Fe-based alloy, alloy member, and method for producing alloy member

Abstract

Provided are: an Fe-based alloy which is unlikely to crack and which is expected to exhibit toughness and thermal cracking resistance; an alloy member; and a method for producing an alloy member.　The Fe-based alloy is characterized: by containing C, Cr, W, Mo and V, with the remainder comprising Fe and unavoidable impurities; having an alloy structure that contains an Fe-BCC phase; in that the Fe-BCC phase contains, in terms of mass%, 3.0-7.0% of C, 2.0-6.0% of Cr, 0.5-4.0% of W, 0.5-4.0% of Mo, 0.5-4.0% of V and 75.0-93.5% of Fe if the total amount of C, Cr, W, Mo, V and Fe is taken to be 100 mass%; in that the alloy has a precipitated carbide in the Fe-BCC phase; and in that the proportion of the Fe-BCC phase is 43.5% or more in terms of areal ratio in a cross-sectional structure observation.

Description

Fe-based alloy, alloy member, and method for manufacturing alloy member

[0001] The present invention relates to an Fe-based alloy, an alloy member, and a method for manufacturing the alloy member.

[0002] Conventionally, tools such as punches and dies for hot precision press working have been made of hot work tool steels with high high-temperature strength, such as SKD8 specified in JIS G 4404, and high-speed tool steels such as SKH51 specified in JIS G 4403. However, these steels have had problems such as susceptibility to settling, wear, breakage, cracking, and heat cracking.

[0003] For example, Patent Document 1 discloses a tool steel containing, in mass %, 0.4 to 0.9% C (carbon), 1.0% or less Si (silicon), 1.0% or less Mn (manganese), 1.5 to 6% of one or both of W (tungsten) and Mo (molybdenum) (1 / 2W+Mo) (however, W is 3% or less), and 0.5 to 3% of one or both of V (vanadium) and Nb (niobium) (V+Nb), in which the average particle size of precipitated carbides dispersed in the matrix is ​​0.5 μm or less and the distribution density is 80×10 ３ pieces / mm ２ A high-speed tool steel characterized by the above is disclosed.

[0004] Japanese Patent Application Laid-Open No. 2004-307963

[0005] In the tool steel of Patent Document 1, coarse primary carbides are formed in the ingot due to solidification segregation during cooling during ingot-making, such as the casting or remelting process of the steel ingot. The presence of these coarse primary carbides promotes the initiation and propagation of cracks, thereby reducing toughness and heat crack resistance. The precipitated carbides preferably have a finely dispersed, uniform structure. To obtain such a structure, soaking at 1200 to 1300°C for 10 to 20 hours is required. However, even after soaking, subsequent quenching and tempering processes are required to obtain forging tools such as dies and punches, as well as molds. This process may result in the precipitation of coarse precipitated carbides, which may reduce toughness and heat crack resistance.

[0006] Therefore, an object of the present invention is to provide an Fe-based alloy, an alloy member, and a method for manufacturing an alloy member that is less susceptible to cracking and is also expected to have toughness and heat crack resistance.

[0007] The present invention provides an Fe-based alloy comprising C, Cr, W, Mo, and V, with the balance being Fe and unavoidable impurity elements, and having an alloy structure including an Fe-BCC phase, wherein the Fe-BCC phase contains, in mass %, 3.0% to 7.0% of C, 2.0% to 6.0% of Cr, 0.5% to 4.0% of W, 0.5% to 4.0% of Mo, 0.5% to 4.0% of V, and 75% to 93.5% of Fe, where the total of C, Cr, W, Mo, V, and Fe is taken as 100%, and wherein carbides are precipitated in the Fe-BCC phase, and the proportion of the Fe-BCC phase is 43.5% or more in terms of area fraction in cross-sectional structural observation.

[0008] Furthermore, it is preferable that the Fe-based alloy as a whole contains, in mass %, C of 0.1% to 2.0%, Cr of 2.0% to 6.0%, W of 0.5% to 4.0%, Mo of 0.5% to 4.0%, V of 0.5% to 4.0%, Si of 1.0% or less, Mn of 1.0% or less, with the balance being Fe and inevitable impurities.

[0009] Furthermore, the Fe-BCC phase preferably contains, in mass%, C of 4.8% or more and 6.0% or less, Cr of 3.9% or more and 6.0% or less, W of 1.5% or more and 3.0% or less, Mo of 2.2% or more and 3.1% or less, and V of 1.5% or more and 3.0% or less.

[0010] The present invention also provides an alloy member comprising at least a portion of the Fe-based alloy.

[0011] The hardness of the Fe-based alloy is preferably 700 HV or more.

[0012] The present invention also provides a method for producing an alloy member, which comprises using an alloy powder containing, by mass%, from 0.1% to 2.0%, C from 2.0% to 6.0%, W from 0.5% to 4.0%, Mo from 0.5% to 4.0%, V from 0.5% to 4.0%, Si from 1.0% to 1.0%, Mn from 1.0% to 1.0%, with the balance being Fe and unavoidable impurities, irradiating the alloy powder with an electron beam or a laser beam to melt and solidify it to form a solidified layer, forming a new solidified layer on the solidified layer, and then repeating this process to obtain an alloy member having a layered structure.

[0013] According to the present invention, it is possible to provide an Fe-based alloy, an alloy member, and a method for manufacturing an alloy member, which are unlikely to crack and are expected to have good toughness and heat crack resistance.

[0014] A diagram illustrating the schematic configuration of an additive manufacturing method. A structural photograph and elemental mapping image of a molded body after quenching treatment. A structural photograph and elemental mapping image of a molded body after quenching treatment and tempering treatment. A structural photograph and elemental mapping image of a molded body (without heat treatment). A structural photograph and elemental mapping image of a molded body after tempering treatment. A structural photograph and elemental mapping image of a conventional forged material after quenching treatment and tempering treatment. A diagram showing the Vickers hardness (HV) of each molded body.

[0015] An embodiment of the present invention will be described below. First, an Fe-based alloy will be described, and then an additive manufacturing method will be described. In the following description, % indicates mass %. In addition, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limit values. In addition, the lower and upper limit values ​​of the numerical range can be combined as appropriate.

[0016] <Fe-Based Alloy> The Fe-based alloy of this embodiment contains C, Cr, W, Mo, and V, with the balance being Fe and inevitable impurity elements. In other words, it is a high-speed tool steel containing C, Cr, W, Mo, V, and Fe. The alloy has an alloy structure including an Fe-BCC phase. The Fe-BCC phase contains, in mass %, 3.0% to 7.0% of C, 2.0% to 6.0% of Cr, 0.5% to 4.0% of W, 0.5% to 4.0% of Mo, 0.5% to 4.0% of V, and 75.0% to 93.5% of Fe, when the total of C, Cr, W, Mo, V, and Fe is taken as 100%. One of its features is that the Fe-BCC phase contains precipitated carbides, and the proportion of the Fe-BCC phase is 43.5% or more in terms of area fraction in cross-sectional structural observation.

