A 70mpa-grade steel plate for hydrogen energy storage and transportation cryogenic vessel and a manufacturing method thereof

Abstract

The application belongs to the field of metal materials, and provides a 70MPa-grade low-temperature container steel plate for hydrogen energy storage and transportation and a manufacturing method thereof.The composition of the steel plate is as follows in terms of percentage by weight: C: 0.15%-0.18%, Si: 0.12%-0.16%, Mn: 0.74%-0.98%, P: ≤0.01%, S: ≤0.01%, Ni: 1.12%-1.44%, Cr: 0.47%-0.75%, V: 0.01%-0.02%, Mo: 0.11%-0.19%, N: 0.022%-0.034%, La: 0.002-0.0028%, and the balance of Fe and inevitable impurities.The manufacturing method comprises smelting, continuous casting, four-stage efficient slab heating, two-stage rolling, two-stage cooling and heat treatment.The steel plate produced by the application has good strength and toughness matching and high and low temperature service performance, and the steel plate has excellent hydrogen-induced cracking resistance, sulfide stress cracking resistance and stress corrosion resistance; the steel plate has good wear resistance, and meets the manufacturing and application requirements of high-performance hydrogen energy storage and transportation steel plate.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and in particular relates to a 70MPa-grade cryogenic container steel plate for hydrogen energy storage and its manufacturing method. Background Technology

[0002] The development of a 70MPa-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 research has shown that while austenitic stainless steel possesses excellent low-temperature toughness, its high cost limits its large-scale application; while traditional low-temperature nickel-based steels, although exhibiting outstanding overall performance, suffer from economic instability due to nickel price fluctuations and complex welding processes. Furthermore, hydrogen energy storage and transportation mainly face the pressure limits and hydrogen embrittlement issues of high-pressure gaseous hydrogen storage, as well as the high energy consumption and insulation requirements of cryogenic liquid hydrogen storage. The development of the 70MPa-grade cryogenic container steel plate aims to promote breakthroughs in hydrogen energy storage and transportation technology by increasing hydrogen storage density and resolving the contradictions in material performance. This material must meet the balance between strength and low-temperature toughness under high pressure, while also possessing resistance to hydrogen embrittlement and corrosion. With the rapid development of the hydrogen energy industry, the demand for efficient and safe hydrogen storage containers in the transportation, industrial, and energy sectors has surged. The limitations of traditional materials in low-temperature and high-pressure environments have made domestic substitution an important direction.

[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 steel plates used in hydrogen storage. Furthermore, the low-temperature performance of the steel plate below -80℃ has not been studied, and the thickness specifications studied are only for large-thickness steel plates of 150mm and above; specific analysis has not been conducted on thinner steel plates applicable to hydrogen energy storage. 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 70MPa grade cryogenic container steel plate for hydrogen energy storage and its manufacturing method, which has good strength and toughness matching, high and low temperature service performance, excellent resistance to hydrogen-induced cracking, sulfide stress cracking and stress corrosion (SSC) performance, good wear resistance, and meets the manufacturing and application requirements of high-performance hydrogen energy storage steel plates.

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

[0006] A 70MPa-grade cryogenic container steel plate for hydrogen energy storage has the following composition by weight percentage: C: 0.15%~0.18%, Si: 0.12%~0.16%, Mn: 0.74%~0.98%, P: ≤0.01%, S: ≤0.01%, Ni: 1.12%~1.44%, Cr: 0.47%~0.75%, V: 0.01%~0.02%, Mo: 0.11%~0.19%, N: 0.022%~0.034%, La: 0.002%~0.0028%, with the balance being Fe and unavoidable impurities.

[0007] Furthermore, the C / La ratio in the steel plate is ≥62.

[0008] Furthermore, the Ni / N ratio in the steel plate is ≥35.

[0009] Furthermore, the Mn / C ratio in the steel plate is 4~6.5.

[0010] Furthermore, the Cr / 50V ratio in the steel plate should be ≤1.

[0011] Furthermore; in the steel plate, 0.25≤Pcm=C+Si / 30+(Mn+Cr) / 20+Ni / 60≤0.30.

[0012] Furthermore, the microstructure of the steel plate is refined sorbite + ferrite + nanoscale spherical bainite, with the following volume percentages: refined sorbite : ferrite : nanoscale spherical bainite = (5~7): (3~5): (2~4), with a grain size of 8~9, and the distance between the lamellar structures of sorbite is no greater than 88nm, and the diameter of the spherical bainite is 21~42nm; the second phase particles in the steel plate are uniformly dispersed, wherein the size of the second phase particles Cr (C and / or N) and V (C and / or N) is ≤45nm, and the size of the spherical second phase particles La (O and / or S and / or N) with a size no greater than 12nm is ≤25nm.

