CO2 corrosion resistant steel, preparation method thereof and steel product

Abstract

The invention relates to CO2 corrosion resistant steel as well as a preparation method and a steel product thereof. The CO2 corrosion resistant steel comprises the following chemical components in percentage by mass: 0.10%-0.16% of C, 0.15%-0.40% of Si, 0.50%-0.70% of Mn, 4.90%-5.50% of Cr, 0.25%-0.80% of Mo, 0.02%-0.04% of Al, less than or equal to 0.020% of P, less than or equal to 0.01% of S, less than or equal to 0.15% of Cu, less than or equal to 0.20% of Ni and the balance of iron and inevitable impurities. According to the CO2 corrosion resistant steel, on the basis that Cr, Mo and Al are added, harmful elements such as P and S are reduced, the content of gases such as O, N and H is reduced, the alloying proportioning principle is fully utilized, the obdurability matching of all the elements is excellent, and the mechanical property and CO2 corrosion resistance of a product are improved; and meanwhile, through cooperation of Mo and Cr elements, the corrosion resistance of the steel can be improved, use of precious metal can be reduced, and the preparation cost is reduced.

Description

Technical Field

[0001] The present application relates to the field of alloy technology, and in particular to a CO2 corrosion resistant steel and a preparation method and steel product thereof. Background Art

[0002] In the process of oil and gas field exploitation and development, corrosion is a serious problem that exists from beginning to end. It not only causes huge economic losses to the oil field, but also often brings some catastrophic consequences, such as casualties, shutdown and environmental pollution. At present, the common types of corrosion in oil fields are electrochemical corrosion caused by H2S, CO2, dissolved oxygen, dissolved salts, and biological corrosion caused by microorganisms such as sulfate-reducing bacteria. With the continuous deterioration of oil and gas well exploitation conditions and the increasing water content, the development of deep H2S and CO2 oil and gas layers is increasing.

[0003] According to the degree of CO2 corrosion from low to high, oilfield enterprises select corresponding steel grades, such as L80-3Cr, N80-5Cr, and L80-13Cr. As the service time of steel increases, the serious corrosion problem of oil casing in high water-content oil wells is exposed. The corrosion type is mainly local corrosion, and the maximum corrosion rate is 0.3-5mm / a. Well logging shows that the severe corrosion section is 1400mm-2200m, and the casing damage section is mainly below the dynamic liquid level.

[0004] In order to solve the problem of internal corrosion, some technologies have adopted two anti-corrosion methods: internal coating of steel pipes and injection of corrosion inhibitors. However, in actual production, the oil casing with internal coatings will inevitably have problems such as mechanical scratches and local shedding, which will affect the protection effect. The injection of corrosion inhibitors has the problems of large on-site workload, high management difficulty, and poor local corrosion prevention effect. Traditional anti-corrosion technology cannot fully meet the actual production requirements. The traditional 13Cr product has a high Cr content, and the price of Cr is high, resulting in high production costs. Summary of the invention

[0005] Based on this, it is necessary to provide a CO2 corrosion resistant steel with good CO2 corrosion resistance and low cost, and a preparation method and steel products thereof.

[0006] The first aspect of the present application provides a CO2 corrosion resistant steel, which comprises the following chemical components, calculated by mass percentage: C: 0.10%~0.16%, Si: 0.15%~0.4%, Mn: 0.50%~0.70%, Cr: 4.9%~5.5%, Mo: 0.25%~0.80%, Al: 0.02%~0.04%, P≤0.020%, S≤0.010%, Cu≤0.15%, Ni≤0.20%, and the remainder is iron and unavoidable impurities.

[0007] The above-mentioned CO2 corrosion resistant steel includes C, Si, Mn, Cr, Mo, Al, P, S, Cu and Ni in specific proportions, and a steel with good CO2 corrosion resistance is provided through the synergistic effect of the proportions of each component. Among them, in the above-mentioned CO2 corrosion resistant steel, a small amount of Mo and Al elements are added on the basis of adding a specific amount of Cr element. Cr, Mo and Al interact with each other to form a dense oxide film, which can prevent the invasion of corrosive media and improve the ability of steel to resist pitting corrosion and uniform corrosion; further, because the price of Mo element is expensive, the addition of Al element can not only greatly improve the material's CO2 corrosion resistance, but also reduce the use of precious metals and reduce costs. At the same time, on the basis of adding Cr, Mo and Al, the above-mentioned CO2 corrosion resistant steel reduces the harmful elements of P and S, reduces the content of gases such as O, N and H, and makes full use of the alloying ratio principle. The strength and toughness of each element are well matched, and the mechanical properties of the product are improved.

