Methods of surface-treating metal lamination-molded object and of manufacturing metal lamination-molded object, and metal lamination-molded object

Abstract

To provide a method of surface-treating a metal lamination-molded object allowing for improving the strength of a metal lamination-molded object.SOLUTION: A method of surface-treating a metal lamination-molded object containing iron- or nickel-based metal, includes: a polishing step that polishes a surface of the metal lamination-molded object and a hardening step that hardens the surface of the metal lamination-molded object, the metal lamination-molded object having a surface arithmetic average roughness of 6.5 μm or smaller.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a surface treatment method for a metal additive manufacturing product, a method for manufacturing a metal additive manufacturing product, and a metal additive manufacturing product. [Background technology]

[0002] BACKGROUND ART A known additive manufacturing method is to irradiate powder material with a laser beam or an electron beam, form a shape layer by layer, and build up the resulting structure to form a three-dimensional object.

[0003] Patent Document 1 discloses a method for manufacturing a molded object in which a material powder having a relatively low carbon content is used as the material powder to form a molded object by layered manufacturing, and then the molded object is subjected to a carburizing treatment. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-119208 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the manufacturing method described in Patent Document 1 leaves room for improvement in terms of the strength of the shaped object.

[0006] A main object of the present disclosure is to provide a surface treatment method for a metal additive manufacturing object that can improve the strength of the metal additive manufacturing object. [Means for solving the problem]

[0007] The aspects of the present disclosure that solve the above problems are as follows. [1] A surface treatment method for a metal additive manufacturing object containing an iron-based metal or a nickel-based metal, comprising: a polishing step of polishing the surface of the metal additive manufacturing object; and a hardening step of hardening the surface of the metal additive manufacturing object. The arithmetic mean roughness of the surface of the metal additive manufacturing product is 6.5 μm or less. A method for surface treatment of metal additive manufacturing objects.

[0008] [2] The surface treatment method of a metal additive manufacturing object according to [1], wherein the polishing step is carried out by a fluid polishing treatment or an electrolytic polishing treatment.

[0009] [3] The surface treatment method of a metal additive manufacturing product according to [1] or [2], wherein the hardening step is carried out by gas nitriding or gas carburizing.

[0010] [4] The surface treatment method of a metal additive manufacturing product according to [3], wherein the gas nitriding treatment or gas carburizing treatment is performed under a reduced pressure atmosphere.

[0011] [5] The surface treatment method for a metal additive manufacturing product according to any one of [1] to [4], wherein the surface hardness of the metal additive manufacturing product is 650 HV or more.

[0012] [6] A surface treatment method for a metal additive manufacturing object according to any one of [1] to [5], further comprising a halogenation treatment step of heating and holding the metal additive manufacturing object in a halogen-based gas atmosphere before the curing step.

[0013] [7] A method for manufacturing a metal additive manufacturing object containing an iron-based metal or a nickel-based metal, comprising: a polishing step of polishing the surface of the metal additive manufacturing object; a hardening step of hardening a surface of the metal additive manufacturing object, The arithmetic mean roughness of the surface of the metal additive manufacturing product is 6.5 μm or less. A method for manufacturing metal additive manufacturing objects.

[0014] [8] Contains iron-based metals or nickel-based metals, The arithmetic mean roughness of the surface is 6.5 μm or less, Surface hardness is 650HV or more Metal additive manufacturing.

[0015] [9] The metal additive manufacturing product according to [8], having a bending strength of 900 MPa or more.

[0016]

[10] A metal additive manufacturing product according to [8] or [9], which has a surface treatment layer containing nitrogen or carbon. [Effects of the Invention]

[0017] According to the present disclosure, it is possible to provide a surface treatment method for a metal additive manufacturing product that can improve the strength of the metal additive manufacturing product. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows displacement-stress curves obtained by bending tests of metal additive manufacturing objects of Examples 1 and 2 and Comparative Examples 1 and 2. [Figure 2] 10 is a cross-sectional micrograph of the metal additive manufacturing products of Example 8 and Comparative Example 8. [Figure 3] 1 is a graph showing the cross-sectional hardness distribution in the depth direction from the surface of the metal additive manufacturing objects of Examples 2 and 8 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments of the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiments. The elements listed below can be combined arbitrarily, and the scope of the present invention is intended to include all modifications within the scope of the claims and equivalents to the scope of the claims. Furthermore, in this specification, the upper and lower limit values ​​exemplified for numerical ranges can be arbitrarily combined to form new numerical ranges. For example, when "A or more and B or less" and "C or more and D or less" are described, the ranges "A or more and D or less" and "C or more and B or less" can also be included in the numerical range.

