JPH0967624A - Production of high strength oil well steel pipe excellent in sscc resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To industrially produce an oil well steel pipe having high strength and excellent sulfide stress corrosion cracking resistance (SSCC resistance) at a low cost by specifying a chemical composition and controlling the maximum grain size of nonmetallic inclusions in a product. SOLUTION: A steel pipe, having a composition consisting of, by weight, 0.15-0.30% C, 0.05-1.00% Si, 0.20-1.50% Mn, <=0.02% P, 0.3-1.5% Cr, 0.10-1.00% Mo, 0.01-0.07% Al, <=0.015% N, <=0.0015% S, 0.0002-0.0010% Ca, one or more kinds among 0.01-0.05% Nb, 0.01-0.05% Ti, 0.01-0.10% V, and 0.001-0.005% B, and the balance Fe, is prepared. This steel pipe is hardened from a temp. in the range not lower than the Ac3 transformation point and lower than the crystal coarsening initiating temp. and then tempered at a temp. not higher than the Ac1 transformation point. By this method, the maximum grain size of nonmetallic inclusions in a product can be controlled to <=20μm and nonmetallic inclusions can be finely dispersed, by which SSCC resistance can be remarkably improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a steel pipe having high strength and excellent resistance to sulfide stress corrosion cracking (hereinafter referred to as SSCC resistance), which is suitable for oil wells and gas wells.

[0002]

2. Description of the Related Art In recent years, oil wells and natural gas gas wells have been excavated in deep oil fields that have not been neglected in the past, due to the depletion of petroleum resources expected in the near future,
Development is being actively conducted on a global scale in areas such as the sour gas field where development was once abandoned.

[0003] Such oil wells and gas wells are generally extremely deep with a depth of several thousand meters, and have a shape in which long oil well pipes and gas well pipes (hereinafter collectively referred to as oil well pipes) are suspended. Since the pipe is heavily loaded, it is required to have high strength. Further, the atmosphere of the oil well and the gas well is often an extremely severe corrosive environment containing H ₂ S, CO ₂ , Cl ^−, etc. under a wet condition, and thus the corrosion resistance, particularly the SSC resistance
Oil well pipes with excellent C properties are required. Therefore, for oil well pipes for drilling oil wells and gas wells, and for oil collection, gas collection, etc., the requirements for high strength and corrosion resistance, particularly SSCC resistance, have become more severe than ever before.

From such a viewpoint, the conventional oil country tubular goods are usually manufactured by quenching and tempering an oil country tubular goods manufactured from Mn-Cr steel or Cr-Mo steel. That is, quenching and tempering of oil country tubular goods contribute to strengthening and toughness, and the tempered martensite structure is SSC resistant.
Shows excellent performance in C property. However, SSCC resistance and strength have a contradictory relationship, and higher strength requires higher SSCC resistance. For this reason, conventionally, S resistance
Yield strength of 655-758N /
The limit was mm ² .

As a method for producing an oil country tubular good having a yield strength of 690 N / mm ² or more, C: 0.15 to 0.45%, Si:
0.1-1.0%, Mn: 0.3-1.8%, sol.
Al: 0.01% or less, Ti: 0.005-0.1%
And Zr: 0.01 to 0.2%, one or more,
N: {0.002+ [Ti (%) + Zr (%)] / 8}
% Or less, AlN: 0.005% or less, and the remainder is a low alloy steel pipe consisting essentially of Fe, after quenching from 880 to 980 ° C., then tempering at 600 to 730 ° C. and 600 to 730 In the temperature range of ℃, plastic working is performed once or multiple times so that the total strain amount becomes 1 to 20%,
After that, quenching from 800 to 950 ℃ and 600 to 7
A method of performing tempering at 30 ° C. (JP-A-1-28332)
No. 2), C: 0.15 to 0.50%, Si: 0.1
0-1.0%, Mn: 0.3-1.8%, Cr: 0.0
4% or less, Mo: 0.82 to 3.0%, sol. Al:
0.005 to 0.07%, including N: 0.01% or less,
If necessary, Nb: 0.005 to 0.10%, Ti:
0.005-0.15%, B: 0.0010-0.00
50%, Zr: 0.01 to 0.2% of one type or two or more types, and the balance of Fe and unavoidable impurities is applied to a steel pipe at 840 to 950 ° C. for 0.1 to 2.0 hours. From heating to quenching, then 0.1 at 600-740 ℃
A method of tempering for up to 5.0 hours (Japanese Patent Laid-Open No. 3-2044)
No. 3 gazette) is proposed.

