WO2025013666A1 - Fe-Cr-Ni ALLOY MATERIAL - Google Patents

Abstract

Provided is an Fe-Cr-Ni alloy material having high strength and decreased strength anisotropy. This Fe-Cr-Ni alloy material comprises, in mass%, C at 0.030% or less, Si at 0.01-1.00%, Mn at 0.01-2.00%, P at 0.040% or less, S at 0.0050% or less, Al at 0.01-0.50%, Ni at over 36.5% to 54.0%, Cr at 19.0-27.5%, Mo at 2.00-11.50%, Cu at 0.01-3.00%, N at 0.010-0.500%, Co at 0.01-2.00%, O at 0.010% or less, with the remainder being Fe and impurities. The Fe-Cr-Ni alloy material has a microstructure where the standard deviation of the crystal grain size number of austenite grains is 0.60 or less, and the tensile yield strength is 758 MPa or more.

Description

Fe-Cr-Ni alloy material

This disclosure relates to alloy materials, and more specifically to Fe-Cr-Ni alloy materials.

Oil wells and gas wells (hereinafter, oil wells and gas wells are collectively referred to as "oil wells") use oil well alloy materials, such as oil well tubular goods. Many oil wells are in sour environments that contain corrosive hydrogen sulfide. In this specification, a sour environment means an acidic environment that contains hydrogen sulfide. A sour environment may contain not only hydrogen sulfide but also carbon dioxide. Materials used in such sour environments are required to have excellent corrosion resistance.

Materials that require excellent corrosion resistance include, for example, 18-8 stainless steel materials such as SUS304H, SUS316H, SUS321H, and SUS347H, and Fe-Cr-Ni alloy materials such as Alloy800H, which is specified as NCF800H in the JIS standard. Fe-Cr-Ni alloy materials have superior corrosion resistance compared to 18-8 stainless steels. Fe-Cr-Ni alloy materials are also more economical than Ni-based alloy materials such as Alloy617. For this reason, Fe-Cr-Ni alloy materials are sometimes used as alloy materials for oil wells used in sour environments.

　JP Patent Publication No. 2-217445 (Patent Document 1) and WO 2015/072458 (Patent Document 2) propose an alloy material for oil wells that has 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%, Mn: 1.0-2.0%, N: 0.015% or less, B: 0.10% or less, C: 0.10% or less, Al: 0.30% or less, P: 0.03% or less, S: 0.02% or less, with the balance being essentially 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 steel has a chemical composition consisting of Al: 0.03-0.20%, REM: 0.01-0.074%, W: 0-less than 8.0%, Co: 0-2.0%, one or more of Ca and Mg: 0.0003-0.01% in total, one or more of Ti, Nb, Zr, and V: 0-0.5% in total, with the balance being Fe and impurities, among the impurities being C: 0.03% or less, P: 0.03% or less, S: 0.001% or less, and O: 0.01% or less, and a 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

In recent years, as oil wells have become deeper, there has been a demand for higher strength oil well alloys. In other words, Fe-Cr-Ni alloys intended for use as oil well alloys are required to have high strength.

In recent oil wells, in addition to vertical wells that are drilled straight down vertically, inclined wells are also on the rise. Inclined wells are formed by drilling the well by bending the extension direction from vertical downward to horizontal. By including a portion that extends horizontally (horizontal well), inclined wells can cover a wide area of the strata in which production fluids such as crude oil and gas are buried, and the production efficiency of the production fluids can be improved.

On the other hand, when used in such inclined wells, the alloy material may be subjected to compressive forces. In this case, it is preferable that the alloy material has high not only tensile yield strength but also compressive yield strength. In other words, it is preferable that Fe-Cr-Ni alloy materials intended for use in inclined wells not only have high strength but also have reduced strength anisotropy. However, in the above Patent Documents 1 and 2, only the tensile yield strength is considered as the strength of the Fe-Cr-Ni alloy material. In other words, the above Patent Documents 1 and 2 do not consider the strength anisotropy of the alloy material.

The objective of this disclosure is to provide an Fe-Cr-Ni alloy material that has high strength and reduced strength anisotropy.

The Fe-Cr-Ni alloy material according to the present disclosure has
In mass percent,
C: 0.030% or less,
Si: 0.01-1.00%,
Mn: 0.01-2.00%,
P: 0.040% or less,
S: 0.0050% or less,
Al: 0.01-0.50%,
Ni: more than 36.5 to 54.0%,
Cr: 19.0-27.5%,
Mo: 2.00-11.50%,
Cu: 0.01-3.00%,
N: 0.010-0.500%,
Co: 0.01-2.00%,
O: 0.010% or less,
V: 0 to 0.50%,
Nb: 0 to 0.10%,
Ti: 0 to 0.40%,
W: 0 to 3.0%,
Sn: 0 to 0.010%,
Ca: 0-0.0100%,
B: 0 to 0.0100%,
Mg: 0 to 0.0100%,
Rare earth elements: 0 to 0.100%, and
The balance is Fe and impurities,
In the microstructure, the standard deviation of the grain size number of the austenite grains is 0.60 or less;
The tensile yield strength is 758 MPa or more.

The Fe-Cr-Ni alloy material disclosed herein has high strength and reduced strength anisotropy.

FIG. 1 is a diagram showing the relationship between the standard deviation σ of the grain size number and the anisotropy index AI (=compressive YS/tensile YS) in this embodiment.

The inventors first focused on Fe-Cr-Ni alloy materials with a tensile yield strength of 110 ksi (758 MPa) or more as Fe-Cr-Ni alloy materials with high strength. Next, the inventors investigated the strength anisotropy of Fe-Cr-Ni alloy materials with a tensile yield strength of 758 MPa or more from the viewpoint of chemical composition.

As a result, the inventors found that the composition is, by mass%, C: 0.030% or less, Si: 0.01-1.00%, Mn: 0.01-2.00%, P: 0.040% or less, S: 0.0050% or less, Al: 0.01-0.50%, Ni: over 36.5-54.0%, Cr: 19.0-27.5%, Mo: 2.00-11.50%, Cu: 0.01-3.00%, N: 0.010-0.500%, Co: 0.01-2.00%, O: 0.010 %, V: 0-0.50%, Nb: 0-0.10%, Ti: 0-0.40%, W: 0-3.0%, Sn: 0-0.010%, Ca: 0-0.0100%, B: 0-0.0100%, Mg: 0-0.0100%, rare earth elements: 0-0.100%, and the balance being Fe and impurities, it is believed that an Fe-Cr-Ni alloy material with a tensile yield strength of 758 MPa or more and further reducing strength anisotropy is possible.

On the other hand, even in Fe-Cr-Ni alloy materials with the above-mentioned chemical composition, if they have a tensile yield strength of 758 MPa or more, strength anisotropy may be large. Therefore, the inventors conducted detailed studies on reducing the strength anisotropy of alloy materials with the above-mentioned chemical composition and a tensile yield strength of 758 MPa or more.

