Steel for 120ksi steel-grade sulfur-resistant oil well pipe, production method of steel, sulfur-resistant oil well pipe, heat treatment method and application of sulfur-resistant oil well pipe

Abstract

The invention provides steel for a 120ksi steel-grade sulfur-resistant oil well pipe, a production method of the steel, the sulfur-resistant oil well pipe, a heat treatment method and application of the sulfur-resistant oil well pipe. The steel comprises the following components: 0.60-0.80% of Cr, 0.80-1.00% of Mo, 0.050-0.100% of Nb, 0.015-0.035% of Al, 0.10-0.20% of V, 0.25-0.30% of C, 0.15-0.35% of Si, 0.50-0.70% of Mn, less than or equal to 0.010% of P, less than or equal to 0.0015% of S and the balance of Fe and other inevitable impurities. Compared with the prior art, the medium-carbon micro-alloying components, the pure steel smelting technology and the heat treatment technology are matched, dispersed and refined second phase structures are distributed on a tempered sorbite matrix in the room temperature state, the total series of non-metallic inclusions is lower than 1.0 level, and the product has good obdurability and excellent hydrogen sulfide corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the field of alloy steel, and in particular relates to a 120ksi steel grade sulfur-resistant oil well pipe steel and a production method thereof, a sulfur-resistant oil well pipe and a heat treatment method and application thereof, which are suitable for deep well mining with a depth of ≥8000m. Background Art

[0002] With the continuous exploitation of oil and gas over the past few decades or even a century, shallow oil and gas resources have been exhausted. The exploration and development of oil and gas in deep wells containing highly corrosive hydrogen sulfide gas is the future development trend. Steel is directly in contact with crude oil containing wet corrosive hydrogen sulfide gas. H atoms produced by the electrochemical reaction of crude oil containing hydrogen sulfide enter the steel and induce sulfide stress corrosion cracking (SSC) in the form of brittle fracture. It is currently recognized that the most commonly used to manufacture SSC-resistant oil well pipes is the Cr-Mo series with tempered martensite microstructure. As the strength increases, the material becomes more and more sensitive to corrosion. It is a major challenge to ensure high strength of the material while also having excellent corrosion resistance.

[0003] The invention patent with publication number CN114855084A published on August 5, 2022 discloses a 120ksi steel grade high-strength, high-toughness, high-grade sulfur-resistant drill pipe joint hot-rolled round steel and its preparation method. In the technical solution disclosed in the patent, the main principle is to obtain tempered martensite structure by adding microalloying elements such as Cr, Mo, and Nb. However, its Cr content exceeds 1.10%, and a higher content of Cr is prone to precipitate large-sized Cr at the grain boundary. 23 C 6 , which has a negative impact on the material's resistance to hydrogen sulfide. And the hydrogen sulfide stress corrosion threshold passed is only 65% ​​SMYS, which cannot meet the safety requirements for use in wells deeper than 8,000m.

[0004] The Chinese invention patent with publication number CN 114277310 A published on April 5, 2022, discloses an anti-H 2 S-corroded oil casing and its manufacturing method. In the technical solution disclosed in the patent, the main principle is to add micro-alloy elements such as Cr, Mo, Nb, V, etc., and then smelt, refine, vacuum treat in VD furnace and continuously cast to obtain tube blanks. However, the yield strength of the material in the patent is greater than 758MPa. As the drilling depth increases to more than 8,000 meters, its strength cannot meet the demand.

[0005] Therefore, it is very necessary to provide a steel for oil well pipes that has excellent corrosion resistance while ensuring high material strength, and can be used in oil wells above 8,000 meters. Summary of the invention

[0006] The object of the present invention is to provide a 120ksi steel grade sulfur-resistant oil well pipe steel and a production method thereof, and to obtain an oil well pipe steel having high material strength and excellent corrosion resistance by optimizing the composition.

[0007] Another object of the present invention is to provide a sulfur-resistant oil well pipe and a heat treatment method, wherein the sulfur-resistant oil well pipe is produced by using the above-mentioned 120ksi steel grade sulfur-resistant oil well pipe steel, and the sulfur-resistant oil well pipe is obtained by a designed heat treatment method, and the tensile strength is ≥940MPa, the yield strength is ≥830MPa, and the impact energy at -20℃ is ≥100J.

