CN114015848A - Needle-shaped ferrite type high-strength steel bar and preparation method thereof - Google Patents
Needle-shaped ferrite type high-strength steel bar and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
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- 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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
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- 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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/08—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement
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- 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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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Abstract
The invention belongs to the technical field of hot-rolled ribbed steel bars for reinforced concrete structures, and particularly relates to a needle-shaped ferrite type high-strength steel bar and a preparation method thereof. The steel in the steel bar comprises the following chemical components in parts by weight: 0.25-0.35% of C, 0.40-0.80% of Si, 1.40-1.80% of Mn, less than or equal to 0.030% of P, less than or equal to 0.030% of S, 0.02-0.04% of Nb, 0.09-0.15% of V, 0.15-0.45% of Cr, 0.010-0.019% of N, and the balance of Fe and inevitable impurity elements. The invention is prepared by adopting high C, Si and Mn component design and V, Nb combined microalloying mode and combining a rolling self-tempering process under the existing process equipment condition of a production plant, and on the premise of keeping the ductility of the material, 700 MPa-grade steel bars with excellent comprehensive performance are produced, the yield strength is more than or equal to 700MPa, the tensile strength is more than or equal to 830MPa, the elongation after fracture is more than or equal to 14 percent, the total elongation under maximum force is more than or equal to 9 percent, and the invention has good earthquake resistance and meets the requirements of high-rise and large-span earthquake-resistant structures.
Description
Technical Field
The invention belongs to the technical field of hot-rolled ribbed steel bars for concrete, and particularly relates to an acicular ferrite type high-strength steel bar and a preparation method thereof.
Background
Compared with the common reinforcing steel bar, the high-strength reinforcing steel bar has the advantages of high strength, excellent comprehensive performance, energy conservation, environmental protection, long service life, high safety performance and the like. The developed foreign countries have already eliminated the steel bars with lower strength level such as 335MPa, the countries such as English, Germany, Australia and French have widely adopted the high-strength steel bars with 500MPa yield strength, the high-strength steel bars with 600MPa yield strength have also been widely applied, and the high-strength steel bars with 700MPa yield strength are actively developed and popularized. In recent years, with the coming of a series of high-strength steel bar popularization and application policies in China, the percentage of the use amount of the high-strength steel bars is increased year by year. At present, HRB500 high-strength steel bars in China are produced and used in large scale, 600 MPa-level high-strength steel bars in China are successfully researched and developed by a micro-alloying process, and GB/T1499.2-2018 incorporates the 600 MPa-level high-strength steel bars and is formally implemented in 2018, 11 and 1. With the continuous emergence of high-rise and large-span buildings in China and the requirements of national policies of energy conservation and emission reduction and light weight of building steel, the 700 MPa-level high-strength steel bar can be predicted to be the directional development of market demands.
Chinese patent publication No. CN103643167A discloses 'a 700MPa grade green heat treatment high strength steel bar and a processing method thereof', the steel bar comprises the following components: 0.18 to 0.3 percent of C, 0.6 to 0.9 percent of Si and 1.3 to 1.9 percent of Mn; 0.05-0.1% of Cr, 0.01-0.05% of Nb, 0.10-0.20% of V, 0.01-0.03% of Ni, B: 0.002-0.004%, P < 0.023%, S < 0.023%, and the balance Fe. The following disadvantages exist: tempering induction heater heating, grain stabilization treatment and the like, and the process is complex and is not beneficial to the popularization of large-scale industrial production.
Chinese patent publication No. CN103898408A discloses 'a 700 MPa-level screw steel bar and a production method thereof', the steel bar comprises the following components: 0.28-0.32% of C, 0.40-0.80% of Si, 1.20-1.60% of Mn1, 0.18-0.24% of V, 0.02-0.06% of Nb, 0.02-0.10% of Ni and 20-300ppm of N; optional ingredients: 0.001-0.020% of Ti, 0.01-0.05% of Mo and 0.02-0.10% of Cu or the combination of more than two of the components; the balance of Fe and inevitable impurities. The method has the following defects: the N content is too high, so that the defects of subcutaneous bubbles and the like of the continuous casting billet are easily caused, and the plasticity index and the timeliness of the reinforcing steel bar are influenced.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a preparation method of a needle-shaped ferrite type high-strength and high-plasticity hot-rolled ribbed steel bar.
