High-strength, high-toughness and low-yield-ratio Q550MPa-grade steel plate for bridge and production method thereof

Abstract

The invention discloses a Q550MPa-grade steel plate for a high-strength, high-toughness and low-yield-ratio bridge and a production method of the Q550MPa-grade steel plate. The steel plate comprises the following chemical components: 0.05%-0.09% of C, 0.20%-0.50% of Si, 1.40%-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.006% of S, 0.15%-0.25% of Ni, 0.25%-0.40% of Cr, 0.20%-0.40% of Mo, 0.025%-0.035% of Nb, 0.020%-0.040% of total Al, 0.005%-0.010% of N, 0.40%-0.47% of CEV, less than or equal to 0.22% of Pcm and the balance of Fe and inevitable impurities. The production method comprises the steps of smelting, casting, heating, rolling, water cooling and heat treatment. The steel plate has the advantages of high strength, high toughness, low yield ratio, good welding performance and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel smelting, and particularly relates to a Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio, and a production method thereof. Background Art

[0002] With the rapid development of China's economy, in order to meet the needs of China's transportation, the country needs to build a large number of railways and highways. Under the comprehensive influence of certain geological conditions and urban construction conditions, the construction of bridges has also been put on the agenda. Steel structure bridges have the advantages of short construction period, being applicable to the construction of long-span bridges, and long service life.

[0003] As an important part of modern transportation infrastructure, the design and construction of long-span bridges have extremely high requirements for materials. In bridge construction, high-strength, high-toughness and low-yield-ratio Q550MPa grade steel has become the main structural material due to its excellent mechanical properties, light self-weight and high fatigue resistance. The main characteristics of this steel are as follows: (1) For seismic resistance requirements, for Q550MPa grade bridge steel, the yield ratio requirement is ≤0.86; (2) The minimum yield strength is 550MPa, the minimum tensile strength is 645MPa, and the maximum is 750MPa; (3) Good low-temperature toughness, -40°C, 120J. After novelty search, the mainly produced ones at home and abroad are 550MPa grade weathering bridge steel. Weathering bridge steel contains a relatively high content of Cu and Ti, which has an obvious effect on refining the grains of the steel plate, but the cost is relatively high. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio, and a production method thereof. The steel plate has good seismic performance and low-temperature impact toughness, as well as high strength, and can meet the requirements of long-span bridges in the field of bridge steel structures.

[0005] In order to achieve the above purpose, the technical solution of the present invention is as follows: A Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio, which is composed of the following chemical components by weight percentage: C: 0.05% - 0.09%, Si: 0.20% - 0.50%, Mn: 1.40% - 1.60%, P≤0.015%, S≤0.006%, Ni: 0.15% - 0.25%, Cr: 0.25% - 0.40%, Mo: 0.20% - 0.40%, Nb: 0.025% - 0.035%, Al 全: 0.020% - 0.040%, N: 0.005% - 0.010%, carbon equivalent CEV: 0.40 - 0.47, welding crack sensitivity coefficient Pcm ≤ 0.22, with the balance being Fe and inevitable impurities. Among them, the carbon equivalent CEV calculation formula: CEV(%) = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15; the welding crack sensitivity coefficient Pcm calculation formula: Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B.

[0006] Furthermore, for the Q550MPa grade steel plate for high-strength, high-toughness and low yield ratio bridges of the present invention, its thickness is 8 - 50 mm.

[0007] Furthermore, for the Q550MPa grade steel plate for high-strength, high-toughness and low yield ratio bridges of the present invention, the yield strength ≥ 550 MPa, the tensile strength ≥ 660 MPa, the yield ratio < 0.86, the elongation > 16%, and the impact energy AKv at -40°C > 120 J.

