JP6859921B2 - Stainless steel materials and stainless steel pipes - Google Patents

Description

The present invention relates to stainless steel materials and stainless steel pipes, and more particularly to stainless steel materials and stainless steel pipes for oil wells and geothermal wells.

Steel pipes are used to mine and extract oil and natural gas, and to extract steam for geothermal power generation. Since oil and natural gas exist deep underground, high strength is required for steel pipes used in oil wells. In addition, the oil well has a completely different environment depending on the area and depth. In particular, the content of the content and the hydrogen sulfide gas (H 2 _S) of carbon dioxide (CO ₂₎ is significantly different for each oil well. For example, some oil wells have high carbon dioxide and hydrogen sulfide gas contents. On the other hand, in another oil well, the content of carbon dioxide gas may be high, but the content of hydrogen sulfide gas may be remarkably low. The characteristics required for steel pipes differ depending on the environment of these wells.

In recent years, in order to cope with soaring crude oil prices and natural gas prices, the development of deeper oil wells and deeper natural gas wells has been promoted. Furthermore, against the background of growing awareness of renewable energy, the development of deeper geothermal wells is being promoted in geothermal wells that collect steam for geothermal power generation.

Such deep oil wells, deep natural gas wells (hereinafter, both are collectively abbreviated as "deep depth oil wells") and deep underground hot wells are generally extremely deep. Furthermore, the atmosphere of deep oil wells and deep geothermal wells is _{harsh, at high temperatures and containing carbon dioxide (CO 2} ), plus acids such as chloride ions (Cl ⁻ ) or sulfuric acid (H ₂ SO _4). It is a corrosive environment. Therefore, excellent carbon dioxide gas corrosion resistance is required for steel materials used as materials for steel pipes used in such deep oil wells and deep geothermal wells.

In corrosive environments such as deep oil wells and deep geothermal wells, martensitic stainless steel (so-called "13% Cr steel") containing about 13% Cr in mass%, which has excellent carbon dioxide gas corrosion resistance, is used. The steel pipe used has been used. However, as oil wells and geothermal wells become deeper, the environment becomes hotter and higher pressure, and in addition, the partial pressure of _{CO 2 becomes higher.} Therefore, there is a demand for a steel pipe having sufficient carbon dioxide corrosion resistance even in a harsher carbon dioxide environment.

It is generally known that carbon dioxide corrosion resistance at high temperatures can be improved by increasing the Cr content. Therefore, in recent years, a steel material having improved carbon dioxide corrosion resistance at high temperatures has been proposed based on martensitic stainless steel by further increasing the amount of Cr as compared with the conventional one.

In Japanese Patent Application Laid-Open No. 2005-336599 (Patent Document 1), the content of Cr, Ni, Mo, Cu and C is optimized, and the content of C and N is adjusted to a certain level or less so that the temperature is 150 ° C. or higher. High-strength stainless steel pipes for line pipes have been proposed, which have excellent CO ₂ corrosion resistance, excellent sulfide stress corrosion cracking resistance even in a hydrogen sulfide environment, and excellent weldability.

In Japanese Patent Application Laid-Open No. 2006-016637 (Patent Document 2), the contents of C, Ni, Si, Mn, V, Al, N and O are optimized based on 13% Cr steel, and further, Mo, Cu, Nb. By adding Ti and Ti, a high-strength stainless steel pipe for oil wells having excellent _{CO 2 corrosion resistance at 170 ° C. or higher has been proposed.}

In Japanese Patent Application Laid-Open No. 2007-332431 (Patent Document 3), by adding Ni, Mo and V and reducing the contents of S, Si, Al and O, CO ₂ corrosion resistance and pipe expansion property are obtained. Stainless steel pipes for oil wells that have both of these characteristics have been proposed.

All of the stainless steels proposed in Patent Documents 1 to 3 show good carbon dioxide gas corrosion resistance in a _{CO 2 environment of about 200 ° C.} However, in deep oil wells and deep geothermal wells, which are deeper than before, the environment becomes even higher than that assumed in Patent Documents 1 to 3. In deep oil wells and deep geothermal wells, for example, the high temperature environment exceeds 250 ° C. Further, in such a high temperature environment, there is _{an environment containing not only CO 2} but also chloride ions and sulfuric acid. Therefore, in the conventional steel pipe as disclosed in Patent Documents 1 to 3, for example _{, a deep oil well environment containing CO 2} and Cl ⁻ at about 250 ° C., or CO ₂ and sulfuric acid at about 250 ° C. Stable desired corrosion resistance (particularly, carbon dioxide corrosion resistance in a strong acid environment containing chloride ions or sulfuric acid) in a high temperature / strong acid CO _{2 environment such as a deep geothermal well environment containing} There was a problem of not showing.

In order to solve such a problem, in Japanese Patent Application Laid-Open No. 2008-297599 (Patent Document 4), stainless steel containing Cr and Cu is _{immersed in a high-pressure CO 2} environment, and a film having an anticorrosion function is formed on the surface layer. A stainless steel material that exhibits excellent corrosion resistance even in a high-temperature CO _{2 environment at 250 ° C. by being formed has been proposed.}

On the other hand, it is known that a two-phase stainless steel composed of a ferrite phase and an austenite phase having a further increased Cr content has sufficient corrosion resistance in a _{high-temperature CO 2 corrosion environment as it is.}

Japanese Unexamined Patent Publication No. 2005-336599 Japanese Unexamined Patent Publication No. 2006-0166637 Japanese Unexamined Patent Publication No. 2007-332431 Japanese Unexamined Patent Publication No. 2008-297599

However, the stainless steel proposed in Patent Document 4 _{requires an anticorrosion film forming treatment in a high-pressure CO 2} environment in order to exhibit excellent corrosion resistance, and has a problem that the manufacturing cost increases.

In addition, the two-phase stainless steel composed of a ferrite phase and an austenite phase can achieve the strength of 125 ksi class (862 MPa or more), which is the strength required for steel pipes used in deep oil wells and deep geothermal wells, as it is heat-treated. Can not. Therefore, when this duplex stainless steel is used for deep oil wells and deep geothermal wells, cold working is required, and there is a problem that the manufacturing cost is higher than that of steel materials based on martensitic stainless steel. ..