In order to solve the technical problem, the technical scheme is that the preparation method of the needle-shaped ferrite type high-strength steel bar comprises the following steps:
s1, weighing molten iron and scrap steel with the mass ratio of 85:15 as steelmaking raw materials, loading the scrap steel into a steelmaking furnace, then pouring the molten iron, adding 95-105kg/t of slag-making materials, after the charging is finished, inserting an oxygen lance into the furnace from the top of the furnace, blowing in high-pressure oxygen flow with the purity of more than 99.6 percent, enabling the oxygen to directly generate oxidation reaction with the high-temperature molten iron, stopping blowing when the weight content of C in crude molten steel is more than or equal to 0.06 percent, the weight content of P and S is less than or equal to 0.025 percent, and the temperature is 1650-;
s2, the steel ladle enters a refining furnace within 10 minutes after tapping, the temperature of molten steel in the steel ladle is ensured to be more than or equal to 1550 ℃, an electrode starts to heat after the molten steel enters a station, the heating speed is 3-4 ℃/min, the heating time is less than or equal to 15 minutes, wollastonite 0-5.5kg/t of molten steel and lime 2.3-6.5kg/t of molten steel are added, argon is always introduced during the operation period to carry out bottom argon blowing operation, the flow of the argon is subject to slight fluctuation of the molten steel and no slag layer breaking, and refining is stopped when the components of the molten steel reach a set target and the temperature of the molten steel reaches 1550-;
s3, after refining is stopped, the molten steel within less than or equal to 10 minutes flows out of the LF furnace refining station and enters a continuous casting platform to be cast into a steel billet, the steel ladle adopts full-process protection casting in the casting process, the open casting time is not more than 25 seconds, the tundish adopts a quick-change metering nozzle, and the open casting time is not more than 10 seconds when the metering nozzle is changedThe flow rate of the cooling water of the crystallizer is 100-3The cooling specific water amount of the secondary cooling area is 0.5-0.8L/kg, and the diagonal length difference of the billet is less than or equal to 7 mm;
s4, the poured steel billet enters a heating furnace, the steel billet is heated to 1100-plus-1200 ℃ in the heating furnace to form an austenite structure, the temperature is kept for 60-90min to obtain the steel billet for the rolled steel bar, the temperature of the steel billet for the rolled steel bar is reduced to 1050-plus-minus temperature 1150 ℃, then rolling is started, the rolled piece is subjected to rough rolling and intermediate rolling and then enters a water cooling section for first cooling, the surface temperature of the steel billet is cooled to below 850 ℃, the surface temperature of the steel billet is below 850 ℃ after the steel billet leaves the water cooling section, the core 950-plus-minus temperature is 1000 ℃, first self-tempering is generated, the surface temperature is increased to 900-plus-minus 950 ℃, and then finish rolling is carried out to roll the steel bar with the required specification;
s5, cooling the finish-rolled steel bar for the second time, rapidly cooling the surface temperature of the steel bar to 400-450 ℃, then discharging the steel bar from the water cooling section to enter a roller conveyor, performing the second self-tempering on the roller conveyor, and cooling the steel bar in an upper cooling bed when the surface temperature of the steel bar is 750-800 ℃, thus obtaining the acicular ferrite type high-strength steel bar.
The preparation method of the needle-shaped ferrite type high-strength steel bar is further improved as follows:
preferably, the slagging material in step S1 is one or two or more of quicklime, dolomite, and limestone.
Preferably, the steel furnace in step S1 is an electric furnace or a converter.
Preferably, the refining furnace in step S2 is an LF furnace, or a combination of an LF furnace and any one of an RH furnace, a VOD furnace, and a VD furnace.
