Nickel-free low-temperature steel applied to LNG storage tank and preparation method therefor

Abstract

A nickel-free low-temperature steel applied to an LNG storage tank and a preparation method therefor. The low-temperature steel comprises the following components in percentage by mass: C: 0.01-0.06%; Si: 0.1-0.2%; Mn: 22.0-28.0%; Al: 3.5-4.5%; Ti: 0.01-0.08%; Nb: 0.01-0.06%; Mo: 0.05-0.15%; P≤0.010%; S≤0.006%; N≤0.005%; and the balance being iron and inevitable impurities. The impact absorption energy of the low-temperature steel at room temperature reaches 260 J or more, and the impact absorption energy at -196°C reaches 190 J or more, solving the problem of poor low-temperature toughness of conventional austenitic low-temperature steel.

Description

Nickel-free low-temperature steel applied to LNG storage tank and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of steel materials, and in particular to a nickel-free low-temperature steel applied to LNG storage tanks and a preparation method thereof. BACKGROUND

[0002] In recent years, the proportion of natural gas in the energy consumption structure is increasing, and the demand is also increasing year by year. Under normal pressure, if gaseous natural gas is cooled to below -162 DEG C to condense into liquefied natural gas (LNG), its volume is only 1 / 600 of the original gaseous volume, which can greatly improve the storage and transportation efficiency and reduce the use cost. At present, the transportation and storage of liquefied natural gas mainly rely on LNG vehicles, LNG ships and large LNG receiving stations. The large-scale exploitation and application of natural gas provide a broad market and development opportunity for the energy storage and transportation equipment manufacturing industry under low-temperature service conditions, and also promote the development of low-temperature steel for LNG storage tanks.

[0003] The LNG storage tank is generally composed of two layers of steel shells, and the middle is filled with thermal insulation materials. The inner tank material is directly in contact with liquid natural gas, so it is required to have good low-temperature toughness, sufficient strength, good process performance, processing performance and corrosion resistance at -162 DEG C. The 9% Ni steel alloy element has low cost, good welding performance, and still has good comprehensive mechanical properties at -196 DEG C. Therefore, the 9% Ni steel gradually replaces aluminum alloy, austenitic stainless steel and Ni-Cr alloy and becomes the main material for LNG storage tanks.

[0004] As for the existing low-temperature steel, Ni is the most basic and important alloying element, which can improve the strength and toughness matching of ferrite phase and increase the toughness through the way of stabilizing austenite phase, so that the ductile-brittle transition temperature is significantly reduced, but the large amount of addition of Ni increases the material cost. In addition, the low yield strength is another technical problem of single-phase austenitic low-temperature steel; and the existing high-manganese austenitic low-temperature steel also has the problems of poor low-temperature toughness, low yield strength, performance anisotropy and the like.

[0005] SUMMARY

[0006] To solve the above problems, in one aspect, the application provides a nickel-free cryogenic steel applied to LNG storage tanks, which comprises the following components in percentage by mass: C: 0.01-0.06%; Si: 0.1-0.2%; Mn: 22.0-28.0%; Al: 3.5-4.5%; Ti: 0.01-0.08%; Nb: 0.01-0.06%; Mo: 0.05-0.15%; P≤0.010%; S≤0.006%; N≤0.005%; and the rest is iron and inevitable impurities.

[0007] Further, the room temperature structure of the cryogenic steel is single-phase austenite.

[0008] A large number of nanoscale carbon nitride precipitation particles are dispersedly distributed on the austenite matrix, and the stacking fault energy of the austenite is between 25-55 mJ / m 2 , and the plastic deformation mechanism is mainly twinning-induced plasticity (TWIP).

[0009] Further, the density of the cryogenic steel is ≤7.2 g / cm 3 .

[0010] The yield strength of the cryogenic steel is 440-500 MPa, the tensile strength is 650-750 MPa, the elongation after fracture is 45-58%, the yield strength ratio is ≤0.68, the room temperature impact absorption energy is ≥260 J, the -196 ℃ impact absorption energy is ≥190 J, the density of the cryogenic steel itself is ≤7.2 g / cm 3 , and the weight reduction relative to pure iron is >8.5%.