[0008] Furthermore, the production method of the Q550MPa grade steel plate for high-strength, high-toughness and low yield ratio bridges of the present invention includes the following steps: (1) Smelting: According to the above chemical composition ratio, primary smelting, LF refining, Ca treatment, and VD vacuum treatment are carried out in sequence; (2) Casting: The molten steel after smelting is cast, and the casting superheat is controlled at 15 - 25°C to obtain a continuous casting billet; (3) Heating: The cast billet is heated in a continuous furnace, the maximum heating temperature is 1200°C - 1230°C, the soaking time in the soaking section ≥ 60 min, and the total heating time ≥ 10 min / mm; (4) Rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1050 - 1150°C, the reduction rate per pass ≥ 15%, and the cumulative reduction rate is 30 - 50%; the second stage is the finish rolling stage, the starting rolling temperature ≤ 950°C, the finishing rolling temperature is 800 - 830°C, and the cumulative reduction rate is 40 - 70%; (5) Water cooling: The rolled steel plate is controlled to cool in an ACC rapid cooling device, the water inlet temperature is controlled at 750 - 790°C, the cooling rate ≥ 10°C / s, the recrystallization temperature is 500 - 600°C, and the steel plate is stacked and slowly cooled after being taken off the production line to prevent internal cracks from forming due to the inability of the internal stress of the steel plate to be released in time; (6) Heat treatment: The steel plate is subjected to quenching + tempering treatment. The quenching temperature is 820 ± 10°C, the total heating time is 2.5 - 3 min / mm, the tempering temperature is 500 ± 10°C, and the total heating time is 2.5 - 3 min / mm.

[0009] The steel plate of the present invention adopts the chemical composition design of C-Si-Mn-Ni-Cr-Mo-Nb series bainitic steel. Through low-carbon composition design and TMCP + quenching + tempering process, a Q550MPa grade steel plate with a thickness of 8mm - 50mm suitable for long-span bridges is produced.

[0010] The C content has an obvious influence on the hardenability and strength of the steel plate. If the C content is too high, the low-temperature impact toughness of the steel plate will be severely deteriorated. Therefore, the C content is designed to be 0.05% - 0.09%. The Si element significantly improves the strength of the steel plate through solid solution strengthening. However, too high Si content will increase the hardness of the steel plate and deteriorate the low-temperature impact toughness. Therefore, the Si content is designed to be 0.2% - 0.5%. The Mn content is 1.40 - 1.60%, which mainly plays the role of solid solution strengthening, reducing the phase transformation temperature and increasing the strength of the steel plate. The Nb content is 0.025 - 0.035%. It forms a "Cottrell atmosphere" by pinning at the austenite boundary, thereby preventing the growth of austenite grains and achieving the purpose of grain refinement. In addition, during the cooling of the TMCP process, the Nb element precipitated at high temperature combines with C and N to form Nb(C, N) compounds. The precipitation of these Nb(C, N) compounds will hinder the movement of dislocations, thereby achieving the purpose of precipitation strengthening. The Ni content is 0.15% - 0.25%. The role of the Ni element is to expand the austenite region. The expansion of the austenite region can increase the supercooling degree of the steel plate, thus achieving the effects of refined structure and fine grain strengthening. In addition, it can also increase the deformation ability of the steel, improve the stability and strength of the alloy, and improve the low-temperature impact toughness of the steel plate. The Cr and Mo elements can significantly improve the hardenability of the steel plate and form solid solution strengthening in the steel plate to increase the strength of the steel plate. The N content is 0.005% - 0.010%, and its main role is to refine grains; nitrogen promotes the precipitation of carbonitrides at the austenite-ferrite phase interface, playing a role in preventing the growth of ferrite grains, and thus refining ferrite grains. The lower limits of the contents of impurity elements such as P and S are not restricted and are reduced as much as possible under the condition permitted by the process equipment to achieve the purpose of pure steel quality and uniform structure.

[0011] The technical solution of the present invention has the following beneficial technical effects: (1) The steel plate has a high yield strength and is suitable for long-span bridge structures.

[0012] (2) The steel plate has good seismic performance and a low yield ratio, and the yield ratio < 0.86.

