JP7748007B2 - NiCrFe alloy material - Google Patents

Description

This disclosure relates to NiCrFe alloy materials.

In facilities such as primary oil and gas processing facilities and chemical plants, the alloys used come into contact with process fluids containing sulfides and/or chlorides. Therefore, the alloys used in these facilities require excellent corrosion resistance. Examples of materials requiring excellent corrosion resistance include 18-8 stainless steels such as SUS304H, SUS316H, SUS321H, and SUS347H, as well as NiCrFe alloys, such as Alloy800H, which is specified as NCF800H in the JIS standard. NiCrFe alloys offer superior corrosion resistance compared to 18-8 stainless steels. Furthermore, NiCrFe alloys are more economical than Ni-based alloys, such as Alloy617. Therefore, NiCrFe alloys are sometimes used as alloys with excellent corrosion resistance.

Japanese Patent Publication No. 2-217445 (Patent Document 1) and International Publication No. 2015/072458 (Patent Document 2) propose alloy materials with excellent corrosion resistance.

The alloy material described in Patent Document 1 is an Fe-Cr-Ni alloy containing Ni: 27-32%, Cr: 24-28%, Cu: 1.25-3.0%, Mo: 1.0-3.0%, Si: 1.5-2.75%, and Mn: 1.0-2.0%, with N: 0.015% or less, B: 0.10% or less, V: 0.10% or less, C: 0.10% or less, Al: 0.30% or less, P: 0.03% or less, and S: 0.02% or less, with the balance consisting essentially of Fe and impurities. Patent Document 1 describes this alloy material as having high strength, galling resistance, and corrosion resistance under stress.

The alloy material described in Patent Document 2 is a Ni-Cr alloy material, and contains, in mass %, Si: 0.01 to 0.5%, Mn: 0.01 to less than 1.0%, Cu: 0.01 to less than 1.0%, Ni: 48 to less than 55%, Cr: 22 to 28%, Mo: 5.6 to less than 7.0%, N: 0.04 to 0.16%, sol. The alloy has a chemical composition consisting of Al: 0.03 to 0.20%, REM: 0.01 to 0.074%, W: 0 to less than 8.0%, Co: 0 to 2.0%, one or more of Ca and Mg: 0.0003 to 0.01% in total, one or more of Ti, Nb, Zr, and V: 0 to 0.5% in total, and the balance being Fe and impurities, wherein the impurities are C: 0.03% or less, P: 0.03% or less, S: 0.001% or less, and O: 0.01% or less, and the dislocation density ρ satisfies the formula (7.0×10 ¹⁵ ≦ρ≦2.7×10 ¹⁶ - 2.67×10 ¹⁷ × [REM (%)]). Patent Document 2 describes that this alloy material has excellent hot workability and toughness, as well as excellent corrosion resistance (resistance to stress corrosion cracking at high temperatures exceeding 200°C and in environments containing hydrogen sulfide), and has a yield strength (0.2% yield strength) of 965 MPa or more.

Japanese Patent Application Publication No. 2-217445 International Publication No. 2015/072458

As mentioned above, Patent Documents 1 and 2 disclose alloy materials with excellent corrosion resistance. However, NiCrFe alloy materials with excellent corrosion resistance may also be obtained by techniques other than those disclosed in Patent Documents 1 and 2.

In the construction and repair of facilities such as primary oil and gas processing facilities and chemical plants, welding of NiCrFe alloy materials is sometimes performed. Therefore, NiCrFe alloy materials used in facilities such as primary oil and gas processing facilities and chemical plants are required to have not only excellent corrosion resistance but also excellent weldability. Here, excellent weldability means that weld cracks (cracks occurring near the weld) are less likely to occur. However, Patent Documents 1 and 2 do not consider the weldability of the alloy materials.

The purpose of this disclosure is to provide a NiCrFe alloy material having excellent corrosion resistance and excellent weldability.

The NiCrFe alloy material according to the present disclosure has
In mass%,
C: 0.002-0.030%,
Si: 0.05-0.50%,
Mn: 0.10 to 1.50%,
P: 0.050% or less,
S: 0.0200% or less,
Ni: 29.0-40.0%,
Cr: 24.00-30.00%,
Mo: 5.0 to 7.5%,
N: 0.20-0.40%,
Al: 0.50% or less,
Ca: 0.0002 to 0.0040%, and
B: 0.0001 to 0.0050%,
The balance is composed of Fe and impurities.
It has a chemical composition that satisfies formula (1).
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %.

The NiCrFe alloy material according to the present disclosure has
In mass%,
C: 0.002-0.030%,
Si: 0.05-0.50%,
Mn: 0.10 to 1.50%,
P: 0.050% or less,
S: 0.0200% or less,
Ni: 29.0-40.0%,
Cr: 24.00-30.00%,
Mo: 5.0 to 7.5%,
N: 0.20-0.40%,
Al: 0.50% or less,
Ca: 0.0002 to 0.0040%, and
B: 0.0001 to 0.0050%, and further
Cu: 0.40% or less,
W: 1.00% or less,
Sn: 0.50% or less,
Co: 0.50% or less,
V: 0.50% or less,
Nb: 0.50% or less,
Ti: 0.50% or less,
Zr: 0.200% or less,
Hf: 0.200% or less,
Ta: 0.50% or less, and
Rare earth elements: 0.0030% or less, containing one or more elements selected from the group consisting of
The balance is composed of Fe and impurities.
It has a chemical composition that satisfies formula (1).
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %.

The NiCrFe alloy material disclosed herein has excellent corrosion resistance and excellent weldability.

FIG. 1 is a diagram showing the relationship between the value of D (=8.5×Mn+19.5×Ni−12.43×Cr−42.4×Mo−10250×Ca+1250×B−74.3776) in this example and the total length (mm) of ductility-dip cracks.

First, the inventors investigated the corrosion resistance of NiCrFe alloy materials from the perspective of chemical composition. As a result, the inventors found that the following components, by mass, are desirable: C: 0.002-0.030%, Si: 0.05-0.50%, Mn: 0.10-1.50%, P: 0.050% or less, S: 0.0200% or less, Ni: 29.0-40.0%, Cr: 24.00-30.00%, Mo: 5.0-7.5%, N: 0.20-0.40%, Al: 0.50% or less, Cu: 0-0.40%. %, W: 0-1.00%, Sn: 0-0.50%, Co: 0-0.50%, V: 0-0.50%, Nb: 0-0.50%, Ti: 0-0.50%, Zr: 0-0.200%, Hf: 0-0.200%, Ta: 0-0.50%, and rare earth elements: 0-0.0030%.

