Steel for corrosion-resistant casing pipe for deep oil and gas exploitation, production method of steel, corrosion-resistant casing pipe, heat treatment process of corrosion-resistant casing pipe and application of corrosion-resistant casing pipe

Abstract

The invention provides steel for a corrosion-resistant casing pipe for deep oil and gas exploitation, a production method of the steel, the corrosion-resistant casing pipe as well as a heat treatment process and application of the corrosion-resistant casing pipe. The steel comprises the following components in percentage by weight: 0.60-0.80% of Cr, 0.70-0.90% of Mo, 0.040-0.080% of Nb, 0.050-0.100% of Ti, 0.0020-0.0040% of B, 0.020-0.050% of Al, 0.060-0.120% of V, 0.25-0.32% of C, 0.20-0.40% of Si, 0.60-0.80% of Mn, less than or equal to 0.012% of P, less than or equal to 0.0020% of S, 0.0010-0.0020% of RE and the balance of Fe and inevitable impurities. Compared with the prior art, the product is produced through components and a heat treatment process, and has good obdurability and excellent hydrogen sulfide corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the field of alloy steel, and in particular relates to a steel for corrosion-resistant casing for deep oil and gas exploitation, a production method thereof, a corrosion-resistant casing, a heat treatment process thereof and an application thereof. Background Art

[0002] With the rapid development of the world economy, human society's demand and dependence on oil resources are increasing. Therefore, the intensity of oil resource exploitation is constantly increasing, and the difficulty of its exploitation is also increasing. Oil casing that only meets the API standard can no longer meet the use requirements. There is an urgent need for high-performance non-API oil well pipes, such as deep well exploitation, hot heavy oil exploitation, and exploitation in hydrogen sulfide corrosive environments. This requires that special oil pipes must have corresponding special performance under special geological exploitation conditions. When ordinary casing is used for the exploitation of oil and gas resources containing hydrogen sulfide, the casing will often suddenly break when the force is far lower than its own yield strength under the use stress and wet hydrogen sulfide environment. In the case of light, the casing string or the entire well will be scrapped, and in the case of severe cases, it will cause a blowout, causing hydrogen sulfide to overflow with oil and gas, causing great damage to the entire drilling rig and the surrounding ecological environment. Therefore, the development of such oil and gas resources requires high-strength and toughness SCC-resistant casing products.

[0003] The Chinese invention patent with publication number CN 108004462 A published on May 8, 2018, discloses a hydrogen sulfide stress corrosion cracking resistant oil casing and its manufacturing method. The casing product disclosed in the patent is designed based on the Mn-Cr system, and micro-alloy elements Ti and B are added to manufacture an 80-90ksi steel grade hydrogen sulfide stress corrosion resistant oil casing. However, its performance is low and cannot meet the use requirements.

[0004] The patent with publication number CN 114277310 A published on April 5, 2022, discloses a hot-rolled steel for high-strength and tough oil well pipes, which is obtained by adding microalloy elements such as Cr, Mo, Nb, and V, smelting, refining, VD furnace vacuum treatment and continuous casting to obtain a pipe blank. However, the yield strength of the material in this patent is greater than 758MPa. As the drilling depth increases to more than 8,000 meters, its strength cannot meet the demand. Summary of the invention

[0005] The invention provides a corrosion-resistant casing steel for deep oil and gas exploitation and a production method thereof. The 120ksi steel grade corrosion-resistant casing steel is obtained by optimizing the composition.

[0006] The present invention provides a corrosion-resistant casing and a heat treatment process thereof. The corrosion-resistant casing produced by using the above-mentioned deep oil and gas exploitation corrosion-resistant casing steel is combined with a suitable heat treatment process, and its yield strength is ≥828MPa, 0℃KV 2 ≥110J, with good toughness and excellent resistance to hydrogen sulfide corrosion.

[0007] The invention provides an application of a corrosion-resistant casing for deep well mining with a depth of ≥8000m.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A steel for corrosion-resistant casing for deep oil and gas production, comprising the following components in percentage by mass:

[0010] Cr: 0.70~0.90%, Mo: 0.70~0.90%, Nb: 0.030~0.060%, Ti: 0.050~0.100%, B: 0.0020~0.0040%, Al: 0.020~0.050%, V: 0.040~0.080%, C: 0.22~0.27%, Si: 0.20~0.40%, Mn: 0.60~0.80%, P≤0.012%, S≤0.0020%, RE: 0.0010~0.0020%, the balance is Fe and inevitable impurities.

