CN111455261B - Nitrogen-rich vanadium microalloyed large-specification 400MPa high-strength-toughness anti-seismic steel bar and preparation method thereof - Google Patents

Nitrogen-rich vanadium microalloyed large-specification 400MPa high-strength-toughness anti-seismic steel bar and preparation method thereof Download PDF

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CN111455261B
CN111455261B CN202010411857.8A CN202010411857A CN111455261B CN 111455261 B CN111455261 B CN 111455261B CN 202010411857 A CN202010411857 A CN 202010411857A CN 111455261 B CN111455261 B CN 111455261B
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nitrogen
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cooling
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陈伟
赵宇
李金柱
陈必胜
武天寿
邓家木
苏灿东
杨春雷
文玉兵
赵亮
刘红兵
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Wuhan Iron and Steel Group Kunming Iron and Steel Co Ltd
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C21D2211/00—Microstructure comprising significant phases
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Abstract

The invention discloses a nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength-toughness anti-seismic steel bar and a preparation method thereof, wherein the steel bar comprises the following chemical components in percentage by weight: 0.20-0.25 wt% of C, 0.55-0.70 wt% of Si, 1.42-1.58 wt% of Mn, 0.014-0.023 wt% of V, less than or equal to 0.045wt% of S, less than or equal to 0.045wt% of P, 0.0095-0.0125 wt% of N, and the balance of Fe and inevitable impurities; the preparation method comprises the working procedures of molten steel smelting, deoxidation alloying, molten steel argon station refining, molten steel casting, billet heating and billet controlled rolling and controlled cooling, and vanadium-containing pig iron is added into a steel ladle for steel-making tapping to replace expensive vanadium-nitrogen alloy, so that the content of V in the molten steel is increased, and the alloying cost is greatly reduced; a very small amount of silicon-nitrogen alloy and high-nitrogen vanadium alloy are added in the deoxidation alloying process, so that the nitrogen content in the molten steel is obviously increased on the basis that the steel contains a certain V content, and the full play of the V strengthening effect in the rolling process is promoted; the steel bar has the advantages of low cost, excellent and stable process mechanical property, fine and uniform microstructure, excellent anti-seismic property and the like.

Description

Nitrogen-rich vanadium microalloyed large-specification 400MPa high-strength-toughness anti-seismic steel bar and preparation method thereof
Technical Field
The invention belongs to the technical field of metallurgy, and particularly relates to a nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength and toughness anti-seismic steel bar with low production cost and strong process applicability and controllability and a preparation method thereof.
Background
Hot rolled ribbed bars are the primary reinforcing material for reinforced concrete building structures, carrying stress and strain loads in the structure, such as tensile, compressive and strain loads. At present, the annual output of hot-rolled ribbed steel bars in China is about 2 hundred million tons, and the hot-rolled ribbed steel bars are steel materials which are most used for the construction of national economic building engineering structures. With the continuous development of buildings in China towards high-rise, large-span and anti-seismic structures, the development of fine-grained anti-seismic steel bars with high toughness and excellent comprehensive performance is one of the important tasks of improving the technical level and adjusting the product structure in the steel industry.
After the GB/T1499.2-2018 standard is implemented, domestic hot-rolled ribbed steel bar production enterprises basically adopt a vanadium microalloying process to produce straight ribbed steel bars, and simultaneously, through optimizing chemical component control and a rolling process, the Vickers hardness of macroscopic metallographic phase, microstructure and section of the steel bars is ensured to meet the new standard inspection requirements.
At present, related research reports of HRB400E straight anti-seismic steel bar production technology after GB/T1499.2-2018 standard implementation are reported in China, a vanadium-nitrogen microalloying process is mainly adopted, the V content in large-specification HRB400E steel with the nominal diameter of 32mm or more is controlled to be 0.030-0.040 wt%, and the large-specification HRB400E steel bar with the nominal diameter of 32mm or more, the macroscopic metallographic phase, the section Vickers hardness and the microstructure of which meet the GB/T1499.2-2018 standard requirements, is obtained by controlling the rolling temperature and rolling passes.
Therefore, the development of a production process of the HRB400E straight anti-seismic steel bar with the nominal diameter of 32mm or more and the large specification with low production cost is necessary, and at present, the preparation method for producing the large-specification 400MPa high-strength and high-toughness anti-seismic steel bar by adopting the nitrogen-rich vanadium microalloying process is not reported.
Disclosure of Invention
The invention aims to provide a nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength and high-toughness anti-seismic reinforcing steel bar, and the invention aims to provide a preparation method of the nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength and high-toughness anti-seismic reinforcing steel bar.
The first purpose of the invention is realized in such a way that the nitrogen-rich vanadium microalloyed large-specification 400MPa high-strength and toughness anti-seismic steel bar has the following chemical components in percentage by weight: 0.20 to 0.25wt% of C, 0.55 to 0.70wt% of Si, 1.42 to 1.58wt% of Mn, 0.014 to 0.023wt% of V, less than or equal to 0.045wt% of S, less than or equal to 0.045wt% of P, 0.0095 to 0.0125wt% of N, and the balance of Fe and inevitable impurities.
