JP6456986B2 - Ultra-high strength and ultra-tough oil well pipe and method for producing the same - Google Patents

Description

  The present invention relates to a metallurgical product and a manufacturing method thereof, and more particularly to an oil well pipe and a manufacturing method thereof.

  Currently, the development of oil and gas resources in Fukai and Ultra-Fukai around the world is increasingly emphasized. The oil field reserves in the western part of Japan are extremely deep and the geological structure is complicated. Since the deepest oil and gas well exceeds 8000 m, the demand for the strength of the oil well pipe for mining the oil and gas well is remarkably improved. As is well known, as the steel grade increases and the yield strength of the material increases, the hardness of the material increases correspondingly, the toughness of the material decreases gradually, and the material's resistance to surface defects increases. Sensitivity may be further increased. Oil well pipes for mining deep wells and ultra deep wells have very high demands on strength and toughness. Satisfying high strength and improving the toughness index as much as possible to ensure the safety of production use.

  However, steel strength, toughness and plasticity generally have a trade-off relationship. That is, steel with high strength is generally lower in plasticity and toughness. Similarly, increasing the plasticity and toughness of steel reduces the strength of the steel. Then, it is very difficult to develop a steel material having high toughness and high strength. At present, the strength of an oil well pipe capable of realizing industrial application is 170 ksi, but the impact toughness of the oil well pipe is only 50-80 J. According to the relevant teaching literature, the impact toughness of high strength steel used for pressure vessels needs to reach 10% of its yield strength. In doing so, each major oil field in the country, such as the Tarim oil field, submitted similar standards for oil well pipe performance for Fukai and Ultra-Fukai. However, the impact toughness performance of high strength steels with an existing strength of 150 ksi (yield strength 1034 MPa) or higher is much lower than the standard.

  Chinese Patent Document CN101586450A (publication date: August 27, 2008, name: “oil well pipe having high strength and high toughness and manufacturing method thereof”) relates to a steel grade for oil well pipe. The chemical element components (wt%) of the steel types are: C: 0.22 to 0.4%, Si: 0.17 to 0.35%, Mn: 0.45 to 0.60%, Cr: 0.95 -1.10%, Mo: 0.70-0.80%, Al: 0.015-0.040%, Ni <0.20%, Cu <0.20%, V: 0.070-0. 100%, Ca> 0.0015%, P <0.010%, S <0.003%, and the balance is iron. The document provided a method for manufacturing the oil well pipe. The method included 1) distribution refining, 2) continuous casting and continuous rolling, and 3) pipe processing. The strength of the steel grade in this document is 1100 Mpa, but the lateral impact toughness is only 90 J, and the toughness index is lower.

  Chinese Patent Document CN101250671A (Release Date: November 25, 2009, Name: “Oil Well Pipe with High Strength and Toughness and Method for Producing the Same”) relates to a steel grade for oil well pipe. The chemical element components (wt%) of the steel types are: C: 0.16-0.28, Si: ≦ 0.5, Mn: 0.3-1.10, Cr: 0.3-1.10, Mo : 0.60 to 0.95, Al: 0.015 to 0.060, of which acid-soluble Als / Al ≧ 0.8, Ni: <0.60, Cu: 0.05 to 0.25, V: 0.06-0.20, Ca> 0.0015, Nb: ≦ 0.05, Ti: ≦ 0.05, P <0.010, S <0.002, O: <0.0024, H : <0.0002, N: <0.008, B: 0.0 to 0.005, and the balance is iron. The oil well pipe of the literature has a lateral impact toughness of only 80 J and a lower index of toughness.

  Japanese Patent Document JP Hei 11-131189A (Release Date: May 18, 1999, Name: “Method for Producing Type 1 Steel Pipe”) disclosed a method for producing Type 1 steel pipe. In this manufacturing method, after heating in a temperature range of 750 to 400 ° C., rolling was performed in a deformation amount range of 20% or 60% or more, and a steel pipe product having a yield strength of 950 Mpa or more and good toughness was obtained. Submitted that. However, this method has a high degree of difficulty in rolling because of the low heating temperature. When the rolling temperature is lowered, a martensite structure is likely to be generated. The fine structure is a fine structure that is not allowed for oil well pipe products.

