35MPa-grade low-temperature container steel plate for hydrogen energy storage and transportation and manufacturing method thereof

Abstract

The invention belongs to the field of metal materials, and provides a 35MPa-grade low-temperature container steel plate for hydrogen energy storage and transportation and a manufacturing method thereof.The steel plate is prepared from, by weight, 0.12%-0.14% of C, 0.25%-0.38% of Si, 1.25%-1.41% of Mn, smaller than or equal to 0.01% of P, smaller than or equal to 0.005% of S, 0.16%-0.28% of Ni, 0.2%-0.3% of Cr, 0.03%-0.05% of Ti, 0.052%-0.064% of Nb, 0.02%-0.032% of N, 0.0012%-0.0024% of Ce and the balance Fe and inevitable impurities. The manufacturing method comprises the steps of electric furnace smelting, continuous casting, three-stage efficient slab heating, three-stage design rolling, two-stage cooling and short-time tempering heat treatment. The steel plate produced by the method has good obdurability matching and high and low temperature service performance, and meets the manufacturing and application requirements of the high-performance steel plate for hydrogen energy storage and transportation.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a 35MPa grade cryogenic container steel plate for hydrogen energy storage and its manufacturing method. Background Technology

[0002] The development of a 35MPa grade special steel plate is urgently needed to address the shortcomings of traditional cryogenic container steel plates in the field of hydrogen energy storage and transportation. Previous studies have shown that while austenitic stainless steel possesses excellent low-temperature toughness, its high cost limits its large-scale application; while 9% Ni steel, although exhibiting outstanding overall performance, suffers from economic instability due to nickel price fluctuations, and its welding process is complex. Furthermore, the existing steel plates have not yet achieved an ideal balance between strength and toughness at extreme low temperatures of -196℃, making it difficult to fully meet the high safety requirements of hydrogen energy storage and transportation.

[0003] The publicly disclosed invention patent "A 130mm~150mm Thick Ultra-Low Temperature Steel Plate and Its Production Method" (CN104561772A) describes a steel plate composed of the following weight percentages: C: 0.06~0.09%, Si: 0.25~0.40%, Mn: 1.60~1.70%, P: <0.010%, S: <0.003%, Nb: 0.02~<0.03%, Ni: 0.60~0.70%, Als: 0.20~0.40%, with the remainder being Fe and residual elements. The tensile strength / yield strength levels are relatively low, making it difficult to meet the requirements for higher strength hydrogen storage steel plates. Furthermore, the low-temperature performance of the steel plate below -80℃ has not been studied, and the thickness specifications are only studied for large thicknesses of 150mm and above; thinner thicknesses are not specifically analyzed. Therefore, it is not suitable for the production of high-density hydrogen storage steel. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a 35MPa grade cryogenic container steel plate for hydrogen energy storage with good strength and toughness matching, excellent high and low temperature service performance, resistance to hydrogen-induced cracking, resistance to sulfide stress cracking and stress corrosion (SSC), and good wear resistance, as well as its manufacturing method.

[0005] The objective of this invention is achieved as follows:

[0006] A 35MPa-grade cryogenic container steel plate for hydrogen energy storage has the following composition by weight percentage: C: 0.12%~0.14%, Si: 0.25%~0.38%, Mn: 1.25%~1.41%, P: ≤0.01%, S: ≤0.005%, Ni: 0.16~0.28%, Cr: 0.2%~0.3%, Ti: 0.03~0.05%, Nb: 0.052~0.064%, N: 0.02~0.032%, Ce: 0.0012~0.0024%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, in the steel plate, Pcm ≤ 0.25, Pcm = C + Si / 30 + (Mn + Cr) / 20 + Ni / 60 ≤ 0.25.

[0008] Furthermore, the Mn / C ratio in the steel plate is ≥10.

[0009] Furthermore; 3N / (4Ni×Ti) ≥ 2 in the steel plate.

[0010] Furthermore, in the steel plate, Cr ≤ Nb / 5Ti.

[0011] Furthermore, in the steel plate, Pcm≤0.25, Pcm=C+Si / 30+(Mn+Cr) / 20+Ni / 60≤0.25.

[0012] Furthermore, the thickness of the steel plate is 8~65mm; the microstructure of the steel plate is uniform and refined sorbite + ferrite + nanoscale spherical bainite, with a grain size of 7~9; the distance between the lamellar structures of the sorbite is no greater than 82nm, and the diameter of the spherical bainite is 25~36nm; the second phase particles in the steel plate are uniformly dispersed, wherein the size of the second phase particles Cr (C and / or N), Ti (C and / or N), and Nb (C and / or N) is ≤48nm, and the diameter of the second phase particles spherical Ce (O / S / N) is ≤10nm.

[0013] Furthermore, the volume ratio of various microstructures in the steel plate is sorbite: ferrite: bainite = (5~6): (6~8): (2~3).