Here, the Fe-Cr-Ni alloy material having the above-mentioned chemical composition has a microstructure consisting of austenite. In this specification, "microstructure consisting of austenite" means that phases other than austenite are negligibly small. Therefore, the inventors have focused on the austenite grains of an Fe-Cr-Ni alloy material having the above-mentioned chemical composition and a tensile yield strength of 758 MPa or more, and have conducted detailed studies on methods for reducing the strength anisotropy of the alloy material.

As a result of detailed investigations by the present inventors, it has become clear that in an Fe-Cr-Ni alloy material having the above-mentioned chemical composition and a tensile yield strength of 758 MPa or more, the standard deviation σ of the grain size number in the microstructure affects the strength anisotropy of the alloy material. This point will be specifically explained using the drawings. Figure 1 is a diagram showing the relationship between the standard deviation σ of the grain size number and the anisotropy index AI in this embodiment. Figure 1 was created using the standard deviation σ of the grain size number and the anisotropy index AI for an embodiment described later in which the configuration other than the standard deviation σ of the grain size number satisfies the conditions of this embodiment.

Referring to FIG. 1, in an Fe-Cr-Ni alloy material having the above-mentioned chemical composition and a tensile yield strength of 758 MPa or more, if the standard deviation σ of the grain size number is 0.60 or less, the anisotropy index AI can be increased to 0.700 or more. On the other hand, if the standard deviation σ of the grain size number exceeds 0.60, the anisotropy index AI drops to less than 0.700. Therefore, the Fe-Cr-Ni alloy material according to this embodiment satisfies the above-mentioned chemical composition, has a tensile yield strength of 758 MPa or more, and further, the standard deviation σ of the grain size number is 0.60 or less. As a result, the Fe-Cr-Ni alloy material according to this embodiment can reduce strength anisotropy.

The details of why the strength anisotropy of an alloy material can be reduced by setting the standard deviation σ of the grain size number to 0.60 or less are not clear. However, it has been proven by the examples described below that the strength anisotropy can be reduced by satisfying the above-mentioned chemical composition, having a tensile yield strength of 758 MPa or more, and further setting the standard deviation σ of the grain size number to 0.60 or less.

The Fe-Cr-Ni alloy material of this embodiment, which was completed based on the above findings, has the following features:

[1]
In mass percent,
C: 0.030% or less,
Si: 0.01-1.00%,
Mn: 0.01 to 2.00%,
P: 0.040% or less,
S: 0.0050% or less,
Al: 0.01-0.50%,
Ni: more than 36.5 to 54.0%,
Cr: 19.0-27.5%,
Mo: 2.00-11.50%,
Cu: 0.01-3.00%,
N: 0.010-0.500%,
Co: 0.01-2.00%,
O: 0.010% or less,
V: 0-0.50%,
Nb: 0 to 0.10%,
Ti: 0 to 0.40%,
W: 0 to 3.0%,
Sn: 0 to 0.010%,
Ca: 0-0.0100%,
B: 0 to 0.0100%,
Mg: 0 to 0.0100%,
Rare earth elements: 0 to 0.100%, and
The balance is Fe and impurities,
In the microstructure, the standard deviation of the grain size number of the austenite grains is 0.60 or less;
The tensile yield strength is 758 MPa or more.
Fe-Cr-Ni alloy material.

[2]
The Fe-Cr-Ni alloy material according to [1],
V: 0.01-0.50%,
Nb: 0.01 to 0.10%,
Ti: 0.01-0.40%,
W: 0.1-3.0%,
Sn: 0.001 to 0.010%,
Ca: 0.0001-0.0100%,
B: 0.0001 to 0.0100%,
Mg: 0.0001 to 0.0100%, and
Rare earth elements: containing one or more elements selected from the group consisting of 0.001 to 0.100%;
Fe-Cr-Ni alloy material.

[3]
Seamless alloy pipe for oil wells.
The Fe-Cr-Ni alloy material according to [1] or [2].

The shape of the Fe-Cr-Ni alloy material according to this embodiment is not particularly limited. The shape of the Fe-Cr-Ni alloy material according to this embodiment may be a plate, a rod with a circular cross section, or a tube. That is, the Fe-Cr-Ni alloy material according to this embodiment may be an alloy plate, a rod with a circular cross section, or an alloy pipe. The alloy pipe may be a seamless alloy pipe or a welded alloy pipe. When the alloy material is an oil well alloy pipe, it is preferably a seamless alloy pipe.

The Fe-Cr-Ni alloy material according to this embodiment will be described in detail below. Unless otherwise specified, "%" for elements means mass %.

[Chemical composition]
The chemical composition of the Fe-Cr-Ni alloy material according to this embodiment contains the following elements.

C: 0.030% or less Carbon (C) is an unavoidably contained impurity. That is, the lower limit of the C content is more than 0%. If the C content is too high, Cr carbides will be generated at the grain boundaries even if the contents of other elements are within the range of this embodiment. Cr carbides increase the cracking sensitivity at the grain boundaries. As a result, the corrosion resistance of the alloy material decreases. Therefore, the C content is 0.030% or less. The preferred upper limit of the C content is 0.028%, more preferably 0.025%, more preferably 0.020%, and even more preferably 0.015%. It is preferable that the C content is as low as possible. However, an extreme reduction in the C content significantly increases the manufacturing cost. Therefore, when considering industrial production, the preferred lower limit of the C content is 0.001%, and even more preferably 0.003%.

Si: 0.01~1.00%
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 range of this embodiment. If the Si content is too high, the hot workability of the alloy material decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Si content is 0.01 to 1.00%. The lower limit of the Si content is preferably 0.05%, more preferably 0.10%, and even more preferably 0.20%. The upper limit of the Si content is preferably 0.90%, and even more preferably is 0.80%, and more preferably 0.70%.

Mn: 0.01-2.00%
Manganese (Mn) deoxidizes and desulfurizes the alloy. 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. If the Mn content is too high, the hot workability of the alloy material is reduced even if the contents of other elements are within the ranges of this embodiment. Therefore, the Mn content is set to 0.01 to 2.00%. The lower limit of the Mn content is preferably 0.10%, more preferably 0.20%, and even more preferably 0.30%. The upper limit of the Mn content is preferably 1.80%. , more preferably 1.60%, more preferably 1.50%, more preferably 1.30%, and even more preferably 1.00%.

P: 0.040% or less Phosphorus (P) is an impurity that is inevitably contained. That is, the lower limit of the P content is more than 0%. P segregates at grain boundaries. Therefore, if the P content is too high, the hot workability and corrosion resistance of the alloy material will decrease even if the contents of other elements are within the range of this embodiment. Therefore, the P content is 0.040% or less. The preferred upper limit of the P content is 0.035%, more preferably 0.030%, and even more preferably 0.025%. The P content is preferably as low as possible. However, an extreme reduction in the P content significantly increases the manufacturing cost. Therefore, in consideration of industrial production, the preferred lower limit of the P content is 0.001%, more preferably 0.002%, and even more preferably 0.003%.