[0011] The RE is at least one of the rare earth elements La and Ce;

[0012] The composition of the steel for corrosion-resistant casing for deep oil and gas exploitation also meets the following requirements: T.O+[N]≤120ppm; Sn, Sb, As, Pb, Bi≤0.010%.

[0013] The composition of the deep oil and gas production corrosion-resistant casing steel also satisfies: M = -2.0 × % Si + 1.0

[0014] ×%Mn+1.3×%Mo+3.0×%B+2.0×(%V+%Ti+%Nb)≥1.30%. Each element represents its mass percentage content in steel.

[0015] The composition of the deep oil and gas production corrosion-resistant casing steel also satisfies: W = -5 × (% Si + % Mn) + 12

[0016] ×%Mo+10×%Cr+22×(%Ti+%B)+18×%V+20×%Nb≥14.50%. Each element represents its mass percentage content in steel.

[0017] The present invention provides a method for producing corrosion-resistant casing steel for deep oil and gas exploitation, comprising the following process flow:

[0018] Hot metal pretreatment → converter smelting → LF furnace refining → RH vacuum degassing → continuous casting.

[0019] The molten iron pretreatment uses Mg-based and CaO-based desulfurizers to remove sulfur from the molten iron to less than 0.001%.

[0020] The converter smelting: deoxidation and alloying are carried out during steel tapping, and the amount of slag is strictly controlled, and the smelting end point P is ≤ 0.006%.

[0021] The LF furnace refining: elements such as C, Si, Mn, Cr, Nb, Mo, V, Ti, and B are adjusted to target values, the white slag retention time is ≥20 minutes, and the smelting cycle is ≤80 minutes.

[0022] The RH vacuum degassing: pure degassing time ≥ 25 min, soft blowing time ≥ 20 min, [H] ≤ 1.0 ppm after vacuum treatment, at least one of rare earth elements La and Ce is added to make the rare earth element content 0.0010-0.0020%.

[0023] The continuous casting: the superheat of the tundish is controlled to be 30-70°C above the liquidus line, and an immersion nozzle is used for pouring with protective slag to prevent secondary oxidation and absorb floating inclusions in the molten steel. The continuous casting billet diameter D and the drawing speed v should meet D = -137 × v 2 -178×v+1032, where the unit of continuous casting billet diameter D is mm, the unit of casting speed v is m / min, and the unit of crystallizer electromagnetic stirring evaluation rate f 1 Should be consistent with the continuous casting billet diameter D, D / f 1 =200; terminal electromagnetic stirring frequency f 2 Should be consistent with the continuous casting billet diameter D, D / f 2 =100; where crystal electromagnetic stirring frequency f 1 The unit is Hz, the end electromagnetic stirring frequency f 2 The unit of continuous casting billet diameter D is mm to ensure the quality of the billet. When calculating, just substitute the value before the unit into the formula.

[0024] Continuous casting produces round billets of Φ150mm to Φ250mm.

[0025] The present invention provides a corrosion-resistant casing, which is produced by using the above-mentioned steel for corrosion-resistant casing for deep oil and gas exploitation.

[0026] The corrosion-resistant casing has a small-angle grain boundary ratio of ≥30% and a dislocation density of 3×10 13 -7×10 13 / m -2 The austenite grain size is ≥8.5, and the A, B, C, and D non-metallic inclusions in the steel are not greater than 1.0.

[0027] The room temperature mechanical properties of the corrosion-resistant casing include yield strength ≥828MPa, tensile strength ≥900MPa, and 0℃KV 2 ≥110J, elongation ≥16%;

[0028] The corrosion-resistant casing has a loading strength of 75% SMYS, H 2 The steel passed the hydrogen sulfide corrosion test under the conditions of S partial pressure of 0.1MPa and temperature of 25°C using the American standard NACE TM0177 method A, and no fracture occurred during the test for 720 hours.

[0029] The present invention provides a heat treatment process for a corrosion-resistant casing, wherein the heat treatment method includes normalizing and quenching and tempering treatment, specifically: normalizing first, then quenching, and finally tempering.

