Ultra-high strength steel for key equipment of large hydropower station and manufacturing method thereof

Abstract

The present invention relates to an ultra-high strength steel for key equipment of a large hydropower station and a manufacturing method thereof. The chemical composition of the steel is C: 0.06%-0.11%; Si: 0.05%-0.095%; Mn: 0.60%-1.10%; P≤0.008%; S≤0.0015%; Ni: 0.66%-0.79%; Cr: 0.66%-0.80%; Mo: 0.71%-0.90%; V: 0.061%-0. 09%; N: 0.01% ~ 0.03%; Zr: 0.02% ~ 0.05%; Al: 0.02% ~ 0.045%; [O] ≤ 8ppm; [H] ≤ 1.5ppm, the balance is Fe and impurities; the integrated design of composition and manufacturing process ensures the uniform and stable performance of the steel plate; the produced steel plate has ultra-high strength, good plasticity, cold bending performance and welding performance; and the production process is short, the cost is low and the efficiency is high.

Description

Technical Field

[0001] The present invention relates to the technical field of hydropower steel manufacturing, and in particular to ultra-high strength steel for key equipment of large hydropower stations and a manufacturing method thereof. Background Art

[0002] At present, the highest strength level of hydropower steel widely used in my country is 800MPa, but with the development trend of large-scale hydropower stations, the use requirements of steel plate strength level will be further improved. As key equipment of hydropower stations, pressure pipes, turbine volutes and other components have complex working environments, which not only require the steel plates to have high strength and toughness and good welding performance, but also require the steel plates to be purified and homogenized to meet high standards of safety use requirements.

[0003] The present invention provides a 30-80 mm thick ultra-high strength steel for key equipment of large hydropower stations and a manufacturing method thereof. The produced steel plate not only has an ultra-high strength of 1000 MPa, but also has good -40°C impact toughness, cold bending performance and welding performance, which fully meets the use requirements of ultra-high strength steel for a new generation of large hydropower stations.

[0004] The present invention is different from the existing domestic steel in chemical composition and production process design, such as:

[0005] The Chinese patent application with publication number CN108504960 A discloses "a 1000MPa grade low crack hydropower steel plate for large hydropower projects and its production method", which is different from the present invention in that the steel plate composition design adopts high Ni (1.0-2.0%) and adds elements such as Cr, Mo, Nb, V, and Ti. The production adopts die casting + blanking + reheating controlled rolling and controlled cooling + offline quenching and tempering process, and the production process is complicated.

[0006] The Chinese patent application with publication number CN 108359879 A discloses "a DQ-T method for a 1000MPa grade hydropower steel plate with a thickness of no more than 60mm". The steel plate composition is designed to be C: 0.09-0.18, Mn: 0.80-1.60%, Ni (0.9-2.6%), Mo (0.3-0.65%), and a certain amount of Cu, Cr, Mo, Nb, V, Ti, B and other elements are added to control Pcm≤0.29. The alloy content is relatively high and the Pcm is relatively high. The production process is two-stage controlled rolling + online quenching + high temperature tempering, which is different from the present invention.

[0007] The Chinese patent application with publication number CN 108193137 A discloses "a DQ-QT production method for 1000MPa grade hydropower steel plate with a thickness of no more than 80mm". The carbon content and Pcm of the steel plate composition design are relatively high, which is not conducive to welding; the production process adopts two-stage controlled rolling + online quenching + offline tempering, which is different from the present invention.

[0008] The Chinese patent application with publication number CN 113652607 A discloses "a 1000MPa grade tempered steel plate for hydropower and its production method", involving a steel plate with a thickness of ≤56mm, a composition of high Ni (1.0-1.7%) + Cr + Mo alloying design, V + Ti micro-alloying, and a relatively high Al element and a trace B element; the production process is two-stage controlled rolling + offline tempering, and the composition and process design are different from the present invention.

