1. Introduction to converter steelmaking
Converter steelmaking involves blowing oxygen into molten pig iron to oxidize impurities such as silicon and manganese. A large amount of heat is released during the oxidation process (containing 1% silicon can increase the temperature of pig iron by 200 degrees Celsius), which can reach a sufficiently high temperature in the furnace. Therefore, converter steelmaking does not require the use of additional fuel. The basic tasks of steelmaking are decarburization, dephosphorization, desulfurization, deoxidation, removal of harmful gases and non-metallic inclusions, raising temperature and adjusting composition. It can be summarized as: “four removals” (carbon, oxygen, phosphorus and sulfur), “two removals” (removal of gases and inclusions), and “two adjustments” (composition and temperature). The main technical means used are: oxygen supply, slagging, heating, adding deoxidizer and alloying operations.
The purpose of converter smelting is to oxidize carbon and other impurities (such as silicon and manganese) in pig iron to produce steel with better physical, chemical and mechanical properties than iron.
The difference between steel and pig iron: The first is the carbon content. In theory, steel is generally called steel with a carbon content less than 2.11%. Its melting point is 1450-1500°C, while the melting point of pig iron is 1100-1200°C. Carbon and iron elements in steel form Fe3C solid solution. As the carbon content increases, its strength and hardness increase, while its plasticity and impact toughness decrease. Steel has very good physical, chemical and mechanical properties, and can be used for deep processing such as drawing, pressing, rolling, punching and drawing. It has a wide range of uses.
2. Introduction to the principles of converter smelting
Converter steelmaking is carried out in a converter. The shape of the converter is like a pear, with refractory bricks on the inner wall and many small holes (tuyeres) on the side of the furnace. Compressed air is blown into the furnace through these small holes, which is also called a side-blown converter. At the beginning, the converter is horizontal, liquid pig iron at 1300 degrees Celsius is injected into it, and a certain amount of quicklime is added, and then air is blown in and the converter is turned to make it stand upright. At this time, the surface of the liquid pig iron reacts violently, causing iron, silicon, and manganese to oxidize (FeO, SiO2, MnO,) to form slag. The convection effect of the molten steel and slag is used to spread the reaction throughout the furnace. After a few minutes, when only a small amount of silicon and manganese remain in the molten steel, the carbon begins to oxidize, generating carbon monoxide (exothermic) and causing the molten steel to boil violently. A huge flame appeared at the furnace mouth due to the burning of overflowing carbon monoxide. Finally, phosphorus is also oxidized and further forms ferrous phosphate. Ferrous phosphate reacts with quicklime to form stable calcium phosphate and calcium sulfide, which together become slag. When the phosphorus and sulfur gradually decrease, the flame recedes, and brown steam of ferric oxide appears at the furnace mouth, it indicates that the steel has been made. At this time, the blast should be stopped immediately, the converter should be turned to a horizontal position, the molten steel should be poured into the molten steel ladle, and deoxidizer should be added for deoxidation. The whole process only takes about 15 minutes. If oxygen is blown from the bottom of the furnace, it is a bottom-blown converter; if oxygen is blown from the top, it is a top-blown converter.
3. Introduction to converter smelting process
The basic smelting process of one furnace of steel in a converter. The operation process of smelting a furnace of steel in a top-blown converter mainly consists of the following six steps:
(1) Tap the furnace, pour slag, check the furnace lining and tilting equipment, and make necessary repairs and repairs;
(2) Tilt the furnace, add scrap steel, add molten iron, and straighten the furnace body (to the vertical position);
(3) Lower the gun and start blowing, and add the first batch of slag at the same time (at first, the noise in the furnace is loud, red smoke comes out from the furnace mouth, and then a dark red flame is emitted. After 3 to 5 minutes, the silicon manganese oxygen is almost finished, and the carbon The oxygen reaction gradually becomes more intense, the flame at the furnace mouth becomes larger, and the brightness increases. At the same time, the slag melts and the noise weakens);
(4) After 3 to 5 minutes, add the second batch of slag and continue blowing (the carbon in the steel gradually decreases as blowing proceeds, and the flame becomes weak after about 12 minutes, so stop blowing);
(5) Turn down the furnace, measure temperature, take samples, and determine the additional blowing time or tapping;
(6) Tap out the steel and at the same time (add the calculated alloy into the ladle) perform deoxidation and alloying.
4. Introduction to the main process equipment of converter steelmaking
Converter
The furnace body can be rotated and is used for metallurgical furnaces for blowing steel or matte. The converter body is made of steel plates, cylindrical in shape, and lined with refractory materials. It is heated by chemical reaction heat during blowing and does not require an external heating source. It is the most important steelmaking equipment and can also be used for copper and nickel smelting.
AOD refining furnace
AOD, argon oxygen decarburization refining furnace, is a proprietary process for stainless steel smelting. AOD furnace types include 3t, 6t, 8t, 10t, 18t, 25t, 30t, etc. according to the capacity. The level of equipment has also evolved from semi-automatic control to intelligent computer control for smelting stainless steel.
VOD refining furnace
VOD refining furnace (vacuumoxygen decarburization) is an external refining furnace that performs oxygen blowing decarburization in a vacuum state. It mainly refines chromium-nickel stainless steel, ultra-low carbon steel, ultra-pure ferritic stainless steel and pure iron. Put the primary molten steel into a refining package and put it into a sealed vacuum tank for oxygen blowing, decarburization, desulfurization, degassing, temperature adjustment, and chemical element adjustment.
LF refining furnace
LF (ladle furnace) furnace is a ladle refining furnace with heating and stirring functions. Heating is usually done by electrode heating, and stirring is done by bottom breathable bricks.
Oxygen gun
The oxygen lance is the main equipment for oxygen supply in the converter. It consists of a nozzle, a gun body and a tail structure. The nozzle is made of forged and cut copper with good thermal conductivity, or is also pressure cast. The shapes of nozzles include Laval type, straight type and spiral type. The most commonly used nozzle at present is the porous Laval type nozzle. The Laval type nozzle is a contraction-expansion contraction type nozzle. When the ratio of outlet oxygen pressure to inlet oxygen pressure pout/p0<0.528, a supersonic jet is formed.
Converter tilting system
Tilt furnace system: frequency conversion speed regulation (frequency converter + motor + reducer + large gear)
Tilt furnace mechanism: The tilting furnace mechanism consists of tracks, tilting furnace cylinders, cradle platforms, horizontal support mechanisms and supports.