C: 0.15 to 0.40%, Si:
0.1-1.0%, Mn: 0.3-1.0%, Cr:
0.1-1.5%, Mo: 0.1-1.0%, Al:
0.01 to 0.10%, P: 0.015 or less, S: 0.
005% or less, N: 0.003 to 0.015%, and if necessary, Nb: 0.01 to 0.
10%, V: 0.01 to 0.10%, Ti: 0.005
~ 0.050%, B: 0.0001-0.0050%,
Ca: 0.0005 to 0.0100%, Cu: 0.1
Steel containing 0.5% or more of 0.5% and the balance being Fe and inevitable impurities is quenched from a temperature range of Ac3 transformation point or more and less than the grain coarsening start temperature, and then this is quenched. After heating again to a temperature range of Ac3 transformation point or higher and lower than the crystal grain coarsening start temperature, quenching is performed again from that temperature range and then tempering at a temperature of Ac1 transformation point or lower, or crystal grain coarsening of Ac3 transformation point or higher. After heating to a temperature range lower than the starting temperature, tempering at a temperature of (Ac1 transformation point −50 ° C.) or lower, and then heating it again to a temperature range of Ac3 transformation point or higher and lower than the crystal grain coarsening start temperature. A method of quenching again from the temperature range and then tempering at a temperature below the Ac1 transformation point (Japanese Patent Laid-Open No. 59-232220),
C: 0.30% or less, Si: 0.05 to 1.00%, M
n: 0.30 to 1.00%, P: 0.03% or less, S:
0.03% or less, Cr: 0.30 to 1.50%, Mo:
0.10-2.00%, Al: 0.01-0.05%,
N: 0.015% or less is included, Nb: 0.01 to 0.0
4%, V: 0.03 to 0.10%, Ti: 0.01 to
0.05%, B: 0.0010 to 0.0050%, C
a: In a method for producing a high-strength corrosion-resistant steel pipe, which contains one or more of 0.0010 to 0.0050% and the balance is Fe and unavoidable impurities, and the quenching and tempering is repeated twice for the steel pipe. A method in which complete bending is performed in the cold or warm after the first quenching and tempering, and a slight bending is performed in the warm after the second quenching and tempering, or no bending is performed. Two
No. 87381) has been proposed.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the method disclosed in Japanese Laid-Open Patent Publication No. 322 and Japanese Unexamined Patent Publication No. 3-20443, a large number of heat treatments are required because the plastic working is performed after the first quenching and tempering and the quenching and tempering is performed again.
Manufacturing cost increases and becomes expensive. Also, Japanese Unexamined Patent Publication No.
The methods disclosed in Japanese Patent No. 232220 and Japanese Patent Application Laid-Open No. 5-287381 disclose quenching and tempering twice as in the methods disclosed in Japanese Patent Application Laid-Open Nos. 1-283322 and 3-20443. A large number of heat treatments are required, and there is a drawback that the manufacturing cost increases and becomes expensive.

As described above, in order to satisfy both the high strength of 690 N / mm ² or more and the SSCC resistance, many methods have been proposed to obtain a fine grain tempered martensite structure by secondary working. For example, Japanese Patent Laid-Open No. 5-287
Even steel pipes manufactured by the method of Japanese Patent No. 381 have SS resistance.
NACE constant load test (room temperature,
0.5% CH ₃ was added to 5% NaCl aqueous solution saturated with H ₂ S.
When a constant load is applied to a round bar tensile test piece with a diameter of 6.4 mm in a solution containing COOH, and SSCC resistance is evaluated by a limit load stress that does not break in 720 hours), a high yield strength is obtained. The material sometimes has a phenomenon of breaking on the high load stress side in a short time from time to time, and has a problem in SSCC resistance performance.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to reduce the steel pipe suitable for oil wells having a high strength of 690 N / mm ² or more and excellent SSCC resistance commensurate with the high strength. SSCC resistant to be industrially manufactured at low cost
An object of the present invention is to provide a method for producing a high-strength steel pipe for oil wells having excellent properties.

[0010]

Means for Solving the Problems As a result of detailed investigation of the test piece after the sulfide stress corrosion cracking test in order to achieve the above object, the inventors found that the occurrence of sulfide stress corrosion cracking was Ca.
-Al-O based large non-metallic inclusions and extended MnS
It was clarified that the non-metallic inclusions in the system were the starting points.
Therefore, the present inventors conducted various investigations on the influence of alloy components on SSCC resistance, and controlled the maximum particle size of non-metallic inclusions in the product to 20 μm or less by limiting the range to a predetermined chemical component range. It is possible to disperse non-metallic inclusions minutely and significantly improve SSCC resistance, especially S,
It was clarified that this can be achieved by limiting the content of Ca to a minute amount, and the present invention was reached.

