A kind of sulfur-resistant steel for oil well pipe and its preparation method

Abstract

The invention discloses a sulfur-resistant steel for oil well pipe and a preparation method thereof, which belongs to the technical field of steel for oil well pipe, and solves the problem that a variety of alloy elements are added to the steel for oil well pipe in the prior art, resulting in high cost; the sulfur-resistant performance and toughness of the existing steel for oil well pipe cannot be improved at the same time. The components of the sulfur-resistant steel for oil well pipe include, by mass percentage: C: 0.45% to 0.55%, Si: 0.51% to 0.60%, Mn: 0.05% to 0.15%, Mo: 0.75% to 0.85%, Cr: 1.41% to 1.55%, V: 0.31% to 0.35%, Al: 0.4% to 0.5%, Cu: 0.9% to 1.1%, P: ≤0.010%, S: ≤0.003%, and the balance is Fe and unavoidable impurities. The sulfur-resistant steel for oil well pipe of the invention has high strength, good toughness and good corrosion resistance.

Description

Technical Field

[0001] The invention relates to the technical field of steel for oil well pipes, and in particular to sulfur-resistant steel for oil well pipes and a preparation method thereof. Background Art

[0002] As the shallow and easily exploitable oil and gas resources are almost exhausted, there is an urgent need to explore and exploit some deep oil and gas fields containing highly corrosive hydrogen sulfide gas. The increase in the depth of oil wells, the high temperature and high pressure environment in deep wells, and the highly corrosive hydrogen sulfide gas will put forward more stringent requirements on the strength and resistance to sulfide stress corrosion cracking of oil well pipes. The existing oil well pipes on the market can no longer meet the service requirements in deep and highly corrosive environments, and it is urgent to develop the next generation of high-grade sulfur-resistant oil well pipe steel.

[0003] The resistance of oil well pipe to hydrogen sulfide stress corrosion cracking is closely related to its original austenite grain size, matrix structure, inclusions, second phase and dislocations. High-grade sulfur-resistant pipes at home and abroad currently use 13Cr stainless steel and nickel-based alloys, but the price is relatively expensive.

[0004] At present, most of the steel used for oil well pipes contains alloys such as Ti, Nb, and Ni, which results in high cost, or the strength of some steel used for oil well pipes cannot meet the service requirements in deep and highly corrosive environments. Summary of the invention

[0005] In view of the above situation, the present invention aims to provide a sulfur-resistant oil well pipe steel and a preparation method thereof, so as to solve one of the following technical problems: (1) a variety of alloy elements are added to the existing oil well pipe steel, which has a high cost; (2) the sulfur resistance and toughness of the existing oil well pipe steel cannot be improved at the same time.

[0006] The purpose of the present invention is mainly achieved through the following technical solutions:

[0007] On the one hand, the present invention provides a sulfur-resistant steel for oil well pipes, wherein the components of the sulfur-resistant steel for oil well pipes include, by mass percentage, C: 0.45%-0.55%, Si: 0.51%-0.60%, Mn: 0.05%-0.15%, Mo: 0.75%-0.85%, Cr: 1.41%-1.55%, V: 0.31%-0.35%, Al: 0.4%-0.5%, Cu: 0.9%-1.1%, P: ≤0.010%, S: ≤0.003%, and the balance is Fe and unavoidable impurities.

[0008] Furthermore, in the composition of sulfur-resistant oil well pipe steel, Mo+C is controlled to be 1.2% to 1.3%.

[0009] Furthermore, in the composition of the sulfur-resistant oil well pipe steel, the C / V value is controlled to be 1.3 to 1.7.

[0010] Furthermore, the components of the sulfur-resistant oil well pipe steel are, by mass percentage, C: 0.47% to 0.55%, Si: 0.51% to 0.60%, Mn: 0.05% to 0.15%, Mo: 0.75% to 0.83%, Cr: 1.431% to 1.55%, V: 0.31% to 0.35%, Al: 0.41% to 0.5%, Cu: 0.9% to 1.1%, P: ≤0.010%, S: ≤0.003%, and the balance is Fe and unavoidable impurities.

[0011] Furthermore, the room temperature microstructure of the sulfur-resistant oil well pipe steel has a matrix of tempered troostite, with VC precipitate phase and copper-rich phase dispersed in the matrix.

[0012] Furthermore, the room temperature microstructure grain size of the sulfur-resistant oil well pipe steel is below 20 μm.

