CN114717377A - Continuous casting thick steel plate and production method thereof - Google Patents

Continuous casting thick steel plate and production method thereof Download PDF

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Publication number
CN114717377A
CN114717377A CN202210291053.8A CN202210291053A CN114717377A CN 114717377 A CN114717377 A CN 114717377A CN 202210291053 A CN202210291053 A CN 202210291053A CN 114717377 A CN114717377 A CN 114717377A
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less
steel plate
equal
thick steel
continuous casting
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CN114717377B (en
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麻晗
镇凡
王耀
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Institute Of Research Of Iron & Steel shagang jiangsu Province
Jiangsu Shagang Steel Co ltd
Jiangsu Shagang Group Co Ltd
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Jiangsu Shagang Group Co Ltd
Zhangjiagang Hongchang Steel Plate Co Ltd
Jiangsu Shagang Iron and Steel Research Institute Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/28—Manufacture of steel in the converter
    • C21C5/36—Processes yielding slags of special composition
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/114—Treating the molten metal by using agitating or vibrating means
    • B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/02—Dephosphorising or desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/064—Dephosphorising; Desulfurising
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/072—Treatment with gases
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Treatment Of Steel In Its Molten State (AREA)

Abstract

The invention discloses a continuous casting type thick steel plate and a production method thereof. The method adopts the technological processes of molten iron pre-desulfurization, converter smelting, LF refining, RH vacuum refining, continuous casting, casting blank heating, controlled rolling and cooling, wherein: smelting steel in a converter with primary slag according to a double-slag remaining method, wherein the temperature of a molten pool is 1350-1400 ℃ in a dephosphorization period, the basicity of the primary deslagging slag is 1.8-2.0, the basicity of the total iron is 12-15%, and the basicity of the secondary deslagging slag is 3.5-4.0, and the basicity of the total iron is 15-18%; performing controlled rolling and cooling according to the carbon equivalent; if the carbon equivalent is less than 0.65, rolling a steel plate with the thickness of 50-120 mm in two stages, and then carrying out MULPIC accelerated cooling; if the carbon equivalent is more than or equal to 0.65, rolling a steel plate with the thickness of 50-165 mm in a single stage, and then directly feeding the steel plate to a cooling bed for natural air cooling to room temperature. The invention improves the performance uniformity of the thick steel plate with high production efficiency and low cost.

Description

Continuous casting thick steel plate and production method thereof
Technical Field
The invention belongs to the technical field of steel smelting, and relates to a production method of a continuous casting type thick steel plate and a thick steel plate prepared by the production method.
Background
The thick steel plate is mainly applied to the fields of naval vessels, ships, maritime workers, containers, molds, energy sources, large buildings and the like, and is a key material for advanced manufacturing industry. In recent years, with the development of technology, the demand for thick steel plates has increased. Not only is a thick steel plate required to have high strength, high toughness, fatigue resistance, and good surface quality, but also good uniformity of properties in the thickness direction of the steel plate is required.
For a continuous casting steel plate, namely a steel plate formed by adopting a continuous casting billet, the thickness of the continuous casting billet is correspondingly required to be larger along with the increase of the thickness of the steel plate. However, in the production and preparation of the current continuous casting slab thick steel plate, the continuous casting slab has the defects of serious core segregation, looseness and the like due to the fact that the thickness of the continuous casting slab is too large; and, when the continuous casting slab is rolled into a steel plate, the core deformation infiltration effect is poor, and the core defect is difficult to eliminate. Furthermore, the performance uniformity of the existing continuous casting thick steel plate is poor, and the quality of the thick steel plate is greatly reduced.
The final performance uniformity of the steel plate can be improved only by adding the processes of electroslag remelting, forging and the like to the conventional continuous casting thick steel plate or by using a thin continuous casting blank with small thickness to perform plate blank welding compounding (i.e. a plurality of thin blanks are compounded and welded into a thick compound blank), and the problems of high production cost, low production efficiency, long flow path, high energy consumption and the like can be derived by the methods.
Disclosure of Invention
In order to solve the problem of poor performance uniformity of the conventional continuous casting type thick steel plate, the invention aims to provide a production method of a continuous casting type thick steel plate and a thick steel plate manufactured by the production method, which can improve the performance uniformity of the thick steel plate with high production efficiency, low energy consumption and short process.
To achieve the above objects, one embodiment provides a method for producing a continuously cast thick steel plate, including the steps of:
(1) carrying out steel making by adopting the processes of molten iron pre-desulfurization, converter smelting, LF refining and RH vacuum refining; in the smelting process of the converter, dephosphorization, primary deslagging, deep dephosphorization, secondary deslagging and tapping are sequentially carried out in the converter with primary slag, the temperature of a molten pool in the dephosphorization period is 1350-1400 ℃, the basicity of slag in the primary deslagging is 1.8-2.0, the total iron in the slag is 12-15%, the basicity of slag in the secondary deslagging is 3.5-4.0, the total iron in the slag is 15-18%, the tapping temperature is 1640-1660 ℃, and the P is less than or equal to 0.006%; in the LF refining process, alloy is added, strong argon blowing is carried out for no more than 5min at the flow rate of 600-800 NL/min, and the whole argon blowing is carried out at the flow rate of 200-400 NL/min for the rest of time; in the RH vacuum refining process, the vacuum degree is less than or equal to 2mbar, and the molten steel is kept stand for 15-18 min after tapping;
(2) continuously casting the steel discharged in the RH vacuum refining process into a continuous casting billet with the thickness of 320 mm; during the process, full-protection casting is adopted, the casting superheat degree is 25-30 ℃, secondary cooling zone electromagnetic stirring is carried out at the frequency of 4-5 Hz and the current of 500-600A, and dynamic soft reduction is adopted for continuous casting, and the reduction is 5-8% of the thickness of a continuous casting blank;
(3) carrying out four-stage heating on the continuous casting billet according to the heat recovery section of less than or equal to 900 ℃, the first heating section of 1000-1100 ℃, the second heating section of 1100-1170 ℃ and the soaking section of 1190-1230 ℃;
(4) calculating the carbon equivalent according to the chemical components of the continuous casting billet and the following formula, and performing controlled rolling and cooling on the continuous casting billet according to the calculation result;
carbon equivalent of C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15
If the obtained carbon equivalent is less than 0.65, firstly carrying out recrystallization zone rolling in a way that initial rolling is 1020-1060 ℃, final rolling is 990-1010 ℃, the first pass secondary reduction is more than or equal to 45mm, the last pass secondary reduction is more than or equal to 30mm and the reduction of each pass is reduced progressively, and then carrying out non-recrystallization zone rolling in a way that initial rolling is 830-880 ℃, final rolling is 780-810 ℃, the last pass secondary reduction is less than or equal to 10mm, the rest passes reduction is more than or equal to 25mm and the reduction of each pass is reduced progressively to prepare a steel plate of 50-120 mm; carrying out MULPIC accelerated cooling on the obtained steel plate, wherein the start cooling temperature is more than or equal to 750 ℃, the water pressure is 1.8-2.2 MPa, and the final cooling temperature is 280-380 ℃, and then air cooling to room temperature;
if the obtained carbon equivalent is more than or equal to 0.65, carrying out recrystallization zone rolling in a way that the initial rolling is 1020-1060 ℃, the final rolling is 960-990 ℃, the first pass rolling reduction is more than or equal to 45mm, the last pass rolling reduction is more than or equal to 30mm, and the rolling reduction of each pass is gradually reduced to prepare a steel plate with the thickness of 50-165 mm; the obtained steel plate is directly put on a cooling bed for natural air cooling to room temperature.
