Fe-based alloy powder for laminate shaping having excellent shaping crack resistance and high thermal conductivity, and laminate shaped body using same

Abstract

The present invention addresses the problem of providing: a powder which is for laminate shaping and with which even when a manufactured shaped body is a large shaped body, cracks are less likely to occur in the shaped body itself and / or at the interface between the shaped body and a laminate base material, and a shaped body having high thermal conductivity can be manufactured; and a shaped body manufactured by a laminate shaping method using said powder for laminate shaping. To solve the problem, provided are: a powder for laminate shaping having a predetermined composition and satisfying expression A of [Ni]-0.2[Cr]≥1.8, expression B of [Ni]-2.0[Cr]≤-8.0, and expression C of [Ni]+0.6[Cr]≤11.0 (in expressions A-C, [Ni] represents the value of a Ni content (mass%) and [Cr] represents the value of a Cr content (mass%)); and a shaped body manufactured by a laminate shaping method using said powder for laminate shaping.

Description

Fe-based alloy powder for additive manufacturing with excellent resistance to cracking during manufacturing and high thermal conductivity, and additive manufacturing body using the same

[0001] The present invention relates to an additive manufacturing powder used in additive manufacturing (also known as a 3D printer method, three-dimensional modeling method, additive manufacturing, or additive manufacturing method), and to shaped bodies manufactured by additive manufacturing using the additive manufacturing powder, which become various tools such as molds.In particular, the present invention relates to an additive manufacturing powder that can be used to manufacture shaped bodies that have high resistance to molding cracking, so that the shaped bodies produced do not crack even when they are large, high thermal conductivity, and also have high mechanical properties, and to a shaped body manufactured by additive manufacturing using the additive manufacturing powder.

[0002] In this specification, "high resistance to cracking during additive manufacturing" means that cracks are less likely to occur in the molded body itself (especially in the areas that become notches) and / or at the interface between the molded body and the molding base material (also called the additive base material) due to thermal stresses, etc., associated with the rapid melting, cooling, and solidification that occurs during additive manufacturing.

[0003] Unlike conventional manufacturing methods, additive manufacturing is capable of manufacturing components with complex shapes or three-dimensional structures, and in recent years has seen remarkable technological development and an expansion of its range of applications. Under these circumstances, studies are underway to apply additive manufacturing to various tools, and in particular, practical application is progressing in die-casting molds that have complex cooling water pipes with three-dimensional structures inside.

[0004] Such tools are used to machine various parts, and their shapes and sizes vary depending on the machining method or part shape.

[0005] In general, additive manufacturing (AM) involves rapidly melting and solidifying raw material powder or wire by heating it for a short time using a narrowly focused heat source such as a laser or electron beam, and then repeating this process to build up solidified layers, thereby enabling the production of parts with complex three-dimensional shapes. In AM, only a portion of the part is heated, melted, and solidified, which generates thermal stress due to local solidification shrinkage, thermal expansion, and thermal contraction. If the material being manufactured or the base material is hard and brittle, it will not be able to withstand the thermal stress, resulting in cracks in the manufactured object itself and / or at the interface between the manufactured object and the base material.

[0006] Such thermal stresses become even greater when a large object is additively manufactured, resulting in increased likelihood of cracks during manufacturing. Generally, high-hardness alloys such as SKD61, a material specified by the JIS standard, are often used for tools, making them prone to cracks during manufacturing. Therefore, the application of additive manufacturing to tools has traditionally been limited to small tools with relatively low thermal stress.

[0007] In recent years, M Ｓ Using an alloy with a low point, Ｓ A method has been proposed in which additive manufacturing is performed in a state where the material is preheated to near the melting point, thereby maintaining the soft, ductile austenite phase rather than the hard, brittle martensite phase during manufacturing, thereby suppressing cracks during manufacturing. Ｓ Lowering the score can be an indicator of improved resistance to molding cracking.

[0008] The surfaces of tools used in hot working, such as die-casting dies (hot working tools), rise in temperature when they come into contact with the high-temperature parts (workpieces) being processed, causing damage such as heat checking. Furthermore, areas that experience particularly rapid temperature increases can become seized. To avoid these problems, it is important to efficiently cool the surface of the hot working tools. By using alloys with high thermal conductivity as the material for the hot working tools, the cooling effect of water-cooled pipes and other devices installed inside the hot working tools can be maximized, even to the surface of the hot working tools.

