CN111893402A - Ultralow-temperature weather-resistant bridge steel and production method thereof - Google Patents

Ultralow-temperature weather-resistant bridge steel and production method thereof Download PDF

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Publication number
CN111893402A
CN111893402A CN202010962123.9A CN202010962123A CN111893402A CN 111893402 A CN111893402 A CN 111893402A CN 202010962123 A CN202010962123 A CN 202010962123A CN 111893402 A CN111893402 A CN 111893402A
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equal
steel
less
temperature
cooling
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许少普
王英杰
朱书成
李忠波
张涛
于飒
康文举
郑海明
赵湖
朱先兴
王希彬
任义
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Nanyang Hanye Special Steel Co Ltd
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Nanyang Hanye Special Steel Co Ltd
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    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04Removing impurities by adding a treating agent
    • C21C7/06Deoxidising, e.g. killing
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21CPROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04Removing impurities by adding a treating agent
    • C21C7/068Decarburising
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING 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
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C1/00Making alloys
    • C22C1/02Making alloys by melting
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/02Ferrous alloys, e.g. steel alloys containing silicon
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/04Ferrous alloys, e.g. steel alloys containing manganese
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/06Ferrous alloys, e.g. steel alloys containing aluminium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/002Bainite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/005Ferrite
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/009Pearlite
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02PCLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00Technologies related to metal processing
    • Y02P10/20Recycling

Abstract

The invention discloses an ultra-low temperature weather-resistant bridge steel and a production method thereof, wherein the ultra-low temperature weather-resistant bridge steel comprises the following chemical components: C. si, Mn, P, S, Als, Nb, V, Cu, Cr, N, Ti, and the balance of Fe and residual elements; the obtained steel plate structure contains more than 70% of quasi-polygonal ferrite, less than 20% of bainite and less than 10% of pearlite, the carbon equivalent Ceq is less than or equal to 0.43%, the yield strength is more than 420MPa, and the impact energy at-100 ℃ is more than or equal to 120J. In the aspect of component design, the influence of various alloy elements on the toughness is comprehensively considered, the idea of low-carbon microalloying is adopted, the alloy cost is reduced, and meanwhile, good impact toughness is obtained; TMCP rolling is adopted in the production process, the whole process flow is shortened, the heat treatment link is eliminated, and the benefits of improving logistics transportation and reducing production cost are remarkable.

Description

Ultralow-temperature weather-resistant bridge steel and production method thereof
Technical Field
The invention belongs to the technical field of steel smelting, and particularly relates to ultralow-temperature weather-resistant bridge steel and a production method thereof.
Background
Weather-resistant bridge steel, namely bridge steel resisting atmospheric corrosion, is formed by adding a small amount of corrosion-resistant elements such as chromium, nickel, copper, phosphorus and the like into common bridge steel, and has the characteristics of toughness, ductility, molding, welding and cutting, abrasion, high temperature, fatigue resistance and the like of high-quality steel; the weather resistance is 2-8 times of that of common steel, and the coating performance is 1.5-10 times of that of common steel. At present, the strength grade and the toughness of the steel for bridges in China are continuously improved, and the welding performance is continuously improved. Steel for railway bridges, steel for highway bridges and steel for sea-crossing bridges become main bodies of steel for bridges in China. The high-strength and ultralow-temperature performance weather-resistant bridge steel conforming to the development requirements of the times is a main direction for the development of bridge steel in China. At present, the quality grade of steel in GB/T714-2015 structural steel for bridges is only specified to E grade in the standard, but the E grade standard cannot meet the requirement on high-strength ultralow-temperature weather-resistant bridge steel in severe environment, and the development of ultralow-temperature impact (-100 ℃ impact energy is more than or equal to 120J) weather-resistant bridge steel becomes necessary.
Disclosure of Invention
The invention aims to provide ultralow-temperature weather-resistant bridge steel and a production method thereof.
In order to achieve the aim, the invention is realized by the following mode that the ultralow-temperature weather-resistant bridge steel comprises the following chemical components in percentage by mass: c: 0.06-0.08%, Si: 0.20 to 0.35%, Mn: 1.1-1.2%, P is less than or equal to 0.018%, S: less than or equal to 0.005 percent, Als: 0.015-0.035%, Nb: 0.02-0.04%, V: less than or equal to 0.03%, Cu: 0.27 to 0.33%, Cr: 0.40 to 0.50%, Ni: 0.30-0.40%, Ti: less than or equal to 0.02 percent, and the balance of Fe and residual elements;
the structure of the steel sheet contains more than 70% of quasi-polygonal ferrite, less than 20% of bainite, and less than 10% of pearlite;
the carbon equivalent Ceq of the steel plate is less than or equal to 0.43 percent, the yield strength is more than 420MPa, and the impact energy at-100 ℃ is more than or equal to 120J.
