Production method of low-cost and high-strength deformed steel bar

Abstract

The invention discloses a low-cost and high-strength deformed steel bar production method which is characterized by comprising the steps of molten iron pretreatment, converter smelting, LF furnace refining, square billet continuous casting production, heating and rolling. The low-cost and high-strength deformed steel bar is prepared from the following chemical components in percentage by weight: 0.20 to 0.25 percent of C, 0.30 to 0.35 percent of Si, 1.00 to 1.25 percent of Mn, less than or equal to 0.030 percent of P, less than or equal to 0.025 percent of S, 0.005 to 0.01 percent of Nb, 0.005 to 0.01 percent of V, 0.025 to 0.030 percent of N and the balance of Fe and other inevitable impurities. The invention aims to provide the production method of the low-cost and high-strength deformed steel bar so as to solve the problems of high production cost and large fluctuation of comprehensive mechanical properties of finished products in the rolling process of the deformed steel bar in the prior art.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a production method of low-cost, high-strength threaded steel. Background Art

[0002] With the acceleration of global urbanization, the construction industry is booming. The construction of infrastructure such as high-rise buildings, large bridges, roads, and railways places extremely high demands on the strength, toughness, and durability of structural materials. Rebar has good adhesion to concrete due to its ribbed surface and can effectively transfer stress, making it an indispensable key material in building structures. At a time when seismic design requirements are becoming increasingly stringent, the excellent performance of rebar can ensure that buildings maintain structural integrity under natural disasters such as earthquakes, thereby promoting the large-scale production of rebar. For example, in high-rise buildings, vertical load-bearing structures require a large amount of high-strength rebar to support the building's own weight and withstand various loads, which has prompted steel companies to continuously optimize production processes to meet the construction industry's demand for rebar quality and quantity.

[0003] In addition, after a long period of development, the steel industry has made significant progress in raw material processing, smelting technology, and rolling technology, laying a solid foundation for rebar production. In terms of raw materials, the mining and beneficiation technology of high-quality iron ore has been improved, as well as the improvement of the scrap steel recycling system, which ensures a stable and high-quality supply of raw materials for rebar production. For example, advanced beneficiation technology can effectively remove impurities in iron ore, improve the grade of iron concentrate, and thus improve the purity and quality of rebar. In the smelting process, the continuous innovation of converter steelmaking and electric furnace steelmaking technology can more accurately control the chemical composition and temperature of molten steel, and achieve precise adjustment of the content of elements such as carbon, silicon, manganese, phosphorus, and sulfur to meet the composition requirements of rebars of different strength grades. For example, by optimizing the converter blowing process, the carbon content in the molten steel can be accurately controlled to produce rebars that meet specific strength standards. In terms of rolling technology, advanced technologies such as controlled rolling and controlled cooling, and split rolling have gradually developed from traditional rolling methods. Controlled rolling and controlled cooling technology can refine grains by controlling parameters such as temperature and deformation during the rolling process, thereby improving the comprehensive performance of rebar; the split rolling technology significantly improves production efficiency, reduces production costs, and makes rebar more competitive in the market, which has effectively promoted the expansion of rebar production scale and the improvement of quality. Summary of the invention

[0004] The purpose of the present invention is to provide a low-cost, high-strength threaded steel production method to solve the problems of high production cost and large fluctuations in the comprehensive mechanical properties of finished products during the rolling process of threaded steel in the above-mentioned prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for producing threaded steel with low cost and high strength, comprising: molten iron pretreatment - converter smelting - LF furnace refining - billet continuous casting production - heating - rolling; wherein:

[0007] Hot metal pretreatment: Before smelting, hot metal is first desulfurized to reduce the sulfur content in the molten steel. Passivated magnesium particles are used for desulfurization. Nitrogen is sprayed into the hot metal. The particle diameter of the passivated magnesium should be controlled at 0.5-2.0 mm. The content exceeding this range is not more than 5%. The spraying amount is 0.4-0.5 kg / t iron. The passivated magnesium reacts with the sulfur in the hot metal to form slag, and the sulfur content in the hot metal is finally reduced to below 0.005%.

