Weathering and earthquake-resistant steel bar with yield strength of 430 MPa and manufacturing method thereof

Abstract

The present invention provides a weather-resistant and earthquake-resistant steel bar with a yield strength of 430MPa and a manufacturing method thereof, belonging to the technical field of hot-rolled steel bar production. The chemical composition of the weather-resistant and hot-rolled earthquake-resistant steel bar is calculated by weight percentage: C: 0.20% to 0.25%, Si: 0.35% to 0.65%, Mn: 0.90% to 1.20%, Nb: 0.005 to 0.015%, O: <0.005%, N: <0.006%, RE: 0.045 to 0.055%, P: <0.035%, S: <0.030%, and the rest is Fe and unavoidable impurities. The embodiment of the present invention adopts a reasonable composition design of Nb and rare earth, optimizes the process conditions of smelting and rolling, obtains a fine and uniform ferrite + pearlite structure, and ensures that it has good high strength and earthquake resistance, as well as atmospheric corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of hot-rolled steel bar production, and in particular to a weather-resistant and earthquake-resistant steel bar with a yield strength of 430 MPa and a manufacturing method thereof. Background Art

[0002] Hot-rolled ribbed steel bars for concrete (hereinafter referred to as steel bars) are the largest single steel variety in my country, accounting for more than 20% of my country's crude steel output for a long time. In addition, more than 60% of my country's regions are in earthquake-prone areas. Therefore, the product upgrade and quality improvement of earthquake-resistant steel bars are not only related to the safety of buildings and people's lives and property, but also to the high-quality development of the steel industry and the "carbon peak and carbon neutrality" strategy. It is of great significance.

[0003] At present, the national standard for hot-rolled ribbed steel bars for concrete implemented in my country is GB / T 1499.2-2018. The standard puts forward requirements for steel bar strength grade, production process and metallographic structure. The lowest grade HRB400 (E) in the standard requires a lower yield strength of more than 400MPa and a tensile strength of more than 540MPa. HRB400E that meets seismic requirements also requires a strength-yield ratio (measured tensile strength / measured lower yield strength) of not less than 1.25, a yield-to-standard ratio (measured lower yield strength / 400MPa) of not more than 1.30, and a total elongation at maximum force of not less than 9%.

[0004] Since the yield strength of hot-rolled steel bars usually decreases due to aging (usually the yield strength of hot-rolled steel bars off the production line decreases the most after aging for about half a month), most steel bar manufacturers require the lower yield strength of HRB400 (E) off-line inspection to be higher than 420MPa. In addition, certain regions and engineering applications also require steel bars to be resistant to atmospheric corrosion. Currently, stainless steel bars and surface-coated steel bars are applied to the above fields, but they are difficult to meet the requirements because of their low cost-effectiveness or environmental pollution. Therefore, it is necessary to develop hot-rolled earthquake-resistant steel bars that take into account high strength, atmospheric corrosion resistance, and economy.

[0005] Patent publication number CN 111187980 discloses a rare earth micro-alloyed high-strength construction steel bar and a production method thereof. The high-strength construction steel bar is produced by alloying C, Si, Mn and RE. Since the solid solution strengthening effect of RE is relatively small, the production of high-strength construction steel bars by adding RE alone is unsatisfactory. The embodiments in the patent also confirm that even if 0.05% RE is added, the lower yield strength of the 32mm diameter steel bar produced is 415-421MPa; the 18mm diameter steel bar produced by adding 0.032% RE is even as low as 414MPa. Because the yield strength decreases during the aging process after hot rolling of the steel bar, the yield strength of the steel bar produced by this method is at risk of not meeting the performance requirements of HRB400 (E) in standard GB / T 1499.2-2018.

[0006] Patent publication number CN 114657447 ​​discloses rare earth corrosion-resistant hot-rolled ribbed steel bars, but does not involve performance indicators such as maximum force elongation and strength-to-yield ratio related to the seismic performance of steel bars, and it is unknown whether it has seismic performance. The mechanical performance data of the embodiment reflects that the yield strength of the 14mm diameter steel bar produced by the chemical composition of 0.24C-0.48Si-1.30Mn-0.10Cr-0.02Cu-0.0168RE (0.0058% La + 0.0110% Ce) is 419MPa, which is low. After aging, the yield strength of the steel bar will decrease, which also reflects that the yield strength surplus of the rare earth corrosion-resistant hot-rolled ribbed steel bar of the invention is insufficient, and it is difficult to stably meet the performance requirements of HRB400E in the standard GB / T1499.2-2018.

