Steel plate for pressure vessel for hydrogen storage and preparation method of steel plate

Abstract

The invention discloses a steel plate for a pressure vessel for hydrogen storage and a preparation method of the steel plate. The steel plate comprises, by weight, 0.08%-0.15% of C, 0.10%-0.40% of Si, 0.50%-1.10% of Mn, smaller than or equal to 0.010% of P, smaller than or equal to 0.002% of S, 0.80%-1.30% of Ni, 0.30%-0.65% of Cr, 0.40%-0.70% of Mo, 0.03%-0.08% of V, 0.3%-0.6% of Cu, 0.03%-0.05% of Als, 0.0005%-0.0030% of B and the balance Fe and other inevitable impurities. The thickness of the steel plate is 10-80 mm, the yield strength is larger than or equal to 760 MPa, the tensile strength is larger than or equal to 810 MPa, the ductility is 17-20%, the impact energy at the temperature of-60 DEG C is larger than or equal to 110 J, the relative ductility under the 10 MPa hydrogen environment is larger than or equal to 91%, and the relative reduction of area is larger than or equal to 90%. The steel plate disclosed by the invention has better plasticity and low-temperature impact toughness while ensuring ultrahigh strength, and is an ultrahigh-toughness steel plate for the pressure vessel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically, it relates to a steel plate for a pressure vessel used for hydrogen storage and a method for preparing the same. Background Technology

[0002] Currently, high-pressure gaseous hydrogen storage technology is the most widely used due to its fast charging and discharging speed and simple container structure. However, most existing high-pressure gaseous hydrogen storage technologies focus on small-scale high-pressure hydrogen storage tanks or large-scale low-pressure hydrogen storage containers. For small-scale high-pressure hydrogen storage tanks, the main method to increase the hydrogen storage pressure is to increase the tank thickness, but the maximum volume at 70 MPa is only 300 L. For large-scale low-pressure hydrogen storage tanks, the largest volume currently available in China can reach 1000 m³. 3 However, both types of hydrogen storage materials have hydrogen storage pressures below 3 MPa. During operation, issues such as energy consumption, hydrogen storage capacity, and storage pressure cannot meet the current requirements for large-scale, economical, and safe hydrogen storage and transportation. Therefore, achieving high-reliability, low-cost, large-capacity, and easy-to-manufacture high-pressure hydrogen storage equipment materials is a core technology that must be mastered. Steel pressure hydrogen storage materials, benefiting from relatively mature production technology and low cost, are important materials for future low-cost, large-capacity, high-pressure hydrogen storage equipment. The key technical characteristics of this type of material are: large thickness, ultra-high strength, weldability, good strength-toughness matching, resistance to hydrogen corrosion, and resistance to hydrogen embrittlement. Currently, this type of material is at the forefront of research worldwide, possessing both extremely high technical barriers and huge market potential. In the latest GB / T 713.6 standard formed in 2023, the highest yield strength level has reached 690 MPa, but the impact toughness requirement (≥80J) is relatively low, still lagging behind international advanced levels. Furthermore, for pressure vessel steel plates used for hydrogen storage, no clear technical requirements have been made regarding the hydrogen compatibility of the steel plates, leaving a technological gap in this field in China.

[0003] Patent CN101643888A discloses "a low weld crack sensitivity steel with a tensile strength of 700MPa and its production method." The disclosed chemical composition of the steel, by weight percentage, is: C: 0.08–0.12%, Si: 0.15–0.40%, Mn: 1.00–2.00%, P≤0.015%, S≤0.006%, Ni: 0.25–0.55%, Mo: 0.15–0.00%. The steel plate contains 0.28% Fe, 0.02-0.10% V, 0.18-0.30% Cu, 0.15-0.30% Cr, 0.008-0.020% Ti, and 0.0007-0.0027% B, with the remainder being Fe and unavoidable inclusions. The actual product of this patented steel plate can only meet the requirement of tensile strength Rm≥690MPa, but for low-temperature impact toughness, it only requires an impact energy ≥47J at -20℃, which is at a relatively low level.

