Oil casing and preparation method thereof

Abstract

The invention discloses an oil casing and a preparation method thereof, and relates to the technical field of petroleum pipe manufacturing. The oil casing comprises the following chemical components by mass percentage: C 0.25%-0.30%, Si 0.65%-0.75%, Mn 1.15%-1.25%, P 0%-0.015%, S 0%-0.005%, Cr 0.50%-0.70%, Ni 0.15%-0.25%, Ti 0.01%-0.05%, Zr 0.01%-0.05%, Nb 0.01%-0.05%, Ca 0.015%-0.025%, Al 0.015%-0.025%, N 0%~0.005%, N+H+O≤0.008%, the balance is Fe and inevitable impurities, it has excellent comprehensive properties, low cost, high strength, sufficient plasticity and toughness.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum pipe manufacturing, in particular to an oil casing and a preparation method thereof. Background Art

[0002] With the continuous development of oil and gas resources, the proportion of deep wells, ultra-deep wells, special structure wells, and special process wells is increasing, which puts forward a huge demand for high-strength and ultra-high-strength oil casing (oil pipes and casings). In order to ensure the mechanical properties and performance of high-strength and ultra-high-strength oil casing, it is necessary to optimize the chemical composition and preparation process. For example, in the chemical composition design, more expensive alloy elements are usually added, such as 1% to 1.2% of Cr, 0.50% to 0.80% of Mo, etc., and even a certain amount of Cu and Ni are added. In order to ensure the mechanical properties of the oil casing, a total of 0.1% to 0.2% of Nb, V, Ti and other micro-alloying elements and rare earth (Re) elements are often added. The large amount of alloying elements adds a significant increase in production and manufacturing costs. In addition, in the usual hot rolling process of oil casing, due to the lack of effective controlled rolling and controlled cooling process, the role of micro-alloying elements such as Nb, V, and Ti is not fully exerted, resulting in the strengthening and toughening effect of the oil casing is not ideal. Therefore, without significantly increasing the preparation cost, how to further optimize the composition design of high-strength and ultra-high-strength oil casing and comprehensively regulate the corresponding preparation process has become an important topic in the research and development of high-strength and ultra-high-strength oil casing. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an oil casing and a preparation method thereof, aiming to provide an oil casing with relatively low cost and excellent comprehensive performance of high strength, sufficient plasticity and toughness, so as to meet the needs of high-strength oil casing for efficient development of oil and gas under complex working conditions.

[0004] The technical solution of the present invention is as follows:

[0005] In a first aspect of the present invention, there is provided an oil casing, wherein the oil casing comprises the following chemical components in terms of mass percentage:

[0006] C 0.25%~0.30%, Si 0.65%~0.75%, Mn 1.15%~1.25%, P 0%~0.015%, S0%~0.005%, Cr 0.50%~0.70%, Ni 0.15%~0.25%, Ti 0.01%~0.05%, Zr 0.01%~0.05%, Nb 0.01%~0.05%, Ca 0.015%~0.025%, Al 0.015%~0.025%, N 0%~0.005%, N+H+O≤0.008%, and the balance is Fe and unavoidable impurities.

[0007] Optionally, the oil casing comprises the following chemical components by mass percentage:

[0008] C 0.25%~0.27%, Si 0.65%~0.69%, Mn 1.15%~1.20%, P 0.010%~0.012%, S 0.003%~0.005%, Cr 0.50%~0.59%, Ni 0.15%~0.20%, Ti 0.01%~0.04%, Zr 0.01%~0.05%, Nb 0.01%~0.04%, Ca 0.015%~0.019%, Al 0.015%~0.018%, N 0%~0.005%, N+H+O≤0.008%, and the balance is Fe and unavoidable impurities.

[0009] Optionally, the oil casing comprises the following chemical components by mass percentage:

[0010] C 0.28%~0.30%, Si 0.71%~0.75%, Mn 1.22%~1.25%, P 0.010%~0.012%, S 0.002%~0.003%, Cr 0.62%~0.70%, Ni 0.17%~0.25%, Ti 0.02%~0.05%, Zr 0.02%, Nb 0.02%~0.05%, Ca 0.020%~0.025%, Al 0.021%~0.025%, N0%~0.005%, N+H+O≤0.008%, and the balance is Fe and unavoidable impurities.

