A steel plate for a crude oil storage tank having a yield strength of 690mpa and a method of manufacturing the same

Abstract

The present application provides a yield strength 690MPa crude oil storage tank steel plate and its manufacturing method, the composition of the steel plate is as follows in percentage by weight: C: 0.05%~0.10%, Si: 0.10%~0.30%, Mn: 1.00%~2.00%, P: ≤0.010%, S: ≤0.005%, V: 0.10%~0.20%, Ti: 0.05%~0.10%, Al: 0.0025%~0.0045%, N: 0.002%~0.006%, B: 0.0005%~0.0015%, W: 0.002%~0.004%, the balance is Fe and inevitable impurities; the manufacturing method comprises smelting, continuous casting, heating, rolling, heat treatment; the steel plate produced by the application is bainite tempering structure, the carbide size in the structure is between 1~4μm, and is uniformly distributed, eliminating the damage of massive ferrite to the strength of the steel plate, so that the steel plate has good strength and toughness ratio, still has excellent strength and toughness after simulated post-weld heat treatment; after large line energy 70~110kJ / cm large line welding, the performance of the heat affected zone is: yield strength R eL ≥690MPa, tensile strength R m : 750~880MPa, elongation A ≥18%, -20℃KV2≥80J.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and particularly relates to a steel plate for crude oil storage tanks with a yield strength of 690 MPa and its manufacturing method. Background Technology

[0002] Petroleum is a vital energy pillar for the development of every nation, and strategic petroleum reserves are the primary means of ensuring petroleum security. Petroleum influences various aspects of my country's national economic development and the improvement of people's quality of life. Crude oil, in particular, has a large demand and wide application, and its inherent flammability, explosiveness, and volatility mean that its transportation and storage are always accompanied by risks. Storage tanks, with their advantages of small surface area, light weight, short manufacturing cycle, and small footprint, are a widely used gas-liquid storage container in the petrochemical industry. Therefore, with the steady growth of my country's petroleum demand and the continuous strengthening of petroleum reserves, the construction of reserve depots and large crude oil storage tanks has reached an unprecedented peak.

[0003] While the industrial production technology for steel used in domestic crude oil storage tanks and the manufacturing technology for large tanks have become largely mature, the construction of ultra-large oil storage tanks with a capacity of 150,000 cubic meters is urgently needed as crude oil storage tanks gradually develop towards larger sizes and higher parameters. However, the use of older grades of high-strength steel for crude oil storage tanks results in excessively thick steel plates, making welding difficult and hindering tank construction. Furthermore, the production of these steel plates wastes the capacity of existing advanced medium-thick plate rolling mills on production lines, increasing process costs and delivery times. Therefore, based on this demand, it is necessary to develop a new type of steel plate for crude oil storage tanks that not only possesses high strength and toughness but also excellent comprehensive performance. Currently, existing domestic steel plates for crude oil storage tanks cannot meet the high strength requirements; therefore, researching a steel plate for crude oil storage tanks with a yield strength of 690 MPa has become an urgent task for the steel industry.

[0004] The patent document "Heat Treatment Method for Thin-gauge Quenched and Tempered 12MnNiVR Steel Plate" (CN108265161A) uses a conventional quenching and tempering heat treatment process, but its yield strength is difficult to reach 690MPa, which cannot meet the requirements.

[0005] The patent document "High-strength and Toughness Steel Plate for Crude Oil Storage Tanks with Low Welding Crack Sensitivity Coefficient and Resistance to High-Temperature PWHT Softening and its Manufacturing Method" (CN105671436A) has the following chemical composition: C 0.07-0.12%, Si 0.15-0.30%, Mn 1.40-1.60%, S≤0.010%, P≤0.015%, Mo 0.05-0.15%, Ni 0.20-0.35%, Nb 0.015-0.035%, V 0.030-0.060%, Ti 0.010-0.030%, Alt 0.015-0.045%, with the remainder being Fe and unavoidable trace impurities. The steel produced by this design composition and manufacturing process cannot meet the yield strength of 690MPa, and the heat treatment time is relatively long, affecting production efficiency.

