Oil casing with high strength, high toughness and large strain performance and preparation method thereof

Abstract

This invention discloses an oil well casing with high strength, high toughness, and large strain performance, and its preparation method, belonging to the field of oil and gas development casing preparation technology. The oil well casing disclosed in this invention, possessing high strength, high toughness, and large strain performance, is micro-alloyed by adding alloying elements Mn, Si, Cr, Ni, Mo, Al, Nb, and V to medium-low carbon, while controlling the content of harmful elements such as P, S, O, H, and N. This ensures that the final composition meets the requirements of oil and gas wells under complex operating conditions for large strain casing. According to relevant experimental results, the yield strength of the oil well casing with the above composition reaches 110 kSi, 125 kSi, and 140 kS, respectively, with a yield strength ratio ≤0.89~0.93 and a uniform elongation ≥15~20%, meeting the practical requirements of oil and gas wells under complex operating conditions.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development casing preparation technology, specifically relating to an oil casing with high strength, high toughness and large strain performance and its preparation method. Background Technology

[0002] With the development of the global oil and gas industry, the oil and gas exploration and development environment is becoming increasingly complex. Deep-sea, deep-layer, low-permeability, shale oil and gas, and tapping the potential of old oilfields are the current focus of development. There are more and more special structure wells such as directional wells and extended reach wells. Most shale oil and gas and low-permeability oil and gas wells need to be enhanced for production. During the well construction process, casing deformation often occurs, sometimes reaching 30-50%, which leads to the inability of bridge plugs to be properly set, reduces the number of fracturing stages, reduces the production of single wells, and shortens the life of oil and gas wells. When the casing deformation is severe, drilling plug operations cannot be completed, and even wellbore integrity failure may occur.

[0003] Studies have shown that the main failure mechanism of casing is deformation caused by shear and crush stress. The main controlling factors depend primarily on the relative magnitude and distribution of the casing string's load-bearing capacity and the applied load. These factors are related to the casing's material properties and structural dimensions, formation conditions (natural fractures, formation inhomogeneity), and fracturing operation parameters (pressure, flow rate, number of cycles, etc.). Load factors mainly include internal and external pressure, axial tension and compression, bending, additional stress generated by fracturing pressure and its temperature changes, uneven stress, fault slip, natural fracture propagation, hydraulic fracture propagation, and their mutual interference. In addition to optimizing wellbore trajectory (controlling formation conditions), optimizing fracturing technology (improving fracturing load conditions), and adopting new methods for integrated wellbore deformation coordination to alleviate casing deformation, improving the casing string's load-bearing capacity is crucial for preventative measures. The casing's load-bearing capacity is manifested in the casing's material strength (steel grade), structural strength (material strength and structural dimensions), toughness (brittle fracture resistance), and uniform deformation resistance (yield-to-tensile strength ratio, uniform elongation).

[0004] Traditional casing string design methods are stress-based, requiring the working stress to be lower than the material's yield strength, meaning that plastic deformation of the casing (string) is not allowed during use. However, in reality, due to variations in wellbore curvature and azimuth, the wellbore trajectory exhibits an irregular spatial shape. Furthermore, the implementation of production enhancement measures such as fracturing can cause localized plastic deformation of the casing. This places demands on the casing's plastic deformation capacity (yield-to-strength ratio, uniform elongation). Controlling the plastic deformation of the casing within an allowable range ensures the safe use of deformed casing. This necessitates the adoption of strain-based casing (string) design, which in turn leads to the development and application of casings that combine high strength, high toughness, and large strain performance.

[0005] To date, apart from high-strain casing used in heavy oil steam thermal recovery wells, there are few reports of high-strain casing applications internationally. For N80 and lower grade casings, although strain-based casing string design methods are not employed, and no requirements are specified for casing strain performance, the low strength and high elongation (including uniform elongation) of most casings easily meet the high-strain performance requirements of strain-based casing string design methods. However, for P110 and higher grade casings, due to the inverse relationship between strength, plasticity, and toughness, it is often difficult to simultaneously meet the requirements. In fact, a significant portion of P110 and higher grade casings have a yield strength ratio exceeding 0.93, some even reaching 0.98. An excessively high yield strength ratio leads to a significant decrease in the material's ability to undergo uniform plastic deformation, severely reducing safety in use. Based on relevant research results and engineering experience, it is proposed to control the yield strength ratio of the casing below 0.93 or even lower to meet the safety requirements of the casing string application based on strain-based design methods. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide an oil casing with high strength, high toughness and large strain performance and its manufacturing method, so as to solve the technical problem that the existing casing cannot meet the large strain requirements of oil and gas wells under complex working conditions.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] This invention discloses an oil casing that combines high strength, high toughness, and large strain performance. The oil casing comprises, by mass percentage: C: 0.23%–0.29%, Si: 0.65%–0.85%, Mn: 1.30%–1.50%, P≤0.015%, S≤0.005%, Cr: 0.90%–1.20%, Ni: 0.30%–0.50%, Mo: 0.25%–0.35%, Al: 0.07%–0.12%, Ca: 0.016%–0.024%, O+H+N≤0.008%, Nb: 0.04%–0.09% or V: 0.04%–0.09%, with the balance being Fe and other unavoidable impurities.