[0007] Patent publication number CN 114657460 discloses a rare earth and nitrogen microalloyed HRB400E coiled steel bar, which produces HRB400E coiled steel bar with a diameter of 6mm-12mm by C (0.18-0.25%)-Si (0.20-0.60%)-Mn (0.8-1.25%)-N (0.006-0.012%)-RE (0.0015-0.0045%)-V (and / or Nb) (0.005-0.025%). The invention has limited strengthening effect of carbonitride formed by trace RE and carbon and nitrogen, and does not involve the production of HRB400E straight spiral steel bar with larger diameter. In addition, the upper limit of nitrogen (N) in the above two patent publications is 0.012%. A higher N content will combine with rare earth, which is not conducive to the solid solution of rare earth in molten steel and affects the corrosion resistance. Summary of the invention

[0008] The purpose of the present invention is to at least partially solve the above technical problems, and to provide a weather-resistant and earthquake-resistant steel bar with a yield strength of 430 MPa and a manufacturing method thereof. The embodiments of the present invention adopt a reasonable composition design of Nb and rare earth, optimize the process conditions of smelting and rolling, obtain a fine and uniform ferrite + pearlite structure, and ensure that it has good high strength and earthquake resistance, as well as atmospheric corrosion resistance.

[0009] In one aspect of the present invention, a weather-resistant earthquake-resistant steel bar with a yield strength of 430 MPa is provided, and the chemical composition of the weather-resistant hot-rolled earthquake-resistant steel bar is as follows by weight percentage: C: 0.20%~0.25%, Si: 0.35%~0.65%, Mn: 0.90%~1.2%, Nb: 0.005~0.015%, O: <0.005%, N: <0.006%, RE: 0.045~0.055%, P: <0.035%, S: <0.030%, and the rest is Fe and unavoidable impurities.

[0010] In some embodiments, the metallographic structure of the weather-resistant and earthquake-resistant steel bar includes only ferrite and pearlite.

[0011] In some embodiments, the RE rare earth element is one of the five elements of lanthanum, cerium, praseodymium, neodymium, and yttrium, or any combination thereof, wherein the weight ratio of the RE rare earth element to the sum of the three elements of O, N, and S is: RE / (O+S+N)≤3.

[0012] In another aspect of the present invention, a method for manufacturing the above-mentioned weather-resistant and earthquake-resistant steel bar with a yield strength of 430 MPa is provided, comprising the following steps:

[0013] (1) Converter smelting: Control the amount of scrap steel charged, add desulfurized molten iron for smelting, and after reaching the end composition and tapping temperature, perform deoxidation and alloying;

[0014] (2) Argon station refining: molten steel is refining in the argon blowing station;

[0015] (3) Continuous casting: The molten steel is cast on a continuous casting platform, and a preheated rare earth cored wire is fed into the continuous casting crystallizer. A continuous casting billet of 150 mm to 170 mm is obtained at a continuous casting speed of 3.0 to 4.0 m / min, and the billet is directly sent down for rolling;

[0016] (4) Controlled rolling: During the rolling process, the rough rolling temperature of the continuous casting billet is greater than 950°C. After rolling by the intermediate rolling mill, the final rolling temperature of the finishing process is controlled to be 800-850°C, so that the post-rolling temperature of the steel bar is lower than the austenite non-recrystallization temperature of the steel bar;

[0017] (5) Weak cooling after rolling: The steel bar is weakly cooled after final rolling, and the surface temperature of the steel bar is controlled at the austenite-ferrite phase transition temperature. Phase transformation occurs immediately after the steel bar is rolled, and the final steel bar obtains a metallographic structure of only ferrite and pearlite.

[0018] In some embodiments, the temperature of the steel bar rises after final rolling but is still lower than the austenite non-recrystallization temperature of the steel bar, so that the grain size of the steel bar is in a refined non-recrystallized state.