[0013] Furthermore; the steel plate thickness is 42~95mm; at room temperature, at 1 / 2 length of the steel plate: tensile strength 870~894MPa, yield strength 804~824MPa, elongation after fracture A≥35%; at 1 / 4 length of the steel plate: tensile strength 870~898MPa, yield strength 812~830MPa, elongation after fracture A≥29%; at -60℃, the average transverse impact energy KV2 ≥290J; at 1 / 4 length of the steel plate: tensile strength 880~912MPa. Yield strength 812~834MPa, elongation after fracture A≥27%; under -80℃ conditions, the average transverse impact energy KV2 ≥285J; at 1 / 4 of the steel plate: tensile strength 906~919MPa, yield strength 821~862MPa, elongation after fracture A≥26.5%; NDDT of the steel plate ≤-100℃; at a temperature range of 450~550℃ and a preset stress of 260~400MPa, the fracture time of the steel plate in the creep test is not less than 6800h.

[0014] Furthermore, 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- In the test 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 had 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 0.0027 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 0.00073cm. 3 Steel plates have good wear resistance.

[0015] The rationale for the design of the components in this invention is as follows:

[0016] Carbon (C) is the main element ensuring the strength of steel plates and also determines their toughness. To ensure the strength of steel plates and meet the strength requirements of 70MPa-grade low-temperature steel plates for hydrogen energy storage, the C content in the steel plates should be optimized and controlled. On the other hand, the hardenability of steel plates affects the uniformity of microstructure and properties across the entire thickness of thick steel plates. When the C content of the steel plate is within a certain range, it ensures that the steel plate has good wear resistance and excellent service performance. However, excessively high C content will affect the machinability of the steel. To ensure good low-temperature toughness of the steel plate, this invention sets the C content range to 0.15%~0.18%.

[0017] Si is commonly used in steel as a reducing agent and oxidizing agent. In this invention, some of the Si comes from the Si element in the spheroidizing agent, reducing the introduction of other impurities. Furthermore, adding an appropriate amount of Si to the steel improves its wear resistance, elastic limit, yield strength, and yield ratio. Since the steel plates are mainly used in the manufacture of low-temperature steel plates for hydrogen energy storage, there are certain requirements for high internal purity and strict control of inclusion size and quantity to resist hydrogen. Excessive Si content in the steel plate can easily lead to excessive large-size inclusions, which is detrimental to the low-temperature service performance of the steel plate. Therefore, this invention sets the Si content range to 0.12%~0.16%.

[0018] Mn plays a fundamental role in steel. It significantly expands the austenite region, ensuring the critical temperature range, while simultaneously improving the uniformity and refining the microstructure, thus acting as a solid solution strengthening agent. This increases the strength and hardness of the steel while maintaining hardenability. Furthermore, it is relatively inexpensive. However, to reduce the impact of MnS inclusions on the hydrogen-induced cracking resistance of steel plates, this invention sets the Mn content range to 0.74%~0.98%. C and Mn work synergistically, utilizing solid solution strengthening, phase transformation regulation, complementary mechanical properties, and process optimization to significantly improve the strength, toughness, wear resistance, and machinability of steel plates. Therefore, the Mn / C ratio is controlled within the range of 4~6.5.

[0019] S and P are harmful elements in steel. In order to ensure the purity of steel, reduce large-sized inclusions inside the steel plate and ensure good plasticity and toughness, they must be strictly controlled. Therefore, this invention limits P to ≤ 0.01% and S to ≤ 0.01%.

[0020] Ni and N: Both are austenite-stabilizing elements affecting microstructure and composition. Ni can expand the γ-phase region and form an infinite solid solution, significantly improving the strength, plasticity, and low-temperature toughness of steel. In this invention, the synergistic effect of Ni and N is utilized to achieve positive results. The addition of N can further enhance this effect; partial substitution of N makes austenite more stable, preventing martensitic transformation during cold working, while reducing the amount of Ni used. Regarding the impact on mechanical properties, N significantly improves the strength of steel through solid solution strengthening, grain refinement, and precipitation hardening (such as VN nitride in this invention) without sacrificing plasticity. The solid solution strengthening effect of Ni is superimposed, allowing the steel to maintain high strength while still possessing good low-temperature toughness. In terms of creep resistance and fatigue performance: N improves the high-temperature creep strength of steel, while Ni improves high-temperature oxidation resistance; the two synergistically enhance the service performance of steel in high-temperature environments. In terms of improving unique properties, N is enriched at the passivation film / metal interface, inhibiting the autocatalytic process of pitting corrosion, and synergistically forms a corrosion-resistant surface layer with elements such as Cr and Mo. Ni (Ni) stabilizes the austenitic microstructure, reduces the precipitation of harmful phases, and further enhances the corrosion resistance of the steel plate. Ni refines the grain size and reduces softening in the heat-affected zone, while Ni reduces the susceptibility to weld cracking; their synergistic effect ensures weldability. Furthermore, Ni is a scarce resource, while Ni is abundant and inexpensive. Partial substitution with Ni can significantly reduce alloy costs while simultaneously upgrading performance. Therefore, the Ni content is controlled at 1.12–1.44%, and the Ni content is controlled at 0.022–0.034%, with a preferred Ni / N ratio of ≥35.

