JPH11302801A - High Cr-high Ni alloy with excellent stress corrosion cracking resistance - Google Patents

Abstract

(57) [Summary] [Problem] A hydrogen sulfide partial pressure of 150 to 25 with a pressure of 1 to 10 atm.
High Cr- which has excellent resistance to hydrogen sulfide stress corrosion cracking in a high temperature environment of 0 ° C, is inexpensive, and has excellent hot workability.
Provide high Ni alloy. SOLUTION: In weight%, Si: 0.05 to 1.0%, M
n: 0.1 to 1.5%, Cr: 20.0 to 35.0%,
Ni: 25.0 to 50.0%, Cu: 0.5 to 8.0
%, Mo: 0.01 to 3.0%, sol. Al: 0.0
1 to 0.3%, N: 0.15% or less, REM: 0 to 0.
10%, Y: 0 to 0.20%, Mg: 0 to 0.1%, C
a: 0 to 0.1%, C, P, and S in the impurities are 0.05% or less, 0.03% or less, and 0.01% or less, respectively, and the formula “% Cu ≧ 1.2− 0.4 (% Mo-1.
4) A high Cr-high Ni alloy satisfying ² ). This alloy is M
When the o content is 1.5% or less, hot workability is remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an austenitic high Cr-high Ni alloy used for oil wells and gas wells (hereinafter simply referred to as "oil wells"). More specifically, in a highly corrosive hydrogen sulfide environment, the corrosion resistance represented by stress corrosion cracking resistance is excellent, and the Mo content conventionally used in these alloy systems is small, so that economic efficiency is low. Also, the present invention relates to an austenitic high Cr-high Ni alloy excellent in hot workability and suitable for industrial production.

[0002]

2. Description of the Related Art Hydrogen sulfide contained in petroleum, natural gas, and the like has a strong corrosiveness to metallic materials, and is used in alloys that are used by being exposed to a liquid containing such hydrogen sulfide. Is required to have excellent corrosion resistance. Examples of alloys used in environments in contact with liquids containing hydrogen sulfide include drilling pipes for oil and natural gas wells, pipes for these flow lines, plates for geothermal power generation equipment, and plates for exhaust gas desulfurization equipment. is there. In particular, in recent years, the wells for extracting oil and natural gas have been remarkably deepened, and the environment has become increasingly severe, and contains many corrosive substances such as carbon dioxide and hydrogen sulfide. As oil wells increase, embrittlement of materials due to corrosion and the like has become a major problem.

[0003] Among them, in an environment at a high temperature of about 200 ° C and containing a large amount of hydrogen sulfide at a partial pressure of about 10 atm, the main factors of the corrosion are cracks generated under stress load conditions in a specific environment. This is so-called stress corrosion cracking. Therefore, alloys used in an environment containing hydrogen sulfide are required to have excellent resistance to corrosion cracking. As a material having corrosion resistance in such a hydrogen sulfide environment, Ni-Cr- containing a large amount of about 30 to 50% of Ni and containing 3% or more of an expensive element such as Mo or W is conventionally used. The Mo (or W) -Fe-based austenitic alloy exhibits excellent corrosion resistance.
Nos. 9660 and 62-9661.

[0004] For example, the alloys disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 62-9660 have Ni, C, which are effective components, in order to have stress corrosion cracking resistance in accordance with the temperature conditions of the use environment.
After limiting the contents of r, Mo and W to a predetermined range, 1% by weight or less of Cu and / or 2% by weight
It contains the following Co. For this reason, since these conventional alloys contain expensive Mo or W as an essential component, there is a problem that the price of the alloy is high.

The above-mentioned conventional alloy has a hydrogen sulfide partial pressure of 10
It is very expensive because it is intended to be used in a severe environment of about atm and around 200 ° C. Also,
On the other hand, Japanese Patent Application Laid-Open No. 8-176746 discloses a relatively inexpensive Cu characterized by a low hydrogen sulfide partial pressure of 0.1 atm or less, a temperature of about 150 ° C., and the absence of Mo. A high Cr-high Ni alloy containing is shown.

However, this alloy has a partial pressure of hydrogen sulfide of 0.3.
When it is about 1 atm, it has excellent corrosion resistance, but when the hydrogen sulfide partial pressure is as high as about 5 atm or more, sufficient corrosion resistance cannot be obtained. Further, as described above, Ni-Cr-M
Austenitic alloys based on o (or / and W) -Fe are expensive and uneconomical. Further, the addition of Mo, W, etc., is not suitable for production on a commercial scale since it reduces the hot workability.

