Weathering resistant steel with high Si, low Ni and no Nb and production method thereof

Abstract

The invention discloses weathering resistant steel with high Si, low Ni and no Nb and a production method thereof, the weathering resistant steel comprises the following components: C, Si, Mn, Ti, Cr, Cu, Als, P, S, Ca, a trace amount of Ni, and the balance of Fe and inevitable impurities, and the contents of the components simultaneously meet the following conditions: (1) 6Mn + 108Cu is more than or equal to 32% and less than or equal to 40%; (2) 3.2 Cr + 1.6 Cu-0.33 P is greater than or equal to 1.6% and less than or equal to 2.1%; (3) the atmospheric corrosion resistance index I is greater than or equal to 6.0%; the production method comprises the following steps: heating a casting blank to 1130-1150 DEG C, and placing the casting blank in a furnace for 200-240 minutes; two-stage controlled rolling is carried out, the rolling temperature of the first stage is 980-1050 DEG C, the initial rolling temperature of the second stage is 890-950 DEG C, and the final rolling temperature is 810-850 DEG C; water cooling is conducted after rolling, the initial cooling temperature is 750-810 DEG C, the cooling speed is 15-20 DEG C / S, and the self-tempering temperature is 600-650 DEG C; according to the steel disclosed by the invention, through reasonable component design, in particular, key alloys are strictly combined and added according to a proportion, and meanwhile, a reasonable production process is supplemented, so that the obtained steel plate integrates excellent mechanical property, appearance quality and high corrosion resistance, precious alloys are greatly reduced, the production cost is low, the market competitiveness is high, and the steel plate belongs to a green and economical product.

Description

Technical Field

[0001] The invention relates to the technical field of steel material manufacturing, in particular to a high-Si, low-Ni and Nb-free weathering steel and a production method thereof. Background Art

[0002] Weathering steel first appeared in Europe. With the improvement of people's requirements for building quality and environmental protection, the application of weathering steel in the domestic construction field has been continuously expanding. In recent years, the domestic weathering steel industry has continuously increased its investment in technology, continuously optimized product quality, and continuously improved various indicators. However, the current production of weathering steel is still basically based on experience to select alloy elements. Precious alloys such as Ni, Cr, Cu, Nb and other elements are added in large amounts, which greatly increases its production cost compared to ordinary structural steel, hindering its promotion and popularization in the market; on the other hand, weathering steel generally contains phosphorus, which reduces the toughness of the steel plate and increases its brittleness, causing problems with welding and recycling.

[0003] In view of the above problems, it is necessary to further strengthen research and development, optimize the alloy element ratio and production process, improve the corrosion resistance and environmental adaptability of weathering steel, and strengthen market promotion and popularization to improve consumers' awareness and acceptance of weathering steel. There are many reports on the production of weathering steel plates in China, and patents have also been applied for.

[0004] The Chinese patent application with publication number CN107475624A discloses a titanium-containing thick-gauge weathering steel and a production method thereof, which adopts a composition design of low C, medium Mn and Cr+Ni+Cu, and adds 0.030-0.045% Nb alloy, and the alloy cost is high.

[0005] The Chinese patent application with publication number CN107881429A discloses a hot-rolled high-strength weathering steel and a manufacturing method thereof, wherein the chemical composition is as follows: C: 0.05-0.07%; Si: 0.5-0.6%; Mn: 0.8-1.0%; P: 0.03-0.07%; S: ≤0.005%; Cr: 0.25-0.35%; Cu: 0.25-0.35%; Ti: 0.09-0.11%, and the rest is iron and unavoidable impurities; the Ti content of this steel is 0.09-0.11%, and excessive Ti content will deteriorate the low-temperature toughness and welding performance of the steel. At the same time, its P content is 0.03-0.07%, which is easy to cause serious internal segregation, and the impact on thick-gauge steel plates is particularly severe.

