Patent Application
20240141459
This application is based on and claims priority under 35 USC 119 from Japanese Patent Applications No. 2022-174050 filed on Oct. 31, 2022 and No. 2023-128787 filed on Aug. 7, 2023, the contents of which are incorporated herein by reference.
The present invention relates to a Ni-based alloy and a method for manufacturing the same, and a Ni-based alloy member, and more particularly, relates to a Ni-based alloy excellent in impact resistance, wear resistance, and corrosion resistance, and a method for manufacturing the same, and a Ni-based alloy member composed of such a Ni-based alloy.
Examples of an alloy generally excellent in wear resistance include (a) tool steel (for example, SKD11 (G 4404: 2015)) and (b) martensitic stainless steel (for example, SUS440C).
However, these Fe—Cr—C alloys are inferior in corrosion resistance, and thus are not suitable for use in environments such as in seawater where corrosion resistance is required.
Examples of an alloy with high corrosion resistance that generally withstands seawater includes (a) austenitic stainless steel (for example, SUS316L(G 4305: 2012)), (b) titanium alloys, and (c) nickel alloys (for example, 718 alloy, 625 alloy).
However, these alloys are lower in hardness than tool steels or martensitic stainless steels and significantly inferior in wear resistance to them.
Furthermore, applications of such highly corrosion-resistant alloys with excellent wear resistance include members for oil and gas drilling. Such members are processed from shaped materials, round bars or wires produced by hot forging or hot rolling. Therefore, it is also important for these alloys to have sufficient hot workability for mass production.
In order to solve this problem, various proposals have been made in the related art.
For example, Patent Literature 1 discloses a Ni-based high-strength heat-resistant alloy obtained by manufacturing an ingot containing 0.1 mass % or less of C, predetermined amounts of Si, Mn, Cr, and Al, with the balance being Ni and unavoidable impurities, and then subjecting the ingot to hot forging, solution heat treatment, and aging treatment.
Patent Literature 1 also describes that (A) by such a method, a Ni-based alloy in which γ′ phase and a phase are compositely precipitated can be obtained, and (B) in addition to the γ′ phase, composite precipitation of the α phase, which mainly contains Cr, provides a Ni-based alloy with high strength, high-temperature stability, high hardness, high corrosion resistance, and non-magnetism.
Patent Literature 2 discloses a Ni-based alloy obtained by manufacturing an ingot containing more than 0.10 mass % and 1.0 mass % or less of C, predetermined amounts of Cr, Al and V, with the balance being Ni and impurities, and then subjecting the ingot to hot forging, solution heat treatment, and aging treatment.
Patent Literature 2 also describes that (A) in the case where the C content exceeds 0.10 mass %, hard particles (Cr-based carbides containing V) are crystallized in the matrix, resulting in a significant improvement in wear resistance, and (B) when Cr is consumed to form carbides, the amount of Cr dissolved in the matrix decreases, and therefore the precipitation amount of α phase during aging treatment decreases, making it impossible to obtain high hardness, and (C) in the case where V is added to the Ni-based alloy, part of the Cr in the Cr-based carbide is replaced with V, and the amount of Cr consumed to form the carbides is reduced, resulting in high hardness after aging treatment.
As described in Patent Literature 1, the composite precipitation of the γ′ phase and the α phase (Cr) can be used to obtain a Ni-based alloy with a Vickers hardness exceeding 600 HV at room temperature. This Ni-based alloy is excellent in hot workability and also has corrosion resistance in a seawater environment. However, this Ni-based alloy does not include a microstructure in which hard coarse carbides are dispersed as the tool steel or the martensitic stainless steel, and therefore, wear resistance thereof is low for hardness thereof.
By using the method described in Patent Literature 2, a Ni-based alloy in which Cr-based carbides containing V are dispersed in the matrix is obtained. This Ni-based alloy is excellent in wear resistance since hard particles are contained therein. In order to prevent a decrease in hardness due to a decrease in dissolved Cr, this Ni-based alloy has a preferable lower limit of the Cr content of 36 mass %, and partially replaces Cr in the Cr carbide with V. However, although such a microstructure contributes to an improvement in hardness, it also causes a decrease in toughness. Especially, since a large impact is applied to a member for oil and gas drilling during drilling, the Ni-based alloy described in Patent Literature 2 is not suitable for a member for oil and gas drilling in terms of an impact property.
The problem to be solved by the present invention is to provide a Ni-based alloy suitable as a material for various members requiring impact resistance, wear resistance, and corrosion resistance, and a method for manufacturing the same.
Another problem to be solved by the present invention is to provide a Ni-based alloy member composed of such a Ni-based alloy.