[0008] In some embodiments, the mass percentage of the Cr and the mass percentage of the Mo satisfy the following relationship:

[0009] ω Mo / ω Cr ≥0.05; where ω Mo and ω Cr They respectively represent the mass percentage of each element component in the CO2 corrosion resistant steel.

[0010] In some embodiments, the chemical composition further comprises 0.01% to 0.04% V by mass.

[0011] In some embodiments, the mass percentage of C is 0.10% to 0.15%; and / or,

[0012] The mass percentage of Si is 0.20% to 0.30%; and / or,

[0013] The mass percentage of Cr is 5.20% to 5.50%; and / or,

[0014] The mass percentage of Mo is 0.25% to 0.4%; and / or,

[0015] The mass percentage of S is 0-0.006%; and / or,

[0016] The mass percentage of Cu is 0-0.035%; and / or,

[0017] The mass percentage of Ni is 0-0.040%.

[0018] In some embodiments, the steel is a seamless tube.

[0019] In some embodiments, the yield strength of the steel is 550 MPa to 760 MPa; and / or,

[0020] The tensile strength of the steel is ≥ 685 MPa; and / or,

[0021] The elongation of the steel is ≥ 20%; and / or,

[0022] The longitudinal full-size impact strength of the steel is ≥80J; and / or,

[0023] The Rockwell hardness of the steel is ≤24HRC.

[0024] The second aspect of the present application provides a method for preparing the above-mentioned CO2 corrosion resistant steel, comprising the following steps:

[0025] Preparing a casting ingot according to the chemical composition of the CO2 corrosion resistant steel;

[0026] The ingot is subjected to hot rolling treatment, quenching treatment and tempering treatment in sequence.

[0027] In some embodiments, the hot rolling process comprises the following steps:

[0028] The ingot is heated to a preset temperature, pierced, and then rolled and reduced in diameter by a continuous rolling mill to obtain a rolled seamless steel pipe.

[0029] In some embodiments, the temperature of the quenching treatment is 910° C. to 930° C., and the cooling method of the quenching treatment is water cooling; and / or,

[0030] The temperature of the tempering treatment is 600°C to 630°C.

[0031] A third aspect of the present application provides a steel product, comprising the CO2 corrosion resistant steel described in the first aspect. DETAILED DESCRIPTION

[0032] In order to facilitate the understanding of the present invention, the present invention is described more comprehensively below. And preferred embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0034] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0035] The weight of the relevant components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also indicate the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the description of the embodiments of the present invention, it is within the scope disclosed in the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiments of the present invention may be a mass unit known in the chemical industry such as μg, mg, g, kg, etc.

[0036] In one embodiment of the present application, a CO2 corrosion steel is provided, which includes the following chemical components, calculated by mass percentage: C: 0.10%~0.16%, Si: 0.15%~0.40%, Mn: 0.50%~0.70%, Cr: 4.9%~5.50%, Mo: 0.25%~0.80%, Al: 0.02%~0.04%, P≤0.02%, S≤0.01%, Cu≤0.15%, Ni≤0.20%, and the remainder is iron and unavoidable impurities.

[0037] The above-mentioned CO2 corrosion resistant steel includes C, Si, Mn, Cr, Mo, Al, P, S, Cu and Ni in specific proportions, and a steel with good CO2 corrosion resistance is provided through the synergistic effect of the proportions of each component. Among them, in the above-mentioned CO2 corrosion resistant steel, a small amount of Mo and Al elements are added on the basis of adding a specific amount of Cr element. Cr, Mo and Al interact with each other to form a dense oxide film, which can prevent the invasion of corrosive media and improve the ability of steel to resist pitting corrosion and uniform corrosion; further, because the price of Mo element is expensive, the addition of Al element can not only greatly improve the material's CO2 corrosion resistance, but also reduce the use of precious metals and reduce costs. At the same time, on the basis of adding Cr, Mo and Al, the above-mentioned CO2 corrosion resistant steel reduces the harmful elements of P and S, reduces the content of gases such as O, N and H, and makes full use of the alloying ratio principle. The strength and toughness of each element are well matched, and the mechanical properties of the product are improved.

[0038] C is an economical element that can improve the hardenability and strength of steel; but if the content is too high, it will form coarse carbides with Cr, which will have an adverse effect on the impact toughness of the steel. Therefore, in the CO2 corrosion resistant steel of the present application, the mass percentage of C is controlled within the range of 0.10% to 0.16%. As an example, in the CO2 corrosion resistant steel, the mass percentage of C can be 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15% or 0.16%. Furthermore, the mass percentage of C in the CO2 corrosion resistant steel can be a range value consisting of any two of the above point values ​​as end values. Preferably, the mass percentage of C in the CO2 corrosion resistant steel is 0.10%~0.15%.