[0020] The surface treatment method of a metal additive manufacturing product according to the present disclosure includes a polishing step and a hardening step. The polishing step is a step of polishing the surface of the metal additive manufacturing product. The hardening step is a step of hardening the surface of the metal additive manufacturing product.

[0021] Although the details of why the effects of the present disclosure are achieved are unclear, it is presumed that the following mechanism is responsible. Metal materials, such as metal additive manufacturing products, generally have a tendency to become brittle and less able to adapt to deformation due to surface hardening. Furthermore, metal additive manufacturing products obtained by additive manufacturing have uneven surfaces due to lamination marks and adhesion of metal material particles. The depressions on the surface of the product have a higher stress concentration than other areas. It is presumed that when a metal additive manufacturing product with an uneven surface is subjected to a surface hardening treatment to form a treatment layer (hardened layer) on the surface of the product, stress concentration occurs in the depressions, causing localized deformation and resulting in destruction of the treatment layer and a decrease in mechanical strength. In other words, hardening the surface of an object with an uneven surface reduces mechanical strength compared to when the surface hardening treatment is not performed. In the surface treatment method for a metal additive manufacturing product of the present disclosure, a polishing process and a hardening process are performed to form a treatment layer with a smooth surface on the surface of the metal additive manufacturing product. This reduces stress concentration in recesses on the surface of the molded object and disperses deformation, effectively improving mechanical strength through hardening and presumably improving wear resistance and durability.

[0022] Metal additive manufacturing (AM) products are three-dimensional objects made by using an additive manufacturing method. Examples of AM methods include extruding molten metal material to form layers, spraying wire or powdered metal material onto the surface while melting it with a laser beam or the like, laminating the layers, colliding and bonding powdered metal material at high speed to form layers, and melting and laminating the surface of powdered metal material with a laser beam or the like. Metal AM products can be formed using, for example, a known 3D printer.

[0023] In the surface treatment method of the embodiment, the metal material used for the metal additive manufacturing product contains an iron-based metal or a nickel-based metal. The iron-based metal or nickel-based metal is not particularly limited as long as it is a material that can be subjected to additive manufacturing and the polishing and hardening processes described below. Examples include carbon steel, alloy steel, stainless steel, maraging steel, and nickel-based alloy. From the viewpoints of strength improvement, durability, and ease of adjusting the nitrogen or carbon concentration in the treatment layer, the metal material is preferably an alloy steel or stainless steel containing 0.5% or more of a component that forms nitrides or carbides (e.g., Cr, Ti, Al, V, etc.), and more preferably an alloy steel or stainless steel (e.g., SUS304, SUS316, etc.) containing 5% or more of the above component. The metal material may be used alone or in combination of two or more.

[0024] The shape of a metal additive manufacturing object manufactured by an additive manufacturing method is not particularly limited. The metal additive manufacturing object may have, for example, an internal structure with a complex shape. The metal additive manufacturing object may have, for example, an internal hollow structure such as a lattice structure in which a lattice-like framework is periodically arranged.

[0025] The thickness of a metal additive manufacturing product manufactured by additive manufacturing is not particularly limited, but is preferably 3 mm or less, more preferably 1 mm or less, from the viewpoints of ease of forming a treatment layer, durability of the metal additive manufacturing product, and strength improvement effects, and is preferably 0.1 mm or more, from the viewpoint of effectively suppressing embrittlement. In this specification, the "thickness of a metal additive manufacturing product" refers to the dimension in the thickness direction of the metal additive manufacturing product. For example, if the metal additive manufacturing product is pipe-shaped, the thickness of the metal additive manufacturing product refers to the dimension between the outer peripheral surface and the inner peripheral surface of the pipe, and if the metal additive manufacturing product is plate-shaped, the thickness of the metal additive manufacturing product refers to the dimension between the front and back surfaces of the plate.

[0026] The surface treatment method according to the embodiment includes a polishing step in which a polishing treatment is performed to polish the surface of the metal additive manufacturing object.

[0027] Examples of polishing techniques include fluid polishing, blast polishing, electrolytic polishing, grindstone polishing, etc. Among these, fluid polishing and electrolytic polishing are preferred from the viewpoint of ease of polishing unevenness on the internal surface.