[0009] This invention also discloses a method for preparing the above-mentioned oil casing with high strength, high toughness, and large strain performance, comprising the following steps:

[0010] S1: After steelmaking, and with the addition of modifying components, the composition of the molten steel obtained is the same as that of the oil casing as described in claim 1.

[0011] S2: The molten steel is continuously cast to obtain a rod-shaped continuous casting billet;

[0012] S3: After heating the bar-shaped continuous casting billet, it is pierced and then hot rolled to obtain the pre-treated sleeve;

[0013] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness and large strain performance is obtained.

[0014] Furthermore, in S1, the steelmaking process employs electric arc furnace steelmaking or oxygen-blown converter steelmaking; the electric arc furnace steelmaking uses sponge iron and high-quality scrap steel as raw materials; the oxygen-blown converter steelmaking uses blast furnace molten iron and high-quality scrap steel as raw materials.

[0015] Furthermore, in S1, after adding modified components, ladle refining and vacuum degassing are carried out to obtain molten steel.

[0016] Furthermore, in S2, the continuous casting process employs electromagnetic stirring and light reduction techniques to control the center segregation of the rod-shaped continuous casting billet.

[0017] Further, in S3, the heating temperature of the rod-shaped continuous casting billet is 1185-1215℃, and the heating time is 90-120 min; the piercing temperature is 1150-1200℃; the hot rolling temperature is 1000-1130℃; after hot rolling, it is cooled in air to obtain a pretreated sleeve.

[0018] Furthermore, in S4, the heat treatment is a heat treatment process involving heating in a protective atmosphere furnace, quenching, and high-temperature tempering.

[0019] The quenching process parameters are: quenching temperature of 900-920℃, holding time of 50-70min, internal and external water spray quenching, and cooling rate ≥30℃ / s;

[0020] The process parameters for high-temperature tempering are as follows: the temperature for high-temperature tempering is 570℃~650℃, and the tempering time is 90~120min.

[0021] Furthermore, in S4, after the pre-treated sleeve undergoes heat treatment and post-treatment, it also needs to undergo hot straightening, tempering, and water cooling treatment in sequence; the temperature of the hot straightening is 520℃~600℃; the temperature of the tempering is 520~600℃, and the time is 90~120min.

[0022] Furthermore, after water cooling, thread machining is performed to obtain an oil casing that combines high strength, high toughness, and large strain performance.

[0023] Furthermore, the threading process involves machining API standard threads or special threads onto the pipe section.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention discloses an oil casing possessing high strength, high toughness, and large strain performance. Microalloying is achieved by adding alloying elements Mn, Si, Cr, Ni, Mo, Al, Nb, and V to a medium-low carbon content. A medium-low carbon content of 0.23%–0.29% is beneficial for improving the steel's plasticity and toughness. However, excessively low carbon content is detrimental to improving the steel's hardenability and strength; excessively high carbon content is also detrimental to improving both plasticity and toughness. Based on the aforementioned carbon content, the addition of Mn, Si, Cr, Ni, Mo, Al, Nb, and V strengthens the steel, improving hardenability and thus strength with minimal impact on the yield strength ratio. This also improves the hardenability and tempering stability, as well as the strength and plasticity. Furthermore, the addition of Al, which combines with oxygen or nitrogen to form finely distributed oxides or nitrides, plays a crucial role in refining the grain size and simultaneously improving both strength and toughness. The steel contains deoxidizers and nitrogen-fixing agents; V is added to the steel to form VC and VN with C and N in the steel, which can inhibit the growth of austenite grains and refine the grains, thereby improving strength and toughness; Nb is added to the steel to form NbC and NbN with C and N in the steel, which can also inhibit the growth of austenite grains and refine the grains, thereby improving strength and toughness; Ca is added to the steel to improve the properties and morphology of inclusions, thereby improving the plasticity and toughness of the steel, and the effect is better when Ca / S≥2; in addition, the content of harmful elements such as P, S, O, H, and N is controlled so that the final composition can meet the requirements of oil and gas wells for high-strain casing under complex working conditions; according to relevant experimental results, the oil casing with the above composition, which combines high strength, high toughness and high strain performance, has yield strengths of 110ksi, 125ksi and 140ks respectively, yield strength ratio ≤0.89~0.93, and uniform elongation ≥15~20%, which can meet the practical requirements of complex working conditions in oil and gas wells.

[0026] This invention also discloses a method for preparing the above-mentioned oil casing with high strength, high toughness, and large strain performance. After adopting an innovative composition design, continuous casting, piercing, heat treatment, and post-treatment are carried out to obtain fine and uniform tempered sorbite, reducing the influence of residual stress on casing performance. This results in an oil casing with excellent mechanical properties, which can meet the requirements of oil and gas wells with complex working conditions for high-strength and large-strain casing. The preparation method is simple to operate and easy to realize industrial production. Detailed Implementation

[0027] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0028] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0029] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0030] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0031] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0032] This invention provides an oil casing that combines high strength, high toughness, and large strain performance. In order to ensure that the requirements of the strain-based casing string design method for casing strength, toughness, and large strain performance (yield-to-tensile ratio, uniform elongation) are met, its chemical composition and manufacturing process must be rationally designed.

