A quenched and tempered steel plate for pressure vessels with high strength and toughness and a manufacturing method thereof

Abstract

The invention relates to a quenched and tempered steel plate for a pressure vessel with high strength and toughness. The chemical composition of the steel plate is as follows by mass percentage: C: 0.07%-0.10%, Si: 0.15%-0.30%, Mn: 0.75%-1.00%, P≤0.010%, S≤0.003%, Ni: 0.80%-1.00%, Cr: 0.55%-0.85%, Mo: 0.10%-0.20%, Ti: 0.01%-0.02%, V: 0.10%-0.20%, Al: 0.03%-0.04%, Cu≤0.04%, Zr: 0.006%-0.010%, N: 0.003%-0.005%, Cr+V+Zr≤0.95%, and the balance is Fe and unavoidable impurities. The steel plate of the present invention has a tensile strength of 850 to 1000 MPa, a yield strength of ≥700 MPa, a transverse impact absorption energy of ≥100 J at -50°C, an elongation A of ≥21%, and a low welding crack sensitivity coefficient Pcm of less than 0.22.

Description

Technical Field

[0001] The present invention relates to the field of steel manufacturing for pressure vessels, and in particular to a quenched and tempered steel plate for pressure vessels with high strength and toughness and a manufacturing method thereof. Background Art

[0002] Quenched and tempered steel plates for pressure vessels are used in the petroleum, chemical, and power plant industries, primarily for the manufacture of structural components for equipment such as reactors, heat exchangers, spherical tanks, oil and gas tanks, and boiler drums. The storage of chemical and petroleum products is crucial to national development and energy security, making pressure vessel steel an irreplaceable tool. This has led to an increase in both the demand for and technical requirements for ambient and low-temperature oil and liquefied natural gas storage tanks.

[0003] To ensure safety, reduce weight, and meet durability / damage tolerance design criteria, high-pressure vessels place extremely high demands on material toughness, low-temperature performance, and weldability. As pressure vessel equipment becomes increasingly larger and the size of stationary storage tanks increases, the demand for higher-quality, tougher quenched and tempered steel plates for pressure vessels also increases. Currently, the steel plates commonly used are thicker to achieve these large-scale requirements, increasing tank manufacturing costs and making welding of extra-thick steel plates more difficult.

[0004] The existing patent CN201410810733.1 "A quenched and tempered high-strength steel with a yield strength of 700 MPa and its production method" states that its chemical composition is: C: 0.06-0.13%, Si: 0.10-0.30%, Mn: 0.80-1.60%, Cr: 0.20-0.70%, Mo: 0.10-0.30%, Ni: 0-0.30%, Nb: 0.010-0.030%, Ti: 0.010-0.030%, V: 0.010-0 .030%, B:0.0005-0.0030%, Al:0.02-0.06%, Ca:0.001-0.004%, N:0.002-0.005%, P≤0.020%, S≤0.010%, O≤0.008%, the rest are Fe and unavoidable impurities, the yield strength of the steel plate is 700-850MPa, the tensile strength is 750-900MPa, but the elongation is greater than 14%, the impact energy at -40℃ is greater than 40J, and the strength and toughness of the steel plate is at a relatively low level.

[0005] Existing patent CN202110832553.3, "A High-Strength and Toughness Alloy Structural Steel and Its Preparation Method," achieves improved toughness by adding more Ni and Cu. However, this results in increased cost, and the reduction in Mn content significantly impacts strength. The elongation of the steel plate after quenching and tempering is too low. In response to this, it is urgent to develop a high-strength and toughness quenched and tempered steel plate for pressure vessels and its preparation method through novel composition design. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high-strength and high-toughness quenched and tempered steel plate for pressure vessels, which is suitable for containers such as petroleum and liquefied natural gas storage.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions:

[0008] A high-strength and toughness quenched and tempered steel plate for a pressure vessel, wherein the chemical composition of the steel plate is as follows by mass percentage: C: 0.07%-0.10%, Si: 0.15%-0.30%, Mn: 0.75%-1.00%, P≤0.010%, S≤0.003%, Ni: 0.80%-1.00%, Cr: 0.55%-0.85%, Mo: 0.10%-0.20%, Ti: 0.01%-0.02%, V: 0.10%-0.20%, Al: 0.03%-0.04%, Cu≤0.04%, Zr: 0.006%-0.010%, N: 0.003%-0.005%, Cr+V+Zr≤0.95%, and the balance being Fe and unavoidable impurities.

