550MPa High-Performance Pipeline Thick Steel Plate and Its Production Method

Abstract

This invention belongs to the field of metallic materials and provides a 550MPa high-performance thick steel plate for pipelines and its production method. The composition of the steel plate, by weight percentage, is as follows: C: 0.035%~0.065%, Si: 0.15%~0.50%, Mn: 1.45%~1.59%, Nb: 0.025%~0.045%, V≤0.06%, N: 0.0040%~0.008%, Ni: 0.05 The composition is as follows: Cu ≤ 0.15%, Cr ≤ 0.05%–0.20%, Al ≤ 0.005%–0.015%, Ca ≤ 0.0020%–0.0045%, Zr ≤ 0.003%, La ≤ 0.004%, Ti ≤ 0.010%, P ≤ 0.008%, S ≤ 0.0015%, H ≤ 0.00015%, O ≤ 0.0015%, with the balance being iron and unavoidable impurities. Based on the composition design of this invention, a production method employing high homogenization heating, two-stage low-temperature roughing rolling + high-penetration deformation of the thickness section, rapid cooling of the intermediate waiting billet, two-stage finishing rolling + intermediate waiting + second-stage low-temperature two-phase region rolling, and differentiated water cooling was used to obtain fine bainitic ferrite + polygonal ferrite, giving the steel plate excellent comprehensive properties.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and particularly relates to a 550MPa high-performance pipeline wide and thick steel plate and its production method. In particular, it relates to a high-performance pipeline steel plate and its production method that has multi-dimensional comprehensive technical characteristics such as strength, plasticity, toughness, strain resistance, corrosion resistance, aging resistance, fatigue resistance and thick wall, suitable for manufacturing energy transmission pipelines in 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] Related patent document 1: "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 composition adopts a design scheme with high Nb (0.08%~0.12%) and high Mo (0.20%~0.40%), 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] Related patent document 2: "An X80M deep-sea strain-resistant pipeline steel plate and rolling process" (CN109234623A) provides a deep-sea pipeline steel plate with a high Ni (0.65%~0.85%) and high Mo (0.31%~0.36%) design scheme, which has excessively high alloy content and cost.

[0007] Related patent document 3: "An X80 pipeline steel with excellent toughness in the heat-affected zone of the circumferential welded 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 rough rolling reduction rate of ≥25% and a final rolling temperature of ≤960℃, is not suitable for the production of wide and thick steel plates, and has high equipment requirements.

[0008] Related patent document 4: "Thick-walled low-temperature resistant pipeline steel and its manufacturing method" (CN116288017A) provides a low-temperature resistant pipeline steel, which also adopts a high Ni (0.35%~0.50%) design.

[0009] In summary, existing technologies still fall short in the research on wide and thick steel plates with widths of 1200–4370 mm for 550 MPa thick-walled high-performance pipelines that possess comprehensive technical characteristics such as high strength, high uniform elongation, low-temperature toughness, high strain, corrosion resistance, aging resistance, and fatigue 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 solution to the technical challenge of multi-dimensional coupling of comprehensive indicators such as high strength, high uniform elongation, low temperature toughness, high strain, corrosion resistance, and aging resistance of wide and thick steel plates with a width of 1200-4370mm for high-performance pipelines operating under complex conditions. This solution addresses the technical challenge of producing a wide and thick steel plate for 550MPa high-performance pipelines and its production method.

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

[0012] A 550MPa high-performance pipeline thick steel plate, the composition of which is as follows by weight percentage: C: 0.035%~0.065%, Si: 0.15%~0.50%, Mn: 1.45%~1.59%, Nb: 0.025%~0.045%, V≤0.06%, N: 0.0040%~0.008%, Ni: 0.05%~0.15%, Cu<0.10%, Cr: 0.05%~0.20%, Al: 0.005%~0.015%, Ca: 0.0020%~0.0045%, Zr≤0.003%, La≤0.004%, 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, in the steel plate, (La / 139+Ca / 40) / (S / 32):2~6.

[0014] Furthermore, the Nb+V content in the steel plate is 0.040% to 0.090%.

[0015] Furthermore, CE in steel plates IIW Controlled within 0.320%–0.370%, CE Pcm Controlled within 0.140% to 0.165%, of which CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0016] Furthermore, the microstructure of the steel plate consists of bainitic ferrite and polygonal ferrite, wherein the volume percentage of polygonal ferrite is 20%–80%, and the average grain cross-sectional area of ​​polygonal ferrite is ≤86μm. 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 35%.

