A 120 ksi grade steel for sour oil well pipe and a production method, a sour oil well pipe and a heat treatment method and application thereof

Abstract

The application provides a 120ksi-grade sulfur-resistant oil well pipe steel and a production method, a sulfur-resistant oil well pipe and a heat treatment method and application thereof, and the composition is as follows: Cr 0.60-0.80%, Mo 0.80-1.00%, Nb 0.050-0.100%, Al 0.015-0.035%, V 0.10-0.20%, C 0.25-0.30%, Si 0.15-0.35%, Mn 0.50-0.70%, P≤0.010%, S≤0.0015%, and the rest is Fe and other inevitable impurities. Compared with the prior art, the application adopts medium-carbon micro-alloying components, pure steel smelting technology and heat treatment process, and in the room temperature state, a tempered sorbite matrix with dispersed and refined second phase structure is obtained, non-metallic inclusions are all lower than 1.0 grade, and the product has good strength and toughness and excellent hydrogen sulfide corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel, and particularly relates to a 120ksi grade sulfur-resistant oil well pipe steel and its production method, sulfur-resistant oil well pipe and heat treatment method and application, which is suitable for deep well mining at a depth ≥8000m. Background Technology

[0002] With the continuous exploitation of oil and gas over the past few decades, even a century, shallow oil and gas resources have been exhausted. Exploration and development of oil and gas in deep wells containing highly corrosive hydrogen sulfide gas is the future trend. When steel comes into direct contact with crude oil containing moist, corrosive hydrogen sulfide gas, hydrogen atoms generated by the electrochemical reaction of the hydrogen sulfide-containing crude oil enter the steel, inducing brittle fracture, specifically sulfide stress corrosion cracking (SSC). Currently, it is generally accepted that Cr-Mo series materials with tempered martensitic microstructures are most commonly used to manufacture SSC-resistant well casings. As strength increases, materials become increasingly sensitive to corrosion; ensuring high strength while maintaining excellent corrosion resistance is a significant challenge.

[0003] The invention patent CN114855084A, published on August 5, 2022, discloses a hot-rolled round steel bar for high-strength, high-toughness, and high-grade sulfur-resistant drill pipe joints of 120ksi steel grade and its preparation method. The main principle of the disclosed technical solution is to obtain a tempered sorbite structure by adding microalloying elements such as Cr, Mo, and Nb. However, its Cr content exceeds 1.10%, and the high Cr content easily leads to the precipitation of large-sized Cr deposits at the grain boundaries. 23 C6 negatively impacts the material's resistance to hydrogen sulfide. Furthermore, the hydrogen sulfide stress corrosion threshold value is only 65% ​​SMYS, which is insufficient for safe use in wells exceeding 8000m in depth.

[0004] Chinese invention patent CN 114277310 A, published on April 5, 2022, discloses an oil casing pipe resistant to H2S corrosion and its manufacturing method. The main principle of the disclosed technical solution is to obtain a pipe blank by adding microalloying elements such as Cr, Mo, Nb, and V, followed by smelting, refining, vacuum treatment in a VD furnace, and continuous casting. However, the yield strength of the material in this patent is greater than 758 MPa, which is insufficient to meet the requirements as drilling depths increase to over 8000 meters.

[0005] Therefore, it is essential to provide a steel for oil well pipes that can guarantee high strength while also having excellent corrosion resistance, so that it can be used in oil wells deeper than 8,000 meters. Summary of the Invention

[0006] The purpose of this invention is to provide a 120ksi grade anti-sulfur oil well pipe steel and its production method. Through composition optimization, an oil well pipe steel that ensures high strength while also having excellent corrosion resistance is obtained.

[0007] Another objective of this invention is to provide a sulfur-resistant oil well pipe and a heat treatment method. The invention utilizes the aforementioned 120ksi grade sulfur-resistant oil well pipe steel to produce sulfur-resistant oil well pipes. Through a designed heat treatment method, a sulfur-resistant oil well pipe is obtained with a tensile strength ≥940MPa, a yield strength ≥830MPa, and an impact energy ≥100J at -20℃.

