700mpa high performance heavy-gauge pipe line steel plate and method of producing the same

Abstract

The application belongs to the field of metal materials, and provides a 700MPa high-performance wide-thick steel plate for pipelines and a production method thereof.The composition of the steel plate takes C, Mn and Cr as basic strengthening elements, and through the addition of La, Zr, Ca and other elements, the inclusions are complexly regulated, Nb and V are complexly added, N is controlled, and the addition of Ti and Al is reduced, so that the Nb and V can play the roles of micro-alloy solid solution, precipitation and fine grain, the strength, aging resistance and weldability are improved, and the hydrogen trap effect is played to improve the corrosion resistance; a small amount of Ni and Cu is added to improve the strength and corrosion resistance; the production method comprises smelting, continuous casting, heating, rough rolling, finish rolling and cooling; and the steel plate produced by the application is suitable for service under the conditions of multiple-dimensional comprehensive technical characteristics such as strength, plasticity, toughness, strain, corrosion resistance, aging resistance and thick wall.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to 700MPa high-performance pipeline thick steel plates and their production methods, which are especially suitable for manufacturing energy transmission pipelines for complex service conditions such as marine, high-altitude and high-low temperature cycles. Background Technology

[0002] Pipelines are the most economical and rational mode of transportation for long-distance energy transmission and a fundamental guarantee for energy strategy. With the continuous development of the economy and society, my country has become the world's largest energy consumer. To ensure energy supply, the pace of oil and gas capacity construction in key areas such as deep energy, non-deep energy, and renewable energy is accelerating, as are the development of new technologies, models, and business forms for renewable energy and energy storage. This has placed more stringent requirements on the service environment and transport media of energy pipelines, and has also brought new opportunities and challenges to the development of pipeline materials for complex conditions such as marine environments, high-altitude cold regions, and high-low temperature cycles.

[0003] To meet service requirements, high-performance pipeline steel plates operating under complex conditions must possess a combination of technical characteristics, including high strength, high uniform elongation, low-temperature toughness, high strain resistance, corrosion resistance, aging resistance, and fatigue resistance. Simultaneously, they must also have thick-walled dimensions to meet high-pressure transportation and safety requirements.

[0004] Currently, there has been some research on high-performance pipeline steel plates for service under complex conditions. Some patents and literature have been found through searching, but the contents recorded therein are significantly different from those of the technical solution of this invention in terms of composition, production method, performance, and microstructure design. In particular, this invention has significant advantages in the coupling of multi-dimensional technical features.

[0005] The paper "Steel with excellent low-temperature toughness and elongation and low yield ratio for high-strength thick pipelines and its manufacturing method" (CN113166905A) provides a high-performance pipeline steel plate. The design scheme adopts a high Nb (0.08%~0.12%) and high Mo (0.20%~0.40%) composition, which results in excessively high alloy costs. The microstructure is mainly composed of acicular ferrite and bainitic ferrite, which leads to weak strain capacity.

[0006] The paper "An X80M Deep-Sea Strain-Resistant Pipeline Steel Plate and Rolling Process" (CN109234623B) provides a deep-sea pipeline steel plate with a high Ni (0.65%~0.85%) and high Mo (0.31%~0.36%) composition, resulting in excessively high alloy content and cost.

[0007] The paper "An X80 pipeline steel with excellent toughness in the heat-affected zone of the circumferential weld joint and its preparation method" (CN117821851A) provides a high-strength and high-toughness pipeline steel with a high Ni design (0.30%~0.45%) and high Nb (0.09%~0.12%). It has high cost, requires a reduction rate of ≥25% in the last pass of rough rolling and a rolling temperature of ≤960℃ in the last pass, and is not suitable for the production of wide and thick steel plates. It also has high requirements for equipment capabilities.

[0008] The paper "Steel for Large Thick-Walled Low-Temperature Pipelines and Its Manufacturing Method" (CN116288017A) provides a steel for low-temperature pipelines, which also adopts a high Ni (0.35%~0.50%) design.

[0009] In summary, existing technologies still fall short in their research on 700MPa thick-walled high-performance pipeline steel plates and their production technologies that possess comprehensive technical characteristics such as high strength, high uniform elongation, low-temperature toughness, high strain, corrosion resistance, and aging resistance, which are suitable for complex conditions. Summary of the Invention

[0010] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a 700MPa high-performance pipeline thick steel plate and its production method that are suitable for service conditions with multi-dimensional comprehensive technical characteristics such as strength, plasticity, toughness, strain, corrosion resistance, aging resistance, fatigue resistance and thick wall.

[0011] The objective of this invention is achieved as follows:

[0012] A 700MPa high-performance pipeline thick steel plate, the composition of which, by weight percentage, is as follows: C: 0.035%–0.060%, Si: 0.15%–0.50%, Mn: 1.75%–1.90%, Nb: 0.030%–0.055%, V≤0.10%, N: 0.0040%–0.012%, Ni: 0.05%–0.20%, Cu: 0.01%–0.15%. %, Cr: 0.15%~0.50%, Mo: 0.05%~0.15%, Al: 0.005%~0.015%, Ca: 0.0020%~0.0055%, Zr≤0.003%, La≤0.005%, Ti≤0.010%, P≤0.008%, S≤0.0015%, H≤0.00015%, O≤0.0015%, with the balance being iron and unavoidable impurities.

[0013] Furthermore, the Nb+V content in the steel plate is 0.045% to 0.135%.

[0014] Furthermore, in the steel plate, (La / 139+Ca / 40) / (S / 32):2~6.

[0015] Furthermore, CE in steel platesIIW Controlled within 0.42% to 0.49%, CE Pcm The content should be controlled between 0.17% and 0.20%, of which CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15;

[0016] CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0017] Furthermore, the microstructure of the steel plate includes bainitic ferrite and polygonal ferrite, wherein the volume percentage of polygonal ferrite is 15%–75%, and the average grain cross-sectional area of ​​polygonal ferrite is ≤85μm. 2 The matrix contains fine precipitates with a size ≤30 nm that are dispersedly distributed. The precipitates consist of nitrides and carbides containing one or both of Nb and V elements. Preferably, the microstructure of the steel plate may also include granular bainite with a volume percentage not exceeding 25%.

