Iron-based sintered body and method for manufacturing an iron-based sintered body

Abstract

The present disclosure aims to provide an iron-based sintered body that has strength and elongation equivalent to existing iron-based sintered bodies (Fe-Cu-C system, sintering temperature 1120°C) while reducing energy consumption during sintering and other processes. [Solution] An iron-based sintered body according to one aspect of the present disclosure contains, as elements, Cu: 3.5% by mass or more and 6.5% by mass or less, P: 0.25% by mass or more and 0.56% by mass or less, and C: 0.3% by mass or more and 1.2% by mass or less, and the area ratio of undiffused Cu in the cross-section of the sintered body is 0.5% or more and 2.5% or less.

Description

Technical Field

[0001] The present disclosure relates to an iron-based sintered body and a method for manufacturing the iron-based sintered body.

Background Art

[0002] Today, the realization of carbon neutrality is desired. From this perspective, even in the manufacturing process of sintered bodies, reduction of energy consumption is required. On the other hand, sintered bodies are also required to have excellent mechanical properties such as strength and elongation.

[0003] In the manufacturing process of sintered bodies, the energy consumption during sintering is the largest and accounts for about 40% of the whole. Therefore, there is a demand for a technology capable of manufacturing a sintered body excellent in strength and elongation while reducing the energy consumption during sintering.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

[0006] Non-patent document 1 describes a method for producing an iron-based sintered body using a raw material powder containing 3.28% by mass of Cu-8.4%P powder, sintered at 1121°C. However, the method described in non-patent document 1 results in high energy consumption during sintering, which is contrary to carbon neutrality.

[0007] Furthermore, Non-Patent Document 2 describes a method for producing an iron-based sintered body by using a raw material powder containing Cu3P powder and sintering it at 970°C to 1120°C. However, Cu3P has a high melting point, resulting in high energy consumption during powder production. In addition, the method described in Non-Patent Document 2 makes it difficult to maintain sufficient elongation of the sintered body.

[0008] On the other hand, Patent Document 1 describes a method for producing an iron-based sintered body by compressing a raw material powder, which is mainly composed of partially diffused alloy powder with a copper content of 10 to 30% by mass, and further blended with tin powder and solid lubricant powder, to form a compact, and then sintering this compact at 820°C to 900°C. According to this method, the sintering temperature is low, so it is thought that energy consumption during sintering can be reduced. However, according to this method, it is difficult to produce a sintered body with sufficient strength.

[0009] This disclosure has been made in view of these circumstances and aims to provide an iron-based sintered body that has strength and elongation equivalent to existing iron-based sintered bodies (Fe-Cu-C system, sintering temperature 1120°C) while reducing energy consumption during sintering and other processes. [Means for solving the problem]

[0010] An iron-based sintered body according to one aspect of this disclosure contains, as elements, Cu: 3.5% by mass or more and 6.5% by mass or less, P: 0.25% by mass or more and 0.56% by mass or less, and C: 0.3% by mass or more and 1.2% by mass or less, and the area ratio of undiffused Cu in the cross-section of the sintered body is 0.5% or more and 2.5% or less. [Effects of the Invention]

[0011] An iron-based sintered body according to one aspect of this disclosure has strength and elongation equivalent to that of a current iron-based sintered body (Fe-Cu-C system, sintering temperature 1120°C), while reducing energy consumption during sintering and raw material powder production. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a flowchart illustrating a method for manufacturing an iron-based sintered body according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a graph showing the relationship between sintering temperature and compression ring strength for each sample in the examples. [Figure 3] Figure 3 is a graph showing the relationship between the surface hardness and compression strength of each sample sintered at a sintering temperature of 1050°C in the examples. [Figure 4] Figure 4 is a graph showing the relationship between compression ring strength and fracture strain for each sample sintered at a sintering temperature of 1050°C in the examples. [Modes for carrying out the invention]

[0013] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0014] (1) An iron-based sintered body according to one aspect of the present disclosure contains, as elements, Cu: 3.5% by mass or more and 6.5% by mass or less, P: 0.25% by mass or more and 0.56% by mass or less, and C: 0.3% by mass or more and 1.2% by mass or less, and the area ratio of undiffused Cu in the cross-section of the sintered body is 0.5% or more and 2.5% or less.

