CN115874113A - Low-temperature-resistant steel for oil well pipe and preparation method thereof - Google Patents
Low-temperature-resistant steel for oil well pipe and preparation method thereof Download PDFInfo
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Abstract
The invention discloses low-temperature-resistant steel for an oil well pipe and a preparation method thereof, belongs to the technical field of steel for the oil well pipe, and solves the problem that austenite low-temperature oil well pipe steel in the prior art is poor in low-temperature toughness. The steel for the low-temperature-resistant oil well pipe comprises the following components in percentage by mass: 0.02 to 0.10 percent of C, 2.0 to 6.5 percent of Mn, 0.02 to 0.10 percent of V, 0.20 to 0.60 percent of Mo, 0.01 to 0.02 percent of Ti, less than or equal to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities. The low-temperature-resistant steel for the oil well pipe has higher strength level, higher toughness and better low-temperature fracture toughness.
Description
Technical Field
The invention relates to the technical field of steel for oil well pipes, in particular to low-temperature-resistant steel for oil well pipes and a preparation method thereof.
Background
In order to meet the increasing demand of world economy on oil and gas resource consumption, oil and gas resource exploration and exploitation gradually extend to high-altitude, deep-land and deep-sea areas. According to the existing prediction, the reserves of the arctic oil and gas exceed billions of tons, and the reserves of the antarctic oil and gas exceed billions of tons, and countries have expanded a new round of competition for the speaking right of resources of south and arctic. The major problem facing polar oil and gas production is the extremely low temperature environment (-94.2 c), which presents a serious challenge to the selection of materials for key components of oil and gas production. Oil well pipes are the core components for oil and gas production, and the quality of the oil well pipes is directly related to the service life, production efficiency and production cost of the oil well. The oil well pipe for operation in high and cold area needs to bear high strength load of hundreds or even thousands of atmospheres, and also needs to avoid brittle fracture in low temperature environment, and severe service condition. Therefore, more severe and special performance requirements are provided for the oil well pipe for oil and gas exploitation: the toughness, especially the low-temperature fracture toughness of the material under the ultralow temperature environment; the temperature difference of fluid inside and outside the pipe body, the temperature difference between the bottom of the well and the surface of the well, and the alternating stress fatigue performance of cold and hot circulation; the steam flooding method has the requirements of heat resistance/cold resistance and the like on oil well pipe materials. The use environment temperature of the low-temperature/ultralow-temperature oil well pipe developed in Russia and France reaches below minus 60 ℃, and the research and development of various oil casing materials used in ultralow-temperature and ultralow-temperature environments are not developed in China. Therefore, key materials for polar environment oil and gas resource development equipment are urgently to be developed to guarantee the energy strategic development of China.
At present, the material selection of foreign low-temperature oil well pipes mainly comprises two types: one is ferritic low-temperature steel, such as low-Ni steel, nickel-chromium-molybdenum steel and other low alloy steels; another is austenitic low temperature steel, such as high and medium alloyed steels like 6Ni steel, 9Ni steel, 36Ni steel, etc. The austenitic low-temperature steel has good low-temperature toughness, generally has no ductile-brittle transition temperature, is safer to use, but is high in price and difficult to apply to large-batch oil well pipes. The ferrite low-temperature steel is low in price, but has obvious ductile-brittle transition temperature and poor low-temperature toughness, brittle failure is easy to occur in the using process, and huge economic loss is brought to oil and gas exploitation. In order to ensure certain low-temperature toughness, the existing low-temperature oil well pipe is generally selected from materials with high Ni content, so that the alloy cost is expensive.
Disclosure of Invention
In view of the above circumstances, the present invention aims to provide a low temperature resistant steel for oil country tubular goods and a method for producing the same, which can solve at least one of the following problems: (1) The cost of the austenite low-temperature oil well pipe steel in the prior art is high; (2) In the prior art, the low-temperature toughness of the ferrite low-temperature oil well pipe steel is poor.
The purpose of the invention is mainly realized by the following technical scheme:
in one aspect, the invention provides a low temperature resistant steel for an oil well pipe, which comprises the following components in percentage by mass: 0.02 to 0.10 percent of C, 2.0 to 6.5 percent of Mn, 0.02 to 0.10 percent of V, 0.20 to 0.60 percent of Mo, 0.01 to 0.02 percent of Ti, less than or equal to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
In one possible design, the composition of the steel for a low temperature resistant oil well pipe comprises, in mass percent: 0.04 to 0.10 percent of C, 3.0 to 6.5 percent of Mn, 0.04 to 0.10 percent of V, 0.30 to 0.60 percent of Mo, 0.011 to 0.02 percent of Ti, 0.2 to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
In one possible design, the room temperature structure of the low temperature resistant oil well pipe steel is a 'tempered sorbite + retained austenite' mixed structure, and a dispersed and refined second phase is distributed on a matrix.