Here, in NiCrFe alloy materials containing the above-mentioned chemical composition, weld cracks have sometimes occurred when welding. Specifically, detailed studies by the inventors have revealed that NiCrFe alloy materials containing the above-mentioned chemical composition are prone to ductility-dip cracking, a type of weld cracking. Ductility-dip cracking is a type of weld cracking in which grain boundaries exposed to high temperatures during welding lose ductility and are unable to withstand thermal contraction due to cooling, resulting in cracking. In other words, if the grain boundaries of NiCrFe alloy materials having the above-mentioned chemical composition can be strengthened, it may be possible to suppress the occurrence of ductility-dip cracking.

Therefore, the inventors focused on calcium (Ca) and investigated ways to suppress ductility-dip cracking. Specifically, when welding is performed on an alloy material having the above-mentioned chemical composition, sulfur (S) may segregate at grain boundaries in the heat-affected zone (hereinafter referred to as the HAZ (heat-affected zone)) of the weld. If S segregates at the grain boundaries, the grain boundary's bonding strength decreases, and the alloy may not be able to withstand thermal contraction due to cooling, causing cracking. The inventors therefore suspected that ductility-dip cracking may occur in an alloy material having the above-mentioned chemical composition. In other words, the inventors believed that adding 0.0002 to 0.0040% Ca in addition to the above-mentioned chemical composition could fix the S in the alloy material as CaS, thereby suppressing ductility-dip cracking in the alloy material.

On the other hand, even in alloy materials that contain 0.0002 to 0.0040% Ca in addition to the above chemical composition, weld cracks have sometimes occurred. Specifically, in alloy materials that contain 0.0002 to 0.0040% Ca in addition to the above chemical composition, liquation cracking has sometimes occurred among weld cracks. Liquation cracking is a type of weld crack that occurs in the HAZ near the fusion line and refers to cracking caused by localized melting.

The inventors therefore focused on boron (B) and investigated ways to suppress liquation cracking. Specifically, B strengthens grain boundaries at high temperatures and suppresses liquation cracking. On the other hand, if the B content is too high, B segregates at grain boundaries and melts in the high-temperature region near the fusion line, thereby promoting liquation cracking. In other words, by adding 0.0001 to 0.0050% B and 0.0002 to 0.0040% Ca to the above-mentioned chemical composition, it is possible to suppress the occurrence of both ductility-dip cracking and liquation cracking, potentially improving the weldability of the alloy material.

That is, the inventors have determined that the composition of the alloy is, by mass%, C: 0.002 to 0.030%, Si: 0.05 to 0.50%, Mn: 0.10 to 1.50%, P: 0.050% or less, S: 0.0200% or less, Ni: 29.0 to 40.0%, Cr: 24.00 to 30.00%, Mo: 5.0 to 7.5%, N: 0.20 to 0.40%, Al: 0.50% or less, Ca: 0.0002 to 0.0040%, B: 0.0001 to 0.00 It was thought that a NiCrFe alloy material consisting of the following composition may be able to achieve both corrosion resistance and weldability: 50%, Cu: 0-0.40%, W: 0-1.00%, Sn: 0-0.50%, Co: 0-0.50%, V: 0-0.50%, Nb: 0-0.50%, Ti: 0-0.50%, Zr: 0-0.200%, Hf: 0-0.200%, Ta: 0-0.50%, rare earth elements: 0-0.0030%, and the balance being Fe and impurities.

The present inventors have manufactured various NiCrFe alloy materials having the above-mentioned chemical composition and have further studied the occurrence of weld cracks in detail. As a result, the present inventors have found that the NiCrFe alloy material having the above-mentioned chemical composition not only has excellent corrosion resistance but also can suppress the occurrence of both ductility-dip cracking and liquation cracking by satisfying the following formula (1):
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %.

D is defined as: D = 8.5 x Mn + 19.5 x Ni - 12.43 x Cr - 42.4 x Mo - 10250 x Ca + 1250 x B - 74.3776. Figure 1 shows the relationship between the value of D and the total length (mm) of ductility-dip cracks in this example. Figure 1 was created using the value of D and the total length (mm) of ductility-dip cracks for examples described below that satisfy the chemical composition described above. The total length (mm) of ductility-dip cracks was determined using the method described below. Furthermore, no liquation cracking was observed in any of the examples shown in Figure 1, and the examples had excellent corrosion resistance.

Referring to Figure 1, in alloy materials satisfying the above-mentioned chemical composition, when D is 0.0 or less, liquation cracking was suppressed, but the total length of the ductility-dip cracks was 4.0 mm or more, and ductility-dip cracking could not be suppressed. Furthermore, referring to Figure 1, in alloy materials satisfying the above-mentioned chemical composition, when D is 6.5 or more, liquation cracking was suppressed, but the total length of the ductility-dip cracks was 4.0 mm or more, and ductility-dip cracking could not be suppressed. In other words, in alloy materials satisfying the above-mentioned chemical composition, when D is greater than 0.0 and less than 6.5, excellent corrosion resistance is achieved, and both liquation cracking and ductility-dip cracking can be suppressed.

Therefore, the NiCrFe alloy material according to this embodiment has the above-mentioned chemical composition, and D is greater than 0.0 and less than 6.5. As a result, the NiCrFe alloy material according to this embodiment can achieve both excellent corrosion resistance and excellent weldability.

The gist of the NiCrFe alloy material of this embodiment, which was completed based on the above findings, is as follows:

[1]
In mass%,
C: 0.002-0.030%,
Si: 0.05-0.50%,
Mn: 0.10 to 1.50%,
P: 0.050% or less,
S: 0.0200% or less,
Ni: 29.0-40.0%,
Cr: 24.00-30.00%,
Mo: 5.0 to 7.5%,
N: 0.20-0.40%,
Al: 0.50% or less,
Ca: 0.0002 to 0.0040%, and
B: 0.0001 to 0.0050%,
The balance is composed of Fe and impurities.
Having a chemical composition that satisfies formula (1):
NiCrFe alloy material.
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %.

[2]
In mass%,
C: 0.002-0.030%,
Si: 0.05-0.50%,
Mn: 0.10 to 1.50%,
P: 0.050% or less,
S: 0.0200% or less,
Ni: 29.0-40.0%,
Cr: 24.00-30.00%,
Mo: 5.0 to 7.5%,
N: 0.20-0.40%,
Al: 0.50% or less,
Ca: 0.0002 to 0.0040%, and
B: 0.0001 to 0.0050%, and further
Cu: 0.40% or less,
W: 1.00% or less,
Sn: 0.50% or less,
Co: 0.50% or less,
V: 0.50% or less,
Nb: 0.50% or less,
Ti: 0.50% or less,
Zr: 0.200% or less,
Hf: 0.200% or less,
Ta: 0.50% or less, and
Rare earth elements: 0.0030% or less, containing one or more elements selected from the group consisting of
The balance is composed of Fe and impurities.
Having a chemical composition that satisfies formula (1):
NiCrFe alloy material.
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %.

[3]
[2] The NiCrFe alloy material according to
The chemical composition is
Cu: 0.40% or less,
W: 1.00% or less,
Sn: 0.50% or less, and
Co: 0.50% or less, containing one or more elements selected from the group consisting of
NiCrFe alloy material.