[0013] (3) It has good low-temperature toughness, and the impact energy is above 120J under the condition of -40°C. Specific embodiments

[0014] The technical solution of the present invention will be further described in detail below through examples. Example 1

[0015] In this embodiment, the high-strength, high-toughness and low yield-strength ratio Q550MPa steel plate for bridges has the following chemical composition by weight percentage: C: 0.05%, Si: 0.20%, Mn: 1.60%, P: 0.013%, S: 0.006%, Ni: 0.25%, Cr: 0.25%, Mo: 0.40%, Nb: 0.035%, Al 全 : 0.020%, N: 0.006%, CEV: 0.46, Pcm: 0.18, and the balance is Fe and inevitable impurities; the thickness of the steel plate is 8mm, and its production method is as follows: (1) Smelting: Converter smelting is carried out according to the above chemical composition ratio, and after smelting is completed, it is sent to the LF refining furnace for refining; When the ladle temperature is ≥1660°C, it is lifted to the VD furnace for vacuum treatment. 150m of Ca-Fe wire is added before vacuum, the vacuum degree is 66Pa, and the vacuum holding time is 18 minutes to ensure good argon blowing throughout the process.

[0016] (2) Casting: The molten steel after smelting is cast, and the casting superheat is controlled at 15°C to obtain a continuous casting billet; (3) Heating: The continuous casting billet is heated in a continuous furnace, the highest heating temperature is 1200°C, the soaking time in the soaking section is 60min, and the total heating time is 10min / mm; (4) Rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1050°C, the reduction rate per pass is 15%, and the cumulative reduction rate is 30%; The second stage is the finish rolling stage, the starting rolling temperature is 950°C, the finishing rolling temperature is 830°C, and the cumulative reduction rate is 40%; (5) Water cooling: The rolled steel plate is controlled to cool in the ACC rapid cooling device, the water inlet temperature is 790°C, the cooling rate is 18°C / s, and the recrystallization temperature is 599°C; After the steel plate is taken off the production line, it is stacked and slowly cooled for 24 hours to prevent internal cracks from forming due to the failure of the internal stress of the steel plate to be released in time; (6) Heat treatment: The steel plate is subjected to quenching + tempering treatment, the quenching temperature is 830°C, the total heating time is 2.5min / mm, the tempering temperature is 510°C, and the total heating time is 3min / mm.

[0017] The yield strength of the steel plate in this embodiment is 573MPa, the tensile strength is 672MPa, the yield ratio is 0.853, the elongation is 22%, and the impact energy AKv (transverse) at -40°C is: 88.3J, 81.7J, 101.5J. (The national standard "Steel for Bridge Structures" requires that the impact performance of a 8mm-thick steel plate ≥60J). Example 2

[0018] In this embodiment, the Q550MPa grade steel plate for high-strength, high-toughness and low yield ratio bridges has the following chemical composition by weight percentage: C: 0.075%, Si: 0.38%, Mn: 1.46%, P: 0.014%, S: 0.004%, Ni: 0.15%, Cr: 0.38%, Mo: 0.26%, Nb: 0.025%, Al 全 : 0.031%, N: 0.0074%, CEV: 0.46, Pcm: 0.20, and the balance is Fe and inevitable impurities; the thickness of the steel plate is 20mm, and its production method is as follows: (1) Smelting: Electric furnace smelting is carried out according to the above chemical composition ratio, and after smelting is completed, it is sent to the LF refining furnace for refining; when the ladle temperature is 1665°C, it is lifted to the VD furnace for vacuum treatment. 150m of Ca wire is added before vacuum, the vacuum degree is 69Pa, and the vacuum holding time is 20 minutes to ensure good argon blowing throughout the process.

[0019] (2) Casting: The molten steel after smelting is cast, and the casting superheat is controlled at 25°C to obtain a continuous casting billet; (3) Heating: The continuous casting billet is heated in a continuous furnace, the highest heating temperature is 1214°C, the soaking time in the soaking section is 70min, and the total heating time is 11min / mm; (4) Rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1080°C, the reduction rate per pass is 15%, and the cumulative reduction rate is 45%; the second stage is the finish rolling stage, the starting rolling temperature is 860°C, the finishing rolling temperature is 819°C, and the cumulative reduction rate is 70%; (5) Water cooling: The rolled steel plate is controlled to cool in the ACC rapid cooling device, the water inlet temperature is 769°C, the cooling rate is 15°C / s, and the recrystallization temperature is 559°C; after the steel plate is taken off the production line, it is stacked and slowly cooled for 24 hours to prevent internal cracks from forming due to the failure of the internal stress of the steel plate to be released in time; (6) Heat treatment: The steel plate is subjected to quenching + tempering treatment, the quenching temperature is 810°C, the total heating time is 3.0min / mm, the tempering temperature is 496°C, and the total heating time is 2.5min / mm.

