Steel plate for a submarine pipeline and method of manufacturing the same

Abstract

The present application relates to a kind of steel plate for submarine pipeline and its manufacturing method, belong to low alloy high strength steel technical field, at least one of the problems in the prior art steel plate strength, toughness, plasticity and large strain capacity is insufficient, the stability of using under submarine environment is not good.The present application provides a kind of steel plate for submarine pipeline, the specific composition of the steel plate is as follows by mass percent: C:0.045%~0.060%, Si:0.18%~0.25%, Mn:1.20%~1.50%, P:0~0.012%, S:0~0.0030%, Cr:0.10%~0.20%, Ni:0.06%~0.12%, Mo:0.06%~0.10%, V:0.025%~0.035%, Nb:0.025%~0.035%, Ti:0.012%~0.020%, the balance is Fe.The thickness specification of the above steel plate is 28.6mm, suitable for manufacturing the outer diameter of 1219mm submarine pipeline steel pipe, steel plate microstructure feature is polygonal ferrite and bainite dual phase, steel plate has excellent strength, toughness, plasticity and large strain capacity, suitable for complex submarine environment.

Description

Technical Field

[0001] This invention relates to the field of low-alloy high-strength steel technology, and in particular to a steel plate for submarine pipelines and its manufacturing method. Background Technology

[0002] With onshore oil and gas resources becoming increasingly depleted, extraction is becoming more difficult and costly, leading to a shift towards the seabed, especially deep-sea areas. The seabed holds abundant oil and gas resources, accounting for more than one-third of the world's total. Offshore gas pipelines are the primary means of transporting oil and gas from offshore oil and gas production platforms to land, serving as an indispensable lifeline for offshore oil and gas field development and production. While pipeline steel products have been successfully deployed in large quantities onshore, the performance requirements for steel pipes are much more stringent in the complex marine environment. With the continuous development of steel production technology, subsea pipeline steel with a diameter of no more than 813 mm has been successfully developed, but research and development of thick-walled subsea pipeline steel with a diameter of 1219 mm is currently lacking.

[0003] Currently, publicly available literature on submarine pipeline steel has issues such as insufficient strength, toughness, plasticity, and large strain capacity, especially insufficient toughness in low-temperature environments. During use / service in the special underwater environment, it is prone to cracking, damage, and deformation. The underwater environment also brings great difficulties to the maintenance and replacement of pipelines. In reality, it is difficult to replace damaged submarine pipelines; repairs can only be carried out in various forms, and it is difficult to guarantee the quality and durability of the repairs.

[0004] Therefore, it is necessary to develop a type of pipeline steel that has excellent strength, toughness, plasticity and large strain capacity under special underwater environments (high pressure, low temperature, etc.). Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a steel plate for submarine pipelines and a method for manufacturing the same, in order to solve at least one of the problems of insufficient strength, toughness, plasticity and large strain capacity of existing submarine pipeline steel, especially insufficient toughness in low-temperature environments.

[0006] This invention discloses a steel plate for submarine pipelines. The specific composition of the steel plate, by mass percentage, is as follows: C: 0.045%–0.060%, Si: 0.18%–0.25%, Mn: 1.20%–1.50%, P: 0–0.012%, S: 0–0.0030%, Cr: 0.10%–0.20%, Ni: 0.06%–0.12%, Mo: 0.06%–0.10%, V: 0.025%–0.035%, Nb: 0.025%–0.035%, Ti: 0.012%–0.020%, with the balance being Fe.

[0007] Specifically, the steel plate has a dual-phase structure of polygonal ferrite and bainite, wherein the proportion of polygonal ferrite is between 70% and 80%, and the structure is uniformly distributed.

[0008] Specifically, the longitudinal uniform elongation of the steel plate is not less than 14%.

[0009] Specifically, the Charpy impact energy of the steel plate at -30℃ is not less than 300J.

[0010] The present invention also discloses a method for manufacturing the steel plate, specifically including the following steps:

[0011] S1: Molten steel with the target metallurgical composition obtained through smelting;

[0012] S2: Continuously cast molten steel into slabs;

[0013] S3: Preheat the slab and perform controlled rolling to obtain a semi-finished steel plate;

[0014] S4: Controlled cooling of the semi-finished steel plate to obtain the finished steel plate.