[0019] In some embodiments, in step (5) of post-rolling weak cooling, the surface temperature of the steel bar is controlled at 720-780° C. After the steel bar is subjected to weak cooling after rolling, a phase change occurs immediately, and dispersed and fine Nb(C,N) is precipitated to improve the strength.

[0020] In some embodiments, the solid solution of Nb and rare earth improves the hardenability of supercooled austenite, while weak cooling after rolling maintains the fine grain size inside the steel bar after final rolling and retains more nucleation sites, so that the steel bar undergoes phase transformation to obtain fine ferrite + pearlite; weak cooling after rolling forms a dense α-FeOOH protective layer on the surface of the steel bar containing niobium and rare earth.

[0021] In some embodiments, in the continuous casting process of step (3), molten steel is cast on a continuous casting platform, a preheated rare earth cored wire with a diameter of 5 mm to 8 mm is fed into the continuous casting crystallizer, and the continuous casting speed is controlled at 3.0 to 4.0 m / min, and finally a continuous casting square billet with a diameter of 150 mm to 170 mm is obtained, which is directly sent down for steel rolling.

[0022] In some embodiments, in step (2) argon station refining, the molten steel after alloying is sent to the bottom of the argon station for mixing by blowing argon gas, the oxygen content in the molten steel is less than 0.005%, the nitrogen content is less than 0.006%, and the content of C, Si, Mn, and Nb elements in the molten steel is adjusted to a preset composition range.

[0023] In some embodiments, in step (1) converter smelting: scrap steel is loaded into the converter and molten iron is added, the amount of scrap steel added is required to be no more than 15% of the molten iron, and the scrap steel needs to be preheated to above 600°C in advance; the molten iron added is required to be desulfurized by KR pretreatment, the sulfur content of the molten iron entering the furnace is ≤0.005%, and the temperature before adding to the converter is ≥1300°C; after oxygen blowing smelting, the end point C is controlled within the range of 0.06-0.10%, the tapping temperature is controlled at 1600°C-1660°C, the liquid nitrogen content of the steel at the end of smelting is <0.004%, P≤0.025%, and S≤0.012% for tapping; when the tapping amount is 1 / 2-3 / 4, silicon manganese alloy, ferrosilicon and ferroniobium are added for deoxidation and alloying, and all are added before tapping.

[0024] The weather-resistant and earthquake-resistant steel bar with a yield strength of 430 MPa and the manufacturing method thereof according to the embodiment of the present invention have at least one of the following advantages:

[0025] The embodiments of the present invention adopt a reasonable composition design of Nb and rare earth components, optimize the process conditions of smelting and rolling, and obtain a fine and uniform ferrite + pearlite structure, thereby ensuring that it has good high strength and seismic resistance, as well as atmospheric corrosion resistance.

[0026] Its performance indicators after hot rolling meet the requirements of lower yield strength ≥430MPa, tensile strength ≥575MPa, total elongation at maximum force ≥12%, strength-yield ratio ≥1.30, and yield-to-standard ratio ≤1.12; and after half a month of natural aging, the lower yield strength is ≥422MPa, the tensile strength is ≥570MPa, the total elongation at maximum force ≥12%, the strength-yield ratio is ≥1.32, and the yield-to-standard ratio is ≤1.09.

[0027] The performance before and after aging meets the HRB400E performance requirements in GB / T 1499.2, and has a good margin and good atmospheric corrosion resistance, ensuring the safety of the steel bars during use, a shorter production process and lower energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of the preferred embodiments in conjunction with the accompanying drawings, in which:

[0029] Figure 1 It is a schematic flow chart of a method for preparing weather-resistant and earthquake-resistant steel bars with a yield strength of 430 MPa according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0031] In view of the above analysis, the present invention adopts Nb and rare earth as micro-alloying elements, combined with controlled rolling and post-rolling weak cooling process technology, to provide a weather-resistant hot-rolled earthquake-resistant steel bar with a yield strength of 430MPa and a manufacturing method thereof. It not only meets the HRB400E performance requirements in GB / T 1499.2 after hot rolling and aging, but also has good atmospheric corrosion resistance, and the size covers a diameter of 10mm to 32mm.

