Iron was the dominant metal for use in building and machinery until the modern era. Iron is still the main component of steel but when impurities are removed in the steel-making process, a stronger, lighter material results (steel). Steel is used in almost all modern buildings, automobiles, aircraft and appliances.
Basic Oxygen Steel-Making (BOS) is the most efficient and popular modern steel-making process. Carbon rich pig-iron is heated until it is molten. Then it is put into a ladle (large container). The molten iron is pre-treated to remove impurities like silicon, sulfur and phosphorus. The iron is then moved into the BOS container and a lance is dropped inside that will blow 99 percent pure oxygen into the iron at a speed greater than Mach 1.
Ignition and Alloy Making
The blast of pure oxygen ignites the carbon in the steel. Carbon leaves in the form of carbon dioxide and carbon monoxide. Other chemical impurities also burn off. Once the process is complete, the steel is combined with certain elements to make alloys according to customer specifications. Carbon steel has added carbon. Stainless steel has added chromium and nickel. Titanium steel has added titanium.