[0006] The patent document "Steel Plate for Large Thickness Ultra-Low Temperature High Toughness Spherical Tank and its Rolling Method" (CN112795839A) designs a chemical composition of C: 0.06-0.09%, Si≤0.55%, Mn 1.30-1.60%, P≤0.012%, S≤0.005%, Ni 0.40-0.70%, Nb 0.020-0.030%, Alt 0.020-0.050%, with the balance being Fe and other elements. However, the strength of the designed large-thickness steel plate is lower than the designed yield strength of 690MPa, and the mechanical properties of the thick steel plate after welding heat treatment are difficult to guarantee, affecting subsequent processing.

[0007] Therefore, in view of the above situation, it is urgent to develop a new type of high-strength steel by adjusting the manufacturing method and designing new components, and to develop a steel plate for crude oil storage tanks with a yield strength of 690MPa and its manufacturing method. Summary of the Invention

[0008] The purpose of this invention is to overcome the above-mentioned problems and deficiencies and provide a crude oil storage tank steel plate with a yield strength of 690 MPa, which has a bainitic tempered structure, eliminates the damage of ferrite to the strength of the steel plate, has a good strength-toughness ratio, good high heat input welding performance, and a bainitic tempered structure, as well as a method for manufacturing the same.

[0009] The objective of this invention is achieved as follows:

[0010] A steel plate for crude oil storage tanks with a yield strength of 690 MPa, the steel plate having the following composition by weight percentage: C: 0.05%–0.10%, Si: 0.10%–0.30%, Mn: 1.00%–2.00%, P: ≤0.010%, S: ≤0.005%, V: 0.10%–0.20%, Ti: 0.05%–0.10%, Al: 0.0025%–0.0045%, N: 0.002%–0.006%, B: 0.0005%–0.0015%, W: 0.002%–0.004%, with the balance being Fe and unavoidable impurities.

[0011] Furthermore, in the steel plate, V / C = 1.5 to 3.5.

[0012] Furthermore, the microstructure of the steel plate is a bainitic tempered structure, and the carbide size in the structure is 1-4 μm.

[0013] Furthermore, the steel plate has a thickness of 10–50 mm and a yield strength R. eL ≥700MPa, tensile strength R m 800~920MPa, elongation A≥18%, KV2≥100J at -20℃; simulated mechanical yield strength Re of steel plate after post-weld heat treatment. L ≥690MPa, tensile strength R m 780~900MPa, elongation A≥18%, KV2≥100J at -20℃.

[0014] Furthermore, the heat-affected zone properties of the steel plate after welding with a high heat input of 70-110 kJ / cm: yield strength R eL ≥690MPa, tensile strength R m 750~880MPa, elongation A≥18%, KV2≥80J at -20℃.

[0015] The rationale for this invention is as follows:

[0016] C: In steel, C forms various carbides or solid solutions with alloying elements to strengthen the steel. It is an element that directly improves the strength of steel plates. However, excessive C content leads to high Pcm and CEV, resulting in poor toughness and weldability. Therefore, to ensure a good balance of low-temperature toughness, high strength, and weldability in steel plates during use, the C content is limited to 0.05-0.10%.

[0017] Si: Si is an element in steel that increases carbon activity, inhibits carbide coarsening, and can dissolve in ferrite to improve the strength and hardenability of steel plates. Within a certain range, it can also lower the ductile-brittle transition temperature and improve the plasticity of steel. Therefore, the Si content is limited to 0.10-0.30%.

[0018] Mn: Mn, combined with Si in steel, achieves excellent deoxidation effects. Mn strengthens steel plates through solid solution, improving their toughness, hot workability, and sulfide distribution, while preventing hot cracking. Furthermore, increasing Mn content enhances the stability of austenite in the steel, reduces the critical cooling rate, significantly improves hardenability, and increases the stability of the tempered structure. Appropriate Mn content enables the weld heat-affected zone to possess high strength and toughness; therefore, Mn content is limited to 1.00-2.00%.

[0019] P: P is a harmful element in steel, which greatly affects low-temperature impact toughness and is also an element that is very prone to segregation. This invention controls P within a low range, so the P content is controlled below 0.010%.

[0020] S: S is also a harmful element in steel, easily forming MnS in steel, which can easily become the initiation point for hot cracks during welding, and also has a significant impact on the toughness of the weld heat-affected zone. Therefore, S should be controlled below 0.005%.