[0014] Furthermore, at room temperature, at the half-section of the steel plate, the tensile strength is 700~756MPa, the yield strength is 582~625MPa, and the elongation after fracture (A) is ≥30%; at the quarter-section of the steel plate, the tensile strength is 705~763MPa, the yield strength is 584~625MPa, and the elongation after fracture (A) is ≥30%; under -60℃ conditions, the average transverse impact energy (KV2) of the steel plate is ≥220J, and at the quarter-section of the steel plate, the tensile strength is 714~773MPa, and the yield strength is 595~633MPa. Pa, elongation after fracture A≥29%; under -80℃ conditions, the average transverse impact energy KV2≥212J, at 1 / 4 of the steel plate: tensile strength 716~776MPa, yield strength 600~640MPa, elongation after fracture A≥29%; NDDT of the steel plate≤-100℃; in the temperature range of 450~550℃, with a preset stress of 180~320MPa, the fracture time of the steel plate in the creep test is not less than 6500h, that is, good strength and toughness matching and high and low temperature service performance.

[0015] According to the hydrogen-induced cracking (HIC) test in GB / T8650-2006 and NACETM0284 "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. According to GB / T4157-2006 and NACETM0177-20 1. In the test "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 solutions A and B was not greater than 0.0029 g / m. 2 •h; Tested according to GB / T3960-2016 "Plastics Sliding Friction and Wear Test Method", the results show that the volumetric wear of the steel plate is no greater than 0.00062 cm. 3 The steel plate has good wear resistance; that is, the steel plate has excellent strength, low temperature toughness, service performance and plate shape. The (8~65) mm thickness specification steel plate meets the manufacturing and application requirements of high performance hydrogen energy storage steel plate.

[0016] The rationale for the design of the components in this invention is as follows:

[0017] Carbon (C) is a crucial element determining the strength and toughness of steel plates. When the C content in a steel plate is low, its strength, hardness, and hardenability are difficult to guarantee, its wear resistance decreases, and its service performance is affected. However, excessively high C content can negatively impact the machinability of the steel. To ensure good low-temperature toughness and prevent an increase in the ductile-brittle transition temperature range, this invention sets the C content range to 0.12%~0.14%.

[0018] Si is commonly used in steel as a reducing agent and oxidizing agent. In this patent, some of the Si comes from the Si element introduced into the spheroidizing agent, reducing the negative impact of other impurities. On the other hand, adding an appropriate amount of Si to steel improves its wear resistance, elastic limit, yield strength, and yield ratio. However, excessive Si content in steel plates can easily lead to excessive large-size inclusions, which is detrimental to the low-temperature performance of the steel plate. Therefore, this invention sets the Si content range to 0.25%~0.38%.

[0019] In steel, manganese (Mn) acts as an austenite-expanding element, typically dissolved in ferrite and austenite to maintain the critical temperature range of the steel plate. It also ensures the uniformity of the microstructure in quenched and tempered steel, refining the microstructure and strengthening it. This increases the steel's strength and hardness while maintaining hardenability. Furthermore, it is relatively inexpensive. However, to reduce the impact of MnS inclusions on the steel plate's resistance to hydrogen-induced cracking, this invention sets the Mn content range to 1.25%~1.41%. Through synergistic effects, C and Mn significantly improve the strength, toughness, wear resistance, and machinability of the steel plate by utilizing solid solution strengthening, phase transformation regulation, complementary mechanical properties, and process optimization. Therefore, the Mn / C ratio is controlled to be ≥10.

[0020] S and P are harmful elements in steel. To ensure the purity and toughness of steel, they must be strictly controlled. Therefore, this invention limits P to ≤ 0.01% and S to ≤ 0.005%.

[0021] Adding appropriate amounts of nickel to steel plates can optimize their crystal structure, making them less prone to fracture under external forces while maintaining good low-temperature plasticity and toughness. Ni atoms, integrated into the metal matrix, impede dislocation movement through lattice distortion, thereby increasing the material's strength. Ni also forms intermetallic compounds (such as Ni3(Ti) phase) with elements like Ti. These precipitated phases effectively pin dislocations and grain boundaries, significantly improving the material's creep resistance. Ni promotes the formation of a stable and dense oxide film on the steel plate, thus enhancing its corrosion resistance. However, considering the high cost of Ni, this patent chooses to substitute it by adding a certain amount of nitrogen (N) to reduce the amount of Ni used, controlling the content to Ni: 0.16~0.28%.

[0022] Nitrogen (N) is a strong austenite-forming element, and its ability to stabilize austenite is approximately tens of times that of nickel (calculated on an equivalent basis). "Nitrogen-substituted nickel" can significantly reduce alloy costs while maintaining or improving austenite stability. When N exists in steel in solid solution form, it significantly improves the strength of the steel plate through solid solution strengthening, ensuring that the low-temperature toughness of the steel plate is not reduced. Excessive N will reduce the stacking fault energy (SFE), requiring optimization of the content to balance strength and low-temperature toughness. Simultaneously, it readily combines with Ti in the steel plate to form fine, dispersed titanium nitrides, enhancing the steel plate's properties and ensuring a good strength-toughness balance. Therefore, the N content should be controlled at N: 0.02~0.032%, while ensuring that the 3N / (4Ni×Ti) ratio is not less than 2.