[0008] At -20℃, KV2≥100J, with a loading strength of 80% SMYS, H2S partial pressure of 0.1MPa, and a temperature of 25℃, the test was conducted using the American standard NACE TM0177 Standard A method. The test passed the hydrogen sulfide corrosion resistance test, and no fracture occurred after 720 hours of testing. The test also took into account strength, toughness, and corrosion resistance.

[0009] The final objective of this invention is to provide an application of sulfur-resistant oil well tubing for deep well mining at a depth of ≥8000m.

[0010] The specific technical solution of this invention is as follows:

[0011] A 120ksi grade sulfur-resistant oil well pipe steel comprises the following components by weight percentage:

[0012] Cr: 0.60–0.80%, Mo: 0.80–1.00%, Nb: 0.050–0.100%, Al: 0.015–0.035%, V: 0.10–0.20%, C: 0.25–0.30%, Si: 0.15–0.35%, Mn: 0.50–0.70%, P≤0.010%, S≤0.0015%, with the remainder being Fe and other unavoidable impurities.

[0013] The composition of the 120ksi grade sulfur-resistant oil well pipe steel also meets the following requirements: T.O+[N]≤120ppm; and the five harmful elements Sn, Sb, As, Pb, and Bi are controlled at ≤0.010%.

[0014] The composition of the 120ksi grade sulfur-resistant oil well tubing steel also satisfies: X = -2 × %Si + 1.0 × %Mn + 1.3 × %Mo + 2.0 × (%Nb + %V) ≥ 1.62%. Each element represents its mass percentage content in the steel.

[0015] The composition of the 120ksi grade sulfur-resistant oil well pipe steel also satisfies: Y = -0.5 × (%Si + %Mn) + 1.2 × %Mo + 1.0 × %Cr + 2.0 × %Nb + 1.8 × %V ≥ 1.60%.

[0016] Each element represents its mass percentage content in the steel.

[0017] This invention provides a method for producing 120ksi grade sulfur-resistant oil well tubing steel, comprising the following process flow:

[0018] Electric arc furnace smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

[0019] The electric arc furnace smelting process involves deoxidation and alloying of the tapped steel, while strictly controlling the amount of slag. The final smelting result is S≤0.030% and P≤0.120%.

[0020] The LF furnace refining process involves adjusting elements such as C, Si, Mn, Cr, Mo, V, and Nb to target values, maintaining white slag for ≥20 minutes, and completing a smelting cycle of ≤80 minutes.

[0021] The RH vacuum degassing process has the following parameters: pure degassing time ≥ 25 min, soft blowing time ≥ 20 min, and [H] ≤ 1.0 ppm after vacuum treatment.

[0022] Calcium treatment is an effective means of modifying the morphology of sulfides in cast billets. It not only modifies primary Al₂O₃ inclusions in the billets into liquid calcium aluminate inclusions, improving the castability of molten steel during continuous casting, but also, during the cooling process, Ca preferentially combines with S to form CaS, lowering the precipitation temperature of MnS inclusions and reducing the amount of MnS inclusions precipitated. The Ca / S ratio ranges from 0.8 to 2.0. Here, the effective calcium-sulfur ratio Ca / S is defined by the following formula:

[0023] Ca / S=[T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS;

[0024] Where TS is the mass fraction of total sulfur in steel, 10 -6 That is, the sulfur content in the composition; T.Ca is the total calcium mass fraction in the steel, 10 -6 TO represents the total oxygen mass fraction in the steel, 10 -6 .

[0025] For continuous casting: the superheat of the tundish is controlled at 20-50°C above the liquidus line; the billet diameter (D, mm) and casting speed (v, m / min) should conform to D = 3256 × v 3 -2494×v 2-500×v+874. Continuous casting yields round billets ranging from 380mm to 700mm. Here, the unit for the billet diameter D is mm, and the unit for the casting speed v is m / min. The design ensures billet quality based on the relationship between the billet diameter and casting speed. In actual production, the billet diameter D is generally limited to 380mm, 450mm, 500mm, 600mm, and 700mm. When calculating the above formula, simply substitute the values ​​before the units into the formula.

