An ultrahigh-strength weather-resistant reinforcing bar and a production method thereof

Abstract

The application relates to the technical field of ultrahigh-strength steel, and provides an ultrahigh-strength weather-resistant steel bar and a production method thereof.The production method of the ultrahigh-strength weather-resistant steel bar comprises the following steps: preheating waste steel, smelting the waste steel after preheating and smelting auxiliary materials in an electric arc furnace, controlling a smelting end point, transferring the molten steel after electric arc furnace smelting into an LF refining furnace, adding stainless steel waste into the LF refining furnace for refining, adding alloy fine-tuning components, controlling the molten steel component at the refining end point, performing whole-process protective casting on the molten steel after refining, obtaining a continuous casting billet, performing rolling, tempering and cooling treatment on the continuous casting billet after heat supplement, and obtaining the ultrahigh-strength weather-resistant steel bar.The ultrahigh-strength weather-resistant steel bar has a finished product tensile strength Rm of greater than or equal to 1000 Mpa, a yield strength Rel of greater than or equal to 800 Mpa, and a breaking elongation A of greater than or equal to 10%.

Description

Technical Field

[0001] This invention relates to the field of ultra-high strength steel technology, specifically to an ultra-high strength weather-resistant steel bar and its production method. Background Technology

[0002] As the core load-bearing component of concrete structures, steel reinforcement directly determines the safe service life of infrastructure projects and building structures through its strength, toughness, ductility, and weather resistance. It also affects the structure's resistance to collapse under natural disasters or extreme loads. Developing new high-strength, weather-resistant steel reinforcement can significantly improve the safety factor of infrastructure and building projects, effectively preventing major accidents and huge losses of life and property caused by material failure.

[0003] Currently, high-strength steel bars with a strength of 400MPa and above are widely used in domestic engineering construction, with models such as HRB400E and HRB500E accounting for over 60% of the market share. However, due to cost control constraints, domestically produced high-strength steel bars still lag significantly behind international advanced levels in terms of alloying control, impurity element control, steel purity, welding performance, and fatigue resistance, and some high-end products still rely on imports.

[0004] In terms of mechanical properties, the yield strength ratio (0.8-0.9) and elongation at break (≥15%) of domestically produced HRB500E grade high-strength steel bars are lower than those of American grade 75 steel bars (yield strength ratio ≤0.85, elongation ≥18%). The HT590 grade seismic steel bars developed in Japan perform even better, maintaining 2 / 3 of the yield strength in a high-temperature environment of 600℃, significantly leading similar fire-resistant steel bar products in China.

[0005] In terms of weather resistance, European and American countries have significantly improved the corrosion resistance of steel bars used in marine engineering by adding alloying elements such as chromium and nickel, extending their service life by more than 50% compared to ordinary steel bars in China. In contrast, China mainly relies on post-treatment technologies such as epoxy resin coating, which are not only more expensive, but also have limited long-term service stability.

[0006] In terms of steel bar preparation, China's short-process steelmaking technology has developed rapidly in recent years. However, there is still a gap with developed countries in key aspects such as intelligent graded utilization of scrap steel and precise control of refining processes. This is one of the core reasons why the quality of domestic steel bars is inferior to that of similar products from the United States, Japan and Europe.

[0007] Steel reinforcement is the core load-bearing component of concrete structures, and its strength, toughness, plasticity, and weather resistance directly determine the safe service life of infrastructure projects and building structures. With the increase in infrastructure projects in high-altitude and cold regions, higher requirements are being placed on the collapse resistance and corrosion resistance of steel reinforcement in extreme environments. Summary of the Invention

[0008] This invention addresses the problem of obtaining ultra-high strength weather-resistant steel bars at low cost in the prior art by providing an ultra-high strength weather-resistant steel bar and its production method.

[0009] The technical method of the present invention is as follows:

[0010] A method for producing ultra-high strength weather-resistant steel bars, the method comprising the following steps:

[0011] S1. Preheat the scrap steel;

[0012] S2. The preheated scrap steel is smelted together with steelmaking auxiliary materials in an electric arc furnace, and the C content at the end of the smelting is controlled to be 0.07-0.15 wt.% and the P content is 0.015-0.025 wt.%. The steelmaking auxiliary materials include lime, lightly calcined dolomite and carbon powder.