[0032] In one embodiment, the chemical composition of the weather-resistant hot-rolled earthquake-resistant steel bars with a yield strength of 430 MPa according to the present invention is calculated by weight percentage: C: 0.20% to 0.25%, Si: 0.35% to 0.65%, Mn: 0.90% to 1.20%, Nb: 0.005 to 0.015%, O: <0.005%, N: <0.006%, RE: 0.045 to 0.055%, P: <0.035%, S: <0.030%, and the rest is Fe and unavoidable impurities.

[0033] Specifically, RE is one of the five elements of lanthanum, cerium, praseodymium, neodymium and yttrium or any combination thereof, wherein the weight ratio of RE to the sum of the three elements of O, N and S is: RE / (O+S+N)≤3.

[0034] The role and proportion of each element in the embodiment of the present invention are as follows:

[0035] Carbon (C): Carbon is the most effective and cheap element for improving the strength of steel bars. As the C content increases, the tensile strength and yield strength of the steel increase accordingly. In order to ensure the strength without reducing the corrosion resistance due to excessive C content, therefore, in the embodiments of the present invention, the C content is limited to 0.20-0.25%.

[0036] Silicon (Si): Silicon is a commonly used deoxidizing element and has a strong solid solution strengthening effect, which is beneficial to improving the strength of steel. Therefore, in the embodiments of the present invention, the content range of Si is limited to 0.35-0.65%.

[0037] Manganese (Mn): Manganese is an important strengthening element and a good deoxidizer and desulfurizer. Too low Mn cannot guarantee the strength of the steel, but too high Mn has an adverse effect on the center segregation of the steel billet and is prone to cracks during welding. Therefore, in the embodiments of the present invention, its content is limited to 0.90-1.20%.

[0038] Phosphorus (P) and sulfur (S): impurity elements in steel, and S and Mn are easy to generate long strips of MnS inclusions, which affect the mechanical properties and corrosion resistance of steel bars. The content of S and P should be as low as possible without significantly increasing the cost. Therefore, in the embodiments of the present invention, they are controlled below 0.035% and 0.030%, respectively, preferably, controlled within 0.030% and 0.025%, respectively.

[0039] Niobium (Nb): Niobium is a strong carbonitride-forming element, which can increase the austenite non-recrystallization temperature of steel. Austenite non-recrystallization zone rolling can be carried out at a higher rolling temperature; in addition, the precipitation strengthening effect of Nb in the controlled rolling process can pin austenite grains through the strain-induced precipitation of Nb carbonitrides, refine austenite grains and improve toughness. The solubility of Nb in iron is greater than that in the rust layer, and it forms a solid solution with iron, which can increase the electrochemical potential of the steel matrix, thereby improving the corrosion resistance of the steel. At the same time, it is economical to use while meeting the performance requirements. Therefore, in the embodiment of the present invention, its content is set at 0.005-0.015%.

[0040] Oxygen (O) and nitrogen (N): In order to avoid the reaction between O and N content and rare earth and affect the recovery rate of rare earth, the content must be controlled within 0.005% and 0.006% respectively. In addition, on the one hand, nitrogen will promote the precipitation of niobium. In order to reduce the precipitation of niobium before rolling as much as possible, more niobium is precipitated after rolling, so as to give full play to the strengthening effect of niobium; on the other hand, a high nitrogen content will lead to a decrease in the strength of steel bars after aging, so the nitrogen content is limited. It should be pointed out that because the continuous casting billet smelted in the present invention is directly sent to the rolling mill for rolling, it also avoids the long-term contact of the billet with the nitrogen and oxygen atmosphere in the heating furnace, reduces its reaction with rare earth, and is beneficial to the corrosion resistance of the steel bar.

