Steel plate with high low-temperature impact toughness for high-strength storage tank and manufacturing method

Abstract

The invention relates to the technical field of high-strength steel plate production, in particular to a high-strength storage tank steel plate with high and low temperature impact toughness and a manufacturing method, and the steel plate comprises the following chemical components: 0.16%-0.18% of C, 0.15%-0.32% of Si, 0.93%-1.14% of Mn, less than or equal to 0.015% of P, less than or equal to 0.01% of S, 0.051%-0.12% of Cr, 0.06%-0.08% of Mo, 0.011%-0.023% of Nb, 0.0049%-0.011% of Ta, 0.020%-0.045% of Alt and the balance of Fe and impurities. By matching with a production process of molten iron spheroidizing inoculation treatment, optimized two-stage rolling and efficient short-time heat treatment, the finished steel plate has high strength, good low-temperature toughness and formability and excellent plate shape; and meanwhile, good structure uniformity and good corrosion resistance are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-strength steel plate production, and in particular to a high-strength steel plate for storage tanks with high and low-temperature impact toughness and a manufacturing method thereof. Background Art

[0002] With the increasing economic development and energy demand, the reserves of strategic oil and natural gas have become one of the indicators to measure the sustainable development capacity of each country's economy. The demand for large-scale oil and liquefied natural gas storage tanks is increasing. Due to the influence of the storage environment, new and higher requirements are also put forward for the service performance of steel plates used in storage tanks in complex and harsh environments such as low temperatures.

[0003] The performance requirements for oil and liquefied natural gas storage tanks include: (1) High strength; usually the tensile strength is required to be above 490MPa to ensure that it can withstand internal pressure and external loads; at the same time, the yield strength must meet specific standards to ensure that it is not easily deformed when subjected to stress. (2) Good low-temperature performance, maintaining good toughness at low temperatures to prevent brittle fracture, and at the same time having high fracture toughness to prevent crack propagation. (3) Excellent welding performance, requiring the joint strength after welding to be equivalent to that of the parent material, and the welding process to be highly adaptable and applicable to a variety of welding methods (such as manual welding, automatic welding, etc.). (4) Corrosion resistance, able to resist environmental corrosion, including corrosion from the atmosphere, water, chemical media, etc., and not prone to stress corrosion cracking under stress environments. (5) Good processing performance, easy to cold-bend, adapt to complex shapes, and easy to cut and process to reduce processing difficulty. (6) High dimensional accuracy and surface quality, thickness, width, and length must meet standards to ensure installation accuracy; the surface should be flat and free of defects to reduce stress concentration. (7) Good fatigue resistance, with high fatigue strength under cyclic loads, which is conducive to extending service life. (8) Good resistance to hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSCC), not easy to crack in hydrogen-containing environments, and not easy to cause stress corrosion cracking in sulfide-containing environments. In addition, it is necessary to comply with relevant standards and specifications, such as API, ASTM, EN and other international or industry standards.

[0004] Chinese patent application publication number CN110106445A discloses a "high-strength and low-temperature toughness steel for offshore platform casting nodes and its preparation method." The steel plate is composed of the following components by weight: C: 0.03-0.10%, Si: 0.1-0.3%, Mn: 1.1-1.6%, Cr: 0.1-0.3%, Mo: 0-0.4%, V: 0-0.02%, Nb: 0.02-0.04%, Ni: 0.4-0.8%, La + Ce ≤ 0.06%, P ≤ 0.025%, S ≤ 0.015%, with the balance being Fe and unavoidable impurities. Heat treatment includes quenching, quenching, and tempering. This offshore platform casting node steel not only has high yield strength but also exhibits excellent low-temperature impact toughness, achieving a yield strength of 600 MPa and a -40°C impact toughness of 2140 J / cm. However, the steel plate contains expensive alloy elements such as Cr and Ni, and the added amount is high, resulting in high production costs. Multi-stage heat treatment is not only time-consuming, but also further increases production costs.