[0013] The present invention also provides a method for preparing sulfur-resistant steel for oil well pipes, which is used to prepare the above-mentioned sulfur-resistant steel for oil well pipes. The preparation method comprises:

[0014] Step 1: smelting and pouring to obtain a billet or ingot;

[0015] Step 2: subjecting the billet or ingot to high temperature homogenization treatment and then rolling it to obtain a rough pipe;

[0016] Step 3: After quenching the rough pipe, high-temperature tempering is performed to obtain sulfur-resistant oil well pipe steel.

[0017] Furthermore, the specific steps of step 2 include: heating the billet or ingot to 1150-1200° C. in a heating furnace, and keeping it at 1150-1200° C. for 1-3 hours, and performing piercing hot rolling and cooling after taking it out of the furnace to obtain a rough pipe of the required size.

[0018] Furthermore, in step 2, the final rolling temperature of hot rolling is controlled at 850-900°C.

[0019] Furthermore, the holding temperature of quenching is 820-900°C, and the holding temperature of high temperature tempering is 700-800°C.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] a) The sulfur-resistant oil well pipe steel provided by the present invention ensures that the matrix structure of the steel of the present invention is tempered troostite by precisely controlling the mass percentage of elements such as C, Si, Mn, Cr, Mo, V, Cu, Al, etc. in the steel and controlling the coordinated quantitative relationship of some elements, and a large number of fine dispersed precipitates (such as VC and copper-rich phase) are present on the matrix, thereby ensuring that the sulfur-resistant oil well pipe steel of the present invention has a high strength level, high toughness and good SSCC resistance.

[0022] b) In the preparation method of the present invention, by precisely controlling each step and process parameters, "tempered troostite structure + VC, copper-rich phase precipitation" is obtained, and due to the increase in tempering temperature, the dislocation density in the test steel is significantly reduced, and the harm of reversible hydrogen traps to sulfur resistance is reduced. Among them, the tempered troostite has good toughness and plasticity matching and excellent anti-SSCC performance as the matrix structure. At the same time, the copper-rich phase is an FCC structure, and its H solid solubility is much higher than the BCC structure of the matrix. It can be used as a hydrogen trap to absorb more H and improve the matrix's anti-SSCC performance. The precipitated VC phase can not only improve the strength and toughness of the pipe through the effect of precipitation strengthening, but also can be used as an irreversible hydrogen trap to accommodate more H, improve the matrix's anti-SSCC performance, and pin the grain boundaries during the quenching process, refine the grains, and improve the anti-SSCC performance. Only by heat treatment within the composition, steps and temperature range of the present invention can the strength and toughness of the steel of the present invention be matched, and all reach the required range.

[0023] c) The sulfur-resistant oil well pipe steel of the present invention has good comprehensive properties, for example, yield strength ≥962MPa (e.g. 962-995MPa), tensile strength ≥1060MPa (e.g. 1062-1120MPa), 0°C impact energy ≥175J (e.g. 177-210J), with reference to NACE TM0177-2016 standard, currently has passed A method A solution, H 2 The sulfur partial pressure is 0.1 MPa, the loading stress is 85% (733 MPa) of the minimum yield strength, and the experimental temperature is 24° C. The sulfur-resistant oil well pipe steel of the present invention has high strength, good toughness and good corrosion resistance.

[0024] d) The sulfur-resistant oil well pipe steel provided by the present invention does not add expensive alloy elements such as Nb and Ni, which greatly reduces the production cost. The preparation method of the present invention is simple and suitable for large-scale production and application.

[0025] Other features and advantages of the present invention will be described in the following description, and part of them will become obvious from the description, or will be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the contents particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings are only for the purpose of illustrating specific embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0027] Figure 1 The microstructure diagram of the steel of Example 1 of the present invention;

[0028] Figure 2 The microstructure diagram of the steel of Example 2 of the present invention;

[0029] Figure 3 This is a microstructure diagram of the steel of Example 3 of the present invention. DETAILED DESCRIPTION

[0030] Preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used to explain the principles of the present invention together with the embodiments of the present invention.