Therefore, it has sufficient carbon dioxide corrosion resistance in the above-mentioned high temperature / strong acid CO ₂ environment of about 250 ° C., and in particular, carbon dioxide corrosion resistance in a strong acid environment containing chloride ions or sulfuric acid (hereinafter, strong acid / carbon dioxide gas). There has been a demand for a steel material having (referred to as corrosiveness) and having a strength of 125 ksi class (862 MPa or more) as it is heat-treated.

An object of the present invention is to provide a stainless steel material having high strength as it is heat-treated and further having excellent strong acid / carbon dioxide corrosion resistance in a high temperature environment.

The stainless steel material of the present embodiment has a mass% of C: 0.040% or less, Si: 0.05 to 1.0%, Mn: 0.010 to 0.30%, and Cr: more than 18.0%. 21.0% or less, Cu: 1.5 to 4.0%, Ni: 3.0 to 6.0%, sol. Al: 0.001 to 0.100%, Mo: 0 to 0.60%, W: 0 to 2.0%, Co: 0 to 0.30%, Ti: 0 to 0.10%, V: 0 ~ 0.15%, Zr: 0 to 0.10%, Nb: 0 to 0.10%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, REM: 0 to 0.05% , B: 0 to 0.005%, and the balance consists of Fe and impurities. Of the impurities, P, S, O, and N are P: 0.050% or less, S: less than 0.0020%, respectively. Ferrite phase having a chemical composition of O: 0.020% or less and N: 0.020% or less, satisfying the formulas (1) and (2), and a volume ratio of 20.0 to 60.0%. , 1.0 to 10.0% austenite phase, and a microstructure with the balance consisting of maltensite.
15.0 ≦ 616-706 (C + N) -22Si-24Mn-24Ni-18Cr-8Cu-16Mo ... (1)
20.0 ≤ Cr + Cu ≤ 24.5 ... (2)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (1) and the formula (2).

The stainless steel pipe of the present embodiment is made of a stainless steel material having the above chemical composition.

The stainless steel material and the stainless steel pipe of the present embodiment have high strength as they are heat-treated, and further have excellent strong acid / carbon dioxide corrosion resistance in a high temperature environment.

FIG. 1 is a diagram showing the relationship between the Cr content of the stainless steel material, the total content of Ni and Cu, and the structure after quenching. FIG. 2 is a diagram in which the line segment L1 in FIG. 1 is moved to the line segment L2.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.

The present inventors have investigated the strength of stainless steel materials and the corrosion resistance to carbon dioxide in a high temperature environment, in particular, the corrosion resistance to strong acid and carbon dioxide in a strong acid environment containing chloride ions or sulfuric acid. As a result, the following findings were obtained.

It is known that increasing the Cr content is effective for enhancing the carbon dioxide corrosion resistance in a high temperature environment. If the Cr content is increased, the strong acid / carbon dioxide gas corrosiveness in an environment containing chloride ions or sulfuric acid can also be increased. However, if the content of Cr, which is a ferrite stabilizing element, is simply increased, the microstructure becomes a two-phase structure composed of ferrite and austenite, or an austenite single-phase structure. In this case, it is difficult to obtain strength of 125 ksi class (862 MPa or more) as it is heat-treated. That is, the higher the Cr content is preferable in consideration of the relationship with the strong acid / carbon dioxide gas corrosiveness, but the Cr content is limited in consideration of the relationship with the strength.

Therefore, the present inventors examined the chemical composition, structure, and strength of the stainless steel material.

FIG. 1 is a diagram showing the relationship between the Cr content of the stainless steel material, the total content of Ni and Cu, and the structure after quenching. The horizontal axis in FIG. 1 represents the Cr content. The vertical axis in FIG. 1 represents the total content of Ni and Cu. With reference to FIG. 1, as the content of Cr, which is a ferrite stabilizing element, increases, the structure after quenching changes from a single phase of martensite (region M in FIG. 1) to a two-phase structure of martensite and ferrite (a two-phase structure of martensite and ferrite (region M in FIG. 1). In FIG. 1, it changes to region M + F) and ferrite single phase (region F in FIG. 1). Further, the line segment L1 in FIG. 1 is a line indicating the boundary of the chemical composition that causes martensitic transformation by quenching. The region above the line segment L1 does not undergo martensitic transformation due to quenching. That is, if the contents of Ni and Cu, which are austenite stabilizing elements, are too high, quenching does not cause martensitic transformation (that is, austenite becomes a single phase) (region A in FIG. 1). The intensity is low in the two-phase structure of ferrite and austenite (region F and region A in FIG. 1) or in the austenite single phase (region A in FIG. 1). On the other hand, in the case of the two-phase structure of martensite and ferrite (region M + F in FIG. 1), strength of 125 ksi class (862 MPa or more) can be obtained without heat treatment.

Conventionally, in order to obtain a two-phase structure of martensite and ferrite, it has been considered that the Cr content is limited to about 18.0%. If more Cr is contained, the microstructure is mainly composed of ferrite and / or austenite, and strength cannot be obtained. Therefore, conventionally, the Cr content is set to about 18.0% at the maximum within the range of the chemical composition that can obtain the two-phase structure of martensite and ferrite (region Y in FIG. 1), as in Patent Document 4. It has been considered difficult to further improve the corrosion resistance other than to improve the corrosion resistance by forming an anticorrosion film.

However, the present inventors have found a method for obtaining high strength even when the Cr content is further increased to more than 18.0% by adjusting the chemical composition other than Cr, unlike the conventional method. The present inventors have focused on the relationship between the chemical composition that causes martensitic transformation (line segment L1 in FIG. 1) and the Cr content, which have not been investigated so far.

As a result of various studies, the present inventors have found that the position of the line segment L1 can be changed by adjusting the contents of C, Si, Mn, Ni, Cr, Cu, Mo and N. Based on this finding, the present inventors adjusted the content of the above-mentioned elements to move the line segment L1 and martensite in a chemical composition having a Cr content of more than 18.0% (region X in FIG. 1). We have come to the conclusion that a two-phase structure of sites and ferrite can be obtained.

FIG. 2 is a diagram in which the content of each element described above is adjusted to move the line segment L1 to the line segment L2. By adjusting the contents of C, Si, Mn, Ni, Cr, Cu, Mo and N described above with reference to FIG. 2, martensite can be obtained in a chemical composition for which martensite could not be obtained so far. Will be able to. (Region X in FIG. 1). As a result, it is possible to achieve both a Cr content of more than 18.0%, which has been considered difficult in the past, and a two-phase structure of martensite and ferrite. That is, it is possible to achieve both high strength of stainless steel and strong acid / carbon dioxide corrosion resistance.