[0004] Patent CN104532159A discloses "a quenched and tempered high-strength steel with a yield strength of 700 MPa and its production method." The disclosed chemical composition of the steel (by weight percentage) is: C: 0.06–0.13%, Si: 0.10–0.30%, Mn: 0.80–1.60%, Cr: 0.20–0.70%, Mo: 0.10–0.30%, Ni: 0–0.30%, Nb… The composition of the steel plate is as follows: 0.010–0.030% Fe, Ti: 0.010–0.030%, V: 0.010–0.030%, B: 0.0005–0.0030%, Al: 0.02–0.06%, Ca: 0.001–0.004%, N: 0.002–0.005%, P≤0.020%, S≤0.010%, O≤0.008%, with the remainder being Fe and unavoidable impurities. The actual yield strength of this patented steel plate is 700–850 MPa, and the tensile strength is 750–900 MPa, but the elongation is >14%, and the impact energy at -40℃ is >40 J. The ductility and toughness of the steel plate are relatively low.

[0005] Patent CN111566242A discloses "Steel for Pressure Vessels with Excellent Resistance to Hydrogen-Induced Cracking and its Manufacturing Method," with the disclosed chemical composition of the steel as follows (weight percentage): C: 0.06–0.25%, Si: 0.05–0.50%, Mn: 1.0–2.0%, Al: 0.005–0.40%, P≤0.010%, S≤0.0010%, Nb: 0.001–0.0%. The composition is as follows: 3%, V: 0.001–0.03%, Ti: 0.001–0.03%, Cr: 0.01–0.20%, Mo: 0.05–0.15%, Cu: 0.01–0.50%, Ni: 0.05–0.50%, Mg: 0.0005–0.0050%, Ca: 0.0005–0.0050%, O ≤ 0.0020%, balance Fe and other unavoidable impurities. The hot-rolled steel plate described in this patent has a thickness of only 5–65 mm. Although it has relatively good resistance to hydrogen-induced cracking, its tensile strength is below 600 MPa, which is relatively low. Summary of the Invention

[0006] To address the technical problems of low tensile strength and low ductility in existing steel plates, this invention provides a steel plate for pressure vessels used in hydrogen storage and its preparation method.

[0007] The steel plate for pressure vessels used for hydrogen storage provided by this invention has the following composition by weight: C 0.08-0.15%, Si 0.10-0.40%, Mn 0.50-1.10%, P≤0.010%, S≤0.002%, Ni 0.80-1.30%, Cr 0.30-0.65%, Mo 0.40-0.70%, V 0.03-0.08%, Cu 0.3-0.6%, Als 0.03-0.05%, B 0.0005-0.0030%, with the remainder being Fe and other unavoidable impurities.

[0008] The steel plate has a thickness of 10-80mm, a yield strength of ≥760MPa, a tensile strength of ≥810MPa, an elongation of 17-20%, an impact energy of ≥110J at -60℃, a relative elongation of ≥91% in a 10MPa hydrogen environment, and a relative reduction of area of ​​≥90%. It is an ultra-high strength and toughness steel plate for pressure vessels.

[0009] The present invention provides a method for preparing steel plates for pressure vessels used for hydrogen storage, comprising the following steps:

[0010] 1) Heating process

[0011] A step-by-step heating method is adopted, with the preheating section temperature controlled below 650℃, the first heating section temperature at 750~850℃, the second heating section temperature at 850~950℃, the third heating section temperature at 950~1200℃, and the soaking section temperature at 1160~1200℃, during which all alloying elements are completely dissolved. The total heating time coefficient is 1.0~1.2H, where H is the thickness of the continuously cast billet.

[0012] 2) Rolling process

[0013] A two-stage controlled rolling mode is adopted. The initial rolling temperature of the roughing stage is 1030-1130℃; the intermediate billet in the finishing stage is heated to 830℃-990℃, the thickness of the intermediate billet is 2-5 times the thickness of the finished product, the cumulative reduction rate of the last three passes of finishing rolling is 25%-40%, and the final rolling temperature is controlled within the range of 780-850℃.

