Cobalt-based alloy product and method for producing the same

Abstract

The present invention relates to a Co-based alloy product containing a polycrystal of a Co-based alloy, and a method for manufacturing the Co-based alloy product, wherein the Co-based alloy contains: 0.001 mass % ≤ C < 0.100 mass %; 9.0 mass % ≤ Cr < 20.0 mass %; 2.0 mass % ≤ Al < 5.0 mass %; 13.0 mass % ≤ W < 20.0 mass %; and 39.0 mass % ≤ Ni < 55.0 mass %, with the remainder being Co and unavoidable impurities, wherein the Co-based alloy product contains segregation crystal cells formed inside grains of the polycrystal, the average size of the segregation crystal cells is 1 μm or more and 100 μm or less, and the segregation crystal cells contain Al and Cr.

Description

Technical Field

[0001] The present invention relates to a cobalt-based alloy product and a method for manufacturing the cobalt-based alloy product. Background Art

[0002] Cobalt (Co)-based alloy materials and nickel (Ni)-based alloy materials are typical heat-resistant alloy materials, and therefore are also called superalloys, and are widely used as high-temperature components of turbines (e.g., gas turbines and steam turbines). Although the material cost of Co-based alloy materials is higher than that of Ni-based alloy materials, Co-based alloy materials have excellent corrosion resistance and wear resistance, and are easy to cause solid solution strengthening. Therefore, Co-based alloy materials have been used as fixed blades and combustor parts of turbines.

[0003] Conventional Co-based alloy materials include, for example, the Co-based alloy described in Patent Document 1. Patent Document 1 discloses a Co-based alloy whose composition contains 0.001 mass%≤C<0.100 mass%, 9.0 mass%≤Cr<20.0 mass%, 2.0 mass%≤Al<5.0 mass%, 13.0 mass%≤W<20.0 mass%, and 39.0 mass%≤Ni<55 mass%, the balance being Co and inevitable impurities, and among the inevitable impurities, the contents of Mo, Nb, Ti, and Ta are Mo<0.010 mass%, Nb<0.010 mass%, Ti<0.010 mass%, and Ta<0.010 mass%. Patent Document 1 indicates that a Co-based alloy having a higher high temperature strength than a conventional Co-based alloy and having hot workability equal to or higher than that of a conventional Co-based alloy can be provided, and thus suitable for forging.

[0004] Patent Document 1: JP-A-2012-041627

[0005] Non-patent literature 1: Xiangfang Xu, et al.: Enhancing mechanical properties of wire+arc additively manufactured INCONEL 718

[0006] superalloy through in-process thermomechanical processing,Material

[0007] and Design,160(2018)1042-1051 Summary of the invention

[0008] In recent years, additive manufacturing (AM) has been used to manufacture industrial products as a method that can easily manufacture complex shapes that are difficult to manufacture by conventional processing methods such as machining and casting. In AM technology, wire additive manufacturing (hereinafter referred to as "WAM") using wire as a raw material has advantages such as fast forming speed, low equipment cost, and good material yield, and as a technology for manufacturing large metal parts, it has attracted the attention of the industrial manufacturing sector. For example, in non-patent document 1, in order to apply the WAM method to the manufacture of high-temperature parts of turbines, a forming method using a Ni-based alloy such as INCONEL (registered trademark of Huntington Alloys Corporation) 718 was studied. However, compared with conventional Ni-based alloy forging materials, the mechanical strength of the WAM formed product made of the Ni-based alloy is significantly reduced, and sufficient performance is not obtained. Therefore, it is desirable to develop a WAM formed product whose strength is not significantly lower than that of conventional Ni-based alloy forging materials and Co-based alloy forging materials, and whose high-temperature strength is similar to that thereof.

[0009] In view of the above situation, an object of the present invention is to provide a Co-based alloy product and a method for manufacturing the Co-based alloy product by a WAM method, wherein the strength of the Co-based alloy product is not significantly reduced compared with the products using conventional Ni-based alloy forging materials and Co-based alloy forging materials, the high-temperature strength of the Co-based alloy product is similar to that of the products using conventional Ni-based alloy forging materials and Co-based alloy forging materials, and an improved yield is achieved.

[0010] That is, the present invention relates to the following configurations (1) to (20).

[0011] (1) A Co-based alloy product comprising a polycrystal of a Co-based alloy,

[0012] Co-based alloys include:

[0013] 0.001 mass%≤C<0.100 mass%;

[0014] 9.0 mass%≤Cr<20.0 mass%;

[0015] 2.0 mass%≤Al<5.0 mass%;

[0016] 13.0 mass % ≤ W < 20.0 mass %; and

[0017] 39.0 mass%≤Ni<55.0 mass%,

[0018] The balance is Co and unavoidable impurities.