[0039] The addition of Si can play a role in deoxidation and improving the corrosion resistance of steel; however, Si has poor thermal conductivity and poor plasticity. If too much Si is added, the impact toughness of CO2 corrosion resistant steel will deteriorate sharply. Therefore, the mass percentage of Si in the CO2 corrosion resistant steel of this application is controlled at 0.15%~0.40%. As an example, in CO2 corrosion resistant steel, the mass percentage of Si can be 0.15%, 0.16%, 0.18%, 0.20%, 0.21%, 0.22%, 0.24%, 0.25%, 0.26%, 0.28%, 0.30%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.38% or 0.40%. Further, the mass percentage of Si in CO2 corrosion resistant steel can be a range value composed of any two of the above point values ​​as end values. Preferably, the mass percentage of Si in CO2 corrosion resistant steel is 0.20%~0.30%.

[0040] Mn is an economical element. Adding appropriate Mn can play a role in solid solution strengthening, improve the toughness of steel and increase the strength of steel. When the Mn content is too high, the wear resistance and hardness of the steel will be significantly improved, but the toughness of the steel will be significantly reduced. Therefore, the mass percentage of Mn in the CO2 corrosion resistant steel of this application is controlled at 0.50% to 0.70%. As an example, in the CO2 corrosion resistant steel, the mass percentage of Mn can be 0.50%, 0.52%, 0.54%, 0.55%, 0.56%, 0.58%, 0.60%, 0.62%, 00.64%, 0.65%, 0.66%, 0.68%, 0.69% or 0.70%. Furthermore, the mass percentage of Mn in the CO2 corrosion resistant steel can be a range value composed of any two of the above point values ​​as end values.

[0041] P is a harmful element. When it is segregated at the grain boundary, it will lead to a decrease in impact performance. Therefore, the mass percentage of P in CO2 corrosion resistant steel is ≤ 0.02%. As an example, the mass percentage of P in CO2 corrosion resistant steel can be 0, 0.005%, 0.01%, 0.011%, 0.012%, 0.013%, 0.015%, 0.016%, 0.018% or 0.020%. Furthermore, the mass percentage of P in CO2 corrosion resistant steel can be a range value consisting of any two of the above point values ​​as end values.

[0042] The S element easily forms MnS inclusions with Mn and forms segregation in the steel pipe, so its content must be strictly controlled. The mass percentage of S in the CO2 corrosion resistant steel of this application is ≤0.01%. As an example, the mass percentage of S can be 0, 0.001%, 0.0015%, 0.002%, 0.0022%, 0.0024%, 0.0027%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009% or 0.01%. Furthermore, the mass percentage of S in the CO2 corrosion resistant steel can be a range value consisting of any two of the above point values ​​as end values. Preferably, the mass percentage of S in the CO2 corrosion resistant steel is 0~0.006%.

[0043] Cr is an element that can expand the austenite zone, which can improve the hardenability of steel, increase the tempering temperature of steel, and increase the high-temperature strength of steel. Cr can form a dense passivation film on the metal surface (especially iron-based alloys such as stainless steel). The passivation film is mainly composed of Cr oxides (such as Cr2O3) and may also contain iron oxides (such as FeO) to form a composite passivation film (such as FeO·Cr2O3); the passivation film has stable and complete characteristics, and is very firmly bonded to the base metal, which can effectively isolate the base from the corrosive medium, thereby inhibiting further oxidation or corrosion of the steel base.

[0044] Furthermore, the addition of Cr can significantly increase the electrode potential of the iron-based alloy. According to the n / 8 law, when the atomic ratio of Cr (i.e., the ratio of the number of Cr atoms to the total number of alloy atoms) increases, the electrode potential of the alloy will increase in a jump-like manner; this increase in electrode potential makes the alloy more difficult to be oxidized, thereby improving its corrosion resistance. Due to the increase in electrode potential, the alloy is more susceptible to passivation reaction in the corrosive medium, that is, a passivation film is formed on the surface to inhibit further corrosion of the matrix. The enhancement of this passivation tendency is also one of the important reasons why Cr improves the corrosion resistance of the alloy. Considering the oil well corrosion environment and cost, the mass percentage of Cr in the CO2 corrosion-resistant steel in this application is controlled to 4.90%~5.50%. As an example, the mass percentage of Cr in the CO2 corrosion-resistant steel can be 4.90%, 5.00%, 5.05%, 5.10%, 5.15%, 5.20%, 5.25%, 5.30%, 5.35%, 5.37% or 5.40%. Furthermore, the mass percentage of Cr in the CO2 corrosion resistant steel can be a range value consisting of any two of the above point values ​​as end values. Preferably, the mass percentage of Cr in the CO2 corrosion resistant steel is 5.20% to 5.50%.