[0015] Specifically, the smelting process in step S1 is converter smelting and LF and / or RH refining.

[0016] Specifically, the continuous casting process in step S2 is as follows: molten steel is poured under full protection. During the continuous casting process, a superheat of 20-30°C above the liquidus, a casting speed of 1.0-1.3 m / min, and a dynamic light reduction process with a total reduction of 4-6 mm are adopted to finally obtain a slab with a thickness of 300 mm.

[0017] Specifically, the preheating process in step S3 is as follows: the slab is heated to a furnace temperature of 1120-1180℃, the heating time in the soaking zone is not less than 90 minutes, and the total heating time is 150-270 minutes.

[0018] Specifically, the controlled rolling process in step S3 includes a roughing rolling section and a finishing rolling section;

[0019] The roughing process is as follows: the heated slab is rolled in both transverse and longitudinal directions for a total of 5 passes to obtain an intermediate slab with a thickness of 110 mm. The first two passes are transverse rolling to widen the slab to 3700-3900 mm, and the last three passes are longitudinal rolling. The reduction rate of the fourth pass is ≥20%, the reduction rate of the fifth pass is ≥24%, and the rolling temperature of the last pass is 1050-1100℃.

[0020] The finishing rolling process is as follows: the obtained intermediate billet is rolled in 7 passes, the finishing rolling entry temperature is ≤940℃, the 7th rolling temperature is 850℃~880℃, and a semi-finished hot-rolled steel plate with a target thickness of 28.6mm is obtained.

[0021] Specifically, the steps for controlling cooling in step S4 are as follows:

[0022] First stage: Spray water to rapidly cool the semi-finished steel plate at a rate of 15-20℃ / s, cooling it to 735-775℃;

[0023] The second stage: The semi-finished steel plate is slowly cooled in the air to 680-720℃;

[0024] The third stage: the semi-finished steel plate is rapidly cooled by water spraying at a rate of 20-30℃ / s, until it reaches 460-500℃;

[0025] The fourth stage involves using a stacking slow cooling process, where semi-finished steel plates are stacked in a dry, sheltered place and allowed to cool naturally in the air for at least 10 hours to obtain finished steel plates.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] 1. The steel plate for submarine pipelines disclosed in this invention has high strength, toughness, and plasticity, especially excellent toughness / large strain capacity under low temperature environment.

[0028] This invention utilizes a rational alloy element design, combining carbon with microalloying elements such as Nb, V, and Ti to form carbide precipitation, effectively suppressing austenite recrystallization, pinning grain boundaries, refining grains, and improving the strength and toughness of the steel plate. Solid-soluble elements such as Si and Mn effectively reduce carbide enrichment at grain boundaries, lowering stress concentration and improving the low-temperature toughness of the steel. Combined with the rational design of continuous casting and rolling process parameters, the microstructure of the continuously cast billet in the intermediate stages is made uniform, reducing center segregation. The roughing process employing first horizontal rolling and then longitudinal rolling reduces the anisotropy of the steel plate. A controlled cooling process combining 5 passes of roughing and 7 passes of finishing rolling is rationally matched to regulate the formation of a fine-grained polygonal ferrite and bainite dual-phase microstructure in the steel plate, promoting the full precipitation of second-phase particles and the homogenization of the substructure, thereby improving the strength and toughness of the steel plate and ensuring the safe operation of the subsea pipeline.

[0029] 2. The performance parameters of the steel plate provided by this invention are as follows:

[0030] Transverse tensile properties: transverse yield strength 420~560MPa, tensile strength 540~760MPa, yield ratio not greater than 0.72, elongation at break not less than 40%; minimum Charpy impact energy obtained at -30℃ not less than 300J; drop hammer toughness tear area (DWTT) obtained at -20℃ not less than 95%; longitudinal tensile properties: longitudinal yield ratio not greater than 0.72, uniform elongation not less than 14%.

