Ultra-thick, ultra-high-strength steel for large hydropower engineering and its manufacturing method

Abstract

The invention relates to an ultra-thick, ultra-high-strength steel for large-scale hydropower engineering and a manufacturing method thereof. The chemical components of the steel are C: 0.10%-0.15%; Si: 0.06%-0.10%; Mn: 0.90%-1.50%; P≤0.008%; S≤0.001%; ​​Ni: 1.75%-2.4%; Cr: 0.55%-0.75%; Mo: 0.75%-1.2%; Ti: 0.07%-0.11%; N: 0.015%-0.025%; CeO2: 0.10%-0.20%; Al: 0.02%-0.04%; [H]≤1.5ppm; [O]≤8ppm; the remainder is Fe and impurities. The steel is designed with low carbon, low manganese, Ni+Cr+Mo+Ti low alloying composition, combined with electroslag remelting + rolling + offline tempering heat treatment process, and utilizing the grain refinement effect of high melting point Ti (CN) and CeO2 to achieve high permeability rolling production of thick electroslag billets, and finally obtain ultra-thick and ultra-high strength steel plates with a grain size of 7.5 or above, a thickness of 110 to 160 mm, and 1000 MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of hydropower steel manufacturing, and in particular to an ultra-thick, ultra-high-strength large-scale hydropower engineering steel and a manufacturing method thereof. Background Art

[0002] With the large-scale development trend of hydropower projects, the strength level of hydropower steel will be further improved, and at the same time, the thickness of steel plates will exceed 100mm. The increase in steel plate thickness will bring a series of problems such as reduced Z-axis performance, uneven structure, and high production costs. In addition, the special performance requirements of hydropower steel will further increase the difficulty of production.

[0003] The existing domestic production methods for 1000MPa strength grade steel are mainly concentrated on thickness specifications below 100mm, and the composition design and process design are greatly different from the present invention.

[0004] The Chinese patent application with publication number CN108385034A discloses "a LGB-QT production method for a 1000MPa grade hydropower steel plate with a thickness of no more than 100mm". The chemical composition of the steel plate is: C0.12-0.21%, Si0.30-0.80%, Mn0.95-1.65%, P≤0.01%, S≤0.002%, Ni≤4.50%, Cr0.20-0.90%, Cu≤0.20%, Alt≤0.10%, Nb≤0.15%, Mo≤0.50%, V≤0.20%, Ti≤0.08%, B≤0.005%, and the balance is Fe. The LGB-Q&T preparation method of the steel plate is: smelting and continuous casting according to the set composition, two-stage controlled rolling after heating, then controlled cooling to room temperature, and finally quenching and tempering. The steel plate produced by the method has a thickness of no more than 100 mm, is designed with a low alloy composition of Ni+Cr+Mo, and uses Nb, V and Ti for controlled rolling and controlled cooling production, which is different from the composition and production process of the present invention.

[0005] The Chinese patent application with publication number CN113399948A discloses "a method for producing 1000MPa hydropower steel with a thickness of more than 100mm". Two 250-350mm thick continuous casting billets are welded together and then rolled and heat treated. Specifically, the method includes the steps of billet welding, vacuuming, rolling and heat treatment after the continuous casting billet size and composite surface are processed accordingly. It belongs to the technical field of rolled composite thick plate manufacturing. The composition of the cast billet used is also different from that of the present invention, and it does not involve the Z-direction performance of the steel plate. For composite plates with a thickness of more than 100mm, the performance safety is relatively low.

[0006] The Chinese patent application with publication number CN108504960A discloses "a 1000MPa grade low crack hydropower steel plate for large hydropower projects and its production method", including the following chemical components in mass percentage: C: 0.06-0.17%, Si: ≤0.15%, Mn: 0.8-2.0%, P: ≤0.010%, S: ≤0.003%, Ni: 1.0-2.0%, Cu: 0.10-0.25%, Cr: 0.3-1.5%, Mo: 0.4-0.7%, V+Nb+Ti: ≤0.1%, Als: 0.015-0.045%, Ce≤0.020%, CEV≤0.64%, Pcm≤0.28%, and the rest are Fe and residual elements. The product has the advantages of high strength, high toughness, low crack sensitivity, good surface quality and good weldability, but the thickness of the steel plate produced is only 10 to 50 mm.

