Maraging steel powder for laminate molding, maraging steel laminate molded article, and method for producing same

Abstract

Provided is a maraging steel powder with which it is possible to obtain a laminated molded article having excellent thermal fatigue life characteristics and little deformation after molding while minimizing Co content. A maraging steel powder for laminate molding, which contains, in mass%, 0.02% or less of C, 0.1%-0.3% of Si, 16%-20% of Ni, 0.1% or less of Co, 2.7%-3.5% of Mo, 1.5%-2.5% of Ti, 0.01% or less of Al, and the balance of Fe and unavoidable impurities, and a laminate molded article of maraging steel, which contains, in mass%, 0.02% or less of C, 0.1%-0.3% of Si, 16%-20% of Ni, 0.1% or less of Co, 2.7%-3.5% of Mo, 1.5%-2.5% of Ti, 0.01% or less of Al, and the balance of Fe and unavoidable impurities. The steel sheet comprises 0.02% or less of C, 0.1%-0.3% of Si, 16%-20% of Ni, 0.1% or less of Co, 2.7%-3.5% of Mo, 1.5%-2.5% of Ti, 0.01% or less of Al, and the balance Fe and unavoidable impurities.

Description

Technical Field

[0001] This invention relates to a method for manufacturing martensitic aging steel powder for laminated molding, martensitic aging steel laminated moldings, and martensitic aging steel laminated moldings. Background Technology

[0002] Recently, stacking molding has attracted much attention as a method for easily forming metal products (parts) with complex shapes using near-net-shape technology. Stacking molding is generally also known as additive manufacturing, specifically three-dimensional (3D) printing. Types of stacking molding include powder spraying and powder bed molding. Powder spraying involves melting metal powder while irradiating it with a heat source, while powder bed molding involves melting and solidifying metal powder laid flat on a platform by irradiating it with a heat source, repeating this process to stack the metal. Stacking molding can significantly reduce the number of machining steps required to produce metal products with complex shapes, thus allowing the use of difficult-to-machine metal materials. Furthermore, difficult-to-machine metal materials are often high-strength, enabling the production of metal products with complex shapes and long lifespans. One application of near-net-shape machining of such complex three-dimensional shapes is die casting molds.

[0003] As a high-strength metallic material, martensitic aging steel is a representative example. Martensitic aging steel, for example, is an age-hardening type of ultra-high-strength steel containing approximately 18% by mass Ni, with the addition of age-hardening elements such as Co, Mo, Ti, and Al. Furthermore, due to its excellent toughness, martensitic aging steel is effective in extending the lifespan of various tools and structural parts by using it as the material. Moreover, a method for manufacturing laminated products using martensitic aging steel in metallic materials via the aforementioned lamination molding method has been proposed (Patent Document 1).

[0004] Because martensitic aging steel powder exhibits excellent strength and toughness in its shaped state and after aging treatment, it is suitable for the stacking and shaping of the aforementioned die-casting molds. As for martensitic aging steels used in this mold application, 300 ksi (kilopound-force per square inch) grade martensitic aging steels are known, typically with a composition of Fe-18%Ni-9%Co-5%Mo.

[0005] On the other hand, when using the powder bed method in laminated molding, powder or dust may be released into the atmosphere from the powder to the mold, especially powder or dust containing added Co, which requires management to control its impact on human health. Furthermore, since the addition of Co increases costs, low-Co maraging steel powder is required. For example, the applicant of this application has proposed a powder for laminated molding, which is formed from maraging steel composed of the following components by mass percent: C: 0.1% or less, Ni: 14%–22%, Co: 0%–5%, Mo: 0.1%–15.0%, Ti: 0.1%–5.0%, Al: 3.0% or less, with the remainder being Fe and impurities. The powder described in Patent Document 2, having the alloy composition described above, can reduce Ti segregation and improve the toughness of the maraging steel laminated product (Patent Document 2).

