CN118974299A - Alloy - Google Patents

Abstract

Provided is an alloy material which has sufficient creep strength in a high-temperature environment and which can achieve both excellent stress relaxation crack resistance and excellent weld heat crack resistance. The alloy material of the present disclosure contains, in mass%, C:0.050 to 0.100%, si: less than 1.00%, mn: less than 1.50%, P: less than 0.035%, S: less than 0.0015%, cr: 19.00-23.00%, ni: 30.00-35.00%, N: less than 0.100%, al:0.15 to 0.70 percent of Ti:0.15 to 0.70%, and B:0.0010 to 0.0050 percent, and the balance of Fe and impurities, wherein the formula (1) and the formula (2) are satisfied, al+Ti is more than 0.60 and less than 1.20 (1), and Ti/Al (2) is more than or equal to 1.12.

Description

Alloy

Technical Field

The present disclosure relates to an alloy material, and more particularly to an alloy material that can be used in a high-temperature environment.

Background Art

Alloy materials used in steam reforming devices, ethylene decomposition furnaces, heating furnace tubes for petroleum refining and petrochemical plants, and polysilicon manufacturing devices are used in high-temperature environments of 500 to 1000°C. Therefore, alloy materials used in such high-temperature environments are required to have high creep strength and excellent corrosion resistance in high-temperature environments. As alloy materials used in such high-temperature environments, alloy 800, alloy 800H, and alloy 800HT are known.

Alloy 800, Alloy 800H, and Alloy 800HT contain a large amount of Cr and Ni. Therefore, it is known that these alloy materials have excellent corrosion resistance at high temperatures. These alloy materials also contain Al and Ti. Therefore, when used in a high temperature environment, γ' (gamma prime) phase (Ni ₃ (Al, Ti)) is generated in the alloy materials. Through precipitation strengthening based on the γ' phase, these alloy materials have excellent creep strength.

However, in alloy 800, alloy 800H, and alloy 800HT, welding hot cracks are easily generated in the heat-affected zone (HAZ) during welding. Moreover, as described in non-patent documents 1 and 2, these alloy materials may generate stress relaxation cracks during use in a high-temperature environment. Therefore, alloy materials having the same chemical composition as alloy 800, alloy 800H, and alloy 800HT are required to have excellent resistance to welding hot cracks and excellent resistance to stress relaxation cracks.

In order to improve the stress relaxation cracking resistance of the above alloy material, methods of limiting the total content of Al and Ti and performing heat treatment after welding have been proposed in the past. However, if the total content of Al and Ti is limited, sufficient creep strength cannot be obtained. In addition, when heat treatment is performed after welding, there are cases where the construction cost becomes high or heat treatment cannot be performed after welding due to equipment design.

The technology for improving the stress relaxation crack resistance of alloy materials containing Al and Ti is disclosed by International Publication No. 2018/066579. In this document, in order to achieve excellent stress relaxation crack resistance in a high temperature environment, attention is paid to the γ' phase generated in the alloy material during use in a high temperature environment. In this document, in order to generate an appropriate amount of γ' phase during use in a high temperature environment, the chemical composition of the alloy material is adjusted. Therefore, it is recorded in Patent Document 1 that excellent stress relaxation crack resistance can be obtained during use in a high temperature environment.

Prior art literature

Patent Literature

Patent Document 1: International Publication No. 2018/066579

Non-patent literature

Non-patent document 1: Hans van Wortel: “Control of Relaxation Cracking in Austenitic High Temperature Components”, CORROSION 2007 (2007), NACE, Paper No. 07423

Non-patent document 2: Richard Colwell and Cathleen Shargay: "Alloy 800H: Materialand fabrication challenges associated with the mitigation of stressrelaxation cracking", ASME Pressure Vessels&Piping Conference 2020, PaperNo.2020-21842

Summary of the invention

Problem that the invention aims to solve

The alloy material described in Patent Document 1 can also obtain excellent stress relaxation crack resistance in a high temperature environment. However, excellent stress relaxation crack resistance in a high temperature environment can also be obtained by other methods. Moreover, Patent Document 1 does not provide any research on achieving both excellent stress relaxation crack resistance and excellent welding hot crack resistance.

An object of the present disclosure is to provide an alloy material having sufficient creep strength in a high temperature environment and capable of achieving both excellent stress relaxation cracking resistance and excellent welding hot cracking resistance.

Solutions for solving problems

The chemical composition of the alloy material disclosed in the present invention is expressed in mass %.

C: 0.050～0.100％,

Si: 1.00% or less,

Mn: 1.50% or less,

P: 0.035% or less,

S: 0.0015% or less,

Cr: 19.00～23.00％,

Ni: 30.00～35.00％,

N: 0.100% or less,

Al: 0.15-0.70%,

Ti: 0.15-0.70%,

B: 0.0010～0.0050％,

Nb: 0-0.30%,

Ta: 0～0.50％,

V: 0～1.00％,

Zr: 0～0.10％,

Hf: 0～0.10％,

Cu: 0-1.00%,

Mo: 0-1.00%,

W: 0～1.00％,

Co: 0-1.00%,

Ca: 0～0.0200％,

Mg: 0～0.0200％,

Rare earth elements: 0 to 0.1000%, and

The balance is Fe and impurities.

The chemical composition satisfies formula (1) and formula (2),

0.60＜Al+Ti＜1.20 (1),

1.12≤Ti/Al (2),

In formula (1) and formula (2), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

Effects of the Invention

The alloy material disclosed in the present invention has sufficient creep strength in a high temperature environment, and can achieve both excellent stress relaxation crack resistance and excellent welding hot crack resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a mechanism of stress relaxation cracking occurring in an alloy material having a content of each element in a chemical composition within the range of the present embodiment during use in a high temperature environment.

DETAILED DESCRIPTION

From the perspective of chemical composition, the present inventors first studied alloy materials that have sufficient creep strength in a high temperature environment and can combine excellent stress relaxation crack resistance and excellent welding hot crack resistance. As a result, the present inventors believed that if the alloy material has the following chemical composition, it is possible to have sufficient creep strength in a high temperature environment and combine excellent stress relaxation crack resistance and excellent welding hot crack resistance: in terms of mass %, C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.100% or less, Al: 0.1 5～0.70%, Ti: 0.15～0.70%, B: 0.0010～0.0050%, Nb: 0～0.30%, Ta: 0～0.50%, V: 0～1.00%, Zr: 0～0.10%, Hf: 0～0.10%, Cu: 0～1.00%, Mo: 0～1.00%, W: 0～1.00%, Co: 0～1.00%, Ca: 0～0.0200%, Mg: 0～0.0200%, rare earth elements: 0～0.1000%, and the balance is Fe and impurities.

The inventors of the present invention have also studied a method for improving the creep strength in a high temperature environment in an alloy material having the above-mentioned chemical composition. As a result, it was found that if the following formula (1) is satisfied in an alloy material having the above-mentioned range of each element content in the chemical composition, the creep strength in a high temperature environment is sufficiently improved.

0.60＜Al+Ti＜1.20 (1)

In the formula (1), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

The present inventors have also studied the balance between excellent stress relaxation crack resistance and excellent welding hot crack resistance. Specifically, the present inventors first investigated the mechanism of stress relaxation cracking when the alloy material having the above chemical composition is used in a high temperature environment. As a result, the present inventors obtained the following insights.

FIG. 1 is a diagram for explaining the mechanism of stress relaxation cracking in an alloy material having a content of each element in the chemical composition within the range of the present embodiment during use in a high temperature environment. The horizontal axis of FIG. 1 represents time. The vertical axis of FIG. 1 represents elongation or strain. The curve CRD0 of FIG. 1 represents creep rupture elongation. The curve IS0 represents the strain accumulated in the Cr-poor region within the grain with creep deformation.

In general, alloy materials used in high temperature environments are subjected to solution treatment in the manufacturing process of the alloy materials to dissolve the precipitates in the alloy materials. In the manufacturing process, the precipitates are fully dissolved in the alloy materials, so that the γ' phase is generated during use in the high temperature environment. By precipitation strengthening based on the γ' phase, a higher creep strength can be obtained.

When such an alloy material is used in a high temperature environment, the creep rupture elongation CRD0 gradually decreases with the passage of time from the beginning of use in the high temperature environment as shown in Figure 1. On the other hand, the above-mentioned γ' phase is generated inside the alloy material from the beginning of use in the high temperature environment (that is, the beginning of the stress relaxation process).

During the use of alloy materials in high temperature environments, not only the above-mentioned γ' phase is generated, but also TiC is generated. Due to the generation of TiC, Cr-poor regions are generated near the grain boundaries. In the Cr-poor regions, the strength is lower than that in other regions within the grains. Therefore, during the stress relaxation process, creep strain tends to concentrate in the Cr-poor regions. The dislocations that constitute the strain are captured by TiC in the Cr-poor regions. As time passes, the amount of TiC generated in the Cr-poor regions increases. Therefore, the amount of dislocations captured by TiC also increases. Therefore, the creep strain amount IS0 in the Cr-poor regions also increases. At time t0 when the increased creep strain amount IS0 exceeds the creep rupture elongation CRD0, stress relaxation cracks occur in the alloy material.

