Sintered component and method for manufacturing sintered component

Abstract

This sintered component has a composition which contains 8.0-20.0 mass% of nickel, 10.0-28.0 mass% of chromium, 0.0-4.0 mass% of molybdenum, 0.0-2.0 mass% of manganese, 0.0-3.0 mass% of silicon, 0.0-2.0 mass% of carbon, 0.0-1.0 mass% of aluminum, 0.0-4.0 mass% of tungsten, 0.0-3.0 mass% of copper, 0.0-1.0 mass% of niobium, 0.0-2.0 mass% of boron, and 0.0-1.5 mass% of nitrogen, with the remainder comprising iron and unavoidable impurities. The composition contains more than 0.0 mass% of at least one element that is selected from the group consisting of molybdenum, silicon, carbon, aluminum, tungsten, copper, niobium, boron, and nitrogen. This sintered component is non-magnetic, has a Rockwell hardness of 71 HRB or more, and satisfies all of the following (A), (B), (C), and (D) with respect to the Cr equivalent and the Ni equivalent in the Schaeffler diagram modified by Schneider. (A) Cr equivalent (mass%) = Cr + 2Si + 1.5Mo + 5V + 5.5Al + 1.75Nb + 1.5Ti + 0.75W ≥ 13, (B) Ni equivalent (mass%) = Ni + Co + 0.5Mn + 0.3Cu + 30C + 25N ≥ 18, (C) Ni equivalent + 0.80 × Cr equivalent - 25.33 ≥ 0, (D) Ni equivalent - 1.44 × Cr equivalent + 14.52 ≥ 0

Description

Sintered parts and manufacturing method for sintered parts

[0001] This application claims priority to Japanese Patent Application No. 2024-030365, filed February 29, 2024, and incorporates by reference the entire contents of said Japanese application.

[0002] Patent Document 1 discloses an austenitic stainless steel that can be used in various applications requiring strength, ductility, and corrosion resistance. This austenitic stainless steel is obtained by melting and casting an alloy of a predetermined composition to form an ingot, hot working the ingot to form a steel material of a desired shape, and then subjecting it to solution heat treatment.

[0003] Whether a certain composition becomes austenite or forms other phases such as ferrite is determined by the compounding ratio of nickel (Ni) and chromium (Cr) to iron (Fe). The Schaeffler's phase diagram is known as an index of austenite stabilization. In the Schaeffler's phase diagram, the contribution of specific elements other than Ni and Cr as ferrite stabilizing elements is expressed as a Cr equivalent, which is converted to the amount of Cr, and the degree of their contribution as austenite stabilizing elements is expressed as a Ni equivalent, which is converted to the amount of Ni. Non-Patent Document 1 discloses a Schaeffler's phase diagram improved by Schneider. In the Schaeffler's phase diagram improved by Schneider, elements corresponding to the Cr equivalent and Ni equivalent have been added.

[0004] Japanese Patent Application Laid-Open No. 2008-127590

[0005] Toshio Fujita, Koji Shibata, Mitsuru Tanino, "Design and Theory of Steel Materials", Maruzen Co., Ltd., 1981, pp. 149-150

[0006] The sintered part of the present disclosure has a composition containing 8.0 to 20.0 mass% nickel, 10.0 to 28.0 mass% chromium, 0.0 to 4.0 mass% molybdenum, 0.0 to 2.0 mass% manganese, 0.0 to 3.0 mass% silicon, 0.0 to 2.0 mass% carbon, 0.0 to 1.0 mass% aluminum, 0.0 to 4.0 mass% tungsten, 0.0 to 3.0 mass% copper, 0.0 to 1.0 mass% niobium, 0.0 to 2.0 mass% boron, 0.0 to 1.5 mass% nitrogen, and the balance being iron and unavoidable impurities. The composition contains more than 0.0 mass% of at least one element selected from the group consisting of molybdenum, silicon, carbon, aluminum, tungsten, copper, niobium, boron, and nitrogen. The sintered part of the present disclosure is non-magnetic, has a Rockwell hardness of 71 HRB or more, and has Cr equivalent and Ni equivalent in the Schaeffler phase diagram modified by Schneider that satisfy all of the following (A), (B), (C), and (D): (A) Cr equivalent (mass%) = Cr+2Si+1.5Mo+5V+5.5Al+1.75Nb+1.5Ti+0.75W≧13 (B) Ni equivalent (mass%) = Ni+Co+0.5Mn+0.3Cu+30C+25N≧18 (C) Ni equivalent + 0.80 x Cr equivalent - 25.33≧0 (D) Ni equivalent - 1.44 x Cr equivalent + 14.52 ≧ 0

[0007] FIG. 1 is a schematic diagram showing an example of a sintered part according to an embodiment. FIG. 2 is a Schaeffler phase diagram improved by Schneider. FIG. 3 is a schematic diagram showing another example of a sintered part according to an embodiment. FIG. 4 is a schematic diagram illustrating a method for manufacturing a sintered part according to an embodiment. FIG. 5 is a flowchart showing an example of steps in the method for manufacturing a sintered part according to an embodiment. FIG. 6 is a flowchart showing another example of steps in the method for manufacturing a sintered part according to an embodiment. FIG. 7 is a diagram showing the composition of a sintered part according to an embodiment. FIG. 8 is a diagram showing the composition of a sintered part according to an embodiment. FIG. 9 is a diagram showing the composition of a sintered part according to an embodiment. FIG. 10 is a diagram showing the sintering temperature and sintered density of a sintered part according to an embodiment. FIG. 11 is a diagram showing the sintering temperature and sintered density of a sintered part according to an embodiment. FIG. 12 is a diagram showing the sintering temperature and sintered density of a sintered part according to an embodiment. FIG. 13 is a diagram showing the Rockwell hardness, 0.2% proof stress, and relative permeability of a sintered part according to an embodiment. FIG. 14 is a diagram showing the Rockwell hardness, 0.2% proof stress, and relative permeability of a sintered part according to an embodiment. FIG. 15 is a diagram showing the Rockwell hardness, 0.2% proof stress, and relative permeability of a sintered part according to an embodiment.

[0008] [Problem to be Solved by the Present Disclosure] In the fields of MRI (Magnetic Resonance Imaging) and electronic devices, there is a demand for parts with complex shapes made of non-magnetic, high-strength austenitic steel. Precipitation-hardened non-magnetic, high-strength austenitic steel has the problem of high raw material costs due to its high Ni content and the need for a furnace for aging precipitation. High-nitrogen non-magnetic, high-strength austenitic steel has the problem of high processing costs when manufacturing parts with complex shapes. The technology of Patent Document 1 requires hot working an ingot into the desired shape, which results in poor processability and makes it difficult to manufacture parts with complex shapes.

[0009] An object of the present disclosure is to provide a sintered part that is non-magnetic and has high strength. Another object of the present disclosure is to provide a method for producing a sintered part that is highly productive.

[0010] [Advantages of the Present Disclosure] The sintered part of the present disclosure is non-magnetic and has high strength.

[0011] [Description of Embodiments of the Present Disclosure] One method for mass-producing parts with complex shapes is to press-molde powder to produce a compact, and then heat-treat the compact. Parts manufactured from powder of Fe (iron)-Ni (nickel)-Cr (chromium) austenitic steel, such as SUS304 or SUS316, which is a non-magnetic material, do not have very high strength. While adding elements that contribute to precipitation hardening to austenitic steel can improve strength, there is a problem in that the powder itself becomes hard and cannot be press-molded.

[0012] As a result of extensive research, the inventors have discovered that by using a primary powder that is hard enough to be press-formed and a secondary powder that can be alloyed with the primary powder during sintering, it is possible to ultimately manufacture non-magnetic, high-strength components. In particular, the elements that make up the secondary powder are selected so that they can diffuse into the primary powder during press-forming of a powder mixture of the primary powder and the secondary powder, and subsequent sintering. First, embodiments of the present disclosure will be listed and described.

