Process for producing extreme size x80 pipeline steel in high water temperature season

Abstract

The application discloses a process method for producing a limited specification X80 pipeline steel in a high water temperature season, and ideal mechanical properties and organizational morphology are obtained through control of components, heating, rolling, cooling, and laminar flow cooling water temperature and the like processes and technologies. 50 The steel is composed of acicular ferrite+granular bainite+M-A, in particular, the M-A component content is controlled to be 4-8%, and the average size of the short axis of the austenite grain of the large-angle grain boundary is 7.4um. The yield strength of the steel is 605-635MPa, the tensile strength is 720-750MPa, the elongation after fracture A is 35-40%, the yield strength ratio is ≤0.85, the low-temperature impact energy (-60℃) is 400-430J, the impact shear area is 100%, the -40℃ drop hammer shear area is 95-100%, and the requirements of the X80 pipeline steel standard are completely met. The steel can be used in pipeline engineering prone to large plastic deformation such as liquefied sedimentation, ground slip deformation and submarine pipeline laying.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a process method for producing X80 pipeline steel of extreme specifications during high water temperature seasons. Background Technology

[0002] With the sustainable development of the national economy, the domestic energy market has experienced a supply shortage, with a significant gap between oil and natural gas demand, greatly stimulating the development of exploration operations. To meet the growing domestic energy demand, efforts are being made to actively search for new oil and gas fields, especially natural gas resources, which have seen significant breakthroughs in recent years. The import of oil and gas resources from neighboring countries has also been put on the agenda. The transportation of oil and gas resources, including natural gas, is now primarily focused on pipeline construction.

[0003] Pipeline transportation is a crucial method for transporting oil and natural gas over long distances. To improve operational efficiency and reduce costs, pipeline transportation is evolving towards larger diameters, thicker walls, and higher pressures. The use of thick-gauge, high-strength, high-toughness, and highly weldable hot-rolled steel coils for oil and gas pipelines has become a future trend. Currently, the China-Russia natural gas pipeline effectively alleviates the natural gas shortage in Northeast China and will also optimize the energy structure of the Beijing-Tianjin-Hebei region. It will have a positive and far-reaching impact on improving air pollution in the Beijing-Tianjin-Hebei region and promoting energy structure adjustment in the Yangtze River Delta region.

[0004] Generally, producing X80 pipeline steel of extreme specifications during high water temperature seasons presents the following challenges: The 25.6mm thick X80 coils place extremely high demands on the cooling capacity of hot rolling mills. Under current equipment and technological conditions, hot continuous rolling mills struggle to achieve this cooling capacity, especially during high water temperature seasons (summer), when the cooling water temperature cannot reach the required level. Due to its high strength grade, 25.6mm thick X80 pipeline steel causes significant impact on equipment, leading to severe damage. Current technology for producing thicker X80 steel sometimes results in low yield strength and excessive yield-to-tensile ratio. Currently, the production efficiency and yield of extreme specifications X80 are low. The performance of this type of extreme specification X80 pipeline steel mainly depends on: 1. the alloying elements added in the composition design and their proportions; 2. the proportion of hard and soft phases in the microstructure; and 3. the morphology and size of the grains after rolling.

[0005] In the prior art, patent CN114058978A discloses X80 pipeline steel with low-temperature toughness. It incorporates expensive elements such as Mo, Ni and Nb in its composition design. The Mo content is 0.20-0.35%, the Ni content is 0.30-0.80%, and the Nb content is 0.04-0.08%, resulting in high alloy costs. In addition, cooling the steel plate to 450-550°C by controlling the cooling rate at 15-30°C / s is a conventional control method. Patent CN111910126A discloses a thick-gauge, high-toughness X80 pipeline steel and its production method. Its chemical composition is C: 0.04–0.08%, Cr: 0.15–0.25%, Nb: 0.07–0.08%, Ti: 0.015–0.025%, with a total cumulative reduction rate of 56.7–60.0%. The steel plate is rapidly cooled at a rate of 60–80℃ / s, a relatively fast cooling rate that is difficult to achieve in production. Patent CN111961957A discloses an X80 grade pipeline steel plate that exhibits both seawater corrosion resistance and resistance to large deformation, and its manufacturing method. It incorporates high chromium, high nickel, and high molybdenum in its composition, resulting in higher costs. The steel plate is formed using a two-stage controlled rolling process, employing DQ rapid cooling and ACC slow cooling sequentially after hot rolling, which is difficult to implement in production. Summary of the Invention