[0009] Furthermore, when machining parts using hot tools, the hot tools must cool after machining one part before machining the next part. Being able to efficiently (in a short time) cool the hot tools to a specified temperature has the advantage of shortening the part machining cycle and increasing part production efficiency.

[0010] Additive manufacturing bodies made of Fe-based alloys that have high resistance to cracking during manufacturing and high thermal conductivity are described, for example, in Patent Documents 1 and 2. In Patent Documents 1 and 2, the variable A (= 15C + Mn + 0.5Cr + Ni) is regulated to be within a certain range. The major difference between the main components of Patent Documents 1 and 2 is the Cr content, with Patent Document 1 having a generally higher Cr content than Patent Document 2.

[0011] Patent Document 1 regulates the contents of various elements and also regulates the variable A to more than 10 and less than 20. As described above, Patent Document 1 has a high Cr content, and therefore the Ni content is low in order to control the variable A, and does not fully consider the properties in the opposite range of low Cr content (12% or less) and high Ni content (4% or more).

[0012] Patent Document 2 regulates the contents of various elements and also regulates the variable A to more than 11.5 and less than 20. As described above, Patent Document 2 has a low Cr content, and therefore a high Ni content is required to control the variable A, and the properties in the opposite range of a high Cr content (6% or more) and a low Ni content (7% or less) are not sufficiently considered.

[0013] JP 2023-71145 A JP 2023-71110 A

[0014] The problem that the present invention aims to solve is to provide a powder for additive manufacturing that can produce a molded object having high thermal conductivity and that is less likely to develop cracks at the interface between the molded object and the layered base material, even if the molded object is large, and to provide a molded object manufactured by an additive manufacturing method using the powder for additive manufacturing.

[0015] The inventors conducted detailed studies focusing on the range where the Cr content is 6 to 12% and the Ni content is 4 to 7%, and the vicinity thereof. As a result, they found that by specifying a range in the vicinity of the above ranges, in which a balance between Cr and Ni is achieved, surrounded by formulas A, B, and C, and by specifying components other than Cr and Ni within desired ranges, a powder for additive manufacturing with excellent properties can be obtained.

[0016] In order to solve the above problems, the present invention provides the following inventions. [1] In mass%, C: 0.11% or more and 0.29% or less, Cr: 6.1% or more and 9.9% or less, Ni: 3.1% or more and 6.9% or less, Si: 0% or more and 0.9% or less, Mn: 0% or more and 0.9% or less, P: 0% or more and 0.024% or less, S: 0% or more and 0.024% or less, O: 0% or more and 0.100% or less, N: 0% or more and 0.150% or less, 1 or more selected from Mo and W: 0%≦(Mo+W / 2)≦1.4%, V: 0% or more and 0.7% or less, Al: 0% or more and 0.045% or less, Cu: 0% or more and 4.5% or less, and the balance: Fe and unavoidable impurities, and Formula A: [Ni]-0.2[Cr]≧1.8, A powder for additive manufacturing that satisfies the following: Formula B: [Ni] - 2.0 [Cr] ≦ -8.0; and Formula C: [Ni] + 0.6 [Cr] ≦ 11.0 (In Formulas A to C, [Ni] represents the Ni content (% by mass), and [Cr] represents the Cr content (% by mass).) [2] The powder for additive manufacturing according to [1], containing one or more elements selected from O: more than 0% and 0.100% or less, and N: more than 0% and 0.150% or less. [3] The powder for additive manufacturing according to [1] or [2], containing one or more elements selected from Mo and W: 0% < (Mo + W / 2) ≦ 1.4%, V: more than 0% and 0.7%, Al: more than 0.045%, and Cu: more than 0% and 4.5% or less. [4] A shaped body manufactured by an additive manufacturing method using the powder for additive manufacturing according to any one of [1] to [3].

[0017] According to the present invention, there is provided a powder for additive manufacturing that can produce a molded object having high thermal conductivity, even if the molded object produced is large, and that is less likely to develop cracks at the molded object itself and / or at the interface between the molded object and the layered base material, and a molded object produced by an additive manufacturing method using the powder for additive manufacturing.