[0009] A high-strength and toughness quenched and tempered steel plate for pressure vessels has a tensile strength of 850-1000 MPa, a yield strength of 700 MPa or more, a -50°C impact transverse impact absorption energy of 100 J or more, an elongation of 21% or more, and a low welding crack sensitivity coefficient Pcm of less than 0.22.

[0010] The effects of the above chemical elements are analyzed as follows:

[0011] Carbon forms various carbides with alloying elements in steel, strengthening it and directly increasing the strength of steel plates. Every 0.1% increase in carbon in steel can increase tensile strength by approximately 70 MPa. However, this increase in carbon content reduces plasticity and toughness, worsens weldability, and increases hardenability, making welding more difficult and requiring higher preheat temperatures. Therefore, the carbon content is limited to 0.07% to 0.10%.

[0012] Si is an effective deoxidizer in steel, and a certain amount of Si can increase the strength of steel plates, improve their hardenability and resistance to high-temperature oxidation, but at the expense of plasticity and toughness. If the Si content is too high, the impact toughness of the heat-affected zone will deteriorate, so the Si content is limited to 0.15% to 0.30%.

[0013] Manganese (Mn) improves steel plate strength and hardness through solid solution strengthening. It can lower the quenching temperature and austenite transformation temperature, increase undercooling, refine grain size, and reduce weld crack sensitivity. Higher Mn content increases production costs and is prone to forming MnS with S. Therefore, Mn is limited to 0.75% to 1.00%.

[0014] P is a harmful element in steel and is also an element that is prone to segregation. Therefore, its content should be kept low during the steelmaking process. However, considering cost factors and meeting application requirements, the P content is controlled within a range that does not affect performance, so it is controlled below 0.010%.

[0015] S is also a harmful element in steel and has a great influence on the toughness of steel. However, considering the operability and cost of steelmaking, the S content is controlled below 0.003%.

[0016] Ni is the main element that stabilizes austenite in steel. Ni can exist in austenite and ferrite in a solid solution with Fe, which can improve the strength of steel, refine grains, reduce the ductile-brittle transition temperature and weld crack sensitivity. Ni reduces the resistance to dislocation movement in steel, relaxes stress, and then changes the substructure of the matrix, thereby improving the toughness of steel, especially low-temperature toughness. Ni is also a nitrogen-fixing element in steel, so the Ni content is limited to between 0.80% and 1.00%.

[0017] Cr, as the main element in this patent, can inhibit the transformation of ferrite and pearlite in steel, shifting the transformation of bainite to the low-temperature zone, and improving the toughness and hardenability of the steel. During the heat treatment process, the Cr23C6 type carbides formed dissolve and solid-solute in the matrix, which can refine the grains and improve the tempering stability of the steel. Therefore, the Cr content is controlled between 0.55% and 0.85%.

[0018] Mo in steel is an element that reduces the austenite region and promotes ferrite transformation. Mo can dissolve in austenite and ferrite to increase the strength of the steel through solid solution strengthening, while also suppressing the occurrence of temper brittleness. Therefore, the Mo content is between 0.10% and 0.20%.

[0019] V, the primary element in this patent, dissolves into austenite at high temperatures, increasing the steel's hardenability. V ensures the steel's strength and hardness through precipitation strengthening, and appropriately increasing V can improve the core strength of thick steel plates through dispersion strengthening. Microalloying increases the formation of V (C, N) carbonitrides in the steel, and these carbides are relatively stable, inhibiting grain boundary movement and grain growth, thereby improving the steel's toughness and tempering stability. Therefore, V is limited to 0.10% to 0.20%.