[0031] The invention provides a sulfur-resistant steel for oil well pipes. The components of the sulfur-resistant steel for oil well pipes include, by mass percentage, C: 0.45%-0.55%, Si: 0.51%-0.60%, Mn: 0.05%-0.15%, P: ≤0.010%, S: ≤0.003%, Mo: 0.75%-0.85%, Cr: 1.41%-1.55%, V: 0.31%-0.35%, Al: 0.4%-0.5%, Cu: 0.9%-1.1%, and the balance is Fe and unavoidable impurities.

[0032] Specifically, in the composition of the sulfur-resistant oil well pipe steel, Mo+C is controlled to be 1.2% to 1.3%, C+Cr+Mo is controlled to be 2.70% to 2.90%, and the C / V value is controlled to be 1.3 to 1.7.

[0033] The following is a detailed description of the effects and dosage of the components in the present invention:

[0034] C: Carbon is a solid solution strengthening element. When the C content in steel is low, its strength and hardness are generally low. The increase in C content can not only increase the strength and hardness of steel, but also shift the CCT curve of steel to the right, reduce the critical cooling rate of martensitic phase transformation, and increase the hardenability of steel. However, too high C content will reduce the plasticity and toughness of steel, making its welding performance poor. Too high C content will lead to excessive strength of steel and high sensitivity to hydrogen-induced cracking, which is not conducive to the SSCC resistance of oil well pipes. Therefore, the C content is controlled between 0.45% and 0.55%.

[0035] Si: Si is a ferrite-forming element and has a strong solid solution strengthening effect, which can increase the hardness and strength of steel, making the steel have better yield and tensile strength. Therefore, the content of Si in the present invention is controlled at 0.51% to 0.60%.

[0036] Mn: Mn is a strong austenite forming element, which is beneficial to increase the hardenability of the material and is a significant strengthening element. However, the increase in Mn content will reduce the material's resistance to sulfide stress cracking. When the Mn content exceeds 0.15%, the material's resistance to sulfide stress cracking is reduced. However, when the Mn content is less than 0.15%, it is beneficial to convert sulfur into sulfide and discharge it during the smelting process, improve the metallurgical quality of steel, and thus improve the resistance to sulfide stress cracking. Therefore, the Mn content is controlled at 0.05% to 0.15%.

[0037] P: P is an impurity in steel and is not conducive to toughness. In the present invention, the P content is controlled to be ≤0.010%.

[0038] S: S seriously deteriorates the hydrogen sulfide stress corrosion resistance of steel and is easy to combine with Mn to form MnS inclusions. The stress area at the tip of the MnS inclusion is easy to become the initiation site of sulfide stress cracking. In the present invention, its content is controlled to ≤ 0.003%.

[0039] Mo: Mo can significantly improve the hardenability and ensure that the steel can obtain martensite structure during quenching; at the same time, adding Mo element can improve the tempering resistance, ensure that when tempering at a higher temperature, the dislocation density of the steel is reduced, the hydrogen diffusion aggregation is reduced, and the resistance to sulfide stress cracking is improved. When the Mo+C content is ≤1.3%, MC and M 3 C-type carbides, and the carbides are dispersed and refined as the Mo content increases, which is beneficial to improve the distribution of diffusible hydrogen and improve the steel's resistance to sulfide stress cracking; however, when the Mo+C content is greater than 1.3%, it is easy to form M 2 C and M 6 C-type carbide is not conducive to the resistance to sulfide stress corrosion; when the Mo+C content is less than 1.2%, the resistance to sulfide stress cracking is low. Therefore, in the present invention, the Mo content is controlled to be 0.75% to 0.85%, and the Mo+C is controlled to be 1.2% to 1.3%, for example, the Mo+C is 1.22% to 1.3%.

[0040] Cr: Cr plays a role in sulfur-resistant steel, similar to Mo. Cr is also an element that improves the hardenability of pipes. It works synergistically with Mo to improve the hardenability. The total amount of C+Cr+Mo should be above 2.7% so that martensitic structure can be obtained after quenching. When the Cr content is ≥1.6%, it is easy to form coarse M distributed along the grain boundaries. 7 C 3 and M 23 C6 Type precipitation particles are the source of hydrogen-induced cracks. In contrast, when the Cr content is ≤1.55%, fine carbides are easily formed, which can act as a benign "hydrogen trap" to improve the distribution of hydrogen atoms in the steel and improve the material's resistance to sulfide stress cracking. When the Cr content is less than 1.41%, the resistance to sulfide stress cracking is low, so the Cr content is controlled at 1.41% to 1.55%. Taking all factors into consideration, C+Cr+Mo is controlled to be 2.70% to 2.90%.