That is, according to the present invention, C: 0.15 to 0.
30%, Si: 0.05 to 1.00%, Mn: 0.20
~ 1.50%, P: 0.02% or less, Cr: 0.3 ~
1.5%, Mo: 0.10 to 1.00%, Al: 0.0
1 to 0.07%, N: 0.015% or less, S: 0.00
15% or less, including Ca: 0.0002 to 0.0010%, and Nb: 0.01 to 0.05%, Ti: 0.0
1 to 0.05%, V: 0.01 to 0.10%, B: 0.
001 to 0.005% of 1 or 2 or more, the balance is Fe and unavoidable impurities to the steel pipe, quenching from a temperature of Ac ₃ transformation point or more, less than the crystal coarsening start temperature, Then, it is a method for producing a high-strength steel pipe for oil wells having excellent SSCC resistance, which is characterized by performing tempering at a temperature not higher than the Ac ₁ transformation point.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the chemical components of the oil well steel pipe of the present invention will be described below. C is an essential element for securing the strength and toughness of steel, but if it is less than 0.15%, it is not sufficient, and if it exceeds 0.30%, quench cracking occurs during quenching, so 0.15% It was set to 0.30%.

Si is an element necessary for deoxidation and securing strength, but if less than 0.05%, deoxidation is not sufficient,
If it exceeds 1.00%, the toughness will deteriorate, so 0.0
It was set to 5 to 1.00%.

Mn is an element necessary for deoxidation and securing strength like Si, but if it is less than 0.20%, deoxidation is not sufficient, and if it exceeds 1.50%, toughness is deteriorated. It was set to 0.20 to 1.50%.

P is an impurity present in the steel and impairs the cleanliness of the steel and deteriorates the toughness and ductility.

Cr is an element necessary to secure hardenability and corrosion resistance, but if it is less than 0.3%, its effect is not sufficient, and if it exceeds 1.5%, hydrogen penetration into the steel is promoted. , Deteriorates SSCC resistance, so 0.3-1.5%
And

Mo is an element which, like Cr, improves hardenability and corrosion resistance, increases temper softening resistance, enables high temperature tempering even with high strength, and improves SSCC resistance. If it is less than 0.1%, the effect is not sufficient, and if it exceeds 1.00%, the effect is saturated, and coarse carbides are generated, conversely degrading toughness and SSCC resistance, so 0.10 to 1.00% And

Al is an element effective in deoxidizing and ensuring toughness, but if it is less than 0.01%, its effect is not sufficient,
If it exceeds 0.07%, alumina-based cluster-like inclusions are generated and the toughness deteriorates, so 0.01 to 0.07%
And

N is an element necessary for forming AlN that controls SSCC resistance, but if it exceeds 0.015%, corrosion resistance,
Since it deteriorates the toughness, it is set to 0.015% or less.

Similar to P, S is an impurity that is inevitably present in the steel and impairs the cleanliness of the steel and deteriorates the toughness and ductility. Therefore, the smaller the content, the better, and the Mn elongated in the product stage.
Since S is formed and the SSCC resistance is remarkably obtained,
It was set to 0.0015% or less.

Ca improves toughness by controlling the morphology of inclusions,
It is an element effective in improving SSCC resistance, but 0.0002
%, The effect is not sufficient, and if it exceeds 0.0010%, Ca-Al-O system cluster-like non-metallic inclusions may be scattered locally, and sulfide stress corrosion cracking occurs during the corrosion resistance test. Since it is the starting point of 0.0002 ~
It was set to 0.0010%.

Further, Ti, Nb, V and B are elements effective for improving SSCC resistance, and it is decided to add one or more of them.

In both Ti and Nb, crystal grains are refined,
It is an element that improves toughness and SSCC resistance,
If less than 0.01%, the effect is not sufficient, 0.05%
When the value exceeds 1.0, the effect is saturated, and NbC precipitates increase to deteriorate the SSCC resistance.
It was set to 01 to 0.05%.

V is an element that enhances the temper softening resistance, but if it is less than 0.01%, its effect is not sufficient and 0.1
If it exceeds 0%, the toughness deteriorates, so 0.01 to 0.1
0%.

B is an element effective for improving the hardenability and the SSCC resistance, but if it is less than 0.001%, its effect is not sufficient, and if it exceeds 0.005%, the toughness deteriorates, so 0.001 Was made 0.005%.

