A thick-gauge low-cost 1000mpa-grade hydroelectric steel and a production method thereof

Abstract

The application discloses a kind of thick gauge low-cost 1000MPa grade hydroelectric steel and its production method, and the chemical composition of steel plate is as follows: C:0.06~0.11%, Mn:0.55~0.95%, Cu:0.20~0.32%, Cr:0.20~0.60%, Mo:0.22~0.52%, Ni:0.80~1.40%, Al:0.32~0.52%, Ti:0.004~0.010%, B:0.001~0.003%, Zr:0.001~0.003%, N≤0.0030%, P≤0.008%, S≤0.003%, O≤0.003%, the balance is Fe and inevitable impurities;Production method includes converter smelting, LF refining, VD treatment, continuous casting, controlled rolling, quenching and tempering heat treatment process.The steel plate of the application has high strength, high super-low temperature impact toughness and excellent welding performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel production, and particularly relates to a thick-gauge low-cost 1000MPa-grade hydropower steel and a production method thereof. BACKGROUND

[0002] With the rapid economic development, energy consumption has increased dramatically, and over-reliance on non-renewable energy sources such as oil and coal has caused serious air pollution and global warming. Under the guidance of the "double carbon" policy, it has become an inevitable trend to vigorously develop clean energy such as hydropower, which has further increased the demand and performance requirements for materials used in hydropower station construction.

[0003] In recent years, pumped storage power stations with large site topography have developed rapidly, and the high water level puts a lot of pressure on the steel pipe, so the comprehensive mechanical properties of the steel plate are increasingly required. With the rapid development of science and technology, large and giant power stations will continue to adopt new materials, new technologies and new processes.

[0004] In the future, with the rapid development of large hydropower projects, the steel used for dam water diversion pipe manufacturing and key facilities such as ribbed plates, branch pipes and spiral cases has higher requirements for yield strength, tensile strength, low-temperature toughness and weldability. At present, there is still a blank in the domestic construction of steel for large drop and super-high head hydropower stations. In order to promote the rapid development of the national hydropower industry, it is imperative to develop high-strength and lightweight hydropower steel.

[0005] A high-strength HY950CF steel plate for hydropower engineering and a production method thereof are disclosed in Chinese patent application CN 115747657A. The chemical composition (wt%) is as follows: C: 0.09-0.12, Si: 0.15-0.25, Mn: 0.30-0.60, P≤0.010, S≤0.003, Als: 0.020-0.040, Nb: 0.02-0.03, V: 0.04-0.1, Cr: 1.2-1.6, Ni: 2.4-2.8, Cu: 0.8-1.0, Mo: 0.2-0.3, Re: 0.0015-0.0025, and the rest is Fe and residual elements, and the carbon equivalent Ceq is less than 0.7. The disadvantages of this method are as follows: the expensive alloy Cr and Ni are added in large amounts, the cost is high; the carbon equivalent is too high, the welding performance is poor; the double quenching process is adopted in the heat treatment process, the process is complex, and the treatment cost is high.

[0006] Chinese patent application CN 117026098A discloses a hydroelectric steel and a preparation method thereof. The chemical composition (wt%) of the hydroelectric steel is: C: 0.05-0.08; Si≤0.20; Mn: 0.6-1.2; P≤0.015; S≤0.004; Cr: 0.5-0.9; Ni: 4.0-4.8; Mg: 0.005-0.008; La: 0.012-0.018; Zr: 0.02-0.03; N: 0.008-0.015; and the balance is Fe and inevitable impurities. The disadvantage of the method is that the expensive alloy Cr and Ni are added in large amounts, resulting in high cost.

