Method for manufacturing a shaped article using Fe-based alloy powder

Abstract

To provide a method for producing a molded article having excellent mechanical properties such as hardness and toughness.SOLUTION: A method for producing a molded article includes: a step of molding an article of a predetermined shape by melting and solidifying Fe-based alloy powder as raw material, which comprises, in mass%, Ni: 15.0-21.0%, Mo: 0.01-10.0%, Al: 0.01-3.00%, Co: 0.45% or less (excluding the case of Co being 0%), Ti: 0.10-6.00%, Nb: 2.0% or less (excluding the case of Nb being 0%), with the balance being Fe and inevitable impurities; a step of subjecting the molded article to a solution heating treatment at 910-1030°C; and an aging heat treatment step of treating the molded article at 450-550°C for 1.0-6.0 hours.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a manufacturing method for obtaining a shaped article using an Fe-based alloy powder suitable for processes involving rapid melting and rapid solidification, such as three-dimensional layer manufacturing methods, thermal spraying methods, laser coating methods, and build-up welding methods. In particular, it relates to a manufacturing method for obtaining a shaped article using an Fe-based alloy powder suitable for a layer manufacturing method by a powder bed method (powder bed fusion bonding method) as a raw material.

Background Art

[0002] 3D printers have started to be used for manufacturing shaped articles made of metal. This 3D printer manufactures shaped articles by a layer manufacturing method. Representative methods of the metal layer manufacturing method include a powder bed method (powder bed fusion bonding method) and a metal deposition method (directed energy deposition method). In the powder bed method, the irradiated part of the spread powder melts and solidifies by irradiation with a laser beam or an electron beam. Due to this melting and solidification, the powder particles bond to each other. The irradiation is selectively performed on a part of the metal powder, and the part where the irradiation is not performed does not melt, and a bonding layer is formed only in the part where the irradiation is performed.

[0003] On top of the formed bonding layer, new metal powder is further spread, and these metal powders are irradiated with a laser beam or an electron beam. Then, by the irradiation, the metal particles melt and solidify, and a new bonding layer is formed. Also, the new bonding layer is bonded to the existing bonding layer.

[0004] By sequentially repeating the melting and solidification by irradiation, the aggregate of the bonding layers gradually grows. By this growth, a shaped article having a three-dimensional shape is obtained. When such a layer manufacturing method is used, a shaped article having a complex shape can be easily obtained.

[0005] As a powder bed-based additive manufacturing method, a metal powder for metal photofabrication is used, which is a mixture of "iron-based powder" and "one or more powders selected from the group consisting of nickel, nickel-based alloys, copper, copper-based alloys, and graphite". A powder layer forming step of laying these metal powders, a sintered layer forming step of irradiating the powder layer with a beam to form a sintered layer, and a removal step of cutting the surface of the fabricated object are repeated to form a sintered layer, and a procedure for manufacturing a three-dimensional shaped object is disclosed (see Patent Document 1).

[0006] For alloys for structures in the aerospace field, etc., strength and fatigue resistance are required. For such applications, for example, maraging steel is suitable.

[0007] Therefore, a laminated object made of maraging steel having a main component of Fe and containing C: 0.1% or less, Ni: 14 to 22%, Co: 0 to 5%, Mo: 0.1 to 15%, Ti: 0.1 to 5%, and Al: 3% or less has been proposed (see Patent Document 2). In this invention, C is contained in the raw material powder.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] For structural materials, molds, etc. in the aerospace field, since it is required to be excellent in strength, fatigue resistance, and toughness, it is generally preferable to apply maraging steel having excellent properties in those characteristics. However, conventional maraging steels achieve high strength by precipitating intermetallic compounds such as Ni 3 Mo phase and Ni 3 Ti phase, etc.

[0010] In the fields of aerospace and space, in structural materials, molds, etc., by applying the additive manufacturing method, there are various advantages such as shortening the manufacturing time and increasing the design freedom, so 3D printers including the additive manufacturing method have begun to be used. Therefore, in the present invention, a method for manufacturing a shaped article made of maraging steel using the additive manufacturing method is considered.

