CN115852248B - V-Nb composite microalloyed 650 MPa-level anti-seismic steel bar and production method thereof - Google Patents
V-Nb composite microalloyed 650 MPa-level anti-seismic steel bar and production method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 127
- 239000010959 steel Substances 0.000 title claims abstract description 127
- 239000002131 composite material Substances 0.000 title claims abstract description 26
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 24
- 238000005096 rolling process Methods 0.000 claims abstract description 46
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 35
- 238000001816 cooling Methods 0.000 claims abstract description 32
- 238000000034 method Methods 0.000 claims abstract description 20
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 17
- 238000005266 casting Methods 0.000 claims abstract description 16
- 238000007670 refining Methods 0.000 claims abstract description 14
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 12
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 12
- 229910001562 pearlite Inorganic materials 0.000 claims abstract description 11
- 239000012535 impurity Substances 0.000 claims abstract description 8
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 7
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 7
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 6
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 28
- 229910052786 argon Inorganic materials 0.000 claims description 14
- 238000009749 continuous casting Methods 0.000 claims description 11
- 238000003723 Smelting Methods 0.000 claims description 10
- 238000010438 heat treatment Methods 0.000 claims description 10
- 239000000203 mixture Substances 0.000 claims description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims description 5
- 235000011941 Tilia x europaea Nutrition 0.000 claims description 5
- 239000004571 lime Substances 0.000 claims description 5
- 238000005452 bending Methods 0.000 claims description 3
- 239000000498 cooling water Substances 0.000 claims description 3
- 238000002791 soaking Methods 0.000 claims description 3
- 229910052882 wollastonite Inorganic materials 0.000 claims description 3
- 239000010456 wollastonite Substances 0.000 claims description 3
- 239000002344 surface layer Substances 0.000 abstract description 9
- 239000002893 slag Substances 0.000 abstract description 4
- 230000000052 comparative effect Effects 0.000 description 23
- 239000000047 product Substances 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 6
- 238000007664 blowing Methods 0.000 description 6
- 238000013461 design Methods 0.000 description 6
- 239000006104 solid solution Substances 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 230000001276 controlling effect Effects 0.000 description 5
- 230000003111 delayed effect Effects 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 229910001563 bainite Inorganic materials 0.000 description 4
- 239000003795 chemical substances by application Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- PNXOJQQRXBVKEX-UHFFFAOYSA-N iron vanadium Chemical compound [V].[Fe] PNXOJQQRXBVKEX-UHFFFAOYSA-N 0.000 description 4
- 238000001953 recrystallisation Methods 0.000 description 4
- 238000010079 rubber tapping Methods 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 229910000628 Ferrovanadium Inorganic materials 0.000 description 3
- 229910001294 Reinforcing steel Inorganic materials 0.000 description 3
- SKKMWRVAJNPLFY-UHFFFAOYSA-N azanylidynevanadium Chemical compound [V]#N SKKMWRVAJNPLFY-UHFFFAOYSA-N 0.000 description 3
- 238000011161 development Methods 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000011150 reinforced concrete Substances 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 238000005728 strengthening Methods 0.000 description 3
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 3
- 229910000720 Silicomanganese Inorganic materials 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000004567 concrete Substances 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000010410 layer Substances 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 230000002787 reinforcement Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 description 1
- 238000004873 anchoring Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000006477 desulfuration reaction Methods 0.000 description 1
- 230000023556 desulfurization Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000003014 reinforcing effect Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Classifications
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- 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
Abstract
The invention provides V-Nb composite microalloyed 650 MPa-level anti-seismic steel bars and a production method thereof, wherein the components are as follows: 0.25 to 0.29 percent of C, 0.55 to 0.80 percent of Si,1.40 to 1.60 percent of Mn, 0.150 to 0.190 percent of V, 0.015 to 0.035 percent of Nb, 0.021 to 0.030 percent of N, less than or equal to 0.030 percent of P, less than or equal to 0.030 percent of S, and the balance of Fe and other unavoidable impurities. In the production process, the LF furnace refining adopts a low-alkalinity slag system, so that the purity and the castability of molten steel are improved; the small square billet adopts a low casting speed and weak cooling process to obtain a small square billet with high surface quality; after rolling, the cooling speed is controlled, so that a surface acicular ferrite, a core ferrite and pearlite microstructure is obtained, and the steel bar has good toughness performance; the thickness of acicular ferrite on the surface layer of the steel bar is adjusted through the cooling speed after rolling, the strength-to-deflection ratio of the steel bar is improved, and the requirement of high strength and earthquake resistance is met.