[0031] 3. The steel plate manufacturing process provided by this invention is simple, and the required raw materials and equipment are all common materials / equipment on the market, which are easy to obtain. Moreover, the amount of alloying elements added is low, and the cost is controllable. The process conditions are relatively mild, making it suitable for large-scale production and widespread application.

[0032] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0033] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0034] Figure 1 This is an optical metallographic photograph of the steel plate used for the subsea pipeline in Example 1;

[0035] Figure 2 This is a scanning electron microscope tissue photograph of the steel plate used for the subsea pipeline in Example 1. Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0037] This invention discloses a steel plate for submarine pipelines. The specific composition of the steel plate, by mass percentage, is as follows: C: 0.045%–0.060%, Si: 0.18%–0.25%, Mn: 1.20%–1.50%, P: 0–0.012%, S: 0–0.0030%, Cr: 0.10%–0.20%, Ni: 0.06%–0.12%, Mo: 0.06%–0.10%, V: 0.025%–0.035%, Nb: 0.025%–0.035%, Ti: 0.012%–0.020%, with the balance being Fe.

[0038] The roles / synergistic effects of each component and the basis for selecting their content are as follows:

[0039] Carbon: C can combine with microalloying elements such as Nb, V, and Ti to form carbide precipitation, which can inhibit austenite recrystallization and also play a role in precipitation strengthening. It pins grain boundaries, refines grains, and plays a role in fine grain strengthening, thereby improving the mechanical properties of the product. Too low a carbon content will lead to embrittlement of the grain boundaries in the microstructure, while too high a carbon content will increase the hardenability of pipeline steel, affecting the toughness and weldability of the pipe. A carbon content of 0.045% to 0.060% can effectively improve the strength and toughness of steel plates used for submarine pipelines.

[0040] Silicon: Si is a solid-soluble element. Increasing the silicon content will lead to an increase in strength and hardness, but excessive silicon will cause grain coarsening, which is detrimental to strength and toughness. Therefore, the Si content should be 0.18% to 0.25%.

[0041] Manganese: Mn is an important solid solution element that can effectively reduce the aggregation of carbides on grain boundaries, refine grains, and improve the strength and toughness of steel. However, excessive Mn can affect the weldability of steel. Therefore, the Mn content should be 1.20% to 1.50%.

[0042] Phosphorus and sulfur: P and S elements can contaminate steel and are impurity elements in steel. The purity of steel has an important impact on its mechanical properties, but excessive pursuit of the removal of P and S elements may lead to increased costs. Therefore, it is sufficient to control the P content to 0-0.012% and the S content to 0-0.0030%.

[0043] Nickel, chromium, and molybdenum: Ni, Cr, and Mo are hardenable elements. Appropriate addition can improve the strength and hardness of steel, but it has an adverse effect on low-temperature impact toughness. Through theoretical analysis and experimental verification, the alloy steel exhibits excellent comprehensive performance when the three elements are in the following ranges: Cr: 0.10%~0.20%, Ni: 0.06%~0.12%, and Mo: 0.06%~0.10%.

[0044] Niobium (Nb) is a solid-solution element that promotes austenitization in steel. It interacts with dislocations, hindering dislocation and grain boundary slip, delaying recrystallization, and expanding the recrystallization temperature range, which is beneficial for refining ferrite grains. During controlled rolling and cooling, it promotes the dispersed precipitation of Nb (C,N), playing a role in precipitation strengthening and thus improving the strength of the steel. A Nb content of 0.025%–0.035% is sufficient to achieve good results.

[0045] Vanadium (V) is beneficial for the formation of nanoscale VC precipitation, providing precipitation strengthening. It can effectively refine grains and improve the strength and toughness of steel. V is a hardenability element that can increase the dislocation density in the steel microstructure and improve the microhardness of the steel. A V content of 0.025% to 0.035% can achieve good results.

[0046] Titanium (Ti): During controlled rolling and cooling, Ti can induce precipitation at grain boundaries, pinning them and preventing the continued growth of recrystallized grains, effectively refining the grains. However, excessive Ti forming Ti(C,N) can act as nucleation sites for microcracks, which is detrimental to the low-temperature toughness of steel. Therefore, it is advisable to control the Ti content to 0.012%–0.020%.