By satisfying the formula (1) in which the chemical composition defines the relationship between the elements affecting the position of the line segment L1, the structure is sufficiently contained in martensite even if the Cr content is more than 18.0%. be able to.
15.0 ≦ 616-706 (C + N) -22Si-24Mn-24Ni-18Cr-8Cu-16Mo ... (1)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (1).

On the other hand, in order to enhance the strong acid / carbon dioxide gas corrosiveness, it is effective to contain Cu in addition to Cr. Therefore, when the chemical composition satisfies the formula (2) that defines the total content of Cr and Cu, the strong acid / carbon dioxide gas corrosiveness containing chloride ion or sulfuric acid is enhanced.
20.0 ≤ Cr + Cu ≤ 24.5 ... (2)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (2).

On the other hand, most of the conventional stainless steel materials for oil wells often contain a large amount of Mo in order to enhance the sulfide stress cracking resistance. However, Mo has been a factor in increasing the cost of stainless steel materials used in oil well environments where the hydrogen sulfide content is remarkably low. The stainless steel material of the present embodiment is intended to enhance the strong acid / carbon dioxide gas corrosiveness rather than the sulfide stress cracking resistance. Therefore, the Mo content may be lower than that of the stainless steel material whose main purpose is to improve the sulfide stress cracking resistance.

As described above, by adjusting the content of the element that affects the position of the line segment L1 according to the formula (1), it is possible to achieve both a Cr content of more than 18.0% and a structure containing a sufficient amount of martensite. Become. As a result, it is possible to achieve both a strength of 125 ksi class (862 MPa or more) and a strong acid / carbon dioxide gas corrosiveness in a high temperature environment exceeding 250 ° C. only by heat treatment. Further, by adding Cu in addition to Cr according to the formula (2), the strong acid / carbon dioxide gas corrosiveness is enhanced. Therefore, it is possible to provide a stainless steel material suitable for a deep oil well or a deep geothermal well.

The stainless steel material of the present embodiment completed based on the above findings has a mass% of C: 0.040% or less, Si: 0.05 to 1.0%, Mn: 0.010 to 0.30%, and so on. Cr: more than 18.0% and 21.0% or less, Cu: 1.5 to 4.0%, Ni: 3.0 to 6.0%, sol. Al: 0.001 to 0.100%, Mo: 0 to 0.60%, W: 0 to 2.0%, Co: 0 to 0.30%, Ti: 0 to 0.10%, V: 0 ~ 0.15%, Zr: 0 to 0.10%, Nb: 0 to 0.10%, Ca: 0 to 0.010%, Mg: 0 to 0.010%, REM: 0 to 0.05% , B: 0 to 0.005%, and the balance consists of Fe and impurities. Of the impurities, P, S, O, and N are P: 0.050% or less, S: less than 0.0020%, respectively. Ferrite phase having a chemical composition of O: 0.020% or less and N: 0.020% or less, satisfying the formulas (1) and (2), and a volume ratio of 20.0 to 60.0%. , 1.0 to 10.0% austenite phase, and a microstructure with the balance consisting of maltensite.
15.0 ≦ 616-706 (C + N) -22Si-24Mn-24Ni-18Cr-8Cu-16Mo ... (1)
20.0 ≤ Cr + Cu ≤ 24.5 ... (2)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (1) and the formula (2).

The stainless steel material of the present embodiment has high strength as it is heat-treated, and further has excellent strong acid / carbon dioxide gas corrosion resistance in a high temperature environment.

Preferably, the chemical composition is selected from the group consisting of Mo: 0.02 to 0.60%, W: 0.01 to 2.0%, and Co: 0.01 to 0.30% 1 Contains seeds or two or more.

In this case, the corrosion resistance of the stainless steel material is further enhanced.

Preferably, the chemical composition is Ti: 0.005 to 0.10%, V: 0.005 to 0.15%, Zr: 0.005 to 0.10%, and Nb: 0.005 to 0. .Contains one or more selected from the group consisting of 10%.

In this case, the strength of the stainless steel material is further increased.

Preferably, the chemical composition is Ca: 0.0005 to 0.010%, Mg: 0.0005 to 0.010%, REM: 0.0005 to 0.05%, and B: 0.0005% to. Contains one or more selected from the group consisting of 0.005%.

In this case, the hot workability of the stainless steel material is improved.

The stainless steel pipe of the present embodiment is made of a stainless steel material having any of the above chemical compositions.

Hereinafter, the stainless steel material of the present embodiment will be described in detail.

[Chemical composition]
The chemical composition of the stainless steel material of the present embodiment contains the following elements. Unless otherwise specified,% for an element means mass%.

C: 0.040% or less Carbon (C) is inevitably contained. C precipitates as carbide during tempering. In this case, the carbon dioxide gas corrosiveness of the stainless steel material at a high temperature is lowered. Further, if the C content is too high, the amount of retained austenite produced during quenching increases. In this case, in order to reduce the amount of retained austenite produced, the Cu and Ni contents effective for strength and toughness must be reduced. Therefore, the C content is 0.040% or less. The upper limit of the C content is preferably 0.030%, more preferably 0.020%, further preferably 0.015%, and most preferably 0.010%. The lower the C content, the better. However, considering the cost of decarburization in the steelmaking process, the lower limit of the C content is preferably 0.001%, more preferably 0.002%, still more preferably 0.004%. Yes, most preferably 0.005%.

Si: 0.05-1.0%
Silicon (Si) deoxidizes stainless steel materials. If the Si content is too low, this effect cannot be obtained. On the other hand, if the Si content is too high, the hot workability of the stainless steel material is lowered. Therefore, the Si content is 0.05 to 1.0%. The upper limit of the Si content is preferably 0.9%, more preferably 0.7%, still more preferably 0.6%, and most preferably 0.5%. The lower limit of the Si content is preferably 0.06%, more preferably 0.08%, still more preferably 0.10%, and most preferably 0.12%.

Mn: 0.010 to 0.30%
Manganese (Mn) deoxidizes stainless steel materials. If the Mn content is too low, this effect cannot be obtained. On the other hand, if the Mn content is too high, austenite tends to remain excessively after quenching and tempering, and the volume fraction of retained austenite may exceed 10%. In this case, the strength of the stainless steel material after tempering decreases. Therefore, the Mn content is 0.010 to 0.30%. The upper limit of the Mn content is preferably 0.27%, more preferably 0.25%, still more preferably 0.22%, and most preferably less than 0.20%. The lower limit of the Mn content is preferably 0.015%, more preferably 0.030%, still more preferably 0.035%, and most preferably 0.050%.