[0013] (1) A sintered part according to an embodiment of the present disclosure has a composition containing 8.0 to 20.0% by mass of nickel, 10.0 to 28.0% by mass of chromium, 0.0 to 4.0% by mass of molybdenum, 0.0 to 2.0% by mass of manganese, 0.0 to 3.0% by mass of silicon, 0.0 to 2.0% by mass of carbon, 0.0 to 1.0% by mass of aluminum, 0.0 to 4.0% by mass of tungsten, 0.0 to 3.0% by mass of copper, 0.0 to 1.0% by mass of niobium, 0.0 to 2.0% by mass of boron, and 0.0 to 1.5% by mass of nitrogen, with the remainder being iron and unavoidable impurities. The composition contains more than 0.0 mass % of at least one element selected from the group consisting of molybdenum, silicon, carbon, aluminum, tungsten, copper, niobium, boron, and nitrogen. The sintered part according to an embodiment of the present disclosure is non-magnetic, has a Rockwell hardness of 71 HRB or more, and has Cr equivalent and Ni equivalent in the Schaeffler phase diagram modified by Schneider that satisfy all of the following (A), (B), (C), and (D): (A) Cr equivalent (mass%) = Cr+2Si+1.5Mo+5V+5.5Al+1.75Nb+1.5Ti+0.75W≧13 (B) Ni equivalent (mass%) = Ni+Co+0.5Mn+0.3Cu+30C+25N≧18 (C) Ni equivalent + 0.80 x Cr equivalent - 25.33≧0 (D) Ni equivalent - 1.44 x Cr equivalent + 14.52 ≧ 0

[0014] The sintered part has high strength due to the above composition. The sintered part can be nonmagnetic because the Ni equivalent and Cr equivalent of the Schaeffler phase diagram improved by Schneider satisfy specific ranges. As described below, the sintered part is manufactured by a method in which powder is press-molded to produce a compact and then the compact is sintered. Sintered parts manufactured by this method can have complex shapes. Sintered parts manufactured by this method have excellent productivity.

[0015] (2) The sintered part of (1) above may have a 0.2% yield strength of 300 MPa or more.

[0016] A sintered part having a 0.2% yield strength of 300 MPa or more has high strength.

[0017] (3) A method for producing a sintered part according to an embodiment of the present disclosure includes Step A of preparing a primary powder and a secondary powder, Step B of mixing the primary powder and the secondary powder to prepare a mixed powder, Step C of press-molding the mixed powder to prepare a compact, and Step D of sintering the compact. The primary powder has a composition containing 8.0 to 20.0 mass% nickel, 10.0 to 28.0 mass% chromium, 0.0 to 4.0 mass% molybdenum, 0.0 to 2.0 mass% manganese, 0.0 to 4.0 mass% tungsten, 0.0 to 3.0 mass% silicon, 0.0 to 3.0 mass% copper, 0.0 to 1.0 mass% niobium, and the balance being iron and unavoidable impurities. The element constituting the secondary powder is at least one selected from the group consisting of carbon, silicon, molybdenum, aluminum, tungsten, copper, niobium, boron, and nitrogen.

[0018] In the above-described method for producing a sintered part, the primary powder has the above-described composition and is therefore a relatively soft iron-based alloy, so that a mixed powder containing this primary powder can be press-molded. If press-molding is possible, sintered parts with complex shapes can be easily produced.

[0019] In the above-described method for producing a sintered part, the mixed powder contains a secondary powder of a specific element, which diffuses and alloys with the iron-based alloy during sintering. The alloying of the specific element with the iron-based alloy increases the strength of the produced sintered part. While the strength of a sintered part produced using only a primary powder is low, using a mixed powder in which the primary powder is mixed with a secondary powder allows for press molding, and the strength of the sintered part obtained after sintering is high. In the above-described method for producing a sintered part, the sintering does not result in the formation of at least one of a ferrite phase and martensitic transformation, so the produced sintered part is nonmagnetic.

[0020] (4) In the method for producing a sintered part according to (3) above, the composition of the mixed powder may be such that the Cr equivalent and Ni equivalent of the Schaeffler phase diagram improved by Schneider satisfy all of the following conditions (A), (B), (C), and (D): (A) Cr equivalent (mass %) = Cr + 2Si + 1.5Mo + 5V + 5.5Al + 1.75Nb + 1.5Ti + 0.75W ≧ 13 (B) Ni equivalent (mass %) = Ni + Co + 0.5Mn + 0.3Cu + 30C + 25N ≧ 18 (C) Ni equivalent + 0.80 × Cr equivalent - 25.33 ≧ 0 (D) Ni equivalent - 1.44 × Cr equivalent + 14.52 ≧ 0

[0021] When the composition of the mixed powder satisfies all of the above (A), (B), (C), and (D), at least one of a ferrite phase and a martensitic transformation is unlikely to occur during sintering, and the produced sintered part is likely to be nonmagnetic.

[0022] (5) In the method for producing a sintered part according to (3) or (4), the Vickers hardness of the primary powder may be 200 HV or less.

[0023] If the Vickers hardness of the main powder is 200 HV or less, the mixed powder containing the main powder can be easily press-molded.

[0024] (6) In any one of the methods for producing a sintered part described in (3) to (5), the mixed powder may have a composition containing 8.0% by mass or more and 20.0% by mass or less of nickel, 10.0% by mass or more and 28.0% by mass or less of chromium, 0.0% by mass or more and 4.0% by mass or less of molybdenum, 0.0% by mass or more and 2.0% by mass or less of manganese, 0.0% by mass or more and 3.0% by mass or less of silicon, 0.0% by mass or more and 2.0% by mass or less of carbon, 0.0% by mass or more and 1.0% by mass or less of aluminum, 0.0% by mass or more and 4.0% by mass or less of tungsten, 0.0% by mass or more and 3.0% by mass or less of copper, 0.0% by mass or more and 1.0% by mass or less of niobium, 0.0% by mass or more and 2.0% by mass or less of boron, 0.0% by mass or more and 1.5% by mass or less of nitrogen, with the remainder being iron and inevitable impurities. The composition may include greater than 0.0 wt.% of at least one element selected from the group consisting of molybdenum, silicon, carbon, aluminum, tungsten, copper, niobium, boron, and nitrogen.

[0025] When the mixed powder has the above composition, the sintered part produced using this mixed powder tends to have high strength.

[0026] (7) The method may be any one of the methods for producing a sintered part described in (3) to (6) above, which produces the sintered part described in (1) or (2) above.

[0027] According to the above manufacturing method, a non-magnetic and high-strength sintered part can be obtained.

[0028] (8) In any of the methods for manufacturing a sintered part described in (3) to (7), the elements constituting the secondary powder may include carbon, and in the step of preparing the mixed powder, the primary powder and the secondary powder may be mixed so that the carbon content in the mixed powder is 0.1 mass % or more and 2.0 mass % or less.

[0029] If the mixed powder contains carbon within the above range, the mixed powder containing the auxiliary powder can be press-molded, and the strength of the sintered part obtained after sintering tends to be high.

[0030] (9) In any of the methods for manufacturing a sintered part described in (3) to (8), the elements constituting the secondary powder may include silicon, and in the step of preparing the mixed powder, the primary powder and the secondary powder may be mixed so that the silicon content in the mixed powder is 0.1 mass % or more and 3.0 mass % or less.

[0031] If the mixed powder contains silicon within the above range, the mixed powder containing the auxiliary powder can be press-molded, and the strength of the sintered part obtained after sintering tends to be high.

[0032] (10) In the method for manufacturing a sintered part according to any one of (3) to (9), the elements constituting the secondary powder may include molybdenum, and in the step of preparing the mixed powder, the primary powder and the secondary powder may be mixed so that the molybdenum content in the mixed powder is 0.1 mass % or more and 4.0 mass % or less.

[0033] If the mixed powder contains molybdenum within the above range, the mixed powder containing the auxiliary powder can be press-molded, and the strength of the sintered part obtained after sintering tends to be high.

[0034] (11) In the method for manufacturing a sintered part according to any one of (3) to (10) above, in the step of preparing the primary powder and the secondary powder, the primary powder may be prepared by a water atomization method.

[0035] The primary powder produced by the water atomization method is excellent in productivity and in formability during press molding.

[0036] (12) In the method for producing a sintered part according to any one of (3) to (11) above, in the step of sintering the compact, the relative density of the compact may be set to 85% or more.

[0037] If the relative density of the compact is 85% or more, the produced sintered part will have a high density. As described above, since the primary powder is made of a relatively soft iron-based alloy, the compact can be press-molded so that the relative density is 85% or more.