[0011] In another aspect, the application further provides a preparation method of the nickel-free cryogenic steel applied to LNG storage tanks as described above, which comprises the following steps:

[0012] (1) forging: forging the cast blank into a forged blank with a thickness of 60-80 mm;

[0013] (2) hot rolling: uniformly treating the forged blank at 1150-1200 ℃ for 60-120 min, and then performing multi-pass hot rolling, and cooling to room temperature to obtain a hot-rolled plate with a thickness of 10-15 mm;

[0014] (3) tempering: heating the hot-rolled plate to 650-720 ℃, holding for 30-60 min, and then cooling to room temperature.

[0015] Further, in step 2, the hot rolling temperature of the forged blank is 950-1100 ℃.

[0016] Further, in step 2, the single-pass hot rolling deformation of the forged blank is >15%, the strain rate is >15 s -1 , and the total reduction is >80%.

[0017] Further, in step 2, the calcined billet is cooled to room temperature by water quenching after hot rolling, and the open cooling temperature of the hot-rolled billet is 900-950℃.

[0018] Further, in step 1, the forging temperature of the cast billet is 1000-1100℃.

[0019] Further, the preparation method of the cast billet comprises:

[0020] melting the metal raw material;

[0021] casting the molten steel obtained by melting into a casting mold to obtain a cast billet with the same chemical composition as the low-temperature steel.

[0022] The component design idea of the nickel-free low-temperature steel in the application is as follows:

[0023] Mn and Ni are both austenite stabilizing elements, which can expand the austenite phase region and increase the content of austenite in the room temperature structure, and even make the room temperature structure of the steel single-phase austenite. Replacing nickel with manganese can greatly reduce the alloy cost of the low-temperature steel and improve the economy of the low-temperature steel. However, due to the high C content of the steel, the impact toughness of the steel at-196℃ is often difficult to reach the performance standard of the traditional 9%Ni steel; therefore, the application proposes a nickel-free low-temperature steel applied to LNG storage tanks.

[0024] The mass fraction of C is 0.01-0.06%, and the ultra-low carbon design is mainly to avoid the segregation of C elements at the austenite grain boundary during hot forming, inhibit the precipitation of brittle carbides and inclusions at the austenite grain boundary, so as to ensure that the low-temperature steel has good low-temperature toughness; at the same time, the ultra-low carbon design can also make the low-temperature steel have good cold forming performance and welding performance.

[0025] The mass fraction of Si is 0.1-0.2%, and the main role of Si is to ensure the tensile strength of the low-temperature steel through solid solution strengthening, secondly, appropriate Si content can inhibit the segregation of Mn and P, which is beneficial to improve the low-temperature toughness of the low-temperature steel. In addition, low Si design is beneficial to improve the weldability, cold formability and fatigue resistance of the low-temperature steel.

[0026] The mass fraction of Mn is 22.0-28.0%, and Mn is the replacement element of Ni in the application, and high Mn design is mainly to expand the austenite phase region under the premise of ultra-low carbon design, improve the thermal stability of austenite at low temperature, and ensure that the room temperature structure of the low-temperature steel is single-phase austenite; high Mn content can also ensure the strength of the low-temperature steel through solid solution strengthening; in addition, with the increase of 1% Mn in the low-temperature steel, the density of the low-temperature steel can be reduced by 0.0085g / cm 3The high manganese design can also achieve a certain lightweight effect. Controlling the mass fraction of Mn to be within 32% can avoid the generation of brittle intermediate phase beta-Mn, and improve the strength of the low-temperature steel.

[0027] The mass fraction of Al is 3.5-4.5%, and Al can effectively improve the stacking fault energy of austenite and improve the mechanical stability of austenite at low temperature. Therefore, the medium aluminum design is mainly used to control the stacking fault energy of austenite to be within 25-55 mJ / m 2 2, and make the Gibbs free energy difference of martensitic phase change > 0 J / mol, so that the deformation mechanism is mainly TWIP, thereby ensuring that the low-temperature steel has good strength and plasticity matching at low temperature. In addition, the density of the low-temperature steel can be reduced by 0.101 g / cm 3 3 for every 1% increase in Al, and the weight of the low-temperature steel is reduced by about 1.3% compared with pure iron. Therefore, the medium aluminum design can also achieve a certain amount of lightweight of the low-temperature steel.