[0020] The addition of Ti refines the grain size and delays the recrystallization of the high-temperature austenite in steel. Ti also strengthens the steel after solid solution, improving its hardenability. Therefore, Ti is limited to 0.01% to 0.02%.

[0021] Al acts as a deoxidizer in steel and forms fine and dispersed AlN with N in the steel, which inhibits grain growth and improves the strength and impact toughness of the steel. Therefore, the Al content is limited to 0.03% to 0.04%.

[0022] Cu, as an element that expands the austenite region, has a decreasing solubility in ferrite as the temperature decreases. Through proper heat treatment, it can cause precipitation strengthening in the structure, increasing the strength of the steel and improving the yield strength ratio, as well as improving the corrosion resistance of the alloy steel. Therefore, the Cu content is controlled below 0.04%.

[0023] A method for manufacturing a quenched and tempered steel plate for a pressure vessel with high strength and toughness, comprising smelting, continuous casting, heating, rolling, and heat treatment, wherein:

[0024] 1) Smelting: Before the end of the oxygen top-blown converter, VN alloy is added and nitrogen is blown into the molten iron to ensure that the nitrogen content is between 0.003% and 0.005%, so that nitrogen combines with V, Ti, and Zr elements to form a precipitate;

[0025] 2) Rolling: The starting temperature of rough rolling is 1100-1150℃, the roller speed is controlled at 0.8-1.0m / s, the first pass reduction is controlled at 20%, the remaining single pass reduction is controlled at 15%-17%, and the total rough rolling reduction is ≥75%. In this stage, large deformation is used for rapid rolling to ensure that the dynamic recrystallization of the steel plate during the rough rolling process is complete; the starting temperature of finishing rolling is 935±30℃, the last pass rolling temperature is controlled at 810-840℃ in the non-crystallization zone, the roller speed is controlled at 0.5-0.7m / s, and the finishing single pass reduction is guaranteed to be 9-11%, and the total finishing pass reduction is ≥28%; small deformation rolling is used in this stage to ensure grain refinement of the steel plate;

[0026] 3) Heat treatment: The quenching temperature is controlled at 950±10℃, the tempering temperature is controlled at 640±10℃, and after the heat treatment, air cooling is performed on the cooling bed at room temperature; the steel plate structure is tempered bainite + bainite, and the grain size is 8 to 10.

[0027] The smelting process includes: firstly, pre-treating the molten iron; after alloying, argon is blown into the ladle, and then the molten iron is refined in an LF furnace to adjust the composition and undergo deep dephosphorization and desulfurization treatment to reduce the phosphorus content in the molten iron to less than 0.010 and the sulfur content to less than 0.003, ensuring that the argon soft blowing time is ≥5 minutes and the refining time is 30 to 60 minutes; then, RH vacuum treatment is used to further refine and adjust the composition, and the vacuum treatment time is 60 to 90 minutes to allow inclusions in the molten steel to fully float.

[0028] The continuous casting process: the casting billet is cast under argon protection throughout the casting process, the billet drawing speed is controlled at 0.7-1.1 m / min, the secondary cooling water volume is controlled at more than 5000 L / min, the casting superheat is controlled at 15-25°C, and the billet straightening temperature is controlled at 1000±50°C.

[0029] The heating process is as follows: the casting billet is first heated to 600°C in a constant temperature furnace, the holding time is controlled at 50-60 minutes, and then heated to 1250-1300°C in a continuous heating furnace, the heating rate is 1.4-2.0 min / mm, and the billet is kept warm for 240-300 minutes after reaching the temperature. The billet discharge temperature is controlled at 1180-1220°C.

[0030] The heat treatment process is as follows: after rolling, the steel plate is stacked and slowly cooled, and the slow cooling time is guaranteed to be ≥24h, and then a quenching + tempering heat treatment process is performed, the quenching heating rate is 1.3~2.0min / mm, the holding time is 30~60min, the tempering heating rate is 1.1~1.6min / mm, and the holding time is 30~60min. After the heat treatment is completed, it is cooled to room temperature on a cooling bed.