[0006] Furthermore, as a common issue in articles manufactured by lamination forming (laminated articles), the generation of strain caused by residual stress is known. As a method to suppress such strain in carbon steel or martensitic stainless steel accompanied by martensitic phase transformation, for example, a method has been proposed as follows: by taking into account the martensitic phase transformation initiation temperature (Ms point) of the raw material powder, the temperature is adjusted between multiple layers of the laminated article by a temperature regulating mechanism of the lamination forming device, thereby mitigating the strain in the laminated article (Patent Document 3).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2011 / 149101

[0010] Patent Document 2: Japanese Patent Application Publication No. 2020-45567

[0011] Patent Document 3: Japanese Patent No. 6295001 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] In the absence of a stacking forming device with a temperature control mechanism as described in Patent Document 3, the stacked formed product may sometimes deform or crack due to strain caused by the thermal shrinkage of the material during forming. In particular, low-Co martensitic aging steel with less than 1% Co tends to have a larger deformation amount compared to general 300 ksi grade products, thus requiring further suppression of deformation.

[0014] On the other hand, one characteristic required for die-casting molds is that they are less prone to cracking due to thermal fatigue (improved thermal fatigue life). To obtain a mold with good thermal fatigue life, a mold material is needed that exhibits high-temperature strength, as well as good room-temperature ductility and toughness after heat treatment of the shaped laminated product (tempered material). Therefore, the object of this invention is to provide a martensitic aging steel powder that yields laminated products with minimal deformation and excellent thermal fatigue life characteristics even with significant reduction in Co, and laminated products obtained using said powder.

[0015] Technical means to solve the problem

[0016] The present invention was made in view of the aforementioned issues.

[0017] That is, one aspect of the present invention is a martensitic aging steel powder for laminated forming, which, by mass%, comprises: C: less than 0.02%, Si: 0.04% to 0.3%, Ni: 16% to 20%, Co: less than 0.1%, Mo: 2.7% to 3.5%, Ti: 1.5% to 2.5%, Al: less than 0.01%, with the remainder being Fe and unavoidable impurities.

[0018] Another aspect of the present invention is a martensitic aging steel laminate, which, by mass%, comprises: C: less than 0.02%, Si: 0.04% to 0.3%, Ni: 16% to 20%, Co: less than 0.1%, Mo: 2.7% to 3.5%, Ti: 1.5% to 2.5%, Al: less than 0.01%, with the remainder being Fe and unavoidable impurities.

[0019] Another aspect of the present invention is a method for manufacturing a maraging steel laminate, comprising: a powder layer forming step, wherein the maraging steel powder for the laminate is laid flat in a layer; and a melting and solidification step, wherein the laid maraging steel powder for the laminate is successively melted and solidified by passing it through a scanning heat source having a diameter larger than the D50 of the maraging steel powder for the laminate, thereby forming a solidified layer, and the powder layer forming step and the melting and solidification step are repeated to obtain the laminate.

[0020] The effects of the invention

[0021] Through this invention, laminated products with minimal deformation and excellent thermal fatigue life characteristics can be obtained even with extreme reduction in Co. Attached Figure Description

[0022] [ Figure 1 [Image] is a schematic diagram of a warpage measurement test piece used for strain evaluation. Detailed Implementation

[0023] This invention comprises a composition of C: 0.02% or less, Si: 0.04% to 0.3%, Ni: 16% to 20%, Co: 0.1% or less, Mo: 2.7% to 3.5%, Ti: 1.5% to 2.5%, Al: 0.01% or less, with the remainder being Fe and unavoidable impurities. First, the rationale for limiting the composition of the martensitic aging steel for laminated forming as specified in this invention will be described. Furthermore, unless otherwise specified, "%" indicates "mass %".

[0024] C (carbon): below 0.02%

[0025] To obtain a high-toughness, low-carbon martensitic structure characteristic of maraging steel, carbon (C) needs to be limited to below 0.02%. When C exceeds 0.02%, the toughness decreases in the shaped state (the state after lamination shaping without heat treatment), and cracking may occur due to strain caused by thermal shrinkage. Preferably, it is below 0.01%. On the other hand, C can also be used as a deacidifying agent in the smelting process; since it is difficult to manufacture without adding it, the lower limit can be set, for example, to 0.001%.