In one possible design, the residual austenite volume fraction in the room temperature structure of the low temperature resistant oil well pipe steel is greater than or equal to 5%.
In another aspect, the present invention provides a method for producing a steel for a low temperature resistant oil well pipe, the method comprising:
step 1, smelting and pouring to obtain a casting blank or an ingot;
step 2, performing high-temperature homogenization treatment on the casting blank or the casting ingot, and then rolling to obtain a pierced billet;
and 3, quenching the pierced billet twice and then tempering to obtain the low-temperature-resistant steel for the oil well pipe with the tempered sorbite and residual austenite structures.
In one possible design, step 2 includes: heating the casting blank or the ingot in a heating furnace to 1100-1200 ℃, preserving the heat for 1-3 h at 1100-1200 ℃, and performing perforation hot rolling and cooling after discharging to obtain a pierced billet.
In one possible design, in step 2, the pierced billet is formed by water spray cooling after exiting the rolling mill.
In one possible design, step 3 includes:
s301, primary quenching: heating the pierced billet to a temperature higher than the austenitizing temperature, preserving heat, and then quenching to room temperature;
s302, secondary quenching: heating the quenched pierced billet to the temperature of a two-phase region, preserving heat, and then quenching to room temperature to obtain a steel pipe;
s303, tempering: and (3) putting the steel pipe into a tempering furnace, heating to 650-680 ℃ along with the furnace, preserving heat for 0.5-2 h, and then air-cooling to room temperature to obtain the low-temperature-resistant steel for the oil well pipe with the tempered sorbite and residual austenite structures.
In a possible design, S301, heating the pierced billet to 880-920 ℃, and preserving heat for 0.5-2 h.
In a possible design, in S302, the quenched pierced billet is heated to 750-800 ℃ and is kept warm for 0.5-2 h.
Compared with the prior art, the invention has the following beneficial effects:
a) The steel for the low-temperature-resistant oil well pipe provided by the invention ensures that the tempered sorbite + residual austenite (volume fraction is more than or equal to 5%) of the steel and the dispersed and refined structure of the second phase are distributed on the matrix by accurately controlling the mass percentages of elements such as C, si, mn, V, mo and the like in the steel and combining the processes of quenching and tempering twice, so that the steel for the low-temperature-resistant oil well pipe has higher strength level, higher toughness and better low-temperature fracture toughness. Ensuring that the steel of the invention can meet excellent mechanical properties. The invention can form a low-cost solution without adding alloy elements such as Cr, ni and the like.
b) The invention obtains a structure of 'tempered sorbite + residual austenite + a structure of a matrix distributed with dispersed and refined second phase' by controlling the process, wherein the volume fraction of the residual austenite is more than or equal to 5 percent, thereby obtaining ideal matching of room-temperature toughness and low-temperature fracture toughness; the strength and toughness of the steel of the present composition can only be matched by heat treatment within the composition, procedure and temperature ranges of the present invention, all to the required range.
c) The low-temperature-resistant steel for the oil well pipe, which is prepared by adopting the components and the method, has good comprehensive mechanical property, the yield strength is more than or equal to 555MPa, the tensile strength is more than or equal to 620MPa, the yield ratio is more than 0.8, the elongation is more than or equal to 25 percent, and the impact toughness at the temperature of minus 60 ℃ is more than or equal to 180J; the steel of the invention ensures the service performance requirement of extremely cold environment, and the component system also greatly reduces the alloy cost.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a microstructure diagram of a steel of example 1 of the present invention;
FIG. 2 is a microstructure diagram of a steel of example 2 of the present invention;
FIG. 3 is a microstructure diagram of a steel of example 5 of the present invention;
FIG. 4 is a microstructure diagram of the steel of example 6 of the present invention.
Detailed Description
The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention.