[0038] (13) In the method for producing a sintered part according to any one of (3) to (12) above, in step D, the compact may be heated at a temperature of 1000°C or higher and 1300°C or lower.

[0039] Heating the compact at a temperature within the above range can improve the bonding strength between the powders, and heating the compact at a temperature within the above range can cause the specific elements in the secondary powder to diffuse and be alloyed with the iron-based alloy, thereby improving the strength of the sintered part after sintering.

[0040] (14) The method for producing a sintered part according to (13) above may further include a step of cooling the sintered body obtained by sintering the molded body at a cooling rate of 5°C / sec or more, and then heat-treating the sintered body at a temperature of 400°C or more and 1000°C or less after cooling.

[0041] By cooling the sintered body and subjecting it to heat treatment at a temperature within the above range, specific elements are precipitated, and the precipitates can further improve the strength of the sintered part.

[0042] (15) In the method for manufacturing a sintered part according to any one of (3) to (14) above, in the step of sintering the compact, an atmospheric gas containing nitrogen may be introduced into a sintering furnace to heat the compact.

[0043] When a compact is heated in a nitrogen-containing atmosphere, nitrogen can dissolve in the composition of the compact, which tends to increase the strength of the sintered part obtained after sintering.

[0044] [Details of the embodiments of the present disclosure] Specific examples of the sintered part and the method for manufacturing a sintered part of the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or equivalent parts. In each drawing, for the sake of convenience, some components may be exaggerated or simplified. The dimensional ratios of each part in the drawings may also differ from the actual ratios. Note that the present invention is not limited to these examples, but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0045] <Sintered Component> A sintered component 10 will be described with reference to Figures 1 to 3. The sintered component 10 has a specific composition. The sintered component 10 is non-magnetic and has high strength.

[0046] <Composition> The sintered part 10 is made of an iron-based alloy. The iron-based alloy contains Ni (nickel) and Cr (chromium) as essential elements. The iron-based alloy also contains at least one element selected from the group consisting of C (carbon), Si (silicon), Mo (molybdenum), Al (aluminum), W (tungsten), Cu (copper), Nb (niobium), B (boron), and N (nitrogen) as essential elements. The iron-based alloy may also contain Mn (manganese). The iron-based alloy contains the elements listed above, with the remainder consisting of iron and unavoidable impurities. The content ratio of each element in the composition of the sintered part 10 is the amount contained in the iron-based alloy when the entire iron-based alloy of the sintered part 10 is taken as 100% by mass.

[0047] As will be described later with reference to Figure 4, the sintered part 10 is produced by a method in which a mixed powder 3 of a main powder 1 and a secondary powder 2 is press-molded to produce a compact 5, and then the compact 5 is sintered. The sintered part 10 produced by this method has a composition in which the iron-based alloy of the main powder 1 is alloyed with the constituent elements of the secondary powder 2. Depending on the composition of the iron-based alloy that makes up the main powder 1 and the elements that make up the secondary powder 2, the contents of Mo, Mn, Si, C, Al, W, Cu, Nb, B, and N may be 0 mass %, excluding unavoidable amounts.

[0048] Ni: Ni is an austenite-forming element that contributes to stabilizing the austenite phase. The Ni content in the sintered part 10 is 8.0% by mass or more and 20.0% by mass or less. A Ni content of 8.0% by mass or more stabilizes the austenite phase, making it easier to maintain non-magnetic properties. A Ni content of 20.0% by mass or less reduces the amount of Ni, which is generally expensive, used, making it easier to reduce costs. The Ni content may be 12.0% by mass or more and 20.0% by mass or less, 12.0% by mass or more and 18.0% by mass or less, or 12.0% by mass or more and 15.0% by mass or less.

[0049] <Cr> Cr is an element that contributes to improving the corrosion resistance of the sintered part 10. The Cr content in the sintered part 10 is 10.0 mass% or more and 28.0 mass% or less. A Cr content of 10.0 mass% or more facilitates improving the corrosion resistance of the sintered part 10. If the Cr content is too high, Fe-Cr intermetallic compounds such as the σ phase are likely to precipitate, which may lead to embrittlement of the sintered part 10. A Cr content of 28.0 mass% or less facilitates reducing embrittlement of the sintered part 10. The Cr content may be 15.0 mass% or more and 28.0 mass% or less, 16.0 mass% or more and 25.0 mass% or less, 17.0 mass% or more and 20.0 mass% or less, or 17.0 mass% or more and 18.0 mass% or less. The Cr content may be 10.0 mass% or more and 20.0 mass% or less.

[0050] <> Mo is a solution strengthening element that contributes to improving the strength of the sintered part 10. The Mo content in the sintered part 10 is 0.0% by mass or more and 4.0% by mass or less. The Mo content is, for example, 1.0% by mass or more and 4.0% by mass or less. A Mo content of 1.0% by mass or more facilitates improving the strength of the sintered part 10. If the Mo content is too high, the sintered part 10 is likely to transform to a body-centered cubic (bcc) structure. If the Mo content is 4.0% by mass or less, the transformation to a bcc structure is difficult. The Mo content may be 1.5% by mass or more and 3.0% by mass or less.

[0051] <> The iron-based alloy constituting the primary powder 1 ( FIG. 4 ), which is the raw material powder of the sintered part 10, may contain Mn. If the iron-based alloy constituting the primary powder 1 contains Mn, the sintered part 10 may also contain Mn. The Mn content in the sintered part 10 is 0.0 mass % or more and 2.0 mass % or less. If the primary powder 1 is produced by atomization, the primary powder 1 may contain approximately 0.5 mass % of Mn. If the primary powder 1 is produced by water atomization, the iron-based alloy is melted in air, so the Mn content, which tends to oxidize more easily than Fe, is preferably low, for example, 2.0 mass % or less.

[0052] <Si> Si is an element that makes Fe less susceptible to oxidation. Furthermore, when Si is included together with C, it contributes to solid-solution strengthening and contributes to improving the strength of the sintered part 10. When Si is included together with at least one of W and Mo, it easily forms compounds, which contributes to improving the strength of the sintered part 10. The Si content in the sintered part 10 is 0.0 mass% or more and 3.0 mass% or less. The Si content is, for example, 0.1 mass% or more and 3.0 mass% or less. A Si content of 0.1 mass% or more makes Fe less susceptible to oxidation. Because Si contributes to solid-solution strengthening, if the primary powder 1 ( FIG. 4 ), which is the raw material powder for the sintered part 10, contains a large amount of Si, the primary powder 1 itself becomes hard and difficult to press-form. The Si content of the iron-based alloy of the sintered part 10 depends on the Si content in the primary powder 1. The fact that the Si content of the iron-based alloy of the sintered part 10 is 3.0% by mass or less means that the Si content of the main powder 1 is 3.0% by mass or less, and that the sintered part 10 was produced by press molding. The Si content may be 0.5% by mass or more and 3.0% by mass or less.

[0053] <<C>> Carbon (C) is an interstitial solution strengthening element that contributes to improving the strength of the sintered part 10 and stabilizing the austenite phase. The C content in the sintered part 10 is 0.0% by mass or more and 2.0% by mass or less. The C content is, for example, 0.1% by mass or more and 2.0% by mass or less. A C content of 0.1% by mass or more facilitates improving the strength of the sintered part 10. If the C content is too high, carbides are likely to be formed during sintering, which may reduce the corrosion resistance of the sintered part 10. If large carbides are formed, the strength of the sintered part 10 may also be reduced. A C content of 2.0% by mass or less improves the strength of the sintered part 10 while minimizing the reduction in corrosion resistance. The C content may be 0.2% by mass or more and 0.5% by mass or less.

[0054] <<Al>> Al is a solid-solution strengthening element that contributes to improving the strength of the sintered part 10. The Al content in the sintered part 10 is 0.0% by mass or more and 1.0% by mass or less. The Al content is, for example, 0.3% by mass or more and 1.0% by mass or less. An Al content of 0.3% by mass or more facilitates improving the strength of the sintered part 10. If the Al content is too high, the iron-based alloy is more likely to transform into a body-centered cubic (bcc) structure. If the Al content is 1.0% by mass or less, transformation to bcc is difficult. Al melts during sintering. If the Al content is too high, pores formed by melting Al tend to coarsen. If the Al content is 1.0% by mass or less, even if pores are formed by melting Al, the pores are less likely to coarsen. The Al content may be 0.3% by mass or more and 0.5% by mass or less.

