Method for producing high-strength, high-thermal-conductivity iron-based alloy laminated molded body

Abstract

To provide a method for producing a high-strength, high-thermal-conductivity iron-based alloy laminated molded body capable of obtaining a laminated molded body difficult to be cracked due to small residual stress.SOLUTION: A method for producing a high-strength and high-thermal-conductivity iron-based alloy laminated molded body by a laser powder bed fusion method, wherein the Ms point is more than 220°C, using an iron-based alloy powder containing 0.40 mass% or less of C, 7 mass% or less of Cr, and 90 mass% or more of Fe, and when the area energy density EA is defined as EA=P / (v σ), the laminated molded body is fabricated at P (laser power (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)) such that the area energy density EA is 3 J / mm2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a high-strength, high-thermal-conductivity iron-based alloy additive manufacturing product. [Background technology]

[0002] Conventionally, additive manufacturing methods have been proposed. For example, Patent Document 1 discloses an additive manufacturing method for obtaining a three-dimensional object by laminating a plurality of solidified layers, the method comprising: a material layer forming step of forming a material layer in a modeling region where a desired three-dimensional object is to be formed; and a solidification step of scanning a laser beam or an electron beam in a predetermined scanning direction to irradiate a predetermined irradiation region of the material layer with the laser beam or the electron beam to form a solidified layer, the method being repeated for each divided layer obtained by dividing the three-dimensional object into a predetermined thickness; and a stress control layer, which is one or more of the plurality of solidified layers, is a layer that is formed by laminating a plurality of solidified layers in a region where a compressive stress is applied. The present invention describes an additive manufacturing method in which the laser beam or the electron beam is scanned over the compressive stress-applying portion in a scanning direction different from that of the non-compressive stress-applying portion, such that the compressive stress-applying portion expands more than the non-compressive stress-applying portion, or the non-compressive stress-applying portion shrinks more than the compressive stress-applying portion, based on the relationship between the scanning direction and the amount of expansion or contraction during temperature change or heat treatment. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7096405 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention provides a method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing product, which can produce an additive manufacturing product that is less likely to crack due to low residual stress. [Means for solving the problem]

[0005] The present invention includes the following (1) to (6). (1) A method for manufacturing a high-strength, high-thermal-conductivity iron-based alloy additive manufacturing object by laser powder bed fusion, An iron-based alloy powder having an Ms point of more than 220°C and containing 0.40 mass% or less of C, 7 mass% or less of Cr, and 90 mass% or more of Fe is used, When the energy density per area is defined as EA = P / (v σ), the energy density per area EA is 3 J / mm 2 This is a method for manufacturing high-strength, high-thermal conductivity iron-based alloy additive manufacturing objects using the above P (laser output (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)). (2) The method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing product according to (1) above, further comprising using the iron-based alloy powder containing at least one of the following compositions or satisfying formula (1): Si content is 0.5% by mass or less, Mn content is 1.0% by mass or less, Ni content is 3% by mass or less, V content is 0.7% by mass or less, Mo+0.5W≦4.0mass%: Formula (1) (3) Energy density per area EA is 3 to 6 J / mm 2 The method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing object according to (1) above is performed by setting P (laser output (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)) such that: (4) When the energy density per volume EV is defined as P / (v w t), the energy density per volume EV is 70 J / mm 3 This is a method for producing a high-strength, high-thermal conductivity iron-based alloy layered shaped product according to any one of (1) to (3) above, in which the product is shaped with the above-mentioned P (laser output (W)), v (scanning speed (mm / s)), w (hatching width (mm)), and t (layer thickness (mm)). (5) When the energy density per volume EV is defined as P / (v w t), the energy density per volume EV is 90 to 150 J / mm3 The method for producing a high-strength, high-thermal conductivity iron-based alloy layered shaped product according to any one of (1) to (4) above, is performed by forming the product at P (laser output (W)), v (scanning speed (mm / s)), w (hatching width (mm)), and t (layer thickness (mm)) such that: (6) A method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing object according to any one of (1) to (5) above, in which the manufacturing is carried out in an Ar atmosphere. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing product, which can produce an additive manufacturing product that is less likely to crack due to low residual stress. [Brief explanation of the drawings]