[0019] The Co-based alloy product includes segregation cells formed inside grains of a polycrystalline body, the average size of the segregation cells is 1 μm to 100 μm, and the segregation cells include Al and Cr.

[0020] (2) The Co-based alloy product according to (1), wherein the Co-based alloy further comprises at least one element selected from the group consisting of:

[0021] Mo≤3.0 mass%;

[0022] Nb≤2.0 mass%;

[0023] Ti≤2.0 mass%; and

[0024] Ta≤2.0 mass%.

[0025] (3) The Co-based alloy product according to (1) or (2), wherein the Co-based alloy further comprises at least one element selected from the group consisting of:

[0026] 0.001 mass%≤B<0.020 mass%;

[0027] 0.0001 mass%≤Zr<0.010 mass%;

[0028] Mg≤0.10 mass%; and

[0029] Ca≤0.20 mass%.

[0030] (4) The Co-based alloy product according to (1) or (2), wherein the 0.2% proof stress of the Co-based alloy product at 800°C is 650 MPa or more.

[0031] (5) The Co-based alloy product according to (3), wherein the 0.2% proof stress of the Co-based alloy product at 800°C is 650 MPa or more.

[0032] (6) The Co-based alloy product according to (1) or (2), wherein the tensile strength of the Co-based alloy product at 800° C. is 850 MPa or more.

[0033] (7) The Co-based alloy product according to (3), wherein the tensile strength of the Co-based alloy product at 800° C. is 850 MPa or more.

[0034] (8) The Co-based alloy product according to (1) or (2), further comprising a γ' phase coherently precipitated inside the grains.

[0035] (9) The Co-based alloy product according to (3), further comprising a γ' phase coherently precipitated inside the grains.

[0036] (10) A method for producing a Co-based alloy product according to (1) or (2), the method comprising:

[0037] a step of preparing a wire material comprising a Co-based alloy;

[0038] The step of additive manufacturing the wire to obtain a Co-based alloy shaped product;

[0039] The step of solution heat treating the Co-based alloy shaped product at a temperature below 1,150°C; and

[0040] A step of performing aging heat treatment after solution heat treatment to obtain a Co-based alloy product.

[0041] (11) A method for producing a Co-based alloy product according to (3), the method comprising:

[0042] a step of preparing a wire material comprising a Co-based alloy;

[0043] The step of additive manufacturing the wire to obtain a Co-based alloy shaped product;

[0044] The step of solution heat treating the Co-based alloy shaped product at a temperature below 1,150°C; and

[0045] A step of performing aging heat treatment after solution heat treatment to obtain a Co-based alloy product.

[0046] (12) The method according to (10),

[0047] Here, before the solution heat treatment, the Co-based alloy formed product includes segregation cells formed inside the grains of the polycrystalline body, and the average size of the segregation cells is 1 μm or more and 100 μm or less.

[0048] (13) The method according to (11),

[0049] Here, before the solution heat treatment, the Co-based alloy formed product includes segregation cells formed inside the grains of the polycrystalline body, and the average size of the segregation cells is 1 μm or more and 100 μm or less.

[0050] (14) The method according to (12), wherein the Co-based alloy product obtained by the aging heat treatment contains a γ' phase coherently precipitated inside the grains.

[0051] (15) The method according to (13), wherein the Co-based alloy product obtained by the aging heat treatment contains a γ' phase coherently precipitated inside the grains.

[0052] (16) The method according to (10), wherein the additive manufacturing uses an electron beam, a laser or a CMT as a heat source.

[0053] (17) The method according to (10), wherein the solution heat treatment is performed at a temperature of 800°C to 1,050°C.

[0054] (18) The method according to (11), wherein the solution heat treatment is performed at a temperature of 800°C to 1,050°C.

[0055] (19) The method according to (10), wherein in the aging heat treatment, the Co-based alloy formed product is held at 900°C for 24 hours and then held at 800°C for 24 hours.

[0056] (20) The method according to (11), wherein in the aging heat treatment, the Co-based alloy formed product is held at 900°C for 24 hours and then held at 800°C for 24 hours.

[0057] The present invention can provide a Co-based alloy product and a method for manufacturing the Co-based alloy product, wherein the strength of the Co-based alloy product does not significantly decrease compared with products using conventional Ni-based alloy forging materials and Co-based alloy forging materials, and the high-temperature strength of the Co-based alloy product is the same as or better than that of products using conventional Ni-based alloy forging materials and Co-based alloy forging materials.

[0058] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The SEM (scanning electron microscope) observation photographs show the structure of the Co-based alloy after forming (heat source: cold metal transition (CMT)), the structure after solution heat treatment, and the structure after aging heat treatment.

