Maraging steel powder for additive fabrication, maraging steel additively fabricated article, and method for manufacturing same

Abstract

Provided is a maraging steel powder from which it is possible to obtain, while reducing Co as much as possible, an additively fabricated article having excellent thermal fatigue life characteristics and exhibiting little deformation after being shaped.　Provided are: a maraging steel powder for additive fabrication comprising, in mass%, no more than 0.02% C, 0.1-0.3% Si, 16-20% Ni, no more than 0.1% Co, 2.7-3.5% Mo, 1.5-2.5% Ti, and no more than 0.01% Al, the remaining portion being Fe and unavoidable impurities; and a maraging steel additively fabricated article comprising no more than 0.02% C, 0.1-0.3% Si, 16-20% Ni, no more than 0.1% Co, 2.7-3.5% Mo, 1.5-2.5% Ti, and no more than 0.01% Al, the remaining portion being Fe and unavoidable impurities.

Description

Maraging steel powder for additive manufacturing, maraging steel additively manufactured product, and manufacturing method thereof

[0001] The present invention relates to a maraging steel powder for additive manufacturing, a maraging steel additive-molded product, and a method for manufacturing a maraging steel additive-molded product.

[0002] Recently, additive manufacturing (AM) has been attracting attention as a means for easily forming complex metal products (components) in near-net shapes. AM, commonly referred to as 3D printing, is an additive manufacturing technology. Examples of AM methods include the powder spray method, in which metal powder is irradiated with a heat source to melt and layer the resulting material, and the powder bed method, in which metal powder spread on a stage is irradiated with a heat source to melt and solidify the powder, layering the resulting material. AM allows for the production of complex metal products with largely eliminated conventional machining processes, allowing the use of difficult-to-process metal materials. Furthermore, since difficult-to-process metal materials are primarily high-strength metal materials, it is possible to produce complex metal products with long durability. One application for near-net processing of such complex three-dimensional shapes is die-casting molds.

[0003] Maraging steel is a typical example of a high-strength metallic material. Maraging steel is an age-hardening, ultra-high strength steel made by adding age-hardening elements such as Co, Mo, Ti, and Al to steel containing, for example, approximately 18% by mass of Ni. Furthermore, since maraging steel also has excellent toughness, using maraging steel as a material for various tools and structural components is effective in extending the lifespan of these products. Furthermore, an additively manufactured product using maraging steel as a metallic material and fabricated by the above-mentioned additive manufacturing method has been proposed (Patent Document 1).

[0004] Maraging steel powder has excellent strength and toughness both as-formed and after aging treatment, making it suitable for the additive manufacturing of the die-casting dies described above. A known maraging steel used for such dies is a 300 ksi (kilogram-force per square inch) grade maraging steel, whose typical composition is Fe-18%Ni-9%Co-5%Mo.

[0005] On the other hand, when using the powder bed method for additive manufacturing (AM), powder and dust may be released into the atmosphere during the process from powder production to the final product. Powder and dust containing Co, in particular, require careful management to minimize their impact on human health. Furthermore, because the addition of Co increases costs, there is a demand for low-Co maraging steel powder. For example, the present applicant has proposed a powder for AM consisting of a maraging steel with a composition, by mass, of 0.1% or less of C, 14-22% of Ni, 0-5% of Co, 0.1-15.0% of Mo, 0.1-5.0% of Ti, 3.0% or less of Al, and the balance being Fe and impurities. The powder described in Patent Document 2, which has the above-mentioned alloy composition, can reduce Ti segregation and improve the toughness of maraging steel AM products (Patent Document 2).

[0006] Furthermore, a common problem with articles manufactured by additive manufacturing (additive manufactured products) is the occurrence of distortion due to residual stress. As a method for suppressing the above-mentioned distortion in carbon steel or martensitic stainless steel that undergoes martensitic transformation, for example, a method has been proposed in which the martensitic transformation start temperature (Ms point) of the raw material powder is taken into consideration, and temperature adjustment is performed between multiple layers of the additive manufactured product using a temperature adjustment mechanism of the additive manufactured product, thereby alleviating distortion in the additive manufactured product (Patent Document 3).

