A high-grade SSC-resistant oil well pipe steel, a production method thereof, a produced oil well pipe, a heat treatment process and application

Abstract

The application provides a high-grade SSC-resistant oil well pipe steel and a production method, a produced oil well pipe, a heat treatment process and an application thereof, the composition of the steel is as follows: Cr 0.95-1.20%, Ni 0.40-0.60%, Mo 0.75-0.95%, Ti 0.030-0.050%, B 0.0010-0.0030%, Al 0.020-0.045%, V 0.10-0.20%, RE 0.0010-0.0020%, C 0.25-0.30%, Si 0.15-0.30%, Mn 0.60-0.75%, P ≤0.010%, S ≤0.0015%, and the rest is Fe and other inevitable impurities. Through the optimization of the component design, the production method and the heat treatment process, the oil well pipe obtained has good strength and toughness and excellent hydrogen sulfide corrosion resistance, and can be used for the exploitation of ten-thousand-meter oil wells.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of alloy steel, and particularly relates to a high-grade steel for oil well pipe resistant to SSC (sulfide stress cracking) and a production method thereof, a produced oil well pipe, a heat treatment process and application. BACKGROUND

[0002] With the continuous exploitation of oil and gas in the past few decades or even a century, the shallow oil and gas resources have been exhausted in advance, and oil and gas exploration and development in deep wells containing high corrosive hydrogen sulfide (H2S) gas requires that the material has excellent corrosion resistance while ensuring high strength. The 125 ksi grade (at least 862 MPa yield strength) steel on the market cannot meet the requirements for working in high corrosive deep wells, and there is an urgent need for higher-grade SCC-resistant oil well pipe products.

[0003] Currently, many studies are trying to develop 135 ksi grade sulfur-resistant oil well pipe, but the developed 135 ksi grade sulfur-resistant oil well pipe is difficult to meet the requirements of strength and toughness while considering H2S corrosion, especially difficult to pass the NACE TM0177 standard A solution test.

[0004] A 125 ksi grade sulfur-resistant oil well pipe and a manufacturing method thereof are disclosed in Chinese Patent No. CN110616366A, which was published on December 27, 2019, and the composition thereof is: C: 0.20-0.30%, Si: 0.1-0.5%, Mn: 0.2-0.6%, Cr: 0.30-0.70%, Mo: 0.60-1.00%, V: 0.10-0.20%, Nb: 0.01-0.06%, Ti: 0.015-0.035%, W: 0.20-0.60%, Al≤0.1%, N≤0.008%, and the balance is Fe and other unavoidable impurities. The Cr-Mo-W system is used to obtain the 125 ksi grade sulfur-resistant oil well pipe, and the low-temperature toughness is not disclosed.

[0005] Chinese Patent No. CN103160752A, which was published on June 19, 2013, discloses a high-strength seamless steel pipe with excellent low-temperature toughness and a manufacturing method thereof, and the composition thereof is: C: 0.15%-0.20%, Si: 0.20%-0.30%, Mn: 0.20%-0.50%, P: ≤0.010%, S: ≤0.003%, Cr: 0.6%-0.8%, Mo: 0.4%-0.7%, Ni: 1.0%-1.4%, Nb: 0.01%-0.035%, and Als: 0.01%-0.05%. The Cr-Mo-Ni system is used to obtain the 125 ksi grade oil well pipe, and although the toughness is greatly improved,

[0006] -60℃ impact energy reaches 40J or above, but no guarantee of anti-sulfur performance.

[0007] Therefore, it is necessary to provide a steel for oil well pipe which has high toughness and meets the index requirements and has anti-H2S corrosion. SUMMARY

[0008] The present application aims to provide a high-grade SSC-resistant steel for oil well pipe and a production method thereof, which is able to pass through a small-diameter continuous casting round billet and is suitable for electric furnace production by component design.

[0009] The present application also aims to provide an oil well pipe and a heat treatment process thereof, which is obtained by using the high-grade SSC-resistant steel for oil well pipe, and by the designed heat treatment process, a dispersed and refined second phase is distributed on a tempering sorbite matrix at room temperature, a low dislocation density and a high proportion of high-angle grain boundaries are obtained, and the morphology of type II MnS is improved, the concentration of H atoms is reduced, so that the material has good strength and toughness and excellent hydrogen sulfide corrosion resistance.