[0030] The normalizing, heating temperature is W1=AC3+30~50℃, holding time t1 is determined by the steel pipe wall thickness S, t1=3.5×S, air cooling. Wherein, the unit of heating temperature W1 is ℃, the unit of holding time t1 is min, and the unit of steel pipe wall thickness S is mm.

[0031] The quenching, heating temperature W2 = AC3 + 30 ~ 50 ° C, holding time t2 is determined by the steel pipe wall thickness S, t1 = 3.2 × S, water cooling. Among them, the unit of heating temperature W is ° C, the unit of holding time t2 is min, and the unit of steel pipe wall thickness S is mm.

[0032] Tempering: Tempering temperature is 680-720°C, holding time t3 is determined by the steel pipe wall thickness S, t3=6×S, air cooling. The unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm.

[0033] Normalizing as a pretreatment can refine the original coarse grains, which can improve the strength and toughness of the steel and lay a good foundation for the subsequent quenching and tempering treatment. The purpose of quenching and tempering heat treatment is to obtain fine tempered troostite. The heat treatment temperature is set according to the AC3 temperature of the material to ensure that the material can be completely austenitized. The holding time is determined according to the wall thickness of the material, and the purpose is also to ensure that it can be completely austenitized.

[0034] Furthermore, the corrosion-resistant casing is directly produced by continuous casting of round billets, and the process of producing the corrosion-resistant casing is: continuous casting of round billets→heating→pipe threading→sizing→heat treatment→steel pipe grinding→steel pipe flaw detection→finishing→flaw detection→packaging and warehousing.

[0035] The invention provides an application of a corrosion-resistant casing for deep well mining with a depth of ≥8000m.

[0036] The design ideas of the present invention are as follows:

[0037] C: Ensures the strength of steel, improves hardenability and thus increases the percentage of martensite transformation; in addition, increasing the C content can increase the number of carbides precipitated during tempering, and these carbides are good H traps: but too high a C content will not only cause segregation itself, but will also greatly increase the segregation of Mn and P, thereby reducing the SSC resistance, so the C content is controlled at 0.22-0.27%.

[0038] Mn: improves the strength and permeability of steel, but Mn is an element that is easily segregated. Excessive Mn content is easy to segregate with S and P at the grain boundaries, so it is not good for the anti-SSC performance. The Cr and Mo contents designed in the present invention are relatively high, which are sufficient to ensure the hardenability and strength of the steel, so the Mn content is controlled at 0.60-0.80%.

[0039] Cr: Improves strength and hardenability, improves corrosion resistance, but excessive Cr content will precipitate large Cr at the grain boundary during tempering 23 C 6 Carbides are not conducive to H resistance 2 S stress corrosion resistance, so the Cr content is controlled at 0.70-0.90%.

[0040] Mo: It is an important solid solution strengthening and tempering precipitation strengthening element, and it also improves the hardenability of steel. Mo carbides precipitate during high temperature tempering, which increases the tempering resistance. Therefore, sufficient Mo must be added to ensure high strength and high tempering temperature. In addition, Mo can also reduce the segregation of P at the grain boundary by reducing the diffusion coefficient of P. However, when Mo is too high, coarse Mo will also form. 2 C and M 6 C carbides are not conducive to H resistance 2 S stress corrosion resistance, so the Mo content is controlled at 0.70-0.90%.

[0041] V: Its role in quenched and tempered steel is to inhibit tempering softening and increase tempering temperature. During high temperature tempering, VC carbides are precipitated to play a precipitation strengthening role, thus ensuring that the dislocation density of the steel is reduced during high temperature tempering, improving the SSC resistance, and ensuring the high strength requirement of 120ksi; however, when the V content in the steel exceeds a certain upper limit, the SSC resistance will no longer be improved, so the V content is controlled at 0.040-0.080%.

[0042] Nb: It can improve the temper softening resistance of steel, allowing the material to be tempered at a higher temperature. It can also further reduce the dislocation density that serves as a reversible hydrogen trap, which can effectively improve the SSC resistance. However, if the Nb content is too high, it may lead to the appearance of oversized chain and block NbN inclusions during the steelmaking process, reducing the material performance, so the Nb content is controlled at 0.030% to 0.060%.