[0011] In conventional maraging steel, Co has the role of reducing the solid solution amount of Mo. Even when the content of Co is small, precipitates containing Mo precipitate, but when the amount of Co is large, Mo is more likely to precipitate. As a result, many intermetallic compounds such as Ni 3 Mo phases are precipitated, so Co is contained. Thus, Co contributes to the strengthening by the formation of intermetallic compounds.

[0012] On the other hand, since Co is also an austenite stabilizing element, it may suppress the martensite transformation. When the martensite transformation is suppressed, even if heat treatment is carried out, a relatively low-strength austenite phase remains, and excellent strength cannot be obtained. Furthermore, since Co is a substance subject to the regulations on the prevention of specific chemical substance hazards, it is preferable not to contain Co.

[0013] However, when conventional heat treatment is applied to low-Co or Co-free maraging steel, a brittle phase (Laves phase) is formed, resulting in low mechanical properties, particularly toughness. Therefore, it has been difficult to obtain mechanical properties equivalent to those of a melt material containing a large amount of Co (Rockwell hardness of 51 to 55 HRC and Charpy impact value of 16.0 to 26.0 J / cm 2 level).

[0014] The inventors have found that, for Co-free maraging steel, by controlling the solution heat treatment at 910 to 1030 °C and the aging heat treatment at 450 to 550 °C with a treatment time of 1.0 to 6.0 hours, the precipitation of the Laves phase can be suppressed and the decrease in toughness can be prevented. Furthermore, when this heat treatment is performed, precipitates composed of Ti, Al, and Mo are formed, so a shaped article having high strength can be obtained. As a result, it has been found that high strength and high toughness can be achieved simultaneously, even though the steel contains no Co or only a small amount of Co (low Co).

[0015] Here, in the present invention, those with Co of 0.45% or less by mass are referred to as low Co. In order to prevent the suppression of martensitic transformation, it is desirable that the Co be low Co of 0.45% or less.

[0016] An object of the present invention is to provide a method for manufacturing a shaped article having excellent mechanical properties such as hardness and toughness by using precipitates different from the Laves phase, which is produced in a process involving rapid melting and rapid solidification, for an Fe-based alloy powder that does not contain Co or contains 0.45% or less of Co.

Means for Solving the Problems

[0017] When the temperature of the solution heat treatment is increased for maraging steel regardless of the presence or absence of Co, grain coarsening occurs, so there is concern about a decrease in strength. In maraging steel that requires high strength, in order to prevent grain coarsening, the solution heat treatment is often carried out at a temperature of 900 °C or lower. The inventors focused on the Laves phase, which is a cause of toughness reduction, for Co-free or low Co maraging steel, and found that the precipitation of the Laves phase can be suppressed by deliberately increasing the temperature of the solution heat treatment to 910 °C or higher.

[0018] In addition, since the additive manufacturing method involves different rapid solidification processes after melting, the crystal grains of the obtained shaped article are fine. Therefore, it has been found that even when the temperature of the solution heat treatment is 910 °C or higher, grain coarsening can be avoided.

[0019] Furthermore, by controlling the aging heat treatment, it has been found that it is possible to improve the strength, and that maraging steel shaped bodies containing low Co and no Co can achieve both high strength and high toughness.

[0020] Therefore, a first means for solving the problems of the present invention is, by mass%, Ni: 15.0 to 21.0%, Mo: 0.01 to 10.0%, Al: 0.01 to 3.00%, Co: 0.45% or less (however, the case where Co is 0% is included), Ti: 0.10 to 6.00%, Nb: 2.0% or less (however, the case where Nb is 0% is included), using an Fe-based alloy powder composed of the balance Fe and unavoidable impurities as a raw material, a step of melting and solidifying to form a shaped body of a predetermined shape, a step of solution heat-treating the shaped body at 910 to 1030°C, and an aging heat treatment step of treating at 450 to 550°C for 1.0 to 6.0 hours, which is a method for manufacturing a shaped body.