The second purpose of the invention is realized in such a way that the preparation method of the nitrogen-rich vanadium microalloyed large-size 400MPa high-strength and toughness anti-seismic steel bar comprises the working procedures of molten steel smelting, deoxidation alloying, molten steel argon station refining, molten steel casting, billet heating and billet controlled rolling and controlled cooling, and specifically comprises the following steps:
a. smelting molten steel: scrap steel, pig iron and molten iron are mixed according to the ratio of 110-140 kg/tSteel、20kg/tSteel、920～950kg/tSteelThe mixture is added into an LD converter, then conventional top-bottom composite blowing is carried out, conventional lime, light-burned dolomite and magnesite balls are added for slagging, and the addition amount of the lime is 24-28 kg/tSteelThe addition amount of the light-burned dolomite is 17-22 kg/tSteelThe adding amount of the magnesite balls is 1.0-2.0 kg/tSteelControlling the end point carbon content to be more than or equal to 0.07wt% and the tapping temperature to be less than or equal to 1660 ℃; 6.0-7.0 kg/t of steel ladle before tappingSteelAdding the following vanadium-containing pig iron in mass ratio: 3.5wt% of C, 0.40wt% of Si, 0.65wt% of Mn, 1.00-1.20 wt% of V, 0.205wt% of P, 0.075wt% of S and the balance of Fe and inevitable impurities, adding vanadium-containing pig iron into a steel ladle, and baking for 3-5 minutes; adding vanadium-containing pig iron before tapping and baking the bottom of a steel ladle according to the proportion of 1.0kg/tSteelAdding the following slag washing desulfurizer in mass ratio for slag washing: al (Al)2O3 21.5wt%，SiO25.2wt%, 46.5wt% of CaO, 9.2wt% of Al, 6.5wt% of MgO6, and the balance of Fe and inevitable impurities, wherein a whole bottom nitrogen blowing process is adopted in the tapping process, and the nitrogen flow is controlled to be 15-20 NL/min; the chemical components of the scrap steel comprise 0.20-0.26 wt% of C, 0.40-0.65 wt% of Si, 1.25-1.60 wt% of Mn, 0.032-0.047 wt% of P, 0.028-0.045 wt% of S, and the balance of Fe and inevitable impurities; 3.2-3.5 wt% of pig iron chemical components C, 0.25-0.45 wt% of Si, 0.50-0.75 wt% of Mn, 0.075-0.095 wt% of P, 0.020-0.045 wt% of S, and the balance of Fe and inevitable impurities; the molten iron comprises 4.2-4.8 wt% of chemical components C, 0.15-0.40 wt% of Si, 0.95-1.25 wt% of Mn, 0.080-0.115 wt% of P, less than or equal to 0.040wt% of S and the balance of Fe and inevitable impurities, wherein the temperature of the molten iron is more than or equal to 1270 ℃;
b. and (3) deoxidation alloying: tapping the molten steel, and when the amount of the molten steel in the ladle is more than 1/4, carrying out the following deoxidation alloying sequence: silico-aluminum-calcium deoxidizer → silicon carbide → ferrosilicon → silicomanganese → high carbon ferromanganese → silicon-nitrogen alloy → high nitrogen vanadium alloy, the following substances are added into the steel ladle in sequence: at a rate of 1.0kg/tSteelAdding the following silicon-aluminum-calcium deoxidizer in mass ratio: 32.5wt% of Si, 16.8wt% of Ca, 10.6wt% of Al and the balance of Fe and inevitable impurities; at a rate of 1.8kg/tSteelIn the following mass ratioSilicon carbide: 82.5wt% of SiC, 26.5wt% of C, 0.053wt% of P, 0.035wt% of S and the balance of inevitable impurities; according to 5.5-7.2 kg/tSteelAdding the following ferrosilicon in percentage by mass: 73.5wt% of Si, and the balance of Fe and inevitable impurities; according to the weight of 11.4-14.1 kg/tSteelAdding the following silicon-manganese alloy in mass ratio: 65.2wt% of Mn, 17.3wt% of Si, 1.8wt% of C, and the balance of Fe and inevitable impurities; at 7.5kg/tSteelAdding the following high-carbon ferromanganese in mass ratio: 75.3wt% of Mn, 7.1wt% of C, and the balance of Fe and inevitable impurities; at a rate of 0.10kg/tSteelAdding the following silicon-nitrogen alloy in mass ratio: 46.5wt% of Si, 35.6wt% of N, 1.35wt% of C, 0.020wt% of P, 0.018wt% of S and the balance of Fe and inevitable impurities; at a rate of 0.08kg/tSteelAdding the following high-nitrogen vanadium alloy in mass ratio: v77.6 wt%, N19.5 wt%, C1.25 wt%, P0.075 wt%, S0.045 wt%, and the balance Fe and inevitable impurities; when the amount of the molten steel in the steel ladle reaches 4/5, the alloy is added; after tapping, hoisting the molten steel to an argon station for refining treatment;
c. refining in a molten steel argon station: hoisting the molten steel to an argon station, connecting a nitrogen band, starting nitrogen, blowing nitrogen at the flow rate of 20-25 NL/min for 4 minutes, and adding a molten steel covering agent, wherein the adding amount is controlled to be 1.0kg/tSteelThen, hoisting the molten steel to a casting station;
d. casting molten steel: the temperature of the tundish is 1525-1545 ℃, the drawing speed is 2.8-3.0 m/min, and the flow of cooling water of the crystallizer is 140-150 m3H, adopting an R9m straight-arc continuous straightening 5-flow small square billet casting machine to cast the molten steel in the step c into a billet with the cross section of 165mm multiplied by 165mm under the condition that the secondary cooling specific water amount is 1.9-2.1L/kg;
e. heating a steel billet: d, conveying the steel billets obtained in the step d into a heating furnace with the furnace temperature of 1050-1100 ℃ in a soaking section, heating for 60 minutes, and pushing the steel billets to a full-continuous bar mill for rolling after steel is tapped;
f. controlling rolling and cooling of steel billets: carrying out rough rolling on the billet obtained in the step e for 6 passes under the rolling condition that the speed is 0.4-0.5 m/s; then carrying out medium rolling for 4 passes under the rolling condition with the speed of 2.5-3.0 m/s(ii) a Then the steel plate enters a pre-water cooling device before finish rolling to carry out controlled cooling before finish rolling, wherein the cooling water amount is 50-60 m3The finish rolling temperature of the steel bar after pre-water cooling is controlled to be 950-1000 ℃; finally, finish rolling for 2-3 passes under the rolling condition with the speed of 8.0-9.0 m/s; performing controlled cooling on the rolled steel through 3 short pipe water cooling section devices (each length is 2.0 meters, and the interval between every two water cooling sections is 0.4 meter), starting 2 water pumps, wherein the pressure of each water pump is 1.5-1.8 MPa; and naturally cooling the steel bars to room temperature in a cooling bed after controlled cooling to obtain the 400MPa high-strength and high-toughness anti-seismic steel bars with the nominal diameter of 32-40mm, wherein the temperature control, rolling pass and controlled cooling parameters of the steel are specifically determined according to different specification requirements.