[0043] Ti, B: When Ti and B are added together, B is concentrated at the grain boundary, reducing the grain boundary vacancy concentration and reducing hydrogen diffusion, thereby improving the SSC resistance. When the Ti content is too high, in addition to forming coarse carbides, it will also increase the bainite and M / A islands in the steel, thereby reducing the SSC resistance. Therefore, the Ti content is controlled at 0.050-0.100%, and the B content is controlled at 0.0020-0.0040%.

[0044] RE: Rare earth elements can change the morphology of inclusions from elongated to spherical, fix rare earth oxides and sulfides around the grain boundaries, inhibit the growth of grains, refine grains to improve impact toughness, ductility and corrosion resistance, and reduce the sensitivity to hydrogen-induced cracking. Therefore, the RE content is controlled at 0.0010-0.0020%.

[0045] P, S and five harmful elements: P, S and five harmful elements Sn, Sb, As, Pb, Bi are impurity elements in steel, which significantly reduce the material's SSC resistance. Their content in steel should be reduced as much as possible. P is easy to form segregation in steel, and the stress zone at the tip of MnS inclusions is easy to become the starting point of sulfide stress cracking. Therefore, P, S and five harmful elements should be controlled at ≤0.012%, ≤0.0020% and ≤0.010% respectively.

[0046] TO and [N]: Oxygen in steel easily forms oxide inclusions, especially type B inclusions along the rolling direction. The presence of free nitrogen increases the brittleness of the material and impairs its toughness. The total amount of T.O + [N] should be ≤120ppm.

[0047] In order to ensure the good low-temperature toughness of steel, the ratio of Si, Mo, Mn, Nb, Ti, V, and B needs to be limited. Since Si is easy to segregate at the austenite grain boundary, it reduces the crystal bonding force, deteriorates the low-temperature toughness, and increases the temper brittleness, so the coefficient of Si is -2.0. Mn can significantly affect the variant selection during the phase transformation process, increase the types of variants in the phase transformation, and thus improve the low-temperature toughness, so the coefficient of Mn is 1.0; Mo can improve the hardenability of steel, effectively reduce the segregation of impurity elements such as P, S, and As at the grain boundary, and effectively improve the low-temperature toughness of steel, so the coefficient of Mo is 1.3; B can stabilize the carbide phase in steel, prevent grain boundary dissolution and grain growth, and can also reduce the precipitation of brittle phase at the grain boundary, improve the toughness of the grain boundary, and increase the low-temperature toughness of steel, so the coefficient of B is 3.0; Ti, Nb, and V can precipitate fine MC carbides, refine the structure and improve the tempering stability of steel, thereby improving the low-temperature toughness, so the coefficients of Ti, Nb, and V are 2.0:

[0048] That is, M=-2.0×%Si+1.0×%Mn+1.3×%Mo+3.0×%B+2.0×(%V+%Ti+%Nb)≥1.30%.

[0050] In order to ensure the steel has good hydrogen sulfide corrosion resistance, the ratio of Si, Mn, Cr, Mo, Nb, V, Ti, and B needs to be limited. Since Si and Mn are easily segregated at the austenite grain boundary, the crystal bonding force is reduced, resulting in uneven microstructure and decreased corrosion resistance, so the coefficient is -5. Mo can improve the hardenability of steel, effectively reduce the segregation of impurity elements such as P and S at the grain boundary, and precipitate carbide Mo during tempering. 2 C can become a trap to capture H, effectively improving the sulfur resistance of steel, so the coefficient of Mo is 12; the MC-type carbides precipitated by Nb and V can effectively inhibit grain growth, and as irreversible H traps, greatly improve the SSC resistance. In addition, it can improve the steel's resistance to temper softening, reduce the material's dislocation density, and improve the SSC resistance. According to relevant research, the ability of NbC to capture hydrogen is greater than that of VC, so the coefficient of V is 18, and the coefficient of Nb is 20; Ti carbides are irreversible traps for hydrogen. When Ti and B are added in combination, B also toughens the grain boundaries, and its solid solubility increases due to Ti solidifying N. B is segregated at the grain boundaries, significantly improving hardenability, increasing martensite content, and effectively reducing the Mn content in steel; on the other hand, B reduces hydrogen diffusion by reducing the vacancy concentration at the grain boundaries. Therefore, the coefficients of Ti and B are 22. The irreversible H hydrogen traps provided by Cr can effectively capture H atoms, slow down the diffusion rate of H atoms, and improve the SSC resistance, so the coefficient of Cr is 10:

[0051] That is -5×(%Si+%Mn)+12×%Mo+10×%Cr+22×(%Ti+%B)+18×%V+20×%Nb≥14.50%.

