HIGHLY CORROSION-RESISTANT Ni-BASED ALLOY

Abstract

To provide a Ni-based alloy that exhibits extremely superior corrosion resistance and has proper hardness.SOLUTION: This Ni-based alloy comprises Cr: 20 mass% or more and 26 mass% or less, Mo: 12 mass% or more and 22 mass% or less, Al: 1.0 mass% or more and 3.0 mass% or less, Nb: 0.0 mass% or more and 2.0 mass% or less, and Ti: 0.0 mass% or more and 2.0 mass% or less. The metal structure of this Ni-based alloy has multiple crystal grains each including the grain boundary and the intragranular region. An average grain size DG of the crystal grains is 10 μm or more. An area ratio PI of an intermetallic compound phase is 10.0% or less. The intragranular region comprises a matrix and multiple γ' phases dispersed in the matrix. The intragranular region contains 20.0 mass% or more of Cr and 12.0 mass% or more of Mo.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a precipitation hardened Ni-based alloy containing Cr, Mo and Al. [Background technology]

[0002] Traditionally, surface-hardening materials with excellent corrosion and wear resistance have included various alloys, such as Ni-based and Co-based alloys. In recent years, surface-hardening techniques aimed at improving corrosion and wear resistance have been widely used in various industrial fields. However, the environments in which they are used are becoming increasingly harsh, resulting in the demand for higher performance surface-hardening materials. Furthermore, carbon-neutral policies often necessitate different operating environments than before. Due to these diverse applications and changing operating environments, the required properties and operating environments are becoming increasingly diverse, such as specialization in corrosion resistance, wear resistance, crack resistance, and high toughness, and conventional materials are no longer able to meet these demands.

[0003] Ni-based alloys are suitable for applications requiring corrosion resistance and wear resistance. JP 2021-38453 A discloses a Ni-based alloy containing Cr, Mo, and Al. In this alloy, a γ' phase precipitates in the matrix upon aging treatment. This γ' phase strengthens the matrix. This alloy has high hardness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-38453 Summary of the Invention [Problem to be solved by the invention]

[0005] The Ni-based alloy described in the aforementioned Cited Document 1 was designed to have excellent properties in both corrosion resistance and wear resistance, resulting in a hardness of approximately 450 HV (45.3 HRC in HRC equivalent) after aging, i.e., during use. In the examples, the hardness was 380 HV or higher (38.8 HRC or higher in HRC equivalent). It is clear that this hardness is influenced not only by γ' but also by the amount of Mo compounds and grain size. It is well known that there is a correlation between hardness and grain size, and the harder the material, the finer the grain size. Furthermore, in high-speed steels, the greater the amount of carbide precipitation, the harder the material generally becomes. Corrosion of this material progresses from the grain boundaries and around the compounds. Therefore, this material, with its fine grains and compound precipitation, cannot be said to have sufficient corrosion resistance.

[0006] Furthermore, even if the material has a similar composition, if it is an ingot (not made from atomized powder, which is produced by a rapid cooling process), the crystal grain size will be coarser, but it will be much larger, about 1 mm. Furthermore, because it is not rapidly cooled, elements such as Cr and Mo, which are effective in corrosion resistance, cannot be dissolved in large amounts in the Ni matrix, and instead precipitate as compounds. This results in low hardness, a large amount of compound precipitation, and a low amount of Cr and Mo in the matrix, which degrades the corrosion resistance not only of the grain boundaries and around the compounds, but also of the matrix itself.

[0007] Other proposed alloys are corrosion-resistant and wear-resistant, with hard particles such as borides dispersed in a Ni-based alloy. However, while the addition of B to the alloy results in dispersed borides in the alloy, the precipitation of borides improves hardness, and once borides have precipitated, they are difficult to redissolve, resulting in concerns about hot workability, as the hardness cannot be changed.