[0028] In blast polishing, abrasive grains are sprayed onto the surface of a metal additive manufacturing product. Examples of blast polishing include wet blasting and shot blasting. Examples of abrasive grains include hard particles such as glass, various ceramics, and stainless steel. The average grain size of the abrasive grains is preferably 1 μm or more and 80 μm or less. The discharge pressure in blast polishing can be adjusted appropriately depending on the grain size of the abrasive grains, and may be, for example, 0.1 MPa to 1 MPa. The processing time for blast polishing can be adjusted appropriately depending on the surface roughness, material, etc. of the metal additive manufacturing product, and is, for example, 1 to 15 minutes, and preferably 3 to 15 minutes.

[0029] In the fluid polishing process, an abrasive fluid containing abrasive grains is flowed onto the metal additive manufacturing product. The abrasive grains contained in the abrasive fluid may be made of the same material as the abrasive grains used in the blast polishing process described above. The processing time for the fluid polishing can be adjusted appropriately depending on the surface roughness, material, etc. of the metal additive manufacturing product, but is typically 1 to 15 minutes, and preferably 3 to 10 minutes.

[0030] In electrolytic polishing, the surface of a metal additive manufacturing product is polished by electrolysis using an electrolytic polishing solution. Examples of components of the electrolytic polishing solution include phosphoric acid, chromic acid, sulfuric acid, and combinations thereof. The electrolytic polishing time can be adjusted appropriately depending on the surface roughness and material of the metal additive manufacturing product, but is typically 1 to 15 minutes, and preferably 5 to 15 minutes.

[0031] The surface treatment method of the embodiment includes a curing step. In the curing step, a hardening treatment is performed to harden the surface of the metal additive manufacturing object. In the surface treatment method of the embodiment, the order of the polishing step and the hardening step is not particularly limited, and the hardening step may be performed after the polishing step, or the polishing step may be performed after the hardening step.

[0032] One example of a hardening treatment method is chemical surface hardening. Chemical surface hardening is a method in which a hardening component acts on the surface of a material to form a treated layer (hardened layer) on the surface of the treatment target. By forming a treated layer on the surface of a metal additive manufacturing product, the hardness is significantly improved compared to when no treated layer is provided, allowing the product to exhibit excellent strength, wear resistance, and durability.

[0033] Examples of chemical hardening methods include nitriding and carburizing, with gas nitriding and gas carburizing being preferred. By diffusing and infiltrating nitrogen and / or carbon into a metal additive manufacturing product using gas nitriding or gas carburizing, a treatment layer including a compound layer containing nitrogen and / or carbon can be uniformly formed over the entire surface of the metal additive manufacturing product. For metal additive manufacturing products with complex shapes, plating and coating methods often fail to form a coating inside the complex structure or in areas where multiple structures come into contact with each other. By using gas nitriding or gas carburizing, a treatment layer can be successfully formed over the entire surface, even in such areas.

[0034] In gas nitriding, a metal additive manufacturing product is heated and held in an atmosphere containing a nitriding source gas, thereby diffusing and penetrating nitrogen into the surface of the metal additive manufacturing product as a base material. Gas nitriding can be any of gas nitriding, gas soft nitriding, and vacuum nitriding.

[0035] Gas nitriding and gas soft-nitriding can be performed by heating and holding a metal additive manufacturing product in a nitriding or soft-nitriding gas atmosphere, i.e., an atmosphere in which NH3 is used as a nitrogen source and, as necessary, N2, H2, CO, CO2, etc. Vacuum nitriding can be performed by heating and holding a metal additive manufacturing product in a reduced-pressure nitriding or soft-nitriding atmosphere, i.e., an atmosphere in which NH3 is used as a nitrogen source and, as necessary, N2, H2, CO, CO2, etc.

[0036] In gas carburizing, a metal additive manufacturing product is heated and held in an atmosphere containing a carburizing source gas, causing carbon to diffuse and penetrate into the surface of the metal additive manufacturing product as a base material. Either gas carburizing or vacuum carburizing can be used as the gas carburizing process.

[0037] Gas carburizing can be performed by heating and holding a metal additive manufacturing object in a carburizing gas atmosphere, i.e., an atmosphere in which CO or C2H2, etc. is used as the carburizing source, and optionally N2, H2, CO, CO2, etc. Vacuum carburizing can be performed by heating and holding a metal additive manufacturing object in a reduced pressure carburizing atmosphere, i.e., an atmosphere in which CO or C2H2, etc. is used as the carburizing source, and optionally N2, H2, CO, CO2, etc.

