A steel plate for 820MPa cryogenic storage tanks and its manufacturing method

Abstract

This invention belongs to the field of metallic materials, and particularly relates to a steel plate for 820MPa cryogenic storage tanks and its manufacturing method. The chemical composition of the steel, by weight percentage, is: C: 0.18%–0.21%, Si: 0.15%–0.37%, Mn: 0.87%–0.96%, P≤0.01%, S≤0.005%, Ni: 0.41%–0.48%, Mo: 0.03%–0.08%, Nb: 0.12%–0.18%, Ce: 0.001%–0.0015%, with the balance being Fe and unavoidable inclusions. This invention, through a novel chemical composition design, employs a three-stage / two-stage efficient slab heating regime, an optimized three-stage rolling process, a two-stage cooling process, a high-temperature short-time tempering heat treatment, and a special manufacturing process, to obtain a high-strength, highly uniform, extra-thick steel plate for containers with excellent comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a steel plate for 820MPa cryogenic storage tanks and its manufacturing method. Background Technology

[0002] With the increasing global demand for green energy, the demand for storage and transportation facilities for liquefied petroleum gas (LPG), natural gas, and hydrogen energy, as important and efficient energy sources, has increased significantly. Cryogenic storage tanks are one of the core pieces of equipment in the LPG industry chain, and their performance directly affects the safety, economy, and efficiency of energy storage. Steel plates, as a key material in the manufacture of cryogenic storage tanks, must meet multiple requirements, including extremely high strength, excellent low-temperature toughness, good weldability, and corrosion resistance.

[0003] Patent document CN102286692A discloses "a tempered steel for low temperature use and its manufacturing method," wherein the steel plate is composed of the following components by weight percentage: C: 0.040%–0.080%, Si ≤ 0.15%, Mn: 1.20%–1.60%, P ≤ 0.015%, S ≤ 0.003%, Als ≤ 0.010%, Cu: 0.05%–0.35%, Ni: 0.10%–0.40%, Mo: 0.10%–0.30%, Ti: 0.007%–0.012%, V: 0.020%–0.050%, N… The composition of the elements is as follows: Mn: 0.0055%–0.0085%, B: 0.0008%–0.0020%, Ca: 0.001%–0.004%, and the content of the above elements satisfies the following relationships: 15≤Mn / C≤30; Ni equivalent ≥0.25%; Ti / N between 1.0 and 2.0; B ≥0.714(N-0.292Ti-0.518Als); Ni / Cu ≥1.0; Ca / S between 1.0 and 3.0 and 1.0×10-4≤(%Ca)×(%S)0.28≤1.5×10-3; the remainder is iron and unavoidable inclusions. The tensile strength / yield strength level is relatively low, making it difficult to meet the requirements for higher strength storage tank steel plates; the influence of Pcm values ​​on the steel plate was not investigated, and the low-temperature impact performance of the steel plate below -50℃ was not studied. Therefore, it is not suitable for the large-scale production of high-strength storage tank steel.

[0004] Patent document CN114107819A discloses a "low-temperature nickel steel resistant to high tempering parameter SR embrittlement and its manufacturing method". The steel plate is composed of the following components by weight percentage: C 0.025%~0.060%, Si≤0.15%, Mn 0.45%~0.85%, P≤0.012%, S≤0.0020%, Cu 0.10%~0.40%, Ni 2.80%~3.80%, Cr 0.10%~0.30%, Mo 0.05%~0.30%, Als 0.040%~0.070%, Ti 0.006%~0.012%, Nb 0.008%~0.025%, N≤0.0040%, Ca 0.001%~0.003%, balance Fe and unavoidable inclusions. The high content of Ni and Cr elements in the elemental composition of the steel plate increases the production cost; the Pcm value is crucial for steel used in cryogenic storage tanks, but no relevant research has been conducted in this application; the impact performance was only studied at -101℃, and the impact performance at lower temperature environments was not covered; no index requirements were proposed for the HIC / SCC resistance of the steel plate, and the strength level of the steel plate is low, making it unsuitable for large-scale production of high-strength cryogenic storage tank steel.

[0005] Patent document CN102691007A discloses a "low-temperature extra-thick steel plate resistant to high tempering parameter PWHT embrittlement and its manufacturing method," wherein the steel plate is composed of the following components by weight percentage: C 0.030%–0.070%, Si ≤0.15%, Mn 1.30%–1.60%, P ≤0.013%, S ≤0.0025%, and Al 0.040%–0.070%. The steel plate contains Cu 0.10%–0.40%, Ni 0.25%–0.65%, Cr 0.10%–0.30%, Mo 0.05%–0.25%, Ti 0.007%–0.013%, Nb 0.010%–0.030%, V 0.020%–0.050%, N ≤0.0045%, Ca 0.001%–0.004%, residual iron, and unavoidable inclusions. The high Ni and Cr content in the steel plate's composition increases production costs. The Pcm value is crucial for steel used in cryogenic storage tanks, but this invention lacks relevant research. Furthermore, impact performance was only studied at -70℃ and -80℃, without addressing impact performance at even lower temperatures. No HIC / SCC resistance requirements were specified, and the steel plate's strength grade is low, making it unsuitable for large-scale production of high-strength cryogenic storage tank steel.