[0008] For the reasons mentioned above, the corrosion resistance of the Ni-based alloy disclosed in JP 2021-38453 A is insufficient in severe corrosive environments. The applicant's intention is as follows: By imparting age hardenability to the matrix by utilizing the additive elements Al, Nb, and Ti, machinability is obtained. During ST, the γNi phase is soft (25 HRC or less), which is advantageous in terms of workability. On the other hand, aging treatment hardens the alloy through the precipitation of γ' phases such as Ni3Al, or Ni3(Al,Nb) and / or Ni3(Al,Ti) phases, resulting in high hardness (30-38 HRC).

[0009] Furthermore, because corrosion occurs preferentially around the intermetallic compound phase (Ni-Cr-Mo) and at the grain boundaries, excellent corrosion resistance (hydrofluoric acid resistance) was achieved by controlling the amount of intermetallic compound phase precipitation and grain size so that the area ratio of the intermetallic compound phase precipitated at the grain boundaries was 10% or less and the average grain size was 10μm or more. Furthermore, by maintaining high concentrations of Cr and Mo in the matrix consisting of γ and γ' (Cr content of 20% or more, Mo content of 12% or more), corrosion resistance (hydrofluoric acid resistance) within the grains was also excellent.

[0010] The object of the present invention is to provide a Ni-based alloy that has extremely excellent corrosion resistance and appropriate hardness. [Means for solving the problem]

[0011] The highly corrosion-resistant Ni-based alloy disclosed in this specification is Cr: 20% by mass or more and 26% by mass or less, Mo: 12% by mass or more and 22% by mass or less, Al: 1.0 mass% or more and 3.0 mass% or less Nb: 0.0 mass% or more and 2.0 mass% or less and Ti: 0.0 mass% or more and 2.0 mass% or less The balance is Ni and unavoidable impurities. The metal structure of this Ni-based alloy has a plurality of crystal grains, each of which has a grain boundary and an intragranular region. The average crystal grain size DG is 10 μm or more. The area fraction PI of the intermetallic compound phase is 10.0% or less. The intragranular region contains a matrix and a plurality of γ' phases dispersed in the matrix. The intragranular region contains 20.0 mass% or more of Cr and 12.0 mass% or more of Mo.

[0012] Preferably, the size DP of each γ' phase is 1.0 μm or less.

[0013] Preferably, the area is 1.0 x 10 4 μm 2 The sum (L1+L2) of the total length L1 of all grain boundaries appearing in a cross section and the total perimeter L2 of all intermetallic compound phases appearing in this cross section is 2000 μm or less.

[0014] Preferably, the area is 1.0 x 10 4 μm 2 The number NI of intermetallic compound phases appearing in a cross section is 600 or less.

[0015] Preferably, the average grain size DI of the intermetallic phase is equal to or less than 8 μm. [Effects of the Invention]

[0016] Unlike conventional alloys, we have discovered that by using a structure specialized for corrosion resistance, this material has a minimum level of hardness during machining and hardness during use. This highly corrosion-resistant Ni-based alloy has extremely excellent corrosion resistance. This Ni-based alloy has appropriate hardness. This Ni-based alloy is suitable for use in severe corrosive environments. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a backscattered electron image of the metal structure of a highly corrosion-resistant Ni-based alloy according to one embodiment, observed with a scanning electron microscope. [Figure 2]FIG. 2 is a chart showing the results of X-ray diffraction of the metal structure of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, preferred embodiments will be described in detail with reference to the drawings as appropriate.

[0019] [composition] The highly corrosion-resistant Ni-based alloy according to this embodiment has the following properties: Cr: 20% by mass or more and 26% by mass or less, Mo: 12% by mass or more and 22% by mass or less, and Al: 1.0 mass% or more and 3.0 mass% or less This Ni-based alloy further contains Nb: 0.0 mass% or more and 2.0 mass% or less and / or Ti: 0.0 mass% or more and 2.0 mass% or less Preferably, the balance is Ni and unavoidable impurities.