[0017] Furthermore, the steel plate thickness is 25–40 mm, the transverse yield strength can reach 420–490 MPa, the transverse tensile strength can reach 570–630 MPa, the transverse yield-to-tensile ratio is ≤0.79, the average transverse impact energy at -60℃ is ≥250 J, the average transverse impact energy in the weld heat-affected zone at -20℃ is ≥150 J, and the transverse DWTT shear area at -45℃ is ≥85%; the longitudinal yield strength can reach 400–480 MPa, the longitudinal tensile strength can reach 550–620 MPa, the longitudinal yield-to-tensile ratio is <0.78, the longitudinal uniform elongation (UEL) is ≥10%, and the longitudinal strain hardening index (n) is ≥0.11. At 5℃, the CTOD is ≥0.6mm. After aging at 280℃ for 4 hours, the longitudinal yield strength can reach 420~490MPa, the longitudinal tensile strength can reach 560~640MPa, the longitudinal uniform elongation UEL is ≥9%, the longitudinal yield strength ratio is ≤0.80, 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 2~6MPa 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.

[0018] The rationale for the design of the components in this invention is as follows:

[0019] 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 0.065%.

[0020] 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%.

[0021] 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 1.45% to 1.59%.

[0022] Nitrogen (Nb) is a good element for improving strength and toughness. During solid solution treatment, it acts as a solute drag, and during precipitation, it strengthens and inhibits grain growth by refining the grains. In particular, it can form fine Nb (CN) precipitates under appropriate processes, which have beneficial effects such as strengthening, refining grains, and reducing aging tendency. However, if the Nb content is too high, it will delay the formation of polygonal ferrite, and the heating temperature of the continuously cast billet needs to be increased to ensure the solid solution 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 0.025% and 0.045%.

[0023] 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 ≤0.06%.

[0024] Controlling Nb+V between 0.040% and 0.090% 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.

[0025] 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 0.008% by combining the addition of Nb, V and other elements.

[0026] 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 0.15%.

[0027] 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 to be below 0.10%.

[0028] 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 0.05% to 0.20%.

[0029] 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%.

[0030] 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 0.0045%.

[0031] 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 ≤ 0.003%.

[0032] 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 ≤0.004%.

[0033] 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.

[0034] 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%.

[0035] 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%.

[0036] 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%.

[0037] This invention CE IIW Controlled within 0.320%–0.370%, CE Pcm By controlling the concentration between 0.140% and 0.165%, the strength and toughness requirements of the steel plate can be met, while also reducing the tendency for welding cracking, thus giving the steel plate good weldability.

[0038] The second technical solution of the present invention is to provide a production method for 550MPa high-performance pipeline thick steel plates, including smelting, continuous casting, rough rolling, heating, finish rolling and cooling;

[0039] Smelting: including converter smelting and ladle refining;

[0040] The converter employs top and bottom blowing and dual-slag smelting, with slag-blocking tapping. The slag layer thickness is ≤40mm. Lime and fluorite are added in a 4 / 1 to 5 / 1 ratio to create top slag. The basicity of the refining slag is controlled between 4 and 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 performed according to the N content control requirements. The converter's dual-slag smelting and slag-blocking tapping ensure low-phosphorus tapping and reduce phosphorus reversion. Sulfur reversion; vacuum control degree ≤ 0.5 torr, vacuum treatment time ≥ 15 min, nitrogen blowing treatment can be carried out according to N content control requirements; converter double slag smelting and slag-blocking tapping can ensure low phosphorus tapping and reduce phosphorus and sulfur reversion; controlling slag basicity and FeO+MnO in slag can ensure slag reducing ability 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; the control of RH vacuum degree and vacuum treatment time can effectively ensure the treatment effect;

[0041] Continuous casting:

[0042] The pre-cast steel decanting time should be ≥10 min; the superheating temperature of the continuously cast billet should be 5–35℃; the residence time of the molten steel in the tundish during casting should be ≥360 s; the dynamic light reduction of the billet should be ≥5 mm; the continuous casting speed should be controlled within the range of 0.6–1.2 m / min; the center segregation of the continuously cast billet should be ≤C0.5 grade; the center porosity should be ≤0.5 grade; and the inclusions of types A, B, C, and D should be ≤1.0 grade. Controlling the pre-cast steel decanting time, the superheating temperature during casting, and the residence time in the tundish can effectively remove inclusions, control segregation, and homogenize the temperature of the molten steel. Controlling the dynamic light reduction and the continuous casting speed can reduce segregation, decrease the fluctuation of the liquid level in the crystallizer, reduce the tendency for defects to occur, and effectively improve the quality of the billet. Controlling center segregation, center porosity, and inclusions can effectively improve service performance such as corrosion resistance.

[0043] heating:

[0044] 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 in heating stages 1 and 2 is 5–15℃ / min, the average heating rate in heating stage 3 is 2–5℃ / min, the average heating rate in the soaking stage is 0.1–0.5℃ / min, the total heating time is 0.9–1.6 min / mm, the furnace exit temperature is 1100–1150℃, and the temperature difference between the thickness section is ≤30℃.