[0020] The yield strength of the steel plate in this embodiment is 581MPa, the tensile strength is 689MPa, the yield ratio is 0.843, the elongation is 23.5%, and the impact energy AKv (transverse) at -40°C is: 165.3J, 170.7J, 273.3J. Example 3

[0021] In this embodiment, the Q550MPa grade steel plate for high-strength, high-toughness and low yield ratio bridges has the following chemical composition by weight percentage: C: 0.067%, Si: 0.32%, Mn: 1.50%, P: 0.012%, S: 0.006%, Ni: 0.19%, Cr: 0.33%, Mo: 0.31%, Nb: 0.030%, Al 全 : 0.028%, N: 0.0065%, CEV: 0.46, Pcm: 0.19, and the balance is Fe and inevitable impurities; the thickness of the steel plate is 30mm, and its production method is as follows: (1) Smelting: Electric furnace smelting is carried out according to the above chemical composition ratio. After smelting is completed, it is sent to the LF refining furnace for refining; when the ladle temperature is 1650°C, it is lifted to the VD furnace for vacuum treatment. 150m of Ca wire is added before vacuum, the vacuum degree is 66Pa, and the vacuum holding time is 19 minutes to ensure good argon blowing throughout the process.

[0022] (2) Casting: The molten steel after smelting is cast, and the casting superheat is controlled at 22°C to obtain a continuous casting billet; (3) Heating: The continuous casting billet is heated in a continuous furnace, the maximum heating temperature is 1210°C, the soaking time in the soaking section is 60min, and the total heating time is 12min / mm; (4) Rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1150°C, the reduction per pass is 15%, and the cumulative reduction is 39%; the second stage is the finish rolling stage, the starting rolling temperature is 880°C, the finishing rolling temperature is 810°C, and the cumulative reduction is 60%; (5) Water cooling: The rolled steel plate is controlled to cool in the ACC rapid cooling device, the water inlet temperature is 774°C, the cooling rate is 12°C / s, and the recrystallization temperature is 546°C; after the steel plate is taken off the production line, it is stacked and slowly cooled for 24 hours to prevent internal cracks from forming due to the failure of the internal stress of the steel plate to be released in time; (6) Heat treatment: The steel plate is subjected to quenching + tempering treatment, the quenching temperature is 820°C, the total heating time is 3min / mm, the tempering temperature is 500°C, and the total heating time is 3min / mm.

[0023] The yield strength of the steel plate in this embodiment is 591MPa, the tensile strength is 701MPa, the yield ratio is 0.843, the elongation is 26%, and the impact energy AKv (transverse) at -40°C is 296J, 300J, 299J. Example 4

[0024] In this embodiment, the high-strength, high-toughness and low yield-strength ratio Q550MPa steel plate for bridges has the following chemical composition by weight percentage: C: 0.087%, Si: 0.47%, Mn: 1.42%, P: 0.008%, S: 0.005%, Ni: 0.23%, Cr: 0.28%, Mo: 0.32%, Nb: 0.032%, Al 全 : 0.037%, N: 0.0085%, CEV: 0.46, Pcm: 0.21, and the balance is Fe and unavoidable impurities; the thickness of the steel plate is 36mm, and its production method is as follows: (1) Smelting: Electric furnace smelting is carried out according to the above chemical composition ratio, and after smelting is completed, it is sent to the LF refining furnace for refining; when the ladle temperature is 1665°C, it is lifted to the VD furnace for vacuum treatment. 150m of Ca-Fe wire is added before vacuum, the vacuum degree is 66Pa, and the vacuum holding time is 20 minutes to ensure good argon blowing throughout the process.