[0007] International Publication No. 2011 / 149101 Japanese Patent Application Laid-Open No. 2020-45567 Japanese Patent No. 6295001

[0008] In the case of an additive manufacturing device without a temperature control mechanism, such as that proposed in Patent Document 3, strain caused by thermal contraction of the material during manufacturing can sometimes cause deformation or cracking in the additively manufactured product. In particular, low-Co maraging steels with less than 1% Co tend to exhibit greater deformation compared to typical 300 ksi-grade steels, making further suppression of deformation necessary. Meanwhile, one of the characteristics required for die-casting molds is their resistance to cracking due to thermal fatigue (improved thermal fatigue life). To obtain a mold with a long thermal fatigue life, mold materials are required that have high-temperature strength and good room-temperature ductility and toughness when heat-treated after manufacturing (tempered material) of the additively manufactured product. Therefore, the objective of the present invention is to provide a maraging steel powder that can minimize Co content and produce additively manufactured products with minimal deformation and excellent thermal fatigue life characteristics, and additively manufactured products made from the same.

[0009] The present invention has been made in view of the above-mentioned problems. Specifically, one aspect of the present invention is a maraging steel powder for additive manufacturing, which contains, by mass%, 0.02% or less C, 0.04 to 0.3% Si, 16 to 20% Ni, 0.1% or less Co, 2.7 to 3.5% Mo, 1.5 to 2.5% Ti, 0.01% or less Al, the balance being Fe and unavoidable impurities. Another aspect of the present invention is a maraging steel additive manufactured product, which contains, by mass%, 0.02% or less C, 0.04 to 0.3% Si, 16 to 20% Ni, 0.1% or less Co, 2.7 to 3.5% Mo, 1.5 to 2.5% Ti, 0.01% or less Al, the balance being Fe and unavoidable impurities. Another aspect of the present invention is a method for producing a maraging steel additive manufacturing product, comprising: a powder layer formation step of spreading the above-mentioned maraging steel powder for additive manufacturing in the form of layers; and a melting and solidifying step of successively melting and solidifying the spread maraging steel powder for additive manufacturing using a scanning heat source having a diameter larger than D50 of the maraging steel powder for additive manufacturing to form a solidified layer, in which the powder layer formation step and the melting and solidifying step are repeated to obtain the additive manufacturing product.

[0010] According to the present invention, even if the Co content is reduced as much as possible, it is possible to obtain an additively manufactured product that has little deformation after additive manufacturing and has excellent thermal fatigue life characteristics.

[0011] FIG. 1 is a schematic diagram of a warpage measurement specimen used in strain evaluation.

[0012] The present invention has a chemical composition consisting of 0.02% or less C, 0.04-0.3% Si, 16-20% Ni, 0.1% or less Co, 2.7-3.5% Mo, 1.5-2.5% Ti, 0.01% or less Al, and the balance being Fe and unavoidable impurities. First, the reasons for the composition limitations of the maraging steel for additive manufacturing specified in the present invention will be described. Unless otherwise specified, "%" refers to "mass %." C (carbon): 0.02% or less. To obtain the high-toughness, low-carbon martensitic structure characteristic of maraging steel, C must be limited to 0.02% or less. If C exceeds 0.02%, the toughness of the as-manufactured steel (i.e., the state after additive manufacturing without heat treatment) decreases, and cracks may occur due to strain caused by thermal contraction. Preferably, C is 0.01% or less. On the other hand, C can also be used as a deoxidizer in the melting process, and since it is difficult to eliminate it from the manufacturing process, the lower limit can be set at, for example, 0.001%.

[0013] Si (silicon): 0.04 to 0.3% Si is an element that improves strength, and its content should be 0.04% or more. On the other hand, excessive addition of Si reduces the toughness of the tempered material, which is necessary for improving thermal fatigue life characteristics, so the Si content should be at most 0.3%. In order to further improve toughness, the upper limit of the Si content is preferably set to 0.2%, and more preferably to 0.15%.

