Fe-based alloys and metal powders for molten solidification molding

Abstract

To provide an Fe base alloy for melt solidification molding in which cracking is hard to generate in a molded object when being used for melt solidification molding such as lamination molding, and capable of obtaining a build-up layer, a lamination molded object or the like having high hardness, and a metal powder having an average composition equal to the same.SOLUTION: An Fe base alloy for melt solidification molding has a composition comprising 18.0≤Co<25.0 mass%, 12.0≤Mo+W / 2≤20.0 mass%, 0.2≤Mn≤5.0 mass% and 0.5≤Ni≤10.0 mass%, and the balance Fe with inevitable impurities, and satisfies 58≤Co+3(Mo+W / 2)≤95 and A / B≥1.6; where A=Co+Ni+3Mn and B=Mo+W / 2+Si. A metal powder is made of the one having an average composition equal to that of the Fe base alloy for melt solidification molding.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an Fe-based alloy and metal powder for fusion solidification forming. More specifically, when used for fusion solidification forming such as build-up welding and additive manufacturing, it is difficult for cracks to occur during forming, and an Fe-based alloy for fusion solidification forming that can obtain a formed product with high hardness, and a metal powder having an average composition equivalent thereto are concerned.

Background Art

[0002] High wear resistance is required for dies and sliding members for cold working. Generally, wear resistance is correlated with hardness, and the higher the hardness, the better the wear resistance. In particular, as alloys that can obtain high hardness, high-speed tool steels, Co-based superalloys, Ni-based superalloys, etc. can be mentioned. However, since these alloys have poor workability, there is a problem that when a large volume is removed by machining, the tool wears severely and the processing cost becomes high. In recent years, with the development of additive manufacturing technology, it has become possible to form these difficult-to-machine materials in a state close to the finished product. Therefore, various proposals have been made for metal powders for additive manufacturing.

[0003] For example, Patent Document 1 discloses an alloy powder containing 25 to 35 wt% of Co, 10 to 17.5 wt% of Mo, and Fe. The same document describes that when additive manufacturing is performed using an alloy powder having such a composition and the formed product is heat-treated at 400°C to 700°C, the hardness required for a wear-resistant member can be obtained.

[0004] Patent Document 2 does not relate to a metal powder for additive manufacturing, but a main body obtained by HIP-treating an alloy powder (carbon-free precipitation hardening type Fe-Co-Mo / W-N alloy powder) containing a predetermined amount of Co, Mo, W, and N and the balance being Fe, and a coating formed on the surface of the main body by PVD method or CVD method are provided in a tool (coated metal product). The document states that when the main body is fabricated using powder metallurgy, a structure is obtained in which each phase is finely dispersed.

[0005] In additive manufacturing processes, the structure is formed by rapid solidification, and thermal stress is generated during the process. Therefore, if the toughness of the fabricated object is insufficient in its solidified state, there was a problem that the object would crack during the process due to thermal stress.

[0006] In this regard, Patent Document 1 discloses a powder for additive manufacturing that can be aged at low temperatures. However, when the alloy powder described in Patent Document 1 is applied to additive manufacturing, ferrite phases may precipitate in the manufactured object depending on the component balance and cooling conditions. In the areas where the ferrite phase has precipitated, a martensitic structure cannot be obtained after cooling, resulting in coarse grains and making the manufactured object prone to cracking due to thermal stress during the process. Furthermore, the alloy powder described in Patent Document 1 contains a relatively large amount of Co. Co has become difficult to obtain and expensive in recent years due to increased demand for applications such as lithium-ion batteries.