[0041] V: The carbides precipitated from V during quenching can refine the grains by pinning the grain boundaries. The carbides precipitated during tempering can not only play a precipitation strengthening effect, improve the toughness of the steel, but also improve the high-temperature tempering resistance. When the V content in the steel is ≤0.35%, the C content dissolved in the steel will decrease, reducing the appearance of banded structure and reducing the SSCC sensitivity. However, when the V content in the steel is greater than 0.35%, the toughness of the material will be significantly reduced. Therefore, in the present invention, the V content is controlled to be 0.31% to 0.35%, and the C / V value is controlled to be 1.3 to 1.7, for example, the C / V value is controlled to be 1.35 to 1.68.

[0042] Cu: Cu is one of the elements that effectively improves corrosion resistance. Cu can precipitate a copper-rich phase after tempering, which is a typical FCC structure. The solubility of H element in the FCC structure is much higher than that in the BCC structure of the matrix. Therefore, the copper-rich phase can dissolve a large amount of hydrogen ions and improve the anti-SSCC performance of the pipe. Therefore, the Cu content in the present invention is 0.9% to 1.1%.

[0043] Al: Al is an essential element for steel deoxidation and can also increase the tempering temperature of steel. The increase in tempering temperature is beneficial to reducing the dislocation density in steel, weakening the harmful effects of reversible hydrogen traps, and improving the SSCC resistance. Therefore, the Al content in the present invention is 0.4% to 0.5%.

[0044] In order to further improve the comprehensive performance of the above-mentioned sulfur-resistant oil well pipe steel, the components of the above-mentioned sulfur-resistant oil well pipe steel can be calculated by mass percentage: C: 0.47% to 0.55%, Si: 0.51% to 0.60%, Mn: 0.05% to 0.15%, Mo: 0.75% to 0.83%, Cr: 1.431% to 1.55%, V: 0.31% to 0.35%, Al: 0.41% to 0.5%, Cu: 0.9% to 1.1%, P: ≤0.010%, S: ≤0.003%, and the balance is Fe and unavoidable impurities.

[0045] Specifically, the room temperature microstructure of the above sulfur-resistant oil well pipe steel has a matrix of tempered troostite, with VC precipitated phase and copper-rich phase dispersed on the matrix.

[0046] Specifically, the grain size of the room temperature microstructure of the sulfur-resistant oil well pipe steel is less than 20 μm, for example, 10 to 19 μm.

[0047] Specifically, in the room temperature microstructure of the sulfur-resistant oil well pipe steel, the volume fraction of the copper-rich phase is ≥1%, for example, 1% to 1.5%.

[0048] Specifically, in the room temperature microstructure of the sulfur-resistant oil well pipe steel, the size of the VC precipitated phase is substantially nanometer-scale, and the shape is mostly spherical, for example, the size of the VC precipitated phase is 10 to 60 nm.

[0049] Specifically, the mass fraction of the VC precipitated phase is 0.4% to 0.8%.

[0050] Specifically, the dislocation density of the above sulfur-resistant oil well pipe steel is 2.01×10 9 cm -2 ~2.08×10 10 cm -2 .

[0051] The present invention also provides a method for preparing the above-mentioned sulfur-resistant oil well pipe steel, comprising:

[0052] Step 1: smelting and pouring to obtain a billet or ingot;

[0053] Step 2: subjecting the billet or ingot to high temperature homogenization treatment and then rolling it to obtain a rough pipe;

[0054] Step 3: After quenching the rough pipe, high-temperature tempering is performed to obtain sulfur-resistant oil well pipe steel.

[0055] Specifically, in the above step 1, a converter, an electric furnace or an induction furnace may be used for smelting, and continuous casting may be used to produce billets, or mold casting may be used to produce ingots.

[0056] Specifically, the role of the above step 2 is to ensure that all alloy elements are dissolved and exist in the matrix in the form of solid solution. Considering that the holding temperature is too high or the holding time is too long, the austenite grains will grow excessively or even overheat, affecting the final performance of the material; the holding temperature is too low or the holding time is too short, resulting in the steel being unable to be completely austenitized or the alloy elements are not fully dissolved, and the steel composition is uneven, affecting the performance. Therefore, the specific steps of controlling the above step 2 include: heating the billet or ingot to 1150-1200°C (for example, 1160°C, 1170°C, 1180°C, 1190°C) in a heating furnace, and keeping it at 1150-1200°C for 1-3 hours, and after being taken out of the furnace, piercing hot rolling and cooling are performed to obtain a rough pipe of the required size.