[0060] Figure 2 The SEM observation photographs show the structure of the Co-based alloy after forming (heat source: CMT), the structure after solution heat treatment, and the structure after aging heat treatment.

[0061] Figure 3 This is a SEM observation photograph showing the structure of the Co-based alloy after forming (heat source: electron beam).

[0062] Figure 4 The following is a SEM observation photograph showing the structure obtained by forming a Co-based alloy (heat source: electron beam) and then performing a solution heat treatment and an aging heat treatment.

[0063] Figure 5: is a metallographic structure photograph taken with an optical microscope, which shows the structure obtained by performing solution heat treatment and aging heat treatment after forging a Co-based alloy. DETAILED DESCRIPTION

[0064] The Co-based alloy product and the method for manufacturing the Co-based alloy product according to the present invention are described below according to the process of the manufacturing method. In this specification, "Co-based alloy formed product" refers to a formed product obtained by additive manufacturing of a Co-based alloy wire without heat treatment, and "Co-based alloy product" refers to a target object obtained by solution heat treatment and aging heat treatment of a Co-based alloy formed product.

[0065] As described above, the method for manufacturing a Co-based alloy product according to the present invention includes (1) a step of preparing a wire material containing a Co-based alloy, (2) a step of additively manufacturing the wire material to obtain a Co-based alloy formed product (additive manufacturing step), (3) a step of solution heat treating the Co-based alloy formed product at a temperature below 1,150° C. (solution heat treatment step); and (4) a step of performing aging heat treatment after the solution heat treatment to obtain a Co-based alloy product (aging heat treatment step). Each step is described in detail below.

[0066] (1) Preparation of Co-based alloy wire

[0067] The Co-based alloy according to the present invention contained in the wire to be subjected to wire additive manufacturing and contained in the Co-based alloy product has a composition containing the following elements, with the balance being Co and unavoidable impurities. The kind of the added element, the content range of the composition, and the reason for limiting the content range are as follows.

[0068] (a) 0.001 mass% ≤ C < 0.100 mass%

[0069] C combines with W and Cr, thus contributing to the formation of carbides in the grains and at the grain boundaries. The precipitation of grain-shaped carbides at the grain boundaries is mainly effective in strengthening the grain boundaries and improving hot workability and high temperature strength. The improvement in grain boundary strength particularly improves high temperature elongation and area shrinkage, and is therefore very effective in improving tensile properties and creep rupture properties. In order to obtain such an effect, the C content needs to be 0.001% by mass or more. The C content is preferably 0.005% by mass or more.

[0070] On the other hand, when the C content is too high, the strength characteristics are reduced by the increase in the intragranular strength caused by the increase in carbide formation in the grains and the precipitation of film-like carbides at the grain boundaries. Therefore, the C content needs to be less than 0.100 mass%. The C content is preferably less than 0.050 mass%.

[0071] An important feature of the Co-based alloy according to the present invention is that carbides with an optimal morphology are precipitated by optimizing the C content, the Cr content, and the W content, thereby improving high temperature ductility and obtaining significant performance improvements. The term "carbide" herein refers to all kinds of carbides each containing C and one of Cr and / or W as a main component.

[0072] (b) 9.0 mass%≤Cr<20.0 mass%

[0073] Cr combines with O to form a dense Cr2O3 layer as a surface layer, and is therefore effective in improving oxidation resistance. In the case where the Cr content is too low, it is difficult to form a dense Cr2O3 layer, and therefore sufficient oxidation resistance cannot be obtained. Cr also combines with C to form various carbides in the grains and at the grain boundaries, and therefore contributes to improving hot workability and high temperature ductility. In order to obtain such an effect, the Cr content needs to be 9.0% by mass or more. The Cr content is preferably 10.0% by mass or more, and more preferably 10.5% by mass or more.

[0074] On the other hand, when the Cr content is too high, this causes a decrease in melting point and a decrease in high temperature mechanical properties. Therefore, the Cr content needs to be less than 20.0 mass %. The Cr content is preferably less than 19.5 mass %, and more preferably less than 18.5 mass %.

[0075] An important feature of the Co-based alloy according to the present invention is that the high temperature ductility is significantly improved by optimizing the Cr content to allow precipitation of carbides with the best morphology.

[0076] (c) 2.0 mass%≤Al<5.0 mass%

[0077] Al is the L of Co3(Al,W) 12 An element that stabilizes the type intermetallic compound phase (γ' phase) and is an element necessary for precipitating the metastable γ' phase as a stable phase to improve the high temperature strength characteristics. When the Al content is too low, the γ' phase cannot be formed in an amount sufficient to improve the strength properties. Similar to Cr, Al is also an element that improves oxidation resistance by forming Al2O3. In order to obtain such an effect, the Al content needs to be 2.0 mass% or more. The Al content is preferably 2.5 mass% or more, and more preferably 3.0 mass% or more.