[4]
[2] The NiCrFe alloy material according to
The chemical composition is
V: 0.50% or less,
Nb: 0.50% or less,
Ti: 0.50% or less,
Zr: 0.200% or less,
Hf: 0.200% or less, and
Ta: 0.50% or less, containing one or more elements selected from the group consisting of
NiCrFe alloy material.

[5]
[2] The NiCrFe alloy material according to
The chemical composition is
Rare earth elements: 0.0030% or less,
NiCrFe alloy material.

The gist of the NiCrFe alloy material according to this embodiment can be further described as follows:

[1]
In mass%,
C: 0.002-0.030%,
Si: 0.05-0.50%,
Mn: 0.10 to 1.50%,
P: 0.050% or less,
S: 0.0200% or less,
Ni: 29.0-40.0%,
Cr: 24.00-30.00%,
Mo: 5.0 to 7.5%,
N: 0.20-0.40%,
Al: 0.50% or less,
Ca: 0.0002-0.0040%,
B: 0.0001 to 0.0050%,
Cu: 0 to 0.40%,
W: 0-1.00%,
Sn: 0 to 0.50%,
Co: 0 to 0.50%,
V: 0-0.50%,
Nb: 0 to 0.50%,
Ti: 0 to 0.50%,
Zr: 0-0.200%,
Hf: 0-0.200%,
Ta: 0 to 0.50%,
Rare earth elements: 0 to 0.0030%, and
The balance is composed of Fe and impurities.
Satisfying formula (1),
NiCrFe alloy material.
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %.

[2]
[1] The NiCrFe alloy material according to
Cu: 0.01-0.40%,
W: 0.01-1.00%,
Sn: 0.01-0.50%,
Co: 0.01 to 0.50%,
V: 0.01-0.50%,
Nb: 0.01 to 0.50%,
Ti: 0.01 to 0.50%,
Zr: 0.001-0.200%,
Hf: 0.001-0.200%,
Ta: 0.01 to 0.50%, and
Rare earth elements: containing one or more elements selected from the group consisting of 0.0001 to 0.0030%;
NiCrFe alloy material.

The NiCrFe alloy material according to this embodiment will be described in detail below. Note that "%" for elements means mass % unless otherwise specified.

[Chemical composition]
The chemical composition of the NiCrFe alloy material according to this embodiment contains the following elements.

C: 0.002-0.030%
Carbon (C) deoxidizes the alloy. C also increases the strength of the alloy material. If the C content is too low, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the C content is too high, the weld heat-affected zone is likely to become sensitized during welding even if the contents of other elements are within the ranges of this embodiment. Therefore, the C content is 0.002 to 0.030%. The preferred lower limit of the C content is 0.003%, more preferably 0.005%, and even more preferably 0.007%. The preferred upper limit of the C content is 0.025%, more preferably 0.023%, and even more preferably 0.020%.

Si: 0.05-0.50%
Silicon (Si) deoxidizes the alloy. If the Si content is too low, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Si content is too high, inclusions are likely to form, and the corrosion resistance of the alloy material will decrease, even if the contents of other elements are within the ranges of this embodiment. Therefore, the Si content is 0.05 to 0.50%. A preferred lower limit of the Si content is 0.07%, more preferably 0.10%, and even more preferably 0.12%. A preferred upper limit of the Si content is 0.35%, more preferably 0.30%, and even more preferably 0.25%.

Mn: 0.10-1.50%
Manganese (Mn) deoxidizes the alloy. Mn is also an austenite-forming element and stabilizes austenite in the alloy material. If the Mn content is too low, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mn content is too high, inclusions are likely to form, and the corrosion resistance of the alloy material will decrease, even if the contents of other elements are within the ranges of this embodiment. Therefore, the Mn content is 0.10 to 1.50%. The preferred lower limit of the Mn content is 0.20%, more preferably 0.30%, and even more preferably 0.40%. The preferred upper limit of the Mn content is 1.40%, more preferably 1.30%, and even more preferably 1.20%.

P: 0.050% or less Phosphorus (P) is an unavoidable impurity. That is, the lower limit of the P content is greater than 0%. P segregates at grain boundaries. Therefore, if the P content is too high, even if the contents of other elements are within the ranges of this embodiment, the alloy material's cracking susceptibility increases and the weldability of the alloy material decreases. Therefore, the P content is 0.050% or less. The preferred upper limit of the P content is 0.045%, more preferably 0.040%, and even more preferably 0.030%. The P content is preferably as low as possible. However, an extreme reduction in the P content significantly increases manufacturing costs. Therefore, considering industrial production, the preferred lower limit of the P content is 0.001%, more preferably 0.002%, even more preferably 0.003%, and even more preferably 0.005%.

S: 0.0200% or less Sulfur (S) is an unavoidable impurity. That is, the lower limit of the S content is greater than 0%. S segregates at grain boundaries. Therefore, if the S content is too high, the cracking susceptibility of the alloy material increases even if the contents of other elements are within the ranges of this embodiment. In this case, inclusions are more likely to form, and the corrosion resistance of the alloy material decreases. Therefore, the S content is 0.0200% or less. A preferred upper limit of the S content is 0.0100%, more preferably 0.0050%, and even more preferably 0.0030%. The S content should be as low as possible. However, an extreme reduction in the S content significantly increases manufacturing costs. Therefore, considering industrial production, a preferred lower limit of the S content is 0.0001%, more preferably 0.0003%.

Ni: 29.0-40.0%
Nickel (Ni) is an austenite-forming element and stabilizes austenite in the alloy material. Ni also enhances the corrosion resistance of the alloy material. If the Ni content is too low, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Ni content is too high, the manufacturing cost will increase significantly even if the contents of other elements are within the ranges of this embodiment. If the Ni content is too high, the weldability of the alloy material may also be reduced. Therefore, the Ni content is 29.0 to 40.0%. The preferred lower limit of the Ni content is 29.5%, and more preferably 30.0%. The preferred upper limit of the Ni content is 39.0%, and more preferably 38.0%.

Cr:24.00~30.00%
Chromium (Cr) improves the corrosion resistance of alloy materials. Cr may also improve the weldability of alloy materials. If the Cr content is too low, the above effects cannot be fully achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Cr content is too high, even if the contents of other elements are within the ranges of this embodiment, intermetallic compounds such as the σ phase are more likely to form, which may actually reduce the corrosion resistance of the alloy material. If the Cr content is too high, the weldability of the alloy material may also be reduced. Therefore, the Cr content is 24.00 to 30.00%. The preferred lower limit of the Cr content is 24.50%, and more preferably 25.00%. The preferred upper limit of the Cr content is 29.00%, and more preferably 28.00%.