Therefore, when the partial pressure of hydrogen sulfide is 1 atm or more,
In addition, the development of inexpensive corrosion-resistant alloys that have sufficient corrosion resistance in extremely severe high-temperature hydrogen sulfide environments with temperatures as high as 150 ° C or higher, and that are excellent in hot workability and suitable for industrial production. It was strongly desired.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydrogen sulfide partial pressure as high as about 1 to 10 atm and a temperature of 15 to 15 atm.
It is excellent in terms of economy because it is excellent in corrosion resistance to hydrogen sulfide under a high temperature environment of 0 to 250 ° C and is composed of inexpensive alloy elements. An object of the present invention is to provide a high Cr-high Ni alloy suitable for excellent industrial production.

[0009]

The gist of the present invention is to provide a (1) high Cr-high Ni alloy excellent in stress corrosion cracking resistance in a hydrogen sulfide environment and a (2) hydrogen sulfide environment described below. Cr- excellent in stress corrosion cracking resistance and hot workability under high temperature
High Ni alloy.

(1) Si: 0.05 to 1.0% by weight
%, Mn: 0.1-1.5%, Cr: 20.0-35.
0%, Ni: 25.0 to 50.0%, Cu: 0.5 to
8.0%, Mo: 0.01-3.0%, sol. Al:
0.01 to 0.3%, N: 0.15% or less, REM: 0
~ 0.10%, Y: 0 ~ 0.20%, Mg: 0 ~ 0.1
%, Ca: 0 to 0.1%, and the balance consists of Fe and unavoidable impurities, and C, P, and S in the impurities are each 0.0%.
A high Cr-high Ni alloy containing 5% or less, 0.03% or less, 0.01% or less and containing Cu satisfying the following formula.

Cu ≧ 1.2-0.4 (% Mo-1.4) ² Here, the symbol of element represents the content (% by weight) of each element in the steel.

(2) The high Cr-high Ni alloy according to the above (1), wherein the content of Mo is 1.5% by weight or less.

The present invention has been completed based on the following findings. That is, the present inventors have studied various alloy components in order to improve the stress corrosion cracking resistance of a high Cr-high Ni alloy under a high temperature environment of 150 ° C. or higher, where the partial pressure of hydrogen sulfide is as high as 1 atm or higher. As a result of examining the effects in detail, the following was found.

That is, in the case of a high Cr-high Ni alloy containing Mo, an Ni sulfide film is formed on the outer layer to exhibit an environment shielding effect from the hydrogen sulfide environment, and the inner layer Cr
An oxide film forms. And, conventionally, it was thought that Mo only contributes to the stable formation of the Cr oxide film of the inner layer. However, a more detailed investigation revealed the following.

In the case of a high Cr—high Ni alloy containing more than 3% of Mo, the initial outer layer coating exposed to the corrosive environment contains Mo sulfide in addition to Ni sulfide.
o also plays a part in the environmental blocking effect similarly to Ni. However, the outer coating after prolonged exposure in a corrosive environment,
Only the extremely thin portion of the outermost layer becomes a single-layer film of Ni sulfide and is stabilized, and Mo mainly acts to maintain the stability of the inner Cr oxide film.

On the other hand, in order to reduce the alloy cost, a high Cr-
In a high Ni alloy, the amount of Mo sulfide contained in the initial outer layer coating exposed to the corrosive environment is not only extremely reduced, but is not included at all in the extreme case, and the environmental barrier effect of the outer layer coating is not sufficient. Sufficient corrosion resistance cannot be secured.

Therefore, it is necessary to add an alloy component which forms as a sulfide in the initial outer layer film and exerts a sufficient environmental shielding effect instead of Mo. The following experiment was conducted, paying attention to the fact that it has the property of easily generating. That is, the Mo content and the Cu content were variously changed within the range of 0.1 to 3%.
% Cr-35% Ni alloy was examined for its resistance to hydrogen sulfide corrosion (resistance to hydrogen sulfide stress corrosion cracking). The hydrogen sulfide stress corrosion test was performed under the following conditions.

