Low-cost, high-toughness, non-quenched and tempered n80 oil well pipe and manufacturing method therefor

Abstract

Disclosed in the present invention is a low-cost, high-toughness, non-quenched and tempered N80 oil well pipe. In addition to Fe and inevitable impurities, the oil well pipe also contains the following chemical elements, in percentage by mass: C: 0.35-0.45%, Si: 0.10-0.35%, Mn: 1.6-1.8%, Ti: 0.02-0.25%, and V≤0.05%. Further disclosed in the present invention is a manufacturing method for the oil well pipe, comprising the steps of: performing smelting and continuous casting to obtain a pipe blank; performing heating, perforation and continuous rolling on the pipe blank; performing online water cooling to 450-550°C; air cooling: controlling an air cooling rate to 30-50°C / min; reheating: controlling a reheating temperature Treheating to 880-950°C and holding time t to 20-40 min; and stretch reducing. By optimizing the alloy design, and using a low-cost element Ti for microalloying, the oil well pipe manufactured by the method can meet product performance requirements without the need for quenching and tempering heat treatment.

Description

A low-cost, high-toughness, non-tempered N80 oil well tubing and its manufacturing method Technical Field

[0001] This invention relates to a steel pipe and its manufacturing method, and more particularly to an oil well pipe and its manufacturing method. Background Technology

[0002] Non-conditioned N80 oil well tubing is delivered in rolled condition, which involves fewer processes and lower energy consumption, making it one of the most widely used products in oil and gas wells.

[0003] However, on the one hand, with the continuous development of the petroleum industry, higher requirements have been placed on the cost control of N80 oil well tubing. On the other hand, the product performance of N80 oil well tubing is difficult to control stably, especially the impact toughness, which is often lower than the standard requirements (0℃ full-size longitudinal impact energy ≥27J, 3 / 4-size impact energy ≥22J, 1 / 2-size impact energy ≥15J).

[0004] Currently, N80 seamless oil well tubing generally adopts a V alloying design, such as 36Mn2V, 36Mn2VN, and 40Mn2V, which exerts a strengthening effect through a large number of carbon and nitrogen dispersed precipitates of V and micro-alloying strengthening elements.

[0005] For example, Chinese patent document CN109136786A, published on January 4, 2019, entitled "Non-quenched and tempered N80 grade oil casing and its preparation method," discloses a non-quenched and tempered N80 grade oil casing and its preparation method. The chemical composition is: C: 0.28–0.32%, Si: 0.25–0.40%, Mn: 1.55–1.70%, P ≤ 0.015%, S ≤ 0.008%, Nb: 0.011–0.020%, V: 0.05–0. The alloy composition is as follows: 0.08%, Ti: 0.007~0.013%, Al: 0.010~0.040%, N: 0.013~0.017%, Cr<0.10%, Ni≤0.10%, Cu≤0.10%, As≤0.020%, Sn≤0.020%, Pb≤0.01%, Sb≤0.01%, Bi≤0.01%, and Sn+As+Pb+Sb+Bi≤0.035%, with the balance being Fe. It is strengthened by adding multiple alloying elements and microalloying.

[0006] For example, Chinese patent document CN109609850A, published on April 12, 2019, entitled "A High-Strength Oil Pipe and its Preparation Method," discloses a high-strength oil pipe and its preparation method. Its chemical composition is C: 0.35-0.39%, Si: 0.25-0.55%, Mn: 1.45-1.65%, P: ≤0.012%, S: ≤0.005%, Al: 0.01-0.04%, Cr: 0.2-0.4%, Ti: 0.005-0.02%, Nb: 0.015-0.04%, V: 0.02-0.055%, N: 0.013-0.017%, Ca: 0.0005-0.005%, with the balance being Fe and unavoidable impurities. The longitudinal full-size impact energy at 0℃ is ≥33J.

[0007] However, these oil well pipes are more expensive because they use more alloying elements. Summary of the Invention

[0008] One of the objectives of this invention is to provide a low-cost, high-toughness untreated N80 oil well tubing. This low-cost, high-toughness untreated N80 oil well tubing achieves high toughness through optimized alloy design and micro-alloying using low-cost Ti elements, without requiring heat treatment.