[0005] The Chinese patent application with application publication number CN107475487A discloses "a method for producing low-carbon, low-alloy, high-strength and high-low-temperature toughness steel castings". The steel plate is composed of the following components in weight percentage: C: 0.16~0.24%, Si≤0.60%, Mn≤1.20%, P≤0.04%, S≤0.045%, Cr: 0.45~0.9%, Mo: 0.3~0.8%, Ni: 0.6~1.2%, and the balance is Fe and unavoidable impurity elements. The product's performance requirements include a tensile strength of ≥780MPa, a yield strength of ≥630MPa, an elongation of ≥13%, a reduction of area of ​​≥35%, and an average impact toughness of ≥27J at -40°C (Akv). The production process involves casting steel parts using a casting process, followed by heat treatment. The castings are heated to a quenching temperature of AC3+80°C to AC3+120°C, held at this temperature for 4 to 8 hours, and then continuously cooled in brine. The steel contains a high amount of Ni, which increases production costs. Furthermore, the steel only utilizes a quenching heat treatment process, requiring a total heat treatment time of over 4 hours. This significantly consumes heat treatment resources and does not meet the requirements for efficient production. Furthermore, since the castings are directly heat treated without rolling, the uniformity of the steel plate structure is difficult to ensure, and defects are difficult to eliminate.

[0006] The present invention optimizes the smelting process, employs a molten iron spheroidization inoculation process, and employs protected pouring throughout the entire process to improve molten steel purity, reduce inclusion levels in the ingot, and refine the original grain structure. Two-stage controlled rolling further optimizes the internal structure of the steel plate, improving the plate shape and ensuring production efficiency. A highly efficient heat treatment process adjusts the material's internal structure while ensuring the service performance of the finished steel plate, improving its mechanical properties and processing performance. The method for producing high-strength storage tanks with high and low-temperature impact toughness provided by the present invention is suitable for large-scale, efficient production of steel for storage tanks. Summary of the Invention

[0007] The present invention provides a high-strength steel plate for storage tanks with high and low-temperature impact toughness and a manufacturing method. Through a unique chemical composition design and a production process of "molten iron spheroidization inoculation treatment + optimized two-stage rolling + efficient short-time heat treatment", the produced steel plate has a thickness of 8 to 80 mm, has high strength, good low-temperature toughness and formability, and excellent plate shape; at the same time, it has good structural uniformity and good corrosion resistance; and can meet the manufacturing and use requirements of high-performance steel plates for storage tanks.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: A high-strength steel plate for storage tanks with high and low-temperature impact toughness has the following chemical compositions by weight: C: 0.16%-0.18%, Si: 0.15%-0.32%, Mn: 0.93%-1.14%, P≤0.015%, S≤0.01%, Cr: 0.051%-0.12%, Mo: 0.06%-0.08%, Nb: 0.011%-0.023%, Ta: 0.0049%-0.011%, Alt: 0.020%-0.045%, and the balance being Fe and unavoidable impurities.

[0009] The metallographic structure of the finished steel plate is refined ferrite + sorbite structure, and the volume ratio of sorbite to ferrite is 2.3~3.1. The grain size of the finished steel plate is 7~9. According to the volume ratio, the Cr in the second phase particles is 2.3~3.1. 23 C6:MoC:NbC:TaC=1~1.2:0.5~0.9:0.5~0.7:0.2~0.4, and the second phase particle size is 40~60nm.

[0010] The properties of the finished steel plate are: at room temperature, 720MPa≤yield strength≤795MPa, 595MPa≤tensile strength≤670MPa, elongation≥25%; at -60℃, transverse impact energy International 2 The average value is ≥120J, and the single impact energy value is ≥90J; the sum of the non-metallic inclusion grades is not greater than 1.0.