[0009] The Chinese patent application with publication number CN 113388775 A discloses "a method for producing 1000MPa high-strength steel plates for hydropower engineering". The steel plates are designed with low carbon and Ni+Cr+Mo+V+Ti low-alloy components, which are different from the present invention. The production process adopts two-stage controlled rolling, in which the second stage adopts low-temperature controlled rolling and ultra-fast cold treatment after rolling. It has very high requirements on the low-temperature rolling capability of the rolling mill equipment and the cooling rate of the online cooling equipment. The rolling production efficiency is low, and the thick plate production process is very difficult to control, and the quality stability is difficult to fully control. Summary of the invention

[0010] The present invention provides an ultra-high strength steel for key equipment of a large hydropower station and a manufacturing method thereof. The steel adopts a low-carbon, low-manganese, Ni+Cr+Mo low alloying, and V+N micro-alloying composition design, and controls Ceq and Pcm at the same time, thereby obtaining the required performance and improving the weldability of the steel plate. Through the integrated design of the composition and the manufacturing process, a tempered bainite structure with a full-thickness cross-section grain size of 9 or more of a 30-80 mm thick ultra-high strength hydropower steel is obtained, thereby ensuring uniform and stable performance of the steel plate. The produced steel plate has ultra-high strength, good plastic toughness, cold bending performance and welding performance; and the production process is short, the cost is low, and the efficiency is high.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] An ultra-high strength steel for key equipment of a large hydropower station, the chemical composition of the steel by weight percentage is C: 0.06% to 0.11%; Si: 0.05% to 0.095%; Mn: 0.60% to 1.10%; P≤0.008%; S≤0.0015%; Ni: 0.66% to 0.79%; Cr: 0.66% to 0.80%; Mo: 0.71% to 0.90%; V: 0.061% to 0.09%; N: 0.01% to 0.03%; Zr: 0.02% to 0. 05%; Al: 0.02% ~ 0.045%; [O] ≤ 8ppm; [H] ≤ 1.5ppm, the balance is Fe and unavoidable impurities; in addition: carbon equivalent Ceq ≤ 0.60%, and Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14; welding crack sensitivity coefficient Pcm ≤ 0.25%, and Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B.

[0013] Furthermore, the tensile strength of the steel plate at room temperature is ≥1000MPa, the yield strength is ≥900MPa, the elongation after fracture is ≥15%; the impact absorption energy at -40°C is ≥150J; the 180° cold bending d=2a is qualified, and the -40°C strain aging impact absorption energy is ≥100J.

[0014] A method for manufacturing ultra-high strength steel for key equipment of a large hydropower station. The steel plate manufacturing process includes converter smelting, LF refining, RH refining, continuous casting, slow cooling of ingots, heating, controlled rolling, online quenching heat treatment, straightening and offline tempering heat treatment; the main control process is as follows:

[0015] 1) Smelting; ensure that non-metallic inclusions in steel are ≤ 0.5 level;

[0016] 2) Continuous casting: control the tundish superheat to 10-20°C, the continuous casting billet drawing speed to 1.3-1.5 m / min, and use a light reduction method at the end of continuous casting with a reduction of 4-6 mm;

[0017] 3) Slow cooling of the ingot: After the continuous casting ingot comes off the production line, it is stacked and slowly cooled for more than 40 hours;

[0018] 4) Heating; the temperature of the soaking section is 1090-1150°C, and the soaking time is 2.5-4h;

[0019] 5) Controlled rolling: Use high temperature, high pressure and fast rolling process. The starting rolling temperature is 1040-1100℃, the pass reduction rate is greater than 15%; the final rolling temperature is ≥920℃;

[0020] 6) Online quenching heat treatment; cooling temperature ≥ 900 ° C, cooling rate 10 ~ 19 ° C / s, cooling to room temperature;

[0021] 7) Offline tempering heat treatment; the tempering holding temperature is 580-630°C, the holding time is 3-8 min / mm, and the steel is air-cooled to room temperature after being taken out of the furnace.

[0022] Furthermore, the stacking slow cooling adopts a stacking method.

[0023] Furthermore, the thickness of the continuous casting billet is 250-300 mm, and the thickness of the finished steel plate is 30-80 mm.

[0024] Furthermore, the continuous casting billet is descaled by high pressure water after leaving the heating furnace.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) The steel plate adopts low carbon, low manganese, Ni+Cr+Mo low alloying, and V+N micro alloying composition design. While obtaining the required performance, the weldability of the steel plate is improved by controlling Ceq≤0.60% and Pcm≤0.25%, thereby effectively ensuring the welding quality and welding efficiency of the steel plate in the construction of hydropower projects;

[0027] 2) The clean steel smelting process is adopted, combined with a unique continuous casting process, to reduce the level of non-metallic inclusions in the steel (≤0.5 level), eliminate the looseness in the center of the ingot, and reduce segregation (below 0.5 level), thus obtaining high-quality and pure continuous casting ingots;