[0021] 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. This inhibits the spheroidization and graphitization of pearlite and cementite at high temperatures, preventing strength loss due to microstructure degradation and ensuring the high-temperature creep resistance of the steel plate. Cr also extends the incubation period of the isothermal transformation curve of supercooled austenite, improves hardenability, and ensures uniform hardening of thick container steel plates. On the other hand, Cr forms a dense Cr2O3 passivation film on the steel surface, fixing free oxygen in the steel plate and effectively blocking the corrosion of oxidizing media (such as H2S and Cl⁻). Especially in low-temperature (below -60℃) high-pressure hydrogen environments, it can reduce the hydrogen permeation rate, ensuring the corrosion resistance, oxidation resistance, and hydrogen resistance of the steel plate. To ensure good toughness, plasticity, processing performance, and service performance of the steel plate, this invention sets the Cr content range to Cr: 0.47%~0.75%.

[0022] In steel, v combines with c and n to form nanoscale vN / vc precipitates. During hot working, these precipitates pin grain boundaries, inhibiting austenite grain growth, refining the ferrite / pearlite microstructure, and improving low-temperature impact toughness. V carbides act as hydrogen traps, capturing diffusible hydrogen atoms, reducing hydrogen segregation concentration at grain boundaries, and simultaneously increasing the hydrogen-induced crack (HIC) initiation stress threshold, ensuring good resistance to HIC cracking and service performance in hydrogen-exposed environments. The dispersed vN particles, through the Orowan strengthening mechanism, ensure the yield strength of the steel plate while maintaining a relatively ideal elongation after fracture, thus ensuring a good strength-toughness balance. In this invention, the v content is set in the range of 0.01~0.02%.

[0023] In terms of Cr-V synergistic effect, composite strengthening and microstructure optimization: the superposition of solid solution strengthening of Cr and precipitation strengthening of V improves the low-temperature impact performance of the steel plate while ensuring good tensile strength. Cr inhibits the coarsening of V(C,N) at high temperatures, while VV(C,N) promotes the uniform distribution of Cr carbides at grain boundaries, forming a "two-phase strengthening network" and delaying the strength decrease caused by long-term high-temperature aging. In terms of synergistic improvement of service performance, the passivation film of Cr and the hydrogen trapping effect of V form dual protection, giving the steel plate good resistance to H corrosion and meeting the stringent safety requirements of hydrogen energy storage and transportation; Cr increases the recrystallization temperature, and V reduces overheat sensitivity, enabling precise control of deformation strengthening and phase transformation during hot working of the steel plate, improving production efficiency while ensuring the excellent performance of the steel plate. Therefore, preferably, in this invention, Cr / 50V is controlled to be ≤1, and the particle size of the second-phase Cr / V carbides / nitrides is within the range of ≤48nm.

[0024] La significantly enhances the overall performance of steel plates through multiple mechanisms, including purifying molten steel, modifying inclusion morphology, refining grain size, and improving low-temperature toughness and corrosion resistance. Specifically, La combines with impurities such as oxygen and sulfur to form high-melting-point compounds, effectively purifying the molten steel and reducing stress concentration. Nanoscale spherical Ce(O / S / N) particles simultaneously inhibit grain growth, refine the grain structure, and improve microstructure uniformity, laying the foundation for improved low-temperature toughness. Furthermore, La enhances the corrosion resistance of the steel plate by forming a dense corrosion product layer and may reduce hydrogen diffusion and accumulation in the steel, lowering the risk of hydrogen embrittlement. These effects collectively improve the safety and reliability of the steel plate in extreme environments, providing crucial protection for hydrogen energy storage and transportation equipment. Moreover, considering overall production costs, this invention sets the La content to 0.002~0.0028%. La refines carbides to the nanoscale and improves their distribution, working in conjunction with the solid solution strengthening of C to enhance the strength of the steel plate while ensuring ultra-toughness in low-temperature impact resistance. La-modified inclusions reduce hydrogen segregation, while La-C compounds act as hydrogen traps, mitigating the risk of hydrogen embrittlement. Furthermore, the synergy between La and C optimizes weldability. Through mechanisms such as carbide regulation, inclusion modification, hydrogen embrittlement suppression, and weldability optimization, La and C achieve synergistic improvements in strength, toughness, and resistance to hydrogen embrittlement in 70MPa cryogenic container steel plates, providing a high-performance, low-cost solution for hydrogen energy storage and transportation equipment. Therefore, controlling the C / La ratio to ≥62 is preferred.