[0006] Patent document CN109423579A discloses "an ultra-low cost, SR-resistant low-temperature nickel steel plate and its manufacturing method", the weight percentage of its composition is as follows: C: 0.040~0.070%, Si≤0.15%, Mn: 0.90~1.20%, P≤0.012%, S≤0.0020%, Cu: 0.10~0.35%, Ni: 1.00~1.50%, Mo: 0.05~0.30%, Als: 0.040~0.070%, Ti: 0.007~0.014%, Nb: 0.008~0.025%, N≤0.0040%, Ca: 0.0010~0.0035%, with the remainder being Fe and unavoidable impurities. The high Ni content in the elemental composition of the steel plate increases the production cost; the Pcm value is crucial for steel used in cryogenic storage tanks, but this invention has not conducted relevant research; furthermore, no research has been done on steel plates with a thickness of 30-50mm; no specific research has been conducted on the HIC / SCC resistance of the steel plate; and the steel plate has a low strength level, making it unsuitable for large-scale production of high-strength cryogenic storage tank steel.

[0007] Patent document CN110747409A discloses "a low-nickel steel for cryogenic storage tanks and its manufacturing method," wherein the steel composition is: C: 0.05-0.15%, Si: 0.20-0.60%, Mn: 1.0-1.70%, Ni: 0.30-1.0%, Cr: 0.20-0.70%, Mo: 0.20-0.70%, Nb: 0.01-0.05%, Ti: 0.01-0.05%, S: ≤0.005%, P: ≤0.008%, with the balance being Fe and impurities. The high Ni content in the steel composition increases production costs. Furthermore, the Pcm value is crucial for cryogenic storage tank steel, but this invention lacks relevant research. Additionally, no research has been conducted on the steel's performance in service environments below -80℃ or its HIC / SCC properties, making it unsuitable for large-scale production of high-strength cryogenic storage tank steel.

[0008] Patent document CN102719745A discloses "High-strength Low-Temperature Steel with Excellent Resistance to HIC and SSC and its Manufacturing Method", wherein C: 0.030%~0.060%, Si: ≤0.10%, Mn: 1.10%~1.40%, P: ≤0.012%, S: ≤0.002%, Als: ≤0.010%, Cu: 0.15%~0.35%, Ni: 0.15%~0.40%, Mo: 0.10%~0.30%, Nb: 0.015%~0.045%, Ti: 0.007%~0.016%, N: 0.0025%~0.0055%, Ca: 0.001%~0.003%, with the remainder being Fe and unavoidable impurities; the impact performance was only studied at -50℃, and the impact performance at lower temperatures was not covered. No requirements were put forward for the HIC / SCC resistance of the steel plate, and the strength level of the steel plate is low, which is not suitable for the large-scale production of high-strength cryogenic storage tank steel. Summary of the Invention

[0009] The purpose of this invention is to provide an 820MPa grade cryogenic storage tank steel plate and its manufacturing method. Through a novel chemical composition design, a three-stage efficient slab heating regime, an optimized three-stage rolling process, an efficient cooling process, a two-stage straightening process, and a short-time tempering heat treatment, a high-strength cryogenic storage tank steel plate with excellent comprehensive performance and a thickness of 22-46mm is obtained. The steel plate has high strength, good low-temperature toughness and service performance, and excellent plate shape, meeting the manufacturing and application requirements of high-performance storage tank steel plates. This invention has low cost and is suitable for large-scale production and use.

[0010] To achieve the above objectives, the present invention employs the following technical solution:

[0011] A type of steel plate for 820MPa cryogenic storage tanks, with the following chemical composition by weight percentage: C: 0.18%–0.21%, Si: 0.15%–0.37%, Mn: 0.87%–0.96%, P≤0.01%, S≤0.005%, Ni: 0.41%–0.48%, Mo: 0.03%–0.08%, Nb: 0.12%–0.18%, Ce: 0.001%–0.0015%, and Mn / C = 4.3~5.2, Ni / Ce = 255~420, Ni ≥ Mo / Nb; the balance is Fe and unavoidable inclusions; at the same time, the values ​​of Pcm = C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B are required to be in the range of 0.235~0.285, and the values ​​of CE = C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15 are required to be in the range of 0.35~0.42.

[0012] The reasons for limiting the amounts of each chemical element (C, Si, Mn, P, S, Ni, Mo, Nb, Ce) in steel plates are detailed below:

[0013] Carbon (C) is a crucial element affecting the properties of steel plates, significantly influencing their strength, toughness, and corrosion resistance. By adding a certain amount of C, the strength, hardness, and wear resistance of the steel plate are ensured through the formation of solid solutions and carbides. Simultaneously, to ensure that the toughness of the steel plate is not affected and to guarantee a good balance of toughness and plasticity even at low temperatures, this invention sets the C content range to 0.18%–0.21%.

