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CN116254471B - A 1000MPa grade easy-to-weld extra-thick hydropower steel and a manufacturing method thereof - Google Patents

A 1000MPa grade easy-to-weld extra-thick hydropower steel and a manufacturing method thereof Download PDF

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CN116254471B
CN116254471B CN202310167172.7A CN202310167172A CN116254471B CN 116254471 B CN116254471 B CN 116254471B CN 202310167172 A CN202310167172 A CN 202310167172A CN 116254471 B CN116254471 B CN 116254471B
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steel
equal
rolling
hydropower
temperature
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CN116254471A (en
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胡海洋
隋轶
王勇
孙殿东
陈捷
高天宇
张瀚宁
王爽
颜秉宇
欧阳鑫
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Angang Steel Co Ltd
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B9/00—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals
    • C22B9/10—General processes of refining or remelting of metals; Apparatus for electroslag or arc remelting of metals with refining or fluxing agents; Use of materials therefor, e.g. slagging or scorifying agents
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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Abstract

本发明涉及一种1000MPa级易焊接特厚水电用钢及其制造方法，钢中化学成分为C：0.08％～0.12％；Si：0.05％～0.09％；Mn：0.50％～0.80％；P≤0.008％；S≤0.001％；Ni：1.35％～1.75％；Mo：0.71％～0.95％；Nb：0.05％～0.08％；B：0.0035％～0.005％；Ca：0.001％～0.004％；Al：0.03％～0.07％；[H]≤1.5ppm；[O]≤8ppm；1＜Mo/Mn＜2；余量为Fe和杂质；本发明采用低碳、Ni+Mo+Nb+B成分体系，同时控制Ceq及Pcm，配合独特的生产工艺，保证钢板具有高强韧性及良好的焊接性能。

The present invention relates to a 1000MPa grade easy-to-weld extra-thick hydroelectric steel and a manufacturing method thereof. The chemical components of the steel are C: 0.08%-0.12%; Si: 0.05%-0.09%; Mn: 0.50%-0.80%; P≤0.008%; S≤0.001%; Ni: 1.35%-1.75%; Mo: 0.71%-0.95%; Nb: 0.05%-0.08%; B: 0 .0035%～0.005%; Ca: 0.001%～0.004%; Al: 0.03%～0.07%; [H]≤1.5ppm; [O]≤8ppm; 1＜Mo/Mn＜2; the balance is Fe and impurities; The present invention adopts low carbon, Ni+Mo+Nb+B component system, controls Ceq and Pcm at the same time, and cooperates with a unique production process to ensure that the steel plate has high strength and toughness and good welding performance.

Description

1000 MPa-level easily-welded extra-thick steel for hydropower and manufacturing method thereof
Technical Field
The invention relates to the technical field of manufacturing of 1000 MPa-level steel plates, in particular to 1000 MPa-level easily-welded extra-thick hydropower steel and a manufacturing method thereof.
Background
In recent years, the use of clean energy has been further developed by the development of carbon peaks and carbon neutralization targets. Hydropower, one of the clean energy sources, does not produce any carbon emissions or pollution, and is renewable, and thus becomes a serious issue in the development of clean energy sources. The large-scale construction of the hydropower engineering enables 800 MPa-level hydropower steel to be widely applied, and meanwhile, demands are also put forward for 1000 MPa-level steel plates.
The steel for hydropower has excellent properties such as toughness, weldability, cold formability and the like, and the requirements for various properties are more strict for 1000 MPa-level hydropower steel. Because of the high difficulty in producing 1000 MPa-level high-strength hydropower steel, only few steel factories can produce the high-strength hydropower steel at home and abroad at present.
The Chinese patent publication No. CN102653846B discloses a large-thickness easily-welded quenched and tempered high-strength steel plate for hydropower and a production method thereof, wherein the steel plate consists of the following chemical components in percentage by weight, ：C：0.15％～0.18％,Si：0.15％～0.35％,Mn：0.90％～1.00％,P≤0.012％,S≤0.005％,Ni：1.52％～1.60％,Cr：0.30％～0.40％,Nb：0.020％～0.030％,Al：0.020％～0.050％,Mo：0.20％～0.30％,V：0.055％～0.065％,B：0.0007％～0.0015％,Ti：0.015％～0.025％, and the balance of Fe and unavoidable impurities. The production method of the steel plate comprises the following steps of electric furnace smelting, LF/VD refining, die casting, steel ingot heating, rolling, water cooling after rolling, heat stacking, heat treatment and finished product production. The maximum thickness of the large-thickness easy-welding quenched and tempered high-strength steel plate for hydropower can reach 230mm, and the steel plate has the characteristics of good welding performance, low yield ratio, excellent low-temperature impact toughness and good thickness direction performance, but has lower overall strength, yield strength of only more than 440MPa and tensile strength of only 540-720 MPa.