Mo: 5.0-7.5%
Molybdenum (Mo) enhances the corrosion resistance of alloy materials. If the Mo content is too low, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Mo content is too high, even if the contents of other elements are within the ranges of this embodiment, intermetallic compounds such as the σ phase are more likely to form, and the corrosion resistance of the alloy material may actually decrease. If the Mo content is too high, the weldability of the alloy material may also decrease. Therefore, the Mo content is 5.0 to 7.5%. The preferred lower limit of the Mo content is 5.1%, more preferably 5.3%, and even more preferably 5.5%. The preferred upper limit of the Mo content is 7.4%, more preferably 7.2%, and even more preferably 7.0%.

N: 0.20-0.40%
Nitrogen (N) dissolves in the alloy material and increases the strength of the alloy material. N may also increase the corrosion resistance of the alloy material. If the N content is too low, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the N content is too high, the weldability of the alloy material will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the N content is 0.20 to 0.40%. The preferred lower limit of the N content is 0.21%, more preferably 0.22%, and even more preferably 0.23%. The preferred upper limit of the N content is 0.39%, more preferably 0.37%, and even more preferably 0.36%.

Al: 0.50% or less Aluminum (Al) deoxidizes the alloy and is an impurity contained in the alloy material. That is, the lower limit of the Al content is greater than 0%. If the Al content is too high, even if the contents of other elements are within the ranges of this embodiment, excessive Al oxides will be generated, reducing the corrosion resistance of the alloy material. Therefore, the Al content is 0.50% or less. A preferred upper limit of the Al content is 0.45%, more preferably 0.40%, and even more preferably 0.35%. However, an extreme reduction in the Al content significantly increases manufacturing costs. Therefore, considering industrial production, a preferred lower limit of the Al content is 0.01%, more preferably 0.03%, and even more preferably 0.05%. Note that the Al content referred to in this specification refers to "total Al," i.e., the T-Al content.

Ca: 0.0002-0.0040%
Calcium (Ca) stabilizes and neutralizes S in the alloy material as sulfides, thereby suppressing ductility-dip cracking in the alloy material and improving the weldability of the alloy material. If the Ca content is too low, the above effect cannot be fully achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Ca content is too high, even if the contents of other elements are within the ranges of this embodiment, coarse oxides are formed in the alloy material, promoting ductility-dip cracking in the alloy material and actually reducing the weldability of the alloy material. Therefore, the Ca content is 0.0002 to 0.0040%. The preferred lower limit of the Ca content is 0.0003%, more preferably 0.0005%, even more preferably 0.0008%, and even more preferably 0.0010%. The preferred upper limit of the Ca content is 0.0035%, even more preferably 0.0030%.

B: 0.0001-0.0050%
Boron (B) strengthens grain boundaries at high temperatures, suppresses liquation cracking of the alloy material, and improves the weldability of the alloy material. If the B content is too low, the above effects cannot be fully achieved even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the B content is too high, B segregates at grain boundaries, promoting liquation cracking of the alloy material and actually reducing the weldability of the alloy material. Therefore, the B content is 0.0001 to 0.0050%. The preferred lower limit of the B content is 0.0003%, more preferably 0.0005%, even more preferably 0.0008%, and even more preferably 0.0010%. The preferred upper limit of the B content is 0.0045%, more preferably 0.0040%, and even more preferably 0.0035%.

The balance of the chemical composition of the NiCrFe alloy material according to this embodiment consists of Fe and impurities. Here, "impurities" refers to substances that are mixed in from raw materials such as ore and scrap, or the manufacturing environment, during the industrial production of the NiCrFe alloy material, and are acceptable to the extent that they do not significantly adversely affect the effects of the NiCrFe alloy material according to this embodiment.

[Optional element]
The chemical composition of the NiCrFe alloy material according to this embodiment may further contain, in place of a portion of Fe, one or more elements selected from the group consisting of Cu, W, Sn, and Co. All of these elements improve the corrosion resistance of the alloy material.

Cu: 0.40% or less Copper (Cu) is an optional element and does not necessarily need to be contained. That is, the Cu content may be 0%. When contained, Cu enhances the corrosion resistance of the alloy material. Even if even a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content is too high, the hot workability of the alloy material will deteriorate even if the contents of other elements are within the ranges of this embodiment. Therefore, the Cu content is 0 to 0.40%, and when Cu is contained, the Cu content is 0.40% or less. The preferred lower limit of the Cu content is more than 0%, more preferably 0.01%, even more preferably 0.02%, and even more preferably 0.04%. The preferred upper limit of the Cu content is 0.38%, even more preferably 0.35%, and even more preferably 0.30%.

W: 1.00% or less Tungsten (W) is an optional element and does not necessarily need to be contained. That is, the W content may be 0%. When contained, W enhances the corrosion resistance of the alloy material. W also enhances the strength of the alloy material through solid solution strengthening. Even if even a small amount of W is contained, the above effects can be obtained to some extent. However, if the W content is too high, the hot workability of the alloy material will deteriorate even if the contents of other elements are within the ranges of this embodiment. Therefore, the W content is 0 to 1.00%, and when W is contained, the W content is 1.00% or less. The preferred lower limit of the W content is more than 0%, more preferably 0.01%, even more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the W content is 0.95%, even more preferably 0.90%, and even more preferably 0.85%.

Sn: 0.50% or less Tin (Sn) is an optional element and does not necessarily need to be contained. That is, the Sn content may be 0%. When contained, Sn enhances the corrosion resistance of the alloy material. Even if even a small amount of Sn is contained, the above effect can be obtained to some extent. However, if the Sn content is too high, the hot workability of the alloy material will deteriorate even if the contents of other elements are within the ranges of this embodiment. Therefore, the Sn content is 0 to 0.50%, and when Sn is contained, the Sn content is 0.50% or less. The preferred lower limit of the Sn content is more than 0%, more preferably 0.01%, even more preferably 0.02%, and even more preferably 0.03%. The preferred upper limit of the Sn content is 0.45%, even more preferably 0.40%, and even more preferably 0.35%.

Co: 0.50% or less Cobalt (Co) is an optional element and does not necessarily need to be contained. That is, the Co content may be 0%. When contained, Co enhances the corrosion resistance of the alloy material. Even if even a small amount of Co is contained, the above effect can be obtained to some extent. However, if the Co content is too high, the manufacturing cost will increase dramatically even if the contents of other elements are within the ranges of this embodiment. Therefore, the Co content is 0 to 0.50%, and when Co is contained, the Co content is 0.50% or less. The preferred lower limit of the Co content is more than 0%, more preferably 0.01%, even more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Co content is 0.45%, even more preferably 0.40%, and even more preferably 0.35%.

The chemical composition of the NiCrFe alloy material according to this embodiment may further contain one or more elements selected from the group consisting of V, Nb, Ti, Zr, Hf, and Ta in place of a portion of the Fe. All of these elements increase the strength of the alloy material.

