500mpa grade fatigue-resistant and corrosion-resistant wide and thick steel plate for deep sea submarine pipeline and production method thereof

Abstract

The present application belongs to the field of metal materials, and provides a 500MPa-grade anti-fatigue and corrosion-resistant wide and thick steel plate for deep-sea seabed pipeline and a production method thereof. In the composition, low C, Mn and Al are designed, and elements such as Mg, Ce and Ca are used for complex regulation of inclusions. Through the composite addition of Nb and V, N is controlled, and the content of Ti and Al is reduced, so as to promote Nb and V to play the roles of micro-alloy solid solution, precipitation and fine grain, improve the strength and weldability, play the hydrogen trap role, improve the corrosion resistance, and the fatigue life of the steel plate produced by the present application is ≥2×10 6 6 times under high stress, the fatigue stress amplitude is 30kpsi, the CTOD at-45℃ is ≥0.6mm, the anti-HIC corrosion performance meets the corrosion qualification of NACE standard A solution for 96 hours, the anti-SSCC corrosion performance meets the non-fracture under 90% stress loading for 720 hours of saturated H2S solution immersion and no visible crack under 10 times magnification observation, and the complex and severe service requirements of deep-sea seabed pipeline steel are met.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a wide and thick steel plate for 500MPa-grade fatigue-resistant and corrosion-resistant deep-sea subsea pipelines and its production method. Background Technology

[0002] The ocean is rich in oil and natural gas, and offshore oil and gas has become a major growth point for new oil and gas production capacity. As shallow-sea oil and gas resource development gradually reaches its peak, future offshore oil and gas exploration will increasingly move towards the deep sea, making the service conditions of subsea oil and gas pipelines even more demanding. During their service life, deep-sea subsea pipelines not only withstand high pressure in deep water but also complex loads such as ocean currents, uneven seabeds, and platform movement; moreover, the deep-sea oil and gas they transport often contains H2S and Cl-. - Corrosive media; at the same time, the design life of deep-sea subsea pipelines is usually required to be 30 years or more. Therefore, in summary, the steel used for deep-sea subsea pipelines must have high strength and toughness, as well as excellent comprehensive properties such as fatigue resistance, corrosion resistance, and crush resistance.

[0003] Currently, there has been some research on wide and thick steel plates with a width range of 1200 to 4370 mm for deep-sea subsea pipelines. Some patents and documents have been found through searching, but the contents described therein are significantly different from the components, production methods, performance, and microstructure design of the technical solution of this invention.

[0004] Relevant patent document 1: "A production method of low hardness acid-resistant submarine pipeline steel X65MOS" (publication number: CN118422044A) provides an X65 grade acid-resistant submarine pipeline steel, which adopts a high Nb (0.075%~0.085%) and high Cu (0.20%~0.25%) alloy design, resulting in high alloy cost; it requires a reduction rate of ≥30% in the last three passes of rough rolling, and the cooled steel plate is subjected to induction heating tempering, which places high demands on production equipment.

[0005] Related patent document 2: "A thick-walled high acid-resistant pipeline steel and its production method" (publication number: CN118996275A) provides an acid-resistant pipeline steel with a high Ni design (0.50%~0.60%) in the composition, which has high cost, requires a reduction rate of ≥22% in the last pass of rough rolling, has high requirements for equipment capacity, and does not pay attention to fatigue resistance.

[0006] Related patent document 3: "A steel plate for thick-walled pipelines with excellent HIC resistance and its manufacturing method" (publication number: CN118814089A) provides a pipeline steel with good HIC resistance. However, it also has a high content of Ni, Cu and Mo alloys and adopts a high final rolling and low final cooling process, which is not conducive to the precipitation effect of microalloys such as Nb and V. Moreover, it also does not take fatigue resistance into account.

[0007] Related patent document 4: "An acid-resistant subsea pipeline steel and its preparation method" (publication number: CN106566991A) provides an acid-resistant subsea pipeline steel, which also adopts a design with high Ni, Mo and other precious alloys, and does not take fatigue resistance into account in terms of performance.

[0008] In summary, existing technologies still fall short in the research on thick steel plates for deep-sea subsea pipelines and their production technologies, which combine multiple dimensions of size, mechanical properties, and service performance, including thick walls, strength, toughness, fatigue resistance, and corrosion resistance. Summary of the Invention

[0009] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate for deep-sea subsea pipelines, and its production method, which solves the technical problems of the dimensional specifications, mechanical properties, and service performance of thick steel plates with a width of 1200-4370mm for deep-sea subsea pipelines.

[0010] The objective of this invention is achieved as follows:

[0011] The composition employs a low-C, Mn, and Al design to effectively reduce segregation and suppress harmful inclusions. The addition of elements such as Mg, Ce, and Ca allows for the composite control of inclusions, reducing their quantity and size and promoting their uniform distribution. Combined with ultra-low P, S, H, and O content and continuous casting billet quality control, fatigue resistance and corrosion resistance are effectively improved. The addition of Nb and V, along with appropriate N control and reduced Ti and Al addition, promotes the microalloying, precipitation, and grain refinement effects of Nb and V, improving strength and weldability while also providing a certain hydrogen trapping effect, thus enhancing corrosion resistance. The addition of small amounts of Ni and Cu balances strength and corrosion resistance. This design meets the complex and demanding service requirements of deep-sea subsea pipeline steel.

[0012] A 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate for deep-sea subsea pipelines, the composition of which, by weight percentage, is as follows: C: 0.015%–0.035%, Si: 0.20%–0.45%, Mn: 0.90%–1.35%, Nb: 0.015%–0.050%, V: 0.010%–0.050%, N: 0.0030%–0.0080%, Ni: 0.01%–0.10%, Cu 0.05%~0.15%, Cr: 0.15%~0.30%, Mg: 0.0010%~0.0050%, Ca: 0.0010%~0.0040%, Ce≤0.005%, Ti≤0.010%, Mo<0.10%, Al<0.010%, P≤0.010%, S≤0.0015%, H≤0.0001%, O≤0.0015%, with the balance being iron and unavoidable impurities.