[0014] Ni (Nickel): 16-20% Ni is a fundamental element necessary for a maraging steel to function as a maraging steel, forming intermetallic compounds with Ti, Al, Mo, etc., and contributing to improved strength. For this reason, in the present invention, the Ni content is set to 16% or more. A preferred lower limit for the Ni content is 17%. On the other hand, if the Ni content is too high, the austenite structure is stabilized, making it difficult to form a martensite structure. For this reason, in the present invention, the Ni content is set to 20% or less. A preferred upper limit for the Ni content is 19%.

[0015] Co (cobalt): 0.1% or less. In this invention, the Co content is reduced in consideration of the ease of managing the effects on human health and the high cost of Co itself. Furthermore, in this invention, it has been discovered that by extremely reducing the Co content, which has the effect of lowering the solid solubility limit of Mo, to 0.1% or less, the effect of improving the toughness of the tempered material is exerted. This is thought to be because reducing excessive precipitation of Mo-based intermetallic compounds improves the toughness necessary for thermal fatigue life characteristics. The preferred upper limit is 0.05%, and more preferably 0.01%. Although it is ideal to add no Co (0%), this is difficult in manufacturing, so the lower limit can be set to, for example, 0.0005%.

[0016] Mo (molybdenum): 2.7 to 3.5% Mo is an intermetallic compound that is present in the alloy during aging treatment. ３Mo is an element that forms Mo to precipitation-strengthen or solid-solution-strengthen the metal structure, thereby improving strength and improving thermal fatigue life. Furthermore, the addition of Mo lowers the Ms point in compositions such as low-Co maraging steel. In the case of an additive manufacturing device without a temperature control mechanism, the temperature during manufacturing may be close to room temperature depending on the manufacturing conditions. However, lowering the Ms point to room temperature can reduce deformation due to thermal contraction by utilizing the effect of mitigating thermal contraction due to martensitic transformation expansion. For this reason, in the present invention, the Mo content is preferably 2.7% or more. On the other hand, if the Mo content is too high, excessive coarse intermetallic compounds are formed with Fe, reducing the toughness of the tempered material required for thermal fatigue life characteristics. Furthermore, the addition of excessive Mo lowers the Ms point more than necessary, making it difficult to form a martensitic structure. For this reason, in the present invention, the Mo content is preferably 3.5% or less.

[0017] Ti (titanium): 1.5 to 2.5% Ti is the strengthening phase of Ni in the structure after aging treatment. ３ Mo forms Ti and provides the high-temperature strength necessary for thermal fatigue life characteristics. Therefore, in the present invention, the Ti content is set to 1.5% or more. For the same reasons as above, the Ti content is preferably 1.7% or more, more preferably 1.9% or more. On the other hand, if the Ti content is too high, significant Ti segregation occurs in the structure during solidification, and this significant Ti segregation may remain in the structure after aging treatment, resulting in a decrease in the toughness of the tempered material necessary for thermal fatigue life characteristics. Therefore, in the present invention, the Ti content is set to 2.5% or less. For the same reasons as above, the Ti content is preferably 2.3% or less, more preferably 2.1% or less. Furthermore, in the present invention, in order to stably obtain the precipitation strengthening effect of Mo and Ti described above, it is preferable that Ti + Mo be 4.5 to 5.5%. A more preferable upper limit of Ti + Mo is 5.2%.

[0018] Al (aluminum): 0.01% or less. Al forms intermetallic compounds with Ni and has the effect of precipitation strengthening the metal structure. However, if the content is too high, nonmetallic inclusions in the metal structure may increase, reducing toughness. Therefore, the content is set to 0.01% or less. The preferred upper limit is 0.007%, and the more preferred upper limit is 0.005%. Furthermore, since the strength provided by intermetallic compounds can be achieved by adding Mo or Ti, the number of elements handled can be reduced, eliminating the need for manufacturing control steps. While it is ideal to add no Al (0%), this is difficult to achieve in manufacturing, so the lower limit can be set to, for example, 0.0001%. The basic composition of the present invention selectively contains the above elements, with the balance consisting of Fe and unavoidable impurities.

