This is what I want:
1, classified by smelting method:
Open hearth steel: including carbon steel and low alloy steel. According to the different lining materials, it can be divided into acid open hearth steel and alkaline open hearth steel.
Converter steel: including carbon steel and low alloy steel. According to the position of oxygen blowing, converter steel has three types: bottom blowing, side blowing and oxygen top blowing.
Electric furnace steel: mainly alloy steel. According to the different types of electric furnaces, there are four kinds of electric arc furnace steel, induction furnace steel, vacuum induction furnace steel and electroslag furnace steel.
Boiling steel, killed steel and semi-killed steel: differentiated by deoxidation degree and gating system.
2, according to the chemical composition classification:
Carbon steel: It is an alloy of iron and carbon. It is reported that in addition to iron and carbon, it also contains elements such as silicon, manganese, phosphorus and sulfur. According to the different carbon content, it can be divided into three kinds of low-carbon (C: 0.60%) steel. Steel with carbon content below 0.04% is called industrial pure iron.
Ordinary low alloy steel: a small amount of alloying elements (such as silicon, calcium, titanium, niobium, boron and rare earth elements, etc. The total amount does not exceed 3%) is added on the basis of low-carbon plain carbon steel. Steel grades with better comprehensive properties can be obtained.
Alloy steel: It is a kind of steel containing one or more appropriate alloying elements and has good special properties. According to the total content of alloying elements, it can be divided into low alloy (total: 10%) steels.
3, according to the purpose of classification:
Structural steel: according to different uses, it can be divided into two types: construction steel and mechanical steel. Building steel is used to build boilers, ships, bridges, factories and other buildings. Mechanical steel is used to manufacture machines or mechanical parts.
Tool steel: high carbon steel and medium carbon steel used for manufacturing various tools, including carbon tool steel, alloy tool steel and high-speed tool steel.
Special steel: special steel with special physical and chemical properties, including stainless acid-resistant steel, heat-resistant steel, electrothermal alloy and magnetic material.
Common smelting methods
1, converter steelmaking:
A steelmaking method using liquid pig iron as main raw material without external heat source. Its main feature is to use the physical heat of liquid pig iron in the converter and the heat generated by the chemical reaction between various components in pig iron such as carbon, manganese, silicon and phosphorus and oxygen sent into the furnace as the smelting heat source to make steel. In addition to molten iron, there are slagging materials (lime, timely, fluorite, etc. ); In order to adjust the temperature, scrap steel and a small amount of cold pig iron and ore can also be added. Converter can be divided into alkaline (lined with magnesia or dolomite) and acidic (lined with siliceous materials) according to the properties of refractory lining. According to the gas blown into the furnace, it is divided into bottom blowing, top blowing and side blowing; According to the gas used, it is divided into air converter and oxygen converter. Acid converter can't remove sulfur and phosphorus from pig iron, so it must use high-quality pig iron, so its application range is limited. Basic converter is suitable for steelmaking with high phosphorus pig iron, which has been greatly developed in western Europe. Because of the high nitrogen content and limited raw materials, the blown converter steel can not be mixed with more scrap steel, which has not been popularized internationally. Oxygen top-blown converter came out in 1952, and now it has become the main steelmaking method in the world. On the basis of oxygen top-blown converter steelmaking, in order to blow high phosphorus pig iron, lime powder oxygen top-blown converter steelmaking appeared. With the successful development of oxygen bottom blowing port technology, Germany and France built oxygen bottom blowing converters in 1967 respectively. After introducing this technology in 197 1 year, the United States developed a converter with bottom blowing oxygen and lime powder for smelting phosphorus-containing pig iron. 1975, France and Luxembourg successfully developed the top-bottom combined blowing converter steelmaking method.