  An object of the present invention is to provide an ultra-high strength and ultra-high toughness oil well pipe. The oil well pipe has ultra-high strength and ultra-high toughness, and its strength is 150 ksi steel grade or higher, and its 0 ° transverse Charpy impact is 10% or more of the yield strength of 150 ksi steel grade. It can satisfy the requirements of strength and toughness submitted to the oil well pipe by the oil and gas field of Ultra Fukai.

  In order to achieve the above object, the present invention has submitted the following ultra-high strength and ultra-tough oil well pipe.

Ultra-high strength and ultra-tough oil well pipes are expressed in mass percentages of chemical elements.
C: 0.12-0.18%;
Si: 0.1 to 0.4%;
Mn: 1.1-1.6%;
Cr: 0.1 to 0.4%;
Mo: 0.2-0.5%;
Nb: 0.02-0.04%;
Ti: 0.02 to 0.05%;
B: 0.0015 to 0.005%;
Al: 0.01 to 0.05%;
Ca: 0.0005 to 0.005%;
N ≦ 0.008%,
And 0 <(Ti-3.4N) ≦ 0.02%, Ti / B ≧ 10 is satisfied,
The balance is Fe and other inevitable impurities.

  Inevitable impurities in this technical plan are mainly P and S elements, and are controlled so that P ≦ 0.015% and S ≦ 0.003%.

  The design principle for each chemical element in the ultra-high strength / ultra-tough oil well pipe of the present invention is as follows.

  C: C is an element that forms carbides, and can improve the strength of steel. When the C content is lower than 0.12 wt%, the hardenability of the steel is lowered and the toughness of the steel is lowered. When the content of C is higher than 0.18 wt%, the segregation of the steel is remarkably deteriorated and the toughness of the steel is also lowered. In order to achieve the demand for high strength and high toughness of the oil country tubular goods, it is necessary to make the content of C element 0.12 to 0.18 wt% in the technical solution of the present invention.

  Si: Si dissolves in ferrite and can improve the yield strength of steel. However, it is not desirable that the amount of Si element added is too high. If the Si element is too high, the workability and toughness of the steel deteriorate. If the Si element is less than 0.1 wt%, the oil well pipe is likely to be oxidized. Then, the Si content should be 0.10 to 0.40 wt%.

  Mn: Mn is an austenite forming element and can improve the hardenability of steel. In the steel type system of the ultra-high strength and ultra-tough oil well pipe of the present invention, if the Mn content is less than 1.1 wt%, the hardenability of the steel is significantly reduced, and the martensite ratio of the steel is reduced. Decrease and reduce the toughness of the steel. When the Mn content exceeds 1.6 wt%, the structure segregation in the steel is remarkably increased, which affects the uniformity of the hot rolled structure and the impact performance. Based on this cause, the Mn content was 1.10 to 1.60 wt% in the technical solution of the present invention.

Cr: Cr is an element that strongly improves the hardenability of steel and is an element that forms strong carbides. Strong carbides precipitated during tempering can improve the strength of the steel. However, if the Cr content exceeds 0.4 wt%, coarse M ₂₃ C ₆ carbide is likely to be precipitated at the crystal boundaries, so that the toughness of the steel is lowered. If the Cr content is less than 0.1 wt%, it is difficult to improve the hardenability of the steel, so the effect of addition is not clear. In the ultra-high strength / ultra-tough oil well pipe of the present invention, the Cr content was designed to be 0.1 to 0.4 wt%.

  Mo: Mo improves the strength and tempering stability of steel mainly by the form of carbide and solid solution strengthening. In the technical solution of the present invention, since the C content is low, when the Mo content exceeds 0.5 wt% or more, Mo hardly forms a carbide precipitation phase with C, which causes waste of the added alloy. If the Mo content is less than 0.2 wt%, the strength of the oil well pipe cannot satisfy the requirement for high strength. Based on the cause, in the present invention, the Mo content is set to 0.2 to 0.5 wt%.