[0011] A second aspect of the present invention provides a method for preparing an oil casing, comprising the steps of:

[0012] According to the embodiment of the present invention, the chemical components of the oil casing as described above are batched, smelted, and continuously cast to obtain a continuously cast billet;

[0013] The continuous casting billet is subjected to hot piercing, hot continuous rolling and heat treatment to obtain a tube billet;

[0014] The tube blank is subjected to heat straightening and heat sizing, and thread processing to obtain the oil casing.

[0015] Optionally, after smelting and continuous casting, the step of obtaining the continuous casting billet specifically includes:

[0016] The raw materials obtained by batching are subjected to oxygen-blown converter smelting, external refining and vacuum degassing in sequence to obtain molten steel;

[0017] The molten steel is cast into a rod-shaped continuous casting billet.

[0018] Optionally, the step of obtaining a tube billet after hot piercing, hot rolling and heat treatment of the continuous casting billet specifically includes:

[0019] The continuous casting billet is heated at a temperature of 1170-1220°C for 100-120min, then hot-pierced at a temperature of 1140-1190°C, hot-rolled at a temperature of 900-1150°C, the final rolling temperature is controlled to be 900-920°C, and after internal and external water spray quenching, it is tempered at a temperature of 590-610°C for 60-75min and then water-cooled to obtain a tube billet.

[0020] Optionally, the step of obtaining a tube billet after hot piercing, hot rolling and heat treatment of the continuous casting billet specifically includes:

[0021] The continuous casting billet is heated at a temperature of 1170-1220° C. for 100-120 min, then hot-pierced at a temperature of 1140-1190° C., hot-rolled at a temperature of 900-1150° C., the final rolling temperature is controlled to be 900-920° C., and after internal and external water spray quenching, it is tempered at a temperature of 640-660° C. for 60-75 min and then water-cooled, reheated to 880-900° C., kept warm for 60-90 min, tempered at a temperature of 570-590° C. for 90-120 min and then water-cooled to obtain a tube billet.

[0022] Optionally, the step of obtaining the oil casing after hot straightening and hot sizing the tube blank and threading the tube blank specifically includes:

[0023] The tube blank is subjected to heat straightening and heat sizing at a temperature of 550-660° C., water cooling, and thread processing to obtain the tube blank.

[0024] Beneficial effects: The oil casing provided by the present invention has excellent comprehensive performance, relatively low cost, high strength, sufficient plasticity and toughness. The yield strength level of the oil casing reaches 125ksi and 140ksi steel grades respectively, the tensile strength is greater than or equal to 1045MPa, the elongation is greater than or equal to 23%, and the 0℃ Charpy V-notch impact toughness is greater than or equal to 83J, which can meet the needs of high-strength oil casing with excellent comprehensive performance for oil and gas benefit development under complex working conditions. DETAILED DESCRIPTION

[0025] The present invention provides an oil casing and a preparation method thereof. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0027] An embodiment of the present invention provides an oil casing, wherein the oil casing includes the following chemical components in terms of mass percentage:

[0028] C 0.25%~0.30%, Si 0.65%~0.75%, Mn 1.15%~1.25%, P 0%~0.015%, S0%~0.005%, Cr 0.50%~0.70%, Ni 0.15%~0.25%, Ti 0.01%~0.05%, Zr 0.01%~0.05%, Nb 0.01%~0.05%, Ca 0.015%~0.025%, Al 0.015%~0.025%, N 0%~0.005%, N+H+O≤0.008%, and the balance is Fe and unavoidable impurities.

[0029] In terms of chemical composition design, the embodiment of the present invention ensures that the oil casing has sufficient strength, plasticity and toughness without significantly increasing the preparation cost. It adopts medium and low C content, adds Mn, adds a small amount of Cr, Si and Ni, Ti-Nb-Zr composite microalloying, adopts Al, Si fully deoxidized killed steel and pure steel technology, and Ca treatment is performed on the steel liquid, so that the oil casing has excellent comprehensive performance, relatively low cost, high strength, sufficient plasticity and toughness, and compared with Ti-Nb, Ti-Nb-V composite microalloyed high-strength oil casing, the strength, plasticity and toughness are significantly improved, and the safety and reliability of complex oil and gas well operations are improved. The yield strength level of the oil casing reaches 125ksi and 140ksi steel grades respectively, the tensile strength is greater than or equal to 1045MPa, the elongation is greater than or equal to 23%, and the 0℃ Charpy V-notch impact toughness is greater than or equal to 83J, which can meet the needs of high-strength oil casing with excellent comprehensive performance for oil and gas benefit development under complex working conditions.