[0047] Specifically, the steel plate has a dual-phase structure of polygonal ferrite and bainite, wherein the proportion of polygonal ferrite is between 70% and 80%, and the structure is uniformly distributed.

[0048] Polygonal ferrite (PF) is a proeutectoid ferrite formed at high transformation temperatures and slow cooling rates, exhibiting an equiaxed, regular grain shape. PF has low dislocation density and substructure, thus exhibiting low strength and high plasticity. Bainite is divided into granular bainite (GB) and bainitic ferrite (BF). Bainitic microstructure is an intermediate-temperature transformation microstructure formed at rapid cooling rates, primarily through a mixed shear and diffusion phase transformation mechanism. GB and BF contain abundant bainite laths and have high dislocation density, resulting in higher strength than PF.

[0049] When the PF content is 70%–80% and the bainite content is 20%–30%, the high-plasticity PF combined with the high-strength bainite structure is rationally distributed, resulting in a good balance of strength and toughness in the steel.

[0050] Specifically, the specific performance parameters of the steel plate are as follows:

[0051] Transverse tensile properties: transverse yield strength 420~560MPa, tensile strength 540~760MPa, yield ratio not greater than 0.72, elongation at break not less than 40%; minimum Charpy impact energy obtained at -30℃ not less than 300J; drop hammer toughness tear area (DWTT) obtained at -20℃ not less than 95%; longitudinal tensile properties: longitudinal yield ratio not greater than 0.72, uniform elongation not less than 14%.

[0052] Submarine pipelines undergo significant longitudinal deformation during laying and service. Therefore, the steel used in submarine pipelines must possess excellent longitudinal deformation capacity. The steel plate of this invention has a low longitudinal yield strength ratio and a high longitudinal uniform elongation, providing excellent longitudinal deformation capacity. Simultaneously, some submarine environments are at low temperatures, requiring high low-temperature toughness. The product of this invention exhibits excellent Charpy impact toughness and DWTT performance, ensuring the safe operation of the pipeline.

[0053] The present invention also discloses a method for manufacturing the steel plate, specifically including the following steps:

[0054] S1: Molten steel with the target metallurgical composition obtained through smelting;

[0055] S2: Continuously cast molten steel into slabs;

[0056] S3: Preheat the slab and perform controlled rolling to obtain a semi-finished steel plate;

[0057] S4: Controlled cooling of the semi-finished steel plate to obtain the finished steel plate.

[0058] Specifically, the smelting process in step S1 is converter smelting and LF and / or RH refining.

[0059] Specifically, the continuous casting process in step S2 is as follows: molten steel is poured under full protection. During the continuous casting process, a superheat of 20-30°C above the liquidus, a casting speed of 1.0-1.3 m / min, and a dynamic light reduction process with a total reduction of 4-6 mm are adopted to finally obtain a slab with a thickness of 300 mm.

[0060] By using the above process, the continuous casting billet obtained in the intermediate stage can have lower center segregation, thereby giving the final steel plate product good low-temperature toughness.

[0061] Specifically, the preheating process in step S3 is as follows: the slab is heated to a furnace temperature of 1120-1180℃, the heating time in the soaking zone is not less than 90 minutes, and the total heating time is 150-270 minutes.

[0062] Heating at 1120–1180℃ can homogenize austenite grains, allow alloying elements in the slab to diffuse sufficiently, thereby further reducing element segregation and ensuring adequate solid solution of the second phase.

[0063] Specifically, the controlled rolling process in step S3 includes a roughing rolling section and a finishing rolling section;

[0064] The roughing process is as follows: the heated slab is rolled in both transverse and longitudinal directions for a total of 5 passes to obtain an intermediate slab with a thickness of 110 mm. The first two passes are transverse rolling to widen the slab to 3700-3900 mm, and the last three passes are longitudinal rolling. The reduction rate of the fourth pass is ≥20%, the reduction rate of the fifth pass is ≥24%, and the rolling temperature of the last pass is 1050-1100℃.

[0065] By employing a transverse rolling followed by longitudinal rolling process, the required steel plate width can be obtained while reducing the difference in mechanical properties between the transverse and longitudinal directions. Through proper matching of rolling passes, reduction rate, and rolling temperature, austenite grains can be fully recrystallized, achieving the goal of refining the austenite grains and resulting in a final steel plate product with excellent strength and toughness.