In order to solve the above-mentioned problems, a Ni-based alloy according to the first embodiment of the present invention consists of:
A Ni-based alloy member according to the first embodiment of the present invention is composed of the Ni-based alloy according to the first embodiment of the present invention.
A Ni-based alloy according to the second embodiment of the present invention consists of:
A Ni-based alloy member according to the second embodiment of the present invention is composed of the Ni-based alloy according to the second embodiment of the present invention.
A method for manufacturing a Ni-based alloy, the method including:
The method for manufacturing a Ni-based alloy according to the present invention, the method may further include:
In the case where the raw material of the Ni-based alloy containing a relatively large amount of C is melted and cast, an ingot containing the massive α-Cr phase and crystallized coarse M23C6-type carbide particles can be obtained. If necessary, the obtained ingot is subjected to the primary hot working, homogenization heat treatment, and secondary hot working, and then solution heat treatment at a relatively low temperature, so that a fine massive α-Cr phase remains without being dissolved. As a result, the fine massive α-Cr phase functions as pinning particles, and during the solution heat treatment, coarsening of the γ phase can be prevented. Furthermore, when the aging treatment is applied to the Ni-based alloy after the solution heat treatment, the cellular structure is formed on the entire inside of the γ phase.
The Ni-based alloy according to the present invention is excellent in corrosion resistance and hot workability due to an optimized composition thereof. The Ni-based alloy after the aging treatment exhibits high wear resistance since the coarse M23C6-type carbide particles are dispersed in a matrix. Furthermore, the Ni-based alloy after the aging treatment exhibits high strength due to the inclusion of the cellular structure. Since an initial γ phase is fine, the cellular structure is also fine, and high toughness (that is, high impact resistance) is also exhibited.
Hereinafter, an embodiment of the present invention will be described in detail.
The Ni-based alloy according to the first embodiment of the present invention consists of the following elements, with the balance being Ni and unavoidable impurities. Types of additive elements, component ranges thereof, and reasons for limitation thereof are as follows.
(1) 0.10 Mass %<C≤0.30 Mass %:
C is an element for forming hard carbides (M23C6-type carbides) that ensure wear resistance. In the case where an amount of C is too small, an amount of the hard carbide decreases and the wear resistance decreases. In order to obtain a sufficient wear resistance, it is necessary that the amount of C exceeds 0.10 mass %. The amount of C is preferably 0.12 mass % or more, and more preferably 0.14 mass % or more.
On the other hand, in the case where the amount of C becomes excessive, hot workability deteriorates. Therefore, it is necessary that the amount of C is 0.30 mass % or less. The amount of C is preferably 0.28 mass % or less, and more preferably 0.26 mass % or less.
(2) Si≤0.50 Mass %:
Si is an element included as an impurity. Since Si lowers strength and toughness of the Ni-based alloy, the smaller a content thereof, the better. In order to prevent deterioration in the strength and toughness, it is necessary that an amount of Si is 0.50 mass % or less. The amount of Si is preferably 0.10 mass % or less.
(3) Mn≤0.50 Mass %:
Mn is an element included as an impurity. On the other hand, Mn fixes S included in the Ni-based alloy as MnS, and has an effect of preventing deterioration of the hot workability due to S. Therefore, the Ni-based alloy may include Mn.
However, in the case where an amount of S is sufficiently small (for example, in the case where the amount of S is 0.002 mass % or less), it is not necessary to add Mn. The addition of Mn more than necessary may cause deterioration of performance of the Ni-based alloy. Therefore, it is necessary that an amount of Mn is 0.50 mass % or less. The amount of Mn is preferably 0.10 mass % or less.
(4) P≤0.030 Mass %:
P is an element included as an impurity. Since P deteriorates the hot workability, the smaller a content thereof, the better. In order to prevent the deterioration in the hot workability, it is necessary that an amount of P is 0.030 mass % or less. The amount of P is preferably 0.010 mass % or less, and more preferably 0.005 mass % or less.
(5) S≤0.010 Mass %:
S is an element included as an impurity. Since S deteriorates the hot workability, the smaller a content thereof, the better. In order to prevent the deterioration in the hot workability, it is necessary that the amount of S is 0.010 mass % or less. The amount of S is preferably 0.003 mass % or less, and more preferably 0.002 mass % or less.
(6) Cu≤3.00 Mass %:
Cu has an effect of improving corrosion resistance of the Ni-based alloy. Therefore, the Ni-based alloy may include Cu.
However, in the case where an amount of Cu becomes excessive, the hot workability may deteriorate. Therefore, it is necessary that the amount of Cu is 3.00 mass % or less. The amount of Cu is preferably 2.50 mass % or less, and more preferably 2.00 mass % or less.