[0033] In terms of composition design, it is proposed to use medium and low carbon, add alloying elements Mn, Si, Cr, Ni, Mo, and Al, microalloy Nb and V, control harmful elements such as P, S, O, H, and N in the steel, perform Al-Si full deoxidation, and treat the molten steel with Ca; increase the content of Mn and Si elements that have a smaller impact on the yield strength ratio.

[0034] The functions and content ranges of the main elements are as follows:

[0035] Carbon (C) is the main strengthening element in steel. Using medium to low carbon content is beneficial for improving the plasticity and toughness of steel, but too low a carbon content is detrimental to improving the hardenability of the steel, which is also unfavorable for increasing its strength; too high a carbon content is detrimental to improving the plasticity and toughness of the steel. It is advisable to control the carbon content within the range of 0.23% to 0.29%.

[0036] Si: It has a solid solution strengthening effect in steel and has little effect on the yield strength ratio. It is also an important deoxidizer. It should be controlled within the range of 0.65% to 0.85%.

[0037] Mn: It is dissolved in steel to improve the hardenability of the steel, thereby increasing its strength, and has little effect on the yield strength ratio. It should be controlled within the range of 1.30% to 1.50%.

[0038] Cr: It is dissolved in steel to improve its hardenability and tempering stability, thereby increasing its strength. However, excessive content will increase costs. It should be controlled within the range of 0.90% to 1.20%.

[0039] Ni: It is dissolved in steel to improve its hardenability and thus its strength. Its addition can also improve the plasticity and toughness of steel, but too high a content will increase the cost. It should be controlled within the range of 0.30% to 0.50%.

[0040] Mo: It is dissolved in steel to improve the hardenability and tempering stability of steel, thereby increasing the strength of the steel. At the same time, adding Mo can suppress the segregation of Mn and P, improve uniformity, and improve the temper brittleness of steel. The effect is better when Mo / P ≥ 15, but too high a content will increase the cost. It is advisable to control it in the range of 0.25% to 0.35%.

[0041] Al: When combined with oxygen or nitrogen, it forms fine and uniformly distributed oxides or nitrides, which can refine grains and improve strength and toughness. It is also an important deoxidizer and nitrogen fixative. However, excessive content will affect the hot working properties of steel. It should be controlled within the range of 0.07% to 0.12%.

[0042] V: When added to steel, it combines with C and N to form VC and VN, which inhibit austenite grain growth and refine the grains, thereby improving strength and toughness. However, excessive VC and VN content can impair the plasticity and toughness of the steel and increase costs. It is advisable to control it within the range of 0.04% to 0.09%.

[0043] Nb: When added to steel, it forms NbC and NbN with the steel, which can inhibit the growth of austenite grains and refine the grains, thereby improving strength and toughness. However, excessive content will result in excessive NbC and NbN, which will impair the plasticity and toughness of the steel and increase costs. It is advisable to control it within the range of 0.04% to 0.09%.

[0044] Ca: Adding it to steel can improve the properties and morphology of inclusions, thereby increasing the plasticity and toughness of the steel. The effect is better when Ca / S ≥ 2. It is advisable to control it within the range of 0.016% to 0.024%.

[0045] P: A harmful element that mainly affects the plasticity and toughness of steel. P should be controlled to ≤0.015%.

[0046] S: A harmful element that primarily affects the plasticity and toughness of steel. It is advisable to control S to ≤0.005%.

[0047] O, H, and N are harmful elements that mainly affect the plasticity and toughness of steel. The total O+H+N content should ideally be controlled to ≤0.008%.

[0048] In summary, the composition of the large strain bushing, by mass percentage, is as follows: C: 0.23%–0.29%, Si: 0.65%–0.85%, Mn: 1.30%–1.50%, P≤0.015%, S≤0.005%, Cr: 0.90%–1.20%, Ni: 0.30%–0.50%, Mo: 0.25%–0.35%, Nb: 0.04%–0.09% or V: 0.04%–0.09%, Al: 0.07%–0.12%, Ca: 0.016%–0.024%, O+H+N≤0.008%, with the balance being Fe and other unavoidable impurities.

[0049] The present invention also discloses the above-mentioned method for preparing oil casing, which mainly involves steelmaking (including ladle refining and vacuum degassing), continuous casting, hot rolling in the austenitic region, heat treatment, hot straightening, stress relief tempering and other processes to obtain a fine and uniform microstructure in the material, thereby achieving a reasonable match between the material's strength, plasticity and toughness; in order to control the yield strength, the final rolling temperature is increased, a higher hot straightening temperature is adopted, and stress relief tempering and other measures are used.

[0050] Specifically, the following steps are included:

[0051] S1: After steelmaking, and with the addition of modifying components, the composition of the molten steel obtained is the same as that of the oil casing as described in claim 1.