Description
Technical Field
The invention belongs to the field of alloys, and particularly relates to a V-Nb composite microalloyed 650 MPa-level anti-seismic steel bar and a production method thereof.
Background
The Europe is in a part of countries other than earthquake zones, the ductility requirement on the steel bars is not high, and high-strength steel bars with the pressure of 500MPa or more are mostly adopted. The ASTM A615-2015, ASTM A706-2014 and ACI318-2014 formulated by the concrete society of materials and test are all used as the current steel bar use standard; wherein, ASTM A615-2015 divides the plain carbon round bar and the ribbed carbon bar into 40 grade (280 MPa), 60 grade (420 MPa), 75 grade (520 MPa) and 80 grade (550 MPa) according to the intensity, and mainly recommends 60 grade and more. Since 2004, korea has been devoted to the development of ultra-high strength anti-seismic bars of 800MPa and 1000MPa levels, and has gradually solved the problems of construction process, connection anchoring, crack control, etc. in the application. In japan, in order to improve the earthquake-resistant performance of buildings, ultra-high strength steel bars of the order of yield strength 685 to 1275MPa have been developed and used for the construction of high-rise buildings. The current industry development trend is to phase out low-strength steel bars, develop, upgrade and gradually popularize steel bars with high strength, low temperature resistance, corrosion resistance and other comprehensive properties.
The national standard of the 2 nd part hot rolled ribbed steel bars of reinforced concrete steel, which is formally implemented in 11.1.2018, is GB/T1499.2-2018, the HRB600 is incorporated, and the market application prospect of the high-strength steel bars of 600MPa and above is wide along with the research and development and the exemplary application of the high-strength steel bars of 600 MPa.
Modern building structures are developing towards super high-rise and large span, and the bearing capacity of the structures is remarkably improved because the strength of high-strength steel bars is far higher than that of common steel bars. For reinforced concrete high-rise buildings, the cross-sectional area of the reinforced concrete high-rise buildings can be reduced on the premise of unchanged bearing capacity by using the high-strength reinforcing steel bars, so that the dead weight of the building structure is reduced, the load born by a structural foundation is further reduced, and meanwhile, the clean space of the structure can be effectively increased.
The design value of the tensile strength of the 650 MPa-level high-strength steel bar is 820MPa, which is higher than 51% of the design value of the tensile strength of the 400 MPa-level steel bar, and is 540MPa, the strength performance is excellent, the 400 MPa-level steel bar is replaced in a large-span member (bent and pulled), a large-eccentric compression member and a member with larger live load, a large amount of steel can be saved, the problems of fat beam and column and the like in a building structure can be solved, the use area of the building is increased, the structural design is more reasonable, the use function of the building is improved, and the environment-friendly and economic and social benefits are obvious.
With the improvement of the strength of the steel bars, the anti-seismic performance is more difficult to realize, and China belongs to multi-seismic countries, and has great demands on the anti-seismic performance of the steel bars, at present, the related reports and patents of the high-strength anti-seismic steel bars at 600MPa and 635MPa are available, and the related reports and patents of the high-strength anti-seismic steel bars at 650MPa are not available.