[0030] Among them, C is the most important strengthening element in steel. Increasing the C content can significantly improve the hardenability of steel and thus increase its strength, but too high a C content will damage the plasticity and toughness of the steel. Taking all factors into consideration, the C content should be controlled within the range of 0.25% to 0.30%.

[0031] Si is usually used as a permanent element and deoxidizer in steel, and is generally controlled within the range of 0.15% to 0.40%. An appropriate amount of Si can improve the hardenability of steel, thereby improving strength, corrosion resistance and tempering stability, but too high a content will increase the segregation tendency of steel, promote the formation of banded structure, and thus damage the plasticity and toughness of steel. Taking all factors into consideration, the Si content in the embodiment of the present invention is preferably controlled within the range of 0.65% to 0.75%.

[0032] Mn is mainly used to improve the hardenability of steel and thus improve its strength, and can partially replace the more expensive Cr element, but the Mn element has a greater tendency to segregate, and too high a content will lead to uneven organizational structure and performance. Taking all factors into consideration, the Mn content in this embodiment is preferably controlled within the range of 1.15% to 1.25%.

[0033] Cr is mainly used to improve the hardenability and tempering stability of steel, thereby improving the strength of steel. Since this embodiment adopts a higher Mn content and adds a certain amount of Si, the amount of Cr added can be appropriately reduced to reduce costs while ensuring performance. Taking all factors into consideration, the Cr content should be controlled within the range of 0.50% to 0.70%.

[0034] Ni is mainly used to improve the hardenability of steel, thereby improving the strength and low-temperature toughness of steel. In this embodiment, since a relatively high Mn content is used and a certain amount of Si is added, in order to reduce costs, a solution of not adding Mo and adding a small amount of Ni is adopted to reduce costs while ensuring performance. Taking comprehensive considerations, the Ni content should be controlled within the range of 0.15% to 0.25%.

[0035] Ti is added to steel to deoxidize and fix nitrogen. It forms TiC and TiN with C and N in steel, which hinders the growth of austenite grains and refines grains, thereby improving strength and toughness. However, too high a content will form too many Ti carbon and nitrogen compounds, which will increase the brittleness of the steel and increase the cost. Taking all factors into consideration, the Ti content should be controlled within the range of 0.01% to 0.05%.

[0036] Nb is added to steel to form NbC and NbN with C and N in the steel, which has the effect of hindering the growth of austenite grains and refining grains, thereby improving strength and toughness. However, too high a content will form too many Nb carbon and nitrogen compounds, which will increase the brittleness of the steel and increase the cost. Taking all factors into consideration, the Nb content should be controlled within the range of 0.01% to 0.05%.

[0037] Zr is added to steel to deoxidize, remove nitrogen and desulfurize. It forms ZrC and ZrN with C and N in steel, refines grains, and thus improves strength and toughness. However, too high a content will increase the brittleness of the steel and increase costs. Taking all factors into consideration, the Zr content should be controlled within the range of 0.01% to 0.05%. In the embodiment of the present invention, Ti-Nb-Zr composite microalloying is used to obtain a better strengthening and toughening effect than single microalloying elements Ti, Nb, V or Zr.

[0038] Ca can improve the properties and morphology of inclusions, thereby increasing the toughness and corrosion resistance of steel. The Ca content should be controlled at 0.015% to 0.025%.

[0039] Al and oxygen form fine and evenly distributed oxides, which can refine the grains and improve the strength and toughness. It is also an important deoxidizer. The Al content should be controlled within the range of 0.015% to 0.025%.

[0040] P is a harmful impurity element that mainly affects the plasticity and toughness of steel. The P content should be controlled within the range of 0% to 0.015%.

[0041] S is a harmful impurity element that mainly affects the plasticity and toughness of steel. The S content should be controlled within the range of 0% to 0.005%.

[0042] N, H and O are harmful gas elements, which mainly affect the plasticity and toughness of steel. The content should be controlled within the range of N+H+O≤0.008% (i.e. the total content of N, H and O is less than or equal to 0.008%), among which the N content should be controlled within the range of 0% to 0.005%.