As described above, the increase in creep strain, which is the main cause of stress relaxation cracking, occurs in the Cr-poor region, and the Cr-poor region is generated due to the generation of TiC. Therefore, the present inventors believe that stress relaxation cracking is more affected by TiC than by the γ' phase. Therefore, the present inventors paid attention to TiC in the alloy material during the stress relaxation process.

The inventors of the present invention first thought that the generation of TiC can be suppressed during the stress relaxation process. In order to suppress TiC, the Ti content in the alloy material can be reduced. However, if the Ti content does not satisfy formula (1), sufficient γ' phase is not generated during use in a high temperature environment. In this case, sufficient creep strength cannot be obtained in a high temperature environment.

Therefore, the inventors of the present invention reversed the idea and thought of: instead of suppressing the generation of TiC, a certain degree of TiC is generated in the alloy material before use in a high temperature environment. And, using such an alloy material, the stress relaxation crack resistance was investigated. As a result, it was found that the stress relaxation crack resistance was improved.

When the alloy material contains a certain amount of TiC before use in a high temperature environment, a certain amount of TiC is generated in the manufacturing process of the alloy material. Due to the pinning effect of the TiC, the grains in the alloy material become fine. If the grains in the alloy material are fine, the creep rupture elongation increases from CRD0 to CRD1.

Moreover, in the initial stage of the stress relaxation process, TiC is generated in the Cr-poor region as in the previous case. However, for the alloy material before being used in a high temperature environment, TiC already exists in a certain amount. Therefore, in the initial stage of the stress relaxation process, the generation of TiC is saturated. And after the generation of TiC is saturated, the TiC that has been generated coarsens. Due to the coarsening of TiC, the dislocations captured by TiC are separated from TiC. As a result, the amount of creep strain accumulated in the Cr-poor region is reduced. Therefore, the amount of creep strain accumulated in the Cr-poor region becomes a curve such as IS1 in Figure 1.

The peak value of creep strain IS1 is formed at the initial stage of the stress relaxation process. The peak time of creep strain IS1 is equivalent to the time when the generation of TiC is saturated. In the initial stage of the stress relaxation process, the creep rupture elongation CRD1 is higher than the peak value of creep strain IS1. In addition, if the creep strain IS1 exceeds the peak value, it will gradually decrease over time. Therefore, the time when creep rupture elongation CRD1 intersects with creep strain IS1 is later than time t0. As a result, the stress relaxation crack resistance is improved.

Furthermore, as described above, when the alloy material contains a certain amount of TiC, the crystal grains in the alloy material become finer. Therefore, the resistance to welding hot cracking during welding is also improved. Therefore, it is possible to achieve both excellent stress relaxation cracking resistance and excellent welding hot cracking resistance.

In addition, if the grains become fine, there is a possibility that the creep strength will decrease. However, as mentioned above, the alloy material contains a certain degree of TiC in advance, and when used in a high temperature environment, not only the γ' phase but also TiC is generated. The existing TiC and the newly generated TiC during use in a high temperature environment precipitate strengthen the alloy material. Therefore, it is possible to maintain sufficient creep strength in a high temperature environment.

Based on the above findings, the present inventors studied the appropriate amount of TiC in an alloy material in order to have sufficient creep strength in a high temperature environment and to achieve both excellent stress relaxation cracking resistance and excellent welding hot cracking resistance. As a result, the following findings were obtained.

In order to generate a certain amount of TiC in an alloy material having the contents of each element in the chemical composition within the above range, the Ti content must be higher than the Al content. Specifically, the Ti content and the Al content are assumed to satisfy the formula (2).

1.12≤Ti/Al (2)

In the formula (2), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

If the content of each element in the chemical composition is within the above range and satisfies formula (1) and formula (2), an appropriate amount of TiC is present in the alloy material. In this case, stress relaxation cracking resistance can be improved, and welding hot cracking resistance during welding construction is also improved. In addition, when used in a high temperature environment, sufficient creep strength can be obtained due to the formation of γ' phase and TiC.

The alloy material of the present embodiment completed based on the above findings has the following configuration.

[1] An alloy material having a chemical composition in mass % as follows:

C: 0.050～0.100％,

Si: 1.00% or less,

Mn: 1.50% or less,

P: 0.035% or less,

S: 0.0015% or less,

Cr: 19.00～23.00％,

Ni: 30.00～35.00％,

N: 0.100% or less,

Al: 0.15-0.70%,

Ti: 0.15-0.70%,

B: 0.0010～0.0050％,

Nb: 0-0.30%,

Ta: 0～0.50％,

V: 0～1.00％,

Zr: 0～0.10％,

Hf: 0～0.10％,

Cu: 0-1.00%,

Mo: 0-1.00%,

W: 0～1.00％,

Co: 0-1.00%,

Ca: 0～0.0200％,

Mg: 0～0.0200％,

Rare earth elements: 0 to 0.1000%, and

The balance is Fe and impurities.

The chemical composition satisfies formula (1) and formula (2),

0.60＜Al+Ti＜1.20 (1),

1.12≤Ti/Al (2),

Wherein, the content of the corresponding element in the chemical composition of the alloy material is substituted in mass % at each element symbol in formula (1) and formula (2).

[2] The alloy material according to [1], wherein, when the Ti content in the residue obtained by electrolytic extraction is defined as [Ti] _R in mass%, the alloy material further satisfies the formula (3),

0.050＜[Ti] _R ＜0.72Ti-0.01(Ti/Al)-0.11 (3),

Wherein, the content of the corresponding element in the chemical composition of the alloy material is substituted in mass % at each element symbol in formula (3).

[3] The alloy material according to [1] or [2], wherein

The alloy material contains a

Nb: 0.01-0.30%,

Ta: 0.01～0.50%

V: 0.01～1.00％,

Zr: 0.01～0.10%,

Hf: 0.01～0.10％,

Cu: 0.01～1.00%,

Mo: 0.01～1.00%,

W: 0.01～1.00％,

Co: 0.01～1.00%,

Ca: 0.0001～0.0200％,

Mg: 0.0001-0.0200%, and

Rare earth elements: one or more elements of the group consisting of 0.001 to 0.1000%.

The alloy material of the present embodiment will be described in detail below. In addition, "%" related to an element means mass % unless otherwise specified.

[Characteristics of the alloy material of this embodiment]

The alloy material of this embodiment has the following characteristics.

(Feature 1)

The chemical composition is as follows in mass %: C: 0.050-0.100%, Si: 1.00% or less, Mn: 1.50% or less, P: 0.035% or less, S: 0.0015% or less, Cr: 19.00-23.00%, Ni: 30.00-35.00%, N: 0.100% or less, Al: 0.15-0.70%, Ti: 0.15-0.70%, B: 0.0010-0.0 050%, Nb: 0～0.30%, Ta: 0～0.50%, V: 0～1.00%, Zr: 0～0.10%, Hf: 0～0.10%, Cu: 0～1.00%, Mo: 0～1.00%, W: 0～1.00%, Co: 0～1.00%, Ca: 0～0.0200%, Mg: 0～0.0200%, rare earth elements: 0～0.1000%, and the balance is Fe and impurities.

(Feature 2)

The chemical composition of feature 1 also satisfies formula (1).

0.60＜Al+Ti＜1.20 (1)

In the formula (1), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

(Feature 3)

The chemical composition of feature 1 also satisfies formula (2).

1.12≤Ti/Al (2)

In the formula (2), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

The alloy material of the present embodiment satisfies the above-mentioned features 1 to 3. Therefore, the alloy material of the present embodiment has sufficient creep strength in a high temperature environment, and can achieve both excellent stress relaxation crack resistance and excellent welding hot crack resistance. Features 1 to 3 are described below.

[For (Feature 1) Chemical composition]

The chemical composition of the alloy of the present embodiment contains the following elements.

C: 0.050～0.100%

Carbon (C) improves the creep strength of the alloy material in a high temperature environment. If the C content is less than 0.050%, the above-mentioned effects cannot be fully obtained even if the contents of other elements are within the ranges of the present embodiment.

On the other hand, if the C content exceeds 0.100%, even if the contents of other elements are within the range of the present embodiment, _M23C6 type Cr carbides are generated at the grain boundaries. In this case, Cr _- poor regions are generated at the grain boundaries, thereby reducing the stress relaxation cracking resistance of the alloy material.

Therefore, the C content is 0.050 to 0.100%.

The lower limit of the C content is preferably 0.053%, more preferably 0.055%, further preferably 0.057%, further preferably 0.060%.

