JP2000178692A - 655Nmm-2 CLASS LOW-C HIGH-Cr ALLOY OIL WELL PIPE WITH HIGH STRESS CORROSION CRACKING RESISTANCE, AND ITS MANUFACTURE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 655Nmm-2 class low-C high-Cr alloy oil well pipe usable without causing stress corrosion cracking even under the environment containing hydrogen sulfide in large amounts while maintaining corrosion resistance by simultaneously improving the stress corrosion cracking resistance and toughness of the conventional high strength martensitic stainless steel, and its manufacturing method. SOLUTION: The 655Nmm-2 class low-C high-Cr alloy oil well pipe having high stress corrosion cracking resistance is composed of an alloy steel which has a composition consisting of, by weight, 0.005-0.05% C, 12-16% Cr, <=1.0% Si, 0.05-0.3% Mn, 3.5-6.0% Ni, 1.5-2.5% Mo, 0.01-0.05% V, <=0.02% N, and the balance Fe with inevitable impurities and satisfying the relation of 705-25[% Ni]+5[%Cr]+25[%Mo]>=680.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength martensitic stainless steel having excellent resistance to stress corrosion cracking and a method for producing the same.
655 with high stress corrosion cracking resistance in environments containing wet carbon dioxide gas and wet hydrogen sulfide in natural gas drilling and transportation
The present invention relates to a Nmm- ² class low C high Cr alloy oil country tubular good and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, petroleum and natural gas produced in recent years often include a large amount of wet carbon dioxide gas and wet hydrogen sulfide. In excavation and transportation, 13Cr stainless steel or the like is used in place of conventional carbon steel. Martensitic stainless steel has been used. However, conventional martensitic stainless steels have excellent corrosion resistance to wet carbon dioxide gas (hereinafter simply referred to as corrosion resistance), but have insufficient stress corrosion cracking resistance to wet hydrogen sulfide (hereinafter simply referred to as stress corrosion cracking resistance). There has been a demand for a martensitic stainless steel having improved stress corrosion cracking resistance while maintaining strength, toughness, and corrosion resistance.

As those satisfying the requirements of stress corrosion cracking resistance in addition to strength, toughness and corrosion resistance, Japanese Patent Publication Nos. 61-3391, 58-199850 and 61-2.
No. 07550 is disclosed.

On the other hand, a martensitic stainless steel having improved stress corrosion cracking resistance in an environment where the partial pressure of hydrogen sulfide exceeds 0.01 atm has been proposed.
JP-A-174859 and JP-A-62-54063 are disclosed.

[0005]

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

Further, Japanese Patent Application Laid-Open No. Sho 60-174859,
The steels described in JP-A-62-54063 cannot completely prevent stress corrosion cracking due to hydrogen sulfide.

Further, from the viewpoint of strength, in any of the above-mentioned martensitic stainless steels, when an attempt is made to increase the strength, the toughness and the stress corrosion cracking resistance are significantly deteriorated. There was also a problem that one had to sacrifice one sex. for that 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 simultaneously required.

An object of the present invention is to improve the stress corrosion cracking resistance and toughness of a conventional high-strength martensitic stainless steel at the same time in order to solve the above-mentioned problems in the prior art, thereby maintaining corrosion resistance. Another object of the present invention is to provide a 655 Nmm- 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 method for producing the same.

Here, the target performance was set as follows in view of the performance required for steel pipes for drilling and transporting oil and natural gas containing carbon dioxide and hydrogen sulfide.

Strength: 655 Nmm ^-2 or more at 0.2% proof stress 7
58Nmm ^-2 or less. Toughness: Absorbed energy value (referred to as Charpy impact value) of Charpy / full size test piece at -20 ° C is 100
J or more. Corrosion resistance: 5% NaCl solution, 180 ° C, 30 atm CO ₂
Corrosion rate is 0.5 mm / y or less under the above environment.

Stress corrosion cracking resistance: 4 * 1 on a test piece in a 5% NaCl solution saturated with hydrogen sulfide gas at 0.1 atm.
A strain is applied at a rate of 0 ^-6 sec ^-1 , and the rupture time thereof is 90% or more of the rupture time performed in the atmosphere.