[0017] (Fe-BCC Phase) The Fe-BCC phase is generally a structure containing α-Fe and martensite formed when an Fe-based alloy is cooled from a high temperature. Here, in the case of an Fe-BCC phase obtained by a method with a fast melting and solidification rate, i.e., a fast cooling rate, such as an Fe-BCC phase obtained using an additive manufacturing method, it refers to a structure containing martensite of an Fe-based alloy in which C is supersaturated in solid solution, and such an Fe-BCC phase is hard. In the Fe-based alloy of this embodiment, the Fe-BCC phase contains 3.0% to 7.0% C, 2.0% to 6.0% Cr, 0.5% to 4.0% W, 0.5% to 4.0% Mo, 0.5% to 4.0% V, and 75.0% to 93.5% Fe. The Fe-BCC phase can be evaluated using electron backscattering diffraction (EBSD). The evaluation method using EBSD will be described later.

[0018] (C: 3.0 to 7.0%) C combines with elements that form carbides, such as Cr, W, Mo, and V, to precipitate carbides. The precipitated carbides (precipitated carbides) are, for example, M ６This produces a composite carbide in which C-type and MC-type carbides are precipitated in combination, thereby improving the wear resistance of Fe-based alloys, alloy members, and their manufactured products. Furthermore, a portion of the C dissolves in the matrix, strengthening the matrix. Therefore, by setting the C content in the Fe-BCC phase to 3.0% or more, the hardness of the Fe-BCC phase can be ensured through both the strengthening of the matrix and the formation of fine carbides within the matrix crystal grains. On the other hand, by setting the C content in the Fe-BCC phase to 7.0% or less, excessive formation of carbides within the matrix grains can be suppressed, ensuring toughness. The C content is preferably 4.0% to 7.0%, and more preferably 4.8% to 6.0%.

[0019] (Cr: 2.0 to 6.0%) Cr combines with C to form carbides, improving wear resistance and also contributing to improved hardenability. By setting the Cr content in the Fe-BCC phase to 2.0% or more, the amount of carbides formed within the matrix grains can be optimized, thereby improving wear resistance and hardenability. On the other hand, by setting the Cr content in the Fe-BCC phase to 6.0% or less, the amount of carbides formed within the matrix grains can be prevented from becoming excessive, ensuring toughness. The Cr content is preferably 3.0% to 6.0%, and more preferably 3.9% to 6.0%.

[0020] (W: 0.5 to 4.0%) W combines with C to form carbides, contributing to improved wear resistance. It also contributes to ensuring strength in high-temperature environments, making it particularly effective in improving the wear resistance of dies used in high-temperature environments. By setting the W content in the Fe-BCC phase to 0.5% or more, it dissolves in the matrix, increasing heat treatment hardness and improving wear resistance. On the other hand, by setting the W content in the Fe-BCC phase to 4.0% or less, excessive formation of carbides within matrix grains can be suppressed, ensuring toughness. The W content is preferably 1.0% to 3.5%, and more preferably 1.5% to 3.0%.

[0021] (Mo: 0.5 to 4%) Mo combines with C to form carbides, improving wear resistance and also contributing to improved hardenability. By making the Mo content in the Fe-BCC phase 0.5% or more, it dissolves in the matrix grains, increasing heat treatment hardness, and thus improving wear resistance. On the other hand, by making the Mo content in the Fe-BCC phase 4.0% or less, it is possible to prevent excessive formation of carbides in the matrix grains and ensure toughness. The Mo content is preferably 1.5% to 3.5%, and more preferably 2.2% to 3.1%.

[0022] (V: 0.5 to 4.0%) V combines with C to form carbides, contributing to improved wear resistance and seizure resistance. By setting the V content in the Fe-BCC phase to 0.5% or more, fine, non-aggregating carbides are precipitated within the matrix grains by heat treatment, increasing softening resistance in high-temperature ranges and high-temperature yield strength. In addition, the matrix crystal grains are refined, improving toughness and raising the A1 transformation point, which, combined with excellent high-temperature yield strength, improves heat crack resistance. On the other hand, by setting the V content in the Fe-BCC phase to 4.0% or less, excessive carbide formation within the matrix grains can be suppressed, ensuring toughness. The V content is preferably 1.0% to 3.5%, and more preferably 1.5% to 3.0%.

[0023] (Carbide) Carbide containing C and at least one of Cr, W, Mo, and V (hereinafter referred to as precipitated carbide) precipitates in the Fe-BCC phase. In the Fe-BCC phase, C combines with carbide-forming elements such as Cr, W, Mo, and V to form hard carbides, which are effective in improving wear resistance. Furthermore, C has the effect of strengthening the matrix by dissolving partially in the matrix. A phase containing precipitated carbides can be referred to as a carbide phase. Cr, V, Mo, and W are concentrated more in the carbide phase than in the Fe-BCC phase, and C is particularly abundant in this region. The carbide phase contains, for example, 12% to 15% C, 3% to 5% Cr, 3% to 9% W, 5% to 12% Mo, 15% to 45% V, and 15% to 60% Fe.

[0024] Furthermore, since the precipitated carbides are appropriately refined, cracks are less likely to occur, resulting in an Fe-based alloy with excellent toughness and heat crack resistance. The size of the precipitated carbides is refined to an average circle-equivalent diameter of 1.5 μm or less. The average circle-equivalent diameter is preferably 0.50 μm to 1.45 μm, and more preferably 1.1 μm to 1.45 μm. For example, when using EBSD, the average diameter can be determined from carbides that are visible when the area of ​​the observation field (region area) is 200 × 200 (μm) and the magnification is 400 times or more.

[0025] (Fe-BCC Phase Proportion) The higher the proportion of the Fe-BCC phase, the more uniform the metal structure becomes, and it is expected that, for example, local distortion due to external stress is less likely to occur, and therefore cracks are less likely to occur. Specifically, the proportion of the Fe-BCC phase, in terms of area ratio in cross-sectional structure observation of the alloy to be observed, is 43.5% or more, and preferably 43.8% or more. There is no particular upper limit, but it can be, for example, 60.0% or less, 50.0% or less, or 45.0% or less.

[0026] (Circle-equivalent average particle diameter of Fe-BCC phase) Furthermore, since a finer circle-equivalent average particle diameter of the Fe-BCC phase can improve the mechanical strength of the alloy member, the circle-equivalent average particle diameter is preferably 8.50 μm or less, more preferably 7.30 μm or less, even more preferably 5.50 μm or less, and even more preferably 5.30 μm or less.