[0014] Si is an essential element in steel because it readily combines with oxygen (O) to purify the steel and improve its corrosion resistance. Si can dissolve in ferrite and austenite, providing solid solution strengthening and increasing strength and hardness. However, excessive addition, especially for steel plates operating in low-temperature environments and requiring high corrosion resistance, can lead to increased non-metallic inclusions and increased brittleness. Therefore, this invention sets the Si content range to 0.15%–0.37%.

[0015] Manganese (Mn) is an important solid solution strengthening element in steel, playing a role in refining grain size. A certain amount of Mn in steel can suppress the hot brittleness caused by sulfur (S), thereby improving the hot working properties of the steel. However, Mn easily forms large-sized MnS with S, which agglomerates at grain boundaries, affecting the steel plate's resistance to hydrogen-induced cracking, sulfide stress cracking, and stress corrosion. Therefore, this invention sets the Mn content range to 0.87%–0.96%. To ensure the strength of the steel plate without sacrificing low-temperature toughness and corrosion resistance, this invention controls the Mn / C ratio to be between 4.3 and 5.2.

[0016] P and S are harmful elements in steel. In order to ensure the purity and toughness of steel, as well as the good corrosion resistance and other service performance of steel plates, they must be strictly controlled. Therefore, this invention limits P to ≤ 0.01% and S to ≤ 0.005%.

[0017] Ni, an important alloying element in low-temperature steel, can ensure the toughness and plasticity of steel without sacrificing its strength level. Ni in steel can expand and stabilize the austenite phase region, lowering the ductile-brittle transition temperature of the steel plate. Ni strengthens steel through solid solution and refines grains, enhancing its plastic deformation capacity, strength, and wear resistance. Adding Ni to steel can extend its service life in corrosive media and improve its corrosion resistance and other service properties. This invention sets the Ni content range to 0.41%–0.48%.

[0018] Mo exists in steel in two forms: firstly, it is dissolved in the matrix, acting as solid solution strengthening; secondly, it combines with carbon in the steel plate to form carbides that are dispersed in the matrix, pinning dislocations and preventing grain growth, thus acting as grain refinement strengthening. The interaction of these two forms ensures a good balance of strength and toughness in the steel plate and lowers its ductile-brittle transition temperature. In chloride-containing environments, Mo significantly improves the steel's resistance to pitting corrosion; and it inhibits the diffusion of hydrogen in the steel, thereby improving the steel plate's resistance to hydrogen-induced cracking. However, excessive Mo increases the temper brittleness of the steel plate and significantly increases production costs. Therefore, this invention sets the Mo content range to 0.03%–0.08%.

[0019] Nitrogen (Nb) is a strong carbide / nitride element. In steel, it forms precipitated strengthening phases such as Nb(C, N), increasing the area of ​​nucleation at grain boundaries and subgrain boundaries, inhibiting grain growth, and the fine, dispersed distribution of Nb(C, N) plays a dispersion strengthening role, ensuring a balance between strength and toughness, as well as low-temperature toughness. Regarding its impact on the corrosion resistance of steel, Nb has a high affinity for C and N, forming stable carbides that limit corrosion at grain boundaries and hydrogen-induced cracking, thereby improving the steel's corrosion resistance. However, excessively high Nb content can lead to abnormal growth of second-phase particles, increasing the brittleness of the steel and negatively affecting its low-temperature performance. Therefore, the recommended Nb content is 0.12%–0.18%.

[0020] The synergistic effect of Ni, Mo, and Nb in steel plates is manifested in the following aspects: Regarding strength and toughness, Nb refines the grain, while Ni and Mo improve the toughness of the matrix, achieving a balance of high strength, high toughness, and good low-temperature performance. In terms of corrosion resistance, Ni and Mo enhance corrosion resistance, while Nb reduces corrosion-sensitive areas by refining the grain. Regarding wear resistance, Mo and Nb increase hardness, while Ni improves toughness, ensuring good wear resistance of the steel plate. Therefore, in this invention, Ni% ≥ Mo / Nb is controlled.

[0021] Adding Ce to steel alters the temperature trend during tempering, slowing down the precipitation of carbides and reducing the formation of network carbides. This increases the uniformity of the second-phase particle distribution, resulting in steel plates with excellent strength and sufficient toughness. Ce-rich phase particles in steel act as heterogeneous nucleation sites, agglomerating within the grains, reducing interfacial energy, increasing the total grain boundary area, hindering grain boundary migration, and tending to reduce crack initiation and propagation pathways. This improves the steel plate's machinability and hot plasticity, reduces the possibility of quenching cracking, and simultaneously ensures the steel plate's corrosion resistance. Ce readily combines with O, S, C, etc., in steel to form fine, dispersed second-phase particles, and can reduce the agglomeration of harmful elements such as P and low-melting-point impurities at grain boundaries, reducing temper brittleness and comprehensively and effectively improving the steel's mechanical properties. However, considering production costs, this invention controls the Ce content within the range of 0.001% to 0.0015%. Meanwhile, to ensure a good balance of strength and toughness, low-temperature performance, and excellent service performance, the Ni / Ce ratio is controlled between 255 and 420.

