This article introduces the converter steelmaking, converter smelting principle and technological process and its main equipment. And explained the primary, secondary and tertiary flue gas of the converter.
Key words: converter steelmaking; principle; process flow; main equipment
Introduction to Converter Steelmaking
Converter steelmaking is to blow oxygen into molten pig iron to oxidize impurities such as silicon and manganese. During the oxidation process, a large amount of heat is released (1% silicon can increase the temperature of pig iron by 200 degrees Celsius), which can make the furnace reach a high enough temperature. 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, increase of temperature and adjustment of composition. It can be summarized as: “four removals” (carbon, oxygen, phosphorus and sulfur), “two removals” (degassing and removal of inclusions), and “two adjustments” (composition and temperature). The main technical means used are: oxygen supply, slagging, temperature rise, adding deoxidizer and alloying operation.
The purpose of converter smelting: 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: first is the carbon content. In theory, the carbon content is generally less than 2.11%, which is called steel. Its melting point is 1450-1500 ℃, while the melting point of pig iron is 1100-1200 ℃. In steel, carbon and iron elements form Fe3C solid solution. As the carbon content increases, its strength and hardness increase, while 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, and has a wide range of uses.
Introduction to the principle 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 side-blown converter. At the beginning, the converter is in a horizontal position, and 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 violent reaction on the surface of the liquid pig iron oxidizes iron, silicon, and manganese (FeO, SiO2, MnO,) to form slag, and the convection of the molten steel and slag makes the reaction spread throughout the furnace. After several minutes, when only a small amount of silicon and manganese were left in the molten steel, the carbon began to oxidize, generating carbon monoxide (heat release) to make the molten steel violently boil. A huge flame appeared at the furnace mouth due to the burning of overflowing carbon monoxide. Finally, phosphorus is also oxidized and further produces ferrous phosphate. Ferrous phosphate reacts with quicklime to generate stable calcium phosphate and calcium sulfide, which together become slag. When the phosphorus and sulfur are gradually reduced, the flame recedes, and brown steam of ferroferric oxide appears at the furnace mouth, it indicates that the steel has been smelted. At this time, the blast should be stopped immediately, and the converter should be turned to a horizontal position, and the molten steel should be poured into the 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.
Introduction to converter smelting process
The basic smelting process of converter steel. The operation process of smelting a heat of steel in a top-blown converter mainly consists of the following six steps:
(1) Tapping and slag dumping in the upper furnace, check the furnace lining and tilting equipment, etc., and carry out necessary repairs and repairs;
(2) Tilt the furnace, add scrap steel, add molten iron, and shake the furnace body (to a vertical position);
(3) The lowering gun is blown, and the first batch of slag is added at the same time (the noise in the furnace is loud at first, red smoke comes out from the furnace mouth, and then a dark red flame is sprayed out; after 3 to 5 minutes, the silicon manganese oxide is almost finished, and the carbon The oxygen reaction becomes more and more intense, the flame at the furnace mouth becomes larger, and the brightness increases; at the same time, the slag melts and the noise decreases);
(4) After 3 to 5 minutes, add the second batch of slag and continue blowing (the carbon in the steel gradually decreases as the blowing progresses, and after about 12 minutes, the flame is weak and the blowing is stopped);
(5) Invert the furnace, measure temperature, take samples, and determine the blowing time or tapping;
(6) Tap out the steel, and at the same time (add the calculated alloy into the ladle) carry out deoxidation alloying.
Introduction of Main Process Equipment for Converter Steelmaking
The furnace body can be rotated and is used for metallurgical furnaces for blowing steel or blowing matte. The furnace body of the converter is made of steel plate, which is cylindrical and lined with refractory materials. It is heated by chemical reaction heat during blowing and does not need 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. According to the capacity of AOD furnace, there are 3t, 6t, 8t, 10t, 18t, 25t, 30t and so on. The level of equipment has also been developed from semi-automatic control to intelligent computer control to smelt stainless steel.
VOD refining furnace
VOD refining furnace (vacuumoxygen decarburization) is an out-of-furnace 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 initial molten steel into a refining bag 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 generally carried out by electrode heating, and stirring is carried out through the bottom air-permeable brick.
The oxygen lance is the main equipment for oxygen supply to the converter, which is composed of a nozzle, a lance body and a tail structure. The nozzle is made of copper with good thermal conductivity through forging and cutting, and it is also made of pressure casting. The shape of the nozzle is Laval type, straight type and spiral type. At present, the most widely used is the porous Laval nozzle. The Laval type nozzle is a contraction-expansion contraction nozzle hole, when the ratio of outlet oxygen pressure to inlet oxygen pressure pout/p0<0.528 forms a supersonic jet.
Converter tilting system
Tilting furnace system: frequency conversion speed regulation (inverter + motor + reducer + large gear)
Tilting mechanism: The tilting mechanism is composed of rails, tilting cylinders, cradle platforms, horizontal support mechanisms and supports.