2, oxygen top-blown converter steelmaking:
A converter steelmaking method, or LD method, uses pure oxygen to blow molten iron from the top of the converter to form steel; In the United States, it is usually called BOF method, also known as BOP method. This is the main method of modern steelmaking. The furnace is an upright crucible-shaped container, and an upright water-cooled oxygen gun is inserted into the furnace from the top to supply oxygen. The furnace body can be tilted. The charge is usually molten iron, scrap steel and slagging materials; A small amount of cold pig iron and iron ore can also be added. Blow high-pressure pure oxygen (containing more than O 299.5%) downward from the top of the molten pool with an oxygen lance, remove silicon, manganese, carbon and phosphorus from the molten iron by oxidation, and slag for dephosphorization and desulfurization. The heat generated by the oxidation of various elements heats the liquid metal in the molten pool, making the molten steel reach the current chemical composition and temperature. Mainly used for smelting non-alloy steel and low alloy steel; But through refining, it can also be used to smelt alloy steel such as stainless steel.
3, oxygen bottom blowing converter steelmaking:
The invention relates to a converter steelmaking method. Oxygen is blown into a molten pool in the converter through an oxygen nozzle at the bottom of the converter to smelt molten iron into steel. Its characteristics are: the height and diameter of the furnace are relatively small; The furnace bottom is flat and can be quickly disassembled and replaced; The tuyere, distributor system and oxygen supply system on the furnace body replace the oxygen lance system of the oxygen top-blown converter. Oxygen bottom-blown converter has the advantages of smooth blowing, less splashing, less smoke and dust, low iron oxide content in slag, and higher metal yield 1% ~ 2% than oxygen top-blown converter. The use of powdery slagging materials, because of its fine particles and large specific surface area, increases the reaction interface, so slagging is fast, which is beneficial to desulfurization and dephosphorization. This method is especially suitable for blowing medium phosphorus pig iron, so it is most widely used in western Europe.
4, continuous steelmaking:
No matter how many heats, raw materials (molten iron and scrap steel) are continuously added from one end of the furnace, and finished products (molten steel) are continuously discharged from the other end of the furnace. The idea of continuous steelmaking process appeared as early as19th century. Due to the potential advantages of small equipment, simple and stable process, many countries have carried out a large number of experiments of various methods, including tank method, spray method and foam method, but they have not been put into industrial production so far.
5, mixed steelmaking:
A steelmaking method in which one furnace steelmaking, another electric furnace smelting reduced slag or reduced slag and alloy, and then mixing at a certain height. This method can improve the quality of steel by treating the steelmaking water of open hearth furnace, converter and electric furnace. Rushing and mixing can increase the contact area between slag and steel, accelerate chemical reaction, deoxidize and desulfurize, and have the function of adsorbing and polymerizing gases and inclusions, thus improving the purity and quality of steel.
6, combined blowing converter steelmaking:
On the basis of top-blown and bottom-blown oxygen converter steelmaking methods, combining their advantages and overcoming their disadvantages, a new steelmaking method is developed, that is, different gases are blown into the bottom of the original top-blown converter to improve the stirring of the molten pool. At present, most countries in the world adopt this steelmaking method, and have developed various types of combined blowing converter steelmaking technologies, such as BSC-BAP method developed by British Steel Company, which uses air +N2 or Ar2 as bottom blowing gas and N2 as cooling gas. The KMS method developed by klokner-Max Metallurgical Plant in Germany uses a naturally protected bottom gun to inject coal and oxygen into the molten pool from the bottom, the K-BOP method developed by Kawasaki Iron and Steel Company in Japan injects oxygen mixed lime powder accounting for 30% of the total oxygen into the molten pool from the bottom, and the LD method developed by Nippon Steel Company, which injects oxygen accounting for 0/0%-20% of the total oxygen/KLOC from the bottom and cools it with propane or natural gas.
7, top blowing oxygen open hearth steelmaking:
Since the mid-1950s, the 1 ~ 5 water-cooled oxygen lance has been inserted into the melting chamber from the top of the furnace and directly blown into the melting pool in open hearth production. This method improves the dynamic conditions of molten pool reaction, changes the thermal effect of carbon-oxygen reaction from endothermic to exothermic, and improves the thermal conditions. Productivity has been greatly improved.