[0031] Compared with the existing technology, the beneficial effects of the present invention are:

[0032] This invention reduces the Mn content and increases the Ni content in the steel, ensuring sufficient strength and good low-temperature toughness. To ensure high strength and toughness of the steel plate, the V content of the alloying element is increased, and Ti is added to the steel. After microalloying, V and Nb, through solid solution strengthening and dispersion strengthening, ensure high strength, toughness, and hardenability of the steel plate after quenching and tempering. Increasing the Cr content improves the toughness and hardenability of the steel, refines the grain size after quenching and tempering, and improves the tempering stability of the steel. Adding Zr refines the grain size, increases strength, and provides the steel plate with good weldability and low-temperature performance. The steel plate structure is tempered bainite + bainite, with a grain size of 8 to 10. These measures ensure the steel plate's high strength and toughness.

[0033] The steel plate of the present invention has a tensile strength of 850-1000 MPa, a yield strength of ≥700 MPa, a -50°C impact transverse impact absorption energy of ≥100 J, an elongation of ≥21%, and a low welding crack sensitivity coefficient Pcm of less than 0.22.

[0034] The present invention regulates the contents of V, Ti and Zr before the end of the oxygen top-blown converter, and then improves the micro-alloying effect of the alloy elements after combining LF furnace refining + RH vacuum treatment. In the continuous casting process, full-process protective casting is adopted to ensure the purity of the steel billet. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 2 is the metallographic structure diagram of the steel plate of the present invention. DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means more than two.

[0038] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0039] A high-strength and toughness quenched and tempered steel plate for a pressure vessel, wherein the chemical composition of the steel plate is as follows by mass percentage: C: 0.07%-0.10%, Si: 0.15%-0.30%, Mn: 0.75%-1.00%, P≤0.010%, S≤0.003%, Ni: 0.80%-1.00%, Cr: 0.55%-0.85%, Mo: 0.10%-0.20%, Ti: 0.01%-0.02%, V: 0.10%-0.20%, Al: 0.03%-0.04%, Cu≤0.04%, Zr: 0.006%-0.010%, N: 0.003%-0.005%, Cr+V+Zr≤0.95%, and the balance being Fe and unavoidable impurities.

[0040] A method for manufacturing a quenched and tempered steel plate for a pressure vessel with high strength and toughness, comprising the following specific steps:

[0041] 1) Smelting

[0042] The molten iron is first pretreated. Before the end of the oxygen top-blown converter, VN alloy and nitrogen are added to ensure that the nitrogen content in the molten iron is 0.003-0.005%. N combines with V, Ti, and Zr elements to form precipitates. After argon is blown in the ladle, LF furnace refining is used for deep dephosphorization and desulfurization to reduce the phosphorus content in the molten iron to less than 0.010 and the sulfur content to less than 0.003. The argon soft blowing time is ensured to be ≥5 minutes, and the refining time is 30-60 minutes. RH vacuum treatment is then used for further refining and composition adjustment. The vacuum treatment time is 60-90 minutes to fully float the inclusions in the molten steel, ensure the purity of the molten steel, and provide sufficient time for the micro-alloying treatment of the molten steel.

[0043] 2) Continuous casting

[0044] The casting process of the billet is carried out under argon protection throughout the casting process. At the end of the solidification of the continuous casting billet, a heavy reduction method is adopted, and the total reduction is controlled at 40-50 mm. The billet drawing speed is strictly controlled at 0.7-1.1 m / min, the secondary cooling water volume is controlled at more than 5000 L / min, the casting superheat is guaranteed to be 15-25 ° C, and the billet straightening temperature is controlled at 1000±50 ° C. The precipitates formed by the combination of N and V, Ti, and Zr elements in the steel inhibit the growth of billet grains during the casting process, improve the surface quality of the billet, eliminate defects such as segregation and looseness inside the billet, and make the billet structure uniform.

[0045] 3) Heating

[0046] The casting billet is first heated to 600℃ in a constant temperature furnace, and the holding time is controlled at 50-60min. It is then heated to 1250-1300℃ in a continuous heating furnace, with a heating rate of 1.4-2.0min / mm. After reaching the temperature, it is kept warm for 240-300min. The billet discharge temperature is controlled at 1180-1220℃ to ensure that the continuous casting billet is completely austenitized during the heating process and the precipitates in the steel are dissolved.

