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

Abstract

Provided are: an Fe-based alloy which is not susceptible to cracking and is expected to have toughness and heat crack resistance; an alloy member; a product; and a method for producing an alloy member.　An Fe-based alloy is characterized by having an alloy structure containing C, Cr, W, Mo, and V, the remainder being Fe and unavoidable impurity elements, and including an Fe-BCC phase, wherein: the Fe-BCC phase contains 3-7 mass% of C, 2-6 mass% of Cr, 0.5-4 mass% of W, 0.5-4 mass% of Mo, 0.5-4 mass% of V, and 75-90 mass% of Fe; a carbide is precipitated in the Fe-BCC phase; and the average equivalent circular grain size of the carbide is 1.30 μm or less.

Description

[Technical Field]

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

[0002] Conventionally, 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, have been used for tools such as punches and dies used in hot precision press working. However, these steels have had problems such as being prone 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, 1.0% or less Si, 1.0% or less Mn, 1.5 to 6% of one or both of W and Mo (1 / 2W+Mo) (however, W is 3% or less), and 0.5 to 3% of one or both of V and Nb (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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-307963 Summary of the Invention [Problem to be solved by the invention]

[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 is required at 1200 to 1300°C for 10 to 20 hours. However, even after soaking, quenching and tempering are still required in subsequent processes to obtain forging tools such as dies and punches, and 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 that is less susceptible to cracking and is expected to have high toughness and heat crack resistance, an alloy member, a product thereof, and a method for manufacturing the alloy member. [Means for solving the problem]

[0007] To achieve the above-mentioned object, the first invention is 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% to 7% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, and 75% to 90% Fe, and wherein precipitated carbides are precipitated in the Fe-BCC phase, and the average circle-equivalent diameter of the precipitated carbides is 1.30 μm or less. The average circle-equivalent diameter of the precipitated carbides can be determined by calculating the average area of ​​the precipitated carbides within an observation field using electron backscattering diffraction (EBSD), and then calculating the circle-equivalent diameter from the area. When the total area is the sum of the areas of the Fe-BCC phase, the Fe-FCC phase, and the zero solution portion, The ratio of the precipitated carbides is , the area ratio obtained by dividing the area of ​​the zero solution portion by the total area, It is less than 0.38%.

[0008] Furthermore, it is desirable that the Fe-BCC phase occupies 96% or more of the alloy structure in terms of area ratio.

[0009] It is also desirable that the average circle-equivalent grain size of precipitated carbides is 0.60 μm or more.

[0010] Furthermore, it is desirable that the Fe-based alloy as a whole contains, in mass%, C from 0.1% to 2%, Cr from 2% to 6%, W from 0.5% to 4%, Mo from 0.5% to 4%, V from 0.5% to 4%, Si from 1.0% to 1.0%, Mn from 1.0% to 4%, Co from 4% to 4%, with the balance being Fe and inevitable impurity elements.

[0011] It is also preferable that the alloy further contains either Si or Mn, or both, and that, in mass %, Si is 1.0% or less and Mn is 0.1% or more and 1.0% or less.

[0012] It is desirable that the Fe-based alloy as a whole further contains 0.5% to 4% of Co, and that the Fe-BCC phase further contains 0.5% to 4% of Co, in mass %.

[0013] According to the first invention, fine precipitated carbides are dispersed in the Fe-BCC phase, making it possible to obtain an Fe-based alloy that is less susceptible to cracking and is also expected to have high toughness and heat crack resistance.

[0014] A second aspect of the present invention is an alloy member characterized by comprising, at least in part, the Fe-based alloy according to the first aspect of the present invention.

[0015] The Fe-based alloy is formed on the surface of the base material of the alloy member, and the hardness of the surface layer is preferably 350 HV or more.

[0016] According to the second aspect of the present invention, it is possible to obtain an alloy member which is less susceptible to cracking and is expected to have high toughness and heat crack resistance.

[0017] Furthermore, by forming an alloy layer made of the Fe-based alloy according to the first aspect on the surface of the base material, a member having excellent surface toughness and heat crack resistance can be obtained. Furthermore, even if a portion of the surface is damaged, for example, the damaged portion can be easily repaired by forming a new alloy layer by buildup only on the damaged portion, and an alloy member having excellent toughness and heat crack resistance can be obtained.

[0018] The alloy member may be an alloy member having, on the surface layer of the Fe-based alloy, one or more of a nitride layer, a compound layer, and a ceramic coating layer.

[0019] Furthermore, by forming a nitride layer, a compound layer, or a ceramic coating layer on the surface, higher durability can be achieved.

[0020] A third invention is a manufactured product characterized by comprising, at least in part, the alloy member according to the second invention.

[0021] According to the third aspect of the present invention, it is possible to obtain a product that is less susceptible to cracking and is expected to have high toughness and heat crack resistance.

[0022] Particularly suitable examples of such products include hot stamping dies, cold forging dies, and cold press dies that are used after being repaired.