The invention provides a low-temperature-resistant steel for an oil well pipe, which comprises the following components in percentage by mass: 0.02 to 0.10 percent of C, 2.0 to 6.5 percent of Mn, 0.02 to 0.10 percent of V, 0.20 to 0.60 percent of Mo, 0.01 to 0.02 percent of Ti, less than or equal to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
The function and amount of the components contained in the present invention are specifically described below:
c: carbon is a typical interstitial solid solution strengthening element, and increasing the content of carbon element in the alloy is an effective way to improve the strength of the alloy, but too high content of carbon can cause severe reduction of the toughness and plasticity of the material. Researches find that the carbon content has remarkable influence on the form of a martensite structure, and the martensite form in the high-carbon steel mainly comprises sheet martensite (twin crystal martensite), so that the high-carbon steel has high strength and extremely poor plasticity; when the carbon content is less than 0.3%, the martensite structure is mainly lath martensite, and a small amount of sheet martensite exists between lath martensite; when the carbon content is reduced by 0.26% or less, the martensite structure is almost entirely lath martensite, i.e., dislocation-type martensite. On the premise of the same strength, the dislocation type martensite has the advantages of better toughness, lower ductile-brittle transition temperature, smaller notch sensitivity and the like compared with the twin crystal type martensite, and has the same performance even after tempering. Therefore, in order to ensure that the steel for the low temperature resistant oil well pipe has good low temperature toughness matching, the content of C in the steel for the low temperature resistant oil well pipe is controlled to be 0.02 to 0.10 percent.
Si: si is a deoxidizer in steel making and has a solid solution strengthening effect, but excessive Si is unfavorable for the toughness and hydrogen sulfide corrosion resistance of steel. Therefore, the content of Si in the present invention is controlled to be 0.50% or less.
Mn: the addition of manganese can reduce the martensite transformation temperature Ms and increase the content of the retained austenite, and particularly, when the content of Mn in the steel is more than or equal to 3 percent, the resistance to the decomposition of the retained austenite can be effectively improved. However, too high Mn content greatly improves the stability of the retained austenite, so that the retained austenite does not undergo phase transformation even in the presence of high plastic deformation, which is not favorable for improving the ductility of the workpiece. Therefore, the Mn content is controlled to be in the range of 2.0 to 6.5% in the present invention.
V: v can refine crystal grains in the pipe penetrating process, form carbide in the heat treatment tempering process to play a role in precipitation strengthening, and can improve the high-temperature tempering resistance and ensure that the dislocation density of steel is reduced in the high-temperature tempering process; however, when the content of V in steel is too high, the toughness of the material is significantly reduced, and thus, the content of V is controlled to 0.02% to 0.10% in the present invention.
Mo: mo is an element for expanding hardenability, and can delay the transformation from austenite to bainite in the continuous cooling process; meanwhile, the tempering stability of the steel is improved in the high-temperature tempering process of the Mo element, so that the steel is ensured to have good toughness, and the steel is ensured to have good comprehensive mechanical properties under higher strength. In the invention, the content of Mo is controlled to be 0.20-0.60%.
Al: al is an element necessary for deoxidation of steel, so that introduction of Al into steel cannot be completely avoided, but when the Al content exceeds 0.1%, the casting process of steel is adversely affected, so that the inventors limited the mass percentage of acid-soluble aluminum in the present invention to ais: less than or equal to 0.05 percent.
P: p belongs to impurities in steel, which is not beneficial to weldability and toughness, and the content of P is controlled to be less than or equal to 0.010 percent.
S: s seriously deteriorates the corrosion resistance and the toughness of the steel, and the content of the S is controlled to be less than or equal to 0.0030 percent in the invention.
Ti: the titanium element is very active, has strong affinity with elements such as carbon, sulfur, nitrogen and the like, and mainly exists in the form of titanium compounds in steel. The fine dispersed TiC or TiN formed in the solidification process can be used as nucleation particles to play a role in refining grains, so that the strength and toughness of the steel are improved. In addition, titanium and sulfur combine to form TiS, which inhibits the formation of MnS and reduces the hazards of MnS, thereby contributing to the impact properties of the steel. However, when the titanium content is too high, coarse nitride or sulfide particles formed on the grain boundary are likely to be a crack source of brittle fracture, and the impact toughness is seriously degraded. Therefore, in the present invention, only the micro Ti treatment is performed, and the Ti content is preferably controlled to 0.01 to 0.02%.
