JP2019112687A - Ni-BASED HEAT RESISTANT ALLOY - Google Patents

Abstract

To provide a Ni-based heat resistant alloy having excellent creep strength and creep rupture ductility.SOLUTION: There is provided a Ni-based heat resistant alloy having a chemical composition containing, C≤0.10%, Si≤1.0%, Mn≤1.0%, P≤0.01%, S≤0.001%, O≤0.002%, Cr:15.0% or more and less than 28.0%, Al:over 0.5% and 2.5% or less, Ti:0.1-2.0%, Nb:0.1-2.0%, B:0.0005-0.01%, Mo:over 0% and 16.0% or less, W:over 0% and 16.0% or less, Nd:0.01-0.5%, Fe≤15.0%, Co:0-25.0%, Zr:0-0.2%, V:0-1.5%, Hf:0-1.0%, Mg:0-0.05%, Ca:0-0.05%, Sc:0-0.5%, Y:0-0.5%, La:0-0.5%, Ce:0-0.5%, Ta:0-8.0%, Re:0-8.0% and the balance:Ni with impurities, satisfying [3.0≤Mo+0.5 W≤18.0], [0.30≤Al/(Al+Ti+Nb)≤0.60], [0.20≤Ti/(Al+Ti+Nb)≤0.50], [0<Nb/(Al+Ti+Nb)≤0.50], and having number density of Nd lump existing on a crystal particle boundary of 10/μm or more, average concentration of P at an intermediate position of Nd lumps each other on the crystal particle boundary of 0.002 mass% or less.SELECTED DRAWING: None

Description

  The present invention relates to a Ni-based heat-resistant alloy.

In recent years, energy saving, effective use of resources, and reduction of CO ₂ gas emissions for environmental protection have become one of the problems to be solved for energy problems, and have become an important industrial policy. In the case of a power generation boiler for burning fossil fuel, a reactor for the chemical industry, etc., a highly efficient super-supercritical pressure boiler or reactor is advantageous. Along with this, construction of ultra-supercritical pressure boilers, in which the temperature and pressure of steam are increased for high efficiency, has been promoted all over the world. Specifically, it is planned to raise the steam temperature which has been around 600 ° C. up to 650 ° C. or more, or even 700 ° C. or more.

  Due to the high temperature and pressure increase of steam, the boiler superheater tube and the reactor tube for chemical industry, and the thick plate and forged products as heat and pressure resistant members are raised to temperatures of 700 ° C or more during operation. It becomes. Therefore, not only high-temperature strength and high-temperature corrosion resistance, but also long-term stability of metal structure and good creep rupture ductility and creep-fatigue properties are required for materials used for a long time in such severe environments. Ru.

  Furthermore, in maintenance such as repair after long-term use, it is necessary to carry out operations such as cutting, processing, and welding on a material which has been subjected to long-term aging. Therefore, not only the characteristics as a new material but also the soundness as an aged material is strongly required for the heat-resistant material.

Patent Documents 1 to 8 disclose Ni-based alloys used under the severe high-temperature environment as described above. In these documents, Mo and / or W are contained to achieve solid solution strengthening, and Al and Ti are contained to form an intermetallic compound γ ′ phase, specifically, Ni ₃ (Al, Ti) It utilizes precipitation strengthening. Among these, since the Ni-based alloys disclosed in Patent Documents 4 to 6 contain 28% or more of Cr, a large amount of α-Cr phase having a bcc structure is also precipitated.

  Patent Document 9 discloses that creep strength is improved by adjusting the matching strain of a Ni-based single crystal superalloy.

  Patent Document 10 discloses an austenitic steel whose high-temperature strength is enhanced by containing a large amount of additive elements such as Mn and Cr.

  Patent Document 11 discloses a Ni-based alloy containing predetermined amounts of Mo and W, and further, predetermined amounts of Nd and B. This document further describes improving the hot workability and creep rupture strength at high temperatures by limiting the total content of Sb, Zn and As.

  Patent Document 12 discloses a Ni-based heat-resistant alloy in which the grain boundaries are reinforced with carbides or borides while defining the balance of the contents of Al, Ti, and Nb constituting the γ 'phase that strengthens the grains. ing.

  Patent Document 13 discloses a Ni-based heat-resistant alloy in which the balance of the volume fraction of the matrix phase of gamma prime (γ ') and the contents of Nb and Mo is specified.

JP-A-51-84726 Japanese Patent Application Laid-Open No. 51-84727 JP-A-7-150277 Unexamined-Japanese-Patent No. 7-216511 JP-A-8-127848 JP-A-8-218140 JP-A-9-157779 Japanese Patent Application Publication No. 2002-518599 Unexamined-Japanese-Patent No. 2003-49231 Japanese Patent Application Laid-Open No. 61-179834 WO 2010/038826 Unexamined-Japanese-Patent No. 2013-216939 JP, 2016-56436, A

  In the Ni-based alloys disclosed in Patent Documents 1 to 8, the γ 'phase and the α-Cr phase precipitate. Therefore, the creep rupture ductility under high temperature is low compared to the conventional austenitic steel etc., and in particular, when it is used for a long period of time, the secular change occurs and the ductility is greatly reduced compared to the new material.

  The Ni-based alloy disclosed in Patent Document 9 is a single crystal alloy and can not be used for applications where ductility and processability are required in a structure such as a steel pipe material. The austenitic steel disclosed in Patent Document 10 can not obtain high breaking strength when the Ni content is 50% or more. The Ni-based alloy disclosed in Patent Document 11 may have low creep strength and creep rupture ductility after long-term use at high temperatures.

  In addition, since the Ni-based heat-resistant alloy disclosed in Patent Document 12 strengthens the grain boundaries with carbides or borides, the strength may decrease in a high temperature environment of 800 ° C. or higher. Although the Ni-based heat-resistant alloy disclosed in Patent Document 13 has excellent creep strength and creep rupture ductility, there is still room for further improvement.