[0023] The above-mentioned Fe-based alloy members and products can be obtained by forming them using additive manufacturing methods using metal powders of the desired composition.

[0024] The fourth invention is a method for producing an alloy part, characterized by using an alloy powder containing, by mass%, 0.1% to 2% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, 1.0% or less Si, 1.0% or less Mn, 4% or less Co, with the remainder being Fe and unavoidable impurities, spraying the alloy powder onto a substrate while moving it, irradiating the sprayed alloy powder with an electron beam or a laser beam to melt and solidify it to form a solidified layer, and repeating the melting and solidification process to obtain the alloy part.

[0025] It is also preferable that the Si content is 0.1% or more and 1.0% or less, and the Mn content is 0.1% or more and 1.0% or less.

[0026] Preferably, the alloy powder further contains Co, and the Co content is, in mass %, 0.5% to 4%.

[0027] Furthermore, it is preferable that the obtained alloy part be subjected to at least one of a quenching treatment in which the alloy part is held at 1000°C or higher and 1400°C or lower, and then cooled in oil or water, and a tempering treatment in which the alloy part is held at 400°C or higher and 700°C or lower.

[0028] Furthermore, it is preferable that the method further comprises a surface treatment step of performing a surface treatment on the obtained alloy member, and the surface treatment step is a nitriding treatment or film formation by a PVD method. By performing the surface treatment step, higher durability can be obtained.

[0029] According to the fourth aspect of the present invention, it is possible to obtain a method for manufacturing an alloy member that is less susceptible to cracking and is expected to have high toughness and heat crack resistance.

[0030] In addition, in the melting and solidifying step, it is desirable that the thickness of the solidified layer be 0.1 mm or more and 5 mm or less. [Effects of the Invention]

[0031] 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 that are less likely to crack and are expected to have high toughness and heat crack resistance.

Brief Description of Drawings

[0032] [Figure 1] A diagram illustrating a schematic configuration of an additive manufacturing method. [Figure 2-A] A microstructure photograph of the alloy member of the present invention after quenching treatment. [Figure 2-B] A microstructure photograph of the formed body of FIG. 2A after tempering treatment. [Figure 2-C] A microstructure photograph of the formed body of the alloy member of the present invention when not heat-treated. [Figure 2-D] A microstructure photograph of the formed body of FIG. 2C after tempering treatment. [Figure 2-E] A microstructure photograph of a conventional forged material after quenching treatment and tempering treatment. [Figure 3] A diagram showing the Vickers hardness (HV) of each formed body.

Embodiments for Carrying Out the Invention

[0033] Hereinafter, an embodiment of the present invention will be described. First, the Fe-based alloy will be described, and then the additive manufacturing method will be described. In the following description, % indicates mass%. Also, in this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. Further, the lower limit value and the upper limit value of the numerical range can be combined as appropriate.

[0034] <Fe-based alloy> The Fe-based alloy of this embodiment contains C, Cr, W, Mo, and V, with the balance being Fe and unavoidable 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, by mass%, 3% to 7% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, and 75% to 90% Fe. Carbides precipitate in the Fe-BCC phase, and the carbides have an average circle-equivalent grain size of 1.3 μm or less.

[0035] (C: 3-7%) Carbon combines with carbide-forming elements such as Cr, W, Mo, and V to form hard complex carbides, improving the wear resistance of alloy members and their products. Carbon also dissolves partially in the matrix, strengthening it. By limiting the C content in the Fe-BCC phase to 3% 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 grains. On the other hand, by limiting the C content in the Fe-BCC phase to 7% or less, excessive formation of carbides within the matrix grains can be suppressed, ensuring toughness.

[0036] (Cr: 2-6%) Cr combines with C to form carbides, improving wear resistance and hardenability. By setting the Cr content in the Fe-BCC phase to 2% or more, the amount of carbides formed within the matrix grains can be optimized, improving wear resistance and hardenability. On the other hand, by setting the Cr content in the Fe-BCC phase to 6% or less, the amount of carbides formed within the matrix grains can be prevented from becoming excessive, ensuring toughness.

[0037] (W:0.5~4%) 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% or less, excessive carbide formation within the matrix grains can be suppressed, ensuring toughness.

[0038] (Mo: 0.5-4%) Mo combines with C to form carbides, improving wear resistance and contributing to improved hardenability. By setting the Mo content in the Fe-BCC phase to 0.5% or more, it dissolves in the matrix grains, increasing heat treatment hardness and improving wear resistance. On the other hand, by setting the Mo content in the Fe-BCC phase to 4% or less, excessive formation of carbides in the matrix grains can be suppressed, ensuring toughness.

[0039] (V:0.5~4%) 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 upon heat treatment, increasing softening resistance at high temperatures and improving high-temperature yield strength. Furthermore, the matrix grains are refined, improving toughness and raising the A1 transformation point, which, combined with the 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% or less, excessive carbide formation within the matrix grains can be suppressed, ensuring toughness.