[0009] To achieve the above objectives, this invention proposes a low-cost, high-toughness, unconditioned N80 oil well tubing, which, in addition to Fe and unavoidable impurities, contains the following chemical elements in weight percentage:

[0010] C: 0.35~0.45%, Si: 0.10~0.35%, Mn: 1.60~1.80%, Ti: 0.02~0.25%, V≤0.05%.

[0011] Preferably, the low-cost, high-toughness, non-tempered N80 oil well tubing of the present invention contains the following chemical elements in weight percentage:

[0012] C: 0.35–0.45%, Si: 0.10–0.35%, Mn: 1.60–1.80%, Ti: 0.02–0.25%, V ≤ 0.05%; balance is Fe and unavoidable impurities.

[0013] In this invention, the commonly used alloying element V is not a necessary element, and its content can be zero. This invention controls the content of low-cost C, Si, and Mn elements, and combines them with Ti microalloying. The carbonitrides of Ti inhibit austenite growth, and the fine grain strengthening can improve both strength and impact energy. Moreover, Ti is relatively inexpensive, which helps to reduce costs, thereby obtaining a low-cost, high-toughness, non-quenched and tempered N80 oil well tubing.

[0014] Specifically, in the low-cost, high-toughness, non-tempered N80 oil well tubing described in this invention, the design principles of each chemical element are as follows:

[0015] C: In the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, carbon (C) is the main strengthening element, which can improve the strength of the steel. However, when the mass percentage of C is too high, it is detrimental to toughness and easily leads to the formation of abnormal structures. Therefore, in the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, the mass percentage of C is controlled between 0.35% and 0.45%.

[0016] Si: In the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, Si is a commonly used deoxidizer and has a strong solid solution strengthening effect on ferrite. Considering that soft-phase ferrite is beneficial to impact toughness, the mass percentage content of Si should not be too high. Therefore, in the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, the mass percentage content of Si is controlled between 0.10% and 0.35%.

[0017] Mn: In the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, Mn is one of the important alloying and strengthening elements, which can effectively improve hardenability and strength while maintaining low cost. However, when the mass percentage of Mn is too high, it tends to promote microstructure segregation. Therefore, in the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, the mass percentage of Mn is controlled between 1.60% and 1.80%.

[0018] Ti: In the low-cost, high-toughness, untreated N80 oil well tubing of this invention, Ti is the strongest carbide-forming element. Ti carbonitrides can significantly refine austenite grains, but when the mass percentage of Ti is too high, production control becomes difficult, and large-size precipitates can impair performance. Therefore, in the low-cost, high-toughness, untreated N80 oil well tubing of this invention, the mass percentage of Ti is controlled between 0.02% and 0.25%.

[0019] V: In the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, vanadium (V) is dissolved in austenite, which can improve the hardenability of the steel. Simultaneously, the dispersed vanadium carbonitride can refine the grains and improve performance, but its price is relatively high. Therefore, in the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, the mass percentage content of vanadium is controlled to V ≤ 0.05%.

[0020] Preferably, in the low-cost, high-toughness, unconditioned N80 oil well tubing of the present invention, unavoidable impurities include P and S, wherein: P≤0.015% and S≤0.004%.

[0021] In the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, the main impurities are phosphorus (P) and sulfur (S), and their contents should be as low as possible when conditions permit. In particular, P and S segregate significantly in steel, which is detrimental to plasticity and toughness. When the mass percentage of S is too high, it will generate MnS, which impairs low-temperature impact energy. Therefore, in the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention, the mass percentage of P can be controlled to P ≤ 0.015%, and the mass percentage of S can be controlled to S ≤ 0.004%.

[0022] Preferably, in the low-cost, high-toughness, non-tempered N80 oil well tubing of the present invention, the mass percentage content of chemical elements also satisfies the following:

[0023] Si+Mn+5Ti+30V<3.50%;

[0024] 2C + Mn + 10Ti > 2.80%.

[0025] In a preferred embodiment of the invention, in addition to C, the composition control further includes Si, Mn, Ti, and V. Ti and V (especially V) have relatively high costs, therefore the content of added element Si+Mn+5Ti+30V needs to be controlled to < 3.5% to reduce the alloy cost of the product. Simultaneously, N80 has certain strength performance requirements. In this design, C, Mn, and Ti (especially Ti) are key strengthening elements, and the content of 2C+Mn+10Ti needs to be controlled to > 2.8% to ensure that the performance meets the requirements.