[0007] On the other hand, the alloy powder described in Patent Document 2 is a powder intended for molding by HIP, and not a powder intended for use in additive manufacturing. Furthermore, the alloy powder described in Patent Document 2 contains components that cause cracking when used in additive manufacturing (for example, 25% Co, 19.2% Mo, etc.). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-084286 [Patent Document 2] U.S. Patent Application Publication No. 2009 / 0007992 Specification [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The problem that the present invention aims to solve is to provide an Fe-based alloy for molten solidification molding that, when used in molten solidification molding such as build-up welding and additive manufacturing, is less prone to cracking in the molded object and can produce a high-hardness build-up layer, additively manufactured object, etc. Another problem that the present invention aims to solve is to provide a metal powder having an average composition equivalent to that of such Fe-based alloys for molten solidification molding. [Means for solving the problem]

[0010] To solve the above problems, the Fe-based alloy for molten solidification molding according to the present invention is 18.0 ≤ Co < 25.0 mass%, 12.0 ≤ Mo + W / 2 ≤ 20.0 mass%, 0.2 ≤ Mn ≤ 5.0 mass%, and, 0.5 ≤ Ni ≤ 10.0 mass% It contains, with the remainder consisting of Fe and unavoidable impurities. The gist of this is that the following equations (1) and (2) are satisfied.

[0011] 58 ≤ Co + 3(Mo + W / 2) ≤ 95 …(1) A / B ≥ 1.6 …(2) however, A = Co + Ni + 3Mn, B = Mo + W / 2 + Si, When Mo, Si, and / or W are not included, the calculations in equation (1) and / or equation (2) are performed with Mo=0, Si=0, and / or W=0.

[0012] The metal powder according to the present invention consists of a material whose average composition is equivalent to that of the Fe-based alloy for molten solidification molding according to the present invention. [Effects of the Invention]

[0013] In Fe-Co-Mo alloys, Co is (a) Function as an austenite phase stabilizing element, (b) During aging treatment, it has the function of precipitating fine particles composed of Fe-Co-Mo-based compounds (μ-phase) in the matrix and is provided with. Therefore, if the Co content is simply reduced in order to reduce the cost of the Fe-based alloy, not only does the precipitation amount of the μ-phase as the precipitation strengthening phase decrease, but the ferrite phase is likely to precipitate during solidification. When such an Fe-based alloy is applied to additive manufacturing, when the ferrite phase precipitates in the formed object, the martensite structure cannot be obtained after cooling, so the crystal grains become coarser. As a result, the formed object is likely to crack.

[0014] On the other hand, when an appropriate amount of Ni and Mn are added while suppressing the Co content to the minimum necessary, the precipitation of the ferrite phase during solidification is suppressed, and an appropriate amount of μ-phase can be precipitated by aging treatment. As a result, when powder made of such an Fe-based alloy is used for fusion solidification forming such as overlay welding and additive manufacturing, cracks are less likely to occur in the formed object, and a high-hardness overlay layer, additive manufactured object, etc. can be obtained.

Brief Description of the Drawings

[0015] [Figure 1] It is a photograph of a cross section perpendicular to the welding length direction of the overlay welded part obtained in Example 11. [Figure 2] It is a diagram showing the relationship between the position and hardness in the width direction of the overlay welded parts obtained in Example 11 and Comparative Example 8.

Modes for Carrying Out the Invention

[0016] Hereinafter, an embodiment of the present invention will be described in detail. [1. Fe-based alloy for fusion solidification forming] [1.1. Composition] The Fe-based alloy for fusion solidification forming according to the present invention (hereinafter, also simply referred to as "Fe-based alloy") contains the following elements, and the balance consists of Fe and inevitable impurities. The types of additive elements, their composition ranges, and the reasons for their limitation are as follows.

[0017] [1.1.1. Main constituent elements] (1) 18.0 ≤ Co < 25.0 mass%: Co has the function of promoting the precipitation of the reinforcing phase, the μ phase, and the function of increasing the stability of austenite at high temperatures. Therefore, if the Co content is too low, the amount of μ phase precipitation will be insufficient, and the hardness will decrease significantly. Accordingly, the Co content needs to be 18.0 mass% or more. Preferably, the Co content is 20.0 mass% or more, and more preferably 22.0 mass% or more. On the other hand, if the Co content becomes excessive, not only will the effect of increasing hardness saturate, but manufacturing costs will also increase. Therefore, the Co content needs to be less than 25.0 mass%.