[0045] Mo can play the role of solid solution strengthening and precipitation strengthening in steel, and can also improve the hardenability and tempering temperature of steel, inhibit temper brittleness and significantly improve the high temperature strength of steel. The addition of Mo enhances the stability of the passivation film of CrMo steel, making it more difficult to be destroyed by corrosive media such as CO2. In addition, the carbide of Mo also helps to form a denser and more stable passivation film layer, improving the corrosion resistance of steel. However, the Mo element is expensive. Considering the economy, the mass percentage of Mo in the CO2 corrosion-resistant steel of this application is controlled to 0.20%~0.80%. As an example, the mass percentage of Mo can be 0.20%, 0.25%, 0.30%, 0.32%, 0.35%, 0.36%, 0.38%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75% or 0.80%. Furthermore, the mass percentage of Mo in the CO2 corrosion resistant steel can be a range value formed by any two of the above point values ​​as end values. Preferably, the mass percentage of Mo in the CO2 corrosion resistant steel is 0.25% to 0.4%.

[0046] Al has a significant effect on improving the corrosion effect of iron-based materials in a CO2 environment. This is mainly due to its ability to form a dense oxide film (such as Al2O3), which has good chemical stability and density, and can effectively isolate the base material from the corrosive medium (such as CO2 aqueous solution). When elements such as Al and Cr coexist in CO2 corrosion-resistant steel, the stability of the passivation film on the surface of the material can be significantly improved and the corrosion rate can be reduced. Al within a certain range can improve the tensile strength, but when the Al content exceeds a certain limit, the effect of improving the strength is no longer significant, and may even cause uneven organization and lead to performance degradation. For example, the impact toughness decreases, and the impact performance changes from ductile fracture characteristics to brittle fracture characteristics. Therefore, the mass percentage of Al in the CO2 corrosion-resistant steel of this application is controlled to be 0.02%~0.04%. As an example, the mass percentage of Al may be 0.02%, 0.024%, 0.025%, 0.026%, 0.028%, 0.030%, 0.032%, 0.034%, 0.035%, 0.036%, 0.038%, 0.039% or 0.04%. Further, the mass percentage of Al in the CO2 corrosion resistant steel may be a range value consisting of any two of the above point values ​​as end values.

[0047] It can be understood that "Cu≤0.15%" means that the mass percentage of Cu in the CO2 corrosion resistant steel of the present application can be 0%, 0.01%, 0.014%, 0.015%, 0.016%, 0.018%, 0.019%, 0.02%, 0.021%, 0.022%, 0.025%, 0.03%, 0.04%, 0.05%, 0.06%, 0.08%, 0.10%, 0.12%, 0.14% or 0.15%. Further, the mass percentage of Cu in the CO2 corrosion resistant steel can be a range value consisting of any two of the above point values ​​as end values. Preferably, the mass percentage of Cu in the CO2 corrosion resistant steel is 0~0.015%.

[0048] It can be understood that "Ni≤0.20%" means that the mass percentage of Ni in the CO2 corrosion resistant steel of the present application can be 0%, 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.036%, 0.038%, 0.039%, 0.04%, 0.042%, 0.05%, 0.10%, 0.12%, 0.15% or 0.20%. Furthermore, the mass percentage of Ni in the CO2 corrosion resistant steel can be a range value consisting of any two of the above point values ​​as end values. Preferably, the mass percentage of Ni in the CO2 corrosion resistant steel is 0~0.040%.

[0049] In some embodiments, the mass percentage of Cr, the mass percentage of Mo, and the mass percentage of Al satisfy the following relationship:

[0050] ω Mo / ω Cr ≥0.05, where ω Mo and ω Cr Respectively represent the mass percentage of each element component in CO2 corrosion resistant steel. Mo / ω Cr The value is 0.05~0.08. A certain amount of Mo and Cr is guaranteed in CO2 corrosion resistant steel. When the Mo content reaches a certain amount, it has a synergistic effect on corrosion resistance. The addition of Mo can enhance the stability of the protective passivation film of the Cr element and the matrix. Mo and Cr have similar electronic structures, low metal activity, and are difficult to form a complex with the medium, which helps to maintain the integrity of the passivation film. In addition, Mo can also promote the formation of a denser and more uniform passivation film structure, further improving the corrosion resistance of the alloy.

