A steel plate for vessels with a low yield strength ratio of 690 MPa and its manufacturing method.

Abstract

This invention proposes a low yield strength ratio steel plate for containers with a yield strength of 690 MPa and its manufacturing method. The steel plate composition, by weight percentage, is as follows: C: 0.04%–0.08%, Si: 0.10%–0.30%, Mn: 1.00%–2.00%, P: ≤0.010%, S: ≤0.005%, Nb: 0.10%–0.50%, V: 0.10%–0.50%, Ti: 0.02%–0.08%, Cr: 0.30%–0.60%, Ni: 0.60%–1.20%, Cu: 0.40%–0.80%, Al: 0.0035%–0.0055%, with the balance being Fe and unavoidable impurities. The production process of steel plates includes smelting, continuous casting, heating, rolling, cooling, and heat treatment. The final steel plate has a microstructure of tempered bainitic structure (90%–94% by volume) plus a small amount of ferrite (6%–10% by volume). The yield strength R of the steel plate... eL ≥690MPa, tensile strength R m 780~930MPa, yield strength ratio R eL / R m ≤0.85, elongation A≥18%, low-temperature impact toughness KV2≥100J at -70℃. The steel plate underwent a simulated post-weld heat treatment process to test its mechanical properties. The simulated post-weld heat treatment temperature was 550~650℃, and the holding time was 120~480min. Its mechanical properties were as follows: yield strength R... eL ≥690MPa, tensile strength R m 780~930MPa, yield strength ratio R eL / R m ≤0.85, elongation A≥18%, low temperature impact toughness KV2≥100J at -70℃.

Description

Technical Field

[0001] This invention relates to the field of metallic materials, and in particular to a low yield strength ratio steel plate for containers with a yield strength of 690 MPa and a method for manufacturing the same. Background Technology

[0002] Currently, as medium and heavy plates are developed towards high strength and lightweight, steel plates are strengthened through various mechanisms to improve strength. However, the yield strength ratio will inevitably increase. For steel plates used in special applications such as storage tanks, offshore platforms, and construction, strict requirements are placed on the yield strength ratio for safety reasons. Therefore, the lower the yield strength ratio, the greater the reliability of the steel plate when subjected to stress exceeding the yield point, and the higher the safety of the steel plate.

[0003] In recent years, the increasing frequency of earthquakes worldwide has made reducing the damage to pressure vessels a key concern. Furthermore, the safe operation of large pressure vessels in the chemical and nuclear power sectors is crucial to the stability of industrial production and energy supply, as well as the safety of people's lives and property. Therefore, pressure vessels face severe risks of damage when encountering earthquakes.

[0004] The chemical composition designed in CN117448695A, "A Steel Plate for Impact-Resistant Butane Pressure Vessels," is C 0.10%–0.20%, Si 0.20%–0.45%, Mn 1.60%–1.80%, Al 0.025%–0.045%, P≤0.015%, S≤0.005%, V 0.065%–0.085%, Nb 0.027%–0.045%. The designed final rolling temperature is relatively high, which easily leads to an increase in yield strength and thus a higher yield-to-tensile ratio. The chemical composition used in CN113913588A, "A Heat Treatment Method for Low-Carbon Equivalent Seismic-Resistant Vessel Steel Plates," is C 0.08%–0.10%, Si 0.25%–0.34%, Mn 1.30%–1.35%, P≤0.009%, S≤0.0025%, Mo… The designed heat treatment process has a large tempering temperature control range, which can easily lead to larger grains and reduced strength in the steel plate. CN117431465A, "A Manufacturing Method for a High-Toughness, Low-Yield-Strength 700MPa Grade Steel Plate," designs the chemical composition as follows: C 0.07%–0.010%, Si 0.10%–0.35%, Mn 1.4%–1.7%, P≤0.010%, S≤0.002%, Nb 0.1%–0.3%, V 0.3%–0.5%, Ti 0.01%–0.02%, Cu 0%–0.25%, Ni 0.2%–0.5%, Mo 0.1% to 0.3%, Alt 0.020% to 0.060%, the balance being Fe and unavoidable impurities, and it is made into slabs by continuous casting, and then processed by controlled rolling and cooling + heat treatment. However, the steel plate has low strength and high yield strength.