8, electric arc furnace steelmaking:
A steelmaking method for melting metals and other materials by using the thermal effect of electric arc. Three-phase AC arc furnace for steelmaking is the most common direct heating arc furnace. In the process of steelmaking, because there is no gas in the furnace, oxidation or reduction atmosphere and conditions can be formed according to the technological requirements, so it can be used to smelt high-quality non-alloy steel and alloy steel. According to the capacity per ton of furnace, EAF can be divided into ordinary power EAF, high power EAF and ultra-high power EAF. The development of EAF steelmaking to high power and ultra-high power aims to shorten smelting time, reduce power consumption, improve productivity and reduce costs. With the emergence of high-power and ultra-high-power electric furnaces, electric arc furnaces have become melting furnaces, and all refining processes are carried out in refining devices. In recent ten years, DC arc furnace has developed rapidly because of low electrode consumption, small voltage fluctuation and low noise, and can be used to smelt high-quality steel and ferroalloy.
9. Set-top box method:
The original text is Sumitomo top-bottom combined blowing process, which is a top-bottom combined blowing converter steelmaking method developed by Sumitomo Metal Company of Japan. This method combines the advantages of oxygen top-blown converter steelmaking and oxygen bottom-blown converter steelmaking. When it is used to blow low carbon steel, the dephosphorization effect is good and the cost is obviously reduced. The bottom blowing gas used is O2, CO2, N2, etc. On the basis of STB method, STB-P top powder spraying method was developed, which further improved the dephosphorization conditions of high carbon steel and was used to refine stainless steel.
10, relative humidity method:
Also known as cyclic vacuum treatment. Developed by Ruhrstahl/Hershey, Germany. There are two conduits under the vacuum chamber into which molten steel is injected. After vacuumizing, the molten steel rises to a certain height, and then inert gas Ar is blown into the riser to drive the molten steel into the vacuum chamber for vacuum treatment, and then flows back to the ladle through another conduit. The vacuum chamber is equipped with an alloy supply system. This method has become the main method for vacuum treatment of molten steel in large capacity ladle (> > 80t).
1 1、RH—OB:
RH oxygen blowing method. Oxygen blowing is added to the vacuum cycle degassing (RH) process to increase the temperature. For refined stainless steel, decarburization reaction can be carried out under reduced pressure first; When it is used to refine ordinary steel, the load of converter can be reduced. Aluminum can also be used to raise the temperature.
12, OBM-S method:
The original text is oxygen-bottom Maxhutte—Scarp, which is a steelmaking method of oxygen bottom-blown converter with natural gas or propane as the cooling medium of bottom-blown oxygen lance, and was invented by German Maxhutte-Klockner factory. OBM-S is to install a side oxygen lance on the cover of OBM oxygen bottom-blown converter, and the bottom oxygen lance injects gas and natural gas to preheat the scrap, so as to increase the scrap ratio.
13, NK-CB method:
The original text is NKK combined blowing system, which is a top-bottom combined blowing converter steelmaking method established by Japan Steel Pipe Company in 1973, that is, a small amount of gas (Ar, CO2, N2) is blown from the bottom of the furnace at the same time of top blowing to strengthen the stirring of steel slag and control the partial pressure of CO in molten steel. This method adopts perforated brick nozzle, which can reduce the cost when it is used to smelt low carbon steel. Using it to smelt high carbon steel is beneficial to dephosphorization. This method should be combined with hot metal pretreatment process.
14、MVOD:
The method of adding a water-cooled oxygen gun to the equipment of VAD method to make it blow oxygen under vacuum to decarbonize. Because decarburization under vacuum is an exothermic reaction, the vacuum heating measures of VAD method can be omitted. The operation process is the same as VOD method.
15, LF method:
The original text is ladle furnace, which is a ladle furnace refining method developed by Japan Special Steel Company (Datong Special Steel Company) in 197 1 year. Its equipment and technology are composed of argon stirring, submerged arc heating and alloy supply system. The advantages of this process are: the chemical composition and temperature of molten steel can be accurately controlled; Reduce the content of inclusions; The yield of alloying elements is high. LF furnace has become an indispensable external refining equipment between steelmaking furnace and continuous casting machine.