S: 0.0050% or less Sulfur (S) is an impurity that is inevitably contained. That is, the lower limit of the S content is more than 0%. S segregates at grain boundaries. Therefore, if the S content is too high, the hot workability of the alloy material decreases even if the contents of other elements are within the range of this embodiment. Therefore, the S content is 0.0050% or less. The preferred upper limit of the S content is 0.0040%, more preferably 0.0030%, and even more preferably 0.0020%. The S content is preferably as low as possible. However, an extreme reduction in the S content significantly increases the manufacturing cost. Therefore, when considering industrial production, the preferred lower limit of the S content is 0.0001%, more preferably 0.0003%, and even more preferably 0.0005%.

Al: 0.01~0.50%
Aluminum (Al) deoxidizes the alloy. It also forms oxides to fix oxygen and improve the hot workability of the alloy. It also improves the impact resistance and corrosion resistance of the alloy. If the Al content is too low, the above-mentioned effect cannot be sufficiently obtained even if the contents of the other elements are within the range of this embodiment. On the other hand, if the Al content is too high, the other element contents are not sufficiently obtained. Even if the amount is within the range of this embodiment, excessive Al oxides are generated, and the hot workability of the alloy material is rather deteriorated. Therefore, the Al content is set to 0.01 to 0.50%. The lower limit of the Al content is preferably 0.02%, more preferably 0.03%, and even more preferably 0.05%. The upper limit of the Al content is preferably 0.45%. The Al content is more preferably 0.40%, and even more preferably 0.30%. The Al content in this specification means the content of "acid-soluble Al", that is, sol. Al. .

Ni: more than 36.5 to 54.0%
Nickel (Ni) is an austenite-forming element and stabilizes austenite in the alloy material. If the Ni content is too low, the above effect cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment. On the other hand, Ni may increase strength anisotropy. Therefore, if the Ni content is too high, the strength anisotropy of the alloy material may increase even if the contents of other elements are within the range of this embodiment. Therefore, the Ni content is more than 36.5 to 54.0%. The preferred lower limit of the Ni content is 36.6%, more preferably 37.0%, more preferably 38.0%, and even more preferably 40.0%. The preferred upper limit of the Ni content is 53.5%, more preferably 53.0%, and even more preferably 52.0%.

Cr: 19.0-27.5%
Chromium (Cr) enhances the corrosion resistance of the alloy material. Cr may also reduce the strength anisotropy of the alloy material. If the Cr content is too low, the contents of other elements may be within the range of this embodiment. On the other hand, if the Cr content is too high, the hot workability of the alloy material is deteriorated even if the contents of other elements are within the range of this embodiment. In this case, intermetallic compounds such as the σ phase are more likely to form, and the corrosion resistance of the alloy material decreases. Therefore, the Cr content is 19.0 to 27.5%. Cr Content The preferred lower limit of the Cr content is 19.5%, more preferably 20.0%, further preferably 21.0%, and further preferably 22.0%. The preferred upper limit of the Cr content is 27. 0%, and more preferably 26.5%.

Mo: 2.00-11.50%
Molybdenum (Mo) contributes to the stabilization of the corrosion protective film and improves the corrosion resistance of the alloy material. Mo also increases the strength of the alloy material by solid solution strengthening. If the Mo content is too low, the alloy material containing other elements will have a high corrosion resistance. On the other hand, if the Mo content is too high, the alloy may not be able to obtain the above-mentioned effects even if the contents of the other elements are within the ranges of the present embodiment. The hot workability of the material is reduced. In this case, the manufacturing cost is also significantly increased. Therefore, the Mo content is 2.00 to 11.50%. The preferred lower limit of the Mo content is 2.20%. The upper limit of the Mo content is preferably 11.20%, more preferably 11.00%, and even more preferably 10. .80%, and more preferably 10.00%.

Cu: 0.01~3.00%
Copper (Cu) contributes to stabilizing the corrosion protection film and enhances the corrosion resistance of the alloy material. If the Cu content is too low, the above effect will not be achieved even if the contents of other elements are within the range of this embodiment. On the other hand, if the Cu content is too high, the hot workability of the alloy material is reduced even if the contents of other elements are within the ranges of this embodiment. The lower limit of the Cu content is preferably 0.02%, more preferably 0.05%, still more preferably 0.10%, and still more preferably 0. The upper limit of the Cu content is preferably 2.80%, more preferably 2.50%, and even more preferably 2.00%.

N: 0.010-0.500%
Nitrogen (N) increases the strength of the alloy material by solid solution strengthening. If the N content is too low, the above effect cannot be sufficiently obtained even if the contents of other elements are within the range of this embodiment. On the other hand, if the N content is too high, the corrosion resistance of the alloy material may decrease even if the contents of other elements are within the range of this embodiment. The lower limit of the N content is preferably 0.015%, more preferably 0.020%, still more preferably 0.030%, and still more preferably 0.050%. The upper limit of the N content is preferably 0.495%, more preferably 0.480%, and still more preferably 0.450%.

Co:0.01~2.00%
Cobalt (Co) stabilizes austenite in the alloy material. If the Co 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 Co content is too high, the manufacturing cost will increase significantly even if the contents of other elements are within the range of this embodiment. Therefore, the Co content is 0.01 to 2.00%. The lower limit of the Co content is preferably 0.02%, more preferably 0.03%, further preferably 0.05%, and further preferably 0.10%. The upper limit is 1.50%, more preferably 1.20%, further preferably 1.00%, and further preferably 0.90%.

O: 0.010% or less Oxygen (O) is an impurity that is inevitably contained. That is, the lower limit of the O content is more than 0%. O forms oxides. Therefore, if the O content is too high, even if the contents of other elements are within the range of this embodiment, coarse oxides are formed in the alloy material, and the hot workability of the alloy material is reduced. In this case, the corrosion resistance of the alloy material is further reduced. Therefore, the O content is 0.010% or less. The preferred upper limit of the O content is 0.008%, more preferably 0.005%. The O content is preferably as low as possible. However, an extreme reduction in the O content significantly increases the manufacturing cost. Therefore, in consideration of industrial production, the preferred lower limit of the O content is 0.0001%, more preferably 0.001%, and even more preferably 0.002%.

The remainder of the chemical composition of the Fe-Cr-Ni alloy material according to this embodiment is composed of Fe and impurities. Here, impurities refer to substances that are mixed in from raw materials such as ore, scrap, or the manufacturing environment when the Fe-Cr-Ni alloy material is industrially manufactured, and are acceptable to the extent that they do not significantly adversely affect the effects of the Fe-Cr-Ni alloy material according to this embodiment.

[Optional element]
The chemical composition of the Fe-Cr-Ni alloy material according to the present embodiment may further contain one or more elements selected from the group consisting of V, Nb, and Ti, all of which increase the strength of the alloy material.