In order to further improve the overall performance of the steel for low temperature resistant oil well pipes, the steel for low temperature resistant oil well pipes may have a composition including, in mass percent: 0.04 to 0.10 percent of C, 3.0 to 6.5 percent of Mn, 0.04 to 0.10 percent of V, 0.30 to 0.60 percent of Mo, 0.011 to 0.02 percent of Ti, 0.2 to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
The invention also provides a preparation method of the steel for the low-temperature-resistant oil well pipe, which comprises the following steps:
step 1, smelting and pouring to obtain a casting blank or an ingot;
step 2, performing high-temperature homogenization treatment on the casting blank or the casting ingot, and then rolling to obtain a pierced billet;
and 3, carrying out quenching twice on the pierced billet and then tempering to obtain the low-temperature-resistant oil well pipe steel with the tempered sorbite and residual austenite structures.
Specifically, in the step 1, a converter, an electric furnace or an induction furnace can be adopted for smelting, and continuous casting or die casting can be adopted for producing a casting blank or a casting ingot.
Specifically, the step 2 has the function of ensuring that the alloy elements are completely dissolved and exist in the matrix in a solid solution state, and considering that the final performance of the material is influenced by excessive growth and even overheating of austenite grains caused by overhigh heat preservation temperature or overlong heat preservation time; the heat preservation temperature is too low or the heat preservation time is too short, so that the steel cannot be completely austenitized or the alloy elements are not sufficiently dissolved, the components of the steel are not uniform, and the performance is influenced. Therefore, the specific steps for controlling step 2 include: heating the casting blank or the ingot to 1100-1200 ℃ in a heating furnace, preserving the heat for 1-3 h at 1100-1200 ℃, and carrying out perforation hot rolling and cooling after discharging to obtain the pierced billet with the required size.
Specifically, in the step 2, a pierced billet is formed by water spray cooling after being taken out of the rolling mill.
Specifically, in the step 2, the finish rolling temperature of the hot rolling is 850 ℃ or higher, for example, 900 ℃ or higher.
Specifically, the specific steps of step 3 include:
s301, primary quenching: heating the pierced billet to a temperature higher than the austenitizing temperature, preserving heat, and then quenching to room temperature;
s302, secondary quenching: heating the quenched pierced billet to the temperature of the two-phase region, preserving the heat, and then quenching to the room temperature to obtain a steel pipe;
s303, tempering: and (3) putting the steel pipe into a tempering furnace, heating to 650-680 ℃ along with the furnace, preserving heat for 0.5-2 h, and then air-cooling to room temperature to obtain the low-temperature-resistant steel for the oil well pipe with the tempered sorbite and residual austenite structures.
Specifically, in S301, the first quenching is to heat the pierced billet to a temperature above the austenitizing temperature and keep the temperature for a period of time to ensure that all micro-alloying elements are dissolved in the matrix, and then quenching is performed to room temperature to obtain a complete martensite structure, and the alloying elements are fully dissolved in the solution. Considering that the final performance of the material is influenced by overhigh temperature or overlong heat preservation time which causes the excessive growth and even overheating of austenite crystal grains; the heat preservation temperature is too low or the heat preservation time is too short, so that the steel cannot be completely austenitized or the alloy elements are not sufficiently dissolved, the components of the steel pipe are not uniform, and the performance is influenced. Therefore, the pierced billet is controlled to be heated to 880-920 ℃ (the heating rate is controlled to be 4-40 ℃/S), and the temperature is kept for 0.5-2 h.
Specifically, in S302, the second quenching is to heat the pierced billet to a certain temperature in a two-phase region, at which only a part of martensite is transformed into austenite, and keep the temperature for a certain time to fully diffuse the alloying elements into the austenite, at which time the austenite enriched with the alloying elements becomes relatively stable, so that a part of the martensite is transformed into martensite during the subsequent quenching process, and a part of the austenite remains at room temperature to become residual austenite in the matrix; the microstructure at this time is "martensite + retained austenite". In the step, the heating is controlled to 750-800 ℃ (the heating rate is controlled to be 4-40 ℃/S), and the temperature is kept for 0.5-2 h.
Specifically, in S303, the heating temperature of the tempering process is lower than the austenite transformation temperature, so that the process mainly includes the steps of tempering the martensite to be transformed into a fine sorbite structure, and simultaneously precipitating dispersed and refined second phases of various types, such as VC, moC, and the like, in the matrix to perform the precipitation strengthening function.
Specifically, in step S303, the steel pipe is placed in a tempering furnace and heated to 650-680 ℃ along with the furnace at a heating rate of 4-40 ℃/S.