(Hydrogen sulfide stress corrosion test conditions): Test solution: 20% NaCl + 0.5% CH ₃ COOH Test gas S: 7 atm H ₂ S + 10 atm CO ₂ Test temperature: 180 ° C. Immersion time: 720 hours Additional stress: 125 ksi (87.75 kgf) / M
m ² ) Test piece: 100 mm width × 2 mm thickness × 75 mm length, U-notch of 0.25 mm formed at the center in the length direction 4
Point Bending Test Piece FIG. 1 is a diagram showing the results of the examination. In the figure, a circle indicates that hydrogen sulfide stress corrosion cracking did not occur, and a black circle indicates that hydrogen sulfide stress corrosion cracking occurred. I have.

As can be seen from FIG. 1, the relationship between the content of Mo and Cu is expressed by the formula "% Cu ≧ 1.2-0.4 (% Mo-
It was found that when 1.4) ² ) was satisfied, excellent hydrogen sulfide stress corrosion cracking resistance was ensured even if the Mo content was reduced to 3% or less.

Here, the reason why the contents of Mo and Cu are regressed by the above equation in order to obtain a stable film structure for exhibiting excellent corrosion resistance will be considered. Under the environment where the alloy of the present invention is used, Mo sulfide is the most stable among the sulfides of Mo, Ni, and Cu. Therefore, when the Mo content is in the range of about 1.5 to 3%, the effect of Mo on the film formation becomes dominant. Therefore, Mo
As the content decreases, the formation of Mo sulfide in the initial film becomes unstable, and the stability of the film as a whole decreases. However, this reduction is compensated for by Cu sulfide and forms a stable Mo / Ni / Cu sulfide film.

On the other hand, when Mo becomes 1.5% or less, the generation of Mo sulfide becomes unstable, and the film structure becomes N
It changes to a film mainly composed of i / Cu sulfide. In this region, the effect of Cu and Ni acting on the film formation becomes large, but the presence of Mo competes with the effect of the film formation. For this reason, since the film structure is not stabilized even after a long period of time, the inner Cr oxide layer is not sufficiently formed, and conversely, Mo impairs the stability of the film.

Further, when the Mo content is reduced and the content is less than 0.1%, the effect of M on the initial film formation is reduced.
The effect of o becomes extremely small. Conversely, even with a small amount of Cu added, a Ni / Cu sulfide film is sufficiently formed stably. It is considered that as a result of such a combination of the phenomena, the above expression is established between the Mo content and the Cu content.

In addition, conventional high Cr-high N containing a large amount of Mo
The i-alloy had high high-temperature strength and poor hot workability, and could not be applied to a highly productive Mannesmann-mandrel mill tube production method. Therefore, in order to enable application to the Mannesmann-mandrel mill pipe-making method, the effect of each additive element was examined from the viewpoint of high-temperature strength. As a result, the reduction of the Mo content significantly reduces the high-temperature strength,
% Does not significantly affect the change in high-temperature strength. In particular, if the Mo content is 1.5% or less, C
The hot workability is remarkably improved while maintaining the excellent corrosion resistance due to the addition of u, and the product (steel pipe) can be manufactured without any problem by applying to the Mannes mandrel mill tube manufacturing method.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The chemical composition of the alloy according to the present invention will be described below. The unit of the content of each element means “% by weight”.

Si: Si is a component necessary as a deoxidizing agent for the alloy, and its effect is obtained at a content of 0.05% or more. However, if the content exceeds 1%, the hot workability decreases. For this reason, the Si content is set to 0.05 to 1%. The preferred range is 0.2-0.5%.

Mn: Mn is a component necessary as a deoxidizing agent for the alloy, similar to Si described above, and its effect is 0.1%.
It is obtained with the above content. However, the content is 1.5
%, The hot workability decreases. For this reason, the Mn content is set to 0.1 to 1.5%. The preferred range is 0.
5 to 0.75%.

Cr: Cr is a main component constituting the alloy of the present invention, and is effective in improving hydrogen sulfide corrosion resistance represented by stress corrosion cracking resistance in the presence of Ni described later. Component. However, if the content is less than 20%, the effect cannot be obtained. On the other hand, if the content exceeds 35%, the effect is saturated, and excessive addition is not preferable from the viewpoint of economy. Therefore, the Cr content is 20 to
35%. The preferred range is 22-30%.

Ni: Ni has the effect of improving hydrogen sulfide corrosion resistance. However, if the content is less than 25%, the Ni sulfide film will not be formed insufficiently on the outer surface of the alloy, so that the effect of Ni cannot be obtained. On the other hand, if the content exceeds 50%, the effect is saturated and the price of the alloy is increased, which impairs the economic efficiency. Therefore, the Ni content is set to 25 to 50%. The preferred range is 27-45%.

