An ultra-high strength and high ductility oil casing and a manufacturing method thereof

Abstract

The application discloses a kind of superhigh strength high plasticity petroleum casing, it contains Fe and inevitable impurity, it also contains the following each chemical element with mass percentage content as follows: C:0.1-0.2%, Si:0.5-0.8%, Mn:1.9-2.8%, Cr:0.6-1.5%, Mo:0.4-0.8%, V:0.10-0.20%, Ni:0.3-0.7%, Ca:0.0005-0.005%, Al:0.01-0.05%, Nb:0.02-0.04%.The application also discloses a kind of superhigh strength high plasticity petroleum casing manufacturing method, it includes the following steps: smelting and continuous casting, to obtain round billet;Perforation;Rolling: control finish rolling temperature is 920~980 ℃;Two-phase region quenching+tempering heat treatment;Wherein steel pipe is heated to austenitizing temperature Ac3-(10~30) ℃, after 30-60min water quenching;Then tempering.Heat straightening.

Description

Technical Field

[0001] This invention relates to a type of steel and a method for manufacturing the same, and more particularly to an oil casing and a method for manufacturing the same. Background Technology

[0002] The working environment in ultra-deep wells is complex, with high temperature and pressure, and some blocks contain thick, high-pressure salt layers (high-pressure formations). These exert complex forces of tension, compression, bending, and torsion on the casing, making it highly susceptible to failure. The casing deforms differently under varying formation stresses. Some fractures occur due to necking under axial tension, while others result in shear deformation under shear forces. When the casing has high plasticity, it undergoes minor deformation but does not fracture, maintaining the integrity of the tubing string and allowing for normal operation. However, when the casing has low plasticity and fractures, normal production cannot proceed. Therefore, casing for deep and ultra-deep wells needs to possess both high strength and high plasticity.

[0003] Uniform elongation is an important indicator of plasticity, referring to the maximum percentage increase in length of a specimen before fracture in a tensile test. It is a crucial parameter for measuring a material's ability to undergo plastic deformation; a higher uniform elongation indicates better plasticity, meaning the material is more capable of uniform deformation under external forces and less prone to fracture.

[0004] Existing patent literature touches upon the aforementioned areas, but all are limited to the strength, toughness, or crush resistance of the casing, failing to study the uniform elongation rate of the casing. For example:

[0005] Chinese patent document with publication number CN103194693A and publication date July 10, 2013, entitled "A High-Strength and High-Toughness Oil Casing and Its Manufacturing Method", discloses a high-strength and high-toughness oil casing and its manufacturing method. It uses "high-frequency welding (HFW) + online heat treatment of weld + thermal tension reduction + full pipe heat treatment" technology to manufacture Q125 steel grade oil casing.

[0006] Chinese patent document CN102296239A, published on December 28, 2011, entitled "A High-Strength Anti-Crush Oil Casing Pipeline and Its Manufacturing Method," discloses a high-strength anti-crush oil casing pipeline and its manufacturing method. The outer diameter of the pipeline is [missing information]. The wall thickness of the tubing is 10.7 mm to 12.9 mm, and the uniform elongation is not mentioned.

[0007] Chinese patent document CN102747300A, published on October 24, 2012, entitled "A High-Strength and High-Toughness Seamless Steel Pipe for Structures and Its Manufacturing Method", discloses a high-strength and high-toughness seamless steel pipe for structures and its manufacturing method. The pipe has a yield strength of not less than 890 MPa, a tensile strength of not less than 960 MPa, an elongation of not less than 14%, a longitudinal impact energy of not less than 120 J at -20℃, and a longitudinal impact energy of not less than 75 J at -40℃. Furthermore, the welded area of ​​the seamless steel pipe has a longitudinal impact energy of not less than 55 J at -20℃ and a longitudinal impact energy of not less than 47 J at -40℃. Summary of the Invention

[0008] One of the objectives of this invention is to provide an ultra-high strength and high plasticity oil casing with high strength and uniform elongation, and to ensure the safety of the casing in the complex and harsh environment of ultra-deep wells by improving the strength and plasticity of the material.