[0019] Furthermore, the maraging steel powder for additive manufacturing of the present invention preferably has an N (nitrogen) content of 0.030% or less by mass. N (nitrogen) is an element that is inevitably incorporated into the metal powder from the raw materials and the atmosphere during the melting and pulverization processes during the metal powder manufacturing process. If the N (nitrogen) content is too high, it bonds with Ti, Mo, etc. in the additive manufacturing product to form a large amount of nitrides. These nitrides may act as fracture initiation points and reduce the toughness of the tempered material. For this reason, in the present invention, the N (nitrogen) content is preferably 0.030% or less, more preferably 0.020% or less, and even more preferably 0.005% or less. However, N is an element that is inevitably mixed in during general additive manufacturing powder manufacturing processes, such as gas atomization. The maraging steel powder for additive manufacturing according to one embodiment of the present invention can tolerate an N (nitrogen) content of 0.001% or more from the viewpoint of suppressing internal defects in the additive manufactured product and ensuring sufficient toughness.

[0020] The maraging steel powder for additive manufacturing of the present invention preferably has an O (oxygen) content of 0.040% or less. O (oxygen) is an element that is inevitably incorporated into the metal powder from the raw materials and the atmosphere in the melting and pulverization processes during the metal powder manufacturing process. O (oxygen) bonds with Ti and other elements to form oxides inside and on the surface of the metal powder. These oxides may act as fracture initiation points and reduce toughness. For this reason, in the present invention, the O (oxygen) content is preferably 0.040% or less, more preferably 0.030% or less, and even more preferably 0.020% or less.

[0021] The maraging steel powder for additive manufacturing of the present invention can tolerate an O (oxygen) content of 0.005% or more, or 0.010% or more, from the viewpoint of suppressing internal defects in the additive manufacturing product and ensuring sufficient toughness.

[0022] The maraging steel powder for additive manufacturing of the present invention can be produced by, for example, gas atomization, water atomization, disk atomization, plasma atomization, rotating electrode atomization, etc. Among these, gas atomization is a method in which a melted raw material prepared to have a desired composition is heated to above its melting point by high-frequency induction heating, melted, and then the molten metal flows out through a fine hole. An inert gas such as argon gas or nitrogen gas is injected into the melted metal, which is then finely pulverized and rapidly solidified to obtain a powder. This gas atomization method can use scrap metal or raw metal materials as the melted raw material. Compared to plasma atomization and rotating electrode atomization, which require the preparation of a raw material with a desired composition and shape in advance, gas atomization can be produced at a lower cost, making it suitable as a method for producing the metal powder for additive manufacturing of the present invention.

[0023] The maraging steel powder for additive manufacturing of the present invention preferably has a 50% particle size (hereinafter referred to as "D50") of a cumulative particle size distribution based on volume of 10 to 250 μm. By setting the D50 of the metal powder for additive manufacturing of the present invention to 250 μm or less, the powder can be easily melted, and the formation of internal defects in the additive manufacturing product can be suppressed. Furthermore, by setting the D50 of the metal powder for additive manufacturing of the present invention to 10 μm or more, the metal powder is less susceptible to the influence of moisture and other factors in the atmosphere during handling and additive manufacturing, ensuring good flowability. The cumulative particle size distribution of the additive manufacturing powder of the present invention is expressed as a cumulative volumetric particle size distribution, and the D50 can be expressed as a measurement value obtained by the laser diffraction scattering method specified in JIS Z 8825.