[0008] -20℃KV 2 ≥100J, loading strength is 80% SMYS, H 2 Under the condition of S partial pressure of 0.1MPa and temperature of 25℃, the American standard NACE TM0177 standard A method was adopted to pass the hydrogen sulfide corrosion test. No fracture occurred during the test for 720h, while taking into account strength, toughness and corrosion resistance.

[0009] The last object of the present invention is to provide an application of sulfur-resistant oil well pipe for deep well mining with a depth of ≥8000m.

[0010] The specific technical solutions of the present invention are as follows:

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

[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%, and the rest are Fe and other inevitable impurities.

[0013] The composition of the 120ksi steel 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 within ≤0.010%.

[0014] The composition of the 120ksi grade sulfur-resistant oil well pipe 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 indicates its mass percentage content in steel.

[0017] The present invention provides a method for producing 120ksi steel grade sulfur-resistant oil well pipe 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: steel is deoxidized and alloyed, and the amount of slag is strictly controlled, and the smelting end point S is ≤ 0.030%, and P is ≤ 0.120%.

[0020] The LF furnace refining: elements such as C, Si, Mn, Cr, Mo, V, Nb are adjusted to target values, the white slag retention time is ≥20 minutes, and the smelting cycle is ≤80 minutes.

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

[0022] Calcium treatment is an effective means to modify the morphology of sulfides in the ingot. Calcium treatment not only 2 O 3 The inclusions are modified into liquid calcium aluminate inclusions, which improves the castability of the molten steel during the continuous casting process. During the cooling process, Ca combines with S to form CaS, which reduces the precipitation temperature of MnS inclusions and reduces the precipitation amount of MnS inclusions. The Ca / S range is 0.8 to 2.0, and the effective calcium-sulfur ratio Ca / S formula is defined as:

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

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

[0025] The continuous casting: the tundish superheat is controlled to be 20-50℃ above the liquidus line, and the continuous casting billet diameter (D, mm) and the casting speed (v, m / min) should meet D = 3256 × v 3 -2494×v 2-500×v+874. Continuous casting obtains 380mm~700mm round billets. Among them, the unit of continuous casting billet diameter D is mm, and the unit of drawing speed v is m / min. The quality of the billet is guaranteed according to the relationship between the diameter and drawing speed of the continuous casting billet. In actual production, the diameter D of the round billet is generally limited to 380mm, 450mm, 500mm, 600mm, and 700mm. When calculating with the above formula, just directly substitute the value before the unit into the formula for calculation.

[0026] The rolling process is as follows: Φ380mm~Φ700mm continuous casting round billets are rolled into Φ90mm~Φ250mm round steel. The billets are sent into a walking-beam heating furnace, and the heating temperature of the round steel is ≥1230°C. The diameter D of the continuous casting billet and the heating time t should meet 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. When calculating with the above formula, the value before the unit can be directly substituted into the formula for calculation. The starting rolling temperature is ≥1180°C, the final rolling temperature is 700~950°C, and after rolling, an insulation cover is used or the billet is placed in a slow cooling pit for slow cooling, and (finishing) the product is formed. The diameter of the continuous casting billet is closely related to the heating time. Generally speaking, the larger the diameter of the continuous casting billet, the longer the heating time. Calculated according to the formula D=180+0.42t of the present invention, the quality of the steel is guaranteed.

[0027] The sulfur-resistant oil well pipe provided by the present invention is produced by adopting the above-mentioned 120ksi steel grade sulfur-resistant oil well pipe steel.

[0028] The structure of the sulfur-resistant oil well pipe is tempered troostite with an area accounting for more than 98%, and the austenite grain size is ≥8.5.

[0029] The sulfur-resistant oil well pipe has a small-angle grain boundary ratio of ≥30% and a dislocation density of 2.0×10 13 / m -2 ~5.0×10 13 / m -2 ; Class A inclusions are level 0, Class B, C or D non-metallic inclusions are no more than level 1.0, and the sum of Class A, B, C and D inclusions is no more than level 2.5.