Preferably, the steel billet in the step S3 comprises the following chemical components in parts by weight: 0.25-0.35% of C, 0.40-0.80% of Si, 1.40-1.80% of Mn, less than or equal to 0.030% of P, less than or equal to 0.030% of S, 0.02-0.04% of Nb, 0.09-0.15% of V, 0.15-0.45% of Cr, 0.010-0.019% of N, and the balance of Fe and inevitable impurity elements.
Preferably, the cross-section of the billet in the step S3 is 150 × 150mm2。
Preferably, in step S3, a protective sleeve is used for full-protection casting, and the protective sleeve is made of quartz.
In order to solve another technical problem, the invention adopts the technical scheme that the needle-shaped ferrite-type high-strength steel bar is prepared by any one of the preparation methods.
Compared with the prior art, the invention has the beneficial effects that:
1) the chemical components of the acicular ferrite high-strength steel bar are designed by adopting V, Nb combined microalloying components, wherein V is added from VN (16) alloy, and N in the VN (16) is added with original N of molten steel (generally 0.0045-0.0065% of N content), so that the N in the steel can meet the content requirement. The microalloying elements V and C, N are utilized to form fine dispersed V (C, N) particles, particularly fine dispersed VN particles, and the strong precipitation strengthening effect is achieved.
The microalloying element Nb in the raw material has the characteristics of larger atom size than Fe, easy segregation on crystal boundary and strong dragging effect on the crystal boundary, and inhibits the recrystallization growth of crystal grains; in addition, interstitial mesophases such as NbC and NbN formed in steel by Nb prevent the migration of sub-grain boundaries during recrystallization, and thus, the steel can strengthen fine grains.
N of the raw material and the microalloying element V, Nb can form fine dispersed and precipitated particles, and the effects of precipitation strengthening and fine grain strengthening are achieved. However, too much N causes age hardening of the steel, and decreases the toughness of the steel.
The addition of Cr to the raw materials can improve the hardenability of steel, refine pearlite structure, have obvious secondary hardening effect, further improve the strength of the steel bar and simultaneously improve the corrosion resistance of the steel bar.
2) According to the invention, micro-alloying component design is adopted, and a rolling self-tempering process is combined, under the condition of the existing process equipment of a steel enterprise, on the premise of keeping the ductility of the material, 700 MPa-grade steel bars with excellent comprehensive performance are produced, the yield strength is more than or equal to 700MPa, the tensile strength is more than or equal to 830MPa, the elongation after fracture is more than or equal to 14%, the total elongation under the maximum force is more than or equal to 9%, the strength of the steel bars is greatly improved, and the ductility index is ensured at the same time.
The heating temperature of the steel billet is controlled to be 1100-plus 1200 ℃, an austenite structure is formed, the steel is tapped and then is cooled for the first time, the surface temperature of the rolled piece after the intermediate rolling is rapidly cooled to be below 850 ℃, the surface of the rolled piece is below 850 ℃ after the rolled piece is taken out of a water cooling section, the core part of the rolled piece is about 1000 ℃, the rolled piece generates the first self-tempering, the heat of the core part of the rolled piece is diffused to the surface, the core part temperature of the rolled piece is reduced, the surface temperature of the rolled piece is increased to 900-plus 950 ℃, and the situation that the austenite structure can not enter a finishing mill for rolling until the austenite structure is too large is ensured. By controlling the temperature of the finishing mill, an acicular ferrite structure is obtained, the strength of the steel bar is greatly improved, and meanwhile, the ductility index of the steel bar is kept.
And after finish rolling, carrying out secondary cooling, after the rolled piece is taken out of a finishing mill, rapidly cooling the surface of the rolled piece to about 450 ℃ and the center of the rolled piece to about 850 ℃, then enabling the rolled piece to enter a conveying roller way, generating secondary self-tempering on the conveying roller way, after the rolled piece reaches a cooling bed, enabling the temperature of the cooling bed on the rolled piece to be 750-plus 800 ℃, and then carrying out tissue transformation on austenite to form an acicular ferrite + pearlite structure, wherein the acicular ferrite structure is a chain structure and has fine grains, so that the acicular ferrite structure has higher strength and ductility.
