CN108570601B - Low-carbon bainite weathering steel and production method thereof - Google Patents

Low-carbon bainite weathering steel and production method thereof Download PDF

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CN108570601B
CN108570601B CN201810495185.6A CN201810495185A CN108570601B CN 108570601 B CN108570601 B CN 108570601B CN 201810495185 A CN201810495185 A CN 201810495185A CN 108570601 B CN108570601 B CN 108570601B
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彭宁琦
罗登
刘丹
范明
李中平
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Hunan Valin Xiangtan Iron and Steel Co Ltd
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
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    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite

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Abstract

The chemical components of the steel in percentage by weight are C = 0.03-0.08, Si = 0.50-0.80, Mn = 1.00-1.80, P is less than or equal to 0.015, S is less than or equal to 0.005, Al = 0.02-0.05, Ti = 0.008-0.020, Nb is less than or equal to 0.020, Cu = 0.50-0.80, Ni = 0.50-1.00, Ca is less than or equal to 0.006, Ca/S is greater than or equal to 1.5, and the balance is Fe and inevitable impurity elements; mo and Cr are selectively added, wherein Mo is less than or equal to 0.30 percent, and Cr is less than or equal to 0.30 percent. The microstructure of the steel consists of more than 95% of carbon-free bainite, a small amount of austenite on a crystal boundary and a Cu-Ni aging precipitation phase, the yield strength is more than or equal to 485MPa, the tensile strength is more than or equal to 585MPa, the elongation after fracture is more than or equal to 25%, and the Charpy impact energy at 40 ℃ is more than or equal to 120J. The low-carbon bainite weathering steel has the advantages of clean steel quality, uniform structure, low internal stress, good surface quality and excellent weathering resistance.

Description

Low-carbon bainite weathering steel and production method thereof
Technical Field
The invention belongs to the technical field of low alloy steel production, and particularly relates to low-carbon bainite weathering steel and a production method thereof.
Background
Weathering steel, also called atmospheric corrosion resistant steel, often has small amounts of alloying elements such as Cu, P, Cr, Ni, Mo, etc. added. Compared with plain carbon steel, the weathering steel has better atmospheric corrosion resistance; compared with stainless steel, the weathering steel not only has greatly reduced cost, but also has mechanical properties and welding properties which can more easily meet the requirements of various projects. Therefore, the weathering steel is widely applied in the fields of bridges, maritime workers, containers, railway carriages and the like.
Early studies on weathering steel focused on the improvement of the ability of the addition of alloying elements to combat atmospheric corrosion. As with the ASTM G101 standard in the United states, the atmospheric corrosion resistance index I ≧ 6.0, where I =26.01Cu +3.88Ni +1.2Cr +1.49Si +17.28P-7.29CuNi-9.1NiP-33.39 CuCu; with reference to the Japanese JISF standard, the atmospheric corrosion resistance index J >1.0, wherein J =1/[ (1.0-0.16C) × (1.05-0.05Si) × (1.04-0.016Mn) × (1.0-0.5P) × (1.0+1.9S) × (1.0-0.1Cu) × (1.0-0.12Ni) × (1.0-0.3Mo) × (1.0-1.7Ti) ]. And a series of weathering resistant steels such as 09CuPCrNi, 09CuPTiRe, Q450NQR1, Corten A, ASTM A709 HSP, JIS G3114 SMA have been developed. Then, people begin to carry out deep research on the anti-atmospheric corrosion mechanism of the weathering steel, and except for discussing the synergistic action mechanism of the alloy elements on the self weather resistance of a steel matrix and the composition, structure and physical and chemical properties of a rust layer, the influence mechanism of the structure uniformity on the corrosion of the micro-galvanic couple is gradually known, and the micro-area potential difference is caused by the non-uniformity of the structure of the steel in phase composition, inclusion, second phase precipitation, segregation, banding, dislocation and the like to form a corrosion micro-galvanic couple, so that the corrosion behavior and the corrosion rate of the weathering steel are directly influenced.
For example, U.S. Pat. No. 6,56833 discloses a thermomechanical controlled rolling high-strength low-yield-ratio weathering steel, Japanese patent JP61012849 discloses a seawater corrosion resistant low-carbon steel produced by a hot rolling rapid cooling and self tempering process, and a Q + T process, for example Chinese patent CN100455692C discloses a quenching and tempering process. There are also weathering steels used in a normalized or annealed state, but the microstructure is usually composed of ferrite + pearlite, while there is a micro-couple effect between cementite and ferrite in the pearlite, as the anode ferrite dissolves, the cathode cementite lamella gradually accumulates on the surface, so that the cathode area gradually increases, causing the continuous accelerated corrosion of the pearlite.