  An object of the present invention is to solve the above problems and to provide a Ni-based heat resistant alloy having excellent creep strength and creep rupture ductility.

  The present invention was made in order to solve the above-mentioned subject, and makes the following Ni basis heat-resistant alloys a summary.

(1) Chemical composition is in mass%,
C: 0.10% or less,
Si: 1.0% or less,
Mn: 1.0% or less,
P: 0.01% or less,
S: 0.001% or less,
O: 0.002% or less,
Cr: 15.0% or more and less than 28.0%,
Al: more than 0.5% and less than 2.5%,
Ti: 0.1 to 2.0%,
Nb: 0.1 to 2.0%,
B: 0.0005 to 0.01%,
Mo: more than 0% and 16.0% or less,
W: more than 0%, 16.0% or less,
Nd: 0.01 to 0.5%,
Fe: 15.0% or less,
Co: 0 to 25.0%,
Zr: 0 to 0.2%,
V: 0 to 1.5%,
Hf: 0 to 1.0%,
Mg: 0 to 0.05%,
Ca: 0 to 0.05%,
Sc: 0 to 0.5%,
Y: 0 to 0.5%,
La: 0 to 0.5%,
Ce: 0 to 0.5%,
Ta: 0 to 8.0%,
Re: 0 to 8.0%,
Remainder: Ni and impurities,
Satisfy the following formulas (i) to (iv),
Nd lumps are present at grain boundaries, and the number density per unit length of the grain boundaries of the Nd lumps is 10 / μm or more,
On the grain boundaries, the average concentration of P at an intermediate position between adjacent Nd masses is, in mass%, 0.002% or less.
Ni-based heat-resistant alloy.
3.0 ≦ Mo + 0.5 W ≦ 18.0 (i)
0.30 ≦ Al / (Al + Ti + Nb) ≦ 0.60 (ii)
0.20 ≦ Ti / (Al + Ti + Nb) ≦ 0.50 (iii)
0 <Nb / (Al + Ti + Nb) ≦ 0.50 (iv)
However, each element symbol in the above formula represents the content (% by mass) of each element contained in the alloy, and is zero when not contained.

(2) The chemical composition is in mass%,
Co: over 5.0% to 25.0% or less,
Zr: 0.005 to 0.2%,
V: 0.02 to 1.5%,
Hf: 0.005 to 1.0%,
Mg: 0.0005 to 0.05%,
Ca: 0.0005 to 0.05%,
Y: 0.001 to 0.5%,
La: 0.001 to 0.5%,
Ce: 0.001 to 0.5%,
Ta: 0.01 to 8.0%, and
Re: 0.01 to 8.0%,
Containing one or more selected from
Ni base heat-resistant alloy as described in said (1).

(3) The volume fraction of the γ 'phase of the matrix phase is 25.0% or less,
Grain boundary coverage is 70.0% or more,
Ni base heat-resistant alloy as described in said (1) or (2).

(4) The volume fraction of the grain boundary sigma phase is 10.0% or less,
The volume fraction of the Laves phase of the mother phase is 5.0% or less,
Ni base heat-resistant alloy in any one of said (1) to (3).

  According to the present invention, a Ni-based heat-resistant alloy having excellent creep strength and creep rupture ductility can be obtained.

It is the mapping figure which showed an example of the measurement result by an atom probe. It is a figure for demonstrating grain boundary coverage.

  The inventors of the present invention, based on the Ni-based heat-resistant alloy disclosed in Patent Document 13, repeated intensive studies on methods of further improving creep strength and creep rupture ductility, and obtained the following findings.

  P contained as an impurity in the alloy is known to segregate at grain boundaries and cause grain boundary embrittlement. Therefore, it is desirable to reduce the P content in the alloy as much as possible. However, since the extreme reduction of the P content leads to an increase in the smelting cost, the current situation is that a certain degree of mixing is inevitable.

  Therefore, the present inventor examined a method for rendering P contained unavoidably included harmless. As a result, it was found that Nd contained in the alloy causes Nd to agglomerate in a massive manner at grain boundaries and to capture P to be harmless.

  In addition, by collecting P segregating at grain boundaries, the concentration of P can be reduced in regions other than the portion where massive Nd (also referred to as “Nd block” in the following description) exists. It becomes possible to prevent intergranular embrittlement.

  The present invention has been made based on the above findings. Hereinafter, each requirement of the present invention will be described in detail.

1. Chemical composition The reasons for limitation of each element are as follows. In the following description, “%” of the content means “mass%”.

C: 0.10% or less Carbon (C) is an element effective in forming a carbide to improve creep strength. In addition, grain boundary precipitation enhances grain boundary strength and contributes to the improvement of creep ductility. However, if the C content is too high, the amount of undissolved carbides in the solution state (solid solution state) increases, and the C content does not contribute to the improvement of creep strength and creep ductility. Furthermore, the toughness and the weldability are reduced. Therefore, the C content is 0.10% or less.

  In addition, when it is desired to realize high temperature creep strength by intermetallic compounds that are more stable than carbides at high temperatures for a long time, carbides precipitate at grain boundaries when the C content increases, so the precipitation amount of intermetallic compounds at grain boundaries As a result, the grain boundary stability on the high temperature long time side can not be maintained. In that case, the C content is preferably less than 0.01%. On the other hand, when it is desired to obtain the above effect, the C content is preferably 0.001% or more, and more preferably 0.002% or more.

Si: 1.0% or less Silicon (Si) deoxidizes the alloy. However, when the Si content is excessive, the weldability and the hot workability are reduced. Therefore, the Si content is 1.0% or less. The Si content is preferably less than 1.0%, more preferably 0.8% or less, and still more preferably 0.5% or less. If the deoxidizing action is sufficiently ensured by other elements, the Si content may not have a lower limit. In order to stably obtain effects such as deoxidation, oxidation resistance and water vapor oxidation resistance, the Si content is preferably 0.01% or more, and more preferably 0.02% or more. Preferably, it is more preferably 0.04% or more.