[0078] On the other hand, when the Al content is too high, this causes a decrease in melting point and a decrease in high temperature properties (hot workability and high temperature ductility). Therefore, the Al content needs to be less than 5.0 mass %. The Al content is preferably less than 4.5 mass %, and more preferably less than 4.3 mass %.

[0079] The term "L of Co3(Al,W) 12The term "γ'-type intermetallic compound phase (γ' phase)" also refers to a γ' phase in which some Co sites and / or (Al, W) sites are substituted by other elements, as well as a γ' phase composed of Co, Al and W.

[0080] (d) 13.0 mass%≤W<20.0 mass%

[0081] W is the L of Co3(Al,W) 12 W is an element that stabilizes the type intermetallic compound phase (γ' phase) and is an element necessary for forming the γ' phase that is effective for high temperature strength. When the W content is too low, the γ' phase cannot be formed in an amount sufficient to improve the strength. W combines with C to form various carbides. The precipitation of grain boundary carbides is effective for improving high temperature strength characteristics, especially high temperature ductility (elongation and area reduction). In order to obtain such an effect, the W content needs to be 13.0 mass% or more. The W content is preferably 14.5 mass% or more, and more preferably 15.0 mass% or more.

[0082] On the other hand, when the W content is too high, W forms harmful phases in the grains and at the grain boundaries, resulting in a significant decrease in hot working properties, wherein the harmful phases are represented by μ phases shown by A7B6. Therefore, the W content needs to be less than 20.0 mass %. The W content is preferably less than 19.0 mass %, and more preferably less than 18.0 mass %.

[0083] "A7B6 compounds (μ phase)" are compounds derived from Co7W6, and these compounds also include compounds in which some A sites (Co sites) are substituted by Ni, Cr, Al, Fe, etc., and some B sites (W sites) are substituted by Ta, Nb, Ti, Zr, etc.

[0084] (e) 39.0 mass%≤Ni<55.0 mass%

[0085] Ni replaces the Co site to form (Co,Ni)3(Al,W) 12 Type intermetallic compound phase. Ni is evenly distributed in the matrix phase γ and the strengthening phase γ'. In particular, when a part of the Co site of the γ' phase is replaced by Ni, the solid solution temperature of the γ' phase rises to improve the high temperature strength characteristics. In order to obtain such an effect, the Ni content needs to be 39.0 mass% or more. The Ni content is preferably 41.0 mass% or more, and more preferably 43.0 mass% or more.

[0086] On the other hand, when the Ni content is too high, the melting point of the matrix phase γ decreases, resulting in a decrease in hot workability. Therefore, the Ni content needs to be less than 55.0 mass %. The Ni content is preferably less than 52.0 mass %, and more preferably less than 50.0 mass %.

[0087] (f) Mo≤3.0 mass%

[0088] Mo stabilizes the μ phase and contributes to the solid solution strengthening of the γ phase as the matrix phase. Therefore, it is effective to add Mo together with W. However, too high a Mo content reduces oxidation resistance. From these viewpoints, the preferred range of the Mo content is 3.0 mass % or less.

[0089] (g) Nb≤2.0 mass%

[0090] (h)Ta≤2.0 mass%

[0091] Nb and Ta stabilize γ'-(Ni,Co)3(Al,W,Ti,Nb,Ta). However, excessive inclusions therein cause the intermetallic compound δ-Ni3(Nb,Ta) to precipitate in the form of plates at the grain boundaries, resulting in reduced creep strength. From these viewpoints, the preferred range of each of the Nb content and the Ta content is 2.0 mass % or less.

[0092] (i) Ti≤2.0 mass%

[0093] Like Nb and Ta, Ti stabilizes γ'-(Ni,Co)3(Al,W,Ti,Nb,Ta). However, excessive inclusions therein cause the intermetallic compound η-Ni3Ti to precipitate in the form of plates at the grain boundaries, resulting in reduced creep strength. From these viewpoints, the preferred range of the Ti content is 2.0 mass % or less.

[0094] In addition to the above-mentioned elements, the Co-based alloy according to the present invention may further contain one or more of the following elements. The kinds of the optional additional elements, the content ranges of the components, and the reasons for limiting the content ranges are as follows.

[0095] (j) 0.001 mass%≤B<0.020 mass%

[0096] (k) 0.0001 mass% ≤ Zr < 0.010 mass%

[0097] B and Zr each serve as an element for strengthening the grain boundary and contribute to improving hot workability. From the viewpoint of obtaining such effects, the B content is preferably 0.001 mass % or more, and the Zr content is preferably 0.0001 mass % or more.

