CN115181908A - Ultra-thick 460 MPa-grade steel plate in service in extremely cold region and preparation method thereof - Google Patents
Ultra-thick 460 MPa-grade steel plate in service in extremely cold region and preparation method thereof Download PDFInfo
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- 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
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C—CHEMISTRY; METALLURGY
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- 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
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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Abstract
The invention provides a 460 MPa-grade steel plate with extremely-thick service specification in an extremely-cold region and a preparation method thereof; the steel plate comprises the following chemical components in percentage by mass: c: 0.08-0.10%, si: 0.20-0.40%, mn: 1.50-1.65%, P is less than or equal to 0.013%, S is less than or equal to 0.005%, nb: 0.030-0.040%, ti:0.010-0.020%, V:0.030% -0.045%, cr:0.15-0.25%, ni: 0.20-0.30%, al: 0.020-0.050%, the balance of Fe and inevitable impurity elements, wherein CEV is less than or equal to 0.43%, and Pcm is less than or equal to 0.22%. The extra-thick 460MPa steel plate has the advantages of high toughness, low temperature resistance and easy welding, and the thickness of the finished steel plate is 80-100mm.
Description
Technical Field
The invention belongs to the technical field of production of ultra-high strength marine steel plates, and particularly relates to a 460 MPa-grade steel plate with a super-thick service specification in an extremely cold region and a preparation method thereof.
Background
With the increasing shortage of world energy, developed countries in the world increase the development of marine resources, and a large number of energy development projects are developed near the arctic. In order to meet the use requirements of various large engineering facilities in service in polar environment, development of ultra-thick steel plates with high strength, low temperature resistance and easy welding is urgently needed.
Patent CN109594013A discloses a longitudinal impact energy KV 2 The steel plate comprises the following components in percentage by mass: c:0.06 to 0.08%, si:0.20 to 0.30%, mn: 1.45-1.65%, P: less than or equal to 0.015 percent, S: less than or equal to 0.008 percent, nb:0.025 to 0.035%, ti:0.010-0.020%, cu:0.15 to 0.25%, ni:0.15-0.25%, cr:0.15-0.25%, als:0.024-0.034%, rare earth Ce:0.0005-0.0030% and the balance of Fe and inevitable impurities, and the steel plate obtained by the patent has weather resistance requirements, so that Cu and Ce are added to improve the corrosion resistance; however, the steel plate is not suitable for polar environment, the maximum thickness of the finished steel plate is only 40mm, and the use requirement of the super-thick steel plate on toughness, particularly the uniformity of the performance in the thickness direction, is difficult to meet at present.
Patent CN111139402B discloses a method for manufacturing an economical polar low-temperature structural steel plate, which comprises the following components in percentage by weight: 0.04-0.10%, si:0.15-0.40%, mn:1.20-1.40%, nb:0.020-0.050%, V:0.020-0.050%, ti:0.010-0.030%, als:0.015 to 0.050%, ni:0.10-0.40%, P < 0.010%, S < 0.003%, CEV < 0.40%, the rest is Fe and inevitable impurity, this patent discloses the method for preparing 80mm extra thick steel plate under the condition of 3.25 low compression ratio, need to carry on 890-910 duC normalizing heat treatment to refine the crystalline grain, homogeneous structure after rolling, but the yield strength of the steel plate prepared of this invention is 340-420MPa, it is difficult to realize the enhancement of the intensity, can't meet the use requirement above 460MPa grade to the intensity grade of the extra thick steel plate.
Patent CN103938108A discloses a 460MPa grade low compression ratio high toughness marine steel plate and a production method thereof, wherein the steel plate comprises the following chemical components by weight percentage: c:0.04-0.07%, si:0.2-0.4%, mn:1.0-1.5%, P is less than or equal to 0.010%, S is less than or equal to 0.003%, ni:0.2-0.5%, cu:0.2-0.5%, cr:0.2-0.4%, mo:0.1-0.3%, nb:0.02 to 0.05%, ti:0.01-0.025%, and the balance of Fe and inevitable impurities; because the content of C in the steel is 0.04-0.07%, and alloying elements such as Mo, cu, cr and the like are added, the tempering heat treatment at 580-700 ℃ is needed after rolling, and the method not only leads to cost improvement, but also is not beneficial to ensuring the welding performance of the steel.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a 460 MPa-grade steel plate with extremely-cold region service extra-thick specification and a preparation method thereof. The extra-thick 460MPa steel plate has the advantages of high toughness, low temperature resistance and easy welding, and the thickness of the finished steel plate is 80-100mm.