[0013] Furthermore, the Nb+V content in the thick steel plate is 0.050% to 0.090%.

[0014] Furthermore, in the thick steel plate, (Ce / 140+Mg / 24+Ca / 40) / (S / 32)=4~7.

[0015] Furthermore, in the thick steel plate, CE IIW The concentration is 0.29%–0.35%, CE Pcm Controlled within 0.12% to 0.15%, 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 thick steel plate is acicular ferrite + polygonal ferrite + granular bainite, wherein, by volume percentage: polygonal ferrite accounts for 10% to 55% of the volume, and the average grain cross-sectional area of ​​acicular ferrite is ≤70μm. 2 The average grain cross-sectional area of ​​polygonal ferrite is ≤100μm. 2 The matrix contains fine precipitates with a size ≤30nm that are diffusely distributed. The precipitates are composed of Nb, V nitrides and carbides.

[0018] Furthermore, the thickness of the wide and thick steel plate is 25-40mm, the transverse yield strength can reach 420-540MPa, the transverse tensile strength can reach 535-600MPa, the transverse yield-to-tensile ratio is ≤0.88, the average transverse impact energy at -60℃ is ≥300J, the average transverse impact energy at -20℃ in the weld heat-affected zone is ≥180J, and the transverse DWTT shear area at -45℃ is ≥85%; the longitudinal yield strength can reach 400-520MPa, the longitudinal tensile strength can reach 515-0.580MPa, the longitudinal uniform elongation UEL is ≥8%, and the longitudinal yield-to-tensile ratio is ≤0.87; the fatigue life under high stress is ≥2*10 6 The fatigue stress amplitude is 30 kpsi; the CTOD at -45℃ is ≥0.6 mm; the HIC corrosion resistance meets the requirements of CLR≤5%, CTR≤2%, and CSR≤0.5% after 96 hours of corrosion in NACE standard A solution; the SSCC corrosion resistance meets the requirements of no fracture after 720 hours of immersion in saturated H2S solution under 90% stress loading and no visible cracks under 10x magnification; the manufactured fatigue-resistant and corrosion-resistant deep-sea subsea pipeline meets the requirements of X60 and X65 grades.

[0019] The rationale for the design of the components in 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, C ≥ 0.015% is required. However, an increase in C will lead to banded structure and increased segregation, which will reduce fatigue resistance, corrosion resistance, plasticity and toughness. Therefore, in this invention, C is controlled at 0.015% to 0.035%.

[0021] Si acts as a deoxidizer. Since it is necessary to better utilize the precipitation of Nb, V and N, this invention adopts a low Al design. Therefore, Si is used to replace Al to perform the deoxidation function. At the same time, it can also be used for solid solution, which can play a 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 0.20% to 0.45%.

[0022] Mn is an effective and inexpensive strengthening element that can improve hardenability and achieve a certain effect of refining and homogenizing the grains in the thickness section. However, excessive manganese content can easily form hard phase bands, induce central segregation, increase the non-uniformity of the structure, and reduce weldability, corrosion resistance and fatigue resistance. Therefore, in this invention, the Mn content is controlled at 0.90% to 1.35%.

[0023] Nitrogen (Nb) is a good element for improving strength and toughness. During solution treatment, it acts as a solute drag, and during precipitation, it strengthens and inhibits grain growth by refining the grains. In addition, Nb can weaken the tendency of banded structure, which is beneficial to improving corrosion resistance. 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 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 is controlled at 0.015% to 0.050%.

[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 through grain boundary aggregation or precipitation combined with C and N, refine grains, reduce the formation of central hard phase banded structures, improve the uniformity of microstructure in the thickness section of the steel plate, 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 0.010% to 0.050%. Preferably, Nb+V is controlled at 0.050% to 0.090% to ensure the effects of solid solution, grain refinement, and phase transformation control. Moreover, it makes the precipitated phase fine and dispersed, while improving the economics of product design.

[0025] N: Since this invention adds Nb and V and adopts a low C design, N is a key element in this invention that combines with Nb, V and other elements to form fine precipitates. Therefore, the N content is not less than 0.0030%. However, if the N content is too high, the precipitate will coarsen, toughness will deteriorate, and hard bands will increase. Therefore, this invention controls the N content to be between 0.0030% and 0.0080% by combining the amount of Nb, V and other elements added.

[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 more will affect 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 0.01% to 0.10%.

[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 at 0.05% to 0.15%.

[0028] Cr can compensate for the strength loss caused by low C and low Mn design, and is also economical; it can increase hardenability, improve the uniformity of the microstructure of the thickness section, inhibit the pearlite transformation, and reduce the Baossinger effect before and after pipeline steel pipe making; at the same time, it is beneficial to improve corrosion resistance; however, excessive Cr content will deteriorate toughness and weldability, so the present invention controls the Cr content at 0.15% to 0.30%.

[0029] Mg has deoxidation and desulfurization effects. It can spheroidize and refine inclusions by controlling the morphology and size of sulfide and oxide inclusions, which is beneficial to reduce anisotropy, improve toughness and corrosion resistance. It can also act as a phase deformation nucleus to refine grains. However, excessive addition will lead to a decrease in yield and an increase in inclusions. Therefore, the Mg content in this invention is 0.0010% to 0.0050%.

[0030] Ca can alter the composition, structure, and morphology of inclusions, improve HIC resistance, enhance toughness and performance uniformity, and also improve weldability. However, excessive Ca content can lead to a decrease in cleanliness. Therefore, the Ca content in this invention is controlled at 0.0010% to 0.0040%.

[0031] Ce readily forms high-melting-point oxygen and sulfide compounds, promoting inclusion modification and removal, and improving corrosion resistance and fatigue resistance. Furthermore, it has a certain effect on promoting solidification and phase deformation nucleation, refining grains. However, excessively high Ce content can reduce the effectiveness of inclusion removal and control, and is also uneconomical. Therefore, this invention controls the Ce content to ≤0.005%. Preferably, (Ce / 140+Mg / 24+Ca / 40) / (S / 32) is controlled between 4 and 7, which is beneficial for obtaining good additive effects, achieving inclusion modification, and improving corrosion resistance and fatigue resistance.