[0007] The Chinese invention patent with the authorization announcement number CN103451562B discloses a "quenched and tempered large thickness easy-to-weld Z-direction high-strength steel plate for hydropower and its production method", which includes smelting, continuous casting, electroslag remelting, heating, rolling, water cooling after rolling, hot stacking, and heat treatment processes, and is smelted from the following mass percentage components: C≤0.18%, Si≤0.60%, Mn≤1.80%, P≤0.012%, S≤0.005%, Ni≤2.00%, Mo≤0.70%, Cr≤1.5%, Cu≤0.5%, Nb≤0.060%, Al≥0.020%, V≤0.12%, Ti≤0.05%, B≤0.004%, N≤0.015%, and the balance is Fe and unavoidable impurities. Compared with the invention, the chemical composition design of the steel is different and the production process is also different. The steel plate described in the invention is produced by controlled rolling and controlled cooling + quenching and tempering heat treatment, and the heating time is as long as 30 hours. The entire production process is cumbersome, the production rhythm is slow, and the production cost is high. In addition, the room temperature tensile strength of the steel plate produced by the invention is only 542-621MPa, which is quite different from the strength of the steel plate of the present invention; the impact energy of the steel plate described in the invention at -20℃ is distributed from 78J to 300J, which shows that the impact performance fluctuates greatly, while the present invention has stable impact performance at 1 / 4 and 1 / 2 of the plate thickness at -40℃. Summary of the invention

[0008] The present invention provides an ultra-thick, ultra-high-strength steel for large hydropower engineering and a manufacturing method thereof, which adopts a low-carbon, low-manganese, Ni+Cr+Mo+Ti low-alloying composition design, cooperates with an electroslag remelting + rolling + offline quenching and tempering heat treatment process, and utilizes high melting point Ti(CN), CeO 2The effect of grain refinement realizes the high-permeability rolling production of thick electroslag billets, and finally obtains ultra-thick and ultra-high-strength steel plates with a grain size of 7.5 or above, a thickness of 110 to 160 mm, and a grade of 1000 MPa.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] An ultra-thick, ultra-high-strength steel for large hydropower projects, wherein the chemical composition of the steel is, by weight percentage, C: 0.10% to 0.15%; Si: 0.06% to 0.10%; Mn: 0.90% to 1.50%; P≤0.008%; S≤0.001%; ​​Ni: 1.75% to 2.4%; Cr: 0.55% to 0.75%; Mo: 0.75% to 1.2%; Ti: 0.07% to 0.11%; N: 0.015% to 0.025%; CeO 2 : 0.10%~0.20%; Al: 0.02%~0.04%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and unavoidable impurities.

[0011] Furthermore, the room temperature tensile strength of the finished steel plate is ≥950MPa, the yield strength is ≥885MPa, the elongation after fracture is ≥15%; the -40°C impact absorption energy is >150J; the Z-direction cross-sectional shrinkage is >55%; and the non-ductile transition temperature TNDT is ≤-45°C.

[0012] A method for manufacturing ultra-thick ultra-high strength steel for large hydropower engineering, the steel plate manufacturing process includes steel billet electroslag remelting, electroslag billet annealing, heating, rolling, and offline quenching and tempering heat treatment; the control process is as follows:

[0013] 1) Electroslag remelting of steel billets: Blow argon into the crystallizer for 15 to 20 minutes before remelting, with an argon flow rate of 7 to 9 m 3 / h; during remelting, the melting rate is controlled at 560-620kg / h, and the cooling water volume of the crystallizer is 55-65m 3 / h, water temperature is controlled at 26~33℃; the current setting value in the slagging stage is 16000~22000A, and the current setting value in the feeding stage is 8000~12000A and maintained for 10~15min;

[0014] 2) Electroslag billet annealing: After demoulding, the electroslag billet is slowly cooled, the slow cooling pit is preheated to 400-500°C, the electroslag billet is kept warm for more than 15 hours, and then slowly cooled to room temperature;