[0022] The steel plate of this invention has a microstructure of troostite + spheroidal bainite with a grain size of 8 to 9, wherein the size of the spheroidal bainite is no greater than 60 nm, the interlamellar spacing is between 22 and 36 nm, and the total inclusion grade of the steel plate is ≤1.0.

[0023] The mechanical properties of the steel plate are: tensile strength R at room temperature m Its strength is 820-876 MPa, and its yield strength R is 820-876 MPa. el With a tensile strength of 730–785 MPa, elongation A ≥ 26%, and HBW ≤ 180; and a tensile strength R at -70℃. m Its strength is 840–910 MPa, and its yield strength R is 100 MPa. el The strength is 790–805 MPa, elongation A ≥ 22%, HBW ≤ 200, and average transverse impact energy KV2 ≥ 245 J; under temperature conditions of -196℃, the yield strength R m The yield strength is 1100–1220 MPa, and the yield strength R is 1100–1220 MPa. el The pressure is 845–942 MPa, A ≥ 18%, HBW ≤ 240, and the lateral impact energy KV2 value ≥ 195 J.

[0024] According to the hydrogen-induced cracking test in GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", the crack sensitivity (CSR%), crack length ratio (CLR%), and crack width ratio (CTR%) of the steel plate are all 0; according to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Pitting Corrosion of Stainless Steel with Ferric Chloride", the corrosion rate of the steel plate is not greater than 0.0026 g / m. 2 •h.

[0025] According to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics", the volumetric wear of the steel plate should not exceed 0.0032 cm. 3 .

[0026] The thickness of the finished steel plate of this invention is 22-46mm.

[0027] A method for manufacturing steel plates for 820MPa cryogenic storage tanks includes smelting, continuous casting, heating, rolling, cooling, straightening, and heat treatment; specifically, it includes the following steps:

[0028] 1) Smelting Process: Steelmaking takes place in a converter, using high-quality scrap steel and molten iron as raw materials. The charge size is controlled between 91 and 110 mm, and the iron content is controlled above 73% to ensure steel purity, shorten process time, and reduce the difficulty of subsequent processes. Strict control is maintained over the converter dephosphorization and decarburization parameters. Decarburization oxygen blowing is controlled at 405–480 s; to effectively reduce the harmful element P content, dephosphorization oxygen blowing is controlled at 512–660 s, controlling the phosphorus mass fraction in the molten steel to below 0.01%; further deep desulfurization is performed in an LF refining furnace, with desulfurization oxygen blowing controlled at 722–840 s, controlling the sulfur content below 0.005%; degassing is completed in an RH furnace, with the initial temperature controlled at 1606–1629℃ and the oxygen blowing rate controlled at 14–19 m³ / s. 3 The net circulation time is 702–780 s, and the pre-casting settling time is 392–419 s. By optimizing the smelting process parameters, steel oxidation is reduced, the content of inclusions in the steel is controlled, internal defects are reduced, and the internal quality of the cast billet is improved.

[0029] 2) Continuous casting process: After vacuum breaking, slab continuous casting machine is used for casting. The key is to control the casting temperature. The casting temperature of molten steel in the tundish is 1580-1596℃, the superheat is set at 3.5-5℃, and the billet pulling speed during casting is 14-21mm / s. The original as-cast structure is refined through high-temperature casting. Electromagnetic stirring process is used, with the stirring speed controlled at 0.63-0.82m / s and the current intensity at 542-556A to ensure the quality and homogeneity of the billet. A light reduction process for the continuous casting billet is adopted to further improve the internal quality of the billet and reduce defects such as segregation and voids. The light reduction rate is controlled at 2-4%, and the reduction rate is controlled at 3.6-5.5mm / s. The billet is stacked and slow cooled after leaving the line. The stacking and slow cooling time is 24-36 hours, and the number of stacked surfaces is 3-4.

[0030] 3) Heating Process: The continuously cast slab is sent to a heating furnace for heating. The slab undergoes segmented heating before being removed from the furnace. A three-stage heating process is adopted, with the first heating stage at a temperature range of 992–1038℃, the second heating stage at 1230–1254℃, and the soaking stage at 1065–1098℃. The heating rate is controlled at 7–10℃ / min, and the total furnace time for the slab is controlled at 2.4–3.6 hours. By using segmented and high-efficiency heating, the uniformity of the internal structure of the steel billet is further improved, the original size of precipitated phase particles is controlled, overheating of the steel plate is avoided, and heating efficiency is improved. This ensures the uniformity of the internal structure and properties of the steel plate, reduces the impact of large inclusions on the service performance of the steel plate, and fully releases the internal stress of the steel plate. At the same time, ensuring uniform temperature inside and outside the steel billet is beneficial for further processing.