  Nb: Nb is an element of fine crystals and precipitation strengthening in steel, and compensates for a decrease in strength due to a reduction in the C content. When the Nb content is less than 0.02 wt%, the addition action is not clear. When the Nb content exceeds 0.04 wt%, coarse Nb (CN) is easily formed, and thus the toughness of the steel is lowered. Then, in the technical solution of the present invention, the Nb content is controlled to 0.02 to 0.04 wt%.

  Ti: Ti is an element that forms strong carbonitrides, can remarkably reduce austenite grains in steel, and compensates for a decrease in strength due to a reduction in C content. If the Ti content is> 0.05 wt%, coarse TiN is likely to be formed, which may reduce the toughness of the material. If the Ti content is less than 0.02 wt%, Ti cannot sufficiently react with N to form TiN, so that B in the steel may react with N to form a brittle phase of BN. Reduce toughness. In the ultra-high strength / ultra-tough oil well pipe of the present invention, it is necessary to control the Ti content to 0.02 to 0.05 wt%.

  B: B is an element that significantly improves the hardenability of steel. In steel types with low C content, B element can solve the problem of deterioration of hardenability due to reduction of C content. When the B content is less than 0.0015 wt%, the effect of improving the hardenability of the steel is not remarkable. If the B content exceeds 0.005 wt%, a BN brittle phase is likely to be formed, so that the toughness of the steel is reduced. Then, in the technical solution of the present invention, the B content is set to 0.0015 to 0.005 wt%.

  Al: Al element is a good deoxygenated solid nitrogen element, and can refine crystal grains. The content is preferably 0.01 to 0.05% by weight percentage.

  Ca: Ca is an element that purifies the steel liquid, can promote MnS spheroidization, and can improve the impact toughness of the steel material. However, if the Ca content is too high, coarse non-metallic foreign matter tends to be formed in the steel. Then, in the technical solution of the present invention, the Ca content is controlled to 0.0005 to 0.005 wt%.

N: In this technical scheme, it is preferable to make the content of N element as small as possible.
At the same time, in order to avoid that the toughness index of the steel material is lowered due to B and N forming a BN brittle phase, and to ensure that Ti and N are sufficiently bonded, Ti, B and N Needs to satisfy the following formula.

0 <(Ti-3.4N) ≦ 0.02%; and Ti / B ≧ 10.
Moreover, the ultra-high strength / ultra-tough oil well pipe of the present invention further contains a V element. The V element range is 0 <V ≦ 0.1 wt%.

  V element can make crystal grains in steel finer. The carbide formed with the element can greatly improve the strength of the steel. However, the enhancement effect is not clear when the amount of V element added becomes constant. If it does so, with respect to the technical solution of this invention, if V element is added, the addition amount will be <= 0.10 wt%.

  Furthermore, the microstructure in the ultra-high strength and ultra-tough oil well pipe of the present invention is tempered sorbite.

  The microstructure in the steel is tempered sorbite so that the wellbore acquires a good toughness formulation. The seed microstructure has the highest toughness. The seed microstructure is converted from a martensite structure. The more martensite structures formed after quenching the steel material, the more tempered sorbite structures obtained thereafter.

  Branch crystals are segregated during the setting process of the steel tube dough, and a large amount of segregation zones exist in the rolled tube. Since the segregation zone is rich in alloy elements such as C, Mn, Cr and Mo and the distribution of alloy components is uneven in the local area, the carbides formed in the segregation zone are many and coarse. At the same time, the hardness and strength of the steel in the segregation zone is higher, so its toughness is lower. In order to reduce the component segregation of the oil country tubular goods, means for reducing alloy elements such as C, Mn, Cr and Mo may be used. On the other hand, the microstructure of the steel material is tempered sorbite in order for the oil well pipe to obtain a good toughness blend. The seed microstructure has the highest toughness. The seed microstructure is converted from a martensite structure. The more martensite structures formed after quenching the steel material, the more tempered sorbite structures obtained thereafter. In this case, improving the hardenability and obtaining a larger martensite structure is a key point for guaranteeing the toughness of the material. Adopting measures to acquire low segregation structure by reducing alloy elements such as C, Mn, Cr and Mo and improve the toughness of steel should reduce the hardenability of steel, and toughness of steel Is further reduced. Based on this content, high strength and high toughness steel grades need to reasonably balance steel segregation and hardenability. The technical solution of the present invention adopts a low-carbon and low-alloy component system to obtain a low segregation microstructure, and further adds B and Ti to improve hardenability and increase steel toughness. And ensure uniform tempering sorbite.