[0051] In some embodiments, the above-mentioned CO2 corrosion resistant steel also includes 0.01% to 0.04% V by mass percentage. As an example, the mass percentage of V in the CO2 corrosion resistant steel can be 0.01%, 0.02%, 0.025%, 0.029%, 0.03% or 0.04%. Further, the mass percentage of V in the CO2 corrosion resistant steel can be a range value consisting of any two of the above point values ​​as end values. Further adding V element components to the steel can improve the density and uniformity of the steel, thereby indirectly helping to improve the corrosion resistance of the steel. Especially in an environment containing corrosive media such as chloride ions, the corrosion resistance of V-CrMo steel is more prominent.

[0052] In some embodiments, the CO2 corrosion resistant steel includes the following chemical components, measured by mass percentage: C: 0.10%~0.15%, Si: 0.20%~0.30%, Mn: 0.50%~0.70%, Cr: 5.20%~5.50%, Mo: 0.25%~0.40%, Al: 0.02%~0.04%, P≤0.02%, S≤0.01%, Cu: 0~0.035%, Ni: 0~0.040%, and the balance iron and unavoidable impurities.

[0053] In some embodiments, the CO2 corrosion resistant steel is a profile, which can be a plate, a rod or a pipe.

[0054] In some embodiments, the CO2 corrosion resistant steel is a seamless pipe.

[0055] In some embodiments, the yield strength of the CO2 corrosion resistant steel is 550MPa to 760MPa. As an example, the yield strength of the CO2 corrosion resistant steel may be 550MPa, 552MPa, 560MPa, 570MPa, 580MPa, 590MPa, 600MPa, 610MPa, 620MPa, 630MPa, 640MPa, 650MPa, 660MPa, 670MPa, 680MPa, 690MPa, 700MPa, 710MPa, 720MPa, 730MPa, 740MPa, 750MPa, 758MPa or 760MPa. Further, the yield strength of the CO2 corrosion resistant steel may be a range value consisting of any two of the above point values ​​as end values.

[0056] In some embodiments, the tensile strength of the CO2 corrosion resistant steel is ≥ 685 MPa. As an example, the tensile strength of the CO2 corrosion resistant steel may be 685 MPa, 690 MPa, 700 MPa, 710 MPa, 720 MPa, 730 MPa, 740 MPa, 750 MPa, 760 MPa, 780 MPa, 790 MPa or 800 MPa. Further, the tensile strength of the CO2 corrosion resistant steel may be any other value greater than 685 MPa. Preferably, the tensile strength of the CO2 corrosion resistant steel is 685 MPa to 770 MPa.

[0057] In some embodiments, the elongation of CO2 corrosion resistant steel is ≥20%. Elongation refers to the ratio of the total elongation length to the original length after the material is stretched and broken under force; it reflects the plastic deformation ability of the material when subjected to tension. As an example, the elongation of CO2 corrosion resistant steel can be 20%, 21%, 21.5%, 22%, 22.5%, 23%, 23.5%, 24%, 24.5%, 25%, 26% or 28%. Furthermore, the elongation of CO2 corrosion resistant steel can be any other value greater than 20%. Preferably, the elongation of CO2 corrosion resistant steel is 20%~25%.

[0058] In some embodiments, the longitudinal full-size 10*10mm (referring to the steel material with a thickness of 10mm and a width of 10mm) impact strength of CO2 corrosion resistant steel is ≥80J. Longitudinal full-size impact strength refers to the ability of a material to resist damage under the action of a longitudinal impact force. As an example, the longitudinal full-size impact strength of CO2 corrosion resistant steel may be 80J, 90J, 100J, 105J, 110J, 115J, 120J, 125J, 130J, 135J or 140J. Furthermore, the longitudinal full-size impact strength of CO2 corrosion resistant steel may be any other value greater than 80J. Preferably, the longitudinal full-size impact strength of CO2 corrosion resistant steel is 90J~140J.

[0059] In some embodiments, the transverse full-size 10*10mm impact strength of CO2 corrosion resistant steel is ≥60J. Transverse full-size impact strength refers to the ability of a material to resist damage when subjected to a transverse impact force. As an example, the longitudinal full-size impact strength of CO2 corrosion resistant steel may be 60J, 65J, 70J, 80J, 90J, 100J, 105J, 110J, 115J or 120J. Furthermore, the transverse full-size 10*10mm impact strength of CO2 corrosion resistant steel may be any other value greater than 60J. Preferably, the transverse full-size 10*10mm impact strength of CO2 corrosion resistant steel is 60J~120J.

