CN100412222C - Seamless steel tubes and pipes for use in oil well - Google Patents

Abstract

The seamless steel pipe for oil wells of the present invention, which can be manufactured with an effective mechanism capable of realizing energy saving and has excellent strength stability, contains C: 0.14 to 0.35%, Si: 0.05 to 1.0%, Mn: 0.05 to 2.0%, Cr: 0.05 to 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 the product of the Al content and the N content corrected by Ti and V The value is 0.00001 to 0.00050, and the remainder is composed of Fe and impurities. Among the impurities, P is 0.025% or less, and S is 0.01% or less. It is preferable to contain Ti, V, Nb, or B to improve hardenability and sulfide stress corrosion cracking resistance, and to contain Ca, Mg, or REM to improve the morphology of inclusions to improve sulfide stress corrosion cracking resistance.

Description

Oil well seamless steel pipe

technical field

The present invention relates to a seamless steel pipe for oil wells, and more specifically, to a seamless steel pipe for oil wells with little variation in strength such as tensile strength and excellent strength stability.

Background technique

Compared with welded pipes, high-reliability seamless steel pipes are mostly used in harsh oil well environments and high-temperature environments, and generally require higher strength, improved toughness, and improved acid corrosion (sour) resistance on the basis of stable strength.

For example, JP-A-2001-73086 discloses that the content of V, Nb, Ti, Cr, and Mo satisfies a prescribed relational expression, and by quenching and tempering the seamless steel pipe thus adjusted, it is possible to suppress the Formation of M ₂₃ C ₆ type carbides, resulting in seamless steel pipes with high toughness and high corrosion resistance.

In order to meet these requirements, it is important to stabilize the strength, and in particular, to narrow the strength range in steel pipes where acid corrosion resistance is considered necessary. In addition, in general oil well pipes, the oil well pipe may be partially deformed due to the external pressure in the oil well due to the strength variation (strength deviation) of the steel pipe, and the strength stability of the steel pipe becomes an essential element.

Conventionally, in order to stabilize the strength, it is preferable to form a uniform tempered martensitic structure in steel pipes. In order to adjust the hardenability, it is necessary to narrow the content of elements such as C, Mn, Cr, and Mo, but this alone cannot Achieve stable strength. In addition, recently, for the purpose of improving production efficiency, reducing energy use, and rationalizing costs, in-line heat treatment has been adopted instead of existing off-line heat treatment. In this in-line heat treatment, there is a problem that the hardenability changes due to the change in the grain size of prior austenite, and stable strength cannot be obtained.

As described above, in order to suppress the change in hardenability caused by the change in the prior austenite grain size, etc., and obtain a seamless steel pipe for oil well with stable high strength, high toughness and acid corrosion resistance, there are still necessary requirements. The problem to be solved.

Contents of the invention

In view of the above circumstances, the present invention aims to provide a seamless steel pipe for oil wells that can be manufactured with an effective mechanism capable of saving energy and has excellent strength stability.

In order to solve the above-mentioned problems, the present inventors studied the production of seamless steel pipes for oil wells with excellent strength stability based on the existing problems, and found the following (a) to (d) The main recognition, thereby make the present invention complete.

(a) In order to reduce the change in steel strength due to the change in the hardenability of the steel pipe, it is very important to control the amount of AlN precipitation in the steel within a predetermined range, and it is necessary to set the Al content (mass %) as an index, The concentration product of the N content (mass %) (hereinafter also referred to as "corrected N content") corrected based on the Ti and V content of the nitrides (hereinafter also referred to as "Al × {N-14 ×(Ti/144+V/153)}"), the value is adjusted in the range of 0.00001-0.00050.

(b) The reason for adjusting the value of concentration product, Al×{N−14×(Ti/144+V/153)} within the range of (a) above is as follows. That is, when the value of the concentration product exceeds 0.00050 and becomes high, the amount of AlN precipitated increases, so the coarsening of crystal grains is suppressed, and the hardenability of the steel pipe decreases. On the other hand, when the value of the concentration product is less than 0.00001, since the amount of AlN precipitated decreases, crystal grains become coarse, and the hardenability of the steel pipe increases. In order to suppress the variation in quenching of the steel pipe thus generated and stabilize the strength, it is necessary to adjust the value of the concentration product to fall within the range described in (a) above.

(c) In order to improve the hardenability, ensure the strength of the steel pipe, and prevent the reduction of toughness, the content of C, Si, Mn and Cr can be adjusted. In addition, in order to improve the hardenability and improve the resistance to sulfide stress corrosion cracking, the Mo content can be adjusted. , which are valid respectively.