[0098] On the other hand, in the case where the B or Zr content is too high, this leads to a decrease in workability. Therefore, the B content is preferably less than 0.020 mass %, and the Zr content is preferably less than 0.010 mass %.

[0099] (l)Mg≤0.10 mass%

[0100] (m)Ca≤0.20 mass%

[0101] Mg and Ca each pin S to contribute to improving hot workability. From the viewpoint of obtaining such effects, it is preferable to add Mg and Ca.

[0102] On the other hand, when the Mg or Ca content is too high relative to the S content, a compound of Mg or Ca is formed, and this causes a decrease in workability. Therefore, the Mg content is preferably 0.10 mass % or less, and the Ca content is preferably 0.20 mass % or less.

[0103] Herein, in the Co-based alloy of the present invention, the balance other than the above elements is Co and inevitable impurities. As inevitable impurities, the components described below may be included. Examples of inevitable impurities include Si≤0.60 mass%, Mn≤0.50 mass%, Fe≤1.0 mass%, and S≤0.010 mass%.

[0104] S segregates at the grain boundaries, causing a significant decrease in hot workability. Therefore, the S content is preferably 0.010 mass % or less.

[0105] Too much Si and Mn inclusions lead to a decrease in hot workability. Therefore, the contents of Si and Mn are preferably Si≤0.60 mass% and Mn≤0.50 mass%, respectively.

[0106] In other embodiments of the present invention, in addition to the above components of the above embodiments, less than 5.0% by mass of Fe may be included. Fe has the same effect as Co, so it is effective to reduce costs by replacing Co with Fe. However, excessive inclusion of Fe may lead to reduced creep strength and oxidation resistance. Therefore, in the case where Fe may be included, the content of Fe is preferably less than 5.0% by mass, and more preferably less than 1.0% by mass.

[0107] (2) Additive manufacturing steps

[0108] As a heat source for wire additive manufacturing using Co-based alloy wire, any one of electron beam, laser or CMT (cold metal transition) can be used. The conditions for additive manufacturing are not particularly limited as long as the structure of the Co-based alloy described later can be obtained. In the case of using an electron beam, the output of the heat source is preferably less than 42kW, and the forming speed is preferably more than 3.18kg / hr and less than 11.34kg / hr. In the case of using CMT, the output of the heat source is preferably more than 42.6W and less than 28.75kW, and the forming speed is preferably more than 1.6kg / hr and less than 3.5kg / hr.

[0109] Whichever heat source is used, the control step is preferably such that the output P (kW) of the heat source and the amount of additive manufacturing per unit time period V (kg / hr) have a relationship satisfying 0.0426<P<42 and 1.6<V<11.34.

[0110] Preferably, the Co-based alloy formed product after additive manufacturing includes a structure formed by melting and solidification, wherein segregation cells with an average size of 1 μm or more and 100 μm or less are formed in the grains of the matrix phase (γ phase) as a polycrystal. The average size of the segregation cell is a value obtained by selecting ten segregation cells from an observation photograph taken with a SEM (scanning electron microscope) and averaging the lengths of the segregation cells. The segregation cell in the present invention refers to a cell of a structure in the process of forming a dendritic structure, or at least one structure in a dendritic structure, which is formed during the melting and solidification process in additive manufacturing. In the observation photograph taken with SEM, there is a difference in brightness / darkness between the inside of the cell and the boundary area between the cells; the term "segregation cell" refers to a dark part or an area surrounded by a light part. The difference in brightness / darkness in the SEM observation photograph refers to a difference between the average composition inside the cell and the average composition of the boundary area. Therefore, in the segregation cell, a given alloy component is located inside the cell and at the boundary area.

[0111] (3) Solution heat treatment step

[0112] After the Co-based alloy formed product is formed, a solution heat treatment is performed. Regarding the heat treatment conditions, it is preferably treated at a certain temperature, above which the residual stress after forming is fully released and the segregation cell does not disappear. Specifically, the temperature is lower than 1,150°C, preferably 800°C or higher and less than 1,150°C, more preferably 800°C or higher and 1,050°C or lower, and further preferably 800°C or higher and 1,000°C or lower. The time is preferably determined according to the heat treatment temperature. An example of a heat treatment condition may be to keep the formed product at 1,050°C for 2 hours.