[0018] Furthermore, the steel plate thickness is 25.4–40 mm, with a transverse yield strength of 490–590 MPa, a transverse tensile strength of 710–800 MPa, a transverse yield-to-tensile ratio ≤0.75, an average transverse impact energy ≥240 J at -60℃, an average transverse impact energy ≥150 J in the weld heat-affected zone at -20℃, and a transverse DWTT shear area ≥85% at -45℃; the longitudinal yield strength is 460–570 MPa, the longitudinal tensile strength is 700–780 MPa, the longitudinal yield-to-tensile ratio <0.75, the longitudinal uniform elongation (UEL) ≥10%, and the longitudinal strain hardening index (n) ≥0.11. At 5℃, the CTOD is ≥0.6mm. After aging at 280℃ for 4 hours, the longitudinal yield strength can reach 470~590MPa, the longitudinal tensile strength can reach 710~780MPa, the longitudinal uniform elongation UEL is ≥9%, the longitudinal yield strength ratio is ≤0.76, the longitudinal strain hardening index n is ≥0.10, and the fatigue life meets the requirement of 20,000 cycles under simulated service pressure of 4~12MPa and temperature of -40~50℃ without fatigue failure. The SSCC corrosion resistance meets the requirement of no fracture after immersion in saturated H2S solution for 720 hours under 90% stress loading and no visible cracks under 10x magnification.

[0019] The rationale for the composition design of this invention is as follows:

[0020] C is a fundamental strengthening and phase transformation control element. It can play a role through interstitial solid solution, precipitation by combining with Nb and V, and promoting microstructure transformation at medium and low temperatures. Therefore, it is necessary to ensure the lower limit of C. However, an increase in C will deteriorate plasticity and toughness, leading to an increase in banded structure and segregation. Therefore, in this invention, C is controlled at 0.035% to 0.060%.

[0021] Si acts as a deoxidizer. Since it is necessary to better utilize the precipitation effect of Nb, V and N, this invention adopts a low Al design. Therefore, Si is used to replace Al to play a deoxidizing role. At the same time, it can also play a solid solution strengthening role. However, if its content is too high, it will cause a decrease in toughness, plasticity and weldability. Therefore, the Si range in this invention is 0.15% to 0.50%.

[0022] Mn is an effective and inexpensive strengthening element and is the basic strengthening element in this invention. It can improve hardenability, increase the uniformity of cooling in the thickness direction of thick-walled steel plates, and has a certain grain refinement effect. However, excessive manganese content can easily form hard phase bands, induce central segregation, increase the non-uniformity of the structure, and reduce toughness, weldability and corrosion resistance. Therefore, in this invention, the Mn content is controlled at 1.75% to 1.90%.

[0023] Nitrogen (Nb) is an excellent element for enhancing strength and toughness. During solution treatment, it acts as a solute drag, and during precipitation, it strengthens the grains and inhibits grain growth by refining them. In particular, under appropriate processes, it can form fine Nb (CN) precipitates, which have beneficial effects such as strengthening, refining grains, and reducing aging tendency. However, excessive Nb content will delay the formation of polygonal ferrite, requiring an increase in the heating temperature of the continuously cast billet to ensure the solution treatment effect. This leads to coarse austenite grains, increased energy consumption, and may also worsen weldability and inhibit the formation of V precipitates. Therefore, the Nb content should be controlled between 0.030% and 0.055%.

[0024] V has the effects of solid solution, precipitation, and grain refinement. During the rolling and cooling of pipeline steel, it can promote ferrite nucleation, refine grains, reduce the formation of central hard phase banded structure, improve the uniformity of microstructure of steel plate thickness section, increase hydrogen trapping, and improve acid corrosion resistance. However, excessive V content is detrimental to toughness and weldability. Therefore, in this invention, V is controlled at ≤0.10%.

[0025] Controlling Nb+V between 0.045% and 0.135% ensures the effects of solid solution, fine grains, and phase transformation control. It also makes the precipitated phase fine and dispersed, while improving the economics of product design.

[0026] N: In this invention, N forms fine precipitates with V and Nb, which play a role in strengthening and refining grains. Therefore, N is a key element in this invention, with a content of not less than 0.0040%. However, if the N content is too high, the precipitate will coarsen, toughness will deteriorate, and hard band structure will increase. Therefore, in this invention, the N content is controlled at 0.0040% to 0.012% by combining the addition of Nb, V and other elements.

[0027] Ni can improve low-temperature toughness and strength, prolong the austenite phase transformation, reduce the critical cooling rate, and inhibit the pearlite transformation; it can also reduce Cu embrittlement and improve corrosion resistance. However, on the one hand, Ni is expensive and adding too much affects economic efficiency; on the other hand, Ni will increase the tendency of HIC in low hydrogen pressure environments. Therefore, the Ni content in this invention is controlled at 0.05% to 0.20%.

[0028] Cu can improve strength and corrosion resistance, and increase hardenability, but too high a Cu content is detrimental to toughness and welding. In this invention, the Cu content is controlled at 0.01% to 0.15%.

[0029] Cr can effectively improve tensile strength and is economical; it can increase hardenability, which is beneficial to improving the uniformity of microstructure in the thickness direction. Moreover, it has a weaker inhibition of the transformation of austenite to polygonal ferrite, which is conducive to increasing the "hardness difference" between soft and hard phases in the microstructure, making it easier to control strain and yield strength ratio; at the same time, it is beneficial to improve corrosion resistance. However, excessive Cr content will deteriorate toughness and weldability. In this invention, the Cr content is controlled at 0.15% to 0.50%.

[0030] Mo can promote the refinement of hard phase structure and low-temperature phase transformation, improve hardenability, reduce phase transformation temperature, and refine grains; however, Mo will inhibit ferrite transformation, which is not conducive to the control of multiphase structure and strain properties, and will also lead to increased costs. Therefore, the present invention controls the Mo content to 0.05% to 0.15%.

[0031] Al is a deoxygenating element. Excessive content will promote the increase of inclusions. Moreover, Al will reduce free N and affect the formation of NbN and VN. In this invention, the Al content is controlled at 0.005% to 0.015%.

[0032] Ca can change the composition and morphology of inclusions, improve corrosion resistance, improve toughness and performance uniformity, and is also beneficial to improve weldability. However, excessive Ca content will lead to a decrease in cleanliness. Therefore, the Ca content in this invention is controlled at 0.0020% to 0.0055%.

[0033] Zr can play a role in deoxidation and inclusion control. Zr oxides can achieve a fine and dispersed distribution in molten steel, reducing the harmfulness of inclusions and improving toughness. At the same time, Zr compounds can also promote phase deformation nucleation and refine grains, which is beneficial to improving strength and toughness. In addition, Zr can also provide toughness after welding. However, if the Zr content is too high, the toughness will decrease. Therefore, in this invention, Zr ≤ 0.030%.

[0034] La has a deep purifying effect on molten steel. It has a strong tendency to combine with O and S to form fine, dispersed, and highly stable inclusions, reducing stress concentration and deformation cracking tendency, and effectively improving corrosion resistance. La can also inhibit grain growth and promote microstructure refinement during high-temperature heating and phase transformation, effectively improving low-temperature toughness and weldability. Moreover, La can reduce the diffusion rate of H, increase the density of the corrosion-resistant oxide film on the surface, and thus improve corrosion resistance. However, excessively high La content will reduce the effect of inclusion removal and control, and is also detrimental to economic efficiency. Therefore, this invention controls the La content to ≤0.005%.