In order to achieve the purpose, the invention provides a 460 MPa-grade steel plate with ultra-thick service specification in an extremely cold region in a first aspect, which adopts the following technical scheme:
a460 MPa grade steel plate with super-thick service specification in an extremely cold region comprises the following chemical components in percentage by mass: c:0.08% to 0.10% (e.g. 0.082%, 0.085%, 0.088%, 0.09%, 0.093%, 0.095%, 0.098%), si:0.20% to 0.40% (e.g., 0.21%, 0.25%, 0.27%, 0.30%, 0.35%, 0.37%, 0.39%), mn: 1.50-1.65% (such as 1.52%, 1.55%, 1.57%, 1.59%, 1.60%, 1.62%, 1.64%), P is less than or equal to 0.013%, S is less than or equal to 0.005%, nb:0.030% to 0.040% (such as 0.031%, 0.033%, 0.034%, 0.035%, 0.037%, 0.38%, 0.39%), ti:0.010% to 0.020% (e.g., 0.011%, 0.012%, 0.014%, 0.015%, 0.017%, 0.018%, 0.019%), V:0.030 to 0.045% (e.g., 0.032%, 0.034%, 0.035%, 0.037%, 0.040%, 0.042%, 0.044%), cr:0.15% to 0.25% (e.g., 0.16%, 0.18%, 0.19%, 0.20%, 0.21%, 0.23%, 0.24%), ni:0.20% to 0.30% (e.g., 0.21%, 0.23%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%), al: 0.020-0.050% (such as 0.022%, 0.025%, 0.028%, 0.030%, 0.035%, 0.040%, 0.045%), and the balance of Fe and inevitable impurity elements, wherein CEV (carbon equivalent) is less than or equal to 0.43%, and Pcm (welding sensitivity coefficient) is less than or equal to 0.22%.
Wherein, CEV = C + Mn/6+ (Cr + Mo + V)/5 + (Ni + Cu)/15, wherein the element symbols represent the mass percentage of the corresponding elements in the steel plate;
pcm = C + Si/30+ Mn/20+ Cu/20+ Ni/60+ Cr/20+ Mo/15+ V/10+5B, and the element symbols in the formula represent the mass percentage content of corresponding elements in the steel plate.
In the extra-thick 460 MPa-grade steel plate in service in the extremely cold region, as a preferred embodiment, the inevitable impurity elements comprise, by mass, H less than or equal to 0.0002%, O less than or equal to 0.003%, N less than or equal to 0.005%, and B less than or equal to 0.0005%.
In the 460 MPa-grade steel plate with extra-thick service specification in the extremely cold region, as a preferred embodiment, the thickness of the steel plate is 80-100mm (such as 82mm, 85mm, 88mm, 90mm, 93mm, 95mm and 98 mm), the yield strength of the steel plate is more than or equal to 460MPa, the tensile strength of the steel plate is 540-675 MPa (such as 550MPa, 580MPa, 600MPa, 625MPa, 640MPa, 650MPa and 670 MPa), the transverse impact energy at 40 ℃ is more than or equal to 200J, and the CTOD characteristic value at 40 ℃ is more than or equal to 0.5mm.
The invention adopts low C design to ensure the welding performance of the steel plate, ensures the strength by adding the alloy element Cr and carrying out micro-alloying by utilizing Nb, V and Ti, and simultaneously ensures the low-temperature performance by adding the alloy element Ni. The design of the components ensures that the steel plate has good toughness, low temperature resistance and welding performance.
The effects of the main components in the ultra-thick 460MPa steel plate in service in the extremely cold region are as follows:
c: c is a solid-solution strengthening element in steel, and can significantly improve the strength of steel sheet, but it reduces the plasticity and toughness of steel, and significantly deteriorates the weldability. In order to ensure that the marine steel has better construction performance in a severe environment of a polar region, save the consumption of welding and subsequent heat treatment and improve the plastic toughness performance, the low-C design is an effective way in the chemical composition design. Therefore, the content of C in the invention is controlled to be 0.08-0.10%.
Cr: for super thick gauge steel, cr can increase the strength while improving the uniformity of properties in the thickness direction. In the invention, the Cr content is controlled to be 0.15-0.25%; if the Cr content is more than 0.25%, it results in the formation of Cr-Mn composite oxides having a low melting point, easily causes surface cracks in the steel sheet during hot working, and also seriously deteriorates weldability.
Nb: nb can effectively prevent the recovery and recrystallization of the deformed austenite in the rolling stage, has the effect of refining grains, and also has the function of precipitation strengthening, but is limited by C and influenced by the heating temperature, nb with too high content cannot be fully dissolved, and the waste of precious alloy is caused invisibly; therefore, the Nb content is controlled to be 0.030% to 0.040% in the present invention.
Ti: ti is a strong N element, when a slab is continuously cast, the added Ti and N can form a fine high-temperature stable TiN precipitated phase, the fine TiN particles can effectively prevent austenite grains from growing when a casting blank is reheated, the low-temperature impact toughness of the steel plate is improved, but when the content is too high, large-particle TiN is easily formed to lose the fine grain effect, the alloy cost and the performance of the steel plate are comprehensively considered, and the Ti content is controlled to be 0.010-0.020%.
V: v is a refined grain element in the steel and also has a precipitation strengthening effect, but excessive V element addition easily causes precipitation growth of coarse V compounds to deteriorate low-temperature impact toughness; therefore, the V content is controlled to be 0.030% -0.045%.