Disclosure of Invention
The invention aims to provide high-weather-resistance low-carbon bainite weathering steel with good comprehensive mechanical properties and a production method thereof, wherein the yield strength of the steel is more than or equal to 485MPa, the tensile strength is more than or equal to 585MPa, the elongation after fracture is more than or equal to 25%, the Charpy impact energy at 40 ℃ is more than or equal to 120J, and the corrosion resistance of the steel is obviously better than that of the traditional low-carbon bainite steel in a neutral salt spray test.
The technical scheme of the invention is as follows:
the low-carbon bainite weathering steel comprises, by weight, C = 0.03-0.08, Si = 0.50-0.80, Mn = 1.00-1.80, P is less than or equal to 0.015, S is less than or equal to 0.005, Al = 0.02-0.05, Ti = 0.008-0.020, Nb is less than or equal to 0.020, Cu = 0.50-0.80, Ni = 0.50-1.00, Ca is less than or equal to 0.006, Ca/S is greater than or equal to 1.5, and the balance of Fe and inevitable impurity elements.
The steel component can also contain one or two of Mo less than or equal to 0.30 percent and Cr less than or equal to 0.30 percent.
The production method of the low-carbon bainite weathering steel with the chemical composition of the steel adopts a converter, an LF furnace and an RH furnace to smelt molten steel and continuously cast into a plate blank, the plate blank is cooled to room temperature in a heaping mode and then subjected to surface grinding, then the plate blank is reheated, rolled and finished, a heat treatment process of normalizing, accelerated cooling and isothermal aging is carried out after surface shot blasting, and finally the performance is sampled and detected. The key process steps comprise: ca treatment is carried out after the LF furnace and the RH furnace, the Ca line is fed after the LF furnace is more than or equal to 200m, the Ca line is fed after the RH furnace is more than or equal to 300m, and the soft argon blowing time is more than or equal to 12min after the Ca treatment; protective pouring is adopted for continuous casting, the superheat degree is 10-20 ℃, the steel passing amount is 3.0-3.5 t/min, the vibration frequency of a crystallizer is 250-300 times/min, and the amplitude is 2-4 mm; reheating the plate blank at 1200-1250 ℃, soaking for 1-2 h, controlling the rolling finishing temperature at 800-850 ℃, and cooling in air after rolling; normalizing at 850-880 ℃, and keeping the temperature for 1-2 h; after normalizing, the accelerated cooling rate is more than or equal to 10 ℃/s, and the final cooling temperature is 550-600 ℃; then directly carrying out isothermal aging at 550-600 ℃ for 2-4 h; and air cooling to obtain the finished product of the weathering steel after aging.
The detection shows that the microstructure of the weathering steel produced by the method is composed of more than 95% of non-carbon bainite, a small amount of austenite on a grain boundary and a Cu-Ni aging precipitation phase.
The design principle of the steel grade components of the invention is as follows:
carbon: the low carbon is beneficial to the toughness and weldability of the bainite, but if the carbon content is too low, the strength of the bainite is influenced, and the smelting is difficult for industrial production; in order to obtain most of the same type of non-carbon bainite tissues, the formation of pearlite, cementite and other carbides is inhibited, and the higher potential difference between the tissues and the matrix tissue is prevented, so that the atmospheric corrosion resistance is improved. Therefore, the invention adopts a low-carbon design, and the carbon content is determined to be 0.03-0.08%.
Silicon: silicon has pitting corrosion resistance and pitting corrosion resistance
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Figure 663647DEST_PATH_IMAGE002
Ion corrosion and the like, and particularly when the silicon content is higher, the silicon-rich oxide film formed on the surface has better marine atmosphere and industrial atmosphere corrosion resistance; silicon is a non-carbide-forming element, suppresses the formation of carbides such as cementite, and diffuses supersaturated carbon in the carbon-free bainite into austenite, thereby contributing to the weather resistance of the steel. However, an excessively high silicon content is disadvantageous in controlling the surface quality and inclusions of the steel, and also in toughness and weldability of the steel. The invention determines the range of the silicon content to be 0.50-0.80%.
Manganese: manganese is an important tough element and can promote bainite transformation. The compounding of Mn, Ca and Cu is beneficial to counteracting the harmful effect of sulfur on weather resistance. However, manganese is likely to segregate, and a MnS band-shaped structure is formed, which is a disadvantageous structure affecting weather resistance. The range of the manganese content determined by the invention is 1.00-1.80%.