(7) 30.0 Mass %≤Cr≤39.0 Mass %:
Cr is an element necessary to ensure the hardness and wear resistance of the Ni-based alloy. In the Ni-based alloy according to the present invention, the hardness is ensured by a lamellar structure of an α phase (Cr) and a γ/γ′ phase. Therefore, it is necessary that an amount of Cr is 30.0 mass % or more. The amount of Cr is preferably 34.0 mass % or more.
On the other hand, in the case where the amount of Cr is excessive, an amount of a massive α-Cr phase with poor deformability becomes excessive, thereby deteriorating the hot workability. Therefore, it is necessary that the amount of Cr is 39.0 mass % or less. The amount of Cr is preferably 38.0 mass % or less.
(8) Mo≤3.00 Mass %:
Mo is an element included as an impurity. A content of Mo as an impurity is usually 0.1 mass % or less. On the other hand, Mo has an effect of improving the corrosion resistance. Therefore, the Ni-based alloy may include Mo.
However, in the case where an amount of Mo becomes excessive, the hot workability may deteriorate. Therefore, it is necessary that the amount of Mo is 3.00 mass % or less. The amount of Mo is preferably 2.50 mass % or less, and more preferably 2.00 mass % or less.
(9) Fe≤3.00 Mass %:
Fe is an element included as an impurity. Since Fe deteriorates the corrosion resistance of the Ni-based alloy, the smaller a content thereof, the better. In order to prevent the deterioration in the corrosion resistance, it is necessary that an amount of Fe is 3.00 mass % or less. The amount of Fe is preferably 1.00 mass % or less.
(10) 2.00 Mass %≤Al≤5.00 Mass %:
Al is an element necessary for obtaining a high-strength Ni-based alloy by forming Ni3Al (γ′ phase). In order to obtain such an effect, it is necessary that an amount of Al is 2.00 mass % or more. The amount of Al is preferably 3.00 mass % or more.
On the other hand, in the case where the amount of Al becomes excessive, the hot workability may deteriorate. Therefore, it is necessary that the amount of Al is 5.00 mass % or less. The amount of Al is preferably 4.50 mass % or less, and more preferably 4.00 mass % or less.
(11) O≤0.0100 Mass %:
O is an element included as an impurity, and the smaller a content thereof, the better. In order to prevent deterioration in the performance of the Ni-based alloy, it is necessary that an amount of O is 0.0100 mass % or less.
(12) N≤0.050 Mass %:
N is an element included as an impurity, and the smaller a content thereof, the better. In order to prevent deterioration in the performance of the Ni-based alloy, it is necessary that an amount of N is 0.050 mass % or less.
(13) Nb≤0.50 Mass %:
(14) V≤0.50 Mass %:
(15) Ti≤0.50 Mass %:
(16) Ta≤0.50 Mass %:
(17) W≤0.50 Mass %:
Nb, V, Ti, Ta, and W are all elements included as impurities. These elements combine with C and/or N in the Ni-based alloy to form carbides (MC), nitrides (MN), and/or carbonitrides (M (C, N)) (hereinafter collectively referred to as “MC-type carbonitrides”). Fine MC-type carbonitrides contribute to an improvement in hardness, but cause a deterioration in toughness. In the case where contents of these elements become excessive, C in the Ni-based alloy is consumed to form the MC-type carbonitrides. As a result, formation of a M23C6-type carbide is inhibited, and the wear resistance deteriorates. Therefore, it is necessary that the content of each of these elements is 0.50 mass % or less. The lower the contents of these elements, the better, and the content of each of these element is preferably 0.40 mass % or less, and more preferably 0.30 mass % or less.
(18) 0.0010 Mass %≤B≤0.0100 Mass %:
(19) 0.0010 Mass %≤Mg≤0.0100 Mass %:
(20) 0.0010 Mass %≤Ca≤0.0100 Mass %:
All of B, Mg and Ca are elements that improve the hot workability. The Ni-based alloy may include only one of B, Mg, and Ca, or may include two or more thereof. Addition of two or more elements thereof is effective for improving the hot workability.
In the case where an amount of B, Mg, or Ca is too small, the hot workability may deteriorate.
Therefore, it is necessary that the amount of each of B, Mg, or Ca is 0.0010 mass % or more.
On the other hand, in the case where the amount of each of B, Mg, or Ca is excessive, hard inclusions containing B, Mg, and/or Ca are formed, and the toughness of the Ni-based alloy may deteriorate. Therefore, it is necessary that the amount of each of B, Mg, or Ca is 0.0100 mass % or less.
The Ni-based alloy according to the present embodiment is obtained by
Therefore, the Ni-based alloy according to the present embodiment includes a microstructure in which the M23C6-type carbide and the massive α-Cr phase are dispersed in the austenite phase (γ phase). The composition of the γ phase is uniquely determined according to the raw material composition, a precipitation amount of the M23C6-type carbide, and a precipitation amount of the massive α-Cr phase. The γ phase becomes a cellular structure by aging treatment. Details of the cellular structure will be described later.