[0035] The ratio of (La / 139+Ca / 40) / (S / 32) should be controlled between 2 and 6 to achieve a good additive effect, effectively control sulfur compound inclusions, and improve corrosion resistance.

[0036] Ti can form high-melting-point precipitates, thereby inhibiting grain growth and refining grains, which is beneficial to improving toughness; however, excessive Ti content will inhibit the formation of Nb and V precipitates. In this invention, the Ti content is controlled to be ≤0.010%.

[0037] P and S are harmful impurity elements; P reduces low-temperature toughness, and this invention controls P to ≤0.008%; an increase in S content will promote the formation of S-containing inclusions, leading to a decrease in corrosion resistance, therefore, S≤0.0015%.

[0038] Increased H and O content can lead to decreased toughness, increased inclusions, and reduced corrosion resistance. Therefore, this invention controls H ≤ 0.00015% and O ≤ 0.0015%.

[0039] The second technical solution of the present invention is to provide a production method for 700MPa high-performance pipeline thick steel plate, including smelting, continuous casting, heating, rough rolling, finish rolling and cooling;

[0040] Smelting: including converter smelting and ladle refining

[0041] The converter adopts top and bottom blowing and double slag smelting, with slag blocking during steel tapping. The slag layer thickness is ≤40mm. Lime and fluorite are added in a ratio of 4 / 1 to 5 / 1 to form top slag. The basicity of the refining slag is controlled at 4 to 7, and the weight percentage of FeO + MnO in the slag is controlled to be ≤1%. After refining and deoxidation, Ti, La, and Zr are added in that order. The RH vacuum degree is ≤0.5 torr, and the vacuum treatment time is ≥15 min. After vacuum treatment, nitrogen blowing is carried out according to the N content control requirements of the finished steel plate.

[0042] Converter double-slag smelting and slag-blocking tapping can ensure low-phosphorus steelmaking and reduce phosphorus and sulfur reversion; controlling slag basicity and FeO+MnO in slag can ensure slag reducing capacity and fluidity, fully desulfurize and deoxidize, and reduce inclusions; the order of adding Ti, La and Zr after refining and deoxidation can more effectively improve the element recovery rate; controlling RH vacuum degree and vacuum treatment time can effectively ensure the treatment effect.

[0043] Continuous casting:

[0044] The quenching time before molten steel is loaded onto the casting machine is ≥10 min; the superheating temperature of the continuously cast billet is 5~30℃; the dwell time of molten steel in the tundish during casting is ≥360s; the dynamic light reduction of the billet is ≥5mm; the continuous casting speed control range is 0.6~1.2m / min; the center segregation of the continuously cast billet is ≤C0.5 grade; the center porosity is ≤0.5 grade; and the inclusions of categories A, B, C, and D are ≤1.0 grade.

[0045] Pre-cast steel calming, pouring superheat, and tundish dwell time control can effectively remove inclusions, control segregation, and homogenize steel temperature. Dynamic light reduction and constant casting speed control can reduce segregation, decrease crystallizer surface fluctuations, reduce defect generation tendency, and effectively improve billet quality. Control of center segregation, center porosity, and inclusions can effectively improve service performance such as corrosion resistance.

[0046] heating:

[0047] The continuously cast billet undergoes multi-stage heating, including preheating, heating stage 1, heating stage 2, heating stage 3, and soaking. The average heating rate in heating stages 1 and 2 is 4–12℃ / min, the average heating rate in heating stage 3 is 2–6℃ / min, and the average heating rate in the soaking stage is 0.1–0.7℃ / min. The total heating time is 0.9 min / mm–1.6 min / mm, the tapping temperature is 1100–1150℃, and the temperature difference across the thickness section is ≤30℃. The multi-stage heating and control of the total heating time improve heating efficiency. The relatively low tapping temperature inhibits austenite grain growth and allows the main alloying elements to dissolve, while Nb precipitates remain in a partially dissolved state, further preventing grain growth. Controlling the temperature difference across the thickness section ensures heating uniformity.

[0048] Rough rolling:

[0049] Before roughing, 2-4 passes of high-pressure water descaling and cooling are performed, with an average cooling rate of 0.5-2℃ / s. Roughing consists of two stages, with each rolling pass undergoing spray cooling. The end temperature of the first stage roughing is 1050-1080℃, and the end temperature of the second stage roughing is 950-1020℃. In the second stage of roughing, each pass is sprayed with descaling water from the mill, and the total deformation rate is ≥35%, with a deformation rate of 16%-20% per pass. A high-low-high cycle is used for the variable passes, and the roughing rolling speed is 1.0m / s-1.8m / s. Preferably, rapid water cooling is performed between the two stages of roughing, with an average cooling rate of 2-6℃ / s and a cooling time of 10-45s. High-pressure water descaling and cooling before rough rolling can remove the scale generated during heating. At the same time, it lowers the billet temperature and increases the temperature gradient of the thickness section, which is beneficial for low-temperature rough rolling and deformation penetration. The second stage of rough rolling, which combines rapid water cooling before rolling, low-temperature rolling, and process spray cooling, can achieve low-temperature rolling and high-penetration deformation of the thickness section, improving production efficiency. At the same time, it suppresses the tendency of recrystallized austenite growth. Combined with the deformation rate and low-speed rolling in the second stage of rough rolling, it can achieve beneficial effects such as refining the microstructure near the thickness center and improving the uniformity of microstructure properties. The use of high-low-high cycle pass variables in the second stage of rough rolling helps to reduce the risk of increased rolling passes and reduced pass deformation rate caused by the difference between the actual rolling torque and the controlled simulation torque in the low-temperature rolling stage, ensuring the realization of the low-temperature + high pass deformation rate process.

[0050] Finishing rolling:

[0051] The finishing rolling process consists of two stages. The first stage starts at a temperature of 800–870°C and ends at 760–800°C. Then, after a 30–80 second warming period, the second stage of finishing rolling begins, ending at 730–760°C. The deformation rate during the finishing rolling stage is 60%–75%. Preferably, after rough rolling, the billet is rapidly cooled to 20–60°C above the starting temperature of the finishing rolling process, with an average cooling rate of 2–12°C / s, and then allowed to warm up to the starting temperature of the finishing rolling process.

[0052] The deformation rate in the finishing rolling stage ensures sufficient deformation of austenite in the finishing rolling zone, increasing deformation energy and nucleation sites, and refining grains; rapid cooling of the intermediate warming billet can effectively suppress austenite growth in the high-temperature zone; the finishing rolling stage adopts a two-stage + intermediate warming + second-stage low-temperature two-phase zone rolling, which on the one hand can promote the precipitation of carbonitrides such as Nb and V, playing a role in strengthening, refining grains, and pinning; on the other hand, it can obtain a sufficient proportion of polygonal ferrite, improving plasticity, toughness and strain performance.

