15Ni steel for ultralow-temperature liquid hydrogen storage tank and preparation method of 15Ni steel

Abstract

The invention discloses 15Ni steel for an ultralow-temperature liquid hydrogen storage tank and a preparation method of the 15Ni steel, and belongs to the technical field of metallurgy. The 15Ni steel comprises the following chemical components in percentage by mass: 0.02%-0.07% of C, 0.10%-0.30% of Si, 0.20%-0.80% of Mn, 0.15%-0.30% of Mo, 0.020%-0.050% of Al, 12.5%-15.5% of Ni, 0.0015%-0.0060% of N, less than or equal to 0.008% of P, less than or equal to 0.002% of S, less than or equal to 0.020% of Nb, less than or equal to 0.080% of V, less than or equal to 0.020% of Ti and the balance of Fe and inevitable impurities. The preparation method comprises the procedures of smelting, continuous casting, heating, rolling and heat treatment. The steel plate produced by the invention has excellent ultralow temperature (-269 DEG C) impact toughness, effectively solves the problems of brittle phase martensite precipitation and low strength of stainless steel at a low temperature of-196 DEG C, can replace stainless steel to be widely used for manufacturing large ultralow temperature liquid hydrogen storage tanks, and has wide application prospects.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a 15Ni steel for cryogenic liquid hydrogen storage tanks and its preparation method. Background Technology

[0002] With the increasing global demand for clean energy, liquid hydrogen, as a highly efficient energy carrier with zero carbon emissions, has shown enormous application potential in aerospace, shipping, and new energy fields. However, the storage and transportation of liquid hydrogen requires materials that can maintain excellent mechanical properties in ultra-low temperature environments (-253℃ to -269℃), which places extremely high demands on the low-temperature toughness, strength, and stability of structural materials. Currently, austenitic stainless steel, due to its face-centered cubic (FCC) structure, is less prone to brittle fracture at low temperatures, making it a primary candidate material for liquid hydrogen storage tanks. However, this type of material has significant limitations: its room temperature yield strength is only about 200 MPa, which is insufficient to meet the high-strength requirements of large storage tanks, leading to increased tank wall thickness and weight, severely restricting the economic viability and large-scale development of the liquid hydrogen supply chain.

[0003] To overcome this technical bottleneck, researchers at home and abroad are committed to developing high-strength and high-toughness low-temperature steel. Nickel (Ni), as an austenite stabilizing element, plays a core role in the design of low-temperature steel. Although traditional 9Ni steel can maintain good toughness at -196℃ (liquid nitrogen temperature), it still faces the risk of martensitic transformation at liquid hydrogen temperature (below -253℃), resulting in a sharp drop in toughness. Further increasing the nickel content to more than 15% can significantly reduce the martensitic transformation temperature (Ms), but the alloy cost, process complexity and microstructure control difficulty of high-nickel steel are greatly increased. In the existing technology, high-nickel steel often faces the following technical challenges: (1) Segregation of alloying elements (such as P and S) at the austenite grain boundaries, which leads to grain boundary embrittlement; (2) Insufficient stability of reverse-transformed austenite at ultra-low temperatures, which easily transforms into brittle martensite; (3) Difficulty in balancing strength and toughness. Although high nickel content improves low-temperature toughness, it may sacrifice strength or weldability.

[0004] In terms of microstructure control, conventional quench-and-temper (QT) processes struggle to achieve stable austenite retention in high-nickel steels. Studies have shown that two-phase heat treatment can promote the formation of reverse-transformed austenite, but its volume fraction and carbon and nitrogen enrichment directly affect low-temperature stability. Furthermore, while the addition of molybdenum (Mo) can improve hardenability, excessive amounts can lead to carbide precipitation, deteriorating toughness and failing to meet the pressure requirements of liquid hydrogen storage tanks.