  Correspondingly, the present invention further provides a method for producing an ultra-high strength and ultra-tough oil well pipe. The method includes a refining process, a continuous casting process, a piercing process, a rolling process, a sizing process, and a heat treatment process.

  Furthermore, in the continuous casting step of the production method of the ultra-high strength / ultra-tough oil well pipe of the present invention, the superheat degree of the molten steel is made less than 30 ° C., and the pulling speed of continuous casting is set to 1.8 to 2.2 m / min.

  The reason for controlling the pulling speed of continuous casting to 1.8 to 2.2 m / min is to reduce component segregation in the steel.

  Preferably, in the method for producing an ultra-high strength / ultra-tough oil country tubular good of the present invention, in the drilling step, the round billet obtained in the continuous casting step is uniformly heated in a furnace at 1200 to 1240 ° C. The drilling temperature is 1180-1240 ° C.

  More preferably, in the manufacturing method of the ultra-high strength / ultra-tough oil well pipe of the present invention, the final rolling temperature is set to 900 to 950 ° C. in the rolling step.

  More preferably, in the method for manufacturing an ultra-high strength / ultra-tough oil country tubular good according to the present invention, the sizing temperature is 850 to 900 ° C. in the sizing step.

  More preferably, in the method for producing an ultra-high strength / ultra-tough oil country tubular good according to the present invention, in the heat treatment step, the austenitizing temperature is set to 900 to 930 ° C., and after quenching for 30 to 60 minutes, 450 to 550 is performed. Tempering is performed at a temperature of 50 to 80 minutes, and finally heat sizing is performed at a temperature of 400 to 550 ° C.

  A lower tempering temperature was used to allow the steel to gain higher temperatures, thus improving toughness and significantly reducing the cost of alloy addition.

  The ultra-high strength and ultra-high toughness oil well pipe of the present invention is a steel grade of 150 ksi or more, and is used for manufacturing an oil well pipe having ultra-high strength and ultra-high toughness.

  The 150 ksi steel grade oil well pipe obtained from the ultra-high strength / high toughness oil well pipe of the present invention has a yield strength of 1034 to 1241 MPa, a tensile strength ≧ 1103 MPa, and an elongation of 20% to 30%. Yes, the 0 ° transverse Charpy impact is 10% or more (≧ 120 J) of the yield strength of the 150 ksi steel grade, and the tough / brittle transition temperature is −70 ° C. or less.

  The 155 ksi steel grade oil well pipe obtained with the ultra high strength / high toughness oil well pipe of the present invention has a yield strength of 1069 to 1276 MPa, a tensile strength ≧ 1138 MPa, and an elongation of 20% to 25%. Yes, the 0 ° transverse Charpy impact is 10% or more (≧ 120 J) of the yield strength of the 155 ksi steel grade, and the tough / brittle transition temperature is −60 ° C. or less.

  The ultra-high strength and ultra-tough oil well pipe of the present invention increases the hardenability of steel by adding B. Therefore, by replacing alloy elements such as Cr and Mo added to ordinary steel grade, The alloy addition cost is reduced, the strength is high, and the toughness is good.

  The manufacturing method of the ultra-high strength / ultra-tough oil well pipe of the present invention has made it possible to obtain higher strength and better toughness of the steel material by controlling the heat treatment process. The process operation is simple and it is easy to realize large-scale production manufacturing, so it has good economic benefits.

The metal structure of the ultra-high strength / ultra-tough oil well pipe in Example A5 is shown. The precipitation phase morphology of the ultra-high strength and ultra-tough oil well pipe in Example A5 was shown. The metal structure of the oil well pipe in Comparative Example B1 is shown. The precipitation phase form of the oil well pipe in Comparative Example B2 was shown. The precipitation phase form of the oil well pipe in Comparative Example B3 was shown.

  Hereinafter, the ultra-high strength / ultra-tough oil well pipe of the present invention and the manufacturing method thereof will be further described based on specific examples. However, specific embodiments and related descriptions are not unduly limited to the technical solutions of the present invention.