[0043] In one embodiment, the oil casing comprises the following chemical components by mass percentage:

[0044] C 0.25%~0.27%, Si 0.65%~0.69%, Mn 1.15%~1.20%, P 0.010%~0.012%, S 0.003%~0.005%, Cr 0.50%~0.59%, Ni 0.15%~0.20%, Ti 0.01%~0.04%, Zr 0.01%~0.05%, Nb 0.01%~0.04%, Ca 0.015%~0.019%, Al 0.015%~0.018%, N 0%~0.005%, N+H+O≤0.008%, and the balance is Fe and unavoidable impurities.

[0045] In this embodiment, the oil casing has good comprehensive performance, the room temperature yield strength reaches the 125ksi steel grade requirement, the room temperature yield strength is 951-962MPa, the tensile strength is 1045-1057MPa, the elongation is 28%, and the 0°C Charpy V-notch impact toughness is 103-106J, which can meet the needs of high-strength oil casing for efficient development of oil and gas fields under complex working conditions.

[0046] In one embodiment, the oil casing comprises the following chemical components by mass percentage:

[0047] C 0.28%~0.30%, Si 0.71%~0.75%, Mn 1.22%~1.25%, P 0.010%~0.012%, S 0.002%~0.003%, Cr 0.62%~0.70%, Ni 0.17%~0.25%, Ti 0.02%~0.05%, Zr 0.02%, Nb 0.02%~0.05%, Ca 0.020%~0.025%, Al 0.021%~0.025%, N0%~0.005%, N+H+O≤0.008%, and the balance is Fe and unavoidable impurities.

[0048] In this embodiment, the oil casing has good comprehensive performance, the room temperature yield strength reaches the 140ksi steel grade requirement, the room temperature yield strength is 1057-1066MPa, the tensile strength is 1149-1159MPa, the elongation is 23%, and the 0°C Charpy V-notch impact toughness is 83-88J, which can meet the needs of high-strength oil casing for efficient development of oil and gas fields under complex working conditions.

[0049] In addition to the reasonable design of chemical composition and proportion content, the comprehensive performance of the oil casing and tubing also requires the manufacturing process to affect the final performance of the oil casing and tubing. Different chemical composition designs require different manufacturing processes to make the oil casing and tubing play the best performance. The embodiment of the present invention develops a manufacturing process that matches the chemical composition of the above-mentioned proportion content, mainly through steelmaking (including refining outside the furnace, vacuum degassing), continuous casting, hot perforation, hot rolling and controlled rolling and cooling in the austenite zone, heat treatment, hot straightening and hot sizing, etc., so that the oil casing and tubing obtain a fine and uniform microstructure to achieve a reasonable match between the strength and plastic toughness of the oil casing and tubing. The heat treatment process of hot rolling and controlled rolling and controlled cooling direct quenching + high temperature tempering is used to replace the commonly used process of hot rolling followed by cooling and reheating for tempering heat treatment, which can further reduce costs while ensuring that the performance meets the requirements. Specifically, the embodiment of the present invention also provides a method for preparing an oil casing and tubing, which includes the steps of:

[0050] S1. After batching, smelting and continuous casting of the chemical composition of the oil casing according to the embodiment of the present invention, a continuous casting billet is obtained;

[0051] S2, performing hot piercing, hot rolling and heat treatment on the continuous casting billet to obtain a tube billet;

[0052] S3, hot straightening and hot sizing the tube blank, and thread processing are performed to obtain the oil casing.

[0053] The chemical composition and manufacturing process of the embodiment of the present invention are used together to achieve the effects of economy, strength improvement and toughness improvement. The preparation method of the present invention obtains the expected organizational structure and performance for the oil casing with the above chemical composition, gives full play to the performance of the oil casing, has low cost, and the process parameters in the process are easy to control, and the obtained oil casing has stable performance.

[0054] In step S1, in one embodiment, after smelting and continuous casting, the step of obtaining the continuous casting billet specifically includes:

[0055] The raw materials obtained by batching are successively subjected to oxygen-blown converter smelting, refining outside the furnace and vacuum degassing, and Si-Ca wire is fed to perform deformation control treatment on inclusions in the steel to obtain molten steel;

[0056] The molten steel is cast into a rod-shaped continuous casting billet.