V: 0.50% or less Vanadium (V) is an optional element and does not necessarily need to be contained. That is, the V content may be 0%. When contained, V forms carbonitrides with C and N, etc., thereby increasing the strength of the alloy material. Even if even a small amount of V is contained, the above effect can be obtained to some extent. However, if the V content is too high, even if the contents of other elements are within the ranges of this embodiment, the strength becomes too high, promoting ductility-dip cracking of the alloy material and thereby reducing the weldability of the alloy material. Therefore, the V content is 0 to 0.50%, and when V is contained, the V content is 0.50% or less. The preferred lower limit of the V content is more than 0%, more preferably 0.01%, even more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the V content is 0.45%, even more preferably 0.40%, and even more preferably 0.35%.

Nb: 0.50% or less Niobium (Nb) is an optional element and does not necessarily need to be contained. That is, the Nb content may be 0%. When contained, Nb forms carbonitrides with C and N, increasing the strength of the alloy material. Even if even a small amount of Nb is contained, the above effect can be obtained to some extent. However, if the Nb content is too high, even if the contents of other elements are within the ranges of this embodiment, the strength becomes too high, promoting ductility-dip cracking of the alloy material and thereby reducing the weldability of the alloy material. Therefore, the Nb content is 0 to 0.50%, and when Nb is contained, the Nb content is 0.50% or less. The preferred lower limit of the Nb content is more than 0%, more preferably 0.01%, even more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Nb content is 0.45%, even more preferably 0.40%, and even more preferably 0.35%.

Ti: 0.50% or less Titanium (Ti) is an optional element and does not necessarily need to be contained. That is, the Ti content may be 0%. When contained, Ti forms carbonitrides with C and N, increasing the strength of the alloy material. Even if even a small amount of Ti is contained, the above effect can be achieved to some extent. However, if the Ti content is too high, even if the contents of other elements are within the ranges of this embodiment, the strength becomes too high, promoting ductility-dip cracking of the alloy material and thereby reducing the weldability of the alloy material. Therefore, the Ti content is 0 to 0.50%, and when Ti is contained, the Ti content is 0.50% or less. The preferred lower limit of the Ti content is more than 0%, more preferably 0.01%, even more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Ti content is 0.45%, even more preferably 0.40%, and even more preferably 0.35%.

Zr: 0.200% or less Zirconium (Zr) is an optional element and does not necessarily need to be contained. That is, the Zr content may be 0%. When contained, Zr forms carbonitrides and increases the strength of the alloy material. Even if even a small amount of Zr is contained, the above effect can be achieved to some extent. However, if the Zr content is too high, even if the contents of other elements are within the ranges of this embodiment, the strength becomes too high, promoting ductility-dip cracking of the alloy material and reducing the weldability of the alloy material. Therefore, the Zr content is 0 to 0.200%, and when Zr is contained, the Zr content is 0.200% or less. The preferred lower limit of the Zr content is more than 0%, more preferably 0.001%, even more preferably 0.002%, even more preferably 0.003%, and even more preferably 0.005%. The preferred upper limit of the Zr content is 0.180%, even more preferably 0.150%, and even more preferably 0.120%.

Hf: 0.200% or less Hafnium (Hf) is an optional element and does not necessarily need to be contained. That is, the Hf content may be 0%. When contained, Hf forms carbonitrides and increases the strength of the alloy material. Even if even a small amount of Hf is contained, the above effect can be obtained to some extent. However, if the Hf content is too high, the strength becomes too high even if the contents of other elements are within the ranges of this embodiment, promoting ductility-dip cracking of the alloy material and thereby reducing the weldability of the alloy material. Therefore, the Hf content is 0 to 0.200%, and when Hf is contained, the Hf content is 0.200% or less. The preferred lower limit of the Hf content is more than 0%, more preferably 0.001%, even more preferably 0.002%, even more preferably 0.003%, and even more preferably 0.005%. The preferred upper limit of the Hf content is 0.180%, even more preferably 0.150%, and even more preferably 0.120%.

Ta: 0.50% or less Tantalum (Ta) is an optional element and does not necessarily need to be contained. That is, the Ta content may be 0%. When contained, Ta forms carbonitrides and increases the strength of the alloy material. Even if even a small amount of Ta is contained, the above effect can be obtained to some extent. However, if the Ta content is too high, even if the contents of other elements are within the ranges of this embodiment, the strength becomes too high, promoting ductility-dip cracking of the alloy material and thereby reducing the weldability of the alloy material. Therefore, the Ta content is 0 to 0.50%, and when Ta is contained, the Ta content is 0.50% or less. The preferred lower limit of the Ta content is more than 0%, more preferably 0.01%, even more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the Ta content is 0.45%, even more preferably 0.40%, and even more preferably 0.35%.

The chemical composition of the NiCrFe alloy material according to this embodiment may further contain rare earth elements in place of a portion of the Fe.

Rare Earth Elements: 0.0030% or Less Rare earth elements (REM) are optional elements and do not necessarily need to be present. That is, the REM content may be 0%. When present, REM neutralizes S in the alloy material by fixing it as sulfides, thereby improving the hot workability of the alloy material. Even if even a small amount of REM is present, the above effect can be achieved to some extent. However, if the REM content is too high, even if the contents of other elements are within the ranges of this embodiment, coarse oxides will form in the alloy material, thereby reducing the hot workability of the alloy material. Therefore, the REM content is 0 to 0.0030%, and when REM is present, the REM content is 0.0030% or less. The preferred lower limit of the REM content is greater than 0%, more preferably 0.0001%, even more preferably 0.0005%, even more preferably 0.0008%, and even more preferably 0.0010%. The upper limit of the REM content is preferably 0.0025%, and more preferably 0.0020%.

In this specification, REM refers to one or more elements selected from the group consisting of scandium (Sc), atomic number 21; yttrium (Y), atomic number 39; and the lanthanides lanthanum (La), atomic number 57, to lutetium (Lu), atomic number 71. In addition, REM content in this specification refers to the total content of these elements.

[Regarding formula (1)]
The NiCrFe alloy material according to this embodiment has the above-described chemical composition and also satisfies the following formula (1).
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %.

D (= 8.5 x Mn + 19.5 x Ni - 12.43 x Cr - 42.4 x Mo - 10250 x Ca + 1250 x B - 74.3776) is an index of ductility-dip cracking and liquation cracking in NiCrFe alloy materials having the above-mentioned chemical composition. In alloy materials satisfying the above-mentioned chemical composition, when D is 0.0 or less, the occurrence of liquation cracking can be suppressed, but the occurrence of ductility-dip cracking cannot be suppressed. Furthermore, in alloy materials satisfying the above-mentioned chemical composition, when D is 6.5 or more, the occurrence of liquation cracking can be suppressed, but the occurrence of ductility-dip cracking cannot be suppressed.