[0021] V: As the main element in this invention, V can dissolve into austenite at high temperatures. After solution treatment, it can strengthen the steel and improve its hardenability and strength. The increased precipitation of V(C,N) can also inhibit grain boundary movement and grain growth, further improving the toughness and tempering stability of the steel. V has a very strong affinity for C atoms, and the V-containing carbides formed can improve the strength of the steel and have high-temperature stability, allowing the steel to maintain a fine-grained structure at high temperatures, greatly reducing the overheating sensitivity of the steel and improving the weldability of the steel plate. If the V content is too high, the carbide size will be too large. Therefore, V is limited to 0.10-0.20%, and V / C: 1.5-3.5.

[0022] Ti: As the main element in this invention, Ti can significantly refine grains. Ti has a strong affinity for C and N, and the carbides, nitrides, or carbonitrides formed have very high dissolution temperatures. During heating, undissolved carbonitride particles increase the nucleation sites for austenite and hinder austenite grain growth at high temperatures. Fine nitrides greatly inhibit austenite grain coarsening at high welding temperatures, and during cooling, they refine the microstructure of the heat-affected zone and improve toughness. Therefore, the Ti content is limited to 0.05-0.10%.

[0023] Al: In steel, Al can deoxidize, fix nitrogen, improve toughness, and refine grain structure. Al can also reduce the formation of boron and nitrogen (BN) in steel and increase the content of dissolved boron (B) in steel. Appropriate Al content can improve the yield and tensile strength of the weld heat-affected zone, but excessive Al can lead to the formation of larger oxides, reducing the low-temperature impact toughness of the steel plate. Therefore, the Al content is limited to 0.0025-0.0045%.

[0024] Nitrogen (N): In steel, nitrogen mainly precipitates as VN or V(CN) during the austenite-ferrite transformation, inhibiting austenite grain growth and improving the steel's strength and low-temperature toughness. Therefore, the nitrogen content is limited to 0.002-0.006%.

[0025] B: During the two-stage rolling process, the segregation of dissolved boron at the original austenite grain boundaries occupies the nucleation sites of ferrite on the original austenite grain boundaries, inhibiting ferrite formation; B can promote the transformation of bainite structure, thereby improving the hardenability of the steel plate; and B can inhibit grain boundary slip and grain growth, enhance grain boundary strengthening, and ensure fine grain structure in the weld. Therefore, B is limited to 0.0005-0.0015%.

[0026] W: W, as the main element in this invention, forms refractory carbides in steel, increasing hardenability, reducing the heat sensitivity of the steel plate, and ensuring high strength in the weld heat-affected zone of the steel plate; at the same time, it can refine the grains and improve the tempering resistance of the steel plate. Therefore, the W content is limited to 0.002-0.004%.

[0027] The second technical solution of the present invention is to provide a method for manufacturing a steel plate for crude oil storage tanks with a yield strength of 690 MPa, including smelting, continuous casting, heating, rolling and heat treatment;

[0028] (1) Smelting: Iron pretreatment is adopted, with iron temperature of 1350~1410℃; during refining treatment, LF time is 25-35min, RH time is 25-35min, and vacuum degree is ≤5.0mbar.

[0029] (2) Continuous casting: The tundish steel pouring temperature is 1340-1400℃. The preferred continuous casting process uses a light reduction technique, with a reduction of 2-4 mm; the billet pulling speed is 0.70-0.85 m / min; the secondary cooling water flow rate is 5500-6000 L / min; the superheat is 20-35℃; and the straightening temperature is 970-990℃. The light reduction technique involves slightly reducing the billet at the point where it is about to solidify to reduce center segregation.

[0030] (3) Heating: The heating of the continuously cast billet is divided into a preheating section, a heating section and a soaking section; the temperature range of the heating section is 1170~1210℃; the temperature range of the soaking section is 1160~1200℃; the total time in the furnace is 150~200min. By heating the billet in three stages, the core temperature of the billet reaches 1160~1200℃, ensuring that the billet structure is completely austenitic.

[0031] (4) Rolling: After the billet exits the furnace, a two-stage controlled rolling and cooling technology is adopted. In the roughing stage, the initial rolling temperature is 1130-1170℃, the roll speed is 0.6-0.8m / s, and the single-pass reduction rate is 11%-16%; in the finishing stage, the initial rolling temperature is 840-900℃, the final rolling temperature is 790-850℃, the roll speed is 0.5-0.6m / s, and the single-pass reduction rate is 13%-18%; in the cooling stage, the initial cooling temperature is 750-810℃, and the final cooling temperature is 450-500℃; after cooling, the steel plate is straightened, and the straightening speed is controlled at 1.0-1.8m / s; finally, the steel plate is stacked and slowly cooled, with a slow cooling temperature of 400-450℃ and a slow cooling time of 1000-1200min. Through two-stage rolling, using high-reduction, slow-roll-speed rolling, the deformation storage energy in the microstructure is increased, the time for dynamic recrystallization is extended, and the grains are refined; by controlling cooling, the ferrite transformation is suppressed, and the bainite transformation is promoted to be complete; by straightening the steel plate, the residual stress generated inside the steel plate due to cooling is eliminated, ensuring good plate shape.

