1, feeding
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 steelmaking operation.
2. Slagging
Slagging: the operation of adjusting slag composition, alkalinity, viscosity and reaction ability in iron and steel production. The purpose is to train metals with required composition and temperature through slag-metal reaction.
For example, the operation of oxygen top-blown converter slagging and oxygen blowing is to generate slag with sufficient fluidity and alkalinity, which can transfer enough oxygen to the metal surface, so that sulfur and phosphorus can be reduced below the upper limit of planned steel grade, and the amount of splashing and slag overflow during oxygen blowing can be reduced as much as possible.
3. Slagging
Slag discharge: Slag discharge or skimming operation during smelting according to different smelting conditions and purposes. If smelting by single slag method, the oxide slag must be scraped off at the end of oxidation; When making reducing slag by double slag method, all original oxide slag must be discharged to prevent phosphorus from flowing back.
4, molten pool stirring
Molten pool stirring: providing energy to the metal molten pool to make the molten metal and slag move, thus improving the kinetic conditions of metallurgical reaction. The stirring of molten pool can be realized by gas, machinery, electromagnetic induction and other methods.
5. Phosphorus removal
Chemical reaction for reducing phosphorus content in molten steel. Phosphorus is one of the harmful impurities in steel. Steel containing more phosphorus is easy to be brittle when used at room temperature or lower, which is called "cold brittleness". The higher the carbon content in steel, the more serious the brittleness caused by phosphorus. Generally, the phosphorus content in ordinary steel does not exceed 0.045%, and high-quality steel requires less phosphorus.
Phosphorus in pig iron mainly comes from phosphate in iron ore. The thermodynamic stability of phosphorus oxide and iron oxide is similar. Under the reduction condition of blast furnace, almost all phosphorus in the burden is reduced and dissolved in molten iron. If phosphorus compounds cannot be removed by mineral processing, dephosphorization can only be carried out outside the furnace or in the alkaline steelmaking furnace.
Understanding and solving the problem of dephosphorization in iron is of special significance in the history of iron and steel production development. The large-scale industrial production of steel began with the acid converter steelmaking method invented by H.Bessemer in 1856. But acid converter steelmaking can't dephosphorize; The lack of low-phosphorus iron ore has seriously hindered the development of steel production.
1879, S.Thomas invented the basic converter steelmaking process, which can treat high phosphorus molten iron. Then the principle of dephosphorization of alkaline slag is extended to open hearth steelmaking, so that a large number of phosphorus-containing iron ores can be used for steelmaking, which has made great contributions to the development of modern iron and steel industry.
The dephosphorization reaction of alkaline slag is carried out at the interface between slag and phosphorus-containing molten iron. Phosphorus P reacts with oxygen O in molten steel to form gaseous P2O5.
6, electric furnace bottom blowing
Electric furnace bottom blowing: according to the process requirements, N2, Ar, CO2, CO, CH4, O2 and other gases are blown into the furnace molten pool through the nozzle placed at the bottom of the furnace to accelerate melting and promote the metallurgical reaction process.
Bottom blowing process can shorten smelting time, reduce energy consumption, improve dephosphorization and desulfurization operations, increase the amount of residual manganese in steel and improve the yield of metals and alloys. It can make the composition and temperature of molten steel more uniform, thus improving the quality of steel, reducing the cost and improving the productivity.
7. Melting period
Melting period: The melting period of steelmaking is mainly open hearth and electric furnace steelmaking. The melting period of EAF steelmaking is called the melting period from electrification to complete melting of charge, and the melting period of open hearth steelmaking is called the melting period from completion of molten iron to complete melting of charge. The task of the melting period is to melt and raise the temperature of the burden as soon as possible, and to make slag during the melting period.
8. Oxidation stage
Oxidation stage and decarbonization stage: the oxidation stage of common EAF steelmaking usually refers to the process stage from charge dissolution, sampling analysis to removal of oxide slag. Some people think that it started with blowing oxygen or adding ore to decarburize.
The main task of oxidation stage is to oxidize carbon and phosphorus in molten steel; Removing gas and impurities; The molten steel is heated uniformly to raise the temperature. Decarburization is an important operation process in the oxidation stage. In order to ensure the purity of steel, decarbonization is required to be greater than 0.2%. With the development of external refining technology, oxidation refining of EAF is mostly carried out in ladle or refining furnace.
9. Refining period
Refining period: In the process of steelmaking, some elements and compounds harmful to steel quality are selected into gas phase or discharged or floated into slag by chemical reaction through slagging and other methods, so that they are discharged from molten steel.
10, reduction period
Reduction period: In common EAF steelmaking operation, the period from the end of oxidation to tapping is usually called reduction period. Its main task is to produce reduced slag for diffusion, deoxidation, desulfurization, chemical composition control and temperature regulation. The reduction period was cancelled in the steelmaking operation of high-power and ultra-high-power EAF.
1 1, refining outside the furnace
Refining outside the furnace: the steelmaking process of moving the molten steel preliminarily refined in the steelmaking furnace (converter, electric furnace, etc.). ) to another container for refining, also known as secondary metallurgy. Therefore, the steelmaking process is divided into two steps: primary smelting and refining. Primary smelting: melting, dephosphorization, decarbonization and main alloying of furnace charge in oxidizing atmosphere.
Refining: degassing, deoxidation, desulfurization, inclusion removal and fine-tuning of molten steel composition in vacuum, inert gas or reducing atmosphere. The advantages of two-step steelmaking are: improving steel quality, shortening smelting time, simplifying technological process and reducing production cost. There are many kinds of out-of-furnace scouring, which can be roughly divided into atmospheric out-of-furnace scouring and vacuum out-of-furnace scouring. According to different treatment methods, it can be divided into ladle treatment type external refining and ladle refining type external refining.
The advantages of two-step steelmaking are: improving steel quality, shortening smelting time, simplifying technological process and reducing production cost. There are many kinds of out-of-furnace scouring, which can be roughly divided into atmospheric out-of-furnace scouring and vacuum out-of-furnace scouring. According to different treatment methods, it can be divided into ladle treatment type external refining and ladle refining type external refining.
12, molten steel stirring
Molten steel stirring: the stirring of molten steel during refining outside the furnace. It homogenizes the composition and temperature of molten steel and promotes metallurgical reaction.
Most metallurgical reactions are phase interface reactions, and the diffusion speed of reactants and products is the limiting link of these reactions. In the static state, the metallurgical reaction speed of molten steel is very slow, for example, it takes 30 ~ 60 minutes for desulfurization of static molten steel in electric furnace; When refining in the furnace, the molten steel can be desulfurized by stirring for only 3-5 minutes.
When the molten steel is still, the inclusions float and are removed, and the removal speed is slow; When stirring molten steel, the removal rate of inclusions increases exponentially, which is related to the intensity and type of stirring, the characteristics and concentration of inclusions.
13, ladle feeding
Ladle wire feeding: the method of feeding the powder with deoxidizing, desulfurizing and fine-tuning components wrapped with iron sheets into the ladle through a wire feeder, or directly feeding aluminum wires and carbon wires for Ca-Si tapping for deep desulfurization, calcium treatment and fine-tuning of carbon and aluminum components in steel. It also has the functions of purifying molten steel and improving the shape of nonmetallic inclusions.