[0055] <W> W is a solution strengthening element that contributes to improving the strength of the sintered part 10. The W content in the sintered part 10 is 0.0% by mass or more and 4.0% by mass or less. The W content is, for example, 0.5% by mass or more and 4.0% by mass or less. A W content of 0.5% by mass or more facilitates improving the strength of the sintered part 10. A W content of 4.0% by mass or less reduces the amount of W, which is generally expensive, used, making it easier to reduce costs. The W content may be 0.8% by mass or more and 1.0% by mass or less, or 1.0% by mass or more and 4.0% by mass or less.

[0056] Cu: Cu is an element added as needed and contributes to stabilizing the austenite phase. The Cu content in the sintered part 10 is 0.0% by mass or more and 3.0% by mass or less. The Cu content is, for example, 1.0% by mass or more and 3.0% by mass or less. A Cu content of 1.0% by mass or more facilitates improving the strength of the sintered part 10. Because Cu melts at a temperature lower than the sintering temperature of the Fe-Ni-Cr iron-based alloy, which is the primary raw material, excessive Cu content may coarsen pores formed during melting. Furthermore, there is a limit to the amount of Cu that can be dissolved in Fe, which may result in the formation of unintended Cu-based precipitates. A Cu content of 3.0% by mass or less reduces the coarsening of pores and the formation of unintended Cu-based precipitates, and the formation of fine Cu-based precipitates may improve hardness. The Cu content may be 1.0 mass % or more and 2.0 mass % or less.

[0057] Cu is contained in the iron-based alloy that constitutes, for example, the main powder 1 (FIG. 4). For example, some austenitic steel powders, such as SUS304 or SUS316, contain about 2 mass% Cu. Furthermore, some commercially available austenitic steel powders produced by atomization contain Cu. By using these powders, the sintered part 10 contains Cu.

[0058] Nb: Nb is an element added as needed. When the content of elements other than Fe is low, Nb forms a Laves phase, thereby contributing to improving the yield strength of the sintered part 10. The Nb content in the sintered part 10 is 0.0 mass% or more and 1.0 mass% or less. The Nb content is, for example, 0.1 mass% or more and 1.0 mass% or less. When C is not contained, an Nb content of 0.1 mass% or more forms a Laves phase or a metastable phase, which easily improves the strength of the sintered part 10. When C is contained, an Nb content of 0.1 mass% or more forms NbC-based carbides, which easily improves the strength of the sintered part 10. When the Nb content is 0.1 mass% or more, under conditions with high carbon or nitrogen contents, Nb forms nonmagnetic alloy carbides or carbonitrides, which have a pinning effect on austenite grains, improving toughness. Since there is a limit to the amount of Nb that can dissolve in Fe, if the Nb content is too high, it is difficult to obtain the above-mentioned effects. If the Nb content is 1.0 mass% or less, the strength of the sintered part 10 can be improved and costs can be easily reduced. The Nb content may be 0.3 mass% or more and 0.5 mass% or less.

[0059] <> B is an interstitial solid-solution strengthening element that contributes to improving the strength of the sintered part 10. The B content in the sintered part 10 is 0.0% by mass or more and 2.0% by mass or less. The B content is, for example, 0.2% by mass or more and 2.0% by mass or less. A B content of 0.2% by mass or more facilitates improving the strength of the sintered part 10. B has a low solid solubility limit in iron-based alloys and can precipitate Fe- and Cr-based borides. Fe- and Cr-based borides are magnetic. A B content of 2.0% by mass or less makes it difficult to precipitate Fe- and Cr-based borides. Furthermore, a B content of 2.0% by mass or less reduces the amount of B used, which is expensive compared to other elements, and facilitates cost reduction. The B content may be 0.2% by mass or more and 1.0% by mass or less, or 0.2% by mass or more and 0.5% by mass or less.

[0060] <<N>> N is an interstitial solution strengthening element that contributes to improving the strength of the sintered part 10 and stabilizing the austenite phase. The N content in the sintered part 10 is 0.0 mass% or more and 1.5 mass% or less. The N content is, for example, 0.1 mass% or more and 1.2 mass% or less. If the N content is 0.1 mass% or more, the strength of the sintered part 10 is easily improved.

[0061] The iron-based alloy forming the sintered part 10 has a Cr equivalent and Ni equivalent satisfying all of the following (A), (B), (C), and (D) in the Schaeffler phase diagram improved by Schneider: (A) Cr equivalent (mass %) = Cr + 2Si + 1.5Mo + 5V + 5.5Al + 1.75Nb + 1.5Ti + 0.75W ≥ 13 (B) Ni equivalent (mass %) = Ni + Co + 0.5Mn + 0.3Cu + 30C + 25N ≥ 18 (C) Ni equivalent + 0.80 × Cr equivalent - 25.33 ≥ 0 (D) Ni equivalent - 1.44 × Cr equivalent + 14.52 ≥ 0

[0062] FIG. 2 shows the Schaeffler phase diagram improved by Schneider. In the phase diagram shown in FIG. 2, the vertical axis represents the Ni equivalent and the horizontal axis represents the Cr equivalent. In the phase diagram, "A" represents the austenite phase, "M" represents the martensite phase, and "F" represents the ferrite phase. In the Schaeffler phase diagram improved by Schneider, specific elements other than Ni and Cr are expressed as Cr equivalents, which convert the contribution of the elements as ferrite stabilizing elements into Cr amounts, and Ni equivalents, which convert the contribution of the elements as austenite stabilizing elements into Ni amounts. Although (A) above lists V (vanadium), Ti (titanium), and Co (cobalt), V and Ti are not included in the composition of the sintered part 10. Therefore, V and Ti are zero in the calculation of (A) above. Co is zero in the calculation of (B) above.

[0063] An iron-based alloy whose Cr equivalent and Ni equivalent satisfy all of (A), (B), (C), and (D) in the Schaeffler phase diagram improved by Schneider can stably maintain the austenite phase. An iron-based alloy that satisfies all of (A), (B), (C), and (D) above is less likely to undergo at least one of ferrite phase and martensitic transformation. Therefore, the sintered part 10 is nonmagnetic.

[0064] <<Nonmagnetic>> In this disclosure, nonmagnetic is defined as a relative permeability of 1 or more and 1.02 or less. A sintered part 10 with a relative permeability of 1.02 or less can be used for various nonmagnetic parts. The relative permeability may be 1.01 or less, 1.001 or less, or 1.0001 or less. As long as the relative permeability does not exceed 1.02, it is acceptable for various magnetic phases to be generated in very small amounts.

[0065] The sintered component 10 may include a phase other than the austenite phase, namely, a non-magnetic precipitate phase 11, as shown in Figure 3. The precipitate phase 11 can be identified using X-ray diffraction (XRD) or scanning electron microscopy (SEM).

[0066] <Relative Density> The relative density of the sintered part 10 is, for example, 85% or more. A sintered part 10 with a relative density of 85% or more has a high density. The relative density of the sintered part 10 may be 90% or more, 95% or more, 97% or more, or 99% or more. The relative density of the sintered part 10 can be determined in the same manner as the relative density of the compact 5, which will be described later.

[0067] <Rockwell Hardness> The Rockwell hardness of the sintered component 10 is 71 HRB or more. A sintered component 10 having a Rockwell hardness of 71 HRB or more has excellent wear resistance. The Rockwell hardness of the sintered component 10 may be 75 HRB or more, 80 HRB or more, or 85 HRB or more.

[0068] <0.2% Yield Strength> The 0.2% yield strength of the sintered component 10 is, for example, 300 MPa or more. A sintered component 10 having a 0.2% yield strength of 300 MPa or more has excellent strength. The 0.2% yield strength of the sintered component 10 may be 350 MPa or more, 400 MPa or more, or 450 MPa or more.

[0069] <Method for Manufacturing Sintered Part> A method for manufacturing a sintered part will be described with reference to Figures 4 to 6. The method for manufacturing a sintered part includes the following steps A, B, C, and D. Step A: Prepare a main powder 1 and a secondary powder 2. Step B: Mix the main powder 1 and the secondary powder 2 to produce a mixed powder 3. Step C: Press-molde the mixed powder 3 to produce a compact 5. Step D: Sinter the compact 5.