[0038] The treatment temperature (atmospheric temperature) of the gas nitriding treatment and gas carburizing treatment can be appropriately determined depending on the material of the metal additive manufacturing product and the desired characteristics of the treatment layer. The temperature of the gas nitriding treatment and gas carburizing treatment correlates with the diffusion rate of nitrogen and carbon, and affects the thickness and surface hardness of the treatment layer. If the treatment temperature is too low, the diffusion rate of nitrogen and carbon will be low, and the thickness of the treatment layer will be small. If the treatment temperature is too high, the thickness of the treatment layer will be excessive and economical. The treatment temperature of the gas nitriding treatment and gas carburizing treatment is, for example, 350°C or higher and 1000°C or lower, preferably 400°C or higher and 950°C or lower.

[0039] The treatment time (holding time) for the gas nitriding treatment and gas carburizing treatment can be appropriately determined depending on the material of the metal additive manufacturing product and the desired characteristics of the treated layer. The treatment time for the gas nitriding treatment and gas carburizing treatment correlates with the diffusion rate of nitrogen and carbon, and affects the thickness and surface hardness of the treated layer. If the treatment time is too short, the diffusion of nitrogen and carbon will be insufficient, resulting in a small thickness of the treated layer. If the treatment time is too long, the treated layer will be excessively thick and will be less economical. The treatment time for the gas nitriding treatment is, for example, 10 minutes to 50 hours, preferably 20 minutes to 30 hours. The treatment time for the gas carburizing treatment is, for example, 10 minutes to 80 hours, preferably 20 minutes to 60 hours.

[0040] When gas nitriding or gas carburizing is performed in the hardening step, it is preferably performed under a reduced pressure atmosphere. By performing gas nitriding or gas carburizing in a reduced pressure atmosphere, it becomes easier for the nitriding source gas or carburizing source gas to reach the fine details of the metal additive manufacturing product. Even for metal additive manufacturing products with complex internal structures, a uniform treatment layer can be formed on the internal surface of the metal additive manufacturing product, further improving the strength of the metal additive manufacturing product.

[0041] The pressure of the reduced pressure atmosphere is preferably 0.1 kPa to 50 kPa, more preferably 1 kPa to 40 kPa. If the pressure is less than 0.1 kPa, the concentration of the processing gas is low, and the surface nitrogen concentration or surface carbon concentration of the resulting processing layer is likely to be low. If the pressure is more than 50 kPa, the processing gas may not be sufficiently distributed throughout the metal additive manufacturing product.

[0042] In the surface treatment method according to the embodiment, it is preferable to include a halogenation treatment step before the hardening step. The halogenation treatment step is a step in which the metal additive manufacturing object is heated and held in a halogen-based gas atmosphere. For example, by performing the halogenation treatment before a hardening step such as a gas nitriding treatment or a gas carburizing treatment, the passive film formed on the surface of the metal additive manufacturing object containing an iron-based metal or a nickel-based metal can be replaced with a halogenated film that is easily permeable by nitrogen or carbon, facilitating the formation of a subsequent treatment layer. When the hardening step is performed after the polishing step, it is preferable to perform the halogenation step after the polishing step and before the hardening step.

[0043] In the halogenation treatment, a heating furnace capable of controlling the atmosphere is used, and the metal additive manufacturing object is heated and held in a halogen-containing atmospheric gas. This activates the surface of the metal additive manufacturing object. The halogen used in the atmospheric gas can be a halogen-based gas (e.g., F2, Cl2, etc.) or a halogen compound gas (e.g., HCl, NF3, etc.), preferably NF3. A single halogen may be used alone, or two or more halogen compounds may be used in combination. The atmospheric gas may be a mixed gas of a halogen-based gas or halogen compound gas with nitrogen gas or an inert gas. The concentration of the halogen-based gas or halogen compound gas in the mixed gas can be, for example, 0.5% by volume or more and 20% by volume or less.

[0044] The temperature and time of the halogenation treatment can be determined appropriately depending on the material of the metal additive manufacturing product and the desired properties of the treatment layer. The temperature of the halogenation treatment is, for example, 200°C or higher and 550°C or lower, preferably 300°C or higher and 450°C or lower. The time of the halogenation treatment is, for example, 10 minutes to 3 hours, preferably 30 minutes to 2 hours.