Publication number CN 114015848A, publication date 2022.2.8: the invention relates to an acicular ferrite type high-strength steel bar and a preparation method thereof. The steel in the steel bar comprises the following chemical components in 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 unavoidable impurity elements. According to the invention, under the existing technological equipment conditions of a production plant, a high C, si and Mn component design and V, nb combined microalloying mode is adopted, and the rolling self-tempering technology is combined to prepare the steel bar with excellent comprehensive performance, the yield strength is more than or equal to 700MPa, the tensile strength is more than or equal to 830MPa, the elongation after breaking is more than or equal to 14%, the total elongation under the maximum force is more than or equal to 9%, the steel bar has good anti-seismic performance, and the requirements of high-rise and large-span anti-seismic structures are met. The strength of the steel bar produced by the method is high, but the strength-to-yield ratio performance is not described, and the strength-to-yield ratio is smaller than 1.25 from the implementation effect.
The invention provides an N-reinforced high-strength anti-seismic steel bar and a production method thereof, wherein the publication number of the N-reinforced high-strength anti-seismic steel bar is CN 111850395A, and the publication date of the N-reinforced high-strength anti-seismic steel bar is 2020, 10 and 30. The steel bar comprises the following chemical components in percentage by weight: c:0.20% -0.26%, si:0.40% -0.80%, mn:1.00% -1.60%, V:0.05% -0.12%, nb:0.01% -0.02%, N:0.036% -0.06%, and the balance of Fe and unavoidable impurities; wherein the relation [ C ]/[ V ] is more than or equal to 2.5 and [ V ]/[ N ] is less than or equal to 4.0; the production method comprises an electric furnace or converter smelting process, a refining process, a continuous casting process, a billet heating process, a continuous rolling process and a cooling bed cooling process which are sequentially executed; in the heating procedure, the heating temperature is 1200-1280 ℃; in the cooling process of the cooling bed, the upper cooling bed temperature is more than 1120 ℃, and the cooling speed of the cooling bed is less than or equal to 1.5 ℃/s. The invention not only realizes reinforcement of the steel bar by improving the content of N element, but also avoids the problem of plasticity easily caused by N reinforcement, and the product has high strength and shock resistance, low cost and realizes the technical development of the N reinforced high-strength steel bar. The steel bars produced by the method belong to the 630MPa level and can not reach the 650MPa level.
The prior art does not reach 650MPa grade steel bars with a strength to deflection ratio greater than 1.25.
Disclosure of Invention
The invention aims to provide a V-Nb composite microalloying 650 MPa-level anti-seismic steel bar and a production method thereof, wherein the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar can be used for manufacturing anti-seismic steel bars with the normal temperature yield strength of more than 670MPa by obtaining a surface acicular ferrite, core ferrite and pearlite microstructure according to components and production process.
The specific technical scheme of the invention is as follows:
a V-Nb composite microalloying 650 MPa-level anti-seismic steel bar comprises the following components in percentage by mass: 0.25 to 0.29 percent of C, 0.55 to 0.80 percent of Si,1.40 to 1.60 percent of Mn, 0.150 to 0.190 percent of V, 0.015 to 0.035 percent of Nb, 0.021 to 0.030 percent of N, less than or equal to 0.030 percent of P, less than or equal to 0.030 percent of S, and the balance of Fe and other unavoidable impurities.
The V-Nb composite microalloying 650 MPa-level anti-seismic steel bar has the components meeting Ceq less than or equal to 0.58 percent, and Ceq=C+Mn/6+ (Cr+V+Mo)/5+ (Cu+Ni)/15;
the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar has an A value of more than or equal to 1.7 and less than or equal to 2.6; a value= (0.27 x [ V ] +0.15 x [ Nb ])/[ N ]. The proper nitrogen content in the steel is controlled, the precipitation strengthening and precipitation strengthening effects of microalloying elements V and Nb in the steel can be fully exerted, and meanwhile, the plasticity of the steel is prevented from being reduced due to the excessively high nitrogen content.
Each element in the formula expresses the content of the element in the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar by 100;
the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar has acicular ferrite on the surface and acicular ferrite on the surface layer with the tissue thickness of 100-350 mu m; a core ferrite + pearlite microstructure;
the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar has normal-temperature mechanical properties: yield strength R eL More than or equal to 670MPa, tensile strength R m Not less than 850MPa, and strong-bending ratio R m /R eL More than or equal to 1.27, the elongation A after breaking is more than or equal to 18 percent, and the maximum force total elongation A gt ≥9.5％。
The invention provides a production method of V-Nb composite microalloyed 650 MPa-level anti-seismic steel bars, which comprises the following process flows:
batching, converter smelting, LF furnace refining, billet continuous casting, heating, bar rolling mill rolling, controlled cooling, steel bar finished product, bundling and warehousing.
