steps of steel making

Feeding: The operation of adding raw materials such as molten iron or scrap steel to the electric furnace or converter is the first step of the steelmaking operation.
Slagging: The operation of adjusting the slag composition, alkalinity, viscosity, and reaction ability in the production of steel and iron. The purpose is to smelt the metal with the required composition and temperature through the steel blast furnace slag-metal reaction. For example, the slagging and oxygen blowing operations of the oxygen top-blowing converter are to generate slag with sufficient fluidity and basicity, which can transfer enough oxygen to the metal surface to reduce the sulfur and phosphorus below the upper limit of the planned steel grade. And to minimize the amount of splashing and slag overflow during oxygen blowing.
Slagging: The slagging or slagging operation is adopted in the smelting process according to different smelting conditions and purposes in the electric arc furnace steelmaking. For example, when the single slag method is used for smelting, the oxidation slag must be removed at the end of oxidation; when the double slag method is used to make reduction slag, the original oxidation slag must be completely released to prevent phosphorus from returning.
Molten pool stirring: Supply energy to the molten metal pool to make the molten metal and molten slag move to improve the kinetic conditions of the metallurgical reaction. The stirring of the molten pool can be achieved using gas, mechanical, electromagnetic induction, and other methods.
Dephosphorization reduces the chemical reaction of phosphorus content in molten steel. Phosphorus is one of the harmful impurities in the steel. Steel with a lot of phosphorus, when used at room temperature or lower, is prone to brittleness, which is called “cold brittleness”. The higher the carbon content in steel, the more serious the embrittlement caused by phosphorus. Generally, it is stipulated that the phosphorus content of ordinary steel does not exceed 0.045%, and high-quality steel requires less phosphorus. The phosphorus in pig iron mainly comes from phosphate in iron ore. Phosphorus oxide and iron oxide have similar thermodynamic stability. Under the reducing conditions of the blast furnace, almost all of the phosphorus in the charge is reduced and dissolved in the molten iron. If the beneficiation cannot remove phosphorus compounds, dephosphorization can only be performed outside the (high) furnace or in an alkaline steelmaking furnace. Understanding and solving the problem of dephosphorization in iron is of special significance in the history of steel production. The large-scale industrial production of steel began in 1856 with the acid converter steelmaking method invented by H. Bessemer. However, acid converter steelmaking cannot be rephosphorized; and iron ore with low phosphorus content is scarce, which seriously hinders the development of steel production. In 1879, Thomas (S.Thomas) invented the alkaline converter steelmaking method that can treat the high-phosphorus molten iron. The principle of dephosphorization of alkaline slag was then extended to open-hearth steelmaking so that a large amount of phosphorus-containing iron ore can be used The production of steel has made a significant contribution to the development of the modern steel industry.
Electric furnace bottom blowing: N2, Ar, CO2, CO, CH4, O2, and other gases are blown into the molten pool in the furnace according to the process requirements through the nozzle placed at the bottom of the furnace to accelerate the melting and promote the metallurgical reaction process. . The use of bottom blowing technology can shorten smelting time, reduce power consumption, improve dephosphorization and desulfurization operations, increase the amount of residual manganese in steel, and increase the yield of metals and alloys. And can make the molten steel composition and temperature more uniform, thereby improving steel quality, reducing costs, and increasing productivity.
Melting period: The melting period of steelmaking is mainly for open-hearth and electric furnace steelmaking. The melting period of electric arc furnace steelmaking is called the melting period from the start of electrification to the complete melting of the furnace steel and the open-hearth furnace steelmaking from the completion of the molten iron to the completion of the charge. The task of the melting period is to melt and heat the charge as soon as possible and make the slag in the melting period.
Oxidation period and decarburization period: The oxidation period of ordinary power electric arc furnace steelmaking usually refers to the process stage from the dissolution of the furnace charge, the sampling, and analysis to the completion of the oxidation slag. Some think it started from blowing oxygen or adding ore to decarbonize. The main task of the oxidation period is to oxidize the carbon and phosphorus in the molten steel; remove the gas and inclusions; to heat the molten steel uniformly. Decarburization is an important process in the oxidation period. To ensure the purity of steel, the amount of decarburization is required to be greater than about 0.2%. With the development of refining technology outside the furnace, most of the oxidation refining of the electric arc furnace is moved to the ladle or refining furnace.
Refining period: The process operation in which some elements and compounds that are harmful to the quality of steel are selected into the gas phase or discharged or floated into the slag through chemical reactions through slagging and other methods to remove them from the molten steel. period. The continuous caster discharges the billet. The continuous caster discharges the billet.
Reduction period: In ordinary power electric arc furnace steelmaking operations, the period from the end of oxidation to the completion of slagging and tapping is usually called the reduction period. Its main task is to create reduced slag for diffusion, deoxidation, desulfurization, chemical composition control, and temperature adjustment. High-power and ultra-power electric arc furnace steelmaking operations have canceled the reduction period.
Out-of-furnace refining: The steelmaking process in which the molten steel that has been smelted in a steelmaking furnace (converter, electric furnace, etc.) is moved to another vessel for refining, also called secondary metallurgy. Therefore, the steelmaking process is divided into two steps: primary smelting and refining. Primary refining: The charge is melted, phosphorized, decarburized, and main alloyed in a furnace with an oxidizing atmosphere. Refining: Degas, deoxidize, desulfurize, remove inclusions and fine-tune the composition of the molten steel in a vacuum, inert gas, or reducing atmosphere container. The advantages of dividing steelmaking into two steps are: it can improve the quality of steel, the steelmaking workshop can shorten the smelting time, simplify the process and reduce the production cost. There are many types of out-of-furnace refining, which can be roughly divided into two types: out-of-furnace refining under atmospheric pressure and out-of-furnace refining under vacuum. According to different treatment methods, it can be divided into ladle processing type furnace refining and ladle refining type furnace refining.
Molten steel stirring: the stirring of molten steel during the refining process outside the furnace. It homogenizes the composition and temperature of molten steel and can promote metallurgical reactions. Most metallurgical reaction processes are phase interface reactions, and the diffusion rate of reactants and products is the limiting link of these reactions. When molten steel is in a static state, its metallurgical reaction speed is very slow. For example, it takes 30 to 60 minutes to desulfurize the molten steel in an electric furnace; while it takes only 3 to 5 minutes to stir the molten steel in the furnace refining. When molten steel is in a static state, the inclusions are removed by floating upwards, and the removal speed is slow; when the molten steel is stirred, the removal speed of the inclusions increases exponentially and is related to the stirring strength, type, and characteristics and concentration of the inclusions.
Wire feeding to the ladle: Feed the steel ladle with deoxidizing, desulfurizing, and fine-tuned powders, such as Ca-Si powder, or directly feeding aluminum wire, carbon wire, etc. into the ladle through the wire feeding machine for deep desulfurization of molten steel, Calcium treatment and the method of fine-tuning the composition of carbon and aluminum in steel. It also has the function of cleaning molten steel and improving the morphology of non-metallic inclusions.

13 steps of steel making

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