[0011] A method for manufacturing high-strength steel plates for storage tanks with high and low temperature impact toughness, the production process includes smelting, continuous casting, heating, rolling and heat treatment; the specific process is as follows: 1) Smelting: During the smelting process, a spheroidizing inoculant containing 4% to 5% magnesium by weight is added. The oxygen blowing time for dephosphorization is controlled at 7 to 10 minutes, and the oxygen blowing time for decarburization is controlled at 4 to 6 minutes, and the weight percentage of phosphorus in the molten steel is controlled within 0.01%. LF refining is used for deep desulfurization to control the weight percentage of sulfur in the molten steel below 0.01%. During RH vacuum degassing, the oxygen blowing rate is controlled at 3.66 to 4.32 m³ / t steel·min, the net circulation time of the molten steel is 20 to 34 minutes, and the calming time before pouring is 4 to 7 minutes. 2) Continuous casting: After breaking the vacuum, the slab continuous casting machine is used for casting. The pouring temperature of the molten steel in the tundish is 1511-1546°C, the superheat is controlled at 12-19°C, and the casting speed during casting is 0.8-1.4m / min. Electromagnetic stirring and / or light reduction process of the continuous casting slab are used, in which the reduction rate is controlled at 4%-6%. 3) Heating: The slab is heated in two stages before leaving the furnace. The temperature range of the first heating stage is 1045-1102°C, and the temperature range of the second heating stage is 1215-1235°C. The total heating time of the slab is controlled at 3.2-5.6 hours. 4) Rolling: Two-stage controlled rolling is adopted; in the first stage, the starting rolling temperature of the recrystallization zone is 1120-1160℃, the finishing rolling temperature is 1020-1070℃, the rolling speed is 3.6-4.4m / s, and the single-pass reduction rate is 13%-16%; in the second stage, the starting rolling temperature of the non-recrystallization zone is 920-940℃, the finishing rolling temperature is 820-850℃, and the single-pass reduction rate adopts a "large and small reciprocating cycle" method, in which the large reduction rate is 10%-15% and the small reduction rate is 5%-8%; 5) Heat treatment: Short-time normalizing heat treatment is adopted. In the first stage, the heating temperature is controlled at 890-920℃ and the holding time is 10-26min. In the second stage, the steel plate is air-cooled to room temperature after being taken out of the furnace, and the cooling rate is controlled at 1.1-2.8℃ / s.

[0012] In the smelting process, scrap steel and molten iron are used as raw materials, and the weight percentage of the molten iron is controlled to be above 73%.

[0013] After continuous casting, the ingots are stacked and slowly cooled off the production line for no less than 36 hours.

[0014] During the rolling process, after the first stage of rolling is completed, the steel plate waiting time is controlled to be 30 to 55 seconds.

[0015] The thickness of the finished steel plate is 8 to 80 mm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) Composition design: Based on strengthening elements such as C, Si, and Mn, appropriate amounts of alloying elements such as Cr, Mo, Nb, and Ta are added, while the content of harmful elements P and S is strictly controlled. Combined with the optimized production process, a refined "ferrite + sorbite" structure (grain size is 7 to 9 levels) is obtained, and by volume ratio, the second phase particles Cr 23 C6: MoC: NbC: TaC = (1-1.2): (0.5-0.9): (0.5-0.7): (0.2-0.4), the second phase particle size is 40-60nm, and the second phase particles of the alloying elements are evenly dispersed, ensuring the steel plate's strong plasticity, low-temperature toughness, and corrosion resistance; (2) The mechanical properties of the steel plate for storage tanks obtained through unique composition design and production process are as follows: at room temperature, 720MPa≤ tensile strength≤795MPa, 595MPa≤ yield strength≤670Mpa, elongation≥25%; at -60℃, the transverse impact strength International 2 The average value is ≥120J, and the single value of impact energy is ≥90J; at the same time, the steel plate has good organizational uniformity, and the sum of the non-metallic inclusion grades is not greater than 1.0.