[0070] One of the features of the method for manufacturing a sintered part is the use of a main powder 1 made of a relatively soft iron-based alloy and a secondary powder 2 that can be alloyed with the main powder 1 during sintering. Because the main powder 1 is made of a relatively soft iron-based alloy, a mixed powder 3 containing this main powder can be press-molded. Because the mixed powder 3 contains the secondary powder 2 made of a specific element, the specific element diffuses and is alloyed with the iron-based alloy during sintering. The specific element is alloyed with the iron-based alloy to form the composition of the sintered part 10 described above.

[0071] <Step A> In step A, a primary powder 1 is prepared (S1 in FIG. 5), and a secondary powder 2 is prepared (S2 in FIG. 5).

[0072] [Main Powder] Main powder 1 is made of an iron-based alloy. The iron-based alloy contains Ni and Cr as essential elements. The iron-based alloy may contain Mo, Mn, W, Si, Cu, and Nb. The iron-based alloy contains the elements listed above, with the remainder being iron and unavoidable impurities. The content ratio of each element in the composition of main powder 1 is the amount contained in the iron-based alloy when the entire iron-based alloy of main powder 1 is taken as 100 mass%.

[0073] The iron-based alloy of main powder 1 has a composition containing 8.0 mass% or more and 20.0 mass% or less of Ni, 10.0 mass% or more and 28.0 mass% or less of Cr, 0.0 mass% or more and 4.0 mass% or less of Mo, 0.0 mass% or more and 2.0 mass% or less of Mn, 0.0 mass% or more and 4.0 mass% or less of W, 0.0 mass% or more and 3.0 mass% or less of Si, 0.0 mass% or more and 3.0 mass% or less of Cu, 0.0 mass% or more and 1.0 mass% or less of Nb, with the balance being Fe and unavoidable impurities.

[0074] The content ratio of each element in the composition of the main powder 1 is adjusted by the elements and the content ratio of those elements in the auxiliary powder 2, which will be described later. The main powder 1 and the auxiliary powder 2 may contain the same elements. In this case, the content ratios of each element in the main powder 1 and the auxiliary powder 2 are adjusted so that the composition of the sintered part 10 to be manufactured is the above-described composition. For example, if the auxiliary powder 2 contains Mo, the content ratios of Mo in the main powder 1 and the auxiliary powder 2 are each adjusted so that the Mo content in the sintered part 10 is 1.0 mass% or more and 4.0 mass% or less. If the auxiliary powder 2 contains Mo, the main powder 1 may or may not contain Mo. If the auxiliary powder 2 does not contain Mo, the main powder 1 may or may not contain Mo. The content ratios of Si, W, Cu, and Nb in the main powder 1 are also adjusted depending on whether they are contained in the auxiliary powder 2.

[0075] The Vickers hardness of the main powder 1 is, for example, 200 HV or less. The Vickers hardness of the main powder 1 can be changed by adjusting the content ratio of each element in the composition of the main powder 1. A main powder 1 with a Vickers hardness of 200 HV or less is suitable for press molding. The lower the Vickers hardness of the main powder 1, the easier it is to press mold. The Vickers hardness of the main powder 1 may be 180 HV or less, or 150 HV or less. The Vickers hardness is determined by embedding the main powder 1 in resin, polishing the resin so that some of the particles constituting the main powder 1 are exposed, and measuring the exposed particles. The number of measurements is, for example, 10 or more.

[0076] {Average Particle Size of the Main Powder} The average particle size of the main powder 1 is, for example, 20 μm or more and 200 μm or less. If the average particle size of the main powder 1 is 20 μm or more, the main powder 1 is easy to handle. If the average particle size of the main powder 1 is 200 μm or less, the main powder 1 is easy to press-form, and it is easy to manufacture a high-density sintered part 10. The average particle size of the main powder 1 may be 20 μm or more and 100 μm or less, 50 μm or more and 200 μm or less, or 50 μm or more and 100 μm or less. The average particle size of the main powder 1 is the particle size at which the cumulative volume in the volumetric particle size distribution measured by a laser diffraction particle size analyzer becomes 50%.

[0077] The primary powder 1 can be produced by, for example, water atomization. The primary powder 1 produced by water atomization has excellent productivity and excellent moldability during press molding. The primary powder 1 may also be produced by gas atomization, melt spinning, rotating electrode, reduction, or other known methods.

[0078] [Secondary Powder] The element constituting the secondary powder 2 is at least one selected from the group consisting of C, Si, Mo, Al, W, Cu, Nb, B, and N. Secondary powder 2 may contain the same elements as those contained in the iron-based alloy constituting the main powder 1. In this case, the amount of secondary powder 2 is adjusted according to the elements contained in the iron-based alloy constituting the main powder 1 and the content ratio of those elements.

[0079] The secondary powder 2 is composed of at least one powder selected from the group consisting of a powder of a simple element, a powder of an alloy, and a powder of a compound. The secondary powder 2 may be composed only of a powder of a simple element. When the secondary powder 2 is composed only of a powder of a simple element, it may be composed of one type of powder consisting of a single simple element, or may be composed of multiple powders consisting of different simple elements. Figure 4 shows an example in which the secondary powder 2 is composed of a first powder 21, a second powder 22, and a third powder 23 each consisting of a different simple element. Specific examples of the first powder 21, the second powder 22, and the third powder 23 will be described later. For ease of understanding, in Figure 4, the first powder 21 is shown as a pentagon, the second powder 22 as a triangle, and the third powder 23 as a circle.

[0080] The auxiliary powder 2 may be composed of a powder of a single element and a powder of an alloy. The auxiliary powder 2 may be composed of a powder of a single element, a powder of an alloy, and a powder of a compound. The auxiliary powder 2 may be composed of only an alloy powder, or only a powder of a compound. The auxiliary powder 2 may be composed of an alloy powder and a powder of a compound. The alloy powder or the powder of a compound constituting the auxiliary powder 2 is composed of two or more elements selected from the group consisting of C, Si, Mo, Al, W, Cu, Nb, B, and N. The alloy powder or the powder of a compound constituting the auxiliary powder 2 may be an intermediate product in the industrial smelting process of ore, or may be a powder produced by an atomization method. The auxiliary powder 2 may be a powder of a carbide such as SiC or WC, or a powder of MoSi ２ The powder may be a silicide powder such as the above.

[0081] <<Average Particle Size of the Sub Powder>> The average particle size of the sub powder 2 is, for example, 1 μm or more and 5 μm or less. Whether the sub powder 2 is composed of a powder of a single element, a powder of an alloy, or a powder of a compound, the average particle size of the sub powder 2 is, for example, 1 μm or more and 5 μm or less. If the average particle size of the sub powder 2 is 1 μm or more, the sub powder 2 is easy to handle. If the average particle size of the sub powder 2 is 5 μm or less, press molding is easy, and it is easy to manufacture a high-density sintered part 10. The average particle size of the sub powder 2 may be 2 μm or more. The average particle size of the sub powder 2 may be 4 μm or less or 3 μm or less. The average particle size of the sub powder 2 may be 1 μm or more and 4 μm or less, or 2 μm or more and 4 μm or less. The average particle size of the various powders that make up the sub powder 2 is the particle size at which the cumulative volume in the volumetric particle size distribution measured by a laser diffraction particle size analyzer becomes 50%.

[0082] <Step B> In step B, the primary powder 1 and the secondary powder 2 are mixed to prepare a mixed powder 3 (S3 in FIG. 5).

[0083] The content of the auxiliary powder 2 relative to the mixed powder 3 is, for example, 0.1 mass% or more and 10.0 mass% or less. If the content of the auxiliary powder 2 relative to the mixed powder 3 is 0.1 mass% or more, the strength of the sintered part 10 to be manufactured is easily improved. If the content of the auxiliary powder 2 relative to the mixed powder 3 is 10.0 mass% or less, the content of the main powder 1 in the mixed powder 3 is relatively high, making it easier to press-form the mixed powder 3. The content of the auxiliary powder 2 relative to the mixed powder 3 may be 0.3 mass% or more and 10.0 mass% or less, 0.3 mass% or more and 5.0 mass% or less, or 1.0 mass% or more and 3.0 mass% or less. The content of the auxiliary powder 2 relative to the mixed powder 3 may be 3.0 mass% or more and 5.0 mass% or less.