The Chinese patent application with publication number of CN108504960A discloses a 1000 MPa-level low-crack hydroelectric steel plate for large-scale hydroelectric engineering and a production method thereof, wherein the thickness of the steel plate is 10-50 mm, and the steel plate comprises the following chemical components ：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％, in percentage by mass and other Fe and residual elements. The steel plate is produced by adopting a low-C and high-Ni (1.0-2.0%) +Cr+Mo component design and adopting a die casting, cogging, reheating, rolling and cooling control and off-line tempering process, ceq is less than or equal to 0.64%, pcm is less than or equal to 0.28%, and the production process is complex.
The Chinese patent application with publication number CN114058960A discloses a high-strength high-toughness easily-welded nano steel with thickness of 25-60 mm and high strength of 1000MPa and a preparation method thereof, and the balance of Fe and unavoidable impurities according to the mass percentage of alloy elements ,C：0.03～0.08,Si：0.2～0.4,Mn：0.7～1.1,P≤0.01,S≤0.0015,Cu：1.5～2.5,Ni：6.0～8.0,Cr：0.5～0.8,Mo：0.45～0.6,Nb：0.02～0.1,Ti：0.01～0.05,Al：0.005～0.05,, and the method comprises the following steps of smelting and refining-die casting or continuous casting-rolling-heat treatment. The yield strength of the nano steel is more than or equal to 1000MPa, the Charpy V notch impact energy at-84 ℃ at the 1/4 and 1/2 thickness of the steel plate is more than or equal to 200J, and the elongation is more than or equal to 15%. The steel plate contains high Cu (1.5-2.5%), high Ni (6-8%) components, the carbon equivalent amount is up to more than 0.65%, and the alloy cost is high.
The publication number CN104532157A discloses a quenched and tempered high-strength steel with yield strength of 900-1000 MPa and a production method thereof, wherein the steel comprises the chemical components of ：C0.16～0.20％,Si0.10～0.30％,Mn0.80～1.60％,Cr0.20～0.70％,Mo0.10～0.45％,Ni0.10～0.50％,Nb0.010～0.030％,Ti0.010～0.030％,V0.010～0.050％,B0.0005～0.0030％,Al0.02～0.06％,Ca0.001～0.004％,N0.002～0.005％,P≤0.020％,S≤0.010％,O≤0.008％,, fe and unavoidable impurities in percentage by weight, and ：Ceq0.51～0.60％,Ceq＝C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15;3.7≤Ti/N≤7.0;1.0≤Ca/S≤3.0;0.8％≤Mo+0.8Ni+0.4Cr+6V≤1.3％. adopts a controlled rolling and controlled cooling and off-line quenching and tempering process, the yield strength of the produced steel plate is 900-1080 MPa, the tensile strength is 950-1200 MPa, the elongation is more than 10%, and the impact power at-40 ℃ is more than 40J. However, the steel plate adopts a higher C (0.16-0.2%), ni+Cr+Mo+B component system, and trace elements Nb, V, ti, N are added, the elongation of the steel plate after fracture is less than 15%, and the impact absorption energy at-40 ℃ is less than 120J.
Therefore, the prior art generally has the problems of high carbon equivalent, insufficient performance and the like.