The upper limit of the C content is preferably 0.095%, more preferably 0.090%, further preferably 0.085%, further preferably 0.080%.

Si: 1.00% or less

Silicon (Si) is inevitably contained. That is, the Si content is greater than 0%. Si deoxidizes the alloy in the steelmaking process. Si also improves the oxidation resistance of the alloy material in a high temperature environment. As long as a small amount of Si is contained, the above-mentioned effect can be obtained to a certain extent even if the content of other elements is within the range of this embodiment. However, if the Si content is greater than 1.00%, the resistance to welding hot cracking is reduced even if the content of other elements is within the range of this embodiment. Therefore, the Si content is less than 1.00%.

The lower limit of the Si content is preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.12%, and still more preferably 0.15%.

The upper limit of the Si content is preferably 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, more preferably 0.60%, more preferably 0.55%, and more preferably 0.50%.

Mn: 1.50% or less

Manganese (Mn) is inevitably contained. That is, the Mn content is greater than 0%. Mn deoxidizes the weld of the alloy material during welding. Mn also stabilizes austenite. As long as a small amount of Mn is contained, the above-mentioned effect can be obtained to some extent. However, if the Mn content is greater than 1.50%, even if the contents of other elements are within the scope of the present embodiment, it is easy to generate σ phase (sigma phase) when used in a high temperature environment. The σ phase reduces the toughness and creep ductility of the alloy material in a high temperature environment. Therefore, the Mn content is less than 1.50%.

The lower limit of the Mn content is preferably 0.01%, more preferably 0.05%, more preferably 0.10%, more preferably 0.40%, more preferably 0.50%, and still more preferably 0.60%.

The upper limit of the Mn content is preferably 1.45%, more preferably 1.40%, more preferably 1.35%, more preferably 1.30%, more preferably 1.25%, and still more preferably 1.20%.

P: 0.035% or less

Phosphorus (P) is inevitably contained. That is, the P content is greater than 0%. P segregates at the grain boundaries of the alloy material during high-heat welding. If the P content is greater than 0.035%, even if the contents of other elements are within the range of this embodiment, the above-mentioned segregation occurs, and the stress relaxation cracking resistance decreases. Therefore, the P content is 0.035% or less.

The P content is preferably as low as possible. However, excessive reduction of the P content will increase the manufacturing cost of the alloy material. Therefore, considering the usual industrial production, the preferred lower limit of the P content is 0.001%, more preferably 0.002%, and more preferably 0.005%.

The upper limit of the P content is preferably 0.030%, more preferably 0.025%, further preferably 0.020%, further preferably 0.015%.

S: 0.0015% or less

Sulfur (S) is inevitably contained. That is, the S content is greater than 0%. S segregates at the grain boundaries of the alloy material during high-heat input welding. If the S content is greater than 0.0015%, even if the contents of other elements are within the range of this embodiment, the above-mentioned segregation occurs, and the stress relaxation cracking resistance decreases. Therefore, the S content is 0.0015% or less.

The S content is preferably as low as possible. However, excessive reduction of the S content will increase the manufacturing cost of the alloy material. Therefore, considering normal industrial production, the preferred lower limit of the S content is 0.0001%, and more preferably 0.0002%.

The upper limit of the S content is preferably 0.0012%, more preferably 0.0010%, further preferably 0.0008%, further preferably 0.0006%.

Cr: 19.00～23.00%

Chromium (Cr) improves the corrosion resistance of the alloy material in a high temperature environment. If the Cr content is less than 19.00%, even if the content of other elements is within the range of the present embodiment, the above-mentioned effect cannot be fully obtained. On the other hand, if the Cr content is greater than 23.00%, even if the content of other elements is within the range of the present embodiment, the stability of austenite in a high temperature environment is reduced. In this case, the creep strength of the alloy material is reduced. Therefore, the Cr content is 19.00 to 23.00%.

The lower limit of the Cr content is preferably 19.20%, more preferably 19.40%, and further preferably 19.60%.

The upper limit of the Cr content is preferably 22.50%, more preferably 22.00%, more preferably 21.50%, more preferably 21.00%, more preferably 20.50%, and more preferably 20.00%.

Ni: 30.00～35.00％

Nickel (Ni) stabilizes austenite and improves the creep strength of the alloy material in a high temperature environment. If the Ni content is less than 30.00%, even if the contents of other elements are within the range of the present embodiment, the above effects cannot be fully obtained. On the other hand, if the Ni content is greater than 35.00%, the above effects are saturated. Moreover, the cost of raw materials becomes high. Therefore, the Ni content is 30.00 to 35.00%.

The preferred lower limit of the Ni content is 30.20%, more preferably 30.40%, more preferably 30.60%, more preferably 30.80%, more preferably 31.20%, more preferably 31.40%, and more preferably 31.60%.

The upper limit of the Ni content is preferably 34.50%, more preferably 34.00%, more preferably 33.50%, and further preferably 33.00%.

N: 0.100% or less

It is inevitable to contain nitrogen (N). That is, the N content is greater than 0%. N is dissolved in the matrix (parent phase) to stabilize the austenite. The solid-solution N also forms fine nitrides in the alloy material during use in a high-temperature environment. The fine nitrides strengthen the Cr-poor region, thereby improving the stress relaxation crack resistance of the alloy material. The fine nitrides generated during use in a high-temperature environment also improve the creep strength through precipitation strengthening. As long as a small amount of N is contained, the above-mentioned effects can be obtained to some extent. However, if the N content is greater than 0.100%, coarse TiN is generated even if the content of other elements is within the range of this embodiment. Coarse TiN reduces the toughness of the alloy material. Therefore, the N content is less than 0.100%.

The preferred lower limit of the N content is 0.001%.

The preferred upper limit of the N content is 0.090%, more preferably 0.080%, more preferably 0.070%, more preferably 0.060%, more preferably 0.050%, more preferably 0.040%, more preferably 0.030%, more preferably 0.020%, and more preferably 0.010%.

Al: 0.15～0.70%

Aluminum (Al) deoxidizes the alloy material in the steelmaking process. Al also improves the oxidation resistance of the alloy material in a high temperature environment. Al also generates a γ' phase in a high temperature environment, improving the creep strength of the alloy material in a high temperature environment. If the Al content is less than 0.15%, even if the content of other elements is within the range of this embodiment, the above-mentioned effects cannot be fully obtained.

On the other hand, if the Al content is greater than 0.70%, even if the content of other elements is within the range of the present embodiment, a large amount of γ' phase is generated in the manufacturing process of the alloy material. In this case, the hot workability in the manufacturing process of the alloy material is reduced. If the Al content is greater than 0.70%, TiC cannot be fully generated. In this case, the grains in the alloy material based on TiC become insufficiently fine. Therefore, during the welding construction of the alloy material, the resistance to welding hot cracking is reduced in the welding heat affected zone of the alloy material. Moreover, the amount of Ti that satisfies formula (1) is reduced, so the TiC that is precipitated and strengthened at 700°C is reduced and the creep strength of the alloy material is not high enough. Moreover, TiC is not fully generated in the initial stage of the stress relaxation process. Therefore, the resistance to stress relaxation cracking in a high temperature environment is reduced.

Therefore, the Al content is 0.15 to 0.70%.

The lower limit of the Al content is preferably 0.17%, more preferably 0.19%, further preferably 0.21%, further preferably 0.23%.

The upper limit of the Al content is preferably 0.65%, more preferably 0.60%, more preferably 0.57%, more preferably 0.55%, more preferably 0.53%, more preferably 0.51%, more preferably 0.45%, and more preferably 0.40%.

In addition, the Al content is the content (mass %) of the so-called total Al (Total Al).

Ti: 0.15～0.70%

Titanium (Ti) combines with Ni and Al in a high temperature environment to generate γ' phase, thereby improving the creep strength of the alloy material in a high temperature environment. If the Ti content is less than 0.15%, even if the content of other elements is within the range of the present embodiment, the above-mentioned effect cannot be fully obtained. On the other hand, if the Ti content is greater than 0.70%, even if the content of other elements is within the range of the present embodiment, coarse TiC is generated. In this case, during the welding construction of the alloy material, the resistance to welding hot cracking is reduced in the welding heat affected zone of the alloy material. If the Ti content is greater than 0.70%, a large amount of γ' phase is also generated in the manufacturing process of the alloy material. In this case, the hot workability in the manufacturing process of the alloy material is reduced. Therefore, the Ti content is 0.15 to 0.70%.

The lower limit of the Ti content is preferably 0.17%, more preferably 0.19%, further preferably 0.21%, further preferably 0.25%.

The upper limit of the Ti content is preferably 0.65%, more preferably 0.60%, more preferably 0.59%, more preferably 0.57%, more preferably 0.55%, more preferably 0.50%, and more preferably 0.45%.