[0053] cool down:

[0054] After rolling, the steel plates undergo two-stage cooling after pre-straightening. The initial water cooling temperature is 700–730℃, and the final water cooling temperature at the top of the steel plate is 160–280℃. During water cooling, the water flow rate in the first 5–7 groups of upper manifolds is 350 L / m. 2 *min~550L / m 2 *min, the remaining upper manifold water flow rate is 180L / m 2 *min~300L / m 2 *min, the water-cooling system roller conveyor first decelerates and then accelerates, with a deceleration rate of 0.01–0.05 m / s. The deceleration transition point is at the head of the steel plate exiting the cooling system. The final cooling temperature gradually decreases along the length of the steel plate, with the head of the steel plate having an average final cooling temperature 20–60°C higher than the tail. Post-rolling pre-straightening helps improve the cooling uniformity of the steel plate; controlling the start and end temperatures of water cooling ensures the acquisition of ideal microstructure and substructure; two-stage cooling can suppress high-temperature phase transformation and refine the hard phase structure, while also reducing internal stress, which is beneficial for plate shape control. The temperature difference control between the head and tail of the steel plate corresponds to the difference in water cooling at different positions of the steel plate, which helps improve performance uniformity.

[0055] The beneficial effects of this invention are as follows:

[0056] (1) The composition of this invention uses C, Mn, and Cr as the basic strengthening elements to ensure strength; by adding elements such as La, Zr, and Ca to control the inclusions, the effects of removing S and O are increased, the number and size of inclusions are reduced, and they are made more uniformly distributed. At the same time, they play the role of nucleation particles and grain refinement. Combined with ultra-low P, S, H, and O content and continuous casting billet quality control, the toughness and corrosion resistance are effectively improved. By adding Nb and V in combination, appropriately controlling N and reducing the addition of Ti and Al, Nb and V are promoted to play the role of microalloy solid solution, precipitation and grain refinement, which improves strength, aging resistance and weldability and plays a certain role of hydrogen trapping, thus improving corrosion resistance. The addition of a small amount of Ni and Cu balances the improvement of strength and corrosion resistance.

[0057] (2) This invention creatively proposes a production process such as smelting, heating, rolling and cooling to obtain high strength, high uniform elongation, low temperature toughness, high strain, as well as corrosion resistance, aging resistance and fatigue resistance and ideal microstructure, so as to meet the requirements of high performance pipelines in complex conditions.

[0058] (3) The present invention adopts production methods such as high-purity smelting, high-homogeneity heating, two-stage low-temperature rolling of roughing + high-penetration deformation of thickness section, rapid cooling of intermediate waiting billet, two-stage finishing rolling + intermediate waiting + second-stage low-temperature two-phase region rolling and differentiated water cooling to obtain fine bainitic ferrite + polygonal ferrite, and may also include a microstructure of granular bainite with a volume percentage not exceeding 25% and small-sized precipitates dispersedly, so that the steel plate has good comprehensive performance.

[0059] (3) The thick steel plate with a width of 1200-4370mm used for high-performance pipelines operating under complex conditions described in this invention has a thickness of 25.4-40mm, a transverse yield strength of 490-590MPa, a transverse tensile strength of 710-800MPa, a transverse yield-to-tensile ratio ≤0.75, an average transverse impact energy of ≥240J at -60℃, an average transverse impact energy of ≥150J at -20℃ in the weld heat-affected zone, and a transverse DWTT shear area of ​​≥85% at -45℃; a longitudinal yield strength of 460-570MPa, a longitudinal tensile strength of 700-780MPa, a longitudinal yield-to-tensile ratio <0.75, and a longitudinal uniform elongation UEL ≥1. 0%, longitudinal strain hardening index n≥0.11, CTOD≥0.6mm at -45℃, after aging at 280℃ for 4h, the longitudinal yield strength can reach 470~590MPa, the longitudinal tensile strength can reach 710~780MPa, the longitudinal uniform elongation UEL≥9%, the longitudinal yield strength ratio≤0.76, the longitudinal strain hardening index n≥0.10, the fatigue life meets the requirement of 20000 cycles under simulated service pressure of 4~12MPa and temperature of -40~50℃ without fatigue failure, and the SSCC corrosion resistance meets the requirement of no fracture after 720 hours of saturated H2S solution immersion under 90% stress loading and no visible cracks under 10x magnification. Attached Figure Description

[0060] Figure 1 This is a metallographic image of the microstructure of Example 2 of the present invention. Detailed Implementation

[0061] The present invention will be further illustrated below through examples.

[0062] A 700MPa high-performance pipeline thick steel plate, characterized in that the steel plate's composition by weight percentage is as follows: C: 0.035%~0.060%, Si: 0.15%~0.50%, Mn: 1.75%~1.90%, Nb: 0.030%~0.055%, V≤0.10%, N: 0.0040%~0.012%, Ni: 0.05%~0.20%, Cu: 0.01%~0. 0.15%, Cr: 0.15%~0.50%, Mo: 0.05%~0.15%, Al: 0.005%~0.015%, Ca: 0.0020%~0.0055%, Zr≤0.003%, La≤0.005%, Ti≤0.010%, P≤0.008%, S≤0.0015%, H≤0.00015%, O≤0.0015%, with the balance being iron and unavoidable impurities.

[0063] Furthermore, in steel plates (Nb+V): 0.045%~0.135%.

[0064] Furthermore; in the steel plate, (La / 139+Ca / 40) / (S / 32): 2~6.

[0065] Furthermore, the microstructure of the steel plate consists of bainitic ferrite and polygonal ferrite, wherein the volume percentage of polygonal ferrite is 15%–75%, and the average grain cross-sectional area of ​​polygonal ferrite is ≤85μm. 2 The matrix contains fine precipitates with a size ≤30nm that are diffusely distributed. The precipitates are composed of nitrides and carbides containing one or both of Nb and V elements.

[0066] Furthermore, the microstructure of the steel plate may also include granular bainite with a volume percentage not exceeding 25%.

[0067] Furthermore; steel plate thickness 25.4–40 mm, transverse yield strength 490–590 MPa, transverse tensile strength 710–800 MPa, transverse yield-to-tensile ratio ≤0.75, average transverse impact energy at -60℃ ≥240 J, average transverse impact energy in the weld heat-affected zone at -20℃ ≥150 J, transverse DWTT shear area at -45℃ ≥85%; longitudinal yield strength 460–570 MPa, longitudinal tensile strength reaching 700–780 MPa, longitudinal yield-to-tensile ratio <0.75, longitudinal uniform elongation UEL ≥10%, longitudinal strain hardening index n ≥0.11, -45℃ At ℃, CTOD≥0.6mm, after aging at 280℃ for 4h, longitudinal yield strength 470~590MPa, longitudinal tensile strength 710~780MPa, longitudinal uniform elongation UEL≥9%, longitudinal yield strength ratio≤0.76, longitudinal strain hardening index n≥0.10, fatigue life meets the requirement of 20000 cycles within the simulated service pressure range of 4~12MPa and temperature range of -40~50℃ without fatigue failure, and SSCC corrosion resistance meets the requirement of no fracture after 720 hours of saturated H2S solution immersion under 90% stress loading and no visible cracks under 10x magnification.