In the production of the steel pipe according to the present invention, after the steel having the above-mentioned chemical composition is melted and sufficiently degassed, the casting temperature is controlled while the floating separation of the large cluster inclusions is sufficiently performed. Casting is performed to produce a highly clean steel ingot having excellent SSCC resistance or a bloom by continuous casting. Next, after slab rolling to form a billet having a predetermined diameter, a steel pipe having a predetermined dimension is formed by hot working by the Mannesmann method.

Thereafter, the steel pipe is subjected to quenching and tempering treatment to obtain a tempered martensite structure in which carbides having excellent SSCC resistance are finely dispersed, to obtain a tempered martensite structure in which carbides are finely dispersed. The quenching temperature in this case is in the austenite temperature range above the Ac3 transformation point, but if it is less than 850 ° C., the effect of the hot working in the previous stage remains, and variations in strength occur after tempering. on the other hand,
Since the crystal grain size of which the quenching temperature exceeds 950 ° C. becomes coarse and the SSCC resistance is lowered, it is preferably 850 to 95.
It is in the range of 0 ° C. If the tempering temperature for obtaining a strength of 690 N / mm ² or more is less than 600 ° C, the strength becomes too high and the corrosion resistance deteriorates, and if it exceeds 750 ° C, the desired strength cannot be obtained. Is the range.

[0028]

EXAMPLES Steel No. with the chemical composition shown in Table 1 After melting steels 1 to 8 and performing sufficient degassing, casting is carried out while controlling the casting temperature to allow the floating separation of large cluster-like inclusions to be sufficiently carried out to form a steel ingot or a bloom by continuous casting. After that, slab rolling was carried out to obtain round billets, and hot rolling was carried out from each round billet by the Mannesmann method to produce a seamless steel pipe having an outer diameter of 250 mm and a wall thickness of 15.0 mm. Next, each seamless steel pipe was heated at 920 ° C. for 20 minutes, water-quenched, and then heat treated by changing the tempering temperature to obtain test materials having different strengths. In order to evaluate the cleanliness of each test material, the size of nonmetallic inclusions was measured after micropolishing.

Each test material was subjected to a tensile test to measure the yield point and the tensile strength, and a round bar tensile test piece having a diameter of 6.4 mm and a parallel portion of 25.4 mm was sampled from the center of the wall thickness. Then, the SSCC resistance test specified in NACE TM-0177 Method-A was carried out. In addition, SSCC resistance
The test was carried out by immersing the tensile test piece in a solution of 5% NaCl aqueous solution saturated with H ₂ S and 0.5% CH ₃ COOH at room temperature under a load of 80% of its yield stress for 720 hours. Then, the pass or fail was evaluated by the presence or absence of breakage. The results are shown in Table 2.

[0030]

[Table 1]

[0031]

[Table 2]

As shown in Table 2, steel No. The steel pipes of the present invention produced from Nos. 1 to 4 all passed the test without any breakage in the SSCC resistance test, in which the maximum length of non-metallic inclusions was significantly reduced to 20 μm or less. On the other hand, steel N
o. The comparative steel pipes manufactured from Nos. 5 to 8 are steel Nos. Containing a large amount of S or Ca impurities. On the contrary, Nos. 6, 7, and 8 are steels N in which non-metallic inclusions grow and the Ca content is low.
o. No. 5 could not suppress the growth of non-metallic inclusions, and the maximum length of all non-metallic inclusions exceeded 25 μm.
In the SCC property test, a maximum of 62.5% broke and failed.

[0033]

As described above, according to the method of the present invention, the chemical composition is limited to a specific range to reduce the particle size of the non-metallic inclusions, so that the single quenching and tempering provides excellent SSCC resistance. It is possible to obtain a high-strength steel pipe for oil wells and to supply it at a relatively low cost.

Claims (1)

[Claims] 1. C: 0.15-0.30%, Si: 0.
05-1.00%, Mn: 0.20-1.50%, P:
0.02% or less, Cr: 0.3 to 1.5%, Mo: 0.
10-1.00%, Al: 0.01-0.07%, N:
0.015% or less, S: 0.0015% or less, Ca:
0.0002 to 0.0010%, and Nb:
0.01-0.05%, Ti: 0.01-0.05%,
V: 0.01 to 0.10%, B: 0.001 to 0.00
1% or more of 5% is contained, and the balance is Fe
And a steel pipe composed of unavoidable impurities are quenched from a temperature not lower than the Ac ₃ transformation point and lower than the crystal coarsening start temperature,
Then, a method for producing a high-strength steel pipe for oil wells having excellent SSCC resistance, which is characterized by performing tempering at a temperature not higher than the Ac ₁ transformation point.