The chemical components are selected because:
the main effect of C in the steel grade is to improve the strength, which is unfavorable for other properties, the C in the steel is controlled to be about 0.07 percent, and the strength is rapidly reduced along with the reduction of the C content, so that various microalloy elements are added for compensation;
si can improve the strength limit, yield limit and hardness of the steel, reduce the elongation, shrinkage and impact toughness of the steel, and influence Pcm crack sensitivity index in the bridge steel, so the Si content is low;
mn is a strengthening alloy element of steel, the increase of Mn content can improve the stability of austenite, reduce the critical cooling speed, strengthen ferrite and improve the hardenability of steel, but the content of manganese sulfide inclusion in a casting blank can be increased due to the excessively high Mn content, the internal quality of the casting blank is influenced, in addition, the carbon equivalent is improved due to the excessively high Mn content, the weldability is not good, and the Mn is controlled to be 1.10-1.20% by combining the carbon equivalent requirement of bridge steel;
p, S belongs to harmful elements, which easily gather in the grain boundary, reduce the surface energy of the grain boundary, reduce the brittle fracture stress, and affect the ductile-brittle transition temperature, so the lower the content, the better, P is beneficial to the steel grade, it can significantly improve the strength limit of the steel, improve the stability of atmospheric corrosion resistance, and can improve the weather resistance coefficient in the weathering resistant steel, therefore, P is less than or equal to 0.018%, S is less than or equal to 0.005%;
nb and V are nitrides which are easy to form with N in steel, and the extremely trace amount of Nb and V can enable free N in the steel to basically disappear, so that the influence of the freedom on the brittleness of the steel is reduced, and the nitrides of Nb and V have a large amount of nucleation effects, so that crystal grains are refined and play a pinning effect;
cr has high hardness, high strength, high yield point and high wear resistance, but has little influence on plasticity and toughness, and because the Cr can refine and uniformly distribute tissues, the plasticity and the toughness are good, and the combination of Cr and Ni can greatly improve the strength and the plasticity of steel;
ni not only can strongly improve the strength of the steel, but also can always keep the toughness of the steel at a very high level, the embrittlement temperature is extremely low, and when the nickel is more than 0.3 percent, the embrittlement temperature reaches below-100 ℃;
cu can improve the strength limit of steel, can also improve the impact toughness of low-carbon steel, and obviously improves the corrosion resistance of the steel, but the Cu content of more than 0.5 percent can cause precipitation hardening effect.
Therefore, the ultralow-temperature weather-resistant bridge steel with the thickness of 16-46 mm has the following chemical components in percentage by mass (unit, wt%): c: 0.06-0.08%, Si: 0.20 to 0.35%, Mn: 1.1-1.2%, P is less than or equal to 0.018%, S: less than or equal to 0.005 percent, Als: 0.015-0.035%, Nb: 0.02-0.04%, V: less than or equal to 0.03%, Cu: 0.27 to 0.33%, Cr: 0.40 to 0.50%, Ni: 0.30-0.40%, Ti: not more than 0.02 percent, the balance of Fe and residual elements, and the carbon equivalent Ceq of the steel plate is not more than 0.43 percent. When the thickness is less than or equal to 30mm, V does not need to be added into the steel plate; when the thickness is more than 30mm, the content of V is between 0.02 and 0.03 percent.