[0005] In summary, developing a 15Ni steel possessing ultra-high strength (yield strength ≥ 550 MPa), excellent ultra-low temperature toughness (impact energy ≥ 80 J at -269℃), and structural stability, along with a corresponding efficient and stable preparation process, represents a key breakthrough for the development of liquid hydrogen storage and transportation technology. This invention, through innovative composition design and QLT heat treatment process, successfully solves the aforementioned technical challenges, providing a material foundation for the large-scale construction of the liquid hydrogen supply chain. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a 15Ni steel for cryogenic liquid hydrogen storage tanks and its preparation method. The steel for liquid hydrogen storage tanks produced by the method of this invention has the characteristics of high density, excellent strength-toughness ratio, and low yield strength ratio. Its performance and plate shape fully meet the requirements for use in liquid hydrogen storage tanks.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a 15Ni steel for cryogenic liquid hydrogen storage tanks, wherein the chemical composition and mass percentage of the 15Ni steel plate are as follows: C: 0.02%~0.07%, Si: 0.10%~0.30%, Mn: 0.20%~0.80%, Mo: 0.15%~0.30%, Al: 0.020%~0.050%, Ni: 12.5%~15.5%, N: 0.0015%~0.0060%, P≤0.008%, S≤0.002%, Nb≤0.020%, V≤0.080%, Ti≤0.020%, with the balance being Fe and unavoidable impurities.

[0008] The thickness of the steel plate described in this invention is ≤40mm.

[0009] The steel plate described in this invention has a yield strength ≥550MPa, a tensile strength of 700MPa~850MPa, an elongation A ≥27% at room temperature, and an average transverse impact energy ≥80J at -269℃; at the same time, the yield strength and tensile strength increase sharply at ultra-low temperatures.

[0010] This invention also provides a method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks, the preparation method comprising smelting, continuous casting, heating, rolling, and heat treatment processes; the rolling process adopts a two-stage rolling process; the heat treatment process adopts a two-stage quenching + tempering process, the first quenching is at 800℃~810℃, held at 2.0min / mm~2.5min / mm (calculated based on steel plate thickness in mm), water-cooled after exiting the furnace, and the reddening temperature is ≤200℃; the second quenching is at 650℃~660℃, held at 2.0min / mm~2.5min / mm (calculated based on steel plate thickness in mm), water-cooled after exiting the furnace, and the reddening temperature is ≤200℃; the tempering temperature is 450℃~480℃, the total heating time is 4min / mm, and the total heating time must be ≥70min, and the finished steel plate is obtained after air cooling after exiting the furnace.

[0011] In the smelting process described in this invention, molten steel is first smelted in a primary smelting furnace at a tapping temperature of 1610℃~1630℃. After slag removal, it is refined in an LF furnace to complete Mn and Mo alloying. When the ladle temperature is ≤1610℃, the ladle is hoisted and vacuum treated in a VD furnace. During vacuum treatment, the vacuum degree is ≤66Pa and the vacuum holding time is ≥20min.

[0012] In the continuous casting process described in this invention, the molten steel is continuously cast after smelting, the superheat of the molten steel is 10℃~20℃, the billet pulling speed is 0.65min / mm~0.75min / mm, and electromagnetic stirring and dynamic light reduction technology are carried out during the casting process; the continuously cast billets are stacked and slowly cooled for ≥36h.

[0013] In the heating process described in this invention, the continuously cast billet is heated in a continuous heating furnace with a maximum heating temperature of 1200℃~1230℃, a holding temperature of 1210~1230℃, and a total heating time of ≥12.5min / mm.

[0014] The rolling process described in this invention adopts a two-stage rolling process. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1100℃~1150℃, a single-pass reduction of 20%~30%, a final rolling temperature of 970℃~1000℃, and a cumulative reduction rate of 30%~50%.

[0015] The rolling process described in this invention adopts a two-stage rolling process. The second stage is the austenite non-recrystallization stage. The initial rolling temperature is ≤960℃, the single-pass reduction is 10%~30%, the cumulative reduction rate is 30%~50%, the final rolling temperature is 850℃~920℃, and the ACC water cooling after rolling is 600℃~750℃.

[0016] The testing method for steel plates used in cryogenic liquid hydrogen storage tanks in this invention refers to ASTM A370 and ASTM A751.