[0006] In order to overcome the defects of the existing technology, the present invention, by adjusting the process and controlling the cooling water temperature, obtains X80 pipeline steel with good strength and toughness matching, excellent surface quality and good weldability, while significantly reducing the cost of alloys, and significantly improving the production efficiency and yield.

[0007] To achieve the aforementioned objectives, this invention provides a process for producing X80 pipeline steel of extreme specifications during high water temperature seasons, including top-and-bottom blowing converter smelting, ladle refining, large slab continuous casting, heating, controlled rolling, and controlled cooling. The method comprises the following technical solutions:

[0008] ① The continuous casting billet casting speed is 1.0~1.1m / min, and the continuous casting billet thickness is 250mm.

[0009] ② The continuously cast billet adopts a low-temperature heating process to avoid excessive growth of austenite. The heating temperature is 1140~1160℃ and the heating time is 1.5~2h.

[0010] ③ Rough rolling: Relaxation and temperature waiting in the rough rolling mill, the exit temperature of the rough rolling mill is ≤945℃; the last pass R7 of rough rolling is used as the first pass of finishing rolling.

[0011] The biggest innovation in roughing rolling is using the final pass (R7) of the roughing mill as the first pass of the finishing mill. This utilizes the large deformation of this pass, allowing the F5 stand to be bypassed, increasing the reduction rate of the other finishing mill stands. This allows the austenite grains to be fully flattened and gradually elongated along the rolling direction, forming numerous deformation bands and dislocations within the deformed austenite grains, providing more nucleation sites for ferrite transformation. Furthermore, the elongation of the austenite grains hinders ferrite grain growth, resulting in a finer ferrite microstructure after phase transformation. Therefore, controlling the reduction rate in finishing rolling can significantly improve the strength of the steel. Keeping the total number of passes in the finishing mill constant, and to some extent shifting the reduction later, is beneficial for grain refinement and improved performance.

[0012] In addition, a "0+7" control mode is adopted, that is, R1 is passed empty, and R2 adopts a 7-pass rolling control mode. The deformation amount is increased by 35-38mm in the two passes of the rough rolling head, and the thickness of the intermediate billet is controlled at 68-70mm. By increasing the thickness of the intermediate billet, it is beneficial to increase the reduction of the finishing mill, so that more rolling deformation remains in the non-recrystallized austenite region, thereby achieving the purpose of refining the grains.

[0013] Taking a slab thickness of 70mm as an example, the reduction amount distribution for each pass of roughing rolling is as follows:

[0014] 250mm→215mm→180mm→165mm→130mm→110mm→90mm→70mm.

[0015] ④ Finish rolling

[0016] Breaking away from the conventional rolling pattern, the distribution of reduction rates from F1 to F7 in conventional rolling is changed from large to small. F5 is skipped, and the reduction rate is significantly shifted to the later stages. The pattern is adjusted so that the reduction rates of F3, F4, and F6 in the intermediate mills are high, while the reduction rates of F1, F2, and F7 in the end mills are low. This effectively increases the cumulative deformation below Tnr, making the microstructure of X80 pipeline steel fine and uniform, achieving the purpose of refining grains and increasing toughness, especially improving the low-temperature drop hammer tear performance.

[0017] Before entering the finishing rolling mill, ultra-high pressure water is used for descaling. The descaling water pressure is 38MPa, which can remove the iron oxide scale from the surface of the steel plate.

[0018] The inlet temperature of the finishing mill should be ≤940℃, below the Tnr temperature, to avoid mixed crystal phenomena.