Therefore, the NiCrFe alloy material according to this embodiment has the above-mentioned chemical composition, and D is set to greater than 0.0 and less than 6.5. As a result, the NiCrFe alloy material according to this embodiment can achieve both excellent corrosion resistance and excellent weldability. The preferred lower limit of D is 0.1, more preferably 0.3, and even more preferably 0.5. The preferred upper limit of D is 6.4, more preferably 6.2, even more preferably 6.0, and even more preferably 5.5.

[Corrosion resistance]
The NiCrFe alloy material according to this embodiment has the above-described chemical composition and satisfies formula (1). As a result, the NiCrFe alloy material according to this embodiment has excellent corrosion resistance. The corrosion resistance of the alloy material according to this embodiment can be evaluated by a four-point bending test. Specifically, a test piece is prepared from the NiCrFe alloy material according to this embodiment. When the alloy material is an alloy plate, the test piece is prepared from the center of the plate thickness. When the alloy material is an alloy pipe, the test piece is prepared from the center of the wall thickness. The size of the test piece is, for example, 2 mm thick, 10 mm wide, and 75 mm long. The length direction of the test piece is parallel to the rolling direction of the alloy material.

The test solution is a 25% by mass aqueous solution of sodium chloride. In accordance with ASTM G39-99 (2011), stress is applied to the test specimen by four-point bending. The applied stress is controlled using a strain gauge, and the strain is 0.2%. The stressed test specimen is sealed in an autoclave along with the test jig. The test solution is poured into the autoclave, leaving the gas phase, and the autoclave is sealed to form a test bath. After degassing the test bath, 1 atm of H ₂ S gas is pressurized and sealed into the autoclave, and the test bath is stirred to saturate the H ₂ S gas. The test bath is stirred at 216°C for 240 hours.

In this embodiment, if no cracks are observed after 240 hours in the above four-point bending test, the alloy material is determined to have excellent corrosion resistance. In this specification, "no cracks are observed" means that no cracks are observed when the test piece is observed with the naked eye after the test.

[Weldability]
The NiCrFe alloy material according to this embodiment has the above-described chemical composition and satisfies formula (1). As a result, the NiCrFe alloy material according to this embodiment has not only excellent corrosion resistance but also excellent weldability. In this embodiment, having excellent weldability means that the occurrence of both liquation cracking and ductility-dip cracking can be suppressed. Specifically, the weldability of the NiCrFe alloy material according to this embodiment can be evaluated by a longitudinal Varestraint test described below.

Test pieces are prepared from the NiCrFe alloy material according to this embodiment. If the alloy material is an alloy plate, the test piece is prepared from the center of the plate thickness. If the alloy material is an alloy pipe, the test piece is prepared from the center of the wall thickness. The size of the test piece is, for example, 12 mm thick, 50 mm wide, and 300 mm long. The longitudinal direction of the test piece is parallel to the rolling direction of the alloy material.

One longitudinal end of the test specimen was fixed, and bead-on-plate welding was performed from the fixed end along the longitudinal direction of the test specimen using GTAW (Gas Tungsten Arc Welding). When the molten pool reached near the longitudinal center of the test specimen, stress was applied to the unfixed longitudinal end of the test specimen, causing the test specimen to deform along the curvature of the bending block. In this way, cracks were generated in the test specimen. The welding conditions were a welding current of 200 A, a welding voltage of 12 V, a welding speed of 15 cm/min, and a load strain of 2%.

The area of the test specimen where the crack occurred is wet buffed and then observed with an optical microscope to determine whether it is liquation cracking or ductility-dip cracking. The magnification of the optical microscope observation is not particularly limited as long as the entire crack can be observed. Furthermore, those skilled in the art can distinguish between liquation cracking and ductility-dip cracking. Specifically, for example, a weld crack that occurs in a HAZ away from the fusion line can be determined to be a ductility-dip crack. Furthermore, for example, a crack in a HAZ close to the fusion line can be determined to be a liquation crack. In this way, optical microscope observation is used to determine whether the weld crack that occurred in the test specimen is a liquation crack or a ductility-dip crack.

If liquation cracking is confirmed as a result of optical microscope observation, it is determined that excellent weldability has not been achieved. If liquation cracking is not confirmed as a result of optical microscope observation, the total length of ductility-dip cracks is determined. There are no particular limitations on the total length of ductility-dip cracks. For example, using a photograph generated by optical microscope observation, the crack length can be measured with a ruler and determined from the scale bar. For example, it can also be determined by performing image analysis on the photograph generated by optical microscope observation.

In this embodiment, if the longitudinal Varestraint test conducted under the above-mentioned conditions shows no liquation cracking and the total length of the ductility-dip cracks is less than 4.0 mm, the material is determined to have excellent weldability.

[Shape of alloy material]
The shape of the NiCrFe alloy material according to this embodiment is not particularly limited. The shape of the alloy material may be, for example, a tube, a rod, a wire, a thick plate, a thin plate, or a foil. When the alloy material is in a tube shape, it is preferably a seamless alloy pipe.

[Alloy material applications]
The application of the NiCrFe alloy material according to this embodiment is not particularly limited. The NiCrFe alloy material according to this embodiment can be used, for example, in facilities related to the oil industry, gas industry, petrochemical industry, and chemical industry. Specifically, the NiCrFe alloy material according to this embodiment is suitable for use in facilities such as oil and gas primary processing facilities and chemical plants.

[Manufacturing method]
An example of a method for manufacturing a NiCrFe alloy material according to this embodiment will be described below. Hereinafter, a method for manufacturing a seamless alloy pipe will be described as an example of the NiCrFe alloy material according to this embodiment. The method for manufacturing a seamless alloy pipe includes a process for preparing a raw material (raw material preparation process), a process for manufacturing a mother pipe from the raw material (hot working process), and a process for performing a solution treatment (solution treatment process). It should be noted that the method for manufacturing a NiCrFe alloy material according to this embodiment is not limited to the manufacturing method described below.

[Material preparation process]
In the material preparation process, a NiCrFe alloy having the above-described chemical composition is melted. The NiCrFe alloy may be melted in an electric furnace, an Ar- _O mixed gas bottom blown decarburization furnace (AOD furnace), or a vacuum decarburization furnace (VOD furnace). The melted NiCrFe alloy may be formed into an ingot by an ingot-making method, or into a slab, bloom, or billet by a continuous casting method. If necessary, the slab, bloom, or ingot may be subjected to blooming to produce a billet. A material (slab, bloom, or billet) is produced by the above-described process.

[Hot working process]
In the hot working step, the prepared material is hot worked to produce an intermediate alloy material (blank pipe). The hot working method is not particularly limited and may be any known method. That is, in this embodiment, the hot working may be hot rolling, hot extrusion, or hot forging. In the hot working, the heating temperature of the material is, for example, 1100 to 1300°C.