[0017] The design concept of this invention: 1) This invention employs C, Mn, and N solid solution strengthening, with Ni content controlled within the range of 12.5% ​​to 15.5%. This reduces grain size, ensures stable residual austenite, and suppresses the increase in low-temperature strength, thereby improving toughness at low temperatures. It improves the overall performance of steel through mechanisms such as grain refinement and lowering phase transformation temperature; stabilizes the austenite structure, allowing nickel and iron to dissolve infinitely, expanding the γ-phase region (austenite region), promoting austenite formation, and significantly lowering the critical transformation temperature (e.g., martensitic transformation temperature); inhibits element diffusion: reducing the diffusion rate of elements in the steel and slowing down the microstructure change process; simultaneously, nickel shifts the "C-curve" to the right by reducing the phase transformation driving force. This invention also adds a certain amount of molybdenum to the steel, combining it with molybdenum to improve its hardenability.

[0018] 2) The heat treatment process of the steel plate in this invention adopts a three-stage heat treatment (QLT) process to obtain a fine microstructure and an appropriate amount of stable retained austenite. The microstructure type is 90%M~92% tempered troostite + undissolved ferrite + austenite. First, the steel plate is quenched at an austenitic temperature to obtain a quenched martensite microstructure; then, it is quenched a second time at a two-phase temperature to obtain a sufficient amount of reverse-transformed austenite; finally, it is tempered at a temperature close to Ac1 to enrich austenite stabilizing elements. This heat treatment process ensures the stability of the retained austenite, thereby improving the ultra-low temperature impact toughness of the steel plate.

[0019] The beneficial effects of adopting the above technical solution are as follows: 1. The chemical composition design of this invention adopts C, Mn, and N solid solution strengthening, Ni refines austenite grains, and nickel expands the austenite phase region. Each 1% increase in nickel can reduce Ms (martensite transformation temperature) by about 20°C. Mn is also an element that expands the austenite phase region, and at the same time, it does not form carbides with carbon, thus ensuring the proportion of austenite structure at a temperature of -269°C. Molybdenum is used to form stable carbides, effectively refine the grain structure, significantly improve the hardenability and tempering stability of steel, and reduce brittleness during high-temperature tempering. 2. The present invention has a yield strength ≥550MPa, tensile strength 700MPa~850MPa, elongation A ≥27%, and average transverse impact energy ≥80J at -269℃. It exhibits excellent strength-toughness ratio, high elongation, superior formability, fracture resistance, and high energy absorption capacity. The microstructure consists of 90%~92% tempered troostite + undissolved ferrite + austenite, resulting in a stable and uniform microstructure and good overall uniformity of the steel plate. The small amount of undissolved ferrite and reverse-transformed austenite in the microstructure effectively improves the ultra-low temperature impact toughness of the steel plate. 2. The steel plate produced by this invention has a low yield strength ratio and good strength and toughness properties, especially excellent ultra-low temperature (-269℃) impact toughness. It effectively solves the problems of brittle martensite precipitation, low strength, and thick wall thickness in stainless steel at -169℃. It can replace stainless steel and be widely used in the manufacture of large ultra-low temperature liquid hydrogen storage tanks, with broad application prospects. Detailed Implementation

[0020] A method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks includes smelting, continuous casting, heating, rolling, and heat treatment processes; the specific process steps are as follows: (1) Smelting process: The molten steel is first smelted in the primary smelting furnace, and the tapping temperature is 1610~1630℃. After slag removal, it is refined in the LF furnace to complete the Mn and Mo alloying. When the ladle temperature is ≤1610℃, the ladle is lifted and vacuum treated in the VD furnace. The vacuum degree during vacuum treatment is ≤66Pa and the vacuum holding time is ≥20min.

[0021] (2) Continuous casting process: The molten steel after smelting is continuously cast. The superheat of the molten steel is 10℃~20℃, the billet pulling speed is 0.65min / mm~0.75min / mm, and electromagnetic stirring and dynamic light pressure technology are used in the casting process. The continuously cast billets are stacked and slowly cooled for ≥36h.