[0015] The iron-based sintered body can achieve high strength by including P and C within the above ranges. Furthermore, since the area ratio of undiffused Cu in the cross-section of the iron-based sintered body is 0.5% to 2.5%, it is considered to have good elongation. Moreover, because the area ratio of undiffused Cu in the cross-section of the iron-based sintered body is 0.5% to 2.5%, the sintering temperature can be lowered while maintaining elongation. Therefore, the iron-based sintered body can have strength and elongation equivalent to or better than the current iron-based sintered body (Fe-Cu-C system, sintering temperature 1120°C) while reducing energy consumption during sintering. Furthermore, since the iron-based sintered body does not require the use of Cu3P powder as described in Non-Patent Document 2, energy consumption during raw material powder production can be reduced.

[0016] (2) In (1) above, it is preferable that the content of P relative to the total content of Cu and P per 100 parts by mass be 7.0 parts by mass or more and 9.0 parts by mass or less. According to the inventors' findings, by using phosphorus-containing copper alloy powder having a phosphorus content of 7.0% by mass or more and 9.0% by mass or less, the content of Cu and P is controlled within the above range, and the area ratio of undiffused Cu in the cross-section of the iron-based sintered body is controlled to be 0.5% or more and 2.5% or less, both the strength and elongation of the iron-based sintered body can be increased. Therefore, the desired quality can be easily obtained in the iron-based sintered body if the content of P relative to the total content of Cu and P per 100 parts by mass is 7.0 parts by mass or more and 9.0 parts by mass or less. Furthermore, according to this embodiment, the energy consumption during sintering can be easily and reliably reduced, and the energy consumption during the production of raw material powder can be reduced more easily.

[0017] (3) A method for manufacturing an iron-based sintered body according to another aspect of the present disclosure includes a step of pressure-molding an iron-based raw material powder containing a phosphorus-containing copper alloy powder, and a step of sintering the molded body formed in the step of pressure-molding in an inert gas atmosphere or a reducing gas atmosphere. The iron-based raw material powder contains, as elements, Cu: 3.5% by mass or more and 6.5% by mass or less, P: 0.25% by mass or more and 0.56% by mass or less, and C: 0.3% by mass or more and 1.2% by mass or less, and the sintering temperature in the step of sintering is 850°C or more and 1050°C or less. Further, the method for manufacturing the iron-based sintered body may further include a step of mixing each raw material powder.

[0018] In the method for manufacturing the iron-based sintered body, since the iron-based raw material powder contains P and C within the above ranges, the strength of the obtained iron-based sintered body can be increased. Also, in the method for manufacturing the iron-based sintered body, since Cu is contained within the above range, good elongation can be maintained even when the sintering temperature in the step of sintering is 850°C or more and 1050°C or less. Therefore, the method for manufacturing the iron-based sintered body can reduce the energy consumption during sintering by lowering the sintering temperature while making the strength and elongation of the obtained iron-based sintered body equal to or higher than those of the current iron-based sintered body (Fe-Cu-C system, sintering temperature 1120°C). Furthermore, since the method for manufacturing the iron-based sintered body does not require the use of Cu3P powder as in Non-Patent Document 2, the energy consumption during the production of the raw material powder can be reduced.

[0019] (4) In the above (3), it is preferable that the phosphorus content in the phosphorus-containing copper alloy powder is 7.0% by mass or more and 9.0% by mass or less. According to this aspect, it is easy to obtain an iron-based sintered body of desired quality. Also, according to this aspect, the energy consumption during the production of the raw material powder and during sintering can be easily and surely reduced.

[0020] In this disclosure, "iron-based raw material powder" means a raw material powder (a mixture of raw material powders) that contains iron as the main component (the component with the largest mass content). The lower limit of the iron content in the iron-based raw material powder may be 50% by mass, 70% by mass, 85% by mass, or 90% by mass.

[0021] "The area ratio of undiffused Cu in the cross-section of a sintered body" refers to the area ratio of undiffused Cu obtained by binarizing an image observed with an optical microscope. For example, it refers to the value measured using the Python library OpenCV in the following procedure for an image of an arbitrary cross-section at an observation magnification of 100x: In the HSV color space (H: hue, S: saturation, V: lightness), the range of H: 15 to 25, S: 110 to 220, and V: 240 to 255 is treated as the undiffused Cu region, and 8 connected components are labeled. The area ratio is then calculated by excluding those with 100 pixels or less.

