Manufacturing method of high-strength and high-toughness sleeve

Abstract

The invention discloses a manufacturing method of a high-strength and high-toughness sleeve, and belongs to the field of steel and iron materials for petroleum and natural gas. The chemical components of the casing pipe have specific weight percentages on multiple elements such as C, Si, Mn and the like, and the casing pipe is manufactured through multiple procedures such as molten iron pretreatment and converter smelting. In the manufacturing process, technological parameters of all links, such as RH degassing time, temperature of all stages, annealing heat preservation time and the like, are strictly controlled. The pre-annealed raw material steel coil is low in strength, good in plasticity and toughness and easy to form, and the banded structure is smaller than or equal to grade 2. After a finished pipe is subjected to welding, hot tension reducing and whole pipe heat treatment, Rp0.2 is larger than or equal to 900 MPa, Rm is larger than or equal to 985 MPa, the elongation is larger than or equal to 22%, the longitudinal impact energy of base metal at the temperature of 10 DEG C below zero is larger than or equal to 130 J, and the structure is homogenized tempered sorbite. The problems that a high-strength and high-toughness casing pipe raw material roll is difficult to form and prone to cracking during welding are solved, and the high requirement of unconventional oil and gas exploitation for casing pipe performance is met.

Description

Technical Field

[0001] The present invention relates to the technical field of steel materials for oil and gas, and particularly relates to a manufacturing method for high-strength and high-toughness casing pipes. Background Art

[0002] With the large consumption of conventional oil and gas resources, the exploitation of unconventional oil and gas resources such as shale gas and tight oil has been increasing year by year. The storage environment of unconventional oil and gas fields is complex, and the multi-stage volume fracturing and intensive cutting technology has become an effective means for increasing reserves and production in oil and gas fields. However, such fracturing operations have increasingly high requirements for the strength, toughness, collapse resistance and other properties of oil and gas casing pipes. Therefore, the demand for high-strength and high-toughness large-diameter casing pipes of Q125 and above shows an increasing trend.

[0003] High-strength and high-toughness casing pipes are made of hot-rolled coils as raw materials, and are mainly manufactured into casing pipes through processes such as longitudinal cutting, row-roll forming, HFI welding, on-line heat treatment of welds, weld extrusion sizing, and full-pipe heat treatment. For high-strength grades such as Q125, the yield strength of the finished pipe exceeds 900 MPa. Although the quenching and tempering treatment after pipe manufacturing is the most important for enhancing strength, the strength design and control of the raw material coil cannot be too low, otherwise it will also restrict the mechanical properties and fatigue resistance of the final finished pipe. Generally, a microalloying design of more than 0.20% C + Nb / V / Ti is mostly used, but such high-strength raw material coils will cause difficulties in row-roll forming and make it difficult to roll the pipe. In addition, the casing steel mostly adopts a medium C and medium Mn design, resulting in relatively serious banded structure in the hot-rolled raw material coil itself, increasing the risk of cracking near the weld during SEW welding, and also affecting comprehensive properties such as anti-HIC. Therefore, how to achieve low strength of the raw material coil; easy forming and easy welding during the pipe manufacturing process; and at the same time, good strength and plasticity after quenching and tempering. This is a technical contradiction and problem in the whole process of manufacturing high-strength and high-toughness casing pipes.

[0004] Currently, a number of patents have been applied for regarding high-strength and high-toughness casing pipes and their manufacturing methods in China.

[0005] The invention patent with the publication number CN103194693A discloses a high-strength and high-toughness oil casing and its manufacturing method. Its chemical composition is C: 0.18% - 0.30%, Si: 0.10% - 0.35%, Mn: 1.00% - 1.30%, P: ≤0.018%, S: ≤0.008%, Cr: 0.20% - 1.20%, Ni: 0.10% - 0.65%, Mo: 0.20% - 0.55%, Nb + V + Ti ≤0.08%. The yield strength of this casing is ≥865 MPa, the tensile strength is ≥940 MPa, and the elongation is ≥23.2%. Its raw material coil is directly longitudinally sheared, edge milled, formed by FFX, welded by HFI, hot tension-reduced, and the whole pipe is heat-treated. There are no technical indicators regarding the banded structure and mechanical properties of the raw material coil in this patent, nor any elaboration on the control of forming difficulty. This patent adopts a high-Mo (0.20 - 0.55%) and Cr (0.20 - 1.20%) alloy design, combined with the HFW welding + online heat treatment + quenching and tempering process. The yield strength of the finished pipe is ≥865 MPa, the tensile strength is ≥940 MPa, and the impact energy at 0°C is ≥105 J (transverse). The existing problems are that the strength of the raw material coil is not optimized, the control of the banded structure is insufficient, and the alloy cost is high.

