JP3529701B2 - Martensitic stainless steel for large diameter seamless steel pipes - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to martensitic stainless steel for large diameter seamless steel pipes having excellent weldability suitable for line pipes and the like used in an environment containing wet carbon dioxide and wet hydrogen sulfide.

[0002]

2. Description of the Related Art Steel materials used in pipelines for transporting petroleum and natural gas are required to have excellent corrosion resistance and local weldability according to the operating environment, and carbon steel copper pipes of X50 and X65 grades are required. Often used.

In recent years, the environment containing wet carbon dioxide gas and wet hydrogen sulfide has increased, and the use of stainless steel has come to be considered from the viewpoint of corrosion resistance. However, the existing stainless steel does not always have sufficient properties as a line pipe, and new development has been desired. That is, 0.2% C to 13% Cr steel having good corrosion resistance to an environment containing wet carbon dioxide and wet hydrogen sulfide is an oil country tubular good that does not require welding, and has high preheating to prevent weld cracking. However, it was not suitable for pipelines that require post heat treatment temperature and where local weldability is important. Also, 22% or 25
% Cr and other duplex stainless steels are expensive although they do not require preheating and post heat treatment, and are difficult to use in pipelines that require a large amount of steel materials. Therefore, JP-A-6-1009
43, JP-A-4-268018, and JP-A-8
Japanese Patent Laid-Open No. -100235 and Japanese Patent Laid-Open No. 8-100236 propose 13% Cr steel with a reduced C content. These steels are usually supplied as seamless or UOE steel pipes. In the case of seamless steel pipes, it is possible to manufacture up to a maximum diameter of 40.64 cm (16 inch) outer diameter in the case of seamless steel pipes. Performance is inferior to seamless steel pipe, but minimum outer diameter is 50.8 cm
(20 inches). Steel pipes with a larger diameter have better transport efficiency and can transport crude oil at a lower cost, but at the same time sufficient corrosion resistance and on-site weldability are sufficient in environments containing both wet carbon dioxide and wet hydrogen sulfide. In addition, there was no steel with a large diameter that could meet the demand for steel with good transportation efficiency and pressure resistance.

[0004]

The present invention can be used in an environment containing both wet carbon dioxide and infiltrated hydrogen sulfide,
Provided is a martensitic stainless steel for a large-diameter seamless steel pipe, which has excellent weldability and hot workability, and has a large-diameter steel pipe that has good transport efficiency and pressure resistance.

[0005]

In order to solve the above problems, the present inventors have proposed a method for improving hot workability at around 1000 ° C. which is a main rolling temperature of an expanded mill capable of producing a large diameter seamless steel pipe. Were examined variously. As a result, if P and S are reduced below a predetermined value, 100
It was found that good hot workability can be obtained at around 0 ° C.
The following martensitic stainless steels for large diameter seamless steel pipes were completed.

1. % By mass, C: 0.02% or less, S
i: 0.1 to 0.3%, Mn: 0.1 to 0.3%, P:
0.02% or less, S: 0.002% or less, Cr: 10
13%, Ni: 5-8%, Mo: 1.5-3%, N:
A martensitic stainless steel for a large-diameter seamless steel pipe, which is 0.02% or less, satisfies C + N: 0.02 to 0.04%, and the balance is Fe and inevitable impurities.

2. % By mass, C: 0.02% or less, S
i: 0.1 to 0.3%, Mn: 0.1 to 0.3%, P:
0.02% or less, S: 0.002% or less, Cr: 10
13%, Ni: 5-8%, Mo: 1.5-3%, N:
0.02% or less, W: 0.1 to 3%, Cu: 0.
Contains 1 to 2% of 1-3%, C + N: 0.02
A martensitic stainless steel for large diameter seamless steel pipes which satisfies 0.04% and the balance is Fe and inevitable impurities.

3. % By mass, C: 0.02% or less, S
i: 0.1 to 0.3%, Mn: 0.1 to 0.3%, P:
0.02% or less, S: 0.002% or less, Cr: 10
13%, Ni: 5-8%, Mo: 1.5-3%, N:
0.02% or less, Ti: 0.01 to 0.1%, N
b: 0.01 to 0.1% of 1 type or 2 types, and C
+ N: Martensite stainless steel for large-diameter seamless steel pipes, which satisfies 0.02 to 0.04% and the balance is Fe and inevitable impurities.