Ni: ni is an element for most obviously improving the low-temperature toughness of the super-thick steel plate, and proper Ni is added to reduce the dislocation energy of crystals, thereby being beneficial to the slippage movement of dislocation and improving the impact toughness. However, the Ni content is too high, so that high-viscosity iron scales are easily formed on the surface of the plate blank, and the surface quality and the fatigue performance are influenced; meanwhile, the Ni content is too high, which is not beneficial to ensuring the welding performance; therefore, the Ni content is controlled to be 0.20-0.30 percent in the invention.
Al: al in the steel can fix free N in the steel, improve the low-temperature toughness of a steel plate and a welding HAZ, and the dispersed precipitation of AlN can inhibit the growth of austenite grains in the heating process, uniformly refine the size of the austenite grains and improve the impact toughness; however, the excessive Al content increases the number of inclusions in the steel, increases the size of the inclusions, reduces the internal quality of the steel plate, and affects the hot workability, weldability and machinability of the steel, so the Al content is controlled to be 0.020-0.050% in the invention.
N: when the content is too high, coarse TiN and AlN are formed and precipitated in the prior austenite grain boundary, and the impact toughness and plasticity of the steel plate and a welding heat affected zone are damaged. Meanwhile, N atoms can also be enriched at the defect positions in the steel to form air holes and looseness, so that the mechanical property of the steel plate is further deteriorated; therefore, considering that N is unlikely to be removed from the steel, the N content is controlled to 0.005% or less in the present invention.
B: the steel plate with too high content can be enriched in the grain boundary in the steel plate, so that the grain boundary energy is reduced, a low-temperature phase change structure is formed in the steel plate in the cooling process, and the low-temperature impact property and the fatigue property of the steel plate are reduced; therefore, the content of B in the present invention is 0.0005% or less.
O: elements are remained in a casting blank or diffused to a surface layer, a crystal boundary is easily oxidized to form a brittle oxide interlayer, austenite crystal grains are isolated, so that intergranular cracks are caused in subsequent deformation processing, the strength and the plasticity of the steel plate are obviously reduced, and the content of O is controlled as much as possible; in order to ensure the plasticity and low-temperature toughness of the steel plate, the inclusion in the steel must be reduced, wherein the aluminum oxide inclusion harm is the largest, so the O content in the steel is less than or equal to 0.003 percent.
H: the existence of hydrogen element can generate white spots, so the content of H is controlled to be less than or equal to 0.0002 percent.
CEV: the control of the carbon equivalent index is favorable for ensuring the strength and weldability of the steel plate, and the CEV of the invention is controlled to be less than or equal to 0.43 percent.
Pcm: the control of the cold crack sensitivity coefficient is favorable for ensuring the welding performance of the product, and Pcm of the invention is controlled to be less than or equal to 0.22 percent.
The second aspect of the invention provides a preparation method of the extra-thick 460 MPa-grade steel plate in service in the extremely cold region, which comprises the steps of molten steel converter smelting, LF + RH double refining, continuous casting, casting blank heating, rolling and cooling.
In the preparation method of the 460 MPa-grade steel plate with extra-thick service specification in the extremely cold region, as a preferred embodiment, in the smelting of the molten steel converter, molten iron, scrap steel and a nickel plate after KR treatment are added into the converter, the molten steel is subjected to primary smelting by adopting a double-slag process, the alkalinity of final slag is controlled to be R = 3.0-4.0 (such as 3.2, 3.5 and 3.8), early slag melting in the initial stage is realized, the slag melting in the process is good, and the final slag is completely melted; alloying manganese, ferroniobium, ferrovanadium, ferrochromium and ferrosilicon, wherein the alloying is added when 1/4 of the steel is placed, and the alloying is finished when 3/4 of the molten steel is discharged; adding aluminum-manganese-iron into steel according to the proportion of 3-3.5Kg/t (such as 3.1Kg/t, 3.3Kg/t and 3.4 Kg/t) for deoxidation; preferably, the S in the molten iron is less than or equal to 0.008 percent; preferably, the steel scrap/(molten iron + steel scrap) is less than or equal to 8wt%.
In the preparation method of the 460 MPa-grade steel plate with extra-thick service specification in the extremely cold region, as a preferred embodiment, in the LF + RH double refining, argon-blowing and stirring are performed in the whole LF refining process, aluminum particles and calcium carbide are adopted for deoxidation, a titanium wire is used for adjusting the Ti component, an aluminum wire is used for adjusting the Al component, and the final slag alkalinity is controlled to be more than 2.5; the RH refining adopts the treatment mode, the vacuum degree in the RH furnace is ensured to be less than or equal to 133Pa, the soft argon blowing time is 10-15min (such as 12min, 13min and 14 min), the pure degassing time is more than or equal to 5min, and after the RH refining is finished, calcium-aluminum wires are fed for 1-1.5m/t (such as 1.1m/t, 1.3m/t and 1.4 m/t); preferably, the LF refining time is 40-50min (such as 42min, 45min and 48 min), wherein the soft argon (argon) blowing time is more than or equal to 5min; preferably, the RH refining time is more than or equal to 50min, and the soft argon (Ar) blowing time is more than or equal to 12min.