[0007] [Figure 1] 1A to 1C are schematic diagrams showing the appearance of layered manufactured bodies obtained in Examples and Comparative Examples. [Figure 2] 10 is a photograph of the metal structure of the layered manufactured body obtained in Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will now be described. The present invention is a method for manufacturing high-strength, high-thermal-conductivity iron-based alloy additive manufacturing products using a laser powder bed fusion method. The method uses an iron-based alloy powder with an Ms point above 220°C and containing 0.40 mass% or less of C, 7 mass% or less of Cr, and 90 mass% or more of Fe, and the energy density per area EA is defined as EA = P / (v·σ), and the energy density per area EA is 3 J / mm 2 This is a manufacturing method for high-strength, high-thermal conductivity iron-based alloy additive manufacturing objects, which are created using the above P (laser output (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)). This method of manufacturing a high-strength, high-thermal-conductivity iron-based alloy additive manufacturing product is also referred to below as the "manufacturing method of the present invention."

[0009] In addition, the iron-based alloy powder used in the manufacturing method of the present invention, having a Ms point exceeding 220°C and containing 0.40 mass% or less of C, 7 mass% or less of Cr, and 90 mass% or more of Fe, is also referred to as "the alloy powder of the present invention" hereinafter.

[0010] First, the alloy powder of the present invention will be described.

[0011] The Ms point of the alloy powder of the present invention exceeds 220°C. The higher the Ms point of the alloy powder used as a material, the easier it is for martensite transformation to occur in the shaped body within the additive manufacturing process. On the other hand, when the Ms point is low, the amount of retained austenite in the shaped object increases, and the thermal conductivity decreases. Since the preheating temperature in a general additive manufacturing apparatus is at most 200°C, the Ms point needs to exceed that temperature, i.e., exceed 220°C, in order to promote martensite transformation during additive manufacturing. Preferably, it may be 250°C or higher. However, since retained austenite also contributes to crack suppression, the Ms point may preferably be 370°C or lower, and more preferably 330°C or lower.

[0012] Note that the Ms point is taken as the value calculated using the following regression equation. Ms (°C) = 550 - 361×(%C) - 39×(%Mn) - 35×(%V) - 17×(%Ni) - 20×(%Cr) - 10×(%Cu) - 5×(%Mo + %W) + 15×(%Co) + 30×(%Al) Here, in the formula, (%C), (%Mn), (%V), (%Ni), (%Cr), (%Cu), (%Mo + %W), (%Co), and (%Al) represent the content ratios (mass%) of the respective components of C, Mn, V, Ni, Cr, Cu, (Mo + W), Co, and Al in the alloy powder of the present invention.

[0013] <C: 0.40 mass% or less> C increases the hardness of the martensitic structure and is also an effective element for increasing the strength of the base material by forming carbides in combination with Cr, V, Mo, etc. through tempering heat treatment. However, if it is contained in a large amount in the alloy powder, the hardness of the martensitic structure in the laminated compact becomes too high, increasing the risk of cracking. Therefore, the amount of C contained in the alloy powder needs to be 0.40 mass% or less. In consideration of the strength of the laminated compact, it is preferably contained at 0.10 mass% or more.

[0014] <Cr: 7 mass% or less> Cr is effective for forming carbides in combination with C to increase the strength of the base material and further improving the corrosion resistance, so it may be contained in the alloy powder of the present invention. However, if it is contained in a large amount, excessive carbides are generated during laminated manufacturing, increasing the hardness and causing cracking, so it needs to be 7 mass% or less. The Cr content in the alloy powder of the present invention may be 1.0 mass% or more, and may be 3.0 mass% or more.

[0015] <Fe: 90 mass% or more> When the alloy powder of the present invention contains 90 mass% or more of Fe, the thermal conductivity of the laminated compact obtained by the manufacturing method of the present invention increases. The Fe content in the alloy powder of the present invention is preferably 91 mass% or more.

[0016] As described above, the alloy powder of the present invention has a Ms point exceeding 220°C and contains C of 0.40 mass% or less, Cr of 7 mass% or less, and Fe of 90 mass% or more, but may also contain the following components.

[0017] <Si: 0.5 mass% or less> Si is an element that acts as a deoxidizer, and a small amount of addition may improve the machinability, so it may be contained in the alloy powder of the present invention. However, if it is contained in a large amount, it reduces the thermal conductivity and deteriorates the toughness, causing cracking, so it is preferably 0.5 mass% or less. The Si content in the alloy powder of the present invention may be 0.02% by mass or more, and may be 0.05% by mass or more.