[0017] (3) According to GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", hydrogen induced cracking (HIC) test was carried out. After 96 hours of testing in solution A and solution B, the crack sensitivity CSR (%), crack length rate CLR (%), and crack width rate CTR (%) of the steel plate were all 0, indicating that the steel plate has excellent resistance to hydrogen induced cracking. According to GB / T17897-2016 "Corrosion of Metals and Alloys - Ferric Chloride Pitting Corrosion Test Method for Stainless Steel", the steel plate showed a corrosion rate of no more than 0.005 g / m in solution A and solution B. 2 h; According to the method of GB / T10125-2021 "Artificial atmosphere corrosion test salt spray test", solution a neutral salt spray test, solution b acetic acid salt spray test, and solution c copper accelerated acetic acid salt spray test were carried out. The test time was 72 h. The red rust area of ​​the steel plate was less than 1%, indicating that the steel plate has excellent corrosion resistance. DETAILED DESCRIPTION

[0018] The high-strength steel plate for storage tanks with high and low-temperature impact toughness disclosed by the present invention has the following chemical compositions by weight: C: 0.16%-0.18%, Si: 0.15%-0.32%, Mn: 0.93%-1.14%, P≤0.015%, S≤0.01%, Cr: 0.051%-0.12%, Mo: 0.06%-0.08%, Nb: 0.011%-0.023%, Ta: 0.0049%-0.011%, Alt: 0.020%-0.045%, and the balance being Fe and unavoidable impurities.

[0019] In the high-strength steel plate for storage tanks with high and low-temperature impact toughness described in the present invention, the content range selection and working principle of chemical elements such as C, Si, Mn, P, S, Cr, Mo, Nb, Ta, and Alt are as follows: Carbon is an essential element for increasing steel strength. Low carbon content in steel plates can hinder strength and easily lead to defects such as cracks during cold working or heat treatment, shortening the material's service life and increasing the risk of fracture. However, excessive carbon content can affect the steel's machinability, and oversaturated carbides can negatively impact the steel's low-temperature toughness. Therefore, the present invention sets the carbon content within a range of 0.16% to 0.18%.

[0020] Si acts as a reducing agent and deoxidizer during the steelmaking process. Si is an inexpensive alloying element. Adding an appropriate amount of Si to steel can improve the hardness and strength of the ferrite. However, excessive Si addition (above 0.32%) can increase non-metallic inclusions in steel plates, reduce their plasticity and toughness, and easily become a source of cracks. Therefore, the present invention sets the Si content range to 0.15% to 0.32%.

[0021] Mn can be infinitely dissolved in Fe, increasing steel strength while having a relatively minimal impact on plasticity. Mn is also a strong austenite stabilizer, lowering the lower critical point of steel, increasing the degree of undercooling during austenite cooling, and refining the pearlite structure, thereby improving the mechanical properties of the steel plate. Furthermore, it is relatively inexpensive. However, excessive Mn content can increase the tendency of grain coarsening in the steel; therefore, the present invention sets the Mn content range to 0.93% to 1.14%.

[0022] S and P are harmful elements in steel and must be strictly controlled to ensure the purity and plasticity of the steel. Therefore, the present invention limits P to 0.015% and S to 0.01%.

[0023] Cr has a high affinity for C, forming stable carbides that can remain stable in high-temperature zones, pinning dislocations and causing them to move, thereby refining ferrite grains. Cr also ensures a comprehensive improvement in the hardenability, strength, plasticity, and toughness of the steel plate, especially its low-temperature toughness. When a certain amount of Cr is added to the steel, it readily combines with O, facilitating the formation of a passivation film on the steel plate's surface, preventing the steel surface from coming into direct contact with the external environment and thereby improving the steel plate's corrosion and oxidation resistance. However, adding excessive amounts of Cr can easily generate large carbides, adversely affecting the toughness and plasticity of the steel plate. Therefore, the present invention sets the Cr content range at 0.051% to 0.12%.