(d) If Ti is contained, N is fixed as a nitride, and B can exist in a solid solution state, so the hardenability can be improved. In addition, if V is contained, fine carbides are precipitated during tempering, Thereby, an increase in strength can be realized. Nb forms carbonitrides, and B improves the hardenability to increase the amount of martensite, thereby improving the sulfide stress corrosion cracking resistance. In addition, by containing one or more of Ca, Mg, and REM, the morphology of inclusions can be improved to improve the sulfide stress crack resistance.

The present invention has been made based on the above findings, and its gist includes seamless steel pipes for oil wells as shown in the following (1) to (4).

(1) A seamless steel pipe for oil well, characterized by containing 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 the content of Al, N, Ti and V satisfies the relationship given by the following formula (1), and the remaining The part is composed of Fe and impurities, and the P in the impurities is 0.025% or less, and the S is 0.010% or less.

0.00001≤Al×{N-14×(Ti/144+V/153)}≤0.00050......(1)

In addition, the symbol of the element in Formula (1) represents the content rate (mass %) of each element contained in steel.

(2) A seamless steel pipe for oil well, characterized by containing 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 one or both of Nb: 0.005 to 0.040% and B: 0.0003 to 0.005%, and The content of Al, N, Ti and V satisfies the relationship given by the above formula (1), and the remainder is composed of Fe and impurities. Among the impurities, P is 0.025% or less, and S is 0.010% or less.

(3) A seamless steel pipe for oil well, characterized by containing 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 also contains Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, and REM: 0.0003 to 0.005%. One or two or more, and the content of Al, N, Ti and V satisfies the relationship given by the above formula (1), the remainder is composed of Fe and impurities, and the P in the impurities is 0.025% or less, and the S is 0.010% %the following.

(4) A seamless steel pipe for oil well, characterized by containing 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 one or both of Nb: 0.005 to 0.040% and B: 0.0003 to 0.005%. It also contains one or more of Ca: 0.0003-0.005%, Mg: 0.0003-0.005%, and REM: 0.0003-0.005%, and the content of Al, N, Ti and V satisfies the given by the formula (1) relationship, the remainder is composed of Fe and impurities, P in the impurities is 0.025% or less, and S is 0.010% or less.

In the present invention, "excellent strength stability" means that the strength variation such as the tensile strength of steel is small, and details thereof will be described later.

In addition, in the following description, "mass %" is abbreviated as "%".

Description of drawings

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

Detailed ways

The present invention is a seamless steel pipe for oil well, characterized in that, as described above, it contains 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 the content of Al, N, Ti and V satisfies the relationship given by the above formula (1), and the remainder consists of Composition of Fe and impurities, P in impurities is 0.025% or less, and S is 0.010% or less. Hereinafter, the reason and preferable range which limit the range of this invention as mentioned above are demonstrated in more detail.

C:

C is contained for the purpose of ensuring the strength of the seamless steel pipe for oil well. When the content thereof is less than 0.14%, the hardenability is insufficient and the tempering temperature cannot be raised, making it difficult to secure necessary steel properties. On the other hand, if the content becomes higher than 0.35%, cracking occurs and the toughness deteriorates. From the above reasons, the appropriate range of the C content is 0.14 to 0.35%. In addition, the preferred range of the C content is 0.16 to 0.28%, and the more preferred range is 0.20 to 0.28%.

Si:

Si is an element that not only has a deoxidizing effect, but also has the effect of improving the hardenability of steel and improving the strength. In order to obtain this effect, a content of 0.05% or more is required. However, when the content becomes higher than 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 0.1-0.5%.

Mn:

Mn is an element that has a deoxidizing effect and also has the effect of improving the hardenability of steel and improving the strength. In order to obtain this effect, it needs to be contained in an amount of 0.05% or more. However, when the content becomes higher than 2.0%, component segregation increases and 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 lower toughness. In particular, when the content becomes higher than 0.025%, it significantly lowers toughness. Therefore, the appropriate range of the P content is set to 0.025% or less. In addition, the P content is preferably 0.020% or less.

S:

S is also an impurity in steel, combining with Mn or Ca to form inclusions. If the S content exceeds 0.010%, the toughness and sulfide stress cracking resistance of the steel deteriorate significantly due to inclusions. Therefore, the appropriate range of the S content is set to 0.010% or less. In addition, the S content is preferably 0.005% or less.

Cr:

Cr is an element effective in improving the hardenability of steel, and in order to exhibit this effect, it needs to be contained in an amount of 0.05% or more. However, if the content becomes higher than 1.5%, the toughness and sulfide stress cracking resistance of the steel will 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 0.2-1.2%.