[0066] The finishing rolling process is as follows: the obtained intermediate billet is rolled in 7 passes, the finishing rolling entry temperature is ≤940℃, the 7th rolling temperature is 850℃~880℃, and a semi-finished hot-rolled steel plate with a target thickness of 28.6mm is obtained.

[0067] By properly matching the number of rolling passes, reduction rate, and rolling temperature in the finishing rolling stage, austenite grains can be fully flattened, accumulating a large amount of strain energy, providing a driving force for phase transformation in the cooling stage, increasing nucleation sites, and achieving the goal of refining grains and improving strength and toughness.

[0068] The steel billet is heated to 1120–1180℃ to homogenize its composition before rolling and controlled cooling to achieve the required mechanical properties. A 5-pass roughing and 7-pass finishing rolling process is employed, and different rolling start temperatures, number of passes, reduction amounts, and cooling methods significantly impact the performance of the steel plate. Through the rational design of rolling process parameters, the microstructure of the steel plate is controlled, core defects in the continuously cast billet are improved, grains are refined, toughness and strength are enhanced, and the core and surface are homogenized to achieve the desired performance indicators.

[0069] Specifically, the steps for controlling cooling in step S4 are as follows:

[0070] First stage: Spray water to rapidly cool the semi-finished steel plate at a rate of 15-20℃ / s, cooling it to 735-775℃;

[0071] The second stage: The semi-finished steel plate is slowly cooled in the air to 680-720℃;

[0072] The third stage: the semi-finished steel plate is rapidly cooled by water spraying at a rate of 20-30℃ / s, until it reaches 460-500℃;

[0073] The fourth stage involves using a stacking slow cooling process, where semi-finished steel plates are stacked in a dry, sheltered place and allowed to cool naturally in the air for at least 10 hours to obtain finished steel plates.

[0074] By controlling cooling in the first and second stages, a fine and uniformly distributed polygonal ferrite structure with a certain phase ratio can be obtained; by controlling cooling in the third stage, the untransformed austenite can undergo a phase transformation, thereby transforming into a bainite structure; by controlling cooling in the fourth stage, the second phase particles can be fully precipitated and the substructure can be fully homogenized.

[0075] Ultimately, a dual-phase microstructure of polygonal ferrite and bainite can be obtained, with the proportion of polygonal ferrite between 70% and 80% and the microstructure being uniformly distributed, thus giving the steel plate excellent plasticity and low-temperature toughness.

[0076] Examples and comparative examples:

[0077] According to the metallurgical composition and processing steps of the present invention, the process involves converter smelting, ladle refining, continuous casting, (preheating) controlled rolling, and controlled cooling. The specific composition and parameters are as follows:

[0078] Table 1. Chemical composition and mass percentage (wt.%) of 28.6mm steel plates for X65 grade subsea pipelines.

[0079] 1 0.052 0.20 1.42 0.0095 0.0008 0.16 0.08 0.10 0.025 0.035 0.015 2 0.045 0.23 1.50 0.0100 0.0025 0.10 0.12 0.10 0.034 0.030 0.012 3 0.060 0.18 1.20 0.0085 0.0015 0.12 0.10 0.06 0.035 0.025 0.020 4 0.056 0.25 1.38 0.0090 0.0012 0.20 0.06 0.08 0.032 0.032 0.016

[0080] Table 2 Manufacturing process parameters for 28.6mm steel plates used in X65 grade submarine pipelines

[0081]

[0082] Table 3 Mechanical Properties of 28.6mm Steel Plates for X65 Grade Submarine Pipelines

[0083]

[0084] As can be seen from the mechanical performance parameters of Examples 1 to 4 above, through the innovative design of the metallurgical composition and production process of the present invention, the 28.6mm wide steel plate for X65 grade submarine pipelines has excellent strength and toughness, especially the steel plate has excellent plastic deformation capacity such as low yield strength ratio and high uniform elongation in the longitudinal direction.