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

[0031] The sulfur-resistant oil well pipe has a loading strength of 80% SMYS, H 2 The steel passed the hydrogen sulfide corrosion test under the conditions of S partial pressure of 0.1MPa and temperature of 25°C using the American standard NACE TM0177 method A, and no fracture occurred during the test for 720 hours.

[0032] The invention provides a heat treatment method for sulfur-resistant oil well pipes, which includes two quenching and tempering, specifically: after the first quenching, the second quenching is performed, and finally the tempering is performed.

[0033] The first quenching: heating temperature W1 = AC 3 +30~50℃, the holding time t1 is determined by the steel pipe wall S, t1=3.2×S, water cooling; the unit of heating temperature W is ℃, the unit of holding time t1 is min, and the unit of S is mm. AC 3 The results were obtained by testing with Gleeble-2000D thermal simulation test machine.

[0034] Secondary quenching: heating temperature W2 = W1-20 ° C, holding time t2 is determined by the steel pipe wall S, t2 = 3.2 × S, water cooling; among them, the unit of heating temperature W2 is ° C, the unit of holding time t2 is min, and the unit of steel pipe wall thickness S is 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 the present invention, the first quenching can refine the thick grains of the original structure of the crude steel pipe wall and transform them into quenching structures such as martensite, providing a good organizational foundation for subsequent processing. The second quenching further refines the grains, makes the organization more uniform and dense, reduces organizational defects, and improves the strength and toughness of the material. High-temperature tempering can eliminate the internal stress generated by quenching, reduce the brittleness of the material, decompose the martensite, and form a tempered troostite structure, which effectively improves the toughness of the material while maintaining high strength. After two quenchings and one high-temperature tempering, the strength and toughness of the material are well matched, with both high strength and hardness, and good toughness, and can withstand large impact loads and complex stress changes. At the same time, uniform and fine alloy carbides are precipitated, which serve as irreversible hydrogen traps to improve the material's sulfur resistance. The quenching temperature is set according to the AC3 temperature, and the purpose is to ensure that the material is completely austenitized, and the holding time is selected according to the wall thickness of the material.

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

[0038] The application of the sulfur-resistant oil well pipe provided by the present invention is used for deep well mining with a depth of ≥8000m.

[0039] The design ideas of the present invention are as follows:

[0040] C: ensures the strength of steel, improves hardenability and thus increases the percentage of martensite transformation; in addition, increasing the C content can increase the number of carbides precipitated during tempering, and these carbides are good H traps: but too high a C content will not only cause segregation itself, but will also greatly increase the segregation of Mn and P, thereby reducing the SSC resistance, so the C content is controlled at 0.25-0.30%.

[0041] Mn: improves the strength and permeability of steel, but Mn is an easily segregated element. Excessive Mn content is easily segregated with S and P at the grain boundaries, so it is not good for the anti-SSC performance. The Cr and Mo contents designed in the present invention are relatively high, which are sufficient to ensure the hardenability and strength of the steel, so the Mn content is controlled at 0.50-0.70%.

[0042] Cr: Improves strength and hardenability, improves corrosion resistance, but excessive Cr content will precipitate large Cr at the grain boundary during tempering 23 C 6 Carbides are not conducive to H resistance 2 S stress corrosion resistance, so the Cr content is controlled at 0.60-0.80%.

[0043] Mo: It is an important solid solution strengthening and tempering precipitation strengthening element, and it also improves the hardenability of steel. Mo carbides precipitate during high temperature tempering, which increases the tempering resistance. Therefore, sufficient Mo must be added to ensure high strength and high tempering temperature. In addition, Mo can also reduce the segregation of P at the grain boundary by reducing the diffusion coefficient of P. However, when Mo is too high, coarse Mo will also form. 2 C and M 6 C carbides are not conducive to H resistance 2 S stress corrosion resistance, so the Mo content is controlled at 0.80~1.00%.

[0044] V: Its role in quenched and tempered steel is to inhibit tempering softening and increase tempering temperature. During high temperature tempering, VC carbides are precipitated to play a precipitation strengthening role, thus ensuring that the dislocation density of steel is reduced during high temperature tempering and improving the SSC resistance. However, when the V content in steel exceeds a certain upper limit, the SSC resistance is no longer improved, so the V content is controlled at 0.10-0.20%.