[0057] Specifically, in the above step 2, the holding time t and the temperature, the thickness d of the billet or ingot conform to the following relationship: when the holding temperature is 1150-1180°C, t1=40d, where the unit of t is s and the unit of d is mm; when the holding temperature is greater than 1180°C, t2=30d, where the unit of t is s and the unit of d is mm.

[0058] Specifically, in the above step 2, water spray cooling is used to form a rough pipe after exiting the rolling mill.

[0059] Specifically, in the above step 2, the final rolling temperature of hot rolling is controlled at 850-900° C. (eg, 860° C., 870° C., 880° C., 890° C.) to ensure that a certain amount of VC precipitation phase is precipitated during the rolling process.

[0060] Specifically, the specific steps of the above step 3 include:

[0061] Step 3-1, quenching: heat the rough pipe to the complete austenitization temperature of 820-900°C and keep it at this temperature for 0.5-2h, then quench it to room temperature;

[0062] Step 3-2, high temperature tempering: heat the rough tube to 700-800℃, keep it at this temperature for 2-5h and then air cool it to room temperature.

[0063] Specifically, in the above step 3-1, quenching is to heat the rough pipe to the complete austenitization temperature of 820-900°C and keep it warm for 0.5-2h to ensure that the pipe structure is completely austenitized, and at the same time, VC is not completely dissolved, and a part of it is still precipitated, pinning the grain boundary to prevent the grain boundary from growing, which plays a role in refining the grain and improving the SSCC resistance; then quenching to room temperature to obtain a complete martensitic structure. Although the grain boundary is not obviously grown due to the pinning of VC precipitation, the high temperature or the long holding time has little effect on the final performance and reduces the production efficiency; the holding temperature is too low or the holding time is too short, resulting in the inability of the steel to be completely austenitized, and the steel pipe structure is uneven, affecting the performance. Therefore, the rough pipe is controlled to be heated to 820-900°C (for example, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C) and kept warm for 0.5-2h (for example, 1h, 1.5h, 2h).

[0064] Specifically, in the above step 3-1, if the heating rate is too high, the temperature difference between the surface and the core will be too large, resulting in uneven performance; if the heating rate is too low, the actual heat preservation time will be too long, which is not conducive to strength. Therefore, the heating rate is controlled to be 1 to 4°C / s, such as 2°C / s or 3°C / s.

[0065] Specifically, in the above step 3-2, the high temperature tempering temperature is 700-800°C (e.g., 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C), and the temperature is kept for 2-5h (e.g., 3h, 3.5h, 4h) and then air-cooled to room temperature. Through step 3-2, the quenched martensite structure is transformed into a fine tempered troostite structure, and the comprehensive mechanical properties and SSCC resistance are significantly improved.

[0066] Specifically, in the above step 3-2, the high temperature tempering temperature is 700-800°C, VC can be dispersed and precipitated in large quantities, and the mass fraction of the precipitated VC particles is 0.4%-0.8%. The shape of these nano-scale VC particles is mostly spherical, and this VC precipitated phase can act as an irreversible hydrogen trap to absorb a large amount of H + , reduce the matrix H + Concentration, not easy to serve as the initiation site of hydrogen-induced cracks, improving the anti-SSCC performance.

[0067] Specifically, in the above step 3-2, the high temperature tempering temperature is 700-800°C, and a copper-rich phase is formed. The copper-rich phase, as an FCC structure, can not only improve the toughness of the material, but also absorb and dissolve H diffused into the steel. + , which greatly improves the corrosion resistance of the pipe and enhances its SSCC resistance.

[0068] Specifically, in the above step 3-2, the high temperature tempering temperature is 700-800° C., which can effectively reduce the dislocation density in the steel, reduce the number of reversible hydrogen traps, and enhance the SSCC resistance.

[0069] Specifically, in the above step 3-2, the steel pipe is placed in a tempering furnace and heated to 700-800° C. at a heating rate of 1-4° C. / s (eg, 2° C. / s, 3° C. / s).