[0032] Ti readily forms high-melting-point Ti(CN) precipitation, refining austenite grains; at the same time, it is beneficial to improve the toughness of the heat-affected zone after welding; however, excessive Ti content will inhibit the formation of Nb and V precipitates. In this invention, the Ti content is controlled to ≤0.010%.

[0033] Mo has the effect of strengthening and promoting the transformation of microstructure at medium and low temperatures, which can reduce the phase transformation temperature and refine the grains; however, Mo will inhibit the formation of polygonal ferrite, which is not conducive to the control of soft phase structure, deteriorates toughness, and also leads to increased cost. Therefore, the present invention controls the Mo content to below 0.10%.

[0034] Al is a deoxygenating element, and excessive content will promote the increase of inclusions. Moreover, Al will affect the formation of NbN and VN. In this invention, the Al content is controlled below 0.010%.

[0035] P and S are harmful impurity elements; P reduces low-temperature toughness, and this invention controls P to ≤0.010%; an increase in S content will promote the formation of S-containing inclusions, leading to a decrease in fatigue and corrosion resistance, therefore, S≤0.0015%.

[0036] Increased H and O content leads to decreased toughness, increased inclusions, and affects corrosion resistance and fatigue performance. Therefore, this invention controls H ≤ 0.0001% and O ≤ 0.0015%.

[0037] The present invention controls CEIIW at 0.29% to 0.35% and CEPcm at 0.12% to 0.15%, which can not only meet the strength and toughness requirements of steel plates, but also reduce the tendency of welding cracking, giving the steel plates good weldability.

[0038] The second technical solution of the present invention is to provide a method for producing 500MPa grade fatigue-resistant and corrosion-resistant thick steel plates for deep-sea subsea pipelines, including smelting, continuous casting, heating, rough rolling, finish rolling, and cooling;

[0039] Smelting:

[0040] The converter employs top and bottom blowing and double-slag smelting, with slag blocking during 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, V, Mg, and Ce 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 of the finished steel plate. The quenching time before the molten steel is loaded onto the mill is ≥10 min. The superheating temperature of the continuously cast billet is 5 to 35℃. The residence time of the molten steel in the tundish during casting is ≥380s. The dynamic light reduction of the billet is ≥5mm. The casting speed is controlled within the range of 0.6 to 1.2 m / min. The center segregation of the continuously cast billet is ≤C grade 0.5, the center porosity is ≤0.5, the inclusions of type A and C are ≤0.5, and the inclusions of type B and D are ≤1.0.

[0041] Dual-slag smelting in converters and slag-blocking tapping can ensure low-phosphorus steelmaking and reduce phosphorus and sulfur reversion; controlling slag basicity and FeO+MnO in the slag can ensure the slag's reducing power and fluidity, fully desulfurize and deoxidize, and reduce inclusions; the order of adding Ti, V, Mg, and Ce after refining and deoxidation can more effectively improve element yield; controlling RH vacuum degree and vacuum treatment time can effectively ensure treatment effect; controlling pre-cast steel killing, casting superheat, and tundish residence time can play a good role in inclusion removal, segregation control, and steel temperature homogenization; controlling dynamic light reduction and constant casting speed of continuous casting billets can reduce segregation, reduce crystallizer liquid level fluctuations, reduce defect generation tendency, and effectively improve billet quality; controlling center segregation, center porosity, and inclusions can effectively improve service performance such as corrosion resistance and fatigue resistance.

[0042] Continuous casting:

[0043] 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 6–12℃ / 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 min / mm to 1.6 min / mm, the furnace exit temperature is 1150–1190℃, and the temperature difference between the thickness section is ≤30℃.

[0044] 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 take into account both the austenite grain size and element solid solution requirements. Thickness section temperature difference control can ensure heating uniformity.

[0045] Rough rolling:

[0046] Before roughing, 3 to 5 passes of high-pressure water descaling and cooling are performed, with an average cooling rate of 0.5 to 3℃ / s. Roughing consists of two stages, with each rolling pass undergoing spray cooling. The end temperature of the first stage of roughing is 1080 to 1120℃, and the end temperature of the second stage is 970 to 1020℃. Rapid water cooling is performed between the two stages, with an average cooling rate of 2 to 4℃ / s and a cooling time of 10 to 30 seconds. The total deformation rate of the second stage of roughing is ≥35%, and the deformation rate per pass is 17% to 20%, using a high-low-high cycle of variable passes. The roughing rolling speed is 1.0 m / s to 2.0 m / s.

[0047] High-pressure water descaling and cooling before rough rolling remove scale from the heating process, while simultaneously lowering the billet temperature and increasing the temperature gradient of the thickness section, which is beneficial for low-temperature rough rolling and deformation penetration. Spray cooling in each rolling pass of rough rolling, as well as rapid water cooling + low-temperature rolling + process spray cooling between the two stages, enables 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 achieves 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.

[0048] Finishing rolling:

[0049] The finishing rolling process consists of two stages. The first stage starts at a rolling temperature of 830–880°C and ends at a rolling temperature of 780–820°C. Then, after a 30–90 s interval at intermediate temperature, the second stage of finishing rolling begins, ending at a rolling temperature of 740–770°C. The deformation rate during the finishing rolling stage is 60%–75%. Preferably, 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 2–10°C / s, and then allowed to warm up to the starting temperature of the first stage of finishing rolling.

[0050] The deformation rate in the finishing rolling stage ensures that austenite undergoes sufficient deformation in the finishing rolling zone, increasing deformation energy and nucleation sites, and refining grains. Rapid cooling of the intermediate heated billet can effectively suppress austenite growth in the high-temperature section. The finishing rolling stage adopts a two-stage + intermediate heated process, 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 certain proportion of fine polygonal ferrite, improve toughness, and reduce yield strength ratio.