[0018] <V: 0.7% by mass or less> Since V combines with C to form carbides and is effective in increasing the strength of the base material, it may be contained in the alloy powder of the present invention. However, if it is contained in a large amount, excessive carbides are generated during additive manufacturing, increasing the hardness and causing cracking. Therefore, it is preferably 0.7% by mass or less. The V content in the alloy powder of the present invention may be 0.1% by mass or more, and may be 0.2% by mass or more.

[0019] <Mn: 1% by mass or less> Mn is an element that enhances hardenability and may be contained in the alloy powder of the present invention. However, if it is contained in a large amount, the amount of metal vapor (fume) generated when the alloy powder of the present invention is irradiated with laser light increases, causing defective forming. Therefore, the Mn content in the alloy powder of the present invention is preferably 1% by mass or less. The Mn content in the alloy powder of the present invention may be 0.1% by mass or more, and may be 0.3% by mass or more.

[0020] <Cu: 1% by mass or less> Since Cu is effective in controlling the Ms point, it may be contained in the alloy powder of the present invention. However, if it is contained in a large amount, it causes solidification cracking. Therefore, the Cu content in the alloy powder of the present invention is preferably 1% by mass or less. The Cu content in the alloy powder of the present invention may be 0.001% by mass or more, and may be 0.005% by mass or more.

[0021] <Ni: 3% or less> Ni may be contained in the alloy powder of the present invention to improve toughness. However, if it is contained in a large amount, the Ms point is excessively lowered and the thermal conductivity is also reduced. Therefore, the Ni content in the alloy powder of the present invention is preferably 3% by mass or less. The Ni content in the alloy powder of the present invention may be 0.001% by mass or more, and may be 0.005% by mass or more.

[0022] <Nb, Ta, Ti, Hf: Each 1% by mass or less> Any of these elements can combine with C to form carbides and have the effect of increasing the strength of the base material or improving the hardenability, so they may be contained in the alloy powder of the present invention. However, if contained in a large amount, coarse carbides will be formed, which may cause cracking. Therefore, the content of Nb, Ta, Ti, and Hf in the alloy powder of the present invention is preferably 1% by mass or less, respectively. The content of Nb, Ta, Ti, and Hf in the alloy powder of the present invention may be 0.001% by mass or more, and may be 0.005% by mass or more, respectively.

[0023] <Relationship of Mo + 0.5W: 4% by mass or less> Any of these elements can combine with C to form carbides and have the effect of increasing the strength of the base material or improving the hardenability, so they may be contained in the alloy powder of the present invention. However, if contained in a large amount, coarse carbides will be formed, which may cause cracking. Since the atomic weight of W is about twice that of Mo, the content of Mo and W in the alloy powder of the present invention preferably satisfies Mo + 0.5W ≤ 4% by mass. Note that only one of Mo and W may be contained. The content of Mo and W in the alloy powder of the present invention may be a content that satisfies Mo + 0.5W ≥ 0.5% by mass, and may be a content that satisfies Mo + 0.5W ≥ 0.8% by mass.

[0024] <Al: 1% by mass or less> Al is an element that raises the Ms point and may be contained in the alloy powder of the present invention for controlling the Ms point. However, if contained in a large amount, it will react with impurities O and N to form oxides and nitrides, which may cause cracking. Therefore, the content of Al in the alloy powder of the present invention is preferably 1% by mass or less. The Al content in the alloy powder of the present invention may be 0.001% by mass or more, and may be 0.005% by mass or more.

[0025] <Co: 3 mass% or less> Co is an element that raises the Ms point and may be contained in the alloy powder of the present invention for the control of the Ms point. However, if it is contained in a large amount, the thermal conductivity will decrease. Therefore, the content of Co in the alloy powder of the present invention is preferably 3 mass% or less. The Co content in the alloy powder of the present invention may be 0.001 mass% or more and may be 0.005 mass% or more.