In the preparation method of the 460 MPa-grade steel plate with the service extra-thick specification in the extremely cold region, as a preferred embodiment, in the continuous casting, the whole-process protective casting is adopted, peritectic steel casting powder is used, the liquidus temperature is 1515-1525 ℃ (such as 1518 ℃, 1520 ℃ and 1522 ℃), the superheat degree is less than 20 ℃, and a continuous casting billet with the thickness of 300mm is cast; the pulling speed is 0.90-1.10m/min (such as 0.95m/min, 0.95m/min and 1.0 m/min), and the casting blank is put into a pit and stacked for slow cooling for more than or equal to 72 hours at the solidification tail end of the casting blank at the sector section by adopting a soft reduction mode.
In the preparation method of the 460MPa grade steel plate with the extra-thick service specification in the extremely cold region, as a preferred embodiment, a multi-stage heating mode is adopted in the casting blank heating, the temperature of the first heating stage is 1050-1170 ℃ (such as 1080 ℃, 1100 ℃ and 1150 ℃), the temperature of the second heating stage is 1150-1280 ℃ (such as 1180 ℃, 1200 ℃ and 1250 ℃), the temperature of the soaking stage is 1170-1250 ℃ (such as 1180 ℃, 1200 ℃, 1220 ℃ and 1240 ℃) is not less than 40min, the tapping temperature is 1190-1230 ℃ (such as 1200 ℃, 1210 ℃ and 1220 ℃), and the total heating time is 270-300min (such as 275min, 280min and 290 min); preferably, after the casting blank is heated, high-pressure water dephosphorization treatment is carried out.
The purpose of limiting the heating temperature and the heating time by adopting a multi-stage heating temperature rise mode in the invention is as follows: on one hand, the uniform burning of the casting blank is ensured, and the excessive growth of austenite grains is prevented.
In the preparation method of the 460 MPa-grade steel plate with the extra-thick service specification in the extremely cold region, as a preferred embodiment, in the rolling, the rolling is rough rolling and finish rolling; preferably, the rough rolling is recrystallization rolling, the rough rolling pass is less than or equal to 5 passes, and the pass reduction (single-pass thickness reduction/inlet thickness) of at least 2 passes is more than or equal to 15 percent; preferably, in the rough rolling, for a steel plate with a finished product of 80-90mm (such as 82mm, 85mm, 88 mm) specification, the thickness of the intermediate blank/the finished product after rough rolling is =1.8; for the steel plate with the finished product of 90-100mm (such as 92mm, 95mm and 98 mm), the thickness of the intermediate blank/the thickness of the finished product after rough rolling is =1.5; preferably, the finish rolling is unrecrystallized rolling, the start rolling temperature of the finish rolling is 840-870 ℃ (such as 845 ℃), 850 ℃, 860 ℃ and 865 ℃), and the pass of the finish rolling is less than or equal to 9 passes; more preferably, the finish rolling pass is 7 passes; more preferably, in the finish rolling, the finish rolling start temperature is 850 to 870 ℃ (e.g., 855 ℃, 860 ℃, 865 ℃) for a steel sheet of 80 to 90mm gauge as a finished product, and 840 to 860 ℃ (e.g., 845 ℃, 850 ℃, 855 ℃) for a steel sheet of 90 to 100mm gauge as a finished product.
The thickness of the intermediate blank refers to the thickness of a casting blank after rough rolling is finished; according to the invention, rough rolling is limited to recrystallization rolling, the number of rough rolling passes is less than or equal to 5, and the reduction rate of at least 2 passes is more than or equal to 15%, so that austenite grains are fully refined through a large reduction rate, and a microstructure guarantee is provided for improving the toughness of a thick steel plate. The finish rolling is limited to unrecrystallized rolling, the pass of the finish rolling is less than or equal to 9 passes, so that the deformation accumulation effect among the passes and a forced phase change mechanism induced by defects in deformed austenite crystals are fully utilized, a large number of deformation zones, twin crystals and dislocations are promoted to appear in the austenite crystals, conditions are created for ferrite phase deformation nuclei, and the toughness of the steel plate is improved. The thickness of the intermediate blank obtained after rough rolling is controlled to reasonably distribute the reduction of rough rolling and finish rolling and improve the performance of the steel plate, particularly the uniformity of the core impact toughness and the thickness directional performance.
In the preparation method of the 460MPa grade steel plate with the extra-thick service specification in the extremely cold region, as a preferred embodiment, the cooling is to cool a rolled piece obtained after rolling, in the cooling, the cooling control is firstly carried out, slow cooling or stacking slow cooling is carried out in a slow cooling pit immediately after the cooling control is finished, and the slow cooling time is more than or equal to 48 hours; preferably, in the controlled cooling, the open cooling temperature is 810-830 ℃ (such as 815 ℃, 820 ℃ and 825 ℃), and the final cooling temperature is 585-615 ℃ (such as 590 ℃, 595 ℃, 600 ℃, 605 ℃ and 610 ℃); more preferably, the controlled cooling rate is 3-6 deg.C/s (e.g., 3.2 deg.C/s, 3.5 deg.C/s, 4 deg.C/s, 4.5 deg.C/s, 5 deg.C/s, 5.5 deg.C/s, 5.8 deg.C/s).