[0031] 4) Rolling process: The rolling process adopts a three-stage controlled rolling method. The rolling temperature at the beginning of the first stage recrystallization zone is 1156-1175℃, and the rolling temperature at the end of the first stage is 986-1063℃. The high-temperature rolling reduces the deformation resistance and improves the yield of steel plates. The rolling control process adopts a "large-small-large cycle reduction" with a rolling speed of 4.2-5.3m / s to fully refine the original austenite structure. The large reduction is controlled within the range of 10-14%, and the small reduction is controlled within the range of 6%-8% to ensure sufficient recrystallization of grains and refine the internal structure of the steel plate while ensuring the uniformity of the structure. After the first stage of rolling, the waiting time for the steel plate to reach the set temperature is controlled within the range of 48–55 seconds. In the second stage, the rolling temperature in the non-recrystallization zone begins at 938–975℃ and ends at 842–859℃. A "small-small-large cycle reduction" rolling process is used for single-pass reduction, with small reductions ranging from 3% to 6% and large reductions controlled within 11% to 16%. This "small-small-large cycle reduction" process involves a phase transformation during rolling, increasing the ferrite content in the steel plate, ensuring the required yield strength, further refining the internal structure, increasing the grain boundary area, and further flattening and elongating the austenite grains, thus enhancing the strength-toughness ratio. The third stage is the microstructure strengthening rolling stage, starting at 826–835℃ and ending at 804–821℃. A "small reduction" rolling process is used for single-pass reduction, ranging from 1% to 3%, optimizing the surface microstructure of the steel plate. This process enhances the uniformity of the microstructure, improving the steel plate's strength and corrosion resistance, among other service properties. After rolling, the steel plate is leveled using a concave roll leveler to control the crown within 40–46 μm and the flatness within 0.12–0.22 mm / m. This further refines the internal microstructure of the steel plate, resulting in better control of the overall plate shape.

[0032] 5) Cooling Process: The uniform and fine microstructure further ensures the uniformity of the steel plate's properties and helps optimize the strength-toughness ratio. The fine-grain strengthening mechanism increases the steel plate's strength, thereby further improving its wear resistance and other service performance. Utilizing an online ultra-fast cooling-water-cooling segmented cooling method, combined with mechanisms such as fine-grain strengthening, precipitation strengthening, and phase transformation strengthening, the mechanical properties of the strip steel are significantly improved. The ultra-fast cooling start temperature of the first cooling stage is controlled at 762–770℃, and the cooling rate is controlled at 120–150℃ / s; the water cooling start temperature of the second cooling stage is controlled at 440–456℃, and the cooling rate is controlled at 26–37℃ / s.

[0033] 6) Straightening process: Utilize online hot straightening + cold straightening to ensure production efficiency while further optimizing the steel plate structure and improving the surface quality of the steel plate. Control the number of hot straightening passes to 3 to 7. During the cold straightening process, introduce small-angle grain boundaries to improve the corrosion resistance of the steel plate. Control the starting temperature of cold straightening of the steel plate to 182 to 194℃ and the reduction to 0.8% to 1.6%.

[0034] 7) Heat Treatment Process: Due to the addition of elements such as C, Si, Mn, Ni, Cr, and V to the steel, the rolled steel plate obtains a troostite + spheroidal bainite microstructure with excellent strength and toughness. However, the uneven grain size distribution of the steel plate leads to concentrations of structural and thermal stresses, making it prone to delayed cracking during flame cutting. Therefore, timely heat treatment is necessary to soften and relieve stress. To further control the internal microstructure of the steel plate while ensuring high production efficiency, this invention employs short-time tempering heat treatment to ensure that the steel plate does not lose strength while possessing suitable plasticity, toughness, low-temperature impact toughness, corrosion resistance, and good processing performance. Therefore, the short-time tempering heat treatment temperature is controlled at 625–649℃, the heating rate at 1.9–2.7℃ / s, the holding time at 35–44 min, and the steel is cooled to room temperature in the furnace at a controlled cooling rate of 20–31℃ / s.