[0045] In the surface treatment method of the embodiment, polishing and hardening treatments are performed so that the surface roughness (arithmetic mean roughness Ra) of a metal additive manufacturing product is 6.5 μm or less. The surface roughness of a metal additive manufacturing product corresponds to the surface roughness of the treatment layer formed on the metal additive manufacturing product. When the surface roughness of a metal additive manufacturing product is 6.5 μm or less, the strength of the metal additive manufacturing product is excellent and embrittlement can be effectively suppressed. From the viewpoint of improving strength, the surface roughness of the metal additive manufacturing product is preferably 4.5 μm or less, more preferably 3.2 μm or less, and even more preferably 2.0 μm or less.

[0046] The surface roughness of the metal additive manufacturing product can be adjusted to the desired value by adjusting the processing conditions of the polishing process (e.g., processing time, composition of the abrasive fluid used in the process, composition of the electrolytic polishing solution, etc.) and the processing conditions of the hardening process (e.g., processing temperature, processing time, gas concentration, atmospheric pressure, etc.).

[0047] In the surface treatment method of the embodiment, the thickness of the treatment layer formed on the surface of the metal additive manufacturing product may be adjusted appropriately taking into consideration the material of the metal additive manufacturing product, the thickness and shape of the metal additive manufacturing product, the pressure applied to the metal additive manufacturing product, etc. From the viewpoints of strength and suppression of embrittlement, the thickness of the treatment layer is preferably 0.5 μm or more and 500 μm or less.

[0048] In the surface treatment method of the embodiment, the ratio of the thickness of the treatment layer to the thickness of the metal additive manufacturing object in a cross section substantially perpendicular to the thickness direction of the metal additive manufacturing object (thickness of treatment layer / thickness of metal additive manufacturing object) is preferably 60% or less. When this ratio is 60% or less, embrittlement of the metal additive manufacturing object can be effectively suppressed. From the viewpoint of the strength, durability, etc. of the metal additive manufacturing object, the ratio of the thickness of the treatment layer to the thickness of the metal additive manufacturing object is preferably 1% or more. The ratio of the thickness of the treatment layer to the thickness of the metal additive manufacturing object is more preferably 1% or more and 60% or less, even more preferably 3% or more and 50% or less, and most preferably 4% or more and 20% or less.

[0049] In the surface treatment method of the embodiment, from the viewpoint of improving strength, it is preferable that the treatment layer is formed around the entire circumference of the cross section of the metal additive manufacturing product in a direction approximately perpendicular to the thickness direction, it is more preferable that it is formed on substantially the entire surface of the metal additive manufacturing product, and it is even more preferable that it is formed on the entire surface of the metal additive manufacturing product.

[0050] In the surface treatment method of the embodiment, it is preferable to perform hardening treatment so that the surface nitrogen concentration of the metal additive manufacturing object (treatment layer) is 2.5 wt% or more and 10.0 wt% or less, or the surface carbon concentration is 1.0 wt% or more and 7.0 wt% or less. If the surface nitrogen concentration or surface carbon concentration of the metal additive manufacturing object exceeds the upper limit, embrittlement may occur. If the surface nitrogen concentration or surface carbon concentration of the metal additive manufacturing object falls below the lower limit, the strength and compressive residual stress at the surface may decrease. The surface nitrogen concentration of the metal additive manufacturing object is more preferably 5.0 wt% or more and 9.0 wt% or less. The surface carbon concentration of the metal additive manufacturing object is more preferably 1.5 wt% or more and 6.0 wt% or less.

[0051] In the surface treatment method of the embodiment, it is preferable to perform hardening treatment so that the surface hardness (surface hardness of the treatment layer) of the metal additive manufacturing product is 650 HV or more in Vickers hardness. When the surface hardness of the metal additive manufacturing product is 650 HV or more, durability and abrasion resistance are improved. The surface hardness of the metal additive manufacturing product is more preferably 700 HV or more, even more preferably 800 HV or more, and most preferably 1000 HV or more.

[0052] The thickness and surface hardness of the treated layer of the metal additive manufacturing product can be adjusted to the desired values ​​by adjusting the treatment conditions of the hardening treatment (for example, treatment temperature, treatment time, gas concentration, atmospheric pressure, etc.).

[0053] In the surface treatment method of the embodiment, it is preferable to perform the polishing treatment and hardening treatment so that the bending strength of the metal additive manufacturing product is 900 MPa or more. From the viewpoint of improving the strength of the metal additive manufacturing product, the bending strength of the metal additive manufacturing product is more preferably 950 MPa or more, even more preferably 1000 MPa or more, and most preferably 1100 MPa or more.

