JP2021116432A - Ni-BASED ALLOY AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

To provide a Ni-based alloy and method for producing the same in which the formation of Freckle segregation can be suppressed without reducing production efficiency.SOLUTION: The Ni-based alloy comprises one having a liquid phase density differences Δρ (=ρ0-ρ0.35) of more than -0.050 and less than 0.015. Here, ρ0 is the density (g/cm3) of the mother liquid phase (solid phase ratio: zero) of the Ni alloy, and ρ0.35 is the density of the concentrated liquid phase of the Ni alloy (solid phase ratio: 0.35) (g/cm3). The Ni-based alloy preferably contains 0.05≤C≤0.10 mass%, 11.0≤Cr≤19.0 mass%, 1.0≤Co≤22.0 mass%, 0.5≤Fe≤10.0 mass%, 2.5≤Mo≤5.0 mass%, 1.0≤W≤5.0 mass%, 0.3≤Nb≤2.0 mass%, 3.0≤Al≤4.0 mass%, and 0.2≤Ti≤2.49 mass%, and the balance being Ni and unavoidable impurities.SELECTED DRAWING: Figure 1

Description

The present invention relates to a Ni-based alloy and a method for producing the same, and more particularly to a Ni-based alloy capable of suppressing the formation of Freckell segregation without lowering the production efficiency and a method for producing the same.

A "Ni-based alloy (or Ni-based superalloy)" is an alloy containing Ni as a main component and strengthened by solid solution and / or precipitation by adding Al, Ti, W, Mo, Ta, Cr, etc. To say. Ni-based alloys are excellent in high-temperature strength, corrosion resistance, oxidation resistance, etc., and are therefore used for moving blades and stationary blades of aircraft jet engines and gas turbines for power generation, turbines for turbochargers, and the like. Therefore, various proposals have been made conventionally regarding such Ni-based alloys.

For example, in Patent Document 1,
(A) 0.001 <C <0.100 mass%, 11.0 ≦ Cr <19.0 mass%, 0.5 ≦ Co <22.0 mass%, 0.5 ≦ Fe <10.0 mass%, Si ≦ 0 .1 mass%, 2.0 <Mo <5.0 mass%, 1.0 <W <5.0 mass%, 2.5 ≦ Mo + 1 / 2W <5.5 mass%, S ≦ 0.010 mass%, 0.3 ≦ It contains Nb <2.0 mass%, 3.0 <Al <6.5 mass%, and 0.2 ≦ Ti <2.49 mass%, and the balance consists of Ni and unavoidable impurities.
(B) Assuming that the atomic% of the element M is [M], 0.2 ≦ [Ti] / [Al] × 10 <4.0, and 8.5 ≦ [Al] + [Ti] + [Nb]. A Ni-based superalloy for hot forging that satisfies <13.0 is disclosed.
The document describes that when the amount of Ti is reduced and the amount of Al is increased, both hot forging workability and high-temperature strength characteristics can be achieved at the same time.

Further, in Patent Document 2,
(A) 0.001 <C <0.100 mass%, 11 ≦ Cr <19 mass%, 5 <Co <25 mass%, 0.1 ≦ Fe <4.0 mass%, 2.0 <Mo <5.0 mass%, It contains 1.0 <W <5.0 mass%, 2.0 ≦ Nb <4.0 mass%, 3.0 <Al <5.0 mass%, and 1.0 <Ti <3.0 mass%, and the balance is Consists of Ni and unavoidable impurities
(B) Assuming that the atomic% of the element M is [M], 3.5 ≦ ([Ti] + [Nb]) / [Al] × 10 <6.5, and 9.5 ≦ [Al] + [ A Ni-based superalloy for hot forging that satisfies Ti] + [Nb] <13.0 is disclosed.
The document describes that by optimizing the contents of Al, Ti, and Nb, the solid solution temperature of the γ'phase can be lowered, which enables hot forging at a low temperature. Has been done.

Further, in Patent Document 3,
(A) 0.001 <C <0.100 mass%, 11 ≦ Cr <19 mass%, 5 <Co <25 mass%, 0.1 ≦ Fe <4.0 mass%, 2.0 <Mo <5.0 mass%, 1.0 <W <5.0 mass%, 0.3 ≦ Nb <4.0 mass%, 3.0 <Al <5.0 mass%, 1.0 <Ti <3.4 mass%, and 0.01 ≦ It contains Ta <2.0 mass% and the balance consists of Ni and unavoidable impurities.
(B) Assuming that the atomic% of the element M is [M], 3.5 ≦ ([Ti] + [Nb]) / [Al] × 10 <6.5, and 9.5 ≦ [Al] + [ A Ni-based superalloy for hot forging that satisfies Ti] + [Nb] <13.0 is disclosed.
The document describes that by optimizing the contents of Al, Ti, and Nb, the solid solution temperature of the γ'phase can be lowered, which enables hot forging at a low temperature. Has been done.

Further, Non-Patent Document 1 discloses the result of a reproduction test of streak-like segregation (Freckel segregation) using a horizontal unidirectional solidification test furnace.
In the same document,
(A) The segregation streak grows in the direction of the sum of the solidification direction vector and the movement direction vector of the concentrated liquid phase driven by the difference in specific gravity from the mother liquid phase.
(B) Ni-based superalloys are classified into a floating type in which segregation streaks extend upward from the solidification front surface and a sedimentation type in which the segregation streaks extend downward from the solidification front surface, depending on the components to be added.
(C) ^{The streak segregation tendency of Ni-based superalloys can be sorted out by a method in which the ε × R 1.1} value (ε: cooling rate, R: solidification rate) is set as the critical value for segregation formation.
Is described.