[0015] 3) Heating: The heating and insulation temperature of the electroslag billet is 1250-1300°C, and the insulation time is 3-5h;

[0016] 4) Rolling; the rolling temperature is 1180-1220°C, the total deformation of the first four rolling passes is ≥45mm, and the reduction rate of the first two passes in the last rolling pass is ≥10%; the steel plate is slowly cooled off the line after rolling, and the slow cooling time is not less than 30 hours;

[0017] 5) Offline quenching and tempering heat treatment; quenching temperature is 880-950°C, holding time is 2-5 min / mm, quenching cooling rate is 20-25°C / s; tempering holding temperature is 560-620°C, holding time is 4-8 min / mm.

[0018] Furthermore, the thickness of the electroslag billet is 500-700 mm; the thickness of the finished steel plate is 110-160 mm.

[0019] Furthermore, the electroslag billet is descaled with high-pressure water for 1 to 3 minutes after leaving the heating furnace, and the descaling water pressure is 28 to 33 MPa.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) Adopt low carbon, low manganese, Ni+Cr+Mo+Ti low alloy composition design, and use high melting point Ti(CN), CeO 2 The effect of grain refinement enables high-permeability rolling production of thick electroslag billets, and ultimately obtains ultra-thick and ultra-high-strength steel plates with a grain size of 7.5 or above (finer);

[0022] 2) Produced by electroslag remelting process, the steel has high purity, non-metallic inclusions ≤ 0.5 level, no center looseness and center segregation;

[0023] 3) Using 500-700mm thick electroslag billets, directly rolling finished steel plates at high temperature and high pressure, and using precise offline quenching and tempering heat treatment process to achieve the manufacture of 110-160mm thick 1000MPa grade steel for hydropower engineering; the production process is relatively simple and stable, and the production efficiency is high;

[0024] 4) Through the innovative design of chemical composition and process, the production of thick, homogenized high-strength steel plates has been realized. The mechanical properties of the steel plates at 1 / 4 and 1 / 2 of the thickness are basically the same, with good performance uniformity;

[0025] 5) The room temperature tensile strength of the finished steel plate is ≥950MPa, the yield strength is ≥885MPa, and the elongation after fracture is ≥15%; the impact absorption energy at -40℃ is >150J; the Z-direction section collection rate is >55%; the non-ductile transition temperature TNDT is ≤-45℃, and it has excellent low-temperature toughness, resistance to lamellar tearing and resistance to brittle fracture, which fully meets the requirements for the use of ultra-thick and ultra-high-strength steel in large hydropower projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a typical metallographic structure photograph of the ultra-thick, ultra-high-strength steel for large-scale hydropower engineering described in the present invention. DETAILED DESCRIPTION

[0027] The invention discloses an ultra-thick, ultra-high-strength steel for large hydropower engineering, wherein the chemical components of the steel are, by weight percentage, C: 0.10% to 0.15%; Si: 0.06% to 0.10%; Mn: 0.90% to 1.50%; P≤0.008%; S≤0.001%; ​​Ni: 1.75% to 2.4%; Cr: 0.55% to 0.75%; Mo: 0.75% to 1.2%; Ti: 0.07% to 0.11%; N: 0.015% to 0.025%; CeO 2 : 0.10%~0.20%; Al: 0.02%~0.04%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and unavoidable impurities.

[0028] Furthermore, the room temperature tensile strength of the finished steel plate is ≥950MPa, the yield strength is ≥885MPa, the elongation after fracture is ≥15%; the -40°C impact absorption energy is >150J; the Z-direction cross-sectional shrinkage is >55%; and the non-ductile transition temperature TNDT is ≤-45°C.