[0007] Chinese patent application CN 116219289A discloses a 1000MPa grade high-toughness hydroelectric steel and a production method thereof. The chemical composition (wt%) of the hydroelectric steel is: C: 0.03-0.10, Si: 0.85-1.0, Mn: 0.5-1.0, P≤0.008, S≤0.002, Ni: 0.1-0.5, Cr: 0.91-1.1, Mo: 0.2-0.6, V: 0.09-0.16, N: 0.006-0.012, Zr: 0.005-0.01, Al 0.02-0.05, and O≤15ppm, H≤3ppm, and the balance is Fe and inevitable impurities. Although the method does not add a large amount of expensive alloy such as Cr and Ni, boron element is not added in the composition to improve hardenability, and the impurity nitrogen content is high, which is only suitable for producing steel plates with a thickness of not more than 70mm, and cannot meet the requirements of thick-specification hydroelectric steel products. SUMMARY

[0008] The present application aims at the deficiencies of the prior art, and provides a thick-specification low-cost 1000MPa grade hydroelectric steel and a production method thereof. Through the composition design of low-alloy addition amount, high Al+low Ti+micro Zr strengthening deoxidization and denitrification, high solid-solution boron yield strengthening hardenability, and nano-phase ZrN precipitation strengthening, combined with oxygen and nitrogen control measures in the whole process, a large-thickness high-hardening steel plate is obtained, and the low-cost preparation of thick-specification 1000MPa grade steel plate for hydroelectric station pressure steel pipes is realized, and the steel plate has high strength, high ultra-low temperature impact toughness, and excellent welding performance.

[0009] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0010] A thick-gauge low-cost 1000MPa-grade hydroelectric steel, whose chemical composition and mass percentage content are as follows: C: 0.06-0.11%, Mn: 0.85-0.95%, Cu: 0.24-0.32%, Cr: 0.40-0.60%, Mo: 0.32-0.52%, Ni: 1.30-1.80%, Al: 0.32-0.52%, Ti: 0.004-0.010%, B: 0.001-0.003%, Zr: 0.001-0.003%, Nb: 0.20-0.40%, V: 0.15-0.40%, N≤0.0030%, P≤0.008%, S≤0.003%, O≤0.003%, and the balance being Fe and inevitable impurities.

[0011] Further, the chemical composition of the steel plate satisfies Al / 250+Ti / 5+Zr / 15≤0.004%, carbon equivalent C eq ≤0.55%, welding crack sensitivity coefficient P cm ≤0.25%. Wherein Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14; Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+B.

[0012] Further, the thickness of the steel plate is 70-150 mm, the yield strength is ≥900 MPa, the tensile strength is ≥960 MPa, the elongation after fracture is ≥15%, the low-temperature impact toughness AKV at -80℃ is ≥100 J, and the welding line energy is ≥150 kJ / cm.

[0013] Further, the solid-solution boron yield of the steel plate is >80%.

[0014] Further, the preparation method comprises the following steps: converter smelting→LF refining→VD treatment→continuous casting→controlled rolling→quenching and tempering heat treatment process, and the specific process steps are as follows:

[0015] (1) Converter smelting: blowing time 7-12 min, tapping C content 550-800 ppm, tapping temperature 1580-1600℃.

[0016] (2) LF refining: the time of the pre-temperature-raising and slagging stage is 10-15 min, and a medium-high gear slagging is used during the period, and at the same time, the submerged arc is paid attention to during the whole refining process, the opening degree of the dust removal cover of the LF process is controlled to be 40%-60%, and the bottom blowing gas adopts a full-process argon control mode. A small current and small voltage are used before the formation of the foamed slag, and the current and voltage are sequentially increased with the formation of the foamed slag. After the white slag is refined in the LF furnace, the aluminum wire, ferrotitanium, ferrozirconium and ferroboron are sequentially added, and the power is continuously supplied for 3-5 min, and then the soft argon blowing is performed for more than 20 min before the ladle is lifted.

[0017] (3) VD treatment: holding for 10-16 min under vacuum degree ≤ 60 Pa, N content ≤ 30 ppm, H content ≤ 0.8 ppm.

[0018] (4) Continuous casting process: using submerged entry nozzle, sealing the joint with argon, continuous casting speed 0.7-1.4 m / min, superheat ≤ 13℃.

[0019] (5) Controlled rolling: using two-stage controlled rolling process, first-stage rough rolling temperature 1040℃-1100℃, finish rolling temperature 960℃-1000℃, single pass maximum reduction rate 25%-30%, last 2 passes reduction ≥ 30 mm; second-stage rough rolling temperature 850℃-890℃, finish rolling temperature 800℃-850℃.