Since the Ni-based alloy contains a large amount of alloying elements, macrosegregation called fleckel tends to occur when the alloy is slowly cooled during solidification. Freckell segregation causes a decrease in the mechanical properties (eg, tensile strength) of the material. Therefore, in the production of Ni-based alloys, a production method such as an electroslag redissolving (ESR) method or a vacuum arc redissolving (VAR) method, which is less likely to cause segregation, is generally adopted. However, even when the ESR method or the VAR method is adopted as the method for producing the Ni-based alloy, there is a problem that the larger the size of the ingot, the more easily Feckel segregation occurs during solidification.

On the other hand, when the ESR method or the VAR method is used, if the melting rate of the consumable electrode is slowed down, the cooling rate of the molten metal becomes high. As a result, Freckell segregation can be suppressed. However, with this method, the solidification rate becomes extremely slow, and high production efficiency cannot be obtained.
Furthermore, the critical value produced by Freckel segregation depends on the alloy composition. Therefore, in order to select production conditions that do not cause Freckell segregation and that can obtain high production efficiency, it is necessary to carry out a one-way solidification test for each alloy composition and obtain a critical value by experiment. However, such a method is extremely complicated. In addition, even when the critical value is clarified, it is difficult to adopt manufacturing conditions (manufacturing conditions in which Freckell segregation is unlikely to occur) that actually exceed the critical value in industrial-level production equipment. There are also many.

Japanese Unexamined Patent Publication No. 2015-129341 JP-A-2017-145479 JP-A-2017-145478

Iron and steel, Vol. 95 (2009), No. 8, P613

An object to be solved by the present invention is to provide a Ni-based alloy capable of suppressing the formation of Freckell segregation without lowering the production efficiency and a method for producing the same.
Another problem to be solved by the present invention is to provide a Ni-based alloy having a small decrease in tensile strength due to Flekkel segregation and a method for producing the same.

In order to solve the above problems, the Ni-based alloy according to the present invention comprises a liquid phase density difference Δρ (= ρ _{0 −ρ 0.35} ) of more than −0.050 and less than 0.015.
However,
ρ ₀ ^{is the density (g / cm 3} ) of the mother-liquid phase (solid phase ratio: zero) of the Ni alloy.
ρ _0.35 ^{is the density (g / cm 3} ) of the concentrated liquid phase (solid phase ratio: 0.35) of the Ni alloy.
The Ni-based alloy is
0.05 ≤ C ≤ 0.10 mass%,
11.0 ≤ Cr ≤ 19.0 mass%,
1.0 ≤ Co ≤ 22.0 mass%,
0.5 ≤ Fe ≤ 10.0 mass%,
2.5 ≤ Mo ≤ 5.0 mass%,
1.0 ≤ W ≤ 5.0 mass%,
0.3 ≤ Nb ≤ 2.0 mass%,
3.0 ≤ Al ≤ 4.0 mass%, and
0.2 ≤ Ti ≤ 2.49 mass%
It is preferable that the balance is composed of Ni and unavoidable impurities.

The method for producing a Ni-based alloy according to the present invention is
When Δρ ≧ 0 (floating), the prediction formula expressing the relationship between the liquidus density difference Δρ (= ρ _{0 −ρ 0.35} ) of the Ni-based alloy and the critical value α (= V × R ^{1.1) of Feckel segregation formation} Type) and when Δρ <0 (precipitation type), respectively, the prediction formula acquisition process to be acquired in advance, and the prediction formula acquisition process.
A Δρ calculation step of calculating _{the liquidus density difference Δρ X} of the alloy (X) based on the composition of the alloy (X) to be produced, and
A critical value calculation step of substituting the calculated Δρ _{X into the prediction formula to calculate the critical value α X} of the Freckell segregation formation of the alloy (X).
It includes an alloy manufacturing process for manufacturing the alloy (X) under the condition of _{α X or more.}
However,
ρ ₀ ^{is the density (g / cm 3} ) of the mother-liquid phase (solid phase ratio: zero) of the Ni alloy.
ρ _0.35 ^{is the density (g / cm 3} ) of the concentrated liquid phase (solid phase ratio: 0.35) of the Ni alloy.
V is the cooling rate (° C./min) when the Ni-based alloy solidifies.
R is the solidification rate (° C./min) when the Ni-based alloy solidifies.

When the Ni-based alloy is slowly solidified, the solute is distributed into the solid phase and the liquid phase at a predetermined ratio as the solidification progresses. As a result, during solidification, a concentrated liquid phase having a density different from that of the mother liquid phase is generated. Freckell segregation is thought to grow with the liquid phase density difference Δρ between the mother liquid phase and the concentrated liquid phase as the driving force. In general, the larger the absolute value of Δρ, the larger the Feckel segregation.

On the other hand, each alloy element is roughly classified into an element that increases Δρ, an element that decreases Δρ, and an element that has almost no effect on Δρ. Therefore, if the content of other elements is increased or decreased while maintaining the content of the element essential for obtaining the desired property, Δρ can be kept within a predetermined range. As a result, the formation of Freckell segregation can be suppressed without impairing production efficiency and required properties (eg, high temperature tensile strength).