[0026] Si (silicon): 0.04%~0.3%

[0027] Si is an element that improves strength, and its content is set to 0.04% or more. On the other hand, since excessive addition of Si will reduce the toughness of the quenched and tempered material required to improve thermal fatigue life characteristics, the Si content is set to a maximum of 0.3%. Moreover, in order to further improve toughness, the upper limit of Si content is preferably set to 0.2%, and more preferably to 0.15%.

[0028] Ni (nickel): 16% ~ 20%

[0029] Ni is a fundamental element required for martensitic aging steel because it forms intermetallic compounds with Ti, Al, Mo, etc., which helps improve strength. Therefore, in this 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 austenitic structure is stabilized, making it difficult to form a martensitic structure. Therefore, in this invention, the Ni content is set to 20% or less. A preferred upper limit for the Ni content is 19%.

[0030] Co (Cobalt): less than 0.1%

[0031] In this invention, considering the ease of managing the impact on human health and the high cost of Co itself, the Co content is reduced. Furthermore, in this invention, it has been found that by keeping the Co content, which has the effect of lowering the solid solution limit of Mo, to a very low level of 0.1% or less, the toughness of the tempered material can be improved. This is believed to be because by reducing the excessive precipitation of Mo-based intermetallic compounds, the toughness required for thermal fatigue life characteristics is increased. The preferred upper limit is 0.05%, and a more preferred upper limit is 0.01%. In addition, it is ideal to set Co to be non-added (0%), but since this is difficult to manufacture, the lower limit can be set to, for example, 0.0005%.

[0032] Mo (molybdenum): 2.7% ~ 3.5%

[0033] Mo is an element that, during aging treatment, forms Ni3Mo as an intermetallic compound, thereby strengthening the metal structure through precipitation or solid solution strengthening, thus improving strength and thermal fatigue life. Furthermore, the addition of Mo in compositions such as low-Co martensitic aging steel lowers the Ms point. In the absence of a stacking forming apparatus with a temperature control mechanism, the forming temperature may be near room temperature depending on the forming conditions. However, by lowering the Ms point to near room temperature, the effect of mitigating thermal shrinkage caused by martensitic phase transformation expansion can be effectively utilized, reducing deformation caused by thermal shrinkage. Therefore, in this invention, the Mo content is preferably 2.7% or more.

[0034] On the other hand, if the Mo content is too high, it will excessively form coarse intermetallic compounds with Fe, reducing the toughness of the tempered material required for thermal fatigue life characteristics. Furthermore, excessive Mo addition will lower the Ms point above the desired level, making it difficult to form a martensitic structure. Therefore, in this invention, the Mo content is preferably 3.5% or less.

[0035] Ti (Titanium): 1.5%~2.5%

[0036] Ti is an element that forms Ni3Ti as a reinforcing phase in the microstructure after aging treatment, imparting the high-temperature strength required for thermal fatigue life characteristics. Therefore, in this invention, the Ti content is set to 1.5% or more. Furthermore, for the same reasons mentioned above, the Ti content is preferably 1.7% or more, and more preferably 1.9% or more.

[0037] On the other hand, if the Ti content is too high, significant Ti segregation may occur in the microstructure during solidification, and this significant Ti segregation may remain in the microstructure after aging treatment, reducing the toughness of the tempered material required for thermal fatigue life characteristics. Therefore, in this invention, the Ti content is set to 2.5% or less. Furthermore, for the same reasons, the Ti content is preferably 2.3% or less, more preferably 2.1% or less. Moreover, in this invention, to stably obtain the precipitation strengthening effect brought about by Mo and Ti, the Ti+Mo content is preferably set to 4.5% to 5.5%. A more preferred upper limit for Ti+Mo is 5.2%.

[0038] Al (aluminum): less than 0.01%

[0039] Al and Ni form intermetallic compounds, which have the effect of precipitation strengthening of the metal structure. However, if there is too much, non-metallic inclusions may increase in the metal structure, resulting in decreased toughness. Therefore, it is set to 0.01% or less. The preferred upper limit is 0.007%, and even more preferably 0.005%. In addition, the strength imparted by the intermetallic compounds can be achieved by Mo or Ti, thus reducing the elements to be processed and omitting manufacturing management steps. Furthermore, it is ideal to set Al to be not added (0%), but since it is difficult to manufacture, the lower limit can be set, for example, to 0.0001%. The basic composition of the present invention is set to selectively include the aforementioned element types, with the remainder including Fe and unavoidable impurities.