[0018] The present invention relates to a steel comprising, by mass%, C: 0.11% to 0.29%, Cr: 6.1% to 9.9%, Ni: 3.1% to 6.9%, Si: 0% to 0.9%, Mn: 0% to 0.9%, P: 0% to 0.024%, S: 0% to 0.024%, O: 0% to 0.100%, N: 0% to 0.150%, one or more elements selected from Mo and W: 0%≦(Mo+W / 2)≦1.4%, V: 0% to 0.7%, Al: 0% to 0.045%, Cu: 0% to 4.5%, and the balance: Fe and unavoidable impurities, and the formula A: [Ni]-0.2[Cr]≧1.8, The steel of the present invention is characterized by satisfying the following: Formula B: [Ni] - 2.0 [Cr] ≦ -8.0, and Formula C: [Ni] + 0.6 [Cr] ≦ 11.0 (In formulas A to C, [Ni] represents the Ni content (mass%), and [Cr] represents the Cr content (mass%).) The steel of the present invention is preferably a tool steel. The tool steel is a steel suitable for tools. The tool is preferably a hot work tool. The hot work tool is a tool used in hot working. An example of the hot work tool is a mold, and an example of the mold is a die-casting mold.

[0019] The present invention also relates to a powder made of the steel of the present invention. The powder of the present invention can be used as a powder for molding. The powder for molding is a powder used as a raw material for molding. The molding is preferably additive manufacturing.

[0020] The present invention also relates to a shaped body. The shaped body of the present invention is a shaped body manufactured by a manufacturing method using the powder of the present invention. The manufacturing method is preferably an additive manufacturing method. The shaped body of the present invention is preferably made of the steel of the present invention, as well as the powder of the present invention. The shaped body of the present invention becomes a tool after being subjected to one or more desired processes (e.g., quenching, tempering, cutting, etc.). The tool is preferably a hot-working tool. The description of the hot-working tool is the same as above.

[0021] Examples of methods for producing the powder of the present invention include water atomization, single-roll quenching, twin-roll quenching, gas atomization, disk atomization, and centrifugal atomization. From the viewpoint of spheroidization, the powder of the present invention is preferably a gas-atomized powder. The produced powder may be used as a raw material powder for shaping after adjusting the particle size by sieving or the like.

[0022] Examples of methods for producing a shaped object of the present invention include a rapid melting and quenching solidification process, which involves melting and solidifying the powder of the present invention. Examples of rapid melting and quenching solidification processes include additive manufacturing, thermal spraying, laser coating, and build-up welding. Examples of additive manufacturing methods include powder bed fusion (powder bed method) and directed energy deposition (powder deposition method). Examples of powder bed fusion (powder bed method) include selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM). The powder of the present invention is suitable for additive manufacturing methods, particularly powder bed fusion additive manufacturing methods.

[0023] For example, a 3D printer can be used for the additive manufacturing method. In the powder bed fusion (powder bed method) additive manufacturing method, a laser beam or an electron beam is irradiated onto a spread powder. The irradiation causes the particles to heat up rapidly and melt rapidly. The melted particles then solidify rapidly. The melting and solidification cause the particles to bond together. The irradiation is selectively performed on a portion of the spread powder. The unirradiated portion of the spread powder does not melt. A bonding layer is formed only in the irradiated portion.

[0024] A thin layer of powder is spread on top of the bonding layer, and a portion of the spread powder is irradiated with a laser beam or electron beam. The irradiation causes the particles to rapidly melt. The molten particles then rapidly solidify. The melting and solidification bond the particles in the powder together, forming a new bonding layer. The new bonding layer also bonds with the existing bonding layer.

[0025] By repeating the bonding process through irradiation, the aggregate of bonding layers gradually grows, resulting in an additive manufacturing object with a three-dimensional shape. Additive manufacturing methods make it easy to obtain additive manufacturing objects with complex shapes.

[0026] The Rockwell hardness of the shaped body of the present invention is preferably 45 to 55 HRC, and more preferably 45.6 to 54.5 HRC.

[0027] The thermal conductivity of the shaped body of the present invention is preferably 18.0 W / m K or more, more preferably 18.1 W / m K or more. The upper limit of the thermal conductivity of the shaped body of the present invention is not particularly limited. The thermal conductivity of the shaped body of the present invention may be, for example, 25.6 W / m K or less.

[0028] The Ms point of the shaped object of the present invention is preferably 230° C. or lower, more preferably 222° C. or lower. There is no particular limitation on the lower limit of the Ms point of the shaped object of the present invention. The Ms point of the shaped object of the present invention may be, for example, 132° C. or higher.

[0029] The Rockwell hardness, thermal conductivity and Ms point can be measured by the methods described in the examples.