[0022] (3) Heating process: The continuous casting billet is heated in a continuous heating furnace with a maximum heating temperature of 1200℃~1230℃, a holding temperature of 1210~1230℃, and a total heating time of ≥12.5min / mm; (4) Rolling process: A two-stage rolling process is adopted. The first stage is the austenite recrystallization stage. The initial rolling temperature is 1100℃~1150℃, the single-pass reduction is 20%~30%, the final rolling temperature is 970℃~1000℃, and the cumulative reduction rate is 30%~50%. The second stage is the austenite non-recrystallization stage. The initial rolling temperature is ≤960℃, the single-pass reduction is 10%~30%, the cumulative reduction rate is 30%~50%, the final rolling temperature is 850℃~920℃, and after rolling, the ACC water cooler is set to 600℃~750℃.

[0023] (5) Heat treatment process: The process of two-stage quenching and tempering is adopted. The first quenching is 800℃~810℃, and the holding time is 2.0min / mm~2.5min / mm (calculated based on the thickness of the steel plate in mm). After the steel plate is removed from the furnace, it is water-cooled and the red temperature is ≤200℃. The second quenching is 650℃~660℃, and the holding time is 2.0min / mm~2.5min / mm (calculated based on the thickness of the steel plate in mm). After the steel plate is removed from the furnace, it is water-cooled and the red temperature is ≤200℃. The tempering temperature is 450℃~480℃, the total heating time is 4min / mm, and the total heating time must be ≥70min. After the steel plate is removed from the furnace and air-cooled, the finished steel plate is obtained.

[0024] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0025] This embodiment describes a 15Ni steel for an ultra-low temperature liquid hydrogen storage tank. The chemical composition and mass percentage of the steel plate are shown in Table 1. The metallographic structure is 90% tempered troostite + undissolved ferrite + austenite.

[0026] This embodiment describes a method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks, including smelting, continuous casting, heating, and rolling processes; the specific process steps are as follows: (1) Smelting process: The molten steel is first smelted in the primary smelting furnace and then sent to the LF refining furnace for refining. The slag volume is increased and the slag is flowed multiple times to facilitate P removal. The tapping temperature is 1610℃. After slag removal, the steel is refined in the LF furnace to complete Mn and Mo alloying. The ladle is hoisted when the temperature is 1600℃. The VD furnace is vacuum treated. The vacuum degree is 66Pa during the vacuum treatment. The total vacuum holding time is 21min. (2) Casting process: The molten steel after smelting is continuously cast. The continuous casting process adopts low superheat casting, the superheat of the molten steel is 18℃, the billet pulling speed is 0.70min / mm, the casting process is carried out with electromagnetic stirring and dynamic light reduction technology; the continuously cast billets are stacked and slowly cooled for 36h. (3) Heating process: The continuous casting billet is heated in a continuous heating furnace with a maximum heating temperature of 1230℃, a holding temperature of 1210℃, and a total heating time of 13.0 min / mm; (4) Rolling process: A two-stage rolling process is adopted. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1210℃, a reduction of 20% in the first three passes, a reduction of 10% in a single pass, a final rolling temperature of 980℃, and a cumulative reduction rate of 40%. The second stage is the austenite non-recrystallization stage, with an initial rolling temperature of 960℃, a reduction of 12% in a single pass, a cumulative reduction rate of 45%, and a final rolling temperature of 880℃. After rolling, a semi-finished steel plate is obtained, which is then water-cooled to 655℃ by ACC after rolling. (5) Heat treatment process: First quenching temperature 805℃, holding temperature 2.2 min / mm, water cooling after exiting the furnace, reddening temperature 180℃; Second quenching temperature 655℃, holding temperature 2.2 min / mm, water cooling after exiting the furnace, reddening temperature 185℃; Tempering temperature 450℃, total heating time 70 min, finished steel plate is obtained after air cooling after exiting the furnace.

[0027] The performance indicators of the 15Ni steel plate for the cryogenic liquid hydrogen storage tank in this embodiment are shown in Tables 2 and 3. Example 2

[0028] This embodiment describes a 15Ni steel for an ultra-low temperature liquid hydrogen storage tank. The chemical composition and mass percentage of the steel plate are shown in Table 1. The metallographic structure is 92% tempered troostite + undissolved ferrite + austenite.