[0041] Rare earth (RE): It is active in nature and easily combines with oxygen, sulfur, nitrogen, etc., thus purifying the quality of molten steel and making the steel have good corrosion resistance. During the solidification process of the ingot, rare earth oxysulfides precipitate in the molten steel, acting as nucleation particles to refine dendrites and inhibit the growth of columnar crystals, reduce segregation, shorten the columnar crystal area, and refine equiaxed grains; in addition, the dispersed rare earth sulfides can be variable strip-shaped manganese sulfide inclusions, weakening the electrochemical corrosion of micro-areas in the steel, inhibiting the occurrence and expansion of pitting corrosion, and inducing uniform corrosion; rare earth is conducive to the formation of stable corrosion products α-FeOOH in the rust layer, and promotes the formation of a uniform and dense protective rust layer on the steel surface. The grain boundary segregation of rare earth elements hinders grain boundary migration, inhibits grain growth, and can refine carbides during pearlite transformation. Whether it is to increase the equiaxed crystal ratio of the ingot, refine the columnar crystal or refine the ferrite pearlite structure, the results all have the effect of improving the strength and plastic toughness of the steel. In particular, the refinement of the pearlite lamellae significantly improves the tensile strength of the steel bar, effectively improves the strength-to-yield ratio of the steel bar, and is beneficial to the seismic performance index. Rare earth elements are concentrated at the austenite grain boundaries, hindering the oxidation caused by the diffusion of oxygen through the grain boundaries, making the steel bar have better corrosion resistance. In addition, the interaction between rare earth and Nb inhibits the precipitation of the precipitate phase in the austenite, and promotes the precipitation of the fine dispersed precipitate phase in the ferrite phase region, which is beneficial to improve the effect of Nb precipitation strengthening. However, because rare earths inhibit grain boundary nucleation during the transformation of supercooled austenite structure, increase the incubation period, shift the C curve of proeutectoid ferrite and pearlite transformation to the right, and increase the hardenability of steel, excessive addition of rare earths will lead to the appearance of non-equilibrium structures such as bainite, and the high surface activity of rare earth elements causes the easily generated complex compounds to aggregate into larger particles, as well as RE-Fe brittle intermetallic compounds, which is not conducive to the performance of steel. Therefore, taking the above factors and the cost and yield of rare earth into consideration, the rare earth content of the present invention is 0.045-0.055%, and RE / (O+S+N)≤3 is proposed, which is beneficial to the modification of inclusions by rare earth and can be partially dissolved in steel, both of which are beneficial to corrosion resistance; the addition form is a cored wire with a diameter of 5mm-8mm, and the rare earth element is one or more of the five elements of lanthanum, cerium, praseodymium, neodymium and yttrium. The mixed rare earth wire core alloy composed of the above elements can be added alone or in combination. When adding, the preheated rare earth cored wire is fed into the crystallizer, which can accelerate the melting of the alloy and improve the rare earth yield.

[0042] In another embodiment of the present invention, see Figure 1 , provides a method for manufacturing corrosion-resistant hot-rolled earthquake-resistant steel bars with a yield strength of 430 MPa according to the present invention, comprising the following steps: converter smelting → argon station refining → continuous casting → controlled rolling → weak cooling after rolling;

[0043] Converter smelting: Load scrap steel into the converter and add molten iron. The amount of scrap steel added is required to be no more than 15% of the molten iron, and the scrap steel needs to be preheated to above 600°C in advance. The molten iron added is required to be desulfurized by KR pretreatment, and the sulfur content of the molten iron entering the furnace is ≤0.005%, and the temperature before adding to the converter is ≥1300°C. After oxygen blowing smelting, the end point C is controlled within the range of 0.06-0.10%, and the tapping temperature is controlled at 1600°C-1660°C. The liquid nitrogen content of the steel at the end of smelting is <0.004%, P≤0.025%, and S≤0.012% for tapping. When the tapping amount is 1 / 2-3 / 4, silicon-manganese alloy, ferrosilicon and ferroniobium are added for deoxidation and alloying, and all are added before tapping to 3 / 4.

[0044] During argon station refining, the alloyed molten steel is sent to the bottom of the argon station for argon blowing and mixing. The blowing time is not less than 5 minutes. The oxygen content in the molten steel is less than 0.005%, and the nitrogen content is less than 0.006%. The content of C, Si, Mn and Nb elements in the molten steel is adjusted to the composition range.

