JP2006265668A - Seamless steel pipe for oil well - Google Patents

Abstract

An oil well seamless steel pipe excellent in strength stability that can be manufactured by an efficient means capable of realizing energy saving is provided.
SOLUTION: C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5%, Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1%, and Al: 0.010% or more, and corrected by Al content and Ti and V The product of the N content is 0.00001 to 0.00050, the balance is Fe and impurities, P in the impurities is 0.025% or less, and S is 0.010% or less. It is a steelless pipe. Improve hardenability and sulfide stress corrosion cracking resistance by containing Ti, V, Nb or B, and improve the form of inclusions by adding Ca, Mg or REM, and resist sulfide stress corrosion cracking. It is preferable to improve the property.
[Selection] Figure 1

Description

  The present invention relates to a seamless steel pipe for oil wells, and in particular, relates to a seamless steel pipe for oil wells having little strength fluctuation such as tensile strength and excellent strength stability.

  Seamless steel pipes, which are more reliable than welded pipes, are often used in harsh oil well environments and high-temperature environments, and they have improved strength, improved toughness, and improved sour resistance under stable strength. Always required.

For example, Patent Document 1 discloses an M ₂₃ C ₆ type carbide obtained by quenching and tempering a seamless steel pipe whose V, Nb, Ti, Cr, and Mo contents are adjusted to satisfy a predetermined relational expression. A seamless steel pipe having high toughness and high corrosion resistance by suppressing the formation of is disclosed.

  In order to satisfy these requirements, it is important to stabilize the strength. Particularly in steel pipes that require sour resistance, the strength range is narrowed. Also, in general oil well pipes, the oil well pipes may be partially deformed by the external pressure in the oil wells due to the strength fluctuation (strength variation) of the steel pipes, and the strength stability of the steel pipes is an indispensable element. Yes.

  Conventionally, in order to stabilize the strength, it is preferable to make the steel pipe a uniform tempered martensite structure. In order to adjust the hardenability, the content of elements such as C, Mn, Cr, and Mo is narrowed. However, it was not possible to achieve a stable strength by itself. Furthermore, recently, in-line heat treatment is being adopted instead of the conventional offline heat treatment for the purpose of improving production efficiency, reducing energy consumption, and rationalizing costs. In the in-line heat treatment, there is a problem that the hardenability changes due to the change in crystal grain size of the prior austenite and a stable strength cannot be obtained.

  As described above, in order to obtain a seamless steel pipe for oil wells with stable high strength, high toughness, and sour resistance, it is still necessary to be solved to suppress the variation of hardenability due to the variation of the prior austenite grain size. There are still issues to be solved.

JP 2001-73086 A (Claims and paragraphs [0010] to [0012])

  This invention is made | formed in view of the above situations, The subject is providing the seamless steel pipe for oil wells excellent in strength stability which can be manufactured by the efficient means which can implement | achieve energy saving. There is.

  In order to solve the above-mentioned problems, the present inventors have studied the production of seamless steel pipes for oil wells excellent in strength stability based on the conventional problems, and the following (a) to (d) As a result, the present invention was completed.

  (A) In order to reduce the fluctuation of the steel strength due to the fluctuation of the hardenability of the steel pipe, it is important to control the precipitation amount of AlN in the steel within a predetermined range, and the Al content (mass %) And the N content (mass%) corrected by the Ti and V contents forming the nitride (hereinafter also referred to as “corrected N content”) (hereinafter “Al × {N-14 × (Ti / 144 + V / 153)} ”) is required to be adjusted within a range of 0.00001 to 0.00050.

  (B) The reason for adjusting the concentration product, Al × {N-14 × (Ti / 144 + V / 153)}, within the range of the above (a) is as follows. That is, when the value of the concentration product is higher than 0.00050, the amount of precipitated AlN is increased, so that the coarsening of crystal grains is suppressed and the hardenability of the steel pipe is lowered. On the other hand, if the value of the concentration product is less than 0.00001, the amount of precipitated AlN decreases, so that the crystal grains become coarse and the hardenability of the steel pipe increases. In order to suppress the fluctuation of the hardenability of the steel pipe generated in this way and stabilize the strength, it is necessary to adjust the value of the concentration product within the range described in (a) above.