[0005] Pressure vessel steel plates are mainly made of high-strength quenched and tempered steel, resulting in a generally high yield strength ratio, typically above 0.90. Therefore, to address the aforementioned issues, there is an urgent need to develop a pressure vessel steel plate that meets the requirements of different service environments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a low yield-to-tensile ratio steel plate for vessels with a yield strength of 690 MPa and its manufacturing method. Through a novel chemical composition design and a unique process, the mechanical properties of the obtained steel plate, as well as the mechanical properties simulated after post-weld heat treatment, both meet the following requirements: yield strength R... eL ≥690MPa, tensile strength R m 780~930MPa, yield strength ratio R eL / R mThe steel plate with a thickness of (10-50) mm proposed in this invention has excellent strength and low-temperature performance, and a uniform and fine microstructure, which can meet the requirements for the manufacture and application of high-performance pressure vessel steel. The steel plate has an elongation of ≤0.85 mm, an elongation of A ≥18%, and a low-temperature impact toughness of KV2 ≥100 J at -70℃.

[0007] The objective of this invention is achieved as follows:

[0008] A steel plate for vessels with a low yield strength ratio and a yield strength of 690 MPa, the chemical composition of which is as follows (by weight percentage):

[0009] C: 0.04%–0.08%, Si: 0.10%–0.30%, Mn: 1.00%–2.00%, P: ≤0.010%, S: ≤0.005%, Nb: 0.10%–0.50%, V: 0.10%–0.50%, Ti: 0.02%–0.08%, Cr: 0.30%–0.60%, Ni: 0.60%–1.20%, Cu: 0.40%–0.80%, Al: 0.0035%–0.0055%, with the balance being Fe and unavoidable impurities.

[0010] Furthermore, the composition 4 ≤ Nb / Ti ≤ 8.

[0011] Furthermore, the steel plate R eL ≥690MPa, R m 880~930MPa, R eL / R m ≤0.85, A≥18%, -70℃ low temperature impact toughness KV2≥100J.

[0012] Furthermore, the microstructure of the steel plate is bainite and ferrite, with a bainite volume content of 90% to 94% and a ferrite volume content of 6% to 10%.

[0013] Furthermore, the thickness of the steel plate is 10–50 mm.

[0014] Nb, Ti, and Ni are the main elements of this invention, and the rationale for their design is as follows:

[0015] C: 0.04%~0.08%

[0016] Carbon (C) in steel forms various carbides or solid solutions with alloying elements to strengthen the steel, directly increasing its strength. Excessive C content leads to poor toughness and weldability; furthermore, high C content increases bainite and cementite, increasing the yield strength ratio. Therefore, to ensure good low-temperature impact toughness and high strength in steel plates during use, and to maintain a sufficiently low Ceq (coefficient of mass), the C content is limited to 0.04%–0.08%.

[0017] Si: 0.10%~0.30%

[0018] Si plays a role in deoxidation and solid solution strengthening in steel. Si can inhibit carbide coarsening, and an appropriate amount of Si can expand the ferrite formation range, improve the strength and hardenability of steel plates, and, within a certain range, lower the ductile-brittle transition temperature and improve the plasticity of steel. Therefore, the Si content is limited to 0.10%–0.30%.

[0019] Mn: 1.00%~2.00%

[0020] In steel, manganese (Mn) improves strength and toughness through substitution, grain refinement, and increased ferrite content. It can also reduce the yield strength ratio of steel by increasing tensile strength through solid solution in the Fe matrix. Simultaneously, it improves toughness, hot workability, and sulfide distribution morphology, preventing hot cracking. Furthermore, increasing Mn content enhances the stability of austenite in steel, lowering the critical austenite transformation temperature during cooling. Therefore, the Mn content is limited to 1.00%–2.00%.

[0021] P: ≤0.010%

[0022] Phosphorus (P) is a harmful element in steel, significantly impairing low-temperature impact toughness and being highly prone to segregation. This invention controls P within a low range, thus keeping the P content below 0.010%.

[0023] S: ≤0.005%

[0024] Sulfur (S) is also a harmful element in steel. It easily forms MnS in steel, which can become a source of crack formation during subsequent processing and has a significant impact on the toughness of steel. Therefore, the S content should be controlled below 0.005%.

[0025] Nb: 0.10%~0.50%

[0026] As the main element in this patent, nitrogen (Nb) can suppress austenite recrystallization during the rolling process in steel, increase the dislocation density within the austenite, promote grain refinement, improve the strength and toughness of the steel plate, reduce overheating sensitivity, and also produce solid solution strengthening. It causes a large amount of Nb (C,N) to precipitate at grain boundaries and dislocations. At high Nb contents, Nb segregated at grain boundaries is more likely to precipitate, creating carbon-depleted zones and promoting the nucleation and growth of ferrite at austenite grain boundaries at high temperatures. Therefore, the Nb content is limited to 0.10%–0.50%.