[0006] The invention patent with the publication number CN112522607A discloses a Q125 grade SEW oil casing and its manufacturing method. Its chemical composition is C: 0.15% - 0.25%, Si: ≤0.30%, Mn: 1.00% - 1.50%, P: ≤0.015%, S: ≤0.005%, Mo: 0.10 - 0.50, V: 0.03 - 0.06%, Ti: 0.01 - 0.03%, Cr: 0.20 - 0.60%, Als: 0.02 - 0.035%. This application adopts hot coiling at 650 - 750°C. The yield strength of the hot continuous rolling coil is 400 - 500 MPa, and the tensile strength is 600 - 700 MPa. Subsequently, SEW welding and forming are carried out, followed by quenching and tempering treatment. The yield strength is 905 - 950 MPa, and the tensile strength is 990 - 1100 MPa. It can be seen that before the whole pipe quenching and tempering treatment in this patent, the raw material coil is not preheated. The difference in yield strength between the raw material coil and the finished pipe is relatively small (about 450 MPa). The impact energy of the finished pipe at -10°C is only 85 - 98 J. There is also no introduction on reducing the banded structure in this patent. This patent adopts hot coiling (650 - 750°C) + SEW pipe manufacturing + quenching and tempering treatment, and reduces the Mo content (0.10 - 0.50%). The technical effect is that the yield strength of the raw material coil is 400 - 500 MPa, and the impact energy of the finished pipe is ≥80 J (transverse at -10°C). The existing problems are that the strength of the raw material coil is still relatively high, the low-temperature toughness is insufficient, and the anti-HIC performance is not clear.

[0007] Therefore, how to design and develop a high-strength and tough casing pipe with good overall pipe organization and performance consistency, easy formability and easy weldability. The present invention designs from aspects such as key component design, steelmaking and rolling, pre-annealing treatment of raw material coils, pipe forming, and full-pipe heat treatment, to realize the manufacture of a high-strength and tough casing pipe with an annealed raw material coil, good tissue uniformity, easy formability and easy weldability. Summary of the Invention

[0008] To solve the problems in the prior art, the purpose of the present invention is to provide a manufacturing method for a high-strength and tough casing pipe. The hot-rolled raw material coil of this casing pipe has low strength, good plastic toughness, and easy formability after pre-annealing; the banded structure is well controlled; after full-pipe heat treatment, the casing pipe has more excellent high strength and toughness and other characteristics.

[0009] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0010] The present invention provides a manufacturing method for a high-strength and tough casing pipe, including the following steps: converter smelting, refining, continuous casting, slab reheating, controlled rolling, laminar flow cooling, coiling, welding, hot tension reducing, and full-pipe heat treatment; pre-annealing is adopted before welding, and the pre-annealing step includes: the hot coil is annealed in a bell-type furnace, the annealing cold spot temperature is 700-740 °C, the holding time is 3.5-4.5 h, and the furnace outlet temperature ≤ 85 °C.

[0011] As a further optimized scheme of the present invention, in the coiling step: the coiling temperature is 550-600 °C.

[0012] As a further optimized scheme of the present invention, the chemical composition of the casing pipe and its weight percentage content are: C: 0.20-0.28%, Si: 0.2-0.3%, Mn: 0.8-1.0%, P: ≤ 0.010%, S: ≤ 0.003%, Cr: 0.1-0.3%, Ni: 0.05-0.15%, Cu: 0.10-0.30%, Als: 0.03-0.05%, Ti: 0.020-0.040%, Mo: ≤ 0.03%, B: ≤ 0.0030%, V: 0.045-0.070, and the balance is Fe and unavoidable inclusions.