V: 0 to 0.50%
Vanadium (V) is an optional element and may not be contained. In other words, the V content may be 0%. When contained, V forms carbonitrides with C and N, and increases the strength of the alloy material. 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 range of this embodiment, excessive carbonitrides are formed, and the ductility of the alloy material decreases. Therefore, the V content is 0 to 0.50%. The preferred lower limit of the V content is more than 0%, more preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%. The preferred upper limit of the V content is 0.40%, more preferably 0.30%, more preferably 0.25%, and even more preferably 0.20%.

Nb: 0-0.10%
Niobium (Nb) is an optional element and may not be contained. In other words, the Nb content may be 0%. When Nb is contained, it forms carbonitrides with C and N, and The strength of the alloy material is increased. Even if even a small amount of Nb is contained, the above effect can be obtained to a certain extent. However, if the Nb content is too high, even if the contents of other elements are within the range of this embodiment, Carbonitrides and the like are formed in excess, and the ductility of the alloy material is reduced. Therefore, the Nb content is 0 to 0.10%. The lower limit of the Nb content is preferably more than 0%, and more preferably 0. The upper limit of the Nb content is preferably 0.09%, more preferably 0.08%, and even more preferably 0.07%. More preferably, it is 0.06%, more preferably, it is 0.05%, more preferably, it is 0.04%, and more preferably, it is 0.03%.

Ti: 0-0.40%
Titanium (Ti) is an optional element and may not be contained. In other words, the Ti content may be 0%. When contained, Ti forms carbonitrides with C and N, and The strength of the alloy material is increased. Even if even a small amount of Ti is contained, the above effect can be obtained to a certain extent. However, if the Ti content is too high, even if the contents of other elements are within the range of this embodiment, Carbonitrides and the like are formed in excess, and the ductility of the alloy material is reduced. Therefore, the Ti content is 0 to 0.40%. The lower limit of the Ti content is preferably more than 0%, and more preferably 0. The upper limit of the Ti content is preferably 0.35%, more preferably 0.30%, and more preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%. The content is more preferably 0.20%, and even more preferably 0.10%.

The chemical composition of the Fe-Cr-Ni alloy material according to this embodiment may further contain one or more elements selected from the group consisting of W and Sn. All of these elements increase the corrosion resistance of the alloy material.

W: 0 to 3.0%
Tungsten (W) is an optional element and may not be contained. That is, the W content may be 0%. When contained, W contributes to stabilization of the corrosion protection film and enhances the corrosion resistance of the alloy material. W further enhances the strength of the alloy material by solid solution strengthening. If even a small amount of W is contained, the above effect can be obtained to a certain extent. However, if the W content is too high, the hot workability of the alloy material decreases even if the contents of other elements are within the range of this embodiment. Therefore, the W content is 0 to 3.0%. The preferred lower limit of the W content is more than 0%, more preferably 0.1%, more preferably 0.3%, and even more preferably 0.5%. The preferred upper limit of the W content is 2.8%, more preferably 2.5%, more preferably 2.2%, and even more preferably 2.0%.

Sn: 0-0.010%
Tin (Sn) is an optional element and may not be contained. In other words, the Sn content may be 0%. When contained, Sn enhances the corrosion resistance of the alloy material. Even a small amount of Sn is contained. If the Sn content is too high, however, the hot workability of the alloy material is reduced even if the contents of other elements are within the ranges of this embodiment. The Sn content is 0 to 0.010%. The lower limit of the Sn content is preferably more than 0%, more preferably 0.001%, even more preferably 0.002%, and even more preferably The upper limit of the Sn content is preferably 0.009%, more preferably 0.008%, and still more preferably 0.007%.

The chemical composition of the Fe-Cr-Ni alloy material according to this embodiment may further contain one or more elements selected from the group consisting of Ca, B, Mg, and rare earth elements (REM). All of these elements improve the hot workability of the alloy material.

Ca: 0~0.0100%
Calcium (Ca) is an optional element and may not be contained. In other words, the Ca content may be 0%. When contained, Ca fixes S in the alloy as sulfides, The above effect can be obtained to some extent if even a small amount of Ca is contained. However, if the Ca content is too high, the contents of other elements will not fall within the range of this embodiment. Even if the Ca content is within the range, coarse oxides are formed in the alloy material, and the hot workability of the alloy material is rather deteriorated. Therefore, the Ca content is 0 to 0.0100%. The lower limit is more than 0%, more preferably 0.0001%, even more preferably 0.0005%, even more preferably 0.0009%, even more preferably 0.0011%, and even more preferably is 0.0013%, and more preferably 0.0015%. The upper limit of the Ca content is preferably 0.0090%, more preferably 0.0080%, further preferably 0.0060%, and further preferably 0.0050%.

B: 0-0.0100%
Boron (B) is an optional element and may not be contained. In other words, the B content may be 0%. When contained, B fixes S in the alloy as sulfides, Even if even a small amount of B is contained, the above effects can be obtained to a certain extent. However, if the B content is too high, the contents of other elements will not fall within the range of this embodiment. Even if the B content is within the range, B segregates at grain boundaries, and the hot workability of the alloy material is rather deteriorated. Therefore, the B content is 0 to 0.0100%. The preferable lower limit of the B content is 0. %, more preferably 0.0001%, more preferably 0.0003%, and even more preferably 0.0005%. The upper limit of the B content is preferably 0.0080%, more preferably 0.0060%, still more preferably 0.0040%, still more preferably 0.0030%, and still more preferably 0.0020%. %, more preferably 0.0015%, and even more preferably 0.0010%.

Mg: 0-0.0100%
Magnesium (Mg) is an optional element and may not be contained. In other words, the Mg content may be 0%. When contained, Mg fixes S in the alloy as sulfides, Even if even a small amount of Mg is contained, the above effects can be obtained to some extent. However, if the Mg content is too high, the contents of other elements will not fall within the range of this embodiment. Even if the Mg content is within the range of 0.0100%, coarse oxides are formed in the alloy material, and the hot workability of the alloy material is rather deteriorated. Therefore, the Mg content is 0 to 0.0100%. The lower limit is more than 0%, more preferably 0.0001%, more preferably 0.0003%, and even more preferably 0.0005%. The preferred upper limit of the Mg content is 0.0080%. More preferably, it is 0.0060%, and even more preferably, it is 0.0040%.

Rare earth elements: 0-0.100%
Rare earth elements (REM) are optional elements and may not be included. In other words, the REM content may be 0%. When included, REM fixes S in the alloy as sulfides. Even if even a small amount of REM is contained, the above effect can be obtained to some extent. However, if the REM content is too high, the contents of other elements may be different from those of the present embodiment. Even if the REM content is within the range, coarse oxides are formed in the alloy material, and the hot workability of the alloy material is rather deteriorated. Therefore, the REM content is 0 to 0.100%. The lower limit is preferably more than 0%, more preferably 0.001%, more preferably 0.005%, and even more preferably 0.010%. The upper limit of the REM content is preferably 0.080%. , more preferably 0.060%, and even more preferably 0.050%.