For example, a mother pipe may be manufactured by carrying out the Mannesmann process as the hot working. In this case, the piercing ratio is not particularly limited and may be, for example, 1.0 to 4.0. For example, a mother pipe may be manufactured by carrying out the Eugène-Séjournet process or the Erhardt push bench process (i.e., hot extrusion) as the hot working. Furthermore, the manufactured mother pipe may be subjected to hot rolling using a mandrel mill, reducer, sizing mill, or the like.

[Solution treatment process]
In the solution treatment step, the produced intermediate alloy material (blank pipe) is subjected to solution treatment. The solution treatment method is not particularly limited and may be a well-known method. For example, the blank pipe is loaded into a heat treatment furnace, maintained at a desired temperature, and then rapidly cooled. When the blank pipe is loaded into a heat treatment furnace, maintained at a desired temperature, and then rapidly cooled to perform the solution treatment, the temperature at which the solution treatment is performed (solution temperature) refers to the temperature (°C) of the heat treatment furnace used to perform the solution treatment. In this case, the time for which the solution treatment is performed (solution time) refers to the time for which the blank pipe is maintained at the solution temperature.

Preferably, the solution treatment temperature in the solution treatment process according to this embodiment is set to 1100 to 1300°C. If the solution treatment temperature is too low, precipitates (such as the σ phase, which is an intermetallic compound) may remain in the mother tube after solution treatment. In this case, the corrosion resistance of the manufactured NiCrFe alloy material may decrease. On the other hand, if the solution treatment temperature is too high, the effect of the solution treatment will saturate. Therefore, in this embodiment, the solution treatment temperature in the solution treatment process is preferably set to 1100 to 1300°C.

When the raw tube is loaded into a heat treatment furnace, held at the desired temperature, and then rapidly cooled to perform solution treatment, the solution treatment time is not particularly limited and can be performed under well-known conditions. The solution treatment time is, for example, 5 to 180 minutes. The rapid cooling method is, for example, water cooling.

[Other processes]
The NiCrFe alloy material according to this embodiment can be manufactured by the above manufacturing method. Other processes may be performed on the NiCrFe alloy material according to this embodiment as needed. For example, cold working may be performed on the intermediate alloy material after the hot working process and before the solution treatment process. The cold working may be cold rolling or cold drawing. In this case, the NiCrFe alloy material can be worked to a desired size. For example, the manufactured NiCrFe alloy material may be further cold worked. In this case, the strength of the NiCrFe alloy material is increased.

The above-mentioned manufacturing method has been described as an example of a method for manufacturing a seamless alloy pipe. However, the NiCrFe alloy material according to this embodiment may be in other shapes, such as a plate shape. Similar to the above-mentioned manufacturing method, manufacturing methods for other shapes, such as a plate shape, also include, for example, a material preparation process, a hot working process, and a solution treatment process. Furthermore, the above-mentioned manufacturing method is an example, and the pipe may be manufactured using other manufacturing methods.

The present invention will now be explained in more detail with reference to the following examples.

Alloys having the chemical compositions shown in Tables 1 and 2 were produced using a high-frequency vacuum melting method. Note that a "-" in Tables 1 and 2 indicates that the content of each element was at the impurity level. Specifically, the Cu content, W content, Sn content, Co content, V content, Nb content, Ti content, and Ta content of Test No. 1 were rounded to two decimal places to mean 0%. Furthermore, the Zr content and Hf content of Test No. 1 were rounded to four decimal places to mean 0%. Furthermore, the REM content of Test No. 1 was rounded to five decimal places to mean 0%. The chemical composition of the alloys for each test number and D calculated from the above definition are shown in Table 3.

A 50 kg ingot was produced by vacuum melting using the alloy designated by each code. Each ingot was heated at 1200°C for 24 hours and then hot forged to produce a square bar with a cross section of 50 mm x 50 mm. The resulting square bar was heated at 1200°C for 1 hour and then hot rolled to produce a plate with a thickness of 30 mm. The hot-rolled plate was then cold-rolled to produce a plate (alloy plate) with a thickness of 15 mm. The resulting alloy plate with each test number was subjected to solution treatment by heating at 1200°C for 1 hour and then water-cooling. The alloy plate with each test number was produced using the above process.

[Evaluation test]
The alloy plates with each test number were subjected to the corrosion resistance test and weldability test described below.

[Corrosion resistance test]
A four-point bending test was performed on the alloy plate of each test number using the method described above to evaluate corrosion resistance. Specifically, a test specimen with a thickness of 2 mm, a width of 10 mm, and a length of 75 mm was prepared from the center of the thickness of the alloy plate of each test number. The longitudinal direction of the test specimen corresponded to the rolling direction of the alloy plate. The test solution was a 25 mass% aqueous solution of sodium chloride. In accordance with ASTM G39-99 (2011), the test specimen was subjected to a stress of 0.2% strain by four-point bending, and the test jig was then sealed in an autoclave.

The test solution was poured into an autoclave, leaving the gas phase, and the autoclave was sealed to form a test bath. After degassing the test bath, 1 atm of _H2S gas was pressurized and sealed into the autoclave, and the test bath was stirred to saturate the _H2S gas. The test bath was stirred at 216°C for 240 hours. As a result of the four-point bending test performed under the above conditions, if no cracks were observed in the test specimen after 240 hours, the alloy plate with that test number was determined to have excellent corrosion resistance ("E" (Excellent) in the "Corrosion Resistance" column in Table 3). On the other hand, if cracks were observed in the test specimen after 1500 hours, the alloy plate with that test number was determined to not have excellent corrosion resistance ("NA" (Not Acceptable) in the "Corrosion Resistance" column in Table 3).

[Weldability test]
Among the test numbers, the weldability was evaluated for those test numbers that were judged to have excellent corrosion resistance. That is, the weldability was not evaluated for those test numbers that were judged not to have excellent corrosion resistance ("-" (no evaluation) in the "liquation cracking" column in Table 3). Specifically, the longitudinal Varestraint test was performed by the above-mentioned method on the alloy plates with test numbers that were judged to have excellent corrosion resistance, and the weldability was evaluated.

More specifically, a test specimen measuring 12 mm thick, 50 mm wide, and 300 mm long was prepared from the center of the thickness of the alloy plate of the target test number. The longitudinal direction of the test specimen corresponded to the rolling direction of the alloy plate. One longitudinal end of the test specimen was fixed, and bead-on-plate welding was performed using GTAW from the fixed end in the longitudinal direction of the test specimen. When the molten pool reached the vicinity of the longitudinal center of the test specimen, stress was applied to the unfixed longitudinal end of the test specimen, deforming the test specimen along the curvature of the bending block. In this way, cracks were generated in the test specimen. The welding conditions were a welding current of 200 A, a welding voltage of 12 V, a welding speed of 15 cm/min, and a load strain of 2%.

