1. Primary steelmaking
Steel can be made from 100% recycled materials or a combination of recycled materials and original steel. Original steel is made from iron ore, coke (produced from coal), and lime in a blast furnace. Raw materials are added to the top of the furnace operating at 3000 ° F. As the iron ore melts and mixes with the burning coke, carbon is released into the molten product. Impurities are absorbed by lime to form surface slag, which can be skimmed off from the molten steel. The products at this stage contain about 4% carbon and still contain some impurities. The melted raw steel is transferred to an alkaline oxygen furnace (BOF) that already contains recycled scrap metal. Blow pure oxygen through the molten steel to oxidize excess carbon, forming a finished product with a carbon content of up to 1.5%.
The recycled scrap steel can be reprocessed without adding the original steel in the electric arc furnace. High power arc melts metal at temperatures up to 3000 ° F. As the scrap melts, more batches of scrap can be added to the furnace until its capacity is reached. Once a flat bath of molten steel is obtained, oxygen will be blown through in the same way as BOF. In both cases, the molten steel is taken out of the furnace and further treated in the ladle or steel groove, while removing surface slag containing impurities.
2. Secondary steelmaking
A key aspect of secondary steelmaking is the removal of oxygen. When molten steel begins to solidify, there is oxygen present, which causes the reaction with carbon to release carbon monoxide gas. Controlled deoxidation can be used to change the characteristics of the finished product, thereby changing the suitability of steel for different applications.
Edge sealing steel
Edge sealing steel is a type of steel that has not been deoxidized or partially deoxidized. During the curing process, high levels of carbon monoxide are generated, resulting in good surface quality, but there are many pores.
Sealing steel
The sealing steel initially follows the same pattern as the flanging, but about a minute later, the mold is sealed to suppress the formation of carbon monoxide.
Semi killed steel
Semi killed steel has undergone partial deoxidation before being poured into the mold, typically with a carbon content ranging from 0.15 to 0.3%.
Killed steel
The killed steel has been completely deoxygenated, so carbon monoxide will not form during the solidification process at all. The finished product has a uniform structure and no pores. Add aluminum as the main deoxidizer to the ladle or mold to "kill" the formation of carbon monoxide; However, some applications do not wish to add aluminum to the finished product. The substitute for aluminum is an iron alloy of manganese and silicon or calcium silicide.
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