[0024] Mo plays a major role in solid solution strengthening in steel. The carbides it forms in combination with carbon pin dislocations and grain boundaries, thereby refining grain size and improving the strength and toughness matching of the steel plate. Adding Mo to steel can improve the hardenability of the steel, with an effect stronger than that of chromium but slightly less than that of manganese. When Mo is added to steel plates, it passivates the steel surface in both reducing acid and strong oxidizing salt solutions. Therefore, Mo can generally improve the corrosion resistance of the steel and prevent pitting corrosion in chloride solutions. In summary, adding an appropriate amount of Mo to steel is beneficial for improving the strength, toughness, hardenability, and corrosion resistance of the steel. Therefore, the present invention sets the Mo content range to 0.06% to 0.08%.

[0025] Nb is a strong carbonitriding element, forming interstitial phases such as NbC or NbN in steel. During the recrystallization process, above the critical temperature, the effect of Nb on recrystallization manifests itself as a solute drag mechanism; below the critical temperature, it manifests itself as a precipitation pinning mechanism. Due to the pinning of dislocations by NbC and NbN, the recrystallization time is greatly increased, the area of ​​grain boundaries and subgrain boundaries for nucleation increases, and the effect of inhibiting grain growth is enhanced, thereby refining the microstructure and improving the strength, yield ratio, and low-temperature toughness of the steel plate after normalizing. However, excessively high Nb content will increase the brittleness of the steel plate; therefore, the present invention sets the Nb content range to 0.011% to 0.023%.

[0026] Ta readily combines with carbon in steel, forming relatively stable TaC particles that are evenly dispersed throughout the matrix, acting as precipitation strengthening, thereby increasing the strength of the steel plate. Ta also prevents secondary grain growth during subsequent rolling and heat treatment, refining the grains and improving the impact toughness of the steel plate. Taking cost factors into consideration, the present invention sets the Ta content range to 0.0049% to 0.011%.

[0027] The present invention controls the content of Cr, Mo, Nb and Ta to control the size of precipitated carbide particles within the range of 40 to 60 nm, and Cr 23C6: MoC: NbC: TaC = (1~1.2): (0.5~0.9): (0.5~0.7): (0.2~0.4), maximizing the strengthening effect of the second phase particles, ensuring the purity and uniformity of the steel plate structure, and obtaining good strength-toughness matching, low-temperature performance, and corrosion resistance.

[0028] Al is a commonly used deoxidizer in steel. Adding a small amount of aluminum can refine the grain size and improve the steel's strength and impact toughness. Excessive aluminum content can affect the steel's hot working, welding, and machinability. Therefore, the present invention limits the Al content to 0.020% to 0.045%.

[0029] The present invention provides a method for manufacturing a high-strength steel plate for storage tanks with high and low temperature impact toughness, comprising smelting ( Hot metal spheroidizing inoculation pretreatment + converter dephosphorization + converter decarburization + off-furnace refining + vacuum degassing), continuous casting (stacking slow cooling + ingot cleaning), heating (two-stage heating), rolling (two-stage controlled rolling + slow cooling), heat treatment (short-time normalizing heat treatment), etc.

[0030] This invention utilizes an optimized smelting process (hot metal spheroidizing inoculation pretreatment) combined with an efficient heating method (two-stage heating followed by short-time normalizing heat treatment), combined with a two-stage controlled rolling process, to produce 8-80mm thick steel plates for storage tanks. These plates exhibit uniform microstructure, excellent strength-toughness balance, and excellent low-temperature performance and corrosion resistance. The specific process is as follows: 1. Smelting Process: Molten steel is smelted in a converter (BOF) using high-quality scrap steel and molten iron as raw materials. The weight percentage of the molten iron is controlled at above 73%, ensuring steel purity and reducing the complexity of subsequent processes. A spheroidizing inoculant containing 4% to 5% magnesium (by weight) is added during the smelting process to promote the formation of a uniform and fine primary structure and accelerate the dephosphorization and deoxidation processes. The BOF dephosphorization and decarburization parameters are strictly controlled during the smelting process. To effectively reduce the harmful element phosphorus content, the oxygen blowing time for dephosphorization is controlled at 7 to 10 minutes, and the oxygen blowing time for decarburization is controlled at 4 to 6 minutes. The phosphorus content in the molten steel is kept below 0.01% by weight. Deep desulfurization is performed using LF refining to control the sulfur content in the molten steel to below 0.01% by weight. Degassing is completed in an RH furnace, with the oxygen blowing rate controlled at 3.66 to 4.32 m³ / t-steel / min. The net circulation time for the molten steel is 20 to 34 minutes, and the pre-casting cooling time is 4 to 7 minutes.