[0070] Specifically, in the above step 3, the mechanical properties of the sulfur-resistant oil well pipe steel obtained are as follows: yield strength ≥962MPa (e.g., 962-995MPa), tensile strength ≥1060MPa (e.g., 1062-1120MPa), 0°C impact energy ≥175J (e.g., 177-210J), high strength and toughness, excellent performance; referring to the NACE TM0177-2016 standard, it has passed the A method A solution, H 2 The S partial pressure is 0.1MPa, the loading stress is 85% of the minimum yield strength (733MPa), and the test temperature is 24°C. Good corrosion resistance.

[0071] Examples 1-8

[0072] Embodiments 1-8 of the present invention provide a sulfur-resistant steel for oil well pipe and a preparation method thereof. The components of the steels of Embodiments 1-8 are shown in Table 2 below.

[0073] The preparation method of the sulfur-resistant oil well pipe steel of Examples 1-8 comprises:

[0074] (1) Use converter steelmaking and continuous casting to produce tube billets;

[0075] (2) Using seamless tube forming technology, the tube blank is heated to the homogenization temperature, kept at a constant temperature for a period of time, then taken out of the furnace, pierced and rolled, and after leaving the rolling mill at an appropriate final rolling temperature, water spray cooling is used to form a rough tube;

[0076] (3) The cooled rough pipe is heated to the quenching temperature, kept at the temperature for a certain period of time, and then quenched to room temperature; then the steel pipe is heated to a certain tempering temperature, kept at the temperature for a certain period of time, and then air-cooled to room temperature, and finally sulfur-resistant oil well pipe steel is obtained.

[0077] The specific preparation process parameters of the steel of Examples 1-8 are shown in Table 1 below, the composition is shown in Table 2, the microstructure is shown in Table 3, the mechanical properties are shown in Table 4, and the SSCC resistance is shown in Table 5. The microstructure of Example 1 is shown in Table 1. Figure 1 As shown, the microstructure of Example 2 is as follows Figure 2 As shown, the microstructure of Example 3 is as follows Figure 3 shown.

[0078] Table 1 Process parameters

[0079]

[0080]

[0081] Table 2 Chemical composition (%)

[0082] Element C Si Mn P S Cr Mo V Al Cu C+Mo C+Cr+Mo C / V Example 1 0.49 0.51 0.06 0.008 0.002 1.51 0.77 0.33 0.44 1.01 1.26 2.77 1.48 Example 2 0.48 0.60 0.08 0.007 0.003 1.50 0.82 0.35 0.41 0.95 1.3 2.80 1.37 Example 3 0.50 0.54 0.05 0.009 0.003 1.44 0.8 0.31 0.47 1.04 1.3 2.74 1.61 Example 4 0.52 0.55 0.10 0.006 0.002 1.53 0.77 0.32 0.43 0.98 1.29 2.82 1.63 Example 5 0.48 0.60 0.09 0.008 0.003 1.47 0.75 0.35 0.48 1.05 1.23 2.70 1.37 Example 6 0.48 0.51 0.13 0.005 0.003 1.44 0.82 0.33 0.47 0.99 1.3 2.74 1.45 Example 7 0.51 0.58 0.11 0.006 0.003 1.45 0.76 0.31 0.41 0.96 1.27 2.72 1.65 Example 8 0.51 0.56 0.15 0.007 0.003 1.50 0.79 0.32 0.43 0.91 1.3 2.80 1.59 Comparative Example 1 0.23 0.12 0.25 0.005 0.003 0.68 0.63 0.07 0.05 0.53 0.86 1.54 3.28 Comparative Example 2 0.42 0.33 0.45 0.004 0.002 0.52 1.05 0.12 0.05 0.52 1.47 1.99 3.50 Comparative Example 3 0.49 0.52 0.09 0.005 0.003 1.49 0.76 0.33 0.45 0.99 1.25 2.74 1.48

[0083] Table 3 Microstructure

[0084]

[0085]

[0086] Table 4 Mechanical properties

[0087] Yield strength / MPa Tensile strength / MPa 0℃ impact energy / J Example 1 963 1062 182 Example 2 987 1089 195 Example 3 962 1067 177 Example 4 972 1072 179 Example 5 993 1106 191 Example 6 981 1080 185 Example 7 995 1113 208 Example 8 979 1081 183 Comparative Example 1 871 923 150 Comparative Example 2 892 951 123 Comparative Example 3 868 916 135

[0088] Table 5 Anti-SSCC performance

[0089]

[0090]

[0091] The inventor has conducted a large number of experimental studies during the research process, and now uses some solutions with poor performance as comparative examples.