[0051] cool down:

[0052] After rolling, the steel plates undergo two-stage cooling following pre-straightening. The initial water cooling temperature is 720–760℃, and the final water cooling temperature at the steel plate head is 380–520℃. During water cooling, the water flow rate in the first 5–7 groups of upper manifolds is 250 L / m. 2 ·min~350L / m 2 The remaining water flow rate in the upper manifold is 120 L / m. 2 ·min~230L / m 2 In the water-cooled system, the roller conveyor first decelerates and then accelerates, with a deceleration rate of 0.01 to 0.05 m / s. The deceleration transition point is at the head of the steel plate exiting the cooling system. The final cooling temperature along the length of the steel plate gradually decreases, with the average final cooling temperature at the head of the steel plate being 20 to 70°C higher than that at the tail.

[0053] Pre-straightening after rolling helps improve the cooling uniformity of the steel plate; controlling the start and end temperatures of water cooling can ensure the acquisition of ideal microstructure and substructure; two-stage cooling can suppress high-temperature phase transformation and refine hard phase structure on the one hand, and reduce internal stress on the other hand, which is beneficial to 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.

[0054] The beneficial effects of this invention are as follows:

[0055] (1) The composition of this invention adopts a low C, Mn, and Al design, which effectively reduces segregation and suppresses harmful inclusions; by adding elements such as Mg, Ce, and Ca to control the inclusions, the number and size of inclusions are reduced, and their distribution is made more uniform; coupled with ultra-low P, S, H, and O content and continuous casting billet quality control, fatigue resistance and corrosion resistance are effectively improved. By adding Nb and V, 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 fine grain, which improves strength and weldability and plays a certain role in hydrogen trapping, thus improving corrosion resistance; adding a small amount of Ni and Cu balances the improvement of strength and corrosion resistance. With the smelting, heating, rolling and cooling processes that match the alloy composition, high strength, high toughness, fatigue resistance, corrosion resistance and other comprehensive technical characteristics and ideal microstructure are obtained to meet the complex and harsh service requirements of deep-sea subsea pipeline steel.

[0056] (2) This invention employs high-purity smelting, highly homogenized heating, two-stage low-temperature roughing rolling with high-penetration deformation of the thick section, rapid cooling of the intermediate billet, multi-stage finishing rolling, and differentiated water cooling to obtain a fine microstructure of acicular ferrite, polygonal ferrite, and granular bainite, as well as dispersed small-sized precipitates, giving the steel plate excellent comprehensive properties. Furthermore, this invention features a low deformation rate in the final pass of roughing rolling, low equipment capacity requirements, and no need for further heat treatment after cooling. This results in fewer processes, lower costs, and higher production efficiency.

[0057] (3) The 500MPa grade fatigue-resistant and corrosion-resistant deep-sea subsea pipeline wide and thick steel plate of the present invention has a thickness of 25-40mm, a transverse yield strength of 420-540MPa, a transverse tensile strength of 535-600MPa, a transverse yield-to-tensile ratio ≤0.88, a transverse impact energy average of ≥300J at -60℃, a transverse impact energy average of ≥180J at -20℃ in the weld heat-affected zone, and a transverse DWTT shear area ≥85% at -30℃; a longitudinal yield strength of 400-520MPa, a longitudinal tensile strength of 515-580MPa, a longitudinal uniform elongation UEL ≥8%, and a longitudinal yield-to-tensile ratio ≤0.87; and a fatigue life ≥2×10 under high stress (fatigue stress amplitude 25kpsi). 6 The CTOD is ≥0.6mm at -30℃, and the HIC corrosion resistance meets the requirements of CLR≤5%, CTR≤2%, and CSR≤0.5% after 96 hours of corrosion with NACE standard A solution. The SSCC corrosion resistance meets the requirements of no breakage after 720 hours of immersion in saturated H2S solution under 90% stress loading and no visible cracks under 10x magnification. The fatigue-resistant and corrosion-resistant deep-sea subsea pipelines manufactured meet the requirements of X60 and X65 grades. Attached Figure Description

[0058] Figure 1 This is a metallographic image of the microstructure of Embodiment 2 of the present invention. Detailed Implementation

[0059] A 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate for deep-sea subsea pipelines, the composition of which, by weight percentage, is as follows: C: 0.015%–0.035%, Si: 0.20%–0.45%, Mn: 0.90%–1.35%, Nb: 0.015%–0.050%, V: 0.010%–0.050%, N: 0.0030%–0.0080%, Ni: 0.01%–0.10%, Cu 0.05%~0.15%, Cr: 0.15%~0.30%, Mg: 0.0010%~0.0050%, Ca: 0.0010%~0.0040%, Ce≤0.005%, Ti≤0.010%, Mo<0.10%, Al<0.010%, P≤0.010%, S≤0.0015%, H≤0.0001%, O≤0.0015%, with the balance being iron and unavoidable impurities.

[0060] Furthermore, the 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate CE for deep-sea subsea pipelines described in this invention... IIW Controlled within 0.29%–0.35%, CE Pcm The concentration should be controlled between 0.12% and 0.15%, including CE. IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15;

[0061] CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0062] Furthermore, the Nb+V content in the thick steel plate is 0.050% to 0.090%.

[0063] Furthermore, in the thick steel plate, (Ce / 140+Mg / 24+Ca / 40) / (S / 32)=4~7.

[0064] Furthermore, the microstructure of the thick steel plate is acicular ferrite + polygonal ferrite + granular bainite, wherein, by volume percentage: polygonal ferrite volume percentage 10%–55%, and the average grain cross-sectional area of ​​polygonal ferrite ≤100μm. 2 The average cross-sectional area of ​​acicular ferrite grains is ≤70μm. 2 The matrix contains fine precipitates with a size ≤30nm that are diffusely distributed. The precipitates are composed of Nb, V nitrides and carbides.