[0019] Distribution of finishing mill reduction:

[0020] 70mm→66.5mm→61.3mm→50.8mm→41.7mm→41.7mm→31.6mm→25.6mm

[0021] ⑤ Laminar flow cooling

[0022] To enhance the cooling effect, the temperature of the laminar flow cooling water is limited, and the volume of cooling water is increased. During production in seasons with high water temperatures, liquid nitrogen is added to the laminar flow cooling circulation system or water is transported by fire truck to lower the water temperature and increase the cooling rate, ensuring that the laminar flow cooling water temperature is ≤20℃.

[0023] ⑥ Final rolling and coiling of X80 pipeline steel of extreme specifications: The final rolling temperature is set at 800℃ and the coiling temperature is 360~380℃. The final microstructure is acicular ferrite + bainite + MA, which meets the requirements of low temperature impact toughness (-60℃) and drop hammer tear toughness. The resulting X80 pipeline steel of extreme specifications has good strength and toughness matching, excellent surface quality and good weldability.

[0024] Cooling rate calculation: Cooling rate = Layer cooling temperature drop / (Cooling section length / Speed)

[0025] For X80 pipeline steel, a cooling rate controlled between 30 and 35°C / s can ensure a good balance of strength and toughness.

[0026] The chemical composition (mass percentage) of the X80 pipeline steel produced by the above process is as follows: C: 0.03–0.04%, Si: 0.10–0.20%, Mn: 1.6–1.70%, P≤0.010%, S≤0.001%, Alt: 0.025–0.035%, N≤0.0030%, O≤0.0010%. In addition, the steel composition also contains Cr: 1.0–1.2%, Ti: 0.10–0.15%, V: 0.035–0.055%, with the balance being iron and unavoidable impurities.

[0027] By appropriately increasing the V and Cr content, precipitation strengthening and precipitation enhancement are achieved. Vanadium in acicular ferrite mainly uses V (C, N) as a low-temperature precipitation strengthening phase to improve the strength of the steel. Chromium makes the grains sufficiently small, promotes the cross-generation of slip bands during the transformation process, and reduces the resistance of transformation dislocations. During the heating process, the continuously cast billet is heated at low temperature, which effectively controls the original austenite grain size and prevents excessive growth. Through rough rolling, low-temperature slow rolling with large reduction is used to strengthen the deformation of the high-temperature austenite recrystallization zone, making the austenite grains sufficiently small. Then, by using accelerated cooling process, water cooling is utilized to refine the phase transformation structure and obtain a uniform acicular ferrite + bainite + MA island (MA) structure, which improves the low-temperature impact performance and drop hammer tear performance of the ultimate specification X80 pipeline steel.

[0028] Furthermore, the ultimate specifications of the X80 pipeline steel are 25.6mm × 2000mm, yield strength 605–635MPa, tensile strength 720–750MPa, and elongation after fracture A. 50The yield strength is 35-40%, the yield strength ratio is ≤0.85, the low-temperature impact energy (-60℃) is 400-430J, the impact shear area is 100%, and the drop hammer shear area at -40℃ is 95-100%, which fully meets the requirements of the X80 pipeline steel standard.

[0029] An application of the aforementioned X80 pipeline steel in pipeline engineering projects prone to large plastic deformation. For example, it is widely used in pipeline projects prone to large plastic deformation, such as liquefaction settlement, ground slip deformation, and submarine pipeline laying; it is mainly used in pipelines such as the China-Russia pipeline, the Pakistan pipeline, and the India pipeline, and can also be used in the construction of natural gas and oil pipelines in harsh environments such as seismically active zones, permafrost layers, and landslide areas.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] ①This invention provides the composition and process technology formula for producing X80 pipeline steel of extreme specifications during high water temperature seasons. By controlling the composition, heating, rolling, cooling and other processes and technologies, ideal mechanical properties and microstructure are obtained, especially low temperature impact performance and drop hammer tear performance.

[0032] ②The metallographic structure of this steel consists of acicular ferrite + granular bainite + MA, with MA content of 4-8% and the average short axis size of austenite grains of 7.4μm.