According to the on-line self-tempering process, the heating temperature of the steel billet is controlled to be 1100-1200 ℃, an austenite structure is formed, and the temperature of the steel billet fed into a finishing mill and the temperature of an upper cooling bed are controlled after tapping, so that the steel bar forms an acicular ferrite structure. Therefore, a temperature control device is arranged behind the intermediate mill group to carry out primary cooling on the rolled piece.
The temperature control device before finish rolling is divided into two sections, wherein one section is a cooling section, and the surface temperature of a rolled piece after intermediate rolling is rapidly cooled to below 850 ℃; the first section is a temperature recovery section, after the rolled piece exits from the water cooling section, the surface is below 850 ℃, the core is about 1000 ℃, the rolled piece generates the first self-tempering, the heat of the core is diffused to the surface, the core temperature is reduced, the surface temperature is increased to 900-950 ℃, and the situation that the austenite structure enters the finishing mill for rolling in short time is ensured. In order to obtain an acicular ferrite structure, the finish rolling is followed by secondary cooling.
The finishing mill is provided with a quick cooling device at the rear part, and secondary cooling is carried out on the rolled piece. After the rolled piece is taken out of the finishing mill, the surface of the rolled piece is rapidly cooled to about 450 ℃, the center of the rolled piece is about 850 ℃, then the rolled piece enters a conveying roller way, secondary self-tempering is generated on the conveying roller way, the temperature of the cooling bed on the rolled piece reaches 750-plus 800 ℃ after the rolled piece reaches the cooling bed, then austenite is subjected to tissue transformation to form an acicular ferrite + pearlite structure, and the acicular ferrite structure is a chain structure and has fine grains, so that the high strength and ductility are realized.
The invention selects an electric furnace or a converter as a steelmaking furnace, adopts and carries out ladle refining by an LF furnace, and finally continuously casts the steel billet into 150 or other steel billets, which can be realized by most domestic manufacturers and is suitable for large-scale popularization.
The invention adopts the microalloying and rolling on-line self-tempering process, does not need to increase equipment, and can realize mass industrial production under the condition of the existing process equipment of a steel enterprise to meet the requirements of high-rise and large-span building structures in China.
Drawings
FIG. 1 is a metallographic structure of a steel bar sample prepared in example 1 of the present invention, with a scale of 500nm, in which: the black structure is pearlite, the white structure is acicular ferrite, and the grain size of the ferrite is 9.0 grade.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to embodiments, and all other embodiments obtained by a person of ordinary skill in the art without any creative effort based on the embodiments of the present invention belong to the protection scope of the present invention.
Example 1
The embodiment provides an acicular ferrite type high-strength steel bar and a preparation method thereof, and the preparation method comprises the following steps:
s1, 85% of molten iron and 15% of scrap steel, and the final molten steel component is 0.06% C, and the final molten steel temperature is 1650 ℃;
s2, after the ladle enters an LF furnace refining station, the time of charging is 7 minutes, the temperature of molten steel in the ladle is 1550 ℃, the electrode temperature rise time is 15 minutes, wollastonite 0kg/t molten steel and 6.5kg/t molten steel of lime are added, the components of the molten steel reach the target values, and the temperature is 1550 ℃;
s3, pouring molten steel from the refining station of the LF furnace to the continuous casting table for 10 minutes, opening the ladle for 25 seconds, opening the tundish for 10 seconds when the metering nozzle of the tundish is changed, and cooling water flow of the crystallizer：100m3The cooling specific water amount of the secondary zone is as follows: 0.5L/kg, and the diagonal length difference of the poured billet is 7mm, so as to obtain the billet for rolling the steel bar, wherein the chemical components of the billet are as follows by weight: 0.25% of C, 0.80% of Si, 1.80% of Mn, 0.024% of P, 0.014% of S, 0.15% of V, 0.02% of Nb, 0.15% of Cr, 0.019% of N, and the balance of Fe and inevitable impurity elements;
s4, heating in a heating furnace to 1100 ℃, preserving heat for 90min, cooling a steel billet to 1050 ℃, feeding the rolled piece into a water cooling section after intermediate rolling, cooling the surface temperature of the steel billet to 800 ℃, performing first self tempering after the steel billet exits the water cooling section, increasing the surface temperature to 900 ℃, then performing finish rolling, rolling into a steel bar with required specification, performing second cooling on the steel bar after finish rolling, cooling the surface to 400 ℃, performing second self tempering on a conveying roller way, and controlling the surface temperature of the steel bar after the steel bar is fed into a cooling bed to 750 ℃. A reinforcing bar sample 1 was prepared.