[0025] The second technical solution of the present invention is to provide a method for manufacturing a 70MPa-level hydrogen energy storage cryogenic container steel plate, including smelting, continuous casting, four-stage high-efficiency slab heating, two-stage rolling, two-stage cooling, and heat treatment.

[0026] (1) Smelting: including electric furnace smelting, LF refining, and RH refining;

[0027] Electric arc furnace smelting uses high-quality scrap steel and molten iron as raw materials, controlling the charge size between 72 and 81 mm, and the molten iron mass percentage is above 76%; during the smelting process, the magnesium-silicon spheroidizing agent is added at a rate of 3.4% to 4.5% per ton of steel; the decarburization oxygen blowing time is 261 to 343 s; the dephosphorization oxygen blowing time is 252 to 329 s, controlling the phosphorus mass fraction in the molten steel to be reduced to below 0.01%;

[0028] The LF refining desulfurization and oxygen blowing time is 344~398s, which controls the sulfur content to below 0.01%;

[0029] RH refining starting temperature: 1662~1670℃, oxygen blowing rate: 26~29m³ 3 The net circulation time is 591~652s, and the pre-pouring settling time is 266~321s.

[0030] In the electric arc furnace smelting process, high-quality scrap steel and molten iron are used as raw materials. The size of the charge is controlled between 72 and 81 mm, and the iron content is controlled above 76% to ensure steel purity, shorten process time, and reduce the difficulty of subsequent processes. During smelting, a magnesium-silicon spheroidizing agent is added at a rate of 3.4% to 4.5% per ton of steel to ensure the uniformity of the original microstructure, refine the as-cast grains, and shorten smelting time. Strict control is maintained over dephosphorization and decarburization parameters. Decarburization oxygen blowing is controlled at 261 to 343 seconds; to effectively reduce the content of harmful element P, dephosphorization oxygen blowing is controlled at 252 to 329 seconds, reducing 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 344 to 398 seconds, reducing the sulfur content to below 0.01%; degassing is completed in an RH furnace, with the initial temperature controlled at 1662 to 1670℃ and the oxygen blowing rate controlled at 26 to 29 m³ / s. 3 The net circulation time is 591~652s, and the pre-casting settling time is 266~321s. By optimizing the smelting process parameters, the oxidation of molten steel is reduced, the content of inclusions in the steel is controlled, internal defects are reduced, and the purity of the steel is improved.

[0031] (2) Continuous casting:

[0032] After vacuum breaking, slab continuous casting is used for casting at a casting temperature of 1580~1591℃, a superheat of 13~15℃, and a billet pulling speed of 2.0~2.3mm / s. During continuous casting, a light reduction process and / or electromagnetic stirring process are used to reduce the core segregation of the billet and improve the quality of the billet. The light reduction rate is preferably controlled at 1%~3%, and the current in the electromagnetic stirring process is 396~419A and the frequency is 4~8Hz. The billet is then stacked for slow cooling at a cooling rate of 11~15℃ / h and a stacking slow cooling time of 36~48h.

[0033] 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 1580~1591℃, the superheat is set at 13~15℃, and the casting speed is 2.0~2.3mm / 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 1~3%, the current is 396~419A, and the frequency is 4~8Hz. After the slab is removed from the casting line, it is stacked for slow cooling at a cooling rate of 11~15℃ / h for 36~48h.

[0034] (3) Four-stage high-efficiency slab heating:

[0035] The continuously cast slab is sent to a heating furnace for heating. The slab undergoes four stages of heating before being taken out of the furnace.

[0036] The temperature range of the preheating section is 782~833℃, the temperature range of the low-temperature homogenization section is 987~1010℃, the temperature range of the high-temperature short-time homogenization section is 1151~1192℃, and the holding time is 42~54min; the temperature range of the high-temperature high-efficiency homogenization section is 1222~1256℃.

[0037] The slab heating rate is controlled at 12~19℃ / min, the total time in the furnace is controlled at 3.9~5.4h, and the cooling rate is controlled at 33~42℃ / min.