B: 0.0010～0.0050%

Boron (B) segregates at the grain boundaries in a high temperature environment and increases the grain boundary strength. Therefore, the stress relaxation crack resistance of the alloy material is improved. If the B content is less than 0.0010%, even if the contents of other elements are within the scope of the present embodiment, the above-mentioned effects cannot be fully obtained. On the other hand, if the B content is greater than 0.0050%, even if the contents of other elements are within the scope of the present embodiment, B promotes the formation of Cr carbides at the grain boundaries. In this case, the stress relaxation crack resistance of the alloy material is reduced. Therefore, the B content is 0.0010 to 0.0050%.

The lower limit of the B content is preferably 0.0012%, more preferably 0.0014%, and further preferably 0.0015%.

The upper limit of the B content is preferably 0.0045%, more preferably 0.0040%, further preferably 0.0035%, further preferably 0.0030%.

The balance of the chemical composition of the alloy material of this embodiment is Fe and impurities. Among them, impurities refer to elements mixed from ore, waste materials, or manufacturing environment as raw materials during industrial manufacturing of alloy materials. They are not intentionally contained elements, but are allowed elements within the range that do not have adverse effects on the alloy material of this embodiment. Representative examples of impurities are Sn, As, Zn, Pb, and Sb. The total content of these impurities is less than 0.1%.

[Optional Elements]

The chemical composition of the alloy material of this embodiment may further contain

Nb: 0-0.30%,

Ta: 0～0.50％,

V: 0～1.00％,

Zr: 0～0.10％,

Hf: 0～0.10％,

Cu: 0-1.00%,

Mo: 0-1.00%,

W: 0～1.00％,

Co: 0-1.00%,

Ca: 0～0.0200％,

Mg: 0～0.0200％,

Rare earth elements: one or more elements of the group consisting of 0 to 0.1000% are substituted for a part of Fe.

These optional elements are described below.

[For Group 1: Nb, Ta, V, Zr and Hf]

It is also possible that the chemical composition of the alloy material of the present embodiment further contains one or more elements selected from the group consisting of Nb, Ta, V, Zr and Hf to replace a portion of Fe. These elements are all combined with C to form carbides, reducing solid solution C. Thus, the generation of Cr carbides at the grain boundaries is suppressed in a high temperature environment. Therefore, the generation of Cr-deficient layers is suppressed. As a result, the stress relaxation crack resistance of the alloy material in a high temperature environment is further improved.

Nb: 0～0.30%

Niobium (Nb) is an arbitrary element and may not be contained. That is, the Nb content may also be 0%. When Nb is contained, that is, when the Nb content is greater than 0%, Nb combines with C to form carbides. By forming carbides, C is fixed and the amount of solid solution C in the alloy material is reduced. As a result, the formation of Cr carbides at the grain boundaries is suppressed in a high temperature environment. Therefore, the formation of Cr-poor regions is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. Nb also forms fine nitrides in the alloy material together with N during use in a high temperature environment. The fine nitrides strengthen the Cr-poor regions, thereby improving the stress relaxation crack resistance of the alloy material. The fine nitrides generated during use in a high temperature environment also improve the creep strength through precipitation strengthening. As long as a small amount of Nb is contained, the above-mentioned effects can be obtained to some extent.

However, if the Nb content exceeds 0.30%, even if the contents of other elements are within the ranges of the present embodiment, the weld hot cracking resistance of the weld heat affected zone of the alloy material decreases during welding of the alloy material. Therefore, the Nb content is 0 to 0.30%.

The lower limit of the Nb content is preferably 0.01%, more preferably 0.02%, further preferably 0.05%, further preferably 0.08%.

The upper limit of the Nb content is preferably 0.25%, more preferably 0.20%, and further preferably 0.15%.

Ta: 0～0.50%

Tantalum (Ta) is an arbitrary element and may not be contained. That is, the Ta content may also be 0%. When Ta is contained, that is, when the Ta content is greater than 0%, Ta combines with C to form carbides. By forming carbides, C is fixed and the amount of solid solution C in the alloy material is reduced. As a result, the formation of Cr carbides at the grain boundaries is suppressed in a high temperature environment. Therefore, the formation of Cr-poor areas is suppressed. As a result, the stress relaxation cracking resistance of the alloy material is improved. As long as a small amount of Ta is contained, the above-mentioned effect can be obtained to some extent.

However, if the Ta content exceeds 0.50%, even if the contents of other elements are within the ranges of the present embodiment, the resistance to hot cracking in the heat-affected zone of the alloy material decreases during welding of the alloy material. Therefore, the Ta content is 0 to 0.50%.

The lower limit of the Ta content is preferably 0.01%, more preferably 0.02%, further preferably 0.05%, further preferably 0.08%.

The upper limit of the Ta content is preferably 0.45%, more preferably 0.40%, further preferably 0.35%, further preferably 0.30%.

V: 0～1.00%

Vanadium (V) is an arbitrary element and may not be contained. That is, the V content may also be 0%. When V is contained, that is, when the V content is greater than 0%, V combines with C to form carbides. By forming carbides, C is fixed and the amount of solid solution C in the alloy material is reduced. As a result, the formation of Cr carbides at the grain boundaries is suppressed in a high temperature environment. Therefore, the formation of Cr-poor areas is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. As long as a small amount of V is contained, the above-mentioned effect can be obtained to some extent.

However, if the V content exceeds 1.00%, even if the contents of other elements are within the ranges of the present embodiment, the weld hot cracking resistance of the weld heat affected zone of the alloy material decreases during welding of the alloy material. Therefore, the V content is 0 to 1.00%.

The lower limit of the V content is preferably 0.01%, more preferably 0.02%, further preferably 0.04%, further preferably 0.06%.

The upper limit of the V content is preferably 0.80%, more preferably 0.50%, more preferably 0.40%, more preferably 0.35%, and further preferably 0.30%.

Zr: 0～0.10%

Zirconium (Zr) is an arbitrary element and may not be contained. That is, the Zr content may also be 0%. When Zr is contained, that is, when the Zr content is greater than 0%, Zr combines with C to form carbides. C is fixed by forming carbides, and the amount of solid solution C in the alloy material is reduced. As a result, the formation of Cr carbides at the grain boundaries is suppressed in a high temperature environment. Therefore, the formation of Cr-poor areas is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. As long as a small amount of Zr is contained, the above-mentioned effect can be obtained to some extent.

However, if the Zr content exceeds 0.10%, even if the contents of other elements are within the ranges of the present embodiment, the weld hot cracking resistance of the weld heat affected zone of the alloy material decreases during welding of the alloy material. Therefore, the Zr content is 0 to 0.10%.

The lower limit of the Zr content is preferably 0.01%, more preferably 0.02%.

The upper limit of the Zr content is preferably 0.09%, more preferably 0.08%, further preferably 0.07%, further preferably 0.06%.

Hf: 0～0.10%

Hafnium (Hf) is an arbitrary element and may not be contained. That is, the Hf content may also be 0%. When Hf is contained, that is, when the Hf content is greater than 0%, Hf combines with C to form carbides. C is fixed by forming carbides, and the amount of solid solution C in the alloy material is reduced. As a result, the formation of Cr carbides at the grain boundaries is suppressed in a high temperature environment. Therefore, the formation of Cr-poor areas is suppressed. As a result, the stress relaxation crack resistance of the alloy material is improved. As long as a small amount of Hf is contained, the above-mentioned effect can be obtained to some extent.

However, if the Hf content exceeds 0.10%, even if the contents of other elements are within the ranges of the present embodiment, the weld hot cracking resistance of the weld heat affected zone of the alloy material decreases during welding of the alloy material. Therefore, the Hf content is 0 to 0.10%.

The lower limit of the Hf content is preferably 0.01%, more preferably 0.02%.

The upper limit of the Hf content is preferably 0.09%, more preferably 0.08%, further preferably 0.07%, further preferably 0.06%.

[For Group 2: Cu, Mo, W and Co]

The chemical composition of the alloy material of the present embodiment may further contain one or more elements selected from the group consisting of Cu, Mo, W, and Co, replacing a part of Fe. These elements all increase the creep strength of the alloy material in a high temperature environment.

Cu: 0～1.00%

Copper (Cu) is an arbitrary element and may not be contained. That is, the Cu content may also be 0%. When Cu is contained, that is, when the Cu content is greater than 0%, Cu precipitates as a Cu phase in the grains during use of the alloy material in a high temperature environment. The creep strength of the alloy material is improved by precipitation strengthening. As long as a small amount of Cu is contained, the above-mentioned effect can be obtained to some extent.

However, if the Cu content is greater than 1.00%, even if the contents of other elements are within the range of the present embodiment, the Cu phase is excessively precipitated in the grains. In this case, the strength difference between the grains and the grain boundaries becomes larger. Therefore, the stress relaxation cracking resistance is reduced. Therefore, the Cu content is 0 to 1.00%.