[0057] In step S2, two methods can be used for heat treatment according to different performance requirements of different steel grade oil casing. In some embodiments, for 125ksi steel grade oil casing, the step of obtaining the tube billet after hot perforation, hot rolling and heat treatment of the continuous casting billet specifically includes:

[0058] The continuous casting billet is heated at a temperature of 1170-1220° C. for 100-120 min, then hot-pierced at a temperature of 1140-1190° C., hot-rolled at a temperature of 900-1150° C., the final rolling temperature is controlled to be 900-920° C., the hot-rolled deformation is controlled to be 70%-80%, and after internal and external water spray quenching (cooling rate is 20-50° C. / s), it is tempered at a temperature of 590-610° C. for 60-75 min and then water-cooled to obtain a tube billet.

[0059] In one embodiment, for a 140 ksi steel grade oil casing, the step of obtaining a tube billet after hot perforating, hot rolling and heat treating the continuous casting billet specifically comprises:

[0060] The continuous casting billet is heated at a temperature of 1170-1220° C. for 100-120 min, then hot-pierced at a temperature of 1140-1190° C., hot-rolled at a temperature of 900-1150° C., the final rolling temperature is controlled to be 900-920° C., and after internal and external water spray quenching, it is tempered at a temperature of 640-660° C. for 60-75 min and then water-cooled, reheated to 880-900° C., kept warm for 60-90 min, tempered at a temperature of 570-590° C. for 90-120 min and then water-cooled to obtain a tube billet.

[0061] In the above two embodiments, water cooling after tempering can avoid possible tempering brittleness, and good strengthening and toughening effect can be obtained by accurately controlling the hot rolling deformation, rolling temperature (especially final rolling temperature), and cooling rate; in addition, compared with other similar oil casing, the preparation method provided in this embodiment strengthens the controlled rolling and controlled cooling process, uses the residual heat of rolling for direct quenching, reduces the one-time reheating process, simplifies the heat treatment process, and can further reduce production costs. In addition, a fine and uniform microstructure (grain size of 8 to 9 levels) can be obtained by heat treatment, ensuring that the oil casing has high strength while having sufficient plasticity and toughness. Through hot straightening and hot sizing, the geometric dimensions of the oil casing meet the requirements, and the residual stress of the oil casing is effectively controlled, and the performance of the oil casing is improved, which can meet the needs of high-performance oil casing for the efficient development of oil and gas fields under complex working conditions.

[0062] In step S3, in some embodiments, the step of obtaining the oil casing after hot straightening and hot sizing the tube blank and threading the tube blank specifically includes:

[0063] The tube blank is subjected to heat straightening and heat sizing at a temperature of 550-660° C., water cooling, and thread processing to obtain the tube blank.

[0064] In some embodiments, the thread is an API (American Petroleum Institute) standard thread or a special thread.

[0065] The following describes it in detail through specific embodiments.

[0066] The chemical compositions of the oil pipes and casings used in the following examples and comparative examples are shown in Table 1.

[0067] Table 1. Chemical composition of tubing and casing

[0068]

[0069]

[0070] Note: In each embodiment and comparative example in Table 1, the chemical composition of the tubing and casing also includes N, H, O, Fe and inevitable impurities, wherein the N content is 0.005%, the total content of N, H and O is 0.008%, and Fe and inevitable impurities are the remainder.

[0071] Example 1

[0072] This embodiment provides a method for preparing a tubing and a casing (Ti-Nb-Zr composite microalloying), comprising the following steps:

[0073] Steelmaking: The chemical composition of the oil pipe and casing of Example 1 shown in Table 1 above is used for batching, followed by oxygen-blown converter steelmaking, refining outside the furnace and vacuum degassing, and Si-Ca wire feeding for deformation control of inclusions in the steel to obtain molten steel.

[0074] Continuous casting: The molten steel is cast into rod-shaped continuous casting billets. During the continuous casting process, electromagnetic stirring and soft pressure reduction technology are used to control the segregation in the continuous casting billets.

[0075] Hot piercing, hot rolling and heat treatment: The continuous casting billet is heated in a ring heating furnace with a heating furnace temperature of 1195±10℃ and a heating time of 120min. Then, hot piercing is performed at a temperature of 1165±15℃, and then hot rolling is performed with a starting rolling temperature of 1150℃ and a final rolling temperature of 900℃. The hot rolling deformation is controlled to be 70%. After internal and external water spray quenching (cooling rate of 20℃ / s), it is tempered at a temperature of 600±10℃ for 75min and then water-cooled to obtain a tempered troostite microstructure with a grain size of 8 to obtain a tube billet.