[0013] S3. Transfer the molten steel smelted in the electric arc furnace to the LF refining furnace, and add stainless steel scrap to the LF refining furnace for refining; add alloy fine-tuning components to control the composition of the molten steel at the refining endpoint to contain: C: 0.28-0.30%; Si: 0.80-1.00%; Mn: 1.70~1.90%; S: ≤0.015%; P: 0.025~0.035%; Cu: 0.10-0.15%; Mo: 0.30~0.60%; Cr: 0.20~0.30%; Nb: 0.04-0.05%; V: 0.10~0.35%; O: ≤40ppm; N: 200-250ppm.

[0014] S4. The refined molten steel is cast under full protection to obtain a continuously cast billet.

[0015] S5. After being reheated, the continuously cast billet is rolled, tempered, and cooled to obtain ultra-high strength weather-resistant steel bars.

[0016] In step S1, the scrap steel is selected from one or more of Q195, Q235, Q345, and Q355. The preheating temperature is 800-1000℃.

[0017] In step S2, the refining temperature is controlled at 1620-1650℃, and the refining time is 40-60 minutes. During the refining process, a mixture of nitrogen and natural gas is used for stirring, with a volume ratio of nitrogen to natural gas of 100:1. The stainless steel scrap includes 201 stainless steel scrap and 17-4PH stainless steel scrap; the amount of 201 stainless steel scrap added accounts for 0.6-0.8 wt.% of the total scrap; the amount of 17-4PH stainless steel scrap added accounts for 0.3-0.5 wt.% of the total scrap.

[0018] In step S3, the step of adding alloys to fine-tune the composition includes: after the electric arc furnace tapping reaches 1 / 4, sequentially adding metallic aluminum particles, silicon-carbon alloy, silicon-manganese alloy, ferromolybdenum, vanadium-nitrogen alloy, and niobium-phosphorus alloy with the steel stream; and completing the addition of the above alloys when the ladle molten steel reaches 4 / 5. The refining temperature is controlled at 1620 or 1600℃, and the refining time is 40-60 minutes. During the refining process, nitrogen and argon are used for alternating stirring; the basicity of the protective slag in the LF refining furnace is controlled at 2.2-2.7, and the white slag is maintained for more than 10 minutes.

[0019] In step S5, before entering rolling, the continuously cast billet is dynamically reheated using an induction heater at a temperature of 980-1000℃, and the temperature difference between the head and tail of the billet is controlled within 10℃. The rolling process consists of rough rolling, head trimming, tail trimming, and finish rolling. The rough rolling temperature is 935-965℃ for 1 minute, rolling the billet into round bars with a diameter of 40-60mm. Then, head and tail trimming are completed. The finish rolling temperature is 830-850℃ for 10 seconds, rolling into steel bar products with a diameter of 12-20mm. After rolling, the steel bar products are rapidly cooled to below 300℃ within 8-10 seconds. The tempering process uses high-temperature tempering at a temperature of 820-840℃ for 30-40 minutes. The cooling process includes: cooling the tempered billet to below 350°C, immersing it in an 8-10 wt.% potassium silicate aqueous solution and stirring for 5-8 seconds, then removing it and air-cooling it to room temperature.

[0020] The present invention also provides an ultra-high strength weather-resistant steel bar produced by the above method, wherein the matrix structure of the ultra-high strength weather-resistant steel bar is bainite and a small amount of ferrite, the yield strength is ≥800MPa, the tensile strength is ≥1000MPa, and the elongation is ≥12%; after a 24-hour neutral salt spray corrosion test, the rust area of ​​the ultra-high strength weather-resistant steel bar is ≤5%.