Phosphorus: phosphorus is one of the most effective alloying elements for improving atmospheric corrosion resistance. The combination of P and Cu can promote the formation of hydroxyl oxide with protective effect and inhibit the further corrosion. However, phosphorus is a harmful impurity in steel, so that cold brittleness of the steel is easily caused, and welding performance is not favorable, and particularly in the isothermal aging process related to the invention, grain boundary segregation of phosphorus makes high-temperature temper brittleness difficult to avoid. Therefore, the invention adopts a low-phosphorus design and limits the phosphorus content to be not more than 0.015 percent.
Sulfur: sulfur is a harmful impurity in steel, reduces ductility, toughness, and weldability of steel, and impairs corrosion resistance of steel. Therefore, the invention adopts a low-sulfur design, and the sulfur content is limited to be not more than 0.005 percent.
Aluminum: aluminum is a deoxidizer in steel and a certain amount is required to control the oxygen content, but an increase in the aluminum content increases the number of B-type inclusions in steel, resulting in an increase in the number of corrosion sources. Although high aluminum content has a corrosion resistance similar to that of silicon, high aluminum content promotes the graphitization tendency of steel and causes difficulties in the processes of smelting, casting, rolling, etc. The composition of proper amount of Al and Ca is favorable for reducing the number of the inclusions, changing the shapes of the inclusions and being favorable for the weather resistance of the steel. The invention determines the aluminum content to be 0.02% -0.05%.
Titanium: TiN formed by micro-titanium treatment can effectively pin austenite crystal boundaries and is beneficial to controlling the growth of austenite crystal grains, but when the titanium content is higher, large-size liquated TiN is easily generated, and the mechanical property and the corrosion resistance of steel are influenced. The range of the determined titanium content is 0.008% -0.020%.
Niobium: niobium is a microalloying element and has the function of refining grains, but a second phase of niobium is precipitated and grown to form a large amount of corrosion micro batteries, so that the electrochemical corrosion process is accelerated, and the formation of upper bainite is easily induced by excessively high niobium content in the normalizing, accelerated cooling and isothermal aging processes. The upper limit of the niobium content is determined to be 0.020%.
Copper: copper is an austenite stabilizing element and can improve the strength and low temperature toughness of steel. Copper in the steel has excellent corrosion resistance, and the effect is more obvious particularly in industrial atmosphere or marine atmosphere. At the grain boundary of the non-carbon bainite, the aging precipitation of epsilon-Cu and the comprehensive micro-couple action with austenite are beneficial to improving the intergranular corrosion resistance, and the pitting corrosion resistance and the chloride stress corrosion resistance are also obviously improved. However, excessive copper is added, which easily causes problems of copper brittleness, surface quality of casting blank and internal cracking. The invention determines the copper content to be 0.50-0.80%.
Nickel: nickel is an austenite stabilizing element, can obviously improve the low-temperature toughness of steel, can effectively prevent the copper brittleness of the steel, and improves the weather resistance of the steel, particularly in harsh environment conditions with higher chloride ions. However, nickel is a precious metal, and too high content of nickel easily causes the pressing of iron scale, and affects the state, structure and uniformity of the iron scale on the surface of the finished steel plate, thereby affecting the weather resistance of the steel. The range of the nickel content determined by the invention is 0.50% -1.00%.
Calcium: calcium can improve the weather resistance of steel, form CaS and CaO, and inhibit MnS and Al2O3Damage to atmospheric corrosion resistance; on the other hand, CaS and CaO are dissolved in the electrolyte membrane of the rust layer, so that the alkalinity of a corrosion interface is increased, the corrosivity of the corrosion interface is reduced, and the rust liquid hanging phenomenon in use of the weathering steel can be effectively avoided. However, excessive addition produces coarse inclusions. Therefore, the upper limit of the calcium content determined by the invention is 0.006%, and Ca/S is more than or equal to 1.5.
Molybdenum: molybdenum can strongly delay ferrite transformation and promote bainite formation, but the formation of lath bainite is promoted due to the excessively high content of molybdenum, and molybdenum carbide is precipitated at grain boundaries, so that the corrosion of the grain boundaries is promoted, and the aging precipitation of Cu-Ni on the grain boundaries is also influenced. Therefore, molybdenum may be selectively added in the present invention, and the upper limit of the content thereof is determined to be 0.30%.