Cr: More than 18.0% and 21.0% or less Chromium (Cr) is indispensable for ensuring strong acid / carbon dioxide corrosion resistance in an environment containing _{CO 2 and chloride ions or sulfuric acid at about 250 ° C.} It is an element. If the Cr content is too low, this effect cannot be obtained. On the other hand, since Cr is a ferrite-forming element, if the Cr content is too high, the amount of ferrite in the stainless steel material becomes excessively large, and the strength of the stainless steel material decreases. Therefore, the Cr content is more than 18.0% and 21.0% or less. The upper limit of the Cr content is preferably 20.8%, more preferably 20.5%, still more preferably 20.3%, and most preferably 20.2%. The lower limit of the Cr content is preferably 18.3%, more preferably 18.5%, further preferably 18.7%, and most preferably 18.8%.

Cu: 1.5-4.0%
Copper (Cu) precipitates as fine Cu particles during tempering to increase the strength of the stainless steel material. Further, Cu enhances the strong acid / carbon dioxide gas corrosiveness in a high temperature environment containing chloride ions or sulfuric acid. If the Cu content is too low, these effects cannot be obtained. On the other hand, if the Cu content is too high, the martensitic transformation does not proceed sufficiently during quenching, and the amount of retained austenite becomes excessively large. In this case, the strength of the stainless steel material decreases. Therefore, the Cu content is 1.5 to 4.0%. The upper limit of the Cu content is preferably 3.8%, more preferably 3.5%, still more preferably 3.2%, and most preferably 3.0%. The lower limit of the Cu content is preferably 1.6%, more preferably 1.7%, still more preferably 1.8%, and most preferably 1.9%.

Ni: 3.0-6.0%
Nickel (Ni) is an austenite-forming element that stabilizes austenite at high temperatures. Therefore, Ni increases the amount of martensite at room temperature and enhances the strength of the stainless steel material. Ni further enhances the strong acid / carbon dioxide corrosiveness in a high temperature environment such as containing chloride ions or sulfuric acid. If the amount of Ni is too low, these effects cannot be obtained. On the other hand, if the Ni content is too high, a stable two-phase structure of ferrite and martensite cannot be obtained. That is, austenite tends to remain excessively after quenching and tempering, and the strength of the stainless steel material after tempering decreases. Therefore, the Ni content is 3.0 to 6.0%. The upper limit of the Ni content is preferably 5.8%, more preferably 5.5%, still more preferably 5.2%, and most preferably 5.0%. The lower limit of the Ni content is preferably 3.2%, more preferably 3.4%, further preferably 3.6%, and most preferably 3.8%.

sol. Al: 0.001 to 0.100%
Aluminum (Al) deoxidizes stainless steel materials. sol. If the Al content is too low, this effect cannot be obtained. On the other hand, sol. If the Al content is too high, the effect will be saturated. sol. If the Al content is too high, inclusions are further generated, and the strong acid / carbon dioxide corrosiveness and toughness in a high temperature environment containing chloride ions or sulfuric acid are lowered. Therefore, sol. The Al content is 0.001 to 0.100%. sol. The upper limit of the Al content is preferably 0.080%, more preferably 0.060%, further preferably 0.055%, and most preferably 0.050%. sol. The lower limit of the Al content is preferably 0.005%, more preferably 0.008%, still more preferably 0.010%, and most preferably 0.015%.

The rest of the chemical composition of the stainless steel material according to this embodiment consists of Fe and impurities. Here, the impurities in the chemical composition are mixed from ore, scrap, or the manufacturing environment as a raw material when the stainless steel material is industrially manufactured, and have an adverse effect on the stainless steel material of the present embodiment. It means what is allowed within the range not given.

[About arbitrary elements]
The stainless steel material of the present embodiment may contain the following optional elements.

Mo: 0-0.60%
Molybdenum (Mo) is an optional element and may not be contained. Mo enhances strong acid / carbon dioxide corrosiveness in a high temperature environment containing chloride ions or sulfuric acid. If even a small amount of Mo is contained, the above effect can be obtained. On the other hand, since Mo is a ferrite-forming element, if the Mo content is too high, ferrite is excessively generated in the stainless steel material. In this case, the strength of the stainless steel material decreases. Therefore, the Mo content is 0 to 0.60%. The upper limit of the Mo content is preferably 0.58%, more preferably 0.56%, still more preferably 0.54%, and most preferably 0.52%. The lower limit of the Mo content is preferably 0.02%, more preferably 0.04%, still more preferably 0.05%, and most preferably 0.06%.

W: 0-2.0%
Tungsten (W) is an optional element and may not be contained. Like Mo, W enhances the strong acid / carbon dioxide corrosiveness in a high temperature environment containing chloride ions or sulfuric acid. If even a small amount of W is contained, the above effect can be obtained. On the other hand, since W is a ferrite forming element, if the W content is too high, ferrite is excessively generated in the stainless steel material, and the strength of the stainless steel material is lowered. Therefore, the W content is 0 to 2.0%. The upper limit of the W content is preferably 1.8%, more preferably 1.5%, still more preferably 1.3%, and most preferably 1.0%. The lower limit of the W content is preferably 0.01%, more preferably 0.02%.

Co: 0 to 0.30%
Cobalt (Co) is an optional element and may not be contained. Like Mo and W, Co enhances the strong acid / carbon dioxide corrosiveness in a high temperature environment containing chloride ions or sulfuric acid. However, if the Co content is too high, the manufacturability is lowered and the manufacturing cost is also high. Therefore, the Co content is 0 to 0.30%. The upper limit of the Co content is preferably 0.25%, more preferably 0.23%, still more preferably 0.20%, and most preferably 0.18%. The lower limit of the Co content is preferably 0.01%, more preferably 0.02%.

Ti: 0 to 0.10%
Titanium (Ti) is an optional element and may not be contained. When contained, Ti precipitates as fine precipitates during tempering to increase the strength of the stainless steel material. If even a small amount of Ti is contained, the above effect can be obtained. On the other hand, if the Ti content is too high, the strong acid / carbon dioxide gas corrosiveness and toughness in a high temperature environment containing chloride ions or sulfuric acid are lowered. Therefore, the Ti content is 0 to 0.10%. The upper limit of the Ti content is preferably 0.08%, more preferably 0.05%. The lower limit of the Ti content is preferably 0.005%, more preferably 0.010%.