[0029] The present invention discloses a method for manufacturing ultra-thick ultra-high strength large-scale hydropower engineering steel, wherein the steel plate manufacturing process includes steel billet electroslag remelting, electroslag billet annealing, heating, rolling, and offline quenching and tempering heat treatment; the control process is as follows:

[0030] 1) Electroslag remelting of steel billets: Blow argon into the crystallizer for 15 to 20 minutes before remelting, with an argon flow rate of 7 to 9 m 3 / h; during remelting, the melting rate is controlled at 560-620kg / h, and the cooling water volume of the crystallizer is 55-65m 3 / h, water temperature is controlled at 26~33℃; the current setting value in the slagging stage is 16000~22000A, and the current setting value in the feeding stage is 8000~12000A and maintained for 10~15min;

[0031] 2) Electroslag billet annealing: After demoulding, the electroslag billet is slowly cooled, the slow cooling pit is preheated to 400-500°C, the electroslag billet is kept warm for more than 15 hours, and then slowly cooled to room temperature;

[0032] 3) Heating: The heating and insulation temperature of the electroslag billet is 1250-1300°C, and the insulation time is 3-5h;

[0033] 4) Rolling; the rolling temperature is 1180-1220°C, the total deformation of the first four rolling passes is ≥45mm, and the reduction rate of the first two passes in the last rolling pass is ≥10%; the steel plate is slowly cooled off the line after rolling, and the slow cooling time is not less than 30 hours;

[0034] 5) Offline quenching and tempering heat treatment; quenching temperature is 880-950°C, holding time is 2-5 min / mm, quenching cooling rate is 20-25°C / s; tempering holding temperature is 560-620°C, holding time is 4-8 min / mm.

[0035] Furthermore, the thickness of the electroslag billet is 500-700 mm; the thickness of the finished steel plate is 110-160 mm.

[0036] Furthermore, the electroslag billet is descaled with high-pressure water for 1 to 3 minutes after leaving the heating furnace, and the descaling water pressure is 28 to 33 MPa.

[0037] The reasons for the composition design of the ultra-thick, ultra-high-strength large-scale hydropower engineering steel described in the present invention are as follows:

[0038] (1) C: Carbon dissolves in steel to form interstitial solid solution, which plays a role in solid solution strengthening. It can form fine carbides with Ti element, which plays a role in precipitation strengthening and can also improve the hardenability of steel. However, the increase in carbon content will damage the welding performance and low temperature toughness of steel. Therefore, the C content of the present invention is controlled to 0.10% to 0.15%.

[0039] (2) Si: It is used as a reducing agent and deoxidizing agent, and plays a certain role in solid solution strengthening. If the Si content is too high, the plasticity and welding performance of the steel will be reduced, so the Si content in the steel of the present invention is controlled to be 0.06% to 0.10%.

[0040] (3) Mn: A good deoxidizer and desulfurizer in steel; it has a certain solid solution strengthening effect in steel and can improve the strength and hardenability of the steel plate. However, too much manganese can easily cause segregation and deteriorate the toughness of the steel plate. Therefore, the present invention controls the Mn content to 0.90% to 1.50%.

[0041] (4) P and S: Both are harmful elements. P can cause cold brittleness of steel, while S can cause hot brittleness of steel and is prone to segregation, which has a significant adverse effect on the low-temperature toughness and welding performance of steel. Therefore, the lower the content of both, the better. In the present invention, P≤0.008% and S≤0.001% in steel are controlled.

[0042] (5) Ni: Its main functions in the present invention are: 1) lowering the transition temperature and improving the hardenability of the steel plate; 2) playing the role of solid solution strengthening and improving the low-temperature toughness of the steel plate; 3) promoting the formation of fine lath martensite; 4) being used in combination with Cr and Mo, the steel plate obtains comprehensive mechanical properties with good strength and toughness after quenching and tempering heat treatment. The present invention controls the Ni content to be 1.75% to 2.4%.

[0043] (6) Cr: Chromium can react with carbon to form fine dispersed carbides, thus improving the strength and toughness of the steel plate. During quenching, it can reduce the minimum cooling rate for obtaining martensitic structure, making it easier to obtain martensitic structure. It can reduce the content of residual austenite, thereby obtaining a good tempered structure during tempering and improving the strength and toughness of the steel plate. It can also improve the thermodynamic stability of alloy infiltrates such as (FeCr)3C precipitated during tempering in the steel, thus reducing the aggregation rate of carbides during tempering. When used in combination with Mo, the steel plate can have good comprehensive properties after quenching and tempering heat treatment. However, too high a Cr content will reduce the welding performance of the steel. Therefore, the Cr content is controlled to be 0.55% to 0.75% in the present invention.