An “average grain diameter of γ phase” refers to a value measured by a line segment method.
The smaller an average grain diameter of the γ phase before the aging treatment, the smaller an average grain diameter of the cellular structure formed by the aging treatment. As the average grain diameter of the cellular structure becomes smaller, the toughness (that is, impact resistance) of the Ni-based alloy after the aging treatment is improved. In order to obtain such an effect, it is necessary that the average grain diameter of the γ phase is 50 μm or less.
1.2.2. M23C6-Type Carbide
The Ni-based alloy according to the present embodiment includes the M23C6-type carbide. A coarse M23C6-type carbide contributes to improvement of the wear resistance of the Ni-based alloy. In the present invention, M is mainly Cr, but may contain other elements (for example, Fe, or Mo) depending on manufacturing conditions.
Note that the word “mainly” means that M contains 90 mass % or more of Cr.
Examples of a method for forming the M23C6-type carbide in the Ni-based alloy include (a) a method of crystallizing carbides during casting, and (b) a method of precipitating carbides during hot working and/or homogenization heat treatment.
In the case where more than 0.1 mass % of C is added to the raw material containing predetermined amounts of Ni, Cr, and Al, the coarse M23C6-type carbide can be crystallized during casting.
On the other hand, even in the case where the amount of C included in the raw material is 0.1 mass % or less, the M23C6-type carbide can be precipitated during hot working and/or during homogenization heat treatment. However, the precipitated carbide often has an average particle diameter of less than 1.0 μm. The fine precipitated carbide is poor in the effect of improving the wear resistance.
Therefore, in order to improve the wear resistance, it is preferable to use the crystallized carbide.
A “circle equivalent particle diameter of the M23C6-type carbide” refers to a diameter of a circle having an area equal to a cross-sectional area of the M23C6-type carbide when a cross section of the Ni-based alloy is observed with a microscope (SEM-EBSD).
An “average circle equivalent particle diameter of the M23C6-type carbide” refers to an average value of circle equivalent particle diameters measured for ten freely selected M23C6-type carbides when the cross section of the Ni-based alloy is observed with a microscope (SEM-EBSD) at a magnification of 1500 times.
The M23C6-type carbide remains almost as it is even after the aging treatment and contributes to the improvement in the wear resistance of the Ni-based alloy after the aging treatment. The larger the average circle equivalent particle diameter of the M23C6-type carbide is, the higher the wear resistance is obtained. In order to obtain such an effect, it is necessary that the average circle equivalent particle diameter of the M23C6-type carbide is 1.0 μm or more. The average circle equivalent particle diameter is preferably 2.0 μm or more, and more preferably 5.0 μm or more.
An upper limit of the average circle equivalent particle diameter of the M23C6-type carbide is not particularly limited, but in the case where the crystallized carbide is used, the average circle equivalent particle diameter thereof is usually 100 μm or less.
A “content of the M23C6-type carbide” refers to a value obtained by (a) extracting a test material having a predetermined size from the Ni-based alloy, (b) anodic dissolving a part of the test material for approximately 2 hours to 5 hours at a current density of 25 mA/cm2 by constant current electrolysis using a 10 volume % acetylacetone-1 mass % tetramethylammonium chloride-methanol solution (10% AA solution) as an electrolytic solution, (c) suction filtering the solution obtained by anodic dissolution using a microfilter with a pore size of 0.1 μm, and (d) dividing a mass of electrolytic extraction residue deposited on the microfilter by a difference in mass of the test material before and after the electrolytic extraction.
The higher the content of the M23C6-type carbide is, the higher the wear resistance is obtained. In order to obtain such an effect, the content of the M23C6-type carbide is preferably 0.3 mass % or more. The content is more preferably 0.5 mass % or more.
On the other hand, in the case where the content of the M23C6-type carbide becomes excessive, the hot workability may deteriorate.
Therefore, the content of the M23C6-type carbide is preferably 3.5 mass % or less. The content is more preferably 3.0 mass % or less.
The “massive α-Cr phase” means an α-Cr phase precipitated at grain boundaries of the γ phase. The massive α-Cr phase is different from the fine plate-like α-Cr phase contained in the lamellar structure formed by the aging treatment. The massive α-Cr phase essentially includes Cr.
A “circle equivalent particle diameter of the massive α-Cr phase” refers to a diameter of a circle having an area equal to a cross-sectional area of the massive α-Cr phase in the case where a cross section of the Ni-based alloy is observed with a microscope (SEM-EBSD).