[0014] 3) Cooling process

[0015] Cooling is controlled by ACC cooling method, and the red-hot temperature of the steel plate is 620-690℃;

[0016] 4) Heat treatment process

[0017] The heat treatment process includes offline quenching heat treatment, two-phase quenching heat treatment, and tempering heat treatment. The offline quenching heat treatment involves reheating the cooled steel plate to 880–910℃, with a furnace time coefficient of 1.5–1.8 min / mm, and then water-cooling the steel plate to room temperature after removal from the furnace. The two-phase quenching heat treatment involves reheating the cooled steel plate to 830–850℃, with a furnace time coefficient of 1.5–1.8 min / mm, and then water-cooling the steel plate to room temperature after removal from the furnace. The tempering heat treatment involves reheating the quenched steel plate to 650–680℃, with a furnace time coefficient of 2.5–4.0 min / mm, and then air-cooling the steel plate to room temperature after removal from the furnace.

[0018] In the rolling process, the compression ratio of the continuously cast billet is not less than 4. The specific value can be determined according to the thickness of the continuously cast billet and the thickness of the finished product, and is generally 4 to 46.

[0019] Invention Mechanism: The roles of each element in the design composition of the quenched and tempered steel of this invention are as follows:

[0020] Carbon (C) is the most effective element for increasing the strength of steel plates. An increase of 0.1% in carbon content can raise the tensile strength by approximately 70 MPa. However, increasing carbon content reduces plasticity and toughness, and worsens the weldability of the steel plate. Carbon has the most significant impact on the hardenability and cold cracking tendency of the weld heat-affected zone. The carbon content of 690 MPa grade low-alloy ultra-high strength steel plates, both domestically and internationally, is typically controlled below 0.15%. The strength loss caused by reduced carbon content is compensated for through microalloying and process optimization.

[0021] Si can significantly improve the strength and hardness of steel, while enhancing its resistance to high-temperature oxidation. However, excessive silicon in steel can also reduce weldability and negatively impact the surface quality of the steel plate.

[0022] Mn primarily enhances the strength of steel plates through solid solution strengthening, while simultaneously lowering the initiation and termination points of austenite transformation, expanding the austenite phase region, and inhibiting the transformation of austenite to ferrite. The manganese content should generally not exceed 2.0%, as excessive amounts can lead to problems such as center segregation and poor weldability in the steel plate.

[0023] P and S: Both are harmful elements. Sulfur easily forms inclusions and segregates in steel, impairing the formability of the steel plate; phosphorus easily forms severe segregation bands, increasing the grade of banded structure and leading to increased anisotropy of the steel plate. Therefore, the content of phosphorus and sulfur should be controlled at a low level as much as possible.

[0024] Ni: Nickel increases the nucleation work of ferrite during the austenite-ferrite phase transformation, promoting the transformation of granular bainite structure; and nickel reduces the frictional resistance of dislocation movement at low temperatures, increasing stacking fault energy, thus improving the low-temperature toughness of steel plates. According to first-principles calculations, Ni has extremely strong hydrogen resistance in the matrix and grain boundaries, and at the same time, it is necessary to ensure the low-temperature toughness of thick plates.

[0025] Cr: Chromium reduces the diffusion rate of carbon, inhibits the transformation of ferrite and pearlite, shifts the bainite transformation to the lower temperature region, and lowers the bainite phase transformation point. Simultaneously, according to first-principles calculations, Cr also exhibits strong resistance to hydrogen in the matrix and grain boundaries.

[0026] Mo: Molybdenum effectively delays high-temperature transformation in steel and has almost no effect on bainitic transformation, which is particularly beneficial for obtaining bainitic microstructure. At the same time, according to the first Scheringer principle, Mo has a certain degree of hydrogen resistance at grain boundaries.

[0027] V: By controlling vanadium precipitation, VC can be interphased during the austenite-ferrite transformation process or randomly precipitated in the ferrite matrix, thus playing a precipitation strengthening role. Simultaneously, increasing the nitrogen content in steel can promote VCN precipitation at the austenite-ferrite phase interface, effectively inhibiting ferrite grain growth and refining the grain size. Furthermore, the precipitated VCN phase can act as a hydrogen trap, reducing the material's hydrogen sensitivity.

[0028] Cu: Copper has a significant strengthening effect on alloy steel and can improve its toughness, significantly enhancing its plasticity and ductility. Adding an appropriate amount of copper can ensure the physical strength of steel after high-temperature tempering. Furthermore, Cu is the second most potent hydrogen-removing element after Ni, which helps prevent hydrogen embrittlement. Maintaining a certain Cu / Ni ratio can effectively prevent copper embrittlement.