[0044] (7) Mo: It can be dissolved in ferrite, austenite and carbide to play a role in solid solution strengthening; it can improve the hardenability of steel; improve the stability of carbides and inhibit the aggregation and growth of infiltrates during tempering; it can be used in combination with Cr and Mn to reduce or inhibit the temper brittleness caused by other elements, ensuring that the steel plate has stable high strength and toughness after heat treatment. The present invention controls the Mo content to 0.75% to 1.2%.

[0045] (8) Ti: It can form a large number of fine dispersed carbonitrides, which can refine the cast structure and prevent the growth of austenite grains during high-temperature heating and rolling, thereby refining the grains; Ti can modify the sulfides in steel, forming a large number of nano-sized sulfide particles and dispersing them, thereby reducing the adverse effects of sulfides on steel properties; solid solution Ti can not only play a solid solution strengthening role, but also improve the hardenability of the steel plate; high melting point TiN can prevent the grain coarsening of the welding heat affected zone and improve the welding performance of the steel plate. Therefore, the Ti content in the present invention is controlled to be 0.07% to 0.11%.

[0046] (9) N: Nitrogen plays the following roles in the present invention: 1) It plays the role of solid solution strengthening; 2) It expands the austenite phase region, forms and stabilizes austenite; 3) It forms fine TiN particles with Ti, improves the as-cast structure, and prevents the austenite grains from coarsening during heating; 4) It forms AlN with Al, and refines the grains. The present invention controls the N content to be 0.015% to 0.025%.

[0047] (10)CeO 2 : Add high melting point CeO to the molten steel 2Powder, increase the nucleation core, promote the solidification of molten steel, refine the cast structure; refine the Ti (CN) particles and promote the dispersion distribution; can increase the resistance of grain boundaries to dislocation movement and improve the toughness of steel plates. 2 The content is 0.10%~0.20%.

[0048] (11) Al: plays a certain role in deoxidation and refines the grains. The Al content in the present invention is controlled to be 0.02% to 0.04%.

[0049] (12) H and O: H and O have adverse effects on the properties of the steel plate. The present invention controls [H]≤1.5ppm and [O]≤8ppm.

[0050] The manufacturing process of the ultra-thick ultra-high strength steel for large hydropower engineering described in the present invention is: electroslag remelting of steel billet - electroslag billet annealing - heating - rolling - off-line quenching and tempering heat treatment - ultrasonic flaw detection - performance inspection, and the main control process is as follows:

[0051] 1. In order to ensure that the compression ratio of the steel billet to the steel plate is greater than 3, thereby effectively controlling the lamellar tearing resistance of the steel plate and the uniformity of the structural properties along the thickness section, the present invention adopts an electroslag billet with a thickness of 500 to 700 mm for rolling production of the steel plate. Electroslag remelting belongs to a secondary refining method, which has the advantages of deep purification of steel quality, improvement of the crystal structure of the steel billet, elimination of central porosity and central segregation, and homogenization of the structural properties of the steel plate, and is very suitable for the production of the steel described in the present invention.

[0052] The electroslag remelting consumable electrode adopts a steel billet that meets the chemical composition requirements of the present invention. During the electroslag remelting process, the power system, slag system, slag amount and filling ratio are strictly controlled. Before remelting, argon is blown into the crystallizer for 15 to 20 minutes, and the argon flow rate is 7 to 9m3 / h; during remelting, the melting rate is controlled at 560 to 620kg / h, the crystallizer cooling water volume is 55 to 65m3 / h, and the water temperature is controlled at 26 to 33°C; the current setting value in the slag melting stage is 16000 to 22000A, and the current setting value in the shrinkage compensation stage is 8000 to 12000A and maintained for 10 to 15 minutes. After demolding, the electroslag billet needs to enter the slow cooling pit for slow cooling. The slow cooling pit is preheated to 400 to 500°C in advance. The electroslag billet is kept at this temperature for more than 15 hours, and then slowly cooled to room temperature before leaving the pit. The purpose of long-term annealing is to eliminate the thermal stress and organizational stress of the electroslag billet, improve the cast structure, and disperse the precipitates.