[0023] Cr is a strong carbide-forming element. In steel, Cr readily combines with C / N to form fine chromium carbide particles that remain stable even at high temperatures. These stable second-phase particles pin dislocations, further preventing dislocation movement, increasing grain boundary area, reducing austenite grain size, and inhibiting grain growth. This ensures a good balance of strength and toughness in the steel plate, while also guaranteeing its high-temperature creep resistance. Furthermore, Cr has a high affinity for O, fixing free O in the steel plate and improving its corrosion resistance and oxidation resistance. Cr also increases the hardness of the steel plate, thus ensuring good wear resistance. To ensure good toughness, plasticity, weldability, and resistance to hydrogen-induced cracking, this invention sets the Cr content range to 0.2%~0.3%.

[0024] Ti has a high affinity for C and N in steel, and Ti (C / N) particles significantly improve the yield and tensile strength of steel plates through dispersion. Simultaneously, due to its ability to inhibit austenite grain growth, it refines the microstructure while enhancing strength and toughness, ensuring the low-temperature service performance of the steel plate. Ti (C / N) particles distributed at grain boundaries reduce the segregation and diffusion of hydrogen atoms at grain boundaries, lowering the susceptibility to hydrogen-induced cracking and ensuring good resistance to hydrogen embrittlement and corrosion. Ti is also an important element for ensuring good creep rupture performance of steel plates, as it forms refined second-phase particles with C and N that remain stable even at high temperatures, ensuring higher load-bearing capacity and creep life at high temperatures. In this invention, the Ti content is set in the range of 0.03~0.05%.

[0025] Nitrogen (Nb) is a strong carbide / nitride element that forms stable carbides in steel, expanding the recrystallization zone and significantly refining the grain structure, ensuring a good balance of strength and toughness in the steel plate. Nb-(C / N) microalloying plays a precipitation strengthening role in steel, acting as a heterogeneous nucleation core to effectively refine the lamellar structure, reduce lamellar distance, and control the sorbite lamellar distance to no more than 82 nm. With appropriate heat treatment, vanadium carbides / nitrides are dispersed and distributed in the steel, thus improving its strength and toughness, as well as its weldability and resistance to intergranular corrosion. However, excessively high Nb content leads to the aggregation and growth of second-phase particles in the steel plate, increasing its brittleness. Therefore, the Nb content is typically between 0.052% and 0.064%, while emphasizing the synergistic strengthening effect of elements in the steel plate, with Cr% ≤ Nb / 5Ti. The particle size of the second-phase Cr / Nb / Ti carbides / nitrides is controlled to be ≤ 48 nm.

[0026] Ce functions in steel through a three-pronged mechanism: First, it reacts with oxygen / sulfur in inclusions such as manganese sulfide and alumina to form high-melting-point compounds, purifying the molten steel. Second, nanoscale spherical Ce (O / S / N) particles (≤10nm) significantly improve the high and low temperature performance of the steel plate by pinning grain boundaries and reducing the segregation of harmful elements. Finally, the microalloying effect of Ce requires strict control; excessive addition will form large, pointed inclusions, which will impair resistance to hydrogen-induced cracking and corrosion. Therefore, its effect is extremely sensitive to the size and morphology of inclusions. Furthermore, considering overall production costs, this patent sets the Ce content at 0.0012~0.0024%.

[0027] The second technical solution of the present invention is to provide a manufacturing method for a 35MPa grade hydrogen energy storage cryogenic container steel plate, including smelting, continuous casting, three-stage slab heating, controlled rolling and controlled cooling, and tempering heat treatment.

[0028] (1) Electric furnace smelting:

[0029] Smelting includes electric furnace smelting, LF refining, and RH refining;

[0030] Electric furnace smelting uses scrap steel and molten iron as raw materials, with a charge size of 82~94mm and a molten iron mass percentage of over 78%. During the smelting process, the magnesium-silicon spheroidizing agent is added at a rate of 3.9%~4.8% per ton of steel, the decarburization oxygen blowing time is 263~368s, and the dephosphorization oxygen blowing time is 286~394s, reducing the phosphorus content in the molten steel to below 0.01%.

[0031] Deep desulfurization is carried out using an LF refining furnace, with a desulfurization and oxygen blowing time of 392~438s, controlling the sulfur content to below 0.005%.

[0032] Degassing is completed in an RH refining furnace, with an initial temperature of 1652~1664℃ and an oxygen blowing rate of 21~25m³.3 The net circulation time is 575~660s, and the pre-pouring settling time is 298~340s.

[0033] Electric arc furnace smelting uses high-quality scrap steel and molten iron as raw materials, controlling the charge size between 82 and 94 mm and the molten iron content above 78% to ensure steel purity, shorten process time, and reduce the difficulty of subsequent processes. Magnesium-silicon spheroidizing agents are added during smelting, at a rate of 3.9% to 4.8% per ton of steel, to ensure the uniformity of the original microstructure, refine the as-cast grains, and shorten smelting time. Strict control was exercised over the setting of dephosphorization and decarburization smelting parameters. Decarburization oxygen blowing was controlled at 263-368 s; to effectively reduce the content of harmful element P, dephosphorization oxygen blowing was controlled at 286-394 s, reducing the phosphorus mass fraction in the molten steel to below 0.01%; further deep desulfurization was carried out using an LF refining furnace, with desulfurization oxygen blowing controlled at 392-438 s, reducing the sulfur content to below 0.005%; degassing was completed in an RH furnace, with the initial temperature controlled at 1652-1664℃, oxygen blowing rate controlled at 21-25 m³, net circulation time at 575-660 s, and pre-casting settling time at 298-340 s. Through the optimized setting of smelting process parameters, the oxidation of molten steel was reduced, the content of inclusions in the steel was controlled, internal defects were reduced, and the purity of the steel was improved.