[0060] In some embodiments, the Rockwell hardness of the CO2 corrosion resistant steel is ≤24HRC. As an example, the Rockwell hardness of the CO2 corrosion resistant steel may be 24HRC, 23HRC, 22HRC, 20.5HRC, 20HRC, 19.5HRC, 19HRC, 18.5HRC, 18HRC, 17.5HRC, 17HRC or 16HRC. Further, the Rockwell hardness of the CO2 corrosion resistant steel may be any other value less than 24HRC. Preferably, the Rockwell hardness of the CO2 corrosion resistant steel is 16HRC to 23HRC.

[0061] In some embodiments, the CO2 corrosion resistant steel is in a carbon dioxide corrosion environment, the electrochemical self-corrosion potential is in the range of -580mv~700mv, the uniform corrosion rate is ≤0.12mm / a, and the maximum pitting corrosion rate is ≤0.20mm / a. Furthermore, the uniform corrosion rate is 0.01mm / a~0.12mm / a, and the maximum pitting corrosion rate is 0.05mm / a~0.20mm / a.

[0062] Another embodiment of the present application further provides a method for preparing the above-mentioned CO2 corrosion resistant steel, comprising the following preparation steps:

[0063] Preparation of ingots according to the chemical composition of CO2 corrosion resistant steel;

[0064] The ingot is subjected to hot rolling treatment, quenching treatment and tempering treatment in sequence.

[0065] In some embodiments, the step of preparing a casting ingot according to the chemical composition of CO2 corrosion resistant steel comprises:

[0066] The ingredients are prepared according to the chemical composition ratio of CO2 corrosion resistant steel, and then smelting, refining, vacuum degassing and casting are carried out in sequence.

[0067] In some embodiments, the batching is performed using molten iron, scrap iron or pig iron with an iron content of more than 50% by mass as the raw material.

[0068] In some embodiments, the melting temperature is 1500°C to 1800°C.

[0069] In some embodiments, the above refining adopts conventional refining methods in the art.

[0070] In some embodiments, the quenching step includes keeping the hot rolled ingot at 910°C to 930°C and then water cooling it to 20°C to 40°C.

[0071] In some embodiments, the holding time (in min) of the quenching treatment is 3 to 5 times the thickness of the hot rolled ingot in mm. As an example, the hot rolled ingot is tubular, and the thickness of the hot rolled ingot is the thickness of the tube wall; when the thickness of the tube wall is 10 mm, the holding time of the quenching treatment can be controlled to be 30 min to 50 min.

[0072] In some embodiments, the tempering treatment temperature is 600°C to 630°C.

[0073] In some embodiments, the tempering heating time (in minutes) is 3 to 5 times the thickness of the hot rolled ingot in mm. As an example, the hot rolled ingot is tubular, and the thickness of the hot rolled ingot is the thickness of the tube wall; when the thickness of the tube wall is 10 mm, the tempering heating time can be controlled to be 30 minutes to 50 minutes.

[0074] In some embodiments, the hot rolling process comprises the following steps:

[0075] The ingot is heated to a preset temperature, pierced, and then rolled and reduced in diameter using a continuous rolling mill to obtain a rolled seamless steel pipe.

[0076] It can be understood that the sizing reduction process is a conventional sizing reduction process.

[0077] In some embodiments, the preset temperature is 1240°C to 1280°C. As an example, the preset temperature may be 1240°C, 1245°C, 1250°C, 1255°C, 1260°C, 1265°C, 1270°C, 1275°C or 1280°C. Further, the preset temperature may be a range value consisting of any two of the above point values ​​as end values. Performing the piercing process after heating the ingot to the preset temperature range is beneficial to subsequent piercing and continuous rolling deformation.

[0078] In some embodiments, a PQF continuous rolling mill or an MPM continuous rolling mill is used for the rolling process.

[0079] In some embodiments, the lubrication speed of the continuous rolling mandrel in the continuous rolling mill is 1000 mm / s.

[0080] In some embodiments, the temperature of the continuous rolling mandrel in the continuous rolling mill is 80° C. to 120° C. As an example, the temperature of the continuous rolling mandrel can be 80° C., 85° C., 90° C., 95° C., 100° C., 105° C., 110° C., 115° C. or 120° C. Further, the temperature of the continuous rolling mandrel can be a range value consisting of any two of the above point values ​​as end values.

[0081] In some embodiments, the method for preparing CO2 corrosion resistant steel further comprises performing heat straightening treatment on the tempered steel pipe.

[0082] In some embodiments, the temperature of the straightening treatment is ≥ 480° C. Further, the temperature of the straightening treatment is 480° C. to 580° C.

[0083] In some embodiments, the method for preparing CO2 corrosion resistant steel further comprises sequentially performing flaw detection, water pressure and thread processing on the steel pipe after heat straightening treatment.

[0084] In one embodiment, a steel product is provided, which includes the above-mentioned CO2 corrosion resistant steel.