The cooling speed is controlled to be 3-6 ℃/s. If the start cooling temperature is lower than 810 ℃ or the cooling speed is lower than 3 ℃/s, a large amount of austenite is converted into ferrite and pearlite before or in the cooling process, and the high strength requirement of the product is difficult to ensure; if the start cooling temperature is higher than 830 ℃ or the cooling speed is higher than 6 ℃/s, more bainite and martensite structures can be formed in the cooling process, and the impact toughness of the product is influenced.
After the rolling is finished, the strength and toughness of the steel plate can be effectively improved by reasonably controlling the cooling process (controlled cooling); and after the controlled cooling is finished, moving the steel plate into a slow cooling pit or stacking for slow cooling, wherein the slow cooling time is more than or equal to 48h, so that the phase change process is fully performed, and the tissue uniformity of the thick steel plate is improved.
Compared with the prior art, the invention has the advantages that:
(1) The comprehensive performance is excellent: the invention adopts Nb, V and Ti microalloying technology, adds Cr and Ni alloy elements, combines reasonable rolling and cooling control process, combines plastic deformation and cooling after rolling with solid phase change, fully exerts the effects of solid solution strengthening, precipitation strengthening and fine grain strengthening, and obtains the steel plate with excellent comprehensive properties of high strength, low temperature resistance, easy welding and the like. The yield strength of the product is more than or equal to 460MPa, the tensile strength is 540-675 MPa, the transverse impact energy at minus 40 ℃ is more than or equal to 200J, the CTOD characteristic value at minus 40 ℃ is more than or equal to 0.5mm, and the technical support is provided for developing steel plate products which can be widely applied to ocean engineering in extremely cold regions.
(2) The toughness in the thickness direction is uniform: the invention provides a high-quality casting blank raw material by controlling the components, the purity and the gas content in the steelmaking process; the process of heating, rolling and controlled cooling after rolling is scientifically designed, and deformation is caused to permeate into the center of the steel plate by means of measures such as large reduction in a rough rolling stage, reasonable two-stage reduction distribution and the like, so that a high-toughness tissue is obtained in the whole thickness section, and the safety of a product in a polar service environment is guaranteed.
(3) Breaks through the limit of the super-thick specification steel plate on the compression ratio, and provides a process method for producing the high-homogeneity super-thick specification steel plate under the condition of low compression ratio (for example, the rolling compression ratio of the 100mm thick steel plate is only 3 in the invention).
Drawings
FIG. 1 is a metallographic structure of a near-surface portion of a 90mm thick steel plate obtained in example 2 of the present invention.
FIG. 2 is an SEM image of the near-surface position of a 90mm thick steel plate obtained in example 2 of the present invention.
FIG. 3 shows the metallographic structure of a steel plate having a thickness of 1/4 of that of a 90mm thick steel plate obtained in example 2 of the present invention.
FIG. 4 is an SEM image of the position of 1/4 of the thickness of a 90mm thick steel plate obtained in example 2 of the present invention.
FIG. 5 shows a metallographic structure of a steel plate of 90mm thickness at the position corresponding to 1/2 of the thickness thereof, obtained in example 2 of the present invention.
FIG. 6 is an SEM image of the position of 1/2 of the thickness of a 90mm thick steel plate obtained in example 2 of the present invention
Detailed Description
The invention is described below with reference to the accompanying drawings and examples, and the invention relates to a 460MPa grade extra-thick steel plate in service in extremely cold regions and a preparation method thereof. It should be understood that these examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. It should be understood that various changes and modifications can be made by one skilled in the art after reading the disclosure of the present invention, and equivalents fall within the scope of the invention as defined by the appended claims.
The test methods in the following examples are all conventional methods unless otherwise specified, and can be performed according to techniques or conditions described in literature in the art or according to product specifications. The starting materials described in the following examples are all commercially available from the public.
The specific embodiment of the invention provides a preparation method of a super-thick specification 460MPa steel plate in service in an extremely cold region, which comprises the steps of molten steel converter smelting, LF + RH double refining, continuous casting, casting blank heating, rolling and cooling, and specifically comprises the following steps:
(1) Smelting in a molten steel converter
Adding molten iron (S in the molten iron is less than or equal to 0.008%) subjected to KR treatment, scrap steel (scrap steel/(molten iron + scrap steel)) is less than or equal to 8wt%, and a nickel plate into a converter, carrying out primary smelting on the molten steel by adopting a double-slag process, and controlling the final slag alkalinity to be R = 3.0-4.0, so as to realize early slagging in the initial stage, good slagging in the process and thorough slagging in the final stage; alloying manganese, ferroniobium, ferrovanadium, ferrochromium and ferrosilicon, wherein the alloy is added when 1/4 of the steel is discharged, and the addition is finished when 3/4 of the molten steel is discharged; adding aluminum ferromanganese into the steel according to the proportion of 3-3.5kg/t for deoxidation.
(2) LF + RH double refining
And (3) blowing argon at the bottom and stirring in the whole LF refining process, deoxidizing by adopting aluminum particles and calcium carbide, adjusting Ti components by using a titanium wire, adjusting Al components by using an aluminum wire, controlling the alkalinity of final slag to be more than 2.5, and performing LF refining for 40-50min, wherein the soft argon blowing time is more than or equal to 5min.