[0021] The beneficial effects of this invention are:

[0022] I. This invention uses scrap steel such as Q195, Q235, Q345, Q355, 201 stainless steel, and 17-4PH stainless steel as the main raw materials, supplemented with ferromanganese, silicon carbide, vanadium-nitrogen alloy, niobium-phosphorus alloy, etc., and adopts an electric arc furnace primary refining-LF refining furnace refining-continuous casting-direct rolling process to produce ultra-high strength weather-resistant steel bars. The finished product has a tensile strength Rm≥1000Mpa, yield strength Rel≥800Mpa, and elongation after fracture A≥10%. The main components are designed with low carbon, high manganese, and high silicon composition. By adding Mo element to expand the bainite transformation zone, a mixed metallographic structure of bainite and ferrite is obtained under certain cooling rate conditions. The fine grain strengthening effect and solid solution strengthening effect brought by V, Cr and Nb composite microalloying technology are utilized, and the P and N element content is precisely controlled to fully utilize the strengthening ability of P and N elements to further improve the strength and toughness of the steel bars.

[0023] II. In order to significantly improve the tensile strength and yield strength of steel bars and ensure that the steel bars have a certain elongation, this invention reduces the sulfur content in molten steel to 0.010% based on general iron and steel metallurgical technology. In the refining furnace process section, the nitrogen content is controlled at 200~240ppm. The continuous casting process adopts a full-process protective casting process. The continuous casting machine speed is maintained at 3.3~3.7m / min. The continuously cast billet is heated to 980~1000℃ by an induction heater before entering the rolling mill for rolling. The temperature of entering the finishing mill is 830~850℃, and the high-temperature tempering temperature is 820~840℃. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the preparation process of a high-strength weather-resistant steel bar.

[0025] Figure 2 Low-magnification metallographic morphology of the steel bars prepared by the process in Example 1;

[0026] Figure 3 High-magnification metallographic morphology of the steel bars prepared by the process in Example 1;

[0027] Figure 4 Low-magnification metallographic morphology of the steel bars prepared by the process in Example 2;

[0028] Figure 5 The image shows the high-magnification metallographic morphology of the steel bars prepared by the process in Example 2. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a method for producing ultra-high strength weather-resistant steel bars, such as... Figure 1 As shown, the method includes the following steps:

[0031] S1. Preheat the scrap steel.

[0032] In this embodiment, the preheating temperature is 800-1000℃. Preheating can remove oil, paint, zinc plating, and other impurities from the surface of scrap steel, reducing their impact on the quality of the steel.

[0033] In this embodiment, the scrap steel is selected from one or more of Q195, Q235, Q345, and Q355.

[0034] S2. The preheated scrap steel is smelted together with steelmaking auxiliary materials in an electric arc furnace, and the C content at the end of the smelting process is controlled to be 0.07-0.15 wt.% and the P content is controlled to be 0.015-0.025 wt.%.

[0035] In this embodiment, the composition of the electric furnace slag at the refining endpoint is controlled as follows: TFe≤20%, R=2.0~2.5.

[0036] In this embodiment, the stainless steel scrap includes 201 stainless steel scrap and 17-4PH stainless steel scrap; the amount of 201 stainless steel scrap added accounts for 0.6-0.8 wt.% of the total scrap; the amount of 17-4PH stainless steel scrap added accounts for 0.3-0.5 wt.% of the total scrap.

[0037] In this embodiment, the steelmaking auxiliary materials include lime, light-burned dolomite, and carbon powder. The lime has the following composition: CaO 93.0%, MgO 1.1%, SiO2 0.5%, S 0.025%, and loss on ignition 3.5%. The light-burned dolomite has the following composition: CaO 48.5%, MgO 29.0%, SiO2 2.5%, S 0.05%, and loss on ignition 3.5%. The carbon powder has the following composition: C 85.0%, volatile matter 6.0%, ash content 8.5%, and moisture 0.5%.

[0038] In this embodiment, the refining temperature is controlled at 1620-1650℃, and the refining time is 40-60 minutes.

[0039] In this embodiment, during the refining process, a mixture of nitrogen and natural gas (also known as a fuel gas mixture) is used for stirring, with a volume ratio of nitrogen to natural gas of 100:1. Stirring is used to improve the uniformity of the composition and further remove impurities such as oxygen.