[0027] [Method of Calculating the Fe-BCC Phase Ratio and the Average Circle-Equivalent Grain Size] The Fe-BCC phase ratio and the average circle-equivalent grain size described above can be calculated as follows. First, for an arbitrary cross-sectional structure of an alloy, for example, when the alloy is produced by an additive manufacturing method, a phase map is obtained from image data of a field of view (observation field) observed using EBSD on an arbitrary cross-section obtained by cutting the alloy in a direction perpendicular to the stacking direction. Here, the arbitrary cross-section can be, for example, a Y-Z plane, where the building direction is X, the stacking direction is Z, and the axis perpendicular to both X and Z is Y. For example, an RGB image can be used as the image data. Furthermore, the image data is obtained when the area of ​​the observation field is 100 μmm ２ ~500μm ２The phase map obtained by EBSD is divided into each color (red, green, blue), and only the Fe-BCC portion is extracted. The noise in this image is removed using a filter, and the image is binarized and inverted (for example, the original red portion (Fe-BCC phase) is displayed as black).

[0028] Then, the observation field is segmented into the Fe-BCC phase portion and the rest using the Watershed method. Ａ ) is the total area of ​​the Fe-BCC phase determined to be the Fe-BCC phase by segmentation (S Ｆ ) is the proportion (S Ｆ / S Ａ ) can be used as the proportion of the Fe-BCC phase. Furthermore, by calculating the circle-equivalent grain size of each Fe-BCC phase within the segmented observation field and averaging them, it is possible to calculate the circle-equivalent average grain size forming the Fe-BCC phase (the circle-equivalent average grain size of the Fe-BCC phase).

[0029] Specifically, the phase map obtained by EBSD is first divided into a red area (Fe-BCC phase), a blue area (mainly Fe-FCC phase), and a green area (area that is neither Fe-BCC nor Fe-FCC phase; hereafter referred to as the "zero solution area"). This division (segmentation) of the phase map makes it possible to determine the proportion of the Fe-BCC phase and precipitated carbides in the structure. By displaying the image of the divided red area in black and white, the Fe-BCC phase appears white.

[0030] By inverting this black and white display, the blue areas (mainly the Fe-FCC phase) and zero solution areas are displayed in white. By performing this image processing, it is possible to extract the Fe-BCC phase surrounded by the Fe-FCC phase and zero solution areas. The proportion of the Fe-BCC phase can be determined by dividing the total area of ​​the Fe-BCC phase areas by the area of ​​the observation field (e.g., 200 μm × 200 μm).

[0031] Furthermore, the diameter of a circle having the same area as each Fe-BCC phase (the circle-equivalent particle size of the Fe-BCC phase) is determined, and the circle-equivalent particle sizes of all the Fe-BCC phases present within the field of view are arithmetically averaged to determine the average circle-equivalent particle size of the Fe-BCC phase.

[0032] (Proportion and Circle-Equivalent Average Particle Diameter of Precipitated Carbide) The precipitated carbide is preferably appropriately refined. By being appropriately refined, cracks are less likely to occur, and excellent toughness and heat crack resistance, as well as excellent wear resistance, can be expected. For example, the circle-equivalent average particle diameter of the precipitated carbide is preferably 1.0 μm or more and 5.0 μm or less, more preferably 1.2 μm or more and 2.5 μm or less, and even more preferably 1.35 μm or more and 2.0 μm or less. Furthermore, the proportion is preferably 0.5% or more, more preferably 1.0% or more, and even more preferably 2.5% or more. If the proportion of precipitated carbide is 0.5% or more, excellent wear resistance can be expected, and the higher the proportion, the more remarkable the effect can be expected.

[0033] [Method for Calculating the Percentage of Precipitated Carbide and the Average Circle-Equivalent Diameter] The zero solution portion can be displayed by subtracting the image of the divided blue portion from the image in which the Fe-BCC phase is displayed in white, i.e., the image in which the blue portion (mainly the Fe-FCC phase) and the zero solution portion are displayed in white. This zero solution portion is a portion that is neither the Fe-BCC phase nor the Fe-FCC phase and corresponds to the precipitated carbide portion. The percentage of precipitated carbide can then be determined by dividing the total area occupied by the precipitated carbide portions within the observation field by the area of ​​the observation field (e.g., 200 μm × 200 μm). Furthermore, the diameter of a circle that has the same area as each precipitated carbide within the observation field (the circle-equivalent diameter of the precipitated carbide) is calculated, and the circle-equivalent diameter of the precipitated carbide determined for all precipitated carbides present within the field of view is arithmetically averaged to calculate the circle-equivalent diameter of the precipitated carbide.

[0034] Each structure can be evaluated using Energy-Dispersive X-ray Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD) associated with a Scanning Electron Microscope (SEM).

[0035] The analysis conditions may be, for example, a scanning electron microscope with an acceleration voltage of 15 kV, a working distance from the objective lens to the surface of the object to be observed of 10 mm, and an observation magnification of 3000x. Furthermore, the element distribution evaluation method using EDS involves obtaining the element distribution by EDS area analysis in the same field of view of the SEM. For example, when analyzing precipitated carbides, the target elements may be, for example, C, Cr, W, Mo, V, Fe, and O. The Fe-BCC phase can also be analyzed in the same manner as above.

[0036] The alloy structure of the Fe-based alloy of this embodiment is made up of 43.5% or more of the Fe-BCC phase, and fine precipitated carbides are uniformly dispersed in the Fe-BCC phase, so cracks originating from the carbides are unlikely to occur, and even if cracks do occur, they are so uniformly dispersed that they are unlikely to propagate, thereby improving toughness and heat crack resistance.

[0037] The Fe-based alloy as a whole contains, in mass%, 0.1% to 2.0% C, 2% to 6.0% Cr, 0.5% to 4.0% W, 0.5% to 4.0% Mo, 0.5% to 4.0% V, and the balance being Fe and inevitable impurity elements.

[0038] Furthermore, either Si or Mn, or both, may be further contained, and it is preferable that Si is 1.0% or less and Mn is 1.0% or less, in mass %. Si is expected to improve oxidation resistance. The above range is preferable in consideration of workability. Mn is expected to have the effects of improving wear resistance and hardenability and reducing embrittlement. The above range is preferable in consideration of the effects of embrittlement due to quench cracking and residual γ.