[0013] As a further optimized scheme of the present invention, the chemical composition of the casing pipe needs to meet the following constraint conditions:

[0014] .

[0015] Constraint condition formula A d , which is used to limit the severity of the banded structure in the raw material coil before pre-annealing, and at the same time prevent the hardenability from being too strong, and form martensite bands in the raw material coil before pre-annealing.

[0016] As a further optimization solution of the present invention, the raw material coil after pre-annealing: Rp 0.2 : 340 - 370 MPa, R m : 550 - 575 MPa, yield ratio < 0.65, elongation 30 - 35%, longitudinal impact energy at -10°C > 90 J, banded structure ≤ grade 2.

[0017] As a further optimization solution of the present invention, the steps of welding, hot stretch reducing and full-tube heat treatment include: the pre-annealed raw material coil is welded into a straight-seam pipe blank by HFW, then heated to 920 - 1000°C for hot stretch reducing, and then undergoes heat treatment of quenching at 890 - 920°C and tempering at 540 - 580°C, and finally a casing is obtained.

[0018] As a further optimization solution of the present invention, for the casing after heat treatment: Rp 0.2 ≥900 MPa, R m ≥985 MPa, elongation ≥ 25%, longitudinal impact energy of the base metal at -10°C ≥ 130 J.

[0019] As a further optimization solution of the present invention, in the BOF smelting and refining steps: the RH refining degassing time ≥ 16 min, the tundish superheat is controlled at 20 - 30°C, electromagnetic rolls and dynamic soft reduction are used during continuous casting, and the cast slab is slowly cooled in the soaking pit for ≥ 72 h.

[0020] As a further optimization solution of the present invention, in the slab reheating, controlled rolling and laminar cooling steps: the slab heating furnace outlet temperature is 1180 - 1220°C, the holding time is 120 - 160 min, the finish rolling temperature of the finishing mill is 820 - 860°C, full descaling is performed for R1 + R2 in rough rolling, super high pressure of 30 - 40 MPa is used for secondary descaling, and descaling is used between the finishing mill stands.

[0021] As a further optimization solution of the present invention, the heated slab is rolled into a hot rolled coil with a thickness of 10 - 16 mm through rough rolling and finishing rolling.

[0022] As a further optimization solution of the present invention, in the low-temperature coiling step: the thermal coil tower overflow during coiling should ≤ 10 mm.

[0023] For the pre-annealed high-strength and high-toughness casing of the present invention, the key design concept of the chemical composition lies in:

[0024] C: As the most crucial element affecting strength and toughness in steel for oil well casings, the reasons are as follows: (1) After pipe manufacturing, tempered sorbite is obtained through high-temperature tempering. The morphology and distribution of its carbides are the key to achieving good strength-toughness matching. When the C content is too low, the proportion of carbides in tempered sorbite is relatively small, especially affecting the tensile strength. When the C content is too high, it significantly affects the plasticity and toughness after heat treatment. (2) Increasing the C content is the key to improving the fatigue resistance and service life of steel for continuous oil pipes. However, excessive C will form a relatively serious banded structure, restricting properties such as weldability and HIC resistance. Considering the above factors, the C content is 0.20 - 0.28%.

[0025] Si: On the one hand, as an element that expands the austenite region, Si exists in a solid solution state in austenite, which not only promotes the formation of martensite but also promotes the formation of ferrite tissue in the air-cooling stage, expanding the cooling process window for the formation of soft-phase ferrite tissue in the air-cooling section. On the other hand, Si can significantly improve the corrosion resistance. However, too high a Si content will significantly reduce the plasticity and toughness of the steel, and too thick reddish-brown scale formed by too high Si will also affect the surface quality of the steel plate. Therefore, the Si content is controlled at 0.2 - 0.3%.