The converter smelting comprises the following steps: controlling the end point C of the converter to be 0.06-0.15%, wherein P is less than or equal to 0.020%; adding lime during tapping 1/5 molten steel, and adding deoxidizing agent and alloy during tapping 1/3, wherein the sequence is as follows: slag material, silicomanganese, vanadium nitrogen and ferrovanadium, and carburant.
Refining in the LF furnace: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding lime and wollastonite for slagging, wherein the alkalinity is R1.2-1.8, the slagging time is more than or equal to 10 minutes, and adding alloy for adjusting Si, mn, V, nb before and during refining according to the analysis result of the components before entering an LF furnace. And (5) carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 10min.
And (3) continuously casting the small square billets: the whole-course protection casting is adopted, a protection sleeve and an argon seal are adopted between a ladle and a tundish, the tundish is protected by using a molten steel covering agent and argon blowing, a submerged nozzle is adopted between the tundish and a crystallizer, and a primary cooling and secondary cooling combined mode is adopted. Wherein the primary cooling water flow is 105-120 m 3 And/h, the secondary cooling specific water quantity is 0.4-0.50 l/kg, the superheat degree is 15-35 ℃, the drawing speed is 1.9-2.3 m/min, the casting process is stable in liquid level, drawing speed and superheat degree, and the defect-free casting blank is obtained.
And (3) rolling the bar: the invention can realize the rolling of the steel bar with phi 12-32mm, and in order to meet the requirement of the rolling process and enable the carbon and nitride of V, nb to be dissolved in austenite in a solid solution way, the steel bar is firstly heated, the heating temperature is controlled to 1150-1250 ℃, the soaking time is more than 25min, and the full solid solution of Nb and V elements is ensured. The heated casting blank enters a continuous rolling unit for rolling, the initial rolling temperature is 1000-1100 ℃, the rolling is completed in an austenite recrystallization region to realize recrystallization refinement, the final rolling temperature is 980-1100 ℃, the higher final rolling temperature ensures the uniformity of component tissues, the casting blank is cooled by passing water after rolling, the cooling speed after rolling is 15.0-23.5 ℃/s, the casting blank is cooled to 830-900 ℃, the surface layer acicular ferrite tissues are obtained, and the thickness of the surface layer acicular ferrite tissues is 100-350 mu m. And then the steel is naturally cooled to normal temperature by a cooling bed, so that the toughness and the strength-to-flexibility ratio of the steel are improved.
The design idea of the invention is as follows:
c: the C element is necessary for obtaining high strength and hardness. In order to obtain high strength required at 650MPa, the C content is required to be 0.25% or more, but too high C content greatly increases the density of movable dislocation in the steel, affecting the toughness of the steel, and thus, the C content in the steel is properly increased. The C content is preferably controlled to be 0.25-0.29%.
Si: si is the main deoxidizing element in steel and is used as solid solution hardening element to improve strength, but Si can obviously improve deformation resistance of steel, and excessive Si content reduces plasticity and toughness of steel, increases activity of C and reduces oxygen content in steel. Therefore, the Si content is controlled to be 0.55-0.80%.
Mn: mn is an effective element for deoxidation and desulfurization, and can also improve the strength of steel. However, too high Mn content results in too high residual austenite content after transformation, and too low bainite transformation temperature results in too low yield strength and yield ratio of the steel. Thus controlling the Mn content to be 1.40-1.60%.