[0068] A method for producing 700MPa high-performance pipeline thick steel plates includes smelting, continuous casting, heating, rough rolling, finish rolling, and cooling.

[0069] heating:

[0070] The continuously cast billet adopts a multi-stage heating process, including preheating, heating stage 1, heating stage 2, heating stage 3, and soaking. The average heating rate of heating stage 1 and heating stage 2 is 4-12℃ / min, the average heating rate of heating stage 3 is 2-6℃ / min, the average heating rate of soaking stage is 0.1-0.7℃ / min, the total heating time is 0.9min / mm-1.6min / mm, the furnace exit temperature is 1100-1150℃, and the temperature difference of the thickness section is ≤30℃.

[0071] Rough rolling:

[0072] Before roughing, 2 to 4 passes of high-pressure water descaling and cooling are performed, with an average cooling rate of 0.5 to 2℃ / s. Roughing consists of two stages, with each rolling pass undergoing spray cooling. The end temperature of the first stage of roughing is 1050 to 1080℃, and the end temperature of the second stage is 950 to 1020℃. The total deformation rate of the second stage of roughing is ≥35%, with a deformation rate of 16% to 20% per pass and a high-low-high cycle of variable passes. The rolling speed of roughing is 1.0 m / s to 1.8 m / s.

[0073] Finishing rolling:

[0074] The finishing rolling process consists of two stages. The initial rolling temperature of the first finishing rolling stage is 800–870℃, and the final rolling temperature of the first finishing rolling stage is 760–800℃. Then, after a 30–80 second warming period, the second finishing rolling stage begins, with a final rolling temperature of 730–760℃. The deformation rate of the finishing rolling stage is 60%–75%.

[0075] cool down:

[0076] After rolling, the steel plate undergoes pre-straightening and two-stage cooling. The initial water cooling temperature is 700–730℃, and the final water cooling temperature at the top of the steel plate is 160–280℃. During water cooling, the water flow rate of the first 5–7 sets of upper manifolds is 350 L / m. 2 ˙min~550L / m 2 The remaining water flow rate in the upper manifold is 180–300 L / m. 2 ·min, the water-cooled system roller conveyor first decelerates and then accelerates, with an acceleration / deceleration rate of 0.01~0.05m / s. The acceleration / deceleration transition point is the head of the steel plate exiting the cooling system. The final cooling temperature along the length of the steel plate gradually decreases. The average final cooling temperature at the head of the steel plate is 20~60℃ higher than that at the tail.

[0077] Further; smelting: including converter smelting and ladle refining;

[0078] The converter adopts top and bottom blowing and double slag smelting, with slag blocking during steel tapping. The slag layer thickness is ≤40mm. Lime and fluorite are added in a ratio of 4 / 1 to 5 / 1 to form top slag. The basicity of the refining slag is controlled at 4 to 7, and the weight percentage of FeO + MnO in the slag is controlled to be ≤1%. After refining and deoxidation, Ti, La, and Zr are added in the order of Ti, La, and Zr. The RH vacuum degree is ≤0.5 torr, and the vacuum treatment time is ≥15 min. After vacuum treatment, nitrogen blowing is carried out according to the N content control requirements of the finished steel plate.

[0079] Continuous casting:

[0080] The molten steel should be cooled for at least 10 minutes before being poured onto the casting machine. The superheating temperature of the continuously cast billet should be 5-30°C. The dwell time of the molten steel in the tundish during pouring should be at least 360 seconds. The dynamic light reduction of the billet should be at least 5 mm. The continuous casting speed should be at least 0.6-1.2 m / min. The center segregation of the continuously cast billet should be at least grade C0.5. The center porosity should be at least grade 0.5. The inclusions of types A, B, C, and D should be at least grade 1.0.

[0081] Furthermore, rapid water cooling is applied between the two stages of rough rolling, with an average cooling rate of 2–6 °C / s and a cooling time of 10–45 s.

[0082] Furthermore, after rough rolling, the intermediate billet is rapidly cooled to 20-60°C above the starting temperature of the first stage of finishing rolling, with an average cooling rate of 2-12°C / s, and then cooled to the starting temperature of the first stage of finishing rolling.

[0083] According to the component ratio of the technical solution, the present invention involves smelting, continuous casting, heating, rough rolling, finish rolling, and cooling. The composition of the steel in the present invention is shown in Table 1. The main process parameters for smelting the steel in the present invention are shown in Table 2. The main process parameters for continuous casting of the steel in the present invention are shown in Table 3. The main process parameters for heating the steel in the present invention are shown in Table 4. The main process parameters for rough rolling of the steel in the present invention are shown in Table 5. The main process parameters for finish rolling of the steel in the present invention are shown in Table 6. The main process parameters for cooling the steel in the present invention are shown in Table 7. The microstructure of the steel in the present invention is shown in Table 8. The mechanical properties of the steel in the present invention are shown in Table 9. The longitudinal tensile properties after aging are shown in Table 10. The fatigue resistance and corrosion resistance of the steel in the present invention are shown in Table 11.