[0052] In the present invention, the added alloying elements such as Ti, V, and Nb can form fine carbides, pin the grain boundaries, hinder dislocation movement, refine the grains, and also serve as irreversible hydrogen traps to improve the sulfur resistance of the steel. The addition of RE rare earth can improve the morphology of inclusions, thereby improving the sulfur resistance of the material. At the same time, a uniform and fine tempered martensite structure can be obtained through the smelting of pure steel and the subsequent heat treatment process, which is conducive to the precipitation of a large number of fine alloy carbides.

[0053] Compared with the prior art, the optimized alloy composition system, combined with appropriate pure steel control and heat treatment process, can obtain a dispersed and refined second phase distributed on the tempered troostite matrix at room temperature, with a lower dislocation density and a higher proportion of small-angle grain boundaries, so that the material has good strength and toughness and excellent resistance to hydrogen sulfide corrosion, and the produced corrosion-resistant casing can be used in deep wells with a depth of ≥8000m. The present invention provides a 120ksi steel grade corrosion-resistant casing steel that can be produced by small-diameter continuous casting round billets and is suitable for converter production. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 The average misorientation map of the cores in the EBSD of Example 1, the average misorientation of the cores is 1.77°;

[0055] Figure 2 In the EBSD map of the core average misorientation of Comparative Example 2, the average core average misorientation is 3.42°. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] Example 1-Example 3

[0058] A steel for corrosion-resistant casing for deep oil and gas production includes the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0059] Comparative Example 1-Comparative Example 3

[0060] A steel for corrosion-resistant casing for deep oil and gas production includes the following components in mass percentage: as shown in Table 1, the remainder not shown in Table 1 is Fe and unavoidable impurities.

[0061] Table 1 Composition of various examples and comparative steels (wt%)

[0062]

[0063]

[0064] In Table 1, the same rare earth raw materials are used in the examples and comparative examples, but the contents of RE (lanthanum and cerium) are controlled differently. In addition, the five harmful elements Sn, Sb, As, Pb and Bi are controlled at ≤ 0.010%.

[0065] The production method of the corrosion-resistant casing steel for deep oil and gas production described in the above embodiments and comparative examples includes the following process flow:

[0066] Hot metal pretreatment → converter smelting → LF furnace refining → RH vacuum degassing → round billet continuous casting.

[0067] The molten iron pretreatment uses Mg-based and CaO-based desulfurizers to remove sulfur from the molten iron to 0.001%, and the post-slag bright surface is ≥80%;

[0068] The converter smelting: deoxidation and alloying are carried out during steel tapping, and the amount of slag is strictly controlled, and the smelting end point P is 0.006%.

[0069] The LF furnace refining: elements such as C, Si, Mn, Cr, Nb, Mo, V, Ti, and B are adjusted to target values, the white slag retention time is 21 minutes, and the smelting cycle is 76 minutes.

[0070] The RH vacuum degassing: pure degassing time is 25 minutes, soft blowing time is 25 minutes, [H] after vacuum treatment is 0.9 ppm, and rare earth elements La and Ce are added to make their content 0.0010-0.0020%.

[0071] The continuous casting: the tundish superheat is controlled to be 47°C above the liquidus line, an immersion nozzle is used for pouring with protective slag to prevent secondary oxidation and absorb floating inclusions in the molten steel, a 200mm diameter continuous casting round billet is produced, the drawing speed is 1.90m / min, and the continuous casting billet diameter D and the drawing speed v should meet D=-137×v 2 -178×v+1032, where the unit of continuous casting billet diameter D is mm, and the unit of casting speed v is m / min. The crystallizer electromagnetic stirring frequency is 1.0Hz, and the end electromagnetic stirring frequency is 2.0Hz, which is consistent with the crystallizer electromagnetic stirring evaluation rate f 1 and continuous casting billet diameter D, D / f 1 =200; in line with the end electromagnetic stirring frequency f 2 Should be consistent with the continuous casting billet diameter D, D / f 2 =100.