V: v is an excellent deoxidizer for steel, and vanadium is added into the steel to refine structure grains and improve strength and toughness. V forms V (C, N) precipitated phase with N, C element in steel, has stronger precipitation strengthening effect, but because the bainite transformation temperature is lower, V diffusion is restrained in the transformation process, so that a large amount of V is solid-solved in the steel, but because V is a strong carbide forming element, the solid-solved V can obviously play a role in refining ferrite, thereby ensuring high yield ratio, vanadium carbonitride has stronger trap energy, can trap hydrogen to uniformly disperse in crystal, restrain hydrogen diffusion and grain boundary segregation, and further improve the delayed fracture resistance of the steel. The V content is too high and the cost is high, so the V content is controlled to be 0.15-0.19%.
Nb: the Nb element can obviously refine grains, and the grain refinement not only can improve the toughness of the steel, but also can improve the delayed fracture resistance of the high-strength steel, and can also improve the corrosion resistance because the grains are finer. The Nb content cannot be too high, and too high Nb promotes bainite transformation, resulting in an increase in the bainite content and a decrease in the plasticity of the steel. Therefore, the range of Nb can be controlled to be 0.015 to 0.035%.
S and P: impurity elements such as S, P are aggregated at grain boundaries, so that the delayed fracture resistance is greatly reduced. The P element can form micro segregation when molten steel is solidified, and then the P element is biased to a grain boundary when heated at an austenitizing temperature, so that the brittleness of the steel is obviously increased, the delayed fracture sensitivity of the steel is increased, and particularly the low-temperature performance is influenced; the S element forms Mn S inclusion and segregation in grain boundary, so that the delayed fracture sensitivity of the steel is increased, and therefore, the content of P, S is controlled to be less than or equal to 0.030% of P and less than or equal to 0.030% of S.
N: n precipitates V (C, N) and Nb (C, N) in steel, the strength of the steel can be obviously improved, but too high N content can deteriorate the strength-to-yield ratio performance of the steel, so that proper N content is the key for ensuring the strength-to-yield ratio performance of high-strength steel bars, and the N content is determined according to the V and Nb content of the steel, and is required to be 1.7-A= (0.27-V+0.15-Nb) V/N-2.6. The A value is ensured to meet the requirement by controlling the proportion of vanadium nitrogen and vanadium iron.
The invention aims to solve the problems that 650MPa grade steel bars have low strength-to-deflection ratio and cannot meet the requirement of anti-seismic performance, and the microstructure of acicular ferrite, core ferrite and pearlite on the surface is obtained through the designed components and process, so that the purposes of high strength and anti-seismic performance are achieved, and the concrete steps are as follows: (1) appropriately increasing the C content and Mn content to increase the strength; (2) The V-Nb composite microalloying is adopted to refine the original austenite grain size, so that the strength is improved, the toughness is improved, and the solid solution V is fully utilized to inhibit C diffusion so as to refine the ferrite size, thereby ensuring high strength and toughness and high strength-to-deflection ratio.
Compared with the prior art, the V-Nb composite microalloying composition design is adopted, so that the purposes of high strength and high toughness are realized; in the production process, the LF furnace refining adopts a low-alkalinity slag system, so that the purity and the castability of molten steel are improved; the small square billet adopts low casting speed and weak cooling process to obtain small square billet with high surface quality, and the surface quality of the steel bar is greatly improved. The best matching of N and V, nb contents in the steel is controlled, so that the strength-to-deflection ratio performance of the steel bar is improved. The ratio of vanadium to nitrogen to ferrovanadium is controlled to ensure that the N content in the steel meets the requirement that A= (0.27 x [ V ] +0.15 x [ Nb ])/[ N ] < 2.6, and the control is stable and the operation is simple; the V-Nb composite microalloying component is combined with a certain cooling speed after rolling to obtain a surface acicular ferrite, core ferrite and pearlite microstructure, so that the steel bar has good toughness performance; the cooling speed after rolling is controlled to be 15.0-23.5 ℃/s, so as to obtain the acicular ferrite structure of the surface layer, and the thickness of the acicular ferrite structure of the surface layer is 100-350 mu m. The produced high-strength anti-seismic steel bar has 650MPa strength performance and anti-seismic performance (the strength-to-deflection ratio is more than or equal to 1.27).