The invention has the beneficial effects that:
1. in the method, a certain amount of vanadium-containing pig iron is added into a steel ladle during steel making and tapping to replace expensive vanadium-nitrogen alloy, so that the content of V in molten steel is increased, and the alloying cost is greatly reduced; a very small amount of silicon-nitrogen alloy and high-nitrogen vanadium alloy are added in the deoxidation alloying process, so that the nitrogen content in molten steel is obviously increased on the basis that the steel contains a certain V content, and the full play of the V strengthening effect in the rolling process is promoted; the steel rolling adopts a lower initial rolling temperature, the lower initial rolling temperature is controlled by pre-water cooling before finish rolling and the multi-section weak controlled cooling process after rolling is carried out, original austenite grains are refined, the nucleation position and the nucleation rate of ferrite grains during the transformation from austenite to ferrite are increased, the ferrite grains are obviously refined, the grain size of the ferrite at the center of the cross section of the steel bar reaches more than 11.5 grades, the fine grain strengthening effect is obvious, and the plastic toughness of the steel is improved; a small amount of vanadium is added into the steel, and nitrogen is added through molten steel, so that the transfer of V from a solid solution state to a carbonitride precipitated phase is promoted, a large amount of finely dispersed V (C, N) and VN precipitated phases are formed and precipitated, the stability of austenite is increased, the phase transition temperature is reduced, and the strengthening effect of the steel is obviously improved; the content of C, Mn in the steel is controlled to be higher, the pearlite content is improved, the structure strengthening effect is improved, and the strength of the steel is obviously improved; by increasing the pearlite content, the tensile strength of the steel is obviously improved, and the seismic performance is improved;
2. the method fully exerts various strengthening effects such as precipitation strengthening, fine grain strengthening, structure strengthening and the like by integrating and innovating chemical component design, converter smelting, deoxidation alloying, continuous casting, steel rolling heating system, rolling temperature and controlled cooling process, and the produced steel bar has the advantages of excellent and stable process mechanical property, fine and uniform microstructure, good plastic toughness, excellent anti-seismic property and the like;
3. the process has the characteristics of low production cost, strong process applicability and controllability and the like, various indexes of the produced steel bar are comprehensively superior to GB/T1499.2-2018, and the production cost is reduced by 75 yuan/T compared with the conventional vanadium microalloying processSteelBy the method, the production cost of the HRB400E steel bar is greatly reduced after GB/T1499.2-2018 is implemented, the market competitiveness of the product is improved, and the method has remarkable economic and social benefits.
Detailed Description
The present invention is further illustrated by the following examples, which are not intended to be limiting in any way, and any modifications or alterations based on the teachings of the present invention are intended to fall within the scope of the present invention.
The nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength-toughness anti-seismic steel bar disclosed by the invention comprises the following chemical components in percentage by weight: 0.20 to 0.25wt% of C, 0.55 to 0.70wt% of Si, 1.42 to 1.58wt% of Mn, 0.014 to 0.023wt% of V, less than or equal to 0.045wt% of S, less than or equal to 0.045wt% of P, 0.0095 to 0.0125wt% of N, and the balance of Fe and inevitable impurities.
The invention relates to a preparation method of a nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength and toughness anti-seismic steel bar, which comprises the working procedures of molten steel smelting, deoxidation alloying, molten steel argon station refining, molten steel casting, billet heating and billet controlled rolling and controlled cooling, and specifically comprises the following steps:
a. smelting molten steel: scrap steel, pig iron and molten iron are mixed according to the ratio of 110-140 kg/tSteel、20kg/tSteel、920～950kg/tSteelThe mixture is added into an LD converter, then conventional top-bottom composite blowing is carried out, conventional lime, light-burned dolomite and magnesite balls are added for slagging, and the addition amount of the lime is 24-28 kg/tSteelThe addition amount of the light-burned dolomite is 17-22 kg/tSteelThe adding amount of the magnesite balls is 1.0-2.0 kg/tSteelControlling the end point carbon content to be more than or equal to 0.07wt% and the tapping temperature to be less than or equal to 1660 ℃; 6.0 to E of steel ladle before tapping7.0kg/tSteelAdding the following vanadium-containing pig iron in mass ratio: 3.5wt% of C, 0.40wt% of Si, 0.65wt% of Mn, 1.00-1.20 wt% of V, 0.205wt% of P, 0.075wt% of S and the balance of Fe and inevitable impurities, adding vanadium-containing pig iron into a steel ladle, and baking for 3-5 minutes; adding vanadium-containing pig iron before tapping and baking the bottom of a steel ladle according to the proportion of 1.0kg/tSteelAdding the following slag washing desulfurizer in mass ratio for slag washing: al (Al)2O3 21.5wt%，SiO25.2wt%, 46.5wt% of CaO, 9.2wt% of Al, 6.5wt% of MgO6, and the balance of Fe and inevitable impurities, wherein a whole bottom nitrogen blowing process is adopted in the tapping process, and the nitrogen flow is controlled to be 15-20 NL/min; the chemical components of the scrap steel comprise 0.20-0.26 wt% of C, 0.40-0.65 wt% of Si, 1.25-1.60 wt% of Mn, 0.032-0.047 wt% of P, 0.028-0.045 wt% of S, and the balance of Fe and inevitable impurities; 3.2-3.5 wt% of pig iron chemical components C, 0.25-0.45 wt% of Si, 0.50-0.75 wt% of Mn, 0.075-0.095 wt% of P, 0.020-0.045 wt% of S, and the balance of Fe and inevitable impurities; the molten iron comprises 4.2-4.8 wt% of chemical components C, 0.15-0.40 wt% of Si, 0.95-1.25 wt% of Mn, 0.080-0.115 wt% of P, less than or equal to 0.040wt% of S and the balance of Fe and inevitable impurities, wherein the temperature of the molten iron is more than or equal to 1270 ℃;
b. and (3) deoxidation alloying: tapping the molten steel in the step a, and when the amount of the molten steel in the ladle is more than 1/4, carrying out the following deoxidation alloying order: silico-aluminum-calcium deoxidizer → silicon carbide → ferrosilicon → silicomanganese → high carbon ferromanganese → silicon-nitrogen alloy → high nitrogen vanadium alloy, the following substances are added into the steel ladle in sequence: at a rate of 1.0kg/tSteelAdding the following silicon-aluminum-calcium deoxidizer in mass ratio: 32.5wt% of Si, 16.8wt% of Ca, 10.6wt% of Al and the balance of Fe and inevitable impurities; at a rate of 1.8kg/tSteelAdding the following silicon carbide in mass ratio: 82.5wt% of SiC, 26.5wt% of C, 0.053wt% of P, 0.035wt% of S and the balance of inevitable impurities; according to 5.5-7.2 kg/tSteelAdding the following ferrosilicon in percentage by mass: 73.5wt% of Si, and the balance of Fe and inevitable impurities; according to the weight of 11.4-14.1 kg/tSteelAdding the following silicon-manganese alloy in mass ratio: 65.2wt% of Mn, 17.3wt% of Si, 1.8wt% of C, and the balance of Fe and inevitable impurities; at 7.5kg/tSteelAdding the following high-carbon ferromanganese in mass ratio: 75.3wt% of Mn, 7.1wt% of C, and the balance of Fe and inevitable impurities; at a rate of 0.10kg/tSteelAdding the following silicon-nitrogen alloy in mass ratio: 46.5wt% of Si, 35.6wt% of N, 1.35wt% of C, 0.020wt% of P, 0.018wt% of S and the balance of Fe and inevitable impurities; at a rate of 0.08kg/tSteelAdding the following high-nitrogen vanadium alloy in mass ratio: v77.6 wt%, N19.5 wt%, C1.25 wt%, P0.075 wt%, S0.045 wt%, and the balance Fe and inevitable impurities; when the amount of the molten steel in the steel ladle reaches 4/5, the alloy is added; after tapping, hoisting the molten steel to an argon station for refining treatment;