[0045] Nb: A large number of research results show that when niobium is precipitated in austenite in the form of carbonitride, the undissolved Nb (C, N) at high temperature and the strain-induced precipitation during rolling can pin the austenite grain boundary, inhibit austenite recrystallization, hinder grain growth, and refine the grains. The precipitated MC carbides are strong hydrogen traps, which effectively improve the material's SSC resistance. However, too high a Nb content will greatly increase the material cost and the improvement in SSC resistance is small, so the Nb content is controlled at 0.050-0.100%.

[0046] P, S and five harmful elements: P, S and five harmful elements: Sn, Sb, As, Pb, Bi as impurity elements in steel, significantly reduce the material's SSC resistance, and their content in steel should be reduced as much as possible. P is easy to form segregation in steel, and the stress zone at the tip of MnS inclusions is easy to become the starting point of sulfide stress cracking. Therefore, P, S and 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 damages the toughness of the material. The present invention controls the total amount of T.O+[N] to ≤120ppm.

[0048] In order to ensure good low-temperature toughness of steel, the ratio of Si, Mo, Mn, Nb and V needs to be limited. Since Si is easy to segregate at the austenite grain boundary, it reduces the crystal bonding force, deteriorates the low-temperature toughness, and increases the temper brittleness, so the coefficient of Si is -2.0. Mn can significantly affect the variant selection during the phase transformation process, increase the types of variants in the phase transformation, and thus improve the low-temperature toughness, so the coefficient of Mn is 1.0; Mo can improve the hardenability of steel, effectively reduce the segregation of impurity elements such as P, S, and As at the grain boundary, and effectively improve the low-temperature toughness of steel, so the coefficient of Mo is 1.3; Nb and V can precipitate fine MC carbides, refine the structure and improve the tempering stability of steel, thereby improving the low-temperature toughness, so the coefficients of 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] In order to ensure the steel has good hydrogen sulfide corrosion resistance, the ratio of Si, Mn, Cr, Mo, V, and Nb needs to be limited. Since Si and Mn are easily segregated at the austenite grain boundary, the crystal bonding force is reduced, resulting in uneven microstructure and decreased corrosion resistance, so 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 the grain boundary, and precipitate carbides during tempering. 2C can become a trap to capture H, effectively improving the anti-sulfur performance of steel, so the coefficient of Mo is 1.2; the MC-type carbides precipitated by V can effectively inhibit grain growth, and as an irreversible H trap greatly improve the anti-SSC performance. In addition, it can improve the steel's resistance to temper softening, reduce the material's dislocation density, and improve the anti-SSC performance, so the coefficient of V is 1.8; Nb can significantly increase the number of irreversible traps and reversible traps in steel. The precipitation of precipitated NbC nanoparticles acts as an effective hydrogen trap to reduce the hydrogen concentration in the defective parts, and the composite addition of Nb and V will reduce the proportion of high-angle grain boundaries and improve the anti-SSC performance, so the coefficient of Nb is 2.0. The irreversible H hydrogen trap provided by Cr can effectively capture H atoms, slow down the diffusion rate of H atoms, and improve the anti-SSC performance, so the coefficient of 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 the prior art, the present invention adopts a medium-carbon microalloying component system, a pure steel smelting technology and a heat treatment process, and adds some microalloying elements to ensure that the material precipitates fine alloy carbides after subsequent heat treatment, while ensuring the hardenability of the material, so that after tempering, a dispersed and refined second phase structure can be obtained on the tempered troostite matrix at room temperature, with a lower dislocation density and a higher proportion of small-angle grain boundaries, and non-metallic inclusions are all below level 1.0, so that the material has good strength and toughness and excellent resistance to hydrogen sulfide corrosion. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is the SEM image of Example 1. A large number of fine alloy carbides are precipitated at the grain boundaries, which is beneficial to the anti-sulfur performance of the material.

[0054] Figure 2 For comparison with the SEM image of Case 1, the grains are coarser than those of the material shown in Example 1, and at the same time, less alloy carbides are precipitated, and the sulfur resistance is poor. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Example 1-Example 3

[0057] A 120 ksi steel grade sulfur-resistant oil well pipe steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and other inevitable impurities.