[0053] 2. The heating and holding temperature of the electroslag billet is 1250-1300℃, and the holding time is 3-5h. Since the steel contains a large amount of dispersed high melting point TiN and CeO 2The particles can effectively prevent the coarsening of austenite grains during the high temperature and long time heating process. Therefore, the present invention appropriately increases the heating temperature, while ensuring the consistency of the temperature inside and outside the electroslag billet and sufficient and uniform austenitization, shortens the heating time of the thick electroslag billet and improves the production efficiency.

[0054] After the electroslag billet comes out of the furnace, it is descaled with high-pressure water for 1 to 3 minutes. The descaling water pressure is 28 to 33 MPa. The purpose is to remove the surface oxide scale and ensure the good surface quality of the steel plate.

[0055] 3. After the electroslag billet is descaled, it is rolled. The rolling temperature is 1180-1220℃. The deformation of the first four rolling passes is ≥45mm, and the reduction rate of the first two passes of the last rolling pass is controlled to be ≥10%. During rolling, the interval between each pass should be as short as possible until the thickness of the finished steel plate is rolled to 110-160mm. Multi-pass rolling at high temperature and high pressure enables the thickness section of the electroslag billet to obtain a certain rolling penetration, improves the deformation consistency of the thick billet, and is conducive to improving the uniformity of organization and performance. And by promoting repeated recrystallization of austenite, the grains are refined and the organization is homogenized. Because the billet is thicker, high-temperature rolling also reduces the load of the rolling mill, ensuring the stable production of steel plates.

[0056] After rolling, the steel plate is put into a slow cooling pit for slow cooling. The slow cooling time is not less than 30 hours, which can fully eliminate the internal stress of the steel plate, reduce the temperature difference between the surface and the center of the steel plate, make the rolling structure more uniform, remove hydrogen from the steel plate, and improve the internal quality of the steel plate.

[0057] 4. After the steel plate is slowly cooled, an offline quenching and tempering heat treatment process is adopted, wherein the quenching temperature is 880-950°C, the holding time is 2-5 min / mm, the quenching cooling rate is 20-25°C / s; the tempering holding temperature is 560-620°C, and the holding time is 4-8 min / mm. The reasonable quenching and tempering heat treatment process ensures that the finished steel plate of the present invention obtains uniform and fine tempered troostite structure and excellent performance.

[0058] Typical metallographic structure photos of the ultra-thick, ultra-high-strength steel for large hydropower engineering projects described in the present invention are as follows: Figure 1 As shown, the structure is tempered martensite.

[0059] The following embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0060] [Example]

[0061] The chemical composition of the steel of each embodiment is shown in Table 1, the electroslag remelting process parameters of each embodiment are shown in Table 2, the heating and rolling process parameters are shown in Table 3, the offline tempering heat treatment process parameters of each embodiment are shown in Table 4, and the properties of the finished steel plates of each embodiment are shown in Table 5.

[0062] Table 1 Chemical composition of steel (%)

[0063]

[0064]

[0065] Table 2 Electroslag remelting process parameters

[0066]

[0067] Table 3 Heating and rolling process parameters

[0068]

[0069] Table 4 Offline quenching and tempering heat treatment process parameters

[0070]

[0071] Table 5 Mechanical properties of steel plates in quenched and tempered state

[0072]