[0034] (2) Continuous casting process:

[0035] The casting temperature is 1570~1582℃, the superheat is set to 11~13℃, and the billet pulling speed is 2.3~2.6mm / s. A continuous casting billet light reduction process and / or electromagnetic stirring process are adopted. In the continuous casting billet light reduction process, the light reduction rate is preferably controlled at 2~4%. In the electromagnetic stirring process, the preferred current is 386~412A and the frequency is 5~9Hz. After the billet is removed from the casting line, it is slowly cooled in a stack at a cooling rate of 13~17℃ / h, and the slow cooling time in the stack is 36~48h.

[0036] After vacuum breaking, slab continuous casting is used for casting. High-temperature casting causes impurities to float to the surface, thus ensuring the internal quality of the original slab. The casting temperature is controlled at 1570~1582℃, the superheat is set at 11~13℃, and the casting speed is 2.3~2.6mm / s. By controlling the casting temperature, the original as-cast microstructure is refined. To optimize the internal quality of the continuously cast slab and reduce defects such as segregation and voids, a light reduction process and / or electromagnetic stirring process are used to reduce the core segregation of the slab and improve the slab quality. The light reduction rate is controlled at 2~4%, the current is 386~412A, and the frequency is 5~9Hz. After the slab is removed from the casting line, it is stacked for slow cooling at a cooling rate of 13~17℃ / h for 36~48h.

[0037] (3) Three-stage high-efficiency slab heating:

[0038] The slab heating adopts a three-stage heating method; the slab heating rate is controlled at 15~24℃ / min, the total furnace time is controlled at 3.1~4.6h, and the cooling rate is controlled at 32~51℃ / min.

[0039] The temperature range of the preheating section is 990~1012℃, the temperature of the high-temperature short-time homogenization section is 1136~1152℃, and the holding time is 36~52min; the temperature of the high-temperature high-efficiency homogenization section is 1244~1259℃.

[0040] The continuously cast slab is fed into a heating furnace for heating, undergoing a three-stage heating process before exiting the furnace. The preheating section has a temperature range of 990~1012℃, the high-temperature short-time homogenization section has a temperature range of 1136~1152℃, and the high-temperature high-efficiency homogenization section has a temperature range of 1244~1259℃. The slab heating rate is controlled at 15~24℃ / min, the total furnace time is controlled at 3.1~4.6h, and the cooling rate is controlled at 32~51℃ / min. This three-stage heating method further improves the uniformity of the internal structure of the slab, controls the original size of precipitated phase particles, fully releases the internal stress of the steel plate, and ensures uniform temperature inside and outside the slab, which is beneficial for further processing.

[0041] (4) Controlled rolling and controlled cooling process:

[0042] The rolling process employs a three-stage controlled rolling method.

[0043] The first stage involves refining the original austenite structure through rolling. The initial rolling temperature is 1078~1113℃, and the final rolling temperature is 981~1041℃. A "large-small-...large reduction rate" rolling control process is adopted, with the large reduction rate controlled within the range of 7%~10% and the small reduction rate within the range of 2%~4%.

[0044] The second stage involves rolling in the two-phase region, with an initial rolling temperature of 960~998℃ and a final rolling temperature of 842~890℃. A "large-large-small-large-...large reduction" rolling control process is employed, controlling the large reduction rate at 8%~11% and the small reduction rate at 4%~5%. This is followed by controlled cooling. First, homogenization-based controlled cooling begins at 830~876℃ with a cooling rate controlled at 43~57℃ / s. Then, precipitation strengthening controlled cooling begins at 514~545℃ with a cooling rate of 141~168℃ / s.

[0045] The third stage is the rolling process to enhance the microstructure and properties. The initial rolling temperature is 276~319℃, the reduction rate is controlled at 2%~4%, and the rolled steel plate is air-cooled.

[0046] The rolling process employs a three-stage controlled rolling and cooling method. The first stage involves refining the original austenite structure through rolling. The initial rolling temperature is 1078~1113℃, and the final rolling temperature is 981~1041℃. The rolling process is controlled by a "large-small-...large reduction rate" approach, with the large reduction rate controlled within the range of 7%~10% and the small reduction rate within the range of 2%~4%. Rolling in the high-temperature austenite region reduces the deformation resistance of the steel plate, fully refines the original austenite structure, ensures sufficient recrystallization of grains, and improves the uniformity of the internal structure of the steel plate while refining the internal structure.