[0029] B: To ensure the hardenability of thick plates, increasing the boron content by a trace amount can significantly improve the hardenability of the steel plate, making it easier for austenite to undergo low-temperature phase transformation and inhibiting ferrite nucleation. To ensure that dissolved boron can fully exert the above-mentioned effects, strong nitride-forming elements such as Ti and Al are generally added to boron-containing steels to consume nitrogen and avoid the formation of large amounts of BN.

[0030] In particular, in order to ensure that the steel plate has excellent hydrogen resistance, the steel plate of the present invention is designed with chemical composition based on first-principles calculations. The hydrogen binding energy after alloying elements are doped in the Fe matrix and at the grain boundaries is calculated. The lower the hydrogen binding energy, the easier it is to bind hydrogen atoms, and the easier it is to cause hydrogen embrittlement.

[0031] The changes in hydrogen binding energy after doping with interstitial atoms (B, N) and substitutional atoms (Cr, Mn, Ni, Cu, Mo and W) in the bcc-Fe structure were calculated based on first-principles calculations.

[0032] Meanwhile, hydrogen atoms tend to accumulate more easily at grain boundaries in steel. When hydrogen atoms accumulate at grain boundaries, it can easily lead to intergranular or transgranular cracking, resulting in material failure. However, when certain alloying elements segregate at grain boundaries, they can change the binding energy of hydrogen atoms at the grain boundaries. Therefore, the influence of each alloying element on the hydrogen binding energy at grain boundaries was calculated.

[0033] Calculations revealed that, overall, Ni, Cr, Mo, and Cu are elements with strong hydrogen-removing properties, which helps prevent hydrogen embrittlement. Therefore, the steel plate composition of this invention focuses on incorporating these four elements.

[0034] The rolled steel plate undergoes a triple heat treatment process: offline quenching, two-phase quenching, and tempering. In the quenching process, the heating temperature is based on the critical point of phase transformation of the steel. The reheating temperature of the rolled steel plate is 880–910℃, with a heating time coefficient of 1.5–1.8 min / mm. During heating, fine and uniform austenite grains are formed. After the steel plate is removed from the furnace, it is quenched to room temperature, meaning the austenite structure transforms into martensite through phase transformation. In the two-phase quenching process, the heating temperature is based on the critical point of phase transformation of the steel. The reheating temperature of the rolled steel plate is 830–850℃, with a heating time coefficient of 1.5–1.8 min / mm. This process retains a small amount of dispersed austenite grains on the martensitic matrix. Ferritic microstructure improves the low-temperature impact toughness of steel plates, lowers the brittle-to-cold transition temperature, and suppresses reversible temper brittleness, laying the foundation for obtaining high toughness without sacrificing strength in subsequent tempering processes. After sub-temperature quenching, the steel plate has high internal stress and is relatively brittle, necessitating tempering. The tempering temperature is 650–680℃, with a furnace time coefficient of 2.5–4.0 min / mm. After exiting the furnace, the steel plate is air-cooled to room temperature to eliminate stress, increase toughness, and adjust strength. After tempering, the steel plate microstructure is dominated by uniform and fine tempered lath bainite. This microstructure has good uniformity, increasing the resistance to crack propagation in locally weak areas, ensuring the steel plate possesses good strength, plasticity, and toughness.

[0035] The present invention has the following beneficial effects:

[0036] 1) Through the design of hydrogen-resistant chemical composition based on first principles, steel plates with a thickness of 10-80mm were obtained. While ensuring ultra-high strength, they also have better plasticity and low-temperature impact toughness, making them an ultra-high strength and toughness pressure vessel steel plate.

[0037] 2) The 10-80mm thick high-performance steel plate has broken through the existing technical bottleneck and filled the gap in the domestic material technology for large high-pressure hydrogen storage containers. In the future, it will promote the formation of a complete and efficient industrial chain prototype for pressure vessel equipment, materials, design, construction, application, safety evaluation, preparation, storage and transportation and end application, laying the foundation for the development, production and application of a new generation of tempered high-strength pressure vessel steel.