[0084] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0085] Example C Si Mn Nb V Nb+V N Ni 1 0.045 0.28 1.79 0.042 0.062 0.104 0.0061 0.14 2 0.056 0.19 1.76 0.038 0.077 0.115 0.0070 0.08 3 0.049 0.41 1.82 0.033 0.036 0.069 0.0059 0.16 4 0.036 0.34 1.81 0.049 0.047 0.096 0.0065 0.07 5 0.053 0.26 1.77 0.053 0 0.053 0.0062 0.12 6 0.046 0.33 1.75 0.044 0.066 0.110 0.0093 0.17 7 0.051 0.46 1.77 0.039 0.055 0.094 0.0057 0.18 8 0.054 0.29 1.84 0.048 0.073 0.121 0.0076 0.08 9 0.048 0.31 1.79 0.035 0 0.035 0.0058 0.15 10 0.055 0.26 1.82 0.044 0.065 0.109 0.0070 0.11 Example Cu Cr Mo Al Ca Zr La Ti 1 0.12 0.27 0.07 0.011 0.0029 0.0018 0.0021 0.006 2 0.13 0.36 0.09 0.008 0.0041 0 0 0.008 3 0.07 0.19 0.12 0.012 0.0025 0.0020 0.0016 0.006 4 0.09 0.38 0.09 0.009 0.0045 0 0.0032 0 5 0.06 0.28 0.13 0.008 0.0026 0.0024 0.0019 0.007 6 0.07 0.26 0.08 0.013 0.0030 0.0015 0.0024 0.008 7 0.09 0.22 0.12 0.007 0.0036 0.0025 0 0 8 0.14 0.39 0.06 0.009 0.0039 0.0016 0.0022 0.008 9 0.11 0.28 0.10 0.008 0.0035 0.0022 0.0031 0.007 10 0.08 0.31 0.13 0.011 0.0021 0.0015 0 0.009 Example P S H O <![CDATA[CE IIW ]]> <![CDATA[CE Pcm ]]> A - 1 0.006 0.0012 0.00010 0.0012 0.441 0.177 2.3 - 2 0.005 0.0010 0.00012 0.0013 0.469 0.190 5.2 - 3 0.006 0.0010 0.00009 0.0010 0.437 0.181 3.0 - 4 0.006 0.0013 0.00010 0.0015 0.452 0.173 5.0 - 5 0.007 0.0010 0.00011 0.0010 0.442 0.178 2.7 - 6 0.006 0.0010 0.00009 0.0012 0.435 0.176 3.7 - 7 0.005 0.0011 0.00010 0.0012 0.443 0.187 4.6 - 8 0.007 0.0013 0.00011 0.0014 0.480 0.195 3.9 - 9 0.007 0.0012 0.00010 0.0011 0.440 0.177 4.3 - 10 0.006 0.0015 0.00009 0.0014 0.472 0.191 1.8 -

[0086] Note: A = (La / 139 + Ca / 40) / (S / 32)

[0087] Table 2 Main process parameters for steelmaking in the embodiments of the present invention

[0088] Example Top slag limestone / fluorite slag alkalinity FeO + MnO weight percentage in slag / % RH vacuum degree / torr Vacuum processing time / min 1 4.2 5.0 0.91 0.4 18 2 4.6 5.8 0.86 0.3 23 3 4.1 4.8 0.95 0.5 16 4 4.2 4.9 0.90 0.4 19 5 4.5 5.6 0.82 0.5 25 6 4.1 4.5 0.92 0.4 21 7 4.7 5.6 0.91 0.3 20 8 4.6 6.1 0.87 0.5 16 9 4.5 5.3 0.89 0.5 18 10 4.2 4.7 0.83 0.4 22

[0089] Table 3 Main process parameters for continuous steel casting in the embodiments of the present invention.

[0090] Example Pre-cure time for molten steel / min Casting superheat / °C Intermediate package dwell time / s Dynamic reduction in continuous casting / mm Continuous casting billet casting speed / m / min Center segregation / grade of continuously cast billet Porosity at the center of continuously cast billet / grade The highest level of inclusions is classified as A, B, C, and D. 1 19 9 386 5.8 0.80 C0.5 0.5 1.0 2 14 23 399 5.2 0.80 C0.5 0.5 1.0 3 20 15 382 5.5 0.80 C0.5 0.5 1.0 4 18 16 387 5.7 0.80 C0.5 0 0.5 5 13 19 408 5.3 0.90 C0.5 0 1.0 6 16 20 395 6.0 0.90 C0.5 0.5 1.0 7 18 18 402 5.1 0.90 C0.5 0 0.5 8 21 12 390 5.3 0.90 C0.5 0 1.0 9 18 24 406 5.5 0.80 C0.5 0.5 1.0 10 15 21 392 5.3 0.90 C0.5 0.5 1.0

[0091] Table 4 Main process parameters for steel heating in embodiments of the present invention

[0092] Example Average heating rate in heating stages 1 and 2 / °C / min Average heating rate in three stages / °C / min Average heating rate of the soaking section / °C / min Total heating time / min / mm Furnace temperature / ℃ Thickness section temperature difference / ℃ 1 7.5 3.8 0.42 1.3 1138 25 2 6.3 4.5 0.30 1.5 1118 21 3 9.1 4.2 0.56 1.0 1123 27 4 6.9 2.8 0.25 1.5 1132 16 5 8.0 5.3 0.28 1.3 1145 20 6 7.2 5.5 0.14 1.2 1129 21 7 10.3 2.9 0.26 1.0 1130 18 8 6.8 4.9 0.35 1.2 1142 16 9 6.0 4.7 0.32 1.5 1146 18 10 8.8 3.0 0.45 1.2 1137 22

[0093] Table 5 Main process parameters for steel roughing in embodiments of the present invention

[0094] Example Number of high-pressure water descaling and cooling passes Average cooling rate of high-pressure water dephosphorization / ℃ / s First-stage roughing finishing temperature / ℃ Second-stage roughing finishing temperature / ℃ Average cooling rate of rapid water cooling between the two stages / ℃ / s Rapid water cooling time between two stages / s Total deformation rate in the second stage of rough rolling / % Deformation rate per pass in the second stage of rough rolling / % Roughing rolling speed / m / s 1 3 0.9 1065 983 2 29 47 16～19 1.5 2 2 0.6 1053 988 3.2 13 50 16～20 1.5 3 2 0.7 1065 990 4.0 12 45 18～19 1.5 4 3 1.1 1059 975 2.3 22 48 17～20 1.5 5 4 1.4 1068 962 2 35 42 16～19 1.0 6 3 1.2 1060 983 2.1 25 39 18～19 1.0 7 2 0.8 1067 1002 2.3 21 38 16～20 1.0 8 4 1.5 1072 1005 2.2 24 40 17～19 1.0 9 3 1.0 1067 992 3 18 48 17～19 1.5 10 4 1.3 1070 984 2.6 23 40 16～20 1.0

[0095] Table 6 Main process parameters for steel finishing in embodiments of the present invention

[0096] Example Deformation rate during finishing rolling stage / % Termination temperature of rapid cooling of intermediate preform at ℃ Intermediate billet temperature - first-stage finishing rolling temperature / ℃ Average cooling rate / ℃ / s First-stage finishing rolling temperature / ℃ First-stage finishing rolling temperature / ℃ Intermediate waiting time / s Two-stage finishing rolling temperature / ℃ 1 73 906 50 3.9 856 786 56 743 2 71 892 44 5.2 848 782 43 745 3 75 895 40 4.0 855 791 65 751 4 70 884 32 3.6 852 788 55 749 5 64 860 39 4.8 821 775 40 738 6 66 858 30 7.5 828 780 52 732 7 67 872 47 9.6 825 779 36 740 8 64 866 36 11.4 830 783 47 743 9 71 890 39 7.0 851 785 41 748 10 65 871 48 8.3 823 776 32 742

[0097] Table 7 Main process parameters for steel cooling in embodiments of the present invention