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, the REM content in this specification refers to the total content of these elements.

[Standard deviation of grain size number σ]
The Fe-Cr-Ni alloy material according to the present embodiment has the above-mentioned chemical composition, and further has a standard deviation σ of the grain size number of the austenite grains of 0.60 or less. As a result, the Fe-Cr-Ni alloy material according to the present embodiment can reduce strength anisotropy even if it has a tensile yield strength of 758 MPa or more.

Here, when the standard deviation σ of the grain size number of the austenite grains is large, it is presumed that there are regions in the alloy material where coarse austenite grains (coarse grains) are unevenly distributed and regions where fine austenite grains (fine grains) are unevenly distributed. In addition, when the tensile yield strength of the Fe-Cr-Ni alloy material having the above-mentioned chemical composition is to be 758 MPa or more, in the manufacturing process described below, cold working or the like is performed after heat treatment such as solution treatment, and strain may be introduced into the alloy material. Therefore, anisotropy in strength may occur depending on the direction in which strain is introduced. Specifically, when cold drawing or cold rolling is performed as cold working, the tensile yield strength is greater than the compressive yield strength.

More specifically, when a tensile test is conducted on an alloy material in which strength anisotropy has been created by applying stress in the tensile direction, in which further stress is applied in the tensile direction, the suppression of dislocation movement becomes dominant. In other words, the ease with which dislocations move during a tensile test does not differ significantly between coarse grains and fine grains. On the other hand, when a compression test is conducted under similar conditions, in which stress is applied in the compression direction, the suppression of dislocation movement during the compression test becomes less effective and the material becomes more susceptible to the effects of grain boundaries. As a result, dislocations move easily in coarse grains during a compression test, but dislocations move less easily in fine grains.

In other words, when strength anisotropy occurs due to the application of stress in the tensile direction, it is presumed that the ease with which dislocations move in the tensile direction differs from the ease with which dislocations move in the compressive direction. Therefore, when there are areas in an alloy material where coarse grains are unevenly distributed and areas where fine grains are unevenly distributed, the ease with which dislocations move in the tensile direction and the difficulty with which dislocations move in the compressive direction may become apparent. In this way, it is presumed that when the standard deviation σ of the crystal grain size number of austenite grains is large, the tensile yield strength is likely to be greater than the compressive yield strength, increasing strength anisotropy.

The inventors speculate that, based on the above mechanism, if the standard deviation σ of the grain size number of the austenite grains of an Fe-Cr-Ni alloy material having the above chemical composition is 0.60 or less, the strength anisotropy can be reduced even if the material has a tensile yield strength of 758 MPa or more. It is possible that, based on a mechanism other than the above mechanism, if the standard deviation σ of the grain size number of the austenite grains of an Fe-Cr-Ni alloy material having the above chemical composition is 0.60 or less, the strength anisotropy can be reduced even if the material has a tensile yield strength of 758 MPa or more. However, as described above, it has been proven by the examples described below that if the standard deviation σ of the grain size number of the austenite grains of an Fe-Cr-Ni alloy material having the above chemical composition is 0.60 or less, the strength anisotropy can be reduced even if the material has a tensile yield strength of 758 MPa or more.

In this embodiment, the preferred upper limit of the standard deviation σ of the grain size number of the austenite grains is 0.58, more preferably 0.55, and even more preferably 0.53. In the Fe-Cr-Ni alloy material according to this embodiment, the smaller the standard deviation σ of the grain size number of the austenite grains, the more preferable. In other words, the lower limit of the standard deviation σ of the grain size number of the austenite grains may be 0.00, 0.05, 0.10, or 0.15.

In the Fe-Cr-Ni alloy material according to this embodiment, the standard deviation σ of the grain size number of the austenite grains can be found by the following method. Specifically, a test piece for microstructure observation is prepared from the Fe-Cr-Ni alloy material according to this embodiment. If the alloy material is in the form of a plate, the test piece is prepared from the center of the plate thickness. If the alloy material is in the form of a tube, the test piece is prepared from the center of the wall thickness. If the alloy material is in the form of a rod with a circular cross section, the test piece is prepared from the R/2 position. In this specification, the R/2 position means the center position of the radius R in a cross section perpendicular to the axial direction. The size of the test piece is not particularly limited as long as it can provide the observation surface described below.

After the observation surface of the prepared test piece is polished to a mirror finish, it is etched using aqua regia (a solution of hydrochloric acid and nitric acid mixed in a ratio of 3:1) to reveal the austenite grain boundaries. From the observation surface, 10 fields of view are selected at random and observed using an optical microscope to generate photographic images. The magnification for microscopic observation can be set appropriately depending on the grain size. Specifically, in microscopic observation, the magnification is set so that the field of view contains, for example, 50 or more grains.

In each field of view, image analysis is performed on the obtained photographic image to measure the grain size number in accordance with ASTM E112 (2021). In other words, one grain size number is obtained for each observation field. At this time, the grain size number of the austenite grains is obtained by rounding off the obtained value to the nearest tenth. The standard deviation of the obtained 10 grain size numbers is calculated and defined as the standard deviation σ of the austenite grain grains. The standard deviation σ of the austenite grain grains is calculated by rounding off the obtained value to the nearest tenth.

In the Fe-Cr-Ni alloy material according to this embodiment, the grain size number of the austenite grains is not particularly limited as long as the standard deviation σ is 0.60 or less. In this embodiment, the lower limit of the grain size number of the austenite grains may be, for example, 4.0, 4.5, or 5.0. In this embodiment, the upper limit of the grain size number of the austenite grains may be, for example, 12.0, 11.5, or 11.0. In this case, the grain size number of the austenite grains means the arithmetic average value of the 10 grain size numbers obtained by the above-mentioned method.

[Tensile yield strength]
The Fe-Cr-Ni alloy material according to the present embodiment has the above-mentioned chemical composition, and further has a standard deviation σ of the grain size number of the austenite grains of 0.60 or less. As a result, the Fe-Cr-Ni alloy material according to the present embodiment has a tensile yield strength of 758 MPa or more, but has reduced strength anisotropy.

As described above, when attempting to obtain a tensile yield strength of 758 MPa or more in an Fe-Cr-Ni alloy material having the above-mentioned chemical composition, strength anisotropy may become high. However, the alloy material according to this embodiment can suppress the manifestation of strength anisotropy due to variations in grain size, because the standard deviation σ of the grain size number of the austenite grains is 0.60 or less. Therefore, the alloy material according to this embodiment can reduce strength anisotropy even if it has a high tensile yield strength of 758 MPa or more.

In this embodiment, the preferred lower limit of the tensile yield strength is 800 MPa, more preferably 830 MPa, and even more preferably 860 MPa. In this embodiment, the upper limit of the tensile yield strength is not particularly limited, and may be, for example, 1240 MPa, 1200 MPa, or 1150 MPa.