[0026] Preferably, the microstructure of the low-cost, high-toughness untreated N80 oil well tubing of the present invention is ferrite + pearlite.

[0027] Preferably, in the low-cost, high-toughness unconditioned N80 oil well tubing of the present invention, the average size of pearlite is 15-25 μm.

[0028] Preferably, the low-cost, high-toughness, untreated N80 oil well tubing of the present invention has a grain size of 7.0 to 8.0.

[0029] Preferably, the yield strength of the low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of the present invention is 552–758 MPa, the tensile strength is ≥689 MPa, and the longitudinal Charpy impact energy at half-size (0°C) is ≥30 J. More preferably, the yield strength is ≥592 MPa and the tensile strength is ≥824 MPa.

[0030] Another objective of this invention is to provide a low-cost, high-toughness, non-quenched and tempered N80 oil well tubing manufacturing method. This manufacturing method employs a controlled rolling and controlled cooling process, which helps to reduce alloy costs and improve product performance.

[0031] To achieve the above objectives, the present invention provides a method for manufacturing low-cost, high-toughness, non-tempered N80 oil well tubing, comprising the following steps performed sequentially:

[0032] S1: Smelting and continuous casting to produce tube blanks;

[0033] S2: Heating, piercing, and continuous rolling of the tube blank;

[0034] S3: Perform online water cooling to cool the tube blank to 450-550℃;

[0035] S4: Air cooling: Control the air cooling rate to 30-50℃ / min;

[0036] S5: Reheating: Control the reheating temperature T 再加热 The temperature range is 880–950℃, and the holding time is 20–40 min.

[0037] S6: Perform tension reduction.

[0038] This invention employs a controlled rolling and cooling process, distinct from traditional methods, involving online controlled cooling including both water and air cooling after rolling and before the steel pipe enters the reheating furnace. This avoids quality issues such as overcooling and uneven cooling that often occur during post-rolling cooling. Furthermore, high-temperature post-rolling cooling prevents the formation of carbonitrides in large-sized Ti particles, thus better leveraging the grain-refining strengthening effect of Ti microalloying. In addition, this process promotes microstructure transformation, and subsequent reheating re-austenitizes the billet, further refining the microstructure. This allows for the production of low-cost N80 oil well tubing that meets performance requirements without adding excessive amounts of expensive microalloying elements.

[0039] Preferably, in step S2 of the manufacturing method of the present invention, the heating temperature is 1180-1250°C.

[0040] Preferably, in step S4 of the manufacturing method of the present invention, the air cooling time is 4 to 6 minutes.

[0041] Preferably, in step S5 of the manufacturing method of the present invention, the heat preservation time t also satisfies: t < (215 - 0.2 × T) 再加热 +0.1 / Ti), where Ti is replaced with the value before the percentage sign of its mass percentage content.

[0042] The low-cost, high-toughness, non-quenched and tempered N80 oil well tubing and its manufacturing method described in this invention have the following advantages and beneficial effects compared to the prior art:

[0043] The low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of this invention achieves product performance requirements through optimized alloy design and micro-alloying using low-cost Ti elements, without the need for quenching and tempering heat treatment.

[0044] In some embodiments, the low-cost, high-toughness, non-tempered N80 oil well tubing of the present invention has a yield strength of 552–758 MPa, a tensile strength ≥689 MPa, and a half-size longitudinal Charpy impact energy ≥30 J at 0°C.

[0045] The manufacturing method of low-cost, high-toughness, non-quenched and tempered N80 oil well tubing described in this invention adopts a different process from traditional controlled rolling and controlled cooling, which helps to reduce alloy costs, improve product performance, avoid quality problems, and ensure stable production. Attached Figure Description

[0046] Figure 1 shows a microstructure photograph of the low-cost, high-toughness, untreated N80 oil well tubing of Embodiment 1 of the present invention under an optical microscope.

[0047] Figure 2 shows a microscopic photograph of the control tube of Comparative Example 1 of the present invention under an optical microscope. Detailed Implementation

[0048] The following will further explain and illustrate the low-cost, high-toughness unconditioned N80 oil well tubing and its manufacturing method according to the present invention with reference to specific embodiments. However, this explanation and illustration do not constitute an undue limitation on the technical solution of the present invention.