c. refining in a molten steel argon station: hoisting the molten steel to an argon station, connecting a nitrogen band, starting nitrogen, blowing nitrogen at the flow rate of 20-25 NL/min for 4 minutes, and adding a molten steel covering agent, wherein the adding amount is controlled to be 1.0kg/tSteelThen, hoisting the molten steel to a casting station;
d. casting molten steel: the temperature of the tundish is 1525-1545 ℃, the drawing speed is 2.8-3.0 m/min, and the flow of cooling water of the crystallizer is 140-150 m3H, adopting an R9m straight-arc continuous straightening 5-flow small square billet casting machine to cast the molten steel in the step c into a billet with the cross section of 165mm multiplied by 165mm under the condition that the secondary cooling specific water amount is 1.9-2.1L/kg;
e. heating a steel billet: d, conveying the steel billets obtained in the step d into a heating furnace with the furnace temperature of 1050-1100 ℃ in a soaking section, heating for 60 minutes, and pushing the steel billets to a full-continuous bar mill for rolling after steel is tapped;
f. controlling rolling and cooling of steel billets: carrying out rough rolling on the billet obtained in the step e for 6 passes under the rolling condition that the speed is 0.4-0.5 m/s; then, carrying out medium rolling for 4 passes under the rolling condition with the speed of 2.5-3.0 m/s; then the steel plate enters a pre-water cooling device before finish rolling to carry out controlled cooling before finish rolling, wherein the cooling water amount is 50-60 m3The finish rolling temperature of the steel bar after pre-water cooling is controlled to be 950-1000 ℃; finally, finish rolling for 2-3 passes under the rolling condition with the speed of 8.0-9.0 m/s; controlling the cooling of the rolled steel by 3 short pipe water cooling section devices with the length of 2.0 meters and the water cooling section interval of 0.4 meter, wherein 2 water pumps are started, and the pressure of each water pump is 1.5-1.8 MPa; after controlled cooling, the steel bar is arrangedAnd naturally cooling the cooling bed to room temperature in air to obtain the target product.
And d, controlling the straightening temperature of the casting blank out of the withdrawal and straightening machine to be more than or equal to 960 ℃.
In the step d, the secondary cooling specific water amount refers to: the ratio of the total water consumption in unit time of the secondary cooling area of the continuous casting machine to the mass of the casting blank passing through the secondary cooling area in unit time is an index of the secondary cooling water spray intensity of continuous casting by taking L/kg as a unit.
In the step e, the steel tapping temperature of the steel billet is 990-1020 ℃;
and in the step f, controlling the temperature of the steel bars on the cooling bed to be 910-930 ℃ after cooling control.
The technological properties, the microstructure and the Vickers hardness difference of the nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength-toughness anti-seismic reinforcing steel bar are shown in tables 1 and 2.
TABLE 1 mechanics performance of large 400MPa high strength and toughness aseismic reinforcing bar technology
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TABLE 2 metallographic structure and Vickers hardness of large 400MPa high-strength and toughness aseismic reinforcing steel bar
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Example 1
a. Smelting molten steel: according to 110kg/t respectivelySteel、20kg/tSteelThe cold charge charging ratio of (1) is that scrap steel (chemical components: C0.20 wt%, Si 0.40wt%, Mn 1.25wt%, P0.032 wt%, S0.028 wt%, and the balance Fe and inevitable impurities) and pig iron (chemical components: C3.2wt%, Si 0.25wt%, Mn 0.50wt%, P0.075 wt%, S0.020 wt%, and the balance Fe and inevitable impurities) are added into an LD converter in the following mass ratio; then according to 950kg/tSteelThe molten iron charging proportion is that molten iron with the following temperature and mass ratio is added into an LD converter: the temperature of molten iron is 1270 ℃, the components of the molten iron are 4.2wt percent of C, 0.15wt percent of Si, 0.95wt percent of Mn, 0.080 wt percent of P and 0.020wt percent of S, and the balance of Fe and inevitable impuritiesPure substance; after waste steel, pig iron and molten iron are added into an LD converter, conventional top-bottom combined blowing is carried out, conventional lime, light-burned dolomite and magnesite balls are added for slagging, and the addition amount of the lime is 24kg/tSteelThe addition amount of light-burned dolomite is 17kg/tSteelThe adding amount of the magnesite balls is 1.0kg/tSteelControlling the end point carbon content to be 0.07wt% and the tapping temperature to be 1645 ℃; 6.0kg/t of steel ladle before tappingSteelAdding the following vanadium-containing pig iron in mass ratio: 3.5wt% of C, 0.40wt% of Si, 0.65wt% of Mn, 1.00wt% of V, 0.205wt% of P, 0.075wt% of S and the balance of Fe and inevitable impurities, adding vanadium-containing pig iron into a steel ladle, and baking for 3 minutes; adding vanadium-containing pig iron before tapping and baking the bottom of a steel ladle according to the proportion of 1.0kg/tSteelAdding the following slag washing desulfurizer in mass ratio for slag washing: al (Al)2O3 21.5wt%，SiO25.2wt%, CaO 46.5wt%, Al 9.2wt%, MgO6.5wt%, and the balance of Fe and inevitable impurities, wherein a whole bottom nitrogen blowing process is adopted in the tapping process, and the nitrogen flow is controlled to be 15 NL/min.
b. And (3) deoxidation alloying: tapping the molten steel smelted in the step a, and when the amount of the molten steel in the ladle is more than 1/4, carrying out the following deoxidation alloying sequence: silico-aluminum-calcium deoxidizer → silicon carbide → ferrosilicon → silicomanganese → high carbon ferromanganese → silicon-nitrogen alloy → high nitrogen vanadium alloy, the following substances are added into the steel ladle in sequence: at a rate of 1.0kg/tSteelAdding the following silicon-aluminum-calcium deoxidizer in mass ratio: 32.5wt% of Si, 16.8wt% of Ca, 10.6wt% of Al and the balance of Fe and inevitable impurities; at a rate of 1.8kg/tSteelAdding the following silicon carbide in mass ratio: 82.5wt% of SiC, 26.5wt% of C, 0.053wt% of P, 0.035wt% of S and the balance of inevitable impurities; at 5.5kg/tSteelAdding the following ferrosilicon in percentage by mass: 73.5wt% of Si, and the balance of Fe and inevitable impurities; at 11.4kg/tSteelAdding the following silicon-manganese alloy in mass ratio: 65.2wt% of Mn, 17.3wt% of Si, 1.8wt% of C, and the balance of Fe and inevitable impurities; at 7.5kg/tSteelAdding the following high-carbon ferromanganese in mass ratio: 75.3wt% of Mn, 7.1wt% of C, and the balance of Fe and inevitable impurities; at a rate of 0.10kg/tSteelIn the following mass ratio of silicon nitrideGold: 46.5wt% of Si, 35.6wt% of N, 1.35wt% of C, 0.020wt% of P, 0.018wt% of S and the balance of Fe and inevitable impurities; at a rate of 0.08kg/tSteelAdding the following high-nitrogen vanadium alloy in mass ratio: v77.6 wt%, N19.5 wt%, C1.25 wt%, P0.075 wt%, S0.045 wt%, and the balance Fe and inevitable impurities; when the amount of the molten steel in the steel ladle reaches 4/5, the alloy is added; and after tapping, hoisting the molten steel to an argon station for refining treatment.