[0026] Mn: It significantly increases the strength through solid solution strengthening. Moreover, a relatively high content of Mn can reduce the critical cooling rate of the steel, significantly improve the hardenability of the steel, and promote the formation of martensite tissue after online quenching. However, Mn has a relatively large segregation coefficient during solidification, easily causing segregation at grain boundaries and forming more MnS inclusions, resulting in poor low-temperature toughness. At the same time, there will also be obvious Mn segregation in the formed banded structure, causing poor HIC resistance. Therefore, low Mn control is adopted: 0.8 - 1.0%.

[0027] Addition of Cr + Ni + Cu + B + Mo: (1) The casing needs to be subjected to integral pipe heat treatment. The microstructure uniformity after quenching + tempering is closely related to the hardenability. Cr, Ni, and Mo are all elements that improve hardenability. In this design, Cr, Ni, and B are used to replace part of Mo to improve the hardenability on the basis of considering economy and form uniform quenched martensite. (2) The addition of Cr + Ni + Cu improves the atmospheric corrosion resistance and HIC resistance. Considering the above, Cr: 0.1 - 0.3%; Ni: 0.05 - 0.15%; Cu: 0.10 - 0.30%; B: ≤0.0030%; Mo: ≤0.03%.

[0028] V and Ti: 1) Combine with C and N to form precipitates such as VC, VN, and TiC, and improve the strength through fine grain and precipitation strengthening effects; 2) Ti simultaneously removes a part of S by forming Ti4C2S2, reduces the S level in the steel, reduces the formation of MnS, and promotes inclusion modification; 3) A part of Ti can inhibit the coarsening of austenite grains in the coarse grain zone during welding. Considering the above reasons, the content of Ti is controlled at 0.020 - 0.040%, and the content of V is controlled at 0.045 - 0.070%.

[0029] The above component design and the whole process control of controlled rolling and controlled cooling, pre-annealing, and pipe-making heat treatment are to obtain a high-strength and tough casing pipe that is easy to form and weld. In order to have good formability and weldability during pipe-making, "medium C + low Mn + Cr + Ni + Cu + Ti + V" microalloying is adopted, and B and Mo are selectively added. Combined with low-temperature coiling + bell annealing, a low-strength raw material coil (yield strength 340 - 370 MPa) is obtained. The annealed coil is significantly softened compared with before pre-annealing, the yield strength is reduced by about 200 MPa, the tensile strength is reduced by about 80 - 100 MPa, and the yield ratio is reduced by about 0.15, greatly reducing the difficulty of the row-roll forming operation. At the same time, the banded structure of the pre-annealed coil is significantly reduced (grade 2) compared with the original hot coil, improving the tissue uniformity near the weld, reducing metal extrusion cracking during HFW welding, and improving the HIC resistance. At the same time, after the whole pipe heat treatment, the pipe body further obtains better strength and toughness (Rp 0.2 ≥900 MPa, R m ≥985 MPa, elongation ≥25%. The longitudinal impact energy of the base metal at -10 °C ≥130 J).

[0030] Starting from multiple aspects such as component design and process control, the present invention effectively solves the technical problems in the manufacture of high-strength and tough casing pipes, and has produced significant beneficial effects in terms of the performance of the raw material coil, the quality of the finished pipe, and the production process:

[0031] The technical solution of the present invention mainly adopts the component design of "medium C + low Mn + Cr / Ni / Cu + Ti + V", and selectively adds B and Mo, through pre-annealing (700 - 740 °C) + low-temperature coiling (550 - 600 °C) + whole pipe heat treatment. The obtained raw material coil has a yield strength of 340 - 370 MPa (a decrease of 40%), a tensile strength reduced to 550 - 575 MPa, a yield ratio <0.65, and a banded structure ≤ grade 2; the finished pipe Rp 0.2≥900 MPa, impact energy at -10°C ≥130 J, no cracks in anti-HIC test. In the prior art, the strength is improved by high-temperature coiling or direct quenching and tempering, but the forming problem caused by the high strength of the raw material coil is not solved. In the present invention, through pre-annealing (700 - 740°C), the yield strength of the raw material coil is reduced to 340 - 370 MPa, significantly reducing the forming difficulty. At the same time, the banded structure ≤ grade 2 (compared with grade 4 of the non-annealed one). Composition co-design: Replace part of the traditional high-Mo alloy with "Cr / Ni / Cu" + selective addition of B, combined with Ti / V microalloying, to improve the anti-HIC performance while reducing costs.