[0008] Converter smelting: The focus of this stage is to ensure that the C and P elements meet the target requirements, with carbon content C ≥ 0.05wt%, P ≤ 0.030wt%, and the tapping temperature is controlled at ≥ 1610℃; in addition, carbon pulling and supplementary blowing, single slag operation, slag blocking tapping, and low-high-low gun position control are adopted for the oxygen supply system, with the gun position of 1.1-1.5m; single slag or double slag is adopted according to the conditions of the molten iron, and the end point basicity is controlled at 2.7-3.5; SiAlMn is used as the final deoxidizer, and appropriate amounts of silicon manganese, manganese iron alloy and vanadium nitrogen alloy are added during the tapping process. The end point control target is to blow once for tapping, and the blowing time is ≤ 1.5min, the tapping carbon is 0.03% ≤ C ≤ 0.05%, and the V content is controlled to be 0.023-0.033wt%;

[0009] LF furnace refining: This stage is mainly to adjust the temperature of molten steel, desulfurize and improve the purity of molten steel. It is heated by graphite electrodes and reduced slag is made to form a reducing atmosphere in the furnace. At the same time, argon is blown at the bottom for stirring throughout the process. According to the steel supply conditions, the composition and temperature are fine-tuned. SiAlCaBa composite deoxidizer is used for deoxidation. BFe is added after sufficient deoxidation. High nitrogen vanadium ferroalloy is added in the later stage of refining, and 38-42 kg of high nitrogen vanadium ferroalloy is added for every 100 tons of molten steel. The soft blowing time is greater than 10 minutes to ensure the uniformity of chemical composition and the floating of inclusions. After refining, the silicon calcium wire is fed and then put into the casting machine.

[0010] Billet continuous casting production: This stage is mainly to prevent the secondary oxidation of molten steel and produce billets with qualified surface and internal quality; molten steel superheat: ΔT≤35℃, target: ΔT≤30℃, casting speed is controlled within the range of 2.2-2.3m / min; asbestos bowl is used for each furnace of steel in the long nozzle of the protective casting ladle, and argon is blown in the long nozzle, so that the T-shaped nozzle does not emit carbon flowers; covering agent is added to the tundish so that the steel liquid surface does not shine; the immersion nozzle is strictly centered, and the immersion nozzle uses a sealing ring; protective slag with a low melting point is used; protective slag is added less and more frequently in the crystallizer, and carbon flowers are not allowed on the steel liquid surface; high-pressure water is used for descaling after leaving the furnace;

[0011] Heating process: the temperature of the preheating section is controlled at 850±50℃, the temperature of the heating section is controlled at 1030±50℃, the temperature of the soaking section is 1060±20℃, and the heating time is 80-100min;

[0012] Rolling process: The technical parameters controlled in the high-speed wire rolling process are as follows:

[0013] Rolling temperature: 1020±20℃;

[0014] Upper cooling bed temperature: 880±20℃;

[0015] The cooling beds are densely packed with spacing less than 10mm.

[0016] Furthermore, 40 kg of high nitrogen vanadium ferroalloy is added to every 100 tons of molten steel.

[0017] Furthermore, the cross section of the ingot is: 150mm×150mm small square billet.

[0018] Furthermore, the chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.20-0.25%, Si: 0.30-0.35%, Mn: 1.00-1.25%, P: ≤0.030%, S: ≤0.025%, Nb: 0.005-0.01%, V: 0.005-0.01%, N: 0.025-0.030%, and the rest is Fe and other inevitable impurities.

[0019] Furthermore, the chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.23%, Si: 0.31%, Mn: 1.25%, P: 0.025%, S: 0.019%, Nb: 0.01%, V: 0.005%, N: 0.025%, and the rest is Fe and other inevitable impurities.