[0027] V: 0.10%~0.50%

[0028] At high temperatures, vanadium (V) can dissolve into austenite, and after solution treatment, it can strengthen the steel and improve its hardenability. V mainly exists in steel as V(C,N), increasing precipitation strengthening to ensure the strength and hardness of the steel plate, reducing overheating sensitivity, and improving thermal stability. Increased V(C,N) precipitation also helps provide coherent interfaces for intragranular ferrite nucleation, pinning them at grain boundaries, inhibiting grain boundary movement and grain growth, and further improving the steel's toughness. Furthermore, V can undergo complex precipitation with inclusions, which is beneficial for deformation-induced ferrite phase transformation. If the V content is too high, not only will the cost increase, but the precipitate size will also increase; therefore, V is limited to 0.10%–0.50%.

[0029] Ti: 0.02%~0.08%

[0030] Ti, as the main element in this patent, is a transition metal element. Adding trace amounts of Ti can precipitate fine precipitates in the billet, preventing austenite grain coarsening during solidification and reheating, thus refining the austenite grain size before rolling. Furthermore, during rolling, it can inhibit grain growth after austenite deformation recrystallization, further refining the grains and reducing the yield strength ratio. The Ti(C,N) particles precipitated at high temperatures remain, and Ti(C,N) can promote the precipitation of Nb and V, resulting in a composite precipitation state. However, when w(Ti) ≥ 0.09%, it reduces the content of acicular ferrite, deteriorating the low-temperature toughness of the steel plate. Therefore, the Ti content is limited to 0.02%–0.08%, and the Nb / Ti ratio is limited to 4–8.

[0031] Cr: 0.30%~0.60%

[0032] Cr is a strong carbide-forming element, which improves the hardenability of steel plates, ensures that bainitic structure can be obtained during controlled cooling, refines the ferrite grain size, and ensures a low yield strength ratio. Cr can also improve the strength and toughness of steel plates, and increasing the Cr content can give the steel plates good corrosion resistance. Therefore, the Cr content in this invention is controlled between 0.30% and 0.60%.

[0033] Ni: 0.60%~1.20%

[0034] Ni is the main element in this patent. As a stable austenite, it can exist in austenite and ferrite in a solid solution with Fe, improving the strength of steel and refining the grain. Adding 1% Ni can increase the strength of steel by about 20 MPa and also improve the low-temperature toughness of steel plates. At the same time, Ni can also reduce the tendency of surface cracking in billets caused by the addition of Cu. However, because Ni is too expensive, it will also make it difficult to remove the iron oxide scale from the steel plate, increasing the cost. Therefore, the Ni content is limited to between 0.60% and 1.20%.

[0035] Cu: 0.40%~0.80%

[0036] As an element that expands the austenite region, Cu's solubility in ferrite decreases with decreasing temperature. Through appropriate heat treatment, it can undergo precipitation strengthening in the microstructure. Furthermore, Cu can help steel plates obtain good low-temperature toughness and improve the corrosion resistance of steel. Therefore, the Cu content is limited to 0.40% to 0.80%.

[0037] Al: 0.0035%~0.0055%

[0038] Al acts as a primary deoxidizer in steel, fixing nitrogen, refining grains, and improving steel toughness. Excessive Al content leads to the formation of larger AlN particles, reducing the low-temperature toughness of the steel plate. Therefore, to ensure more complete deoxidation and nitrogen fixation, the Al content is limited to 0.0035%–0.0055%.

[0039] The second technical solution of the present invention is to provide a manufacturing method for a low yield strength ratio steel plate for containers with a yield strength of 690MPa, with the following process flow: smelting, continuous casting, heating, rolling, cooling, and heat treatment.

[0040] Smelting: Hot metal pretreatment is adopted, with hot metal temperature of 1365~1415℃; during refining treatment, LF time is 35~60min, RH time is 25~40min, and vacuum degree is ≤5.0mbar.

[0041] Continuous casting: The tundish steel pouring temperature is 1370~1400℃, electromagnetic stirring or light reduction technology is used, the billet pulling speed is 0.65~0.85m / min, the secondary cooling water is 4200~4700L / min, the superheat is 18~25℃, and the straightening temperature is 960~1000℃.