16, converter steelmaking method:
1952, Linz Plant of Austrian Iron and Steel Company and Donowitz Plant of Austrian Alpine Mining and Metallurgy Company took the lead in developing oxygen top-blown converter steelmaking method in industry, and named them after their initials. After this law came out, it quickly spread all over the world. The United States calls this method BOF or BOP, which is short for basic oxygen furnace or process. See oxygen top blowing and converter for details.
17, laser diode OTB method:
The original text is LD-OX Gyen Top an Bottom process, which is a top-bottom combined blowing converter steelmaking process developed by Kobayashi Steel Works and Ogawa Plant. It is characterized by adopting a special bottom blowing single-ring slit nozzle (SA nozzle), so that the bottom blowing body can be controlled in a wide range. Inert gas is blown into the bottom.
18, LD-HC method:
The original text is LD-Hainaut Saubre CRM, which is a top-bottom combined blowing converter steelmaking method developed by Belgium for blowing high phosphorus hot metal, that is, LD+ bottom blowing oxygen and protecting the nozzle with hydrocarbons.
19, LD-AC method:
The original text is LD-Arbed-Centre National, a steelmaking method developed by French Iron and Steel Research Institute, which is used to blow high phosphorus hot metal.
20, KS method:
The original steelmaking in Klokner is a converter steelmaking process, with bottom blowing of pulverized coal and oxygen and 100% solid material operation. The proportion of bottom blowing oxygen is 60% ~ 100%.
2 1, K-ES method:
The electric arc furnace steelmaking method combines bottom blowing gas technology, secondary combustion technology and pulverized coal injection technology. It is a technology jointly developed by Tokyo Steelmaking Company of Japan and Kiokner Company of Germany, and coal can be used instead of electricity.
22, FINKL—VAD method:
Arc heating ladle degassing method or vacuum arc degassing method. Characterized in that an arc heating device is added to the cover of the vacuum chamber, and argon gas is used for stirring under vacuum. This method has stable degassing effect, and can be used for desulfurization, decarbonization and addition of a large number of alloys. The equipment is mainly composed of vacuum chamber, arc heating system, alloy supply device, vacuum pumping system and hydraulic system.
23, DH method:
Vacuum treatment device developed by hoddle United Metallurgical Company in Dortmund, Germany. In the vacuum chamber lined with refractory material, the conduit lined with refractory material is inserted into the ladle, and the vacuum chamber or ladle is lowered and lifted periodically, so that a part of molten steel enters the vacuum chamber and returns to the ladle after treatment. The upper part is provided with an alloying device and a vacuum heating and heat preservation device. At present, this equipment has not been built.
24, CLU method:
A refining method of stainless steel. Its principle is the same as that of AOD method, and its purpose is to replace argon with steam. This method was successfully developed by French Creusot-Loire company and Swedish Uddeholm company, and put into production in 1973. Steam is decomposed into H2 and O2 after contacting with molten steel; H2 reduces the partial pressure of carbon monoxide, and the decomposition reaction is endothermic, so the temperature rise of molten steel can be suppressed. However, the oxidation burning loss of chromium is more serious than that of AOD method.
25, casting method:
The original text is sealed argon blowing to adjust the composition, which is an out-of-furnace refining method for fine-tuning the alloy composition under argon sealing. In this method, argon is blown from the bottom of the ladle, after slag is discharged, the dipping hood is lowered, argon is blown continuously, and then alloy trimming components are added. Its advantages are accurate composition control and high alloy yield.
26, CAS-OB method:
The original text is sealed argon blowing blending, which is an external refining method by adding oxygen blowing gun to casting equipment. In addition to fine-tuning the alloy composition, it can also be heated by adding aluminum and blowing oxygen (chemical thermal method), and the heating speed is 5 ~ 13℃/min. This method can accurately control the temperature of molten steel within 3℃, which is beneficial to continuous casting production.