[0039] (C: 0.1 to 2.0%) Carbon (C) combines with carbide-forming elements such as Cr, W, Mo, and V to form hard composite carbides, improving the wear resistance of alloy members and their products. Furthermore, C dissolves partially within the matrix, strengthening the matrix. By limiting the C content in the entire Fe-based alloy to 0.1% or more, the hardness of the entire Fe-based alloy can be ensured through the strengthening of the matrix, the formation of fine carbides within the matrix grains, and the formation of carbides at the matrix grain boundaries. On the other hand, by limiting the C content in the entire Fe-based alloy to 2.0% or less, excessive carbide formation in the entire Fe-based alloy can be suppressed, ensuring the toughness of the entire Fe-based alloy. The C content is preferably 0.5 to 1.5%, and more preferably 0.5 to 1.0%.

[0040] (Cr: 2.0 to 6.0%) Cr (chromium) combines with C to form carbides, improving wear resistance and contributing to improved hardenability. By making the Cr content in the entire Fe-based alloy 2.0% or more, the amount of carbides formed in the entire Fe-based alloy can be optimized, improving wear resistance and hardenability. On the other hand, by making the Cr content in the entire Fe-based alloy 6% or less, the amount of carbides formed in the entire Fe-based alloy can be prevented from becoming excessive, ensuring toughness. The Cr content is preferably 3.0 to 5.0%, and more preferably 4.0 to 5.0%.

[0041] (W: 0.5 to 4.0%) W (tungsten) combines with C to form carbides, contributing to improved wear resistance. It also contributes to ensuring strength in high-temperature environments, making it particularly effective in improving the wear resistance of dies used in high-temperature environments. By making the W content in the entire Fe-based alloy 0.5% or more, it dissolves in the matrix grains, increasing heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving wear resistance. On the other hand, by making the W content in the entire Fe-based alloy 4% or less, excessive carbide formation in the entire Fe-based alloy can be suppressed, ensuring toughness. The W content is preferably 1.0 to 2.5%, more preferably 1.5 to 2.0%.

[0042] (Mo: 0.5 to 4.0%) Mo (molybdenum) combines with C to form carbides, improving wear resistance and contributing to improved hardenability. By making the Mo content in the entire Fe-based alloy 0.5% or more, it dissolves in the matrix grains, increasing heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving wear resistance. On the other hand, by making the Mo content in the entire Fe-based alloy 4% or less, it is possible to prevent excessive carbide formation in the entire Fe-based alloy and ensure toughness. The Mo content is preferably 1.5 to 3.5%, and more preferably 2.0 to 3.5%.

[0043] (V: 0.5 to 4.0%) V (vanadium) combines with C to form carbides, contributing to improved wear resistance and seizure resistance. By setting the V content in the entire Fe-based alloy to 0.5% or more, fine, non-aggregating carbides are precipitated within the matrix grains by heat treatment, increasing softening resistance in high-temperature regions and improving high-temperature yield strength. In addition, the matrix crystal grains are refined, improving toughness and raising the A1 transformation point, which, combined with excellent high-temperature yield strength, improves heat crack resistance. On the other hand, by setting the V content in the entire Fe-based alloy to 4% or less, excessive carbide formation in the entire Fe-based alloy can be suppressed, ensuring toughness. The V content is preferably 1.5 to 3.5%, more preferably 2.0 to 3.0%.

[0044] (Si: 1.0% or less) The Fe-based alloy may also contain Si (silicon). When Si is contained in the entire Fe-based alloy, the Si content in the entire Fe-based alloy is preferably 0.8% or less, more preferably 0.5%, in order to improve oxidation resistance and suppress deterioration of workability. Furthermore, the Si content is preferably 0.1 to 1.0%, more preferably 0.1 to 0.8%, and even more preferably 0.1 to 0.5%.

[0045] (Mn: 1.0% or less) Furthermore, Mn (manganese) may be contained. When Mn is contained in the entire Fe-based alloy, the Mn content in the entire Fe-based alloy is preferably 0.8% or less, more preferably 0.5% or less, in order to improve wear resistance and castability, reduce embrittlement, and suppress embrittlement due to quench cracking and residual γ. Furthermore, 0.1 to 0.8% is preferable, and 0.1 to 0.5% is even more preferable.

[0046] (Inevitable Impurities) Inevitable impurities refer to trace amounts of impurities that are difficult to remove technically due to trace elements mixed into raw materials or reactions with various components that come into contact during the manufacturing process. In the case of the alloy of this embodiment, unavoidable impurities specifically refer to, for example, Al, Cu, N, Ni, O, P, S, and Co. Among these impurities, impurities that should be particularly limited are P, S, O, and N. In mass%, P is preferably 0.03% or less, S is preferably 0.003% or less, O is preferably 0.02% or less, and N is preferably 0.05% or less. Of course, the content of these unavoidable impurities is preferably low, and 0% is even better.

[0047] <Method for manufacturing alloy member> The Fe-based alloy and alloy member of this embodiment are manufactured by a so-called additive manufacturing method, which involves irradiating an alloy powder with an electron beam or a laser beam to melt and solidify the alloy powder to form a solidified layer, forming a new solidified layer on the solidified layer, and then repeating this process to obtain an alloy member with a layered structure. Note that this method may be referred to as an additive manufacturing (layered manufacturing) method in this specification.

[0048] (Alloy Powder) Here, the alloy powder is an Fe-based alloy powder containing the above-mentioned predetermined composition of C, Cr, W, Mo, and V, with the remainder being Fe and inevitable impurity elements. First, predetermined amounts of feed materials for each element are measured so as to obtain an alloy having a predetermined composition range, and these are mixed to produce a raw material powder. This raw material powder is used to obtain an atomized powder. For example, the raw material powder is loaded into a crucible, melted by high frequency, and the molten alloy is dropped from a nozzle below the crucible and sprayed with high-pressure argon to produce a gas-atomized powder. This gas-atomized powder can be classified to obtain an alloy powder.

[0049] The Fe-based alloy powder of this embodiment may be an alloy controlled to satisfy the composition of the Fe-based alloy described above. For example, the Fe-based alloy powder may contain, by mass%, 0.1% to 2.0% C, 2% to 6.0% Cr, 0.5% to 4.0% W, 0.5% to 4.0% Mo, 0.5% to 4.0% V, 1.0% or less Si, and 1.0% or less Mn, with the balance being Fe. More preferably, the Fe-based alloy powder contains 0.5 to 0.9% C, 4.0 to 5.0% Cr, 1.0 to 2.0% W, 2.5 to 3.5% Mo, 2.0 to 3.0% V, 0.8% or less Si, and 0.3% or less Mn, with the balance being Fe and unavoidable impurities.

[0050] When a shaped body is produced using the Fe-based alloy powder of this embodiment, C in the alloy structure of the shaped body combines with carbide-forming elements such as Cr, W, Mo, and V to form hard complex carbides, thereby improving the wear resistance of the alloy member and the product thereof. Furthermore, C dissolves in a portion of the matrix of the alloy structure of the shaped body, strengthening the matrix. By setting the C content in the Fe-based alloy powder to 0.1% or more, the hardness of the alloy structure can be ensured by the effects of strengthening the matrix of the alloy structure, fine carbides formed within the matrix grains, and carbides formed at the matrix grain boundaries. On the other hand, by setting the C content in the Fe-based alloy powder to 2.0% or less, excessive carbide formation in the alloy structure can be suppressed, thereby ensuring the toughness of the Fe-based alloy as a whole.