[0038] 3) By setting up an offline quenching + two-phase quenching + tempering process, the strength, plasticity and toughness of the steel plate are further improved. Attached Figure Description

[0039] Figure 1 The change in hydrogen binding energy after alloying elements are doped into Fe;

[0040] Figure 2 The change in hydrogen binding energy after alloying element doping at grain boundaries;

[0041] Figure 3 This is a microstructure diagram of the steel plate of the present invention. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] Figure 1 The horizontal axis represents the interstitial and substitutional atoms in Fe, and the vertical axis represents the hydrogen binding energy for different doping atoms. When the hydrogen binding energy is less than 0, it indicates that the alloying element easily captures hydrogen atoms from the interstitial sites; while when the hydrogen binding energy is greater than 0, it indicates that the alloying element has a stronger repulsive effect on hydrogen atoms. The 0 eV value on the vertical axis represents the hydrogen binding energy in the absence of any alloying element. Except for the alloying element Mn, all others are positive, indicating that these alloying elements do not easily bind with hydrogen, while values ​​greater than 0.1 eV indicate a strong repulsive effect on hydrogen atoms.

[0044] Figure 2 This indicates the influence of doping with various alloying elements at grain boundaries on the hydrogen binding energy at grain boundaries, and its influence trend and... Figure 1 same.

[0045] Through analysis Figure 1 and Figure 2 In summary, Ni, Cr, Mo, and Cu are elements with strong hydrogen embrittlement properties, which helps prevent hydrogen embrittlement. This is why these four elements are the main components added to the steel plate of this invention.

[0046] The following are embodiments of the technical solution of the present invention:

[0047] Example 1

[0048] The present invention discloses a steel plate for a pressure vessel used for hydrogen storage, the finished product having a thickness of 80 mm, and its composition by weight is: C: 0.15%, Si: 0.38%, Mn: 1.10%, P: 0.08%, S: 0.002%, Ni: 1.28%, Cr: 0.63%, Mo: 0.68%, V: 0.08%, Cu: 0.6%, Als: 0.05%, B: 0.0028%, with the remainder being Fe and other unavoidable impurities.

[0049] Its preparation method includes the following steps:

[0050] 1) Heating process: The 320mm continuous casting billet is heated in a heating furnace using a step heating method. The preheating section temperature is 635℃, the first heating section temperature is 847℃, the second heating section temperature is 942℃, the third heating section temperature is 1193℃, and the soaking section temperature is 1195℃. All alloying elements are completely dissolved. The total heating time coefficient is 1.2H (H is the thickness of the continuous casting billet).

[0051] 2) Rolling process: A two-stage controlled rolling mode is adopted, with a continuous casting billet compression ratio of 4; the initial rolling temperature of the roughing stage is 1035℃, and the roughing stage adopts high temperature, low speed and large reduction rolling; in the finishing stage, the intermediate billet steel plate waiting thickness is 2h (h is the finished product thickness), the waiting temperature is 836℃, the cumulative reduction rate of the last three passes is 26%, the final product thickness is 80mm, and the final rolling temperature is 843℃;

[0052] 3) Cooling process: Cooling is controlled by ACC cooling method, and the red-hot temperature of the steel plate is 687℃;

[0053] 4) Offline quenching heat treatment process: The reheating temperature of the rolled steel plate is 910℃, the furnace time coefficient is 1.8min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace;

[0054] 5) Two-phase quenching heat treatment process: After offline quenching, the steel plate is reheated at 850℃, and the furnace time coefficient is 1.8min / mm. After the steel plate is taken out of the furnace, it is water-cooled to room temperature.

[0055] 6) Tempering heat treatment process: After quenching in the two-phase region, the steel plate is reheated to 650℃, with a furnace time coefficient of 3.0min / mm. After the steel plate is taken out of the furnace, it is air-cooled to room temperature.

[0056] Example 2

[0057] The present invention discloses a steel plate for a pressure vessel used for hydrogen storage, the finished product having a thickness of 70 mm, and its composition by weight is: C: 0.13%, Si: 0.30%, Mn: 1.00%, P: 0.06%, S: 0.002%, Ni: 1.12%, Cr: 0.56%, Mo: 0.55%, V: 0.06%, Cu: 0.5%, Als: 0.04%, B: 0.0020%, with the remainder being Fe and other unavoidable impurities.