[0072] The corrosion-resistant casing is produced by using the corrosion-resistant casing steel for deep oil and gas production in the above embodiments and comparative examples. The specific process flow is: continuous casting of round billets → heating → pipe threading → sizing → heat treatment → steel pipe grinding → steel pipe flaw detection → fine machining → flaw detection → packaging and warehousing.

[0073] Among them, the heat treatment process includes normalizing + quenching and tempering. Specifically: normalizing first, then quenching, and finally tempering.

[0074] The normalizing, heating temperature is W1 = AC3 + 30 ~ 50 ℃, the holding time t1 is determined by the steel pipe wall thickness S, t1 = 3.5 × S, air cooling. Among them, the unit of heating temperature W1 is ℃, the unit of holding time t1 is min, and the unit of steel pipe wall thickness S is mm. 3 The W1 of each embodiment and comparative example satisfies W1=AC 3 +30~50℃.

[0075] The quenching, heating temperature W2 = AC3 + 30 ~ 50 ° C, holding time t2 is determined by the steel pipe wall thickness S, t2 = 3.2 × S, water cooling. Among them, the unit of heating temperature W is ° C, the unit of holding time t2 is min, and the unit of steel pipe wall thickness S is mm.

[0076] Tempering: tempering temperature 680-720°C, holding time t3 determined by the steel pipe wall thickness S, t3=6×S, air cooling. Wherein, the unit of holding time t3 is min, and the unit of steel pipe wall thickness S is mm. The heat treatment parameters of each embodiment and comparative example are shown in Table 2.

[0077] Table 2 List of heat treatment processes for the embodiments of the present invention and comparative examples

[0078]

[0079]

[0080] The performance testing method of the corrosion-resistant casing produced in each embodiment and comparative example is as follows:

[0081] Organization: Take samples from 1 / 2 wall thickness of the cross section at the end of the steel pipe for metallographic and grain size analysis.

[0082] Performance: Take tensile, impact and SSC resistance specimens on the 1 / 2 radius of the steel pipe, and conduct mechanical property tests according to GB / T228 and GB / T229, and conduct SSC resistance tests according to NACE TM0177 standard A method (at a loading strength of 75% SMYS, H 2 The S partial pressure was 0.1 MPa and the temperature was 25°C. The average grain size was observed according to GB / T 6394, and the small angle grain boundaries (2°≤θ≤15°) were observed using EBSD. The results are shown in Table 3.

[0083] Non-metallic inclusions were sampled from the 1 / 2 radius of the steel pipe and tested according to method A in ASTM E45 standard. The results are shown in Table 4.

[0084] Table 3 Performance test results of the embodiments of the present invention and the comparative examples

[0085]

[0086] Table 4 Non-metallic inclusion detection results of the embodiments of the present invention and the comparative examples

[0087]

[0088]

[0089] Embodiments and comparative examples Through the pure steel smelting technology, non-metallic inclusions are well controlled. Figure 1The average misorientation map of the cores in the EBSD of Example 1, the average misorientation of the cores is 1.77°; Figure 2 Compared with the core average orientation difference map in EBSD of Case 2, the average core average orientation difference is 3.42°; the lower the value of the core average orientation difference, the lower the dislocation density of the material, and the lower the dislocation density, the more beneficial it is to the material's anti-sulfur performance.

[0090] The chemical composition and production methods of the steels of Examples 1-3 are properly controlled, their chemical compositions meet the requirements, and the strength, toughness and SSC resistance of the steels are good. The chemical composition of Comparative Example 1 does not meet the requirements of the M formula, so its toughness does not meet the requirements; the chemical composition of Comparative Example 2 does not meet the requirements of the M value and W value, resulting in its sulfur resistance and mechanical properties not meeting the requirements; the chemical composition of Comparative Example 3 does not meet the requirements of the M value and W value, and the heat treatment process is not properly controlled, resulting in very unsatisfactory overall performance.

[0091] The underlined data above do not meet the requirements of the present invention.

[0092] The description of the above embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A steel for corrosion-resistant casing for deep oil and gas exploitation, characterized in that: The deep oil and gas production corrosion-resistant casing steel includes the following mass percentage components: Cr: 0.70~0.90%, Mo: 0.70~0.90%, Nb: 0.030~0.060%, Ti: 0.050~0.100%, B: 0.0020~0.0040%, Al: 0.020~0.050%, V: 0.040~0.080%, C: 0.22~0.27%, Si: 0.20~0.40%, Mn: 0.60~0.80%, P≤0.012%, S≤0.0020%, RE: 0.0010~0.0020%, the balance is Fe and inevitable impurities.