[0020] (6) Quenching and tempering heat treatment: using on-line quenching and off-line tempering process, quenching temperature 890℃-930℃, quenching water volume ≥ 9000 m 3 / h, tempering temperature 570℃-620℃, holding time 4-5 min / mm.

[0021] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0022] (1) Low alloying amount, only a small amount of expensive alloy elements such as Ni, Cr and Mo are used to strengthen the matrix, which greatly reduces the alloy cost of the steel material, and at the same time reduces the carbon equivalent and the welding crack sensitivity coefficient, ensuring the excellent welding performance of the steel material.

[0023] (2) High solid solution boron yield, thereby obtaining strong hardenability of large thickness steel plate. As an alloying element, a small amount of boron can greatly improve the hardenability of steel. The present application optimizes the alloying sequence by using the route of high Al + low Ti + micro Zr strengthening deoxidization and denitrification, adopts the idea of adding aluminum to preserve titanium, adding titanium to preserve zirconium, and adding zirconium to preserve boron, combines the oxygen and nitrogen control measures in the whole process, and uses the Al, Ti and Zr element addition amount relationship formula summarized from a large amount of practical experience, to realize the solid solution boron yield > 80%, thereby obtaining the strong hardenability of large thickness steel plate.

[0024] (3) Nanophase ZrN precipitation strengthening. The addition of a small amount of Zr alloying element not only helps to protect the solid solution yield of boron element and avoid the formation of BN inclusions, but also forms nanoscale ZrN precipitates in the steel matrix through whole process control, which significantly improves the strength and toughness of the steel.

[0025] Through the combination of the above beneficial effects, a thick-gauge 1000 MPa grade steel plate for hydropower station pressure steel pipes is prepared at low cost, and the prepared steel plate has high strength, high ultralow-temperature impact toughness and excellent welding performance. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present application will now be described in detail, which should be considered to be illustrative of the application and not as limiting the application. It will be understood that the detailed description and specific examples, while indicating certain aspects of the application, are given by way of illustration only, since various changes and modifications within the scope of the application will become apparent to those skilled in the art from this detailed description.

[0027] It should be understood that the terms used in the specification are for the purpose of describing particular embodiments only and are not intended to be limiting of the present application. In addition, for a range of values of a parameter, unless otherwise stated, each intervening value by each intervening value, as well as any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these intervening values can independently be included or excluded in the range, and are also encompassed. These smaller ranges are thus each individually disclosed.

[0028] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict, the present specification will control.

[0029] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples presented herein. The specification and examples given should be considered exemplary only, and should not be used to limit the scope or spirit of the application.

[0030] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended and do not exclude additional elements or steps. Example 1

[0031] The water and electricity steel plate thickness of this embodiment is 70 mm, and the chemical composition is: C: 0.07%, Mn: 0.86%, Cu: 0.25%, Cr: 0.52%, Mo: 0.40%, Ni: 1.53%, Al: 0.32%, Ti: 0.005%, B: 0.0012%, Zr: 0.0013%, Nb: 0.22%, V: 0.17%, N: 0.0027%, P: 0.007%, S: 0.0027%, O: 0.0026%, and the balance is Fe and inevitable impurities. The chemical composition satisfies Al / 250+Ti / 5+Zr / 15≤0.004%, carbon equivalent Ceq≤0.55%, and welding crack sensitivity coefficient Pcm≤0.25%; the production method comprises the following steps of converter smelting→LF refining→VD treatment→continuous casting→controlled rolling→quenching and tempering heat treatment process, and the specific process steps are as follows:

[0032] (1) Converter smelting: blowing time is 7.4 min, tapping C content is 562 ppm, and tapping temperature is 1580℃.