Preferably, the respective grades of the A, B, C, D four types of inclusions of the continuous casting billet obtained in the step 2 are less than or equal to 1.0 grade, the sum of the grades is less than or equal to 3.0 grade, and the length-width product of the maximum inclusions is less than or equal to 900 mu m2The density of the inclusions with the equivalent diameter of more than 10 mu m is less than or equal to 8/cm2。
Preferably, the manganese segregation ratio of the cross section of the continuous casting billet obtained in the step 2 is less than or equal to 1.08.
Preferably, the center porosity of the continuous casting billet obtained in the step 2 is less than or equal to 0.5 grade.
Preferably, in the smelting process of the converter, the initial slag amount is more than or equal to 70 kg/ton molten steel, and the slag amount remained in the converter after tapping is 50-60% of the total slag amount of secondary deslagging.
Preferably, in the steel tapping of the RH vacuum refining process, the mass percentage of P is less than or equal to 0.010 percent, S is less than or equal to 0.0035 percent, O is less than or equal to 0.0020 percent, N is less than or equal to 0.0030 percent, H is less than or equal to 0.0001 percent, As is less than or equal to 0.01 percent, and Sn is less than or equal to 0.01 percent.
Preferably, in the molten iron pre-desulfurization process, the arrival temperature of molten iron is more than or equal to 1380 ℃, S is less than or equal to 0.035%, the slag removal rate of the molten iron is more than or equal to 95%, and S is less than or equal to 0.002%.
Preferably, in the converter smelting process, the molten iron after pre-desulfurization and the scrap steel with P less than 0.02%, S less than 0.03%, Sn less than or equal to 0.01% and thickness more than or equal to 3mm are put into a converter for smelting.
Preferably, in the LF refining process, the alloy is added for the first time, strong argon blowing is carried out for no more than 5min at the flow rate of 600-800 NL/min, and the alloy is supplemented, and the strong argon blowing is carried out for no more than 3min at the flow rate of 600-800 NL/min.
Preferably, in the RH vacuum refining process, the degassing time is 20-25 min, and the net circulation treatment time is 8-10 min.
Preferably, in the step 2, during the continuous casting, the full-protection casting is carried out according to the modes of the argon blowing flow rate of 200-220L/min at the long nozzle, the argon blowing flow rate of 4-5L/min at the stopper rod and the argon blowing flow rate of 4-5L/min at the submerged nozzle, and the fluctuation of the liquid level of the crystallizer is less than or equal to 2 mm.
Preferably, in the step 3, if the alloy content of the continuous casting slab is more than or equal to 3.3%, stacking and slow cooling are carried out on the continuous casting slab obtained in the step 2 before four-stage heating, wherein the stacking temperature is more than or equal to 600 ℃, the unstacking temperature is 200-300 ℃, and blank cutting is carried out when the temperature of the continuous casting slab is more than or equal to 100 ℃ after unstacking.
Preferably, in the step 3, the residence time of the two heating sections is 60-90 min, and the residence time of the soaking section is 40-60 min.
Preferably, in the step 4, if the obtained carbon equivalent is less than 0.65, the ratio of water to water is 0.92-0.96, the distance between the side part shields is 100-300 mm, the coefficient of water volume after shielding is 0.90-0.95, the distance between the head part shields is 1200-2500 mm, the coefficient of water volume after shielding is 0.88-0.93, the distance between the tail part shields is 500-1800 mm, and the coefficient of water volume after shielding is 0.92-0.96.
Preferably, the production method further comprises the steps of:
(5) if the obtained carbon equivalent is less than 0.65, carrying out tempering heat treatment according to the tempering temperature of 300-500 ℃, the tempering heating coefficient of 2.2min/mm and the tempering heat preservation time of 20-40 min; if the obtained carbon equivalent is more than or equal to 0.65, tempering heat treatment is carried out according to the tempering temperature of 500-600 ℃, the tempering heating coefficient of 2.2min/mm and the tempering heat preservation time of 20-40 min.
In order to achieve the purpose, one embodiment provides a continuous casting type thick steel plate which is prepared by the production method, wherein the band-shaped structure of the thick steel plate is less than or equal to grade 1, and the strength difference of the whole plate is less than or equal to 50 Mpa.
Furthermore, the strength difference in the thickness direction of the thick steel plate is less than or equal to 35MPa, and the strength difference between the head and the tail is less than or equal to 40 MPa.
Further, the carbon equivalent of the thick steel plate is less than 0.65, and the impact energy A at the temperature of 60 ℃ below zero isKV2The single value is more than 80J, the average value is more than 250J, and the hardness difference in the thickness direction is less than or equal to 20 HV; or the carbon equivalent of the thick steel plate is more than or equal to 0.65, the Rockwell hardness is 30-35 HRC, and the difference between the surface hardness and the core hardness is less than or equal to 2 HRC.
Compared with the prior art, the beneficial effects of one embodiment include: on one hand, the improvement of the purity and the uniformity of the continuous casting billet is realized through the specific design of the operation and the parameters of each procedure in the steel making, the thick continuous casting billet with high purity, low inclusion and high uniformity which cannot be obtained in the prior art is obtained, and the defects of core segregation, core porosity and the like existing when the thickness of the existing continuous casting billet is larger are effectively eliminated; on the other hand, on the premise of the excellent continuous casting billet, the steel rolling technology is improved by combining the carbon equivalent, compared with the prior art, the effect of deformation permeation to the core of the billet is further improved, the defects of core segregation, porosity and the like are improved, and the banded structure can be reduced, so that the thick steel plate with high performance uniformity is finally obtained; in addition, the whole production process of the thick steel plate is simple, the technology of electroslag remelting, forging, quenching, normalizing and the like is not required to be additionally added in the prior art, the core surface uniformity of the steel plate can be greatly improved, the production cost is low, the production efficiency is high, the process is short, the energy consumption is low, the manufacturing of thick steel plate products with different carbon equivalent is realized by the casting technology of the same continuous casting billet, the technical applicability is improved, and the method has extremely high economic benefit and value for industrialization.