[0025] (2) Casting: The molten steel after smelting is cast, and the casting superheat is controlled at 18°C to obtain a continuous casting billet; (3) Heating: The continuous casting billet is heated in a continuous furnace, the highest heating temperature is 1225°C, the soaking time in the soaking section is 63min, and the total heating time is 14min / mm; (4) Rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1110°C, the reduction rate per pass is 15%, and the cumulative reduction rate is 36%; the second stage is the finish rolling stage, the starting rolling temperature is 895°C, the finishing rolling temperature is 807°C, and the cumulative reduction rate is 43%; (5) Water cooling: The steel plate after rolling is controlled to cool in the ACC rapid cooling device, the water inlet temperature is 756°C, the cooling rate is 16°C / s, and the recrystallization temperature is 510°C; after the steel plate is taken off the production line, it is stacked and slowly cooled for 24 hours to prevent internal cracks from forming due to the inability of the internal stress of the steel plate to be released in time; (6) Heat treatment: The steel plate is subjected to quenching + tempering treatment, the quenching temperature is 818°C, the total heating time is 3min / mm, the tempering temperature is 490°C, and the total heating time is 2.9min / mm.

[0026] The yield strength of the steel plate in this embodiment is 569MPa, the tensile strength is 702MPa, the yield-strength ratio is 0.81, the elongation is 28%, and the impact energy AKv (-40°C, transverse) is 300J, 300J, 299J. Example 5

[0027] In this embodiment, the Q550MPa grade steel plate for high-strength, high-toughness and low yield ratio bridges has the following chemical composition by weight percentage: C: 0.083%, Si: 0.44%, Mn: 1.43%, P: 0.011%, S: 0.004%, Ni: 0.21%, Cr: 0.34%, Mo: 0.20%, Nb: 0.025%, Al 全 : 0.035%, N: 0.008%, CEV: 0.44, Pcm: 0.20, and the balance is Fe and inevitable impurities; the thickness of the steel plate is 40mm, and its production method is as follows: (1) Smelting: Electric furnace smelting is carried out according to the above chemical composition ratio. After smelting is completed, it is sent to the LF refining furnace for refining; when the ladle temperature is 1665°C, it is lifted to the VD furnace for vacuum treatment. 150m of Ca wire is added before vacuum, the vacuum degree is 64Pa, and the vacuum holding time is 17 minutes to ensure good argon blowing throughout the process.

[0028] (2) Casting: The molten steel after smelting is cast, and the casting superheat is controlled at 20°C to obtain a continuous casting billet; (3) Heating: The continuous casting billet is heated in a continuous furnace, the maximum heating temperature is 1220°C, the soaking time in the soaking section is 71min, and the total heating time is 16min / mm; (4) Rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1100°C, the reduction rate per pass is 15%, and the cumulative reduction rate is 50%; the second stage is the finish rolling stage, the starting rolling temperature is 885°C, the finishing rolling temperature is 811°C, and the cumulative reduction rate is 56%; (5) Water cooling: The rolled steel plate is controlled to cool in the ACC rapid cooling device, the water inlet temperature is 762°C, the cooling rate is 14°C / s, and the recrystallization temperature is 521°C; after the steel plate is taken off the production line, it is stacked and slowly cooled for 24 hours to prevent internal cracks from forming due to the failure of the internal stress of the steel plate to be released in time; (6) Heat treatment: The steel plate is subjected to quenching + tempering treatment, the quenching temperature is 810°C, the total heating time is 2.5min / mm, the tempering temperature is 492°C, and the total heating time is 2.8min / mm.

[0029] The yield strength of the steel plate in this embodiment is 572MPa, the tensile strength is 679MPa, the yield ratio is 0.842, the elongation is 21.3%, and the impact energy AKv (transverse) at -40°C is 195J, 188J, 224J. Example 6

[0030] In this embodiment, the high-strength, high-toughness and low yield ratio Q550MPa steel plate for bridges has the following chemical composition by weight percentage: C: 0.079%, Si: 0.41%, Mn: 1.44%, P: 0.006%, S: 0.004%, Ni: 0.18%, Cr: 0.40%, Mo: 0.22%, Nb: 0.029%, Al 全 : 0.033%, N: 0.005%, CEV: 0.46, Pcm: 0.20, and the balance is Fe and inevitable impurities; the thickness of the steel plate is 50mm, and its production method is as follows: (1) Smelting: Electric furnace smelting is carried out according to the above chemical composition ratio. After smelting is completed, it is sent to the LF refining furnace for refining; when the ladle temperature is 1665°C, it is lifted to the VD furnace for vacuum treatment. 150m of Ca-Fe wire is added before vacuum, the vacuum degree is 68Pa, and the vacuum holding time is 19 minutes to ensure good argon blowing throughout the process.

