CN116219293A - Super-thick and super-high-power steel for hydroelectric engineering and manufacturing method thereof - Google Patents

Abstract

The invention relates to an ultra-thick, ultra-high-power and large-scale steel for hydropower engineering and a manufacturing method thereof. The chemical composition in the steel is 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 %; : 0.10%～0.20%; Al: 0.02%～0.04%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and impurities. Adopt low carbon, low manganese, Ni+Cr+Mo+Ti low alloying composition design, cooperate with electroslag remelting + rolling + off-line quenching and tempering heat treatment process, and use high melting point Ti(CN) and CeO2 to refine the grain , realized the high penetration rolling production of large-thickness electroslag blanks, and finally obtained ultra-thick and ultra-high-strength steel plates with a grain size of 7.5 and above, 110-160mm thick and 1000MPa grade.

Description

An ultra-thick, ultra-high-strength, large-scale hydropower engineering steel and its manufacturing method

technical field

The invention relates to the technical field of steel manufacturing for hydropower, in particular to an ultra-thick, super-high-strength large-scale steel for hydropower engineering and a manufacturing method thereof.

Background technique

With the development trend of large-scale hydropower projects, the strength level of steel for hydropower will be further improved, and at the same time, the thickness of steel plates will also exceed 100mm. The increase in the thickness of the steel plate will bring about a series of problems such as reduced Z-direction performance, uneven structure, and high production costs. Coupled with the particularity of performance requirements for steel for hydropower, the production difficulty will further increase.

The existing domestic production methods for steel with a strength level of 1000 MPa mainly focus on thickness specifications below 100 mm, and the composition design and process design are quite different from the present invention.

The Chinese patent application with the publication number CN108385034A discloses "a method for producing LGB-QT of a 1000MPa-grade steel plate for hydropower not greater than 100 mm in thickness". 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: 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 treatment. The thickness of the steel plate produced by it is not more than 100mm, and the low alloy composition design of Ni+Cr+Mo is adopted, and Nb, V, Ti are used for controlled rolling and controlled cooling production, which is different from the composition and production process of the present invention.

The Chinese patent application with the publication number CN113399948A discloses "a method for producing 1000MPa hydropower steel with a thickness of 100mm or more", which uses two continuous casting slabs with a thickness of 250-350mm to be rolled and heat-treated after welding. The size of the continuous casting slab and the composite surface are processed accordingly, and then the processes such as billet welding, vacuuming, rolling and heat treatment are carried out; it belongs to the technical field of rolling composite thick plate manufacturing, and the components of the cast slab used are also different from those of the present invention, and are not It involves the Z-direction performance of the steel plate. For the composite plate over 100mm, the performance safety is low.

The Chinese patent application with the publication number CN108504960A discloses "a 1000MPa low-crack hydropower steel plate for large-scale hydropower projects and its production method", including the following chemical components in mass percentages: 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%, others are Fe and residual elements. The product has the advantages of high strength, high toughness, low crack sensitivity, good surface quality, good weldability, etc., but the thickness of the steel plate it produces is only 10-50mm.

The Chinese invention patent with the authorized notification number CN103451562B discloses a "quenched and tempered large-thickness easy-to-weld Z-direction high-strength steel plate for hydropower and its production method", including smelting, continuous casting, electroslag remelting, heating, rolling, After rolling, water cooling, hot stacking, and heat treatment processes are smelted from the following components in mass percentages, 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%, the balance is Fe and unavoidable impurities. Compared with the present invention, the chemical composition design of the steel is different, and the production process is also different. The steel plate described in this invention is produced by the process of controlled rolling and controlled cooling + quenching and tempering heat treatment, and the heating time is as long as 30 hours. The whole 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 this 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 in this invention at -20°C is distributed from 78J to 300J, which shows that the impact performance fluctuates Larger, but the present invention has stable impact performance at -40°C at 1/4 and 1/2 of the plate thickness.

Contents of the invention

The invention provides an ultra-thick, ultra-high-strength, large-scale steel for hydropower engineering and its manufacturing method. It adopts low-carbon, low-manganese, Ni+Cr+Mo+Ti low-alloying composition design, and cooperates with electroslag remelting + rolling + off-line Quenching and tempering heat treatment process, using the effect of high melting point Ti(CN) and _CeO2 to refine the grain, realized the high penetration rolling production of large thickness electroslag blank, and finally obtained the grain size of 7.5 grade and above, 110 ~ 160mm Thick 1000MPa class ultra-thick ultra-high-strength steel plate.