[0021] Its second means is, by mass%, Ni: 15.0 to 21.0%, Mo: 0.01 to 10.0%, Al: 0.01 to 3.00%, Co: 0.45% or less (however, the case where Co is 0% is included), Ti: 0.10 to 6.00%, Nb: 2.0% or less (however, the case where Nb is 0% is included), using an Fe-based alloy powder composed of the balance Fe and unavoidable impurities as a raw material, a step of melting and solidifying to form a shaped body of a predetermined shape, a step of solution heat-treating the shaped body at 910 to 1030°C for 0.5 to 5.0 hours, and an aging heat treatment step of treating at 450 to 550°C for 1.0 to 6.0 hours, It is a method for manufacturing a shaped article.

[0022] The third means is the manufacturing method according to the first or second means, wherein the step of manufacturing the shaped article is a step by a layer manufacturing method in which Fe-based alloy powder is laminated and melted and solidified.

Advantages of the Invention

[0023] By subjecting the Fe-based alloy shaped body according to the present invention to a solution heat treatment at a predetermined temperature, precipitation of the Laves phase can be suppressed. Therefore, even when the Co content is low or Co is not contained, a shaped article having high toughness can be obtained.

[0024] Furthermore, since precipitates composed of Ti, Al, and Mo are formed, a shaped article having high strength can be obtained even though the temperature of the solution treatment is high. Therefore, it is possible to obtain a shaped article having high strength and high toughness and having mechanical properties equivalent to or better than those of the melted material.

[0025] Specifically, when a shaped article is manufactured by heat treatment using the manufacturing method of the present invention, the Rockwell hardness is 50 to 60 HRC, the Charpy impact value is 16.0 to 30.0 J / cm 2 or more, and the room temperature tensile strength of 1700 MPa or more can be obtained.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0027] In the Fe-based alloy powder used for manufacturing the shaped article of the present invention, maraging steel that is Co-free or has extremely low Co content is used as a raw material. Therefore, prior to the description of the manufacturing method of the shaped article of the present invention, the reasons for defining the components and characteristics of the Fe-based alloy used for manufacturing the shaped article of the present invention will be described below. Note that % in the following component compositions is mass %.

[0028] Ni: 15.0 to 21.0%, Ni forms an intermetallic compound with Mo and Al, and is an element for obtaining a shaped article having excellent strength. From this viewpoint, Ni is preferably 15.0% or more, more preferably 16.0% or more, and particularly preferably 17.0% or more. However, since Ni is an element that forms an austenite phase, when a large amount of Ni is added, the martensitic transformation is suppressed and the formation of the martensite phase becomes difficult. From this viewpoint, the content rate of Ni is preferably 21.0% or less. More preferably, Ni is 20.0% or less. Particularly preferably, Ni is 19.5% or less.

[0029] Mo: 0.01 to 10.0%, Mo forms an intermetallic compound with Ti, Fe, and Ni, and is an element for ensuring strength. Mo is required to be 0.01% or more. From this viewpoint, the content rate of Mo is preferably 1.0% or more. However, when a large amount of Mo is added, the toughness decreases. From this viewpoint, Mo is preferably 10.0% or less. More preferably, Mo is 6.0% or less.

[0030] Al: 0.01 to 3.00%, Al forms an intermetallic compound with Ti and Ni, and is an element for obtaining a shaped article having excellent strength and oxidation resistance. From this viewpoint, the content rate of Al is set to 0.01% or more. Further, 0.1% or more is more preferable. However, when a large amount of Al is added, hot cracking is likely to occur in the rapid melting and rapid solidification process. From this viewpoint, the content rate of Al is preferably 3.0% or less. More preferably, Al is 2.5% or less.

[0031] Co: less than 0.45% (however, including the case where Co is 0%). Co is an element that forms an austenite phase. Therefore, when the content rate of Co becomes excessive, it becomes difficult to form a martensite phase. From this perspective, the content rate of Co is set to 0.45% or less. Preferably, Co is 0.30% or less. Co may not be included.

[0032] Ti: 0.10 - 6.00% Ti forms an intermetallic compound with Al and Mo and is an element for ensuring strength and oxidation resistance. From this perspective, the content rate of Ti is set to 0.10 mass% or more. Preferably, Ti is 0.50% or more. However, when a large amount of Ti is added, hot cracking is likely to occur in the rapid melting and rapid solidification process. Therefore, the content rate of Ti is set to 6.0% or less. Preferably, Ti is 4.0% or less.