[0033] ③ The X80 pipeline steel of the specified ultimate specification has a yield strength of 605-635 MPa, a tensile strength of 720-750 MPa, and an elongation after fracture of A. 50 The yield strength is 35-40%, the yield strength ratio is ≤0.85, the low-temperature impact energy (-60℃) is 400-430J, the impact shear area is 100%, and the drop hammer shear area at -40℃ is 95-100%, which fully meets the requirements of the X80 pipeline steel standard. Attached Figure Description

[0034] Figure 1 The CCT curve for X80 pipeline steel according to the present invention;

[0035] Figure 2 Metallographic diagram of X80 pipeline steel in Example 1;

[0036] Figure 3 The image shows the microstructure of X80 austenite grains in Example 1.

[0037] Figure 4 The image shows the metallographic structure of X80 pipeline steel as a comparative example. Detailed Implementation

[0038] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

[0039] The production process for the ultimate specification X80 pipeline steel during high-temperature seasons according to the present invention involves smelting in a 180-ton top-and-bottom combined blowing converter and controlled rolling and cooling production on a 2300mm hot continuous rolling mill. The process flow is as follows: 250mm continuous casting billet → heating → rough rolling "0+7" rolling (relaxation and waiting for temperature) → 7-stand finish rolling (controlled rolling) → ultra-rapid cooling → coiling (controlled phase transformation) → finished product. The chemical composition of the steel plate in the embodiments is shown in Table 1. (Appendix) Figure 1 The CCT curve is for X80 pipeline steel.

[0040] Table 1. Chemical composition (wt%) of the X80 pipeline steel plate of the ultimate specification in the embodiments.

[0041] Example C Si Mn P S Alt Cr Ti V N O Example 1 0.03 0.11 1.62 0.006 0.0007 0.025 1.02 0.10 0.036 0.0022 0.0006 Example 2 0.034 0.16 1.66 0.008 0.0008 0.03 1.10 0.13 0.045 0.0026 0.0008 Example 3 0.04 0.19 1.70 0.010 0.001 0.035 1.19 0.15 0.054 0.0030 0.0010

[0042] Example 1

[0043] A process for producing X80 pipeline steel (25.6mm × 2000mm) in high-temperature seasons, comprising top-and-bottom blowing converter smelting, ladle refining, large slab continuous casting, heating, controlled rolling, and controlled cooling, with specific technical details as follows:

[0044] ① The continuous casting billet casting speed is 1.0m / min, and the continuous casting billet thickness is 250mm.

[0045] ② The continuous casting billet adopts a hot delivery and hot charging process, and the continuous casting billet adopts a low temperature heating process with a heating temperature of 1142℃ and a heating time of 1.5h.

[0046] ③ Rough rolling: Relaxation and temperature waiting in the rough rolling mill, with an exit temperature of 945℃; the last pass of rough rolling, R7, is used as the first pass of finishing rolling.

[0047] The biggest innovation in roughing rolling is using the final pass (R7) of the roughing roll as the first pass of the finishing roll. This utilizes the large deformation of this pass, allowing the F5 stand to be bypassed, increasing the reduction rate of the other finishing mills. This allows the austenite grains to be fully flattened and gradually elongated along the rolling direction, forming numerous deformation bands and dislocations within the deformed austenite grains, providing more nucleation sites for ferrite transformation. Furthermore, the elongation of the austenite grains hinders ferrite grain growth, resulting in a finer ferrite structure after phase transformation. Therefore, controlling the reduction rate in finishing rolling can significantly improve the strength of the steel. Keeping the total number of passes in the finishing section constant, and shifting the reduction to a later stage to some extent, is beneficial for grain refinement and improved performance.

[0048] In addition, a "0+7" control mode is adopted, that is, R1 is passed empty, and R2 adopts a 7-pass rolling control mode. The deformation amount is increased by 35-38mm in the two passes of the rough rolling head, and the thickness of the intermediate billet is controlled at 68-70mm. By increasing the thickness of the intermediate billet, it is beneficial to increase the reduction of the finishing mill, so that more rolling deformation remains in the non-recrystallized austenite region, thereby achieving the purpose of refining the grains.