In order to achieve the above object, the present invention adopts the following technical solutions to realize:

An ultra-thick, ultra-high-strength, and large-scale steel for hydropower engineering. The chemical composition in the steel is 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%; CeO ₂ : 0.10% ～0.20%; Al: 0.02%～0.04%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and unavoidable impurities.

Further, the tensile strength of the finished steel plate at room temperature is ≥ 950MPa, the yield strength is ≥ 885MPa, and the elongation after fracture is ≥ 15%; the impact energy absorbed at -40°C is > 150J; the Z-direction section shrinkage rate is > 55%; there is no ductility transition temperature TNDT≤-45°C.

A method for manufacturing ultra-thick, ultra-high-strength, and large-scale steel for hydropower projects. The steel plate manufacturing process includes electroslag remelting of steel billets, electroslag billet annealing, heating, rolling, and off-line quenching and tempering heat treatment; the control process is as follows:

1) Billet electroslag remelting: before remelting, blow argon gas into the crystallizer for 15-20 minutes, and the flow rate of argon gas is 7-9m ³ /h; 55~65m ³ /h, the water temperature is controlled at 26~33℃; the current setting value in the slag melting stage is 16000~22000A, and the feeding stage current setting value is 8000~12000A and kept for 10~15min;

2) Electroslag billet annealing; slow cooling after electroslag billet demoulding, slow cooling pit preheated to 400-500°C, holding time of electroslag billet for more than 15h, and slow cooling to room temperature;

3) Heating; the heating and holding temperature of the electroslag billet is 1250-1300°C, and the holding time is 3-5h;

4) Rolling; the starting rolling temperature is 1180-1220°C, the total deformation of the first 4 rolling passes is ≥ 45mm, and the reduction ratio of the first 2 passes in the last rolling pass is ≥ 10%; after rolling The steel plate is slowly cooled off the production line, and the slow cooling time is not less than 30 hours;

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

Further, the thickness of the electroslag billet is 500-700 mm; the thickness of the finished steel plate is 110-160 mm.

Further, after the electroslag billet leaves the heating furnace, high-pressure water is used to descale for 1-3 minutes, and the water pressure for descaling is 28-33 MPa.

Compared with prior art, the beneficial effect of the present invention is:

1) It is designed with low carbon, low manganese, Ni+Cr+Mo+Ti low alloying composition, and utilizes the effect of high melting point Ti(CN) and _CeO2 to refine the grains to realize high penetration rolling of large thickness electroslag blanks production, and finally obtain ultra-thick ultra-high-strength steel plates with a grain size of 7.5 and above (finer);

2) Produced by electroslag remelting process, the steel has high purity, non-metallic inclusions ≤ 0.5 grade, no center porosity and center segregation;

3) Using 500-700mm thick electroslag billet, directly rolling the finished steel plate under high temperature and high pressure, and using precise off-line quenching and tempering heat treatment process to realize the manufacture of 110-160mm thick 1000MPa grade steel for hydropower engineering; the production process is relatively simple, Stable, high production efficiency;

4) Through the innovative design of chemical composition and process, the production and manufacture of a large-thickness, homogeneous high-strength steel plate has been realized. The mechanical properties of 1/4 and 1/2 of the thickness of the steel plate are basically the same, with good performance uniformity;

5) The tensile strength of the finished steel plate at room temperature is ≥ 950MPa, the yield strength is ≥ 885MPa, and the elongation after fracture is ≥ 15%; -40°C impact absorption energy > 150J; Z-direction section acceptance rate > 55%; no ductility transition temperature TNDT ≤-45°C, with excellent low-temperature toughness, lamellar tear resistance and brittle fracture resistance, fully meeting the requirements of large-scale hydropower projects for ultra-thick and ultra-high-strength steel.

Description of drawings

Fig. 1 is a typical metallographic structure photo of a kind of ultra-thick, ultra-high-power and large-scale hydropower engineering steel according to the present invention.

Detailed ways

The super-thick, ultra-high-power and large-scale hydropower engineering steel of the present invention, the chemical composition in the steel is 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%; CeO ₂ : 0.10%～0.20%; Al: 0.02%～0.04%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and unavoidable impurities.

Further, the tensile strength of the finished steel plate at room temperature is ≥ 950MPa, the yield strength is ≥ 885MPa, and the elongation after fracture is ≥ 15%; the impact energy absorbed at -40°C is > 150J; the Z-direction section shrinkage rate is > 55%; there is no ductility transition temperature TNDT≤-45°C.