  (C) In order to enhance the hardenability and ensure the strength of the steel pipe and to prevent the toughness from being lowered, adjusting the contents of C, Si, Mn and Cr, and improving the hardenability and resistance to sulfides In order to enhance the stress corrosion cracking property, it is effective to adjust the Mo content.

  (D) When Ti is contained, N can be fixed as a nitride and B can be present in a solid solution state, so that hardenability can be improved, and when V is contained, fine carbides are formed during tempering. By precipitating, the strength can be increased. Nb improves the resistance to sulfide stress corrosion cracking by forming carbonitrides, and B improves the hardenability and increases the amount of martensite. Furthermore, the inclusion of one or more of Ca, Mg, and REM can improve the form of inclusions and improve the resistance to sulfide stress cracking.

  This invention is completed based on said knowledge, The summary exists in the seamless steel pipe for oil wells shown to following (1)-(4).

(1) By mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5% Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Al, N, Ti and V Oil well characterized in that the content satisfies the relationship given by the following formula (1), the balance is Fe and impurities, P in the impurities is 0.025% or less, and S is 0.010% or less Seamless steel pipe.
0.00001 ≦ Al × {N-14 × (Ti / 144 + V / 153)} ≦ 0.00050 (1)
However, the element symbol in the formula (1) represents the content (% by mass) of each element contained in the steel.

  (2) By mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5% , Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Nb: 0.005 to 0.040% And B: one or two of 0.0003 to 0.005% are contained, and the content of Al, N, Ti and V satisfies the relationship given by the formula (1), with the balance being A seamless steel pipe for oil wells comprising Fe and impurities, wherein P in the impurities is 0.025% or less and S is 0.010% or less.

  (3) By mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5% , Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Ca: 0.0003 to 0.005% , Mg: 0.0003 to 0.005% and REM: 0.0003 to 0.005%, and the Al, N, Ti, and V contents are the above (1 ) A seamless steel pipe for oil wells satisfying the relationship given by the formula, wherein the balance consists of Fe and impurities, P in the impurities is 0.025% or less, and S is 0.010% or less.

  (4) By mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5% , Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Nb: 0.005 to 0.040% And B: one or two of 0.0003 to 0.005%, Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, and REM: 0 .0003-0.005% of one or more, and the contents of Al, N, Ti and V satisfy the relationship given by the above formula (1), the balance being Fe and impurities And P in the impurities is 0.025% or less and S is 0.010% or less. .

  In the present invention, “excellent in strength stability” means that there are few fluctuations in strength such as tensile strength of steel, and details thereof will be described later.

  In the following description, “mass%” is also simply expressed as “%”.

  The oil well seamless steel pipe of the present invention is an oil well seamless steel pipe excellent in strength stability that can be manufactured by an effective means capable of realizing energy saving. In particular, even when manufactured through an in-line heat treatment process, variation in hardenability due to variation in grain size of prior austenite crystal grains is suppressed, and stable high strength can be obtained. Therefore, the seamless steel pipe for oil wells of the present invention is suitable as a seamless steel pipe for oil wells produced under energy saving and improved production efficiency.

  In the present invention, as described above, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5 %, Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Al, N, Ti and The V content satisfies the relationship given by the above formula (1), the balance is Fe and impurities, P in the impurities is 0.025% or less, and S is 0.010% or less. It is a seamless steel pipe for oil wells. The reason why the scope of the present invention is limited as described above and the preferred range will be described in more detail below.

C:
C is contained for the purpose of ensuring the strength of the seamless steel pipe for oil wells. If the content is less than 0.14%, the hardenability is insufficient and the tempering temperature cannot be increased, and it is difficult to ensure the required steel performance. On the other hand, when the content rate exceeds 0.35%, burn cracking occurs and toughness deteriorates. For the above reason, the appropriate range of the C content is set to 0.14 to 0.35%. In addition, the preferable range of C content rate is 0.16 to 0.28%, and a more preferable range is 0.20 to 0.28%.

Si:
Si is an element having a deoxidizing action and an action of improving the hardenability of the steel to improve the strength. In order to obtain the effect, it is necessary to set the content to 0.05% or more. However, when the content exceeds 1.0%, the resistance to sulfide stress cracking decreases. Therefore, the appropriate range of the Si content is set to 0.05 to 1.0%. In addition, the preferable range of Si content rate is 0.1 to 0.5%.