[0092] Comparative Example 1

[0093] This comparative example provides a steel for oil well pipes, the components of which are shown in Table 2 above, and the preparation method is the same as that of Example 1, which will not be repeated here. The components of this comparative example do not meet the requirements of the present invention, and the performance is lower than that of the examples of the present invention.

[0094] Comparative Example 2

[0095] This comparative example provides a steel for oil well pipes, the components of which are shown in Table 2 above, and the preparation method is the same as that of Example 1, which will not be repeated here. The components of this comparative example do not meet the requirements of the present invention, and the performance is lower than that of the examples of the present invention.

[0096] Comparative Example 3

[0097] This comparative example provides a steel for oil well pipes, the components of which are the same as those of Example 1. In the preparation method, homogenization is performed at 1135°C for 2 hours, quenching is performed at 750°C for 1.5 hours, and tempering is performed at 600°C for 2 hours. The preparation method of this comparative example does not meet the requirements of the present invention, and the performance is lower than that of the examples of the present invention.

[0098] The main performance test results of the comparative steel are shown in Table 5 above.

[0099] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A sulfur-resistant steel for oil well pipe, characterized in that: The components of the sulfur-resistant oil well pipe steel include, by mass percentage, C: 0.45% to 0.55%, Si: 0.51% to 0.60%, Mn: 0.05% to 0.15%, Mo: 0.75% to 0.85%, Cr: 1.41% to 1.55%, V: 0.31% to 0.35%, Al: 0.4% to 0.5%, Cu: 0.9% to 1.1%, P: ≤0.010%, S: ≤0.003%, and the balance is Fe and unavoidable impurities.

2. The sulfur-resistant steel for oil well pipe according to claim 1, characterized in that: In the composition of the sulfur-resistant oil well pipe steel, Mo+C is controlled to be 1.2% to 1.3%.

3. The sulfur-resistant steel for oil well pipe according to claim 1, characterized in that: In the components of the sulfur-resistant oil well pipe steel, the C / V value is controlled to be 1.3 to 1.

7.

4. The sulfur-resistant steel for oil well pipe according to claim 1, characterized in that: The components of the sulfur-resistant oil well pipe steel are, by mass percentage, C: 0.47%-0.55%, Si: 0.51%-0.60%, Mn: 0.05%-0.15%, Mo: 0.75%-0.83%, Cr: 1.431%-1.55%, V: 0.31%-0.35%, Al: 0.41%-0.5%, Cu: 0.9%-1.1%, P: ≤0.010%, S: ≤0.003%, and the balance is Fe and unavoidable impurities.

5. The sulfur-resistant steel for oil well pipe according to any one of claims 1 to 4, characterized in that: The room temperature microstructure of the sulfur-resistant oil well pipe steel has a matrix of tempered troostite, and VC precipitated phase and copper-rich phase are dispersed on the matrix.

6. The sulfur-resistant steel for oil well pipe according to claim 5, characterized in that: The grain size of the room temperature microstructure of the sulfur-resistant oil well pipe steel is below 20 μm.

7. A method for preparing sulfur-resistant oil well pipe steel, characterized in that: The preparation method is used to prepare the sulfur-resistant oil well pipe steel according to any one of claims 1 to 6, and the preparation method comprises: Step 1: smelting and pouring to obtain a billet or ingot; Step 2: subjecting the billet or ingot to high temperature homogenization treatment and then rolling it to obtain a rough pipe; Step 3: After quenching the rough pipe, high-temperature tempering is performed to obtain sulfur-resistant oil well pipe steel.

8. The preparation method according to claim 7, characterized in that: The specific steps of step 2 include: heating the billet or ingot to 1150-1200° C. in a heating furnace, and keeping it at 1150-1200° C. for 1-3 hours, and performing piercing hot rolling and cooling after taking it out of the furnace to obtain a rough pipe of the required size.

9. The preparation method according to claim 7, characterized in that: In the step 2, the final rolling temperature of hot rolling is controlled at 850-900°C.

10. The preparation method according to any one of claims 7 to 9, characterized in that: The holding temperature of the quenching is 820-900°C, and the holding temperature of the high-temperature tempering is 700-800°C.

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