[0045] Continuous casting process: The molten steel is then cast on the continuous casting platform, and a preheated rare earth cored wire with a diameter of 5mm to 8mm is fed into the continuous casting crystallizer. The continuous casting speed is controlled at 3.0 to 4.0m / min, and finally a 150mm to 170mm continuous casting billet is obtained, which is directly sent to the rolling mill;

[0046] Controlled rolling: Ensure that the surface temperature of the continuous casting billet sent to the rolling workshop is ≥980℃, and the continuous casting billet does not need to be heated to reduce burning loss and save energy; the starting temperature of the rough rolling is >950℃, and after rolling by the intermediate rolling unit, the final rolling temperature of the finishing process is controlled to be 800~850℃. The addition of Nb increases the austenite non-recrystallization temperature T of the steel bar. nr Although the temperature of the steel bar rises after final rolling, the temperature after rolling is lower than T nr , so that the grain size of the steel bar is still in a refined non-recrystallized state, that is, fine grains are obtained by controlling rolling;

[0047] Weak cooling after rolling: The steel bar after final rolling is weakly cooled, and the surface temperature of the steel bar is controlled at 720-780℃, that is, the austenite-ferrite phase transition temperature A r3 After rolling, the steel bar undergoes phase transformation immediately, and finally obtains fine ferrite + pearlite. In addition, the dispersed and fine Nb (C, N) precipitates during weak cooling after rolling, which plays a precipitation strengthening role, thereby ensuring the strength and seismic resistance of the steel bar.

[0048] It is worth pointing out that weak cooling is required immediately after rolling. On the one hand, weak cooling can maintain the fine grain size after final rolling until the phase transformation, and finally obtain a refined phase transformation structure; and the solid solution Nb and rare earth can improve the hardenability of supercooled austenite, while weak cooling maintains the fine grain size inside the steel bar, thereby retaining more nucleation sites, so that the steel bar can transform into fine ferrite + pearlite as soon as possible, thereby avoiding the appearance of bainite structure. On the other hand, weak cooling is also conducive to the formation of a dense and stable α-FeOOH protective layer on the surface of steel bars containing niobium and rare earth, and obtains better atmospheric corrosion resistance.

[0049] The invention obtains hot-rolled weather-resistant and earthquake-resistant steel bars with a lower yield strength of 430 MPa through reasonable design of Nb and rare earth components and a manufacturing method of converter smelting → argon station refining → continuous casting processing → controlled rolling → weak cooling after rolling. The hot-rolled steel bars with a diameter of 10 mm to 32 mm produced in the invention both meet the HRB400E performance requirements in GB / T 1499.2 in the hot-rolled state and after aging, and have a good surplus. Compared with the existing similar steel bar production technology, the invention shortens the production process, saves energy, and gives full play to the coupling effect of Nb and rare earth.

[0050] In the present invention, in view of the high activity of rare earth elements, control requirements for the contents of O, N and S are proposed, and a rare earth alloy cored wire is fed into a crystallizer to improve the rare earth recovery rate. Since the heating of the continuous casting billet is omitted, the corrosion resistance of the steel bar casting billet is reduced due to the reaction of the solid-dissolved rare earth with the oxygen and nitrogen atmosphere in the furnace caused by heating in the heating furnace, thereby ensuring the coupling effect of the rare earth and Nb, so that a dense and stable α-FeOOH protective layer is formed on the surface of the steel bar, which is beneficial to the atmospheric corrosion resistance of the steel bar.

[0051] Compared with the prior art, the hot-rolled corrosion-resistant and earthquake-resistant steel bar with a yield strength of 430 MPa and the manufacturing method thereof described in the embodiment of the present invention have the following advantages:

[0052] The embodiment of the present invention adopts reasonable composition design of Nb and rare earth components, optimizes the process conditions of smelting and rolling, obtains fine and uniform ferrite + pearlite structure, ensures that it has good high strength and seismic resistance, and atmospheric corrosion resistance, and its performance indicators after hot rolling meet the lower yield strength ≥430MPa, tensile strength ≥575MPa, maximum force total elongation ≥12%, strength yield ratio ≥1.30, and yield-to-standard ratio ≤1.12; and after half a month of natural aging, the lower yield strength is ≥422MPa, the tensile strength is ≥570MPa, the maximum force total elongation is ≥12%, the strength yield ratio is ≥1.32, and the yield-to-standard ratio is ≤1.09; the performance before and after aging meets the HRB400E performance requirements in GB / T 1499.2, and has a good surplus, and also has good atmospheric corrosion resistance, ensuring the safety of the steel bars during use, a shorter production process, and lower energy consumption.