c. Refining in a molten steel argon station: hoisting the molten steel to an argon station, connecting a nitrogen band, starting nitrogen, blowing nitrogen at the flow rate of 20NL/min for 4 minutes, adding a molten steel covering agent, and controlling the adding amount to be 1.0kg/tSteelAnd then hoisting the molten steel to a casting station.
d. Casting molten steel: the temperature of the tundish is 1545 ℃, the pulling speed is 2.8m/min, and the flow of cooling water of the crystallizer is 150m3H, adopting an R9m straight-arc continuous straightening 5-machine 5-flow small square billet casting machine to cast the molten steel in the step c into a billet with the section of 165mm multiplied by 165mm under the condition that the secondary cooling specific water amount is 2.1L/kg; the straightening temperature of the casting blank discharged from the withdrawal and straightening machine is controlled at 960 ℃.
e. Heating a steel billet: and d, feeding the steel billets obtained in the step d into a heating furnace with the furnace temperature of the soaking section of 1100 ℃, heating for 60 minutes, wherein the steel tapping temperature of the steel billets is 1020 ℃, and then pushing the steel billets to a full-continuous bar mill for rolling.
f. Controlling rolling and cooling of steel billets: rough rolling the billet steel obtained in the step e for 6 passes under the rolling condition of the speed of 0.5 m/s; then, rolling for 4 passes under the rolling condition with the speed of 3.0 m/s; then the steel plate enters a pre-water cooling device before finish rolling to carry out controlled cooling before finish rolling, wherein the cooling water amount is 50m3The finish rolling temperature of the steel bar after pre-water cooling is controlled to be 1000 ℃; finally, finish rolling is carried out for 3 passes under the rolling condition with the speed of 9.0 m/s; performing controlled cooling on the finish-rolled steel through 3 short pipe water cooling section devices (each length is 2.0 meters, and the interval between each water cooling section is 0.4 meter), starting 2 water pumps, wherein the pressure of each water pump is 1.5 MPa; controlling the temperature of the steel bars on a cooling bed to be 910 ℃ after controlled cooling, and then naturally cooling the steel bars in the cooling bed to room temperature to obtain the large-specification 400MPa high-strength and high-toughness anti-seismic steel bars with the nominal diameter of 32mm and the following chemical components in percentage by weight:0.20wt% of C, 0.55wt% of Si, 1.42wt% of Mn, 0.014wt% of V, 0.028wt% of S, 0.026wt% of P, 0.0095wt% of N, and the balance of Fe and inevitable impurities.
The mechanical properties, the microstructure and the Vickers hardness difference of the high-strength high-toughness anti-seismic steel bar with the nominal diameter of 32mm and 400MPa of the nitrogen-rich vanadium microalloying steel bar in the embodiment 1 are shown in tables 3 and 4.
TABLE 3 mechanical Properties of high-toughness aseismic reinforcing steel bar with nominal diameter of 32mm and 400MPa in example 1
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TABLE 4 metallographic structure and Vickers hardness of high-toughness aseismic reinforcing steel bar of nominal diameter 32mm 400MPa in example 1
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Example 2
a. Smelting molten steel: at 130kg/t respectivelySteel、20kg/tSteelThe cold charge charging ratio of (1) is that scrap steel (chemical components: C0.22 wt%, Si 0.52wt%, Mn 1.42wt%, P0.039 wt%, S0.036 wt%, and the balance Fe and unavoidable impurities) and pig iron (chemical components: C3.4wt%, Si 0.35wt%, Mn 0.62wt%, P0.085 wt%, S0.032 wt%, and the balance Fe and unavoidable impurities) are added into an LD converter in the following mass ratio; then 935kg/tSteelThe molten iron charging proportion is that molten iron with the following temperature and mass ratio is added into an LD converter: the temperature of molten iron is 1280 ℃, the components of the molten iron comprise 4.6wt% of C, 0.29wt% of Si, 1.10wt% of Mn, 0.095wt% of P, 0.035wt% of S and the balance of Fe and inevitable impurities; after waste steel, pig iron and molten iron are added into an LD converter, conventional top-bottom combined blowing is carried out, conventional lime, light-burned dolomite and magnesite balls are added for slagging, and the addition amount of the lime is 26kg/tSteelThe addition amount of light-burned dolomite is 20kg/tSteelThe adding amount of the magnesite balls is 1.0kg/tSteelControlling the end point carbon content to be 0.08wt% and the tapping temperature to be 1655 ℃; 6.5kg/t of ladle before tappingSteelAdding the following vanadium-containing pig iron in mass ratio: 3.5wt% of C, 0.40wt% of Si, 0.65wt% of Mn, 1.10wt% of V, 0.205wt% of P, 0.075wt% of S and the balance of Fe and inevitable impurities, adding vanadium-containing pig iron into a steel ladle, and baking for 4 minutes; adding vanadium-containing pig iron before tapping and baking the bottom of a steel ladle according to the proportion of 1.0kg/tSteelAdding the following slag washing desulfurizer in mass ratio for slag washing: al (Al)2O3 21.5wt%，SiO25.2wt%, CaO 46.5wt%, Al 9.2wt%, MgO6.5wt%, and the balance Fe and inevitable impurities, wherein a whole bottom nitrogen blowing process is adopted in the tapping process, and the nitrogen flow is controlled to be 20 NL/min.
