a proportion of 0.4% by weight and 1.6% by weight, respectively, in relation to the whole in the powder mixed.

[00112] Comparative Example 7: Comparative example for the density difference in the sintered product [00113] In the same way as in Example 1, a sintered alloy test piece was prepared. In Comparative Example 7, a molding pressure during compact molding was greater than in Example 1, and the density before the oxidation treatment was greater.

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For that reason, there were fewer pores within the sintered product, thus the generation of oxides was avoided and an increase in the density of the sintered product after the oxidation treatment was reduced (ie the density difference was reduced).

Comparative Example 8: Comparative example for the hardness of the first hard particles [00114] As in Example 1, sintered alloy test pieces were prepared. Comparative Example 8 differed from Example 1 in that the sintering temperature was higher than in Example 1 and the hardness of the first hard particles of the sintered product after sintering was greater (see Table 1, 650 Hv).

Comparative Example 9 [00115] As in Example 1, a sintered alloy test piece was prepared. Comparative Example 9 differed from Example 1 in that particles including a Co-40Mo-5Cr0.9C alloy corresponding to the hard particles described in JP 2004-156101A were used as the first hard particles, no second hard particles were added and no no oxidation treatment was performed on the sintered product after sintering.

Hardness test [00116] For sintered alloy test pieces according to Examples 1 to 8 and Comparative Examples 1 to 9, the hardness of the first hard particles and the second hard particles were measured using a Vickers micro hardness testing machine with a measuring load of 0.1 kgf. The results are shown in Table 1.

Density measurement test [00117] The masses of the sintered test pieces according to

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26/36 with Examples 1 to 8 and Comparative Examples 1 and 3 to 8 before and after the oxidation treatment were measured. The measured mass was divided by a volume calculated from the size of the test piece, and the densities of the test piece (sintered product) before and after the oxidation treatment were calculated. In addition, a density difference between the before and after the oxidation treatment on the test piece (sintered product) was calculated. The results are shown in Table 1.

Wear test [00118] Using a test machine in FIG. 1, a wear test was performed on the sintered alloy test pieces according to Examples 1 to 8 and Comparative Examples 1 and 3 to 9, and their wear resistances were evaluated. In this test, as shown in FIG. 1, a propane burner 10 was used as a heating source, and a sliding part between a ring-shaped valve seat 12 made of the sintered alloy prepared as above and a valve face 14 of a valve 13 was placed in a combustion atmosphere of propane gas. The valve face 14 was obtained through nitrocarbonization according to EV12 (SEA standard). The temperature of the valve seat 12 was controlled so that it was 250Ό, a load of 25 kgf was applied by a spring 16 when the valve seat 12 was brought into contact with the valve face 14, the valve seat 12 was placed in contact with the face of the valve 14 at 3250 times / min, and the wear test was carried out for 8 hours.

[00119] The total amount of a wear depth in the axial direction of the valve seat 12 and the valve face 14 after the wear test was measured as a wear test wear amount, and a value obtained by dividing the amount wear test wear by value in Comparative Example 9

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27/36 was calculated as a proportion of the amount of wear from the wear test. The results are shown in Table 1.

[00120] FIGS. 3A, 4A, 5A, 6A and 7A show plotted results of the corresponding proportions of the amount of wear from the wear test between Examples 1 to 8 and Comparative Examples 1 and 3 to 9 where the horizontal axis represents the amount of first hard particles added, the amount of second hard particles added, the amount of graphite particles added, the hardness of the first hard particles, and the difference in density in the sintered product in that order.

[00121] In addition, the surfaces of the test pieces after the wear test according to Example 1 and Comparative Example 7 after the wear test were observed under a microscope. The results are shown in Fig. 8A and FIG. 8B. FIG. 8A is an image of the test piece surface according to Example 1 after the wear test and FIG. 8B is an image of the test piece surface according to Comparative Example 7 after the wear test.

[00122] The test pieces of Example 1, Comparative Example 5 and Comparative Example 6 before the wear test were recorded using nital, and the structure of the sintered alloy was observed under a microscope. The results are shown in FIGs. 9A to FIG. 9C. FIG. 9A is an image of the test piece structure according to Example 1, FIG. 9B is an image of the test piece structure according to Comparative Example 5, and FIG. 9C is an image of the test piece structure according to Comparative Example 6.