[0022] [Details of the embodiments of this disclosure] The embodiments of this disclosure will be described in detail below. Note that the numerical values ​​described herein can be arbitrarily combined with the upper and lower limits. In this specification, all possible numerical ranges from the upper to lower limits are described as suitable ranges.

[0023] <Iron-based sintered body> The iron-based sintered body contains, as elements, Cu: 3.5% to 6.5% by mass, P: 0.25% to 0.56% by mass, and C: 0.3% to 1.2% by mass. The area ratio of undiffused Cu in the cross-section of the iron-based sintered body is 0.5% to 2.5%.

[0024] The iron-based sintered body can achieve high strength by including P and C within the above ranges. Furthermore, since the area ratio of undiffused Cu in the cross-section of the iron-based sintered body is 0.5% to 2.5%, it is considered to have good elongation even at low sintering temperatures. Therefore, the iron-based sintered body can have strength and elongation equivalent to or better than the current iron-based sintered body (Fe-Cu-C system, sintering temperature 1120°C) while reducing energy consumption during sintering. Moreover, since the iron-based sintered body does not require the use of Cu3P powder as described in Non-Patent Document 2, energy consumption during raw material powder production can be reduced.

[0025] The iron-based sintered body is manufactured by a process of pressure molding an iron-based raw material powder containing phosphorus-containing copper alloy powder, as described below, and a process of sintering the molded body formed by pressure molding. The iron-based raw material powder includes, for example, iron powder, the phosphorus-containing copper alloy powder, and a carbon material. Additives such as lubricants may also be added to the iron-based raw material powder.

[0026] Examples of the iron powder mentioned above include pure iron powder such as atomized iron powder and reduced iron powder. Examples of the phosphorus-containing copper alloy powder mentioned above include those with a phosphorus content of 7.0% by mass or more and 9.0% by mass or less. Examples of the carbon material mentioned above include graphite powder. Examples of the lubricant mentioned above include metal soaps such as ethylenebis-stearamide, lithium stearate, calcium stearate, and zinc stearate, as well as stearic acid monoamide, fatty acid amide, amide wax, and hydrocarbon wax. The lubricant mentioned above is intended to facilitate the removal of the molded body from the mold during the pressure molding process, and it is not necessary for it to be contained in the molded body after it has been removed from the mold.

[0027] (component) As described above, the iron-based sintered body contains Cu (copper), P (phosphorus), and C (carbon). In the iron-based sintered body, elements other than Cu, P, and C may include Fe (iron) and unavoidable impurities. Furthermore, the unavoidable impurities may originate from the lubricant. The content of the unavoidable impurities in the iron-based sintered body may be 0.05% by mass or less, or 0.01% by mass or less, for each element.

[0028] [Fe] The iron-based sintered body contains Fe as its main component. The lower limit of the Fe content in the iron-based sintered body may be 50% by mass, 70% by mass, 85% by mass, or 90% by mass. On the other hand, the upper limit of the Fe content may be, for example, 96% by mass.

[0029] [Cu and P] Cu is a strong ferrite-strengthening element. Cu is incorporated using the phosphorus-containing copper alloy powder described above. In particular, the phosphorus-containing copper alloy powder may have a phosphorus content of 7.0% by mass or more and 9.0% by mass or less. Such phosphorus-containing copper alloy powder is also called Cu-8%P powder, and it is an intermetallic compound consisting of a Cu solid solution with a melting point of about 714°C and Cu and P. Therefore, because Cu is incorporated using the phosphorus-containing copper alloy powder, the P in the Cu-8%P powder diffuses easily into the iron powder at low temperatures during sintering of the iron-based sintered body, and the bonding strength of the iron powder interface can be sufficiently improved even at sintering temperatures of, for example, 1050°C or lower. As a result, the strength of the iron-based sintered body can be increased while reducing energy consumption during sintering. In addition, undiffused Cu with a melting point of 1084.5°C remains and contributes to deformation, making it easier to maintain good elongation. Furthermore, Cu-8%P is non-toxic and therefore highly safe.