[0113] (4) Aging heat treatment step

[0114] After the solution heat treatment step, an aging heat treatment step is performed. Conventional heat treatment conditions may be used as aging heat treatment conditions, and the aging heat treatment may be performed at a temperature of 500°C to 1,100°C for 1 to 100 hours. A two-stage aging treatment may be performed in which two temperatures are used. In the present embodiment, an example of heat treatment conditions may be to keep the formed product at 900°C for 24 hours and then at 800°C for 24 hours.

[0115] After aging heat treatment, the Co-based alloy product according to the present invention is obtained. As a result of aging heat treatment, the γ' phase coherently precipitates in the grains of the γ phase as the matrix phase of the Co-based alloy, thereby constituting a precipitation strengthening mechanism like the alloy of Patent Document 1 above.

[0116] According to the method for manufacturing a cobalt-based alloy product according to the present invention, additive manufacturing can be performed using a material having high temperature strength. In the case of manufacturing a component using a formed product, the machining allowance (for example, a portion discarded as machining waste powder in machining) can be significantly reduced compared to manufacturing from a forged material. Therefore, productivity can be increased, and an improved yield can be achieved.

[0117] Example

[0118] The high temperature strength of the Co-based alloy products according to the present invention (Examples 1 to 6), products using conventional Co-based alloy forging materials (Comparative Example 4), products using conventional Ni-based alloy formed products (Comparative Examples 1 and 2), and products using conventional Ni-based alloy forging materials (Comparative Example 3) were evaluated. Table 1 shows the alloy compositions (mass %) of Examples 1 to 6 and Comparative Examples 1 to 4. The alloy compositions of Examples 1 to 6 and Comparative Example 4 are COWALOY (a registered trademark of Daido Steel Co., Ltd.), the alloy compositions of Comparative Examples 1 and 2 are INCONEL 625 and INCONEL 718, respectively, and the alloy composition of Comparative Example 3 is WASPALOY (a registered trademark of United States Technologies, Inc.).

[0119]

[0120] The formed products or forged materials of Examples 1 to 6 and Comparative Examples 1 to 4 were each subjected to solution heat treatment and aging heat treatment. The heat treatment conditions are shown in Table 2. In Example 1, the Co-based alloy formed product formed by electron beam was subjected to solution heat treatment and aging heat treatment. In Examples 2 to 6, the Co-based alloy formed products formed by CMT were each subjected to solution heat treatment and aging heat treatment. In Comparative Examples 1 and 2, the WAM formed products of INCONEL 625 and INCONEL 718 were each subjected to solution heat treatment and aging heat treatment. In Comparative Examples 3 and 4, the forged materials of WASPALOY and COWALOY were each subjected to solution heat treatment and aging heat treatment. The reason why the comparative examples differ from the embodiments in terms of heat treatment conditions is that the solution temperature of the strengthening phase and the conditions required for stress removal vary according to the alloy composition. The heat treatment conditions shown in Table 2 are conditions suitable for each alloy composition.

[0121] Table 2

[0122]

[0123] [Observation of metallographic structure]

[0124] Figure 1 and Figure 2 The SEM observation photographs show the structure of the Co-based alloy after forming (heat source: CMT), the structure after solution heat treatment, and the structure after aging heat treatment of Example 2 of the present invention. Figure 1 and Figure 2 In the graph, the light gray part is light elements (aluminum (Al), chromium (Cr), etc.), and the dark gray part is Co, Ni, tungsten (W), etc. These components can be detected by mapping from backscattered electron images.

[0125] like Figure 1 As shown, the structure after forming includes a structure formed by melting and solidification, and includes segregation cells 1 with an average size of 1 μm or more and 100 μm or less in the grains of the matrix phase (γ phase) as a polycrystal. The segregation cell is a characteristic structure that appears in a formed product obtained by wire additive manufacturing of a Co-based alloy material. W carbide precipitates at the boundaries between the segregation cells 1. Segregation cells 1 are also observed in the crystal structure after solution heat treatment and after aging heat treatment. In addition, as Figure 2 As shown, it has Figure 1 At a higher magnification, a γ' phase 2 coherently precipitated in the matrix phase of the Co-based alloy after aging heat treatment was observed. Segregation cells 1 similar to those in Example 2 and a γ' phase 2 precipitated after aging heat treatment were also observed in the Co-based alloy formed products of Examples 3 to 6 (heat source: CMT).

[0126] Figure 3 and Figure 4 This is a SEM observation photograph showing the structure of the Co-based alloy after forming (heat source: electron beam) in Example 1 of the present invention ( Figure 3 ), and the microstructure after solution heat treatment and aging heat treatment ( Figure 4 ).like Figure 3 As shown in FIG. 1 , as in the case of using CMT, after forming using an electron beam as a heat source, a segregated cell 1 was observed in the crystal structure. After solution heat treatment and aging heat treatment, a segregated cell 1 was also observed in the crystal structure. In addition, as Figure 4 As shown, the γ' phase 2 is observed after the aging heat treatment. The shape of the segregation unit cell 1 is different from that of the CMT case, which is caused by the different heat source.