[0010] The last purpose of the present application is to provide an application of the oil well pipe, which can be used for ten-thousand-meter oil well exploitation.

[0011] The specific technical solutions of the present application are as follows:

[0012] A high-grade SSC-resistant steel for oil well pipe, comprising the following components by mass percentage:

[0013] Cr: 0.95-1.20%, Ni: 0.40-0.60%, Mo: 0.75-0.95%, Ti: 0.030-0.050%, B: 0.0010-0.0030%, Al: 0.020-0.045%, V: 0.10-0.20%, RE: 0.0010-0.0020%, C: 0.25-0.30%, Si: 0.15-0.30%, Mn: 0.60-0.75%, P≤0.010%, S≤0.0015%, and the rest is Fe and other inevitable impurities.

[0014] In the composition of the high-grade SSC-resistant steel for oil well pipe, RE is at least one of rare earth elements La and Ce.

[0015] The composition of the high-grade SSC-resistant steel for oil well pipe also satisfies T.O+[N]≤120ppm, and the five harmful elements Sn, Sb, As, Pb and Bi are controlled at ≤0.010%;

[0016] The composition of the high-grade SSC-resistant steel for oil well pipe also satisfies α=-2.0×%Si+1.0

[0017] 1.3 x %Mo + 2.5 x %Ni + 2.0 x %V + 5.0 x %(Ti + B) ≥ 2.90 %. Each element represents its mass percentage content in the steel.

[0018] The composition of the high-grade SSC-resistant oil well pipe steel also satisfies: β = -5 x (%Si + %Mn) + 12

[0019] 10 x %Cr + 22 x (%Ti + %B) + 18 x %V ≥ 18.00 %. Each element represents its mass percentage content in the steel.

[0020] A production method of a high-grade SSC-resistant oil well pipe steel, comprising the following process flow: electric arc furnace smelting → LF furnace refining → RH vacuum degassing → continuous casting.

[0021] The electric arc furnace smelting: tapping for deoxidization and alloying, while strictly controlling the amount of slag.

[0022] The LF furnace refining: C, Si, Mn, Cr, Ni, Mo, V, Ti, B and other elements are adjusted to the target value, white slag retention time ≥ 20 min, and smelting period ≤ 80 min.

[0023] The RH vacuum degassing: pure degassing time ≥ 25 min, soft blowing time ≥ 20 min, [H] ≤ 1.0 ppm after vacuum treatment, and adding any one or several of rare earth elements La or Ce, so that the content of rare earth is 0.0010-0.0020%.

[0024] The continuous casting: the superheat of the tundish is controlled to be 30-70℃ above the liquidus, and the submerged entry nozzle and protective slag are used for pouring to prevent secondary oxidation and absorb the floating inclusions in the liquid steel;

[0025] Continuous casting square billet: the casting speed of 380x450mm continuous casting square billet should be 0.40-0.45m / min;

[0026] Continuous casting round billet: the diameter D of the continuous casting round billet and the casting speed v should satisfy v = 1.83 x (D / 1000) 2 -3.04 x

[0027] (D / 1000)+1.41, wherein the unit of the diameter D of the continuous casting billet is mm, and the drawing speed is m / min; the electromagnetic stirring frequency f1 of the crystallizer and the diameter D of the continuous casting billet should meet D / f1=200; the electromagnetic stirring frequency f2 of the end and the diameter D of the continuous casting billet should meet D / f2=100, wherein the unit of the electromagnetic stirring frequency f1 of the crystallizer is Hz, the unit of the electromagnetic stirring frequency f2 of the end is Hz, and the unit of the diameter D of the continuous casting billet is mm. When calculating, the numerical value before the unit is directly substituted into the formula for calculation. If the drawing speed and the diameter do not match, the macroscopic quality of the continuous casting billet may be poor, thereby affecting the overall performance of the material subsequently. The diameter specification of the continuous casting billet can be selected as: 380mm, 450mm, 500mm, 600mm, and 700mm.