[0051] The composition of the alloy powder can be analyzed using, for example, inductively coupled plasma (ICP) optical emission spectrometry.

[0052] (Additive Manufacturing Method) In one embodiment, a shape is formed by irradiating an Fe-based alloy powder with an electron beam or a laser beam and melting and solidifying it, and this can be used in an appropriate additive manufacturing method. Generally, additive manufacturing methods for metal materials are roughly divided into powder bed fusion (PBF) and directed energy deposition (DED). The method can be applied to both powder bed fusion (PBF) and directed energy deposition (DED), which are additive manufacturing methods for metal materials.

[0053] The PBF method is a method in which metal powder is spread on a base plate (substrate) to form a powder bed, and a beam is irradiated onto the metal powder spread in the target area to melt and solidify the metal powder to create a shape. With the PBF method, a three-dimensional object, i.e., an additive manufactured object, can be produced by repeating the lamination of the powder bed and the melting and solidification of the metal powder each time a two-dimensional object is produced on the powder bed.

[0054] Powder bed fusion (PBF) methods include those that use a laser beam as a heat source and those that use an electron beam as a heat source. The methods that use a laser beam are broadly divided into selective laser melting (SLM) and selective laser sintering (SLS). The methods that use an electron beam are called selective electron beam melting (SEBM, or simply EBM).

[0055] The powder laser melting (SLM) method is a method of melting or sintering metal powder using a laser beam. The powder laser sintering (SLS) method is a method of sintering metal powder using a laser beam. In the SLM and SLS methods using a laser beam, the metal powder is melted and solidified in an inert atmosphere such as nitrogen gas. The Fe-based alloy member of this embodiment can be manufactured by repeatedly performing a melting and solidification process in which the above-mentioned Fe-based alloy powder is irradiated with a heat source such as an electron beam or a laser beam to melt and solidify it and form a solidified layer, thereby stacking further solidified layers on top of the solidified layer.

[0056] The powder electron beam melting (SEBM / EBM) method is a method of melting metal powder using an electron beam as a heat source. The EBM method using an electron beam involves irradiating metal powder with the electron beam and converting the kinetic energy into heat to melt the metal powder. In the EBM method, the electron beam irradiation and the melting and solidification of the metal powder proceed under a high vacuum.

[0057] The directed energy deposition (DED) method involves supplying metal powder to a substrate or an already-formed build area and irradiating it with a beam, melting and solidifying the metal powder supplied to the build area, and creating a shape. The DED method scans the supply of metal powder and the irradiation of the beam two-dimensionally or three-dimensionally, repeatedly depositing solidified metal on an already-formed build area, thereby producing a three-dimensional object, i.e., an additive manufacturing object.

[0058] The DED method is also called the metal deposition method. DED methods include laser metal deposition (LMD), which uses a laser beam as a heat source, and methods that use an electron beam as a heat source. Among DED methods, the method of applying powder cladding to a base material using a laser beam is also called laser powder cladding welding.

[0059] Among various additive manufacturing methods, powder bed fusion (PBF) has the advantage of high shape accuracy of the additively manufactured object. On the other hand, directed energy deposition (DED) has the advantage of enabling high-speed manufacturing. In particular, among the powder bed fusion (PBF) methods, powder laser melting (SLM) enables selective melting and solidification of metal powder by irradiating a powder bed with a micro-beam diameter, each layer of which is several tens of micrometers thick, with a laser.

[0060] In addition, powder particle size may be adjusted by mesh sieving or airflow classification to suit the modeling method of the additive manufacturing method. For example, for modeling powders used in powder bed fusion using electron beams or laser beams, the powder is melted by the laser beam, which serves as the heat source, but coarse powder that is difficult to melt must be removed to minimize the area affected by the heat. Furthermore, highly adhesive fine powder must also be removed to obtain optimal fluidity to ensure powder spreadability.

[0061] For example, when applied to powder bed fusion (PBF), it is preferable to adjust the average particle size (D50) of the alloy powder to a range of 10 to 60 μm. Furthermore, for example, metal powders used in directed energy deposition (DED) require removal of coarse powders that are difficult to melt in order to melt the powder using a laser beam as a heat source. Furthermore, fine powders must also be removed to prevent dust scattering when the powder is supplied to the heat source and ensure fluidity that allows the powder to be easily transported. Therefore, when applying the shaping powder of the present invention to DED, it is preferable to adjust the D50 to a range of 50 to 120 μm. Furthermore, when using an electron beam or plasma as a heat source, it is possible to use coarser metal particles for shaping, so it is preferable to set the D50 to 75 to 250 μm.

[0062] Figure 1 shows the schematic configuration of an additive manufacturing device 1 that uses a laser beam as a heat source for additive manufacturing using a directed energy deposition method. The additive manufacturing device 1 is mainly composed of a powder feed nozzle 3, a focusing lens 5, a protective lens 7, etc. Alloy powder 11 is supplied to the powder feed nozzle 3 and injected into the tip of the powder feed nozzle 3 together with argon gas. A laser beam 9 emitted from a laser oscillator (not shown) is focused by the focusing lens 5 and irradiated near the tip of the powder feed nozzle 3. A protective lens 7 is provided below the focusing lens 5.

[0063] In additive manufacturing, alloy powder 11 is supplied onto a base plate 17 while a powder supply nozzle 3 is moved relative to the base plate 17 (direction A in the figure). A laser beam 9 focused by a focusing lens 5 is irradiated onto the supplied alloy powder 11, forming a molten pool 13 in which the alloy powder 11 melts and solidifies, thereby forming a shaped body 15 (Fe-based alloy). This process is repeated using a program file created using CAD-CAM software to stack shaped bodies 15 on the base plate 17, thereby forming a three-dimensional alloy part at least partially composed of an Fe-based alloy.