Mn: 1.0% or less Manganese (Mn) deoxidizes the alloy. Mn further fixes the impurity S as sulfide to enhance the hot workability of the alloy. On the other hand, when the Mn content is excessive, the formation of a spinel-type oxide film is promoted, and the oxidation resistance at high temperature is lowered. Therefore, the Mn content is 1.0% or less. The Mn content is preferably less than 1.0%, more preferably 0.8% or less, and still more preferably 0.5% or less. The Mn content is preferably 0.01% or more, more preferably 0.02% or more, and more preferably 0.04% or more, in order to stably obtain the action of improving the hot workability. It is further preferred that

P: 0.01% or less Phosphorus (P) is an element contained in the alloy as an impurity, causes intergranular embrittlement during high temperature use, and causes an increase in stress relaxation cracking susceptibility. Therefore, the P content is 0.01% or less. The P content is preferably 0.008% or less, more preferably 0.006% or less.

S: 0.001% or less Sulfur (S) is an element contained in the alloy as an impurity, and segregates and concentrates at grain boundaries during high temperature use, and significantly increases stress relaxation cracking sensitivity. Therefore, the S content is made 0.001% or less. The S content is preferably 0.0008% or less, more preferably 0.0006% or less.

O: 0.001% or less Oxygen (O) is an element contained in the alloy as an impurity, and if contained in large amounts, an oxide is excessively formed, and the workability and ductility decrease. Therefore, the O content is made 0.001% or less. The O content is preferably 0.0008% or less, more preferably 0.0006% or less.

Cr: 15.0% or more and less than 28.0% Chromium (Cr) improves the corrosion resistance of the alloy, such as oxidation resistance, water vapor oxidation resistance, and high temperature corrosion resistance. Further, Cr combines with Nb to form an intermetallic compound and precipitates at grain boundaries to improve the creep strength of the alloy. On the other hand, when the Cr content is excessive, the α-Cr phase and the σ phase are excessively precipitated and coarsened, and creep voids are likely to be formed at the precipitate interface during long-term use. This reduces creep strength and creep rupture ductility and also reduces hot workability. Therefore, the Cr content is 15.0% or more and less than 28.0%. From the viewpoint of the lower limit, the Cr content is preferably higher than 15.0%, more preferably 16.0% or more, and still more preferably 18.0% or more. The Cr content is preferably 27.0% or less, and more preferably 26.0% or less, from the viewpoint of the upper limit.

Al: more than 0.5% to 2.5% or less Aluminum (Al) forms a γ 'phase (Ni ₃ Al) to enhance creep strength. On the other hand, when the Al content is excessive, the precipitation temperature of the γ ′ phase is increased, the volume fraction of the γ ′ phase at high temperature is increased, and the hot workability is reduced. Therefore, the Al content is more than 0.5% and not more than 2.5%. From the viewpoint of the upper limit, the Al content is preferably less than 2.5%, more preferably 2.3% or less, and still more preferably 2.2% or less. From the viewpoint of the lower limit, the Al content is preferably 0.6% or more, and more preferably 0.7% or more. In the present specification, the Al content is sol. It means the content of Al (acid-soluble Al).

Ti: 0.1 to 2.0%
Titanium (Ti) is an element which forms a γ 'phase (Ni ₃ (Al, Ti)) together with Al to enhance the creep strength of the alloy. On the other hand, when the Ti content is excessive, the hot workability is reduced. Therefore, the Ti content is 0.1 to 2.0%. The Ti content is preferably 0.5% or more, and more preferably 1.0% or more. The Ti content is preferably less than 2.0%, more preferably 1.8% or less, and still more preferably 1.7% or less.

Nb: 0.1 to 2.0%
Niobium (Nb) dissolves in the γ 'phase to strengthen the γ' phase. Nb further strengthens the matrix by solid solution. Therefore, Nb enhances the high temperature strength of the alloy. However, if the Nb content is too high, the γ 'phase increases and the amount of Nb dissolved in the matrix (intra-grain) also increases. Therefore, the intragranular structure is extremely strengthened. Furthermore, coarse Nb carbides are formed and the structure becomes weak. Therefore, creep strength and ductility are reduced, and hot workability is also reduced. Therefore, the Nb content is 0.1 to 2.0%. The Nb content is preferably higher than 0.1%, more preferably 0.2% or more, and still more preferably 0.5% or more. The Nb content is preferably less than 2.0%, more preferably 1.8% or less, and still more preferably 1.7% or less.

B: 0.0005 to 0.01%
Boron (B) strengthens the grain boundaries and enhances the creep strength and creep rupture ductility of the Ni-based heat resistant alloy. On the other hand, when the B content is excessive, the weldability is reduced and the creep strength and the creep rupture ductility are also reduced. Therefore, B content is 0.0005 to 0.01%. From the viewpoint of the upper limit, the B content is preferably less than 0.01%, more preferably 0.009% or less, and still more preferably 0.008% or less. From the viewpoint of the lower limit, the B content is preferably higher than 0.0005%, more preferably 0.001% or more, and still more preferably 0.002% or more.

Mo: More than 0% and 16.0% or less Mo (molybdenum) is solid-solved in the matrix and improves the creep strength of the alloy by solid solution strengthening. As described later, in the present invention, it is necessary to set the Mo equivalent within a predetermined range, but when the Mo content is 0%, the workability is deteriorated and the ductility is also reduced. On the other hand, when the Mo content is excessive, the hot workability is reduced. It also forms carbides or nitrides and lowers the high temperature long time strength at 800 ° C. or higher. Therefore, the Mo content is more than 0% and not more than 16.0%. The Mo content is preferably 0.2% or more, and more preferably 0.5% or more. The Mo content is preferably less than 15.0%, more preferably 14.0% or less, and still more preferably 12.0% or less.