[0084] As described above, the auxiliary powder 2 may contain the same elements as those contained in the iron-based alloy that constitutes the main powder 1. In this case, the auxiliary powder 2 is adjusted according to the elements contained in the iron-based alloy that constitutes the main powder 1 and the content ratio of those elements. The content ratio of the auxiliary powder 2 relative to the mixed powder 3 may be selected appropriately depending on the combination of powders that constitute the auxiliary powder 2. An example of the content ratio of each element that constitutes the auxiliary powder 2 will be described below.

[0085] When the elements constituting the auxiliary powder 2 include carbon, the carbon content relative to the mixed powder 3 is, for example, 0.1% by mass or more and 2.0% by mass or less. A carbon content of 0.1% by mass or more facilitates the improvement of the strength of the sintered part 10 produced. If the carbon content is too high, carbides are likely to be formed during sintering, potentially reducing the corrosion resistance of the sintered part 10. If large carbides are formed, the strength of the sintered part 10 may also be reduced. A carbon content of 2.0% by mass or less improves the strength of the sintered part 10 while minimizing the reduction in corrosion resistance. The carbon content relative to the mixed powder 3 may be 0.2% by mass or more and 0.5% by mass or less. In press molding, unlike typical cast steel, the grain size and powder particle size are small, so increasing the carbon content does not result in coarsening of the grains. The precipitated carbides are also not as large as those produced by the ingot manufacturing method, allowing for a correspondingly higher carbon content.

[0086] Even if carbides are generated because the elements constituting the secondary powder 2 contain C, depending on the balance with the content ratio of other elements, NbC-based carbides, M ６ C-based carbide, M ７ C ３ carbides, or M ２３ C ６ Even if these carbides are precipitated, the sintered part 10 produced is non-magnetic.

[0087] Even if C is not contained as the auxiliary powder 2, it can be contained in the manufactured sintered part 10 by carburizing it during sintering or during an additional heat treatment after sintering, as described below. The carburizing treatment is, for example, gas carburizing. Because a press-molded body has voids, the carburizing treatment allows C to penetrate deep into the sintered part 10.

[0088] When the elements constituting the auxiliary powder 2 include Si, the Si content relative to the mixed powder 3 is, for example, 0.1 mass % or more and 3.0 mass % or less. Si is contained together with C, for example. If the Si content is 0.1 mass % or more, the strength of the sintered part 10 to be manufactured is easily improved. If the Si content is 3.0 mass % or less, the strength of the sintered part 10 can be improved and press molding is easy. The Si content relative to the mixed powder 3 may be 1.0 mass % or more and 2.0 mass % or less.

[0089] When the elements constituting the auxiliary powder 2 include Mo, the Mo content relative to the mixed powder 3 is, for example, 0.1% by mass or more and 4.0% by mass or less. Mo is contained together with, for example, C and Si. If the Mo content is 0.1% by mass or more, the strength of the sintered part 10 to be manufactured is easily improved. If the Mo content is 4.0% by mass or less, the amount of Mo used, which is expensive compared to other elements, is small, making it easy to reduce costs. The Mo content relative to the mixed powder 3 may be 2.0% by mass or more and 4.0% by mass or less.

[0090] When the content of Mo is high and the content of C is relatively high, M ７ C ３ carbides or M ２３ C ６When the content of Mo is high and the content of C is relatively low, the Laves phase or metastable phase is likely to be formed. ５ Si ３ Even if a Laves phase is produced, it is acceptable if it is a fine Laves phase.

[0091] The content ratio of the auxiliary powder 2 can be appropriately selected so that the mixed powder 3 has a specific composition. The mixed powder 3 has a composition containing, for example, 8.0 mass% to 20.0 mass% Ni, 10.0 mass% to 28.0 mass% Cr, 0.0 mass% to 4.0 mass% Mo, 0.0 mass% to 2.0 mass% Mn, 0.0 mass% to 3.0 mass% Si, 0.0 mass% to 2.0 mass% C, 0.0 mass% to 1.0 mass% Al, 0.0 mass% to 4.0 mass% W, 0.0 mass% to 3.0 mass% Cu, 0.0 mass% to 3.0 mass% Nb, 0.0 mass% to 1.0 mass% B, 0.0 mass% to 2.0 mass% N, and the remainder being iron and inevitable impurities. The composition of the mixed powder 3 and the composition of the sintered part 10 to be produced may differ depending on the sintering conditions, etc.

[0092] The auxiliary powder 2 is composed of, for example, a first powder 21 made of C, a second powder 22 made of Si, and a third powder 23 made of Mo. The auxiliary powder 2 can be appropriately selected so that the content ratio of each element relative to the mixed powder 3 falls within the above-mentioned range.

[0093] N is, for example, C ３ N ４N is contained in the form of powder. Even if N is not contained in the auxiliary powder 2, it can be contained in the sintered part 10 by solid solution diffusion into the compact 5 or sintered part 10 when an N-containing atmospheric gas is introduced during sintering or cooling. Generally, molded parts obtained by press-molding powder have many open pores, which allows nitrogen to easily penetrate into the molded part. N is not an essential element in the sintered part 10, but it can be unavoidably contained in powders produced by a general atomization method at a concentration of several hundred ppm. Due to this unavoidable N content, N may be contained in the sintered part 10. A high density of the powder before press-molding can deteriorate press moldability. A low N content is less likely to deteriorate press moldability. The N content may be 0 mass% excluding the amount unavoidably contained in at least one of the main powder 1 and the auxiliary powder 2.

[0094] The composition of the mixed powder 3 is, for example, such that the Cr equivalent and Ni equivalent in the Schaeffler phase diagram improved by Schneider satisfy all of the above-mentioned (A), (B), (C), and (D). When the composition of the mixed powder 3 satisfies all of the above-mentioned (A), (B), (C), and (D), at least one of a ferrite phase and a martensitic transformation is unlikely to occur during sintering, and the sintered part 10 produced is likely to be nonmagnetic.

[0095] <<Step C>> In step C, the mixed powder 3 is press-molded (S4 in FIG. 5 ). The press-molding is performed using a die 4. The mixed powder 3 is filled into a cavity formed in the die 4 and pressurized. When the mixed powder 3 is press-molded, a compact 5 corresponding to the shape of the cavity is produced. Because the main powder 1 is made of a relatively soft iron-based alloy, even a compact 5 with a complex shape can be press-molded.

[0096] The press molding can be performed so that the relative density of the compact 5 is 85% or more. If the press molding is performed so that the relative density of the compact 5 is 85% or more, the produced sintered part 10 will have a high density. Because the main powder 1 is made of a relatively soft iron-based alloy, the press molding can be performed so that the relative density of the compact 5 is 85% or more. The press molding may also be performed so that the relative density of the compact 5 is 90% or more, 93% or more, 95% or more, or 97% or more. The relative density of the compact 5 is calculated by (apparent density of the compact 5 / true density of the compact 5) × 100. The apparent density of the compact 5 is calculated in accordance with Archimedes' method. Specifically, the mass of the compact 5 in air and in pure water is measured, and the apparent density of the compact 5 is calculated by "(density of pure water × mass in air) / (mass in air - mass in pure water)." The true density of the compact 5 can be calculated by, for example, performing a component analysis of the compact 5 by inductively coupled plasma optical emission spectroscopy (ICP-OES) or the like to determine the content ratio of each element, and then using this content ratio, the density of each element, and the mass of the compact 5. Here, the true density of the compact 5 can be determined from the basic composition of the mixed powder 3.

[0097] A lubricant (not shown) may be added to the mixed powder 3. The lubricant serves to ensure lubrication between the mold 4 and the mixed powder 3 during press molding. The lubricant improves moldability and makes it easier to increase the density of the compact 5. Known lubricants used in press molding can be used. For example, metal soaps such as lithium stearate or zinc stearate, and amides such as ethylene bisstearamide can be used as lubricants. The lubricant evaporates during sintering, as described below, and therefore does not substantially remain in the manufactured sintered part 10. The lubricant may be applied to the mold 4.