An “average circle equivalent particle diameter of the massive α-Cr phase” is a value calculated using the SEM-EBSD image (phase map) used to calculate the above-mentioned “average circle equivalent particle diameter of the M23C6-type carbide”, and refers to an average value of circle equivalent particle diameters measured for all massive α-Cr phases contained in a freely selected 60 μm×60 μm region.
The Ni-based alloy before the solution heat treatment includes various massive α-Cr phases with different circle equivalent particle diameters. Among these phases, a fine massive α-Cr phase has an effect of preventing coarsening of the γ phase during the solution heat treatment. On the other hand, a coarse massive α-Cr phase is less effective in preventing the coarsening of the γ phase, and may rather deteriorate the hot workability.
Note that the M23C6-type carbide having a circle equivalent particle diameter of 1.0 μm or more has a large particle diameter and thus hardly contribute to the refinement of the γ phase.
In order to prevent coarsening of the γ phase, it is necessary that the average circle equivalent particle diameter of the massive α-Cr phase is 10.0 μm or less. The average circle equivalent particle diameter is preferably 5.0 μm or less, and more preferably 1.0 μm or less.
A “content of the massive α-Cr phase” is a value calculated using the SEM-EBSD image (phase map) used to calculate the above-mentioned “average circle equivalent particle diameter of the M23C6-type carbide”, and refers to a ratio (area ratio) of a total area of the massive α-Cr phase to an area of a freely selected 60 μm×60 μm region.
During the solution heat treatment, the larger the content of the massive α-Cr phase, the easier it is to prevent the coarsening of the γ phase. In order to obtain such an effect, it is necessary to perform the solution heat treatment so that the massive α-Cr phase remains even after the solution heat treatment. The content of the massive α-Cr phase after the solution heat treatment is preferably 2.0 area % or more. The content is more preferably 3.0 area % or more.
On the other hand, in the case where the content of the massive α-Cr phase is excessive, it may be difficult to form a lamellar structure during the subsequent aging treatment. Therefore, the content of the massive α-Cr phase after the solution heat treatment is preferably 12.0 area % or less. The content is more preferably 10.0 area % or less.
Note that in
A Ni-based alloy member according to the first embodiment of the present invention is composed of the Ni-based alloy according to the first embodiment of the present invention.
A shape of the Ni-based alloy member is not particularly limited, and an optimum shape can be selected according to a purpose thereof. Examples of the Ni-based alloy member include shaped materials, round bars, and wires. Note that the “shaped material” is a material that is processed into a shape close to the shape of the member or into the shape of the member by hot forging. A member (product) is obtained by finishing the shaped material. Finishing refers to machining and/or heat treatment.
The Ni-based alloy according to the second embodiment of the present invention consists of the predetermined elements, with the balance being Ni and unavoidable impurities. The types of additive elements, component ranges thereof, and details of reasons for limitations thereof are the same as in the first embodiment, and therefore, descriptions thereof will be omitted.
The “cellular structure” refers to a structure in which a lamellar structure of the α-Cr phase and a γ phase (γ/γ′ phase) in which a γ′ phase (Ni3Al) is precipitated is formed in a state of cell on an entire inside of an austenite phase.
In order to obtain a high strength, it is preferable that the cellular structure is precipitated on the entire inside of the austenite phase.
The Ni-based alloy after the solution heat treatment includes the austenite (initial γ) phase, the M23C6-type carbide, and the massive α-Cr phase. When the Ni-based alloy after the solution heat treatment is subjected to the aging treatment, the lamellar structure of the α-Cr phase and the γ/γ′ phase is formed in the cell state from the grain boundary to the inside of the grain of the initial γ phase, resulting in the cellular structure.
The longer the aging treatment time, the more the cellular structure grows, and eventually the entire of the initial γ phase becomes a cellular structure. The cellular structure contributes to increasing the strength of the Ni-based alloy.
3.2.2. M23C6-type Carbide
The Ni-based alloy according to the present embodiment is obtained by subjecting the Ni-based alloy containing the M23C6-type carbide after the solution heat treatment (Ni-based alloy according to the first embodiment) to the aging treatment. The circle equivalent particle diameter and content of the M23C6-type carbide hardly change before and after the aging treatment. Therefore, the Ni-based alloy according to the present embodiment also contains the M23C6-type carbide. Other points regarding the M23C6-type carbide are as described above, and therefore, descriptions are omitted.
The definitions of the “circle equivalent particle diameter of the M23C6-type carbide” and the “average circle equivalent particle diameter of the M23C6-type carbide” are the same as those in the first embodiment, and therefore, the description thereof will be omitted.