According to the present invention, a method for manufacturing super-thick, super-high-power and large-scale steel for hydropower engineering, the steel plate manufacturing process includes billet electroslag remelting, electroslag billet annealing, heating, rolling, off-line quenching and tempering heat treatment; the control process is as follows:

1) Billet electroslag remelting: before remelting, blow argon gas into the crystallizer for 15-20 minutes, and the flow rate of argon gas is 7-9m ³ /h; 55~65m ³ /h, the water temperature is controlled at 26~33℃; the current setting value in the slag melting stage is 16000~22000A, and the feeding stage current setting value is 8000~12000A and kept for 10~15min;

2) Electroslag billet annealing; slow cooling after electroslag billet demoulding, slow cooling pit preheated to 400-500°C, holding time of electroslag billet for more than 15h, and slow cooling to room temperature;

3) Heating; the heating and holding temperature of the electroslag billet is 1250-1300°C, and the holding time is 3-5h;

4) Rolling; the starting rolling temperature is 1180-1220°C, the total deformation of the first 4 rolling passes is ≥ 45mm, and the reduction ratio of the first 2 passes in the last rolling pass is ≥ 10%; after rolling The steel plate is slowly cooled off the production line, and the slow cooling time is not less than 30 hours;

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

Further, the thickness of the electroslag billet is 500-700 mm; the thickness of the finished steel plate is 110-160 mm.

Further, after the electroslag billet leaves the heating furnace, high-pressure water is used to descale for 1-3 minutes, and the water pressure for descaling is 28-33 MPa.

The compositional design reason of a kind of ultra-thick ultra-high-power large-scale hydropower project steel of the present invention is as follows:

(1) C: Carbon dissolves in steel to form interstitial solid solution, which acts as solid solution strengthening, and can form fine carbides with Ti element, which acts as precipitation strengthening, and can also improve the hardenability of steel. However, the increase of carbon content will damage the weldability and low-temperature toughness of steel, so the content of C in the present invention is controlled at 0.10%-0.15%.

(2) Si: It is used as a reducing agent and deoxidizer, and plays a certain role in solid solution strengthening. If the Si content is too high, the plasticity and weldability of the steel will be reduced, so the Si content in the steel of the present invention is controlled at 0.06%-0.10%.

(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 steel plates. 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 be 0.90%-1.50%.

(4) P and S: Both are harmful elements, P will cause cold brittleness of steel, S will cause hot brittleness of steel, and is easy to segregate, which has obvious adverse effects on low temperature toughness and welding performance of steel, so both The lower the content, the better, and the present invention controls P≤0.008% and S≤0.001% in the steel.

(5) Ni: The functions in the present invention mainly include: 1) reduce the near transition temperature and improve the hardenability of the steel plate; 2) play the role of solid solution strengthening and improve the low temperature toughness of the steel plate; 4) It is used in conjunction with Cr and Mo to make the steel plate obtain 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%.

(6) Cr: Chromium can form fine and dispersed carbides with carbon to improve the strength and toughness of the steel plate; during quenching, it can reduce the minimum cooling rate to obtain martensite structure, and it is easier to obtain martensite structure; reduce retained austenite content, so that a good tempered structure can be obtained during tempering, and the strength and toughness of the steel plate can be improved; the thermodynamic stability of alloy infiltration bodies such as (FeCr)3C and other alloys precipitated in steel can be improved, and the aggregation speed of carbides can be reduced during tempering. ; Used in conjunction with Mo, etc., the steel plate has good comprehensive properties after quenching and tempering heat treatment. However, if the Cr content is too high, the weldability of the steel will be reduced, so the present invention controls the Cr content to be 0.55%-0.75%.

(7) Mo: It can be dissolved in ferrite, austenite and carbide, and plays a role of solid solution strengthening; it can improve the hardenability of steel; improve the stability of carbide, and inhibit the infiltration during tempering Agglomeration and growth; used in conjunction with Cr and Mn to reduce or inhibit temper brittleness caused by other elements, and ensure stable high-strength toughness of the steel plate after heat treatment. The present invention controls the Mo content to be 0.75% to 1.2%.

