JP3491149B2 - High-strength martensitic stainless steel pipe for oil well with excellent strength-toughness balance and method for producing the same - 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 pipes for oil wells, and particularly has a yield strength of YS758MPa.
(110ksi) grade high strength martensitic stainless steel pipe for improving strength-toughness balance. The steel pipe in the present invention includes a seamless steel pipe and a welded steel pipe.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of soaring crude oil prices and depletion of petroleum and natural gas resources that are expected in the near future, deep oil fields and corrosive oil fields and gas fields that have not been previously considered Etc. are being actively developed. Such oil and gas fields are generally located at high depths in so-called frontier areas such as the sea and cold regions, and are often in severe corrosive environments containing carbon dioxide CO ₂ , chlorine ion Cl ^−, etc. There is.

Under such a highly corrosive wet carbon dioxide environment, 0.2% C-13% specified in API SPEC 5CT.
Martensitic stainless steel pipes of Cr have been widely used. This type of steel pipe is usually adjusted by adjusting the heat treatment conditions so that the yield strength is YS80ksi grade or YS95k.
It is used as a ksi grade. With the recent trend toward deeper oil and gas fields, there is a demand for oil well pipes to be used with higher strength, and 0.2% C-13% with high corrosion resistance.
A high-strength martensitic stainless steel pipe having a Cr-based composition and a yield strength YS: 758 MPa (110 ksi) grade has been required.

However, with the conventional method, this 0.2%
Heat treatment is applied to C-13% Cr steel pipe to increase the strength to YS: 758MPa.
When adjusted to (110 ksi) class, the test temperature: Charpy absorbed energy vE- ₁₀ at -10 ° C is only about 30 J and the toughness is low, and the strength-toughness balance is deteriorated, and in the extremely cold regions such as North Sea and Alaska. There was a problem that it became difficult to use.

[0005]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems of the prior art and is suitable for use as a steel pipe for oil wells in oil fields and gas fields in extremely cold regions with high depth and strong corrosiveness. It is an object of the present invention to propose a high-strength martensitic stainless steel pipe for oil wells, which has excellent strength / high toughness and excellent strength-toughness balance, and a method for producing the same. In the present invention, a steel pipe with high strength and high toughness and excellent strength-toughness balance is
YS: Strength of 758MPa (110ksi) or more, test temperature: -10 ℃
Steel pipe having a Charpy absorbed energy vE _-10 of 50 J or more and a (YS) × (vE _-10 ) of 40,000 MPaJ or more.

[0006]

The present inventors have found that the yield strength is
In order to improve the strength-toughness balance of a 0.2% C-13% Cr martensitic stainless steel pipe having YS: 758 MPa (110 ksi) or more, various factors including composition affecting toughness were earnestly studied. As a result, by properly containing Nb and adjusting the heating conditions of the quenching treatment in relation to the C, N, and Nb contents, finally a tempered martensite structure with a fine and toughness can be obtained, -Newly found that the toughness balance is improved.

The present invention is based on these findings.
It was completed after further examination. That is, in the present invention, in mass%, C: 0.17 to 0.22%, Si: 1.0% or less, Mn: 0.25 to 1.0%, P: 0.03% or less, S: 0.005%
Below, Cr: 12 to 14%, Ni: 0.14 to 0.5%, N: 0.06% or less, Nb: 0.02 to 0.07%, or further V: 0.20
% Or less, has a composition consisting of the balance Fe and unavoidable impurities, and has a yield strength: high strength of 758 MPa or more and −10
Charpy absorbed energy at ° C vE- ₁₀ : A high-strength martensitic stainless steel pipe for oil wells having a high toughness of 50 J or more and having an excellent strength-toughness balance.