V: 0 to 0.15%
Vanadium (V) is an optional element and may not be contained. When contained, V precipitates as fine precipitates during tempering to increase the strength of the stainless steel material. If even a small amount of V is contained, the above effect can be obtained. On the other hand, if the V content is too high, the strong acid / carbon dioxide gas corrosiveness and toughness in a high temperature environment containing chloride ions or sulfuric acid are lowered. Therefore, the V content is 0 to 0.15%. The upper limit of the V content is preferably 0.13%, more preferably 0.12%. The lower limit of the V content is preferably 0.005%, more preferably 0.010%, and even more preferably 0.020%.

Zr: 0-0.10%
Zirconium (Zr) is an optional element and may not be contained. When contained, Zr, like Ti and V, precipitates as fine precipitates during tempering to increase the strength of the stainless steel material. If even a small amount of Zr is contained, the above effect can be obtained. On the other hand, if the Zr content is too high, the toughness of the stainless steel material decreases. Therefore, the Zr content is 0 to 0.10%. The upper limit of the Zr content is preferably 0.08%, more preferably 0.05%. The lower limit of the Zr content is preferably 0.005%, more preferably 0.010%.

Nb: 0 to 0.10%
Niobium (Nb) is an optional element and may not be contained. When contained, Nb precipitates as fine precipitates during tempering to increase the strength of the stainless steel material. If even a small amount of Nb is contained, the above effect can be obtained. On the other hand, if the Nb content is too high, the strong acid / carbon dioxide gas corrosiveness and toughness in a high temperature environment containing chloride ions or sulfuric acid are lowered. Therefore, the Nb content is 0 to 0.10%. The upper limit of the Nb content is preferably 0.08%, more preferably 0.05%. The lower limit of the Nb content is preferably 0.005%, more preferably 0.010%.

Ca: 0 to 0.010%
Calcium (Ca) is an optional element and may not be contained. When contained, Ca enhances the hot workability of stainless steel materials. If even a small amount of Ca is contained, the above effect can be obtained. On the other hand, if the Ca content is too high, inclusions will be excessively produced. In this case, the toughness of the stainless steel material and the strong acid corrosion resistance in a high temperature environment such as containing sulfuric acid are lowered. Therefore, the Ca content is 0 to 0.010%. The upper limit of the Ca content is preferably 0.008%, more preferably 0.005%. The lower limit of the Ca content is preferably 0.0005%.

Mg: 0 to 0.010%
Magnesium (Mg) is an optional element and may not be contained. When contained, Mg enhances the hot workability of stainless steel materials. The above effect can be obtained if even a small amount of Mg is contained. On the other hand, if the Mg content is too high, inclusions are excessively formed. In this case, the toughness of the stainless steel material and the strong acid corrosion resistance in a high temperature environment such as containing sulfuric acid are lowered. Therefore, the Mg content is 0 to 0.010%. The upper limit of the Mg content is preferably 0.008%, more preferably 0.005%. The lower limit of the Mg content is preferably 0.0005%.

REM: 0-0.05%
Rare earth elements (REM) are optional elements and may not be contained. Like Ca and Mg, REM enhances the hot workability of stainless steel materials. On the other hand, if the REM content is too high, inclusions of oxides and sulfides are excessively generated, and the toughness of the stainless steel material and the strong acid corrosion resistance in a high temperature environment such as containing sulfuric acid are lowered. Therefore, the REM content is 0-0.05%. The upper limit of the REM content is preferably 0.03%, more preferably 0.02%. The lower limit of the REM content is preferably 0.0005%. Here, REM means 17 elements obtained by adding yttrium (Y) and scandium (Sc) to the elements from lanthanum (La) of element number 57 to lutetium (Lu) of element number 71 in the periodic table. The REM content means the total content of these elements.

B: 0 to 0.005%
Boron (B) is an optional element and may not be contained. When B is added, the hot workability of the stainless steel material is enhanced as in the case of Ca, Mg and REM. On the other hand, if the B content is too high, charcoal boride of Cr is deposited at the grain boundaries, and the toughness of the stainless steel material is lowered. Therefore, the B content is 0 to 0.005%. The upper limit of the B content is preferably 0.004%, more preferably 0.003%. The lower limit of the B content is preferably 0.0005%.

[About impurity elements]
The following elements may be contained as impurities in the chemical composition of the stainless steel material of the present embodiment. The content of these elements is limited for the following reasons.

P: 0.050% or less Phosphorus (P) is an impurity. P segregates at the grain boundaries and lowers the strong acid / carbon dioxide gas corrosiveness of the stainless steel material. Therefore, the P content is 0.050% or less. The upper limit of the P content is preferably 0.045%, more preferably 0.040%, further preferably 0.035%, and most preferably 0.030%. The P content is preferably as low as possible. The lower limit of the P content is not particularly limited, but is, for example, 0.001%.

S: Less than 0.0020% Sulfur (S) is an impurity. S segregates at the grain boundaries and lowers the strong acid / carbon dioxide gas corrosiveness of the stainless steel material. S further reduces the hot workability of the stainless steel material. Therefore, the S content is less than 0.0020%. The upper limit of the S content is preferably 0.0017%, more preferably 0.0015%. The S content is preferably as low as possible. The lower limit of the S content is not particularly limited, but is, for example, 0.0003%.

O: 0.020% or less Oxygen (O) is an impurity. O forms a coarse oxide and reduces the toughness of the stainless steel material and the strong acid corrosion resistance in a high temperature environment such as containing sulfuric acid. Therefore, the O content is 0.020% or less. The upper limit of the O content is preferably 0.015%, more preferably 0.010%. The O content is preferably as low as possible. The lower limit of the O content is not particularly limited, but is, for example, 0.001%.

N: 0.020% or less Nitrogen (N) is an impurity. N forms a coarse nitride. Coarse nitrides serve as the starting point for pitting corrosion and reduce the strong acid corrosion resistance of stainless steel materials in high temperature environments such as those containing sulfuric acid. Therefore, the N content is 0.020% or less. The upper limit of the N content is preferably 0.018%, more preferably 0.015%. The N content is preferably as low as possible. The lower limit of the N content is not particularly limited, but is, for example, 0.001%.