Detailed Description
The technical solutions of the present invention are further described below with reference to specific embodiments, but the scope of protection is not limited to the description.
An embodiment of the invention provides a production method of a continuous casting type thick steel plate and a thick steel plate prepared by the production method. The production method basically adopts the technological processes of molten iron pre-desulfurization, converter smelting, LF refining, RH vacuum refining, continuous casting, casting blank heating, controlled rolling and cooling, and is specifically introduced as follows.
(1) Molten iron pre-desulfurization-converter smelting-LF refining-RH vacuum refining-continuous casting steel-making process
In the molten iron pre-desulfurization process, KR pre-desulfurization is carried out on the molten iron.
In the smelting process of the converter, molten iron (namely molten iron obtained after pre-desulfurization) discharged by KR is poured into the converter with primary slag, a certain proportion of waste steel is merged, then dephosphorization, primary deslagging, deep dephosphorization, secondary deslagging and tapping are sequentially carried out, the temperature of a molten pool during dephosphorization is 1350-1400 ℃, the basicity of molten slag during primary deslagging is 1.8-2.0, 12-15% of total iron in slag, the basicity of molten slag during secondary deslagging is 3.5-4.0, 15-18% of total iron in slag, the tapping temperature is 1640-1660 ℃, and P is less than or equal to 0.006%.
In the LF refining process, converter tapping is transferred into an LF refining furnace for refining, and at least one alloying operation (for example, after the first alloying, whether alloy is supplemented or not is determined as required) is carried out in the whole refining process so as to adjust the chemical composition of molten steel to meet the preset chemical composition. And (2) performing strong argon blowing at a flow rate of 600-800 NL/min for not more than 5min while starting alloy addition (such as primary alloying and alloy supplement) every time (such as performing strong argon blowing at a flow rate of 600-800 NL/min for not more than 5min while adding the alloy for the first time, performing strong argon blowing at a flow rate of 600-800 NL/min for not more than 3min while adding the alloy for the supplement), and performing whole argon blowing at a flow rate of 200-400 NL/min for the rest of time. Therefore, slagging can be promoted, the temperature uniformity of components can be accelerated, and floating removal of inclusions is facilitated.
In the RH vacuum refining process, the steel tapping of the LF furnace is lifted to the RH vacuum furnace for refining. During vacuum refining, the vacuum degree of the RH vacuum furnace is less than or equal to 2mbar, and molten steel in a ladle after tapping is kept stand for 15-18 min on a rotary table. Therefore, the method can realize rapid denitrification and dehydrogenation under low vacuum degree, ensure the content of nitrogen and hydrogen at a lower level, simultaneously stand before casting to strengthen the floating of inclusions, and improve the purity of molten steel.
In the continuous casting process, after the steel discharged in the RH vacuum refining process is stood on a rotary table, a continuous casting billet with the thickness of 320mm is manufactured by adopting a continuous casting machine. And in the period, full-protection casting is adopted, the casting superheat degree is 25-30 ℃, secondary cooling zone electromagnetic stirring is carried out at the frequency of 4-5 Hz and the current of 500-600A, and dynamic soft reduction is adopted in continuous casting, and the reduction is 5-8% of the thickness of the continuous casting billet. Therefore, on one hand, the purity can be ensured, and on the other hand, the method is favorable for reducing the core segregation of the casting blank, improving the equiaxial crystal rate of the casting blank, reducing the core looseness of the casting blank and improving the structure uniformity of the casting blank.
Based on the steelmaking process, the steelmaking quality of the embodiment is excellent, and the continuous casting slab is high in purity and good in uniformity. Specifically, the respective grades of the A, B, C, D four types of inclusions of the obtained continuous casting slab are less than or equal to 1.0 grade, the sum of the grades is less than or equal to 3.0 grade, and the length-width product of the maximum inclusion is less than or equal to 900 mu m2The density of the inclusions with the equivalent diameter of more than 10 mu m is less than or equal to 8/cm2(ii) a The manganese segregation ratio of the cross section is less than or equal to 1.08, and the center porosity is less than or equal to 0.5 level.
Further, in the smelting process of the converter, the primary slag amount is more than or equal to 70 kg/ton of molten steel, namely, the primary slag is paved in the converter in advance according to the total weight of the molten steel to be smelted in the converter; in addition, after the smelting of the converter is finished, the slag remaining amount in the converter after tapping is 50% -60% of the total slag amount of secondary deslagging, and the remaining slag can be used as initial slag for smelting next molten steel.
Furthermore, the continuous casting billet obtained in the continuous casting process has the mass percentage of P less than or equal to 0.010 percent, S less than or equal to 0.0035 percent, O less than or equal to 0.0020 percent, N less than or equal to 0.0030 percent, H less than or equal to 0.0001 percent, As less than or equal to 0.01 percent and Sn less than or equal to 0.01 percent.
Preferably, in the molten iron pre-desulfurization process, the temperature of molten iron arriving at the station is more than or equal to 1380 ℃, S is less than or equal to 0.035%, P is less than or equal to 0.11%, Si is more than or equal to 0.4% and less than or equal to 0.7%, As is less than or equal to 0.01%, and the slagging-off rate of the molten iron leaving the station is more than or equal to 95% and S is less than or equal to 0.002%. Therefore, the desulfurization effect can be improved, the desulfurization pressure is reduced, and the content of harmful elements can be reduced.
In the smelting process of the converter, molten iron after pre-desulfurization and scrap steel with P less than 0.02%, S less than 0.03%, Sn less than or equal to 0.01% and thickness more than or equal to 3mm are put into the converter for smelting.
In the RH vacuum refining process, the degassing time is 20-25 min, and the net circulation treatment time is 8-10 min. Therefore, the floating removal of the inclusion can be further promoted, and the purity is improved.
During continuous casting, full-protection casting is carried out according to the modes of the argon blowing flow of 200-220L/min for the long nozzle, the argon blowing flow of 4-5L/min for the stopper rod and the argon blowing flow of 4-5L/min for the submerged nozzle, so that the serious nitrogen increase in the continuous casting process can be avoided, and the nitrogen increase is less than or equal to 0.0002 percent; and the fluctuation of the liquid level of the crystallizer is less than or equal to 2 mm.