Specifically, in S303, the room-temperature structure of the low-temperature resistant steel for oil country tubular goods is a "tempered sorbite + retained austenite" mixed structure, and a dispersed and refined second phase is distributed on the matrix; wherein the volume fraction of the retained austenite is more than or equal to 5 percent, and the second phase mainly comprises VC and MoC. Preferably, the volume fraction of retained austenite is 8% or more, for example, 8.5% to 20% of retained austenite.
Specifically, the crystal grain size of the room temperature structure of the steel for a low temperature resistant oil well pipe is 30 μm or less, for example, 20 to 30 μm.
Specifically, in S303, the mechanical properties of the steel for low temperature resistant oil country tubular goods obtained are as follows: yield strength is more than or equal to 555MPa (for example, 565MPa to 725 MPa), tensile strength is more than or equal to 620MPa (for example, 673MPa to 836 MPa), yield ratio is more than 0.8 (for example, 0.84 to 0.9), elongation is more than or equal to 25 percent (for example, 30 percent to 38 percent), and impact toughness at-60 ℃ is more than or equal to 180J (for example, more than 200J). The steel achieves the strength level of 80Ksi and above steel grade, and has excellent low-temperature fracture toughness. The steel of the invention has low cost, economy, practicability, good obdurability and good low-temperature fracture toughness.
Examples 1 to 4
The invention provides steel for a low-temperature-resistant oil well pipe and a preparation method thereof in examples 1 to 4, wherein the steel in examples 1 to 4 comprises the following components in percentage by mass: 0.02 to 0.10 percent of C, 2.0 to 6.5 percent of Mn, 0.02 to 0.10 percent of V, 0.20 to 0.60 percent of Mo, 0.01 to 0.02 percent of Ti, less than or equal to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
The preparation method of the steels of examples 1 to 4 includes:
(1) Converter steelmaking and continuous casting are adopted to produce a tube blank;
(2) Heating the tube blank to 1150 ℃ by utilizing a seamless tube forming technology, preserving heat for 2 hours in a constant temperature section, then discharging, piercing and rolling, discharging from a rolling mill at 980 ℃, and then cooling by adopting water spray to form a pierced billet;
(3) Heating the cooled pierced billet to 900 ℃, preserving the heat for 1 hour, and then quenching to room temperature; heating the steel pipe to 780 ℃, preserving heat for 1h, and quenching to room temperature; and finally, putting the steel pipe into a tempering furnace, heating the steel pipe to 660 ℃ along with the furnace at the speed of 5 ℃/S, preserving the heat for 1h, and then air-cooling the steel pipe to room temperature to obtain the low-temperature-resistant steel for the oil well pipe.
The specific compositions of the steels of examples 1 to 4 are shown in table 1 below, the microstructure of the steel of example 1 is shown in fig. 1, the microstructure of the steel of example 2 is shown in fig. 2, the microstructure of the steels of examples 1 to 4 is shown in table 2 below, and the mechanical properties of the steels are shown in table 3 below.
Table 1 chemical composition of the steels of examples 1-4
| Serial number | C | Si | Mn | P | S | V | Mo | Ti |
| Example 1 | 0.05 | 0.28 | 4.0 | 0.007 | 0.0020 | 0.09 | 0.4 | 0.013 |
| Example 2 | 0.07 | 0.23 | 4.5 | 0.009 | 0.0025 | 0.08 | 0.4 | 0.016 |
| Example 3 | 0.09 | 0.30 | 5.2 | 0.008 | 0.0019 | 0.07 | 0.5 | 0.015 |
| Example 4 | 0.097 | 0.27 | 6.5 | 0.008 | 0.0020 | 0.08 | 0.5 | 0.012 |
TABLE 2 microstructures of the steels of examples 1-4
TABLE 3 mechanical Properties of the steels of examples 1-4
Examples 5 to 8
Embodiments 5 to 8 of the present invention provide a low temperature resistant steel for an oil well pipe and a method for preparing the same, the steel of embodiments 5 to 8 comprising, in mass percent: 0.09% of C, 0.30% of Si, 5.2% of Mn, 0.07% of V, 0.50% of Mo, 0.008% of P, 0.019% of S, 0.015% of Ti and the balance of Fe and inevitable impurities.