[0098] Example Initial water cooling temperature / °C Water-cooled steel plate head temperature / ℃ Water flow rate of the first 5-7 groups of upper manifolds / L / m2 * min Other water volume in the upper manifold / L / m2 * min Average final cooling temperature difference from head to tail along length (°C) 1 715 188 7 groups 430 280 28 2 719 225 7 groups 380 260 42 3 721 196 6 groups 490 250 25 4 711 220 5 groups 480 230 36 5 705 186 6 groups 520 280 28 6 707 198 7 groups 550 220 35 7 716 182 7 groups 490 290 30 8 712 207 6 groups 530 260 39 9 719 173 7 groups 520 230 31 10 710 215 5 groups 530 280 42

[0099] Table 8. Microstructure of steel in the embodiments of the present invention

[0100] Example Polygonal ferrite volume percentage / % Granular bainite volume percentage / % Average grain cross-sectional area of ​​polygonal ferrite / μm2 Plate thickness / mm 1 41 12 70 27.5 2 32 23 62 27.5 3 26 10 55 27.5 4 55 18 73 27.5 5 62 8 81 33 6 67 15 75 33 7 43 9 60 33 8 52 20 68 33 9 39 3 96 27.5 10 58 21 84 33

[0101] Table 9 Mechanical properties of steel in the embodiments of the present invention

[0102] Example - Direction Rt0.5 / MPa Rm / MPa Rt0.5 / Rm UEL / % Steel plate KV-60℃ave / J Welding hot zone KV-20℃ave / J DWTTSA-35℃ave / % CTOD-45℃ave / mm n 1-Horizontal 550 755 0.73 -- 306 215 89 -- -- 1-Vertical 525 730 0.72 12.0 -- -- -- 0.79 0.12 2-Horizontal 580 770 0.75 -- 287 203 86 -- -- 2-Vertical 550 755 0.73 11.0 -- -- -- 0.85 0.11 3-Horizontal 550 740 0.74 -- 295 197 90 -- -- 3-Vertical 535 720 0.74 11.5 -- -- -- 0.81 0.11 4-Horizontal 535 750 0.71 -- 303 220 90 -- -- 4-Vertical 510 725 0.70 12.5 -- -- -- 0.88 0.12 5-Horizontal 525 740 0.71 -- 276 205 89 -- -- 5-Vertical 495 725 0.68 13.5 -- -- -- 0.76 0.13 6-Horizontal 510 725 0.70 -- 285 212 87 -- -- 6-Vertical 475 705 0.67 13.5 -- -- -- 0.82 0.12 7-Horizontal 545 750 0.73 -- 296 226 88 -- -- 7-Vertical 510 730 0.70 12.0 -- -- -- 0.78 0.11 8-Horizontal 540 775 0.70 -- 277 209 85 -- -- 8-Vertical 515 745 0.69 12.0 -- -- -- 0.88 0.11 9-Horizontal 540 750 0.72 -- 226 168 85 -- -- 9-Vertical 510 715 0.71 11.5 -- -- -- 0.58 0.11 10-Horizontal 530 760 0.70 -- 249 172 85 -- -- 10-Vertical 510 735 0.69 12.5 -- -- -- 0.67 0.11

[0103] Note: The tensile specimen is a full-thickness rectangular specimen with a parallel test section width of 38.1 mm; the impact specimen size is 10*55*55 mm.

[0104] Table 10. Longitudinal tensile properties of steel after aging according to embodiments of the present invention.

[0105] Example Rt0.5 / MPa Rm / MPa Rt0.5 / Rm UEL / % n 1 540 735 0.73 11.0 0.12 2 555 750 0.74 10.5 0.10 3 535 730 0.73 11.0 0.11 4 520 730 0.71 11.5 0.11 5 510 725 0.70 12 0.12 6 495 715 0.69 12.5 0.12 7 520 725 0.72 10.5 0.10 8 530 750 0.71 11 0.11 9 520 710 0.73 10 0.10 10 525 735 0.71 11 0.10

[0106] Note: The aging process involves holding at 280℃ for 4 hours.

[0107] Table 11 Fatigue resistance and corrosion resistance of the steel of this invention

[0108] Example fatigue test Anti-SSCC test 1 qualified qualified 2 qualified qualified 3 qualified qualified 4 qualified qualified 5 qualified qualified 6 qualified qualified 7 qualified qualified 8 qualified qualified 9 qualified qualified 10 qualified qualified

[0109] Fatigue test: 20,000 fatigue cycles were performed under simulated service pressure of 4–12 MPa and temperature of -40–50 °C. SSCC resistance test: No fracture occurred after immersion in saturated H2S solution (solution A) for 720 hours under 90% stress loading; no visible cracks were observed at 10x magnification.

[0110] The steel plates produced using this invention have a thickness of 25.4–40 mm, a transverse yield strength of 490–590 MPa, a transverse tensile strength of 710–800 MPa, a transverse yield-to-tensile ratio ≤0.75, an average transverse impact energy ≥240 J at -60℃, an average transverse impact energy ≥150 J in the weld heat-affected zone at -20℃, and a transverse DWTT shear area ≥85% at -45℃; a longitudinal yield strength of 460–570 MPa, a longitudinal tensile strength of 700–780 MPa, a longitudinal yield-to-tensile ratio <0.75, a longitudinal uniform elongation (UEL) ≥10%, and a longitudinal strain hardening index (n) ≥0.11. At 5℃, the CTOD is ≥0.6mm. After aging at 280℃ for 4 hours, the longitudinal yield strength is 470~590MPa, the longitudinal tensile strength is 710~780MPa, the longitudinal uniform elongation UEL is ≥9%, the longitudinal yield ratio is ≤0.76, the longitudinal strain hardening index n is ≥0.10, and the fatigue life meets the requirement of 20,000 cycles under simulated service pressure of 4~12MPa and temperature of -40~50℃ without fatigue failure. The SSCC corrosion resistance meets the requirement of no fracture after 720 hours of immersion in saturated H2S solution under 90% stress loading and no visible cracks under 10x magnification. The microstructure of the steel plate is bainitic ferrite + polygonal ferrite, of which the volume percentage of polygonal ferrite is 15%~75%, and the average grain cross-sectional area of ​​polygonal ferrite is ≤85μm. 2 The matrix contains fine precipitates with a size ≤30nm that are diffusely distributed. The precipitates are composed of nitrides and carbides containing one or both of Nb and V elements.