Furthermore, in the Fe-Cr-Ni alloy material of this embodiment, the compressive yield strength is not particularly limited. In this embodiment, the lower limit of the compressive yield strength may be, for example, 600 MPa, 610 MPa, or 630 MPa. In this embodiment, the upper limit of the compressive yield strength may be, for example, less than 1240 MPa, less than 1200 MPa, or less than 1150 MPa. Furthermore, the method of measuring the tensile yield strength and compressive yield strength in this embodiment will be described later.

[Strength anisotropy]
The Fe-Cr-Ni alloy material according to the present embodiment has the above-mentioned chemical composition, and further has a standard deviation σ of the grain size number of the austenite grains of 0.60 or less. As a result, the Fe-Cr-Ni alloy material according to the present embodiment has a reduced strength anisotropy even though it has a tensile yield strength of 758 MPa or more. In this specification, the reduced strength anisotropy means that the anisotropy index AI is 0.700 or more. In this specification, the anisotropy index AI means the ratio (compressive YS/tensile YS) of the compressive yield strength (compressive YS) to the tensile yield strength (tensile YS).

The preferred lower limit of the anisotropy index AI is 0.705, more preferably 0.710, more preferably 0.715, more preferably 0.720, and even more preferably 0.730. The upper limit of the anisotropy index AI is substantially less than 1.000, more preferably 0.999, more preferably 0.990, and even more preferably 0.980.

The anisotropy index AI, tensile yield strength, and compressive yield strength of the Fe-Cr-Ni alloy material according to this embodiment can be determined by the following method. First, the tensile yield strength and compressive yield strength of the Fe-Cr-Ni alloy material according to this embodiment are determined.

Specifically, the tensile yield strength of the Fe-Cr-Ni alloy material according to this embodiment can be determined by the following method. A tensile test is performed according to the method of ASTM E8/E8M (2021). A round bar test piece is prepared from the alloy material according to this embodiment. When the alloy material has a plate shape, a round bar test piece is prepared from the center of the plate thickness. When the alloy material has a tubular shape, a round bar test piece is prepared from the center of the wall thickness. When the alloy material has a rod shape with a circular cross section, a round bar test piece is prepared from the R/2 position. The size of the round bar test piece is, for example, a parallel part diameter of 4 mm and a gauge length of 20 mm. The axial direction of the round bar test piece is parallel to the rolling direction of the alloy material. A tensile test is performed using the round bar test piece at room temperature (25°C) in the air, and the obtained 0.2% offset yield strength is defined as the tensile yield strength (MPa). The tensile yield strength (MPa) is calculated by rounding the obtained value to the nearest tenth.

Similarly, the compressive yield strength of the Fe-Cr-Ni alloy material according to this embodiment can be determined by the following method. A compression test is performed according to ASTM E9 (2019). A cylindrical test piece is prepared from the alloy material according to this embodiment. If the alloy material is plate-shaped, a cylindrical test piece is prepared from the center of the plate thickness. If the alloy material is tubular, a cylindrical test piece is prepared from the center of the wall thickness. If the alloy material is rod-shaped with a circular cross section, a cylindrical test piece is prepared from the R/2 position. The size of the cylindrical test piece is, for example, 4 mm in parallel diameter and 8 mm in length. The axial direction of the cylindrical test piece is parallel to the rolling direction of the alloy material. A compression test is performed using the cylindrical test piece at room temperature (25°C) in the air, and the obtained 0.2% offset yield strength is defined as the compressive yield strength (MPa). The compressive yield strength (MPa) is determined by rounding off the obtained value to the nearest tenth.

The anisotropy index AI (=compression YS/tensile YS) can be calculated using the obtained tensile yield strength (tensile YS) and compression yield strength (compression YS). The anisotropy index AI is calculated by rounding the obtained value to the fourth decimal place.

[Production method]
An example of a method for producing an Fe—Cr—Ni alloy material according to this embodiment will be described below. As an example of the Fe—Cr—Ni alloy material according to this embodiment, a method for producing a seamless alloy pipe will be described below. The method for producing a seamless alloy pipe includes a step of preparing a material (material preparation step), a step of producing a mother pipe from the material (hot working step), a step of cold working the produced mother pipe (first cold working step), a step of performing a solution treatment (solution treatment step), and a step of cold working the solution-treated mother pipe (second cold working step). Note that the method for producing an Fe—Cr—Ni alloy material according to this embodiment is not limited to the production method described below.

[Material preparation process]
In the material preparation process, an Fe—Cr—Ni alloy having the above-mentioned chemical composition is melted. The Fe—Cr—Ni alloy may be melted in an electric furnace, or in an Ar—O ₂ mixed gas bottom blown decarburization furnace (AOD furnace). It may also be melted in a vacuum decarburization furnace (VOD furnace). The melted Fe—Cr—Ni alloy may be made into an ingot by an ingot casting method, or into a slab, bloom, or billet by a continuous casting method. If necessary, the slab, bloom, or ingot may be rolled to produce a billet. The material (slab, bloom, or billet) is produced by the above-mentioned process.

[Hot processing process]
In the hot working step, the prepared material is hot worked to produce an intermediate alloy material (blank pipe). The method of hot working is not particularly limited and may be a well-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, when manufacturing a blank pipe by carrying out the Mannesmann process as hot working, a round billet is pierced and rolled using a piercing machine. In this case, the piercing ratio is not particularly limited and is, for example, 1.0 to 4.0. The blank pipe that has been pierced and rolled may also be hot rolled using a mandrel mill, reducer, sizing mill, etc. to produce a blank pipe.

In this specification, the intermediate alloy material refers to a plate-shaped alloy material when the final product is an alloy plate, a blank tube when the final product is an alloy pipe, and an alloy material with a circular cross section perpendicular to the axial direction when the final product is a solid material with a circular cross section. Here, when the alloy material is a solid material with a circular cross section, the material is first heated in a heating furnace. The heating temperature is not particularly limited, but is, for example, 1100 to 1300°C. The material extracted from the heating furnace is subjected to hot processing to produce an intermediate alloy material with a circular cross section perpendicular to the axial direction. The hot processing is, for example, blooming rolling by a blooming mill, or hot rolling by a continuous rolling mill. The continuous rolling mill has a horizontal stand having a pair of grooved rolls arranged side by side in the vertical direction, and a vertical stand having a pair of grooved rolls arranged side by side in the horizontal direction, alternately arranged. In addition, when the alloy material is an alloy plate, the material is first heated in a heating furnace. The heating temperature is not particularly limited, but is, for example, 1100 to 1300°C. The material extracted from the heating furnace is hot rolled using a blooming mill and a continuous rolling mill to produce intermediate alloy material in the form of alloy plates.