Machinability test [00123] Using a test machine shown in FIG. 2, a machinability test was performed on the test parts

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28/36 of sintered alloy according to Examples 1 to 8 and Comparative Examples 1 and 3 to 9, and their machinability was evaluated. In this test, six test pieces 20 were prepared with an outer diameter of 30 mm, an inner diameter of 22 mm, and a total length of 9 mm for each of Examples 1 to 8 and Comparative Examples 1 and 3 to 9. Using an NC lathe, a test piece 20 rotated at a rotation speed of 970 rpm was cut in a wet type rotation using an aluminum cemented carbide tool and titanium nitride (tool 30) with a cutting depth of 0.3 mm, being fed at 0.08 mm / rev, and over a cutting distance of 320 m. Then, a maximum wear depth of a tool flank 30 was measured as an amount of tool wear using an optical microscope and a value obtained by dividing the amount of tool wear by the value in Comparative Example 9 was calculated as a proportion of the amount of tool wear. The results are shown in Table 1.

[00124] FIGS. 3B, 4B, 5B, 6B and 7B show plotted results of the corresponding proportions of the amount of tool wear between Examples 1 and 3 to 8 and Comparative Examples 1 to 9 where the horizontal axis represents the amount of first hard particles added, the amount of second hard particles added, the amount of graphite particles added, the hardness of the first hard particles, and the difference in density in the sintered product in that order.

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Proportion of the amount of tool wear 0.70 0.90 1.00 Wear test wear ratio sf o 0.13 1.00 Graphite particles Quantity added (% by mass) Oxidation treatment Density difference (g / cm ³ ) 0.04 0.16 After treatment Density (g / cm ³ ) 7.20 B- Before treatment Density (g / cm ³ ) 7.16 6.96 Second hard particles Quantity added (% of mas- sa) CO CO Toughness (Hv) 1100 066 none First hard particles Quantity added (% by mass) 40 40 40 Toughness (Hv) 540 650 880 Sample name tra Comparative Example 7 Comparative Example 8 Comparative Example 9

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Result 1: ideal amount of first hard particles added [00125] As shown in FIG. 3A, the proportions of the amount of wear from the wear test of Examples 1 to 3 were lower than in Comparative Examples 1 and 9. The proportions of the amount of wear from the wear test decreased in the order of Example 2, Example 1 and Example 3. Therefore, when the first hard particles were added, the abrasive wear resistance of the sintered alloy was assumed to be improved. However, in Comparative Example 2, it can be said that the moldability of the molded product has deteriorated because too many hard particles have been added. Based on the above, the ideal amount of first hard particles added was 5% by weight to 50% by weight in relation to the whole powder mixed.

[00126] Here, as shown in FIG. 3B, the proportions of the amount of tool wear in Examples 1 to 3 were lower than in Comparative Example 9. The proportion of amount of tool wear increased in the order of Example 2, Example 1 and Example 3. However, do you think It is noted that when more first hard particles were added than in Example 3, the machinability of the sintered alloy deteriorated and the proportion of tool wear amount increased.

Result 2: ideal amount of second hard particles added [00127] As shown in FIG. 4A, the proportions of the amount of wear from the wear test of Examples 1.4 and 5 and Comparative Example 4 were lower than in Comparative Examples 3 and

9. However, as shown in FIG. 4B, the proportion of the amount of tool wear in Comparative Example 4 was greater than in Examples 1, 4 and 5. Here, when the test piece surface

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32/36 after the wear test was observed, Comparative Example 3 presented more risks due to adhesive wear than the other examples.

[00128] Therefore, it is believed that the second hard particles improved the hardness of the sintered alloy after sintering, prevented the plastic deformation of the iron matrix of the sintered alloy during use, and reduced an adhesive wear of the sintered alloy. Specifically, it is thought that, since the second hard particles did not contain Ni, Co and the like, unlike the first hard particles, the iron matrix around the second hard particles managed to harden more than in the first hard particles, molybdenum carbide precipitated at the grain limit of the iron matrix during sintering, and in this way the hardness of the iron matrix after sintering was improved.

[00129] Based on the above, when the amount of second hard particles added was very small, the sintered alloy surface after the wear test was easily scraped. On the other hand, it is thought that, as in Comparative Example 4, when a quantity of second hard particles added was very large, the sintered alloy after sintering was very hard, and the machinability deteriorated. Based on the above result, the ideal amount of second hard particles added was from 1% by weight to 5% by weight in relation to the whole powder mixed.