[0028] The continuous casting of the application obtains a 380*450mm continuous casting square billet; or a continuous casting round billet with a diameter D of 380mm, 450mm, 500mm, 600mm, and 700mm.

[0029] The application provides a heat treatment process for an oil well pipe, which is used for heat treatment of the oil well pipe produced by using the high-grade SSC-resistant oil well pipe steel.

[0030] The first quenching is performed at a heating temperature W1=AC3+30-50℃, the holding time t1 is determined by the wall thickness S of the steel pipe, t=3.5*S, and water cooling is performed.

[0031] The first tempering is performed at a tempering temperature of 700-730℃, the holding time t2 is determined by the wall thickness S of the steel pipe, t2=6*S, and air cooling is performed.

[0032] The second quenching is performed at a heating temperature W2=W1-20℃, the holding time t3 is determined by the wall thickness S of the steel pipe, t=3.5*S, and water cooling is performed.

[0033] The second tempering is performed at a tempering temperature of 680-710℃, the holding time t4 is determined by the wall thickness S of the steel pipe, t4=6*S, and air cooling is performed.

[0034] The design of the twice quenching process mainly embodies three aspects: first, the quenching process in the first quenching makes the workpiece obtain martensite organization, and after tempering, the martensite decomposes, and in the heating and cooling process of the second quenching, the grains are further refined. The refined grains increase the grain boundary area, so that the diffusion of hydrogen atoms at the grain boundary is more difficult, thereby improving the ability of the material to resist hydrogen sulfide corrosion. Second, the twice quenching can make the alloying elements redistribute between the matrix and the carbide, forming more stable carbide phases, such as carbides of alloying elements such as Cr, Mo, V, Ti, etc. These carbides are dispersedly distributed at the grain boundaries or phase boundaries, play the role of pinning dislocations, and at the same time, improve the corrosion resistance of the material. Third, the twice quenching helps to make the stress distribution in the workpiece more uniform, reducing the stress concentration phenomenon. The 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.

[0035] The purpose of the temperature reduction of the secondary quenching of the present application compared with the primary quenching is to retain the effect of refining the grains in the primary quenching, further adjust the organization, make it more stable and uniform, and at the same time, the lower secondary quenching temperature can reduce the generation of thermal stress and organizational stress, and improve the corrosion resistance of the material. The reason for the reduction of the secondary tempering temperature is to ensure the mechanical properties of the material, and the higher primary tempering temperature is to reduce the stress in the material and improve the sulfur resistance of the material.

[0036] Further, the production process of the oil well pipe includes the above-mentioned heat treatment, and the specific process is: continuous casting round billet→heating→pipe threading→sizing→heat treatment→steel pipe grinding→steel pipe flaw detection→finishing→flaw detection→packaging and warehousing, which can directly produce oil well pipes through small-diameter continuous casting round billets.

[0037] The present application provides an oil well pipe produced by the above-mentioned heat treatment process, and the oil well pipe has a room temperature mechanical property with a yield strength of ≥950MPa, a tensile strength of ≥1050MPa, an impact energy at-20℃ of ≥100J, and an elongation of ≥16%. The oil well pipe passes the hydrogen sulfide corrosion resistance test under the conditions of a loading strength of 75%SMYS, a H2S partial pressure of 0.1MPa, and a temperature of 25℃, using the American standard NACE TM0177 standard A method, and does not break after 720h of testing.

[0038] The grain at the 1 / 2 wall thickness of the end cross section of the oil well pipe is ≥8.5 level; and the organization is: the proportion of the tempered sorbite area is more than 98%.

[0039] The large-angle grain boundary proportion of the oil well pipe is ≤70%, and the dislocation density is 7.0×10 13 / m 2 ~9.0×1013 / m 2 .

[0040] The total of the A, B, C, D and DS inclusions of the oil well pipe is less than 4.0 level, and the A, B, C, D and DS inclusions are not more than 1.0 level.

[0041] The application of the oil well pipe can be used for ten-thousand-meter oil well exploitation.

