JP3485034B2 - 862N / mm2 Class Low C High Cr Alloy Oil Well Pipe Having High Corrosion Resistance and Method of Manufacturing the Same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high-strength martensitic stainless steel excellent in stress corrosion cracking resistance and a method for producing the same, and more specifically, for example, petroleum,
862 with high stress corrosion cracking resistance in environments containing wet carbon dioxide, wet hydrogen sulfide in natural gas drilling and transportation
The present invention relates to an N / mm ² class low C high Cr alloy oil country tubular good and a manufacturing method thereof.

[0002]

2. Description of the Related Art Recently, petroleum and natural gas produced in recent years are increasingly containing a large amount of wet carbon dioxide gas and wet hydrogen sulfide. In excavation and transportation, 13Cr type stainless steel or the like is used instead of conventional carbon steel. Martensitic stainless steels have been used. However, the conventional martensitic stainless steel has excellent corrosion resistance to wet carbon dioxide (hereinafter simply referred to as corrosion resistance), but has sufficient stress corrosion cracking resistance to wet hydrogen sulfide (hereinafter simply referred to as stress corrosion cracking resistance). Instead, a martensitic stainless steel having improved stress corrosion cracking resistance while maintaining strength, toughness, and corrosion resistance has been desired.

Those satisfying the requirements of stress corrosion cracking resistance in addition to strength, toughness and corrosion resistance are disclosed in Japanese Examined Patent Publication No. 61-3391.
JP-A-58-199850 and JP-A-61-207
It is disclosed in Japanese Patent Publication No. 550.

On the other hand, a martensitic stainless steel having improved resistance to stress corrosion cracking in an environment in which the partial pressure of hydrogen sulfide exceeds 0.01 atm has also been proposed, for example, JP-A-60-.
It is disclosed in Japanese Patent No. 174859, Japanese Patent Laid-Open No. 62-54063, and the like.

[0005]

However, the steels described in JP-B-61-3391, JP-A-58-199850, and JP-A-61-207550 contain only a very small amount of hydrogen sulfide. Although it exhibits stress corrosion cracking resistance in the environment, it has a problem that it cannot be used in an environment containing a large amount of hydrogen sulfide because stress corrosion cracking occurs in an environment where the hydrogen sulfide partial pressure exceeds 0.01 atm.

[0006] Further, JP-A-60-174859,
The steels described in JP-A-62-54063 and the like cannot completely prevent stress corrosion cracking due to hydrogen sulfide.

Further, from the viewpoint of strength, the toughness and the stress corrosion cracking resistance of each of the above-mentioned martensitic stainless steels are significantly deteriorated when an attempt is made to increase the strength, so that the strength or the toughness and the stress corrosion cracking resistance are deteriorated. There was also the problem of having to sacrifice one. For this reason, for example, there is a drawback that it cannot be applied to a deep oil well where high strength, stress corrosion cracking resistance, corrosion resistance and toughness are required at the same time.

The object of the present invention is to improve the strength, stress corrosion cracking resistance and toughness of conventional martensitic stainless steel at the same time in order to solve the above problems in the prior art, while maintaining the corrosion resistance. Another object of the present invention is to provide an 862 N / mm ² class low C, high Cr alloy oil country tubular good which can be used without causing stress corrosion cracking even in an environment containing a large amount of hydrogen sulfide, and a manufacturing method thereof.

The target performance is set as follows in view of the performance required for carbon dioxide, petroleum containing hydrogen sulfide, natural gas, and steel pipes for transportation.

Strength: 0.2% yield strength of 862 N / mm ² or more 9
65 N / mm ² or less. Toughness: Absorbed energy value (called Charpy impact value) of Charpy full size test piece at -20 ° C is 100.
J or higher. Corrosion resistance: Corrosion rate of 0.5 mm / y or less in an environment of 5% NaCl solution, 180 ° C., 30 atm CO ₂ .

Stress corrosion cracking resistance: 0.2% on a test piece in a 5% NaCl solution saturated with hydrogen sulfide gas at 0.01 atm.
Load 90% of proof stress and withstand 720 hours or more without breaking.

[0012]

In order to solve the above problems and achieve the object, the present invention uses the following means.

The alloy oil country tubular goods of the first aspect of the present invention, in% by weight,
C: 0.005-0.05%, Cr: 12-16%, S
i: 1.0% or less, Mn: 0.05 to 0.3%, Ni:
3.5-6.0%, Mo: 1.5-2.5%, V: 0.
862 N / mm ² class low C having high corrosion resistance, characterized by containing 01 to 0.05%, N: 0.02% or less, and satisfying the following (1), and the balance being substantially Fe. High Cr
It is an alloy oil country tubular good. 25-25 [% Ni] +5 [% Cr] +25 [% Mo] ≧ 0 ... (1)

The alloy oil country tubular good according to the second aspect of the present invention further comprises the components described in the first aspect of the present invention in Nb: 0.01 to 0.01% by weight.
862 N / mm ² having high corrosion resistance, characterized by containing one or more of 0.1% and Ti: 0.01 to 0.1%
It is a low C, high Cr alloy oil country tubular good.