Drawings
Fig. 1 shows the surface microstructure of the steel bar according to the present invention;
fig. 2 shows acicular ferrite structure on the surface of the steel bar according to the invention;
fig. 3 shows a ferrite + pearlite structure in the core of the reinforcing steel bar according to the present invention.
Detailed Description
Example 1 to example 5
A V-Nb composite microalloying 650 MPa-grade anti-seismic steel bar is shown in Table 1, and the balance which is not shown in Table 1 is Fe and unavoidable impurities.
Comparative example 1-comparative example 5
A V-Nb composite microalloying 650 MPa-grade anti-seismic steel bar is shown in Table 1, and the balance which is not shown in Table 1 is Fe and unavoidable impurities.
TABLE 1 chemical composition (wt%) of the examples of the invention
| Case (B) | C | Si | Mn | V | Nb | N | P | S | Ceq | A value |
| Example 1 | 0.27 | 0.75 | 1.55 | 0.163 | 0.023 | 0.0271 | 0.030 | 0.021 | 0.56 | 1.8 |
| Example 2 | 0.27 | 0.78 | 1.52 | 0.169 | 0.015 | 0.0215 | 0.027 | 0.019 | 0.56 | 2.2 |
| Example 3 | 0.28 | 0.73 | 1.56 | 0.181 | 0.021 | 0.0234 | 0.029 | 0.018 | 0.58 | 2.2 |
| Example 4 | 0.27 | 0.76 | 1.54 | 0.185 | 0.022 | 0.0210 | 0.024 | 0.022 | 0.56 | 2.5 |
| Example 5 | 0.28 | 0.77 | 1.55 | 0.190 | 0.024 | 0.0263 | 0.023 | 0.021 | 0.58 | 2.1 |
| Comparative example 1 | 0.26 | 0.55 | 1.45 | 0.160 | 0.016 | 0.0300 | 0.030 | 0.021 | 0.53 | 1.5 |
| Comparative example 2 | 0.27 | 0.79 | 1.43 | 0.190 | 0.035 | 0.0210 | 0.027 | 0.019 | 0.55 | 2.7 |
| Comparative example 3 | 0.25 | 0.78 | 1.66 | 0.120 | 0.025 | 0.0232 | 0.020 | 0.017 | 0.55 | 1.6 |
| Comparative example 4 | 0.27 | 0.76 | 1.54 | 0.185 | 0.022 | 0.0210 | 0.024 | 0.022 | 0.56 | 2.5 |
| Comparative example 5 | 0.28 | 0.77 | 1.55 | 0.190 | 0.024 | 0.0263 | 0.023 | 0.021 | 0.58 | 2.1 |
The components of comparative examples 1 and 2 satisfy the requirements of the present invention, but the A value does not satisfy the requirements of the present invention. Neither component A nor component A of comparative example 3 satisfies the requirements of the present invention. Comparative example 4 and example 4 have the same composition, and comparative example 5 and example 5 have the same composition.
The production method of the V-Nb composite microalloying 650 MPa-level anti-seismic steel bars of the embodiment and the comparative example comprises the steps of proportioning according to the given chemical composition ratio, smelting in a converter, refining in an LF furnace, continuous casting of small square billets, heating, rolling in a bar mill, controlled cooling, steel bar finished products, bundling and warehousing. The specific operation key points are as follows:
(1) Smelting in a converter: controlling the end point C of the converter to be 0.06-0.15%, wherein P is less than or equal to 0.020%; adding lime during tapping 1/5 molten steel, and adding deoxidizing agent and alloy during tapping 1/3, wherein the sequence is as follows: slag material, silicomanganese, vanadium nitrogen and ferrovanadium, and carburant.
(2) Refining in an LF furnace: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding lime and wollastonite for slagging, wherein the alkalinity is R1.2-1.8, the slagging time is more than or equal to 10 minutes, and adding alloy for adjusting Si, mn, V, nb before and during refining according to the analysis result of the components before entering an LF furnace. And (5) carrying out soft argon blowing treatment before the station is out, wherein the soft argon blowing time is more than or equal to 10min.