[0032] High strength and toughness: After pre-annealing, the elongation of the raw material coil reaches 30 - 35%, the longitudinal impact energy at -10°C > 90 J, and it still has good impact resistance in low-temperature environments, meeting the requirements of complex working conditions. Good tissue uniformity: Pre-annealing makes the banded structure of the raw material coil ≤ grade 2. Compared with the non-annealed raw material coil, the cracking risk near the weld is significantly reduced, and the tissue uniformity near the weld is improved. After hot tension reducing and full-tube heat treatment, the Rp of the finished pipe 0.2 ≥900 MPa, R m ≥985 MPa, elongation ≥25%, longitudinal impact energy of the base metal at -10°C ≥130 J, fully meeting the performance requirements of high-strength, high-toughness, large-diameter casing pipes, and applicable to the exploitation of unconventional oil and gas fields. Tissue homogenization: The pre-annealed coil has a homogenized F + P structure; the structure of the finished pipe is homogenized tempered sorbite. Especially through pre-annealing + quenching and tempering, the adverse effects of the banded structure on weldability and corrosion resistance are eliminated, ensuring the stability and reliability of the pipe body performance. When it bears harsh conditions such as high pressure and corrosion, the performance fluctuation is small, the anti-HIC performance is excellent, and the service life is long. Description of the Drawings

[0033] Figure 1 It is the tissue morphology of the raw material coil after pre-annealing in Example 1 of the present invention. The tissue after pre-annealing is F + P, and the banded structure is grade 1.

[0034] Figure 2 It is the tissue morphology of the raw material coil without pre-annealing (Comparative Example 7). The tissue is F + P, and the banded structure is severe, with the evaluation grade of 4.

[0035] Figure 3 It is the tissue morphology of the finished pipe in Example 1 of the present invention, which is homogenized tempered sorbite. Detailed Embodiments

[0036] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the preferred implementation schemes of the present invention are described below in conjunction with specific embodiments. However, it should be understood that the drawings are only for illustrative purposes and cannot be construed as a limitation to this patent.

[0037] The present invention provides a manufacturing method for high-strength and high-toughness casing pipes. The chemical composition of the casing pipes and their weight percentage contents (wt%) are as follows: C: 0.20 - 0.28%; Si: 0.2 - 0.3%; Mn: 0.8 - 1.0%; P: ≤0.010%; S: ≤0.003%; Cr: 0.1 - 0.3%; Ni: 0.05 - 0.15%; Cu: 0.10 - 0.30%; Als: 0.03 - 0.05%; Ti: 0.020 - 0.040%; B: ≤0.0030%; Mo: ≤0.03%; V: 0.045 - 0.070, and the balance is Fe and unavoidable inclusions.

[0038] The technological process includes: hot metal pretreatment → converter smelting → LF refining → RH refining → continuous casting → slab reheating → controlled rolling → laminar flow cooling → low-temperature coiling → pre-annealing → HFW welding, hot stretch reducing, and full-pipe heat treatment.

[0039] 1) Smelting, refining, and continuous casting processes

[0040] The molten steel is smelted according to the above chemical composition. After the LF refining process, RH refining is carried out. The RH degassing time is ≥16 min to ensure more sufficient deep dehydrogenation, denitrification, and inclusion removal. The superheat of the tundish is controlled within a narrow range of 20 - 30 °C, which can prevent the tundish nozzle from being blocked due to too low temperature and prevent the columnar crystals of the slab from being too coarse due to too high temperature, resulting in aggravated central segregation and further aggravating the banded structure. At the same time, to reduce central porosity and segregation, an electromagnetic roll and dynamic soft reduction are used during the continuous casting process, and the slab is slowly cooled in the soaking pit for ≥72 h.

[0041] 2) Slab heating, controlled rolling, and controlled cooling processes

[0042] The slab heating furnace tapping temperature is 1180 - 1220 °C, and the holding time is 120 - 160 min.