[0026] <Other impurities> The alloy powder of the present invention may contain the components shown below in the amounts shown below. In the present invention, these components are treated as inevitable impurities. P ≦ 0.05 mass%, S ≦ 0.05 mass%, O ≦ 0.05 mass%, N ≦ 0.05 mass%, H ≦ 0.05 mass%, B ≦ 0.01 mass%, Zr ≦ 0.05 mass%, Ag ≦ 0.03 mass%, As ≦ 0.01 mass%, Ca ≦ 0.005 mass%, Sb ≦ 0.03 mass%, Se ≦ 0.03 mass%, Sn ≦ 0.03 mass%, Te ≦ 0.005 mass%, Bi ≦ 0.01 mass%, Pb ≦ 0.03 mass%, Mg ≦ 0.02 mass%, Hg ≦ 0.01 mass%, Cd ≦ 0.01 mass%, REM ≦ 0.01 mass%.

[0027] The alloy powder of the present invention may be mixed with powders having an increased carbon, nitrogen, or oxygen concentration by surface treatment, a plurality of alloy powders having different components, pure metal powders, semi-metal powders, oxide powders, nitride powders, carbide powders, boride powders, silicide powders, organic powders, and carbon powders, etc. However, the content of each component of the above mixed powder is preferably within the scope of the present invention.

[0028] Other aspects of the alloy powder of the present invention may be the same as those of conventionally known materials in the additive manufacturing method. For example, the average particle size D50 may be 20 to 50 μm.

[0029] In the manufacturing method of the present invention, an additive manufacturing object is produced by laser powder bed fusion (L-PBF) using the alloy powder of the present invention as described above. For example, a material layer made of the alloy powder of the present invention as described above is formed in a manufacturing area, and a laser beam is scanned to irradiate predetermined positions of the material layer, thereby sintering or melting the material layer to form a solidified layer. By repeating the formation of material layers and solidified layers, the solidified layers are stacked to produce a high-strength, high-thermal conductivity iron-based alloy additive manufacturing object, which is the desired three-dimensional object.

[0030] In the manufacturing method of the present invention, a conventionally known additive manufacturing apparatus used for additive manufacturing by laser powder bed fusion (L-PBF) can be used. Such an additive manufacturing apparatus includes a chamber, a material layer forming device, and an irradiation device.

[0031] The chamber covers a build area where a desired three-dimensional object is formed. An inert gas of a predetermined concentration is supplied to the chamber from an inert gas supply device. The inert gas is preferably a gas that does not substantially react with the material layer or the solidified layer, and N2 gas, Ar gas, He gas, etc. may be used.

[0032] In the manufacturing method of the present invention, it is preferable to use Ar gas and perform shaping in an Ar atmosphere. Through extensive research, the inventors have found that when manufacturing in an Ar atmosphere, residual stress in high-strength, high-thermal conductivity iron-based alloy additive manufacturing products obtained by the manufacturing method of the present invention is reduced. This is thought to be because Ar gas has a lower thermal conductivity than N2 gas, and the use of Ar gas reduces the cooling rate of the additive manufacturing product during additive manufacturing.

[0033] A window for transmitting laser light is provided on the top surface of the chamber and is made of a material that allows laser light to pass through.

[0034] The material layer forming device is provided inside the chamber and includes a base having a build region and a recoater head disposed on the base, the recoater head being configured to be reciprocally movable in a horizontal axis direction by a recoater head drive device. The recoater head includes a material storage section, a material supply port, and a material discharge port. The material supply port is provided at the top of the material storage section and serves as a receiving port for the alloy powder of the present invention supplied from the material supply unit to the material storage section. The material discharge port is provided at the bottom of the material storage section and discharges the alloy powder of the present invention from the material storage section. The material discharge port preferably has a slit shape extending in the longitudinal direction of the material storage section. Blades are provided on both side surfaces of the recoater head. The blades flatten the alloy powder of the present invention discharged from the material discharge port to form a material layer.

[0035] The modeling area is located above a modeling table, and a desired three-dimensional object is formed in the modeling area. The modeling table is driven by a modeling table drive device and is movable in the vertical direction. During modeling, it is preferable that a base plate be placed on the modeling table, and a first material layer be formed on the base plate.

[0036] In the manufacturing method of the present invention, it is preferable to preheat the base plate. Specifically, it is preferable to preheat the base plate to 120 to 200°C, and more preferably to about 200°C. Preheating the base plate tends to reduce cracking in the high-strength, high-thermal conductivity iron-based alloy additive manufacturing product obtained by the manufacturing method of the present invention.