[0040] S3. Transfer the molten steel smelted in the electric arc furnace to the LF refining furnace, and add stainless steel scrap to the LF refining furnace for refining; add alloy fine-tuning components to control the composition of the molten steel at the refining endpoint to contain: C: 0.28-0.30%; Si: 0.80-1.00%; Mn: 1.70~1.90%; S: ≤0.015%; P: 0.025~0.035%; Cu: 0.10-0.15%; Mo: 0.30~0.60%; Cr: 0.20~0.30%; Nb: 0.04-0.05%; V: 0.10~0.35%; O: ≤40ppm; N: 200-250ppm.

[0041] In this embodiment, the step of adding alloy fine-tuning components includes: after the amount of steel tapped from the electric arc furnace reaches 1 / 4, aluminum particles, silicon-carbon alloy, silicon-manganese alloy, ferromolybdenum, vanadium-nitrogen alloy, and niobium-phosphorus alloy are added sequentially with the steel stream; and the above alloys are added when the amount of molten steel in the ladle reaches 4 / 5.

[0042] In this embodiment, the refining temperature is controlled at 1620 or 1600°C, and the refining time is 40-60 minutes.

[0043] In this embodiment, nitrogen and argon are used alternately for stirring during the refining process; the alkalinity of the protective slag in the LF refining furnace is controlled at 2.2-2.7, and the white slag is maintained for more than 10 minutes.

[0044] S4. The refined molten steel is cast under full protection to obtain a continuously cast billet.

[0045] In this embodiment, the continuous casting section employs full-process protective casting and low-supercooling casting technology. The initial casting temperature is controlled at 1510~1520℃, the secondary cooling water pressure is ≥1.2MPa, the flow rate is 400-500L / min in section I and 300-400L / min in section II. The continuous casting machine speed is 3.3~3.6m / min.

[0046] S5. After being reheated, the continuously cast billet is rolled, tempered, and cooled to obtain ultra-high strength weather-resistant steel bars.

[0047] In this embodiment, before entering the rolling mill, the continuously cast billet is dynamically reheated using an induction heater at a temperature of 980-1000℃, and the temperature difference between the beginning and end of the billet is controlled within 10℃. Two to three induction heaters can be used.

[0048] In this embodiment, rolling is divided into rough rolling, head trimming, tail trimming, and finish rolling. Rough rolling is performed at a temperature of 935–965°C for 1 minute, rolling the continuously cast billet into round bars with a diameter of 40–60 mm. Then, head and tail trimming is completed. Finish rolling is performed at a temperature of 830–850°C for 10 seconds, rolling into steel reinforcement products with a diameter of 12–20 mm. After rolling, the steel reinforcement products are rapidly cooled to below 300°C within 8–10 seconds. Rolling is performed using a rolling mill. Cooling is achieved using water mist cooling.

[0049] In this embodiment, high-temperature tempering is used, with a tempering temperature of 820~840℃ and a tempering time of 30~40min.

[0050] In this embodiment, the cooling process includes: cooling the tempered billet to below 350°C, immersing it in an 8-10 wt.% potassium silicate aqueous solution and stirring for 5-8 seconds, and then removing it and air-cooling it to room temperature.

[0051] The present invention also provides an ultra-high strength weather-resistant steel bar produced by the above method, wherein the matrix structure of the ultra-high strength weather-resistant steel bar is bainite and a small amount of ferrite, the yield strength is ≥800MPa, the tensile strength is ≥1000MPa, and the elongation is ≥12%; after a 24-hour neutral salt spray corrosion test, the rust area of ​​the ultra-high strength weather-resistant steel bar is ≤5%.

[0052] The high-strength, weather-resistant steel rebar obtained by this invention contains trace amounts of alloying elements such as Cr, Ni, Cu, and Mo, which not only enhance the strength and weather resistance of the rebar but also significantly improve its toughness and plasticity. It is suitable for application in harsh, high-altitude, and frigid infrastructure projects.

[0053] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0054] The present invention will be described in detail below through embodiments and experimental examples. However, these are merely examples and do not limit the present invention in any way.