[0058] Its preparation method includes the following steps:

[0059] 1) Heating process: The 320mm continuous casting billet is heated in a heating furnace using a step heating method. The preheating section temperature is 640℃, the first heating section temperature is 823℃, the second heating section temperature is 877℃, the third heating section temperature is 1175℃, and the soaking section temperature is 1182℃. All alloying elements are completely dissolved. The total heating time coefficient is 1.0H (H is the thickness of the continuous casting billet).

[0060] 2) Rolling process: A two-stage controlled rolling mode is adopted, with a continuous casting billet compression ratio of 4.6: the initial rolling temperature of the roughing stage is 1045℃, and the roughing stage adopts high temperature, low speed and large reduction rolling; in the finishing stage, the intermediate billet steel plate waiting thickness is 2h (h is the finished product thickness), the waiting temperature is 855℃, the cumulative reduction rate of the last three passes is 28%, the final product thickness is 70mm, and the final rolling temperature is 837℃;

[0061] 3) Cooling process: Cooling is controlled by ACC cooling method, and the red-hot temperature of the steel plate is 666℃;

[0062] 4) Offline quenching heat treatment process: The reheating temperature of the rolled steel plate is 910℃, the furnace time coefficient is 1.8min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace;

[0063] 5) Two-phase quenching heat treatment process: After offline quenching, the steel plate is reheated at 850℃, and the furnace time coefficient is 1.8min / mm. After the steel plate is taken out of the furnace, it is water-cooled to room temperature.

[0064] 6) Tempering heat treatment process: After quenching in the two-phase region, the steel plate is reheated to 660℃, with a furnace time coefficient of 3.0min / mm. After the steel plate is taken out of the furnace, it is air-cooled to room temperature.

[0065] Example 3

[0066] The present invention discloses a steel plate for a pressure vessel used for hydrogen storage, the finished product having a thickness of 50 mm, and its composition by weight is: C: 0.11%, Si: 0.26%, Mn: 0.93%, P: 0.05%, S: 0.002%, Ni: 1.05%, Cr: 0.52%, Mo: 0.50%, V: 0.05%, Cu: 0.4%, Als: 0.03%, B: 0.0025%, with the remainder being Fe and other unavoidable impurities.

[0067] Its preparation method includes the following steps:

[0068] 1) Heating process: The 320mm continuous casting billet is heated in a heating furnace using a step heating method. The preheating section temperature is 638℃, the first heating section temperature is 753℃, the second heating section temperature is 856℃, the third heating section temperature is 957℃, and the soaking section temperature is 1166℃. All alloying elements are completely dissolved. The total heating time coefficient is 1.1H (H is the thickness of the continuous casting billet).

[0069] 2) Rolling process: A two-stage controlled rolling mode is adopted, with a continuous casting billet compression ratio of 6.4: the initial rolling temperature of the roughing stage is 1063℃, and the roughing stage adopts high temperature, low speed and large reduction rolling; in the finishing stage, the intermediate billet steel plate has a waiting thickness of 2.5h (h is the finished product thickness), the waiting temperature is 881℃, the cumulative reduction rate of the last three passes is 30%, the final product thickness is 50mm, and the final rolling temperature is 812℃;

[0070] 3) Cooling process: Cooling is controlled by ACC cooling method, and the red-hot temperature of the steel plate is 656℃;

[0071] 4) Offline quenching heat treatment process: The reheating temperature of the rolled steel plate is 900℃, the furnace time coefficient is 1.7min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace.

[0072] 5) Two-phase quenching heat treatment process: After offline quenching, the steel plate is reheated at 840℃, and the furnace time coefficient is 1.7min / mm. After the steel plate is taken out of the furnace, it is water-cooled to room temperature.

[0073] 6) Tempering heat treatment process: After quenching in the two-phase region, the steel plate is reheated to 670℃, with a furnace time coefficient of 2.5min / mm. After the steel plate is taken out of the furnace, it is air-cooled to room temperature.

[0074] Example 4

[0075] The present invention discloses a steel plate for a pressure vessel used for hydrogen storage, the finished product having a thickness of 25 mm, and its composition by weight is: C: 0.10%, Si: 0.20%, Mn: 0.78%, P: 0.08%, S: 0.002%, Ni: 0.93%, Cr: 0.46%, Mo: 0.46%, V: 0.04%, Cu: 0.35%, Als: 0.04%, B: 0.0015%, with the remainder being Fe and other unavoidable impurities.