[0030] The Cu content in the iron-based sintered body can be adjusted, for example, based on the amount of phosphorus-containing copper alloy powder added. The lower limit of the Cu content in the iron-based sintered body is 3.5 mass%, as described above. Alternatively, the lower limit of the Cu content may be 4.0 mass%, from the viewpoint of improving the strength of the iron-based sintered body and increasing the area ratio of undiffused Cu in the cross-section. On the other hand, the upper limit of the Cu content is 6.5 mass%, as described above, or 6.0 mass%, from the viewpoint of preventing the iron-based sintered body from becoming brittle due to an excessive increase in both Cu and P content, which would prevent the density from increasing.

[0031] P is a strong iron-based strengthening element that solid-solves in iron during sintering, providing solid-solution strengthening. In the iron-based sintered body, P is incorporated using the phosphorus-containing copper alloy powder mentioned above. In particular, the phosphorus-containing copper alloy powder may have a phosphorus content of 7.0% by mass or more and 9.0% by mass or less. By using Cu-8%P as the phosphorus-containing copper alloy powder, energy consumption can be reduced when producing Cu-P powder as a raw material powder for manufacturing the iron-based sintered body. More specifically, Cu-P powder is usually produced by gas atomization or the like, which requires melting Cu and P at a high temperature. In this case, if Cu-8%P is used, the Cu and P can be melted by raising the temperature to 714°C.

[0032] The phosphorus (P) content in the iron-based sintered body can be adjusted, for example, based on the amount of phosphorus-containing copper alloy powder added. The lower limit of the P content in the iron-based sintered body is 0.25% by mass, as described above. Furthermore, the lower limit of the P content may be 0.30% by mass or 0.32% by mass, from the viewpoint of improving the strength of the iron-based sintered body. On the other hand, the upper limit of the P content may be 0.56% by mass or 0.50% by mass, from the viewpoint of suppressing the embrittlement of the iron-based sintered body, as described above.

[0033] As described above, Cu and P may be blended using the phosphorus-containing copper alloy powder. Therefore, the P content may be 7.0 parts by mass or more and 9.0 parts by mass or less per 100 parts by mass of the total Cu and P content. According to the inventors' findings, by using phosphorus-containing copper alloy powder with a phosphorus content of 7.0% by mass or more and 9.0% by mass or less, the Cu and P content can be controlled within the above range, and the area ratio of undiffused Cu in the cross-section of the iron-based sintered body can be set to 0.5% or more and 2.5% or less, thereby increasing both the strength and elongation of the iron-based sintered body. Therefore, the desired quality can be easily obtained in the iron-based sintered body by setting the P content to 7.0 parts by mass or more and 9.0 parts by mass or less per 100 parts by mass of the total Cu and P content. Furthermore, according to this embodiment, energy consumption during raw material powder production and sintering can be easily and reliably reduced.

[0034] [C] Carbon (C) is a strong iron-based strengthening element. The lower limit of the C content in the iron-based sintered body is 0.3% by mass, as mentioned above, but it may also be 0.5% by mass. On the other hand, the upper limit of the C content is 1.2% by mass, as mentioned above, but it may also be 1.0% by mass. If the C content exceeds the upper limit, the effect of improving strength tends to diminish.

[0035] Undiffused Cu is present in the cross-section of the iron-based sintered body. The presence of undiffused Cu makes it easier to maintain good elongation in the iron-based sintered body. In other words, when Cu and P are blended with the phosphorus-containing copper alloy powder, the P diffuses into the iron early, contributing to increased strength, while the presence of undiffused Cu allows for appropriate control of toughness and ductility, making it easier to achieve both strength and elongation.

[0036] As mentioned above, the lower limit of the area ratio of undiffused Cu in the cross-section of the iron-based sintered body is 0.5%, but it may also be 0.6% or 0.7%. On the other hand, since Cu is added as Cu-P, the upper limit of the above area ratio is 2.5%, as mentioned above, but it may also be 2.2% or 2.0%, from the viewpoint that the P concentration may become too high and cause embrittlement (density may not increase).

[0037] The iron-based sintered body can achieve both strength and elongation. The lower limit of the compression ring strength of the iron-based sintered body is preferably 770 MPa, but may also be 800 MPa, 850 MPa, 880 MPa, or 900 MPa. On the other hand, the upper limit of the compression ring strength of the iron-based sintered body may be, for example, 1100 MPa or 1000 MPa.