[0049] The reduction amount distribution for each pass of roughing rolling is as follows:

[0050] 250mm→215mm→180mm→165mm→130mm→110mm→90mm→70mm.

[0051] ④ Finish rolling

[0052] Breaking away from the conventional rolling pattern, the distribution of reduction rates from F1 to F7 in conventional rolling is changed from large to small. F5 is skipped, and the reduction rate is significantly shifted to the later stages. The pattern is adjusted so that the reduction rates of F3, F4, and F6 in the intermediate mills are high, while the reduction rates of F1, F2, and F7 in the end mills are low. This effectively increases the cumulative deformation below Tnr, making the microstructure of X80 pipeline steel fine and uniform, achieving the purpose of refining grains and increasing toughness, especially improving the drop hammer tear performance.

[0053] Before entering the finishing rolling mill, ultra-high pressure water is used for descaling. The descaling water pressure is 38MPa, which can remove the iron oxide scale from the surface of the steel plate.

[0054] The inlet temperature of the finishing mill is 940℃, below the Tnr temperature, to avoid mixed crystal formation.

[0055] Distribution of finishing mill reduction:

[0056] 70mm→66.5mm→61.3mm→50.8mm→41.7mm→41.7mm→31.6mm→25.6mm

[0057] ⑤ Laminar flow cooling

[0058] To enhance the cooling effect, the temperature of the laminar cooling water is limited and the volume of cooling water is increased. During production in seasons with high water temperatures, liquid nitrogen is added to the laminar cooling circulation system or fresh water from the Taizi River is transported by fire truck to lower the water temperature and increase the cooling rate, ensuring that the laminar cooling water temperature is 19℃.

[0059] ⑥ Final rolling and coiling of X80 pipeline steel of extreme specifications: The final rolling temperature is set at 800℃ and the coiling temperature is 380℃. The low-temperature final rolling and low-temperature coiling process is adopted to obtain the final microstructure as acicular ferrite + bainite + MA microstructure, which meets the requirements of low-temperature impact toughness and drop hammer tear toughness, and obtains X80 pipeline steel of extreme specifications with good strength and toughness matching, excellent surface quality and good weldability.

[0060] Cooling rate calculation: Cooling rate = Layer cooling temperature drop / (Cooling section length / Speed)

[0061] For X80 pipeline steel, a cooling rate controlled at 30℃ / s can ensure a good balance of strength and toughness.

[0062] The metallographic structure of the X80 pipeline steel in Example 1 is shown in the attached figure. Figure 2 The microstructure consists of acicular ferrite + granular bainite + austenite (MA), with the MA content controlled at 5%. The microstructure of X80 austenite grains in Example 1 is as follows: Figure 3 As shown, the average size of the short axis of the large-angle grain boundaries is 7.4 μm. The comprehensive mechanical properties of the steel plate in Example 1 are shown in Table 2.

[0063] Example 2

[0064] A process for producing X80 pipeline steel (25.6mm × 2000mm) in high-temperature seasons, comprising top-and-bottom blowing converter smelting, ladle refining, large slab continuous casting, heating, controlled rolling, and controlled cooling, with specific technical details as follows:

[0065] ① The continuous casting billet casting speed is 1.05m / min, and the continuous casting billet thickness is 250mm.

[0066] ② The continuous casting billet adopts a hot delivery and hot charging process, and the continuous casting billet adopts a low temperature heating process with a heating temperature of 1151℃ and a heating time of 1.7h.

[0067] ③ Roughing: Relaxation and temperature waiting in the roughing mill unit, the outlet temperature of the roughing mill is 940℃;

[0068] The rolling process adopts a 7-pass control mode with R1 blank pass and R2 pass. The deformation amount of the rough rolling head is 37mm in two passes, and the thickness of the intermediate billet is controlled at 68mm.