[0018] (2) 12.0 ≤ Mo + W / 2 ≤ 20.0 mass%: Mo and W, like Co, have the functions of promoting the precipitation of the strengthening phase, the μ phase, and increasing the stability of austenite at high temperatures, respectively. Furthermore, since the atomic weight of W is approximately twice that of Mo, similar effects can be obtained by replacing all or part of Mo with twice the amount of W. However, if the amount of (Mo + W / 2) is too low, the amount of μ phase precipitation will be insufficient, and high-hardness molded objects may not be obtained. Therefore, the amount of (Mo + W / 2) needs to be 12.0 mass% or more. Preferably, the amount of (Mo + W / 2) is 14.0 mass% or more. On the other hand, if the amount of (Mo+W / 2) is excessive, the volume fraction of the μ phase may become too large, which can reduce the toughness of the fabricated object. Therefore, the amount of (Mo+W / 2) must be 20.0 mass% or less. Preferably, the amount of (Mo+W / 2) is 16.0 mass% or less.

[0019] (3) 0.2 ≤ Mn ≤ 5.0 mass%: Mn has the function of acting as a deoxidizing agent and inhibiting ferrite formation. Therefore, if the Mn content is too low, when such powder is applied to melt-solidification molding, the ferrite phase will precipitate during molding, making the molded object prone to cracking. Accordingly, the Mn content needs to be 0.2 mass% or more. Preferably, the Mn content is 0.5 mass% or more, and more preferably 0.7 mass% or more. On the other hand, if the Mn content is excessive, the amount of retained austenite in the molded object increases, which may result in insufficient hardness. Therefore, the Mn content needs to be 5.0 mass% or less. Preferably, the Mn content is 3.0 mass% or less, and more preferably, 1.0 mass% or less.

[0020] (4) 0.5 ≤ Ni ≤ 10.0 mass%: Ni has the function of suppressing ferrite formation. Therefore, if the Ni content is too low, when such powder is applied to melt-solidification molding, the ferrite phase will precipitate during molding, making the molded object prone to cracking. Accordingly, the Ni content needs to be 0.5 mass% or more. Preferably, the Ni content is 0.8 mass% or more, and more preferably 1.0 mass% or more. On the other hand, if the nickel content is excessive, the amount of retained austenite in the fabricated object increases, which may result in insufficient hardness. Therefore, the nickel content should be 10.0 mass% or less.

[0021] [1.1.2. Sub-constituent elements] The Fe-based alloy according to the present invention may further contain one or more elements in addition to the elements described above. The types of additive elements, their component ranges, and the reasons for their limitations are as follows.

[0022] (1) 0 ≤ Si ≤ 1.0 mass %: Si has the function of both a deoxidizing agent and a function of promoting the precipitation of the μ phase, and can be added as needed. However, if the Si content is excessive, the precipitation of the μ phase is excessively promoted, and the μ phase is more likely to crystallize from the liquid phase. As a result, the toughness of the fabricated object may deteriorate. Therefore, a Si content of 1.0 mass% or less is preferable. More preferably, the Si content is 0.5 mass% or less, and even more preferably, 0.3 mass% or less.

[0023] (2) 0 ≤ W ≤ 20.0 mass%: As mentioned above, W, like Mo, has the function of promoting the precipitation of the reinforcing phase, the μ phase, and the function of increasing the stability of austenite at high temperatures, so all or part of Mo can be replaced with W. However, if the W content is excessive, the volume fraction of the μ phase may become too large, and the toughness of the fabricated object may decrease. Therefore, the W content is preferably 20.0 mass% or less. More preferably, the W content is 15.0 mass% or less.