[0020] In a structure in which borides are dispersed and precipitated by the addition of B, the boride precipitation improves hardness, but once the borides precipitate, they are difficult to redissolve, and there is a concern about hot workability, as hardness cannot be changed. On the other hand, this alloy does not substantially contain B. Instead, Al, Nb, and Ti, whose solid solubility limits in Ni change with temperature, are added, so that the hard phase can be redissolved in γNi by heat treatment, and this alloy has excellent machinability. In the present invention, machinability refers to the ease of plastic working performed before heat treatment such as aging treatment is performed.

[0021] [Example of manufacturing method] In the production of this Ni-based alloy, a raw material is first obtained by powder metallurgy. The raw material powder for powder metallurgy can be obtained by atomization. A preferred atomization method is gas atomization. In gas atomization, the raw material is placed in a container (quartz crucible) with a small hole at the bottom. The raw material is heated and melted in a high-frequency induction furnace in an argon gas or nitrogen gas atmosphere. Argon gas or nitrogen gas is sprayed onto the raw material flowing out of the small hole. The raw material is rapidly cooled and solidified, yielding a powder.

[0022] This powder is classified as necessary. The classified powder is filled into a capsule made of carbon steel. The inside of this capsule is vacuum-evacuated, and the capsule is then sealed to obtain a billet. This billet is then subjected to HIP (hot isostatic pressing). The preferred pressure for HIP is 50 MPa or more and 300 MPa or less, and the preferred sintering temperature is 1000°C or more and 1350°C or less. A green body (raw material) is obtained by HIP. The raw material may also be obtained by other pressure methods other than HIP, such as a solidification molding method by hot extrusion.

[0023] This material is then subjected to solution treatment. In solution treatment, the material is held in an environment of 1150°C to 1250°C for 1 to 30 minutes. The material is then cooled, typically by water cooling. This solution treatment results in a metal structure containing many crystal grains. There is no γ' phase in the material after this solution treatment. This material can then be subjected to mechanical plastic working.

[0024] Next, this material is subjected to aging treatment. In aging treatment, the material is kept in an environment of 650°C for 16 hours. After that, the material is cooled. Typically, the cooling is by air cooling. This aging treatment causes the γ' phase to precipitate.

[0025] [Metal structure] This alloy has a polycrystalline metal structure. Each crystal grain has intragranular and intergranular regions. The intragranular regions contain a matrix and numerous γ' phases. The γ' phases precipitate through solution treatment, aging, etc., and are dispersed in the matrix. Figure 1 shows a backscattered electron image of this metal structure observed with a scanning electron microscope. Figure 2 shows the results of X-ray diffraction of this metal structure.

[0026] [Grains] According to the findings of the present inventors, corrosion in Ni-based alloys can progress along grain boundaries. In Ni-based alloys with large grains, the total length of all grains is shorter than that of Ni-based alloys with small grains. In other words, corrosion along grain boundaries can be suppressed. From this perspective, the average grain size DG of the grains is preferably 10 μm or more, more preferably 25 μm or more, and particularly preferably 50 μm or more. It is well known that there is a correlation between hardness and grain size, and the harder the alloy, the finer the grain size. Furthermore, in high-speed steels, the greater the amount of carbide precipitation, the harder the alloy. Therefore, from the viewpoint of high hardness and homogeneity of Ni-based alloys, the average grain size DG is preferably 120 μm or less, more preferably 100 μm or less, and particularly preferably 90 μm or less.

[0027] The average grain size DG is measured based on a backscattered electron image obtained by a scanning electron microscope.

[0028] By employing powder metallurgy with atomization (described in detail below) and the aforementioned solution treatment, it is possible to obtain alloys with an average grain size DG of 120 μm or less. By creating a homogeneous microstructure through atomization and then dissolving hard phases and intermetallic compounds in the γNi through the aforementioned solution treatment, it is possible to obtain alloys with an average grain size DG of 10 μm or more. This is because the sufficient dissolution of Cr, Mo, and other elements in the γNi reduces the number of precipitates, which in turn reduces the pinning effect originating from these precipitates, resulting in coarsening of the grains (10 μm or more).