[0053] According to the chemical composition and production process of the present invention, the actual chemical composition of the steel bar of the present invention is shown in Table 1, the actual process parameters of the present invention for producing steel bars of various specifications are shown in Table 2, the performance results after rolling off the production line are shown in Table 3, and the performance results after aging for half a month are shown in Table 4. It can be seen from Tables 3 and 4 that the present invention produces 10mm~32mm hot-rolled steel bars with various indicators: yield strength ≥422MPa, tensile strength ≥570MPa, maximum force elongation ≥12%, tensile strength / yield strength ≥1.30, yield strength / yield strength characteristic value ≤1.12, with good margin and good atmospheric corrosion resistance.

[0054] Table 1 Smelting components in the steel of the present invention (wt%)

[0055]

[0056]

[0057] Table 2 Actual process parameters of the steel examples of the present invention

[0058] Table 3 Mechanical properties and atmospheric corrosion resistance of the steel bars of the present invention after being tested

[0059] Table 4 Mechanical properties and atmospheric corrosion resistance of the steel bar of the present invention after aging for half a month

[0060]

[0061]

[0062] The steel bars produced according to the above technical solution of the present invention have the following excellent properties:

[0063] (1) Lower yield strength ≥ 430 MPa, tensile strength ≥ 575 MPa, tensile strength / yield strength ≥ 1.30, measured yield strength / yield strength characteristic value ≤ 1.12, and total elongation at maximum force ≥ 12%;

[0064] (2) After aging for half a month, the lower yield strength is ≥422MPa, the tensile strength is ≥570MPa, the tensile strength / yield strength is ≥1.32, the measured yield strength / yield strength characteristic value is ≤1.09, and the maximum force total elongation is ≥12%; the corrosion rate of the industrial atmosphere test (g / (m 2 ·h))≤0.13.

[0065] Although some embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the present general inventive concept, the scope of which is defined by the claims and their equivalents.

Claims

1. A weather-resistant and earthquake-resistant steel bar with a yield strength of 430 MPa, characterized in that: The chemical composition of the weathering hot-rolled earthquake-resistant steel bar is as follows by weight percentage: C: 0.20% to 0.25%, Si: 0.35% to 0.65%, Mn: 0.90% to 1.16%, Nb: 0.005 to 0.012%, O: <0.005%, N: <0.006%, S: <0.030%, RE: 0.045 to 0.055%, P: <0.035%, and the rest is Fe and unavoidable impurities. The molten steel of the weather-resistant hot-rolled earthquake-resistant steel bar is only processed by continuous casting, controlled rolling and weak cooling after rolling to obtain the weather-resistant earthquake-resistant steel bar, wherein In the continuous casting process, the molten steel is cast on the continuous casting platform, the preheated rare earth core wire is fed into the continuous casting crystallizer, and the continuous casting billet of 150mm~170mm is obtained at a continuous casting speed of 3.0~4.0m / min, and is directly sent down for rolling; In the controlled rolling step: during the rolling process, the rough rolling start temperature of the continuous casting square billet is greater than 950°C, and after rolling by the intermediate rolling mill, the final rolling temperature of the finishing rolling process is controlled to be 800-850°C, so that the post-rolling temperature of the steel bar is lower than the austenite non-recrystallization temperature of the steel bar; In the post-rolling weak cooling step: the steel bar after final rolling is weakly cooled, and the surface temperature of the steel bar is controlled at the austenite-ferrite phase transition temperature of 720-780°C. The steel bar undergoes a phase transition immediately after rolling, and the steel bar finally obtains a metallographic structure of only ferrite and pearlite. The RE rare earth element is any one of the five elements of lanthanum, cerium, praseodymium, neodymium and yttrium or any combination thereof, and the weight ratio of the RE rare earth element to the sum of the three elements of O, N and S is: RE / (O+S+N) ≤3.