[0076] Its preparation method includes the following steps:

[0077] 1) Heating process: The 220mm continuous casting billet is heated in a heating furnace using a step heating method. The preheating section temperature is 627℃, the first heating section temperature is 803℃, the second heating section temperature is 893℃, the third heating section temperature is 1110℃, and the soaking section temperature is 1173℃. All alloying elements are completely dissolved. The total heating time coefficient is 1.2H (H is the thickness of the continuous casting billet).

[0078] 2) Rolling process: A two-stage controlled rolling mode is adopted, with a continuous casting billet compression ratio of 8.8: the initial rolling temperature of the roughing stage is 1093℃, and the roughing stage adopts high temperature, low speed and large reduction rolling; in the finishing stage, the intermediate billet steel plate waiting thickness is 3h (h is the finished product thickness), the waiting temperature is 937℃, the cumulative reduction rate of the last three passes is 31%, the final product thickness is 25mm, and the final rolling temperature is 803℃;

[0079] 3) Cooling process: Cooling is controlled by ACC cooling method, and the red-hot temperature of the steel plate is 638℃;

[0080] 4) Offline quenching heat treatment process: The reheating temperature of the rolled steel plate is 880℃, the furnace time coefficient is 1.6min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace;

[0081] 5) Two-phase quenching heat treatment process: After offline quenching, the steel plate is reheated at 840℃, and the furnace time coefficient is 1.6min / mm. After the steel plate is taken out of the furnace, it is water-cooled to room temperature.

[0082] 6) Tempering heat treatment process: After quenching in the two-phase region, the steel plate is reheated to 670℃, with a furnace time coefficient of 4.0min / mm. After the steel plate is taken out of the furnace, it is air-cooled to room temperature.

[0083] Example 5

[0084] The present invention discloses a steel plate for a pressure vessel used for hydrogen storage, the finished product having a thickness of 10 mm, and its composition by weight is: C: 0.08%, Si: 0.11%, Mn: 0.5%, P: 0.07%, S: 0.002%, Ni: 0.82%, Cr: 0.32%, Mo: 0.42%, V: 0.03%, Cu: 0.3%, Als: 0.035%, B: 0.0028%, with the remainder being Fe and other unavoidable impurities.

[0085] Its preparation method includes the following steps:

[0086] 1) Heating process: The 150mm continuous casting billet is heated in a heating furnace using a step heating method. The preheating section temperature is 636℃, the first heating section temperature is 783℃, the second heating section temperature is 921℃, the third heating section temperature is 1020℃, and the soaking section temperature is 1186℃. All alloying elements are completely dissolved. The total heating time coefficient is 1.1H (H is the thickness of the continuous casting billet).

[0087] 2) Rolling process: A two-stage controlled rolling mode is adopted, with a continuous casting billet compression ratio of 15: the initial rolling temperature of the roughing stage is 1127℃, and the roughing stage adopts high temperature, low speed and large reduction rolling; in the finishing stage, the intermediate billet steel plate waiting thickness is 5h (h is the finished product thickness), the waiting temperature is 983℃, the cumulative reduction rate of the last three passes is 37%, the final product thickness is 10mm, and the final rolling temperature is 782℃;

[0088] 3) Cooling process: Cooling is controlled by ACC cooling method, and the red-hot temperature of the steel plate is 622℃;

[0089] 4) Offline quenching heat treatment process: The reheating temperature of the rolled steel plate is 880℃, the furnace time coefficient is 1.5min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace.

[0090] 5) Two-phase quenching heat treatment process: After offline quenching, the steel plate is reheated at 830℃, and the furnace time coefficient is 1.5min / mm. After the steel plate is taken out of the furnace, it is water-cooled to room temperature.

[0091] 6) Tempering heat treatment process: After quenching in the two-phase region, the steel plate is reheated to 680℃, with a furnace time coefficient of 4.0min / mm. After the steel plate is taken out of the furnace, it is air-cooled to room temperature.