W: more than 0% and 16.0% or less Tungsten (W) dissolves in the matrix and improves the creep strength of the alloy by solid solution strengthening. In addition, Laves phase precipitates at grain boundaries to improve grain boundary strength. As described later, in the present invention, it is necessary to set the Mo equivalent within a predetermined range, but when the W content is 0%, the Laves phase becomes thermally unstable and the grain boundary precipitation amount decreases. On the other hand, when the W content is excessive, the hot workability is reduced. Therefore, the W content is more than 0% and not more than 16.0%. The W content is preferably 1.0% or more, and more preferably 2.0% or more. The W content is preferably 14.0% or less, more preferably 12.0% or less.

Nd: 0.01 to 0.5%
Neodymium (Nd) is an element having the function of collecting and detoxifying P as well as aggregating in bulk at grain boundaries. On the other hand, when the Nd content is excessive, inclusions such as oxides increase and the hot workability and the weldability decrease. Therefore, the Nd content is 0.01 to 0.5%. The Nd content is preferably 0.03% or more, more preferably 0.05% or more. The Nd content is preferably 0.3% or less, more preferably 0.1% or less.

Fe: 15.0% or less Iron (Fe) is an element that improves the hot workability of a Ni-based heat-resistant alloy. Also, Laves phase precipitates at grain boundaries to improve grain boundary strength. On the other hand, when the Fe content is excessive, the tissue stability is reduced. Therefore, the Fe content is 15.0% or less. The Fe content is preferably 10.0% or less, more preferably less than 5.0%. Moreover, in order to stabilize the Laves phase which is a metastable phase and to suppress the formation of the σ phase, the Fe content is preferably 1.0% or less, more preferably less than 0.1%. preferable. In order to obtain the above effects, the Fe content is preferably 0.02% or more, more preferably 0.04% or more, and still more preferably 0.06% or more.

  In the chemical composition of the Ni-based heat-resistant alloy of the present invention, the balance is Ni and impurities. Here, “impurity” is a component mixed in due to various factors such as ore, scrap, etc. and various factors in the manufacturing process when the alloy is industrially manufactured, and it is acceptable within a range not adversely affecting the present invention Means one.

  In addition, if Ni content is 40.0% or more, the fall of ductility can be suppressed even if it makes other elements contain and creep strength is raised. When the Ni content is too low, intragranular deformation resistance increases significantly and creep rupture ductility decreases. Therefore, the Ni content is preferably 40.0% or more.

  The Ni-based heat-resistant alloy of the present invention may further contain one or more elements selected from Co, Zr, V, Hf, Mg, Ca, Sc, Y, La, Ce, Ta and Re. .

Co: 0 to 25.0%
Cobalt (Co) is distributed in the γ phase and the γ ′ phase and mainly acts as a solid solution strengthening element. Furthermore, Co solid solution in γ ′ greatly reduces the lattice constant and reduces matching lattice strain. Therefore, Co improves creep strength and creep rupture ductility. The increase in elongation at break corresponds to the decrease in lattice strain due to the inclusion of Co. Furthermore, Co lowers the precipitation temperature of the embrittlement phase σ phase, and spreads the γ + γ ′ two-phase region excellent in the strength and ductility balance in the grains. Therefore, Co may be contained as needed.

  However, when the Co content is excessive, the ductility improvement effect is saturated. In addition, excessive solid solution of Co significantly strengthens the matrix and reduces the hot workability. Therefore, the Co content is 25.0% or less. The Co content is preferably less than 25.0%, more preferably 22.0% or less, and still more preferably 20.0% or less. In order to stably obtain the effects described above, the Co content is preferably more than 5.0%, more preferably 7.0% or more, and still more preferably 10.0% or more.

Zr: 0 to 0.2%
Zirconium (Zr) is distributed between the intragranular γ 'phase and the grain boundaries, and stabilizes the intragranular γ' phase in the grains as Ti. At grain boundaries, it acts as a grain boundary solid solution element like B, and enhances the creep strength and creep rupture ductility of the Ni-based heat-resistant alloy. Therefore, Zr may be contained as needed. However, when the Zr content is excessive, the Zr distributed inside the grains excessively strengthens the grains and reduces the hot workability. Furthermore, part of Zr forms coarse (Zr, Nb) carbides as inclusions, and the creep strength of the alloy decreases. Therefore, the Zr content is 0.2% or less. The Zr content is preferably less than 0.2%, more preferably 0.1% or less, and still more preferably 0.05% or less. In order to stably obtain the above effects, the Zr content is preferably 0.005% or more, more preferably 0.01% or more, and further preferably 0.02% or more. preferable.

V: 0 to 1.5%
Vanadium (V) may be contained as necessary because it is an element that forms carbonitrides or intermetallic compounds to increase creep strength. However, when the V content is excessive, the ductility and toughness decrease due to the occurrence of high temperature corrosion and the precipitation of the embrittled phase. Therefore, the V content is 1.5% or less. The V content is preferably less than 1.5%, more preferably 1.2% or less, and still more preferably 1.0% or less. In order to stably obtain the effects described above, the V content is preferably 0.02% or more, more preferably 0.04% or more, and further preferably 0.06% or more. preferable.

Hf: 0 to 1.0%
Hafnium (Hf) is an element mainly contributing to grain boundary strengthening to enhance creep strength, and may be contained as necessary. However, when the Hf content is excessive, the hot workability and the weldability decrease. Therefore, the Hf content is 1.0% or less. The Hf content is preferably less than 1.0%, more preferably 0.8% or less, and still more preferably 0.5% or less. In order to stably obtain the above-described effects, the Hf content is preferably 0.005% or more, more preferably 0.008% or more, and further preferably 0.01% or more. preferable.

  The V and Hf may be contained alone or in combination of two or more. When V and Hf are contained, the preferable total content of these elements is 2.5% or less.