[0065] The thickness of the wide and thick steel plate is 25-40 mm, with a transverse yield strength of 420-540 MPa, a transverse tensile strength of 535-600 MPa, a transverse yield-to-tensile ratio ≤0.88, a transverse impact energy average of ≥300 J at -60℃, a transverse impact energy average of ≥180 J at -20℃ in the weld heat-affected zone, and a transverse DWTT shear area ≥85% at -45℃; a longitudinal yield strength of 400-520 MPa, a longitudinal tensile strength of 515-580 MPa, a longitudinal uniform elongation UEL ≥8%, and a longitudinal yield-to-tensile ratio ≤0.87; and a fatigue life ≥2 × 10⁻⁶ under a high-stress fatigue amplitude of 30 kpsi. 6 The corrosion resistance is as follows: CTOD ≥ 0.6 mm at -45℃; HIC corrosion resistance meets the requirements of CLR ≤ 5%, CTR ≤ 2%, and CSR ≤ 0.5% after 96 hours of corrosion with NACE standard A solution; SSCC corrosion resistance meets the requirements of no breakage after 720 hours of immersion in saturated H2S solution under 90% stress loading and no visible cracks under 10x magnification.

[0066] A method for preparing a 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate for deep-sea subsea pipelines includes smelting, continuous casting, heating, rough rolling, finish rolling, and cooling.

[0067] Rough rolling:

[0068] Before rough rolling, 3 to 5 passes of high-pressure water descaling and cooling are performed, with an average cooling rate of 0.5 to 3℃ / s. Rough rolling consists of two stages. Each rolling pass of rough rolling is sprayed with cooling. The end temperature of the first stage of rough rolling is 1080 to 1120℃. The total deformation rate of the second stage of rough rolling is ≥35%, and the deformation rate of each pass is 18% to 21%, with a high-low-high cycle of variable passes. The rolling speed of rough rolling is 1.0 to 2.0 m / s, and the end temperature of the second stage of rough rolling is 970 to 1020℃.

[0069] Finishing rolling:

[0070] The finishing rolling process consists of two stages. The initial rolling temperature of the first stage is 830–880℃, and the final rolling temperature of the first stage is 780–820℃. After waiting for 30–90 seconds, the second stage of finishing rolling begins, and the final rolling temperature of the second stage is 740–770℃. The deformation rate during the finishing rolling stage is 60%–75%.

[0071] cool down:

[0072] After rolling, the steel plates undergo two-stage cooling after pre-straightening. The initial water cooling temperature is 720–760℃, and the final water cooling temperature at the top of the steel plate is 380–520℃. During water cooling, the water flow rate in the first 5–7 groups of upper manifolds is 250–350 L / m. 2 The remaining water flow rate in the upper manifold is 120–230 L / m. 2 In the water-cooled system, the roller conveyor first decelerates and then accelerates, with a deceleration rate of 0.01 to 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, and the average final cooling temperature at the head of the steel plate is 20 to 70°C higher than that at the tail.

[0073] Furthermore, the slab is rapidly water-cooled between the two stages of rough rolling, with an average cooling rate of 2–4 °C / s and a cooling time of 10–30 s.

[0074] 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 2-10°C / s, until it reaches the starting temperature of the first stage of finishing rolling.

[0075] Furthermore, 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 4 / 1 to 5 / 1 ratio to create 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, V, Mg, and Ce 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 required according to the N content in the finished steel plate. The quenching time of molten steel before being loaded onto the machine is ≥10 min. The superheating temperature of the continuously cast billet is 5 to 35℃. The residence time of molten steel in the tundish during casting is ≥380s. The dynamic light reduction of the billet is ≥5mm. The casting speed is controlled within the range of 0.6 to 1.2 m / min. The center segregation of the continuously cast billet is ≤C grade 0.5, the center porosity is ≤0.5, the inclusions of type A and C are ≤0.5, and the inclusions of type B and D are ≤1.0.

[0076] Furthermore, 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 6–12℃ / 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 min / mm–1.6 min / mm, the furnace exit temperature is 1150–1190℃, and the temperature difference between the thickness section is ≤30℃.

[0077] The present invention will be further illustrated below through examples.

[0078] The composition 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 steel in this embodiment of the invention are shown in Table 4. The main process parameters for rough rolling of the steel in this embodiment of the invention are shown in Table 5. The main process parameters for finish rolling of the steel in this embodiment of the invention are shown in Table 6. The main process parameters for cooling and the microstructure of the steel in this embodiment of the invention are shown in Table 7. The mechanical properties of the steel in this embodiment of the invention are shown in Table 8. The corrosion resistance of the steel in this invention is shown in Table 9.

[0079] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0080] Example C Si Mn Nb V N Ni Cu Cr Mg Ca Nb+V 1 0.032 0.29 1.33 0.038 0.031 0.0066 0.05 0.12 0.23 0.0032 0.0025 0.069 2 0.027 0.38 1.29 0.020 0.048 0.0071 0.09 0.07 0.28 0.0015 0.0028 0.068 3 0.019 0.41 1.28 0.029 0.036 0.0050 0.07 0.13 0.22 0.0018 0.0035 0.065 4 0.031 0.36 1.08 0.016 0.040 0.0062 0.09 0.10 0.26 0.0043 0.0017 0.056 5 0.028 0.27 1.34 0.032 0.028 0.0047 0.06 0.09 0.19 0.0022 0.0020 0.060 6 0.033 0.35 1.19 0.028 0.045 0.0060 0.08 0.13 0.25 0.0025 0.0032 0.073 7 0.024 0.43 1.28 0.018 0.047 0.0055 0.05 0.08 0.29 0.0036 0.0013 0.065 8 0.034 0.31 1.18 0.046 0.039 0.0065 0.09 0.14 0.22 0.0015 0.0024 0.085 Comparative Example 1 0.032 0.29 1.31 0.021 0.017 0.0054 0.07 0.11 0.21 0.0027 0.0030 0.038 Comparative Example 2 0.027 0.33 1.27 0.042 0.031 0.0062 0.08 0.13 0.27 0.0012 0.0022 0.073 Example Ce A Ti Mo Al <![CDATA[CE IIW ]]> <![CDATA[CE Pcm ]]> P S H O - 1 0 5.2 0.007 0 0.005 0.317 0.130 0.008 0.0012 0.00009 0.0010 - 2 0.0031 4.5 0 0.05 0 0.328 0.131 0.009 0.0011 0.0001 0.0013 - 3 0 4.3 0 0.08 0.006 0.313 0.124 0.008 0.0012 0.0001 0.0012 - 4 0.0026 5.9 0 0.09 0 0.302 0.127 0.006 0.0013 0.00008 0.0009 - 5 0.0045 4.3 0.006 0.06 0.008 0.317 0.126 0.010 0.0013 0.0001 0.0013 - 6 0.0018 5.3 0.009 0.08 0 0.320 0.134 0.008 0.0012 0.00008 0.0010 - 7 0.0033 6.0 0.007 0.06 0.005 0.325 0.130 0.007 0.0011 0.00009 0.0015 - 8 0.0025 4.5 0.005 0.05 0.006 0.308 0.130 0.006 0.0010 0.0001 0.0012 - Comparative Example 1 0.0022 4.4 0 0.06 0.007 0.320 0.130 0.007 0.0010 0.00008 0.0010 - Comparative Example 2 0.0018 3.1 0.006 0.08 0.005 0.329 0.131 0.009 0.0012 0.0001 0.0013 -