[0020] Furthermore, the chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.22%, Si: 0.32%, Mn: 1.10%, P: 0.021%, S: 0.017%, Nb: 0.01%, V: 0.009%, N: 0.030%, and the rest is Fe and other inevitable impurities.

[0021] Furthermore, the chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.21%, Si: 0.34%, Mn: 1.25%, P: 0.019%, S: 0.020%, Nb: 0.008%, V: 0.006%, N: 0.028%, and the rest is Fe and other inevitable impurities.

[0022] The main functions of each element:

[0023] Carbon (C) is the most important strengthening element. The right amount of carbon can significantly increase the strength of rebar. For example, as the carbon content increases, the yield strength and tensile strength of the rebar will increase, allowing the rebar to withstand greater tension and compression. However, too high a carbon content will reduce the toughness and weldability of the rebar.

[0024] Silicon (Si) is added as a deoxidizer. It can remove oxygen from molten steel and reduce defects such as pores in steel. At the same time, silicon can also increase the strength and hardness of steel bars and enhance their corrosion resistance. To a certain extent, silicon can make steel bars more durable in harsh environments.

[0025] Manganese (Mn) mainly plays the role of deoxidation and desulfurization. Sulfur is a harmful element in steel, which will make the steel hot brittle. Manganese combines with sulfur to form manganese sulfide, thereby reducing the harmful effects of sulfur. Manganese can also improve the strength and toughness of steel bars, making them less likely to break when subjected to external forces and enhancing their earthquake resistance.

[0026] Phosphorus (P) is generally an impurity element. It can improve the strength of steel to a certain extent, but too high a phosphorus content will make the steel bar brittle at low temperatures, a phenomenon known as cold brittleness. Therefore, in the production of threaded steel bars, the phosphorus content must be strictly controlled to ensure the performance of the steel bars in various use environments.

[0027] Sulfur (S) is also an impurity element. Sulfur can cause hot brittleness in steel, which means that steel is prone to cracks and other defects during hot working. Therefore, the sulfur content should be reduced as much as possible during the production process to ensure the quality and performance of the steel bars.

[0028] Niobium (Nb) can refine grains. During the solidification process of steel, niobium prevents the growth of austenite grains and refines the grains. This can improve the strength and toughness of steel bars, because fine-grained steel has higher strength, and when subjected to external forces, fine grains can make deformation more uniform, and it is not easy to cause local stress concentration and fracture. At the same time, adding niobium can improve the welding performance of steel bars, improve the quality of welds, reduce welding defects, and ensure the stability of steel bar connections during construction and other processes.

[0029] Nitrogen (N) can play a certain strengthening role. It can dissolve into ferrite to form interstitial solid solution, produce solid solution strengthening effect, thereby improving the yield strength and tensile strength of steel bars. At the same time, an appropriate amount of nitrogen can improve the corrosion resistance of steel bars. It can combine with other elements in steel to form a dense protective film or change the process of corrosion reaction, thereby enhancing the durability of threaded steel bars in complex environments (such as humid environments containing certain corrosive media).

[0030] Vanadium (V) can produce precipitation strengthening effects. During the heat treatment of steel, vanadium will form fine, dispersed carbides and nitrides with elements such as carbon and nitrogen, such as VC (vanadium carbide) and VN (vanadium nitride). These compounds can effectively hinder dislocation movement in the steel matrix, significantly improve the yield strength and tensile strength of the steel bar, and enable the steel bar to withstand greater external forces. It can also refine the grains. During the solidification and phase transformation of steel, vanadium and its compounds can inhibit grain growth and refine ferrite grains, thereby improving the strength and toughness of the steel bar. The fine grain structure makes the steel bar deform more evenly when subjected to stress, helps prevent fractures caused by local stress concentration, and enhances the comprehensive mechanical properties of the steel bar.