[0009] To achieve the above objectives, the present invention provides an ultra-high strength and high plasticity oil casing, which contains Fe and unavoidable impurities, and also contains the following chemical elements in the following mass percentages:

[0010] C: 0.1-0.2%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.1 0-0.20%, Ni: 0.3-0.7%, Ca: 0.0005-0.005%, Al: 0.01-0.05%, Nb: 0.02-0.04%.

[0011] Furthermore, in the ultra-high strength and high plasticity oil casing described in this invention, the mass percentage content of each element is as follows:

[0012] C: 0.1-0.2%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.10-0.20%, Ni: 0.3-0.7%, Ca: 0.0005-0.005%, Al: 0.01-0.05%, Nb: 0.02-0.04%; balance Fe and other unavoidable impurities.

[0013] In this invention, an ultra-high strength, high-plasticity oil casing achieves a tempered sorbite + retained austenite microstructure through composition and heat treatment processes. During plastic deformation, the retained austenite undergoes the TRIP effect under stress, and a large amount of the stable gradient-distributed retained austenite transforms into hard martensite. The formation of martensite causes volume expansion, increasing the dislocation density in the tempered sorbite, enhancing the coordinated deformation ability between the phases, significantly improving the uniform elongation of the material, and enhancing the uniform deformation capability of the casing, thus preventing casing rupture.

[0014] Specifically, the design principles of each chemical element in the ultra-high strength and high plasticity oil casing of this invention are as follows:

[0015] C: In the ultra-high strength and high plasticity oil casing of this invention, element C is a precipitate-forming element that can improve the strength of the steel. When the mass percentage of element C is too low, the hardenability of the steel will decrease, making it difficult to simultaneously ensure high strength. When the mass percentage of element C is too high, element C will also form a large number of coarsened precipitates with elements Cr and Mo, and significantly aggravate the segregation of the steel, resulting in a significant decrease in plasticity and toughness. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage of element C is controlled between 0.1% and 0.2%.

[0016] Si: In the ultra-high strength and high plasticity oil casing of this invention, Si promotes the diffusion of carbon into austenite and inhibits the precipitation of cementite in austenite. It not only plays a role in solid solution strengthening but also promotes carbon enrichment in austenite, improving the stability of retained austenite. However, the mass percentage of Si in the steel should not be too high, as excessive Si will deteriorate the workability and toughness of the steel; when the mass percentage of Si is too low, the effect of improving the stability of retained austenite is not significant. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage of Si is controlled between 0.5% and 0.8%.

[0017] Mn: In the ultra-high strength and high plasticity oil casing of this invention, Mn is an austenite-forming element that can stabilize austenite in steel, slow down the ferrite transformation rate, reduce carbon diffusion from ferrite to austenite, and increase the amount of retained austenite, which is beneficial to improving the uniform elongation of the material. To achieve the desired microstructure control, the Mn content needs to be controlled above 1.9%. However, when the mass percentage of Mn is too high, it will significantly increase microstructure segregation in the steel, affecting the uniformity and impact performance of the hot-rolled microstructure. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage of Mn is controlled between 1.9% and 2.8%.

[0018] Cr: In the ultra-high strength and high plasticity oil casing described in this invention, Cr is an element that strongly improves hardenability and is also a strong precipitate-forming element. During tempering, it can precipitate precipitates, increasing the strength of the steel. However, when the mass percentage of Cr is too high, coarse precipitates (M-type precipitates) are easily formed at the grain boundaries. 23 C6 precipitates reduce toughness; when the mass percentage of Cr is too low, hardenability is poor, and sufficient toughness cannot be guaranteed. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage of Cr is controlled between 0.6% and 1.5%.