[0037] The irradiation device is provided above the chamber and irradiates an irradiation area of ​​the material layer formed in the building region with laser light in accordance with preset irradiation conditions, thereby melting or sintering the alloy powder of the present invention present at the irradiated position and solidifying it.

[0038] The irradiation conditions include the intensity of the laser light, the size of the spot diameter, the scanning speed, the thickness of the division layer, and the like. The irradiation area exists within the modeling area and roughly coincides with an area surrounded by the outline shape of the three-dimensional model in a predetermined divided layer. The irradiation device includes a light source, a collimator, a focus control unit, and a scanning device.

[0039] The light source generates laser light, and the laser light may be, for example, a fiber laser, a CO2 laser, or a YAG laser, as long as it can sinter or melt the alloy powder of the present invention. The collimator includes a collimator lens and converts the laser light output from the light source into parallel light. The focus control unit includes a focus control lens and a motor that moves the focus control lens back and forth along the optical axis direction, and adjusts the beam diameter, i.e., spot diameter, of the laser light on the surface of the material layer by adjusting the focal position of the laser light converted into parallel light by the collimator. The scanning device is, for example, a galvanometer scanner, and includes an X-axis galvanometer mirror, a Y-axis galvanometer mirror, and an X-axis actuator and a Y-axis actuator that rotate the X-axis galvanometer mirror and the Y-axis galvanometer mirror to desired angles, respectively. The laser light that passes through the focus control unit is two-dimensionally scanned onto the upper surface of the material layer in the modeling area by the X-axis galvanometer mirror and the Y-axis galvanometer mirror. Here, the X-axis direction and the Y-axis direction are horizontal directions that are perpendicular to each other.

[0040] The control device of such an additive manufacturing device controls the material layer forming device, irradiation device, etc. in accordance with the project file, and additive manufacturing is performed. The project file is created, for example, by a CAM (Computer Aided Manufacturing) device and sent to the control device via a communication line or storage medium. The control device and CAM device are configured by any combination of hardware such as a CPU, RAM, ROM, auxiliary storage device, and input / output interface, and software. The project file may include instructions for laser light scanning patterns such as island patterns and stripe patterns.

[0041] In the manufacturing method of the present invention, when the energy density per area EA is defined as EA = P / (v·σ), for example, using the conventionally known additive manufacturing device as described above, the energy density per area EA is 3 J / mm 2 The model is created using the above P (laser output (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)).

[0042] In the additive manufacturing process of iron-based alloy powder, martensitic transformation occurs in the manufactured object during additive manufacturing. The inventors have discovered that if additive manufacturing is repeated under conditions of high energy density per area, this martensitic structure is tempered during manufacturing, reducing residual stress and making it possible to obtain an additive manufactured object that is less likely to crack. 2 The present inventors have found that an energy density per area EA of at least 1000 kJ / cm is required. However, an excessive increase in the energy density per area can promote the generation of defects inside the object or increase the surface roughness of the object, causing cracks. 2 It is preferable to set it as follows: Energy density per area EA is 3 to 6 J / mm 2 It is more preferable to perform shaping with P (laser output (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)) such that:

[0043] In the manufacturing method of the present invention, when the energy density per volume EV is defined as P / (v·w·t), the energy density per volume EV is 70 J / mm 3 It is preferable to perform shaping with the above P (laser output (W)), v (scanning speed (mm / s)), w (hatching width (mm)), and t (layer thickness (mm)).

[0044] The energy density per volume EV contributes to the amount of defects in the printed object, and if it is too small or too large, the number of defects increases. When the energy density per volume is defined as EV = P / (v w t), the energy density per volume EV is 70 to 150 J / mm 3 (More preferably 90 to 150 J / mm 3It is more preferable to perform molding with P (laser output (W)), v (scanning speed (mm / s)), w (hatching width (mm)), and t (layer thickness (mm)) such that

[0045] In the manufacturing method of the present invention, P (laser output (W)), v (scanning speed (mm / s)), σ (laser spot diameter (mm)), w (hatching width (mm)), and t (lamination thickness (mm)) can be set as irradiation conditions in the irradiation device.