[0026] The rolling process involves rolling continuously cast round billets of Φ380mm~Φ700mm into round bars of Φ90mm~Φ250mm. The billets are fed into a walking beam furnace, and the heating temperature of the round bars is ≥1230℃. The diameter D of the continuously cast billet and the heating time t should conform to the formula D=180+0.42t, where the unit of the diameter D is mm and the unit of the heating time t is min. When calculating the above formula, simply substitute the values ​​before the units into the formula. The initial rolling temperature is ≥1180℃, and the final rolling temperature is 700~950℃. After rolling, the billets are cooled slowly using an insulation cover or a slow cooling pit (for finishing). There is a close relationship between the diameter of the continuously cast billet and the heating time; generally, the larger the diameter, the longer the heating time. Calculations according to the formula D=180+0.42t of this invention ensure the quality of the steel.

[0027] The present invention provides a sulfur-resistant oil well pipe, which is produced using the above-mentioned 120ksi grade sulfur-resistant oil well pipe steel.

[0028] The microstructure of the sulfur-resistant oil well casing is tempered sorbite with an area ratio of over 98% and an austenite grain size of ≥8.5.

[0029] The sulfur-resistant oil well casing has a small-angle grain boundary ratio of ≥30% and a dislocation density of 2.0×10⁻⁶. 13 / m -2 ~5.0×10 13 / m -2 Inclusions of type A are classified as grade 0, and non-metallic inclusions of types B, C, or D are all classified as grade 1.0. The total of inclusions of types A, B, C, and D is not greater than grade 2.5.

[0030] The room temperature mechanical properties of the sulfur-resistant oil well pipe are as follows: tensile strength ≥940MPa, yield strength ≥830MPa, impact energy at -20℃ ≥100J, and elongation ≥16%.

[0031] The sulfur-resistant oil well tubing, under a load strength of 80% SMYS, an H2S partial pressure of 0.1 MPa, and a temperature of 25°C, passed the hydrogen sulfide corrosion resistance test using the American standard NACE TM0177 Standard A method, and did not break after 720 hours of testing.

[0032] This invention provides a heat treatment method for sulfur-resistant oil well tubing, comprising two quenching processes and tempering. Specifically, after a first quenching, a second quenching is performed, followed by a final tempering.

[0033] The first quenching process involves a heating temperature of W1 = AC3 + 30 to 50°C, a holding time t1 determined by the steel pipe wall temperature S, t1 = 3.2 × S, and water cooling. The unit of heating temperature W is °C, the unit of holding time t1 is min, and the unit of S is mm. AC3 was obtained using a Gleeble-2000D thermal simulation testing machine.

[0034] Secondary quenching: heating temperature W2 = W1 - 20℃, holding time t2 is determined by the steel pipe wall thickness S, t2 = 3.2 × S, water cooling; where heating temperature W2 is in ℃, holding time t2 is in min, and steel pipe wall thickness S is in mm.

[0035] Tempering: Tempering temperature 680~720℃, holding time t3 is determined by the steel pipe wall thickness S, t=6×S, air cooling; where the unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

[0036] In this invention, the first quenching refines the thick, coarse grains of the original steel pipe, transforming them into martensite and other quenched structures, providing a good microstructure foundation for subsequent processing. The second quenching further refines the grains, making the microstructure more uniform and dense, reducing structural defects, and improving the material's strength and toughness. High-temperature tempering eliminates the internal stress generated by quenching, reduces the material's brittleness, and decomposes the martensite to form tempered sorbite, effectively improving the material's toughness while maintaining high strength. After two quenchings and one high-temperature tempering, the material achieves a good balance of strength and toughness, possessing both high strength and hardness and good toughness, capable of withstanding large impact loads and complex stress changes. Simultaneously, uniform and fine alloy carbides precipitate, acting as irreversible hydrogen traps to improve the material's sulfur resistance. The quenching temperature is set based on AC3 temperature to ensure complete austenitization of the material, and the holding time is selected according to the material's wall thickness.