27.ASEA-SKF method:
Ladle refining method developed in Sweden. Using low frequency electromagnetic stirring, atmospheric arc heating, slag refining in ladle, vacuum degassing in another station, equipped with oxygen gun, oxygen can be blown to reduce pressure and decarbonize. In order to improve the refining effect, argon can also be blown through the perforated brick at the bottom of the ladle and alloy can be added to adjust the composition of molten steel.
28, AOD method:
Argon-oxygen decarbonization is the main refining method for smelting low carbon stainless steel. 1964 was successfully developed by American carbide company, and 1968 was used in practical production. Its metallurgical principle is to dilute CO with Ar, reduce its partial pressure, and achieve the effect of vacuum, thus removing carbon to a very low level. The furnace body and transmission device of AOD are similar to those of converter. The air holes are arranged on the side wall near the furnace bottom, and the mixed gas of Ar+O2 is blown into the furnace, and the raw material is molten steel in the primary melting furnace. The blowing process is divided into oxidation stage, reduction stage and refining stage. It has become the main production process of stainless steel.
Special metallurgical method
Include electroslag remelting, vacuum metallurgy, plasma metallurgy, electron beam melting, zone melting and other steelmaking methods. Some high-tech or special-purpose steels that require ultra-high purity can be refined by special metallurgical methods if they cannot meet the requirements by ordinary steelmaking and external refining.
Electroslag remelting: a refining process, also known as ESR, in which molten steel is cast or forged into electrodes and remelted twice by slag resistance heat. Its heat source comes from the resistance heat of slag. During remelting, the consumable electrode is immersed in the slag, and the current passes through the ionized slag, so that the temperature of the slag is much higher than the melting point of the molten consumable electrode. The consumable electrode inserted into the slag melts to form droplets, which can be washed and refined by their own weight through the slag pool, and then enter the metal melting pool under the condition of reducing air pollution. Forming a thin slag skin between the ingot and the crystallizer wall not only slows down the radial cooling, but also improves the surface quality of the finished ingot. With the help of water cooling at the bottom of the mold, it solidifies into a remelted ingot with less axial crystallization tendency and segregation, which improves the hot working plasticity.
Plasma metallurgy: a metallurgical process with plasma flow as heat source, that is, using plasma gun to convert electric energy into heat energy in directional plasma jet. Plasma jet has the characteristics of stable arc, concentrated heat and extremely high temperature. The working temperature of some plasma guns is as high as 5000 ~ 20000℃. Plasma gun can use inert gas (Ar) and reducing gas (H2) as media to achieve different metallurgical purposes. Plasma furnaces can be used to smelt high melting point metals and active metals, and to purify metals or alloys. Plasma technology is also used in the treatment of waste dust in iron and steel plants and the production of ferroalloys.
Jet metallurgy: in order to accelerate the physical and chemical reaction between liquid metal and materials, powder materials are sent into liquid metal by gas jet to complete metallurgical reaction, also known as powder jet metallurgy. This process is widely used in hot metal pretreatment and ladle refining to achieve the purpose of desulfurization, deoxidation, fine-tuning of components and denaturation of inclusions. The process has fast reaction speed and high material utilization rate.
Regional melting: the process of refining metals by using the solubility difference of impurity elements in liquid and solid phases proposed by W.G.Pfann in 1952. Its working principle is: assuming that a small piece of metal in a uniform solid metal bar melts into liquid, if this small piece of liquid area moves slowly from left to right, the impurities will be redistributed every time it moves, and the effect is equivalent to driving the impurities to the right. After repeated for many times, the left metal can reach high purity.
Vacuum metallurgy: metallurgical process under the condition of less than 0. 1MPa to ultra-high vacuum [133.3x (< 760 ~10-12) pa], including refining, melting, remelting, refining, forming and heat treatment of metals and alloys. The main purposes are: ① to reduce the pollution of gas relative to metal; (2) reducing the content of gases or volatile impurities dissolved in metals; ③ Promote the chemical reaction with gaseous products; ④ Avoid pollution caused by refractory containers. Meet the requirements of high-performance metal materials and new metal materials. With the need of producing new high-performance metal materials such as electrothermal materials, electrical alloys, soft magnetic alloys and high-temperature nickel-based alloys, various vacuum melting methods have been developed, including vacuum resistance melting, vacuum induction melting, vacuum arc remelting, electron beam melting and electroslag remelting.