[0052] S2: The molten steel is continuously cast to obtain a rod-shaped continuous casting billet;

[0053] S3: After heating the bar-shaped continuous casting billet, it is pierced and then hot rolled to obtain the pre-treated sleeve;

[0054] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness and large strain performance is obtained.

[0055] Preferably, in terms of billet preparation process, the main processes are steelmaking (including ladle refining and vacuum degassing), continuous casting, hot rolling in the austenitic region, heat treatment, hot straightening, stress relief tempering, etc., to obtain a fine and uniform microstructure of the material, so as to achieve a reasonable match between the material strength, plasticity and toughness; in order to control the yield strength, the final rolling temperature is increased, a higher hot straightening temperature is adopted, and stress relief tempering and other measures are adopted.

[0056] Preferably, it includes the following steps:

[0057] ① Steelmaking: Batching, electric furnace or oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in the steel, refining outside the furnace and vacuum degassing to obtain the above-mentioned oil casing composition of molten steel.

[0058] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. During the continuous casting process, electromagnetic stirring and light reduction technology are used to control the center segregation of the continuous casting billet.

[0059] ③ Piercing and Hot Rolling: The resulting bar-shaped continuous casting billet is heated in an annular furnace at a temperature of 1185℃~1215℃ for 90~120 min. Hot piercing is then performed at 1150℃~1200℃, followed by hot rolling at 1000℃~1130℃. After air cooling, the billet is sawn to the appropriate length. Using a higher final rolling temperature is beneficial for obtaining a lower yield strength ratio and a larger uniform plastic deformation elongation.

[0060] ④ Heat Treatment and Post-treatment: A protective atmosphere furnace heating, quenching + high-temperature tempering heat treatment process is adopted. The quenching temperature should be controlled at 900℃~920℃, the holding time is 50~70min, internal and external water spray quenching, and the cooling rate is ≥30℃ / s to ensure that the quenched structure is basically complete martensite. The tempering temperature is controlled at 570℃~650℃, and the tempering time is 90~120min to obtain fine and uniform tempered sorbite with a grain size of grade 8 or finer. After tempering, water cooling is performed to avoid possible temper brittleness. After heat treatment, hot straightening is performed at a straightening temperature controlled at 520℃~600℃, followed by water cooling. To reduce the influence of residual stress on the performance of the sleeve, after hot straightening, tempering is performed at 520℃~600℃ for 90~120 minutes, followed by water cooling. Then, non-destructive testing is performed.

[0061] ⑤ Thread machining: API standard threads or special threads can be machined on pipe sections according to user requirements, and magnetic particle testing can be performed on the threads.

[0062] The oil casing produced by this invention using an appropriate manufacturing process possesses excellent comprehensive performance, combining high strength, high toughness, and large strain properties. Its yield strength levels can reach 110 ksi, 125 ksi, and 140 ksi, respectively, corresponding to a room temperature yield strength greater than 758–965 MPa, a tensile strength greater than 862–1034 MPa, a yield-to-tensile ratio ≤0.89–0.93, a total elongation ≥15–20%, a uniform elongation ≥10–15%, and a Charpy impact toughness ≥80–100 J. This meets the requirements of oil and gas wells under complex operating conditions for high-strength, large-strain casing.

[0063] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0064] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0065] Example 1

[0066] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0067] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0068] The composition of the molten steel, by mass percentage, includes: C: 0.24%, Si: 0.70%, Mn: 1.32%, P: 0.010%, S: 0.003%, Cr: 0.90%, Ni: 0.33%, Mo: 0.27%, V: 0.04%, Al: 0.09%, Ca: 0.016%, O+H+N: 0.007%, with the balance being Fe and other unavoidable impurities;

[0069] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0070] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0071] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃±10℃, the holding time is 50min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 640℃±10℃, the tempering time is 90min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 590℃±10℃, and then water cooling is performed. After hot straightening, tempering is carried out at 590℃±10℃ for 90min, followed by water cooling, and then non-destructive testing is performed.

[0072] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0073] The oil casing obtained in Example 1, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 861 MPa, a tensile strength greater than 978 MPa, a yield-to-tensile ratio of 0.88, a total elongation of 23%, a uniform elongation of 16%, and a Charpy impact toughness of 105 J.

[0074] Example 2

[0075] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0076] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0077] The composition of the molten steel, by mass percentage, includes: C: 0.23%, Si: 0.65%, Mn: 1.30%, P: 0.011%, S: 0.002%, Cr: 0.96%, Ni: 0.30%, Mo: 0.31%, V: 0.044%, Al: 0.07%, Ca: 0.019%, O+H+N: 0.005%, with the balance being Fe and other unavoidable impurities;

[0078] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0079] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0080] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 50min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 640℃-110℃, the tempering time is 90min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 590℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 590℃-110℃ for 90min, followed by water cooling, and then non-destructive testing is performed.

[0081] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0082] The oil casing obtained in Example 2, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 853 MPa, a tensile strength greater than 958 MPa, a yield-to-tensile ratio of 0.89, a total elongation of 24%, a uniform elongation of 17%, and a Charpy impact toughness of 113 J.