[0028] The mass fraction of Ti and Nb in the low-temperature steel is 0.01-0.08% and 0.01-0.06% respectively. Adding trace amounts of Ti and Nb mainly utilizes the precipitation strengthening of carbide particles to ensure the strength of the low-temperature steel. However, due to the low C content in the low-temperature steel, too high Ti and Nb content cannot play an effective strengthening effect, but can increase the alloy cost of the low-temperature steel. In addition, adding Ti and Nb elements to the low-temperature steel can increase the recrystallization temperature of the steel, so that the low-temperature steel can be rolled at a higher temperature, thereby improving the deformation storage energy and crystal defects in the deformed austenite structure, which provides nucleation sites for the precipitation of carbide particles, and further promotes the precipitation strengthening effect of the low-temperature steel.

[0029] The mass fraction of Mo is 0.05-0.15%, which can improve the diffusion activity of C atoms, promote the combination of Ti, Nb and C, and promote the precipitation of TiC, NbC and other precipitates with Mo atoms in a complex form. In addition, the addition of Mo can refine the size of the precipitate particles, so that Ti and Nb can play a better precipitation strengthening effect.

[0030] The mass fraction of P, S and N in the raw material is ≤0.010%, ≤0.006% and ≤0.005% respectively. P is easy to form serious segregation band and increase the band structure level of the low-temperature steel. S is easy to form MnS inclusions and segregation in high manganese steel. N is easy to form coarse liquid precipitation TiN with Ti in the high temperature zone, so that Ti in the low-temperature steel loses the precipitation strengthening effect. For high manganese austenitic low-temperature steel, the low-temperature toughness is very sensitive to the content of P, S and N. Therefore, the content of P, S and N in the steel should be controlled within the minimum range as much as possible.

[0031] In the preparation process of the low-temperature steel, the action mechanism of hot rolling and tempering process is as follows:

[0032] The forging blank is homogenized before hot rolling, the basic principle is to select lower heating temperature and shorter holding time as far as possible under the premise of ensuring complete austenitization and homogenization of alloying elements, and to prevent grain coarsening. For Al-deoxidized ultra-low carbon steel, uneven grain coarsening is easily caused when heated below 1100 DEG C, thereby deteriorating the performance of the steel. Therefore, the austenite homogenization temperature is controlled at 1150-1200 DEG C, and the holding time is controlled at 60-120 min. For austenitic steel, the main purpose of hot rolling is to obtain uniform and fine austenite grains through dynamic recovery and dynamic recrystallization, and to promote grain refinement after hot rolling from the genetic organization. The hot rolling temperature is controlled in the range of 950-1100 DEG C, which can ensure that the austenite is deformed in the complete recrystallization zone, the single-pass hot rolling deformation is > 15%, the strain rate is > 15 s -1 , the total reduction is > 80%, and the austenite grains can achieve good recrystallization refinement effect. Since the Mn and Al contents of the present application are high, the material has good hardenability, and the cast blank is water-cooled from 900-950 DEG C to room temperature after hot rolling, which can inhibit the generation of low-temperature transformation structure and coarse carbides during the cooling process, improve the low-temperature toughness of the low-temperature steel, and at the same time, the rapid cooling after hot rolling can also avoid the coarsening of austenite grains, which is beneficial to improve the comprehensive mechanical properties of the low-temperature steel.

[0033] Fine-grain strengthening and precipitation strengthening are two main strengthening ways of low-carbon microalloyed steel, and the dispersed precipitation particles of microalloying elements such as Nb and Ti can strengthen the matrix through the dragging effect on dislocations, and can also refine the grains through the pinning effect on grain boundaries, thereby improving the strength of the steel. However, water quenching after hot rolling is not conducive to the diffusion and precipitation of solid solution elements. Therefore, the hot-rolled plate is high-temperature tempered at 650-720 DEG C (austenite single-phase zone) and held for 30-60 min, mainly to promote the nanoscale carbonitride of microalloying elements such as Nb, Ti and Mo to precipitate, so as to further improve the precipitation strengthening effect of the material. In addition, for this high-manganese phase-change-free austenitic steel, tempering at 650-720 DEG C can prevent phase transformation and austenite grain coarsening, eliminate residual stress generated during quenching, eliminate segregation of elements such as C and Mn, thereby improving the uniformity of the structure and performance, and avoiding cracking of the steel plate during forming.