It is a figure which shows the relationship between the liquid-phase density difference Δρ and VR ^1.1. 2 (A) to 2 (F) are diagrams showing the effect of the difference Δx in the contents of C, Cr, Co, Fe, Mo, or W on the liquid phase density difference Δρ, respectively. 3A to 3D are diagrams showing the effect of the difference Δx in the contents of Nb, Ti, Zr, or Al on the liquidus density difference Δρ, respectively.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Ni-based alloy]
[1.1. composition]
[1.1.1. Main constituent elements]
The Ni-based alloy according to the present invention comprises an alloy in which the liquidus density difference Δρ is within a predetermined range. The details of the liquidus density difference Δρ will be described later. The composition of the Ni-based alloy according to the present invention is not particularly limited as long as the liquidus density difference Δρ satisfies the conditions described later.
The Ni-based alloy according to the present invention preferably contains the following elements, and the balance is composed of Ni and unavoidable impurities. The types of additive elements, their component ranges, and the reasons for their limitation are as follows.

(1) 0.05 ≤ C ≤ 0.10 mass%:
C combines with Cr, Nb, Ti, W, Mo and the like to produce various carbides. Among the carbides, those having a high solid solution temperature (Nb-based and Ti-based carbides) suppress the coarsening of crystal grains at high temperatures due to the pinning effect, and contribute to the improvement of hot workability. Further, Cr-based, Mo-based, and W-based carbides are deposited at the grain boundaries to strengthen the grain boundaries, thereby contributing to the improvement of mechanical properties. In order to obtain such an effect, the C content is preferably 0.05 mass% or more.

On the other hand, when the C content becomes excessive, the amount of carbide becomes excessive. As a result, the structure becomes non-uniform due to segregation of carbides, and hot workability and mechanical properties deteriorate due to excessive precipitation of intergranular carbides. Therefore, the C content is preferably 0.1 mass% or less.

(2) 11.0 ≦ Cr ≦ 19.0 mass%:
Cr is an essential element for forming a protective oxide film of _{Cr 2} O _{3 and improving corrosion resistance and oxidation resistance.} Further, Cr combines with C to form Cr ₂₃ C ₆ carbide, which contributes to the improvement of strength characteristics. In order to obtain such an effect, the Cr content is preferably 11.0 mass% or more. The Cr content is preferably 12.0 mass% or more, more preferably 12.3 mass% or more.

On the other hand, Cr is a ferrite stabilizing element. Therefore, when the Cr content becomes excessive, austenite becomes unstable and the formation of the embrittled phase σ phase and Laves phase is promoted. As a result, the hot workability and the mechanical properties such as strength and impact value are deteriorated. Therefore, the Cr content is preferably 19.0 mass% or less. The Cr content is preferably 17.0 mass% or less, more preferably 16.0 mass% or less.

(3) 1.0 ≤ Co ≤ 22.0 mass%:
Co dissolves in the austenite phase, which is the parent phase of the Ni-based alloy, to improve workability. In addition, Co promotes the precipitation of the γ'phase and improves the high temperature strength such as tensile properties. In order to obtain such an effect, the Co content is preferably 1.0 mass% or more. The Co content is preferably 15.0 mass% or more, more preferably 19.0 mass% or more.
On the other hand, since Co is expensive, excessive addition leads to high cost. Therefore, the Co content is preferably 22.0 mass% or less.

(4) 0.5 ≤ Fe ≤ 10.0 mass%:
Fe dissolves in the austenite phase, which is the parent phase of the Ni-based alloy. If the amount of Fe is small, there is no effect on the strength characteristics and workability. Further, Fe is a component that may be mixed in the raw material at the time of alloy production, and although the Fe content becomes large depending on the selection of the raw material, it leads to a reduction in the raw material cost. In order to obtain such an effect, the Fe content is preferably 0.5 mass% or more. The Fe content is preferably 0.95 mass% or more, and more preferably 1.0 mass% or more.
On the other hand, when the Fe content becomes excessive, the strength decreases. Therefore, the Fe content is preferably 10.0 mass% or less. The Fe content is preferably 7.0 mass% or less, more preferably 5.0 mass% or less.

(5) 2.5 ≤ Mo ≤ 5.0 mass%:
Mo is a solid solution strengthening element and is solid solution into the austenite phase, which is the parent phase of the Ni-based alloy, to strengthen the alloy. In addition, Mo binds to C to form carbides, strengthens grain boundaries, and contributes to improvement of mechanical strength. In order to obtain such an effect, the Mo content is preferably 2.5 mass% or more. The Mo content is preferably 3.0 mass% or more.
On the other hand, when the Mo content becomes excessive, the formation of σ phase and Laves phase, which are harmful phases, is promoted, and hot workability and mechanical properties are deteriorated. Therefore, the Mo content is preferably 5.0 mass% or less.

(6) 1.0 ≤ W ≤ 5.0 mass%:
W is a solid solution strengthening element and is solid solution into the austenite phase, which is the parent phase of the Ni-based alloy, to strengthen the alloy. Further, W combines with C to form carbides, strengthens grain boundaries, and contributes to improvement of mechanical strength. In order to obtain such an effect, the W content is preferably 1.0 mass% or more. The W content is preferably 2.0 mass% or more, and more preferably 2.5 mass% or more.
On the other hand, when the W content becomes excessive, the formation of the σ phase and the Raves phase, which are harmful phases, is promoted, and the hot workability and mechanical properties are deteriorated. Therefore, the W content is preferably 5.0 mass% or less. The W content is preferably 4.5 mass% or less, more preferably 4.0 mass% or less.