[0047] The second stage involves rolling in the two-phase region, with an initial rolling temperature of 960-998℃ and a final rolling temperature of 842-890℃. A "large-large-small-large-...large reduction rate" controlled rolling process is employed, controlling the large reduction rate at 8-11% and the small reduction rate at 4-5%. As the grain boundary area increases, the ferrite nucleation rate increases during subsequent phase transformations, significantly refining the internal structure of the steel plate. Austenite grains are further flattened and elongated. Following rolling, a first-stage homogenization controlled cooling stage is performed, with a starting temperature of 830-876℃ and a cooling rate controlled at 23-37℃ / s. By controlling the cooling rate and temperature during rolling, abnormal grain growth in the steel plate is reduced, primary network carbide precipitation is prevented, dislocation movement caused by deformation is decreased, and the internal microstructure of the steel plate is optimized. The second stage of precipitation strengthening controlled cooling is then carried out, with the starting temperature controlled at 514~545℃ and the cooling rate at 91~108℃ / s. Through high-rate cooling, the austenite hardening state is maintained, nucleation is promoted, the microstructure is refined, strain-induced precipitation is suppressed, more microalloying elements are retained, the precipitation strengthening effect is improved, and the mechanical properties of the steel plate are enhanced.

[0048] The third stage of rolling is the microstructure and performance enhancement rolling stage. The initial rolling temperature is 276~319℃, and the reduction rate is controlled at 2~4%. The rolled steel plate is air-cooled. This further improves the uniformity of the steel plate microstructure, introduces more small-angle grain boundaries on the steel plate surface, further ensures the wear resistance, corrosion resistance and other service performance of the steel plate, releases the internal stress of the steel plate, and optimizes the control of the steel plate shape.

[0049] 5. Heat treatment:

[0050] The heat treatment is a short-time tempering heat treatment. The short-time tempering heat treatment temperature of the steel is 625~648℃, the heating rate is controlled at 0.7~1.0min / mm, the holding time is 25~42min, and the cooling rate is 39~46℃ / min.

[0051] Because of the addition of elements such as C, Si, Mn, Ni, Cr, Mo, Nb, and Ce to the steel, the rolled steel plate obtains a ferrite + sorbite + spheroidal bainite structure 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 structure 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 ductility, toughness, low-temperature impact toughness, corrosion resistance, and good processing performance. Therefore, the short-time tempering heat treatment stage of the steel is controlled at a temperature of 625~648℃, a heating rate of 0.7~1.0 min / mm, a holding time of 25~42 min, and a cooling rate of 39~46℃ / min.

[0052] The beneficial effects of this invention are as follows:

[0053] (1) Based on the strengthening elements of C, Si and Mn, by adding appropriate amounts of alloying elements such as Ni, Cr, Nb and Ce, and optimizing the control of N element, while strictly controlling the content of harmful elements P and S, and combining the production process optimization, a uniform and refined composition of sorbite + ferrite + nanoscale spherical bainite is obtained. The volume ratio of various microstructures of the steel plate is sorbite: ferrite: bainite = (5~6): (6~8): (2~3); the grain size is 7~9, the distance between the lamellar structures of sorbite is no more than 82nm, and the spherical bainite is between 25~36nm; the size is within the range of ≤48nm. The second phase particles Cr (C and / or N), Ti (C and / or N), Nb (C and / or N) particles are uniformly dispersed and the spherical Ce (O / S / N) with a diameter of no more than 10nm are also included. This ensures the high plasticity and low temperature toughness of the steel plate, while ensuring that the steel plate has good corrosion resistance and wear resistance.

[0054] (2) The mechanical properties of the steel plates for storage tanks obtained through a unique production process are as follows: at room temperature, the tensile strength at 1 / 2 of the steel plate ranges from 700 to 756 MPa, the yield strength ranges from 582 to 625 MPa, and the elongation after fracture (A) is ≥30%; at 1 / 4 of the steel plate, the tensile strength ranges from 705 to 763 MPa, the yield strength ranges from 584 to 625 MPa, and the elongation after fracture (A) is ≥30%; at -60℃, the average transverse impact energy (KV2) is ≥220 J; at 1 / 4 of the steel plate, the tensile strength ranges from 714 to 773 MPa. The yield strength ranges from 595 to 633 MPa, and the elongation after fracture (A) is ≥29%. Under conditions of -80℃, the average transverse impact energy (KV2) is ≥212 J. At 1 / 4 of the steel plate, the tensile strength ranges from 716 to 776 MPa, the yield strength ranges from 600 to 640 MPa, and the elongation after fracture (A) is ≥29%. The NDDT of the steel plate is ≤-100℃. At a temperature range of 450 to 550℃ and a preset stress of 180 to 320 MPa, the fracture time in the endurance test of the steel plate is not less than 6500 h, indicating good strength and toughness matching and high and low temperature service performance.

[0055] (3) According to the hydrogen-induced cracking (HIC) test in GB / T8650-2006 and NACETM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", after 96 hours of testing in solution A and solution B, the crack sensitivity CSR (%), crack length ratio CLR (%), and crack width ratio CTR (%) of the steel plate are all 0, indicating that the steel plate has excellent resistance to hydrogen-induced cracking. According to GB / T4157-2006 and NACETM0177-2 01. In the test "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 solutions A and B was not greater than 0.0029 g / m. 2 •h; Tested according to GB / T3960-2016 "Plastics Sliding Friction and Wear Test Method", the results show that the volumetric wear of the steel plate is no greater than 0.00062 cm. 3 The steel plate has good wear resistance; that is, the steel plate has excellent strength, low temperature toughness, service performance and plate shape. The (8~65) mm thickness specification steel plate meets the manufacturing and application requirements of high performance hydrogen energy storage steel plate.