[0045] Multi-stage heating of continuously cast billets and control of total heating time are beneficial to improving heating efficiency. The relatively low tapping temperature can inhibit austenite grain growth on the one hand, and at the same time, allow the main alloying elements to dissolve, while the Nb precipitates are in a partially dissolved state, further preventing grain growth; control of the temperature difference in the thickness section can ensure heating uniformity.

[0046] Rough rolling:

[0047] Before roughing, 2-4 passes of high-pressure water descaling and cooling are performed, with an average cooling rate of 0.5-3℃ / s. Roughing consists of two stages, with spray cooling in each rolling pass. The end temperature of the first stage is 1040-1080℃, and the end temperature of the second stage is 960-1020℃. The total deformation rate in the second stage is ≥35%, with a deformation rate of 18%-22% per pass, using a high-low-high cycle of variable passes. The rolling speed is 1.0 m / s-2.0 m / s. Preferably, rapid water cooling is performed between the two stages of roughing, with an average cooling rate of 2-5℃ / s and a cooling time of 15-50 s.

[0048] 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.

[0049] Finishing rolling:

[0050] The finishing rolling process consists of two stages. The initial rolling temperature of the first stage is 800–880°C, and the final rolling temperature of the first stage is 760–800°C. Then, after a 30–90 s intermediate warming period, the second stage of finishing rolling begins, with a final rolling temperature of 730–760°C. The deformation rate during the finishing rolling stage is 60%–75%. Preferably, after rough rolling, the intermediate warming billet is rapidly cooled to 20–40°C above the starting temperature of the finishing rolling, with an average cooling rate of 2–8°C / s, and then allowed to warm up to the starting temperature of the finishing rolling.

[0051] The deformation rate during the finishing rolling stage ensures sufficient deformation of austenite within the finishing rolling zone, increasing deformation energy and nucleation sites, and refining grain size. Rapid cooling of the intermediate preheating billet effectively inhibits austenite growth in the high-temperature zone. The finishing rolling stage employs a two-stage process plus intermediate preheating and a second-stage low-temperature two-phase rolling. On one hand, this promotes the precipitation of carbonitrides such as Nb and V, playing a role in strengthening, refining grain size, and pinning. On the other hand, it obtains a sufficient proportion of polygonal ferrite, improving plasticity, toughness, and strain performance. Post-rolling pre-straightening helps improve the cooling uniformity of the steel plate.

[0052] cool down:

[0053] After rolling, the steel plates undergo two-stage cooling after pre-straightening. The initial water cooling temperature is 690–730℃, and the final water cooling temperature at the top of the steel plate is 150–260℃. During water cooling, the water flow rate in the first 5–7 groups of upper manifolds is 400 L / m. 2 ·min~550L / m 2 The remaining water flow rate in the upper manifold is 150 L / m. 2 ·min~300L / 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 30~60℃ higher than that at the tail.

[0054] 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 hard phase structure, while reducing internal stress and facilitating plate shape control. The temperature difference between the beginning and end of the steel plate corresponds to the difference in water cooling at different positions of the steel plate, which helps to 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 inclusions, the effects of desulfurization and deoxygenation 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, controlling N appropriately and reducing the addition of Ti and Al, Nb and V are promoted to play the role of microalloying 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. A small amount of Ni and Cu is added to balance the improvement of strength and corrosion resistance. A Mo-free design is adopted to promote the formation of polygonal ferrite and reduce costs. High strength, high uniform elongation, low temperature toughness, high strain and comprehensive technical characteristics such as corrosion resistance, aging resistance and fatigue resistance, as well as ideal microstructure are obtained to meet the requirements of high-performance pipelines serving under complex conditions.

[0057] (2) The present invention adopts production methods such as high-purity smelting, high-homogeneity heating, two-stage low-temperature rolling of rough rolling + 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 microstructure of granular bainite with a volume percentage not exceeding 35% and small-sized precipitates dispersedly, so that the steel plate has good comprehensive performance.