Example 2
The embodiment provides an acicular ferrite type high-strength steel bar and a preparation method thereof, and the preparation method comprises the following steps:
s1, 85% of molten iron and 15% of scrap steel, and the final molten steel components are 0.07% of C, and the final molten steel temperature is 1665 ℃;
s2, after the ladle enters an LF furnace refining station, the time of charging is 6 minutes, the temperature of molten steel in the ladle is 1560 ℃, the temperature rise time is 14 minutes, 2.75kg/t of wollastonite molten steel and 4.4kg/t of lime are added, the components of the molten steel reach the target value, and the temperature is 1560 ℃;
s3, pouring molten steel from an LF refining station to a continuous casting table for 9 minutes, opening a ladle for pouring for 23 seconds, opening a metering nozzle of a tundish for pouring for 9 seconds, and cooling water flow of a crystallizer: 115m3The cooling specific water amount of the secondary zone is as follows: 0.65L/kg, and the difference of the diagonal lengths of the cast billets is 6mm, so as to obtain the billets for rolling the steel bars, wherein the chemical compositions of the billets are as follows by weight: 0.30% of C, 0.60% of Si, 1.60% of Mn, 0.022% of P, 0.013% of S, 0.12% of V, 0.03% of Nb, 0.30% of Cr, 0.015% of N, and the balance of Fe and inevitable impurity elements;
s4, heating the steel billet in a heating furnace to 1150 ℃, preserving heat for 75min, cooling the steel billet to 1100 ℃, enabling the rolled piece to enter a water cooling section after intermediate rolling, rapidly cooling the surface temperature of the steel billet to 825 ℃, performing first self-tempering after the steel billet exits the water cooling section, increasing the surface temperature to 925 ℃, then performing finish rolling, rolling the steel billet into a steel bar with required specification, performing second cooling on the steel bar after finish rolling, rapidly cooling the surface temperature of the steel bar to 425 ℃, performing second self-tempering on a conveying roller bed, and enabling the surface temperature of the steel bar after the steel bar is fed into a cooling bed to be 775 ℃. Reinforcing bar sample 2 was prepared.