[0037] The production method of the sulfur-resistant oil well pipe is as follows: hot-rolled round steel → heating → pipe threading → sizing → heat treatment → steel pipe grinding → steel pipe flaw detection → precision machining → flaw detection → packaging and warehousing.

[0038] This invention provides an application of a sulfur-resistant oil well pipe for deep well mining at a depth of ≥8000m.

[0039] The design concept of this invention is as follows:

[0040] C: Ensures the strength of steel and improves hardenability, thereby increasing the percentage of martensite transformation; in addition, increasing the C content can increase the amount of carbides precipitated during tempering, which are good H traps; however, excessively high C content will not only cause segregation itself, but also greatly increase the segregation of Mn and P, thereby reducing the resistance to SSC, so the C content should be controlled at 0.25-0.30%.

[0041] Mn: Improves the strength and hardenability of steel, but Mn is an element that is prone to segregation. Excessive Mn content is prone to segregation with S and P at grain boundaries, which is detrimental to the resistance to SSC. The Cr and Mo content designed in this invention is relatively high, which is sufficient to ensure the hardenability and strength of the steel. Therefore, the Mn content is controlled at 0.50 to 0.70%.

[0042] Cr: Improves strength and hardenability, and enhances corrosion resistance; however, excessive Cr content can cause large Cr deposits to precipitate at grain boundaries during tempering. 23 C6 carbides are not conducive to resistance to H2S stress corrosion, so the Cr content is controlled at 0.60-0.80%.

[0043] Mo (Mo) is an important solid solution strengthening and temper precipitation strengthening element, and it also improves the hardenability of steel. Mo carbides precipitate during high-temperature tempering, increasing tempering resistance; therefore, sufficient Mo must be added to ensure high strength and high tempering temperature. Additionally, Mo can reduce P segregation at grain boundaries by decreasing the diffusion coefficient of P. However, excessive Mo content can lead to the formation of coarse M2C and M6C carbides, which are detrimental to resistance to H2S stress corrosion. Therefore, the Mo content is controlled between 0.80% and 1.00%.

[0044] In quenched and tempered steel, volatile organic compounds (V) play a role in inhibiting temper softening and increasing the tempering temperature. During high-temperature tempering, the precipitation of V carbides provides precipitation strengthening, thus ensuring a reduction in dislocation density and improving resistance to precipitated sclerosis (SSC) during high-temperature tempering. However, if the V content in the steel exceeds a certain upper limit, the SSC resistance will no longer improve; therefore, the V content is controlled between 0.10% and 0.20%.

[0045] Nb: Numerous studies have shown that when niobium precipitates in austenite as carbonitrides, undissolved Nb(C,N) at high temperatures and strain-induced precipitation during rolling can pin austenite grain boundaries, inhibit austenite recrystallization, hinder grain growth, and refine grains. Furthermore, the precipitated MC-type carbides are strong hydrogen traps, effectively improving the material's resistance to susceptibility ...

[0046] P, S, and the five harmful elements: P, S, Sn, Sb, As, Pb, and Bi, as impurity elements in steel, significantly reduce the material's resistance to stress cracking (SSC), and their content in steel should be minimized. P readily forms segregations in steel, while the stress zones at the tips of MnS inclusions easily become the initiation sites for sulfide stress cracking. Therefore, the content of P, S, and the five harmful elements should be controlled at ≤0.010%, ≤0.0015%, and ≤0.010%, respectively.

[0047] TO and [N]: Oxygen in steel easily forms oxide inclusions, especially type B inclusions along the rolling direction. The presence of free nitrogen increases the brittleness of the material and impairs its toughness. In this invention, the total amount of T.O+[N] should be controlled to be ≤120ppm.

[0048] To ensure good low-temperature toughness in steel, the proportions of Si, Mo, Mn, Nb, and V need to be carefully controlled. Since Si tends to segregate at austenite grain boundaries, reducing crystallization bonding strength, worsening low-temperature toughness, and increasing temper brittleness, the coefficient for Si is -2.0. Mn significantly affects the selection of variants during phase transformation, increasing the variety of variants and thus improving low-temperature toughness; therefore, the coefficient for Mn is 1.0. Mo improves the hardenability of steel and effectively reduces the segregation of impurities such as P, S, and As at grain boundaries, effectively improving low-temperature toughness; therefore, the coefficient for Mo is 1.3. Nb and V precipitate fine MC carbides, refining the microstructure and improving the tempering stability of the steel, thereby enhancing low-temperature toughness; therefore, the coefficients for Nb and V are 2.0.