[0049] Examples 1-8 and Comparative Examples 1-4

[0050] The low-cost, high-toughness, non-quenched and tempered N80 oil well tubing of Examples 1-8 of the present invention and the comparative steel tubing of Comparative Examples 1-4 were prepared by the following steps:

[0051] (1) Smelting: The steelmaking process is carried out by converter steelmaking, ladle refining and vacuum degassing.

[0052] (2) Continuous casting: Continuous casting is used to form billets, and the superheat of molten steel is controlled to be ≤35℃.

[0053] (3) Piercing and rolling: The continuous casting billet is heated to 1180~1250℃, and then pierced and rolled continuously.

[0054] (4) Online water cooling: The rolled rough tubes are water cooled online to 450-550℃.

[0055] (5) Air cooling: Air cooling rate is 30-50℃ / min, and air cooling time is 4-6min.

[0056] (6) Reheating: Reheating temperature T 再加热 Set the temperature to 880–950℃ and keep warm for 20–40 minutes.

[0057] In some embodiments, the heat preservation time t can be further satisfied within the above-mentioned range of 20 to 40 minutes, provided that: t < 215 - 0.2 × T 再加热 +0.1 / Ti, where Ti is the value before the percentage sign of its mass percentage content.

[0058] (7) Tension reduction: The inlet temperature of sizing is ≥850℃, and the cooling bed is rolled and air-cooled after sizing.

[0059] Table 1 lists the mass percentage of each chemical element in the low-cost, high-toughness unquenched and tempered N80 oil well tubing of Examples 1-8 of the present invention and the comparative steel tubing of Comparative Examples 1-4.

[0060] Table 1. (wt%, balance Fe and other unavoidable impurities besides P and S)

[0061] Table 2 lists the specific process parameters of the low-cost, high-toughness unquenched and tempered N80 oil well tubing of Examples 1-8 of the present invention and the comparative steel tubing of Comparative Examples 1-4.

[0062] Table 2.

[0063] It should be noted that in Table 2, the online water cooling temperature of Comparative Example 1 and Comparative Example 2 is "-", indicating that they do not perform online water cooling.

[0064] Samples were taken from the low-cost, high-toughness unquenched and tempered N80 oil well tubing of Examples 1-8 and the control steel tubing of Comparative Examples 1-4, and their microstructure was observed. The observation results are listed in Table 3. Among them:

[0065] Microstructure observation: Metallographic samples were taken, polished, etched with nitric acid and alcohol, and then microstructure was observed using a metallographic microscope;

[0066] Average pearlite size: Metallographic observation at 500×, several fields of view were taken for each sample to measure the pearlite size through a metallographic microscope, and the average value was calculated;

[0067] Grain size level: Referencing standard GB / T 6394-2017 "Method for determination of average grain size of metals", the intercept method is used for measurement, and the grain size level number G is calculated and determined.

[0068] Table 3 lists the microstructure observation results of the low-cost, high-toughness unquenched and tempered N80 oil well pipes of Examples 1-8 of the present invention and the comparative steel pipes of Comparative Examples 1-4.

[0069] Table 3.

[0070] As can be seen from Table 3 above, the microstructure of the low-cost, high-toughness untreated N80 oil well tubing of Examples 1-8 prepared by the method of the present invention is ferrite + pearlite, the average size of the pearlite is between 15 and 25 μm, and the grain size is between 7.0 and 8.0.

[0071] Figure 1 shows a microstructure photograph of the low-cost, high-toughness, untreated N80 oil well tubing of Embodiment 1 of the present invention under an optical microscope.

[0072] As shown in Figure 1, the microstructure of the low-cost, high-toughness, non-quenched and tempered N80 oil well pipe of Embodiment 1 of the present invention at room temperature is ferrite + pearlite. The structure is uniform, with many fine ferrite structures, and the pearlite size is between 15 and 25 μm.

[0073] Figure 2 shows a microscopic photograph of the control tube of Comparative Example 1 of the present invention under an optical microscope.

[0074] As shown in Figure 2, the microstructure of the control tube in Comparative Example 1 of the present invention is mostly bulk pearlite, with a pearlite size greater than 30 μm.