[0012]

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

(1) The alloy oil country tubular goods of the present invention. In weight percent,
C: 0.005 to 0.05%, Cr: 12 to 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.
High stress corrosion cracking resistance, characterized by comprising an alloy steel containing 0.01 to 0.05%, N: 0.02% or less, and satisfying the following formula (3), the balance being Fe and unavoidable impurities. 655 Nmm ^-2 class low C high Cr alloy oil country tubular goods having 705-25 [% Ni] +5 [% Cr] +25 [% Mo] ≧ 680 (3)

(2) The alloy oil country tubular goods according to the present invention further comprise, as an alloy steel component, Nb: 0.01 to 0.1% by weight,
The 655 Nmm- ² class low C high Cr alloy oil country tubular good having high stress corrosion cracking resistance according to claim 1, characterized in that it contains one or more of Ti: 0.01 to 0.1%. .

(3) In the production method of the present invention, after hot working an alloy steel having the composition described in the above (1) or (2), the austenitizing temperature is not less than the Ac ₃ point and not more than 980 ° C. After austenitizing so that the C content [% C] and the austenitizing temperature satisfy the following formula (4), cooling is performed, then the _first tempering is performed at a temperature of 1 point or more and ₃ points or less of Ac, and after cooling, The second tempering is performed at a temperature of 550 ° C. or higher and _one point of Ac or lower, and the carbide after tempering is uniformly precipitated in the grains and does not preferentially precipitate at the grain boundaries. 655Nmm ^-2 class low C high Cr
This is a method for manufacturing an alloy oil country tubular good.

Log [% C] ≧ −12900 * [[austenitizing temperature (° C.)] + 273] ⁻¹ +9.72 (4)

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have obtained the following findings.

It is effective to increase Cr to improve the corrosion resistance of martensitic stainless steel. However, an increase in Cr, on the other hand, forms a δ-ferrite phase and degrades strength and toughness. Therefore, the austenite forming element N
Although there is a method of suppressing the formation of the δ-ferrite phase by increasing i, there is a limitation in terms of the tempering temperature in increasing Ni. An increase in C is also effective in suppressing the formation of the δ-ferrite phase, but its content should be rather limited because carbides precipitate during tempering and deteriorate corrosion resistance and stress corrosion cracking resistance.

Further, if austenite is formed at a relatively low temperature of not less than the Ac ₃ point and all C is not dissolved, the same effect as when reducing the C content by suppressing carbide precipitation during tempering can be recognized. .

On the other hand, generally, when the strength of steel is increased, toughness and stress corrosion cracking resistance are deteriorated. However, V is contained in an appropriate amount, and carbide is dispersed as fine precipitates in the stainless steel matrix 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 particularly necessary to control the tempering conditions.

Based on the above findings, the present inventors considered that the low C high Cr alloy oil country tubular goods should contain a certain amount of V and 655 Nmm ^{− The} heat treatment conditions are adjusted within a certain range in order to stably obtain the ^second- class strength, and carbides are uniformly dispersed and precipitated in the grains, resulting in high toughness that could not be achieved with conventional martensitic stainless steel A new martensitic stainless steel (low C high Cr alloy oil country tubular good) having high strength and excellent stress corrosion cracking resistance and a method for producing the same have been found, and the present invention has been completed.

That is, the present invention limits the alloy composition and production conditions to the following ranges, and simultaneously improves the strength, stress corrosion cracking resistance and toughness of conventional martensitic stainless steel while maintaining corrosion resistance. Can be used without causing stress corrosion cracking even in an environment containing a large amount of hydrogen sulfide.
5Nmm- ² class low C high Cr alloy oil country tubular goods can be provided.

The reasons for adding the components, the reasons for limiting the components, and the reasons for limiting the production conditions in the present invention are described below.

(1) Component composition range: C: 0.005 to 0.05% C is a strong austenite-forming element and is also an essential element for obtaining high strength. However, during tempering, it combines with Cr to form carbides and precipitates,
Deterioration of stress corrosion cracking resistance and toughness. If the C content is less than 0.005%, sufficient strength cannot be obtained,
If it exceeds 5%, remarkable deterioration is recognized, so 0.005%
To 0.05%.

Cr: 12 to 16% Cr is a basic element constituting martensitic stainless steel and is an important element exhibiting corrosion resistance. However, if the content is less than 12%, sufficient corrosion resistance can be obtained. Without
If it exceeds 16%, δ-
Since the amount of ferrite phase formed increases and the strength and toughness deteriorate, the content is set to 12 to 16%.

Si: 1.0% or less Si is an element necessary as a deoxidizing material, but is also a strong ferrite-forming element. When contained in excess of 1.0%, it promotes the formation of a δ-ferrite phase. Therefore, it is set to 1.0% or less.

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

Ni: 3.5-6.0% Ni is an element that is extremely effective in improving corrosion resistance and forming austenite, but when it is less than 3.5%, its effect is small, while the content increases. Then the transformation point (Ac
₁ point) to lower the tempering temperature to 6.0.
% As the upper limit.