[0042] The design idea of the present application is as follows:

[0043] C: ensure the strength of the steel, improve the hardenability to increase the percentage of martensite transformation; in addition, increasing the C content can increase the number of carbonides precipitated during tempering, which are good H traps; but too high C content not only causes its own segregation, but also greatly increases the segregation of Mn and P, thereby reducing the anti-SSC performance, so the C content is controlled at 0.25-0.30%.

[0044] Mn: increase the strength and hardenability of the steel, but Mn is an easy segregation element, and too much Mn is easy to segregate with S and P at the grain boundary, thus being unfavorable for the anti-SSC performance; for the high Cr and Mo content designed in the present application, the hardenability and strength of the steel are sufficient, so the Mn content is controlled at 0.60-0.75%.

[0045] Ni: Ni is an austenite stabilizing element, has the effect of expanding the phase region, increases the stability of supercooled austenite, and improves the hardenability of the steel. Ni is the main element for improving low-temperature toughness, which reduces the stacking fault energy of the steel crystals, makes the dislocation more easily slip under low-temperature conditions, thereby preventing stress concentration under low-temperature conditions and achieving excellent low-temperature toughness, but too high Ni content will deteriorate the anti-SSC performance of the steel. Therefore, the Ni content is controlled at 0.40-0.60%.

[0046] Cr: increase the strength and hardenability, and improve the corrosion resistance, but too high Cr content will precipitate large-size Cr 23 C6 carbides at the grain boundary during tempering, which is not conducive to the H2S stress corrosion resistance, so the Cr content is controlled at 0.95-1.20%.

[0047] Mo: is an important solid solution strengthening and tempering precipitation strengthening element, and also improves the hardenability of the steel. Mo carbides are precipitated during high-temperature tempering to improve the tempering resistance, so 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, but when Mo is too high, coarse M2C and M6C carbides will be formed, which is not conducive to the H2S stress corrosion resistance, so the Mo content is controlled at 0.75-0.95%.

[0048] V: The function of V in the controlled rolling and controlled cooling steel is to restrain the temper softening and to increase the tempering temperature. The VC carbide precipitates during the high temperature tempering and plays the role of precipitation strengthening, thus ensuring the steel to reduce the dislocation density during the high temperature tempering and to improve the SSC resistance, and also ensuring the high strength requirement of 135 ksi. However, the SSC resistance will not be improved when the V content exceeds a certain upper limit, so the V content is controlled in the range of 0.10-0.20%.

[0049] Ti, B: When Ti and B are added together, B is segregated at the grain boundary to reduce the grain boundary vacancy concentration and to reduce the hydrogen diffusion, thus improving the SSC resistance. When the Ti content is too high, in addition to forming coarse carbides, the bainite and M / A islands in the steel will also increase, thus reducing the SSC resistance. Therefore, the Ti content is controlled in the range of 0.030-0.050%, and the B content is controlled in the range of 0.0010-0.0030%.

[0050] RE: The rare earth element can change the strip-shaped MnS in the steel into spherical sulfide, which can reduce the concentration of hydrogen atoms at the strip-shaped MnS inclusions and reduce the hydrogen-induced crack sensitivity. Therefore, the RE content is controlled in the range of 0.0010-0.0020%.

[0051] P, S and the five harmful elements: P, S and the five harmful elements Sn, Sb, As, Pb and Bi are impurity elements in the steel, which can significantly reduce the SSC resistance of the material, so their contents in the steel should be reduced as much as possible. P is easy to form segregation in the steel, and the MnS inclusion tip stress area is easy to become the starting position of sulfide stress cracking. Therefore, the P, S and the five harmful elements should be controlled in the range of ≤0.010%, ≤0.0015% and ≤0.010%, respectively.

[0052] T.O and [N]: The oxygen in the steel is easy to form oxide inclusions, especially the B-type inclusions along the rolling direction, and the presence of free nitrogen increases the brittleness of the material and damages the toughness of the material. The total amount of T.O + [N] should be ≤120 ppm.