As described above, the larger the average circle equivalent particle diameter of the M23C6-type carbide is, the higher the wear resistance is obtained. In order to obtain such an effect, it is necessary that the average circle equivalent particle diameter of the M23C6-type carbide is 1.0 μm or more. The average circle equivalent particle diameter is preferably 2.0 μm or more, and more preferably 5.0 μm or more.
The upper limit of the average circle equivalent particle diameter of the M23C6-type carbide is not particularly limited, but the average circle equivalent particle diameter is usually 100 μm or less.
The definition of the “content of the M23C6-type carbide” is the same as in the first embodiment, and therefore, the description thereof is omitted.
As described above, the higher the content of the M23C6-type carbide is, the higher the wear resistance is obtained. In order to obtain such an effect, the content of the M23C6-type carbide is preferably 0.3 mass % or more. The content is more preferably 0.5 mass % or more.
The Ni-based alloy according to the present embodiment is obtained by subjecting the Ni-based alloy containing the massive α-Cr phase after the solution heat treatment (Ni-based alloy according to the first embodiment) to the aging treatment.
The circle equivalent particle diameter and content of the massive α-Cr phase hardly change before and after the aging treatment. Therefore, the Ni-based alloy according to the present embodiment also contains the massive α-Cr phase. Other points regarding the massive α-Cr phase are as described above, and therefore, descriptions are omitted.
The definitions of the “circle equivalent particle diameter of the massive α-Cr phase” and the “average circle equivalent particle diameter of the massive α-Cr phase” are the same as those in the first embodiment, and therefore, the description thereof will be omitted.
The size of the massive α-Cr phase contained in the Ni-based alloy before the aging treatment affects the refinement of the γ phase, but the size of the massive α-Cr phase contained in the Ni-based alloy after the aging treatment does not significantly affect properties of the Ni-based alloy after the aging treatment.
Since the size of the massive α-Cr phase hardly changes before and after the aging treatment, in the case where the average circle equivalent particle diameter of the massive α-Cr phase after the solution heat treatment is 10.0 μm or less, the average circle equivalent particle diameter of the massive α-Cr phase after the aging treatment is also 10.0 μm or less.
The definition of the “content of the massive α-Cr phase” is the same as in the first embodiment, and therefore, the description thereof is omitted.
The content of the massive α-Cr phase contained in the Ni-based alloy before the aging treatment affects the refinement of the γ phase, but the content of the massive α-Cr phase contained in the Ni-based alloy after the aging treatment does not significantly affect properties of the Ni-based alloy after the aging treatment.
Since the content of the massive α-Cr phase hardly changes before and after the aging treatment, in the case where the content of the massive α-Cr phase after the solution heat treatment is 2.0 area % to 12.0 area %, the content of the massive α-Cr phase after the aging treatment is also 2.0 area % to 12.0 area %.
Although it cannot be determined in
The “0.2% proof stress” refers to a value measured in accordance with JIS Z 2241:2011.
The Ni-based alloy according to the present embodiment includes the cellular structure, and thus exhibits a high 0.2% proof stress. By optimizing manufacturing conditions, the 0.2% proof stress at 25° C. becomes 1300 MPa or more. By further optimizing the manufacturing conditions, the 0.2% proof stress at 25° C. becomes 1500 MPa or more.
The “absorption energy” refers to a value measured in accordance with JIS Z 2242:2018.
The Ni-based alloy according to the present embodiment includes the fine cellular structure, and thus exhibits high toughness.
By optimizing the manufacturing conditions, the absorption energy at 25° C. becomes 40 J (10R notch) or more. By further optimizing the manufacturing conditions, the absorption energy at 25° C. becomes 50 J (10R notch) or more.
A Ni-based alloy member according to the second embodiment of the present invention is composed of the Ni-based alloy according to the second embodiment of the present invention.
A shape of the Ni-based alloy member is not particularly limited, and an optimum shape can be selected according to a purpose thereof. Examples of the Ni-based alloy member include shaped materials, round bars, and wires.
A method for manufacturing the Ni-based alloy according to the present invention includes: (a) a first step of obtaining an ingot by melting and casting a raw material blended to have a predetermined composition, (b) a second step of obtaining a primary hot-worked product by subjecting the ingot to the primary hot working, as necessary, (c) a third step of obtaining a homogenized heat-treated product by subjecting the ingot or the primary hot-worked product to the homogenization heat treatment, as necessary, (d) a fourth step of obtaining a secondary hot-worked product by subjecting the ingot, the primary hot-worked product, or the homogenized heat-treated product to secondary hot working, and (e) a fifth step of obtaining the Ni-based alloy according to the first embodiment of the present invention by subjecting the secondary hot-worked product to the solution heat treatment.