[0085] Transverse tensile properties: transverse yield strength 420-560 MPa, tensile strength 540-760 MPa, yield-to-tensile ratio not greater than 0.72, elongation at break not less than 40%; minimum Charpy impact energy obtained at -30℃ not less than 300 J; drop hammer toughness tear area (DWTT) obtained at -20℃ not less than 95%; longitudinal tensile properties: longitudinal yield strength 400-510 MPa, tensile strength 580-700 MPa, longitudinal yield-to-tensile ratio not greater than 0.72, uniform elongation not less than 14%.

[0086] The optical metallographic microstructure of the pipeline steel plate in Example 1 is as follows: Figure 1 As shown, the scanning electron microscope micrographs of tissue are as follows: Figure 2 As shown. (Through) Figure 1 and Figure 2 It can be seen that the pipeline steel of Example 1 has a two-phase structure of uniformly distributed polygonal ferrite and bainite, with the ferrite phase accounting for approximately 75% and the second phase being bainite. Analysis showed that the ferrite phase proportions of Examples 2, 3, and 4 were 74%, 78%, and 71%, respectively, with the second phase being bainite.

[0087] The present invention also provides three comparative examples for comparison with the above-described embodiments 1 to 4.

[0088] Table 4. Chemical composition and mass percentage (wt.%) of comparative steel plates

[0089] 1 0.042 0.18 1.56 0.0078 0.0010 0.02 0.24 0.16 0.15 0.002 0.050 0.015 2 0.062 0.25 1.15 0.0090 0.0020 0.14 0.26 0.18 0.16 0.004 0.052 0.014 3 0.055 0.22 1.45 0.010 0.0015 - 0.15 0.10 0.08 0.030 0.030 0.016

[0090] Table 5. Manufacturing process parameters for comparative steel plates

[0091]

[0092] Table 6 Mechanical properties of comparative steel plates

[0093]

[0094]

[0095] In Comparative Example 1, the lower C content increased the smelting cost, and the higher levels of alloying elements such as Mn, Cr, Ni, Mo, and Nb compared to the Example 1 increased the alloy cost. In Comparative Example 2, Cu was added, and the higher levels of alloying elements such as Cr, Ni, Mo, and Nb compared to the Example 2 also increased the alloy cost. Therefore, overall, the metallurgical costs of Comparative Example 1 and Comparative Example 2 are higher than those of the Example 1.

[0096] Meanwhile, Comparative Example 1 uses a direct rapid cooling process, and Comparative Example 2 uses a two-stage cooling process of slow air cooling + rapid water cooling. Neither of these processes can obtain the excellent fine-grained ferrite + bainite dual-phase microstructure characteristics found in the examples. This is not conducive to improving the low-temperature toughness and longitudinal deformation capacity of the steel plate. Therefore, Comparative Examples 1 and 2 are inferior to the examples in terms of performance parameters such as low-temperature toughness, longitudinal yield strength ratio, and uniform elongation.

[0097] The alloy composition of Comparative Example 3 is within the scope of this invention application, but its manufacturing process is different from that of this invention application. In particular, a two-stage cooling process is used in the cooling stage, resulting in coarse and unevenly distributed ferrite structure. At the same time, due to the high cooling rate and low final cooling temperature, the bainite structure has higher hardness. These structural characteristics lead to Comparative Example 3 having high strength but poor low-temperature toughness and plasticity, which cannot meet the mechanical performance requirements for steel used in submarine pipelines.

[0098] By comparing the mechanical properties of the embodiments and the comparative examples, it can be seen that the products of the present invention, through the design of reasonable metallurgical elements and manufacturing process parameters, have better low-temperature toughness and deformation properties such as longitudinal yield strength ratio and uniform elongation. Compared with the ordinary pipeline steel of the comparative examples, the products have better performance and meet the requirements for laying submarine pipeline steel.