[0030] In this specification, the "quenched and tempered hardness" of a shaped body refers to the hardness of a shaped body that has been quenched after shaping and then tempered. However, because additive manufacturing involves rapid melting, rapid cooling, and solidification, even an additively manufactured body may be in a pseudo-quenched state after additive manufacturing. Therefore, additively manufactured bodies may be used after only tempering or stress relief heat treatment without quenching after additive manufacturing. In such cases, the "quenched and tempered hardness" of an additively manufactured body refers to the hardness of an additively manufactured body that has been only tempered or stress relief heat treatment without quenching after additive manufacturing.

[0031] The steel of the present invention contains C, Cr, and Ni as essential components. The steel of the present invention may contain one or more optional components selected from Si, Mn, P, S, O, N, Mo, W, V, Al, and Cu. In the steel of the present invention, the balance other than the essential components and optional components is Fe and unavoidable impurities.

[0032] In one embodiment, the steel of the present invention contains one or more selected from Si, Mn, P, and S. In another embodiment, the steel of the present invention contains one or more selected from Si, Mn, P, and S, and one or more selected from O and N. In yet another embodiment, the steel of the present invention contains one or more selected from Si, Mn, P, and S, and one or more selected from Mo, W, V, Al, and Cu. In yet another embodiment, the steel of the present invention contains one or more selected from Si, Mn, P, and S, one or more selected from O and N, and one or more selected from Mo, W, V, Al, and Cu.

[0033] The reasons for specifying the contents of the essential elements (C, Cr, and Ni) and optional elements (one or more selected from Si, Mn, P, S, O, N, Mo, W, V, Al, and Cu) of the steel of the present invention will be explained below. The "%" for the content of each element is mass%.

[0034] C: 0.11% or more and 0.29% or less. C is an essential component for obtaining high quench-and-temper hardness by dissolving in the martensite matrix phase and precipitating fine carbides. However, if the C content is less than 0.11%, high quench-and-temper hardness cannot be obtained. Therefore, the C content is 0.11% or more, preferably 0.12% or more, and more preferably 0.13% or more. On the other hand, if the C content exceeds 0.29%, the hardness of the as-formed shaped body becomes excessively high, deteriorating the forming crack resistance. Therefore, the C content is 0.29% or less, preferably 0.24% or less, and more preferably 0.19% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0035] Cr: 6.1% or more and 9.9% or less Cr has the effect of improving hardenability and corrosion resistance, and also has the effect of improving M Ｓ Cr is an important essential component in the steel of the present invention because it has the effect of reducing the number of defects. Furthermore, tool steels are often used while being cooled with industrial water or the like, and therefore, corrosion resistance to prevent rusting is also required, so the addition of Cr is also essential in this respect. However, if the Cr content is less than 6.1%, the low M Ｓ Therefore, the Cr content is 6.1% or more, preferably 7.1% or more, and more preferably 8.1% or more. On the other hand, if the Cr content exceeds 9.9%, the thermal conductivity will be significantly reduced. Therefore, the Cr content is 9.9% or less, preferably 9.4% or less, and more preferably 9.3% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0036] Ni: 3.1% or more and 6.9% or less Ni has the effect of improving hardenability and corrosion resistance, and also has the effect of improving M. Ｓ Ni is an important essential component in the steel of the present invention because it has the effect of reducing the number of defects. Furthermore, tool steels are often used while being cooled with industrial water or the like, and therefore, corrosion resistance to prevent rusting is also required, so the addition of Ni is also essential in this respect. However, if the Ni content is less than 3.1%, the low M ＳTherefore, the Ni content is 3.1% or more, preferably 3.5% or more, and more preferably 3.7% or more. On the other hand, if the Ni content exceeds 6.9%, the thermal conductivity is significantly reduced. Therefore, the Ni content is 6.9% or less, preferably 5.4% or less, and more preferably 4.9% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0037] Si: 0% or more and 0.9% or less Si is an optional component, and the Si content may be 0% or more. Since Si has the effect of improving the flowability of the molten alloy, adding it appropriately can reduce the likelihood of nozzle clogging during powder production by atomization. When Si is added, the Si content is preferably 0.1% or more. On the other hand, if the Si content exceeds 0.9%, the thermal conductivity decreases. Therefore, the Si content is preferably 0.9% or less, more preferably 0.7% or less, and even more preferably 0.4% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0038] Mn: 0% or more and 0.9% or less Mn is an optional component, and the Mn content may be 0% or more. Mn has the effect of improving the flowability of the molten alloy, so adding it appropriately can reduce the likelihood of nozzle clogging during powder production by atomization. When Mn is added, the Mn content is preferably 0.1% or more. On the other hand, if the Mn content exceeds 0.9%, the thermal conductivity decreases. Therefore, the Mn content is preferably 0.9% or less, more preferably 0.4% or less, and even more preferably 0.3% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0039] P: 0% or more and 0.024% or less P is an optional component, and the P content may be 0% or more. Although P is a typical impurity, adding trace amounts has the effect of improving the flowability of the molten alloy. Therefore, adding an appropriate amount of P can reduce nozzle clogging during powder production by atomization. The P content is preferably 0.001% or more. On the other hand, if the P content exceeds 0.024%, solidification cracking is more likely to occur during additive manufacturing. Therefore, the P content is preferably 0.024% or less, more preferably 0.014% or less, and even more preferably 0.004% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values. The same effect can be obtained whether P is contained as an impurity or intentionally added.