(7) 0.3 ≦ Nb ≦ 2.0 mass%:
Nb combines with C to form MC-type carbides with a relatively high solid solution temperature. Therefore, when Nb is added, coarsening of crystal grains after solution heat treatment is suppressed due to the pinning effect, and high-temperature strength characteristics and hot workability are improved. Further, Nb replaces the Al site of the γ'phase _{(Ni 3} Al), which is a strengthening phase, together with _{Ti, and becomes Ni 3} (Al, Ti, Nb) to solidify and strengthen the γ'phase. In order to obtain such an effect, the Nb content is preferably 0.3 mass% or more. The Nb content is preferably 0.7 mass% or more, more preferably 1.0 mass% or more.

On the other hand, when the Nb content becomes excessive, the solid solution temperature of the γ'phase rises and the hot workability decreases. In addition, a Laves phase, which is an embrittlement phase, is formed, which causes a decrease in high-temperature strength. Therefore, the Nb content is preferably 2.0 mass% or less. The Nb content is preferably 1.5 mass% or less.

(8) 3.0 ≤ Al ≤ 4.0 mass%:
_{Al acts as a forming element of the γ'phase (Ni 3} Al), which is a strengthening phase, and is an element particularly important for improving high-temperature strength characteristics. Further, Al raises the solid solution temperature of the γ'phase, but has a smaller effect on the rise in the solid solution temperature than Nb and Ti. Rather, Al has the effect of increasing the amount of γ'phase precipitated in the aging temperature range while suppressing the rise in the solid solution temperature of the γ'phase. Further, Al combines with O _{to form a protective oxide film composed of Al 2 O 3,} which is also effective in improving corrosion resistance and oxidation resistance. In order to obtain such an effect, the Al content is preferably 3.0 mass% or more. The Al content is preferably 3.5 mass% or more.

On the other hand, when the Al content becomes excessive, the solid solution temperature of the γ'phase rises. In addition, the amount of γ'phase precipitated may increase and the hot workability may decrease. Therefore, the Al content is preferably 4.0 mass% or less.

(9) 0.2 ≤ Ti ≤ 2.49 mass%:
Ti combines with C to form MC-type carbides with a relatively high solid solution temperature. Therefore, when Ti is added, coarsening of crystal grains after solution heat treatment is suppressed due to the pinning effect, and high-temperature strength characteristics and hot workability are improved. Further, Ti replaces the Al site of the γ'phase _{(Ni 3} Al), which is a strengthening phase, together with _{Nb, and becomes Ni 3} (Al, Ti, Nb) to solidify and strengthen the γ'phase. In order to obtain such an effect, the Ti content is preferably 0.2 mass% or more. The Ti content is preferably 0.23 mass% or more, more preferably 0.5 mass% or more.

On the other hand, when the Ti content becomes excessive, the solid solution temperature of the γ'phase rises and the hot workability decreases. In addition, a Laves phase, which is an embrittlement phase, is formed, which causes a decrease in high-temperature strength. Therefore, the Ti content is preferably 2.49 mass% or less. The Ti content is preferably 2.0 mass% or less.

[1.1.2. Sub-components]
The Ni-based alloy may further contain one or more of the following elements in addition to the main constituent elements described above. The types of additive elements, their component ranges, and the reasons for their limitation are as follows.

(10) 0.09 ≤ Si ≤ 0.15 mass%:
When Si is added, a scale layer of Si oxide is formed and the oxidation resistance is improved. In order to obtain such an effect, the Si content is preferably 0.09 mass% or more.
However, when the Si content becomes excessive, Si segregates to form a locally low melting point portion, which lowers the hot workability. Therefore, the Si content is preferably 0.15 mass% or less. The Si content is preferably 0.10 mass% or less.

(11) 1.0 ≤ Ta ≤ 2.0 mass%:
Ta combines with C to form MC-type carbides with a relatively high solid solution temperature. Therefore, when Ta is added, coarsening of crystal grains after solution heat treatment is suppressed due to the pinning effect, and high-temperature strength characteristics and hot workability are improved. Further, Ta replaces the Al site of the γ'phase _{(Ni 3} Al), which is a strengthening phase, together with Nb and Ti, _{and becomes Ni 3} (Al, Ti, Nb, Ta) to solidify and strengthen the γ'phase. .. In order to obtain such an effect, the Ta content is preferably 1.0 mass% or more.

On the other hand, when the Ta content becomes excessive, the solid solution temperature of the γ'phase rises and the hot workability decreases. In addition, a Laves phase, which is an embrittlement phase, is formed, which causes a decrease in high-temperature strength. Therefore, the Ta content is preferably 2.0 mass% or less. The Ta content is preferably 1.5 mass% or less.

(12) 0.001 ≤ B ≤ 0.03 mass%:
B segregates at the grain boundaries to strengthen the grain boundaries and improve workability and mechanical properties. In order to obtain such an effect, the B content is preferably 0.001 mass% or more. The B content is preferably 0.01 mass% or more.
On the other hand, when the B content becomes excessive, ductility is lost due to excessive segregation at the grain boundaries, and hot workability is lowered. Therefore, the B content is preferably 0.03 mass% or less. The B content is preferably 0.025 mass% or less, more preferably 0.02 mass% or less.

(13) 0.04 ≤ Zr ≤ 0.1 mass%:
Zr segregates at the grain boundaries to strengthen the grain boundaries and improve workability and mechanical properties. In order to obtain such an effect, the Zr content is preferably 0.04 mass% or more. The Zr content is preferably 0.045 mass% or more.
On the other hand, when the Zr content becomes excessive, ductility is lost due to excessive segregation at the grain boundaries, and hot workability is lowered. Therefore, the Zr content is preferably 0.1 mass% or less.