[0043] The heated slab is rolled into a hot-rolled coil with a thickness of 10 - 16 mm through rough rolling and finish rolling. The finish rolling final rolling temperature is 820 - 860 °C; to reduce the influence of surface decarburization and intergranular oxidation caused by subsequent raw material coil annealing, low-temperature coiling is adopted, and the coiling temperature is 550 - 600 °C.

[0044] Full descaling is carried out for R1 + R2 in rough rolling, and 30 - 40 MPa ultra-high pressure is used for secondary descaling. Descaling is carried out between the finish rolling stands, which can significantly improve the removal effect of the dense oxide layer and reduce the scale spalling during box annealing.

[0045] During coiling, the thermal coil tower overflow should be ≤10 mm to ensure smooth entry into the box annealing furnace and prevent coil damage during vertical stacking.

[0046] 3) Pre-annealing

[0047] The hot coil is annealed in a bell-type furnace. The annealing cold spot temperature is 700 - 740 °C, the holding time is 3.5 - 4.5 h, and the furnace outlet temperature is ≤ 85 °C.

[0048] 4) HFW welding, hot stretch reducing, and full tube heat treatment

[0049] After the HFW welding forms a straight seam tube blank, the tube blank is heated to 920 - 1000 °C by medium-frequency induction heating and then undergoes hot stretch reducing; then the tube is heat-treated by quenching at 890 - 920 °C + tempering at 540 - 580 °C.

[0050] The technical solution of the present invention will be further described below through specific examples and comparative examples.

[0051] The main chemical components of the examples and comparative examples are shown in Table 1, the main rolling process parameters are shown in Table 2, and the mechanical properties are shown in Table 3.

[0052] Table 1 Chemical compositions of the examples and comparative examples of the present invention

[0053]

[0054] Table 2 Main process parameters of the processes of the examples and comparative examples

[0055]

[0056] Table 3 Mechanical properties, impact properties, and HIC resistance properties of the examples and comparative examples

[0057]

[0058] From Figure 1 It can be seen that the structure after pre-annealing is F + P, the banded structure is grade 1. Combining the data in Table 3, the banded structure of the pre-annealed raw material coil is ≤ grade 2. According to the HIC test specified in NACE - 2016 TM0284, no cracks are found. For comparative example 7 without pre-annealing ( Figure 2 ), the banded structure is severe, and the evaluation grade is 4. When the same HIC test is carried out, cracks appear. Therefore, it can be seen from the above that good tissue uniformity improves the tissue uniformity near the weld, reduces the risk of extrusion cracking, and also improves the comprehensive properties such as HIC resistance. Balance between strength and plasticity: The strength of the pre-annealed raw material steel coil decreases, Rp 0.2 is 340 - 370 MPa, R m is 550 - 575 MPa, the yield ratio < 0.65, and the elongation rate reaches 30 - 35%. It can be seen from Table 3 that Rp of the pre-annealed raw material coil in Example 1 0.2It is 341 MPa, with an elongation of 35.0%. While ensuring a certain strength, it has good plasticity. Compared with Comparative Example 7 without pre-annealing (Rp0.2 is 570 MPa), it is easier to form and can effectively reduce the difficulty of the forming operation of the planetary roll forming. High toughness: The longitudinal impact energy at -10 °C > 90 J. For example, in Example 1, the impact energy of the raw material coil at -10 °C reaches 113 / 109 / 111 J, with good toughness, which can meet the anti-impact requirements during subsequent processing and use.

[0059] After welding, hot stretch reducing, and full-tube heat treatment, the strength, plasticity, and toughness of the casing are further improved. Rp 0.2 ≥900 MPa, R m ≥985 MPa, elongation ≥ 25%, and the longitudinal impact energy of the base material at -10 °C ≥ 130 J. For example, in Example 1, the Rp of the finished pipe 0.2 is 903 MPa, R m is 987 MPa, elongation 26.5%, impact energy at -10 °C 154 / 148 / 150 J, which can meet the high requirements for the strength and toughness of the casing in the exploitation of unconventional oil and gas fields. Microstructure homogenization: Figure 3 The microstructure of the finished pipe shown is homogenized tempered sorbite, ensuring the stability and reliability of the casing performance, enabling it to withstand complex pressures and environments during use.

