How structural steel is made?
There are two basic processes in use today in the United States for the manufacture of structural steel. Hot-rolled shapes including wide-flange sections, angles and channels are produced in steel mills utilizing Electric Arc Furnaces (EAF). Hollow Steel Sections (HSS) are manufactured from rolls of sheet steel that may have originally been produced in either a Basic Oxygen Furnace (BOF) or an EAF. Plate steel may also have been produced through either a BOF or EAF process.
The EAF process uses steel scrap as its basic feedstock material. Scrap from old automobiles, appliances, industrial waste and curbside recycling collection is melted in large electric furnaces. Impurities skimmed from the liquid steel and chemical additives are introduced to bring the steel to its desired metallurgical balance. The liquid steel is then cast into a beam blank that is similar in shape to a steel beam. The beam blanks are cooled, reheated and then passed through a series of rollers forming the beam into its precise geometric shape. The beams are then straightened, cut into standard shipping lengths, cooled and prepared for shipment. The recycled content of structural steel produced using the EAF process averages near 90%.
The BOF process used to make steel plate or rolled sheet steel is the more traditional method using iron ore and coke. Iron ore is melted in a coke (a processed form of coal) fired blast furnace and then transferred to a ladle. The molten iron in the ladle is chemically pretreated and introduced along with steel scrap into the basic oxygen furnace where the entire mix is melted together while oxygen is introduced into the middle of the mix through a water-cooled lance. The molten mix is then poured into a ladle for rolling into sheet or plate. The recycled content of steel produced using the BOF process averages near 25%.
HSS is produced by forming rolled sheet steel of the desired thickness into the geometric shape specified.
Structural Steel – MSC – August 2007