[0073] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An ultra-thick, ultra-high-strength steel for large hydropower projects, characterized in that: The chemical composition of the steel is calculated by weight as follows: C: 0.10% ~ 0.15%; Si: 0.06% ~ 0.10%; Mn: 0.90% ~ 1.50%; P ≤ 0.008%; S ≤ 0.001%; ​​Ni: 1.75% ~ 2.4%; Cr: 0.55% ~ 0.75%; Mo: 0.81% ~ 1.2%; Ti: 0.07% ~ 0.11%; N: 0.015% to 0.025%; CeO2: 0.10% to 0.20%; Al: 0.02% to 0.04%; [H] ≤ 1.5ppm; [O] ≤ 8ppm; the balance is Fe and unavoidable impurities; The finished steel plate has a room temperature tensile strength of ≥950MPa, a yield strength of ≥885MPa, and an elongation of ≥15%; -40℃ impact absorption energy>150J; Z-direction cross-sectional shrinkage>55%; non-ductile transition temperature TNDT≤-45℃; the steel plate manufacturing process includes billet electroslag remelting, electroslag billet annealing, heating, rolling, and offline quenching and tempering heat treatment; the control process is as follows: 1) Electroslag remelting of steel billets: Blow argon into the crystallizer for 15 to 20 minutes before remelting, with an argon flow rate of 7 to 9 m 3 / h; during remelting, the melting rate is controlled at 560-620kg / h, and the cooling water volume of the crystallizer is 55-65m 3 / h, water temperature is controlled at 26~33℃; the current setting value in the slagging stage is 16000~22000A, and the current setting value in the feeding stage is 8000~12000A and maintained for 10~15min; 2) Electroslag billet annealing: After demoulding, the electroslag billet is slowly cooled, the slow cooling pit is preheated to 400-500°C, the electroslag billet is kept warm for more than 15 hours, and then slowly cooled to room temperature; 3) Heating: The heating and insulation temperature of the electroslag billet is 1250-1300°C, and the insulation time is 3-5h; 4) Rolling: The rolling temperature is 1180-1220℃, the deformation of each of the first four rolling passes is ≥45mm, and the total reduction rate of the two passes before the last rolling pass is ≥10%; the steel plate is slowly cooled off the line after rolling, and the slow cooling time is not less than 30 hours; 5) Offline quenching and tempering heat treatment; quenching temperature is 910-950°C, holding time is 2-5 min / mm, quenching cooling rate is 20-25°C / s; tempering holding temperature is 560-620°C, holding time is 4-8 min / mm.

2. A method for manufacturing ultra-thick, ultra-high-strength large-scale hydropower engineering steel as claimed in claim 1, characterized in that: The steel plate manufacturing process includes electroslag remelting of steel billets, electroslag billet annealing, heating, rolling, and offline quenching and tempering heat treatment; the control process is as follows: 1) Electroslag remelting of steel billets: Blow argon into the crystallizer for 15 to 20 minutes before remelting, with an argon flow rate of 7 to 9 m 3 / h; during remelting, the melting rate is controlled at 560-620kg / h, and the cooling water volume of the crystallizer is 55-65m 3 / h, water temperature is controlled at 26~33℃; the current setting value in the slagging stage is 16000~22000A, and the current setting value in the feeding stage is 8000~12000A and maintained for 10~15min; 2) Electroslag billet annealing: After demoulding, the electroslag billet is slowly cooled, the slow cooling pit is preheated to 400-500°C, the electroslag billet is kept warm for more than 15 hours, and then slowly cooled to room temperature; 3) Heating: The heating and insulation temperature of the electroslag billet is 1250-1300°C, and the insulation time is 3-5h; 4) Rolling: The rolling temperature is 1180-1220℃, the deformation of each of the first four rolling passes is ≥45mm, and the total reduction rate of the two passes before the last rolling pass is ≥10%; the steel plate is slowly cooled off the line after rolling, and the slow cooling time is not less than 30 hours; 5) Offline quenching and tempering heat treatment; quenching temperature is 910-950°C, holding time is 2-5 min / mm, quenching cooling rate is 20-25°C / s; tempering holding temperature is 560-620°C, holding time is 4-8 min / mm.

3. The method for manufacturing ultra-thick, ultra-high-strength large-scale hydropower engineering steel according to claim 2, characterized in that: The thickness of the electroslag billet is 500-700 mm; the thickness of the finished steel plate is 110-160 mm.

4. The method for manufacturing ultra-thick, ultra-high-strength large-scale hydropower engineering steel according to claim 2, characterized in that: After the electroslag billet comes out of the heating furnace, it is descaled by high-pressure water for 1 to 3 minutes, and the descaling water pressure is 28 to 33 MPa.

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