[0049] That is, X=-2×%Si+1.0×%Mn+1.3×%Mo+2.0×(%Nb+%V)≥1.62%.

[0050] To ensure good resistance to hydrogen sulfide corrosion in steel, the proportions of Si, Mn, Cr, Mo, V, and Nb need to be limited. Since Si and Mn tend to segregate at the austenite grain boundaries, reducing the crystal bonding force and causing uneven microstructure, the corrosion resistance is reduced. Therefore, the coefficient is -0.5. Mo can improve the hardenability of steel, effectively reduce the segregation of impurity elements such as P and S at grain boundaries, and precipitate Mo2C carbides during tempering, which can act as traps for H, effectively improving the steel's resistance to sulfur dioxide (SSC). Therefore, the coefficient for Mo is 1.2. The precipitated MC-type carbides from V can effectively inhibit grain growth and, as irreversible H traps, greatly improve resistance to SSC. In addition, it can improve the steel's resistance to tempering softening, reduce the dislocation density of the material, and improve SSC resistance. Therefore, the coefficient for V is 1.8. Nb can significantly increase the number of irreversible and reversible traps in steel. The precipitation of NbC nanoparticles acts as an effective hydrogen trap, reducing the hydrogen concentration at defect sites. Furthermore, the combined addition of Nb and V reduces the proportion of large-angle grain boundaries, improving SSC resistance. Therefore, the coefficient for Nb is 2.0. Cr provides irreversible H hydrogen traps that can effectively capture H atoms, slow down the diffusion rate of H atoms, and improve SSC resistance. Therefore, the coefficient for Cr is 1.0.

[0051] That is, Y=-0.5×(%Si+%Mn)+1.2×%Mo+1.0×%Cr+2.0×%Nb+1.8×%V≥1.60%.

[0052] Compared with existing technologies, this invention uses a medium-carbon microalloying composition system, pure steel smelting technology and heat treatment process in combination. The addition of some microalloying elements ensures that fine alloy carbides are precipitated in the material after subsequent heat treatment. At the same time, it ensures the hardenability of the material, so that after tempering, a dispersed and refined second phase structure is obtained on the tempered sorbite matrix at room temperature. It has a low dislocation density and a high proportion of small-angle grain boundaries, and the non-metallic inclusions are all below grade 1.0. As a result, the material has good strength and toughness and excellent resistance to hydrogen sulfide corrosion. Attached Figure Description

[0053] Figure 1 The SEM image of Example 1 shows a large number of fine alloy carbides precipitated at the grain boundaries, which is beneficial to the material's sulfur resistance.

[0054] Figure 2 To compare with the SEM image of Case 1, the grains are coarser than those of the material shown in Example 1, and there is less alloy carbide precipitation, resulting in poorer sulfur resistance. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Examples 1-3

[0057] A 120ksi grade anti-sulfur oil well pipe steel comprises the following composition by mass percentage as shown in Table 1, with the remainder not shown in Table 1 being Fe and other unavoidable impurities.

[0058] Comparative Examples 1-3

[0059] A 120ksi grade anti-sulfur oil well pipe steel comprises the following composition by mass percentage as shown in Table 1, with the remainder not shown in Table 1 being Fe and other unavoidable impurities.