[0040] Furthermore, the martensitic aging steel powder for laminated forming according to the present invention preferably contains 0.030% or less N (nitrogen) by mass%. Nitrogen is an element that is inevitably introduced into the metal powder from the raw materials or the atmosphere of the melting and pulverizing processes during the metal powder manufacturing process. If the content of nitrogen is too high, it will combine with Ti, Mo, etc. in the laminated forming to form a large amount of nitrides. These nitrides act as the starting point for damage, and there is a concern that they will reduce the toughness of the tempered material. Therefore, in the present invention, the content of nitrogen is preferably 0.030% or less, more preferably 0.020% or less, and even more preferably 0.005% or less.

[0041] However, nitrogen (N) is an element that is inevitably mixed in during the manufacturing processes of general laminated forming powders, such as gas atomization. From the viewpoint of suppressing internal defects in laminated forming articles and ensuring sufficient toughness, one aspect of the martensitic aging steel powder for laminated forming of the present invention allows for the content of 0.001% or more of nitrogen (N).

[0042] The martensitic aging steel powder for layered forming of the present invention preferably contains 0.040% or less of oxygen (O). O is an element that is inevitably introduced into the metal powder from the raw materials or the atmosphere of the melting and pulverizing processes during the manufacturing process of the metal powder. O combines with Ti and the like to form oxides inside or on the surface of the metal powder. These oxides act as the starting point for damage, and there is a concern that they reduce toughness. Therefore, in the present invention, the content of O is preferably 0.040% or less, more preferably 0.030% or less, and even more preferably 0.020% or less.

[0043] From the viewpoint of suppressing internal defects in laminated products and ensuring sufficient toughness, the martensitic aging steel powder for laminated products of the present invention may contain more than 0.005% or more or more 0.010% O (oxygen).

[0044] The maraging steel powder for layered shaping according to the present invention can be manufactured, for example, by gas atomization, water atomization, disk atomization, plasma atomization, or rotating electrode method. The gas atomization method involves heating a molten raw material prepared in a manner that yields the desired composition to above its melting point using high-frequency induction heating. After melting, an inert gas such as argon or nitrogen is injected into the molten metal flowing through fine orifices, thereby finely pulverizing the molten metal and rapidly cooling it to obtain powder. The gas atomization method can use scrap metal or coarse metal raw materials as the molten raw material. Compared to plasma atomization or rotating electrode methods, which require pre-preparation of raw materials with the desired composition and shape, it can be manufactured at a low cost, making it a preferred method for obtaining the metal powder for layered shaping according to the present invention.

[0045] The martensitic aging steel powder for laminated forming according to the present invention preferably has a 50% particle size (hereinafter referred to as "D50") of 10 μm to 250 μm based on the volumetric cumulative particle size distribution. Regarding the metal powder for laminated forming according to the present invention, by setting its D50 to 250 μm or less, the powder melts more easily, and the formation of internal defects in laminated forming articles can be suppressed.

[0046] Furthermore, regarding the metal powder for lamination forming according to the present invention, by setting its D50 to 10 μm or more, it is less susceptible to the effects of moisture and the like in the atmosphere of metal powder handling or lamination forming, thus ensuring good flowability.

[0047] Furthermore, the cumulative particle size distribution of the shaping powder of the present invention is represented by the cumulative volumetric particle size distribution, and its D50 can be represented by the measured value based on the laser diffraction scattering method specified in Japanese Industrial Standards (JIS) Z 8825.

[0048] The maraging steel powder for layered forming of the present invention can also have its D50 adjusted by using methods such as sieving and classifying with a sieve or air classifying, according to the described method. For example, regarding the metal powder for layered forming used in the powder bed method, the metal powder is melted by a laser beam that serves as a heat source. On the other hand, in order to minimize the range of heat-affected zones, it is necessary to remove coarse metal powder that is difficult to melt. In addition, in order to obtain optimal flowability to ensure the spreadability of the metal powder, it is also necessary to remove fine metal powder with high adhesion. Therefore, when applying the maraging steel powder for layered forming of the present invention to the powder bed method, it is preferable to adjust the D50 to a range of 10 μm to 53 μm. The preferred upper limit of D50 is 40 μm, and the preferred lower limit of D50 is 20 μm.