Mn:
Mn is an element having a deoxidizing action and an action of improving the hardenability of the steel to improve the strength. In order to obtain the effect, it is necessary to contain 0.05% or more. However, when the content exceeds 2.0%, component segregation increases and the toughness decreases. Therefore, the appropriate range of the Mn content is set to 0.05 to 2.0%.

P:
P is an impurity element in steel and segregates at grain boundaries to cause toughness reduction. In particular, when its content exceeds 0.025%, toughness is significantly reduced. Therefore, the appropriate range of the P content is set to 0.025% or less. The P content is preferably 0.020% or less.

S:
S is also an impurity in the steel and combines with Mn or Ca to form inclusions. If the S content exceeds 0.010%, the deterioration of the toughness of the steel and the resistance to sulfide stress cracking increases due to the inclusions. Therefore, the appropriate range of the S content is set to 0.010% or less. The S content is preferably 0.005% or less.

Cr:
Cr is an element effective for enhancing the hardenability of steel, and it is necessary to contain 0.05% or more in order to exert the effect. However, if the content exceeds 1.5%, the toughness and sulfide stress cracking resistance of the steel decrease. Therefore, the appropriate range of the Cr content is set to 0.05 to 1.5%. In addition, the preferable range of Cr content rate is 0.2 to 1.2%.

Mo:
Mo is an element effective for enhancing the hardenability of the steel to ensure high strength and for enhancing the resistance to sulfide stress cracking. In order to obtain these effects, the Mo content needs to be 0.05% or more. However, when the Mo content exceeds 2.0%, the toughness and the resistance to sulfide stress cracking decrease. For the above reason, the appropriate range of the Mo content is set to 0.05 to 2.0%. In addition, the preferable range of Mo content is 0.1 to 0.8%.

Al:
Al is an element having a deoxidizing action and effective in enhancing the toughness and workability of steel. On the other hand, if the Al content is less than 0.010%, the amount of solid solution C increases, and as a result, the strength increases remarkably. Therefore, the appropriate range of Al content is set to 0.010% or more. In addition, the preferable upper limit of Al content rate is 0.080%.

Reasons for limiting the contents of Al, N, Ti and V according to the relational expression (1):
As described above, the concentration product of Al content and N content, the reason for adjusting the value of Al × {N-14 × (Ti / 144 + V / 153)} to the range of values represented by the following formula (1) Is as follows.
0.00001 ≦ Al × {N-14 × (Ti / 144 + V / 153)} ≦ 0.00050 (1)
The concentration product, Al × {N-14 × (Ti / 144 + V / 153)}, is an index indicating the degree of precipitation of AlN in the steel, and when the concentration product value becomes higher than 0.00050, The precipitation amount of AlN in the steel increases. As a result, coarsening of crystal grains is suppressed, and the hardenability of the steel pipe is lowered. On the other hand, if the value of the concentration product is less than 0.00001, the precipitation amount of AlN in the steel decreases, resulting in coarsening of crystal grains and an increase in the hardenability of the steel pipe. For these reasons, the appropriate range of the concentration product value for suppressing the fluctuation of the hardenability due to the decrease in the hardenability and excessive increase of the steel pipe generated as described above and stabilizing the strength is the above (1 ) To be 0.00001 to 0.00050. Note that a preferable range of the concentration product is 0.00003 to 0.0003.

  FIG. 1 is a diagram showing the influence of Al and the corrected N content on the fluctuation of the yield strength YS of a steel pipe subjected to quenching and tempering treatment.

  In the figure, the magnitude of the fluctuation of the yield strength YS of the steel pipe was evaluated by the equation (2) described later. That is, a circle mark in the figure indicates that the intensity fluctuation is small, and a circle mark indicates that the intensity fluctuation is large.

  As shown in the figure, the appropriate ranges of the Al content rate and the corrected N content rate satisfy the above formula (1), and the Al content rate is 0.010% or more.

  Below, the component and composition of the 1st group and 2nd group which are contained as needed are demonstrated.

  The first group is Ti, V, Nb and B, and contains one or more of these elements as necessary.

Ti:
Ti is an element that makes N exist in a solid solution state in the steel during quenching by fixing N in the steel as a nitride, thereby exhibiting the effect of improving hardenability. Although it is not necessary to make it contain, said effect can be acquired by making it contain. However, if the Ti content exceeds 0.05%, it will remain in the steel as coarse nitrides, reducing the resistance to sulfide stress cracking. For the above reason, the content range when Ti is contained is set to 0 to 0.05%. In addition, the preferable range of content rate is 0.005-0.025%.