[0038] The lower limit of the fracture strain of the iron-based sintered body may be 2.8%, 2.9%, or 3.0%. On the other hand, the upper limit of the fracture strain of the iron-based sintered body may be, for example, 3.5% or 3.4%. "Fracture strain" refers to the strain applied until fracture occurs, and is measured by dividing the displacement in the compression ring test by the initial outer diameter.

[0039] <Method for manufacturing an iron-based sintered body> Next, with reference to Figure 1, a method for manufacturing an iron-based sintered body according to one embodiment of the present disclosure will be described. The method for manufacturing an iron-based sintered body (hereinafter also simply referred to as "the manufacturing method") comprises a step S1 of pressurizing an iron-based raw material powder containing phosphorus-containing copper alloy powder, and a step S2 of sintering the molded body formed in the pressurizing step S1 in an inert gas atmosphere or a reducing gas atmosphere. The manufacturing method may further comprise a step of mixing each raw material powder. In the mixing step, the iron-based raw material powder can be obtained by mixing each raw material powder. The iron-based raw material powder contains, as elements, Cu: 3.5% to 6.5% by mass, P: 0.25% to 0.56% by mass, and C: 0.3% to 1.2% by mass. The sintering temperature in the sintering step S2 is 850°C to 1050°C.

[0040] This manufacturing method allows for increased strength of the resulting iron-based sintered body by ensuring that the iron-based raw material powder contains P and C within the specified ranges. Furthermore, by including Cu within the specified ranges and setting the sintering temperature in step S2 to between 850°C and 1050°C, this manufacturing method allows for a reduction in sintering temperature while maintaining the strength and elongation of the resulting iron-based sintered body. Therefore, this manufacturing method can reduce energy consumption during sintering and contribute to carbon neutrality by lowering the sintering temperature while achieving strength and elongation equivalent to or greater than that of existing iron-based sintered bodies (Fe-Cu-C system, sintering temperature 1120°C). Moreover, since this manufacturing method does not require the use of Cu3P powder as described in Non-Patent Document 2, energy consumption during raw material powder production can be reduced.

[0041] (Pressure molding process) In step S1, the iron-based raw material powder is pressure-molded using a molding die. The molding die can be shaped according to the intended use of the resulting iron-based sintered body. The molded body obtained in step S1 may be, for example, ring-shaped.

[0042] The iron-based raw material powder used in the pressure molding process S1 may be a mixture of multiple types of raw material powders. Examples of the raw material powders include the iron powder, phosphorus-containing copper alloy powder, and carbon material mentioned above in the iron-based sintered body. Additives such as lubricants may also be added to the iron-based raw material powder. The iron-based raw material powder may consist of the iron powder, the phosphorus-containing copper alloy powder, and the carbon material. The iron-based raw material powder may be obtained by mixing the multiple types of raw material powders in a mixer. An example of the mixer is a V-type mixer. Note that the lubricant is not included as an active ingredient in the resulting iron-based sintered body. Therefore, in this disclosure, the lubricant is not included in the iron-based raw material powder. The content of each element in the iron-based raw material powder may be the same as the content of each element in the iron-based sintered body mentioned above.

[0043] The upper limit of the median particle size of the phosphorus-containing copper alloy powder described above may be 100 μm, 60 μm, 50 μm, or 40 μm, from the viewpoint of suppressing the decrease in strength due to the slow diffusion rate of Cu. On the other hand, the lower limit of the median particle size may be 25 μm or 30 μm, from the viewpoint of handling ease, etc. Note that "median particle size" refers to the median value when approximately 10 g is measured using Microtrac.

[0044] The phosphorus content in the above-mentioned phosphorus-containing copper alloy powder may be 7.0% by mass or more and 9.0% by mass or less. In other words, the above-mentioned phosphorus-containing copper alloy powder may be Cu-8%P powder. According to this embodiment, it is easy to obtain an iron-based sintered body of the desired quality. Furthermore, according to this embodiment, energy consumption during raw material powder production and sintering can be easily and reliably reduced.

[0045] For example, the molding conditions in the pressure molding process S1 include a density of 7 ± 0.02 g / cm³. 3 This can be done. The molding temperature in the pressure molding process S1 can be, for example, 10°C or more and 50°C or less.

[0046] (Sintering process) In the sintering step S2, energy consumption is reduced by lowering the sintering temperature, while simultaneously improving the strength and elongation of the resulting iron-based sintered body. Furthermore, in the sintering step S2, oxidation of the molded body is prevented by sintering it in an inert gas atmosphere or a reducing gas atmosphere. Examples of the inert gas include nitrogen gas and argon gas. Examples of the reducing gas include hydrogen gas.