[0049] By using the manufacturing method described later to laminate the martensitic aging steel powder for lamination forming according to the present invention, a martensitic aging steel laminate containing, by weight %: C: 0.02% or less, Si: 0.04% to 0.3%, Ni: 16% to 20%, Co: 0.1% or less, Mo: 2.7% to 3.5%, Ti: 1.5% to 2.5%, Al: 0.01% or less, with the remainder being Fe and unavoidable impurities. Preferably, the Ti+Mo content is 4.5% to 5.5%. The laminated product exhibits low deformation due to thermal shrinkage and excellent thermal fatigue life characteristics. Die-casting molds are the most preferred application for the laminated product, but it may also be applicable to other molds such as plastic molds that require internal cooling mechanisms. Furthermore, it may also be applicable to the repair of molds using powder spraying for lamination forming. In addition, it is not limited to molds and may also be applicable to various tools or gears and other components using martensitic aging steel.

[0050] Next, the manufacturing method of the present invention, which uses the martensitic aging steel powder of the present invention to obtain the laminated articles of the present invention, will be described. Furthermore, the manufacturing steps described below can be applied, for example, to the powder bed method.

[0051] In the manufacturing method of the present invention, the following steps are performed: a step of spreading the prepared martensitic aging steel powder (hereinafter also referred to as "metal powder") for layering into a layer, and a step of successively melting the spread metal powder through a scanning heat source having a diameter larger than the D50 of the metal powder and solidifying it, thereby forming a solidified layer. Then, by repeating the step of spreading the metal powder into a layer and the step of forming the solidified layer, multiple layered solidified layers are formed, thereby producing the layered shape of the present invention. The scanning heat source can be, for example, a laser or an electron beam. Moreover, by making the diameter of the scanning heat source larger than the D50 of the metal powder, the aggregate of metal powder can be melted uniformly, which is preferable in this respect.

[0052] In the manufacturing method of the present invention, the laser power during simultaneous scanning and irradiation of the metal powder can be 50 W to 350 W, the scanning speed can be 200 mm / s to 2000 mm / s, and the scanning interval can be 0.02 mm to 0.20 mm. Here, if the layer thickness of each laser scan is too large, heat cannot be transferred to the entire sheet of metal powder during laser irradiation, the metal powder cannot melt sufficiently, and internal defects are promoted. On the other hand, if the layer thickness of each scan is too small, the number of layers required to reach the desired size of the stacked product increases, and the time required for the stacking and forming process increases. Therefore, the layer thickness of each scan is preferably set to 10 μm to 200 μm. A more preferred lower limit for the layer thickness is 20 μm, and a more preferred upper limit is 100 μm.

[0053] In the manufacturing method of the present invention, in order to impart the mechanical properties required for use as a metal article (part), it is preferable to perform an aging treatment on the component in a laminated state (a state after lamination without heat treatment). Aging treatment of the laminated article of the present invention allows various intermetallic compounds to precipitate in the microstructure, which is useful in this respect, for example, adjusting the hardness to 40 Rockwell Hardness (HRC) to 55 HRC. The aging treatment temperature is preferably set to 400°C or higher. More preferably, it is 450°C or higher, even more preferably 500°C or higher, and even more preferably 550°C or higher. By increasing the aging treatment temperature, the strength improvement effect resulting from the precipitation of Ni3Ti can be obtained. However, if the aging treatment temperature is too high, the intermetallic compounds become coarse, and the strength expected from the amount of intermetallic compound precipitation cannot be sufficiently obtained. Therefore, the aging treatment temperature is preferably set to 700°C or lower. More preferably, it is 650°C or lower, even more preferably 640°C or lower, and even more preferably 630°C or lower. It can also be set to below 600℃.