[0024] The maraging steel powder for additive manufacturing of the present invention may have its D50 adjusted by mesh sieving or airflow classification, depending on the method described above. For example, metal powder for additive manufacturing used in the powder bed method must be melted by a laser beam, which serves as a heat source, while coarse metal powder that is difficult to melt must be removed to minimize the area affected by the heat. Furthermore, highly adhesive fine metal powder must also be removed to obtain optimal fluidity for ensuring the layability of the metal powder. Therefore, when applying the maraging steel powder for additive manufacturing of the present invention to the powder bed method, it is preferable to adjust the D50 to a range of 10 to 53 μm. The preferred upper limit of D50 is 40 μm, and the preferred lower limit of D50 is 20 μm.

[0025] By additively manufacturing the maraging steel powder for additive manufacturing of the present invention using the manufacturing method described below, it is possible to obtain a maraging steel additively manufactured product comprising, by mass%, 0.02% or less C, 0.04 to 0.3% Si, 16 to 20% Ni, 0.1% or less Co, 2.7 to 3.5% Mo, 1.5 to 2.5% Ti, 0.01% or less Al, and the balance being Fe and unavoidable impurities. Preferably, the Ti+Mo ratio is 4.5 to 5.5. This additively manufactured product exhibits minimal deformation due to thermal contraction and excellent thermal fatigue life characteristics. While die-casting molds are the most preferred application example for this additively manufactured product, it may also be applicable to other molds requiring internal cooling mechanisms, such as plastic molds. It may also be applicable to repairing molds manufactured using the powder spray additive manufacturing method. Furthermore, it is not limited to molds, and may also be applicable to components such as various tools and gears that use maraging steel.

[0026] Next, we will explain the manufacturing method of the present invention, which can produce the additive manufacturing product of the present invention using the maraging steel powder of the present invention. The manufacturing process described below can be applied to, for example, the powder bed method. The manufacturing method of the present invention includes the steps of: spreading the prepared maraging steel powder for additive manufacturing (hereinafter also referred to as "metal powder") in layers; and sequentially melting and solidifying the spread metal powder using a scanning heat source having a diameter larger than the D50 of the metal powder to form solidified layers. The layered metal powder spreading step and the solidified layer forming step are then repeated to form multiple solidified layers, thereby producing the additive manufacturing product of the present invention. The scanning heat source can be, for example, a laser or an electron beam. Furthermore, using a scanning heat source with a diameter larger than the D50 of the metal powder is preferable because it allows for uniform melting of the metal powder aggregates.

[0027] In the manufacturing method according to the present invention, when the metal powder is irradiated with a laser while being scanned, the laser output can be set to 50 to 350 W, the scanning speed to 200 to 2000 mm / sec, and the scanning pitch to 0.02 to 0.20 mm. Here, if the layer thickness per laser scan is too large, heat is not easily transferred to the entire spread metal powder during laser irradiation, causing the metal powder to not melt sufficiently, which promotes the formation of internal defects. On the other hand, if the layer thickness per scan is too small, the number of layers required to achieve the desired size of the additive manufacturing product increases, lengthening the time required for the additive manufacturing process. For this reason, the layer thickness per scan is preferably set to 10 to 200 μm. A more preferred lower limit of the layer thickness is 20 μm, and a more preferred upper limit of the layer thickness is 100 μm.