[0034] The present application has the following beneficial effects compared with the prior art due to the use of the above technical scheme:

[0035] 1) The low-temperature steel of the present application has a room temperature impact absorption energy of more than 260 J and an impact absorption energy at -196 DEG C of more than 190 J, solving the problem of poor low-temperature toughness of traditional austenitic low-temperature steel.

[0036] 2) The low-temperature steel of the present application has a yield strength of 440-500 MPa, a yield strength ratio of ≤0.68, and a post-break elongation of not less than 45-58%, thus solving the problem of low yield strength of traditional austenitic low-temperature steel without affecting plasticity.

[0037] 3) The low-temperature steel of the present application has better plasticity and low-temperature toughness than 9% Ni steel, and the alloy cost of the low-temperature steel is greatly reduced by using manganese instead of nickel, and the density of the low-temperature steel is reduced by more than 8.5% compared with pure iron by increasing the lattice constant and reducing the atomic weight, thus realizing the lightweight of the low-temperature steel. BRIEF DESCRIPTION OF DRAWINGS

[0038] Fig. 1 is an SEM microstructure morphology diagram of the low-temperature steel in Example 1 of the present application;

[0039] Fig. 2 is an EBSD microstructure morphology diagram of the low-temperature steel in Example 2 of the present application;

[0040] Fig. 3 is a TEM morphology diagram of the nano-precipitates formed on the austenitic matrix of the low-temperature steel in Example 3 of the present application. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0042] The present application provides a nickel-free low-temperature steel applied to LNG storage tanks, which comprises the following components in percentage by mass: C: 0.01-0.06%; Si: 0.1-0.2%; Mn: 22.0-28.0%; Al: 3.5-4.5%; Ti: 0.01-0.08%; Nb: 0.01-0.06%; Mo: 0.05-0.15%; P≤0.010%; S≤0.006%; N≤0.005%; and the rest is iron and inevitable impurities.

[0043] The low-temperature steel and the preparation method thereof will be further described below through Examples 1-3.

[0044] Example 1

[0045] The embodiment provides a nickel-free low-temperature steel applied to an LNG storage tank, which comprises the following components in percentage by mass: 0.05% of C, 0.2% of Si, 24.4% of Mn, 4.0% of Al, 0.06% of Ti, 0.03% of Nb, 0.1% of Mo, 0.007% of P, 0.005% of S, 0.003% of N, and the rest is iron and inevitable impurities.

[0046] The low-temperature steel has a single-phase austenite room-temperature metallographic structure, a yield strength of 455 MPa, a tensile strength of 675 MPa, a post-break elongation of 53%, a room-temperature impact absorption energy of 298 J, a -196 DEG C impact absorption energy of 206 J, and a density of 7.19 g / cm 3 , and a weight loss of 8.6% relative to pure iron.

[0047] The preparation method of the low-temperature steel in the embodiment is as follows:

[0048] Metal raw materials such as electrolytic manganese with a purity of 99.90%, high-purity aluminum blocks with a purity of 99.99%, graphite rods and industrial pure iron are put into a vacuum induction melting furnace for smelting according to a certain ratio, so that a molten steel with the same composition as the low-temperature steel is obtained, and the molten steel obtained through smelting is cast into a copper casting mold to obtain a casting blank.

[0049] The riser of the casting blank is cut off, the casting blank is heated to 1200 DEG C for homogenization treatment for 120 min, and then the casting blank is forged into a 80mm-thick forged blank at 1050-1100 DEG C.

[0050] The forged blank is heated to 1200 DEG C for homogenization treatment for 120 min, and then is sequentially subjected to 7 passes of hot rolling to obtain a 15mm-thick hot-rolled plate, the rolling mill reduction schedule is 80mm→68mm→54mm→44mm→35mm→28mm→21mm→15mm, the starting rolling temperature is 1083 DEG C, the final rolling temperature is 958 DEG C, the total reduction is 81.25%, and the hot-rolled plate is water quenched to room temperature after hot rolling, and the starting cooling temperature is 937 DEG C.

[0051] The quenched hot-rolled plate is heated to 680 DEG C in a vacuum induction heating furnace, is kept for 50 min, and then is air cooled to room temperature to obtain a low-temperature steel plate.