4. % By mass, C: 0.02% or less, S
i: 0.1 to 0.3%, Mn: 0.1 to 0.3%, P:
0.02% or less, S: 0.002% or less, Cr: 10
13%, Ni: 5-8%, Mo: 1.5-3%, N:
0.02% or less, W: 0.1 to 3%, Cu: 0.
1 to 2% of 1-3%, Ti: 0.01 to 0.1
%, Nb: 0.01 to 0.1% of one or two, and C + N: 0.02 to 0.04% is satisfied, and the balance is F.
Martensitic stainless steel for large diameter seamless steel pipe consisting of e and inevitable impurities.

In addition, these methods have an outer diameter of 4
It is effective for large diameter seamless steel pipe of 0.64 to 66.04 cm (16 to 26 inches).

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for adding each additive component and the reason for limiting the addition range of the present invention will be described below.

C: 0.02% or less It is an element that forms carbides with Cr in steel and enhances the strength, but if added in excess, it reduces the amount of Cr effective for corrosion resistance. Moreover, since the hardness of the heat affected zone of welding is increased and a heat treatment after welding is required, the upper limit is made 0.02%.

Si: 0.1 to 0.3% Although it is added as a deoxidizer, if it is 0.1% or less, it has no effect. On the other hand, if it is added excessively, delta ferrite is crystallized, so that the phase balance is increased. In order to maintain the above, it is necessary to increase the amount of Ni, so the upper limit is made 0.3%.

Mn: 0.1 to 0.3% It is added as a deoxidizing agent on steelmaking, but if it is 0.1% or less, its effect is not obtained and hot workability is deteriorated. On the other hand, if added excessively, the corrosion resistance in a carbon dioxide gas and hydrogen sulfide environment decreases, so the upper limit is made 0.3%.

P: 0.02% or less If P is 0.04% or less, it does not affect the corrosion resistance of the steel of the present invention, but 0.02% in order to obtain good hot workability. % Or less.

S: 0.002% or less If S is 0.01% or less, it does not affect the corrosion resistance of the steel of the present invention, but 0.002% to obtain good hot workability. % Or less.

Cr: 10 to 13% This is an element effective for improving the corrosion resistance in an environment containing wet carbon dioxide, but if it is less than 10%, the effect cannot be obtained. Corrosion resistance improves as the content increases, but since the amount of Ni, which is a strong ferrite-forming element and is a costly austenite-forming element, is required to form a martensite structure, the upper limit is 13%.

Ni: 5-8% This is an element necessary for obtaining a martensite structure.
If it is less than 5%, the ferrite phase increases, and the toughness and corrosion resistance are impaired. On the other hand, if it exceeds 8%, it is an expensive element and the economical efficiency is lowered, so the content range is made 5 to 8%.

Mo: 1.5 to 3% This is an element effective for corrosion resistance, but if it is less than 1.5%, its effect is not sufficient. Since it is a ferrite-forming element, if it is added in excess of 3%, the phase balance is maintained and expensive Ni needs to be increased. Therefore, the upper limit is made 3%.

N: 0.02% or less An element that forms a nitride with Cr in steel and enhances the strength, but if added in excess, it reduces the amount of Cr effective for corrosion resistance. Moreover, since the hardness of the heat affected zone of welding is increased and a heat treatment after welding is required, the upper limit is made 0.02%.

W: 0.1 to 3%, Cu: 0.1 to 3% Both are effective elements for strength and corrosion resistance. If added, if less than 0.1%, the effect is not sufficient and 3%. %, The hot workability deteriorates, so the content is made 0.1 to 3%.

Ti: 0.01 to 0.1%, Nb: 0.0
1 to 0.1% All are elements that form carbides with C in steel and improve the strength and toughness by the effect of refining the crystal grains.
When added, if less than 0.01%, the effect is not sufficient,
If the content exceeds 0.1%, the effect is saturated, so 0.01 to 0.
1%

C + N: 0.02 to 0.04% The individual elements of C and N are added within the above-mentioned limited range, but the present invention further defines C + N. In order to obtain a predetermined strength, the content is made 0.02% or more, and in order to suppress the hardness of the weld heat affected zone, it is made 0.04% or less.

The steel of the present invention may be melted by any method such as a converter, an electric furnace, or a combined hot water thereof, as long as it has a predetermined composition range. After melting, a continuous casting machine or a mold is used to form a billet, or a steel ingot is hot-rolled into a billet, and then hot-rolled to form a steel pipe, and a target strength is obtained by heat treatment.
The heat treatment may be performed by cooling or normalizing after processing to obtain a transformed martensite structure, and then tempering to adjust the strength.

