Deoxidation post-treatment method for Q355B series aluminum-containing steel grade

Abstract

The invention discloses a Q355B series aluminum-containing steel grade deoxidation post-treatment method, which belongs to the technical field of metallurgy, and comprises the following steps: converter tapping pre-deoxidation: in the converter tapping process, sequentially adding silicon manganese alloy, silicon iron, lime and carbon powder for pre-deoxidation; lF refining deep deoxidation: after the molten steel reaches an LF furnace, performing oxygen determination analysis, and adding aluminum blocks, aluminum wires and aluminum particles for deep deoxidation according to an oxygen content calculation result; in the LF refining process, the total adding amount of lime is controlled to be 1400 kg / 200 tons of steel, and the argon blowing stirring time is optimized to be 180 s; inclusions are controlled, specifically, low-melting-point MnO-SiO2 composite oxide is generated through silicon-manganese and silicon-iron pre-deoxidation, the average size of B-type inclusions is reduced to a first target value, and the area proportion is reduced to a second target value. According to the method, joint optimization of deoxidation, desulfurization and inclusion control is achieved in a post-deoxidation mode of'silicon-manganese and silicon-iron pre-deoxidation + LF aluminum deep deoxidation '.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and in particular relates to a post-deoxidation method for Q355B series aluminum-containing steel. Background Technology

[0002] 355B steel series, as a low-alloy high-strength structural steel, possesses excellent comprehensive mechanical properties and weldability, and is widely used in important fields such as bridge engineering, high-rise buildings, shipbuilding, and heavy machinery structures. In the original smelting process, aluminum deoxidation was usually concentrated during the converter tapping stage. This practice resulted in significantly unstable aluminum recovery rates, generally fluctuating only between 75% and 80%. Simultaneously, concentrated aluminum addition easily promotes the formation of large amounts of high-melting-point alumina inclusions. These inclusions are difficult to float and remove, easily causing nozzle blockage during continuous casting and adversely affecting the internal cleanliness and surface quality of the cast billet.

[0003] Furthermore, significant shortcomings exist in the deoxidation and desulfurization processes. The timing of quicklime addition lacks precise control, and the argon blowing and stirring parameters are not adequately matched to the desulfurization reaction, resulting in large fluctuations in desulfurization efficiency, with actual desulfurization rates typically ranging from 55% to 65%. This inefficient and unstable desulfurization further increases alloy consumption and prolongs the smelting cycle, ultimately driving up alloy costs and impacting overall production economics and the stability of steel quality. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a post-deoxidation method for Q355B series aluminum-containing steel, which achieves joint optimization of deoxidation, desulfurization and inclusion control through a post-deoxidation method of "silicon-manganese and silicon-iron pre-deoxidation + LF aluminum deep deoxidation".

[0005] The purpose of this invention is to provide a post-deoxidation method for Q355B series aluminum-containing steel, comprising the following steps: Pre-deoxidation during converter tapping: During the converter tapping process, silicon-manganese alloy, ferrosilicon, quicklime, and carbon powder are added sequentially for pre-deoxidation; LF refining deep deoxidation: After the molten steel arrives at the LF furnace, oxygen analysis is performed first. Based on the oxygen content calculation results, aluminum blocks, aluminum wires, and aluminum granules are added for deep deoxidation. Desulfurization optimization: During the LF refining process, the total amount of quicklime added is controlled at 1400kg / 200 tons of steel, and the argon blowing and stirring time is optimized to 180s; Inclusion control: By pre-deoxidizing silicon manganese and silicon iron to generate low-melting-point MnO-SiO2 composite oxide, the average size of type B inclusions is reduced to the first target value and the area ratio is reduced to the second target value.

[0006] Preferably, during the pre-deoxidation process of converter steel tapping, the amount of silicon-manganese alloy added is 1705.94 kg / 200 tons of steel, and the amount of quicklime added is 500 kg / 200 tons of steel.

[0007] Preferably, during the pre-deoxidation process of converter tapping, the amount of slag is controlled, and soft slag-blocking plugs are used to ensure that the slag layer thickness is ≤55mm.

[0008] Preferably, during the LF refining and deep deoxidation process, the total aluminum content is controlled at 133 kg / 200 tons of steel, so that the acid-soluble aluminum content in the steel is stabilized at 0.020% to 0.040%.

[0009] Preferably, in the deep deoxidation process of LF refining, the slag basicity of the LF refining furnace needs to be controlled at 9-18, and the FeO+MnO content in the slag ≤1.0%.