[0064] In the directed energy deposition method, a (three-dimensional) additive manufacturing device is used to rapidly melt the surface of a substrate, such as a base plate, a molded object, or a die, by irradiating it with a laser. A raw material powder is then supplied into the resulting molten pool, where it is rapidly cooled and solidified. This series of processes is repeated to create a molded object. The molded object formed on the base plate corresponds to the Fe-based alloy component of this embodiment. Furthermore, in the case of mold repair, a manufactured product can be obtained. Additive manufacturing conditions are determined appropriately taking into account the particle size and composition of the raw material powder, the size, shape, and properties of the molded object, production efficiency, etc., and for the alloy of this embodiment, the additive manufacturing conditions can be selected, for example, from the following ranges:

[0065] <Additive Manufacturing Conditions> The thickness of each layer during additive manufacturing can be, for example, 0.1 mm to 1.0 mm, preferably 0.4 to 0.8 mm. The thickness of the first layer of Fe-based alloy formed on the surface of the base material (base plate) (the thickness from the interface of the base material to the surface of the first layer of Fe-based alloy, including the dilution layer near the interface) is 0.1 mm to 1 mm. The thickness of the entire layer from the interface of the base material to the surface of the Fe-based alloy (including the dilution layer near the interface) is preferably 0.1 mm to 5 mm to prevent peeling of the Fe-based alloy from the base material and cracking of the Fe-based alloy itself. Here, the dilution layer refers to a layer that dissolves with the base material during molding of the first layer of Fe-based alloy, resulting in a mixture of the compositions of both the base material and the first layer of Fe-based alloy.

[0066] Next, the laser beam diameter is preferably about 3 mm at the irradiation position. The laser output is preferably 1500 to 2500 W. The laser scanning speed is preferably 500 to 1000 mm / min. The powder supply rate is preferably 10 to 20 g / min.

[0067] The density of the energy input by laser irradiation to rapidly melt the raw material powder (energy density of the heat source: J / mm) is preferably 90 to 300 J / mm, and more preferably 180 to 240 J / mm. If the energy density is too low, the defect rate increases, and the supplied powder will no longer melt, making it difficult to maintain the shape of the shaped object. On the other hand, if the energy density is too high, a wide area of ​​the base plate or shaped object centered on the laser irradiation position will melt, again making it difficult to maintain the shape of the shaped object. The energy density E (J / mm) can be calculated using the laser output P (W) and the laser scanning speed v (mm / min) as P / v x 60.

[0068] (Heat Treatment) The Fe-based alloy of this embodiment may be quenched to improve hardness, and if costs and the like are within an acceptable range, may be additionally tempered to remove quenching stress and improve toughness. For example, in the case of quenching, the alloy may be held at 1180 to 1220°C for 10 to 60 minutes, followed by cooling in oil or water. Cooling in oil is more preferable to prevent distortion and quench cracking. Quenching and cooling may also be performed using a salt bath. Tempering is a heat treatment process in which the alloy is held at 400 to 700°C, and preferably held at 560 to 580°C for 2 to 6 hours, followed by air cooling.

[0069] (Hardness) The hardness of the surface layer of the Fe-based alloy or alloy member of this embodiment can be evaluated by Vickers hardness HV (hereinafter referred to as hardness), and is desirably 350 HV or more, preferably 500 HV or more. For example, the hardness can be measured by setting the indentation load of a Vickers indenter to 0.5 kg and the dwell time during indentation to 10 seconds, and determining the hardness from the length of the diagonal line of the indentation formed on the measurement surface by indentation of the indenter.

[0070] The method may further include a surface treatment step in which the obtained alloy component is subjected to a surface treatment. The surface treatment step is, for example, a nitriding treatment or a film formation by a PVD method on the surface layer of the Fe-based alloy, such as a nitride layer, a compound layer, or a ceramic coating layer. In these surface treatment steps, a coating that is harder than the Fe-based alloy formed by additive manufacturing can be formed on the surface layer of the Fe-based alloy, thereby further strengthening the surface of the alloy component obtained by additive manufacturing and improving its wear resistance.

[0071] [Product] The product having at least a part of the alloy member obtained in this way is not particularly limited, but is particularly suitable for, for example, a hot stamping die, a cold forging die, and a cold pressing die. In this case, even if a part of the surface of the die is damaged, it can be easily repaired by forming an alloy layer of the present invention by buildup only on the damaged part. In this case, the die repaired with the Fe-based alloy according to this embodiment is less likely to crack and has excellent toughness and heat crack resistance.

[0072] To obtain a shaped body of the desired composition, the raw materials for each element shown in Table 1 were weighed out in predetermined amounts, mixed, and loaded into a crucible. The raw materials were then subjected to high-frequency melting in a vacuum, and the molten alloy was dropped from a nozzle below the crucible and sprayed with high-pressure argon to produce a gas-atomized powder. This gas-atomized powder was then classified to obtain an Fe-based alloy powder with a particle size of 53 to 106 μm and a D50 of 75.8 μm. The composition of the obtained Fe-based alloy powder is shown in Table 1, and its particle size distribution is shown in Table 2.

[0073]

[0074] Next, using a directed energy deposition 3D additive manufacturing device (LASERTEC65 3D Hybrid manufactured by DMG Mori Seiki Co., Ltd.), raw material powder was supplied to a molten pool formed by laser irradiation on a base plate, and melted and solidified to produce a shaped body (alloy member) measuring 3 mm in width, 80 mm in length, and approximately 10 mm in stack height. The additive manufacturing conditions were as follows: Maraging steel (YAG300 manufactured by Proterial Co., Ltd. (YAG is a registered trademark of Proterial Co., Ltd.) was used for the base plate.

[0075] (Additive manufacturing conditions) Thickness of one layer during additive manufacturing: 0.47 mm Laser beam diameter: approximately 3 mm Laser output: 2400 W Laser scanning speed: 600 mm / s Energy density: 240 J / mm

[0076] The heat-treated and unheat-treated shaped bodies were evaluated. The shaped body that was only quenched was designated F1, the shaped body that was both quenched and tempered was designated F2, the shaped body that was not heat-treated was designated F3, and the shaped body that was only tempered was designated F4. The quenching treatment involved holding the body at 1200°C for 0.5 hours, followed by cooling in oil. The tempering treatment involved holding the body at 560°C for 4 hours, followed by air cooling.

[0077] First, the molded bodies F1 and F2 were observed and evaluated using an SEM. The test specimens for evaluation were prepared by cutting a portion of the molded body into small pieces, embedding them in resin, and then polishing the cut surfaces of the embedded molded bodies to a mirror finish. The observation magnification was 3000x. Furthermore, elemental analysis of the same field of view was performed using an EDS attached to the SEM. Eight elements were analyzed: C, Cr, Fe, Mo, O, V, and W.

[0078] 2A to 2E show examples of SEM and EDS images. Figure 2A shows SEM and EDS images obtained by observing the cross-sectional structure of a cross section of the alloy of the following alloys: body F1, which was subjected to only quenching as a heat treatment; body F2, which was subjected to quenching and tempering; body F3, which was not subjected to heat treatment; and body F4, which was subjected to only tempering. Figure 2E shows SEM and EDS images of a forged material F0 made from an alloy of the same composition by a conventional powder metallurgy method. This forged material F0 was sintered from powder, forged, and then subjected to the same quenching and tempering treatments as above.