In the present invention, C: 0.17-0.
22%, Si: 1.0% or less, Mn: 0.25 to 1.0%, P: 0.03%
Below, S: 0.005% or less, Cr: 12-14%, Ni: 0.01-0.
5%, N: 0.001 to 0.06%, Nb: 0.01 to 0.07%,
Alternatively, it further contains V: 0.20% or less, preferably,
A steel pipe having a composition consisting of the balance Fe and unavoidable impurities, and temperature: (Ac ₃ transformation point) to 1100 ° C., time: within the range of 60 to 1800 s and the following formula (1) T + 100log (t / 60) −500 (C + N) ) -4000 Nb ≤ 880 (1) where, T: heating temperature (° C), t: holding time (s), C, N, Nb: content of each element (mass%) T satisfying the heating temperature T Oil well with a good balance of strength and toughness, which is characterized by performing a quenching treatment of austenizing at (° C.) and a holding time t (s), then cooling, and then performing a tempering treatment at a temperature of Ac ₁ transformation point or lower. It is a method for producing a high-strength martensitic stainless steel pipe for use.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The high strength martensitic stainless steel pipe for an oil well according to the present invention has a yield strength YS: 758 MPa (110 ks).
i) and high strength, and Charpy absorbed energy vE _{-10 at} -10 ℃ has high toughness of 50 J or more.
S) x (vE- ₁₀ ) is 40,000 MPaJ or more, which is a high-strength steel pipe for oil wells with excellent strength-toughness balance and excellent corrosion resistance.

Next, the reason for limiting the chemical composition of the high-strength steel pipe for oil wells of the present invention will be explained. In the following, mass% is simply referred to as%. C: 0.17 to 0.22% C is an important element for ensuring the strength of the martensitic stainless steel pipe, and in the present invention, the content of 0.17% or more is required. On the other hand, if the content exceeds 0.22%,
Toughness decreases. Therefore, C is limited to 0.17 to 0.22%.

Si: 1.0% or less Si is an element that acts as a deoxidizer and increases the strength of the martensitic stainless steel pipe.
If the content exceeds 0%, the hot workability is deteriorated, and further the carbon dioxide corrosion resistance is deteriorated. Therefore, in the present invention, Si
Was limited to 1.0% or less. In addition, preferably 0.1 to 0.5
%.

Mn: 0.25 to 1.0% Mn is an element that increases the strength of the martensitic stainless steel pipe. In the present invention, the content of 0.25% or more is required to secure the desired strength, but 1.0% If the content exceeds 1, the toughness deteriorates. Therefore, Mn is limited to the range of 0.25 to 1.0%. The content is preferably 0.3 to 0.7%.

P: 0.03% or less P is an element that increases strength but reduces ductility and toughness, and further deteriorates corrosion resistance. It is desirable to reduce P as much as possible. However, the extreme reduction causes a rise in manufacturing cost. Therefore, in the present invention, the content is limited to 0.03% or less, which is a range that can be implemented industrially at a relatively low cost and does not extremely deteriorate the toughness and corrosion resistance. In addition, preferably 0.02
It is 5% or less.

S: 0.005% or less S is an element that remarkably deteriorates hot workability, and it is desirable to reduce S as much as possible in order to improve productivity in the steel pipe manufacturing process, but an extreme reduction causes an increase in manufacturing cost. Invite.
If it is reduced to 0.005% or less, it is possible to manufacture a steel pipe in a normal process. Therefore, in the present invention, S is limited to 0.005% or less. The content is preferably 0.003% or less.

Cr: 12 to 14% Cr is an element that forms a protective film and increases corrosion resistance such as carbon dioxide corrosion resistance and carbon dioxide stress corrosion cracking resistance. From the viewpoint of corrosion resistance, Cr is contained at 12% or more. But need 14%
If it is contained in excess of 1.0, the hot workability in the steel pipe manufacturing process will be deteriorated. Therefore, in the present invention, Cr is limited to the range of 12 to 14%.

Ni: 0.14 to 0.5% Ni strengthens the protective film and increases corrosion resistance, and
It is an element that increases strength and toughness .
Include at least 14 %. On the other hand, if the content exceeds 0.5%, strength may decrease. Therefore, in the present invention, 0.
It was limited to the range of 14 % to 0.5%. In addition, preferably 0.14
~ 0.3%.

N: 0.06% or less N is an element that significantly increases pitting corrosion resistance, and is 0.0010
%, It is desirable to contain it, but if it exceeds 0.06%, the effect is saturated and the risk of lowering the toughness increases. Therefore, N is limited to 0.06% or less. In addition, it is preferably 0.01 to 0.04%.

Nb: 0.02 to 0.07% Nb is an important element in the present invention, and contributes to improvement of toughness through refinement of austenite grains. Nb forms fine nitriding carbides during quenching and heating to form fine austenite grains, and finally improves the strength and toughness of steel pipe as a fine tempered martensite structure after heat treatment. Such effects are recognized when the content is 0.02 % or more, but the content exceeding 0.07% rather deteriorates the toughness. Therefore, in the present invention, Nb
Was limited to the range of 0.02 to 0.07%. In addition, preferably 0.
It is from 02 to 0.06%.