[1.2. Liquid phase density difference]
[1.2.1. Suitable range of Δρ]
The Ni-based alloy according to the present invention comprises an alloy having a liquid phase density difference Δρ of more than −0.05 and less than 0.015. Here, the "liquid phase density difference Δρ" means a value represented by the following equation (1).
Δρ ＝ ρ ₀ −ρ _0.35 … (1)
However,
ρ ₀ ^{is the density (g / cm 3} ) of the mother-liquid phase (solid phase ratio: zero) of the Ni alloy.
ρ _0.35 ^{is the density (g / cm 3} ) of the concentrated liquid phase (solid phase ratio: 0.35) of the Ni alloy.

When the Ni-based alloy is slowly solidified, dendrite nuclei are formed on the casting wall, and the dendrite grows toward the inside of the mold. At this time, the solute is distributed into the solid phase and the liquid phase at a predetermined ratio. Normally, as the solidification progresses, the solute is swept out from the solid phase, so that the concentration of the solute in the liquid phase increases. As a result, a concentrated liquid phase having a density different from that of the mother liquid phase (solid phase ratio: zero) may be generated during solidification. The difference between the density of the mother-liquid phase and the density of the concentrated liquid phase (difference in liquid-phase density) Δρ differs depending on the solid phase ratio. _{In the present invention, the density ρ 0.35} of the concentrated liquid phase when the solid phase ratio is 0.35 is used for calculating the liquid phase density difference Δρ. This is because Δρ is often the maximum when the solid phase ratio is 0.35.

Freckell segregation is thought to grow with the liquid phase density difference Δρ between the mother liquid phase and the concentrated liquid phase as the driving force. Therefore, in general, the smaller the absolute value of Δρ, the less likely it is that Feckel segregation will occur.
In order to produce an ingot having an industrial size (for example, a diameter of about 150 mm to 1000 mm) and having no Freckell segregation in a general-purpose manufacturing facility, Δρ is more than -0.050 and less than 0.015. Must be.

[1.2.2. Relationship between Δρ and the critical value α of Freckell segregation]
The “critical value α for Feckel segregation formation” means a value represented by the following equation (2).
α = V × R ^1.1 … (2)
However,
V is the cooling rate (° C./nin) when the Ni-based alloy solidifies.
R is the solidification rate (mm / min) when the Ni-based alloy solidifies.

It is known that there is a correlation between the critical value α (= V × R ^1.1 ) for the formation of Freckell segregation and Δρ, and that Freckell segregation is likely to occur when the cooling conditions during solidification fall below the critical value α. ..
Therefore, even when the critical value α under the actual manufacturing conditions is unknown, if Δρ can be known, it is possible to accurately predict whether or not Freckell segregation is generated to some extent.
Further, when Δρ is in the above range, it is difficult for Freckell segregation to occur, but when Freckell segregation still occurs, it means that the cooling condition is below the critical value α. In such a case, the content of the alloying element should be changed so that the absolute value of Δρ becomes smaller, or the cooling condition should be higher than the critical value α (that is, the quenching condition should be obtained). ), The manufacturing method and / or the manufacturing conditions may be changed.

Various empirical formulas have been conventionally proposed as empirical formulas expressing the relationship between Δρ and α. However, conventionally, it is common to discuss the relationship between Δρ and α without distinguishing whether the alloy is a floating type (Δρ ≧ 0) or a sedimentation type (Δρ <0). rice field.

On the other hand, the correlation between Δρ and α differs greatly depending on whether the alloy is a floating type (Δρ ≧ 0) or a sedimentation type (Δρ <0). This point is the first finding found by the inventors of the present application. Therefore, if the prediction formula expressing the relationship between Δρ and α is divided into the case of the floating type (Δρ ≧ 0) and the case of the sedimentation type (Δρ <0) and obtained in advance, the Flekkel segregation The presence or absence can be predicted with some accuracy.

The relationship between Δρ and α (prediction formula) generally differs depending on the type of alloy. However, for a group of alloys that can be considered to have similar composition and properties, α can be estimated using a set of prediction formulas.
Here, "a group of alloys that can be regarded as having similar compositions and properties" is defined as
(A) Contains the same main constituent elements
(B) It has the same crystal structure and has the same crystal structure.
(C) An alloy having similar physical and chemical properties.

For example, when the alloy is a Ni-based alloy containing the above-mentioned main constituent elements and the Ni-based alloy is a floating type (Δρ ≧ 0), it is preferable to use the following formula (3) as the prediction formula. On the other hand, when the Ni-based alloy is of the precipitation type (Δρ <0), it is preferable to use the following formula (4) as the prediction formula.
V × R ^1.1 = 353.42Δρ + 4.11 ・ ・ ・ (3)
V × R ^1.1 = 167.64 Δρ −0.29 ・ ・ ・ (4)
Note that "V × R ^1.1 " does not actually take a negative value, but when Δρ takes a negative value, V × R ^1.1 is represented by a negative value for convenience.

Since the equilibrium partition coefficient of the solute is known, Δρ can be calculated by theoretical calculation once the alloy composition is determined. On the other hand, the critical value α of the alloy having a certain composition can be obtained by a unidirectional solidification test (specifically, a vertical unidirectional solidification test is preferable, but the present invention is not limited to this). for that reason,
(A) From a group of alloys, a plurality (preferably two or more) of alloy compositions having Δρ significantly different from each other, one having Δρ ≧ 0 and the other having Δρ <0, are selected.
(B) A solidification test was performed on each of the selected alloy compositions.
(C) The Δρ obtained from the theoretical calculation and the critical value α (= V × R ^1.1 ) obtained from the solidification test are divided into a straight line when Δρ ≧ 0 and when Δρ <0, respectively. By regressing, a prediction formula can be obtained.