The RH refining adopts the treatment mode, the vacuum degree in the RH furnace is ensured to be within 133Pa, the soft argon blowing time is 10-15min, and the pure degassing time is more than or equal to 5min; after the RH treatment is finished, feeding calcium aluminum wires for 1-1.5m/t, preferably, the soft argon blowing time is more than or equal to 12min, and the RH refining time is more than or equal to 50min.
(3) Continuous casting
The whole-process protective casting is adopted, peritectic steel covering slag is used, the liquidus temperature is 1515-1525 ℃, the superheat degree is less than 20 ℃, a continuous casting billet with the thickness of 300mm is obtained, the drawing speed is 0.90-1.10m/min, the light reduction technology is adopted at the solidification tail end of a casting billet in a sector section, the casting billet enters a pit, and the stacking and slow cooling are more than or equal to 72 hours.
(4) Heating of casting blanks
The casting blank cold charging method comprises the steps of cold charging and charging a casting blank, wherein a multi-stage heating mode is adopted, the temperature of a first heating section is 1050-1170 ℃, the temperature of a second heating section is 1150-1280 ℃, the temperature of a soaking section is 1170-1250 ℃, soaking time is not less than 40min, tapping temperature is 1190-1230 ℃, and the total heating time is 270-300min, so that a hot casting blank is obtained; and then carrying out high-pressure water dephosphorization treatment on the hot casting blank.
(5) Rolling of
Rolling the hot cast blank subjected to the high-pressure water dephosphorization treatment, wherein the rolling process comprises two stages of rough rolling and finish rolling; the rough rolling is recrystallization rolling, the rough rolling pass is less than or equal to 5 passes, and the pass reduction (single-pass thickness reduction/inlet thickness) of at least 2 passes is ensured to be more than or equal to 15 percent; the finish rolling is non-recrystallization rolling, the start rolling temperature of the finish rolling is 840-870 ℃, and the pass of the finish rolling is less than or equal to 9.
(6) After the cooling rolling is finished, controlling the cooling, wherein the starting cooling temperature is 810-830 ℃, the final cooling temperature is 585-615 ℃, and the cooling speed is 3-6 ℃/s; after the controlled cooling is finished, moving the steel plate into a slow cooling pit or stacking and slow cooling, wherein the slow cooling time is more than or equal to 48h; the specific process parameters of rolling and controlled cooling are shown in the table 1.
Table 1 shows the specific process parameters of rolling and cooling control
The present invention will be described in further detail with reference to specific examples.
Example 1: a preparation method of a 460 MPa-grade steel plate with extra-thick service specification in an extremely cold region comprises the following steps:
according to the chemical components shown in the table 2, (1) molten steel converter smelting and (2) LF + RH double refining are carried out to obtain high-cleanness molten steel, and (3) continuous casting is carried out to obtain a continuous casting billet with the thickness of 300 mm. (Steps 1/2/3 are as described above)
(4) Heating a casting blank: adopting a multi-stage heating mode, wherein the temperature of the first heating section is 1050-1170 ℃, the temperature of the second heating section is 1150-1280 ℃, the temperature of the soaking section is 1210-1240 ℃, the soaking time is 50min, the tapping temperature is 1230 ℃, and the total heating time is 300min;
(5) Rolling: 5 passes of rough rolling (5 th pass), wherein the reduction rates of the 3 rd pass and the 4 th pass are respectively 19.3 percent and 23.7 percent, and the thickness of the intermediate blank is 145mm after the rough rolling is finished; the initial rolling temperature of the finish rolling is 870 ℃, and the steel plate with the thickness of 80mm is obtained after 7 times of finish rolling (7 th pass).
(6) And (3) cooling: and (3) carrying out controlled cooling on the steel plate at the speed of 6 ℃/s, wherein the opening cooling temperature is 825 ℃, the final cooling temperature is 610 ℃, and after the controlled cooling is finished, moving the steel plate into a slow cooling pit for slow cooling for more than 48 h.
Example 2: a preparation method of a 460 MPa-grade steel plate with a super-thick service specification in an extremely cold region comprises the following steps:
according to the chemical components shown in the table 2, (1) molten steel converter smelting and (2) LF + RH double refining are carried out to obtain high-cleanness molten steel, and (3) continuous casting is carried out to obtain a continuous casting billet with the thickness of 300 mm. (Steps 1/2/3 are as defined above)
(4) Heating a casting blank: and adopting a multi-stage heating mode, wherein the temperature of the first heating section is 1050-1170 ℃, the temperature of the second heating section is 1150-1280 ℃, the temperature of the soaking section is 1200-1230 ℃, the soaking time is 40min, the tapping temperature is 1210 ℃, and the total heating time is 270min.
(5) Rolling: the rolling reduction rates of the rough rolling of 5 passes are respectively 15.7 percent and 19.1 percent, and the thickness of the intermediate blank is 135mm after the rough rolling is finished; the initial rolling temperature of the finish rolling is 860 ℃, and the steel plate with the thickness of 90mm is obtained after 9 passes of finish rolling (the 9 th pass).