[0069] The reduction amount distribution for each pass of roughing rolling is as follows:

[0070] 250mm→213mm→176mm→164mm→132mm→108mm→92mm→68mm.

[0071] ④ Finish rolling

[0072] F5 is skipped, and the reduction ratio distribution from F1 to F7 is changed from large to small. The reduction ratio is significantly shifted to the end, and the mode is adjusted so that the reduction ratio of the intermediate mills F3, F4, and F6 is high, and the reduction ratio of the end mills F1, F2, and F7 is low.

[0073] Before entering the finishing mill, ultra-high pressure water descaling is used, with a descaling water pressure of 38 MPa. The inlet temperature of the finishing mill is 936℃.

[0074] Distribution of finishing mill reduction:

[0075] 70mm→65.7mm→62.8mm→48.5mm→40.7mm→40.7mm→30.5mm→25.6mm

[0076] ⑤ Laminar flow cooling: Laminar flow cooling water temperature 18℃.

[0077] ⑥ Final rolling and coiling of X80 pipeline steel (limit specification): The final rolling temperature was set at 800℃, the coiling temperature at 370℃, and the cooling rate was controlled at 33℃ / s. The comprehensive mechanical properties of the steel plate in Example 2 are shown in Table 2.

[0078] Example 3

[0079] A process for producing X80 pipeline steel (25.6mm × 2000mm) in high-temperature seasons, comprising top-and-bottom blowing converter smelting, ladle refining, large slab continuous casting, heating, controlled rolling, and controlled cooling, with specific technical details as follows:

[0080] ① The continuous casting billet casting speed is 1.1m / min, and the continuous casting billet thickness is 250mm.

[0081] ② The continuous casting billet adopts a hot delivery and hot charging process, and the continuous casting billet adopts a low temperature heating process with a heating temperature of 1159℃ and a heating time of 2.0h.

[0082] ③ Roughing: Relaxation and temperature waiting in the roughing mill unit, the outlet temperature of the roughing mill is 938℃;

[0083] The rolling process adopts a 7-pass control mode with R1 blank pass and R2 pass. The deformation amount of the rough rolling head is 38mm in two passes, and the thickness of the intermediate billet is controlled at 67mm.

[0084] The reduction amount distribution for each pass of roughing rolling is as follows:

[0085] 250mm→212mm→174mm→163mm→130mm→105mm→90mm→67mm.

[0086] ④ Finish rolling

[0087] F5 is passed empty, using a mode where the reduction rates of intermediate mills F3, F4, and F6 are high, while the reduction rates of end mills F1, F2, and F7 are low.

[0088] Before entering the finishing mill, ultra-high pressure water descaling is used, with a descaling water pressure of 38 MPa. The inlet temperature of the finishing mill is 935℃.

[0089] Distribution of finishing mill reduction:

[0090] 67mm→63.5mm→60.5mm→45.2mm→38.7mm→38.7mm→29.5mm→25.6mm

[0091] ⑤ Laminar flow cooling: Laminar flow cooling water temperature 18℃.

[0092] ⑥ Final rolling and coiling of X80 pipeline steel (limit specification): The final rolling temperature was set at 800℃, the coiling temperature at 360℃, and the cooling rate was controlled at 35℃ / s. The comprehensive mechanical properties of the steel plate in Example 3 are shown in Table 2.

[0093] Comparative Example

[0094] Using existing X80 pipeline steel as a comparative example, the existing X80 pipeline steel has a yield strength of not less than 555 MPa, a tensile strength of not less than 625 MPa, a Charpy impact energy of 300 J at -20℃, and a DWTT shear area of ​​85% at -15℃. The comprehensive mechanical properties of the steel plate of the comparative example are shown in Table 2.

[0095] The metallographic structure of the existing X80 pipeline steel (comparative example) is shown in the attached figure. Figure 4 As shown, the microstructure consists of polygonal ferrite + bainite + MA, with an MA content of 14.1%. Excessive MA content is not conducive to increasing low-temperature impact toughness.