[0079] 2A to 2E, in addition to confirming the structure indicated by the gray shading, a phase map was also obtained using EBSD using the method described above. The field of view (also referred to as the field of view area) was 200 μm × 200 μm. Furthermore, elemental analysis was performed on the Fe-BCC phase and precipitated carbides within the field of view. The six elements analyzed were C, Cr, W, Mo, V, and Fe.

[0080] The elemental analysis was performed on the Fe-BCC phase 50 at part A shown in FIGS. 2A, 2B, 2C, 2D, and 2E, and on the precipitated carbides 52 at part B shown in FIGS. 2A, 2B, 2C, 2D, and 2E.

[0081] Table 3 shows the composition of the Fe-BCC phase and precipitated carbides for the shaped bodies F1 to F4 and the forged material F0. Table 3 shows the results when the sum of C, Cr, W, Mo, V, and Fe is taken as 100%. Although not included in the elemental analysis this time, the Fe-BCC phase may contain Si and Mn. Note that for F3, the size and proportion of the precipitated carbides were extremely small and below the resolution of the detection device, resulting in large errors depending on the analysis location, and as a result, no numerical values ​​were listed, as proper measurement was not possible.

[0082]

[0083] As shown in Table 3, the Fe-BCC phase of F1 contained 84.4% Fe, 4.9% C, 4.4% Cr, 1.7% W, 2.5% Mo, and 2.2% V. The precipitated carbides contained 19.8% Fe, 14.7% C, 3.9% Cr, 8.3% W, 10.6% Mo, and 42.8% V.

[0084] The Fe-BCC phase of F2 contained 82.0% Fe, 5.8% C, 4.8% Cr, 2.1% W, 3.0% Mo, and 2.3% V. The precipitated carbides contained 55.3% Fe, 12.2% C, 4.3% Cr, 4.0% W, 6.2% Mo, and 18.0% V.

[0085] The Fe-BCC phase of F3 contained 83.7% Fe, 5.3% C, 3.8% Cr, 2.4% W, 2.2% Mo and 2.6% V.

[0086] The Fe-BCC phase of F4 contained 82.5% Fe, 4.9% C, 4.7% Cr, 2.1% W, 3.3% Mo, and 2.5% V. The precipitated carbides contained 43.0% Fe, 11.5% C, 5.6% Cr, 6.1% W, 9.0% Mo, and 24.6% V.

[0087] The Fe-BCC phase of F0 contained 84.9% Fe, 4.7% C, 3.8% Cr, 2.0% W, 3.2% Mo, and 1.4% V. The precipitated carbides contained 47.1% Fe, 12.9% C, 4.7% Cr, 6.2% W, 7.6% Mo, and 21.5% V.

[0088] On the other hand, the composition of the precipitated carbides showed different trends among the shaped bodies F1 to F4. In the shaped body F1, which was only subjected to quenching, the V (vanadium) carbide and the composite carbides of Mo and W with Fe were difficult to decompose, and the C derived from these carbides did not dissolve in the Fe-BCC phase, which is thought to be why the concentrations of V, Mo, and W in the precipitated carbides were high.

[0089] In the shaped body F2 that had been subjected to quenching and tempering treatments, it was confirmed that V, Mo, and W had precipitated in the precipitated carbides due to the quenching and tempering treatments, but it is believed that the proportions of V, Mo, and W in the precipitated carbides were relatively low due to the precipitation of carbides of the main components Fe and Cr as well.

[0090] Regarding the shaped body F4, which was only subjected to tempering, it can be assumed that the shaped body was subjected to a short-term quenching treatment using a heat source in the additive manufacturing process, and therefore it can be assumed that it has undergone a thermal history similar to that of the shaped body F2, which was subjected to quenching and tempering treatment. This is because, as can be seen from the above analysis results, the shaped body F4, like F2, contains V, Mo, and W in the precipitated carbides, and in addition, carbides of the main components Fe and Cr are also precipitated, and the proportions of V, Mo, and W in the precipitated carbides are relatively lower than those of the shaped body F1.

[0091] The non-heat-treated shaped body F3 had a high cooling rate after shaping, and although fine carbides precipitated locally, it is presumed that their size was below the resolution of the detector.

[0092] The forged and pressed material F0 was subjected to quenching and tempering treatment under the same conditions as F2, and tempering treatment under the same conditions as F4. However, the composition of the precipitated carbides was significantly different between the formed body F2 and the forged and pressed material F0. This is thought to be due to the fact that the additive manufacturing method used to create the formed body has a faster cooling rate from the molten state to the solidified state, i.e., the melting and solidification rate, than the forged and pressed material.

[0093] For the above-mentioned bodies F1 to F0, the electron diffraction patterns generated when the surfaces of the bodies F1 to F0 were irradiated with an electron beam were measured by EBSD. As a result, bodies F1 to F0 were confirmed to have a BCC structure and therefore an Fe-BCC phase. Although bodies F1 to F4 and forged material F0 were subjected to different heat treatments and manufacturing processes, they were originally derived from powders of the same composition, and therefore no significant differences were observed in the elemental composition of the Fe-BCC phase.

[0094] Next, using the method described above, the proportion of the Fe-BCC phase in the field of view, the circle-equivalent average grain size of the Fe-BCC phase, the proportion of precipitated carbides in the field of view, and the circle-equivalent average grain size of the precipitated carbides were calculated. Table 4 shows the proportion of the Fe-BCC phase, the circle-equivalent average grain size of the Fe-BCC phase, the proportion of precipitated carbides, and the circle-equivalent average grain size of the precipitated carbides for the shaped bodies F1 to F4 and the forged material F0.

[0095]

[0096] As shown in Table 4, the proportion of the Fe-BCC phase, in terms of area percentage, was higher in the formed bodies F1 to F4 (43.8% to 56.2%) than in the forged material F0, which was 43.3%. Furthermore, the proportions of the Fe-BCC phase in the formed body F3, which was not subjected to heat treatment, and the formed body F4, which was subjected to only tempering, were 45.1% and 56.2%, respectively, which were higher than those in the formed body F1, which was subjected to only quenching, and the formed body F2, which was subjected to quenching and tempering.

[0097] The proportion of precipitated carbides was highest in the formed body F2 at 5.95%, followed by the formed body F1 at 2.79%, the formed body F4 at 0.13%, and the formed body F3 at 0.064%. The proportion of precipitated carbides in the forged material F0 was 3.73%. From these results, it was confirmed that the proportion of precipitated carbides in the formed bodies F3 and F4 was lower than that in the formed bodies F1, F2, and the forged material F0.

