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Analysis:

Pig iron, ore or processed scrap steel, oxygen, etc. are the main raw materials

< p> Steelmaking methods can generally be divided into three methods: converter steelmaking, open hearth steelmaking and electric furnace steelmaking. They are introduced as follows:

1. Converter steelmaking method The oxidant used in this steelmaking method is oxygen. Blow air into the 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.

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 (tuyere) 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 the brown steam of ferric oxide appears at the furnace mouth, it indicates that the steel has been smelted. 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 the air is blown from the bottom of the furnace, it is a low-blowing converter.

With the development of oxygen production technology, oxygen top-blown converters (also side-blown converters) are now commonly used. This kind of converter blows high-pressure industrial pure oxygen, and the reaction is more violent, which can further improve production efficiency and steel quality.

2. Open-hearth steelmaking method (open-hearth steelmaking method is also called Martin method)

Open-hearth steelmaking uses the air introduced into the oxidant and the oxides in the charge, (scrap iron , scrap steel, iron ore). The heat required for the reaction is provided by burning gaseous fuel (blast furnace gas, generator gas) or liquid fuel (heavy oil).

The hearth of an open-hearth furnace is a trough made of refractory bricks, which is covered by a furnace roof made of refractory bricks. There is a charging port on the front wall of the open-hearth furnace, and the charging machine loads the furnace materials from here. Close the door made of refractory bricks while smelting. There are burners at both ends of the furnace, and each burner has two holes for introducing fuel and hot air, or for guiding furnace gas from the furnace.

The raw materials used in open-hearth steelmaking are scrap steel, scrap iron, iron ore and solvents (limestone and quicklime). When smelting begins, the fuel burns on the fuel surface when it encounters the introduced hot air, with temperatures as high as 1800 degrees Celsius. The heat is directly transferred from the flame to the charge, causing the charge to melt quickly (the melting point of iron is 1535 degrees Celsius, and that of steel is slightly lower). At the same time, part of the melted pig iron generates ferrous oxide, and the impurities silicon and manganese in the pig iron are oxidized by the ferrous oxide and become slag. Because there is excess limestone in the furnace, impurities such as phosphorus and sulfur generate calcium phosphate and calcium sulfide and become slag. Secondly, the carbon also undergoes oxidation, producing carbon monoxide that emerges from the molten metal as if the metal is boiling.

When the reaction is about to be completed, add deoxidizer and remove the slag regularly. When smelting is about to be completed, it is necessary to check whether the composition of the steel meets the requirements based on pre-furnace analysis (using a rapid analysis method, which can be completed in a few minutes). Technetium-smelting steel flows from the steel tap into a molten steel ladle, and is then poured from the molten ladle into a mold to be cast into products or steel ingots.

In order to increase the furnace temperature, the gaseous fuel must be preheated in the regenerator (as shown in Figures I, II, III, IV).

Not only liquid pig iron can be added to the open hearth, but also solid pig iron, scrap iron and iron ore after pinching can be added. In addition, if 30% oxygen-enriched air is used to blow air in the open-hearth furnace and oxygen is blown into the molten metal at the same time, the productivity can be increased by 80%, the smelting time can be shortened by 2 to 4 hours, and fuel and oxygen-enriched air can be saved. No preheating required either.

3. Electric furnace steelmaking method Steel can also be smelted in an electric furnace that uses electricity as the heat source. Using electric furnaces to make steel can produce high-quality alloy steel. There are many types of electric furnaces, and the most widely used one is the electric arc furnace.