[0083] Example 3

[0084] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0085] S1: Batching, electric arc furnace steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0086] The composition of the molten steel, by mass percentage, includes: C: 0.26%, Si: 0.72%, Mn: 1.37%, P: 0.008%, S: 0.002%, Cr: 1.03%, Ni: 0.35%, Mo: 0.32%, V: 0.051%, Al: 0.08%, Ca: 0.021%, O+H+N: 0.006%, with the balance being Fe and other unavoidable impurities;

[0087] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0088] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0089] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 50min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 640℃-110℃, the tempering time is 90min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 590℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 590℃-110℃ for 90min, followed by water cooling, and then non-destructive testing is performed.

[0090] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0091] The oil casing obtained in Example 3, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 856 MPa, a tensile strength greater than 962 MPa, a yield ratio of 0.89, a total elongation of 24%, a uniform elongation of 17%, and a Charpy impact toughness of 117 J.

[0092] Example 4

[0093] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0094] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0095] The composition of the molten steel, by mass percentage, includes: C: 0.25%, Si: 0.73%, Mn: 1.35%, P: 0.0111%, S: 0.002%, Cr: 0.93%, Ni: 0.37%, Mo: 0.32%, V: 0.056%, Al: 0.10%, Ca: 0.020%, O+H+N: 0.005%, with the balance being Fe and other unavoidable impurities;

[0096] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0097] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0098] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 50min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 640℃-110℃, the tempering time is 90min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 590℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 590℃-110℃ for 90min, followed by water cooling, and then non-destructive testing is performed.

[0099] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0100] The oil casing obtained in Example 4, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 869 MPa, a tensile strength greater than 988 MPa, a yield-to-tensile ratio of 0.88, a total elongation of 23%, a uniform elongation of 16%, and a Charpy impact toughness of 108 J.

[0101] Example 5

[0102] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0103] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0104] The composition of the molten steel, by mass percentage, includes: C: 0.27%, Si: 0.72%, Mn: 1.38%, P: 0.008%, S: 0.002%, Cr: 0.98%, Ni: 0.40%, Mo: 0.29%, V: 0.062%, Al: 0.11%, Ca: 0.022%, O+H+N: 0.004%, with the balance being Fe and other unavoidable impurities;

[0105] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0106] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0107] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 50min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 640℃-110℃, the tempering time is 90min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 590℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 590℃-110℃ for 90min, followed by water cooling, and then non-destructive testing is performed.

[0108] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0109] The oil casing obtained in Example 5, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 865 MPa, a tensile strength greater than 983 MPa, a yield-to-tensile ratio of 0.88, a total elongation of 23%, a uniform elongation of 16%, and a Charpy impact toughness of 119 J.

[0110] Example 6

[0111] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0112] S1: Batching, electric arc furnace steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0113] The composition of the molten steel, by mass percentage, includes: C: 0.24%, Si: 0.68%, Mn: 1.36%, P: 0.009%, S: 0.003%, Cr: 1.06%, Ni: 0.45%, Mo: 0.30%, V: 0.080%, Al: 0.10%, Ca: 0.018%, O+H+N: 0.006%, with the balance being Fe and other unavoidable impurities;

[0114] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0115] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0116] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 60min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 610℃-110℃, the tempering time is 100min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 560℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 560℃-110℃ for 100min, followed by water cooling, and then non-destructive testing is performed.

[0117] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0118] The oil casing obtained in Example 6, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 951 MPa, a tensile strength greater than 1045 MPa, a yield-to-tensile ratio of 0.91, a total elongation of 21%, a uniform elongation of 15%, and a Charpy impact toughness of 109 J.

[0119] Example 7

[0120] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0121] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0122] The composition of the molten steel, by mass percentage, includes: C: 0.27%, Si: 0.71%, Mn: 1.44%, P: 0.010%, S: 0.003%, Cr: 1.09%, Ni: 0.37%, Mo: 0.28%, V: 0.083%, Al: 0.09%, Ca: 0.020%, O+H+N: 0.005%, with the balance being Fe and other unavoidable impurities;

[0123] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0124] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0125] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 60min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 610℃-110℃, the tempering time is 100min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 560℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 560℃-110℃ for 100min, followed by water cooling, and then non-destructive testing is performed.

[0126] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0127] The oil casing obtained in Example 7, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 959 MPa, a tensile strength greater than 1054 MPa, a yield-to-tensile ratio of 0.91, a total elongation of 21%, a uniform elongation of 15%, and a Charpy impact toughness of 106 J.

[0128] Example 8

[0129] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0130] S1: Batching, electric arc furnace steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0131] The composition of the molten steel, by mass percentage, includes: C: 0.25%, Si: 0.65%, Mn: 1.39%, P: 0.012%, S: 0.003%, Cr: 1.03%, Ni: 0.43%, Mo: 0.26%, V: 0.070%, Al: 0.10%, Ca: 0.017%, O+H+N: 0.007%, with the balance being Fe and other unavoidable impurities;

[0132] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0133] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0134] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 60min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 610℃-110℃, the tempering time is 100min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 560℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 560℃-110℃ for 100min, followed by water cooling, and then non-destructive testing is performed.