[0029] This embodiment describes a method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks, including smelting, continuous casting, heating, and rolling processes; the specific process steps are as follows: (1) Smelting process: The molten steel is first smelted in the primary smelting furnace and then sent to the LF refining furnace for refining. The slag volume is increased and the slag is flowed multiple times to facilitate P removal. The tapping temperature is 1625℃. After slag removal, the steel is refined in the LF furnace to complete Mn and Mo alloying and then carry out metallic manganese alloying. The ladle is hoisted when the temperature is 1605℃ and the VD furnace is vacuum treated. The vacuum degree is 66Pa and the total vacuum holding time is 20min. (2) Casting process: The molten steel after smelting is continuously cast. The continuous casting process adopts low superheat casting, the superheat of the molten steel is 19℃, the billet pulling speed is 0.65min / mm, the casting process is carried out with electromagnetic stirring and dynamic light reduction technology; the continuously cast billets are stacked and slowly cooled for 36h. (3) Heating process: The continuous casting billet is heated in a continuous heating furnace with a maximum heating temperature of 1230℃ and a holding temperature of 1230℃. The total heating time is 12min / mm. (4) Rolling process: A two-stage rolling process is adopted. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1150℃, a reduction of 20% in the first three passes, a reduction of 10% in a single pass, a final rolling temperature of 980℃, and a cumulative reduction rate of 43%. The second stage is the austenite non-recrystallization stage, with an initial rolling temperature of 955℃, a reduction of 11% in a single pass, a cumulative reduction rate of 38%, a final rolling temperature of 890℃, and ACC water cooling to 700℃. (5) Heat treatment process: First quenching temperature 800℃, holding temperature 2.3 min / mm, water cooling after exiting the furnace, reddening temperature 175℃; Second quenching temperature 668℃, holding temperature 2.3 min / mm, water cooling after exiting the furnace, reddening temperature 185℃; Tempering temperature 465℃, total heating time 100 min, finished steel plate is obtained after air cooling after exiting the furnace.

[0030] The performance indicators of the 15Ni steel plate for the cryogenic liquid hydrogen storage tank in this embodiment are shown in Tables 2 and 3. Example 3

[0031] This embodiment describes a 15Ni steel for an ultra-low temperature liquid hydrogen storage tank. The chemical composition and mass percentage of the steel plate are shown in Table 1. The metallographic structure is 91% tempered troostite + undissolved ferrite + austenite.

[0032] This embodiment describes a method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks, including smelting, continuous casting, heating, and rolling processes; the specific process steps are as follows: (1) Smelting process: The molten steel is first smelted in the primary smelting furnace and then sent to the LF refining furnace for refining. The slag volume is increased and the slag is flowed multiple times to facilitate P removal. The tapping temperature is 1620℃. After slag removal, the steel is refined in the LF furnace to complete Mn and Mo alloying. The ladle is lifted when the temperature is 1630℃ and vacuum treatment is performed in the VD furnace. The vacuum degree is 66Pa and the total vacuum holding time is 20min. (2) Casting process: The molten steel after smelting is continuously cast. The continuous casting process adopts low superheat casting, the superheat of the molten steel is 20℃, the billet pulling speed is 0.75min / mm, the casting process is carried out with electromagnetic stirring and dynamic light reduction technology; the continuously cast billets are stacked and slowly cooled for 36h. (3) Heating process: The continuous casting billet is heated in a continuous heating furnace with a maximum heating temperature of 1230℃, a holding temperature of 1225℃, and a total heating time of 12.5min / mm; (4) Rolling process: A two-stage rolling process is adopted. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1150℃, a reduction of 20% in the first three passes, a reduction of 10% in a single pass, a final rolling temperature of 980℃, and a cumulative reduction rate of 40%. The second stage is the austenite non-recrystallization stage, with an initial rolling temperature of 955℃, a reduction of 12% in a single pass, a cumulative reduction rate of 45%, a final rolling temperature of 910℃, and ACC water cooling to 650℃ after rolling. (5) Heat treatment process: First quenching temperature 810℃, holding temperature 2.5 min / mm, water cooling after exiting the furnace, reddening temperature 195℃; Second quenching temperature 660℃, holding temperature 2.5 min / mm, water cooling after exiting the furnace, reddening temperature 200℃; Tempering temperature 450℃, total heating time 160 min, finished steel plate is obtained after air cooling after exiting the furnace.