Mg: 0 to 0.05%
Ca: 0 to 0.05%
Sc: 0 to 0.5%
Y: 0 to 0.5%
La: 0 to 0.5%
Ce: 0 to 0.5%
Magnesium (Mg), calcium (Ca), scandium (Sc), yttrium (Y), lanthanum (La) and cerium (Ce) are all necessary elements because they have the function of fixing S and O which are impurities. You may make it contain according to.

  As described above, in the present invention, P is collected and detoxified by Nd lumps. However, when the alloy contains a large amount of S and O, Nd is also bonded to those elements, and tends to form coarse sulfides or oxides. Among the above elements, in particular, Ca, La and Ce have higher affinity for S than Nd, and Mg, Sc and Y have higher affinity for O than Nd. Therefore, the inclusion of these elements suppresses the formation of sulfides and oxides of Nd, and enables efficient collection of P.

Further, Sc, Y, La and Ce further enhance the adhesion of the Cr ₂ O ₃ protective film on the alloy surface, and in particular, enhance the oxidation resistance at the time of repeated oxidation. These elements further strengthen grain boundaries to increase creep strength and strain at break.

  However, when the content of Mg and Ca is excessive, the cleanliness is reduced and the hot workability and ductility are reduced. Therefore, the contents of Mg and Ca are both 0.05% or less. The content of Mg and Ca is preferably less than 0.05%, more preferably 0.02% or less, and still more preferably 0.01% or less. In order to stably obtain the effects described above, at least one of the content of Mg and Ca is preferably 0.0005% or more, more preferably 0.0008% or more, and 0.001% or more It is further preferred that

  Furthermore, when the contents of Sc, Y, La and Ce become excessive, inclusions such as oxides increase and the hot workability and weldability decrease. Therefore, the contents of Sc, Y, La and Ce are all 0.5% or less. The content of each of these elements is preferably less than 0.5%, more preferably 0.3% or less, and still more preferably 0.15% or less. In order to stably obtain the above-described effects, it is preferable to set any of the contents of these elements to 0.001% or more, more preferably 0.002% or more, and 0.003% or more It is further preferred that

  The above Mg, Ca, Y, La and Ce can be contained alone or in combination of two or more. The preferable total content of these elements is 0.94% or less. Moreover, when it is desired to sufficiently obtain the effect of fixing S, it is preferable to set the total content of one or more selected from Ca, La and Ce to 0.001% or more. Similarly, when it is desired to sufficiently obtain the effect of fixing O, it is preferable to set the total content of one or more selected from Mg, Sc and Y to 0.001% or more.

Ta: 0 to 8.0%
Re: 0 to 8.0%
Both tantalum (Ta) and rhenium (Re) form carbonitrides and form a solid solution in the matrix to increase creep strength. These elements are further dissolved in the γ 'phase to increase the high temperature strength. Therefore, these elements may be contained as needed. However, when the content of these elements is excessive, the processability and mechanical properties are degraded. Accordingly, the Ta content and the Re content are each 8.0% or less. The Ta content and the Re content are each preferably less than 8.0%, more preferably 7.0% or less, and still more preferably 6.0% or less. In order to stably obtain the effects described above, at least one of the contents of Ta and Re is preferably 0.01% or more, more preferably 0.1% or more, and more preferably 0.5% or more It is further preferred that

  The above Ta and Re can be contained alone or in combination of two. The preferable total content of these elements is 14.0% or less.

In the above component systems, excellent creep strength and creep rupture ductility can be obtained by setting the Mo equivalent within the following range. Specifically, 750 ° C. obtained using Larson-Miller parameter method, the creep rupture time at 100MPa becomes ¹⁰⁵ hours or more, and 750 ° C., creep rupture ductility at 100MPa is more than 20%.
3.0 ≦ Mo + 0.5 W ≦ 18.0 (i)
However, each element symbol in the above formula represents the content (% by mass) of each element contained in the alloy, and is zero when not contained.

The following formulas (ii) to (iv) indicate the ratios of the Al content, the Ti content, and the Nb content to the total of the Al, Ti and Nb contents, respectively.
0.30 ≦ Al / (Al + Ti + Nb) ≦ 0.60 (ii)
0.20 ≦ Ti / (Al + Ti + Nb) ≦ 0.50 (iii)
0 <Nb / (Al + Ti + Nb) ≦ 0.50 (iv)
However, each element symbol in the above formula represents the content (% by mass) of each element contained in the alloy, and is zero when not contained.

  The Ni-based heat-resistant alloy according to the present invention satisfies the above formulas (ii) to (iv) in addition to the chemical composition being in the range described above. When the above formulas (ii) to (iv) are satisfied, the balance between the individual solid solution effects of Ti and Nb and the precipitation strengthening of the γ ′ phase is good. That is, in this case, excellent creep strength and creep rupture ductility can be obtained by a significant increase in strength due to precipitation strengthening and ductility and strength increase due to solid solution strengthening.

2. As described above, it is possible to prevent intergranular embrittlement by forming massive Nd at grain boundaries and trapping P to render it harmless. In order to obtain this effect, it is necessary that Nd lumps exist at grain boundaries, and the number density per unit length of grain boundaries of Nd lumps be 10 / μm or more. Here, the Nd lump is an aggregation of Nd, and has a size of about 5 to 25 nm. In the present invention, an aggregate of Nd having an equivalent circle diameter of 5 nm or more is defined as Nd lump.

  The upper limit of the number density of Nd lumps need not be particularly defined, but if it is excessive, the grain boundary coverage by the Laves phase may be reduced. Therefore, the number density of Nd lumps is preferably 400 / μm or less, more preferably 100 / μm or less.

  Then, it is necessary to collect most of P segregated in grain boundaries by Nd lumps and to reduce the concentration of P in the region other than the portion where the Nd lumps are present. Specifically, on the grain boundary, the average concentration of P at an intermediate position between adjacent Nd masses needs to be set to 0.002% or less by mass%.