b. And (3) deoxidation alloying: tapping the molten steel smelted in the step a, and when the amount of the molten steel in the ladle is more than 1/4, carrying out the following deoxidation alloying sequence: silico-aluminum-calcium deoxidizer → silicon carbide → ferrosilicon → silicomanganese → high carbon ferromanganese → silicon-nitrogen alloy → high nitrogen vanadium alloy, the following substances are added into the steel ladle in sequence: at a rate of 1.0kg/tSteelAdding the following silicon-aluminum-calcium deoxidizer in mass ratio: 32.5wt% of Si, 16.8wt% of Ca, 10.6wt% of Al and the balance of Fe and inevitable impurities; at a rate of 1.8kg/tSteelAdding the following silicon carbide in mass ratio: 82.5wt% of SiC, 26.5wt% of C, 0.053wt% of P, 0.035wt% of S and the balance of inevitable impurities; at 6.4kg/tSteelAdding the following ferrosilicon in percentage by mass: 73.5wt% of Si, and the balance of Fe and inevitable impurities; at 12.7kg/tSteelAdding the following silicon-manganese alloy in mass ratio: 65.2wt% of Mn, 17.3wt% of Si, 1.8wt% of C, and the balance of Fe and inevitable impurities; at 7.5kg/tSteelAdding the following high-carbon ferromanganese in mass ratio: 75.3wt% of Mn, 7.1wt% of C, and the balance of Fe and inevitable impurities; at a rate of 0.10kg/tSteelAdding the following silicon-nitrogen alloy in mass ratio: 46.5wt% of Si, 35.6wt% of N, 1.35wt% of C, 0.020wt% of P, 0.018wt% of S and the balance of Fe and inevitable impurities; at a rate of 0.08kg/tSteelAdding the following high-nitrogen vanadium alloy in mass ratio: v77.6 wt%, N19.5 wt%, C1.25 wt%, P0.075 wt%, S0.045 wt%, and the balance Fe and inevitable impurities; when the amount of the molten steel in the steel ladle reaches 4/5, the alloy is added; and after tapping, hoisting the molten steel to an argon station for refining treatment.
c. Refining in a molten steel argon station: hoisting the molten steel to an argon station, connecting a nitrogen band, starting nitrogen, blowing nitrogen at the flow rate of 25NL/min for 4 minutes, adding a molten steel covering agent, and controlling the adding amount to be 1.0kg/tSteelAnd then hoisting the molten steel to a casting station.
d. Casting molten steel: the temperature of the tundish is 1535 ℃, the pulling speed is 2.9m/min, and the flow of cooling water of the crystallizer is 145m3H, adopting an R9m straight-arc continuous straightening 5-machine 5-flow small square billet casting machine to cast the molten steel in the step c into a billet with the section of 165mm multiplied by 165mm under the condition that the secondary cooling specific water amount is 2.0L/kg; the straightening temperature of the casting blank discharged from the withdrawal and straightening machine is controlled to be 980 ℃.
e. Heating a steel billet: and d, feeding the steel billet obtained in the step d into a heating furnace with the furnace temperature of a soaking section of 1070 ℃, heating for 60 minutes, wherein the steel tapping temperature of the steel billet is 1000 ℃, and then pushing the steel billet to a full-continuous bar mill for rolling.
f. Controlling rolling and cooling of steel billets: rough rolling the billet steel obtained in the step e for 6 passes under the rolling condition of the speed of 0.5 m/s; then, rolling for 4 passes under the rolling condition with the speed of 3.0 m/s; then the steel plate enters a pre-water cooling device before finish rolling to carry out controlled cooling before finish rolling, wherein the cooling water amount is 60m3The finish rolling temperature of the steel bar after pre-water cooling is controlled to be 980 ℃; finally, finish rolling is carried out for 2 passes under the rolling condition with the speed of 8.0 m/s; performing controlled cooling on the finish-rolled steel through 3 short pipe water cooling section devices (each length is 2.0 meters, and the interval between each water cooling section is 0.4 meter), starting 2 water pumps, wherein the pressure of each water pump is 1.6 MPa; controlling the temperature of the steel bars on a cooling bed to be 920 ℃ after controlled cooling, and then naturally cooling the steel bars in the cooling bed to room temperature to obtain the large-size 400MPa high-strength and high-toughness anti-seismic steel bars with the nominal diameter of 36mm and the following chemical components in percentage by weight: 0.22wt% of C, 0.63wt% of Si, 1.50wt% of Mn, 0.018wt% of V, 0.034wt% of S, 0.038wt% of P, 0.0110wt% of N, and the balance of Fe and inevitable impurities.
The process mechanical property, microstructure and Vickers hardness difference of the nitrogen-rich vanadium microalloyed high-strength high-toughness anti-seismic steel bar with the nominal diameter of 36mm and 400MPa in the embodiment 2 are shown in tables 5 and 6.
TABLE 5 mechanical Properties of high-toughness aseismic reinforcing steel bar of example 2 with nominal diameter of 36mm and 400MPa
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TABLE 6 metallographic structure and Vickers hardness of high-toughness aseismic reinforcing steel bar of example 2 with nominal diameter of 36mm and 400MPa
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Example 3
a. Smelting molten steel: according to 140kg/t respectivelySteel、20kg/tSteelThe charge ratio of the cold charge is that scrap steel (chemical components: C0.26 wt%, Si 0.65wt%, Mn 1.60wt%, P0.047 wt%, S0.045 wt%, and the balance Fe and unavoidable impurities) and pig iron (chemical components: C3.5wt%, Si 0.45wt%, Mn 0.75wt%, P0.095 wt%, S0.045 wt%, and the balance Fe and unavoidable impurities) are added into an LD converter according to the following mass ratio; then according to 920kg/tSteelThe molten iron charging proportion is that molten iron with the following temperature and mass ratio is added into an LD converter: the temperature of molten iron is 1300 ℃, the components of the molten iron comprise 4.8wt% of C, 0.40wt% of Si, 1.25wt% of Mn, 0.115wt% of P, 0.040wt% of S and the balance of Fe and inevitable impurities; after waste steel, pig iron and molten iron are added into an LD converter, conventional top-bottom combined blowing is carried out, conventional lime, light-burned dolomite and magnesite balls are added for slagging, and the addition amount of the lime is 28kg/tSteelThe addition amount of the light-burned dolomite is 22kg/tSteelThe adding amount of the magnesite balls is 2.0kg/tSteelControlling the final carbon content to be 0.09wt% and the tapping temperature to be 1660 ℃; the steel ladle before tapping is 7.0kg/tSteelAdding the following vanadium-containing pig iron in mass ratio: 3.5wt% of C, 0.40wt% of Si, 0.65wt% of Mn, 1.20wt% of V, 0.205wt% of P, 0.075wt% of S and the balance of Fe and inevitable impurities, adding vanadium-containing pig iron into a steel ladle, and baking for 3-5 minutes; adding vanadium-containing pig iron before tapping and baking the bottom of a steel ladle according to the proportion of 1.0kg/tSteelAdding the following slag washing desulfurizer in mass ratio for slag washing: al (Al)2O321.5wt%，SiO25.2wt%, CaO 46.5wt%, Al 9.2wt%, MgO6.5wt%, and the balanceThe steel tapping process adopts a whole bottom blowing nitrogen process for Fe and inevitable impurities, and the nitrogen flow is controlled to be 20 NL/min.