[0060] Table 1 Chemical composition (wt%) of embodiments and comparative examples of the present invention

[0061] steel grades C Si Mn Cr Mo Nb V Al Example 1 0.26 0.23 0.57 0.73 0.93 0.092 0.18 0.026 Example 2 0.29 0.18 0.54 0.75 0.98 0.085 0.15 0.028 Example 3 0.26 0.22 0.59 0.71 0.88 0.073 0.12 0.023 Comparative Example 1 0.28 0.33 0.61 0.68 0.89 0.068 0.15 0.025 Comparative Example 2 0.28 0.30 0.65 0.62 0.82 0.052 0.11 0.029 Comparative Example 3 0.27 0.28 0.58 0.63 0.81 0.057 0.13 0.019 steel grades P S T.Ca [N] TO X value Y value Ca / S Example 1 0.007 0.0012 0.0025 0.0041 0.0018 1.86 1.95 1.00 Example 2 0.008 0.0009 0.0028 0.0049 0.0018 1.92 2.01 1.53 Example 3 0.009 0.0010 0.0022 0.0056 0.0021 1.68 1.72 0.84 Comparative Example 1 0.008 0.0013 0.0020 0.0050 0.0023 1.54 1.68 0.47 Comparative Example 2 0.008 0.0009 0.0021 0.0056 0.0016 1.44 1.43 1.19 Comparative Example 3 0.007 0.0011 0.0022 0.0064 0.0020 1.45 1.52 0.82

[0062] In Table 1, T.Ca is the actual data obtained through equipment measurement. Additionally, the levels of the five harmful elements Sn, Sb, As, Pb, and Bi are controlled to ≤0.010%.

[0063] The production method of the 120ksi grade sulfur-resistant oil well pipe steel described in the various embodiments and comparative examples includes the following process flow: electric arc furnace smelting → LF furnace refining → RH vacuum degassing → continuous casting → rolling.

[0064] The electric arc furnace smelting process involves deoxidation and alloying of the tapped steel, while strictly controlling the amount of slag. The final smelting result is S≤0.030% and P≤0.120%.

[0065] LF furnace refining: C, Si, Mn, Cr, Nb, Mo, V and other elements are adjusted to the target values, white slag is maintained for ≥20 min, and the smelting cycle is ≤80 min.

[0066] RH vacuum degassing: pure degassing time ≥25min, soft blowing time ≥20min, [H] ≤1.0ppm after vacuum treatment, calcium treatment is performed, and the effective calcium-sulfur ratio Ca / S controlled by each example and comparative example is shown in Table 1, Ca / S=[T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS.

[0067] Continuous casting: The superheat in the tundish is controlled at 20-50°C above the liquidus. The casting specification is a round billet with a diameter D = 450mm. In actual production, a 450mm diameter continuous casting round billet is produced at a superheat of 45°C and a casting speed of 0.44m / min. This satisfies the requirement that the continuous casting billet diameter (D, mm) and casting speed (v, m / min) conform to D = 3256v. 3 -2494×v 2 -500×v+874.

[0068] Φ450mm continuously cast round billets are rolled into Φ150mm hot-rolled round bars. The billets are then fed into a walking beam furnace, heated to a temperature ≥1230℃, and held for 642 minutes, conforming to D=180+0.42t. The initial rolling temperature is ≥1180℃, and the final rolling temperature is 700~950℃. After rolling, the billets are either placed under an insulation cover or placed in a slow cooling pit for slow cooling.

[0069] The above embodiments and comparative examples use 120ksi grade sulfur-resistant oil well pipe steel for the production of sulfur-resistant oil well pipes. The specific pipe manufacturing route is as follows: Φ150mm hot-rolled round steel → heating → pipe threading → sizing → heat treatment → steel pipe grinding → steel pipe flaw detection → finishing → flaw detection → packaging and warehousing.

[0070] The heat-treated body consists of: first quenching, then second quenching, and finally tempering.

[0071] The first quenching process involves a heating temperature of W1 = AC3 + 30~50℃, a holding time t1 determined by the steel pipe wall thickness S, t1 = 3.2 × S, and water cooling. The unit for heating temperature W1 is ℃, the unit for holding time t1 is min, and the unit for steel pipe wall thickness S is mm. AC3 was obtained using a Gleeble-2000D thermal simulation testing machine. In all embodiments and comparative examples, W1 satisfies W1 = AC3 + 30~50℃.