[0135] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0136] The oil casing obtained in Example 8, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 944 MPa, a tensile strength greater than 1049 MPa, a yield-to-tensile ratio of 0.90, a total elongation of 20%, a uniform elongation of 14%, and a Charpy impact toughness of 93 J.

[0137] Example 9

[0138] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0139] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0140] The composition of the molten steel, by mass percentage, includes: C: 0.26%, Si: 0.71%, Mn: 1.42%, P: 0.010%, S: 0.003%, Cr: 1.01%, Ni: 0.40%, Mo: 0.33%, V: 0.074%, Al: 0.09%, Ca: 0.023%, O+H+N: 0.006%, with the balance being Fe and other unavoidable impurities;

[0141] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0142] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0143] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 60min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 610℃-110℃, the tempering time is 100min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 560℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 560℃-110℃ for 100min, followed by water cooling, and then non-destructive testing is performed.

[0144] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0145] The oil casing obtained in Example 9, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 947 MPa, a tensile strength greater than 1052 MPa, a yield-to-tensile ratio of 0.90, a total elongation of 20%, a uniform elongation of 14%, and a Charpy impact toughness of 98 J.

[0146] Example 10

[0147] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0148] S1: Batching, electric arc furnace steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0149] The composition of the molten steel, by mass percentage, includes: C: 0.28%, Si: 0.65%, Mn: 1.37%, P: 0.012%, S: 0.002%, Cr: 1.05%, Ni: 0.39%, Mo: 0.31%, V: 0.09%, Al: 0.11%, Ca: 0.018%, O+H+N: 0.007%, with the balance being Fe and other unavoidable impurities;

[0150] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0151] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0152] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 60min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 610℃-110℃, the tempering time is 100min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 560℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 560℃-110℃ for 100min, followed by water cooling, and then non-destructive testing is performed.

[0153] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0154] The oil casing obtained in Example 10, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 954 MPa, a tensile strength greater than 1048 MPa, a yield-to-tensile ratio of 0.91, a total elongation of 21%, a uniform elongation of 15%, and a Charpy impact toughness of 102 J.

[0155] Example 11

[0156] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0157] S1: Batching, electric arc furnace steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0158] The composition of the molten steel, by mass percentage, includes: C: 0.26%, Si: 0.75%, Mn: 1.45%, P: 0.009%, S: 0.003%, Cr: 1.1%, Ni: 0.46%, Mo: 0.48%, Nb: 0.053%, Al: 0.10%, Ca: 0.021%, O+H+N: 0.005%, with the balance being Fe and other unavoidable impurities;

[0159] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0160] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0161] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 70min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 580℃-110℃, the tempering time is 120min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 530℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 530℃-110℃ for 120min, followed by water cooling, and then non-destructive testing is performed.

[0162] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0163] The oil casing obtained in Example 11, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 1051 MPa, a tensile strength greater than 1142 MPa, a yield strength ratio of 0.92, a total elongation of 17%, a uniform elongation of 11%, and a Charpy impact toughness of 89 J.

[0164] Example 12

[0165] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0166] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0167] The composition of the molten steel, by mass percentage, includes: C: 0.25%, Si: 0.77%, Mn: 1.43%, P: 0.010%, S: 0.001%, Cr: 1.20%, Ni: 0.45%, Mo: 0.35%, Nb: 0.090%, Al: 0.12%, Ca: 0.019%, O+H+N: 0.006%, with the balance being Fe and other unavoidable impurities;

[0168] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0169] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0170] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 70min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 580℃-110℃, the tempering time is 120min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 530℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 530℃-110℃ for 120min, followed by water cooling, and then non-destructive testing is performed.

[0171] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0172] The oil casing obtained in Example 12, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 1047 MPa, a tensile strength greater than 1126 MPa, a yield-to-tensile ratio of 0.93, a total elongation of 18%, a uniform elongation of 12%, and a Charpy impact toughness of 93 J.

[0173] Example 13

[0174] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0175] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0176] The composition of the molten steel, by mass percentage, includes: C: 0.28%, Si: 0.70%, Mn: 1.50%, P: 0.008%, S: 0.001%, Cr: 1.13%, Ni: 0.50%, Mo: 0.32%, Nb: 0.066%, Al: 0.09%, Ca: 0.024%, O+H+N: 0.004%, with the balance being Fe and other unavoidable impurities;

[0177] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0178] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0179] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 70min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 580℃-110℃, the tempering time is 120min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 530℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 530℃-110℃ for 120min, followed by water cooling, and then non-destructive testing is performed.

[0180] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0181] The oil casing obtained in Example 12, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 1045 MPa, a tensile strength greater than 1124 MPa, a yield-to-tensile ratio of 0.93, a total elongation of 18%, a uniform elongation of 12%, and a Charpy impact toughness of 85 J.