Chromium: chromium enables the rust layer to form a compact oxide film, and improves the passivation capability of steel, thereby effectively improving the atmospheric corrosion resistance of the steel. However, chromium tends to increase the high temperature temper brittleness and chromium carbides are coarser than molybdenum. Therefore, the present invention can selectively add chromium, and the upper limit of the content thereof is determined to be 0.30%.
The production method of the invention is set according to the following steps: the invention adopts calcium treatment and ensures the soft blowing time, so that the steel quality is clean, and the impurities are modified; the casting steel of the invention adopts low superheat degree and low drawing speed (low steel flux), which is beneficial to improving dendrite segregation; aiming at the high-silicon high-copper weathering steel, the crystallizer is vibrated at high frequency and low amplitude, and the surface of the plate blank is polished, so that the surface quality of the plate blank is ensured, the surface iron scale is removed, and the primary iron scale pressing which is easily caused by high-nickel high-silicon is prevented; the invention adopts higher-temperature heating, rolling and air cooling after rolling, and aims to improve the uniformity of components and tissues and reduce the degree of banded tissues; by adopting the heat treatment process of normalizing, accelerated cooling and isothermal aging, the invention not only can obtain a microstructure consisting of more than 95 percent of carbon-free bainite, a small amount of austenite on a crystal boundary and a Cu-Ni aging precipitation phase to form a large anode and a small cathode, and fully play the corrosion resistance role of copper and nickel, thereby reducing the corrosion rate, simultaneously enabling the obtained structure to be more uniform and balanced, reducing the dislocation density, eliminating the stress and being beneficial to improving the corrosion resistance; the invention performs shot blasting on the surface before the heat treatment process, so as to ensure that the iron scale on the surface of the finished product is uniformly distributed after the heat treatment, and a layer of red Fe with compact structure is covered on the surface layer with higher FeO proportion and better adhesion2O3The scale structure has a good protection effect on corrosion of base steel, and therefore a lower normalizing temperature is adopted, the heat preservation time is properly prolonged, a temperature range of 880-950 ℃ where scale is prone to peeling is avoided, and the aging temperature and time are properly adopted, so that aging precipitation of Cu-Ni and pre-eutectoid transformation of FeO are controlled.
The invention has the beneficial effects that: (1) the low-carbon bainite weathering steel of the invention does not improve the weathering resistance by adding phosphorus, and has good low-temperature toughness and weldability; (2) the weathering steel has clean steel quality, uniform structure and low internal stress; (3) the production method of the low-carbon bainite weathering steel provided by the invention has a stable and controllable process. The finished steel plate produced by the production method has stable mechanical property and good surface quality; (4) the invention comprehensively considers the corrosion resistance of alloy elements on a matrix and a rust layer, particularly on a grain boundary, and the influence of the structure uniformity, the internal stress, the surface iron scale structure and the like on the weather resistance, and achieves the purpose of high weather resistance of the weather-resistant steel by finely preparing the chemical composition and the structure characteristics and the feasible process control of the industrial production suitable for the chemical composition and the structure characteristics. In addition, the low-carbon bainite weathering steel also has good seawater corrosion resistance.
Drawings
FIG. 1 is a photograph of the microstructure of the lower bainite weathering steel of example 1 of the present invention.
FIG. 2 is a graph comparing the corrosion weight loss ratio of the low bainite weathering steel of example 1 of the present invention and the conventional low bainite steel in a 5% NaCl solution.
FIG. 3 is a microscopic corrosion morphology diagram of the low bainite weathering steel of example 1 of the present invention after being etched in 5% NaCl solution for 10 days.
FIG. 4 is a microscopic corrosion morphology of the selected conventional lower bainite steel after being etched in a 5% NaCl solution for 10 days.
Detailed Description
The present invention will be further described with reference to the following examples and accompanying drawings.
Example 1
The steel has a chemical composition in weight percent of C =0.05, Si =0.62, Mn =1.25, P =0.012, S =0.0013, Al =0.033, Ti =0.014, Nb =0.012, Cu =0.66, Ni =0.80, Ca =0.0027, and the balance of Fe and unavoidable impurity elements.
The production process of the steel comprises the following steps: smelting molten steel according to the components by adopting a converter, an LF furnace and an RH furnace, continuously casting the molten steel into a plate blank, carrying out surface grinding after the plate blank is cooled to room temperature, then reheating the plate blank for rolling and finishing, carrying out a heat treatment process of normalizing, accelerated cooling and isothermal aging after surface shot blasting, and finally sampling and detecting the performance.