(2) Steel rolling process of heating, controlled rolling and cooling casting blank
The continuous casting billet is heated in four stages according to the heat recovery section of less than or equal to 900 ℃, the first heating section of 1000-1100 ℃, the second heating section of 1100-1170 ℃ and the soaking section of 1190-1230 ℃. So, through the rate of rise of temperature of control blank at each section, can prevent on the one hand that the blank heaies up too fast, avoids the heart table difference in temperature too big, can make alloy element effectively dissolve on the other hand again, avoids the problem that the oxidation scaling loss is serious and the tissue is big.
Preferably, a hot charging process can be adopted, and the temperature of the continuous casting billet in a heating furnace is more than or equal to 100 ℃.
In the embodiment, the carbon equivalent is calculated according to the following formula according to the chemical components of the continuous casting billet, and the continuous casting billet is subjected to controlled rolling and cooling according to the calculation result;
carbon equivalent of C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15 … formula
Specifically, when the obtained carbon equivalent is less than 0.65, carrying out recrystallization zone rolling in a way that initial rolling is 1020-1060 ℃, final rolling is 990-1010 ℃, first pass secondary reduction is not less than 45mm, last pass secondary reduction is not less than 30mm, and reduction of each pass is reduced, and then carrying out non-recrystallization zone rolling in a way that initial rolling is 830-880 ℃, final rolling is 780-810 ℃, last pass secondary reduction is not more than 10mm, rest pass reduction is not less than 25mm, and reduction of each pass is reduced to prepare a steel plate with the thickness of 50-120 mm; and then, carrying out MULPIC accelerated cooling on the obtained steel plate, wherein the start cooling temperature is more than or equal to 750 ℃, the water pressure is 1.8-2.2 MPa, and the final cooling temperature is 280-380 ℃, and then carrying out air cooling to the room temperature. So, combine the control of temperature, the decrement in the rolling of two stages and cooling temperature, hydraulic control, when can reduce the rolling mill load, promote rolling efficiency, do benefit to warp and permeate to the blank core, improve defects such as core segregation, loose, in addition, can also make after rolling to organize and accumulate a large amount of deformation zones in to obtain tiny tissue in the cooling, improve the low temperature toughness of steel sheet.
If the obtained carbon equivalent is more than or equal to 0.65, carrying out recrystallization zone rolling in a way that the initial rolling is 1020-1060 ℃, the final rolling is 960-990 ℃, the first pass rolling reduction is more than or equal to 45mm, the last pass rolling reduction is more than or equal to 30mm, and the rolling reduction of each pass is gradually reduced to prepare a steel plate with the thickness of 50-165 mm; the obtained steel plate is directly put on a cooling bed for natural air cooling to room temperature. Therefore, the control of the temperature and the rolling reduction in the single-stage rolling and the cooling scheme are combined, so that the load of a rolling mill can be reduced, the rolling efficiency is improved, the structure can be fully recrystallized and refined, meanwhile, the deformation and the penetration to the center of the blank are facilitated, the defects of center segregation, looseness and the like are improved, and the banded structure can be reduced.
As described above, the thick steel plate obtained in the present embodiment is excellent in strength, toughness, and fatigue properties, and has uniform structure properties. Specifically, the method comprises the following steps: the band-shaped structure of the thick steel plate is less than or equal to 1 grade, the strength difference of the whole plate is less than or equal to 50MPa, particularly the strength difference in the thickness direction is less than or equal to 35MPa, and the strength difference between the head and the middle is less than or equal to 40 MPa; and, what is moreThe carbon equivalent of the thick steel plate is less than 0.65 (namely the carbon equivalent of the continuous casting billet is less than 0.65), and the impact energy A is 60 ℃ below zeroKV2The single value is more than 80J, the average value is more than 250J, and the hardness difference in the thickness direction is less than or equal to 20 HV; or the carbon equivalent of the thick steel plate is more than or equal to 0.65 (namely the carbon equivalent of the continuous casting slab is more than or equal to 0.65), the Rockwell hardness is 30-35 HRC, and the difference between the surface hardness and the core hardness is less than or equal to 2 HRC.
In summary, according to the production method of the embodiment, on one hand, through specific design of operation and parameters of each process in steel making, improvement of purity and uniformity of the continuous casting billet is realized, a thick continuous casting billet with high purity, low inclusion and high uniformity, which cannot be obtained in the prior art, is obtained, and defects of core segregation, core porosity and the like existing in the prior continuous casting billet with large thickness are effectively eliminated; on the other hand, on the premise of the excellent continuous casting billet, the steel rolling technology is improved by combining with carbon equivalent, compared with the prior art, the effect of deformation permeation to the core of the billet is further improved, the defects of core segregation, looseness and the like are improved, and the banded structure can be reduced, so that the thick steel plate with high performance uniformity is finally obtained; in addition, the whole production process of the thick steel plate is simple, the production cost is low, the production efficiency is high, the process is short, the energy consumption is low, the manufacturing of thick steel plate products with different carbon equivalent is realized by the casting technology of the same continuous casting billet, the technical applicability is improved, and the method has strong economic benefits and values for industrialization.
Further preferably, if the alloy content of the continuous casting slab is more than or equal to 3.3%, stacking and slow cooling are carried out on the continuous casting slab obtained in the step 2 before four-stage heating, wherein the stacking temperature is more than or equal to 600 ℃, the unstacking temperature is 200-300 ℃, and blank cutting is carried out when the temperature of the continuous casting slab is more than or equal to 100 ℃ after unstacking. Therefore, whether the continuous casting billet is stacked or not is designed according to the alloy content, the core defect of the continuous casting billet can be reduced, the core-surface difference can be further reduced, and the cracking risk can be avoided.
In addition, the residence time of the two heating sections is preferably 60-90 min, and the residence time of the soaking section is preferably 40-60 min.
Preferably, if the obtained carbon equivalent is less than 0.65, the ratio of water to water is 0.92-0.96, the distance between the edge part shields is 100-300 mm, the coefficient of water volume after shielding is 0.90-0.95, the distance between the head part shields is 1200-2500 mm, the coefficient of water volume after shielding is 0.88-0.93, the distance between the tail part shields is 500-1800 mm, and the coefficient of water volume after shielding is 0.92-0.96. The edge/head/tail shielding means shielding a partial area of the water cooling device corresponding to the edge/head/tail of the steel plate to reduce the amount of water sprayed toward the edge/head/tail of the steel plate, the shielding distance is also the length of the shielded area of the water cooling device, and the water amount coefficient after shielding is the ratio of the amount of water shielded in the shielded area to the amount of water not shielded.