[0006] The above patents either add too much precious alloys or add too high P, Ti and other elements that are not conducive to the comprehensive performance of the steel plate, which does not meet the overall requirements of green and economical weather-resistant structural steel demanded by the current market. Therefore, the development of a low-cost and high-performance weather-resistant steel has become an urgent problem to be solved in the industry at this stage. Summary of the invention

[0007] The purpose of the present invention is to solve the problems that the current methods for producing weathering steel generally have high content of precious metal alloys, high cost, or too high content of P and Ti elements, which affect the comprehensive performance of the steel plate. A weathering steel with high Si, low Ni and no Nb and a production method thereof are proposed. The method of the present invention uses a trace amount of alloy and controls a relatively low P content to obtain a steel plate with a thickness of 8 to 100 mm without equipment modification, with intact surface quality, no defects such as cracks, a yield strength of 435 to 509 MPa, a tensile strength of 625 to 673 MPa, a yield strength ratio of ≤0.78, a steel plate with an impact of 180 to 283 J at -20°C, and a corrosion rate of ≤1.245 g / m 2 ˑh steel plate production method.

[0008] The invention discloses a weathering steel with high Si, low Ni and no Nb, comprising the following chemical components in percentage by mass: C: 0.12-0.14%, Si: 0.45-0.55%, Mn: 1.25-1.45%, Ti: 0.008-0.015%, Cr: 0.40-0.50%, Ni: 0.08-0.15%, Cu: 0.20-0.30%, Als: 0.015-0.030%, P≤0.015%, S≤0.004%, and the rest are Fe and unavoidable impurities, and the contents of the above elements satisfy the following relationship at the same time: (1) 32%≤6Mn+108Cu≤40%; (2) 1.6%≤3.2Cr+1.6Cu-0.33P≤2.1%; (3) Atmospheric corrosion resistance index: I=26.0lCu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29Cu•Ni-9.10Ni•P-33.39Cu²≥6.0%.

[0009] The weathering steel finished plate produced by the present invention has a thickness specification of 8-100 mm, a good surface quality of the steel plate, no crack defects, a yield strength of 435-509 MPa, a tensile strength of 625-673 MPa, a yield strength ratio of ≤0.78, an impact of 180-283 J at -20°C, and a corrosion rate of ≤1.245 g / m 2 ·h.

[0010] The present invention provides a method for producing high-Si, low-Ni and Nb-free weathering steel, comprising: KR hot metal desulfurization → converter top and bottom combined blowing smelting → inclusion calcium treatment → LF furnace refining → vacuum treatment → continuous casting → holding pit slow cooling → billet heating → rolling mill rolling → steel plate stack cooling → finishing, wherein: (1) KR hot metal desulfurization: deep desulfurization process is adopted, the S content of hot metal entering the converter is ≤ 0.003%, and the hydrogen content is < 1.0 ppm; (2) Ferromanganese, ferrosilicomanganese and ferrochrome are added when 1 / 3 of the steel is tapped from the converter, and are added before 2 / 3 to 3 / 4 of the steel is tapped. Nickel plates and copper plates are added after the steel is tapped. The vacuum pressure during vacuum treatment is ≤67Pa, and the vacuum holding time is ≥15min. (3) During the continuous casting process, the secondary cooling water straightening temperature is controlled at 920-930°C, the pulling speed is controlled at 0.80-0.90 m / min, the lifting and lowering pulling speed fluctuation is controlled within ±0.05 m / min, the superheat is controlled within the range of 10-25°C, and the continuous casting is performed into 200-300 mm thick ingots; (4) The casting is heated to 1130-1150°C at a heating rate of 7-8 min / mm, and the furnace time is controlled at 200-240 min; (5) The rolling mill adopts two-stage controlled rolling: the first stage rolling temperature is controlled at 980-1050°C to roll into an intermediate billet, the second stage start rolling temperature is controlled at 890-950°C, and the final rolling load temperature is 810-850°C; (6) Water cooling is used for cooling after rolling, the cooling temperature is controlled at 750-810℃, the cooling rate is controlled at 15-20℃ / S, and the roller speed during ACC cooling is limited to 0.8-1.2m / s, and the red-return temperature is controlled at 600-650℃.

[0011] The reasons for limiting the main chemical components of the weathering steel of the present invention are as follows: C: Carbon is one of the indispensable elements in steel for improving the strength of steel. When the C content is lower than 0.12%, the above-mentioned strengthening effect of C is weakened, making the strength of the invented steel insufficient; when the C content is too high, it will increase the welding cold crack sensitivity coefficient, strongly reduce the low-temperature toughness of the substrate and the welding heat-affected zone, and affect the hot and cold processing performance, so the C content is controlled at 0.12-0.14%.