[0075] In addition, samples were taken again from the low-cost, high-toughness unquenched and tempered N80 oil well tubing of Examples 1-8 and the comparative steel tubing of Examples 1-4, and their mechanical properties were tested. The results are listed in Table 4.

[0076] Tensile properties: Take longitudinal arc-shaped tensile specimens and conduct room temperature tensile tests in accordance with standard GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Tensile testing at room temperature" to test yield strength and tensile strength;

[0077] Impact toughness: Take longitudinal V-shaped impact specimens and conduct 0℃ impact KV8 test according to standard GB / T 229-2020 "Metallic Materials Charpy Pendulum Impact Test Method".

[0078] Table 4 lists the mechanical property test results of the low-cost, high-toughness unquenched and tempered N80 oil well pipes of Examples 1-8 of the present invention and the comparative steel pipes of Comparative Examples 1-4.

[0079] Table 4.

[0080] As can be seen from Table 4 above, the yield strength of the low-cost, high-toughness, non-quenched and tempered N80 oil well pipes of Examples 1-8 prepared by the method of the present invention is between 592 and 693 MPa, the tensile strength is above 824 MPa, and the longitudinal Charpy impact energy at half size at 0℃ is greater than 30 J.

[0081] It should be noted that the scope of protection of the prior art in this invention is not limited to the embodiments given in this application. All prior art that does not contradict the solution of this invention, including but not limited to prior patent documents, prior publications, prior public uses, etc., can be included in the scope of protection of this invention.

[0082] Furthermore, 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.

[0083] 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 non-conditioned N80 oil well tubing, characterized in that, In addition to Fe and unavoidable impurities, the tube contains the following chemical elements in percentage by mass: C: 0.35~0.45%, Si: 0.10~0.35%, Mn: 1.60~1.80%, Ti: 0.02~0.25%, V≤0.05%.

2. The non-conditioned N80 oil well tubing as described in claim 1, characterized in that, The tube contains the following chemical elements in percentage by mass: C: 0.35–0.45%, Si: 0.10–0.35%, Mn: 1.60–1.80%, Ti: 0.02–0.25%, V ≤ 0.05%; balance is Fe and unavoidable impurities.

3. The non-conditioned N80 oil well tubing as described in claim 1 or 2, characterized in that, The unavoidable impurities include P and S, wherein P ≤ 0.015% and S ≤ 0.004%.

4. The non-conditioned N80 oil well tubing as described in claim 1 or 2, characterized in that, The mass percentage of chemical elements in the tube also satisfies the following conditions: Si+Mn+5Ti+30V < 3.50%; 2C+Mn+10Ti > 2.80%.

5. The non-conditioned N80 oil well tubing as described in claim 1 or 2, characterized in that, The microstructure of the tube is ferrite + pearlite.

6. The non-conditioned N80 oil well tubing as described in claim 5, characterized in that, The average size of pearlite is 15–25 μm.

7. The non-conditioned N80 oil well tubing as described in claim 1 or 2, characterized in that, The grain size of the tube is grade 7.0 to 8.

0.

8. The non-conditioned N80 oil well tubing as described in claim 1 or 2, characterized in that, The tube has a yield strength of 552–758 MPa, a tensile strength of ≥689 MPa, preferably ≥824 MPa, and a longitudinal Charpy impact energy of ≥30 J at half-size at 0°C.

9. A method for manufacturing non-conditioned N80 oil well tubing as described in any one of claims 1-8, characterized in that, The method includes the following steps performed sequentially: S1: Smelting and continuous casting to produce tube blanks; S2: Heating, piercing, and continuous rolling of the tube blank; S3: Perform online water cooling to cool the tube blank to 450-550℃; S4: Air cooling: Control the air cooling rate to 30-50℃ / min; S5: Reheating: Control the reheating temperature T 再加热 The temperature range is 880–950℃, and the holding time is 20–40 min. S6: Perform tension reduction.

10. The method as described in claim 9, characterized in that, In step S2, the heating temperature is 1180–1250°C.

11. The method as described in claim 9, characterized in that, In step S4, the air cooling time is 4 to 6 minutes.

12. The method as described in claim 9, characterized in that, In step S5, the heat preservation time t also satisfies: t < (215 - 0.2 × T) 再加热 +0.1 / Ti), where Ti is replaced with the value before the percentage sign of its mass percentage content.

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