[0010] Preferably, in the desulfurization optimization process, argon blowing and stirring are divided into three stages: the initial stage (0-60s) is weak stirring to promote slag formation, the transition stage (60-180s) is strong stirring to accelerate desulfurization, and the stable stage (180-200s) is to maintain dynamic balance to avoid slag entrainment in molten steel.

[0011] Preferably, during the desulfurization optimization process, the argon flow rate is 30NL / min to 120NL / min to promote the desulfurization reaction.

[0012] Preferably, the desulfurization rate is stable at 81.2%.

[0013] Preferably, during the inclusion control process, the average size of Class B inclusions is reduced to 8.5µm and the area percentage is reduced to 0.05%.

[0014] Preferably, the chemical composition of Q355B series aluminum-containing steel should meet the following requirements: C 0.016%~0.20%, Si 0.10%~0.25%, Mn 0.40%~0.45%, P≤0.035%, S≤0.010%, Ti 0.040%~0.055%, Ni≤0.3%, Alt≥0.005%.

[0015] The advantages and technical effects of this invention are as follows: This invention employs a post-deoxidation process of "silicon-manganese and ferrosilicon pre-deoxidation + LF aluminum deep deoxidation," implementing deoxidation operations in stages during the LF refining process, achieving synergistic optimization of deoxidation, desulfurization, and inclusion control. The process first uses silicon-manganese and ferrosilicon for preliminary deoxidation, reducing some oxygen content and creating favorable conditions for subsequent deep deoxidation. Then, deep deoxidation is carried out in the LF furnace using aluminum wire or aluminum granules, significantly reducing dissolved oxygen in the steel, promoting the desulfurization reaction, and effectively controlling the morphology and distribution of inclusions.

[0016] After applying this method, the cleanliness of molten steel was significantly improved, and the average oxygen content at the LF refining endpoint was stably controlled at 4.5 × 10⁻⁶. -5 The process significantly reduced the formation of alumina inclusions. The average length of Class B alumina inclusions decreased from 16.2µm in the original process to approximately 8.5µm, resulting in smaller and fewer inclusions and improved billet quality. Simultaneously, desulfurization efficiency was significantly improved, with an average desulfurization rate of approximately 85%, enhancing the steel's crack resistance. Furthermore, alloy consumption costs were reduced by 21.07 yuan / ton of steel, effectively resolving the problems of excessive aluminum consumption, large fluctuations in inclusion control, and unstable desulfurization effects in the original process, thus combining economic benefits with quality advantages. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below. The described embodiments are only some examples of the present invention, and not all examples. Obviously, the illustrated embodiments of the present invention demonstrate characteristic technical solutions. Based on the embodiments of the present invention, any other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0018] A post-deoxidation method for Q355B series aluminum-containing steel, specifically including: Pre-deoxidation during converter tapping: During the converter tapping process, ferrosilicon, quicklime, and carbon powder are added sequentially for pre-deoxidation. The amount of ferrosilicon added is 1705.94 kg / 200 tons of steel, and the amount of quicklime added is 500 kg / 200 tons of steel. The amounts of ferrosilicon and carbon powder added are adjusted according to the specific steel grade and deoxidation requirements to ensure deoxidation effectiveness and steel quality.

[0019] LF Refining Deep Deoxidation: After the molten steel arrives at the LF furnace, it first undergoes oxygen analysis to accurately determine its oxygen content. Based on the analysis results, deoxidizers such as aluminum blocks, aluminum wires, and aluminum granules are calculated and added appropriately for deep deoxidation. The method of aluminum addition is selected comprehensively based on the smelting rhythm and mixing effect to ensure a thorough and uniform deoxidation reaction. The total amount of aluminum added is controlled at 133 kg per 200 tons of molten steel, thereby stabilizing the acid-soluble aluminum content in the steel within the target range of 0.020%-0.040%, ensuring that the deoxidation effect meets refining requirements and creating favorable steel conditions for subsequent processes.

[0020] Desulfurization optimization: In the LF refining process, desulfurization optimization measures include strictly controlling the total amount of quicklime added to the standard of 1400 kg / 200 tons of steel, optimizing the argon blowing and stirring time to 180 seconds, and adjusting the argon flow rate within the range of 30 NL / min-120 NL / min. These parameter adjustments effectively promoted the desulfurization reaction, improved sulfur removal efficiency by enhancing stirring and gas flow, and thus maintained a stable desulfurization rate of around 82%, for example, maintaining a stable desulfurization rate of 81.2%, thereby improving the overall quality of the molten steel.