2. The corrosion-resistant casing steel for deep oil and gas exploitation according to claim 1 is characterized in that: The composition of the steel for corrosion-resistant casing for deep oil and gas production also satisfies: M=-2.0×%Si+1.0×%Mn+1.3×%Mo+3.0×%B+2.0×(%V+%Ti+%Nb)≥1.30%.

3. The corrosion-resistant casing steel for deep oil and gas exploitation according to claim 1 is characterized in that: The composition of the steel for corrosion-resistant casing for deep oil and gas production also satisfies: W=-5×(%Si+%Mn)+12×%Mo+10×%Cr+22×(%Ti+%B)+18×%V+20×%Nb≥14.50%.

4. A method for producing corrosion-resistant casing steel for deep oil and gas exploitation according to any one of claims 1 to 3, characterized in that: The production method comprises the following process flow: Hot metal pretreatment → converter smelting → LF furnace refining → RH vacuum degassing → round billet continuous casting.

5. The production method according to claim 4, characterized in that: The continuous casting: the continuous casting billet diameter D and the drawing speed v meet D = -137 × v 2 -178×v+1032, where the unit of the continuous casting billet diameter D is mm, and the unit of the pulling speed v is m / min; the crystallizer electromagnetic stirring frequency f1 is consistent with the continuous casting billet diameter D, D / f1=200; the terminal electromagnetic stirring frequency f2 is consistent with the continuous casting billet diameter D, D / f2=100; where the unit of the crystallizer electromagnetic stirring frequency f1 is Hz, the terminal electromagnetic stirring frequency f2 is Hz, and the unit of the continuous casting billet diameter D is mm.

6. A corrosion-resistant casing, characterized in that: The method is obtained by using the steel for corrosion-resistant casing for deep oil and gas exploitation as described in any one of claims 1 to 3.

7. The corrosion-resistant casing according to claim 6, characterized in that: The corrosion-resistant casing has a small-angle grain boundary ratio of ≥30% and a dislocation density of 3×10 13 -7×10 13 / m -2 ; The austenite grain size is ≥8.5, and the non-metallic inclusions of types A, B, C, and D in the steel are not greater than level 1.

0.

8. The corrosion-resistant casing according to claim 6 or 7, characterized in that: The room temperature mechanical properties of the corrosion-resistant casing include yield strength ≥828MPa, tensile strength ≥900MPa, 0°C KV2 ≥110J, and elongation ≥16%.

9. The corrosion-resistant casing according to any one of claims 6 to 8, characterized in that: The corrosion-resistant casing passed the hydrogen sulfide corrosion test using the American standard NACE TM0177 standard A method at a loading strength of 75% SMYS, a H2S partial pressure of 0.1 MPa, and a temperature of 25°C, and no fracture occurred during the test for 720 hours.

10. A heat treatment process for the corrosion-resistant casing according to any one of claims 6 to 9, characterized in that: The heat treatment process includes: normalizing first, quenching second, and tempering last.

11. The heat treatment process according to claim 10, characterized in that: For the normalizing, the heating temperature is W1=AC3+30~50℃, the holding time t1 is determined by the steel pipe wall thickness S, t1=3.5×S, and air cooling; wherein the unit of the heating temperature W1 is ℃, the unit of the holding time t1 is min, and the unit of the steel pipe wall thickness S is mm.

12. The heat treatment process according to claim 10, characterized in that: For the quenching, the heating temperature W2=AC3+30~50℃, the holding time t2 is determined by the steel pipe wall thickness S, t1=3.2×S, and water cooling; wherein the unit of the heating temperature W is ℃, the unit of the holding time t2 is min, and the unit of the steel pipe wall thickness S is mm.

13. The heat treatment process according to claim 10, characterized in that: The tempering: the tempering temperature is 680-720°C, the holding time t3 is determined by the steel pipe wall thickness S, t3=6×S, and air cooling; wherein the unit of the holding time t3 is min, and the unit of the steel pipe wall thickness S is mm.

14. An application of the corrosion-resistant casing according to any one of claims 6 to 9, characterized in that: Used for deep well mining with a depth of ≥8000m.

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