Result 3: ideal amount of graphite particles added [00130] As shown in FIG. 5A, the proportions of the amount of wear from the wear test of Examples 1, 6 and 7 and Comparative Example 6 were lower than in Comparative Examples 5 and

9. However, as shown in FIG. 5B, the proportion of the amount of tool wear in Comparative Example 6 was greater than in Examples 1, 6 and 7.

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33/36 [00131] As shown in FIG. 9A, in the sintered alloy structure shown in Example 1, a perlite structure was formed. However, as shown in FIG. 9C, in the sintered alloy structure shown in Comparative Example 6, a cementite structure was formed due to an increased amount of graphite particles. As a result, the proportion of tool wear in Comparative Example 6 was thought to be greater than in Examples 1, 6 and 7.

[00132] On the other hand, it is thought that, as shown in FIG. 9B, in the sintered alloy structure shown in Comparative Example 5, since the structure had ferrite as a major part of it, the proportion of the amount of wear from the wear test in Comparative Example 5 was greater than in Examples 1, 6 and 7 and Comparative Example 6. For this reason, the ideal amount of graphite particles added in which it was possible to hold a perlite structure in the iron matrix after sintering was 0.5% by mass to 1.5% by weight. mass in relation to all the mixed powder.

Result 4: ideal hardness of the first hard particles [00133] As shown in FIG. 6A, the proportions of the amount of wear from the wear test of Examples 1, 3, 5 and 8 and Comparative Example 8 were smaller than in Comparative Example 9. However, as shown in FIG. 6B, the proportion of the amount of tool wear in Comparative Example 8 was greater than in Examples 1, 3, 5 and 8.

[00134] It is thought that, since the hardness of the first hard particles in Comparative Example 9 was greater than in Examples 1, 3, 5 and 8 and in Comparative Example 8, a counterpart component became more worn, and the proportion of the amount of wear from the wear test of Example 9 was greater than in the other examples. On the other hand, it is thought that, in Examples 1, 3, 5 and 8, since the

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34/36 hardness (Hv) of the first hard particles was less than in Comparative Example 8 and was 600 or less, the proportions of the amount of tool wear in Examples 1, 3, 5 and 8 were lower than in Comparative Example 8 Here, in Examples 1, 3, 5 and 8, it can be said that, since the first hard particles with a hardness of 400 Hv or more were guaranteed, the wear resistance was guaranteed.

[00135] Therefore, the hardness of the first hard particles after sintering is preferably in the range of 400 to 600 Hv. Here, in consideration of the second hard particles that improved the wear resistance of the iron matrix, in the condition of the amplitude above the added amount, it was necessary that the hardness of the second hard particles be greater than the hardness of the first hard particles and exceed by minus 600 Hv.

Result 5: ideal density difference in the sintered product [00136] As shown in FIG. 7A, the proportions of the amount of wear from the wear test of Examples 1 to 8 were less than in Comparative Examples 7 and 9. As shown in FIG. 7B, the proportion of the amount of tool wear in Comparative Example 9 was greater than in Examples 1 through 8 and Comparative Example 7.

[00137] In Comparative Example 7, since a difference in density between the before and after the oxidation treatment in the sintered product was less than 0.05 g / cm ³ , an amount of oxides that mainly includes triferro tetroxide in the sintered product it was less than in the sintered products of Examples 1 to 8. For that reason, metal contact with a counterpart component was promoted, and as shown in FIG. 8B, in the test piece (sintered product) of Comparative Example 7, and adhesive wear with a counterpart component is thought to have been accelerated. For another

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35/36 On the other hand, in Examples 1 to 8, the wear resistance of the sintered alloy was thought to be greater than in Comparative Example 7, since there was almost no adhesive wear (for example, see Example 1, Figure 8A). Therefore, it was necessary to carry out an oxidation treatment so that a difference in density between the before and after the oxidation treatment in the sintered product would become 0.05 g / cm ³ or more.

Example 9: ideal particle size of the second hard particles [00138] As in Example 1, a sintered alloy test piece was prepared. Example 9 was an example for evaluating an ideal particle size of the second hard particles. Example 9 differed from Example 1 in that, like the second hard particles, second hard particles classified to have a particle size (granularity) in a range greater than 75 pm and 100 pm or less were used.