Example A1-A5 and Comparative Examples B1-B4
The oil well pipe of Example A1-A5 and Comparative Example B1-B4 was manufactured as the following process.

  1) Refining: The composition of mass percentage of each chemical element in Examples A1-A5 and Comparative Examples B1-B4 was controlled as shown in Table 1.

  2) Continuous casting: A tube material was formed by continuous casting, the superheat degree of the molten steel was set to less than 30 ° C, and the pulling speed of continuous casting was set to 1.8 to 2.2 m / min.

  3) Drilling: The round billet obtained in the continuous casting process was uniformly heated in a ring furnace at 1200 to 1240 ° C., so that the drilling temperature was 1180 to 1240 ° C.

4) Rolling: The final rolling temperature was 900 to 950 ° C.
5) Sizing: The sizing temperature was 850 to 900 ° C.

  6) Heat treatment: Austenitizing temperature is 900 to 930 ° C, quenching is performed after incubation for 30 to 60 minutes, tempering is performed at 450 to 550 ° C, incubation time is set to 50 to 80 minutes, and finally heat sizing is performed at 400 to 550 ° C. Went.

  Table 1 listed the mass percentage formulations for each chemical element in Example A1-A5 and Comparative Examples B1-B4.

  Table 2 lists the parameters of each step of Example A1-A5 and Comparative Example B1-B4.

  Table 3 shows the mechanical performance of the oil well pipes in Examples A1-A5 and Comparative Examples B1-B4.

  As can be seen from Table 3, all of the oil well pipes in Examples A1-A5 had a yield strength of ≧ 1050 Mpa (achieved a strength of 150 ksi grade or higher), a tensile strength of ≧ 1090 Mpa, and 0 ° lateral impact. Gong was ≧ 128 J, the elongation was ≧ 23%, and the tough / brittle transition temperature was ≦ −60 ° C. That is, since all of the oil well pipes in Examples A1-A5 had ultra high strength and ultra high toughness, they are suitable for manufacturing oil well pipes for mining Fukai and ultra deep wells. On the other hand, Mn and Cr in Comparative Example B1 exceeded the range limited to the technical solution of the present invention, B and Ti were not added in Comparative Example B2, and C in Comparative Example B3, Mn, Cr and Mo exceeded the range limited to the technical solution of the present invention, and Ti and N elements in Comparative Example B4 were 0 <(Ti-3.4N) ≦ 0.02%, Ti / Since the condition of B ≧ 10 was sometimes not satisfied, the mechanical performance of at least one term of the oil well pipe in Comparative Examples B1-B4 did not achieve the standard of the high strength and high toughness well pipe.

  FIG. 1 shows the metal structure of the ultra-high strength / ultra-tough oil well pipe in Example A5, and FIG. 2 shows the precipitated phase morphology of the ultra-high strength / ultra-tough oil well pipe in Example A5.

  As shown in FIG. 1, no band-like structure formed by component segregation in the metal structure of the oil well pipe in Example A5 has been found. As shown in FIG. 2, the carbide of the precipitated phase of the oil well pipe in Example A5 is fine and the distribution thereof is uniform. Then, the ultra-high strength / ultra-tough oil well pipe in Example A5 had a strength of 150 ksi steel grade or higher, and its 0 ° lateral impact toughness was 120 J or higher.

FIG. 3 shows the metal structure of the oil well pipe in Comparative Example B1.
Since the contents of C and Mn in Comparative Example B1 were lower, the hardenability of the steel was lowered. As shown in FIG. 3, since more ferrite structure exists in the metal structure of Comparative Example B1, the strength of the oil well pipe after heat treatment is insufficient, and the 0 ° lateral impact effect is not high. If it does so, it cannot adapt to processing into a super high strength and super high toughness oil well pipe.

  FIG. 4 shows the precipitated phase morphology of the oil well pipe in Comparative Example B2, and FIG. 5 shows the precipitated phase morphology of the oil well pipe in Comparative Example B3.

  Since a large amount of segregation zones exist in the tube after rolling due to branching segregation during the tube dough condensation process, as shown in FIG. 4, the segregation zones of Comparative Example B2, such as C, Mn, Cr, and Mo Since the alloy elements are concentrated and the distribution of the alloy components is uneven in the local area, the carbides formed in the segregation zone are many and coarse.