In order to ensure the required performance of the ultralow-temperature weather-resistant bridge steel with the thickness of 16-46 mm, even higher than the performance requirement, the invention adopts the following production method measures: the steel plate is obtained by cleanly smelting molten steel, protecting and casting the whole process of the continuous casting steel casting process, and heating, dephosphorizing, rolling and cooling and heap cooling a casting blank, and the method specifically comprises the following steps:
(1) smelting clean molten steel: KR pretreatment, converter smelting and VD + LF + VD smelting are carried out on the molten iron to obtain clean molten steel; wherein: after the molten iron is stirred and desulfurized by KR, the molten iron S is ensured to be less than or equal to 0.005 percent, the desulfurization period is less than or equal to 21min, and the desulfurization temperature is reduced by less than or equal to 20 ℃; after the smelting in the converter is finished, the tapping temperature is more than or equal to 1560 ℃, the C is more than or equal to 0.05 percent and less than or equal to 0.08 percent, and the P is less than or equal to 0.009 percent; finishing the VD + LF + VD smelting, controlling the temperature of the molten steel leaving the station to be 1565-1570 ℃, and controlling the H content to be less than or equal to 1.2 ppm;
(2) continuous casting: the superheat degree of a tundish is 10-25 ℃, the whole process is protected for casting, a protective pipe needs to be sleeved within 1min after a ladle is cast, the molten steel surface does not turn red in the tundish casting process, the argon blowing amount of a stopper rod is controlled in the steel casting process, and the slight fluctuation of the liquid level of a crystallizer is ensured; the stacking cooling is required to be more than or equal to 24 hours after the casting blank is off-line;
(3) heating a casting blank: the temperature of the preheating section is less than or equal to 950 ℃, the temperature of the heating section is 1210-1230 ℃, the temperature of the heat preservation section is 1200-1220 ℃, and the total heating time is 10-12 min/cm;
(4) and (3) dephosphorization: heating the casting blank, removing phosphorus for the first time, then reloading the casting blank into a heating furnace for secondary heating, wherein the heating temperature is 1200-1220 ℃, the heating time is 4-6 min, and tapping and removing phosphorus again after the secondary heating;
(5) rolling and cooling control: after dephosphorization is carried out on the casting blank, temperature-controlled rolling is carried out immediately; the initial rolling temperature of rough rolling is more than or equal to 980 ℃, the steel feeding speed is 1.5m/S, the accumulated reduction rate is more than or equal to 60%, the steel airing thickness is the thickness of a finished product plus 50-80 mm, and the finished product enters an IC for cooling at the cooling speed of less than or equal to 3 ℃/S; the initial rolling temperature of finish rolling is controlled to be 810-890 ℃, the final rolling temperature is controlled to be 790-870 ℃, the steel plate after final rolling slowly advances for 40-90S on a rear roller way of a rolling mill to enter ACC for rapid cooling, the cooling speed is controlled to be 7-12 ℃/S, and the temperature of red return is 590-630 ℃;
(6) and (3) cooling in a heaped mode: and (3) after the steel plate is taken off line, putting the steel plate into a slow cooling pit for stack cooling, wherein the stack cooling temperature is 350-450 ℃, and the stack cooling time is more than or equal to 24 hours.
In some embodiments, the structure of the steel sheet obtained by the above process contains more than 70% of quasi-polygonal ferrite, less than 20% of bainite, and less than 10% of pearlite.
In some embodiments, the steel plate has a yield strength of more than 420MPa and an impact energy of more than or equal to 120J at-100 ℃ through performance detection.
The invention has the beneficial effects that:
in the aspect of component design, the influence of various alloy elements on the strength and toughness is comprehensively considered, a low-carbon microalloying thought is adopted, low-C and low-Mn elements such as Nb and V in a certain range and weather-resistant component elements such as Cr, Ni and Cu are added, and then the steel plate structure is positioned by taking ferrite as the main part and containing a small amount of pearlite and bainite through corresponding process measures.
The molten steel smelting adopts VD + LF + VD technology, the first VD is for decarbonization and deoxidation, oxygen dissolved in the molten steel is dissociated out to react with carbon through vacuum decompression, the purpose of decarbonization and deoxidation is achieved, and the carbon content is required to be at the lower limit of the standard; the middle LF furnace smelting is to raise the temperature of molten steel, add alloy elements, refine and remove slag inclusion under the action of blowing argon and adding white slag, correspondingly increase the carbon content in the process of adding the alloy elements, but in the required range, add aluminum wires in the LF furnace for further deoxidation; and the final VD furnace treatment is to further reduce the pressure in vacuum, release the hydrogen content in the molten steel, further remove impurities and obtain high-quality molten steel.
The process can ensure that more than 95% of iron scale on the surface of the casting blank can be removed by adopting the secondary heating and the secondary phosphorus removal, and mainly solves the problem by adopting the method of the secondary heating and the secondary phosphorus removal because Ni is added into steel components and the primary iron scale on the surface of the casting blank can not be completely removed by a normal method after the casting blank is heated.