[0111] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A 700MPa high-performance pipeline wide and thick steel plate, characterized in that, The composition of the steel plate, by weight percentage, is as follows: C: 0.035%–0.060%, Si: 0.15%–0.50%, Mn: 1.81%–1.90%, Nb: 0.038%–0.055%, V≤0.10%, N: 0.0040%–0.012%, Ni: 0.05%–0.20%, Cu: 0.01%–0.15%, Cr: 0.15%–0.50%, Mo: 0.05%–0.15%, Al: 0.00 5%~0.015%, Ca: 0.0020%~0.0055%, Zr≤0.003%, La≤0.005%, Ti≤0.010%, P≤0.008%, S≤0.0015%, H≤0.00015%, O≤0.0015%, with the balance being iron and unavoidable impurities; steel plate thickness 25.4~40mm, transverse yield strength 490~590MPa, transverse tensile strength 710~800MPa, transverse yield ratio ≤0.

75. The average transverse impact energy at -60℃ is ≥240J, and the average transverse impact energy at -20℃ in the weld heat-affected zone is ≥150J. The transverse DWTT shear area at -45℃ is ≥85%. The longitudinal yield strength is 460~570MPa, the longitudinal tensile strength is 700~780MPa, the longitudinal yield ratio is <0.75, the longitudinal uniform elongation UEL is ≥10%, the longitudinal strain hardening index n is ≥0.11, and the CTOD at -45℃ is ≥0.6mm. After aging at 280℃ for 4 hours, the longitudinal yield strength is... 470~590MPa, longitudinal tensile strength 710~780MPa, longitudinal uniform elongation UEL≥9%, longitudinal yield ratio≤0.76, longitudinal strain hardening index n≥0.10, fatigue life meets the requirement of 20,000 cycles within the simulated service pressure range of 4~12MPa and temperature range of -40~50℃ without fatigue failure, and SSCC corrosion resistance meets the requirement of no fracture after 720 hours of saturated H2S solution immersion under 90% stress loading and no visible cracks under 10x magnification.

2. The 700MPa high-performance pipeline thick steel plate according to claim 1, characterized in that, In steel plates, (Nb+V): 0.045%~0.135%.

3. The 700MPa high-performance pipeline thick steel plate according to claim 1, characterized in that, In steel plates, (La / 139+Ca / 40) / (S / 32): 2~6.

4. The 700MPa high-performance pipeline thick steel plate according to claim 1, characterized in that, The microstructure of the steel plate consists of bainitic ferrite and polygonal ferrite, with polygonal ferrite comprising 15%–75% by volume and an average grain cross-sectional area ≤85μm. 2 The matrix contains fine precipitates with a size ≤30nm that are diffusely distributed. The precipitates are composed of nitrides and carbides containing one or both of Nb and V elements.

5. The 700MPa high-performance pipeline thick steel plate according to claim 1, characterized in that, The microstructure of the steel plate also includes granular bainite, which accounts for no more than 25% of the volume.

6. A method for producing a 700MPa high-performance pipeline thick steel plate as described in any one of claims 1-5, comprising smelting, continuous casting, heating, rough rolling, finish rolling, and cooling; characterized in that: heating: The continuously cast billet adopts a multi-stage heating process, including preheating, heating stage 1, heating stage 2, heating stage 3, and soaking. The average heating rate of heating stage 1 and heating stage 2 is 4-12℃ / min, the average heating rate of heating stage 3 is 2-6℃ / min, the average heating rate of soaking stage is 0.1-0.7℃ / min, the total heating time is 0.9min / mm-1.6min / mm, the furnace exit temperature is 1100-1150℃, and the temperature difference of the thickness section is ≤30℃. Rough rolling: Before roughing, 2 to 4 passes of high-pressure water descaling and cooling are performed, with an average cooling rate of 0.5 to 2℃ / s. Roughing consists of two stages, with each rolling pass undergoing spray cooling. The end temperature of the first stage of roughing is 1050 to 1080℃, and the end temperature of the second stage is 950 to 1020℃. The total deformation rate of the second stage of roughing is ≥35%, with a deformation rate of 16% to 20% per pass and a high-low-high cycle of variable passes. The rolling speed of roughing is 1.0 m / s to 1.8 m / s. Finishing rolling: The finishing rolling process consists of two stages. The initial rolling temperature of the first finishing rolling stage is 800–870℃, and the final rolling temperature of the first finishing rolling stage is 760–800℃. Then, after a 30–80 second warming period, the second finishing rolling stage begins, with a final rolling temperature of 730–760℃. The deformation rate of the finishing rolling stage is 60%–75%. cool down: After rolling, the steel plate undergoes pre-straightening and two-stage cooling. The initial water cooling temperature is 700–730℃, and the final water cooling temperature at the top of the steel plate is 160–280℃. During water cooling, the water flow rate of the first 5–7 sets of upper manifolds is 350 L / m. 2 ˙min~550L / m 2 The remaining water flow rate in the upper manifold is 180–300 L / m. 2 ·min, the water-cooled system roller conveyor first decelerates and then accelerates, with an acceleration / deceleration rate of 0.01~0.05m / s. The acceleration / deceleration transition point is the head of the steel plate exiting the cooling system. The final cooling temperature along the length of the steel plate gradually decreases. The average final cooling temperature at the head of the steel plate is 20~60℃ higher than that at the tail.

7. The method for producing 700MPa high-performance pipeline thick steel plates according to claim 6, characterized in that: Smelting: including converter smelting and ladle refining; The converter adopts top and bottom blowing and double slag smelting, with slag blocking during steel tapping. The slag layer thickness is ≤40mm. Lime and fluorite are added in a ratio of 4 / 1 to 5 / 1 to form top slag. The basicity of the refining slag is controlled at 4 to 7, and the weight percentage of FeO + MnO in the slag is controlled to be ≤1%. After refining and deoxidation, Ti, La, and Zr are added in the order of Ti, La, and Zr. The RH vacuum degree is ≤0.5 torr, and the vacuum treatment time is ≥15 min. After vacuum treatment, nitrogen blowing is carried out according to the N content control requirements of the finished steel plate. Continuous casting: The molten steel should be cooled for at least 10 minutes before being poured onto the casting machine. The superheating temperature of the continuously cast billet should be 5-30°C. The dwell time of the molten steel in the tundish during pouring should be at least 360 seconds. The dynamic light reduction of the billet should be at least 5 mm. The continuous casting speed should be at least 0.6-1.2 m / min. The center segregation of the continuously cast billet should be at least grade C0.

5. The center porosity should be at least grade 0.

5. The inclusions of types A, B, C, and D should be at least grade 1.

0.

8. The method for producing 700MPa high-performance pipeline thick steel plates according to claim 6, characterized in that: Rapid water cooling is applied between the two stages of rough rolling, with an average cooling rate of 2–6℃ / s and a cooling time of 10–45s.

9. The method for producing 700MPa high-performance pipeline thick steel plates according to claim 6, characterized in that: After rough rolling, the intermediate billet is rapidly cooled to 20-60°C above the first stage rolling temperature of finishing rolling, with an average cooling rate of 2-12°C / s. Then, it is allowed to warm up to the first stage rolling temperature of finishing rolling.

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