[0052] As shown in FIG. 1 of the accompanying drawings, the SEM microstructure diagram of the low-temperature steel after tempering treatment in the embodiment is shown, the microstructure type is equiaxed austenite, and a large number of annealing twins are distributed on the austenite matrix.

[0053] Embodiment 2

[0054] The embodiment provides a nickel-free low-temperature steel applied to an LNG storage tank, which comprises the following components in percentage by mass: 0.04% of C, 0.12% of Si, 25.2% of Mn, 4.4% of Al, 0.08% of Ti, 0.05% of Nb, 0.11% of Mo, 0.005% of P, 0.003% of S, 0.003% of N, and the rest is iron and inevitable impurities.

[0055] The low-temperature steel has a metallographic structure of single-phase austenite, a yield strength of 473 MPa, a tensile strength of 696 MPa, a post-break elongation of 54%, a room-temperature impact absorption energy of 295 J, a -196 DEG C impact absorption energy of 204 J, and a density of 7.14 g / cm 3 , and a weight loss of 9.3% relative to pure iron.

[0056] The preparation method of the low-temperature steel in the embodiment is as follows:

[0057] Metallic manganese with a purity of 99.90%, high-purity aluminum blocks with a purity of 99.99%, graphite rods, industrial pure iron and other metal raw materials are put into a vacuum induction melting furnace for smelting according to a certain ratio, so that molten steel with the same composition as the low-temperature steel is obtained, and the molten steel obtained by smelting is cast into a copper casting mold to obtain a casting blank.

[0058] The riser of the casting blank is cut off, the casting blank is heated to 1200 DEG C for homogenization treatment for 120 min, and then the casting blank is forged into a 80mm-thick forged blank at 1050-1100 DEG C.

[0059] The forged blank is heated to 1150 DEG C for homogenization treatment for 120 min, and then is sequentially subjected to 7-pass hot rolling to obtain a 15mm-thick hot-rolled plate, the rolling mill reduction schedule is 80mm→68mm→54mm→44mm→35mm→28mm→21mm→15mm, the starting rolling temperature is 1097 DEG C, the final rolling temperature is 954 DEG C, the total reduction is 83.3%, and the hot-rolled plate is water quenched to room temperature after hot rolling, and the starting cooling temperature is 931 DEG C.

[0060] The hot-rolled plate after quenching is heated to 720 DEG C in a vacuum induction heating furnace, is kept for 50 min, and then is air cooled to room temperature to obtain a low-temperature steel plate.

[0061] As shown in FIG. 2 of the accompanying drawings, the EBSD pattern of the microstructure of the low-temperature steel after tempering treatment in the embodiment is shown.

[0062] Embodiment 3

[0063] The embodiment provides a nickel-free low-temperature steel applied to an LNG storage tank, which comprises the following components in percentage by mass: 0.05% of C, 0.15% of Si, 24.8% of Mn, 4.2% of Al, 0.07% of Ti, 0.04% of Nb, 0.09% of Mo, 0.006% of P, 0.004% of S, 0.004% of N, and the rest is iron and inevitable impurities.

[0064] The low-temperature steel has a metallographic structure of single-phase austenite, a yield strength of 461 MPa, a tensile strength of 688 MPa, a post-break elongation of 52%, a room-temperature impact absorption energy of 289 J, a -196 DEG C impact absorption energy of 197 J, and a density of 7.17 g / cm 3 , and a weight loss of 8.9% relative to pure iron.

[0065] The preparation method of the low-temperature steel in the embodiment is as follows:

[0066] Metallic manganese with a purity of 99.90%, high-purity aluminum blocks with a purity of 99.99%, graphite rods, and industrial pure iron are put into a vacuum induction melting furnace according to a certain ratio to be smelted, so that the same molten steel as the low-temperature steel is obtained, and the molten steel obtained by smelting is cast into a copper casting mold to obtain a casting blank.

[0067] The riser of the casting blank is cut off, the casting blank is heated to 1200 DEG C for homogenization treatment for 120 min, and then the casting blank is forged into a 60 mm thick forged blank at 1050-1100 DEG C.