The TMCP rolling is adopted, the whole process flow is shortened, the heat treatment link is eliminated, and the benefits of improving logistics transportation and reducing production cost are remarkable. The rough rolling adopts high-temperature low-speed high-reduction rolling, the accumulated reduction rate is more than or equal to 60 percent, the grain refinement of the internal structure of the billet is realized, and the IC rapid cooling is used for cooling the steel plate to the temperature below the temperature of an austenite non-recrystallization region before finish rolling, so that the early transformation of more quasi-polygonal ferrite, acicular ferrite and the like is realized; the rapid cooling is to obtain bainite and pearlite, wherein the ferrite has high ductility and high impact toughness, and the bainite and pearlite have higher tensile strength and higher yield strength. The finish rolling temperature is controlled below a non-recrystallization area, different finish rolling temperatures are controlled according to different thicknesses of the steel plates, and the thinner the steel plate is, the closer the start rolling temperature and the finish rolling temperature are to the upper limit, and the thicker the steel plate is, the closer the start rolling temperature and the finish rolling temperature are to the lower limit, with the thickness of 30mm as a limit; and after finishing rolling, slowly advancing the steel plate on a rear roller way of a rolling mill for 40-90 seconds, wherein the lower the roller speed of the steel plate is, the slower the steel plate advances, the longer the corresponding advancing time is, the temperature balance between the center and the surface of the steel plate is realized, and the transformation of each tissue of a middle-temperature area is promoted through the physical metallurgy process of deformed austenite dislocation recovery and continuous precipitation of microalloy elements, so that a final target tissue is generated, and the purpose of grain refinement is achieved.
Drawings
The technical features of the present invention will be further described with reference to the accompanying drawings and embodiments.
FIG. 1 is a 200-fold enlarged schematic representation of the metallographic structure of a 40mm thick steel plate in example 3.
FIG. 2 is a 500-fold enlarged view of the metallographic structure of a 40mm thick steel plate in example 3.
Detailed Description
The steel plate compositions of the different thickness examples are designed as follows:
the requirements of trace elements are as follows:
and (3) carrying out KR desulfurization, converter, argon station, VD decarburization, LF refining, VD vacuum treatment, continuous casting, casting blank cutting and cooling in heap, casting blank heating, dephosphorization, rolling control and cooling control, and cooling in heap on molten iron to obtain a finished steel plate. The specific production process is as follows:
KR molten iron pretreatment: the desulfurizer uses Mg powder, CaO or Mg powder and CaO, the slag before and after the molten iron arrives at the station must be removed, the thickness of the slag layer on the liquid surface is ensured to be less than or equal to 20mm, the molten iron is stirred and desulfurized by KR to ensure that the S content of the molten iron is less than or equal to 0.005 percent, the desulfurization period is less than or equal to 21min and the desulfurization temperature drop is less than or equal to 20 ℃.
b. Smelting in a converter: smelting by adopting a normal ladle, wherein the S content of molten iron is required to be less than or equal to 0.030%; and (3) converter end point control: the tapping temperature is more than or equal to 1600 ℃, the C is more than or equal to 0.05 percent and less than or equal to 0.08 percent, the P is less than or equal to 0.009 percent, argon is not blown in the tapping process, and any deoxidizer and alloy are not added into the molten steel.
c. An argon station: after the molten steel arrives at the argon station, sampling argon, temporarily forbidding to add alloy, aluminum wires or auxiliary materials into the molten steel, and forbidding to blow argon. The molten steel is directly hoisted to a VD furnace for vacuum treatment, a VD decarburization process is carried out, and the off-station temperature is controlled according to the temperature of more than or equal to 1560 ℃.
VD decarburization: after the molten steel reaches a VD seat, a main operator firstly measures the temperature; then adding a proper amount of iron scale according to the carbon content after argon, wherein the iron scale adding amount is referred as follows:
post argon C/%) <0.04% ≤0.04-0.05% ≥0.05-0.06%
The addition amount of iron scale/Kg 0 40 100
Maintaining the pressure for more than 8min after vacuumizing, improving the argon blowing strength in the pressure maintaining process for improving the decarburization effect, ensuring the diameter of a naked eye to be more than 400mm in a vacuum state, and adding 4.0m/t of aluminum wire after finishing decarburization.