The preparation method of the steels of examples 5 to 8 includes:
(1) Converter steelmaking and continuous casting are adopted to produce a tube blank;
(2) Heating the tube blank to 1120 ℃ by utilizing a seamless tube forming technology, preserving heat for 2.5 hours in a constant temperature section, then discharging, piercing and rolling, discharging from a rolling mill at 950 ℃, and then cooling by adopting water spray to form a pierced billet;
(3) Firstly, heating the cooled pierced billet to 910 ℃, preserving heat for 1h, and then quenching to room temperature; then heating the steel pipe to 750 ℃ and 780 ℃ respectively, preserving heat for 1h, and quenching to room temperature; and finally, placing the steel pipe into a tempering furnace at the speed of 5 ℃/S, heating the steel pipe to 660 ℃ and 680 ℃ along with the furnace, preserving the heat for 1h, and then cooling the steel pipe to room temperature in air. Specific heat treatment process parameters are shown in table 4.
The microstructure of the steel of example 5 is shown in fig. 3, the microstructure of the steel of example 6 is shown in fig. 4, the microstructure results of the steels of examples 5 to 8 are shown in table 5, and the mechanical properties of the steels are shown in table 6 below.
Table 4 heat treatment process of steels of examples 5 to 8
| Serial number | Heat preservation temperature of secondary quenching | Tempering temperature |
| Example 5 | 750℃ | 660℃ |
| Example 6 | 750℃ | 680℃ |
| Example 7 | 780℃ | 660℃ |
| Example 8 | 780℃ | 680℃ |
TABLE 5 microstructures of the steels of examples 5-8
TABLE 6 mechanical Properties of the steels of examples 5-8
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. The steel for the low-temperature-resistant oil well pipe is characterized by comprising the following components in percentage by mass: 0.02 to 0.10 percent of C, 2.0 to 6.5 percent of Mn, 0.02 to 0.10 percent of V, 0.20 to 0.60 percent of Mo, 0.01 to 0.02 percent of Ti, less than or equal to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
2. The steel for low temperature resistant oil well pipes according to claim 1, characterized in that the components of the steel for low temperature resistant oil well pipes comprise, in mass percent: 0.04 to 0.10 percent of C, 3.0 to 6.5 percent of Mn, 0.04 to 0.10 percent of V, 0.30 to 0.60 percent of Mo, 0.011 to 0.02 percent of Ti, 0.2 to 0.50 percent of Si, less than or equal to 0.05 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, and the balance of Fe and inevitable impurities.
3. The steel for low temperature resistant oil well pipes according to claim 1, characterized in that the room temperature structure of the steel for low temperature resistant oil well pipes is a "tempered sorbite + retained austenite" mixed structure, and dispersed, refined second phases are distributed on the matrix.
4. The steel for a low temperature-resistant oil well pipe as claimed in claim 3, wherein the steel for a low temperature-resistant oil well pipe has a residual austenite volume fraction of not less than 5% in a room temperature structure.
5. A method for producing a steel for a low temperature resistant oil well pipe, characterized by comprising, for producing the steel for a low temperature resistant oil well pipe according to any one of claims 1 to 4:
step 1, smelting and pouring to obtain a casting blank or an ingot;
step 2, performing high-temperature homogenization treatment on the casting blank or the casting ingot, and then rolling to obtain a pierced billet;
and 3, quenching the pierced billet twice and then tempering to obtain the low-temperature-resistant steel for the oil well pipe with the tempered sorbite and residual austenite structures.
6. The method for preparing according to claim 5, wherein the step 2 comprises: heating the casting blank or ingot to 1100-1200 ℃ in a heating furnace, preserving the heat for 1-3 h at 1100-1200 ℃, and carrying out perforation hot rolling and cooling after discharging to obtain a pierced billet.
7. The method according to claim 6, wherein in the step 2, the pierced billet is formed by water spray cooling after being discharged from the rolling mill.
8. The method for preparing according to claim 5, wherein the step 3 comprises:
s301, primary quenching: heating the pierced billet to a temperature higher than the austenitizing temperature, preserving heat, and then quenching to room temperature;
s302, secondary quenching: heating the quenched pierced billet to the temperature of the two-phase region, preserving the heat, and then quenching to the room temperature to obtain a steel pipe;
s303, tempering: and (3) putting the steel pipe into a tempering furnace, heating to 650-680 ℃ along with the furnace, preserving heat for 0.5-2 h, and then air-cooling to room temperature to obtain the low-temperature-resistant steel for the oil well pipe with the tempered sorbite and residual austenite structures.
9. The preparation method according to claim 8, wherein in S301, the pierced billet is heated to 880-920 ℃ and is kept at the temperature for 0.5-2 h.
10. The preparation method according to claim 8 or 9, wherein in S302, the quenched pierced billet is heated to 750-800 ℃ and is kept at the temperature for 0.5-2 h.
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