[0019] Mo: In the ultra-high strength and high plasticity oil casing of this invention, Mo mainly improves the strength and tempering stability of the steel through precipitates and solid solution strengthening. In this invention, the carbon content is relatively low. When the mass percentage of Mo is too high, it has little effect on improving the steel strength, easily leading to alloy waste; when the mass percentage of Mo is too low, the strength is difficult to reach the 140ksi steel grade. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage of Mo is controlled between 0.4% and 0.8%.

[0020] V: In the ultra-high strength and high plasticity oil casing described in this invention, vanadium (V) is a typical precipitation strengthening element that can compensate for the decrease in strength caused by the reduction in carbon content. When the mass percentage of V is too high, coarse V(CN) atoms are easily formed, thereby reducing toughness. Therefore, in the ultra-high strength and high plasticity oil casing described in this invention, the mass percentage of V is controlled between 0.10% and 0.20%.

[0021] Ni: In the ultra-high strength and high plasticity oil casing of this invention, Ni can promote the formation of austenite structure, ensuring the presence of residual austenite in the rolled steel, which is beneficial for improving the uniform elongation of the material and enhancing its impact toughness. However, when the mass percentage of Ni is higher than 0.7%, the cost is high and the effect of increasing the austenite ratio is not significant; when the mass percentage of Ni is lower than 0.3%, it cannot effectively increase the proportion of residual austenite. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage of Ni is controlled between 0.3% and 0.7%.

[0022] In the ultra-high strength and high plasticity oil casing of this invention, Ca can purify molten steel and promote MnS spheroidization, thereby improving impact toughness. However, when the mass percentage content of Ca is too high, it easily forms coarse non-metallic inclusions. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage content of Ca is controlled between 0.0005% and 0.005%.

[0023] Al: In the ultra-high strength and high plasticity oil casing of this invention, Al is a traditional deoxidizing and nitrogen-fixing element that can refine grains. Considering that it will reduce the yield strength ratio of the material, the Al content should not be too high. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage content of Al is controlled between 0.01% and 0.05%.

[0024] Nb: In the ultra-high strength and high plasticity oil casing of this invention, Nb is a grain-refining and precipitation-strengthening element that can compensate for the decrease in strength caused by the reduction in carbon content. When the mass percentage of Nb is higher than 0.04%, coarse Nb(CN) is easily formed, thereby reducing toughness. When the mass percentage of Nb is lower than 0.02%, the strengthening effect is not obvious. Therefore, in the ultra-high strength and high plasticity oil casing of this invention, the mass percentage of Nb is controlled between 0.02% and 0.04%.

[0025] Furthermore, in the unavoidable impurities of the ultra-high strength and high plasticity oil casing described in this invention: P≤0.015%, S≤0.005%.

[0026] In the above-described technical solution of the present invention, both P and S are harmful impurity elements. In order to obtain steel with better performance and higher quality, the content of P and S should be reduced as much as possible when the technology allows.

[0027] Furthermore, the microstructure of the ultra-high strength and high plasticity oil casing described in this invention is tempered sorbite + retained austenite.

[0028] Furthermore, in the ultra-high strength and high plasticity oil casing described in this invention, the area percentage of retained austenite is 6-12%.

[0029] Furthermore, the performance of the ultra-high strength and high plasticity oil casing described in this invention meets the following requirements: yield strength of 965-1170 MPa, tensile strength ≥1034 MPa, uniform elongation ≥12%, and transverse Charpy impact energy at 0℃ ≥80 J.

[0030] Another objective of this invention is to provide a method for manufacturing ultra-high strength and high plasticity oil casing, which is simple in process and easy to implement for mass production.

[0031] To achieve the above objectives, the present invention provides a method for manufacturing ultra-high strength and high plasticity oil casing, comprising the following steps:

[0032] Smelting and continuous casting to obtain round billets;

[0033] perforation;

[0034] Rolling: Control the final rolling temperature to 920–980℃;

[0035] Two-phase quenching and tempering heat treatment; wherein the steel pipe is heated to the austenitizing temperature Ac3-(10~30)℃, held for 30-60min and then water quenched; then tempered.