[0031] By optimizing the smelting process parameters, the oxidation of molten steel can be effectively prevented and the inclusion content in the steel can be controlled to achieve the purpose of purifying the purity of the steel.

[0032] 2. Continuous Casting Process: After breaking vacuum, casting is performed using a slab continuous caster. Key control is placed on the casting temperature. The tundish steel casting temperature is maintained between 1511°C and 1546°C, with superheat controlled between 12°C and 19°C. The casting rate is maintained between 0.8 and 1.4 m / min. Low-temperature casting is employed to refine the original as-cast structure. To control defects such as central segregation and porosity in the continuously cast slabs, electromagnetic stirring and / or light reduction are employed, with a reduction rate of 4% to 6%. The slabs are stacked and slowly cooled off the production line for at least 36 hours.

[0033] 3. Heating Process: The continuously cast slab is heated in a heating furnace. The slab is heated in two stages before exiting the furnace. The temperature range of the first heating stage is 1045-1102°C, and the temperature range of the second heating stage is 1215-1235°C. The total heating time of the slab is controlled at 3.2-5.6 hours.

[0034] The two-stage heating method improves the slab's plasticity, reduces its deformation resistance, and achieves uniform temperature inside and outside the slab, facilitating further processing. It also further improves the uniformity of the slab's internal structure. When the heating temperature in the first heating stage is below 1045°C, coarse precipitates in the continuous casting slab cannot be dissolved, resulting in incomplete austenitization of the steel plate. Furthermore, the final rolling temperature in the first stage cannot be guaranteed. When the heating temperature in the second heating stage is above 1235°C, fine precipitates in the slab are likely to re-dissolve and cause excessive grain growth.

[0035] 4. Rolling process: adopt two-stage controlled rolling method.

[0036] The first stage of recrystallization begins at a temperature of 1120-1160°C, and the final rolling temperature is 1020-1070°C to fully refine the original austenite structure. High-deformation rapid rolling is employed at a rolling speed of 3.6-4.4 m / s, with a single initial reduction ratio of 13%-16%. This fully recrystallizes, refines the internal structure of the steel plate, and improves structural uniformity. After the first stage of rolling, the steel plate is held at temperature for 30-55 seconds.

[0037] In the second stage, the starting rolling temperature of the non-recrystallization zone is 920-940°C, and the final rolling temperature is 820-850°C. The single-pass reduction rate adopts a cyclic system, that is, a "large and small reciprocating cycle" method, in which the large reduction rate is controlled in the range of 10%-15%, and the small reduction rate is controlled in the range of 5%-8%.

[0038] By adopting the method of "reciprocating large and small reduction rates", as the grain boundary area increases, the ferrite nucleation rate increases in the subsequent phase transformation process, the internal structure of the steel plate is fully refined, the austenite grains are further flattened and elongated, and the stress in the steel plate is released, thereby optimizing the steel plate shape control.

[0039] 5. Heat Treatment: Due to the addition of elements such as C, Mn, Cr, Mo, Nb, and Ta to the steel, the rolled steel plate acquires a "ferrite + sorbite" structure with excellent strength and toughness. However, the grain size distribution of the rolled steel plate is uneven, leading to concentrated structural and thermal stresses, which can easily cause delayed cracking during flame cutting. Therefore, heat treatment should be used promptly to soften and relieve stress.