The manufacturing method of the third invention of the present invention is, in weight percent,
C: 0.005-0.05%, Cr: 12-16%, S
i: 1.0% or less, Mn: 0.05 to 0.3%, Ni:
3.5-6.0%, Mo: 1.5-2.5%, V: 0.
After hot working an alloy steel containing 01 to 0.05% and N: 0.02% or less and satisfying the following (1), 100 ° C or less after austenitizing at a temperature of AC ₃ points or more and 980 ° C or less 862N having high corrosion resistance, characterized in that it is cooled to a temperature of 610 ° C. and then tempered at a temperature of 610 ° C. or lower and 540 ° C. or higher to uniformly precipitate carbides after tempering within the grain and not preferentially precipitate at grain boundaries. / mm ² Class C low Cr high Cr alloy oil country tubular goods manufacturing method. 25-25 [% Ni] +5 [% Cr] +25 [% Mo] ≧ 0 ... (1)

The production method of the fourth invention of the present application is the same as the components described in the third invention of the present application, further containing Nb: 0.01 to 0.01% by weight.
0.12%, Ti: 0.01 to 0.1% of one or more kinds are contained, and 862N / mm ² class low C high Cr alloy oil well having high corrosion resistance according to the third aspect of the present invention. It is a method of manufacturing a tube.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies to solve the above problems, the present inventors have obtained the following findings.

Increasing Cr is effective for improving the corrosion resistance of martensitic stainless steel. However, increasing Cr, on the other hand, produces a δ-ferrite phase, deteriorating strength and toughness. Therefore, there is a method of suppressing the generation of the δ-ferrite phase by increasing the amount of Ni which is an austenite forming element, but the increase of Ni is limited in terms of tempering temperature. Increasing C is also effective in suppressing the formation of the δ-ferrite phase, but carbides precipitate during tempering, which rather deteriorates corrosion resistance and stress corrosion cracking resistance, so its content should be rather limited.

On the other hand, generally, when the strength of steel is increased, the toughness and the stress corrosion cracking resistance are deteriorated, but an appropriate amount of V is contained and the carbide is dispersed as a fine precipitate in the matrix of this stainless steel by heat treatment. By doing so, it is possible to increase the strength without deteriorating them.

However, in order to uniformly disperse and precipitate fine V carbides, it is necessary to control the tempering conditions.

Based on the above findings, the present inventors have considered that the restriction of the metal structure due to the increase of Cr as described above is included in the low C high Cr alloy oil country tubular goods in a certain amount of V, and 862 N / In order to stably obtain mm ² grade strength, the heat treatment conditions were adjusted within a certain range to uniformly disperse and precipitate carbides within the grains, which was not possible with conventional martensitic stainless steels. The present invention has been completed by discovering a new martensitic stainless steel (low C high Cr alloy oil country tubular good) having high toughness, high strength and excellent stress corrosion cracking resistance, and a method for producing the same.

That is, the present invention limits the alloy composition and manufacturing conditions to the following ranges to improve the stress corrosion cracking resistance and toughness of the conventional high-strength martensitic stainless steel and maintain the corrosion resistance, 862 N / mm that can be used in environments containing a large amount of hydrogen sulfide without causing stress corrosion cracking
^{A second} class low C, high Cr alloy oil country tubular good can be provided.

The reasons for adding the components, the reasons for limiting the components, and the reasons for limiting the manufacturing conditions in the present invention will be described below.

(1) Component composition range C: 0.005 to 0.05% C is a strong austenite forming element, and is an element essential for obtaining high strength. However, at the time of tempering, it combines with Cr to form carbides and precipitates.
It deteriorates stress corrosion cracking resistance and toughness. If the C content is less than 0.005%, sufficient strength cannot be obtained, and 0.0
If it exceeds 5%, the deterioration becomes remarkable, so 0.005 to 0.
The content is set to 05%.

Cr: 12 to 16% Cr is a basic element that constitutes martensitic stainless steel, and is an important element that exhibits corrosion resistance. However, if the content is less than 12%, sufficient corrosion resistance can be obtained. No
If it exceeds 16%, no matter how the other alloying elements are adjusted, δ-
The amount of ferrite phase produced increases, and the strength and toughness deteriorate, so the content is made 12 to 16%.

Si: 1.0% or less Si is an element necessary as a deoxidizer, but it is also a strong ferrite forming element, and if it is contained in an amount exceeding 1.0%, the formation of a δ-ferrite phase is promoted. Therefore, it is 1.0% or less.