V: 0.20% or less V also has an effect of increasing strength without deteriorating toughness like Nb, and can be contained together with Nb if necessary. The effect of increasing the strength becomes noticeable at 0.03% or more, but if the content exceeds 0.20%, the toughness deteriorates. Therefore, it is preferable to limit V to 0.20% or less. Incidentally, it is more preferably 0.03 to 0.10%.

Remaining Fe and Inevitable Impurities The balance other than the above chemical components is Fe and inevitable impurities. As unavoidable impurities, Al: 0.05% or less,
O: 0.006% or less is acceptable. Al: 0.05% or less Al acts as a deoxidizing agent, but the content exceeding 0.05% deteriorates the toughness, so it is preferable to limit the content to 0.05% or less.

O: 0.006% or less O is bound to other elements to form various oxides, which significantly reduces hot workability, toughness, and corrosion resistance, so it is preferable to reduce O as much as possible, but up to 0.006% acceptable. Next, a method for manufacturing the martensitic stainless steel pipe for oil wells of the present invention will be described. First, the chemical composition limit
The reason for the decision will be explained. C: 0.17 to 0.22 % C ensures the strength of martensitic stainless steel pipe.
It is an important element in order, in the present invention, at least 0.17%
Requires inclusion. On the other hand, if the content exceeds 0.22 %,
Toughness decreases. Therefore, C is limited to 0.17 to 0.22%
It was Si : 1.0 % or less Si acts as a deoxidizer, and at the same time, martensite
Although it is an element that increases the strength of stainless steel pipes, 1.
If the content exceeds 0 %, the hot workability is deteriorated and
Carbon dioxide corrosion resistance decreases. Therefore, in the present invention, Si
Was limited to 1.0 % or less. In addition, preferably 0.1 to 0.5
%. Mn : 0.25 ~ 1.0 % Mn increases the strength of martensitic stainless steel pipe
It is an element that allows the strength of the present invention to ensure the desired strength.
Content of 0.25 % or more is required, but content of more than 1.0 % is required.
Existence deteriorates toughness. For this reason, Mn is of 0.25 to 1.0%
Limited to the range. Incidentally, it is preferably 0.3 to 0.7 %.
It P: 0.03 % or less P increases strength but decreases ductility and toughness.
In addition, it is an element that deteriorates corrosion resistance and is reduced as much as possible.
It is desirable to do. However, extreme reductions in manufacturing costs
Cause soaring. Therefore, in the present invention, it is industrially relatively inexpensive.
Cost-effective and does not significantly deteriorate toughness and corrosion resistance.
The range is limited to 0.03 % or less. In addition, preferably 0.02
It is 5 % or less. S: 0.005 % or less S is an element that significantly deteriorates hot workability.
Reduce as much as possible to improve productivity in the manufacturing process
However, an extreme reduction leads to an increase in manufacturing cost.
If it is reduced to 0.005 % or less, steel pipes can be manufactured in the normal process.
Therefore, in the present invention, S is 0.005 % or less.
Limited The content is preferably 0.003 % or less. Cr: 12 ~ 14% Cr is耐炭acid gas corrosion resistance and form a protective coating,耐炭acid gas
It is an element that increases corrosion resistance such as stress corrosion cracking resistance, and
From the viewpoint of food habits, it is necessary to contain 12 % or more, but 14 %
If it is contained in excess of 100%, the hot workability in the steel pipe manufacturing process will deteriorate.
To do. Therefore, in the present invention, Cr is limited to the range of 12 to 14 %.
did. Ni: 0.01 ~ 0.5% Ni, as well as to increase the corrosion resistance to strengthen a protective coating,
It is an element that increases strength and toughness .
01 % or more is contained. On the other hand, the content exceeding 0.5 % is strength.
May cause a decline. Therefore, in the present invention, 0.
It was limited to the range of 01 % to 0.5 %. In addition, preferably 0.1
It is ~ 0.3 %. N: 0.06 % or less N is an element that significantly increases pitting corrosion resistance, and 0.0010
% Or more, it is desirable to contain more than 0.06 %.
However, the effect is saturated and the risk of reducing toughness increases.
Big Therefore, N is limited to 0.06 % or less.
It was In addition, it is preferably 0.01 to 0.04 %. Nb : 0.01 to 0.07 % Nb is an important element in the present invention, and is austenite grain.
Contributes to the improvement of toughness through the refinement of Nb is quenching and heating
At times, it forms fine carbonitrides and forms fine austenite grains.
After heat treatment, finally fine tempered martensite structure
As to improve the strength and toughness of the steel pipe. Such an effect
Although it is recognized in the content of 0.01% or more, containing more than 0.07%
On the contrary, it deteriorates toughness. Therefore, in the present invention, Nb
Was limited to the range of 0.01 to 0.07 %. In addition, preferably 0.
It is from 02 to 0.06 %. V: 0.20 % or less V also increases the strength without degrading the toughness like Nb .
It has an effect and can be contained together with Nb if necessary . Increased strength
The effect of addition becomes noticeable at 0.03 % or more
However, if the content exceeds 0.20 %, the toughness deteriorates. others
Therefore, V is preferably limited to 0.20 % or less. In addition,
More preferably, it is 0.03 to 0.10 %. The balance Fe and unavoidable impurities The balance other than the above-mentioned chemical components is preferably Fe and impurities.
It is an unavoidable impurity. As inevitable impurities, Al : 0.
05 % or less and O: 0.006 % or less are acceptable. Al deoxidized
Acts as an agent, but containing more than 0.05 % deteriorates toughness.
Order to, preferably limited to 0.05% or less. O
Forms various oxides by combining with other elements, and hot working
Can significantly reduce the toughness, toughness and corrosion resistance
However, 0.006 % is not acceptable.
It