[0040] To further control the internal structure of the steel plate while ensuring high production efficiency, the present invention utilizes a short-time normalizing heat treatment. This ensures that the steel plate maintains strength while maintaining appropriate plasticity, low-temperature impact toughness, corrosion resistance, and good processability. The first stage of the short-time normalizing heat treatment involves heating to a temperature of 890-920°C for a holding time of 10-26 minutes. In the second stage, the steel plate is air-cooled to room temperature after exiting the furnace, with a cooling rate of 1.1-2.8°C / s.

[0041] The metallographic structure of the finished steel plate is refined ferrite + sorbite structure, and the volume ratio of sorbite to ferrite is 2.3~3.1. The grain size of the finished steel plate is 7~9. According to the volume ratio, the Cr in the second phase particles is 2.3~3.1. 23 C6:MoC:NbC:TaC=(1~1.2):(0.5~0.9):(0.5~0.7):(0.2~0.4), and the second phase particle size is 40~60nm.

[0042] The properties of the finished steel plate are: at room temperature, 720MPa≤ tensile strength≤795MPa, 595MPa≤ yield strength≤670Mpa, elongation≥25%; at -60℃, transverse impact strength International 2 The average value is ≥120J, and the single impact energy value is ≥90J; the sum of the non-metallic inclusion grades is not greater than 1.0.

[0043] The thickness of the finished steel plate is 8 to 80 mm.

[0044] In order to more intuitively embody the present invention, the embodiments of the present invention are further described in conjunction with examples. The following examples are only preferred specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solution that can be obviously obtained by a person skilled in the art within the technical scope disclosed in the present invention, including simple changes or equivalent replacements, is within the scope of protection of the present invention.

[0045] Example:

[0046] Table 1 shows the chemical composition of the steel in each embodiment and comparative example, Table 2 shows the smelting, continuous casting and heating process parameters of the steel in each embodiment and comparative example, Table 3 shows the rolling and heat treatment process parameters of the steel in each embodiment and comparative example, Table 4 shows the test results of the grain size and inclusion grade evaluation of the finished steel plates in each embodiment and comparative example, and Table 6 shows the test results of corrosion resistance (hydrogen cracking resistance test, pitting corrosion test, salt spray test) of the finished steel plates in each embodiment and comparative example.

[0047] Table 1: Chemical composition of steel (wt%, %)

[0048] Table 2: Steel smelting, continuous casting and heating process parameters

[0049] Table 3: Steel rolling and heat treatment process parameters

[0050] Table 4: Mechanical properties of finished steel plates

[0051] Table 5: Test results of grain size and inclusion grade evaluation of finished steel plate

[0052] Table 6: Test results of corrosion resistance of finished steel plates (hydrogen-induced cracking test, pitting test, and salt spray test)

[0053] From the above examples, it can be concluded that the mechanical properties of the steel plate for storage tanks with a thickness of 8 to 80 mm provided by the present invention are as follows: at room temperature, 720 MPa ≤ tensile strength ≤ 795 MPa, 595 MPa ≤ yield strength ≤ 670 MPa, and elongation ≥ 25%; at -60 ° C, the transverse impact strength International 2 The average value is ≥120J, and the single value of impact energy is ≥90J; the sum of non-metallic inclusion grades is not greater than 1.0, and the corrosion resistance is excellent.

[0054] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A high-strength steel plate for storage tanks with high and low temperature impact toughness, characterized in that: The chemical composition by weight percentage is C: 0.16%~0.18%, Si: 0.15%~0.32%, Mn: 0.93%~1.14%, P≤0.015%, S≤0.01%, Cr: 0.051%~0.12%, Mo: 0.06%~0.08%, Nb: 0.011%~0.023%, Ta: 0.0049%~0.011%, Alt: 0.020%~0.045%, and the balance is Fe and unavoidable impurities.

2. The high-strength steel plate for storage tanks with high and low temperature impact toughness according to claim 1, characterized in that: The metallographic structure of the finished steel plate is refined ferrite + sorbite structure, and the volume ratio of sorbite to ferrite is 2.3~3.

1. The grain size of the finished steel plate is 7~9. According to the volume ratio, the Cr in the second phase particles is 2.3~3.