[First cold working process]
In the first cold working step, the produced intermediate alloy material (blank pipe) is subjected to cold working. In this embodiment, the cold working may be cold drawing, or cold rolling. When cold rolling is performed, for example, a continuous rolling mill equipped with a plurality of cold rolling stands may be used. That is, in the first cold working step according to the present embodiment, a known cold rolling mill may be used. The cold working may be performed under known conditions. Specifically, the temperature of the intermediate alloy material (base pipe) during cold working may be, for example, room temperature to 300°C.

In the first cold working step according to the present embodiment, a preferred cold working ratio R1 (%) is 5% or more. Here, the cold working ratio R1 means the reduction rate of the cross-sectional area of the intermediate alloy material (blank tube) from before the start of the first cold working step to after the end of the first cold working step. Specifically, when the cross-sectional area of the blank tube before the first cold working step is defined as S0(1) and the cross-sectional area of the blank tube after the first cold working step is defined as S1(1), the cold working ratio R1 (%) of the first cold working step is defined by the following formula (A).
R1 (%) = 100 (1-S1(1)/S0(1)) (A)

If the cold working rate R1 is 5% or more, recrystallization during heat treatment is promoted in the solution treatment process described below. As a result, the standard deviation σ of the grain size number of the manufactured Fe-Cr-Ni alloy material can be stably reduced. Therefore, in this embodiment, it is preferable that the cold working rate R1 in the first cold working process is 5% or more. In this embodiment, the upper limit of the cold working rate R1 in the first cold working process is not particularly limited, but is, for example, 30%.

[Solution treatment process]
In the solution treatment process, a solution treatment is performed on the intermediate alloy material (blank pipe) that has been subjected to cold working. The method of the solution treatment is not particularly limited and may be a well-known method. For example, the blank pipe is loaded into a heat treatment furnace, held at a desired temperature, and then quenched. When the blank pipe is loaded into a heat treatment furnace, held at a desired temperature, and then quenched to perform the solution treatment, the temperature at which the solution treatment is performed (solution temperature) means the temperature (°C) of the heat treatment furnace for performing the solution treatment. In this case, the time for which the solution treatment is performed (holding time) means the time for which the blank pipe is held at the solution temperature.

Preferably, in the solution treatment process according to this embodiment, when the intermediate alloy material (base tube) is heated to the solution temperature, the residence time at 900 to 1050°C is 9 minutes or more. In the intermediate alloy material having the above-mentioned chemical composition, recrystallization and grain growth are likely to proceed at 900°C or higher. Therefore, if the residence time at 900 to 1050°C is too short, temperature variations in the intermediate alloy material are likely to occur, and recrystallization and grain growth are likely to become non-uniform. On the other hand, if the residence time at 900 to 1050°C is 9 minutes or more, recrystallization and grain growth are likely to become uniform. In this case, recrystallization is further likely to be promoted in the heat treatment at 1060°C or higher. As a result, the standard deviation σ of the grain size number of the manufactured Fe-Cr-Ni alloy material can be stably reduced.

Therefore, in this embodiment, the residence time at 900 to 1050°C during heating in the solution treatment process is preferably 9 minutes or more. In this embodiment, a more preferable lower limit for the residence time at 900 to 1050°C during heating in the solution treatment process is 10 minutes. Note that if the residence time at 900 to 1050°C is too long, the above-mentioned effect saturates. Therefore, in this embodiment, the upper limit for the residence time at 900 to 1050°C during heating in the solution treatment process is, for example, 60 minutes. The upper limit for the residence time at 900 to 1050°C during heating in the solution treatment process may be 45 minutes or 30 minutes.

Preferably, the solution temperature in the solution treatment step according to this embodiment is 1060 to 1300°C. If the solution temperature is too low, precipitates (such as the σ phase, which is an intermetallic compound) may remain in the blank tube after solution treatment. In this case, the corrosion resistance of the manufactured Fe-Cr-Ni alloy material may decrease. On the other hand, if the solution temperature is too high, the effect of the solution treatment is saturated. Therefore, in this embodiment, it is preferable to set the solution temperature in the solution treatment step to 1060 to 1300°C.

When the blank tube is loaded into a heat treatment furnace, held at the desired temperature, and then rapidly cooled to perform solution treatment, there are no particular limitations on the holding time, and the process may be carried out under well-known conditions. The holding time is, for example, 5 to 180 minutes. The rapid cooling method is, for example, water cooling.

[Second cold working process]
In the cold working step, the solution-treated intermediate alloy material (blank tube) is cold worked to produce an Fe—Cr—Ni alloy material. As described above, in this embodiment, the cold working is In other words, in the second cold working step according to the present embodiment, the known cold working is performed in the same manner as in the first cold working step. Specifically, the temperature of the intermediate alloy material (base pipe) during cold working may be, for example, room temperature to 300°C.

In the second cold working step according to the present embodiment, a preferred cold working ratio R2 (%) is 5 to 50%. Here, the cold working ratio R2 means a reduction ratio of a cross-sectional area of an intermediate alloy material (blank tube) from before the start of the second cold working step to after the end of the second cold working step. Specifically, when the cross-sectional area of the blank tube before the second cold working step is defined as S0(2) and the cross-sectional area of the Fe-Cr-Ni alloy material after the second cold working step is defined as S1(2), the cold working ratio R2 (%) is defined by the following formula (B).
R2 (%) = 100 (1-S1(2)/S0(2)) (B)

If the cold working rate R2 is 5 to 50%, the tensile yield strength of the Fe-Cr-Ni alloy material after the second cold working process can be stably set to 758 MPa or more. Therefore, it is preferable that the cold working rate R2 is 5 to 50%.

In this embodiment, it is preferable that the cold working rate R1 (%) of the first cold working step and the cold working rate R2 (%) of the second cold working step satisfy the above-mentioned range, and the total cold working rate in the manufacturing process is not particularly limited.

The above manufacturing method allows the production of the Fe-Cr-Ni alloy material according to this embodiment. In the above manufacturing method, the method for producing seamless alloy pipes has been described as one example. However, the Fe-Cr-Ni alloy material according to this embodiment may be in other shapes, such as a plate shape. Similar to the above manufacturing method, a manufacturing method for other shapes, such as a plate shape, also includes, for example, a material preparation step, a hot working step, a solution treatment step, and a cold working step. Furthermore, the above manufacturing method is one example, and the material may be produced by other manufacturing methods. The present invention will be described in more detail below with reference to examples.

Alloys having the chemical compositions shown in Tables 1A and 1B were produced by high-frequency vacuum melting. In Table 1B, "-" means that the content of each element is at the impurity level. Specifically, the W content of A is rounded off to one decimal place and is 0%. Similarly, the V content, Nb content, and Ti content of A are rounded off to one decimal place and are 0%. Similarly, the Sn content and REM content of A are rounded off to the fourth decimal place and are 0%. Similarly, the Ca content, B content, and Mg content of A are rounded off to the fifth decimal place and are 0%.