[0024] (3) 10.0 ≤ Mo ≤ 20.0 mass%: As mentioned above, Mo, like W, has the function of promoting the precipitation of the reinforcing phase, the μ phase, and the function of increasing the stability of austenite at high temperatures, so all or part of W can be replaced with Mo. However, if the Mo content is too low, the amount of μ phase precipitation will be insufficient, and high hardness may not be obtained. Therefore, a Mo content of 10.0 mass% or more is preferable. A more preferable Mo content is 12.0 mass% or more, and even more preferable is 14.0 mass% or more. On the other hand, if the Mo content is excessive, the volume fraction of the μ phase may become too large, which can reduce toughness. Therefore, the Mo content is preferably 20.0 mass% or less. More preferably, the Mo content is 16.0 mass% or less.

[0025] (4) P ≤ 0.05 mass %: P is an unavoidable impurity that is introduced during manufacturing. P segregates at grain boundaries, reducing the toughness of the molded product. Therefore, a P content of 0.05 mass% or less is preferable. A P content of 0.03 mass% or less is even more preferable. The lower the P content, the better.

[0026] (5) S ≤ 0.05 mass %: S is an unavoidable impurity that is introduced during manufacturing. S segregates at grain boundaries, reducing the toughness of the molded product. Therefore, a S content of 0.05 mass% or less is preferable. A S content of 0.03 mass% or less is even more preferable. The lower the S content, the better.

[0027] [1.1.3. Inevitable Impurities] In the Fe-based alloy according to the present invention, the following components may be present in the amounts shown below. In such cases, these components are treated as unavoidable impurities in the present invention. Cr≦0.5mass%, C≦0.1mass%, Cu≦0.5mass%, Al≦0.2mass%, N≦0.1mass%, O≦0.1mass%, Sn≦0.05mass%, Nb≦0.05mass%, Ta≦0.05mass%, Ti≦0.5mass%, Zr≦0.05mass%, B≦0.02mass%, Ca≦0.01mass%, Se≦0.03mass%, Te≦0.03mass%, Bi≦0.03mass%, Pb≦0.05mass%, Mg≦0.02mass%, REM≦0.01mass%.

[0028] [1.2. Ingredient Balance] The Fe-based alloy according to the present invention must satisfy the following formulas (1) and (2). 58 ≤ Co + 3(Mo + W / 2) ≤ 95 …(1) A / B ≥ 1.6 …(2) however, A = Co + Ni + 3Mn, B = Mo + W / 2 + Si, When Mo, Si, and / or W are not included, the calculations in equation (1) and / or equation (2) are performed with Mo=0, Si=0, and / or W=0.

[0029] [1.2.1. Formula (1)] "Co+3(Mo+W / 2)" serves as an indicator of the amount of μ phase precipitated (hereinafter also referred to as "indicator C"). If indicator C becomes too small, high hardness cannot be obtained. Therefore, indicator C needs to be 58 or higher. Preferably, indicator C is 61 or higher, and more preferably 64 or higher. On the other hand, if index C becomes too large, the volume fraction of the μ phase becomes too large, which can significantly degrade the toughness of the fabricated object. Therefore, index C needs to be 95 or less. Preferably, index C is 85 or less, and more preferably 80 or less.

[0030] [1.2.2. Formula (2)] In equation (2), "A" represents the equivalent weight of the austenite phase stabilizing element. In equation (2), "B" represents the equivalent weight of the ferrite phase stabilizing element. Furthermore, the "A / B" in equation (2) (hereinafter also referred to as the "equivalent ratio") represents the ratio of the equivalent weight of the austenite phase stabilizing element to the equivalent weight of the ferrite phase stabilizing element.

[0031] If the equivalence ratio becomes too low, when such powder is applied to melt-solidification molding, the ferrite grain boundaries become the starting points for cracks, making the molded object prone to cracking. Therefore, the equivalence ratio needs to be 1.6 or higher. Preferably, the equivalence ratio is 1.7 or higher. On the other hand, if the equivalence ratio becomes too large, the amount of retained austenite may increase, leading to a decrease in hardness. Therefore, an equivalence ratio of less than 2.4 is preferable. More preferably, the equivalence ratio is 2.2 or less.