[0036] Thermal straightening.

[0037] In this invention, the austenitizing temperature is limited to Ac3-(10~30)℃ to obtain a final tempered sorbite and retained austenitic ferrite multiphase structure, thereby ensuring the proportion of each microstructure in the steel and improving the work hardening index. It should be noted that in step (4), Ac3 = 910-203 [C]. 1 / 2 -15.2[Ni]+44.7[Si]+104[V]+31.5[Mo]+13.1[W], where C, Ni, Si, V, Mo and W represent their respective mass percentages, and the values ​​substituted into the above limiting formula should include the values ​​before the percentage sign.

[0038] Furthermore, in the smelting and continuous casting steps of the manufacturing method described in this invention, the continuous casting speed is controlled to be 1.8 to 2.4 m / min.

[0039] Furthermore, in the piercing step of the manufacturing method described in this invention, the round blank is homogenized at 1220-1270°C, and then pierced at a piercing temperature of 1150-1210°C.

[0040] Furthermore, in the rolling step of the manufacturing method described in this invention, the sizing temperature is 800–880°C.

[0041] Furthermore, in the tempering step of the manufacturing method described in this invention, the tempering temperature is controlled at 550–630°C, and the holding time is 60–90 min.

[0042] The ultra-high strength and high plasticity oil casing and its manufacturing method described in this invention have the following advantages and beneficial effects:

[0043] The ultra-high strength and high plasticity oil casing of this invention, through reasonable composition design, achieves high strength, uniform elongation, and low cost, thereby solving the problem of poor plasticity in existing high-strength casings and improving the safe service capability of the casing in downhole applications.

[0044] In some embodiments, the ultra-high strength and high plasticity oil casing of the present invention has a yield strength of 965-1170 MPa, a tensile strength of ≥1034 MPa, a uniform elongation of ≥12%, and a transverse Charpy impact energy of ≥80 J at 0℃.

[0045] The manufacturing method of the ultra-high strength and high plasticity oil casing described in this invention is simple and easy to implement for mass production. Detailed Implementation

[0046] The ultra-high strength and high plasticity oil casing and its manufacturing method described in this invention will be further explained and described below with reference to specific embodiments. However, this explanation and description do not constitute an improper limitation on the technical solution of this invention.

[0047] Examples 1-5 and Comparative Examples 1-8

[0048] The ultra-high strength and high plasticity oil casings of Examples 1-5 and the control pipes of Comparative Examples 1-8 of this invention were all prepared using the following steps:

[0049] (1) Smelting and continuous casting to obtain round billets;

[0050] (2) Perforation;

[0051] (3) Rolling: Control the final rolling temperature to 920~980℃;

[0052] (4) Two-phase quenching + tempering heat treatment; wherein the steel pipe is heated to the austenitizing temperature Ac3-(10~30)℃, held for 30-60min and then water quenched; then tempered.

[0053] (5) Thermal straightening.

[0054] It should be noted that the chemical element composition and related process design of the ultra-high strength and high plasticity oil casings in Examples 1-5 of this invention all meet the design specifications of this invention. However, the chemical element content of the control tubes in Comparative Examples 1-6 does not conform to the design of this invention, and the process parameters of Comparative Examples 7-8 do not conform to the design of this invention.

[0055] Table 1 lists the mass percentage of each chemical element in the ultra-high strength and high plasticity oil casing of Examples 1-5 of the present invention and the control pipes of Comparative Examples 1-8.