Disclosure of Invention
The invention provides 1000 MPa-level easy-to-weld extra-thick steel for hydropower and a manufacturing method thereof, wherein a low-carbon, ni+Mo+Nb+B component system is adopted, ceq and Pcm are controlled at the same time, and a unique production process is matched, so that the steel plate has high toughness and good welding performance.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
The steel for the ultra-thick water and electricity easy to weld at the level of 1000MPa comprises the following chemical components in percentage by weight, wherein the balance of C：0.08％～0.12％;Si：0.05％～0.09％;Mn：0.50％～0.80％;P≤0.008％;S≤0.001％;Ni：1.35％～1.75％;Mo：0.71％～0.95％;Nb：0.05％～0.08％;B：0.0035％～0.005％;Ca：0.001％～0.004％;Al：0.03％～0.07％;[H]≤1.5ppm;[O]≤8ppm;1＜Mo/Mn＜2; is Fe and unavoidable impurities, and the steel further satisfies that the carbon equivalent Ceq is less than 0.50 percent, ceq=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14, the welding crack sensitivity coefficient Pcm is less than or equal to 0.25 percent, and pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B.
Further, the room temperature tensile strength of the finished steel plate is more than or equal to 980MPa, the yield strength is more than or equal to 900MPa, the elongation after breaking is more than or equal to 20%, the impact absorption energy at-40 ℃ is more than or equal to 200J, the Z-direction tensile reduction of area is more than 60%, the ductile-free transition temperature is TNDT ℃ less than or equal to-50 ℃, and the impact absorption energy at-40 ℃ of a welded joint under the welding heat input of 10-100 kJ/cm is more than or equal to 150J.
A manufacturing method of 1000 MPa-level easily-welded extra-thick hydropower steel comprises the following steps:
1) Adopting a converter smelting and external refining mode, and carrying out calcium treatment on molten steel during external refining to ensure that the rating thickness of nonmetallic inclusion in the steel is less than or equal to 0.5 level;
2) The method comprises the steps of casting, controlling the superheat degree of a tundish to be 15-25 ℃ in the casting process, the casting blank pulling speed to be 1.3-1.6 m/min, adopting a gas-water spraying mode for secondary cooling water, the cooling speed to be 100-150 ℃/m, adopting an electromagnetic stirring mode for a solidification tail end, and controlling the electromagnetic stirring current to be 300-350A and the frequency to be 4-6 Hz;
3) Stacking and slow cooling, namely stacking and slow cooling the continuous casting billets for more than 40 hours after the continuous casting billets are offline, wherein the center segregation rating of the casting billets is less than or equal to 0.5 grade;
4) Heating, namely heating the continuous casting billet in a heating furnace, wherein the temperature of a soaking section is 1170-1210 ℃, and the soaking time is 2.5-3.5 h;
5) The rolling is carried out by adopting two-stage control, wherein the rolling is carried out in a first-stage recrystallization zone, the initial rolling temperature is 1120-1150 ℃, the pass rolling reduction is 10-25%, the final rolling temperature is 990-1020 ℃, the intermediate billet is cooled to 860-880 ℃ by water, the rolling is carried out in a second-stage non-recrystallization zone, the total rolling reduction is more than 60%, and the final rolling temperature is controlled to 710-740 ℃;
6) And performing heat treatment after rolling, wherein an off-line quenching and tempering heat treatment mode is adopted, the quenching heat preservation temperature is 850-890 ℃, the heat preservation time is 2-5 min/mm, the tempering heat preservation temperature is 570-620 ℃, and the heat preservation time is 2-6 min/mm.
Further, the thickness of the continuous casting blank is 300-450 mm, the thickness of the intermediate blank is 2-3 times the thickness of the finished steel plate, and the thickness of the finished steel plate is 70-110 mm.
Further, high-pressure water is adopted to remove scales after the continuous casting billet is discharged from the furnace.