[0038] The continuously cast slab is fed into a heating furnace for heating, undergoing four stages of heating before being removed from the furnace. The preheating stage has a temperature range of 782~833℃, the low-temperature homogenization stage has a temperature range of 987~1010℃, the high-temperature short-time homogenization stage has a temperature range of 1151~1192℃ with a holding time of 42~54 min, and the high-temperature high-efficiency homogenization stage has a temperature range of 1222~1256℃. The slab heating rate is controlled at 12~19℃ / min, the total furnace time is controlled at 3.9~5.4 h, and the cooling rate is controlled at 33~42℃ / min. This four-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 internal and external temperatures of the slab, which is beneficial for further processing.

[0039] (4) Two-stage rolling:

[0040] The rolling process employs a two-stage controlled rolling method.

[0041] The first stage involves refining the original austenite structure through rolling. The initial rolling temperature is 1058~1096℃, and the final rolling temperature is 961~998℃. 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%.

[0042] The second stage is the two-phase region rolling process, with an initial rolling temperature of 946~974℃ and a final rolling temperature of 847~880℃. The rolling process adopts a "reduction rate" rolling control process, and the reduction rate of the second stage two-phase region rolling is 6%~10%.

[0043] The rolling process employs a two-stage controlled rolling method. The first stage involves refining the original austenite structure, with an initial rolling temperature of 1058–1096℃ and a final rolling temperature of 961–998℃. A "large-small-...large reduction rate" rolling control process is used, controlling the large reduction rate within 7%–10% and the small reduction rate within 2%–4%. Rolling in the high-temperature austenite region reduces the steel plate's deformation resistance, fully refines the original austenite structure, ensures sufficient grain recrystallization, and improves the uniformity of the internal structure while refining the steel plate's internal structure. The second stage involves rolling in the two-phase region, with an initial rolling temperature of 946–974℃ and a final rolling temperature of 847–880℃. A "reduction rate decreasing" rolling control process is used, controlling the reduction rate in the second-stage two-phase region rolling within 6%–10%. As the grain boundary area increases, the ferrite nucleation rate increases during subsequent phase transformations, further refining the internal structure of the steel plate, and further flattening and elongating the austenite grains.

[0044] (5) Two-stage cooling:

[0045] The first stage is a homogenization and controlled cooling stage, with a starting temperature of 835~876℃ and a cooling rate of 26~34℃ / s; the second stage is a precipitation enhancement and controlled cooling stage, with a starting temperature of 512~539℃ and a cooling rate of 86~104℃ / s.

[0046] The first stage is a homogenization controlled cooling stage, with a cooling start temperature of 835~876℃ and a cooling rate controlled at 26~34℃ / s. By controlling the cooling rate and temperature during the rolling process, abnormal grain growth in the steel plate is reduced, primary network carbide precipitation is prevented, dislocation movement caused by deformation is reduced, and the internal microstructure of the steel plate is optimized. The second stage is a precipitation strengthening controlled cooling stage, with a starting temperature of 512~539℃ and a cooling rate of 86~104℃ / 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.

[0047] (6) Heat treatment:

[0048] The heat treatment of the steel plate is as follows: in the low-temperature mold welding heat treatment stage, the temperature is controlled at 555~592℃, the heating rate is 0.6~0.9min / mm, and the holding time is 165~200min; in the high-temperature mold welding heat treatment stage, the temperature is controlled at 605~642℃, the heating rate is 0.8~1.1min / mm, the holding time is 45~60min, and the cooling rate is controlled at 36~49℃ / min.

[0049] Because of the addition of elements such as C, Si, Mn, Ni, Cr, Mo, V, La, and N, the steel plate, after rolling, exhibits a ferrite + sorbite + 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 a two-stage die welding heat treatment to ensure that the steel plate's strength is not compromised, while simultaneously imparting suitable ductility, toughness, low-temperature impact toughness, corrosion resistance, and good machinability. Therefore, the temperature for the low-temperature die welding heat treatment stage of the steel plate is controlled at 555~592℃, the heating rate is controlled at 0.6~0.9min / mm, and the holding time is in the range of 165~200min; the temperature for the high-temperature die welding heat treatment stage is controlled at 605~642℃, the heating rate is controlled at 0.8~1.1min / mm, the holding time is in the range of 45~60min, and the cooling rate is controlled at 36~49℃ / min.

[0050] The beneficial effects of this invention are as follows:

[0051] (1) Based on the strengthening elements of C, Si, and Mn, by adding appropriate amounts of Ni, Cr, V, and La alloying elements, optimizing and controlling the N element, and strictly controlling the content of harmful elements P and S, and combining with the production process optimization, a uniform and refined composition of sorbite + ferrite + nanoscale spherical bainite is obtained. The ratio of the three by volume percentage is (5~7):(3~5):(2~4), the grain size is 8~9, and the distance between the lamellar structures of sorbite is no greater than 88nm, and the spherical bainite is between 21~42nm. The second phase particles in the steel plate are uniformly dispersed, of which the size of the second phase particles Cr (C and / or N) and V (C and / or N) is ≤45nm, and the size of the spherical second phase particles La (O and / or S and / or N) with a size no greater than 12nm is ≤25nm. 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.