[0058] (3) The thick steel plate for high-performance pipelines with 550MPa service under complex conditions described in this invention has a thickness of 25-40mm, a transverse yield strength of 420-490MPa, a transverse tensile strength of 570-630MPa, a transverse yield-to-tensile ratio ≤0.79, a transverse impact energy average of ≥250J at -60℃, a transverse impact energy average of ≥150J at -20℃ in the weld heat-affected zone, and a transverse DWTT shear area ≥85% at -45℃; a longitudinal yield strength of 400-480MPa, a longitudinal tensile strength of 550-620MPa, a longitudinal yield-to-tensile ratio <0.78, a longitudinal uniform elongation UEL ≥10%, and a longitudinal strain hardness The strain hardening index n≥0.11, CTOD≥0.6mm at -45℃, longitudinal yield strength can reach 420-490MPa after aging at 280℃ for 4h, longitudinal tensile strength can reach 560-640MPa, longitudinal uniform elongation UEL≥9%, longitudinal yield ratio≤0.80, longitudinal strain hardening index n≥0.10, fatigue life meets the requirement of 20,000 cycles under simulated service pressure of 2~6MPa and temperature 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. Attached Figure Description

[0059] Figure 1 This is a metallographic image of the microstructure of Example 2 of the present invention. Detailed Implementation

[0060] This invention provides a 550MPa high-performance thick steel plate for pipelines. The composition of the steel plate, by weight percentage, is as follows: C: 0.035%~0.065%, Si: 0.15%~0.50%, Mn: 1.45%~1.59%, Nb: 0.025%~0.045%, V≤0.06%, N: 0.0040%~0.008%, Ni: 0.05%~0.15%, Cu<0.10%, Cr: 0.05%~0.20%, Al: 0.005%~0.015%, Ca: 0.0020%~0.0045%, Zr≤0.003%, La≤0.004%, Ti≤0.010%, P≤0.008%, S≤0.0015%, H≤0.00015%, O≤0.0015%, with the balance being iron and unavoidable impurities.

[0061] Furthermore, in the steel plate, (La / 139+Ca / 40) / (S / 32):2~6.

[0062] Furthermore, the Nb+V content in the steel plate is 0.040% to 0.090%.

[0063] Furthermore, CE in steel plates IIWControlled within 0.320%–0.370%, CE Pcm Controlled within 0.140% to 0.165%, of which CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0064] The production method of a 550MPa high-performance pipeline thick steel plate includes smelting, continuous casting, rough rolling, heating, finish rolling, and cooling.

[0065] heating:

[0066] 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 in heating stages 1 and 2 is 5-15℃ / min, the average heating rate in heating stage 3 is 2-5℃ / min, the average heating rate in the soaking stage is 0.1-0.5℃ / min, the total heating time is 0.9min / mm-1.6min / mm, the furnace exit temperature is 1100-1150℃, and the temperature difference between the thickness section is ≤30℃.

[0067] Rough rolling:

[0068] 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 1040 to 1080℃, and the end temperature of the second stage is 960 to 1020℃. The total deformation rate of the second stage of roughing is ≥35%, with a deformation rate of 18% to 22% per pass and a high-low-high cycle of variable passes. The rolling speed of roughing is 1.0 m / s to 2.0 m / s.

[0069] Finishing rolling:

[0070] The finishing rolling process consists of two stages. The initial rolling temperature of the first stage is 800–880℃, and the final rolling temperature of the first stage is 760–800℃. Then, after a 30–90 s interval at the intermediate temperature, the second stage of finishing rolling begins, with a final rolling temperature of 730–760℃. The deformation rate during the finishing rolling stage is 60%–75%.

[0071] cool down:

[0072] After rolling, the steel plate undergoes two-stage cooling after pre-straightening. The initial water cooling temperature is 690–730℃, and the end water cooling temperature at the head of the steel plate is 150–260℃. The roller conveyor of the water cooling system first decelerates and then accelerates, with a deceleration rate of 0.01–0.05 m / s. The point where the head of the steel plate exits the cooling system is the point of acceleration / deceleration transition. The final cooling temperature along the length of the steel plate gradually decreases, and the average final cooling temperature at the head of the steel plate is 30–60℃ higher than that at the tail.

[0073] Further; smelting: including converter smelting and ladle refining;

[0074] 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.

[0075] Continuous casting:

[0076] The quenching time before molten steel is loaded onto the casting machine is ≥10 min; the superheating temperature of the continuously cast billet is 5~35℃; the residence 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 A, B, C, and D types are ≤1.0 grade.

[0077] Furthermore, rapid water cooling is applied between the two stages of roughing, with an average cooling rate of 2–5℃ / s and a cooling time of 15–50s. After roughing, the intermediate billet is rapidly cooled to 20–40℃ above the starting temperature of the first stage of finishing, with an average cooling rate of 2–8℃ / s, and then cooled to the starting temperature of the first stage of finishing.

[0078] Furthermore; during water cooling, the water flow rate for the first 5-7 groups of upper manifolds is 400-550 L / m. 2 •min, the remaining upper manifold water flow rate is 150~300L / m 2 ·min.

[0079] The present invention will be further illustrated below through examples.

[0080] According to the component ratio of the technical solution, the embodiments of the present invention carry out smelting, continuous casting, heating, rough rolling, finish rolling and cooling.