[0092] Structural characterization

[0093] Figure 3 This is a microstructure diagram of the steel plate of the present invention. The structure of the steel plate is mainly composed of tempered sorbite and ferrite.

[0094] Performance testing

[0095] The mechanical properties and hydrogen compatibility of the steel plates prepared in Examples 1 to 5 were tested in accordance with GB / T228.1, GB / T 229, GB / T 232, and GB / T 34542.2. The test results are shown in Tables 1 and 2.

[0096] Table 1. Test results of mechanical properties of steel plates in Examples 1-5

[0097]

[0098] Table 2. Results of 10MPa hydrogen environment compatibility test on steel plates in Examples 1-5

[0099]

[0100] As can be seen, the 10-80mm thick ultra-high strength and toughness pressure vessel steel plates for hydrogen storage obtained in Examples 1-5 above exhibit excellent comprehensive performance, good strength-toughness balance, and satisfactory cold bending forming performance. The actual yield strength of the steel plates is ≥760MPa, tensile strength is ≥810MPa, elongation is 17-20%, impact energy at -60℃ is ≥110J, relative elongation at 10MPa hydrogen environment is ≥91%, and relative reduction of area is ≥90%.

Claims

1. A steel plate for a pressure vessel used for hydrogen storage, characterized in that, Its composition by weight is as follows: C 0.08-0.15%, Si 0.10-0.40%, Mn 0.50-1.10%, P≤0.010%, S≤0.002%, Ni 0.80-1.30%, Cr 0.30-0.65%, Mo 0.40-0.70%, V 0.03-0.08%, Cu 0.3-0.6%, Als 0.03-0.05%, B 0.0005-0.0030%, with the remainder being Fe and other unavoidable impurities.

2. The steel plate for a pressure vessel used for hydrogen storage according to claim 1, characterized in that: The steel plate has a yield strength ≥760MPa, a tensile strength ≥810MPa, an elongation of 17~20%, an impact energy of -60℃ ≥110J, a relative elongation of ≥91% under 10MPa hydrogen environment, and a relative reduction of area ≥90%.

3. The steel plate for a pressure vessel used for hydrogen storage according to claim 1 or 2, characterized in that: The thickness of the steel plate is 10-80 mm.

4. A method for preparing a steel plate for a pressure vessel for hydrogen storage as described in claim 1 or 2, characterized in that, The process includes the following steps: 1) Heating process A step-by-step heating method is adopted, with the preheating section temperature controlled below 650℃, the first heating section temperature at 750~850℃, the second heating section temperature at 850~950℃, the third heating section temperature at 950~1200℃, and the soaking section temperature at 1160~1200℃, during which all alloying elements are completely dissolved. The total heating time coefficient is 1.0~1.2H, where H is the thickness of the continuously cast billet. 2) Rolling process A two-stage controlled rolling mode is adopted. The initial rolling temperature of the roughing stage is 1030-1130℃; the intermediate billet in the finishing stage is heated to 830℃-990℃, the thickness of the intermediate billet is 2-5 times the thickness of the finished product, the cumulative reduction rate of the last three passes of finishing rolling is 25%-40%, and the final rolling temperature is controlled within the range of 780-850℃. 3) Cooling process Cooling is controlled by ACC cooling method, and the red-hot temperature of the steel plate is 620-690℃; 4) Heat treatment process The heat treatment process includes offline quenching heat treatment, two-phase zone quenching heat treatment, and tempering heat treatment. The offline quenching heat treatment involves reheating the cooled steel plate to 880–910℃, with a furnace time coefficient of 1.5–1.8 min / mm, followed by water cooling to room temperature after removal from the furnace. The two-phase zone quenching heat treatment involves reheating the cooled steel plate to 830–850℃, with a furnace time coefficient of 1.5–1.8 min / mm, followed by water cooling to room temperature after removal from the furnace. The tempering heat treatment involves reheating the quenched steel plate to 650–680℃, with a furnace time coefficient of 2.5–4.0 min / mm, followed by air cooling to room temperature after removal from the furnace. The compression ratio of the continuously cast billet in the rolling process is not less than 4.

5. The method for preparing a steel plate for a pressure vessel for hydrogen storage according to claim 4, characterized in that: The compression ratio of the continuously cast billet in the rolling process is 4 to 46.

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