[0085] In one embodiment, the steel product includes but is not limited to oil casing.

[0086] In order to make the purpose, technical solutions and advantages of the present invention more concise and clear, the present invention is described with the following specific embodiments, but the present invention is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present invention, which can be used to describe the present invention and cannot be understood as limiting the scope of the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0087] In order to better illustrate the present invention, the present invention is further described below in conjunction with an embodiment. The following is a specific embodiment of producing CO2 corrosion resistant steel with a specification of φ139.7*9.17mm.

[0088] Embodiment 1~5

[0089] The preparation methods of Examples 1 to 5 and Comparative Examples 1 to 5 of the present application are basically the same, the only difference being that the chemical composition of the CO2 corrosion resistant steel is different. The chemical composition of the CO2 corrosion resistant steel prepared in each Example and Comparative Example is shown in Table 1.

[0090] The preparation methods of Examples 1 to 5 and Comparative Examples 1 to 5 are:

[0091] (1) Batching: According to the chemical composition ratio in Table 1, use more than 50% molten iron + scrap steel or pig iron as the raw material batching.

[0092] (2) Smelting: The raw materials prepared in step (1) are placed in an electric arc furnace and smelted at 1615°C to 1630°C; then, the raw materials are refined outside the furnace, argon gas is introduced for 15 minutes for vacuum degassing, and then the melt is introduced into a mold for casting to obtain a round tube ingot.

[0093] (3) Hot rolling: The ingot is heated to 1240~1280℃ in a ring furnace, then pierced, rolled and reduced by an MPM continuous rolling mill to obtain a rolled seamless steel pipe. During the piercing process, due to the high Cr content and high rolling resistance of the material, the ordinary piercing die head and guide plate are easily damaged, so molybdenum-based head and guide plate are used; when rolling by a continuous rolling mill, the continuous rolling mandrel lubrication speed is 1000mm / s, and the mandrel temperature is controlled at 80℃.

[0094] (4) Heat treatment: Place the rolled seamless steel pipe in a walking beam quenching furnace and heat it to 910℃~930℃; then cool it to 20℃~40℃ by internal spraying, external showering and rotary water cooling; then the steel pipe enters a walking beam tempering furnace with a tempering temperature of 600℃.

[0095] (5) Straightening: The heat-treated steel pipe is straightened at 480°C, and then subjected to flaw detection, water pressure and thread processing to obtain CO2 resistant oil casing.

[0096] The chemical compositions of the steel materials of various embodiments and comparative examples are shown in Table 1.

[0097] Table 1

[0098]

[0099] Performance Testing

[0100] Room temperature tensile test: The yield strength, tensile strength and elongation of the steel prepared in each embodiment and comparative example were tested according to IOS 6892-1 standard.

[0101] Impact test (A kv / J): According to ASTM 370, the steel materials prepared in the examples and comparative examples were subjected to impact tests at 0°C.

[0102] Corrosion test: in accordance with JB / T7901-1999 and GB / T 15890-2001 standards. A simulated corrosion test was conducted in a high-temperature autoclave; according to the typical water quality of oil wells, a laboratory simulated test solution was prepared. The formula of the simulated test solution is shown in Table 2 below.

[0103] Table 2

[0104]

[0105] The prepared simulation test solution is placed in a high-temperature autoclave, and the steel pipes prepared in each embodiment and comparative example are immersed in the simulation test solution. The high-temperature autoclave is heated to 60°C, and CO2 gas is introduced to maintain the CO2 pressure in the autoclave at 0.21Mpa and the total gas pressure at 5.0Mpa; the test period is 168h. After the test is completed, the corrosion rate of the sample is calculated. The sample corrosion rate is calculated as follows:

[0106] Uniform corrosion rate (mm / a) = [8.76×10 7 × (M-M1)] / (S×T×D),

[0107] Where: M is the mass of the sample before the test, in g;

[0108] M1 is the mass of the sample after the test, in g;

[0109] S is the total area of ​​the sample, in cm 2 ;

[0110] T is the test time, in h;

[0111] D is the density of the material, and its value is 7900kg / m 3 .

[0112] Maximum pitting rate (mm / a) = maximum pitting depth (mm) × 365 / T (day) (this formula comes from NACE SP0775-2013 standard).

[0113] The performance test data of the steel prepared in each embodiment and comparative example are shown in Tables 3-4 below.

[0114] Table 3

[0115]

[0116] Table 4

[0117]

[0118] From the performance test data in Tables 3 and 4, it can be seen that the steels obtained in Examples 1 to 5 using the technical solution of the present application not only have higher yield strength, tensile strength and elongation, but also have better toughness; in particular, the steels have better resistance to CO2 corrosion, with a uniform corrosion rate of only 0.05 mm / a to 0.08 mm / a, and a maximum pitting rate of 0.11 mm / a to 0.14 mm / a.