[0081] The composition (wt%) of the steel in this embodiment of the invention is shown in Table 1. The main process parameters for smelting the steel in this embodiment of the invention are shown in Table 2. The main process parameters for continuous casting of the steel in this embodiment of the invention are shown in Table 3. The main process parameters for heating the continuously cast billet of the steel in this embodiment of the invention are shown in Table 4. The main process parameters for heating the continuously cast billet and rough rolling of the steel in this embodiment of the invention are shown in Table 5. The main process parameters for finishing rolling and cooling of the steel in this embodiment of the invention are shown in Table 6. The main process parameters for cooling of the steel in this embodiment of the invention are shown in Table 7. The microstructure of the steel in this invention is shown in Table 8. The mechanical properties of the steel in this embodiment of the invention are shown in Table 9. The longitudinal tensile properties after aging of the steel in this embodiment of the invention are shown in Table 10. The fatigue resistance and corrosion resistance of the steel in this invention are shown in Table 11.

[0082] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0083] Example C Si Mn Nb V Nb+V N Ni Cu Cr La 1 0.052 0.15 1.55 0.026 0.042 0.068 0.0058 0.07 0 0.08 0.0026 2 0.035 0.43 1.59 0.044 0.035 0.079 0.0071 0.14 0.09 0.17 0.0034 3 0.063 0.22 1.46 0.028 0.052 0.080 0.0062 0.08 0.06 0.15 0 4 0.044 0.34 1.52 0.032 0.038 0.07 0.0065 0.10 0.08 0.08 0.0032 5 0.056 0.27 1.49 0.043 0 0.043 0.0053 0.06 0.09 0.10 0.0019 6 0.042 0.38 1.55 0.041 0.026 0.067 0.0049 0.11 0.07 0.15 0.0013 7 0.061 0.25 1.48 0.030 0.045 0.075 0.0068 0.08 0.06 0.18 0.0028 8 0.048 0.29 1.53 0.035 0.020 0.055 0.0055 0.11 0.05 0.11 0.0037 9 0.046 0.35 1.50 0.033 0.041 0.074 0.0062 0.08 0.06 0.13 0.0010 10 0.055 0.33 1.47 0.023 0.012 0.035 0.0051 0.12 0.09 0.16 0.0029 Example Al Ca Zr Ti P S H O <![CDATA[CE IIW ]]> <![CDATA[CE Pcm ]]> A 1 0.008 0.0024 0 0.008 0.005 0.0012 0.00012 0.0012 0.339 0.144 2.1 2 0.012 0.0041 0.0027 0 0.008 0.0014 0.00015 0.0015 0.356 0.148 4.3 3 0.007 0.0027 0.0018 0.005 0.006 0.0011 0.00009 0.0011 0.356 0.160 3.1 4 0.010 0.0033 0.0021 0.008 0.006 0.0012 0.00012 0.0011 0.333 0.145 4.1 5 0.012 0.0035 0.0013 0.007 0.007 0.0015 0.00010 0.0012 0.334 0.150 3.3 6 0.007 0.0025 0.0025 0 0.005 0.0011 0.00012 0.001 0.348 0.148 3.2 7 0.008 0.0038 0.0017 0.006 0.006 0.0010 0.00008 0.0009 0.362 0.161 5.5 8 0.011 0.0026 0.0012 0.005 0.008 0.0011 0.00010 0.0012 0.340 0.146 3.8 9 0.012 0.0021 0.0021 0.006 0.005 0.0015 0.00011 0.0010 0.340 0.148 1.9 10 0.008 0.0035 0.0018 0.009 0.008 0.0012 0.00010 0.0013 0.348 0.155 4.3

[0084] Note: A = (La / 139 + Ca / 40) / (S / 32)

[0085] Table 2 Main process parameters for steelmaking in the embodiments of the present invention

[0086] Example Top slag limestone / fluorite slag alkalinity FeO + MnO weight percentage in slag / % RH vacuum degree / torr Vacuum processing time / min 1 4.8 6.1 0.86 0.4 17 2 4.3 5.0 0.82 0.5 20 3 4.6 5.2 0.91 0.5 16 4 4.2 4.5 0.95 0.4 21 5 4.3 4.7 0.91 0.4 19 6 4.5 4.9 0.88 0.3 17 7 4.2 4.3 0.85 0.5 15 8 4.6 5.2 0.82 0.5 23 9 4.3 5.1 0.85 0.5 18 10 4.5 5.4 0.89 0.4 22

[0087] Table 3 Main process parameters for continuous steel casting in the embodiments of the present invention.