[0012] Si: Silicon can play a role in solid solution strengthening and deoxidation in steel. When the Si content is high, a Si-rich protective film can be formed on the surface of the steel. Si can also refine the α-FeOOH rust layer and stabilize it. Especially when used in combination with Cu, Cr, and P, it can improve the atmospheric corrosion resistance of weathering steel. However, when the Si content is greater than 0.60%, it is harmful to the toughness of the steel. Therefore, the Si content is controlled at 0.45-0.55%.

[0013] Mn: Manganese can be dissolved into cementite to form Mn-containing alloy cementite. It is an austenite stabilizing element and can improve the strength of steel within a certain range. However, as the Mn content increases, the density of the rust layer will be reduced. Therefore, the Mn content is controlled at 1.25-1.45%.

[0014] Cu: Copper can effectively improve the atmospheric corrosion resistance of steel. Its electrode potential is relatively high. It reacts with the matrix as a cathode contact, accelerates the formation of a stable oxide film, produces a passivation effect, plays an anti-corrosion role, and reduces the corrosion rate of steel. On the other hand, when the copper content reaches 0.2%, Cu atoms are precipitated on the surface of the steel in a free state, forming a uniformly dispersed Cu-rich phase in the rust layer, which forms a copper oxide compound that is closely attached to the steel matrix, so that the formed rust layer is protective and slows down the corrosion of the matrix. In addition, copper can improve the strength of steel through solid solution strengthening. Therefore, the Cu content is limited to 0.2-0.3%.

[0015] At the same time, it is limited to 32≤6Mn+108Cu≤40 to maximize the corrosion resistance of Mn on Cu-containing steel.

[0016] Cr: Chromium is the most effective passivation element. Its passivation effect forms a dense oxide film on the surface of weathering steel. This oxide film isolates the contact between the substrate and the external dielectric. Chromium is conducive to the refinement of α-FeOOH, preventing the invasion of corrosive ions such as chloride ions, and inhibiting further corrosion of steel. In addition, chromium can also effectively improve the hardenability of steel and improve the plasticity and toughness of steel. Therefore, the Cr content is controlled at 0.40-0.50%.

[0017] P: Phosphorus is an element that is easy to segregate. It is easy to segregate in parts of steel, thereby reducing the plasticity, low-temperature toughness and welding performance of steel. Therefore, the P content is limited to ≤0.015%. However, when it is added together with alloying elements such as Cr and Cu, it can effectively prevent the rust layer formed on the surface of the steel plate from being reduced when it encounters water, making the rust layer more stable and significantly improving the atmospheric corrosion resistance of the steel; therefore, it is strictly limited to 1.6≤3.2Cr+1.6Cu-0.33P≤2.1. When the above component combination requirements are not met, the corrosion resistance of the steel is very poor.

[0018] Ni: Nickel can increase the self-corrosion potential of the steel matrix, thereby increasing the stability of the steel matrix and improving the corrosion resistance of the steel. On the other hand, nickel in the form of oxides can increase the density of the rust layer, thereby improving the atmospheric corrosion resistance of the steel. At the same time, adding a certain amount of nickel alloy to the steel can effectively improve the thermal cracking phenomenon caused by copper during the rolling process; in addition, nickel exists in the form of solid solution in the steel, which can improve the stability of austenite, inhibit the precipitation of proeutectoid ferrite, and increase the strength and tough-brittle transition temperature of the steel. By controlling rolling and cooling, controlling the reasonable organizational structure, the mechanical properties of the steel can be effectively improved; however, the cost of nickel plates is high, and adding too much Ni alloy is bound to cause a substantial increase in costs, so the Ni content is controlled within the range of 0.08-0.15%.

[0019] Ti: Titanium is a strong deoxidizer in steel, which can make the internal structure of steel dense, refine grains, reduce aging sensitivity and cold brittleness, improve welding performance, and adding a certain amount of Ti can also reduce the longitudinal and transverse performance differences. In addition, titanium has greater resource and cost advantages than strengthening elements such as niobium and vanadium, so the designed Ti content is: Ti: 0.008~0.015%.

[0020] Als: Aluminum is used as a deoxidizing and nitrogen fixing agent during steelmaking. It refines grains, inhibits the aging of low-carbon steel, improves the toughness of steel at low temperatures, and can also improve the oxidation resistance of steel. Therefore, the Als content is controlled at 0.015-0.030%.