[0028] 3) The process of directly quenching to room temperature after high permeability rolling in the recrystallization zone at a lower heating temperature replaces the offline re-quenching process, simplifies the process flow, improves production efficiency and reduces production costs;

[0029] 4) Through the integrated design of composition and manufacturing process, the tempered troostite structure with a grain size of 9 or above (finer) in the full-thickness section of 30-80mm thick ultra-high-strength hydropower steel was finally obtained, ensuring the uniform and stable performance of the steel plate;

[0030] 5) The tensile strength of the finished steel plate at room temperature is ≥1000MPa, the yield strength is ≥900MPa, and the elongation after fracture is ≥15%; the impact absorption energy at -40℃ is ≥150J; the 180° cold bending (d=2a) is qualified, and the -40℃ strain aging impact absorption energy is ≥100J. It has ultra-high strength, good plasticity, cold bending performance and welding performance, and fully meets the use requirements of steel for key equipment of large hydropower stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a typical metallographic structure photograph of the ultra-high strength steel used for key equipment of a large hydropower station described in the present invention. DETAILED DESCRIPTION

[0032] The ultra-high strength steel for key equipment of a large hydropower station described in the present invention has the following chemical compositions by weight: C: 0.06%-0.11%; Si: 0.05%-0.095%; Mn: 0.60%-1.10%; P≤0.008%; S≤0.0015%; Ni: 0.66%-0.79%; Cr: 0.66%-0.80%; Mo: 0.71%-0.90%; V: 0.061%-0.09%; N: 0.01%-0.03%; Zr: 0.02%-0.03%; 0.05%; Al: 0.02%~0.045%; [O]≤8ppm; [H]≤1.5ppm, the balance is Fe and unavoidable impurities; in addition: carbon equivalent Ceq≤0.60%, and Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14; welding crack sensitivity coefficient Pcm≤0.25%, and Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5B.

[0033] Furthermore, the tensile strength of the steel plate at room temperature is ≥1000MPa, the yield strength is ≥900MPa, the elongation after fracture is ≥15%; the impact absorption energy at -40°C is ≥150J; the 180° cold bending d=2a is qualified, and the -40°C strain aging impact absorption energy is ≥100J.

[0034] A method for manufacturing ultra-high strength steel for key equipment of a large hydropower station. The steel plate manufacturing process includes converter smelting, LF refining, RH refining, continuous casting, slow cooling of ingots, heating, controlled rolling, online quenching heat treatment, straightening and offline tempering heat treatment; the main control process is as follows:

[0035] 1) Smelting; ensure that non-metallic inclusions in steel are ≤ 0.5 level;

[0036] 2) Continuous casting: control the tundish superheat to 10-20°C, the continuous casting billet drawing speed to 1.3-1.5 m / min, and use a light reduction method at the end of continuous casting with a reduction of 4-6 mm;

[0037] 3) Slow cooling of the ingot: After the continuous casting ingot comes off the production line, it is stacked and slowly cooled for more than 40 hours;

[0038] 4) Heating; the temperature of the soaking section is 1090-1150°C, and the soaking time is 2.5-4h;

[0039] 5) Controlled rolling: Use high temperature, high pressure and fast rolling process. The starting rolling temperature is 1040-1100℃, the pass reduction rate is greater than 15%; the final rolling temperature is ≥920℃;

[0040] 6) Online quenching heat treatment; cooling temperature ≥ 900 ° C, cooling rate 10 ~ 19 ° C / s, cooling to room temperature;

[0041] 7) Offline tempering heat treatment; the tempering holding temperature is 580-630°C, the holding time is 3-8 min / mm, and the steel is air-cooled to room temperature after being taken out of the furnace.

[0042] Furthermore, the stacking slow cooling adopts a stacking method.

[0043] Furthermore, the thickness of the continuous casting billet is 250-300 mm, and the thickness of the finished steel plate is 30-80 mm.

[0044] Furthermore, the continuous casting billet is descaled by high pressure water after leaving the heating furnace.

[0045] The reasons for designing the chemical composition of the ultra-high strength steel for key equipment of a large hydropower station described in the present invention are as follows:

[0046] (1) C: In the present invention, the main functions of carbon are: 1) dissolving in steel to form interstitial solid solution, which plays a role in solid solution strengthening; 2) forming fine carbides with V and Zr elements, which play a role in precipitation strengthening during heating, rolling deformation and heat treatment, and can effectively improve the strength of the steel plate. However, in the present invention, too high a carbon content will damage the welding performance of the steel plate. Therefore, the C content is designed to be 0.06% to 0.11%.