[0088] 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 16 24 402 5.8 0.95 C0.5 0 1.0 2 13 26 393 5.3 0.95 C0.5 0.5 0.5 3 18 17 385 5.9 0.95 C0.5 0.5 1.0 4 20 12 388 5.2 0.95 C0.5 0 0.5 5 18 15 373 5.3 0.80 C0.5 0 0.5 6 17 19 390 5.5 0.80 C0.5 0 1.0 7 21 13 377 5.2 0.80 C0.5 0.5 1.0 8 15 22 389 5.6 0.80 C0.5 0 1.0 9 19 18 383 5.3 0.95 C0.5 0.5 1.0 10 17 13 380 5.5 0.80 C0.5 0.5 1.0

[0089] Table 4. Main process parameters for heating the continuously cast steel billet in the embodiments of the present invention.

[0090] 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 6.4 4.2 0.36 1.2 1124 20 2 10.2 3.1 0.15 1.5 1142 17 3 7.5 3.9 0.21 1.2 1131 14 4 7.1 2.3 0.48 1.3 1137 23 5 8.9 3.0 0.23 1.0 1145 15 6 6.2 4.5 0.40 1.0 1130 19 7 7.8 3.7 0.25 1.6 1116 16 8 7.0 2.5 0.36 1.3 1123 20 9 6.8 3.3 0.39 1.1 1135 19 10 8.1 3.0 0.25 1.3 1127 14

[0091] Table 5. Main process parameters for rough rolling of continuously cast steel billets in the embodiments of the present invention.

[0092] 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 The total deformation rate in the second stage of rough rolling is ≥35%. Deformation rate per pass in the second stage of rough rolling / % Roughing rolling speed / m / s 1 3 1.1 1051 978 2.2 25 48 18～21 1.5 2 4 1.5 1066 1006 2.5 18 45 19～21 1.5 3 3 1.0 1062 993 2.3 21 47 18～22 1.5 4 3 1.2 1057 980 2.2 26 43 18～20 1.5 5 4 1.3 1070 968 2 40 36 18～20 1.0 6 2 0.7 1046 990 2 21 38 19～20 1.0 7 2 0.5 1048 997 2.2 17 40 18～21 1.0 8 2 0.7 1055 971 2.1 31 38 18～22 1.0 9 3 0.9 1064 984 2.3 27 45 18～21 1.5 10 3 1.0 1052 972 2.6 18 37 18～20 1.0

[0093] Table 6 Main process parameters of steel finishing process in the embodiments of the present invention

[0094] Example Deformation rate / % 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 71 895 33 2.7 862 784 65 738 2 68 891 21 4 870 787 78 746 3 66 887 28 4.2 859 775 60 743 4 71 902 36 3.1 866 791 46 751 5 63 855 31 5.5 824 773 38 741 6 68 863 28 5.3 835 780 41 745 7 65 852 32 6.9 820 768 32 739 8 67 861 30 4.6 831 771 39 735 9 69 892 27 4.0 865 779 56 742 10 65 869 32 3.8 837 768 40 740

[0095] Table 7 Main process parameters of steel cooling process in embodiments of the present invention

[0096] Example Initial water cooling temperature / °C Water-cooled end 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) 1 703 176 6 groups of 500 240 37 2 712 192 7 groups 540 170 42 3 715 195 6 groups 430 280 32 4 722 243 5 groups 520 230 51 5 716 188 7 groups 510 240 35 6 724 197 6 groups 550 250 46 7 715 173 6 groups of 500 300 40 8 711 181 7 groups 520 250 33 9 710 197 6 groups 520 220 46 10 712 175 7 groups of 500 260 35

[0097] Table 8 Microstructure of the steel of the present invention

[0098] Example Polygonal ferrite volume percentage / % Granular bainite volume percentage / % Average grain cross-sectional area of ​​polygonal ferrite / μm2 Plate thickness / mm 1 65 6 72 26 2 40 22 62 26 3 46 17 55 26 4 37 29 59 26 5 49 9 67 31 6 33 13 52 31 7 57 0 60 31 8 63 9 68 31 9 60 13 81 26 10 56 11 70 31

[0099] Table 9 Mechanical properties of steel in the embodiments of the present invention

[0100] 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-45℃ave / % CTOD-45℃ave / mm n 1-Horizontal 440 585 0.75 -- 284 170 92 -- -- 1-Vertical 415 570 0.73 13.5 -- -- -- 0.93 0.13 2-Horizontal 475 615 0.77 -- 273 194 89 -- -- 2-Vertical 455 595 0.76 11.5 -- -- -- 0.85 0.11 3-Horizontal 460 610 0.75 -- 280 191 90 -- -- 3-Vertical 435 585 0.74 12.0 -- -- -- 0.92 0.12 4-Horizontal 460 590 0.78 -- 291 205 89 -- -- 4-Vertical 440 570 0.77 11.0 -- -- -- 1.03 0.12 5-Horizontal 445 585 0.76 -- 267 199 88 -- -- 5-Vertical 425 565 0.75 12.0 -- -- -- 0.88 0.12 6-Horizontal 470 595 0.79 -- 285 208 86 -- -- 6-Vertical 445 575 0.77 11.5 -- -- -- 1.05 0.11 7-Horizontal 455 610 0.75 -- 281 185 89 -- -- 7-Vertical 440 600 0.73 12.5 -- -- -- 1.10 0.13 8-Horizontal 435 580 0.75 -- 272 192 88 -- -- 8-Vertical 410 560 0.73 13.5 -- -- -- 0.94 0.13 9-Horizontal 465 590 0.79 -- 251 173 83 -- -- 9-Vertical 435 570 0.76 12.5 -- -- -- 0.76 0.10 10-Horizontal 455 595 0.76 -- 238 154 85 -- -- 10-Vertical 430 565 0.76 12.0 -- -- -- 0.69 0.12