[0035] This invention optimizes the smelting process, employs a pretreatment process for molten iron, ensures full-process protective casting, and combines electromagnetic stirring with light reduction technology to improve the purity of molten steel, guarantee the internal quality of the cast billet, strictly control the influence of elements such as P, S, and O, and ensure the internal quality of the cast billet, fundamentally guaranteeing the service performance of the steel plate. A segmented, high-efficiency three-stage slab heating process is adopted to shorten processing time, improve production efficiency, and ensure efficient heat conduction within the cast billet. Through three-stage controlled rolling combined with efficient cooling and two-stage straightening technology, the uniformity of the internal structure of the steel plate is further optimized, ensuring uniform and excellent mechanical properties, improving plate shape, and guaranteeing good corrosion resistance and low-temperature resistance. A high-temperature, short-time tempering heat treatment process improves the strength-toughness ratio while adjusting the microstructure of the material, improving the mechanical properties of the steel plate and ensuring its service performance. This invention provides an 820MPa grade low-temperature storage tank steel plate and its manufacturing method, suitable for large-scale, high-efficiency, high-strength low-temperature storage tank steel production.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] 1) Based on the strengthening elements C, Si, and Mn, appropriate amounts of alloying elements Ni, Mo, Nb, and Ce are added, while strictly controlling the content of harmful elements P and S. Combined with the optimization of the production process, uniform and refined troostite + spherical bainite is obtained. The total inclusion grade of the steel plate is ≤1.0, the grain size is 8 to 9, the size of the spherical bainite is no greater than 60nm, the interlamellar spacing is between 22 and 36nm, and the second phase particles (mainly Ce (O / S / C) and Mo and Nb (C / N)) with a size below 35nm are uniformly dispersed, which ensures the steel plate's strength, plasticity, low-temperature toughness, corrosion resistance, wear resistance and other service performance.

[0038] 2) The mechanical properties of the steel plates for storage tanks obtained through a unique production process are characterized by the tensile strength R of the steel plate at room temperature. m Its strength is 820-876 MPa, and its yield strength R is 820-876 MPa. el For a strength of 730–785 MPa, elongation A ≥ 26%, HBW ≤ 180; tensile strength R at -70℃. m Its strength is 840–910 MPa, and its yield strength R is 100 MPa. el The steel plate has a strength of 790–805 MPa, elongation A ≥ 22%, HBW ≤ 200, and average transverse impact energy KV2 ≥ 245 J; under conditions of -196℃, the yield strength R of the steel plate is... m The strength is 1100-1220 MPa, and the yield strength R is... el With a strength of 845–942 MPa, an A value of ≥18%, an HBW value of ≤240, and an average transverse impact energy KV2 value of ≥195 J, the steel plate exhibits uniform performance and a good balance of strength and toughness, as well as excellent low-temperature service performance.

[0039] 3) According to the hydrogen-induced cracking (HIC) test in GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", after 96 hours of testing in solutions A and B, the crack susceptibility (CSR) (%), crack length ratio (CLR) (%), and crack width ratio (CTR) (%) of the steel plate were all 0, indicating excellent resistance to hydrogen-induced cracking (HIC) of the steel plate; according to GB / T4157-2006 and NACE-TM017 According to the test standard 7-201 "Resistance of Metals to Sulfide Stress Cracking and Stress Corrosion in H2S Environment", the steel plate was subjected to tensile stress test in an acidic aqueous solution containing hydrogen sulfide. The results showed that no cracks appeared in the sample, indicating that the steel plate has excellent resistance to sulfide stress cracking and stress corrosion (SSC). According to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Pitting Corrosion of Stainless Steel with Ferric Chloride", the corrosion rate of the steel plate in both solution A and solution B was not greater than 0.0026 g / m³. 2 •h. According to the neutral salt spray test (NSS test) in GB / T10125-2021 "Artificial Atmosphere Corrosion Test: Salt Spray Test", the proportion of red rust after 48 hours is not greater than 10%, which shows that the steel plate has excellent corrosion resistance.

[0040] 4) Tests were conducted according to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics". The results showed that the volumetric wear of the steel plate was no greater than 0.0032 cm. 3 Steel plates have good wear resistance. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0042] The production method adopted in this invention is: molten iron pretreatment—vacuum degassing—continuous casting (with electromagnetic stirring and light reduction) treatment—stacking and slow cooling—slab cleaning—three-stage high-efficiency slab heating—three-stage controlled rolling—high-efficiency cooling process—two-stage straightening treatment + short-time tempering heat treatment, to produce steel plates for storage tanks with a thickness of 22-46mm. The produced steel plates have uniform microstructure and properties, good strength and toughness matching, and excellent corrosion resistance and wear resistance.

[0043] Table 1 shows the chemical composition of the embodiments of the present invention; Table 2 shows the steel smelting-continuous casting and heating process parameters of the embodiments; Table 3 shows the steel rolling, cooling and heat treatment process parameters of the embodiments; Table 4 shows the final mechanical properties of the embodiments; Table 5 shows the evaluation test results of microstructure grain size and second phase particles; Table 6 shows the evaluation test results of microstructure inclusion grade of the steel plate of the embodiments; Table 7 shows the service performance test results of the embodiments - corrosion resistance (hydrogen-induced cracking test, stress corrosion resistance test, pitting corrosion test, salt spray test) test, and friction and wear test results.

[0044] Table 1 Chemical composition (wt, %) of the examples

[0045]

[0046] Table 2 Smelting-continuous casting and heating process parameters for the examples

[0047]

[0048] Table 3 shows the process parameters for steel rolling, cooling, and heat treatment in the examples.