Mo:

Mo is an element that improves the hardenability of steel to ensure high strength, and is effective in improving 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 rate exceeds 2.0% and becomes high, toughness and sulfide stress crack resistance will fall. For the reasons described above, the appropriate range of the Mo content is set to 0.05 to 2.0%. In addition, the preferable range of Mo content rate is 0.1-0.8%.

Al:

Al is an element that has a deoxidizing effect and is effective in improving the toughness and workability of steel. Also, when the Al content is less than 0.010%, the amount of solid solution C increases, resulting in a significant increase in strength. Therefore, the appropriate range of the Al content is set to 0.010% or more. In addition, the preferable upper limit of the Al content is 0.080%.

Reasons for limiting the Al, N, Ti, and V content in relational expression (1):

As described above, the concentration product of the Al content and the N content, Al×{N-14×(Ti/144+V/153)}, is adjusted to a value represented by the following formula (1). The reason for the range is as follows.

0.00001≤Al×{N-14×(Ti/144+V/153)}≤0.00050......(1)

The above-mentioned concentration product, the value of Al×{N-14×(Ti/144+V/153)}, is an index indicating the degree of AlN precipitation in the steel, and if the value of the concentration product exceeds 0.00050 and becomes high, the steel The amount of AlN precipitation increases. As a result, the coarsening of crystal grains is suppressed, and the hardenability of the steel pipe decreases. On the other hand, when the value of the concentration product is less than 0.00001, the amount of AlN precipitated in the steel decreases, and as a result, the crystal grains become coarse, and the hardenability of the steel pipe increases. For these reasons, the decrease in hardenability of the steel pipe that occurs as described above and the change in hardenability associated with an excessive increase are suppressed, and the value of the concentration product for stabilizing the strength is set as shown in the above (1). The appropriate range of is 0.00001 to 0.00050. In addition, the preferable range of the value of a concentration product is 0.00003-0.0003.

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

In the same figure, the magnitude of the variation in the yield strength YS of the steel pipe was evaluated by the formula (2) described later. That is, the ○ mark in the figure indicates that the intensity variation is small, and the ● mark indicates that the intensity variation is large.

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

Hereinafter, the components and compositions of the first group and the second group to be contained as necessary will be described.

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

Ti:

Ti is an element that fixes N in the steel as a nitride and causes B to exist in a solid solution state in the steel during quenching, thereby exhibiting the effect of improving hardenability. It may or may not be contained, but by containing it, the above-mentioned action can be obtained. However, if the content of Ti becomes higher than 0.05%, it will remain as coarse nitrides in the steel and reduce the resistance to sulfide stress cracking. From the above reasons, the range of the content rate when Ti is contained is made 0 to 0.05%. In addition, the preferable range of content rate is 0.005-0.025%.

B:

B is an element that improves the hardenability and increases the amount of martensite to improve the resistance to sulfide stress corrosion cracking, and its content has this effect even at the impurity level. It may or may not be contained, but in order to obtain this effect more remarkably, a content rate of 0.0003% or more is preferable. However, when the B content becomes higher than 0.005%, the toughness of steel decreases. Therefore, the range of the content rate when B is contained is set to 0.0003 to 0.005%. In addition, the preferable range of content rate is 0.0003-0.003%.

V:

V is an element that acts to increase the strength of steel by being precipitated as fine carbides during tempering. It may or may not be contained, but the effect mentioned above can be acquired by containing it. On the other hand, if the content becomes higher than 0.3%, the toughness of steel will decrease. From these reasons, when V is contained, the range of the V content rate is 0 to 0.3%.

Nb:

Nb is an element that prevents the coarsening of crystal grains by forming carbonitrides in a high-temperature region, thereby improving the toughness and sulfide stress corrosion cracking resistance of steel. It may or may not be contained, but this effect can be acquired by making a content rate 0.005 % or more. On the other hand, when the content becomes higher than 0.040%, the carbonitrides are excessively coarsened and the resistance to sulfide stress cracking is reduced. Therefore, the range of the Nb content when it is contained is made 0.005 to 0.040%. In addition, the preferable range of content rate is 0.010-0.030%.

Group 2 is Ca, Mg and REM.

These elements may or may not be contained, but when they are contained, any of them react with S in the steel to form sulfides, thereby improving the form of inclusions and improving the resistance to sulfide stress cracking of steel. effect. When the above-mentioned effect is desired, one or more of Ca, Mg, and REM (rare earth elements such as Ce, La, and Y) are selected and contained at 0.0005% or more, respectively, so that the effect can be obtained. On the other hand, if the content of any one of the elements exceeds 0.005%, the purity of the steel decreases due to the increase in the amount of inclusions in the steel, and the resistance to sulfide stress cracking decreases. From the above-mentioned reasons, the range of the content rate when these elements are contained is set to 0.0005% to 0.005% for any element.