[0029] [matrix] The main component of the matrix is ​​Ni. In this matrix, Cr or Mo is dissolved in Ni as a solid solution. This matrix has excellent corrosion resistance.

[0030] [γ' phase] The γ' phase precipitates in the matrix during aging. In this γ' phase, Ni is bonded to Al, Nb, or Ti. Examples of γ' phase compositions include Ni3Al, Ni3(Al,Nb), and Ni3(Al,Ti). The alloy has low hardness before the γ' phase precipitates. Therefore, this alloy is easy to process. The alloy has high hardness after the γ' phase precipitates. Furthermore, because the γ' phase is finely dispersed in the matrix, it contributes to the uniformity of the alloy's hardness. There is no unevenness or segregation like in wrought materials. Therefore, this alloy has excellent wear resistance. This alloy is precipitation hardenable.

[0031] The size DP of each γ' phase is 1.0 μm or less. This γ' phase is too small to be observed with a scanning electron microscope. This γ' phase contributes to the high hardness and uniformity of the alloy. From these viewpoints, the size DP is preferably 0.7 μm or less, and particularly preferably 0.5 μm or less. The size DP is preferably 0.1 μm or more.

[0032] The size DP is measured by observation using a transmission electron microscope.

[0033] The γ' phase, with a size DP of 1.0 μm or less, can be precipitated by the aging treatment described above. The γ' phase precipitates when Al, Nb, and Ti, whose solid solubility in Ni changes depending on the temperature, are added.

[0034] [Grain boundary] The grain boundaries may contain precipitated intermetallic compounds. Examples of such intermetallic compounds include Ni-Cr-Mo. According to the findings of the present inventors, corrosion in Ni-based alloys may progress not only along grain boundaries but also along the intermetallic compounds. In Ni-based alloys with a small amount of intermetallic compounds, corrosion along these intermetallic compounds may be suppressed. From this perspective, the area fraction PI of the intermetallic compound phase is preferably 10.0% or less, more preferably 9.0% or less, and particularly preferably 8.0% or less. This area fraction PI is preferably 0.5% or more.

[0035] The area fraction PI was measured by capturing an observation image based on a backscattered electron image obtained with a scanning electron microscope. This observation image was then subjected to image processing (binarization) to calculate the area fraction occupied by the intermetallic compound phase.

[0036] The aforementioned solution treatment can be used to obtain a Ni-based alloy with an area fraction PI of 10.0% or less. The temperature and holding time listed in Table 1 have a large effect on how much intermetallic compounds are dissolved in γNi. The subsequent aging treatment is only for γ' precipitation, and has little effect on the amount of precipitation (area fraction) of intermetallic compounds.

[0037] Corrosion areas occur around grain boundaries and intermetallic compound phases, so reducing these areas improves corrosion resistance. From the perspective of suppressing corrosion in intermetallic compounds, the average grain size DI of the intermetallic compound phase is preferably 8 μm or less, more preferably 7 μm or less, and particularly preferably 6 μm or less. The average grain size DI is preferably 1 μm or more.

[0038] The average particle size DI is measured based on a backscattered electron image obtained by a scanning electron microscope.

[0039] The aforementioned solution treatment can be used to obtain Ni-based alloys with an average grain size DI of 8 μm or less. Even at this size, the temperature and holding time listed in Table 1 have a significant effect. The subsequent aging treatment is solely responsible for γ' precipitation, and has little effect on the grain size of the intermetallic compounds.

[0040] From the viewpoint of corrosion inhibition in intermetallic compounds, the area is 1.0 × 10 4 μm 2 The number NI of intermetallic compound phases appearing in a cross section is preferably 600 or less, more preferably 550 or less, and particularly preferably 500 or less. Since intermetallic compounds have a pinning effect, a sufficiently hard Ni-based alloy can be obtained by the precipitation of these intermetallic compounds. From this viewpoint, the number NI is preferably 150 or more.

[0041] The number NI is measured based on backscattered electron images obtained by a scanning electron microscope.