The lower limit of the Cu content is preferably 0.01%, more preferably 0.02%, more preferably 0.05%, more preferably 0.10%, more preferably 0.15%, and more preferably 0.20%.

The upper limit of the Cu content is preferably 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.60%, more preferably 0.55%, and still more preferably 0.50%.

Mo: 0～1.00%

Molybdenum (Mo) is an arbitrary element and may not be contained. That is, the Mo content may be 0%. When Mo is contained, that is, when the Mo content is greater than 0%, Mo improves the creep strength of the alloy material by solid solution strengthening during use of the alloy material in a high temperature environment. As long as a small amount of Mo is contained, the above-mentioned effect can be obtained to some extent.

However, if the Mo content is greater than 1.00%, even if the contents of other elements are within the range of the present embodiment, intermetallic compounds such as LAVES phases are generated in the grains. In this case, secondary induced precipitation hardening increases and the strength difference between the grains and the grain boundaries increases. Therefore, stress relaxation cracking resistance decreases. Therefore, the Mo content is 0 to 1.00%.

The lower limit of the Mo content is preferably 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.04%, more preferably 0.05%, more preferably 0.10%, more preferably 0.20%, and more preferably 0.30%.

The upper limit of the Mo content is preferably 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, and further preferably 0.60%.

W: 0～1.00%

Tungsten (W) is an arbitrary element and may not be contained. That is, the W content may be 0%. When W is contained, that is, when the W content is greater than 0%, W improves the creep strength of the alloy material by solid solution strengthening during use of the alloy material in a high temperature environment. As long as a small amount of W is contained, the above-mentioned effect can be obtained to some extent.

However, if the W content is greater than 1.00%, even if the contents of other elements are within the range of the present embodiment, intermetallic compounds such as the LAVES phase are generated in the grains. In this case, secondary induced precipitation hardening increases and the strength difference between the grains and the grain boundaries increases. Therefore, the stress relaxation cracking resistance decreases. Therefore, the W content is 0 to 1.00%.

The lower limit of the W content is preferably 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.04%, more preferably 0.05%, and more preferably 0.10%.

The upper limit of the W content is preferably 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.65%, more preferably 0.60%, and more preferably 0.50%.

Co: 0～1.00%

Cobalt (Co) is an arbitrary element and may not be contained. That is, the Co content may be 0%. When Co is contained, that is, when the Co content is greater than 0%, Co stabilizes austenite and improves the creep strength of the alloy material in a high temperature environment. As long as a small amount of Co is contained, the above-mentioned effect can be obtained to some extent.

However, if the Co content exceeds 1.00%, the raw material cost becomes high. Therefore, the Co content is 0 to 1.00%.

The lower limit of the Co content is preferably 0.01%, more preferably 0.02%, more preferably 0.03%, more preferably 0.05%, and still more preferably 0.10%.

The upper limit of the Co content is preferably 0.90%, more preferably 0.80%, more preferably 0.70%, more preferably 0.60%, and still more preferably 0.50%.

[For Group 3: Ca, Mg and rare earth elements (REM)]

The chemical composition of the alloy material of the present embodiment may further contain one or more elements selected from the group consisting of Ca, Mg, and rare earth elements (REM) in place of a portion of Fe. These elements improve the hot workability of the alloy material.

Ca: 0～0.0200%

Calcium (Ca) is an arbitrary element and may not be contained. That is, the Ca content may be 0%. When Ca is contained, that is, when the Ca content is greater than 0%, Ca fixes O (oxygen) and S (sulfur) as inclusions, thereby improving the hot workability of the alloy material. Ca also fixes S and suppresses the grain boundary segregation of S. Therefore, during the welding construction of the alloy material, the welding heat affected zone (HAZ) of the alloy material improves the resistance to welding hot cracking. As long as a small amount of Ca is contained, the above-mentioned effect can be obtained to some extent.

However, if the Ca content exceeds 0.0200%, even if the contents of other elements are within the ranges of the present embodiment, the cleanliness of the alloy material decreases, and the hot workability of the alloy material decreases. Therefore, the Ca content is 0 to 0.0200%.

The lower limit of the Ca content is preferably 0.0001%, more preferably 0.0002%, further preferably 0.0005%, further preferably 0.0010%.

The upper limit of the Ca content is preferably 0.0150%, more preferably 0.0100%, more preferably 0.0080%, more preferably 0.0050%, and still more preferably 0.0040%.

Mg: 0～0.0200%

Magnesium (Mg) is an arbitrary element and may not be contained. In other words, the Mg content may be 0%.

When Mg is contained, that is, when the Mg content is greater than 0%, Mg fixes O (oxygen) and S (sulfur) as inclusions, thereby improving the hot workability of the alloy material. Mg also fixes S to suppress the grain boundary segregation of S. Therefore, during the welding of the alloy material, the HAZ of the alloy material improves the resistance to welding hot cracking. As long as a small amount of Mg is contained, the above effect can be obtained to some extent.

However, if the Mg content exceeds 0.0200%, even if the contents of other elements are within the ranges of the present embodiment, the cleanliness of the alloy material decreases, and the hot workability of the alloy material decreases. Therefore, the Mg content is 0 to 0.0200%.

The lower limit of the Mg content is preferably 0.0001%, more preferably 0.0002%, further preferably 0.0005%, further preferably 0.0010%.

The upper limit of the Mg content is preferably 0.0150%, more preferably 0.0100%, more preferably 0.0080%, more preferably 0.0050%, and still more preferably 0.0040%.

Rare earth elements: 0～0.1000%

Rare earth elements (REM) are arbitrary elements and may not be contained. That is, the REM content may be 0%. When REM is contained, that is, when the REM content is greater than 0%, REM fixes O (oxygen) and S (sulfur) as inclusions, thereby improving the hot workability of the alloy material. REM also fixes S and suppresses the grain boundary segregation of S. Therefore, during the welding construction of the alloy material, the resistance to welding hot cracking is improved in the HAZ of the alloy material. As long as a small amount of REM is contained, the above-mentioned effect can be obtained to some extent.

However, if the REM content exceeds 0.1000%, even if the contents of other elements are within the ranges of the present embodiment, the cleanliness of the alloy material decreases, and the hot workability of the alloy material decreases. Therefore, the REM content is 0 to 0.1000%.

The lower limit of the REM content is preferably 0.0001%, more preferably 0.0005%, further preferably 0.0010%, further preferably 0.0020%.

The upper limit of the REM content is preferably 0.0800%, more preferably 0.0600%, and further preferably 0.0400%.

The REM in this specification contains at least one element of Sc, Y, and lanthanoid elements (La with atomic numbers 57 to Lu with atomic numbers 71), and the REM content means the total content of these elements.

[For (Feature 2) Formula (1)]

The chemical composition of the alloy material of the present embodiment also satisfies the formula (1).

0.60＜Al+Ti＜1.20(1)

In the formula (1), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

It is defined as F1 = Al + Ti. F1 is an index of the amount of γ' phase generated. In the alloy material of this embodiment, γ' phase is generated during use in a high temperature environment. The creep strength of the alloy material in a high temperature environment is improved by this γ' phase.

Even if the content of each element in the chemical composition is within the range of the present embodiment, if F1 is 0.60 or less, a sufficient amount of γ' phase is not generated in the alloy material in a high temperature environment. In this case, the creep strength of the alloy material in a high temperature environment decreases.

On the other hand, even if the content of each element in the chemical composition is within the range of the present embodiment, if F1 is 1.20 or more, a large amount of γ' phase is excessively generated in the alloy material. In this case, the welding hot cracking resistance of the alloy material decreases. Therefore, F1 is greater than 0.60 and less than 1.20.

The preferred lower limit of F1 is 0.62, more preferably 0.64, more preferably 0.66, more preferably 0.68, and still more preferably 0.70.

The preferred upper limit of F1 is 1.15, more preferably 1.10, more preferably 1.05, more preferably 1.00, and still more preferably 0.95.

[For (Feature 3) Formula (2)]

The chemical composition of the alloy material of this embodiment also satisfies the formula (2).

1.12≤Ti/Al(2)

In the formula (2), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

It is defined as F2 = Ti/Al. F2 is an indicator of the stress relaxation cracking resistance of an alloy material in a high temperature environment.

In a high temperature environment, in order to take into account both creep strength and stress relaxation crack resistance, in the alloy material of the present embodiment, the Ti content is increased relative to the Al content. In this case, the alloy material contains a certain amount of TiC. Therefore, TiC is used to refine the grains in the alloy material. As a result, the creep rupture elongation of the alloy material in a high temperature environment is improved. In the alloy material of the present embodiment, the Ti content is also increased relative to the Al content, and the generation of TiC is saturated in the initial stage of the stress relaxation process. After the generation of TiC is saturated, TiC coarsens over time. As a result, the amount of creep strain accumulated in the Cr-poor region forms a peak value in the initial stage of the stress relaxation process. Afterwards, the amount of creep strain decreases over time. As a result, the stress relaxation crack resistance in a high temperature environment is improved. If F2 is less than 1.12, the above effect cannot be fully obtained. Therefore, F2 is above 1.12.