Mo: 1.5 to 2.5% Mo is an element particularly effective for stress corrosion cracking resistance and corrosion resistance, but its effect does not appear at a content of less than 1.5%. %, The upper limit is set to 2.5% because an excessive δ-ferrite phase appears.

V: 0.01-0.05% V is a strong carbide-forming element, and makes fine carbides precipitate uniformly in the grains and does not preferentially precipitate at the grain boundaries, thereby making the crystal grains finer, thereby reducing the stress resistance. It improves corrosion cracking properties and 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 0.1.
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 the content exceeds 0.02%, it becomes a nitride during tempering and precipitates, and the corrosion resistance, stress corrosion cracking resistance and toughness deteriorate, so the content is set to 0.02% or less. 705-25 [% Ni] +5 [% Cr] +25 [% M
o] ≧ 680

This is because the Ac ₁ point and the main additive elements (Ni, C
r, Mo). When the Ac ₁ point decreases, it becomes difficult to obtain a sufficient tempered martensite structure, and the stress corrosion cracking resistance deteriorates. Therefore, 7
05-25 [% Ni] +5 [% Cr] +25 [% Mo]
The composition must satisfy ≧ 680.

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

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

The inevitable impurities include P and S. When P is 0.04% or less and S is 0.01% or less, the stress corrosion cracking resistance aimed at by the present invention can be secured. Also, there is no problem in the production of an electric resistance welded steel pipe made of a seamless steel pipe or a hot rolled steel sheet. However, these are all elements that deteriorate the hot workability and stress corrosion cracking resistance of steel, and the smaller the number, the more preferable.

By adjusting the composition to the above range, the stress corrosion cracking resistance and toughness of the high-strength martensitic stainless steel are improved at the same time, and while maintaining the corrosion resistance, the stress corrosion corrosion resistance is maintained even in an environment containing a large amount of hydrogen sulfide. It is possible to obtain a 655 Nmm ^{- 2} class low C high Cr alloy oil country tubular good (martensitic stainless steel) that can be used without cracking.

The steel having such characteristics can be manufactured by the following manufacturing method. (2) Steel production process The steel adjusted to the above-mentioned component composition range is melted in a converter or an electric furnace, and is made 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,
Cooling after austenitizing at Ac ₃ point or higher 980 ° C. or less of the temperature, and then after cooling performed first tempering at temperatures below ₃ points Ac ₁ point or more Ac, 2 time at further 550 ° C. or higher Ac ₁ point below the temperature Tempering.

[0039] (a) austenitizing temperature: The Ac ₃ point or more 980 ° C. or less austenitizing temperature Ac less than ₃ points, since no effect of quenching not austenitized is obtained, the lower limit is Ac ₃
Points. On the other hand, when the heating temperature exceeds 980 ° C., the crystal grains become coarse, not only cannot obtain sufficient strength, but also
Since the toughness deteriorates, the upper limit is set to 980 ° C. The cooling after austenitization is preferably performed at a temperature of 100 ° C. or lower in order to obtain a full martensite phase.

(B) log [% C] ≧ −12900 * [[austenitizing temperature (° C.)] + 273] ⁻¹ +9.72 This is a formula showing the solubility of C when austenitized in the alloy steel of the present invention. It is. If the austenitizing temperature is low, not all C will form a solid solution and carbides will precipitate. For this reason, while reducing the amount of carbide precipitated during tempering,
Since the number of precipitation sites is reduced, it is difficult to refine the carbide. As described above, C combines with Cr at the time of tempering and precipitates as carbides, deteriorating corrosion resistance, stress corrosion cracking resistance, and toughness. Therefore, when the austenitizing temperature is adjusted and carbide is precipitated during austenitizing, the same effect as when C is reduced can be obtained, and a steel excellent in corrosion resistance, stress corrosion cracking resistance and toughness can be obtained. . Therefore, it is necessary to satisfy log [% C] ≧ −12900 * [[austenitizing temperature (° C.)] + 273] ⁻¹ +9.72.