[0028] In the manufacturing method according to the present invention, it is preferable to perform aging treatment on the as-additively manufactured member (i.e., a state in which heat treatment has not been performed after additive manufacturing) in order to impart the mechanical properties necessary for use as a metal product (component). The aging treatment of the additively manufactured product of the present invention is useful in that it precipitates various intermetallic compounds in the structure, for example, adjusting the hardness to 40 to 55 HRC, thereby obtaining superior high strength and high toughness. The aging temperature is preferably 400°C or higher, more preferably 450°C or higher, even more preferably 500°C or higher, and even more preferably 550°C or higher. By increasing the aging temperature, Ni ３The effect of improving strength due to the precipitation of Ti can be obtained. However, if the aging temperature is too high, the intermetallic compounds will coarsen, and the strength expected from the amount of precipitation of the intermetallic compounds will not be obtained sufficiently. Therefore, the aging temperature is preferably 700°C or less. More preferably, it is 650°C or less, even more preferably 640°C or less, and even more preferably 630°C or less. It can also be 600°C or less. The aging time (holding time at the aging temperature) is preferably 60 minutes or more, more preferably 100 minutes or more, and even more preferably 150 minutes or more. By extending the aging time, the amount of various intermetallic compounds increases. However, if the aging time is too long, the intermetallic compounds will coarsen and the strength will decrease. Therefore, the aging time is preferably 600 minutes or less, more preferably 400 minutes or less, and even more preferably 200 minutes or less. Furthermore, since the aging treatment is performed to adjust (temper) the hardness to a specific value while measuring the hardness as needed, the aging treatment time per treatment may be set within the preferred range described above and performed multiple times. In the heat treatment of additively manufactured products, the melting and rapid cooling during manufacturing sometimes double as quenching treatment, so unlike general ingot materials, the solution treatment may be omitted and the as-manufactured product may be directly aged. The manufacturing method of the present invention has been described above, but the maraging steel powder for additive manufacturing of the present invention is not limited to the manufacturing method described above. For example, it can also be applied to a direct metal deposition method in which the powder is sprayed directly onto a heat source and welded to a substrate.

[0029] In the manufacturing method according to the present invention, a solution treatment may be performed before the aging treatment described above to improve mechanical properties and eliminate segregation. The solution treatment temperature is preferably 800°C or higher, more preferably 850°C or higher, even more preferably 900°C or higher, and even more preferably 950°C or higher. Increasing the solution treatment temperature improves the effect of eliminating segregation formed during additive manufacturing. However, if the solution treatment temperature is too high, prior austenite grains will coarsen, resulting in a decrease in the strength and toughness of the additively manufactured product. Therefore, the solution treatment temperature is preferably 1200°C or lower, more preferably 1100°C or lower, and even more preferably 1050°C or lower. The solution treatment time (holding time at the solution treatment temperature) is preferably 10 minutes or longer, more preferably 30 minutes or longer, and even more preferably 45 minutes or longer. Increasing the solution treatment time improves the effect of eliminating segregation formed during additive manufacturing. However, if the solution treatment time is too long, the prior austenite grain size will become coarse. Therefore, the solution treatment time is preferably 120 minutes or less, more preferably 100 minutes or less, and even more preferably 80 minutes or less. Some additively manufactured products are used as composites by additively manufacturing another material on a base material. When an additively manufactured product is used in a mold, a composite may be made by additively manufacturing a maraging steel on a general tool steel. Tool steels are usually quenched before use; for example, the quenching temperature of the general hot work tool steel SKD61 is around 1000°C. When an additively manufactured product is used as a composite, the quenching of the tool steel and the solution treatment of the maraging steel can be combined.

[0030] Example 1: Each metal raw material was prepared to have the component composition shown in Table 1, then charged into a high-frequency induction melting furnace and melted. The molten metal was pulverized with argon gas to obtain a gas-atomized powder. The resulting atomized powder was subjected to mesh sieving and airflow classification to adjust the particle size, resulting in powders for additive manufacturing (AM) examples and comparative examples with a D50 of 35 μm. Each of the resulting metal powders for additive manufacturing was used to produce additive manufacturing products under the manufacturing conditions shown in Table 2 using a GE Additive Mlab Cusing 200R. Table 3 shows the component compositions of the resulting AM products.

[0031]

[0032]

[0033]

[0034] First, the deformation of the additively manufactured products was measured. First, cantilever-shaped test pieces shown in FIG. 1 were fabricated on a base plate as additively manufactured products for the present invention and comparative examples. Next, the cutting portion of the support portion shown in FIG. 1 was cut using wire electric discharge machining, causing warping of the beam portion due to accumulated strain. This confirmed that the greater the warping, the greater the accumulated strain in the additively manufactured product. Next, the height of the measurement point at the end of the beam portion relative to the base plate was measured before and after cutting the support portion. As shown in Table 4, the deformation of the additively manufactured products made of the Co-free maraging steel of the present invention examples was less than that of the low-Co maraging steel of the comparative examples, confirming that the additively manufactured products of the present invention can suppress deformation in the as-manufactured state even when the Co content is minimized.