[0031] Compared with the prior art, the beneficial technical effects of the present invention are:

[0032] The invention can stably produce low-cost, high-strength threaded steel with excellent performance and small fluctuation in the comprehensive mechanical properties of the finished product. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with embodiments:

[0034] This embodiment provides a method for producing low alloy seawater corrosion resistant steel, which includes the steps of molten iron pretreatment - converter smelting - LF furnace refining - billet continuous casting production - heating - rolling.

[0035] The specific ingredients of each embodiment are as follows:

[0036] Example 1: The designed chemical composition of the low-cost, high-strength threaded steel is required to be calculated in percentage as follows: C: 0.23%, Si: 0.31%, Mn: 1.25%, P: 0.025%, S: 0.019%, Nb: 0.01%, V: 0.005%, N: 0.025%, and the rest is Fe and other unavoidable impurities.

[0037] Example 2: The designed chemical composition of the low-cost, high-strength threaded steel is required to be calculated in percentage as follows: C: 0.22%, Si: 0.32%, Mn: 1.10%, P: 0.021%, S: 0.017%, Nb: 0.01%, V: 0.009%, N: 0.030%, and the rest is Fe and other unavoidable impurities.

[0038] Example 3: The designed chemical composition of the low-cost, high-strength threaded steel is required to be calculated in percentage as follows: C: 0.21%, Si: 0.34%, Mn: 1.25%, P: 0.019%, S: 0.020%, Nb: 0.008%, V: 0.006%, N: 0.028%, and the rest is Fe and other unavoidable impurities.

[0039] The process parameters for rolling low-cost, high-strength threaded steel in various embodiments are shown in Table 1:

[0040] Table 1: Process parameters for rolling low-cost, high-strength threaded steel in various embodiments:

[0041]

[0042]

[0043] The mechanical properties of low-cost, high-strength threaded steel bars rolled in various embodiments are shown in Table 2:

[0044] Table 2: Mechanical properties of the seawater corrosion resistant steel after rolling in various embodiments:

[0045] Example <![CDATA[R (p0.2) / MPa]]> <![CDATA[R m / MPa]]> A％ Strength-to-yield ratio 1 612 752 27.1 1.23 2 641 761 28.0 1.19 3 622 744 25.2 1.20

[0046] The room temperature impact energy of low-cost, high-strength threaded steel rolled in various embodiments is shown in Table 3:

[0047] Table 3: Room temperature impact energy of low-cost, high-strength rebar rolled in various embodiments

[0048] Example Impact energy at room temperature / J 1 96.2 2 89.9 3 94.0

[0049] Through random sampling of the above production results, it can be seen from Table 2 that the low-cost, high-strength threaded steel has good yield strength and tensile strength. It can be seen from Table 3 that its room temperature impact energy is large, indicating that its toughness is good.