The preferred lower limit of F2 is 1.13, more preferably 1.15, more preferably 1.30, more preferably 1.40, and still more preferably 1.50.

The upper limit of F2 is not particularly limited. From the viewpoint of improving the oxidation resistance of the alloy material, the upper limit of F2 is preferably 4.00, more preferably 3.90, more preferably 3.70, more preferably 3.50, and more preferably 3.30.

[Preferred Forms of the Alloy Material of the Present Embodiment]

Preferably, the alloy material of the present embodiment satisfies Features 1 to 3, and further satisfies the following Feature 4.

(Feature 4)

When the Ti content in mass % in the residue obtained by the electrolytic extraction method is defined as [Ti] _R , the formula (3) is satisfied.

0.050＜[Ti] _R ＜0.72Ti-0.01(Ti/Al)-0.11(3)

In the formula (3), the content of the corresponding element in the chemical composition of the alloy material is substituted in mass %.

Feature 4 will be described below.

[For (Feature 4) Formula (3)]

[Ti] _R, which is the Ti content in the residue, is an indicator of the amount of TiC in the alloy material. In order to achieve both excellent stress relaxation cracking resistance and excellent welding hot cracking resistance, the amount of TiC and the amount of solid solution Ti in the alloy material are preferably appropriate.

If [Ti] _R is greater than 0.050, a certain amount of TiC is present in the alloy material before the alloy material is used in a high temperature environment. In this case, a pinning effect caused by TiC can be obtained. Therefore, the grains in the alloy material are refined. As a result, the creep rupture elongation of the alloy material in a high temperature environment is improved. Moreover, before the alloy material is used in a high temperature environment, a certain amount of TiC already exists in the alloy material. Therefore, as described above using FIG. 1, in high temperature use, the generation of TiC is saturated in the initial stage of the stress relaxation process. As a result, the creep strain amount in the Cr-poor region also forms a peak value in the initial stage of the stress relaxation process. Afterwards, as time passes, the creep strain amount decreases. As a result, stress relaxation cracks of the alloy material in a high temperature environment are further suppressed.

On the other hand, if [Ti] _R is less than F3 (= 0.72Ti-0.01(Ti/Al)-0.11), the amount of TiC in the alloy material is appropriate and not excessive. If it is assumed that there is an excessive amount of TiC in the alloy material, welding hot cracks caused by TiC will occur during the welding construction of the alloy material. In other words, if [Ti] _R is less than F3, the resistance to welding hot cracking of the alloy material is further improved. In addition, if it is assumed that there is an excessive amount of TiC in the alloy material, sufficient γ' phase is not generated during use in a high temperature environment. In this case, the creep strength does not increase in a high temperature environment. In other words, if [Ti] _R is less than F3, the creep strength of the alloy material is further improved. Therefore, it is preferred that [Ti] _R is greater than 0.050 and less than F3 (= 0.72Ti-0.01(Ti/Al)-0.11).

[Ti] The lower limit of _R is more preferably 0.055, more preferably 0.060, more preferably 0.065, more preferably 0.070, and still more preferably 0.075.

[Ti] A more preferred upper limit (F3) of _R is 0.72Ti-0.01(Ti/Al)-0.15, more preferably 0.72Ti-0.01(Ti/Al)-0.18, and even more preferably 0.72Ti-0.01(Ti/Al)-0.20.

[[Ti] _R measurement method]

[Ti] _R can be measured using the following electrowinning method.

The test piece is collected from a position at a depth of 1 mm or more from the surface of the alloy material. The size of the test piece is not particularly limited. For example, the test piece is 10 mm in diameter and 70 mm in length.

The surface of the collected test piece was polished by about 50 μm using the preliminary electrolytic polishing to obtain a new surface. The electrolytically polished test piece was formally electrolyzed at a current value of 270 mA using an electrolyte (10% acetylacetone + 1% tetraammonium + methanol). At this time, the electrolysis depth was set to about 31 μm. The electrolyte after the formal electrolysis was passed through a 0.2 μm filter to capture the residue. The obtained residue was acid-decomposed, and the mass (g) of Ti in the residue was determined by ICP (inductively coupled plasma) emission analysis. In addition, the mass (g) of the test piece before the formal electrolysis and the mass (g) of the test piece after the formal electrolysis were measured. In addition, the value obtained by subtracting the mass of the test piece after the formal electrolysis from the mass of the test piece before the formal electrolysis was defined as the mass (g) of the parent material that was formally electrolyzed. The mass of Ti in the residue was divided by the mass of the parent material that was formally electrolyzed to determine the Ti content (mass %) in the residue. That is, [Ti] _R (mass %) as the Ti content in the residue was determined based on the following formula.

[Ti] _R = Ti mass in the residue/base material mass × 100

[Effect of alloy materials]

The alloy material of the present embodiment satisfies the above-mentioned characteristics 1 to 3. As a result, the alloy material of the present embodiment has sufficient creep strength in a high temperature environment, and can achieve both excellent stress relaxation crack resistance and excellent welding crack resistance. If the alloy material of the present embodiment further satisfies characteristic 4, the creep strength and welding hot crack resistance are further improved.

[Microstructure of alloy materials]

The microstructure of the alloy material of the present embodiment is austenite.

[Shape of alloy material]

The shape of the alloy material of this embodiment is not particularly limited. The alloy material may be an alloy tube or an alloy plate. The alloy material may also be an alloy rod. Preferably, the alloy material of this embodiment is an alloy tube.

[Method for producing alloy material]

The manufacturing method of the alloy material of the present embodiment that satisfies characteristics 1 to 4 is described. The manufacturing method described later is an example of the manufacturing method of the alloy material of the present embodiment. Therefore, the alloy material that satisfies characteristics 1 to 4 can also be manufactured by other manufacturing methods other than the manufacturing method described later. However, the manufacturing method described later is a preferred example of the manufacturing method of the alloy material of the present embodiment.

The method for producing the alloy material according to the present embodiment includes the following steps.

(Process 1) Preparation process

(Process 2) Hot working process

(Process 3) Cold working process

(Step 4) Heat treatment step

In the hot working step of step 2, the following condition 1 is satisfied.

(Condition 1)

The heating temperature T1 (° C.) and the holding time t1 (minutes) of the heating temperature T1 during heating before hot working are within the following ranges.

T1: 1100～1280℃

t1: 3 to 120 minutes

Furthermore, in the heat treatment step of step 4, the following condition 2 is satisfied.

(Condition 2)

The heat treatment temperature T2 (° C.) and the holding time t2 (minutes) of the heat treatment temperature T2 in the heat treatment step are within the following ranges.

T2: 1050～1300℃

t2: 1 to 60 minutes

Hereinafter, each step will be described.

[(Process 1) Preparation process]

In the preparation step, a billet having the chemical composition of the above-mentioned feature 1 is prepared. The billet may be supplied from a third party or may be manufactured. The billet may be an ingot, a slab, a bloom, or a billet.

When manufacturing a billet, the billet is manufactured using the following method. Molten steel having the above-mentioned chemical composition is manufactured. The manufactured molten steel is used to manufacture an ingot by an ingot casting method. The manufactured molten steel can also be used to manufacture a slab, a bloom, or a billet by a continuous casting method. The manufactured ingot, slab, or billet can also be subjected to hot working to manufacture a billet. For example, a cylindrical billet can also be manufactured by hot forging a steel ingot, and the billet is used as a billet. In this case, the temperature of the billet immediately before hot forging is not particularly limited, and is, for example, 1000 to 1300°C. The method for cooling the billet after hot forging is not particularly limited.

[(Process 2) Hot working process]

In the hot working step, the blank prepared in the preparation step is hot worked to produce an intermediate alloy material. The intermediate alloy material may be, for example, an alloy tube, an alloy plate, or an alloy rod.

When the intermediate alloy material is an alloy tube, the following processing is performed in the hot working process. First, a cylindrical billet is prepared. A through hole is formed along the central axis of the cylindrical billet by mechanical processing. The cylindrical billet with the through hole is heated. The heated cylindrical billet is subjected to hot extrusion represented by a glass lubricant high-speed extrusion method to manufacture the intermediate alloy material (alloy tube). A hot stamping tube method can also be implemented to replace the hot extrusion method.