[0033] The performance indicators of the 15Ni steel plate for the cryogenic liquid hydrogen storage tank in this embodiment are shown in Tables 2 and 3. Example 4

[0034] This embodiment describes a 15Ni steel for an ultra-low temperature liquid hydrogen storage tank. The chemical composition and mass percentage of the steel plate are shown in Table 1. The metallographic structure is 90% tempered troostite + undissolved ferrite + austenite.

[0035] This embodiment describes a method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks, including smelting, continuous casting, heating, and rolling processes; the specific process steps are as follows: (1) Smelting process: The molten steel is first smelted in the primary smelting furnace and then sent to the LF refining furnace for refining. The slag volume is increased and the slag is flowed multiple times to facilitate P removal. The tapping temperature is 1620℃. After slag removal, the steel is refined in the LF furnace to complete Mn and Mo alloying. When the ladle temperature is 1600℃, the ladle is vacuum treated in the VD furnace. The vacuum degree is 66Pa and the total vacuum holding time is 21min. (2) Casting process: The molten steel after smelting is continuously cast. The continuous casting process adopts low superheat casting, the superheat of the molten steel is 20℃, the billet pulling speed is 0.68min / mm, the casting process is carried out with electromagnetic stirring and dynamic light reduction technology; the continuously cast billets are stacked and slowly cooled for 36h. (3) Heating process: The continuous casting billet is heated in a continuous heating furnace with a maximum heating temperature of 1200℃, a holding temperature of 1230℃, and a total heating time of 12.5min / mm; (4) Rolling process: A two-stage rolling process is adopted. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1150℃, a reduction of 20% in the first three passes, a reduction of 10% in a single pass, a final rolling temperature of 985℃, and a cumulative reduction rate of 40%. The second stage is the austenite non-recrystallization stage, with an initial rolling temperature of 960℃, a reduction of 13% in a single pass, a cumulative reduction rate of 46%, a final rolling temperature of 880℃, and ACC water cooling to 610℃ after rolling.

[0036] (5) Heat treatment process: First quenching temperature 800℃, holding temperature 2.2 min / mm, water cooling after exiting the furnace, reddening temperature 120℃; Second quenching temperature 660℃, holding temperature 2.2 min / mm, water cooling after exiting the furnace, reddening temperature 125℃; Tempering temperature 480℃, total heating time 70 min, finished steel plate is obtained after air cooling after exiting the furnace.

[0037] The performance indicators of the 15Ni steel plate used in the cryogenic liquid hydrogen storage tank of this embodiment are shown in Tables 2 and 3. Example 5

[0038] This embodiment describes a 15Ni steel for an ultra-low temperature liquid hydrogen storage tank. The chemical composition and mass percentage of the steel plate are shown in Table 1. The metallographic structure is 91.5% tempered troostite + undissolved ferrite + austenite.