[0033] (2) LF refining: the time of the pre-temperature-raising and slagging stage is 10 min, and a medium-high gear slagging is used during the period, and at the same time, the submerged arc is paid attention to during the whole refining process, the opening degree of the dust removal cover of the LF process is controlled at 42%, and the bottom blowing gas adopts the whole process argon control mode. Before the formation of the foamed slag, a small current and small voltage operation is used, and with the formation of the foamed slag, the current and voltage are sequentially increased. After the white slag is refined in the LF furnace, the aluminum wire, ferrotitanium alloy, zirconium-iron alloy and boron-iron alloy are sequentially added, and the power is continuously supplied for about 3 min, and then the soft argon blowing is performed for 20 min.

[0034] (3) VD treatment: the pressure maintaining time is controlled to be 10 min under the vacuum degree of 58 Pa, the N content is 29 ppm, and the H content is 0.4 ppm.

[0035] (4) Continuous casting process: the submerged entry nozzle is used, the butt joint is sealed by argon, the continuous casting speed is 1.4 m / min, and the superheat is 12℃.

[0036] (5) Controlled rolling: two-stage controlled rolling process is adopted, the first stage rolling temperature is 1040℃, the final rolling temperature is 960℃, the single pass maximum reduction rate is 25%, and the last 2 passes reduction amount is 31 mm; the second stage rolling temperature is 860℃, and the final rolling temperature is 800℃.

[0037] (6) Quenching and tempering heat treatment: online quenching and offline tempering process is adopted, quenching temperature is 890℃, quenching water volume is 9000 m 3 / h, tempering temperature is 570℃, and holding time is 4.0 min / mm.

[0038] The steel plate of the embodiment has a yield strength of 930 MPa, a tensile strength of 1020 MPa, an elongation of 16.3% after fracture, a low-temperature impact toughness AKV of 172 J at -80 ℃, a welding heat input of 176 kJ / cm, and a solid-solution boron yield of 83.4%. Example 2

[0039] The water and electricity steel plate of the embodiment has a thickness of 90 mm and a chemical composition comprising C: 0.07%, Mn: 0.88%, Cu: 0.27%, Cr: 0.40%, Mo: 0.40%, Ni: 1.40%, Al: 0.52%, Ti: 0.005%, B: 0.0017%, Zr: 0.0017%, Nb: 0.20%, V: 0.20%, N: 0.0028%, P: 0.007%, S: 0.0025%, O: 0.0027%, and the balance of Fe and inevitable impurities; the chemical composition satisfies Al / 250+Ti / 5+Zr / 15≤0.004%, a carbon equivalent Ceq≤0.55%, and a welding crack sensitivity coefficient Pcm≤0.25%; and the production method comprises the following steps of converter smelting, LF refining, VD treatment, continuous casting, controlled rolling, and quenching and tempering heat treatment processes.

[0040] (1) Converter smelting: the blowing time is 8 min, the tapping C content is 550 ppm, and the tapping temperature is 1584 ℃.

[0041] (2) LF refining: the time of the pre-temperature-raising and slagging stage is 11 min, a medium-high gear slagging is used during the period, and the submerged arc is paid attention to during the whole refining process; the opening degree of the dust removal cover of the LF process is controlled to be 40%, and the bottom blowing gas adopts a whole-process argon control mode; a small current and small voltage operation is used before the formation of the foamed slag, and the current and voltage are sequentially increased with the formation of the foamed slag; the aluminum wire, ferrotitanium, ferrozirconium, and ferroboron are sequentially added after the white slag refining in the LF furnace, and the power is continuously supplied for about 3 min, and then the ladle is lifted after soft argon blowing for 22 min.

[0042] (3) VD treatment: the pressure holding time is controlled to be 12 min under a vacuum degree of 55 Pa, the N content is 28 ppm, and the H content is 0.65 ppm.

[0043] (4) Continuous casting process: a submerged entry nozzle is used, the butt joint is sealed by argon, the continuous casting speed is 1.2 m / min, and the superheat is 12 ℃.

[0044] (5) Controlled rolling: a two-stage controlled rolling process is used, the first-stage rolling temperature is 1060 ℃, the final rolling temperature is 980 ℃, the single pass maximum reduction rate is 27%, and the last two passes are reduced by 30 mm; the second-stage rolling temperature is 870 ℃, and the final rolling temperature is 820 ℃.