The method for manufacturing the Ni-based alloy according to the present invention may further include: (f) a sixth step of obtaining a rough-worked product by roughing the Ni-based alloy (solution-heat-treated product) after the solution heat treatment, and (g) a seventh step of obtaining the Ni-based alloy according to the second embodiment of the present invention by subjecting the rough-worked product or the solution-heat-treated product to the aging treatment.
First, the raw material blended to have a predetermined composition is melted and cast to obtain the ingot (first step).
The method and conditions for melting and casting are not particularly limited, but the melting is preferably vacuum melting using a vacuum induction furnace. The larger a mold size during casting, the more likely non-uniform distribution of the crystallized carbide occurs due to a non-uniform cooling rate. Therefore, the ingot may be subjected to secondary melting such as electro slag remelting (ESR).
After the secondary melting is applied, an ingot in which the crystallized carbide is uniformly distributed is obtained.
Next, if necessary, the ingot is subjected to the primary hot working to obtain the primary hot-worked product (second step).
The “primary hot working” refers to blooming rolling or blooming forging. A temperature of the primary hot working is preferably 900° C. to 1150° C.
The primary hot working can be omitted. However, after the ingot is subjected to the primary hot working, casting defects in the ingot can be eliminated and a coarse cast solidified structure can be destroyed. The ingot can be made into a predetermined shape such as a slab, bloom, or billet.
5.3. Third Step
Next, if necessary, the ingot or the primary hot-worked product is subjected to the homogenization heat treatment to obtain the homogenized heat-treated product (third step).
A temperature of the homogenization heat treatment is preferably 1200° C. to 1280° C. A treatment time is preferably 12 hours or more.
The homogenization heat treatment can be omitted. However, after the ingot or the primary hot-worked product is subjected to the homogenization heat treatment, segregation of components can be mitigated.
5.4. Fourth Step
Next, the ingot, the primary hot-worked product, or the homogenized heat-treated product is subjected to the secondary hot working to obtain the secondary hot-worked product (fourth step).
The secondary hot working is performed to form the ingot, the primary hot-worked product, or the homogenized heat-treated product into a predetermined shape (for example, a plate, a bar, a wire rod, or a shaped material). A method for the secondary hot working is not particularly limited, and an optimum method can be selected according to a purpose thereof. Examples of the method for the secondary hot working include hot rolling and hot forging.
The secondary hot working is preferably performed in a temperature range of 900° C. to 1200° C. This is because in the case where the temperature of the secondary hot working is too high or too low, cracks are likely to occur during working.
5.5. Fifth Step
Next, the secondary hot-worked product is subjected to the solution heat treatment (fifth step). As a result, the Ni-based alloy according to the first embodiment of the present invention is obtained.
After forming into a material having a predetermined shape by the secondary hot working, the material is subjected to the solution heat treatment. In this case, it is important not to allow the massive α-Cr phase to dissolve completely during the solution heat treatment, and intentionally leave a small amount of the fine massive α-Cr phase. In this way, the structure is refined, and the toughness can be ensured.
In the case where a temperature for the solution heat treatment is too low, the amount of the massive α-Cr phase becomes excessive, making it difficult to form the cellular structure during the subsequent aging treatment. Therefore, the temperature for the solution heat treatment is preferably 980° C. or higher.
On the other hand, in the case where the temperature for the solution heat treatment is too high, the massive α-Cr phase is completely dissolved and crystal grains are coarsened. As a result, the toughness of the Ni-based alloy is lowered. Therefore, the temperature for the solution heat treatment is preferably 1080° C. or lower.
A time of approximately 0.5 hours to 1 hour is sufficient for the solution heat treatment.
After holding for a predetermined time at the solution heat treatment temperature, the material is quenched. In this case, in the case where a cooling rate is too slow, there is concern that the cellular structure may be partially formed during cooling. Cracking may occur in the case where the cellular structure is partially formed during cooling. The hardness may also increase, and roughing such as cutting may become difficult. Therefore, as for the cooling method, it is preferable to use a technique that provides a cooling rate higher than that of oil cooling. The faster the cooling rate, the better.
Next, if necessary, the solution-heat-treated product is subjected to roughing to obtain the rough-worked product (sixth step).
The roughing is performed as necessary. A roughing method is not particularly limited, and an optimum method can be selected according to a purpose thereof. Examples of the roughing method include cutting and cold working.
Next, the rough-worked product or the solution-heat-treated product is subjected to the aging treatment (seventh step). As a result, the Ni-based alloy according to the second embodiment of the present invention is obtained.
The aging treatment is performed to form a cellular structure of a lamellar structure of the α-Cr phase and the γ/γ′ phase inside the γ phase, which is a matrix phase. A temperature for the aging treatment is usually 500° C. to 800° C. A time for the aging treatment is usually 1 hour to 50 hours. Cooling after the aging treatment may be air cooling.