[0182] Example 14

[0183] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0184] S1: Batching, electric arc furnace steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0185] The composition of the molten steel, by mass percentage, includes: C: 0.27%, Si: 0.85%, Mn: 1.46%, P: 0.010%, S: 0.003%, Cr: 1.15%, Ni: 0.48%, Mo: 0.34%, Nb: 0.040%, Al: 0.11%, Ca: 0.020%, O+H+N: 0.005%, with the balance being Fe and other unavoidable impurities;

[0186] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0187] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0188] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 70min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 580℃-110℃, the tempering time is 120min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 530℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 530℃-110℃ for 120min, followed by water cooling, and then non-destructive testing is performed.

[0189] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0190] The oil casing obtained in Example 14, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 1054 MPa, a tensile strength greater than 1146 MPa, a yield-to-tensile ratio of 0.92, a total elongation of 17%, a uniform elongation of 11%, and a Charpy impact toughness of 87 J.

[0191] Example 15

[0192] A method for manufacturing an oil casing that combines high strength, high toughness, and large strain performance includes the following steps:

[0193] S1: Batching, oxygen-blown converter steelmaking, feeding Si-Ca wire to modify inclusions in steel, followed by ladle refining and vacuum degassing to obtain molten steel with the following composition;

[0194] The composition of the molten steel, by mass percentage, includes: C: 0.29%, Si: 0.72%, Mn: 1.48%, P: 0.008%, S: 0.003%, Cr: 1.18%, Ni: 0.47%, Mo: 0.33%, Nb: 0.078%, Al: 0.10%, Ca: 0.022%, O+H+N: 0.006%, with the balance being Fe and other unavoidable impurities;

[0195] S2: The molten steel is continuously cast to obtain a bar-shaped continuous casting billet; electromagnetic stirring and light reduction technology are used in the continuous casting process to control the center segregation of the continuous casting billet.

[0196] S3: The bar-shaped continuous casting billet is heated in an annular heating furnace at a temperature of 1200-115℃ for 100 minutes. It is then hot-pierced at 1150℃-1200℃, hot-rolled at 1000℃-1130℃, and then air-cooled and sawn to a suitable length to obtain a pre-treated sleeve.

[0197] S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness, and large strain performance is obtained. The heat treatment and post-treatment adopt a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process. The quenching temperature is 910℃-110℃, the holding time is 70min, and the internal and external water spray quenching is carried out with a cooling rate ≥30℃ / s. The tempering temperature is 580℃-110℃, the tempering time is 120min, and water cooling is performed after tempering. After heat treatment, hot straightening and stress relief tempering are required. The straightening temperature is controlled at 530℃-110℃, and then water cooling is performed. After hot straightening, tempering is carried out at 530℃-110℃ for 120min, followed by water cooling, and then non-destructive testing is performed.

[0198] S5: According to user requirements, API standard threads or special threads can be machined on the pipe section, and magnetic particle testing can be performed on the threads.

[0199] The oil casing obtained in Example 15, which combines high strength, high toughness, and large strain performance, has a room temperature yield strength greater than 1059 MPa, a tensile strength greater than 1151 MPa, a yield-to-tensile ratio of 0.92, a total elongation of 17%, a uniform elongation of 11%, and a Charpy impact toughness of 96 J.

[0200] In the above embodiments, the steelmaking process adopts electric arc furnace steelmaking or oxygen-blown converter steelmaking; electric arc furnace steelmaking uses sponge iron and high-quality scrap steel as raw materials; the oxygen-blown converter steelmaking uses blast furnace molten iron and high-quality scrap steel as raw materials.

[0201] Table 1 shows the chemical composition of oil casings with yield strength levels of 110 ksi, 125 ksi, and 140 ksi in Examples 1 to 15, respectively. In each example, the balance is Fe and unavoidable impurities.

[0202] Table 1 shows the chemical composition of the oil casing in the embodiments.

[0203] serial number C Si Mn P S Cr Ni Mo Nb V Al Ca O+H+N 1(110ksi) 0.24 0.70 1.32 0.010 0.003 0.90 0.33 0.27 - 0.040 0.09 0.016 0.007 2(110ksi) 0.23 0.65 1.30 0.011 0.002 0.96 0.30 0.31 - 0.044 0.07 0.019 0.005 3(110ksi) 0.26 0.72 1.37 0.008 0.002 1.03 0.35 0.25 - 0.051 0.08 0.021 0.006 4 (110 ksi) 0.25 0.73 1.35 0.011 0.002 0.93 0.37 0.32 - 0.056 0.10 0.020 0.005 5 (110 ksi) 0.27 0.72 1.38 0.008 0.002 0.98 0.40 0.29 - 0.062 0.11 0.022 0.004 6 (125 ksi) 0.24 0.68 1.36 0.009 0.003 1.06 0.45 0.30 - 0.080 0.10 0.018 0.006 7 (125 ksi) 0.27 0.71 1.44 0.010 0.003 1.09 0.37 0.28 - 0.083 0.09 0.020 0.005 8 (125 ksi) 0.25 0.65 1.39 0.012 0.003 1.03 0.43 0.26 - 0.070 0.10 0.017 0.007 9 (125 ksi) 0.26 0.71 1.42 0.010 0.003 1.01 0.40 0.33 - 0.074 0.09 0.023 0.006 10 (125 ksi) 0.28 0.65 1.37 0.012 0.002 1.05 0.39 0.31 - 0.090 0.11 0.018 0.007 11 (140 ksi) 0.26 0.75 1.45 0.009 0.003 1.10 0.46 0.48 0.053 - 0.10 0.021 0.005 12 (140 ksi) 0.25 0.77 1.43 0.010 0.001 1.20 0.45 0.35 0.090 - 0.12 0.019 0.006 13 (140 ksi) 0.28 0.70 1.50 0.008 0.001 1.13 0.50 0.32 0.066 - 0.09 0.024 0.004 14 (140 ksi) 0.27 0.85 1.46 0.010 0.003 1.15 0.48 0.34 0.040 - 0.11 0.020 0.005 15 (140 ksi) 0.29 0.72 1.48 0.008 0.003 1.18 0.47 0.33 0.078 - 0.10 0.022 0.006