[0054] Furthermore, the aging treatment time (the holding time at the aging treatment temperature) is preferably set to 60 minutes or more. More preferably, it is 100 minutes or more, and even more preferably, it is 150 minutes or more. By extending the aging treatment time, the amount of various intermetallic compounds increases. However, if the aging treatment time is too long, the intermetallic compounds become coarser, and the strength decreases. Therefore, the aging treatment time is preferably set to 600 minutes or less. More preferably, it is 400 minutes or less, and even more preferably, it is 200 minutes or less. In addition, in order to adjust to a specific hardness (tempering) while measuring the hardness at any time, the aging treatment time for each time can be set within the above-preferred range and performed multiple times. Furthermore, in the heat treatment of laminated shaped articles, since the melting and rapid cooling during shaping sometimes also take into account quenching, unlike general smelted materials, the solidification treatment is sometimes omitted, and the aging treatment is performed directly from the shaped state. The manufacturing method of the present invention has been described above. However, the martensitic aging steel powder for laminated forming of the present invention is not limited to the manufacturing method of the present invention. For example, it can also be applied to direct metal deposition methods in which the powder is directly sprayed onto a heat source and deposited onto a substrate.

[0055] In the manufacturing method of the present invention, a solution treatment may be performed to improve mechanical properties or eliminate segregation before the aging treatment. The solution treatment temperature is preferably set to 800°C or higher. More preferably, 850°C or higher. Furthermore, it is more preferably 900°C or higher, and even more preferably 950°C or higher. By increasing the solution treatment temperature, the effect of eliminating segregation formed during lamination is improved. However, if the solution treatment temperature is too high, the original austenite grains coarsen, thus reducing the strength and toughness of the laminated product. Therefore, the solution treatment temperature is preferably set to 1200°C or lower. More preferably, 1100°C or lower, and even more preferably 1050°C or lower.

[0056] The solution treatment time (holding time at the solution treatment temperature) is preferably set to 10 minutes or more. More preferably, it is 30 minutes or more, and even more preferably, it is 45 minutes or more. By extending the solution treatment time, the effect of eliminating segregation formed during lamination is improved. However, if the solution treatment time is too long, the original austenite grain size becomes coarser. Therefore, the solution treatment time is preferably set to 120 minutes or less. More preferably, it is 100 minutes or less, and even more preferably, it is 80 minutes or less. Here, in the laminated products, there are also laminated products used as composites by laminating other materials on the base material. When using laminated products in a mold, sometimes a composite is made by laminating martensitic aging steel on a general tool steel. Tool steel is usually used after quenching, for example, the quenching temperature of general hot work tool steel SKD61 is around 1000°C. When using laminated products as composites, the quenching of tool steel and the solution treatment of martensitic aging steel can be taken into account.

[0057] Example

[0058] (Example 1)

[0059] After preparing the raw metal materials according to the composition shown in Table 1, they were placed in a high-frequency induction melting furnace and melted. The molten metal was then pulverized using argon gas to obtain gas-atomized powder. The obtained atomized powder was sieved and classified using a sieve and airflow classification to adjust the particle size, resulting in a layered molding powder with a D50 of 35 μm, which serves as an example and comparative example of the present invention. For each of the obtained layered molding metal powders, layered molding articles were produced using a Mlab cusing 200R manufactured by GE Additive Manufacturing Co., Ltd., under the molding conditions shown in Table 2. The composition values ​​of the obtained layered molding articles are shown in Table 3.

[0060] [Table 1]

[0061]

[0062] [Table 2]

[0063]

[0064] [Table 3]

[0065]

[0066] First, the deformation of the stacked articles was measured. First, stacked articles, which are examples of the present invention and comparative examples, were fabricated on a base plate. Figure 1 The test piece shown is in the shape of a cantilever beam. Next, in... Figure 1 The cut section of the support shown was cut by wire electrical discharge machining, and the beam warped due to the accumulated strain. This confirms that the greater the warping, the more strain accumulates in the layered structure.

[0067] Next, the height of the measuring point at the end of the beam portion, with the base plate as the reference, was measured before and after the support portion was cut. As shown in Table 4, it was confirmed that the deformation of the laminated product containing the Co-free martensitic aging steel of the present invention was less than that of the low-Co martensitic aging steel of the comparative example. The laminated product of the present invention can suppress deformation in the forming state even if the Co content is minimized.