[0040] (Fe-BCC phase) The Fe-BCC phase is a structure containing α-Fe and martensite that generally forms when an Fe-based alloy is cooled from a high temperature. Because of the high cooling rate, the Fe-BCC phase is a structure containing martensite in an Fe-based alloy with a supersaturated C solid solution, and is hard. The Fe-BCC phase contains 3% to 7% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, and 75% to 90% Fe. The Fe-BCC phase can be characterized using electron backscattering diffraction (EBSD). The EBSD evaluation method is described below.

[0041] (carbide) Carbides containing at least one of Cr, W, Mo, and V (hereinafter also referred to as precipitated carbides) are precipitated in the Fe-BCC phase. Carbide-forming elements such as Cr, W, Mo, and V combine with C (carbon) in the Fe-BCC phase 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. The phase containing precipitated carbides can be referred to as the carbide phase. The carbide phase is a region where Cr, V, Mo, and W are more concentrated than in the Fe-BCC phase, and where C is abundant. The carbide phase contains, for example, 7% to 11% C, 3% to 7% Cr, 1% to 5% W, 1% to 5% Mo, 1% to 5% V, and 75% to 90% Fe.

[0042] 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. Specifically, the size of the precipitated carbides is refined to an average circle-equivalent grain size of 1.30 μm or less. The average circle-equivalent grain size is preferably 0.50 μm to 1.1 μm, and more preferably 0.60 μm to 1.1 μm. For example, when using EBSD, the average grain size can be determined from carbides that are visible at a magnification of 400 times or more.

[0043] (Method of calculating the average particle diameter equivalent to a circle) The circle-equivalent average grain size of precipitated carbides in the Fe-BCC phase can be calculated as follows: First, the phase map obtained by EBSD (e.g., RGB image, field of view: 200 × 200 μm) is divided into each color (red, green, blue), and only the precipitated carbide area is extracted.

[0044] 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). By dividing the phase map in this way, the proportion of the Fe-BCC phase and precipitated carbides in the structure can be determined. By displaying the image of the divided red area (Fe-BCC phase) in black and white, the Fe-BCC phase appears white.

[0045] The blue area (mainly the Fe-FCC phase) and the green area (zero solution area) are displayed in white. If the total area is the sum of the areas of the red area (Fe-BCC phase), the blue area (mainly the Fe-FCC phase), and the zero solution area, the value obtained by dividing the red area (Fe-BCC phase) by the total area can be rephrased as the Fe-BCC layer ratio (area ratio).

[0046] By subtracting the image of the divided blue area (mainly the Fe-FCC phase) from this inverted black-and-white image, the zero solution area can be displayed. This zero solution area is the area that is neither the Fe-BCC nor the Fe-FCC phase, and corresponds to the precipitated carbide area. Next, by calculating the average area of ​​the precipitated carbide area within the field of view and then calculating the circle-equivalent diameter of that area, the circle-equivalent average diameter of the precipitated carbide in the Fe-BCC phase can be calculated.

[0047] Each structure can be evaluated using energy-dispersive X-ray spectroscopy (EDS) and electron backscattering diffraction (EBSD) associated with a scanning electron microscope (SEM).

[0048] 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 observation surface 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, Co, and O, and Si and Mn may also be included. The Fe-BCC phase can also be analyzed in the same manner as above.

[0049] Furthermore, the higher the proportion of the Fe-BCC phase, the more uniform the metal structure becomes, and since local distortion due to, for example, external stress is less likely to occur, the effect of suppressing cracks can be expected. Specifically, the proportion of Fe-BCC, in terms of area ratio, is preferably 96% or more, more preferably 97% or more, even more preferably 98% or more, and even more preferably 99% or more.

[0050] The structure of the Fe-based alloy of this embodiment is such that 96% or more of the alloy structure is occupied by the Fe-BCC phase, and fine carbides are precipitated in the Fe-BCC phase, making it difficult for cracks to occur originating from the carbides. Even if cracks do occur, they are uniformly dispersed and therefore do not easily propagate. This improves toughness and heat crack resistance.

[0051] The Fe-based alloy as a whole contains, in mass %, 0.1% to 2% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, 1.0% or less Si, 1.0% or less Mn, 4% or less Co, and the remainder being Fe and unavoidable impurity elements.

[0052] (C: 0.1 to 2%) Carbon 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. Carbon also dissolves partially in the matrix, strengthening it. By limiting the C content in the Fe-based alloy to 0.1% or more, the hardness of the Fe-based alloy as a whole 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 Fe-based alloy to 2% or less, the formation of excessive carbides in the Fe-based alloy as a whole can be suppressed, ensuring the toughness of the Fe-based alloy as a whole.

[0053] (Cr: 2-6%) Cr combines with C to form carbides, improving wear resistance and hardenability. By making the Cr content in the entire Fe-based alloy 2% 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.

[0054] (W:0.5~4%) 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 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 also forms carbides 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, it is possible to prevent excessive carbide formation in the entire Fe-based alloy, ensuring toughness.