[1.2.3. How to adjust Δρ]
In Ni-based alloys, the alloying elements are
(A) Elements whose Δρ increases as the content increases (hereinafter, also referred to as “positive elements”),
(B) Elements whose Δρ decreases as the content increases (hereinafter, also referred to as “negative elements”), and
(C) Elements that have little effect on Δρ even if the content is increased or decreased (hereinafter, also referred to as "neutral elements")
It is roughly divided into.
Therefore, Δρ can be maintained within a predetermined range by increasing or decreasing the content of each alloy element according to the purpose. Further, by optimizing the selection of alloying elements that increase or decrease the content, it is possible to suppress the formation of Feckel segregation without impairing the production efficiency and the required properties (for example, high temperature tensile strength).

Examples of positive elements include Al and the like.
Examples of the negative element include Mo, Nb, Ti, Zr, C, W (provided that the content is 2.5 mass% or more).
Examples of the neutral element include Cr, Co, Fe, and W (provided that the content is 2.5 mass% or less).

[1.3. High temperature tensile strength]
By optimizing the content of alloying elements, it is possible to obtain a Ni-based alloy that is substantially free of Flekkel segregation. Further, when such a Ni-based alloy is appropriately heat-treated, a Ni-based alloy having a structure in which the γ'phase is precipitated in the matrix phase and having a high high-temperature tensile strength can be obtained.
Specifically, when the content of each alloy element and the heat treatment conditions are optimized, the tensile strength at 650 ° C. becomes 1200 MPa or more.
When the content of the alloying element is further optimized, the tensile strength at 650 ° C. becomes 1300 MPa or more.

[2. Manufacturing method of Ni-based alloy]
The method for producing a Ni-based alloy according to the present invention is
When Δρ ≧ 0 (floating), the prediction formula expressing the relationship between the liquidus density difference Δρ (= ρ _{0 −ρ 0.35} ) of the Ni-based alloy and the critical value α (= V × R ^{1.1) of Feckel segregation formation} Type) and when Δρ <0 (precipitation type), respectively, the prediction formula acquisition process to be acquired in advance, and the prediction formula acquisition process.
A Δρ calculation step of calculating _{the liquidus density difference Δρ X} of the alloy (X) based on the composition of the alloy (X) to be produced, and
A critical value calculation step of substituting the calculated Δρ _{X into the prediction formula to calculate the critical value α X} of the Freckell segregation formation of the alloy (X).
It includes an alloy manufacturing process for manufacturing the alloy (X) under the condition of _{α X or more.}
However,
ρ ₀ ^{is the density (g / cm 3} ) of the mother-liquid phase (solid phase ratio: zero) of the Ni alloy.
ρ _0.35 ^{is the density (g / cm 3} ) of the concentrated liquid phase (solid phase ratio: 0.35) of the Ni alloy.
V is the cooling rate (° C./min) when the Ni-based alloy solidifies.
R is the solidification rate (° C./min) when the Ni-based alloy solidifies.

Specifically, the alloy manufacturing process
(A) A melting and casting step in which raw materials blended to have a predetermined composition are melted and cast under conditions of _{α X or higher.}
(B) A soaking process in which the obtained ingot is homogenized and heat-treated, and
(C) A hot working step of performing hot working on the material after homogenization heat treatment, and
(D) A solution heat treatment step of performing a solution heat treatment on the material after hot working,
(E) It is provided with an aging treatment step of performing an aging treatment on the material after the solution heat treatment.

[2.1. Prediction formula acquisition process]
First, when the prediction formula expressing the relationship between the liquid phase density difference Δρ (= ρ _{0 −ρ 0.35} ) of the Ni-based alloy and the critical value α (= V × R ^{1.1) of the Freckel segregation formation is Δρ ≧ 0.} It is divided into (floating type) and the case where Δρ <0 (precipitation type), and each is acquired in advance (prediction formula acquisition step). Since the details of the prediction formula acquisition process are as described above, the description thereof will be omitted.

[2.2. Δρ calculation process]
_{Next, the liquidus density difference Δρ X} of the alloy (X) is calculated based on the composition of the alloy (X) to be produced (Δρ calculation step). Since the details of the Δρ calculation step are as described above, the description thereof will be omitted.

[2.3. Critical value calculation process]
Next, the calculated Δρ _X is substituted into the prediction formula, and the critical value α _X of the Freckell segregation formation of the alloy (X) is calculated (critical value calculation step). The details of the critical value calculation step are as described above, and thus the description thereof will be omitted.

[2.4. Alloy manufacturing process]
Next, the alloy (X) is manufactured under the condition of _{α X or higher (alloy manufacturing step).}
[2.4.1. Melting / casting process]
First, the raw materials blended so as to have a predetermined composition are _{melted and cast under the condition of α X} or more (melting / casting step). The melting / casting method and conditions are not particularly limited, and the optimum method and conditions can be selected according to the purpose. Examples of the melting / casting method include an electroslag remelting (ESR) method and a vacuum arc remelting (VAR) method.

[2.4.2. Homogenization heat treatment process]
Next, the obtained ingot is subjected to a homogenizing heat treatment. The homogenization heat treatment is performed to remove segregation generated during casting. The conditions of the homogenizing heat treatment are not particularly limited as long as such effects are obtained. Usually, the homogenizing heat treatment is performed by heating and holding the ingot under the conditions of temperature: 1100 ° C. to 1220 ° C. and time: 10 hr or more.