  In the present invention, the number density of Nd lumps and the average concentration of P at an intermediate position between the Nd lumps are determined as follows.

  First, a needle-like sample is collected so as to include grain boundaries. The size of the needle-like sample is such that the bottom has a diameter of 50 to 100 nm and the height is about 300 nm. Then, an analysis of the needle-like sample is performed using an energy compensated laser-assisted local electrode atom probe (hereinafter simply referred to as “atom probe”).

  FIG. 1 is a mapping diagram showing an example of a measurement result by an atom probe. In FIG. 1, the part in which the Nd lump exists is shown enlarged, and it can be seen that P is collected in the Nd lump.

  From the mapping map as described above, the number density of Nd is determined by calculating the number of Nd lumps present in crystal grain boundaries having a length of about several 10 nm contained in the needle-like sample. At the same time, the concentration of P at an intermediate position between Nd masses is measured. The measurement is performed on 5 samples and the average value is adopted.

  The grain boundaries can be identified by referring to the mapping diagrams of C, Ni, C, and Al in the same field of view. And, the measurement of the P concentration is performed in the direction which does not coincide with the longitudinal direction of the needle-like sample and which is substantially perpendicular to the grain boundary.

  The other metal structures are not particularly limited, but in order to stabilize the structure and ensure excellent creep strength and creep rupture ductility, it is preferable to satisfy the following conditions.

The volume fraction of the γ 'phase of the matrix phase: 25.0% or less The volume fraction (vol.%) Of the γ' phase of the matrix phase is the volume fraction of Ni particles in the matrix phase (γ phase) It means volume fraction. Depending on the process, the γ 'phase may be precipitated at the grain boundaries, but in the present invention, only the γ' phase precipitated in the grains is considered.

  If the volume fraction of the γ ′ phase is too high, the matching lattice strain may increase and the intragranular ductility may decrease. Furthermore, since the precipitation temperature of the γ 'phase is increased, the hot workability may be reduced. Therefore, the volume fraction of the γ 'phase is preferably 25.0% or less. By setting the volume fraction of the γ ′ phase in the above range, the balance between strength and ductility is maintained, and excellent high temperature strength (creep strength), ductility and hot workability (break elongation) can be obtained. Although the lower limit of the volume fraction of the γ ′ phase of the matrix phase is not particularly provided, if the volume fraction of the γ ′ phase is too low, the required creep strength may not be obtained. Therefore, the volume fraction of the γ 'phase is preferably 10.0% or more.

  The volume fraction of the mother phase γ 'phase is measured by the following method. X-ray diffraction measurement is performed on a Ni-based heat-resistant alloy, and volume fraction analysis is performed by structure optimization by the X-ray Rietveld method using a two-phase model of the matrix phase (γ phase) and the γ ′ phase. Here, the γ 'phase precipitated at the grain boundaries is not detected by X-ray diffraction measurement because it is thin film-like and sparse. That is, the γ 'phase detected in the X-ray diffraction measurement is the γ' phase precipitated in the γ grains. Therefore, the volume fraction of the γ 'phase can be determined by analyzing the volume fraction by the above-mentioned X-ray diffraction method.

  The volume fraction of the γ ′ phase can also be measured by image analysis using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). In this case, the area ratio of the γ 'phase precipitated in the γ particles is determined by image analysis, and the determined area ratio is defined as the volume fraction of the γ' phase.

Grain boundary coverage: 70.0% or more Grain boundary coverage is the ratio (%) of the length of grain boundaries covered by precipitates to the total length of grain boundaries of crystal grains (γ phase). In the present invention, the grain boundary coverage measured in the state before the Ni-based heat resistant alloy is put to use, that is, at the time of new material is adopted.

  When the alloy deforms, stress concentrates on grain boundaries. If the grain boundaries are covered with precipitates, this stress can be dispersed. Therefore, the higher the grain boundary coverage, the higher the strength of the alloy. If the grain boundary coverage is 70.0% or more, excellent creep strength can be obtained. The grain boundary coverage is preferably 80.0% or more. On the other hand, if the grain boundary coverage is too high, there are no sites for deformation, and ductility may sometimes decrease depending on the volume fraction of the intragranular γ 'phase. Therefore, the grain boundary coverage is preferably 90.0% or less.

Grain boundary coverage is calculated by the following method. A sample is taken from any place of the Ni-based heat-resistant alloy. From the collected sample, an area of about 60 × 50 μm ^{2 is} observed in five fields of view. A scanning electron microscope (SEM) is used for observation. FIG. 2 is a schematic view of the observed area. The total length L of grain boundaries in the region is measured. And length A1-An of each grain boundary part (total n pieces) covered with the precipitate is measured. Based on the obtained L and A1 to An, grain boundary coverage (%) in each region (5 in total) is determined based on the following formula (A). The average of the obtained five grain boundary coverages is defined as grain boundary coverage (%).
Grain boundary coverage = (A1 + A2 + A3 + ... + An) / L (A)

  The precipitates precipitated at the grain boundaries in the present embodiment are mainly intermetallic compounds. However, in calculating the grain boundary coverage, if it is covered by any precipitate such as carbide, boride, etc. in addition to the intermetallic compound, it is covered by the precipitate in the above formula (A). Calculate as grain boundary part.

Volume fraction of sigma phase at grain boundary: 10.0% or less When the volume fraction of sigma phase at grain boundary exceeds 10.0%, the change from Laves phase to sigma phase advances rapidly under high temperature environment Most of the Laves phase present at grain boundaries changes to the σ phase. As a result, the grain boundary σ phase coarsens at an early stage, and a void is generated around the σ phase, and a non-precipitation zone is formed in the vicinity of the grain boundary to weaken the structure, which may lead to early breakage. Therefore, it is preferable to set the volume fraction of the σ phase at grain boundaries to 10.0% or less.