[0098] <<Step D>> In step D, the press-molded compact 5 is sintered to obtain a sintered body (S5 in FIG. 5). FIG. 4 shows an example in which the compact 5 is sintered in a furnace 6. Sintering improves the bonding strength between the powders. During sintering, the constituent elements of the auxiliary powder 2 diffuse, and the iron-based alloy of the main powder 1 and the constituent elements of the auxiliary powder 2 are alloyed. A sintered part 10 obtained in step D is shown in FIG. 1.

[0099] During sintering, the compact 5 is heated at a temperature not exceeding the melting point of the alloy constituting the sintered part 10, for example, at a temperature of 1000°C or higher and 1300°C or lower. A sintering temperature of 1000°C or higher can improve the bonding strength between the powders. A sintering temperature of 1000°C or higher facilitates diffusion of the constituent elements of the auxiliary powder 2, facilitating alloying between the iron-based alloy of the main powder 1 and the constituent elements of the auxiliary powder 2. A sintering temperature of 1300°C or lower makes it difficult for the compact 5 to shrink during sintering. The sintering temperature may be 1100°C or higher and 1300°C or lower, or 1200°C or higher and 1300°C or lower. Sintering may be performed by batch processing, in which a predetermined amount of compacts 5 is heated at once in a furnace 6. In the case of batch processing, the sintering holding time is, for example, 1 hour to 10 hours or lower, or 1 hour to 5 hours or lower. The sintering atmosphere may be, for example, a vacuum, nitrogen gas, hydrogen gas, or argon gas. The sintering may be a continuous process in which the compact 5 is continuously heated.

[0100] During sintering, the compact 5 may be heated in an atmospheric gas containing nitrogen (N) introduced into the sintering furnace. Heating the compact 5 in an atmospheric gas containing N can result in N dissolving in the composition of the compact 5. The N dissolving tends to increase the strength of the sintered part 10 obtained after sintering. The N solubility limit basically depends on the Cr content. However, the amount of N dissolved can be adjusted by changing heating conditions such as the sintering temperature, sintering holding time, and atmospheric gas.

[0101] <<Step E>> Although not shown in Fig. 4, step E may be performed after step D. In step E, the sintered part 10 is cooled at a cooling rate of 10°C / sec or more (S6 in Fig. 6), and then heat-treated at a temperature of 400°C to 1000°C (S7 in Fig. 6). Steps S1 to S5 in Fig. 6 are the same as steps S1 to S5 in Fig. 5.

[0102] Cooling the sintered part 10 at a cooling rate of 5°C / sec or more makes it less likely to transform into bcc. The cooling rate may be 10°C / sec or more. However, the cooling rate should preferably be, for example, 20°C / sec or less. Rapid cooling within the cooling rate range of 5°C / sec or more and 20°C / sec or less makes it easier for the iron-based alloy alloyed during sintering to become uniform. Cooling methods include, for example, gas cooling, water cooling, and oil cooling.

[0103] During cooling, an atmospheric gas containing N may be introduced into a cooling vessel to cool the sintered part 10. When the sintered part 10 is cooled in an atmospheric gas containing N, N can dissolve in the composition of the sintered part 10. The dissolution of N tends to increase the strength of the sintered part 10 obtained after cooling and heat treatment.

[0104] After cooling, heat treatment at a temperature of 400°C to 1000°C precipitates specific elements, further improving the strength of the sintered part 10. The holding time for the heat treatment is, for example, 4 hours to 100 hours, or 4 hours to 10 hours. The sintered part 10 obtained in step E is shown in Figure 2. The black circles in Figure 2 indicate the precipitate phase 11.

[0105] The sintered part 10 is produced by the above-described method for producing a sintered part. In other words, the above-described method for producing a sintered part involves performing steps A, B, C, and D to produce the above-described sintered part 10. Because the primary powder 1 has a specific composition and is made of a relatively soft iron-based alloy, the mixed powder 3 containing this primary powder 1 can be press-molded. The sintered part 10 produced by press-molding can have a complex shape. For ease of explanation, the drawings show the sintered part 10 as a simple rectangular, schematic, two-dimensional shape; however, the sintered part 10 can be produced in any three-dimensional shape that can be press-molded.

[0106] [Test Example] Sintered parts made of iron-based alloys were produced and the sintered parts were evaluated.

[0107] <Description of Samples> A mixed powder of the primary powder and the secondary powder was press-molded to produce a green body, and the green body was sintered to produce sintered parts of Samples No. 1 to No. 58 and Samples No. 101 to No. 123.

[0108] First, for each sample, the prepared main powder and auxiliary powder were mixed to produce a mixed powder. The compositions of the main powder and auxiliary powder were selected so that the sintered part would have the composition shown in Figures 7 to 9. In Figures 7 to 9, elements in the column labeled "Main Powder" are contained only in the main powder, elements in the column labeled "Main Powder / Auxiliary Powder" are contained in at least one of the main powder and auxiliary powder, and elements in the column labeled "Auxiliary Powder" are contained only in the auxiliary powder. In Figures 7 to 9, elements in the column labeled "As Sintered" are contained in the atmosphere during sintering. The composition of the sintered part is composed of elements contained in the main powder, elements contained in the auxiliary powder, and elements contained in the atmosphere during sintering. The numerical values ​​of the compositions shown in Figures 7 to 9 are rounded to one decimal place.

[0109] In Samples No. 103, 104, 105, and 109, the content of a specific element in the primary powder was higher than in the other samples. In Samples No. 120 to 123, no secondary powder was used. That is, the Si and Mo contained in the sintered parts of Samples No. 120 to 123 were contained in the primary powder. In Samples No. 1 to 58, the Vickers hardness of the primary powder was 200 HV or less.

[0110] The prepared mixed powder was press-molded to prepare a cylindrical compact having a diameter of 11 mm and a height of 20 mm. The press-molding load was 8 ton / cm. ２ (784 MPa).

[0111] The prepared compacts were dewaxed at 500°C for 1 hour and then sintered. The sintering temperatures were as shown in Figures 10 to 12. The sintering holding time was 1 hour for all samples. For Samples No. 1 to 58, Samples No. 101 to 110, Samples No. 112 to 114, and Samples No. 121 to 123, a nitrogen-containing atmosphere gas was introduced into the sintering furnace to sinter the compacts. Due to the nitrogen in the atmosphere gas during sintering, the produced sintered parts contained nitrogen in the proportions shown in Figures 7 to 9. For Samples No. 111 and Samples No. 115 to 120, an Ar (argon)-containing atmosphere gas was introduced into the sintering furnace to sinter the compacts. That is, for Samples No. 111 and Samples No. 115 to 120, an Ar (argon)-containing atmosphere gas was introduced into the sintering furnace to sinter the compacts. In No. 120, N was intentionally not included, and the nitrogen content in the composition of the sintered part obtained after sintering was 0.0 mass %. Figures 10 to 12 also show the sintered density.

[0112] <Composition of Sintered Parts> The composition of each sample was measured using an ICP (Inductively Coupled Plasma) optical emission spectrometer, a carbon / sulfur analyzer, and an oxygen / nitrogen analyzer. The ICP optical emission spectrometer used was an ICPS-8100 manufactured by Shimadzu Corporation. The carbon / sulfur analyzer used was a CS-744 manufactured by LECO Corporation. The oxygen / nitrogen analyzer used was an EMGA-920 manufactured by Horiba, Ltd. In addition, the Cr equivalent and Ni equivalent of the Schaeffler phase diagram improved by Schneider were calculated for each sample. In Figures 7 to 9, columns (A), (B), (C), and (D) represent values ​​calculated using the following formulas. The values ​​(A), (B), (C), and (D) shown in Figures 7 to 9 were calculated using the measured composition values ​​of the sintered parts before rounding. (A) Cr equivalent (mass%) = Cr + 2Si + 1.5Mo + 5V + 5.5Al + 1.75Nb + 1.5Ti + 0.75W (B) Ni equivalent (mass%) = Ni + Co + 0.5Mn + 0.3Cu + 30C + 25N (C) Ni equivalent + 0.80 x Cr equivalent - 25.33 (D) Ni equivalent - 1.44 x Cr equivalent + 14.52

[0113] <Rockwell Hardness> The Rockwell hardness of each sample was measured using an electric digital Rockwell hardness tester ARD-A, scale B, manufactured by Akashi Seisakusho Co., Ltd. The results are shown in Figs. 13 to 15.