[0032] (5) Heat treatment: After slow cooling in the stack, the steel plates are tempered at a temperature of 610-630℃ and held for 100-250 minutes to ensure that the steel plate structure is fully transformed into bainitic tempered structure. Through tempering heat treatment, the steel plate structure is uniform and is bainitic tempered structure, which can improve the mechanical properties of the steel plate.

[0033] The beneficial effects of this invention are as follows:

[0034] 1. This invention features a simple composition design. Based on a low carbon content, sufficient amounts of V and Ti are added to enhance the steel plate's strength through precipitation strengthening. V dissolves into austenite at high temperatures, improving the steel's hardenability. During smelting, V and C form stable, refractory carbides that refine the grain size and reduce the steel's overheat sensitivity. Simultaneously, the precipitation and dispersion strengthening effects of V ensure sufficient strength and toughness, significantly refining the grain size. Ti has a strong affinity for C and N, forming compounds with high dissolution temperatures. During heating, undissolved carbonitride particles increase austenite nucleation sites and hinder austenite grain growth at high temperatures. During cooling, this refines the microstructure of the weld and heat-affected zone, improving toughness. Furthermore, the addition of W and B further refines the grain size, improving the steel plate's hardenability and tempering resistance. This composition ensures the steel plate exhibits excellent high heat input welding performance.

[0035] 2. The manufacturing method of this invention is reasonable. By employing controlled rolling and cooling combined with tempering heat treatment, the finished product microstructure is ensured to be a bainitic tempered microstructure with carbide sizes between 1 and 4 μm and uniform distribution. This eliminates the damage to the steel plate's strength caused by blocky ferrite, resulting in a steel plate with a good strength-toughness ratio. Even after simulated welding heat treatment, it still exhibits excellent strength and toughness. By straightening the steel plate, the flatness is controlled within 1 to 4 mm.

[0036] 3. The steel plate of this invention has a thickness of 10-50 mm and a yield strength R. eL ≥700MPa, tensile strength R m 800~920MPa, elongation A≥18%, -20℃KV2≥100J. Simulated post-weld heat treatment steel plate performance: ReL≥690MPa, Rm:780~900MPa, A≥18%, -20℃KV2≥100J.

[0037] 4. Properties of the heat-affected zone after steel plates are welded with a high heat input of 70–110 kJ / cm: Yield strength R eL ≥690MPa, tensile strength R m 750~880MPa, elongation A≥18%, KV2≥80J at -20℃. Detailed Implementation

[0038] The present invention will be further illustrated below through examples.

[0039] (1) Heating: The heating of the continuously cast billet is divided into a preheating section, a heating section and a soaking section; the temperature range of the heating section is 1170~1210℃; the temperature range of the soaking section is 1160~1200℃; the total time in the furnace is 150~200min;

[0040] (2) Rolling: After the billet exits the furnace, a two-stage controlled rolling and cooling technology is adopted. In the roughing stage, the initial rolling temperature is 1130-1170℃, the roll speed is 0.6-0.8m / s, and the single-pass reduction rate is 11%-16%; in the finishing stage, the initial rolling temperature is 840-900℃, the final rolling temperature is 790-850℃, the roll speed is 0.5-0.6m / s, and the single-pass reduction rate is 13%-18%; in the cooling stage, the initial cooling temperature is 750-810℃, and the final cooling temperature is 450-500℃; after cooling, the steel plate is straightened, and the straightening speed is controlled at 1.0-1.8m / s; then the steel plate is stacked and slowly cooled, with a slow cooling temperature of 400-450℃ and a slow cooling time of 1000-1200min.

[0041] (3) Heat treatment: After stacking and slow cooling, the steel plates are tempered at a temperature of 610-630℃ and held for 100-250 minutes.