[0127] Comparative Examples 1 and 2 are WAM formed products manufactured using an electron beam as a heat source. As in the WAM formed products according to the present invention, the presence of a dendrite structure (segregation cell) formed by melting and solidification was observed in Comparative Examples 1 and 2. However, due to the difference in alloy composition, in Comparative Examples 1 and 2, no γ' phase was observed after aging heat treatment. Meanwhile, in Comparative Examples 3 and 4, products were manufactured by forging, and no segregation cell according to the present invention was observed.

[0128] For reference, a metallographic structure photograph of a forged product (the structure obtained by solution heat treatment and aging heat treatment after forging) taken with an optical microscope is shown in Figure 5 It can be seen that the forged structure 3 has been formed and it is different from the segregated unit cell according to the present invention.

[0129] Next, the following test was performed to evaluate the high temperature strength.

[0130] [Tensile test]

[0131] A test specimen having a test portion diameter of 8 mm and a length of 90 mm was cut out from each product. Tensile tests were performed on these specimens at room temperature and 800° C. to determine 0.2% proof stress, tensile strength, and elongation at break. The evaluation results obtained from these tests are shown in Table 3. Incidentally, the results of Comparative Example 2 are the results given in Non-Patent Document 1, but Table 3 does not show the values ​​evaluated at 800° C. because the document does not disclose this result.

[0132] Table 3

[0133]

[0134] As shown in Table 3, it can be seen that the Co-based alloy products of Examples 1 to 6 of the present invention have higher 0.2% proof stress at room temperature and 800° C. and higher tensile strength at room temperature and 800° C. than the products of Comparative Examples 1 and 2. The reason why the strength of the Co-based alloy products according to the present invention is higher than that of Comparative Examples 1 and 2 is that the γ' phase constituting the precipitation strengthening mechanism is coherently precipitated in the grains of the γ phase which is the matrix phase of the Co-based alloy.

[0135] Compared with the product using the forged material in Comparative Example 3, the other examples except Example 5 have lower room temperature 0.2% proof stress, and each of Examples 1 to 6 has a lower room temperature tensile strength than Comparative Example 3. Compared with the product using the forged material in Comparative Example 4, the room temperature 0.2% proof stress of Examples 1 to 6 is reduced by up to 130 MPa, and the room temperature tensile strength is reduced by up to 259 MPa (each difference between Comparative Example 4 and Example 6). However, with respect to the 0.2% proof stress at 800°C and the tensile strength at 800°C, the 0.2% proof stress and tensile strength of Examples 1 to 6 are higher than those of the product using the forged material in Comparative Example 3. Compared with the product using the forged material in Comparative Example 4, the 0.2% proof stress at 800°C of Examples 1 to 6 differs by up to 98 MPa, and the tensile strength at 800°C differs by up to 57 MPa (each difference between Comparative Example 4 and Example 3), indicating that these differences are smaller than the corresponding values ​​at room temperature.

[0136] It can be seen that the room temperature strength (0.2% proof stress, tensile strength) of the Co-based alloy product according to the present invention (product of WAM formed product using COWALOY) is slightly lower than that of the product using conventional forged COWALOY material, but higher than that of formed products using INCONEL 625 and INCONEL 718. Regarding the strength at 800°C, it can be seen that it is possible to ensure high temperature strength equal to or higher than that of the product using conventional Ni-based (WASPALOY) alloy forging material and the product using Co-based alloy (COWALOY) forging material.

[0137] As described above, it is demonstrated that the present invention can provide a Co-based alloy product and a method for manufacturing the Co-based alloy product using WAM, wherein the strength of the Co-based alloy product is not significantly lower than that of products using conventional wrought Ni-based alloy materials and wrought Co-based alloy materials, and the high-temperature strength is equal to or better than that of products using conventional wrought Ni-based alloy materials and wrought Co-based alloy materials, and the manufacturing method achieves an improvement in yield.

[0138] The present invention is not limited to the embodiments given above, and includes various modifications. For example, for ease of understanding, these embodiments are used to describe the present invention in detail, and the present invention is not limited to the embodiments including all configurations described therein. Some configurations of the embodiments can be replaced by the configurations of other embodiments, and the configurations of the embodiments can also be added to the configurations of other embodiments. In addition, with respect to some configurations of each embodiment, another configuration can be added, eliminated or replaced.

[0139] This application is based on Japanese Patent Application No. 2021-160757 filed on September 30, 2021 and Japanese Patent Application No. 2022-091284 filed on June 6, 2022, and the disclosed contents of the above applications are incorporated herein by reference.