[About the formula]
The chemical composition of the stainless steel material of the present embodiment has an appropriate content of each of the above elements and satisfies the following formulas (1) and (2). As a result, it is possible to achieve both high strength only by heat treatment and excellent acid / carbon dioxide corrosion resistance in a high temperature environment.

[About equation (1)]
The chemical composition satisfies the formula (1).
15.0 ≦ 616-706 (C + N) -22Si-24Mn-24Ni-18Cr-8Cu-16Mo ... (1)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (1).

It is defined as Fn1 = 616-706 (C + N) -22Si-24Mn-24Ni-18Cr-8Cu-16Mo. Fn1 is an index showing the chemical composition from which martensite can be obtained. If the content of each of the above elements is appropriate and Fn1 is appropriate, a two-phase structure of martensite and ferrite, which will be described later, can be obtained even if the Cr content exceeds 18.0%. This structure has a sufficiently high volume fraction of the martensite phase (hereinafter referred to as martensite fraction). This increases the strength of the stainless steel material. That is, only by adjusting Fn1, it is possible to achieve both strong acid / carbon dioxide corrosiveness in a high temperature environment containing chloride ions or sulfuric acid and strength of 125 ksi class (862 MPa or more) only by heat treatment. If Fn1 is less than 15.0, the martensite fraction decreases and the strength of the stainless steel material decreases. Therefore, 15.0 ≦ Fn1. The lower limit of Fn1 is preferably 40.0, more preferably 50.0, still more preferably 60.0, and most preferably 70.0. The upper limit of Fn1 is not particularly limited, but in consideration of the manufacturing cost, it is preferably 300, more preferably 250, further preferably 200, and most preferably 150.

[About equation (2)]
The chemical composition satisfies the formula (2).
20.0 ≤ Cr + Cu ≤ 24.5 ... (2)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (2).

It is defined as Fn2 = Cr + Cu. Fn2 is an index showing strong acid / carbon dioxide gas corrosiveness in a high temperature environment containing chloride ions or sulfuric acid. If the content of each of the above elements is appropriate and Fn2 is appropriate, the strong acid / carbon dioxide gas corrosiveness is enhanced. If Fn2 is less than 20.0, the strong acid / carbon dioxide gas corrosiveness of the stainless steel material is lowered. On the other hand, if Fn2 exceeds 24.5, the ferrite fraction or the retained austenite fraction becomes excessively high, and the strength of the stainless steel material decreases. Therefore, 20.0 ≦ Fn2 ≦ 24.5. The upper limit of Fn2 is preferably 24.2, more preferably 24.0, still more preferably 23.8, and most preferably 23.5. The lower limit of Fn2 is preferably 20.3.

[About equation (3)]
Preferably, the chemical composition further satisfies formula (3).
0.35 ≤ Cu / Ni ≤ 1.0 ... (3)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (3).

It is defined as Fn3 = Cu / Ni. Fn3 is an index showing the strength and hot workability of the stainless steel material. If the content of each of the above elements is appropriate and Fn3 is appropriate, the strength and hot workability of the stainless steel material will be further enhanced. When Fn3 is 1.0 or less, the ratio of the Ni content to the Cu content is sufficiently high, and the hot workability of the stainless steel material is enhanced. On the other hand, when Fn3 is 0.35 or more, the ratio of the Cu content to the Ni content is sufficiently high, the effect of strengthening the precipitation of Cu at the time of tempering is enhanced, and the strength of the stainless steel material is further enhanced. Therefore, it is preferable that 0.35 ≦ Fn3 ≦ 1.0. The upper limit of Fn3 is more preferably 0.9, still more preferably 0.8, and most preferably 0.7. The lower limit of Fn3 is more preferably 0.40, further preferably 0.45, and most preferably 0.50.

[About microstructure]
The stainless steel material of the present embodiment is a duplex stainless steel material of ferrite and martensite. Specifically, the microstructure of the stainless steel material contains a ferrite phase of 20.0 to 60.0% and an austenite phase of 1.0 to 10.0% by volume fraction, and the balance is composed of martensite.

The ferrite phase in the microstructure enhances the strong acid / carbon dioxide corrosiveness in a high temperature environment such as containing chloride ions or sulfuric acid. If the volume fraction of the ferrite phase (hereinafter referred to as the ferrite fraction) is too low, the above effect cannot be obtained. On the other hand, if the ferrite fraction is too high, the strength and toughness of the stainless steel material will decrease. Therefore, the ferrite fraction is 20.0 to 60.0%. The upper limit of the ferrite fraction is preferably 58.0%, more preferably 55.0%, still more preferably 52.0%. The lower limit of the ferrite fraction is preferably 20.5%, more preferably 21.0%.

Residual austenite after tempering enhances the toughness of stainless steel. If the volume fraction of retained austenite (volume fraction of the austenite phase, hereinafter also referred to as retained austenite fraction) is too low, the above effect cannot be obtained. On the other hand, if the retained austenite fraction is too high, the yield strength of the stainless steel material is lowered, and the yield strength of 862 MPa or more cannot be stably obtained. Therefore, the retained austenite fraction is 1.0 to 10.0%. The upper limit of the retained austenite fraction is preferably 9.5%, more preferably 9.0%. The lower limit of the retained austenite fraction is preferably 1.5%, more preferably 2.0%.

[Measurement method of volume fraction of each phase in microstructure]
The ferrite fraction (volume%), retained austenite fraction (volume%), and martensite fraction (volume%) in the microstructure of the stainless steel material in the present embodiment are measured by the following methods.

[Measurement method of ferrite fraction]
First, a test piece for microstructure observation is collected from the stainless steel material. If the stainless steel material is a steel plate, the cross section of the surface of the test piece perpendicular to the plate width direction of the steel plate (hereinafter referred to as the observation surface) is polished. If the stainless steel material is a steel pipe, bar steel, or wire rod, the cross section (observation surface) of the surface of the test piece perpendicular to the axial direction of the stainless steel material is polished. Next, the observation surface after polishing is etched with a mixed solution of aqua regia and glycerin. Ferrite is identified on the etched observation surface. Then, the area ratio of the specified ferrite is measured by a point calculation method based on JIS G0555 (2003). Assuming that the measured area fraction is equal to the volume fraction, this is defined as the ferrite fraction (volume%).