(6) And (3) cooling: and (3) carrying out controlled cooling on the steel plate at the speed of 6 ℃/s, wherein the starting cooling temperature is 819 ℃, the final cooling temperature is 605 ℃, and after the controlled cooling is finished, moving the steel plate into a slow cooling pit for slow cooling for more than 48 h.
The metallographic structure and SEM images of the steel sheet obtained in this example are shown in fig. 1 to 6, the near surface is a mixed structure of acicular ferrite and lower bainite, and the thickness 1/4 position and the center are a lower bainite structure of polygonal ferrite + a small amount of pearlite + dispersed distribution.
Example 3: a preparation method of a 460 MPa-grade steel plate with a super-thick service specification in an extremely cold region comprises the following steps:
according to the chemical components shown in the table 2, (1) molten steel converter smelting and (2) LF + RH double refining are carried out to obtain high-cleanness molten steel, and (3) continuous casting is carried out to obtain a continuous casting billet with the thickness of 300 mm. (Steps 1/2/3 are as defined above)
(4) Heating a casting blank: adopting a multi-stage heating mode, wherein the temperature of the first heating stage is 1050-1170 ℃, the temperature of the second heating stage is 1150-1280 ℃, the temperature of the soaking stage is 1170-1200 ℃, the soaking time is 45min, the tapping temperature is 1190 ℃, and the total heating time is 280min;
(5) Rolling: 5 passes of rough rolling (5 th pass), wherein the reduction rates of 3 rd pass and 4 th pass are respectively 16.5 percent and 20.2 percent, and the thickness of the intermediate blank is 150mm after the rough rolling is finished; and the initial rolling temperature of finish rolling is 850 ℃, and the steel plate with the thickness of 100mm is obtained after 7 times of finish rolling.
(6) And (3) cooling: and (3) carrying out controlled cooling on the steel plate at the speed of 5 ℃/s, wherein the start cooling temperature is 810 ℃, the end cooling temperature is 590 ℃, and after the controlled cooling is finished, moving the steel plate into a slow cooling pit for slow cooling for more than 48 h.
Comparative example 1
Comparative example 1 no controlled cooling was performed in (6) cooling, and after rolling was completed, the steel sheet was directly moved into a slow cooling pit for a period of more than 48 hours; the rest is the same as in example 1.
Comparative example 2
Comparative example 2 in (6) cooling: carrying out controlled cooling on the steel plate at the speed of 9 ℃/s, wherein the starting cooling temperature is 825 ℃, the final cooling temperature is 610 ℃, and after the controlled cooling is finished, moving the steel plate into a slow cooling pit for slow cooling for more than 48h; the rest is the same as in example 1.
Performance testing
The steel sheets obtained in examples 1 to 3 of the present invention and comparative examples 1 to 2 were subjected to performance tests, tensile tests were referred to, and the specific results are shown in tables 3 and 4.
Table 3 shows the tensile properties and impact properties of the steel sheets obtained in examples 1-3 and comparative examples 1-2, the yield strength of examples 1-3 is not less than 460MPa, the tensile strength is 540-675 MPa, and the elongation after fracture is not less than 17%; the transverse impact energy at minus 40 ℃ is more than or equal to 200J, and the uniformity of the performance in the thickness direction is good. In comparative example 1, controlled cooling was not performed after rolling, but direct slow cooling was performed, so that the structure was mainly ferrite + pearlite, the strength was low, and the impact toughness was good. In comparative example 2, the cooling speed after rolling is high, so that the structure contains more bainite and even martensite, and although the strength is high, the yield ratio is high, the impact toughness is extremely poor, and the use of the product is greatly restricted.
Table 4 shows the results of the CTOD tests performed on the steel sheets obtained in examples 1 to 3 in accordance with ISO 12135-2016: CTOD is more than or equal to 0.5mm at minus 40 ℃.
TABLE 2 chemical composition (wt%) of steel sheets in inventive examples 1-3 and comparative examples 1-2
TABLE 3 Properties of Steel sheets according to examples 1 to 3 of the present invention and comparative examples 1 to 2
TABLE 4 CTOD test of steel sheets according to examples 1 to 3 of the present invention
The above description is only exemplary of the invention and should not be taken as limiting the invention, as any modification, equivalent replacement, or improvement made within the spirit and principle of the invention is intended to be covered by the appended claims.
Claims (10)
1. A460 MPa-grade steel plate with super-thick service specification in an extremely cold region is characterized in that the steel plate comprises the following chemical components in percentage by mass: c: 0.08-0.10%, si: 0.20-0.40%, mn: 1.50-1.65%, P is less than or equal to 0.013%, S is less than or equal to 0.005%, nb: 0.030-0.040%, ti:0.010% -0.020%, V:0.030% -0.045%, cr:0.15% -0.25%, ni: 0.20-0.30%, al: 0.020-0.050%, the balance of Fe and inevitable impurity elements, wherein CEV is less than or equal to 0.43%, and Pcm is less than or equal to 0.22%.