[0054] The present embodiment can provide a method for manufacturing a metal additive manufacturing product. The method for manufacturing a metal additive manufacturing product of the embodiment includes a polishing step and a hardening step similar to the above-described method for surface treatment of a metal additive manufacturing product.

[0055] A method for manufacturing a metal additive manufacturing object according to an embodiment is a method for manufacturing a metal additive manufacturing object containing an iron-based metal or a nickel-based metal, the method comprising: a polishing step of polishing a surface of the metal additive manufacturing object; and a hardening step of hardening the surface of the metal additive manufacturing product, wherein the arithmetic mean roughness of the surface of the metal additive manufacturing product is 6.5 μm or less. The method for manufacturing a metal additive manufacturing product may further include a shaping step of shaping a metal material by an additive manufacturing method.

[0056] In this embodiment, a metal additive manufacturing product can be provided. The metal additive manufacturing product of the embodiment is a metal additive manufacturing product that has been treated by the above-described method for surface treatment of a metal additive manufacturing product.

[0057] The metal additive manufacturing object of the embodiment contains an iron-based metal or a nickel-based metal, and has a surface with an arithmetic mean roughness of 6.5 μm or less and a surface hardness of 650 HV or more.

[0058] In the metal additive manufacturing product of the embodiment, it is preferable that the bending strength is 900 MPa or more. In the metal additive manufacturing product of the embodiment, it is preferable that the surface is provided with a treatment layer containing nitrogen or carbon.

[0059] The uses of the metal additive manufacturing products of the embodiments are not particularly limited. Because the metal additive manufacturing products of the embodiments have excellent strength, durability, and abrasion resistance, they can be suitably used in products that use metal materials but emphasize lightweight design, such as parts for automobiles, aerospace vehicles including drones, bicycles, molds, and wearable products. Specific examples of uses of metal additive manufacturing products include automobile parts such as frames and rotating shafts, and mobile phone parts for watches, eyeglasses, smartphones, and the like. [Example]

[0060] The present invention will be explained in more detail below based on examples and comparative examples, but it is not intended that the present invention be limited to these examples.

[0061] (Manufacturing of metal additive manufacturing) [Example 1] A 3D printer, which uses a laser beam to melt and layer the surface of metal powder, was used to additively fabricate stainless steel (SUS316) pipe-shaped additively manufactured objects (outer diameter φ4 mm, thickness 1 mm, length 80 mm). The outer surface of the resulting pipe-shaped additively manufactured object was then shot-blasted. The blasting process was performed using a gravity-type manual blasting device, with glass beads (average particle size 45 μm or less) as abrasives, at a discharge pressure of 0.3 MPa and a processing time of 3 minutes. The inner surface of the pipe-shaped additively manufactured object was then subjected to fluid polishing. The fluid polishing process consisted of a slurry containing a water-soluble solvent and ceramic abrasives as the abrasive fluid, which was injected at high pressure from one end of the pipe-shaped additively manufactured object to the other end.

[0062] After the polishing treatment, the metal additive manufacturing object was subjected to a fluorination treatment (halogenation treatment). The fluorination treatment conditions were a mixed gas of NF3:N2 = 10:90 (volume %) as the atmospheric gas, a treatment temperature of 350°C, and a treatment time (holding time) of 1 hour. After the fluorination treatment, the metal additive manufacturing object was subjected to a gas nitriding treatment. The gas nitriding treatment conditions were a mixed gas of NH3 = 100 volume %, an atmospheric pressure of 1 kPa to 20 kPa, a treatment temperature of 570°C, and a treatment time (holding time) of 5 hours. In this way, a metal additive manufacturing object of Example 1 was obtained.

[0063] [Examples 2 to 8, Comparative Examples 1 to 8] Metal additive manufacturing objects of Examples 2 to 8 and Comparative Examples 1 to 8 were obtained in the same manner as Example 1, except that the material, shape, and various processing conditions of the metal additive manufacturing object were as shown in Table 1. In Examples 3 to 5 and 7 and Comparative Examples 4 to 7, stainless steel (SUS304) was used as the metal material to produce plate-shaped metal additive manufacturing objects (width 30 mm, length 50 mm, thickness 0.5 mm). In Example 6, stainless steel (SUS304) was used as the metal material to produce a plate-shaped metal additive manufacturing object (width 30 mm, length 50 mm, thickness 1.5 mm).