[0045] (6) Quenching and tempering treatment: on-line quenching and off-line tempering process, quenching at 900 °C, quenching water volume 9000 m 3 / h, tempering temperature 580 °C, holding time 4.2 min / mm.

[0046] The steel plate of this example has yield strength 925 MPa, tensile strength 1008 MPa, elongation after fracture 16.0%, low temperature impact toughness AKV at -80 °C 169 J, welding heat input 174 kJ / cm, and solid solution boron yield 82.7%. Example 3

[0047] The water and electricity steel plate of this example has thickness 120 mm, and the chemical composition includes C: 0.09%, Mn: 0.92%, Cu: 0.30%, Cr: 0.57%, Mo: 0.48%, Ni: 1.70%, Al: 0.47%, Ti: 0.008%, B: 0.0024%, Zr: 0.0025%, Nb: 0.32%, V: 0.34%, N: 0.0027%, P: 0.006%, S: 0.0025%, O: 0.0024%, and the balance is Fe and inevitable impurities; the chemical composition satisfies Al / 250+Ti / 5+Zr / 15≤0.004%, carbon equivalent Ceq≤0.55%, and welding crack sensitivity coefficient Pcm≤0.25%; the production method includes the processes of converter smelting, LF refining, VD treatment, continuous casting, controlled rolling, and quenching and tempering treatment, and the specific process steps are as follows:

[0048] (1) Converter smelting: blowing time 8 min, tapping C content 670 ppm, tapping temperature 1590 °C.

[0049] (2) LF refining: the time of the pre-temperature-raising and slagging stage is 13 min, and a medium-high gear slagging is used during the stage, and at the same time, the submerged arc is paid attention to during the whole refining process, the opening degree of the dust removal cover of the LF process is controlled at 52%, and the bottom blowing gas adopts the whole process argon control mode. Small current and small voltage operation is used before the formation of foamed slag, and the current and voltage are sequentially increased with the formation of foamed slag. After the white slag is refined in the LF furnace, aluminum wire, ferrotitanium, zirconium-iron alloy, and boron-iron alloy are sequentially added, and power is continuously supplied for about 4.5 min, and then soft argon blowing is performed for 24 min.

[0050] (3) VD treatment: the holding time is controlled to be 14 min under the vacuum degree of 58 Pa, the N content is 29 ppm, and the H content is 0.75 ppm.

[0051] (4) Continuous casting process: a submerged nozzle is used, the butt joint is sealed with argon, the continuous casting speed is 1.0 m / min, and the superheat is 11 °C.

[0052] (5) Controlled rolling: two-stage controlled rolling process was adopted, the first stage was open rolling at 1090 °C and finish rolling at 990 °C, the single pass maximum reduction was 29%, and the last two passes were 32 mm; the second stage was open rolling at 860 °C and finish rolling at 810 °C.

[0053] (6) Quenching and tempering heat treatment: on-line quenching and off-line tempering process was adopted, quenching at 910 °C, quenching water volume was 10000 m 3 / h, tempering temperature was 600 °C, and holding time was 4.6 min / mm.

[0054] The steel plate of the example has yield strength of 930 MPa, tensile strength of 995 MPa, elongation after fracture of 15.7%, low temperature impact toughness AKV of 126 J at -80 °C, welding line energy of 155 kJ / cm, and solid solution boron yield of 82.3%. Example 4

[0055] The water and electricity steel plate of the example has thickness of 150 mm, and the chemical composition comprises: C: 0.11%, Mn: 0.95%, Cu: 0.32%, Cr: 0.60%, Mo: 0.52%, Ni: 1.80%, Al: 0.45%, Ti: 0.010%, B: 0.003%, Zr: 0.003%, Nb: 0.40%, V: 0.40%, N: 0.0026%, P: 0.006%, S: 0.0024%, O: 0.0024%, and the balance is Fe and inevitable impurities; the chemical composition satisfies Al / 250+Ti / 5+Zr / 15≤0.004%, carbon equivalent Ceq≤0.55%, and welding crack sensitivity coefficient Pcm≤0.25%; the production method comprises the steps of converter smelting, LF refining, VD treatment, continuous casting, controlled rolling, and quenching and tempering heat treatment process, and the specific process steps are as follows:

[0056] (1) Converter smelting: blowing time was 12 min, C content of tapping was 800 ppm, and tapping temperature was 1600 °C.