[0047] (2) Si: Si is used in the present invention to improve the yield strength of steel and play a certain role in solid solution strengthening. Considering the adverse effects of silicon on the plasticity and welding properties of steel, the present invention designs the Si content to be 0.05% to 0.095%.

[0048] (3) Mn: It is used to improve the hardenability of steel and dissolve in the ferrite matrix during quenching heat treatment, thereby improving the heat treatment performance of steel. In addition, manganese also plays a certain role in deoxidation and desulfurization in the present invention. However, too high manganese content can easily deteriorate the uniformity of steel plate performance and welding performance. Therefore, the designed Mn content is 0.60% to 1.10%.

[0049] (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, the better. The present invention requires that P≤0.008% and S≤0.0015% in steel.

[0050] (5) Ni: used to expand the austenite zone during heating, improve recrystallization rolling conditions, and thus refine and homogenize the rolled structure; used to reduce the critical transformation temperature of steel, reduce the diffusion rate of each element in steel, improve hardenability, and ensure that the steel plate obtains a uniform and stable tempered martensite structure along the thickness section after quenching and tempering heat treatment; nickel is added in combination with chromium, molybdenum, etc., so that the steel can obtain comprehensive mechanical properties with good matching of strength and toughness after heat treatment. However, nickel is a precious metal, and its content should be reduced while meeting the composition design requirements of the steel of the present invention. Therefore, the Ni content of the present invention is designed to be 0.66% to 0.79%.

[0051] (6) Cr: used to improve the hardenability of steel; form a continuous solid solution with Fe to improve the strength and hardness of steel; improve the thermodynamic stability of alloy infiltrates such as (FeCr)3C precipitated during tempering, prevent the decomposition of carbides, and thus reduce the aggregation rate of carbides during tempering; Cr is used in combination with Mo, etc. to make tempered steel have good comprehensive properties. However, in the present invention, too high a Cr content will reduce the low-temperature toughness and welding performance of the steel, so the Cr content in the steel of the present invention is controlled to be 0.66% to 0.80%.

[0052] (7) Mo: It can be dissolved in ferrite and austenite to improve the hardenability of steel; it can form carbon and nitride, refine the grains and improve the strength of steel; Mo is 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. However, considering the influence of molybdenum on welding performance, the Mo content of the present invention is designed to be 0.71% to 0.90%.

[0053] (8) V: It forms fine dispersed VC and VN with carbon and nitrogen. On the one hand, it reduces the growth of austenite grains when the ingot is heated, and on the other hand, it inhibits the recrystallization of deformed austenite during rolling, thereby refining the grains; it plays a precipitation strengthening role during cooling and tempering; it inhibits the strain aging embrittlement of steel, ensuring that the steel plate has good strain aging low-temperature impact performance; it is dissolved in austenite to improve the hardenability of steel. The V content of the present invention is designed to be 0.061% to 0.09%.

[0054] (9) N: In the present invention, an appropriate amount of nitrogen is added to promote the precipitation of V (C, N), and VN is precipitated in the austenite region through recrystallization controlled rolling and quenching heat treatment, thereby increasing the nucleation density of ferrite and refining the ferrite grains; N and Zr form high melting point ZrN, which is used to improve the as-cast structure and prevent the coarsening of high temperature austenite grains during reheating; N and Al form AlN, which can refine the grains. The present invention controls the N content to be 0.01% to 0.03%.

[0055] (10) Zr: It forms nano-scale high melting point ZrC and ZrN in steel, which can effectively improve the structure of continuous casting billet and prevent the coarsening of austenite recrystallization grains during high temperature rolling; reduce the strain aging tendency and temper brittleness of steel, and improve the low temperature toughness and strain aging impact performance of steel; it can refine the structure of welding heat affected zone and improve the welding performance of high-strength steel; it can improve the corrosion resistance of steel and increase the service life and safety of hydropower steel. The present invention controls the Zr content to 0.02% to 0.05%.

[0056] (11) Al: It plays a certain deoxidation role and can form AlN with N, refine austenite grains, and improve the low-temperature toughness of steel. According to needs, the Al content of the present invention is controlled within 0.02% to 0.045%.