[Measurement method of retained austenite fraction]
The retained austenite fraction is determined using X-ray diffraction. First, a 15 mm × 15 mm × 2 mm test piece is collected from a stainless steel material. Next, using the collected test pieces, the (200) plane and the (211) plane of the ferrite (α phase), the (200) plane, the (220) plane and the (311) plane of the austenite (γ phase), respectively. The X-ray diffraction profile of is measured, and the integrated intensity of each surface is calculated. After the calculation, the retained austenite fraction Vγ is obtained for each combination of each surface of the α phase and each surface of the γ phase (6 sets in total) using the following equation.
Vγ = 100 / (1+ (Iα × Rγ) / (Iγ × Rα))
Here, "Iα" in the equation is the integrated intensity of the α phase, and "Iγ" is the integrated intensity of the γ phase. “Rα” is the crystallographic theoretically calculated value of the α phase, and “Rγ” is the crystallographically calculated theoretically calculated value of the γ phase. The average value of the volume fraction Vγ of each of the above surfaces is defined as the retained austenite fraction (volume%).

[Measurement method of martensite fraction]
Of the microstructure of the stainless steel material of the present embodiment, the rest other than ferrite and retained austenite is composed of martensite. The martensite fraction is calculated by the following formula.
Martensite fraction = 100- (ferrite fraction + retained austenite fraction)

[Stainless steel]
The shape of the stainless steel material of the present embodiment is not particularly limited. The stainless steel material may be, for example, a steel pipe, a steel plate, a steel bar, or a wire rod.

[Production method]
As an example of the method for manufacturing the stainless steel material of the present embodiment, the method for manufacturing the seamless steel pipe will be described. A material having a chemical composition satisfying the content of each of the above-mentioned elements and the formulas (1) and (2) is prepared. The material may be a slab produced by a continuous casting method (including round CC) or a steel slab produced from the slab. Further, a steel piece produced by hot-working an ingot produced by the ingot method may be used.

The prepared material is placed in a heating furnace or a soaking furnace and heated to, for example, 1100 to 1300 ° C. Subsequently, the heated material is hot-processed to produce a raw tube. For example, the Mannesmann method is carried out as hot working. Specifically, the material is drilled and rolled by a drilling machine to make a raw pipe. Subsequently, the raw pipe is further rolled by a mandrel mill or a sizing mill. Hot extrusion may be carried out as hot working, or hot forging may be carried out. The temperature of hot working is, for example, 1000 to 1300 ° C.

The raw tube after hot working is quenched and tempered, and the strength is adjusted so that the yield strength is 862 MPa or more (125 ksi class). The quenching temperature is 800 to 1050 ° C. The preferred tempering temperature is 650 ° C. or lower.

The stainless steel material produced by the above steps has high strength as it is heat-treated, and preferably has a yield strength of 862 MPa or more. The stainless steel material is also excellent in strong acid / carbon dioxide gas corrosiveness in a high temperature environment containing chloride ions or sulfuric acid.

In the above-mentioned method for manufacturing a stainless steel material, a method for manufacturing a seamless steel pipe has been described as an example. However, the method for producing the stainless steel material of the present embodiment is not limited to the above-mentioned production method. When the stainless steel material is not a seamless steel pipe, the stainless steel material of the present embodiment can be produced by hot working in the same temperature range as the above manufacturing method, and quenching and tempering treatment. Further, the stainless steel material of the present embodiment can obtain high strength even as it is heat-treated without being cold-worked. However, cold working, heat treatment, or the like may be carried out if necessary.

The molten steel having the chemical composition shown in Table 1 was melted in a vacuum high-frequency melting furnace to produce a 50 kg ingot. Among the chemical compositions shown in Table 1, test numbers 1 to 20 are examples of the present invention, and test numbers 21 to 26 are comparative examples outside the scope of the present invention.

Each ingot was heated at 1200 ° C. for 3 hours. The heated ingot was hot forged to obtain a steel material having a thickness of 45 mm and a width of 60 mm. The steel material was heated at 1230 ° C. for 1 hour. The heated steel material was hot-rolled to produce a steel plate having a plate thickness of 13 mm. The steel sheet after hot rolling was hardened and tempered. In quenching, the steel sheet was heated at 950 ° C. for 15 minutes and then water-quenched. The hardened steel sheet was tempered at 550 ° C. for 30 minutes and then air-cooled.

Using the steel sheets of each test number after quenching and tempering, a microstructure observation test, a tensile test, and a corrosion test in _{a high-temperature strong acid CO 2 environment were carried out.}

[Microstructure observation test (measurement of volume fraction of each phase)]
A test piece for microstructure observation was collected from the steel plate of each test number. Of the surface of the collected test piece, the cross section (observation surface) perpendicular to the plate width direction of the steel plate was polished. The observed surface after polishing was etched with a mixed solution of aqua regia and glycerin. Using the etched observation surface, the ferrite fraction (volume%) was determined by the above-mentioned measuring method. The results are shown in Table 2.

A 15 mm × 15 mm × 2 mm test piece was collected from the steel plate of each test number. Using the collected test piece, the retained austenite fraction (volume%) was determined by the above-mentioned measuring method. The results are shown in Table 2.

Based on the obtained ferrite fraction and retained austenite fraction, the martensite fraction (volume%) was determined by the above method. The results are shown in Table 2.

[Tensile test]
Round bar tensile test pieces were collected from the central part of the thickness of the steel plate of each test number. The longitudinal direction of the round bar tensile test piece was a direction parallel to the rolling direction of the steel sheet (L direction). The diameter of the parallel portion of the round bar tensile test piece was 6 mm, and the distance between the gauge points was 40 mm. A tensile test was carried out on the collected round bar tensile test pieces at room temperature to determine the yield strength (0.2% proof stress). The results are shown in Table 2.

[Corrosion test in high temperature strong acid CO _{2 environment]}
First, corrosion test pieces were collected from the steel plates of each test number. The test piece had a length of 40 mm, a width of 10 mm, and a thickness of 3 mm, and had a hole having a diameter of 3 mm for hanging on a jig. Next, the weight of this test piece was measured. Subsequently, the test piece was immersed in the test solution shown in test condition A or test condition B, and the test piece was stored in the autoclave while being immersed in the test solution. The inside of the autoclave was adjusted to the test gas atmosphere and test temperature shown in test condition A or test condition B, respectively. The test time was 336 hours.

Test condition A
Test solution: 25 mass% NaCl aqueous solution Test gas: 30 barCO ₂
Test temperature: 250 ° C

Test condition B
Test solution: 0.01 mol / L H ₂ SO ₄ aqueous solution Test gas: 30 barCO ₂
Test temperature: 250 ° C

The weight of the test piece after the end of the test time was measured, and the corrosion weight loss of each test piece was determined based on the amount of change in weight before and after the test. From the obtained corrosion weight loss, the annual corrosion amount (mm / y) of the steel sheet of each test number was calculated. The results are shown in Table 2.