[0050] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing low-cost, high-strength threaded steel, characterized in that: include: Hot metal pretreatment - converter smelting - LF furnace refining - billet continuous casting production - heating - rolling; including: Hot metal pretreatment: Before smelting, hot metal is first desulfurized to reduce the sulfur content in the molten steel. Passivated magnesium particles are used for desulfurization. Nitrogen is sprayed into the hot metal. The particle diameter of the passivated magnesium should be controlled at 0.5-2.0 mm. The content exceeding this range is not more than 5%. The spraying amount is 0.4-0.5 kg / t iron. The passivated magnesium reacts with the sulfur in the hot metal to form slag, and the sulfur content in the hot metal is finally reduced to below 0.005%. Converter smelting: The focus of this stage is to ensure that the C and P elements meet the target requirements, and the carbon content C≥ 0.05wt%, P≤0.030wt%, and the tapping temperature is controlled to be ≥1610℃; in addition, carbon pulling and supplementary blowing, single slag operation, slag blocking tapping are adopted, and the oxygen supply system adopts low-high-low gun position control, and the gun position is 1.1-1.5m; single slag or double slag is adopted according to the conditions of molten iron, and the end point basicity is controlled according to 2.7-3.5; SiAlMn is used as the final deoxidizer, and appropriate amounts of silicon manganese, manganese iron alloy and vanadium nitrogen alloy are added during the tapping process. The end point control target is to blow once for tapping, and the blowing time is ≤1.5min, the tapping carbon is 0.03%≤C≤0.05%, and the V content is controlled to be 0.023~0.033wt%; LF furnace refining: This stage is mainly to adjust the temperature of molten steel, desulfurize and improve the purity of molten steel. It is heated by graphite electrodes and reduced slag is made to form a reducing atmosphere in the furnace. At the same time, argon is blown at the bottom for stirring throughout the process. According to the steel supply conditions, the composition and temperature are fine-tuned. SiAlCaBa composite deoxidizer is used for deoxidation. BFe is added after sufficient deoxidation. High nitrogen vanadium ferroalloy is added in the later stage of refining, and 38-42 kg of high nitrogen vanadium ferroalloy is added for every 100 tons of molten steel. The soft blowing time is greater than 10 minutes to ensure the uniformity of chemical composition and the floating of inclusions. After refining, the silicon calcium wire is fed and then put into the casting machine. Billet continuous casting production: This stage is mainly to prevent the secondary oxidation of molten steel and produce billets with qualified surface and internal quality; molten steel superheat: ΔT≤35℃, target: ΔT≤30℃, casting speed is controlled within the range of 2.2-2.3m / min; asbestos bowl is used for each furnace of steel in the long nozzle of the protective casting ladle, and argon is blown in the long nozzle, so that the T-shaped nozzle does not emit carbon flowers; covering agent is added to the tundish so that the steel liquid surface does not shine; the immersion nozzle is strictly centered, and the immersion nozzle uses a sealing ring; protective slag with a low melting point is used; protective slag is added less and more frequently in the crystallizer, and carbon flowers are not allowed on the steel liquid surface; high-pressure water is used for descaling after leaving the furnace; Heating process: the temperature of the preheating section is controlled at 850±50℃, the temperature of the heating section is controlled at 1030±50℃, the temperature of the soaking section is 1060±20℃, and the heating time is 80-100min; Rolling process: The technical parameters controlled in the high-speed wire rolling process are as follows: Rolling temperature: 1020±20℃; Upper cooling bed temperature: 880±20℃; The cooling beds are densely packed with spacing less than 10mm.

2. The method for producing low-cost, high-strength threaded steel according to claim 1, characterized in that: Add 40 kg of high nitrogen vanadium ferroalloy to every 100 tons of molten steel.

3. The method for producing low-cost, high-strength threaded steel according to claim 1, characterized in that: The cross section of the ingot is: 150mm×150mm small square ingot.

4. The method for producing low-cost, high-strength threaded steel according to claim 1, characterized in that: The chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.20-0.25%, Si: 0.30-0.35%, Mn: 1.00-1.25%, P: ≤0.030%, S: ≤0.025%, Nb: 0.005-0.01%, V: 0.005-0.01%, N: 0.025-0.030%, and the rest is Fe and other inevitable impurities.

5. The method for producing low-cost, high-strength threaded steel according to claim 4, characterized in that: The chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.23%, Si: 0.31%, Mn: 1.25%, P: 0.025%, S: 0.019%, Nb: 0.01%, V: 0.005%, N: 0.025%, and the rest is Fe and other inevitable impurities.

6. The method for producing low-cost, high-strength threaded steel according to claim 4, characterized in that: The chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.22%, Si: 0.32%, Mn: 1.10%, P: 0.021%, S: 0.017%, Nb: 0.01%, V: 0.009%, N: 0.030%, and the rest is Fe and other inevitable impurities.

7. The method for producing low-cost, high-strength threaded steel according to claim 4, characterized in that: The chemical composition of the low-cost, high-strength threaded steel includes, in percentage, C: 0.21%, Si: 0.34%, Mn: 1.25%, P: 0.019%, S: 0.020%, Nb: 0.008%, V: 0.006%, N: 0.028%, and the rest is Fe and other inevitable impurities.

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