[0025]

EXAMPLES Steels having the chemical composition shown in Table 1 were melted in a combined hot water of a converter and an electric furnace, made into a billet with a continuous casting machine, and then hot with a plug mill at 40.64 cm (16 inch).
Machined into steel pipe with an outer diameter. Then, it is hot worked into a steel tube having an outer diameter of 50.8 cm (20 inch) by an expanding mill, and a target strength is obtained by heat treatment. The heat treatment was carried out by cooling after processing to obtain a transformed martensite structure and then tempering to adjust the strength. The surface properties after rolling were observed, and the case where no maintenance was required was passed. Furthermore, the corrosion resistance and weldability of these steel pipes were investigated. The stress corrosion cracking test (SSC test) as a test for evaluating the corrosion resistance to wet hydrogen sulfide was based on the test method of NACE TM0177. A test piece loaded with 90% of the proof stress was saturated with 0.01 atm of hydrogen sulfide at room temperature.
It was soaked in a 25% NaCl aqueous solution with H = 4.5 for 720 hours, and the case where it did not break was regarded as a pass. The weldability test uses a duplex stainless steel welding rod to measure the hardness of the heat-affected zone when welding with Manual TIG.
A value of 350 Hv or less was passed.

Table 2 shows the test results. The steels A and B of the present invention show good surface properties after rolling and need no maintenance. Also, in the corrosion resistance and weldability tests, the steel of the present invention showed good results and passed.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

As described above, according to the present invention,
Martensitic stainless steel showing excellent corrosion resistance in an environment containing both wet carbon dioxide and wet hydrogen sulfide, excellent weldability and hot workability, and a large diameter steel pipe with good transport efficiency and pressure resistance. It can be used for oil and natural gas line pipes and has a remarkable industrial effect.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yama ▲ saki ▼ Ichio Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Toshio Suzuki 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Yusuke Minami 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Tatsuo Ono 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. In-company (72) Inventor Kumino Giuseppe Piazza Caduit 6 Lulio 1944 Numero 1 (56) References 2000-178697 (JP, A) JP 11-140594 (Diamondine (Bergamo), Italy) JP, a) JP flat 9-316611 (JP, a) JP flat 3-120337 (JP, a) (58 ) investigated the field (Int.Cl. ^7, D Name) C22C 38/00 - 38/60

Claims (5)

(57) [Claims] 1. C: 0.02% or less by mass%, Si:
0.1-0.3%, Mn: 0.1-0.3%, P: 0.
02% or less, S: 0.002% or less, Cr: 10-13
%, Ni: 5-8%, Mo: 1.5-3%, N: 0.0
C + N: 0.02 to 0.04% is satisfied at 2% or less,
Martensitic stainless steel for large diameter seamless steel pipes, the balance of which is essentially Fe and unavoidable impurities. 2. In mass%, C: 0.02% or less, Si:
0.1-0.3%, Mn: 0.1-0.3%, P: 0.
02% or less, S: 0.002% or less, Cr: 10-13
%, Ni: 5-8%, Mo: 1.5-3%, N: 0.0
2% or less, further W: 0.1-3%, Cu: 0.1-3
% Of 1 or 2 and C + N: 0.02 to 0.
Martensite stainless steel for large diameter seamless steel pipes, which satisfies 04% and the balance is substantially Fe and unavoidable impurities. 3. C: 0.02% or less by mass%, Si:
0.1-0.3%, Mn: 0.1-0.3%, P: 0.
02% or less, S: 0.002% or less, Cr: 10-13
%, Ni: 5-8%, Mo: 1.5-3%, N: 0.0
2% or less, further Ti: 0.01 to 0.1%, Nb:
0.01 to 0.1% of 1 type or 2 types, and C +
N: 0.02 to 0.04% is satisfied, and the balance is substantially F.
Martensitic stainless steel for large diameter seamless steel pipe consisting of e and inevitable impurities. 4. C: 0.02% or less, Si:
0.1-0.3%, Mn: 0.1-0.3%, P: 0.
02% or less, S: 0.002% or less, Cr: 10-13
%, Ni: 5-8%, Mo: 1.5-3%, N: 0.0
2% or less, further W: 0.1-3%, Cu: 0.1-3
%, One or two, Ti: 0.01 to 0.1%, N
b: 0.01 to 0.1% of 1 type or 2 types, and C
+ N: Martensite stainless steel for large diameter seamless steel pipes, which satisfies 0.02 to 0.04% and the balance is substantially Fe and unavoidable impurities. 5. An outer diameter of 40.64 to 66.04 cm (1
The martensitic stainless steel according to any one of claims 1 to 4, which is 6 to 26 inches).