Further, under the corrosion condition A, for each test piece after the test, the presence or absence of pitting corrosion on the surface of the test piece was confirmed using a magnifying glass having a magnification of 10 times. The results are shown in Table 2.

[Evaluation results]
Under the test condition A, if the annual corrosion amount was less than 0.050 (mm / y), it was determined that the strong acid / carbon dioxide gas corrosiveness was good. Under the test condition B, if the annual corrosion amount was less than 0.100 (mm / y), it was determined that the strong acid / carbon dioxide gas corrosiveness was good.

With reference to Tables 1 and 2, the steel sheets of Test Nos. 1 to 20 had a chemical composition in which the content of each element was appropriate and the formulas (1) and (2) were satisfied. Therefore, the steel sheets of test numbers 1 to 20 had a high yield strength of 862 MPa or more. Further, the steel sheets of test numbers 1 to 20 had a low corrosion rate and no pitting corrosion under any of the test conditions A and B assuming the environment of the deep oil well and the deep geothermal well. Therefore, the steel sheets of test numbers 1 to 20 have high strength as they are heat-treated, and further have excellent strong acid / carbon dioxide corrosion resistance in an environment containing _{CO 2 and chloride ions or sulfuric acid at 250 ° C.} Indicated.

Further, the steel sheets of test numbers 1 to 19 having a chemical composition satisfying the formula (3) are compared with the steel sheets of the test number 20 having a chemical composition (Fn3 = 0.32) not satisfying the formula (3). The yield strength (YS) was even higher.

On the other hand, in test number 21, the Cr content was too low. In test number 21, Fn2 was as low as 18.9, which did not satisfy the formula (2). Therefore, in the corrosion test, the annual corrosion amount of the test condition A of the steel sheet of the test number 21 was 0.120 mm / y, and further pitting corrosion occurred. Further, the steel sheet of test number 21 had an annual corrosion amount of 0.280 mm / y under test condition B. In test number 21, the strong acid / carbon dioxide gas corrosiveness was inferior.

In test number 22, the Cu content was too low. In test number 22, Fn2 was as low as 19.9, which did not satisfy the formula (2). Therefore, the steel sheet of test number 22 had a low yield strength of 351.3 MPa. Further, in the corrosion test, the steel sheet of test number 22 had an annual corrosion amount of 0.160 mm / y under test condition B, and was inferior in strong acid / carbon dioxide gas corrosiveness.

In test number 23, the Ni content was too high. In test number 23, Fn1 was as low as 14.3, which did not satisfy the formula (1). Therefore, the steel sheet of Test No. 23 had a high retained austenite fraction of 32.5% by volume and a low yield strength of 405.4 MPa.

In the chemical composition of the steel sheet of Test No. 24, although the content of each element was appropriate, Fn1 was as low as 7.5 and did not satisfy the formula (1). Therefore, the steel sheet of Test No. 24 had a high retained austenite fraction of 47.2% by volume and a low yield strength of 386.7 MPa.

In the chemical composition of the steel sheet of Test No. 25, although the content of each element was appropriate, Fn2 was as high as 24.7 and did not satisfy the formula (2). Therefore, the steel sheet of Test No. 25 had a high retained austenite fraction of 11.7% by volume and a low yield strength of 537.9 MPa.

In the chemical composition of the steel sheet of Test No. 26, although the content of each element was appropriate, Fn2 was as low as 19.8 and did not satisfy the formula (2). Therefore, in the corrosion test, the annual corrosion amount of the test condition A of the steel sheet of test number 26 was 0.142 mm / y, and further pitting corrosion occurred. The steel sheet of test number 26 further had an annual corrosion amount of 0.268 mm / y under test condition B. In test number 26, the strong acid / carbon dioxide gas corrosiveness was inferior.

The embodiments of the present invention have been described above. However, the embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

M Martensite phase M + F Two-phase structure of martensite phase and ferrite phase F ferrite phase A austenite phase

Claims (5)

By mass%
C: 0.040% or less,
Si: 0.05-1.0%,
Mn: 0.010 to 0.30%,
Cr: More than 18.0% and 21.0% or less,
Cu: 1.5-4.0%,
Ni: 3.0-6.0%,
sol. Al: 0.001 to 0.100%,
Mo: 0-0.60%,
W: 0-2.0%,
Co: 0-0.30%,
Ti: 0 to 0.10%,
V: 0 to 0.15%,
Zr: 0-0.10%,
Nb: 0 to 0.10%,
Ca: 0-0.010%,
Mg: 0-0.010%,
REM: 0-0.05%,
B: 0 to 0.005% and
The rest consists of Fe and impurities
Of the impurities, P, S, O, and N are each.
P: 0.050% or less,
S: less than 0.0020%,
O: 0.020% or less, and
N: 0.020% or less,
A chemical composition satisfying the formulas (1) and (2),
By volume fraction,
A stainless steel material having a ferrite phase of 20.0 to 60.0%, an austenite phase of 1.0 to 10.0%, and a microstructure in which the balance is martensite.
15.0 ≦ 616-706 (C + N) -22Si-24Mn-24Ni-18Cr-8Cu-16Mo ... (1)
20.0 ≤ Cr + Cu ≤ 24.5 ... (2)
Here, the content (mass%) of each element is substituted for each element symbol in the formula (1) and the formula (2). The stainless steel material according to claim 1.
The chemical composition is
Mo: 0.02 to 0.60%,
W: 0.01 to 2.0% and
Co: 0.01-0.30%
A stainless steel material containing one or more selected from the group consisting of. The stainless steel material according to claim 1 or 2.
The chemical composition is
Ti: 0.005 to 0.10%,
V: 0.005 to 0.15%,
Zr: 0.005 to 0.10% and
Nb: 0.005 to 0.10%
A stainless steel material containing one or more selected from the group consisting of. The stainless steel material according to any one of claims 1 to 3.
Ca: 0.0005 to 0.010%,
Mg: 0.0005 to 0.010%,
REM: 0.0005-0.05% and
B: 0.0005% to 0.005%
A stainless steel material containing one or more selected from the group consisting of. A stainless steel pipe made of the stainless steel material according to any one of claims 1 to 4.

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