(8) Ti: It can form a large number of fine and dispersed carbonitrides, which can not only refine the as-cast structure, but also prevent the growth of austenite grains and refine the grains during high temperature heating and rolling; Ti can deteriorate The sulfides in the steel form a large number of nano-sized sulfide particles and distribute them in a dispersed manner, thereby reducing the adverse effects of sulfides on the properties of the steel; 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 grain coarsening in the welding heat-affected zone and improve the welding performance of the steel plate. Therefore, the content of Ti in the present invention is controlled to be 0.07%-0.11%.

(9) N: The role of nitrogen in the present invention mainly includes: 1) play the role of solid solution strengthening; 2) expand the austenite phase region, form and stabilize austenite; 3) form fine TiN particles with Ti, Improve the as-cast structure and prevent the coarsening of austenite grains during heating; 4) form AlN with Al to refine the grains. The present invention controls the N content to be 0.015% to 0.025%.

(10) CeO ₂ : Add high melting point CeO ₂ powder to the molten steel to increase the nucleation core, promote the solidification of the molten steel, and refine the as-cast structure; refine the Ti(CN) particles and promote the dispersion distribution; it can improve the grain boundary The resistance to dislocation movement improves the strength and toughness of the steel plate. The content of _CeO2 added in the present invention is 0.10%-0.20%.

(11) Al: It plays a certain role in deoxidation and refines the grains. In the present invention, the Al content is controlled at 0.02% to 0.04%.

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

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

1. In order to ensure that the compression ratio between the steel billet and the steel plate is greater than 3, so as to effectively control the lamellar tear resistance of the steel plate and the uniformity of the structure and performance along the thickness section, the present invention uses an electroslag billet with a thickness of 500-700mm for rolling of the steel plate production. Electroslag remelting belongs to the secondary refining method, which has the advantages of deep cleaning of steel quality, improvement of slab crystal structure, elimination of center porosity and center segregation, and homogenization of steel plate structure and performance, and is very suitable for the production of steel described in the present invention.

The electroslag remelting consumable electrode adopts the steel billet meeting the chemical composition requirements of the present invention, and the electric power system, slag system, slag amount and filling ratio are strictly controlled during the electroslag remelting process. Before remelting, blow argon gas into the crystallizer for 15-20 minutes, the flow rate of argon gas is 7-9m3/h; during re-melting, the melting speed is controlled at 560-620kg/h, the cooling water volume of the crystallizer is 55-65m3/h, and the water temperature is controlled At 26-33°C; the setting value of the current in the slag removal stage is 16000-22000A, and the current setting value in the feeding stage is 8000-12000A and keep it for 10-15min. After demoulding, the electroslag billet needs to enter the slow cooling pit for slow cooling. The slow cooling pit is preheated to 400-500°C, and the electroslag billet is kept at this temperature for more than 15 hours, and then slowly cooled to room temperature to exit the pit. The purpose of long-term annealing is to eliminate the thermal stress and structural stress of the electroslag billet, improve the as-cast structure, and disperse the precipitates.

2. The heating and holding temperature of the electroslag billet is 1250-1300°C, and the holding time is 3-5 hours. Since the steel contains a large number of dispersed TiN and _CeO2 particles with high melting point, it can effectively prevent the coarsening of austenite grains during high temperature and long heating process. Therefore, the present invention appropriately increases the heating temperature, and while ensuring consistent internal and external temperatures of the electroslag billet and sufficiently uniform austenitization, shortens the heating time of the large-thickness electroslag billet and improves production efficiency.

After the electroslag billet is out of the furnace, high-pressure water is used to descale for 1-3 minutes, and the descaling water pressure is 28-33MPa. The purpose is to remove the surface oxide scale and ensure the good surface quality of the steel plate.

3. The electroslag billet is rolled after descaling, the rolling start temperature is 1180-1220°C, the deformation of the first 4 rolling passes is ≥ 45mm, and the first 2 passes of the last rolling pass are controlled. Ratio ≥ 10%. During rolling, the interval between each pass should be as short as possible until the thickness of the finished steel plate (110-160mm) is reached. The multi-pass rolling under high temperature and high pressure makes the thickness section of the electroslag billet obtain a certain rolling penetration, improves the deformation consistency of the large thickness billet, and is conducive to improving the uniformity of structure and performance. And by promoting repeated recrystallization of austenite, the grains are refined and the structure is homogenized. Because the billet is thicker, high-temperature rolling also reduces the load on the rolling mill and ensures stable production of steel plates.