b. And (3) deoxidation alloying: tapping the molten steel smelted in the step a, and when the amount of the molten steel in the ladle is more than 1/4, carrying out the following deoxidation alloying sequence: silico-aluminum-calcium deoxidizer → silicon carbide → ferrosilicon → silicomanganese → high carbon ferromanganese → silicon-nitrogen alloy → high nitrogen vanadium alloy, the following substances are added into the steel ladle in sequence: at a rate of 1.0kg/tSteelAdding the following silicon-aluminum-calcium deoxidizer in mass ratio: 32.5wt% of Si, 16.8wt% of Ca, 10.6wt% of Al and the balance of Fe and inevitable impurities; at a rate of 1.8kg/tSteelAdding the following silicon carbide in mass ratio: 82.5wt% of SiC, 26.5wt% of C, 0.053wt% of P, 0.035wt% of S and the balance of inevitable impurities; at 7.2kg/tSteelAdding the following ferrosilicon in percentage by mass: 73.5wt% of Si, and the balance of Fe and inevitable impurities; at 14.1kg/tSteelAdding the following silicon-manganese alloy in mass ratio: 65.2wt% of Mn, 17.3wt% of Si, 1.8wt% of C, and the balance of Fe and inevitable impurities; at 7.5kg/tSteelAdding the following high-carbon ferromanganese in mass ratio: 75.3wt% of Mn, 7.1wt% of C, and the balance of Fe and inevitable impurities; at a rate of 0.10kg/tSteelAdding the following silicon-nitrogen alloy in mass ratio: 46.5wt% of Si, 35.6wt% of N, 1.35wt% of C, 0.020wt% of P, 0.018wt% of S and the balance of Fe and inevitable impurities; at a rate of 0.08kg/tSteelAdding the following high-nitrogen vanadium alloy in mass ratio: v77.6 wt%, N19.5 wt%, C1.25 wt%, P0.075 wt%, S0.045 wt%, and the balance Fe and inevitable impurities; when the amount of the molten steel in the steel ladle reaches 4/5, the alloy is added; and after tapping, hoisting the molten steel to an argon station for refining treatment.
C. Refining in a molten steel argon station: hoisting the molten steel to an argon station, connecting a nitrogen band, starting nitrogen, blowing nitrogen at the flow rate of 25NL/min for 4 minutes, adding a molten steel covering agent, and controlling the adding amount to be 1.0kg/tSteelAnd then hoisting the molten steel to a casting station.
d. Casting molten steel: cooling the crystallizer at 1525 deg.C and 3.0m/minThe water flow is 140m3H, adopting an R9m straight-arc continuous straightening 5-machine 5-flow small square billet casting machine to cast the molten steel in the step c into a billet with the section of 165mm multiplied by 165mm under the condition that the secondary cooling specific water amount is 1.9L/kg; the straightening temperature of the casting blank discharged from the withdrawal and straightening machine is controlled to be 1000 ℃.
e. Heating a steel billet: and d, feeding the steel billet obtained in the step d into a heating furnace with the furnace temperature of 1050 ℃ in a soaking section, heating for 60 minutes, wherein the steel tapping temperature of the steel billet is 990 ℃, and then pushing the steel billet to a full-continuous bar mill for rolling.
f. Controlling rolling and cooling of steel billets: rough rolling the billet steel obtained in the step e for 6 passes under the rolling condition of the speed of 0.4 m/s; then rolling for 4 passes under the rolling condition with the speed of 2.5 m/s; then the steel plate enters a pre-water cooling device before finish rolling to carry out controlled cooling before finish rolling, wherein the cooling water amount is 60m3The finish rolling temperature of the steel bar after pre-water cooling is controlled to be 950 ℃; finally, finish rolling is carried out for 2 passes under the rolling condition with the speed of 8.0 m/s; performing controlled cooling on the finish-rolled steel through 3 short pipe water cooling section devices (each length is 2.0 meters, and the interval between each water cooling section is 0.4 meter), starting 2 water pumps, wherein the pressure of each water pump is 1.8 MPa; controlling the temperature of the steel bar on a cooling bed to be 930 ℃ after controlled cooling, and then naturally cooling the steel bar in the cooling bed to room temperature to obtain the large-size 400MPa high-strength and high-toughness anti-seismic steel bar with the nominal diameter of 40mm and the following chemical components in percentage by weight: 0.25wt% of C, 0.70wt% of Si, 1.58wt% of Mn, 0.023wt% of V, 0.045wt% of S, 0.045wt% of P, 0.0125wt% of N, and the balance of Fe and inevitable impurities.
The mechanical properties, the microstructure and the Vickers hardness difference of the nitrogen-rich vanadium microalloyed high-strength high-toughness anti-seismic steel bar with the nominal diameter of 40mm and 400MPa in the embodiment 3 are shown in tables 7 and 8.