And e, LF refining: low-carbon alloys (low-carbon ferromanganese and low-carbon ferrochromium) are adopted, and high-carbon alloys are strictly forbidden. The slag must turn white or yellow-white after heating, the white slag retention time is more than or equal to 30min, and the final slag after refining is required to be foamed white slag with good fluidity and proper viscosity; and strictly executing a soft argon blowing process, and strictly prohibiting explosion blowing. The deoxidizer is mainly calcium carbide and aluminum particles, the Als in the process is controlled to be 0.010-0.030%, if the Als content in the heated alloy is below 0.015%, an aluminum wire can be added after the alloy is added, and the reference addition amount is controlled according to 2m/t steel. All alloy elements in the refining link are controlled according to target values, and C, Mn prohibits simultaneous lower limit or simultaneous upper limit.
VD degassing: controlling the arrival temperature of the molten steel to be 1610-1615 ℃, and maintaining the pressure in vacuum for 13-16 min, wherein the argon blowing strength must be improved in the pressure maintaining process to ensure that the diameter of a single naked eye is more than 500 mm; ferrotitanium is added at the first time after the air break, and an aluminum wire is added, wherein the aluminum wire is controlled according to the steel of 1.0-1.5 m/t; after the ferrotitanium and the aluminum wire are added, the soft argon blowing time is required to be more than 5 min; the final H content is less than or equal to 1.2ppm, and the VD leaving-station temperature is controlled to be 1565-1570 ℃.
g. Continuous casting: electromagnetic stirring is adopted for continuous casting steel, the casting is protected in the whole process, a protective tube is sleeved 1min after a large ladle is opened, the liquid level of the steel is ensured not to be red in the pouring process of a middle ladle, the argon blowing amount of a stopper rod is reasonably controlled in the steel casting process, and the liquid level fluctuation of a crystallizer is ensured to be slight; the stacking cooling is required to be more than or equal to 24 hours after the casting blank is off-line.
h. And (3) heating the casting blank, wherein the temperature of a preheating section is 850-950 ℃, the temperature of a heating section is 1210-1230 ℃, the temperature of a heat preservation section is 1200-1220 ℃, and the total heating time is controlled according to 10 min/cm.
i. And (3) dephosphorization, namely, rapidly dephosphorizing the cast blank after primary heating and tapping, then reloading the cast blank into a soaking section of a heating furnace for secondary heating, wherein the secondary heating time is 4-6 min, carrying out secondary dephosphorization and rolling on the cast blank after secondary heating, and removing more than 95% of the primary iron sheet on the surface after secondary heating and dephosphorization.
j. Rolling and controlling cold, namely rolling by adopting a double-stand rolling mill under controlled temperature, rapidly feeding and rolling the billet after secondary dephosphorization, wherein the initial rolling temperature of rough rolling is more than or equal to 980 ℃, the steel feeding speed is 1.5m/s, the cumulative reduction rate is more than or equal to 60%, the steel airing thickness is 60-100 mm, the billet enters an IC for cooling after the rough rolling is finished, the water outlet temperature is controlled to be 850-900 ℃, and the billet is subjected to air cooling and temperature equalization on a roller way; the start rolling temperature of finish rolling is controlled to be 810-890 ℃, the finish rolling temperature is controlled to be 790-870 ℃, after finish rolling is finished, the steel wire is slowly moved on a rear roller way for about 40-90S, enters ACC for quick cooling, and the red return temperature is 560-590 ℃.
k. And (4) stacking and cooling, namely, after the steel plate is taken off line, entering a slow cooling pit, wherein the temperature is 350-450 ℃, and the slow cooling time is 24 hours.
48 batches of the 4 embodiments are produced in a co-production mode and controlled according to the process, wherein the yield strength is 452MPa on average, the tensile strength is 565MPa on average, the elongation is 25 percent on average, the impact energy is 216J on average at the temperature of minus 100 ℃, and the weather resistance coefficient I is more than or equal to 6.4; all performance indexes reach, even exceed, the standard of TMCP rolling Q420qENH weather-resistant bridge steel in GB/T714-2015. The mechanical property indexes (average values) of the examples are as follows:
FIGS. 1 and 2 are schematic views of the metallographic structure of a 40mm thick steel plate in example 3, magnified 200 times and 500 times, respectively: more than 70% of quasi-polygonal ferrite, less than 20% of bainite and less than 10% of pearlite, with a grain size of grade 10.
4 examples 48 batches of products were tested for external inspection and flaw detection: the quality control rate of the steel plate is 100%, flaw detection is carried out according to GB/T2970-2004, and all the flaw detection is combined to one level.