Compared with the prior art, the invention has the beneficial effects that:
1) The design of a low-carbon, ni+Mo+Nb+B component system is adopted, and meanwhile, the Mo/Mn is controlled to be less than 1 and less than 2, the Ceq is controlled to be less than 0.5%, and the Pcm is less than or equal to 0.25%, so that the guarantee on alloy components is provided for the steel plate with high strength and toughness and good welding performance;
2) The converter and external refining mode is adopted to control P in steel to be less than or equal to 0.008 percent, S to be less than or equal to 0.001 percent, H to be less than or equal to 1.5ppm and O to be less than or equal to 8ppm, and a proper calcium treatment process is matched, so that the purity of the steel is improved, nonmetallic inclusion in the steel is reduced, and the grade of the nonmetallic inclusion is less than or equal to 0.5 grade;
3) According to the design characteristics of alloy components in steel, a recrystallization region and a non-recrystallization region are adopted to control rolling, and the core structure and performance of the extra-thick plate are effectively improved through multi-pass high-permeability deformation and microalloy strengthening mechanisms, so that the lamellar tearing resistance of the steel plate is improved;
4) The production and the manufacture of the steel for the easy-to-weld hydropower with the thickness of 70-110 mm and the tensile strength of 1000MPa are realized by the design of a low-carbon, ni+Mo+Nb+B component system and the combination of controlled rolling and off-line tempering heat treatment process, and the steel plate has excellent toughness and welding performance;
5) The room temperature tensile strength of the steel plate is more than or equal to 980MPa, the yield strength is more than or equal to 900MPa, the elongation after breaking is more than or equal to 20%, the impact absorption energy of-40 ℃ is more than or equal to 200J, the Z-direction tensile reduction of area is more than 60%, the ductile transition temperature is TNDT ℃ or less than or equal to-50 ℃, the impact absorption energy of the welded joint at-40 ℃ under the welding heat input of 10-100 kJ/cm is more than or equal to 150J, the steel plate has excellent low temperature toughness and weldability, and the use requirement of a large hydropower station on 1000 MPa-level easily-welded extra-thick hydropower steel can be completely met.
Drawings
FIG. 1 is a photograph of a typical metallographic structure of a 1000MPa grade easily welded extra-thick steel for hydropower according to the invention.
Detailed Description
The 1000 MPa-level easy-to-weld extra-thick steel for hydropower comprises the following chemical components in percentage by weight, wherein the balance of Fe and unavoidable impurities is C：0.08％～0.12％;Si：0.05％～0.09％;Mn：0.50％～0.80％;P≤0.008％;S≤0.001％;Ni：1.35％～1.75％;Mo：0.71％～0.95％;Nb：0.05％～0.08％;B：0.0035％～0.005％;Ca：0.001％～0.004％;Al：0.03％～0.07％;[H]≤1.5ppm;[O]≤8ppm;1＜Mo/Mn＜2;, the carbon equivalent Ceq is less than 0.50%, ceq=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14, the welding crack sensitivity coefficient Pcm is less than or equal to 0.25%, and pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B.
Further, the room temperature tensile strength of the finished steel plate is more than or equal to 980MPa, the yield strength is more than or equal to 900MPa, the elongation after breaking is more than or equal to 20%, the impact absorption energy at-40 ℃ is more than or equal to 200J, the Z-direction tensile reduction of area is more than 60%, the ductile-free transition temperature is TNDT ℃ less than or equal to-50 ℃, and the impact absorption energy at-40 ℃ of a welded joint under the welding heat input of 10-100 kJ/cm is more than or equal to 150J.
The invention relates to a manufacturing method of 1000 MPa-level easily-welded extra-thick steel for hydropower, which comprises the following steps:
1) Adopting a converter smelting and external refining mode, and carrying out calcium treatment on molten steel during external refining to ensure that the rating thickness of nonmetallic inclusion in the steel is less than or equal to 0.5 level;
2) The method comprises the steps of casting, controlling the superheat degree of a tundish to be 15-25 ℃ in the casting process, the casting blank pulling speed to be 1.3-1.6 m/min, adopting a gas-water spraying mode for secondary cooling water, the cooling speed to be 100-150 ℃/m, adopting an electromagnetic stirring mode for a solidification tail end, and controlling the electromagnetic stirring current to be 300-350A and the frequency to be 4-6 Hz;
3) Stacking and slow cooling, namely stacking and slow cooling the continuous casting billets for more than 40 hours after the continuous casting billets are offline, wherein the center segregation rating of the casting billets is less than or equal to 0.5 grade;
4) Heating, namely heating the continuous casting billet in a heating furnace, wherein the temperature of a soaking section is 1170-1210 ℃, and the soaking time is 2.5-3.5 h;
5) The rolling is carried out by adopting two-stage control, wherein the rolling is carried out in a first-stage recrystallization zone, the initial rolling temperature is 1120-1150 ℃, the pass rolling reduction is 10-25%, the final rolling temperature is 990-1020 ℃, the intermediate billet is cooled to 860-880 ℃ by water, the rolling is carried out in a second-stage non-recrystallization zone, the total rolling reduction is more than 60%, and the final rolling temperature is controlled to 710-740 ℃;
6) And performing heat treatment after rolling, wherein an off-line quenching and tempering heat treatment mode is adopted, the quenching heat preservation temperature is 850-890 ℃, the heat preservation time is 2-5 min/mm, the tempering heat preservation temperature is 570-620 ℃, and the heat preservation time is 2-6 min/mm.