[0021] At the same time, the atmospheric corrosion resistance index is strictly limited: I=26.0lCu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29Cu•Ni-9.10Ni•P-33.39Cu²≥6.0%, which makes the steel have good atmospheric corrosion resistance.

[0022] In addition to requiring the content range of individual elements in the composition, the present invention also specifically limits the content of the above elements to simultaneously satisfy the following three relationships: (1) 32≤6Mn+108Cu≤40, (2) 1.6≤3.2Cr+1.6Cu-0.33P≤2.1, (3) atmospheric corrosion resistance index I≥6.0, in order to maximize the atmospheric corrosion resistance through the interaction of different elements while ensuring the mechanical properties of the steel plate.

[0023] The reasons for setting the main production process parameters of the steel of the present invention are as follows: Smelting stage: deep desulfurization of molten iron, composite blowing at the top and bottom of the converter, and RH vacuum treatment are used to ensure that the hydrogen content of the molten steel is less than 1.0ppm, P≤0.006%, and S≤0.002%, laying a good foundation for the high quality of the ingot; the continuous casting secondary cooling water straightening temperature is controlled at 920-930℃, the pulling speed is controlled at 0.80-0.90m / min, and the ingot is continuously cast into 200-300mm thick ingot, and the superheat is controlled within the range of 10-25℃. The above parameters are controlled to reduce the gas content inside the ingot, so that the shell thickness of the ingot can grow evenly during the continuous casting process, reducing the occurrence of defects such as surface cracks.

[0024] Ingot heating stage: the ingot is heated to 1130-1150℃ at a heating rate of 7-8min / mm, and the furnace time is controlled within 200-240min to shorten the time of Cu liquefaction and severe enrichment; the heating furnace gas is controlled to a weak reducing atmosphere to reduce the enrichment of Cu in the oxide layer and the steel matrix caused by the oxidation of the slab surface, avoid the two-dimensional extrusion of the edge in the horizontal and vertical directions, and reduce the probability of cracks.

[0025] Rolling stage: The rolling mill adopts two-stage controlled rolling. The rolling temperature of the first stage is controlled at 980-1050℃, and the intermediate billet is rolled. The second stage rolling temperature is controlled at 890-950℃, and the final rolling load temperature is 810-850℃. The cooling adopts water cooling after rolling, the cooling temperature is controlled at 750-810℃, the cooling rate is controlled at 15-20℃ / S, the cooling roller speed is 0.8-1.2m / s, and the red-returning temperature is controlled at 600-650℃. In order to form a certain proportion of quasi-polygonal ferrite, acicular ferrite and granular bainite structure, and at the same time ensure uniform structure at different positions in the thickness, ensure good plasticity and toughness of the steel plate and low yield strength ratio.

[0026] The technical solution provided by the present invention breaks the traditional luxurious alloy combination of weathering steel, replaces the precious Ni alloy with cheap Si, removes the Nb alloy addition, and through special alloy ratio and heating, controlled rolling and controlled cooling process, ensures the intact surface quality and excellent plasticity of the steel plate while also having good corrosion resistance. The finished steel plate produced has a thickness of 8 to 100 mm, good appearance quality, high corrosion resistance, and a yield strength of 435 to 509 MPa, a tensile strength of 625 to 673 MPa, a yield strength ratio of ≤0.78, an impact of -20°C of 180 to 283 J, and a corrosion rate of ≤1.245 g / m 2 ·h.

[0027] The steel produced by the present invention has the following beneficial effects: (1) Simple chemical composition design, low precious alloy and harmful elements added, it is a green and economical product; (2) The short-process technology eliminates the need for additional equipment upgrades and post-rolling heat treatment, greatly shortening the production cycle, improving production and contract delivery efficiency, and achieving a win-win situation for steel mills and users; (3) The products produced have a wide range of thickness, high strength, excellent low-temperature toughness and low yield strength ratio, as well as good corrosion resistance. They are high value-added products with universal promotion significance. DETAILED DESCRIPTION

[0028] In order to better explain the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments. The following embodiments are merely exemplary of the technical solution of the present invention and do not limit the present invention in any form. The serial numbers of the following embodiments are only for description and do not represent the advantages and disadvantages of the embodiments.