[0042] The aforementioned solution treatment can be used to obtain a Ni-based alloy with an NI of 600 or less. Even at this size, the temperature and holding time listed in Table 1 have a significant effect. The subsequent aging treatment is only responsible for γ' precipitation, and has little effect on the number of intermetallic compounds.

[0043] From the viewpoint of corrosion resistance, the area is 1.0 × 10 4 μm 2 The sum (L1+L2) of the total length L1 of all grain boundaries appearing in a cross section and the total perimeter L2 of all intermetallic compound phases appearing in this cross section is preferably 2000 μm or less, more preferably 1700 μm or less, and particularly preferably 1500 μm or less. From the viewpoint of hardness, the sum (L1+L2) is preferably 500 μm or more.

[0044] The sum (L1 + L2) was measured by acquiring an observation image based on a backscattered electron image obtained with a scanning electron microscope. This observation image was then subjected to image processing (binarization) to calculate the sum of the total length L1 of all grain boundaries appearing in the cross section and the total perimeter L2 of all intermetallic compound phases appearing in this cross section.

[0045] The aforementioned solution treatment can be used to obtain a Ni-based alloy with a sum (L1 + L2) of 2000 μm or less. Even at this size, the temperature and holding time listed in Table 1 have a significant effect. The subsequent aging treatment, due solely to γ' precipitation, has little effect on the sum of the total length L1 of all grain boundaries appearing in the cross section and the total perimeter L2 of all intermetallic compound phases appearing in this cross section.

[0046] From the viewpoint of machinability such as cutting, the hardness HS of the material after solution treatment but before aging treatment is preferably 25HRC or less, more preferably 23HRC or less, and particularly preferably 22HRC or less. This hardness HS is preferably 10HRC or more.

[0047] From the viewpoint of wear resistance, the hardness HA of the Ni-based alloy after aging treatment is preferably 30 HRC or more, more preferably 32 HRC or more, and particularly preferably 33 HRC or more. This hardness HA is preferably 40 HRC or less.

[0048] The Ni-based alloy disclosed in JP 2021-38453 A places emphasis on wear resistance through precipitation hardening. However, the corrosion resistance of this Ni-based alloy in severe corrosive environments is insufficient. The inventors have identified that the causes of corrosion lie in grain boundaries and intermetallic compounds, and have succeeded in improving the corrosion resistance of Ni-based alloys. The hardness of the Ni-based alloy of the present invention is lower than that of the Ni-based alloy disclosed in JP 2021-38453 A, but it can withstand use in severe corrosive environments.

[0049] Chromium Cr dissolves in Ni and contributes to the corrosion resistance of the alloy. Cr particularly contributes to corrosion resistance against various acids. From the viewpoint of corrosion resistance, the Cr content is preferably 20% by mass or more, and more preferably 22% by mass or more. Excess Cr leads to the precipitation of excess intermetallic compounds. Ni-based alloys containing excess intermetallic compounds have poor corrosion resistance. From the viewpoints of corrosion resistance and cost, the Cr content is preferably 26% by mass or less, and more preferably 25% by mass or less.

[0050] [Molybdenum (Mo)] Mo dissolves in Ni and contributes to the corrosion resistance of the alloy. Mo particularly contributes to corrosion resistance against non-oxidizing acids such as hydrochloric acid, sulfuric acid, acetic acid, and phosphoric acid. From the viewpoint of corrosion resistance, the Mo content is preferably 12 mass% or more, more preferably 13 mass% or more, and particularly preferably 14 mass% or more. Excess Mo leads to the precipitation of excess intermetallic compounds. Ni-based alloys containing excess intermetallic compounds have poor corrosion resistance. From the viewpoints of corrosion resistance and cost, the Mo content is preferably 22 mass% or less, more preferably 20 mass% or less, and particularly preferably 18 mass% or less.