  The volume fraction of the sigma phase of the grain boundary can be measured by image analysis using energy selective backscattering (EsB) attached to the SEM. In this case, the area ratio of the σ phase of the grain boundary is obtained by image analysis, and the obtained area ratio is defined as a volume fraction.

Volume fraction of Laves phase of matrix: 5.0% or less The volume fraction (vol.%) Of Laves phase of the matrix means the volume fraction of Laves phase precipitated in the matrix. If the volume fraction of the Laves phase contained in the matrix phase is too high, there is a possibility that creep damage may be promoted by stress concentration in the grains by the Laves phase. Therefore, the volume fraction of the Laves phase of the parent phase is preferably 5.0% or less.

  The volume fraction of the mother phase Laves phase is measured by the following method. The SEM image is arbitrarily observed in five fields of view with an arbitrary cross section, and the area ratio of the acicular precipitates in the grains is calculated by image processing. The average value is taken as the volume fraction of the Laves phase of the mother phase.

3. Manufacturing Method The manufacturing conditions of the Ni-based heat-resistant alloy according to the present invention are not particularly limited, but can be manufactured by using the manufacturing method described below. In the following example, a method of manufacturing a Ni-based heat-resistant alloy tube will be described.

  As described above, although it is necessary to form Nd lumps at grain boundaries, Nd can combine with O and S contained in the alloy as impurities to form coarse inclusions. When these inclusions are generated, it is difficult to obtain the P collection effect. Therefore, in order to collect P efficiently, it is desirable in the melting step that O and S be fixed as other compounds before adding Nd. That is, the timing of the addition of Nd in the melting step is important.

  Specifically, in the melting step, it is preferable to first add one or more selected from Mg, Ca, Y, La and Ce to fix S and O, and then add Nd. Finally, the chemical composition is adjusted to satisfy the above-mentioned definition.

  Next, a billet is produced from the alloy produced by the above method by continuous casting or the like, and thereafter, it is made into a hollow billet. The hollow billet is manufactured by, for example, machining, vertical perforation or centrifugal casting. Subsequently, hot extrusion is performed on the hollow billet.

  As an example of the hot extrusion processing, the hot extrusion processing by the Eugene Sejourne method will be described. First, the hollow billet is heated. The heated hollow billet is housed in the container of the hot extrusion device. The mandrel is inserted into the core hole of the hollow billet contained in the container, and the hollow billet is pushed forward by the stem. A die is placed in front of the container. The hollow billet pushed forward by the stem is pushed in a tube from between the die and the mandrel. The Ni-based heat-resistant alloy pipe is manufactured by the above-described hot extrusion processing. Cold working such as cold rolling and / or cold drawing may be further performed on the Ni-based heat-resistant alloy pipe after the hot extrusion processing.

  The manufactured alloy tube is subjected to solution heat treatment (solution heat treatment). Specifically, solution heat treatment is performed by equalizing an alloy tube to 1000 to 1200 ° C. The holding time is not particularly limited, and is, for example, 1 to 2 hours.

  The first aging heat treatment is performed on the solution treated alloy tube. Specifically, the first aging heat treatment is performed by soaking the alloy tube at 750 to 950 ° C. The holding time depends on the chemical composition of the alloy tube and the soaking temperature, and is, for example, 2 to 400 hours. If the content of each element of the Ni-based alloy is in the above-mentioned range, mainly the intermetallic compounds are precipitated at the grain boundaries by the first aging heat treatment. At this time, the soaking temperature and the holding time are adjusted so that the grain boundary coverage is 70% or more. The? 'Phase is simultaneously formed by the first aging heat treatment.

  In addition, formation of Nd lump and collection of P are performed also by the first aging heat treatment. However, after carrying out the above-mentioned first aging heat treatment, the second aging heat treatment is carried out in order to further promote the collection of P by Nd lumps. Further, even when the precipitation amount of the γ 'phase by the first aging heat treatment is insufficient, it is possible to further precipitate the γ' phase by the second aging treatment.

  Specifically, the second aging heat treatment is performed by soaking the first aging heat treated alloy tube at 600 to 700 ° C. for 1 to 10 hours. The second aging heat treatment adjusts the soaking temperature and the holding time such that the volume fraction of the γ ′ phase is 25.0% or less. By performing the heat treatment in the temperature range in which the Laves phase hardly precipitates, it is possible to perform aggregation of Nd lumps and collection of P while suppressing coarsening of the Laves phase.

  In the above, the manufacturing method of the alloy pipe was demonstrated as Ni-based heat-resistant alloy. However, the Ni-based heat resistant alloy may be manufactured in a shape other than a pipe, for example, the Ni-based heat resistant alloy may be a plate.

  EXAMPLES Hereinafter, the present invention will be more specifically described by way of examples, but the present invention is not limited to these examples.

  An alloy having the chemical composition shown in Table 1 was produced. Each alloy having the above chemical composition was melted in a high frequency vacuum melting furnace to produce a 25 kg ingot. In the melting process, first, elements other than Nd, Mg, Ca, Sc, Y, La and Ce were added to adjust the components. Then, these elements were added as necessary in the order of introduction shown in Table 2 to perform final adjustment of the components. In addition, in the injection | pouring order of Table 2, it means that the element connected by ", (comma)" is simultaneously added.

  Subsequently, each ingot was heated to 1160 ° C. The heated ingot was hot forged to produce a plate having a thickness of 25 mm. After completion of the hot forging, the plate was air cooled. The air-cooled plate was further hot forged to produce a plate of 15 mm in thickness. Then, solution treatment and aging heat treatment (first aging heat treatment or first and second aging heat treatment) were performed on each plate material having a thickness of 15 mm under the conditions shown in Table 2.

  Next, the structure of each alloy was measured according to the following procedure.