[0033] Nb: 2.0% or less (however, including the case where Nb is 0) Nb is an optional additional component that may be added when ensuring strength. However, when the addition amount is large, the toughness decreases, so it is set to 2.0% or less.

[0034] D50 / TD: 0.2 - 20.0 The ratio of D50 (μm), which is the average particle diameter, to TD (Mg / m 3 ), "D50 / TD", is an index indicating the balance between the fluidity and formability of the powder. When D50 / TD is less than 0.2, the fluidity of the powder decreases due to pulverization, and the density of the formed object decreases. However, when D50 / TD is greater than 20, a part of the powder remains melted and sintered during laminated forming and remains as a defect. Therefore, it is preferable that D50 / TD is 0.2 - 20.0.

[0035] In the measurement of the average particle diameter D50, the total volume of the powder is taken as 100%, and a cumulative curve is obtained. The particle diameter at the point on this curve where the cumulative volume is 50% is the average particle diameter D50. The average particle diameter D50 is measured by the laser diffraction scattering method. As an apparatus suitable for this measurement, the laser diffraction / scattering type particle size distribution measuring apparatus "Microtrac MT3000" manufactured by Nikkiso Co., Ltd. can be mentioned. In the cell of this apparatus, the powder is flowed in together with pure water, and the particle diameter is detected based on the light scattering information of the particles.

[0036] The tap density is measured in accordance with the provisions of "JIS Z 2512". In the measurement, about 50 g of powder is filled into a cylinder with a volume of 100 cm 3 and the density is measured. The measurement conditions are as follows. Drop height: 10 mm Number of tap times: 200 times

[0037] [Particle size of Fe-based alloy powder] The average particle diameter of the Fe-based alloy powder is preferably 10 μm or more and 100 μm or less. A powder with an average particle diameter of 10 μm or more has excellent fluidity. From this viewpoint, the average particle diameter is more preferably 20 μm or more, and particularly preferably 30 μm or more. From a powder with an average particle diameter of 100 μm or less, a shaped article with a large relative density can be obtained. From this viewpoint, the average particle diameter is more preferably 80 μm or less, and particularly preferably 60 μm or less.

[0038] [Manufacturing method of Fe-based alloy powder] As manufacturing methods of the powder, water atomization method, single-roll rapid cooling method, twin-roll rapid cooling method, gas atomization method, disk atomization method, and centrifugal atomization method are exemplified. Preferred manufacturing methods are the single-roll cooling method, gas atomization method, and disk atomization method. Mechanical milling or the like may be applied to the powder. As milling methods, ball milling method, bead milling method, planetary ball milling method, attritor method, and vibration ball milling method are exemplified.

[0039] The powder used for additive manufacturing is preferably produced by gas atomization from the perspective of spheroidization. In the present invention, in the following examples, gas atomization will be taken as an example for explanation.

[0040] [Modeling] As a method for producing a shaped object, there is a rapid melting and rapid solidification process, which is a process of melting and solidifying metal powder. Specific examples of this process include three-dimensional additive manufacturing, thermal spraying, laser coating, and build-up welding. In particular, the Fe-based alloy powder of the present invention is suitable for the powder bed fusion type three-dimensional additive manufacturing method and can form a large-sized shaped object with high density.

[0041] As the three-dimensional additive manufacturing method, for example, a 3D printer can be used. In the powder bed fusion method (powder bed method) among the additive manufacturing methods, the Fe-based alloy powder of the present invention spread on the powder bed is irradiated with a laser beam or an electron beam. By the irradiation, the particles are rapidly heated and rapidly melted. The melted particles then rapidly solidify. By this melting and solidification, the particles are bonded to each other. The irradiation is selectively performed on a part of the spread Fe-based alloy powder. Among the spread powder, the part where the irradiation is not performed does not melt. A bonding layer is formed only in the part where the irradiation is performed.

[0042] On the bonding layer, the Fe-based alloy powder is further thinly spread. A part of this Fe-based alloy powder is irradiated with a laser beam or an electron beam. By the irradiation, the particles are rapidly melted. The melted particles then rapidly solidify. By this melting and solidification, the particles in the powder are bonded to each other, and a new bonding layer is formed. The new bonding layer is also bonded to the existing bonding layer.