[0081] Note: A = (Ce / 140 + Mg / 24 + Ca / 40) / (S / 32)

[0082] Table 2 Main process parameters for steelmaking in the embodiments of the present invention

[0083] Example Top slag limestone / fluorite slag alkalinity FeO + MnO weight percentage in slag / % RH vacuum degree / torr Vacuum processing time / min 1 4.5 5.3 0.78 0.4 18 2 4.2 4.7 0.90 0.5 16 3 4.6 5.8 0.84 0.4 21 4 4.2 5.5 0.82 0.5 16 5 4.3 4.9 0.95 0.3 19 6 4.8 6.0 0.74 0.3 20 7 4.1 5.3 0.86 0.5 15 8 4.6 4.6 0.90 0.4 18 Comparative Example 1 4.1 4.8 0.95 0.5 21 Comparative Example 2 4.5 5.3 0.92 0.5 19

[0084] Table 3 Main process parameters for continuous steel casting in the embodiments of the present invention.

[0085] 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 Class A and C inclusions are the highest level. Class B and D inclusions are the highest level. 1 17 21 395 5.9 0.80 C0.5 0 0.5 0.5 2 18 16 400 5.3 0.80 C0.5 0.5 0.5 1.0 3 21 20 402 5.5 0.80 C0.5 0.5 0 0.5 4 17 13 392 6.1 0.80 C0.5 0 0.5 1.0 5 19 15 387 5.8 0.95 C0.5 0 0.5 1.0 6 16 18 405 5.2 0.95 C0.5 0 0.5 0.5 7 23 21 406 5.8 0.95 C0.5 0.5 0.5 0.5 8 21 28 412 5.5 0.95 C0.5 0.5 0.5 1.0 Comparative Example 1 16 29 401 5.2 0.80 C0.5 0.5 0.5 0.5 Comparative Example 2 19 26 393 5.5 0.95 C0.5 0.5 1.0 1.5

[0086] Table 4 Main process parameters for steel heating in embodiments of the present invention

[0087] Example Average heating rate in heating stage 1 and heating stage 2 / °C / min Average heating rate in three stages / °C / min Average heating rate of the soaking zone / °C / min Total heating time / min / mm Furnace temperature / ℃ Thickness section temperature difference / ℃ 1 6.7 4.5 0.47 1.3 1182 18 2 8.3 2.8 0.36 1.5 1158 12 3 8.1 3.3 0.15 1.2 1163 23 4 11.5 3.0 0.12 1.6 1176 10 5 9.2 4.1 0.35 1.2 1165 21 6 7.5 3.5 0.28 1.1 1169 25 7 6.6 4.3 0.39 1.3 1180 19 8 8.5 4.6 0.26 1.0 1178 26 Comparative Example 1 9.0 3.2 0.45 1.2 1172 16 Comparative Example 2 8.1 2.7 0.34 1.5 1185 13

[0088] Table 5 Main process parameters for steel roughing in embodiments of the present invention

[0089] 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 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 4 1.1 1105 1001 2.3 24 43 18～20 1.5 2 3 0.8 1090 1006 2.5 12 48 19～20.5 1.5 3 3 0.8 1087 997 2.2 16 45 18～21 1.5 4 4 1.5 1115 992 2.3 20 42 18.5～20 1.5 5 4 1.5 1100 981 2.5 15 39 19～21 1.0 6 4 1.3 1093 989 2.6 21 37 18～20.5 1.0 7 5 2.1 1102 986 2.1 27 40 18.5～20 1.0 8 5 2.4 1106 1002 2.1 22 36 18.5～21 1.0 Comparative Example 1 4 1.3 1095 993 2.2 18 42 18～20 1.5 Comparative Example 2 3 0.9 1102 997 2.7 15 37 18.5～20.5 1.0

[0090] Table 6 Main process parameters for steel finishing in embodiments of the present invention

[0091] 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 72 912 46 2.8 866 813 73 767 2 68 890 37 8.2 853 805 58 758 3 72 895 40 6.0 855 808 52 765 4 70 903 43 3.9 860 801 60 762 5 66 865 32 5.1 833 788 42 750 6 64 881 36 5.5 845 794 39 752 7 68 872 42 8.0 830 789 45 744 8 66 864 26 8.9 838 785 37 745 Comparative Example 1 70 886 29 5.2 857 812 63 758 Comparative Example 2 65 871 31 4.5 840 790 47 742

[0092] Table 7 Main process parameters and microstructure of steel cooling in embodiments of the present invention

