The process of adding raw materials, such as molten iron or scrap steel, into the electric furnace marks the initial step of electric arc furnace steelmaking operations.
This operation involves modifying the slag composition, alkalinity, viscosity, and reactivity during steel and iron production. For instance, oxygen blowing aims to create slag with sufficient fluidity and alkalinity to effectively transfer oxygen to the metal surface, thereby reducing sulfur and phosphorus levels below the specified limits for the planned steel grade. This minimizes the amount of slag splashing and spillage.
In electric arc furnace steelmaking, slag removal or slagging operations are employed based on varying smelting conditions and objectives. For example, when using the single-slag method, oxidation slag must be removed at the end of the oxidation stage. Conversely, when employing the double-slag method to produce reduction slag, the original oxidation slag must be completely released to prevent phosphorus reversion.
Energy is supplied to the molten metal pool to induce movement in both the molten metal and slag, enhancing the kinetic conditions for metallurgical reactions. Stirring can be achieved through gas, mechanical, electromagnetic induction, or other methods.
This chemical reaction aims to reduce the phosphorus content in molten steel. Phosphorus is a detrimental impurity in steel, causing brittleness, known as "cold brittleness," at room temperature or lower. The higher the carbon content in steel, the more severe the embrittlement caused by phosphorus. Typically, ordinary steel is specified to have a phosphorus content not exceeding 0.045%, with high-quality steel requiring even lower levels.
Through nozzles placed at the furnace bottom, gases such as N₂, Ar, CO₂, CO, CH₄, and O₂ are blown into the molten pool according to process requirements. This accelerates melting and promotes metallurgical reactions, shortening smelting time, reducing power consumption, improving dephosphorization and desulfurization operations, increasing residual manganese content in steel, and enhancing metal and alloy yields. It also results in more uniform molten steel composition and temperature, improving steel quality, reducing costs, and increasing productivity.
The melting period in steelmaking primarily pertains to open-hearth and electric furnace steelmaking. For electric arc furnace steelmaking, it refers to the period from the start of electrification until the complete melting of furnace steel spikes. In open-hearth steelmaking, it spans from the completion of molten iron charging to the melting of the charge. The main task during this period is to melt and heat the charge as quickly as possible and to form slag.
The oxidation period in ordinary power electric arc furnace steelmaking typically refers to the stage from charge dissolution, sampling, and analysis to the completion of oxidation slag formation. Some consider it to begin with oxygen blowing or ore addition for decarburization. The main tasks are to oxidize carbon and phosphorus in the molten steel, remove gases and inclusions, and uniformly heat the molten steel. Decarburization is a crucial process during this period, requiring a decarburization amount greater than approximately 0.2% to ensure steel purity. With advancements in external refining technology, most oxidation refining in electric arc furnaces has shifted to ladles or refining furnaces.
During the steelmaking process, harmful elements and compounds are removed from the molten steel through chemical reactions, slagging, and other methods. These substances are transferred into the gas phase, discharged, or floated into the slag, improving steel quality. The continuous caster then discharges the billet.
In ordinary power electric arc furnace steelmaking operations, the period from the completion of slagging at the end of oxidation to tapping is known as the reduction period. Its main tasks include creating reducing slag for diffusion, deoxidation, desulfurization, chemical composition control, and temperature adjustment. High-power and ultra-high-power electric arc furnace steelmaking operations have eliminated the reduction period.
This steelmaking process involves transferring molten steel initially produced in a steelmaking furnace (converter, electric furnace, etc.) to another vessel for refining, also known as secondary metallurgy. The process is divided into two steps: primary smelting and refining. Primary smelting involves melting, dephosphorizing, decarburizing, and main alloying in a furnace with an oxidizing atmosphere. Refining entails degassing, deoxidizing, desulfurizing, removing inclusions, and fine-tuning the molten steel's composition in a vacuum, inert gas, or reducing atmosphere container. Dividing steelmaking into two steps improves steel quality, shortens smelting time, simplifies the process, and reduces production costs. External refining methods can be broadly categorized into atmospheric pressure and vacuum refining, with further divisions based on treatment methods into ladle processing type and ladle refining type.
Stirring molten steel during external refining homogenizes its composition and temperature, promoting metallurgical reactions. Most metallurgical reactions occur at phase interfaces, with the diffusion rate of reactants and products being the limiting factor. Static molten steel has a slow metallurgical reaction rate; for example, desulfurization in an electric furnace takes 30 to 60 minutes, whereas stirring in furnace refining takes only 3 to 5 minutes. Inclusions are removed more slowly by floating upwards in static molten steel; stirring exponentially increases their removal rate, depending on stirring intensity, type, and inclusion characteristics and concentration.
This method involves feeding deoxidation, desulfurization, and fine-tuning powders, such as Ca-Si powder, or directly feeding aluminum wire, carbon wire, etc., into the steel ladle through a wire feeder. This achieves deep desulfurization, calcium treatment, and fine-tuning of molten steel composition, including carbon and aluminum. It also cleans the molten steel and improves the morphology of non-metallic inclusions.
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