[0101] Table 10. Longitudinal tensile properties of embodiments of the present invention after aging.

[0102] Example Rt0.5 / MPa Rm / MPa Rt0.5 / Rm UEL / % n 1 430 575 0.75 12.5 0.12 2 475 605 0.79 10 0.10 3 450 585 0.77 11 0.10 4 445 580 0.77 11 0.11 5 435 580 0.75 11.5 0.12 6 455 570 0.80 10 0.10 7 450 605 0.74 12 0.12 8 430 560 0.77 12 0.11 9 450 575 0.78 11.5 0.095 10 440 560 0.79 11.0 0.105

[0103] Note: The aging process involves holding at 280℃ for 4 hours.

[0104] Table 11 Fatigue resistance and corrosion resistance of the steel of this invention

[0105] Example fatigue test SSCC corrosion resistance test 1 No fatigue failure occurred. qualified 2 No fatigue failure occurred. qualified 3 No fatigue failure occurred. qualified 4 No fatigue failure occurred. qualified 5 No fatigue failure occurred. qualified 6 No fatigue failure occurred. qualified 7 No fatigue failure occurred. qualified 8 No fatigue failure occurred. qualified 9 No fatigue failure occurred. qualified 10 No fatigue failure occurred. qualified

[0106] Notes: Fatigue test: 20,000 fatigue cycles were performed under simulated service pressure of 2-6 MPa and temperature of -40-50℃. SSCC corrosion resistance test: No fracture occurred after immersion in saturated H2S solution (solution A) for 720 hours under 90% stress loading conditions; no visible cracks were observed at 10x magnification.

[0107] As can be seen from the above, the microstructure of the steel plate produced by applying the present invention is bainitic ferrite + polygonal ferrite, wherein the volume percentage of polygonal ferrite is 20% to 80%, and the average grain cross-sectional area of ​​polygonal ferrite is ≤86μm. 2 The matrix contains fine precipitates with a size ≤30nm dispersedly, and the precipitates consist of nitrides and carbides containing one or both of Nb and V elements. The microstructure of the steel plate may also include granular bainite with a volume percentage not exceeding 35%. The steel plate thickness is 25-40mm, with a transverse yield strength of 420-490MPa, a transverse tensile strength of 570-630MPa, a transverse yield-to-tensile ratio ≤0.79, a transverse impact energy average of ≥250J at -60℃, a weld heat-affected zone transverse impact energy average of ≥150J at -20℃, and a transverse DWTT shear area ≥85% at -45℃; longitudinal yield strength is 400-480MPa, longitudinal tensile strength is 550-620MPa, a longitudinal yield-to-tensile ratio <0.78, a longitudinal uniform elongation UEL ≥10%, a longitudinal strain hardening index n ≥0.11, and a CT at -45℃. OD≥0.6mm, after aging at 280℃ for 4h, longitudinal yield strength 420~490MPa, longitudinal tensile strength 560~640MPa, longitudinal uniform elongation UEL≥9%, longitudinal yield ratio≤0.80, longitudinal strain hardening index n≥0.10, fatigue life meets the requirement of 20000 cycles under simulated service pressure of 2~6MPa and temperature 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.