The steel having the above composition is melted by a generally known melting method such as a converter or an electric furnace, and is continuously cast or ingot-
It is preferable to make a steel pipe material by slabbing. These steel pipe materials are a normal seamless steel pipe manufacturing process, that is, heated, perforated by a Mannesmann perforator, hot-rolled by using a slant rolling mill such as a plug mill system and a mandrel system, and a seamless steel pipe having a predetermined dimension. Preferably. The seamless steel pipe has a martensite structure as it is rolled, but is then subjected to quenching treatment and tempering treatment in order to impart desired strength and toughness.

The heating conditions for the quenching treatment are temperature: (Ac ₃ transformation point) to 1100 ° C., time: 60 to 1800 s, and the following equation (1) T + 100log (t / 60) -500 (C + N) -4000Nb. ≤ 880 (1) Where, T: heating temperature (° C), t: holding time (s), C, N, Nb: content of each element (mass%), heating temperature T (° C) And it is preferable to austenitize for the holding time t (s).

When the heating temperature is lower than (Ac ₃ transformation point), the heating temperature is too low to obtain a perfect austenite structure. On the other hand, if it exceeds 1100 ° C, the austenite grains become coarse and the toughness deteriorates. If the holding time is less than 60 s,
The heating temperature of the steel pipe cannot be made uniform. On the other hand, if it exceeds 1800 s, the productivity of heat treatment will decrease. In the quenching treatment of the present invention, within the above-mentioned heating temperature and holding time, and
The material is heated to austenite at a heating temperature T (° C.) and a holding time t (s) satisfying the formula (1) related to the amounts of (C + N) and Nb.

When the heating temperature and holding time for austenitization do not satisfy the expression (1), that is, the left side of the expression (1) QP = T + 100log (t / 60) -500 (C + N) -4000.
When Nb exceeds 880 and the formula (1) is not satisfied, the austenite grains become coarse and the toughness of the steel pipe deteriorates. The proper range of the heating temperature and the holding time of the quenching treatment changes depending on the (C + N) amount and the Nb amount. As an example, for example, (C + N)
Fig. 1 shows the range of suitable austenitizing conditions when Nb changes to 0.02, 0.04, and 0.06% at 0.22%. In the case of (C + N): 0.22%, Nb: 0.02%,
In the case of (C + N): 0.22% and Nb: 0.04%, (C + N)
In the case of N): 0.22% and Nb: 0.06%, the area is.

After being austenitized under the above heating conditions, it is cooled to obtain a martensite structure. The cooling conditions are not particularly limited and may be air cooling or water cooling,
A martensite structure can be obtained even with air cooling. The steel pipe that has been quenched and cooled to room temperature is then
c Tempering is performed at a temperature below the ₁ transformation point. It is preferable to temper at a temperature of 500 to 650 ° C.