[0042] 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 1190~1230℃; the temperature range of the soaking section is 1170~1210℃; the total time in the furnace is 240~300min. By heating the billet in three stages, the heating temperature of the billet is made uniform, ensuring that the billet microstructure is fully austenitic.

[0043] 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 1120–1160℃, the roll speed is 0.5–0.7 m / s, and the single-pass reduction rate is 13%–17%. In the finishing stage, the initial rolling temperature is 840–920℃, the final rolling temperature is 780–810℃, the roll speed is 0.6–0.8 m / s, and the single-pass reduction rate is 9%–13%. In the cooling stage, the initial cooling temperature is 730–780℃, and the final cooling temperature is 490–540℃. After cooling, the steel plates are stacked for slow cooling at 420–450℃ for 720–1080 min. The thickness of the rolled steel plate is 10–50 mm. Large deformation rolling during the roughing stage continuously increases the deformation energy stored within the austenite grains. Due to the pinning and dragging effects of Ti and Nb second-phase particles, the recrystallization behavior of deformed grains is hindered, promoting the formation of fine ferrite grains to obtain excellent mechanical properties and reduce the yield strength ratio. The microstructure consists of bainite and a small amount of ferrite.

[0044] Heat treatment: After slow cooling in stacks, the steel plates undergo normalizing heat treatment at a temperature of 885–905℃ for 30–60 minutes. After removal from the furnace, the plates are cooled to 450–500℃ and then air-cooled. This normalizing heat treatment combined with controlled cooling ensures that the steel plate maintains its strength while possessing suitable ductility, toughness, low-temperature performance, and a low yield strength ratio. Furthermore, it ensures a uniform microstructure, consisting of tempered bainitic structure (90%–94% by volume) plus a small amount of ferrite (6%–10% by volume). This heat treatment enhances the mechanical properties of the steel plate.

[0045] The beneficial effects of this invention are as follows:

[0046] This invention, based on strengthening elements C, Si, and Mn, reduces the C content and adds sufficient amounts of Nb and Ti. The second-phase particles of Ti promote the precipitation of Nb and V, exhibiting a composite precipitation effect. This precipitation strengthening and grain refinement ensure sufficient strength in the steel plate. The pinning effect of the second-phase particles and the dragging effect of solid solution atoms promote the formation of fine ferrite within the grains, ensuring a low yield strength ratio. The addition of Ni increases the low-temperature toughness of the steel plate. The resulting steel plate possesses sufficient strength, good low-temperature performance, and excellent mechanical properties simulating post-weld heat treatment.

[0047] 1. This invention, through a novel composition design and a unique production process, yields a low yield-to-tensile ratio steel plate for containers with a yield strength of 690 MPa. The steel plate thickness ranges from 10 to 50 mm. After normalizing heat treatment and controlled cooling, the steel plate exhibits good low-temperature impact toughness at -70℃ and high strength properties. Its mechanical properties are: Yield strength R... eL ≥690MPa, tensile strength R m780~930MPa, yield strength ratio R eL / R m ≤0.85, elongation A≥18%, low temperature impact toughness KV2≥100J at -70℃.

[0048] 2. A low yield strength ratio steel plate for containers with a yield strength of 690 MPa, wherein the steel plate microstructure is bainitic tempered microstructure (volume content of 90-94%) + a small amount of ferrite (volume content of 6-10%).

[0049] 3. The steel plate of this invention undergoes a simulated post-weld heat treatment process to test its mechanical properties. The simulated post-weld heat treatment temperature is 550–650℃, and the holding time is 120–480 min. Its mechanical properties are as follows: yield strength R... eL ≥690MPa, tensile strength R m 780~930MPa, yield strength ratio R eL / R m ≤0.85, elongation A≥18%, low temperature impact toughness KV2≥100J at -70℃. Detailed Implementation

[0050] The present invention will be further illustrated below through examples.

[0051] According to the component ratio of the technical solution, the embodiments of the present invention carry out smelting, continuous casting, heating, rolling, cooling and heat treatment.

[0052] heating

[0053] The continuous casting billet heating process is divided into a preheating section, a heating section, and a soaking section; the temperature range of the heating section is 1190–1230℃; the temperature range of the soaking section is 1170–1210℃; and the total furnace time is 240–300 min.