[0072] Secondary quenching: Heating temperature W2 = W1 - 20℃, holding time t2 is determined by the steel pipe wall thickness S, t2 = 3.2 × S, water cooling. Wherein, heating temperature W is in ℃, holding time t2 is in min, and steel pipe wall thickness S is in mm.

[0073] Tempering: Tempering temperature 680~720℃, holding time t3 is determined by the steel pipe wall thickness S, t3=6×S, air cooling. The unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

[0074] The heat treatment parameters for each embodiment and comparative example are shown in Table 2.

[0075] Table 2 lists the heat treatment processes of the embodiments and comparative examples of the present invention.

[0076]

[0077] The performance testing methods for the steel pipes produced in each embodiment and comparative example are as follows:

[0078] Organization: Samples were taken from half the wall thickness of the end cross section of the steel pipe for metallographic and grain size analysis.

[0079] Performance: Tensile, impact, and SSC resistance specimens were taken from half the radius of the steel pipe. Mechanical property tests were conducted according to GB / T228 and GB / T229, and SSC resistance tests were conducted according to NACE TM0177 Standard A (at a loading strength of 80% SMYS, H2S partial pressure of 0.1 MPa, and temperature of 25℃). Average grain size was observed according to GB / T 6394, and small-angle grain boundaries (2°≤θ≤15°) were observed using EBSD. The results are shown in Table 3.

[0080] Non-metallic inclusions: Samples were taken from 1 / 2 radius of the hot-rolled round steel and tested according to Method A of ASTM E45. The properties are shown in Table 4.

[0081] Table 3. Performance testing results of embodiments and comparative examples of the present invention.

[0082]

[0083]

[0084] Table 4 Requirements for Non-metallic Inclusion Levels (Unit: Level)

[0085]

[0086] Examples 1-3, through pure steel smelting technology, showed good control of non-metallic inclusions. The chemical composition and production methods of the steels in Examples 1-3 were appropriately controlled, meeting the requirements for chemical composition, and exhibiting good strength, toughness, and SSC resistance. Comparative Example 1, however, suffered from poor control of chemical composition and Ca / S ratio, resulting in the presence of Class A non-metallic inclusions. Furthermore, the sum of the four types of non-metallic inclusions was 4.5, and the X value did not meet the requirements, leading to poor toughness and sulfur resistance. Comparative Example 2, due to poor control of chemical composition, resulted in both X and Y values ​​failing to meet requirements, leading to poor mechanical properties and sulfur resistance. Comparative Example 3, with its inappropriate chemical composition and heat treatment process, resulted in unsatisfactory overall performance.

[0087] The data underlined above do not meet the requirements of this invention.

[0088] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A sulfur resistant oil country tubular goods characterized by, The anti-sulfur oil well pipe is produced by using 120 ksi steel grade anti-sulfur oil well pipe steel; The 120 ksi steel grade anti-sulfur oil well pipe steel comprises the following mass percentage components: Cr: 0.60~0.80%, Mo: 0.80~1.00%, Nb: 0.050~0.100%, Al: 0.015~0.035%, V: 0.10~0.20%, C: 0.25~0.30%, Si: 0.15~0.35%, Mn: 0.50~0.70%, P≤0.010%, S≤0.0015%, and the rest is Fe and other inevitable impurities; The components of the 120 ksi steel grade anti-sulfur oil well pipe steel also satisfy: X=-2×%Si+1.0×%Mn+1.3×%Mo+2.0×(%Nb+%V)≥1.62%; The components of the 120 ksi steel grade anti-sulfur oil well pipe steel also satisfy: Y=-0.5×(%Si+%Mn)+1.2×%Mo+1.0×%Cr+2.0×%Nb+1.8×%V≥1.60%; The heat treatment method of the anti-sulfur oil well pipe is: after primary quenching, secondary quenching is performed, and finally tempering is performed; The primary quenching: heating temperature W1=AC3+30~50℃, holding time t1 is determined by the pipe wall S, t1=3.2×S, water cooling; wherein, the unit of heating temperature W is ℃, the unit of holding time t1 is min, and the unit of S is mm; AC3 is obtained by testing by using Gleeble-2000D thermal simulation tester; The secondary quenching: heating temperature W2=W1-20℃, holding time t2 is determined by the pipe wall S, t2=3.2×S, water cooling; wherein, the unit of heating temperature W2 is ℃, the unit of holding time t2 is min, and the unit of pipe wall thickness S is mm; The tempering: tempering temperature 680~720℃, holding time t3 is determined by the pipe wall thickness S, t=6×S, air cooling; wherein, the unit of holding time t3 is min, and the unit of pipe wall thickness S is mm.