[0064] In Table 1, "before hardening treatment" in the polishing treatment order indicates that the polishing treatment was performed before hardening treatment, and "after hardening treatment" indicates that the polishing treatment was performed after hardening treatment. The electropolishing conditions in Example 2 and Comparative Example 3 were an electropolishing solution containing phosphoric acid, chromic acid, and sulfuric acid as its main components, a voltage of 12 V, and a solution temperature of the electropolishing solution ranging from room temperature to 100°C. The shot blast polishing conditions in Examples 3, 4, and 7 and Comparative Examples 5 to 7 were the same as in Example 1, except that the treatment time was as shown in Table 1. The wet blast polishing conditions in Examples 5 and 6 were as follows: a manual wet blasting machine was used, ceramic abrasive grains (median particle size 5 μm or less) were used, the discharge pressure was 0.4 MPa, and the treatment time was as shown in Table 1. In all of Examples 3 to 5 and 7 and Comparative Examples 4 to 7, shot blast polishing was performed on both sides of the plate-shaped metal additive manufacturing object. The fluorination treatment conditions in Examples 2 to 8 and Comparative Examples 2 to 8 were the same as in Example 1.

[0065] [Measurement and evaluation methods] The metal additive manufacturing objects of each example and comparative example were measured for their properties and evaluated for their strength using the following methods. The measurement and evaluation results are shown in Table 2.

[0066] (Surface hardness) The surface hardness was measured using a micro-Vickers hardness tester under a load of 50 g. The surface hardness is the average value of hardness measured at any five points on the surface of the metal additive manufacturing product.

[0067] (Treatment layer thickness) The thickness of the treated layer was measured by observing each metal additive manufacturing object using a digital microscope with a length measurement function. The thickness of the treated layer was the average value of the thicknesses of the treated layer measured at any three points on the cross section of the metal additive manufacturing object.

[0068] (surface roughness Ra) For each of the metal additive manufacturing products of Examples and Comparative Examples, the surface roughness Ra of the outer surface of the metal additive manufacturing product was measured using a contact surface roughness measuring device. Furthermore, each of the pipe-shaped metal additive manufacturing products of Examples 1 and 2 and Comparative Examples 1 to 3 was cut along the axial direction of the pipe, and the surface roughness Ra of the inner surface of the metal additive manufacturing product was measured using a scanning confocal laser microscope. The surface roughness Ra is the average value of the surface roughness measured at three points on the surface of the metal additive manufacturing product.

[0069] (bending strength) A three-point bending test was performed on each metal additive manufacturing product to determine its bending strength, which was then evaluated as its strength. A bending strength of 900 MPa was deemed to be good. In the three-point bending test, a universal testing machine was used at room temperature to support each metal additive manufacturing product at two supports, with the center of the distance between the supports set as the load point. A force was applied to the load point by moving an indenter vertically downward to measure the load applied to the load point indenter. The maximum load applied to the load point indenter was measured, and the bending strength was calculated based on the obtained maximum load. The bending strength was the average value of the bending strengths calculated for three randomly selected metal products. The test conditions used were as follows: ·Distance between fulcrums: 35mm ·Indenter radius: 5mm ·Fulcrum radius: 5mm Indenter pressing speed: 5mm / min

[0070] (surface nitrogen concentration and surface carbon concentration) The surface nitrogen concentration or surface carbon concentration was measured for the metal additive manufacturing objects of Examples 1 and 2 and Comparative Examples 1 and 2. The surface nitrogen concentration and surface carbon concentration were measured on the surface of the metal additive manufacturing object using energy dispersive X-ray spectroscopy (EDX). The surface nitrogen concentration and surface carbon concentration are the average values ​​of concentrations measured at any three points on the surface of the metal additive manufacturing object. The surface nitrogen concentration of Example 1 was 5.3 wt %, the surface carbon concentration of Example 2 was 1.5 wt %, the surface nitrogen concentration of Comparative Example 2 was 5.4 wt %, and the surface carbon concentration of Comparative Example 3 was 1.5 wt %.

[0071] [Table 1]

[0072] [Table 2]

[0073] 1 shows displacement-stress curves obtained by bending tests of the metal additive manufacturing products of Examples 1 and 2 and Comparative Examples 1 and 2. The horizontal axis of the graph represents displacement (mm), and the vertical axis represents stress (MPa).

[0074] As shown in Table 2 and Figure 1, the metal additive manufacturing products of each example, which underwent a polishing process and a hardening process and had an arithmetic mean roughness of the surface of the metal additive manufacturing product of 6.5 μm or less, were confirmed to have superior strength to the metal additive manufacturing products of the comparative examples.