[0093] Example Initial water cooling temperature / °C Water-cooled steel plate head temperature / ℃ <![CDATA[Water volume of the first 5 - 7 upper headers / L / m 2 ·min]]> <![CDATA[Remaining upper header water volume / L / m 2 ·min]]> Average final cooling temperature difference from head to tail along length (°C) Water-cooled roller conveyor speed increase / decrease rate / m / s Polygonal ferrite volume percentage / % Average cross-sectional area of ​​acicular ferrite grains / μm2 Average grain cross-sectional area of ​​polygonal ferrite / μm2 Plate thickness / mm 1 759 469 6 groups 300 150 35 0.04 21 37 55 28.6 2 743 482 5 groups 330 130 42 0.02 39 46 61 28.6 3 752 430 6 groups 270 210 39 0.03 18 45 48 28.6 4 748 406 7 groups 300 190 50 0.05 28 39 52 28.6 5 741 394 6 groups 330 220 28 0.03 41 30 65 32 6 735 382 7 groups 310 210 55 0.05 49 33 68 32 7 732 405 7 groups 290 220 43 0.04 43 38 59 32 8 728 412 5 groups 350 190 41 0.03 54 40 73 32 Comparative Example 1 749 446 6 groups 280 180 36 0.04 32 74 118 28.6 Comparative Example 2 730 398 6 groups 330 200 49 0.03 47 59 92 32

[0094] Table 8 Mechanical properties of steel in embodiments of the present invention

[0095] 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 / % <![CDATA[Fatigue life (30 kpsi) / 10 6 > CTOD-45℃ave / mm 1-Horizontal 490 565 0.87 -- 351 239 88 -- -- 1-Vertical 465 550 0.85 9.0 -- -- -- 3.5 1.08 2-Horizontal 460 550 0.84 -- 390 247 90 -- -- 2-Vertical 430 530 0.81 11 -- -- -- 4.2 1.13 3-Horizontal 505 580 0.87 -- 335 230 87 -- -- 3-Vertical 485 555 0.87 8.5 -- -- -- 3.2 0.95 4-Horizontal 470 575 0.82 -- 374 219 88 -- -- 4-Vertical 450 545 0.83 9.0 -- -- -- 3.8 1.05 5-Horizontal 460 560 0.82 -- 355 227 86 -- -- 5-Vertical 445 540 0.82 11 -- -- -- 4.0 1.10 6-Horizontal 445 560 0.79 -- 370 251 88 -- -- 6-Vertical 415 535 0.78 12 -- -- -- 4.0 1.18 7-Horizontal 455 565 0.81 -- 339 215 88 -- -- 7-Vertical 430 545 0.79 11 -- -- -- 3.7 1.15 8-Horizontal 435 545 0.80 -- 362 256 87 -- -- 8-Vertical 410 525 0.78 12 -- -- -- 3.9 1.18 Comparative Example 1 - Horizontal 475 560 0.85 277 192 82 2.3 0.87 Comparative Example 1 - Longitudinal 450 545 0.83 11.5 -- -- -- Comparative Example 2 - Horizontal 460 555 0.83 296 203 80 2.6 0.90 Comparative Example 2 - Longitudinal 430 535 0.80 11

[0096] 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.

[0097] Table 9 Corrosion resistance of the steel of this invention

[0098] Example Anti-HICCLR / % Anti-HICCTR / % Anti-HICCSR / % Anti-SSCC 1 0 0 0 qualified 2 0 0 0 qualified 3 0 0 0 qualified 4 0 0 0 qualified 5 0 0 0 qualified 6 0.5 0.1 0.005 qualified 7 0 0 0 qualified 8 0 0 0 qualified Comparative Example 1 1.0 0.6 0.006 qualified Comparative Example 2 2.8 2.2 0.062 qualified

[0099] Note: HIC corrosion resistance test conditions: corrosion by NACEA solution for 96 hours; SSCC corrosion resistance test conditions: no fracture occurred after immersion in saturated H2S solution (solution A) for 720 hours under 90% stress loading, and no visible cracks were observed when magnified 10 times.

[0100] As can be seen from the above, the microstructure of the thick steel plate produced using this invention is acicular ferrite + polygonal ferrite + granular bainite, wherein, by volume percentage: polygonal ferrite volume percentage 10%~55%, and the average grain cross-sectional area of ​​polygonal ferrite ≤100μm. 2 The average cross-sectional area of ​​acicular ferrite grains is ≤70μm. 2The matrix contains fine precipitates with a size ≤30nm dispersedly, and the precipitated phases are composed of Nb, V nitrides and carbides. The thickness of the wide and thick steel plate is 25–40mm, with a transverse yield strength of 420–540MPa, a transverse tensile strength of 535–600MPa, a transverse yield-to-tensile ratio ≤0.88, an average transverse impact energy ≥300J at -60℃, an average transverse impact energy ≥180J in the weld heat-affected zone at -20℃, and a transverse DWTT shear area ≥85% at -45℃; longitudinal yield strength is 400–520MPa, longitudinal tensile strength is 515–580MPa, longitudinal uniform elongation UEL ≥8%, and a longitudinal yield-to-tensile ratio ≤0.87; fatigue life at a high stress fatigue amplitude of 30kpsi is ≥2×10⁻⁶. 6 The corrosion resistance is as follows: CTOD ≥ 0.6 mm at -45℃; HIC corrosion resistance meets the requirements of CLR ≤ 5%, CTR ≤ 2%, and CSR ≤ 0.5% after 96 hours of corrosion with NACE standard A solution; SSCC corrosion resistance meets the requirements of no breakage after 720 hours of immersion in saturated H2S solution under 90% stress loading and no visible cracks under 10x magnification.