[0052] (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 870 to 894 MPa, the yield strength ranges from 804 to 824 MPa, and the A% is ≥35; at 1 / 4 of the steel plate, the tensile strength ranges from 870 to 898 MPa, the yield strength ranges from 812 to 830 MPa, and the A% is ≥29; under -60℃ conditions, the average transverse impact energy KV2 is ≥290 J; at 1 / 4 of the steel plate, the tensile strength ranges from 880 to 912 MPa, and the yield strength is ≥290 J. The strength range is 812~834MPa, A%≥27; under -80℃ conditions, the average transverse impact energy KV2 is ≥285J; at 1 / 4 of the steel plate: tensile strength range is 906~919MPa, yield strength range is 821~862MPa, A%≥26.5; the NDDT of the steel plate is ≤-100℃; at a temperature range of 450~550℃ and a preset stress of 260~400MPa, the fracture time of the steel plate in the creep test is not less than 6800h, which means good strength and toughness matching and high and low temperature service performance.

[0053] (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 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 both solution A and solution B was not greater than 0.0027 g / m. 2 According to GB / T3960-2016 "Test Method for Sliding Friction and Wear of Plastics", the test results show that the volumetric wear of the steel plate is no greater than 0.00073 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, and the thickness specification of (42~95) mm meets the manufacturing and application requirements of high-performance hydrogen energy storage steel plates. Detailed Implementation

[0054] The present invention will be further illustrated below through examples.

[0055] According to the component ratio of the technical solution, the embodiments of the present invention carry out smelting, continuous casting, four-stage high-efficiency slab heating system, two-stage design rolling, two-stage cooling, and two-stage mold welding heat treatment.

[0056] (1) Continuous casting:

[0057] After vacuum breaking, slab continuous casting machine is used for casting, with casting temperature of 1580~1591℃, superheat of 13~15℃, and billet pulling speed of 2.0~2.3mm / s; continuous casting billet light reduction process and / or electromagnetic stirring process are adopted, and the billet is put into the stack for slow cooling after leaving the line, with a cooling rate of 11~15℃ / h and a stacking slow cooling time of 36~48h;

[0058] (2) Four-stage high-efficiency slab heating:

[0059] The continuously cast slab is sent to the heating furnace for heating. The slab undergoes four stages of heating before being taken out of the furnace. The slab heating rate is 12~19℃ / min, the total time in the furnace is 3.9~5.4h, and the cooling rate is 33~42℃ / min.

[0060] The temperature range of the preheating section is 782~833℃, the temperature range of the low-temperature homogenization section is 987~1010℃, the temperature range of the high-temperature short-time homogenization section is 1151~1192℃, and the holding time is 42~54min; the temperature range of the high-temperature high-efficiency homogenization section is 1222~1256℃.

[0061] (3) Two-stage rolling:

[0062] The rolling process employs a two-stage controlled rolling method.

[0063] The first stage involves refining the original austenite structure through rolling. The initial rolling temperature is 1058~1096℃, and the final rolling temperature is 961~998℃. 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%.

[0064] The second stage is the two-phase region rolling process, with an initial rolling temperature of 946~974℃ and a final rolling temperature of 847~880℃. It adopts a "reduction rate" rolling control process, and the reduction rate in the second stage of the two-phase region rolling is 6%~10%.

[0065] (4) Two-stage cooling:

[0066] The first stage is a homogenization and controlled cooling stage, with a starting temperature of 835~876℃ and a cooling rate of 26~34℃ / s; the second stage is a precipitation enhancement and controlled cooling stage, with a starting temperature of 512~539℃ and a cooling rate of 86~104℃ / s.

[0067] (5) Heat treatment:

[0068] For the low-temperature die welding heat treatment stage of steel plates, the temperature is controlled at 565~582℃, the heating rate is 0.6~0.9min / mm, and the holding time is 165~200min; for the high-temperature die welding heat treatment stage, the temperature is controlled at 605~612℃, the heating rate is 0.8~1.1min / mm, the holding time is 45~60min, and the cooling rate is controlled at 36~49℃ / min.