[0098] The average circle-equivalent particle size of precipitated carbides was the largest for shaped body F3 at 1.42 μm, followed by shaped body F2 at 1.41 μm, shaped body F1 at 1.39 μm, for forged material F0 at 1.33 μm, and for shaped body F4 at 1.14 μm.

[0099] The proportion of precipitated carbides or the average circle-equivalent grain size were smaller in the shaped bodies F3 and F4 than in the shaped bodies F1 and F2. Because the cooling rate during production was high and the carbide formation time was short in the shaped bodies F1 to F4, it is thought that the amount of carbides formed inside the alloy (shaped body) in the pre-heat treatment state was smaller than in the forged material F0.

[0100] Furthermore, since bodies F3 and F4 were not quenched, it was difficult for the carbides present in the unheated bodies to decompose, and for C to dissolve and diffuse into the Fe-BCC phase, which is thought to be why there was insufficient C to bond with carbide-forming elements such as Cr, W, Mo, and V contained in the Fe-based alloy, making it difficult for carbides to form, resulting in a smaller proportion of precipitated carbides and a smaller average circle-equivalent grain size.From the above, it was confirmed that bodies F1 to F4 have a higher proportion of the Fe-BCC phase than forged material F0.

[0101] Furthermore, the Fe-BCC phase ratio of the formed bodies F1 to F4 is 43.5% or more in terms of area ratio, which means that the structure can be said to be more uniform. Furthermore, although it is not possible to simply compare the formed bodies F1 to F4, which are additively manufactured products, with the forged material F0, the formed bodies F1 to F4 have a higher ratio of the Fe-BCC phase than F0.

[0102] Therefore, with the shaped bodies F1 to F4, it is expected that cracks will not easily occur because local distortion due to external stress, for example, will not easily occur. Furthermore, with the shaped bodies F1 to F4, the circle-equivalent average particle size of the precipitated carbides is small and the precipitated carbides are fine, so it is expected that cracks will not easily occur and that the Fe-based alloys will have excellent toughness, heat crack resistance, and wear resistance.

[0103] Furthermore, in F1 and F2, the average circle-equivalent grain size of the Fe-BCC phase is 7.0 μm or less, the proportion of precipitated carbides exceeds 0.1%, and the size of the Fe-BCC phase is not too large, with carbides precipitated in the Fe-BCC phase. Therefore, it can be expected that these steels will have even better mechanical strength, toughness, heat crack resistance, and wear resistance.

[0104] [Hardness] Next, the hardness of the shaped bodies F1 to F4 and the forged material F0 was measured using a Vickers hardness tester. The measurement conditions were a Vickers indenter indentation load of 0.5 kg and a dwell time of 10 seconds during indentation, and the hardness was determined from the length of the diagonal line of the indentation formed on the measurement surface by indentation of the indenter. Five measurements were taken, and the average value was calculated. The results are shown in Table 5.

[0105]

[0106] As shown in Table 5, the hardness of the shaped body F1, which was subjected to only quenching, was 725 HV, and the hardness of the shaped body F2, which was subjected to quenching and tempering, was 710 HV. The hardness of the shaped body F3, which was not subjected to heat treatment (no heat treatment), was 408 HV, and the hardness of the shaped body F4, which was subjected to only tempering, was 405 HV. From this, it was confirmed that if it is desired to improve the wear resistance, it is preferable to at least harden the shaped body, as with the shaped bodies F1 and F2.

[0107] As mentioned above, the shaped body F1 that was subjected to only quenching treatment, the shaped body F2 that was subjected to quenching treatment and tempering treatment, the shaped body F3 that was not subjected to heat treatment, and the shaped body F4 that was subjected to only tempering treatment have a proportion of Fe-BCC phase of 43.5% or more, as shown in Table 4, and therefore have a uniform structure and can suppress the occurrence of localized distortion due to, for example, external stress, and are therefore expected to be less susceptible to cracking.

[0108] Furthermore, as shown in Table 4, the shaped body F1, which was subjected to only quenching treatment, and the shaped body F2, which was subjected to quenching and tempering treatment, have average circle-equivalent particle sizes of precipitated carbides of 1.39 μm and 1.41 μm, respectively, which are suitably refined, making them less susceptible to cracking, and are expected to have excellent toughness, heat crack resistance, and wear resistance.

[0109] REFERENCE SIGNS LIST 1... additive manufacturing device 3... powder supply nozzle 5... focusing lens 7... protective lens 9... laser beam 11... alloy powder 13... molten pool 15... shaped body 17... base plate 50... Fe-BCC phase 52... precipitated carbide

Claims

1. An Fe-based alloy comprising C, Cr, W, Mo, and V, with the balance being Fe and unavoidable impurity elements, having an alloy structure including an Fe-BCC phase, wherein the Fe-BCC phase contains, in mass%, when the sum of C, Cr, W, Mo, V, and Fe is taken as 100%, C is 3.0% to 7.0%, Cr is 2.0% to 6.0%, W is 0.5% to 4.0%, Mo is 0.5% to 4.0%, V is 0.5% to 4.0%, and Fe is 75.0% to 93.5%, and has precipitated carbides precipitated in the Fe-BCC phase, and the proportion of the Fe-BCC phase is 43.5% or more in terms of area ratio in cross-sectional structure observation.

2. The Fe-based alloy according to claim 1, characterized in that the Fe-based alloy as a whole has, in mass%, C of 0.1% or more and 2.0% or less, Cr of 2.0% or more and 6.0% or less, W of 0.5% or more and 4.0% or less, Mo of 0.5% or more and 4.0% or less, V of 0.5% or more and 4.0% or less, Si of 1.0% or less, Mn of 1.0% or less, with the balance being Fe and the unavoidable impurities.

3. An Fe-based alloy according to claim 1 or 2, characterized in that the Fe-BCC phase contains, by mass%, C of 4.8% or more and 6.0% or less, Cr of 3.9% or more and 6.0% or less, W of 1.5% or more and 3.0% or less, Mo of 2.2% or more and 3.1% or less, and V of 1.5% or more and 3.0% or less.

4. An alloy member comprising at least a part of the Fe-based alloy according to claim 1.

5. The alloy part according to claim 4, characterized in that the hardness of the Fe-based alloy is 700 HV or more.

6. A method for manufacturing an alloy part, comprising using an alloy powder containing, by mass%, C from 0.1% to 2.0%, Cr from 2.0% to 6.0%, W from 0.5% to 4.0%, Mo from 0.5% to 4.0%, V from 0.5% to 4.0%, Si from 1.0% or less, Mn from 1.0% or less, with the balance being Fe and unavoidable impurities, irradiating the alloy powder with an electron beam or laser beam to melt and solidify it to form a solidified layer, forming a new solidified layer on the solidified layer, and then repeating this operation to obtain an alloy part having a layered structure.

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