In the above description, the seamless steel pipe has been described as an example, but the steel pipe is not limited to this. Needless to say, a welded steel pipe may be used.
For example, a steel pipe material having the above-mentioned composition is formed into a steel strip by hot rolling, and after subjecting the steel strip to the quenching and tempering treatment described above, a normal electric resistance welded pipe manufacturing process, that is, according to forming-welding-straightening, a predetermined The size may be an electric resistance welded steel pipe. Further, in the state of the steel strip, after being rolled as it is, it is possible to perform an ordinary electric resistance welded pipe manufacturing process to obtain an electric resistance welded steel pipe, and then subject the above-mentioned quenching and tempering treatment to the entire electric resistance welded steel pipe.

[0028]

EXAMPLE Steels having the compositions shown in Table 1 were melted in a converter and made into a billet by a continuous casting method. These billets were heated, pipe-formed by a Mannesmann mandrel type mill, rolled and air-cooled to obtain seamless steel pipes. Then, these steel pipes are shown in Table 2.
Yield strength YS75
8MPa (110ksi) grade steel pipe was used.

Tensile tests and Charpy impact tests were carried out on these steel pipes to investigate the tensile properties and impact properties.
In the tensile test, a round bar test piece within 6 mm from the longitudinal direction of these steel pipes was sampled, and the yield strength YS, tensile strength TS, and elongation El were measured. In the impact test, JIS No. 4 test pieces were sampled from the longitudinal direction of these steel pipes, and Charpy absorbed energy vE _-10 at -10 ° C was measured.

[0030]

[Table 1]

[0031]

[Table 2]

In all the examples of the present invention, the yield strength YS: 758M.
-10 in spite of the high strength of Pa (110ksi) grade
The absorbed energy (vE _-10 ) at 50 ° C is as high as 50 J or more, indicating excellent toughness. In addition, the strength-toughness balance (YS) x (vE- ₁₀ ) is also higher than that of the conventional steel pipe at 40,000 MPaJ or more, and the steel tube has an excellent strength-toughness balance. On the other hand, in the comparative example which is out of the scope of the present invention and subjected to the quenching treatment, the toughness is significantly deteriorated.

As described above, it can be seen that the steel pipe of the present invention has high strength, high toughness, excellent strength-ductility balance, and excellent properties as an oil well steel pipe.

[0034]

As described above, according to the present invention, it is possible to inexpensively provide a martensitic stainless steel pipe for an oil well having high strength and high toughness, an excellent strength-toughness balance, and excellent corrosion resistance. In addition, the martensitic stainless steel pipe for oil wells of the present invention can be used in oil wells in extremely cold regions at high depths and in harsh environments, and has a marked industrial effect.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a range of quenching and heating conditions of the present invention.

Front Page Continuation (72) Inventor Yuichi Kitahiro 1-1, Kawasaki-cho, Handa-shi, Aichi Kawasaki Steel Co., Ltd. Chita Works (56) References JP-A-4-210453 (JP, A) (58) Survey Areas (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 6/00 102 C21D 9/08

Claims (2)

(57) [Claims] 1. In mass%, C: 0.17 to 0.22%, Si: 1.0% or less, Mn: 0.25 to 1.0%, P: 0.03% or less, S: 0.005% or less, Cr: 12 to 14%, Ni: 0.14 to 0.5%, N: 0.06% or less, Nb: 0.02 to 0.07%, or V: 0.20% or less, balance
A strength characterized by having a composition consisting of Fe and inevitable impurities, and having a high yield strength: 758 MPa or higher and a Charpy absorbed energy at −10 ° C. v E _-10 : high toughness of 50 J or higher. -High-strength martensitic stainless steel pipe for oil wells with excellent toughness balance. 2. In mass%, C: 0.17 to 0.22%, Si: 1.0% or less, Mn: 0.25 to 1.0%, P: 0.03% or less, S: 0.005% or less, Cr: 12 to 14%, Ni: 0.01 to 0.5%, N: 0.06% or less, Nb: 0.01 to 0.07%, or V: 0.20% or less, in a steel pipe having a composition of temperature: (Ac ₃ transformation point) to 1100 ° C, time: 60 to 18
Heating temperature T within the range of 00s and satisfying the following formula (1)
Oil well with a good balance of strength and toughness, which is characterized by performing a quenching treatment of austenizing at (° C.) and a holding time t (s), then cooling, and then performing a tempering treatment at a temperature of Ac ₁ transformation point or lower. For manufacturing high-strength martensitic stainless steel pipes for automobiles. Note T + 100log (t / 60) -500 (C + N) -4000Nb ≦ 880 (1) where T: heating temperature (° C), t: retention time (s), C, N, Nb: content of each element Amount (mass%)