In addition, instead of hot extrusion, piercing and rolling by the Mannesmann method can be performed to manufacture alloy tubes. In this case, the cylindrical billet is heated. The heated cylindrical billet is subjected to piercing and rolling by a piercer. In the case of piercing and rolling, the piercing ratio is not particularly limited, and is, for example, 1.0 to 4.0. The pierced and rolled cylindrical billet is further hot-rolled by a continuous tube mill, a reducing mill, a sizing mill, etc. to form a hollow tube billet (alloy tube). The cumulative cross-sectional reduction rate in the hot working process is not particularly limited, and is, for example, 20 to 80%. In the case of manufacturing alloy tubes by hot working, the temperature of the hollow tube billet just after the hot working (finishing temperature) is preferably above 800°C.

When the intermediate alloy material is an alloy plate, the hot working step uses, for example, one or more rolling mills equipped with a pair of work rolls to heat a billet such as a slab and hot-roll the heated billet using the rolling mill to produce an alloy plate.

In the hot working step, the above-mentioned condition 1 is satisfied. That is, the heating temperature T1 (° C.) and the holding time t1 (minutes) at the heating temperature T1 during heating before hot working are within the following ranges.

T1: 1100～1280℃

t1: 3 to 120 minutes

Preferably, in the hot working step, the following condition 3 is satisfied.

(Condition 3)

The heating temperature T1 (° C.) and the holding time t1 (minutes) of the heating temperature T1 satisfy the following formula (A).

800≤T1×LOG(t1)≤2100(A)

It is defined as FA = T1 x LOG (t1). FA affects the amount of TiC in the alloy material after manufacture.

When FA is 800 or more, a sufficient amount of TiC is generated during heating before hot working. Therefore, in the alloy material after production, [Ti] _R is greater than 0.050.

On the other hand, if FA is 2100 or less, TiC is generated in an appropriate amount during heating before hot working. Therefore, in the alloy material after production, [Ti] _R is less than F3 (= 0.72Ti-0.01(Ti/Al)-0.11). Therefore, FA is preferably 800 to 2100.

The lower limit of FA is more preferably 820, more preferably 840, more preferably 860, more preferably 1000, and even more preferably 1200.

The upper limit of FA is more preferably 2050, more preferably 2000, more preferably 1950, and even more preferably 1850.

[(Process 3) Cold working process]

The cold working process is implemented as needed. In other words, the cold working process may not be implemented. In the case of implementation, the cold working is implemented after the intermediate alloy material is pickled. In the case where the intermediate alloy material is an alloy tube or an alloy bar, the cold working is, for example, cold drawing. In the case where the intermediate alloy material is an alloy plate, the cold working is, for example, cold rolling. The cold working process can be implemented to achieve the manifestation of recrystallization and graining. The cross-sectional reduction rate in the cold working process is not particularly limited, for example, 10 to 90%.

[(Step 4) Heat treatment step]

In the heat treatment step, the intermediate alloy material after the hot working step or the cold working step is heat treated to adjust the amount of TiC and the size of the crystal grains in the alloy material.

In the heat treatment step, the above-mentioned condition 2 is satisfied. That is, the heat treatment temperature T2 (° C.) and the heat treatment temperature T2 holding time t2 (minutes) are within the following ranges.

T2: 1050～1300℃

t2: 1 to 60 minutes

Preferably, in the heat treatment step, the following condition 4 is satisfied.

(Condition 4)

The heat treatment temperature T2 (° C.) and the holding time t2 (minutes) of the heat treatment temperature T2 satisfy the following formula (B).

2600≤T2×(LOG(t2)+2)≤4400(B)

It is defined as FB=T2×(LOG(t2)+2). FB affects the amount of TiC in the alloy material after production in the same manner as FA.

When FB is 2600 or more, a sufficient amount of TiC is generated in the alloy material after production. Therefore, [Ti] _R is larger than 0.050.

On the other hand, if FB is 4400 or less, TiC is generated in an appropriate amount in the alloy material after production. Therefore, [Ti] _R is less than 0.72Ti-0.01(Ti/Al)-0.11. Therefore, FB is preferably 2600 to 4400.

A further preferred lower limit of FB is 2650, further preferably 2700, and further preferably 2750.

A more preferred upper limit of FB is 4350, more preferably 4300, more preferably 4250, more preferably 4000, and even more preferably 3800.

After the intermediate alloy material is held at the heat treatment temperature T2 (° C.) for the holding time t2 (minutes), the intermediate alloy material is cooled. The cooling method is preferably rapid cooling (water cooling).

Preferably, the following condition 5 is also satisfied in the heat working step and the heat treatment step.

(Condition 5)

0.30≤FA/FB(C)

Defined as FC = FA / FB. FC, like FA and FB, affects the amount of TiC in the alloy material after manufacture. If FC is 0.30 or more, it is easy to obtain a sufficient amount of TiC in the alloy material after manufacture. Therefore, [Ti] _R is greater than 0.050.

Therefore, FC is preferably 0.30 or more.

The lower limit of FC is more preferably 0.33, more preferably 0.35, and even more preferably 0.38.

The upper limit of FC is not particularly limited. The upper limit of FC is, for example, 0.60.

The alloy material of the present embodiment can be manufactured by the above process. The above manufacturing method is an example of the manufacturing method of the alloy material of the present embodiment. Therefore, the manufacturing method of the alloy material of the present embodiment is not limited to the above manufacturing method. As long as the features 1 to 3 are satisfied, or as long as the features 1 to 4 are satisfied, the manufacturing method of the alloy material is not limited to the above manufacturing method.

[Method for manufacturing a welded joint of alloy material]

The welded joint of the alloy material according to the present embodiment can be produced by the following method.

As a base material, an alloy material of the present embodiment is prepared. A groove is formed on the prepared base material. Specifically, a groove is formed at the end of the base material using a well-known processing method. The groove shape can be a V shape, a U shape, an X shape, or other shapes other than a V shape, a U shape, and an X shape.

The welded joint is manufactured by welding the prepared base metal. Specifically, two base metals with grooves are prepared. The grooves of the prepared base metals are butted against each other. Then, a pair of butted groove ends are welded using a well-known welding material to form a weld metal having the above-mentioned chemical composition. The welding material is, for example, AWS standard name: ERNiCr-3. However, the welding material is not limited thereto.

The welding method may form a single layer of weld metal or may be a multi-layer cladding method. Examples of the welding method include TIG welding (GTAW), coated metal arc welding (SMAW), flux-cored arc welding (FCAW), gas metal arc welding (GMAW), and submerged arc welding (SAW). The welded joint of the alloy material of the present embodiment can be manufactured using the above manufacturing process.

Example

The effects of the alloy material of the present embodiment will be further specifically described using examples. The conditions in the following examples are an example of conditions used to confirm the feasibility and effects of the alloy material of the present embodiment. Therefore, the alloy material of the present embodiment is not limited to this example of conditions.

[Manufacturing of alloy materials]

Steel ingots having the chemical compositions shown in Table 1-1 and Table 1-2 were produced. The shape of the steel ingot was a cylinder with an outer diameter of 120 mm, and the mass of the steel ingot was 30 kg.

[Table 1-1]

TABLE 1-1

[Table 1-2]

TABLE 1-2

“-” in Table 1-2 means that the content of the corresponding element is below the impurity level.

The produced steel ingot was subjected to hot forging to produce a billet (alloy plate) having a thickness of 30 mm. The heating temperature of the steel ingot during hot forging was 1000 to 1300°C.

The manufactured billet was subjected to a hot working process. Specifically, the billet was heated in a heating furnace. The heating temperature T1 in the hot working process was 1100 to 1280°C, and the holding time t1 of the heating temperature T1 was 3 to 120 minutes. The FA value is shown in Table 2. The heated billet was hot rolled to produce an intermediate alloy material (alloy plate) with a thickness of 15 mm.

[Table 2]

TABLE 2

The intermediate alloy material was subjected to a heat treatment process. The heat treatment temperature T2 in the heat treatment process was 1050-1300°C, and the holding time t2 of the heat treatment temperature T2 was 1-60 minutes. The FB value and the FC value are shown in Table 2. The intermediate alloy material after the holding time t2 was water-cooled to room temperature. The alloy material (alloy plate) of each test number was manufactured using the above process.

[Evaluation test]

The following evaluation tests were carried out using the produced alloy materials.

(Test 1) [Ti] _R measurement test

(Test 2) Creep strength evaluation test

(Test 3) Stress relaxation crack resistance evaluation test

(Test 4) Welding hot crack resistance evaluation test

Hereinafter, each evaluation test will be described.

[(Test 1) [Ti] _R measurement test]

A test piece was collected from a position at a depth of 1 mm or more from the surface of the alloy material of each test number. The size of the test piece was 10 mm in diameter × 70 mm in length. Based on the above-mentioned [[Ti] _R measurement method], the Ti content [Ti] _R (mass %) in the residue was obtained. The obtained [Ti] _R is shown in the "[Ti] _R (mass %)" column in Table 2.