[0055] (Mo: 0.5-4%) Mo combines with C to form carbides, improving wear resistance and contributing to improved hardenability. By making the Mo content in the Fe-based alloy 0.5% or more, not only does it dissolve in the matrix grains, increasing heat treatment hardness, but carbides are also formed at the matrix grain boundaries, improving wear resistance. On the other hand, by making the Mo content in the Fe-based alloy 4% or less, it is possible to prevent the formation of excessive carbides in the Fe-based alloy as a whole, thereby ensuring toughness.

[0056] (V:0.5~4%) V combines with C to form carbides, contributing to improved wear resistance and seizure resistance. By setting the V content in the Fe-based alloy to 0.5% or more, fine, non-aggregating carbides are precipitated within the matrix grains upon heat treatment, increasing softening resistance at high temperatures and improving high-temperature yield strength. Furthermore, the matrix grains are refined, improving toughness and raising the A1 transformation point, which, combined with excellent high-temperature yield strength, improves heat crack resistance. Meanwhile, by setting the V content in the Fe-based alloy to 4% or less, excessive carbide formation in the Fe-based alloy as a whole can be suppressed, ensuring toughness.

[0057] Furthermore, it is preferable that the steel further contains either Si or Mn, or both, with Si being 0.1% to 1.0% by mass and Mn being 0.1% to 1.0% by mass. Si is expected to improve oxidation resistance. The above ranges are desirable in consideration of workability. Mn is expected to have the effects of improving wear resistance and hardenability and reducing embrittlement. The above ranges are desirable in consideration of the effects of embrittlement due to quench cracking and residual γ.

[0058] (Si:1.0% or less) The Fe-based alloy may also contain Si. When Si is contained in the entire Fe-based alloy, the content of Si in the entire Fe-based alloy is preferably 0.1% or more and 1.0% or less in order to improve oxidation resistance and suppress deterioration of workability.

[0059] (Mn:1.0% or less) Furthermore, Mn may be contained. When Mn is contained in the entire Fe-based alloy, the content of Mn in the entire Fe-based alloy is preferably 0.1% or more and 1.0% or less in order to improve wear resistance and hardenability, reduce embrittlement, and suppress embrittlement due to quench cracking and residual γ.

[0060] (Co:4.0% or less) In addition to the above elements, the Fe-based alloy may contain Co. In order to improve the softening resistance of the matrix and suppress a decrease in toughness in the entire Fe-based alloy, the content of Co in the entire Fe-based alloy is preferably 4.0% or less, and more preferably 0.5% or more and 4% or less.

[0061] (unavoidable impurities) Inevitable impurities refer to trace amounts of impurities that are technically difficult to remove, such as 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 Ti. 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.

[0062] <Method of manufacturing alloy member> The Fe-based alloy and alloy member of this embodiment can be obtained by spraying alloy powder onto a substrate while moving it, irradiating the sprayed alloy powder with an electron beam or laser beam to melt and solidify it to form a solidified layer, stacking another solidified layer on top of the solidified layer, and repeating this process. This is a so-called additive manufacturing method. Note that this specification may also be referred to as a layered manufacturing method.

[0063] (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 consisting of Fe and inevitable impurity elements. First, predetermined amounts of feed materials for each element are measured so as to obtain an alloy with 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, high-frequency melted, 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 then be classified to obtain an alloy powder.

[0064] The Fe-based alloy powder of this embodiment may be alloyed to satisfy the above-mentioned composition of the Fe-based alloy, for example, by mass % of 0.1% to 2% C, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, 4.0% or less Co, 1.0% or less Si, 1.0% or less Mn, and the remainder being Fe and unavoidable impurities.

[0065] When a shaped body is manufactured 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 double carbides, which has the effect of improving the wear resistance of the alloy member and its manufactured products. In addition, C dissolves in a part of the matrix of the alloy structure of the shaped body, thereby strengthening the matrix.

[0066] 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, forming fine carbides within the grains of the matrix, and forming carbides at the grain boundaries of the matrix. On the other hand, by setting the C content in the Fe-based alloy powder to 2% or less, the formation of excessive carbides in the alloy structure can be suppressed, and the toughness of the Fe-based alloy as a whole can be ensured.

[0067] Cr combines with C to form carbides, improving the wear resistance of the alloy structure of the shaped body and also contributing to improved hardenability. By setting the Cr content in the Fe-based alloy powder to 2% or more, the amount of carbides formed in the alloy structure of the shaped body can be optimized, improving the wear resistance and hardenability of the alloy structure. On the other hand, by setting the Cr content in the entire Fe-based alloy to 6% or less, the amount of carbides formed in the alloy structure of the shaped body can be prevented from becoming excessive, ensuring toughness.