[2.4.3. Hot forging process]
Next, the material after the homogenization heat treatment is hot forged. Hot forging is performed to destroy the coarse cast structure and miniaturize the structure. The conditions for hot forging are not particularly limited as long as such effects are exhibited. Usually, hot forging is performed by heating the material under the conditions of 1100 ° C. to 1160 ° C., forging under the condition of forging end temperature: 1100 ° C., and then air-cooling. The hot forging may be continuously performed after the homogenizing heat treatment without cooling the material to room temperature.

[2.4.4.4. Solution heat treatment process]
Next, the material after hot forging is subjected to solution heat treatment. The solution heat treatment is performed to make the material austenite single phase. The conditions of the solution heat treatment are not particularly limited as long as such effects are obtained. Usually, the solution heat treatment is performed by heating and cooling the material under the conditions of temperature: 1000 ° C. to 1160 ° C. × heating time: 3 hr to 5 hr. Examples of the cooling method include air cooling, impulse cooling, oil cooling, and water cooling.

[2.4.5. Aging process]
Next, the material after the solution heat treatment is subjected to an aging treatment. The aging treatment is carried out to precipitate the γ'phase in the mother phase. The conditions of the aging treatment are not particularly limited as long as they exert such an effect. Usually, the aging treatment is performed by heating the material at 700 ° C. to 900 ° C. for 10 hr to 24 hr. After heat treatment, it is cooled by air cooling.

[3. Action]
When the Ni-based alloy is slowly solidified, the solute is distributed into the solid phase and the liquid phase at a predetermined ratio as the solidification progresses. As a result, during solidification, a concentrated liquid phase having a density different from that of the mother liquid phase is generated. Freckell segregation is thought to grow with the liquid phase density difference Δρ between the mother liquid phase and the concentrated liquid phase as the driving force. In general, the larger Δρ, the larger the Freckel segregation.

On the other hand, each alloy element is roughly classified into an element that increases Δρ, an element that decreases Δρ, and an element that has almost no effect on Δρ. Therefore, if the content of other elements is increased or decreased while maintaining the content of the element essential for obtaining the desired property, Δρ can be kept within a predetermined range. As a result, the formation of Freckell segregation can be suppressed without impairing production efficiency and required properties (eg, high temperature tensile strength).

(Examples 1 to 24, Comparative Examples 1 to 7)
[1. Preparation of sample]
50 kg of Ni-based alloys having the chemical components shown in Table 1 were melted in a high-frequency induction furnace. The molten ingot was subjected to a homogenization heat treatment at 1100 to 1220 ° C. for 16 hours. Then, a rod having a diameter of 30 mm was hot forged.
Next, the hot forged material was subjected to a solution heat treatment at 1000 to 1160 ° C. Further, the material after the solution heat treatment was subjected to one-step or two-step or more aging treatment at 700 to 900 ° C.

[2. Test method]
[2.1. Calculation of liquidus density difference Δρ]
Thermophysical properties calculation software: JMatPro using (R), the density was calculated [rho _0.35 thickening liquid phase when the density [rho ₀ of the mother liquid phase and solid phase ratio is 0.35. Further, the liquid phase density difference Δρ was calculated from the density of the mother liquid phase and the density of the concentrated liquid phase.

[2.2. VR ^1.1 Forecast]
When the calculated liquidus density difference Δρ was a floating type (Δρ ≧ 0), it was substituted into the above equation (3) to obtain ^{VR 1.1.}
When the calculated liquidus density difference Δρ is a sedimentation type (Δρ <0), it is substituted into the above equation (4) to obtain ^{VR 1.1.}

[2.3. Presence or absence of freckle defects]
The prepared sample was cut, and the cut surface was observed with a macrostructure to confirm the presence or absence of Freckell defects.
[2.4. High temperature tensile test]
After the solution heat treatment of the forged material, one step or two or more steps of aging treatment were carried out. Then, a sample having a parallel portion diameter of 8 mm and a gauge point distance of 40 mm was prepared and subjected to a high-temperature tensile test in accordance with JIS G 0567. The test temperature was 650 ° C.

[3. result]
Table 1 shows the results. Further, FIG. 1 shows the relationship between the liquid phase density difference Δρ and VR ^1.1. From Table 1 and FIG. 1, the following can be seen.

(1) When the liquidus density difference Δρ was more than −0.05 and less than 0.015, an ingot without Freckell defects was obtained.
(2) If a Freckell defect occurs during casting, the high-temperature tensile strength is low even after aging treatment. On the other hand, when the Freckell defect did not occur during casting, the high-temperature tensile strength was 1200 MPa or more due to the aging treatment.

(Example 25)
[1. Test method]
The composition of Example 1 was used as the base composition. The liquidus density difference Δρ was calculated by theoretical calculation for the sample in which the content of some elements contained in the base composition was increased or decreased. Further, the critical value α (predicted value) of Feckel segregation was calculated using the above-mentioned equations (3) and (4).

[2. result]
It was estimated how Δρ changes when the element (M) content deviates from the base composition by Δx (mass%). 2 (A) to 2 (F) show the influence of the difference Δx in the contents of C, Cr, Co, Fe, Mo, or W on the liquid phase density difference Δρ, respectively. 3 (A) to 3 (D) show the influence of the difference Δx in the contents of Nb, Ti, Zr, or Al on the liquid phase density difference Δρ, respectively. The following can be seen from FIGS. 2 and 3.