[0032] [1.3. Shape] In the present invention, the shape of the Fe-based alloy is not particularly limited. Examples of Fe-based alloy shapes include ingots, rods, tubes, wires, and powders. In particular, powder is suitable as a raw material for melt-solidification molding.

[0033] [2. Metal powder] The metal powder according to the present invention consists of a metal powder whose average composition is equivalent to that of the Fe-based alloy for molten solidification molding according to the present invention. Preferably, the metal powder has an average particle size of 10 μm or more and 300 μm or less.

[0034] [2.1. Ingredients] "The average composition is equivalent to that of Fe-based alloys for molten solidification molding" means that (a) The metal powder consists of an aggregate of one type of metal particles having the same composition, and each individual metal particle is within the compositional range described above. (b) The metal powder consists of a mixture of two or more metal particles having different compositions, and each individual metal particle is within the above-mentioned range of components, or (c) The metal powder consists of a mixture of two or more metal particles having different compositions, and one or more of the metal particles are not within the above-mentioned component range, but the average value of the overall composition of the metal powder is within the above-mentioned component range. It refers to.

[0035] When a metal powder consists of a mixture of two or more metal particles having different compositions, each metal particle may be a pure metal particle containing a single metal element, or it may be an alloy particle containing two or more metal elements. When the metal powder consists of a mixture, its average composition can be obtained, for example, by taking a sample of about 10 g from the mixture and analyzing it using methods such as X-ray fluorescence analysis, combustion infrared absorption spectroscopy, or plasma emission spectroscopy. The details of the metal powder composition (average composition) are the same as those of the Fe-based alloy described above, so the explanation will be omitted.

[0036] [2.2. Average particle size] "Average particle size" refers to the number frequency D 50(μm), that is, the cumulative particle size (median diameter) of 50 percent of the powder. D 50 For example, as a method of measurement, (a) A method of measurement using a particle distribution analyzer based on laser diffraction and scattering, (b) A method of measurement using a particle image analyzer, (c) Method of measurement using a Coulter counter, These are some examples. In the present invention, "D 50 When this term is used, it refers to the median diameter measured by a particle distribution analyzer based on laser diffraction and scattering. The average particle size and particle size distribution of metal powder can be controlled by the manufacturing conditions and classification conditions of the metal powder.

[0037] In melt-solidification molding using metal powder, a nozzle is sometimes used to supply the metal powder to the molding area. In this case, if the average particle size of the metal powder becomes too small, the fluidity of the metal powder decreases, making it difficult to stably supply the metal powder. Therefore, the average particle size of the metal powder is preferably 10 μm or larger. Preferably, the average particle size is 50 μm or larger, and more preferably, 80 μm or larger.

[0038] On the other hand, if the average particle size of the metal powder becomes too large, the larger particles may clog the nozzle, making it impossible to supply the powder stably. Therefore, the average particle size of the metal powder is preferably 300 μm or less. Preferably, the average particle size is 200 μm or less, and more preferably 150 μm or less.

[0039] [2.3. Particle shape] The particle shape of individual metal particles contained in the metal powder is not particularly limited. The metal particles may be spherical or irregularly shaped. Spherical metal particles are preferred for obtaining high fluidity.

[0040] [2.4. Surface coating] The metal particles may have their surfaces coated with nanoparticles. "Nanoparticles" refer to inorganic compound particles with a diameter of 1 nm to 100 nm. Coating the surface of metal particles with certain types of nanoparticles can sometimes suppress the aggregation of metal particles. Examples of nanoparticles that have the effect of suppressing metal particle aggregation include metal oxides such as silica (SiO2), alumina (Al2O3), manganese oxide (MnO), iron oxide (Fe2O3), calcium oxide (CaO), and magnesium oxide (MgO).

[0041] When coating the surface of metal particles with nanoparticles, if the coating amount is too small, it may not be possible to sufficiently suppress the aggregation of the metal particles. Therefore, a nanoparticle content of 0.005 mass% or more is preferable. On the other hand, if the amount of nanoparticle coating is excessive, the nanoparticles may become inclusions, which may reduce the strength and / or toughness of the molded object when melt-solidification molding is performed. Therefore, the nanoparticle content is preferably 0.05 mass% or less.