[0046] P (laser power (W)) is the energy density per area EA = P / (v σ) = 3 J / mm 2 The laser power may be adjusted within the range above. However, excessive laser power tends to generate metal vapor (fumes) and spatter, resulting in increased surface roughness and molding defects. Therefore, it is preferable to set it to 1000 W or less, and more preferably 500 W or less. On the other hand, if the laser power is too low, it becomes difficult to melt the powder. Therefore, it is preferable to set it to 100 W or more, and more preferably 210 W or more.

[0047] v (scanning speed (mm / s)) is the energy density per area EA = P / (v σ) = 3 J / mm 2 The scanning speed may be adjusted within a range of 1000 mm / s or more. However, if the scanning speed is too high, the melting of the powder becomes unstable, leading to an increase in surface roughness. Therefore, it is preferable to set it to 1000 mm / s or less, and more preferably 700 mm / s or less. On the other hand, if the scanning speed is too low, the molding speed will decrease and productivity will be impaired. Therefore, it is preferable to set it to 200 mm / s or more, and more preferably 300 mm / s or more.

[0048] σ (laser spot diameter (mm)) is the energy density per area EA = P / (v σ) = 3 J / mm 2 The laser spot diameter may be adjusted within the above range. If the laser spot diameter is too small or too large, it will promote the generation of spatter and lead to an increase in molding defects. Therefore, the laser spot diameter is preferably in the range of 0.05 to 0.30 mm, and more preferably 0.10 to 0.26 mm.

[0049] w (hatching width (mm)) is the energy density per volume EV = P / (v w t) of 70 J / mm 3 The hatching width may be adjusted within the range above. However, if the hatching width is too large, it will lead to an increase in molding defects. Therefore, it is preferable to set it to 0.40 mm or less, and more preferably 0.30 mm or less. On the other hand, if the hatching width is too small, the molding speed will decrease and productivity will be impaired. Therefore, it is preferable to set it to 0.05 mm or more, and more preferably 0.08 mm or more.

[0050] t (layer thickness (mm)) is the energy density per volume EV = P / (v w t) of 70 J / mm 3 The thickness may be adjusted within the range above. However, if the layer thickness is too large, it will lead to an increase in surface roughness and molding defects. Therefore, it is preferable to set it to 0.100 mm or less, and more preferably 0.070 mm or less. On the other hand, if the layer thickness is too small, the molding speed will decrease, reducing productivity, and it will be difficult to form a uniform material layer made of the alloy powder of the present invention. Therefore, it is preferable to set it to 0.030 mm or more, and more preferably 0.050 mm or more.

[0051] Furthermore, in order to reduce surface roughness, the surface layers such as the outer periphery (contour) and down skin of the layered object may be shaped by appropriately changing the irradiation conditions. [Example]

[0052] The present invention will be described with reference to examples, but the present invention is not limited to the examples described below.

[0053] In each of the examples and comparative examples, an iron-based alloy powder having the composition shown in Table 1 was used, and additive manufacturing was carried out by laser powder bed fusion under the manufacturing conditions shown in Table 2. Two types of approximately rectangular pillar-shaped additive manufactured objects were obtained for each of the Examples and Comparative Examples. The appearance of these additive manufactured objects is shown in Figure 1. Figure 1(a) is a schematic side view of the additive manufactured objects obtained in each of the Examples and Comparative Examples, and Figure 1(b) is a schematic end view. As shown in Figure 1, the additive manufactured objects obtained in each of the Examples and Comparative Examples were approximately rectangular pillar-shaped with cutouts at the ends. As shown in Figure 1(a), the additive manufactured objects obtained in the Examples and Comparative Examples had a side width of 80 mm and an end width of 15 mm. Two types were manufactured, one with a height (width in the manufacturing direction) of 25 mm and the other with a height of 35 mm. Furthermore, the cutouts in the layered objects obtained in the examples and comparative examples have a height (width in the building direction) of 10 mm and are formed from 2.5 mm to 12.5 mm from the bottom surface. As shown in Figure 1(a), the cutouts form a right-angled isosceles triangle when viewed from the side.

[0054] In each of the examples and comparative examples, the presence or absence of cracks in the notched portions of the layered manufactured bodies with heights of 25 mm and 35 mm was confirmed. The results are shown in Table 2.