2. The sulfur resistant oil country tubular goods of claim 1, wherein, The small-angle grain boundary ratio of the anti-sulfur oil well pipe is greater than or equal to 30%, and the dislocation density is 2.0*10 13 / m -2 ~5.0*10 13 / m -2 ; the A-type inclusions are 0 grade, the B, C or D-type non-metallic inclusions are all not greater than 1.0 grade, and the total of A, B, C and D types is not greater than 2.5 grade.

3. The sulphur resistant oil country tubular goods according to claim 1 or 2, characterized in that, The room temperature mechanical properties of the anti-sulfur oil well pipe are: tensile strength≥940 MPa, yield strength≥830 MPa, and-20℃ impact energy≥100 J; the anti-sulfur oil well pipe passes the anti-sulfur hydrogen corrosion test under the conditions of loading strength of 80%SMYS, H2S partial pressure of 0.1 MPa, and temperature of 25℃, using the American standard NACE TM0177 standard A method, and no fracture occurs after 720 h of test.

4. The sulfur-resistant oil country tubular good of claim 1 or 2, wherein The production method of the 120 ksi steel grade anti-sulfur oil well pipe steel comprises the following technological process: Electric arc furnace smelting→LF furnace refining→RH vacuum degassing→round billet continuous casting→rolling.

5. The sulfur resistant oil country tubular goods of claim 4, wherein, The RH vacuum degassing is performed by calcium treatment, and the effective calcium sulfur ratio Ca / S formula is: Ca / S=[T.Ca-(0.31+0.02×T.Ca)×(0.99×T.O-5.44)] / 1.25×T.S; the range of Ca / S is 0.8~2.0; where T.S is the total mass fraction of sulfur in the steel, 10 -6 ; T.Ca is the total calcium mass fraction in the steel, 10 -6 ; T.O is the total oxygen mass fraction in steel, 10 -6 .

6. The sulfur resistant oil country tubular goods of claim 4, wherein, The continuous casting: the diameter D of the continuously cast billet and the casting speed v satisfy D = 3256 x v 3 - 2494 x v 2 - 500 x v + 874, wherein the unit of the diameter D of the continuously cast billet is mm, and the unit of the casting speed v is m / min.

7. The sulfur resistant oil country tubular goods of claim 4, wherein, The rolling: the diameter D of the continuous casting billet and the heating time t should satisfy D=180+0.42t, wherein the unit of the diameter D of the continuous casting billet is mm, and the unit of the heating time t is min.

8. A method of heat treating a sulphur resistant oil well pipe according to any one of claims 1 to 7, characterized in that, The heat treatment is: after primary quenching, secondary quenching is carried out, and finally tempering is carried out. The primary quenching: the heating temperature W1=AC3+30~50℃, the holding time t1 is determined by the steel pipe wall S, t1=3.2×S, and water cooling; wherein the unit of the heating temperature W is ℃, the unit of the holding time t1 is min, and the unit of S is mm; AC3 is obtained by testing with a Gleeble-2000D thermal simulation testing machine device; The secondary quenching: the heating temperature W2=W1-20℃, the holding time t2 is determined by the steel pipe wall S, t2=3.2×S, and water cooling; wherein the unit of the heating temperature W2 is ℃, the unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm; The tempering: the tempering temperature is 680~720℃, the holding time t3 is determined by the steel pipe wall thickness S, t=6×S, and air cooling; wherein the unit of the holding time t3 is min, and the unit of the steel pipe wall thickness S is mm.

9. Use of the sulphur-resistant oil well pipe according to any one of claims 1 to 7, characterized in that, It is used for exploitation in a deep well with a depth of ≥8000m.

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