[0096] Table 2 Mechanical properties of steel plates in each embodiment and comparative example

[0097] Example Kv2 / J DWTT / % Rt0.5 / MPa Rm / MPa The ratio of yield strength Comparative Example 300(-20℃) 85(-15℃) 575 632 0.91 Example 1 430(-60℃) 100(-40℃) 605 720 0.84 Example 2 421(-60℃) 98(-40℃) 614 740 0.83 Example 3 400(-60℃) 95(-40℃) 635 750 0.84

[0098] Compared with existing X80 pipeline steel, the product of this invention can still have a high Charpy impact energy and impact shear area at temperatures of -60℃ or lower, and still have a good drop hammer tear area (DWTT) at -40℃. The yield strength ratio is low, indicating that the product of this invention has good low-temperature toughness, and its yield strength and tensile strength are higher than those of existing X80 pipeline steel.

[0099] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A process for producing X80 pipeline steel of extreme specifications during high water temperature seasons, including top and bottom blowing converter smelting, ladle refining, large slab continuous casting, heating, controlled rolling, and controlled cooling processes, characterized in that... The method includes the following technical solutions: The chemical composition of the X80 pipeline steel of the specified limit specification is as follows (by mass percentage): C: 0.03%–0.04%, Si: 0.10%–0.20%, Mn: 1.60%–1.66%, P≤0.010%, S≤0.001%, Alt: 0.025%–0.035%, N≤0.0030%, O≤0.0010%; in addition, the steel also contains Cr: 1.0%–1.2%, Ti: 0.10%–0.15%, V: 0.035%–0.055%, with the balance being iron and unavoidable impurities. ① The continuous casting billet casting speed is 1.0~1.1m / min, and the continuous casting billet thickness is 250mm; ② The continuous casting billet adopts a low-temperature heating process, with a heating temperature of 1140℃~1159℃ and a heating time of 1.5~2h; ③ Rough rolling: Relaxation and temperature waiting in the rough rolling mill, the outlet temperature of the rough rolling mill is ≤945℃; the last pass of rough rolling R7 is used as the first pass of finishing rolling; the rough rolling adopts the "0+7" control mode, that is, R1 is passed empty, R2 adopts the rolling 7-pass control mode, the last pass of R2 is used as the first pass of finishing rolling, the large reduction makes the grains after rough rolling sufficiently refined and uniform, the deformation of the first two passes of rough rolling is increased by 35~38mm, and the thickness of the intermediate billet is controlled to be 68~70mm; ④ Finishing rolling: Adjust the rolling mode to a mode with high reduction rates in intermediate mills F3, F4, and F6, empty pass in F5, and low reduction rates in end mills F1, F2, and F7, to increase the cumulative deformation below Tnr; use ultra-high pressure water descaling before finishing rolling, with a descaling water pressure of 38MPa; finish rolling inlet temperature ≤940℃; ⑤ Laminar flow cooling: The temperature of the laminar flow cooling water is ≤20℃; the formula for calculating the cooling rate is: Cooling rate = Laminar cooling temperature drop / (Cooling section length / speed); The cooling rate is controlled at 33~35℃ / s; ⑥ Final rolling and coiling of X80 pipeline steel of extreme specification: The final rolling temperature is set at 800℃, and the coiling temperature is 360℃~380℃; The microstructure of the X80 pipeline steel consists of acicular ferrite + granular bainite + MA, with MA content of 4% to 8% and the average short axis size of austenite grains of 7.4 μm. The ultimate specifications of the X80 pipeline steel are 25.6mm × 2000mm, yield strength 605~635MPa, tensile strength 720~750MPa, and elongation after fracture A. 50 The yield strength is 35% to 40%, the yield strength ratio is ≤0.85, the impact energy at -60℃ is 400 to 430 J, the impact shear area is 100%, and the drop hammer shear area at -40℃ is 95% to 100%.

2. The application of X80 pipeline steel of extreme specification prepared by the method described in claim 1 in pipeline engineering where large plastic deformation is likely to occur.

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