[0057] (12) H and O: Hydrogen and oxygen are harmful elements in the steel of the present invention. In order to reduce the influence of H and O on the properties of the steel and improve the purity and homogeneity of the steel, the present invention controls [H] ≤ 1.5 ppm and [O] ≤ 8 ppm.

[0058] (13) Ceq, Pcm: As two important indicators for measuring the welding performance of steel plates, carbon equivalent and welding crack sensitivity coefficient should be as small as possible. A large amount of outdoor welding work is required in hydropower projects, and the quality of steel plate welding directly affects the project progress and construction cost. The steel described in the present invention has ultra-high strength, which requires the addition of a certain amount of alloy elements. Therefore, Ceq≤0.60% and Pcm≤0.25% are controlled to ensure that the mechanical properties of the steel plate meet the use requirements while ensuring that it has good welding performance.

[0059] The ultra-high strength steel for key equipment of a large hydropower station described in the present invention has a manufacturing process of a steel plate as follows: molten iron pretreatment - converter smelting - LF refining - RH refining - continuous casting - slow cooling of ingot - heating - controlled rolling - online quenching heat treatment - straightening - offline tempering heat treatment - ultrasonic flaw detection - performance inspection. The present invention mainly controls the following production processes:

[0060] 1. To ensure that the steel of the present invention has excellent comprehensive properties, the pure steel production process is used for smelting. P≤0.008%, S≤0.0015%, [H]≤1.5ppm, [O]≤8ppm in the steel are controlled to ensure that the non-metallic inclusions in the steel are ≤0.5 level. By adding 0.02% to 0.05% Zr to the steel, the formation of nano-scale high melting point ZrC and ZrN is promoted. These fine and dispersed particles can serve as nucleation centers during the solidification of the molten steel, reduce coarse columnar crystals, dendritic structures and segregation, and improve the cast structure.

[0061] 2. During the casting process, the tundish superheat is controlled at 10-20℃, the billet pulling speed is 1.3-1.5m / min, and the light pressure reduction method is adopted at the end of continuous casting, with a pressure reduction of 4-6mm. Reasonable casting process not only improves the internal quality of the billet, eliminates the center looseness, reduces the center segregation, but also improves production efficiency.

[0062] 3. After the continuous casting billet is off the line, it is slowly cooled for more than 40 hours in stacking. The stacking adopts the method of surrounding stacking. Other hot billets should be set above, below, left and right of the continuous casting billet to reduce the temperature drop rate of the billet and reduce the temperature difference at different positions of the billet, so as to further homogenize the as-cast structure, reduce the internal stress of the billet, reduce the segregation of the billet, and ensure that the center segregation of the billet is ≤0.5, laying the foundation for obtaining excellent steel plate performance. The thickness of the continuous casting billet is preferably 250-300mm.

[0063] 4. The continuous casting billet is heated in a heating furnace (preferably a walking beam heating furnace) with a soaking section temperature of 1090-1150°C and a soaking time of 2.5-4 hours. A certain amount of V is added to the steel of the present invention, and a lower heating temperature retains some V (CN) particles, which can effectively prevent the movement of austenite grain boundaries and reduce the growth of austenite grains; a reasonable soaking time ensures that the continuous casting billet is heated evenly and austenitized sufficiently.

[0064] 5. After the continuous casting billet is taken out of the furnace, high-pressure water is used for descaling. The rolling process adopts high-temperature, high-pressure and fast rolling process. The starting rolling temperature is 1040-1100℃, the pass reduction rate is greater than 15%, and the interval between passes should be as short as possible to avoid the growth of recrystallized grains until the thickness of the finished steel plate is reached, and the final rolling temperature is ≥920℃.

[0065] 6. After rolling, the online direct quenching process is adopted, the cooling temperature is ≥900℃, the cooling rate is 10~19℃ / s, and it is cooled to room temperature. In order to obtain the martensitic structure, the high density dislocation in the rolling is maintained, the grain growth after rolling is reduced, and the steel plate obtains the quenched state performance with higher strength. In addition, part of the carbonitride is dissolved in the austenite during high temperature rolling, thereby improving the hardenability of the steel plate during quenching, so that the steel plate can obtain a uniform martensitic structure along the thickness section, and ensure the uniformity and stability of the steel plate performance.