<Measurement of Nd Mass Number Density and Average Concentration of P at an Intermediate Position between Nd Mass>
First, a needle-like sample was collected so as to include grain boundaries. The size of the needle-like sample is about 50 to 100 nm in diameter at the bottom and about 300 nm in height. Then, analysis of the needle-like sample was performed using an atom probe (manufactured by CAMECA, LEAP4000X-HR).

  Then, the number density of Nd lumps was determined by calculating the number of Nd lumps present in crystal grain boundaries having a length of about several 10 nm contained in the needle-like sample. At the same time, the concentration of P at an intermediate position between Nd chunks was measured. These measurements were performed on 5 samples, and the average value was adopted.

<Measurement of volume fraction of matrix γ ′ phase>
X-ray diffraction was performed on each alloy. The output voltage and current of the X-ray were 40 kV and 40 mA, and the target was Cu. From the obtained X-ray diffraction pattern, the structure was optimized by the Rietveld method, and the volume fraction of the γ 'phase was determined.

<Measurement of grain boundary coverage>
For each alloy, an area of about 60 × 50 μm ² was observed in five fields of view by SEM. Then, as shown in FIG. 2, after measuring the total length L of the grain boundaries in the region, lengths A1 to An of each grain boundary portion (total of n) covered with the precipitates were measured. Based on the obtained L and A1 to An, grain boundary coverage (%) in each region (5 in total) was determined based on the following formula (A). The average of the obtained five grain boundary coverages was taken as the grain boundary coverage (%).
Grain boundary coverage = (A1 + A2 + A3 + ... + An) / L (A)

<Measurement of volume fraction of grain boundary sigma phase and mother phase Laves phase>
The volume fraction of the grain boundary sigma phase and the matrix Laves phase was measured by image analysis using EsB. Specifically, the area ratio of the σ phase of the grain boundary and the Laves phase of the base material was determined by image analysis, and the determined area ratio was defined as the volume fraction of each phase.

  Subsequently, a creep rupture test was performed according to the following procedure. A round bar with a diameter of 6 mm and a gauge length of 30 mm parallel to the longitudinal direction from the thickness direction central part of each plate material subjected to aging heat treatment (first aging heat treatment or first and second aging heat treatment) Test pieces were produced by machining. The creep rupture test was performed using the produced round bar tensile test piece.

  The creep strength and the creep rupture ductility of each alloy were evaluated as follows by the creep rupture test. Specifically, a creep rupture test was carried out at a load of 130 MPa, 100 MPa or 80 MPa in the atmosphere at 850 ° C. to determine the rupture time and the elongation at break. Furthermore, the obtained fracture time was converted by the Larson-Miller parameter (LMP) method and regressed to calculate creep strength equivalent to 100 MPa, which was used as an index of creep strength. In addition, the elongation at break is used as an index of creep rupture ductility.

  The results are shown together in Table 2.

As can be seen from Table 2, Test No. 2 satisfies all the requirements of the chemical composition of the present invention. At 1 to 20, the elongation at break was 20% or more, and the value of LMP was 26000 or more, which resulted in excellent creep strength and creep rupture ductility. On the other hand, test No. 1 which is a comparative example. In 21 to 35, at least one of creep strength and creep rupture ductility was inferior.

Claims (4)

The chemical composition is in mass%,
C: 0.10% or less,
Si: 1.0% or less,
Mn: 1.0% or less,
P: 0.01% or less,
S: 0.001% or less,
O: 0.002% or less,
Cr: 15.0% or more and less than 28.0%,
Al: more than 0.5% and less than 2.5%,
Ti: 0.1 to 2.0%,
Nb: 0.1 to 2.0%,
B: 0.0005 to 0.01%,
Mo: more than 0% and 16.0% or less,
W: more than 0%, 16.0% or less,
Nd: 0.01 to 0.5%,
Fe: 15.0% or less,
Co: 0 to 25.0%,
Zr: 0 to 0.2%,
V: 0 to 1.5%,
Hf: 0 to 1.0%,
Mg: 0 to 0.05%,
Ca: 0 to 0.05%,
Sc: 0 to 0.5%,
Y: 0 to 0.5%,
La: 0 to 0.5%,
Ce: 0 to 0.5%,
Ta: 0 to 8.0%,
Re: 0 to 8.0%,
Remainder: Ni and impurities,
Satisfy the following formulas (i) to (iv),
Nd lumps are present at grain boundaries, and the number density per unit length of the grain boundaries of the Nd lumps is 10 / μm or more,
On the grain boundaries, the average concentration of P at an intermediate position between adjacent Nd masses is, in mass%, 0.002% or less.
Ni-based heat-resistant alloy.
3.0 ≦ Mo + 0.5 W ≦ 18.0 (i)
0.30 ≦ Al / (Al + Ti + Nb) ≦ 0.60 (ii)
0.20 ≦ Ti / (Al + Ti + Nb) ≦ 0.50 (iii)
0 <Nb / (Al + Ti + Nb) ≦ 0.50 (iv)
However, each element symbol in the above formula represents the content (% by mass) of each element contained in the alloy, and is zero when not contained. The chemical composition is, in mass%,
Co: over 5.0% to 25.0% or less,
Zr: 0.005 to 0.2%,
V: 0.02 to 1.5%,
Hf: 0.005 to 1.0%,
Mg: 0.0005 to 0.05%,
Ca: 0.0005 to 0.05%,
Y: 0.001 to 0.5%,
La: 0.001 to 0.5%,
Ce: 0.001 to 0.5%,
Ta: 0.01 to 8.0%, and
Re: 0.01 to 8.0%,
Containing one or more selected from
The Ni-based heat-resistant alloy according to claim 1. The volume fraction of the γ 'phase of the mother phase is 25.0% or less,
Grain boundary coverage is 70.0% or more,
The Ni-based heat-resistant alloy according to claim 1 or 2. The volume fraction of grain boundary sigma phase is 10.0% or less,
The volume fraction of the Laves phase of the mother phase is 5.0% or less,
The Ni-based heat-resistant alloy according to any one of claims 1 to 3.