The production process of the steel comprises the following key process parameters: feeding a Ca line 250m behind the LF furnace for soft argon blowing for 15min, feeding a Ca line 350m behind the RH furnace for soft argon blowing for 18 min; protective pouring is adopted for continuous casting, the superheat degree is 12-14 ℃, the steel passing amount is 3.2t/min, the vibration frequency of a crystallizer is 280 times/min, and the amplitude is 3 mm; the slab reheating temperature is 1230 ℃, the soaking time is 100min, the rolling finishing temperature is 828 ℃, and the slab is air-cooled after rolling; normalizing at 860 ℃ and keeping the temperature for 1.5 h; after normalizing, the accelerated cooling rate is 16.3 ℃/s, and the final cooling temperature is 575 ℃; then directly carrying out isothermal aging at the temperature of 580 ℃ for 3 h; and air cooling after aging.
The microstructure of the lower bainite weathering steel of example 1 was observed as shown in fig. 1. The microstructure of the steel sheet of example 1 was uniform and consisted of 95% or more of bainite free from carbon, a small amount of austenite at grain boundaries, and a Cu-Ni age-precipitated phase.
The steel plate of the example 1 is tested for mechanical properties, and has a yield strength of 505MPa, a tensile strength of 590MPa, an elongation after fracture of 31 percent and a Charpy impact work of 153/156/155J at-40 ℃.
Referring to GB/T10125-1997 standard, the neutral salt spray test is carried out on the low-carbon bainite weathering steel of the embodiment 1, the test solution is a 5% NaCl solution, the test periods are 1, 2, 4, 7, 10, 20 and 30 days respectively, the corrosion weight loss rate of each period is measured, and the corrosion morphology is observed.
The traditional low-carbon bainite steel is adopted for comparison tests, and the selected traditional low-carbon bainite steel comprises the following components in percentage by weight: c =0.06, Si =0.20, Mn =1.55, P =0.009, S =0.0020, Al =0.028, Ti =0.017, Nb =0.041, Cu =0.03, Ni =0.12, Ca =0.0007, Mo =0.10, Cr =0.18, and the balance Fe and unavoidable impurity elements. The traditional low-carbon bainite steel is produced by adopting a TMCP (thermal mechanical control processing) process, the microstructure comprises acicular ferrite, granular bainite and a small amount of polygonal ferrite, the yield strength is 532MPa, the tensile strength is 634MPa, the elongation after fracture is 44 percent, and the Charpy impact energy at 40 ℃ is 357/351/384J.
According to the corrosion test scheme of the low-bainite weathering steel of example 1, the corrosion weight loss rate of the conventional low-bainite steel is also measured and the corrosion morphology is observed.
Fig. 2 shows a comparison of corrosion weight loss ratios of the two steels. It is apparent that the corrosion resistance of the lower bainite weathering steel of example 1 is superior to that of the conventional lower bainite steel.
The micro-corrosion morphology of the lower bainite weathering steel of example 1 after being etched for 10 days is shown in fig. 3, and the micro-corrosion morphology of the conventional lower bainite steel after being etched for 10 days is shown in fig. 4. As can be seen from the figure, a large number of shallow disc-shaped pitting corrosion is formed on the surface of the sample, but the traditional low-carbon bainite steel has larger pitting caliber and depth, and large-area corrosion spots are formed. The results show that the lower bainite weathering steel of example 1 has better corrosion resistance.
Example 2
The steel has a chemical composition in weight percent of C =0.04, Si =0.65, Mn =1.23, P =0.013, S =0.0015, Al =0.030, Ti =0.016, Nb =0.015, Cu =0.64, Ni =0.82, Ca =0.0026, Mo =0.11, Cr =0.17, and the balance of Fe and unavoidable impurity elements.
The production process of the steel comprises the steps of adopting a converter, an LF furnace and an RH furnace, smelting molten steel according to the components, continuously casting the molten steel into a plate blank, carrying out surface grinding after the plate blank is cooled to room temperature, then reheating the plate blank for rolling and finishing, carrying out a heat treatment process of normalizing, accelerated cooling and isothermal aging after surface shot blasting, and finally sampling and detecting the performance.