Sol. Al: Al is the above Si, Mn
Similarly, it is necessary as a deoxidizer for alloys. To obtain the effect, sol. Al content of 0.01% or more is required. However, when the content exceeds 0.3%, the hot workability decreases. Therefore, sol. Al content is 0.
01-0.3%. The preferred range is 0.1 to 0.1
5%.

Cu: Cu is the most characteristic element for the alloy of the present invention. Further, Cu has a function of significantly improving the corrosion resistance to hydrogen sulfide in a hydrogen sulfide environment, and the effect is obtained at a content of 0.5% or more. However, if the content exceeds 8%, the effect is saturated, and conversely, the hot workability decreases. Therefore, the Cu content is set to 0.5 to 8%. The preferred range is 1-6%.

However, as described above, the Cu content is determined by the formula “% Cu ≧ 1.2-0.4 (% Mo-1.4)
² ”must be satisfied.

Mo: Mo is a characteristic element of the alloy of the present invention next to Cu described above. Further, Mo has an effect of improving the corrosion resistance to hydrogen sulfide in a hydrogen environment, but is very expensive. Therefore, in the present invention, the upper limit of the content is 3% from the viewpoint of economy. . On the other hand, the effect is 0.01% when added together with Cu.
It is obtained with the above content. For this reason, the Mo content is 0.1.
01 to 3%. The preferred range is 0.05-2%.

However, as described above, the Mo content is determined by the formula “% Cu ≧ 1.2-0.4 (% Mo-1.4)
² ”must be satisfied.

From the viewpoint of hot workability, the upper limit is preferably set to 1.5%. The reason is that, when the content of Mo exceeds 1.5%, the high-temperature strength is increased, the hot workability is reduced, and it becomes difficult to manufacture an alloy pipe by the Mannesmann-mandrel mill pipe manufacturing method. It is.

C: If the content of C exceeds 0.05%, it reacts with Nb and V existing as impurities to form coarse carbides. Furthermore, continuous Cr
It forms carbides and increases susceptibility to stress corrosion cracking at grain boundaries. Therefore, the upper limit is set to 0.05%. A preferred upper limit is 0.03%.

P: P is contained as an unavoidable impurity, but if its content exceeds 0.03%, the sensitivity to stress corrosion cracking in a hydrogen sulfide environment increases. Therefore, the upper limit is set to 0.03% or less. A preferred upper limit is 0.02%.

S: Like S, S is contained as an unavoidable impurity, and when its content exceeds 0.01%, the hot workability is significantly reduced. Therefore, the upper limit is set to 0.01%. The hot workability is significantly improved when the content of S is reduced to 0.0007% or less. Therefore, when hot working under severe conditions is required, the S content is preferably set to 0.0007% or less.

N: N may not be added. However,
The high Cr-high Ni alloy targeted by the present invention usually contains about 0.01% of N as an unavoidable impurity, similarly to the above P and S. However, if N is positively added, the strength can be increased without deteriorating the corrosion resistance.

That is, the high Cr-high Ni alloy pipe is usually made into a product by performing cold working for strength adjustment after hot working. At that time, in the case of an alloy pipe having a low N content, it is necessary to impart a working ratio (cross-section reduction rate) exceeding 30% in order to secure a desired strength. In this case, the corrosion resistance (stress corrosion cracking resistance) decreases, but if N is added positively, the desired strength can be ensured by cold working with a workability of 30% or less, and the corrosion resistance (stress corrosion cracking resistance) is reduced. ) Does not decrease.

Therefore, when it is necessary to further improve the strength by cold working with a working ratio of 30% or less,
N can be positively added. The effect is 0.0
It is obtained with a content of 2% or more. On the other hand, when its content is 0.1.
If it exceeds 15%, hot workability is reduced. Further, the strength becomes too high, so that it becomes difficult to adjust the strength level by cold working, and the sensitivity to stress corrosion cracking in a hydrogen sulfide environment is rather increased. Therefore, the N content when actively added is 0.02 to 0.15%, preferably 0.05 to
It is desirable to set it to 0.1%.

REM (rare earth element), Mg, Ca, Y These components are added as needed. If you add
Since the hot workability is improved, if it is necessary to ensure more excellent hot workability, one or more selected from these can be added. But,
If the content of any of the elements is less than 0.001%, the above effects cannot be obtained. On the other hand, the content is REM,
If the content of Mg and Ca exceeds 0.1% and the content of Y exceeds 0.2%, coarse oxides are formed, which causes a reduction in hot workability. Therefore, the content of these elements when added is 0.001 to 0.1% for REM, Mg and Ca, and 0.001 for Y.
It is desirable to set it to 1 to 0.2%.