Claims (4)

1. The ultra-low temperature weather-resistant bridge steel is characterized by comprising the following chemical components in percentage by mass: c: 0.06-0.08%, Si: 0.20 to 0.35%, Mn: 1.1-1.2%, P is less than or equal to 0.018%, S: less than or equal to 0.005 percent, Als: 0.015-0.035%, Nb: 0.02-0.04%, V: less than or equal to 0.03%, Cu: 0.27 to 0.33%, Cr: 0.40 to 0.50%, Ni: 0.30-0.40%, Ti: less than or equal to 0.02 percent, and the balance of Fe and residual elements;
the steel sheet has a structure containing more than 70% of quasi-polygonal ferrite, less than 20% of bainite, and less than 10% of pearlite;
the carbon equivalent Ceq of the steel plate is less than or equal to 0.43 percent, the yield strength is more than 420MPa, and the impact energy at-100 ℃ is more than or equal to 120J.
2. The ultra-low temperature weather-resistant bridge steel as claimed in claim 1, wherein the thickness of the steel plate is 16-46 mm.
3. The ultra-low temperature weather-resistant bridge steel as claimed in claim 1, wherein when the thickness of the steel plate is less than or equal to 30mm, V is not contained in chemical components; when the thickness of the steel plate is more than 30mm, the content of V is between 0.02 and 0.03 percent.
4. The method for producing ultra-low temperature weather-resistant bridge steel according to claim 1, which is characterized by comprising the following steps: the steel plate is obtained by cleanly smelting molten steel, protecting and casting the whole process of the continuous casting steel casting process, and heating, dephosphorizing, rolling and cooling and heap cooling a casting blank, and the method specifically comprises the following steps:
(1) smelting clean molten steel: KR pretreatment, converter smelting and VD + LF + VD smelting are carried out on the molten iron to obtain clean molten steel; wherein: after the molten iron is stirred and desulfurized by KR, the molten iron S is ensured to be less than or equal to 0.005 percent, the desulfurization period is less than or equal to 21min, and the desulfurization temperature is reduced by less than or equal to 20 ℃; after the smelting in the converter is finished, the tapping temperature is more than or equal to 1560 ℃, the C is more than or equal to 0.05 percent and less than or equal to 0.08 percent, and the P is less than or equal to 0.009 percent; finishing the VD + LF + VD smelting, controlling the temperature of the molten steel leaving the station to be 1565-1570 ℃, and controlling the H content to be less than or equal to 1.2 ppm;
(2) continuous casting: the superheat degree of a tundish is 10-25 ℃, the whole process is protected for casting, a protective pipe needs to be sleeved within 1min after a ladle is cast, the molten steel surface does not turn red in the tundish casting process, the argon blowing amount of a stopper rod is controlled in the steel casting process, and the slight fluctuation of the liquid level of a crystallizer is ensured; the stacking cooling is required to be more than or equal to 24 hours after the casting blank is off-line;
(3) heating a casting blank: the temperature of the preheating section is less than or equal to 950 ℃, the temperature of the heating section is 1210-1230 ℃, the temperature of the heat preservation section is 1200-1220 ℃, and the total heating time is 10-12 min/cm;
(4) and (3) dephosphorization: heating the casting blank, removing phosphorus for the first time, then reloading the casting blank into a heating furnace for secondary heating, wherein the heating temperature is 1200-1220 ℃, the heating time is 4-6 min, and tapping and removing phosphorus again after the secondary heating;
(5) rolling and cooling control: after dephosphorization is carried out on the casting blank, temperature-controlled rolling is carried out immediately; the initial rolling temperature of rough rolling is more than or equal to 980 ℃, the steel feeding speed is 1.5m/S, the accumulated reduction rate is more than or equal to 60%, the steel airing thickness is the thickness of a finished product plus 50-80 mm, and the finished product enters an IC for cooling at the cooling speed of less than or equal to 3 ℃/S; the initial rolling temperature of finish rolling is controlled to be 810-890 ℃, the final rolling temperature is controlled to be 790-870 ℃, the steel plate after final rolling slowly advances for 40-90S on a rear roller way of a rolling mill to enter ACC for rapid cooling, the cooling speed is controlled to be 7-12 ℃/S, and the temperature of red return is 590-630 ℃;
(6) and (3) cooling in a heaped mode: and (3) after the steel plate is taken off line, putting the steel plate into a slow cooling pit for stack cooling, wherein the stack cooling temperature is 350-450 ℃, and the stack cooling time is more than or equal to 24 hours.
CN202010962123.9A 2020-09-14 2020-09-14 Ultralow-temperature weather-resistant bridge steel and production method thereof Pending CN111893402A (en)

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