[0039] This embodiment describes a method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks, including smelting, continuous casting, heating, and rolling processes; the specific process steps are as follows: (1) Smelting process: The molten steel is first smelted in the primary smelting furnace and then sent to the LF refining furnace for refining. The slag volume is increased and the slag is flowed multiple times to facilitate P removal. The tapping temperature is 1620℃. After slag removal, the steel is refined in the LF furnace to complete Mn and Mo alloying. When the ladle temperature is 1600℃, the ladle is vacuum treated in the VD furnace. The vacuum degree is 66Pa and the total vacuum holding time is 20min. (2) Casting process: The molten steel after smelting is continuously cast. The continuous casting process adopts low superheat casting, the superheat of the molten steel is 10℃, the billet pulling speed is 0.65min / mm, the casting process is carried out with electromagnetic stirring and dynamic light reduction technology; the continuously cast billets are stacked and slowly cooled for 36h. (3) Heating process: The continuous casting billet is heated in a continuous heating furnace with a maximum heating temperature of 1230℃ and a holding temperature of 1230℃. The total heating time is 12min / mm. (4) Rolling process: A two-stage rolling process is adopted. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1100℃, a reduction of 20% in the first three passes, a reduction of 10% in a single pass, a final rolling temperature of 985℃, and a cumulative reduction rate of 40%. The second stage is the austenite non-recrystallization stage, with an initial rolling temperature of 960℃, a reduction of 10% in a single pass, a cumulative reduction rate of 40%, a final rolling temperature of 880℃, and ACC water cooling to 680℃ after rolling. (5) Heat treatment process: First quenching temperature 905℃, holding temperature 2.0 min / mm, water cooling after exiting the furnace, reddening temperature 180℃; Second quenching temperature 655℃, holding temperature 2.0 min / mm, water cooling after exiting the furnace, reddening temperature 185℃; Tempering temperature 470℃, total heating time 120 min, finished steel plate is obtained after air cooling after exiting the furnace.

[0040] The performance indicators of the 15Ni steel plate used in the cryogenic liquid hydrogen storage tank of this embodiment are shown in Tables 2 and 3. Example 6

[0041] This embodiment describes a 15Ni steel for an ultra-low temperature liquid hydrogen storage tank. The chemical composition and mass percentage of the steel plate are shown in Table 1. The metallographic structure is 92% tempered troostite + undissolved ferrite + austenite.

[0042] This embodiment describes a method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks, including smelting, continuous casting, heating, and rolling processes; the specific process steps are as follows: (1) Smelting process: The molten steel is first smelted in the primary smelting furnace and then sent to the LF refining furnace for refining. The slag volume is increased and the slag is flowed multiple times to facilitate P removal. The tapping temperature is 1630℃. After slag removal, the steel is refined in the LF furnace to complete Mn and Mo alloying. When the ladle temperature is 1600℃, the ladle is vacuum treated in the VD furnace. The vacuum degree is 66Pa and the total vacuum holding time is 21min. (2) Casting process: The molten steel after smelting is continuously cast. The continuous casting process adopts low superheat casting, the superheat of the molten steel is 18℃, the billet pulling speed is 0.71min / mm, the casting process is carried out with electromagnetic stirring and dynamic light reduction technology; the continuously cast billet is stacked and slowly cooled for 36h. (3) Heating process: The continuous casting billet is heated in a continuous heating furnace with a maximum heating temperature of 1230℃, a holding temperature of 1220℃, and a total heating time of 12.5min / mm; (4) Rolling process: A two-stage rolling process is adopted. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1100℃, a reduction of 20% in the first three passes, a single-pass reduction of 10%, a final rolling temperature of 985℃, and a cumulative reduction rate of 40%. The second stage is the non-recrystallization stage of austenite, with an initial rolling temperature of 955℃, a single-pass reduction of 12%, a cumulative reduction rate of 45%, a final rolling temperature of 885℃, and ACC water cooling to 720℃ after rolling. (5) Heat treatment process: First quenching temperature 905℃, holding temperature 2.5 min / mm, water cooling after exiting the furnace, reddening temperature 190℃; Second quenching temperature 655℃, holding temperature 2.5 min / mm, water cooling after exiting the furnace, reddening temperature 185℃; Tempering temperature 460℃, total heating time 80 min, finished steel plate is obtained after air cooling after exiting the furnace.

[0043] The performance indicators of the 15Ni steel plate used in the cryogenic liquid hydrogen storage tank of this embodiment are shown in Tables 2 and 3.

[0044] Table 1 Chemical composition and mass percentage (%) of 15Ni steel plates used in liquid hydrogen storage tanks of Examples 1-6

[0045] Note: The balance of components in Table 1 represents Fe and unavoidable impurities.