[0054] Rolling

[0055] A two-stage controlled rolling and cooling technology is adopted. In the roughing stage, the initial rolling temperature is 1120-1160℃, the roll speed is 0.5-0.7m / s, and the single-pass reduction rate is 13%-17%. In the finishing stage, the initial rolling temperature is 840-920℃, the final rolling temperature is 780-810℃, the roll speed is 0.6-0.8m / s, and the single-pass reduction rate is 9-13%.

[0056] cool down

[0057] The initial cooling temperature during the cooling stage is 730–780℃, and the final cooling temperature is 490–540℃. After cooling, the steel plates are stacked and cooled slowly at a temperature of 420–450℃ for 720–1080 min.

[0058] Heat treatment

[0059] After being stacked and slowly cooled, the steel plates undergo normalizing heat treatment and controlled cooling. The normalizing temperature is 885–905℃, the holding time is 30–60 minutes, and the temperature is cooled to 450–500℃.

[0060] Furthermore, the molten iron temperature during the smelting process is 1365–1415℃; during refining, the LF time is 35–60 min, the RH time is 25–40 min, and the vacuum degree is ≤5.0 mbar.

[0061] Furthermore, during the continuous casting process, the molten steel pouring temperature in the tundish is 1370–1400℃, electromagnetic stirring or light pressure technology is used, the billet pulling speed is 0.65–0.85 m / min, the secondary cooling water is 4200–4700 L / min, the superheat is 18–25℃, and the straightening temperature is 960–1000℃.

[0062] The embodiments are detailed in the embodiments of the present invention. These embodiments are only general descriptions of the present invention and do not limit the scope of the present invention. Table 1 shows the chemical composition of the embodiments, Table 2 shows the smelting and continuous casting parameters of the embodiments, Table 3 shows the heating and rolling parameters of the embodiments, Table 4 shows the cooling, slow cooling and heat treatment parameters of the embodiments, Table 5 shows the mechanical properties of the embodiments, and Table 6 shows the mechanical properties of the embodiments after simulated post-weld heat treatment.

[0063] Table 1 Chemical composition (wt%) of the examples

[0064] Example C Si Mn P S Nb V Ti Cr Ni Cu Al Nb / Ti 1 0.04 0.12 1.03 0.003 0.001 0.16 0.15 0.03 0.3 0.64 0.40 0.0036 5.3 2 0.04 0.29 1.85 0.008 0.003 0.2 0.50 0.04 0.45 1.12 0.46 0.0038 5.0 3 0.06 0.30 1.50 0.009 0.004 0.42 0.35 0.06 0.48 0.81 0.54 0.0036 7.0 4 0.04 0.24 1.98 0.009 0.004 0.32 0.48 0.07 0.43 1.20 0.67 0.0048 4.6 5 0.06 0.15 1.31 0.009 0.004 0.25 0.41 0.06 0.37 1.15 0.52 0.0046 4.2 6 0.08 0.23 1.19 0.005 0.002 0.44 0.33 0.06 0.5 1.00 0.74 0.0041 7.3 7 0.04 0.24 1.24 0.004 0.001 0.42 0.38 0.07 0.45 0.98 0.46 0.0050 6.0 8 0.05 0.30 1.90 0.006 0.002 0.37 0.46 0.05 0.6 1.10 0.78 0.0053 7.4 9 0.08 0.19 1.8 0.010 0.005 0.38 0.38 0.05 0.53 0.85 0.48 0.0038 7.6 10 0.05 0.19 1.92 0.006 0.002 0.32 0.46 0.06 0.34 1.18 0.65 0.0042 5.3 11 0.05 0.25 1.70 0.008 0.003 0.3 0.43 0.06 0.41 1.20 0.57 0.0055 5.0 12 0.07 0.22 1.63 0.005 0.002 0.28 0.33 0.05 0.34 0.92 0.46 0.0040 5.6 13 0.07 0.25 1.45 0.008 0.003 0.14 0.41 0.03 0.56 1.02 0.72 0.0050 4.7 14 0.06 0.17 1.10 0.007 0.003 0.29 0.22 0.04 0.48 0.72 0.80 0.0048 7.3 15 0.07 0.27 1.37 0.010 0.005 0.39 0.27 0.05 0.53 1.08 0.52 0.0055 7.8

[0065] Table 2 Smelting and Continuous Casting Parameters for Examples

[0066]

[0067] Table 3 Heating and rolling parameters for the embodiments

[0068]

[0069] Table 4 Cooling, slow cooling, and heat treatment parameters for the embodiments

[0070]

[0071] Table 5 Mechanical properties of the examples

[0072]

[0073] Table 6 Mechanical properties of simulated post-weld heat treatment in embodiments of the present invention.