After the steel plate is rolled, it goes off-line and enters the slow cooling pit for slow cooling. The slow cooling time is not less than 30 hours, fully eliminates the internal stress of the steel plate, reduces the temperature difference between the surface and the center of the steel plate, further homogenizes the rolling structure, and removes the hydrogen in the steel plate, improving The internal quality of the steel plate.

4. After the steel plate is slowly cooled, the off-line quenching and tempering heat treatment process is adopted, wherein the quenching temperature is 880-950°C, the holding time is 2-5min/mm, the quenching cooling rate is 20-25°C/s; the tempering and holding temperature is 560-620 ℃, the holding time is 4~8min/mm. Reasonable quenching and tempering heat treatment process ensures that the finished steel plate of the present invention obtains uniform and fine tempered sorbite structure and excellent performance.

A photo of a typical metallographic structure of an ultra-thick, ultra-high-strength, large-scale hydropower engineering steel according to the present invention is shown in Figure 1, and the structure is tempered sorbite.

The following examples are carried out on the premise of the technical solutions of the present invention, and detailed implementation methods and specific operation processes are provided, but the protection scope of the present invention is not limited to the following examples.

【Example】

The chemical composition of each embodiment steel 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, and the off-line quenching and tempering heat treatment process of each embodiment The parameters are shown in Table 4, and the properties of the finished steel plates of each embodiment are shown in Table 5.

Table 1 Chemical Composition of Steel (%)

Table 2 Electroslag remelting process parameters

Table 3 heating and rolling process parameters

Table 4 off-line quenching and tempering heat treatment process parameters

Table 5 Mechanical properties of steel plate in quenched and tempered state

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (5)

1. An ultra-thick, ultra-high-strength, large-scale steel for hydropower engineering, characterized in that the chemical composition in the steel is calculated by weight percentage as 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%; ; CeO ₂ : 0.10%-0.20%; Al: 0.02%-0.04%; [H]≤1.5ppm; [O]≤8ppm; the balance is Fe and unavoidable impurities. 2. A super-thick, ultra-high-power and large-scale steel for hydropower engineering according to claim 1, characterized in that the tensile strength of the finished steel plate at room temperature is ≥ 950 MPa, the yield strength is ≥ 885 MPa, and the elongation after fracture is ≥ 15%; Impact absorption energy at -40°C > 150J; Z-direction area reduction > 55%; non-ductile transition temperature TNDT ≤ -45°C. 3. A method for manufacturing ultra-thick, ultra-high-power, large-scale hydropower engineering steel as claimed in claim 1 or 2, wherein the steel plate manufacturing process includes electroslag remelting of steel billets, electroslag billet annealing, heating, rolling, off-line Quenching and tempering heat treatment; the control process is as follows: 1) Billet electroslag remelting: before remelting, blow argon gas into the crystallizer for 15-20 minutes, and the flow rate of argon gas is 7-9m ³ /h; 55~65m ³ /h, the water temperature is controlled at 26~33℃; the current setting value in the slag melting stage is 16000~22000A, and the feeding stage current setting value is 8000~12000A and kept for 10~15min; 2) Electroslag billet annealing; slow cooling after electroslag billet demoulding, slow cooling pit preheated to 400-500°C, holding time of electroslag billet for more than 15h, and slow cooling to room temperature; 3) Heating; the heating and holding temperature of the electroslag billet is 1250-1300°C, and the holding time is 3-5h; 4) Rolling; the rolling start temperature is 1180-1220°C, the deformation of each pass in the first 4 rolling passes is ≥45mm, and the total reduction rate of the 2 passes before the last rolling pass is ≥10%; After rolling, the steel plate is slowly cooled off the production line, and the slow cooling time is not less than 30 hours; 5) Off-line quenching and tempering heat treatment; quenching temperature is 880-950°C, holding time is 2-5min/mm, quenching cooling rate is 20-25°C/s; tempering holding temperature is 560-620°C, holding time is 4-5 8min/mm. 4 . The method for manufacturing ultra-thick, ultra-high-power and large-scale steel for hydropower engineering according to claim 3, characterized in that, the thickness of the electroslag billet is 500-700 mm; the thickness of the finished steel plate is 110-160 mm. 5. A method for manufacturing ultra-thick, ultra-high-power, large-scale hydropower engineering steel according to claim 3, characterized in that, after the electroslag billet leaves the heating furnace, high-pressure water is used for descaling for 1 to 3 minutes, and the water pressure for descaling is 1-3 minutes. It is 28 ~ 33MPa.

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