The alloy of the present invention contains B, Sn, As, and S as unavoidable impurities other than C, P, and S described above.
b, Bi, Pb and Zn may each be contained in a range of 0.1% or less, and even in this case, the characteristics of the alloy of the present invention are not impaired at all.

The alloy of the present invention and products such as alloy tubes using the alloy as a base material can be manufactured by manufacturing equipment and manufacturing methods usually used for commercial production. For example, melting of an alloy is performed by an electric furnace, an Ar-O ₂ mixed gas bottom-blown decarburizing furnace (AOD furnace), and a vacuum decarburizing furnace (VOD furnace).
And so on. The molten metal may be cast into an ingot, or may be cast into a rod-shaped billet or the like by a continuous casting method. When an alloy tube is produced from these billets, for example, an extrusion tube method such as the Eugene Sejunel method or a Mannesmann tube method can be used. In particular, the alloy according to the second aspect of the present invention is preferably manufactured by the Mannesmann tube method. In addition, the pipe making conditions such as the billet heating temperature before the pipe making are the same as those of the conventional high Cr-
It may be the same as the case of the high Ni alloy.

The alloy pipe after hot working has a working degree of 3%.
It is preferable to apply a cold work of 0% or less to adjust the strength and make a product tube.

[0045]

EXAMPLES Table 1 shows the characteristics of the alloy of the present invention.
The following 15 alloys were melted. After melting these alloys in an electric furnace and adjusting the composition to the target chemical composition,
It was manufactured by a method of performing decarburization and desulfurization treatment using an AOD furnace. The obtained molten metal weighs 1500 kg and has a diameter of 500 kg.
mm ingot. In addition, among the 16 alloys shown in Table 1, Nos. 1 to 9 are examples of the present invention, and Nos. 10 to 1
6 is an alloy of a comparative example.

[0046]

[Table 1]

Each of the ingots having the chemical compositions shown in Table 1 was subjected to the following treatment. First, 125 ingots
Heat to 0 ℃, hot forging at 1200 ℃, 150m in diameter
m. Further, it was cut into a length of 1000 mm to obtain an extruded pipe billet. Next, this billet was formed into a tube having a diameter of 60 mm, a wall thickness of 5 mm, and a length of about 20 m using a hot tube extruded tube by the Eugene Sejournel method, and its hot workability was examined. In addition, a billet similar to the above was made into a tube having a diameter of 60 mm, a wall thickness of 7 mm, and a length of about 20 m by a Mannesmann-mandrel mill tube manufacturing method.
The hot workability was investigated.

Among them, the tube obtained by hot tube extrusion was subjected to a solution treatment under the conditions of holding at 1100 ° C. for 0.5 hour and then cooling with water. Furthermore, the 0.2% proof stress is 125 ksi grade (87.75 to 98.28 kg) by performing cold working with a working ratio (cross-section reduction rate) of 25%.
f / mm ² ) to obtain a product tube.

A test piece 1 having the shape and dimensions shown in FIG. 2 and having a U-notch 2 formed in the center in the longitudinal direction thereof was sampled from these product tubes, and this test piece 1 was bent into a bending jig shown in FIG. After setting to 3 and applying a predetermined bending, the steel sheet was subjected to a hydrogen sulfide corrosion test as it was, and the hydrogen sulfide corrosion resistance (hydrogen sulfide stress corrosion cracking resistance) was investigated. The hydrogen sulfide corrosion test was performed under the following conditions.

(Hydrogen sulfide corrosion test conditions): Test solution: 20% NaCl + 0.5% CH ₃ COOH Test gas: 7 atm H ₂ S + 10 atm CO ₂ Test temperature: 180 ° C. Immersion time: 720 hours Applied stress: 125 ksi (87.75 kgf / m)
m ² ) On the other hand, the hot workability was evaluated by visually observing the inner surface of the tube after the tube was formed by extruding the tube with a hot tube, and evaluating the presence or absence of flaws generated during the tube forming. In the case of a Mannesmann-mandrel mill tube, the tube was cut at a position of 1000 mm from the end of the tube after the tube was manufactured, and evaluated by the presence or absence of occurrence of molten double cracks in the thickness direction of the cross section of the tube.