[0047] The upper limit of the sintering temperature in the sintering process S2 is 1050°C. In this manufacturing method, when the phosphorus-containing copper alloy powder is Cu-8%P powder, the powder is composed not only of intermetallic compounds but also of solid solutions and intermetallic compounds. Therefore, the phosphorus in Cu-8%P diffuses easily into the iron powder at low temperatures, making it easier to increase strength even during low-temperature sintering. As a result, sufficient strength can be obtained even when the sintering temperature is 1050°C. On the other hand, the lower limit of the sintering temperature is 850°C as described above, but it may also be 900°C or 950°C. By setting the sintering temperature above the lower limit, sufficient phosphorus can diffuse into the iron powder during sintering, thereby obtaining sufficient strength.

[0048] The sintering time in step S2 can be, for example, 10 minutes or more and 60 minutes or less. The upper limit of the sintering time may be, for example, 50 minutes or 40 minutes.

[0049] [Other embodiments] The above embodiments do not limit the configuration of the present invention. Therefore, the above embodiments allow for the omission, substitution, or addition of components of each part of the above embodiments based on the description herein and common technical knowledge, and all such omissions, substitutions, or additions should be interpreted as falling within the scope of the present invention. [Examples]

[0050] The present invention will be described in detail below based on examples, but the present invention should not be interpreted as being limited based on the description of these examples.

[0051] [Sample preparation] [No.1 to No.6] A composite powder containing iron powder, phosphorus-containing copper alloy iron powder (Cu-8.0%P) with a phosphorus content of 8.0% by mass and a median particle size of 35 μm, graphite powder, and a lubricant consisting of ethylene bis-stearamide, in the proportions shown in Table 1, was mixed in a V-type mixer for 30 minutes. The resulting mixed powder had a density of approximately 7.0 g / cm³. 3 The material was pressure-molded into a ring shape using a molding die (pressure molding step S1). The molded body obtained in pressure molding step S1 was then heat-treated in a nitrogen gas atmosphere at the sintering temperature shown in Table 1 for 30 minutes (sintering step S2) to produce an iron-based sintered body. In this example, the median particle size was determined by the median value when approximately 10 g was measured using a microtrac. Iron-based sintered bodies were produced for No. 1 and No. 2 at sintering temperatures of 900°C, 1050°C, and 1120°C, respectively. On the other hand, iron-based sintered bodies were produced for No. 3 to No. 6 only at a sintering temperature of 1050°C.

[0052] [No.7] A composite powder containing iron powder, copper powder with a median particle size of 60 μm, graphite powder, and a lubricant consisting of ethylenebis-stearamide in the proportions shown in Table 1 was processed using the same procedure as for Nos. 1 to 6 at the sintering temperatures shown in Table 1 to produce an iron-based sintered body. The iron-based sintered body produced at a sintering temperature of 1120°C in No. 7 is presented as an example of a so-called current iron-based sintered body (Fe-Cu-C system, sintering temperature 1120°C).

[0053] [No.8] A composite powder containing iron powder, copper powder with a median particle size of 32 μm, graphite powder, and a lubricant consisting of ethylenebis-stearic acid amide in the proportions shown in Table 1 was processed using the same procedure as for Nos. 1 to 6 at the sintering temperature shown in Table 1 to produce an iron-based sintered body.

[0054] [No.9] A composite powder containing iron powder, tin-containing copper alloy iron powder (Cu-10.0%Sn) with a tin content of 10.0% by mass and a median particle size of 40 μm, graphite powder, and a lubricant consisting of ethylene bis-stearamide, in the proportions shown in Table 1, was processed using the same procedure as for Nos. 1 to 6 at the sintering temperature shown in Table 1 to produce an iron-based sintered body.

[0055] [No.10] A composite powder containing iron powder, tin-containing copper alloy iron powder (Cu-33.0%Sn) with a tin content of 33.0% by mass and a median particle size of 26 μm, graphite powder, and a lubricant consisting of ethylene bis-stearamide, in the proportions shown in Table 1, was processed using the same procedure as for Nos. 1 to 6 at the sintering temperature shown in Table 1 to produce an iron-based sintered body.