[0057] (2) LF refining: the time of the pre-temperature-raising and slagging stage was 15 min, and a medium-high gear slagging was used during the period, and at the same time, the arc burying was paid attention to during the whole refining process, the opening degree of the dust removal cover of the LF process was controlled at 60%, and the bottom blowing gas used the whole process control argon mode. Small current and small voltage operation was used before the formation of the foamed slag, and then the current and voltage were increased in turn with the formation of the foamed slag. After the white slag was refined in the LF furnace, the aluminum wire, ferrotitanium, zirconium-iron alloy and boron-iron alloy were sequentially added, and the power was continued to be supplied for about 5 min, and then the ladle was lifted after soft argon blowing for 25 min.

[0058] (3) VD treatment: the pressure holding time was controlled to be 16 min under the vacuum degree of 60 Pa, the N content was 30 ppm, and the H content was 0.77 ppm.

[0059] (4) Continuous casting process: using submerged entry nozzle, sealing the joint with argon, continuous casting speed 0.7 m / min, superheat 13°C.

[0060] (5) Controlled rolling: using two-stage controlled rolling process, first stage rough rolling temperature 1100°C, finish rolling temperature 1000°C, single pass maximum reduction rate 30%, last 2 passes reduction 39 mm; second stage rough rolling temperature 890°C, finish rolling temperature 850°C.

[0061] (6) Quenching and tempering heat treatment: using on-line quenching and off-line tempering process, quenching at 930°C, quenching water volume 12000 m 3 / h, tempering temperature 620°C, holding time 5.0 min / mm.

[0062] The steel plate of this example has yield strength 904 MPa, tensile strength 967 MPa, elongation after fracture 15.1%, low temperature impact toughness AKV at -80°C 110 J, welding heat input 153 kJ / cm, and solid solution boron yield 80.5%. Example 5

[0063] The water and electricity steel plate of this example has thickness 100 mm, and the chemical composition consists of: C: 0.10%, Mn: 0.91%, Cu: 0.24%, Cr: 0.43%, Mo: 0.38%, Ni: 1.62%, Al: 0.49%, Ti: 0.004%, B: 0.002%, Zr: 0.001%, Nb: 0.27%, V: 0.26%, N: 0.0025%, P: 0.007%, S: 0.0026%, O: 0.0025%, the balance being Fe and unavoidable impurities; the chemical composition satisfies Al / 250+Ti / 5+Zr / 15≤0.004%, carbon equivalent Ceq≤0.55%, and welding crack sensitivity coefficient Pcm≤0.25%; the production method includes the processes of converter smelting→LF refining→VD treatment→continuous casting→controlled rolling→quenching and tempering heat treatment, and the specific process steps are as follows:

[0064] (1) Converter smelting: blowing time 9 min, tapping C content 610 ppm, tapping temperature 1596°C.

[0065] (2) LF refining: the time of the early stage of temperature increase and slagging is 14 min, during which the medium and high grade slagging is used, and at the same time, the submerged arc is paid attention to during the whole refining process, the dust cover opening degree of the LF process is controlled at 48%, and the bottom blowing gas adopts the whole process argon control mode. Small current and small voltage operation is used before the formation of foamed slag, and with the formation of foamed slag, the current and voltage are increased in turn. After the white slag is refined in the LF furnace, the aluminum wire, ferro-titanium, ferro-zirconium and ferro-boron are sequentially added, and the power is continued to be sent for about 4 min, and then the ladle is lifted for 23 min of soft argon blowing.

[0066] (3) VD treatment: the pressure holding time is controlled at 15 min under the vacuum degree of 57 Pa, the N content is 27 ppm, and the H content is 0.53 ppm.