1. 23 C6:MoC:NbC:TaC=1~1.2:0.5~0.9:0.5~0.7:0.2~0.4, and the second phase particle size is 40~60nm.

3. The high-strength steel plate for storage tanks with high and low temperature impact toughness according to claim 1, characterized in that: The properties of the finished steel plate are: at room temperature, 720MPa≤ tensile strength≤795MPa, 595MPa≤ yield strength≤670MPa, elongation≥25%; at -60℃, transverse impact strength KV 2 The average value is ≥120J, and the single impact energy value is ≥90J; the sum of the non-metallic inclusion grades is not greater than 1.

0.

4. A method for manufacturing a high-strength steel plate for storage tanks having high and low temperature impact toughness according to any one of claims 1 to 3, characterized in that: The production process includes smelting, continuous casting, heating, rolling and heat treatment; the specific process is as follows: 1) Smelting: During the smelting process, a spheroidizing inoculant containing 4% to 5% magnesium by weight is added. The oxygen blowing time for dephosphorization is controlled at 7 to 10 minutes, and the oxygen blowing time for decarburization is controlled at 4 to 6 minutes, and the weight percentage of phosphorus in the molten steel is controlled within 0.01%. LF refining is used for deep desulfurization to control the weight percentage of sulfur in the molten steel below 0.01%. During RH vacuum degassing, the oxygen blowing rate is controlled at 3.66 to 4.32 m³ / t steel·min, the net circulation time of the molten steel is 20 to 34 minutes, and the calming time before pouring is 4 to 7 minutes. 2) Continuous casting: After breaking the vacuum, the slab continuous casting machine is used for casting. The pouring temperature of the molten steel in the tundish is 1511-1546°C, the superheat is controlled at 12-19°C, and the casting speed during casting is 0.8-1.4m / min. Electromagnetic stirring and / or light reduction process of the continuous casting slab are used, in which the reduction rate is controlled at 4%-6%. 3) Heating: The slab is heated in two stages before leaving the furnace. The temperature range of the first heating stage is 1045-1102°C, and the temperature range of the second heating stage is 1215-1235°C. The total heating time of the slab is controlled at 3.2-5.6 hours. 4) Rolling: Two-stage controlled rolling is adopted; in the first stage, the starting rolling temperature of the recrystallization zone is 1120-1160℃, the finishing rolling temperature is 1020-1070℃, the rolling speed is 3.6-4.4m / s, and the single-pass reduction rate is 13%-16%; in the second stage, the starting rolling temperature of the non-recrystallization zone is 920-940℃, the finishing rolling temperature is 820-850℃, and the single-pass reduction rate adopts a "large and small reciprocating cycle" method, in which the large reduction rate is 10%-15% and the small reduction rate is 5%-8%; 5) Heat treatment: Short-time normalizing heat treatment is adopted. In the first stage, the heating temperature is controlled at 890-920℃ and the holding time is 10-26min. In the second stage, the steel plate is air-cooled to room temperature after being taken out of the furnace, and the cooling rate is controlled at 1.1-2.8℃ / s.

5. The method for manufacturing a high-strength steel plate for storage tanks with high and low temperature impact toughness according to claim 4, characterized in that: During the smelting process, scrap steel and molten iron are used as raw materials, and the weight percentage of molten iron is controlled at more than 73%.

6. The method for manufacturing a high-strength steel plate for storage tanks with high and low temperature impact toughness according to claim 4, characterized in that: After continuous casting, the ingots are stacked and slowly cooled off the production line for no less than 36 hours.

7. The method for manufacturing a high-strength steel plate for storage tanks having high and low temperature impact toughness according to claim 4, characterized in that: During the rolling process, after the first stage of rolling is completed, the steel plate waiting time is controlled at 30 to 55 seconds.

8. The method for manufacturing a high-strength steel plate for storage tanks with high and low temperature impact toughness according to claim 4, characterized in that: The thickness of the finished steel plate is 8 to 80 mm.

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