[0055] Furthermore, the 25 mm high layered manufactured bodies obtained in each example were cut at any point in a direction parallel to the height direction (the end surface as shown in Figure 1(b)), and the cut surfaces were mirror-polished. After that, the metal structure of the cut surfaces was photographed using an optical microscope. A photograph of the metal structure obtained for the additive manufacturing product obtained in Example 7 is shown in Figure 2. Note that Figure 2 is a composite of consecutive photographs taken at 50x magnification using an optical microscope. After that, the image was binarized using the image processing software ImageJ, and the area ratio of the internal defects was calculated. 2 The test was carried out within the above range, and the area ratio of internal defects was measured. The results are shown in Table 2. The area ratio of internal defects is preferably 1% or less.

[0056] Furthermore, those in which no cracks occurred in the cutout portion of the 25 mm high layered molded object and in which the cutout portion of the 35 mm high layered molded object had an internal defect area ratio of 1% or less were judged to be "very good (◯)". In addition, the cutouts in the 25 mm high and 35 mm high additively molded objects did not crack, but the area rate of internal defects was over 1%. These were judged to be "good (△)." In addition, a 25 mm high additively manufactured object in which no cracks occurred only in the cutout portion and the area rate of internal defects was 1% or less was also judged to be "good (△)." Furthermore, when cracks occurred in both the cutout portion of the 25 mm high layered object and the cutout portion of the 35 mm high layered object, the object was judged to be "fail (x)". The results are shown in Table 2.

[0057] [Table 1]

[0058] [Table 2]

[0059] As shown in Table 2, in all of Examples 1 to 36 within the scope of the present invention, no cracks occurred in the notched portion of the 25 mm high layered object. On the other hand, cracks occurred in both the cutouts of the 25 mm-high and 35 mm-high additive manufacturing products obtained in Comparative Example 1. This is thought to be due to the low energy density per area EA, which resulted in excessively large residual stress. In Comparative Example 2, the energy density per area EA was 3 J / mm 2 Despite these factors, cracks occurred. This is thought to be due to the high V and Cr content, which caused the precipitation of carbides, making the molded product excessively hard, and the large amount of Si content, which reduced toughness. In Comparative Example 3, the energy density per area EA was 3 J / mm 2 Despite these factors, cracks occurred. This is presumably due to the high C content, which resulted in the martensitic structure of the molded product becoming excessively hard.

Claims

1. A method for manufacturing a high-strength, high-thermal-conductivity iron-based alloy additive manufacturing body by laser powder bed fusion, comprising: An iron-based alloy powder having an Ms point of more than 220°C and containing 0.40 mass% or less of C, 7 mass% or less of Cr, and 90 mass% or more of Fe is used, When the energy density per area EA is defined as EA = P / (v σ), the energy density per area EA is 3 J / mm 2 This is a method for manufacturing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing object, which is manufactured using the above-mentioned P (laser output (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)).

2. The method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing product according to claim 1, further comprising using the iron-based alloy powder which further contains at least one of the following compositions or satisfies formula (1): Si content is 0.5% by mass or less, Mn content is 1.0% by mass or less, Ni content is 3% by mass or less, V content is 0.7% by mass or less, Mo+0.5W≦4.0% by mass: formula (1)

3. Energy density per area EA is 3 to 6 J / mm 2 3. The method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing object according to claim 1 or 2, wherein P (laser output (W)), v (scanning speed (mm / s)), and σ (laser spot diameter (mm)) satisfy the following conditions:

4. When the energy density per volume EV is defined as P / (v w t), the energy density per volume EV is 70 J / mm 3 3. The method for producing a high-strength, high-thermal conductivity iron-based alloy layered shaped product according to claim 1 or 2, wherein the shaping is performed with the above-mentioned P (laser output (W)), v (scanning speed (mm / s)), w (hatching width (mm)), and t (layer thickness (mm)).

5. When the energy density per volume EV is defined as P / (v w t), the energy density per volume EV is 90 to 150 J / mm 3 3. The method for producing a high-strength, high-thermal conductivity iron-based alloy layered shaped product according to claim 1 or 2, wherein the shaping is performed with P (laser output (W)), v (scanning speed (mm / s)), w (hatching width (mm)), and t (layer thickness (mm)) such that

6. The method for producing a high-strength, high-thermal conductivity iron-based alloy additive manufacturing product according to claim 1 or 2, wherein the product is manufactured in an Ar atmosphere.

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