[(Test 2) Creep strength evaluation test]

The following creep strength evaluation test was performed on the alloy material (alloy plate) of each test number.

Creep rupture test pieces according to JIS Z 2271:2010 were collected from the center of the plate width and the center of the plate thickness of the alloy material (alloy plate) of each test number. The cross section of the parallel part of the creep rupture test piece perpendicular to the axial direction is circular. The outer diameter of the parallel part is 6mm and the length is 30mm. The length direction of the creep rupture test piece is parallel to the rolling direction of the alloy plate.

The collected creep rupture test pieces were used to perform a creep rupture test in accordance with JIS Z 2271: 2010. Specifically, the creep rupture test pieces were heated to 700° C. Thereafter, the creep rupture test was performed. The test stress was set to 80 MPa. In the test, the creep rupture time (hours) was determined.

The creep strength was evaluated as follows based on the obtained creep rupture time.

Evaluation E (Excellent): Creep rupture time is longer than 4000 hours

Evaluation G (Good): Creep rupture time is 2000 to 4000 hours

Evaluation B (Bad): Creep rupture time is shorter than 2000 hours

In the case of evaluation G or evaluation E, it was judged that excellent creep strength was obtained. The evaluation results are shown in the "Creep Strength" column in Table 2.

[(Test 3) Stress relaxation crack resistance evaluation test]

The following stress relaxation cracking resistance evaluation test was performed on the alloy material (alloy plate) of each test number.

A square test piece was collected from the center of the plate width and the center of the plate thickness of the alloy material (alloy plate) of each test number. The cross section of the square test piece perpendicular to the length direction was set to a 10mm×10mm rectangle. The length of the square test piece was set to 100mm. The length direction of the square test piece was parallel to the rolling direction of the alloy material (alloy plate).

The following thermal history was applied to the collected square test piece using a high-frequency thermal cycler. Specifically, the square test piece was heated from room temperature to 1300°C at 70°C/second in the atmosphere. After that, it was kept at 1300°C for 180 seconds. After that, the square test piece was cooled to room temperature at a cooling rate of 50°C/second. By applying the above thermal history to the square test piece, a welding simulation test piece was produced.

A stress relaxation test according to ASTM E328-02 was conducted using a welded simulated test piece. Specifically, a test piece for the stress relaxation test was made from a welded simulated test piece. The test piece was a flanged creep test piece with a length of 80 mm and a distance between points GL = 30 mm. An initial cold strain of 20% was applied to the test piece using a test fixture for flexural displacement load. The test fixture with the test piece to which the cold strain was applied was placed in a heating furnace and maintained at 650°C for 300 hours.

The results of the stress relaxation test according to AST ME328-02 were evaluated as follows.

Evaluation E (Excellent): The test piece did not break after 300 hours.

Evaluation G (Good): The test piece broke after 200 to 300 hours.

Evaluation B (Bad): The test piece broke in less than 200 hours

In the case of evaluation G or evaluation E, it was judged that excellent stress relaxation cracking resistance was obtained. The evaluation results are shown in the "Stress Relaxation Cracking Resistance" column in Table 2.

[(Test 4) Welding hot crack resistance evaluation test]

A test piece with a thickness of 12 mm, a width of 40 mm, and a length of 300 mm was collected, centered at the center of the plate width and the center of the plate thickness of the alloy material (alloy plate) of each test number. The following longitudinal adjustable restrained crack test was performed on the collected test piece.

Specifically, TIG welding was performed in the longitudinal direction of the center of the plate width of the test piece under welding conditions of welding current 200A, voltage 12V, and speed 15cm/min. During TIG welding, bending stress was instantaneously applied parallel to the welding direction to apply 2% strain to the surface layer.

The portion including the site where the welding crack was generated due to the application of the bending stress was cut out to a size that could be observed with an optical microscope. The size of the cut sample was 40 mm×40 mm×12 mm.

The oxide scale on the surface of the welded part of the cut sample was removed by polishing. Afterwards, the presence of cracks in the HAZ was measured using a 100x optical microscope, and the length of the cracks was measured if cracks occurred. Specifically, the length of the crack propagated in the direction perpendicular to the welding direction (the length in the direction perpendicular to the welding direction) was measured starting from the boundary between the weld metal and the HAZ. The length of all cracks generated in the test piece in the direction perpendicular to the welding direction was calculated. The sum of the lengths of these cracks was defined as the total crack length (mm). The total crack length was calculated in each of the two test pieces. The arithmetic mean of the total crack lengths calculated was defined as the average total crack length.

The welding hot crack resistance was evaluated as follows based on the obtained average total crack length.

Evaluation E (Excellent): Average total crack length is less than 2.0 mm

Evaluation G (Good): Average total crack length greater than 2.0 to less than 3.0 mm

Evaluation B (Bad): Average total crack length is 3.0 mm or more

In the case of evaluation G or evaluation E, it was judged that excellent resistance to welding hot cracking was obtained. The evaluation results are shown in the column "Resistance to welding hot cracking" in Table 2.

[Test results]

Table 2 shows the test results.

Referring to Table 1-1, Table 1-2, and Table 2, in Test Nos. 1 to 35, the alloy material satisfies Characteristics 1 to 3. Therefore, sufficient creep strength is obtained in a high temperature environment. In addition, excellent stress relaxation crack resistance and excellent welding hot crack resistance are obtained.

Moreover, in test numbers 1 to 28, the manufacturing conditions FA satisfied the formula (A), FB satisfied the formula (B), and FC satisfied the formula (C). As a result, in test numbers 1 to 28, the alloy material satisfied not only the characteristics 1 to 3 but also the characteristic 4. Therefore, in test numbers 1 to 28, the evaluation E was obtained in the creep strength evaluation test, the stress relaxation cracking resistance evaluation test, and the welding hot cracking resistance evaluation test, and further excellent creep strength, stress relaxation cracking resistance, and welding hot cracking resistance were obtained.

On the other hand, in Test No. 36, the Al content was too high, so sufficient stress relaxation crack resistance and welding hot crack resistance could not be obtained. In addition, sufficient creep strength could not be obtained.

In Test No. 37, although the contents of the elements in the chemical composition were appropriate, F1 was less than the lower limit of the formula (1), so that sufficient creep strength could not be obtained.

In Test No. 38, although the contents of the elements in the chemical composition were appropriate, F1 was greater than the upper limit of the formula (1). Therefore, sufficient resistance to welding hot cracking could not be obtained.

In Test No. 39, although the contents of the elements in the chemical composition were appropriate, F2 was less than the lower limit of Formula (2). As a result, sufficient stress relaxation cracking resistance could not be obtained.

The embodiments of the present invention have been described above. However, the above embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above embodiments, and can be implemented by appropriately changing the above embodiments without departing from the gist thereof.

Claims (3)

1. An alloy material comprises the following chemical components in percentage by mass: 0.050 to 0.100 percent,

Si: less than 1.00%,

Mn: less than 1.50 percent,

P: less than 0.035 percent,

S: less than 0.0015 percent,

Cr：19.00～23.00％、

Ni：30.00～35.00％、

N:0.100% or less,

Al：0.15～0.70％、

Ti：0.15～0.70％、

B：0.0010～0.0050％、

Nb：0～0.30％、

Ta：0～0.50％、

V：0～1.00％、

Zr：0～0.10％、

Hf：0～0.10％、

Cu：0～1.00％、

Mo：0～1.00％、

W：0～1.00％、

Co：0～1.00％、

Ca：0～0.0200％、

Mg：0～0.0200％、

Rare earth element: 0 to 0.1000%, and the balance of Fe and impurities,

The chemical composition satisfies the formula (1) and the formula (2),

0.60＜Al+Ti＜1.20 (1)，

1.12≤Ti/Al (2)，

Wherein the content of the corresponding element in the chemical composition of the alloy material is substituted in mass% at each element symbol in the formula (1) and the formula (2).

2. The alloy material according to claim 1, wherein,

When the content of Ti in mass% in the residue obtained by the electrowinning method is defined as [ Ti ] _R, the alloy material also satisfies the formula (3),

0.050＜[Ti]_R＜0.72Ti-0.01(Ti/Al)-0.11 (3)，

Wherein the content of the corresponding element in the chemical composition of the alloy material is substituted in mass% at each element symbol in the formula (3).

3. Alloy material according to claim 1 or 2, wherein,

The alloy material contains a material selected from the group consisting of

Nb：0.01～0.30％、

Ta：0.01～0.50％、

V：0.01～1.00％、

Zr：0.01～0.10％、

Hf：0.01～0.10％、

Cu：0.01～1.00％、

Mo：0.01～1.00％、

W：0.01～1.00％、

Co：0.01～1.00％、

Ca：0.0001～0.0200％、

Mg:0.0001 to 0.0200 percent, and

Rare earth element: 0.001 to 0.1000% of more than 1 element of the group consisting of.