[0068] The forged blank is heated to 1150 DEG C for homogenization treatment for 120 min, and then is sequentially subjected to 6 passes of hot rolling to obtain a 10 mm thick hot-rolled plate, the rolling mill reduction schedule is 60 mm→51 mm→43 mm→35 mm→26 mm→18 mm→10 mm, the starting rolling temperature is 1092 DEG C, the final rolling temperature is 955 DEG C, the total reduction is 83.3%, and the hot-rolled plate is water quenched to room temperature after hot rolling, and the starting cooling temperature is 929 DEG C.

[0069] The hot-rolled plate after quenching is heated to 650 DEG C in a vacuum induction heating furnace, is kept for 60 min, and then is air cooled to room temperature to obtain a low-temperature steel plate.

[0070] As shown in FIG. 3 of the accompanying drawings, the TEM morphology of the nano-precipitates formed by micro-alloy elements on the austenite matrix of the low-temperature steel after tempering treatment is shown.

[0071] It should be understood by those skilled in the art that the present application can be implemented in many other specific forms without departing from the spirit and scope of the present application. Although the embodiments of the present application have been described, it should be understood that the present application should not be limited to this embodiment, and those skilled in the art can make changes and modifications within the spirit and scope of the present application as defined in the appended claims.

Claims

1. A nickel-free cryogenic steel for LNG storage tanks, characterized in that, comprises the following components by mass percent: C: 0.01-0.06%; Si: 0.1-0.2%; Mn: 22.0-28.0%; Al: 3.5-4.5%; Ti: 0.01-0.08%; Nb: 0.01-0.06%; Mo: 0.05-0.15%; P≤0.010%; S≤0.006%; N≤0.005%; and the balance being iron and inevitable impurities. comprises the following components by mass percent: C: 0.01-0.06%; Si: 0.1-0.2%; Mn: 22.0-28.0%; Al: 3.5-4.5%; Ti: 0.01-0.08%; Nb: 0.01-0.06%; Mo: 0.05-0.15%; P≤0.010%; S≤0.006%; N≤0.005%; and the balance being iron and inevitable impurities. comprises the following components by mass percent: C: 0.01-0.06%; Si: 0.1-0.2%; Mn: 22.0-28.0%; Al: 3.5-4.5%; Ti: 0.01-0.08%; Nb: 0.01-0.06%; Mo: 0.05-0.15%; P≤0.010%; S≤0.006%; N≤0.005%; and the balance being iron and inevitable impurities.

2. The nickel-free cryogenic steel for LNG storage tanks according to claim 1, characterized in that, The room temperature structure of the low-temperature steel is single-phase austenite.

3. The nickel-free cryogenic steel for LNG storage tanks according to claim 1, characterized in that, Density of the low-temperature steel is ≤ 7.2 g / cm 3 .

4. A method for producing a nickel-free cryogenic steel for LNG storage tanks according to any one of claims 1 to 3, characterized in that, comprises the following steps: (1) forging: forging the cast blank into a forged blank with a thickness of 60-80 mm; (2) hot rolling: homogenizing the forged blank at 1150-1200°C for 60-120 min, then performing multi-pass hot rolling, and cooling to room temperature to obtain a hot-rolled plate with a thickness of 10-15 mm; (3) tempering: heating the hot-rolled plate to 650-720°C, holding for 30-60 min, and then cooling to room temperature.

5. The method of producing a nickel-free cryogenic steel for LNG storage tanks according to claim 4, characterized in that, In step 2, the hot-rolling temperature of the forged blank is 950-1100°C.

6. The method of producing a nickel-free cryogenic steel for LNG storage tanks according to claim 4, characterized in that, In step 2, the single-pass hot rolling deformation of the forging blank is > 15%, the strain rate is > 15 s -1 , and the total reduction is > 80%.

7. The method of producing a nickel-free cryogenic steel for LNG storage tanks according to claim 4, characterized in that, In step 2, the forged blank is cooled to room temperature by water quenching after hot rolling, and the open-cooling temperature of the forged blank after hot rolling is 900-950°C.

8. The method of producing a nickel-free cryogenic steel for LNG storage tanks according to claim 4, characterized in that, In step 1, the forging temperature of the cast blank is 1000-1100°C.

9. The method of producing a nickel-free cryogenic steel for LNG storage tanks according to claim 4, characterized in that, The method for preparing the cast blank comprises: smelting a metal raw material; casting the molten steel obtained by smelting into a casting mold to obtain a cast blank with the same chemical composition as the low-temperature steel.

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