Therefore, the optimized water ratio, the water quantity coefficient after shielding and the shielding distance are adopted, and the uniformity of the plate shape and the temperature is ensured, so that the uniformity of the performance of the whole plate is ensured.
In addition, in another variation, a tempering heat treatment process may be additionally added after the cooling process of the foregoing embodiment, so that the structural uniformity of the thick steel plate obtained by the foregoing embodiment is further improved. Specifically, if the obtained carbon equivalent is less than 0.65, carrying out tempering heat treatment according to the tempering temperature of 300-500 ℃, the tempering heating coefficient of 2.2min/mm and the tempering heat preservation time of 20-40 min; if the obtained carbon equivalent is more than or equal to 0.65, carrying out tempering heat treatment according to the tempering temperature of 500-600 ℃, the tempering heating coefficient of 2.2min/mm and the tempering heat preservation time of 20-40 min.
The following provides 2 preferred embodiments of the present invention to further illustrate the technical solution of the present invention. Of course, these 2 examples are only preferred implementations of the many variations that are encompassed by this embodiment, and not all.
Example 1
The embodiment provides a thick steel plate, and the production flow is as follows:
(1) pre-desulphurisation of molten iron
KR pre-desulfurization is carried out on 170 tons of molten iron; the arrival temperature of molten iron is 1400 ℃, the S content is 0.035%, the C content is 4.51%, the P content is 0.11%, the Si content is 0.40%, and the As content is 0.01%; the slag removing rate of the molten iron discharged from the station is more than or equal to 95 percent, the S content is 0.001 percent, and the temperature is 1380 ℃;
(2) smelting in a converter
Pouring the molten iron discharged from the KR into a 180-t converter with primary slag, adding high-quality waste steel according to the proportion of (waste steel + molten iron) to (15: 100), and then sequentially carrying out dephosphorization, primary deslagging, deep dephosphorization, secondary deslagging and tapping;
wherein P in the high-quality scrap steel is less than 0.02 percent, S is less than 0.03 percent, Sn is 0.01 percent, and the thickness of the scrap steel is more than or equal to 3 mm;
the temperature of a molten pool is 1400 ℃ in the dephosphorization period, the basicity of the slag in the primary deslagging is 2.0, the total iron in the slag is 12%, the basicity of the slag in the secondary deslagging is 3.5, and the total iron in the slag is 15%, the tapping temperature is 1660 ℃, the P content is 0.006%, and the C content is 0.04%, the slag is retained in the tapping mode by adopting a slag stopper and a slag stopping rod, and the residual slag amount is 60% of the total slag amount in the secondary deslagging.
(3) LF refining
Transferring the converter tapping into an LF refining furnace for refining;
during refining, the steel plate obtained finally comprises the following chemical components in percentage by mass: 0.030-0.060% of C, 0.10-0.20% of Si, 1.58-1.72% of Mn, 0.20-0.30% of Cr, 0.48-0.60% of Ni, 0.28-0.38% of Cu, 0.05-0.10% of Mo, 0.035' 0.045% of Nb, 0.009-0.020% of Ti, 0.009-0.018% of V, 0.020-0.040% of Al, and the balance of Fe and impurities, and carrying out at least one alloying operation;
argon is blown at the bottom in the whole refining period, strong argon blowing is carried out for no more than 5min at the flow rate of 600NL/min while the alloy is added for the first time, and strong argon blowing is carried out for no more than 3min at the flow rate of 600NL/min while the alloy is added. And the argon is blown in the whole process according to the flow of 200NL/min in the rest time, the stirring and the overturning can not be carried out violently, and the molten steel is not allowed to be exposed by bottom blowing stirring.
And in the refining process, a high-efficiency slag surface deoxidizer is used for deoxidation, calcium carbide is strictly forbidden, 800kg of lime and a proper amount of fluorite are added for slag regulation, and white slag is rapidly produced for desulfurization.
(4) RH vacuum refining
Hoisting the steel discharged from the LF furnace to an RH vacuum furnace for refining;
during vacuum refining, the vacuum degree of an RH vacuum furnace is less than or equal to 2mbar, the degassing time is 20min, the net cycle processing time is 10min, and molten steel in a steel ladle after tapping is kept stand for 15min on a rotary table.
(5) Continuous casting
After the steel tapping of the RH vacuum refining process is finished by standing on a rotary table, manufacturing a continuous casting blank with the thickness of 320mm and the width of 1850mm by adopting a continuous casting machine;
during continuous casting, performing full-protection casting according to the modes of argon blowing flow of a long nozzle of 200L/min, argon blowing flow of a stopper rod of 4-5L/min, argon blowing flow of an immersion nozzle of 4-5L/min and covering agent in a tundish; in addition, argon blowing is started in the tundish 5 minutes before casting, and the argon blowing is stopped after the addition of the covering agent of the tundish in the first round is finished;
and (3) carrying out secondary cooling zone electromagnetic stirring at the casting superheat degree of 25-30 ℃ and at the frequency of 4-5 Hz and the current of 500-600A, wherein the continuous casting adopts dynamic soft reduction, the reduction is 25mm, and the drawing speed is 0.65 m/min.
The chemical components of the obtained continuous casting billet in percentage by mass are as follows: 0.043 percent of C, 0.15 percent of Si, 1.65 percent of Mn, 0.25 percent of Cr, 0.53 percent of Ni, 0.33 percent of Cu, 0.06 percent of Mo, 0.040 percent of Nb, 0.015 percent of Ti, 0.012 percent of V, 0.030 percent of Al, the balance of Fe and impurities, less than or equal to 0.010 percent of impurity element P, less than or equal to 0.0035 percent of S, less than or equal to 0.0020 percent of O, 0.0030 percent of N, less than or equal to 0.0001 percent of H, less than or equal to 0.01 percent of As, and less than or equal to 0.01 percent of Sn;
after the obtained continuous casting billet is subjected to sampling and pickling, the surface of the continuous casting billet has no cracks, and the internal quality of the continuous casting billet is good; the detection shows that the respective grades of the A, B, C, D four types of inclusions are all 0.5 grade, the sum of the grades is 2.0 grade, and the length-width product of the largest inclusion is 800 mu m2The density of inclusions with an equivalent diameter of 10 μm or more is 7/cm2(ii) a The manganese segregation ratio of the cross section is 1.05, and the center porosity is 0.5 grade.