[0021] Inclusion control: Low-melting-point MnO-SiO2 composite oxides are generated by pre-deoxidation of silicon manganese and silicon iron, reducing high-melting-point Al2O3 inclusions. This reduces the average size of Class B inclusions from 16.2µm to 8.5µm and the area percentage from 0.13% to 0.05%.

[0022] Inclusion control is a crucial step in steelmaking, and its core lies in optimizing the composition and morphology of oxide inclusions through a rational deoxidation process. In this process, ferrosilicon and silicon manganese are used for pre-deoxidation, promoting the formation of a large number of dispersed low-melting-point MnO-SiO2 composite oxides. These composite oxides easily aggregate and float in molten steel, thus significantly reducing the probability of high-melting-point alumina inclusions. After this process, the average size of type B inclusions (mainly alumina) was effectively reduced from 16.2µm to 8.5µm, and their area ratio in the metallographic observation field also decreased from 0.13% to 0.05%, indicating a significant improvement in the quantity and size distribution of inclusions. This control measure not only improves the purity of molten steel but also helps improve the macrostructure and mechanical properties of the cast billet.

[0023] Based on the above preferred embodiments, the following non-limiting optimization features may also be included: During the pre-deoxidation process of converter steelmaking, in order to effectively improve the purity of molten steel and the deoxidation effect, the amount of slag fed into the ladle must be strictly controlled to avoid excessive slag entering the ladle. Soft slag plugs are typically used for slag blocking. These plugs have good high-temperature resistance and flexibility, effectively isolating the molten slag and reducing the risk of slag falling into the ladle. The key requirement is to ensure that the slag layer thickness is strictly controlled within ≤55 mm to meet production process specifications, guarantee the smooth progress of subsequent refining processes, and ensure the final steel quality.

[0024] In the deep deoxidation process of LF refining, the LF refining furnace requires strict control of the slag basicity, i.e., the mass ratio of CaO to SiO2, maintaining it within the range of 9 to 18. Simultaneously, the total content of FeO and MnO in the slag must be ensured not to exceed 1.0%. These measures aim to effectively reduce the oxidation loss of aluminum in the molten steel, thereby increasing aluminum yield, reducing alloy waste, and improving the purity of the molten steel and the quality of the final product. By precisely controlling these parameters, the deoxidation effect can be optimized, ensuring the stability and economy of the smelting process.

[0025] In the desulfurization optimization process, argon blowing and stirring are key methods aimed at promoting metallurgical reactions and improving desulfurization efficiency through gas agitation. The entire process is divided into three distinct stages: the initial stage (0-60 seconds) uses a weak stirring intensity, mainly to promote slag formation, allowing the slag phase to fully form and cover the surface of the molten steel, creating conditions for subsequent desulfurization; the transition stage (60-180 seconds) increases the stirring intensity, accelerating the mass transfer of sulfides from the molten steel to the slag phase through strong agitation, thereby effectively reducing the sulfur content; the stabilization stage (180-200 seconds) maintains a moderate stirring intensity to maintain the dynamic balance of the steel-slag interface, preventing excessive stirring from causing slag entrainment in the molten steel, ensuring the stability of the desulfurization effect, and avoiding secondary pollution. Parameter control in each stage is crucial to the final desulfurization effect.

[0026] This invention applies to Q355B series low-alloy high-strength structural steel, whose chemical composition must meet the following requirements: C 0.016%~0.20%, Si 0.10%~0.25%, Mn 0.40%~0.45%, P≤0.035%, S≤0.010%, Ti 0.040%~0.055%, Ni≤0.3%, Alt≥0.005%.

[0027] The core of this invention lies in: Staged deoxidation: Pre-deoxidation is carried out using silicon-manganese alloy and ferrosilicon during converter tapping to generate low-melting-point MnO-SiO2 composite oxide; during LF refining, aluminum is precisely added through oxygen analysis to achieve deep deoxidation in the LF furnace.

[0028] Process parameter optimization: The total amount of quicklime added is 1400kg / 200 tons of steel, and the argon blowing time is optimized to 180s to ensure that the desulfurization rate is stable at around 82%.

[0029] Inclusion plasticity control: Modify Al2O3 alumina inclusions using deoxidation products of ferrosilicon manganese and ferrosilicon to improve the inclusion flotation rate in molten steel.