[0029] Table 1 below is a list of chemical composition values ​​(wt, %) of the steel plates of various embodiments of the present invention and the comparative examples; Table 2 below is a list of the main process parameter values ​​of the key processes of the steel plates of various embodiments of the present invention and the comparative examples; Table 3 below is a list of main performance test results of steel plates of various embodiments of the present invention and comparative examples; Table 4 below is a list of corrosion resistance test results of the steel plates of various embodiments of the present invention and the comparative examples.

[0030] A production method of high Si, low Ni and Nb-free weathering steel in each embodiment of the present invention comprises: KR molten iron desulfurization → converter top and bottom combined blowing smelting → inclusion calcium treatment → LF furnace refining → vacuum treatment → continuous casting → holding pit slow cooling → ingot heating → rolling mill rolling → steel plate stack cooling → finishing, wherein: (1) KR hot metal desulfurization: deep desulfurization process is adopted, the S content of hot metal entering the converter is ≤ 0.003%, and the hydrogen content is < 1.0 ppm; (2) Ferromanganese, ferrosilicomanganese and ferrochrome are added when 1 / 3 of the steel is tapped from the converter, and are added before 2 / 3 to 3 / 4 of the steel is tapped. Nickel plates and copper plates are added after the steel is tapped. The vacuum pressure during vacuum treatment is ≤67Pa, and the vacuum holding time is ≥15min. (3) During the continuous casting process, the secondary cooling water straightening temperature is controlled at 920-930°C, the pulling speed is controlled at 0.80-0.90 m / min, the lifting and lowering pulling speed fluctuation is controlled within ±0.05 m / min, the superheat is controlled within the range of 10-25°C, and the continuous casting is performed into 200-300 mm thick ingots; (4) The casting is heated to 1130-1150°C at a heating rate of 7-8 min / mm, and the furnace time is controlled at 200-240 min; (5) The rolling mill adopts two-stage controlled rolling: the first stage rolling temperature is controlled at 980-1050°C to roll into an intermediate billet, the second stage start rolling temperature is controlled at 890-950°C, and the final rolling load temperature is 810-850°C; (6) Water cooling is used for cooling after rolling, the cooling temperature is controlled at 750-810℃, the cooling rate is controlled at 15-20℃ / S, and the roller speed during ACC cooling is limited to 0.8-1.2m / s, and the red-return temperature is controlled at 600-650℃.

[0031] Table 1 List of chemical composition values ​​of steel plates of various embodiments of the present invention and comparative examples (wt, %)

[0032] Table of main process parameter values ​​for key processes of steel plates in various embodiments of the present invention and comparative examples

[0033] Table 3 Main performance test results of steel plates of various embodiments of the present invention and comparative examples

[0034] Table 4 Corrosion resistance test results of steel plates of various embodiments of the present invention and comparative examples

[0035] The corrosion resistance test adopts a weekly immersion corrosion test. The corrosion rate is calculated and evaluated by calculating the weight loss of each test sample after 72 hours of corrosion. Specific scheme: The test samples are immersed in NaHSO with a concentration of 0.01 mol / L and a solution temperature of 45°C. 3 Each cycle time is 1 hour, the immersion time of each cycle is 15 minutes, 4 parallel samples are taken in each group, and the experimental results are taken as the average value of their weight loss.

[0036] It can be seen from Table 3 above that the 8-100 mm thick steel plates produced by the composition and production process designed by the present invention have good surface quality, no defects such as cracks, a yield strength of 435-509 MPa, a tensile strength of 625-673 MPa, a yield strength ratio of ≤0.78, and a -20°C impact of 180-283 J. On the other hand, comparative examples 1 and 2 both have crack defects to varying degrees, and the strength fluctuates greatly, and cannot meet the requirements of high strength, low yield strength ratio and excellent low-temperature toughness.

[0037] It can be seen from Table 4 above that the corrosion rate of the 8-100 mm thick steel plate produced by the composition and production process designed by the present invention is ≤1.245 g / m 2 h, while the comparative examples 1 and 2 both reached 2.5 g / m 2 ˑh or more.