[0042] Further; Smelting: Iron pretreatment is adopted, with iron temperature of 1350~1410℃; during refining treatment, LF time is 25~35min, RH time is 25~35min, and vacuum degree is ≤5.0mbar.

[0043] Further; Continuous casting: tundish steel pouring temperature 1340~1400℃, billet pulling speed 0.70~0.85m / min, secondary cooling water 5500~6000L / min, superheat 20~35℃, straightening temperature 970~990℃.

[0044] Furthermore, a light reduction technique is used during the continuous casting process, with the reduction amount controlled at 2-4 mm.

[0045] According to the component ratio of the technical solution, the embodiments of the present invention involve smelting, continuous casting, heating, rolling, and heat treatment. The composition of the steel in the embodiments of the present invention is shown in Table 1. The main process parameters for smelting and casting of the steel in the embodiments of the present invention are shown in Table 2. The main process parameters for heating and rolling of the steel in the embodiments of the present invention are shown in Table 3. The process parameters for cooling, slow cooling, and heat treatment of the steel in the embodiments of the present invention are shown in Table 4. The properties of the steel in the embodiments of the present invention are shown in Table 5. The properties of the steel after simulated post-weld heat treatment in the embodiments of the present invention are shown in Table 6. The mechanical properties of the heat-affected zone after high heat input welding in the embodiments of the present invention are shown in Table 7.

[0046] Table 1. Composition (wt%) of steel in embodiments of the present invention

[0047] Example C Si Mn P S V Ti N B W Al V / C 1 0.09 0.13 1.03 0.001 0.001 0.12 0.05 0.002 0.0005 0.002 0.0025 1.3 2 0.05 0.16 1.80 0.002 0.002 0.16 0.08 0.003 0.0009 0.002 0.0025 3.2 3 0.05 0.27 1.19 0.001 0.001 0.10 0.06 0.003 0.0007 0.002 0.0038 2.0 4 0.06 0.16 1.97 0.007 0.005 0.19 0.07 0.006 0.0014 0.003 0.0029 3.2 5 0.06 0.14 1.71 0.007 0.005 0.18 0.10 0.002 0.0006 0.002 0.0026 3.0 6 0.07 0.28 1.62 0.004 0.003 0.13 0.06 0.005 0.0015 0.004 0.0040 1.9 7 0.05 0.17 1.57 0.01 0.005 0.10 0.10 0.003 0.001 0.003 0.0031 2.0 8 0.07 0.28 1.53 0.006 0.005 0.12 0.06 0.005 0.0014 0.004 0.0035 1.7 9 0.08 0.22 1.09 0.001 0.002 0.20 0.10 0.002 0.0006 0.003 0.0033 2.5 10 0.05 0.20 1.46 0.008 0.005 0.10 0.10 0.003 0.0008 0.002 0.0032 2.0 11 0.08 0.29 1.35 0.002 0.002 0.17 0.09 0.004 0.0012 0.004 0.0037 2.1 12 0.09 0.15 1.3 0.005 0.004 0.18 0.09 0.004 0.0011 0.004 0.0028 2.0 13 0.10 0.30 1.27 0.003 0.003 0.15 0.08 0.005 0.0013 0.004 0.0039 1.5 14 0.10 0.23 1.88 0.009 0.005 0.17 0.09 0.002 0.0007 0.004 0.0027 1.7 15 0.09 0.25 1.48 0.006 0.004 0.19 0.06 0.006 0.0013 0.003 0.0039 2.1

[0048] Table 2 Main process parameters for steel smelting and casting in the embodiments of the present invention.

[0049]

[0050] Table 3 Main process parameters for steel heating and rolling in the embodiments of the present invention.

[0051]

[0052] Table 4. Process parameters for steel cooling, slow cooling, and heat treatment in embodiments of the present invention.

[0053]

[0054] Table 5 Properties of the steel in the embodiments of the present invention

[0055]

[0056] Table 6 Mechanical properties of steel after post-weld heat treatment in embodiments of the present invention

[0057]

[0058] Note: The heat treatment temperature for mold welding is 560-640℃, and the holding time is 120-240min.

[0059] Table 7 Mechanical properties of the heat-affected zone after high heat input welding in the embodiments of the present invention.

[0060]

[0061] Note: The maximum heat input for welding is 70-110 kJ / cm.