(C) Tempering temperature: the first time was Ac₁Above the point Ac_Three
Point or less, the second time is 550 ° C or more Ac₁As described above, the tempering treatment is performed to uniformly fine V carbides.
First, they are dispersed and precipitated, resulting in poor toughness and stress corrosion cracking resistance.
It is indispensable to increase the strength without increasing the strength.
Set the first tempering temperature to Ac₁Above the point Ac_ThreeAfter cooling to below the point,
Set the second tempering temperature to 550 ℃ or more₁Below the point
And 655Nmm^-2Class strength can be obtained stably
You. The first tempering temperature is Ac₁Above the point Ac_ThreeBelow the point
But the temperature is Ac _ThreeBeyond the point, again austenite
And hardened, the upper limit is Ac_ThreePoint.
Also, Ac₁Below the point, the effect of the second tempering
The lower limit is Ac₁Point. Also,
The second tempering temperature is 550 ℃ or more Ac₁Below the point
But the temperature is Ac₁Beyond the point, partial austenia
The formation of hardened parts due to the formation of toughness and stress
To degrade corrosion cracking, the upper limit is Ac₁Point. Ma
If the temperature is lower than 550 ° C., the strength of the steel itself increases and the toughness increases.
And the lower limit is 550 to deteriorate the stress corrosion cracking resistance.
° C.

The effects of the present invention will be proved by the following examples.

[0043]

EXAMPLES Specific examples of the present invention will be described below. The present inventors have proposed invention steels 1-A to 1 having the chemical compositions shown in Table 1.
3-Metal and comparative steels a to c were melted as test steels, hot-rolled into steel plates having a thickness of 12 mm, heated, austenitized, cooled to 100 ° C. or lower, and then tempered twice. , Under the following conditions, mechanical properties (strength, toughness),
A test of corrosion resistance and stress corrosion cracking resistance was performed.

Strength: 0.2% yield strength Toughness: Absorbed energy value (Charpy impact value) of Charpy full-size specimen at -20 ° C. Corrosion resistance: 5% NaCl solution, 180 ° C., 30 atmospheres CO ₂
Corrosion rate for 2 weeks under the following environment: Stress corrosion cracking resistance: Strain was applied to a test specimen at a rate of 4 * 10 ^-6 sec ^-1 in a 5% NaCl solution saturated with hydrogen sulfide gas at 0.1 atm. Then, the rupture time (the rupture time in the environment) was determined, and the stress corrosion cracking resistance was evaluated based on the ratio to the rupture time (the rupture time in the atmosphere) performed in the atmosphere and the rupture time in the environment / the rupture time in the atmosphere.

Table 2 shows the transformation temperatures of Ac ₁ and Ac ₃ , the heating temperature (quenching temperature), and the tempering temperature of the steel. Table 3 shows the results of tests on mechanical properties, corrosion resistance and stress corrosion cracking resistance.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

In the method of the present invention, "1 to 3-A" is 0.2
The% yield strength 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 comparison methods "1 to 3" and "a to
As for “c”, any of the components, the heating temperature, and the tempering temperature are out of the range of the present invention, and the test results also fail to achieve the targets of the corrosion resistance and the stress corrosion cracking resistance.

[0051]

According to the present invention, by specifying the alloy composition and the manufacturing conditions, 655 Nmm ^-2 class having good corrosion resistance to carbon dioxide gas corrosion as well as stress corrosion cracking resistance in an environment containing a large amount of hydrogen sulfide. It has become possible to provide a low C high Cr alloy oil country tubular good.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yusuke Minami, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Katsumi Masamura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo No. Nippon Kokan Co., Ltd. F-term (reference) 4K042 AA06 CA07 CA08 CA09 CA10 CA11 CA13 DA02 DC02

Claims (3)

[Claims] 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:
655 Nmm ^-2 low C high with high stress corrosion cracking resistance characterized by containing 0.02% or less and satisfying the following formula (1), and made of alloy steel comprising the balance of Fe and unavoidable impurities. Cr alloy oil well tube. 705-25 [% Ni] +5 [% Cr] +25 [% Mo] ≧ 680 (1) 2. The alloy steel component further comprises N in weight%.
b: 0.01~0.1%, Ti: characterized in that it comprises one or more of 0.01~0.1%, 655Nmm having high stress corrosion cracking resistance according to claim 1 ^- Class ² low C high C
r alloy oil well tube. 3. After hot working an alloy steel having the composition according to claim 1 or 2, the austenitizing temperature is Ac _3.
Austenitizing so that the C content in steel [% C] and the austenitizing temperature satisfy the following formula (2), and then cooling, and then the first time at a temperature between ₁ point of Ac and ₃ points of Ac or less. After cooling and tempering, Ac
655 Nm with high stress corrosion cracking resistance characterized in that the second tempering is performed at a temperature of ₁ point or less, and the carbide after tempering is uniformly precipitated in the grains and does not preferentially precipitate at the grain boundaries.
Manufacturing method of m- ² class low C high Cr alloy oil country tubular goods. log [% C] ≧ -12900 * [[Austenitizing temperature (℃)] + 273] ^-1 +9.72… (2)