Mn: 0.05 to 0.3% Mn is an austenite forming element which is effective as a deoxidizing and desulfurizing agent and which suppresses the appearance of the δ-ferrite phase. However, Mn is harmful to the stress corrosion cracking resistance, and the upper limit is 0.3%. If the content is 0.05% or less, deoxidation is insufficient and inclusions increase, so the Mn content is set to 0.05 to 0.3%.

Ni: 3.5 to 6.0% Ni is an element that is extremely effective in improving corrosion resistance and forming austenite, but if it is less than 3.5%, its effect is small, while the content increases. Then the transformation point (A
6.0 to lower tempering temperature by lowering _C1 point)
% Is the upper limit.

Mo: 1.5 to 2.5% Mo is an element particularly effective for stress corrosion cracking resistance and corrosion resistance, but if the content is less than 1.5%, the effect does not appear and 2.5 %, The excess δ-ferrite phase appears, so the upper limit is made 2.5%.

V: 0.01 to 0.05% V is a strong carbide-forming element, which finely precipitates fine carbides in the grains uniformly and does not preferentially precipitate at grain boundaries to make the crystal grains finer and to reduce stress resistance. It not only improves corrosion cracking properties, but also contributes to strength improvement. However, it is also a ferrite forming element and increases the δ-ferrite phase. If the content is less than 0.01%, the effect of improving stress corrosion cracking resistance does not appear, and if it exceeds 0.05%, the effect is saturated, and δ
-Since the ferrite phase increases, the content is 0.01 to 0.
05%.

N: 0.02% or less N is an element harmful to the improvement of corrosion resistance, but is also an austenite forming element. If it is contained in excess of 0.02%, it will precipitate as a nitride during tempering, and the corrosion resistance, stress corrosion cracking resistance and toughness will deteriorate, so the content is made 0.02% or less.

25-25 [% Ni] +5 [% Cr] +2
5 [% Mo] ≧ 0 This is A_C1Relationship between points and main additive elements (Ni, Cr, Mo)
It is an expression that gives a relation. A _C1When the point drops, enough baking
It becomes difficult to obtain the restored martensite structure,
Strength corrosion cracking property deteriorates. Therefore, 25-25 [% N
i] +5 [% Cr] +25 [% Mo] ≧ 0
Need to

In the present invention, in addition to the above basic components, one or more of the following selective components (Nb, Ti) may be contained. (Selective component) Nb: 0.01 to 0.1%, Ti: 0.0
1-0.1%

Nb and Ti are strong carbide-forming elements, and by precipitating fine carbides, the crystal grains are refined,
Improves stress corrosion cracking resistance. However, it is also a ferrite forming element and increases the δ-ferrite phase. If the content is less than 0.01%, the effect of improving the stress corrosion cracking resistance does not appear, and if it exceeds 0.1%, the effect is saturated, and
Since the δ-ferrite phase increases, the content of both Nb and Ti is set to 0.01 to 0.1%.

The unavoidable impurities include P and S. If P is 0.04% or less and S is 0.01% or less, the stress corrosion cracking resistance targeted by the present invention can be secured. In addition, no hindrance appears in the production of seamless steel pipes or electric resistance welded steel pipes made of hot rolled steel plate. However, all of these are elements that deteriorate the hot workability and stress corrosion cracking resistance of steel, and the smaller the content, the better.

By adjusting the above composition range.
The resistance of conventional high-strength martensitic stainless steel
Improves corrosion resistance and toughness to maintain corrosion resistance
In addition, stress corrosion cracking occurs even in an environment containing a large amount of hydrogen sulfide
862 N / mm that can be used without ²Grade low C high Cr alloy oil well
Capable of obtaining pipes (martensitic stainless steel)
Becomes Steel with such characteristics can be manufactured by the following manufacturing method.
It can be manufactured.

(2) Steel manufacturing process Steel adjusted to the above composition range is melted in a converter or an electric furnace and cast into a slab by an ordinary ingot casting method or a continuous casting method. After manufacturing it into a seamless steel pipe by hot working,
A _C After austenitizing at a temperature of ₃ points or more and 980 ° C or less 1
Cool to a temperature below 00 ° C, then 540 ° C below 610 ° C
Tempering is performed at a temperature of ℃ or more.