[0056] (4) This invention, through optimized alloy composition and utilizing microalloying theory, fundamentally ensures the superior internal structure and service performance of the steel plate. The smelting process is optimized by employing an optimized molten iron treatment process combined with full-process protective casting to improve the purity of the molten steel, increase the purity of the cast billet, reduce the influence of elements such as P, S, and O, and control the original microstructure grain size. A three-stage optimized slab heating process is adopted to improve production efficiency and ensure the quality of the cast billet. The three-stage controlled rolling technology further optimizes the internal structure of the steel plate, improves the plate shape, and ensures production efficiency. A rationally designed two-stage cooling process is used to control and ensure the service performance of the steel plate. An optimized heat treatment process (short-time tempering system) is used to improve production efficiency, reduce production costs, and ensure a balance between strength and toughness while adjusting the microstructure of the material, improving the mechanical properties of the steel plate, and perfecting the service performance of the steel plate in all thickness directions. This invention provides a 35MPa-grade hydrogen energy storage cryogenic container steel plate and its manufacturing method, suitable for the production and manufacturing of steel for large-scale, high-efficiency storage tanks. Detailed Implementation

[0057] The present invention will be further illustrated below through examples.

[0058] According to the component ratio of the technical solution, the embodiments of the present invention carry out smelting, continuous casting, three-stage high-efficiency slab heating, controlled rolling and cooling, and heat treatment.

[0059] (1) Continuous casting:

[0060] Continuous casting process:

[0061] The casting temperature is 1570~1582℃, the superheat is set to 11~13℃, and the billet pulling speed is 2.3~2.6mm / s. The continuous casting billet is subjected to a light reduction process and / or an electromagnetic stirring process; the billet is placed in a stack for slow cooling after leaving the casting line, with a cooling rate of 13~17℃ / h and a stacking slow cooling time of 36~48h.

[0062] (2) Three-stage high-efficiency slab heating:

[0063] The slab heating adopts a three-stage heating method; the slab heating rate is controlled at 15~24℃ / min, the total furnace time is controlled at 3.1~4.6h, and the cooling rate is controlled at 32~51℃ / min.

[0064] The temperature range of the preheating section is 990~1012℃, the temperature of the high-temperature short-time homogenization section is 1136~1152℃, and the holding time is 36~52min; the temperature of the high-temperature high-efficiency homogenization section is 1244~1259℃.

[0065] (3) Controlled rolling and controlled cooling

[0066] The rolling process employs a three-stage controlled rolling method.

[0067] The first stage involves refining the original austenite structure through rolling. The initial rolling temperature is 1078~1113℃, and the final rolling temperature is 981~1041℃. The rolling process is controlled by a "large-small-...large reduction ratio" and the large reduction ratio is controlled within the range of 7%~10%, while the small reduction ratio is controlled within the range of 2%~4%.

[0068] The second stage involves rolling in the two-phase region, with an initial rolling temperature of 960~998℃ and a final rolling temperature of 842~890℃. A "large-large-small-large-...large reduction" control rolling process is employed, controlling the large reduction rate at 8%~11% and the small reduction rate at 4%~5%. This is followed by controlled cooling. First, homogenization-based controlled cooling begins at 830~876℃ with a cooling rate controlled at 23~37℃ / s. Then, precipitation strengthening controlled cooling begins at 514~545℃ with a cooling rate of 91~108℃ / s.

[0069] The third stage is the rolling microstructure and performance enhancement rolling stage, with an initial rolling temperature of 276~319℃, a reduction rate of 2%~4%, and air cooling of the rolled steel plate.

[0070] (4) Heat treatment:

[0071] The short-time tempering heat treatment temperature is 625~648℃, the heating rate is controlled at 0.7~1.0min / mm, the holding time is 25~42min, and the cooling rate is 39~46℃ / min.

[0072] Furthermore; smelting includes electric furnace smelting, LF refining, and RH refining;

[0073] Electric arc furnace smelting uses scrap steel and molten iron as raw materials, with a charge size of 82-94mm and a molten iron content of over 78%. During smelting, a magnesium-silicon spheroidizing agent is added at a rate of 3.9%-4.8% per ton of steel, with decarburization and oxygen blowing times of 263-368s and dephosphorization and oxygen blowing times of 286-394s, reducing phosphorus content in the molten steel to below 0.01%. Deep desulfurization is performed in an LF refining furnace, with a desulfurization and oxygen blowing time of 392-438s, controlling the sulfur content below 0.005%. Degassing is completed in an RH refining furnace, starting at a temperature of 1652-1664℃ and an oxygen blowing rate of 21-25m³. 3 The net circulation time is 575~660s, and the pre-pouring settling time is 298~340s.