[0042] [2.5. Usage] The metal powder according to the present invention can be used as a raw material powder for melt solidification molding. Here, "melt solidification molding method" refers to a method of forming all or part of an object by melting metal powder using various heat sources, and then solidifying and depositing the molten metal powder. "To form the entire object" means to form the entire object solely through the melting, solidification, and deposition of metal powder. "Forming a part of a molded object" means adding a new layer that constitutes another part of the molded object to the surface of a substrate that constitutes a part of the molded object by melting, solidifying, and depositing metal powder (for example, repairing a mold).

[0043] Among the melt-solidification molding methods, a typical example is, (a) Direct Energy Deposition (DED) method, (b) Powder bed melting method, (c) Plasma overlay welding method, These are some examples.

[0044] Among these methods, "Directed Energy Deposition (DED)" refers to a method in which molten metal is selectively deposited onto existing components or substrates by irradiating them with a laser or electron beam while supplying metal powder. The DED method allows for repeated deposition of metal layers and enables the deposition of metal into various shapes such as linear, wall-like, and lumpy forms. By using a device that uses a laser as a heat source, the volume of molten metal deposited can be reduced, suppressing quality degradation due to the mixing of components that occurs at the interface with the deposition material. Therefore, various materials such as Fe-based alloys, Ni-based alloys, and Co-based alloys can be used as the deposition material.

[0045] "Powder bed fusion" refers to a fabrication method in which slice data in units of tens of micrometers is created based on three-dimensional data (e.g., STL data) generated by 3D-CAD, and then a laser is selectively scanned and irradiated onto a powder bed using the obtained slice data to build up sintered layers. "Plasma overlay welding" is a method of welding in which a plasma arc is generated between an electrode and a substrate, metal powder is introduced into the arc to melt the metal powder, and the metal is built up on the surface of the substrate.

[0046] [3. Method for producing metal powder] The metal powder according to the present invention can be manufactured using methods such as gas atomization, water atomization, plasma atomization, plasma rotation electrode method, and centrifugal atomization. Alternatively, the powder obtained in this manner may be combined with a spheroidization treatment using a reducing thermal plasma.

[0047] Among these methods, "gas atomization" refers to a method of obtaining metal powder by melting alloy raw materials in an induction melting furnace, etc., and blowing high-pressure gas onto the molten metal while it falls from the bottom of a tundish, thereby pulverizing and solidifying the molten metal. Inert gases such as nitrogen, argon, and helium are used as the high-pressure gas. The gas atomization conditions are not particularly limited, and the optimal conditions can be selected according to the purpose.

[0048] It is preferable to produce metal powder using the gas atomization method, and then perform classification to adjust the average particle size and particle size distribution. Classification methods include, for example, dry cyclones, wet cyclones, dry sieves, and ultrasonic sieves. When metal powder with controlled average particle size and particle size distribution is used, dense molded objects can be obtained when applied to melt solidification molding. Furthermore, if necessary, two or more metal powders with different compositions may be mixed to adjust the composition.

[0049] [4. Effect] In Fe-Co-Mo alloys, Co is (a) Function as an austenite phase stabilizing element, (b) Function to precipitate fine particles consisting of Fe-Co-Mo compounds (μ phase) in the matrix during aging treatment. It is equipped with. Therefore, simply reducing the amount of Co in Fe-based alloys to lower costs not only reduces the amount of μ phase (which acts as a precipitation strengthening phase) that precipitates, but also makes it easier for the ferrite phase to precipitate during solidification. When such Fe-based alloys are applied to additive manufacturing, if the ferrite phase precipitates in the fabricated object, the grain becomes coarse because a martensitic structure cannot be obtained after cooling. As a result, the fabricated object becomes more prone to cracking.