[0053] In order to ensure the good low temperature toughness of the steel, the proportioning of Si, Mo, Mn, Ni, Ti, V and B needs to be limited. Since Si is easy to segregate at the austenite grain boundary, the crystallization binding force is reduced, the low temperature toughness is deteriorated, and the temper brittleness is increased, so the coefficient of Si is -2.0. Mn can significantly affect the variant selection in the phase transformation process, increase the variant type 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 the 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 the steel, so the coefficient of Mo is 1.3; Ni can significantly reduce the ductile-brittle transition temperature of the steel and improve the low temperature toughness, so the coefficient of Ni is 2.5; V can precipitate fine MC carbides, refine the structure and improve the temper stability of the steel, thereby improving the low temperature toughness, so the coefficient of V is 2.0; when Ti and B act together, the refining effect is more significant. The carbonitride formed by Ti provides more nucleation sites for the segregation of B at the grain boundary, so that B can more effectively play a role in inhibiting the migration of the grain boundary. The two cooperate with each other to further improve the degree of grain refinement, thereby improving the low temperature toughness of the material, so the coefficient of Ti and B is 5.0.

[0054] That is, α = -2.0 × %Si + 1.0 × %Mn + 1.3 × %Mo + 2.5 × %Ni + 2.0 × %V + 5.0 × (%Ti + B%) ≥ 2.90%.

[0055] In order to ensure the good hydrogen sulfide corrosion resistance of the steel, the proportioning of Si, Mn, Cr, Mo, V, Ti and B needs to be limited. Since Si and Mn are easy to segregate at the austenite grain boundary, the crystallization binding force is reduced, the microstructure is not uniform, and the corrosion resistance is reduced, so the coefficient is -5. Mo can improve the hardenability of the steel, effectively reduce the segregation of impurity elements such as P and S at the grain boundary, and precipitate Mo2C carbides during the tempering process, which can become H traps, thereby effectively improving the hydrogen resistance of the steel, so the coefficient of Mo is 12; the MC type carbides precipitated by V can effectively inhibit grain growth, and as irreversible H traps, greatly improve the SSC resistance, in addition, can improve the temper softening resistance of the steel, reduce the dislocation density of the material, and improve the SSC resistance, so the coefficient of V is 18; the carbonitride of Ti is an irreversible hydrogen trap. When Ti and B are added together, B also toughens the grain boundary, and the solid solution amount increases due to the N fixation of Ti. B segregates at the grain boundary, significantly improves the hardenability and increases the martensite content, effectively reduces the content of Mn in the steel; on the other hand, B reduces the vacancy concentration of the grain boundary, thereby reducing the diffusion of hydrogen. Therefore, the coefficient of Ti and B is 22. The irreversible H hydrogen trap provided by Cr can effectively capture H atoms, slow down the diffusion rate of H atoms, and improve the SSC resistance, so the coefficient of Cr is 10.

[0056] That is, β = -5x(%Si+%Mn) + 12x%Mo + 10x%Cr + 22x(%Ti+%B) + 18x%V >= 18.00%.

[0057] The inventors found that the inclusions in the steel material (especially MnS inclusions) are the main cause of hydrogen-induced cracking and the starting point of HIC, and the hydrogen-induced cracking caused by inclusions is first determined by its morphology, and the strip-shaped MnS is more harmful than the elliptical one. By reasonable refining process, addition of rare earth elements and control of the refining process, the content of MnS

[0058] The aspect ratio of the morphology is less than 3, and the two ends are relatively smooth. Reducing the content of type II MnS in the steel and controlling the morphology can effectively improve the SSC resistance of the steel.

[0059] The suitable component system and the twice quenching and tempering heat treatment process of the present application ensure the mechanical properties and hydrogen sulfide resistance of the material, and the smelting technology of clean steel reduces the influence of non-metallic inclusions and component segregation in the steel on the performance of the material.

[0060] Compared with the prior art, the present application adopts an optimized alloy component system, combined with suitable steelmaking process and heat treatment process, to obtain a dispersed and refined second phase on a tempered sorbite matrix at room temperature, a low dislocation density and a high proportion of high-angle grain boundaries, while improving the morphology of type II MnS and reducing the aggregation concentration of H atoms, so that the material has good strength and toughness and excellent hydrogen sulfide corrosion resistance. It can be applied to the exploitation of ten-thousand-meter oil wells. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 It is the EBSD size grain boundary map of Example 1, and the proportion of high-angle grain boundaries is 65%;

[0062] Figure 2 It is the EBSD size grain boundary map of Comparative Example 1, and the proportion of high-angle grain boundaries is 78%. DETAILED DESCRIPTION

[0063] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0064] Examples 1-3

[0065] A high-grade SSC-resistant oil well pipe steel, comprising the following mass percentage components: as shown in Table 1, the balance of Table 1 being Fe and inevitable impurities.