[0043] By repeating the bonding by irradiation, the aggregate of the bonding layers gradually grows. By this growth, a shaped object having a three-dimensional shape is obtained. By this additive manufacturing method, a shaped object with a complex shape can be easily obtained.

[0044] [Sphericity] The sphericity of the powder is preferably 0.80 to 0.95. Powders with a sphericity of 0.80 or more have excellent fluidity. Therefore, the sphericity is more preferably 0.83 or more, and particularly preferably 0.85 or more. On the other hand, when the sphericity is close to 1, the reflectivity of the laser increases, so the efficiency of the laser energy in the powder decreases. Therefore, from the viewpoint of suppressing laser reflection, it is preferable that the powder has a sphericity of 0.95 or less. Therefore, the sphericity is more preferably 0.93 or less, and particularly preferably 0.90 or less.

[0045] In the measurement of sphericity, a test piece in which the powder is embedded in resin is prepared. This test piece is subjected to mirror polishing, and the polished surface is observed with an optical microscope. The magnification of the microscope is 100 times. Image analysis is performed on 20 randomly extracted particles, and the sphericity of these particles is measured. The average of the 20 measured values is the sphericity of the powder. Sphericity means the ratio of the maximum length of one powder particle to the length in the direction perpendicular to the maximum length.

[0046] [Heat treatment] For the shaped article using the Fe-based alloy powder, instead of using the as-formed non-heat-treated shaped article as it is, by passing through the steps of solution heat treatment and aging heat treatment for the non-heat-treated shaped article, a shaped article with the desired properties of the present invention can be obtained.

[0047] By controlling the solution heat treatment, the precipitation of the Laves phase is suppressed, and a supersaturated martensite structure is obtained. By controlling the aging heat treatment, intermetallic compounds containing Ti, Al, Mo, etc. are precipitated in the martensite phase. Due to these intermetallic compounds, a shaped article excellent in mechanical properties, particularly strength, can be obtained.

[0048] [Solution heat treatment] Solution heat treatment temperature: 910 - 1030 °C Treatment time: preferably 0.5 - 5.0 hours When the solution heat treatment temperature is 910 °C or higher, the precipitation of the Laves phase is suppressed. Furthermore, a martensite structure in which alloying elements are sufficiently solid-solved can be obtained. From this perspective, the solution heat treatment temperature shall be 910 °C or higher. Preferably, the solution heat treatment temperature is 950 °C or higher. However, when the temperature exceeds 1030 °C, grain coarsening becomes remarkable, resulting in a decrease in strength. Therefore, the solution heat treatment temperature is set to 910 - 1030 °C.

[0049] By reaching the above-mentioned solution heat treatment temperature, the Laves phase can be suppressed, and a martensite structure in which alloying elements are sufficiently solid-solved can be obtained. In terms of suppressing the precipitation of the Laves phase, the solution heat treatment time at the temperature of the present invention is preferably 0.5 hours or more. However, if the solution heat treatment time is too long, the grain size becomes coarsened, resulting in a decrease in strength. Therefore, the solution treatment time at 910 - 1030 °C is preferably 0.5 - 5.0 hours. More preferably, the solution treatment time is 0.5 - 4.0 hours.

[0050] [Ageing heat treatment] Treatment temperature: 450 - 440 °C Treatment time: 1.0 - 6.0 hours If the ageing heat treatment temperature is 450 °C or higher, a structure in which intermetallic compounds such as TiAl and TiMo are sufficiently precipitated can be obtained. Therefore, the ageing heat treatment temperature shall be 450 °C or higher. Preferably, it is 470 °C or higher. And in the ageing at a temperature of 550 °C or lower, the solid solution of alloying elements into the matrix phase is suppressed. Furthermore, grain coarsening is suppressed. However, when exceeding 550 °C, it becomes difficult to suppress the solid solution into the matrix phase and grain coarsening. Therefore, the ageing heat treatment temperature is set to 550 °C or lower. Preferably, it is 530 °C or lower.