[0040] S: 0% or more and 0.024% or less S is an optional component, and the S content may be 0% or more. Although S is a typical impurity, adding a small amount has the effect of improving the flowability of the molten alloy. Therefore, adding an appropriate amount of S can reduce nozzle clogging during powder production by atomization. The S content is preferably 0.001% or more. On the other hand, if the S content exceeds 0.024%, solidification cracking is more likely to occur during additive manufacturing. The S content is preferably 0.024% or less, more preferably 0.014% or less, and even more preferably 0.004% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values. The same effect can be obtained whether S is contained as an impurity or intentionally added.

[0041] O: 0% or more and 0.100% or less O is an optional component, and the O content may be 0% or more. O is an impurity that is inevitably mixed in mainly during powder production by gas atomization. If the O content exceeds 0.100%, gas is generated during additive manufacturing, and pores remain inside the molded object. Therefore, the O content is preferably 0.100% or less, more preferably 0.050% or less, and even more preferably 0.030% or less. On the other hand, it is difficult to keep the O content below 0.003%, so 0.003% or more of O may be unavoidably contained. The O content may be, for example, 0.012% or more. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0042] N: 0% or more and 0.150% or less N is an optional component, and the N content may be 0% or more. N is an impurity that is inevitably mixed in mainly during powder production by gas atomization. If the N content exceeds 0.150%, gas is generated during additive manufacturing, and pores remain inside the molded object. Therefore, the N content is preferably 0.150% or less, more preferably 0.120% or less, and even more preferably 0.090% or less. On the other hand, it is difficult to keep the N content below 0.003%, so it is acceptable for 0.003% or more of N to be unavoidably contained. The N content may be, for example, 0.007% or more. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0043] The steel of the present invention may optionally contain one or more elements selected from Mo, W, V, Al, and Cu. The reasons for including one or more elements selected from Mo, W, V, Al, and Cu as optional added elements will be explained below.

[0044] (Mo + W / 2): 0% or more and 1.4% or less Mo and W are optional components, and the Mo content and the W content may each be 0% or more than 0%. Mo and W are components that promote secondary hardening during tempering and increase quench-temper hardness, and one or more elements selected from Mo and W can be added as needed. (Mo + W / 2) may be 0% or more than 0%. "Mo" in (Mo + W / 2) represents the Mo content (%), and "W" in (Mo + W / 2) represents the W content (%). When one or more elements selected from Mo and W are added, (Mo + W / 2) is preferably 0.1% or more. On the other hand, if (Mo + W / 2) exceeds 1.4%, the thermal conductivity decreases. Therefore, when one or more elements selected from Mo and W are added, (Mo+W / 2) is preferably 1.4% or less, more preferably 0.2% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0045] V: 0% or more and 0.7% or less V is an optional component, and the V content may be 0% or more than 0%. The V content may be, for example, 0.2% or more. V is a component that promotes secondary hardening during tempering and increases quench-temper hardness, and can be added as needed, but excessive addition reduces thermal conductivity. Therefore, the V content is preferably 0.7% or less, more preferably 0.2% or less, and more preferably 0% (no addition). Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0046] Al: 0% or more and 0.045% or less. Al is an optional component, and the Al content may be 0% or more. Al forms nitrides and suppresses grain coarsening during quenching, and can be added as needed. The Al content is preferably 0.001% or more, more preferably 0.002% or more. However, if the Al content exceeds 0.045%, the formation of excess Al nitrides reduces toughness. It also reduces thermal conductivity. Therefore, the Al content is preferably 0.045% or less, more preferably 0.025% or less, and even more preferably 0.009% or less. Each of the above lower limits may be combined with any of the above upper limits. Note that Al may be intentionally added or may be mixed in from refractories used in gas atomization melting. In either case, the effect of Al inclusion is similar.