Heating temperature: A _C3 point or more and 980 ° C. or less If the heating temperature is less than A _C3 point, austenite does not occur and the effect of quenching cannot be obtained, so the lower limit was made A _C3 point. On the other hand, when the heating temperature exceeds 980 ° C., the crystal grains become coarse, sufficient strength cannot be obtained, and the toughness deteriorates. Therefore, the upper limit is 980 ° C. (The cooling after austenitization is performed in order to obtain a full martensite phase, 10
Cool to a temperature below 0 ° C. )

B. Tempering temperature: 610 ° C. or lower and 540 ° C. or higher, as described above, the tempering treatment uniformly disperses and precipitates fine carbides of V, and does not deteriorate the toughness and stress corrosion cracking resistance. It is essential for strengthening.
The tempering temperature is 610 ° C or lower and 540 ° C or higher, but if the temperature exceeds 610 ° C, 852 N / mm ² or higher of 0.2
% Yield strength cannot be obtained, so the upper limit is 610 ° C. If it is lower than 540 ° C, the target 0.2% proof stress or SSC resistance cannot be obtained, so the lower limit is made 540 ° C.

[0040]

EXAMPLES Specific examples of the present invention will be described below. The inventors made inventive steels 1 to 3 and comparative steels a to c having the chemical compositions shown in Table 1 as test steels and hot rolled them into steel plates having a thickness of 12 mm.

After the subsequent heat treatment, the product is
As a result, the mechanical properties (strength, toughness), corrosion resistance and stress corrosion cracking resistance were tested under the following conditions.

Strength: 0.2% yield strength Toughness: Absorbed energy value (Charpy impact value) of Charpy full size test piece at -20 ° C Corrosion resistance: 5% NaCl solution, 180 ° C, 30 atmosphere CO ₂ 2 weeks corrosion rate Stress corrosion cracking resistance (SSC): 0.2% on a test piece in a 5% NaCl solution saturated with hydrogen sulfide gas at 0.01 atm
Existence of rupture after 720 hours of loading 90% of proof stress

Table 2 shows the A _C1 , A _C3 transformation temperature, heating temperature, and tempering temperature of the steel. Table 3 shows the results of testing the mechanical properties, corrosion resistance and stress corrosion cracking resistance.

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

The heat treatment according to the method of the present invention "1
In “3-A”, the 0.2% proof stress and the Charpy impact value all exceeded the target values. The corrosion resistance and stress corrosion cracking resistance also cleared the target values.

On the other hand, the comparative examples "1 to 3" and "a to c"
-E "indicates that any of the components, the heating temperature, and the tempering temperature are out of the range of the present invention, so the test result is 0.2%.
The yield strength, corrosion resistance and stress corrosion cracking resistance have not reached the target.

[0049]

EFFECTS OF THE INVENTION According to the present invention, by specifying the alloy composition and manufacturing conditions, the toughness is excellent, and the corrosion resistance to carbon dioxide corrosion as well as the stress corrosion cracking resistance in an environment containing a large amount of hydrogen sulfide are good. 862N / mm ² class low C high C
It has become possible to obtain r-alloy oil country tubular goods.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Masamura, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (56) Reference JP-A-10-130787 (JP, A) JP 2000-144337 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/10 C21D 9/08

Claims (4)

(57) [Claims] 1. C: 0.005-0.05 by weight%
%, Cr: 12 to 16%, Si: 1.0% or less, Mn:
0.05-0.3%, Ni: 3.5-6.0%, Mo:
1.5-2.5%, V: 0.01-0.05%, N:
862N / mm ² class low C high Cr alloy oil country tubular good having high corrosion resistance, characterized in that it contains 0.02% or less and satisfies the following (1), and the balance is substantially Fe. 25-25 [% Ni] +5 [% Cr] +25 [% Mo] ≧ 0 ... (1) 2. The composition according to claim 1, further comprising Nb: 0.01-0.1% and Ti: 0.01-0.
862N / mm ² class low C high Cr alloy oil country tubular good having high corrosion resistance, characterized by containing at least one of 1%. 3. C: 0.005 to 0.05 by weight%
%, Cr: 12 to 16%, Si: 1.0% or less, Mn:
0.05-0.3%, Ni: 3.5-6.0%, Mo:
1.5-2.5%, V: 0.01-0.05%, N:
After hot working an alloy steel containing 0.02% or less and satisfying the following (1), it is austenitized at a temperature of A _C3 point or more and 980 ° C. or less, and then cooled to a temperature of 100 ° C. or less, and then 610 ° C. 862 N / mm with high corrosion resistance, characterized in that after tempering at a temperature of 540 ° C. or higher, carbides after tempering precipitate uniformly in the grains and do not preferentially precipitate at grain boundaries.
^A method for producing a ^second class low C, high Cr alloy oil country tubular good. 25-25 [% Ni] +5 [% Cr] +25 [% Mo] ≧ 0 ... (1) 4. The composition according to claim 3, further comprising Nb: 0.01-0.1% and Ti: 0.01-0.
4. 1% or more of 1% is included, It is characterized by the above-mentioned.
862N / mm ² class low C high Cr alloy oil country tubular good having a high corrosion resistance as described in 1.