(6) Heating of casting blanks
Adopting a hot charging process, and feeding the continuous casting billet obtained in the continuous casting process into a furnace with the temperature being more than or equal to 100 ℃; then, four-section heating of a heat recovery section, a first heating section, a second heating section and a soaking section is adopted in the heating furnace, wherein the heat recovery section is less than or equal to 900 ℃, the first heating section is 1000-1100 ℃, the second heating section is 1100-1170 ℃ and the residence time is 60-90 min, and the soaking section is 1190-1230 ℃ and the residence time is 40-60 min;
(7) two-stage controlled rolling
The first stage is rolling in a recrystallization zone, the initial rolling temperature is 1043 ℃, the final rolling temperature is 995 ℃, a high reduction rolling process is adopted, the first pass secondary reduction is 45mm, the last pass secondary reduction is 33mm, and the reduction of each pass is gradually reduced;
the second stage is rolling in a non-recrystallization region, the initial rolling temperature is 840 ℃, the final rolling temperature is 790 ℃, a high reduction rolling process is adopted, the final reduction is 10mm, the reduction of the rest passes is more than or equal to 25mm, and the reduction of each pass is reduced progressively;
after the second stage of rolling is finished, the thickness of the obtained steel plate is 100 mm;
(8) MULPIC controlled Cooling
The start cooling temperature is 764 ℃, the water pressure is 2.0MPa, the water-to-water ratio is 0.93, the final cooling temperature is 320 ℃, and then the air cooling is carried out to the room temperature;
during water cooling, the distance of the edge part shield is 150mm, the water yield coefficient after shielding is 0.90, the distance of the head part shield is 1500mm, the water yield coefficient after shielding is 0.89, the distance of the tail part shield is 1000mm, and the water yield coefficient after shielding is 0.96;
the band-shaped structure of the thick steel plate is less than or equal to level 1, the strength difference of the whole plate is less than or equal to 50MPa, the yield strength of each part of the whole plate is more than or equal to 470MPa, and the tensile strength is more than or equal to 610 MPa; especially the strength difference in the thickness direction is less than or equal to 35MPa, and the strength difference between the head and the tail is less than or equal to 40 MPa; in addition, the impact energy of the thick steel plate at-60 ℃ is 322J, 310J and 331J, and the hardness difference in the thickness direction is less than or equal to 18 HV;
(9) tempering heat treatment
Tempering the thick steel plate air-cooled to room temperature at 350 deg.C for 30min, with a tempering heating coefficient of 2.2min/mm (i.e. the tempering heating time is 100mm × 2.2 min/mm-220 min);
sampling and detecting the steel plate again after treatment, wherein the strength difference of the whole plate is less than or equal to 46MPa, the yield strength of each part of the whole plate is greater than or equal to 460MPa, and the tensile strength is greater than or equal to 590 MPa; the strength difference in the thickness direction is less than or equal to 32MPa, and the strength difference between the head and the tail is less than or equal to 38 MPa; the impact energy of the thick steel plate is 325J, 332J and 323J at the temperature of minus 60 ℃, and the hardness difference in the thickness direction is less than or equal to 16 HV.
Example 2
The embodiment provides a thick steel plate, and the production flow is as follows:
(1) pre-desulphurisation of molten iron
KR pre-desulfurization is carried out on 168 tons of molten iron; the arrival temperature of molten iron is 1380 ℃, the S content is 0.030%, the C content is 4.55%, the P content is 0.105%, the Si content is 0.45%, and the As content is 0.01%; the slag removing rate of the molten iron discharged from the station is more than or equal to 95 percent, the S content is 0.001 percent, and the temperature is 1350 ℃;
(2) smelting in a converter
Pouring the molten iron discharged from the KR into a 180-t converter with primary slag, adding high-quality waste steel according to the proportion of (waste steel + molten iron) to (15: 100), and then sequentially carrying out dephosphorization, primary deslagging, deep dephosphorization, secondary deslagging and tapping;
wherein P in the high-quality steel scrap is less than 0.02 percent, S is less than 0.03 percent, Sn is 0.01 percent, and the thickness of the steel scrap is 10 mm;
the temperature of a molten pool is 1350 ℃ in the dephosphorization period, the slag alkalinity of the primary deslagging is 1.8, the total iron in the slag is 15%, the slag alkalinity of the secondary deslagging is 4.0, the total iron in the slag is 18%, the tapping temperature is 1640 ℃, the P content is 0.005%, and the C content is 0.05%, the slag is retained in the tapping mode of a slag stopper and a slag stopping rod, and the slag remaining amount is 50% of the total slag amount in the secondary deslagging.
(3) LF refining
Transferring the converter tapping into an LF refining furnace for refining;
during refining, the steel plate obtained finally comprises the following chemical components in percentage by mass: 0.35-0.40% of C, 0.25-0.35% of Si, 1.50-1.60% of Mn, 1.65-1.75% of Cr, 0.18-0.26% of Mo and the balance of Fe and impurities, and carrying out at least one alloying operation;
argon gas is blown at the bottom in the whole refining period, strong argon blowing is carried out for 4min at the flow rate of 800NL/min while the alloy is added for the first time, and strong argon blowing is carried out for 3min at the flow rate of 800NL/min while the alloy is supplemented. And the argon is blown in the whole process at the flow rate of 400NL/min in the rest time, the stirring and the overturning can not be carried out violently, and the molten steel is not allowed to be exposed by bottom blowing stirring.
In the refining process, a high-efficiency slag surface deoxidizer is used for deoxidation, 700kg of lime and a proper amount of fluorite are added for slag regulation, and white slag is rapidly produced for desulfurization.
(4) RH vacuum refining
Hoisting the tapping of the LF furnace to an RH vacuum furnace for refining;
during vacuum refining, the vacuum degree of the RH vacuum furnace is less than or equal to 2mbar, the degassing time is 25min, the net cycle processing time is 8min, and molten steel in a steel ladle after tapping is kept stand for 18min on a rotary table.
(5) Continuous casting
After the steel tapping of the RH vacuum refining process is finished by standing on a rotary table, manufacturing a continuous casting blank with the thickness of 320mm and the width of 1850mm by adopting a continuous casting machine;
during continuous casting, full-protection casting is carried out according to the modes of 220L/min of argon blowing flow of a long nozzle, 5L/min of argon blowing flow of a stopper rod, 5L/min of argon blowing flow of an immersion nozzle and covering agent in the middle; in addition, the tundish starts to blow argon 5 minutes before casting, and the argon blowing is stopped after the tundish covering agent in the first round is added;
the casting superheat degree is 30 ℃, the secondary cooling zone electromagnetic stirring is carried out at the frequency of 5Hz and the current of 500A, the continuous casting adopts dynamic soft reduction, the reduction is 20mm, and the drawing speed is 0.65 m/min.