[0051] When the ageing heat treatment time is 1.0 hours or more, a structure in which intermetallic compounds such as TiAl and TiMo are sufficiently precipitated can be obtained. Therefore, the treatment time shall be 1.0 hours or more. However, when the ageing heat treatment time is long, the grain size becomes coarsened, resulting in a decrease in strength. Therefore, the treatment time is set to 6.0 hours or less. Preferably, the treatment time is 5.0 hours or less.

[0052] [Physical properties of the shaped object after heat treatment] A shaped object with a Rockwell hardness of 50 HRC or more is excellent in strength. From this viewpoint, a Rockwell hardness of 50 HRC or more is preferable. And a shaped object with a Rockwell hardness of 60 HRC or less is excellent in toughness and durability. On the other hand, when the Rockwell hardness exceeds 60 HRC, there may be a problem in toughness and durability. From this viewpoint, a Rockwell hardness of 60 HRC or less is preferable.

[0053] A shaped object with a Charpy impact value of 16.0 J / cm 2 or more is excellent in toughness. Therefore, the Charpy impact value is preferably 16.0 J / cm 2 or more, and more preferably 20.0 J / cm 2 or more. On the other hand, when the Charpy impact value is large, the strength tends to decrease. From this viewpoint, the Charpy impact value is preferably 30.0 J / cm 2 or less.

[0054] A shaped object with a room temperature tensile strength of 1700 MPa or more is excellent in strength. Therefore, the room temperature tensile strength is preferably 1700 MPa or more, and more preferably 1800 MPa or more. On the other hand, when the room temperature tensile strength is large, the toughness tends to decrease. From this viewpoint, the room temperature tensile strength is preferably 2200 MPa or less.

[0055] [Relative density] The relative density of the shaped object subjected to heat treatment is preferably 90% or more. This shaped object has few defects inside the shaped object and is excellent in hardness. From this viewpoint, the relative density is more preferably 93% or more, and even more preferably 95% or more.

[0056] The relative density is calculated based on the ratio between the density of a 10 mm square test piece produced by a layered manufacturing method or the like and the bulk density of the powder as the raw material. The density of the 10 mm square test piece is measured by the Archimedes method. The bulk density of the powder is measured by a dry density measuring instrument.

[0057] In the measurement of bulk density, it is measured by the constant volume expansion method using He gas substitution. As an apparatus suitable for this measurement, the dry automatic densitometer "AccuPyc1330" manufactured by Shimadzu Corporation can be mentioned. The powder is filled in the cell of this apparatus to measure the density.

[0058] [Examples] The raw materials consisting of the chemical components described in Examples 1 to 18 and Comparative Examples 1 to 9 in Table 1 and the balance of Fe and inevitable impurities were gas atomized to obtain Fe-based alloy powders. First, in a vacuum, using an alumina crucible, the raw materials having a predetermined composition were heated by high-frequency induction heating and melted. Then, the molten metal was dropped from a nozzle with a diameter of 5 mm located under the crucible. Next, argon gas was sprayed toward this molten metal to obtain a large number of particles. These particles were classified to remove particles with a diameter exceeding 63 μm, and Fe-based alloy powders were obtained.

[0059]

Table 1

[0060]

Table 2

[0061] [Modeling] Using this powder as a raw material, by using the layer manufacturing method with a three-dimensional layer manufacturing apparatus (EOS-M280), the laying and irradiation of the powder were repeated to obtain an as-built object with a predetermined shape (for example, a cube with a side length of 10 mm).

[0062] [Heat Treatment] This as-built object was solution heat-treated under the conditions shown in Table 1. The cooling method at this time was air cooling. After the solution heat treatment, aging heat treatment was performed under the conditions shown in Table 1. The cooling method at this time was air cooling.

[0063] [Relative Density of the As-built Object] The density of the shaped object was measured by the Archimedes method. The relative density of the shaped object was calculated from the bulk density of the powder measured by a dry-type automatic densitometer "AccuPyc1330". It was confirmed that the relative density of all the shaped objects was 99% or more.