Further, the thickness of the continuous casting blank is 300-450 mm, the thickness of the intermediate blank is 2-3 times the thickness of the finished steel plate, and the thickness of the finished steel plate is 70-110 mm.
Further, high-pressure water is adopted to remove scales after the continuous casting billet is discharged from the furnace.
The chemical composition design reason of the 1000 MPa-level easily-welded extra-thick steel for hydropower is as follows:
(1) The C has the function of solid solution strengthening, and can form tiny carbide with Nb and Mo, thereby playing the role of effective precipitation strengthening in the heating, rolling deformation and heat treatment processes. However, the increase of the carbon content is unfavorable for the welding performance of the steel, so that the C content is controlled to be 0.08% -0.12% in the invention.
(2) Si, which plays a role of solid solution strengthening and can improve the hardenability and tempering resistance of steel. However, the welding performance of the steel is reduced due to the fact that the Si content is too high, so that the Si content in the steel is controlled to be 0.05% -0.09%.
(3) Mn is capable of improving the hardenability of steel and has the function of solid solution strengthening, and more importantly, the Mn-Mo alloy steel plate has the advantages that the Mn is matched with Mo for use, and the Mn/Mn is controlled to be 1< Mo/Mn <2, so that the formation of an alloy penetrating body in the long-time tempering process is inhibited, the toughness of the steel plate after heat treatment is improved, and the welding performance of the steel plate is improved. However, an increase in manganese content reduces the weldability of the steel. Therefore, the Mn content in the steel is controlled to be 0.50% -0.80%.
(4) P, S, which are harmful elements, wherein P damages the low-temperature toughness of the steel plate, S is easy to form sulfide inclusions in the steel, the impact toughness of the steel is reduced, and the welding performance is damaged, so that the lower the content of the P is, the better the lower the content of the P is, the less than or equal to 0.008%, and the S is, the less than or equal to 0.001% in the steel.
(5) Ni is used for expanding an austenite region, so that the effective implementation of the controlled rolling process is facilitated, the adjacent transformation temperature is reduced, the low-temperature toughness of the steel plate is improved, ferrite is strengthened, the controlled cooling structure is refined, and the hardenability of the steel plate is improved. However, the increase of the nickel content is unfavorable for improving the welding performance, so the invention controls the Ni content to be 1.35% -1.75%.
(6) Mo has the main effects of 1) playing a certain solid solution strengthening role, 2) improving the hardenability of steel, 3) improving the stability of carbide and further improving the strength of steel, and 4) inhibiting the formation of alloy penetrating body in the long-time tempering process by being matched with Mn and controlling the content of Mo/Mn to be 1< 2, improving the toughness of the steel plate after heat treatment and improving the welding performance of the steel plate. Considering the influence of molybdenum on welding performance, the method controls the content of Mo to be 0.71% -0.95%.
(7) Nb has the main functions of 1) preventing austenite grains from growing when a steel billet is heated and increasing the coarsening temperature of the grains, 2) preventing the migration of grain boundaries and preventing coarsening of recrystallized grains due to the interaction of niobium dissolved in austenite and dislocation during rolling in a recrystallization zone, 3) pinning austenite subgrain and promoting ferrite nucleation by fine niobium carbonitride precipitated through deformation during rolling in a non-recrystallization zone, 4) expanding the range of the non-recrystallization zone of austenite, which is beneficial to the implementation of a controlled rolling process, 5) improving the hardenability of the steel, and 6) inhibiting the generation of Fe (C, B) 6 and ensuring that boron in the steel exists basically in the form of solid solution boron. Therefore, the Nb content in the steel is controlled to be 0.05% -0.08%.
(8) And B, improving the hardenability of the steel and improving the strength of the steel after controlled cooling and tempering. The excessive boron content can cause segregation and reduce the toughness of the steel, so that the content of B in the steel is controlled to be 0.0035% -0.005%.