[0066] Comparative Examples 1-3

[0067] A high-grade SSC-resistant oil well pipe steel, comprising the following mass percentage components: as shown in Table 1, the balance of Table 1 being Fe and inevitable impurities.

[0068] Table 1 Steel components (wt%) of each example and comparative example

[0069]

[0070] The same rare earth raw material is used in each example and comparative example in Table 1, and the RE content is controlled to be different. In addition, the five harmful elements Sn, Sb, As, Pb and Bi are controlled to be ≤0.010%.

[0071] The production method of the high-grade SSC-resistant oil well pipe steel of each example and comparative example comprises the following process flow: electric arc furnace smelting→LF furnace refining→RH vacuum degassing→round billet continuous casting.

[0072] The electric arc furnace smelting: tapping for deoxidization and alloying, while strictly controlling the amount of slag.

[0073] The LF furnace refining: C, Si, Mn, Cr, Ni, Mo, V, Ti, B and other elements are adjusted to the target value, the white slag retention time is ≥20 min, and the smelting period is ≤80 min.

[0074] The RH vacuum degassing: the pure degassing time is ≥25 min, the soft blowing time is ≥20 min, the [H] after vacuum treatment is ≤1.0 ppm, and any one or several of the rare earth elements La or Ce is added, so that the content of rare earth is 0.0010-0.0020%.

[0075] The continuous casting: using a submerged entry nozzle and a protective slag for pouring to prevent secondary oxidation and absorb the floating inclusions in the liquid steel, producing a diameter of 450 mm continuous casting round billet, the superheat is 47℃, the withdrawal speed is 0.41 m / min, and it meets v=1.83×(D / 1000) 2 -3.04×(D / 1000)+1.41; the crystallizer electromagnetic stirring frequency is 2.25 Hz, the terminal electromagnetic stirring frequency is 4.5 Hz, D / f1=200 is met, and D / f2=100 is not met.

[0076] In the actual production of the steel of each example and comparative example, the control is carried out within the above process range, so that the production can be realized.

[0077] The oil well pipe produced by using the steel of each of the above embodiments and the comparative example and the pipe production route are as follows: the cast blank produced above → hot-rolled round steel → heating → pipe piercing → sizing → heat treatment → steel pipe grinding → steel pipe flaw detection → finishing → flaw detection → packaging and warehousing.

[0078] The heat treatment includes twice quenching and twice tempering. Specifically, first quenching is performed, then first tempering is performed, then second quenching is performed, and finally second tempering is performed.

[0079] The first quenching is performed at a heating temperature W1 = AC3 + 30-50℃, the holding time t1 is determined by the wall thickness S of the steel pipe, t1 = 3.5×S, and water cooling is performed. The unit of the heating temperature W1 is ℃, the unit of the holding time t1 is min, and the unit of the wall thickness S of the steel pipe is mm. AC3 is obtained by testing by using a Gleeble-2000D thermal simulation testing machine. The W1 of each of the embodiments and the comparative example satisfies W1 = AC3 + 30-50℃.

[0080] The first tempering is performed at a tempering temperature of 700-730℃, the holding time t2 is determined by the wall thickness S of the steel pipe, t2 = 6×S, and air cooling is performed. The unit of the holding time t2 is min, and the unit of the wall thickness S of the steel pipe is mm.

[0081] The second quenching is performed at a heating temperature W2 = W1-20℃, the holding time t3 is determined by the wall thickness S of the steel pipe, t3 = 3.5×S, and water cooling is performed. The unit of the heating temperature W2 is ℃, the unit of the holding time t3 is min, and the unit of the wall thickness S of the steel pipe is mm.

[0082] The second tempering is performed at a tempering temperature of 680-710℃, the holding time t4 is determined by the wall thickness S of the steel pipe, t4 = 6×S, and air cooling is performed. The unit of the holding time t4 is min, and the unit of the wall thickness S of the steel pipe is mm.