[0064] [Measurement of hardness of shaped object] A heat-treated test piece with a size of 10 mm square (10×10×10 mm) was prepared, and a load of 10 kgf, which is the basic load, was applied to the test surface with an indenter equipped with a diamond steel ball having a tip radius of 0.2 mm. Next, a load of 110 kgf, which is the test load of 100 kgf added to the basic load, was applied to the test piece to plastically deform this test piece. Next, the load was returned to the reference load of 10 kgf, and the depth of the permanent indentation from the reference surface was measured. From this depth, the Rockwell hardness HRC was calculated using a conversion formula. The measurement was performed before and after the heat treatment. The results are shown in Tables 1 and 2.

[0065] [Measurement of Charpy impact value] In order to confirm the toughness of the shaped object, a Charpy impact test with a 2 mm U-notch was carried out in accordance with JIS Z 2242 on a 2 mm V-notch test piece (10 mm square, 55 mm long), which is a JIS No. 4 test piece subjected to heat treatment. The average value of three measurements was taken as the Charpy impact value, and the results are shown in Tables 1 and 2.

[0066] [Tensile properties at room temperature] A JIS 14A No. φ5 test piece (diameter 5 mm, gauge length 25 mm) was prepared, and a tensile test was carried out in accordance with the JIS regulations. The maximum tensile stress σ (σ = measured load F / cross-sectional area S) applied during the test was taken as the tensile strength, and the results are shown in Tables 1 and 2.

[0067] [TEM observation] For the heat-treated shaped body, a thin-film sample was prepared by FIB (focused ion beam) processing. This sample was observed with a transmission electron microscope (TEM), and the composition of the precipitate was specified at 10 randomly extracted locations (one location is a region of 2 μm square). The results of Example 12 are shown in Fig. 1, and the results of Comparative Example 8 are shown in Fig. 2. In Example 12, the precipitate is a precipitate composed of Ti, Al, and Mo, whereas in Comparative Example 8, the Laves phase has precipitated.

[0068] As described above, since the shaped article manufactured by the procedure of the example of the present invention has been subjected to appropriate solution treatment and aging treatment, precipitation of the Laves phase can be suppressed, and the toughness of the shaped article is in the range of 16 to 30 J / mm 2 and is excellent. Furthermore, precipitation of an intermetallic compound composed of Ti, Al, and Mo can be confirmed, and the strength is in the range of 1700 to 2200 MPa and is excellent. Also, all of the hardness values satisfied 50 HRC or more. Thus, based on the method of the example, a shaped article having both high strength and high toughness can be obtained.

[0069] Regarding the comparative example, as also illustrated in Fig. 2, the Laves phase has precipitated, and a shaped article with high toughness could not be obtained. Thus, by performing the manufacturing method of the present invention, a shaped article excellent in strength and toughness can be obtained.

Claims

1. By mass percentage, Ni: 15.0 to 21.0%, Mo: 0.01 to 10.0%, Al: 0.01 to 3.00%, Co: 0.45% or less (however, the case where Co is 0% is included), Ti: 0.10 to 6.00%, Nb: 2.0% or less (however, the case where Nb is 0% is included), Using an Fe-based alloy powder composed of the balance Fe and unavoidable impurities as a raw material, A step of melting and solidifying to form a shaped article of a predetermined shape, A step of solution heat-treating the shaped article at 910 to 1030 °C, Including an aging heat-treatment step of treating at 450 to 550 °C for 1.0 to 6.0 hours, A method for manufacturing a shaped article.

2. By mass percentage, Ni: 15.0 to 21.0%, Mo: 0.01 to 10.0%, Al: 0.01 to 3.00%, Co: 0.45% or less (however, the case where Co is 0% is included), Ti: 0.10 to 6.00%, Nb: 2.0% or less (however, the case where Nb is 0% is included), Using an Fe-based alloy powder composed of the balance Fe and unavoidable impurities as a raw material, A step of melting and solidifying to form a shaped article of a predetermined shape, A step of solution heat-treating the shaped article at 910 to 1030 °C for 0.5 to 5.0 hours, Including an aging heat-treatment step of treating at 450 to 550 °C for 1.0 to 6.0 hours, A method for manufacturing a shaped article.

3. The manufacturing method according to claim 1 or 2, wherein the step of manufacturing the shaped article is a step by a laminated manufacturing method in which Fe-based alloy powder is laminated and melted and solidified.

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