[0069] Furthermore; smelting includes electric furnace smelting, LF refining, and RH refining;

[0070] In the electric arc furnace smelting process, high-quality scrap steel and molten iron are used as raw materials, with a charge size of 72~81mm and a molten iron mass percentage of over 76%. During the smelting process, the magnesium-silicon spheroidizing agent is added at a rate of 3.4%~4.5% per ton of steel. The decarburization oxygen blowing time is 261~343s, and the dephosphorization oxygen blowing time is 252~329s, controlling the phosphorus mass fraction in the molten steel to be reduced to below 0.01%.

[0071] The LF refining desulfurization and oxygen blowing time is 344~398s, which controls the sulfur content to below 0.01%;

[0072] RH refining starting temperature: 1662~1670℃, oxygen blowing rate: 26~29m³ 3 The net circulation time is 591~652s, and the pre-pouring settling time is 266~321s.

[0073] Further details: During continuous casting, the reduction rate of the continuously cast billet under light pressure is 1% to 3%; the current in the electromagnetic stirring process is 396 to 419 A, and the frequency is 4 to 8 Hz.

[0074] 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 cooling 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 grain size and second-phase particles in the microstructure of the steels in the embodiments and comparative examples of this invention are shown in Table 8. The evaluation results of microstructure and inclusions in the steels in the embodiments and comparative examples of this invention are shown in Table 9. The experimental results of service performance of the steels in the embodiments and comparative examples of this invention are shown in Table 10.

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] Based on the above results, it can be concluded that the steel plate with a thickness of (42~95) mm provided by this invention achieves the following results: at half-length: tensile strength range of 870~894 MPa, yield strength range of 804~824 MPa, elongation after fracture A≥35%; at quarter-length: tensile strength range of 870~898 MPa, yield strength range of 812~830 MPa, elongation after fracture A≥29%; under -60℃ conditions, the average transverse impact energy KV2 ≥290 J; and at quarter-length: tensile strength range of 880~912 MPa. a. Yield strength ranges from 812 to 834 MPa, elongation after fracture A ≥ 27%; under -80℃ conditions, the average transverse impact energy KV2 ≥ 285 J; at 1 / 4 of the steel plate: tensile strength ranges from 906 to 919 MPa, yield strength ranges from 821 to 862 MPa, elongation after fracture A ≥ 26.5%; NDDT of the steel plate ≤ -100℃; total inclusion grade of the steel plate ≤ 1.0, grain size is grade 8 to 9; microstructure consists of sorbite + ferrite + nanoscale spherical bainite, the proportion of the three by volume percentage ranges from (5 to 7) :): (3~5): (2~4), and the distance between the lamellar structures of sorbite is not greater than 88nm, and the spherical bainite is between 21~42nm; the second phase particles in the steel plate are uniformly dispersed, wherein the size of the second phase particles Cr (C and / or N) and V (C and / or N) is ≤45nm, and the size of the spherical second phase particles La (O and / or S and / or N) with a size not greater than 12nm is ≤25nm. Within a temperature range of 450~550℃ and a preset stress of 260~400MPa, the steel plate exhibits a creep rupture test fracture time of no less than 6800h; 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 0.0027 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 0.00073cm.3 The 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 (42~95) mm meets the manufacturing and application requirements of high-performance hydrogen energy storage steel plates.

[0086] 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 70MPa-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: 0.15%~0.18%, Si: 0.12%~0.16%, Mn: 0.74%~0.98%, P: ≤0.01%, S: ≤0.01%, Ni: 1.12~1.44%, Cr: 0.47%~0.75%, V: 0.01%~0.02%, Mo: 0.11%~0.19%, N: 0.022%~0.034%, La: 0.002%~0.0028%, with the balance being Fe and unavoidable impurities; The microstructure of the steel plate is refined sorbite + ferrite + nanoscale spherical bainite, with the following volume percentages: refined sorbite : ferrite : nanoscale spherical bainite = (5~7): (3~5): (2~4), with a grain size of 8~9, and the distance between the lamellar structures of sorbite is no greater than 88nm, and the diameter of the spherical bainite is 21~42nm; the second phase particles in the steel plate are uniformly dispersed, wherein the size of the second phase particles Cr (C and / or N) and V (C and / or N) is ≤45nm, and the size of the spherical second phase particles La (O and / or S and / or N) with a size no greater than 12nm is ≤25nm; The steel plate thickness is 42~95mm; at room temperature, at half the length of the steel plate: tensile strength 870~894MPa, yield strength 804~824MPa, elongation after fracture... A ≥35%, at 1 / 4 of the steel plate: tensile strength 870~898MPa, yield strength 812~830MPa, elongation after fracture A ≥29%; Transverse impact energy at -60℃ KV 2 Average value ≥290J, at 1 / 4 of the steel plate, tensile strength 880~912MPa, yield strength 812~834MPa, elongation after fracture A ≥27%; Transverse impact energy at -80℃ KV 2 Average value ≥285J, at 1 / 4 of the steel plate: tensile strength 906~919MPa, yield strength 821~862MPa, elongation after fracture A ≥26.5%; NDDT of steel plate ≤-100℃; When the temperature is in the range of 450~550℃ and the preset stress is 260~400MPa, the fracture time of steel plate in the endurance test is not less than 6800h.