[0068] [Table 4]

[0069]

[0070] (Example 2)

[0071] Next, to confirm the mechanical properties of the laminated product, the same laminated product as that produced in Example 1 was subjected to heat treatment under the conditions shown in Table 5, with a hardness of 46 HRC ± 1 HRC and 52 HRC ± 1 HRC. Here, Samples No. 4 to No. 7 are samples that underwent heat treatment on Sample No. 1 of Example 1, Samples No. 8 to No. 11 are samples that underwent heat treatment on Sample No. 2 of Example 1, and Samples No. 12 to No. 15 are samples that underwent heat treatment on Sample No. 3. Regarding the samples that underwent solution treatment, the heat treatment was assumed to be a case where martensitic aging steel was laminated on general tool steel to form a composite, taking into account both the quenching and solution treatment of the tool steel, and the temperature and time were determined. In addition, the aging treatment time was 3 hours each time. The hardness was determined by Rockwell hardness test in accordance with JIS Z 2245. Tensile test pieces were collected horizontally relative to the stacking direction of the tempered laminated product and subjected to 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.

[0072] [Table 5]

[0073]

[0074] Table 6 shows the 550°C-0.2% yield strength (high-temperature yield strength), room-temperature reduction of area, and 2 mm U-notch Charpy impact value (indicating toughness) of the HRC quenched and tempered material without solid melting treatment and aging treatment (52). Table 7 shows the 550°C-0.2% yield strength (high-temperature yield strength), room-temperature reduction of area, and 2 mm U-notch Charpy impact value (indicating toughness) of the HRC quenched and tempered material without solid melting treatment and aging treatment (46). When comparing materials quenched and tempered to the same hardness, the examples of the present invention show higher high-temperature yield strength and Charpy impact value than the comparative examples. Based on the above results, it is confirmed that the present invention can obtain laminated products with thermal fatigue life characteristics exceeding those of conventional low-Co martensitic aging steels under heat treatment conditions that omit solid melting treatment.

[0075] [Table 6]

[0076]

[0077] [Table 7]

[0078]

[0079] Table 8 shows the 550°C-0.2% yield strength (high-temperature yield strength), room-temperature reduction of area, and 2 mm U-notch Charpy impact value (indicating toughness) of the HRC quenched and tempered material after solution treatment at 1020°C and aging treatment at 52°C. Table 9 shows the 550°C-0.2% yield strength (high-temperature yield strength), room-temperature reduction of area, and 2 mm U-notch Charpy impact value (indicating toughness) of the HRC quenched and tempered material after solution treatment at 1020°C and aging treatment at 46°C. When comparing materials quenched and tempered to the same hardness, the present invention shows higher high-temperature yield strength and Charpy impact value than the comparative examples. It has been confirmed that even under the heat treatment conditions of quenching and solution treatment of tool steel, where martensitic aging steel is laminated and formed into a composite on general tool steel, the present invention can obtain laminated products with thermal fatigue life characteristics exceeding those of conventional low-Co martensitic aging steel.

[0080] [Table 8]

[0081]

[0082] [Table 9]

[0083]

Claims

1. A martensitic aging steel powder for layered molding, comprising, by mass%, less than 0.02% C, 0.04% to 0.3% Si, 16% to 20% Ni, less than 0.1% Co, 2.7% to 3.5% Mo, 1.5% to 2.5% Ti, less than 0.01% Al, with the remainder being Fe and unavoidable impurities.

2. A martensitic aging steel laminate, comprising, by mass%, less than 0.02% C, 0.04% to 0.3% Si, 16% to 20% Ni, less than 0.1% Co, 2.7% to 3.5% Mo, 1.5% to 2.5% Ti, less than 0.01% Al, with the remainder being Fe and unavoidable impurities.

3. A method for manufacturing a martensitic aging steel laminated product, comprising: a powder layer forming step, wherein the martensitic aging steel powder for laminated product as described in claim 1 is spread into a layer; and In the melting and solidification process, the flat, layered martensitic aging steel powder for shaping is successively melted and solidified by a scanning heat source having a diameter larger than the D50 of the layered martensitic aging steel powder, thereby forming a solidified layer. The powder layer forming process and the melting and solidification process are repeated to obtain a laminated product.

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