[0067] (4) Continuous casting process: the submerged entry nozzle is used, the joint is sealed with argon, the continuous casting speed is 0.9 m / min, and the superheat is 11 ℃.

[0068] (5) Controlled rolling: two-stage controlled rolling process is adopted, the first stage rolling temperature is 1050 ℃, the final rolling temperature is 970 ℃, the single pass maximum reduction rate is 26%, and the last 2 passes reduction amount is 33 mm; the second stage rolling temperature is 850 ℃, and the final rolling temperature is 810 ℃.

[0069] (6) Quenching and tempering heat treatment: online quenching and offline tempering process is adopted, quenching at 920 ℃, quenching water amount is 9500 m 3 / h, tempering temperature is 590 ℃, and holding time is 4.5 min / mm.

[0070] The yield strength of the steel plate of the example is 921 MPa, the tensile strength is 978 MPa, the elongation after fracture is 16.2%, the low temperature impact toughness AKV at-80 ℃ is 104 J, the welding line energy is 175 kJ / cm, and the solid solution boron yield is 81.4%. Example 6

[0071] The water and electricity steel plate thickness of this embodiment is 130 mm, and its chemical composition is composed of C: 0.06%, Mn: 0.85%, Cu: 0.29%, Cr: 0.55%, Mo: 0.32%, Ni: 1.30%, Al: 0.40%, Ti: 0.007%, B: 0.001%, Zr: 0.0022%, Nb: 0.35%, V: 0.15%, N: 0.0029%, P: 0.006%, S: 0.0027%, O: 0.0028%, and the balance of Fe and inevitable impurities; the chemical composition satisfies Al / 250+Ti / 5+Zr / 15≤0.004%, carbon equivalent Ceq≤0.55%, and welding crack sensitivity coefficient Pcm≤0.25%; and its production method comprises the following steps of converter smelting→LF refining→VD treatment→continuous casting→controlled rolling→quenching and tempering heat treatment process.

[0072] (1) Converter smelting: blowing time is 10 min, the C content of tapping is 730 ppm, and the tapping temperature is 1593℃.

[0073] (2) LF refining: the time of the pre-temperature-raising and slagging stage is 12 min, and a medium-high gear slagging is used during the period, and at the same time, the submerged arc is paid attention to during the whole refining process, the opening degree of the dust removal cover of the LF process is controlled to be 57%, and the bottom blowing gas adopts the whole process argon control mode. A small current and small voltage operation is used before the formation of the foamed slag, and then the current and voltage are increased in turn. After the white slag is refined in the LF furnace, the aluminum wire, ferrotitanium alloy, zirconium-iron alloy and boron-iron alloy are sequentially added, and the power is continued to be supplied for about 4 min, and then the ladle is lifted after soft argon blowing for 25 min.

[0074] (3) VD treatment: the pressure maintaining time is controlled to be 13 min under the vacuum degree of 58 Pa, the N content is 28 ppm, and the H content is 0.58 ppm.

[0075] (4) Continuous casting process: the submerged entry nozzle is adopted, the joint is sealed by argon, the continuous casting speed is 1.1 m / min, and the superheat is 12℃.

[0076] (5) Controlled rolling: two-stage controlled rolling process is adopted, the first stage rolling temperature is 1070℃, the final rolling temperature is 980℃, the single pass maximum reduction rate is 28%, and the last two passes are reduced by 35 mm; the second stage rolling temperature is 880℃, and the final rolling temperature is 830℃.

[0077] (6) Quenching and tempering heat treatment: the online quenching and offline tempering process is adopted, the quenching temperature is 900℃, the quenching water volume is 11000 m 3 / h, the tempering temperature is 610℃, and the holding time is 4.3 min / mm.

[0078] The steel plate of the embodiment has yield strength of 917 MPa, tensile strength of 984 MPa, elongation of 16.9%, low-temperature impact toughness AKV of 143 J at-80℃, welding line energy of 169 kJ / cm, and solid-solution boron yield of 85.3%.