Using the alloys with each code, 50 kg of ingots with each test number were produced by ingot casting. The obtained ingots with each test number were heated at 1200°C for 3 hours and then hot forged to produce square bars with a cross section of 50 mm x 50 mm. The obtained square bars were heated at 1200°C for 1 hour and then hot rolled to produce plates (alloy plates) with a plate thickness of 30 mm. A first cold working process was performed on the obtained alloy plates with each test number. The cold working rate R1 (%) of the first cold working performed on the alloy plates with each test number is shown in Table 2.

A solution treatment was carried out on the alloy plates of each test number that had been subjected to the first cold working. In the solution treatment, the alloy plates that had been subjected to the first cold working were heated and held at the solution temperature (°C) shown in Table 2 for the holding time (min) shown in Table 2, and then water-cooled. The holding time at 900-1050°C when heating to the solution temperature is shown in the "Holding time (min)" column in Table 2.

A second cold working process was carried out on the alloy plates of each test number that had been subjected to solution treatment. The cold working ratio R2 (%) of the second cold working process carried out on the alloy plates of each test number is shown in Table 2. Note that in test numbers 4 and 20, cold drawing was carried out as the cold working process. In each test number except test numbers 4 and 20, cold rolling was carried out as the cold working process.

The total cold working ratio R (%) of the cold working performed on the alloy plate of each test number is shown in Table 2. In this example, the total cold working ratio R (%) is defined by the following formula (C).
R (%) = R1 (%) + R2 (%) (C)
Here, the cold working rate (%) of the first cold working is substituted for R1 in the formula (C), and the cold working rate (%) of the second cold working is substituted for R2.

[Evaluation test]
The alloy plates having each test number produced by the above method were subjected to a grain size number measurement test and a strength anisotropy measurement test, which will be described below.

[Grain size number measurement test]
A grain size number measurement test was performed on the alloy plate of each test number to determine the standard deviation σ of the grain size number. Specifically, the test pieces prepared by the above-mentioned method were subjected to microscopic observation by the above-mentioned method. Image analysis was performed on the photographic images obtained by microscopic observation to measure the grain size number in accordance with ASTM E112 (2021). Table 3 shows the grain size numbers obtained in 10 fields of view for each test number. Table 3 shows the average value and standard deviation σ of the grain size numbers obtained from the 10 grain size numbers obtained.

[Strength anisotropy measurement test]
A strength anisotropy measurement test was carried out on the alloy plate of each test number to obtain the anisotropy index AI. Specifically, the tensile yield strength (MPa) and the compressive yield strength (MPa) were first obtained by the above-mentioned method. Specifically, a round bar test piece for a tensile test and a cylindrical test piece for a compression test were prepared from the center of the plate thickness of the alloy plate of each test number. The round bar test piece had a parallel part diameter of 4 mm and a gauge length of 20 mm. The cylindrical test piece had a parallel part diameter of 4 mm and a length of 8 mm. The axial direction of the round bar test piece and the cylindrical test piece was parallel to the rolling direction of the alloy plate.

A tensile test was performed on the round bar test pieces at room temperature (25°C) in air in accordance with ASTM E8/E8M (2021). The 0.2% offset yield strength obtained by the tensile test was defined as the tensile yield strength (MPa). Furthermore, a compression test was performed on the cylindrical test pieces at room temperature (25°C) in air in accordance with ASTM E9 (2019). The 0.2% offset yield strength obtained by the compression test was defined as the compressive yield strength (MPa). The ratio of the compressive yield strength (compressive YS) to the obtained tensile yield strength (tensile YS) (compressive YS/tensile YS) was calculated and defined as the anisotropy index AI. For the alloy plates with each test number, the obtained tensile yield strength is shown in the "Tensile YS (MPa)" column of Table 3, the compressive yield strength is shown in the "Compressive YS (MPa)" column of Table 3, and the anisotropy index AI is shown in the "Anisotropy Index AI" column of Table 3.

[Evaluation Results]
Referring to Tables 1A to 3, all of the alloy plates of Test Nos. 1 to 23 had appropriate chemical compositions. Furthermore, the standard deviation σ of the grain size number of these alloy plates was 0.60 or less. As a result, the tensile yield strength of these alloy plates was 758 MPa or more. Furthermore, the anisotropy index AI was 0.700 or more, and the strength anisotropy was reduced.

On the other hand, the alloy plate of test number 24 had too high a Ni content. As a result, although this alloy plate had a tensile yield strength of 758 MPa or more, the anisotropy index AI was less than 0.700, and the strength anisotropy was not reduced.

The alloy plate with test number 25 had too low a Cr content. As a result, although this alloy plate had a tensile yield strength of 758 MPa or more, the anisotropy index AI was less than 0.700, and the strength anisotropy was not reduced.

The alloy plates of test numbers 26 and 27 had too low a cold working ratio R1 in the first cold working process. As a result, the standard deviation σ of the grain size number of these alloy plates exceeded 0.60. As a result, although these alloy plates had a tensile yield strength of 758 MPa or more, the anisotropy index AI was less than 0.700, and the strength anisotropy was not reduced.

The alloy plates of test numbers 28 and 29 had too short a residence time at 900-1050°C during heating in the solution treatment process. As a result, the standard deviation σ of the grain size number of these alloy plates exceeded 0.60. As a result, although these alloy plates had a tensile yield strength of 758 MPa or more, the anisotropy index AI was less than 0.700, and the strength anisotropy was not reduced.

The above describes the 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 (3)

In mass percent,
C: 0.030% or less,
Si: 0.01-1.00%,
Mn: 0.01 to 2.00%,
P: 0.040% or less,
S: 0.0050% or less,
Al: 0.01-0.50%,
Ni: more than 36.5 to 54.0%,
Cr: 19.0-27.5%,
Mo: 2.00-11.50%,
Cu: 0.01-3.00%,
N: 0.010-0.500%,
Co: 0.01-2.00%,
O: 0.010% or less,
V: 0-0.50%,
Nb: 0 to 0.10%,
Ti: 0 to 0.40%,
W: 0 to 3.0%,
Sn: 0 to 0.010%,
Ca: 0-0.0100%,
B: 0 to 0.0100%,
Mg: 0 to 0.0100%,
Rare earth elements: 0 to 0.100%, and
The balance is Fe and impurities,
In the microstructure, the standard deviation of the grain size number of the austenite grains is 0.60 or less;
The tensile yield strength is 758 MPa or more.
Fe-Cr-Ni alloy material. The Fe-Cr-Ni alloy material according to claim 1,
V: 0.01-0.50%,
Nb: 0.01 to 0.10%,
Ti: 0.01-0.40%,
W: 0.1-3.0%,
Sn: 0.001 to 0.010%,
Ca: 0.0001-0.0100%,
B: 0.0001 to 0.0100%,
Mg: 0.0001 to 0.0100%, and
Rare earth elements: containing one or more elements selected from the group consisting of 0.001 to 0.100%;
Fe-Cr-Ni alloy material. Seamless alloy pipe for oil wells.
The Fe-Cr-Ni alloy material according to claim 1 or 2.

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