Steelmaking

Steel mill with two arc furnaces.

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Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.

Modern processes

Modern steelmaking processes are broken into two categories: primary and secondary steelmaking. Primary steelmaking uses mostly new iron as the feedstock, usually from a blast furnace. Secondary steelmaking uses scrap steel as the primary raw material.

Primary steelmaking

Basic oxygen steelmaking (BOS, BOF, Linz-Donawitz-Verfahren, LD-converter) is a method of primary steelmaking in which carbon-rich molten pig iron is made into steel. The LD-converter is named after the Austrian placenames Linz and Donawitz (a district of Leoben). The vast majority of steel manufactured in the world is produced using the basic oxygen furnace. Modern furnaces will take a charge of iron of up to 350 tons and convert it into steel in less than 40 minutes. The LD converter is a refined version of the Bessemer converter where blowing of air is replaced with blowing oxygen.

Blowing oxygen through molten pig iron lowers the carbon content of the alloy and changes it into low-carbon steel.

The process is known as basic due to the pH of the refractories - calcium oxide and magnesium oxide - that line the vessel to withstand the high temperature of molten metal.

Secondary steelmaking

An electric arc furnace (EAF) is a furnace that heats charged material by means of an electric arc.

Arc furnaces range in size from small units of approximately one ton capacity (used in foundries for producing cast iron products) up to about 400 ton units used for secondary steelmaking. Arc furnaces used in research laboratories and by dentists may have a capacity of only a few dozen grams. Electric arc furnace temperatures can be up to 1,800 degrees Celsius. Arc furnaces differ from induction furnaces in that the charge material is directly exposed to the electric arc, and the current in the furnace terminals passes through the charged material.

History

The earliest means of producing steel was in a bloomery. Early modern methods of producing steel were often labour-intensive and highly skilled arts. See:

• finery forge, in which the German finery process could be managed to produce steel.
• blister steel and crucible steel.

An important aspect of the industrial revolution was the development of large-scale methods of producing forgeable metal (bar iron or steel). The puddling furnace was initially a means of producing wrought iron, but was later applied to steel production.

The real revolution in steelmaking only began at the end of the 1850s. The Bessemer converter was the first successful mass steelmaking process, followed by the open hearth furnace.

See also

• Argon oxygen decarburization
• Blast furnace
• Decarburization
• FINEX
• Flodin process
• Steel mill

External links

• U.S. Steel Gary Works Photograph Collection, 1906-1971
• Scrap steel for steelmaking facilities information reference compendium