[0030] The technical effects include: Aluminum consumption was reduced by 32%, resulting in a saving of 21.07 yuan per ton of steel in alloy costs. The total oxygen content in steel is ≤4.5×10⁻⁶. -5The number of Class B inclusions decreased by 45%; The desulfurization rate increased from 50% to 82%, and the refining cycle was shortened by 5-10 minutes. Specific Implementation Steel grade for smelting: Q355B series, steel output 200 tons / furnace; When tapping steel from the converter: add 1,705.94 kg of silicon-manganese alloy, 200 kg of ferrosilicon, 500 kg of quicklime, and 140 kg of carbon powder. Control the slag discharge to ≤ 5 kg / ton of steel. LF refining: After the oxygen level is determined at the station, add 205.28 kg of aluminum blocks, 46.78 kg of aluminum wire, and 10 kg of aluminum powder. The total amount of quicklime is 1400 kg. Purge argon for 180 seconds (flow rate 60 NL / min). Results: The mean oxygen content of LF was 4.5 × 10⁻⁶. -5 The desulfurization rate was 81.2%, and the area of ​​inclusions accounted for 0.05%.

[0032] Comparative example, The difference from the specific embodiment is that the amount of quicklime added is increased to 1650 kg; Results: The desulfurization rate was only 82.5%, with no significant increase, confirming that 1400kg is the economic value; This invention achieves cost reduction and efficiency improvement through post-deoxygenation and parameter adjustment, and is suitable for large-scale production.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A post-deoxidation method for Q355B series aluminum-containing steel, characterized in that, include: Pre-deoxidation during converter tapping: During the converter tapping process, silicon-manganese alloy, ferrosilicon, quicklime, and carbon powder are added sequentially for pre-deoxidation; LF refining deep deoxidation: After the molten steel arrives at the LF furnace, oxygen analysis is performed first. Based on the oxygen content calculation results, aluminum blocks, aluminum wires, and aluminum granules are added for deep deoxidation. Desulfurization optimization: During the LF refining process, the total amount of quicklime added is controlled at 1400kg / 200 tons of steel, and the argon blowing and stirring time is optimized to 180s; Inclusion control: By pre-deoxidizing silicon manganese and silicon iron to generate low-melting-point MnO-SiO2 composite oxide, the average size of type B inclusions is reduced to the first target value and the area ratio is reduced to the second target value.

2. The deoxidation post-processing method for Q355B series aluminum-containing steel according to claim 1, characterized in that, During the pre-deoxidation process of converter steelmaking, the amount of silicon-manganese alloy added is 1705.94 kg / 200 tons of steel, and the amount of quicklime added is 500 kg / 200 tons of steel.

3. The deoxidation post-processing method for Q355B series aluminum-containing steel according to claim 1, characterized in that, During the pre-deoxidation process of converter tapping, the amount of slag is controlled, and soft slag-blocking plugs are used to ensure that the slag layer thickness is ≤55mm.

4. The deoxidation post-processing method for Q355B series aluminum-containing steel according to claim 1, characterized in that, During the deep deoxidation process of LF refining, the total aluminum content is controlled at 133 kg / 200 tons of steel, so that the acid-soluble aluminum content in the steel is kept stable at 0.020% to 0.040%.

5. The post-deoxidation method for Q355B series aluminum-containing steel according to claim 1, characterized in that, During the deep deoxidation process of LF refining, the slag basicity of the LF refining furnace needs to be controlled between 9 and 18, and the FeO+MnO content in the slag should be ≤1.0%.

6. The deoxidation post-processing method for Q355B series aluminum-containing steel according to claim 1, characterized in that, During the desulfurization optimization process, argon blowing and stirring are divided into three stages: the initial stage (0-60s) is characterized by weak stirring to promote slag formation, the transition stage (60-180s) is characterized by strong stirring to accelerate desulfurization, and the stable stage (180-200s) is characterized by maintaining dynamic equilibrium to avoid slag entrainment in molten steel.

7. The deoxidation post-processing method for Q355B series aluminum-containing steel according to claim 1, characterized in that, During the desulfurization optimization process, the argon flow rate is 30NL / min to 120NL / min to promote the desulfurization reaction.

8. The deoxidation post-processing method for Q355B series aluminum-containing steel according to claim 7, characterized in that, The desulfurization rate remained stable at 81.2%.

9. The post-deoxidation method for Q355B series aluminum-containing steel according to claim 1, characterized in that, During the inclusion control process, the average size of Class B inclusions was reduced to 8.5µm, and the area percentage was reduced to 0.05%.

10. The post-deoxidation method for Q355B series aluminum-containing steel according to claim 1, characterized in that, The chemical composition of Q355B series aluminum-containing steel must meet the following requirements: C 0.016%~0.20%, Si 0.10%~0.25%, Mn 0.40%~0.45%, P≤0.035%, S≤0.010%, Ti 0.040%~0.055%, Ni≤0.3%, Alt≥0.005%.