[0079] The above-described embodiments are merely preferred modes of the present application and are not intended to limit the scope of the present application. Various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. A thick-gauge, low-cost 1000MPa grade hydroelectric steel, characterized in that, The chemical composition and mass percentage of the hydroelectric steel plate are as follows: C: 0.06–0.11%, Mn: 0.85–0.95%, Cu: 0.24–0.32%, Cr: 0.40–0.60%, Mo: 0.32–0.52%, Ni: 1.30–1.80%, Al: 0.32–0.52%, Ti: 0.004–0.010%, B: 0.001–0.00%. 3%, Zr: 0.001~0.003%, Nb: 0.20~0.40%, V: 0.15~0.40%, N≤0.0030%, P≤0.008%, S≤0.003%, O≤0.003%, with the balance being Fe and unavoidable impurities; the chemical composition of the steel plate satisfies Al / 250+Ti / 5+Zr / 15≤0.004%; the thickness of the steel plate is 70~150 mm, yield strength ≥900 MPa, tensile strength ≥960 MPa, elongation after fracture ≥15%, low-temperature impact toughness AKV ≥100 J at -80℃, and welding heat input ≥150 kJ / cm.

2. The thick-gauge, low-cost 1000MPa grade hydroelectric steel according to claim 1, characterized in that, The steel plate has a carbon equivalent Ceq ≤ 0.55% and a welding crack sensitivity coefficient Pcm ≤ 0.25%. Among them, Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14; Pcm=C+Si / 30+(Mn+ Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+B.

3. The thick-gauge, low-cost 1000MPa grade hydroelectric steel according to claim 1, characterized in that, The boron recovery rate of the steel plate is >80%.

4. A method for producing thick-gauge, low-cost 1000MPa grade hydroelectric steel according to any one of claims 1 to 3, comprising the following steps: converter smelting → LF refining → VD treatment → continuous casting → controlled rolling → quenching and tempering heat treatment, characterized in that, In the LF refining process, the initial heating and slag-forming stage lasts for 10-15 minutes, during which medium-to-high grade slag is used. At the same time, attention is paid to submerging the arc throughout the refining process. The opening of the dust collector cover in the LF process is controlled at 40%-60%, and the bottom blowing gas adopts the full-process controlled argon mode. After refining white slag in the LF furnace, aluminum wire, titanium-iron alloy, zirconium-iron alloy, and boron-iron alloy are added in sequence, and power is continued for 3-5 minutes. Then, soft blowing of argon is performed for more than 20 minutes before the ladle is lifted.

5. The method for producing thick-gauge, low-cost 1000MPa grade hydroelectric steel according to claim 4, characterized in that, The converter smelting process is as follows: blowing time 7-12 min, steel C content 550-800 ppm, and steel tapping temperature 1580-1600℃.

6. The method for producing thick-gauge, low-cost 1000MPa grade hydroelectric steel according to claim 4, characterized in that, The VD treatment process involves maintaining a vacuum of ≤60 Pa for 10–16 min, with N content ≤30 ppm and H content ≤0.8 ppm.

7. The method for producing thick-gauge, low-cost 1000MPa grade hydroelectric steel according to claim 4, characterized in that, The continuous casting process is as follows: an immersion nozzle is used, the joint is sealed with argon gas, the casting speed is 0.7 to 1.4 m / min, and the superheat is ≤13℃.

8. The method for producing thick-gauge, low-cost 1000MPa grade hydroelectric steel according to claim 4, characterized in that, The controlled rolling process adopts a two-stage controlled rolling process. In the first stage, the initial rolling temperature is 1040℃~1100℃, the final rolling temperature is 960℃~1000℃, the maximum reduction rate per pass is 25%~30%, and the reduction amount of the last two passes is ≥30 mm. In the second stage, the initial rolling temperature is 850℃~890℃, and the final rolling temperature is 800℃~850℃.

9. The method for producing thick-gauge, low-cost 1000MPa grade hydroelectric steel according to claim 4, characterized in that, The quenching and tempering heat treatment process employs online quenching and offline tempering, with a quenching temperature of 890℃~930℃ and a quenching water volume ≥9000 m³. 3 / h, tempering temperature 570℃~620℃, holding time 4~5 min / mm.