[0047] Cu: 0% or more and 4.5% or less Cu is an optional component, and the Cu content may be 0% or more than 0%. Cu does not relatively reduce the thermal conductivity, and Ｓ It is a component that can lower the M Ｓ Cu may be added as needed to lower the temperature. It may also be added from the viewpoint of improving corrosion resistance. The Cu content is preferably 0.1% or more, more preferably 0.2% or more. On the other hand, excessive addition of Cu reduces thermal conductivity. Therefore, the Cu content is preferably 4.5% or less, more preferably 2.9% or less, and even more preferably 0.4% or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0048] The steel of the present invention satisfies the following formulae A to C: Formula A: [Ni] - 0.2 [Cr] ≥ 1.8 Formula B: [Ni] - 2.0 [Cr] ≤ -8.0 Formula C: [Ni] + 0.6 [Cr] ≤ 11.0

[0049] In formulas A to C, [Ni] represents the Ni content (% by mass), and [Cr] represents the Cr content (% by mass). For example, if the Ni content is 4.0% by mass and the Cr content is 9.0% by mass, [Ni] is 4.0 and [Cr] is 9.0.

[0050] When the steel of the present invention satisfies formulas A to C, it is possible to identify the region surrounded by formulas A, B, and C where Cr and Ni are balanced, and it is possible to selectively capture steel with excellent properties. Note that Cr and Ni are added in larger amounts than other elements, and have a greater influence on these formulas.

[0051] The reasons for defining formulas A to C will be explained below.

[0052] Formula A: [Ni]-0.2[Cr]≧1.8 The value of [Ni]-0.2[Cr] is determined by the balance between Cr and Ni. Ｓ Cr is a carbide-forming component, and Ni is a non-carbide-forming component. The balance between these two components affects the carbide formation behavior, including secondary hardening, and the resulting martensite phase components of the matrix, which affects not only hardness but also M. Ｓ When the value of [Ni]-0.2[Cr] is less than 1.8, the Cr content relative to the Ni content is excessively high, and a large amount of Cr carbide is generated, resulting in a deficiency of C in the matrix, which leads to a decrease in M. Ｓ The score will be higher. Ｓ It is a point-decreasing component. Therefore, the value of [Ni]-0.2[Cr] is 1.8 or more, preferably 1.9 or more, and more preferably 2.0 or more. The upper limit of [Ni]-0.2[Cr] is not particularly limited. The value of [Ni]-0.2[Cr] may be, for example, 7.0 or less, or 6.0 or less. Each of the above lower limit values ​​may be combined with any of the above upper limit values.

[0053] Formula B: [Ni]-2.0[Cr]≦-8.0 The value of [Ni]-2.0[Cr] is an important parameter for controlling the thermal conductivity to a high level by the balance between Cr and Ni. Cr is a carbide-forming component, and Ni is a non-carbide-forming component. The balance between these two components affects the carbide formation behavior, including secondary hardening, and the resulting composition of the martensite phase in the matrix, and affects not only hardness but also M. ＳThis also affects the thermal conductivity. If the value of [Ni]-2.0[Cr] exceeds -8.0, the Cr content relative to the Ni content is excessively low, the amount of Cr carbide produced is excessively small, and the C content in the matrix becomes excessive, resulting in low thermal conductivity. C is a component that reduces thermal conductivity. Therefore, the value of [Ni]-2.0[Cr] is -8.0 or less, preferably -9.0 or less, and more preferably -11.0 or less. The lower limit of [Ni]-2.0[Cr] is not particularly limited. The value of [Ni]-2.0[Cr] may be, for example, -18.0 or more, or -17.0 or more. Each of the above lower limits may be combined with any of the above upper limits.