Example

In order to confirm the effect of the seamless steel pipe for oil wells of the present invention, the following tests were conducted and the results were evaluated.

From 22 types of test steels with the chemical composition shown in Table 1 and Table 2, a steel billet with an outer diameter of 225 mm was produced, and after it was heated to 1250 ° C, it was manufactured according to the Mannesmann mandrel. Pipe method, forming a seamless steel pipe with an outer diameter of 244.5 mm and a wall thickness of 13.8 mm. Then, this seamless steel pipe was subjected to quenching and tempering treatment, and a tensile test piece was taken.

Here, quenching is water quenching performed after uniform heating at 950° C. for 5 minutes, and tempering is performed by soaking the quenched steel pipe at 650° C. for 30 minutes. In addition, the above-mentioned treatment conditions are examples, and the quenching and tempering treatments of the seamless steel pipe of the present invention are not limited thereto.

In addition, the tensile test is to take an arc-shaped tensile test piece from the longitudinal direction of the pipe steel for the tensile test at the parallel section specified in 5CT of the API standard, and perform the tensile test to measure the yield strength YS (MPa ).

In addition, the variation (variation) of the yield strength YS was obtained based on the above-mentioned measurement results, and the strength stability was evaluated, which are also shown in Table 2 above.

In addition, in Table 2, the fluctuation of the yield strength YS was calculated|required by the following method, and evaluated based on two stages. That is, the above-mentioned tensile test was carried out 10 times (number of N = 10) on the test steel of each steel number, and when the relationship of the following formula (2) was satisfied, it was regarded as good (○) as the fluctuation of TS was small , when the relation of the formula (2) is not satisfied, the fluctuation of YS is considered bad (×).

Each YS≤average YS-3×each YS standard deviation......(2)

Here, the "average TS" is the average YS of all the test steels (22 types) provided in the test, "each YS" is the average YS of the target steel (1 type), and then "each YS standard "Deviation" is the standard deviation of the target steel (one type).

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 with a low Al content rate, and steel numbers with a low Al content rate, and the concentration product, Al×{N-14×(Ti/144+V/153)} value is high In Test No. 16 of Steel No. 16, the variation of yield strength YS was large in any of them, and the strength stability was poor. In addition, regardless of whether the Al content rate is within the range of the present invention, test numbers 17 to 22 of steel numbers 17 to 22 having a high concentration product, Al×{N-14×(Ti/144+V/153)} were used. , in any of them, the fluctuation of YS is large, and the strength stability is poor.

On the other hand, in test numbers 1 to 12 using steel numbers 1 to 12 which are the steels of the present invention satisfying all the conditions specified in the present invention, any variation in YS was small, and the strength stability was good. In particular, in test Nos. 6, 7, 8 and 10 using steel Nos. 6, 7, 8 and 10 containing Ti, V, Nb or B, higher strength and durability were obtained due to improvement in hardenability, etc. Sulfide stress corrosion cracking resistance, and in test numbers 6, 8, 9, and 10 containing one or more of Ca, Mg, and REM, higher resistance to sulfide stress cracking was obtained.

Industrial application

The seamless steel pipe for oil wells of the present invention is a seamless steel pipe for oil wells that can be manufactured with an effective mechanism capable of saving energy and has excellent strength stability. In particular, in the case of manufacturing through an in-line heat treatment process, variations in hardenability due to variations in the grain size of prior austenite grains can be 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 with strength stability produced with energy saving and improved production efficiency, and can be widely used in terms of rationalization of the manufacturing process and expansion of applications. Be applicable.

Claims (4)

1. A seamless steel pipe for oil wells, characterized by containing 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% to 0.080%, and the content of Al, N, Ti and V satisfies the relationship given by the following formula (1), and the remaining The part is composed of Fe and impurities, and the P in the impurities is less than 0.025%, and the S is less than 0.010%. 0.00001≤Al×{N-14×(Ti/144+V/153)}≤0.00050……(1) However, the symbol of the element in the formula (1) represents the content rate of each element contained in the steel, and the unit is mass %. 2. The seamless steel pipe for oil well according to claim 1, wherein instead of a part of the Fe, one of Nb: 0.005 to 0.040% and B: 0.0003 to 0.005% or 2 kinds. 3. The seamless steel pipe for oil wells according to claim 1, further comprising Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, and REM: 0.0003 to 1 or more of 0.005%. 4. The seamless steel pipe for oil wells according to claim 2, wherein instead of a part of the Fe, Ca: 0.0003 to 0.005%, Mg: 0.0003 to 0.005%, and REM: 0.0003 to 1 or more of 0.005%.

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