[0050] In contrast, by adding appropriate amounts of Ni and Mn while keeping the Co content to the minimum necessary, the precipitation of the ferrite phase during solidification is suppressed, and an appropriate amount of μ phase can be precipitated by aging treatment. As a result, when powder made from such an Fe-based alloy is used in molten solidification molding such as build-up welding and additive manufacturing, cracks are less likely to occur in the manufactured object, and a high-hardness build-up layer, additively manufactured object, etc., can be obtained. [Examples]

[0051] (Examples 1-10, Comparative Examples 1-7) [1. Sample Preparation] [1.1. Preparation of Metal Powders] Seventeen types of metal powders, as shown in Table 1, were prepared using the gas atomization method. Note that elements not listed in the table may be present as impurities within specified limits.

[0052] [Table 1]

[0053] [1.2. Fabrication of built-up sculptures] Objects were fabricated using the prepared metal powder and a DED (Depositional Energy Deposition) laser metal additive manufacturing system (metal 3D printer) to confirm their hardness and microstructure. A flat SKD61 plate (50 × 70 × 10 mm) was used as the substrate. The fabrication conditions were as follows. The fabrication conditions were adjusted as needed to achieve a density of 98% or higher. Laser output: 1500~2000W Powder flow rate: 5~10g / min Feed rate: 100~1000mm / min Dimensions of the printed object: Height 5-10mm x Width 10-12mm x Length 60-70mm

[0054] [2. Test Method] [2.1. Cracks] Penetrant testing was performed on the fabricated object to check for cracks at the interface between the fabricated object and the substrate.

[0055] [2.2. Hardness 1 (Hardness as molded)] The printed object was cut into 5mm thick slices, and the cross-sections were polished with sandpaper. The Rockwell hardness (JIS Z2245) was measured at the center of the cross-section of the printed object.

[0056] [2.3. Hardness 3 (Hardness after aging treatment)] The fabricated object was cut into 5mm thick slices. The cut slices were placed in an air furnace heated to 600°C and held for 30 minutes, after which they were air-cooled. This process is also referred to as "aging treatment." After air-cooling, the oxide film on the slices was removed with abrasive paper, and the Rockwell hardness (JIS Z2245) was measured at the center of the cross-section of the fabricated object.

[0057] [3. Results] The results are shown in Table 2. From Table 2, the following can be seen: (1) Comparative Examples 1, 6, and 7 showed cracks in the fabricated objects. This is thought to be because the A / B ratio was less than 1.6, causing cracks to occur at the ferrite grain interface. (2) Comparative Example 2 showed no cracking and had high hardness. However, the manufacturing cost was high due to the large amount of Co added. (3) Comparative Examples 3 and 4 have low hardness (hardness 2) after aging treatment. This is thought to be because the Co+3(Mo+W / 2) content was less than 58, resulting in insufficient precipitation of the μ phase. (4) Comparative Example 5 has a low hardness (hardness 2) after aging treatment. This is thought to be because the amount of Mn is excessive, resulting in a large amount of soft retained austenite in the structure. (5) In all of Examples 1 to 10, no cracks occurred, and the hardness (hardness 2) after aging treatment also increased.

[0058] [Table 2]

[0059] (Example 11, Comparative Example 8) [1. Sample Preparation] A 5 kg steel ingot having the composition shown in Table 3 was prepared in a vacuum induction melting furnace. The steel ingot was heated at 1200°C for 5 hours and then forged to a cross-sectional size of 30 mm x 30 mm. A φ1.6 mm round bar was cut from the forged steel billet by wire electrical discharge machining and used as a welding rod for welding testing.