Example 3
The embodiment provides an acicular ferrite type high-strength steel bar and a preparation method thereof, and the preparation method comprises the following steps:
s1, 85% of molten iron and 15% of scrap steel, and the final molten steel components are 0.08% C, and the final molten steel temperature is 1680 ℃;
s2, after the ladle enters an LF furnace refining station, the time of charging is 5 minutes, the temperature of molten steel in the ladle is 1570 ℃ for 13 minutes, 5.5kg/t of wollastonite and 2.3kg/t of lime are added into the molten steel, the components of the molten steel reach the target values, and the temperature is 1570 ℃;
s3, the casting time of molten steel from the refining station of the LF furnace to the continuous casting table is 8 minutes, the open casting time of a ladle is 21 seconds, the open casting time of a tundish is 8 seconds when a fixed-diameter water gap is changed, and the flow rate of cooling water of a crystallizer is as follows: 130m3H, the cooling specific water amount of the secondary zone is 0.8L/kg, the diagonal length difference of the cast steel billet is 5mm, and the steel billet for rolling the steel bar is obtained, wherein the chemical components of the steel billet are as follows by weight: 0.35% of C, 0.40% of Si, 1.80% of Mn, 0.022% of P, 0.013% of S, 0.09% of V, 0.04% of Nb, 0.45% of Cr, 0.010% of N, and the balance of Fe and inevitable impurity elements;
s4, heating the steel billet in a heating furnace to 1200 ℃, preserving heat for 60min, cooling the steel billet to 1150 ℃, feeding the rolled piece into a water cooling section after intermediate rolling, rapidly cooling the surface temperature of the steel billet to 850 ℃, performing first self-tempering after the steel billet exits the water cooling section, increasing the surface temperature to 950 ℃, then performing finish rolling, rolling to obtain the steel bar with required specification, performing second cooling on the steel bar after finish rolling, rapidly cooling the surface temperature of the steel bar to 450 ℃, then feeding the steel bar out of the water cooling section into a conveying roller way, and after second self-tempering is performed on the conveying roller way, feeding the steel bar on a cooling bed to 800 ℃. A reinforcing bar sample 3 was prepared.
The parameters of the low-temperature rolling process of the embodiment of the invention are shown in table 1.
TABLE 1 Low temperature Rolling Process parameters for the examples of the invention
The steel bar samples prepared in examples 1 to 3 were subjected to performance tests, and the metallographic structure is shown in fig. 1, and it can be seen from fig. 1 that the grain size of the steel bar is grade 10, and the structure of the steel bar is ferrite and pearlite. And the acicular ferrite has a chain structure and fine grains, so that the steel bar has higher strength and ductility.
The mechanical properties of the examples of the invention are shown in Table 2.
TABLE 2 mechanical Properties of the examples of the invention
Wherein: reLIs the yield strength; rmIs tensile strength; a is elongation after fracture; a. thegtElongation at maximum force. The technical requirement that the mechanical property reaches 700MPa grade high-strength anti-seismic steel bar is demonstrated.
The test results in Table 3 show that 700 MPa-grade steel bars with excellent comprehensive performance are produced by V, Nb composite microalloying component design and a rolling self-tempering process under the condition of the existing process equipment of steel enterprises and on the premise of keeping the ductility of the material, the yield strength is more than or equal to 700MPa, the tensile strength is more than or equal to 830MPa, the elongation after fracture is more than or equal to 14%, the total elongation under the maximum force is more than or equal to 9%, and the mechanical property technical requirements of the 700 MPa-grade high-strength anti-seismic steel bars can be met.
It should be understood by those skilled in the art that the foregoing is only illustrative of several embodiments of the invention, and not of all embodiments. It should be noted that many variations and modifications are possible to those skilled in the art, and all variations and modifications that do not depart from the gist of the invention are intended to be within the scope of the invention as defined in the appended claims.