[0056] [No.11] A composite powder containing iron powder, tin (Sn) with a median particle size of 27 μm, graphite powder, and a lubricant consisting of ethylenebis-stearamide in the proportions shown in Table 1 was processed using the same procedure as for Nos. 1 to 6 at the sintering temperature shown in Table 1 to produce an iron-based sintered body.

[0057] (Surface hardness) Surface hardness was measured using a standard Rockwell hardness test. The results are shown in Table 1.

[0058] (Pressure test) The compression ring strength was measured using a 50-ton press tester, taking into account the load and displacement. The measurement results are shown in Table 1. Figure 2 shows the relationship between the sintering temperature and compression ring strength for each sample. Figure 3 shows the relationship between the surface hardness and compression ring strength for each sample sintered at a temperature of 1050°C.

[0059] (Fracture strain) The fracture strain was determined by dividing the displacement in the compression ring test by the initial outer diameter. The measurement results are shown in Table 1. Figure 4 shows the relationship between the compression ring strength and fracture strain for each sample sintered at a sintering temperature of 1050°C.

[0060] (Percentage of undiffused Cu area) The fraction of undiffused Cu in the cross-section of the iron-based sintered body was measured using the following procedure. For optical microscope images of an arbitrary cross-section of an iron-based sintered body at a magnification of 100x, the Python library OpenCV was used to label the area in the HSV color space (H: hue, S: saturation, V: lightness) with 8 linked components, defining the range of H: 15 to 25, S: 110 to 220, and V: 240 to 255 as the undiffused Cu region. The percentage of the area was then calculated by excluding pixels smaller than 100 pixels.

[0061] [Table 1]

[0062] As shown in Table 1 and Figure 2, Nos. 1 to Nos. 6 containing Cu-8.0%P (especially Nos. 4 to Nos. 6 containing 4 mass% or more of Cu-8.0%P) achieve strength (compression ring strength) equivalent to or greater than that of the iron-based sintered body No. 7, which is sintered at 1120°C, even when the sintering temperature is 1050°C. Furthermore, it is presumed that Nos. 4 to Nos. 6 containing 4 mass% or more of Cu-8.0%P will also achieve superior strength at sintering temperatures of 900°C or higher when compared to Nos. 9 to Nos. 11, which are sintered at 1120°C.

[0063] Furthermore, as shown in Table 1, Nos. 1 to 6 (especially Nos. 4 to 6 containing 4% by mass or more of Cu-8.0%P) exhibit elongation (fracture strain) and surface hardness equivalent to or better than that of the iron-based sintered body No. 7, which is sintered at 1120°C, even when the sintering temperature is 1050°C. Moreover, as shown in Figures 3 and 4, improvements in strength and surface hardness are observed with increasing Cu-8.0%P content, while no decrease in elongation is observed.

[0064] Thus, the iron-based sintered body according to this disclosure can reduce energy consumption during sintering by lowering the sintering temperature, and also exhibits excellent strength and elongation.

Claims

1. Iron-based sintered body, As an element, Cu: 3.5% by mass or more and 6.5% by mass or less, P: 0.25% by mass or more and 0.56% by mass or less, C: 0.3% by mass or more and 1.2% by mass or less Includes, An iron-based sintered body in which the area ratio of undiffused Cu in the cross-section of the sintered body is 0.5% or more and 2.5% or less.

2. The iron-based sintered body according to claim 1, wherein the content of P is 7.0 parts by mass or more and 9.0 parts by mass or less per 100 parts by mass of the total content of Cu and P.

3. A process of pressure molding an iron-based raw material powder containing phosphorus-containing copper alloy powder, The process of sintering the molded body formed in the above pressure molding process in an inert gas atmosphere or a reducing gas atmosphere. Equipped with, The above iron-based raw material powder contains, as elements, Cu: 3.5% by mass or more and 6.5% by mass or less, P: 0.25% by mass or more and 0.56% by mass or less, C: 0.3% by mass or more and 1.2% by mass or less Includes, A method for manufacturing an iron-based sintered body, wherein the sintering temperature in the above sintering step is 850°C or higher and 1050°C or lower.

4. The method for producing an iron-based sintered body according to claim 3, wherein the phosphorus content in the phosphorus-containing copper alloy powder is 7.0% by mass or more and 9.0% by mass or less.

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