(3) Continuous casting of small square billets: and adopting small square billet continuous casting. The whole-course protection casting is adopted, a protection sleeve and an argon seal are adopted between a ladle and a tundish, the tundish is protected by using a molten steel covering agent and argon blowing, a submerged nozzle is adopted between the tundish and a crystallizer, and a mode of combining secondary cooling and electromagnetic stirring of the crystallizer is adopted. Wherein the primary cooling water flow is 105-120 m 3 And/h, the secondary cooling specific water quantity is 0.4-0.50 l/kg, the superheat degree is 15-35 ℃, the drawing speed is 1.9-2.3 m/min, the casting process is stable in liquid level, drawing speed and superheat degree, and the defect-free casting blank is obtained.
(4) Rolling the bar: the invention can realize the rolling of the steel bar with phi 12-32mm, and ensures that the elements Nb and V are fully dissolved in the solid solution for the requirement of the rolling process and the solid solution of the carbon and the nitride of V, nb in the austenite, wherein the heating temperature is controlled to 1150-1250 ℃, and the soaking time is more than 25 min. The heated casting blank enters a continuous rolling unit for rolling, the initial rolling temperature is 1000-1100 ℃, the rolling is completed in an austenite recrystallization region to realize recrystallization refinement, the final rolling temperature is 980-1100 ℃, the higher final rolling temperature ensures the uniformity of component tissues, the casting blank is cooled by passing water after rolling, the cooling speed after rolling is 15.0-23.5 ℃/s, the casting blank is cooled to 830-900 ℃, the surface layer acicular ferrite tissues are obtained, and the thickness of the surface layer acicular ferrite tissues is 100-350 mu m. And then the steel is naturally cooled to normal temperature by a cooling bed, so that the toughness and the strength-to-flexibility ratio of the steel are improved.
The parameters of the converter smelting, LF refining and billet continuous casting production process of each example and comparative example are shown in Table 2.
Table 2 technological parameters of the converter smelting, LF refining, billet continuous casting production in examples and comparative examples
The rolling process parameters of the bars in the embodiment 1 to the embodiment 5 are shown in the table 3, and the microstructure of the produced steel bar is surface acicular ferrite, core ferrite and pearlite. The bar rolling process parameters of comparative example 1, comparative example 2, comparative example 3 and comparative example 5 are shown in table 3, and the microstructure of the produced steel bar is surface acicular ferrite, core ferrite + pearlite. Comparative example 4 the bar rolling process parameters are shown in table 3, and the microstructure of the produced steel bar is ferrite + pearlite.
Table 3 the parameters of the rolling process for the steel bars according to the embodiment of the invention
The properties of the rebars produced in each example are shown in Table 4.
Table 4 mechanical properties of the reinforcing bars according to the examples of the present invention
The data of the horizontal lines drawn in the above table are data which do not satisfy the requirements of the present invention.
The 650 MPa-level anti-seismic steel bar produced by the method has a needle-shaped ferrite layer with a certain thickness on the surface, as shown in figure 1, and the mechanical property of the steel bar is regulated by controlling the thickness of the needle-shaped ferrite layer on the surface layer, so that the best matching of the strength and the strength-to-yield ratio is achieved, the strength-to-yield ratio is more than 1.27, and the requirement of the anti-seismic steel bar is met. The surface microstructure is shown in fig. 2, which is acicular ferrite structure, the core microstructure is shown in fig. 3, which is ferrite + pearlite structure. The mechanical properties of the reinforcing steel bars of the embodiments of the invention are as follows: the mechanical properties at normal temperature can be as follows: yield strength R eL More than or equal to 670MPa, tensile strength R m Not less than 850MPa, and strong-bending ratio R m /R eL More than or equal to 1.27, the elongation A after breaking is more than or equal to 18 percent, and the maximum force total elongation A gt More than or equal to 9.5 percent. And each embodiment obtains high surface quality billet, and the surface quality of the steel bar is excellent.