Claims (8)
1. The preparation method of the needle-shaped ferrite high-strength steel bar is characterized by comprising the following steps of:
s1, weighing molten iron and scrap steel with the mass ratio of 85:15 as steelmaking raw materials, loading the scrap steel into a steelmaking furnace, then pouring the molten iron, adding 95-105kg/t of slag-making materials, after the charging is finished, inserting an oxygen lance into the furnace from the top of the furnace, blowing in high-pressure oxygen flow with the purity of more than 99.6 percent, enabling the oxygen to directly generate oxidation reaction with the high-temperature molten iron, stopping blowing when the weight content of C in crude molten steel is more than or equal to 0.06 percent, the weight content of P and S is less than or equal to 0.025 percent, and the temperature is 1650-;
s2, the steel ladle enters a refining furnace within 10 minutes after tapping, the temperature of molten steel in the steel ladle is ensured to be more than or equal to 1550 ℃, an electrode starts to heat after the molten steel enters a station, the heating speed is 3-4 ℃/min, the heating time is less than or equal to 15 minutes, wollastonite 0-5.5kg/t of molten steel and lime 2.3-6.5kg/t of molten steel are added, argon is always introduced during the operation period to carry out bottom argon blowing operation, the flow of the argon is subject to slight fluctuation of the molten steel and no slag layer breaking, and refining is stopped when the components of the molten steel reach a set target and the temperature of the molten steel reaches 1550-;
s3, after the refining is stopped, the molten steel is discharged from the LF refining station and enters a continuous casting platform within 10 minutes or less, a steel billet is cast, the steel ladle adopts full-process protection casting in the casting process, the open casting time is not more than 25 seconds, the tundish adopts a quick-change sizing nozzle, the open casting time is not more than 10 seconds when the sizing nozzle is changed, the flow of the cooling water of the crystallizer is 100-130m3The cooling specific water amount of the secondary cooling area is 0.5-0.8L/kg, and the diagonal length difference of the billet is less than or equal to 7 mm;
s4, the poured steel billet enters a heating furnace, the steel billet is heated to 1100-plus-1200 ℃ in the heating furnace to form an austenite structure, the temperature is kept for 60-90min to obtain the steel billet for the rolled steel bar, the temperature of the steel billet for the rolled steel bar is reduced to 1050-plus-minus temperature 1150 ℃, then rolling is started, the rolled piece is subjected to rough rolling and intermediate rolling and then enters a water cooling section for first cooling, the surface temperature of the steel billet is cooled to below 850 ℃, the surface temperature of the steel billet is below 850 ℃ after the steel billet leaves the water cooling section, the core 950-plus-minus temperature is 1000 ℃, first self-tempering is generated, the surface temperature is increased to 900-plus-minus 950 ℃, and then finish rolling is carried out to roll the steel bar with the required specification;
s5, cooling the finish-rolled steel bar for the second time, rapidly cooling the surface temperature of the steel bar to 400-450 ℃, then discharging the steel bar from the water cooling section to enter a roller conveyor, performing the second self-tempering on the roller conveyor, and cooling the steel bar in an upper cooling bed when the surface temperature of the steel bar is 750-800 ℃, thus obtaining the acicular ferrite type high-strength steel bar.
2. The method for preparing an acicular ferrite type high-strength steel bar according to claim 1, wherein the slagging material in step S1 is one or two or more of quicklime, dolomite, and limestone.
3. The method for producing the acicular ferrite-type high-strength steel bar according to claim 1, wherein the steel-making furnace of step S1 is an electric furnace or a converter.
4. The method of claim 1, wherein the refining furnace in step S2 is an LF furnace, or a combination of an LF furnace and any one of an RH furnace, a VOD furnace, and a VD furnace.
5. The method for preparing the acicular ferrite type high-strength steel bar according to claim 1, wherein the billet in the step S3 comprises the following chemical components in parts by weight: 0.25-0.35% of C, 0.40-0.80% of Si, 1.40-1.80% of Mn, less than or equal to 0.030% of P, less than or equal to 0.030% of S, 0.02-0.04% of Nb, 0.09-0.15% of V, 0.15-0.45% of Cr, 0.010-0.019% of N, and the balance of Fe and inevitable impurity elements.
6. The method for producing an acicular ferrite-type high-strength reinforcing steel bar according to claim 1,the cross section of the billet in the step S3 is 150 x 150mm2。
7. The method for preparing the acicular ferrite-type high-strength steel bar according to claim 1, wherein the step S3 is performed by using a protective sleeve for full-process protective casting, wherein the protective sleeve is made of quartz.
8. An acicular ferrite-type high-strength reinforcing steel bar obtained by the process according to any one of claims 1 to 7.
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| CN115233104A (en) * | 2022-07-28 | 2022-10-25 | 宁夏钢铁(集团)有限责任公司 | HRB400E anti-seismic steel bar and processing technology thereof |
| CN115652202A (en) * | 2022-10-21 | 2023-01-31 | 陕钢集团产业创新研究院有限公司 | 700 MPa-grade high-strength low-yield-ratio hot-rolled steel bar and production method thereof |
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