[0051] [Aluminum (Al)] Al precipitates as a γ' phase (such as Ni3Al phase, Ni3(Al,Nb) phase, or Ni3(Al,Ti) phase) and contributes to the hardness and wear resistance of Ni-based alloys. From this viewpoint, the Al content is preferably 1.0 mass% or more, more preferably 1.2 mass% or more, and particularly preferably 1.3 mass% or more. Excessive Al leads to the precipitation of excess intermetallic compounds. Ni-based alloys containing excess intermetallic compounds have poor corrosion resistance. From the viewpoint of corrosion resistance, the Al content is preferably 3.0 mass% or less, more preferably 2.7 mass% or less, and particularly preferably 2.5 mass% or less.

[0052] [Niobium (Nb)] Nb precipitates as a γ' phase (such as Ni3(Al,Nb) phase) and contributes to the hardness and wear resistance of Ni-based alloys. From this viewpoint, the Nb content is preferably 0.2 mass% or more, more preferably 0.4 mass% or more, and particularly preferably 0.6 mass% or more. Excessive Nb leads to the precipitation of excess intermetallic compounds. Ni-based alloys containing excess intermetallic compounds have poor corrosion resistance. From the viewpoint of corrosion resistance, the Nb content is preferably 2.0 mass% or less, more preferably 1.8 mass% or less, and particularly preferably 1.65 mass% or less. Nb is not an essential element. Therefore, the Nb content may be below the detection limit.

[0053] [Titanium (Ti)] Ti precipitates as a γ' phase (such as a Ni3(Al,Yi) phase) and contributes to the hardness and wear resistance of Ni-based alloys. From this viewpoint, the Ti content is preferably 0.2 mass% or more, more preferably 0.4 mass% or more, and particularly preferably 0.6 mass% or more. Excessive Ti leads to the precipitation of excess intermetallic compounds. Ni-based alloys containing excess intermetallic compounds have poor corrosion resistance. From the viewpoint of corrosion resistance, the Ti content is preferably 2.0 mass% or less, more preferably 1.8 mass% or less, and particularly preferably 1.6 mass% or less. Ti is not an essential element. Therefore, the Ti content may be below the detection limit.

[0054] [Intragranular components] As described above, the interior of the grains contains a matrix and numerous γ' phases. The interior of the grains contains 20.0 mass% or more of Cr and 12.0 mass% or more of Mo. Because the interior of the grains contains sufficient Cr and Mo, the amount of intermetallic compounds in this Ni-based alloy is small. In this Ni-based alloy, corrosion along the intermetallic compounds can be suppressed. Because the pinning effect due to the precipitation of intermetallic compounds is small, the average grain size DG of the crystal grains in this Ni-based alloy is sufficiently large. In this Ni-based alloy, corrosion along the crystal grains can be suppressed. From these viewpoints, the Cr content PCr in the grains is more preferably 20.5 mass% or more, and particularly preferably 21.0 mass% or more. This content PCr is preferably 25.0 mass% or less. The Mo content PMo in the grains is more preferably 12.5 mass% or more, and particularly preferably 13.0 mass% or more. This content PMo is preferably 20.0 mass% or less.

[0055] The amount of Cr and Mo in the grains was measured using an energy dispersive X-ray analyzer (EDS). Elemental analysis in the grains was measured by detecting characteristic X-rays.

[0056] Rapid cooling of the molten metal during atomization makes it possible to obtain a Ni-based alloy containing sufficient Cr and Mo within the grains, and this is also achieved by dissolving Cr and Mo sufficiently in γNi through the above-mentioned solution treatment. [Example]

[0057] The effects of the Ni-based alloys according to the examples will be clarified below, but the scope of the present specification should not be construed as being limited based on the descriptions of these examples.

[0058] [Example 1] Raw materials having a predetermined composition were prepared. The raw materials were heated in an alumina crucible in an argon gas atmosphere using high-frequency induction heating. The raw materials were melted by this heating to obtain a molten metal. The molten metal was dropped from a 5 mm diameter nozzle located below the crucible. Nitrogen gas was sprayed onto the molten metal to obtain a powder. The powder was classified to adjust the particle size to 500 μm or less. The composition of this powder is shown in Table 1 below. The powder was filled into a capsule made of carbon steel with a diameter of 100 mm and a height of 100 mm. The capsule was evacuated under vacuum. The capsule was sealed to obtain a billet. The billet was subjected to HIP molding. The HIP temperature was 1200°C. A rod-shaped compact was obtained by HIP. The compact was then subjected to solution treatment under the conditions shown in Table 1 below. This compact was subjected to aging treatment at a temperature of 650° C. for 16 hours, followed by air cooling, to obtain a Ni-based alloy according to Example 1.