[0119] The carbon content of Comparative Example 1 is too high, which exceeds the scope of this application. The CO2 uniform corrosion rate of the steel prepared therefrom reaches 0.36 mm / a, and the maximum pitting rate reaches 0.31 maximum pitting rate. The Mn content of Comparative Example 2 is too high, which exceeds the scope of this application. The CO2 uniform corrosion rate of the steel prepared therefrom reaches 0.34 mm / a, and the maximum pitting rate reaches 0.26 mm / a. The Cr content in Comparative Example 3 is lower than the scope of this application. The CO2 uniform corrosion rate of the steel prepared therefrom reaches 0.25 mm / a, and the maximum pitting rate reaches 0.30 mm / a. In Comparative Example 4, the Mo content is reduced, and it is not within the scope of this application. The maximum pitting rate and uniform corrosion rate of the steel prepared in Comparative Example 4 are accelerated to 0.35 mm / a and 0.44 mm / a, respectively. In Comparative Example 5, the Al content is reduced and is not within the scope of the present application; the maximum pitting rate and uniform corrosion rate of the steel prepared in Comparative Example 5 are accelerated to 0.19 mm / a and 0.22 mm / a respectively. It can be seen that the CO2 corrosion resistance of the steel prepared in Comparative Examples 1 to 5 is inferior to that of Examples 1 to 5. The present application significantly improves the CO2 corrosion resistance of the steel by strictly controlling the components of each element.

[0120] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0121] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A CO2 corrosion resistant steel, characterized in that: Calculated by mass percentage, it includes the following chemical components: C: 0.10%~0.16%, Si: 0.15%~0.40%, Mn: 0.50%~0.70%, Cr: 4.90%~5.50%, Mo: 0.25%~0.80%, Al: 0.02%~0.04%, P≤0.02%, S≤0.01%, Cu≤0.15%, Ni≤0.20%, and the remainder is iron and unavoidable impurities.

2. The CO2 corrosion resistant steel according to claim 1, characterized in that: The mass percentage of the Cr and the mass percentage of the Mo satisfy the following relationship: ω Mo / ω Cr ≥0.05; where ω Mo and ω Cr They respectively represent the mass percentage of each element component in the CO2 corrosion resistant steel.

3. The CO2 corrosion resistant steel according to claim 1, characterized in that: Calculated by mass percentage, the chemical composition also includes 0.01% to 0.04% V.

4. The CO2 corrosion resistant steel according to any one of claims 1 to 3, characterized in that: The mass percentage of C is 0.10% to 0.15%; and / or, The mass percentage of Si is 0.20% to 0.30%; and / or, The mass percentage of Cr is 5.20% to 5.50%; and / or, The mass percentage of Mo is 0.25% to 0.4%; and / or, The mass percentage of S is 0-0.006%; and / or, The mass percentage of Cu is 0-0.035%; and / or, The mass percentage of Ni is 0-0.040%.

5. The CO2 corrosion resistant steel according to any one of claims 1 to 3, characterized in that: The CO2 corrosion resistant steel is a seamless pipe.

6. The CO2 corrosion resistant steel according to claim 5, characterized in that: The yield strength of the CO2 corrosion resistant steel is 550MPa-760MPa; and / or, The tensile strength of the CO2 corrosion resistant steel is ≥ 685 MPa; and / or, The elongation of the CO2 corrosion resistant steel is ≥ 20%; and / or, The longitudinal full-size impact strength of the CO2 corrosion resistant steel is ≥80J; and / or, The Rockwell hardness of the CO2 corrosion resistant steel is ≤24HRC.

7. The method for preparing steel according to any one of claims 1 to 6, characterized in that: The steps include: Preparing a casting ingot according to the chemical composition of the CO2 corrosion resistant steel; The ingot is subjected to hot rolling treatment, quenching treatment and tempering treatment in sequence.

8. The preparation method according to claim 7, characterized in that: The hot rolling process comprises the following steps: The ingot is heated to a preset temperature, pierced, and then rolled and reduced in diameter by a continuous rolling mill to obtain a rolled seamless steel pipe.

9. The preparation method according to any one of claims 7 to 8, characterized in that The temperature of the quenching treatment is 910° C. to 930° C., and the cooling method of the quenching treatment is water cooling; and / or, The temperature of the tempering treatment is 600°C to 630°C.

10. A steel product, characterized in that: Including the CO2 corrosion resistant steel as described in any one of claims 1 to 6.

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