B:
B is an element that has the effect of improving the hardenability and improving the resistance to sulfide stress corrosion cracking by increasing the amount of martensite, even if its content is at the impurity level. Have Although it is not necessary to make it contain, in order to acquire the effect more notably, it is preferable to make it the content rate of 0.0003% or more. However, if the B content exceeds 0.005%, the toughness of the steel decreases. Therefore, the content range when B is contained is set to 0.0003 to 0.005%. In addition, the preferable range of content rate is 0.0003 to 0.003%.

V:
V is an element having an effect of increasing the strength of steel by being precipitated as fine carbides during tempering. Although it is not necessary to make it contain, said effect can be acquired by making it contain. On the other hand, if the content exceeds 0.3%, the toughness of the steel decreases. For these reasons, the range of the V content when V is contained is set to 0 to 0.3%.

Nb:
Nb is an element having an effect of preventing coarsening of crystal grains by forming carbonitride in a high temperature region and improving the toughness and resistance to sulfide stress corrosion cracking of steel. Although it is not necessary to make it contain, the effect can be acquired by making content rate 0.005% or more. On the other hand, if the content exceeds 0.040%, the carbonitride becomes excessively coarse, and the resistance to sulfide stress cracking is lowered. Then, the range of Nb content rate when making it contain was 0.005 to 0.040%. In addition, the preferable range of content rate is 0.010 to 0.030%.

  The second group is Ca, Mg and REM.

  These elements may or may not be included, but if included, both improve the form of inclusions by reacting with S in steel to form sulfides, It has the effect of improving the resistance to sulfide stress cracking of steel. When it is desired to obtain the above effect, one or more selected from Ca, Mg and REM (rare earth elements such as Ce, La, and Y) should be contained in an amount of 0.0005% or more. Thus, the effect can be obtained. On the other hand, if the content of any of these elements exceeds 0.005%, the amount of inclusions in the steel increases, thereby reducing the cleanliness of the steel and reducing the resistance to sulfide stress cracking. For the above reasons, the range of the content when these elements are contained is set to 0.0005 to 0.005% for any element.

  In order to confirm the effect of the seamless steel pipe for oil well of the present invention, the following test was conducted and the result was evaluated.

  Billets having an outer diameter of 225 mm were manufactured from 22 types of test steels having the chemical composition shown in Tables 1 and 2, and after heating them to 1250 ° C., the outer diameter was 244.5 mm by the Mannesmann mandrel manufacturing method. And formed into a seamless steel pipe having a wall thickness of 13.8 mm. Subsequently, the seamless steel pipe was quenched and tempered, and a tensile test piece was collected.

  Here, the quenching was performed by uniformly heating at 950 ° C. for 5 minutes and then water quenching, and the tempering was performed by soaking the steel tube after quenching at 650 ° C. for 30 minutes. . In addition, said process conditions are an example and the hardening and tempering process of the seamless steel pipe of this invention are not restricted to this.

  In addition, the tensile test was performed by collecting a tensile test piece having a circular section in the parallel part specified by API standard 5CT from the longitudinal direction of the steel pipe for tensile test, and performing the tensile test to yield strength YS (MPa). Was measured.

  Furthermore, the fluctuation (variation) in the yield strength YS was obtained based on the above measurement results, and the strength stability was evaluated.

  In Table 2, the variation of the yield strength YS was determined by the following method and evaluated in two stages. That is, when the above tensile test was carried out 10 times (N number = 10) for the test steel of each steel number and the relationship of the following formula (2) was satisfied, the fluctuation of YS was small and good (◯), A case where the relationship of the formula (2) is not satisfied is defined as a failure (x) with a large variation in YS.

Each YS ≦ average YS-3 × YS standard deviation (2)
Here, “average YS” is the average YS of all test steels (22 types) subjected to the test, “each YS” is the average YS of the target test steel (1 type), and “each YS standard deviation” "Represents the standard deviation of the target test steel (type 1), respectively.

  Test numbers 1 to 12 are examples of the present invention using steel numbers 1 to 12 which are steels of the present invention, and test numbers 13 to 22 are comparative examples using steel numbers 13 to 22 which are comparative steels.