TABLE 7 mechanics performance of high strength and toughness aseismic reinforcing steel bar with nominal diameter of 40mm and 400MPa of example 3
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TABLE 8 metallographic structure and Vickers hardness of high-toughness aseismic reinforcing steel bar of example 3 having nominal diameter of 40mm and 400MPa
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Claims (5)

1. A preparation method of a nitrogen-vanadium-enriched microalloyed large-specification 400MPa high-strength-toughness anti-seismic steel bar comprises the following chemical components in percentage by weight: 0.20-0.25 wt% of C, 0.55-0.70 wt% of Si, 1.42-1.58 wt% of Mn, 0.014-0.023 wt% of V, less than or equal to 0.045wt% of S, less than or equal to 0.045wt% of P, 0.0095-0.0125 wt% of N, and the balance of Fe and inevitable impurities; the preparation method comprises the working procedures of molten steel smelting, deoxidation alloying, molten steel argon station refining, molten steel casting, billet heating and billet rolling and cooling control, and is characterized by comprising the following steps:
a. smelting molten steel: scrap steel, pig iron and molten iron are mixed according to the ratio of 110-140 kg/tSteel、20kg/tSteel、920~950kg/tSteelThe mixture is added into an LD converter, then conventional top-bottom composite blowing is carried out, conventional lime, light-burned dolomite and magnesite balls are added for slagging, and the addition amount of the lime is 24-28 kg/tSteelThe addition amount of the light-burned dolomite is 17-22 kg/tSteelThe adding amount of the magnesite balls is 1.0-2.0 kg/tSteelControlling the end point carbon content to be more than or equal to 0.07wt% and the tapping temperature to be less than or equal to 1660 ℃; 6.0-7.0 kg/t of steel ladle before tappingSteelAdding the following vanadium-containing pig iron in mass ratio: 3.5wt% of C, 0.40wt% of Si, 0.65wt% of Mn, 1.00-1.20 wt% of V, 0.205wt% of P, 0.075wt% of S and the balance of Fe and inevitable impurities, adding vanadium-containing pig iron into a steel ladle, and baking for 3-5 minutes; adding vanadium-containing pig iron before tapping and baking the bottom of a steel ladle according to the proportion of 1.0kg/tSteelAdding the following slag washing desulfurizer in mass ratio for slag washing: al (Al)2O3 21.5wt%，SiO2 5.2wt%, CaO 46.5wt%, Al 9.2wt%, MgO6.5wt%, and the balance of Fe and inevitable impurities, wherein a whole bottom nitrogen blowing process is adopted in the tapping process, and the nitrogen flow is controlled to be 15-20 NL/min; the chemical components of the scrap steel comprise 0.20-0.26 wt% of C, 0.40-0.65 wt% of Si, 1.25-1.60 wt% of Mn, 0.032-0.047 wt% of P, 0.028-0.045 wt% of S, and the balance of Fe and inevitable impurities; 3.2-3.5 wt% of pig iron chemical components C, 0.25-0.45 wt% of Si, 0.50-0.75 wt% of Mn, 0.075-0.095 wt% of P, 0.020-0.045 wt% of S and the balance ofFe and inevitable impurities; the molten iron comprises 4.2-4.8 wt% of chemical components C, 0.15-0.40 wt% of Si, 0.95-1.25 wt% of Mn, 0.080-0.115 wt% of P, less than or equal to 0.040wt% of S and the balance of Fe and inevitable impurities, wherein the temperature of the molten iron is more than or equal to 1270 ℃;
b. and (3) deoxidation alloying: tapping the molten steel in the step a, and when the amount of the molten steel in the ladle is more than 1/4, carrying out the following deoxidation alloying order: silico-aluminum-calcium deoxidizer → silicon carbide → ferrosilicon → silicomanganese → high carbon ferromanganese → silicon-nitrogen alloy → high nitrogen vanadium alloy, the following substances are added into the steel ladle in sequence: at a rate of 1.0kg/tSteelAdding the following silicon-aluminum-calcium deoxidizer in mass ratio: 32.5wt% of Si, 16.8wt% of Ca, 10.6wt% of Al and the balance of Fe and inevitable impurities; at a rate of 1.8kg/tSteelAdding the following silicon carbide in mass ratio: 82.5wt% of SiC, 26.5wt% of C, 0.053wt% of P, 0.035wt% of S and the balance of inevitable impurities; according to 5.5-7.2 kg/tSteelAdding the following ferrosilicon in percentage by mass: 73.5wt% of Si, and the balance of Fe and inevitable impurities; according to the weight of 11.4-14.1 kg/tSteelAdding the following silicon-manganese alloy in mass ratio: 65.2wt% of Mn, 17.3wt% of Si, 1.8wt% of C, and the balance of Fe and inevitable impurities; at 7.5kg/tSteelAdding the following high-carbon ferromanganese in mass ratio: 75.3wt% of Mn, 7.1wt% of C, and the balance of Fe and inevitable impurities; at a rate of 0.10kg/tSteelAdding the following silicon-nitrogen alloy in mass ratio: 46.5wt% of Si, 35.6wt% of N, 1.35wt% of C, 0.020wt% of P, 0.018wt% of S and the balance of Fe and inevitable impurities; at a rate of 0.08kg/tSteelAdding the following high-nitrogen vanadium alloy in mass ratio: v77.6 wt%, N19.5 wt%, C1.25 wt%, P0.075 wt%, S0.045 wt%, and the balance Fe and inevitable impurities; when the amount of the molten steel in the steel ladle reaches 4/5, the alloy is added; after tapping, hoisting the molten steel to an argon station for refining treatment;
c. refining in a molten steel argon station: hoisting the molten steel to an argon station, connecting a nitrogen band, starting nitrogen, blowing nitrogen at the flow rate of 20-25 NL/min for 4 minutes, and adding a molten steel covering agent, wherein the adding amount is controlled to be 1.0kg/tSteelThen, hoisting the molten steel to a casting station;
d. casting molten steel: the temperature of the tundish is 1525-1545 ℃, the drawing speed is 2.8-3.0 m/min, and the flow of cooling water of the crystallizer is 140-150 m3H, adopting an R9m straight-arc continuous straightening 5-flow small square billet casting machine to cast the molten steel in the step c into a billet with the cross section of 165mm multiplied by 165mm under the condition that the secondary cooling specific water amount is 1.9-2.1L/kg;
e. heating a steel billet: d, conveying the steel billets obtained in the step d into a heating furnace with the furnace temperature of 1050-1100 ℃ in a soaking section, heating for 60 minutes, and pushing the steel billets to a full-continuous bar mill for rolling after steel is tapped;
f. controlling rolling and cooling of steel billets: carrying out rough rolling on the billet obtained in the step e for 6 passes under the rolling condition that the speed is 0.4-0.5 m/s; then, carrying out medium rolling for 4 passes under the rolling condition with the speed of 2.5-3.0 m/s; then the steel plate enters a pre-water cooling device before finish rolling to carry out controlled cooling before finish rolling, wherein the cooling water amount is 50-60 m3The finish rolling temperature of the steel bar after pre-water cooling is controlled to be 950-1000 ℃; finally, finish rolling for 2-3 passes under the rolling condition with the speed of 8.0-9.0 m/s; controlling the cooling of the rolled steel by 3 short pipe water cooling section devices with the length of 2.0 meters and the water cooling section interval of 0.4 meter, wherein 2 water pumps are started, and the pressure of each water pump is 1.5-1.8 MPa; and naturally cooling the steel bars to room temperature in a cooling bed after cooling control, and obtaining the target object.
2. The preparation method according to claim 1, wherein the straightening temperature of the cast blank discharged from the withdrawal straightening machine in the step d is controlled to be not less than 960 ℃.
3. The preparation method according to claim 1, wherein the steel blank tapping temperature in the step e is 990-1020 ℃.
4. The preparation method of claim 1, wherein the temperature of the cooling bed on the steel bar after controlled cooling in the step f is controlled to be 910-930 ℃.
5. The nitrogen-vanadium-enriched microalloyed large-size 400MPa high-strength and toughness anti-seismic steel bar obtained by the preparation method according to any one of claims 1 to 4 comprises the following chemical components in percentage by weight: 0.20 to 0.25wt% of C, 0.55 to 0.70wt% of Si, 1.42 to 1.58wt% of Mn, 0.014 to 0.023wt% of V, less than or equal to 0.045wt% of S, less than or equal to 0.045wt% of P, 0.0095 to 0.0125wt% of N, and the balance of Fe and inevitable impurities.
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