Steel manufacturing is a multi-stage process that begins by smelting iron ore into cast iron in a blast furnace. This initial stage involves layering iron ore with coke, a type of fuel, and crushed limestone within the furnace. The coke is ignited with a high volume of air, leading to the creation of carbon monoxide, which acts to reduce the iron ore to pure iron.
During this smelting process, limestone plays a crucial role by forming slag. Slag captures impurities within the molten iron, such as silica, phosphorus, and alumina, and floats above the molten metal, allowing for easy separation. The purified molten iron is then drained and moved to the next stage for steel processing.
However, this molten iron typically contains excess carbon and other impurities which must be removed to create quality steel. This is done through the basic oxygen process, in which a water-cooled lance is dipped into a mixture of molten iron and scrap metal. The addition of lime and fluorspar flux helps to form slag by reacting with phosphorus, which is then discarded.
After refining, the composition of the steel can be further modified by introducing new metallic elements to meet specific requirements. The steel is then ready to be shaped; it is either poured into molds to form ingots or processed through a strand-casting machine. Ingot molds are large, with diameters and heights that can span several feet.
The final step in steel manufacturing involves continuously casting the refined steel into thick, rough shapes known as beam blanks or blooms, which are then ready for further processing into various steel products.