[0075] Examples 1, 2, and 8 and Comparative Examples 1, 2, and 8 confirmed that examples in which polishing was performed on the inner peripheral surface of a metal additive manufacturing product had significantly higher bending strength than comparative examples in which polishing was not performed, demonstrating significant improvements in strength. Each of the Examples and Comparative Examples confirmed that setting the surface roughness of a metal additive manufacturing product to 6.5 μm or less can increase bending strength and improve strength. Examples 1, 2, and 8 and Comparative Examples 1 to 3 and 8 revealed that if the surface of the treatment layer is not sufficiently smoothed, the hardening treatment does not have an effect and bending strength is not sufficiently improved. Furthermore, Comparative Examples 2 and 3 suggest that if the surface nitrogen concentration of a metal additive manufacturing product exceeds 2.5 wt % or the surface carbon concentration exceeds 1.0 wt %, the iron may form compounds with nitrogen and carbon, resulting in increased sensitivity to surface roughness and reduced strength.

[0076] Examples 3 to 6 and Comparative Examples 4 to 7 confirmed that the strength of a metal additive manufacturing product can be improved by performing a hardening treatment and a blast polishing treatment to reduce the surface roughness to 6.5 μm or less. The polishing treatment may be performed either before or after the hardening treatment. Since wet blasting can improve surface roughness in a shorter treatment time than shot blasting, it was found that wet blast polishing can be expected to improve the productivity of surface roughness adjustment.

[0077] Fig. 2 shows cross-sectional micrographs of the metal additive manufacturing products of Example 8 and Comparative Example 8. As is clear from Fig. 2, the surface of the treated layer of the metal additive manufacturing product of Example 8 is smoothed, while the surface of the treated layer of the metal additive manufacturing product of Comparative Example 8 has surface irregularities that occurred during additive manufacturing, and the surface of the treated layer is not smoothed.

[0078] Fig. 3 is a graph showing the cross-sectional hardness distribution (Vickers hardness) in the depth direction from the surface of the metal additive manufacturing objects of Examples 2 and 8 and Comparative Example 1. The horizontal axis of the graph represents the depth from the surface (µm), and the vertical axis represents the hardness (HV) of the metal additive manufacturing object. As shown in Fig. 3, in Examples 2 and 8, sufficient hardness was obtained even at a certain depth. The hardness at a depth of 10 µm from the surface of the metal additive manufacturing object of Example 8 was 1238 µm, and the hardness at a depth of 10 µm from the surface of the metal additive manufacturing object of Example 2 was 863 µm.

Claims

1. A surface treatment method for a metal additive manufacturing object containing an iron-based metal or a nickel-based metal, comprising: a polishing step of polishing the surface of the metal additive manufacturing object; and a hardening step of hardening the surface of the metal additive manufacturing object. The arithmetic mean roughness of the surface of the metal additive manufacturing product is 6.5 μm or less. A method for surface treatment of metal additive manufacturing objects.

2. The polishing step is carried out by a fluid polishing process or an electrolytic polishing process. The surface treatment method for a metal additive manufacturing product according to claim 1 .

3. The hardening process is carried out by gas nitriding or gas carburizing. The surface treatment method for a metal additive manufacturing product according to claim 1 or 2.

4. The gas nitriding or gas carburizing treatment is carried out in a reduced pressure atmosphere. The surface treatment method for a metal additive manufacturing product according to claim 3 .

5. The surface hardness of the metal additive manufacturing product is 650 HV or more. The surface treatment method for a metal additive manufacturing product according to claim 1 or 2.

6. a halogenation treatment step of heating and holding the metal additive manufacturing object in a halogen-based gas atmosphere before the curing step; The surface treatment method for a metal additive manufacturing product according to claim 1 or 2.

7. A method for manufacturing a metal additive manufacturing object containing an iron-based metal or a nickel-based metal, comprising: a polishing step of polishing the surface of the metal additive manufacturing object; a hardening step of hardening a surface of the metal additive manufacturing object, The arithmetic mean roughness of the surface of the metal additive manufacturing product is 6.5 μm or less. A method for manufacturing metal additive manufacturing objects.

8. Contains an iron-based metal or a nickel-based metal, The arithmetic mean roughness of the surface is 6.5 μm or less, Surface hardness is 650HV or more Metal additive manufacturing.

9. Bending strength is 900 MPa or more The metal additive manufacturing product according to claim 8.

10. The surface is provided with a treatment layer containing nitrogen or carbon. The metal additive manufacturing product according to claim 8 or 9.

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