Since the strength the Ni-based alloy and the toughness (impact property) thereof are in a trade-off relation, it is preferable to set the aging treatment conditions in consideration of the target strength and toughness.
For example, in the case where a Ni-based alloy having a 0.2% proof stress of 1300 MPa or more and an impact property of 50 J (10R notch) or more, with an emphasis on toughness, is desired, it is preferable to set the aging treatment temperature to 710° C. to 750° C. and the aging treatment time to approximately 16 hours.
Alternatively, in the case where a Ni-based alloy having a 0.2% proof stress of 1500 MPa or more and an impact property of 40 J (TOR notch) or more, with an emphasis on strength, is desired, it is preferable to set the aging treatment temperature to 600° C. to 700° C. and the aging treatment time to approximately 16 hours.
In the case where the raw material of the Ni-based alloy containing a relatively large amount of C is melted and cast, an ingot containing the massive α-Cr phase and crystallized coarse M23C6-type carbide particles can be obtained. If necessary, the obtained ingot is subjected to the primary hot working, homogenization heat treatment, and secondary hot working, and then solution heat treatment at a relatively low temperature, so that a fine massive α-Cr phase remains without being dissolved. As a result, the fine massive α-Cr phase functions as pinning particles, and during the solution heat treatment, coarsening of the γ phase can be prevented. Furthermore, when the aging treatment is applied to the Ni-based alloy after the solution heat treatment, the cellular structure is formed on the entire inside of the γ phase.
The Ni-based alloy according to the present invention is excellent in corrosion resistance and hot workability due to an optimized composition thereof. The Ni-based alloy after the aging treatment exhibits high wear resistance since the coarse M23C6-type carbide particles are dispersed in a matrix. Furthermore, the Ni-based alloy after the aging treatment exhibits high strength due to the inclusion of the cellular structure. Since an initial γ phase is fine, the cellular structure is also fine, and high toughness (that is, high impact resistance) is also exhibited.
In a vacuum induction furnace, 50 kg of a raw material having a composition shown in Table 1 was vacuum melted to obtain an ingot. The obtained ingot was subjected to the homogenization heat treatment at 1200° C. for 24 hours, and then hot forging in a temperature range of 900° C. to 1200° C. to produce a round bar with a diameter of 24 mm. The round bar was subjected to the solution heat treatment at 1050° C. for 1 hour, and then cooled with water. The round bar was further subjected to the aging treatment at 720° C. for 16 hours and then air-cooled.
Using the line segment method, the average grain diameter of the γ phase contained in the Ni-based alloy after the solution heat treatment was measured. First, a photograph of a metal structure of the round bar was captured with an optical microscope (magnification: 100 times).
Next, a total of ten different straight lines of five vertical lines and five horizontal lines were drawn on the captured photograph, and for each of the straight lines, a value (=L/n) obtained by dividing a length (L) of the straight line by the number (n) of crystal grains whose boundaries intersect with the straight line was calculated. Further, an average grain diameter was calculated by calculating an average value thereof.
2.2. Weight Fraction of M23C6-Type Carbide
Using an electrolytic extraction method, a weight fraction of the M23C6-type carbide contained in the Ni-based alloy after the aging treatment was measured.
A tensile test was performed at room temperature in accordance with JIS Z 2241:2011 to measure 0.2% proof stress and elongation.
A Charpy impact test (notch R: 10 mm) was performed in accordance with JIS Z 2242:2018 to measure absorption energy.
The wear resistance was evaluated in accordance with ASTM G65 Procedure A. A weight change (g) of a wheel before and after the test was measured with a test load of 30 Lbf (13.608 kg), a sand flow rate of 320 g/min, a wheel diameter of 8.68″ (220.472 mm), and a wheel width of 0.5″ (12.7 mm).
Table 2 shows results. The followings can be found from Table 2.
Comparative Example 2 has a high 0.2% proof stress, but a small elongation and a small absorption energy. It is considered that this is because the amount of C is excessive and V is contained.
Compared with Comparative Example 2, Comparative Example 3 had smaller elongation and absorption energy. It is considered that this is because the solution heat treatment temperature was too high, and the average grain diameter of the γ phase after the solution heat treatment exceeded 50 μm.
Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention.
The present application is based on Japanese Patent Applications No. 2022-174050 filed on Oct. 31, 2022 and No. 2023-128787 filed on Aug. 7, 2023, and the contents thereof are incorporated herein by reference.
The Ni-based alloy according to the present invention can be used for members for oil and gas drilling, various shaped materials including a shaped material for members for oil and gas drilling, round bars, wires, and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-174050 | Oct 2022 | JP | national |
| 2023-128787 | Aug 2023 | JP | national |