The results of these investigations are also shown in Table 1. The hydrogen sulfide corrosion resistance was evaluated as “good: を” when no crack or pitting occurred in the above-described hydrogen sulfide corrosion test, and as “bad” when it occurred. The hot workability was evaluated as “good:」 ”for hot extruded pipes where no flaws occurred during pipe making by visual observation, and“ poor ”for those which were observed. Yoshi: × ”. Further, as for the pipes made of a Mannesmann-mandrel mill, those with no occurrence of split cracks were evaluated as “hot workability: good”, and those with cracks were evaluated as “defective hot workability: ×”. And

As is clear from the results shown in Table 1, the alloys of the present invention (Nos. 1 to 9) were all excellent in hydrogen sulfide corrosion resistance. In addition, regarding hot workability, the No. 3 alloy having a high Mo content of 2.8% cracked into two pieces of molten steel, making commercial production by the Mannesmann-mandrel mill tube method impossible. All were good except for the above.

On the other hand, the alloys of Comparative Examples (Nos. 10-1)
Of the 5), the alloys of Nos. 10 and 11 each had good hot workability, but the content of Mo and Cu was within the range specified in the present invention, and the formula “% Cu ≧ 1” .2-0.4
(% Mo-1.4) ² ], but Cr or N
Since the content of i is lower than the lower limit specified in the present invention,
Hydrogen sulfide corrosion resistance was poor.

The alloys of Nos. 12 and 13 are Mo and C
Although the content of u is within the range specified in the present invention, the formula “%
Cu ≧ 1.2−0.4 (% Mo−1.4) ² ”, the hydrogen sulfide corrosion resistance was poor. Among them, the alloy of No. 12 had a high Mo content of 2.8%, so that the molten double cracks occurred, and commercial production by the Mannesmann-mandrel mill pipe manufacturing method was impossible. Was.

Further, the alloy of No. 14 had good hot workability, but was poor in hydrogen sulfide corrosion resistance because it did not contain Cu.

The alloy of No. 15 has the formula “% Cu ≧ 1.2−
0.4 (% Mo-1.4) ² ], and the hydrogen sulfide corrosion resistance was good, but the Cu content was 9.4%, which exceeded the upper limit specified in the present invention. , Hot workability was poor.

The alloy of No. 16 has the formula “% Cu ≧ 1.2−
0.4 (% Mo-1.4) ² ], but the content of N is 0.18%, which exceeds the upper limit specified in the present invention. there were.

[0058]

The high Cr-high Ni alloy of the present invention has a high hydrogen sulfide partial pressure of about 1 to 10 atm and a temperature of 150 to 2 atm.
Excellent resistance to hydrogen sulfide corrosion under high temperature environment of 50 ° C. In addition, the alloy is inexpensive because the effective Mo content is small. Moreover, it has excellent hot workability and is suitable for industrial production.

[Brief description of the drawings]

FIG. 1 is a view showing the influence of Cu content and Mo content on stress corrosion cracking resistance.

FIGS. 2A and 2B are views showing the shape and dimensions of a notched four-point bending test piece used in a hydrogen sulfide corrosion test of an example, wherein FIG. 2A is a plan view, FIG. FIG. 3C is an enlarged view of the cutout portion.

3A and 3B are diagrams showing a relationship between a bending applying jig and a test piece, wherein FIG. 3A is a front view showing a set state, and FIG. 3B is a front view showing a stress applying state on the test piece. .

[Explanation of symbols]

 1: test piece, 2: U notch, 3: bending jig.

Claims (2)

[Claims] (1) Si: 0.05-1%, Mn:
0.1-1.5%, Cr: 20-35%, Ni: 25-
50%, Cu: 0.5 to 8%, Mo: 0.01 to 3%,
sol. Al: 0.01 to 0.3%, N: 0.15% or less, REM: 0 to 0.1%, Y: 0 to 0.2%, Mg:
0 to 0.1%, Ca: 0 to 0.1%, the balance being Fe
And unavoidable impurities, and C, P, S in the impurities
Are 0.05% or less, 0.03% or less, and 0.01, respectively.
%, And the relationship between the contents of Cu and Mo satisfies the following expression: a high Cr-high Ni alloy excellent in stress corrosion cracking resistance in a hydrogen sulfide environment. Cu ≧ 1.2−0.4 (Mo−1.4) ² Here, the symbol of element represents the content (% by weight) of each element in the steel. 2. The high Cr-high Ni composition according to claim 1, wherein the Mo content is 1.5% by weight or less. alloy.