[0056] Table 1. (wt%, balance Fe and other unavoidable impurities besides P and S)

[0057] serial number C Si Mn Cr Mo V Ni Ca Al Nb P S Example 1 0.1 0.6 2.2 0.6 0.4 0.10 0.3 0.0005 0.01 0.040 0.008 0.003 Example 2 0.12 0.5 1.9 0.9 0.5 0.18 0.2 0.0008 0.02 0.020 0.010 0.001 Example 3 0.16 0.8 2.5 1.0 0.6 0.15 0.6 0.0012 0.03 0.030 0.011 0.002 Example 4 0.18 0.7 2.8 1.2 0.7 0.12 0.7 0.0030 0.04 0.025 0.012 0.005 Example 5 0.20 0.6 2.4 1.5 0.8 0.20 0.5 0.0050 0.05 0.035 0.015 0.002 Comparative Example 1 0.10 0.6 1.4 0.6 0.4 0.10 0.3 0.0005 0.01 0.040 0.008 0.003 Comparative Example 2 0.10 0.6 3.5 0.6 0.4 0.10 0.3 0.0005 0.01 0.040 0.008 0.003 Comparative Example 3 0.05 0.1 2.5 1.0 0.6 0.15 0.6 0.0012 0.03 0.030 0.011 0.002 Comparative Example 4 0.25 1.2 2.5 1.0 0.6 0.15 0.6 0.0012 0.03 0.030 0.011 0.002 Comparative Example 5 0.12 0.5 1.9 0.4 0.5 0.18 0.1 0.0008 0.02 0.020 0.010 0.001 Comparative Example 6 0.12 0.5 1.9 2 0.5 0.18 0.9 0.0008 0.02 0.020 0.010 0.001 Comparative Example 7 0.16 0.8 2.5 1.0 0.6 0.15 0.6 0.0012 0.03 0.030 0.011 0.002 Comparative Example 8 0.16 0.8 2.5 1.0 0.6 0.15 0.6 0.0012 0.03 0.030 0.011 0.002

[0058] Table 2 lists the specific process parameters of the ultra-high strength and high plasticity oil casing of Examples 1-5 and the comparative pipes of Comparative Examples 1-8 of the present invention.

[0059] Table 2.

[0060]

[0061]

[0062] Samples were taken from the ultra-high strength and high plasticity oil casings of Examples 1-5 of the present invention and the control tubes of Comparative Examples 1-8. After polishing, the microstructure of the samples was observed by scanning electron microscopy, and the test results are listed in Table 3.

[0063] Table 3 lists the microstructure test results of the ultra-high strength and high plasticity oil casings of Examples 1-5 of the present invention and the control pipes of Comparative Examples 1-8.

[0064] Table 3.

[0065] serial number Microorganism Residual austenite area percentage (%) Example 1 Tempered sorbite + retained austenite 6 Example 2 Tempered sorbite + retained austenite 8 Example 3 Tempered sorbite + retained austenite 10 Example 4 Tempered sorbite + retained austenite 11 Example 5 Tempered sorbite + retained austenite 12 Comparative Example 1 Tempered sorbite + retained austenite 2 Comparative Example 2 Tempered sorbite + retained austenite 13 Comparative Example 3 Tempered sorbite + retained austenite 5 Comparative Example 4 Tempered sorbite + retained austenite 5 Comparative Example 5 Tempered sorbite + retained austenite 4 Comparative Example 6 Tempered sorbite + retained austenite 10 Comparative Example 7 Tempered sorbite + retained austenite 3 Comparative Example 8 Tempered sorbite + retained austenite 4

[0066] As can be seen from Table 3, the microstructure of the ultra-high strength and high plasticity oil casings of Examples 1-5 prepared by the present invention is tempered sorbite + retained austenite, wherein the area percentage of retained austenite is between 6-12%.

[0067] In addition, samples of the ultra-high strength and high plasticity oil casing from Examples 1-5 and the control casings from Comparative Examples 1-8 were taken again and their performance was tested. The test results are listed in Table 4. The relevant test procedures are as follows:

[0068] Mechanical property testing:

[0069] Tensile test: Tensile properties at room temperature are tested according to GB / T 228.1-2000 standard.

[0070] Impact test: The impact energy test at 0℃ was conducted according to GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method".