[0046] Table 2 Performance Indicators of 15Ni Steel Plates Used in Liquid Hydrogen Storage Tanks of Examples 1-6

[0047] Table 3 Performance indicators of 15Ni steel plates used in liquid hydrogen storage tanks of Examples 1-6

[0048] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A type of 15Ni steel for cryogenic liquid hydrogen storage tanks, characterized in that, The chemical composition and mass percentage of the 15Ni steel plate are as follows: C: 0.02%–0.07%, Si: 0.10%–0.30%, Mn: 0.20%–0.80%, Mo: 0.15%–0.30%, Al: 0.020%–0.050%, Ni: 12.5%–15.5%, N: 0.0015%–0.0060%, P≤0.008%, S≤0.002%, Nb≤0.020%, V≤0.080%, Ti≤0.020%, with the balance being Fe and unavoidable impurities.

2. The 15Ni steel for a cryogenic liquid hydrogen storage tank according to claim 1, characterized in that, The steel plate has a thickness of ≤40mm and a metallographic structure of 90%~92% tempered troostite + undissolved ferrite + austenite.

3. The 15Ni steel for a cryogenic liquid hydrogen storage tank according to claim 1, characterized in that, The steel plate has a yield strength of ≥550MPa at room temperature, a tensile strength of 700MPa~850MPa, an elongation A of ≥27%, and an average transverse impact energy of ≥80J at -269℃.

4. A method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks according to any one of claims 1-3, characterized in that, The preparation method includes smelting, continuous casting, heating, rolling and heat treatment processes; the rolling process adopts a two-stage rolling process. The heat treatment process employs a two-stage quenching and tempering process. The first quenching is at 800℃~810℃, held for 2.0min / mm~2.5min / mm, followed by water cooling after removal from the furnace, with a reddening temperature ≤200℃. The second quenching is at 650℃~660℃, held for 2.0min / mm~2.5min / mm (calculated based on the steel plate thickness in mm), followed by water cooling after removal from the furnace, with a reddening temperature ≤200℃. The tempering temperature is 450℃~480℃, with a total heating time of 4min / mm, and the total heating time must be ≥70min. After air cooling after removal from the furnace, the finished steel plate is obtained.

5. The method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks according to claim 4, characterized in that, In the smelting process, the molten steel is first smelted in a primary smelting furnace at a tapping temperature of 1610℃~1630℃. After slag removal, it is refined in an LF furnace to complete Mn and Mo alloying. When the ladle temperature is ≤1610℃, the ladle is lifted and vacuum treated in a VD furnace. During vacuum treatment, the vacuum degree is ≤66Pa and the vacuum holding time is ≥20min.

6. The method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks according to claim 4, characterized in that, In the continuous casting process, the molten steel is continuously cast after smelting, with a superheat of 10℃~20℃ and a billet pulling speed of 0.65min / mm~0.75min / mm. Electromagnetic stirring and dynamic light reduction technology are used in the casting process. The continuously cast billets are stacked and slowly cooled for ≥36h.

7. A method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks according to any one of claims 4-6, characterized in that, In the heating process, the continuously cast billet is heated in a continuous heating furnace with a maximum heating temperature of 1200℃~1230℃, a holding temperature of 1210~1230℃, and a total heating time of ≥12.5min / mm.

8. A method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks according to any one of claims 4-6, characterized in that, The rolling process adopts a two-stage rolling process. The first stage is the austenite recrystallization stage, with an initial rolling temperature of 1100℃~1150℃, a single-pass reduction of 20%~30%, a final rolling temperature of 970℃~1000℃, and a cumulative reduction rate of 30%~50%.

9. A method for preparing 15Ni steel for cryogenic liquid hydrogen storage tanks according to any one of claims 4-6, characterized in that, The rolling process adopts a two-stage rolling process. The second stage is the austenite non-recrystallization stage. The initial rolling temperature is ≤960℃, the single-pass reduction is 10%~30%, the cumulative reduction rate is 30%~50%, the final rolling temperature is 850℃~920℃, and the ACC water cooling after rolling is 600℃~750℃.

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