[0068] W combines with C to form carbides, contributing to improving the wear resistance of the alloy structure of the shaped body. 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-based alloy powder to 0.5% or more, the W dissolves in the matrix grains in the alloy structure, increasing heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving the wear resistance of the alloy structure. On the other hand, by setting the W content in the Fe-based alloy powder to 4% or less, excessive carbide formation in the alloy structure can be suppressed, ensuring toughness.

[0069] Mo combines with C to form carbides, improving the wear resistance of the alloy structure of the shaped body and also contributing to improved hardenability. By setting the Mo content in the Fe-based alloy powder to 0.5% or more, Mo dissolves in the matrix grains in the alloy structure, increasing the heat treatment hardness, and carbides are also formed at the matrix grain boundaries, improving the wear resistance of the alloy structure. On the other hand, by setting the Mo content in the Fe-based alloy powder to 4% or less, excessive carbide formation in the alloy structure can be suppressed, ensuring toughness.

[0070] V combines with C to form carbides, contributing to improved wear resistance and seizure resistance of the alloy structure of the shaped body. By setting the V content in the Fe-based alloy powder to 0.5% or more, fine, non-aggregating carbides are precipitated within the matrix grains in the alloy structure upon heat treatment, increasing the softening resistance of the alloy structure in the high-temperature range and improving high-temperature yield strength. Furthermore, the matrix grains in the alloy structure are refined, improving toughness and raising the A1 transformation point. This, combined with the excellent high-temperature yield strength, improves heat crack resistance. Meanwhile, by setting the V content in the Fe-based alloy powder to 4% or less, excessive carbide formation within the alloy structure can be suppressed, ensuring toughness.

[0071] For example, an Fe-based alloy powder containing, by mass, 0.1% to 2% C, 0.1% to 1.0% Si, 0.1% to 1.0% Mn, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, and the remainder being Fe and unavoidable impurity elements can be used. It is preferable that the powder contains either Si or Mn, or both.

[0072] When the Fe-based alloy powder contains Si, the content in the Fe-based alloy powder is preferably 0.1% to 1.0% in order to improve the oxidation resistance of the alloy structure of the shaped body and suppress a decrease in workability.When the Fe-based alloy powder contains Mn, the content in the Fe-based alloy powder is preferably 0.1% to 1.0% in order to improve the wear resistance and hardenability of the alloy structure of the shaped body, reduce embrittlement, and suppress embrittlement due to quench cracking and residual γ.

[0073] In addition to the above elements, Co can also be contained. To prevent a decrease in the toughness of the alloy structure of the shaped body, the content of Co in the Fe-based alloy as a whole is preferably 4% or less. To improve the softening resistance of the matrix of the alloy structure, it is preferably 0.5% or more.

[0074] Therefore, when Co is contained, it is preferable to use an Fe-based alloy powder containing 0.1% to 2% C, 0.1% to 1.0% Si, 0.1% to 1.0% Mn, 2% to 6% Cr, 0.5% to 4% W, 0.5% to 4% Mo, 0.5% to 4% V, 0.5% to 4% Co, and the remainder being Fe and unavoidable impurity elements.

[0075] The composition of the alloy powder can be analyzed using, for example, high-frequency inductively coupled plasma (ICP) optical emission spectrometry.

[0076] As an embodiment in which an Fe-based alloy powder is irradiated with an electron beam or a laser beam to melt and solidify it to form a shape, either Powder Bed Fusion (PBF) or Directed Energy Deposition (DED), which are additive manufacturing methods for metal materials, can be applied.

[0077] For example, the Fe-based alloy member of this embodiment can be manufactured by repeatedly performing a melting and solidifying process in which the 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 laminating a further solidified layer on the solidified layer. Alternatively, for example, the directed energy deposition method can be used to spray alloy powder onto a substrate while moving it, and then irradiate the sprayed alloy powder with an electron beam or a laser beam to melt and solidify it and form a solidified layer, repeating this melting and solidifying process, thereby laminating a further solidified layer on the solidified layer, thereby obtaining the alloy member (shaped body) of this embodiment.

[0078] 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.

[0079] For example, when applying the powder bed fusion (PBF) method, it is preferable to adjust the average particle size (D50) of the alloy powder to a range of 10 to 53 μm. Furthermore, for example, metal powders used in directed energy deposition methods must be melted by a laser beam, which serves as a heat source, so coarse powder that is difficult to melt must be removed. Furthermore, fine powder must also be removed to prevent dust scattering when the powder is supplied to the heat source and to ensure fluidity that allows the powder to be easily transported. Therefore, when applying the powder for molding of the present invention to directed energy deposition methods, it is preferable to adjust the D50 to a range of 53 to 106 μm. On the other hand, when using an electron beam or plasma as a heat source, it is possible to mold using coarser metal particles, so it is preferable to set the D50 to 75 to 250 μm.

[0080] 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 the 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.

[0081] 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 of the alloy powder 11, which is then solidified to form 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.