[0071] Table 4 lists the performance test results of the ultra-high strength and high plasticity oil casings of Examples 1-5 and the control casings of Comparative Examples 1-8.

[0072] Table 4.

[0073]

[0074] As can be seen from Table 4 above, the yield strength of the ultra-high strength and high plasticity oil casings of Examples 1-5 prepared by the present invention is between 965 and 1170 MPa, the tensile strength is greater than 1034 MPa, the uniform elongation is greater than or equal to 2%, and the transverse Charpy impact energy at 0℃ is greater than 80 J. They have high strength and uniform elongation, which can ensure the service safety of the casing in the complex and harsh environment of ultra-deep wells.

[0075] In the comparative examples, the mass percentage of Mn in Comparative Examples 1-2 exceeded the range defined in this invention; the mass percentage of C and Si in Comparative Examples 3-4 exceeded the range defined in this invention; the mass percentage of Ni and Cr in Comparative Examples 5-6 exceeded the range defined in this invention; and the heat treatment temperature of the two-phase region in Comparative Examples 7 and 8 exceeded the range defined in this invention. As a result, at least one mechanical property of the comparative sleeves in Comparative Examples 1-8 failed to meet the standard of high-strength and high-plasticity sleeves, and their overall performance was inferior to that of the sleeves in the various embodiments of this invention.

[0076] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0077] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A high-strength, high-plasticity oil casing, containing Fe and unavoidable impurities, characterized in that, It also contains the following chemical elements in the following percentages by mass: C: 0.1-0.2%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.1 0-0.20%, Ni: 0.3-0.7%, Ca: 0.0005-0.005%, Al: 0.01-0.05%, Nb: 0.02-0.04%.

2. The ultra-high strength, high plasticity oil casing as described in claim 1, characterized in that, Its elemental mass percentage content is as follows: C: 0.1-0.2%, Si: 0.5-0.8%, Mn: 1.9-2.8%, Cr: 0.6-1.5%, Mo: 0.4-0.8%, V: 0.10-0.20%, Ni: 0.3-0.7%, Ca: 0.0005-0.005%, Al: 0.01-0.05%, Nb: 0.02-0.04%; balance Fe and other unavoidable impurities.

3. The ultra-high strength, high plasticity oil casing as described in claim 1 or 2, characterized in that, In unavoidable impurities: P ≤ 0.015%, S ≤ 0.005%.

4. The ultra-high strength, high plasticity oil casing as described in claim 1 or 2, characterized in that, Its microstructure consists of tempered sorbite and retained austenite.

5. The ultra-high strength, high plasticity oil casing as described in claim 4, characterized in that, The area percentage of retained austenite is 6-12%.

6. The ultra-high strength, high plasticity oil casing as described in claim 1 or 2, characterized in that, Its performance meets the following requirements: yield strength of 965~1170MPa, tensile strength ≥1034MPa, uniform elongation ≥12%, and transverse Charpy impact energy at 0℃ ≥80J.

7. The method for manufacturing ultra-high strength and high plasticity oil casing as described in any one of claims 1-6, characterized in that, It includes the following steps: Smelting and continuous casting to obtain round billets; perforation; Rolling: Control the final rolling temperature to 920–980℃; Two-phase quenching and tempering heat treatment; wherein the steel pipe is heated to the austenitizing temperature Ac3-(10~30)℃, held for 30-60min and then water quenched; then tempered. Thermal straightening.

8. The manufacturing method as described in claim 7, characterized in that, During the smelting and continuous casting steps, the continuous casting speed is controlled at 1.8–2.4 m / min.

9. The manufacturing method as described in claim 7, characterized in that, In the piercing step, the round blank is homogenized at 1220-1270℃, and then pierced at 1150-1210℃.

10. The manufacturing method as described in claim 7, characterized in that, During the rolling process, the sizing temperature is 800–880℃.

11. The manufacturing method as described in claim 7, characterized in that, During the tempering process, the tempering temperature is controlled at 550–630℃, and the holding time is 60–90 min.

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