[0055] Example 1

[0056] Using scrap steel of Q195, Q235, Q345, and Q355 in any proportion as raw material, the scrap steel is preheated using gas heating to a temperature of 800℃. Then, the preheated scrap steel is smelted together with steelmaking auxiliary materials in an electric arc furnace at a temperature of 1650℃ for 40 minutes. During the smelting process, a mixture of nitrogen and natural gas is used for stirring, with the room temperature volume ratio of nitrogen to natural gas being 100:1. The final concentrations are controlled as C: 0.09% and P: 0.025%. Electric furnace slag composition: TFe: 18%, R=2.3; steelmaking auxiliary materials: lime (CaO 93.0%, MgO 1.1%, SiO2 0.5%, S 0.025%, loss on ignition 3.5%) 21kg / t, lightly calcined dolomite (CaO 48.5%, MgO 29.0%, SiO2 2.5%, S 0.05%, loss on ignition 3.5%) 7kg / t, carbon powder (C 85.0%, volatile matter 6.0%, ash 8.5%, moisture 0.5%) 15kg / t.

[0057] The molten steel refined in the electric arc furnace is transferred to a ladle refining furnace for further refining. Simultaneously, surface-cleaned scrap steel products such as 201 stainless steel and 17-4PH stainless steel are added to the ladle refining furnace in a specific ratio as cold steel, and refined together with the molten steel. The refining temperature is controlled at 1620℃, and the refining time is 40 minutes. The amount of 201 stainless steel scrap added accounts for 0.8 wt.% of the total scrap steel, and the amount of 17-4PH stainless steel scrap added accounts for 0.3 wt.%. During the refining process, ferromanganese, ferromolybdenum, and silicon-carbon alloys are added to adjust the composition of the molten steel. Nitrogen and argon gases are alternately used for stirring during refining to ensure compositional uniformity and increase nitrogen content. The main components of the molten steel, after adjustment, are controlled as follows: C: 0.29%; Si: 0.95%; Mn: 1.78%; S: 0.010%; P: 0.030%; Cu: 0.15%; Mo: 0.3%; Cr: 0.25%; Nb: 0.045%; V: 0.20%; O: 25ppm; N: 240ppm; the balance being Fe and unavoidable impurities.

[0058] The continuous casting section employs full-process protective casting. When the molten steel temperature drops to 1515℃, the secondary cooling water pressure is 1.25MPa, the water flow rate in section I is 450L / min, and the water flow rate in section II is 350L / min. The continuous casting machine speed is 3.54m / min. During casting, an appropriate amount of argon gas is blown into the tundish protective cover for protection to reduce oxidation of the continuous casting billet surface.

[0059] The continuously cast billet is conveyed to the continuous rolling production line via a conveyor line equipped with an insulation cover for continuous rolling. During the conveying process, the billet temperature is monitored using infrared thermography, and controlled by opening and closing the insulation cover and using air cooling. Before entering the roughing mill, the billet is dynamically reheated using two induction heaters to 1000℃ before entering the rolling mill. Rolling consists of roughing, head trimming, tail trimming, and finishing. Roughing is performed at 945℃ for 1 minute, rolling the billet into a 50mm diameter round bar. Head and tail trimming are then completed. Finishing is performed at 840℃ for 10 seconds, rolling into a 14mm diameter steel bar. After rolling, the steel bar is rapidly cooled to below 300℃ within 8-10 seconds. Tempering is performed at a high temperature of 820℃ for 35 minutes. After the steel bars are cooled to 350℃, they are completely immersed in a 10% potassium silicate aqueous solution and stirred and cooled for 8 seconds. After that, ultra-high strength weather-resistant steel bar products can be obtained.

[0060] The high-strength weather-resistant steel bar product obtained in Example 1 has a matrix structure of bainite + a small amount of ferrite, a yield strength of 875 MPa, a tensile strength of 1050 MPa, and an elongation of 13.4%. After a 24-hour neutral salt spray corrosion test, the rust area is <1%.

[0061] Figure 2 and Figure 3 The image shows the metallographic structure of the steel bars prepared using the process in Example 1. As can be seen from the image, the main metallographic structure is bainite (gray) and a small amount of ferrite (white).