[0060] [Table 3]

[0061] Next, the obtained welding rods were used to build up the SKD61 plate using the TIG welding method. The TIG welding conditions were as follows: Welding current: Approximately 100A Wire insertion direction: Forward Gas flow rate: Approximately 5-10 L / min (Ar) Weld length: 50mm Number of welds: 3 passes / layer in width direction × 5 layers in height direction Pass overlap rate: Aiming for 50% Cooling between layers: After the nth layer (1≦n≦4) of build-up welding is completed and the temperature of the build-up area drops below 150°C, the (n+1)th layer of build-up welding is performed. Preheating: None Weaving: None

[0062] [2. Test Method] The welded section, cut perpendicular to the weld length, was embedded in resin and mechanically polished until it reached a mirror finish. A Vickers hardness test was then performed on the mirror-polished surface. Figure 1 shows a photograph of a cross-section of the build-up weld obtained in Example 11, perpendicular to the weld length direction. In Figure 1, the left region, the center region, and the right region correspond to the build-up weld regions of the first pass, second pass, and third pass, respectively. Vickers hardness was measured at the halfway point in the weld height direction (indicated by the dashed line in Figure 1) at 0.5 mm intervals in the weld width direction (in the direction of the dashed line in Figure 1).

[0063] [3. Results] Figure 2 shows the relationship between the position in the width direction and the hardness of the build-up welds obtained in Example 11 and Comparative Example 8. Note that "position = zero mm" on the horizontal axis of Figure 2 corresponds to the position of the left end of the dashed line in Figure 1. In Comparative Example 8, the hardness of the heat-affected zone (the region with a position of 0 to 5 mm) increased, and a region with a hardness exceeding 800 Hv appeared. This is thought to be because the region where martensite was generated in the first pass of build-up welding was reheated during the second pass of build-up welding and underwent age hardening.

[0064] In contrast, in Example 11, despite having almost the same amounts of Co and Mo as in Comparative Example 8, which have a significant impact on hardness after heat treatment, the hardness of the heat-affected zone was lower than that of Comparative Example 8. This is thought to be because the addition of an appropriate amount of Ni lowered the martensitic transformation onset temperature (Ms). In other words, because Ms was lowered, the second pass of overlay welding was performed before the martensitic transformation of the first pass of overlay welding was completed, thus suppressing age hardening. Furthermore, in both Example 11 and Comparative Example 8, the hardness at the 5-10 mm position was 600 Hv or less. This is thought to be because this corresponds to the final 5th layer, 3rd pass, and age hardening did not occur because it was not affected by heat after the build-up.

[0065] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0066] The metal powder according to the present invention can be used as a raw material powder for manufacturing and repairing wear-resistant parts such as molds and sliding members using additive manufacturing or build-up welding. Furthermore, due to its characteristics, the present invention is also suitable for use as a wire for welding or additive manufacturing.

Claims

1. 18.0≦Co<25.0 mass%, 12.0≦Mo+W / 2≦20.0mass%, 0.2 ≤ Mn ≤ 5.0 mass%, and, 0.5≦Ni≦10.0mass% It contains, with the remainder consisting of Fe and unavoidable impurities. An Fe-based alloy for molten solidification molding that satisfies the following formulas (1) and (2). 58≦Co+3(Mo+W / 2)≦95…(1) A / B≧1.6…(2) however, A=Co+Ni+3Mn, B=Mo+W / 2+Si, When Mo, Si, and / or W are not included, the calculations in equation (1) and / or equation (2) are performed with Mo = 0, Si = 0, and / or W = 0.

2. 0 ≤ Si ≤ 1.0 mass%, and / or, 0≦W≦20.0mass% The Fe-based alloy for molten solidification molding according to claim 1, further comprising:

3. A metal powder having an average composition equivalent to that of the Fe-based alloy for molten solidification molding described in claim 1 or 2. However, the above statement that "the average composition is equivalent to that of Fe-based alloys for molten solidification molding" means that (a) The metal powder consists of an aggregate of one type of metal particles having the same composition, and each of the metal particles is within the composition range described in claim 1 or 2. (b) The metal powder consists of a mixture of two or more metal particles having different compositions, and each of the metal particles is within the composition range described in claim 1 or 2, (c) The metal powder consists of a mixture of two or more metal particles having different compositions, and one or more of the metal particles are not within the composition range described in claim 1 or 2, but the average value of the composition of the entire metal powder is within the composition range described in claim 1 or 2. It refers to.

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