[0076] Hot straightening and hot sizing: The tube blank is hot straightened and hot sized at a temperature of 570±10℃ and then water-cooled. After API standard thread processing, the thread is subjected to magnetic particle inspection to obtain oil pipes and casings respectively.

[0077] Example 2

[0078] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb-Zr composite microalloying), which is basically the same as that of Embodiment 1, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Embodiment 2 shown in Table 1 above.

[0079] Example 3

[0080] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb-Zr composite microalloying), which is basically the same as that of Embodiment 1, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Embodiment 3 shown in Table 1 above.

[0081] Comparative Example 1

[0082] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb composite microalloying), which is basically the same as that of Example 1, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Comparative Example 1 shown in Table 1 above.

[0083] Comparative Example 2

[0084] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb-V composite microalloying), which is basically the same as that of Example 1, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Comparative Example 2 shown in Table 1 above.

[0085] Example 4

[0086] This embodiment provides a method for preparing a tubing and a casing (Ti-Nb-Zr composite microalloying), comprising the following steps:

[0087] Steelmaking: The oil pipe and casing of Example 4 are prepared according to their chemical compositions shown in Table 1 above, and then subjected to oxygen-blown converter steelmaking, refining outside the furnace and vacuum degassing, and Si-Ca wire is fed to control deformation of inclusions in the steel to obtain molten steel.

[0088] Continuous casting: The molten steel is cast into rod-shaped continuous casting billets. During the continuous casting process, electromagnetic stirring and soft pressure reduction technology are used to control the segregation in the continuous casting billets.

[0089] Hot piercing, hot rolling and heat treatment: the continuous casting billet is heated in a ring heating furnace with a heating furnace temperature of 1195±10℃ and a heating time of 120min, and then hot piercing is performed at a temperature of 1165±15℃, and then hot rolling is performed with a starting rolling temperature of 1150℃ and a final rolling temperature of 900℃, and the hot rolling deformation is controlled to be 70%. After internal and external water spray quenching (cooling rate of 20℃ / s), it is tempered at 650±10℃ for 60min and then water cooled, reheated to 890±10℃ and kept warm for 75min, internal and external water spray quenching (cooling rate of 20℃ / s), tempered at 580±10℃ for 120min and then water cooled to obtain a tempered troostite microstructure with a grain size of 9 to obtain a tube billet.

[0090] Hot straightening and hot sizing: The tube blank is hot straightened and hot sized at a temperature of 550±10℃ and then water-cooled. After API standard thread processing, the thread is subjected to magnetic particle inspection to obtain oil pipes and casings respectively.

[0091] Example 5

[0092] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb-Zr composite microalloying), which is basically the same as that of Embodiment 4, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Embodiment 5 shown in Table 1 above.

[0093] Example 6

[0094] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb-Zr composite microalloying), which is basically the same as that of Embodiment 4, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Embodiment 6 shown in Table 1 above.

[0095] Comparative Example 3

[0096] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb composite microalloying), which is basically the same as that of Embodiment 4, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Comparative Example 3 shown in Table 1 above.

[0097] Comparative Example 4

[0098] This embodiment provides a method for preparing an oil pipe and a casing (Ti-Nb-V composite microalloying), which is basically the same as that of Example 4, except that the ingredients are prepared according to the chemical composition of the oil pipe and the casing of Comparative Example 4 shown in Table 1 above.

[0099] The oil pipes and casings prepared in the examples and comparative examples were subjected to room temperature yield strength test, tensile strength test, elongation test, and 0°C Charpy V-notch impact toughness test. The results are shown in Table 2 below.

[0100] Table 2 Performance results of tubing and casing in examples and comparative examples

[0101]

[0102]

[0103] In summary, the Ti-Nb-Zr composite microalloyed tubing and casing obtained by the present invention after appropriate preparation process has excellent comprehensive performance, the yield strength can reach Q125 steel grade and 140ksi steel grade respectively, and has good plasticity and toughness. Compared with Ti-Nb and Ti-Nb-V composite microalloyed tubing and casing, the strength, plasticity and toughness are significantly improved (see Table 2 for details), and the safety and reliability of complex oil and gas well operations are improved. Compared with other similar tubing and casing, the controlled rolling and controlled cooling process is strengthened, the heat treatment process is simplified, and the preparation cost is reduced, which can meet the needs of high-performance tubing and casing for the efficient development of oil and gas fields under complex working conditions.