[0082] In the directed energy deposition method, a three-dimensional additive manufacturing device is used to rapidly melt the surface of a base material such as a base plate, a molded object, or a die by irradiating it with a laser. Then, raw material powder is 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 is the Fe-based alloy component of this embodiment. Furthermore, in the case of mold repair, a finished 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 conditions can be selected, for example, from the following ranges:

[0083] The thickness of one layer during additive manufacturing is, 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 plate is 0.1 mm to 1 mm. The thickness of the entire layer from the interface with the base material to the surface of the Fe-based alloy 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 when the Fe-based alloy is molded, and in which the compositions of both the base material and the first layer of Fe-based alloy are mixed.

[0084] 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 200 to 2000 mm / min, more preferably 500 to 1000 mm / min. The powder supply rate is preferably 10 to 20 g / min.

[0085] The energy density (heat source energy density: J / mm) input by laser irradiation to melt the raw material powder is preferably 90 to 300 J / mm, more preferably 180 to 240 J / mm. If the energy density is too low, the defect rate increases, and the supplied powder becomes difficult to melt, making it difficult to maintain the shape of the molded object. On the other hand, if the energy density is too high, the base plate or the molded object itself will melt over a wide area centered on the laser irradiation position, making it difficult to maintain the shape of the molded object. The energy density E (J / mm) can be calculated using the laser output P (W) and laser scanning speed v (mm / min) as E = P / v × 60.

[0086] (Heat treatment) The Fe-based alloy of this embodiment may be subjected to quenching treatment after shaping to improve hardness, or, if costs and the like are within an acceptable range, may be subjected to additional tempering treatment to remove quenching stress and improve toughness. Regarding heat treatment conditions, in the case of quenching treatment, for example, the holding temperature may be 1000 to 1400°C, more preferably 1100 to 1300°C, and even more preferably 1150 to 1280°C. The holding time may be 0.1 to 5 hours, more preferably 0.1 to 2 hours. Cooling can be performed in oil or water, but cooling in oil is more preferable to prevent distortion and quench cracking. Quenching and cooling may also be performed using a salt bath.

[0087] When tempering is performed, the temperature may be maintained at 400 to 700°C, more preferably 560 to 580°C. The temperature may be maintained for 1 to 10 hours, more preferably 2 to 6 hours. Cooling is preferably performed by air cooling.

[0088] Carbide precipitates when carbon (C) dissolves or diffuses into the Fe-BCC phase and combines with carbide-forming elements such as Fe, W, Mo, and V. Therefore, by performing heat treatment that facilitates carbon dissolution and diffusion into the Fe-BCC phase, carbide precipitates in the Fe-BCC phase and is appropriately refined.

[0089] For example, quenching promotes the decomposition of carbides present in the shaped body and facilitates the diffusion of carbon, which bonds with carbide-forming elements such as Fe, W, Mo, and V, into the Fe-BCC phase, thereby facilitating the formation of precipitated carbides. Therefore, alloys that have undergone quenching have a higher proportion of precipitated carbides than alloys that have not undergone quenching. Furthermore, it can be assumed that the diffusion of carbon disperses the precipitated carbides, reducing their mean circle-equivalent particle size.

[0090] (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.

[0091] 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 may involve, for example, nitriding or forming a film on the surface layer of the Fe-based alloy by a PVD method, such as a nitride layer, a compound layer, or a ceramic coating layer. These surface treatment steps can form a coating on the surface layer of the Fe-based alloy that is harder than an Fe-based alloy formed by additive manufacturing, thereby further strengthening the surface of the alloy component obtained by additive manufacturing and improving its wear resistance.

[0092] <Product> The manufactured product having at least a part of the alloy member thus obtained is not particularly limited, but is particularly suitable for, for example, a hot stamping die, a cold forging die, and a cold press die. In this case, even if a part of the surface of the die is damaged, the damaged part 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. [Example]

[0093] To obtain a shaped body with 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 resulting raw materials were then melted by high-frequency induction in a vacuum. The molten alloy was then 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. The composition of the resulting Fe-based alloy powder is shown in Table 1, and its particle size distribution is shown in Table 2.

[0094] [Table 1] [Table 2]

[0095] 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 rapid melting and rapid solidification were performed to create a 3 mm wide, 80 mm long, and approximately 10 mm high structure. 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.

[0096] Layer thickness when additive manufacturing: 0.47mm Laser beam diameter: approx. 3mm Laser power: 2400W Laser scanning speed: 600mm / s Energy density: 240J / mm

[0097] The shaped bodies were evaluated by heat-treating and not heat-treating. The shaped body that was only quenched was designated F1, the shaped body that was 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.

[0098] 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 surface of the embedded molded body to a mirror finish. The observation magnification was 3000x. Eight elements were analyzed: C, Co, Cr, Fe, Mo, V, W, and O.