Vacuum arc melting: the process of remelting metals and alloys by electric arc heating under vacuum (10-2 ~/kloc-0-1pa), also known as VAR method. The process is as follows: the water-cooled copper crucible is used as the positive electrode, and the consumable electrode to be melted is connected to the virtual electrode that enters the furnace body through sliding seal as the negative electrode; Input low-voltage DC current, strike an arc between the electrode and the bottom of the crucible, and remelt the metal and alloy by arc heating. With the melting of consumable electrode, consumable electrode is remelted into remelting ingot with uniform composition, dense structure, high purity and less segregation by controlling the descending speed of electrode. It is not only used for remelting active metals and refractory metals, but also used for remelting high-temperature alloys and special steels with strict requirements.
Vacuum electron beam melting: under high vacuum (133.3x10-4 ~133.3x10-8pa), the material to be melted (as anode) is bombarded by an electron gun, and then it is dropped into a water-cooled copper crystallizer to solidify into ingots. Ingots are continuously extracted by mechanical devices. This method can adjust the energy distribution and control the melting speed. The purity of electron beam remelting materials is higher than other vacuum melting methods. Suitable for melting tungsten, molybdenum and their alloys, advanced alloy steel, high temperature alloy, ultra-pure metal and other metals.
Vacuum resistance melting: a melting method that uses the heat generated by current passing through a conductor as a heat source under vacuum conditions. Generally, indirect heating is used, and electric heaters transfer heat energy to materials in the furnace. The atmosphere in the resistance furnace can be inert or protective as required. Vacuum resistance furnace can be designed as melting furnace or heat treatment furnace.
Vacuum induction melting: the process of melting metals and alloys under vacuum by using induced electrothermal effect. Select the power frequency according to the charge and capacity. It can be divided into high frequency (> 104 Hz), intermediate frequency (50 ~ 104 Hz) and power frequency (50 or 60Hz). Induction furnaces are divided into two categories: cored (closed tank type) and coreless (crucible type). The former has high electrothermal efficiency and high power factor, but it needs melting point and low melting temperature, which is suitable for continuous melting of single variety; The latter has high melting temperature and low electrothermal efficiency, and is suitable for melting special steel and nickel-based alloy. Vacuum induction melting is widely used in the production of superalloy, high strength steel and ultra-high strength steel.
Steelmaking process
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 slagging and oxygen blowing operation of oxygen top-blown converter is to generate slag with sufficient fluidity and alkalinity, 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.
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.
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.
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.
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 the start of electrification to the complete melting of charge, and the melting period of open hearth steelmaking is called the melting period from the end of molten iron mixing to the 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.
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.
Refining period: the process operation period in which some elements and compounds harmful to steel quality are selected into the gas phase or discharged or floated into slag through chemical reaction, so as to be excluded from molten steel.
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. At present, the reduction period has been cancelled for steelmaking operations of high-power and ultra-high-power electric arc furnaces.
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, 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 are removed by floating, 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 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 deep desulfurization, calcium treatment and fine-tuning of carbon and aluminum components in steel during tapping with Ca-Si. It also has the functions of purifying molten steel and improving the shape of nonmetallic inclusions.
Ladle treatment: short for ladle treatment external refining. 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.
Ladle 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 is blown into molten steel, which does not participate in metallurgical reaction, but each small bubble rising in 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.
Pre-alloying: the operation process of adding one or more alloying elements to molten steel to 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: the 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.
Increasing 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: control to make the chemical composition and temperature of metal meet the planned tapping requirements at the end of steelmaking and blowing in oxygen converter. There are two ways to control the end point: increasing carbon and pulling carbon.
Tapping: tapping operation when the temperature and composition of molten steel meet the specific requirements of steelmaking varieties. Pay attention to prevent slag from flowing into ladle when tapping. When tapping, additives for adjusting the temperature, composition and deoxidation of molten steel are added to ladle or tapping flow.