[0058] Comparative Example 1-Comparative Example 3

[0059] A 120 ksi steel grade sulfur-resistant oil well pipe steel comprises the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and other inevitable impurities.

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

[0061] Steel Type 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 Type 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 measured by the equipment. In addition, the five harmful elements Sn, Sb, As, Pb, and Bi are controlled at ≤0.010%.

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

[0064] The electric arc furnace smelting: steel is deoxidized and alloyed, and the amount of slag is strictly controlled, and the smelting end point S is ≤ 0.030%, and P is ≤ 0.120%.

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

[0066] RH vacuum degassing: pure degassing time ≥ 25 min, soft blowing time ≥ 20 min, [H] ≤ 1.0 ppm after vacuum treatment, calcium treatment is carried out, and the effective calcium-sulfur ratio Ca / S controlled in each embodiment 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 tundish superheat is controlled 20-50℃ above the liquidus line. Continuous casting specifications: round billet with diameter D=450mm. In actual production, the continuous casting round billet with diameter of 450mm is produced, the superheat is 45℃, and the pulling speed is 0.44m / min. The continuous casting billet diameter (D, mm) and the pulling speed (v, m / min) meet D=3256v 3 -2494×v 2 -500×v+874.

[0068] The Φ450mm continuous casting round billet is rolled into Φ150mm hot-rolled round steel, and the billet is sent to a step-beam heating furnace, with a heating temperature of ≥1230℃ and a holding time of 642min, which meets D=180+0.42t. The starting rolling temperature is ≥1180℃, the final rolling temperature is 700~950℃, and after rolling, a heat preservation cover is used or the billet is put into a slow cooling pit for slow cooling.

[0069] The above embodiments and comparative examples of 120ksi grade sulfur-resistant oil well pipe steel are used to produce sulfur-resistant oil well pipes. The specific pipe manufacturing route is: 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 is: subjected to primary quenching, secondary quenching, and finally tempering.

[0071] The first quenching: heating temperature W1 = AC 3 +30~50℃, the holding time t1 is determined by the steel pipe wall S, t1=3.2×S, water cooling. Among them, the unit of heating temperature W1 is ℃, the unit of holding time t1 is min, and the unit of steel pipe wall thickness S is mm. AC 3 The W1 of each embodiment and comparative example satisfies W1=AC 3 +30~50℃.

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

[0073] Tempering: Tempering temperature is 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 of each embodiment and comparative example are shown in Table 2.

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

[0076]

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

[0078] Organization: Take samples from 1 / 2 wall thickness of the cross section at the end of the steel pipe for metallographic and grain size analysis.

[0079] Performance: Take tensile, impact and SSC resistance specimens on the 1 / 2 radius of the steel pipe, and conduct mechanical property tests according to GB / T228 and GB / T229, and conduct SSC resistance tests according to NACE TM0177 standard A method (at a loading strength of 80% SMYS, H 2 The S partial pressure was 0.1 MPa and the temperature was 25°C. The average grain size was observed according to GB / T 6394, and the small angle grain boundaries (2°≤θ≤15°) were observed using EBSD. The results are shown in Table 3.

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

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

[0082]

[0083]

[0084] Table 4 Non-metallic inclusion level requirements (unit: level)

[0085]

[0086] In Example 1-Example 3, the non-metallic inclusions are well controlled through the pure steel smelting technology. The chemical composition and production methods of the steels of Examples 1-3 are properly controlled, and their chemical composition meets the requirements, and the strength, toughness and SSC resistance of the steel are good. Comparative Example 1 is that the chemical composition and Ca / S are not well controlled, resulting in the appearance of Class A non-metallic inclusions. At the same time, the sum of the four types of non-metallic inclusions is 4.5, and the X value does not meet the requirements, resulting in poor toughness and sulfur resistance of the material; Comparative Example 2 is due to poor control of chemical composition, and both the X value and the Y value do not meet the requirements, resulting in poor mechanical properties and sulfur resistance of the material; Comparative Example 3 has improper chemical composition and heat treatment process, resulting in unsatisfactory overall performance.

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

[0088] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and 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 present invention should be within the protection scope of the present invention.

Claims

1. A 120ksi steel grade sulfur-resistant oil well pipe steel, characterized in that: The 120ksi steel grade sulfur-resistant oil well pipe steel includes the following components in mass percentage: 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 are Fe and other inevitable impurities.

