Fe2O3+3CO==2Fe+3CO2 (high temperature)
Fe3O4+2CO==3Fe+2CO2 (high temperature)
C+O2==CO2 (high temperature)
C+CO2==2CO (high temperature)
Iron-making is to mix iron ore or sintered pellets, manganese ore, limestone and coke in a certain proportion, and then send them to the bunker, and then send them to the blast furnace, where hot air of about 1000℃ is blown from the lower part of the blast furnace, so that the coke burns to generate a large amount of high-temperature reducing gas, thereby heating the materials and causing them to undergo chemical reactions. At about 1 100℃, the iron ore begins to soften and melts at 1400℃, forming molten iron and liquid slag, which are layered in the furnace. After that, iron tapping and slag tapping operations are carried out.
The nature of raw materials and fuels, products and by-products, and the environmental conditions of production have brought a series of potential occupational hazards to ironworkers. For example, ore and coke will produce a lot of dust in the process of transportation, loading and unloading, crushing and screening, sintering and screening; The equipment, facilities and pipelines are densely arranged in the tapping yard in front of the blast furnace, with many kinds of operations, concentrated personnel and the most concentrated dangerous and harmful factors. For example, high temperature radiation in front of the furnace will produce a lot of smoke and dust, and molten iron and slag will explode when they meet water. Damage caused by taphole machine and crane, etc. Gas leakage in ironworks will be poisoned, and blast furnace gas mixed with air will explode with great power. Dust explosion can occur when soot powder is injected; In addition, there is noise in the ironmaking area and damage to machines and vehicles. So many dangerous factors threaten the life safety and health of production personnel.
Steelmaking is a smelting process in which pig iron, scrap steel and slagging materials are used as raw materials, and steel is produced through heating and melting, slagging, dephosphorization, oxidation and decarbonization, degassing, reduction and deoxidation, desulfurization and impurity removal.
Steelmaking process:
Input raw materials
Adding raw materials such as molten iron or scrap steel into electric furnace or converter is the first step of steelmaking operation.
Slagging: the operation of adjusting slag composition, alkalinity, viscosity and reaction ability in iron and steel production. The purpose is to smelt metal 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. taphole
According to different smelting conditions and purposes, slag discharge or slag scraping operations are taken in the smelting process. 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.
Molten pool stirring
Energy is supplied to the molten metal 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.
phosphorous 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.
Electric furnace bottom blowing
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 according to the process requirements, so as to accelerate the 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.
melting stage
The melting period of steelmaking is mainly open hearth and electric furnace steelmaking. EAF steelmaking starts from electrifying to charging.
The melting period is called the melting period until all materials are melted, and the open hearth steelmaking is called the melting period from the beginning of mixing molten iron to the complete melting of the burden. 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.
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 oxidation 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%.
refining period
In the process of steelmaking, some elements and compounds harmful to the quality of steel are selected into the gas phase or discharged or floated into the slag by chemical reaction through slagging and other methods, thus being excluded from the molten steel.
Reduction period
In the common EAF steelmaking operation, the time 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. At present, the reduction period has been cancelled for steelmaking operations of high-power and ultra-high-power electric arc furnaces.
External refining
The steelmaking process of moving molten steel that has been preliminarily melted in a steelmaking furnace (converter, electric furnace, etc.). ) refining in another container is also called 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, deoxidizing, desulfurizing, removing inclusions and fine-tuning the composition of molten steel in a container with 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 refining outside the furnace, which can be roughly divided into two kinds: atmospheric refining and vacuum refining. According to different treatment methods, it can be divided into ladle treatment type external refining and ladle refining type external refining.
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. In the static state of molten steel, inclusions * float up 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.
Ladle feeding
The method of deep desulfurization, calcium treatment and carbon-aluminum fine-tuning of steel by feeding the powder of deoxidizing, desulfurization and fine-tuning components wrapped by iron sheets into a ladle or directly feeding aluminum wires and carbon wires.
Ladle treatment
Short for external refining of ladle treatment. Its characteristics are short refining time (about 10 ~ 30 minutes), single refining task, no heating device to compensate for the temperature drop of molten steel, simple process operation and low equipment investment. It has devices for degassing and desulfurizing molten steel, controlling composition and changing the shape of inclusions. Such as vacuum cycle degassing method (RH, DH), ladle vacuum argon blowing method (Gazid), ladle powder spraying treatment method (IJ, TN, SL) and so on.
Barrel refining
Short for ladle refining outside the furnace. Its characteristic is that the refining time is longer than that of ladle treatment (about 60 ~ 180 minutes). It has many refining functions and heating devices to compensate for the temperature drop of molten steel. Suitable for refining all kinds of high alloy steel and special performance steel (such as ultra-pure steel). Vacuum oxygen blowing decarburization (VOD), vacuum arc heating degassing (VAD), ladle refining (ASEA-SKF), closed argon blowing fine tuning (CAS), etc. , all belong to this category; Similarly, there is argon-oxygen decarbonization (AOD).
Inert gas treatment
Inert gas Ar is blown into molten steel. This gas itself does not participate in metallurgical reaction, but each small bubble rising from molten steel is equivalent to a "small vacuum chamber" (the partial pressure of H2, N2 and CO in the bubble is close to zero), which has the function of "gas washing". The principle of stainless steel production by out-of-furnace refining method is to apply the equilibrium relationship between carbon, chromium and temperature under different CO partial pressures. Refining decarbonization with inert gas and oxygen can reduce the partial pressure of CO in carbon-oxygen reaction. At lower temperature, the carbon content decreases and chromium is not oxidized.
Prealloying
The operation process of adding one or more alloying elements to molten steel to make it meet the requirements of finished steel composition specification is called alloying. In most cases, deoxidation and alloying are carried out at the same time, and part of the deoxidizer added to steel is consumed by deoxidation of steel and converted into deoxidation products to be discharged; The other part is absorbed by molten steel and plays an alloying role. Before the deoxidation operation is completely completed, the alloying effect of the alloy added at the same time with the deoxidizer is absorbed by molten steel, which is called prealloying.
Composition control
: Operation to ensure that all components of finished steel meet the standard requirements. Composition control runs through every link from batching to tapping, but the key point is to control the composition of alloying elements 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 steel, it is controlled according to the middle and lower limits.
Increase silicon
At the end of blowing, the silicon content in molten steel is extremely low. In order to meet the requirements of various steel grades for silicon content, a certain amount of silicon must be added in the form of alloy. Besides being used as the consumption part of deoxidizer, it also increases the silicon in molten steel. The amount of silicon added should be accurately calculated and should not exceed the allowable range of steel blowing.
Terminal control
At the end of steelmaking and blowing in oxygen converter, the chemical composition and temperature of metal should be controlled to meet the tapping requirements of planned steel grades. There are two ways to control the end point: increasing carbon and pulling carbon.
Tap, tap
When the temperature and composition of molten steel meet the specified requirements of steelmaking varieties, the operation of discharging molten steel. Pay attention to prevent slag from flowing into ladle when tapping. Additives used to adjust the temperature, composition and deoxidation of molten steel are added to ladle or tapping flow when tapping, which is also called deoxidation alloying.