  Test numbers 13 to 15 using steel numbers 13 to 15 having a low Al content, and a low Al content and a high concentration product, Al × {N-14 × (Ti / 144 + V / 153)} In each of the test numbers 16 using the steel number 16, the yield strength YS greatly fluctuated, and the strength stability was poor. In addition, although the Al content is within the range of the present invention, the test number using steel numbers 17 to 22 having a high concentration product, Al × {N-14 × (Ti / 144 + V / 153)}. In any of 17-22, the fluctuation of YS was large and the strength stability was poor.

  On the other hand, in Test Nos. 1 to 12 using Steel Nos. 1 to 12 that are all steels of the present invention that satisfy all of the conditions defined in the present invention, the fluctuation of YS was small and the strength stability was good. It was. In particular, in test numbers 6, 7, 8 and 10 using steel numbers 6, 7, 8 and 10 containing Ti, V, Nb or B, higher strength and sulfide stress corrosion resistance due to improved hardenability, etc. Crackability was obtained, and in Test Nos. 6, 8, 9 and 10 containing one or more of Ca, Mg and REM, higher sulfide stress crack resistance was obtained.

  The oil well seamless steel pipe of the present invention is an oil well seamless steel pipe excellent in strength stability that can be manufactured by an effective means capable of realizing energy saving. In particular, even when manufactured through an in-line heat treatment process, variation in hardenability due to variation in grain size of prior austenite crystal grains is suppressed, and stable high strength can be obtained. Accordingly, the seamless steel pipe for oil wells of the present invention is suitable as a seamless steel pipe for oil wells having strength stability that is produced while saving energy and improving production efficiency, and is widely used for both rationalization of manufacturing processes and expansion of applications. Applicable to.

It is a figure which shows the influence of Al and correction | amendment N content rate on the fluctuation | variation of the yield strength YS of the steel pipe which performed the quenching tempering process.

Claims (4)

In mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5%, Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1%, and Al: 0.010% or more, and Al, N, Ti, and V contents are The oil well seamless characterized by satisfying the relationship given by the following formula (1), the balance being Fe and impurities, P in the impurities being 0.025% or less and S being 0.010% or less Steel pipe.
0.00001 ≦ Al × {N-14 × (Ti / 144 + V / 153)} ≦ 0.00050 (1)
However, the element symbol in the formula (1) represents the content (% by mass) of each element contained in the steel. In mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5%, Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Nb: 0.005 to 0.040% and B: One or two of 0.0003 to 0.005% are contained, and the contents of Al, N, Ti and V satisfy the relationship given by the following formula (1), with the balance being Fe and impurities A seamless steel pipe for oil wells, wherein P in impurities is 0.025% or less and S is 0.010% or less.
0.00001 ≦ Al × {N-14 × (Ti / 144 + V / 153)} ≦ 0.00050 (1)
However, the element symbol in the formula (1) represents the content (% by mass) of each element contained in the steel. In mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5%, Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Ca: 0.0003 to 0.005%, Mg: It contains one or more of 0.0003 to 0.005% and REM: 0.0003 to 0.005%, and the Al, N, Ti, and V contents are represented by the following formula (1) A seamless steel pipe for oil wells satisfying a given relationship, the balance being Fe and impurities, wherein P in the impurities is 0.025% or less and S is 0.010% or less.
0.00001 ≦ Al × {N-14 × (Ti / 144 + V / 153)} ≦ 0.00050 (1)
However, the element symbol in the formula (1) represents the content (% by mass) of each element contained in the steel. In mass%, C: 0.14-0.35%, Si: 0.05-1.0%, Mn: 0.05-2.0%, Cr: 0.05-1.5%, Mo: 0.05 to 2.0%, Ti: 0 to 0.05%, V: 0 to 0.1% and Al: 0.010% or more, and Nb: 0.005 to 0.040% and B: One or two of 0.0003 to 0.005% are contained, and Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, and REM: 0.0003 to Containing one or more of 0.005% and satisfying the relationship in which the Al, N, Ti and V contents are given by the following formula (1), the balance consists of Fe and impurities, A seamless steel pipe for oil wells, wherein P in impurities is 0.025% or less and S is 0.010% or less.
0.00001 ≦ Al × {N-14 × (Ti / 144 + V / 153)} ≦ 0.00050 (1)
However, the element symbol in the formula (1) represents the content (% by mass) of each element contained in the steel.

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