[0074]

[0075] Note: The heat treatment temperature for mold welding is 550-650℃, and the holding time is 120-480 min.

[0076] As can be seen from the above, the mechanical properties of the low yield-to-tensile ratio steel plate for vessels with a yield strength of 690 MPa (10-50 mm) provided by this invention are as follows: yield strength R eL ≥690MPa, tensile strength R m 780~930MPa, yield strength ratio R eL / R m ≤0.85, elongation A≥18%, low-temperature impact toughness KV2≥100J at -70℃, uniform and fine microstructure throughout the thickness, high strength, low yield strength ratio, good low-temperature performance and excellent mold-welded mechanical properties.

[0077] 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 method for manufacturing a low yield-to-tensile ratio steel plate for containers with a yield strength of 690 MPa, comprising smelting, continuous casting, heating, rolling, cooling, and heat treatment, characterized in that, heating The continuous casting billet heating process is divided into a preheating section, a heating section, and a soaking section; the temperature range of the heating section is 1190~1230℃; the temperature range of the soaking section is 1170~1210℃; and the total furnace time is 240~300 minutes. Rolling A two-stage controlled rolling and cooling technology is adopted. In the roughing stage, the initial rolling temperature is 1120~1160℃, the roll speed is 0.5~0.7m / s, and the single-pass reduction rate is 13%~17%. In the finishing stage, the initial rolling temperature is 840~920℃, the final rolling temperature is 780~810℃, the roll speed is 0.6~0.8m / s, and the single-pass reduction rate is 9%~13%. cool down The initial cooling temperature during the cooling stage is 730~780℃, and the final cooling temperature is 490~540℃. After cooling, the steel plates are stacked and slowly cooled at a temperature of 420~450℃ for 720~1080 min. Heat treatment After stacking and slow cooling, the steel plates undergo normalizing heat treatment and controlled cooling. The normalizing temperature is 885~905℃, the holding time is 30~60min, and the controlled cooling is 450~500℃. A steel plate for containers with a low yield-to-tensile ratio and a yield strength of 690 MPa, comprising the following components by weight percentage: C: 0.04%~0.08%, Si: 0.10%~0.30%, Mn: 1.00%~2.00%, P: ≤0.010%, S: ≤0.005%, Nb: 0.10%~0.50%, V: 0.10%~0.50%, Ti: 0.02%~0.08%, Cr: 0.30%~0.60%, Ni: 0.60%~1.20%, Cu: 0.40%~0.80%, Al: 0.0035%~0.0055%, with the balance being Fe and unavoidable impurities; The microstructure of the steel plate consists of bainite and ferrite, with a bainite volume content of 90%~94% and a ferrite volume content of 6%~10%.

2. The method for manufacturing a low yield strength ratio steel plate for containers with a yield strength of 690 MPa according to claim 1, characterized in that, The component is 4≤Nb / Ti≤8.

3. The method for manufacturing a low yield-to-tensile ratio steel plate for containers with a yield strength of 690 MPa according to claim 1, characterized in that, The steel plate has a ReL≥690MPa, Rm:780~930MPa, ReL / Rm≤0.85, A≥18%, and a low-temperature impact toughness KV2≥100J at -70℃.

4. The method for manufacturing a low yield strength ratio steel plate for containers with a yield strength of 690 MPa according to claim 1, characterized in that, The thickness of the steel plate is 10~50mm.

5. The method for manufacturing a low yield strength ratio steel plate for containers with a yield strength of 690 MPa according to claim 1, characterized in that, The smelting process involves a molten iron temperature of 1365~1415℃; during refining, the LF process lasts 35~60min, the RH process lasts 25~40min, and the vacuum degree is ≤5.0mbar.

6. The method for manufacturing a low yield-to-tensile ratio steel plate for containers with a yield strength of 690 MPa according to claim 1, characterized in that, During the continuous casting process, the molten steel pouring temperature in the tundish is 1370~1400℃, electromagnetic stirring or light reduction technology is used, the billet pulling speed is 0.65~0.85m / min, the secondary cooling water is 4200~4700L / min, the superheat is 18~25℃, and the straightening temperature is 960~1000℃.

Images