The key technological parameters in the production method are as follows: feeding a Ca line 250m behind the LF furnace for soft argon blowing for 12min, feeding a Ca line 350m behind the RH furnace for soft argon blowing for 20 min; protective pouring is adopted for continuous casting, the superheat degree is 14-15 ℃, the steel passing amount is 3.2t/min, the vibration frequency of a crystallizer is 280 times/min, and the amplitude is 3 mm; the slab reheating temperature is 1236 ℃, the soaking time is 1.5h, the rolling finishing temperature is 830 ℃, and the slab is air-cooled after rolling; normalizing at 860 deg.C for 100 min; after normalizing, the accelerated cooling rate is 13.6 ℃/s, and the final cooling temperature is 580 ℃; then directly carrying out isothermal aging at the temperature of 580 ℃ for 3 h; and air cooling after aging.
The microstructure of the lower bainite weathering steel of example 2 was observed, and the microstructure consisted of 95% or more of non-carbon bainite, a small amount of austenite at grain boundaries, and a Cu — Ni aged precipitate phase.
The steel plate of the example 2 is tested for mechanical properties, and has the yield strength of 518MPa, the tensile strength of 613MPa, the elongation after fracture of 28 percent and the Charpy impact work of 142/138/136J at the temperature of-40 ℃.

Claims (2)

1. A low-carbon bainite weathering steel is characterized in that: the steel comprises the following chemical components, by weight, 0.03-0.08% of C, 0.50-0.80% of Si, 1.00-1.80% of Mn, 0.015% or less of P, 0.005% or less of S, 0.02-0.05% of Al, 0.008-0.020% of Ti, 0.020% or less of Nb, 0.50-0.80% of Cu, 0.50-1.00% of Ni, 0.006% or less of Ca, 0.30% or less of Mo, 0.30% or less of Cr, 1.5% or more of Ca/S and the balance of Fe and inevitable impurity elements; smelting molten steel by adopting a converter, an LF furnace and an RH furnace, continuously casting the molten steel into a plate blank, carrying out surface grinding after the plate blank is cooled in a heaped mode to room temperature, then reheating the plate blank for rolling and finishing, carrying out a heat treatment process of normalizing, accelerated cooling and isothermal aging after surface shot blasting, and finally sampling and detecting the performance, wherein the key process steps comprise: ca treatment is carried out after the LF furnace and the RH furnace, the Ca line is fed after the LF furnace is more than or equal to 200m, the Ca line is fed after the RH furnace is more than or equal to 300m, and the soft argon blowing time is more than or equal to 12min after the Ca treatment; protective pouring is adopted for continuous casting, the superheat degree is 10-20 ℃, the steel passing amount is 3.0-3.5 t/min, the vibration frequency of a crystallizer is 250-300 times/min, and the amplitude is 2-4 mm; reheating the plate blank at 1200-1250 ℃, soaking for 1-2 h, controlling the rolling finishing temperature at 800-850 ℃, and cooling in air after rolling; normalizing at 850-880 ℃, and keeping the temperature for 1-2 h; after normalizing, the accelerated cooling rate is more than or equal to 10 ℃/s, and the final cooling temperature is 550-600 ℃; then directly carrying out isothermal aging at 550-600 ℃ for 2-4 h; and air cooling to obtain the finished product of the weathering steel after aging.
2. A production method of low-carbon bainite weathering steel according to claim 1, adopting a converter, an LF furnace and an RH furnace to smelt molten steel and continuously cast into a plate blank, performing heap cooling to room temperature, then performing surface grinding, then reheating, rolling and finishing the plate blank, performing a heat treatment process of normalizing, accelerated cooling and isothermal aging after surface shot blasting, and finally sampling and detecting performance, and is characterized in that the key process steps comprise: ca treatment is carried out after the LF furnace and the RH furnace, the Ca line is fed after the LF furnace is more than or equal to 200m, the Ca line is fed after the RH furnace is more than or equal to 300m, and the soft argon blowing time is more than or equal to 12min after the Ca treatment; protective pouring is adopted for continuous casting, the superheat degree is 10-20 ℃, the steel passing amount is 3.0-3.5 t/min, the vibration frequency of a crystallizer is 250-300 times/min, and the amplitude is 2-4 mm; reheating the plate blank at 1200-1250 ℃, soaking for 1-2 h, controlling the rolling finishing temperature at 800-850 ℃, and cooling in air after rolling; normalizing at 850-880 ℃, and keeping the temperature for 1-2 h; after normalizing, the accelerated cooling rate is more than or equal to 10 ℃/s, and the final cooling temperature is 550-600 ℃; then directly carrying out isothermal aging at 550-600 ℃ for 2-4 h; and air cooling to obtain the finished product of the weathering steel after aging.
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