[0114] <0.2% Yield Strength> The 0.2% yield strength of each sample was measured in accordance with JIS Z 2241:2022. A 100 kNN tensile tester manufactured by Tokyo Koki Testing Instruments Co., Ltd. was used. The test was carried out at a crosshead displacement rate of 0.5 mm / min. The results are shown in Figs. 13 to 15.

[0115] <Relative Permeability> The relative permeability of each sample was measured using a vibrating sample magnetometer VSM-5 manufactured by Toei Scientific Industry Co., Ltd. The results are shown in Figs.

[0116] Samples No. 1 to No. 58 had a Rockwell hardness of 71 HRB or more, a 0.2% proof stress of 300 MPa or more, and a relative magnetic permeability of 1.02 or less. Because Samples No. 1 to No. 58 contain auxiliary powders composed of specific elements in the mixed powder, the specific elements diffuse and are alloyed with the iron-based alloy during sintering, resulting in sintered parts with a specific composition, and a Rockwell hardness of 71 HRB or more and a 0.2% proof stress of 300 MPa or more. Because Samples No. 1 to No. 58 have a specific composition, the above (A), (B), (C), and (D) calculated from the Schaeffler phase diagram improved by Schneider satisfy specific ranges, which is believed to be why they are nonmagnetic. Samples No. 1 to No. 58 Samples No. 1 to No. 58 were manufactured by a method in which a main powder of a specific composition was used to press a compact to produce a sintered part with a specific composition, and then the compact was sintered. Therefore, it is believed that Samples No. 1 to No. 58 can be pressed into complex shapes while maintaining high strength.

[0117] REFERENCE SIGNS LIST 1 Primary powder 2 Secondary powder 21 First powder 22 Second powder 23 Third powder 3 Mixed powder 4 Mold 5 Compact 6 Furnace 10 Sintered part 11 Precipitate phase

Claims

1. nickel in an amount of 8.0% by mass or more and 20.0% by mass or less; chromium in an amount of 10.0 mass% or more and 28.0 mass% or less; Molybdenum: 0.0% by mass or more and 4.0% by mass or less; manganese of 0.0% by mass or more and 2.0% by mass or less; silicon of 0.0 mass % or more and 3.0 mass % or less, Carbon is more than 0.0 mass% and not more than 2.0 mass%; aluminum in an amount of 0.0 mass % or more and 1.0 mass % or less; tungsten in an amount of 0.0 mass % or more and 4.0 mass % or less; Copper: 0.0% by mass or more and 3.0% by mass or less; Niobium: 0.0% by mass or more and 1.0% by mass or less; Boron: 0.0% by mass or more and 2.0% by mass or less; The composition contains more than 0.0 mass% and not more than 1.5 mass% nitrogen, with the balance being iron and unavoidable impurities; It is non-magnetic and Rockwell hardness is 71 HRB or more, A sintered part having a Cr equivalent and a Ni equivalent that satisfy all of the following (A), (B), (C), and (D): (A) Cr equivalent (mass%) = Cr+2Si+1.5Mo+5V+5.5Al+1.75Nb+1.5Ti+0.75W≧13 (B) Ni equivalent (mass%) = Ni + Co + 0.5Mn + 0.3Cu + 30C + 25N≧18 (C) Ni equivalent + 0.80 x Cr equivalent - 25.33≧0 (D) Ni equivalent - 1.44 x Cr equivalent + 14.52≧0

2. 2. The sintered part according to claim 1, wherein the 0.2% proof stress is 300 MPa or more.

3. preparing a primary powder and a secondary powder; mixing the primary powder and the secondary powder to prepare a mixed powder; a step of press-molding the mixed powder to produce a molded body; and sintering the compact. The main powder is nickel in an amount of 8.0% by mass or more and 20.0% by mass or less; chromium in an amount of 10.0 mass% or more and 28.0 mass% or less; Molybdenum: 0.0% by mass or more and 4.0% by mass or less; manganese of 0.0% by mass or more and 2.0% by mass or less; tungsten in an amount of 0.0 mass % or more and 4.0 mass % or less; silicon of 0.0 mass % or more and 3.0 mass % or less, Copper: 0.0% by mass or more and 3.0% by mass or less; The composition contains 0.0 mass% or more and 1.0 mass% or less of niobium, with the balance being iron and inevitable impurities, The element constituting the secondary powder is at least one selected from the group consisting of carbon, silicon, molybdenum, aluminum, tungsten, copper, niobium, boron, and nitrogen. Manufacturing methods for sintered parts.

4. 4. The method for producing a sintered part according to claim 3, wherein the mixed powder has a composition in which the Cr equivalent and Ni equivalent satisfy all of the following (A), (B), (C), and (D): (A) Cr equivalent (mass%) = Cr+2Si+1.5Mo+5V+5.5Al+1.75Nb+1.5Ti+0.75W≧13 (B) Ni equivalent (mass%) = Ni + Co + 0.5Mn + 0.3Cu + 30C + 25N≧18 (C) Ni equivalent + 0.80 x Cr equivalent - 25.33≧0 (D) Ni equivalent - 1.44 x Cr equivalent + 14.52≧0

5. 5. The method for producing a sintered part according to claim 3, wherein the main powder has a Vickers hardness of 200 HV or less.

6. The mixed powder is nickel in an amount of 8.0% by mass or more and 20.0% by mass or less; chromium in an amount of 10.0 mass% or more and 28.0 mass% or less; Molybdenum: 0.0% by mass or more and 4.0% by mass or less; manganese of 0.0% by mass or more and 2.0% by mass or less; silicon of 0.0 mass % or more and 3.0 mass % or less, Carbon is 0.0 mass % or more and 2.0 mass % or less, aluminum in an amount of 0.0 mass % or more and 1.0 mass % or less; tungsten in an amount of 0.0 mass % or more and 4.0 mass % or less; Copper: 0.0% by mass or more and 3.0% by mass or less; Niobium: 0.0% by mass or more and 1.0% by mass or less; Boron: 0.0% by mass or more and 2.0% by mass or less; The composition contains 0.0 mass % or more and 1.5 mass % or less of nitrogen, with the balance being iron and unavoidable impurities, 5. The method for producing a sintered part according to claim 3 or claim 4, wherein the composition contains more than 0.0% by weight of at least one element selected from the group consisting of molybdenum, silicon, carbon, aluminum, tungsten, copper, niobium, boron and nitrogen.

7. A method for producing a sintered part according to claim 3 or 4, which produces the sintered part according to claim 1 or 2.

8. The elements constituting the secondary powder include carbon, 5. The method for producing a sintered part according to claim 3, wherein in the step of preparing the mixed powder, the primary powder and the secondary powder are mixed together so that a carbon content in the mixed powder is 0.1% by mass or more and 2.0% by mass or less.

9. The elements constituting the secondary powder include silicon, 5. The method for producing a sintered part according to claim 3, wherein in the step of preparing the mixed powder, the primary powder and the secondary powder are mixed together so that a silicon content in the mixed powder is 0.1% by mass or more and 3.0% by mass or less.

10. The elements constituting the secondary powder include molybdenum, 5. The method for producing a sintered part according to claim 3, wherein in the step of preparing the mixed powder, the primary powder and the secondary powder are mixed together so that a molybdenum content in the mixed powder is 0.1% by mass or more and 4.0% by mass or less.

11. 5. The method for producing a sintered part according to claim 3, wherein in the step of preparing the primary powder and the secondary powder, the primary powder is prepared by a water atomization method.

12. 5. The method for producing a sintered part according to claim 3, wherein in the step of producing the compact, the relative density of the compact is set to 85% or more.

13. 5. The method for producing a sintered part according to claim 3, wherein the step of sintering the compact comprises heating the compact at a temperature of 1000°C or higher and 1300°C or lower.

14. 14. The method for producing a sintered part according to claim 13, further comprising the steps of cooling the sintered body obtained by sintering the compact at a cooling rate of 5°C / sec or more, and then heat treating the sintered body at a temperature of 400°C or more and 1000°C or less after cooling.

15. 5. The method for producing a sintered part according to claim 3, wherein in the step of sintering the compact, the compact is heated by introducing a nitrogen-containing atmospheric gas into a sintering furnace.