[0062] Example 2

[0063] Using scrap steel of Q195, Q235, Q345, and Q355 in any proportion as raw material, the scrap steel is preheated using gas heating to a temperature of 1000℃. Then, the preheated scrap steel is smelted together with steelmaking auxiliary materials in an electric arc furnace at a temperature controlled at 1620℃ for 60 minutes. During the smelting process, a mixture of nitrogen and natural gas is used for stirring, with a nitrogen-to-natural gas volume ratio of 100:1 at room temperature. The steelmaking auxiliary materials include: lime (CaO 93.0%, MgO 1.1%, SiO2 0.5%, S 0.025%, loss on ignition 3.5%) 21 kg / t, and lightly calcined dolomite (CaO 48.5%, MgO 29.0%, SiO2 0.0%)... 2.5%, S0.05%, loss on ignition 3.5%) 7kg / t, carbon powder (composition C85.0%, volatile matter 6.0%, ash 8.5%, moisture 0.5%) 15kg / t.

[0064] Molten steel refined in an electric arc furnace is transferred to a ladle refining furnace for further refining. Simultaneously, surface-cleaned scrap steel products such as 201 stainless steel and 17-4PH stainless steel are added to the ladle refining furnace in a specific ratio as cold steel, and refined together with the molten steel. The refining temperature is controlled at 1600℃, and the refining time is 60 minutes. The amount of 201 stainless steel scrap added accounts for 0.6 wt.% of the total scrap steel, and the amount of 17-4PH stainless steel scrap added accounts for 0.5 wt.%. During the refining process, ferromanganese, ferromolybdenum, and silicon-carbon alloys are added to adjust the composition of the molten steel. Nitrogen and argon gases are alternately used for stirring during refining to ensure compositional uniformity and to increase nitrogen content. The mass percentages of the main components of the molten steel after adjustment are as follows: carbon: 0.28%; silicon: 1.00%; manganese: 1.90%; sulfur: 0.012%; phosphorus: 0.035%; Cu: 0.15%; Cr: 0.20%; Mo: 0.35%; Nb: 0.05%; V: 0.25%; O: 22ppm; N: 248ppm.

[0065] The continuous casting section employs full-process protective casting. When the molten steel temperature drops to 1510℃, the secondary cooling water pressure is 1.27MPa, the water flow rate in section I is 452L / min, and the water flow rate in section II is 345L / min. The continuous casting machine speed is 3.49m / min. During casting, an appropriate amount of argon gas is blown into the tundish protective cover for protection to reduce oxidation of the continuous casting billet surface.

[0066] The continuously cast billet is conveyed to the continuous rolling production line via a conveyor line equipped with an insulation cover for continuous rolling. During the conveying process, the billet temperature is monitored using infrared thermography, and controlled by opening and closing the insulation cover and using air cooling. Before entering the roughing mill, the billet is dynamically reheated using two induction heaters to a temperature of 990°C before entering the rolling mill. Rolling consists of roughing, head trimming, tail trimming, and finishing. Roughing is performed at 950°C for 1 minute, rolling the billet into a 45mm diameter round bar. Head and tail trimming are then completed. Finishing is performed at 845°C for 10 seconds, rolling the billet into a 19mm diameter steel bar. After rolling, the steel bar is rapidly cooled to below 300°C within 8-10 seconds. Tempering is performed at a high temperature of 835°C for 35 minutes. After the steel bars are cooled to 340℃, they are completely immersed in a 10% potassium silicate aqueous solution and stirred and cooled for 5 seconds. After that, ultra-high strength weather-resistant steel bar products can be obtained.

[0067] The high-strength weather-resistant steel bar product obtained in Example 2 has a matrix structure of bainite + trace ferrite, a yield strength of 840 MPa, a tensile strength of 1090 MPa, and an elongation of 13.2%. After a 24-hour neutral salt spray corrosion test, the rust area is <1%.

[0068] Figure 4 andFigure 5 The image shows the metallographic structure of the steel bars prepared using the process in Example 2. As can be seen from the image, the main metallographic structure is bainite (gray) and a small amount of ferrite (white).

[0069] Table 1. Tensile property test results of high-strength weather-resistant steel bars prepared by the method of the present invention.