[0059] [Examples 2-12 and Comparative Examples 1-8] Ni-based alloys according to Examples 2-12 and Comparative Examples 1-8 were obtained in the same manner as in Example 1, except that the raw material compositions and solution treatment conditions were as shown in Table 1 below.

[0060] [Corrosion resistance] A test piece was cut from a Ni-based alloy. The size of this test piece was 10 mm x 10 mm x 15 mm. The mass of this test piece was measured. This test piece was immersed in a 10% aqueous solution of hydrofluoric acid for 10 hours. The temperature of this aqueous solution was 40°C. The mass of the test piece was then measured. The amount of mass loss due to immersion was calculated and ranked according to the following criteria. A: Reduction amount is 0.3g / m 2 / h or less. B: Reduction amount is 0.3g / m 2 / h and above 0.5g / m 2 / h or less. C: Reduction amount is 0.5g / m 2 / h and above 1.0 g / m 2 / h or less. D: Reduction amount is 1.0g / m 2 More than / h. The results are shown in Table 2 below.

[0061] [Hardness] The compact after the solution treatment but before the aging treatment was polished to obtain a test piece whose upper and lower surfaces were parallel. The Rockwell hardness HS of this test piece was measured. Furthermore, the Ni-based alloy after the aging treatment was polished to obtain a test piece whose upper and lower surfaces were parallel. The Rockwell hardness HA of this test piece was measured. These results are shown in Table 2 below.

[0062] [Table 1]

[0063] [Table 2]

[0064] As is clear from Table 2, the Ni-based alloys of each example have excellent corrosion resistance. The hardness HS of these Ni-based alloys before aging is small. These Ni-based alloys have excellent workability before aging. Furthermore, the hardness HA of these Ni-based alloys after aging is moderately large. These Ni-based alloys also have excellent wear resistance. [Industrial Applicability]

[0065] The highly corrosion-resistant Ni-based alloy described above is suitable for various members used in corrosive or high-temperature environments.

Claims

1. Cr: 20% by mass or more and 26% by mass or less, Mo: 12% by mass or more and 22% by mass or less, Al: 1.0% by mass or more and 3.0% by mass or less Nb: 0.0 mass% or more and 2.0 mass% or less and Ti: 0.0% by mass or more and 2.0% by mass or less and the balance being Ni and unavoidable impurities, The metal structure has a plurality of crystal grains, each of which has grain boundaries and intragranular regions; The average crystal grain size DG of the crystal grains is 10 μm or more, the area fraction PI of the intermetallic compound phase is 10.0% or less, The interior of the grains contains a matrix and a plurality of γ' phases dispersed in the matrix, The precipitation-hardened, highly corrosion-resistant Ni-based alloy contains 20.0 mass % or more of Cr and 12.0 mass % or more of Mo within the grains.

2. 2. The highly corrosion-resistant Ni-based alloy according to claim 1, wherein the size DP of each γ' phase is 1.0 μm or less.

3. The area is 1.0 x 10 ４ μm ２ 3. The highly corrosion-resistant Ni-based alloy according to claim 1, wherein the sum (L1 + L2) of a total length L1 of all grain boundaries appearing in a cross section of

4. The area is 1.0 x 10 ４ μm ２ 3. The highly corrosion-resistant Ni-based alloy according to claim 1, wherein the number NI of intermetallic compound phases appearing in a cross section of

5. 3. The highly corrosion-resistant Ni-based alloy according to claim 1, wherein the intermetallic compound phase has an average grain size DI of 8 μm or less.

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