[0047] 4) Rolling

[0048] After the steel billet is taken out of the furnace, rough rolling is carried out, the starting rolling temperature is controlled at 1100-1150℃, the roller speed is controlled at 0.8-1.0m / s, and the first pass reduction rate is controlled at 20%, the single pass reduction rate is controlled at 15-17%, the total rough rolling reduction rate is ≥75%, the finishing rolling start temperature is 935±30℃, the final rolling temperature is controlled at 810-840℃ in the non-crystallization zone, the roller speed is controlled at 0.5-0.7m / s, and the finishing rolling single pass reduction rate is guaranteed to be 9-11%, and the total finishing pass reduction rate is ≥28%.

[0049] 5) Heat treatment

[0050] After rolling, the steel plate is stacked and slowly cooled, and the slow cooling time is guaranteed to be ≥24h, and then the quenching + tempering heat treatment process is carried out. The quenching temperature is 950±10℃, the quenching heating rate is 1.3~2.0min / mm, and the holding time is 30~60min. The tempering temperature is 640±10℃, the tempering heating rate is 1.1~1.6min / mm, and the holding time is 30~60min. After the heat treatment is completed, it is air-cooled to room temperature on the cooling bed. The steel plate structure is tempered bainite + bainite, and the grain size is 8~10 levels, ensuring that the steel plate has good comprehensive mechanical properties after heat treatment.

[0051] The preferred embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, and these simple modifications all fall within the scope of protection of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner unless there is any contradiction. In order to avoid unnecessary repetition, the present invention will no longer describe various possible combinations separately. In addition, the various different embodiments of the present invention can also be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

[0052] To make the objectives, technical solutions, and technical effects of the present invention more clear, the technical solutions in the embodiments of the present invention are now clearly and completely described. However, the embodiments described below are only some of the embodiments of the present invention, not all of them. In combination with the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0053] The chemical composition of the embodiment is shown in Table 1; the smelting and continuous casting process is shown in Table 2. The thickness of the ingot is 200-300 mm, and then the ingot is rolled into a steel plate with a thickness of 60-80 mm in a 5500 mm wide and heavy plate rolling mill. The rolling process is shown in Table 3; various mechanical property tests are carried out after the heat treatment method of quenching and tempering treatment. The heat treatment process is shown in Table 4; the test results are shown in Tables 5 and 6.

[0054] Table 1 Chemical composition of the examples (wt%)

[0055]

[0056] Table 2 Example smelting and continuous casting process

[0057]

[0058]

[0059] Table 3 Example rolling process

[0060]

[0061] Table 4 Example heat treatment process

[0062]

[0063]

[0064] Table 5 Mechanical properties of the embodiment in the quenched and tempered heat treatment state

[0065]

[0066] Table 6 Grain size and non-metallic inclusion test results

[0067]

[0068]

[0069] Steel plate samples were taken for room temperature tensile testing. The tests were conducted in accordance with GB / T 228.1-2010, "Tensile Testing of Metallic Materials - Part 1: Room Temperature Test Methods," and the tensile tests were performed on the specimens. The measured elongation (A%) values ​​were above 21%, and the tensile strength (Rm) values ​​were above 850 MPa, indicating that the steel plate possesses high toughness and a good balance of toughness and strength. The calculated Pcm values ​​were both below 0.22. This demonstrates the steel plate's low weld crack susceptibility. Metallographic photographs show that the steel plate's microstructure is composed of tempered bainite and bainite, with a uniform distribution of microstructures. The steel plate also fully meets the requirements of the Ti level flaw detection standard in NB / T 47013.3-2018.