(9) Ca is used for modifying oxide and sulfide inclusion in molten steel, improving the cleanliness of the molten steel, refining grains, improving the toughness of a steel plate and improving the lamellar tearing resistance of the extra-thick plate. However, excessive Ca easily forms large-sized compounds and damages the toughness of the steel plate, so the invention controls the content of Ca in the steel to be 0.001-0.004%
(10) Al plays a certain role in deoxidizing, can form AlN, refines grains and improves the toughness of the steel plate. The Al content is controlled to be 0.03% -0.07%.
(11) H and O have adverse effects on the performance of the steel plate, and the invention controls [ H ] to be less than or equal to 1.5ppm and [ O ] to be less than or equal to 8ppm.
The invention relates to a manufacturing method of 1000 MPa-level easily-welded extra-thick steel for hydropower. The design principle is as follows:
1. The steel billet smelting adopts a converter and external refining mode, P in steel is controlled to be less than or equal to 0.008 percent, S is controlled to be less than or equal to 0.001 percent, H is controlled to be less than or equal to 1.5ppm, O is controlled to be less than or equal to 8ppm, and calcium treatment is carried out on molten steel in an external refining process to denature impurities in the molten steel, improve the purity of the steel, enable nonmetallic impurities in the molten steel to be sphericized, enable the thickness grade to be not more than 0.5 grade, improve the fluidity of the molten steel and improve the cast structure.
2. The superheat degree of the tundish is controlled to be 15-25 ℃ in the casting process, the casting blank pulling speed is 1.3-1.6 m/min, the secondary cooling water adopts a gas-water spraying mode, the cooling speed is 100-150 ℃ per m, and the internal and external temperature drop balance of the casting blank is ensured, and no crack exists. The solidification tail end adopts an electromagnetic stirring mode, the electromagnetic stirring current is 300-350A, the frequency is 4-6 Hz, the equiaxial crystal bands are enlarged and thinned, the distribution of inclusions is improved, shrinkage cavities of casting blanks are eliminated, and center porosity and center segregation are reduced.
3. Stacking and slow cooling the continuous casting blanks for more than 40 hours after the continuous casting blanks are off line, promoting the cast structure to be further homogenized, reduces the internal stress of the casting blank, reduces the segregation of the casting blank, ensuring that the segregation of the casting blank is less than or equal to 0.5 level. The thickness of the continuous casting billet is preferably 300-450 mm.
4. The continuous casting blank is heated in a heating furnace (preferably a stepping heating furnace), the temperature of a soaking section is 1170-1210 ℃, the soaking time is 2.5-3.5 h, and under the heating process, the casting blank is uniformly heated, austenitized is sufficient and coarsening tendency does not exist.
5. The casting blank is taken out of the furnace the scale is removed by high-pressure water, and then adopting two-stage control rolling. In the first stage, the recrystallization zone is rolled, the initial rolling temperature is 1120-1150 ℃, the pass reduction rate is 10-25%, the interval time between rolling passes is reduced as much as possible, austenite grains are prevented from growing, the thickness of the intermediate blank is 2-3 times that of the finished steel plate, and the final rolling temperature is 990-1020 ℃. And (3) cooling the intermediate blank to 860-880 ℃ by water, rolling in a second stage of non-recrystallization zone, wherein the total rolling reduction is more than 60%, and the final rolling temperature is controlled to 710-740 ℃.
6. The rolled steel plate is subjected to off-line quenching and tempering heat treatment, wherein the quenching heat preservation temperature is 850-890 ℃, the heat preservation time is 2-5 min/mm, the tempering heat preservation temperature is 570-620 ℃, and the heat preservation time is 2-6 min/mm. The reasonable tempering process ensures that the steel plate has excellent toughness.
A typical metallographic structure photo of the 1000 MPa-level easily-welded extra-thick hydropower steel is shown in figure 1, and the structure in the steel is tempered sorbite.
The following examples are given by way of illustration of detailed embodiments and specific procedures based on the technical scheme of the present invention, but the scope of the present invention is not limited to the following examples.
[ Example ]
The chemical composition of the steel in each example is shown in table 1, the continuous casting and heating process parameters of the steel in each example are shown in table 2, the rolling and heat treatment process parameters of the steel in each example are shown in table 3, and the mechanical properties of the finished steel plate in each example are shown in table 4.
