What is the steelmaking process flow?

Slagging: the operation of adjusting the composition, alkalinity, viscosity and reaction ability of slag in the production of steel and iron. The purpose is to refine the metal with the required composition and temperature through the slag-metal reaction. For example, oxygen top-blowing converter slagging and oxygen blowing operations are to generate slag with sufficient fluidity and basicity to reduce sulfur and phosphorus below the upper limit of the planned steel grade, and to prevent splashing and slag overflow during oxygen blowing. Minimize the amount.
Slagging: The slagging or slagging operation adopted during the smelting process according to different smelting conditions and purposes during electric arc furnace steelmaking. For example, when smelting with single slag method, the oxidation slag must be removed at the end of oxidation; when using double slag method 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 slag move to improve the kinetic conditions of the metallurgical reaction. The stirring of the molten pool can be achieved by means of gas, mechanical, electromagnetic induction and other methods.
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 a 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 it can make the composition and temperature of the molten steel more uniform, thereby improving the quality of steel, 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 until the charge is completely melted, and the open-hearth 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 up 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 dissolving the furnace charge, sampling and analyzing 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; make the molten steel uniformly heated. Decarburization is an important process in the oxidation period. In order 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 period in which some elements and compounds 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.
Reduction period: In ordinary power electric arc furnace steelmaking operations, the period from the completion of slagging at the end of oxidation to 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. At present, the reduction period of high-power and ultra-power electric arc furnace steelmaking operations has been cancelled.
Out-of-furnace refining: The steelmaking process in which the molten steel that has been initially 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, dephosphorized, decarburized and main alloyed in an oxidizing atmosphere furnace. Refining: Degas, deoxidize, desulfurize, remove inclusions and fine-tune components in a container of vacuum, inert gas or reducing atmosphere. The benefits of dividing steelmaking into two steps are: it can improve the quality of steel, shorten the smelting time, simplify the process and reduce production costs. 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 the 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 at rest, its metallurgical reaction speed is very slow. For example, it takes 30 to 60 minutes for molten steel to desulfurize in an electric furnace; while it takes only 3 to 5 minutes to stir molten steel in furnace refining. When the molten steel is at rest, the inclusions will float up and remove, and the removal speed will be slow; when the molten steel is stirred, the removal speed of the inclusions increases exponentially, and is related to the stirring strength, type, and the characteristics and concentration of the inclusions.
Ladle wire feeding: the steel ladle is fed into the ladle with iron-clad powders for deoxidation, desulfurization and fine-tuning, such as Ca-Si powder, or directly fed into aluminum wire, carbon wire, etc., for deep desulfurization and calcium treatment of molten steel And methods to fine-tune the carbon and aluminum components in steel. It also has the function of cleaning molten steel and improving the morphology of non-metallic inclusions.
Ladle treatment: Abbreviation for out-of-furnace refining of ladle treatment. It is characterized by short refining time (approximately 10-30 minutes), single refining task, no heating device to compensate for the decrease in molten steel temperature, simple process operation and low equipment investment. It has devices for molten steel degassing, desulfurization, composition control and changing the shape of inclusions. Such as vacuum cycle degassing method (RH, DH), ladle vacuum argon blowing method (Gazid), ladle powder spraying method (IJ, TN, SL), etc. are all in this category.
Ladle Refining: Abbreviation for ladle refining outside furnace. It is characterized by longer refining time than ladle treatment (about 60-180 minutes), has a variety of refining functions, has a heating device that compensates for the decrease in molten steel temperature, and is suitable for various high-alloy steels and special-performance steels (such as ultra-pure steel). Species) refinement. Vacuum oxygen blowing decarburization method (VOD), vacuum arc heating degassing method (VAD), ladle refining method (ASEA-SKF), closed argon blowing composition fine adjustment method (CAS), etc., all belong to this category; similar to this There is also argon oxygen decarburization (AOD).
Inert gas treatment: blowing inert gas into the molten steel. This gas itself does not participate in the metallurgical reaction, but each small bubble rising from the molten steel is equivalent to a “small vacuum chamber” (the H2, N2, CO in the bubble) The partial pressure is close to zero), which has the effect of “air washing”. The principle of the production of stainless steel by the out-of-furnace refining method is to apply the equilibrium relationship between carbon chromium and temperature under different CO partial pressures. Refining and decarburization by adding oxygen with inert gas can reduce the CO partial pressure in the carbon-oxygen reaction. Under lower temperature conditions, the carbon content is reduced without chromium being oxidized.
Pre-alloying: The process of adding one or several alloying elements to the molten steel to meet the compositional specifications of the finished steel is called alloying. In most cases, deoxidation and alloying are carried out at the same time. Part of the deoxidizer added to the steel is consumed by the deoxidation of the steel and converted into deoxidation products to be discharged; the other part is absorbed by the molten steel for alloying. Before the deoxidation operation is completely completed, the alloying effect of the alloy added at the same time as the deoxidizer is absorbed by the molten steel is called pre-alloying.
Composition control: The operation to ensure that the composition of the finished steel all meets the requirements of the standard. Composition control runs through every link from batching to tapping, but the focus is on the control of alloying element composition during alloying. For high-quality steel, it is often required to accurately control the composition in a narrow range; generally, under the premise of not affecting the performance of the steel, the middle and lower limits are controlled.
Increased silicon: At the end of blowing, the silicon content in molten steel is extremely low. In order to meet the requirements for silicon content of each steel grade, a certain amount of silicon must be added in the form of alloy material. In addition to being used as a deoxidizer, it also increases the silicon in the molten steel. The amount of added silicon must be accurately calculated and should not exceed the allowable range of the steel type.
End point control: At the end point of oxygen converter steelmaking (the end of oxygen blowing), the chemical composition and temperature of the metal can simultaneously meet the tapping requirements of the planned steel grade. There are two methods of end-point control: increasing carbon method and pulling carbon method.
Steel tapping: The operation of releasing molten steel when the temperature and composition of the molten steel meet the specified requirements of the steel type. When tapping steel, attention should be paid to prevent molten slag from flowing into the ladle. The additives used to adjust the temperature, composition and deoxidation of molten steel are added to the ladle or the tapping stream during the tapping process.