2. The extremely cold region in-service extra thick specification 460 MPa-grade steel plate according to claim 1, wherein the unavoidable impurity elements include, by mass, H ≤ 0.0002%, O ≤ 0.003%, N ≤ 0.005%, and B ≤ 0.0005%.
3. The extremely cold region service extra-thick 460 MPa-grade steel plate according to claim 1 or 2, wherein the thickness of the steel plate is 80-100mm, the yield strength of the steel plate is not less than 460MPa, the tensile strength is 540-675 MPa, the transverse impact energy at-40 ℃ is not less than 200J, and the CTOD characteristic value at-40 ℃ is not less than 0.5mm.
4. The preparation method of the extra-thick-gauge 460 MPa-grade steel plate used in the extremely cold region according to any one of claims 1 to 3, characterized by comprising the steps of molten steel converter smelting, LF + RH double refining, continuous casting, billet heating, rolling and cooling.
5. The preparation method according to claim 4, wherein in the molten steel converter smelting, molten iron, scrap steel and nickel plates after KR treatment are added into a converter, a double-slag process is adopted for molten steel primary smelting, and the alkalinity of final slag is controlled to be R = 3.0-4.0, so that early slag formation in the initial stage is achieved, slag formation in the process is good, and the final slag is completely formed; alloying manganese, ferroniobium, ferrovanadium, ferrochromium and ferrosilicon, wherein the alloying is added when 1/4 of the steel is placed, and the alloying is finished when 3/4 of the molten steel is discharged; adding aluminum-manganese-iron for deoxidation according to 3-3.5Kg/t steel; preferably, the S in the molten iron is less than or equal to 0.008 percent; preferably, the steel scrap/(molten iron and steel scrap) is less than or equal to 8wt%.
6. The preparation method according to claim 4 or 5, characterized in that in the LF + RH double refining, argon is blown to the bottom and stirred in the whole LF refining process, aluminum particles and calcium carbide are used for deoxidation, a titanium wire is used for adjusting Ti component, an aluminum wire is used for adjusting Al component, and the alkalinity of final slag is controlled to be more than 2.5; the RH refining adopts the treatment mode, the vacuum degree in the RH furnace is ensured to be less than or equal to 133Pa, the soft argon blowing time is 10-15min, the pure degassing time is more than or equal to 5min, and after the RH refining is finished, calcium aluminum wires are fed for 1-1.5m/t; preferably, the LF refining time is 40-50min, wherein the soft argon blowing time is more than or equal to 5min; preferably, the RH refining time is more than or equal to 50min, and the soft argon blowing time is more than or equal to 12min.
7. The preparation method according to any one of claims 4 to 6, characterized in that in the continuous casting, the whole-process protective casting is adopted, peritectic steel casting powder is used, the liquidus temperature is 1515-1525 ℃, the superheat degree is less than 20 ℃, and a continuous casting billet with the thickness of 300mm is obtained by casting; the pulling speed is 0.90-1.10m/min, the casting blank enters a pit at the solidification tail end of the casting blank at the sector section by adopting a soft reduction mode, and the stacking and slow cooling are more than or equal to 72h.
8. The preparation method according to any one of claims 4 to 7, characterized in that in the casting blank heating, a multi-stage heating temperature rise mode is adopted, the temperature of the first heating section is 1050-1170 ℃, the temperature of the second heating section is 1150-1280 ℃, the temperature of the soaking section is 1170-1250 ℃, the soaking time is not less than 40min, the tapping temperature is 1190-1230 ℃, and the total time of heating temperature rise is 270-300min; preferably, after the casting blank is heated, high-pressure water dephosphorization treatment is carried out.
9. The production method according to any one of claims 4 to 8, wherein, in the rolling, the rolling is rough rolling and finish rolling; preferably, the rough rolling is recrystallization rolling, the number of rough rolling passes is less than or equal to 5, and the pass reduction rate of at least 2 passes is more than or equal to 15%; preferably, in the rough rolling, for a steel plate with a finished product of 80-90mm specification, the thickness of the intermediate blank/the thickness of the finished product after the rough rolling =1.8; for the steel plate with the finished product of 90-100mm specification, the thickness of the intermediate blank/the thickness of the finished product after rough rolling =1.5; preferably, the finish rolling is unrecrystallized rolling, the start rolling temperature of the finish rolling is 840-870 ℃, and the pass of the finish rolling is less than or equal to 9; more preferably, the finish rolling pass is 7 passes; more preferably, in the finish rolling, the finish rolling start temperature is 850 to 870 ℃ for a steel sheet of 80 to 90mm gauge as a finished product, and 840 to 860 ℃ for a steel sheet of 90 to 100mm gauge as a finished product.
10. The preparation method according to any one of claims 4 to 9, wherein the cooling is to cool the rolled piece obtained after rolling, in the cooling, controlled cooling is firstly carried out, slow cooling is carried out in a slow cooling pit or stacking slow cooling is carried out immediately after the controlled cooling is finished, and the slow cooling time is more than or equal to 48h; preferably, in the controlled cooling, the start cooling temperature is 810-830 ℃, and the end cooling temperature is 585-615 ℃; more preferably, the cooling rate for controlled cooling is 3-6 deg.C/s.
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