[0049]

[0050] Table 4. Final Mechanical Properties of Examples

[0051]

[0052] Table 5 shows the results of the microstructure grain size and second-phase particle evaluation tests.

[0053]

[0054] Table 6. Results of the test for evaluating the inclusion grade of the steel plates in the examples.

[0055]

[0056] Table 7 shows the service performance test results of the examples.

[0057]

[0058] Based on the above results, it can be concluded that the tensile strength R of the steel plate with a thickness of (22-46) mm provided by this invention at room temperature is [missing information]. m Its strength is 820-876 MPa, and its yield strength R is 820-876 MPa. el With a tensile strength of 730–785 MPa, elongation A ≥ 26%, and HBW ≤ 180; and a tensile strength R at -70℃. m Its strength is 840–910 MPa, and its yield strength R is 100 MPa. elThe tensile strength is 790–805 MPa, elongation A ≥ 22%, HBW ≤ 200, and average transverse impact energy KV2 ≥ 245 J; under temperature conditions of -196℃, the tensile strength R... m The strength is 1100-1220 MPa, and the yield strength R is... el The steel plate has an energy rating of 845–942 MPa, an alumina (A) of ≥18%, an HBW of ≤240, and a transverse impact energy (KV2) of ≥195 J. The total inclusion grade of the steel plate is ≤1.0. The microstructure consists of troostite and spheroidal bainite with a grain size of 8–9. The size of the spheroidal bainite is no greater than 60 nm. The interlayer spacing is between 22 and 36 nm. The second phase particles (mainly Ce (O / S / C) and Mo and Nb (C / N)) with a size below 35 nm are uniformly dispersed. The steel plate exhibits excellent corrosion resistance across its entire thickness (resistance to hydrogen-induced cracking, sulfide stress cracking and stress corrosion, and pitting corrosion). Specifically, according to the hydrogen-induced cracking (HIC) test in GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", after 96 hours of testing in solutions A and B, the crack susceptibility (CSR) (%), crack length ratio (CLR) (%), and crack width ratio (CTR) (%) are all 0, indicating excellent resistance to hydrogen-induced cracking (HIC). According to GB / T... According to tests 4157-2006 and NACE-TM0177-201 "Resistance of Metals to Sulfide Stress Cracking and Stress Corrosion in H2S Environments," tensile stress tests were conducted on steel plates in acidic aqueous solutions containing hydrogen sulfide. The results showed no cracks appearing in the samples, indicating excellent resistance to sulfide stress cracking and stress corrosion (SSC). According to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Pitting Corrosion of Stainless Steel with Ferric Chloride," the corrosion rate of the steel plate in solutions A and B was not greater than 0.0026 g / m³. 2 • h. According to the neutral salt spray test (NSS test) in GB / T10125-2021 "Artificial Atmosphere Corrosion Test: Salt Spray Test", the proportion of red rust after 48 hours is not greater than 10%; according to GB / T3960-2016 "Plastics Sliding Friction and Wear Test Method", the results show that the volumetric wear of the steel plate is not greater than 0.0032 cm. 3 The steel plate has good wear resistance. That is, the steel plate has strength, low temperature toughness, good service performance and excellent plate shape. The (22~46) mm thickness specification steel plate meets the manufacturing and application requirements of high performance storage tank steel plates.

Claims

1. A steel plate for 820MPa grade cryogenic storage tanks, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.18%–0.21%, Si: 0.15%–0.37%, Mn: 0.87%–0.96%, P≤0.01%, S≤0.005%, Ni: 0.41%–0.48%, Mo: 0.03%–0.08%, Nb: 0.12%–0.18%, Ce: 0.001%–0.0015%, and Mn / C = 4.3–5.

2. Ni / Ce = 255~420, Ni ≥ Mo / Nb; the balance is Fe and unavoidable inclusions; at the same time, the values ​​of Pcm% = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B are required to be in the range of 0.235~0.285, and the values ​​of CE% = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 are required to be in the range of 0.35~0.

42. The microstructure of the steel plate is troostite + spheroidal bainite, with a grain size of 8 to 9. The size of the spheroidal bainite is no greater than 60 nm, the interlamellar spacing is between 22 and 36 nm, and the total inclusion grade of the steel plate is ≤1.

0.

2. The steel plate for an 820MPa cryogenic storage tank according to claim 1, characterized in that, The mechanical properties of the steel plate are: tensile strength R at room temperature m Its strength is 820-876 MPa, and its yield strength R is 820-876 MPa. el With a tensile strength of 730–785 MPa, elongation A ≥ 26%, and HBW ≤ 180; and a tensile strength R at -70℃. m Its strength is 840–910 MPa, and its yield strength R is 100 MPa. el The tensile strength is 790–805 MPa, elongation A ≥ 22%, HBW ≤ 200, and average transverse impact energy KV2 ≥ 245 J; under temperature conditions of -196℃, the tensile strength R... m The strength is 1100-1220 MPa, and the yield strength R is... el The pressure is 845–942 MPa, A ≥ 18%, HBW ≤ 240, and the transverse impact energy KV2 value ≥ 195 J.