[0031] (2) Casting: The molten steel after smelting is cast, and the casting superheat is controlled at 23°C to obtain a continuous casting billet; (3) Heating: The continuous casting billet is heated in a continuous furnace, the maximum heating temperature is 1216°C, the soaking time in the soaking section is 72min, and the total heating time is 13min / mm; (4) Rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1090°C, the reduction per pass is 15%, and the cumulative reduction is 47%; the second stage is the finish rolling stage, the starting rolling temperature is 865°C, the finishing rolling temperature is 814°C, and the cumulative reduction is 62%; (5) Water cooling: The rolled steel plate is controlled to cool in the ACC rapid cooling device, the water inlet temperature is 765°C, the cooling rate is 10°C / s, and the recrystallization temperature is 533°C; after the steel plate is taken off the production line, it is stacked and slowly cooled for 24 hours to prevent internal cracks from forming due to the failure of the internal stress of the steel plate to be released in time; (6) Heat treatment: The steel plate is subjected to quenching + tempering treatment, the quenching temperature is 811°C, the total heating time is 2.6min / mm, the tempering temperature is 495°C, and the total heating time is 2.6min / mm.

[0032] The yield strength of the steel plate in this embodiment is 568MPa, the tensile strength is 688MPa, the yield ratio is 0.83, the elongation is 23%, and the impact energy AKv (transverse) at -40°C is 155J, 276J, 300J.

Claims

1. A Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio, characterized in that, It is composed of the following chemical components by weight percentage: C: 0.05% - 0.09%, Si: 0.20% - 0.50%, Mn: 1.40% - 1.60%, P ≤ 0.015%, S ≤ 0.006%, Ni: 0.15% - 0.25%, Cr: 0.25% - 0.40%, Mo: 0.20% - 0.40%, Nb: 0.025% - 0.035%, Al 全 : 0.020% - 0.040%, N: 0.005% - 0.010%, carbon equivalent CEV: 0.40 - 0.47, welding crack sensitivity coefficient Pcm ≤ 0.22, and the balance is Fe and inevitable impurities.

2. The Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio according to claim 1, characterized in that, The thickness of the steel plate is 8 - 50 mm.

3. The Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio according to claim 1, characterized in that, The yield strength of the steel plate is ≥550 MPa, the tensile strength is ≥660 MPa, the yield ratio is <0.86, the elongation is >16%, and the impact energy AKv at -40°C is >120 J.

4. The production method of the Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio based on claim 1, characterized in that, It includes smelting, casting, heating, rolling, water cooling and heat treatment.

5. The production method of the Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio according to claim 4, characterized in that, The heating: The continuous casting billet is heated in a continuous furnace, the maximum heating temperature is 1200°C - 1230°C, the soaking time is ≥60 min, and the total heating time is ≥10 min / mm.

6. The production method of the Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio according to claim 4, characterized in that, The rolling: The two-stage rolling method is adopted. The first stage is the rough rolling stage, the rolling temperature is 1050 - 1150°C, the reduction per pass is ≥15%, and the cumulative reduction is 30 - 50%; the second stage is the finish rolling stage, the starting rolling temperature is ≤950°C, the finishing rolling temperature is 800 - 830°C, and the cumulative reduction is 40 - 70%.

7. The production method of the Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio according to claim 4, characterized in that, The water cooling: The rolled steel plate is controlled to cool in an ACC rapid cooling device, the water inlet temperature is controlled at 750 - 790°C, the cooling rate is ≥10°C / s, the recrystallization temperature is 500 - 600°C, and the steel plate is stacked and slowly cooled after being taken off the production line.

8. The production method of the Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio according to claim 4, characterized in that, The heat treatment: The steel plate is subjected to quenching + tempering treatment.

9. The production method of the Q550MPa grade steel plate for bridges with high strength, high toughness and low yield ratio according to claim 7, characterized in that, The quenching temperature is 820 ± 10°C, and the total heating time is 2.5 - 3 min / mm; the tempering temperature is 500 ± 10°C, and the total heating time is 2.5 - 3 min / mm.