[0099] Figures 2A to 2E show examples of acquired SEM images. Figure 2A is an SEM image of a shaped body F1 that was subjected to only quenching as a heat treatment, and Figure 2B is an SEM image of a shaped body F2 that was subjected to quenching and tempering. Figure 2C is an SEM image of a shaped body F3 that was not subjected to heat treatment (no heat treatment), Figure 2D is an SEM image of a shaped body F4 that was subjected to tempering only, and Figure 2E is an SEM image of a forged material F0 (powder sintered, forged, and then heat-treated (quenching and tempering)) made by conventional powder metallurgy, which has the same composition.

[0100] 2A to 2E, the structure indicated by the gray shading can be seen. The phase map was obtained using the method described above, and elemental analysis was performed within the field of view. Here, the area of ​​the field of view (also called the field of view area) was 200 μm × 200 μm.

[0101] Table 3 shows the composition of the Fe-BCC phase and carbides in F2, which was quenched and tempered. The Fe-BCC phase was analyzed at position A in Figure 2B, and the precipitated carbides (sometimes simply referred to as carbides) were analyzed at position B in Figure 2B. Table 4 also shows the results of an analysis of the Fe-BCC phase in F3, which was not heat-treated (no heat treatment), at position C in Figure 2C. For F0, the Fe-BCC phase was analyzed at the position D in FIG. 2E, and the carbides were analyzed at the position E in FIG. 2E. The results are shown in Table 5.

[0102] [Table 3] [Table 4] [Table 5]

[0103] As shown in Table 3, for F2, both the Fe-BCC phase and the carbides contained primarily Fe. The C, Cr, W, Mo, V, and Co content of the Fe-BCC phase was 5.0%, 4.2%, 1.8%, 2.1%, 1.1%, 1.3%, and 84.5% Fe, respectively. The C, Cr, W, Mo, V, and Co content of the Fe-BCC phase were 3%-7%, 2%-6%, 0.5%-4%, 0.5%-4%, 0.5%-4%, and 75%-90% Fe. The carbides were 8.9%, 4.8%, 2.5%, 3.3%, 2.5%, and 78.1% Fe. Electron diffraction patterns generated during electron beam irradiation were measured using EBSD, confirming that the Fe-BCC phase had a BCC structure.

[0104] As shown in Table 4, the C, Cr, W, Mo, V, and Co contents of the Fe-BCC phase for F3 were 4.9% C, 4.2% Cr, 1.9% W, 2.2% Mo, 1.2% V, 1.3% Co, and 84.5% Fe, with the ranges of 3%-7% C, 2%-6% Cr, 0.5%-4% W, 0.5%-4% Mo, 0.5%-4% V, and 75%-90% Fe. Carbides could not be analyzed because their area was too small and beyond the resolution of the analytical instrument. One possible reason for the lack of carbide precipitation in F3 is that the lack of heat treatment hindered carbide decomposition and the dissolution and diffusion of C into the Fe-BCC phase. This resulted in a lack of C to bond with carbide-forming elements such as Cr, W, Mo, and V, making carbide formation difficult.

[0105] Next, the circle-equivalent average particle size of precipitated carbides in the Fe-BCC phase was calculated. Table 6 shows the ratio of the Fe-BCC phase and precipitated carbides and the circle-equivalent average particle size of precipitated carbides in the Fe-BCC phase for F1 to F4 and F0.

[0106] [Table 6]

[0107] As shown in Table 6, the proportion of the Fe-BCC phase was 96.0% or more for all of F1 to F4, with 99.4% for F1, which was subjected to only quenching treatment, 99.5% for F2, which was subjected to both quenching and tempering treatment, 99.8% for F3, which was not subjected to quenching or tempering treatment (no heat treatment), and 99.9% for F4, which was subjected to only tempering treatment.

[0108] Furthermore, the proportion of precipitated carbides in the shaped bodies F1 to F4 was 0.27% for F1 and 0.38% for F2, confirming that the precipitated carbides were moderately precipitated within the Fe-BCC phase. On the other hand, the proportions of precipitated carbides in F3 and F4 were 0.012% and 0.009%, respectively, confirming that the proportions of precipitated carbides within the Fe-BCC phase were lower than those in F1 and F2.

[0109] Furthermore, the circle-equivalent average particle size of precipitated carbides was 1.08 μm for F1 and F2, which confirmed that they were refined.Furthermore, it was 0.58 μm for F3 and 0.50 μm for F4, which confirmed that the precipitated carbides were also refined for F3 and F4.

[0110] The reason why the proportion of precipitated carbides in F1 and F2 is larger than that in F3 and F4 is presumably due to differences in the amount of precipitated carbides resulting from the presence or absence of heat treatment. The absence of quenching in F3 and F4 likely makes it difficult for carbides to decompose, or for C to dissolve or diffuse into the Fe-BCC phase. This, in turn, makes it difficult for carbides to form due to a lack of C to bond with carbide-forming elements such as Cr, W, Mo, and V contained in the Fe-based alloy. Therefore, it is believed that the difficulty in carbide formation in F3 and F4 is the reason for the smaller proportion of precipitated carbides and the smaller mean circle-equivalent particle size of precipitated carbides.