[0083] The heat treatment processes of each of the embodiments and the comparative example are shown in Table 2.

[0084] Table 2 List of heat treatment processes of the embodiments and the comparative example of the application

[0085]

[0086] The performance detection method of the oil well pipe produced by each of the embodiments and the comparative example is as follows:

[0087] Organization: Sampling from the 1 / 2 wall thickness of the cross section of the steel pipe end for metallographic and grain size analysis.

[0088] Performance: Tensile, impact, SSC resistance samples were taken from the 1 / 2 radius of the steel pipe, mechanical property tests were carried out according to GB / T228, GB / T229, and EBSD was used to observe and analyze high-angle grain boundaries (15°≤θ≤62.5°). The SSC resistance test was carried out according to NACE TM0177 standard A method (under the conditions of loading strength of 75% SMYS, H2S partial pressure of 0.1 MPa, and temperature of 25℃), and the average grain size was observed according to GB / T6394. The results are shown in Table 3.

[0089] Non-metallic inclusions were sampled from the 1 / 2 radius of the steel pipe, and tested according to the A method in ASTM E45 standard, and the performance is shown in Table 4.

[0090] Table 3 Performance detection situation list of the inventive examples and the comparative examples

[0091]

[0092]

[0093] Table 4 Non-metallic inclusion detection situation of the inventive examples and the comparative examples

[0094]

[0095] The chemical composition, production method, and performance of the steel of Example 1, Example 2, and Example 3 are all properly controlled, the chemical composition meets the requirements, and the strength and toughness and SSC resistance of the steel are all good. The chemical composition of Comparative Example 1 is suitable, but the β value does not meet the requirements, even if it is produced according to the heat treatment process of the application, but the product grain is large, the proportion of high-angle grain boundaries is high, and the material substructure angle is more than 70%, which will affect the sulfur resistance of the material, so the SSC resistance of Comparative Example 1 is very poor. The chemical composition of Comparative Example 2 is suitable, but the α value does not meet the requirements, even if it is produced according to the heat treatment process of the application, but the product grain is large, the strength and low temperature toughness are reduced. The chemical composition of Comparative Example 3 is properly controlled, but the heat treatment process is improper, resulting in unsatisfactory overall performance.

[0096] The above underlined data do not meet the requirements of the application.

[0097] The above description of the embodiments is to facilitate those of ordinary skill in the art to understand and use the application. Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without having to go through creative labor. Therefore, the application is not limited to the above embodiments, and improvements and modifications made by those skilled in the art without departing from the scope of the application should be within the scope of protection of the application.

Claims

1. An oil well pipe, characterized by, The oil well pipe is produced by using high-grade SSC-resistant oil well pipe steel, and the high-grade SSC-resistant oil well pipe steel comprises the following components by mass percentage: Cr: 0.95-1.20%, Ni: 0.40-0.60%, Mo: 0.75-0.95%, Ti: 0.030-0.050%, B: 0.0010-0.0030%, Al: 0.020-0.045%, V: 0.10-0.20%, RE: 0.0010-0.0020%, C: 0.25-0.30%, Si: 0.15-0.30%, Mn: 0.60-0.75%, P≤0.010%, S≤0.0015%, and the rest is Fe and other inevitable impurities. The components of the high-grade SSC-resistant oil well pipe steel also satisfy: α=-2.0×%Si+1.0×%Mn+1.3´%Mo+2.5×%Ni+2.0×%V+5.0%×(Ti+B)≥2.90%。 The components of the high-grade SSC-resistant oil well pipe steel also satisfy: β=-5×(%Si+%Mn)+12×%Mo+10×%Cr+22×(%Ti+%B)+18×%V≥18.00%。 The oil well pipe produced by using the high-grade SSC-resistant oil well pipe steel is subjected to heat treatment, and the heat treatment is as follows: first quenching, then first tempering, then second quenching, and finally second tempering. The first quenching is as follows: heating temperature W1=AC3+30-50℃, holding time t1 is determined by the pipe wall thickness S, t=3.5×S, and water cooling; wherein, the unit of the heating temperature W1 is ℃, the unit of the holding time t1 is min, and the unit of the pipe wall thickness S is mm. The first tempering is as follows: tempering temperature 700-730℃, holding time t2 is determined by the pipe wall thickness S, t2=6×S, and air cooling; wherein, the unit of the holding time t2 is min, and the unit of the pipe wall thickness S is mm. The second quenching is as follows: heating temperature W2=W1-20℃, holding time t3 is determined by the pipe wall thickness S, t=3.5×S, and water cooling; wherein, the unit of the heating temperature W2 is ℃, the unit of the holding time t3 is min, and the unit of the pipe wall thickness S is mm. The second tempering is as follows: tempering temperature 680-710℃, holding time t4 is determined by the pipe wall thickness S, t4=6×S, and air cooling; wherein, the unit of the holding time t4 is min, and the unit of the pipe wall thickness S is mm.