[0108] 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 550MPa high-performance pipeline thick steel plate, characterized in that, The composition of the steel plate, by weight percentage, is as follows: C: 0.035%–0.065%, Si: 0.15%–0.50%, Mn: 1.45%–1.59%, Nb: 0.025%–0.045%, V≤0.06%, N: 0.0040%–0.008%, Ni: 0.05%–0.15%, Cu<0.10%, Cr: 0.05%–0.20%, Al: 0.005%–0.015%, Ca The composition of the steel plate is as follows: 0.0020%~0.0045%, Zr≤0.003%, La≤0.004%, Ti≤0.010%, P≤0.008%, S≤0.0015%, H≤0.00015%, O≤0.0015%, with the balance being iron and unavoidable impurities; the microstructure of the steel plate is bainitic ferrite + polygonal ferrite, wherein the volume percentage of polygonal ferrite is 20%~80%, and the average grain cross-sectional area of ​​polygonal ferrite is ≤86μm. 2 The matrix contains fine precipitates with a size ≤30nm dispersedly, and the precipitates are composed of nitrides and carbides containing one or both of Nb and V elements; the steel plate thickness is 25-40mm, the transverse yield strength is 420-490MPa, the transverse tensile strength is 570-630MPa, the transverse yield ratio is ≤0.79, the average transverse impact energy at -60℃ is ≥250J, the average transverse impact energy in the weld heat-affected zone at -20℃ is ≥150J, and the transverse DWTT shear area at -45℃ is ≥85%; the longitudinal yield strength is 400-480MPa, the longitudinal tensile strength is 550-620MPa, the longitudinal yield ratio is <0.78, and the longitudinal uniform elongation UEL is ≥ 10%, longitudinal strain hardening index n≥0.11, CTOD≥0.6mm at -45℃, after aging at 280℃ for 4h, longitudinal yield strength 420~490MPa, longitudinal tensile strength 560~640MPa, longitudinal uniform elongation UEL≥9%, longitudinal yield ratio≤0.80, longitudinal strain hardening index n≥0.10, fatigue life meets the requirement of 20000 cycles under simulated service pressure 2~6MPa and temperature -40~50℃ without fatigue failure, 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 550MPa high-performance pipeline thick steel plate according to claim 1, characterized in that, In steel plates, (La / 139+Ca / 40) / (S / 32): 2~6.

3. The 550MPa high-performance pipeline thick steel plate according to claim 1, characterized in that, Nb+V: 0.040%~0.090%.

4. The 550MPa 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 35% of the volume.

5. A method for producing a 550MPa high-performance pipeline thick steel plate as described in any one of claims 1-4, comprising smelting, continuous casting, rough rolling, heating, 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 in heating stages 1 and 2 is 5-15℃ / min, the average heating rate in heating stage 3 is 2-5℃ / min, the average heating rate in the soaking stage is 0.1-0.5℃ / min, the total heating time is 0.9min / mm-1.6min / mm, the furnace exit temperature is 1100-1150℃, and the temperature difference between 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 1040 to 1080℃, and the end temperature of the second stage is 960 to 1020℃. The total deformation rate of the second stage of roughing is ≥35%, with a deformation rate of 18% to 22% per pass and a high-low-high cycle of variable passes. The roughing rolling speed is 1.0 to 2.0 m / s. Finishing rolling: The finishing rolling process consists of two stages. The initial rolling temperature of the first stage is 800–880℃, and the final rolling temperature of the first stage is 760–800℃. Then, after a 30–90 s interval at the intermediate temperature, the second stage of finishing rolling begins, with a final rolling temperature of 730–760℃. The deformation rate during the finishing rolling stage is 60%–75%. cool down: After rolling, the steel plate undergoes two-stage cooling after pre-straightening. The initial water cooling temperature is 690–730℃, and the end water cooling temperature at the head of the steel plate is 150–260℃. The roller conveyor of the water cooling system first decelerates and then accelerates, with a deceleration rate of 0.01–0.05 m / s. The point where the head of the steel plate exits the cooling system is the point of acceleration / deceleration transition. The final cooling temperature along the length of the steel plate gradually decreases, and the average final cooling temperature at the head of the steel plate is 30–60℃ higher than that at the tail.

6. The method for producing a 550MPa high-performance pipeline thick steel plate according to claim 5, characterized in that: Smelting: including converter smelting and ladle refining; The converter adopts top and bottom combined 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, the vacuum treatment time is ≥15 min, and nitrogen blowing is carried out after vacuum treatment according to the N content control requirements. Continuous casting: The quenching time before molten steel is loaded onto the casting machine is ≥10 min; the superheating temperature of the continuously cast billet is 5~35℃; the residence 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 A, B, C, and D types are ≤1.0 grade.

7. The method for producing a 550MPa high-performance pipeline thick steel plate according to claim 5, characterized in that: Rapid water cooling is performed between the two stages of roughing, with an average cooling rate of 2-5℃ / s and a cooling time of 15-50s. After roughing, the intermediate billet is rapidly cooled to 20-40℃ above the starting temperature of the first stage of finishing, with an average cooling rate of 2-8℃ / s. Then, it is allowed to warm up to the starting temperature of the first stage of finishing.

8. The method for producing a 550MPa high-performance pipeline thick steel plate according to claim 5, characterized in that: When water-cooled, the water flow rate of the first 5 to 7 groups of upper manifolds is 400 to 550 L / m. 2 •min, the remaining upper manifold water flow rate is 150~300L / m 2 ·min.

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