[0104] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. An oil casing, characterized in that: The oil casing is composed of the following chemical components by mass percentage: C 0.25%~0.30%, Si 0.65%~0.75%, Mn 1.15%~1.25%, P 0%~0.015%, S 0%~0.005%, Cr0.50%~0.70%, Ni 0.15%~0.25%, Ti0.01%~0.05%, Zr 0.01%~0.05%, Nb 0.01%~0.05%, Ca 0.015%~0.025%, Al0.015%~0.025%, N 0%~0.005%, N+H+O≤0.008%, the balance is Fe and unavoidable impurities; The microstructure of the oil casing is tempered troostite, and the grain size is 8-9.

2. The oil casing according to claim 1, characterized in that: The oil casing is composed of the following chemical components by mass percentage: C 0.25% ~ 0.27%, Si 0.65% ~ 0.69%, Mn 1.15% ~ 1.20%, P 0.010% ~ 0.012%, S 0.003% ~ 0.005%, Cr 0.50% ~ 0.59%, Ni 0.15% ~ 0.20%, Ti 0.01% ~ 0.04%, Zr 0.01% ~ 0.05%, Nb 0.01% ~ 0.04%, Ca 0.015% ~ 0.019%, Al 0.015% ~ 0.018%, N 0% ~ 0.005%, N+H+O ≤ 0.008%, and the balance is Fe and unavoidable impurities.

3. The oil casing according to claim 1, characterized in that: The oil casing is composed of the following chemical components by mass percentage: C 0.28% ~ 0.30%, Si 0.71% ~ 0.75%, Mn 1.22% ~ 1.25%, P 0.010% ~ 0.012%, S 0.002% ~ 0.003%, Cr 0.62% ~ 0.70%, Ni 0.17% ~ 0.25%, Ti 0.02% ~ 0.05%, Zr 0.02%, Nb 0.02% ~ 0.05%, Ca 0.020% ~ 0.025%, Al 0.021% ~ 0.025%, N 0% ~ 0.005%, N+H+O ≤ 0.008%, and the balance is Fe and unavoidable impurities.

4. A method for preparing an oil casing, characterized in that: Includes steps: After batching, smelting and continuous casting according to the chemical composition of the oil casing according to any one of claims 1 to 3, a continuous casting billet is obtained; The continuous casting billet is subjected to hot piercing, hot continuous rolling and heat treatment to obtain a tube billet; The tube blank is subjected to heat straightening and heat sizing, and thread processing to obtain the oil casing.

5. The preparation method according to claim 4, characterized in that: After smelting and continuous casting, the steps of obtaining the continuous casting billet specifically include: The raw materials obtained by batching are subjected to oxygen-blown converter smelting, external refining and vacuum degassing in sequence to obtain molten steel; The molten steel is cast into a rod-shaped continuous casting billet.

6. The preparation method according to claim 4, characterized in that: After the continuous casting billet is subjected to hot piercing, hot rolling and heat treatment, the step of obtaining a tube billet specifically comprises: The continuous casting billet is heated at a temperature of 1170-1220°C for 100-120min, then hot-pierced at a temperature of 1140-1190°C, hot-rolled at a temperature of 900-1150°C, the final rolling temperature is controlled to be 900-920°C, and after internal and external water spray quenching, it is tempered at a temperature of 590-610°C for 60-75min and then water-cooled to obtain a tube billet.

7. The preparation method according to claim 4, characterized in that: After the continuous casting billet is subjected to hot piercing, hot rolling and heat treatment, the step of obtaining a tube billet specifically comprises: The continuous casting billet is heated at a temperature of 1170-1220° C. for 100-120 min, then hot-pierced at a temperature of 1140-1190° C., hot-rolled at a temperature of 900-1150° C., the final rolling temperature is controlled to be 900-920° C., and after internal and external water spray quenching, it is tempered at a temperature of 640-660° C. for 60-75 min and then water-cooled, reheated to 880-900° C., kept warm for 60-90 min, tempered at a temperature of 570-590° C. for 90-120 min and then water-cooled to obtain a tube billet.

8. The preparation method according to claim 4, characterized in that: The step of obtaining the oil casing after hot straightening and hot sizing the tube blank and threading the tube blank specifically includes: The tube blank is subjected to heat straightening and heat sizing at a temperature of 550-660° C., water cooling, and thread processing to obtain the tube blank.

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