2. The 70MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, The C / La ratio in the steel plate is ≥62.

3. The 70MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, The Ni / N ratio in the steel plate is ≥35.

4. The 70MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, The Mn / C ratio in the steel plate is 4~6.

5.

5. The 70MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 1, characterized in that, The Cr / 50V ratio in the steel plate is ≤1.

6. A method for manufacturing a 70MPa-grade cryogenic container steel plate for hydrogen energy storage as described in any one of claims 1-5, characterized in that: It includes smelting, continuous casting, four-stage high-efficiency slab heating, two-stage rolling, two-stage cooling, and heat treatment; (1) Continuous casting: After vacuum breaking, slab continuous casting machine is used for casting, with casting temperature of 1580~1591℃, superheat of 13~15℃, and billet pulling speed of 2.0~2.3mm / s; continuous casting billet light reduction process and / or electromagnetic stirring process are adopted, and the billet is put into the stack for slow cooling after leaving the line, with a cooling rate of 11~15℃ / h and a stacking slow cooling time of 36~48h; (2) Four-stage high-efficiency slab heating: The continuously cast slab is sent to the heating furnace for heating. The slab undergoes four stages of heating before being taken out of the furnace. The slab heating rate is 12~19℃ / min, the total time in the furnace is 3.9~5.4h, and the cooling rate is 33~42℃ / min. The temperature range of the preheating section is 782~833℃, the temperature range of the low-temperature homogenization section is 987~1010℃, the temperature range of the high-temperature short-time homogenization section is 1151~1192℃, and the holding time is 42~54min; the temperature range of the high-temperature high-efficiency homogenization section is 1222~1256℃. (3) Two-stage rolling: The rolling process employs a two-stage controlled rolling method. The first stage involves refining the original austenite structure through rolling. The rolling temperature starts at 1058~1096℃ and ends at 961~998℃. A "large-small-...large reduction rate" control rolling process is adopted, with a large reduction rate of 7%~10% and a small reduction rate of 2%~4%. The second stage is the two-phase region rolling, with an initial rolling temperature of 946~974℃ and a final rolling temperature of 847~880℃. It adopts a "reduction rate" rolling control process, and the reduction rate in the second stage of the two-phase region rolling is 6%~10%. (4) Two-stage cooling: The first stage is a homogenization and controlled cooling stage, with a starting temperature of 835~876℃ and a cooling rate of 26~34℃ / s; the second stage is a precipitation enhancement and controlled cooling stage, with a starting temperature of 512~539℃ and a cooling rate of 86~104℃ / s. (5) Heat treatment: The heat treatment of the steel plate is as follows: in the low-temperature mold welding heat treatment stage, the temperature is controlled at 555~592℃, the heating rate is 0.6~0.9min / mm, and the holding time is 165~200min; in the high-temperature mold welding heat treatment stage, the temperature is controlled at 605~642℃, the heating rate is 0.8~1.1min / mm, the holding time is 45~60min, and the cooling rate is controlled at 36~49℃ / min.

7. The method for manufacturing a 70MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 6, characterized in that: Smelting includes electric furnace smelting, LF refining, and RH refining; In the electric arc furnace smelting process, high-quality scrap steel and molten iron are used as raw materials, with a charge size of 72~81mm and a molten iron mass percentage of over 76%. During the smelting process, the magnesium-silicon spheroidizing agent is added at a rate of 3.4%~4.5% per ton of steel. The decarburization oxygen blowing time is 261~343s, and the dephosphorization oxygen blowing time is 252~329s, controlling the phosphorus mass fraction in the molten steel to be reduced to below 0.01%. The LF refining desulfurization and oxygen blowing time is 344~398s, which controls the sulfur content to below 0.01%; RH refining starting temperature: 1662~1670℃, oxygen blowing rate: 26~29m³ 3 The net circulation time is 591~652s, and the pre-pouring settling time is 266~321s.

8. The method for manufacturing a 70MPa-grade hydrogen energy storage cryogenic container steel plate according to claim 6, characterized in that: During continuous casting, the reduction rate of the continuously cast billet under light pressure is 1% to 3%; the current in the electromagnetic stirring process is 396 to 419 A, and the frequency is 4 to 8 Hz.

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