[0035]

[0036] Example 2 Next, to confirm the mechanical properties of the additively manufactured product, the same additively manufactured product as in Example 1 was heat-treated under the conditions shown in Table 5 and tempered to hardnesses of 46±1 HRC and 52±1 HRC. Samples 4 to 7 were heat-treated Sample 1 from Example 1, Samples 8 to 11 were heat-treated Sample 2 from Example 1, and Samples 12 to 15 were heat-treated Sample 3 from Example 1. For the solution-treated samples, the temperature and time were determined based on the heat treatment that combines quenching and solution treatment of the tool steel when additively manufacturing a maraging steel on a general tool steel to form a composite. The aging treatment time was 3 hours per cycle. Hardness was measured using a Rockwell hardness test in accordance with JIS Z 2245. Tensile test specimens were taken from the tempered additive manufacturing product in a direction horizontal to the lamination direction, and a high-temperature tensile test at 550°C and a room-temperature tensile test at 22°C in accordance with JIS Z 2241, as well as a 2 mm U-notch Charpy impact test in accordance with JIS Z 2242, were performed.

[0037]

[0038] Table 6 shows the 550°C-0.2% yield strength (high-temperature yield strength), room-temperature reduction, and 2mm U-notch Charpy impact value, which indicates toughness, for the 52HRC tempered material without solution treatment and aging, and Table 7 shows the 46HRC tempered material without solution treatment and aging. When compared with materials tempered to the same hardness, the inventive example exhibited higher high-temperature yield strength and Charpy impact value than the comparative example. These results confirm that the present invention, under heat treatment conditions that omit solution treatment, can produce additively manufactured products with thermal fatigue life properties that exceed those of conventional low-Co maraging steel.

[0039]

[0040]

[0041] Table 8 shows the 550°C-0.2% yield strength (high-temperature yield strength), room-temperature draw, and 2mm U-notch Charpy impact value, which indicates toughness, for the solution-treated, 1020°C-aging, 52HRC tempered material, and Table 9 shows the solution-treated, 1020°C-aging, 46HRC tempered material. When compared with materials tempered to the same hardness, the inventive example exhibited higher high-temperature yield strength and Charpy impact value than the comparative example. It was confirmed that the present invention can produce additively manufactured products with thermal fatigue life properties superior to those of conventional low-Co maraging steels, even under heat treatment conditions that combine quenching and solution treatment of the tool steel, such as when a maraging steel is additively manufactured on a conventional tool steel to form a composite.

[0042]

[0043]

Claims

1. Maraging steel powder for additive manufacturing consisting of, by mass%, C: 0.02% or less, Si: 0.04-0.3%, Ni: 16-20%, Co: 0.1% or less, Mo: 2.7-3.5%, Ti: 1.5-2.5%, Al: 0.01% or less, and the balance: Fe and unavoidable impurities.

2. A maraging steel additively manufactured product consisting of, by mass%, C: 0.02% or less, Si: 0.04-0.3%, Ni: 16-20%, Co: 0.1% or less, Mo: 2.7-3.5%, Ti: 1.5-2.5%, Al: 0.01% or less, and the balance: Fe and unavoidable impurities.

3. A method for manufacturing an additive manufacturing product of maraging steel, comprising: a powder layer forming step of spreading the maraging steel powder for additive manufacturing according to claim 1 in the form of layers; and a melting and solidifying step of successively melting and solidifying the spread maraging steel powder for additive manufacturing using a scanning heat source having a diameter larger than D50 of the maraging steel powder for additive manufacturing to form a solidified layer, wherein the powder layer forming step and the melting and solidifying step are repeated to obtain an additive manufacturing product.

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