[0140] 1: Segregation cell formed in the matrix phase of Co-based alloy

[0141] 2: Coherent precipitation of γ' phase in the matrix phase of Co-based alloy

[0142] 3: Forge the organization.

Claims

1. A Co-based alloy product, comprising: Polycrystalline of Co-based alloy; A gamma phase as a matrix phase within the grains of the polycrystalline body; segregated unit cells formed in the gamma phase within the grains of the polycrystalline body; and The γ' phase coherently precipitated inside the grains of the polycrystalline body, The Co-based alloy comprises: 0.001 mass%≤C<0.100 mass%; 9.0 mass%≤Cr<20.0 mass%; 2.0 mass%≤Al<5.0 mass%; 13.0 mass % ≤ W < 20.0 mass %; and 39.0 mass%≤Ni<55.0 mass%, The balance is Co and unavoidable impurities. wherein the average size of the segregation unit cell is 1 μm or more and 100 μm or less, and the segregation unit cell contains Al and Cr, The segregation cell refers to a cell of a tissue in the process of forming a dendrite structure, or at least one tissue in a dendrite structure. The segregation cell is a region surrounded by a boundary region in the SEM observation photograph.

2. The Co-based alloy product according to claim 1, wherein the Co-based alloy further comprises at least one element selected from the group consisting of: Mo≤3.0 mass%; Nb≤2.0 mass%; Ti≤2.0 mass%; and Ta≤2.0 mass%.

3. The Co-based alloy product according to claim 1 or 2, wherein the Co-based alloy further comprises at least one element selected from the group consisting of: 0.001 mass%≤B<0.020 mass%; 0.0001 mass%≤Zr<0.010 mass%; Mg≤0.10 mass%; and Ca≤0.20 mass%. 4 . The Co-based alloy product according to claim 1 , wherein the 0.2% proof stress of the Co-based alloy product at 800° C. is 650 MPa or more. 5 . The Co-based alloy product according to claim 3 , wherein the 0.2% proof stress of the Co-based alloy product at 800° C. is 650 MPa or more. 6 . The Co-based alloy product according to claim 1 , wherein the tensile strength of the Co-based alloy product at 800° C. is 850 MPa or more. 7 . The Co-based alloy product according to claim 3 , wherein the tensile strength of the Co-based alloy product at 800° C. is 850 MPa or more.

8. A method for manufacturing a Co-based alloy product according to claim 1 or 2, the method comprising: A step of preparing a wire material comprising the Co-based alloy; A step of additively manufacturing the wire to obtain a Co-based alloy shaped product; The step of subjecting the Co-based alloy shaped product to a solution heat treatment at a temperature below 1,150°C; as well as A step of performing aging heat treatment after the solution heat treatment to obtain the Co-based alloy product.

9. A method for manufacturing a Co-based alloy product according to claim 3, the method comprising: A step of preparing a wire material comprising the Co-based alloy; A step of additively manufacturing the wire to obtain a Co-based alloy shaped product; The step of subjecting the Co-based alloy shaped product to a solution heat treatment at a temperature below 1,150°C; as well as A step of performing aging heat treatment after the solution heat treatment to obtain the Co-based alloy product.

10. The method according to claim 8, in, Before the solution heat treatment, the Co-based alloy formed product includes segregation cells formed inside grains of a polycrystalline body, and an average size of the segregation cells is 1 μm or more and 100 μm or less.

11. The method according to claim 9, in, Before the solution heat treatment, the Co-based alloy formed product includes segregation cells formed inside grains of a polycrystalline body, and an average size of the segregation cells is 1 μm or more and 100 μm or less. 12 . The method according to claim 10 , wherein the Co-based alloy product obtained by the aging heat treatment comprises a γ′ phase coherently precipitated inside the grains. 13 . The method according to claim 11 , wherein the Co-based alloy product obtained by the aging heat treatment comprises a γ′ phase coherently precipitated inside the grains.

14. The method according to claim 8, wherein the additive manufacturing uses an electron beam, a laser or a CMT as a heat source.

15. The method according to claim 8, wherein: The solution heat treatment is performed at a temperature of 800°C to 1,050°C.

16. The method according to claim 9, wherein: The solution heat treatment is performed at a temperature of 800°C to 1,050°C.

17. The method according to claim 8, wherein: In the aging heat treatment, the Co-based alloy formed product was maintained at 900° C. for 24 hours and then maintained at 800° C. for 24 hours.

18. The method according to claim 9, wherein: In the aging heat treatment, the Co-based alloy formed product was maintained at 900° C. for 24 hours and then maintained at 800° C. for 24 hours.

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