[0062] The steel plate produced using this invention has a bainitic tempered microstructure. The steel plate has a thickness of 10–50 mm and a yield strength R0. eL ≥700MPa, tensile strength R m 800~920MPa, A≥18%, -20℃ KV2≥100J. Simulated mechanical properties of steel plate after post-weld heat treatment: yield strength R. eL ≥690MPa, tensile strength R m 780~900MPa, A≥18%, -20℃ KV2≥100J. Yield strength R of the heat-affected zone of welded steel plate. eL ≥690MPa, tensile strength R m :750~880MPa, A≥18%, -20℃KV2≥80J.

[0063] To illustrate the present invention, the present invention has been appropriately and sufficiently described above through embodiments. The above embodiments are only for illustrating the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Any modifications, equivalent substitutions, improvements, etc., should be included within the protection scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A steel plate for crude oil storage tanks with a yield strength of 690 MPa, characterized in that, The composition of the steel plate, by weight percentage, is as follows: C: 0.05%~0.10%, Si: 0.10%~0.30%, Mn: 1.00%~2.00%, P: ≤0.010%, S: ≤0.005%, V: 0.10%~0.20%, Ti: 0.05%~0.10%, Al: 0.0025%~0.0045%, N: 0.002%~0.006%, B: 0.0005%~0.0015%, W: 0.002%~0.004%, with the balance being Fe and unavoidable impurities; the steel plate thickness is 10~50mm, and the yield strength R... eL ≥700MPa, tensile strength R m 800~920MPa, elongation A ≥18%, -20℃ KV 2 ≥100J; the welding energy of the steel plate is 70-110J. kJ / The heat-affected zone properties after welding a large wire of cm are the yield strength R. eL ≥690MPa, tensile strength R m 750~880MPa, elongation A≥18%, -20℃ KV 2 ≥80J.

2. The steel plate for crude oil storage tanks with a yield strength of 690 MPa according to claim 1, characterized in that, The V / C ratio in the steel plate is 1.5~3.

5.

3. The steel plate for crude oil storage tanks with a yield strength of 690 MPa according to claim 1, characterized in that, The microstructure of the steel plate is a bainitic tempered structure, with carbide sizes ranging from 1 to 4 μm.

4. A method for manufacturing a steel plate for crude oil storage tanks with a yield strength of 690 MPa as described in any one of claims 1-3, comprising smelting, continuous casting, heating, rolling, and heat treatment; characterized in that: (1) Heating: The heating of the continuously cast billet is divided into a preheating section, a heating section and a soaking section; the temperature range of the heating section is 1170~1210℃; the temperature range of the soaking section is 1160~1200℃; the total time in the furnace is 150~200min. (2) Rolling: After the billet exits the furnace, a two-stage controlled rolling and cooling technology is adopted; the initial rolling temperature of the roughing stage is 1130~1170℃, the roll speed is 0.6~0.8m / s, and the single-pass reduction rate is 11%~16%; the initial rolling temperature of the finishing stage is 840~900℃, the final rolling temperature is 790~850℃, the roll speed is 0.5~0.6m / s, and the single-pass reduction rate is 13%~18%; the initial cooling temperature of the cooling stage is 750~810℃, and the final cooling temperature is 450~500℃; after cooling, the steel plate is straightened, and the straightening speed is controlled at 1.0~1.8m / s; The steel plates are then stacked and cooled slowly at a temperature of 400-450℃ for 1000-1200 minutes. (3) Heat treatment: After stacking and slow cooling, the steel plates are tempered at a temperature of 610~630℃ and held for 100~250min.

5. The method for manufacturing a crude oil storage tank steel plate with a yield strength of 690 MPa according to claim 4, characterized in that: Smelting: Hot metal pretreatment is adopted, with hot metal temperature of 1350~1410℃; during refining treatment, LF time is 25~35min, RH time is 25~35min, and vacuum degree is ≤5.0mbar.

6. The method for manufacturing a crude oil storage tank steel plate with a yield strength of 690 MPa according to claim 4, characterized in that: Continuous casting: tundish steel pouring temperature 1340~1400℃, billet speed 0.70~0.85m / min, secondary cooling water 5500~6000L / min, superheat 20~35℃, straightening temperature 970~990℃.

7. The method for manufacturing a crude oil storage tank steel plate with a yield strength of 690 MPa according to claim 6, characterized in that: Light reduction is used in the continuous casting process, with a reduction amount of 2~4mm.

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