[0070] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and basic spirit of the invention, and the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a high-strength and high-toughness quenched and tempered steel plate for pressure vessels, characterized in that: The chemical composition of the steel plate is as follows by mass percentage: C: 0.07% to 0.10%, Si: 0.15% to 0.30%, Mn: 0.75% to 1.00%, P≤0.010%, S≤0.003%, Ni: 0.80% to 1.00%, Cr: 0.55% to 0.85%, Mo: 0.10% to 0.20%, Ti: 0.01% to 0.02%, V: 0.10% to 0.20%, Al: 0.03% to 0.04%, Cu≤0.04%, Zr: 0.006% to 0.010%, N: 0.003% to 0.005%, Cr+V+Zr≤0.95%, and the balance is Fe and unavoidable impurities; The manufacturing method includes smelting, continuous casting, heating, rolling, and heat treatment, among which: 1) Smelting: Before the end of the oxygen top-blown converter, VN alloy is added and nitrogen is blown into the molten iron to ensure that the nitrogen content is between 0.003% and 0.005%; 2) Rolling: The starting temperature of rough rolling is 1100-1150℃, the roller speed is controlled at 0.8-1.0m / s, the first pass reduction is controlled at 20%, and the remaining single pass reduction is controlled at 15%-17%. The total rough rolling reduction is ≥75%. In this stage, large deformation is used for rapid rolling. The starting temperature of finishing rolling is 935±30℃, and the final pass rolling temperature is controlled at 810-840℃ in the non-crystallization zone. The roller speed is controlled at 0.5-0.7m / s to ensure that the finishing single pass reduction is 9-11% and the total finishing pass reduction is ≥28%. Small deformation rolling is used in this stage. 3) Heat treatment: The quenching temperature is controlled at 950±10℃, the tempering temperature is controlled at 640±10℃, and after the heat treatment, it is air-cooled to room temperature on a cooling bed; the steel plate structure is tempered bainite + bainite, and the grain size is 8 to 10.

2. The method for manufacturing a high-strength and toughness quenched and tempered steel plate for pressure vessels according to claim 1, wherein: The steel plate has a tensile strength of 850 to 1000 MPa, a yield strength of ≥700 MPa, a transverse impact absorption energy of ≥100 J at -50°C, an elongation of ≥21%, and a welding crack sensitivity coefficient Pcm lower than 0.

22.

3. The method for manufacturing a high-strength and toughness quenched and tempered steel plate for pressure vessels according to claim 1, wherein: The smelting process includes: firstly, pre-treating the molten iron; after alloying, argon is blown into the ladle, and then the molten iron is refined in an LF furnace to adjust the composition and undergo deep dephosphorization and desulfurization treatment to reduce the phosphorus content in the molten iron to less than 0.010 and the sulfur content to less than 0.003, ensuring that the argon soft blowing time is ≥5 minutes and the refining time is 30 to 60 minutes; then, RH vacuum treatment is used to further refine and adjust the composition, and the vacuum treatment time is 60 to 90 minutes.

4. The method for manufacturing a high-strength and toughness quenched and tempered steel plate for pressure vessels according to claim 1, wherein: The continuous casting process: the casting billet is cast under argon protection throughout the casting process, the billet drawing speed is controlled at 0.7-1.1 m / min, the secondary cooling water volume is controlled at more than 5000 L / min, the casting superheat is controlled at 15-25°C, and the billet straightening temperature is controlled at 1000±50°C.

5. The method for manufacturing a high-strength and toughness quenched and tempered steel plate for pressure vessels according to claim 1, wherein: The heating process is as follows: the billet is first heated to 600°C, the holding time is controlled at 50-60 minutes, then heated to 1250-1300°C, the heating rate is 1.4-2.0 min / mm, and the temperature is kept for 240-300 minutes after reaching the temperature. The billet out-of-furnace temperature is controlled at 1180-1220°C.

6. The method for manufacturing a high-strength and toughness quenched and tempered steel plate for pressure vessels according to claim 1, wherein: The heat treatment process is as follows: after rolling, the steel plate is stacked and slowly cooled, and the slow cooling time is guaranteed to be ≥24h, and then a quenching + tempering heat treatment process is performed, the quenching heating rate is 1.3~2.0min / mm, the holding time is 30~60min, the tempering heating rate is 1.1~1.6min / mm, and the holding time is 30~60min. After the heat treatment is completed, air cooling at room temperature is performed on the cooling bed.

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