[0204] Table 2 summarizes the parameters of the casing materials in Examples 1 to 15 after appropriate preparation processes, demonstrating excellent comprehensive properties such as strength, plasticity, and toughness. These parameters include: room temperature yield strength of 853–1059 MPa, tensile strength of 958–1151 MPa, yield-to-tensile ratio of 0.88–0.93, total elongation of 17–24%, uniform elongation of 11–17%, and Charpy impact toughness of 85–119 J at 0°C. These properties can meet the requirements of high-strength, high-strain casing in complex oil and gas well conditions.

[0205] Table 2. Heat treatment process and performance of oil casing in the examples.

[0206]

[0207] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing an oil casing possessing high strength, high toughness, and large strain performance, characterized in that, Includes the following steps: S1: After steelmaking, modified components are added to make the composition of the molten steel the same as that of oil casing. The composition of the oil casing, by mass percentage, includes: C: 0.23%~0.29%, Si: 0.65%~0.85%, Mn: 1.30%~1.50%, P≤0.015%, S≤0.005%, Cr: 0.90%~1.20%, Ni: 0.30~0.50%, Mo: 0.25%~0.35%, Al: 0.07%~0.12%, Ca: 0.016%~0.024%, O+H+N≤0.008%, Nb: 0.04%~0.09% or V: 0.04%~0.09%, with the balance being Fe and other unavoidable impurities; S2: The molten steel is continuously cast to obtain a rod-shaped continuous casting billet; S3: After heating the bar-shaped continuous casting billet, it is pierced and then hot rolled to obtain the pre-treated sleeve; S4: After heat treatment and post-treatment of the pretreated casing, an oil casing with high strength, high toughness and large strain performance is obtained. In S3, the heating temperature of the rod-shaped continuous casting billet is 1185~1215℃, and the heating time is 90~120min; the piercing temperature is 1150~1200℃; the hot rolling temperature is 1000~1130℃; after hot rolling, it is cooled in air to obtain a pretreated sleeve. In S4, after the pre-treated sleeve undergoes heat treatment and post-treatment, it also needs to undergo hot straightening, tempering and water cooling in sequence; the temperature of hot straightening is 520℃~600℃; the temperature of tempering is 520~600℃, and the time is 90~120min. The oil casing has a room temperature yield strength of 853–1059 MPa, a tensile strength of 958–1151 MPa, a yield-to-tensile ratio of 0.88–0.93, a total elongation of 17–24%, a uniform elongation of 11–17%, and a Charpy impact toughness of 85–119 J at 0°C.

2. The method for preparing an oil casing with high strength, high toughness, and large strain performance according to claim 1, characterized in that, In S1, the steelmaking process adopts electric arc furnace steelmaking or oxygen-blown converter steelmaking; the electric arc furnace steelmaking uses sponge iron and high-quality scrap steel as raw materials; the oxygen-blown converter steelmaking uses blast furnace molten iron and high-quality scrap steel as raw materials.

3. The method for preparing an oil casing with high strength, high toughness, and large strain performance according to claim 1, characterized in that, In S1, after adding modified components, ladle refining and vacuum degassing are carried out to obtain molten steel.

4. The method for preparing an oil casing with high strength, high toughness, and large strain performance according to claim 1, characterized in that, In S2, the continuous casting process uses electromagnetic stirring and light reduction technology to control the center segregation of the rod-shaped continuous casting billet.

5. The method for preparing an oil casing with high strength, high toughness, and large strain performance according to claim 1, characterized in that, In S4, the heat treatment is a heat treatment process of heating in a protective atmosphere furnace, quenching and high-temperature tempering. The quenching process parameters are: quenching temperature of 900~920℃, holding time of 50~70min, internal and external water spray quenching, and cooling rate ≥30℃ / s; The process parameters for high-temperature tempering are: the tempering temperature is 570~650℃, and the tempering time is 90~120min.

6. The method for preparing an oil casing with high strength, high toughness, and large strain performance according to claim 1, characterized in that, After water cooling, the threads are machined to obtain an oil casing that combines high strength, high toughness, and large strain performance.

7. The method for preparing an oil casing with high strength, high toughness, and large strain performance according to claim 6, characterized in that, The threading process involves machining API standard threads or special threads onto pipe sections.

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