[0074] Furthermore, during continuous casting, the light reduction rate is controlled at 2% to 4%.

[0075] Furthermore, during the electromagnetic stirring process in continuous casting, the current is 386~412A and the frequency is 5~9Hz.

[0076] The composition of the steels in the embodiments and comparative examples of this invention is shown in Table 1. The main process parameters for smelting the steels in the embodiments and comparative examples of this invention are shown in Table 2. The main process parameters for continuous casting of the steels in the embodiments and comparative examples of this invention are shown in Table 3. The main process parameters for heating the steels in the embodiments and comparative examples of this invention are shown in Table 4. The main process parameters for rolling the steels in the embodiments and comparative examples of this invention are shown in Table 5. The main process parameters for the cold zone and heat treatment of the steels in the embodiments and comparative examples of this invention are shown in Table 6. The mechanical properties of the steels in the embodiments and comparative examples of this invention are shown in Table 7. The evaluation results of the grain size and second-phase particles of the steels in the embodiments and comparative examples of this invention are shown in Table 8. The evaluation results of the microstructure and inclusions of the steels in the embodiments and comparative examples of this invention are shown in Table 9. The experimental results of the service performance of the steels in the embodiments and comparative examples of this invention are shown in Table 10.

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087] Based on the above results, it can be concluded that the production specifications (8~65) mm thickness provided by this invention have the following characteristics: At 1 / 2 length of the steel plate: tensile strength ranges from 700 to 756 MPa, yield strength ranges from 582 to 625 MPa, and elongation after fracture (A) ≥ 30%; At 1 / 4 length of the steel plate: tensile strength ranges from 705 to 763 MPa, yield strength ranges from 584 to 625 MPa, and A ≥ 30%; Under -60℃ conditions, the average transverse impact energy (KV2) ≥ 220 J; At 1 / 4 length of the steel plate: tensile strength ranges from 714 to 773 MPa, yield strength ranges from 595 to 633 MPa, and elongation after fracture (A) ≥ 29%; At -80℃... Under these conditions, the average transverse impact energy KV2 is ≥212J. At 1 / 4 of the steel plate: tensile strength ranges from 716 to 776 MPa, yield strength ranges from 600 to 640 MPa, and elongation after fracture A ≥29%; the NDDT of the steel plate is ≤-100℃; the total inclusion grade of the steel plate is ≤1.0, and the grain size is 7 to 9; the microstructure consists of sorbite + ferrite + nanoscale spherical bainite, and the volume percentage ratio of the three is sorbite:ferrite:bainite = (5~6):(6~8):(2~3), and the distance between the lamellar structures of sorbite is not greater than 82nm, and the spherical bainite is between 25 and 36nm. The second phase Cr / Nb carbide particles with a size of ≤48nm are uniformly dispersed and the spherical Ce (O / S / N) particles with a size of not greater than 10nm are uniformly distributed. Within a temperature range of 450~550℃ and a preset stress of 180~320MPa, the steel plate exhibits a creep rupture test fracture time of no less than 6500h; it possesses good corrosion resistance (resistance to hydrogen-induced cracking, H2S corrosion, and pitting corrosion) and wear resistance. Specifically, according to the hydrogen-induced cracking (HIC) test in GB / T8650-2006 and NACETM0284 "Evaluation Method for Hydrogen-Induced Cracking Resistance of Pipeline Steel and Pressure Vessel Steel", after 96h testing in solutions A and B, the crack susceptibility CSR (%), crack length ratio CLR (%), and crack width ratio CTR (%) are all [missing data]. The steel plate exhibits excellent resistance to hydrogen-induced cracking. According to GB / T4157-2006 and NACETM0177-201 "Metals in H2S Environment - Resistance to Sulfide Stress Cracking and Stress Corrosion", the steel plate underwent tensile stress testing in an acidic aqueous solution containing hydrogen sulfide. The results showed no cracks appearing in the samples, demonstrating 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 no greater than 0.0029 g / m³. 2 •h; Tested according to GB / T3960-2016 "Plastics Sliding Friction and Wear Test Method", the results show that the volumetric wear of the steel plate is no greater than 0.00062 cm. 3The steel plate has good wear resistance. That is, the steel plate has excellent strength, low temperature toughness, service performance and plate shape, and the thickness specification of (8~65) mm meets the manufacturing and application requirements of high-performance hydrogen energy storage steel plates.

[0088] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A 35MPa-grade cryogenic container steel plate for hydrogen energy storage, characterized in that, The composition of the steel plate by weight percentage is as follows: C: 0.12%~0.14%, Si: 0.25%~0.38%, Mn: 1.25%~1.41%, P: ≤0.01%, S: ≤0.005%, Ni: 0.16%~0.28%, Cr: 0.2%~0.3%, Ti: 0.03~0.05%, Nb: 0.052~0.064%, N: 0.02~0.032%, Ce: 0.0012~0.0024%, with the balance being Fe and unavoidable impurities; the microstructure of the steel plate is uniform refined sorbite + ferrite + nanoscale spherical bainite.