The components of comparative example 1 and comparative example 2, while satisfying the requirements of the present invention, have a value a that does not satisfy the requirements of the present invention; even if produced according to the required process and parameters, the product performance still cannot meet the requirements of the invention. The component A and the component B of the comparative example 3 do not meet the requirements of the invention, and even if the product is produced according to the required process and parameters, the product performance still cannot meet the requirements of the invention. Comparative example 4 and example 4 have the same composition and meet the requirements of the present invention, but in production, bar rolling is not controlled according to the requirements of the present invention, the cooling rate after rolling and the upper cooling bed temperature cannot meet the requirements of the present invention, and the product performance is significantly lower than the present invention. Comparative example 5 and example 5 were identical in composition, but in production, the continuous casting process was not controlled according to the requirements of the present invention, and the properties were satisfied, but net-shaped cracks were formed on the surface of the continuous casting slab, resulting in streak-shaped cracks on the surface of the steel bar.
Claims (6)
1. The V-Nb composite microalloyed 650 MPa-level anti-seismic steel bar is characterized by comprising the following components in percentage by mass: 0.25 to 0.29 percent of C, 0.55 to 0.80 percent of Si,1.40 to 1.60 percent of Mn, 0.150 to 0.190 percent of V, 0.015 to 0.035 percent of Nb, 0.021 to 0.030 percent of N, less than or equal to 0.030 percent of P, less than or equal to 0.030 percent of S, and the balance of Fe and other unavoidable impurities;
the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar has the components of A value which is more than or equal to 1.7 and less than or equal to 2.6; a value= (0.27× [ V ] +0.15× [ Nb ])/[ N ];
the production method comprises the following process flows: batching, converter smelting, LF furnace refining, billet continuous casting, heating, bar rolling mill rolling, controlled cooling, steel bar finished product, bundling and warehousing;
and (3) rolling the bar: the heating temperature is controlled at 1150-1250 ℃, the soaking time is more than 25min, the initial rolling temperature is 1000-1100 ℃, the final rolling temperature is 980-1100 ℃, the cooling is carried out through water after rolling, the cooling is cooled to 830-900 ℃, and the cooling speed after rolling is 15.0-23.5 ℃/s;
the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar has surface acicular ferrite and surface acicular ferrite tissue thickness of 100-350 mu m; a core ferrite + pearlite microstructure;
the V-Nb composite microalloying 650 MPa-level anti-seismic steel bar has normal-temperature mechanical properties: yield strength R eL More than or equal to 670MPa, tensile strength R m Not less than 850MPa, and strong-bending ratio R m /R eL More than or equal to 1.27, the elongation A after breaking is more than or equal to 18 percent, and the maximum force total elongation A gt ≥9.5%。
2. The V-Nb composite micro-alloyed 650 MPa-grade anti-seismic steel bar of claim 1, wherein the V-Nb composite micro-alloyed 650 MPa-grade anti-seismic steel bar composition satisfies Ceq +.0.58%.
3. A method for producing the V-Nb composite micro-alloyed 650 MPa-grade earthquake-resistant steel bar according to claim 1 or 2, characterized in that the production method comprises the following process flows: batching, converter smelting, LF furnace refining, billet continuous casting, heating, bar rolling mill rolling, controlled cooling, steel bar finished product, bundling and warehousing.
4. A production method according to claim 3, characterized in that the converter smelting: the end point C of the converter is controlled to be 0.06-0.15%, and P is less than or equal to 0.020%.
5. A production method according to claim 3, characterized in that the LF furnace refines: argon is blown to the bottom of the whole ladle, and the argon flow is based on the condition that molten steel does not splash the ladle; adding lime and wollastonite for slagging, wherein the alkalinity R is 1.2-1.8, and the slagging time is more than or equal to 10 minutes.
6. A production method according to claim 3, characterized in that the billet is continuously cast: the flow rate of primary cooling water is 105-120 m 3 And/h, the secondary cooling specific water amount is 0.4-0.50 l/kg, the superheat degree is 15-35 ℃, and the pulling speed is 1.9-2.3 m/min for low-speed casting.
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