Table 1 chemical composition (wt%) of steel
Table 2 continuous casting and heating process parameters of steel
Table 3 parameters of the rolling and heat treatment process for steels
TABLE 4 mechanical Properties of quenched and tempered Steel plate
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

Claims (4)

1. A manufacturing method of 1000 MPa-level easily-welded extra-thick steel for hydropower is characterized in that the steel comprises the following chemical components in percentage by weight, wherein the balance of C：0.08%～0.12%;Si：0.05%～0.09%;Mn：0.50%～0.80%;P≤0.008%;S≤0.001%;Ni：1.35%～1.75%;Mo：0.71%～0.95%;Nb：0.05%～0.08%;B：0.0035%～0.005%;Ca：0.001%～0.004%;Al：0.03%～0.07%;[H]≤1.5ppm;[O]≤8ppm;1＜Mo/Mn＜2; is Fe and unavoidable impurities, the carbon equivalent Ceq is less than 0.50%, ceq=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14, the welding crack sensitivity coefficient Pcm is less than or equal to 0.25%, and pcm=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B;
the manufacturing method of the 1000 MPa-level easily-welded extra-thick hydropower steel comprises the following steps of:
1) Adopting a converter smelting and external refining mode, and carrying out calcium treatment on molten steel during external refining to ensure that the rating thickness of nonmetallic inclusion in the steel is less than or equal to 0.5 level;
2) The method comprises the steps of casting, controlling the superheat degree of a tundish to be 15-25 ℃ in the casting process, the casting blank pulling speed to be 1.3-1.6 m/min, adopting a gas-water spraying mode for secondary cooling water, the cooling speed to be 100-150 ℃/m, adopting an electromagnetic stirring mode for a solidification tail end, and controlling the electromagnetic stirring current to be 300-350A and the frequency to be 4-6 Hz;
3) Stacking and slow cooling, namely stacking and slow cooling the continuous casting billets for more than 40 hours after the continuous casting billets are offline, wherein the center segregation rating of the casting billets is less than or equal to 0.5 grade;
4) Heating, namely heating the continuous casting billet in a heating furnace, wherein the temperature of a soaking section is 1170-1210 ℃, and the soaking time is 2.5-3.5 h;
5) The rolling is carried out by adopting two-stage control, wherein the rolling is carried out in a first-stage recrystallization zone, the initial rolling temperature is 1120-1150 ℃, the pass rolling reduction is 10-25%, the final rolling temperature is 990-1020 ℃, the intermediate billet is cooled to 860-880 ℃ by water, the rolling is carried out in a second-stage non-recrystallization zone, the total rolling reduction is more than 60%, and the final rolling temperature is controlled to 710-740 ℃;
6) And performing heat treatment after rolling, wherein an off-line quenching and tempering heat treatment mode is adopted, the quenching heat preservation temperature is 850-890 ℃, the heat preservation time is 2-5 min/mm, the tempering heat preservation temperature is 570-620 ℃, and the heat preservation time is 2-6 min/mm.
2. The method for manufacturing 1000 MPa-level easily-welded extra-thick steel for hydropower stations, which is characterized in that the room-temperature tensile strength of a finished steel plate is equal to or more than 980MPa, the yield strength is equal to or more than 900MPa, the elongation after fracture is equal to or more than 20%, the impact absorption energy at-40 ℃ is equal to or more than 200J, the Z-direction tensile reduction of area is equal to or more than 60%, the ductile-free transition temperature is TNDT ℃ or less than-50 ℃, and the impact absorption energy at-40 ℃ of a welded joint under the welding heat input of 10-100 kJ/cm is equal to or more than 150J.
3. The method for manufacturing 1000 MPa-level easily-welded extra-thick steel for hydropower according to claim 1, wherein the thickness of the continuous casting blank is 300-450 mm, the thickness of the intermediate blank is 2-3 times the thickness of the finished steel plate, and the thickness of the finished steel plate is 70-110 mm.
4. The method for manufacturing 1000 MPa-level easily-welded extra-thick steel for hydropower stations, according to claim 1, characterized in that high-pressure water is adopted for descaling after the continuous casting billet is discharged from the furnace.
CN202310167172.7A 2023-02-27 2023-02-27 A 1000MPa grade easy-to-weld extra-thick hydropower steel and a manufacturing method thereof Active CN116254471B (en)

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