[0054] Formula C: [Ni] + 0.6[Cr] ≦ 11.0 The value of [Ni] + 0.6[Cr] is an important parameter for controlling the quenching and tempering hardness by the balance between Cr and Ni. If the addition amounts of both Cr and Ni are excessively high, austenite becomes overly stabilized, and this soft austenite tends to remain without sufficient decomposition, resulting in insufficient hardness. If the value of [Ni] + 0.6[Cr] exceeds 11.0, the retained austenite becomes stable, and insufficient hardness cannot be obtained. Therefore, the value of [Ni] + 0.6[Cr] is 11.0 or less, preferably 10.5 or less, and more preferably 10.0 or less. The lower limit of [Ni] + 0.6[Cr] is not particularly limited. The value of [Ni] + 0.6[Cr] may be, for example, 5.0 or more or 6.0 or more. Each of the above lower limits may be combined with any of the above upper limits.

[0055] The present invention will be described below based on examples and comparative examples. Note that the examples are examples of embodiments of the present invention, and the scope of the present invention is not limited to only the examples.

[0056] [Production of Raw Material Powders] Table 1 shows the component compositions of the powders of Examples 1 to 24, and Table 2 shows the component compositions of the powders of Comparative Examples 1 to 16. The units for each component composition are mass %. The remainder of each component composition is Fe and unavoidable impurities. Powders having the component compositions listed in Examples 1 to 24 in Table 1 and those having the component compositions listed in Comparative Examples 1 to 16 in Table 2 were each obtained by gas atomization. The specific powder production procedure is as follows. First, in a vacuum and argon atmosphere, the melted raw materials placed in an alumina crucible were melted by high-frequency heating. Next, the molten alloy was poured from a 5 mm diameter nozzle at the bottom of the crucible and immediately atomized with high-pressure argon gas. This atomization breaks the molten alloy into fine droplets, which cool and solidify as they fall through the tower of the atomization device, becoming alloy powder. This alloy powder was sieved using a sieve with 63 μm openings, and the powder that passed through the sieve was used as the raw material powder in the subsequent additive manufacturing.

[0057] Additive manufacturing was performed using a laser-heated powder bed type device (EOS-M290 manufactured by EOS Corporation) under the standard manufacturing conditions (MS1 conditions) for maraging steel set in the device, with a preheating temperature of 180°C. Annealed S45C steel was used as the base material for the plate, and a 20 mm x 20 mm x 20 mm block was manufactured on top of this.

[0058] [Evaluation] The molded block was cut by wire cutting, and the obtained test pieces were evaluated for hardness, thermal conductivity, and M Ｓ was used to evaluate the points.

[0059] [Hardness (HRC)] Using a 10 mm square block-shaped test piece, the hardness (HRC) of the surface parallel to the lamination direction was measured using a Rockwell hardness tester in accordance with JIS Z 2245:2016.

[0060] [Thermal Conductivity (W / m·K)] Using a disk-shaped test piece having a diameter of 5 mm and a thickness of 1 mm, the thermal conductivity (W / m·K) at room temperature was measured by a laser flash method.

[0061] [M Ｓ Point (°C)] M ＳThe thermal expansion characteristics were measured using a Formaster tester using a cylindrical test piece with a diameter of 3 mm and a length of 10 mm. Ｓ The maximum heating temperature was 1050°C.

[0062] Hardness, thermal conductivity and M Ｓ The evaluation results for these points are shown in Tables 1 and 2. In Tables 1 and 2, "Formula A" represents the value of [Ni]-0.2[Cr] (hereinafter, sometimes referred to as "the value of Formula A"), "Formula B" represents the value of [Ni]-2.0[Cr] (hereinafter, sometimes referred to as "the value of Formula B"), and "Formula C" represents the value of [Ni]+0.6[Cr] (hereinafter, sometimes referred to as "the value of Formula C").

[0063] Hardness, thermal conductivity and M Ｓ Based on the evaluation results, specimens with a hardness of 45 to 55 HRC, a thermal conductivity of 18.0 W / m·K or more, and an Ms point of 230° C. or less were judged to be good.

[0064] In some examples, the test pieces obtained by cutting with a wire cutter were tempered at the following temperatures. Specifically, the test pieces were held at tempering temperatures of 525°C for Example 3, 600°C for Example 9, 575°C for Example 14, and 625°C for Example 22 for one hour, followed by air cooling, and the tempering treatment was repeated twice. The test pieces used for evaluating hardness and thermal conductivity were tempered, but the M Ｓ This was not done on the specimens used for point evaluation.