[0070]

[0071] Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible subranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the range referred to.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for producing ultra-high strength weather-resistant steel bars, characterized in that, The method includes the following steps: S1. Preheat the scrap steel; S2. The preheated scrap steel is smelted together with steelmaking auxiliary materials in an electric arc furnace, and the C content at the end of the smelting is controlled to be 0.07-0.15 wt.% and the P content is 0.015-0.025 wt.%. The steelmaking auxiliary materials include lime, lightly calcined dolomite and carbon powder. S3. Transfer the molten steel smelted in the electric arc furnace to the LF refining furnace, and add stainless steel scrap to the LF refining furnace for refining; add alloy fine-tuning components to control the composition of the molten steel at the refining endpoint to contain: C: 0.28-0.30%; Si: 0.80-1.00%; Mn: 1.70~1.90%; S: ≤0.015%; P: 0.025~0.035%; Cu: 0.10-0.15%; Mo: 0.30~0.60%; Cr: 0.20~0.30%; Nb: 0.04-0.05%; V: 0.10~0.35%; O: ≤40ppm; N: 200-250ppm. S4. The refined molten steel is cast under full protection to obtain a continuously cast billet. S5. After being reheated, the continuously cast billet is rolled, tempered, and cooled to obtain ultra-high strength weather-resistant steel bars.

2. The method according to claim 1, characterized in that, The step of adding alloys to fine-tune the composition includes: after the amount of steel tapped from the electric arc furnace reaches 1 / 4, adding aluminum particles, silicon-carbon alloy, silicon-manganese alloy, ferromolybdenum, vanadium-nitrogen alloy, and niobium-phosphorus alloy in sequence with the steel stream; and completing the addition of the above alloys when the amount of molten steel in the ladle reaches 4 / 5.

3. The method according to claim 1, characterized in that, The scrap steel is selected from one or more of Q195, Q235, Q345, and Q355.

4. The method according to claim 1, characterized in that, The preheating temperature is 800-1000℃.

5. The method according to claim 1, characterized in that, The refining temperature is controlled at 1620-1650℃, and the refining time is 40-60 minutes. During the refining process, a mixture of nitrogen and natural gas is used for stirring, and the volume ratio of nitrogen to natural gas is 100:

1.

6. The method according to claim 1, characterized in that, The stainless steel scrap includes 201 stainless steel scrap and 17-4PH stainless steel scrap; the amount of 201 stainless steel scrap added accounts for 0.6-0.8 wt.% of the total scrap; the amount of 17-4PH stainless steel scrap added accounts for 0.3-0.5 wt.% of the total scrap.

7. The method according to claim 1, characterized in that, The refining temperature is controlled at 1620 or 1600℃, and the refining time is 40-60 minutes.

8. The method according to claim 1, characterized in that, During the refining process, nitrogen and argon are used for alternating stirring; the alkalinity of the protective slag in the LF refining furnace is controlled at 2.2-2.7, and the white slag is maintained for more than 10 minutes.

9. The production method according to claim 1, characterized in that, Before entering the rolling mill, the continuously cast billet is dynamically heated by an induction heater at a temperature of 980-1000℃, and the temperature difference between the head and tail of the continuously cast billet is controlled within 10℃. The rolling process is divided into rough rolling, head cutting, tail cutting, and finish rolling. The rough rolling temperature is 935-965℃ and the time is 1 minute, rolling the continuously cast billet into round bars with a diameter of 40-60mm. Then, the head and tail are cut off. The finish rolling temperature is 830-850℃ and the finish rolling time is 10 seconds, rolling into steel bar products with a diameter of 12-20mm. After rolling, the steel bar products are rapidly cooled to below 300℃ within 8-10 seconds. The tempering is high-temperature tempering, with a tempering temperature of 820~840℃ and a tempering time of 30~40min; The cooling process includes: cooling the tempered billet to below 350°C, immersing it in an 8-10 wt.% potassium silicate aqueous solution and stirring for 5-8 seconds, then removing it and air-cooling it to room temperature.

10. An ultra-high strength weather-resistant steel bar produced by the method according to any one of claims 1-9, characterized in that, The ultra-high strength weather-resistant steel bar has a matrix structure of bainite and a small amount of ferrite, a yield strength ≥800MPa, a tensile strength ≥1000MPa, and an elongation ≥12%. After a 24-hour neutral salt spray corrosion test, the rust area of ​​the ultra-high strength weather-resistant steel bars is ≤5%.

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