[0038] In summary, the weather-resistant structural steel produced by the present invention is designed with reasonable ingredients, especially the key alloys are added in a strict combination according to a certain proportion, and their beneficial effects are maximized. At the same time, a reasonable heating, rolling and cooling system is used. The steel plate finally obtained combines excellent mechanical properties, appearance quality and high corrosion resistance, and achieves the following effects: the surface quality of the 8-100 mm thick steel plate produced is intact, without defects such as cracks, the yield strength is 435-509 MPa, the tensile strength is 625-673 MPa, the yield strength ratio is ≤0.78, the -20°C impact is 180-283 J, and the corrosion rate is ≤1.245 g / m 2 ˑh, low production cost, better performance than the same category of steel plates on the market, strong market competitiveness, suitable for wide promotion.

[0039] The above embodiments are only specific examples for explaining the present invention and do not limit the present invention in any form. Any non-substantial changes made by anyone based on the above contents and forms without departing from the protection scope of the claims of the present invention shall be deemed to fall within the protection scope of the claims of the present invention. The present invention is not limited to the above specific implementation examples.

Claims

1. A weathering steel with high Si, low Ni and no Nb, characterized in that The chemical composition comprises the following mass percentages: C: 0.12-0.14%, Si: 0.45-0.55%, Mn: 1.25-1.45%, Ti: 0.008-0.015%, Cr: 0.40-0.50%, Ni: 0.08-0.15%, Cu: 0.20-0.30%, Als: 0.015-0.030%, P≤0.015%, S≤0.004%, and the rest are Fe and unavoidable impurities, and the contents of the above elements satisfy the following relationship at the same time: (1) 32%≤6Mn+108Cu≤40%; (2) 1.6%≤3.2Cr+1.6Cu-0.33P≤2.1%; (3) Atmospheric corrosion resistance index: I=26.0lCu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29Cu·Ni-9.10Ni·P-33.39Cu²≥6.0%.

2. The high Si, low Ni and Nb-free weathering steel according to claim 1, characterized in that: The thickness of the finished weathering steel plate is 8-100mm, the surface quality of the steel plate is intact, without crack defects, the yield strength is 435-509MPa, the tensile strength is 625-673MPa, the yield strength ratio is ≤0.78, the impact at -20℃ is 180-283J, and the corrosion rate is ≤1.245g / m 2 ·h.

3. A method for producing a high-Si, low-Ni and Nb-free weathering steel as claimed in claim 1 or 2, comprising: KR hot metal desulfurization → converter top and bottom combined blowing smelting → inclusion calcium treatment → LF furnace refining → vacuum treatment → continuous casting → holding pit slow cooling → billet heating → rolling mill rolling → steel plate stack cooling → finishing, characterized by: (1) KR hot metal desulfurization: deep desulfurization process is adopted, the S content of hot metal entering the converter is ≤ 0.003%, and the hydrogen content is < 1.0 ppm; (2) Ferromanganese, ferrosilicomanganese and ferrochrome are added when 1 / 3 of the steel is tapped from the converter, and are added before 2 / 3 to 3 / 4 of the steel is tapped. Nickel plates and copper plates are added after the steel is tapped. The vacuum pressure during vacuum treatment is ≤67Pa, and the vacuum holding time is ≥15min. (3) During the continuous casting process, the secondary cooling water straightening temperature is controlled at 920-930°C, the pulling speed is controlled at 0.80-0.90 m / min, and the fluctuation of the lifting and lowering pulling speed is controlled within ±0.05 m / min, and the continuous casting is performed into 200-300 mm thick ingots; (4) The billet is heated to 1130-1150°C and the furnace time is controlled at 200-240 minutes; (5) The rolling mill adopts two-stage controlled rolling: the first stage rolling temperature is controlled at 980-1050°C to roll into an intermediate billet, the second stage start rolling temperature is controlled at 890-950°C, and the final rolling load temperature is 810-850°C; (6) Water cooling is used for cooling after rolling, the cooling temperature is controlled at 750-810℃, the cooling rate is controlled at 15-20℃ / S, and the roller speed during ACC cooling is limited to 0.8-1.2m / s, and the red-return temperature is controlled at 600-650℃.

4. The method for producing high Si, low Ni and Nb-free weathering steel according to claim 3, characterized in that: In step (3), the superheat during the continuous casting process is controlled within the range of 10 to 25°C.

5. The method for producing high Si, low Ni and Nb-free weathering steel according to claim 3, characterized in that: In step (4), the ingot is heated to a temperature of 1130-1150° C. at a heating rate of 7-8 min / mm.

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