[0065]

[0066]

[0067] All of the test pieces additively manufactured using the powders of Examples 1 to 24 satisfy the component composition and formulas A to C defined in the present invention. The test pieces additively manufactured using the powders of Examples 1 to 24 had hardnesses of 45.6 to 54.5 HRC, which were the hardness required for machine tools or parts such as molds, but were not too hard, and did not cause cracking during manufacturing. Appropriate quenched and tempered hardness was also obtained. Furthermore, the test pieces additively manufactured using the powders of Examples 1 to 24 had Ms points kept low at 132 to 222 °C, making it easier to suppress cracking during manufacturing. Furthermore, the test pieces additively manufactured using the powders of Examples 1 to 24 had thermal conductivities of 18.1 W / m·k or higher, demonstrating good thermal conductivity.

[0068] In Comparative Example 1, the amount of C is too small, and hardness is not obtained. In Comparative Example 2, the value of formula B is off the high side, and the amount of Cr relative to Ni is low, so the amount of Cr carbide produced is too small, and C in the matrix becomes excessive, resulting in low thermal conductivity. In Comparative Example 3, the value of formula A is off, and M Ｓ The points are too high, and the molding crack resistance is poor. In Comparative Example 4, the value of formula C is not met, and hardness is not obtained. In addition, the thermal conductivity is low and poor. In Comparative Example 5, the value of formula A is not met, and M Ｓ The points are too high, and the molding crack resistance is poor. In Comparative Example 6, the value of Formula C is off, and hardness is not obtained. The thermal conductivity is also low and poor. In Comparative Example 7, the value of Formula B is off to the high side, and the thermal conductivity is low and poor. In Comparative Example 8, the value of Formula A is off, and M Ｓ The points are too high, and the molding crack resistance is poor. In Comparative Example 9, the value of formula C is not met, and hardness is not obtained. In addition, the thermal conductivity is low and poor. In Comparative Example 10, the value of formula A is not met, and M Ｓ The point is too high, and the resistance to cracking during molding is poor. In Comparative Example 11, the value of formula C is out of range, and hardness is not obtained. The thermal conductivity is also low and poor. In Comparative Example 12, the amount of C is too much, and the hardness of the molded product is too high, so the resistance to cracking during molding is poor. In Comparative Example 13, the amount of Cr is too little, and M ＳThe point is not lowered. Comparative Example 14 has an excessive amount of Cr, and the thermal conductivity is low and inferior. Comparative Example 15 has an insufficient amount of Ni, and the value of formula A is not obtained. Ｓ The points are too high, and the molding crack resistance is poor. In Comparative Example 16, the value of formula C is out of range, and the hardness is not obtained. In addition, the thermal conductivity is low and poor.

[0069] The powder for additive manufacturing of the present invention is M Ｓ The powder for additive manufacturing of the present invention has a suppressed spot temperature and is less likely to crack during manufacturing, making it suitable for additive manufacturing. The additive manufacturing method using the powder for additive manufacturing of the present invention has excellent thermal conductivity and sufficient hardness, making it suitable for industrial machinery applications such as hot tool parts, and also for mold applications.

Claims

1. In mass%, C: 0.11% or more and 0.29% or less, Cr: 6.1% or more and 9.9% or less, Ni: 3.1% or more and 6.9% or less, Si: 0% or more and 0.9% or less, Mn: 0% or more and 0.9% or less, P: 0% or more and 0.024% or less, S: 0% or more and 0.024% or less, O: 0% or more and 0.100% or less, N: 0% or more and 0.150% or less, one or more elements selected from Mo and W: 0%≦(Mo+W / 2)≦1.4%, V: 0% or more and 0.7% or less, Al: 0% or more and 0.045% or less, Cu: 0% or more and 4.5% or less, and the balance: Fe and unavoidable impurities; and Formula A: [Ni]-0.2[Cr]≧1.8, A powder for additive manufacturing that satisfies the following conditions: Formula B: [Ni] - 2.0 [Cr] ≦ -8.0; and Formula C: [Ni] + 0.6 [Cr] ≦ 11.0 (In Formulas A to C, [Ni] represents the Ni content (mass%), and [Cr] represents the Cr content (mass%).) 2. The powder for additive manufacturing according to claim 1, containing one or more selected from O: more than 0% and 0.100% or less, and N: more than 0% and 0.150% or less.

3. The powder for additive manufacturing according to claim 1 or 2, containing one or more selected from Mo and W: 0% < (Mo + W / 2) ≦ 1.4%, V: more than 0% and 0.7% or less, Al: more than 0% and 0.045% or less, and Cu: more than 0% and 4.5% or less.

4. A shaped body manufactured by an additive manufacturing method using the powder for additive manufacturing according to any one of claims 1 to 3.

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