2. The 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, The Mn / C ratio in the steel plate is ≥10.

3. The 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, In steel plates, 3N / (4Ni×Ti)≥2.

4. The 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, In steel plates, Cr ≤ Nb / 5Ti.

5. The 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, The thickness of the steel plate is 8~65mm; the grain size of the microstructure of the steel plate is grade 7~9; the distance between the lamellar structures of sorbite is no greater than 82nm, and the diameter of the spherical bainite is 25~36nm; the second phase particles in the steel plate are uniformly dispersed, wherein the size of the second phase particles Cr (C and / or N), Ti (C and / or N), and Nb (C and / or N) is ≤48nm, and the diameter of the second phase particles spherical Ce (O / S / N) is ≤10nm.

6. The 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, At room temperature, the tensile strength of a steel plate at half its length is 700~756MPa, the yield strength ranges from 582~625MPa, and the elongation after fracture is... A ≥30%; 1 / 4 section of steel plate: tensile strength 705~763MPa, yield strength 584~625MPa, elongation after fracture A ≥30%; Transverse impact energy of steel plate under -60℃ conditions KV 2 Average value ≥220J, at 1 / 4 of the steel plate, tensile strength 714~773MPa, yield strength 595~633MPa, elongation after fracture A ≥29%; Transverse impact energy at -80℃ KV 2 Average value ≥212J, at 1 / 4 of the steel plate: tensile strength 716~776MPa, yield strength 600~640MPa, elongation after fracture A ≥29%; NDDT of steel plate ≤-100℃; When the temperature is in the range of 450~550℃ and the preset stress is 180~320MPa, the fracture time of steel plate in the endurance test is not less than 6500h.

7. A method for manufacturing a 35MPa-grade cryogenic container steel plate for hydrogen energy storage as described in any one of claims 1-6, characterized in that: This includes smelting, continuous casting, three-stage slab heating, controlled rolling and cooling, and tempering heat treatment; (1) Continuous casting: The casting temperature is 1570~1582℃, the superheat is 11~13℃, the billet pulling speed is 2.3~2.6mm / s, and the continuous casting billet light reduction process and / or electromagnetic stirring process are adopted; the billet is put into the stack for slow cooling after leaving the line, the cooling rate is 13~17℃ / h, and the stacking slow cooling time is 36~48h. Three-stage slab heating: The slab heating rate is controlled at 15~24℃ / min, the total time in the furnace is controlled at 3.1~4.6h, and the cooling rate is controlled at 32~51℃ / min; The temperature range of the preheating section is 990~1012℃, the temperature of the high-temperature short-time homogenization section is 1136~1152℃, and the holding time is 36~52min; the temperature of the high-temperature homogenization section is 1244~1259℃. Controlled rolling and controlled cooling: The rolling process employs a three-stage controlled rolling and cooling method. The first stage involves refining the original austenite structure through rolling. The initial rolling temperature is 1078~1113℃, and the final rolling temperature is 981~1041℃. The rolling process is controlled by a "large-small-...large reduction rate" with a large reduction rate of 7%~10% and a small reduction rate of 2%~4%. The second stage involves rolling in the two-phase region, with an initial rolling temperature of 960~998℃ and a final rolling temperature of 842~890℃. A "large-large-small-large-...large reduction rate" control rolling process is employed, with a large reduction rate of 8%~11% and a small reduction rate of 4%~5%. This is followed by controlled cooling. First, homogenization-based controlled cooling begins at 830~876℃, with a cooling rate controlled at 23~37℃ / s. Then, a precipitation strengthening controlled cooling stage is performed, with an initial temperature of 514~545℃ and a cooling rate of 91~108℃ / s. The third stage is the rolling microstructure and performance enhancement rolling stage, with an initial rolling temperature of 276~319℃, a reduction rate of 2%~4%, and air cooling of the rolled steel plate. Tempering heat treatment: The tempering heat treatment temperature is 625~648℃, the heating rate is controlled at 0.7~1.0min / mm, the holding time is 25~42min, and the cooling rate is 39~46℃ / min.

8. The method for manufacturing a 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 7, characterized in that: Smelting includes electric furnace smelting, LF refining, and RH refining; Electric furnace smelting uses scrap steel and molten iron as raw materials, with a charge size of 82~94mm and a molten iron mass percentage of over 78%. During the smelting process, the magnesium-silicon spheroidizing agent is added at a rate of 3.9%~4.8% per ton of steel, the decarburization oxygen blowing time is 263~368s, and the dephosphorization oxygen blowing time is 286~394s, reducing the phosphorus content in the molten steel to below 0.01%. Deep desulfurization is carried out using an LF refining furnace, with a desulfurization and oxygen blowing time of 392~438s, controlling the sulfur content to below 0.005%. Degassing is completed in an RH refining furnace, with an initial temperature of 1652~1664℃ and an oxygen blowing rate of 21~25m³. 3 The net circulation time is 575~660s, and the pre-pouring settling time is 298~340s.

9. The method for manufacturing a 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 8, characterized in that: During continuous casting, the light reduction rate is controlled at 2% to 4%.

10. The method for manufacturing a 35MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 8, characterized in that: During the electromagnetic stirring process in continuous casting, the current is 386~412A and the frequency is 5~9Hz.

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