Comparative Example 10: Comparative example for the ideal particle size of the second hard particles [00139] In the same way as in Example 1, a sintered alloy test piece was prepared. Comparative Example 10 is a comparative example for evaluating an ideal particle size of the second hard particles. Comparative Example 10 differed from Example 1 in that, like the second hard particles, the second hard particles classified to have a particle size in a range greater than 100 pm and 150 pm or less were used. Here, the test piece according to Comparative Example 10 was a sintered alloy included within the scope of the present invention and was defined as Comparative Example 10 for convenience in order to allow comparison with Examples 1 and 9.

[00140] In the same way as in Example 1, the wear test and the machining test were performed on the test pieces of Example

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36/36 and Comparative Example 10, and a wear test wear amount and a tool wear amount were measured. The results are shown in FIG. 10A and in FIG. 10B together with the results above from Example 1.

[00141] FIG. 10A is a graph showing the results of the proportions of the amount of wear from the wear test in Examples 1 and 9 and in Comparative Example 10 and FIG. 10B is a graph showing the results of the proportions of the amount of tool wear in Examples 1 and 9 and Comparative Example 10.

Result 6: ideal particle size of the second hard particles [00142] As shown in FIG. 10A, the proportions of the amount of wear from the wear test of Examples 1 and 9 and Comparative Example 10 were similar. However, as shown in FIG. 10B, the proportions of the amount of tool wear in Examples 1 and 9 were lower than in Comparative Example 10, and the proportion of amount of tool wear in Example 1 was the lowest among the examples. This is because, in Comparative Example 10, since the particle size of the second hard particles was very large, the machinability of the test piece (sintered product) deteriorated in some cases. Based on this result, the particle size (maximum particle size) of the second hard particles was preferably in a range of 100 μ m or less, and more preferably, the particle size (maximum particle size) of the second hard particles were in an interval of 75 pm or less.

[00143] Although the modalities of the present invention have been described in detail above, the present invention is not limited to these modalities, and various design modifications can be made.

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1/2

Claims (3)

1. Method of production of a sintered, wear-resistant iron-based alloy, comprising: a molding process in which a mixed powder including hard particles, graphite particles and iron particles is compactly molded into a molded product for a sintered alloy; and a sintering process in which the molded product for the sintered alloy is sintered while the C of the graphite particles of the molded product for the sintered alloy diffuses into the hard particles and iron particles, the production method of the base sintered alloy wear-resistant iron, characterized by the fact that the hard particles include the first hard particles and the second hard particles, where the first hard particles include Mo: 20% by weight to 70% by weight, Ni: 5% by weight at 40% by mass, Co: 5% by mass to 40% by mass, Mn: 1 by mass% to 20% by mass, Si: 0.5% by mass to 4.0% by mass, and C: 0, 5% by mass to 3.0% by mass, with the balance including Fe and unavoidable impurities when an amount of the first hard particles is defined as 100% by mass, where the second hard particles include Mo: 60% by mass at 70 % by mass, and Si: 2.0% by mass or less, with the balance including Fe and unavoidable impurities when a quantity of the second hard particles is defined as 100% by mass, where the mixed powder includes the first hard particles from 5% by mass to 50% by mass, the second hard particles from 1% by mass to 5% by mass, and graphite particles at 0.5 mass% to 1.5 mass% when a total amount of the first 870180025516, dated 29/03/2018, pg. 127/141 2/2 ras hard particles, second hard particles, graphite particles and iron particles are defined as 100% by mass, and where, in the sintering process, sintering is carried out so that the hardness of the first particles becomes 400 to 600 Hv and the hardness of the second hard particles exceeds 600 Hv, after the sintering process, an oxidation treatment is carried out with a sintered product, sintered from the product molded to the sintered alloy so that a part of the iron contained in an iron matrix derived from the iron particles becomes triferro tetroxide, and the oxidation treatment is carried out so that a difference between a density of the sintered product before the oxidation treatment and a density of the sintered product after the oxidation treatment becomes 0.05 g / cm ³ or more. Method according to claim 1, characterized in that 10% by mass or less of Cr is additionally added to the first hard particles when the amount of the first hard particles is defined as 100% by mass. Method according to claim 1 or 2, characterized in that the particle size of the second hard particles is in the range of 100 μm or less. Petition 870180025516, of 03/29/2018, p. 128/141 1/10