[0066] 7. The steel plate is subjected to offline tempering heat treatment, with a tempering holding temperature of 580-630°C and a holding time of 3-8 min / mm. It is air-cooled to room temperature after leaving the furnace. A reasonable tempering process is adopted to promote the formation of equiaxed grains, promote the transformation of cementite into fine special carbides, improve the dispersion strengthening effect, and enable the steel plate to obtain a stable tempered troostite structure and well-matched strength and toughness.

[0067] Typical metallographic structure photos of ultra-high strength steel for key equipment of large hydropower stations described in the present invention are as follows: Figure 1As shown, the microstructure of the finished steel plate is tempered troostite.

[0068] 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.

[0069] [Example]

[0070] The chemical composition of the steel in each embodiment is shown in Table 1, the continuous casting, slow cooling and heating process parameters in each embodiment are shown in Table 2, the rolling and post-rolling heat treatment process parameters in each embodiment are shown in Table 3, and the mechanical properties of the finished steel plate in each embodiment are shown in Table 4.

[0071] Table 1 Chemical composition of steel (%)

[0072]

[0073] Table 2 Continuous casting, slow cooling and heating process parameters Process parameters

[0074]

[0075] Table 3 Rolling and post-rolling heat treatment process parameters

[0076]

[0077] Table 4 Mechanical properties of steel plates in quenched and tempered state

[0078]

[0079] 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. A method for manufacturing ultra-high strength steel for key equipment of a large hydropower station, characterized in that: The chemical composition of the steel is calculated by weight as follows: C: 0.06% ~ 0.11%; Si: 0.05% ~ 0.095%; Mn: 0.60% ~ 1.10%; P ≤ 0.008%; S ≤ 0.0015%; Ni: 0.66% ~ 0.79%; Cr: 0.66% ~ 0.80%; Mo: 0.71% ~ 0.90%; V: 0.061% ~ 0.09%; N: 0.01% ~ 0.03%; Zr: 0.02% ~ 0.05%; Al: 0.02% ~ 0.045%; [O] ≤ 8ppm; [H] ≤ 1.5ppm, the balance is Fe and unavoidable impurities; in addition, the carbon equivalent Ceq ≤ 0.60%, and Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4+ V / 14; welding crack sensitivity coefficient Pcm≤0.25%, and Pcm= C+ Si / 30+ Mn / 20+ Cu / 20+ Ni / 60+ Cr / 20 + Mo / 15+ V / 10+ 5B; The steel plate manufacturing process includes converter smelting, LF refining, RH refining, continuous casting, slow cooling of ingot, heating, controlled rolling, online quenching heat treatment, straightening and offline tempering heat treatment; the main control processes are as follows: 1) Smelting; ensure that non-metallic inclusions in steel are ≤0.5 level; 2) Continuous casting: control the tundish superheat to 10-20°C, the continuous casting billet drawing speed to 1.3-1.5m / min, and use a light reduction method at the end of continuous casting with a reduction of 4-6mm; 3) Slow cooling of the ingot; the thickness of the continuous casting ingot is 250-300mm; the continuous casting ingot is stacked and slowly cooled for more than 40 hours after it comes off the production line, and the stacking and slow cooling adopts the stacking method; 4) Heating: The temperature of the soaking section is 1090-1150°C, and the soaking time is 2.5-4h; high-pressure water is used to descale the continuous casting billet after it leaves the heating furnace; 5) Controlled rolling; adopt high temperature and high pressure rapid rolling process; the starting rolling temperature is 1040~1100℃, the pass reduction rate is greater than 15%; the final rolling temperature is ≥920℃; 6) Online quenching heat treatment; cooling temperature ≥ 900 ° C, cooling rate 10 ~ 19 ° C / s, cooling to room temperature; 7) Offline tempering heat treatment; the tempering holding temperature is 580-630℃, the holding time is 3-8min / mm, and it is air-cooled to room temperature after being taken out of the furnace.

2. The method for manufacturing ultra-high strength steel for key equipment of a large hydropower station according to claim 1, characterized in that: The thickness of the finished steel plate is 30-80mm; the tensile strength of the finished steel plate at room temperature is ≥1000MPa, the yield strength is ≥900MPa, and the elongation after fracture is ≥15%; the impact absorption energy at -40℃ is ≥150J; the 180° cold bending d=2a is qualified, and the -40℃ strain aging impact absorption energy is ≥100J.

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