  As shown in FIG. 5, since the alloy elements such as C, Cr, and Mo in Comparative Example B3 exceeded the range limited to the technical solution of the present invention, segregation of the oil well pipe after the heat treatment became severe. When segregation became severe, the toughness of the oil well pipe became insufficient and the toughness index of steel was lowered.

  It should be noted that the above are only specific embodiments of the present invention. The present invention is not limited to the embodiments described above, and there are many similar variations. Variations obtained directly or associable by those skilled in the art directly from the disclosed contents of the present invention also belong to the protection scope of the present invention.

Claims (9)

In terms of mass percentage of chemical elements, C: 0.12 to 0.18%, Si: 0.1 to 0.4%, Mn: 1.1 to 1.6%, Cr: 0.1 to 0.4 %, Mo: 0.2-0.5%, Nb: 0.02-0.04%, Ti: 0.02-0.05%, B: 0.0015-0.005%, Al: 0.0. 01 to 0.05%, Ca: 0.0005 to 0.005%, N ≦ 0.008%, and 0 <(Ti-3.4N) ≦ 0.02%, Ti / B ≧ 10 satisfied, Ri balance Fe and other inevitable impurities der,
Its microstructure is tempered sorbite,
Its yield strength is 1034 to 1241 MPa, tensile strength is 1103 MPa or more, elongation is 20% to 30%, 0 ° transverse Charpy impact is 120 J or more, and tough and brittle transition temperature is −70 ° C. or less. Ultra-high strength and ultra-tough oil well pipe characterized by In terms of mass percentage of chemical elements, C: 0.12 to 0.18%, Si: 0.1 to 0.4%, Mn: 1.1 to 1.6%, Cr: 0.1 to 0.4 %, Mo: 0.2-0.5%, Nb: 0.02-0.04%, Ti: 0.02-0.05%, B: 0.0015-0.005%, Al: 0.0. 01 to 0.05%, Ca: 0.0005 to 0.005%, N ≦ 0.008%, and 0 <(Ti-3.4N) ≦ 0.02%, Ti / B ≧ 10 Satisfied, the balance is Fe and other inevitable impurities,
Its microstructure is tempered sorbite,
The yield strength is 1069 to 1276 MPa, the tensile strength is 1138 MPa or more, the elongation is 20% to 25%, the 0 ° transverse Charpy impact is 120 J or more, and the tough brittle transition temperature is −60 ° C. ultra high strength and ultra high-toughness OCTG you equal to or less than. The ultra-high strength and ultra-tough oil well pipe according to claim 1 or 2 , further comprising an element V in a range of 0 <V ≦ 0.1 wt%. Refining process, step continuous casting, perforation step, rolling step, the sizing method of manufacturing an ultra-high strength, ultra high-toughness OCTG according to any one of claims 1 to 3, characterized in that it comprises a heat treatment step. The super high strength and super strength according to claim 4 , wherein in the continuous casting step, the superheat degree of the molten steel is set to less than 30 ° C, and the pulling speed of the continuous casting is set to 1.8 to 2.2 m / min. A method for producing a tough oil well pipe. 5. The drilling process according to claim 4 , wherein the round billet obtained in the continuous casting process is uniformly heated in a furnace at 1200 to 1240 ° C. to set the drilling temperature to 1180 to 1240 ° C. 5. Manufacturing method of ultra-high strength and ultra-tough oil well pipe. The method for producing an ultra-high strength and ultra-tough oil well pipe according to claim 4 , wherein a final rolling temperature is set to 900 to 950 ° C in the rolling step. 5. The method for producing an ultrahigh strength / ultra high toughness well pipe according to claim 4 , wherein a sizing temperature is 850 to 900 ° C. in the sizing step. In the heat treatment step, the austenitizing temperature is set to 900 to 930 ° C., quenched after holding for 30 to 60 min, tempered at 450 to 550 ° C., set to 50 to 80 min, and finally heated at 400 to 550 ° C. Sizing is performed, The manufacturing method of the ultra-high-strength and ultra-tough oil well pipe of Claim 4 .

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