2. A method for manufacturing the weather-resistant and earthquake-resistant steel bar with a yield strength of 430 MPa as claimed in claim 1, comprising the following steps: (1) Converter smelting: Control the amount of scrap steel charged, add desulfurized molten iron for smelting, and after reaching the end composition and tapping temperature, perform deoxidation and alloying; (2) Argon station refining: molten steel enters the argon station for refining; (3) Continuous casting: The molten steel is cast on the continuous casting platform, and the preheated rare earth cored wire is fed into the continuous casting crystallizer. The continuous casting billet of 150mm~170mm is obtained at a continuous casting speed of 3.0~4.0m / min and is directly sent to the steel rolling workshop; (4) Controlled rolling: During the rolling process, the rough rolling start temperature of the continuous casting billet is greater than 950°C. After rolling by the intermediate rolling mill, the final rolling temperature of the finishing process is controlled to be 800~850°C, so that the post-rolling temperature of the steel bar is lower than the austenite non-recrystallization temperature of the steel bar; (5) Weak cooling after rolling: The steel bar is weakly cooled after final rolling. The surface temperature of the steel bar is controlled at the austenite-ferrite phase transformation temperature of 720~780℃. Phase transformation occurs immediately after the steel bar is rolled, and the final steel bar obtains a metallographic structure of only ferrite and pearlite.

3. The method for manufacturing weather-resistant and earthquake-resistant steel bars with a yield strength of 430 MPa according to claim 2, characterized in that: After final rolling, the temperature of the steel bar rises but is still lower than the austenite non-recrystallization temperature of the steel bar, so that the grain size of the steel bar is in a refined non-recrystallized state.

4. The method for manufacturing weather-resistant and earthquake-resistant steel bars with a yield strength of 430 MPa according to claim 3, characterized in that: In the post-rolling weak cooling of step (5), the surface temperature of the steel bar is controlled at 720-780°C. After the steel bar is subjected to weak cooling after rolling, a phase change immediately occurs, and dispersed and fine Nb(C,N) is precipitated.

5. The method for manufacturing weather-resistant and earthquake-resistant steel bars with a yield strength of 430 MPa according to claim 4, characterized in that: The solid-dissolved Nb and rare earth improve the hardenability of supercooled austenite, while weak cooling after rolling can maintain the fine grain size inside the steel bar after final rolling and retain more nucleation sites, so that the steel bar undergoes phase transformation immediately after rolling, thereby obtaining fine ferrite + pearlite. Weak cooling after rolling forms a dense α-FeOOH protective layer on the surface of the steel bar containing niobium and rare earth.

6. The method for manufacturing weather-resistant and earthquake-resistant steel bars with a yield strength of 430 MPa according to any one of claims 2 to 5, characterized in that: During the continuous casting process in step (3), molten steel is poured onto a continuous casting platform, a preheated rare earth cored wire with a diameter of 5 mm to 8 mm is fed into the continuous casting crystallizer, and the continuous casting speed is controlled at 3.0 to 4.0 m / min. Finally, a continuous casting billet with a diameter of 150 mm to 170 mm is obtained and directly sent down for rolling.

7. The method for manufacturing weather-resistant and earthquake-resistant steel bars with a yield strength of 430 MPa according to claim 6, characterized in that: In step (2) argon station refining, the alloyed molten steel is sent to the bottom of the argon station for argon blowing to mix evenly, so that the oxygen content in the molten steel is less than 0.005%, and the nitrogen content is less than 0.006%, and the content of C, Si, Mn and Nb elements in the molten steel is adjusted to a preset composition range.

8. The method for manufacturing weather-resistant and earthquake-resistant steel bars with a yield strength of 430 MPa according to claim 7, characterized in that: In step (1) converter smelting: scrap steel is loaded into the converter and molten iron is added, the amount of scrap steel added is required to be no more than 15% of the molten iron, and the scrap steel needs to be preheated to above 600°C in advance; the molten iron added is required to be desulfurized by KR pretreatment, the sulfur content of the molten iron entering the furnace is ≤0.005%, and the temperature before adding to the converter is ≥1300°C; after oxygen blowing smelting, the end point C is controlled within the range of 0.06-0.10%, the steel tapping temperature is controlled within the range of 1600°C-1660°C, the liquid nitrogen content of the steel at the end point of smelting is <0.004%, P≤0.025%, and S≤0.012% for steel tapping; when the steel tapping amount is 1 / 2-3 / 4, silicon-manganese alloy, ferrosilicon and ferroniobium are added for deoxidation and alloying, and the addition is completed before 3 / 4 of the steel is tapped.

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