(1) The influence of Δx on Δρ was significantly different depending on the type of element (M). The element (M) is roughly classified into those in which Δρ increases, those in which Δρ decreases, and those in which Δρ does not increase or decrease as Δx increases.
(2) Among the elements (M), Al and Mo were found to have a large change in Δρ with a slight change in Δx.
(3) Among the elements (M), it was found that for Mo, Nb, and Ti, Δρ decreased as Δx increased.
(4) Among the elements (M), Cr, Co, Fe, and W are the amount of change in Δρ that accompanies the change in Δx from a negative value to a value of zero, and the value of Δx from a value of zero to a positive value. It was found that the amount of change in Δρ with the change of was different in two stages.
(5) Among the elements (M), it was found that Δρ of Al increases as Δx increases.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The Ni-based alloy according to the present invention can be used for moving blades, stationary blades, turbochargers and the like of turbines.

Claims (13)

A Ni-based alloy having a liquidus density difference Δρ (= ρ _{0 −ρ 0.35} ) of more than −0.05 and less than 0.015.
However,
ρ ₀ ^{is the density (g / cm 3} ) of the mother-liquid phase (solid phase ratio: zero) of the Ni alloy.
ρ _0.35 ^{is the density (g / cm 3} ) of the concentrated liquid phase (solid phase ratio: 0.35) of the Ni alloy. 0.05 ≤ C ≤ 0.10 mass%,
11.0 ≤ Cr ≤ 19.0 mass%,
1.0 ≤ Co ≤ 22.0 mass%,
0.5 ≤ Fe ≤ 10.0 mass%,
2.5 ≤ Mo ≤ 5.0 mass%,
1.0 ≤ W ≤ 5.0 mass%,
0.3 ≤ Nb ≤ 2.0 mass%,
3.0 ≤ Al ≤ 4.0 mass%, and
0.2 ≤ Ti ≤ 2.49 mass%
The Ni-based alloy according to claim 1, wherein the balance is composed of Ni and unavoidable impurities. 0.09 ≤ Si ≤ 0.15 mass%,
0.001 ≤ B ≤ 0.03 mass%, and
0.04 ≤ Zr ≤ 0.1 mass%
The Ni-based alloy according to claim 2, further comprising any one or more elements selected from the group consisting of. The Ni-based alloy according to claim 2 or 3, further comprising 1.0 ≦ Ta ≦ 2.0 mass%. The Ni-based alloy according to any one of claims 1 to 4, wherein the tensile strength at 650 ° C. is 1200 MPa or more. The Ni-based alloy according to any one of claims 1 to 5, wherein the tensile strength at 650 ° C. is 1300 MPa or more. When Δρ ≧ 0 (floating), the prediction formula expressing the relationship between the liquidus density difference Δρ (= ρ _{0 −ρ 0.35} ) of the Ni-based alloy and the critical value α (= V × R ^{1.1) of Feckel segregation formation} Type) and when Δρ <0 (precipitation type), respectively, the prediction formula acquisition process to be acquired in advance, and the prediction formula acquisition process.
A Δρ calculation step of calculating _{the liquidus density difference Δρ X} of the alloy (X) based on the composition of the alloy (X) to be produced, and
A critical value calculation step of substituting the calculated Δρ _{X into the prediction formula to calculate the critical value α X} of the Freckell segregation formation of the alloy (X).
A method for producing a Ni-based alloy, which comprises an alloy manufacturing step for manufacturing the alloy (X) under the condition of _{α X or more.}
However,
ρ ₀ ^{is the density (g / cm 3} ) of the mother-liquid phase (solid phase ratio: zero) of the Ni alloy.
ρ _0.35 ^{is the density (g / cm 3} ) of the concentrated liquid phase (solid phase ratio: 0.35) of the Ni alloy.
V is the cooling rate (° C./min) when the Ni-based alloy solidifies.
R is the solidification rate (° C./min) when the Ni-based alloy solidifies. The method for producing a Ni-based alloy according to claim 7, wherein the alloy (X) has a liquidus density difference Δρ (= ρ _{0 −ρ 0.35) of more than −0.050 and less than 0.015.} The alloy (X) is
0.05 ≤ C ≤ 0.10 mass%,
11.0 ≤ Cr ≤ 19.0 mass%,
1.0 ≤ Co ≤ 22.0 mass%,
0.5 ≤ Fe ≤ 10.0 mass%,
2.5 ≤ Mo ≤ 5.0 mass%,
1.0 ≤ W ≤ 5.0 mass%,
0.3 ≤ Nb ≤ 2.0 mass%,
3.0 ≤ Al ≤ 4.0 mass%, and
0.2 ≤ Ti ≤ 2.49 mass%
The method for producing a Ni-based alloy according to claim 7 or 8, wherein the balance is composed of Ni and unavoidable impurities. The alloy (X) is
0.09 ≤ Si ≤ 0.15 mass%,
0.001 ≤ B ≤ 0.03 mass%, and
0.04 ≤ Zr ≤ 0.1 mass%
The method for producing a Ni-based alloy according to claim 9, further comprising any one or more elements selected from the group consisting of. The method for producing a Ni-based alloy according to claim 9 or 10, wherein the alloy (X) further contains 1.0 ≦ Ta ≦ 2.0 mass%. The method for producing a Ni-based alloy according to any one of claims 7 to 11, wherein the alloy (X) has a tensile strength of 1200 MPa or more at 650 ° C. The method for producing a Ni-based alloy according to any one of claims 7 to 12, wherein the alloy (X) has a tensile strength of 1300 MPa or more at 650 ° C.

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