The area of the test specimen where the crack occurred was wet-buffed and then observed under an optical microscope to determine whether it was liquation cracking or ductility-dip cracking. If the identified crack was liquation cracking, it was determined that liquation cracking had been confirmed in the alloy sheet with that test number ("NA" (Not Acceptable) in the "Liquation Cracking" column in Table 3). If the identified crack was ductility-dip cracking, it was determined that liquation cracking had not been confirmed in the alloy sheet with that test number ("E" (Excellent) in the "Liquation Cracking" column in Table 3).

For test specimens in which no liquation cracking was observed, the total length of the ductility-dip cracks was determined. The total length of the ductility-dip cracks was determined by measuring the ductility-dip crack length with a ruler from photographs generated by optical microscope observation and comparing it with a scale bar. The obtained ductility-dip crack lengths (mm) are shown in Table 3.

[Evaluation results]
Referring to Tables 1 to 3, the alloy plates of Test Nos. 1 to 15 had appropriate chemical compositions, and D was greater than 0.0 and less than 6.5. As a result, these alloy plates had excellent corrosion resistance, no liquation cracking was observed, and further, the total length of ductility-dip cracks was less than 4.0 mm. That is, these alloy plates had excellent corrosion resistance and excellent weldability.

On the other hand, the alloy plates of test numbers 16 to 19 had D of 0.0 or less. As a result, the total length of ductility-dip cracks was 4.0 mm or more. In other words, these alloy plates did not have excellent weldability.

Alloy plates with test numbers 20 to 23 had a D of 6.5 or more. As a result, the total length of ductility-dip cracks in these alloy plates was 4.0 mm or more. In other words, these alloy plates did not have excellent weldability.

The alloy sheets of test numbers 24 and 25 did not contain Ca or B, and furthermore, D was 6.5 or more. As a result, the total length of ductility-dip cracks in these alloy sheets was 4.0 mm or more. In other words, these alloy sheets did not have excellent weldability.

The alloy plate of test number 26 had too low a N content. As a result, this alloy plate did not have excellent corrosion resistance.

The alloy plate of test number 27 had an excessively high N content. As a result, the total length of ductility-dip cracks in this alloy plate was 4.0 mm or more. In other words, this alloy plate did not have excellent weldability.

The alloy plate of test number 28 had an excessively low Ca content. As a result, the total length of ductility-dip cracks in this alloy plate was 4.0 mm or more. In other words, this alloy plate did not have excellent weldability.

The alloy sheets of test numbers 29 and 30 had too high a Ca content. As a result, the total length of ductility-dip cracks in these alloy sheets was 4.0 mm or more. In other words, these alloy sheets did not have excellent weldability.

The alloy plate of test number 31 had a B content that was too low, and furthermore, D was 6.5 or more. As a result, liquation cracking was confirmed in this alloy plate. In other words, this alloy plate did not have excellent weldability.

The alloy plates of test numbers 32 and 33 had too high a B content and a D of 6.5 or more. As a result, liquation cracking was confirmed in these alloy plates. In other words, these alloy plates did not have excellent weldability.

The alloy plate of test number 34 had too low a Ni content and a D of 0.0 or less. As a result, this alloy plate did not have excellent corrosion resistance.

The alloy plate of test number 35 had an excessively high Ni content. As a result, the total length of ductility-dip cracks in this alloy plate was 4.0 mm or more. In other words, this alloy plate did not have excellent weldability.

The alloy plate of test number 36 had too low a Cr content. As a result, the total length of ductility-dip cracks in this alloy plate was 4.0 mm or more. In other words, this alloy plate did not have excellent weldability.

The alloy plate of test number 37 had an excessively high Cr content. As a result, the total length of ductility-dip cracks in this alloy plate was 4.0 mm or more. In other words, this alloy plate did not have excellent weldability.

The alloy plate of test number 38 had too low a Mo content. As a result, this alloy plate did not have excellent corrosion resistance.

The alloy plate of test number 39 had too high a Mo content and too low a N content. As a result, the total length of ductility-dip cracks in this alloy plate was 4.0 mm or more. In other words, this alloy plate did not have excellent weldability.

The alloy plate with test number 40 had too high a V content. As a result, this alloy plate did not have excellent corrosion resistance.

The alloy plate with test number 41 had too high a P content. As a result, liquation cracking was confirmed in this alloy plate. In other words, this alloy plate did not have excellent weldability.

The above describes embodiments of the present disclosure. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by modifying the above-described embodiments as appropriate within the scope of the spirit of the present disclosure.

Claims (5)

In mass%,
C: 0.002-0.030%,
Si: 0.05-0.50%,
Mn: 0.10 to 1.50%,
P: 0.050% or less,
S: 0.0200% or less,
Ni: 29.0-40.0%,
Cr: 24.00-30.00%,
Mo: 5.0 to 7.5%,
N: 0.20-0.40%,
Al: 0.50% or less,
Ca: 0.0002 to 0.0040%, and
B: 0.0001 to 0.0050%,
The balance is composed of Fe and impurities.
Having a chemical composition that satisfies formula (1):
NiCrFe alloy material.
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %. In mass%,
C: 0.002-0.030%,
Si: 0.05-0.50%,
Mn: 0.10 to 1.50%,
P: 0.050% or less,
S: 0.0200% or less,
Ni: 29.0-40.0%,
Cr: 24.00-30.00%,
Mo: 5.0 to 7.5%,
N: 0.20-0.40%,
Al: 0.50% or less,
Ca: 0.0002 to 0.0040%, and
B: 0.0001 to 0.0050%, and further
Cu: 0.40% or less,
W: 1.00% or less,
Sn: 0.50% or less,
Co: 0.50% or less,
V: 0.50% or less,
Nb: 0.50% or less,
Ti: 0.50% or less,
Zr: 0.200% or less,
Hf: 0.200% or less,
Ta: 0.50% or less, and
Rare earth elements: 0.0030% or less, containing one or more elements selected from the group consisting of
The balance is composed of Fe and impurities.
Having a chemical composition that satisfies formula (1):
NiCrFe alloy material.
0.0<8.5 × Mn + 19.5 × Ni − 12.43 × Cr − 42.4 × Mo − 10250 × Ca + 1250 × B − 74.3776 < 6.5 (1)
Here, the element symbols in formula (1) are substituted with the contents of the corresponding elements in mass %. The NiCrFe alloy material according to claim 2,
The chemical composition is
Cu: 0.40% or less,
W: 1.00% or less,
Sn: 0.50% or less, and
Co: 0.50% or less, containing one or more elements selected from the group consisting of
NiCrFe alloy material. The NiCrFe alloy material according to claim 2,
The chemical composition is
V: 0.50% or less,
Nb: 0.50% or less,
Ti: 0.50% or less,
Zr: 0.200% or less,
Hf: 0.200% or less, and
Ta: 0.50% or less, containing one or more elements selected from the group consisting of
NiCrFe alloy material. The NiCrFe alloy material according to claim 2,
The chemical composition is
Rare earth elements: 0.0030% or less,
NiCrFe alloy material.