[0099] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A steel plate for submarine pipelines, characterized in that: The specific composition of the steel plate, by mass percentage, is as follows: C: 0.045%–0.060%, Si: 0.18%–0.25%, Mn: 1.20%–1.50%, P: 0–0.012%, S: 0–0.0030%, Cr: 0.10%–0.20%, Ni: 0.06%–0.12%, Mo: 0.06%–0.10%, V: 0.025%–0.035%, Nb: 0.025%–0.035%, Ti: 0.012%–0.020%, with the balance being Fe; The steel plate has a dual-phase structure of polygonal ferrite and bainite, wherein the proportion of polygonal ferrite is between 70% and 80%, and the structure is uniformly distributed. The method for manufacturing the steel plate specifically includes the following steps: S1: Molten steel with the target metallurgical composition obtained through smelting; S2: Continuously cast molten steel into slabs; S3: Preheat the slab and perform controlled rolling to obtain a semi-finished steel plate; S4: Controlled cooling of the semi-finished steel plate to obtain the finished steel plate; The specific steps for controlling cooling as described in step S4 are as follows: First stage: Spray water to rapidly cool the semi-finished steel plate at a rate of 15-20℃ / s, cooling it to 735-775℃; The second stage: The semi-finished steel plate is slowly cooled in the air to 680-720℃; The third stage: the semi-finished steel plate is rapidly cooled by water spraying at a rate of 20-30℃ / s, until it reaches 460-500℃; The fourth stage involves using a stacking slow cooling process, where semi-finished steel plates are stacked in a dry, sheltered place and allowed to cool naturally in the air for at least 10 hours to obtain finished steel plates.

2. The steel plate according to claim 1, characterized in that: The longitudinal uniform elongation of the steel plate is not less than 14%.

3. The steel plate according to claim 1, characterized in that: The steel plate has a Charpy impact energy of not less than 300J at -30℃.

4. A method for manufacturing the steel plate according to any one of claims 1 to 3, characterized in that, Specifically, the following steps are included: S1: Molten steel with the target metallurgical composition obtained through smelting; S2: Continuously cast molten steel into slabs; S3: Preheat the slab and perform controlled rolling to obtain a semi-finished steel plate; S4: Controlled cooling of the semi-finished steel plate to obtain the finished steel plate; the specific steps of controlled cooling in step S4 are as follows: First stage: Spray water to rapidly cool the semi-finished steel plate at a rate of 15-20℃ / s, cooling it to 735-775℃; The second stage: The semi-finished steel plate is slowly cooled in the air to 680-720℃; The third stage: the semi-finished steel plate is rapidly cooled by water spraying at a rate of 20-30℃ / s, until it reaches 460-500℃; The fourth stage involves using a stacking slow cooling process, where semi-finished steel plates are stacked in a dry, sheltered place and allowed to cool naturally in the air for at least 10 hours to obtain finished steel plates.

5. The manufacturing method according to claim 4, characterized in that: The smelting process in step S1 is converter smelting and LF and / or RH refining.

6. The manufacturing method according to claim 4, characterized in that: The specific process of continuous casting in step S2 is as follows: molten steel is poured under full protection. During the continuous casting process, a superheat of 20-30°C above the liquidus, a casting speed of 1.0-1.3 m / min, and a dynamic light reduction process with a total reduction of 4-6 mm are adopted to finally obtain a slab with a thickness of 300 mm.

7. The manufacturing method according to claim 4, characterized in that: The specific process of preheating in step S3 is as follows: the slab is heated to a furnace temperature of 1120-1180℃, the heating time in the soaking zone is not less than 90 minutes, and the total heating time is 150-270 minutes.

8. The manufacturing method according to claim 4, characterized in that: The controlled rolling process described in step S3 includes a roughing rolling section and a finishing rolling section; The roughing process is as follows: the heated slab is rolled in both transverse and longitudinal directions for a total of 5 passes to obtain an intermediate slab with a thickness of 110 mm. The first two passes are transverse rolling to widen the slab to 3700-3900 mm, and the last three passes are longitudinal rolling. The reduction rate of the fourth pass is ≥20%, the reduction rate of the fifth pass is ≥24%, and the rolling temperature of the last pass is 1050-1100℃. The finishing rolling process is as follows: the obtained intermediate billet is rolled in 7 passes, the finishing rolling entry temperature is ≤940℃, the 7th rolling temperature is 850℃~880℃, and a semi-finished hot-rolled steel plate with a target thickness of 28.6mm is obtained.

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