2. The 120ksi grade sulfur-resistant oil well pipe steel according to claim 1, characterized in that: The composition of the 120ksi grade sulfur-resistant oil well pipe steel also satisfies: X=-2×%Si+1.0×%Mn+1.3×%Mo+2.0×(%Nb+%V)≥1.62%.

3. The 120ksi grade sulfur-resistant oil well pipe steel according to claim 1, characterized in that: 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%.

4. A method for producing the 120 ksi grade sulfur-resistant oil well pipe steel according to any one of claims 1 to 3, characterized in that: The production method comprises the following process flow: Electric arc furnace smelting → LF furnace refining → RH vacuum degassing → round billet continuous casting → rolling.

5. The production method according to claim 4, characterized in that: The RH vacuum degassing is performed for calcium treatment, and the effective calcium-sulfur ratio Ca / S is controlled by the formula: Ca / S=[T.Ca-(0.31+0.02×T.Ca)×(0.99×TO-5.44)] / 1.25×TS; Ca / S range is 0.8~2.0; Where TS is the total sulfur content in steel, 10 -6 ; T.Ca is the total calcium mass fraction in steel, 10 -6 ; TO is the total oxygen mass fraction in steel, 10 -6 .

6. The production method according to claim 4, characterized in that: The continuous casting: the continuous casting billet diameter D and the casting speed v meet D = 3256 × v 3 -2494×v 2 -500×v+874, where the unit of continuous casting billet diameter D is mm and the unit of casting speed v is m / min.

7. The production method according to claim 4, characterized in that: The rolling: the continuous casting billet diameter D and the heating time t should meet D=180+0.42t, wherein the unit of the continuous casting billet diameter D is mm, and the unit of the heating time t is min.

8. A sulfur-resistant oil well pipe, characterized in that: The sulfur-resistant oil well pipe is produced by using the 120ksi steel grade sulfur-resistant oil well pipe steel as described in any one of claims 1 to 3.

9. The sulfur-resistant oil well pipe according to claim 8, characterized in that: The sulfur-resistant oil well pipe has a small-angle grain boundary ratio of ≥30% and a dislocation density of 2.0×10 13 / m -2 ~5.0×10 13 / m -2 ; Class A inclusions are level 0, Class B, C or D non-metallic inclusions are no more than level 1.0, and the sum of Class A, B, C and D inclusions is no more than level 2.

5.

10. The sulfur-resistant oil well pipe according to claim 8 or 9, characterized in that: The room temperature mechanical properties of the sulfur-resistant oil well pipe are as follows: tensile strength ≥940MPa, yield strength ≥830MPa, and impact energy at -20°C ≥100J; the sulfur-resistant oil well pipe passes the hydrogen sulfide corrosion test using the American standard NACE TM0177 standard A method at a loading strength of 80% SMYS, a H2S partial pressure of 0.1MPa, and a temperature of 25°C, and no fracture occurs during the test for 720 hours.

11. A heat treatment method for sulfur-resistant oil well pipe according to any one of claims 8 to 10, characterized in that: The heat treatment comprises: first quenching, second quenching and finally tempering.

12. The heat treatment method according to claim 11, characterized in that: The primary quenching: heating temperature W1 = AC3 + 30 ~ 50 ° C, holding time t1 is determined by the steel pipe wall S, t1 = 3.2 × S, water cooling; wherein the unit of heating temperature W is ° C, the unit of holding time t1 is min, and the unit of S is mm. AC3 is tested using the Gleeble-2000D thermal simulation test machine.

13. The heat treatment method according to claim 11, characterized in that: The secondary quenching: heating temperature W2 = W1-20°C, holding time t2 is determined by the steel pipe wall S, t2 = 3.2×S, water cooling; wherein, the unit of heating temperature W2 is °C, the unit of holding time t2 is min, and the unit of steel pipe wall thickness S is mm.

14. The heat treatment method according to claim 11, characterized in that: The tempering: the tempering temperature is 680-720°C, 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.

15. An application of the sulfur-resistant oil well pipe according to any one of claims 8 to 10, characterized in that: Used for deep well mining with a depth of ≥8000m.

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