The chemical components of the obtained continuous casting billet in percentage by mass are as follows: 0.38 percent of C, 0.31 percent of Si, 1.56 percent of Mn, 1.70 percent of Cr, 0.22 percent of Mo, and the balance of Fe and impurities, wherein the impurity element P is less than or equal to 0.010 percent, the S is less than or equal to 0.0035 percent, the O is less than or equal to 0.0020 percent, the N is 0.0030 percent, the H is less than or equal to 0.0001 percent, the As is less than or equal to 0.01 percent, and the Sn is less than or equal to 0.01 percent;
after the obtained continuous casting billet is subjected to sampling and pickling, the surface of the continuous casting billet has no cracks, and the internal quality of the continuous casting billet is good; the detection shows that the respective grades of A, B, C, D four types of inclusions are all 0.5 grade, the sum of the grades is 2.0 grade, and the length-width product of the largest inclusion is 900 mu m2The density of inclusions with an equivalent diameter of 10 μm or more is 8 pieces/cm2(ii) a The manganese segregation ratio of the cross section is 1.05, and the center porosity is 0.5 grade.
(6) Heating of casting blanks
Stacking and slowly cooling the continuous casting billets obtained in the continuous casting process, wherein the stacking temperature is more than or equal to 600 ℃, the unstacking temperature is 200-300 ℃, and cutting the billets when the temperature of the continuous casting billets is more than or equal to 100 ℃ after unstacking;
then, a hot charging process is adopted, the cut continuous casting slab is charged into a furnace with the temperature being more than or equal to 100 ℃; then, four-section heating of a heat recovery section, a first heating section, a second heating section and a soaking section is adopted in the heating furnace, wherein the heat recovery section is less than or equal to 900 ℃, the first heating section is 1000-1100 ℃, the second heating section is 1100-1170 ℃ and the residence time is 60-90 min, and the soaking section is 1190-1230 ℃ and the residence time is 40-60 min;
(7) single stage controlled rolling
Rolling in a recrystallization zone, wherein the initial rolling temperature is 1020-1060 ℃, the final rolling temperature is 960-990 ℃, a high reduction rolling process is adopted, the first pass reduction is more than or equal to 45mm, the last pass reduction is more than or equal to 30mm, and the reduction of each pass is gradually reduced;
after the rolling is finished, the thickness of the obtained steel plate is 160 mm;
(8) cooling down
An air cooling process is adopted, the steel plate obtained by rolling is controlled not to be cooled by water, and the steel plate is directly put on a cooling bed to be naturally cooled to room temperature by air;
the band-shaped structure of the thick steel plate is less than or equal to level 1, the strength difference of the whole plate is less than or equal to 50MPa, the yield strength of each part of the whole plate is more than or equal to 700MPa, and the tensile strength of each part of the whole plate is more than or equal to 1050 MPa; especially the strength difference in the thickness direction is less than or equal to 35MPa, and the strength difference between the head and the tail is less than or equal to 40 MPa; in addition, the Rockwell hardness of the thick steel plate is 31-33 HRC, and the difference between the surface hardness and the core hardness is 2 HRC;
(9) tempering heat treatment
Tempering the thick steel plate which is air-cooled to room temperature, wherein the tempering temperature is 500-600 ℃, the tempering heating coefficient is 2.2min/mm (namely the tempering heating time is 160mm multiplied by 2.2 min/mm-352 min), and the tempering heat preservation time is 20-40 min;
sampling and detecting the steel plate again after treatment, wherein the strength difference of the whole plate is less than or equal to 46MPa, the yield strength of each part of the whole plate is more than or equal to 650MPa, and the tensile strength is more than or equal to 950 MPa; the strength difference in the thickness direction is less than or equal to 32MPa, and the strength difference between the head, the middle and the tail is less than or equal to 38 MPa; the Rockwell hardness of the thick steel plate is 28-30 HRC, and the difference between the surface hardness and the core hardness is less than or equal to 1.8 HRC.
The detailed description set forth above is merely a specific description of possible embodiments of the present invention and is not intended to limit the scope of the invention, which is intended to include within the scope of the invention equivalent embodiments or modifications that do not depart from the technical spirit of the present invention.

Claims (18)

1. A production method of a continuous casting type thick steel plate is characterized by comprising the following steps:
(1) carrying out steel making by adopting the processes of molten iron pre-desulfurization, converter smelting, LF refining and RH vacuum refining; in the smelting process of the converter, dephosphorization, primary deslagging, deep dephosphorization, secondary deslagging and tapping are sequentially carried out in the converter with primary slag, the temperature of a molten pool in the dephosphorization period is 1350-1400 ℃, the basicity of slag in the primary deslagging is 1.8-2.0, the total iron in the slag is 12-15%, the basicity of slag in the secondary deslagging is 3.5-4.0, the total iron in the slag is 15-18%, the tapping temperature is 1640-1660 ℃, and the P is less than or equal to 0.006%; in the LF refining process, alloy is added, strong argon blowing is carried out for no more than 5min at the flow rate of 600-800 NL/min, and the whole argon blowing is carried out at the flow rate of 200-400 NL/min for the rest of time; in the RH vacuum refining process, the vacuum degree is less than or equal to 2mbar, and the molten steel is kept stand for 15-18 min after tapping;
(2) continuously casting the steel discharged in the RH vacuum refining process into a continuous casting billet with the thickness of 320 mm; during the process, full-protection casting is adopted, the casting superheat degree is 25-30 ℃, secondary cooling zone electromagnetic stirring is carried out at the frequency of 4-5 Hz and the current of 500-600A, and dynamic soft reduction is adopted for continuous casting, and the reduction is 5-8% of the thickness of a continuous casting blank;
(3) carrying out four-stage heating on the continuous casting billet according to the heat recovery section of less than or equal to 900 ℃, the first heating section of 1000-1100 ℃, the second heating section of 1100-1170 ℃ and the soaking section of 1190-1230 ℃;
(4) calculating the carbon equivalent according to the chemical components of the continuous casting billet and the following formula, and performing controlled rolling and cooling on the continuous casting billet according to the calculation result;
carbon equivalent of C + Mn/6+ (Cr + Mo + V)/5+ (Cu + Ni)/15
If the obtained carbon equivalent is less than 0.65, firstly carrying out recrystallization zone rolling in a way that initial rolling is 1020-1060 ℃, final rolling is 990-1010 ℃, the first pass secondary reduction is more than or equal to 45mm, the last pass secondary reduction is more than or equal to 30mm and the reduction of each pass is reduced progressively, and then carrying out non-recrystallization zone rolling in a way that initial rolling is 830-880 ℃, final rolling is 780-810 ℃, the last pass secondary reduction is less than or equal to 10mm, the rest passes reduction is more than or equal to 25mm and the reduction of each pass is reduced progressively to prepare a steel plate of 50-120 mm; carrying out MULPIC accelerated cooling on the obtained steel plate, wherein the start cooling temperature is more than or equal to 750 ℃, the water pressure is 1.8-2.2 MPa, and the final cooling temperature is 280-380 ℃, and then air cooling to room temperature;
if the obtained carbon equivalent is more than or equal to 0.65, carrying out recrystallization zone rolling in a way that the initial rolling is 1020-1060 ℃, the final rolling is 960-990 ℃, the first pass rolling reduction is more than or equal to 45mm, the last pass rolling reduction is more than or equal to 30mm, and the rolling reduction of each pass is gradually reduced to prepare a steel plate with the thickness of 50-165 mm; the obtained steel plate is directly put on a cooling bed for natural air cooling to room temperature.