2. The oil well pipe according to claim 1, characterized by The oil well pipe has grain size of ≥8.5 level at the cross section 1 / 2 wall thickness; the oil well pipe has large-angle grain boundary proportion of ≤70%, dislocation density of 7.0×10 13 / m 2 ~9.0×10 13 / m 2 ; the oil well pipe has total A-type, B-type, C-type, D-type and DS-type inclusions of <4.0 level, and the A-type, B-type, C-type, D-type and DS-type inclusions are not more than 1.0 level.

3. The oil well pipe according to claim 1, characterized by The oil well pipe has the following room temperature mechanical properties: yield strength≥950MPa, and impact energy at-20℃≥100J; the oil well pipe passes the hydrogen sulfide corrosion resistance test under the conditions of loading strength of 75%SMYS, H2S partial pressure of 0.1MPa, and temperature of 25℃, and does not break after 720h of test according to the American standard NACE TM0177 standard A method.

4. The oil well pipe according to claim 1, characterized by The production method of the high-grade SSC-resistant oil well pipe steel comprises the following technological process: electric arc furnace smelting, LF furnace refining, RH vacuum degassing, and round billet continuous casting.

5. The oil well pipe according to claim 4, characterized by The continuous casting: continuous casting round billet: continuous casting round billet diameter D, and the casting speed v should meet v = 1.83 x (D / 1000) 2 -3.04 x (D / 1000) + 1.41, wherein the unit of continuous casting billet diameter D is mm, the casting speed is m / min; the mold electromagnetic stirring frequency f1 and the continuous casting billet diameter D should meet D / f1 = 200; the terminal electromagnetic stirring frequency f2 and the continuous casting billet diameter D should meet D / f2 = 100, wherein the unit of mold electromagnetic stirring frequency f1 is Hz, the unit of terminal electromagnetic stirring frequency f2 is Hz, and the unit of continuous casting billet diameter D is mm.

6. A heat treatment process for oil well pipe as claimed in any one of claims 1 to 5, characterized in that, The heat treatment comprises: first quenching, then tempering, then secondary quenching, and finally secondary tempering; The first quenching is: heating temperature W1=AC3+30~50℃, holding time t1 is determined by the thickness S of the steel pipe, t=3.5×S, water cooling; wherein, the unit of the heating temperature W1 is ℃, the unit of the holding time t1 is min, and the unit of the thickness S of the steel pipe is mm; The first tempering is: tempering temperature 700~730℃, holding time t2 is determined by the thickness S of the steel pipe, t2=6×S, air cooling; wherein, the unit of the holding time t2 is min, and the unit of the thickness S of the steel pipe is mm; The second quenching is: heating temperature W2=W1-20℃, holding time t3 is determined by the thickness S of the steel pipe, t=3.5×S, water cooling; wherein, the unit of the heating temperature W2 is ℃, the unit of the holding time t3 is min, and the unit of the thickness S of the steel pipe is mm; The second tempering is: tempering temperature 680~710℃, holding time t4 is determined by the thickness S of the steel pipe, t4=6×S, air cooling; wherein, the unit of the holding time t4 is min, and the unit of the thickness S of the steel pipe is mm.

7. Use of the oil well pipe according to any one of claims 1 to 5, characterized in that It is used for the exploitation of ten-thousand-meter oil well.

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