3. The steel plate for an 820MPa cryogenic storage tank according to claim 1, characterized in that, According to the hydrogen-induced cracking test in GB / T8650-2006 and NACE-TM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", the crack sensitivity (CSR%), crack length ratio (CLR%), and crack width ratio (CTR%) of the steel plate are all 0; according to GB / T17897-2016 "Corrosion of Metals and Alloys - Test Method for Pitting Corrosion of Stainless Steel with Ferric Chloride", the corrosion rate of the steel plate is not greater than 0.0026 g / m. 2 •h.

4. The steel plate for an 820MPa cryogenic storage tank according to claim 1, characterized in that, According to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics", the volumetric wear of the steel plate should not exceed 0.0032 cm. 3 .

5. The steel plate for an 820MPa grade cryogenic storage tank according to claim 1, characterized in that, The thickness of the finished steel plate is 22-46mm.

6. A method for manufacturing 820MPa grade cryogenic storage tank steel plate as described in any one of claims 1-5, comprising smelting, continuous casting, heating, rolling, cooling, straightening, and heat treatment; characterized in that, Specifically, it includes: The heating process includes a three-stage heating process, wherein the temperature range of the first heating stage is 992–1038℃, the temperature range of the second heating stage is 1230–1254℃, and the temperature range of the soaking stage is 1065–1098℃; the heating rate is controlled at 7–10℃ / min, and the total time the slab is in the furnace is controlled at 2.4–3.6 hours. The rolling process includes: a three-stage controlled rolling method, with the first stage recrystallization zone starting at a rolling temperature of 1156–1175℃ and ending at 986–1063℃; a "large-small-large cycle reduction" rolling control process is adopted, with a rolling speed of 4.2–5.3 m / s, and the large reduction range controlled at 10%–14%, the small reduction range controlled at 6%–8%, and the waiting time for the steel plate after the first stage of rolling controlled at 48–55 s. In the second stage, the rolling temperature in the non-recrystallization zone starts at 938–975℃ and ends at 842–859℃. A "small-small-large cycle reduction" rolling process is used to control the reduction per pass, with small reductions ranging from 3% to 6% and large reductions ranging from 11% to 16%. In the third stage, the rolling temperature starts at 826–835℃ and ends at 804–821℃. A "small reduction" rolling process is used to control the reduction per pass, with a reduction range of 1% to 3%. The cooling process includes: controlling the starting temperature of the ultra-rapid cooling in the first cooling section of the steel plate to be 762-770℃ and the cooling rate to be 120-150℃ / s; and controlling the starting temperature of the water cooling in the second cooling section to be 440-456℃ and the cooling rate to be 26-37℃ / s. The straightening process includes: controlling the number of hot straightening passes to 3 to 7; controlling the starting temperature of cold straightening of the steel plate to be 182 to 194°C, and the reduction to be 0.8% to 1.6%; The heat treatment includes: short-time tempering heat treatment of steel with a controlled temperature of 625-649℃, a heating rate of 1.9-2.7℃ / s, a holding time of 35-44 min, and furnace cooling to room temperature with a controlled cooling rate of 20-31℃ / s.

7. The method for manufacturing steel plates for 820MPa-grade cryogenic storage tanks according to claim 6, characterized in that, The smelting process includes: controlling the charge size to be between 91 and 110 mm, and controlling the molten iron content to be above 73%; controlling decarburization oxygen blowing to be between 405 and 480 s; controlling dephosphorization oxygen blowing to be between 512 and 660 s; performing deep desulfurization treatment in an LF refining furnace, with desulfurization oxygen blowing controlled to be between 722 and 840 s; and completing degassing in an RH furnace, with the initial temperature controlled to be between 1606 and 1629 °C and the oxygen blowing rate controlled to be between 14 and 19 m³. 3 The net circulation time is 702–780 s, and the pre-pouring settling time is 392–419 s.

8. The method for manufacturing steel plates for 820MPa cryogenic storage tanks according to claim 6, characterized in that, The continuous casting process includes: a tundish steel pouring temperature of 1580–1596℃, a superheat setting of 3.5–5℃, and a billet pulling speed of 14–21 mm / s; an electromagnetic stirring process, controlling the stirring speed at 0.63–0.82 m / s and the current intensity at 542–556 A; a continuous casting billet light reduction process, with a light reduction rate controlled at 2%–4% and a reduction rate controlled at 3.6–5.5 mm / s; and the billet undergoing slow cooling in a stacked manner after being removed from the casting line, with a stacking time of 24–36 hours and a stacking surface number of 3–4.

9. The method for manufacturing steel plates for 820MPa cryogenic storage tanks according to claim 6, characterized in that, After rolling, the plate is leveled by a concave roll leveler to control the crown to 40-46 μm and the flatness of the steel plate to 0.12-0.22 mm / m.

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