2. The method of producing a continuously cast thick steel plate as claimed in claim 1, wherein the A, B, C, D-type inclusions in the slab obtained in step 2 are rated at 1.0 or less and the sum of the ratings is 3.0 or less, and the length-width product of the largest inclusion is 900 μm or less2The density of the inclusions with the equivalent diameter of more than 10 mu m is less than or equal to 8/cm2。
3. The method for producing a continuously cast thick steel plate as claimed in claim 1, wherein the manganese segregation ratio of the cross section of the slab obtained in the step 2 is 1.08 or less.
4. The method for producing a continuously cast thick steel plate as claimed in claim 1, wherein the center porosity of the continuously cast slab obtained in step 2 is not more than 0.5.
5. The method for producing a continuously cast thick steel plate as claimed in claim 1, wherein the amount of the primary slag is not less than 70 kg/ton of molten steel in the converter smelting step, and the amount of the slag remaining in the converter after tapping is 50 to 60% of the total amount of the slag of the secondary deslagging.
6. The method for producing a continuously cast thick steel plate As claimed in claim 1, wherein the continuously cast slab obtained in step 2 has a mass percentage of P of 0.010% or less, S of 0.0035% or less, O of 0.0020% or less, N of 0.0030% or less, H of 0.0001% or less, As of 0.01% or less, and Sn of 0.01% or less.
7. The method for producing a continuously cast thick steel plate as claimed in claim 6, wherein in the molten iron pre-desulfurization step, the temperature of molten iron arriving at the station is not less than 1380 ℃, S is not more than 0.035%, and the slag removal rate of leaving the station is not less than 95% and S is not more than 0.002%.
8. The method of producing a continuously cast thick steel plate as claimed in claim 6, wherein the molten iron after preliminary desulfurization and scrap steel having a P content of less than 0.02%, an S content of less than 0.03%, an Sn content of less than or equal to 0.01%, and a thickness of not less than 3mm are charged into a converter for smelting in a converter smelting process.
9. The method for producing a continuously cast thick steel plate as claimed in claim 6, wherein the degassing time is 20 to 25min and the net circulation treatment time is 8 to 10min in the RH vacuum refining step.
10. The method for producing a continuously cast thick steel plate according to claim 6, wherein in the step 2, full-protection casting is performed in a manner that the argon blowing flow rate of the long nozzle is 200-220L/min, the argon blowing flow rate of the stopper rod is 4-5L/min, and the argon blowing flow rate of the submerged nozzle is 4-5L/min during continuous casting, and the fluctuation of the liquid level of the crystallizer is less than or equal to 2 mm.
11. The method for producing a continuously cast thick steel plate as claimed in claim 1, wherein in the LF refining step, strong argon blowing is performed at a flow rate of 600 to 800NL/min for not more than 5min while the alloy is first added, and strong argon blowing is performed at a flow rate of 600 to 800NL/min for not more than 3min while the alloy is supplemented.
12. The method for producing a continuously cast thick steel plate according to claim 1, wherein in the step 3, if the alloy content of the continuously cast slab is not less than 3.3%, the continuously cast slab obtained in the step 2 is stacked and slowly cooled at a stacking temperature of not less than 600 ℃ and a unstacking temperature of 200 to 300 ℃ before the four-stage heating, and the slab is cut at a continuous slab temperature of not less than 100 ℃ after the unstacking.
13. The method for producing a continuously cast thick steel plate as claimed in claim 1, wherein in step 3, the residence time in the two heating zones is 60 to 90min, and the residence time in the soaking zone is 40 to 60 min.
14. The method for producing a continuously cast thick steel plate as claimed in claim 1, wherein in step 4, if the obtained carbon equivalent is less than 0.65, the ratio of water supply to water discharge is 0.92 to 0.96, the distance between the edge shield and the edge shield is 100 to 300mm, the water yield coefficient after shielding is 0.90 to 0.95, the distance between the head shield and the end shield is 1200 to 2500mm, the water yield coefficient after shielding is 0.88 to 0.93, the distance between the tail shield and the end shield is 500 to 1800mm, and the water yield coefficient after shielding is 0.92 to 0.96.
15. The method for producing a continuously cast thick steel plate as claimed in claim 1, further comprising the steps of:
(5) if the obtained carbon equivalent is less than 0.65, carrying out tempering heat treatment according to the tempering temperature of 300-500 ℃, the tempering heating coefficient of 2.2min/mm and the tempering heat preservation time of 20-40 min; if the obtained carbon equivalent is more than or equal to 0.65, carrying out tempering heat treatment according to the tempering temperature of 500-600 ℃, the tempering heating coefficient of 2.2min/mm and the tempering heat preservation time of 20-40 min.
16. A continuously cast thick steel plate, characterized in that it is produced by the production method according to any one of claims 1 to 15, and the steel plate has a ribbon structure of grade 1 or less and has a total plate strength difference of 50MPa or less.
17. The continuously cast thick steel plate as claimed in claim 16, wherein the thick steel plate has a thickness direction strength difference of 35MPa or less and a head-to-tail strength difference of 40MPa or less.
18. The continuously cast thick steel plate as claimed in claim 16, wherein the thick steel plate has a carbon equivalent of < 0.65 and an impact work a of-60 ℃KV2The single value is more than 80J, the average value is more than 250J, and the hardness difference in the thickness direction is less than or equal to 20 HV;
or the carbon equivalent of the thick steel plate is more than or equal to 0.65, the Rockwell hardness is 30-35 HRC, and the difference between the surface hardness and the core hardness is less than or equal to 2 HRC.
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