[0101] 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 thick steel plate for deep-sea subsea pipelines with 500MPa-grade fatigue resistance and corrosion resistance, characterized in that, The composition of the steel plate, by weight percentage, is as follows: C: 0.015%–0.035%, Si: 0.20%–0.45%, Mn: 0.90%–1.35%, Nb: 0.015%–0.050%, V: 0.010%–0.050%, N: 0.0030%–0.0080%, Ni: 0.01%–0.10%, Cu: 0.05%–0.15%, Cr: 0.15%–0.30%, Mg: 0.0015%–0.0050%, Ca: 0.00 The composition is 10%–0.0040%, Ce≤0.005%, Ti≤0.010%, Mo<0.10%, Al<0.010%, P≤0.010%, S≤0.0015%, H≤0.0001%, O≤0.0015%, with the balance being iron and unavoidable impurities; the microstructure of the thick steel plate is acicular ferrite + polygonal ferrite + granular bainite, wherein, by volume percentage: polygonal ferrite volume percentage 10%–55%, average grain cross-sectional area of ​​polygonal ferrite ≤100μm. 2 The average cross-sectional area of ​​acicular ferrite grains is ≤70μm. 2 The matrix contains fine precipitates with a size ≤30nm dispersedly, and the precipitates are composed of Nb, V nitrides and carbides; the thickness of the wide and thick steel plate is 25-40mm, the transverse yield strength is 420-540MPa, the transverse tensile strength is 535-600MPa, the transverse yield ratio is ≤0.88, the average transverse impact energy at -60℃ is ≥300J, the average transverse impact energy at -20℃ in the weld heat-affected zone is ≥180J, and the transverse DWTT shear area at -45℃ is ≥85%; the longitudinal yield strength is 400-520MPa, the longitudinal tensile strength is 515-580MPa, the longitudinal uniform elongation UEL is ≥8%, and the longitudinal yield ratio is ≤0.87; the fatigue life at a high stress fatigue amplitude of 30kpsi is ≥2×10 6 The corrosion resistance is as follows: CTOD ≥ 0.6 mm at -45℃; HIC corrosion resistance meets the requirements of CLR ≤ 5%, CTR ≤ 2%, and CSR ≤ 0.5% after 96 hours of corrosion with NACE standard A solution; SSCC corrosion resistance meets the requirements of no breakage after 720 hours of immersion in saturated H2S solution under 90% stress loading and no visible cracks under 10x magnification.

2. The 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate for deep-sea subsea pipelines according to claim 1, characterized in that, The Nb+V content in the thick steel plate is 0.050% to 0.090%.

3. The 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate for deep-sea subsea pipelines according to claim 1, characterized in that, In the thick steel plate, (Ce / 140+Mg / 24+Ca / 40) / (S / 32)=4~7.

4. A method for preparing a 500MPa grade fatigue-resistant and corrosion-resistant thick steel plate for deep-sea subsea pipelines as described in any one of claims 1-3, comprising smelting, continuous casting, heating, rough rolling, finish rolling, and cooling; characterized in that: Rough rolling: Before rough rolling, 3 to 5 passes of high-pressure water descaling and cooling are performed, with an average cooling rate of 0.5 to 3℃ / s. Rough rolling consists of two stages. Each rolling pass of rough rolling is sprayed with cooling. The end temperature of the first stage of rough rolling is 1080 to 1120℃. The total deformation rate of the second stage of rough rolling is ≥35%, and the deformation rate of each pass is 18% to 21%, with a high-low-high cycle of variable passes. The rolling speed of rough rolling is 1.0 to 2.0 m / s, and the end temperature of the second stage of rough rolling is 970 to 1020℃. Finishing rolling: The finishing rolling process consists of two stages. The initial rolling temperature of the first stage is 830–880℃, and the final rolling temperature of the first stage is 780–820℃. After waiting for 30–90 seconds, the second stage of finishing rolling begins, and the final rolling temperature of the second stage is 740–770℃. The deformation rate during the finishing rolling stage is 60%–75%. cool down: After rolling, the steel plates undergo two-stage cooling after pre-straightening. The initial water cooling temperature is 720–760℃, and the final water cooling temperature at the top of the steel plate is 380–520℃. During water cooling, the water flow rate in the first 5–7 groups of upper manifolds is 250–330 L / m. 2 The remaining water flow rate in the upper manifold is 120–230 L / m. 2 In the water-cooled system, the roller conveyor first decelerates and then accelerates, with a deceleration rate of 0.01 to 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, and the average final cooling temperature at the head of the steel plate is 20 to 70°C higher than that at the tail.

5. The method for preparing 500MPa grade fatigue-resistant and corrosion-resistant thick steel plates for deep-sea subsea pipelines according to claim 4, characterized in that: The slab is rapidly water-cooled between the two stages of rough rolling, with an average cooling rate of 2-4℃ / s and a cooling time of 10-30s.

6. The method for preparing 500MPa grade fatigue-resistant and corrosion-resistant thick steel plates for deep-sea subsea pipelines according to claim 4, characterized in that: After rough rolling, the intermediate billet is rapidly cooled to 20-60°C above the first stage of finishing rolling temperature, with an average cooling rate of 2-10°C / s, and then cooled to the first stage of finishing rolling temperature.

7. The method for preparing 500MPa grade fatigue-resistant and corrosion-resistant thick steel plates for deep-sea subsea pipelines according to claim 4, characterized in that: The converter adopts top and bottom blowing and double slag smelting, with slag blocking during 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 at 4 to 7, and the weight percentage of FeO + MnO in the slag is controlled to be ≤1%. After refining and deoxidation, Ti, V, Mg, and Ce 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 required according to the N content in the finished steel plate. The quenching time of molten steel before being loaded onto the machine is ≥10 min. The superheating temperature of the continuously cast billet is 5 to 35℃. The residence time of molten steel in the tundish during casting is ≥380s. The dynamic light reduction of the billet is ≥5mm. The casting speed is controlled within the range of 0.6 to 1.2 m / min. The center segregation of the continuously cast billet is ≤C grade 0.5, the center porosity is ≤0.5, the inclusions of type A and C are ≤0.5, and the inclusions of type B and D are ≤1.

0.

8. The method for preparing 500MPa grade fatigue-resistant and corrosion-resistant thick steel plates for deep-sea subsea pipelines according to claim 4, characterized in that: 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 6–12℃ / 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 1150–1190℃, and the temperature difference between the thickness section is ≤30℃.

Images