[0060] The present invention has been described in detail above in combination with the embodiments. However, the present invention is not limited to the above embodiments. Within the knowledge scope of those of ordinary skill in the art to which the present invention pertains, various changes can be made without departing from the gist of the present invention. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A manufacturing method of a high-strength and high-toughness casing, comprising the following steps: converter smelting, refining, continuous casting, reheating of slab, controlled rolling, laminar flow cooling, coiling, welding, hot tension reducing and full-tube heat treatment; characterized in that, Pre-annealing is adopted before welding. The pre-annealing step includes: the hot coil is annealed in a bell-type furnace, the annealing cold spot temperature is 700 - 740 °C, the holding time is 3.5 - 4.5 h, and the furnace outlet temperature ≤ 85 °C.

2. The manufacturing method of the high-strength and high-toughness casing according to claim 1, characterized in that, In the coiling step: the coiling temperature is 550 - 600 °C.

3. The manufacturing method of the high-strength and high-toughness casing according to claim 1, wherein The chemical composition and its weight percentage content of the casing are: C: 0.20 - 0.28%, Si: 0.2 - 0.3%, Mn: 0.8 - 1.0%, P: ≤ 0.010%, S: ≤ 0.003%, Cr: 0.1 - 0.3%, Ni: 0.05 - 0.15%, Cu: 0.10 - 0.30%, Als: 0.03 - 0.05%, Ti: 0.020 - 0.040%, Mo: ≤ 0.03%, B: ≤ 0.0030%, V: 0.045 - 0.070, and the balance is Fe and unavoidable inclusions.

4. The manufacturing method of the high-strength and high-toughness casing according to claim 3, characterized in that The chemical composition of the casing needs to meet the following constraint conditions: 。 5. The manufacturing method of the high-strength and high-toughness casing according to any one of claims 1-4, characterized in that, The raw material coil after pre-annealing: Rp 0.2 :340~370MPa,R m : 550~575MPa, yield strength ratio <0.65, elongation 30~35%, -10℃ longitudinal impact energy >90J, banded structure ≤level 2.

6. The manufacturing method of the high-strength and high-toughness casing according to claim 1, characterized in that, The welding, hot stretch reducing and full-tube heat treatment steps include: the pre-annealed raw material coil is welded into a straight-seam tube blank by HFW, then heated to 920 - 1000 °C for hot stretch reducing, and then undergoes heat treatment of quenching at 890 - 920 °C and tempering at 540 - 580 °C, and finally the casing is obtained.

7. The manufacturing method of the high-strength and high-toughness casing according to claim 6, characterized in that, Casing after heat treatment: Rp 0.2 ≥ 900 MPa, R m ≥ 985 MPa, elongation ≥ 25%, longitudinal impact energy of base metal at -10 °C ≥ 130 J.

8. The manufacturing method of the high-strength and high-toughness casing according to claim 1, characterized in that, In the converter smelting and refining steps: the RH refining degassing time ≥ 16 min, the tundish superheat is controlled at 20 - 30 °C, the electromagnetic roll and dynamic soft reduction are used during continuous casting, and the cast slab is slowly cooled in a heat preservation pit for ≥ 72 h.

9. The manufacturing method of the high-strength and high-toughness casing according to claim 1, characterized in that, In the slab reheating, controlled rolling and laminar cooling steps: the slab furnace outlet temperature is 1180 - 1220 °C, the holding time is 120 - 160 min, the finish rolling temperature of the finishing mill is 820 - 860 °C, full descaling is carried out for the roughing R1 + R2, 30 - 40 MPa ultra-high pressure is used for the secondary descaling, and descaling is used between the finishing mill stands.

10. The manufacturing method of the high-strength and high-toughness casing according to claim 9, characterized in that, The heated slab is rolled into a hot-rolled coil with a thickness of 10 - 16 mm through roughing and finishing rolling.

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