[0111] Furthermore, when comparing F0 with F1 and F2, F1 and F2, which were produced using additive manufacturing methods like those in this example, have a faster cooling rate than the precipitation rate of the precipitated carbides because the alloy powder is melted and then immediately cooled and solidified. One of the reasons for this is thought to be that the faster cooling rate shortens the holding time in the temperature range where precipitated carbides can be formed, and the amount of carbides formed inside the alloy (shaped body) in the pre-heat treatment state is originally smaller than that of F0.

[0112] As described above, the shaped bodies F1 to F4 have a small circle-equivalent average particle size of the precipitated carbides, and the fineness of the precipitated carbides makes them less susceptible to cracking, resulting in Fe-based alloys with excellent toughness and heat crack resistance. In particular, the circle-equivalent average particle size of the precipitated carbides in the shaped bodies F1 and F2 is 1.08 μm, and the moderate fineness of the precipitated carbides makes them Fe-based alloys with excellent wear resistance. Furthermore, while the proportion of the Fe-BCC phase in the forged material F0 is 95.7%, the proportion of the Fe-BCC phase in the shaped bodies F1 to F4 is 99% or more, resulting in a more uniform structure. Therefore, for example, it can be expected that cracking will be less likely to occur because localized distortion due to external stress will be less likely to occur.

[0113] [Hardness] The hardness of the resulting molded body was measured using a Vickers hardness tester. Measurements were taken at five points, and the average value was calculated. The results are shown in Table 7, and a comparison with the forged material is shown in Figure 3.

[0114] [Table 7]

[0115] As shown in Table 7, the hardness of the shaped body F1, which was subjected to only quenching treatment, was 600 HV, and the hardness of the shaped body F2, which was subjected to quenching and tempering treatment, was 578 HV. The hardness of the shaped body F3, which was not subjected to heat treatment (no heat treatment), was 409 HV, and the hardness of the shaped body F4, which was subjected to only tempering treatment, was 408 HV. From this, it was confirmed that if it is desired to improve the wear resistance, it is preferable to harden the shaped body as in the case of the shaped bodies F1 and F2.

[0116] As mentioned above, the quenched body F1, the quenched and tempered body F2, the unheated body F3, and the tempered body F4 all have a homogeneous structure due to the Fe-BCC phase ratio of 99% or more, as shown in Table 6. Therefore, it is expected that cracks will not occur because localized distortion due to external stress is unlikely to occur. Furthermore, the quenched body F1 and the quenched and tempered body F2 have a moderately fine, circle-equivalent average particle diameter of precipitated carbides of 1.08 μm, as shown in Table 6. Therefore, cracks will not occur easily, and they are expected to have excellent toughness, heat crack resistance, and wear resistance. [Explanation of symbols]

[0117] 1. Additive manufacturing equipment 3. Powder supply nozzle 5. Focusing lens 7. Protective lens 9. Laser beam 11. Alloy powder 13. Weld pool 15. Sculptural body 17···Base plate 50...Fe-BCC phase 52 Fine precipitates

Claims

1. including C, Cr, W, Mo and V; In mass%, C is 0.1% or more and 2% or less, Cr is 2% or more and 6% or less, W is 0.5% or more and 4% or less, Mo is 0.5% or more and 4% or less, V is 0.5% or more and 4% or less, Si is 1.0% or less, containing 1.0% or less of Mn, 4% or less of Co, and the balance being Fe and inevitable impurity elements; having an alloy structure including an Fe-BCC phase, The alloy has precipitated carbides precipitated in the Fe-BCC phase, The precipitated carbides have an average circle-equivalent particle size of 1.30 μm or less, When the total area is the sum of the areas of the Fe-BCC phase, the Fe-FCC phase, and the zero solution portion, The proportion of the precipitated carbides is 0.38% or less in terms of an area ratio obtained by dividing the area of ​​the zero solution portion by the total area, The Fe-BCC phase accounts for 96% or more of the alloy structure in terms of area ratio. An Fe-based alloy characterized by:

2. 2. The Fe-based alloy according to claim 1, wherein the average circle-equivalent grain size of the precipitated carbides is 0.60 μm or more.

3. 3. The Fe-based alloy according to claim 1, wherein the Si content is 0.1% or more and 1.0% or less, and the Mn content is 0.1% or more and 1.0% or less, in mass %.

4. 2. The Fe-based alloy according to claim 1, wherein the Co content is, in mass %, 0.5% to 4%.

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

6. 6. The alloy member according to claim 5, wherein the Fe-based alloy has a hardness of 350 HV or more.

7. 7. The alloy member according to claim 5, wherein the outermost layer of the Fe-based alloy is provided with at least one of a nitride layer, a compound layer, and a ceramic coating layer.

8. A manufactured product comprising at least a part of the alloy member according to claim 7.

9. 9. The article of manufacture according to claim 8, which is a warm forging die, a die casting die, a hot stamping die, a cold forging die or a cold pressing die.

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